Synthesis, Structures, and Aggregation-Induced Emission Properties of Distyrylbenzene Derivatives Containing Fluorine Groups.

Distyrylbenzene derivatives with substituents on the vinylene moieties have been studied due to interest in their optoelectronic properties. In this study, we focused on distyrylbenzene derivatives with monofluoroolefin structures, expecting intermolecular H-F interactions in the solid state. UV-vis and fluorescence spectra of the obtained compounds were measured and compared with those of unsubstituted distyrylbenzene. The crystal structures of each compound were determined by single crystal X-ray diffraction and Hirshfeld surface analysis to understand the intermolecular contacts.

Parallel synthesis of donor-acceptor π-conjugated polymers by post-element transformation of organotitanium polymer.

The donor-acceptor type π-conjugated polymers having heterole units were prepared by the reaction of a regioregular organometallic polymer having both reactive titanacyclopentadiene and electron-donor thiophene-2,5-diyl units in the main chain with electrophiles such as diphenyltin dichloride, dichlorophenylphosphine, and diiodophenylarsine. For example, a polymer having electron-accepting phosphole unit was obtained in 54% yield whose number-average molecular weight (Mn) and molecular weight distribution (Mw/Mn) were estimated as 3,000 and 1.9, respectively. The obtained polymer exhibits a high highest occupied molecular orbital (HOMO) and low lowest unoccupied molecular orbital (LUMO) energy levels (-5.13 eV and -3.25 eV, respectively) due to the electron-donating thiophene and electron-accepting phosphole units. Reflecting upon the alternating structure of thiophene and phosphole, the polymer exhibits a band gap energy level (Eg) of 1.78 eV which is narrower than that of a derivative of poly(thiophene) (Eg = 2.25 eV).

Site-Selective Synthesis and Concurrent Immobilization of Imine-Based Covalent Organic Frameworks on Electrodes Using an Electrogenerated Acid.

Imine-based covalent organic frameworks (COFs) are crystalline porous materials with prospective uses in various devices. However, general bulk synthetic methods usually produce COFs as powders that are insoluble in most of the common organic solvents, arising challenges for the subsequent molding and fixing of these materials on substrates. Here, we report a novel synthetic methodology that utilizes an electrogenerated acid (EGA), which is produced at an electrode surface by electrochemical oxidation of a suitable precursor, acting as an effective Brønsted acid catalyst for imine bond formation from the corresponding amine and aldehyde monomers. Simultaneously, it provides the corresponding COF film deposited on the electrode surface. The COF structures obtained with this method exhibited high crystallinities and porosities, and the film thickness could be controlled. Furthermore, such process was applied for the synthesis of various imine-based COFs, including a three-dimensional (3D) COF structure.

Synthesis of Cationic Azatriphenylene Derivatives by Electrochemical Intramolecular Pyridination and Characterization of Their Optoelectronic Properties.

Here, a facile and selective synthesis method for cationic azatriphenylene derivatives was established by electrochemical intramolecular cyclization, where atom-economical C-H pyridination without a transition-metal catalyst or an oxidant is a key step. The proposed protocol is a practical strategy for the late-stage introduction of cationic nitrogen (N+) into π-electron systems and broadens the scope of molecular design of N+-doped polycyclic aromatic hydrocarbons.

AC-Bipolar Electropolymerization of 3,4-Ethylenedioxythiophene in Ionic Liquids.

Recently, alternating current (AC)-bipolar electropolymerization of 3,4-ethylenedioxythiophene (EDOT) has been reported to produce poly(3,4-ethylenedioxythiophene) (PEDOT) fibers from the terminals of bipolar electrodes in acetonitrile solution (MeCN) containing low concentrations of supporting salts in a template-free manner. Here, we extend such methodology in ionic liquid (IL) media. Three kinds of ILs, diethylmethyl(2-methoxyethyl)ammonium tetrafluoroborate ([DEME][BF4]), 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), and diethylmethyl(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl)imide ([DEME][TFSI]), with different electric field transmission efficiencies and diffusion coefficients were employed as solvents for the AC-bipolar electropolymerization of EDOT. A variety of PEDOT morphologies were obtained in these three ILs, showing a relationship with the physicochemical properties of the ILs. We successfully confirmed the growth of PEDOT fibers in ILs and systematically discussed the factors that influenced their growth.

