Department of Chemistry, University of Coimbra, Rua Larga, 3004-535 Coimbra, Portugal.
Phys Chem Chem Phys. 2013 Sep 28;15(36):15204-13. doi: 10.1039/c3cp52056k.
A comprehensive spectral and photophysical investigation of four donor-acceptor-donor (DAD) oligomers consisting of electron-deficient 2,1,3-benzothiadiazole or quinoxaline moieties linked to electron-rich thienyl or bithienyl units has been undertaken. Additionally, a bis(dithienyl) substituted naphthalene was also investigated. The D-A-D nature of these oligomers resulted in the presence of an intramolecular charge transfer (ICT) state, which was further substantiated by solvatochromism studies (analysis with the Lippert-Mataga formalism). Hereby, significant differences have been obtained for the fluorescence quantum yields of the oligomers in the non-polar solvent methylcyclohexane vs. the polar ethanol. The study was further complemented with the determination of the optimized ground-state molecular geometries for the oligomers together with the prediction of the lowest vertical one-electron excitation energy and the relevant molecular orbital contours using DFT calculations. The electronic transitions show a clear HOMO to LUMO charge-transfer character. In contrast to the thiophene oligomers (the oligothiophenes with n = 1-7), where the intersystem crossing (ISC) yield decreases with n, the studied DAD oligomers were found to show an increase in the ISC efficiency with the number of (donor) thienyl units.
我们对由缺电子的 2,1,3-苯并噻二唑或喹喔啉部分与富电子噻吩或双噻吩单元连接而成的四个给体-受体-给体（DAD）寡聚物进行了全面的光谱和光物理研究。此外，还研究了双（二噻吩基）取代的萘。这些寡聚物的 D-A-D 性质导致了分子内电荷转移（ICT）态的存在，溶剂化变色研究（用 Lippert-Mataga 形式进行分析）进一步证实了这一点。因此，在非极性溶剂甲基环己烷和极性乙醇中，寡聚物的荧光量子产率存在显著差异。该研究还通过确定寡聚物的优化基态分子几何形状以及使用 DFT 计算预测最低垂直单电子激发能和相关分子轨道轮廓来补充。电子跃迁显示出明显的 HOMO 到 LUMO 电荷转移特征。与噻吩寡聚物（n = 1-7 的寡噻吩）不同，其中系间窜越（ISC）产率随 n 降低，所研究的 DAD 寡聚物被发现随着（供体）噻吩单元数量的增加，ISC 效率增加。
