C2 Symmetry Research Articles

Merging bound states in the continuum-driven ultrahigh sensing figure of merit in all-dielectric metasurfaces

Radiation-free photonic bound states in the continuum (BIC) in metasurfaces allow ultrahigh quality (Q) factor and strongly confined mode volume, which are extremely advantageous in the development of ultrasensitive microcavity sensors. However, the conventional isolated BICs are susceptible to failure due to symmetry breaking caused by fabrication imperfection and nonzero incident angle. Here, we propose a silicon nitride-based metasurface with multiple BIC merging. The merging of accidental BIC and symmetry-protected BIC can increase the Q-factor near the Brillouin zone Γ point and thus robustly induces a figure of merit (FOM) of refractive index sensing at small incident angles two orders of magnitude higher than that in isolated BIC configuration. Specifically, the FOM in merging BIC reaches 108 at a 2° incident angle. The BIC merging can be universally achieved in square lattices with C4 symmetry, and slower decay of Q-factor and higher FOM can further occur in hexagonal lattices benefiting from higher-order topological charges. The advantage of merging BIC is also maintained when considering in-plane and out-of-plane symmetry breaking. These results offer a unique design path for high-performance metasurface sensors and can be extended to other high-Q applications such as low-threshold lasers, nonlinear frequency conversion, and low-loss waveguides.

Solid-State NMR Analysis of the Dynamics of Cofactors: Comparison of Heliobacterial and Purple Bacterial Reaction Centers.

Photosynthetic reaction centers (RCs) serve as natural engines converting solar energy to chemical energy. Understanding the principles of efficient charge separation and light-induced electron transfer (ET) between the chlorophyll-type pigments might guide the synthesis for artificial photosynthetic systems. We present detailed insight into the dynamics at the atomic level using solid-state NMR techniques applied to the RCs of Heliobacillus (Hb.) mobilis (HbRCs) and the purple bacterium Rhodobacter (R.) sphaeroides (PbRCs). It is assumed that heliobacteria were among the first phototrophic organisms; therefore, their RC can be regarded as ancient. They are constructed homodimerically with perfect C2 symmetry, enabling ET over both branches of cofactors. Modern RCs of R. sphaeroides wild-type (WT) have higher redox power and are functionally highly asymmetric. The dynamics of the cofactors in both RCs has been explored using nuclear hyperpolarization, induced by the solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) effect. Based on the individual incorporation of 13C positions of the cofactors (through supplementation by 13C-δ-aminolevulinic acid), photo-CIDNP magic-angle spinning (MAS) NMR experiments provide access to the local dynamics of the cofactors along the ET path over a broad range of time scales. Theoretical analysis of the dynamic deformation of these macrocycles is also discussed in terms of function. The dynamics observed in HbRCs appears to be correlated to ET. The cofactors in PbRC are significantly less dynamic than those in the HbRC. Relevance for efficiency and redox properties are discussed.

Liquid Crystal Behavior of Uniform Short Rods Made from Computationally Designed Parallel Coiled Coil Building Blocks.

Parallel, homotetrameric coiled coils were computationally designed using 29 amino acid peptides. These parallel coiled coils, called "bundlemers", have C2 symmetry, with all N-termini displayed from one end of the nanoparticle and all C-termini from the opposite end. This anisotropic display of the peptide termini allowed for the functionalization of two sets of nanoparticles with either maleimide or thiol functionality at the N-terminal region of the constituent peptides. The thiol-Michael conjugation reaction between the N-terminal end of complementary bundlemer nanoparticles formed monodisperse, rigid bundlemer dimer, called "dibundlemer", rods. The constituent, individual bundlemer nanoparticles were characterized with small-angle X-ray scattering (SAXS), Förster resonance energy transfer (FRET), and circular dichroism (CD) spectroscopy to confirm the parallel assembly of the coiled coils, consistent with the computational design. The dibundlemer rods were characterized with SAXS to reveal the uniform dibundlemer nature of the rods. Optical birefringence is observed in concentrated samples of the rods, with polarized optical microscopy (POM) revealing a nematic liquid crystalline behavior.

