We stumbled on a very curious observation in the summer of 2018 with DABQDI molecules provided by Olivier Siri‘s team.
While evaluating its experimental suitability for 1d coordination with metals, which has already proven to be fruitful, we noticed the molecules forming chain-like structures even before we introduced metal adatoms.
The low temperature SPM results are sublime: unusual mechanical stability, distinctive intermolecular bonding, and near-Fermi electronic states lighting up at the ends of the chains.
It took an extraordinary cast of theorists hailing from Pavel’s core group, FZU, Charles, Reykjavik, & Madrid Universities to unravel this puzzle and explain these observations as concerted proton tunneling causing a delocalization of electrons.
“Significance of Nuclear Quantum Effects in Hydrogen Bonded Molecular Chains”, ACS Nano, 2021. 10.1021/acsnano.1c02572
Marina Castelli studied the phthalocyanine containing magnesium (MgPc) via 5K scanned probe microscopies extensively during her PhD.
‘Routine’ STM characterisation showed that the molecules were interacting with one another on the Ag100 surface.
ncAFM showed identical contrast for all molecules, pointing to an electronic origin to the observed changes in appearance.
Our key observation was to track the shape of the occupied LUMO for different pairwise distances, an electronic feature that otherwise remained isoenergetic.
With multipass dI/dV mapping we were able to quantitatively track from four- to two-fold rotational symmetry, over distances out to ~3 nm. We found the spatial extent of this attractive hybridization quite surprising.