Biphenyl Unit Research Articles

Biphenyl Containing Shape Memory Epoxy Resin with Post‐heating Adjustable Properties

AbstractShape memory epoxy resin (SMEP) with tailorable properties has gained wide attention. Herein, a series of photocured diphenyl epoxy with excellent shape memory effects, based on the epoxy monomer diglycidyl ether of biphenyl (DGEBP) and M‐xylylenediamine (MXDA), is fabricated. Fourier transform infrared spectrometer (FTIR) is used to verify the mix‐curing process. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), polarized light microscope (POM), and X‐ray diffraction (XRD) are applied to analyze the microstructure of the film. The molar ratio of the raw material and the post‐heating could tune the crosslinking density, which allows the prepared epoxy resin to present a tailorable shape memory effect. Besides, this epoxy resin exhibits an excellent triple‐shape memory effect due to the wide transition temperature. It is worth of noting that post‐heating induced the self‐assembly of biphenyl unit of the lamellar structure due to π–π interactions that causes an adjustable shape memory effect. This work offers a novel SMEP with potential application in the thermal history trace field.

13C NMR investigations and molecular order of nematogens with biphenyl and bithiophene at terminus

ABSTRACT Four rod-like mesogens in which biphenyl and bithiophene units are located at one terminus are synthesised and the occurrence of enantiotropic nematic phase is established by hot-stage optical polarising microscopy and differential scanning calorimetry. For biphenyl based mesogens (BP-1 and BP-2), the mesophase is observed irrespective of number of phenyl rings in the amine moiety. For bithiophene (BT-1), on the other hand, the mesophase is only noted when the amine component has two rings. The mesophase range for BP-1 is found to be 163.7◦C and for BT-1 and BP-2, the values are 84.7◦C and 11.1◦C, respectively. BP-1 and BT-1 are subjected to 13C NMR investigation in nematic phase to determine the local order and accordingly, oriented 1D 13C and 2D SAMPI-4 NMR experiments are accomplished. The remarkable feature of the SAMPI-4 spectrum of BP-1 measured at 145◦C in nematic phase is observation of the 13C-1H dipolar coupling value of 16.67 kHz for terminal carbon (C18). For BT-1, however, the dipolar coupling value for C18 is found to be 8.60 kHz in nematic phase (138◦C). Such large values of 13C-1H dipolar couplings for the terminal ring carbons of the nematogens offer orientation of the rings of the core unit directly.

Second-order NLO response in chiral ferroelectric liquid crystals: Molecular and bulk consideration

Nonlinear optical (NLO) properties of three chiral smectic liquid crystals were investigated by Hyper-Rayleigh Scattering (HRS) and the Second-Harmonic Generation (SHG) methods. The HRS measurements of two compounds (MHPOBC and D16), with the biphenyl unit in their center, in solution demonstrate the quadratic NLO activity. The third compound (D17), having three isolated phenyl rings in the core, does not exhibit the NLO activity. The NLO properties in smectic phases of all investigated compounds have been also studied by wide-field second-harmonic and two-photon fluorescence microscopy confirming noncentrosymmetry for compounds with biphenyl π coupling (MHPOBC and D16).

Selective alkane co-inclusion by methylene- and adamantane-bridged macrocycle with biphenyl units

A methylene- and adamantane-bridged macrocycle with biphenyl units showed selective co-inclusion of n-hexane among the hexane isomers through crystallization. In the use of n-pentane or n-heptane, inclusion crystals with alkanes were not formed.

Polycarbazole and its derivatives: progress, synthesis, and applications

Polycarbazole and its derivatives encompass nitrogen-containing aromatic heterocyclic conducting polymers having excellent optoelectronic properties, high charge carrier mobility, and excellent morphological stability, which make them potential candidates in the field of nanodevices, rechargeable batteries and electrochemical transistors. Engrossingly, carbazole moieties can be electropolymerized in two different methods resulting in the formation of poly(2,7-carbazole)s or poly(3,6-carbazole)s derivatives because the 2,7 and 3,6 positions are more active than the others. The fundamental difference between these two polymers is in the bandgap energies and effectual conjugation length. Poly(2,7-carbazole) exhibits more extended conjugation length because of the presence of lower bandgap energy values and the presence of poly para phenylene (PPP) like structure. The pysico-chemical characteristics of the polymers, revamped by employing substituents at various positions and synthetic methods, leading to the generation of highly efficient materials for a wide range of optoelectronic applications. At present, much intrinsically conducting polymers (ICPs) like polythiophene (PT), poly (p-phenylene) (PPP), polypyrrole (PPY), and polyaniline (PANI) have been diligently investigated. Among these carbazole units are more advantageous because of their intriguing properties includes the presence of bridged biphenyl unit providing a material with a lower bandgap, the inexpensive raw material (9H-carbazole), and the natural functionalizing ability of nitrogen atom. The predominant objective of this review is to effectuate a comprehensive study of carbazole based conducting polymers, its derivatives, applications, and various synthesis methods.