Diamagnetic Precursor to Biradical by Means of a Thermal Trigger: A Head-to-Tail (N-O)2 Four-Membered Ring Formed in Naphthalene-1,8-diyl Bis(tert-butyl Nitroxide).

The title compound was synthesized, and ESR and magnetic analysis revealed diamagnetic properties below 400 K. The crystal structure analysis clarified that the molecule possesses an approximate C2 symmetry with a head-to-tail (N-O)2 four-membered ring. The N···O distances are 2.349(4) - 2.374(4) Å, belonging to the class found in diamagnetic phases of dimerized nitroxide materials. A zero-field splitting pattern appeared in the solid-state ESR around 440 K on heating. The density functional theory (DFT) calculations supported the formation of a biradical.

CuI/CuII Chiral Homoleptic Complexes: Study of Self‐Recognition and Self‐Discrimination

AbstractThe formation of ML2 homoleptic copper(I) and copper(II) complexes from bidentate chiral ligands with C2 symmetry, comprising three types of substituents (namely benzyl, indanyl and phenyl groups), was investigated. The formation of homochiral or heterochiral complexes can be influenced by the nature of the substituents and the geometry induced by the oxidation state of the metal. All the complexes were isolated and characterized, in particular in the solid state by X‐ray diffraction studies. In solution, cyclic voltammetry was used to study ligand association and discrimination induced by the CuI/CuII transition.

Synthesis, Structure, and Optical Property of Tris(biaryldiyl)metal Complexes Consisting of Group 9 Elements.

We report the synthesis and characterization of tris(biphenyl-2,2'-diyl)metal complexes of trivalent group 9 elements (1M, M = Co, Rh, Ir) and their nonplanarly π-extended analogs, tris(1,1'-binaphthyl-2,2'-diyl)metal complexes (2M, M = Rh, Ir). Single crystal X-ray crystallography reveals the distorted octahedral geometry with an approximate C3 symmetry of trianionic complexes 1M (M = Co, Rh, Ir) and 2M (M = Rh, Ir), which are contacted by three Li+ ions in the crystal. Complex 1Ir exhibits yellow luminescence in THF with a photoluminescence quantum yield (ΦPL) of up to 0.73, along with a distinctive photophysical property, namely, a concentration dependence of the emission wavelength from 530 to 580 nm. This is a characteristic property of 1Ir and has not been observed in its isoelectronic analog, tris(2-phenylpyridinato)iridium(III) (Ir(ppy)3). The concentration-dependent optical properties originate from the dissociation equilibria of Li+ ions from the anionic chromophore. Complex 2Ir also exhibits luminescence at 715 nm in THF, with a notable bathochromic shift from 1Ir through the π-extension. The findings offer insights into the photophysical properties of homoleptic organo-transition metal complexes, providing the foundation for the design of related transition metal complexes.

5]Helicene Based π-Conjugated Macrocycles with Persistent Figure-Eight and Möbius Shapes: Efficient Synthesis, Chiral Resolution and Bright Circularly Polarized Luminescence.

π-Conjugated chiral shape-persistent molecular nanocarbons hold great potential as chiroptical materials, though their synthesis remains a considerable challenge. Here, we present a simple approach using Suzuki coupling of a [5]helicene building block with various aromatic units, enabling the one-pot synthesis of a series of chiral macrocycles with persistent figure-eight and Möbius shapes. Single-crystal structures of 7 compounds were solved, and 22 enantiomers were separated by preparative chiral HPLC. A notable pyrene-bridged figure-eight macrocycle, with its rigid, fully π-conjugated and overcrowded structure, exhibited pure excimer emission and outstanding circularly polarized luminescence (CPL) properties, including a large dissymmetric factor (|glum| = 3.8 × 10-2) and significant CPL brightness (BCPL = 710.5 M-1cm-1). This method provides a versatile synthetic platform for producing various chiral D2-symmetric figure-eight macrocycles and singly or triply twisted Möbius macrocycles with C2 and D3 symmetry, offering tunable chiroptical properties for CPL applications.

