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

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

Donor–Acceptor Conjugated Polymers with Dithienocarbazoles as Donor Units: Effect of Structure on Semiconducting Properties

A series of donor–acceptor (D–A) conjugated polymers (CPs) comprising dithieno­[2,3-<i>b</i>;7,6-<i>b</i>]­carbazole (<b>C1</b>) or dithieno­[3,2-<i>b</i>;6,7-<i>b</i>]­carbazole (<b>C2</b>) as D unit and thienopyrroledione (<b>TPD</b>), isoindigo (<b>IID</b>), or diketopyrrolopyrrole (<b>DPP</b>) as A unit were synthesized, and their semiconducting properties were investigated with organic field-effect transistors (OFETs). Because of different bonding geometry of <b>C1</b> and <b>C2</b>, the CPs based on these isomeric D units have distinct backbone conformation. The CPs based on <b>C1</b> unit and all three A units show strong backbone curvature. In consequence, these polymers all formed amorphous films and exhibited low OFET mobility in the level of 10^–3 cm²/(V s). <b>P­(TPD-C2)</b> and <b>P­(DPP-C2)</b>, which comprise <b>C2</b> and <b>TPD</b> or <b>DPP</b>, both display pseudo-straight-shaped backbones and formed ordered films with the polymer backbones adopting edge-on orientation respective to the substrates. Accordingly, <b>P­(TPD-C2)</b> and <b>P­(DPP-C2)</b> exhibited the highest mobility of 0.31 and 1.36 cm²/(V s), respectively. However, <b>P­(IID-C2)</b> could only form amorphous films probably owing to its highly stiff backbone, leading to a moderate OFET mobility (2.96 × 10^–2 cm²/(V s)). This implies that large fused aromatics are promising building blocks for high-mobility D–A CPs when polymer backbone conformation and rigidity are appropriately manipulated

Low-Band-Gap Conjugated Polymers of Dithieno[2,3‑<i>b</i>:7,6‑<i>b</i>]carbazole and Diketopyrrolopyrrole: Effect of the Alkyl Side Chain on Photovoltaic Properties

Four donor–acceptor (D–A) conjugated polymers of dithieno­[2,3-<i>b</i>;7,6-<i>b</i>]­carbazole (DTC) and diketopyrrolopyrrole, which have different alkyls on the nitrogen atom in the DTC unit and are named as <b>P-C8C8</b>, <b>P-C5C5</b>, <b>P-C12</b>, and <b>P-C10</b>, respectively, have been synthesized for studying the effect of the alkyl side chains on the optoelectronic properties of the polymers. All polymers are soluble in various organic solvents and exhibit identical optical band gaps (<i>E</i>_g^opt) of ∼1.3 eV and highest occupied molecular orbital energy levels of ∼−5.1 eV. Organic thin-film transistors and bulk heterojunction polymer solar cells (BHJ PSCs) with phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) as the electron-accepting material were fabricated via solution spin-casting. Compared to the polymers substituted by branched alkyl chains, the polymers with straight alkyl chains show higher hole mobility. Of these polymers, <b>P-C10</b> exhibits the highest field effect mobility up to 0.011 cm²/V·s. The alkyl chain on the DTC unit has a strong impact on the film morphology of polymer:PC₇₁BM blends. Severe phase separation was found for polymers containing branched alkyl chains, and those with straight alkyl chains formed uniform films featuring fine phase separation. An open-circuit voltage (<i>V</i>_oc) of 0.72 V, a short-circuit current density (<i>J</i>_sc) of 13.4 mA/cm², a fill factor (FF) of 62%, and a power conversion efficiency (PCE) of 5.9% were demonstrated for BHJ PSCs based on the <b>P-C10</b>:PC₇₁BM [1:3 (w/w)] blend film

Donor–Acceptor Conjugated Polymers Based on Indacenodithiophene Derivative Bridged Diketopyrrolopyrroles: Synthesis and Semiconducting Properties

