In-Plane and Tilt Reorientation of p-Methoxyazobenzene Side Chains Tethered to Liquid Crystalline Polymethacrylates by Irradiation with 365 nm Light

Abstract

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.

Photoalignment and Photoinduced Molecular Reorientation of Photosensitive Materials

“…5,6,9,90 Additionally, thermal enhancement of the photoinduced optical anisotropy of the liquid-crystalline azobenzenecontaining polymethacrylates has been observed. 91,92 For example, polymethacrylate with 4-methoxyazobenzene side groups 30 displays thermally enhanced in-plane or out-of-plane molecular reorientation, depending on the length of the alkylene spacer and the amount of the axis-selectively formed cis isomers, as illustrated in Figure 8. 76,92 Furthermore, Seki et al have investigated the control of the microphase separation direction in diblock copolymers containing azobenzene groups by adjusting the polarization of the exposed LP light.…”

Synthesis and liquid crystalline behavior of phosphorus-containing aliphatic–aromatic copoly(ester-imide)s

“…Liquid crystalline polymers are particularly attractive due to their potential applications in optical switching, optical data storage, and optical display [18][19][20].…”

Pendant triazole ring assisted mesogen containing side chain liquid crystalline polymethacrylates: Synthesis and characterization

“…4,5 A number of nemetogens were copolymerized with various azobenzene containing side chain polymers for analysing their photo alignment with respect to switching property of azobenzene unit. [6][7][8][9] During the past decades large number of liquid crystalline compounds containing heterocyclic units have been synthesized. [10][11][12] Interest in such compounds arises from incorporation of heteroatoms can result in prominent changes in the corresponding liquid crystalline phases and/or physical property of the observed phases, because most of the usual heteroatoms (S, O and N) introduced are chemically classified as more polarizable than carbon.…”