On the relationship between the radiative rate constant and the fluorescence intensity in organic fluorophores

In this Letter we explore the relationship between the radiative constant, kr, and the lineshape of an emission spectrum for fluorescent organic molecules, in particular tryptophan. We make a number of judicious approximations to the expression given by Strickler and Berg in conjunction with the log-normal function for the lineshape. Our result is a closed form expression for kr in terms of the inverse maximum wavelength λmax−1 which compares well with recent experimental findings for tryptophan residues in proteins.