A Chichibabin's Hydrocarbon-Based Molecular Cage: The Impact of Structural Rigidity on Dynamics, Stability, and Electronic Properties.

A three-dimensional π-conjugated polyradicaloid molecular cage c-Ph14, consisting of three Chichibabin's hydrocarbon motifs connected by two benzene-1,3,5-triyl bridgeheads, was synthesized. Compared with its linear model compound l-Ph4, the prism-like c-Ph14 has a more rigid structure, which shows significant impact on the molecular dynamics, stability, and electronic properties. A higher rotation energy barrier for the quinoidal biphenyl units was determined in c-Ph14 (15.64 kcal/mol) than that of l-Ph4 (11.40 kcal/mol) according to variable-temperature NMR measurements, leading to improved stability, a smaller diradical character, and an increased singlet-triplet energy gap. The pressure-dependent Raman spectroscopic studies on the rigid cage c-Ph14 revealed a quinoidal-to-aromatic transformation along the biphenyl bridges. In addition, the ellipsoidal cavity in the cage allowed selective encapsulation of fullerene C70 over C60, with an associate constant of about 1.43 × 104 M-1. Moreover, c-Ph14 and l-Ph4 exhibited similar redox behavior and their cationic species (c-Ph146+ and l-Ph42+) were obtained by chemical oxidation, and the structures were identified by X-ray crystallographic analysis. The biphenyl unit showed a twisted conformation in l-Ph42+ and remained coplanarity in c-Ph146+. Notably, molecules of c-Ph146+ form a one-dimensional columnar structure via close π-π stacking between the bridgeheads.

Axially Chiral Biphenyl Compound-Based Thermally Activated Delayed Fluorescent Materials for High-Performance Circularly Polarized Organic Light-Emitting Diodes.

To boost intrinsic circularly polarized luminescence (CPL) properties of chiral emitters, an axially chiral biphenyl unit is inlaid in thermally activated delayed fluorescent (TADF) skeleton, urging the participation of chiral source in frontier molecular orbital distributions. A pair of enantiomers, (R)‐BPPOACZ and (S)‐BPPOACZ, containing the cyano as electron‐withdrawing moieties and carbazole and phenoxazine as electron‐donating units are synthesized and separated. The circularly polarized TADF enantiomers exhibit both high photoluminescence quantum yield of 86.10% and excellent CPL activities with maximum dissymmetry factor |g PL| values of almost 10−2 in solution and 1.8 × 10−2 in doped film, which are among the best values of previously reported small chiral organic materials. Moreover, the circularly polarized organic light‐emitting diodes based on the TADF enantiomers achieve the maximum external quantum efficiency of 16.6% with extremely low efficiency roll‐off. Obvious circularly polarized electroluminescence signals with |g EL| values of 4 × 10−3 are also recorded.

Catalytic one-handed helix-induction and memory of amphiphilic poly(biphenylylacetylene)s in water

A series of amphiphilic biphenylylacetylene-based homo- and copolymers (PBPAs) carrying chiral and/or achiral oligo(ethylene glycol) pendants at the 4′-position of the biphenyl units were synthesized and the amplification of the macromolecular helicity through noncovalent and/or covalent chiral interactions followed by the memory of the helicity were investigated in both water and organic solvents. The macromolecular helicity was efficiently induced in the homopolymers of achiral monomers through specific encapsulation of a catalytic amount of hydrophobic chiral guests in water and their induced helicities were stably memorized in water after complete removal of the optically-active guests, while an excess helical sense was not biased at all in the homopolymers in toluene. One-handed macromolecular helicities were also efficiently induced in the chiral homopolymers through chiral information transfer from covalently linked optically-active pendants with a point chirality to biphenyl units with a dynamic axial chirality, whose helical senses were almost perfectly inverted in water and organic solvents. The achiral/chiral copolymers displayed a unique bidirectional (P and M) strong chiral amplification of the macromolecular helicity in water and toluene assisted by the solvent-induced helix-inversion, and their macromolecular helicities were further enhanced or inverted through encapsulation of a catalytic amount of enantiomeric alcohols in water, which could be further memorized in water after removing the encapsulated guests. We also demonstrated that the left- and right-handed circularly polarized lights could be generated through chirality transfer from the one-handed helical polymers with a macromolecular helicity memory, consisting entirely of achiral monomer units, to an achiral fluorescent dye in the blended films. Importantly, the resulting luminescence dissymmetry factors (ca. 2 × 10–3) were virtually the same as those of chiral homopolymers composed of the optically-pure repeating units.

