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ACID‐BASE EQUILIBRIA OF THE EXCITED SINGLET AND TRIPLET STATES AND THE SEMI‐REDUCED FORM OF ACRIDINE ORANGE
Author(s) -
Kellmann Arlette,
Lion Yves
Publication year - 1979
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.1751-1097.1979.tb07042.x
Subject(s) - acridine orange , chemistry , acridine , excited state , singlet state , flash photolysis , photochemistry , cationic polymerization , triplet state , fluorescence , chromophore , kinetics , molecule , atomic physics , reaction rate constant , organic chemistry , apoptosis , biochemistry , physics , quantum mechanics
Abstract— The acid‐base equilibria of the excited singlet and triplet states of acridine orange (AO) were studied by flash‐photolysis and fluorometric methods. The dye is a stronger base in the first excited singlet state (pK s = 13.3) than in the triplet and ground states (pK r = 10.3: pK c , = 10.2); acridine orange follows the trend observed with some other heterocyclic compounds, viz. pK s > pK r = pK, c . At room temperature, an anomalous fluorescence occurs from the dye in basic media: the assignment of this emission is discussed. The semi‐reduced dye was studied as a function of pH. In a large pH range (3–14), only the protolytic equilibrium between the cationic (AOH 2 + ) and the neutral (AOH) radicals was observed; the pK value corresponding to this equilibrium was found to be in the range of pH 5–6.