Dual wavelength in situ photoalignment for stable planar alignment of nematic liquid crystals

We present a two-step in situ photoalignment method for achieving stable planar alignment of nematic liquid crystals. Monodomain and multidomain planar alignments were efficiently induced by employing photochromic side chain polyimides with linearly polarized visible light. Subsequently, the induced alignment was effectively stabilized by UV-curable reactive mesogens (RMs). For efficient alignment control and stabilization, two processes were performed separately by using different wavelengths of exposed light (i.e., dual wavelength in situ photoalignment). The polymerized RM-layers acted as new alignment layers, by overcoating the pristine PI-alignment layers. As a result, the reversible photochromic PI-layer lost its function as an alignment layer and thus the LC alignment became irreversible and stable. Therefore, the proposed dual wavelength in situ photoalignment can be beneficially adopted for practical device applications.