Circularly Polarized Luminescence of a Stereogenic Curved Paraphenylene Anchoring a Chiral Binaphthyl in Solution and Solid State

Invited for the cover of this issue are Masashi Hasegawa, Yoshitane Imai, Yasuhiro Mazaki and co-workers at Kitasato University, Kindai University and Osaka University. The image depicts a stereogenic twisted cycloparaphenylene that exhibits circularly polarized luminescence in a polymethyl methacrylate thin film. Read the full text of the article at 10.1002/chem.202004283.

Reversible Color and Shape Changes of Nanostructured Fibers of a Macrocyclic π-Extended Thiophene Hexamer Promoted by Adsorption and Desorption of Organic Vapor

A phenyl-substituted macrocyclic π-extended thiophene hexamer 1, composed of four thienylene-ethynylene and two thienylene-vinylene units, has a solid-state structure in which π-π, CH-π, and van der Waals interactions occur. Slow addition of acetone to a solution of 1 in CS₂ produces a yellow nanostructured fiber 1-A containing a 1:1.5:1 ratio of 1, acetone, and CS₂. Over a 2 min period at 25 °C, 1-A gradually changes to an orange fiber 1-B containing a 1:0.5:1 ratio of 1, acetone, and CS₂. On exposure to acetone vapor, 1-B regenerates 1-A (vapochromism), and removal of all solvents from 1-A and 1-B generates a red-orange fiber 1-C, which upon brief immersion in acetone/CS₂ produces 1-A. Furthermore, 1-C is converted to orange yellow fiber 1-D upon exposure to acetone vapor for 1 s at 25 °C. Analysis of the horizontal and vertical profiles of the X-ray diffraction (XRD) patterns shows that removal of solvent from 1-A reversibly creates 1-B in conjunction with a shape and size change along with arching.

Thermal Expansion of Incompressible U2S3-Type Nb2N3 Synthesized in a Diamond Anvil Cell

A novel niobium nitride, U₂S₃-type Nb₂N₃, has been successfully synthesized by nitridation of δ-NbN above approximately 30 GPa in a laser-heated diamond anvil cell. Nb₂N₃ crystallizes in the same orthorhombic structure (space group: Pnma) as η-Ta₂N₃. Nb₂N₃ consists of regular-shaped polyhedra, and the bulk modulus has been determined to K₀ = 300(2) GPa. The low-temperature X-ray diffraction measurements have been successfully conducted for the tiny novel Nb₂N₃ between 297.7(5) and 106.3(3) K under ambient pressure. Nb₂N₃ shows no structural phase transition down to 106.3(3) K, and investigation of the linear thermal expansion coefficients yields α_a = 3.36(9) × 10^-6 K^-1, α_b = 5.39(10) × 10^-6 K^-1, α_c = 6.77(15) × 10^-6 K^-1, respectively. Our study reveals that the incompressible novel nitride shows low thermal expansion behavior, which offers new insights for the development of functional nitrides and their crystal chemistry.

Selenacalix[4]selenophene: Synthesis, Structure, and Gel Formation of Cyclic Selenoether of Selenophene

A selenacalix[4]selenophene derivative, a cyclic selenophene oligomer linked with divalent selenium atoms, was successfully synthesized via a one-pot cyclization reaction using 2,5-dibromo-3,4-bis(4-t-butylphenyl)selenophene and (Bu₃Sn)₂Se. The X-ray analysis revealed an annular geometry consisting of two sets of vertical and horizontal selenophene pairs. The observed geometry was preserved by intermolecular Se···Se and Se···π interactions, leading to a one-dimensional array. This self-assembled network results in a supramolecular gel, despite the absence of any hydrogen bonding sites.

