Organic Donor-Acceptor-Donor Trimers Nanoparticles Stabilized by Amphiphilic Block Copolymers for Photocatalytic Generation of H2.

Photocatalytic generation of H2 via water splitting emerges as a promising avenue for the next generation of green hydrogen due to its low carbon footprint. Herein, a versatile platform is designed to the preparation of functional π-conjugated organic nanoparticles dispersed in aqueous phase via mini-emulsification. Such particles are composed of donor-acceptor-donor (DAD) trimers prepared via Stille coupling, stabilized by amphiphilic block copolymers synthesized by reversible addition-fragmentation chain transfer polymerization. The hydrophilic segment of the block copolymers will not only provide colloidal stability, but also allow for precise control over the surface functionalization. Photocatalytic tests of the resulting particles for H2 production resulted in promising photocatalytic activity (≈0.6 mmol g-1 h-1). This activity is much enhanced compared to that of DAD trimers dispersed in the water phase without stabilization by the block copolymers.

Tuning the Aggregates of Thiophene-based Trimers by Methyl Side-chain Engineering for Photocatalytic Hydrogen Evolution.

Organic π-conjugated semiconductors (OCSs) have recently emerged as a promising alternative to traditional inorganic materials for photocatalysis. However, the aggregation of OCSs in photocatalytic aqueous solution caused by self-assembly, which closely relates to the photocatalytic activity, has not yet been studied. Here, the relationship between the aggregation of 4,7-Bis(thiophen-2-yl) benzothiadiazole (TBT) and the photocatalytic activity was systematically investigated by introducing and varying the position of methyl side chains on the two peripheral thiophene units. Experimental and theoretical results indicated that the introduction of -CH3 group at the 3-position of TBT resulted in the smallest size and best crystallinity of aggregates compared to that of TBT, 4- and 5-positions. As a result, TBT-3 exhibited an excellent photocatalytic activity towards H2 evolution, ascribed to the shorten charge carrier transport distance and solid long-range order. These results suggest the important role of aggregation behavior of OCSs for efficient photocatalysis.

Synthesis and Characterization of Vanillin-Based π-Conjugated Polyazomethines and Their Oligomer Model Compounds.

The synthesis of π-conjugated polymers via an environmentally friendly procedure is generally challenging. Herein, we describe the synthesis of divanillin-based polyazomethines, which are derived from a potentially bio-based monomer. The polymerization is performed in 5 min under microwave irradiation without any metallic catalyst, with water as the only by-product. The vanillin-based polyazomethines were characterized by SEC, TGA, and UV-Vis spectroscopy. Model compounds were designed and characterized by X-ray diffraction and UV-Vis spectroscopy. The structure/properties study of vanillin-based azomethines used as models allowed us to unequivocally confirm the E configuration and to highlight the cross-conjugated nature of divanillin-based polymers.

Optical Gain in Semiconducting Polymer Nano and Mesoparticles.

The presence of excited-states and charge-separated species was identified through UV and visible laser pump and visible/near-infrared probe femtosecond transient absorption spectroscopy in spin coated films of poly[N-9″-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) nanoparticles and mesoparticles. Optical gain in the mesoparticle films is observed after excitation at both 400 and 610 nm. In the mesoparticle film, charge generation after UV excitation appears after around 50 ps, but little is observed after visible pump excitation. In the nanoparticle film, as for a uniform film of the pure polymer, charge formation was efficiently induced by UV excitation pump, while excitation of the low energetic absorption states (at 610 nm) induces in the nanoparticle film a large optical gain region reducing the charge formation efficiency. It is proposed that the different intermolecular interactions and molecular order within the nanoparticles and mesoparticles are responsible for their markedly different photophysical behavior. These results therefore demonstrate the possibility of a hitherto unexplored route to stimulated emission in a conjugated polymer that has relatively undemanding film preparation requirements.

Design of Potassium-Selective Mixed Ion/Electron Conducting Polymers.

An approach providing cation-selective poly-(3,4-ethylenedioxythiophene)(PEDOT):polyelectrolyte-mixed conductors is presented in this communication based on the structural modification of this ambivalent (ionic and electronic conductive) polymer complex. First, an 18-crown-6 moiety is integrated into the styrene sulfonate monomer structure as a specific metal cation scavenger particularly targeting K+ versus Na+ detection. This newly functionalized monomer is characterized by 1 H NMR titration to evaluate the ion selectivity. Aqueous PEDOT dispersion inks containing the polymeric ion-selective moieties are designed and their electrical and electrochemical properties analyzed. These biocompatible inks are the first proof-of-concept step towards ion selectivity in view of their interfacing with biological cells and microorgans of interest in the field of biosensors and physiology.

