Controlling Charge Transport of Organic Semiconductors and Molecules via Edge-On Gating Effect

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Non-technical AbstractThis project is focused on synthesis of model molecular transistors and investigation of their physical properties. The research can help to find answers for the limitations faced in miniaturization of electronic systems. Synthetic approaches to these molecular systems are shown to be feasible and techniques for electric measurements on single molecules are operational. Preliminary results indicate proper chemical functions can switch electric current on and off, similar to functioning of transistors. With support from the Solid State and Materials Chemistry program in the Division of Materials Research, this research team is pursuing extensive synthetic efforts to prepare a series of new compounds with different structures and functions. Theoretical studies are performed to calculate and understand the electric properties of molecules. This project provides an excellent educational platform for students, especially an effective incubator to encourage minority students into a career path of scientific research. This project includes a plan for recruiting these students. The proposed work is an interdisciplinary effort that integrates chemistry, materials science, physics and nanoscience to explore new science and materials, and requires extensive innovations in synthetic approaches and applications of modern characterization techniques to gain insight into the electronic properties of molecular materials. It thus offers a broad spectrum of research and educational opportunities for students. Students working in this program gain necessary knowledge and training to be future leaders in the area of organic/material chemistry and organic electronic materials. New materials generated can have potential impact on electronic industries.Technical AbstractThis project is aimed at synthesis of model molecular transistors based on cyclophane building motif, and investigating the edge-on chemical gating effect on electronic properties of semiconducting molecules and materials. The cyclophane moiety contains a perpendicular pyridine unit that is connected to the conjugated semiconducting molecules with two vinyl groups. Thus, the pi-system in pyridine ring is orthogonal to that in semiconducting wire. The gating end is not directly conjugated with the semiconducting entity, closely resembling a gate electrode in FET. The molecular system developed resembles a field effect transistor, but allows using break-junction Scanning Tunneling Spectroscopy techniques to investigate the gating effect. The research effort is focused on edge-on chemical gating effect, by which various functional groups with different electronic properties are introduced to the para-position of the perpendicular pyridine ring. These substituents behave like applied gating voltage, allowing for detailed physical investigation to gain insight into in controlling charge transport. This project devotes extensive synthetic efforts to prepare a series of new compounds with different gating moieties, conjugation lengths, and electronic properties. This team has set up a Scanning Tunneling Spectroscopy system to characterize the charge transport behavior of molecules, which include single molecular conductance, electron tunneling barriers and chemical gating correlation with functional groups. Theoretical studies help to calculate and understand the charge density changes in the gating pyridine moiety, which was shown to be a parameter correlated to the charge transport conductance. Ideas for possible applications of the gating effect are pursued, including proton triggered switch and photoinduced switch