Trivalent Titanium Salen Complex: Thermally Robust and Highly Active Catalyst for Copolymerization of CO₂ and Cyclohexene Oxide

A trivalent titanium complex combining salen ligand (salen-H₂<i>N,N</i>-bis­(3,5-di-<i>tert</i>-butylsalicylidene)-1,2-benzenediamine) was synthesized as catalyst for copolymerization of CO₂ and cyclohexene (CHO). In combination with onium salt [PPN]­Cl, (Salen)­Ti­(III)Cl showed impressive activity and selectivity, yielding completely alternating copolymer without the formation of cyclohexene carbonate (CHC), with turnover frequency (TOF) of 557 h^–1 at 120 °C, which was more than 10 times higher than that of our previously reported (Salalen)­Ti­(IV)­Cl, and close to the Cr counterparts. In addition to the biocompatibility of Ti, thermally robust character resulting from the reducibility of trivalent Ti was industrially desirable

Reversible Sol–Gel Transition of Oligo(<i>p</i>‑phenylenevinylene)s by π–π Stacking and Dissociation

Methyl sulfide terminated <i>trans</i>-oligo­(<i>p</i>-phenylenevinylene) derivatives (<b>OPV</b><i><b>n</b></i>, <i><b>n</b></i> is the number of phenyl rings) were synthesized, and reversible sol–gel transition was observed in a variety of organic solvents. Investigations with UV–vis, fluorescence, and ¹H NMR spectroscopy revealed that aromatic π–π stacking and van der Waals forces were important in the formation of the gels, with the former being the main driving force for sol–gel transition. The π-conjugation length showed a key influence on self-assembly and gelation property: the gel-to-sol transition temperature (<i>T</i>_gel) increased with π-conjugation length. The gels of <b>OPV4–7</b> can self-assemble into one-dimensional fibers with different sizes and shapes, depending on their π-conjugation length. On the basis of X-ray diffraction measurements and spectroscopic data, a self-assembly model was proposed. Our observation may be useful for designing functional π-gelators based on π–π stacking

Enhancing Molecular Conductance of Oligo(<i>p</i>‑phenylene ethynylene)s by Incorporating Ferrocene into Their Backbones

Designing and preparing the molecular wires with good charge transport performance is of crucial importance to the development of molecular electronics. By incorporating ferrocene into molecular backbones, we successfully enhanced the molecular conductance of OPEs in both tunneling and hopping conduction regimes. Furthermore, we found that the increase degree of molecular conductance in the hopping regime is much more than that in the tunneling regime. Via this approach, the molecular conductance of a long molecule exceeds the molecular conductance of a short one at room temperature. A theoretical calculation provided a possible and preliminary explanation for these novel phenomena in terms of molecular electronic structures. The current work opens the opportunity for designing excellent charge transport performance molecules. An increasing number of new types of molecular wires with this unusual phenomenon are expected to be discovered in the future

White Electroluminescence from All-Phosphorescent Single Polymers on a Fluorinated Poly(arylene ether phosphine oxide) Backbone Simultaneously Grafted with Blue and Yellow Phosphors

On the basis of a fluorinated poly­(arylene ether phosphine oxide) backbone with both high triplet energy and appropriate HOMO/LUMO levels, highly efficient all-phosphorescent single white-emitting polymers were designed and successfully synthesized via a “two-step addition” strategy. Simultaneous blue and yellow triplet emissions were achieved to generate white electroluminescence with a promising luminous efficiency as high as 18.4 cd/A (8.5 lm/W, 7.1%) and CIE coordinates of (0.31, 0.43)

Blue Thermally Activated Delayed Fluorescence Polymers with Nonconjugated Backbone and Through-Space Charge Transfer Effect

We demonstrate novel molecular design for thermally activated delayed fluorescence (TADF) polymers based on a nonconjugated polyethylene backbone with through-space charge transfer effect between pendant electron donor (D) and acceptor (A) units. Different from conventional conjugated D–A polymers with through-bond charge transfer effect, the nonconjugated architecture avoids direct conjugation between D and A units, enabling blue emission. Meanwhile, spatial π–π interaction between the physically separated D and A units results in both small singlet–triplet energy splitting (0.019 eV) and high photoluminescence quantum yield (up to 60% in film state). The resulting polymer with 5 mol % acceptor unit gives efficient blue electroluminescence with Commission Internationale de l’Eclairage coordinates of (0.176, 0.269), together with a high external quantum efficiency of 12.1% and low efficiency roll-off of 4.9% (at 1000 cd m^–2), which represents the first example of blue TADF nonconjugated polymer

Controlled Synthesis of Polyfluorenes via Kumada Catalyst Transfer Polycondensation with Ni(acac)₂/dppp as the Catalyst

A new catalyst system, i.e., nickel acetylacetonate/1,3-bis­(diphenylphosphino)­propane (Ni­(acac)₂/dppp), was explored to catalyze the Kumada catalyst transfer polycondensation (KCTP) of three fluorene monomers with different substituents at 9-position. The “living” nature of the polymerization was confirmed by polymerization kinetic studies, “monomer addition” experiment and block copolymerizations. As a result, poly­(9,9-dioctylfluorene)­s (PF8s) with the number-average molecular weights (<i>M</i>_ns) in the range 2.8–62.2 kDa and polydispersity indices (PDIs) of ∼1.20 were successfully synthesized in a controlled manner. The syntheses of fluorene-fluorene and fluorene-thiophene diblock copolymers with <i>M</i>_ns up to 46 kDa were also demonstrated. A complex, i.e. Ni­(dppp)­(acac)₂, with an octahedral coordination geometry was isolated and confirmed by X-ray crystallographic analysis. The polymerization experiments indicated that the in situ formed Ni­(dppp)­(acac)₂ should be the active catalyst. To the best of our knowledge, this is the first report on the controlled synthesis of polyfluorenes (PFs) via KCTP

