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

Swagat K Mohapatra; Khaled Al Kurdi; Samik Jhulki; Georgii Bogdanov; John Bacsa; Maxwell Conte; Tatiana V Timofeeva; Seth R Marder; Stephen Barlow

doi:10.3762/bjoc.19.121

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

Beilstein J Org Chem. 2023 Nov 1:19:1651-1663. doi: 10.3762/bjoc.19.121. eCollection 2023.

Authors

Swagat K Mohapatra^{1

2}, Khaled Al Kurdi¹, Samik Jhulki¹, Georgii Bogdanov³, John Bacsa⁴, Maxwell Conte¹, Tatiana V Timofeeva³, Seth R Marder^{1

5

6

7}, Stephen Barlow^{1

5

7}

Affiliations

¹ Center for Organic Photonics and Electronics and School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 80007, United States.
² Department of Industrial and Engineering Chemistry, Institute of Chemical Technology-Indian Oil Campus, ITT Kharagpur Extension Center, Bhubaneswar 751013 Odisha, India.
³ Department of Chemistry, New Mexico Highlands University, Las Vegas, New Mexico 87701, United States.
⁴ Crystallography Lab, Emory University, Atlanta, Georgia 30322, United States.
⁵ Renewable and Sustainable Energy Institute (RASEI), University of Colorado Boulder, Boulder, Colorado 80309, United States.
⁶ Department of Chemical and Biological Engineering and Department of Chemistry, University of Colorado Boulder, Boulder, Colorado 80309, United States.
⁷ National Renewable Energy Laboratory, Chemistry and Nanoscience Center, Golden, Colorado, 80401, United States.

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).

Keywords: benzoimidazole; crystal structure; kinetics; n-dopant; reduction.

Grants and funding

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. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.