Triazole‐fused indolo[2,3‐a]carbazoles: synthesis, structures, and properties

The synthesis, structure, and photophysical and electrochemical properties of triazole fused indolo[2,3‐a]carbazole derivatives 2‐5 are reported. The key step involved in the synthesis of triazole fused indolo[2,3‐a]carbazole derivatives is the Cadogan ring closing reaction. 2‐Hexyl‐5,6‐dinitro‐2H‐benzo[d][1,2,3]triazoles having 4,7‐diaryl capping were subjected to the Cadogan cyclization reaction to obtain compounds 2‐5. In contrast to thiadiazole‐fused indolo[2,3‐a]carbazole 1, bromination of triazole‐fused indolo[2,3‐a]carbazole 4 afforded only meta‐dibrominated product with respect to the nitrogen of fused pyrrole rings on treatment with both N‐bromosuccinimide (NBS) and elemental bromine. These compounds showed positive solvatochromism in their emission spectra. Incorporation of electron‐donating substituent in the indole moiety resulted in the elevation of the highest occupied molecular orbital (HOMO) level. Density functional theory (DFT) calculations were performed to support the experimental findings.