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.     

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.     

Films of Highly Disperse Electrodeposited Poly(N‐vinylcarbazole)–Graphene Oxide Nanocomposites

The electrodeposition of polymer nanocomposite thin films of PVK–GO is demonstrated. Highly exfoliated and stable graphene oxide (GO) solutions are prepared by incorporating poly(N‐vinylcarbazole) (PVK) through mixing. Enhanced stability up to 30 d is observed in both aqueous and organic solvents. TGA, XRD, FTIR, and UV‐vis measurements confirm nanocomposite formation. CV enables electrodeposition of the films. The presence of GO on the PVK–GO surface is confirmed by the appearance of the C=O and OH stretching vibrations, attributed to the carboxylic and hydroxyl groups of GO. AFM measurements show homogeneous and well‐defined film morphology.     

A Study of Diphenylfumaronitrile and Furan‐Substituted Diketopyrrolopyrrole Alternating Copolymer and Its Thin‐Film Transistors

A fused aromatic furan‐substituted diketopyrrolopyrrole and novel diphenylfumaronitrile conjugated building blocks are used for the synthesis of an alternating copolymer ( DPFN‐DPPF ) via Suzuki polycondensation. In this paper, the first attempt to use the diphenylfumaro­nitrile building block for the synthesis of conjugated polymer is described. The number‐average and weight‐average ­molecular weights calculated for DPFN‐DPPF are 20 661 and 66 346 g mol^?1, respectively. The optical bandgap calculated for DPFN‐DPPF is 1.53 eV whereas the highest occupied molecular orbital (HOMO) value calculated by photoelectron spectroscopy in air (PESA) is 5.50 eV. The calculated HOMO value is lower, which is suitable for stable organic electronic devices. DPFN‐DPPF polymer is used as an active layer in bottom‐contact bottom‐gate organic thin‐film transistor devices and the thin film exhibits a hole mobility of 0.20 cm² V^?1 s^?1 in air.

     

Formation of Macrocycles in the Synthesis of Poly(N‐(2‐ethylhexyl)carbazol‐3,6‐diyl)

A series of polymerizations of 3,6‐dibromo‐9‐(2‐ethylhexyl)carbazole was carried out in different monomer concentrations using standard Yamamoto reaction conditions. It was found that the molecular weight of the resulting poly(N‐(2‐ethylhexyl)carbazol‐3,6‐diyl) strongly depends on the monomer concentration in the reaction mixture. Matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) measurements confirmed the formation of low‐molar‐mass cyclic oligomers of the 3,6‐disubstituted carbazole. In this paper we describe, for the first time, the formation of large amounts of a cyclic tetramer and of higher macrocycles in the synthesis of poly(N‐alkyl‐3,6‐carbazoles) by the Yamamoto method. This seems to be a limiting factor in the synthesis of high molecular weight poly(N‐alkyl‐3,6‐carbazole)s. The optical, thermal, and electrochemical properties of poly(N‐(2‐ethylhexyl)carbazol‐3,6‐diyl) have been investigated. Poly(N‐(2‐ethylhexyl)carbazol‐3,6‐diyl) is thermally stable, with 5% weight loss at 460 °C in nitrogen. The polymer exhibits a weak blue fluorescence with a maximum at 425 nm. Poly(N‐(2‐ethylhexyl)carbazol‐3,6‐diyl) is electrochemically stable, its highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels are ?5.0 and ?1.6 eV, respectively.

     

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.     

Isoindigo (IID)‐Based Semiconductor with F⋯S Interaction Locked Conformation for High‐Performance Ambipolar Bottom‐Gate Top‐Contact Field‐Effect Transistors

The development of high‐performance ambipolar polymer semiconductors is critical to organic electronics. Herein, isoindigo (IID)‐based copolymers PIIDDTBT and PIIDDTffBT are synthesized and characterized. Both polymers have suitable highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels for hole and electron injection. Density functional theory calculation reveals F?S intramolecular interactions are formed in PIIDDTffBT , which locks the molecular conformation and leads to a more planar backbone. Thin film transistor characterization shows both polymers display ambipolar charge carrier transport behavior. The hole/electron mobilities are 0.29/0.1 cm² V^?1 s^?1 for PIIDDTffBT and 0.053/0.013 cm² V^?1 s^?1 for PIIDDTBT in the bottom‐gate/top‐contact (BGTC) device structures. The hole/electron mobilities of PIIDDTffBT are one of the highest values for IID‐based ambipolar polymer transistors in BGTC device structure. Atomic force microscopy and X‐ray diffraction results reveal PIIDDTffBT films have higher film quality, crystallinity, and more ordered microstructures, being ascribed to the F?S interactions locked backbone. These results demonstrate that the introduction of F?S interactions is an effective strategy to design high‐performance ambipolar polymer semiconductors.     