Tailoring the Chemical Composition of LiMPO4 (M = Mg, Co, Ni) Orthophosphates To Design New Inorganic Pigments from Magenta to Yellow Hue.

New inorganic pigments with intense and saturated coloration have been prepared by a solid-state route and exhibit a large color scale from magenta to yellow. Indeed, yellow and magenta are two of the three subtractive model's colors with wide application in printing or displays as e-book readers. To develop yellow and magenta hue, we focused on cobalt- and nickel-based orthophosphates thanks to the chemical stability, low density, low price, and easy preparation of such a pigment class. All of these orthophosphates crystallize with the well-known olivine-type structure (orthorhombic Pnma space group) where transition metals are stabilized in a distorted octahedral site. This paper deals with the optical absorption properties of various orthophosphates, the correlations with structural features, and their colorimetric parameters (in L*a*b* color space). The LiCo1- xMg xPO4 series show near-magenta color with tunable luminosity, while the LiNiPO4 compound exhibits a frank yellow coloration. Co2+ (4T1) and Ni2+ (4A2) chromophore ions occupy a more or less distorted octahedral site, leading to tuning of the intensity of the d-d electronic transitions in the visible and near-IR ranges and providing a subtractive color scale; i.e., a LiCo1- xNi xPO4 solid solution possesses a very rich panel of colors between the two yellow and magenta extremes. It is worth noting that the crystal-field splitting and B Racah parameter have been estimated in a first approximation on the basis of the Tanabe-Sugano diagram and lead to the conclusion of a slightly higher crystal-field splitting of around 0.9 eV for Ni2+ ions and similar ß covalent parameters, despite the same crystallographic sites of both of these transition metals.

Aqueous PCDTBT:PC71 BM Photovoltaic Inks Made by Nanoprecipitation.

The fabrication of organic solar cells from aqueous dispersions of photoactive nanoparticles has recently attracted the interest of the photovoltaic community, since these dispersions offer an eco-friendly solution for the fabrication of solar cells, avoiding the use of toxic solvents. In this work, aqueous dispersions of pure poly[n-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl-C71 -butyric acid methyl ester (PC71 BM) nanoparticles, as well as of composite PC71 BM:PCDTBT nanoparticles, are prepared using the nanoprecipitation postpolymerization method. These dispersions are subsequently used to form the active layer of organic photovoltaic cells. Thin films of PC71 BM and PCDTBT are obtained by spray deposition of the nanoparticles' dispersions, and are characterized using a combination of spectroscopic and microscopic techniques. Photovoltaics that incorporate these active layers are fabricated thereafter. The impact of the annealing temperature and of the composition of the active layer on the efficiency of the solar cells is studied.

Core-Shell Double Gyroid Structure Formed by Linear ABC Terpolymer Thin Films.

The synthesis and self-assembly in thin-film configuration of linear ABC triblock terpolymer chains consisting of polystyrene (PS), poly(2-vinylpyridine) (P2VP), and polyisoprene (PI) are described. For that purpose, a hydroxyl-terminated PS-b-P2VP (45 kg mol-1 ) building block and a carboxyl-terminated PI (9 kg mol-1 ) are first separately prepared by anionic polymerization, and then are coupled via a Steglich esterification reaction. This quantitative and metal-free catalyst synthesis route reveals to be very interesting since functionalization and purification steps are straightforward, and well-defined terpolymers are produced. A solvent vapor annealing (SVA) process is used to promote the self-assembly of frustrated PS-b-P2VP-b-PI chains into a thin-film core-shell double gyroid (Q230 , space group: Ia3¯d) structure. As terraces are formed within PS-b-P2VP-b-PI thin films during the SVA process under a CHCl3 vapor, different plane orientations of the Q230 structure ((211), (110), (111), and (100)) are observed at the polymer-air interface depending on the film thickness.

Material challenges for solar cells in the twenty-first century: directions in emerging technologies.

Photovoltaic generation has stepped up within the last decade from outsider status to one of the important contributors of the ongoing energy transition, with about 1.7% of world electricity provided by solar cells. Progress in materials and production processes has played an important part in this development. Yet, there are many challenges before photovoltaics could provide clean, abundant, and cheap energy. Here, we review this research direction, with a focus on the results obtained within a Japan-French cooperation program, NextPV, working on promising solar cell technologies. The cooperation was focused on efficient photovoltaic devices, such as multijunction, ultrathin, intermediate band, and hot-carrier solar cells, and on printable solar cell materials such as colloidal quantum dots.

Templated Sub-100-nm-Thick Double-Gyroid Structure from Si-Containing Block Copolymer Thin Films.

