Glycoluril–tetrathiafulvalene molecular clips: on the influence of electronic and spatial properties for binding neutral accepting guests

Abstract

SummaryGlycoluril-based molecular clips incorporating tetrathiafulvalene (TTF) sidewalls have been synthesized through different strategies with the aim of investigating the effect of electrochemical and spatial properties for binding neutral accepting guests. We have in particular focused our study on the spacer extension in order to tune the intramolecular TTF···TTF distance within the clip and, consequently, the redox behavior of the receptor. Carried out at different concentrations in solution, electrochemical and spectroelectrochemical experiments provide evidence of mixed-valence and/or π-dimer intermolecular interactions between TTF units from two closed clips. The stepwise oxidation of each molecular clip involves an electrochemical mechanism with three one-electron processes and two charge-coupled chemical reactions, a scheme which is supported by electrochemical simulations. The fine-tunable π-donating ability of the TTF units and the cavity size allow to control binding interaction towards a strong electron acceptor such as tetrafluorotetracyanoquinodimethane (F4-TCNQ) or a weaker electron acceptor such as 1,3-dinitrobenzene (m-DNB).

Metalla‐Assembled Electron‐Rich Tweezers: Redox‐Controlled Guest Release Through Supramolecular Dimerization

“…Interestingly, both self‐assembled structures OxM 4 L 2 and (NaphM 4 L 2 ) 2 show a significant splitting of the oxidation wave, providing evidence of electronic interactions between the DTF units. A similar splitting was already reported in the case of TTF‐based molecular tweezers and was ascribed to the formation of mixed‐valence and π‐dimer species . From a mechanistic point of view, the electrochemical process observed for the (NaphM 4 L 2 ) 2 dimer consists of two successive oxidations, each involving two electrons (Figure a).…”

Tuning the structure and the properties of dithiafulvene metalla-assembled tweezers

“…The CV of the latter exhibits a splitting of the redox wave corresponding to the DTF units, with 2 reversible oxidations occurring at E1 ox = 0.49 V and E2 ox = 0.63 V vs Fc/Fc + , suggesting that both tips of the tweezer do not behave independently. Such splitting has already been reported in the case of molecular tweezers bearing TTF 40 and more recently with DTF tips, 33 and was ascribed to the formation of mixedvalence and π-dimer species upon oxidation. The abovementioned estimated distance of 8.5 Å between both panels in Pd2L3Pyr2 should in principle allow the sandwiching of a planar aromatic species between both tips, 41, 42 including a selfintercalation of two molecular tweezers if no other species is present in solution.…”

“…Such behavior is similar to the one reported by E. Levillain and P. Hudhomme for TTF-based molecular clips. 40 Thanks to the modelling of cyclic voltammetry experiments, these authors could demonstrate that the stepwise oxidation process follows a square scheme involving both neutral and radical cation species, which interact either inside or outside the cavity ( Figure S5a). This difference of the CV behavior between Pd2L3Pyr2 and Pd2L4Pyr2, is therefore correlated to the distance separating both tips of the tweezer: whereas Pd2L3Pyr2 can bind a planar guest in the cavity through the simultaneous contribution of both tips (S … S distance 8.5 Å) ( Figure S5b), Pd2L4Pyr2 (S … S distance 15 Å) cannot.…”

Real-time absorption spectroelectrochemistry: From solution to monolayer

“…Nevertheless, a real-time A-SEC devoted to very low absorbance measurements is undoubtedly an asset for examining more thoroughly electrochemical mechanism in solution (e.g. see reference [39]) within redox-responsive materials (e.g. see reference [40]) or in surface-confined redox species [27,28,35,37] and it should facilitate the establishment of detailed structureproperties and structure-reactivity relationships at nanoscale.…”