Systematic Investigation of a Novel Low‐Bandgap Terpolymer Library via Inkjet Printing: Influence of Ink Properties and Processing Conditions

The thin‐film properties of a polymer library consisting of novel conjugated low‐bandgap poly(diketopyrrolopyrrole‐co‐benzothiadiazole‐co‐fluorene) (poly(DPP‐co‐BTD‐co‐F)) polymers are investigated. The content of the monomer units in the copolymers is systematically varied. Structure–property relationships are obtained for the ink characteristics, the film formation qualities, and their optical properties. Toluene/o‐DCB in a ratio 90/10 and a concentration of 5 mg mL^?1 is found to be a suitable solvent system for all polymers. The polymer compositions and the choice of solvent have a significant influence on the film properties. Inkjet printing is shown to be a suitable technique for the preparation of thin‐film libraries that subsequently can be characterized by combinatorial screening tools.     

The Photoelectric Properties of Polymer Acceptors Containing Oxadiazole and Thiadiazole

By the introduction of electron‐deficient five‐membered heterocycles 1,3,4‐oxadiazole (OZ) or 1,3,4‐thiadiazole (TZ) moieties, two new A₁–D–A₂–D‐type polymer acceptors containing naphthalene diimide, named PNOZ and PNTZ, are prepared and applied for all‐polymer solar cells. Both polymer acceptors possess deeply lowest unoccupied molecular orbital (LUMO) energy levels below −4.0 eV and show broad absorption spectra in the range of 300–800 nm. Compared with PNOZ, PNTZ shows broader and stronger absorption, slightly higher lying LUMO level and better microphase separation size. Employing PNTZ as the acceptor material and PTB7 as the donor material, the all‐polymer solar cells based on PTB7/PTNZ (1:1, by weight) give the best power conversion efficiency of 2.58% with a short‐circuit current density (J _sc) of 10.05 mA cm⁻², an open‐circuit voltage (V _oc) of 0.70 V, and a fill factor (FF) of 0.37 due to the formation of a well‐optimized, bicontinuous network of the donor and acceptor polymer domains.

     

Novel Supramolecular Polymers Based on Zinc‐Salen Chromophores for Efficient Light‐Emitting Diodes

Summary: A novel series of supramolecular polymers based on zinc‐salen chromophores were readily prepared via ligand‐metal coordination. These polymers were characterized by FT‐IR, NMR, GPC and elemental analysis. All the polymers were readily soluble in common organic solvents and had substantially good thermal properties. Cyclic voltammetry revealed they had LUMO energy levels ranging from −3.20 to −3.23 eV and HOMO energy levels ranging from −6.13 to −6.15 eV. The polymer films can emit strong green photoluminescence (PL) with relatively high quantum efficiencies of 42–51%. Light‐emitting diodes with the configuration ITO/PEDOT/polymer/BCP/Alq₃/LiF/Al were efficient green emitters, with maximum current efficiencies of 0.9–2.3 cd · A⁻¹. The preliminary EL results thus suggest that these polymers are potential candidates for efficient green emission in polymer LEDs.

Structures of polymers produced.     

Direct Insertion Mass Spectrometric Analysis of Thermal Degradation of Poly(2‐alkyl‐2‐oxazoline)

Direct pyrolysis mass spectrometry is applied to investigate the thermal behavior of poly(2‐isopropyl‐2‐oxazoline) (PIPOX, a thermoresponsive polymer) and poly[2‐(3‐butenyl)‐2‐oxazoline] (PBOX, a “clickable” polymer). It is found that the thermal degradation of PIPOX is started by a loss of side chains. At slightly higher temperatures the degradation of the polymer backbone occurs by random chain scission processes. In the case of PBOX, vinyl polymerization of the side chains produces chains with variable thermal stabilities. The number of repeating units of the polymer has almost no effect on the thermal behavior of PIPOX, but significantly affects both thermal stability and degradation product distribution of PBOX.     

