LOG-NORMAL DESCRIPTION OF FLUORESCENCE-SPECTRA OF ORGANIC FLUOROPHORES

The smooth fluorescence bands of various organic fluorophores of diffe rent classes (e.g. indole, tryptophan, tyrosine, phthalimides, quinine sulfate, aminopyridines, acetylanthracenes) in different ionization s tates of their substituents and dissolved in various solvents can be a ccurately fitted on the frequency (wavenumber) scale by the four-param etric log-normal distribution curves up to the far spectral wings, Thi s fact suggests that the lognormal function is a good analytical descr iption for smooth emission spectra of so-called complex molecules, Exa mination of log-normal parameters of 126 spectra of several tryptophan derivatives measured in different ionization states in various solven ts revealed a straight-linear relation between three shape parameters of the lognormal function, namely, the positions of spectral maxima an d of the two half-maximal amplitudes, This fact indicates that only on e parameter is needed to describe the band shape for the set of trypto phan derivatives, A similar linearity was also observed for the series of spectra of 1- and 2-acetylanthracenes or 3-amino-N-methylphthalimi des when varying the solvent, As a result, the spectral maximum positi on can entirely determine the shape of emission spectra of a series of a fluorophore derivatives in any environmental condition, Such a simp lified mathematical representation significantly facilitates the probl em of analytical resolution of composite fluorescence spectra, for ins tance, those of proteins.