Pieter G. Schouten

Peripherally Octasubstituted Phthalocyanines with Branched Alkoxy Chains

Abstract Phthalocyanines (H2Pc) octasubstituted with branched alkoxy chains were synthesized: 2,3,9,10,16,17,23,24- octakis(3,7-dimethyloctoxy)phthalocyanine (1a) and 2,3,9,10,16,17,23,24-octakis(3,7,11-trimethyldodecoxy)phthalocyanine (1b). Their mesomorphic properties were studied by DSC, polarization microscopy and X-ray diffraction. Compound 1a, which was initially crystalline at room temperature, maintains its mesomorphic structure on cooling back to room temperature. Compound 1b is mesomorphic at room temperature. It shows a D ho→D hd transition at 34[ddot]C and a transition of unknown nature at 173[ddot]C. Both compounds display a D→I transition.

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.

Evidence of a chiral superstructure in the discotic mesophase of an optically active phthalocyanine

In the liquid crystalline phase of optically active phthalocyanine (S)-1 the columns are helically distorted, as has been shown by circular dichroism experiments on a Langmuir-Blodgett film of (S)-1 and by small angle X-ray diffraction studies, and confirmed by time-resolved microwave conductivity measurements.

The disperse kinetics of intercolumnar charge recombination in pulse-irradiated mesomorphic phthalocyanines

Abstract Peripherally octa-alkoxy substituted phthalocyanines, PcOC n , with n the alkyl chain length, self-organise into columnar stacks with a central core of Pc macrocyles surrounded by a saturated hydrocarbon mantle. The decay of the radiation-induced conductivity following pulsed ionization of these materials is mainly due to charge recombination via intercolumnar tunneling of electrons through the intervening hydrocarbon barrier which is varied from 10 A to 20 A thick ( n = 6 to 18). Despite the well-organised super-lattice structure of the materials, as evidenced by small-angle X-ray diffraction patterns, the decay kinetics are very disperse. They can, under most conditions, be well described by the Kohlrausch expression, σ ( t ) = σ (0)exp[− t / Γ ) α ], with α values between 0.2 and 0.8. The kinetic dispersion and negative thermal activation found are ascribed to conformational deformations and fluctuations within the hydrocarbon barrier.

Microwave conductivity in the columnar, discotic mesophase of undoped, peripherally octa-alkoxy substituted phthalocyanines

Abstract A large microwave conductivity, up to 0.2 Sm −1 , is found in the discotic mesophase of peripherally octa-alkoxy substituted phthalocyanines for straight- and branched- alkyl chain monomeric compounds and for axially (polysiloxane) and coaxially (polymethacrylate) polymerised materials.

Charge transport in mesomorphic phthalocyanines studied by pulse-radiolysis time-resolved microwave conductivity

The pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) technique has been used to obtain information on the transport of charge within columnarly stacked, peripherally octaalkoxy-substituted phthalocyanines. Data are presented on the one-dimensional, intracolumnar charge mobility and on the timescale of quasi-two-dimensional intercolumnar electron tunnelling. Particular attention is paid to materials that are liquid-crystalline at room temperature, because of their potential technological importance in optoelectric charge transport layers and molecular semiconductor devices. The relevance of the data to channeled charge transport in aligned thin layers is discussed.

Charge Migration in Supramolecular Stacks of Porphyrins and Phthalocyanines

Abstract Information on the factors controlling the mobility of charge carriers in columnar aggregates of aromatic macrocycles is obtained from studies of the radiation-induced and dark microwave conductivity.