Advanced materials and architecture for organic, printable and bio-inspired photonics

Resume : Perylene bisimides (PBIs) are dyes and pigments known for combining high absorption and emission in the visible region with their thermal and photochemical stability. Non-conventional H-bonded aggregation driven by free-imide groups has been reported to promote alternative J-type aggregate formation in non-polar solvents. J-aggregates are highly desired thanks to their bathochromically shifted absorption and fluorescence (by exciton coupling), together with hyperchromicity and superradiance compared to the monomer. Herein we present the water soluble analogue PBI4 showing interesting aggregation in water and in solid state. Unlike hydrophobic precursors, PBI4 aggregates in water upon increasing temperature indicating an entropy-driven self-assembly. Temperature dependent Resonance Raman (RR) spectroscopy at different wavelengths was employed for the structural characterization of PBI4 in aqueous solution versus toluene and in aggregated thin films. In order to gain insights on the structure of the aggregate, theoretical calculations of the normal modes of PBI4 with the use of Gaussian were performed to correlate the varied vibrational fingerprint upon aggregation to specific structural changes. These assignments indicate a distortion of the perylene core upon aggregation, where the bonds along the perylene long axis lengthen and the ones perpendicular to that shorten, suggesting a head-to-tail arrangement. Complementary FT-IR measurements provides further information on the aggregation process.

Resume : Organic semiconductors (small molecules, oligomers and polymers) are materials where unique optical and electronic properties often originate from a tailored chemical structure[1-3]. During the past few decades a vast number of organic semiconductors for organic light emitting diodes (OLEDs)[4], organic field effect transistors (OFETs)[5-7] and organic photovoltaics (OPVs)[8-10] have been developed and various chemical modifications are used in order to engineer and optimize the chemical structure towards enhanced device performance through the synergistic expertise of chemists, material scientists, physicists, and engineers. It is therefore evident that the enormous potential for practical applications from organic electronics increases the value of this research field[11]. Polymeric semiconductors represent the most challenging category from the class of the organic semiconductors. The ability to control and optimize their chemical structure for different optoelectronic applications involves many parameters such as: (i) molecular weight, (ii) bond length alternation (BLA), (iii) planarity, (iv) aromatic resonance energy (ERes), (v) substituents and (vi) intermolecular interactions[8,12]. Nowadays, the proper design of polymeric semiconductors has been focused on the way with which the optoelectronic properties of the polymers and the resulting device performance can be affected. For example, the role of the ionization energy of the donor (D) and the electron affinity of the acceptor (A) moieties in the backbone of donor-acceptor (D-A) conjugated polymers affecting the positioning of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels and consequently on the optical energy gap of the polymer[8,12-17] is well understood. Moreover, the influence of the molecular weight[18-23], homocoupling defects[24,25], isomeric structures of the functional monomers[15,26-28], electron donating or accepting side groups[29] as well as, side chains with different nature regarding length and/or branching together with their positioning onto the polymeric backbone[30-38] and end group effect[39] have been studied and explained. However, it is of outmost importance to gain an in depth understanding on the role of the chemical structure in (i) the establishment of the tendency for supramolecular self-assembly and corresponding morphological features and (ii) the optoelectronic properties of the polymeric semiconductors and the corresponding device performance. Achieving these correlations, next generation polymeric semiconductors shall be attractive candidate materials of choice for high performance organic electronic applications. In this study, the dependence of optoelectronic, microscopic (supramolecular packing) and macroscopic (morphology variation and device performance) properties by the rational design of the chemical structures of new D-A semiconducting polymers consisting of indacenodithiophene, indacenodithienothiophene or benzodithiophene derivatives as the electron donating (D) units and various electron withdrawing building blocks (A) such as benzothiadiazole, quinoxaline and thienopyrrolodione is reported.[40- Extensive studies were performed in both single-component polymer films and their blends with fullerene derivatives. Understanding the specific structure-properties relations will lead to significant advancement in the area of organic electronics (such as organic photovoltaics and organic photodetectors) since it will set new design rules towards further optimization of polymer chemical structures to enhance the device performances. References 1. Z. B. Henson, Κ. Müllen, G. C. 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Rapid Commun. 2017, 38, 1600614. 44. C. L. Chochos, N. Leclerc, N. Gasparini, N. Zimmerman, E. Tatsi, A. Katsouras, D. Moschovas, E. Serpetzoglou, I. Konidakis, S. Fall, P. Lévêque, T. Heiser, M. Spanos, V. G. Gregoriou, E. Stratakis, T. Ameri, C. J. Brabec, A. Avgeropoulos, J. Mater. Chem. A 2017, 5, 25064. 45. C. L. Chochos, R. Singh, V. G. Gregoriou, M. Kim, A. Katsouras, E. Serpetzoglou, I. Konidakis, E. Stratakis, K. Cho, A. Avgeropoulos, 2017, under consideration.

Resume : Poly(phenylene methylene) (PPM), a forgotten class of hydrocarbon polymer, can readily be synthesized in large quantities on laboratory scale (>150 g) and in absence of solvents by catalytic polymerization of benzyl chloride with SnCl4. The polymer can be processed easily into fibres, films and foams. TGA analysis revealed an exceptionally high decomposition temperature around 470 °C [1]. Surprisingly, PPM shows photoluminescence in the range of 400–600 nm. However, the fluorescence cannot be induced by π-electron delocalization of alternating double and single bonds. Instead, extended investigations indicate homoconjugation as the origin of the photoluminescence [2]. Homoconjugation can occur only in certain chemical structures in which individual π-electron systems can overlap through space across electronically isolating groups, e.g. a methylene group [3]. Importantly, impurities, π-stacking and aggregation/crystallization were excluded as the cause of fluorescence [2]. Remarkably, PPM exhibits a long photoluminescence lifetime of 8.55 ns in thin films and a high quantum efficiency of 69% in solution. We assume that poly(phenylene methylene) can serve as an example of a new class of fluorescent polymers characterized by homoconjugation. [1] A. Braendle, et al., J. Polym. Sci. Part A Polym. Chem., 2018, 56, 309. [2] A. Braendle, et al., J. Polym. Sci. Part B Polym. Phys., 2017, 55, 707. [3] L. T. Scott, Pure Appl. Chem. 1986, 58, 105.

Resume : Conjugated polymers are an attractive class of fluorescent organic materials for optoelectronic applications owing to their tuneable properties through variation of chemical structure, processability and electronic conductivity. In condensed phases, materials that can emit colourful fluorescence are useful for a wide range of applications, from organic light-emitting diodes and photovoltaic devices to wavelength-tuneable lasers. However, in highly concentrated amounts, complexities arise regarding photophysical processes such as energy migration/transfer, charge separation and excimer formation.[1] We present the synthesis and characterisation of a series of encapsulated diketopyrrolopyrrole red-emitting conjugated polymers. The novel materials display extremely high fluores-cence quantum yields in both solution (>70%) and thin film (>20%). Both the absorption and emission spectra show clearer, more defined features compared to their naked counterparts demonstrating the suppression of inter and intra-molecular aggregation. We find that the encapsulation results in decreased energetic disorder and a dramatic in-crease in backbone co-linearity as evidenced by STM. This study paves the way for DPP to be used in emissive solid state applications and demonstrates a novel method to reduce structural disorder in conjugated polymers.[2] References [1] Pan, C.,et al. Angew. Chemie - Int. Ed. 2013 52, 10775–10779 [2] Leventis et al. J. Am. Chem. Soc. 2018, 140, 5, 1622-1626

Resume : The exploitation of aggregation for boosting the efficiency of organic chromophores has provided a paradigm shift among luminescence management strategies, which had largely been dominated by the concern of limiting aggregation, and is now a promising approach in the area of organic light-emitting diodes (OLEDs). Here, we present a class of emitters based on 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY), which is a well-known fluorophore otherwise affected by aggregation, functionalised with different aggregation-induced emission (AIE) luminogens. Thanks to this modification, we could tune the photoluminescence (PL) from the green to the NIR, and obtain PL efficiencies above 50 % in the solid-state. Most importantly, we observed an enhancement of the AIE and 100 % efficiencies by blending the red/NIR fluorophores with a commercially available polyfluorene matrix. Residual PL from the host matrix could be minimised thanks to efficient energy transfer, therefore maintaining good spectral purity. By incorporating these metal-free blends in OLEDs, we obtained electroluminescence (EL) peaked in the range 650—700 nm with up to 1.8 % efficiency and 2 mW/cm2 radiance, which are remarkably high for red/NIR emitting and solution-processed OLEDs. Further optimisation of the performance could make such OLEDs suitable for integration in pulse oximeters, given that the 650—700 nm EL affords both optimal tissue penetration and contrast between oxygenated and deoxygenated haemoglobin.

Resume : We report on a solution-processable near-infrared emitting curcuminoid derivative containing two triphenylamine donor groups and one acetylacetonate boron difluoride acceptor unit [1]. This dye with a bio-inspired backbone derived from curcumin exhibits an efficient thermally-activated delayed fluorescence activity at room temperature with a maximum emission wavelength above 700 nm in thin films and is used as emitter in organic light-emitting diodes with a maximum external quantum efficiency of about 10% and a maximum radiance value of 3 x 106 mW sr-1 m-2. In contrast to most thermally activated delayed fluorescent dyes used in high-efficiency organic electroluminescent devices, the curcuminoid derivative also exhibits excellent amplified spontaneous emission properties in doped organic thin films with a threshold as low as 7 microJ/cm2 for an emission peak wavelength around 750 nm. The simultaneous observation of highly efficient thermally-activated delayed fluorescence and amplified spontaneous emission is explained by the strong overlap between the hole and electron wavefunctions involved in the optical transition together with a nonadiabatic coupling effect between the low-lying excited states. These results demonstrate for the first time that thermally-activated delayed fluorescent emitters are of strong interest for high performance near-infrared organic electroluminescence and lasing. [1] D. H. Kim et al. Nature Photonics, in press, DOI: 10.1038/s41566-017-0087-y

Resume : Emerging organic light-emitting electronic devices such as organic light-emitting transistors and lasers need materials combining high luminescence and efficient charge transport. Doping of the materials by highly luminescent molecules is an efficient approach to control and enhance the material luminescence. Here, we introduce the concept of self-doping according to which a higher luminescent dopant emerges as a byproduct in the course of the host material synthesis, and demonstrate how the dopant controls the luminescence of organic semiconducting crystals. As the host material, we synthesized thiophene(T)-phenylene(P) co-oligomers (TPCO) with the conjugated core P2TP and various end groups. We show that the self-dopant with the conjugated core P4TP present in the synthesized host with a concentration of ~1%. The dopant content was checked by luminescent and photothermal spectroscopies. We show that photoluminescence (PL) in the self-doped single crystals is controlled by Förster resonant energy transfer (FRET) from the host TPCO to the higher luminescent TPCO dopant. Time-resolved PL data and Monte-Carlo simulations indicate that the Förster radius and the exciton diffusion length in the self-doped crystals are close. We demonstrate that self-doping also operates in various 5-ring TPCO and in 4-ring oligophenylene single crystals. We conclude that self-doping is a promising route to control and enhance the luminescent properties of organic semiconducting materials.

