Bidirectional energy transfer between the triplet T-1 state of photofrin and singlet oxygen in deuterium oxide

Singlet oxygen ((1)Delta (g)) was generated by the photoactivated photosens itizer photofrin, which is clinically approved for photodynamic therapy (PD T). Using a new infrared sensitive photomultiplier, the complete time depen dence of singlet oxygen luminescence in D2O was measured. All relevant rela xation rates and rate constants for the triplet T-1 state of photofrin and for singlet oxygen were determined. For the first time, an effective back t ransfer of energy from singlet oxygen to the triplet state of photofrin was found, affecting the rise and decay rates of the luminescence of singlet o xygen. (C) 2001 Elsevier Science B.V. All rights reserved.