Quenching of Anthracene Fluorescence by Carbon Tetrachloride and Carbon Tetrabromide

Abstract

Quenching of Anthracene fluorescence probably results from collisions between the quencher and excited anthracene molecules. In solution, strong quenchers may quench in two ways. The quencher may be alongside the anthracene molecule at the moment of excitation or it may diffuse to the excited molecule before fluorescence has been emitted. These two types of quenching, static and diffusion quenching, might be distinguishable by the addition of a weak quencher. An equation is derived suggesting that addition of a weak quencher will reduce the diffusion quenching but leave the static quenching unchanged. To test this equation, quenching by CCl₄ (weak quencher) in benzene and in cyclohexane, and by CBr₄ (strong quencher) in benzene, in benzene/CCl₄ mixtures and in cyclohexane was measured with a specially constructed accurate fluorimeter. Quenching by CBr₄ in the presence of CCl₄ is only approximately in agreement with the derived equation. Quenching by both CCl₄ and CBr₄ is altered by a change of solvent from benzene to cyclohexane.