Resume : Linear porphyrin oligomers joined by π-conjugated linkers at their meso positions show efficient electron delocalization in their neutral state. Moreover, the readily formed radical cations of a butadiyne-linked family of oligomers were previously reported to be delocalized over 2-3 porphyrin units, regardless of the length of the chain. To date, however, there is little systematic investigation on the effect of the linkage on this delocalization. As a consequence of the shortening of the distance between chromophores, single-acetylene linked porphyrin oligomers are known to show even more pronounced electronic communication in their neutral state, as evidenced by their NIR absorption features. Here we present an investigation on the radical cations of the single-acetylene linked arrays of N = 1-3, 5 porphyrin units. These radical cations were generated in solution by chemical oxidation, and probed by EPR spectroscopy. By carefully selecting appropriate side chains that prevent aggregation and provide solubility, this series was extended to unprecedented oligomer lengths (N > 10). The results shed light on the distribution of the polaron over the backbone of this type of π-conjugated linear oligomers. [1] K. Susumu, P. R. Frail, P. J. Angiolillo, M. J. Therien, J. Am. Chem. Soc. 2006, 128, 8380-8381. [2] M. D. Peeks, C. E. Tait, P. Neuhaus, G. M. Fischer, M. Hoffmann, R. Haver, A. Cnossen, J. R. Harmer, C. R. Timmel, H. L. Anderson, J. Am. Chem. Soc. 2017, 139, 10461-10471. [3] M. Rickhaus, A. Vargas Jentzsch, L. Tejerina, I. Grübner, M. Jirasek, T. D. W. Claridge, H. L. Anderson, J. Am. Chem. Soc. 2017, 139, 16502-16505.

Resume : In order to improve the ambient contrast ratio in organic light emitting diodes (OLEDs), a circular polarizer (CP) has been used to suppress ambient light reflection. However, the use of a CP has many drawbacks such as decreased flexibility, increased cost, and more than 50% absorption loss of the OLED. In this work, we report that patterned MoS2 nanosheets obtained by mechanical rubbing (R-MoS2), ion-beam treatment (I-MoS2), and rubbing/ion-beam treatment (RI-MoS2) can efficiently function as hole transport layers and templates for alignment of an emissive layer {poly(9,9-dioctylfluorene-alt-benzothiadiazole), poly [(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo [2,1,3]thiadiazol-4,8-diyl)] (F8BT)} with a nematic liquid crystal phase toward highly efficient polarized OLEDs. The Electroluminescence (EL) spectrum of the N-MoS2-based OLED is clearly unchanged under different rotation angles of the polarizer, indicating that the OLED fabricated on N-MoS2 is not polarized. In contrast, the EL spectra of the R-MoS2-, I-MoS2-, and RI-MoS2-based OLEDs dropped dramatically as the polarizer was rotated. The maximum polarization ratios for the R-MoS2-, I-MoS2-, and RI-MoS2-based OLEDs are approximately 19.8, 21.7, and 166.7, respectively, at 540 nm. The average polarization ratios for the emission spectra of the R-MoS2-, I-MoS2-, and RI-MoS2-based OLEDs were calculated to be 11.5, 12.3, and 62.5, respectively. These data suggest that RI-MoS2 is the optimal hole transport layer for high-efficiency polarized OLEDs. ACKNOWLEDGEMENT This research was supported in part by National Research Foundation of Korea (NRF) grants provided by the Korean government (MSIP) (Nos. 2015K1A3A1A59073839, 2017H1D8A1030599, 2017K1A3A1A67014432) and in part by Korea Agency for Infrastructure Technology Advancement grant funded by Ministry of Land, Infrastructure and Transport (17IFIP-B133622-01).

Resume : Cesium lead halide perovskite nanostructures such as nanoparticles, nanosheets and nanorods have attracted an increasing interest since their promising light-emitting applications. However, the photophysics behind them is not yet clear. Herein, the emission properties of CsPbBr3 nanosheets (NSs) are investigated by using steady-state and transient photoluminescence (PL) spectroscopic techniques. Two kinds of excitonic emissions are observed at low temperatures < 80 K under the conditions of low excitation level. They are revealed to stem from the radiative recombination of trapped and free excitons by examining their spectral features, emission intensity dependence on the excitation power and PL lifetime. Some surface states and structural defects inevitably induced in the synthesis process of CsPbBr3 NSs may be responsible for trapping centers of excitons. The thermal migration from the trapped excitons to the free excitons with the rise of temperature is found and modeled quantitatively. These results and findings shed some light on the luminescence mechanism of CsPbBr3 NSs.

Resume : Stretchable optoelectronic devices which can be conformally attached and mounted to the human body to monitor physiological parameters, generate powers and communicate with external electronics are of great interest. In this respect, a few stretchable optoelectronic devices including stretchable light-emitting diodes (LEDs), stretchable solar cells, and stretchable photodetectors have been investigated. However, realization of high performance devices has been retarded due to difficulty in securing durability and stabilityof the devices. In this presentation, we propose a new approach for fabrication of various stretchable optoelectronic devices. Some examples of stretchable ultraviolet (UV), visible, and infrared (IR) photodetectors and organic light-emitting diodes (OLEDs) which have stretchability in uniaxial and multiaxial directions are demonstrated by adopting a unique geometric engineering of the layers in the devices. In our approach, stretchable photodetectors and OLEDs are fabricated directly on a three-dimensionally micro-patterned stretchable substrate composed of curvilinearly connected bumps and valleys; this structure allows for efficient absorption of stretching strain. This approach enables the optoelectronic devices to sustain large stretching strain in all directions through efficient absorption of stretching in lateral direction. Furthermore, the devices can be easily and conformally attached to a human body, allowing us to achieve the stable response of the device to UV, visible, and IR light during human activities. Based on those features, the stretchable optoelectronic devices may providea great promise for applications in future stretchable and wearable electronics and internet of humans.

Resume : Zeolitic imidazolate frameworks (ZIFs), a subclass of metal-organic frameworks (MOFs), have been recently employed in various fields such as gas separation, catalysis, water purification and drug delivery.1 Their high importance is due to their chemical and thermal stability in addition to the flexibility of their design. ZIFs have been synthesized solvothermally or at room temperature using organic solvents (e.g. methanol, DMF) or pure water.2 The control of size and morphology of crystals has been achieved using reverse microemulsion methods, microwave, ultrasound-assisted syntheses and coordination modulation methods.1-3 Herein, we investigate a new synthesis method where ZIF crystals are produced using the reaction-diffusion framework (RDF) in a gel medium at room temperature. The method is based on the diffusion of an outer solution of the organic linker or mixed linkers into an agar gel containing the inner metal ions Zn(II) where a precipitation reaction takes place leading to the formation of the ZIF crystals. A facile method to produce Zeolitic Imidazolate Frameworks (ZIF-8, ZIF-67 and solid- solution ZIFs (mixed Co and Zn)) is reported. ZIF crystals are produced via a reaction- diffusion framework (RDF) by diffusing an outer solution at a relatively high concentration of the 2-methyl imidazole linker (HmIm) into an agar gel matrix containing the divalent metal (zinc (II) and/or cobalt (II)) at room temperature. Accordingly, a propagating supersaturation wave, initiated at the interface between the outer solution and the gel matrix leads to a precipitation front endowed with a gradient of crystal sizes ranging between 100 nm and 55 μm along the same reaction tube. While the precipitation fronts of ZIF-8 and ZIF-67 travel the same distance for the same initial conditions, ZIF-8 crystals therein are consistently smaller than the ZIF-67 crystals due to the disparity of their rate of nucleation and growth. The effects of temperature, the concentration of the reagents, and the thickness of the gel matrix on the growth of the ZIF crystals are investigated. We also show that by using RDF, we can envisage the formation mechanism of the ZIF crystals, which consists of the aggregation of ZIF nanospheres to form the ZIF-8 dodecahedrons. Moreover, using RDF the formation of a solid-solution ZIF via the incorporation of Co(II) and Zn(II) cations within the same framework is achieved in a controlled manner. Finally, we demonstrate that doping ZIF-8 by Co(II) enhances the photodegradation of methylene blue dye under visible light irradiation without hydrogen peroxide. References [1] Eddaoudi, M.; Kim, J.; Rosi, N.; Vodak, D.; Wachter, J.; O'keeffe, M.; Yaghi, O. M. Science 2002, 295, 469-472. [2] Rosi, N. L.; Eckert, J.; Eddaoudi, M.; Vodak, D. T.; Kim, J.; O'keeffe, M.; Yaghi, O. M. Science 2003, 300, 1127-1129. [3]Saliba, D.; Ammar, M.; Rammal, M.; Al-Ghoul, M.; Hmadeh, M. J. Am. Chem. Soc., 2018, DOI: 10.1021/jacs.7b11589.

Resume : The value of the work function of molybdenum trioxide (MoO3) electrodes has been widely debated in the literature. Here, we use electroabsorption measurements to characterize, non-invasively, finished conjugated polymer sandwich structures with MoO3 anodic interlayers and investigate the energy-level line-up in these systems, suitable for photonics devices, such as polymer light-emitting and photovoltaic diodes. We measure built-in voltages of ~ 1.77 ± 0.10 V in structures with calcium counterelectrodes, similar to those measured when MoO3 is replaced by poly(3,4-ethylene dioxythiophene) doped with poly(styrene sulfonate), PEDOT:PSS, (1.95 ± 0.04 V) from which we extract a work function value of ~ 5.1 eV for MoO3. This is consistent within 0.1 eV with the value we also measure by Kelvin probe under nitrogen, but significantly lower than reported in past studies via ultraviolet photoelectron spectroscopy (up to ~ 6.9 eV) thereby showing the strong dependence of MoO3 work function on the details of the deposition and post-deposition environmental parameters. Photovoltaic diodes incorporating our MoO3 films displayed power conversion efficiencies comparable or slightly better than our reference devices with PEDOT:PSS anodes.

Resume : We report the investigation of the optical properties of a class of highly emissive and atomically precise graphene quantum dots (GQDs), a derivative of dibenzo[hi,st]ovalene (DBOV-Mes), blended with poly(9,9-dioctylfluorene-alt-benzothiadiazole (F8BT), a light-emitting polymer largely used for optoelectronics applications. Differently from GQDs generated via a top-down approach, our compound, specifically designed and synthesized, has an atomically controlled dot dimension and substituents, thus well-defined optical properties. DBOV-Mes was blended at 0.5, 1, 2.5 and 5 w/w % with F8BT showing a marked red-NIR fluorescence emission (ranging from 630 nm to 740 nm depending on the dopant loading) with a maximum fluorescence quantum yield of 82 ± 4 % in the solid state. Furthermore, thanks to efficient energy transfer, green emission from the host polymer is efficiently quenched, thereby affording optimal spectral purity. Part of the red emission from the blends is due to relatively long living (up to ~ 20 ns) intermolecular species, which have been investigated via time-correlated single photon counting technique (TCSPC). Finally, we used such blends as active layers to fabricate red-NIR emitting organic light-emitting diodes (OLEDs), which showed max external quantum efficiency of 0.67% at a current density of ~ 100 mA/cm2. This is the first report of successful incorporation of DBOV-Mes in fully solution-processed OLEDs, and paves the way for the use of such unique, atomically tuneable, GQD molecules for optoelectronic applications.

