Bipyridine Units Research Articles

Individually Tunable Energy Levels of Oligomers Based on N-B←N Units.

Opto-electronic properties and device performance of organic semiconductors are mainly determined by energy levels of their frontier molecular orbitals, e.g. lowest unoccupied molecular orbital (ELUMO) and highest occupied molecular orbital (EHOMO) in the ground state, first singlet state (ES1) and first triplet state (ET1) in the excited state. These energy levels are always intricately intertwined. Herein, we report a series of monodisperse oligomers based on double B←N bridged bipyridine (BNBP) units. With the increasing number of repeating units, the oligomers exhibit gradually downshifted ELUMO and nearly unchanged EHOMO due to the different distribution of the frontier molecular orbitals of the oligomers. Moreover, the oligomers exhibit gradually decreasing ES1 and nearly unchanged ET1 because of the different contributions of the charge transfer component in the excited state. This work provides new insight into energy level tuning of organic semiconductors, which is important for high-performance organic opto-electronic devices.

Individually Tunable Energy Levels of Oligomers Based on N−B←N Units

AbstractOpto‐electronic properties and device performance of organic semiconductors are mainly determined by energy levels of their frontier molecular orbitals, e.g. lowest unoccupied molecular orbital (ELUMO) and highest occupied molecular orbital (EHOMO) in the ground state, first singlet state (ES1) and first triplet state (ET1) in the excited state. These energy levels are always intricately intertwined. Herein, we report a series of monodisperse oligomers based on double B←N bridged bipyridine (BNBP) units. With the increasing number of repeating units, the oligomers exhibit gradually downshifted ELUMO and nearly unchanged EHOMO due to the different distribution of the frontier molecular orbitals of the oligomers. Moreover, the oligomers exhibit gradually decreasing ES1 and nearly unchanged ET1 because of the different contributions of the charge transfer component in the excited state. This work provides new insight into energy level tuning of organic semiconductors, which is important for high‐performance organic opto‐electronic devices.

Synthesis, Structure, and Properties of Nontrivial Iridium(III) Complexes Based on Anthracene-Decorated Benzimidazole Ligand.

Reactions of iridium trichloride hydrate with bulky 2-(9-anthracenyl)-1-phenyl-benzimidazole (anbi) in the presence of N-donor ligands afforded a number of unique noncyclometalated complexes, while attempts to prepare a common μ-chloro-bridged bis-cyclometalated dimer systematically gave a monocyclometalated complex cis-[Ir(C,N-anbi)(N-anbi)Cl2] instead. The obtained complexes were characterized by 1H NMR, high-resolution mass spectrometry, single-crystal and powder X-ray diffraction, UV-vis spectroscopy, and cyclic voltammetry. The noncyclometalated complexes fac-[Ir(N-anbi)(N^N)Cl3)], where N^N are 4,4'-disubstituted 2,2'-bipyridines, are octahedral and contain the anthracene and 2,2'-bipyridine units in a close cofacial arrangement. These complexes were found to be exceptionally inert to the chloride ligand exchange even in the presence of silver triflate, forming a rare trinuclear Ir-μ-Cl3-Ag-μ-Cl3-Ir structure instead. In the monocyclometalated complex, the Ir(III) ion is pentacoordinated in a rare square-pyramidal geometry, where the bulky anthracene fragment is involved in the steric shielding of the metal center. This is in line with the results of gas-phase density functional theory calculations, demonstrating that the experimentally observed structure is energetically most preferable. The monocyclometalated complex is deeply colored due to intense charge-transfer absorption bands in the range 450-650 nm with ε = 2000-5000 M-1 cm-1, superior to the noncyclometalated complexes. The synthesis, structures, and properties of the new complexes are discussed in the context of the related mono-, bis-, and noncyclometalated iridium(III) compounds.

Synthesis and luminescent properties of five-six-membered bis(metallacyclic) platinum(II) complexes bearing polypyridine alkynes

A series of five-six-membered bis(metallacyclic) Pt(II) complexes bearing a 2,2′-bipyridine (BPY) or 2,2′:6′,2"-terpyridine (TPY) ethynyl ligand were synthesized and characterized. The structures of N^C*N-coordinated Pt(II) complexes (−)-1 and (−)-5 were confirmed by single crystal X-ray diffraction, displaying a slightly distorted square-planar coordination environment around the Pt(II) centers. Compared to N^N*C-coordinated Pt(II) derivatives ((−)-2, (−)-4 and (−)-6), N^C*N-coordinated complexes ((−)-1, (−)-3 and (−)-5) demonstrate a more significant AIE property with a sharp luminescence variation in response to water content. In addition, due to the existence of the pendent BPY or TPY unit, N^C*N-coordinated Pt(II) complexes show a luminescence response to Zn2+ ions. Cytotoxicity and cell imaging of luminescent five-six-membered bis(metallacyclic) Pt(II) complexes with polypyridine alkynes have been evaluated.

