Electric-Field-Induced Chirality in Columnar Liquid Crystals.

We describe a novel class of tetraphenylbenzene-based discotic molecules with exceptional self-assembling properties. Absorption and fluorescence studies confirmed the formation of J-type aggregates in solution. The discotic mesogens also show an enhancement of the emission upon aggregation. Interestingly, these discotic molecules displayed enantiotropic hexagonal columnar liquid crystal (LC) phases that can be switched into a helical columnar organization by application of an electric field. The helical columns arise from the electric-field-induced tilt of the polar fluorobenzene ring that directs all of the peripheral phenyl groups into a propeller-like conformation with respect to the central benzene core. A cooperative assembly process of these propeller-shaped molecules resolves into a helical columnar organization, in which the preferred helical sense is obtained from the stereogenic center proximate to the polar carbon-fluorine bond. The ease of inducing chirality in columnar LCs by an electric field presents opportunities to create next-generation chiral materials for a variety of applications.

Metallocalix[4]arene Polymers for Gravimetric Detection of N-Nitrosodialkylamines.

N-Nitrosamines are found in food, drugs, air, water, and soil. They pose a significant risk to human health because of their carcinogenicity; consequently, materials that can be used to selectively and sensitively detect nitrosamines are needed. In this work, we designed and synthesized two polymers bearing calix[4]arene or 4-tert-butylcalix[4]arene tungsten-imido complexes (PCalixH and PCalixtBu) as N-nitrosodimethylamine (NDMA) receptors. The interaction between metallocalix[4]arene monomers/polymers and NDMA was confirmed by 1H NMR and IR spectroscopy. Single-crystal X-ray analysis further revealed that the host-guest interaction is based on binding of the terminal oxygen of NDMA to tungsten within the calixarene cavity. Gravimetric detection of NDMA was performed on a quartz crystal microbalance (QCM) in air. Both polymers show responses to NDMA, with PCalixtBu exhibiting a low theoretical limit of detection of 5 ppb for NDMA. The sensor also shows high selectivity toward NDMA and moderate humidity tolerance. This work provides a sensitive sensor for detection of NDMA and also offers a class of new, selective, and efficient NDMA receptors for the future design of NDMA sensors and NDMA extraction materials.

Cyclopentadienone Derivative Dimers as Tunable Photoswitches.

A series of photoswitchable cyclopentadienone derivative dimers bearing bromo, thienyl, 4-(dimethylamino)phenyl, 3-pyridinyl, 4-nitrophenyl and cyano groups was designed and facilely synthesized. Photoswitching properties such as the photoconversions in the photostationary state (PSS), the thermal kinetics and thermal half-lives of photoisomers were systematically investigated. These photoswitches show high fatigue resistance and large photoconversions in the PSS. This work proves that the photoswitching properties of photoswitches based on cyclopentadienone dimers can be tuned by substitution groups and also pave the way to functionalize the cyclopentadienone derivative dimer-based photoswitch, which is important for its future applications.

Azulene-Pyridine-Fused Heteroaromatics.

Azulene, a nonbenzenoid bicyclic aromatic hydrocarbon with unique electronic structure, is a promising building block for constructing nonbenzenoid π-conjugated systems. However, azulene-fused (hetero)aromatics remain rare as a result of limited synthetic methods. We report herein the unexpected synthesis of azulene- and pyridine-fused heteroaromatics Az-Py-1, a seven fused ring system with 30π electrons, by reductive cyclization of a 1-nitroazulene. The structure of Az-Py-1 was unambiguously confirmed by single-crystal X-ray analysis, and analogues Az-Py-2-Az-Py-6 were also synthesized, demonstrating that this is an effective method for constructing azulene- and pyridine-fused heteroaromatics. Theoretical calculations and photophysical and electrochemical studies of Az-Py-1-Az-Py-6 suggest their potential as semiconductors, and the single-crystal ribbons of Az-Py-1 show high hole mobilities up to 0.29 cm2 V-1 s-1.

Triindolo-Truxene Derivatives: Design, Synthesis, and Fine-Tuning of Electronic Properties and Molecular Assembly through Molecular Engineering.

Triindolo-truxene, a C3 -symmetric molecule with a large π-conjugated plane, has six methylene carbon atoms and three aromatic carbon atoms that can be facilely functionalized. Herein, butyl, carbonyl, cyano, and/or malononitrile groups were introduced at six methylene carbon atoms (6-, 14-, 22- or 8-, 16-, 24-positions) and/or three aromatic carbon atoms (2-, 10-, and 18-positions) of triindolo-truxene to produce eight derivatives. Their photophysical properties, electrochemical properties, and molecular assembly can be effectively modulated by substituents and substitution patterns. Incorporation of electron-deficient groups led to redshifts in both the absorption and emission of these derivatives and also lowered their HOMO and LUMO levels. Different substitution patterns resulted in the different intramolecular donor-acceptor interactions. Electron-deficient substituents at the methylene carbon atoms in the 6-, 14-, and 22-positions led to intramolecular charge transfer from the fluorene arms to the truxene core, whereas the corresponding substitutions at the methylene carbon atoms in the 8-, 16-, and 24-positions resulted in intramolecular charge transfer from the truxene core to the fluorene arms. The molecular packing in single crystals and molecular aggregation in solution are also influenced by the substituents and substitution patterns. This work provides a straightforward strategy to alter the properties of triindolo-truxene.

Stable Diindeno-Fused Corannulene Regioisomers with Open-Shell Singlet Ground States and Large Diradical Characters.