Two indacenodithiophene derivative bridged diketopyrrolopyrroles (DPP), i.e., 2,7-bis­(2,5-bis­(2-decyl­tetradecyl)-3,6-dioxo-4-(thiophen-2-yl)-2,3,5,6-tetrahydro­pyrrolo­[3,4-<i>c</i>]­pyrrol-1-yl)-<i>s</i>-indaceno­[1,2-<i>b</i>:5,6-<i>b</i>′]­dithiophene-4,9-dione (DDPP-PhCO) and 2,2′-(2,7-bis­(2,5-bis­(2-decyl­tetradecyl)-3,6-dioxo-4-(thiophen-2-yl)-2,3,5,6-tetrahydro­pyrrolo­[3,4-<i>c</i>]­pyrrol-1-yl)-<i>s</i>-indaceno­[1,2-<i>b</i>:5,6-<i>b</i>′]­dithiophene-4,9-diylidene)­dimalononitrile (DDPP-PhCN), were developed via intramolecular Friedel–Crafts acylation and Knoevenagel condensation. A series of donor–acceptor (D–A) conjugated polymers were synthesized by Stille or direct arylation polycondensation with these two novel units as acceptors and vinyl or thiophene derivatives as donors. The polymers with DDPP-PhCO as acceptor unit exhibited optical bandgaps (<i>E</i>_g^opt) of ca. 1.2 eV and the highest occupied molecular orbital (HOMO) energy levels of ∼−5.3 eV with the difference less than 0.1 eV, and their lowest unoccupied molecular orbital (LUMO) levels were in the range of −3.73 to −3.91 eV. The polymer based on DDPP-PhCN showed similar HOMO level (−5.29 eV) but remarkably lower LUMO level (−4.21 eV). Top-gate/bottom-contact (TGBC) organic field-effect transistors (OFETs) of all the polymers exhibited ambipolar transport behavior with the highest hole mobility (μ_h) and electron mobility (μ_e) up to 1.09 and 0.44 cm² V^–1 s^–1, respectively, in air. Owing to their favorable molecular orientation and frontier molecular orbital distribution, the polymers based on DDPP-PhCO displayed much higher hole and electron mobilities than that based on DDPP-PhCN

Donor–Acceptor Conjugated Polymers Based on Dithieno[3,2‑<i>b</i>:3′,2′‑<i>b</i>′]naphtho[1,2‑<i>b</i>:5,6‑<i>b</i>′]dithiophene: Synthesis and Semiconducting Properties

A polycyclic aromatic unit comprising six rings, i.e., 5,11-bis­(2-octyl­dodecyl)­dithieno­[3,2-<i>b</i>:3′,2′-<i>b</i>′]­naphtho­[1,2-<i>b</i>:5,6-<i>b</i>′]­dithiophene (DTNDT), was developed. Four donor–acceptor (D–A) conjugated polymers, which are named <b>P-BT</b>, <b>P-2FBT</b>, <b>P-IID</b>, and <b>P-DPP</b>, were synthesized with DTNDT as the D-unit and 2,1,3-benzo­thiadiazole (BT), 5,6-difluoro­benzo­[<i>c</i>]­[1,2,5]­thiadiazole (2FBT), isoindigo (IID), and diketo­pyrrolo­pyrrole (DPP) as the A-unit, respectively. All four polymers are thermally stable with decomposition temperature above 390 °C and show pseudo-straight-shaped backbones. Their ordered thin films were prepared via solution spin-casting, in which conjugated backbones mainly adopted edge-on alignment on the substrate. The semiconducting properties of the polymers were characterized with bottom gate and top contact (BGTC) organic thin film transistors (OTFTs). All four polymers showed p-type transport behavior, and the hole mobilities were 0.023, 0.078, 0.50, and 1.80 cm²/(V s) for <b>P-BT</b>, <b>P-2FBT</b>, <b>P-IID</b>, and <b>P-DPP</b>, respectively. <b>P-DPP</b> exhibited the highest film order, a short π–π stacking distance (3.52 Å), and therefore the highest device mobility