Department of Materials Science and Engineering, University of Florida, PO Box 116400, Gainesville, Florida 32611, United States.
Department of Chemistry, University of Florida, PO Box 117200, Gainesville, Florida 32611, United States.
ACS Appl Mater Interfaces. 2023 May 31;15(21):25134-25147. doi: 10.1021/acsami.2c05946. Epub 2022 Jun 29.
It was recently reported that the most popular electron-accepting units introduced to π-conjugated oligomers studied for organic photovoltaic applications are susceptible to unwanted and even destructive photochemical reactions. The consequences of / photoisomerization of the popular 2-(1,1-dicyanomethylene)rhodanine (RCN) unit on the optical and morphological properties of a homologous series of RCN-functionalized oligothiophenes are studied here. Oligomers consisting of one, two, or three thiophene units were studied as pure isomers and with isomer compositions of 25, 53, and 45%, respectively, for / mixtures. Solutions of isomers and / mixtures were characterized by UV-vis and photoluminescence spectroscopy, wherein changes to optical properties were evaluated on the basis of isomer content. X-ray diffraction of thin-film / mixtures reveals crystalline domains of both and forms after thermal annealing for mono- and bithiophene oligomers, with greater interplanar spacing for crystalline domains than the counterparts along the substrate normal direction. The surface morphology viewed by atomic force microscopy also shows fiberlike structures for the form with a much larger aspect ratio than for the domains in the bithiophene oligomer. Optical characterization reveals drastic changes in the solid state upon introduction of the form for the mono- and bithiophene derivatives, whereas subtle consequences are noted for the terthiophene analogue. Most notably, a 132 nm redshift in maximum absorption occurs for the bithiophene oligomer films containing 53% isomer compared to the pure counterpart. Finally, although solid-state photoisomerization experiments find no evidence of → isomerization in polycrystalline films, → isomerization is observed and becomes more restrictive in films with higher crystallinity (i.e., after thermal annealing). This structure-property study, which elucidates the consequences of the RCN configuration on solid-state packing and optical properties, is expected to guide the development of more efficient and stable organic optoelectronic devices.
最近有报道称，在研究用于有机光伏应用的π-共轭寡聚物时，引入的最受欢迎的电子受体单元容易发生不需要的甚至破坏性的光化学反应。本文研究了在同一系列 RCN 功能化寡噻吩中，常见的 2-(1,1-二氰基亚甲基)罗丹宁（RCN）单元的光异构化对其光学和形态性质的影响。研究了由一个、两个或三个噻吩单元组成的低聚物，作为纯异构体和 25%、53%和 45%的 异构体组成的混合物进行研究。通过紫外-可见光谱和光致发光光谱对 异构体和混合物的溶液进行了表征，其中根据异构体含量评估了光学性质的变化。对于单和双噻吩低聚物，热退火后，/混合物的 X 射线衍射显示出 和 两种形式的结晶域，与沿基底法向的 晶面间距相比， 晶面间距更大。原子力显微镜观察到的表面形貌也显示出 形式的纤维状结构，其纵横比远大于双噻吩低聚物中的 畴。光学特性表明，在引入 形式后，单和双噻吩衍生物在固态中会发生剧烈变化，而在三噻吩类似物中则只有细微的变化。最值得注意的是，与纯 相比，含有 53% 异构体的双噻吩低聚物薄膜的最大吸收发生了 132nm 的红移。最后，尽管固态光异构化实验在多晶 薄膜中没有发现 → 异构化的证据，但观察到 → 异构化，并且在结晶度更高的薄膜中（即热退火后）变得更受限制。这项结构-性质研究阐明了 RCN 构型对固态堆积和光学性质的影响，有望指导更高效、更稳定的有机光电设备的发展。
