Reversible actuating and writing behaviours of a head-to-side connected main-chain photochromic liquid crystalline polymer

A photochromic liquid crystalline (LC) polymer {4-butoxy-2′-(4-hex-5- enyloxy)-4′-(4-hex-5-enyl-oxybenzyloxy)azobenzene, abbreviated as PLCP} was newly synthesized via the acrylic diene metathesis polymerization (H. J. Choi, et al., J. Mater. Chem., 2009, 19, 7124). Utilizing the combined techniques of differential scanning calorimetry, cross-polarized optical microscopy, and wide-angle X-ray diffraction (WAXD), it was realized that PLCP formed a nematic (N) phase below the isotropization temperature (T_NI = 145 °C) and the N phase turned to the glassy N phase below the glass transition temperature (T_g = 24 °C). Especially, two-dimensional (2D) WAXD of the uniaxially oriented PLCP fibre indicated that the N phase contains the synclinically tilted smectic C (SmC)-type cybotactic clusters in which the molecular packing structure is related to the head-to-side connected chemical structure of PLCP. Without introducing any chemical crosslinks, PLCP fibres and films were reversibly deformed by exposing to ultraviolet and visible light. Additionally, we demonstrated the rewritable micro-patterned PLCP film. Because of the wireless remote-controlled actuating behaviours of PLCP combined with its excellent processability, PLCP can be applied in optoelectronic and bio-mimetic devices.