Phase Behavior of a Hydrogen-Bonded Polymer with Lamella-to-Cylinder Transition: Complex of Poly(4-vinylpyridine) and Small Dendritic Benzoic Acid Derivative

Phase behavior of a supramolecular system based on poly­(4-vinylpyridine) (P4VP) and 3,4,5-tris­(dodecyloxy)­benzoic acid (TDBA) [P4VP­(TDBA)_<i>x</i>, where <i>x</i> is the molar ratio of TDBA to P4VP repeating unit] was investigated by means of FTIR, differential scanning calorimetry, polarized optical microscopy, and X-ray scattering method. The intermolecular hydrogen-bonding interaction between P4VP and TDBA is confirmed by FTIR. While almost all of the added TDBA molecules are hydrogen bonded to the P4VP chains at <i>x</i> < ∼0.60, the hydrogen-bonding interaction becomes incomplete at <i>x</i> > 0.60 and saturates at <i>x</i> > 0.90. The phase structure of P4VP­(TDBA)_<i>x</i> is composition dependent. At <i>x</i> < ∼0.30, the complex is homogeneous. With ∼0.30 < <i>x</i> < ∼0.60, P4VP­(TDBA)_<i>x</i> forms a lamella phase, of which the long period is proportional to 1/<i>x</i>. Further adding TDBA causes a lamella-to-cylinder transition. At <i>x</i> > ∼0.60, the lattice parameter of the cylinder or hexagonal columnar (Φ_H) phase decreases with increasing <i>x</i>. Considering the microphase separation between the polar part and the nonpolar part of alkyl tails, the lamella-to-cylinder transition can be understood using a volumetric argument. We consider that the large nonpolar part of TDBA enhances the microphase separation of P4VP­(TDBA)_<i>x</i>, and moreover, the fan-like shape of TDBA facilitates the formation of Φ_H phase. We also roughly estimated the domain size of the P4VP chains in the microphase-separated mesophase. For both the lamellar and Φ_H phase, increasing <i>x</i> results in stronger confinement on the P4VP chains. During the lamella-to-cylinder transition the confinement imposed by the TDBA molecules may be partially released, which favors the Φ_H phase formation

Combined Main-Chain/Side-Chain Liquid Crystalline Polymer with Main-Chain On the basis of “Jacketing” Effect and Side-Chain Containing Azobenzene Groups

Combining the concept of “flexible spacer” which can bring liquid crystalline (LC) properties to the side-chains and the side-group “jacketing” effect which can result in main-chain with rod-like conformation, we have synthesized a new combined main-chain/side-chain LC polymer based on radical polymerization, poly(2,5-bis{[6-(4-methoxy-4′-oxy-azobenzene)hexyl]oxycarbonyl}styrene) (denoted as P1) with two azobenzene groups per repeating unit. The chemical structures of P1 and the corresponding monomer were characterized using various techniques with satisfactory analysis data. The phase structures and transitions of P1 were investigated using differential scanning calorimetry, polarized optical microscope, and one- and two-dimensional (1D and 2D) wide-angle X-ray diffraction. We identify that P1 can form a hierarchically ordered structure with double orderings on both the nanometer and subnanometer length scales. Most likely, the thick main-chains of P1 obtained by “jacketing” the central rigid portion of terephthalate side-chain to the polyethylene backbone construct a 2D centered rectangular scaffold, which is stable until the sample becomes completely isotropic. The packing of side-chains inside the main-chain scaffold undergoes the transitions of smectic B- (SmB-) like ↔ smecitc A (SmA)-like ↔ isotropic. The confinement arising from the scaffold induces the SmB-like packing and enhances the stability of SmA-like structure. The hierarchically ordered structure of P1 renders a biaxial orientation with the side-chains perpendicular to the main-chains. We compared P1 with an end-on side-chain LC polymer of poly(4-{[6-(4-methoxy-4′-oxy-azobenzene)hexyl]oxycarbonyl}styrene) (denoted as P2). P2 bearing one mesogenic group per repeating unit forms a monolayer SmA phase, with the transition temperature much lower than that of P1. Upon UV irradiation, in contrast to that P2 will become isotropic, P1 can still exhibit LC behavior after the azobenzene groups adopt cis conformation

Enantioselective Access to Triaryl-2-pyrones with Monoaxial or Contiguous C–C Diaxes via Oxidative NHC Catalysis

