CdS clusters in the quantized size regime ( almost-equal-to 30 angstrom radius) have been synthesized in several media, including homogeneous organic solution, reverse micelles, and polymers (carboxymethylamylose). Particle size is controlled by the medium, but the photophysical properties of the clusters, as prepared, do not depend strongly on the medium. However, the associated photochemical reactivity can depend strongly on the reaction medium. We have used the well studied photochemical oxidative fragmentation of alpha,beta-amino alcohols as a benchmark reaction to examine the cluster photochemical reactivity as potential excited state electron acceptors. Initially, addition of amine to irradiated cluster suspensions leads to decreased nonradiative decay and increased emission corresponding to adsorption of the amine at previous deep trap sites on the cluster surface. At this stage, no organic products are formed: the (chemically) adsorbed species are essentially inert to oxidation. As amine concentration is further increased, a rapid onset of quenching occurs with associated oxidative cleavage of the amino alcohol. This reaction corresponds to oxidation of solvated and/or physisorbed amine. Thus, in contrast to reduction processes which are favored by surface adsorption, corresponding oxidation processes can be disfavored by adsorption, if the reactive lone pair becomes involved in surface bonding. The amino alcohol concentration at which reaction occurs depends on the distribution of reagent within the (micro)environment. Finally, the organic photochemical aspects of the reaction including high quantum yields are briefly considered.
