•Tetrathiafulvalene-based receptors are an emerging area in molecular recognition.•TTF holds great potential as a building block for receptor construction.•Acyclic and cyclic receptors as well as coordination cages with TTFs are discussed.•Promising applications lie in the field of sensorics and functional materials.Tetrathiafulvalenes (TTFs) are popular building blocks on the scene of supramolecular chemistry, where they play various roles ranging from electron rich guest moieties in interlocked supramolecular architectures to structural elements of ion sensors. In this review, we discuss so far rather neglected role of TTFs as active elements of binding sites in molecular receptors. We consider several recent design concepts of molecular receptors with architectures of molecular tweezers, macrocycles, and metal-coordinated cages that contain two or more TTF, extended TTF, or pyrrolo-TTF moieties. High affinity to electron-deficient guests and redox activity allowed their use for the construction of functional supramolecular materials and sensors, as well as pave the way for other practical applications.Figure optionsDownload full-size imageDownload as PowerPoint slide

Redox-active liposomes are prepared by the incorporation of tetrathiafulvalene–cholesterol conjugate 1 in phospholipid vesicles. The oxidation of tetrathiafulvalene (TTF) on the surface of the liposomes in aqueous solution is monitored by UV-vis spectroscopy. It is shown that metastable (TTF+˙)2 π-dimers of the mono-oxidized cation radical are formed due to the high local concentration of TTF groups in the lipid membrane. These dimers can be further stabilized by the addition of cucurbit[8]uril or by reduction of the lateral mobility in the membrane by variation of the lipid composition.

Two bromomethylated azobenzene derivatives were characterized by X-ray crystallography at 100 K after fast cooling, and showed disorder of the central N-atoms. The structures were re-determined over a range of temperatures, providing evidence for dynamic disorder due to pedal motion of the central NN bond. Using van't Hoff plots, thermodynamic parameters for the pedal motion were determined. Computationally very cheap Atom–Atom-Force Field (AA-CLP) calculations were employed, which showed that the differences in dynamic disorder enthalpy between the two compounds are predominantly due to intermolecular interactions. AA-CLP calculations and gas phase electronic structure calculations were employed to show the link between intermolecular interactions and activation energy for pedal motion.

Herein we report the first synthesis of a monopyrrolo-tetrathiafulvalene (MPTTF) with two alkyl substituents, performed using a triphenylphosphine-mediated coupling reaction. An Ullmann-type N-arylation reaction was used to prepare a calixarene-based bis-MPTTF receptor, as well as an arylated mono-MPTTF derivative. Complexation studies with electron-deficient compounds showed strongly enhanced affinity of the alkyl-substituted MPTTF derivatives in comparison with the non-substituted MPTTF analogues.

•Acylation of alcohols with acryloyl chloride in the presence of pyridine fails due to the β-addition of pyridine.•Three types of pyridinium derivatives were identified in the reaction mixture.•The mechanism of the reactions was explored using NMR and MS.•Simple synthetic approaches are now available to prepare various pyridinium derivatives.Direct acylation reactions of alcohols with acid chlorides in the presence of pyridine leads to the formation of unexpected pyridinium derivatives as major products. Although this phenomenon was briefly reported several decades ago, a detailed structure elucidation of the intermediates and ionic products was missing. In this study, the formed pyridinium products are structurally characterized and the underlying reaction mechanism is discussed. The addition of reactants in the order acryloyl chloride—R-OH—pyridine yields a structure P1, which was tentatively proposed before. However, if the order of reactant addition was changed, that is, R-OH was added to a mixture of acryloyl chloride and pyridine, two new types of pyridinium derivatives (P2 and P3) were observed. Their formation implies the unprecedented β-addition of pyridine to acryloyl chloride followed by a Michael addition of the nucleophilic α-carbon or by an alkylation of the activated carboxyl group. The proposed reaction mechanism is supported by a detailed structural analysis of intermediates and products.

