  We present an \emph{ab initio} study of the role of interference effects in
the thermal conductance of single-molecule junctions. To be precise, using a
first-principles transport method based on density functional theory, we
analyze the coherent phonon transport in single-molecule junctions based on
several benzene and oligo-phenylene-ethynylene derivatives. We show that the
thermal conductance of these junctions can be tuned via the inclusion of
substituents, which induces destructive interference effects and results in a
decrease of the thermal conductance with respect to the unmodified molecules.
In particular, we demonstrate that these interference effects manifest as
antiresonances in the phonon transmission, whose energy positions can be
controlled by varying the mass of the substituents. Our work provides clear
strategies for the heat management in molecular junctions and more generally in
nanostructured metal-organic hybrid systems, which are important to determine,
how these systems can function as efficient energy-conversion devices such as
thermoelectric generators and refrigerators.
