Banana-shaped Molecules Research Articles

Spontaneous breaking of chiral symmetry in achiral bent-core liquid crystals: Excluded volume effect.

Bent-Core banana-shaped molecules exhibit tilted polar smectic phases with macroscopically chiral layer order even though the constituent molecules are achiral in nature. Here, we show that the excluded volume interactions between the bent-core molecules account for this spontaneous breaking of chiral symmetry in the layer. We have numerically computed excluded volume between two rigid bent-core molecules in a layer using two types of model structures of them and explored the different possible symmetries of the layer that are favored by the excluded volume effect. For both model structures of the molecule, the C_{2} symmetric layer structure is favored for most values of tilt and bending angle. However, the C_{s} and C_{1} point symmetries of the layer are also possible for one of the model structures of the molecules. We have also developed a coupled XY-Ising model and performed Monte Carlo simulation to explain the statistical origin of spontaneous chiral symmetry breaking in this system. The coupled XY-Ising model accounts for the experimentally observed phase transitions as a function of temperature and electric field.

Uniaxial and biaxial nematic phases in binary mixtures of banana-shaped molecules

We introduce a mean-field theory to describe uniaxial and biaxial nematic phases in binary mixtures of banana-shaped molecules. We extend our previous theory for pure banana-shaped molecules to the binary mixtures and calculate phase diagrams on the temperature-concentration plane. We predict uniaxial-biaxial nematic phase transitions and Landau points in the binary mixtures. The biaxial nematic phases of banana-shaped molecules are promoted by mixing the two components with different bend angles.

Mitochondrial COA7 is a heme-binding protein with disulfide reductase activity, which acts in the early stages of complex IV assembly

Cytochrome c oxidase (COX) assembly factor 7 (COA7) is a metazoan-specific assembly factor, critical for the biogenesis of mitochondrial complex IV (cytochrome c oxidase). Although mutations in COA7 have been linked to complex IV assembly defects and neurological conditions such as peripheral neuropathy, ataxia, and leukoencephalopathy, the precise role COA7 plays in the biogenesis of complex IV is not known. Here, we show that loss of COA7 blocks complex IV assembly after the initial step where the COX1 module is built, progression from which requires the incorporation of copper and addition of the COX2 and COX3 modules. The crystal structure of COA7, determined to 2.4 Å resolution, reveals a banana-shaped molecule composed of five helix-turn-helix (α/α) repeats, tethered by disulfide bonds. COA7 interacts transiently with the copper metallochaperones SCO1 and SCO2 and catalyzes the reduction of disulfide bonds within these proteins, which are crucial for copper relay to COX2. COA7 binds heme with micromolar affinity, through axial ligation to the central iron atom by histidine and methionine residues. We therefore propose that COA7 is a heme-binding disulfide reductase for regenerating the copper relay system that underpins complex IV assembly.

Twist-bend nematics and heliconical cholesterics: a physico-chemical analysis of phase transitions and related specific properties

ABSTRACT Certain nematic liquid crystals, for example, those formed by banana-shaped molecules, can exhibit a low-temperature twist-bend nematic (Ntb) phase. Upon addition of chiral dopants, a chiral version of the twist-bend phase (N*tb) can be observed below the conventional chiral nematic (N*) phase, while under electric field the N* phase is transformed into a specific state known as ‘oblique helicoidal cholesteric’. In this work, we have studied the well-known Ntb-forming system CB7CB:CB6OCB with addition of 5CB and chiral dopants (ChDs) using optical microscopy, differential scanning calorimetry (DSC), and measurements of temperature-dependent optical transmission using optical microscopy. Effects of 5CB and different chiral dopants (of steroid or non-steroid nature) upon thermal stability of Ntb phase were analysed, and selective reflection in the visible range could be observed in the N* phase with a sufficiently high ChD content. As a peculiar feature, sharp unwinding of the cholesteric helix was observed at lower temperatures when approaching the N*tb phase, which appears to be similar to the helix unwinding close to the smectic-A transition.

Banana-Shaped Nonfullerene Acceptor Molecules for Highly Stable and Efficient Organic Solar Cells

Banana-Shaped Nonfullerene Acceptor Molecules for Highly Stable and Efficient Organic Solar Cells

Nematic-isotropic phase transitions of banana-shaped molecules with gauche- and trans-conformations

A mean field theory is introduced to describe nematic phases of a banana-shaped molecule of a bend angle (θB ) with an axial chirality. We here take into account internal rotations: gauche- and trans-states, of the C-C bonds on the alkyl chains of the banana-shaped molecules. Using the Boltzmann statistics, the mean rotation angle is given as a function of temperature and the bond energy difference between the gauche- and the trans-states. We calculate phase diagrams on the temperature–bend angle plane and find six uniaxial and biaxial nematic phases with Landau points, depending on the bond energy.

