C O M M U N I C A T I O N S
On the other hand, at the intensity of g1.5 W/cm2, one can see
that the transmittance of the probe beam decayed to ∼10%. This
result implies that the homogeneous alignment in the azotolane
moieties (Figure 2a) is almost destroyed upon irradiation of light
(Figure 2b). In other words, the high value of ∆n in the
homogeneously aligned state can be effectively converted to the
change in ∆n by the photoinduced change in the alignment of the
azotolane moieties. Actually, the calculated values of the change
in ∆n were g0.65 at the intensity of g1.5 W/cm2 even in the glassy
state. Further irradiation of the pump beam increased the transmit-
tance gradually. The increase is ascribed to the generation of a new
alignment upon irradiation of s-polarized light (parallel to the
rubbing direction); namely, the azotolane moieties become aligned
perpendicular to the electronic vector of the actinic beam due to
the reorientation process as mentioned above (Figure 2c). From
these results, we have revealed that the azotolane moiety with a
higher content of the azo unit enhances the change in ∆n
remarkably.
In summary, we have developed highly birefringent LCPs
containing a long azotolane moiety and have investigated the effects
of the structural factors on the photoinduced alignment change.
Specifically, the azotolane LCP with two azobenzene units showed
the most efficient change in ∆n (g0.65). The molecular architecture
is useful for extensive optical applications in high performance
photonic devices (such as high-density optical recording, as well
as holographic and multibit recording) and photoswitching materials.
Acknowledgment. We are grateful to Prof. Yu Nagase for
measuring the wide-angle X-ray diffraction. This work was
supported by a Grant-in-Aid for Scientific Research (S) 16105004
from the Japan Society for the Promotion of Science (JSPS).
Figure 2. Effect of light intensity on the change in transmittance at 20 °C.
Probe beam: 633 nm. (a-c) Plausible mechanism of the change in
alignment of the azotolane moieties in film 4 upon irradiation of the pump
beam: (a) homogeneously aligned state before irradiation, (b) destruction
of the alignment in the azotolane moieties by irradiation of the beam, (c)
reorientation of the azotolane moieties by isomerization cycles. Film
thickness: 330 nm.
Supporting Information Available: Additional data and synthetic
preparations. This material is available free of charge via the Internet
indicated ordinary wavelength dispersion of ∆n; with a decrease
in wavelength the value of ∆n increased due to resonant enhance-
ment.
References
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