Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, 100190 Beijing, People's Republic of China.
J Chem Phys. 2011 Jul 7;135(1):014304. doi: 10.1063/1.3606579.
Aggregation-induced emission (AIE) phenomenon has attracted much attention in recent years due to its potential applications in optoelectronic devices, fluorescence sensors, and biological probes. Restriction of intramolecular rotation has been proposed as the cause of this unusual phenomenon. Rational design of AIE luminogens requires quantitative descriptions of its mechanism. 2,3-dicyano-5,6-diphenylpyrazine (DCDPP) with "free" phenyl rings is an AIE active compound, whereas 2,3-dicyanopyrazino [5,6-9,10] phenanthrene (DCPP) with "locked" phenyl rings is not. Quantum chemistry calculations coupled with our thermal vibration correlation function formalism for the radiative and non-radiative decay rates reveal that the radiative decay rates for both DCPP and DCDPP are close to each other for all the temperatures, but the non-radiative decay processes are very different. For DCDPP, the low-frequency modes originated from the phenyl ring twisting motions are strongly coupled with the electronic excited state, which dissipate the electronic excitation energy through mode-mixing (Duschinsky rotation effect), and the non-radiative decay rate strongly increases with temperature. For DCPP, however, such mode-mixing effect is weak and the non-radiative decay rate is insensitive to temperature. These findings rationalize the fact that DCDPP is AIE active but DCPP is not, and are instructive to further development of AIE luminogens.
聚集诱导发光（AIE）现象近年来引起了广泛关注，因为它在光电设备、荧光传感器和生物探针等领域具有潜在的应用。分子内旋转的限制被认为是这种不寻常现象的原因。AIE 发光体的合理设计需要对其机制进行定量描述。具有“自由”苯环的 2,3-二氰基-5,6-二苯基吡嗪（DCDPP）是一种 AIE 活性化合物，而具有“锁定”苯环的 2,3-二氰基吡嗪并[5,6-9,10]菲（DCPP）则不是。量子化学计算结合我们的热振动相关函数形式理论，用于辐射和非辐射衰减速率，揭示了对于所有温度，DCPP 和 DCDPP 的辐射衰减速率都非常接近，但非辐射衰减过程却非常不同。对于 DCDPP，来自苯环扭曲运动的低频模式与电子激发态强烈耦合，通过模式混合（杜欣斯基旋转效应）耗散电子激发能，而非辐射衰减速率随温度的升高而强烈增加。然而，对于 DCPP，这种模式混合效应较弱，非辐射衰减速率对温度不敏感。这些发现合理地解释了 DCDPP 是 AIE 活性的而 DCPP 不是的事实，并且对进一步开发 AIE 发光体具有指导意义。
