Redox-Regulated Rotary Motion of a Bis(9-triptycyl)-TTFV System

A Proof-of-Principle Design for Through-Space Transmission of Unidirectional Rotary Motion by Molecular Photogears

The construction of molecular photogears that can achieve through-space transmission of the unidirectional double-bond rotary motion of light-driven molecular motors onto a remote single-bond axis is a formidable challenge in the field of artificial molecular machines. Here, we present a proof-of-principle design of such photogears that is based on the possibility of using stereogenic substituents to control both the relative stabilities of two helical forms of the photogear and the double-bond photoisomerization reaction that connects them. The potential of the design was verified by quantum-chemical modeling through which photogearing was found to be a favorable process compared to free-standing single-bond rotation ("slippage"). Overall, our study unveils a surprisingly simple approach to realizing unidirectional photogearing.

Electrostatically-gated molecular rotors

The ability to control molecular-scale motion using electrostatic interactions was demonstrated using an N-phenylsuccinimide molecular rotor with an electrostatic pyridyl-gate. Protonation of the pyridal-gate forms stabilizing electrostatic interactions in the...

Theoretical study on pentiptycene molecular brake: photoinduced isomerization and photoinduced electron transfer

The isomerization of the double bond plays an important role in the braking and de-braking of the light-controlled molecular brake. Therefore, the pentiptycene-type (Pp-type) light-controlled molecular brake system ((E)- and (Z)-4'-pentiptycyl vinyl-[1,1'-biphenyl]-4-carbonitrile) containing the C = C double bond was theoretically studied. Combining the 6-31G(d) basis set, the ωB97XD functional with dispersion correction was applied to implement the (E)-configuration and (Z)-configuration initial optimization. Next, using the 6-311G(d,p) basis set, the relaxed potential energy surface scans of the rotation angle were operated, and then the optimization calculations of the transition states at the extremum high points. Analyzing the stagnation points and the rotational transition states on the potential energy profiles, the rotation mechanism and basic energy parameters of the molecular brake were obtained. Then, the DFT computations at ground states and the TD-DFT computations of vertical excitation energy were put into practice at the accuracy of the def-TZVP basis set for the two configurations, and using the natural transition orbital (NTO) analyses combining the excitation energies and absorption spectra, the electronic transition characteristics and electron transfer properties of light-controlled molecular brake were studied. Afterwards, in order to investigate the photoinduced isomerization reaction, the C = C double bond was scanned on the relaxed potential energy surface, and the intermediates of the isomerization reaction were searched and analyzed; thus, the braking mechanism of the light-controlled molecular brake was proposed.

Molecular Gears: From Solution to Surfaces

This review highlights the major efforts devoted to the development of molecular gears over the past 40 years, from pioneering covalent bis-triptycyl systems undergoing intramolecular correlated rotation in solution, to the most recent examples of gearing systems anchored on a surface, which allow intermolecular transmission of mechanical power. Emphasis is laid on the different strategies devised progressively to control the architectures of molecular bevel and spur gears, as intramolecular systems in solution or intermolecular systems on surfaces, while aiming at increased efficiency, complexity and functionality.

Gear Slippage in Molecular Bevel Gears Bridged with a Group 14 Element

Ditriptycilmethanes are known as molecular bevel gears because the two triptycil groups show correlated rotation. In this report, molecular bevel gears bridged with a group 14 element, bis(methyltriptycil)X (X = SiH₂, GeH₂, GeF₂), were synthesized, and their gearing properties were investigated. Gear slippage, that is an error in gear rotation, is observed in high-temperature solutions of molecular bevel gears. Heavy atom derivatives undergo gear slippage more easily due to the long bond lengths and wide angles between the two triptycil units and the bridging group 14 element. Activation energies of gear slippages were estimated by temperature-dependent NMR spectroscopy and DFT calculations, and theoretical thermodynamic parameters for gear slippage were found to be in excellent agreement with experimental values. The results indicate that theoretical calculations for gear rotation in molecular bevel gears can accurately reproduce experimental phenomena.

