Spectroscopic studies of nile red in organic solvents and polymers

We have studied the spectroscopic properties of nile red (NR), a highly fluorescent laser dye, in organic solvents, binary solvent mixtures and polymers. Spectroscopic studies reveal remarkable changes in the absorption and emission band positions and intensities as a function of the polarity of the medium. Such large changes have been attributed to the twisted intramolecular charge transfer (TICT) state of the molecule in polar medium. Experimental results show that the molecule is sensitive to the polarity of its microenvironment and is an excellent probe for systems presenting restricted geometries. We have incorporated NR into thin films of poly(methyl methacrylate) (PMMA) and poly(vinyl alcohol) (PVA); it is found that the micropolarity in PVA is greater than that in PMMA; in PVA, the micropolarity corresponds to that of a binary mixture of acetonitrile and water, whereas in PMMA, the micropolarity corresponds closely to that of pure acetonitrile.