High‐Performance Photorefractive Composite Based on Non‐conjugated Main‐Chain,Hole‐Transporting Polymer

The photorefractivity of a non‐conjugated main‐chain polymeric composite, composed of electron‐rich N,N‐di‐toly‐N,N′‐diphenylbiphenyldiamine doped with 2‐{3‐[(E)‐2‐(piperidino)‐1‐ethenyl]‐5,5‐dimethyl‐2‐cyclohexenylidene}‐malononitrile (P‐IP‐DC) and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM), is studied using two‐beam coupling and degenerate four‐wave mixing at 633 nm. The N,N′‐di‐toly‐N,N′‐diphenylbiphenyldiamine‐based composite shows a gain coefficient of 215 cm^?1 at 80 V μm^?1 with s‐polarized beams and a diffraction efficiency of 67% at 30 V μm^?1, with a response time of the diffraction efficiency of 344 ms at T_g + 4.6 °C. Comparing the photorefractive grating response time of the 3,3′‐dicarbazole‐containing polymer composite with that of the N,N′‐di‐toly‐N,N′‐diphenylbiphenyldiamine‐based composite shows that the former is more than three times faster.     

Solid‐State Dye‐Sensitized Solar Cells with Conjugated Polymers as Hole‐Transporting Materials

DSCs are a promising alternative to conventional silicon‐based solar cells owing to their low cost and relatively high efficiency. However, the utilization of a liquid electrolyte containing the iodine/iodide redox couple in traditional DSCs brings practical problems for their long‐term application, which leads to rapid development of SDSCs based on inorganic p‐type semiconductors or organic HTMs. In this review, we summarize the current research on SDSCs using conjugated polymer as HTM. Special attention is paid to understand the effects of polymer HTM structure and deposition process on SDSC performance. The limiting factors for SDSC energy conversion efficiency are discussed and strategies to improve device performance are proposed.

     

Syntheses of New 3,6‐Carbazole‐Based Donor/Acceptor Conjugated Copolymers for Optoelectronic Device Applications

The syntheses, properties, and optoelectronic device characteristics of four new 3,6‐carbazole‐based donor/acceptor conjugated copolymers are reported. Such copolymers are used to explore the effects of acceptor strength and backbone coplanarity on the electronic and optoelectronic properties. The optical bandgaps of the studied copolymers are PCzQ (2.29 eV) > PCzDTQ (1.91 eV) > PCzTP (1.75 eV) > PCzDTTP (1.49 eV), which are much smaller than the parent poly(3,6‐carbazole). The power conversion efficiency of the photovoltaic cells fabricated from blends of copolymer/PC₆₁BM or PC₇₁BM reached 1.01 and 1.73% by varying the film thickness or blend ratio. The experimental results suggest the potential application of 3,6‐carbazole acceptor conjugated copolymers in optoelectronic devices.

     

New Carbazole‐Based Copolymers as Amorphous Hole‐Transporting Materials for Multilayer Light‐Emitting Diodes

New carbazole‐based copolymers, which contain various concentrations of 9‐alkyl‐3,6‐carbazole fragments in the main chain connected via alkylene spacers, have been synthesized by Ni(0)‐catalyzed Yamamoto‐type aryl‐aryl coupling reactions. Full characterization of the copolymer structure by NMR spectroscopy and elemental analysis is presented. These compounds represent amorphous materials of high thermal stability with glass transition temperatures of 151–162 °C and thermal decomposition starting at temperatures >390 °C. UV‐Vis absorption and photoluminescence emission of the copolymers confirmed that the effectively conjugated segment in the 3,6‐linked carbazole‐type copolymers is limited to dyads (dimeric units). However, copolymers with varying concentrations of the oligocarbazole chromophores demonstrate different charge injection and transport properties in multilayer light‐emitting diodes with the copolymers as the hole transport and Alq₃ as the electroluminescent/electron transport layer. The device based on a copolymer composed of oligocarbazole blocks with an average length of around four carbazoles exhibited the best overall performance with a turn‐on voltage of 3.5 V, a maximal photometric efficiency of 4.1 cd · A^?1 and maximum brightness of about 4 200 cd · m^?2.

