Coverage-Dependent Luminescence from Two-Dimensional Systems of Covalently Attached Perylene Fluorophores on Silica

Photophysical processes occurring in two-dimensional systems of perylene derivatives covalently attached to planar silica surfaces are studied using a combination of steady-state and time-resolved measurements. Monomeric emission is observed for low fluorophore densities (below 0.15 nm(-2)). A broad emission feature centered around 530 nm is observed for high fluorophore densities (above 0.44 nm(-2)) and is attributed to excimer-like emission from partially overlapping perylene moieties. No distinct emission feature from the fully relaxed excimer state is observed, although the presence of a small fraction of such sites is inferred from both steady-state and time-resolved measurements. A one-carbon chain is used to anchor the fluorophore to the surface by the reaction of perylene-3-methanol with free hydroxyl and strained siloxane sites, likely hindering the ability of neighboring molecules to form a fully relaxed excimer state. Analysis of fluorescence decay profiles indicates energy migration between sites occurs even for low fluorophore densities.