J.F. van der Pol

Homologous series of liquid-crystalline metal free and copper octa-n-alkoxyphthalocyanines

Abstract Two series of discotic liquid crystals, one based on metal-free and the other on copper containing phthalocyanine (Pc) as the central core and eight peripherally n-alkoxy groups (C6–C12) as substituents have been synthesized and their mesomorphic properties and structural parameters have been determined. These compounds represent a series totally devoid of polymorphism, the mesophase in all cases being Dho. In the solid state an orthorhombic two dimensional lattice with four molecules per unit cell and a presumably tilted stacking is present, while in the mesophase the planes of the molecules are on average perpendicular to the direction of the stacks. The aggregation behaviour of the C8, C10 and C12 homologues was studied as a function of solvent polarity and of concentration. The electrical properties of the copper complexes of the n-dodecoxy and n-octoxy derivatives have been determined by means of complex impedance spectroscopy and compared with those of the non-mesogenic CuPc.

The affordance of anchored discussion for the collaborative processing of academic texts

A system for “anchored discussion” is compared with a system for traditional forum discussion (Blackboard), and their collaborative and communicative affordances for the collaborative processing of academic texts are investigated. Results show that discussion in the system for anchored discussion is more directed at processing the meaning of texts than discussion in the traditional forum, which is more oriented towards the sharing of personal opinions and experiences. This difference in orientation produces a more constructive collaboration in the system for anchored discussion, versus a more debate-like collaboration in the forum discussion. Additionally, while messages in the traditional forum resemble usual discussion or email conversation and contain social and regulative comments, discussion in the system for anchored discussion is seen to be more efficient and “to-the-point.” We conclude that for collaborative text comprehension by undergraduate students, anchored discussion might be more suitable than traditional forum discussion. Finally, the observed differences can be explained by the stronger defined collaborative context in the system for anchored discussion, which focuses participants’ collaborative intentions and their frames of reference.

Luminescence and energy migration in the solid state and in the ordered columnar mesophase of peripherally octa-n-dodecoxy-substituted phthalocyanine

Abstract The luminescence of octa- n -dodecoxy-substituted phthalocyanine has been studied as a function of temperature (4.2-400 K). Quenching occurs down to the lowest temperatures and has a low activation energy. The quenching is mainly due to migration to molecules of the analogous copper complex. At the solid → mesophase transition a sharp drop in luminescence intensity occurs which is explained in terms of a change in the rate of migration to the quenching sites.

Langmuir-Blodgett films of poly(isocyanide)s with different sidechains. 2. poly(3-cholesteryl-6-isocyanohexanoate)

A poly(isocyanide), [RNC <]n, with pendant cholesterol side groups forms stable Langmuir-Blodgett (LB) monolayers at the air-water interface. At high surface pressures, the monolayers are spontaneously transformed into bilayer structures. The monolayer was transferred onto various solid substrates to form LB multilayers. FT-IR, ellipsometry and SAXS indicate that in these multilayers the polymer side chains are oriented perpendicular to the substrate surface.

Polymerized Discotic Liquid Crystals

Octaalkoxyphthalocyanines with six to twelve carbon atoms in each alkoxy chain are liquid crystalline. On heating, a transition to the mesophase occurs in the region between 80 and 120 °C. In this phase, the disc-like molecules are arranged in ordered stacks. These stacks show one-dimensional transport properties. When the alkoxy chains are provided with (meth)acryloyloxy groups at their terminal positions, the molecules can be polymerized in their mesophase. As a consequence of this polymerization the stack structure is retained on cooling to ambient temperature.