The design of stimuli-responsive systems in which supramolecular structure changes in response to external signals, such as the change in voltage of an electrode, is important for many applications, for example, self-healing polymers and gels. In this study, a four H-bond ureidopyrimidinone (UPy) array with an alkyl-pyridinium, (RP), redox center has been synthesized, UPy(RP). This array prefers the tautomer that presents an ADAD H-bond motif in the starting oxidation state. Due to electrostatic repulsions and unfavorable secondary H-bond interactions, this motif would form a dimer with relatively weak H-bonding. Upon 2e- reduction, where 1e- is gained per R-pyridinium redox center, the H-bond strength should increase due to the loss of the repulsive charges, making the nitrogen a stronger hydrogen acceptor. Because the nitrogen is now a better hydrogen acceptor, there could be a possibility of an intermolecular proton transfer. This would encourage the tautomer to have an AADD motif that will make the H-bonding stronger by increasing the favorable secondary H-bond interactions. UPy dimers can exist in two tautomeric forms called pyrimidinol and pyrimidinone. The CV’s of UPy(RP)/PF6 in CH3CN show three reductions. The first occurs at a potential very similar to that seen with simple model compounds. The second is considerably positive of that observed for the model compounds and the third is very close to the second reduction peak of the model compounds. The first reduction is reversible if the scan direction is switched immediately after the peak. As the scan rate increases, the second reduction peak disappears. Going through the second and third reductions also leads to the appearance of new oxidation wave at more positive potentials. To improve the solubility of the UPy array in methylene chloride, TFAB was used as a counterion instead of the PF6. The CV’s of UPy/TFAB array in methylene chloride show similar behavior to that in acetonitrile with an additional fourth reduction wave observed at far negative potential. 1H NMR spectrum of UPy/TFAB at room temperature suggests the presence of two tautomeric forms in methylene chloride. However, at low temperatures, only one tautomer is observed in 1H NMR spectrum that’s believed to be the dimer. Further studies to help elucidate what is actually happening in this system will include taking CV’s at low temperatures in CH2Cl2.

Cyclic voltammetry studies of a redox-responsive 4 H-bond ureidopyrimidinone alkyl-pyridinium capable of self-dimerization

253rd National Meeting (2017)

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