Chiroptical Redox Switching of Tetra‐Cationic Derivatives of Azoniahelicenes

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

On the Physicochemical Properties of Pyridohelicenes

International audienc

On the Supra‐LUMO Interaction: Case Study of a Sudden Change of Electronic Structure as a Functional Emergence

International audienc

Importance of the Anchor Group Position (Para versus Meta) in Tetraphenylmethane Tripods: Synthesis and Self-Assembly Features

The efficient synthesis of tripodal platforms based on tetraphenylmethane with three acetyl-protected thiol groups in either meta or para positions relative to the central sp 3 carbon for deposition on Au (111) surfaces is reported. These platforms are intended to provide a vertical arrangement of the substituent in position 4 of the perpendicular phenyl ring and an electronic coupling to the gold substrate. The self-assembly features of both derivatives are analyzed on Au (111) surfaces by low-temperature ultra-high-vacuum STM, high-resolution X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and reductive voltammetric desorption studies. These experiments indicated that the meta derivative forms a well-ordered monolayer, with most of the anchoring groups bound to the surface, whereas the para derivative forms a multilayer film with physically adsorbed adlayers on the chemisorbed para monolayer. Single-molecule conductance values for both tripodal platforms are obtained through an STM break junction experiment