Biphenyl Unit Research Articles

Narrow‐Band Emission of Asymmetric 1,3‐Substituted Pyrene‐Based Deep‐Blue Emitters and Application in OLEDs

AbstractHigh‐efficiency organic blue light‐emitting materials with narrow‐band emission are fundamental components for constructing high color purity and high resolution in high‐performance organic light‐emitting diode (OLED) devices. Herein, new pyrene‐based blue emitters (8–10) with narrow‐band emission are synthesized by asymmetrically introducing biphenyl and triphenylamine units at the 1‐ and 3‐positions of pyrene, respectively. Due to the steric effect and through‐space conjugation, the synergistic effects of both groups not only boost these emitters 8–10 (CIEy < 0.11) with aggregation‐induced emission (AIE) characteristics and high fluorescence quantum yield (>0.68), but also endow narrow full width at half maxima (FWHM) emission (≤36 nm) in the crystallized state (FWHM ≤ 55 nm in the film state). The EL spectra of pyrene‐based 8–10 in nondoped OLEDs exhibit blue emission with a maximum emission (λmax em) in the range of 448–453 nm (CIEy ≤ 0.12). The compounds 8–10 in doped‐OLEDs show a blue emission with a λmax em in the range of 443–445 nm and CIEy ≤ 0.08, with FWHM emission of 57–61 nm. The compound 10‐based doped OLED displays an impressive EL performance with a maximum brightness of 9756 cd m−2 and a maximum external quantum efficiency of 2.58%.

Nonfullerene Acceptors Bearing Spiro-Substituted Bithiophene Units in Organic Solar Cells: Tuning the Frontier Molecular Orbital Distribution to Reduce Exciton Binding Energy.

The development of nonfullerene acceptors (NFAs), represented by ITIC, has contributed to improving the power conversion efficiency (PCE) of organic solar cells (OSCs). Although tuning the electronic structures to reduce the exciton binding energy (Eb) is considered to promote photocharge generation, a rational molecular design for NFAs has not been established. In this study, we designed and developed two ITIC-based NFAs bearing spiro-substituted bithiophene or biphenyl units (named SpiroT-DCI and SpiroF-DCI) to tune the frontier molecular orbital (FMO) distribution of NFAs. While the highest occupied molecular orbitals (HOMOs) of SpiroF-DCI and ITIC are delocalized in the main π-conjugated framework, the HOMO of SpiroT-DCI is distributed on the bithiophene unit. Reflecting this difference, SpiroT-DCI exhibits a smaller Eb than either SpiroF-DCI or ITIC, and exhibits greater external quantum efficiency in single-component OSCs. Furthermore, SpiroT-DCI shows improved PCEs for bulk-heterojunction OSCs with a donor of PBDB-T, compared with that of either SpiroT-DCI or ITIC. Time-resolved spectroscopy measurements show that the photo-induced intermolecular charge separation is effective even in pristine SpiroT-DCI films. This study highlights the introduction of spiro-substituted bithiophene units that are effective in tuning the FMOs of ITIC, which is desirable for reducing the Eb and improving the PCE in OSCs.

Synthesis, crystal structure and Hirshfeld surface analysis of 4'-cyano-[1,1'-biphen-yl]-4-yl 3-(benz-yloxy)benzoate.

In the title compound, C27H19O3N, the dihedral angle between the aromatic rings of the biphenyl unit is 38.14 (2)° and the C-O-C-C torsion angle in the benz-yloxy benzene fragment is 179.1 (2)°. In the crystal, the mol-ecules are linked by weak C-H⋯O inter-actions forming S(9) chains propagating along [010]. The most important contributions to the Hirshfeld surface arise from H⋯H (32.4%) and C⋯H/H⋯C (37.0%) contacts.

