The purpose of this study is to investigate the fluorescence quenching of 2-naphthol and its derivatives by pyridine, quinoline, and acridine. The process of fluorescence quenching occurs when an electron is transferred from an excited state fluorescing molecule to a quenching molecule. In some cases, a proton-coupled electron transfer can occur between the pair. The B3LYP 6-31*G theoretical calculations are used to predict if proton transfer is expected for the fluorescer-quencher combinations. The Stern-Volmer method uses the data collected from the fluorescence quenching experiments to quantify the quenching rate constant. Cyclic voltammetry experiments and absorbance and emission spectra are used to find the change in free energy of electron transfer. A proton transfer process has a quenching rate constant greater than 1 × 109 M–1 s–1 and a change of free energy of electron transfer greater than 5.8 kcal/mol. The addition of electron-donating or electron-withdrawing substituents to 2-naphthol affects the quenching mechanism. The proton transfer mechanism is validated for several of the fluorescer-quencher pairs.

Investigation of the proton transfer mechanism in fluorescence quenching

ACS Spring 2022

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