Azimuthal Dipolar Rotor Arrays on Surfaces

Abstract

A set of dipolar molecular rotor compounds was designed, synthesized and adsorbed as self-assembled 2D arrays on Ag(111) surfaces. The title molecules are constructed from three building blocks: (a) 4,8,12-trioxatriangulene (TOTA) platforms that are known to physisorb on metal surfaces such as Au(111) and Ag( 111), (b) phenyl groups attached to the central carbon atom that function as pivot joints to reduce the barrier to rotation, (c) pyridine and pyridazine units as small dipolar units on top. Theoretical calculations and scanning tunneling microscopy (STM) investigations hint at the fact that the dipoles of neighboring rotors interact through space through pairs of energetically favorable head-to-tail arrangements.

Molecular machines working at interfaces: physics, chemistry, evolution and nanoarchitectonics

“…For regulation of molecular rotor motions upon dipole moment interference in an array of molecular rotors, dipolar molecular rotor compounds were designed, synthesized, and adsorbed as a self-assembled 2D array on an Ag(111) surface by Herges and co-workers. 80 In this molecular rotor, a 4,8,12-trioxatriangulene platform known to be physisorbed on metal surfaces, a phenyl group that bonds to the central carbon atom and acts as a pivot joint to reduce barriers to rotation, and a small dipole unit at the top, a pyridine and pyridazine units are arranged. Theoretical calculations and STM observation studies suggest that the dipoles of adjacent rotators interact spatially through a pair of energetically favorable head–tail nanoarchitectures.…”

Effect of an axial ligand on the self-assembly of molecular platforms

“…Gas-phase calculations of the molecule (substrate neglected) indicate barrier heights for the rotations of the upper and lower phenyl rings of 460 and 11 meV, respectively. 39 Although the interaction with a Ag substrate may modify in particular the latter barrier height thermal rotation is unlikely at the cryogenic temperature of the measurements (k B T E 0.4 meV). As to rotation induced with the STM tip, the different barrier heights suggest that rotation of the entire biphenyl is more likely than rotation of the upper phenyl ring alone.…”

“…This structure is not surprising and similar patterns were previously observed from triangular functionalized TOTA molecules on C 3 symmetric fcc(111) surfaces. [19][20][21][22][23][24][25]39 The predominant phase b, however, is a superstructure of apparent dimer chains.…”

“…Previous gas phase calculations of biphenyl-TOTA led to closely related results. 39 Because of the large height of the biphenyl ligand STM images are not directly sensitive to the TOTA platform and its orientation on the surface. They rather reveal the orientation of the upper phenyl moiety as shown in Fig.…”