Helix Inversion Controlled by Molecular Motors in Multistate Liquid Crystals

Abstract

Artificial molecular motors and switches are called to contribute in setting materials in motion. [1-5] Ongoing efforts to enable transmission of motion and allow molecular machines to work at larger length scales involve their integration in hydrogels, [6-8] self-assembled monolayers, [9] artificial muscles, [10,11] and polymer materials. [12] The long-range organization and fluidity of liquid crystals accounts for their high responsiveness to small changes in molecular structure or composition, with a special sensitivity to changes in chirality. [13] Therefore, liquid crystals constitute an effective host medium for molecular motors and switches. [14-16] Chiral molecular switches can drive dynamic helix inversion in liquid crystals, [17-24] and artificial molecular motors also induce the formation of chiral nematic liquid crystals that respond to light with large changes in pitch and in the orientation of the helical axis, usually also with chiral inversion at the photostationary state. [25,26] Motordoped cholesteric liquid crystals have supported the discovery of rotating surfaces, [27-29] supramolecular vortices, [30] swimming [31] and reconfigurable chiral droplets, [32] and adaptive optical materials. [33,34] Notably, while being at the forefront of light-responsive and adaptive materials, to date motor-doped liquid crystals have been used primarily for their ability to convert from one helix to another, reversibly. These earlier studies have involved "second generation" motors, for which only the expression of two states was possible, because only two isomers of these motors can be distinguished at room temperature. [35,36] Here, we report the motion of the so-called "first generation" molecular motor in liquid crystals, in a cyclic behavior that involves four distinct isomeric states. These motors induce light-responsive helices in liquid crystals, which readily undergo photomodulation of the liquid crystal phase, including helix inversion. While multistate liquid crystal helices can be designed by mixing chiral dopants, [37,38] using a single chiral dopant-for example, by incorporating multiple light-switchable units, [14,39,40] is a better option as this prevents solubility issues and offers better options for rational design, as predictions on the pitch formed by a mixture of chiral dopants lack reliability, particularly at larger concentrations. Key to the design of molecular motors that are able to drive multistate and photoinvertible helices is that each of the motor states displays a distinctively different shape, i.e., either

Motorized Macrocycle: A Photo‐responsive Host with Switchable and Stereoselective Guest Recognition

“…Fore xample,t he yields of stable-trans-3 and stable-cis-3 were 12 %a nd 54 %, respectively.D etailed procedures of the synthesis are provided in the Supporting Information. Them olecular structures were fully characterized by 1 H, 13 CNMR spectroscopies, and high-resolution mass spectrometry (HR-MS;Supporting Information, Figures S50-S71).…”

“…Light-driven molecular motors [12] based on overcrowded alkenes have been developed as a unique family of photoresponsive units in the last decades. Due to their intrinsic feature of performing unidirectional rotation, molecular motors have been explored as robust and versatile functional units to fabricate many photo-responsive materials, including liquid crystals, [13] soft actuators, [6b, 14] gels, [15] foams, [16] membranes, [17] solid-state surfaces, [18] porous frameworks, [19] and nanocars. [20] The intrinsic axial chirality and photoswitching ability of molecular motors, resulting in multiple stable chiral states with precise control over the sequence of chiral isomer formation, are the key features of asymmetric catalysts and phosphate receptors with adaptive chirality.…”

On the Miscibility of Nematic Liquid Crystals with Ionic Liquids and Joint Reaction for High Helical Twisting Power Product(s)

“…High helical twisting power of the chiral dopants is still of interest among other liquid crystalline materials [ 21 , 44 , 45 , 46 , 47 , 48 ], especially those with new electro-optical functionalities, such as optical tunability [ 44 , 45 ], an electrically tunable reflection band [ 47 ], and blue phases, which are used in systems such as electro-optical modulators [ 48 ].…”

Circularly Polarized Luminescence and SHG Chiral Signals of Helical TPE Macrocycles

“…Circularly polarized luminescence (CPL) materials have great potential applications in 3D displays, [ 1 ] nonlinear optics, [ 2 ] information transmission and storage, [ 3‐4 ] chiral sensors, [ 5 ] asymmetric photochemical reactions, [ 6 ] and biological imaging. [ 7 ] But to get excellent CPL active materials with both high fluorescence quantum yield and high CPL dissymmetric factors is still a challenge.…”