Design, Synthesis, and Study of Main Chain Poly(N-Heterocyclic Carbene) Complexes: Applications in Electrochromic Devices

Phototriggered color modulation of perovskite nanoparticles for high density optical data storage

The perovskite nanocrystals-dichloromethane (PNCs-DCM) with tunable fluorescent color under UV light are a new kind of photoresponsive luminescent materials (PLMs), which are qualified to apply in optical data storage.

Computational investigations of NHC-backbone configurations for applications in organocatalytic umpolung reactions

Density functional theory (DFT) and multiconfigurational self-consistent field theory (MCSCF) methods are employed to investigate variation of the electronic properties of various N-heterocyclic carbenes. Alterations to the backbone by increased or decreased conjugation, heteroatom substitution in the NHC ring, and electron-donating or -withdrawing backbone substituents are modeled. The MCSCF calculations show extensive delocalization of both the highest occupied and lowest unoccupied molecular orbitals for NHCs with polymerizable backbone substituents. The free energies of the intermediates and transition structures for benzoin condensation are also shown to be sensitive to substitution of the NHC backbone. Taken together, these results imply great sensitivity of the reactivity of poly(NHC) catalysts to backbone modification at this moiety. Implications with respect to enhancement of poly(NHC)s employed in umpolung catalysis are discussed.

Imidazole and Benzimidazole Modified Half-Sandwich IridiumIII N-Heterocyclic Carbene Complexes: Synthesis, Anticancer Application, and Organelle Targeting

Herein, we report the synthesis, characterization and anticancer activity of a series of half-sandwich iridium^III imidazole and benzimidazole N-heterocyclic carbene (NHC) anticancer complexes, and the general formula of which can be expressed as [(η⁵-Cp^x)Ir(C^∧N)Cl]Cl (Cp^x: pentamethylcyclopentadienyl (Cp^*) or biphenyl derivatives (Cp^xbiph); C^∧N: imidazole and benzimidazole NHC chelating ligands). Compared with cis-platin, these complexes showed interesting antitumor activity against A549 cells. Complexes could bind to bovine serum albumin (BSA) by means of static quenching mode, catalyze the oxidation of nicotinamide adenine dinucleotide (NADH) and increase the levels of reactive oxygen species (ROS). Meanwhile, these complexes could arrest the cell cycles of A549 cells and influence the mitochondrial membrane potential significantly. Due to the inherent luminescence property, laser confocal test show that complexes could enter cells followed an energy-dependent mechanism and effectively accumulate in lysosome (the value of Pearson's co-localization coefficient is 0.70 after 1 h), further destroy lysosome integrity and induce apoptosis.

Electropolymerizable N-heterocyclic carbene complexes of Rh and Ir with enantiotropic polymorphic phases

New Rh (1) and Ir (2) complexes of an N-heterocyclic carbene (NHC) featuring a terthiophene backbone were synthesized. Single crystal X-ray diffraction studies of 1 and 2 at 100 K and 298 K respectively, revealed two enantiotropic polymorphic phases with similar lattice parameters for each compound. The transition temperature between two crystalline forms for each compound was determined by measuring the percentage of reflections with a different space group ranging from 100 K to 298 K. Both 1 and 2 were also found to catalyze the hydrogen transfer reaction. The conducting metallopolymers poly-1 and poly-2 were synthesized from oxidative electropolymerization of 1 and 2, respectively, in CH₂Cl₂ electrolyte solution on indium tin oxide-(ITO) coated glass. The electrochromic properties of synthesized conducting metallopolymers were studied by UV-vis-NIR spectroelectrochemistry.

Synthesis and electropolymerization of N-heterocyclic carbene complexes of Pd(ii) and Pt(ii) from an emissive imidazolium salt with a terthiophene backbone

The synthesis of an emissive terthiophene-based imidazolium iodide: 1,3-dimethyl-4,6-di(thiophen-2-yl)-thienoimidazol-3-ium iodide (4), the corresponding N-heterocyclic carbene (NHC) preligand, and Pd and Pt-NHC complexes (5a, 5b) are reported. A related Pd-NHC complex (8) with a mono-thiophene backbone has also been synthesized. The solid-state structures were determined by single crystal X-ray diffraction studies. Compounds 4, 5a and 5b were characterized by absorption/emission spectroscopy and an emission-quench phenomenon of 5a was observed. The Pd complexes 5a and 8 were shown to catalyze Heck type C-C bond forming reactions. The compounds with terthiophene backbones (4, 5a, 5b) were electropolymerized onto indium tin oxide (ITO)-coated glass electrodes to yield thin films of conducting metallopolymers (CMPs) (P1-3). UV-vis-NIR spectroelectrochemistry data of P1-3 showed reversible color changes upon oxidation due to the generation of charge carrier species along the polythiophene backbones.

