Photophysics and dynamics of a β-carboline analogue in room temperature ionic liquids

Abstract

Room temperature ionic liquids are rapidly emerging as a new class of media that are ideally suited for various applications including carrying out chemical reactions. In the present article, we report the photophysics of a β-carboline analogue, namely, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), in three room temperature ionic liquids (RTILs), 1-butyl-3-methylimidazolium methyl sulfate ([BMIM][MeSO₄]), 1-butyl-3-methylimidazolium octyl sulfate ([BMIM][C₈SO₄]) and 1-ethyl-3-methylimidazolium methyl sulfate ([EMIM][MeSO₄]). Out of these, [BMIM][C₈SO₄] is a typical RTIL that forms micellar aggregates above a critical micellar concentration (CMC). Steady state absorption, steady state and time resolved fluorescence techniques are used to probe the properties of these systems. The investigation reveals that the photophysics of AODIQ is modified significantly in the micelle-forming RTIL as compared to that in the other two. A comparative study with the fluorophore in [BMIM][C₈SO₄] and a conventional anionic surfactant of a similar hydrophobic chain length from the sodium-n-alkyl sulfate series, viz., sodium octyl sulfate (S₈S), reveals that the fluorophore experiences a more constrained environment in the RTIL micelle as compared to the conventional anionic micelle.