Redox-Gated Tristable Molecular Brakes of Geared Rotation

p-Bis(arylcarbonyl)pentiptycenes 2 (aryl = 4-(trifluoromethyl)phenyl) and 3 (aryl = mesityl) have been prepared and investigated as redox-gated molecular rotors. For 2, rotations about the pentiptycene-carbonyl bond (the α rotation) and about the aryl-carbonyl bond (the β rotation) are independent, and the rotation barriers are 11.3 and 9.5 kcal mol^-1, respectively, at 298 K. In contrast, the α and β rotations in 3 are correlated (geared) in a 2-fold cogwheel pathway between the aryl and the pentiptycene groups with a much lower rotation barrier of 6.5 kcal mol^-1 at 298 K in spite of the bulkier aryl groups. Electrochemical reduction of the neutral forms led first to radical anions (2^•- and 3^•-) and then to a bis(radical anion) for 2^2- but a dianion for 3^2-. The redox operations switch the independent α and β rotations in 2 into a geared rotation in both 2^•- and 2^2- and result in a slow-fast-stop rotation mode for 2-2^•--2^2-. The two redox states 3^•- and 3^2- retain the geared α and β rotations and follow a fast-slow-stop mode for 3-3^•--3^2-. Both molecular systems mimic tristable molecular brakes and display 8-9 orders of magnitude difference in rotation rate through the redox switching.

Intramolecular alkyne–dithiolium cycloaddition: a joint experimental and DFT mechanistic study

The intramolecular alkyne–dithiolium cycloaddition reactions were found to occur through either a concerted or stepwise pathway, depending on the conjugation degree of the alkynyl unit.

EF, Zhao Y. Redox-dependent properties of DTF-endcapped π-oligomers

Solid films of electroactive π-conjugated oligomers show distinct redox behaviour from that in solution, with interesting morphological changes accompanying oxidation.

Multivalent dithiafulvenyl functionalization of dendritic oligo(phenylene vinylene)s with an anthraquinodimethane core

Redox-active dithiafulvenyl endgroups were attached to dendritic oligo(phenylene vinylene)s which contain an anthraquinodimethane core. The ability of these molecules and their polymer thin films to bind with and detect nitrobenzene was demonstrated.

Redox interactions of Au(iii) with carboxylated dithiafulvenes and tetrathiafulvalene analogues in polar organic media

The redox interactions between HAuCl₄ and a series of π-conjugated organic donors, namely carboxylated dithiafulvenes and tetrathiafulvalene vinylogues, were investigated. Interestingly, the dithiafulvene derivative with two carboxylic groups showed the ability to directly induce the formation of Au(0) nanoparticles in dipolar aprotic solvents such as DMF and DMSO.

Tetrathiafulvalene Vinylogue-Fluorene Co-oligomers: Synthesis, Properties, and Supramoleclar Interactions with Carbon Nanotubes

A series of bis(dithiafulvenyl)-end-capped fluorene derivatives was prepared and subjected to a one-pot iodine-promoted oxidative polymerization to yield π-conjugated co-oligomers containing tetrathiafulvalene vinylogue and fluorene repeat units. The resulting π-oligomers were characterized to take either acyclic or cyclic molecular structures, depending on the π-conjugation length of the monomer used for the polymerization. Electronic and electrochemical redox properties were examined by UV-vis spectroscopic and cyclic voltammetric analyses, while the supramolecular interactions of the π-oligomers with single-walled carbon nanotubes were investigated by UV-vis-NIR and Raman spectroscopy.

Carboxylated dithiafulvenes and tetrathiafulvalene vinylogues: synthesis, electronic properties, and complexation with zinc ions

A class of carboxyl and carboxylate ester-substituted dithiafulvene (DTF) derivatives and tetrathiafulvalene vinylogues (TTFVs) has been synthesized and their electronic and electrochemical redox properties were characterized by UV-vis spectroscopic and cyclic voltammetric analyses. The carboxyl-TTFV was applied as a redox-active ligand to complex with Zn(II) ions, forming a stable Zn-TTFV coordination polymer. The structural, electrochemical, and thermal properties of the coordination polymer were investigated by infrared spectroscopy, cyclic voltammetry, powder X-ray diffraction, and differential scanning calorimetric analyses. Furthermore, the microscopic porosity and surface area of the Zn-TTFV coordination polymer were measured by nitrogen gas adsorption analysis, showing a BET surface of 148.2 m(2) g(-1) and an average pore diameter of 10.2 nm.

Dithiafulvenyl-substituted phenylacetylene derivatives: synthesis and structure–property–reactivity relationships

A series of regioisomers for dithiafulvenyl-substituted phenylacetylene derivatives was synthesized and characterized to show structure-dependent electronic properties and different reactivities in their oxidized states.

A TTFV–pyrene-based copolymer: synthesis, redox properties, and aggregation behaviour

A new π-conjugated copolymer containing tetrathiafulvalene vinylogue and pyrene repeat units was synthesized and exhibited reversible redox activity, while the self-aggregation behaviour in the solution phase was responsive to external stimuli such as solvent and pH value.