TABLE OF CONTENTS

Volume 49, Issue 1 (January 2017)

Special Issue: Photo- and Electro-Functional Polymers and Molecular Assemblies

The January 2017 issue of Polymer Journal is a special issue on Photo- and Electro-Functional Polymers and Molecular Assemblies, featuring collections of reviews and articles that include outstanding research on synthesis, functions, and applications of π-conjugated molecular, polymer and liquid-crystalline materials. We would like to thank special issue editors, Prof. Takuma Yasuda, Prof. Wen-Chang Chen and Prof. Takashi Kato for their support with the planning and coordination of this issue.

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Editorial

Special Issue: Photo- and Electro-Functional Polymers and Molecular Assemblies  

Takuma Yasuda, Wen-Chang Chen and Takashi Kato

Polym J 49: 1; doi:10.1038/pj.2016.111

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Focus Reviews

Physical Properties of Polymers

Revealing mechanical and structural properties of molecules on surface by high-resolution atomic force microscopy  

Shigeki Kawai

Polym J 49: 3-11; advance online publication, October 19, 2016; doi:10.1038/pj.2016.106

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The state-of-the-art atomic force microscopy allows us to observe inner structures of single molecules. Such observation is quite beneficial to study single and self-assembled molecules on surface as well as on-surface chemical reaction. This focus review describes recent technical improvement and achievements in the field of on-surface molecule studied with high-resolution atomic force microscopy.

Functional Polymers

Development of donor–acceptor copolymers based on dioxocycloalkene-annelated thiophenes as acceptor units for organic photovoltaic materials  

Yutaka Ie and Yoshio Aso

Polym J 49: 13-22; advance online publication, October 12, 2016; doi:10.1038/pj.2016.96

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A series of dioxocycloalkene-annelated thiophenes was designed to utilize as noble acceptor units in donor–acceptor (D–A) copolymers, and D–A copolymers containing these acceptor units were systematically developed for the application to organic photovoltaics (OPVs). Photophysical and electrochemical properties of these copolymers as well as their photovoltaic performance under the combination with [6,6]-phenyl-Cx-butyric acid methyl ester (x=61 or 71) were summarized. These systematic investigations provide important clues for the development of high-performance D–A-type OPV materials.

Self-assembled Materials

Liquid crystalline organic semiconductors for organic transistor applications  

Hiroaki Iino and Jun-ichi Hanna

Polym J 49: 23-30; advance online publication, October 12, 2016; doi:10.1038/pj.2016.101

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Liquid crystalline organic semiconductors are good candidates for organic transistors because the materials have properties that are beneficial compared with those of polymer materials. Liquid crystalline materials show good solution processability for the fabrication of uniform crystalline thin films. The novel liquid crystalline material 2-phenyl-7-decyl[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-10) exhibits a highly ordered liquid crystal phase, and has good solution processability and high thermal durability to use for creating transistor devices with high mobility, over 10cm2Vs−1, following thermal annealing.

A new class of nanostructured supramolecular organic semiconductors based on intertwined multi-lamellar co-assemblies in π-conjugated liquid-crystalline side-chain polymers  

Yiming Xiao, Danli Zeng, Leszek Mateusz Mazur, Andrea Castiglione, Emmanuelle Lacaze, Benoît Heinrich, Bertrand Donnio, David Kreher, André-Jean Attias, Jean-Charles Ribierre and Fabrice Mathevet

Polym J 49: 31-39; advance online publication, November 9, 2016; doi:10.1038/pj.2016.107

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In this focused review, we provide an overview of our recent work on the design and synthesis of a new type of side-chain liquid crystal π-conjugated polymeric system associating regioregular poly(3-alkylthiophene) backbones with laterally pending π-conjugated mesogenic groups. Several polymeric architectures have been prepared based on different polymer backbone structures and various side groups, providing important insight into the relationships among the polymeric architecture, nano- and macroscale organization and charge transport properties in such self-organized multi-lamellar macromolecular systems.