Di-μ-acetato-bis{[3-benzyl-1-(2,4,6-trimethylphenyl)imidazol-2-ylidene]silver(I)}

The title compound, [Ag2(C2H3O2)2(C19H20N2)2] (2), was readily synthesized by treatment of 3-benzyl-1-(2,4,6-trimethylphenyl)imidazolium chloride with silver acetate. The solution structure of the complex was analyzed by NMR spectroscopy, while the solid-state structure was confirmed by single-crystal X-ray diffraction studies. Compound 2 crystallizes in the triclinic space group P 1 ¯ , with a silver-to-carbene bond length (Ag-CNHC) of 2.084 (3) Å. The molecule resides on an inversion center, so that only half of the molecule is crystallographically unique. The planes defined by the two imidazole rings are parallel to each other, but not coplanar [interplanar distance is 0.662 (19) Å]. The dihedral angles between the imidazole ring and the benzyl and mesityl rings are 77.87 (12) and 72.86 (11)°, respectively. The crystal structure features π-π stacking interactions between the benzylic groups of inversion-related (-x + 1, -y + 1, -z + 1) molecules and C-H ⋯ π interactions.

N-Heterocyclic Carbenes in Materials Chemistry

N-Heterocyclic carbenes (NHCs) have become one of the most widely studied class of ligands in molecular chemistry and have found applications in fields as varied as catalysis, the stabilization of reactive molecular fragments, and biochemistry. More recently, NHCs have found applications in materials chemistry and have allowed for the functionalization of surfaces, polymers, nanoparticles, and discrete, well-defined clusters. In this review, we provide an in-depth look at recent advances in the use of NHCs for the development of functional materials.

Bridged cyclometalated diruthenium complexes for fundamental electron transfer studies and multi-stage redox switching

Four bridged cyclometalated diruthenium systems are highlighted in this Frontier article, including strongly-coupled diruthenium complexes with a short phen-1,4-diyl or a planar pyren-2,7-diyl bridge, redox asymmetric diruthenium complexes characterized by different terminal ligands on the two ends, diruthenium complexes with a urea bridge that allows modulating the degree of electronic coupling, and those with a redox-active amine bridge with varying electronic structures. These complexes posess redox couples with low potentials and intense intervalence charge transfer absorptions in the near-infrared region in the one-electron-oxidized mixed-valent state. They are appealing not only for providing a platform for fundamental electron transfer studies but also as molecular materials with multi-stage redox switching properties.

A Thiophene-Containing Conductive Metallopolymer Using an Fe(II) Bis(terpyridine) Core for Electrochromic Materials

Three Fe(II) bis(terpyridine)-based complexes with thiophene (Fe(L1)₂), bithiophene (Fe(L2)₂), and 3,4-ethylenedioxythiophene (Fe(L3)₂) side chains were designed and synthesized for the purpose of providing two terminal active sites for electrochemical polymerization. The corresponding metallopolymers (poly-Fe(Ln)₂, n = 2 or 3) were synthesized on indium tin oxide (ITO)-coated glass substrates via oxidative electropolymerization of the thiophene-substituted monomers and characterized using electrochemistry, X-ray photoelectron spectroscopy, UV-vis spectroscopy, and atomic force microscopy. The film poly-Fe(L2)₂ was further studied for electrochromic (EC) color-switching properties and fabricated into a solid-state EC device. Poly-Fe(L2)₂ films exhibit an intense MLCT absorption band at 596 nm (ε = 4.7 × 10⁴ M^-1 cm^-1) in the UV-vis spectra without any applied voltage. Upon application of low potentials (between 1.1 and 0.4 V vs Fc⁺/Fc), the obtained electropolymerized film exhibited great contrast with a change of transmittance percentage (ΔT%) of 40% and a high coloration efficiency of 3823 cm² C^-1 with a switching time of 1 s. The film demonstrates commonplace stability and reversibility with a 10% loss in peak current intensity after 200 cyclic voltammetry cycles and almost no loss in change of transmittance (ΔT%) after 900 potential switches between 1.1 and 0.4 V (vs Fc⁺/Fc) with a time interval of 0.75 s. The electropolymerization of Fe(L2)₂ provides convenient and controllable film fabrication. Electrochromic behavior was also achieved in a solid-state device composed of a poly-Fe(L2)₂ film and a polymer-supported electrolyte sandwiched between two ITO-coated glass electrodes.

