Synthesis of π‐Conjugated Organometallic Polymer Networks

The present paper reports the synthesis of π‐conjugated organometallic polymer networks based on poly[2,5‐dioctyloxy‐1,4‐diethynyl‐phenylene‐alt‐2,5,‐bis(2′‐ethylhexyloxy)‐1,4‐phenylene] (EHO‐OPPE), a soluble poly(p‐phenylene ethynylene) (PPE) derivative. The ethynylene moieties of the polymer coordinate to Pt⁰ centers, which act as conjugated cross‐links. These materials are readily accessible through ligand‐exchange reactions between the linear PPE and Pt(styrene)₃. The in‐situ NMR investigation of model reactions of Pt(styrene)₃ with diphenylacetylene (DPA) has shown that the ethynylene moieties comprised in the PPE readily coordinate to Pt⁰ centers under release of the relatively weakly‐bound styrene ligands. Spin‐coating has resulted in cross‐linked films of good optical quality. We also have been able to produce PPE‐Pt‐gels with high solvent content (> 95 wt.‐%). As expected, the coordination of Pt markedly influences the photophysical characteristics of the PPE. The photoluminescence is efficiently quenched, and the absorption maximum in the visible regime experiences a hypsochromic shift.

Ligand‐exchange reaction between EHO‐OPPE and [Pt(PhCH?CH₂)₃] leading to the target EHO‐OPPE‐Pt⁰ networks.     

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.     

Effect of Side Chains on Charge Transport of Anthracene‐Based PPE–PPV Copolymers

The variation of the drift mobility of positive and negative charge carriers in films of anthracene‐containing poly(p‐phenylene‐ethynylene)‐alt‐poly(p‐phenylene‐vinylene)s ( AnE‐PVs ), differently substituted, is investigated as a function of the applied electric field. Branched 2‐ethylhexyl and linear alkoxy side chains of different lengths are considered, as well as well‐defined and random distributions of lateral substituents. The same conditions are used both for the deposition of the polymer films and for their characterization, which allows for the establishment of a clear relationship between the chemical structure and the charge carrier mobility.

     

Blue Emission of a Soluble Poly(p‐phenylene) with a Cross‐Conjugated Bisimidazole‐Based Chromophore

A novel poly(p‐phenylene) ( 6 ) has been synthesized by a cruciform combination of a polyphenylene backbone with 2,2′‐(p‐phenylene)‐bis(4,5‐diphenylimidazole) ( 5 ) as an additional, orthogonal chromophore. Polymer 6 showed in solution and in the solid state, a blue‐green emission, which is obviously arising from the second bisimidazole‐based chromophore. UV‐Vis spectroscopy, and cyclic voltammetry revealed that the optical and electronic properties of 6 were fully determined by the incorporated 2,2′‐(1,4‐phenylene)bisimidazole structure. The bisimidazole unit led to high solubility and, despite the steric demand of the substituents, at the same time to the blue‐green emission of the poly(p‐phenylene) ( 6 ). In addition, the oxidation of 6 with potassium ferricyanide yielded a low bandgap polymer with a quinoid‐type structure and a bandgap of 1.6 eV.

     

Enhanced Photoluminescence,Mesomorphism and Conformation of Liquid‐Crystalline Conjugated Polymers with Terphenyl Mesogen Pendants

A variety of LCCPs containing terphenyl pendants based on polyacetylene, polythiophene, poly(p‐phenylene) and a poly(p‐phenylene) copolymer backbone have been synthesized. The effects of the structural variation on their properties, especially their mesomorphism, photoluminescence and secondary structures, were studied systematically. Longer alkoxy spacer favor stronger light emission and better mesomorphism. Disubstituted polyacetylenes show better developed mesomorphic textures, higher quantum yields and better thermal stability than their corresponding monosubstituted analogs. Steric effects and the “jacket‐ effect” from the mesogens cause the bulky terphenyl mesogen pendants to rotate around the main chain and force the main chain to assume a spiral conformation along the main chain in long range.

     

Investigation of Bimetallic Nickel Catalysts in Catalyst‐Transfer Polymerization of π‐Conjugated Polymers

A comparative study involving bimetallic nickel catalysts designed from disubstituted N,N,N′,N′‐tetra(diphenylphosphanylmethyl)benzene diamine bridging ligands is reported. Catalyst behavior is explored in the Kumada catalyst‐transfer polymerization (KCTP) using poly(3‐hexylthiophene) (P3HT) as the model system. The success of a controlled polymerization is monitored by analyzing monomer conversion, degree of polymerization, end‐group identity, and molecular weight distribution. The characterization of P3HT obtained from KCTP initiated with the bimetallic catalysts shows chain‐growth behavior; however, the presence of Br/Br end‐groups and broader molecular weight distribution reveals a reduced controlled polymerization compared to the commonly employed Ni(dppp)Cl₂. The observed increase in intermolecular chain transfer and termination processes in KCTP initiation with the bimetallic catalysts can be attributed to a weaker Ni(0)‐π‐aryl complex interaction, which is caused by increased steric crowding of the coordination sphere.     

