Photoluminescent Properties of Octadecylrhodamine B in Water, in Alcohols and in Mixed Water‐alcohol Solutions

Fluorescence, excitation and absorption spectra of octadecylrhodamine B (ORB) have been observed in solutions of water, methanol, ethanol and other simple alcohols. A remarkable increase in the ORB fluorescence intensity occurs when the probe is transferred from water to the alcohols. This effect is ascribed to the release of ORB fluorescent monomers from nonfluorescent multimers, which exist predominantly in water. The dependence of the fluorescence intensity on the composition of water‐alcohol binary solvent systems shows that hydrophobic interactions play an important role in the monomer = multimer equilibrium of ORB in these solutions. The fluorescence lifetimes of ORB in the alcohols are also reported.