The solvent polarized continuum model on the basis of the density functional B3LYP/6-31G(D) level was used to study the molecular geometrical structures and orbital energy levels of porphyrin and magnesium porphyrin in the solvents with different polarities such as tetrahydrofuran, dimethysulfoxide, dichloromethane, chloroform, and further the variation of the molecular structure and orbital energy level caused by the solvent effect. The geometrical structures optimized in the solvents above on the time dependent density functional level were then used to calculate the excitation energy, absorption wavelength, oscillator strength and the orbital composition of the electronic transition. According to the calculation results, compared with the geometrical structures of porphyrin and magnesium porphyrin molecules in the vacuum state, the molecular geometrical structures have a little variation in all the solvents considered, which becomes stronger along with the increase in the dielectric constants of the solvents. It was also found that the absorption wavelengths of porphyrin and magnesium porphyrin had the general red shift. The molecular orbital theory was used to give a possible explanation for this variation, and the feasibility of using the theoretical analysis involving solvent effect to check the possibility of porphyrin compounds as a photosensitizer of dye-sensitized solar cells was also discussed.

Key words: density functional theory, molecular structure, molecular orbital, electronic absorption spectra, dye-sensitized solar cell