Electropolymerization without an electric power supply.

Electrifying synthesis is now a common slogan among synthetic chemists. In addition to the conventional two- or three-electrode systems that use batch-type cells, recent progress in organic electrochemical processes has been significant, including microflow electrochemical reactors, Li-ion battery-like technology, and bipolar electrochemistry. Herein we demonstrate an advanced electrosynthesis method without the application of electric power based on the concept of streaming potential-driven bipolar electrochemistry. As a proof-of-concept study, the electrochemical oxidative polymerization of aromatic monomers successfully yielded the corresponding polymer films on an electrode surface, which acted as an anode under the flow of electrolyte in a microchannel without an electric power supply.

Alkali Metal Fluorides in Fluorinated Alcohols: Fundamental Properties and Applications to Electrochemical Fluorination.

Fundamental properties of alkali metal fluorides (MF, M = Cs, K) dissolved in 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) or in 3,3,3-trifluoroethanol (TFE) are investigated, including solubility, conductivity, and viscosity. Solid-state structures of single crystals obtained from CsF/HFIP and CsF/TFE are described for the first time, giving insights into the multiple interactions between fluorinated alcohols and CsF. Applications in electrochemical fluorination reactions are successfully demonstrated.

Pillar[6]quinone: facile synthesis, crystal structures and electrochemical properties.

A novel electron-deficient macrocycle, pillar[6]quinone (P[Q]6), has been synthesized for the first time by both chemical and electrochemical oxidation of pillar[6]arene, showing clear hexagonal columnar stacking in the solid state. Cathodic voltammetric studies of P[Q]6 revealed that three electrons are injected first, followed by stepwise one-electron reductions.

Fabrication of Gradient and Patterned Organic Thin Films by Bipolar Electrolytic Micelle Disruption Using Redox-Active Surfactants.

Bipolar electrochemistry could be regarded as a powerful approach for selective surface modification due to the beneficial feature that a wirelessly controllable potential distribution on bipolar electrodes (BPEs). Herein we report a bipolar electrolytic micelle disruption (BEMD) system for the preparation of shaped organic films. A U-shaped bipolar electrolytic system with a sigmoidal potential gradient on the BPE gave gradient-thin films including various interesting organic compounds, such as a polymerizable monomer, an organic pigment and aggregation induced emission (AIE) molecules. The gradient feature was characterized by UV-Vis absorption, thickness measurements and surface morphology analysis. Corresponding patterned films were also fabricated using a cylindrical bipolar electrolytic setup that enables site-selective application of the potential on the BPE. Such a facile BEMD approach will open a long-term perspective with respect to organic film preparation.

An air-stable organometallic polymer containing titanafluorene moieties obtained by the Sonogashira-Hagihara cross-coupling polycondensation.

The synthesis of a polymer containing alternating titanafluorene and arylene ethynylene moieties is described. The polymerization of a 2,7-dibromo-9-titanafluorene derivative with 1,4-dioctyloxy-2,5-diethynylbenzene is carried out at 70 °C for 48 h in tetrahydrofuran (THF) in the presence of palladium dichloride/4,5-bis(diphenylphosphino)-9,9-dimethylxanthene as a catalyst and diisopropylamine as a base to produce a dark red polymer. The polymer thus obtained is soluble in organic solvents and stable towards both air and moisture. In the UV-vis absorption spectrum of the polymer, the absorption maxima (λmax) are observed at 321 nm and 395 nm, which are bathochromically shifted compared to those of a model compound of the repeating unit, a 2,7-bis(phenylethynyl)titanafluorene derivative (λmax = 309 nm and 364 nm). The optical band gap (Eg) of the polymer is estimated to be 2.8 eV on the basis of the absorption onset, which is narrower than that of the model compound (3.1 eV).

Bis(pentafluorophenyl)-o-carborane and its arylthio derivatives: synthesis, electrochemistry and optical properties.