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Reviews

Functional Polymers

Structure and design of polymers for durable, stretchable organic electronics  

Jonathan Onorato, Viktoria Pakhnyuk and Christine K Luscombe

Polym J 49: 41-60; advance online publication, September 7, 2016; doi:10.1038/pj.2016.76

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Stretchable electronics are an attractive means for producing mechanically robust devices with enhanced utility and can enable novel applications such as conformal solar cells, electronic skin and wearable electronics. Approaches to stretchable organic electronics, specifically polymer solar cell active layer materials, via a molecular design strategy are presented. Further discussion into polymer blends and engineering approaches to producing other types of stretchable electronics is given. The relationships between mechanical and electrical properties of all these materials are discussed and suggestions are given for future areas of research.

Renewable polymeric materials for electronic applications  

Han-Sheng Sun, Yu-Cheng Chiu and Wen-Chang Chen

Polym J 49: 61-73; advance online publication, October 19, 2016; doi:10.1038/pj.2016.95

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Developing renewable polymeric materials for electronics applications is crucial toward next generation of green electronic industry. Current progress on the renewable materials used as the passive and active components in electronics is reviewed, where the correlation between the relationships of chemical structures, morphology and device characteristics is featured. Furthermore, their future perspectives are provided for foreseeable paths in the development of green electronics.

Self-assembled Materials

Integration of electro-active π-conjugated units in nanosegregated liquid-crystalline phases  

Masahiro Funahashi

Polym J 49: 75-83; advance online publication, October 5, 2016; doi:10.1038/pj.2016.91

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Perylene tetracarboxylic bisimide (PTCBI) derivatives bearing oligosiloxane moieties were synthesized. At room temperature, the PTCBI derivatives bearing oligosiloxane chains exhibit a nanosegregated columnar phase in which crystal-like π-stacks are surrounded by a liquid-like mantle. These PTCBI derivatives are soluble in various organic solvents, and thin films can be produced by a spin-coating method. The PTCBI derivatives bearing polymerizable cyclotetrasiloxane rings show the liquid crystalline (LC) phases at room temperature. The spin-coated films of the LC PTCBI derivatives with cyclotetrasiloxane rings can be polymerized and insolubilized by exposure to the vapors of trifluoromethanesulfonic acid.

Liquid crystals in photovoltaics: a new generation of organic photovoltaics  

Manish Kumar and Sandeep Kumar

Polym J 49: 85-111; advance online publication, November 9, 2016; doi:10.1038/pj.2016.109

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Liquid crystals (LCs) have recently gained significant importance in organic photovoltaics (PVs). Power-conversion efficiency up to about 10% has reached in solar cells incorporating LCs. This review presents an overview of the developments in the field of organic PVs with LCs. Comprehensive details of LCs used in bilayer solar cells, bulk heterojunction solar cells and dye-sensitized solar cells have been given. An outlook into the future of this newly emerging, fascinating and exciting field of self-organizing supramolecular LC PV research is provided.

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Original Articles

Polymer Synthesis and Reactions

Double acceptor donor–acceptor alternating conjugated polymers containing cyclopentadithiophene, benzothiadiazole and thienopyrroledione: toward subtractive color organic photovoltaics  

Shu-Wei Chang, Tsuyoshi Muto, Takeshi Kondo, Ming-Jhih Liao and Masaki Horie

Polym J 49: 113-122; advance online publication, September 14, 2016; doi:10.1038/pj.2016.72

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Double acceptor donor–acceptor alternating conjugated copolymers comprising thienopyrroledione, benzothiadiazole, two cyclopentadithiophene groups and their analogs with thiophene or bithiophene units have been synthesized by combinations of direct arylation, Suzuki and Stille coupling and oxidative polymerization. These polymers were used to fabricate bulk heterojunction organic photovoltaic (OPV) devices with fullerene derivatives. The active layer comprising the double acceptor polymer with fullerene derivatives showed a subtractive color resulting from wide-range visible light absorption, which is advantageous for practical OPV applications.

