Effect of methylene spacers in poly(methacrylate)s bearing styrylpyridine side chains on the ability to control liquid crystal alignment

The photochemistry, photoinsolubilization and ability to control surface-as sisted liquid crystal (LC) alignment of poly(methacrylates) tethering styry lpyridine (SP) side chains through methylene spacers (m = 2, 6 and 12) are described. The extent of (2+2) photodimerization and E-to-Z isomerization o f SP side chains was markedly affected by the length of methylene spacers. In the early stage of photoirradiation, the photodimerization took place pr eferentially for SP-polymers with a shorter methylene spacer, whereas the p hotodimerization was accompanied by the E-to-Z photoisomerization for the p olymers with longer spacers even in the early stage of photoirradiation. Ir radiation of thin films with linearly polarized light resulted in the gener ation of dichroism of SP moieties owing to the angular-selective consumptio n of E-isomer, leading to surface-assisted homogeneous LC aligment. The dir ection of LC photoalignment was reversed from perpendicular to parallel ori entation when SP moieties were tethered to polymer backbones through spacer s. The working mechanism of the alignment reversion was discussed, based on the angular-selective E-to-Z photoisomerization and photodimerization.