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AN EPR STUDY ON THE TRIPLET STATE OF PURINE FREE BASE IN AQUEOUS GLASSES AT 77 K
Author(s) -
Arce R.,
Rivera M.
Publication year - 1982
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.1751-1097.1982.tb02638.x
Subject(s) - intersystem crossing , electron paramagnetic resonance , chemistry , free base , excited state , triplet state , ionic bonding , aqueous solution , cationic polymerization , photochemistry , ionic strength , nuclear magnetic resonance , ion , atomic physics , molecule , salt (chemistry) , polymer chemistry , organic chemistry , physics , singlet state
— Since purine free base in aqueous solution exists in different ionic forms at different pHs and most of its photoreactions are likely to involve the triplet excited states of these different ionic forms, electron paramagnetic resonance studies (EPR) have been performed in order to determine intersystem crossing quantum yields and other characteristic parameters of the excited triplet state of these forms. Intersystem crossing yields decrease with a decrease in pH, being 0.62, 0.37 and 0.10 in 8 M NaOH, 8 M NaCIO 4 and 6M H 3 P0 4 glasses, respectively. Differences in triplet decay lifetimes 3.4, 2.5 and 3.1 s, as well as in root mean‐square zero‐field splitting (ZFS) parameter, D * , (0,1304, 0.1512 and 0.1353 cm ‐1 ) are also observed for the anionic, neutral and cationic species of purine free base. The EPR signals of the triplet state of the neutral and anionic forms have been observed simultaneously in the pH range of7–10.