Synthesis of base-acid pair based poly(isatin arylene) membranes for HT-PEMFC applications

Phosphoric acid (PA) doped polymer electrolyte membranes are promising high temperature proton exchange membranes (HT-PEMs) for fuel cells. While PA doped polybenzimidazole (PBI) has been considered as a successful HT-PEM, several issues remain, such as the use of carcinogenic monomer, poor solubility in organic solvents and easy PA loss. To develop more cost-effective, readily synthesized and high-performance HT-PEMs, this study focuses on synthesizing high-performance HT-PEMs based on poly(isatin arylene)s (i.e., PIT and PIB) containing a lactam structure and devoid of ether bonds. These polymers are synthesized from isatin and p-terphenyl (or biphenyl) under superacid catalysis. Subsequently, glycidyl trimethyl ammonium chloride (GTA) is employed as a grafting reagent for PIT and PIB. This ring-opening reaction is accomplished through an efficient and environmentally friendly procedure without any alkaline catalysts. The introduced GTA side chains with quaternary ammonium and hydroxyl groups not only produce microphase separation structures that facilitate proton conduction, but also reduce PA loss. Comparing with PIT-GTA with terphenyl units, the PIB-GTA membrane with short biphenyl units exhibits superior properties. For instance, the PIB-GTA/218.5%PA membrane achieves a high conductivity of 0.103 S cm−1 at 180 °C and a tensile strength of 6.6 MPa at room temperature. Without humidification and backpressure, the PIB-GTA/218.5%PA based H2–O2 single cell displays a peak power density of 632 mW cm−2 at 160 °C. This work presents a straightforward approach to synthesizing GTA grafted poly(isatin arylene) membranes for HT-PEM fuel cells.

Nonfullerene Acceptors Bearing Spiro‐Substituted Bithiophene Units in Organic Solar Cells: Tuning the Frontier Molecular Orbital Distribution to Reduce Exciton Binding Energy

The development of nonfullerene acceptors (NFAs), represented by ITIC, has contributed to improving the power conversion efficiency (PCE) of organic solar cells (OSCs). Although tuning the electronic structures to reduce the exciton binding energy (Eb) is considered to promote photocharge generation, a rational molecular design for NFAs has not been established. In this study, we designed and developed two ITIC‐based NFAs bearing spiro‐substituted bithiophene or biphenyl units (named SpiroT‐DCI and SpiroF‐DCI) to tune the frontier molecular orbital (FMO) distribution of NFAs. While the highest occupied molecular orbitals (HOMOs) of SpiroF‐DCI and ITIC are delocalized in the main π‐conjugated framework, the HOMO of SpiroT‐DCI is distributed on the bithiophene unit. Reflecting this difference, SpiroT‐DCI exhibits a smaller Eb than either SpiroF‐DCI or ITIC, and exhibits greater external quantum efficiency in single‐component OSCs. Furthermore, SpiroT‐DCI shows improved PCEs for bulk‐heterojunction OSCs with a donor of PBDB‐T, compared with that of either SpiroT‐DCI or ITIC. Time‐resolved spectroscopy measurements show that the photo‐induced intermolecular charge separation is effective even in pristine SpiroT‐DCI films. This study highlights the introduction of spiro‐substituted bithiophene units that are effective in tuning the FMOs of ITIC, which is desirable for reducing the Eb and improving the PCE in OSCs.

Para-Phenylenediamine Dimer as a Redox-Active Guest for Supramolecular Systems.

Redox-active components are highly valuable in the construction of molecular devices. We combined two p-phenylenediamines (p-PDA) with a biphenyl (BiPhe) unit to prepare a supramolecular guest 4 consisting of three binding sites for cucurbit[7/8]uril (CBn) and/or cyclodextrins (CD). Supramolecular properties of 4 were investigated using NMR, UV-vis, mass spectrometry and isothermal titration calorimetry. Our analysis revealed that 4 forms higher-order host-guest complexes, wherein a CD unit occupies the central BiPhe site, secured by two CBn units at the terminal p-PDA sites. Additionally, 1 : 1 complexes with α-CD and β-CD, a 1 : 2 complex with γ-CD and 2 : 1 complexes with CB7 and CB8 were identified. Through UV-vis and cyclic voltammetry, redox processes leading to the formation of a stable, deep blue dication diradical of 4 are elucidated. Furthermore, it is demonstrated that CB7 selectively protects oxidised 4 from reduction in the presence of a reducing agent. The supramolecular and redox properties of the structural motif represented by 4 render it an interesting candidate for the construction of supramolecular devices.

Biphenyl tetracarboxylic acid-based metal-organic frameworks: a case of topology-dependent thermal expansion.

