Rotational Isomerism Involving Acetylene Carbon

Ethynylene-linked Figure-Eight Octaphyrin(1.2.1.1.1.2.1.1): Synthesis and Characterization of Its Two Oxidation States

An octaphyrin(1.2.1.1.1.2.1.1) containing two conjugated ethynylene bridges has been synthesized and characterized. The macrocycle reveals complex conformational dynamics dependent on its protonation and oxidation state. The [40]annulenoid macrocycle and its [38]annulenoid oxidized form display residual macrocyclic ring currents. In spite of its low apparent aromaticity the new octaphyrin is a potent chromophore with a vis-NIR absorption profile strongly influenced by the redox and acid-base chemistry.

Comprehensive Look at the Photochemistry of Tolane

Diphenylacetylene (tolane) exhibits a rich photochemistry that depends on the relative orientation of the phenyl rings and the external conditions. Here, state-of-the-art quantum chemical methods based on the algebraic diagrammatic construction scheme for a polarization propagator of second order are employed to investigate the luminescence properties of tolane and its derivatives. It is explained why different derivatives of tolane exhibit different absorption but practically identical fluorescence spectra, why the fluorescence quantum yield and the population of a "dark" state are temperature-dependent, and why initially twisted tolanophanes phosphoresce in glassy media at 77 K while planar ones do not.

Unpicking the determinants of amide NH⋯OC hydrogen bond strength with diphenylacetylene molecular balances

The stereoelectronic properties affecting hydrogen bond strength are investigated with a series of diphenylacetylene-based molecular balances.

Palladium-catalyzed direct ortho-alkynylation of arylalkylacid derivatives at γ and δ positions via an N,O-bidentate directing group

A new N,O-bidentate directing group: first example of the ortho-alkynylation of arylalkylacid derivatives at γ and δ positions.

Chirality imprinting and direct asymmetric reaction screening using a stereodynamic Brønsted/Lewis acid receptor

Molecular recognition, activation and dynamic self-assembly with Brønsted and Lewis acids play a central role across the chemical sciences including catalysis, crystal engineering, supramolecular architectures and drug design. Despite this general advance, the utilization of the corresponding binding motifs for fast and robust quantitative chemosensing of chiral compounds in a complicate matrix has remained challenging. Here we show that a stereodynamic probe carrying complementary boronic acid and urea units achieves this goal with hydroxy carboxylic acids. Synergistic dual-site binding and instantaneous chirality imprinting result in characteristic ultraviolet and CD readouts that allow instantaneous determination of the absolute configuration, enantiomeric excess and concentration of the target compound even in complex mixtures. The robustness and practicality of this strategy for high-throughput screening purposes is demonstrated. Comprehensive sensing of only 0.5 mg of a crude reaction mixture of an asymmetric reduction eliminates cumbersome work-up protocols and minimizes analysis time, labour and waste production.

Determining results of asymmetric reactions can take long periods of time and consume large amounts of organic solvents during work-up and analysis. Here, the authors report a bifunctional organic probe that can bind to chiral hydroxyacids, and provide yield, enantiomeric excess and absolute configuration even with crude mixtures.

Recent advances in copper-mediated chelation-assisted functionalization of unactivated C–H bonds

Recent advances in copper-mediated (both stoichiometric and catalytic) chelation-assisted functionalization of unactivated C–H bonds are reviewed.

Nickel-catalyzed direct alkynylation of C(sp2)–H bonds of amides: an “inverse Sonogashira strategy” to ortho-alkynylbenzoic acids

Nickel-catalyzed direct alkynylation of C(sp²)–H bonds of amides using commercially available, inexpensive 8-aminoquinoline as a removable bidentate directing group is described.

Photophysical properties of symmetrically substituted diarylacetylenes and diarylbuta-1,3-diynes

A series of symmetrically substituted diarylacetylenes and diaryl-1,3-butadiynes were prepared and studied with an emphasis on their spectral and photophysical properties.

Synthesis of Functionalized Mono-, Bis-, and Trisethynyltriptycenes for One-Dimensional Self-Assembly on Surfaces

This paper describes the synthesis of triptycene-based building blocks that are able to interact through hydrogen bonds to form one-dimensional self-assembled motifs on surfaces. We designed 9,10-diethynyltriptycene derivatives functionalized at the ethynyl end groups by a variety of hydrogen-bonding groups for homomolecular recognition and complementary building blocks for heteromolecular recognition. We also present the synthesis of bis- and trisethynyltriptycenes with terminal alkyne functional groups available for on-surface azide-alkyne cycloaddition reaction to expand the potential of the triptycene building block.

Well-defined palladium(ii) complexes for ligand-enabled C(sp(3))-alkynylation

The first example of ligand-enabled C(sp(3))-alkynylation of 8-methylquinoline is reported. The reaction is catalysed by well-defined Pd(ii) complexes. The present C(sp(3))-alkynylation has a broad substrate scope as well as functional group tolerance and proceeds efficiently under mild conditions.