     

Iminoboronate Backbone‐Based Hyperbranched Polymeric Micelles with Fenton‐Like Enhanced ROS Response

Compared to normal cells, there is a relatively high level of reactive oxygen species (ROS) in tumor cells caused by defecting ROS scavenging systems. To this issue, developing ROS‐responsive nanocarriers has been a promising way to cancer therapy. However, it is always difficult for a certain ROS‐responsive nanocarrier to be perfectly triggered due to the complexity of cancerous tissues. Thus, it is pressing to improve the response sensitivity of ROS‐responsive nanocarriers. Herein, the Fenton‐like reaction enhanced ROS response of polymeric nanocarriers of an iminoboronate backbone‐based hyperbranched polymer with metallisable 8‐hyroxyquinoline (HQ) moieties is demonstrated. HQ‐Cu catalytic sites can be formed at the prepared nanocarriers via the complexation of Cu(II) ions and HQ moieties. Upon H₂O₂, hydroxyl radicals (·OH) are quickly generated via the Fenton‐like reaction between H₂O₂ and HQ‐Cu. Then, the oxidative cleavage of iminoboronate moieties can be effectively activated to disrupt the nanocarriers, leading to a rapid release of encapsulated drugs. It is proposed that this kind of polymeric nanocarriers with Cu‐complexed catalyzing‐triggered ROS response may achieve highly effective oxidation therapy.     

Synthesis of Hyperbranched Polypyridine via a Cross Coupling Approach as an n‐Type π‐Conjugated Polymer

The synthesis of an n‐type π‐conjugated hyperbranched polymer, hyperbranched polypyridine, is described. The polymer is obtained by copolymerization of 2,4,6‐tribromopyridine and 2,5‐dibromopyridine via chain‐growth condensation polymerization catalyzed by Ni(dppp)Cl₂. The NMR and fourier transform infrared results indicate the successful introduction of the branching unit into polypyridine by this cross coupling approach. The results of UV–vis spectroscopy and cyclic voltammetry suggest that the introduction of the branching unit contributes to a quick response during electrochemical doping due to the diffusion of dopant enhanced by the hyperbranched structure.     

4,5‐Ethylene‐2,7‐Carbazole‐Based Medium‐Bandgap Conjugated Polymers with Low‐Lying HOMO Levels Toward Efficient Polymer Solar Cells with High Open‐Circuit Voltage

Three medium‐bandgap polymers based on a 4,5‐ethylene‐2,7‐dithienyl carbazole as the electron‐donating unit and different 5,6‐dialkoxy‐2,1,3‐benzothiadiazoles as the electron‐accepting units, are synthesized as polymer donors for photovoltaic applications. The three copolymers possess highest occupied molecular oribital (HOMO) levels around ?5.47 eV and medium bandgaps of about 1.94 eV. The solar cells with polymer:[6,6]‐phenyl C71‐butyric acid methyl ester (PC₇₁BM) = 1:4 as the active layer, show an especially high open‐circuit voltage (V_oc) of 0.95 V and attain good power conversion efficiency up to 5.91%. The hole mobilities of the active layer films, measured by space‐charge‐limited current (SCLC), are up to 3.5 × 10^?4 cm² V^?1 s^?1. Given the favorable medium bandgaps, low‐lying HOMO levels, and good hole mobilities, these copolymers are promising candidates for the construction of a highly efficient front cell to harvest the shorter wavelength band of the solar radiation in a tandem solar cell with high V_oc.

     

Synthesis and Photovoltaic Properties of 1,8‐Carbazole‐Based Donor–Acceptor Type Conjugated Polymers

1,8‐Diethynylcarbazole‐based conjugated polymers were synthesized by the acetylenic oxidative coupling reaction or Pd‐catalyzed Sonogashira reaction of the newly designed 3,6‐dialkylated 1,8‐diethynylcarbazole monomers. In particular, the Sonogashira polycondensation was effective for the preparation of donor–acceptor type alternating copolymers. The UV‐vis absorption and fluorescence spectra of the polymers revealed the strength of the donor–acceptor interactions as well as their self‐assembling features. The combination of electrochemical redox potentials and optical band gaps enabled the estimation of the polymer energy levels. The bulk‐heterojunction solar cells composed of these promising polymers and PCBM exhibited a photoconversion efficiency (PCE) of 0.24%. It was determined that the partial doping of the bulk‐heterojunction layer increased the open‐circuit voltage (V_oc), but decreased the short‐circuit current (J_sc).     

