Polymeric Semiconductors with a Pre‐Specified Alternation of Conjugated Bonds and Metal Clusters

Summary: In this work the first samples of polymeric semiconductors of a new structure are produced. Their electric conductivity is of the order ∼10⁻² Ohm⁻¹ · cm⁻¹ and it increases with temperature. Their synthesis includes a stage of radiation grafting of a matrix‐type on stretched polyamide films. Conducting molecular circuits in such materials include fragments with conjugated bonds and metal clusters. The alternation of these fragments is determined by the polyamide matrix.

Plot of voltage versus current determined for new polymer semiconducting films where fragments with conjugated bonds alternate with silver clusters.     

Synthesis of nonlinear optical polymers with large photoconductive sensitivity and transparency

Novel nonlinear optical (NLO) chromophore, 2-{3-[2-(4-methylsulfonylphenyl)vinyl]carbazol-9-yl}ethanol was synthesized and subsequently reacted with methacryloyl chloride to give a photoconducting NLO monomer ( M1 ). 2-Methylacrylic acid 2-[3-(diphenylhydrazonomethyl)carbazol-9-yl]ethyl ester ( M2 ) was also synthesized as a comonomer to enhance the carrier mobility of the NLO polymer. Photoconducting NLO polymers, P1 and P2 were obtained by the copolymerization of Ml with methyl methacrylate and M2 , respectively. These polymers were well soluble in organic solvents and showed glass transition at 177 °C and 196 °C, respectively. Polymer films of P1 and P2 were optically clear, and were transparent at wavelengths longer than 420 nm. The electro-optic coefficient (r₃₃) of poled P1 films was measured to be ∼5 pm/V at 632.8 nm. The photoconductive sensitivities of P1 and P2 were 6.2 × 10⁻¹⁴ S·cm⁻¹/mW·cm⁻² and 5.6 × 10⁻¹¹ S·cm⁻¹/mW·cm⁻².     

Two-Dimensional Conjugated Polymer Synthesized by Interfacial Suzuki Reaction: Towards Electronic Device Applications

Preparing two-dimensional conjugated polymers (2DCPs) with desirable structures and semiconducting properties is promising but remains a great challenge. Presented here is a new 2DCP, named 2D polytriethyltriindole (2DPTTI), which is efficiently synthesized by a modified interfacial Suzuki reaction from 2,7,12-tribromo-5,10,15-triethyltriindole (2-BrTTI) and 1,4-benzenediboronic acid dipinacol ester (BADE) precursors at room temperature. Wafer-scale free-standing 2DPTTI films with controllable thicknesses between 2.5 and 46.0 nm were obtained by adjusting the experimental conditions. The resulting 2DPTTI films, used as an active layer in organic field effect transistors (OFETs), exhibited typical p-type semiconducting properties and superior UV optoelectronic performance with a photosensitivity of 3.7×10³ and responsivity of 1.4×10³ A W⁻¹, as well as a light-blue fluorescence character. This report provides a general approach for constructing various semiconducting 2DCPs, by an interfacial Suzuki reaction, towards multifunctional organic electronics.     

An Amorphous n-Type Conjugated Polymer with an Ultra-Rigid Planar Backbone

High charge carrier mobility polymer semiconductors are always semi-crystalline. Amorphous conjugated polymers represent another kind of polymer semiconductors with different charge transporting mechanism. Here we report the first near-amorphous n-type conjugated polymer with decent electron mobility, which features a remarkably rigid, straight and planar polymer backbone. The molecular design strategy is to copolymerize two fused-ring building blocks which are both electron-accepting, centrosymmetrical and planar. The polymer is the alternating copolymer of double B←N bridged bipyridine (BNBP) unit and benzobisthiazole (BBTz) unit. It shows a decent electron mobility of 0.34 cm² V⁻¹ s⁻¹ in organic field-effect transistors. The excellent electron transporting property of the polymer is possibly due to the ultrahigh backbone stiffness, small π-π stacking distance, and high molecular weight.     