Double-bridged N–B←N bipyridyl-based airfoil-shaped small molecule dyes: π-bridge regulation on photovoltaic performance

The double-bridged N–B←N bipyridine unit (BNBP) with boron-nitrogen covalent bond and coordination bond can reduce the electronic energy level of the π-conjugated system, resulting in a reduction of band gap and a red shift in the absorption spectrum. Embedding the BNBP building block into organic optoelectronic materials provides a novel possibility in molecule design. In this paper, under the guidance of density functional theory (DFT) calculations, a series of 3D “airfoil-shaped” small molecule donors (SMDs) have been designed and successfully synthesized through Sonogashira, Suzuki and Stille coupling reactions. BNBP is adopted as the central electron-withdrawing unit and strong electron-rich triphenylamine (TPA) as the terminal group. The novel “airfoil-shaped” structure plays a supporting role in reducing the carrier recombination in the active layer. It reveals that molecular design engineering can achieve the expected results by the following steps: Firstly, the introduction of electron-rich alkoxy groups into the end of TPA through side chain engineering helps to improve the solubility and film-forming properties of the materials. Then, the π-bridge regulation not only extends the conjugate structure, but also plays a crucial role in the regulation of photovoltaic properties. It is worth noting that the compound BNBP(3TTPA)2 was synthesized by introducing thiophene oligomer into BNBP-based SMDs for the first time. Finally, the compound BNBP(EDPPTPA)2 was constructed by combining BNBP with DPP dye unit. Its narrow band gap is only 1.36 eV, which is one of the narrowest band gaps in small molecular organic-boron materials. In particular, compared with the starting compound BNBP(ETPA)2, the synergistic effects of DPP and BNBP broaden the edge absorption wavelength to 814 nm, resulting in a red shift of 170 nm. The power conversion efficiency (PCE) of 4.48 % is obtained in BNBP(EDPPTPA)2-based bulk heterojunction (BHJ) organic solar cells (OSCs), which is more than twice that of reference compound BNBP(ETPA)2. This work provides important references for the future development of 3D BNBP-based organic-boron SMDs and the structural regulation of materials through molecular engineering.

Pyridine-Based Covalent Organic Frameworks with Pyridyl-Imine Structures for Boosting Photocatalytic H2O2 Production via One-Step 2e- Oxygen Reduction.

Bipyridine-based covalent organic frameworks (COFs) have emerged as promising contenders for the photocatalytic generation of hydrogen peroxide (H2O2). However, the presence of imine nitrogen alters the mode of H2O2 generation from an efficient one-step two-electron (2e-) route to a two-step 2e- oxygen reduction pathway. In this work, we introduce 3,3'-bipyridine units into imine-based COF skeletons, creating a pyridyl-imine structure with two adjacent nitrogen atoms between the pyridine ring and imine linkage. This unique bipyridine-like architecture can effectively suppress the two-step 2e- ORR process at the single imine-nitrogen site, facilitating a more efficient one-step 2e- pathway. Consequently, the optimized pyridyl-imine COF (PyIm-COF) exhibits a remarkable H2O2 production rate of up to 5850 μmol h-1 g-1, nearly double that of pristine bipyridine COFs. This work provides valuable insight into the rational design of functionalized COFs for enhanced H2O2 production in photocatalysis.

Pyridine‐Based Covalent Organic Frameworks with Pyridyl‐Imine Structures for Boosting Photocatalytic H2O2 Production via One‐Step 2e− Oxygen Reduction

AbstractBipyridine‐based covalent organic frameworks (COFs) have emerged as promising contenders for the photocatalytic generation of hydrogen peroxide (H2O2). However, the presence of imine nitrogen alters the mode of H2O2 generation from an efficient one‐step two‐electron (2e−) route to a two‐step 2e− oxygen reduction pathway. In this work, we introduce 3,3′‐bipyridine units into imine‐based COF skeletons, creating a pyridyl‐imine structure with two adjacent nitrogen atoms between the pyridine ring and imine linkage. This unique bipyridine‐like architecture can effectively suppress the two‐step 2e− ORR process at the single imine‐nitrogen site, facilitating a more efficient one‐step 2e− pathway. Consequently, the optimized pyridyl‐imine COF (PyIm‐COF) exhibits a remarkable H2O2 production rate of up to 5850 μmol h−1 g−1, nearly double that of pristine bipyridine COFs. This work provides valuable insight into the rational design of functionalized COFs for enhanced H2O2 production in photocatalysis.

