Unveiling the interaction between carbon nanodot and IR light emitting fluorescent dyes inside the confined micellar environment

Abstract

In this contribution, using microwave heating of polyethylene glycol (PEG 200), we have prepared carbon nanodot (CND). It is found that in aqueous medium as well as in the micellar solutions of triblock copolymer, P123 and in anionic surface active ionic liquid (SAIL), 1-butyl-3-methylimidazolium n-octylsulfate ([C4mim][C8SO4]) the fluorescence intensity of CND gets quenched in the presence of cationic cyanine dye HITCP and cationic phenoxazine dye Nile blue (NB). Stern-Volmer constant indicates that the quenching of fluorescence intensity is more in the aqueous medium compared to P123 and [C4mim][C8SO4] i.e., (BmimOs) micelles. Time-correlated single photon counting (TCSPC) measurement reveals that the fluorescence quenching is static in nature and the quenching through Förster resonance energy transfer (FRET) process is not dominant here. Addition of both the cationic dye molecules (HITCP and NB) in CND solution generates new excited state absorption peaks in transient absorption measurement. This observation suggests that a transient species is generated through photoinduced electron transfer (PET) between the donor-acceptor pairs and this PET is responsible for the fluorescence quenching of CNDs by the dye molecules. Moreover, this electron transfer kinetics is relatively faster in bulk water compared to that inside P123 and BmimOs micelle due to the intervention of the surfactant molecules between CND and the dye molecules. Therefore, this study provides a new insight about the PET dynamics between CND and fluorescent dye molecules.