Rare Three-Dimensional Uranyl-Biphenyl-3,3'-disulfonyl-4,4'-dicarboxylate Frameworks: Crystal Structures, Proton Conductivity, and Luminescence.

Due to the intrinsic coordination preference of the linear uranyl unit, uranyl-organic frameworks (UOFs) are generally prone to exhibiting low-dimensional structures. Reactions of uranyl nitrate with biphenyl-3,3'-disulfonyl-4,4'-dicarboxylic acid dipotassium salt (K2H2BPDSDC) under different conditions led to three UOFs, namely, {(Me2NH2)[K2(UO2)3(μ3-O)(μ3-OH)2(μ2-OH)(BPDSDC)(H2O)3]·4DMF}n (1), {[K2(UO2)(μ3-O)(BPDSDC)0.5(H2O)2]}n (2), and {(Me2NH2)2.5[K1.5(UO2)(BPDSDC)1.5(H2O)3]}n (3). Compounds 1 and 2 contain one-dimensional (1D) ribbon structures formed from UO22+ units bridged by μ3-O atoms and carboxylate groups. The 1D ribbons in 1 are linked by K+ atoms to form a two-dimensional (2D) layer, which is further pillared by the biphenyl units to give a three-dimensional (3D) framework. For 2, the oxygen atoms of UO22+ units in each 1D ribbon bridge the K+ atoms to form four -[K-O-K]n- infinite chains located above and below the ribbon. The 1D ribbons in 2 are bridged by sulfonate groups to generate a 3D substructure featuring 1D channels occupied by biphenyl moieties. In 3, each mononuclear [(UO2)(COO)3] unit is bridged by three K+ atoms to form a 3D substructure featuring 1D small left-handed and large righted helical channels occluded by biphenyl moieties. Compound 2 exhibits an excellent proton conductivity with the highest conductivity of 1.07 × 10-3 S cm-1. The inner walls of 1D channels of 2 are full of the hydrophilic sulfonate groups, which boost enrichment of the guest water molecules, thus resulting in a high proton conductivity. Finally, temperature dependence of fluorescent studies showed that compounds 1 and 2 display the characteristic uranyl emissions. This work presents the elegant examples of the rarely explored 3D UOFs and expands the potentials of UOFs.

Structurally Isomerized Bis-Biphenyl Moieties Embedded in Hexaphyrin(3.1.1.3.1.1) and Octaphyrin(1.1.1.0.1.1.1.0).

An o-p-biphenyl moiety-incorporated 32π hexaphyrin(3.1.1.3.1.1) is successfully achieved. Replacing ortho with meta connectivity in the biphenyl unit of hexaphyrin leads to the formation of its structural isomer, octaphyrin(1.1.1.0.1.1.1.0). Spectral and structural analyses reveal the lack of planarity in hexaphyrin and the presence of an m-arene unit in octaphyrin, thus affording nonaromatic characteristics.

6,6′-[(3,3′-Di-tert-butyl-5,5′-dimethoxy-1,1′-biphenyl-2,2′-diyl)bis(oxy)]bis(dibenzo[d,f][1,3,2]dioxaphosphepine) benzene monosolvate

The crystal structure of the benzene monosolvate of the well known organic diphosphite ligand BIPHEPHOS, C46H44O8P2·C6H6, is reported for the first time. Single crystals of BIPHEPHOS were obtained from a benzene solution after layering with n-heptane at room temperature. One specific property of this type of diphosphite structure is the twisting of the biphenyl units. In the crystal, C—H...π contacts and π–π stacking interactions [centroid-to-centroid distance = 3.8941 (15) Å] are observed.

