In order to well understand the halogen (F₂, Cl₂, Br₂, I₂, ICl) doping effect on electronic structure of poly(methylphenyl)silane (PMPSi), a theoretical investigation on halogen doped models has been performed using density functional theory (DFT). The optimized structures of PMPSi are obtained at the BH&HLYP/6-31G^* level, and the stagger conformation is the most stable conformation among three isomers. Halogen doped PMPSi were optimized at the BH&HLYP level based on the stagger conformation, and the changes of geometry parameters are compared for PMPSi and halogen doped PMPSi. Furthermore, frontier molecular orbital energies and electronic absorption spectra of halogen doped PMPSi are investigated. The results show that energy of the highest occupied molecular orbital (HOMO) almost keeps the same when PMPSi is doped by halogen, but energy of the lowest unoccupied molecular orbital (LUMO) becomes lower, the energy gap is therefore decreased according to the order Cl₂>F₂>ICl>Br₂>I₂. When PMPSi is doped by halogen, electron transition is assigned to the HOMO-1→LUMO, it leads to red shift of the absorption spectrum of complex, and presents relative strong absorption peak in visible region. Natural bond orbital (NBO) analyses were performed to study the charge distribution of halogen doped PMPSi, it is found that charge transfer from backbone to halogen in the complex. The interaction energies of all the complexes which were corrected for basis set superposition error (BSSE) are from -0.61 to -3.20 kcal/mol. The result what arouse most interest is, the higher polarity of dopant, the larger interaction energy of complex. In addition, the influence of position of dopant on energy gaps and interaction energies of all complexes is discussed in our present work. This study is expected to provide theoretical clues and foundation for future research on improving the photoelectric property of PMPSi.

Key words: poly(methylphenyl)silane, doping effect, energy gap, absorption spectrum, charge transfer