Planar Conformation Research Articles

Conformation and Bonding of Lanthanide(III) Trihalides LnX3 (Ln = La-Lu; X = F, Cl, Br): A Relativistic Local Vibrational Mode Study.

This study employed relativistic methods to investigate the connection between the conformation and bonding properties of 45 lanthanide trihalides LnX3 (Ln: La-Lu; X:F, Cl, Br). Our findings reveal several insights. The proper symmetry exhibited by open-shell LnX3 requires the inclusion of spin-orbit coupling, achieved with 2-component relativistic Hamiltonians. Fluorines (LnF3) primarily exhibit pyramidal structures, while chlorides and bromides tend to yield planar conformations. For a given halide, the strength of Ln-X bonds increases across the lanthanide series, another outcome of the lanthanide contraction. Both strength and covalency of Ln-X bonds decrease upon the halide, i.e., LnF3 > LnCl3 > LnBr3. We introduced a novel parameter, the local force constant associated with the dihedral β(X-Ln-X-X), ka(β), which quantifies the resistance of these molecules to conformational changes. We observed a correlation between ka(β) and the covalency of the Ln-X bond, with higher ka(β) values indicating a stronger covalent character. Finally, the degree of pyramidalization in the LnX3 structures is connected to (i) the extent of charge donation within the molecule and (ii) the greater covalency of the Ln-X bond. These findings provide valuable insights into the interplay between the electronic structure and molecular geometry in LnX3.

Evaluation of the Highly Ordered Structure, Ligature, and Enzymatic Degradation of Poly[(R)-3-hydroxybutyrate-co-4-hydroxybutyrate] Elastic Porous Fibers.

We prepared biocompatible elastic fibers with high porosity and high tensile strength from poly[(R)-3-hydroxybutyrate-co-4-hydroxybutyrate], which is a microbial polyester that can be produced from renewable carbon resources by isothermal crystallization. It was possible to control the pore size by adjusting the isothermal crystallization time. Most of the pores were approximately less than 10 μm in diameter, did not penetrate, and were distributed discontinuously throughout the fibers. The elasticity of the fibers was apparently attributable to the generation of tie molecules with planar zigzag conformations between lamellar crystals and to the deformation of the pores. The ligature area occupied by the porous fibers in surgical knots was reduced by 75% compared with that of nonporous fibers. This is expected to make the ligature more difficult to untie and reduce the feeling of foreign matter. X-ray tomography revealed that the porous fibers had a relatively small fiber diameter owing to the collapse of the porous area. The rate of enzymatic degradation of the porous fibers was more than four times that of nonporous fibers. These results suggest that this elastic porous fiber will have many applications, including in the medical and marine material fields.

Understanding the mechano-fluorochromic enhancement in a cyanoethylene-functionalized pyrene-based luminogen: an experimental and theoretical study

Pyrene-based luminogens have attracted wide attention due to their promising applications in organic electronics, chemical sensing, and bioimaging. In this study, a cyanoethylene-functionalized pyrene-based luminogen CNPyCH3 was designed and synthesized. Experimental results show that CNPyCH3 exhibits distinct photophysical properties in dilute solution and various solid states. The mechano-fluorochromic (MFC) property is more attractive and interesting, as a red shift with enhanced emission was observed upon mechanical stimulation. The intriguing MFC enhancement behavior was further investigated by in-depth theoretical calculations combining Monte Carlo simulations, quantum mechanics/molecular mechanics calculations, and time-dependent density functional theory. It was found that the calculated emission wavelengths for both pristine and ground CNPyCH3 are in good agreement with the experimental values, and that the ground CNPyCH3 has a greater oscillator strength. From the perspective of intermolecular interactions, the weakened π-π interactions induced by the half-switched “face-to-edge” packing modes are beneficial for achieving brighter emission upon grinding. In terms of intramolecular structures, the ground CNPyCH3 has a more planar conformation around the cyanoethylene moiety in the excited-state equilibrium geometry than the pristine CNPyCH3, resulting in the grinding-induced red-shifted emission. Our study provides a unique insight into the MFC enhancement behavior of the pyrene-based luminogens.

