Determination of triplet formation efficiency from kinetic profiles of the ground state recovery.

A procedure is presented which allows determination of the triplet formation efficiency from the analysis of transient ground state bleaching curves obtained after short laser pulse excitation. Crucial factors that control the applicability and the accuracy of the method are discussed, such as a proper choice of the detection wavelength, which allows avoidance of interference from transient absorption. The technique is tested on porphycene and octaethylporphyrin and applied for several porphyrin derivatives used as photodynamic therapy agents.