Pyroelectric activity in polar hemicyanine Langmuir-Blodgett multilayer films

The Langmuir-Blodgett (LB) films of hemicyanine dyes were prepared by LB technique. The films showed pyroelectric effect. The pyroelectric coefficient measured by the method of integrated charges was 12 μC·m^-2·K^-1 at room temperature, and the relationship between the orientation of DAEP dye in the films and temperature was studied by polarized Fourier transform infrared spectroscopy (FTIR) and Second harmonic generation (SHG). It was indicated that the observed pyroelectricity can be ascribed preliminarily to the structure modification of the polar head groups and the deterioration of the film framework (the first-order phase transition) resulted in the change of spontaneous polarization with temperature.