Using sulfur bridge oxidation to control electronic coupling and photochemistry in covalent anthracene dimers
Using sulfur bridge oxidation to control electronic coupling and photochemistry in covalent anthracene dimers
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DOI：
10.1039/c8sc05598j
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发表时间：
2019-08-28
期刊：
影响因子：
8.4
通讯作者：
Bardeen, Christopher J.
中科院分区：
文献类型：
--
作者：
Cruz, Chad D.;Yuan, Jennifer;Bardeen, Christopher J.
CO2束缚的双发色团提供了一个理想的试验场，以开发控制发色团组装中激发态行为的策略。在这项工作中，光谱学和电子结构理论相结合，证明蒽发色团之间的硫连接剂的氧化态不仅控制了分子的光物理，而且控制了分子的光化学。改变硫连接基的氧化态不会改变发色团之间的几何形状，从而允许分离发色团之间的电子效应。以前，我们表明，硫桥连三噻吩二聚体中的激子状态调制的硫孤对电子屏蔽，但硫轨道不直接参与这些状态。在桥蒽二聚体，是目前的论文的主题，未氧化的S接头的原子轨道可以积极地与蒽分子轨道混合，形成新的电子状态，增强电荷转移特性，不同的激子耦合，和快速（亚纳秒）的系统间交叉，这取决于溶剂极性。然而，完全氧化的SO2桥恢复纯粹的通过空间的蒽发色团之间的电子耦合，并抑制系统间的交叉。光激发导致在亚20皮秒时间尺度上的内部转换，或者导致长寿命的发射状态的产生，该发射状态是分子内[4 + 4]光二聚化的可能前体。这些结果说明了共价桥中单个原子的化学修饰不仅可以显着改变分子的光物理，而且可以显着改变分子的光化学。
Covalently tethered bichromophores provide an ideal proving ground to develop strategies for controlling excited state behavior in chromophore assemblies. In this work, optical spectroscopy and electronic structure theory are combined to demonstrate that the oxidation state of a sulfur linker between anthracene chromophores gives control over not only the photophysics but also the photochemistry of the molecules. Altering the oxidation state of the sulfur linker does not change the geometry between chromophores, allowing electronic effects between chromophores to be isolated. Previously, we showed that excitonic states in sulfur-bridged terthiophene dimers were modulated by electronic screening of the sulfur lone pairs, but that the sulfur orbitals were not directly involved in these states. In the bridged anthracene dimers that are the subject of the current paper, the atomic orbitals of the unoxidized S linker can actively mix with the anthracene molecular orbitals to form new electronic states with enhanced charge transfer character, different excitonic coupling, and rapid (sub-nanosecond) intersystem crossing that depends on solvent polarity. However, the fully oxidized SO2 bridge restores purely through-space electronic coupling between anthracene chromophores and inhibits intersystem crossing. Photoexcitation leads to either internal conversion on a sub-20 picosecond timescale, or to the creation of a long-lived emissive state that is the likely precursor of the intramolecular [4 + 4] photodimerization. These results illustrate how chemical modification of a single atom in the covalent bridge can dramatically alter not only the photophysics but also the photochemistry of molecules.