H. Monobe et al., Mesomorphic and photoconductive properties of a mesogenic long-chain tetraphenylporphyrin nickel(II) complex, J MAT CHEM, 11(5), 2001, pp. 1383-1392
A tetraphenylporphinatonickel-based mesogenic compound 5,10,15,20-tetrakis(
4-n-pentadecylphenyl)porphinatonickel(II) (C15TPPNi) was synthesised and it
s mesomorphic and photoconductive properties were investigated. The photoco
nductive properties were compared with those of the metal-free compound. Al
l measurements were carried out for symmetrical ITO/C15TPPNi/ITO type cells
and steady-state currents in the constant temperature conditions were dete
cted. A photocurrent rectification was seen in either the crystal phase or
lamellar mesophase of C15TPPNi. The metal-free compound with pentadecyl cha
ins showed a strong dependence of photocurrent rectification on mesomorphic
phases: the rectification is shown in the cell of crystal and low-temperat
ure lamellar phases and it disappears in the high-temperature lamellar meso
phase. This phenomenon was interpreted in terms of the various mechanisms o
f charged carrier generation with the phase transition, based on the result
s 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 m
esomorphic phase in the ITO/C15TPPNi/ITO cell in comparison with the metal-
free compound.