Molecular Packing and Orientation Transition of Crystalline Poly(2,5‐dihexyloxy‐p‐phenylene)

The effect of thermal treatment on the transition of molecular packing and orientation of the semiconducting poly(2,5‐dihexyloxy‐p‐phenylene) (PPP) film is probed by the combination of in situ 2D grazing incidence X‐ray diffraction (2D GIXD) and selected area electron diffraction (SAED). The structure analysis indicates that PPP crystallizes in an orthorhombic unit cell with a = 21.20 Å, b = 3.78 Å, and c = 4.24 Å. A variation of the annealing temperature from 80 °C to 100 °C demonstrates that the worm‐like morphology in the pristine film melts and develops into nanowires. Furthermore, the molecular orientation transforms from face‐on to edge‐on via thermal annealing. Remarkably, a previously unknown metastable state of “slope” edge‐on with a tilt angle of 51.1° is observed. This orientation change arises from the heterogeneous nucleation and growth of edge‐on PPP crystal during crystallization from the melt.

     

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 and Characterization of Soluble Poly(p‐phenylene) Derivatives for PLED Applications

PPP derivatives with high molecular weights were synthesized and characterized by FT‐IR, ¹H, ¹³C NMR and GPC. The decomposition temperatures of 2a–2c were above 300–400 °C. DSC analysis indicated their nature to be crystalline as all of them exhibited a melt temperature on controlled heating. Optical and electrochemical band gaps was determined using UV/Vis spectroscopy and CV. Single‐layer PLEDs fabricated with 2a–2c displayed high threshold voltages due to high potential barrier for holes. Their EL spectra reveal a small shift in blue peak and the emission form higher wavelength shoulder peak is enhanced.

     

Charge‐Transfer‐Complexed Conjugated Microporous Polymers (CT‐CMPs)

A new concept of the formation of charge transfer (CT) complexes between an intrinsically electron‐donating conjugated microporous polymer and a small molecule acceptor is reported. Spirobifluorene‐based mesoporous organic polymers with high porosity and Brunauer–Emmett–Teller surface area are synthesized by the Suzuki‐coupling reaction of spirobifluorene and pyrene monomers. The simple doping of the synthesized mesoporous, electron‐rich, conjugated polymer with 7,7,8,8‐tetracyanoquinodimethane as an acceptor leads to efficient CT complexation in the electron‐donating mesoporous spaces. This results in a high‐speed synthesis (within 5 s), thermally stable compound (up to about 200 °C), and good control of the concentration of donor–acceptor pairs in the CT complex.     

Screening of Film‐Formation Qualities of Various Solvent Systems for π‐Conjugated Polymers Via Combinatorial Inkjet Printing

A systematic investigation of the relationships between the choice of solvent system and the film quality of inkjet printed π‐conjugated polymer films is presented. Solution properties, such as surface tension and viscosity, have no effect on the final film quality, whereas the boiling point of the solvent and, more specifically, the difference in boiling point between the main and the co‐solvent have a strong influence on the final film quality. New solvent systems are developed based on non‐chlorinated, aromatic solvents that reveal homogeneous films when the difference in boiling point between the main and the co‐solvent is between 90 and 100 °C.     

Design of Open‐Shell π‐Conjugated Microporous Polymer Film with Super‐High Conductivity

Polymers with open‐shell π‐conjugated structure and thiophene‐based building blocks are designed for electropolymerization. These systems are expected to electropolymerize and form solution‐processable conjugated microporous polymer films, which can be used for device fabrications. The designed radical structure has a low highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap, high electronic hopping rate for the hole transfer and electron transfer, and ultimately high conductivity. The eclipsed dimer has higher conductivities than that of staggered dimer. The designed monomer with substituted groups has lower conductivities due to steric effect. The open‐shell systems designed will be promising materials with various applications. Design principles for open‐shell organic materials can be established based on the trends of this paper.     

“Heavy‐Atom” Donor–Acceptor Conjugated Polymers

Heavy‐atom substitution chemistry in donor–acceptor (D–A) conjugated polymers has gained increasing attention in the past few years. Overall, the introduction of “heavy” atoms (below C in group 14; below N in group 15; below S in group 16) into D–A conjugated polymers allows control over properties through relatively straightforward synthetic chemistry, and produces materials with high molecular weights (>20 000 g mol^?1), strong absorption (ε ≈ 40 000 L mol^?1 cm^?1), narrow highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gaps (<1 eV), as well as high charge‐carrier mobility (>10^?2 cm² V^?1 s^?1). This Trend article aims to describe heavy‐atom substitution effects in D–A polymers, and their applications, by systematically examining representative polymer structures.