Exploring Electronic and Conformational Attributes of an Organic Donor‐Bridge‐Acceptor Molecular System

AbstractThis research explores the electronic properties and conformational dynamics of the ZnP‐COPV‐ (Zinc Porphyrin ‐ Carbon bridged Oligo Phenylenevinylene ‐ Fullerene) organic semiconductor via specialized Density Functional Theory (DFT) and Molecular Dynamics (MD) computational techniques. First, through DFT calculations, essential HOMO (Highest Occupied Molecular Orbital), LUMO (Lowest Unoccupied Molecular Orbital), and Molecular Electrostatic Potential (MEP) electronic attributes are meticulously dissected providing insights into the intricate charge transfer processes between the constituent donor‐acceptor moieties. Furthermore, MD simulations are employed to unveil the molecular system's multifaceted conformational flexibility and stability. The Root‐mean‐squared deviation (RMSD), end‐to‐end distance, and torsional angles quantitative analysis of conformational attributes support the carbon‐bridged oligo‐phenylenevinylene (COPV) molecular wire's ‐skeleton planar and rigid conformation. This minimal end‐to‐end distance variation (within Å) compared to the initially extended structure and the constrained torsional motion (within for ZnP‐COPV and for COPV‐) after thermalization showcases COPV's ability to maintain structural rigidity over time, aligning with the concept of effective ‐conjugation. Finally, through the lens of time dependent (TD)‐DFT, the dynamic evolution of the HOMO–LUMO energy gap, TD‐DFT excitation energies and oscillator strengths are explored as the molecular structure transforms over time. The observed energy gap variation underscores the molecule's adaptability in the face of structural modifications, hinting at an intriguing connection between structural stability and enhanced electronic properties. The research provides a comprehensive understanding of the intricate interplay between conformational dynamics and electronic attributes in organic semiconductors, providing quantitative insights crucial for designing stable, high‐performance materials for cutting‐edge optoelectronic applications and helping advance the collective understanding of sustainable energy conversion.

Thieno[3,2-b]thiophene Incorporated Redox Active 22π and 34π Core-Modified Expanded Isophlorinoids.

Incorporation of a thieno[3,2-b]thiophene into an isophlorinoid-like framework alters the aromaticity by extending the macrocyclic π-circuit. Their opto-electronic and aromatic properties significantly differ from other 22π and 34π porphyrinoids. Among the three different 34π hexaphyrins, furan based hexaphyrin adopts a non-aromatic 'figure-of-eight' conformation. Replacing all the furans either by thiophene or selenophene induces a planar conformation with aromatic characteristics. Spectro-electrochemical studies revealed reversible two-electron ring oxidation to yield their 4np dicationic species respectively.

Selective Recognition of the Dimeric NG16 Parallel G-Quadruplex Structure Using Synthetic Turn-On Red Fluorescent Protein Chromophore.

Red fluorescent protein (RFP)-based fluorescent probes that can selectively interact with specific nucleic acids are of great importance for therapeutic and bioimaging applications. Herein, we have reported the synthesis of RFP chromophores for selective recognition of G-quadruplex nucleic acids in vitro and ex vivo. We identified DFHBI-DM as a fluorescent turn-on probe that binds to the dimeric NG16 parallel quadruplex with superior selectivity and sensitivity over various parallel, antiparallel, and hybrid topologies. The binding of DFHBI-DM to NG16 exhibited excellent photophysical properties, including high binding affinity, large Stokes shift, high photostability, and quantum yield. The MD simulation study supports the 1:1 binding stoichiometry. It confirms the planar conformation of DFHBI-DM, which makes strong binding interactions with a flat quartet of NG16 compared to other antiparallel and hybrid topologies. The cell imaging and MTT assays revealed that DFHBI-DM is a biocompatible and efficient fluorescent probe for intracellular imaging of NG16. Overall, these results demonstrated that DFHBI-DM could be an effective fluorescent G4-stabilizing agent for the dimeric NG16 parallel quadruplex, and it could be a promising candidate for further exploration of bioimaging and therapeutic applications.

Stabilization of the Compressed Planar Benzene Dianion in Inverse-Sandwich Rare Earth Metal Complexes.

