Photophysical and photochemical properties of potential porphyrin and chlorin photosensitizers for PDT

Structural and optical properties as well as photophysical and photochemical parameters (excited S-1 and T-1 state lifetimes at 77 K and in the presence of O-2 in solution at 293 K; efficiencies of singlet oxygen, (1) Delta(g), generation) are presented for porphyrins and chlorins with potential for the PDT of cancer: chlorin p(6) and its trimethyl ester, chlorin e(6) and its Na-3 and K-3 salts, purpurin-18 and its monomethylester, 5,10,15,20-tetrakis(3-methoxyphenyl)porphyrin (TPPM), 5,10,15,20-tetrakis(2,4-difluoro-3-methoxyphenyl) (TPPMF) and GaTPP in different solvents (ethanol, toluene, pyridine and buffer pH 7.4) at 77-300 K. It has been shown that for monomeric chlorin e,, chlorin p, and its derivatives the photophysical parameters are similar, as follows: fluorescence lifetimes tau(s) in the presence of oxygen are 3.2-4.5 ns at 293 K; fluorescence quantum yields phi(f) vary from 0.1 to 0.2 depending on the solvent; phosphorescence quantum yields phi(f) are of the order 10(-5); T-f state lifetimes tau(T) = 1.5-2.0 ms al 77 K and 250-390 ns at 293 K in the presence of O-2. By use of the direct kinetic measurement of singlet oxygen emission at 1.27 mu m on laser excitation the quantum yields of (1) Delta(g), generation by chlorins have been measured: phi(Delta) = 0.35-0.68. In this case values of phi(f) and phi(Delta) depend strongly on the solvent, probably because of the formation of aggregates. For TPPM, TPPMF and Ga-TPP the phi(Delta) values measured are higher (0.87-0.98) and are explained by the higher intersystem crossing S-1 --> T-1 quantum yields.