Ion-mediated conformational switches

Molecular switches are ubiquitous in Nature and provide the basis of many forms of transport and signalling. Single synthetic molecules that change conformation, and thus function, reversibly in a stimulus-dependent manner are of great interest not only to chemists but society in general; myriad applications exist in storage, display, sensing and medicine. Here we describe recent developments in the area of ion-mediated switching.

Crystalline arrays of molecular rotors with TIPS-trityl and phenolic-trityl stators using phenylene, 1,2-difluorophenylene and pyridine rotators

Molecular rotors based on substituted-trityl stators provide crystalline arrays capable of supporting different rotators through non-covalent interactions.

Concomitant conformational dimorphism in 1,2-bis(9-anthryl)acetylene

The structure of a concomitant conformational polymorph of an opto-electronic material raises questions about polymorphism.

Experimental and theoretical studies of the spectroscopic properties of simple symmetrically substituted diphenylacetylene derivatives

A series of symmetrically substituted diphenylacetylene derivatives possessing electron-donating or electron-accepting character were prepared and studied with respect to their spectral and photophysical properties.

Bridged tolanes: a twisted tale

The rotational motion of tolanes along their acetylene axis is not fully understood. What happens to the optical and electronic properties if the tolane backbone is forced into a twisted conformation? Several tethers were investigated to obtain tolanophanes, fixing the torsion angle of the two phenyl rings. X-ray crystal structures revealed tether-specific torsion angles in the solid state. The absorption, emission, and excitation spectra were recorded. Twisted tethered tolane conformers showed blue-shifted absorption; emission spectra were all torsionally independent and identical. The tethered tolanes were embedded in a rigid matrix by freezing to 77 K; well-resolved emission spectra were recorded for planar tolanes, but for twisted systems unexpectedly long-lived phosphorescence was observed. How is this triplet emission explained? Quantum chemical calculations (TDDFT/cam-B3LYP/6-31G*) of the unsubstituted tolane showed that intersystem crossing (ISC) is favored with large spin-orbit coupling, which occurs when the molecular orbitals are orthogonal to each other; this is the case at the crossing of S1/T7. Also, a small energy difference between singlet and triplet states is required; we found that ISC can favorably take place at four crossings: S1/T6, S1/T7, S1/T(8,9), S1/T10.

Single rotating molecule-machines: nanovehicles and molecular motors

In the last decade many molecular machines with controlled molecular motions have been synthesized. In the present review chapter we will present and discuss our contribution to the field, in particular through some examples of rotating molecular machines that have been designed, synthesized, and studied in our group. After starting by explaining why it is so important to study such machines as single molecules, we will focus on two families of molecular machines, nanovehicles and molecular motors. The first members of the nanovehicle family are molecules with two triptycenes as wheels: the axle and the wheelbarrow. Then come the four-wheel nanocars. Since triptycene wheels are not very mobile on metallic surfaces, alternative wheels with a bowl-shape structure have also been synthesized and studied on surfaces. The molecular motors are built around ruthenium organometallic centers and have a piano-stool geometry with peripheric ferrocenyl groups.

A surface-bound molecule that undergoes optically biased Brownian rotation

Developing molecular systems with functions analogous to those of macroscopic machine components, such as rotors, gyroscopes and valves, is a long-standing goal of nanotechnology. However, macroscopic analogies go only so far in predicting function in nanoscale environments, where friction dominates over inertia. In some instances, ratchet mechanisms have been used to bias the ever-present random, thermally driven (Brownian) motion and drive molecular diffusion in desired directions. Here, we visualize the motions of surface-bound molecular rotors using defocused fluorescence imaging, and observe the transition from hindered to free Brownian rotation by tuning medium viscosity. We show that the otherwise random rotations can be biased by the polarization of the excitation light field, even though the associated optical torque is insufficient to overcome thermal fluctuations. The biased rotation is attributed instead to a fluctuating-friction mechanism in which photoexcitation of the rotor strongly inhibits its diffusion rate.

A Lewis acid-mediated conformational switch

An isonicotinamide-substituted diphenylacetylene undergoes conformational switching upon recognition of Lewis acids.

Electrophilic alkynylation of ketones using hypervalent iodine

The efficient electrophilic alkynylation of ketones can be performed using hypervalent iodine compounds. This protocol was applied for an aldehyde.

Solvatochromic studies of pull–push molecules containing dimethylaniline and aromatic hydrocarbon linked by an acetylene unit

Pull–push molecules containing dimethylaniline and aromatic hydrocarbon linked by an acetylene unit were studied using spectroscopic methods and DFT theoretical calculations.

Electron-rich carbon nanorings as macrocyclic hosts for fullerenes

Electron-rich cycloparaphenyleneacetylenes as well as their twin "glasses-like" conjugates form stable complexes with fullerenes.