Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
J Phys Chem B. 2010 Apr 22;114(15):4964-72. doi: 10.1021/jp9104954.
Six new thiophene oligomers, here designated as tripodal-like oligothienyl-imidazoles, were synthesized and have been investigated in ethanol solution at room and low temperature. The oligomers bear a common core where two or more thiophenes are linked to one or more imidazole units that further links through its alpha-position to a different number of incremental thiophene units. The study involves a comprehensive spectral and photophysical investigation where the properties of the singlet and triplet states have been investigated regarding absorption, fluorescence and phosphorescence, transient triplet-triplet absorption together with all relevant quantum yields (fluorescence, phi(F), internal conversion, phi(IC), intersystem crossing, phi(T,) and singlet oxygen, phi(Delta)) and lifetimes. In addition, density functional theory quantum chemical calculations were performed to gain a detailed understanding of the molecular geometry and optical properties of the investigated oligomers. From the overall data, the radiative (k(F)) and radiationless (k(NR), k(IC), and k(ISC)) rate constants have been determined and it is shown that, in contrast with the parent oligothiophenes, the radiative competes with the radiationless deactivation channels. The results show that, by comparison with the oligothiophene counterparts, there is an augment of the relative contributions of the internal conversion and fluorescence processes relative to the S(1)~~-->T(1) intersystem crossing. Phosphosphorescence emission was found for the simplest member of the investigated compounds with a low quantum yield (phi(Ph) = 0.009) and a lifetime of 8 micros. The data also show that the introduction of a 4,5-dithienyl-imidazole moiety in a bi- or terthiophene oligomer results in, respectively, a 20-fold and a 3-fold increase of the fluorescence quantum yield relative to their oligothiophene counterparts. The synergy of the structural and photophysical properties, combined with the exceptional thermal stabilities, opens new perspectives related to the copolymerization of oligothiophenes with thienyl-imidazole units with potential application as organic light emitting devices.
六种新的噻吩寡聚物，这里称为三足状寡噻吩-咪唑，被合成并在乙醇溶液中在室温及低温下进行了研究。寡聚物具有一个共同的核心，其中两个或更多的噻吩连接到一个或多个咪唑单元，该咪唑单元进一步通过其α-位连接到不同数量的递增噻吩单元。该研究涉及全面的光谱和光物理研究，其中单重态和三重态的性质已经在吸收、荧光和磷光、瞬态三重态-三重态吸收以及所有相关的量子产率（荧光、phi(F)、内转换、phi(IC)、系间窜越、phi(T,)和单线态氧、phi(Delta))和寿命方面进行了研究。此外，还进行了密度泛函理论量子化学计算，以深入了解所研究寡聚物的分子几何形状和光学性质。从整体数据中，确定了辐射（k(F)）和无辐射（k(NR)、k(IC)和 k(ISC)）速率常数，结果表明，与母体寡噻吩相反，辐射与无辐射失活通道竞争。结果表明，与寡噻吩对应物相比，内部转换和荧光过程的相对贡献相对于 S(1)~~-->T(1)系间窜越增加。在研究化合物中最简单的成员中发现了磷光发射，其量子产率低（phi(Ph)=0.009），寿命为 8 微秒。数据还表明，在双噻吩或三噻吩寡聚物中引入 4,5-二噻吩基-咪唑部分，分别相对于其寡噻吩对应物，荧光量子产率增加了 20 倍和 3 倍。结构和光物理性质的协同作用，加上卓越的热稳定性，为寡噻吩与噻吩基-咪唑单元的共聚开辟了新的前景，有望作为有机发光器件的应用。
