Two-quantum photo-induced radical hydrogenation of porphyrins in solid frozen matrices

A new type of photochemical transformation of porphyrins in solid matrices, taking place as a result of two-quantum photo-excitation of porphyrin molecules to the highest triplet states, destruction of the solvent molecules, and addition of atomic hydrogen liberated in the process of photochemical destruction of the solvent to porphyrin molecules, was investigated. The reaction was conducted in frozen ethereal and alcoholic matrices exposed to radiation with λ=270–380 nm. It has been proposed that the product of this reaction is a radical monohydro-derivative of porphyrin with a structure of the same type as the structure of phlorin. The validity of this proposal was supported by the results of experiments on the separation of electrons from phlorin anions in ethereal matrices exposed to radiation with a wavelength of less than 300 nm. Quantum-chemical calculations of the equilibrium geometry of a phlorin radical and phlorin anion as well as of their energies and oscillator strengths have been performed. The calculated data were in good agreement with the data obtained from the experimental spectra. © Kluwer Academic/Plenum Publishers 1999.