One‐Step Route to Ladder‐Type C–N Linked Conjugated Polymers

A one‐step synthetic method is demonstrated to construct ladder‐type conjugated polymers without the resource to post‐cyclization procedures. The ladder‐type C–N linked conjugated polymers ( P1 and P2 ) and model compounds ( 1 and 2 ) are achieved in high yields. The obtained model compounds and polymers display desirable solubility in commonly used solvents and high thermal stability, which show a promising application in photoelectric material field.     

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.

     

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).     

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.

     

Thieno[3,4‐c]pyrrole‐4,6‐dione‐Based Polymers for Optoelectronic Applications

Over the last decade, great progress has been made in the field of organic electronics. Advancements in organic syntheses as well as in device engineering enabled preparation of polymer solar cells with power conversion efficiency (PCE) exceeding 8%–9%. In search for new polymers suitable for photovoltaic applications, push–pull polymers containing thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) motif as an electron deficient (pull) unit emerged as very promising candidates. This Trend Article summarizes research on TPD‐based polymers with a special emphasis on the structure–property relationships.     

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.

     

Facile Fabrication of Electrochromic Poly(amine‐amide) and Poly(amine‐imide) Films Via Carbazole‐Based Oxidative Coupling Electropolymerization

The synthesis and electrochemical properties of four electropolymerizable monomers featuring an interior aromatic diamide or diimide segment bridged by p‐phenylene units to terminal electroactive carbazole groups are described. Upon electrochemical oxidation, the coupling reactions between carbazole radical cations occur instantly, rendering an efficient electropolymerization process feasible. The electrogenerated polymer films exhibit reversible electrochemical processes and stable color changes upon electro‐oxidation, which can be switched by potential modulation. The remarkable electrochromic behavior of the film is clearly interpreted on the basis of spectroelectrochemical studies.

     

Fluorene‐Based Conjugated Poly(azomethine)s: Synthesis,Photophysical Properties,and Theoretical Electronic Structures

Summary: Soluble conjugated poly(azomethine)s, PFI and PFCI , were synthesized from 2,7‐diformyl‐9,9′‐dioctylfluorene ( DFOF ) with diamines. The replacement of the fluorene ( PFI ) by carbazole ( PFCI ) reduces the ionization potential but enhances the band gap (E_g) due to the kink disorder introduced by the 3,6‐carbazole. The optical absorption or photoluminescence of the synthesized PFI or PFCI is sensitive to good/poor solvent ratio, acid environment, or metal ions. The variation of the planarity on the polymer backbone and intermolecular charge transfer explain the above spectral tuning by chemical species. The theoretical results based on the density functional theory (DFT) suggest that the PFI and PFCI show a non‐coplanar conformation due to steric repulsion force between the adjacent hydrogen atoms. It could be resolved by replacing the fluorene or carbazole ring by thiophene ( PFTI ) or 3,4‐ethylenedioxythiophene ( PFEI ). The coplanar geometry and possible intramolecular charge transfer lead to the E_g of 2.17 and 2.03 eV for the PFTI and PFEI , respectively. The smaller effective mass of the PFTI or PFEI also indicates that both polymers could be p‐type semiconductors for organic electronics.

Chemical structures of fluorene‐based conjugated poly(azomethine)s.     

Polymers for Luminescent Sensing Applications

Polymers are widely used for chemical sensing applications, as a receptor or as a signal transducer. Fluorescent conjugated polymers (CPs) are extensively studied for signaling. Water‐soluble CPs are particularly attractive due to their potential sensing applications in environmental and biorelated fields. The CPs by themselves do not provide specific binding sites by folding into secondary or tertiary structures. Molecularly imprinted polymers (MIPs) are artificial receptors fabricated using the molecular‐imprinting technique. They contain in‐built information about the shape and functionality of specific potential analytes. However, most MIPs do not have optical‐signaling properties. In this article, the recent developments regarding luminescent polymeric sensors are briefly summarized. It will be of great interest if the optical‐signal properties of CPs and the selectivity of MIPs are integrated in an advanced polymeric sensor.

     

Synthesis and Fluorescent Properties of Carbazole‐Substituted Hydroxyethylcelluloses

Carbazole‐substituted hydroxyethylcelluloses (Cz‐HECs) are homogeneously synthesized by reacting hydroxyethylcellulose (HEC) with N‐3′‐bromopropyl carbazole (Br‐Cz). The structure of Cz‐HECs is characterized with elemental analysis and NMR, and the DS of the carbazole is in the range 0.11–0.43, determined from nitrogen content. The fluorescent properties of Cz‐HECs are measured using a spectrofluorimeter. The results show that the fluorescence lifetime increases as the DS increases, and the fluorescent intensity of Cz‐HECs is stronger than that of Br‐Cz. All samples exhibit concentration self‐quenching properties. The addition of acrylonitrile, as an electron acceptor, quenches the emission spectra of Cz‐HECs, and the fluorescence quenching is found to be a dynamic quenching by analyzing with the Stern–Volmer equation.     

