Diindole-annulated naphthalene diimides: synthesis and optical and electronic properties of syn- and anti-isomers.

Here we report a selective method for the core-extension of naphthalene diimide (NDI) with two annulated indole rings leading to carbazolo[2,3-b]carbazole diimides (CbDIs) with exclusive syn-connectivity based on a regioselective nucleophilic substitution reaction of Br4-NDI with arylamines, followed by palladium-catalyzed intramolecular C–C coupling. The oxygen analogues of anti-CbDIs, namely anti-benzofurobenzofuran diimides (anti-BfDIs), were obtained from 2,6-Br2-NDI and 2-bromophenol. The syn- and anti-isomers of CbDIs were unambiguously characterized by single-crystal X-ray analysis. The optical properties of the present core-enlarged NDIs were studied, revealing clear differences in the absorption characteristics of the syn- and anti-isomers of CbDI, on one hand, and CbDI vs BfDI derivatives, on the other hand. Cyclic voltammetry studies showed that the redox properties are dependent on the substituents at the CbDI-core and oxygen atom containing BfDIs are more prone to reduction than the respectiv...