Direct arylation polycondensation for the synthesis of bithiazole-based conjugated polymers and their physical properties  

Junpei Kuwabara, Masahiro Kuramochi, Songlin Liu, Takeshi Yasuda and Takaki Kanbara

Polym J 49: 123-131; advance online publication, September 7, 2016; doi:10.1038/pj.2016.75

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Direct arylation polycondensation using Pd(PCy3)2 as a precatalyst in N,N-diethylpropanamide as a reaction solvent afforded three types of the bithiazole-based conjugated polymers that have been difficult to synthesize under previously reported conditions using N,N-dimethylacetamide. The obtained polymers exhibited aggregation properties and high crystallinity. Control of aggregation was a key factor for increasing the power conversion efficiency of the organic photovoltaic devices fabricated from these polymers.

Functional Polymers

Twisting poly(3-substituted thiophene)s: cyclopolymerization of gemini thiophene monomers through catalyst-transfer polycondensation  

Chunhui Zhao, Kazuhiko Nagura, Masayuki Takeuchi and Kazunori Sugiyasu

Polym J 49: 133-139; advance online publication, July 27, 2016; doi:10.1038/pj.2016.66

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Herein, we demonstrate a new approach to control a structural parameter of polythiophene: the dihedral angle of the backbone. To achieve this, we exploited the unique polymerization mechanism of cyclopolymerization. We designed and synthesized gemini thiophene monomers in which two thiophene monomers are tethered by an alkylene strap and we processed the monomers by using the catalyst-transfer polycondensation method. We found that the dihedral angle in the polythiophene is dictated by the size of the macrocycle formed, thus allowing for the control of the photophysical properties of polythiophenes.

Semi-crystalline A1–D–A2-type copolymers for efficient polymer solar cells  

Thanh Luan Nguyen, Hyosung Choi, Seo-Jin Ko, Taehyo Kim, Mohammad Afsar Uddin, Sungu Hwang, Jin Young Kim and Han Young Woo

Polym J 49: 141-148; advance online publication, September 21, 2016; doi:10.1038/pj.2016.88

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Three types of A1–D–A2 conjugated polymers were synthesized based on thiophene as an electron-rich unit and two similarly structured electron-deficient moieties of benzothiadiazole (BT) and benzotriazole (BTz). The weaker acceptor, BTz, with three alkyl (or alkyloxy) substituents took on a solubilizing role without deteriorating the chain planarity. The absence of alkyl substituents on thiophene induced a deep valence band. Increasing the number of fluorine substituents on BT decreased the frontier orbitals and enhanced the interchain packing. The chain planarity and crystalline interchain organization were facilitated via intra- and/or interchain non-covalent S···O and S···F coulombic interactions. The best power conversion efficiency of 7% was measured for BTzDT2FBT:PC71BM.

Inhibition of solution-processed 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile crystallization by mixing additives for hole injection layers in organic light-emitting devices  

Satoru Ohisa, Yong-Jin Pu, Shogo Takahashi, Takayuki Chiba and Junji Kido

Polym J 49: 149-154; advance online publication, September 28, 2016; doi:10.1038/pj.2016.92

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The inhibition of solution-processed 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN) crystallization by mixing additives was successfully achieved for hole injection layers (HILs) in organic light-emitting devices (OLEDs). Among various additives, the film mixed with pyrazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile (PPDN) showed both transparent appearance and high solvent resistances to an upper layer coating solvent. We applied the HAT-CN mixed with PPDN for an HIL in an OLED including solution-processed four-layer stack. The device showed lower driving voltage and higher luminescent efficiency than a device containing conventional HIL, poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT:PSS).

The synthesis and purification of amphiphilic conjugated donor–acceptor block copolymers  

Valerie D Mitchell, Wallace W H Wong, Mukundan Thelakkat and David J Jones

Polym J 49: 155-161; advance online publication, October 19, 2016; doi:10.1038/pj.2016.97

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Hydrophilic tetraethylene glycol moieties are incorporated into the electron-accepting block of a donor–acceptor block copolymer (BCP) to afford two novel amphiphilic materials based on the P3HT-b-PFTBT scaffold. These amphiphilic BCPs are designed to provide enhanced morphological control as organic photovoltaic active layer materials. The chemical disparity introduced by the hydrophilic side chains enabled the design of a purification system capable of isolating the BCP product, an advantage over previously reported systems.

