The Production and Characterisation of Novel Conducting Redox-active Oligomeric Thin Films from Electrooxidised Indolo[3,2,1-jk]carbazole

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.