1,3-Dimethyl-2,3-dihydrobenzo[
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d ]imidazoles,1H , and 1,1',3,3'-tetramethyl-2,2',3,3'-tetrahydro-2,2'-bibenzo[d ]imidazoles,1 2 , 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 NaBH4to1gH ,1hH , and1iH , and with Na:Hg to1g 2 and1h 2 . 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 reducingE (1 + /1 • ) values, as well as cathodic shifts inE (1 2 •+ /1 2 ) andE (1H •+ /1H ) values. Both the use of 3,4-dimethoxy and 2-aryl substituents accelerates the reaction of the1H species with PC61BM. Because 2-aryl groups stabilize radicals,1b 2 and1g 2 exhibit weaker bonds than1e 2 and1h 2 and thus react with 6,13-bis(triisopropylsilylethynyl)pentacene (VII ) via a “cleavage-first” pathway, while1e 2 and1h 2 react only via “electron-transfer-first”.1h 2 exhibits the most cathodicE (1 2 •+ /1 2 ) value of the dimers considered here and, therefore, reacts more rapidly than any of the other dimers withVII via “electron-transfer-first”. Crystal structures show rather long central C–C bonds for1b 2 (1.5899(11) and 1.6194(8) Å) and1h 2 (1.6299(13) Å). -
Abstract Doping the electron‐transport polymer poly{[
N ,N ′‐bis(2‐octyldodecyl)naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene)} [P(NDI2OD‐T2)] with the bulky, strongly reducing metallocene 1,2,3,4,1′,2′,3′,4′‐octaphenylrhodocene (OPR) leads to an increased bulk conductivity and a decreased contact resistance. While the former arises from low‐level n‐doping of the intrinsic polymer and increased carrier mobility due to trap‐filling, the latter arises from a pronounced accumulation of dopant molecules at an indium tin oxide (ITO) substrate. Electron transfer from OPR to ITO leads to a work function reduction, which pins the Fermi level at the P(NDI2OD‐T2) conduction band and thus minimizes the electron injection barrier and the contact resistance. The results demonstrate that disentangling the effects of electrode modification by the dopant and bulk doping is essential to comprehensively understand doped organic semiconductors.