N-Dopants Based on Dimers of Benzimidazoline Radicals: Structures and Mechanism of Redox Reactions

Siyuan Zhang, Benjamin D. Naab, Evgheni V. Jucov, Sean Parkin, Eric G.B. Evans, Glenn L. Millhauser, Tatiana V. Timofeeva, Chad Risko, Jean Luc Brédas, Zhenan Bao, Stephen Barlow, Seth R. Marder

Research output: Contribution to journalArticlepeer-review

21 Scopus citations

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+/0.5D2 redox potentials - the effective reducing strengths of the dimers - vary little within the series (ca. -1.9V 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. Benzimidazoline dimers are effective n-dopants for organic electronics. Vis-NIR kinetics help elucidate the mechanisms by which they react with acceptors (A); these depend on both the dimer and A and can be rationalized using electrochemistry and dissociation energies (see scheme). X-ray diffraction shows central C-C bond lengths do not correlate with dissociation energy.

Original languageEnglish (US)
Pages (from-to)10878-10885
Number of pages8
JournalChemistry - A European Journal
Volume21
Issue number30
DOIs
StatePublished - Jul 1 2015
Externally publishedYes

Keywords

  • density functional calculations
  • doping
  • reaction mechanism
  • redox chemistry
  • structure elucidation

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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