Photoinduced birefringence of azobenzene polymer at blue excitation wavelengths

Abstract

The photoinduced birefringence resulting from trans–cis–trans isomerizations has been measured in a thin film of azobenzene-functionalized poly(esterimide) at three excitation wavelengths. The excitation wavelengths of 388 and 420 nm have been located at exactly opposite sides of the trans azobenzene absorption band. A third irradiation wavelength was shifted to 438 nm. Distinct saturation levels and growth dynamics of photoinduced birefringence have been observed under the 388- and 420-nm illumination, while very similar characteristics were recorded at 420 and 438 nm. Differences in the obtained birefringence signals have been explained considering the cis isomer absorption and photoisomerization pathways.