Internal Delensing of Cosmic Microwave Background Polarization B-Modes with the POLARBEAR Experiment

Using only cosmic microwave background polarization data from the polarbear experiment, we measure B-mode polarization delensing on subdegree scales at more than 5σ significance. We achieve a 14% B-mode power variance reduction, the highest to date for internal delensing, and improve this result to 22% by applying for the first time an iterative maximum a posteriori delensing method. Our analysis demonstrates the capability of internal delensing as a means of improving constraints on inflationary models, paving the way for the optimal analysis of next-generation primordial B-mode experiments.

Mixed Tb/Dy coordination ladders based on tetra(carboxymethyl)thiacalix[4]arene: a new avenue towards luminescent molecular nanomagnets

The macrocyclic ligand calix[4]arene (L1) and its sulphur-containing analogue thia[4]calixarene (L2) are promising precursors for functional molecular materials as they offer rational functionalization with various organic groups. Here, we present the first example of lanthanide-based coordination polymers built from the macrocyclic thiacalix[4]arene backbone bearing four carboxylic moieties, namely, ligand H₄L3. The combination of H₄L3 with the Tb³⁺ and Dy³⁺ cations led to the formation of 1D ladder-type coordination polymers with the formula [Ln^IIIHL3DMF₃]·(DMF) (where DMF = dimethylformamide and Ln = Tb or Dy, denoted as HL3–Tb and HL3–Dy), which resulted from the coordination of the lanthanide cations with the partially deprotonated ligand HL3³⁻ that behaved as a T-shape connector. The coordination sphere around the metal was completed by the coordinated DMF solvent molecules. By combining both Tb³⁺ and Dy³⁺ cations, isostructural heterobimetallic solid solutions HL3–Tb_1−xDy_x were also prepared. HL3–Tb and HL3–Dy showed visible light photoluminescence originating from the f–f electronic transitions of pale green emissive Tb³⁺ and pale yellow emissive Dy³⁺ with efficient sensitization by the functionalized thia[4]calixarene ligand HL3. In the HL3–Tb_1−xDy_x solid solutions, the Tb/Dy ratio governed both the emission colour as well as the emission quantum yield, which reached even 28% at room temperature for HL3–Tb. Moreover, HL3–Dy exhibited a slow magnetic relaxation effect related to the magnetic anisotropy of the dodecahedral Dy³⁺ complexes, which were well isolated in the crystal lattice by expanded organic spacers.

The single crystals of the two isostructural Tb³⁺- and Dy³⁺-based coordination polymers (HL3–Tb and HL3–Dy) were structurally characterized, and their photophysical properties were investigated, together with their corresponding solid solutions.

Small Structural Changes in the Alkyl Substituents of Macrocyclic π-Extended Thiophene Oligomers Causes a Key Effect on Their Stacking and Functional Properties

Three new macrocyclic π-extended thiophene hexamers composed of four thienylene-ethynylene and two thienylene-vinylene units with or without four alkyl substituents have been synthesized. Despite similar shape-persistent structures in solution, the alkyl substituents control the solid-state structures and morphologies. The unsubstituted hexamer exhibited a planar conformation with a theoretically predicted structure in the solid state; however, the planar hexamer with four ethyl substituents formed a closely stacked columnar crystal structure to exhibit π-π interactions. Interestingly, the hexamer with four butyl substituents adopted both planar and twisted conformations in the solid state, exhibiting polymorphism based on induced-fit stacking of molecules. Thus, the butyl-substituted hexamer produces a mixture of yellow, orange, and red single crystals from toluene/acetone, and X-ray analysis revealed six different conformations. Consequently, the small structural difference in the macrocycles causes a key effect on their functional properties in the solid state, and their morphology governs electrical conductivity and organic field-effect-transistor activity. The polymorphism of the hexamers was applied to the switching of film morphology.

