Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 27, Issue 17, Pages 5509-5520Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.202005211
Keywords
carbazoles; chromo-active materials; density functional theory; diradicals; electronic transitions
Categories
Funding
- MICINN [PID2019-110305GB-I00, PID2019-104293GB-I00, PCI2019-111825-2, PID2019-106114GB-I00]
- Instituto de Salud Carlos III (ISCIII) [RD16/0006/0012]
- Junta de Andalucia [UMA-FEDERJA-080, UMA-FEDERJA-007, P09FQM-4708]
- Generalitat Valenciana [AICO/2018/175]
- National Natural Science Foundation of China [21875279, 21790362]
- Spectroelectrochemistry Reading (a spinout company of the University of Reading)
- European Research Council (ERC) Grant Hecate [695527]
- MCIU/MINECO [CTQ2013-48252-P, CTQ2015-67755-C02-01-R, PGC2018-094814-B-C21]
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This study describes the synthesis and properties of a dicyanomethylene-substituted indolo[3,2-b]carbazole diradical ICz-CN and its chemical behavior under different conditions. Experimental results show that ICz-CN exhibits similar characteristics in different oxidation states and undergoes chromism under certain conditions.
This work describes the synthesis and properties of a dicyanomethylene-substituted indolo[3,2-b]carbazole diradical ICz-CN. This quinoidal system dimerises almost completely to (ICz-CN)(2), which contains two long C(sp(3))-C(sp(3)) sigma-bonds between the dicyanomethylene units. The minor open-shell ICz-CN component in the solid-state mixture was identified by EPR spectroscopy. Cyclic voltammetry and UV-visible spectroelectrochemical data, as well as 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 peculiar cathodic behaviour reflects the co-existence of (ICz-CN)(2) and ICz-CN. 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 a distinctive cathodic response at low overpotentials. Differently from neutral ICz-CN, its radical anion 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 sigma-bond in neutral (ICz-CN)(2) is cleaved in solution and in the solid-state upon soft external stimuli (temperature, pressure), showing a strong chromism from light yellow to blue-green. Notably, in the solid state, the monomeric diradical species is predominantly formed under high hydrostatic pressure (>1 GPa).
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