Quantum-chemical and experimental kinetical investigation of the porphyrin diacids: role of the counterions in non-radiative deactivation of the excited electronic states

The photophysical properties of a series of porphyrin diacids have been studied theoretically at the density functional theory level and experimentally by measuring decay kinetics of S1 and T1 excited states of the diacids. The existence of a new pathway of the effective non-radiative deactivation of the lowest singlet and triplet excited states of the porphyrin diacids due to electron transfer from the acid residues to the porphyrins has been suggested.