Synthesis and Photovoltaic Properties of Donor–Acceptor Copolymer Based on Dithienopyrrole and Thienopyrroledione

A novel donor–acceptor (D–A) type alternating copolymer based on dithieno[3,2‐b:2′,3′‐d]pyrrole (DTP) and thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) was synthesized. The polymer has a broad absorption spectrum in the range of 350–810 nm. The energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the copolymer were ?5.11 and ?3.63 eV, respectively, as determined by cyclic voltammetry. Bulk heterojunction type polymer solar cells based on PDTP‐TPD and PC₇₀BM, showed power conversion efficiency (PCE) up to 1.6% with an open‐circuit voltage of V_OC = 0.66 V, a short‐circuit current of I_SC = 4.98 mA · cm^?2, and a fill factor of FF = 0.50. The V_OC of 0.66 V is the highest value among DTP‐based photovoltaic polymers.

     

Carbazole‐Substituted Triphenylamine and Diketopyrrolopyrrole Alternating Copolymer for Photovoltaic Cells

A new alternating conjugated polymer (PTCDPP) of carbazole‐substituted triarylamine and diketopyrrolopyrrole is prepared and characterized in detail. The polymer exhibits two strong absorption bands at 345 and 600 nm. With highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of ?5.13 eV and ?3.67 eV, PTCDPP displays an energy gap of 1.66 eV. PTCDPP‐based bulk heterojunction solar cells with a structure of fluorinated tin oxide (FTO)/TiO₂/PTCDPP:[6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM)/MoO₃/Ag are fabricated. The devices are optimized by adjusting the composition of the PTCDPP:PCBM active layer, thermal treatment, and addition of processing additives. The device based on PTCDPP:PCBM (1:4, w/w) shows a power conversion efficiency (PCE) of 2.31%, with a short‐circuit current of 4.17 mA cm^?2, an open‐circuit voltage of 0.79 V, and a fill factor of 0.35. The best cell performance (2.65% PCE) is achieved by using 1,8‐diiodooctane (3%, v/v) as a processing additive and annealing the active layer at 80 °C.

     

Thermoresponsive UCST‐Type Behavior of Interpolymer Complexes of Poly(ethylene glycol) and Poly(poly(ethylene glycol) methacrylate) Brushes with Poly(acrylic acid) in Isopropanol

Upper critical solution temperature (UCST)‐type thermoresponsive behavior of poly(ethylene glycol)–poly(acrylic acid) (PEG–PAA) and poly(poly(ethylene glycol) methacrylate)–poly(acrylic acid) (PPEGMA–PAA) interpolymer complexes has been observed in isopropanol. For these investigations, PPEGMA and PAA with various average molecular weights have been synthesized by atom transfer radical polymerization. It has been found that both the PEG and PPEGMA have lower cloud point temperatures (T _cp) than its mixed polymer solutions with PAA, whereas PAA does not show such behavior in the investigated temperature range. These findings indicate the reversible formation of interpolymer complexes with variable structure and composition in the solutions of the polymer mixtures in isopropanol. Increasing the ethylene glycol/acrylic acid molar ratio or the molecular weight of either the PAA or the H‐acceptor PEG component of the interpolymer complexes increases the UCST‐type cloud point temperatures of these interpolymer systems. The polymer–polymer interactions by hydrogen bonds between PAA and PEG or PPEGMA and the correlations between T _cp and structural parameters of the components revealed in the course of these investigations may be utilized for exploring well‐defined UCST‐type material systems for various applications.

     

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.     

Poly(amine‐amide‐imide)s Bearing Pendent N‐Carbazolylphenyl Moieties: Synthesis and Electrochromic Properties

Summary: A series of novel poly(amine‐amide‐imide)s with pendent N‐carbazolylphenyl units that have inherent viscosities of 0.45–0.66 dL · g⁻¹ are prepared from various aromatic bis(trimellitimide)s and the new carbazole‐based aromatic diamine, 4,4′‐diamino‐4″‐N‐carbazolyltriphenylamine, by direct polycondensation. All the polymers are readily soluble in polar organic solvents. Flexible, amorphous, and deep reddish films of poly(amine‐amide‐imide)s can be obtained by solution casting, and have useful levels of thermal stability associated with high glass transition temperatures (307–343 °C), 10% weight‐loss temperatures in excess of 500 °C, and char yields at 800 °C in nitrogen higher than 65%. These polymers exhibit a maximum UV‐vis absorption at 300 nm with a fluorescence emission maxima around 449–454 nm in N‐methyl‐2‐pyrrolidinone solution. The hole‐transporting and electrochromic properties are examined by electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the poly(amine‐amide‐imide) films cast onto an indium tin oxide‐coated glass substrate exhibit a reversible oxidation at 0.84 V and irreversible oxidation redox couples at 1.27 V versus Ag/AgCl in acetonitrile solution, and reveal good stability of electrochromic characteristics, with a color change from yellowish to green at applied potentials ranging from 0.00 to 0.95 V.

