Abstract: We have fully optimized the structures of the oligomers of (PF)_2n and (PFDBO)_n (n=1—4) using DFT/B3LYP method and calculated their P_I(v,a), E_A(v,a), E_HP , E_EP . The absorption spectra data were calculated at ZINDO and TD-DFT levels of theory. We analyzed the rules to the variation of their HOMO-LUMO energy gap with n rising and how the energy gap reflected the spectral properties of the oligomers to deduce the spectral properties of their polymers. We optimized the S₁ excited geometries and studied the emission spectra. Moreover, in the excited geometries all the framework atoms in a molecule are apt to coplanar. Above all, the dramatically twisted segment of seven-membered-ring in PFDBO(dihedral angel between it′s two phenyl ring is 42.5°±0.5°), because of CH₂OCH₂ caused the conjugated backbone broken. So the energy gap of it is broader, which makes in the max absorption and emission wavelengths of PFDBO shorter than PF′s.

Key words: Oligomeric fluorenes, Density functional theory, Absorptive spectrum, Luminescent properties