  The current work investigates candidate building blocks based on molecular
junctions from hydrogen transfer tautomerization in the benzoquinone-like core
of an azophenine molecule with QTAIM and the recently-introduced stress tensor
trajectory analysis. We find that in particular the stress tensor trajectories
are well suited to describe the mechanism of the switching process. The effects
of an Fe-dopant atom coordinated to the quinone ring, as well as F and Cl
substitution of different ring-hydrogens, are investigated and the new QTAIM
and stress tensor analysis is used to draw conclusions on the effectiveness of
such molecules as molecular switches in nano-sized electronic circuits. We find
that the coordinated Fe-dopant greatly improves the switching properties, both
in terms of the tautomerisation barrier that has to be crossed in the switching
process and the expected conductance behavior, while the effects of hydrogen
substitution are more subtle. The absence of the Fe-dopant atom led to impaired
functioning of the switch 'OFF' mechanism as well as coinciding with the
formation of closed-shell H---H bond critical points that indicated a strained
or electron deficient environment. Our analysis demonstrates promise for future
use in design of molecular electronic devices.
