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.

Key words: polymer, density functional theory, optical property