Controlling Molecular Rotary Motion with a Self‐Complexing Lock

Abstract

Biological motors, such as the kinesin or myosin linear and ATPase rotary motor systems, [1] have been a source of inspiration for the development of a variety of artificial molecular mechanical devices [2] (including switches, shuttles, muscles, and rotors) and of elegant molecular motor systems.[3] Selfcomplexing and self-assembling systems [4] represent important dynamic compounds that play a prominent role in the field of molecular recognition and molecular devices. The uses of such supramolecular systems add attractive features to the construction of advanced nanoscale molecular machinery because of their potential to undergo controllable intramolecular complexation in response to a particular stimulus.Of these self-assembling systems, secondary dialkylammonium ions (R 2 NH 2 + ) are well-known for their ability to thread through, for example, a dibenzo [24] [6] have combined both the dibenzo[24]crown-8 and dialkylammonium ion structural motifs into a single system, most of these feature versatile intermolecular complexation rather than unique intramolecular self-complexation.Herein we report the design, characterization, and operation of a lockable [7] light-driven molecular rotary motor featuring a self-complexing [1]pseudorotaxane system. By taking advantage of the complexation between the R 2 NH 2 + and the DB24C8 units in the system, acid-basecontrolled threading-dethreading movements can be utilized to unlock or lock the molecular rotary motor. The design of the molecular system with a self-complexing lock is illustrated in Scheme 1. The molecular system cis-1-H·PF 6 is composed of 1) a second-generation light-driven molecular motor [8][9][10] based on an overcrowded alkene, in which the molecular rotor (2,6-dioxonaphthalene, upper half) rotates 3608 relative to the stator (xanthene, lower half) upon repetitive photochemical trans-cis isomerizations and subsequent thermal irreversible helix inversion steps, 2) a DB24C8 macrocyclic ring incorporated into the xanthene lower stator half, which can act as a socket for the dialkylammonium moiety, and 3) a R 2 NH 2 + moiety attached to the upper rotor half by a short spacer, which can insert itself as a plug into the DB24C8 macrocycle socket. The free OH group at the end of the arm can be easily functionalized to construct interlocked rotaxanes. cis-1-H·PF 6 was prepared in 20 steps (Schemes S1-S4 in the Supporting Information) and characterized by 1 H and 13 C NMR spectroscopy and high-resolution mass spectrometry. [11] The 1 H NMR spectrum (500 MHz, 298 K) of the hexafluorophosphate salt cis-1-H·PF 6 (Figure 1 a), recorded in [D 6 ]DMSO, has similar splitting patterns as the spectrum of the unprotonated cis-1 in CD 2 Cl 2 (Figure 1 b), [6a] which can be rationalized by attributing it to the uncomplexed species, that is, the dialkylammonium ion does not reside inside the DB24C8 cavity.[6c] A more complicated 1 H NMR spectrum of cis-1-H·PF 6 was obtained in CD 2 Cl 2 (Figure 1 c), as is evident in the region d = 3.5-4.4 ppm corresponding to the resonanc...

Artificial molecular motors

“…This work shows that precise control of stereochemical elements is crucial in achieving higher degrees of complexity of motion generated by molecular machines In addition to controlling the direction of rotation by a chemical stimulus, the photochemical step and therefore the whole rotation can also be inhibited by a chemical trigger. 91 The system for which this behaviour has been described consisted of a 2 nd generation overcrowded alkene molecular motor functionalized with a dialkyl ammonium group on the upper half and a dibenzo [24]crown-8-ether attached to the lower half (Scheme 18). It was found by 1 H-NMR spectroscopy that in CD 2 Cl 2 the ammonium group is bound non-covalently to the crown ether.…”

Sailboat‐Shaped Self‐Complexes that Function as Controllable Rotary Switches

“…All reactions were performed under an atmosphere of N 2 . 2‐Methoxycarbonylbis( p ‐phenylene)‐34‐crown‐10 ( 1 ) was synthesized according to a literature procedure . Melting points were determined with an Electrothermal x‐5 melting point apparatus.…”

“…Recently, several self‐complexing systems were developed as molecular switches . Qu and Feringa reported a lockable light‐driven molecular motor based on an overcrowded alkene bearing a dialkylammonium/DB24C8 system as a self‐complexing lock; the acid–base‐controlled threading/dethreading movements were utilized to lock or unlock the molecular motor. Herein, we report a new type of self‐complex, that is, sailboat‐shaped self‐complexes, formed by benzylammoniummethylene‐substituted bis( p ‐phenylene)‐34‐crown‐10 (BPP34C10) ethers.…”

Reprogrammable Assembly of Molecular Motor on Solid Surfaces via Dynamic Bonds

“…[2] Meanwhile, it contains bromo substituents that are facile to be introduced into the framework of molecular motors and functionalized by other functional groups. [13] Here, the molecular motor MS 2 with disulfide bonds was synthesized by Sonogashira coupling and esterification reactions from molecular motor M 1 . The chemical structure of molecular motor MS 2 is well identified by 1 H and 1 C NMR spectroscopy, matrix-assisted laser desorption/ ionization time of flight mass spectrometry (MALDI-TOF), and elemental analysis (see the Supporting Information).…”