Singlet oxygen quantum yields from halogenated chlorins: potential new photodynamic therapy agents

Flash photolysis and photoacoustic calorimetry were used to measure the energy-transfer rates and singlet oxygen quantum yields originated by the triplet states of halogenated tetrakisphenylporphyrins and related chlorins in aerated toluene. The chlorins (lambda (max) approximate to 660 nm, epsilon approximate to 3 x 10(4) M-1 cm(-1)) have long-lived triplet states (>12 mus) in the absence of molecular oxygen, and in its presence the singlet oxygen production quantum yields of the 2-chloro and 2,6-dichlorophenyl derivatives are 0.89 +/- 0.05 and 0.98 +/- 0.02, respectively. The high absorptivity in the red, the photostability and the efficiency of these chlorins in producing singlet oxygen suggests a ground for the development of better sensitisers for photodynamic therapy. (C) 2001 Elsevier Science B.V. All rights reserved.