Light-Driven Control of Polar Order in Ferroelectric Nematic Liquid Crystals

Ferroelectric nematic (N_F) liquid crystals are polar fluids that combine long-range orientational order with spontaneous macroscopic polarization and exceptionally large dielectric permittivity. While these properties make N_F materials attractive for responsive soft devices, incorporating additional functionality remains challenging because polar order is highly sensitive to molecular mismatch. Here we introduce a molecular design strategy that enables optical control of N_F materials using azobenzene-based mesogens structurally matched to the archetypal N_F compound DIO. Two derivatives are themselves ferroelectric nematogens, demonstrating that photoisomerizable mesogens can intrinsically sustain and modulate N_F polar order, with large and reversible light-induced changes in polarization and dielectric permittivity. The same structural matching principle also enables non-N_F azobenzenes to co-assemble with DIO at concentrations up to 20 wt.% while preserving ferroelectric nematic order. In selected blends, light irradiation drives a reversible transition from the ferroelectric nematic state to a low-permittivity state consistent with antiferroelectric smectic order. Together, light and temperature provide complementary handles to navigate this phase landscape of competing ferroelectric and antiferroelectric order. These results provide a molecular design strategy for programming collective polar order in ferroelectric nematic fluids using light-responsive mesogens.