The trimer geometric structures of PPV-like derivatives substituted by CN and CF₃ were optimized using density functional theory (DFT) at B3LYP/6-31G(d) level. The UV absorption spectra of the corresponding compounds were also calculated using time-dependent density functional theory (TD-DFT) at the same level. We analysed the molecular geometric structures, the frontier molecular orbital energy levels and the electron cloud distributing rules of the PPV-like derivatives substituted by CN and CF₃ groups. We simultaneously interpreted the different influence of conjugated CN and non conjugated CF₃ electron withdrawing substituents on photo-electricity properties of their derivatives. The former leads to the red shift of UV absorption spectrum of the corresponding compounds, and the latter leads to the blue shift. The calculations have also shown that the UV absorption spectrum of the compounds calculated by TD-DFT method agrees well with the experimental data. In addition, the LUMO energy levels of the corresponding PPV-like derivatives are lowered and their electron affinities increase with the introduction of the electron withdrawing substituents CN and CF₃. The PPV-like derivatives are all good electron transporting materials.

Key words: PPV-like derivative, UV absorption spectrum, time-dependent density functional theory(TD-DFT), electron withdrawing substituent