Surface photochemistry: the effect of surface modification on the photophysics of naphthalene and pyrene adsorbed on silica gel

The influence of heat treatment and of added coadsorbates on the surface photophysics of pyrene and naphthalene adsorbed on silica gel is reported. When the silica gel surface is partially dehydroxylated, the distribution of pyrene or naphthalene is inhomogeneous, as indicated by multiexponential fluorescence decay and broad emission spectra. Addition of polar coadsorbates renders the surface more homogeneous with singlet lifetimes approaching solution values. The pretreatment and addition of coadsorbates, in the case of pyrene, also influence the relative importance of dynamic excimer formation vis-a-vis ground state association.