Research Interests:
Research in the Hopkins group is centered in inorganic and materials chemistry. We are broadly interested in understanding the relationships among the molecular and electronic structures of inorganic compounds and their photochemical, redox, and catalytic properties, especially as relevant to applications in renewable energy. We are also developing new classes of hybrid functional materials derived from supramolecular assembly on surfaces. Our research incorporates synthetic chemistry, a wide variety of physical characterization methods (steady-state and time-resolved optical and vibrational spectroscopies, electrochemistry, solution and solid-state structural methods, scanning-probe microscopy), and computational studies. Three current areas of interest are:
- Artificial photosynthesis
- Molecular patterning of surfaces
- Conjugated transition-metal materials
Artificial Photosynthesis
We are developing homogeneous molecular systems that store solar energy in chemical fuels, particularly via reactions that result in the reduction of carbon dioxide. A principal goal is to replace conventional (and unproductive) sacrificial reagents in light-driven reactions with renewable redox equivalents, such as water-sourced H2, through integration of photosensitizers with separate oxidative and reductive catalytic cycles. An example of these efforts has been the development of tungsten–alkylidyne photoredox chromophores that photosensitize the transfer of protons and electrons from H2 to reduction catalysts, and which are among the strongest known photochemical reductants.
Molecular Patterning of Surfaces
The synthesis on planar surfaces of 3D supramolecular structures with controlled dimensions offers unique opportunities to precisely position nanoscale and molecular functional modules at addressable interfaces. We are studying the surface chemistry of metalloporphyrins and related molecules in which axial ligands support functional units such as dyes, redox shuttles, and supramolecular receptors, positioning them at specific Cartesian coordinates within the array. An example of this approach is the discovery of gallium(III) porphyrin monolayers that induce the spontaneous self assembly of organized fullerene arrays on graphite under ambient conditions. These hybrid materials are readily extensible to other 2D surfaces formed by graphene and gold, and have potential applications in solar energy conversion, sensing, and catalysis.
Conjugated Transition-Metal Materials
Materials based on π-conjugated organic oligomers and polymers have important applications in solar cell, sensor, and display technologies. One of our goals is to develop metal-containing analogues of conjugated organic materials, in which selected multiply bonded carbon atoms are replaced by metal centers. These centers enhance the optical and redox properties of the hybrid materials and provide new loci for controlling their electronic structures. We have prepared novel π-conjugated compounds from building blocks that contain M–M and M–L multiple bonds and explored how their bonding, structures, and properties compare with organic counterparts. Tungsten-containing oligo-phenylene-ethynylenes, for example, maintain the electronic delocalization of organic OPEs but possess enhanced optical and redox properties that are inaccessible to their organic analogues.
Selected Publications
"Synthesis, Structure, and Bonding of d3 Molybdenum–Oxo Complexes." H. B. Vibbert, A. S. Filatov and M. D. Hopkins, Angew. Chem. Int. Ed. (2020), 59, 10581–10586. DOI: 10.1002/anie.202001379
"Light-Driven Redox Activation of CO2- and H2-Activating Complexes in a Self-Assembled Triad." N. T. La Porte, D. B. Moravec, R. D. Schaller and M. D. Hopkins, J Phys. Chem B (2019), 123, 10980–10989. DOI: 10.1021/acs.jpcb.9b07830
"Thermodynamic and Structural Factors that Influence the Redox Potentials of Tungsten-Alkylidyne Complexes." B. Rudshteyn, H. B. Vibbert, R. May, E. Wasserman, I. Warnke, M. D. Hopkins and V. S. Batista, ACS Catalysis (2017), 7, 6134–6143. DOI: 10.1021/acscatal.7b01636
"Axial Ligand Effects on the Structures of Self-Assembled Gallium–Porphyrin Monolayers on HOPG”. J. M. Kamm, C. P. Iverson, W.-Y. Lau and M. D. Hopkins, Langmuir (2016), 32, 487–495. DOI: 10.1021/acs.langmuir.5b03696
"X-Ray Crystallographic, Multifrequency EPR, and DFT Investigation of the Ni(PCy2NtBu2)2n+ Hydrogen Oxidation Catalyst in the Ni(I) Oxidation State”. J. Niklas, M. Westwood, K. L. Mardis, T. L. Brown, A. M. Pitts-McCoy, M. D. Hopkins and O. G. Poluektov, Inorg. Chem. (2015), 54, 6226–6234. DOI: 10.1021/acs.inorgchem.5b00445
"Electron-Transfer Sensitization of H2 Oxidation and CO2 Reduction Catalysts Using a Single Chromophore”. N. T. La Porte, D. B. Moravec and M. D. Hopkins, PNAS (2014), 111, 9745–9750. DOI: 10.1073/pnas.1321375111
"Electronic, Redox, and Photophysical Consequences of Metal-for-Carbon Substitution in oligo-Phenylene-Ethynylenes”. D. C. O'Hanlon, B. W. Cohen, D. B. Moravec, R. F. Dallinger and M. D. Hopkins, J. Am. Chem. Soc. (2014),136, 3127–3136. DOI: 10.1021/ja411354d