Abstract

A tetraphenylporphinatonickel-based mesogenic compound 5,10,15,20-tetrakis(4-n-pentadecylphenyl)porphinatonickel(II) (C₁₅TPPNi) was synthesised and its mesomorphic and photoconductive properties were investigated. The photoconductive properties were compared with those of the metal-free compound. All measurements were carried out for symmetrical ITO/C₁₅TPPNi/ITO type cells and steady-state currents in the constant temperature conditions were detected. A photocurrent rectification was seen in either the crystal phase or lamellar mesophase of C₁₅TPPNi. The metal-free compound with pentadecyl chains showed a strong dependence of photocurrent rectification on mesomorphic phases: the rectification is shown in the cell of crystal and low-temperature lamellar phases and it disappears in the high-temperature lamellar mesophase. This phenomenon was interpreted in terms of the various mechanisms of charged carrier generation with the phase transition, based on the results of the action spectra and the illumination light intensity dependence of the photocurrent. The improvement of the contact for electric conduction at the interface upon heating was found, which is a special feature of this mesomorphic phase in the ITO/C₁₅TPPNi/ITO cell in comparison with the metal-free compound.