A bridged low band gap A-D-A quaterthiophene as efficient donor for organic solar cells

International audience[small alpha],[small omega]-Bis(dicyanovinyl)quaterthiophene 1 with a median 4,4-diethyl-4H-cyclopenta[2,1-b:3,4-b[prime or minute]]dithiophene has been synthesized. UV-Vis absorption data show that the covalent bridging of the inner 2,2[prime or minute]-bithiophene leads to a significant reduction of the HOMO-LUMO gap essentially due to an increase of the HOMO level as confirmed by electrochemical and theoretical results. X-ray diffraction analysis of a single crystal of 1 shows that except for the out-of-plane ethyl groups, the conjugated system displays a quasi-planar geometry while the molecular packing exhibits strong [small pi]-stacking interactions and multiple short intermolecular contacts. Quaterthiophene 1 has been used as active donor material in organic solar cells of various architectures including bi-layer planar hetero-junctions and hybrid co-evaporated bulk hetero-junctions with C60 as electron acceptor material. A maximum conversion efficiency of 4.30% is obtained with a hybrid co-evaporated device. These results are discussed in terms of structure-properties relationships with reference to the open-chain parent [small alpha],[small omega]-bis(dicyanovinyl)quaterthiophene 2

Triphenylamine/Tetracyanobutadiene-Based π-Conjugated Push–Pull Molecules End-Capped with Arene Platforms:Synthesis, Photophysics, and Photovoltaic Response

π-Conjugated push–pull molecules based on triphenylamine and 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) have been functionalized with different terminal arene units. In solution, these highly TCBD-twisted systems showed a strong internal charge transfer band in the visible spectrum and no detectable photoluminescence (PL). Photophysical and theoretical investigations revealed very short singlet excited state deactivation time of ≈10 ps resulting from significant conformational changes of the TCBD-arene moiety upon photoexcitation, opening a pathway for non-radiative decay. The PL was recovered in vacuum-processed films or when the molecules were dispersed in a PMMA matrix leading to a significant increase of the excited state deactivation time. As shown by cyclic voltammetry, these molecules can act as electron donors compared to C 60. Hence, vacuum-processed planar heterojunction organic solar cells were fabricated leading to a maximum power conversion efficiency of ca. 1.9 % which decreases with the increase of the arene size

Theoretical and Experimental Investigation on the Intersystem Crossing Kinetics in Benzothioxanthene Imide Luminophores, and Their Dependence on Substituents Effects

In spite of their remarkable luminescence properties, benzothioxanthene imide (BTXI an imide containing rylene chromophores) derivatives have been largely overlooked compared to their perylene bisimide and naphthalene bisimide counterparts. Thus their detailed photophysics are much less understood. In this paper, we show how relatively simple structural modifications of the backbone of BTXIs can lead to impressive variations in their Inter-System Crossing kinetics. Thus, through rational engineering of their structure, it is possible to obtain a triplet formation quantum yield that reaches unity, making BTXI a promising class of compounds for triplet-based applications (photodynamic therapy, electroluminescence, etc.).</p

Regioselective Mono and Homo/hetero Dihalogenation of the Benzothioxanthene Monoimide

Through the preparation and characterization of five new derivatives, the regioselective mono and di, homo and hetero, halogenation of the benzothioxanthene (BTXI) core is demonstrated herein. All structurally solved by X-ray crystallography, these complementary functionalized building blocks open doors to the design of new symmetrical and asymmetrical π-conjugated systems based on this promising but still under-explored rylene

From Textile Coloring to Light-emitting Electrochemical Devices: Upcycling of the Isoviolanthrone Vat Dye

Produced at ton scale, vat dyes are major environmental pollutants generated by the textile industry. However, they represent ideal and accessible candidates for chemical upcycling since they are usually composed of large pi-conjugated scaffolds. Based on the valorization of "old" products, waste or even contaminant into high-added value goods, this concept can be easily transposed to the laboratories. As a contribution to the current environmental and ecological transition, we demonstrate herein the valorization/upcycling of wastewaters generated during the dyeing procedure. To do so, the reduced (leuco) form of vat violet 10, also known as isoviolanthrone, was functionalized to afford a readily soluble derivative that was subsequently and successfully used as active material in operating solution processed light-emitting electrochemical cells, that is, from textile dyeing to high-tech application.11Nsciescopu

