Fluorescence quantum yield evaluation of strongly absorbing dye solutions as a function of the excitation wavelength

Abstract

A simple method to evaluate fluorescence quantum yields based on corrected fluorescence emission spectra of dyes in dilute and strongly absorbing solutions using different excitation wavelengths is presented. The method is supported by a detailed knowledge of the apparatus geometry and energy profile of excitation. Several recommended quantum counters were used (9,10-diphenylanthracene, rhodamines 101 and B, cresyl, violet, oxazine 1 and 1-ethyl-4-(4- p-dimethylaminophenyl)-1,3 butadienyl)-quinolinium perchlorate, (LDS 798) to cover the emission range from the UV to the visible and near-IR A curve of correction factor f vs. the optical density of the samples was obtained enabling an accurate determination to be made of the fluorescence quantum yield as a function of concentration and excitation wavelength. A case study of two squaraines (bis[4-(dimethylamino)phenyl]squaraine (HSQ) and bis[4-(dimethylamino)-2-methylphenyl]squaraine (MeSQ)) is presented. The quantum yields of these squaraines were obtained in saturated solutions in dichloromethane and in dilute samples at room temperature. The quantum yields determined are the same for high and low concentrations of the compounds indicating that no aggregation effects occur.