The synthesis of open-shell polycyclic hydrocarbons with large diradical characters is challenging because of their high reactivities. Herein, two diindeno-fused corannulene regioisomers DIC-1 and DIC-2, curved fragments of fullerene C104 , were synthesized that exhibit open-shell singlet ground states. The incorporation of the curved and non-alternant corannulene moiety within diradical systems leads to significant diradical characters as high as 0.98 for DIC-1 and 0.89 for DIC-2. Such high diradical characters can presumably be ascribed to the re-aromatization of the corannulene π system. Although the DIC compounds have large diradical characters, they display excellent stability under ambient conditions. The half-lives are 37 days for DIC-1 and 6.6 days for DIC-2 in solution. This work offers a new design strategy towards diradicaloids with large diradical characters yet maintain high stability.

Porous Polymers Containing Metallocalix[4]arene for the Extraction of Tobacco-Specific Nitrosamines.

We designed porous polymers with a tungsten-calix[4]arene imido complex as the nitrosamine receptor for the efficient extraction of tobacco-specific nitrosamines (TSNAs) from water. The interaction between the metallocalix[4]arene and the TSNA, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (nicotine-derived nitrosamine ketone, NNK) was investigated. We found that the incorporation of the nitrosamine receptor into porous polymers increased their selectivity toward NNK over nicotine. The polymer with an optimal ratio of calixarene-containing and porosity-inducing building blocks showed a high maximum adsorption capacity of up to 203 mg/g toward NNK under sonication, which was among the highest values reported. The adsorbed NNK could be removed from the polymer by soaking it in acetonitrile, enabling the adsorbent to be reused. A similar extraction efficiency to that under sonication could be achieved using the polymer-coated magnetic particles under stirring. We also proved that the material could efficiently extract TSNAs from real tobacco extract. This work not only provides an efficient material for the extraction of TSNAs but also offers a design strategy for efficient adsorbents.

Chelating Phosphine Ligand Stabilized AuNPs in Methane Detection.

The capping reagent plays an essential role in the functional properties of gold nanoparticles (AuNPs). Multiple stimuli-responsive materials are generated via diverse surface modification. The ability of the organic ligand shell on a gold surface to create a porous shell capable of binding small molecules is demonstrated as an approach to detect molecules, such as methane, that would be otherwise difficult to sense. Thiols are the most studied capping ligands of AuNPs used in chemiresistors. Phosphine capping groups are usually seen as stabilizers in synthesis and catalysis. However, by virtue of the pyramidal shape of triarylphosphines, they are natural candidates to create intrinsic voids within the ligand shell of AuNPs. In this work, surface-functionalized (capped) AuNPs with chelating phosphine ligands are synthesized via two synthetic routes, enabling chemiresistive methane gas detection at sub-100 ppm levels. These AuNPs are compared to thiol-capped AuNPs, and studies were undertaken to evaluate structure-property relationships for their performance in the detection of hydrocarbons. Polymer overcoatings applied to the conductive networks of the functionalized AuNP arrays were shown to reduce resistivity by promoting the formation of conduction pathways with decreased core-core distance between nanoparticles. Observations made in the context of developing methane sensors provide insight relevant to applications of phosphine or phosphine-containing surface groups in functional AuNP materials.

Author Correction: Unveiling how intramolecular stacking modes of covalently linked dimers dictate photoswitching properties.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Unveiling how intramolecular stacking modes of covalently linked dimers dictate photoswitching properties.

Covalently linked π-stacked dimers represent the most significant platform for elucidating the relationship between molecular alignments and their properties. Here, we present the one-pot synthesis of two intramolecularly π-stacked dimers and disclose how intramolecular stacking modes dictate photoswitching properties. The dimer, which features cofacially stacked chromophores and geometrically favours intramolecular photochemical [2 + 2] cycloadditions, displays a nearly irreversible photoswitching behaviour. By contrast, the dimer, bearing crosswise stacked chromophores, is geometrically unfavourable for the cycloaddition and exhibits a highly reversible photoswitching process, in which the homolysis and reformation of carbon-carbon single bonds are involved. Moreover, the chiral carbon centres of both dimers endow these photoswitches with chirality and the separated enantiomers exhibit tuneable chiroptical properties by photoswitching. This work reveals that intramolecular stacking modes significantly influence the photochemical properties of π-stacked dimers and offers a design strategy toward chiral photoswitchable materials.

Cocrystallization of Imide-Fused Corannulene Derivatives and C60 : Guest-Induced Conformational Switching and 1:1 Segregated Packing.

A pair of interconvertible stereoisomers of imide-fused corannulene derivatives was mixed with C60 , which resulted in cocrystallization into a 1:1 segregated packing motif through concave-convex π-π interactions. Only one conformation was observed in the cocrystal owing to guest-induced conformational switching. The 1D assemblies of the complex showed promising applications in organic electronics.

Thiophene-fused bowl-shaped polycyclic aromatics with a dibenzo[a,g]corannulene core for organic field-effect transistors.

For the first time, electron-rich thiophene units were fused into the skeleton of corannulene to extend π-surfaces and tune arrangement in single crystals. Two isomeric butterfly-like thiophene-fused dibenzo[a,g]corannulenes (3 and 5) were synthesized. Isomer 3 showed p-type transport properties, with a hole mobility of 0.06 cm(2) V(-1) s(-1).

Corannulene derivatives with low LUMO levels and dense convex-concave packing for n-channel organic field-effect transistors.

Electron-deficient corannulene derivatives incorporating cyano and imide groups into the corannulene core were synthesized, which showed low LUMO (lowest unoccupied molecular orbital) levels and dense convex-concave packing structures in single crystals. These two features help to realize the first n-channel organic field-effect transistors (OFETs) in air based on corannulene derivatives.