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 composite 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, photoisomerization of the appended trans isomer to the corresponding cis isomer takes place both in solution and in the composite cluster. Inefficient photodimerization could be observed by H-1 NMR spectroscopy for cluster 4. The quantum yields for photoisomerization of the composite clusters 3 and 4 were affected by the length of the linker because of distance-dependent through-bond quenching by the metal core.