For the first time, the capture of a planar antiaromatic benzene dianion in between two trivalent rare earth (RE) metal cations, each stabilized by two guanidinate ligands, is reported. The synthesized inverse-sandwich complexes [{(Me3Si)2NC(NiPr)2}2RE]2(µ-ƞ6:ƞ6-C6H6), (RE = Y (1), Dy (2), and Er (3)) feature a remarkably planar benzene dianion, previously not encountered for any metal ion prone to low or absent covalency. The -2 charge localization at the benzene ligand was deduced from the results obtained by single-crystal X-ray diffraction analyses, spectroscopy, magnetometry, and Density Functional Theory (DFT) calculations. In the 1H NMR spectrum of the diamagnetic Y complex 1, the equivalent proton resonance of the bridging benzene dianion ligand is drastically shifted to higher field in comparison to free benzene. This and the calculated highly positive Nucleus-Independent Chemical Shift (NICS) values are attributed to the antiaromatic character of the benzene dianion ligand. The crucial role of the ancillary guanidinate ligand scaffold in stabilizing the planar benzene dianion conformation was also elucidated by DFT calculations. Remarkably, the planarity of the benzene dianion originates from the stabilization of the π-type orbitals of the d-manifold and compression through its strong electrostatic interaction with the two REIII sites.

Stabilization of the Compressed Planar Benzene Dianion in Inverse‐Sandwich Rare Earth Metal Complexes

For the first time, the capture of a planar antiaromatic benzene dianion in between two trivalent rare earth (RE) metal cations, each stabilized by two guanidinate ligands, is reported. The synthesized inverse‐sandwich complexes [{(Me3Si)2NC(NiPr)2}2RE]2(µ–ƞ6:ƞ6–C6H6), (RE = Y (1), Dy (2), and Er (3)) feature a remarkably planar benzene dianion, previously not encountered for any metal ion prone to low or absent covalency. The ‐2 charge localization at the benzene ligand was deduced from the results obtained by single‐crystal X‐ray diffraction analyses, spectroscopy, magnetometry, and Density Functional Theory (DFT) calculations. In the 1H NMR spectrum of the diamagnetic Y complex 1, the equivalent proton resonance of the bridging benzene dianion ligand is drastically shifted to higher field in comparison to free benzene. This and the calculated highly positive Nucleus‐Independent Chemical Shift (NICS) values are attributed to the antiaromatic character of the benzene dianion ligand. The crucial role of the ancillary guanidinate ligand scaffold in stabilizing the planar benzene dianion conformation was also elucidated by DFT calculations. Remarkably, the planarity of the benzene dianion originates from the stabilization of the π‐type orbitals of the d‐manifold and compression through its strong electrostatic interaction with the two REIII sites.

The evolution of flexibility and function in the Fc domains of IgM, IgY, and IgE.

Antibody Fc regions harbour the binding sites for receptors that mediate effector functions following antigen engagement by the Fab regions. An extended "hinge" region in IgG allows flexibility between Fab and Fc, but in both the most primitive antibody, IgM, and in the evolutionarily more recent IgE, the hinge is replaced by an additional domain pair in the homodimeric six-domain Fc region. This permits additional flexibility within the Fc region, which has been exploited by nature to modulate antibody effector functions. Thus, in pentameric or hexameric IgM, the Fc regions appear to adopt a planar conformation in solution until antigen binding causes a conformational change and exposes the complement binding sites. In contrast, IgE-Fc principally adopts an acutely bent conformation in solution, but the binding of different receptors is controlled by the degree of bending, and there is allosteric communication between receptor binding sites. We sought to trace the evolution of Fc conformational diversity from IgM to IgE via the intermediate avian IgY by studying the solution conformations of their Fc regions by small-angle X-ray scattering. We compared four extant proteins: human IgM-Fc homodimer, chicken IgY-Fc, platypus IgE-Fc, and human IgE-Fc. These are examples of proteins that first appeared in the jawed fish [425 million years ago (mya)], tetrapod (310 mya), monotreme (166 mya), and hominid (2.5 mya) clades, respectively. We analysed the scattering curves in terms of contributions from a pool of variously bent models chosen by a non-negative linear least-squares algorithm and found that the four proteins form a series in which the proportion of acutely bent material increases: IgM-Fc < IgY-Fc < plIgE-Fc < huIgE-Fc. This follows their order of appearance in evolution. For the huIgM-Fc homodimer, although none are acutely bent, and a significant fraction of the protein is sufficiently bent to expose the C1q-binding site, it predominantly adopts a fully extended conformation. In contrast, huIgE-Fc is found principally to be acutely bent, as expected from earlier studies. IgY-Fc, in this first structural analysis of the complete Fc region, exhibits an ensemble of conformations from acutely bent to fully extended, reflecting IgY's position as an evolutionary intermediate between IgM and IgE.

