title: Mechanistic study on the solution-phase n-doping of 1,3-dimethyl-2-aryl-2,3-dihydro-1H-benzoimidazole derivatives.
abstract: The discovery of air-stable n-dopants for organic semiconductor materials has been hindered by the necessity of high-energy HOMOs and the air sensitivity of compounds that satisfy this requirement. One strategy for circumventing this problem is to utilize stable precursor molecules that form the active doping complex in situ during the doping process or in a postdeposition thermal- or photo-activation step. Some of us have reported on the use of 1H-benzimidazole (DMBI) and benzimidazolium (DMBI-I) salts as solution- and vacuum-processable n-type dopant precursors, respectively. It was initially suggested that DMBI dopants function as single-electron radical donors wherein the active doping species, the imidazoline radical, is generated in a postdeposition thermal annealing step. Herein we report the results of extensive mechanistic studies on DMBI-doped fullerenes, the results of which suggest a more complicated doping mechanism is operative. Specifically, a reaction between the dopant and host that begins with either hydride or hydrogen atom transfer and which ultimately leads to the formation of host radical anions is responsible for the doping effect. The results of this research will be useful for identifying applications of current organic n-doping technology and will drive the design of next-generation n-type dopants that are air stable and capable of doping low-electron-affinity host materials in organic devices.
authors.affiliation: Departments of Chemical Engineering and Chemistry, Stanford University , 359 N-S Axis Stauffer III, Stanford, California 94303, United States.
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Naab
authors.forename: Song
authors.initials: S
authors.lastname: Guo
authors.forename: Selina
authors.initials: S
authors.lastname: Olthof
authors.forename: Eric G B
authors.initials: EG
authors.lastname: Evans
authors.forename: Peng
authors.initials: P
authors.lastname: Wei
authors.forename: Glenn L
authors.initials: GL
authors.lastname: Millhauser
authors.forename: Antoine
authors.initials: A
authors.lastname: Kahn
authors.forename: Stephen
authors.initials: S
authors.lastname: Barlow
authors.forename: Seth R
authors.initials: SR
authors.lastname: Marder
authors.forename: Zhenan
authors.initials: Z
authors.lastname: Bao
mesh_terms: D004579:Electron Transport; D007093:Imidazoles / Q000737:chemistry*; D007700:Kinetics; D012996:Solutions; D013816:Thermodynamics
chemical_list: D007093:Imidazoles; D012996:Solutions