Competitive photochemical reactivity in a self-assembled monolayer on a colloidal gold cluster

A shell-core cluster 2 produced by depositing a self-assembled monolayer (SAM) of 6-thiohexyl-3-nitro-4-(4'-stilbenoxymethyl)-benzoate (1) on a nanoparticulate gold colloid preserves normal solution-phase photoreactivity of the trans-stilbene and o-nitrobenzyl ether moieties, but shows quenched fluorescence. Nearest-neighbor aggregation is weaker for 1 bound to the roughly spherical colloidal gold particle (in cluster 2) than for analogous stilbenoids: bound to a planar gold surface. Unlike the observed photochemical reactivity of stilbenylalkyl sulfides appended as SAMs on planar gold surfaces, the chromophores present in these shell-core nanocomposites 2 exhibit efficient trans-to-cis photoisomerization and blocked [2 + 2] photodimerization. Wavelength selectivity for photoisomerization and photocleavage proved to be elusive, but tripler sensitization of the geometric isomerization took place without photorelease of the attached group.