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首页> 外文期刊>Chemistry: A European journal >Structure-dependent electronic nature of star-shaped oligothiophenes, probed by ensemble and single-molecule spectroscopy
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Structure-dependent electronic nature of star-shaped oligothiophenes, probed by ensemble and single-molecule spectroscopy

机译：整体和单分子光谱探测的星形寡聚噻吩的结构依赖性电子性质

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We have investigated the photophysical properties of star-shaped oligothiophenes with three terthiophene arms (meta to each other, S3) or six terthiophene arms (ortho-, meta-, and para-arranged, S6) connected to an ethynylbenzene core to elucidate the relationship between their molecular structure and electronic properties by using a combination of ensemble and single-molecule spectroscopic techniques. We postulate two different conformations for molecules S3 and S6 on the basis of the X-ray structure of hexakis(5-hexyl-2-thienlyethynyl)benzene and suggest the coexistence of these conformers by using spectroscopic methods. From the steady-state spectroscopic data of compound S6, we show that the exciton is delocalized over the core structure, but that the meta-linkage in compound S3 prevents the electronic communication between the arms. However, in single-molecule spectroscopic measurements, we observed that some molecules of compound S3 showed long fluorescence lifetimes (about 1.4 ns) in the fluorescence-intensity trajectories, which indicated that π electrons were delocalized along the meta linker. Based on these observations, we suggest that the delocalized exciton is intensely sensitive towards the dihedral angle between the core and the adjacent thiophene ring, as well as to the substituted position of the terthiophene arms. Our results highlight that the fluorescence lifetimes of compounds S3 and S6 are strongly correlated with the spatial location of their excitons, which is mainly affected by their conformation, that is, whether the innermost thiophene rings are facing each other or not. More interestingly, we observed that the difference between the degrees of ring-torsional flexibility of compounds S3 and S6 results in their sharply contrasting fluorescence properties, such as a change in fluorescence intensity as a function of temperature. Written in the stars: The electronic nature of star-shaped oligothiophenes can be controlled by increasing the number of branched arms (see figure), because these structural modifications lead to differences in the ring-torsional flexibility, which determines the degree of exciton delocalization throughout the core structure.
机译：我们研究了星形低聚噻吩的光物理性质，该寡聚噻吩具有三个与乙炔基苯核相连的三噻吩基臂（彼此间互为S3）或六个六噻吩基臂（邻，间和对位排列，S6）。结合使用集成和单分子光谱技术在分子结构和电子性质之间进行分析。基于六（5-己基-2-噻吩乙炔基）苯的X射线结构，我们假设分子S3和S6具有两个不同的构象，并通过光谱方法建议这些构象的共存。从化合物S6的稳态光谱数据来看，我们表明激子在核结构上离域化，但化合物S3中的间位键阻止了臂之间的电子通讯。但是，在单分子光谱测量中，我们观察到化合物S3的某些分子在荧光强度轨迹中显示出较长的荧光寿命（约1.4 ns），这表明π电子沿着亚连接子发生了离域化。基于这些观察，我们建议离域激子对核与相邻噻吩环之间的二面角以及对噻吩臂的取代位置非常敏感。我们的结果表明，化合物S3和S6的荧光寿命与其激子的空间位置密切相关，而激子的空间位置主要受其构象的影响，也就是说，最里面的噻吩环是否彼此面对。更有趣的是，我们观察到化合物S3和S6的环扭转柔性程度之间的差异导致它们的荧光特性发生了鲜明的对比，例如荧光强度随温度的变化。写在星星上：星形寡聚噻吩的电子性质可以通过增加分支臂的数量来控制（见图），因为这些结构修饰导致环扭转柔性不同，这决定了整个激子的离域化程度核心结构。

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