The Production and Characterisation of Novel Conducting Redox‐Active Oligomeric Thin Films From Electrooxidised Indolo[3,2,1‐jk]carbazole

Novel thin‐film materials have been produced from indolo[3,2,1‐jk]carbazole (see picture). These are conducting and redox‐active and, unusually, consist of three distinct covalently coupled luminescent dimer species, consistent with a specific radical‐cation coupling mechanism. magnified image Indolo[3,2,1‐jk]carbazole (IC) has been synthesised on a gram scale by flash vacuum pyrolysis. In contrast to a previous suggestion, IC is planar and it is also highly fluorescent, with a solution quantum yield of 0.41. Electro‐oxidation of IC at a rotating disc electrode resulted in the passage of steady‐state currents and the reproducible formation of conducting, redox‐active films with constituent species that are also highly fluorescent. Unusually for coupled electroactive N‐heterocyclic systems, electrochemical and spectroscopic characterisation revealed the film to consist exclusively of three redox‐active (2,2′, 5,5′ and 2,5′ coupled) IC dimers with no polymeric products. Calculations showed this coupling pattern to be consistent with IC radical‐cation coupling through the accessible sites of highest unpaired electron density. The unusual combination of a high dimer second oxidation potential and a negligible dimer–dimer coupling rate explains the lack of further coupling. The identities of the dimeric species were confirmed by independent syntheses involving the Suzuki–Miyaura coupling of IC boronic acids as the key step. Electro‐oxidation of the IC system therefore offers a ready route to novel conducting, redox‐active molecular films and their redox‐active, luminescent dimer constituents.