Invisible Polymer Walls Enhance Reorientational Optical Nonlinearity in Oligothiophene‐Doped Liquid Crystals

ABSTRACT Dynamic control of optical properties is key to developing high‐performance materials and devices for a wide range of applications, such as optical communication, sensing, laser protection, and signal modulation. Liquid crystals (LCs) are promising materials that can induce a reversible change in optical properties due to photoinduced molecular reorientation. However, the photoinduced molecular reorientation generally requires high light intensity and has been predominantly explored in the uniformly aligned LC system. In this study, we demonstrate that polymer wall‐stabilized oligothiophene dye‐doped LCs (PWLCs) with three‐dimensional molecular orientation fabricated by spatially selective photopolymerization show highly sensitive optical nonlinearity. Incidence of a linearly polarized laser beam on dye‐doped LCs brings about the light‐intensity‐dependent molecular reorientation and resultant optical limiting behavior. The threshold light intensity, at which the nonlinear molecular reorientation occurs, was reduced by approximately 50% compared to uniformly photopolymerized dye‐doped LCs. Furthermore, the PWLCs exhibited clear polarization dependence near the polymer wall, which affects the torque balance of molecular reorientation. Notably, microstructured polymer walls became invisible, while this optically transparent PWLC cell remained significantly sensitive and acted as a high‐performance optical limiter. This electrode‐free LC system will enable the development of all‐optical smart windows.