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).
We systematically investigate the relationships between structural and electronic effects of finite size zigzag or armchair carbon nanotubes of various diameters and lengths, starting from a molecular template of varying shape and diameter, i.e. cyclic oligoacene or oligophenacene molecules, and disclosing how adding layers and/or end-caps (i.e. hemi-fullerenes) can modify their (poly)radicaloid nature. We mostly used tight-binding and finite-temperature density-based methods, the former providing a simple but intuitive picture about their electronic structure, and the latter dealing effectively with strong correlation effects by relying on a fractional occupation number weighted electron density (ρ<sub>FOD</sub>), with additional RAS-SF calculations backing up the<br>latter results. We also explore how minor structural modifications of nanotube end-caps might influence the results, showing that topology, together with the chemical nature of the systems, is pivotal for the understanding of the electronic properties of these and other related systems.
We systematically investigate the relationships between structural and electronic effects of finite size zigzag or armchair carbon nanotubes of various diameters and lengths, starting from a molecular template of varying shape and diameter, i.e. cyclic oligoacene or oligophenacene molecules, and disclosing how adding layers and/or end-caps (i.e. hemi-fullerenes) can modify their (poly)radicaloid nature. We mostly used tight-binding and finite-temperature density-based methods, the former providing a simple but intuitive picture about their electronic structure, and the latter dealing effectively with strong correlation effects by relying on a fractional occupation number weighted electron density (ρ<sub>FOD</sub>), with additional RAS-SF calculations backing up the<br>latter results. We also explore how minor structural modifications of nanotube end-caps might influence the results, showing that topology, together with the chemical nature of the systems, is pivotal for the understanding of the electronic properties of these and other related systems.
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