Preparation of New Hole Transport Polymers via Copolymerization of N,N ′‐Diphenyl‐N,N′‐bis(4‐alkylphenyl)benzidine (TPD) Derivatives with 1,4‐Divinylbenzene

Monomers containing N,N ′,N,N ′‐tetraphenylbenzidine (TPD) were prepared by introducing two alkyl or alkoxy substituents into the p‐position of two of the four phenyl groups in the triphenylamine unit. The monomers were copolymerized with 1,4‐divinylbenzene (DVB) in the presence of p‐toluenesulfonic acid and Lewis acids, such as SnCl₄ and BF₃. The polymerization conditions and the catalyst types showed a marked influence on yield, molecular weight and even polymer structure. ¹H NMR measurements revealed that, by using p‐toluenesulfonic acid as a catalyst, the linkage between the TPD unit and DVB occurs at the p‐position of the phenyl group and at the m‐position of the tolyl group in the TPD unit, whereas, with SnCl₄ or BF₃ catalyst, substitution occurs exclusively at the p‐position of TPD. All polymers are soluble in common organic solvents, which allows the preparation of thin films of good quality. The rigid structure of the polymeric backbone results in a high thermal stability up to 400°C. The results of ionization potential measurements and the redox behavior showed that the introduction of the TPD unit into this kind of polymer backbone does not change its electronic structure. On the basis of high electroactivity, the polymers were successfully used as hole transport layers in two‐layer electroluminescence devices.     

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).     

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.     

High‐Mobility Conjugated Polymers Based on Fused‐Thiophene Building Blocks

Organic field‐effect transistors (OFETs) are a promising cost‐effective alternative to silicon‐based field‐effect transistors, and possess low‐cost, light‐weight, and flexibility advantages. Conjugated polymers based on fused‐thiophene building blocks have received considerable attention in the emerging field of organic electronics. In this review the most recent developments in conjugated polymers based on fused‐thiophene rings for high‐performance OFETs are summarized. The focus is on correlations of polymer chemical structures with properties, such as energy levels, film‐forming property, film morphology, and OFET performance. This structure–property relationship analysis may guide rational structural design and evaluation of organic semiconductors.

     

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.     

Novel Low Bandgap EDOT‐Naphthalene Bisimides Conjugated Polymers: Synthesis,Redox, and Optical Properties

Low band‐gap conjugated polymers based on naphthalene bisimide (NBI) and 3,4‐ethylenedioxythiophene (EDOT) were synthesized by Stille cross‐coupling reaction. The alternating conjugated poly(EDOT‐NBI) ( P1 ) and random poly(EDOT‐NBI) ( P2 ) are both solution‐processable due to the existence of bulky 2,6‐diisopropylphenyl substituent. Their optical and electrochemical properties were characterized. P1 and P2 films show optical band gaps of 1.75 and 1.38 eV estimated from UV‐Vis absorption spectra. Cyclic voltammograms of both polymers display reversible reduction peaks with onset reduction potentials at ?0.55 V for P1 and ?0.61 V for P2 , which correspond to the electron affinity (EA) values (LUMO energy level) of 3.85 and 3.79 eV, respectively. The ionization potential (IP, HOMO level) values of 5.60 eV for P1 and 5.17 eV for P2 were also calculated by combining solid‐state optical and electrochemical data. A double heterojunction device was fabricated. It exhibits an open circuit voltage of 0.30 V and average power conversion efficiency of 0.15%.

     

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.

     

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.     

High‐Yielding Alkyne‐Tetracyanoethylene Addition Reactions: A Powerful Tool for Analyzing Alkyne‐Linked Conjugated Polymer Structures

Poly(o‐phenyleneethynylene) and poly(o‐phenylenebutadiynylene) derivatives are synthesized by the Sonogashira polycondensation or oxidative polymerization of an asymmetric monomer, 3,4‐diethynyl‐N,N‐dihexylaniline. Postfunctionalization of the poly(o‐phenyleneethylene) derivatives is unsuccessful due to the occurrence of undesired side reactions. In contrast, the poly(o‐phenylenebutadiynylene) derivative is converted into the donor–acceptor type polymer without side reactions. The resulting polymer features a well‐defined charge‐transfer (CT) band in the Vis–NIR region and redox activity in both the anodic and cathodic directions. The results suggest that the oxidative polymerization mainly proceeds through the pseudo two‐step pathway.

