Peng Qian, Yi Yuanping, Shuai Zhigang, Shao Jiushu
Key Laboratory of Organic Solids, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing, PR China.
J Am Chem Soc. 2007 Aug 1;129(30):9333-9. doi: 10.1021/ja067946e. Epub 2007 Jul 10.
It is a highly desirable but difficult task to predict the molecular fluorescence quantum efficiency from first principles. The molecule in the excited state can undergo spontaneous radiation, conversion of electronic energy to nuclear motion, or chemical reaction. For relatively large molecules, it is impossible to obtain the full potential energy surfaces for the ground state and the excited states to study the excited-state dynamics. We show that, under harmonic approximation by considering the Duschinsky rotation effect, the molecular fluorescence properties can be quantitatively calculated from first principles coupled with our correlation function formalism for the internal conversion. In particular, we have explained the peculiar fluorescence behaviors of two isomeric compounds, cis,cis-1,2,3,4-tetraphenyl-1,3-butadiene and 1,1,4,4-tetraphenyl-butadiene, the former being nonemissive in solution and strongly emissive in aggregation or at low temperature, and the latter being strongly emissive in solution. The roles of low-frequency phenyl ring twist motions and their Duschinsky mode mixings are found to be crucial, especially to reveal the temperature dependence. As an independent check, we take a look at the well-established photophysics of 1,4-diphenylbutadiene for its three different conformers. Both the calculated radiative and nonradiative rates are in excellent agreement with the available experimental measurements.
从第一性原理预测分子荧光量子效率是一项非常理想但却困难的任务。处于激发态的分子会经历自发辐射、电子能量向核运动的转换或化学反应。对于相对较大的分子，不可能获得基态和激发态的完整势能面来研究激发态动力学。我们表明，在考虑杜什insky旋转效应的简谐近似下，结合我们用于内转换的关联函数形式，可以从第一性原理定量计算分子荧光性质。特别地，我们解释了两种异构体化合物顺，顺 - 1,2,3,4 - 四苯基 - 1,3 - 丁二烯和1,1,4,4 - 四苯基 - 丁二烯的奇特荧光行为，前者在溶液中不发光而在聚集态或低温下强烈发光，后者在溶液中强烈发光。发现低频苯环扭转运动及其杜什insky模式混合的作用至关重要，特别是对于揭示温度依赖性。作为独立验证，我们研究了1,4 - 二苯基丁二烯三种不同构象的成熟光物理性质。计算得到的辐射率和非辐射率与现有的实验测量结果都非常吻合。
