Gas-Phase Electronic Structure of Phthalocyanine Ions: A Study of Symmetry and Solvation Effects

Research into and applications of phthalocyanines (Pc) are mostly connected to their intriguing electronic properties. Here, messenger-type UV-vis spectroscopy of two metal-free ions from the phthalocyanine family, cationic H₂Pc⁺ and H₂PcD⁺, along with their hydrates is performed. They show that the electronic properties of both ions can be traced to those in the conjugate base, Pc^2-, however, they are affected by state splitting due to the reduced symmetry; in the H₂Pc⁺ radical cation, a new band appears due to excitations into the singly-occupied molecular orbital. Quantum chemical spectra modeling reproduces all important features of the measured spectra and provides insight into the nature of electronic transitions. Hydration of the ions has only a mild effect on the electronic spectra, showing the stability of the electronic structure with respect to solvation effects.