Resume : Semiconducting light-emitting materials based on conjugated (macro-)molecules possess enormous technological potential owing to low-cost, large-area solution-based processing and the possibility of tuning the spectral properties by chemical modification. Despite recent progress, several obstacles remain, e.g., (i) decrease of luminescence efficiency and spectral purity upon degradation under ambient conditions and (ii) the frequent compromise between efficiencies of charge transport and luminescence. Here we report the first instance of synthesis and characterisation of fluorescent derivatives of the so-called Magnus Green salt (MGS) – a quasi-1D semiconductor comprising a linear chain of Pt atoms substituted with organic ligands. The resultant hybrid organic-inorganic compounds, termed ‘cyanoplatinates’, have the general formula [Pt(NH2L)4][Pt(CN)4)] where L is an alkyl. Unlike MGS, cyanoplatinates can be solution-processed into thin films. Using ‘matrix-assisted’ assembly we show that their fluorescent properties are enabled by the assembly of dimers into 1D chains, with the emission colour (typically blue-green) governed by the Pt-Pt distance, i.e. the size of the alkyl substituents. The fluorescence of cyanoplatinates is found to be remarkably stable, even following thermal annealing in air at 200 °C, and is preserved after extensive doping using FeCl3. Cyanoplatinates thus represent a promising new strategy for stable next-generation light-emitting materials.

Resume : Encapsulation within a macrocycle is a fundamental approach to enhance photo-physical properties (i.e. luminescence, quantum yields in solid state) and for preventing the aggregation of fluorophores.[1],[2] In this context, an example for a macrocycle interacting with a host by hydrogen bonding is the rotaxination of squaraine dyes into tetralactam macrocycles.[3] Here we show, that this approach can be adapted to indigoids. Indigo displays low solubility and fluorescence caused by its strong inter- and intramolecular hydrogen bonds. However, introduction of a bridge between its functional groups inhibits the formation of inter- and intramolecular hydrogen bonds leading to improved fluorescence properties. The carbonyl groups can be used to bind the indigoid dye to a tetralactam macrocycle with hydrogen bonds, and thus, provide easy access to a supramolecularly encapsulated indigoid. In addition to the supramolecular system, we explored the covalent encapsulation of indigoids.[4] Functional chains with terminal double bonds can be introduced which permit the self-encapsulation following a metathesis reaction. A comparison and results of both encapsulation strategies will be presented. [1] Frampton, M. J.; Anderson, H. L. Angew. Chemie - Int. Ed. 2007, 46, 1028–1064. [2] Taylor, P. N.; Hagan, A. J.; Anderson, H. L. Org. Biomol. Chem. 2003, 1, 3851–3856. [3] Arunkumar, E.; Forbes, C. C.; Noll, B. C.; Smith, B. D. J. Am. Chem. Soc. 2005, 127, 3288–3289. [4] Sugiyasu, K.; Honsho, Y.; Harrison, R. M.; Sato, A.; Yasuda, T.; Seki, S.; Takeuchi, M. J. Am. Chem. Soc. 2010, 132, 14754–14756.

Resume : General photonic glasses are dielectric structures having short-range order and reflect specific wavelength of light corresponding energy of photonic bandgap (PBG). But photonic glasses show low reflectance and chroma and the breakthrough was needed to enhance optical properties. According to Kramers-Kronig relations, real part of refractive index (RI) is changed by controlling imaginary part of RI. Also, some papers recently explain that imaginary part of RI also affects to formation of PBG and in nature, many creatures already adopt pigment in photonic crystal structures. But until now, imaginary part of RI in artificial photonic crystals is not considered. So, we graft imaginary part of RI onto disordered photonic structures by doping absorbing materials and confirm that reflectance increase when absorption band of absorbing materials and PBG of photonic structures are matched. This phenomenon means absorption resonantly interact with reflectance of disordered photonic structures. Also, black materials doping can enhance reflectance and chroma at the same time by absorbing incoherent scattering light. There were no reports of effect of absorbing materials on optical properties enhancement. This study will suggest a new directions of photonic crystal fields and bring improvement of industrial application possibility.

Resume : Self-assembly of block copolymers (BCPs) provides a fascinating approach for creating photonic materials due to their ability to organize into 1D, 2D and 3D periodic microstructures with a long range order. Their periodic dielectric structures allow to modulate the propagation of electromagnetic waves, producing strong structural colors. Here, we demonstrate one-dimensionally periodic block copolymer photonic sensors with full-color tunability as a result of pH changes. The photonic lamellar gels were realized via the self-assembly of a hydrophobic block-hydrophilic block copolymer, polystyrene-b-poly(acrylic acids) (PS-b-PAA). The selective swelling of the PAA domains leads to extremely large tunability of the photonic stop band from blue to red wavelengths as a function of pH changes of aqueous solution. The reversible color changes and swelling behaviors are strongly dependent on the protonation/deprotonation of the acrylic acid groups in the lamellar microdomains. These tunable structural color materials may be attractive for pH-responsive photonic sensors.

Resume : We report the optical and electrooptical characterisation of a novel series of newly synthesised encapsulated diketopyrrolopyrrole (DPP) red-emitting conjugated polymers. The DPP core is sheathed using cyclic sidechains to prevent π-π stacking and formation of non-emissive aggregates. We characterise the optical properties both in solution and in thin films, as well as electroluminescence in organic light-emitting diodes (OLEDs). The novel encapsulated materials display high fluorescence quantum yields in both solutions (>70%) and thin films (>20%). The full extent of the aggregation minimisation is demonstrated when compared to the “naked” counterparts. The latter exhibit significantly lower quantum yields (>3 times) in both solutions and thin films. Both absorption and emission spectra show better defined features compared to their naked counterparts, thereby demonstrating suppression of inter and/or intra-molecular aggregation. This claim if further confirmed by the substantially poorer results of the naked polymers when embedded in OLEDs, that display much broader, featureless and red-shifted spectra, as well as lower external quantum efficiencies (>4 times). These results prove that DPP can be used in emissive solid-state applications and serves as a proof-of-concept for future optoelectronic applications also when low-energy bandgap emitters (with extended conjugation and therefore enhanced tendency to aggregation) are needed (e.g. for near-infrared emission).

Resume : We report the control of spontaneous emission in a flexible all-polymeric microcavity (MC) embedding poly(4,4’-diphenylene diphenylvinylene) (PDPV) as fluorescent material. The full plastic MC reshapes the PDPV photoluminescence (PL) into a sharp emission peak with 6 nm linewidth, which defines a quality factor Q = 90. PDPV exhibits the intriguing aggregation-induced emission (AIE) phenomenon. In dilute solutions, non-radiative decay pathways due to intramolecular rotations quench the PDPV PL (efficiency, Φ = 4%). However, addition of propan-2-ol (IPA), which acts as poor solvent for PDPV, into toluene solutions causes the polymer to aggregate and induces efficient emission. The solutions show unchanged Φ until a ~20% volume of IPA is added. Further addition of IPA leads to a steep increase of Φ, which rises abruptly to 26% at 30% IPA volume in the mixture and reaches 95% when IPA is in a ratio r = 99:1 with toluene. Correspondingly, the PL lifetime of PDPV increases from 0.2 ns (r = 0) to 2.8 ns (r = 99), as the non-radiative constant is reduced by 270 times. In solid state, the AIE effect boosts the Φ value up to 70%, which makes PDPV promising for photonics. We incorporated a PDPV thin film in a MC, consisting of 50 bilayers of poly(9-vinyilcarbazole) and cellulose acetate and tuned on the PL band of PDPV, peaking at 532 nm. We demonstrate an eighteen-fold PL directional enhancement with a 25-times shrinkage of the PL linewidth, paving the way for cheap light management.

Resume : We report the optical properties and electroluminescence of a series of novel low-gap porphyrin oligomers. In these, bulky trihexylsilyl (THS) sidechains are added to the porphyrin cores, so as to maintain high luminescence efficiency in the presence of the extended backbone planarity needed for red and near-infrared (NIR) emission, driving - -pi stacking and ultimately favouring formation of (less emissive) interchain states. We report the optical properties of the oligomers both in solutions and thin films, and the electroluminescence (EL) of the oligomers in blends with the commercial conjugated polymer poly(9,9’-dioctylfluorene-alt-benzothiadiazole) (F8BT). More specifically, we investigated different loadings of the porphyrins in the polymer matrix and carried out optical characterisation by means of UV-VIS absorption, ns-regime time-resolved emission spectroscopy and photoluminescence efficiency (ηPL) measurements using an integrating sphere. We chose the best performing blends, in terms of ηPL, and incorporated them in organic light emitting diodes (OLEDs). With a carefully optimised device architecture including an electron blocking layer (EBL), devices yield up to a maximum EL external quantum efficiency (ηEL) of 3.8 % with almost pure NIR emission (>95 % at λ>700 nm). This value is the highest ηEL reported so far for a NIR heavy-metal free emitter. These results serve as a proof of concept that efficient NIR emission from OLEDs is possible without the use of toxic heavy metals, while maintaining solution processability and low-cost fabrication.

Resume : This work demonstrates a new method for tuning the optical stop band of SiO2-inverse opals. To achieve the goal of ~ 110 nm shift, we take advantage of the opal-growth technique known as “vertical method” where the self-assembly of the sacrificial opal template (made by polystyrene particles) and the infiltration of the matrix material, e.g. silica, take place in a single step. Usually, the central frequency of the photonic stop band (PSB) is tuned by changing the sphere diameters of the opal template. Here we found that controlling the contents of the silica precursor, the PSB blue-shifts from 585 nm to 470 nm, keeping fixed the sphere diameters. The high-quality of our opals is confirmed by the SEM images and the presence in their reflectance and transmittance spectra of the Van Hove-like structures. Furthermore, to verify the performance of these photonic crystals, we study the spontaneous emission of a luminescent organic polymer, e.g. poly(4,4`-diphenylene diphenylvinylene), or briefly PDPV, after its infiltration into the opals. According to the angular dispersion of the PSB, a strong modification of the photoluminescence (PL) spectra and a 75 nm red-shift of the emission peak are detected when increasing the collection angle from 0 to 40°. To conclude, we show how a simple and low-cost modification of the opal fabrication conditions allows controlled tuning of the optical photonic stop band.