A Three-Dimensional Porous Organic Semiconductor Based on Fully sp2-Hybridized Graphitic Polymer

Dimensionality plays an important role in the charge transport properties of organic semiconductors. Although three-dimensional semiconductors, such as Si, are common in inorganic materials, imparting electrical conductivity to covalent three-dimensional organic polymers is challenging. Now, the synthesis of a three-dimensional π-conjugated porous organic polymer (3D p-POP) using catalyst-free Diels–Alder cycloaddition polymerization followed by acid-promoted aromatization is presented. With a surface area of 801 m² g⁻¹, full conjugation throughout the carbon backbone, and an electrical conductivity of 6(2)×10⁻⁴ S cm⁻¹ upon treatment with I₂ vapor, the 3D p-POP is the first member of a new class of permanently porous 3D organic semiconductors.     

Semi‐perfluoroalkylated perylene diimides for conjugated polymers with high molecular weight and high electron mobility

Perylene diimides (PDIs) and their derivatives are excellent semiconductors, while conjugated polymers based on PDIs have limited applications because of their low electron mobility (μ_e) derived from low molecular weight. The reported maximum number‐average molecular weight (M_n) of related polymers is only 21 kDa because PDIs have very poor solubility due to strong π–π stacking of their big planar conjugated cores. Herein, it is found that suitable semi‐perfluoroalkyl groups could enhance the solubility of PDIs significantly, and a series of semi‐perfluoroalkyl modified conjugated polymers with high molecular weight and electron mobility were synthesized. The maximum M_n reaches 94.8 kDa [P(4C_F8C_H‐PDI‐T2)_HW]. In their space‐charge‐limited current (SCLC) devices, all polymers exhibit typical characters of electron transporting semiconductors, and the highest μ_e is up to 8.40 × 10⁻³ cm² V⁻¹ s⁻¹ [P(4C_F8C_H‐PDI‐T2)_HW], which is similar as that of widely used electron transporting semiconductor PC₆₁BM (6.41 × 10⁻³ cm² V⁻¹ s⁻¹). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 116–124     

Dithienylmethanone‐Based Cross‐Conjugated Polymer Semiconductors: Synthesis,Characterization, and Application in Field‐Effect Transistors

Herein, we report the synthesis, characterization, and field‐effect properties of two cross‐conjugated dithienylmethanone (DMO)‐based alternating polymers, namely, PDMO‐S and PDMO‐Se . Both polymers possess high thermal stability, good solubility, and broad absorption spectra. Their electrochemical properties were investigated using cyclic voltammetry, indicating that PDMO‐Se has higher HOMO/LUMO energy levels of −5.49/−3.49 eV than −5.57/−3.58 eV of PDMO‐S . The two polymers exhibited promising charge transport properties with the highest hole mobility of 0.12 cm² V⁻¹ s⁻¹ for PDMO‐S and 0.025 cm² V⁻¹ s⁻¹ for PDMO‐Se . AFM and 2D‐GIXRD analyses demonstrated that the PDMO‐S formed lamellar, edge‐on packing thin film with close π‐π stacking. These findings suggest that cross‐conjugated polymers might be potential semiconducting materials for low‐cost and flexible organic electronics. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1012–1019     

Ion conduction in poly(crown ethers), polyglucosan gels and macroporous polyethylene films

Much work has been reported on ion conduction in solid solutions of salts dissolved in linear and comb-branched poly(ethylene oxide) analogues. There appears to be a limit to the conductivity levels achieved in such systems, and conductivity values rarely exceed σ ∼ 10⁻⁴ Scm⁻¹ at room temperature. To overcome this there has been a move towards more mobile plasticized systems and polymer gel electrolytes are receiving some attention. Gels prepared from N-methyl-2-pyrrolidinone/LiCl and polyglucosans such as cellulose and amylose have been studied and show some promise with ambient σ Ge; 10⁻⁴ Scm⁻¹. Macroporous polyethylene has also been used to support fluid polyethylene glycol/salt systems, but these only reached σ ≥ 10⁻⁵ Scm⁻¹ at ambient temperature. Comb-branch polymers with crown ethers provide systems with respectable room temperature conductivities of between 10⁻⁴ and 10⁻⁵ Scm⁻¹, but these might be improved if the crown ethers could be arranged in regular channels. Ways to achieve this are briefly discussed.     