The large inherent flexibility and highly modular nature of metal-organic frameworks (MOFs) make them ideal candidates for the study of negative thermal expansion (NTE). Among diverse organic ligands, the biphenyl unit, which can unrestrictedly rotate along its C-C single bond, can largely enhance the structural flexibility. Herein, we explored the thermal expansion behaviors of four indium biphenyl tetracarboxylates (BPTCs). Owing to the different dihedral angles of BPTC ligands and coordination mode of In3+, they show distinct topologies: InOF-1 (nti), InOF-2 (unc), InOF-12 (pts) and InOF-13 (nou). Intriguingly, it is found that the thermal expansion is highly dependent on the specific topology. The MOFs featuring mononuclear nodes show normal positive thermal expansion (PTE), and the magnitudes of coefficients follow the trend of InOF-2 < InOF-12 < InOF-13, inversely related to averaged molecular volumes. In contrast, the InOF-1, composed of a 1D chain of corner-shared InO6 octahedrons, shows pronounced NTE. Detailed high-resolution synchrotron powder X-ray diffraction and lattice dynamic analyses shed light on the fact that NTE in the InOF-1 is a synergy effect of the spring-like distortion of the inorganic 1D helical chain and twisting of the BPTC ligands. The present work shows how the topological arrangement of building blocks governs the thermal expansion behaviors.

Development of a light-responsive fluorinated poly(arylene ether) copolymer containing azobenzene groups in the main polymer chain

A novel azo-based polymer with high mechanical and thermal stability is obtained. The polymer exhibits stable birefringence changes, enabling the fabrication of diffraction gratings, showing its potential for various optical applications.

Light-Triggered Enhancement of Fluorescence Efficiency in Organic Cages.

The fluorescence efficiency of excited molecules can be enhanced by many external factors. Here, we showcase a surprising phenomenon whereby light is used as a gating source to increase the fluorescence efficiency of organic cages composed of biphenyl subunits. We show that the enhancement of fluorescence is not due to structural changes or ground-state events. Cryo-fluorescence measurements and kinetic studies suggest a restriction of the phenyl-based structures in the excited state, leading to increased fluorescence, which is also supported by time-resolved measurements. Through computational calculations, we propose that the planarization of the biphenyl units within the cages contributes to emission enhancement. This phenomenon offers insights into the design of optoelectronic structures with improved fluorescence properties.

Mesomorphic, magnetic and DFT studies of biphenyl-based molecule with various substituted anilines

ABSTRACT A new series of liquid crystals consisting of biphenyl unit connected to phenyl core system have been successfully prepared wherein various substituents X= OCH3, F, Cl, Br and I were introduced in the para position of the imine fragment while the length of terminal alkoxy chain of seven carbon atoms was intact. The mesomorphic and thermal studies by POM and DSC exhibit dominant enantiotropic nematic (N) phase. A relatively weak magnetism was detected with vibrating sample magnetometer (VSM) for compounds 3F and 3I at room temperature, wherein the magnetic strength of fluoro-substituted compound appeared stronger than the iodo-substituted compound. The connectivity between the substituents X and their kinetic stability associated with the changes in HOMO-LUMO energy gap value (ΔEgap) supports that the terminal substituents X have great influence on the ΔEgap which can be ascribed to the chemical activity of the compounds. Present study shows an increase in the ΔEgap from OCH 3 < I < Br < Cl < F, where the largest ΔEgap indicates high molecular kinetic stability and low chemical reactivity because adding electrons to high-lying LUMO is energetically unfavourable, resulting in disruption of the molecular packing and reduction of nematogenic, which were validated by DSC and POM.

Towards an in-Depth Understanding of Single-Ion Conducting Polymer Electrolytes for Lithium-Metal Batteries

Recently, we have reported a new polyarylene-based single-ion conducting multi-block copolymer electrolyte providing very high ionic conductivities of about 1 mS cm-1 at ambient temperature and excellent cycling stability of LiNMC811 (LiNi0.8Mn0.1Co0.1O2) cells – even at 0 °C.1–3 Further improvement of this new electrolyte system, however, requires an in-depth understanding of ideally each single functional unit in the polymer.Herein, we present some of our latest results on the experimental and theoretical investigation of stepwise modified copolymers in order to decipher the impact of the different functional groups on the eventual mechanical, thermal, chemical, and electrochemical behavior. This stepwise modification includes, amongst others, the replacement of the biphenyl unit by a series of bisphenol derivatives and the variation of the ionophobic and ionophilic block. The former approach provides the unique opportunity to investigate the influence of the monomer substitution pattern, while the latter unveils some rather unexpected findings concerning the impact of the lithium concentration in the electrolyte. References H.-D. Nguyen et al., Energy Environ. Sci., 11, 3298–3309 (2018).D. Steinle et al., J. Solid State Electrochem., 26, 97–102 (2022).Z. Chen et al., Nano Energy, 77, 105129 (2020).