Novel Carbazole‐Based Ladder‐Type Polymers for Electronic Applications

Summary : New carbazole‐based ladder‐polymers have been prepared utilising a 3,6‐diacyl‐2,7‐dibromocarbazole building block 4 . Suzuki polycondensation of 4 with carbazole‐2,7‐diboronic acid followed by addition of methyl lithium and ring closure with boron trifluoride gave ladder‐polymers 9 with all methine bridges, analogous to ladder‐type poly(para‐phenylene). In very dilute solution, these polymers show blue‐green fluorescence similar to that from the corresponding LPPP. At higher concentrations, a broader red‐shifted emission is seen which suggests that the chains are aggregating in solution. Homopolymerisation of 4 followed by condensation of the carbonyls with boron sulfide produced a novel ladder‐type structure 13 with alternating five‐ and six‐membered rings. This ladder‐polymer displays bright yellow‐green fluorescence. Cyclic voltammetry indicated that these materials have HOMO energy levels comparable to the work function of ITO, making them good candidates for use as hole accepting emissive materials for LEDs.

The ladder polymers synthesised.     

Multilayer Thin Films by Layer‐by‐Layer Assembly of Hole‐ and Electron‐Transport Polyelectrolytes: Optical and Electrochemical Properties

Summary: In this paper, we present the synthesis of a series of p‐type and n‐type semiconducting polyelectrolytes with triarylamine, oxadiazole, thiadiazole and triazine moieties. The synthesized polymeric hole and electron transport materials were examined optically and electrochemically using UV/Vis spectroscopy, PL spectroscopy and CV. Based on the optical and electrochemical data, each of the energy levels were calculated and all values suggested that they were promising hole‐ (p‐type) or electron‐transport (n‐type) materials for devices. Moreover, the synthesized ionic polymers were suitable for LBL thin film deposition from dilute polymer solutions and the multilayers were fully characterized by UV/Vis, PL spectroscopy and CV.

     

Four Simple Structure Carbazole‐Based Conjugated Microporous Polymers with Different Soft Connected Chains

Four carbazole–spacer–carbazole polymers PCz–Cn–Cz (n = 3–6) with the similar topological model structures are designed and prepared by FeCl₃ oxidative coupling polymerization. The Brunauer–Emmett–Teller (BET) specific surface areas of polymers are 862, 870, 768 and 785 m² g^?1, respectively. Interestingly, there are no obvious differences in the domain pore width (centered at 0.5 nm) and the pore size distribution among four polymers, although they have different length soft alkylene chains to interlink same rigid backbone carbazole. Gas adsorption isotherms show that H₂ storage of polymers can be up to 1.33 wt% at 1.0 bar and 77 K, the uptake capacity for CO₂ can reach 16.8 wt% at 1.0 bar and 273 K, CH₄ uptake can reach 2.11 wt% at 1.0 bar and 273 K, and the CO uptake performance can be up to 1.37 wt% at 298 K and 1.0 bar. Selective adsorption of CO₂/N₂ and CO₂/CH₄ calculated using the initial gas uptake slopes shows that these networks display good selectivity with a maximum value of 47.7 (33.8) and 14 (7.3) at 273 K (298 K). The high selective adsorption performances make these materials potential candidates for gas separation and other environmental applications.

     

Size‐Stable Supramolecular Hyperbranched Polymer Vesicles for Redox‐Triggered Double‐Drug Release

Supramolecular polymer vesicles (SPVs) with stimuli‐responsive features are promising multifunctional nanocarriers; however, improving the stability and developing multiple‐drug‐loaded SPVs remain key issues in this field. In this work, cross‐linked supramolecular hyperbranched polymer vesicles (SHPVs) with redox‐responsiveness are first constructed based on an AB₂‐type macromonomer‐synthesized SHP. The obtained cross‐linked SHPVs exhibit much better size stability than those of non‐cross‐linked branched self‐assemblies, and higher double‐drug‐loading capacity compared with linear supramolecular polymer self‐assemblies. Particularly, these cross‐linked SHPVs exhibit a redox‐triggered, controlled double‐drug release behavior upon the addition of H₂O₂.     

