Spatial Factors for Triplet Fusion Reaction of Singlet Oxygen Photosensitization
Abstract
First-principles quantum-chemical description of photosensitized singlet oxygen generation kinetics is challenging due to the intrinsic complexity of the underlying triplet fusion process in a floppy molecular complex with open-shell character. With a quantum-chemical kinetic model specifically tailored to deal with this problem, the reaction rates are investigated as a function of intermolecular incidence direction, orientation, and distance between O2 and the photosensitizer. The adopted photosensitizer, 6-azo-2-thio-thymine, combines practical interest and prototypical variability. The study quantitatively determined maximum singlet oxygen generation rates for fifteen incidence/orientation directions, showing that they span five orders of magnitude between the largest and the smallest rate. Such information may provide a hands-on guideline for the experimental molecular design of new photosensitizers as well as further higher-level theoretical research. TOC graph
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