A Density-Functional Study on the Change of Q/B-Band Intensity Ratio of Zinc Tetraphenylporphyrin in Solvents

摘要

We study the Q/B-band intensity ratio (I_(Q/B)) of zinc tetraphenylporphyrin (ZnTPP) in various solvents from its electronic structure by utilizing the polarizable continuum model and density functional theory (DFT). The selected solvents are benzene, chloroform, dichloromethane, pyridine and methanol. The Q/B-band intensity ratio is simplified by dipole strength of HOMO→LUMO and HOMO-1→LUMO from a two-level system, or f_(Q/B). The results show the linear correlation between the calculated f_(Q/B) and the experimental I_(Q/B). This suggests that I_(Q/B) of ZnTPP in solvents can be studied from dipole strength ratio from a two-level system, where the orbitals are determined by DFT. The change of f_(Q/B) is due to the change of frontier molecular orbital shape of ZnTPP which are dominantly constructed by p_z-orbital. In the core part of ZnTPP, the change of p_z-orbital shape is inversely proportional to the solvent dielectric constant, ε.