Preferential solvation studied by the fluorescence lifetime of acridine in water-alcohol mixtures

Fluorescence lifetimes (τ_F) of acridine have been measured in water-alcohol solvent mixtures at room temperature. The τ_F of acridine in pure water (11.5 ± 0.1 ns) was drastically decreased upon the addition of small amounts of alcohol; i.e. τ_F = 1.2 ± 0.01 ns in 0.5 mole fraction of ethanol in water and τ_F = 0.4 ± 0.01 ns in pure ethanol. The extent of the decrease in τ_F becomes more evident in the following order: methanol < ethanol < propan-1-ol. This is the order of increasing hydrophobic interaction between alcohols and acridine, suggesting that alcohol molecules preferentially solvate acridine in water. Such an observation has been discussed in terms of the degree of preferential solvation.