TIME-RESOLVED EVANESCENT WAVE-INDUCED FLUORESCENCE SPECTROSCOPY .1. DEVIATIONS IN THE FLUORESCENCE LIFETIME OF TETRASULFONATED ALUMINUM PHTHALOCYANINE AT A FUSED-SILICA METHANOL INTERFACE

Evanescent wave induced fluorescence spectroscopy and time-correlated single-photon counting have been combined to provide a method of studying the fluorescence decay profiles of fluorophores at a solid/solution interface. Using these techniques the photophysical properties of tetrasulphonated aluminium phthalocyanine (AIS4Pc) in methanol and water solution have been studied at a fused silica interface. In a poor solvent, such as methanol, AIS4Pc is shown to form an adsorbed monolayer on the fused silica surface and exhibit a fluorescence decay profile that deviates from the simple, first-order, single-exponential kinetics of the bulk solution. By changing the solvent to water, which is a good solvent for AIS4Pc, the surface/bulk differences are not observed. The ability of time-resolved fluorescence spectroscopy to distinguish between concentration and quantum-yield effects on evanescent wave induced fluorescence intensity, is clearly demonstrated.