GO/ionic surfactant inspired photophysical modulation of rhodamine B in Reline with or without additives

Abstract

Photophysical behaviour of rhodamine B (RB) in deep eutectic solvents (DES, formed by quaternary ammonium salt and hydrogen bond donor (HBD) in a specific eutectic ratio) with or without graphene oxide (GO) or ionic surfactants, is less known. The nature of Reline (choline chloride (ChCl): urea (HBD), 1:2), a well-known DES, has been designed by adding glycerol or water as the second HBD for sustained movement of RB. Effects of GO, surfactant, or GO + surfactant, in controlling RB movement, at various sites (GO surface, surfactant micelle, DES surface, or background solvent), have been fluorometrically reported. The basic nature of Reline (pH = 10.38) causes modification of GO surface (deprotonated site) and nature of RB (cationic → zwitter ionic). Above Reline-inspired changes have been found to modify interactions of RB with GO and/or sodium dodecyl sulphate (SDS, an anionic surfactant) or cetyl trimethyl ammonium bromide (CTAB, a cationic surfactant). SDS (10 mMdm−3, < critical micelle concentration (CMC) in Reline) shows ∼ 2.6, 1.6, and 1.4 fold fluorescence intensity enhancement of RB (in water, pure Reline, and methanol, respectively). However, GO and/or CTAB shows quenching behaviour. Further, the fluorescence of RB shows weak dependence on changing the second HBD (water or glycerol). DES-controlled cationic vs zwitterionic form of RB is responsible for the interaction and sustained movement towards GO surface, micellar surface, or negatively charged ion-pair formation (with SDS monomers). Findings of the work have implications in searching potential fluorescent levels/sensors for photophysics, photobiology, or wider vehicle means for sustained drug delivery.