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 triplet sensitization of the geometric isomerization took place without photorelease of the attached group.