Time-programmed helix inversion in phototunable liquid crystals

Aßhoff, Sarah J.; Iamsaard, Supitchaya; Bosco, Alessandro; Cornelissen, Jeroen J. L. M.; Feringa, Bernard; Katsonis, Nathalie

doi:10.1039/c2cc37161h

Cited by 51 publications

(38 citation statements)

References 20 publications

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“…This means that the write-and-erase features of our opto-molecular addressing of liquid crystals can be tuned and optimized by appropriate engineering of the molecular switch. [ 34 ] In particular, the use of photoactive chiral molecular switches with thermal stability is expected to overcome present limitations in terms of perennial recording of localized chiral topological states. [ 35 ] To conclude, we have demonstrated the subnanowatt optical generation, control and morphing of topological defect structures and textures in liquid crystalline materials.…”

Section: Doi: 101002/adma201400811mentioning

confidence: 99%

Subnanowatt Opto‐Molecular Generation of Localized Defects in Chiral Liquid Crystals

et al. 2014

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Section: Doi: 101002/adma201400811mentioning

confidence: 99%

Subnanowatt Opto‐Molecular Generation of Localized Defects in Chiral Liquid Crystals

et al. 2014

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“…[77][78][79][80][81][82][83][84][85] One of the significant merits of these materials as lightdriven chiral dopants is that their photoisomerization causes inversion of the molecular helical conformation, which consequently bestows the capability for handedness inversion to the induced helical superstructures of CLCs. Different generations of this fascinating class of materials have been developed and their ability to induce chirality as well as their capability for handedness inversion in nematic LC hosts studied.…”

Section: Chirality Inversion By Overcrowded Alkenesmentioning

confidence: 99%

“…[81] They observed that both 4b and 4c facilitate handedness inversion of induced CLCs fabricated using E7 as the host, with the rate of relaxation of the CLC helix being determined by the rate of inversion of the molecular helicity of the dopants.A ccordingly,t he relaxation of the CLC helix from the photostationary state can be time-programmed by appropriately editing the chemical structure of the molecular motors. [81] They observed that both 4b and 4c facilitate handedness inversion of induced CLCs fabricated using E7 as the host, with the rate of relaxation of the CLC helix being determined by the rate of inversion of the molecular helicity of the dopants.A ccordingly,t he relaxation of the CLC helix from the photostationary state can be time-programmed by appropriately editing the chemical structure of the molecular motors.…”

Section: Chirality Inversion By Overcrowded Alkenesmentioning

confidence: 99%

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

2016

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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.

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“…Coupling molecular photoswitches with liquid crystals has allowed developing light‐responsive molecular systems with applications ranging from optical memory writing to colorful displays . Combined with (helix‐based) cholesteric liquid crystals, molecular photoswitches have allowed creating and manipulating chiral topological structures, changing reflexion colors and polarization, detecting catalytic reactions, and developing soft rotating devices . When embedded in liquid crystal networks covalently, molecular photoswitches have mediated complex shape transformations, and the conversion of light into work and power by soft polymer machines has been demonstrated also …”

Section: Introductionmentioning

confidence: 99%

Long‐Lived Supramolecular Helices Promoted by Fluorinated Photoswitches

Huang

Orlova

Matt

et al. 2017

Macromol. Rapid Commun.

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light into work and power by soft polymer machines has been demonstrated also. [17] Light-responsive cholesteric liquid crystals can be prepared by dissolving a small percentage of chiral photoswitches in a (achiral) nematic liquid crystal host [4,18] (Figure 1). The propensity of these photoswitches, used as dopants, to induce a twist in a given host is characterized by their helical twisting power (HTP), defined as β = × × − ( ) 1 p c ee , where p is the pitch and corresponds to a full 360° rotation of the molecules along the helical axis, c is the concentration of the dopant in wt%, and ee is the enantiomeric excess of the dopant. Chiral switches are typically characterized by large twisting powers for their chirality and can be amplified across length scales effectively. [6] Azobenzenes are typically used as switchable dopants because their trans-cis photoisomerization is associated with large changes in both the geometry and the dipole moment of the molecule. While rod-like trans-azobenzenes are compatible with the nematic order, the bent-like cis-molecules disturb this molecular order significantly. Consequently, the HTP of the trans and the cis isomers are remarkably different. Moreover, coupling azobenzenes to elements of axial chirality yields both a large HTP in the ground state and a large variation of HTP under irradiation with light, compared to chiral azobenzenes that display point chirality only. [11,[19][20][21][22] Light-driven helix inversion has also been reported, when chiral azobenzene dopants with axial chirality were used as dopants. [23][24][25] However, the lack of thermal stability of the cisisomer remains a limitation to reaching the full potential of complex dynamic behavior in these supramolecular systems.Fluorinated azobenzenes display larger thermal stability than their classical counterparts, primarily because the repulsion between the nitrogen lone pairs that destabilizes the cis-isomer is lifted by electron-withdrawing effect of the fluorine atoms in ortho-position. [26][27][28][29] Here, we combine the axial chirality of a binaphthyl moiety with ortho-fluorination of an azobenzene moiety in molecular photoswitches that induce supramolecular helices in liquid crystals in both forms, and thus we demonstrate the photoengineering of long-lived supramolecular helices in soft matter. Results and DiscussionMolecules 1a and 1b were synthesized from commercially available starting materials. Their photochemistry and performance as dopants were investigated by comparing them to the reference azobenzenes 2a [19] and 2b [20,30] in the same Molecular PhotoswitchesChiral azobenzenes can be used as photoswitchable dopants to control supramolecular helices in liquid crystals. However, the lack of thermal stability of the cis-isomer precludes envisioning the generation of long-lived supramolecular helices with light. Here, this study demonstrates thermally stable and axially chiral azobenzene switches that can be used as chiral dopants to create supramolecular helices from (achiral) nematic liq...

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Time-programmed helix inversion in phototunable liquid crystals

Cited by 51 publications

References 20 publications

Subnanowatt Opto‐Molecular Generation of Localized Defects in Chiral Liquid Crystals

Subnanowatt Opto‐Molecular Generation of Localized Defects in Chiral Liquid Crystals

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

Long‐Lived Supramolecular Helices Promoted by Fluorinated Photoswitches

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