Tunable Complex Stability in Surface Molecular Recognition Mediated by Self-Complementary Quadruple Hydrogen Bonds

We show that surfaces modified with asymmetric 2-ureido-4[1H]-pyrimidinone-hydroxyalkane disulfide adsorbates exhibit efficient and controllable self-complementary molecular recognition of the pyrimidinone moieties. Two novel asymmetric 2-ureido-4[1H]-pyrimidinone-hydroxyalkane disulfide adsorbates, as well as two trifluoromethyl- and ferrocenyl-derivatized external pyrimidinone guests, were synthesized. Self-complementary molecular recognition of the pyrimidinone moieties, mediated by a quadruple donor-donor-acceptor-acceptor array of hydrogen-bonding sites, was studied in self-assembled monolayers on Au by exploiting the dependence of the dimerization constant on the solvent and temperature. Depending on the choice of solvent and temperature, reversible supramolecular recognition between surface-immobilized adsorbates and external guests occurred, as shown by X-ray photoelectron spectroscopy, differential pulse voltammetry, atomic force microscopy, and surface plasmon resonance methods. We observe a surface-enhanced apparent dimerization constant, which depends on the solvent and temperature. This feature allows us to conveniently control the complex stability, which renders these systems highly suitable for the construction of more complex, directionally defined surface-immobilized supramolecular architectures, as well as for the study of pyrimidinone-based supramolecular polymers at surfaces.