卟啉-富勒烯体系光激发电子转移的理论研究

Photoinduced electron transfer in porphyrin-fullerene system:a time-dependent DFT study

在分子水平研究新型人工光俘获材料对于太阳能电池的发展具有重要意义。本文采用TD-DFT方法研究了卟啉-富勒烯(P-C60)体系的光诱导电子转移过程。该过程由三个过程组成:(1)光激发过程,P-C60由基态激发至卟啉局域激发(LE)态;(2)电荷分离(CS)过程形成卟啉至富勒烯的电荷转移(CT)态;(3)电荷重组(CR)过程,CT态返回到基态。我们通过分析分子轨道指认了LE态和CT,并获得了这两个激发态的结构。采用广义Mulliken-Hush(GMH)方法计算体系电荷分离和电荷重组过程的态态间电子耦合,和实验测量的电子转移速率获得定性一致的结果。本工作为分析、预测光诱导电荷转移过程提供了有效的手段。

The study of new artificial light-harvesting system at molecular level is important for the development of organic solar ceils. In this work, the photo-induced electron transfer process of light-harvesting dyad（porphyrin-C60） is investigated with time-de- pendent density functional theory（TD-DFT）calculations. This process could be regarded as three steps, （1）the photo-induced exci- tation of the porphyrin chmmophore yields a local excited（LE） state;（2） the charge separation, in which the charge transfer （CT） state is followed by electron transition from porphyrin to C6o ; （3） the charge recombination, in which the CT state decays and returns to the ground state. The LE and CT states are assigned through the analysis of molecular orbital and their geometries are optimized by TD-DFT calculations. Also the charge separation and charge recombination processes are demonstrated by generalized Mulliken- Hush（GMH） method. The P-C6o in the two processes is approximated as a 2-state system and the electronic coupling that calculat- ed. The values of theoretical electron coupling are in reasonable agreement with the experimental observations. This work provided a useful method to analyse and predict photoinduced electron transfer process.