Foldamer based recognition- and photo-switches for supramolecular electronics – FORESEE

Foldamers, linear oligomers that fold into predefined and stable molecular architectures, possessing specific units for the recognition of substrates or photoswitch are synthesized. The structural characteristics of these compounds are then studied by conventional characterization methods such as NMR and X-ray diffraction. The molecular recognition properties as well as their structural response to external stimuli are tested. The most promising molecules are then modified to be grafted onto gold surfaces, then the properties of electric current conduction are measured.

At the present time, we have produced monolayers of foldamers capable of recognizing strong acids and for which, by protonation of the skeleton of the oligomer, a modification of the conductive properties of these surfaces could be observed. This response is however weak and it is now necessary to design more sensitive oligomers. In a second approach, we have developed oligomers with photosensitive units and we are currently testing the influence of light irradiation on the architecture of these compounds.

These photosensitive compounds will then be deposited on gold surfaces in order to determine the influence of the modifications induced by irradiation on the conductive capacities of the monolayers formed.

An article on the influence of encapsulation of a strong acid on the conductivity of monolayers formed by foldamers.is in preparation.

In complex living organisms, sensing information (sight, smell, taste, touch or hearing) begins with a molecular events which is eventually transduced into charge transport processes, i.e. the propagation of bilayer membrane potentials in neurons, allowing information to be integrated and processed in the brain. In a similar manner, this project aims at making critical steps towards the coupling of synthetic molecular sensors with electron transport in view of the long-term objective of sensor integration into complex electronic devices. Specifically, we will explore the requirements for switching “on” and “off” charge transport through synthetic organic helical aromatic foldamers upon guest binding or light-induced spatial reorganization of covalent and non-covalent interactions.
Molecular nanoelectronics have attracted lots of attention in recent years due to the perspective of miniaturization offered by the use of single molecules as electronic components. Indeed, molecules can be considered as the smallest possible building block for the construction of an electronic circuits. However, this requires integrating functional molecules that can make a transition between high and low conductivity as one of the key steps. Such molecular switches may become basic components in molecular electronic devises. But in the context of a bottom-up approach to create nano-devices, the use of a single molecule is for the moment not realistic and in term of producing long-lived, and commercial devices reproducibly is not pertinent. Attention has then been turn to the production of conducting self-assembled monolayers and conducting AFM as a method of choice for their characterization and operation. This technique, however, has the pre-requirement of having stable and well-organized monolayers of a responsive conducting substrate. The majority of SAMs are made of long alkyl chains that are considered insulating, or are composed of specifically designed substrates for which chemical modifications may create monolayer destabilization and therefore are difficult to be evolved to tune their conductivity properties.
In this project, we propose to use molecular oligomeric helically structured architecture, foldamers developed by partner 1, as a scaffold that forms stable monolayers on surfaces and for which, properties can be adjusted by modification of their sequences without changing their overall external shape and so their self-assembly properties. These aromatic oligoamide has shown self-assembled monolayer formation when anchored on gold surfaces, and C-AFM measurements demonstrated good charge conduction through the formed monolayers, that is along the helices, with little attenuation with helix length, in agreement with the extremely fast photo-induced charge transfer across long distances observed in solution. These molecular architectures also feature interesting recognition properties. It is possible by design to create oligomeric molecular containers that present an inner cavity large enough to accommodate various guest with high affinity and selectivity. This recognition event is expected, when the guest interact with the host oligomer, to modify its conducting property and to result in an electrical signal that can be detected. In another approach, incorporation into the helical backbone of photochromic units, that can modify the electronic property of the oligomer upon irradiation, is also proposed in this project. Photo-active systems offer the advantage to be only driven by light, which can be easily address and often show reversibility, a pre-requirement to produce a switch.
This project will lead to the development of molecular systems capable of transducing a chemical or a light signal into an electrical one analogously to an artificial nose or an artificial eye.