Anick M. van de Craats

Discotic Liquid Crystalline Semiconductors

Our works on discotic liquid crystalline semiconductors are reviewed. Some of them show very fast carrier mobilities. Novel sandwich rare earth metal complex, bis[octakis(alkylthio)phthalocyaninato]lutetium(III), shows a mobility of 0.71 cm 2 /Vs, which is the fastest in liquid crystals at the present time, so far as we know. It was also found that novel octaphenoxy- and/or hexaphenoxy-substituted phthalocyanine-based discotic liquid crystals exhibit spontaneous perfect homeotropic alignment in the tetragonal columnar mesophase. The corresponding polymer films showing the perfect homeotropic alignment at room temperature could be successfully prepared. Such marvelous films can be practically utilized as organic carrier transport materials and solar batteries.

Charge carrier mobilities in the crystalline solid and discotic mesophases of hexakis-hexylthio and hexakis-hexyloxy triphenylene

Abstract The radiation-induced conductivities of bulk samples of hexakis-hexylthio and hexakis-hexyloxy triphenylene, HHTT and HHOT, have been studied from 0 to +100°C using the pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) technique. The one-dimensional, intracolumnar mobility, σμ c , of charge carriers in the various phases is estimated and compared with values obtained using the time-of-flight technique. Temperature independent values of σμ c , of 0.4×10 −4 and 0.08×10 −4 m 2 /Vs are found for the K (crystalline solid) and H (helical columnar mesophase) of HHTT respectively. A much lower value of σμ c ≈ 0.01×10 −4 m 2 /Vs is found for the K phase of HHOT.

Charge mobility in discotic liquid crystalline porphyrins and phthalocyanines measured by PR-TRMC

The pulse-radiolysis time-resolved microwave conductivity technique, “PR-TRMC”, has been used to determine the charge carrier mobility within columnar stacks of mesomorphic discotic porphyrins and phthalocyanines. The influences of temperature, morphology and variations in the primary molecular structure are demonstrated and discussed. Both the mesomorphic and conductive properties are shown to be dramatically influenced by subtle changes in the peripheral alkyl chain structure or the core-to-chain coupling element. Mobilities close to 1 cm2.V−1.s−1 are found in crystalline solids, and well in excess of 0.1 cm2.V−1.s−1 in columnar, liquid crystalline phases. These values which are even larger than those determined by PR-TRMC for conjugated polymers and similar to values found for electrons and holes in organic single crystals.