  We report the formation of self-assembled monolayers of a molecular
photoswitch (azobenzene-bithiophene derivative, AzBT) on cobalt via a thiol
covalent bond. We study the electrical properties of the molecular junctions
formed with the tip of a conductive atomic force microscope under ultra-high
vacuum. The statistical analysis of the current-voltage curves shows two
distinct states of the molecule conductance, suggesting the coexistence of both
the trans and cis azobenzene isomers on the surface. The cis isomer population
(trans isomer) increases (decreases) upon UV light irradiation. The situation
is reversed under blue light irradiation. The experiments are confronted to
first-principle calculations performed on the molecular junctions with the
Non-Equilibrium Green's Function formalism combined with Density Functional
Theory (NEGF/DFT). The theoretical results consider two different molecular
orientations for each isomer. Whereas the orientation does not affect the
conductance of the trans isomer, it significantly modulates the conductance of
the cis isomer and the resulting conductance ON/OFF ratio of the molecular
junction. This helps identifying the molecular orientation at the origin of the
observed current differences between the trans and cis forms. The ON state is
associated to the trans isomer irrespective of its orientation in the junction,
while the OFF state is identified as a cis isomer with its azobenzene moiety
folded upward with respect to the bithiophene core. The experimental and
calculated ON/OFF conductance ratios have a similar order of magnitude. This
conductance ratio seems reasonable to make these Co-AzBT molecular junctions a
good test-bed to further explore the relationship between the spin-polarized
charge transport, the molecule conformation and the molecule-Co spinterface.