Highly Red Emissive Conjugated Homopolymers Based on Double B←N Bridged Bipyridine Unit

Highly Red Emissive Conjugated Homopolymers Based on Double B←N Bridged Bipyridine Unit

Triazine-COF@Silicon nanowire mimicking plant leaf to enhance photoelectrocatalytic CO2 reduction to C2+ chemicals

Triazine-COF@Silicon nanowire mimicking plant leaf to enhance photoelectrocatalytic CO2 reduction to C2+ chemicals

A two-dimensional coordination polymer bearing an Evans-Showell-type polyoxometalate: Synthesis, structure and biological insight†

An Evans-Showell-type polyoxometalate (POM) based coordination polymer (CP), [H2(Co2Mo10H4O38)2(Co3(L)3(HL)2(H2O)6)(HL)2]·14H2O (1), {L = 4,4′-bipyridine}, was synthesized under hydrothermal conditions and structurally characterized by infrared spectroscopy (IR), elemental analysis, powder X-ray diffraction (PXRD), diffuse reflectance spectroscopy (DRS) and single crystal X-ray diffraction methods. In 1, two [Co2Mo10H4O38]6− POMs are joined together via two Co-O interactions to form a dimer which is centrosymmetric. Here, the dimers act as repeating units and are expanded by another crystallographically independent Co ion in the structure. Binding of the cations to the O atoms of the POM and the N atoms of organic ligand resulted in the formation of a 2D CP structure. Compound 1 is the first example of an inorganic-organic polymer architecture constructed from Evans-Showell-type POM in which Co cations act as metal nodes. The topology of 1 can be rationalized as a 2D square lattice (sql) coordination network with point symbol {44.62} in which [Co2Mo10H4O38]6− and 4,4′-bipyridine units act as linkers and the Co cations as nodes. The cytotoxicity effects of the POM were evaluated on the cancer CT26 and normal L929 cell lines by an MTT assay from which an IC50 value of cancer CT26 cells of approximately 366 ppm was obtained, but normal L929 cells did not show significant toxicity.

Europium(III) Functionalized Covalent Organic Framework as Sensitive and Selective Fluorescent Switch for Detection of Uranium.

Uranium poses severe health risks due to its radioactivity and chemical toxicity if released into the environment. Therefore, there is an urgent demand to develop sensing materials in situ monitoring of uranium with high sensitivity and stability. In this work, a fluorescent Eu3+-TFPB-Bpy is synthesized by grafting Eu3+ cation onto TFPB-Bpy covalent organic framework (COF) synthesized through Schiff base condensation of monomers 1,3,5-tris(4-formylphenyl)benzene (TFPB) and 5,5'-diamino-2,2'-bipyridine (Bpy). The fluorescence of Eu3+-TFPB-Bpy is enhanced compared with that of TFPB-Bpy, which is originated from the intramolecular rotations of building blocks limited by the bipyridine units of TFPB-Bpy coordinated with Eu3+. More significantly, Eu3+-TFPB-Bpy is a highly efficient probe for sensing UO22+ in aqueous solution with the luminescence intensity efficiently amplified by complexation of UO22+ with Eu3+. The turn-on sensing capability was derived from the resonance energy transfer occurring from UO22+ to the Eu3+-TFPB-Bpy. The developed probe displayed desirable linear range from 5 nM to 5 μM with good selectivity and rapid response time (2 s) for UO22+ in mining wastewater. This strategy provides a vivid illustration for designing luminescence lanthanide COF hybrid materials with applications in environmental monitoring.

Preparation of a ruthenium complex covalently bonded to multilayer graphene and its evaluation as a photocatalyst.

Multilayer graphene (MLG), obtained by mild sonication of graphite in NMP, was functionalised via 1,3-dipolar cycloaddition with azomethine ylides generated by thermal 1,2-prototropy from various imino esters. The microwave-assisted functionalisation took place in five hours at 100 °C. The resulting MLG, containing substituted proline-based amine functional groups, was characterized using XPS and showed a nitrogen loading three times that obtained for the same transformation performed for five days using convection-assisted heating. The preparation of the imino ester containing a bipyridine unit at the arylidene position allowed for the preparation of the corresponding functionalised MLG, which incorporated the ruthenium atom to achieve a heterogeneous MLG-Ru complex. This supported complex was tested, as a proof of concept, as a photocatalyst of the aerobic oxidative hydroxylation of 4-methoxyphenylboronic acid.

