Synthesis and spectroscopic studies of highly fluorescent, solvatochromic diastereomers with differentially stacked bithiophene-substituted quinoxaline rings

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• 作者：Ryan A. Ciufo ; John J. Kreinbihl ; Sarah R. Johnson ; Jocelyn M. Nadeau ; ^{jocelyn.nadeau@marist.edu}
• 关键词：Quinoxaline ; Bithiophene ; Pi overlap ; Intramolecular excimer ; Charge transfer ; Solvatochromic
• 刊名：Tetrahedron
• 出版年：2017
• 出版时间：5 January 2017
• 年：2017
• 卷：73
• 期：1
• 页码：30-38
• 全文大小：1206 K
• 卷排序：73

文摘

Diastereomeric C-shaped molecules containing closely stacked bithiophene-substituted quinoxaline rings were synthesized and characterized by NMR, UV–vis absorption, and fluorescence spectroscopy. The unique geometry of each diastereomer resulted in different degrees of π-overlap between the bithiophene-substituted quinoxaline ring chromophores, modulating their spectroscopic properties. The donor-acceptor nature of this chromophore gave rise to its positive solvatochromism. 1H NMR and UV–vis absorption spectroscopy confirmed the existence of π-π interactions in the ground state between the quinoxaline rings in both molecules but between the bithiophene rings only in the syn isomer. They exhibited significant emission maxima bathochromic shifts, a strong, positive solvatochromism, increased band broadening, and larger Stokes shifts when compared to a compound with an unstacked chromophore. Additionally, the syn isomer consistently showed λmax,em value red-shifts and larger band broadening and Stokes shifts compared to the anti isomer due to the greater π-overlap in the syn isomer.