Benzoimidazolium-derived dimeric and hydride n-dopants for organic electron-transport materials: impact of substitution on structures, electrochemistry, and reactivity

• Type of Material: Article
• Authors: Swagat K. Mohapatra, Georgia Institute of Technology; Khaled Al Kurdi, Georgia Institute of Technology; Samik Jhulki, Georgia Institute of Technology; Georgii Bogdanov, Ne Mexico Highlands University; John Bacsa, Emory University; Maxwell Conte, Georgia Institute of Technology; Tatiana V. Timofeeva, New Mexico Highlands University; Seth R. Marder, Georgia Institute of Technology; Stephen Barlow, Georgia Institute of Technology
• Language: English
• Date: 2023-11-01
• Publisher: BJOC
• Publication Version: Final Published Version
• Copyright Statement: © 2023, Mohapatra et al.
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): https://doi.org/10.3762/bjoc.19.121
• Title of Journal or Parent Work: Beilstein Journal of Organic Chemistry
• Volume: 19
• Start Page: 1651
• End Page: 1663
• Grant/Funding Information: The work was primarily supported by the National Science Foundation through award DMR-1807797/2216857. Diffraction studies at New Mexico Highlands University were supported by the National Science Foundation’s PREM program through DMR-2122108. SJ was supported by Fulbright-Nehru Postdoctoral Fellowship from the United States-India Educational Foundation and Institute of International Education for (grant no. 2266/FNPDR/2017). This work was also authored in part by the National Renewable Energy Laboratory (NREL), operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308; specifically, some of the data analysis was carried out as part of a Laboratory Directed Research and Development (LDRD) Program at NREL.
• Keywords: n-dopant; crystal structure; reduction; benzoimidazole; kinetics
• Research Categories: Chemistry, Organic

Abstract

1,3-Dimethyl-2,3-dihydrobenzo[d]imidazoles, 1H, and 1,1',3,3'-tetramethyl-2,2',3,3'-tetrahydro-2,2'-bibenzo[d]imidazoles, 12, are of interest as n-dopants for organic electron-transport materials. Salts of 2-(4-(dimethylamino)phenyl)-4,7-dimethoxy-, 2-cyclohexyl-4,7-dimethoxy-, and 2-(5-(dimethylamino)thiophen-2-yl)benzo[d]imidazolium (1g–i+, respectively) have been synthesized and reduced with NaBH4 to 1gH, 1hH, and 1iH, and with Na:Hg to 1g2 and 1h2. Their electrochemistry and reactivity were compared to those derived from 2-(4-(dimethylamino)phenyl)- (1b+) and 2-cyclohexylbenzo[d]imidazolium (1e+) salts. E(1+/1•) values for 2-aryl species are less reducing than for 2-alkyl analogues, i.e., the radicals are stabilized more by aryl groups than the cations, while 4,7-dimethoxy substitution leads to more reducing E(1+/1•) values, as well as cathodic shifts in E(12•+/12) and E(1H•+/1H) values. Both the use of 3,4-dimethoxy and 2-aryl substituents accelerates the reaction of the 1H species with PC61BM. Because 2-aryl groups stabilize radicals, 1b2 and 1g2 exhibit weaker bonds than 1e2 and 1h2 and thus react with 6,13-bis(triisopropylsilylethynyl)pentacene (VII) via a “cleavage-first” pathway, while 1e2 and 1h2 react only via “electron-transfer-first”. 1h2 exhibits the most cathodic E(12•+/12) value of the dimers considered here and, therefore, reacts more rapidly than any of the other dimers with VII via “electron-transfer-first”. Crystal structures show rather long central C–C bonds for 1b2 (1.5899(11) and 1.6194(8) Å) and 1h2 (1.6299(13) Å).