Interaction of telmisartan and related sartans with the programmed cell death-ligand 1 (PD-L1) protein dimer: a molecular docking analysis

BackgroundTelmisartan (TLT) is a prototypic angiotensin receptor blocker largely used to treat hypertension worldwide. In addition to its cardioprotective effects, TLT presents pleiotropic activities and notably displays noticeable anti-inflammatory and antitumor effects. The repression of the programmed cell death-1 (PD-1)/programmed death-ligand 1 (PD-L1) immune checkpoint may be implicated antitumor action of TLT, as it is the case with many other compounds equipped with a biphenyl moiety. We have used molecular modeling to compare the interaction of TLT and derivatives with the PD-L1 dimer protein.ResultsTwo molecules, TLT-dimer and TLT-acylglucuronide, were found to form more stable complexes with PD-L1 than TLT itself. In parallel, the docking analysis performed with a series of 12 sartans led to the identification of Olmesartan as a potential PD-L1 binder. The stacked biphenyl unit of Olmesartan positions the molecule along the groove delimited by the two protein monomers. The flanking tetrazole and imidazole moieties, on each side of the biphenyl unit of Olmesartan, contribute favorably to the protein interaction via specific hydrogen bonding interactions.ConclusionsThe computational analysis suggests a possible binding of Olmesartan to PD-L1 dimer and thus offers novel perspectives for the design of small molecules capable of interrupting the PD-1/PD-L1 immune checkpoint. Experimental studies are warranted to validate the hypothesis.Graphical abstract

Biphenylene-containing polycyclic conjugated compounds.

There has been a growing emphasis on the synthesis of polycyclic conjugated compounds, driven by their distinct structural characteristics that make them valuable candidates for use in cutting-edge technologies. In particular, acenes, a subgroup of polycyclic aromatic compounds, are sought-after synthetic targets due to their remarkable optoelectronic properties which stem from their π-conjugation and planar structure. Despite all these promising characteristics, acenes exhibit significant stability problems when their conjugation enhances. Various approaches have been developed to address this stability concern. Among these strategies, one involves the incorporation of the biphenylene unit into acene frameworks, limiting the electron delocalization through the antiaromatic four-membered ring. This review gives a brief overview of the methods used in the synthesis of biphenylenes and summarizes the recent studies on biphenylene-containing polycyclic conjugated compounds, elucidating their synthesis, and distinct optoelectronic properties.

Low dielectric constant and highly intrinsic thermal conductivity fluorine‐containing epoxy resins with ordered liquid crystal structures

AbstractEpoxy resins with a high dielectric constant and low intrinsic thermal conductivity coefficient cannot meet the current application requirements of advanced electronic and electrical equipment. Therefore, novel fluorine‐containing liquid crystal epoxy compounds (TFSAEy) with fluorinated groups, biphenyl units, and flexible alkyl chains are first synthesized via amidation and esterification reactions. Then, 4,4′‐diaminodiphenylmethane (DDM) is used as a curing agent to prepare the corresponding fluorine‐containing liquid crystal epoxy resins. The obtained dielectric constant (ε) and dielectric loss (tan δ) values of TFSAEy/DDM at 1 MHz are 2.54 and 0.025, respectively, which are significantly lower than those of conventional epoxy resins (E‐51/DDM, 3.52 and 0.038). Additionally, the intrinsic thermal conductivity coefficient (λ) of TFSAEy/DDM is 0.36 W/(m·K), 71.4% higher than that of E‐51/DDM (0.21 W/(m·K)). Meanwhile, the corresponding elastic modulus, hardness, glass transition temperature, and heat resistance index of TFSAEy/DDM are 5.73 GPa, 0.35 GPa, 213.5°C, and 188.7°C, respectively, all superior to those of E‐51/DDM (3.68 GPa, 0.27 GPa, 107.2°C, and 174.8°C), presenting potential application in high‐heating electronic component packaging and printed circuit boards.

