title: n-Dopants Based on Dimers of Benzimidazoline Radicals: Structures and Mechanism of Redox Reactions.
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.
authors.affiliation: School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA 30332-0400 (USA).
authors.forename: Siyuan
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Departments of Chemical Engineering and Chemistry, Stanford University, Stanford, CA 94303 (USA).
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Naab
authors.affiliation: Department of Chemistry, New Mexico Highlands University, Las Vegas, NM 87701 (USA).
authors.forename: Evgheni V
authors.initials: EV
authors.lastname: Jucov
authors.affiliation: Department of Chemistry, University of Kentucky, Lexington, KY 40506 (USA).
authors.forename: Sean
authors.initials: S
authors.lastname: Parkin
authors.affiliation: Department of Chemistry and Biochemistry, University of California - Santa Cruz, Santa Cruz, CA 95064 (USA).
authors.forename: Eric G B
authors.initials: EG
authors.lastname: Evans
authors.affiliation: Department of Chemistry and Biochemistry, University of California - Santa Cruz, Santa Cruz, CA 95064 (USA).
authors.forename: Glenn L
authors.initials: GL
authors.lastname: Millhauser
authors.affiliation: Department of Chemistry, New Mexico Highlands University, Las Vegas, NM 87701 (USA).
authors.forename: Tatiana V
authors.initials: TV
authors.lastname: Timofeeva
authors.affiliation: School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA 30332-0400 (USA).|Department of Chemistry and Center for Applied Energy Research (CAER), University of Kentucky, Lexington, KY 40506-0055 (USA).
authors.forename: Chad
authors.initials: C
authors.lastname: Risko
authors.affiliation: School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA 30332-0400 (USA).|Division of Physical Sciences and Engineering King Abdullah University of Science and Technology, Thuwal, 23955-6900 (Saudi Arabia).
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Brédas
authors.affiliation: Departments of Chemical Engineering and Chemistry, Stanford University, Stanford, CA 94303 (USA). zbao@stanford.edu.
authors.forename: Zhenan
authors.initials: Z
authors.lastname: Bao
authors.affiliation: School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA 30332-0400 (USA). stephen.barlow@chemistry.gatech.edu.
authors.forename: Stephen
authors.initials: S
authors.lastname: Barlow
authors.affiliation: School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA 30332-0400 (USA). seth.marder@chemistry.gatech.edu.
authors.forename: Seth R
authors.initials: SR
authors.lastname: Marder
mesh_terms: D001555:Benzene Derivatives / Q000737:chemistry; D018360:Crystallography, X-Ray; D019281:Dimerization; D004579:Electron Transport; D005609:Free Radicals / Q000737:chemistry*; D048288:Imidazolines / Q000737:chemistry*; D008958:Models, Molecular; D009279:Naphthacenes / Q000737:chemistry; D010084:Oxidation-Reduction; D011789:Quantum Theory; D012666:Semiconductors; D013816:Thermodynamics
chemical_list: D001555:Benzene Derivatives; D005609:Free Radicals; D048288:Imidazolines; D009279:Naphthacenes; C523499:pentacene
keywords: density functional calculations; doping; reaction mechanism; redox chemistry; structure elucidation