This work describes the synthesis and properties of ad icyanomethylene-substituted indolo[3,2-b]carbazole diradical ICz-CN. This quinoidal system dimerises almost completely to (ICz-CN) 2 ,w hich contains two long C(sp 3)À C(sp 3) s-bonds between the dicyanomethylene units. The minor open-shell ICz-CN component in the solid-state mixture was identified by EPR spectroscopy.C yclic voltammetry and UV-visible spectroelectrochemical data, as well as comparison with reference monomerI Cz-Br reveal that the nature of the one-electrono xidation 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 peculiar cathodic behaviour reflects the coexistence of (ICz-CN) 2 and ICz-CN. The involvement of the dicyanomethylene groupss tabilizes the close-lying LUMO and LUMO + 1o f(ICz-CN) 2 and especially ICz-CN comparedt oI Cz-Br,r esulting in ad istinctive cathodic response at low overpotentials. Differently from neutralI Cz-CN, its radicala nion and dianion are remarkably stable under ambient conditions. The UV/Vis(-NIR) electronic transitions in parent (ICz-CN) 2 and ICz-CN and their different redox forms have been assigned convincingly with the aid of TD-DFT calculations. The s-bond in neutral(ICz-CN) 2 is cleaved in solution and in the solid-state upon soft external stimuli (temperature, pressure), showing as trong chromism from light yellow to blue-green. Notably,i nt he solid state, the monomeric diradical species is predominantly formed under high hydrostatic pressure (> 1GPa).