Page 231 - Photoreactive Organic Thin Films

2 | 0 HENNING HENZEL

FIG. 6,26 Atomic-force microscopy 3-D topography image (20 ^im x 20 fim x 200 ran) of the sur-
face-relief grating on 100-layer mixed LBK film of polymer 44 and cadmium stearate deposited on glass
(reproduced from reference 121 with permission. Copyright (1999) American Chemical Society).

71
ation (see Figures 6.16 and 6.19). In the case of the polypeptide with the
longer spacer 38 (n = 6), however, the coupling between the side chain and
the still ordered main chain are too strong to efficiently reorient the azoben-
71 119
zene in the side chain. ' Employing LBK films of copolypeptides 40,
Menzel et al. have shown that photoreorientation is hindered in well-ordered
LBK films of the copolypeptide, even if the aggregation is suppressed by the
introduction of the nonphotochromic biphenyl moiety. So the structure of the
densely packed LBK films is decisive for the hindrance of the photoreorienta-
93
tion but not the aggregation of the chromophores, Employing irradiation
conditions for holographic experiments, the photoisomerization in azoben-
zene films can result in the formation of surface-relief gratings (see Chapter
14), Because the polarization of the writing beams has a distinct effect on the
efficiency of the grating formation, it is supposed that photoreorientation of
120
the chromophores plays a role in the grating formation. Mendo^a et al.
have shown that surface-relief gratings also can be inscribed in LBK films of
121
an azobenzene poly(methacrylate) 44 (see Figure 6.26)

6.6 EXAMPLES OF LBK FILMS WITH A STRUCTURE TAILORED FORTHE DESIRED
APPLICATION

6.6.1 Optical Data Storage
The majority of the applications that have been suggested for photoactive
LBK films are in the area of optical data storage. The level of technical rele-
vance of the proposed systems differs widely. The earliest reports suggested