Dynamics of Preferential Solvation of 5-Aminoquinoline in Hexane-Alcohol Solvent Mixtures.

Dynamics of preferential solvation of 5-aminoquinoline (5AQ) has been studied in hexane-alcohol solvent mixtures. Significant spectral red shift and fluorescence quenching are observed, even for miniscule amounts of alcohols. A nonlinear variation of these parameters, with alcohol mole fraction, indicates dipolar enrichment around 5AQ in its excited state. A nanosecond rise at the red end of emission spectra is ascribed to translational diffusion of alcohol molecules and consequent preferential solvation of 5AQ. Electrostatic stabilization and hydrogen bonding between the dipolar excited state of the fluorophore and polar alcohol molecules are major driving factors here. Time evolution of emission spectra, from those in a predominantly hexane-like environment to those in a predominantly alcohol-like environment, takes place in nanosecond time scale and depends on the alcohol concentration in the mixture. This in agreement with calculations using an existing model. Hence, 5AQ is found to be a suitable fluorescent probe for the study of dynamics in complex systems.