Enlightening dynamic functions in molecular systems by intrinsically chiral light-driven molecular motors

Abstract

Chirality is a fundamental property which plays a major role in chemistry, physics, biological systems and materials science. Chiroptical artificial molecular motors (AMMs) are a class of molecules which can convert light energy input into mechanical work, and they hold great potential in the transformation from simple molecules to dynamic systems and responsive materials. Taking distinct advantages of the intrinsic chirality in these structures and the unique opportunity to modulate the chirality on demand, chiral AMMs have been designed for the development of light-responsive dynamic processes including switchable asymmetric catalysis, chiral self-assembly, stereoselective recognition, transmission of chirality, control of spin selectivity and biosystems as well as integration of unidirectional motion with specific mechanical functions. This review focuses on the recently developed strategies for chirality-led applications by the class of intrinsically chiral AMMs. Finally, some limitations in current design and challenges associated with recent systems are discussed and perspectives towards promising candidates for responsive and smart molecular systems and future applications are presented.

Fig. 1. Selected applications of light-driven molecular motors. (a) Chirality transfer from AMM to a dynamic polymer. Adapted with permission from ref. . Copyright 2007 Wiley-VCH. (b) AMMs embedded in a contractive gel. Adapted with permission from ref. . Copyright 2017, Springer Nature. (c) Electrically driven directional motion of a four-wheeled molecule. Adapted with permission from ref. . Copyright 2011, Springer Nature. (d) Enantiodivergent catalysis by AMMs. (e) Surface-assembled unidirectional molecular motor on a gold surface. Adapted with permission from ref. . Copyright 2005, Springer Nature. (f) Artificial muscle-like function from hierarchical supramolecular assembly of photoresponsive AMMs. Modified with permission from ref. . Copyright 2017, Springer Nature. (g) Embedded AMMs in metal–organic-frameworks. Adapted with permission from ref. . Copyright 2019, Springer Nature. (h) AMMs as chiral dopant in liquid crystal materials.

Fig. 2. (a) Rotary cycle of a chiral first generation molecular motor. (b) Rotary cycle of a chiral second generation molecular motor. (c) Different half-lives of second generation molecular motors and switches in the ground state at 293.15 K. (d) Photoisomerization of bistable photoswitches with distinct chirality. Only the R-enantiomers are shown in this figure.

Fig. 3. (a) Molecular motor based switchable catalyst M1. Light/heat controlled enantioselectivity in asymmetric catalysis by the different states of molecular motor catalyst. (b) Anion binding asymmetric catalysis based on a first generation molecular motor M2.

Fig. 4. (a) First generation molecular motor based chiral phosphorus ligand for transition metal-based asymmetric catalysis. (R,R)-(P,P)-cis-M3 leads to the product with (3S, 4R) configuration while (R,R)-(M,M)-cis-M3 gives the opposite (3R, 4S) chirality. (b) Biphenol based 2nd generation molecular motor M4 as a chiral ligand for asymmetric catalysis. Reproduced with permission from ref. . Copyright 2018, American Chemical Society. (c) Phosphoramidite-hybrid 2nd generation molecular motor M5 as a chiral ligand for asymmetric catalysis. Reproduced with permission from ref. . Copyright 2020, Springer Nature. (d) Transmission of chirality from molecular motor M6 to achiral manganese(III)-salen catalyst used as a photoswitchable catalyst for asymmetric epoxidation.

Fig. 5. (a) Coordination oligomers formed by (P,P)-trans-M7 with Cu(i), and photoisomerization leads to the formation of P’-helicity of (M,M)-cis-M7 with Cu(i). Thermal helix inversion leads to the formation of M’-helicity of (P,P)-cis-M7 with Cu(i). Modified with permission from ref. . Copyright 2017, Springer Nature. (b) Molecular structures of molecular motor M8 in multistate isomers with distinct chirality, and its corresponding assembly structures. Reproduced with permission from ref. . Copyright 2022, American Chemical Society. (c) Schematic representation of photoresponsive assembly transformations of enantiopure M9 and photo-controllable CPL signals. Reproduced with permission from ref. . Copyright 2022, Wiley-VCH.

Fig. 6. (a) Isomerization of M10 and selective chiral guest recognition of M10 in the (M,M)-cis-form and (P,P)-cis-form. (b) Representation of stereoselective guest recognition of molecular motor-based crown ether M11.

Fig. 7. (a) M12 is the initiator to form the poly-isocyanate, whose chains fold into helices. The (M)-trans-M13 shows little influence on the helical poly-isocyanate, thus the polymer helices are racemic. (P)-cis-M13 leads to M-helical polymer. (M)-cis-M13 results in a P-helix polymer. Reproduced with permission from ref. . Copyright 2007, Wiley-VCH. (b) Control over the helicity of polyphenylacetylene using M14 as dopant. Reproduced with permission from ref. . Copyright 2017, the Royal Society of Chemistry.

