Chiroptical Redox Switching of Tetra‐Cationic Derivatives of Azoniahelicenes. Issue 12 (3rd April 2019)

• Record Type: Journal Article
• Authors: Rončević, Igor; Jirásek, Michael; Severa, Lukáš; Reyes‐Gutierrez, Paul Eduardo; Teplý, Filip; Bednárová, Lucie; Hromadová, Magdaléna; Pospíšil, Lubomír
• Is Part Of: ChemElectroChem. Volume 6:Issue 12(2019)
• Page Start: 3002
• Page End: 3008
• Publication Date: 2019-04-03
• Subjects: helquats -- redox switching -- voltammetry -- spectroelectrochemistry -- circular dichroism; Electrochemistry -- Periodicals; 541.37
• DOI: 10.1002/celc.201900204
• Languages: English
• ISSNs: 2196-0216

Abstract

Abstract: New tetra‐ and di‐cationic azoniahelicenes provide electrochemical, spectroelectrochemical and electronic circular dichroism (ECD) data reflecting their differences in electron transfer (ET) kinetics. Di‐cationic helquats containing two seven‐membered rings are irreversibly reduced in two ET steps. Substitution by redox‐active ethenylpyridinium in the α or γ position with respect to nitrogen atoms of the helquat core yields tetra‐cationic derivatives with reversible ET steps and communicating redox centres. Redox‐inactive substituents in di‐cationic azoniahelicenes retain ET irreversibility. Redox switching of ECD of tetra‐cationic enantiomers was observed. Unlike fully aromatic helquat, the ECD response of tetra‐cationic helquats to periodic reduction‐oxidation cycles is slower, owing to a strong adsorption on electrodes. Quantum chemical calculations (DFT) indicate that the first ET step of tetra‐cationic derivative substituted in the γ position yields a folded structure, which favours the internal donor‐acceptor interaction. This explains the spectroelectrochemical differences between both tetra‐cations. Abstract : In the fold : Helquats containing seven‐membered rings substituted with redox‐active ethenylpyridinium in the α or γ position with respect to the nitrogen atoms of the helquat core yield tetra‐cationic derivatives. Reversible electron transfers switch the intensity of the electronic circular dichroism signal of both tetra‐cations. Derivatives substituted in the γ position during the electron transfer undergo structural folding.