Light-activated helical inversion in cholesteric liquid crystal microdroplets

Abstract

Cholesteric liquid crystal (CLC) droplets exhibit nontrivial topological features, which are controlled by the ratio between the cholesteric pitch and the droplet radius. The radial spherical structure (RSS) is of particular interest, as it reveals an onion-like concentric organization of the cholesteric helices, leading to the expression of spherical Bragg microcavities. Using an overcrowded alkene-based unidirectional molecular motor as a dopant, we show that the topological defect structure in the droplet can be activated by illumination. By using appropriate molecular motor concentrations, light can either break the symmetry of topological defects (as observed for the bent-twisted bipolar structure), or it can induce inversion of handedness in an onion-like organization (in the case of RSS). This latter feature may pave the way toward alternative activation modes of lasers based on cholesteric droplets. By also studying CLC droplets once they have reached full photoconversion at photostationary state (PSS), we highlight that the strong influence of confinement on the droplets structure occurs to the same extent after the helix inversion event. Our results are interpreted in terms of numerical simulations of the droplets' structure, which shed light on the major role played by curvature close to the droplets' center, this latter one becoming dominant when the droplet radius is small.

Photoefficient 2nd generation molecular motors responsive to visible light

“…39 However, the UV light used in the original as well as follow-up studies remains one of the major limitations of this technology. 24,[40][41][42] For this reason, we decided to study the efficacy of our novel visible light responsive push-pull motors 1 s and 2 s as switchable chiral dopants to obtain cholesteric E7 liquid crystals. Table 4 gives an overview of the measured helical twisting powers (b) for enantiomerically pure stable isomers and PSS mixtures of motors 1 (l exc ¼ 420 nm) and 2 (l exc ¼ 455 nm).…”

Photoactivated Artificial Molecular Machines that Can Perform Tasks

“…Another interesting aspect of cholesteric liquid crystals is the fact that droplets of these materials exhibit peculiar topological features, such as microcavities, whose properties are determined by the ratio between the cholesteric pitch and the droplet radius. The photoresponsive behavior of cholesteric LC droplets doped with overcrowded alkene molecular motors was the subject of a recent investigation . Experiments and simulations revealed that the light‐induced change of the cholesteric pitch, driven by the switching of the helicity of the molecular motor dopant, can be harnessed to control some properties of the droplet, such as the position of topological defects and the handedness of the radial spherical structure.…”

Driving Smart Molecular Systems by Artificial Molecular Machines

“…Liquid crystals exhibit a highly ordered structure resulting from anisotropy in solution or molten state, which may provide a favorable work environment for molecular machines and therefore to achieve practical functions. Many liquid crystal–doped systems have been designed over the past few decades . In 2006, Feringa et al embedded light‐driven chiral molecular motors into a cholesteric liquid crystal film, forcing this film to adopt the helicity of molecular motors.…”