Molecular Rotor Functionalized with a Photoresponsive Brake

Abstract

A molecular motor that has been previously shown to rotate when fueled by electrons through a scanning tunneling microscope tip has been functionalized with a terarylene photochrome fragment on its rotating subunit. Photoisomerization has been performed under UV irradiation. Variable-temperature 1 H NMR and UV−vis studies demonstrate the rotational motion and its braking action after photoisomerization. The braking action can be reversed by thermal heating. Once the rigid and planar closed form is obtained, the rotation is effectively slowed at lower temperature, making this new rotor a potential motor with an independent response to electrons and light.

Two ‘braking mechanisms’ for tin phthalocyanine molecular rotors on dipolar iron oxide surfaces

“…Achieving control of molecular machines is difficult, but quite nontrivial. To realize the practical application, many problems still keep open for controlling molecular machines, such as how to adjust the rotation speed of a nanoscale molecular rotor, how to directly brake/restart the motion of a molecular motor as well as how to realize the propagation of rotational excitation between adjacent molecules like a macroscopic scale gear set [28][29][30][31] .…”

“…To realize the practical application, many problems still remain open for controlling molecular machines, such as how to adjust the rotation speed of a nanoscale molecular rotor, how to directly stop/restart the motion of a molecular motor and how to realize the propagation of rotational excitation between adjacent molecules such as a macroscopic scale gear set. [28][29][30][31] In the current stage, we naturally associate the role of switches and clutches with machinery, and try to install similar functions on nanomachines. A cap-shaped tin phthalocyanine (SnPc) molecule adsorbed on the surface constitutes a singlemolecule switch, with the central metal ion pointed either down to the surface or up to the vacuum with different distances (d) to the surface 32,33 (Fig.…”

Ruthenium complexes of sterically-hindered pentaarylcyclopentadienyl ligands

“…This group has previously been used by our group as a photoactive brake subunit to hinder the rotation of a molecular motor with the rotational braking observed using both NMR and UV/Visible analysis. 15 …”

“…In our efforts towards the development of photo-controlled molecular machines, we aimed to introduce a terarylene photochrome on the cyclopentadienyl rotating subunit of a ruthenium complex. 15 Given the synthetic cost and sensitivity of the terarylene moiety, the direct oxidative addition of the cyclopentadiene precursor Cp 5Ar H was ruled out and we instead turned our attention to Manners' method, starting from the bromocyclopentadiene carrying four phenyl groups and a terarylene fragment ( Scheme 2 ). Strikingly, its reaction with Ru 3 (CO) 12 was inoperative due to decomposition of the bromine precursor via radical side-reactions, preventing formation of the desired ruthenium complex.…”

E/Z Molecular Photoswitches Activated by Two-Photon Absorption: Comparison between Different Families

“…Scientists have focused their efforts not only on discovering novel photochemical reactions, but also on taking advantage of the ones already known to build useful building blocks [ 1 , 2 , 3 , 4 , 5 ]. Photoactive molecular devices, such as molecular motors, rotors, or switches, are a clear example [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ]. The relevance of this field in the last decade has been acknowledged by the Nobel Prize in Chemistry 2016 awarded to Jean-Pierre Sauvage, Sir J. Fraser Stoddart and Bernard L. Feringa “for the design and synthesis of molecular machines.” Among photoactive molecular devices, molecular switches are the most widely studied, due to their simpler photoactive mechanism and easier implementation in larger systems for applications [ 6 , 11 , 13 ].…”