Third-Generation Light-Driven Symmetric Molecular Motors

Abstract

Symmetric molecular motors based on two overcrowded alkenes with a notable absence of a stereogenic center show potential to function as novel mechanical systems in the development of more advanced nanomachines offering controlled motion over surfaces. Elucidation of the key parameters and limitations of these third-generation motors is essential for the design of optimized molecular machines based on light-driven rotary motion. Herein we demonstrate the thermal and photochemical rotational behavior of a series of third-generation light-driven molecular motors. The steric hindrance of the core unit exerted upon the rotors proved pivotal in controlling the speed of rotation, where a smaller size results in lower barriers. The presence of a pseudo-asymmetric carbon center provides the motor with unidirectionality. Tuning of the steric effects of the substituents at the bridgehead allows for the precise control of the direction of disrotary motion, illustrated by the design of two motors which show opposite rotation with respect to a methyl substituent. A third-generation molecular motor with the potential to be the fastest based on overcrowded alkenes to date was used to visualize the equal rate of rotation of both its rotor units. The autonomous rotational behavior perfectly followed the predicted model, setting the stage for more advanced motors for functional dynamic systems.

Exploring the Mechanism of a Chiral N‐Alkyl Imine‐Based Light‐Driven Molecular Rotary Motor at MS‐CASPT2//CASSCF and MS‐CASPT2//(TD) DFT Levels

“…Although there are still many challenges to be overcome to allow the widespread use of artificial molecular machines, the prospect is promising. Sauvage, Stoddart, and Feringa won the 2016 Nobel Prize in Chemistry for their significant contributions to the design and synthesis of molecular machines, which is an affirmation for the emerging field of artificial molecular machines. Light‐driven molecular rotary motors designed by Feringa et al.…”

“…Sauvage, Stoddart, and Feringa won the 2016 Nobel Prize in Chemistry for their significant contributions to the design and synthesis of molecular machines, which is an affirmation for the emerging field of artificial molecular machines. Light‐driven molecular rotary motors designed by Feringa et al. on the basis of overcrowded alkenes (Figure a) are an important class of molecular machines.…”

“…The sophisticated structures and amazing energy conversion efficiencies of biomolecular machines have attracted the attention of biologists, physicists, and chemists, so analyses of their molecular structures and studies of their operational mechanisms are always hot research topics. With the expansion of experimental and theoretical research, scientists have gradually deepened their appreciation of biomolecular machines; furthermore, they have been inspired to design and synthesize a series of artificial molecular machines with simple structures and different functions. Although there are still many challenges to be overcome to allow the widespread use of artificial molecular machines, the prospect is promising.…”

“…For the single‐molecule machine, light, with the virtues of being clean, easy to control and highly selective, acts as the driving energy; at the same time, the rotor part of the molecular motor can create a unidirectional rotation with respect to the stator part, utilizing the photoinduced cis – trans isomerization of the central C=C double bond, which is an attractive type of movement for application in different fields . At present, with the joint efforts of experimental and theoretical scientists, we have a more profound understanding of the working mechanism of the molecular motor; meanwhile, chemists are constantly improving the operational efficiency and extending the functionality of molecular motors by tuning their structures.…”

“…The development of human civilization is always inseparable from the design and construction of machines that emancipate human beings from heavy labor.S imilarly,p eople have found that biological molecular machines [1][2][3][4][5] also play an important role in nature,a nd they takep art in almost all life activities;f or instance, ATPs ynthase, [1,2,5] which creates the energy storage molecule ATP, is at ypical biomolecular rotary motor.T he sophisticated structures and amazing energy conversion efficiencies of biomolecular machines have attracted the attention of biologists, physicists, and chemists, so analyses of their molecular structures and studies of their operational mechanisms are always hot research topics. With the expansion of experimental and theoretical research, scientists have gradually deepened their appreciation of biomolecular machines;f urthermore, they have been inspired to design and synthesize as eries of artificial molecularm achines [6][7][8][9][10][11][12][13][14][15][16] with simple structures and different functions. Althought here are stillm any challenges to be overcomet oa llow the widespread use of artificial molecular machines,t he prospecti sp romising.…”