Holger Kretzschmann

A new synthesis of soluble poly(1,4-phenylenevinylene)s and poly(2,5-pyrimidinylenevinylene)s

Abstract Alkoxy-substituted 4-methylbenzylideneanilines 2a-f and their pyrimidine analogues 2g,h show an efficient selfcondensation in the alkaline medium KOC(CH 3 ) 3 /DMF. The totally stereoselective reaction yields 3a-h which are transformed by acidic work-up to 4a-h . A narrow distribution of the molecular weight can be achieved.

Unusual lift by shearing mesogenic fluids

Abstract The compounds hexakis- and pentakis[octylthio]benzene showing discotic phases below room temperature were sheared in an oscillation mode under load between a cylinder and a disk of chromium steel at temperatures between 60 and 120[ddot]C. Surprisingly, after some initial wear friction coefficients f decreased to values between 0.005 and 0.001. Under these conditions known lubrication oils cause boundary friction with values some 100 times higher. The nonmesogenic compounds hexakis[2-ethylhexylthio]benzene and hexakis[2-octylthio]benzene behave like known oils. Possible reasons for this promising behaviour of the mesogenic compounds are discussed.

Photochemistry of linear and cyclic oligo- and poly(aryleneethenylene)s — applications in materials science

Abstract A variety of alkoxy-substituted oligo- and poly(aryleneethenylene)s were prepared by applying a new synthetic approach to optimize the photoconductivity, which is strongly influenced by the number, position and length of the side-chains. Measurements of the photodischarge were performed in dispersion layers or cast films. Irradiation in the visible region leads solely to the generation of charge carriers, whereas irradiation in the UV causes primarily a transformation of the benzenoid building blocks to quinoid systems and finally a photopolymerization reaction. The same synthetic procedure can also be used for the preparation of cyclic oligomers. Some alkoxysubstituted triphenanthro[18]annulenes obtained via this route exhibit liquid crystal (LC) properties. The disc-like molecules are arranged in pairs which form photosensitive nematic discotic N D phases. As for the openchained compounds, photopolymerization reactions are observed on irradiation, i.e. the LC phases sustain an irreversible photodegradation.

Photoconductivity of Poly(Arylenevinylene)S and Poly(Hetarylenevinylene)S

Abstract The intramolecular condensation of aromatic Schiff bases leads under strong alkaline conditions to the poly(arylenevinylene)s and poly(hetarylenevi-nylene)s A - H. Due to the extreme stereoselectivity the resulting products are rigid, (E)-configurated polymers. The broad band gap of the unsubstituted intrinsic insulators is decreased by alkoxy substituents. Investigations of the photoconductivity and the photoreactivity, as well as of the AC-conductivity of some undoped, doped and quaternized systems are performed.