Click Functionalization of Aromatic Polymers for Organic Electronic Device Applications

The [2 + 2] cycloaddition–retroelectrocyclization between electron‐rich alkynes and tetracyanoethylene (TCNE)/7,7,8,8‐tetracyanoquinodimethane (TCNQ), yielding the tetracyanated donor–acceptor (D–A) chromophores, is a new class of click chemistry reactions, due to the high efficiencies, no byproducts, and applicability to polymer syntheses. As compared to the conventional click reactions represented by the Cu(I)‐catalyzed azide–alkyne cycloaddition (CuAAC), these new click reactions provide fascinating optoelectronic properties originating from the D–A chromophore structures formed. A series of π‐conjugated aromatic polymers containing electron‐rich alkynes were successfully functionalized by these click reactions, producing novel organic or organometallic materials featuring conducting and photovoltaic properties in thin film electronic devices. This review article describes the recent results of the author's research group. The power of click chemistry is highlighted by the polymer synthesis using CuAAC. This is followed by the alkyne–TCNE/TCNQ postfunctionalization to produce high‐performance aromatic polymers for use as active components in organic electronic devices, such as thin film transistors, organic solar cells and polymer memory devices.

     

Full‐Color Processible Electrochromic Polymers Based on 4,4‐Dioctyl‐Cyclopentadithiophene

Three soluble electrochromic copolymers based on 4,4‐di‐octyl‐cyclopentadithiophene (DOCPDT): PDOCPDT‐OT, PDOCPDT‐PT, and PDOCPDT‐Cz were synthesized and the electrochromic properties were investigated. Colorimetric analysis revealed that red‐colored PDOCPDT‐OT, green‐colored PDOCPDT‐PT and their blue mother polymer PDOCTDT are cathodic coloration polymers. PDOCPDT‐Cz is yellow in its neutral state and shows an anodic electrochromism. The structural flexibility, color diversity, processibility and good electrochromic performance make octyl‐cyclopentadithiophene‐containing polymers prominent candidates for electrochromic applications.

     

Xanthene‐Based Oligothiophene‐Layered Polymers

We synthesized xanthene‐based oligothiophene‐layered polymers containing bithiophenes, terthiophenes, quaterthiophenes and quinquethiophenes by the Suzuki‐Miyaura coupling reaction. The polymers were characterized by various spectroscopic and electrochemical methods. They were well soluble in common organic solvents and thermally stable. Effective π‐π interactions among the layered oligothiophene units in the polymer backbone were not observed in the ground state as well as in the excited state. A possible application of the polymers in opto‐electronic devices such as hole transporting materials is expected.

     

Novel Photo‐Alignment Polymer Layer Capable of Charge Transport

Summary: With the progress of organic electronics, materials possessing various functionalities are attracting much attention. Here we have synthesized a novel photo‐alignment polymer composed of a conjugated carbazole main‐chain and a coumarin side‐chain through nickel(0)‐mediated polymerization. Carbazole is a well‐known hole transporting material and coumarin is also famous for its good photo‐alignment properties. The photochemical reactivity of the coumarin side‐chain was monitored by UV‐vis spectroscopy and the liquid crystal (LC) photo‐alignment direction of the polymer film was proved to be perpendicular to the polarization direction of the irradiated UV light. The highest occupied molecular orbital (HOMO) level of the polymer, measured from both cyclic voltammetry and photoelectron spectroscopy, was ?5.32 eV. Organic light‐emitting diodes (OLEDs) of the configuration [ITO/polymer/NPB/Alq₃/LiF/Al] showed a higher efficiency (2.17%) and brightness (14 000 cd · m^?2) than a control device due to enhanced charge balance.

     

Copolymers of Thiophene and Cyano‐Substituted Phenylene: Facile Tuning of Electronic Energy Levels and their Photovoltaic Application

A series of copolymers of thiophene and different molar ratios of DOCNP have been synthesized and characterized. The copolymers exhibit interesting tunable electronic energy levels and optoelectronic properties. The LUMO energy levels of the copolymers decreased with increasing DOCNP content, while the HOMO levels changed only a little. The copolymer films show broad absorption and high absorption coefficients in the visible region, which could be beneficial to the application as photovoltaic materials in solar cells. The results show that the introduction of a proper amount of electron‐acceptor groups in the polymer main chains induces an extension of the absorption spectra and improves the photovoltaic properties of the copolymers.

