Effect of chemical structures of polyimides on photo-alignment of liquid crystals

Unidirectional liquid crystal (LC) alignment by a polarized UV exposure was examined using various polyimides (PIs) which consist of different tetraca rboxylic dianhydrides and diamines. The dichroic ratios and anchoring energ ies of the LC cells were measured as a function of polarized UV exposure ti me. The results suggest that the unidirectional LC alignment for UV dosage is largely affected by the chemical structures of the PIs used. The LC alig nment properties are summarized with respect to the UV absorption efficienc ies, molecular conformations, and mechanisms of decomposition of the PI fir ms.