Page 133 - Photoreactive Organic Thin Films

112 ZOUHBR SEKKAT AND WOLFGANG KNOLL

0,009
A Initial (trans) State
I / min, UV
+ 3 min. UV

» 6 min. UV
T 12 min. UV

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

B 1-2

1.0-

0.8 H
•fi
o
«j
< 0.6
0 25 50 75 100 125 150
Time, t/rain
0.4-
Monoexponential Fit as
"Guide to the Eye"
0.2-

0.0-
1000 2000 3000 4000 5000 6000
Time, t / min
FIG. 4.2 (a) UV-vis absorption spectra of the azo-silane layer before and after various timed doses
2
of UV (360 nm, ~ 2mW/cm ) irradiation. Cis-»trans photoisomerization by blue (450 nm) irradiation
produced a reverse effect and restored the initial spectra. (B) Real-time kinetics of the thermally
activated cis-wans isomerization, with an inset showing an expanded view of the first points of the
figure. After reference 39, redrawn by permission of ACS.

is shown), demonstrating that the monolayer was in-plane optically
isotropic at that time. The UV-induced dichroism could be erased on
irradiation with impolarized blue light upon which the initial spectra for both
Abs// and Abs x were recovered. Further irradiation with linearly polarized UV
light restores the initial dichroism, and successive cycles of UV (linearly