Mircea Grigoras

Synthesis and Characterization of Linear, Branched and Hyperbranched Triphenylamine-Based Polyazomethines

Novel triphenylamine-based linear, hyperbranched and branched conjugated polyazomethines have been synthesized by free-catalyst solution polycondensation of 1,4-diaminobenzene with 4,4′-diformyl triphenylamine, 4,4′,4′′-triformyl triphenylamine and their mixture in different molar ratios. Linear polyazomethine has a good solubility in organic solvents while branched and hyperbranched polymers are partially soluble. A wholly soluble hyperbranched polyazomethine was obtained by end-capping of polymer at gelation point using a monofunctional aromatic amine, p-anisidine. Characterization of all polymers was made by 1H-NMR, FT-IR and UV-Vis and photoluminescence spectroscopy and thermal methods. Electrochemical behavior of polymers was studied by cyclic voltammetry using thin films cast from THF solution on a platinum disc working electrode in acetonitrile solvent and tetrabutylammonium tetrafluoroborate as electrolyte.

Electrically insulated molecular wires

This paper is an up-to-date mini-review based on literature data and own results regarding synthesis and properties of conducting (pseudo)rotaxane supramolecular structures. Conjugated polymers, such as polyarylene, polyheteroarylene, polyaniline, polyarylenevinylene or polyaryleneimine, were used as axle, while the macrocyclic components were cyclodextrins, cucurbiturils, cyclophanes or crown ethers. Properties of the supramolecular structure such as solubility, thermal or chemical stability, conductivity, etc. can be drastically modified by the inclusion of hydrophobic conjugated polymers inside the macrocycle, without any chemical modification. For instance, the photophysical properties (i.e. quantum yield of fluorescence and electroluminescence) of the supramolecular structures were enhanced when compared with uninsulated conjugated polymers. The doping process is also affected, because the access of a dopant to the conjugated chain is limited only to the uncovered domains of the conjugated chain.

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.

Polyazomethines with Triphenylamine Groups Synthesized by Suzuki Polycondensation Reactions

Two new linear, conjugated triphenylamine-based polyazomethines were synthesized by the Suzuki polycondensation of N,N′-bis[4-(4-bromophenyl)(phenyl)aminobenzylidene]-1,4-phenylendiamine with 2,5-thiophenediboronic acid and 9,9-dioctylfluorene-2,7-diboronic acid, respectively, using Pd(PPh3)4 as catalyst. The obtained structures were characterized by spectral methods (1H-NMR, FT-IR, UV-Vis and fluorescence), as well as by thermal analysis.

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, 1H-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.

Quantum-chemical investigation of the structure and electronic absorption spectra of symmetric triphenylamine oligomers conjugated to vinylene, imine, azine, and ethynylene groups

Based on the density functional theory (DFT) and using the B3LYP and BMK hybrid exchange-correlation functionals, we have studied the structure and electronic-spectral properties of some triphenylamine oligomers that contain various π-electron spacers of end groups and that are of interest as electro- and photoactive materials. Good agreement between calculation results and experimental data on absorption spectra in the visible and UV ranges has been obtained. The nature of visible spectral bands has been elucidated based on interrelations with structural changes of oligomer molecules.

Electrochemically generated networks from poly(4,4′-triphenylamine-co-9,9-dioctyl-2,7-fluorene) with grafts containing carbazole groups

Herein, the synthesis of poly(4,4′-triphenylamine-co-9,9-dioctyl-2,7-fluorene) grafted with oligo N-(2-hydroxyethyl) carbazolyl methacrylate as side chains was performed in two steps. A macromonomer with dibromo-triphenylamine end was firstly synthesized by atom-transfer radical polymerization of N-(2-hydroxyethyl) carbazolyl methacrylate followed by Suzuki polycondensation of the macromonomer with 9,9-dioctylfluorene-2,7-diboronic acid. The graft copolymer was characterized by Fourier-transform infrared spectroscopy (FTIR), 1H and 13C-NMR spectroscopy while the optical properties were investigated by UV–vis and fluorescence methods. Cyclic votammetry studies evidenced that the redox processes were accompanied by the dimerization of carbazole pendant groups and polymer crosslinking with the formation of an insoluble network. The parent polymer was post-modified, in solution or bulk, by electrochemical oxidation leading to a crosslinked and insoluble network having electrochromic properties.

Indolo[3,2-b]carbazole-based poly(arylene ethynylene)s Modulation of their optoelectronic properties by changing the position of substituents

A novel family of indolo[3,2-b]carbazole (ICZ)-based polymers was designed and synthesized using Sonogashira cross-coupling reaction between three bisbromine indolo[3,2-b]carbazoles and 1,4-diethynylbenzene. The new polymers have an arylene ethynylene structure with ICZ moiety interconnected in the main chain by 2,8-, 3,9- or 6,12- positions. The polymers were obtained as partially soluble materials, in chlorinated, aromatic and aprotic polar solvents. The structure of the polymers was studied by spectroscopic methods such as Fourier transform infrared, proton and carbon-13 nuclear magnetic resonance, ultraviolet–visible and photoluminescence spectroscopies, thermogravimetry and molecular weights determined by gel permeation chromatography. Electrochemical properties were investigated by cyclic voltammetry using films cast on platinum disc working electrode. Optical and electronic properties were discussed from the viewpoint of the connection positions of ICZ units in the polymer chain.

Metal complexation of aromatic oligoazomethines bearing cyano groups: An optical and electrochemical study

AbstractTwo new oligoazomethines containing 2,5-diamino-3,4-dicyanothiophene as central unit and, triphenylamine or carbazole at both ends, were characterized in terms of metal ions complexation ability. The influence of various metal ions on their optical properties was investigated by UV-vis and photoluminescence measurements. For both oligomers the presence of ions such as Cu2+, Sn2+, and Hg2+ causes significant modifications of the absorption and emission spectra. The hypsochromic shift of the long wavelength can be correlated with the existence of new coordination complex species that decrease the conjugation pathway. Sn2+ ions act as emission intensifier for both oligomers. Hg2+ ions act as emission quencher for triphenylamine-containing oligoazomethine, while for carbazoleoligoazomethine acts as emission intensifier. The presence of the metal ions in high concentration (9×10−4 M) significantly modifies in time, the colour of the oligomers solutions, and this can be observed even with the naked eye. The cyclic voltammograms recorded after the addition of metal ions revealed new redox peaks which can be assigned to the presence of metal ions- oligoazomethine complexes. The studied oligoazomethines can be employed as selective and sensitive chemosensors for Hg2+, Cu2+, and Sn2+ ions.