Synthesis, characterization, mesogenic properties, and DFT studies of unsymmetrical liquid crystalline dimers of biphenyl

ABSTRACT A series of asymmetrical liquid crystal dimers (E)-4((4(n([1,1’-biphenyl]-4-yloxy)alkoxy)phenyl) diazenyl)benzonitrile (BpnCN) were synthesized, consisting of two distinct rigid cores: 4-cyanoazobenzene and biphenyl units. Characterization was accomplished through various spectroscopic techniques. The mesomorphic properties were explored via polarizing optical microscopy and differential scanning calorimetry. UV–Visible spectroscopy assessed the photophysical properties. The presence of an even number of atoms in the flexible spacer resulted in linear molecular shapes for Bp4CN and Bp6CN, while Bp3CN and Bp5CN showed nonlinearity, explaining their non-mesomorphic properties. Computational studies showed a clear correlation between theoretical and experimental wave numbers. The enhanced stability of the mesophase in Bp4CN and Bp6CN was attributed to their higher aspect ratios, promoting ordered structures within the material. UV–visible spectroscopy of dimer Bp4CN revealed absorption bands at 445 nm (n–π* transitions) and 365 nm (π–π* transitions), with photoisomerization observed under UV exposure, reaching a photostationary state in 2.5 min and reversible isomerization back to the trans form in approximately 2.3 h. Notably, even in the absence of substitutions on the biphenyl core, the dimers in our present series demonstrated an enantiotropic nematic mesophase.

Enabling Stereochemical Communication and Stimuli-Responsive Chiroptical Properties in Biphenyl-Capped Cyclodextrins.

Chiroptical materials are gaining increasing interest due to their innovative character and their applications in optoelectronics and data encryption technologies. Fully harnessing the potential of building blocks from the "chiral pool", such as native cyclodextrins (CDs), as they often lack chromophores suitable for the construction of materials with significant chiroptical properties. Here, we present the synthesis and characterization of a two-level molecular stack consisting of a point-chiral element (CD) and an axially chiral element (biphenyl), capable of effectively translating the overall stereochemical information contained in CDs into stimuli-responsive chiroptical properties. α- and β-permethylated CDs were efficiently capped with two different 2,2'-difunctionalized 1,1'-biphenyl units. In CD derivatives containing the rigid 2,2'-dihydroxy-1,1'-biphenyl cap, two intramolecular hydrogen bonds act synergistically as stereoselective actuators, enabling effective communication between the two levels and the transfer of nonchromophoric stereochemical information from the cyclic-oligosaccharide to the atropoisomeric cap. The chiroptical properties can be finely tuned by external stimuli such as temperature and solvent. The way chirality is transferred from the CD platform to the biphenyl cap was revealed thanks to crystallographic and computational analyses, together with electronic circular dichroism (ECD) studies.

Selective Construction of Borromean Rings andTweezer‐LikeMolecular Assembly Featuring Cp*Rh/Ir Clips forNear‐InfraredPhotothermal Conversion†

Comprehensive SummaryMaking full use of coordination‐driven self‐assembly strategy, we herein described the selective synthesis of a molecular Borromean rings and two cases of “U”‐shaped tweezer‐like molecular assemblies in high yield by using bipyridyl ligands based on biphenyl unit and half‐sandwich binuclear rhodium(III)/iridium(III) building blocks. The selective synthesis was realized by adjusting the length of dipyridyl arms. The utilization of curved U‐shaped bipyridyl ligandL1led to tweezer‐like molecular assemblies. Subsequently, olefinic bonds were introduced to elongate dipyridyl arms obtaining ligandL2. The ligandL2has two stable conformations, U‐shape and Z‐shape, which facilitated the formation of different topologies including the tetranuclear macrocycle and Borromean rings with different building blocks in this work. These structures in solid and solution all have been further confirmed by single‐crystal X‐ray diffraction, NMR analysis, and mass spectrometry. In addition, as an important driving force, π‐π stacking interactions not only played a significant role in the stability of structures but also further triggered photothermal conversion in solution. The experimental results demonstrated that compounds1aand2had good NIR photothermal conversion efficiency (11.83% and 17.76%), and further analysis found the photothermal conversion efficiency had a gradual increase in the trend with the π‐π stacking interactions increasing. This research expands the application of topological structures in materials science and provides a new idea for the synthesis of novel photothermal conversion materials.

