To develop our system, we have used oligo-phenylene ethynylenes (OPEs) as rigid rods, functionalized with squaramide (SQ) units. These compounds were prepared using standard synthetic procedures, which were optimized to obtain the best outputs. Mono-, bis- and tris-SQ OPEs were prepared and studied both in solution, by NMR spectroscopy, and in solid state, by single crystal X-ray diffraction. The crystal structures showed a perfect match between the repeat unit distances in the SQ relay and in the OPE.
SQ-OPE relays were prepared with different director groups in one end of their structure. We observed two opposite orientations of the SQ relays with respect to the OPE rigid rod. The orientation and robustness of the relay was dictated by the hydrogen-bonding properties of the director, thus determining the orientation and interaction capability of a remote SQ unit.
We installed a switchable director into a tris-SQ relay of 2 nm length (a distance similar to the thickness of the lipophilic region of a bilayer membrane). The resulting device responded to a simple chemical messenger, the proton, relaying the conformational change caused by protonation of the director to the end of the scaffold. Addition of a second messenger, a base, caused the recovery of the initial conformational state, which was able to accept subsequent protonation/deprotonation cycles.
The reversible communication device described above was then combined with a chemical fuel to produce an out-of-equilibrium system. The chemical fuel (an acid) caused a message to be relayed down the scaffold, and then the initial “off” state was recovered over time, due to the self-consumption of the fuel.
The results of the SQSig project will afford two publications in wide-interest chemistry journals.
- Chemically fuelled communication along a nanoscale molecular relay. Manuscript under preparation.
- Effect of intramolecular cooperativity on the formation of oligo-squaramide supramolecular polymers.
Those works will be published immediately Open Access, and preprints will be available from on-line repositories.
Scientific meetings have provided a significant opportunity to disseminate our research to our target audiences. Dr. Martínez-Crespo has presented the main results of this project in five conferences (in the UK, the Netherlands, France, Spain and online).
To contribute to the public understanding of science, Dr. Martínez-Crespo participated in the “Science is Wonderful! Activities”, delivering a talk (followed by a discussion) to four groups of secondary school students in Spain. Moreover, a divulgation poster was uploaded to the website of the “European Researchers Night – Catalan Section”.