5]Helicene Based π‐Conjugated Macrocycles with Persistent Figure‐Eight and Möbius Shapes: Efficient Synthesis, Chiral Resolution and Bright Circularly Polarized Luminescence

π‐Conjugated chiral shape‐persistent molecular nanocarbons hold great potential as chiroptical materials, though their synthesis remains a considerable challenge. Here, we present a simple approach using Suzuki coupling of a [5]helicene building block with various aromatic units, enabling the one‐pot synthesis of a series of chiral macrocycles with persistent figure‐eight and Möbius shapes. Single‐crystal structures of 7 compounds were solved, and 22 enantiomers were separated by preparative chiral HPLC. A notable pyrene‐bridged figure‐eight macrocycle, with its rigid, fully π‐conjugated and overcrowded structure, exhibited pure excimer emission and outstanding circularly polarized luminescence (CPL) properties, including a large dissymmetric factor (|glum| = 3.8 × 10−2) and significant CPL brightness (BCPL = 710.5 M‐1cm‐1). This method provides a versatile synthetic platform for producing various chiral D2‐symmetric figure‐eight macrocycles and singly or triply twisted Möbius macrocycles with C2 and D3 symmetry, offering tunable chiroptical properties for CPL applications.

Insights into the gas-phase structure and internal dynamics of diphenylsilane: A broadband rotational spectroscopy study.

The rotational spectrum of diphenylsilane was investigated using chirped-pulse Fourier transform microwave spectroscopy in the frequency range of 2-8 GHz. The lowest energy structure of diphenylsilane has C2 point group symmetry with the C2 symmetry axis coinciding with the binertial axis of the molecule. Through the assignment of the main isotopologue as well as singly substituted heavy-atom isotopologues, including 13C, 29Si, and 30Si, we were able to obtain a comprehensive gas-phase structure of diphenylsilane. The structure of diphenylsilane was compared with its oxygen analogue, diphenylether, including a discussion of the barrier height to the large-amplitude motion of the phenyl rings. Furthermore, the structural comparison was extended to include a range of C-Si bond lengths and bond angles from other organosilicon molecules where the silicon atom is bonded to aliphatic and/or aromatic moieties.

Luminescence and Faraday rotation properties of Tb2O3 and Tb:Y2O3 single crystals

Heavily-doped and fully concentrated 2.78% Tb:Y2O3 and Tb2O3 single crystals with high optical quality and very low levels of impurities have been grown and studied for their luminescence and Faraday rotation properties. Absorption, emission and fluorescence decay measurements performed vs excitation wavelength and temperature and their confrontation with Judd-Ofelt and crystal-field calculations show the contributions of two types of luminescent centers: dominant ones with a 5D4 emission lifetime of 23 μs corresponding to coupled near-neighbor Tb3+ ions, all in C2 symmetry sites, and minority ones with a 5D4 emission lifetime of about 2 ms corresponding to coupled Tb3+ ions in C2 and C3i near-neighbor symmetry sites. Faraday rotation measurements confirm Tb2O3 as the Tb-based Faraday crystalline material with the largest ever measured Verdet constant, at all temperatures and from the visible to the near-infrared. They also show that the dominant luminescent centers contribute more particularly to this large Verdet constant thanks to a favorable crystal-field splitting of their 7F6 ground multiplet and also to the contributions of both types of spin-allowed and spin-forbidden 4f-5d absorption bands.

Solid-solution Er:(Sc,Y)2O3 transparent ceramics: Optical spectroscopy, inhomogeneous line broadening, C3i sites and mid-infrared laser operation

Rare-earth-doped transparent sesquioxide laser ceramics enable engineering of their gain bandwidths via solid-solution compositions exhibiting a strong inhomogeneous spectral line broadening. We report on a detailed spectroscopic study and the first mid-infrared laser operation of Erbium-doped yttria-scandia, (ScxY1−x)2O3, ceramics fabricated by vacuum sintering at 1750 °C from laser-ablated nanoparticles. The effect of the Sc fraction on the spectral and kinetic properties of Er3+ emission around 2.8 μm owing to the 4I11/2 → 4I13/2 is revealed. The inhomogeneous spectral line broadening leading to merging of individual Stark sub-levels of Er3+ multiplets is evidenced by low-temperature spectroscopy. An original method of quantifying the distribution of dopant Er3+ ions over C2 and C3i symmetry sites in the cubic bixbyite structure is suggested based on the transition probabilities derived by the Judd-Ofelt theory. In the parent Er:Y2O3 ceramic, the Er3+ ions nearly follow the ideal distribution with 3/4 of ions residing in C2 sites, and Sc addition skews it in favor of C3i sites. A continuous-wave Er:(Sc,Y)2O3 ceramic laser generated 312 mW at 2716 nm with a slope efficiency of 18.6% and a laser threshold of 128 mW.

