Yee-Hing Lai

Bridged Triphenylamine-Based Dendrimers: Tuning Enhanced Two-Photon Absorption Performance with Locked Molecular Planarity

Triphenylamine derivatives bridged by methylene units afford a near planar molecular platform in a series of one dimer and two oligomers exhibiting increased structural rigidity compared to that of their parent triphenylamines. This series of dendrimers show significantly enhanced two-photon absorptions that are up to 3-fold that of triphenylamines with similar molecular size and structure.

Bridged-triarylamine starburst oligomers as hole transporting materials for electroluminescent devices

Two bridged-triphenylamine starburst molecules were designed and synthesized. Their electrochemical properties were studied in detail using cyclic voltammetry (CV) and square wave voltammetry (SWV) methods. The bridged molecular structure stabilizes the oxidative state and decreases the oxidation potentials, resulting in an increased HOMO energy level. Double-layer sandwich electroluminescence devices were fabricated. The bridged triphenylamine starburst 4 has shown significantly enhanced performance compared with the triphenylamine analog 3 and its ethenyl-linked derivative 6.

Synthesis and electrochemical characterization of a new polymer constituted of alternating carbazole and oxadiazole moieties

Abstract We report herein the synthesis and electrochemical characterization of a novel copolymer containing an electron rich carbazole moiety and an electron deficient oxadiazole unit—poly[N-(2′-ethylhexyl)-carbazole-3,6-diyl-1″,3″,4″-oxadiazole-2″,5″-diyl] (PCO). PCO can be dissolved in THF, CHCl3, xylene, and DMSO. The structure of the polymer is confirmed by FT-IR, NMR and elemental analysis. The optical and electronic properties of the polymer are investigated by UV–Vis absorption spectroscopy and photoluminescence spectroscopy as well as cyclic voltammetry. The results show that the polymer films emit greenish-blue light (λmax 485 nm) upon UV excitation. Both p-doping and n-doping processes are observed in cyclic voltammetric investigation. A comparison between the properties of polycarbazole and polycarbazole–oxadiazole has been presented.

Azulene-containing organic chromophores with tunable near-IR absorption in the range of 0.6 to 1.7 μm

Near-infrared (NIR) absorption in the range of 0.75–2.5 μm is in great demand for a variety of applications but currently the majority of commercial NIR devices are based on inorganic materials due to the limited number of organic materials that are active in this range. Here we present the preparation and optical studies of a new series of stable azulene-containing NIR chromophores whose absorption can be tuned in the range of 0.6–1.7 μm. DFT calculation revealed that the protonation-induced low excitation gap was attributable to the substantial intramolecular charge transfer.

Synthesis and characterization of a cyano-substituted electroluminescent polymer with well-defined conjugation length

Abstract A novel copolymer, poly[1,6–hexanedioxy–1,4–phenylene–1,2–ethenylene–(2,5–dicyano–1,4–phenylene)–1,2–ethenylene–1,4–phenylene] (HCN-PPV), with alternating conjugated and non-conjugated blocks is synthesized by the Wittig reaction. The conjugated block containing one unit of 2,5-dicyano-1,4-phenylene vinylene is linked to a flexible linear hexyl chain spacer by an ether group in the backbone. The polymer is soluble in common organic solvents such as CHCl 3 and CH 2 Cl 2 . The number average molecular weight ( M n ) is 2517 with a polydispersity index of 1.75. The optical bandgap of HCN-PPV is 2.48 eV. λ max of the PL spectrum of the polymer film sample lies at 533 nm, corresponding to green light emission. The polymer also shows good thermal stability with a decomposition temperature of 304°C under air atmosphere. Cyclic voltammetric investigation of the polymer reveals a reversible n -doping process and an irreversible p -doping process. The onset for the n -doping process occurs at −1.48 V (vs. SCE), while the onset for the p -doping process occurs at 1.19 V (vs. SCE). The results imply that HCN-PPV is an n -dope type electroluminescent polymer.

