Optical hysteresis behavior of tetra-nonyl phthalocyanine copper LB film

Langmuir-Blodgett (LB) films of tetra-nonyl phthalocyanine copper (TNPcCu) were prepared. The structure of TNPcCu LB film has been studied by x-ray diffraction and IR reflection absorption spectroscopy. The results show that the TNPcCu LB film forms an ordered structure, in which molecules are arranged in an orderly fashion with phthalocyanine rings oriented nearly perpendicular to the substrate surface and perpendicular to the lifting direction. The optical absorbance at 740 nm of TNPcCu LB film has a hysteresis behavior during heating and cooling. Dipoles of TNPcCu molecules are oriented in an orderly fashion and their vibrations in phase cause the formation of aggregates. When the temperature increases, the dipoles change the ordered orientation into the disordered one, the aggregates are destroyed and the absorbance at 740 nm decreases. When the temperature reduces to the room temperature, the dipoles recover their ordered state, the aggregates restore and the absorbance at 740 nm increases. The reversible phenomena of optical absorbance may be applied to the optical recording devices.