Ultrahigh-Reflectivity Circularly Polarized Mirrors Based on the High-Contrast Subwavelength Chiral Metasurface

The circularly polarized laser sources are core components for many optical applications such as biomedicine, quantum technology, and AR/VR. However, conventional techniques make it difficult to further diminish the size of circularly polarized lasers. Thus, the high-contrast subwavelength chiral metasurface (HCCM) with a 980 nm operating wavelength is numerically investigated. The HCCM is composed of chiral metasurfaces modulating the circular dichroism of reflectance and 6 pairs of Distributed Bragg Reflectors (DBR) with 55% reflectivity. The reason that the HCCM has an ultra-high reflectivity (99.9%) at the operating wavelength of 980 nm is the combination of the optical refractive index difference between the GaAs metasurface and the AlOx substrate and weak destructive interference in the AlOx support layer. In addition, the circular dichroism of the chiral metasurfaces (2.1%) is mainly caused by the displacement of two square air holes in opposite directions, thus transforming the unit cell of the metasurface from C2 symmetry to chiral symmetry. The reflector has the advantages of a simple structure and miniaturization, which is expected to greatly reduce the fabrication difficulty and cost of the circular polarization VCSELs.

Determination of some NSAIDs content in meat by liquid chromatography with tandem mass spectrometry (LC-MS/MS)

Nonsteroidal anti-inflammatory drugs (NSAIDs) are the most widely used group of drugs worldwide for pain relief, anti-inflammation, blood clot prevention, and fever reduction, but they can cause some side effects bad for health if used incorrectly. NSAIDs are on the list of drugs that must be monitored according to Council Directive 96/23/EC. The fact that NSAIDs are also used in animals for anti-inflammation, fever reduction, and pain relief raises concerns that animal products such as meat, eggs, and milk may be contaminated with NSAIDs, affecting human health if consumed like eating right. Therefore, developing a method to analyze NSAIDs in meat products is necessary, contributing to assessing the quality of meat products currently circulating on the market. In this study, 4 common substances in the NSAIDs group were studied and identified by liquid chromatography with tandem mass spectrometry (LC-MS/MS) using a Symmetry C18 chromatographic column with an ESI (+) positive electron spray ionization source and multiple reaction monitoring (MRM) mode. The validity of the method was confirmed according to the guidelines of the Association of Official Analytical Chemists (AOAC). The results showed that the method has good specificity, the linearity range from 5.0 to 100 µg/kg, the detection limit of 1.5 µg/kg, the quantification limit of 5.0 µg/kg; precision and accuracy with relative standard deviation (RSD) less than 11% and recoveries ranging from 81.1 to 111%, meeting AOAC requirements. The method was used to analyze the content of NSAIDs in 15 meat samples in Hanoi. The results showed that 7 samples showed tolfenamic acid exceeding the quantitative limit of the method.

Stability Indicating RP-HPLC Method for Posaconazole Assay Using QbD Approach.

The development and optimization of analytical techniques utilizing the quality by design methodology is essential in the pharmaceutical industry. This approach helps in the direction of identifying and optimizing critical parameters during drug development and assesses their impact on key quality attributes. A stability-indicating RP-HPLC method was developed for quantifying posaconazole in bulk and tablet forms utilizing the quality-by-design approach. The Box-Behnken design optimized buffer flow rate, organic modifier percentage, and temperature, affecting retention time, theoretical plate count, and symmetry factor. Chromatography was performed on a Symmetry C18 column with a mobile phase of 0.01N potassium dihydrogen phosphate and acetonitrile (57.4:42.6% v/v), at a flow rate of 1.11 mL/min, detection at 220 nm, and column temperature of 30°C. Posaconazole’s retention time was 3.663 minutes, with precise, accurate, and linear signals (R² = 0.999). The method is simple, fast, cost-effective, and ideal for routine quality control.

