A comparison of photosensitizing properties of meso-tetraphenylporphin in acetone and in dimethyl sulfoxide

Infrared time and spectral resolved phosphorescence measurements of a lipophylic photosensitizer meso-tetraphenylporphin, were used to compare its ability to generate singlet oxygen at various conditions in two different solvents: clinically used dimethyl sulfoxide and acetone as a standard spectroscopic solvent. Triplet state population of tetraphenylporphin in acetone is mostly quenched by oxygen, whereas in dimethyl sulfoxide the quenching by oxygen is substantially less important and the tetraphenylporphin phosphorescence kinetics are dominated by triplet–triplet quenching. The triplet–triplet quenching rate constant of (3.1±0.5)×109 M−1 s−1was determined. The lifetime of singlet oxygen obtained in acetone was above 50 μs. On the other hand it was only 1.8 μs in air saturated dimethyl sulfoxide, where quenching of singlet oxygen by oxygen was observed. The quantum yield of singlet oxygen production photogenerated by tetraphenylporphin in air saturated dimethyl sulfoxide was found to be only 11% of the value obtained in acetone.