We investigated the relationship between the chemical structure involving the pentacoordinate silicon and the electronic properties of the molecules. The substituent effects on the electronic structures of dibenzo[b,f]silepins containing pentacoordinate silicon were evaluated with two series of position isomers with electron-donor and/or electron-acceptor groups by NMR, UV-vis absorption and photoluminescence spectroscopies. It was found that the electronic structures of the complexes were strongly influenced by the type of substituent on the silicon center. In contrast,the substituents at the dibenzosilepin moiety showed only slight electronic perturbation. In 2,8-diaryl substituted compounds,the electron-donating group induced the emission peak to shift to longer wavelength regions than those observed with an electron-withdrawing group. In 3,7-diaryl substituted dibenzo[b,f] silepins,the introduction of both the fluorine group at the silicon center and the methoxy group on the dibenzosilepin moiety also led to bathochromic shifts in the absorption spectra. This is the first study,to the best of our knowledge,to offer systematic information on the substituent effects on the electronic structure of the pentacoordinate complex.