Calculation of the structure and absorption spectra of phthalocyanines in the gas-phase and in solution

Ab initio calculations have been carried out on both gas-phase and solvated phthalocyanines in order to determine equilibrium structures, vibrational spectra, and electronic spectra. Density functional theory (DFT) optimized geometries have the expected symmetries of D-2h for free-base phthalocyanin e, D-4h for copper phthalocyanine, and C-4v for tin phthalocyanine, whereas Hartree-Fock optimized geometries, which also include lead phthalocyanine, are slightly displaced from the expected symmetries. Both sets of optimize d geometries agree reasonably well with the available experimental structur es. Vibrational spectra, calculated by the Hartree-Fock method, are in part ial agreement with measured spectra, whereas visible absorption spectra cal culated using molecular geometries obtained at three different levels of th eory (DFT, HF, and PM3) showed good agreement with the measured vapor-phase spectra in the Q-band, and using the DFT optimized geometry resulted in ve ry good agreement with measurements in the B-band. The self-consistent reac tion held method for including bulk solvent effects in HF calculations had a small, nearly negligible, effect on the molecular structure of SnPc, wher eas the DFT/COSMO solvation model yielded the predictable result of increas ing the Sn-N bond length by pulling the Sn atom further out of the molecula r plane. (C) 1998 Elsevier Science B.V. All rights reserved.