An intramolecular charge transfer based fluorescent probe for imaging of OCl–

The discovery and utilization of new fluorescent chromophore is indispensable to exploit high performance probes for biological research. Stokes shift is one of the most important properties of chromophore accounting for super-resolution fluorescence imaging. Intramolecular charge transfer (ICT) is one of the fundamental mechanisms for fluorescence that accompanied by large Stokes shifts. Based on the conformational changes between ground and excited states, ICT models can be divided into two types: conformation-steady ICT, whose conformation remains unchanged, and conformation-changeable ICT, which is characterized by the rotation of the chromophore around an axis upon excitation. Herein, we report a new chromophore whose donor and acceptor parts took a butterfly geometry with a dihedral angle of 21° in ground state and a planar conformation upon photo excitation. The bent conformation might be ascribed to the extra conjugated double bond, which made the coplanarity of the chromophore in ground state get worse. The chromophore shows a remarkable Stokes shift over 150 nm and a high fluorescence quantum yieldof 0.62. The limit of detection is 41 nM, which enabled the imaging of basal as well as induced OCl– in different cells. Moreover, the pronounced spectroscopic properties ensure the in vivo monitoring of OCl– in arthritic mice. This finding would shed light on the exploitation of small molecule probes based on new fluorescence chromophore for precise biological imaging.

The Role of the Nitro Group on the Formation of Intramolecular Hydrogen Bond in the Methyl Esters of 1-Vinyl-Nitro-Pyrazolecarboxylic Acids

All reactions involving the nitrogen atom in 3(5)-substituted pyrazoles inevitably lead to a mixture of N-substituted 3- and 5- isomers due to tautomerism. The position of substituent can affect the behavior of N-vinyl isomers, in particular, the ability of some functional groups to form =C-H...O or =C-H...N weak hydrogen bonding type interaction with α-hydrogen of vinyl group due to steric reasons. Moreover, the additional substituents in the pyrazole ring can further influence the possibility and nature of specific intramolecular interactions. Here we have shown the effect of the nitro group on the formation of hydrogen bonds in methyl esters of 1-vinyl-4-nitro-3(5)- and 1-vinyl-5-nitro-3(5)-pyrazole carboxylic acids. A comprehensive study, including synthesis, quantum chemical calculations, NMR and XRD analysis, allowed to conclude that, contrary to expected, in the methyl ester of 1-vinyl-4-nitro-5-pyrazolecarboxylic acid, the formation of a planar conformation is unfavorable, preventing formation of a classical hydrogen bond. On the other hand, there is a hydrogen bond between the nitro group and vinyl group in 1-vinyl-5-nitro-pyrazolecarboxylic acids.

Chlorinated Polythiophene‐Based Donors with Reduced Energy Loss for Organic Solar Cells

