Optoelectronic and charge transport properties of D-n-A type 1,3,5-triazine derivatives: A combined experimental and DFT study.

The synthesis of five D-n-A type star-shaped octupolar molecules is presented in the current work. The exploration of the potential applicability of molecules under study in organic optoelectronics as electron or hole transporting materials is carried out by DFT methods. All the molecules have a 1,3,5-triazine core, which acts as an electron acceptor (A). Phenyl ring and pyridine ring act as electron donors (D) in AZ and PZ series of molecules respectively. The donor and acceptor core are connected by -NH bridge (n). The crystal structure of a molecule in the PZ series is elucidated. Thermogravimetric studies are carried out to confirm the thermal stability of molecules. The frontier molecular orbitals of molecules are characterized with the help of cyclic voltammetry. With the assistance of DFT methodologies, the whole research presented in this work focuses on the electronic excitations, reorganization energies, electron affinity, ionization potential and features of frontier molecular orbitals of molecules. The investigation of the variation of optoelectronic properties of molecules with changing patterns of nucleophilic substitution on 1,3,5-triazine core and presence of a hetero (nitrogen) atom in the donor part of the molecule is also accomplished.

Polysubstituted Hexa-cata-hexabenzocoronenes: Syntheses, Characterization, and Their Potential as Semiconducting Materials in Transistor Applications.

A series of tetra- and octa-substituted hexa-cata-hexabenzocoronenes (cata-HBCs) were synthesized from tetraryl olefins via iodine- and iron chloride-catalyzed oxidative cyclodehydrogenation reactions. The substitutions on the periphery of the parent HBC serve to modify the photophysical properties, highest occupied molecular orbital-lowest unoccupied molecular orbital gaps, and thermal stabilities of the respective derivatives. The crystal structures were determined to display multiple twists in the framework, resulting in different packing motifs depending on the position, type, and number of functional groups on the hexabenzocoronene framework. Nearly perfect co-facial packing to marginally or extensively shifted co-facial stacks were obtained due to substitution. The single crystals of parent HBC were used to fabricate single-crystal field-effect transistors, from which the highest p-channel mobility of 0.51 cm2 V-1 s-1 was measured. Thin-film transistors of selected HBCs were also prepared, and 0.61 cm2 V-1 s-1 was obtained for MeHBC-2. These results attest the potential of these materials as semiconducting materials.

Compact TiO2 films with sandwiched Ag nanoparticles as electron-collecting layer in planar type perovskite solar cells: improvement in efficiency and stability.

Fabrication of perovskite solar cells (PSCs) in a simple way with high efficiency and stability remains a challenge. In this study, silver nanoparticles (Ag NPs) were sandwiched between two compact TiO2 layers through a facile process of spin-coating an ethanolic AgNO3 solution, followed by thermal annealing. The presence of Ag NPs in the electron-transporting layer of TiO2 improved the light input to the device, the morphology of the perovskite film prepared on top, and eliminated leakage current. Photoluminescence and electron mobility studies revealed that the incorporation of Ag NPs in the ETL of the planar PSC device facilitated the electron-hole separation and promoted charge extraction and transport from perovskite to ETL. Hysteresis-free devices with incorporated Ag NPs gave a high average short-circuit current density (J sc) of 22.91 ± 0.39 mA cm-2 and maximum power conversion efficiency of 17.25%. The devices also showed enhanced stability versus a control device without embedded Ag NPs. The possible reasons for the improvement are analyzed and discussed.

Synthesis and Characterization of Contorted Pentabenzo-Fused Coronenes as Semiconducting Materials.

Here, we report the synthesis and characterization of a series of contorted, yet noncentrosymmetrical, polycyclic aromatic hydrocarbons with a pentabenzo-fused coronene as the core framework. The parent pentabenzo[a,d,g,j,m]coronene (PBC) compound is shown to exhibit a shifted and rotated type of π-π stacking interactions, which render this series a semiconducting material. Single-crystal-based field-effect transistor devices of PBC exhibited efficient charge transport behavior, giving a p-channel field-effect mobility of 0.42 cm2 V-1 s-1 and an on/off ratio of 105.

Synthesis, characterization and photocatalytic activity of KAl0.33W1.67O6 and Sn0.5Al0.33W1.67O6xH2O.