Synthesis of linear PEDOT fibers by AC-bipolar electropolymerization in a micro-space  

Masato Ohira, Yuki Koizumi, Hiroki Nishiyama, Ikuyoshi Tomita and Shinsuke Inagi

Polym J 49: 163-167; advance online publication, October 12, 2016; doi:10.1038/pj.2016.100

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Alternating current bipolar electropolymerization of 3,4-ethylenedioxythiophene (EDOT) was performed in the presence of benzoquinone in tetrabutylammonium perchlorate/acetonitrile. The obtained poly(3,4-ethylenedioxythiophene) (PEDOT) was deposited at both ends of bipolar electrode (BPE) gold wires in a linear fiber form (φ=ca. 30μm) owing to limited accessibility of the EDOT monomer to the active site of BPEs in a micro-space. The linear growth of the PEDOT microfibers was demonstrated to be useful for application in circuit wiring.

Effects of branching position of alkyl side chains on ordering structure and charge transport property in thienothiophenedione- and quinacridone-based semiconducting polymers  

Kohsuke Kawabata, Masahiko Saito, Noriko Takemura, Itaru Osaka and Kazuo Takimiya

Polym J 49: 169-176; advance online publication, October 19, 2016; doi:10.1038/pj.2016.103

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To investigate the effect of the branching position of the alkyl side chain of semiconducting polymers, we synthesized two series of semiconducting polymers based on thienothiophene-2,5-dione (PTTD4Ts) and quinacridone (PQA2Ts). The polymer thin films exhibited small but clear differences in their optical absorption spectra and X-ray diffraction patterns, suggesting that the intermolecular interaction in the solid state varied as a function of the branching position. Although PTTD4Ts did not exhibit a clear correlation between the branching position and charge carrier mobility, the mobility of PQA2Ts gradually increased as the branching position moved away from the backbone.

Improvement of short circuit current density by intermolecular interaction between polymer backbones for polymer solar cells  

Tae Ho Lee, Min Hee Choi, Sung Jae Jeon, Seung Jun Nam, Yong Won Han, Jung Rim Haw and Doo-Kyung Moon

Polym J 49: 177-187; advance online publication, November 16, 2016; doi:10.1038/pj.2016.104

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The results of the X-ray diffraction suggest that the dπ-spacing distance for poly(diethylhexyloxy benzo dithiophene-dioctyloxy dithiophene dibenzophenazine (PBDTAFQ) (dπ=3.89Å) was smaller than poly(diethylhexyloxy benzo dithiophene-dioctyloxy dithiophene diphenyl Qu) (PBDTAQ) (dπ=4.36Å) because of fused-phenyl ring derivative. As a result, PBDTAFQ displayed a higher absorbance at the UV–vis absorption spectra in the film state. And, as a consequence, PBDTAFQ showed an improved short current density (JSC) in organic photovoltaic cells. The PBDTAFQ:PC70BM blend devices that were fabricated exhibited a power conversion efficiency of 3.4%.

Supramolecular Polymers

Supramolecular polymerization of hydrogen-bonded rosettes with anthracene chromophores: regioisomeric effect on nanostructures  

Deepak D Prabhu, Keisuke Aratsu, Mitsuaki Yamauchi, Xu Lin, Bimalendu Adhikari and Shiki Yagai

Polym J 49: 189-195; advance online publication, October 19, 2016; doi:10.1038/pj.2016.94

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Regioisomeric introduction of barbituric acid and aliphatic tail units onto anthracene core resulted in distinctly different ππ stacking arrangements upon aggregation in nonpolar solvent, resulting in the formation of supramolecular polymers with either non-helical or helically twisted fibrous morphologies. The difference in the topology of these fibrous nanoaggregates is attributed to the conformational difference of anthracene chromophores with respect to the plane of hydrogen-bonded supermacrocycle.

