Electrical properties and orientations of dye molecules in LB films

Fundamental electrical properties due to orientation of dye molecules were investigated for alternate-layer Langmuir-Blodgett (LB) films of merocyanine dyes (MC) and arachidic acids (C₂₀), and squarylium dye (SQ) LB films. Spontaneous currents below room temperature were repeatedly observed in the alternate-layer LB films of MC and C₂₀. The currents above room temperature remarkably increased with temperature above ~330 K in the first heating stage. The directions of the currents depended upon the orientations of the MC molecules in the alternate LB films. The spontaneous currents were related to the formation of the J aggregate of MC in the alternate LB films. Anisotropy of conduction currents of the SQ LB films was also investigated. The conductivity in the plane was due to the chromophore of the SQ molecules, and it was 10⁴~10⁵ times as much as the perpendicular conduction along the alkyl chains of the molecules. Anisotropic conduction in the plane caused by the orientation of SQ molecules was also observed