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

Abstract

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.

A Minireview on the Scope of Cadogan Cyclization Reactions Leading to Diverse Azaheterocycles

“…Among the synthesized compounds 30 b and 31 b were found to express positive solvatochromism in their emission spectra, indicating the importance of electron‐donating substituents such as methoxy groups in the stabilization of charge separation states. Moreover, these experimental results were also supported by DFT calculations [28] …”

“…In 2020, several triazole fused indolo[2,3-a]carbazole derivatives were synthesized and evaluated for photophysical as well as electrochemical properties by Sirina Ghosh and colleagues. [28] Here, Cadogan cyclization reaction was used as the key route for the preparation of desired molecules as shown in Scheme substitution on both triazole and indolocarbazole scaffolds and even by substitution on the terminal phenyl rings. Among the synthesized compounds 30 b and 31 b were found to express positive solvatochromism in their emission spectra, indicating the importance of electron-donating substituents such as methoxy groups in the stabilization of charge separation states.…”

“…Moreover, these experimental results were also supported by DFT calculations. [28] Fernando and the team developed a new, simple and efficient methodology for the synthesis of the different angular indolocarbazole skeletons through gold-catalysed regioselective cyclization reaction and dioxomolybdenum-catalysed reductive Cadogan cyclization resulting in the two sequential carbazole formation reactions as shown in Scheme 7. [29] The salient features of this methodology are regioselectivity and high yield products.…”

“…In 2020, several triazole fused indolo[2,3‐ a ]carbazole derivatives were synthesized and evaluated for photophysical as well as electrochemical properties by Sirina Ghosh and colleagues [28] . Here, Cadogan cyclization reaction was used as the key route for the preparation of desired molecules as shown in Scheme 6.…”