Branched azomethines based on tris(2-aminoethyl)amine: Impact of imine core functionalization on thermal, electrochemical and luminescence properties

A series of imines based on tris(2-aminoethyl)amine was designed and synthesized to evaluate the effect of core functionalization with biphenyl, pyrene, anthracene, triphenylamine and phenanthrene units on selected properties. Their chemical structure was thoroughly characterized by NMR and FTIR spectroscopy and elemental analysis. All compounds were crystalline (except for imine with triphenylamine units) and melted in the wide temperature range of 99–187 °C, according to the structure of the substituent. DSC measurements revealed that the studied compounds can be converted into amorphous material with glass transition occurring for temperatures between 16 and 55 °C. The imines were electrochemically active and underwent oxidation and reduction processes as found using CV and DPV methods. Density functional theory was employed for optimizing the imines geometry, as well as for calculating HOMO and LUMO orbital energies together with ionization potentials and electron affinities. The absorption and photoluminescence in the UV–Vis spectral range, both in solution and in the solid state as films on glass substrates were studied. When dissolved in chloroform, they emitted light with quantum yields ranging from 0.54 to 22%. In the solid state they exhibited emission in the range of 380–515 nm. The selected compounds were preliminarily tested as components in light emitting diodes. The ability neat azomethines for electroluminescence in diode ITO/PEDOT:PSS/imine/Al was demonstrated.

Dual role of a pyrene derivative as a hole transport material and an emitter in blue fluorescent organic light-emitting diodes

A pyrene derivative, N1,N6-di([1,1′-biphenyl]-4-yl)-N1,N6-bis(9,9-dimethyl-9H-fluoren-2-yl)pyrene-1,6-diamine(PyFB), was investigated as a dual function organic material working as a hole transport material and a sky blue emitter at the same time. A pyrene core was modified with an aromatic amine moiety substituted with a fluorene and a biphenyl unit. The pyrene derived PyFB material showed the highest occupied molecular orbital of −5.5 eV and better hole transport properties than a common hole transport layer. The PyFB also worked as the sky blue emitter and a sky blue organic light-emitting diode developed using the PyFB emitter demonstrated a high external quantum efficiency of 8.5% and a very long lifetime of 56 h up to 95% of initial luminance at 500 cd/m2.

Supramolecular nanostructures constructed by rod-coil molecular isomers: effect of rod sequences on molecular assembly.

Coil-rod-coil molecules, composed of flexible oligoether chains and conjugated rod blocks, have a well-known ability to produce various nanostructures in bulk and in aqueous solution. Herein we report the synthesis and self-assembly of coil-rod-coil molecules based on the sequence of the rod building block and the type of oligoether coil chain. These molecules consist of conjugated rod segments, which are composed of biphenyl, terphenyl, and acetylenic bonds, with chiral oligoether chains as flexible coil segments. The experimental results imply that the sequence of the rod segments markedly influences the self-assembled nanostructures of coil-rod-coil molecules in the bulk state, and that the type of coil chain strongly affects the morphology of the supramolecular nanoassemblies of these molecules in aqueous solution. In the bulk state, molecules 1a and 1b, which contain biphenyl units connected to the end of the coil segments self-organize into a hexagonal perforated lamellar phase, and oblique columnar and body-centred tetragonal structures, respectively. However, molecules 2a and 2b bearing terphenyl units linked to the end of the coil segments self-assemble into lamellar, hexagonal perforated lamellar and hexagonal columnar structures. In aqueous solution, rod-coil molecular isomers with linear chiral oligoether chains self-assemble into helical nanofibres of various lengths. Meanwhile, isomers with chiral oligoether dendron chains self-organize into sheet-like nanoribbons of different sizes.

Impact of intramolecular H bond and n-π* interactions on photophysical and CO2 sensing properties of laterally appended D-π-A triarylboron compounds

Several examples of laterally appended donor-π-acceptor (D-π-A) boron compounds based on a biphenyl unit have been synthesized and fully characterized. Intramolecular H bonds or n-π* interactions have been found to have a great impact on the photophysical/fluorescent properties of these compounds. Some members of these compounds have been found to display fluorescent response toward CO2.

Biphenyl Sulfonic and Disulfonic Acids with Perfluorinated Alkyl Residues

Sulfonic acids serve as interesting, yet not intensively studied alternatives to carboxylic acids as linker units in coordination polymers. In this study, we present the synthesis of hybrid sulfonic acids with polar, rigid biphenyl moieties and disordered highly fluorinated alkyl chains. Consequently, eight biphenyl sulfonic and disulfonic acids with one or two perfluoroalkyl chains were prepared. The key steps within the synthesis include two palladium catalyzed C–C bond formations: The perfluoroalkyl residue is installed by Heck reaction (up to 91 %) using 1H,1H,2H‐perfluorinated alkenes (C6 and C8) and the biphenyl unit is established by a Suzuki coupling (up to 88 %) of boronic acids bearing one or two protected thiol groups. Finally, these thiol groups are converted into the sulfonic acids by N‐chlorosuccinimide mediated oxidation followed by hydrolysis of the respective sulfonyl chloride.

