First-Principles Investigation of Photoisomeric Switching of Vibrational Heat Current across Molecular Junctions

Photoisomeric molecules rearrange their structure when exposed to light, which alters their chemical, electronic, mechanical, as well as vibrational properties. The present study explores the possibilities to tune the thermal transport across molecular junctions by using photoisomeric molecules. The effect of isomeric switching on phonon transport through single-molecule junctions linking two macroscopic reservoirs is investigated using density-functional-theory-based tight-binding calculations and Green-function formalism. The junctions are built using azobenzene and its derivatives (azobiphenyl and azotriphenyl) that display photoisomeric behavior. Effects of system setup on the heat current and the switching coefficient are studied systematically. Dependence on the molecular species, the choice of reservoir, as well as the type of linkers that bind themolecules to the reservoir are investigated with calculating the phonon-transmission spectra and temperature-dependent thermal conductance values. The results show that thermal conductance can be altered significantly by switching the molecule from trans- to cis-configuration since all molecules yield higher conductances in trans-configurations than their cis-configurations at temperatures higher than 50 K. In the low-temperature range, results reveal considerable switching coefficients exceeding 50%. At room temperature, the switching coefficient can be as high as 20%. It is shown that the effect is robust under the variation of both the molecular species and the linkers.