Crystallization and Organic Field-Effect Transistor Performance of a Hydrogen-Bonded Quaterthiophene.

Crystalline thin films of π-conjugated molecules are relevant as the active layers in organic electronic devices. Therefore, materials with enhanced control over the supramolecular arrangement, crystallinity, and thin-film morphology are desirable. Herein, it is reported that hydrogen-bonded substituents serve as additional structure-directing elements that positively affect crystallization, thin-film morphology, and device performance of p-type organic semiconductors. It is observed that a quaterthiophene diacetamide exhibits a denser packing than that of other quaterthiophenes in the single-crystal structure and, as a result, displays enhanced intermolecular electronic interactions. This feature was preserved in crystalline thin films that exhibited a layer-by-layer morphology, with large domain sizes and high internal order. As a result, organic field-effect transistors of these polycrystalline thin films showed mobilities in the range of the best mobility values reported for single-crystalline quaterthiophenes. The use of hydrogen-bonded groups may, thus, provide an avenue for organic semiconducting materials with improved morphology and performance.

Solubility and crystallizability: facile access to functionalized π-conjugated compounds with chlorendylimide protecting groups.

Functional π-conjugated molecules are relevant for the preparation of new organic electronic materials with improved performance. However, their synthesis is often rendered difficult by their inherently low solubility, and the permanent attachment of solubilizing groups may change the properties of the material. Here, we introduced the chlorendylimidyl moiety as a new temporary protecting group for the straightforward large-scale synthesis of protected quarter-, sexi-, octathiophene, and perylene bisimide diamine and dicarboxylic acid derivatives. The obtained chlorendylimides and chlorendylimidyl active esters were highly soluble in organic solvents, and optical spectroscopy confirmed the low tendency of the compounds to aggregate in solution. At the same time, they could be conveniently purified by recrystallization or precipitation. Single-crystal X-ray structures obtained for most compounds showed supramolecular motifs highlighting the role of the rigid, polychlorinated chlorendyl moieties in their crystallization. The obtained protected diamine and dicarboxylic acid derivatives were easily deprotected and converted into various amide-substituted oligothiophenes and perylene bisimides that are of interest as new functional materials for organic electronic thin film or nanowire devices.

Organic thin-film transistors: the passivation of the dielectric-pentacene interface by dipolar self-assembled monolayers.

In organic thin-film transistors (OTFTs), the conducting channel is located near the interface between the organic semiconductor and the oxide dielectric; this interface is crucial for transistor performance. Self-assembled monolayers (SAMs) on the interface reduce the negative influences of the oxide dielectric surface by decreasing the coupling of the carriers at the gate and the role of the active surface defects on transfer. In this paper, we show that SAMs carrying a dipole moment determine the OTFT performance by controlling the charge transfer between the oxide dielectric and the semiconductor. The charges introduced into the semiconductor by this transfer (i.e., residual carriers) lead to a threshold shift to positive values, as well as a decrease in the contact resistance and an increase in the apparent mobility. In this study, other effects of the SAMs, such as the gate potential shift in the channel or a direct reaction between semiconductor and SAM molecules, can be excluded as dominant processes.

Robust self-assembled monolayers of Ru(II) and Os(II) polypyridines on gold surfaces: exploring new potentials.

Metal complexes [M(phtpy)(pztpy)](PF(6))(2) (phtpy = 4'-phenyl-2,2':6',2''-terpyridine, pztpy = 4'-(N-piperazinyl)-2,2':6',2''-terpyridine, M = Ru, Os) were prepared and examined spectroscopically and electrochemically. The piperazine attachment was found to significantly modify the photophysical and electrochemical properties compared to the parent bis-terpyridine complexes, causing a red-shift of the (1)MLCT (23 nm, 53.9 eV) and a substantial cathodic shift of the redox potential (0.3 V for Ru, 0.23 V for Os). Self-assembled monolayers (SAMs) of the complexes on polished gold electrodes were generated simply by the in situ formation of a dithiocarbamate (DTC) anchoring group at the terminal piperazinyl nitrogen on the pztpy ligand. Cyclic voltammetry revealed that the monolayers show excellent reversible behaviour and exceptional stability. The high stability of the SAMs is attributed to the strong bidentate attachment to the gold surface of the DTC tether and the favourable low oxidation potentials of the complexes which result from the electron-rich piperazine nitrogen on the pztpy ligand. Such DTC-based SAMs demonstrate a substantial improvement over commonly-employed thiol-based systems, and offer new scope for future development.

Sublimation not an innocent technique: a case of bis-cyclometalated iridium emitter for OLED.

Isomerization of a neutral bis-cyclometalated iridium(III) complex has been observed for the first time during the preparation of vacuum-processed organic light-emitting devices (OLEDs) and reproduced in solution. Isolation of the isomer revealed a cis organization of the two pyridine rings of the cyclometalating ligands. Photophysical studies show very similar emission properties of the two isomers. However, due to in situ isomerization, it is only possible to prepare vacuum-processed OLED devices having a mixture of isomers.

Luminescence-detected phase transitions in lanthanide-containing liquid crystals.

Complexes between lanthanide nitrates and a pro-mesogenic 18-membered diaza-substituted coronand are luminescent both as powders and liquid crystals (between 87 and 195 degrees C), and the phase transitions are detected by monitoring luminescence intensity and lifetime.