On the photophysical properties of Al-, Ga- and In-hemin complexes: a quantum chemical investigation

Photophysical properties of the recently synthesized Al(III), Ga(III) and In(III)-hemin complexes have been studied, in particular, the most important properties relevant to their proposed use as new photosensitizers for photodynamic therapy (PDT). Minimum energy structures, excitation energies, singlet-triplet energy gaps (Δ<i>E</i>_S₁-T), spin-orbit coupling constants (SOCs), and intersystem kinetic constants were computed at a Gaussian variant of B3LYP coupled with x2c-SVPall and D4 Grimme's dispersion in SMD simulated solvent. To verify whether intersystem crossing here can efficiently occur, the kinetic constants for their fluorescence were determined. Based on our results, the possible deactivation paths were predicted. Furthermore, the possibility of producing superoxide O₂˙^- through type I reactions was examined. The results showed them having photophysical properties that would make them suitable as photosensitizers in antimicrobial photodynamic therapy.