Planar,Stair-Stepped,and Twisted: Modulating Structure and Photophysics in Pyrene- and Benzene-Fused N-Heterocyclic Boranes |
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Authors: | Kelsie E. Krantz Sarah L. Weisflog Nathan C. Frey Dr. Wenlong Yang Dr. Diane A. Dickie Prof. Dr. Charles Edwin Webster Prof. Dr. Robert J. Gilliard Jr. |
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Affiliation: | 1. Department of Chemistry, University of Virginia, 409 McCormick Rd./ PO Box 400319, Charlottesville, VA, 22904 USA;2. Department of Chemistry, Mississippi State University, Box 9573, Mississippi State, MS, 39762 USA |
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Abstract: | Because of their rigidity, polycyclic aromatic hydrocarbons (PAHs) have become a significant building block in molecular materials chemistry. Fusion or doping of boron into PAHs is known to improve the optoelectronic properties by reducing the LUMO energy level. Herein, we report a comprehensive study on the syntheses, structures, and photophysical properties of a new class of fused N-heterocyclic boranes (NHBs), pyrene- and benzene-linked in a “Janus-type” fashion ( 2 – 4 , 6 – 9 , and 11 ). Remarkably, these examples of fused NHBs display fluorescent properties, and collectively their emission spans the visible spectrum. The pyrene-fused NHBs all display blue fluorescence, as the excitations are dominated by the pyrene core. In notable contrast, the emission properties of the benzene-fused analogues are highly tunable and are dependent on the electronics of the NHB fragments (i.e., the functional group directly bound to the boron atoms). Pyrene-fused 2 – 4 and 11 represent the only molecules in which the K-region of pyrene is functionalized with NHB units, and while they exhibit distorted (twisted or stair-stepped) pyrene cores, benzene-fused 6 – 9 are planar. The electronic structure and optical properties of these materials were probed by computational studies, including an evaluation of aromaticity, electronic transitions, and molecular orbitals. |
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Keywords: | coordination chemistry doping N-heterocyclic boranes materials chemistry PAHs |
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