Chlorine-Substituted N-Heteroacene Analogues Acting as Organic Semiconductors for Solution-Processed n-type Organic Field-Effect Transistors

High performance solution processable n-type organic semiconductor is an essential element to realize low-cost, all organic and flexible composite logic circuits. In the design of n-type semiconducting materials, tuning the LUMO level of compounds is a key point. As a strong electron withdrawing unit, the introduction of chlorine atom into the chemical structure can increase the electron affinity of the material and reduce the LUMO energy level. Here, a series chlorine substituted N-heteroacene analogues of 6,7,8,9-tetrachloro-4,11-bis(4-((2-ethylhexyl)oxy)phenyl)-[1,2,5]thiadiazolo[3,4-b]phenazine (O4Cl), 6,7,8,9-tetrachloro-4,11-bis(4-((2-ethylhexyl)thio)phenyl)-[1,2,5]thiadiazolo[3,4-b]phenazine (S4Cl), 1,2,3,4,8,9,10,11-octachloro-6,13-bis(4-((2-ethylhexyl)oxy)phenyl)quinoxalino[2,3-b]phenazine (8Cl) and 12Cl have been synthesized and characterized. Solution-processed organic field-effect transistors (OFETs) based on these four compounds exhibit good electron mobilities of 0.04 cm² V⁻¹ s⁻¹, 0.01 cm² V⁻¹ s⁻¹, 2×10⁻³ cm² V⁻¹ s⁻¹ and 3×10⁻³ cm² V⁻¹ s⁻¹, respectively, under ambient conditions. The results suggest that these chlorine substituted π-conjugated N-heteroacene analogues are promising n-type semiconductors in OFET applications.     

Quinoxaline-based conjugated polymers containing ruthenium(II) bipyridine metal complex

A series of novel quinoxaline-based conjugated polymers which contain a ruthenium(II) bipyridine complex were synthesized by the Suzuki coupling reactions. UV/VIS spectroscopy showed that the spectral features of the polymers are dependent on the amount of metal complex present. Results from excitation and emission spectroscopy suggest an energy transfer between the backbone and the metal complex. The polymers exhibit hole carrier mobilities of ≈ 10⁻⁵ cm² · V⁻¹ · s⁻¹, which is comparable to organic photoconductors.     

A High-Performance n-Type Thermoelectric Polymer from C−H/C−H Oxidative Direct Arylation Polycondensation

n-Type conjugated polymers (CPs) are crucial in the applications of organic electronics. Direct coupling of electron-deficient C−H monomer via selective C−H activation, namely C−H/C−H oxidative direct arylation polycondensation (Oxi-DArP), is an ideal approach toward such CPs. Herein, Oxi-DArP is firstly adopted to synthesize a high-performance n-type CP using a newly developed monomer, i.e., 3,6-di(thiazol-5-yl)-diketopyrrolopyrrole (Tz-5-DPP). Tz-5-DPP based homopolymer PTz - 5 - DPP with a molecular weight of 22 kDa has been synthesized via Oxi-DArP. After n-doping, PTz - 5 - DPP films exhibited electric conductivity values up to 8 S cm⁻¹ and power factors (PFs) up to 106 μW m⁻¹ K⁻². Notably, this PF value is the highest for n-type polymer thermoelectric materials to date. The Oxi-DArP synthesis and the excellent n-type performance of the polymer make this work an important step toward the straightforward and sustainable preparation of high-performance n-type polymer semiconductors.     

An n-Type Polythiophene Derivative with Excellent Thermoelectric Performance

Typical n-type conjugated polymers are based on fused-ring electron-accepting building blocks. Herein, we report a non-fused-ring strategy to design n-type conjugated polymers, i.e. introducing electron-withdrawing imide or cyano groups to each thiophene unit of a non-fused-ring polythiophene backbone. The resulting polymer, n-PT1 , shows low LUMO/HOMO energy levels of −3.91 eV/−6.22 eV, high electron mobility of 0.39 cm² V⁻¹ s⁻¹ and high crystallinity in thin film. After n-doping, n-PT1 exhibits excellent thermoelectric performance with an electrical conductivity of 61.2 S cm⁻¹ and a power factor (PF) of 141.7 μW m⁻¹ K⁻². This PF is the highest value reported so far for n-type conjugated polymers and this is the first time for polythiophene derivatives to be used in n-type organic thermoelectrics. The excellent thermoelectric performance of n-PT1 is due to its superior tolerance to doping. This work indicates that polythiophene derivatives without fused rings are low-cost and high-performance n-type conjugated polymers.     

