Modification of the photophysics of 3-hydroxyflavone in aqueous solutions of imidazolium-based room temperature ionic liquids: a comparison between micelle-forming and non micelle-forming ionic liquids

Abstract

In the present article, we have investigated the photophysical behavior of 3-hydroxyflavone (3HF), an excited state intramolecular proton transfer (ESIPT) probe, in aqueous solutions of two imidazolium-based room temperature ionic liquids (RTILs), one micelle-forming and the other non micelle-forming, exploiting steady state and time resolved fluorometric techniques. The study unveils that the ESIPT process of 3HF is modified substantially in the micelle-forming RTIL as compared to that in the other RTIL. The critical micellar concentration (CMC) of the micelle-forming RTIL has been determined from both steady state and time resolved data. The study suggests that 3HF resides within the micellar phase and experiences a significantly less polar environment in its vicinity than in the non micelle-forming ionic liquid. A comparative study with the probe in the micelle-forming ionic liquid and a conventional anionic surfactant of a similar hydrophobic chain length reveals that 3HF experiences an appreciably less polar environment in the RTIL micelle as compared to the conventional anionic micelle.