     

Synthesis and Optical Properties of π‐Conjugated Polymers Composed of Benzo[1,2‐b:4,5‐b′]dithiophene and Thiophenes Bearing Electron‐Deficient Ethenyl Groups in the Side Chains

π‐Conjugated polymers composed of dialkoxybenzo[1,2‐b:4,5‐b′]dithiophene and thiophenes bearing cyano‐alkoxycarbonylethenyl [? CH?C(CO₂R)CN] and bis(alkoxycarbonyl)ethenyl groups [? CH?C(CO₂R)₂] were prepared. The optical properties of the obtained polymers were investigated by UV‐vis and photoluminescence spectroscopy to demonstrate that the absorption maxima of the polymers were tunable by varying the substituent of thiophene unit. The photoluminescence wavelengths and intensities of the polymer in solution were significantly dependent on the polymer side chain. The HOMO energy level of the polymer was lowered by up to ?5.51 eV by introducing electron‐deficient cyano groups. Polymer solar cells based on the new polymers were fabricated to achieve a PCE of 1.90%.

     

Conjugated Main Chain Azo‐Polymers Based on Polycyclic Aromatic Hydrocarbons

A reductive coupling reaction employing sodium bis(2‐methoxyethoxy) aluminum hydride is used to prepare main chain azo‐polymers comprising of polycyclic aromatic hydrocarbons (naphthalene, anthraquinone, or fluorenone) from their dinitro‐derivatives. The azo‐bridges act as effective means of conjugation and all polymers exhibit differences in the ultra‐violet–visible light absorption and photoluminescence emission spectra depending on the degree of polymerization. Furthermore, in the case of poly(azofluorenone)s and poly(azoanthraquinone)s, these spectra may be modified by changes in the protonation state of the polymers. The lowest unoccupied molecular orbital and highest occupied molecular orbital energy levels and the band gap of poly(azoanthraquinone) are estimated from cyclic voltammetry data and UV–visible absorption of films.     

Facile Synthesis of Ladder‐Type Polyacenes with Perylene‐Fused‐Pyrene Structures

Ladder‐type polyacene (FP2) and model compounds (1c and 2c) with perylene‐fused‐pyrene structures are achieved in high yields by using a Pd(PPh₃)₂Cl₂‐catalyzed Suzuki reaction followed by cyclization with FeCl₃. The obtained model compounds and polyacene display desirable solubility in commonly used solvents and high thermal stability. Fluorescence peak at 614 nm is observed in diluted CH₂Cl₂ solution containing polyacene. Furthermore, the as‐prepared model compound (2c) and polyacene (FP2) are employed as acceptors in bulk‐heterojunction (BHJ) solar cells with PTB7‐Th as electrodonor cells. The 2c‐based solar cell demonstrates a power conversion efficiency of 3.25%.     

The Process of Functional Conjugated Organic Polymers Derived from Triple‐Bond Building Blocks

Polyacetylenes, poly(p‐phenyleneethynylenes), and polydiacetylenes, as conjugated polymers derived from triple‐bond containing building blocks, attain considerable attention because of their electronic and photoconduction properties. In this review, recent studies on the design and synthesis of conjugated polymers derived from triple‐bond building blocks are summarized with an emphasis on the developments in our group in recent years. Our intense attention is focused on constructing different molecular systems with enhanced light‐harvesting efficiency, and determining the functional properties of conjugated organic polymers. The conjugated organic polymers that appear in this review are useful candidates for various potential applications because of their extraordinary optical and electronic properties. The potential applications of the conjugated polymer‐containing systems are explored.

     

Novel Soluble N‐Phenyl‐Carbazole‐Containing PPVs for Light‐Emitting Devices: Synthesis,Electrochemical, Optical,and Electroluminescent Properties

Summary: Novel PPV derivatives (PCA8‐PV and PCA8‐MEHPV) containing N‐phenyl‐carbazole units on the backbone were successfully synthesized by the Wittig polycondensation of 3,6‐bisformyl‐N‐(4‐octyloxy‐phenyl)carbazole with the corresponding tributyl phosphonium salts in good yields. The newly formed and dominant trans vinylene double bonds were confirmed by FT‐IR and NMR spectroscopy. The polymers (with of 6 289 for PCA8‐PV and 7 387 for PCA8‐MEHPV) were soluble in common organic solvents and displayed high thermal stability (T_gs are 110.7 °C for PCA8‐PV and 92.2 °C for PCA8‐MEHPV, respectively) because of the incorporation of the N‐phenyl‐carbazole units. Cyclic voltammetry investigations (onsets: 0.8 V for PCA8‐PV and 0.7 V for PCA8‐MEHPV) suggested that the polymers possess enhanced hole injection/transport properties, which can be also attributed to the N‐phenyl‐carbazole units on the backbone. Both the single‐layer and the double‐layer light‐emitting diodes (LEDs) that used the polymers as the active layer emitted a greenish‐blue or bluish‐green light (the maximum emissions located 494 nm for PCA8‐PV and 507 nm for PCA8‐MEHPV, respectively). Compared with those of the single‐layer devices, the emission efficiencies of the double‐layer devices, in which an electron‐transporting layer (Alq₃) was added, were enhanced by a factor of 10, implying that the better hole‐electron balance is achieved because of the incorporation of the electron‐transporting layer.

The N‐phenyl‐carbazole‐containing polymers synthesized.