Hexyloxy Chains Research Articles

NEW BLUE CROSSLINKABLE POLYMERS FOR ORGANIC LIGHT EMITTING DEVICES

Here, we report on new blue electroluminescence (EL) crosslinkable polymers containing fluorene/phenylene alternating repeating units. Additionally, they contain polymerizable oxetane groups attached through flexible hexyloxy chains to phenylene units of the polymer backbone. The copolymers were synthesized via Pd-catalyzed Suzuki coupling reactions. The copolymers obtained were found to be soluble and easily processable from common organic solvents such as chloroform or toluene and have been characterized by 1H and 13C NMR spectroscopy, FT-IR spectroscopy and elemental analysis. The degree of polymerization has been determined by gel permeation chromatography (GPC). The thermal properties of the copolymers have been characterized by differential scanning calorimetry (DSC). The optical properties of the polymers were investigated in solution by UV/VIS spectroscopy. The polymers were photo-crosslinked in spin-coated thin films to yield insoluble networks.

Stilbenoid dendrimers

The first five generations of the stilbenoid dendrimers 1(n) (n = 1-5) have been prepared by a combined coupled synthesis (between the generations of the dendrons 8-12) and convergent synthesis. Wittig-Horner reactions together with a protecting group technique yield monodisperse compounds of high constitutional and configurational purity. The solubility of the stiff molecules, which have primarily a disklike shape in the first and second generations and a cylindrical shape in the third, fourth, and fifth generations, is governed by the alkoxy chains that are attached to the peripheral benzene rings. The number of stilbene building blocks increases according to the formula 3(2(n)-1) from 3 in the first generation (n = 1) to 93 in the fifth generation (n = 5). Consequently, the molecular mass reaches 24,000 in 1(5)b which contains 144 hexyloxy chains. An exact measurement of the mass is provided by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. In solution, the stilbenoid dendrimers 1(n) exhibit a strong tendency to aggregate, which increases from generation to generation. In the pure state, columnar mesophases Col(hd) (1(1)b, 1(1)c, 1(2)b, and 1(2)c) and Col(ob) (1(2)b, 1(2)c) are formed; intramolecular steric hindrance prevents such ordered arrangements in higher generations 1(n) (n = 3, 4, 5).

A new synthetic route to tribenzo[ a, e, i][12]annulenes

The tribenzo[ a, e, i][12]annulene 10 and the corresponding twofold annulene 14 were prepared on synthetic routes which first led from suitably functionalised starting compounds ( 2, 11) to the 1,2-distyryl- and 1,2,3,4-tetrastyrylbenzene derivatives 9 and 13 with two and four formyl groups, respectively. The cyclisation to 10 and 14 was achieved by applying the McMurry reaction. The extended ring system of compound 14 represents a discotic mesogen. The generation of liquid crystals was obtained with eight hexyloxy chains on the periphery.

Convergent Synthesis of Columnar Twins and Tetramers from Triphenylene Building Blocks – The First Example of a Columnar Spiro-Twin

The novel spiro-twins 3a–f were prepared in three steps by one-pot oxidative coupling of guaiacol (9) and 1,2-dialkoxybenzenes 10a–f, followed by demethylation of the triphenylene 11 and subsequent etherification with the tetrabromide 6. A related strategy gave the tetramers 7a–f in two steps. Whereas derivatives 3a,b and 7a,b with pentyloxy and hexyloxy chains showed isotropic melting behavior, compounds 3c–f and 7c–f with longer alkyl chains displayed columnar mesophases. DSC, polarizing microscopy, X-ray diffraction and molecular modeling studies were used to further characterize the type of mesophase. For the spiro-twin 3 either a rectangular or a hexagonal columnar phase were conceivable. In case of 7f a hexagonal columnar mesophase was assigned.

Orientational ordering in some nematogens deviating from the classical rod-shape

Several new laterally substituted liquid crystalline compounds have been synthesized. They have the same main core which contains four rings (two aromatic, two alicyclic) with two lateral substituents introduced on the same side of one of the inner rings. One of the substituents is a 4-X-benzyloxy group (X=CH3,CN,Cl) and the other is a hexyloxy chain. The presence of the lateral aromatic substituent makes these compounds deviate markedly from the classical rod-shape. However, a wide enantiotropic nematic phase is present for all the compounds. The order parameters of the chain and the para -disubstituted aromatic rings were obtained by using a 2D 13C NMR technique with variable angle spinning. The temperature dependence of the order parameters was estimated using 13C chemical shifts with slow spinning of the sample parallel to the magnetic field. The results indicate that the two lateral substituents are more or less folded back along the mesogenic core. Thus, the flexible lateral chain is found to be roughly aligned with the molecular long axis, whereas the para axis of the less flexible aromatic branch makes a considerable angle with the molecular long axis imposed by the core, substantially increasing the mean width of the molecule. The core ordering does not seem to be influenced by the type and position of the substituents. The folding back of the lateral chain and the substantial tilt of the lateral aromatic branch with respect to the core main axis are confirmed by the X-ray structure of a parent compound.