We present herein an unprecedented stereoselective synthesis of triaryl-2-pyrones with monoaxial or contiguous diaxes from readily available starting materials. This N-heterocyclic carbene catalysis method adopts an atroposelective annulation of 2-aryketones with ynals under oxidative conditions. The annulation includes the construction of one or two axes in a single operation, achieves step economy, and affords axially chiral triaryl-2-pyrones in moderate to good yields, with high to excellent enantioselectivities. DFT calculations of the relative energies of stereoisomers and rotational barriers were performed

Enantioselective Access to Triaryl-2-pyrones with Monoaxial or Contiguous C–C Diaxes via Oxidative NHC Catalysis

We present herein an unprecedented stereoselective synthesis of triaryl-2-pyrones with monoaxial or contiguous diaxes from readily available starting materials. This N-heterocyclic carbene catalysis method adopts an atroposelective annulation of 2-aryketones with ynals under oxidative conditions. The annulation includes the construction of one or two axes in a single operation, achieves step economy, and affords axially chiral triaryl-2-pyrones in moderate to good yields, with high to excellent enantioselectivities. DFT calculations of the relative energies of stereoisomers and rotational barriers were performed

Enantioselective Access to Triaryl-2-pyrones with Monoaxial or Contiguous C–C Diaxes via Oxidative NHC Catalysis

We present herein an unprecedented stereoselective synthesis of triaryl-2-pyrones with monoaxial or contiguous diaxes from readily available starting materials. This N-heterocyclic carbene catalysis method adopts an atroposelective annulation of 2-aryketones with ynals under oxidative conditions. The annulation includes the construction of one or two axes in a single operation, achieves step economy, and affords axially chiral triaryl-2-pyrones in moderate to good yields, with high to excellent enantioselectivities. DFT calculations of the relative energies of stereoisomers and rotational barriers were performed

Enantioselective Access to Triaryl-2-pyrones with Monoaxial or Contiguous C–C Diaxes via Oxidative NHC Catalysis

We present herein an unprecedented stereoselective synthesis of triaryl-2-pyrones with monoaxial or contiguous diaxes from readily available starting materials. This N-heterocyclic carbene catalysis method adopts an atroposelective annulation of 2-aryketones with ynals under oxidative conditions. The annulation includes the construction of one or two axes in a single operation, achieves step economy, and affords axially chiral triaryl-2-pyrones in moderate to good yields, with high to excellent enantioselectivities. DFT calculations of the relative energies of stereoisomers and rotational barriers were performed

Crystal Structure and Molecular Packing Behavior of Poly(2,3-diphenyl-1,4-phenylenevinylene) Derivatives Containing Alkyl Side-Chains

Phase behavior and crystal structure of a series of poly­(2,3-diphenyl-5-alkyl-p-phenylenevinylene) (denoted as DPn-PPV, where n represents the carbon number of the alkyl side-chain, n = 6, 8, 10, 12) were studied using differential scanning calorimetry, one- and two-dimensional (1D and 2D) wide-angle X-ray diffraction (WAXD), and selected area electron diffraction (SAED). The experimental results reveal that DPn-PPV exhibits one crystalline phase at low temperatures. On the basis of 2D WAXD and SAED patterns obtained from the oriented samples, the crystal structures are determined to be orthorhombic for DP6-PPV and monoclinic for DP8-PPV, DP10-PPV, and DP12-PPV. To account for the unusually large unit cell dimensions, we propose that the unit cell of DPn-PPV contains 4 chains (8 chemical repeat units). The complex crystal structure can be attributed to the longitudinal and transverse offsets between the neighboring chains, which shall be mainly due to the requirement of minimizing the steric hindrance caused by the attached pendent groups and maximizing the π–π interaction between the chains. The molecular packing scheme was simulated by using Cerius2 software, of which the result agrees with the experimental data. The polarized UV–vis absorption and polarized solid-state photoluminescence (PL) property of these polymers was also investigated. The PL spectra indicated that the light emitted from the oriented film was preferentially polarized parallel to the shear direction, implying that DPn-PPV may potentially be useful in linearly polarized luminescence devices

Kinetic Resolution of Acyclic Tertiary Propargylic Alcohols by NHC-Catalyzed Enantioselective Acylation

We report herein an efficient NHC-catalyzed kinetic resolution of acyclic tertiary propargylic alcohols that provides them in high to excellent enantioselectivity. This is the first example of kinetic resolution realized by enantioselective acylation. The recovered enantioenriched alcohols can be facilely converted into other valuable compounds such as densely functionalized tertiary alcohols and carbmates in high yields and excellent stereopurity. Density functional theory calculations were performed to determine the reaction mechanism and to understand the origin of enantiodiscrimination