ACID-BASE EQUILIBRIA OF THE EXCITED SINGLET AND TRIPLET STATES AND THE SEMI-REDUCED FORM OF ACRIDINE ORANGE |
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Authors: | Arlette Kellmann Yves Lion |
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Institution: | Laboratoire de Photophysique Moléculaire du CNRS, Universitéde Paris-Sud. 91405 Orsay, France |
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Abstract: | 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 (pKs= 13.3) than in the triplet and ground states (pKr= 10.3: pKc, = 10.2); acridine orange follows the trend observed with some other heterocyclic compounds, viz. pKs > pKr= 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 (AOH2+) 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. |
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