Organic molecules with an aggregation-induced emission (AIE) property have been attracting much attention from the viewpoint of application to solid state emissive materials. For the AIE mechanism, quantum mechanical studies proposed the restriction of the intramolecular motion (RIM) model with the contribution of the conical intersection (CI) and deduced the importance of the restricted access to a conical intersection (RACI) in the potential energy surface (PES). Although these theoretical studies have contributed to the elucidation of AIE phenomena, direct detection of the reaction dynamics is indispensable to clarify the actual PES and the deactivation mechanism. Along this line, we investigated excited state dynamics of the AIE molecule with dibenzoylmethanatoboron difluoride complexes using time-resolved absorption spectroscopies in both visible and infrared (IR) regions. While the reference system of 1,3-bis(4-methoxyphenyl)methanatoboron difluoride (2aBF₂) showed strong emission in solution, the methyl-substituted derivative at the α-position of the dioxaborine ring (2amBF₂) led to the very weak fluorescence in solution but strong emission in the solid state. Time-resolved visible absorption measurements revealed a peak shift and broadening of the stimulated emission in the solution of 2amBF₂, owing to the rapid change of the molecular geometry. With the temporal evolution of time-resolved IR absorption signals and density functional theory (DFT) calculation of these systems, it was deduced that 2amBF₂ has two stable geometries, namely, planar and bending, in the S₁ state and the bending geometry in the S₁ state led to rapid conversion to the S₀ state. These results support the RACI model in the aggregated states, leading to the AIE properties.

中文翻译：

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具有聚集诱导发射特性的 α 取代二苯甲酰基甲氧硼二氟化物复合物几何演化的激发态动力学


从固态发光材料的应用角度来看，具有聚集诱导发射 （AIE） 特性的有机分子已经引起了广泛关注。对于 AIE 机制，量子力学研究提出了锥形交点 （CI） 的贡献对分子内运动 （RIM） 模型的限制，并推断了势能表面 （PES） 中锥形交点 （RACI） 的限制访问的重要性。尽管这些理论研究有助于阐明 AIE 现象，但直接检测反应动力学对于阐明实际的 PES 和失活机制是必不可少的。沿着这条路线，我们在可见光和红外 （IR） 区域使用时间分辨吸收光谱研究了 AIE 分子与二苯甲酰甲氧乙硼二氟化物配合物的激发态动力学。虽然 1,3-双（4-甲氧基苯基）甲氧硼二氟化物 （2aBF₂） 的参比系统在溶液中显示出强发射，但二氧杂硼环 （2amBF₂） α位的甲基取代衍生物导致溶液中荧光非常弱，但在固态下发射很强。时间分辨可见光吸收测量显示，由于分子几何形状的快速变化，2amBF₂ 溶液中受激发射的峰偏移和展宽。随着时间分辨红外吸收信号的时间演化和这些系统的密度泛函理论 （DFT） 计算，推断 2amBF₂ 在 S₁ 状态下具有平面和弯曲两个稳定的几何形状，而 S₁ 状态下的弯曲几何形状导致快速转换为 S₀ 状态。 这些结果支持聚合状态下的 RACI 模型，从而得出 AIE 属性。