Luminol fluorescence quenching by triethyl amine and non-linear Stern-Volmer plot: Solvent effect

The interaction of 3-aminophthalhydrazide (luminol) with a quencher, triethyl amine (TEA) has been studied employing steady-state and nanosecond time resolved emission spectroscopy. The bimolecular rate constant for fluorescence quenching in water is found to be about two orders of magnitude higher than that obtained in 1,4-dioxane (DIO). The Stern-Volmer (S-V) plot for fluorescence quenching exhibits positive deviation from linearity when water is used as solvent. On the other hand, the S-V plot shows negative deviation from linearity when DIO is used as a solvent. The rate constants obtained in ethanol, dimethyl sulphoxide (DMSO) and DIO are found to be similar to the rate constant for diffusional process. The possible interpretation of the quenching mechanism and nature of deviation from S-V plots have been discussed in relation to the strength of interaction between the colliding species. It is shown that the rate of luminol fluorescence quenching is dependent on the nature of the solvent, being particularly fast in aqueous medium.