Collaborative Research: Directing Charge Transport in Hierarchical Molecular Assemblies

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In this project funded by the Macromolecular, Supramolecular and Nanochemistry program of the Chemistry Division, Professor James Batteas of the Texas A & M University and Professor Charles Drain of Hunter College of the City University of New York study the molecular assembly and electron transport properties of molecules that might help in electronic device miniaturization. Moore's Law, which has held for the last four decades, states that the density of transistors on an electronic device "chip" will double approximately every two years, making electronic devices smaller, faster and more powerful. A pressing question is whether Moore's Law will continue into the future or has it reached its fundamental limits. Professors Batteas and Drain study metal-organic complexes known as porphyrinoids, found in nature as the active component of hemoglobin and chlorophyll, to aid in these developments. They design, synthesize and evaluate the conductive properties of porphyrinoids assembled into specific structures on surfaces. Using imaging techniques such as atomic force microscopy (AFM) and scanning tunneling microscopy (STM), the team can place individual molecules into precise arrangements on surfaces and measure not only their assembled structure at the molecular level but also how the structure controls the movement of electrons through the molecules. This research has broader impacts in science and technology, and enables the rational design of potential molecular electronic devices, including enhanced photovoltaics, chemical sensors and molecular electronics. The team also trains students, for broader impacts in education, in fundamental materials chemistry, preparing them for the 21st century high technology jobs sector. Professor Batteas and Professor Drain study how to design, synthesize and evaluate the conductive properties of porphyrinoids assembled on metal surfaces with an eye toward the implementation of hybrid molecular-based devices for photonics applications, including enhanced photovoltaics, chemical sensors and molecular based electronics. The electroactive properties and self-assembly of robust porphyrinoids can be readily tuned through chemical synthesis using simple high yield reactions that facilitate commercial viability, making them attractive targets to be integrated as active components in electronic devices. In this project porphryinoids are assembled on Au surfaces in precise architectures via a combination of nanolithography and directed click-chemical reactions to create nanoscopic assemblies of less than 10 nm in lateral dimension. Characterization methods (time resolved florescence, UV-visible absorption, STM and AFM) are applied to understand how local molecular interactions influence electron transport properties in small molecule assemblies, how spatial confinement of molecules on a surface influence their resulting assembly process and the structures that can be formed, and how the assembled architectures control electron transport. Broader impacts of the research result in an improved fundamental understanding of the assembly and electron transport properties of the porphryiods, with potential to influence molecular electronic device and solar light harvesting applications. Broader impacts through education and outreach incorporate aspects of the work, including atomic scale imaging, nanolithography, molecular self-assembly and nanoscale electronics, into demonstrations for elementary school students as part of a weeklong summer camp on Nanotechnology (at Texas A&M University), and into the undergraduate and graduate classrooms at Texas A&M University and CUNY Hunter College.