The directed self-assembly of diblock copolymer chains (poly(1,1-dimethyl silacyclobutane)-block-polystyrene, PDMSB-b-PS) into a thin film double gyroid structure is described. A decrease of the kinetics of a typical double-wave pattern formation is reported within the 3D-nanostructure when the film thickness on mesas is lower than the gyroid unit cell. However, optimization of the solvent-vapor annealing process results in very large grains (over 10 µm²) with specific orientation (i.e., parallel to the air substrate) and direction (i.e., along the groove direction) of the characteristic (211) plane, demonstrated by templating sub-100-nm-thick PDMSB-b-PS films.

Highly Ordered Nanoring Arrays Formed by Templated Si-Containing Triblock Terpolymer Thin Films.

Laterally ordered nanorings with a periodicity of 38 nm are produced from the directed self-assembly of poly(1,1-dimethylsilacyclobutane)-block-polystyrene-block-poly(methyl methacrylate) thin films on topographically patterned substrates. Such nanoscale arrays with vertically oriented rings are highly desired in technological applications including memory using magnetic recording, metamaterial, waveguide, etc.

Photoactive Donor-Acceptor Composite Nanoparticles Dispersed in Water.

A major issue that inhibits the large-scale fabrication of organic solar modules is the use of chlorinated solvents considered to be toxic and hazardous. In this work, composite particles of poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2',1',3'-benzothiadiazole] (PCDTBT) and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) were obtained in water from a versatile and a ready-to-market methodology based on postpolymerization miniemulsification. Depending on the experimental conditions, size-controlled particles comprising both the electron donor and the electron acceptor were obtained and characterized using transmission electron microscopy (TEM), atomic force microscopy (AFM), small-angle neutron scattering (SANS), UV-visible absorption, and fluorescence spectroscopy. Intimate mixing of the two components was definitely asserted through PCDTBT fluorescence quenching in the composite nanoparticles. The water-based inks were used for the preparation of photovoltaic active layers that were subsequently integrated into organic solar cells.

Anisotropic Lithium Ion Conductivity in Single-Ion Diblock Copolymer Electrolyte Thin Films.

Well-defined single-ion diblock copolymers consisting of a Li-ion conductive poly(styrenesulfonyllithium(trifluoromethylsulfonyl)imide) (PSLiTFSI) block associated with a glassy polystyrene (PS) block have been synthesized via reversible addition fragmentation chain transfer polymerization. Conductivity anisotropy ratio up to 1000 has been achieved from PS-b-PSLiTFSI thin films by comparing Li-ion conductivities of out-of-plane (aligned) and in-plane (antialigned) cylinder morphologies at 40 °C. Blending of PS-b-PSLiTFSI thin films with poly(ethylene oxide) homopolymer (hPEO) enables a substantial improvement of Li-ion transport within aligned cylindrical domains, since hPEO, preferentially located in PSLiTFSI domains, is an excellent lithium-solvating material. Results are also compared with unblended and blended PSLiTFSI homopolymer (hPSLiTFSI) homologues, which reveals that ionic conductivity is improved when thin films are nanostructured.

Laterally Ordered Sub-10 nm Features Obtained From Directed Self-Assembly of Si-Containing Block Copolymer Thin Films.

Laterally ordered sub-10 nm features are produced from the directed self-assembly of poly(1,1-dimethyl silacyclo-butane)-block-poly(methyl methacrylate) (PDMSB-b-PMMA) thin films on sinusoidal azobenzene-containing patterns. The use of sinusoidal surface relief grating enables the formation of very large grain areas (over several µm(2) ) consisting of out-of-plane PMMA cylinders.

Low Bandgap Semiconducting Copolymer Nanoparticles by Suzuki Cross-Coupling Polymerization in Alcoholic Dispersed Media.

The synthesis and formulation of organic semiconductors for the emerging technology of organic electronics requires the use of preparative methods and solvents being environment friendly. Today most of the active layer materials for the organic photovoltaic devices and modules are using chlorinated solvents, which are toxic and hazardous. In this work, the synthesis of poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2',1',3'-benzothiadiazole] (PCDTBT) in propan-1-ol is presented as the dispersant continuous phase in the presence of poly(vinylpyrrolidone) used as stabilizer. Suzuki-Miyaura polycondensation of 9-(9-heptadecanyl)-9H-carbazole-2,7-diboronic acid bis(pinacol) ester and 4,7-bis(2-bromo-5-thienyl)-2,1,3-benzothiadiazole in alcohol dispersion yields colloidally stable nanoparticles of PCDTBT with particles size of 330-1300 nm, depending on the stabilizer concentration. Other reaction parameters are also discussed such as the amount of base or Pd catalyst.

An Alternative Anionic Polyelectrolyte for Aqueous PEDOT Dispersions: Toward Printable Transparent Electrodes.