Cross-Linkable Fluorene-Diphenylamine Derivatives for Electrochromic Applications

Multicolor electrochromic systems based on heat cross-linkable arylamine-substituted fluorene derivatives, FD and FDOMe, are reported. These derivatives with pendant vinyl groups have been synthesized by the Buchwald-Hartwig amination reaction and were well-characterized using various analytical and spectroscopic techniques such as NMR, ESI-MS, and single-crystal X-ray diffraction analysis. FD and FDOMe exhibited thermally activated cross-linking above their melting temperatures, which was confirmed through absorption, differential scanning calorimetry (DSC), FT-IR, and wide-angle X-ray diffraction (WAXD) techniques. Cross-linked FD films (FD-X) on ITO showed two reversible redox peaks at 0.74 and 0.91 V (versus Ag/AgCl) that correspond to the formation of radical cations and dications, respectively. The corresponding redox peaks were observed at 0.6 and 0.8 V for cross-linked FDOMe films (FDOMe-X). Spectroelectrochemical studies of the electrochromic films on ITO revealed multicolor electrochromism of FD-X (colorless-yellow-dark cyan) and FDOMe-X (colorless-brick red-blue) with a color contrast of ∼44% at 485 nm for FD-X and ∼63% at 500 nm for FDOMe-X and good switching stability between the neutral and oxidized states (>300 cycles) with low switching voltages (<0.9 V for the first oxidation and <1.3 V for the second oxidation). Furthermore, fabrication of electrochromic devices using FD-X and FDOMe-X on FTO substrate with PMMA-based solid electrolyte was demonstrated, where the devices exhibited reasonably low switching time between the redox states (<30 s) with good optical contrast.

Three-state near-infrared electrochromism at the molecular scale

Self-assembled monolayer films of a cyclometalated ruthenium complex with a redox-active amine substituent and three carboxylic acid groups have been prepared on ITO electrode surfaces. The obtained thin films show three-state electrochromic switching with low electrochemical potential inputs and high near-infrared absorbance outputs. Thanks to the long retention time of each oxidation states, these films have been used to demonstrate surface-confined flip-flop memory functions with high ON/OFF ratios at the molecular scale.

Tuning of resistive memory switching in electropolymerized metallopolymeric films

A diruthenium complex capped with two triphenylamine units was polymerized by electrochemical oxidation to afford metallopolymeric films with alternating diruthenium and tetraphenylbenzidine structures. The obtained thin films feature rich redox processes associated with the reduction of the bridging ligands (tetra(pyrid-2-yl)pyrazine) and the oxidation of the tetraphenylbenzidine and diruthenium segments. The sandwiched ITO/polymer film/Al electrical devices show excellent resistive memory switching with a low operational voltage, large ON/OFF current ratio (100-1000), good stability (500 cycles tested), and long retention time. In stark contrast, devices with polymeric films of a related monoruthenium complex show poor memory performance. The mechanism of the field-induced conductivity of the diruthenium polymer film is rationalized by the formation of a charge transfer state, as supported by DFT calculations.

Organometallic polymers for electrode decoration in sensing applications

Macromolecules containing metals combine the processing advantages of polymers with the functionality offered by the metal centers. The developments in the area of electrochemical chemo/biosensors based on organometallic polymers are reviewed.

Synthesis and electronic properties of N-heterocyclic carbene-containing conducting polymers with coinage metals

A series of bithiophene based N-heterocyclic carbene (NHC) conducting polymers containing coinage metals (Cu, Ag, and Au) was designed and characterized.

Smart responsive phosphorescent materials for data recording and security protection

Smart luminescent materials that are responsive to external stimuli have received considerable interest. Here we report ionic iridium (III) complexes simultaneously exhibiting mechanochromic, vapochromic and electrochromic phosphorescence. These complexes share the same phosphorescent iridium (III) cation with a N-H moiety in the N^N ligand and contain different anions, including hexafluorophosphate, tetrafluoroborate, iodide, bromide and chloride. The anionic counterions cause a variation in the emission colours of the complexes from yellow to green by forming hydrogen bonds with the N-H proton. The electronic effect of the N-H moiety is sensitive towards mechanical grinding, solvent vapour and electric field, resulting in mechanochromic, vapochromic and electrochromic phosphorescence. On the basis of these findings, we construct a data-recording device and demonstrate data encryption and decryption via fluorescence lifetime imaging and time-gated luminescence imaging techniques. Our results suggest that rationally designed phosphorescent complexes may be promising candidates for advanced data recording and security protection.

A phosphenium cation supported by a seven-membered thiophene based ring system

A novel diamine ligand containing a simple thiophene ring in the backbone has been synthesized. Substitution at the nitrogen atoms with either 2,4,6-trimethylphenyl (Mes) or 2,6-diisopropylphenyl (Dipp) was varied via a condensation reaction between the corresponding aniline and 3,4-diformylthiophene, giving two different ligand derivatives. In onwards chemistry that targeted the cyclic diaminochlorophosphines, the substitution at phosphorus was dependent on the ligand used. For example, when a stoichiometric reaction between PCl3 and thiophene-3,4 diyldimethaneamine (R = Mes) was carried out, the synthesis of a bis-substituted diphosphino- product was isolated. If the R = Dipp ligand derivative was employed, both a 2:1 and 1:1 stoichiometric reaction between PCl3 and the diamine was observed. Nevertheless, the cyclic diaminochlorophosphine (i.e., 1:1 stoichiometry) for R = Dipp was isolated in high yields and the synthesis of the corresponding phosphenium cation was achieved and structurally characterized.