Towards the design of molecular conductance and bithermoelectric switches

Description

Creating functional nanoscale devices using single molecules as active electronic components is the ultimate goal of the field of molecular electronics. Besides their potential to meet the growing demand for miniaturization of electronics, molecular electronics opens up the possibility of de-vices with novel, unforeseen functionalities beyond silicon-based technologies, such as molecu-lar switches. Through a bottom-up quantum chemistry approach, we have shown that expanded porphyrins are flexible enough to switch between different π-conjugation topologies (Mobius, Hückel and twisted-Hückel) encoding distinct electronic properties and aromaticity.[1]. Since these topology/aromaticity switches can be induced by different external stimuli,[2] these mac-rocycles represent a unique platform to develop a novel type of molecular switches for different nanoelectronic applications.

The first application involves the conductance switching in molecular junctions through aroma-ticity and topology changes. In this regard, the electron transport properties of the different states of the switches were carefully investigated with the non-equilibrium Green´s function formalism in combination with density functional theory for various configurations of the gold contacts.[3] Our findings reveal that the negative relationship between conductance and molecu-lar aromaticity or polarizability does not hold for most of the configurations of the molecular junctions, so we devise new selection rules to predict the occurrence of quantum interference around the Fermi level for Hückel and Möbius systems.[4] A second application concerns the design of bithermoelectric switches, an entirely new class of switches that revert the direction of the heat and /or charge transport. Our in-house calculations reveal that the Hückel-Möbius to-pology switch in heptaphyrins causes the Seedbeck coefficient or thermopower to change con-siderably from +50 V/K to -40 V/K.[5] Chemical control over the thermoelectric properties can be achieved through substitution of the linker groups. Overall, our work demonstrates how the concept of aromaticity and molecular topology can be exploited to create a novel type of effi-cient switching devices.

Period	30 Jun 2019
Event title	Current Topics in Theoretical Chemistry (CTTC2019)
Event type	Conference
Location	Quito, Peru
Degree of Recognition	International