Towards solid-state molecular switches
Molecules often possess unique properties that have no parallel in conventional materials, promising new devices with novel functions that cannot be achieved with equivalent solid-state devices. Molecular switches on surface are an appealing example, where different environmental stimuli can trigger them by manipulating for example their charged states. Redox-active molecules are compelling candidates for molecular switches. However, although the switching capability is shown in solution, in order to move towards devices they need to be immobilized in a solid support. The EU-funded project ELECTROMAGIC (Multifunctional surfaces structured with electroactive and magnetic molecules for electronic and spintronic devices) sought to address this by synthesising solid-state molecular switches through preparing self-assembly monolayers (SAMs). By synthesising SAMs based on endohedral metallofullerene (EMF) molecules on a gold substrate, scientists managed to electrically trigger the surface magnetic behaviour by changing the redox state. In addition, the team functionalised a gold surface with two different tetrathiafulvalene molecules, demonstrating the possibility to control its wettability. Moreover, they modulated the surface energy by exchanging the counterions used to stabilise the charge of the oxidised SAMs. Redox states can also act as memory bits. Larger number of states means higher storage capacity of the fabricated molecular switch. Newly synthesised mixed SAMs based on two electro-active molecules would serve as multi-molecular switch. Scientists then proceeded with designing a more complex system, confining the molecules on certain areas of the surface. The aim is to provide a proof-of-concept using nanoparticles that could bind with the molecules on the surface. The system can find application in microfluidic chips that guide the recognition in the channels, sensors for charged biomolecules, or controlled growth of charged polyelectrolytes. The project team also provided key insight into the use of organic radicals in molecular spintronics. Following the preparation of SAM based on organic radicals; experimental results confirmed the role that radicals play on the charge transport across the molecular junctions between the radicals and electrodes. The ability to efficiently control the molecule properties at each redox state opens the way for functional molecular devices that can act as switches, memories or sensors.
Keywords
Solid-state molecular switches, molecular electronics, redox state changes, molecular spintronics, information storage
