Xuduo Bai

Novel soluble polyazomethines with pendant carbazole and triphenylamine derivatives: preparation, characterization, and optical, electrochemical and electrochromic properties

Two series of novel polyazomethines (PAMs) P1–P5, Pa–Pe with an Mn of 1522–7879 g mol−1 were prepared via the direct polycondensation from N,N-Bis(4-aminophenyl)-4-N′-carbazolyl-1,4- phenylenediamine, and N,N-Bis (4-aminophenyl)-N′,N′-di-phenyl-1,4-phenylenediamine with various dicarboxaldehyde such as phthaldialdehyde, 1,3-isophthalaldehyde, terephthalaldehyde, 4,4′-diformyltriphenylamine, 3,5-thiophenedialdehyde. All the polymers were amorphous with good solubility in many organic solvents, such as CHCl3, tetrahydrofuran (THF), N-methyl-2-pyrrolidinone (NMP) and N,N-dimethylacetamide (DMAc), and could be solution-cast into polymer films. All polymers displayed outstanding thermal stabilities, i.e. 20% wt loss in excess of 470 °C under nitrogen. A hybrid density functional theory (DFT) method was used to calculate the optimized geometry and electronic structure of PAMs. The variation of the backbone ring significantly affected the dihedral angles and resulted in the variation of electronic properties. The HOMO and LUMO energy levels of these polymers calculated by electrochemistry and absorption spectra were in the range 4.687–5.189 and 2.366–2.989 eV below the vacuum level, respectively. Our study demonstrated the backbone ring can tune the electronic properties of conjugated PAMs effectively. All obtained PAMs revealed stability of electrochromic characteristics, changing color from original yellowish to red or violet or blue. And multiple reversible colours states were observed upon chemical doping. The properties prove that the polyazomethines are multipurpose materials which will be used in hole-transporting, electrochromic and chemical sensor applications in the near future.

RGO functionalised with polyschiff base: multi-chemical sensor for TNT with acidochromic and electrochromic properties

In this work, we synthesized a conjugated polyschiff base (PSB) from N,N′-bis(4-aminophenyl)-N,N′-bis(β-naphthyl)-bisphenylenediamine and 2,5-thiophene-dialdehyde through condensation polymerization, in which the triphenylamine (TPA) core acted as an electron donor and hole transporting material, subsequently the polymer was directly used to react with graphene in the presence of an excess of N-methylglycine to produce a highly soluble RGO covalently functionalized with PSB. The composite was fully characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectrometry, thermogravimetric analysis (TGA), photoluminescence (PL) spectroscopy, UV-Vis absorption spectroscopy, cyclic voltammetry (CV), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). A stable, highly efficient charge-transfer configuration was disclosed and confirmed. The work function values of the PSB and RGO–PSB were obtained by Kelvin probe force microscopy (KPFM) measurements. The devices based on RGO–PSB also showed nonvolatile resistive switching behavior. This composite exhibited higher electrochemical catalytic activity for trinitrotoluene (TNT) and showed excellent electrochromic, acidochromic, and photochromic properties.

High coloration efficiency and fast switching speed of poly(amic acid-imide)s containing triphenylamine in acidic electrolyte

Two novel poly(amic acid-imide)s (PAA-IMs) were prepared from two electroactive diamines, 4,4′-diamino-4′′-methoxytriphenylamine and 4,4′-diamino-4′′-phenoxytriphenylamine, and pyromellitic dianhydride (PMDA) by conventional polycondensation, followed by partial imidization at 150 °C. The resulting PAA-IMs had significant levels of thermal stability associated with 2% weight-loss temperatures between 195 and 370 °C. Flexible PAA-IM films with light color showed excellent adhesion on the surface of an indium–tin oxide (ITO)-coated glass substrate. The electrochromic properties were examined by electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the PAA-IM films cast onto ITO substrate exhibited a reversible oxidation at 1.26–1.35 V vs. Ag/AgCl in acid electrolyte consisting of acetonitrile and 4-toluene sulfonic acid (MBSA), revealed excellent stability of electrochromic characteristics with a color change from neutral yellowish pale form to the green or blue oxidized form at applied potentials ranging from −0.5 to 1.8 V. The anodically electrochromic PAA-IM films not only showed excellent reversible electrochromic stability with extremely high coloration efficiency (CE = 834 and 523 cm2 C−1) but also exhibited fast switching speed which required 1.7 to 3.8 s for color switching and 0.8 to 1.6 s for bleaching. After over 30 cyclic switches, the PAA-IMs films still exhibited stable electrochemical and electrochromic characteristics.

