Light‐Directed Dynamic Chirality Inversion in Functional Self‐Organized Helical Superstructures

Abstract

Helical superstructures are widely observed in nature, in synthetic polymers, and in supramolecular assemblies. Controlling the chirality (the handedness) of dynamic helical superstructures of molecular and macromolecular systems by external stimuli is a challenging task, but is of great fundamental significance with appealing morphology-dependent applications. Light-driven chirality inversion in self-organized helical superstructures (i.e. cholesteric, chiral nematic liquid crystals) is currently in the limelight because inversion of the handedness alters the chirality of the circularly polarized light that they selectively reflect, which has wide potential for application. Here we discuss the recent developments toward inversion of the handedness of cholesteric liquid crystals enabled by photoisomerizable chiral molecular switches or motors. Different classes of chiral photoresponsive dopants (guests) capable of conferring light-driven reversible chirality inversion of helical superstructures fabricated from different nematic hosts are discussed. Rational molecular designs of chiral molecular switches toward endowing handedness inversion to the induced helical superstructures of cholesteric liquid crystals are highlighted. This Review is concluded by throwing light on the challenges and opportunities in this emerging frontier, and it is expected to provide useful guidelines toward the development of self-organized soft materials with stimuli-directed chirality inversion capability and multifunctional host-guest systems.

Dynamic Helicity Control of Oligo(salamo)-Based Metal Helicates

“…Since the P and M forms are in dynamic equilibrium, we can change the P/M equilibrium ratio by the addition/removal or modification of the chiral auxiliary. This would lead to responsive helicity changes and inversions as described the Section 1.3, which are recognized as one of the hot topics in functional molecular chemistry [18][19][20][21][22][23][24]. ( Figure 3a), we have to convert the enantiomer pair into a diastereomer pair by the introduction of a chiral auxiliary.…”

“…To date, various types of chemical and other stimuli have been used to achieve dynamic helicity inversion of the helical structures such as polymers, metal helicates, etc. [18][19][20][21][22][23][24]. …”

Self-organized cholesteric liquid crystal polymer films with tunable photonic band gap as transparent and flexible back-reflectors for dye-sensitized solar cells

“…[20][21][22][23] The most important property of CLCs is the selective light reflection according to Bragg's law: [24][25][26][27] λ = np where n is the average refractive index of the liquid crystals medium and p is the pitch defined as the distance along the helical axis of one complete rotation. The photonic band gap of these CLCs can be precisely controlled by modulating the helical pitch and twist sense.…”

Instant Locking of Molecular Ordering in Liquid Crystal Elastomers by Oxygen‐Mediated Thiol–Acrylate Click Reactions

“…Molecular orientation from the pre-aligned liquid crystal oligomers can be faithfully transferred to the LCE films,a llowing for preprogrammed shape morphing from two to three dimensions by origami-(folding-only) and kirigami-like (folding with cutting) mechanisms.T he new LCE chemistry also enables widely tunable physical properties,i ncluding nematic-toisotropic phase-transition temperatures (T N-I ), glassy transition temperatures (T g ), and mechanical strains,w ithout disrupting the LC ordering.Reconfigurable soft materials have gained much attention [1] because of their potential in aw ide range of applications, including energy storage devices, [2] smart windows, [3] microfluidics, [4] optics, [5] flexible electronics, [6] artificial muscles, [7] and soft robots. Rapid gelation of LCEs is required to fix molecular ordering within the elastomer network, whichi se ssential for directed shape transformation.…”