Photophysical properties of 3-cyano-7-hydroxy coumarin in reverse micelles

• We report the photophysical properties of 3-cyano-7-hydroxycoumarin (7-CNU) in reverse micelles. • Presence of undissociated molecule (I), the phenolate anion (II) forms of 7-CNU was observed in water containing reverse micelle. • In water containing reverse micelle we observed one iso-emissive point in the emission spectra. • In non-aqueous polar solvent containing reverse micelles undissociated form of 7-CNU is exist. In this article we have studied the photophysics of 3-cyano-7-hydroxycoumarin (7-CNU) in the reverse micelle containing various polar solvents such as water, methanol, acetonitrile, N , N -dimethylformamide, and ethylene glycol by using multiple spectroscopic techniques. We have observed a systematic red shift by 2–3 nm in both absorption and emission spectra as the polar solvent content increased in the reverse micelle. Notably, an iso-emissive point with two distinct shoulders (band I and band II) in the emission spectra of 7-CNU in aqueous reverse micelles showing the existence of two different forms of 7-CNU. In non-aqueous polar solvents containing reverse micelles iso-emissive point was not observed. Further fluorescence emission decays of 7-CNU in reverse micelles were measured to estimate the changes in the lifetime values with increase in the polar solvents content. We have observed a decrease in the average rotational relaxation time of 7-CNU with an increase in the amount of polar solvents in the reverse micelles expect ethylene glycol containing reverse micelles. In the case of ethylene glycol-containing reverse micelles increase in rotational relaxation time of 7-CNU was observed with increase in the ethylene glycol content.