Dynamic Covalent Properties of a Novel Indolo[3,2‐b]carbazole Diradical

This work describes the synthesis and properties of a dicyanomethylene‐susbtituted indolo[3,2‐b]carbazole diradical ICz‐CN.This quinoidal system dimerises almost completely to (ICz‐CN)2 containing two long C(sp3 )‐C(sp 3) σ‐bonds between the dicyanomethylene units . The minor open‐shell ICz‐CN component in the solid state mixture was identify with EPR spectroscopy. The cyclic voltammetric and UV‐vis spectroelectrochemical data, and comparison with reference monomer ICz‐Br reveal that the nature of the one‐electron oxidation of (ICz‐CN)2 at ambient temperature and ICz‐CN at elevated temperature is very similar in all these compounds due to the prevailing localization of their HOMO on the ICz backbone. The involvement of the dicyanomethylene groups stabilizes the close‐lying LUMO and LUMO+1 of (ICz‐CN) 2 and especially ICz‐CN compared to ICz‐Br , resulting in the distinctive cathodic behaviour at low overpotentials. Differently from neutral ICz‐CN , its radical anion and dianion are remarkably stable at ambient conditions. The UV‐Vis(‐NIR) electronic transitions in parent ( ICz‐CN ) 2 and ICz‐CN and their different redox forms have been assigned with the aid of TD‐DFT calculations. The s‐bond cleavage in neutral ( ICz‐CN ) 2 is achieved in solution and in the solid‐state upon soft external stimuli (time, temperature, pressure), showing a strong chromism from light yellow to blue‒green. Notably, in solid state, the predominant formation of the monomeric diradical species is achieved under high hydrostatic pressure conditions (>1 GPa).