A Three‐Dimensional Porous Organic Semiconductor Based on Fully sp2‐Hybridized Graphitic Polymer

Dimensionality plays an important role in the charge transport properties of organic semiconductors. Although three‐dimensional semiconductors, such as Si, are common in inorganic materials, imparting electrical conductivity to covalent three‐dimensional organic polymers is challenging. Now, the synthesis of a three‐dimensional π‐conjugated porous organic polymer (3D p‐POP) using catalyst‐free Diels–Alder cycloaddition polymerization followed by acid‐promoted aromatization is presented. With a surface area of 801 m² g^?1, full conjugation throughout the carbon backbone, and an electrical conductivity of 6(2)×10^?4 S cm^?1 upon treatment with I₂ vapor, the 3D p‐POP is the first member of a new class of permanently porous 3D organic semiconductors.     

Designing Thiophene-Enriched Fully Conjugated 3D Covalent Organic Framework as Metal-Free Oxygen Reduction Catalyst for Hydrogen Fuel Cells

The application of three-dimensional (3D) covalent organic frameworks (COFs) in renewable energy fields is greatly limited due to their non-conjugated skeletons. Here, we design and successfully synthesize a thiophene-enriched fully conjugated 3D COF (BUCT-COF-11) through an all-thiophene-linked saddle-shaped building block (COThTh-CHO). The BUCT-COF-11 exhibits excellent semiconducting property with intrinsic metal-free oxygen reduction reaction (ORR) activity. Using the COF as cathode catalyst, the assembled anion-exchange membrane fuel cells (AEMFCs) exhibited a high peak power density up to 493 mW cm⁻². DFT calculations reveal that thiophene introduction in the COF not only improves the conductivity but also optimizes the electronic structure of the sample, which therefore boosts the ORR performance. This is the first report on the application of COFs as metal-free catalysts in fuel cells, demonstrating the great potential of fully conjugated 3D COFs as promising semiconductors in energy fields.     

Conjugated Copper–Catecholate Framework Electrodes for Efficient Energy Storage

A conjugated copper(II) catecholate based metal–organic framework (namely Cu-DBC) was prepared using a D₂-symmetric redox-active ligand in a copper bis(dihydroxy) coordination geometry. The π-d conjugated framework exhibits typical semiconducting behavior with a high electrical conductivity of ca. 1.0 S m⁻¹ at room temperature. Benefiting from the good electrical conductivity and the excellent redox reversibility of both ligand and copper centers, Cu-DBC electrode features superior capacitor performances with gravimetric capacitance up to 479 F g⁻¹ at a discharge rate of 0.2 A g⁻¹. Moreover, the symmetric solid-state supercapacitor of Cu-DBC exhibits high areal (879 mF cm⁻²) and volumetric (22 F cm⁻³) capacitances, as well as good rate capability. These metrics are superior to most reported MOF-based supercapacitors, demonstrating promising applications in energy-storage devices.     

Laser Spectroscopy and Lifetime Measurements of the S1 State of Tetracyanoquinodimethane (TCNQ) in a Cold Gas-Phase Free-Jet

The S₁ electronic state of 7,7,8,8-Tetracyanoquinodimethane (TCNQ) has been investigated by laser induced fluorescence (LIF), dispersed fluorescence (DF) spectroscopy, and lifetime measurements under jet-cooled conditions in the gas-phase. The LIF spectrum showed a weak origin band at 412.13 nm (24262 cm⁻¹) with prominent progression and combination bands involving vibrations of 327, 1098, and 2430 cm⁻¹. In addition, very strong bands appeared at ∼363.6 nm (3300 cm⁻¹ above the origin). Both the LIF and DF spectra indicate considerable geometric change in the S₁ state. The fluorescence lifetime of S₁ at zero-point level was obtained to be 220 ns. This lifetime is 40 times longer than the radiative lifetime estimated from the S₁−S₀ oscillator strength. Furthermore, the lifetimes of the vibronic bands exhibited drastic energy dependence, indicating a strong mixing with the triplet (T₁) or intramolecular charge-transfer (CT) state. This study is thought to disclose intrinsic nature of TCNQ, which has been well known as a component of organic semiconductors and a versatile p-type dopant.     

