Page 134 - Photoreactive Organic Thin Films

4. PHOTOISOMERIZATION AND PHOTO-ORIENTATION OF AZO DYE IN FILMS OF POLYMER f J 3

polarized)/blue (unpolarized) irradiation have shown that this dichroism can
be written/erased and rewritten without any fatigue over 20 cycles. When the
sample was kept in the dark, the spectra from the relaxed sample was shifted
to higher absorbance due to the thermal back reaction, but the initial
dichroism was retained. It was interesting to see that the absorption of probe
light vertically polarized and that of probe light horizontally polarized was

300 320 340 360 380 400 420 440 460 480 500
Wavelength, A, (nm)

0,009

320 340 360 380 400 420 440 460 480 500
Wavelength, X (nm)

FIG. 4.3 UV-vis absorption spectra of the azo-silane layer before (Initial) and after linearly polarized
2
UV (360 nm, ~ 2mW/cm ) irradiation. The probe light was also linearly polarized and spectra were
obtained for both parallel and perpendicular orientations. The polarization of the irradiation UV light
was rotated by 90 degrees from (A) for (B). After reference 39, redrawn by permission of ACS.