Quenching of Fluorescence by Van Der Waals Forces

Abstract

THE quenching of fluorescence of dyes in solutions has been explained satisfactorily as a chemical reaction in a number of cases. In an interesting paper¹ Weiss has classified some different mechanisms of 'chemical' quenching, such as quenching by ions and by the electronegative oxygen molecule². Furthermore, Weiss has attempted to explain the well-known fact of concentration quenching chemically: according to him the formation of dimers is responsible for the decrease of fluorescent efficiency in solutions with increasing concentration of the fluorescing solute. On the other hand, Franck³ has shown that under certain conditions the electronic energy of an excited dye molecule in solution may serve to form a tautomer by a process of internal conversion. In this way electronic energy is transferred into vibrational energy of nuclei and so the fluorescent efficiency is reduced.