Synthesis of UHMWPE by neutral phosphine-phenolate based nickel catalysts

It is highly interesting to prepare polyethylene with ultra-high molecular weight under homogeneous conditions by nickel based neutral P^O type catalysts. In this contribution, ligand remote electronic effect was explored in some sterically hindered phosphine-phenolate based neutral nickel catalysts Ni1–Ni3 to afford UHMWPE. The maximal activity of these catalysts was found to be 1.33 × 106 g mol−1 h−1, which is quite active. The nickel catalysts retained considerable activity at high temperature of 120 °C showing their good thermal stability. More importantly, all these catalysts are capable of generating UHMWPE with maximum Mn of 2.51 × 106 g mol−1 by Ni2. The minimum distance between the Ni center and the oxygen of the 2,6-dimethoxy-1,1′-biphenyl unit attached with the phosphorous atom in Ni1 was recorded as 3.154 Å, which exactly matches with the van der Waals radii of oxygen and nickel. This provides an effective shield around the metal by preventing chain transfer and resulting to enhance the molecular weight of polymer. Combined with steric the remote substituents effect also crucial both to modulate activity and molecular weight of polymers.

Synthesis and Characterization of Novel Wholly Aromatic Copolyesters Based on 4'-Hydroxybiphenyl-3-Carboxylic and 3-Hydroxybenzoic Acids.

A series of new wholly aromatic (co)polyesters based on m-substituted bifunctional comonomers-4'-hydroxybiphenyl-3-carboxylic (3HBCA) and 3-hydroxybenzoic (3HBA) acids with molar ratios of 3HBCA:3HBA from 0:100 to 60:40, respectively-was synthesized. NMR and FTIR spectroscopy methods proved the full compliance of the copolymer composition with the target ratio of comonomers, as well as high compositional homogeneity (absence of block sequences). The resulting copolyesters have a sufficiently high molecular weight and their intrinsic viscosity values are in the range of 0.6-0.8 dL/g. Thermal analysis showed that all 3HBCA-3HBA copolyesters are amorphous, and with an increase in the content of biphenyl units (3HBCA), the glass transition temperature increases significantly (up to 190 °C). The onset of the intense thermal decomposition of the synthesized polyesters occurs above 450 °C. Thus, this indicates a sufficiently high thermal stability of these polyesters. Rheological measurements have shown that melts of copolyesters with a high content of 3HBCA units exhibit anisotropic properties. At the same time, the method of polarization optical microscopy did not confirm the transition to the liquid crystal state for these polyesters. These results confirm that it is possible to obtain high-performance polyesters based on 3HBCA, but not a mesogenic comonomer. Thus, 3HBCA is a promising comonomer for the synthesis of new thermotropic copolyesters with controlled anisotropic properties.

Tuning Intermolecular Singlet Fission Efficiencies of Perylenediimide Derivatives through Bay Aromatic Substitution†

Comprehensive SummarySinglet fission (SF) has potential applications in high‐efficiency photo‐energy harvesting applications, but its practical application is hindered by the limited number of materials. In this work, we explored the bay aromatic substitution strategy for the design of new perylenediimide (PDI) based SF materials. A series of PDI derivatives with biphenyl or naphthalene units substituted at the bay positions were designed and synthesized to investigate the effects of aromatic substitutes on their photodynamic behaviours. The bay substitutions do not shift the energy level of the PDI core significantly but give rise to different intermolecular coupling strengths in the thin films and affect the intermolecular SF efficiency. Femtosecond transient absorption (fsTA) spectroscopy reveals that appropriate spacing configuration from the bay aromatic substitution groups enhances the SF yields by promoting the interaction of neighbouring PDI cores. Triplet exciton yields of up to 183% have been obtained from these new PDI derivatives, making them potential candidates in future SF‐based optoelectronics.