Harnessing Liquid Crystal Attributes of Near-Unit Photoluminescent Benzothioxanthene Photosensitizers: Photophysical Profiling in Solution, Solid State, and Polymer Matrix Embedding

Liquid crystals (LCs) have garnered significant attention for their unique optical and electrical properties, making them promising candidates in various technological applications such as smart displays, sensors, telecommunications, biomedicals or wearable electronics. In this study, we explore the potential of several highly emissive benzothioxanthene imide (BTI) derivatives as LC materials with a focus on their robustness and temperature-stable emission behavior. By tailoring the molecular structure of BTIs, we have accomplished exceptional emissive properties while maintaining the inherent advantages of LCs, such as their self-organizing ability and responsive nature. We describe the formation of enantiotropic liquid crystals whose mesomorphic properties dependent on the nature, length, and position of the side chain. Moreover, we have investigated the thermal stability of their emission spectra over a wide range of temperature, highlighting their potential use in demanding conditions where precise optical performances are critical. Our findings underscore the importance of molecular design in achieving highly emissive LC materials with enhanced robustness and temperature stability, opening new avenues for the use of BTI derivatives

Harnessing liquid crystal attributes of near-unit photoluminescent benzothioxanthene photosensitizers: photophysical profiling in solution, solid state, and polymer matrix embedding

Liquid crystals (LCs) have garnered significant attention for their unique optical and electrical properties, making them promising candidates in various technological applications such as smart displays, sensors, telecommunications, biomedicals or wearable electronics. In this study, we explore the potential of several highly emissive benzothioxanthene imide (BTI) derivatives as LC materials with a focus on their robustness and temperature-stable emission behavior. By tailoring the molecular structure of BTIs, we have accomplished exceptional emissive properties while maintaining the inherent advantages of LCs, such as their self-organizing ability and responsive nature. We describe the formation of enantiotropic liquid crystals whose mesomorphic properties dependent on the nature, length, and position of the side chain. Moreover, we have investigated the thermal stability of their emission spectra over a wide range of temperature, highlighting their potential use in demanding conditions where precise optical performances are critical. Our findings underscore the importance of molecular design in achieving highly emissive LC materials with enhanced robustness and temperature stability, opening new avenues for the use of BTI derivatives.Depto. de Química InorgánicaFac. de Ciencias QuímicasTRUEpubAPC financiada por la UC

Importance of the Donor:Fullerene Intermolecular Arrangement for High-Efficiency Organic Photovoltaics

The performance of organic photovoltaic (OPV) material systems are hypothesized to depend strongly on the intermolecular arrangements at the donor:fullerene interfaces. A review of some of the most efficient polymers utilized in polymer:fullerene PV devices, combined with an analysis of reported polymer donor materials wherein the same conjugated backbone was used with varying alkyl substituents, supports this hypothesis. Specifically, the literature shows that higher-performing donor–acceptor type polymers generally have acceptor moieties that are sterically accessible for interactions with the fullerene derivative, whereas the corresponding donor moieties tend to have branched alkyl substituents that sterically hinder interactions with the fullerene. To further explore the idea that the most beneficial polymer:fullerene arrangement involves the fullerene docking with the acceptor moiety, a family of benzo­[1,2-b:4,5-b′]­dithiophene–thieno­[3,4-<i>c</i>]­pyrrole-4,6-dione polymers (PBDTTPD derivatives) was synthesized and tested in a variety of PV device types with vastly different aggregation states of the polymer. In agreement with our hypothesis, the PBDTTPD derivative with a more sterically accessible acceptor moiety and a more sterically hindered donor moiety shows the highest performance in bulk-heterojunction, bilayer, and low-polymer concentration PV devices where fullerene derivatives serve as the electron-accepting materials. Furthermore, external quantum efficiency measurements of the charge-transfer state and solid-state two-dimensional (2D) ¹³C­{¹H} heteronuclear correlation (HETCOR) NMR analyses support that a specific polymer:fullerene arrangement is present for the highest performing PBDTTPD derivative, in which the fullerene is in closer proximity to the acceptor moiety of the polymer. This work demonstrates that the polymer:fullerene arrangement and resulting intermolecular interactions may be key factors in determining the performance of OPV material systems