Fig. 10 Change in intensity of diffracted light as a function of
Fig. 8 Typical profiles of the grating formation and the photo-
chemical alignment change in the P3AT6 film. The intensity of the
irradiation time for the P3ATm films. a, P3AT6; b, P3AT9, c, P3AT12.
Films were exposed to (s + s)-polarized writing beams (488 nm) at
writing beams and the pumping beam was adjusted to 250 mW cm22
.
150 mW cm22
.
Conclusion
In summary, we synthesized highly birefringent LCPs contain-
ing an azobenzene group directly connected with a tolane
moiety. One can induce a large change in birefringence
(#0.35) in three LCPs by the photochemical alignment
change. The grating formation in these LCPs could be
attributed to the photoinduced order–disorder change of the
azo-tolane moieties. The formation of gratings takes place
faster in the LCPs having shorter alkyl spacers because the
alignment change in the LCPs possessing short spacer length
could be easily generated by the order–disorder change.
Furthermore the LCP films exhibited high sensitivity as
holographic materials. Therefore it might be possible to use
these LCPs in compact optical systems.
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Effect of spacer length on grating formation
The effect of the spacer length of P3ATm on the diffraction
efficiency was evaluated (Fig. 10). We observed a tendency
that the formation of gratings takes place faster in the LCPs
having shorter alkyl spacers (P3AT6 . P3AT9 . P3AT12).
This tendency could be attributed to the packing density of
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3400 | J. Mater. Chem., 2005, 15, 3395–3401
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