Novel Quantitative Estimation of Rucaparib and Bevacizumab in Rat Plasma Using LC-MS/MS & Study of Pharmacokinetics.

Rucaparib and Bevacizumab‘s bioanalytical evaluation was performed using an easy-to-use, effective, and repeatable LC-MS/ MS technique, with D6-Rucaparib and D6-Bevacizumab serving as internal standards. This work provides a summary of current developments in bioanalytical LC-MS/MS techniques using an organic mobile phase consisting of 50:50 formic acid and acetonitrile IN 0.1% as well as a Waters Symmetry C18 column. The results for stability, matrix effect, accuracy, precision, and recovery were all within allowable bounds. To test the targeted analytes in body fluids using pharmacokinetic research, a simple and efficient approach was created. This application included all accuracy, system appropriateness, linearity, and specificity characteristics that were used successfully for pharmacokinetic investigations in rats and that complied well with USFDA guidelines.

QbD-Driven Approach to Cleaning Method Development and Validation for Darunavir Analysis in Oral Films.

The current investigations involve developing a high-performance liquid chromatographic method that’s simple to operate, fast to establish, accurate, precise, and economical through design-enabled methods. A positive experimental design is offered to utilize the central composite design of pH and the mobile phase, two crucial components of the RP-HPLC technology. The chromatographic conditions were optimized with the release of Design Expert software version 13.0. Symmetry C18 column (4.6×150mm, 5µm) was used in the procedure, along with acetonitrile (20:80 v/v) and potassium dihydrogen orthophosphate buffer pH 4.0 as the mobile phase. There was a 0.70 ml/min flow rate. 263 nm is the wavelength of detection. Darunavir’s sharp, resolved peak was seen 2.3 minutes after swabbed samples from the 10*10 cm SS plate were injected. A linear calibration curve with an R2 of 0.9991 was observed in the concentration range of 0.25 to 25µg/ml. For precision %RSD is 1.03,1.48. Accuracy % concentration 50%,100%,150% mean recovery 99.43-100.53.LOD & LOQ 1.12µg/ml, 3.39µg/ml. Robustness was tested with modest modifications to the wavelength and flow rate. Forced degradation studies were carried out and found to be within the limits. the degradation parameters such as Acid, Base, Oxidative, Photolytic, and thermal degradation parameters are according to the ICH guidelines. % Assay was done for oral films and it was found to be within the limits. Thus, the outcomes unequivocally demonstrated that the QbD technique could be effectively used to enhance the HPLC method for the measurement of darunavir in production settings.

Tri‐ and Hexadentate Poly‐Lewis Acids – Attempts to Unravel the Complex Dynamics of Cage and Capsule Formation in Solution

AbstractTwo tri‐ and two hexadentate poly‐Lewis acids (PLAs) with calyx‐like structures of C3 symmetry containing aluminum‐ and boron‐containing Lewis acidic functions were prepared by tin‐metal exchange reactions. The triply hydrosilylated [12]annulene served as basic framework. It forms a calyx‐like structure by the stereo‐ and regioselective attachment of three SiMeCl2 groups to the planar [12]annulene. The PLA precursors were generated by attaching three or six trimethylstannylethynyl groups to the silicon atoms. Lewis acid functions were introduced using the reagents bis‐(bis(trimethylsilyl)methyl)aluminium hydride (HAl[CH(SiMe3)2]2) and catecholatochloroborane (ClBCat). The complexation behavior of the PLAs towards different Lewis bases was investigated by NMR. Bases included pyridine, polydentate nitrogen‐ and phosphorus‐containing bases. Additionally, three molecules of a bidentate phosphorus‐containing base were captured with hexadentate PLAs. Diffusion NMR experiments provided insight into the aggregation processes: some of the adducts had a significantly larger volume than expected, indicating the formation of larger adducts than the expected 1 : 1 adduct, including larger 2 : 2 adduct cages. The distances between the Lewis acid units and the steric requirement of the attached substituents determine the complexation behavior of the PLAs. Thus, the weak Lewis acidic BCat units show no (tridentate case) or a strong (hexadentate case) interaction with PMe2‐containing bases, if they can act cooperatively.

