title: Measuring the mechanical properties of molecular conformers.
abstract: Scanning probe-actuated single molecule manipulation has proven to be an exceptionally powerful tool for the systematic atomic-scale interrogation of molecular adsorbates. To date, however, the extent to which molecular conformation affects the force required to push or pull a single molecule has not been explored. Here we probe the mechanochemical response of two tetra(4-bromophenyl)porphyrin conformers using non-contact atomic force microscopy where we find a large difference between the lateral forces required for manipulation. Remarkably, despite sharing very similar adsorption characteristics, variations in the potential energy surface are capable of prohibiting probe-induced positioning of one conformer, while simultaneously permitting manipulation of the alternative conformational form. Our results are interpreted in the context of dispersion-corrected density functional theory calculations which reveal significant differences in the diffusion barriers for each conformer. These results demonstrate that conformational variation significantly modifies the mechanical response of even simple porpyhrins, potentially affecting many other flexible molecules.
authors.affiliation: School of Physics &Astronomy, University of Nottingham, Nottingham NG7 2RD, UK.
authors.forename: S P
authors.initials: SP
authors.lastname: Jarvis
authors.affiliation: School of Physics &Astronomy, University of Nottingham, Nottingham NG7 2RD, UK.
authors.forename: S
authors.initials: S
authors.lastname: Taylor
authors.affiliation: Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK.
authors.forename: J D
authors.initials: JD
authors.lastname: Baran
authors.affiliation: School of Chemistry, University of Nottingham, Nottingham NG7 2RD, UK.
authors.forename: N R
authors.initials: NR
authors.lastname: Champness
authors.affiliation: Applied Physics, Division of Materials Science, Department of Engineering Sciences and Mathematics, Luleå University of Technology, SE-971 87 Luleå, Sweden.
authors.forename: J A
authors.initials: JA
authors.lastname: Larsson
authors.affiliation: School of Physics &Astronomy, University of Nottingham, Nottingham NG7 2RD, UK.
authors.forename: P
authors.initials: P
authors.lastname: Moriarty