The Form of the Absorption Bands in Solutions of the Organic Dyes, and a Relation Between Absorption and Fluorescence

To account for the breadth of the absorption and fluorescence bands in solutions and for the fact that the absorption and emission bands are not coincident it is assumed that for a given position relative to the solvent molecules the potential energy of an excited molecule is different from that of a normal molecule, and that the change in the potential energy that occurs during excitation or emission is to be counted as a part of the energy that determines $h\nu$. This leads to a general relation between the intensity of fluorescence $F$ for the frequency $\nu$ and the coefficient of absorption for the same frequency, viz. $F=K^{\prime }\nu e^{-\frac{h\nu }{\mathrm{kT}}}$ in which $K^{\prime }$ is a function of $T$ and probably of $\nu$.