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PROTOLYTIC EQUILIBRIA IN THE LOWEST EXCITED SINGLET STATES OF 2‐HYDROXYQUINOLINE AND 4‐HYDROXYQUINOLINE
Author(s) -
SCHULMAN S. G.,
CAPOMACCHIA A. C.,
TUSSEY B.
Publication year - 1971
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.1751-1097.1971.tb06212.x
Subject(s) - excited state , chemistry , singlet state , titration , tautomer , ground state , 8 hydroxyquinoline , fluorescence , photochemistry , ion , stereochemistry , inorganic chemistry , atomic physics , organic chemistry , physics , quantum mechanics
— Fluorescence spectra of 2‐ and 4‐hydroxyquinoline in a variety of solvents indicate that the lactam‐lactim tautomerism favoring the lactam structure in the ground state also favor the lactam structure in the lowest excited singlet state. Fluorimetric titrations show that the cations of both isomers become slightly more acidic in the lowest excited singlet state and that the anion of the 2 isomer becomes slightly more basic in the excited state. The excited anion of the 4 isomer is either identical in basicity to the ground state anion or does not equilibrate with the quinolone during the lifetime of the excited state. The Forster cycle is found to give a pK α * values in generally poor agreement with those obtained from fluorimetric titrations. The reasons for this are discussed.