Light-Activated Organic Molecular Motors and Their Applications

Abstract

Molecular motors are at the heart of cellular machinery, and they are involved in converting chemical and light energy inputs into efficient mechanical work. From a synthetic perspective, the most advanced molecular motors are rotators that are activated by light wherein a molecular subcomponent rotates unidirectionally around an axis. The mechanical work produced by arrays of molecular motors can be used to induce a macroscopic effect. Light activation offers advantages over biological chemically activated molecular motors because one can direct precise spatiotemporal inputs while conducting reactions in the gas phase, in solution and in vacuum, while generating no chemical byproducts or waste. In this review, we describe the origins of the first light-activated rotary motors and their modes of function, the structural modifications that led to newer motor designs with optimized rotary properties at variable activation wavelengths. Presented are molecular motor attachments to surfaces, their insertion into supramolecular structures and photomodulating materials, their use in catalysis, and their action in biological environments to produce exciting new prospects for biomedicine. CONTENTS 6. Molecular Motors for Applications in Medicine 115 7. Outlook 119 Author Information 120 Corresponding Author 120 ORCID 120 Author Contributions 120 Notes 120 Biographies 120 Acknowledgments 120 References 120

Flexible C−C Bonds: Reversible Expansion, Contraction, Formation, and Scission of Extremely Elongated Single Bonds

“…[23] Thel atter reactivity is more interesting from at opochemical point of view,s ince the solid-state reaction would be applicable for stimuli-responsive systems toward potential applications such as photoswitching,optical recording, and sensing materials. [24][25][26][27][28][29][30][31][32] By controlling the crystal packing structure,i ntermolecular [2+ +2] cyclization could proceed in as ingle-crystal-to-single-crystal (SCSC) manner upon photoirradiation, which has been realized by the aid of soft matter/lattices such as ionic crystals,m etal-organic frameworks,a nd coordination polymers. [33][34][35][36][37][38] Furthermore, only af ew examples exhibit reversible SCSC photocycloaddition and thermal cleavage of ac yclobutane ring, [34][35][36] and none of them are pure neutral organic molecules.…”

“…Another aspect is a structurally fixed cis ‐stilbene moiety in the DBCHT unit, and thus the intramolecular [2+2] cycloaddition reaction could proceed as in DBCHT‐dimer to produce a caged molecule [23] . The latter reactivity is more interesting from a topochemical point of view, since the solid‐state reaction would be applicable for stimuli‐responsive systems toward potential applications such as photoswitching, optical recording, and sensing materials [24–32] . By controlling the crystal packing structure, intermolecular [2+2] cyclization could proceed in a single‐crystal‐to‐single‐crystal (SCSC) manner upon photoirradiation, which has been realized by the aid of soft matter/lattices such as ionic crystals, metal–organic frameworks, and coordination polymers [33–38] .…”

Structural Transition Dynamics in Carbon Electrode‐Based Single‐Molecule Junctions

“…[ 3‐5 ] For example, the configurational changes of photo/electro‐isomeric molecules can be applied to molecular switches, digital storages and other fields. [ 6‐7 ] The conformational transitions, especially the stereoelectronic effects, are critical to chemical reactions and provide new functions for molecular devices. [ 8‐9 ] The conformational changes of biological macromolecules, such as the nucleotide chains, can be used to disease diagnosis and drug discovery.…”

Flexible C−C Bonds: Reversible Expansion, Contraction, Formation, and Scission of Extremely Elongated Single Bonds

“…[23] Thel atter reactivity is more interesting from at opochemical point of view,since the solid-state reaction would be applicable for stimuli-responsive systems toward potential applications such as photoswitching,o ptical recording, and sensing materials. [24][25][26][27][28][29][30][31][32] By controlling the crystal packing structure,i ntermolecular [2+ +2] cyclization could proceed in as ingle-crystal-to-single-crystal (SCSC) manner upon photoirradiation, which has been realized by the aid of soft matter/lattices such as ionic crystals,m etal-organic frameworks,a nd coordination polymers. [33][34][35][36][37][38] Furthermore,o nly af ew examples exhibit reversible SCSC photocycloaddition and thermal cleavage of acyclobutane ring, [34][35][36] and none of them are pure neutral organic molecules.…”