Suppression of Kasha's rule as a mechanism for fluorescent molecular rotors and aggregation-induced emission
Suppression of Kasha's rule as a mechanism for fluorescent molecular rotors and aggregation-induced emission
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DOI：
10.1038/nchem.2612
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发表时间：
2017-01-01
期刊：
影响因子：
21.8
通讯作者：
Aprahamian, Ivan
中科院分区：
文献类型：
--
作者：
Qian, Hai;Cousins, Morgan E.;Aprahamian, Ivan
虽然有一些建议的解释聚集诱导发射，一个现象的应用范围从生物传感器到有机发光二极管，目前的理解的量子力学起源的这一物理行为是有限的。为了解决这个问题，我们评估了一系列基于BF 2-腙的染料的发射特性作为溶剂粘度的函数。这些分子被证明是高效的荧光分子转子。这种性质，除了它们是聚集诱导发射发光体之外，使我们能够更深入地探索它们的发射机制。含时密度泛函理论计算和实验结果表明，发射不是从S-1态，从Kasha的规则预测，而是从更高的能量（>S-1）的状态。此外，我们发现，通过限制转子旋转来抑制内部转换到暗S-1状态增强了荧光，这导致了抑制Kasha规则是粘性溶液和固态中发射的物理机制的建议。
Although there are some proposed explanations for aggregation-induced emission, a phenomenon with applications that range from biosensors to organic light-emitting diodes, current understanding of the quantum-mechanical origin of this photophysical behaviour is limited. To address this issue, we assessed the emission properties of a series of BF2-hydrazone-based dyes as a function of solvent viscosity. These molecules turned out to be highly efficient fluorescent molecular rotors. This property, in addition to them being aggregation-induced emission luminogens, enabled us to probe deeper into their emission mechanism. Time-dependent density functional theory calculations and experimental results showed that the emission is not from the S-1 state, as predicted from Kasha's rule, but from a higher energy (>S-1) state. Furthermore, we found that suppression of internal conversion to the dark S-1 state by restricting the rotor rotation enhances fluorescence, which leads to the proposal that suppression of Kasha's rule is the photophysical mechanism responsible for emission in both viscous solution and the solid state.