Self-assembled Materials

Aggregation-induced delayed fluorescence from phenothiazine-containing donor–acceptor molecules for high-efficiency non-doped organic light-emitting diodes  

Naoya Aizawa, Chao-Jen Tsou, In Seob Park and Takuma Yasuda

Polym J 49: 197-202; advance online publication, September 21, 2016; doi:10.1038/pj.2016.82

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Highly luminescent donor–acceptor molecules based on a phenothiazine donor unit coupled with a xanthone or benzophenone acceptor unit were developed. While both molecules are almost non-luminescent in pure tetrahydrofuran (THF) solution, a strong yellow delayed fluorescence was observed upon their aggregation in THF/water mixtures and in neat films. This result demonstrates the unique aggregation-induced delayed fluorescence (AIDF) characteristics of these molecules. Organic light-emitting diodes (OLEDs) using these AIDF materials as a non-doped emission layer achieved high external electroluminescence quantum efficiencies of up to 11%, which far exceeds the theoretical maximum for conventional fluorescent OLEDs.

π-Conjugated polymer-layered structures: synthesis and self-assembly  

Yuichi Tsuji, Yasuhiro Morisaki and Yoshiki Chujo

Polym J 49: 203-208; advance online publication, September 28, 2016; doi:10.1038/pj.2016.89

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π-Conjugated polymers capped with a boronic acid end-functional group were synthesized by chain-growth Suzuki–Miyaura polycondensation. The obtained polymers were reacted with a π-stacked-polymer scaffold to synthesize graft polymers. The spectroscopic and optical characterization of the obtained graft polymers in the solid state revealed that the original π-conjugated polymers were stacked in a single polymer chain. Direct observations of the obtained graft polymers showed that they self-assembled into spherical or fiber structures depending on the introduced polymers, whereas no ordered structures were formed by the same polymers before the polymer reaction.

Effect of surface treatment on molecular reorientation of polymer-stabilized liquid crystals doped with oligothiophene  

Koji Usui, Erika Katayama, Jing Wang, Kyohei Hisano, Norihisa Akamatsu and Atsushi Shishido

Polym J 49: 209-214; advance online publication, October 19, 2016; doi:10.1038/pj.2016.102

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The molecular orientation of polymer-stabilized nematic liquid crystals (PSLCs) doped with oligothiophene can be easily manipulated using irradiation with linearly polarized light above a threshold intensity. The photoresponsive behavior depended on the initial molecular orientation, as controlled by the surface treatment of PSLC cells. The threshold light intensity for molecular reorientation was successfully reduced by 30% by optimizing the silane coupler concentration because of the decrease in surface anchoring. Thus, weak surface anchoring leads to a reduced threshold light intensity for molecular reorientation.

Alkylated oxygen-bridged V-shaped molecules: impacts of the substitution position and length of the alkyl chains on the crystal structures and fundamental properties in aggregated forms  

Chikahiko Mitsui, Tatsuro Annaka, Ken-ichi Nakamura, Masato Mitani, Daisuke Hashizume, Katsumasa Nakahara, Masakazu Yamagishi, Takanari Ueno, Yuji Tanaka, Masafumi Yano, Daichi Iwasawa, Miki Hasegawa, Hiroyasu Sato, Akihito Yamano, Jun Takeya and Toshihiro Okamoto

Polym J 49: 215-221; advance online publication, November 9, 2016; doi:10.1038/pj.2016.105

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Alkylated dinaphtho[2,3-b:2',3'-d]furan (DNF–V) derivatives are systematically investigated in view of the impact of the substitution position as well as length of alkyl side chains. For both alkylated DNF–VV and DNF–VW derivatives, the solubilities as well as phase-transition temperatures increase as the shorter alkyl chains are attached. Especially, alkylated DNF–VV simultaneously gain the high solubility over 1 wt% and highly stabilized crystal phase up to 199°C. Furthermore, DNF–V derivatives exhibit deep-blue emission in solid state with the quantum efficiency ranging from 17 to 51%.