Electrochemical characterization of arylene vinylene oligomers containing triphenylamine and carbazole units

Arylenevinylene Oligomer-Based Heterostructures on Flexible AZO Electrodes

We investigated the optical and electrical properties of flexible single and bi-layer organic heterostructures prepared by vacuum evaporation with a p-type layer of arylenevinylene oligomers, based on carbazole, 3,3' bis(N hexylcarbazole)vinylbenzene = L13, or triphenylamine, 1,4 bis [4 (N,N' diphenylamino)phenylvinyl] benzene = L78, and an n-type layer of 5,10,15,20-tetra(4-pyrydil)21H,23H-porphyne = TPyP. Transparent conductor films of Al-doped ZnO (AZO) with high transparency, >90% for wavelengths > 400 nm, and low resistivity, between 6.9 × 10-4 Ω·cm and 23 × 10-4 Ω·cm, were deposited by pulsed laser deposition on flexible substrates of polyethylene terephthalate (PET). The properties of the heterostructures based on oligomers and zinc phthalocyanine (ZnPc) were compared, emphasizing the effect of the surface morphology. The measurements revealed a good absorption in the visible range of the PET/AZO/arylenevinylene oligomer/TPyP heterostructures and a typical injection contact behavior with linear (ZnPc, L78) or non-linear (L13) J-V characteristics in the dark, at voltages < 0.4 V. The heterostructure PET/AZO/L78/TPyP/Al showed a current density of ~1 mA/cm2 at a voltage of 0.3 V. The correlation between the roughness exponent, evaluated from the height-height correlation function, grain shape, and electrical behavior was analyzed. Consequently, the oligomer based on triphenylamine could be a promising replacement of donor ZnPc in flexible electronic applications.

Synthesis and optoelectronic characterization of some star-shaped oligomers with benzene and triphenylamine cores

Six star-shaped oligomers containing triphenylamine (D1-D3) and benzene unit (D4-D6) as cores have been synthesized by Wittig condensation or Heck coupling reaction using aromatic aldehydes and triphenylphosphonium salts or aromatic halogenated compounds with vinyl triphenylamine. All oligomers have well-defined molecular structure and high purity. Characterization of the oligomers was made by FT-IR, (1)H-NMR spectroscopy, UV-Vis, and fluorescence spectroscopy. The electrochemical behavior was studied by cyclic voltammetry (CV). The cyclic voltammograms have revealed that oligomers undergo quasireversible or irreversible redox processes. The irreversible process is associated with electrochemical polymerization of oligomers by dimerization of unsubstituted triphenylamine groups. Thermal characterization was accomplished by TGA and DSC methods and evidenced that all oligomers were stable materials until 250°C and have formed stable molecular glasses after first heating scan.

New symmetrical conjugated thiophene-azomethines containing triphenylamine or carbazole units: Synthesis, thermal and optoelectrochemical properties

New oligo- and poly(azomethine)s containing 3,4-dicyanothiophene and triphenylamine or carbazole units were synthesized under condensation reaction conditions. Although the different amino group reactivity, a one-pot synthesis of symmetric conjugated oligoazomethines was possible by judicious choice of solvent and careful control of reagent stoichiometry. Different polycondensation strategies (in solution and bulk polymerization reactions) were applied in order to obtain soluble oligoazomethines and poly(azomethine)s. Their expected chemical structures were confirmed by 1H-NMR and Fourier transform infrared (FT-IR) characterization techniques. Electronic properties of the synthesized oligoazomethines were investigated in different solvents, using UV-Vis and photoluminescence spectroscopy (PL) and these revealed that there is a slight dependency between the solvent polarity and absorption wavelength, while the emissions peaks are shifted at higher wavelength with increasing the solvent polarity. The thermogravimetric and differential scanning calorimetry analysis showed a high thermal stability up to 350 °C and no glass transition temperature. Having in their structure electroactive sites, i.e., carbazole and triphenylamine units, cyclic voltammetry technique was used to investigate the oxido-reduction behavior and to determine the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels.

Synthesis and electrochemical characterization of new linear conjugated arylamine copolymers

New conjugated copolymers having linear structures were synthesized by palladium catalyzed cross-coupling reactions of bis(4-bromophenyl)phenylamine or 4-hydroxymethyl-N,N’-bis(4-bromophenyl)aniline and two bisboronic acids of fluorene or thiophene. The copolymers were obtained as fully or partially soluble materials, in chlorinated and aprotic polar solvents. Having a hydroxymethyl group attached to the para position of the triphenylamine units, the synthesized copolymers can be viewed as functional polymers which were transformed into new ones by employing suitable chemical reactions. A new copolymer was obtained by coupling the hydroxymethyl group of triphenylamine of P35 copolymer, with phenyl isocyanate. The chemical structures and the properties of copolymers were investigated by spectroscopic methods such as 1H nuclear magnetic resonance, Fourier transform infrared, ultraviolet-Vis and photoluminescence spectroscopy. Cyclic voltammetry was performed in order to obtain information about the electrochemical stability and reversibility of the redox processes of copolymers. Electrochemical studies were carried out on films cast on glassy carbon electrode (GCE) or In-Tin oxide (ITO) glass-coated electrode.