Electrically Induced Photonic Assemblies of Faceted ZIF‐8 Crystals Exhibiting Binary Angle‐Dependent Structural Color and Metamerism

ABSTRACT

Electrically tunable structural color has been pursued primarily in ordered photonic crystals (PhCs), where modulation of a sharp Bragg reflection provides an intuitive design handle. However, the dependence of observed color on viewing angles in PhCs limits their use for optical security and information encoding. Extending comparable electrical control to photonic glasses (PhGs), where multiple scattering pathways coexist and angle‐dependent coloration is suppressed, has remained less explored. Here, electrically driven photonic assemblies (PhAs) based on sub‐micron, faceted, zeolitic imidazolate framework‐8 (ZIF‐8) colloids are reported, exhibiting rapid and reversible optical switching under low applied voltages. Unlike conventional spherical colloids, the faceted geometry of the ZIF‐8 particles introduces pronounced angle‐dependent single‐particle scattering. Electric‐field‐induced assembly in liquid environments tunes particle packing and short‐range order, selectively reweighting the relative contributions of Bragg‐like reflection, diffuse scattering, and angle‐dependent single‐particle backscattering. This produces an unusual binary angular response, appearing blue at normal incidence and pink at oblique viewing angles. By designing a second assembly with indistinguishable normal‐incidence color but no angular switching, we further realize a metameric pair suitable to demonstrate two‐factor authentication. Spectroscopy measurements, combined with single‐particle scattering simulations, elucidate how electrically controlled particle packing and disorder govern optical response in metal–organic framework (MOF)‐based PhAs.