Surface functionalization and derivatization of ~25 Angstrom cadmium sulfide nanoclusters: A study of potential molecular electronic components

Semiconductor nanoclusters (or quantum dots) are currently the focus of extensive scientific investigation. Interest in these materials stems primarily from their unique size dependent optical and electronic properties which are the result of Quantum Confinement (or Size) Effect. It has been proposed, and in some instances demonstrated, that these materials have far reaching applications in the areas of catalysis, solar energy conversion, molecular electronics and non-linear optical materials.; To take full advantage of semiconductor colloids and their properties, it is necessary that control over cluster size, stability, and chemical characteristics be achieved. One approach to these issues involves the chemical derivatization of pendant surface functionalities. Unfortunately, semiconductor nanoclusters are often prone to destruction when subjected to standard synthetic procedures, thus, careful consideration must be given when designing methods for cluster chemistry.; The Kinetic Trapping Method, a form of controlled precipitation, employs competitive reactions of thiolate and sulfide anions with cadmium cations to produce size controlled cadmium sulfide nanoclusters. This procedure offers a useful approach for the introduction of a wide variety of surface functionalities onto the surface of cadmium sulfide nanoclusters in the form of a substituted thiolate capping agent. We have chosen to expand upon the existing procedure, developed by Herron and Wang in 1990, as a means to introduce some control over cluster electronic and chemical characteristics.; Found within the following discussion are investigations into the preparation of fourteen distinct functionalized cadmium sulfide nanoclusters with varied surface electronic and chemical characteristics. We also present four novel synthetic methods for the derivatization of two of these nanocluster species which do not disturb the integrity of the semiconductor core. The facility for which the presented procedures chemically modify the nanocluster surfaces indicates that they are useful methodologies for the future attachment of molecular wires and the ultimate incorporation of these materials into molecular electronic devices.; Using the methods for cluster derivatization described herein we have successfully prepared a series of CdS nanoclusters bearing surfaces ranging from long chain aliphatic groups and optically active moieties, to electroactive transition metal complexes. Our studies of the photolability of these materials have yielded invaluable information regarding the effects of the surface electronic properties on core stability. We have found that strongly electron withdrawing (-NO₂) and donating (-NH₂) groups promote cluster photo degradation while electron neutral surface groups provide some increased stability for the cluster toward photolysis.; Electrochemical and emission studies of CdS nanoclusters bearing ruthenium polypyridyl moieties have also demonstrated that electronic communication is mediated by the semiconductor core of the cluster. Here we present the first conclusive evidence that energy band quantization resulting from the Quantum Confinement Effect does not eliminate the semiconductor properties of cadmium sulfide. Thus, it is reasonable to foresee application of these compounds in molecular electronic devices.