科研之友
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摘要
An azo-containing liquid crystalline polymer was irradiated with linearly polarized blue Ar+ light and the resulting linear birefringence and dichroism were monitored. In its amorphous phase, results obtained are typical for azo polymers of similar structure, with the optical constants largest along the direction perpendicular to the laser polarization. In its nematic phase, surprising results are obtained, including two changes in the sign of the dichroism measured at 632.8 nm and, at one point, a quadrupolar transmission profile. Dichroic visible spectra show evidence for two bands of opposite sign in the region of the npi* transition, which are attributed to the trans and cis isomers. In addition to the conventional photoreorientation of azo groups along an axis perpendicular to the polarization direction of the pump, we propose that, under some conditions, a tendency toward parallel alignment occurs as a result of the optical Freedericksz transition.
- 出版日期2003-3-13