Synthesis of 1,2-bis(pentafluorophenyl)-o-carborane and its arylthio-derivatives is reported. The regioselective arylthiolation was successfully achieved via nucleophilic aromatic substitution (SNAr) reaction. A series of bis(perfluoroaryl)-o-carboranes with various para-substituents showed strong multicolor emission in the solid-state (Φf up to 47%), suggesting an aggregation-induced emission (AIE) character in this motif.

Fluoride-Ion-Catalyzed Synthesis of Ladder-type Conjugated Benzobisbenzofurans via Intramolecular Nucleophilic Aromatic Substitution Reaction under Metal-free and Mild Conditions.

The fluoride-ion-catalyzed synthesis of benzobisbenzofuran derivatives is described. Fluorine-containing aryl silyl ethers were reacted with 5 mol % of Bu4NF to give desired compounds in high yield under mild conditions. Syn-selective cyclization reaction was discovered for a particular compound as a kinetic product. Computational analysis revealed that the fluorine substituents in the anti-type benzobisbenzofurans affect the order of the molecular orbitals.

Postfunctionalization of a Perfluoroarene-Containing π-Conjugated Polymer via Nucleophilic Aromatic Substitution Reaction.

Postfunctionalization is a useful strategy to tune the properties of conjugated polymers, while polymer reactions in the main chain of a conjugated backbone are still underexplored. Here we report the postfunctionalization of the main chain of a conjugated polymer via nucleophilic aromatic substitution reaction. Poly(9,9-dioctylfluorene-alt-tetrafluoro-p-phenylene) is used as a precursor to react with thiophenol derivatives in the presence of a base to enable multiple introduction of arylthio groups into the polymer main chain in high yield with preserving the backbone and the dispersity of the precursor polymer. The main chain structure and optoelectronic properties of the resulting polymers were significantly changed, evidenced by spectroscopic analysis of both model compounds and polymers as well as a computational simulation.

Te-Li Exchange Reaction of Tellurophene-Containing π-Conjugated Polymer as Potential Synthetic Tool for Functional π-Conjugated Polymers.

On the basis of the facts that tellurophene-containing π-conjugated polymers are obtainable from organotitanium polymers and that the tellurium atoms in the tellurophene derivatives can be transformed into lithium atoms, the synthesis of reactive lithiated polymer precursor and its transformations into some functionalized π-conjugated polymers are described. A regioregular organometallic polymer having 1,4-dilithio-1,3-butadiene and 9,9-dioctylfluorene-2,7-diyl units is generated by the reaction of a tellurophene-containing polymer having the number-average molecular weight (Mn ) and molecular weight distribution (Mw /Mn ) of 5890 and 1.9, respectively, with n-butyllithium (2.4 equiv.) at -78 °C to -60 °C for 3 h. The lithiated polymer thus prepared is subjected to reactions with electrophiles to produce functionalized π-conjugated polymers. For example, a π-conjugated polymer possessing 1,4-bis(tri-n-butylstannyl)-1,3-butadiene-1,4-diyl unit is obtained in 67% yield by the reaction with tri-n-butyltin chloride (2.4 equiv.) at -60 °C to ambient temperature for 12 h in tetrahydrofuran, whose Mn and Mw /Mn are estimated as 7320 and 2.5, respectively, by size exclusion chromatography. The absorption maximum and onset of the obtained polymer are observed at 380 and 465 nm, respectively, in the UV-vis spectrum, from which the optical band gap of the polymer is estimated as 2.67 eV.

Synthesis of Stannole-Containing π-Conjugated Polymers by Post-Element Transformation of Organotitanium Polymer.

The synthesis of stannole-2,5-diyl-containing π-conjugated polymers by the post-element transformation of a regioregular organotitanium polymer is described. For example, a 1,1-diphenylstannole-containing polymer is obtained in 83% yield by the reaction of a regioregular organotitanium polymer, which is prepared from 1,4-bis(2-ethylhexyloxy)-2,5-diethynylbenzene and a low-valent titanium complex with diphenyltin dichloride at -50 °C to ambient temperature. The number-average molecular weight and molecular weight distribution (Mn and Mw /Mn ) of the stannole-containing polymer are estimated as 4800 and 1.8, respectively. The obtained polymer is found to have the extended π-conjugated backbone and relatively low-lying lowest unoccupied molecular orbital (LUMO) energy level (-3.12 eV), which is supported by its UV-vis absorption spectrum and cyclic voltammetric (CV) analysis. In addition, the stannole-containing polymer is found to be applicable to a chemosensor for fluoride anion where the color and photoluminescence intensity of the polymer solution exhibits a distinct change in the presence of a fluoride anion.

