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

Peripherally octa-alkoxy substituted phthalocyanines, PcOCn, 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 Å to 20 Å 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.