共轭聚合物链中光激发过程的无序效应

Effects of intrachain disorder on photoexcitation in conjugated polymer chains

应用包含链内无序和电子关联的Su-Schriffer-Heeger模型,研究了共轭聚合物链中无序效应在光激发演化过程中的作用,尤其是对激子产率的影响.采用multi-configurational time-dependent Hartree–Fock方法处理电子部分的含时Schrödinger方程,而晶格部分的运动则由经典的牛顿方程决定.研究发现,加入无序后,光激发弛豫后的产物与纯净聚合物链中有着定性的不同.相比于纯净聚合物中光激发下会有一定的概率直接生成极化子对,考虑无序效应后则更趋向于生成激子,并且激子的产率很大程度上依赖于无序的类型和强度.另外还研究了电子-电子相互作用和共轭链长度对激子产率的影响.

The luminescence efficiency of conjugated polymers has been a central topic in the study of light emitting.The effect of disorder plays an important role in generating excitons after the conjugated polymers have been excited by photons.In this paper,by using the Su-Schriffer-Heeger model,which has been modified to include intrachain disorder and electron correlation,we investigate the effects of disorder on the photoexcitation,especially on the yield of excitons in a conjugated polymer chain.We adopt the multi-configurational timedependent Hartree–Fock method to solve the multi-electron time-dependent Schrödinger equation and the Newtonian equation of motion for the lattice vibration.The results show that after the photoexcitation relaxation process,the products of the disordered polymer chain are qualitatively distinct from those of the pure polymer chain.While the pairs of polarons can be generated directly after the photoexcitation in a pure polymer chain,the disorder favors excitons as the products of the photoexcitation,and the yield of excitons depends crucially on the kind and strength of the disorder.Furthermore,the influences of the electron correlation and the conjugation length on the yield of excitons are also discussed.Specifically,we find that in the case of diagonal disorder,when the conjugation length is short and the diagonal disorder is weak,the excitons are mainly generated by the recombination of two lattice defects with a high yield of excitons which will be reduced as the conjugation length increases.The excitons tend to be generated directly with a low yield of excitons which is enlarged as the disorder gets stronger when the conjugation length is long or the diagonal disorder is strong.The on-site Coulomb repulsion favors the generation of excitons as well.The case of off-diagonal disorder is similar to that of diagonal disorder except that the on-site Coulomb potential favors the generation of excitons in the weak disorder regime but depresses the generation of excitons in the strong disorder regime.When both diagonal and off-diagonal disorders are considered,the yield of excitons is dominated by the offdiagonal disorder.We hope that our investigations can provide useful guidance and help for designing organic photoelectric materials and devices.