Fluorescence and photostability studies of anthracene-9-carboxylic acid in different media

摘要

Electronic absorption and fluorescence spectra of anthracene-9-carboxylic acid (ANCA) werestudied in different homogeneous solvents, binary protic/aprotic solvent mixtures and in heterogeneoussolutions of the cationic cetyltrimethyl ammonium bromide (CTAB) micelle. Different chemical species ofANCA were identified spectroscopically in different media. The results are discussed on the basis of a mechanismthat involves two equilibria: acid-base equilibrium and monomer-dimer equilibrium. These equilibriawere found to be very sensitive to the nature of the medium and the concentration of ANCA.Moreover, while it is photostable in most solvents studied, the ANCA was found to be photolabile in aqueousmedia of different pHs. The acid-base catalyzed photodegradation rate was studied by following upabsorption and/or fluorescence intensities as a function of illumination dose. The determined rate of thephotochemical degradation of ANCA depends on the nature of the medium. The first order degradation rateconstant is remarkably enhanced in heterogeneous medium of CTAB. As expected, the determined activationenergy is low (～3.2 kJ.mol-1). This result favors photooxidation process. Anthraquinone was the main photodegradationproduct obtainedvia9,9′-dicarboxylic head-to-head dimer of anthracene that was identifiedby GC-Mass technique.