Helical twisting power enhancement by adding banana-shaped molecules

Banana-shaped molecules with chiral conformations have been widely studied in supramolecular systems. Herein, it was found that the helical twisting power of a chiral dopant was enhanced with the addition of some banana-shaped molecules. The quantum chemistry calculations indicated that the banana-shaped molecules were feasible to form chiral conformations. One of the chiral conformations should prefer to be formed in the cholesteric liquid crystalline mixture.

Controlling the curvature

Liquid Crystals Molecular chirality is often required to make chiral liquid crystalline phases, but liquid crystallinity has also been obtained using curved elongated rods known as bent-core or banana-shaped molecules. Fernandez-Rico et al. developed a method to controllably alter the curvature of the rods using ultraviolet light and a photoresponsive polymer (see the Perspective by Godinho). From a single starting batch can come a family of rods with different curvatures but similar overall rod thickness, length, and length distribution. The researchers explored a range of liquid crystalline phases, including the splay-bend nematic phase that was predicted more than 40 years ago. Science , this issue p. [950][1]; see also p. [918][2] [1]: /lookup/doi/10.1126/science.abb4536 [2]: /lookup/doi/10.1126/science.abd3548

Nanobar Array Assay Revealed Complementary Roles of BIN1 Splice Isoforms in Cardiac T-Tubule Morphogenesis.

Bridging integrator-1 (BIN1) is a family of banana-shaped molecules implicated in cell membrane tubulation. To understand the curvature sensitivity and functional roles of BIN1 splicing isoforms, we engineered vertical nanobars on a cell culture substrate to create high and low curvatures. When expressed individually, BIN1 isoforms with phosphoinositide-binding motifs (pBIN1) appeared preferentially at high-curvature nanobar ends, agreeing well with their membrane tubulation in cardiomyocytes. In contrast, the ubiquitous BIN1 isoform without phosphoinositide-binding motif (uBIN1) exhibited no affinity to membranes around nanobars but accumulated along Z-lines in cardiomyocytes. Importantly, in pBIN1-uBIN1 coexpression, pBIN1 recruited uBIN1 to high-curvature membranes at nanobar ends, and uBIN1 attached the otherwise messy pBIN1 tubules to Z-lines. The complementary cooperation of BIN1 isoforms (comboBIN1) represents a novel mechanism of T-tubule formation along Z-lines in cardiomyocytes. Dysregulation of BIN1 splicing, e.g., during myocardial infarction, underlied T-tubule disorganization, and correction of uBIN1/pBIN1 stoichiometry rescued T-tubule morphology in heart disease.

Twist-bend nematic phases of banana-shaped molecules with an axial chirality

ABSTRACTWe present a mean field theory to describe uniaxial () and biaxial twist-bend nematic () phases of banana-shaped liquid crystalline molecules with an axial chirality. We first derive a tensor order parameter for the banana-shaped molecules as a function of a bend angle (), a torsion angle for the axial chirality, and four orientational order parameters, which describe uniaxial and biaxial nematic phases. Depending on the bend angle and the strength of an oblique twisting power of the banana-shaped molecules, we calculate phase diagrams on the temperaturebend angle plane. We derive the analytical formulas for two Landau points (LPs): one is at the bend angle and the other is at , which depends on the torsion angle. We also find that the phase appears outside the two LP angles and the phase diagrams show a rich variety of phase transitions, such as the second-order uniaxial nematic ( and the second-order phase transitions, etc.

Banana- and pizza-slice-shaped mesogens give a new constrained O(n) ferromagnet universality class.

It has been known that at high density, banana-shaped molecules are packed into a bent configuration locally, giving rise to interesting liquid-crystalline phases such as splay bend and twist bend. These spontaneous bend states can be modeled theoretically by allowing the bend elastic constant in the Frank elastic energy to become negative. Here, we extend this idea to banana-shaped and pizza-slice-shaped molecules with ferrointeractions, which can display both splayed and bent states. We model this by allowing both splay and bend elastic constants in the effective Frank elastic energy to be negative. In particular, we predict two new liquid-crystalline splay-bend phases. Furthermore, using renormalization group analysis, we showed that the phase transition belongs to a new constrained ferromagnet universality class.

Cholesteric-isotropic phase transitions of banana-shaped liquid crystalline molecules

A mean field theory is introduced to describe cholesteric (Ch) phases of banana-shaped liquid crystalline molecules. From a geometric point of view, we derive the tensor order parameter of the banana-shaped molecules as a function of a bend angle () and four orientational order parameters. Using the tensor order parameter, we derive the free energy of the cholesteric phase for the banana-shaped molecules and obtain the approximate formula of a cholesteric-isotropic phase transition (CIT) temperature as a function of the bend angle. We find a cholesteric C phase for < 70.5 or > 109.5 where the the two arm vectors of the banana-shaped molecule tend to parallel to the director and a cholesteric C phase for 70.5 < < 109.5 where the two arm vectors tend to perpendicular to the director. These Ch phases are also distinguished by using the primary axis of the orthogonal molecular axis.