•We report the synthesis of tripodal monopyrrolo-tetrathiafulvalene receptors.•We examine their binding ability toward electron-deficient substrates.•In solution, our receptors bind non-charged molecular guests.•Our receptors display binding to pyridinium ions in the gas phase.We report the synthesis of tripodal receptors with monopyrrolo-tetrathiafulvalene arms 1a,b, based on 1,3,5-substituted 2,4,6-triethylbenzene scaffold. The three converging pyrrolotetrathiafulvalene groups form an electron rich cone-shaped binding site. Molecular hosts 1a,b are capable of binding neutral electron deficient guests in solution, as well as positively charged pyridinium species in the gas phase.

Macrocyclization between tetrathiafulvalene (TTF) dithiolates and bis-bromomethylazobenzenes/bis-bromomethylstilbenes is investigated under high dilution conditions. We show that macrocycles of different size can be formed depending on whether the (Z)- or (E)-isomers of azobenzene (AB) or stilbene are used. This represents the first example of a light-controllable cyclization reaction. The oxidation potential of the small, structurally rigid TTF–AB macrocycle is found to depend on the conformation of the AB moiety, opening the way for the modulation of redox properties by an optical stimulus. DFT calculations show that the out-of-plane distortion of the TTF moiety in this macrocycle is responsible for the variation of its oxidation potential upon photoisomerization of the neighboring AB bridge.

Four upper rim bis-monopyrrolotetrathiafulvalene-calix[4]arene conjugates 2a,b and 3a,b have been efficiently synthesized using a modular construction approach. The new compounds feature a molecular tweezer architecture with a quasi-parallel arrangement of redox-active tetrathiafulvalene (TTF) arms, which serve as the guest binding centers. Complexation studies using UV/vis binding titrations revealed a high affinity of the calixarene–TTF receptors for planar electron-deficient guests, leading to formation of deeply colored charge-transfer complexes in solution. The binding efficiency of the receptors depends on the flexibility of the calixarene scaffolds and the electronic nature of the TTF arms: the highest binding efficiency is shown by receptor 2b, featuring a highly preorganized molecular structure and an electron-rich TTF moiety.

The synthesis of novel upper rim calix[4]arene–tetrathiafulvalene conjugates 1a–d has been performed by bridging the tetrachloromethylated calix[4]arene derivative 4 with the corresponding tetrathiafulvalene-dithiolates. The cyclic voltammetry of 1a–d shows a two-step oxidation behavior, whereas NMR binding titrations showed their binding affinity to pyridinium salts. X-ray structure of 4 features calixarene fixed in the pinched cone conformation; its crystal packing is defined by the network of C–H···Cl weak hydrogen bonds.

Crystal structures of 4,5-bis(bromomethyl)-1,3-dithiole-2-thione (1) and 4,5-bis(bromomethyl)-1,3-dithiol-2-one (2) were determined and analyzed. Both compounds pack in the same C2/c space group and adopt very similar molecular geometries. Patterns of intermolecular contacts, analyzed with the help of Hirshfeld surfaces and fingerprint plots, on the other hand, are remarkably different. The dominant interactions in the packing of 1 are short Br⋯Br contacts and non-classical CH⋯Br hydrogen bonds. For 2, the packing is governed by short CH⋯OC hydrogen bonds, and longer CH⋯Br and S⋯Br contacts play only a secondary role.Highlights► X-ray structures of two heterocyclic compounds were determined and analyzed. ► Hirshfeld surfaces were used for efficient analysis of intermolecular contacts. ► Molecular backbones of both compounds form stacks in the crystal phase. ► Packing of thione is determined by short Br⋯Br and CH⋯Br interactions. ► Packing of ketone is dominated by notably short CH⋯OC hydrogen bonds.

Redox-active liposomes are prepared by the incorporation of tetrathiafulvalene–cholesterol conjugate 1 in phospholipid vesicles. The oxidation of tetrathiafulvalene (TTF) on the surface of the liposomes in aqueous solution is monitored by UV-vis spectroscopy. It is shown that metastable (TTF+˙)2 π-dimers of the mono-oxidized cation radical are formed due to the high local concentration of TTF groups in the lipid membrane. These dimers can be further stabilized by the addition of cucurbit[8]uril or by reduction of the lateral mobility in the membrane by variation of the lipid composition.