Photorefractive Composite Based on a Monolithic Polymer

A new class of photorefractive (PR) composite based on a fully functionalized polymer with high phase‐stability is reported. The polymer containing non‐linear optical (NLO) chromophores and charge‐transporting carbazole moieties is synthesized by a polymer‐analogous reaction. The polymer is doped with plasticizer, NLO dye, and sensitizer to fabricate the PR composite. The NLO dye is the same as the NLO chromophore moiety in the polymer side chain. The PR performance of the composite is evaluated by degenerated four‐wave mixing and two‐beam coupling measurements. A diffraction efficiency of 30% at a relatively low applied electric field of 45 V μm^?1 is achieved. Despite a high concentration of NLO dye, the composites show good stability for a long period without phase separation.     

2D Self‐Assembly of an Amido‐Ended Hydrophilic Hyperbranched Polyester by Copper Ion Induction

The self‐assembly of an amido‐ended hydrophilic hyperbranched polyester (HTDA‐2) into ordered, compact, 2D, tree‐like structures with a diameter of over 500 μm and a trunk‐width of about 3–5 μm by the induction effect of cupric ions is presented. Influencing factors on the morphology of the self‐assemblies, including temperature, time, solvents, concentration, and humidity, investigated by polarizing optical microscopy (POM) and scanning electron microscopy (SEM), are discussed. The self‐assembly mechanism is analyzed by X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD), SEM, and Fourier transform IR (FTIR) spectroscopy. A dimension (D_f) of about 1.50 for the perfect fractal behavior and the crystal behavior of the self‐assemblies are determined.

     

A New Dithienylbenzotriazole‐Based Poly(2,7‐carbazole) for Efficient Photovoltaics

A new dithienyl benzotriazole‐based conjugated polymer was synthesized by Suzuki coupling reaction. The polymer was found to be soluble in common organic solvents, such as chloroform, tetrahydrofuran and chlorobenzene, with excellent film‐forming properties. The structure of the polymer was confirmed by ¹H NMR, the molecular weights determined by GPC and the thermal properties investigated by TGA and DSC. The polymer films exhibited an absorption band in the wavelength range 300 to 610 nm. Preliminary photovoltaic cells based on the composite structure of indium tin oxide (ITO)/PEDOT:PSS/ PCDTBTz:PC ₆₀ BM (1:2 w/w)/Al showed an open‐circuit voltage of 0.92 V, a power conversion efficiency of 2.2% and a short circuit current of 5.33 mA cm^?2.

     

Synthesis and Characterization of a 2,4,6‐Tri(2‐thienyl)pyridine‐Based Conjugated Polymer for OFET Applications

2,4,6‐Tri(2‐thienyl)pyridine is used to synthesize the new conjugated polymer PBDTTPy for OFET applications. The concept of introducing electron‐deficient pyridine repeating units and meta‐linked structures into a conjugated polymer to reduce its HOMO energy level and thereby increase its ambient stability is tested. The absorption spectrum of the polymer thin film displays a large bathochromic shift compared with its solution absorption spectrum. The polymer PBDTTPy shows a typical amorphous structure in the solid state. The first OFET device based on a conjugated polymer with meta‐linked trithienylpyridine units is reported. PBDTTPy exhibits p‐type transport under ambient conditions in a bottom‐gate, top‐contact OFET device with a mobility of 2.4 × 10^?4 cm² V^?1 s^?1.     