     

Design of Random and Semi‐Random Conjugated Polymers for Organic Solar Cells

Significant effort has been devoted to the improvement of organic solar cell performance via the optimization of polymer structure. The expanding scope of conjugated polymer design extends from novel monomers to side‐chain and backbone engineering. These efforts target desired properties for optimal organic photovoltaic performance, including electronic aspects such as optical band gaps, frontier orbital levels, and charge carrier mobilities, as well as physical aspects such as surface energy. Perfectly alternating, donor‐acceptor copolymers represent the state‐of‐the‐art, having low band gaps and demonstrating record efficiencies. However, recent reports indicate significant potential by introducing some degree of randomization to donor‐acceptor copolymers. Specifically, semi‐random copolymers have demonstrated promising photovoltaic performance through incorporation of small ratios of acceptor monomers into a donor‐dominant polymer backbone. Semi‐random polymers have also been found uniquely suited to the optimization of ternary blend solar cells, which benefit from highly tunable randomized structures by means of energy level matching, complementary optical absorption, and directed polymer‐polymer miscibility via surface energy tuning. In this trend article the scope of random and semi‐random polymers, many based on poly(3‐hexyl thiophene), is explored, primarily in the context of solar cell applications. Distinctions between regimes of random copolymers are also defined and discussed.     

Self‐Assembly Behavior and Optical Properties of Poly(3‐thiopheneacetate)/Dialkyldimethylammonium Complexes

Poly(3‐thiopheneacetate)/dialkyldimethylammonium complexes (PTA‐Cn) were prepared by mixing regiorandom poly(3‐thiopheneacetic acid) with dialkyldimethylammonium bromide to study the effect of their self‐assembled structures on the optical properties. The lengths of the alkyl groups in the ammonium salts were varied from decyl (C10) to octadecyl (C18) groups. These complexes showed fully developed layer structures with ordered mesophases. PTA‐C16 and PTA‐C18 with longer alkyl groups showed side‐chain crystalline phases, and PTA‐C10, PTA‐C12, and PTA‐C14 with shorter alkyl groups showed side‐chain crystalline and liquid crystalline phases at room temperature. When PTA‐C18 was heated, a melting transition from side‐chain crystalline to smectic liquid crystalline phase was observed at 41.5 °C. The maximum absorption and emission wavelengths of these complexes increased with increasing alkyl chain length indicating that the π‐conjugated structure of the regiorandom thiophene backbone changes according to the alkyl groups.

     

Grafting Polymers from Poly(2,6‐dimethyl‐1,4‐phenylene oxide) as New Thermoplastics

Graft polymers with poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) as backbones are successfully prepared via two convenient steps. The utilization of semiflexible PPO as backbones offers unique properties for the graft polymers. Thermal, rheological, and phase behaviors of these new graft polymers are well controlled via the precise design of architectural parameters. The disordered microphase separation in melt state and the proper composition of side grafts provide the ease of thermal processing for these graft polymers. The graft density shows impact on the relaxation and mechanical properties of the thermoplastics. This work shows the possibility to use lots of semiflexible engineering polymers as backbones to construct new thermoplastics.

     

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.     

Synthesis of π‐Conjugated Polymer Thin Films by Electropolymerization of Benzodithiophene Derivatives

π‐conjugated polymer thin films are successfully prepared by the electropolymerization of 4,5‐diaryl benzodithiophenes, which are readily obtained by the three‐component coupling reactions of aryl iodides, 1,2‐di(thiophen‐2‐yl)ethyne, and phenylboronic acid, followed by the photochemical annulation. The resulting polymer films exhibit π‐conjugated properties as convinced from their UV–vis absorption spectra and cyclic voltammetric analyses. The electronic properties such as highest occupied molecular orbital (HOMO) energy levels of the resulting polymer films are affected by the 4‐aryl substituents. The π‐conjugated polymer thin films exhibit electrochromism, where the color of the polymer film turns from yellow to blue by oxidation.     

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.     

Synthesis of π‐Conjugated Polymer Possessing Mercapto‐Substituted 1,3‐Butadiene‐1,4‐diyl Units by Reaction of Regioregular Organometallic Polymer Having Titanacyclopentadiene Moieties in the Main Chain

A π‐conjugated polymer having 1,4‐bismercapto‐substituted 1,3‐diene units in the main chain was prepared by the novel polymer reaction of a regioregular organometallic polymer having titanacyclopentadiene‐2,5‐diyls units with benzenesulfenyl chloride. The number‐average molecular weight and the molecular weight distribution of the polymer derived from 1,4‐diethynyl‐2,5‐di(2‐ethylhexyloxy)benzene were estimated to be 5 700 and 1.6, respectively, from the GPC analysis. The π‐conjugated character, photoluminescence behavior both in solid‐state and solutions, and the electron‐donating properties of the π‐conjugated polymer are discussed on the basis of its UV‐vis spectrum, photoluminescence spectrum, and CV analysis.