In-plane and tilt reorientation of p-methoxyazobenzene side chains tethered to liquid crystalline polymethacrylates by irradiation with 365 nm light

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 spin-coated 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 (T-g) 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.