Griffipavixanthone, a novel cytotoxic bixanthone from Garcinia griffithii and G. pavifolia

Abstract A bioactivity-directed fractionation of the extracts of the Malaysian plant Garcinia pavifolia and a phytochemical study of G. griffithii led to the discovery of griffipavixanthone ( 1 ), a novel cytotoxic bixanthone with cyclized prenyl groups providing the xanthone-xanthone linkage. Spectroscopic data and preparation of methylated derivatives allowed for the complete structural elucidation of 1 .

Phenylene-functionalized polythiophene derivatives for light-emitting diodes: their synthesis, characterization and properties

The design, synthesis and characterization of a new series of conjugated polymers, poly[(3-(4′-n-butylphenyl)thiophene-2,5-diyl)(2,5-dialkoxy-1,4-phenylene)(4-(4′-n-butylphenyl)thiophene-2,5-diyl)] are described in this contribution. Three polymers modified by phenyl groups have been successfully synthesized via FeCl3-oxiditive polymerization. The well-defined structure of the polymers is fully verified by elemental analysis, FT-IR, and 1H and 13C NMR spectroscopy. All polymers show good thermal stability and solubility in common organic solvents. The absolute photoluminescence (PL) efficiencies of the polymers in the neat film can be up to 11%. The electrochemical properties of the polymers indicate that their HOMO and LUMO energy levels can be adjusted by means of the aromatic groups both in the side chain and the backbone structure. Yellowish green electroluminescence is achieved from single-layered polymer light-emitting diodes (PLEDs) with the configuration ITO/polymer/Ca or Al.

2,5b,10b,11-tetramethyldihydropyreno[5,6-c]furan: the first furan-isoannelated [14]annulene that sustains as strong a diamagnetic ring current as the parent system

Abstract Relative chemical shifts of internal methyl protons of trans-furano-dimethyldihydropyrene 4 and its parent 3 provide the first evidence that such an isoannelation does not lead to a significant decrease in diatropicity.

A novel property of spider silk: chemical defence against ants

Spider webs are made of silk, the properties of which ensure remarkable efficiency at capturing prey. However, remaining on, or near, the web exposes the resident spiders to many potential predators, such as ants. Surprisingly, ants are rarely reported foraging on the webs of orb-weaving spiders, despite the formidable capacity of ants to subdue prey and repel enemies, the diversity and abundance of orb-web spiders, and the nutritional value of the web and resident spider. We explain this paradox by reporting a novel property of the silk produced by the orb-web spider Nephila antipodiana (Walckenaer). These spiders deposit on the silk a pyrrolidine alkaloid (2-pyrrolidinone) that provides protection from ant invasion. Furthermore, the ontogenetic change in the production of 2-pyrrolidinone suggests that this compound represents an adaptive response to the threat of natural enemies, rather than a simple by-product of silk synthesis: while 2-pyrrolidinone occurs on the silk threads produced by adult and large juvenile spiders, it is absent on threads produced by small juvenile spiders, whose threads are sufficiently thin to be inaccessible to ants.

12,13,25,26-Tetraaza-2,15-dithia[3.3]phenanthrolinophane. Synthesis, conformational study and complexation reactions

Abstract 12,13,25,26-Tetraaza-2,15-dithia[3.3]phenanthrolinophane 7 was prepared from a cyclization reaction of 2,9-bis(bromomethyl)phenanthroline 3. The syn isomer of 7 was kinetically favoured while the anti isomer was the thermodynamically more stable product isolated. The macrocycle 7 formed 1:1 complexes, namely 10 and 11, respectively, with zinc(II) and cadmium(II) ions. A tetragonal-pyrimidal configuration is proposed for these complexes. A comparison of the 1H NMR spectral data of 7, 10 and 11 suggests that the complexation results in a symmetrical structure through the four nitrogen donor atoms. The sulfur atoms in the bridges do not seem to coordinate strongly to the metal ions.