Periodically Clickable Polyesters: Study of Intrachain Self-Segregation Induced Folding, Crystallization, and Mesophase Formation

A series of polyesters based on 2-propargyl-1,3-propanediol or 2,2-dipropargyl-1,3-propanediol or 2-allyl-2-propargyl-1,3-propanediol and 1,20-eicosanedioic acid were prepared by solution polycondensation using the corresponding diacid chloride; these polyesters were quantitatively “clicked” with a fluoroalkyl azide, namely CF₃(CF₂)₇CH₂CH₂N₃, to yield polyesters carrying long-chain alkylene segments in the backbone and either one or two perfluoroalkyl segments located at periodic intervals along the polymer chain. The immiscibility of the alkylene and fluoroalkyl segments causes the polymer chains to fold in a zigzag fashion to facilitate the segregation of these segments; the folded chains further organize in the solid state to form a lamellar structure with alternating domains of alkyl (HC) and fluoroalkyl (FC) segments. Evidence for the self-segregation is provided by DSC, SAXS, WAXS, and TEM studies; in two of the samples, the DSC thermograms showed two distinct endotherms associated with the melting of the individual domains, while the WAXS patterns confirm the existence of two separate peaks corresponding to the interchain distances within the crystalline lattices of the HC and FC domains. SAXS data, on the other hand, reveal the formation of an extended lamellar morphology with an interlamellar spacing that matches reasonably well with those estimated from TEM studies. Interestingly, a smectic-type liquid crystalline phase is observed at temperatures between the two melting transitions. These systems present a unique opportunity to develop interesting nanostructured polymeric materials with precise control over both the domain size and morphology; importantly, the domain sizes are far smaller than those typically observed in traditional block copolymers

Mesomorphic Schiff base amine tethered giant gold nanoparticles

<p>GNP-LC hybrid incorporating giant gold nanoclusters was accessed with tailor made liquid crystalline Schiff base bearing amine function as reactive end group without using any external reducing agent. The liquid crystal phase (smectic C) of the Schiff base remained unaltered in the hybrid material. The ligand and hybrid both exhibited interesting concentration-dependent fluorescence quenching of 9,10-diphenylanthracene when excited at 345 nm wavelength in dichloromethane solution. The GNP-LC hybrid exhibited reasonably good electrical conductivity showing an Arrhenius-type behaviour in the smectic mesophase and a tunnelling behaviour in the crystalline state.</p

Transforming a <i>C</i>₃‑Symmetrical Liquid Crystal to a π‑Gelator by Alkoxy Chain Variation

Rational understanding of the structural features involving different noncovalent interactions is necessary to design a liquid crystal (LC) or an organogelator. Herein, we report the effect of the number and positions of alkoxy chains on the self-assembly induced physical properties of a few π-conjugated molecules. For this purpose, we designed and synthesized three <i>C</i>₃-symmetrical molecules based on oligo­(<i>p</i>-phenylenevinylene), <i><b>C</b></i>_<b>3</b><b>OPV1</b>–<b>3</b>. The self-assembly properties of these molecules are studied in the solid and solution states. All of the three molecules follow the isodesmic self-assembly pathway. Upon cooling from isotropic melt, <i><b>C</b></i>_<b>3</b><b>OPV1</b> having nine alkoxy chains (−OC₁₂H₂₅) formed a columnar phase with two-dimensional rectangular lattice and retained the LC phase even at room temperature. Interestingly, when one of the −OC₁₂H₂₅ groups from each of the end benzene rings is knocked out, the resultant molecule, <i><b>C</b></i>_<b>3</b><b>OPV2</b> lost the LC property, however, transformed as a gelator in toluene and <i>n</i>-decane. Surprisingly, when the −OC₁₂H₂₅ group from the middle position is removed, the resultant molecule <i><b>C</b></i>_<b>3</b><b>OPV3</b> failed to form either the LC or the gel phases

Effect of Pressure on Dielectric and Frank Elastic Constants of a Material Exhibiting the Twist Bend Nematic Phase