Synthesis, electrochromic, halochromic and electro-optical properties of polyazomethines with a carbazole core and triarylamine units serving as functional groups

A series of aromatic polyazomethines (PAMs) were prepared via direct polycondensation from 9-(2-ethylhexyl)-carbazole-3,6-dicarboxaldehyde and six different types of diamine containing triarylamines. The PAMs displayed good solubility in many organic solvents, such as tetrahydrofuran (THF), chloroform (CHCl3) and N,N-dimethylformamide (DMF) which was beneficial for polymer film formation via spin coating, and exhibited outstanding thermal stability. These PAMs exhibited blue-green photoluminescence around 405–520 nm with a quantum yield of up to 48% in a dichloromethane (CH2Cl2) solution. They exhibited halochromic properties with a color change from yellow to red, accompanied by fluorescence quenching after HCl-doping. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the PAMs were determined from cyclic voltammograms to be −5.01 to −4.88 eV and −2.15 to −2.11 eV, respectively. The PAMs films not only had good electrochromic properties with high coloration efficiency, but also generated photovoltage and photocurrent under simulated solar radiation.

Optical, electrochemical, photoelectrochemical and electrochromic properties of polyamide/graphene oxide with various feed ratios of polyamide to graphite oxide

A series of novel multicoloured near-infrared electrochromic polyamide (PA)-based nanocomposites with graphene were successfully prepared via in situ chemical polymerization with various feed ratios of PA to graphene oxide (GO) (PA : GO = 999 : 1, 199 : 1, 49 : 1, 19 : 1, 1 : 0). The prepared nanocomposites were readily soluble in many organic solvents and displayed outstanding thermal resistance, stability of electrochromic characteristics, high coloration efficiency, short switching time, and anodic electrochromic behavior, and showed a good and uniform dispersion of the GO sheets in the PA matrix. The typical, stable photoelectrical response showed that there was charge transfer in the interior of the composites film under illumination, and the enhanced electrochemical performance was also investigated by electrochemical impedance spectroscopy (EIS) technique. The content of GO played a pivotal role in the electron transfer and regulated the conductivity of the composites. The properties prove that the composite is a multipurpose material which will cater for photoelectric conversion and electrochromic application.

Activated nitrogen-enriched carbon/carbon aerogel nanocomposites for supercapacitor applications

Abstract Activated nitrogen-enriched carbon/carbon aerogel nanocomposites (ANC/ACA) were prepared by synthesis of melamine resin/carbon aerogel composites, carbonization and KOH activation. Novel asymmetric supercapacitors consisting of Ni(OH)2/Co(OH)2 as anode and ANC/ACA with different composite ratios as cathode were assembled. The influence of composite ratio on electrochemical performances of materials was detected by cycle voltammetry (CV) and galvanostatic charge/discharge methods. The results of XPS and SEM show that N atoms exist in the ANC/ACA and ANC/ACA shows nanometer and honeycomb structure with more pores. When the composite ratio of ANC/ACA is 12:1, the ANC/ACA shows the highest Cp1 (312.8 F/g) vs 103.4 F/g of ACA and 230.1 F/g of ANC. And the optimal asymmetric supercapacitor with the ANC/ACA as cathode also shows the best electrochemical performances. The optimal supercapacitor is stable over 100 cycles. When the current density is 50 mA/cm2, the Cp2, Ep and P of the optimal supercapacitor are still 57.3 F/g, 9.0 W·h/g and 1 302.1W/kg, respectively.

