Publications

Discotic liquid crystal (LC) molecules readily form columnar supramolecular structures. Because of molecular mobility in the LC state these columnar assemblies can self-heal structural defects to a certain extent. Therefore, conjugated aromatic molecules of the discotic LC state may exhibit exceptional charge carrier transport properties, and thus are potential active materials for use in optoelectronic devices. In this review, a number of discotic LC materials including benzene, triphenylene, hexabenzocoronene, perylene, and phthalocyanine derivatives are reviewed. The emphases are on the correlation between chemical structure and LC properties and some recent developments in the application of these materials in optoelectronic devices such as organic light-emitting diodes (OLED), organic field-effect transistors (OFET), and photovoltaic cells. In addition, studies related to the dynamics of some discotic LC materials are briefly discussed.

A set of conjugated oligo- and polytluorene-tethered fac-Ir(ppy)(3) complexes were synthesized, In addition to steady-state absorption and emission, time-resolved emission spectroscopy was used to systematically study the correlation of photophysical properties with chemical structures. A chain length dependency study showed that both radiative and nonradiative triplet decay rates, as well as the phosphorescence quantum yield, decreased with increasing chain length of the appended oligofluorene. Notably, the complex with oligofluorene tethered to the pyridine tiara to phenyl ring possessed a substantially higher phosphorescence quantum efficiency and shorter lifetime than those of an isomeric complex with the oligofluorene linked to the phenyl ring para to pyridine. Nonetheless, both these two oligomer complexes exhibited an excited state of mixed MLCT. (metal-to-ligand charge transfer) and LC (ligand-centered) transitions, whereas another isomeric complex having an oligofluorene appended to the phenyl ring pant to the iridium ion exhibited a particularly long triplet lifetime (> 100 mu s), indicative of a (LC)-L-3 excited state. A moderately high quantum yield (similar to 0.5) was displayed by this (LC)-L-3-featured phosphor. DEL calculations substantiated the proposition that the attachment of oligofluorene to Ir(ppy)(3) at different positions resulted in varied molecular orbitals, with different relative contribution of MLCT to the emissive excited state. Hence, photophysical properties such as radiative decay rate, lifetime, and quantum yield, etc., were all influenced by the substitution isomerism. As these results indicated that if short lifetime and fast radiative decay were desired, among different substitution patterns appending the conjugated chain to the pyridine unit was the most favorable. Thus, star-shaped complexes with an oligo- or polyfluorene tethered to each of the three pyridine units of Ir(ppy)(3) were prepared. In such a structure, the tris-cyclometalated iridium effected nearly complete intersystem crossing (ISC) in all three ligands across three fluorene units, without compromising the phosphorescence quantum yield. But the study showed that further extending the conjugated ligand resulted in partial ISC or even complete loss of capacity for ISC beyond a certain distance.

Arylene ethynylene macrocycles containing 9,10-anthrylene or 1,4-naphthylene units were synthesized. In chloroform, significant resonance upfield shifting was observed with beta-protons of anthrylene and naphthylene in NMR spectra. This was considered to result from partial stacking of these aromatic units intramolecularly, driven by attractive pi-pi interactions. DFT calculations supported the proposed intramolecular stacking motif. Moreover, a liquid-crystal phase was exhibited by the anthrylene-containing macrocycle, by virtue of the unique discotic shape.

Well-defined 3-dimensional architectures constitute the indispensable structural basis of the versatile, mind-boggling functions of biological macromolecules, such as proteins and nucleic acids. In the past few decades, diversified synthetic systems have been designed to mimic these biological entities in their capability of adopting such specific, higher order structures The relevant research field presents one of the most rapidly developing areas related to supramolecular chemistry The current contribution will focus on the most recent progress related to foldamers consisting of arylene ethynylene building blocks Some of the work features developing novel functions based on previously established arylene ethynylene folding systems, and others have designed and synthesized new arylene ethynylene foldable structures that aim to realize previously uncharted properties (C) 2010 Elsevier B.V. All rights reserved

Crystalline microwires of a phenyleneethynylene (PE) macrocycle self-assembled from solution exhibited superior photoconductive properties. Photoswitches fabricated with single wires afforded nA-scale photocurrents with on/off ratios of ca. 10(3). At a bias of 30 volts highest gain value achieved was up to 4.5. The stable and rapid responses to light qualify these microwire-based devices for excellent photoswitches or photodetectors.