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THE PHOTOSENSITIZERS BENZOPHENOXAZINE and THIAZINES: COMPREHENSIVE INVESTIGATION OF PHOTOPHYSICAL and PHOTOCHEMICAL PROPERTIES
Author(s) -
Becker Ralph S.,
Chakravorti Sankar,
Das Suresh
Publication year - 1990
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/j.1751-1097.1990.tb01962.x
Subject(s) - photochemistry , chemistry , intersystem crossing , singlet oxygen , triplet state , protonation , quantum yield , singlet state , excited state , methanol , singlet fission , fluorescence , oxygen , molecule , organic chemistry , ion , physics , quantum mechanics , nuclear physics
Eight differently substituted title dye compounds have been investigated regarding intersystem crossing, triplet state, fluorescence and singlet excited state pK a properties. In general, non‐halogenated oxazines and thiazines as well as a mono bromooxazine show very low triplet quantum yields, φ T (lT 0.03) and relatively long triplet lifetimes (‐40 μs) in acidic methanol. The φ T data correlate well with known singlet oxygen yields. In basic methanol no triplet transient is observed but a significant yield of a ground state transient protonated (base dye) form is produced with a short lifetime, ‐400 ns. Fluorescence can be seen simultaneously from both the excited base and the protonated base dye forms in basic methanol. For iodinated oxazine or thiazines, the triplet yield increases and can be as high as 0.5 (diiodo case) in acidic methanol. The triplet lifetimes are further shortened to ‐10 μs compared to the non‐iodinated derivatives above. The triplet yields of the iodo compounds are higher or equal to known singlet oxygen yields. In basic methanol triplet yields up to 0.2 can be seen, the triplet lifetime are shortened still further to 1 μs but no observable protonated form is produced (in distinction to the non‐iodinated cases). Consideration is given to the correlation of triplet and singlet oxygen yields, ground and excited pK a properties, spin‐orbit coupling and internal conversion properties, solvent effects, and phototherapeutic activity of these dyes.