Analysis of fluorescence spectra of PRODAN in protic solvents as the superposition of two Gaussian functions

Abstract

The steady-state fluorescence emission spectra of 6-propionyl-2-dimethylaminonaphthalene(PRODAN) in aqueous solutions of methanol, ethanol and 1-propanol were studied in a widerange of concentrations. The flourescence of PRODAN was also studied in aqueous solutions(from 0.003 to 0.021 mole/liter) of dodecyltrimethylammonium bromide (DTAB),a micelle-forming ionic surfactant. In all cases, experimental data, as a function of wavelength,are very well fitted by the sum of two Gaussian functions. In alcohol solutions, the maximumof lower wavelength depends linearly both on concentration and polarizability. In DTABsolutions, the maximum of higher wavelength varies smoothly with concentration, but thelower wavelength maximum changes abruptly at the Critical Micellar Concentration.Results are explained by assuming that the fluorescence emission of PRODAN is originatedin transitions from two excited states which are close in energy but have dissimilar interactionswith the probe environment.