Resume : We report on the sensing of volatile organic compounds including alcohols and aromatic molecules by multi-layered photonic crystals made of commodity polymers. The kinetical analysis of the optical response of these polymer photonic crystals to vapours exposure leads, on one hand, to label-free colorimetric sensors, suitable for the qualitative and quantitative assessment of volatile organic compounds, and on the other, to the determination of the analyte diffusion parameters into the polymer multilayers. We will demonstrate that this simple method offers a new powerful tool for the in-situ assessment of the molecular diffusion coefficient in polymer films, widely used in food packaging and for the encapsulation of optoelectronic devices by mean of simple UV-VIS spectroscopy.

Resume : We have achieved sizable ex-chiral-pool synthesis of enantiopure prolinol functionalized squaraine small molecular compounds with opposite handedness. Early stage aggregation in solution shows formation of H-aggregates with helical stacking. Thermal annealing of spin-casted thin films induces further supramolecular aggregation into J-aggregates with a sharp absorption maximum at 780 nm. By Mueller matrix spectroscopy [1] we show an extraordinary high but true circular dichroism associated with the J-band. The ellipticity well reaches a value of 500 mdeg/nm and an intensive dissymmetry factor of g = 0.75, respectively, and is evenly distributed over the complete thin film area. So far, these values have no documented rival among intrinsic supramolecular circular dichroism, and thereby open new perspectives for the development of organic based chiral photonics and spintronics. [1] O. Arteaga, B. Kahr, Opt. Lett. 38 (2013) 1134.

Resume : In this paper we show large magnitude (sub-)picosecond optical switching of the near infrared (NIR) localized surface plasmon resonances (LSPRs) of colloidal doped metal oxide nanocrystals.[1] Doping levels in the range of 1021 cm-3 result in plasmonic response in wavelength ranges of interest for optical communication.[1,2] For example fluorine-indium codoped cadmium oxide (FICO) nanocrystals display narrow linewidths and high quality factors LSPRs tunable between 1.5 to 3.3 μm by controlling the level of doping.[1-3] Their lower free carrier density with respect to noble metals adds sensitivity to absolute changes in the carrier concentration, delivering a way to modulate their NIR plasmon response.[1,2] In this work we exploited this property to induce large signal modulation in the NIR combined with ultrafast recombination times, making our system interesting for all-optical signal processing at optical communication wavelengths. We show that the plasmon response can be modulated by ultrafast photodoping with a mono-exponential signal recovery, due to the temporarily increased carrier density of up to 7%. Instead when exciting the LSPR an initial sub-picosecond signal change associated to the cooling of the hot carriers is followed by a negligible signal ascribed to the lattice heating. Notably, our results further suggest that a change in carrier effective mass as a result of the non-parabolic conduction band of the doped semiconductor is responsible for the high signal response observed upon plasmon excitation.[1] Both findings are specific to this type of NIR plasmonic material and display new and exciting tools for all-optical signal processing in the NIR. Incorporating such materials as constituents of photonic structures allows actively manipulating the photonic response due to a variation of the dielectric function of the doped metal oxide, opening new pathways for novel optically controllable nanophotonic devices.[4] References [1] Kriegel, I.; Urso, C.; Viola, D.; De Trizio, L.; Scotognella, F.; Cerullo, G.; Manna, L. Ultrafast Photodoping and Plasmon Dynamics in Fluorine–Indium Codoped Cadmium Oxide Nanocrystals for All-Optical Signal Manipulation at Optical Communication Wavelengths. J. Phys. Chem. Lett. 2016, 7, 3873–3881. [2] Kriegel, I.; Scotognella, F.; Manna, L. Plasmonic Doped Semiconductor Nanocrystals: Properties, Fabrication, Applications and Perspectives. Physics Reports 2017, 674, 1–52. [3] Ye, X.; Fei, J.; Diroll, B. T.; Paik, T.; Murray, C. B. Expanding the Spectral Tunability of Plasmonic Resonances in Doped Metal-Oxide Nanocrystals through Cooperative Cation–Anion Codoping. J. Am. Chem. Soc. 2014, 136, 11680–11686. [4] Optically switchable 1D photonic structures, G. M. Paternò, C. Iseppon, A. D’Altri, C. Fasanotti, G. Merati, M. Randi, A. Desii, E. A. A. Pogna, D. Viola, G. Cerullo, F. Scotognella, I. Kriegel, under review Scientific Reports (2017).

Resume : Organic light emitting diodes (OLED) are good candidates for the high-quality flat-panel displays and solid-state lighting applications [1-2]. At present, almost every single commercial OLED product is fabricated by vacuum deposition because of its superlative features, such as precise layer thickness control, high efficiency, and easy multilayer deposition in the intricate devices, which are highly expensive because of low throughput and huge material wastage [2]. To make the resultant products commercially profitable and enable large-area roll-to-roll fabrication, solution-processable OLEDs with higher efficiencies are highly demanded. Charge transporting materials play an important role in OLED performance [2]. A charge transporting material should have the capability to block the carriers of the opposite sign from passing through the organics and recombining at the electrodes [2]. Molecular architecture, thermal stability, morphology, HOMO- LUMO values, ability to block the carriers of opposite charge and charge mobility of charge transporting materials are important for efficient and long lifetime OLEDs [3]. In the present study, we demonstrate a solution-processed novel hole transporting material, 9,9-diethyl-1,3,4-trifluoro-7-(2,4,6-trifluorophenyl)-9H-flourene for highly efficient OLEDs. This HTM exhibit excellent solubility in common organic solvents and robust thermal stability. Taking conventional PO-01 based yellow phosphorescent device for example, at 100 cd/m2, the current efficiency is enhanced from 23.3 to 59.2 cd A-1 and a power efficiency from 14.6 to 28.4 lm W-1, as NPB replaced by reported HTM. The high device efficiency is attributed to rational hole mobility and effective electron confinement. Moreover, the phosphorescent device architecture enables therein an electron trap to facilitate the injection of the minor carriers against that of a hole, leading to a more balanced carrier injection. Key Words: OLED, Hole transporting material, Solution-process References 1. D’Andrade BW, Forrest SR. White Organic Light-Emitting Devices for Solid-State Lighting. Adv. Mater.16: 1585–1595, 2004. 2. Jou JH, Kumar S, Agrawal A, Li TH, Sahoo S., Approaches for fabricating high efficiency organic light emitting diodes, J. Mater. Chem. C 3: 2974-3002, 2015. 3. Gaspar DJ, Polikarpov E. OLED Fundamentals: Materials, Devices, and Processing of Organic Light-Emitting Diodes. ISBN 9781138893962, 2015.

Resume : Fullerene-based acceptors such as PC61BM and PC71BM have been used in the field of organic photovoltaics (OPV) despite of some significant limitations including i) weak absorption of the incident solar spectrum, ii) limited tunability, iii) high synthetic costs, and iv) morphological instability due to fullerene diffusion. As an alternative way to solve the limitations of PC61BM and PC71BM, much attention has been focused on the development of non-fullerene acceptors. Recently, the research on non-fullerene acceptors has progressed rapidly and PCE performances of even up to 13% have been obtained. Here we report novel benzothiadiazole-based linear rod-like non-fullerene acceptors based on a symmetric acceptor-donor–acceptor-donor-acceptor (A2–D–A1–D–A2) structure, which is comprised benzothiadiazole central acceptor unit (A1) flanked by a donor (D) unit and a terminal acceptor unit (A2), mainly attached via a vinyl linkage. We systematically investigated the synthesis, optical and electrochemical properties, and photovoltaic characteristics of the resulting small molecule acceptors and will be presenting structure-performance relationship studies of benzothiadiazole-based non-fullerene acceptors. Benzothiadiazole-based acceptors showed the PCE values over 5.2% and 8.3% combined with P3HT and PCE-10, respectively. The optimization in device fabrication is ongoing and the detailed results will be providing, moreover, this study will give out the benefits of easily synthesized small molecule acceptors with a simple structure, which have greater potential for industrial application than high-efficiency molecules with a complex synthesis.

Resume : In our precedent studies we demonstrated graphenoid surface physical functionalization (HOPG and graphene),1 based on a molecular clip we developed ten years ago.2 In this context, recently we focused to modify our chemical strategy in order to target any type of substrate. Thus, we designed and synthesized new molecular architectures based on the 3D Janus tecton concept, suitable for self-assembly on surface by supramolecular interactions such as coordination, halogen bond or hydrogen bond.3 Here we present two different model pyridyl end-capped molecules: the pedestal P1, and the naked pillar NP pedestal incorporating a cyclophane core. After the attempt of several synthetic routes, P1 and NP were finally obtained in four and nine steps with an overall yield of 71% and 8%, respectively. Both compounds were characterized by NMR and infra-red spectroscopies, the absorption and emission properties being also studied. The pH-dependent absorption and emission were then studied for P1 : the first protonation of the pyridine unit could be easily observed with an isobestic point a 350 and 419 nm, respectively, but the second protonation was just slightly detected and its isobestic point could not be accurately estimated. In addition, the complexation of P1 with complementary entities (palladium II dichloride, terephtalic acid and 1,4-diodobenzene) to form supramolecular network was also investigated by infrared spectroscopy in solid state, the coordination with PdII beuing observed by as strong shift of the C-N bond stretching of the pyridine unit compared to the pedestal alone (1591→1609 cm-1). Finally, different attempts of supramolecular self-assemblies were carried out on surface. P1 behavior was first investigated by STM at the liquid/solid interface : as an exemple, an arrangement of the molecules on HOPG presenting a quasi-square lattice (a = 2.1 nm, b = 2.2 nm, α = 94°) self-assembled by hydrogen bonds between the pyridine unit and the methyl groups borne by the p-xylene core will be described, indicating strong intermolecular interactions between the molecules P1 leading to a supramolecular self-assembly independent of the underlying HOPG structure. [1] a) D Bleger, D Kreher, F Mathevet, A-J Attias, I Arfaoui, G Metgé, L Douillard, C Fiorini-Debuisschert and F Charra, Angewandte Chemie, Int. Ed. (2008), 47(44), 8412. b) D Bleger, F Mathevet, D Kreher, A-J Attias, A Bocheux, S Latil, L Douillard, C Fiorini-Debuisschert and F Charra, Angew. Chem., Int. Ed. (2011), 50 (29), 6562. c) P Du, D Bleger, V Bouchiat, D Kreher, F Mathevet, F Charra and A-J Attias, Beilstein J. Nanotech. (2015), 6, 632. [2] D Bleger, D Kreher, F Mathevet, A-J Attias, G Schull, A Huard, L Douillard, C Fiorini-Debuischert and F Charra, Angewandte Chemie, International Edition (2007), 46(39), 7404. [3] M. Auffray, 2014-2017 PhD, UPMC, unpublished results.