Organic conducting polymers are promising electrode materials for printable organic electronics. One of the most studied conducting polymers is PEDOT: PSS, which is sufficiently conductive and transparent, but which shows some drawbacks, such as hygroscopicity and acidity. A new approach to stabilize PEDOT in aqueous dispersions involves the replacement of PSS with a basic polyanion based on a polystyrene backbone with (trifluoromethylsulfonyl)imide (TSFI) side groups. The PEDOT: PSTFSIK dispersions were obtained by oxidative polymerization of EDOT in an aqueous PSTFSIK solution and were characterized with regard to their composition, morphology, doping, rheological behavior, and optoelectronic performance. The PEDOT: PSTFSIK dispersions showed excellent printability and good optoelectronic performance (238 Ohm sq(-1) at 91% transmittance, σ>260 S cm(-1)) and were successfully integrated as flexible electrodes in OLED and OPV devices.

Preparation of water-free PEDOT dispersions in the presence of reactive polyisoprene stabilizers.

Poly(3,4-ethylenedioxythiophene) nanoparticles with narrow size distribution were prepared in organic dispersant media in the presence of both iron(III) dodecylbenzenesulfonate {Fe(DBS)3}-acting as both an oxidant and a stabilizer-and ω-functionalized polyisoprenes (ω-R-PI) as costabilizers. The effects of the solvent nature and concentration of Fe(DBS)3 on the size and morphology of the PEDOT particles were first studied in the absence of costabilizer. Second, the effects of the molar mass, concentration, and nature of the functional end group of the polyisoprene costabilizer were investigated. PEDOT nano-objects were characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS), and conductivity measurements.

Introducing Photo-Cross-Linkable Functionalities on P(VDF-co-TrFE) Ferroelectric Copolymer.

Ferroelectric polymers have emerged as crucial materials for the development of advanced organic electronic devices. Their recent high-end commercial applications as fingerprint sensors have only increased the amount of scientific interest around them. Despite an ever-larger body of studies focusing on optimizing the properties of ferroelectric polymers by physical means (e. g., annealing, stretching, blending or nano-structuring), post-polymerization chemical modification of such polymers has only recently become a field of active study with great promise in expanding the scope of those polymers. In this work, a solution-based post-polymerization modification method was developed for the safe and facile grafting of a plethora of functional groups to the backbone of commercially available Poly(vinylidene fluoride-co-trifluoroethylene P(VDF-co-TrFE) ferroelectric polymers. To showcase the versatility of this approach, photosensitive groups were grafted onto the polymeric backbone, enabling them to undergo photo-cross-linking. Finally, these modified polymers were used as functional negative photoresists in a photolithographic process, highlighting the potential of this method to integrate ferroelectric fluorinated electroactive polymers into standard electronic microfabrication production lines.

3D-Printed Organic Conjugated Trimer for Visible-Light-Driven Photocatalytic Applications.

Small molecule organic semiconductors (SMOSs) have emerged as a new class of photocatalysts that exhibit visible light absorption, tunable bandgap, good dispersion, and solubility. However, the recovery and reusability of such SMOSs in consecutive photocatalytic reactions is challenging. This work concerns a 3D-printed hierarchical porous structure based on an organic conjugated trimer, named EBE. Upon manufacturing, the photophysical and chemical properties of the organic semiconductor are maintained. The 3D-printed EBE photocatalyst shows a longer lifetime (11.7 ns) compared to the powder-state EBE (1.4 ns). This result indicates a microenvironment effect of the solvent (acetone), a better dispersion of the catalyst in the sample, and reduced intermolecular π-π stacking, which results in improved separation of the photogenerated charge carriers. As a proof-of-concept, the photocatalytic activity of the 3D-printed EBE catalyst is evaluated for water treatment and hydrogen production under sun-like irradiation. The resulting degradation efficiencies and hydrogen generation rates are higher than those reported for the state-of-the-art 3D-printed photocatalytic structures based on inorganic semiconductors. The photocatalytic mechanism is further investigated, and the results suggest that hydroxyl radicals (HO⋅) are the main reactive radicals responsible for the degradation of organic pollutants. Moreover, the recyclability of the EBE-3D photocatalyst is demonstrated in up to 5 uses. Overall, these results indicate the great potential of this 3D-printed organic conjugated trimer for photocatalytic applications.

Conjugated polymer blends for faster organic mixed conductors.

A model mixed-conducting polymer, blended with an amphiphilic block-copolymer, is shown to yield systems with drastically enhanced electro-chemical doping kinetics, leading to faster electrochemical transistors with a high transduction. Importantly, this approach is robust and reproducible, and should be readily adaptable to other mixed conductors without the need for exhaustive chemical modification.