High performance semiconducting polymers containing bis(bithiophenyl dithienothiophene)‐based repeating groups for organic thin film transistors

New dithienothiophene‐containing conjugated polymers, such as poly(2,6‐bis(2‐thiophenyl‐3‐dodecylthiophene‐2‐yl)dithieno[3,2‐b;2′,3′‐d]thiophene, 4 and poly(2,6‐bis (2‐thiophenyl‐4‐dodecylthiophene‐2‐yl)dithieno[3,2‐b;2′,3′‐d]thiophene, 8 have been successfully synthesized via Stille coupling reactions using dodecyl‐substituted thiophene‐based monomers, bistributyltin dithienothiophene, and bistributyltin bithiophene; these polymers have been fully characterized. The main difference between the two polymers is the substitution position of the dodecyl side chains in the repeating group. Grazing‐incidence X‐ray diffraction (GI‐XRD) gave clear evidence of edge‐on orientation of polycrystallites to the substrate. The semiconducting properties of the two polymers have been evaluated in organic thin film transistors (OTFTs). The two conjugated polymers 4 and 8 exhibit fairly high hole carrier mobilities as high as μ_ave = 0.05 cm²/Vs (I_ON/OFF = 3.42 × 10⁴) and μ_ave = 0.01 cm²/Vs, (I_ON/OFF = 1.3 × 10⁵), respectively, after thermal annealing process. The solvent annealed films underwent reorganization of the molecules to induce higher crystallinity. Well‐defined atomic force microscopy (AFM) topography supported a significant improvement in TFT device performance. The hole carrier mobilities of the solvent annealed films are comparable to those obtained for a thermally annealed sample, and were one‐order higher than those obtained with a pristine sample. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Conjugated polymers based on 1,8‐naphthalene monoimide with high electron mobility

1,4,8,9‐Naphthalene diimides (NDIs) with strong electron accepting ability and high stability are excellent building blocks for semiconductor polymers. However, 1,8‐naphthalene monoimide (NMI) with similar structure and energy levels as that of NDI has never been used to construct conjugated polymers because of synthetic difficulty. Herein, 3,6‐dibromo‐NMI (DBNMI) with bulky alkyl groups was obtained effectively in a four‐step synthesis, and three donor‐acceptor (D‐A) type conjugated polymers based on NMI were firstly prepared. These polymers have strong absorption in the range of 300–600 nm, low LUMO level of 3.68 eV, and moderate bandgaps of 2.18 eV. Space charge limiting current measurements indicate these polymers are typical electron transporting materials, and the highest electron mobility is up to 5.8 × 10⁻³ cm² V⁻¹ s⁻¹, which is close to the star acceptor based on NDI (N2200, 5.0 × 10⁻³ cm² V⁻¹ s⁻¹). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 276–281     

Preparation and Physico-Chemical Characteristics of N-Maleoyl Chitosan Films

N-Maleoyl chitosan (N-MC), a water-soluble derivative of chitosan, was synthesized by N-carboxyacylation of chitosan and maleic anhydride. N-MC films were prepared by solvent casting and kept in a desiccator for different time intervals in order to obtain N-MC films with different degrees of cross-linking. The swelling characteristic of N-MC films was investigated. When the ageing time increased from 5 to 30 d, the swelling of the N-MC films decreased from ∼475 to ∼160% and the weight loss decreased from ∼25 to ∼8%, corresponding to the increase in the cross-linking density from 0.86 × 10⁻⁶ to 8.97 × 10⁻⁶ mol · cm⁻³. Additionally, the swelling behavior of the N-MC films was influenced by changes in either the pH or the ionic strength of the media.     

Two‐Dimensional Conjugated Polymer Synthesized by Interfacial Suzuki Reaction: Towards Electronic Device Applications

Preparing two‐dimensional conjugated polymers (2DCPs) with desirable structures and semiconducting properties is promising but remains a great challenge. Presented here is a new 2DCP, named 2D polytriethyltriindole (2DPTTI), which is efficiently synthesized by a modified interfacial Suzuki reaction from 2,7,12‐tribromo‐5,10,15‐triethyltriindole (2‐BrTTI) and 1,4‐benzenediboronic acid dipinacol ester (BADE) precursors at room temperature. Wafer‐scale free‐standing 2DPTTI films with controllable thicknesses between 2.5 and 46.0 nm were obtained by adjusting the experimental conditions. The resulting 2DPTTI films, used as an active layer in organic field effect transistors (OFETs), exhibited typical p‐type semiconducting properties and superior UV optoelectronic performance with a photosensitivity of 3.7×10³ and responsivity of 1.4×10³ A W^?1, as well as a light‐blue fluorescence character. This report provides a general approach for constructing various semiconducting 2DCPs, by an interfacial Suzuki reaction, towards multifunctional organic electronics.