芴-硫芴共聚物的电子结构和光谱性质的理论研究

用DFT-B3LYP方法对低聚物(PF30T)_n n(芴)∶n(硫芴)＝2∶1, 物质的量之比, n＝1～4], (PF50T)_n n(芴)∶n(硫芴)＝1∶1, 物质的量之比, n＝1～4]体系全优化, 得到两系列低聚物的电离能(IP_(a,v))、电子亲和势(EA_(a,v))、空穴抽取能(HEP)、电子抽取能(EEP). 在此基础上用ZINDO和TD-DFT方法计算吸收光谱, 分析了两个系列的HOMO-LUMO能隙随着n递增的变化趋势及硫芴含量对低聚物电子结构和光谱性质的影响, 推断了高聚物的电子和光谱性质. 用ab initio CIS方法优化了低聚物的S₁激发态结构并分析了其与发射光谱的关系. 研究显示: 2,8位引入的硫芴基团, 破坏了链的共轭, 而且随着硫芴含量的增加, HOMO-LUMO能隙变大, 光谱蓝移; 激发态结构趋于共面化.

Theoretical Investigation on Electronic Structure and Optical Proper-ties of Polyfluorene by Copolymerization with Dibenzothiophene

We have full optimized the structures of the oligomers of (PF30T)_n n(fluorene)∶n(dibenzothiophene)＝2∶1, n＝1～4] and (PF50T)_n n(fluorene)∶n(dibenzothiophene)＝1∶1, n＝1～4] with DFT/B3LYP method, and calculated the IP_(a,v), EA_(a,v), HEP and EEP. Using TD-DFT and ZINDO methods on the structures of the optimized oligomers, we analyzed the trend of the variation of HOMO-LUMO gaps with 1/n and the influence on the spectral properties with the increasing of dibenzothiophene, and extrapolated the electronic structure and optical properties of the polymers. We optimized the S₁ excited ge-ometries with ab initio CIS and studied the relation of S₁ state and emission spectra. It shows that all atoms come to coplanar in S₁ state. The results show that, with introducing dibenzothiophene at the 2,8 positions of fluorene, the conjugation is broken, the HOMO-LUMO gaps are broader, and the spectrum is blue-shifted.