Bipyridine-based conjugated microporous polymers for boosted photocatalytic U(VI) separation.

Incorporating bipyridine units into the matrix of conjugated microporous polymers (CMPs) boosts exciton dissociation, charge separation, and oxidation capacity. Consequently, the bipyridine-modified CMPs exhibit an impressive U(VI) separation rate (404 μmol g-1 h-1) under sacrificial agent-free conditions, outperforming the results of its counterparts without bipyridine units and other documented CMPs.

Donor-acceptor moiety functionalized covalent organic frameworks for boosting charge separation and H2 photogeneration

Covalent organic frameworks (COFs) have a broad prospect to be used as a photocatalytic platform to convert solar energy into valuable chemicals due to their tunable structures and rich active catalytic sites. However, constructing COFs with tuned sp2-carbon donor-acceptor moiety remains an enormous challenge. Herein, we synthesized two new fully π-conjugated cyano-ethylene-linked COFs containing benzotrithiophene as functional group by Knoevenagel polycondensation reaction. The accetpor 2,2′-bipyridine unit in BTT-BpyDAN-COF skeleton favored the formation of a intermolecular specific electron transport pathway with the donor benzotrithiophene, and thereby promoted charge separation and transfer efficiency. Specifically, a donor-acceptor (D-A) type BTT-BpyDAN-COF exhibited high hydrogen evolution rate of 10.1 mmol g-1h−1 and an excellent apparent quantum efficiency of 4.83 % under visible light irradiation.

A fully conjugated imidazole-fused perylene phenantroline ruthenium(II) complex in photocatalytic oxidation

In this investigation, the suitability of a specially designed imidazole-fused perylene ruthenium(II) molecule, denoted as Ru-PhP, was explored by employing the photooxidation of 1,5-dihydroxynaphthalene (DHN) to produce Juglone as a model reaction. This distinctive, entirely conjugated compound was synthesized through the reaction between perylene imide anhydride dye (1) and a ruthenium(II) phenanthroline complex (2) in the presence of a Zn(OAc)2 catalyst. Structural analyses of the compound were performed by using general spectroscopic methods including FT-IR, 1H NMR, 13C- NMR, and MALDI-TOF analyses. Various photophysical properties, including the UV–Vis absorption spectrum, fluorescence emission spectrum, and fluorescence quantum yield, were examined. The photochemical studies via indirect method endorsed Ru-PhP as an efficient photosensitizer. Furthermore, Ru-PhP proved to be highly effective in facilitating the photooxidation of DHN to yield juglone. DFT-based natural bond orbital analysis revealed intramolecular charge transfer in Ru(II) coordination environment, with a strong total stabilization energy (25.31 eV) between the ruthenium acceptor and nitrogen donors in the bipyridine and phenanthroline units. The dispersion of HOMO electrons within the imidazole-bridged perylene moiety and the localization of LUMO electrons near Ru(II)-coordinated bipyridine units were observed through Frontier Molecular Orbital and molecular electrostatic potential analyses. Ru-PhP is proposed as photocatalyst for photo redox catalytic organic reactions.

Synthesis and Metal‐Complexation of a Trimer of Dendrimers with Bipyridine Cores in the Center of Conjugated Chains

AbstractTwo types of dendrimers with a bipyridine unit in the center of their rigid backbones were prepared. One dendrimer has two azide groups and the other has one ethynyl terminal. These dendrimers were coupled by the copper‐mediated Hüisgen 1,3‐dipolar cycloadditions of the ethynyl and azide terminals to afford a trimer with three bipyridine cores. The addition of Fe(II) to a solution of the trimer resulted in an absorption change characteristic of the formation of tris(bipyridine)Fe(II) complexes. The structural properties of the tris(bipyridine)Fe(II) core are likely reflected in the conformation of the timer because the bipyridine units are attached to the rigid backbones.

Self-healing luminescent polyurethane with ultrahigh toughness resulting from lanthanide-bipyridine segment and hydrogen bonds

Synthesis and manufacturing a new generation of luminescent elastomers that simultaneously features self-healing efficiency with superior mechanical properties remains a challenge due to the compromise between toughness and self-healing ability. Here, a new class of transparent luminescent materials was synthesized via coordinating lanthanide (Ln3+) to bipyridine (Bpy) units introduced into the polymer backbone prepared by polymerization of Polytetramethylene ether glycol (PTMEG) and 4-methylenedicyclohexyl diisocyanate (HMDI). Relying on collaborative reinforcement of a great number of loosely packed Ln3+-ligand coordination bonds and hydrogen bonds (H-bonds), the prepared luminescent polymers showed an ultrahigh toughness of 373.12 MJ m−3 and a mechanical ultrahigh strength of 33.73 MPa. In addition, the multi-color emission behavior of the luminescent materials can be simply adjusted via tailoring the molar ratio of Eu3+/Tb3+. The luminescent self-healing materials can reversibly respond to acid-base vapor because of protonation/deprotonation of Bpy ligands. We believe luminescent polymers obtained by us with excellent mechanical properties and luminescence off/on switching ability show great potential applications as acid-base detector.