Structural Studies of Piperidino‐Alanes with Halide, Amide and Hydride as further Ligands at Aluminum

AbstractNine different derivatives of piperidino alanes of the general formula (CH2)5N‐AlXY [X=Y=Cl (1), Br (2), I (3); X=(CH2)5N, Y=Cl (4), Br (5), I (6); X=H, Y=Cl (7), Br (8), I (9)] have been synthesized and compared with respect to their structures. All molecules form dimers with an Al2N2 central cycle and aluminum and nitrogen atoms in distorted tetrahedral environments as determined from X‐ray diffraction. The three dihalide derivatives 1, 2 and 3 have C2h (2/m) symmetries in solution of which they maintain the Centro symmetry in the crystal lattice. The bis(piperidino) derivatives 4, 5 and 6 have either C1 (1) symmetry with the bridging piperidino cycles oriented in the same direction (4, 5) or Ci (ī) point symmetry as found for 6 (in solution at least one other isomer is present). Whereas the chlorine derivative 7 has crystallographic Ci (ī) symmetry, the bromine 8 has almost C2 and the iodine 9 crystallographic C2 (2) point symmetry. In solution all derivatives 7, 8, 9 show equilibria between cis (C2) and trans (Ci) isomeric forms (27Al NMR). The longest Al−N bond lengths within the rings are found for 5 (1.969(4) Å) and the shortest for 8 (1.940(4) Å). The ratio of Al⋅⋅⋅Al to N⋅⋅⋅N non‐bonding distances in the almost square rings vary with the bulkiness of the terminal ligands at aluminum.

Trefoil-like COFs membrane fabricated by interfacial polymerization for dye/salt separation

Covalent organic frameworks (COFs) with β-ketoenamine structure have shown notable effectiveness in water treatment. In general, COFs can be constructed by the interfacial polymerization (IP) between a C2 symmetry monomer with para-position reaction groups and a C3, C4 and C6 symmetry functionalized monomer. The constrained availability of para-position monomers limits the diversity of COFs synthesis options, necessitating exploration into non-para-position alternatives. Herein, 2,4,6-triformylphloroglucinol (Tp) and ortho-position monomer o-phenylenediamine (OPD) are employed to fabricate a composite membrane featuring COFs with a special trefoil-like structure by interfacial polymerization method. The optimal OPD-Tp COFs/Nylon nanofiltration (NF) membrane has 99.8 % rejection for CR and only 3.2 % rejection for NaCl. Meanwhile, the pure water permeation flux is 132 L m−2 h−1 bar−1. This study shows the significant potential for dye/salt separation of the prepared COFs composite NF membrane and broadens the monomer selective range for the COFs membrane fabrication.

Terahertz tunable quasi-bound state in the continuum metasurface with high sensitivity based on Dirac semimetal

We have proposed a novel tunable terahertz (THz) quasi-bound states in the continuum (BIC) metasurface based on Dirac semimetal (DS). By modifying the structural parameters of the DS resonator and disrupting the C4 symmetry to induce perturbations, we achieve the conversion of BIC to quasi-BIC with a high Q-factor, reaching up to 1291.3. Moreover, we conducted a systematic analysis of the electric field distribution and surface current density for both symmetric and asymmetric configurations to elucidate the formation mechanism of the quasi-BIC. Furthermore, by varying the Fermi energy of the DS within the range of 0.1–0.2eV, we achieved continuously tunable operation with the operating frequency ranging from 1.179 to 1.248 THz and the transmission from 21.18% to 96.87%. Most notably, we investigated the sensing performance of the device, finding that its refractive index sensitivity and figure of merit (FOM) are 0.301 THz/RIU and 143.3 RIU−1, respectively, highlighting its potential for high-sensitivity applications, particularly in material detection and biomedical diagnostics.