A series of aryl ketones, namely, 11-mercapto-1-phenyl-undecanone (1), 1-(4-hexyl-phenyl)-11-mercaptoundecanone (2), 1-(4-dodecyl-phenyl)-11-mercaptoundecanone (3), 1-[4-(11-mercaptoundecyl)phenyl]hexanone (4), and 1-[4-(11-mercaptoundecyl)phenyl]undecanone (5), anchored as mixed monolayers with one of hexanethiolate, dodecanethiolate, and octadecanethiolate on gold nanoclusters (so-called monolayer-protected clusters, MPCs) were prepared and characterized. The Norrish-Yang type II photoreactivity of these MPCs was investigated in benzene solution to serve as probes of conformational mobility within the monolayer environment. The aryl ketones react efficiently by a Norrish type II reaction (> 75% completion) through their triplet excited state to yield a 1,4-biradical that fragments to give the corresponding alkene and substituted acetophenone-modified MPCs for 1-3 and 4 and 5, respectively. The extent of reaction and the efficiency do not appear to depend on the length of the alkanethiolate coadsorbed onto the MPC or on whether the aryl ketone is further embedded into the monolayer. Notably, there was no evidence for the generation of cyclobutanol products that would be generated from cyclization of the 1,4-biradical or other competing photochemical reactions. The findings of this investigation suggest that the MPC environment is quite dynamic; yet, the exclusive fragmentation products indicate that there are some factors affecting the conformational mobility of the triplet biradical. We further suggest that the reactivity in MPCs may be greatest at the edge/vertexes with larger constraints on the terraces. Regardless, the Norrish type II reactivity yields efficient fragmentation of either acetophenone or alkene moiety, suggesting such MPCs could find use for the controlled release of substrates in solution.