Uniaxial and biaxial nematic phases of banana-shaped molecules and the effects of an external field

ABSTRACTA mean field theory is introduced to describe uniaxial and biaxial nematic phases of banana-shaped liquid crystalline molecules. From a geometric point of view, we derive the tensor order parameter of the banana-shaped molecules as a function of a bend angle and four orientational order parameters. Using the nematic free energy of the Maier-Saupe type, we calculate the phase diagram on the temperaturebend angle () plane and find three uniaxial nematic () and three biaxial nematic () phases, where is the primary axis of the orthogonal molecular axis. We also derive the approximate formulas of a nematic-isotropic phase transition () and a biaxial-uniaxial phase transition () temperature as a function of the bend angle. We also discuss the effects of the external field on the temperature and find the negative dependence of the temperature on the external field.

Design and Synthesis of a Novel Banana-Shaped Functional Molecule via Double Cross-Coupling.

A novel banana-shaped molecule using 2,8-Dimethyl-6H,12H-5,11-methanodibenzo [b,f] [1,5]diazocine (Tröger’s base) as bent-core was synthesized via double Carbon-Carbon cross-coupling reaction. The double Sonogashira cross-coupling reaction was optimized by using Pd(PPh3)2Cl2 as catalyst, CuI as cocatalyst and diisopropylamine as base in place of triethylamine. The structure of this compound was confirmed by 1H-NMR, 13C-NMR, Fourier transform infrared (FT-IR) spectroscopy and mass spectrometry.

Fine Structural Tuning of Thieno[3,2-b] Pyrrole Donor for Designing Banana-Shaped Semiconductors Relevant to Organic Field Effect Transistors

On the basis of the newly synthesized banana-shaped thieno[3,2- b] pyrrole building block [Bulumulla, C.; Gunawardhana, R.; Kularatne, R. N.; Hill, M. E.; McCandless, G. T.; Biewer, M. C.; Stefan, M. C. Thieno[3,2- b] pyrrole-Benzothiadiazole Banana-Shaped Small Molecules for Organic Field Effect Transistors. ACS Appl. Mater. Interfaces 2018, 10, 11818-11825], several small molecules that can be used as organic semiconducting materials were theoretically designed. We have shown that these novel molecules with the donor-π conjugated bridge-acceptor-π conjugated bridge-donor (D-π-A-π-D) building block exhibit superior charge transport properties in organic field-effect transistors (OFETs). A variety of donors, π-bridges, and acceptors are examined, and the structural, electronic, optical, and charge transport properties of designed semiconductors are systematically investigated. The results highlight the impact of the core acceptor in improving the transport properties of the designed molecules. In particular, this work points toward the benzo-bis(1,2,5-thiadiazole) as the most promising acceptor that can be combined with thiophene π-bridge and flanked benzo-thiadiazole terminal units to produce a reasonable candidate for synthesis and for incorporating into OFET materials. For the suggested semiconductor, the small electron reorganization energy and large intramolecular coupling originating from dense π-stacking gave rise to enhanced electron mobility. This strategy can be helpful for further improving the performance of curved small molecules in field-effect devices.

Dielectric properties of liquid crystal formed by laterally fluorine-substituted banana-shaped molecules

ABSTRACT Dielectric spectroscopy in the frequency range from 10−2 to 107 Hz was applied to investigate the dynamics of the relaxation processes in a banana-shaped liquid crystal compound with fluorinated chain segments. The dielectric spectra indicate the presence of two relaxation processes and a conductivity contribution. The high-frequency process shows Arrhenius-like temperature dependence in the B4 and SmCP phases and can be assigned to the hindered rotation of the bent-shaped molecules around their long molecular axis. The low-frequency process can be related to the dynamics of the periodic superstructures in B4 phase and fluctuations of the modulated ferroelectric domains in the SmCP phase. In the B7 (or SmCG) phase, both processes show the nonlinear dependence of the relaxation frequencies especially close to the isotopic phase transition. The dielectric measurements confirm the existence of the SmCP – B7 (or SmCG) second order or weakly first-order phase transition.

Twist-bend nematic phases in binary mixtures of banana-shaped liquid crystalline molecules

ABSTRACTWe present a mean field theory to describe twist-bend nematic () phases in binary mixtures of banana shaped, such as bent-core or dimer, liquid crystalline (LC) molecules with , where is a twist and is a bend elastic constant. We introduce the free energy for the mixtures by taking into account the director-pitch (DP) coupling of the consisting LC molecules ) and calculate the phase diagrams on the temperature-concentration plane. Our theory demonstrates that the isotropic (I), or para-nematic (), nematic (), and phases appear, depending on the strength of the DP coupling parameter and predicts various phase transitions: the first-order and transitions, and the second-order transition, etc., on the temperature-concentration plane. Our theory has a good agreement with the experimental phase diagrams of the mixtures.

