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Photoexcited States of UV Absorbers, Benzophenone Derivatives
Author(s) -
Kumasaka Ryo,
Kikuchi Azusa,
Yagi Mikio
Publication year - 2014
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/php.12257
Subject(s) - phosphorescence , benzophenone , photochemistry , chemistry , acetonitrile , excited state , absorption (acoustics) , singlet oxygen , absorption spectroscopy , singlet state , fluorescence , oxygen , materials science , organic chemistry , optics , atomic physics , physics , composite material
The UV absorption, phosphorescence and phosphorescence‐excitation spectra of benzophenone ( BP ) derivatives used as organic UV absorbers have been observed in rigid solutions at 77 K. The triplet–triplet absorption spectra have been observed in acetonitrile at room temperature. The BP derivatives studied are 2,2′,4,4′‐tetrahydroxybenzophenone ( BP ‐2), 2‐hydroxy‐4‐methoxybenzophenone ( BP ‐3), 2,2′‐dihydroxy‐4,4′‐dimethoxybenzophenone ( BP ‐6), 5‐chloro‐2‐hydroxybenzophenone ( BP ‐7) and 2‐hydroxy‐4‐ n ‐octyloxybenzophenone ( BP ‐12). The energy levels and lifetimes of the lowest excited triplet ( T 1 ) states of these BP derivatives were determined from the first peak of phosphorescence. The time‐resolved near‐ IR emission spectrum of singlet oxygen generated by photosensitization with BP ‐7 was observed in acetonitrile at room temperature. BP ‐2, BP ‐3, BP ‐6 and BP ‐12 show photoinduced phosphorescence enhancement in ethanol at 77 K. The possible mechanism of the observed phosphorescence enhancement is discussed. The T 1 states of 2‐hydroxy‐5‐methylbenzophenone, 4‐methoxybenzophenone and 2,4′‐dimethoxybenzophenone have been studied for comparison.