We report the first investigation on the effect of applied pressure on the now well-known dimer α,ω bis­(4,4′-cyanobiphenyl)­heptane (CB7CB) that exhibits two types of nematic: the regular uniaxial nematic (N) and the recently discovered twist-bend nematic (N_TB) phase. At atmospheric pressure, the thermal behavior of ε_⊥, the permittivity normal to the director in the N phase decreases on entering the N_TB wherein the value represents permittivity orthogonal to the helical axis. Application of pressure initially decreases the magnitude of the change in ε_⊥ and with further increase in pressure exhibits an increase in the value. Such a change in the feature of ε_⊥ is similar to that obtained at room pressure when the monomeric heptyloxy cyanobiphenyl (7OCB) is doped to CB7CB at a high concentration of 50%. The dielectric anisotropy exhibits a trend reversal with temperature, the extent of which is affected at high pressures. Another salient feature of the study is the effect that pressure has on the Frank bend elastic constant K₃₃. Over the pressure range studied K₃₃ enhances by a large factor of 5. In contrast, the splay elastic constant exhibits a much smaller change of only 70%. The pressure–temperature phase boundary has a much smaller slope for the N–N_TB transformation than for the isotropic-N transition. We propose that all these features can be understood in terms of the relative population of the more energetic horseshoe and lower energy extended conformer adopted by the CB7CB molecule. The extended conformer is favored at lower temperatures or at higher pressures. This argument is validated by X-ray diffraction experiments at atmospheric pressure on the binary mixture of CB7CB and 7OCB, mentioned above

Binary System Exhibiting the Nematic to Twist-Bend Nematic Transition: Behavior of Permittivity and Elastic Constants

We describe measurements of the permittivity and Frank elastic constant in the nematic phase of a binary system displaying a transition between the nematic (N) and the recently discovered twist-bend nematic (N_TB) phase. Among the salient features observed are (i) the existence of the N_TB phase even when the system is loaded with a high concentration (∼64 mol %) of a rodlike component; (ii) a clear signature in permittivity of the N–N_TB transition; and (iii) a lower value of the bend elastic constant compared to the splay over a large phase space, with the difference between the two becoming a maximum for an intermediate mixture. These studies further support the surprising idea that the elastic features associated with bent molecules can be further augmented by suitable rodlike additives

Investigation of liquid crystalline property of a new calamitic liquid crystalline system methyl 4-(4ʹ-(4ʹʹ-(decyloxy)benzyloxy) benzylideneamino)benzoate

<p>A new polar calamitic liquid crystal, methyl 4-(4ʹ-(4ʺ-(decyloxy)benzyloxy) benzylideneamino)benzoate (M3BA) containing ether and Schiff base groups as linker with terminal polar ester group, has been synthesised and mesomorphic properties are studied by differential scanning calorimetry, polarising optical microscopy, density functional theory, temperature-dependent X-ray diffraction and temperature-dependent micro- Raman study. The smectic A (SmA) mesophase with focal conic texture has been observed with wide mesomorphic range. Layer thickness in SmA phase is greater than the optimised length of the molecule, indicating partially bilayer SmA phase. Analysis of Raman marker bands of C–H in-plane bending of phenyl rings, C=C stretching of rings, C=N stretching and C=O stretching shows structural changes at molecular level at Cr → SmA phase transition and provides proper intermolecular interactions responsible for dimeric unit in partially bilayer SmA phase.</p

Iron(III) metallomesogen of [N₂O₂] donor Schiff base ligand containing 4-substituted alkoxy chains

<p>Two new square pyramidal iron(III)-complexes of ‘salen’-type Schiff base ligands containing 4-substituted long alkoxy arms on the aromatic rings, [Fe(4-C₁₆H₃₃O)₂salcn)]Cl and [Fe(4-C₁₆H₃₃O)₂salophen)]Cl {salcn = N,Nʹ-cyclohexanebis(salicylideneiminato) and salophen = N,Nʹ-phenylenebis(salicylideneiminato)}, have been successfully synthesised, and their mesomorphic property investigated. The ligands and complexes were characterised by elemental analyses, UV–Vis, FT-IR, ESI–MS, ¹H and ¹³C NMR (for ligands only). The phase behaviour of the iron(III) complexes were ascertained by differential scanning calorimetry, polarising optical microscopy and variable temperature PXRD study. Ligands are non-mesomorphic, however, mesomorphism got induced upon complexation with the iron(III) centre. X-ray diffraction study revealed a layer-like arrangement of the five coordinated mesomorphic iron(III) complexes. The mesophase is stable over a wide range of temperature. The density functional theory calculations were carried out using Gaussian 09 program at B3LYP level using unrestricted 6–31G (d, p) basis set to obtain the optimised geometry of the iron(III) complexes.</p