Comprehensive SummaryThe industrialization of organic solar cells (OSCs) faces challenges due to complex synthesis routes and high costs of organic photovoltaic materials. To address this, we designed and synthesized a series of polythiophene‐based donor materials, PTVT‐T‐xCl (20%Cl, 50%Cl and 100%Cl), by introducing different degrees of chlorine substitution within their conjugated skeletons. The incorporation of chlorine atoms does not change the planar conformation of the conjugated main chain of the control polymer, PTVT‐T, but effectively reduces their HOMO energy levels (≤ –5.3 eV) and alters the crystallinity of the polymers. In addition, when preparing OSC by blending with non‐fused electron acceptor A4T‐16, the non‐radiative energy loss of the three photovoltaic devices gradually decreased with the increase of chlorine content (0.343, 0.278 and 0.189 eV, respectively). Notably, PTVT‐T‐20%Cl exhibited a more moderate nanoscale phase separation with the acceptor, leading to efficient exciton dissociation, lower bimolecular recombination, and thus a favorable current in the OSCs. Consequently, the photovoltaic device based on PTVT‐T‐20%Cl:A4T‐16 achieved a remarkable photovoltaic efficiency of 11.8%. In addition, the PTVT‐T‐xCl series polymers show much lower material‐only‐cost (MOC) values than the other reported photoactive material systems. This work provides the way for the development of low‐cost photovoltaic materials and the industrial application of OSC, overcoming previous limitations posed by high energy losses in polythiophene‐based donors.

High‐Efficiency Deep Red Fluorescent Material with Aggregation Induced Emission and the Application in Organic Light‐Emitting Diodes

AbstractThe development of highly efficient deep red materials with emission wavelength beyond 650 nm remains a big challenge due to the constraints imposed by the energy gap rule. In this work, a donor‐acceptor‐donor type emitter, 4,7‐bis (10‐(4‐(tert‐butyl) phenyl)‐10H‐phenothiazin‐3‐yl) benzo[c][1,2,5] thiadiazole (TBPPTZ) is designed and synthesized. Resulting from the slight twist angle between the donor and acceptor units, TBPPTZ exhibits nearly planar conformation and an extended conjugated structure. TBPPTZ shows a deep red emission peak at 687 nm and aggregation induced emission property with a high photoluminescence quantum yield of 45 % in neat thin film. The optimized organic light‐emitting diode (OLEDs) utilizing TBPPTZ as the non‐doped emissive layer obtains a high external quantum efficiency (EQE) up to 2.51 % with an electroluminescence (EL) peak at 676 nm, aligning with the Commission Internationale de L'Eclairage (CIE) coordinates (0.68, 0.31), which shows a small EQE roll‐off of only 5.6 % at 100 cd m−2. Additionally, the doped OLED achieves an EQE up to 5.09 %, with an EL peak at 656 nm and CIE coordinates of (0.65, 0.34). The findings of this research not only contribute to achieve highly efficient deep red OLEDs but also offer a novel and effective deep red molecular strategy to realize high‐quality OLEDs.

Multifunctional cyanoaryl porphyrazine pigments with push-pull structure of macrocycle framing: Photophysics and possible applications

We report the experimental study of fluorescence properties of three porphyrazine derivatives, distinct in the number of fused aromatic rings in aryl groups contained in the macrocycle frame and/or presence of Pd in the macrocycle, in solutions with biological molecules and in methanol-glycerol mixtures. Spectral and lifetime fluorescence analysis has revealed that all three pigments demonstrated two fluorescence transition bands from the first S1 and the second S2 electronic excited states to the ground state S0, and thus followed the anti-Kasha’s rule. Strong dependence of the quantum yield and lifetimes in the S1 → S0 fluorescence band on solution viscosity was observed. A significant increase of the fluorescence decay times and fluorescence intensity with albumin concentration and with presence of other biological molecules in solution was observed as well. A model of the low-laying energy states of porphyrazine derivatives has been developed for elucidation of the fluorescence properties observed, that took into account several radiative and non-radiative relaxation channels in molecular excited states. In particular, the model suggests that the first electronic excited state consists of planar and bent conformations separated by a potential energy barrier and shows a typical molecular-rotor behavior as a function of solution viscosity. Potential applications of the porphyrazine pigments as viscosity sensors and fluorescence probes were considered.

An Exopolysaccharide from the Cyanobacterium Arthrospira platensis May Utilize CH-π Bonding: A Review of the Isolation, Purification, and Chemical Structure of Calcium-Spirulan.

