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1,3-Dimethyl-2,3-dihydrobenzo[d]imidazoles,1H, and 1,1',3,3'-tetramethyl-2,2',3,3'-tetrahydro-2,2'-bibenzo[d]imidazoles,1₂, 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 to1g₂and1h₂. 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(1₂^•+/1₂) andE(1H^•+/1H) values. Both the use of 3,4-dimethoxy and 2-aryl substituents accelerates the reaction of the1Hspecies with PC₆₁BM. Because 2-aryl groups stabilize radicals,1b₂and1g₂exhibit weaker bonds than1e₂and1h₂and thus react with 6,13-bis(triisopropylsilylethynyl)pentacene (VII) via a “cleavage-first” pathway, while1e₂and1h₂react only via “electron-transfer-first”.1h₂exhibits the most cathodicE(1₂^•+/1₂) value of the dimers considered here and, therefore, reacts more rapidly than any of the other dimers withVIIvia “electron-transfer-first”. Crystal structures show rather long central C–C bonds for1b₂(1.5899(11) and 1.6194(8) Å) and1h₂(1.6299(13) Å). 

The effects of sequential n-doping on a high-electron-mobility naphthalene-diimide-based copolymer poly[( N , N ′-bis(2-decyltetradecyl)-naphthalene-1,8:4,5-bis(dicarboximide)-2,6-diyl)-(selenophene-2,5-diyl)-(benzo[ c ][1,2,5]thiadiazole-4,7-diyl)-(selenophene-2,5-diyl)], PNBS, are reported. Grazing-incidence XRD measurements show that PNBS doped with 2,2′-bis(4-(dimethylamino)phenyl)-1,1′,3,3′-tetramethyl-2,2′,3,3′-tetrahydro-1 H ,1′ H -2,2′-bibenzo[ d ]imidazole, (N-DMBI) 2 , has increased order relative to both the pristine polymer and a film doped with ruthenium pentamethylcyclopentadienyl mesitylene dimer. Films of PNBS optimally doped with (N-DMBI) 2 show electrical conductivities approaching 2 mS cm −1 in air. Temperature-dependent electrical measurements suggest that the polaronic charge carriers are highly localized, which is consistent with the moderate conductivity values obtained.