Interaction of the excited state intramolecular proton transfer probe 3-hydroxy-2-naphthoic acid with poly N-vinyl-2-pyrrolidone polymer in water: An insight into the water structure in the binding region

The enhancement of the excited state intramolecular proton transfer (ESIPT) emission of 3-hydroxy-2-naphthoic acid (3HNA) in presence of poly N-vinyl-2-pyrrolidone (PVP) has been investigated by time resolved fluorescence and anisotropy measurement. In other water soluble polymers and monomers there is no enhancement of the ESIPT emission of 3HNA. The microenvironment of the probe in PVP–water mixture is investigated by comparing the ESIPT emission of 3HNA in mixed solvents of acetonitrile–toluene. The anisotropy, rotational correlation time and the blue shift observed in the ESIPT emission in PVP–water mixture have been ascribed to both the polarity and the motional restriction of the probe imposed by the bound water region of PVP.