Structure and properties of PAI‐2M (bottom left: cyclic voltammetry; bottom right: potential‐step absorptometry).     

Supramolecularly Designed Thermoresponsive Polymers in Different Polymer Backbones

Thermoresponsive polymers in water, for example, poly(N‐isopropylacrylamide) (PNIPAM) are investigated extensively, due to a wide range of biomedical applications. However, the attempts to control thermoresponsiveness are still rare in less or nonpolar media. Herein, the three thermoresponsive homopolymers tethering an N‐butylurea group in the side chain with a different polymer backbone are reported. They exhibit lower critical solution temperature (LCST)‐type and upper critical solution temperature (UCST)‐type thermoresponsiveness depending on association of the urea group in the polymer chain and hydrogen bonding small molecules (effectors) in ternary systems (polymer/effector/organic solvent). The difference of polymer backbone appears as their change of solvophobicity in organic solvents. Poly(methacrylate) backbone needs more amount of the effector in nonpolar organic solvents, and poly(vinyl ether) backbone needs more amount in polar organic solvents. However, the influence of polymer backbone is too little to change the phase transition behavior, and the thermoresponsiveness is dominated by association and dissociation of hydrogen bondings between polymers and effectors. The supramolecular design of the thermoresponsive polymers is strong and extensible for the design of their phase transitions.     

Polyphenylenes and Poly(phenyleneethynylene)s with 9,10‐Anthrylene Subunits

Summary: Light‐emitting conjugated polyphenylenes and poly(phenyleneethynylene)s have been synthesized, which comprise of 9,10‐linked anthracene repeat units with branched alkyl side‐chains (2‐octyldecyl) at the 2,6‐positions with p‐terphenyl ( P1 ), p‐diethynylbenzene ( P2 ), and diphenylacetylene ( P3 ) units. Both Sonogashira‐Hagihara and Suzuki‐Miyaura‐type cross‐coupling reactions under palladium catalysis were used as polycondensation methods. The branched alkyl side chains not only improve the solubility of the resulting copolymers but also prevent stacking in the solid state as evident from the almost identical PL spectra in solution and film. The copolymers P1 and P3 display pure blue emission while P2 exhibits green emission due to the extended π‐system along the polymer backbone. All polymers possess high thermal stability and P1 shows the best solubility and film‐forming ability among the three copolymers investigated. Furthermore, the enhanced color stability of this material is demonstrated by the almost identical PL spectra obtained on annealing at 200 °C.

Alternating copolymers P1 , P2 , and P3 .     

Temperature and pH Dual‐Responsive Behavior of Dendritic Poly(N‐isopropylacrylamide) with a Polyoligomeric Silsesquioxane Core and Poly(2‐hydroxyethyl methacrylate) Shell

Novel temperature and pH dual‐responsive dendritic polyoligomeric silsesquioxane (POSS)–poly(N‐isopropylacrylamide) (PNIPAm)–poly(2‐hydroxyethyl methacrylate) (PHEMA) copolymers are prepared via atom transfer radical polymerization and click reactions. The cloud points (T_c) decrease with decreasing pH from 10.0 to 5.0 due to the weakened inter‐molecular interactions and enhanced intra‐molecular hydrogen bonding, whereas the T_c exhibits a small increase from pH 5.0 to 4.0 because of the better solvation of PHEMA at highly acidic conditions. The above findings are corroborated by the different sizes of aggregates observed by dynamic light scattering. The encapsulation of a fluorescent dye and stimulated release by temperature and pH changes are also demonstrated.     

Design,Synthesis, and Photophysical Property of Strongly Fluorescent Benzofuran–Ethynylene Copolymer

A novel alternating benzofuran–ethynylene copolymer is designed and synthesized through a series of palladium‐catalyzed reactions, and extremely strong fluorescence is observed. The electronic levels of frontier orbitals are estimated by electrochemical and photophysical measurements for copolymer and corresponding monomers. The extension of π‐electron conjugation is shown after polymerization reaction, in which the energy of highest occupied molecular orbital (HOMO) is increased and that of the lowest unoccupied molecular orbital (LUMO) is decreased, simultaneously. The fluorescence quantum yield of this copolymer is as high as 75%, and time‐resolved fluorescence measurement confirms this intrinsic property. A preliminary optoelectronic device is fabricated to test the potential application of this copolymer as an emitting layer. In comparison with other known dibenzofuran‐based materials, moderate performance is obtained. The incorporation of a benzofuran group combining acetylene moiety in a polymeric skeleton provides a novel choice of highly fluorescent materials.