Photophysics of some common fluorescence standards

An accurate study of the fluorescence decay and fluorescence quantum yield of three fluorescence standards is made. From data on 9,10-diphenylanthracene it is concluded that (a) the refractive index squared correction employed in relative quantum yield measurements in right-angle fluorometers is valid, (b) a refractive index squared term is required for the valid comparison of radiative lifetimes of the same molecule measured in different solvents and (c) the fluorescence quantum yield is less than unity and is essentially independent of the solvent (φF = 0.93 ± 0.03 in four non-polar solvents). Further results are presented on the complex kinetics of the fluorescence decay of quinine bisulphate in aqueous H2SO4 solutions; a model is proposed which accounts adequately for these observations. Some results are presented for 2-aminopyridine in aqueous H2SO4 solutions which suggest that this may also be a useful fluorescence standard; we measured φF = 0.66 and τF = 9.6 ns in both 1 and 0.1 N H2SO4 solutions. However, disagreement about these values and the strong temperature dependence of φF that is observed renders this compound less acceptable as a standard than quinine bisulphate in 1 N H2SO4 solution.