     

Bisfuran‐s‐Tetrazine‐Based Conjugated Polymers: Synthesis,Characterization, and Photovoltaic Properties

Bisfuran‐s‐tetrazine (FTz) and its copolymers with cyclopenta[2,1‐b:3,4‐b′]dithiophene (CPDT) and benzo[1,2‐b:4,5‐b′]dithiophene (BDT) (PCPDTFTz and PBDTFTz) are prepared with the alternating s‐tetrazine and CPDT or BDT units bridged by a furan ring. Their optical and electrochemical properties are studied and compared with their thiophene analogs (PCPDTTTz‐out and PCPDTTTz‐in), in which the bridging unit is 4‐hexylthiophene or 3‐hexylthiophene, respectively. Bulk heterojunction (BHJ) solar cells fabricated from these polymers with PC₇₁BM have a power conversion efficiency (PCE) of 0.8%, which is much lower than that from the PCPDTTTz‐out analog (3.2%), due to the low steric hindrance of the furan polymers in the absence of alkyl substitution on the furan ring.     

Homologous Series of 2,5‐Diheptyloxy‐p‐Phenylene Vinylene (DHepO‐PV) Oligomers with Vinyl or 1‐Butenyl End Groups: Synthesis,Isolation, and Microstructure

In this paper we report the synthesis, isolation, and microstructure characterization of 2,5‐diheptyloxy‐p‐phenylene vinylene (PV) oligomers. Two homologous series with their chain length dependent NMR and IR spectra are presented and discussed in detail. To obtain the products, first, oligomer mixtures were synthesized by acyclic diene metathesis (ADMET) polycondensation of 2,5‐diheptyloxy‐1,4‐divinylbenzene. The Schrock‐type alkylidene complex Mo(NPhMe₂)(CHCMe₂Ph) [OCMe(CF₃)₂]₂ served as a catalyst. The polycondensation mixture was used either for the isolation of the oligomers with vinyl end groups or as a feed component for a cross metathesis reaction with 3‐hexene yielding thermally stable derivatives (investigated up to 250 °C) with 1‐butenyl end groups. From the oligomer mixtures, single oligomers up to the octamer (n = 2 … 8) were isolated by means of column chromatography. The monodispersity was determined by means of MALDI‐TOF mass spectrometry. The colors within the homologous series span widely from colorless (monomer) to yellow (trimer) to red (hexamer and upwards). The chain‐length dependence of the NMR spectra is resolved in detail. The presented data could also be used for valuable reference compounds for analogue polymer systems.

Synthesis of diheptyloxy‐PV oligomers by olefin metathesis.     

Dual Tuning of Emission Color and Electron Injection Properties Through in‐situ Chemical Reaction in a Conjugated Polymer Containing 9,10‐Phenanthrenequinone

Three new polymers were obtained through an in situ chemical reaction of the matrix conjugated polymer ( PPQF ) with ortho‐amine compounds. By controlling the conjugation degree of diamine compounds, the emission of PPQF was tuned from weak blue to bright blue, green, and orange for PFBQ , PFBP and PFNP , respectively. The photoluminescence efficiencies were also improved in the same tendency, and the LUMO levels were gradually decreased from ?2.76 and ?3.12 to ?3.40 eV, which was beneficial for electron injection and transport in electronic devices. Thus, a dual tuning for the emission color and electron injection properties were realized through an in situ chemical reaction, which is a novel strategy to design and construct new valuable polymers from one reactive matrix polymer.

     

Synthesis of New Blue Anthracene‐based Conjugated Polymers and Their Applications in Polymer Light‐Emitting Diodes

A series of anthracene‐based conjugated copolymers containing 9,10‐bis(6‐bromonaphthalen‐2‐yl)‐2‐tert‐butylanthracene (BNA) and 2,7‐diphenyl substituted fluorene (DPPF) moieties are prepared via a palladium‐catalyzed Suzuki polymerization. All of the synthesized polymers emit blue light at around 450 nm and show good thermal and color stability. Their electroluminescence spectra remain unchanged at high driving voltage. The double‐layer polymer light‐emitting diode (PLED) fabricated with ITO/PEDOT:PSS/DPPFBNA3/CsF/Al, produces a maximum brightness of 1 650 cd · m^?2 and has a luminance efficiency of 0.39 cd · A^?1. The ITO/PEDOT:PSS/TFB/DPPFBNA3/CsF/Al multilayer PLED, incorporating a TFB layer to facilitate hole transportation, produces a maximum brightness of 5 371 cd · m^?2 and a luminance efficiency of 1.18 cd · A^?1.