Fig. 8. (a) Four-step unidirectional rotation cycle of molecular motor M15. Color changes from left to right correspond to 0, 10, 20, 30, 40, and 80 s of irradiation time, respectively. Adapted with permission from ref. . Copyright 2002, the National Academy of Sciences. (b) Four steps rotary cycle of “first generation” AMMs used in this study. The thin cholesteric layers with recorded patterns were visualized under natural (nonpolarized) light and under left- and right-circular polarized light (LCP and RCP, respectively). Adapted with permission from ref. . Copyright 2020, Wiley-VCH. (c) Spiral droplets reorient their swimming direction in response to light-induced helix inversion. Reproduced with permission from ref. . Copyright 2019, Springer Nature. (d) Molecular-machine-based CPL-emitting LC devices are prepared by mixing AMMs and BODIPYs in different LC mixtures. Reproduced with permission from ref. . Copyright 2022, Wiley-VCH. (e) Molecular rotary motor-based photo-responsive liquid-crystal network (LCN) and structure of the LC monomers and molecular motors as cross-linkers. The obtained ribbon is able to bend upon UV light irradiation (365 nm) or walk over a surface (right top). LC monomers with enantiomerically pure motors (R)-M24 and (S)-M24. The resulting ribbon with R-motor shows left-handed helical motion upon UV light irradiation while the ribbon with S-motor shows right-handed helical motion (right bottom). Reproduced with permission from ref. Copyright 2022, Wiley-VCH.

Fig. 9. (a) Schematic depiction of the four-stage spin polarization switching in electron tunneling through the molecular motor M25 thin film on the Ni (50 nm)-Al₂O₃ (3 nm)-M25 (2–3 nm)-Au (20 nm) or the Ni (50 nm)- Al₂O₃ (3 nm)-M25 (2–3 nm)-PEDOT/PSS (600 nm) cross-bar tunnel junction device. Blue helices represent M25. Reproduced with permission from ref. . Copyright 2019, Springer Nature. (b) Schematic depiction of the four-stage spin polarization switching in electron tunneling through the molecular motor M26 thin film on nickel/gold (Ni/Au) substrate which is corresponding to unidirectional rotation through four helical states. Reproduced with permission from ref. . Copyright 2021, Wiley-VCH.

Fig. 10. (a) Rotation of the cholesteric LC texture and glass rod by M20. Scale bar: 50 μm. Reproduced with permission from ref. . Copyright 2006, Springer Nature. (b) Molecular motor M19 or M20 used as dopant to revolve supramolecular chiral structures in LC materials.

Fig. 11. (a) Structure and cartoon representation of the meso-(R,S-R,S) isomer M27. (b)–(d). STM images of molecular nanocars’ movements with different isomers. Reproduced with permission from ref. . Copyright 2011, Springer Nature.

Fig. 12. (a) Schematic representation of a reticulated irreversible photo-contractive polymer-motor gel with molecular motor M28 incorporated in the network. (b) Images of contraction of gel via UV light irradiation. Reproduced with permission from ref. . Copyright 2015, Springer Nature. (c) Schematic representation of a polymer-motor-modulator gel that could be unbraided by a photoswitchable diarylethene modulator. Modified with permission from ref. 101. Copyright 2017, Springer Nature.

Fig. 13. (a) Schematic illustration of a molecular motor atop a cell membrane (left) which can open the membrane by UV light activation of the motor (right). Reproduced with permission from ref. . Copyright 2017, Springer Nature. (b) Schematic illustration of a surface assembled rotary motor and the light-induced molecular motion is directing the fate of stem cells. (c) The design of a force application platform with the rotary motor M29. Schematic representation of manufacture and activation of anti-CD3 antibody linked to the substrate via rotatable motor or non-rotatable motor. Reproduced with permission from ref. . Copyright 2021, Springer Nature.

Fig. 14. (a) Molecular motor structure M30 and proposed mechanism for the photochemical formation of +3, starting from −1. Thermal relaxation of wound up ±n state via temporary ring-opening in the presence of catalytic amounts of nucleophile. Reproduced with permission from ref. . Copyright 2022, Springer Nature. (b) Molecular whirligig structure M31 and schematic representation of the forward and backward stepwise 180° rotations, leading to new entanglements in the Fig.-of-eight and incorporating 1, 2, or 3 crossings. Reproduced with permission from ref. . Copyright 2022, American Chemical Society.

Fig. 15. (a) Scheme showing the design of the force light boosted metal ion transport with the rotary motor M32. Reproduced with permission from ref. . Copyright 2022, American Chemical Society.

Jinyu Sheng

Daisy R. S. Pooler

Ben L. Feringa