DFT study on the geometric, electronic structure and Raman spectra of 5,15-diphenylporphine

The ground state geometric, electronic structure and Raman spectra of 5,15-diphenylporphine (H2DPP) have been studied using B3LYP/6-31G(d) method and compared with that of well-studied free base porphine (H2P) and meso-tetraphenylporphine (H2TPP). Calculation shows that 5,15-substitution causes remarkable in-plane distortion, whereas the resulting out-of-plane distortion is negligible. The calculated electronic structure of H2DPP is consistent with the absorption spectra compared with H2P and H2TPP. The calculated vibrational frequencies of H2DPP scaled with a single factor of 0.971 agree well with experimental data (the rms error is 8.0 cm−1). The assignment of experimental Raman bands of H2DPP was discussed on the basis of theoretical calculation and the comparison with that of H2P and H2TPP. The splitting of some vibrational modes involving the motion of Cm atom, such as ν1, ν8, and ν10, was observed and was attributed to the diversification of the environment around Cm atoms. As the shift of absorption peaks, the shift of some structure-sensitive Raman bands of H2DPP form that of H2TPP and H2P was attributed to the in-plane nuclear reorganization (IPNR) induced by phenyl-substitution, though the contribution of nonplanarity mechanism could not be excluded completely.