Jiena Weng

Theoretical Studies of Electron Transport in Thiophene Dimer: Effects of Substituent Group and Heteroatom

The electron-transport properties of various substituted molecules based on the thiol-ended thiophene dimer (2Th1DT) are investigated through density functional theory (DFT) combined with nonequilibrium Greens function (NEGF) method. The current-voltage (I-V) curves of all the Au/2Th1DT/Au systems in this work display similar steplike features, while their equilibrium conductances show a large difference and some of these I-V curves are asymmetric distinctly. The results reveal the dependence of conductance on the energy level of the substituted 2Th1DT molecules. Rectification ratios are computed to examine the asymmetric properties of the I-V curves. The rectifying behavior in the 2Th1DT molecule containing the amino group close to the molecular end is more prominent than that in the other molecules. The rectifying behavior is analyzed through transmission spectra and molecular projected self-consistent Hamiltonian (MPSH) states. Slight negative differential resistance (NDR) can be observed in some of the systems. The electron-transport properties of 2Th1DT molecules containing different heteroatoms are also investigated. The results indicate that the current in heteroatom-containing molecules is larger than that in their pristine analogues, and lighter heteroatoms are more favorable than heavier heteroatoms for electron transport of the thiophene dimer.

Encapsulation of metal layers within metal–organic frameworks as hybrid thin films for selective catalysis

A facile encapsulation strategy for the preparation of metal layer/metal–organic framework (metal/MOF) hybrid thin films, by alternately growing MOF thin films and sputter-coating metal layers, is reported. The controlled species of the MOF thin films and metal layers, as well as the designed thickness of MOF thin films, endow the resulting hybrid thin films with improved functional and design flexibility. Importantly, the metal/MOF hybrid thin films, with well-defined sandwich structures, exhibit excellent selective catalytic activity, derived from MOFs acting as molecular sieves and the metal layers providing active sites.

Bipolar luminescent materials containing pyrimidine terminals: synthesis, photophysical properties and a theoretical study

A new series of 4-monosubstituted pyrimidine bipolar materials containing a carbazole (PM1–PM2) or a triphenylamine (PM3–PM5) moiety as the electron donor have been synthesized by a ZnCl2-catalyzed three-component coupling reaction. These 4-monosubstituted pyrimidine compounds were characterized by UV-vis and fluorescence spectroscopy, cyclic voltammetry, as well as density functional theory (DFT) calculations. It was intriguing to find that these 4-monosubstituted pyrimidine compounds exhibited bright fluorescence with excellent quantum yields (∼0.53–0.93) in the blue region. PM1 and PM2 had a lower LUMO than that of CBP (4,4′-di(9H-carbazol-9-yl)biphenyl), meaning that both of them had better electron injection and transfer abilities. The variation tendencies of energy levels and absorption spectra obtained from DFT calculations agreed well with those from experiment. Other electronic properties including ionization potentials (IP), electronic affinities (EA), and reorganization energies (λhole and λelectron) have been theoretically studied as well. These electronic properties could be tuned by introducing a different number of pyrimdin-4-yl moieties onto to the donor fragments. The incorporation of pyrimdin-4-yl can significantly decrease the λelectron and then improve the electron-accepting and hole–electron charge balance abilities. The combined theoretical and experimental studies offer insights into the nature of bipolar molecules containing 4-monosubstituted pyrimidine moieties, and provided a fertile ground for the design of appropriate ambipolar materials for optoelectronic applications.

Effect of pH on the photophysical properties of two new carboxylic-substituted iridium(III) complexes.

Two cyclometalated iridium(III) complexes have been prepared based on 2-(4-diphenylamino-phenyl)-quinoline and incorporating carboxylic acid ethyl ester (–COOC(2)H(5), (TPAQCE)(2)Irpic and carboxylic acid (–COOH, (TPAQCOOH)(2)Irpic) substituents at the 4-position of the quinoline ligand, respectively. The absorption, emission and (1)H NMR spectra of (TPAQCE)(2)Irpic and (TPAQCOOH)(2)Irpic under alkaline or acidic conditions demonstrate that they respond to the pH of the surrounding solvent environment. The deprotonation of the carboxylic acid group significantly blue-shifts the metal-to-ligand charge transfer absorption band of (TPAQCOOH)(2)Irpic by 48 nm and enhances the emission quantum-yield in DMSO. In addition, (1)H-NMR titration reveals that (TPAQCOOH)(2)Irpic is deprotonated into negatively charged (TPAQCOO(−))(2)Irpic in free DMSO-d(6) solution, and the acid-induced N^O ancillary ligands cleavage or replacement in (TPAQCOOH)(2)Irpic could be ignored. A water-soluble near-neutral optical pH probe (TPAQCOOH)(2)Irpic with pK(a) of ~7 is also reported. In aqueous buffer, (TPAQCOOH)(2)Irpic possesses an obvious emission response with an excellent linearity in the pH range of 6.50–8.00, showing a promising application in bioprocessing.

Metal-Organic Framework Wears a Protective Cover for Improved Stability

Metal-organic frameworks (MOFs) with an ordered channel and porosity show great promise for a myriad of purposes. Unfortunately, the coordination bond of metal ions and organic ligands easily weakens in unfavorable environments, which poses a key problem in expanding the application of MOFs. Herein, we report a general and efficient strategy to enhance the stability and preserve the porosity of MOFs by coating them with reduced graphene oxide (rGO). The prepared hybrid material consisted of MOFs and rGO, as the core and the protective shell, respectively. It is worth noting that the obtained MOFs@rGO composite material maintained a well-defined crystal structure and showed good catalytic activity as well as enhanced stability. Notably, this novel and general method of coating MOFs with a thin protective rGO shell will broaden the application fields of MOFs and open up a new avenue for the research of MOFs.

Fabrication of Flexible Transparent Electrode with Enhanced Conductivity from Hierarchical Metal Grids

Flexible transparent conductive electrodes (FTCEs) are essential components for numerous optoelectronic devices. In this work, we have fabricated the hierarchical metal grids (HMG) FTCEs by a facile and low-cost, near-field photolithography strategy. Compared to normal metal grids (MG), the HMG structure can provide distinctly increased conductivity of the electrode yet without obvious reduction of the optical transmittance. This HMG sample possesses excellent optoelectronic performance and high mechanical flexibility, making it a promising component for practical applications.

Novel phosphorescent iridium(III) complexes containing 2-thienyl quinazoline ligands: synthesis, photophysical properties and theoretical calculations

The easy tailoring of organic ligands of iridium(III) complexes provides a facile way to tune their opto-electronic properties for applications in high efficiency phosphorescent light emitting diodes. Herein, a series of yellow and red emitting phosphorescent iridium complexes based on 2-thienyl quinazoline derivatives are successfully synthesized and systematically characterized with various opto-electronic properties. The X-ray crystal structures demonstrate that the iridium centers in the complexes with bulky substituents on the 4-position of quinazolyl rings prefer to chelate with the N atoms in the 1-position of quinazolyl rings. Both experiment and theoretical studies indicate that the steric hindrance along with the electron-donating effect of substituents on the C^N ligands enhances the emission quantum yields, accompanied by significant emission shifts. Two yellow phosphorescent iridium complexes (Ir2 and Ir3) are successfully designed and exhibit moderate emission efficiencies, through the incorporation of bulky ligands with strong electron-donating abilities (piperidine for Ir2 and 2,6-dimethyl-phenoxy for Ir3, respectively). The synergistic effect of electron structure and hindrance of ligand is believed to be a promising strategy for tuning the opto-electronic properties of iridium complexes.