Resume : A non-coherent monochromatic light beam was passed through bacterial biofilm. Output light, after passage through biofilm, was studied, using synchronous scan mode in fluorimeter [1]. By keeping the emission and excitation monochromator at the same wavelength, only elastically scattered light was studied, at each wavelength. The measured light output from biofilm was enhanced, compared to input, due to coherence induction. Such coherence is a signature of Anderson localization. Gold nano-islands and gold nano-networks were synthesized using biofilm as a template. Percolation of gold (conductor) through biofilm template (dielectric) was studied using electron microscopy and Energy Dispersive X-Ray spectroscopy (EDX). Formed nano-composites showed a transition in metal percolation state (i.e. non-percolating to percolating state), as evident from critical enhancement of conductance and associated decrease in capacitance. Plasmonic properties of such gold-biofilm composites were studied using our previously reported method where, for non-coherent monochromatic input light beam, photonic coherence was achieved by passage through biocomposite, decorated with gold atoms. Coherence resulted in light amplification. The extent of enhancement was found to depend on gold precursor concentration. Peaks in the enhancement spectra corresponded to plasmonic peaks of Au. We thus infer that plasmon resonance phenomenon can alter the enhancement profile of light passing through gold-biocomposites. Further, the extent of enhancement showed a sharp transition that corresponded to metal atom percolation through the material. At lower gold concentrations, that is below percolation threshold, times enhancement decreased with increasing gold concentration. Above percolation threshold, times enhancement increased (ultimately saturated) with increasing gold concentration. Hence we conclude that an interplay between plasmon delocalization (due to metal atom percolation) and elastic scattering within biofilm cause this dual change in optical-coherence status and electrical properties of the gold-bio-composites. Such response also indicates that localized plasmonic edge scattering interferes destructively with Anderson localized photons. Whereas with the emergence of connected structures and consequent delocalized (and in phase) plasmon, there is constructive interference between output photons. Percolation threshold was confirmed by measuring current-voltage properties and capacitance- increasing conductance, with a concurrent decrease in capacitance, being the signature of percolation. We propose that biofilm-templated percolation clusters may constitute a family of smart materials that show dual changes in optical and electrical properties subjected to critical changes in the micro-environment. Fusion of the changes in electrical and optical properties also make them a potential candidate for designing smart biosensors. Reference: [1] Ray, Sanhita, and Anjan Kr Dasgupta. "Light Amplification by Biofilm and Its Polarization Dependence." bioRxiv (2017): 139741.

Resume : Electrode design and fabrication play a critical role in promoting the final performance of lithium ion batteries (LIBs). It is very difficult to control the geometry, architecture and porosity of the electrode by the conventional slurry coating techniques. Although free-standing aerogel has been developed for high performance electrode of LIBs, geometry and porosity are hard to adjust. In this work, 3D printing technology was employed to fabricate the aerogel electrode with controlled dimension, porosity, morphology and thickness. This artificial 3D printed aerogel was used as the electrode of LIBs without any additional binder or conductive agent. The cyclic voltammetry and galvanostatic charge/discharge measurements show that the 3D printed aerogel electrode exhibits excellent electrochemical performance.

Resume : Cellulose nanocrystals (CNCs) are remarkable nanoparticles with interesting liquid-crystalline properties, exploitable for cheap and bio-inspired photonics. They self-assemble into chiral nematic left-handed superstructures that selectively reflect left-handed circular polarized light (LCPL) and transmit right-handed circular polarized light. The wavelength of the reflected LCPL depends on the distant of a full rotation of the director and can be tuned extrinsically. In this work we thus explore their potential application for semiconducting devices capable of detecting CPL in the visible light range. For this we use inorganic semiconductors that respond in the desired wavelength, where the CNC films show maximum response. Indium-Gallium-Zinc-Oxide and Silicon are therefore in the spotlight for their photoresponse in the visible and UV region. We report results on the characterization of the CNC films regarding their photonic and electrochemical behavior as electrolytes and their final integration into transistors. Combining the photonic character of the CNC films with the employed light sensible semiconductors, the devices are capable of precise discrimination between LCPL and RCPL signals. These type of devices could find application in photonics, emission, conversion or sensing with CPL but also imaging or spintronics.

Resume : One of the numerous biosensor facilities has been established within our laboratory (FEMTO-ST Institute). In real terms, it is a platform for the biomolecules detection based on micro and nanotechnology, made up especially of a Ti:LiNbO3 (Z-Cut) Fabry-Perot cavity. The interaction between the specific analyte and the sensitive grafted layer on this platform was fairly consistent to achieve the variation in the spectral response. However, there are many technological factors that goes into making this platform enough complex to elicit the desired response. In this work, we will expose the spectral response obtained after reaction in a specific way with the targeted biological entity. Knowing that our system is structured to exhibit a photonic band gap effect, we have observed, after detection, an enlargement and a shift of about 27 nm of this band gap and also an attenuation of the transmitted signal up to 5.7 dB.

Resume : Optical methods represent a powerful and non-invasive tool to stimulate and probe biological matter1,2. In particular, conjugated molecules and macromolecules can offer an optimal platform to interface with cells and living organisms, given their relatively high optical absorption/emission cross sections, versatility in chemical synthesis and, in general, lower toxicity than the inorganic counterparts. In this context, gaining insights into the interaction and stimulation processes is a crucial step for the fabrication of actual medical devices 3,4. In this work, we employ a well-known conjugated polymer, namely poly(3-hexylthiophene), and a newly-synthesized azobenzene molecule to stimulate/influence the activity of living cells. Finally, we test the biocompatibility of such probes, with the view to apply them on a simple animal model. References 1. Rivnay, J., Wang, H., Fenno, L., Deisseroth, K. & Malliaras, G. G. Next-generation probes, particles, and proteins for neural interfacing. Sci. Adv. 3, e1601649 (2017). 2. Antognazza, M. R. et al. Shedding Light on Living Cells. Adv. Mater. 27, 7662–7669 (2015). 3. Martino, N., Ghezzi, D., Benfenati, F., Lanzani, G., Antognazza, M.R. Organic semiconductors for artificial vision. J. Mater. Chem. B. 1, 3768 (2013). 4. Mawad, D., et al. A conducting polymer with enhanced electronic stability applied in cardiac models. Sci. Adv. 2, e1601007 (2016).

Resume : Single-crystal thiophene-phenylene (TPCO) and furan-phenylene co-oligomers (FPCO) have a great potential for the application in optoelectronics and photonic devices, since they combine high luminescence and efficient charge transport. The promising approach to control the luminescent properties of organic semiconductor crystals is their doping by highly luminescent molecules. Recently, we have found that such a luminescent dopant can appear as byproducts in the course of TPCO chemical synthesis [1]. In this work, we report on study of luminescent impurities in single-crystal TPCO and FPCO by photothermal deflection spectroscopy. We detected the impurity absorption features in the TPCO and FPCO single crystals samples, which were grown from the vapor phase and from solution. Using reference samples of TPCO 5,5'-bis(4-(trimethylsilyl)phenyl)-2,2'-bithiophene (TMS-PTTP-TMS) crystals doped with a longer TPCO 5,5'''-bis(4-(trimethylsilyl)phenyl)-2,2':5',2'':5'',2'''-quaterthiophene (TMS-PTTTTP-TMS) and assuming, that the absorption is linearly dependent on the impurity concentration, we can estimate the impurity concentration in other similar samples. And it was observed that impurity distribution may be nonuniform in presented above material at a concentration of impurity 0.7% and more. Taking into account the TPCO and FPCO photoluminescence data, we discuss luminescent and photothermal techniques for study small amounts of dopants. The authors acknowledge funding from Russian Foundation for Basic Research (project #17-02-00841). [1] O.D. Parashchuk et al., 13th International Conference on Organic Electronics - 2017 (ICOE-2017). Book of abstracts. 2017, 48

Resume : Light harvesting management by using microstructural is a promising strategy for enhancing photoactive layer absorption in organic (OSCs) and perovskite solar cells (PSCs). Simple fabrication process of flexible based micro-cone array (MCA) structure textured on transparent polymer substrate was successfully demonstrated in this work for enhancing the photovoltaic performance. The flexible MCA films exhibit both high total transmittance of ~93 % and ultra-high haze of ~94 % in the wide range of visible wavelength and simultaneously shows self-cleaning properties by adjusting the aspect ratio of width and depth of cone array. Both rigid and flexible based OSCs and PSCs shows improvement in power conversion efficiency (PCE) owing to the absorption enhancement in photoactive layer cause by light trapping effect of MCA. Here, we show the flexible transparent conducting electrodes (TCEs) was embedded together with MCA textured. The mechanical properties of flexible MCA based OSCs and PSCs was highly flexible with 98 % retention from initial PCE at both 0 o and oblique incident angle 60 o after 2000 bending cycles at radius of 2 mm. This finding is promising for wearable technology where flexible solar cells device attached on curved objects yet could enhance light harvesting efficiency.

Resume : Some beetles and butterflies feature highly effective nanostructures producing non-bleaching structural colours. White beetles of the genus Cyphochilus, for example, are well-known for their scales producing a nearly perfect whiteness in a very efficient way with an astonishing low amount of material. Inspired by this biological architecture, we developed two techniques allowing for the fabrication of ultra-thin, yet highly scattering, white polymer films. White polymer films can be achieved by foaming with CO2 saturation [1]. By optimising pore diameter and fraction in terms broad-band reflectance through saturation parameters, we obtained very thin films comparable to the biomimetic inspiration. Even 24 µm thick films reflect up to 85% of the incident light. Highly scattering porous polymer films can be also achieved via phase separation [2]. By varying the molecular weight of the polymer, we modified the morphology of the porous films and therefore tuned their scattering properties. The achieved transport mean free paths are in the micrometer range, improving the scattering strength of analogous low-refractive index systems, e.g. standard white paper, by an order of magnitude. The produced porous films show a broadband reflectivity of approximately 75 % whilst only 4 µm thick. Both approaches can be utilized for various applications ranging from extremely white but ultra-thin coatings to scattering particles as potential replacements for titanium dioxide. [1] J. Syurik, R. H. Siddique, A. Dollmann, G. Gomard, M. Schneider, M. Worgull, G. Wiegand, and H. Hölscher. Sci. Rep. 7, 46637 (2017). [2] J. Syurik, G. Jacucci, O. D. Onelli, H. Hölscher, and S. Vignolini. Adv. Funct. Mater. (2018).

Resume : Optical measurements are widely used to monitor biological activities, such as changes in metabolism, gene expression, and ionic concentrations. Bulk heterojunction organic photodetectors have numerous advantages over inorganic technologies but have been limitedly investigated in biomedical applications, with no reported applications in the brain to date. An organic photodetector (OPD) with a simple structure and low leakage current is presented. This makes the optical sensor simple to fabricate and highly sensitive. The potential impact of this system is demonstrated through the application of monitoring intrinsic optical signals, changes in the optical properties of brain tissue related to cell volume and which can be related to biological events such as metabolism and hypoxia. These OPDs have high sensitivity and high temporal resolution, and thus, have a high potential for detecting of a wide range of pathophysiological and physiological events. The tunable properties of OPDs will allow this platform to be adapted to other optically-based sensing applications in living tissues. We anticipate that the simplicity of this OPD combined with its exceptional sensitivity and temporal resolution will prove an invaluable tool for numerous biological applications.

