Title: Molecules in a Hurry to Escape Antiaromaticity
Abstract : Antiaromatic molecules, unless kinetically trapped, fused to aromatic frameworks, or stabilized by chemical modifications, often are short-lived and difficult to work with experimentally—they always find ways of escaping the state of being called “antiaromatic.” Cyclobutadiene, cyclopentadiene, pentalene, and other cyclic, π-conjugated compounds, with formal [4n] ring π-electrons, easily dimerize to get rid of antiaromaticity. Upon irradiation, benzene rather isomerize to fulvene and the very strained benzvalene than stay [4n + 2] π-electron antiaromatic. Many photochemical reactions can be understood by relief of excited-state antiaromaticity. My talk will focus on the effects of antiaromaticity relief on excited-state proton transfer (ESPT) reactions, including excited-state intramolecular proton transfers (ESIPT), biprotonic transfers, dynamic catalyzed transfers, and proton relay transfers. o-Salicylic acid undergoes ESPT only in the “antiaromatic” S1 (1ππ*) state, but not in the “aromatic” S2 (1ππ*) state. Stokes’ shifts of structurally-related compounds (e.g., derivatives of 2-(2-hydroxyphenyl)benzoxazole and hydrogen-bonded complexes of 2-aminopyridine with protic substrates) vary depending on the antiaromaticity of the photoinduced tautomers. Implications of excited-state antiaromaticity for proton-coupled electron transfer in DNA base pairs also will be discussed.
Bio: Judy grew up in the subtropical island of Taiwan. She earned a BS (2004) in Chemistry from Tunghai University, Taiwan, and a PhD (2011) working with Paul Schleyer, at the University of Georgia. In 2015, she began her independent career at the University of Houston, Department of Chemistry. She is interested in studying how light affects proton and...