Solvation Dynamics of Fluorophores with an Anthroyloxy Group at the Heptane/Water Interface as Studied by Time-Resolved Total Internal Reflection Fluorescence Spectroscopy

Abstract

Solvent relaxation processes of 12-(9-anthroyloxy) stearic acid (12-AS) and 4-(9-anthroyloxy) butanoic acid (4-ABA) at the heptane/water interface are examined by time-resolved total internal reflection fluorescence spectroscopy. In a bulk heptane solution containing 3 M ethanol, both 12-AS and 4-ABA show time-dependent fluorescence spectral shifts, and the decay profiles can be analyzed by the two-state kinetics model. The results obtained for the binary mixture of heptane and ethanol can be ascribed to a local enrichment of ethanol molecules around fluorophores, that is, preferential solvation. A similar result is obtained for 12-AS but not for 4-ABA at the heptane/water interface, indicating that the preferential solvation occurs for 12-AS at the heptane/water interface. Since 4-ABA does not show a time-dependent spectral shift at the interface, the fluorophore of 4-ABA is surrounded by more water molecules, by which quenching of fluoresence was accelerated, than 12-AS at the heptane/water interface, and it is located more closely to the water phase than 12-AS.