The CH-π bonding potential of a saccharide is determined primarily by the number of hydrogen atoms available for bonding and is reduced by side groups that interfere with the CH-π bond. Each hydrogen bond increases the total bond energy, while interfering hydroxyl groups and other side groups reduce the bond energy by repulsion. The disaccharide repeating units of Calcium-Spirulan (Ca-SP), a large exopolysaccharide sub fractionated from the supernatant of the cyanobacterium Arthrospira platensis, contain a unique monosaccharide that is completely devoid of hydroxyl groups and side groups on its entire beta surface, leaving five hydrogen atoms available for CH-π bonding in the planar conformation. While planar conformations of independent pyranose rings are rare-to-nonexistent, due to ring strain associated with that conformation, the binding site of a protein could provide the conformational energy needed to overcome that energy barrier. By enabling a planar conformation, a protein could also enable the sugar to form a novel 5-hydrogen CH-π bond configuration. One study of the anticoagulant property of Ca-SP shows that the molecule acts as an activator of Heparin Cofactor II (HC-II), boosting its anticoagulant kinetics by 104. In comparison, the longstanding anticoagulant drug Heparin boosts the HC-II kinetics by 103. The difference may be explained by this unique CH-π configuration. Here, we review current knowledge and experience on the isolation techniques, analytical methods, and chemical structures of Ca-SP. We emphasize a discussion of the CH-π bonding potential of this unique polysaccharide because it is a topic that has not yet been addressed. By introducing the topic of CH-π bonding to the cyanobacterial research community, this review may help to set the stage for further investigation of these unique molecules, their genetics, their biosynthetic pathways, their chemistry, and their biological functions.

Mechanochromic luminescent material with high quantum yield for multi-mode anti-counterfeiting applications

The multi-mode anti-counterfeiting materials, constructed by mechanochromic luminescent materials with high quantum yield, can effectively prevent illegal counterfeiting, but their design and construction still present significant challenges. Herein, a twisting D-A-D conjugated molecule, FBtF, is obtained with a special hybridized local and charge transfer excited state, and shows approximately 100 % photoluminescence quantum yield in the coating film. The self-assembled FBtF microplates exhibit bathochromic-shifted emission from green to orange, accompanied by the photoluminescence quantum yield increase from 47.8 % to 89.0 % upon grinding, which is the highest in reported MCL materials, to the best of our knowledge. In contrast, a D-π-D type molecule (FBenF) and a D-D’-D molecule (FAnF) maintain the blue-emission after grinding. Through mechanistic investigation, the force-induced molecular conformational planarization and the breakage of the intermolecular charge transfer collaboratively lead to the emission-color change and photoluminescence quantum yield increase. The FBtF microplates are designed as ink for anti-counterfeiting applications based on multi-mode output signals, including the UV light-excited image and the grinding-induced emission color change together with the photoluminescence quantum yield increase. The written tags exhibit high stability in various harsh environments, and demonstrate superior anti-counterfeiting performance in practical applications, such as medicine anti-counterfeiting.

New polymorph of N-benzoyl-morpholine-4-carbothioamide with ten crystallographically independent molecules in the asymmetric unit: Crystal structure, Hirshfeld surface analysis and Density functional theory calculations

Herein, facile synthesis, single crystal X-ray diffraction (SC-XRD) structure, Hirshfeld surface (HS) analysis and Density functional theory (DFT) calculations of N-benzoyl-morpholine-4-carbothioamide 5(a) are presented. Hence, the synthesized compound, C12H14N2O2S 5(a), crystallizes in monoclinic crystal system having space group of P 21 with a = 22.2226 (9) Å, b = 11.7520 (3) Å, c = 24.9361 (8) Å, α = 90°, β = 111.054 (4)°, γ = 90°, Z = 20 and V = 6077.6 (4) Å3. The asymmetric unit of 5(a) contains ten crystallographically independent molecules, where the morpholine and benzene rings are in respective chair and planar conformations. In the crystal structure, some of the intermolecular, N—H···O, C—H···O and C—H···S, hydrogen bonds link the molecules into a 2D-network parallel to (010), enclosing R22(10) and R22(24) ring motifs, when viewed down the b-axis direction. Furthermore, contribution of the remaining hydrogen bonds consolidates a 3D-architecture. Similarly, HS analysis clarified the importance of hydrogen atom contacts with the major contributions of H…H (46.7 %), H…S/S…H (21.1 %), H…C/C…H (16.5 %), and H…O/O…H (12.5 %). Thus, hydrogen bond and van der Waals interactions play major role in the crystal packing. Finally, optimum molecular structure of compound 5(a) was related to the experimentally determined one employing DFT at B3LYP/6–311++G(d,p) level. Subsequently, the geometry of the optimized and most stable conformation turned out to be complementary with the crystal structure. The computational calculation of compound 5(a) revealed the molecule to be chemically hard in nature with high energy intrinsic reaction pathway. The associated band gap predicted compound 5(a) to be a wide band gap material. The intrinsic reaction pathway predicts hard-core behavior of the molecule.

