有机分子聚集体中振动分辨光谱的激子耦合效应（英文）

Effect of Intermolecular Excited-state Interaction on Vibrationally Resolved Optical Spectra in Organic Molecular Aggregates

光谱是探究分子间相互作用及发光机理的有效手段.本工作采用Frenkel激子模型和量子力学/分子力学(QM/MM)方法系统研究了一系列聚集诱导发光(AIE)体系和传统荧光(非AIE)体系晶态下的吸收、发射光谱.结果表明,分子内电声子耦合(λ)与分子间激子耦合(J)竞争决定了晶态聚集体的光谱特性.在室温下,当J/λ值大于约0.17时,有机分子聚集体光谱的激子耦合效应将表现明显.例如,对于面对面排列的H聚集体,只有考虑激子耦合效应的理论计算光谱才与其实验光谱吻合很好,即相较于单分子光谱的吸收蓝移、发射减弱并红移.对于AIE体系,因为其J/λ值均小于0.17,AIE聚集体光谱特征主要是由分子内电声子耦合所主导,激子耦合可以忽略不计.

The optical spectra are effective means to reveal the molecular interactions and the luminescent mechanism of the organic molecules in aggregates. Herein, we systematically investigate the crystalline state vibrationally resolved absorption and emission spectra for a series of AIEgens and non-AIEgens by considering intermolecular excited state interaction by using Frenkel-exciton model coupled with quantum mechanics and molecular mechanics （QM/MM） calculations. It is found that the competition between the intramolecular vibronic coupling （2） and the intermolecular exciton coupling （3） governs the crystalline aggregate spectral characters. At room temperature, when J/λ value is larger than a critical value （ca. 0.17）, the exciton coupling would have a large effect on the optical spectra. For face-to-face H-aggregates, only when both intermolecular electrostatic and excitonic couplings are considered, can one obtain calculated vibrationally resolved spectra and well reproduce the experimental results, namely, remarkable blue-shift in absorption but much less red-shift in emission when compared with the gas-phase. The optical spectra of the AIE-active aggregates are determined by the intramolecular vibronic coupling because the ratio J/λ is less than the critical value.