Optical and Structural Properties of ESIPT Inspired HBT-Fluorene Molecular Aggregates and Liquid Crystals.

In bulk materials, positional isomers not only help in understanding how slight difference in molecular structure alters the crystal packing and optical properties, but also play a key role in developing new type of materials for functional applications. A detailed study on the photophysical properties of fluorene-HBT positional isomers in solution and in the solid state providing a molecular level understanding of the factors which influence fluorescence behavior is reported. Two molecules Ia and IIa were synthesized by Suzuki coupling reaction and their photophysical properties were compared to positional isomers Ib and IIb. Crystal structure analyses and density functional theory (DFT) computation studies were performed to understand structure-properties relation and the results reveal that changing substitution pattern has a marked influence on their packing modes and luminescence properties. Strong noncovalent interactions (π-π) in the solid state hamper the excited state intramolecular proton transfer (ESIPT) process which causes fluorescence quenching in the solid state (Ia and IIa = Φf, 28-40%; Ib and IIb = Φf, 55-67%). Compounds show solvent-responsive and aggregation induced emission (AIE) properties. Bent structures of Ia with double and symmetric substitution of ESIPT motifs exhibit particularly unique condensed phase upon heating, confirmed as a nematic liquid crystalline phase, and this is the first report on the ESIPT and AIE active liquid crystalline materials with a banana-shaped molecule.

Anion-templated nanosized silver clusters protected by mixed thiolate and diphosphine.

S2-, MoO42-, and Mo6O228- were successfully employed as templates in the formation of six high-symmetry polynuclear silver clusters as exemplified in the single-crystal X-ray structures of [S@Ag18(tBuC6H4S)16(dppp)4]·DMF·5CH3CN·3CH3OH (1), [MoO4@Ag24(MeC6H4S)12(dppm)6(MoO4)4]·2BF4·C2H5NO (2), [MoO4@Ag24(MeC6H4S)12(dppm)6(MoO4)4]·2CF3SO3 (3), [MoO4@Ag24(MeC6H4S)12(dppf)6(MoO4)4]·2CF3SO3 (4), [MoO4@Ag24(MeC6H4S)12(dppb)6(MoO4)4]·2CF3SO3 (5) and [Mo6O22@Ag46(tBuC6H4S)32(dppm)4(CH3CN)8]·6CF3SO3 (6) (dppp = 1,3-bis(diphenylphosphino)propane, dppm = bis(diphenylphosphino)methane, dppf = 1,1'-bis(diphenylphosphino)ferrocene and dppb = 1,4-bis(diphenylphosphino)butane). Cluster 1 is a S2--centered octadecanuclear banana-shaped molecule. Clusters 2-5 have similar structures consisting of a tetrahedron of a MoO42- core and four MoO42- where three silver atoms cap each face and a pair sits on each edge, giving tetraicosanuclear ball-shaped molecules. Although different diphosphine ligands and silver salts were used in the syntheses, 2-5 contain a common building cluster unit with similar geometry and nuclearity. With (Bu4N)2Mo6O19 as a template, a giant 46-silver-atom cluster encapsulates an in situ modified Mo6O228- unit. The nuclearity and geometry depend on the size and shape of the templates. High-resolution electrospray mass spectrometry (HR-ESI-MS) analyses of 4 indicate its exceptionally high stability in acetonitrile. The solid-state luminescence of 1 as a function of the temperature exhibits thermochromism from red to yellow due to the different intensities of the two bands. This work established a new strategy for the construction of polynuclear silver clusters using an anionic template and mixed S- and P-donor ligands where a promising approach for building novel dual emissive materials is unraveled.

Two-Dimensional Skyrmion Lattice Formation in a Nematic Liquid Crystal Consisting of Highly Bent Banana Molecules.

We synthesized a novel banana-shaped molecule based on a 1,7-naphthalene central core that exhibits a distinct mesomorphism of the nematic-to-nematic phase transition. Both the X-ray profile and direct imaging of atomic force microscopy (AFM) investigations clearly indicates the formation of an anomalous nematic phase possessing a two-dimensional (2D) tetragonal lattice with a large edge (ca. 59 Å) directed perpendicular to the director in the low-temperature nematic phase. One plausible model is proposed by an analogy of skyrmion lattice in which two types of cylinders formed from left- and right-handed twist-bend helices stack into a 2D tetragonal lattice, diminishing the inversion domain wall.