Photophysics and Spectroscopic Properties of Zinc Phthalocyanine Revisited using Quantum Chemistry

This study provides a theoretical evaluation of the photophysical behavior of zinc phthalocyanine (ZnPc) using density functional theory (DFT) and its time-dependent (TD-DFT) approach, based on the combination of the B3LYP hybrid functional and the 6-311+ G(d,p) basis set. The influence of solvation was estimated using IEFPCM (integral equation formalism approach of polarizable continuum model) considering DMSO (dimethyl sulfoxide) as solvent. The simulated absorption spectra were based in the calculation of the first 40 excited states being that the eight most intense peaks could be assigned to the Q and Soret (B) bands. Fluorescence emission wavelength and radiative lifetime were calculated using the TD-DFT approach and compared to experimental data. The ZnPc intersystem crossing (ISC) phenomena was attributed to spin-orbit coupling induced by Zn2+ since the adjacent singlet and triplet states have the same orbital symmetry. The phosphorescence data in gas phase were also compared.