Realizing tunable molecular thermal devices based on photoisomerism-Is it possible?

In this work, we address the question if it is possible to tune the thermal conductance through photoisomerism-capable molecular junctions. Using non-equilibrium molecular dynamics simulations, we study heat flow due to phonons between two silicon leads connected via two classes of photoisomeric molecules-(a) azobenzene and (b) Spiropyran (SP)-Merocyanine (MC) isomers. For the case of azobenzene, isomeric states with different conformations are realized via mechanical strain, while in the case of SP-MC, via a hybridization change. Based on the phononic contribution to thermal conductance, we observe that the thermal conductance of both junctions is rather insensitive to the isomeric state, thereby rendering the tunability of molecular thermal devices rather difficult. Consistent with these observations, the vibrational density of states for different configurations yields very similar spectra. We note that including the effect of electronic contribution to thermal conductance could enhance the tunability of thermal properties, albeit weakly. (C) 2015 AIP Publishing LLC.