Switchable molecular wires featuring quantum interferences for thermoelectric applications – HotElo

Nanotechnology expansion relies not only on the conception of operative nanosize modules and of their assembly, but also on the management of energy flows such as power source and harvesting of generated energy when those nano-systems are in-use. At the micro and macroscopic scales, the use of thermoelectric ability of some bulk materials (capability to reversibly convert heat into electricity) is intensively developed to address the problem of wasted energy. Interestingly, even though thermoelectricity at the nanoscale can also be an efficient solution for energy harvesting, researches in the domain are very limited compared to other areas of nanotechnologies such as molecular electronics, opto-electronics or spintronics. At the nanoscale, functions such as prevention of heating-damages, heat-harvesting or regulation of the temperature of nano-devices at working-temperature are the most obvious applications, while others remain to be discovered taking into account the high level of functionalisation offered by molecular engineering.
Seminal works in the domain recently demonstrated this proof of concept, i. e. the effective ability of molecular based systems to convey thermoelectric properties and has become a growing field of research. The main challenge to reach technologically viable and applicable thermoelectric nano-devices is now to obtain efficient and stable operating molecular-based thermoelectric systems. The first major issue relies on the optimisation of the properties of the molecular part. Our project aims at contributing in this area, by providing and evaluating innovative and stable molecules, specifically designed to generate efficient thermoelectric mechanism when incorporated between electrodes. A subsequent goal of this project will be to be able to drive remotely those thermoelectric properties, a feature that has never been implemented yet. This is a necessary condition to access applications such as nano-generators, information processing, or thermalization. To that regard, our strategy will be to use light as switching stimuli.
The key idea of this project to achieve high thermoelectric systems is to generate quantum interferences in the transmission function around the Fermi level. To target only highly efficient molecular building-blocks, a significant computational screening will be performed and their synthesis and the device fabrication will be done all along the project following the molecular design findings. In contrast with the current researches in this area focused on conjugated organic junctions possessing side groups or modified fullerenes, we will investigate a new route by using organometallic molecular wires, which have the additional advantages to have highly tuneable electronic properties and to be able to combine several functions. We aim at obtaining concomitantly Seebeck coefficient and electrical conductance higher that the best molecular systems known to date. Importantly, we will implement in these systems remote optical on/off switching of thermoelectric ability, a necessary feature for applications.
A joint theoretical-experimental research protocol will be used to efficiently target realistic arrangements and evaluate their potential in a virtuous circular way: (i) the theoretical screening of several families of complexes achieving potentially efficient thermoelectric effect; (ii) the synthesis of the best candidates in each family; (iii) the experimental studies of physical properties of the molecular nano-devices; and (iv) the addition of a switching of the thermoelectric ability to the systems. We will manage the level of risk by targeting families of complexes with established general synthetic routes. This will allow us measuring rapidly the thermoelectric properties of the first built molecular break-junction setups, as well as to highlight the parameters requiring optimization for this computationally-assisted molecular engineering project.