High Refractive Index Hyperbranched Polymers Prepared by Two Naphthalene‐Bearing Monomers via Thiol‐Yne Reaction

High refractive index (HRI) materials play an important role in optic‐electronic devices. In this study, two compounds with high content of naphthalene groups, 1,5‐dithiolnaphthalene and 1,3,5‐tris(naphthalyl–ethylnyl) benzene, are selected as “A₂” and “B₃” monomers, respectively to prepare hyperbranched HRI polymers. Metal‐free radical‐initiated “A₂ + B₃” thiol‐yne polyaddition is conducted successfully at different monomer molar ratios even for those sterically demanding molecules being able to adjust the molar mass as well as RI. Polymers with refractive index up to 1.79 at 589.7 nm are obtained, which are among the highest RI values so far reported for pure polymer‐based materials. The high RI, based on the high molar refraction of naphthalene group, metal‐free and easy one‐pot synthesis, high transparency in the visible area, good thermal stability, good solubility, and easy processability into thin films, make these polymers excellent candidates for optic‐electronic applications.

     

Branched Oligophenylenes with Phenylene–Ethynylene Fragments as Anode Interfacial Layer for Solution Processed Optoelectronics

Two branched oligophenylenethynylenes with phenylene or biphenylene moieties as inter‐nodal fragments are synthesized by the Sonogashira reaction for optoelectronic applications. The branching of polyphenylenethynylenes influences the electro‐optical properties, but cannot be precisely controlled, while its determination is often hardly addressed. The optical investigation, supported by nuclear magnetic resonance (NMR) studies, of oligophenylenethynylenes and the properly synthesized model compounds is performed to get insights on the branching and related effect on the material performance. The proposed branched oligophenylenethynylenes are good ultraviolet emitters in solution, while in solid‐state aggregation phenomena strongly affect emission properties. However, the interactions between π‐electrons on phenylene and ethynylene of neighboring molecules in films enhance intermolecular charge transport (hole mobility = 3.2 × 10^?3 cm² V^?1s^?1) making them optimal candidates as hole transport materials in optoelectronic devices. The insertion of the oligophenylenethynylene film as a hole transporting layer in multilayered solution processes blue, green, and red electroluminescent diodes, enhances OLEDs electro‐optical properties.     

Synthesis of Hyperbranched Polymers via Metal‐Free ATRP in Solution and Microemulsion

Atom transfer radical polymerization (ATRP), as one of the most successful controlled radical polymerization techniques, has been broadly used by polymer chemists and nonspecialists for synthesis of various functional materials, although the use of copper as traditional catalyst often results in undesired color or properties. The first homopolymerization of an initiable monomer, that is, inimer, is reported via metal‐free ATRP using 10‐phenylphenothiazine (Ph‐PTH) as photocatalyst in both solution and microemulsion media. Although polymerizations of inimers in both media can be carried out, only the microemulsion polymerization of methacrylate‐based inimer 1 effectively confines the random bimolecular reaction within each segregated latex and produces hyperbranched polymers with high molecular weight and low polydispersity. Several experimental parameters in the microemulsion polymerization of inimer 1 are subsequently studied, including the Ph‐PTH amount, the solids content of microemulsion, and the light source of irradiation. The results not only provide an effective method to tune the structure and molecular weights of hyperbranched polymers in confined‐space polymerization, but also expand the toolbox of using metal‐free ATRP method for synthesizing highly branched polymers in controlled manner.     

OH‐ and NH2‐Terminated Hyperbranched Polysiloxanes: Controlled Synthesis,Characterization, Toughening,and Reinforcing Epoxy Resin

A new silicon‐containing hyperbranched polysiloxane (HAHBPs) is successfully synthesized via a one‐pot A₂ + B₃ strategy using diethylene glycol and (3‐aminopropyl)triethoxysilane (KH550) under solvent‐free and catalyst‐free conditions. Then, for the first time, the HAHBPs are used to modify epoxy resin E51. TGA results display significantly lower thermal stability compared with that of the neat epoxy resin. Experimental results also show that the addition of HAHBPs simultaneously improves flexural strength and impact strength. In particular, a great increase (2.48 times its original toughness) in the toughness of epoxy resin E51 is achieved with 20 wt% HAHBPs loading. More importantly, fracture morphology and DMA measurements show no obvious phase separation due to the strong interfacial bonds between the HAHBPs and epoxy matrix. These results indicate that the HAHBPs containing OH‐ and NH₂‐ can be a potentially effective epoxy resin toughener.