Photoinduced Size-Controlled Generation of Silver Nanoparticles Coated with Carboxylate-Derivatized Thioxanthones

We report a new strategy for a rapid photoinduced synthesis of monodisperse ligand-coated silver nanoparticles. Such nanoparticles are produced through a very fast reduction of Ag(+) by alpha-aminoalkyl radicals which are first generated from hydrogen abstraction toward an aliphatic amine by the excited triplet state of the 2-substituted thioxanthone series (TX-O-CH(2)-COO(-) and TX-S-CH(2)-COO(-)). The quantum yield of this prior reaction is tuned by the substituent effect on thioxanthones and leads to a kinetic control of the conversion of Ag(+) to Ag(O). Combined with the capping role of a carboxylate function linked to the chromophores, a size regulation of the growing nanoparticles is both promoted and optimized because of a concomitant kinetics adjustment between the photoreduction process and the subsequent functionalization of the nanoparticles. We demonstrate that the optimal adjustment is then obtained with TX-S-CH(2)-COO(-).