Exciplex luminescence studies of the surface polarity of end-capped bonded phases

The fluorescence intensities and emission maxima of surface-bound exciplexes were studied to determine the relative polarity of microparticulate silica before and after derivatization with trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDS). The results indicate that HMDS yields a bonded phase with greater average polarity relative to TMCS at equivalent surface coverages. This difference is attributed to the formation of basic sites on the surface by chemisorption of ammonia generated during derivatization with HMDS. The observation of exciplex emission on silica gel is novel and strongly supports clustering of surface-bound molecules into high-density regions.