Redox-Driven Folding, Unfolding, and Refolding of Bis(tetrathiafulvalene) Molecular Switch

Abstract

We report redox-driven folding, unfolding, and refolding motions of a synthetic molecular system, in which two tetrathiafulvalene (TTF) units are tethered onto a conformationally rigid yet torsionally flexible π-conjugated backbone. Upon oneelectron oxidation, this molecular switch undergoes swiveling motions from a fully relaxed and freely rotating Z-shaped conformation to a compact folded conformation stabilizing πstacked radical species. Subsequent one-electron oxidation produces dicationic intermediates, which either engage in intimate π−π interactions or transition to an open structure. Further oxidation, however, brings the molecule back to the initial conformation to minimize the repulsion between doubly-charged TTF units. Intriguingly, the reaction coordinates of this redox-driven structural change have strong dependence on the environment, such as the solvent (THF vs CH 2 Cl 2 ) and supporting electrolyte (PF 6 − vs B(C 6 F 5 ) 4 − ). With a proper design, factors that are typically considered as "secondary effects" could dictate the solution dynamics and reaction pathways of structural folding and unfolding, all driven by controlled delivery of electrons.

Dimeric Indenofluorene‐Extended Tetrathiafulvalene Motif for Enhanced Intramolecular Complexation

“…TLC was performed using aluminum sheets covered with silica gel coated with a fluorescent indicator. NMR spectra were recorded on at 500 and 126 MHz for 1 H-and 13 C NMR, respectively (using an instrument with a cryoprobe). Deuterated chloroform (CDCl 3 , δ H = 7.26 ppm, δ C = 77.16 ppm), deuterated dichloromethane (CD 2 Cl 2 , δ H = 5.32 ppm, δ C = 54.00 ppm) or deuterated benzene (C 6 D 6 , δ H = 7.16 ppm, δ C = 128.06 ppm) were used as solvents (and references for calibration).…”

“….80 (td, J = 7.5, 1.1 Hz, 2H), 2.87 (t, J = 7.3 Hz, 4H), 2.83 (t, J = 7.3 Hz, 4H), 2.75 (dt, J = 14.6, 7.3 Hz, 8H), 1.77-1.47 (m, 16H), 1.39-1.09 (m, 48H), 0.96-0.81 (m, 24H) ppm. 13 ) m/z = 2083.57319.…”

“…Lee et al [13] published in 2019 work on a TTF dimer which was rigidly linked via a 1,4-bis(2-ethynylphenyl)buta-1,3-diyne moiety. This system underwent redox-driven folding and unfolding upon formation of intramolecular mixed valence complexes and π-dimers.…”

Oxidation triggers guest dissociation during reorganization of an FeII4L6twisted parallelogram

“…We thus envisioned that the incorporation of metallocene ligands into supramolecular capsules with octahedral metal ion vertices could enable the formation of low-symmetry products. Metallocenes are furthermore redox-active, enabling potential stimuli-responsive behavior 42,[45][46][47][48][49][50][51][52][53] that may be used for different host-guest interactions, 45,47,54 such as redox-triggered guest ejection or structural reconguration. 55,56…”

Ethynylphenyl-Derivatized Free Base Porphyrins: Anodic Oxidation Processes and Covalent Grafting onto Glassy Carbon Electrodes

“…reversible when the electrolyte anion is changed from [PF6]to [B(C6F5)4]raises the possibility that the dications [H22] 2+ and [H23] 2+ undergo nucleophilic attack by the [PF6]anion. Although examples of reactions of modestly nucleophilic anions such as [PF6]with highly oxidized organometallic[49][50][51][52] and organic39,53,54 radical cations and dications are known, we are not aware of them being reported for free-base porphyrins in higher oxidation states. Certainly, stronger nucleophiles such as nitrite, hydroxide, and nitrogenous bases are known to react with porphyrin cations at either a meso position or at the  position of a pyrrole ring (see below), giving isoporphyrins and meso-or -substituted porphyrins 16,55-61 .…”