Immobilized polyazomethines containing triphenylamine groups on ITO: synthesis and acidochromic, electrochemical, electrochromic and photoelectronic properties

A new series of polyazomethines (PAMs) containing triphenylamine (TPA) as easily-oxidized units were synthesized as highly soluble materials with electrochromism. 2,5-Bis(hexyloxy)terephthaldehyde and four different kinds of diamine were condensed to construct the PAMs under benign conditions with n values of 21 700–25 400 g mol−1. The color of the PAM solution changed reversibly between light yellow and navy blue with the increase and decrease of pH. The PAMs with a high number of alkyl groups, which could dissolve facilely in many common organic solvents, were grafted onto ITO through siloxane linkages to be cast into tough films. During the electrochemical reoxidation process, the films showed color switching with high coloration efficiency. The HOMO and LUMO levels were determined via cyclic voltammograms combined with the UV-visible spectrum as −5.14 to −4.79 eV and −2.81 to −2.54 eV, respectively, which can be utilized in the hole transporting layer in organic light-emitting diodes (OLEDs) or solar cell (SC) devices.

Synthesis and electrochromic, acidochromic properties of Schiff bases containing triphenylamine and thiophene units

A series of Schiff bases (SBs) were designed and prepared from 2-thiophenecarboxaldehyde and different triphenylamine (TPA) derivatives. The structures of the compounds were characterized by Fourier transform infrared (FT-IR), hydrogen nuclear magnetic resonance (1H NMR). The optical and electrochemical properties were tested by ultraviolet-visible (UV-vis) spectroscopy and cyclic voltammetry (CV) techniques. The SBs exhibited stable and reversible electrochromic properties. Furthermore, multiple reversible colors states were also observed with the change of pH. Consequently, the SBs can be used as electrochromic and acidochromic materials.

Reducing polyazomethine to poly(N-phenylbenzylamine) with near infrared electrochromic, fluorescence and photovoltaic properties

A novel series of solution-processable near-infrared (NIR) electrochromic aromatic poly(N-phenylbenzylamines) (RPAMs) have been synthesized by the reduction of polyazomethines (PAMs). The RPAMs were characterized by FT-IR and 1H NMR spectroscopy. Thermogravimetric analysis (TGA) showed that all the RPAMs were stable, with 5% weight losses recorded above 353 °C in nitrogen atmosphere. All the polymers are readily soluble in common organic solvents such as CHCl3, THF, DMF and DMAc. The RPAMs exhibit a strong blue-green fluorescence with a maximum at 415–514 nm, and the fluorescence quantum yield of RPAM-a in THF is about 18%. The PL intensity and color of the RPAMs changed depending on the value of pH. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of these polymers were determined in the range of −4.51–−5.03 and −1.58–−2.33 eV (vs. the vacuum level) by cyclic voltammetry method consistent with the results of quantum chemical calculation. The polymer films revealed excellent stability of the electrochromic characteristics, with a color change from neutral pale yellowish to a purple doped form at applied potentials ranging from 0.0 to 1.5 V. The RPAMs showed a typical photovoltaic response and the SEM images implied the RPAM would be inclined to self assemble into ball particles.

Hybrid supercapacitors based on polyaniline and activated carbon composite electrode materials

Purpose – The purpose of this paper is to develop feasible composite electrodes with a long cycle life and large specific capacitance and to investigate optimal ratio between aniline and activated carbon materials.Design/methodology/approach – PANI/AC composite electrode materials were synthesised by in situ polymerisation of aniline on activated carbon with ammonium persulphate as oxidant. Hybrid supercapacitors are assembled by putting Ni‐MH battery separator between positive and negative electrodes. The electrochemical performances of PANI/AC composite electrode materials and supercapacitors are studied.Findings – The results show that the optimal ratio between aniline and activated carbon is 1:1.08. The specific capacitance of polyaniline electrode materials is 956 F g−1. The specific capacitance of supercapacitors is 159.37 F g−1. This result could be attributed to the pseudocapacitive effect of Ni(OH)2. Whats more, the activated carbon addition reduced the resistance of polymer electrode materials ...