Quenching mechanism of dimethylaminocyanobiphenyl aggregates by fluorescein in CTAB: An interplay between FRET and electrostatic interactions

Abstract

Fӧrster resonance energy transfer (FRET) is a widely used tool to study micro heterogeneous media. Herein, quenching mechanism of dimethylaminocyanobiphenyl aggregates in CTAB (DMACBA-S; donor) by fluorescein disodium salt (FLU; acceptor) was analyzed using steady-state and time-resolved fluorescence measurements. Even though, the quenching behavior resembled the characteristic FRET phenomenon, unusual spectral shifts in the emission maxima of DMACBA-S and FLU were observed. In-depth analysis of this uncommon spectral shifts and fluorescence decay curves of DMACBA-S in the presence and absence of FLU revealed that the quenching could be due to a combination of FRET and electrostatic interaction between the acceptor and the CTAB micelles which eventually resulted in the rupture of the micelle followed by the formation of weakly fluorescent DMACB aggregates in water (DMACBA-R). By varying the concentration of CTAB, a variation in the contribution from electrostatic interaction towards the quenching mechanism was observed. The study highlights the less known interaction of acceptor with the microheterogenous medium in FRET studies. The present results manifest the need for a deeper analysis of the experimental quenching data to avoid erroneous conclusions.