3-[(Benzo-1,3-dioxol-5-yl)amino]-4-methoxycyclobut-3-ene-1,2-dione: polymorphism and twinning of a precursor to an antimycobacterial squaramide.

The title compound, 3-[(benzo-1,3-dioxol-5-yl)amino]-4-methoxycyclobut-3-ene-1,2-dione, C12H9NO5 (3), is a precursor to an antimycobacterial squaramide. Block-shaped crystals of a monoclinic form (3-I, space group P21/c, Z = 8, Z' = 2) and needle-shaped crystals of a triclinic form (3-II, space group P-1, Z = 4, Z' = 2) were found to crystallize concomitantly. In both crystal forms, R22(10) dimers assemble through N-H...O=C hydrogen bonds. These dimers are formed from crystallographically unique molecules in 3-I, but exhibit crystallographic Ci symmetry in 3-II. Twinning by pseudomerohedry was encountered in the crystals of 3-II. The conformations of 3 in the solid forms 3-I and 3-II are different from one another but are similar for the unique molecules in each polymorph. Density functional theory (DFT) calculations on the free molecule of 3 indicate that a nearly planar conformation is preferred.

Investigating adsorption characteristics and electronic properties of Clar’s Goblet and beyond

Our study explores the structural diversity and stability of Clar’s Goblets (CG) derivatives, nCG-mC, analyzing dihedral angles and bond lengths to reveal various planar and non-planar conformations. We highlight the exceptional stability of 3CG-7C through binding energy assessments. Examining electronic, magnetic, and optical properties, we show how CG unit variations impact energy gaps and molecular orbitals. Functionalizing 3CG-7C enhances stability and electronic properties, suggesting diverse applications. Adsorption studies of chlorinated methane on 3CG-7C-NO demonstrate stable interactions, confirmed by changes in bond lengths and Mulliken charges, underscoring the potential of CG derivatives in various fields.

Cycle endurance and failure in ITO/MEH-PPV/Al resistive switching devices

Improving resistive memory reliability requires understanding some bottlenecks, i.e., control and stability of the memory parameters during endurance cycling and physical degradation that shows up in memories that contain metal oxides. The physical degradation of indium tin oxide/poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene]/aluminum (ITO/MEH-PPV/Al) devices was studied through I–V sweeps and cycle endurance with different compliance currents (IC), in addition to scanning electron microscopy (SEM), energy-dispersive X-Ray spectroscopy (EDS), and Raman spectroscopy. The devices showed a dependence of the conductance quantization G0 in current compliance IC, i.e., the G0 histogram shows different distribution shape after changing IC. After many cycles, the devices presented partial destruction in the active area (physical alteration) followed by memory parameter degradation and finally failing (no commuting anymore). SEM/EDS measurements in the deteriorated region showed that the aluminum electrode was removed and only remnants of the polymer remained. The Raman spectroscopy analyses focused on changes in the polymeric structure caused by the endurance cycle, such as changes in chain planarity, which is related to the band around 966 cm−1 that was shifted to lower wavenumbers (965 cm−1) together with the increase in intensity which indicates less planar conformations when compared to the non-degraded area. Alteration of the conjugation length was evidenced by the contribution around 1581 cm−1. In this case, we can see a shift: of 1581 cm−1 to 1584 cm−1, for the non-degraded area and degraded area, respectively. Both results indicate a decrease in the conjugation length. All these changes show fragmentation of the polymer chain as a result of the endurance cycle.