Resume : Bio-inspired nanostructures mimicking Moth’s eye have been researched for broadband and omnidirectional antireflection (AR) technologies. Despite advances in nanopatterning methods and their fascinating functions, mechanical vulnerability has always been pointed out as a disadvantage of the AR nanostructures. This research suggests a unique AR strategy for producing sustainable AR surfaces by constructing nanopatterns with a transparent shape memory polymer (SMP). A unique SMP with facile shape-recovery and transparency was synthesized through tri-copolymerization, where the transition temperature was specially tuned to near body temperature. A synthetic reaction scheme, chemical composition, and a nanopatterning method for the SMP were introduced. A shape recovery behavior of the SMP nanopatterns was confirmed from scanning electron microscope (SEM) images. Light transmittance of the samples was measured experimentally according to shape state of the SMP nanopatterns, and it was confirmed that the shape recovery function restored the original AR performance. Theoretical transmittance was calculated based on effective medium theory to propose an underlying mechanism of the sustainable AR. Omnidirectional antireflectivity of the nanopatterns was examined by measuring oblique incident transmittance. Sustainable self-cleaning with the SMP nanopatterns was confirmed experimentally. We hope that the unique approach proposed in this study will provide new insights into a field of biomimetic optics.

Resume : Moth-eye-inspired periodic arrangements of nanostructures are highly useful for antireflection applications. There are different methods to create such nanostructures, primarily involving patterning and lithography. Mimicking these structures in an easy, inexpensive and reproducible route is always an advantage. Here we use combination a simple dewetting route and reactive ion etching process to grow silica nanopillars. By using bimetallic nanostructures, we can fine tune the particle sizes and hence control the pillar dimensions. Thin films are metastable in the as-deposited state. When these films are annealed below the melting point they tend to break into individual agglomerates. This process is known as solid-state dewetting and is driven by surface energy minimization [1]. Copper and silver are mutually insoluble, and addition of silver nanoparticles suppresses dewetting of copper thin films and controls the nanoparticles density [2]. Nobel metal nanoparticles such as copper and silver exhibit localized surface plasmon resonance which can be utilized to enhance the optical properties suitable for optoelectronic devices. Bimetallic nanoparticles have excellent optical, electronic and catalytic properties as compared to monometallic nanoparticles [3]. Dewetting is an easy and cost-effective technique to form bimetallic nanoparticles. Initially, we synthesized monometallic and bimetallic nanoparticles by solid state dewetting of copper and copper-silver bilayer films to form mono and bimetallic particles on oxidized silicon substrates. After the formation of nanoparticles, samples are subjected to reactive ion etching for different times. Nanoparticles acts as a mask for nanopillars formation and the pillar heights can be tuned by changing the etching duration. After the formation of nanopillars the metallic particles are removed using nitric acid leaving behind the silica nanopillars. UV – Vis reflectance studies show that the nanopillars exhibit low reflectance around 12% as compared to 45% of bare silicon. References [1] C. V. Thompson, “Solid-State Dewetting of Thin Films,” Annu. Rev. Mater. Res., vol. 42, pp. 399–434, 2012. [2] K. Kumar and P. Swaminathan, “Role of silver nanoparticles in the dewetting behavior of copper thin films,” Thin Solid Films, vol. 642, pp. 364–369, 2017. [3] A. Zaleska-Medynska, M. Marchelek, M. Diak, and E. Grabowska, “Noble metal-based bimetallic nanoparticles : the effect of the structure on the optical , catalytic and photocatalytic properties,” Adv. Colloid Interface Sci., vol. 229, pp. 80–107, 2016.

Resume : Perovskite solar cells (PSC) have been attracting strong interest because of their rising efficiencies coupled with their processing via evaporation and printing techniques. Here we present research focused at developing device architectures and materials, including novel solution-processed transport layers, that produce devices with remarkable performance under artificial indoor illumination. Photovoltaic (PV) cells manufactured on glass achieved the highest power outputs reported for a PV technology under typical 200-400 lx indoor LED illumination with maximum power densities of MPD = 41.6 µW/cm2 at 400 lx (and power conversion efficiencies, PCE, of 27%). For indoor applications, thin flexible devices are particularly interesting because they can be seamlessy integrated on surfaces, even curved ones, although fabrication is complicated by having to maintain processing temperatures below 150 C to avoid deformation of plastic substrates. The quality of low temperature electron transport layers developed was important in achieving not only strong outputs for PV cells under standard test conditions (PCE = 14.8%) but particularly under low intensity indoor illumination (MPD = 19.2 μW/cm2, PCE = 13.3%). The unparalleled performance as indoor light harvesters, paves the way for perovskite solar cells to contribute strongly to the powering of indoor optoelectronics of the future (e.g. smart autonomous indoor wireless sensor networks, internet of things).

Resume : Organometal halide perovskite solar cells (PSCs) have demonstrated high power conversion efficiencies (PCEs) of > 22% yet they face the challenge of long term environmental stability, especially towards ultraviolet (UV) light. In this contribution, we will demonstrate that UV triggered instability of methylammonium lead iodide (CH3NH3PbI3) based solar cells is spectral dependent. For this purpose, two UV light sources (310-316 nm and 360-380 nm) are used to stress PSCs. Only the short UV wavelength region (310-316 nm) is found to degrade the perovskite absorber material. These findings are investigated for different device architectures fabricated with a range of electron transport layers (ETLs) and perovskite material; such degradation occurs regardless of the chosen ETL. However, various ETLs might exhibit different degradation rates depending on the self-stability of ETLs and the nature of their interface with perovskite absorber. Reliability of UV stability assessment of PSCs is evaluated by translating the UV exposure times into sun hours. The photon flux of relevant wavelengths in AM 1.5G spectrum is compared to the UV illumination bands to express the exposure time in terms of sun hours for comparable results. Solution strategies are suggested to effectively suppress this degradation by using luminescent downshifting (LDS) materials or completely get rid of UV instability issue by cutting-off harmful UV wavelengths at cost of negligible loss of photocurrent.

Resume : The demand for large area high-energy radiation detection systems combining high sensitivity and low-cost fabrication, has pushed the research in the last ten years to develop and design both novel materials and device geometries. Organic semiconductors have attracted a great attention1. However, their low atomic number strongly limits the high-energy radiation absorption and, blending the organic solution with high Z nanoparticles2,3 is necessary to maximize their radiation absorption. Hybrid organic-inorganic perovskites have been recently proposed as alternative materials for X- and γ-photon direct detection, thanks to their high Z atoms, combined with high charge mobility4. In this work we report on thin film X-ray detectors made of solution processed Cesium-containing triple cation perovskite, namely Cs0.05(MA0.17FA0.78)Pb(I0.8Br0.2)3 (CsFAMA), where cesium (Cs) has added to mixed organic cations (methylammonium (MA) and formamidinium CH3(NH2)2 + (FA)) and mixed halides (I and Br). Such a triple cation perovskite formulation has been already demonstrated to overcome the thermal and structural instabilities of MA/FA mixture, providing high efficiency perovskite solar cells5. We demonstrate how X-ray detectors based on solution processed CsFAMA thin film possess a high sensitivity, with values up to 80 µC mGy-1 cm-3 in short-circuit conditions, higher than the values reported for MAPbI3 based detector with similar operating conditions4, and up to 1,000 µC mGy-1 cm-3 when operated under small (i.e. -0.4V) reverse bias condition. [1] L. Basiricò et al., Nat. Comm. 7, 13063, 2016. [2] C.A. Mills et al., J. Phys. Appl. Phys., 46, 275102, 2013. [3] A. Ciavatti et al. App.Phys.Lett., 111, 183301, 2017 [4] S. Yakunin et al., Nat. Phot., 9, 444, 2015 [5] Saliba et al., Energy Environ. Sci., 9, 1989, 2016

Resume : Two dimensional hybrid lead halide perovskites, often referred to as self-assembling organic-inorganic quantum well structures sustain strong and stable excitons at room temperature, a desirable characteristic for photonic and quantum optoelectronic applications [1]. Their optical properties exhibit a broad variety of phenomena, ranging from broadband photoluminescence in some compounds [2], the appearance of an excitonic fine structure at low temperatures [3] and biexcitonic emission [4]. Combining optical and structural probes, we elucidate the role of crystal structure in the photophysics of 2D perovskites. Based on comprehensive spectroscopic investigation of (PEA)2PbI4, one of the most widely used 2D perovskites, we discuss the excitonic fine structure using a modified two-dimensional Wannier formalism and show that it depends strongly on lattice fluctuations and crystalline distortion induced by the interlayer organic cation. Using the temperature to control the degree of disorder we demonstrate via two-dimensional electronic spectroscopy that the material exhibits stable biexcitons with values similar to the transition dichalchogenides. Our findings stress the complexity of excitonic properties in this class of hybrid materials. [1] Lanty, et al., J., Phys. Rev. B, 2011, 84, 195449 [2] Cortecchia et al., J. Am. Chem. Soc., 2017, 139 (1), pp 39–42 [3] Straus et al. , J. Am. Chem. Soc., 2016, 138 (42), 13798-13801 [4] T. Ishihara, et al., Surf. Sci., 1992, 267 (1-3), 323-326

Resume : Organic solar cells (OSC) are a promising technology for low-cost, versatile, accessible solar energy. Non-fullerene acceptors (NFA) are a new class of electron accepting material with reportedly high efficiencies (over 11%), tunable molecular energy levels and lower synthesis cost.[1] One such NFA, Eh-IDTBR, was shown to form burn-in free devices (no degradation under illumination in nitrogen) when utilised with PCE11, in contrast to fullerene-based devices.[2] This rapid development of NFA over the past two years provides promise for high performance, stable OSC in the future. However, the intrinsic stability of NFA’s and their degradation in the presence of oxygen are unknown; both of which crucial in understanding NFA long-term stability. Here, a combination of advanced characterisation techniques were used to investigate the intrinsic stability of rhodanine-flanked NFA films and devices. It was observed that NFA stability is strongly linked to the yield of superoxide anions, mediated by NFA LUMO. The results of this study signify new electron acceptors with a low-lying LUMO can be designed to provide improved intrinsic stability. [1] W. Zhao et al., Adv. Mater. 2016, 28, 4734 [2] H. Cha et al., Adv. Mater. 2017, 29, 1701156

Resume : Photonic materials typically require a high degree of order to produce a well-defined optical band gap. While photonic materials in nature are ubiquitous and are known to give rise to brilliant optical signatures, the degree of order in most biological photonic materials is not very high. My presentation focusses on the structural properties of grating-like patterns on the surface of flower petals, the optical signature they produce, and the role they play for their recognition by pollinators (bees). Furthermore, I will give an overview and perspective of the interplay of photonic order and disorder in other organisms, such as butterflies and beetles.

