n‐Dopants Based on Dimers of Benzimidazoline Radicals: Structures and Mechanism of Redox Reactions |
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| Authors: | Evgheni V Jucov Prof Sean Parkin Eric G B Evans Glenn L Millhauser Tatiana V Timofeeva Dr Chad Risko Prof Jean‐Luc Brédas Prof Zhenan Bao Dr Stephen Barlow Prof Seth R Marder |
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| Institution: | 1. Department of Chemistry, New Mexico Highlands University, Las Vegas, NM 87701 (USA);2. Department of Chemistry, University of Kentucky, Lexington, KY 40506 (USA);3. Department of Chemistry and Biochemistry, University of California ‐ Santa Cruz, Santa Cruz, CA 95064 (USA);4. School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA 30332‐0400 (USA);5. Department of Chemistry and Center for Applied Energy Research (CAER), University of Kentucky, Lexington, KY 40506‐0055 (USA);6. Division of Physical Sciences and Engineering King Abdullah University of Science and Technology, Thuwal, 23955‐6900 (Saudi Arabia);7. Departments of Chemical Engineering and Chemistry, Stanford University, Stanford, CA 94303 (USA) |
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| Abstract: | Dimers of 2‐substituted N,N′‐dimethylbenzimidazoline radicals, (2‐Y‐DMBI)2 (Y=cyclohexyl (Cyc), ferrocenyl (Fc), ruthenocenyl (Rc)), have recently been reported as n‐dopants for organic semiconductors. Here their structural and energetic characteristics are reported, along with the mechanisms by which they react with acceptors, A (PCBM, TIPS‐pentacene), in solution. X‐ray data and DFT calculations both indicate a longer C?C bond for (2‐Cyc‐DMBI)2 than (2‐Fc‐DMBI)2, yet DFT and ESR data show that the latter dissociates more readily due to stabilization of the radical by Fc. Depending on the energetics of dimer (D2) dissociation and of D2‐to‐A electron transfer, D2 reacts with A to form D+ and A? by either of two mechanisms, differing in whether the first step is endergonic dissociation or endergonic electron transfer. However, the D+/0.5 D2 redox potentials—the effective reducing strengths of the dimers—vary little within the series (ca. ?1.9 V vs. FeCp2+/0) (Cp=cyclopentadienyl) due to cancelation of trends in the D+/0 potential and D2 dissociation energy. The implications of these findings for use of these dimers as n‐dopants, and for future dopant design, are discussed. |
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| Keywords: | density functional calculations doping reaction mechanism redox chemistry structure elucidation |
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