Effect of excited state self-quenching on singlet oxygen photogeneration using nanosheet surface assembled zinc phthalocyanine

Abstract

The numerous applications of singlet molecular oxygen (¹O₂)-based photosensitized oxidation reactions comprising fascinating processes have been explored. Although phthalocyanines are among the promising chromophores for facilitating ¹O₂ photogeneration via long wavelength visible light region absorption, they tend to form aggregates, which reduce photochemical reaction efficiency. Notably, the aforementioned aggregation of sensitizers can be suppressed by immobilizing the sensitizer on nanomaterial surfaces. However, undesired intramolecular photochemical reactions, such as self-quenching reactions, may also occur in systems on whose surfaces such dyes are densely immobilized. In this study, we investigated the effect of the adsorption density of phthalocyanine onto nanosheet surfaces on the efficiency of ¹O₂ photogeneration, exploring the reaction process based on the photodegradation efficiency of a ¹O₂ scavenger (9,10-antracenediyl-bis(methylene) dimalonoic acid; ADMA) and via steady-state emission and transient absorption spectroscopies. Furthermore, the singlet-oxygen photogeneration efficiency was estimated from the quantum yield (QY) of ADMA decomposition. The results confirmed that the self-quenching of the excited singlet state mainly contributed to decreasing ADMA-photodegradation QY, indicating that the suppression of such self-quenching processes or the promotion of intersystem crossing would improve the photodegradation QY.