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Frequency‐domain Measurement of the PhotodegradationProcess of Fluorescein ¶
Author(s) -
Gaigalas A. K.,
Wang Lili,
Vogt Robert F.
Publication year - 2002
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 - 10.1562/0031-8655(2002)0760022fdmotp2.0.co2
Subject(s) - photodegradation , fluorescein , fluorescence , excited state , photochemistry , chemistry , reaction rate constant , aqueous solution , optics , kinetics , atomic physics , physics , photocatalysis , biochemistry , quantum mechanics , catalysis
ABSTRACT The frequency‐domain technique is applied to measure the photodegradation rate of fluorescein in aqueous solutions. The illuminating light is modulated, and the changes in fluorescence from the illuminated region are detected synchronously. A constant flow rate is imposed on the fluorescein solution to control the mass transport of fluorescein into the illuminated region. The fluorescence response is described by a model that assumes that photodegradation occurs from the triplet excited state. The predictions of the model are consistent with the observed variations in the fluorescence response with flow rate, modulation frequency and incident power. We discuss in this article how the dependence of the model parameters on experimental conditions can be used to infer the photodegradation rate as well as some of the details of the photodegradation mechanism. The results are consistent with the known mechanism of photodegradation of fluorescein. The frequency‐domain technique gives a photodegradation rate of 53 s −1 in an air‐saturated solution and 37 s −1 in solutions purged with argon gas.