Ulrich Berens

High charge-carrier mobility and low trap density in a rubrene derivative

Ciba Specialty Chemistry Inc., 4002 Basel, Switzerland(Dated: February 1, 2008)We have synthesized, crystallized and studied the structural and electric transport properties oforganic molecular crystals based on a rubrene derivative with t-butyl sidegroups at the 5,11 posi-tions. Two crystalline modifications are observed: one (A) distinct from that of rubrene with largerspacings between the naphtacene backbones, the other (B) with a in-plane structure presumablyvery similar compared to rubrene. The electric transport properties reflect the different structures:in the latter phase (B) the in-plane hole mobility of 12cm

Asymmetric hydrogenation reactions mediated by a new class of bicyclic bisphosphinites

Abstract The bicyclic alcohol (−)- 4 was prepared from (−)-bicyclo[3.2.0]hept-2-en-6-one (−)- 1 in 50% yield. The diol (−)- 4 was coupled to selected chlorophosphines 6 – 12 to produce a series of bisphosphinites 13 – 19 in 89–95% yield. From these bisphosphinites were prepared the rhodium complexes 20 – 26 which were characterised by 31 P NMR and used in situ for the asymmetric hydrogenation of α-enamides 27 – 29 . Complexes 21 , 23 – 25 proved to be the superior catalysts for the production of ( R )- N -acetylphenylalanine (91, 84, 90 and 87.5% ee) from 27 and ( S )- N -acetylalanine methyl ester (70, 72, 68 and 71% ee) from 28 .

Amplification of double stereodifferentiation in the asymmetric hydrogenation by a solvent effect

Abstract High diastereoselectivities of more than 96 % leading to ( S )-amino acid menthyl esters were found in the hydrogenation of both the newly prepared enantiomers 3 and 4 of menthyl (Z)-2-N-benzoylamidocinnamate with the rhodium(I)-chelate of (Ph-s-glup-OH) 1 as chiral catalyst in polar solvents. The analogous chelate of (Me-α-glup) 2 forms a mismached pair with the enantiomer 4 giving the ( S )-product in a low diastereoselectivity which can be inversed in the apolar solvent benzene to 86 % of the ( R )-diastereomer. Of particular note is the possibility of obtaining high yields either of ( R )- or ( S )-amino acids with the same catalyst with a single ligand derived from D-glucose.

Quinoid heteropentacenes as promising organic semiconductors for field-effect transistor applications

We report on a quinoid heteropentacene as p-type semiconductor in organic field-effect transistors. Both single crystal and thin-film transistors were fabricated with 7,14-diphenyl-chromeno[2,3-b]xanthene (DPCX). In this small molecule organic semiconductor the field-effect mobility is as high as 0.16 cm2/Vs in single-crystal devices and 0.01 cm2/Vs in thin-film devices. In addition, the devices show favorable properties such as near zero onset/threshold voltages and a small current hysteresis. X-ray diffraction experiments show the molecules to be arranged in slipped stacks and to have a flat backbone in the crystals. For thin films of DPCX the situation is complicated by the coexistence of a thin-film phase with the bulk phase. However, a comparison of DPCX thin films on octadecyltrichlorosilane (OTS)-treated and bare SiO2 gate dielectrics provides clear evidence that the OTS surface treatment leads to organic thin films with a better structural order. The low-cost synthesis and purification of DPCX alo...