A Time-Resolved Thermal-Lensing Investigation of Photosensitization of Singlet Oxygen

Abstract

Dual beam time-resolved thermal-lensing (TRTL) is a sensitive calorimetric tool capable of resolving heat evolution due to radiationless deactivations as either fast or slow with respect to the acoustic transit time τ_a in the system (in our case using focused beams, τ_a ≃ 100 ns). This enables us to obtain information regarding quantum yields and lifetimes of energy storing species. We have previously outlined the characteristics and capabilities of our system with a number of examples [1] and more recently shown its application in evaluating the photosensitizing properties of hematoporphyrin [2], a molecule attracting interest as a sensitizer in photodynamic therapy of cancers. In the present study we have investigated the production of singlet molecular oxygen, O₂(¹∆_g), formed by energy transfer from a variety of triplet sensitizers in oxygen saturated solutions, in an attempt to gain an insight into the properties determining the efficiency of photosensitization.