Two-Level Spatial Modulation of Vibronic Conductance in Conjugated Oligophenylenes on Boron Nitride

Intramolecular current-induced vibronic
excitations are reported
in highly ordered monolayers of quaterphenylene dicarbonitriles at
an electronically patterned boron nitride on copper platform (BN/Cu(111)).
A first level of spatially modulated conductance at the nanometer-scale
is induced by the substrate. Moreover, a second level of conductance
variations at the molecular level is found. Low temperature scanning
tunneling microscopy studies in conjunction with molecular dynamics
calculations reveal collective amplification of the molecule’s
interphenylene torsion angles in the monolayer. Librational modes
influencing these torsion angles are identified as initial excitations
during vibronic conductance. Density functional theory is used to
map phenylene breathing modes and other vibrational excitations that
are suggested to be at the origin of the submolecular features during
vibronic conductance.