Nano sized defect pyrochlore, KAl0.33W1.67O6 (KAW), is prepared through sol-gel method. Divalent tin-doped KAW is obtained at room temperature by ion exchange method using acidified SnCl2 and parent KAW. These materials are characterized by powder X-ray diffraction, thermogravimetric analysis (TGA), scanning electron microscopy-energy dispersive spectra (SEM-EDS), Raman Spectroscopy and X-ray photo electronic spectroscopy. The composition of tin-doped KAW is obtained from chemical analysis, SEM-EDS and TGA methods and written as Sn0.5Al0.33W1.67O6xH2O (x = 1.4-1.5) (SnAW). It crystallizes in cubic lattice with Fd3¯m space group. The band gap energies are found to be 2.82 and 2.21 eV for KAW and SnAW respectively. The observed reduction in the band gap with the introduction of Sn(2+) in defect pyrochlore lattice is due to mixing of 5s state of Sn(2+) with O 2p states leading to an upward shift in the valence band. The Raman spectra of these materials gave more bands than the number expected for defect pyrochlores due to substitutional disorder in 16c sites and displacive disorder of A ions. The photoactivity of SnAW is higher compared to KAW.

Chirality and bioactivity of the sex pheromone of Madeira mealybug (Hemiptera: Pseudococcidae).

Two compounds (trans-1R,3R-chrysanthemyl R-2-methylbutanoate and R-lavandulyl R-2-methylbutanoate) identified from aeration extracts of virgin female Madeira mealybug, Phenacoccus madeirensis Green (Hemiptera: Pseudococcidae), were synthesized and tested in field bioassays in northern Taiwan over a 1-mo period. In total, 1,492 male P. madeirensis were captured in sticky traps. Our results showed that 1 microg of synthetic trans-1R,3R-chrysanthemyl R-2-methylbutanoate released from a plastic tube dispenser was attractive to the mealybugs. Different stereoisomers of chrysanthemyl 2-methylbutanoate also were tested. The insect-produced stereoisomer was the most attractive of all the isomers tested, and the stereochemistry of the acid moiety proved to be more critical than that of the alcohol moiety. The minor component found in extracts, R-lavandulyl R-2-methylbutanoate, alone was not attractive to male Madeira mealybugs nor did it act synergistically or additively with the main component.

High mobility n-channel single-crystal field-effect transistors based on 5,7,12,14-tetrachloro-6,13-diazapentacene.

Heteroaromatic oligomer 5,7,12,14-tetrachloro-6,13-diazapentacene (TCDAP) was characterized and assessed as n-channel material in field-effect transistor applications. A single-crystal transistor based on TCDAP as the channel material exhibits a very high electron mobility of 3.39 cm(2) V(-1) s(-1) and an on/off ratio of ∼1.08 × 10(4) respectively.

Effect of interfacial structure on the transistor properties: probing the role of surface modification of gate dielectrics with self-assembled monolayer using organic single-crystal field-effect transistors.

Single-crystal field-effect transistors based on 2,3-dimethylpentacene have been used to probe the effect of surface modification of the insulating dielectric SiO(2) layer on the transistor characteristics. Self-assembled monolayers (SAMs) of different chain lengths and functional groups were used to systematically modify the structure and property of the semiconductor/dielectric interface. The charge carrier mobility as a function of SAM used for surface modification was analyzed. The character of the terminal functional group, as well as the mechanic treatment (rubbing) of the monolayer, much influences the carrier mobility. Introduction of a polar end group (donor or acceptor type) decreases the mobility compared to a nonpolar end group. Prerubbing of the monolayer serves to increase the charge carrier mobility by a factor of 2-4-fold. The results are interpreted in terms of the orderliness of the monolayer which affects the contact at the monolayer/semiconductor interface, which in turn affects the trapping sites' density or the smoothness of the potential surface that the carriers experience while transporting along the interface.

Use of the curtius rearrangement of acryloyl azides in the synthesis of 3,5-disubstituted pyridines: mechanistic studies.

A series of disubstituted pyridine derivatives was synthesized from the corresponding acryloyl azides by acetic acid-promoted cycloaddition. This represents a novel and convenient synthetic approach to the symmetric 3,5-disubstituted pyridines. The nature of the substituent on the double bond and the utilized solvent were found to be crucial to the yield of pyridines. The reactivity of the acid-promoted cycloaddition increases with the presence of aryl groups, such as phenyl and pyridinyl. We also explored the comprehensive mechanism by the acid-promoted cycloaddition of (13)C-labeled cinnamoyl azide. The symmetric 3,5-disubstituted pyridines were synthesized from acryloyl azides by acetic acid-promoted trimolecular condensation.

Spectroscopic studies on Co(II), Ni(II), Cu(II) and Zn(II) complexes with a N4-macrocylic ligands.

Complexes of cobalt(II), nickel(II), copper(II) and zinc(II) with a new tetraaza macrocyclic ligand have been synthesized and characterized by microanalyses, molar conductance, magnetic susceptibility, mass, thermogravimetric (TGA), IR, 1H and 13C NMR, electronic and ESR spectral studies. All the complexes are found to have the formula [MLX2]x nH2O and are six-coordinated with distorted octahedral geometry.