Resume : The tunability of the photonic band gap of photonic crystals has attracted a significant attention in the last decades, with applications in sensing, lighting, and displays. Here, we present the electric field-induced tuning of the light transmission in a multilayer sandwiched between ITO electrodes, made by alternating layers of silver nanoparticles and titanium dioxide nanoparticles. We show a shift of around 10 nm for an applied voltage of 10 V. The shift can be ascribed to an accumulation of charges at the silver/TiO2 interface due to electric field, resulting in an increase of the number of charges contributing to the plasma frequency in silver. This gives rise to a blue shift of the silver plasmon band, with concomitant blue shift of the photonic band gap. We also propose the fabrication of 1D photonic crystal and microcavities employing a magneto-optical material as TGG (Tb3Ga5O12). With these structures we can observe a shift of 22 nm with a magnetic field of 5 T, at low temperature (8 K). Finally, we describe the possiblity to tune the gap of a doped semiconductor nanoparticle based multilayer by photodoping.

Resume : Quantum confinement of the electronic wave function allows to open a finite band-gap in the graphene electronic structure. For instance, the nanofabrication of 2D graphene nanomesh[1], 1D graphene nanoribbons[2] and 0D graphene quantum dots[3], has paved the way for the development of the promising field of nanographene optoelectronics. In this context, the synthesis of molecular graphene via bottom-up processes permits to obtain monodisperse nanographene, with defined physical and chemical properties[4]. The luminescence features exhibited by molecular graphene[5], in particular, has made these carbon-based materials of great interest for plasmonic and photonic applications, among others. Here, we demonstrate that the optical gain properties of a newly synthesised and very luminescent (absolute PL quantum yield 79%) nanographene molecule, namely dibenzo[hi,st]ovalene (DBOV 1) can be preserved in the solid state by simply blending the active molecule with polystyrene (PS). Interestingly, we were able to observe amplified stimulated emission (ASE) for a nanographene:PS 1% weight ratio at a relatively low power threshold (60 µJ cm-2)[6]. In addition, we show that the stimulated emission signal can be modulate in the fs time-regime (500 fs), by exploiting the spectral overlap between such signal and the absorption of charges. References [1] J. Bai, X. Zhong, S. Jiang, Y. Huang, X. Duan, Nat Nanotechnol, 2010, 5, 190-194. [2] A. Narita et al., Nature chemistry, 2014, 6, 126-132.. [3] B. Trauzettel, D. V. Bulaev, D. Loss, G. Burkard, Nature Physics, 2007, 3, 192-196. [4] A. Narita, X. Y. Wang, X. Feng, K. Mullen, Chem Soc Rev, 2015, 44, 6616-6643. [5] S. J. Zhu et al., Carbon, 2014, 77, 462-472. [6] G.M. Paternò et al., Angewandte Chemie, 2017, 56, 6753-6757.

Resume : We develop fabrication methodologies based on self-assembly of polymers and colloids in order to produce materials and surfaces, in which optically resonant nanostructures induce unusual optical properties for visible wavelengths. We produce anisotropic nanocomposites by the assembly of gold nanoparticles within spontaneously ordered matrices of diblock copolymers. In particular, we study periodic lamellar stacks of layers of gold particles and layers of pure polymer. Detailed structural study and measure of their anisotropic effective dielectric permittivity by spectroscopic ellipsometry show that they constitute hyperbolic metamaterials, allowing for the propagation of large magnitude wavevectors, which would be evanescent in a dielectric. We also study plasmonic nanoclusters made of metallic satellites surrounding a dielectric core by colloidal engineering. The individual clusters present a strong magnetic scattering, as shown by polarization resolved spectroscopic light scattering measurement on a liquid suspension. We interpret this scattering as due to an induced magnetic dipole related to plasmonic current loops between coupled satellite nanoparticles. These complex resonators can then be deposited on surfaces or assembled into a bulk material. Variable angle spectroscopic ellipsometry measurements indicate that a thick dense film of such objects can be described by the magnetic permeability with values between 0.8 and 1.4, over the visible light wavelength range.

Resume : Here we demonstrate, for the first time, lasing action from fully-transparent nanostructured porous silicon (PSi) monolithic microcavities (MCs) infiltrated with a well-known polyfluorene derivative, namely poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO). We fabricated asymmetric PSiMCs with relatively high quality-factor (about 100) operating in the visible region (resonance wavelength at 466 nm) via one-step electrochemical etching of crystalline silicon, followed by thermal oxidation and transfer-printing onto a transparent polydimethylsiloxane (PDMS) slab. The emitter was infiltrated in the transfer-printed PSiMCs via drop-casting at room temperature. Remarkably, the PFO-infiltrated PSiMCs support single-mode lasing at the resonance wavelength of 466 nm, with line width of ~1.3 nm and lasing threshold as low as 5 nJ. Furthermore, time-resolved photoluminescence shows a significant shortening (about 57%) of the emission lifetime in the PSiMC, with respect to non-resonant structures, thus confirming a variation of the radiative decay rate of the excitation due to Purcell effects. Our findings break a new ground on the silicon photonics arena by envisaging the bottom-up integration of low-threshold PSi organic lasers for the next generation of on-chip photonic circuits and networks.

Resume : Current implant technology uses electrical signals at the electrode-neural interface. This approach has fundamental problems which limit both the performance and safety of the implants, bearing high invasiveness. Inducing light sensitivity in living organisms is an alternative approach that provides ground breaking opportunities in neuroscience. Optogenetics is a spectacular demonstration of this, yet limited by the viral transfection of exogenous genetic material. In this talk I will describe approaches to artificially NON-genetically enhance or induce light sensitivity in cells or organism by using light-responsive nanostructures (0.1-1 ?m) or molecular actuators that trigger signaling cascades. The photophysics of actuators is fully characterized, both in vitro as well in vivo, and their effect on cells investigated.

Resume : We aim to develop an artificial photoreceptor based on photovoltaic organic materials for future retinal prosthetic devices. For that, we anticipate a purely photoelectrical stimulation pathway by capacitive coupling of transient photocurrents instead of direct electronic charge injection. By electrophysiological patch clamp recordings, we probe the response of neuronal model cells to photoexcitation by short light pulses, excluding other pathways than a photoelectrical coupling, to be of passive nature only. [1] We finally evoke an active response of the cells by improving the photoreceptor architecture and adapting the stimulation protocol to allow for other excitation pathways, such as photothermal coupling. [2] While the amplitude of the capacitive transient photocurrent is easily exceeding the cellular stimulation threshold, we identify its duration to be well below this threshold. Since the pulse duration appears to be inherently limited by the transient nature of the photocurrent, we tend to rule out the feasibility of the capacitive coupling approach for retinal prosthetic devices, but still emphasize the future perspective of electronically coupling photovoltaic photoreceptors based on soft organic materials. [1] O. S. Abdullaeva, M. Schulz, F. Balzer, J. Parisi, A. Lützen, K. Dedek, M. Schiek, Langmuir 32 (2016) 9297-9302. [2] N. Martino, P. Feyen, M. Porro, C. Bossio, E. Zucchetti, D. Ghezzi, F. Benfenati, G. Lanzani, M. R. Antognazza. Sci. Rep. 5 (2015) 8911.

Resume : Photonic biomedical devices gain in importance in healthcare and become significantly more versatile and compatible with human tissue if their components are readily metabolizable. We demonstrate applications of biodegradable and -resorbable materials as active optoelectronic components and as light outcoupling optics for organic light-emitting devices. We introduce a vitamin B2 derived emitter, riboflavin tetrabutyrate and its utilization in a solution processed organic light-emitting diode (OLED). Addition of tailored side groups changes the vitamin’s solubility to enable the formation of homogeneous and smooth films via solution processing. Using grazing incidence wide-angle X-ray scattering, we show that crystallinity and π π stacking interactions decrease. We demonstrate riboflavin tetrabutyrate OLEDs with a maximum luminance of 10 cd/m2 and external quantum efficiency of 0.02% and 640 nm peak emission which exceed performance of comparable devices by five orders of magnitude.1 Further, we present polycaprolactone as solid polymer electrolyte and its ion dissolving abilities in the active layer of light-emitting electrochemical cells.2 On the light management side we demonstrate widely established light outcoupling solutions using biological polymers (shellac, cellulose etc.) and printing techniques to reduce substrate mode losses in OLEDs. 1. Jürgensen N. et al. ACS Sustain. Chem. Eng.; 2017; 5:5368-5372. 2. Jürgensen N. et al. Sci. Rep.; 2016; 6:36643.

Resume : Thin films spin-casted from anilino-squaraine dyes, blended with a commercial fullerene acceptor, are of interest as possible artificial photoreceptors for vision restoration [1]. Here, we investigate the anilino-squaraine 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl]-squaraine (SQIB) blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) on indium tin oxide (ITO)-coated glass substrates. Depending on the annealing temperature after deposition, two polymorphic phases (monoclinic and orthorhombic) with differing morphological and optical properties form. These phases also exhibit different electric surface potentials determined by Kelvin probe force microscopy. The stability of the films is monitored by atomic force microscopy and spectroscopy during white light illumination and immersion in Ringer’s solution. Bleaching, roughening, and removal of material within days is observed. This aging can be largely suppressed by prior coating with a thin layer of silica, thus providing us a stable platform for proof-of-principle, mechanistic investigations. [1] O. S. Abdullaeva, M. Schulz, F. Balzer, J. Parisi, A. Lützen, K. Dedek, M. Schiek, Langmuir 32, 9297-9302 (2016).