Self-Assembling and Luminescent Properties of Chiral Bisoxadiazole Derivatives in Solution and Liquid-Crystalline Phases

Herein, we report the synthesis, self-assembly, and electroluminescence characteristics of a new green-emitting, pseudodiscoid chiral molecule, OXDC, containing an electron-donating stilbene core and an electron-accepting oxadiazole substituent. The helical organization and specific interaction of the chiral pseudodiscoid molecule resulted in the formation of self-assembled nanofibers with a columnar superstructure. Macroscopic chirality was observed in both the liquid-crystalline phases and the self-assembled nanofibers of OXDC, a feature which was absent in the analogous achiral oxadiazole derivative reported earlier [Sivadas, A. P.; Supergelation via Purely Aromatic π-π Driven Self-Assembly of Pseudodiscotic Oxadiazole Mesogens. J. Am. Chem. Soc. 2014, 136, 5416−5423]. A high-performance organic light-emitting device was demonstrated using OXDC as the emitting material, with a luminous intensity of 10 115 cd m^–2 at 5 V and chromaticity coordinates of (0.32, 0.51)

Reversible Polymorphism, Liquid Crystallinity, and Stimuli-Responsive Luminescence in a Bola-amphiphilic π‑System: Structure–Property Correlations Through Nanoindentation and DFT Calculations

We report the design, synthesis, detailed characterization, and analysis of a new multifunctional π-conjugated bola-amphiphilic chromophore: <i>oligo</i>-(<i>p</i>-phenyleneethynylene)­dicarboxylic acid with dialkoxyoctadecyl side chains (<b>OPE-C</b>_<b>18</b><b>-1</b>). <b>OPE-C</b>_<b>18</b><b>-1</b> shows two polymorphs at 123 K (<b>OPE-C</b>_<b>18</b><b>-1′</b>) and 373 K (<b>OPE-C</b>_<b>18</b><b>-1″</b>), whose crystal structures were characterized via single crystal X-ray diffraction. <b>OPE-C</b>_<b>18</b><b>-1</b> also exhibits thermotropic liquid crystalline property revealing a columnar phase. The inherent π-conjugation of <b>OPE-C</b>_<b>18</b><b>-1</b> imparts luminescence to the system. Photoluminescence measurements on the mesophase also reveal similar luminescence as in the crystalline state. Additionally, <b>OPE-C</b>_<b>18</b><b>-1</b> shows mechano-hypsochromic luminescence behavior. Density functional theory (DFT)-based calculations unravel the origins behind the simultaneous existence of all these properties. Nanoindentation experiments on the single crystal reveal its mechanical strength and accurately correlate the molecular arrangement with the liquid crystalline and mechanochromic luminescence behavior

Reversible Polymorphism, Liquid Crystallinity, and Stimuli-Responsive Luminescence in a Bola-amphiphilic π‑System: Structure–Property Correlations Through Nanoindentation and DFT Calculations

We report the design, synthesis, detailed characterization, and analysis of a new multifunctional π-conjugated bola-amphiphilic chromophore: <i>oligo</i>-(<i>p</i>-phenyleneethynylene)­dicarboxylic acid with dialkoxyoctadecyl side chains (<b>OPE-C</b>_<b>18</b><b>-1</b>). <b>OPE-C</b>_<b>18</b><b>-1</b> shows two polymorphs at 123 K (<b>OPE-C</b>_<b>18</b><b>-1′</b>) and 373 K (<b>OPE-C</b>_<b>18</b><b>-1″</b>), whose crystal structures were characterized via single crystal X-ray diffraction. <b>OPE-C</b>_<b>18</b><b>-1</b> also exhibits thermotropic liquid crystalline property revealing a columnar phase. The inherent π-conjugation of <b>OPE-C</b>_<b>18</b><b>-1</b> imparts luminescence to the system. Photoluminescence measurements on the mesophase also reveal similar luminescence as in the crystalline state. Additionally, <b>OPE-C</b>_<b>18</b><b>-1</b> shows mechano-hypsochromic luminescence behavior. Density functional theory (DFT)-based calculations unravel the origins behind the simultaneous existence of all these properties. Nanoindentation experiments on the single crystal reveal its mechanical strength and accurately correlate the molecular arrangement with the liquid crystalline and mechanochromic luminescence behavior