Oxidation of a Dithieno[3,4-b:3',4'-d]thiophene Cyclic Dimer Containing a Planar Cyclooctatetraene Ring: Retention of High Antiaromaticity During Reactions

One-electron and peracid oxidations of dithieno[3,4-b : 3',4'-d]thiophene cyclic dimer, which contains an antiaromatic planar cyclooctatetraene (COT) core, were conducted. The reaction of the cyclic dimer with SbCl₅ produced isolable radical cation salts. Density functional theory (DFT) calculations showed that the spin density of the radical cation resides not on the COT ring but on the peripheral sulfur and carbon atoms in the thiophene unit with retention of high antiaromaticity based on the nucleus-independent chemical shift (NICS). The peracid oxidation of the cyclic dimer was found to proceed not on the COT ring but on the bridging sulfur atom in the dithienothiophene moiety. The retention of the high antiaromaticity of the COT ring after the sulfoxide formation was experimentally confirmed based on the relative hardness, and also was theoretically supported by NICS calculations. Interestingly, the DFT calculations suggested that the high antiaromaticity does not enhance the reactivity towards the epoxidation on the COT ring.

Crystal structures and electronic properties of Sn3N4 polymorphs synthesized via high-pressure nitridation of tin

Sn₃N₄ polymorphs were synthesized via high-pressure nitridation of tin by means of laser-heated diamond anvil cell technique. This implies new insight into the crystal chemistry and functional materials of group IVA nitrides.

High-Pressure Synthesis and Crystal Structure of MoC-Type Tungsten Nitride by Nitridation with Ammonium Chloride

A novel tungsten nitride, MoC-type WN, was synthesized at 6 GPa and 1200 °C via nitridation of tungsten by ammonium chloride as a nitrogen source. This compound is isostructural with γ'-MoC, which has a hexagonal structure with a space group of P6₃/mmc (No. 194). Micrometer-sized single crystals of MoC-type WN were grown in molten ammonium chloride flux. In addition, NaCl-type WN and WC-type WN were synthesized via nitridation by ammonium chloride at 6 GPa and 1000 °C. Ammonium chloride is appropriate as a nitrogen source for nitride synthesis under high pressure. The new WN phase crystallizes in the hexagonal structure with unit cell parameters of a = 2.89248(2) Å and c = 10.17069(7) Å. The chemical formula of MoC-type WN refined by the Rietveld analysis from powder X-ray diffraction data was WN_0.60(1). The zero-pressure bulk modulus, K₀, of MoC-type WN was determined to be 338(3) GPa, which can be expected to be a hard material.

The POLARBEAR Fourier transform spectrometer calibrator and spectroscopic characterization of the POLARBEAR instrument

We describe the Fourier Transform Spectrometer (FTS) used for in-field testing of the POLARBEAR receiver, an experiment located in the Atacama Desert of Chile which measures the cosmic microwave background (CMB) polarization. The POLARBEAR-FTS (PB-FTS) is a Martin-Puplett interferometer designed to couple to the Huan Tran Telescope (HTT) on which the POLARBEAR receiver is installed. The PB-FTS measured the spectral response of the POLARBEAR receiver with signal-to-noise ratio >20 for ∼69% of the focal plane detectors due to three features: a high throughput of 15.1 sr cm², optimized optical coupling to the POLARBEAR optics using a custom designed output parabolic mirror, and a continuously modulated output polarizer. The PB-FTS parabolic mirror is designed to mimic the shape of the 2.5 m-diameter HTT primary reflector, which allows for optimum optical coupling to the POLARBEAR receiver, reducing aberrations and systematics. One polarizing grid is placed at the output of the PB-FTS and modulated via continuous rotation. This modulation allows for decomposition of the signal into different harmonics that can be used to probe potentially pernicious sources of systematic error in a polarization-sensitive instrument. The high throughput and continuous output polarizer modulation features are unique compared to other FTS calibrators used in the CMB field. In-field characterization of the POLARBEAR receiver was accomplished using the PB-FTS in April 2014. We discuss the design, construction, and operation of the PB-FTS and present the spectral characterization of the POLARBEAR receiver. We introduce future applications for the PB-FTS in the next-generation CMB experiment, the Simons Array.