Overview | Current Projects | Recent Projects | Pie in the Sky 
My interests span analytical chemistry, inorganic chemistry, surface science, and sold-state materials science. Recent research has focused on the forces driving molecules to spontaneously assemble themselves into well-ordered structures on a surface (called self-assembly) and the electrical and optical properties of such systems. These systems have applications as chemical sensors and form the starting point for various forms of nanotechnology related to molecular-based electronics.

Current research in the Van Ryswyk group centers around two major thrusts:

• Experimental investigation of electronic coupling in metalloporphryin dimers and trimers. We use solid-phase organic synthesis, photolysis, and inert atmosphere (glove box) techniques to synthesize metalloporphyrin dimers and trimers. We study the metal-to-metal electronic coupling in these oligomers via observation of the near-infrared intervalence charge-transfer bands in order to make comparisons to predictions generated by Prof. Cave’s group using their recently developed Koopmanns’ Theorem – Generalized Mulliken Hush approach (KT-GMH) based upon semiempirical, Hartree-Fock, and Density Functional Theory-based calculations.

• Lead levels in soil from vehicle emissions. Lead in soil from vehicle emissions is a leading cause of childhood lead poisoning in southern California. We  developed a service-learning module for the general chemistry course at HMC wherein our first-year students will work with local fifth- and sixth-grade students to determine lead levels in soil throughout our community. We utilized statistical sampling methods, gps mapping, microwave-assisted digestion, and atomic absorption analysis in a preliminary study of soil at the Bernard Field Station adjacent to old U.S. Route 66 in Claremont.  The completed project is now part of the HMC core curriculum.  We are working with Vista del Valle and Oakmont elementary schools in the Claremont Unified School District.  See the Vista del Valle – Harvey Mudd College Collaboration in Science, Mathematics, and Writing for more information.
  

All of the work described here is done at Harvey Mudd College with undergraduate coworkers. An example of recent research in my laboratory is shown below. For more information on recent projects, see the following (*denotes undergradute co-author):

• Van Ryswyk, Hal; *Moore, Erin E.; *Joshi, Neel S.; *Zeni, Rebecca J.; Eberspacher, Todd A.; Collman, James P. “Surface-confined metalloporphyrin oligomers.” Angewandte Chemie Int. Ed. 2004, 43, 5827-5830. [PDF]
  
  
• Van Ryswyk, H.; *Gabor, R. S.; *Awasthi, S.; *Bodzin, D. J.; *Orosz, K. S. “Kinetics of metalloporphyrin chemisorption onto monolayer-confined ligands and subsequent distal ligand exchange.” Langmuir 2004, 20, 11815-11817. [PDF]
  
  
• Eberspacher, Todd A.; Collman, James P.; Chidsey, Christopher E.D.; *Donohue, Deirdre L.; Van Ryswyk, Hal “Modular assembly and air-stable electrochemistry of ruthenium porphyrin monolayers” Langmuir 2003, 19, 3814-3821. [PDF]
  

Surface-Confined Metalloporphryin Oligomers

We create monolayer-bound metalloporphyrins via modular self-assembly (scheme I). First the alkanethiolate monolayer self-assembles on gold, then the metalloporphyrin is attached. These metalloporphyrin centers are electroactive, meaning that the metalloporphyrin can be oxidized, with the electron given up by the metalloporphyrin tunneling reversibly to the gold surface underneath the alkanethiol monolayer.

Using electrochemical techniques, we study the rate of metalloporphyrin attachment to the underlying monolayer as a function of metalloporphyrin concentration in the supernatent solution and time. We also study the rate of ligand substitution at the distal (top) site of the monolayer-bound metalloporphyrin. Finally, we study the rate of electron transfer between the metalloporphyrin and the underlying gold surface as a function of the height and composition of the monolayer.

Using spectroscopic and ellipsometric techniques, we study the size and orientation of these structures.

Examples of electrochemical techniques employed in these studies include cyclic voltammetry and fast-scan square-wave voltammetry. Examples of the spectroscopic techniques we use include uv-vis spectroscopy of mono- and multilayers mounted on glass substrates, grazing angle Fourier transform infrared spectroscopy of structures assembled on gold mirrors, and surface-enhanced Fourier transform infrared spectroscopy of structures assembled on gold islands smaller than 100 Å in diameter.

 

Using a monolayer-bound metalloporphyrin as a template, we synthesize metalloporphyrin oligomers (sometimes called "shish-kebab polymers") via bridging axial ligands (scheme II). We study the effects of the bridging ligand upon the electronic (mixed-valence) properties of the metalloporphyrins and their electronic communication with the underlying substrate via electrochemical means.

The results of these studies influence ongoing efforts with one of our collaborators to immobilize models of the cyctochrome c oxidase active center on monolayers as a test bed for mechanistic studies of catalytic oxygen reduction.

 

Wire frame rendering of ruthenium octahydroxyphenylporphyrin attached to a monolayer-based ligand. (The hydrogens along the alkane chain have been omitted.)	Ray-traced rendering of ruthenium octahydroxyphenylporphyrin attached to a monolayer-based ligand. (The hydrogens along the alkane chain have been omitted.)

A brief note regarding molecular electronics...

The "Holy Grail" in much of this research is to develop a better understanding of how individual molecules might be incorporated into molecular-level electronics. The rational for this runs something like the following:

• If you track the personal computer industry, you will note that over the past twenty years the perfomance of computers has tracked a relationship called Moore's Law, which states that the computational power of state-of-the-art computers doubles every 18 months. In order for this to occur, the number of transistors on a CPU chip must also double every 18 months. (Such increases in performance have been realized in the Intel 80x86 chip line.) In order for such advances to occur, the size of an individual transistor must shrink by a factor of 2 every 18 months.

Now here is the problem: The size of the smallest feature you can create with photolithography (the process used to create features on silicon chips) is limited by the wavelength of light used to write these features. It is this physical limit, and the corresponding challenge of making interconnections on this scale which electrical engineers must surmount each and every day to pack more transistors into a smaller and smaller area.

If you are an electrical engineer, how you proceed is fairly straightforward: search for incremental ways to write smaller features, and rake in the money...

If you are a chemist, you begin to wonder, "The smallest object I can imagine which would possess transistor-like qualities is a molecule. If I can make molecules which have transistor-like electrical properties and wire them together in a useful fashion, I will have made the smallest possible electronic circuit!"

Put succinctly, it is the goal of chemists interested in molecular electronics to "beat" the electrical engineers to the smallest possible circuitry. When the EE's get there, the chemists will be waiting for them with molecular-based electronics in hand!

Keywords: monolayer and multilayer self-assembly; molecular electronics, chemical sensors, photoelectrochemistry, electronic coupling.