The distinct O2 quenching mechanism between fluorescence and phosphorescence for dyes adsorbed on silica gel

Abstract

We herein aim to probe the emission quenched by O₂ on silica gel. Our special focus is on the O₂ quenching of the fluorescence of a series of organic D–π–A phosphonium compounds 1–3. The results show that the O₂ quenching rate constants for the fluorescence of 1–3 are on the order of 10¹⁰ M⁻¹ s⁻¹, which are nearly on the same order as those measured for 1–3 and common organic compounds in solution. In yet another approach, the study of O₂ quenching of phosphorescence in the solid phase indicates that the O₂ quenching rate constant for the triplet state, i.e., , is smaller than by two orders of magnitude. Detailed investigation indicates that this distinction stems from the intrinsic O₂ quenching rate constants for the singlet and triplet states subsequent to the formation of collisional complexes. In the absence of the solvent cage effect, is greatly influenced by the formation energy of the O₂–dye CT complex, whereas in the solid phase is a nearly diffusion-controlled rate. Due to the larger distinction between and in the solid phase, O₂ quenching of fluorescence is efficient for dyes in the solid phase. This leads to a feasible application of sensing O₂ with regular fluorescent dyes adsorbed on porous solid substrates.