Fluorescence Quenching in Aromatic Hydrocarbons by Oxygen

Abstract

The role of the possible fluorescence quenching process $S_1\mathrm{\hspace{0.17em}+\hspace{0.17em}}{\mathrm{O}}_2{(}^1{\Sigma }_g^{-}\mathrm{)\hspace{0.17em}\to \hspace{0.17em}T\hspace{0.17em}+\hspace{0.17em}}{\mathrm{O}}_2{(}^1{\Delta }_g)$ which involves energy transfer to oxygen is examined in a number of aromatic hydrocarbons. It is observed that quenching is just as efficient in aromatics where the $S_1\mathrm{–T}$ energy gap is too small (< 7900 cm⁻¹) for excitation of oxygen in the above process as in aromatics where it is allowed energetically. This process cannot therefore account for the general phenomenon of fluorescence quenching by oxygen in aromatics. Evidence bearing on other quenching mechanisms is discussed.