Templated bipolar electrolysis for fabrication of robust Co and Pt nanorods.

The migration of metal ions into a nanoporous electrode was controlled using an electrophoretic effect under the influence of an external electric field based on the concept of bipolar electrochemistry. Robust, uniform and well-aligned arrays of Co and Pt nanorods were observed to form vertically against the electrode.

Synthesis of Poly(3,4-ethylenedioxythiophene)-Platinum and Poly(3,4-ethylenedioxythiophene)-Poly(styrenesulfonate) Hybrid Fibers by Alternating Current Bipolar Electropolymerization.

Alternating current (ac) bipolar electropolymerization of 3,4-ethylenedioxythiophene (EDOT) was performed in the presence of hexachloroplatinate ([PtCl6]2-) or poly(styrenesulfonate) (PSS). We demonstrated that both [PtCl6]2- and PSS were successfully incorporated into electrogenerated poly(3,4-ethylenedioxythiophene) (PEDOT) as dopants to offer hybrid fibers composed of (i) PEDOT and platinum nanoparticles (PtNPs) (PEDOT-Pt hybrid fibers) and (ii) PEDOT and PSS (PEDOT-PSS hybrid fibers), respectively, in one step, grown from the very edges of Au wires used as bipolar electrodes (BPEs).

Buoyant force-induced continuous floating and sinking of Janus micromotors.

A novel bubble-induced ultrafast floating and sinking of micromotors based on the difference between buoyant force and gravity is proposed. Asymmetric micromotors were prepared by modification with Au and Pt layers for the two faces of glassy carbon beads (GCBs) by the bipolar electrodeposition technique. After the accumulation of enough oxygen bubbles by the decomposition of H2O2 at the Pt layer, the upward net force acting on the micromotor drove its movement to the air/solution interface. In order to reverse the direction of net force for the sinking of the micromotors, sodium dodecyl sulfate (SDS) was added into the fuel solution, which could facilitate the release of bubbles and decrease the diameter of the bubbles. However, the lifetime of the bubbles was increased significantly. After the addition of a small amount of salt, the lifetime of the bubbles was obviously reduced. As a consequence, the breakup of bubbles on the micromotor changed the direction of the net force from up to down which pulled the micromotor down to the bottom of the solution. The velocity of the micromotor was dependent on the net force exerted on the micromotor, leading to an ultrafast motion of the micromotor. It still reached 1.2 cm s-1 after 3 h. Moreover, the simple asymmetric deposition technique showed great promise for the further application of the micromotors in bioanalysis and environmental remediation.

In-Plane Growth of Poly(3,4-ethylenedioxythiophene) Films on a Substrate Surface by Bipolar Electropolymerization.

Alternating current (AC) bipolar electropolymerization of 3,4-ethylenedioxythiophene (EDOT) using a gold (Au) wire as a bipolar electrode (BPE) on a substrate surface resulted in gradual growth of the corresponding poly(3,4-ethylenedioxythiophene) (PEDOT) thin film from the terminals of the Au wire on the substrate. Studies to clarify the polymerization behavior were conducted under various electrolytic conditions, including monomer concentration, applied frequency, monomer structure, and substrate material. This method could be used to draw conducting polymer films on a nonconductive substrate, guided by an applied external electric field, and thus has potential for circuit patterning in organic electronic devices.

The controlled synthesis of pillar[6]arene-based hexagonal cylindrical structures on an electrode surface via electrochemical oxidation.

Electrochemical oxidation of pillar[6]arene containing six hydroquinones resulted in the formation of hexagonal cylindrical structures on an electrode surface driven by charge transfer interaction. The electrochemical approach successfully controlled the size and shape of the structures.