4
0
M. Kamruzzaman et al.
demonstrated that the on-off switching of the reflection could be achieved by com-
bination of spontaneous out-of-plane molecular orientation and photoisomerization
of azobenzene group.
Conclusion
Polyethylene imines having azobenzene side chain groups were synthesized success-
fully and fabricated photo-tunable multiply-layered film consisting of PEI6 M and
PVA by alternative spin coating. PEI6 M films showed high dichroism and order
parameter values after annealing and that revealed a well-pronounced tendency
for the development of the out-of-plane order. Also the multiply layered films exhib-
ited reflection of color and the wavelength and intensity of reflection peak could be
tuned by film thickness and the bilayer number respectively. The multiply-layered
ꢀ
film showed a low reflectance after annealing at 85 C because of small difference
in refrective index (n ) of PEI6 M and PVA. But again the reflection of such
0
multiply-layered film was increased by UV light irradiation because of reorientation
of azobenzene groups from out-of-plane order to random state. In all cases
PEI6 M-II single layer as well as multiply-layered films showed quicker response
than PEI6 M-I because of high azo content in PEI6 M-II. So the photochemical con-
trol of the molecular orientation of PEI6 M between random state and the out-of-
plane structures could be achieved by combination of thermal and photochemical
processes. These results were caused due to the transformation of molecular orien-
tation and trans-cis photoisomerization of azobenzene groups. Therefore, these
results may provide promising ways to fabricate novel types of optical elements
and devices for photonic applications.
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