Site Engineering of Covalent Organic Frameworks for Regulating Peroxymonosulfate Activation to Generate Singlet Oxygen with 100 % Selectivity

AbstractSinglet oxygen (1O2) is an excellent reactive oxygen species (ROSs) for the selective conversion of organic matter, especially in advanced oxidation processes (AOPs). However, due to the huge dilemma in synthesizing single‐site type catalysts, the control and regulation of 1O2 generation in AOPs is still challenging and the underlying mechanism remains largely obscure. Here, taking advantage of the well‐defined and flexibly tunable sites of covalent organic frameworks (COFs), we report the first achievement in precisely regulating ROSs generation in peroxymonosulfate (PMS)‐based AOPs by site engineering of COFs. Remarkably, COFs with bipyridine units (BPY‐COFs) facilitate PMS activation via a nonradical pathway with 100 % 1O2, whereas biphenyl‐based COFs (BPD‐COFs) with almost identical structures activate PMS to produce radicals (⋅OH and SO4⋅−). The BPY‐COFs/PMS system delivers boosted performance for selective degradation of target pollutants from water, which is ca. 9.4 times that of its BPD‐COFs counterpart, surpassing most reported PMS‐based AOPs systems. Mechanism analysis indicated that highly electronegative pyridine‐N atoms on BPY‐COFs provide extra sites to adsorb the terminal H atoms of PMS, resulting in simultaneous adsorption of O and H atoms of PMS on one pyridine ring, which facilitates the cleavage of its S−O bond to generate 1O2.

Site Engineering of Covalent Organic Frameworks for Regulating Peroxymonosulfate Activation to Generate Singlet Oxygen with 100% Selectivity.

Singlet oxygen (1O2) is an excellent reactive oxygen species (ROSs) for the selective conversion of organic matter, especially in advanced oxidation processes (AOPs). However, due to the huge dilemma in synthesizing single-site type catalysts, the control and regulation of 1O2 generation in AOPs is still challenging and the underlying mechanism remains largely obscure. Here, taking advantage of the well-defined and flexibly tunable sites of covalent organic frameworks (COFs), we report the first achievement in precisely regulating ROSs generation in peroxymonosulfate (PMS)-based AOPs by site engineering of COFs. Remarkably, COFs with bipyridine units (BPY-COFs) facilitate PMS activation via a nonradical pathway with 100% 1O2, whereas biphenyl-based COFs (BPD-COFs) with almost identical structures activate PMS to produce radicals (•OH and SO4•-). The BPY-COFs/PMS system delivers boosted performance for selective degradation of target pollutants from water, which is ca. 9.4 times that of its BPD-COFs counterpart, surpassing most reported PMS-based AOPs systems. Mechanism analysis indicated that highly electronegative pyridine-N atoms on BPY-COFs provide extra sites to adsorb the terminal H atom of PMS, resulting in simultaneous adsorption of O and H atoms of PMS on one pyridine ring, which facilitates the cleavage of its S-O bond to generate 1O2.

2,2’‐Bipyridine‐Derived Cobalt‐Based Porous Coordination Polymers for Selective Degradation of Anionic Dyes

Abstract2,2’‐Bipyridine‐derived two chelating linkers containing two and three bipyridine units were synthesized and characterized. Solvothermal condensation of these linkers with Co(NO3)2.6H2O generated cobalt‐based porous coordination polymers (Co‐PCPs). The scanning electron microscopy studies revealed the macroporous nature of the Co‐PCPs, with the highest surface area achieved up to 441.1 m2 g−1. The Co‐PCPs were found to be effective catalysts in the degradation of the anionic dyes, methyl orange (MO) and orange 2 (OII), in the presence of sodium borohydride. Also, the synthesized PCPs were found to selectively catalyse the degradation of anionic dyes from a mixture of dyes (~99 % degradation in 55 min). Regeneration studies showed that the PCPs could be regenerated and reused for more than five cycles with ~98 % retention of degradation efficiency and are promising materials for the selective degradation of anionic dyes from wastewater.