Photoinduced orientational behavior of polymethacrylates with side chains (amorphous polymers, pMAz2 and C2MeO, and liquid crystalline polymers, C6MeO and C12MeO) with different alkylene spacer lengths (n ) 2, 6, 12) were investigated by means of polarized Fourier transform infrared (FT-IR) and UV-vis absorption spectroscopy. Being different from pMAz2, C2MeO showed high optical anisotropy due to in-plane orientation and the excellent thermostability even above T g, which can be explained in terms of potential liquid crystallinity to be able to have a tendency to form a well-ordered domain. We observed marked dependence of photoorientation processes on film temperatures of C6MeO. While in-plane orientation was generated in glassy state as well as at 76 °C, irradiation at 90 °C slightly lower than T SN (transition temperature between smectic and nematic phases) gave rise to the distinct transformation from in-plane orientation at the early stage to successive out-of-plane reorientation, which was accompanied by H-aggregation. This situation enabled ones to record optical images in a C6MeO film on the basis of the difference in birefringences between two orientational modes. The biaxial reorientation occurred also for C12MeO, though both in-plane and out-of-plane photoorientation occurred simultaneously at room temperature as well as elevated film temperatures.

We describe here the highly fluorescent self-assembled spherical aggregates of an azobenzene molecule without a specific ionic component in organic solution under UV light illumination. The first stage of trans-to-cis photoisomerization by UV light at 365 nm was followed by a significant enhancement, up to about 1000 times, of the emission from an azobenzene molecule (CN2Azo) with a long alkyl chain, which is due to the spontaneous formation of spherical organic aggregates. Fluorescence emission was further enhanced in the dark, and the quantum yield increased to about 0.3. We also report the significant size and structural changes of the aggregates, from nanometer-scale micelle-like aggregates to micrometer-scale vesicular aggregates, obtained only from the variation in the concentration of an azobenzene derivative. The light-driven azobenzene aggregates show the size and structure dependences of emission wavelength from violet-blue to green-yellow.

The generation of optical anisotropy induced by irradiation with linearly polarized 365 nm light and by oblique irradiation with nonpolarized 365 nm light and subsequent annealing was described for liquid crystalline polymethacrylates with p-methoxyazobenzene side chains. Exposure of the spincoated films of the polymers to linearly polarized UV light of 10-20 mJ/cm 2 doses and subsequent annealing at temperatures close to the glass transition temperatures (Tg) of the polymers led to a marked enhancement of azimuthal reorientation of the azobenzene to give birefringent films exhibiting excellent thermostability of the optical anisotropy. When the spin-coated films of the polymers were irradiated obliquely with nonpolarized 365 nm light of about 15 mJ/cm 2 dose and annealed subsequently, spatially manipulated reorientation of the azobenzene groups was realized, accompanied by the formation of H-aggregation. The orientational direction was controlled simply by the incident direction of UV light. The photogenerated optical anisotropy for both cases was considerably reduced or disappears when exposure doses exceed about 50 mJ/cm 2 . The mechanism for the thermally enhanced generation of optical anisotropy induced by both modes of photoirradiation was discussed on the basis of photoselective E-to-Z photoisomerization of the E-isomer with a transition dipole moment parallel to the electric vector of linearly polarized 365 nm light or perpendicular to the incident direction of nonpolarized UV light.

Unambiguous observation of the reorientation of azobenzene chromophores toward the propagation direction of the actinic light has been performed. Prolonged irradiation of a spin-coated film of liquid crystalline poly[6-{4-(4′-methoxyphenyl)azophenyloxy}hexyl methacrylate] (C6MeO) with 436 nm light for n-π* excitation led to a marked decrease of the π-π* absorption band. Spectral analysis in combination with conoscopic observation revealed that the reorientation of the azobenzene chromophores occurs in such a way that the longitudinal molecular axis of the azobenzene aligns in parallel with the propagation of light to form strong H-aggregates. The tilt orientation of the azobenzene was more readily achieved by irradiation with light at high temperatures near or above the glass transition temperature. Concerning the effect of spacer length on the three-dimensional orientation, the azobenzene groups showed a tendency to orient more homeotropically as the alkylene spacer length increases.