Ben L. Feringa

Photonics and tunable optics are rapidly developing fields that require materials with programmable properties and advanced functionalities. Cholesteric liquid crystals (CLCs) are unique materials that exhibit selective light reflection and can be tuned using stimuli‐responsive small organic molecules. The challenge lies in designing molecules that can convert external signals, such as light, into dynamic and invertible chiral states, which can be transduced to the CLC supramolecular structures inducing large differences in helicity and eventually to macroscopic properties. Here, novel intrinsically chiral phenanthrene‐based diarylethenes as light‐responsive chiral dopants for controlling the supramolecular helical architectures of CLCs are introduced. The substitution pattern and light‐invertible axial chirality of these diarylethenes make them highly compatible with liquid crystals and provide high twisting power. The light‐induced cyclization and molecular chirality transformation result in a wide tunability of the cholesteric helix pitch (reflection colors) and reversible inversion of helical handedness. These findings provide a powerful tool for controlling and manipulating the macroscopic properties of CLCs, opening new avenues for a range of applications, including diffractive optics and photonics, anticounterfeiting tags, and displays.