Resume : Photosynthetic microorganisms represent a plentiful source of photoactive micro/nano structures. Combining such specialized structures optimized by billions of years of evolution with tailored organic molecules paves the way for intriguing new materials for photonics and optoelectronics. The lecture will present two examples of photonic biohybrid materials obtained in our laboratories: i) Supramolecular photoconverters resulting from chemical modification of photosynthetic bacterial enzymes. Chemical modifications are introduced to boost the performance of the resulting hybrids vis-à-vis the native protein[1] and to assemble the photoenzyme molecules onto active surfaces for applications in optoelectronic devices.[2] ii) Photonic nanostructures obtained by in vitro and/or in vivo functionalization of ornate biosilica shells of diatoms microalgae[3] with light-emitting organic molecules.[4] The lecture will discuss the logic behind designing and synthesizing these biohybrid assemblies, highlighting the challenges raised by the controlled functionalization. New concepts for photonic materials’ design and synthesis can be envisaged by combining the biotechnological production and the tools of organic synthesis. References: [1] F. Milano et al. Angew. Chem. Int. Ed. 2012, 51, 11019 [2] A. Operamolla et al. J. Mater. Chem. C 2015, 3, 6471 [3] R. Ragni et al. Adv. Mater. 2017, DOI: 10.1002/adma.201704289 [4] R. Ragni et al. Adv. Funct. Mater. 2018, DOI: 10.1002/adfm.201706214

Resume : Light reflected by a photonic crystal is determined by the structure and the properties of the building materials. The photonic nanoarchitectures occurring in the wing scales of butterflies are nanocomposites of chitin and air [1]. As changes of the surrounding atmosphere affect the reflected light [2], one can obtain qualitative and quantitative information regarding the vapor(s) in the air-vapor mixture. The changes depend on the capillary condensation in the structure, the sample temperature [3], and the surface treatment [4] of the wings, which are major factors of the sensing efficiency. These parameters make the sensing a complex process. Even if a single vapor in artificial air is measured, data preprocessing and multivariate analysis methods are needed for proper determination of the vapor concentration used. We aim the analysis of vapor mixtures in air, in this way approaching the real applications where the sensor is exposed to multiple reagents in the same time. As a first step we investigated different concentrations of ethanol in water. We found that 100% ethanol and 100% H2O have well distinguished responses, while the intermediate concentrations of ethanol fall within the two extremes. Further mixtures will be discussed. [1] L. P. Biró, J. P. Vigneron, Laser Photon. Rev. 2011, 5, 27 [2] R. A. Potyrailo et al. Nat. Photonics 2007, 1, 123–128 [3] K. Kertész et al. Appl. Surf. Sci. 2013, 281, 49–53 [4] G. Piszter et al. Opt Exp 22 (2014) 22649

Resume : Radial p-i-n junctions constructed over vertical silicon nanowires (SiNWs) are advantageous 3D architectures to explore advanced photovoltaic and bio-inspired photo-detection applications. Built upon our previous works on high performance radial junction a-Si:H thin film solar cell,[1-2] we here propose and demonstrate a new radial tandem junction (RTJ) super-rod structure, which consist of coaxially stacking hydrogenated amorphous silicon (a-Si:H) PIN junctions upon SiNWs, resembling to the live retinal cells in terms of both geometry and dimension. Imitating the natural rod or cone cells in human eyes has inspired a biomimetic design of filter-free color sensing photodetector with the aid of 3D nano photonic engineering. These RTJ units enjoy a unique wavelength-selective and cavity-mode assisted light responses in the inner and the outer radial PIN junctions, which are readily tunable to achieve natural RGB color discrimination in the RTJ rod-cells without the need of any filter system.[3] This unique RTJ design could indicate a new 3D implementation of color sensing photodetectors enabled by advanced nano photonic structuring and engineering. Furthermore, we present also a new hybrid radial junction structure that marries inorganic CsPbX3 (X=Cl, Br, I or hybrid among them) perovskite quantum dots (IPQDs) to radial junction structures to achieve ultrafast and highly sensitive ultraviolet (UV) detection in solar-blind spectrum.[4] A fast solar-blind UV detection has been achieved, with rise/fall response time scales of 0.48/1.03 ms and a high responsivity of 54 mA/W@200 nm (or 32 mA/W@ 270 nm), without the need of any external power supply. These results pave the way towards large area manufacturing of high performance Si-based perovskite UV detectors in a scalable and low-cost procedure. References [1] S. Misra, L. Yu, M. Foldyna, P. Roca i Cabarrocas, SOL. ENERG. MAT. SOL. C. 2013, 118, 90. [2] S. Qian, S. Misra, J. Lu, Z. Yu, L. Yu, J. Xu, J. Wang, L. Xu, Y. Shi, K. Chen, P. Roca i Cabarrocas, Appl. Phys. Lett. 2015, 107, 043902. [3] F. Yang, J. Wang, J. Lu, Z. Yu, L. Yu, J. Xu, Y. Shi, K. Chen, P. R. I. Cabarrocas, Advanced Optical Materials 2017, 1700390. [4] J. Lu, X. Sheng, G. Tong, Z. Yu, X. Sun, L. Yu, X. Xu, J. Wang, J. Xu, Y. Shi, K. Chen, Adv. Mater. 2017, 29, 1700400.

Resume : Graphene has focused intensive research in the past ten years due to its unusually and unique properties.[1] In particular, its non-covalent functionalization with organic molecular building blocks has appeared as a promising way to modulate its properties in view of functional applications :[2] this bottom-up elaboration process by physisorption onto graphene of mostly planar molecules (tectons) is now well. More recently, self-assembling building blocks of increasing three-dimensional (3D) complexity emerged, in particular following the so-called Janus tecton paradigm :[3] these systems have been proposed as a platform to attach functional molecular moieties at a controlled distance from graphene.[4] This is why here we report a first fluorescent molecular self-assembly on graphene. More precisely, the quenching of the fluorescence of the adsorbed dye by the adjacent graphene is avoided at the molecular scale based on a spacer approach, through a specifically designed (3D) dual-functionalized self-assembling building block whom synthesis is described. Moreover, the spontaneous ordering of the adsorbed layer is investigated by scanning tunneling microscopy (STM) whereas the resulting optical properties of the whole graphene-dye hybrid system are characterized by absorption and fluorescence micro-spectroscopies.[5] [1] A. K. Geim, Graphene: Status and Prospects. Science, 324 (5934), 1530 (2009). [2] J. M. MacLeod et al., Molecular Self-Assembly on Graphene. Small, 10 (6), 1038 (2008). [3] D Bleger, D. Kreher et al., Angew. Chem., Int. Ed., 50 (29), 6562 (2011). [4] a) P. Du, D. Kreher et al., Beilstein J. Nanotechnology, 6, 632 (2015) b) P. Du, D. Kreher et al., Angew. Chem. Inter. Ed., 53 (38), 10060 (2014). [5] S Le Liepvre, P Du, D Kreher, F Mathevet, A-J Attias, C Fiorini-Debuisschert, L Douillard and F Charra. ACS Photonics (2016), 3 (12), 2291-2296.

Resume : Development of compact two photon pumped lasers (TPPL) converting infra-red radiation into visible is a challenging task nowadays. Organic dyes are often used for creation microlasers since they can be easily assembled into resonators of various shapes. One of the most promising materials for TPPL is DCM (4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran) dye due to its high value of two-photon absorption cross-section. Here we report on the observation of room-temperature two-photon lasing in DCM spherical microresonators made by self-assembly method. Microspheres with the diameter of 5-10 um were studied using a nonlinear-optical microscopy setup based on the titanium-sapphire femtosecond laser operating at the wavelength of 800 nm. The fundamental beam was focused into a spot of 1 um in diameter. We demonstrate that whispering gallery modes (WGM) are excited in the DCM microspheres in the spectral range of the two-photon fluorescence (TPF). Polarization-resolved nonlinear-optical microscopy shows that both TE- and TM-polarized WGMs appear, with the quality factor up to 300 and the free spectral range of 10-20 nm. Lasing effect was observed for individual WGMs as a pronounced deviation of the TPF intensity dependence from quadratic power law and being undisturbed in non-resonant case. Numerical modelling supports the experimental data.

Resume : Organic light emitting transistors (OLETs) integrate light-emission of an OLED with logic functions of a transistor into a single device configuration. This integration provides access to low cost and simplified display pixels as it removes the requirement of separate high mobility-driving transistors. Despite of their technological potential and a tremendous progress in OLETs in last decade, achievement of high luminescence efficiency and higher charge transport in single layer of organic semiconducting materials is a challenging task. Herein, we present small molecule and polymeric material and device structure strategy to achieve high performance in OLETs. These results represent a significant advancement in OLET technology and can be seen as an important milestone towards next generation display, injection lasing and sensor technologies.

Resume : Over the last decade, organic light emitting diode (OLED) has been a great success in application thank to versatile organic characteristics. However, organic laser diode has not been demonstrated yet mainly due to the high lasing threshold under electrical pumping which is several orders higher than available OLED current density. In order to deal with this issue, two aspects can be considered; firstly the ultra short pulsed electrical excitation of OLED allowing higher current density and secondly the fabrication of low laser threshold microcavities in transparent and conductive oxide electrodes. In this context, we previously developed a new design of microwave electrodes on indium tin oxide (ITO) that enable to pump OLED with ultra short electrical pulses (down to 2.5 ns). In this work we present for the first time the design and fabrication of a photonic crystal (PhC) microcavity onto the ITO coplanar waveguide and report the effect of the differents process parameters. The nanostructures have been obtained using ebeam lithography combined with inductively coupled plasma reactive ion etching (ICP-RIE) in boron trichloride (BCl3 ) and chlore (Cl2 ) plasma. The triangular lattice configuration consisting of air holes radius of 210 nm and lattice constant of 290 nm was successfully transfered throught the 300 nm hydrogen silsesquioxane (HSQ) resist mask to the 150 nm thick ITO layer on glass substrate achieving straight and smooth sidewall.

Resume : We create zero-dimensional exciton-polariton condensates at ambient conditions by optically exciting a ladder-type conjugated polymer placed inside a tunable optical microcavity. In the upper mirror of the cavity we define a Gaussian-shaped defect for the in-plane confinement. By detuning the cavity length, we show strong coupling between the excitonic resonance of the conjugated polymer and the individual cavity modes revealing a Rabi splitting of 92 meV. By exciting the system above threshold we observe polariton condensation in the zero-dimensional system. Non-linear emission intensity, spectral line-narrowing and characteristic blue shift are shown as a function of excitation power. In addition, we studied the condensation in momentum space and first order coherence properties. We also demonstrate the possibility to create photonic molecules by adding another Gaussian defect close by. In such a system, the tunnel coupling leads to the formation of bonding and antibonding modes which characterize the formation of the photonic molecule. Our results, represent the basic building blocks for realizing an analog polariton quantum simulator working at ambient conditions.

Resume : The concept of printing nanomaterials paves the way for cheap and scalable fabrication of photonic devices. We present a novel technology for printing nanomaterials on a submicron scale. In this contribution, we mainly focus on submicron lines assembled from metallic nanoparticles. Yet, the XTPL approach allows to print different nanomaterials, e.g., semiconductor nanoparticles. The feature size of the printed structures is in the range between 100 nm to 3 μm, with the width-to-height aspect ratio around 1. The XTPL approach is based on a guided assembly of nanoparticles using the dielectrophoretic attraction. During the printing process, the printing head deposits an ink, i.e., nanoparticles in a liquid solution, on a non-conductive substrate, such as glass or flexible foil. Afterwards an external alternating electric field causes nanoparticles to assemble and form a line. The properties of the lines are tuned by changing 1) amplitude, shape, and frequency of the electrical signal; 2) physicochemical properties of the inks; 3) shape and size distribution of nanoparticles. This technology has been already implemented in the XTPL Submicron Lab Printer. There is a wide range of possible applications of the XTPL approach. One of the most promising is the fabrication of biosensors and lab-on-chip devices. In this regard, the surface of nanoparticles can be functionalized to provide both optical and electrical sensing.