Conjugated Systems Containing Antiaromatic Cyclobutadienoids: Synthesis and Study of the Multifaceted Effects of Local Antiaromaticity

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In this project, funded by the Chemical Structure, Dynamic & Mechanism B Program of the Chemistry Division, Professor Yan Xia of the Department of Chemistry at Stanford University is developing a diverse family of carbon-rich conjugated molecules containing unusual antiaromatic cyclobutadienoids (CBDs) to control and understand the complex effects of antiaromaticity for future organic electronic applications. Conjugated molecules are critical materials for various optical and electronic applications. While they predominantly consist of aromatic frameworks, introducing CBD antiaromatic motifs has long been sought as a novel strategy to achieve favorable molecular properties, but conjugated CBDs are previously challenging to access. The proposed research will generate several unprecedented series of CBD-containing conjugated molecules, new fundamental insights into the control and influence of antiaromaticity, and new types of conjugated materials. This project integrates organic synthesis, design and advanced physical measurement of conjugated materials, and computation, providing a highly interdisciplinary and collaborative environment for training and outreach at graduate, undergraduate, and high school levels for students at Stanford and from the Bay Area.Carbon-rich conjugated molecules are of significant fundamental and technical interest for their optoelectronic properties and applications. Conjugated systems containing 4 pi-electron antiaromatic cyclobutadienoids (CBDs) have been challenging to synthesize, thus limiting the understanding of the multifaceted effects of CBD in extended pi-systems. This project will leverage the methodology that the Professor Xia's group has recently developed to synthesize several series of CBD-containing polycyclic conjugated hydrocarbons with different topologies, sizes of conjugation, conformations, and electronic characteristics. Experimental and computational investigations of these series of molecules will be carried out to answer the following questions: 1) How to modulate the degree of CBD antiaromaticity? 2) How does antiaromaticity affect frontier molecular orbitals, pi-bonding structures and conformations, optoelectronic properties, and carrier mobility? 3) How to tune these molecular properties of aromatic frameworks by designed fusion of CBD motifs?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.