  Molecular devices, as future electronics, seek low-resistivity contacts for
the energy saving. At the same time, the contacts should intensify desired
properties of tailored electronic elements. In this work, we focus our
attention on two classes of organic switches connected to carbon-nanotube leads
and operating due to photo- or field-induced proton transfer (PT) process. By
means of the first-principles atomistic simulations of the ballistic
conductance, we search for atomic contacts which strengthen diversity of the
two swapped I-V characteristics between two tautomers of a given molecular
system. We emphasize, that the low-resistive character of the contacts is not
necessarily in accordance with the switching properties. Very often, the
higher-current flow makes it more difficult to distinguish between the logic
states of the molecular device. Instead, the resistive contacts multiply a
current gear at the tautomeric transition to a larger extent. The low- and
high-bias work regimes set additional conditions, which are fulfilled by
different contacts. In some cases, the peroxide contacts or the direct
connection to the tube perform better than the popular sulfur contact.
Additionally, we find that the switching-bias value is not an inherent property
of the conducting molecule, but it strongly depends on the chosen contacts.
