Acyl and alkyl radicals generated photochemically in a solution containing monolayer-protected gold nanoparticles are shown to efficiently liberate the alkylthiolate ligands into the solution as the thioacetyl or alkyl sulfide, respectively. This radical-induced reaction initiates a coalescence of the gold cores to facilitate an increase in core size. The photoinitiated radical reaction also liberates monolayers from two-dimensional gold surfaces.