Jiwei Cai

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.

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.

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.

Synthesis and electrochromic properties of polyimides with pendent benzimidazole and triphenylamine units

Five novel near-infrared electrochromic aromatic polyimides (PIs) with pendent benzimidazole group were synthesized from 4,4′-diamino-4″-(1-benzylbenzimidazol-2-yl)triphenylamine (named as DBBT) with five different dianhydrides via two-step polymerization process, respectively. The maximum UV-Vis absorption bands of these PIs locate at about 335 nm for solid films due to the π-π* transitions. A reversible pair of distinct redox peaks, that were associated with a noticeable color change from original yellow to blue, was observed in the cyclic voltammetry (CV) test. A new absorption peak emerged at 847 nm in near-infrared (NIR) region with increasing voltage in UV-Vis-NIR spectrum, which indicates that PI can be used as NIR electrochromic material. These novel PIs have good electrochemical stability, appropriate energy levels for the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), in the range of -5.17 eV to -5.20 eV and -2.14 eV to -2.26 eV (versus the vacuum level) determined by cyclic voltammetry method. These values basically consisted with the results of quantum chemical calculation. These polyimides can be used as novel electrochromic and hole transportation materials.

Preparation and characterization, stable bismaleimide-triarylamine polymers with reversible electrochromic properties

A series of novel polyimides were synthesized from bismaleimide containing different diaminetriarylamines by Michael addition reaction. The prepolymer is readily soluble in many common organic solvents, such as CHCl3, Tetrahydrofuran (THF) and N, N-dimethyl formamide (DMF). Prepolymers can be solution-cast into transparent, tough, and flexible films. These aromatic polyimides display good thermal stabilities, i.e. 5% weight-loss temperatures in excess of 200 °C under nitrogen. All obtained polyimides revealed excellent stability of electrochromic characteristics, changing color from original yellowish to green. The energies of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the investigated the polymers were estimated by experimental method are in the range of -4.78 eV to -4.98 eV and -1.64 eV to -2.09 eV vs the vacuum level, respectively. All the polymer films reveal good electrochemical and electrochromic stability under repeatedly switching electrode voltages, with coloration change from the yellow neutral state to green oxidized state.

Fabrication of one-dimensional multifunctional poly-Schiff base bars by anodic aluminum oxide template

A simple strategy has been adopted for the fabrication of 1D nanobars PSB using anodic aluminum oxide template. Scanning electron microscope measurements provided direct evidence that the nanostructure showed a uniform width and depth in the appropriate time during the etch conditions. The electrochemical characteristics and the photovoltaic behaviors of PSB nanobar were characterized by cyclic voltammetry. The 1D conducting polymer nanostructures exhibited improved charge transport properties, and enhanced electrochemical properties, compared to their bulk polymer materials. And it also exhibited excellent electrochromic, acidochromic, and photoelectric characteristics.