Photoreactivity of self-assembled monolayers of azobenzene or stilbene derivatives capped on colloidal gold clusters

Trans-4-methyl-4 '-(-S-(CH2)(n)-O-)azobenzenes (1) with varying alkyl chain lengths (n = 4, 6, 9, 12) and trans-4-methyl-4 '-(-S-(CH2)(n)-O-)stilbenes (2) (n. 6, 7, 8, 9) were used to cap colloidal gold clusters, yielding com posite shell-core nanostructures 3 and 4, respectively. Aggregation of the terminal arene moieties by pi -stacking within the organic shells was weak in these composite particles. Upon irradiation at 350 nm, photoisomerizatio n of the appended trans isomer to the corresponding cis isomer takes place both in solution and in the composite cluster. Inefficient photodimerizatio n could be observed by H-1 NMR spectroscopy for cluster 4. The quantum yiel ds for photoisomerization of the composite clusters 3 and 4 were affected b y the length of the linker because of distance-dependent through-bond quenc hing by the metal core.