Three-dimensional orientational control of molecules by slantwise photoirradiation

When a film of poly[2-(4-phenylazophenyloxy)ethyl methacrylate] is subjected to irradiation with nonpolarized 436 nm light for n-π* excitation at an oblique incident angle with respect to a film surface, dichroism is induced as a result of the reorientation of azobenzene chromophores. The orientational direction is determined reversibly by an incident plane of the light while azobenzene residues reorient in a direction parallel with the light propagation. This procedure is applicable to the generation of tilt angles of nematic liquid crystals assisted by obliquely photoirradiated films as a function of exposure doses, maintaining homogeneous alignment during photoirradiation.