6336-32-9

indolo[3,2-b]carbazole has a large planar and rigid conjugated structure with fused alternating three benzene and two pyrrole rings. It is a heterocyclic analogue of pentacene – one of the most used organic semiconductors – and is considered to be a nitrogen-containing electron-rich heteroacene with a ladder-type structure. It is a potent agonist of the aryl hydrocarbon receptor (AhR) and was found in Brassica family vegetables. Since its electron-donating nature, indolo[3,2-b]carbazole derivative is commonly used as hole transporting, charge injection, host, and electroluminescent materials for OLED and OFET devices with good thermal, chemical, and environmental stability[1].

The nitrogen heteroatoms open up the possibility of functionalization and sensing capabilities, as well as lowering the HOMO energy levels, which renders them air-stable. Additionally, Indolo[3,2-b]carbazole exhibit very strong Nsingle bondH?π interactions, which can enhance charge transport by improving intermolecular interactions and thus result in an improved molecular packing motive. Because of the high glass transition temperature, ICZ compounds possess great thermal and morphological stability under ambient conditions[1].

To a mixed solution of 25.0 g (101.5 mmol) 3,3'-diindolylmethane and 15.1 g (101.5 mmol) triethyl orthoformate in 400 mL of methanol was slowly added 1.4 mL of concentrated sulfuric acid. The reaction mixture was stirred under reflux conditions for 5 hours. Upon completion of the reaction, the reaction solution was cooled to room temperature in an ice water bath. The precipitate precipitated was collected by filtration and washed with 500 mL of methanol to give 19.0 g of brown solid. The solid was analyzed by FD-MS and confirmed to be the target intermediate 2-2 in 73% yield.

[1] Streckaite S, et al. Fluorescence quenching of indolo[3,2-b]carbazole compounds by conformational motions of attached substituents. Dyes and Pigments, 2016; 133: 120-126.
[2] Bintinger J, et al. Synthesis, characterization and printing application of alkylated indolo[3,2-b]carbazoles. Synthetic Metals, 2017; 288: 9-17.