Effects of polarization conditions on molecular orientation in azo-dye compound film

In order to investigate the influence of polarization conditions on azo-dye molecular orientation in films, azo-dye polymer films of guest-host system were prepared by spin-coating method. The average alignment factor of azo-dye molecules in films were investigated by UV-Vis spectra measured before and after corona poling, as well as second harmonic generation at different corona poling conditions. The experimental results show that the average alignment factor of azo-dye films becomes bigger, and second harmonic intensity first increases and then decreases with the increasing of poling temperature. The closer the poling temperature is to the polymer's glass transition temperature, the more likely the molecules are orientated. However, PMMA will fall into a state of viscosity at too high temperature. A part of azo-dye molecules will evaporate easily at high temperature, making the second harmonic intensity decline and the average alignment factor increase. As the film thickness increases, the inhomogeneity of electric field distribution in films increases, which is caused by point-plane corona discharges, the polarization efficiency reduces, and therefore the average alignment factor decreases and the second harmonic intensity first increases and then decreases. (authors)