My students and I combine interests in molecular monolayers and nanoscopic chemical materials in the current topic of Monolayer Protected Clusters (MPCs). These are nanometer-sized metal particles (such as Au, Ag, Pd, and metal alloys) coated with a dense monolayer of thiolate ligands, so that even when dried the metal nanoparticles do not fuse and aggregate. This allows us to treat these materials as large molecules, subject to application of synthetic elaboration of the monolayer (such as with donor/acceptor, fluorophore, ionophore, nucleotide, peptide, etc. groups), and facilitating study of their chemical and physical properties. We have investigated both nanoparticle structure and electron transfer thermodynamics and kinetics, both in solutions and solid-state.

Of particular recent interest has been the discovery of single electron double layer charging, and of core-based, intense nanoparticle luminescence. Other recent work has included: assembly of hybrid nano-structures that combine nanoparticles with single wall carbon nanotubes (swnt), the association of charged nanoparticles with other molecular solutes such as DNA, electron self-exchange reactions within mixed valent films of nanoparticles, NMR, HPLC and CE of nanoparticles, and optically driven electron transfers at nanoparticles.

In these projects, students in the laboratory gain the acquaintance of a wide range of methods in studying the properties of nanoparticles; we are also interested in methods that probe the nanoparticles as platforms for analytical sensors. The methods include electrochemical voltammetry, surface plasmon resonance, vibration/UV-Vis/fluorescence spectroscopies, surface wetting, thermal methods, nmr, nano-titrations, solid state conductivity, metal filming, optical microscopy and TEM, small angle X-ray scattering, and XPS.

An outgrowth of previous work on solvent-free redox polymers on electrodes has been an interest in understanding electron transfer and mass transport dynamics in highly viscous semi-solids. The research consists of a) designing and synthesizing model semi-solids that contain electron donor/acceptor groups (or some other interesting kind of functionality), b) developing methods (microelectrodes) for measuring dynamics properties of the semi-solids such as mass transport (diffusion), electron hopping rates, heterogeneous electron transfer rates, excited state behavior, etc., c) carrying out dynamics measurements on semi-solids in such a way as to try to understand the relationships between microscopic dynamics and structure, and d) to compare the dynamics results, especially for electron transfers, to contemporary electron transfer theory (that has been extensively studied in non-viscous fluids but hardly at all in semi-solids).

The model semi-solids are based on incorporating the molecular dis-organizing effects of polyether oligomers into interesting chemical materials, which have included metal bipyridines, ferrocyanide, viologens, porphyrins and phthalocyanines, perylene, anthraquinone, and DNA and its mononucleotides. These semi-solids are molecular melts and molten salts (room temperature). A recent direction has been the design of donor/acceptor molten salts in which electron transfers can be effected by absorption of photons (i.e., optical electron transfers).

We have discovered that the very high concentrations intrinsic to many of our semi-solid materials are ideal for optical electron transfer research. Another recent and promising direction, in collaboration with Professor Thorp, has been the synthesis of molten salts which contain DNA as the anion and a polyether-tailed quaternary ammonium salt as the cation: a novel "liquid DNA".