Water Dispersed Conducting Polyaniline Nanofibers for High-Capacity Rechargeable Lithium–Oxygen Battery

Water dispersed conducting polyaniline nanofibers doped with phosphate ester have been synthesized and characterized by scanning electron microscopy (SEM), wide-angled X-ray diffraction (WAXD), X-ray photoelectron spectroscopy (XPS), UV–visible spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. Next, a systematic and careful electrochemical test was carried out to deeply investigate their potential application for lithium–oxygen battery. The experimental result showed us that this low cost and easily produced material could catalyze the discharge reaction independently, and after an initial degradation from 3260 to 2320 mAh/g PANI during the first three cycles at current density of 0.05 mA/cm², its discharge capacity kept relatively stable in the next 27 cycles with only a 4% loss, which may provide a new choice for fabrication of high-capacity rechargeable lithium–oxygen battery for practical application

Poly(spirobifluorene)s Containing Nonconjugated Diphenylsulfone Moiety: Toward Blue Emission Through a Weak Charge Transfer Effect

Instead of conjugated dibenzothiophene-<i>S,S</i>-dioxide (DBTSO), we have introduced nonconjugated diphenylsulfone (DPSO) as the electron-deficient unit into the main chain of poly­(spirobifluorene)­s (PSFs). Because of the weaker electron affinity of DPSO relative to DBTSO, the charge transfer from the pendant 2,3,6,7-tetraoctyloxyfluorene to the main chain can be effectively prevented. Consequently, the resultant polymers containing DPSO moiety show pure blue emissions, which is different from DBTSO-based PSFs that exhibit undesired green emissions. With a single-layer device configuration, a peak luminous efficiency of 2.90 cd/A and a maximum luminescence of 14130 cd/m² have been realized for the polymer PSFDPSO03. The corresponding CIE coordinates are (0.17, 0.18), nearly independent of the applied current density from 2 to 592 mA/cm². These results indicate that tuning the electron affinity of the incorporated electron-deficient units is a very promising strategy to control the charge transfer strength for the development of blue-emitting PSFs with high efficiency and stability

Self-Host Blue-Emitting Iridium Dendrimer Containing Bipolar Dendrons for Nondoped Electrophosphorescent Devices with Superior High-Brightness Performance

A novel self-host blue-emitting iridium dendrimer, namely, <b>B-CzPO</b>, has been designed and synthesized via a postdendronization route, where a bipolar carbazole/triphenylphosphine oxide hybrid is selected as the peripheral dendron instead of the p-type oligocarbazole used in unipolar analogue <b>B-CzG2</b>. This structural modification can render <b>B-CzPO</b> with more balanced charge transportation relative to that of <b>B-CzG2</b>. As a result of the significantly reduced efficiency roll-off, the nondoped phosphorescent organic light-emitting diodes (PhOLEDs) of <b>B-CzPO</b> show a superior high-brightness performance, revealing a luminous efficiency of 21.2, 16.1, and 10.5 cd/A at 1000, 5000, and 10 000 cd/m², respectively. Compared with that of <b>B-CzG2</b> (i.e., 7.8 cd/A @5000 cd/m²), more than doubled high-brightness performance is achieved for <b>B-CzPO</b>. The results indicate that the design of self-host phosphorescent dendrimers with a bipolar feature will be a promising strategy to develop efficient nondoped PhOLEDs suitable for high-brightness applications including general illumination and micro displays

Asymmetric Conjugated Molecules Based on [1]Benzothieno[3,2‑<i>b</i>][1]benzothiophene for High-Mobility Organic Thin-Film Transistors: Influence of Alkyl Chain Length

Herein, we report the synthesis and characterization of a series of [1]­benzothieno­[3,2-<i>b</i>]­[1]­benzothiophene (BTBT)-based asymmetric conjugated molecules, that is, 2-(5-alkylthiophen-2-yl)[1]­benzothieno­[3,2-<i>b</i>]­[1]­benzothiophene (BTBT-T<i>n</i>, in which T and <i>n</i> represent thiophene and the number of carbons in the alkyl group, respectively). All of the molecules with <i>n</i> ≥ 4 show mesomorphism and display smectic A, smectic B (<i>n</i> = 4), or smectic E (<i>n</i> > 4) phases and then crystalline phases in succession upon cooling from the isotropic state. Alkyl chain length has a noticeable influence on the microstructures of vacuum-deposited films and therefore on the performance of the organic thin-film transistors (OTFTs). All molecules except for 2-(thiophen-2-yl)[1]­benzothieno­[3,2-<i>b</i>]­[1]­benzothiophene and 2-(5-ethylthiophen-2-yl)[1]­benzothieno­[3,2-<i>b</i>]­[1]­benzothiophene showed OTFT mobilities above 5 cm² V^–1 s^–1. 2-(5-Hexylthiophen-2-yl)[1]­benzothieno­[3,2-<i>b</i>]­[1]­benzothiophene and 2-(5-heptylthiophen-2-yl)[1]­benzothieno­[3,2-<i>b</i>]­[1]­benzothiophene showed the greatest OTFT performance with reliable hole mobilities (μ) up to 10.5 cm² V^–1 s^–1 because they formed highly ordered and homogeneous films with diminished grain boundaries