Collaborative Research: Tuneable cross-conjugated organic semiconductors

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Professors Malika Jeffries-EL of Boston University and Aimee Tomlinson of University of North Georgia are supported by the Macromolecular, Supramolecular, and Nanochemistry (MSN) Program of the Division of Chemistry to develop new carbon-based materials - organic semiconductors - that combine the properties of organic materials with the optical and electronic properties of conventional inorganic semiconductors. These complex materials are of technological importance as they can be fabricated into devices for use in a variety of different areas including energy (solar cells), displays, (light emitting diodes), and electronics (field effect transistors). During the course of this project, conjugated materials based on the cross-like motif are designed by Tomlinson's team using computational methods in order to identify the most promising candidates for synthesis and characterization by the Jeffries-EL group. This research enhances our understanding of how structure impacts its material properties, and how these properties then impact its performance in various applications. In addition to supporting basic research, this grant provides interdisciplinary research experiences for both undergraduate and graduate students. The broader impacts of this grant include the development of highly qualified scientists with extensive experience working on complex interdisciplinary projects in a diverse environment. Since the University of North Georgia is located in the foothills of the Blue Ridge mountain range a number of first generation and underrepresented undergraduates are given the opportunity to be involved in this project. Additionally, Dr. Jeffries-EL fosters interest in materials chemistry in underrepresented high school students through the Achievement, Self-Awareness, Communication, Engagement, Networking and Developmental Skills (ASCEND) outreach program targeting low-income and underrepresented minority students in grades 9-12. The project further advances the field of organic semiconductors through an investigation of structure-property-morphology relationships in cross-conjugated benzobisoxazoles (BBOs). Cross-conjugated molecules, which are systems with two orthogonal conjugation paths that intersect through a central aromatic ring, are especially advantageous for organic semiconducting applications as this arrangement leads to spatial segregation of the frontier molecular orbitals (FMOs). Consequently, it is possible to selectively tune the FMOs and band gaps through aryl group substitution along the various axes as a result of extension of the pi system and inductive effects. The benefits of the approach are that the cross-conjugated platform allows for the opportunity to optimize the material's optical and electronic properties for specific applications. Based on the insights from the previous grant period, there are several opportunities for the rational design of new materials, specifically architectures for narrow band-gap materials for photovoltaic cells and wide band gap materials which can be used as either blue emitters or hosts in organic light emitting diodes. A combination of theory, synthesis, device fabrication and characterization are utilized to identify and generate new materials as well as provide insights on how to design future materials. The simple iterative approach allows for easy synthesis of the target materials and structure-property studies advance the rational design of new materials with characteristics that are tunable and predictable. As such this work is expected to impact the field of organic electronics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.