Intercalated metal\u2013organic frameworks with high electronic conductivity as negative electrode materials for hybrid capacitors

Hybrid capacitors should ideally exhibit high volumetric energy density, favorable low-temperature performance and safe operation. Here we describe a negative electrode comprising an intercalated metal–organic framework, 4,4′-biphenyl dicarboxylate dilithium [4,4′-Bph(COOLi)2], which forms a repeating organic–inorganic layered structure of π-stacked biphenyl and tetrahedral LiO4 units. The electrode shows a stepwise two-electron transfer and has a capacity of 190 mAh g−1 at 0.7 V vs. Li/Li+, which can suppress the lithium metal deposition reaction occurring an internal short circuit. A hybrid capacitor containing 4,4′-Bph(COOLi)2 negative and activated carbon positive electrodes possesses high volumetric energy density of approximately 60 Wh L−1 and good high-rate performance, particularly at the low temperature of 0 °C, because of low charge-transfer resistance along with low activation energy. Hopping mobility calculations suggest the observed low resistance properties are the result of high electron mobility arising from two electron-hopping pathways between adjacent molecules in the π-stacked biphenyl packing layer by lithium intercalation.

Fluorescence-Tuned Silicone Elastomers for Multicolored Ultraviolet Light-Emitting Diodes: Realizing the Processability of Polyhedral Oligomeric Silsesquioxane-Based Hybrid Porous Polymers

Processability has always been a challenge for most insoluble porous materials. Herein, we report a facile approach to realize their processability by physically blending them into a thiol-containing polysiloxane matrix (PMMS) followed by an efficient thiol–ene cross-linking reaction, resulting in novel silicone elastomers. The applied porous materials are polyhedral oligomeric silsesquioxane-based hybrid porous polymers (HPPs), which were prepared by the Heck reactions of octavinylsilsesquioxane with 4,4′-dibrombiphenyl and/or 1,3,6,8-tetrabromopyrene. They exhibit tunable fluorescence with a continuous color change from blue to red by altering the molar ratio of biphenyl and pyrene units. This remarkable fluorescence modulation endows the elastomers incorporated with HPP materials similar multicolor emissions from blue to red depending on the added HPP. It was observed that HPP materials were well dispersed in the polymeric matrix when the amount of HPPs was below 20 mg per gram of PMMS. Furthermore, mu...

Molecular Wires with Controllable π-Delocalization Incorporating Redox-Triggered π-Conjugated Switching Units.

A perfluorobiphenyl-2,2'-diyl dication and its corresponding dihydrophenanthrene-type electron donor are interconvertible upon two-electron transfer. Redox-triggered C-C bond-formation/cleavage caused a drastic change in the torsion angle of the biphenyl unit. Thus, π-delocalization ON/OFF switching was observed as a change in the UV absorption upon electrolysis of the linearly extended analogue with two phenylethynyl groups. A further extended π-system with a molecular length of ca. 3.5 nm, which has two switching units, was synthesized. Spectroelectrograms as well as voltammetric analyses showed that the two units act nearly simultaneously because of the very small inter-unit electrostatic repulsion in the tetracationic state. Thus, the present pair is a promising candidate as a switching unit for "molecular wires" with controllable π-delocalization, in which a higher ON/OFF ratio of delocalization could be realized by incorporating multiple switching units.

Effects of biphenyl groups on the dry sliding behavior of poly (ether-ether-ketone-ketone) copolymers against stainless steel

In this paper, an experimental study was decided to investigate the dependence of tribological property on biphenyl group contents in the polymer chain. A series of biphenyl containing poly (ether-ether-ketone-ketone) copolymers were synthesized by nucleophilic substitution polycondensation, the contents of biphenyl units were controlled by the feed ratio of biphenol to hydroquinone. The sliding wear and friction tests were conducted using a pin-on-disc apparatus against a stainless steel counterpart without any lubricant under dry conditions. The results indicated the friction coefficient decreased with the growing biphenyl contents first and then increased after BP60, associated with the same change of polymer crystallinity, while the specific wear rate exhibited a negative correlation. It was demonstrated that this bridge between polymer structure, crystallinity, and tribological performance was independent of the test conditions. For one specific sample, raising applied load and sliding speed will aggravate the wear work, while the friction coefficient was only distinctly affected by the applied load, having no concern with the sliding speed. Probable mechanisms were discussed by observation of the worn surface using scanning electron microscopy. Within our efforts, a possible molecular design method was proposed to develop potential tribological resins via adjusting one specific group in the backbone.