Toward the Design of Bithermoelectric Switches

In this work, we explore the design of so-called "reversible bithermoelectric switches", molecules which can be switched reversibly between a positive and negative Seebeck coefficient through the application of external stimuli. We focus on heptaphyrins, a class of expanded porphyrins that can be shifted between a Hückel and Möbius topology, and demonstrate that these molecules are promising candidates for such an electronic function. Our calculations lead to the conclusion that the molecular switch between these two π-conjugation topologies causes the thermopower to change considerably from +50 μV/K to -40 μV/K, respectively. We address some of the limitations of our approach and expect that this behavior will be retrieved experimentally as well, although chemical modifications of the molecules and/or electrodes might be required. Bithermoelectric switches could potentially constitute an entirely new class of molecular switches which, instead of switching between an ON and an OFF state (the modus operandi of most molecular switches so far), revert the direction of the heat and/or charge transport. This could potentially lead to a wide range of novel technological applications.