Photophysical behaviour of an opp-dibenzoporphyrin (2,12-diethyl-3,13-dimethyldibenzo[g,q]porphyrin) in micelles and organic solvents

Photophysical parameters relevant to photodynamic therapy have been studied for a novel lipophilic opp-dibenzoporphyrin (DBP), 2,12-diethyl-3,13-dimethyldibenzo[g,q]porphyrin, in N,N-dimethylformamide and TX-100 micelles. The structure of DBP is intermediate between a porphyrin and a phthalocyanine and is associated with higher molar extinction coefficients in the red Q-bands than those found in the haematoporphyrin derivative currently used for photodynamic therapy. The ultrafast measurements on DBP in DMF revealed a fast (ps) lifetime for the second excited singlet state. Observed lifetimes of the first excited singlet state were found to be similar in DMF and TX-100 (12.2 and 14.7 ns), but excited triplet lifetimes were different in the two solvents (0.46 and 2.86 micros). The fluorescent quantum yields of DBP in DMF and TX-100 were twice that of free-base tetraphenylporphyrin and the singlet oxygen quantum yield in DMF and TX-100 was high (0.56-0.65). The combination of stable chemical structure, stronger red-absorption, high singlet oxygen quantum yields, and high fluorescent quantum yields suggests that DBP is an potential chromophore for applications in photodynamic therapy.