     

π‐Conjugated Polymers Consisting of 9,10‐Dihydrophenanthrene Units

π‐Conjugated polymers consisting of 9,10‐disubstituted 9,10‐dihydrophenenthrene, with the substituents octyl, 2‐ethylhexyl, ‐OSiBu₃, etc., units are prepared by organometallic polycondensation. Homopolymers ( PH₂Ph(9,10‐R) ) have a π‐conjugation system similar to that of polymers of 9,9‐dialkylfluorene and show UV‐Vis peaks at ≈380 nm. In addition to the peak at ≈380 nm, some homopolymers give rise to a peak at a longer wavelength, suggesting molecular assembly of the polymers. X‐ray diffraction data support the molecular assembly. The homopolymers show photoluminescence (PL) with PL peaks at ≈430 nm, and PL spectrum of the polymer film is essentially unchanged after heating the polymer film at 150 °C in air. The homopolymers undergo electrochemical p‐doping at about 1.5 V versus Ag⁺/Ag.     

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.

     

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.     

Synthesis of Laser‐Alignable Liquid Crystalline Conducting Polymers

Summary: The synthetic routes to three series of liquid crystal conducting polymers (based on pyrrole, thiophene, and aniline monomers) are reported and the optimum conditions for polymer preparation are described. These polymers show increased conductivity when laser‐aligned, the greatest effect being shown by the N‐substituted pyrrole‐based system. Information on their liquid crystal and spectroscopic properties and other characteristics are also included.

Structure of the monomers M1, M2, and M3.     

Oxidative Coupling Copolymerization of 4‐Methyltriphenylamine with Arenes

A novel synthetic method for the preparation of high‐molecular‐weight conjugated polymers is presented. It consists of the oxidation copolymerization of different arenes with triphenylamine. The structure of the copolymers was characterized by ¹H and ¹³C NMR spectra. The copolymers have good solubility in common organic solvents and are thermally stable. Photoluminescence (PL) spectra (see Figure) showed that the color of emission depends on the type of arene units in the copolymer chain. Cyclic voltammetry (CV) measurements revealed electrochemical activity of the copolymers.

PL spectra of the copolymers.     

π‐Conjugated Polymers Consisting of Isothianaphthene and Dialkoxy‐p‐phenylene Units: Synthesis,Self‐Assembly,and Chemical and Physical Properties

A series of π‐conjugated alternating copolymers consisting of Th‐ITN‐Th and p‐C₆H₂(OR)₂ units were synthesized. XRD indicated that the copolymers assume an interdigitation packing mode, and UV‐Vis spectra revealed a strong tendency for self‐assembly. Upon molecular assembly of the copolymer, the UV‐Vis absorption shifted by about 100 nm to a longer wavelength from that of the single molecule. The copolymers underwent electrochemical oxidation (or p‐doping) and reduction (or n‐doping) at 0.2 and ?2.0 V versus Ag⁺/Ag, respectively. A p‐doped copolymer film showed an electrical conductivity of 182 S · cm^?1, and the temperature dependence of electrical conductivity was measured. The copolymer showed piezochromism and served as a p‐channel material for a field‐effect transistor.

     

Synthesis of Monodisperse Sequence‐Defined Polymers Using Protecting‐Group‐Free Iterative Strategies

The synthesis of “precision” polymers with finely controlled molecular structures is an important new development in synthetic polymer chemistry. This trend is the logical outcome of the continuing evolution of the field of polymer synthesis. Indeed, during the last few decades, synthetic tools, such as living ionic polymerizations, controlled radical polymerizations, and click chemistry, have revolutionized the synthesis of polymers with controlled architectures such as block, graft, star, brush, hyperbranched or cyclic polymers. These aspects being solved, it is now time for polymer chemists to address more challenging questions such as the design of monodisperse polymers and the control of primary (i.e., comonomer sequences), secondary (i.e., single‐chain folding), and tertiary (i.e., single‐chain compartmentalization) structures. Here, new synthetic tools have to be developed or imported from other disciplines such as organic chemistry and biochemistry. For instance, solid‐phase iterative chemistry, which was initially introduced for the synthesis of oligopeptides and oligonucleotides, is an interesting methodology for preparing monodisperse sequence‐defined polymers. However, such approaches are usually time‐consuming and request demanding coupling/capping/deprotection steps. Yet, interesting protecting‐group‐free methodologies have been described in recent years for simplifying and accelerating these processes. These promising new approaches are briefly listed and explained in this article.