Insulated π-Conjugated Azido Scaffolds for Stepwise Functionalization via Huisgen Cycloaddition on Metal Oxide Surfaces

In organic−inorganic hybrid devices, fine interfacial controls by organic components directly affect the device performance. However, fabrication of uniformed interfaces using π-conjugated molecules remains challenging due to facile aggregation by their strong π-π interaction. In this report, a π-conjugated scaffold insulated by covalently linked permethylated α-cyclodextrin moiety with an azido group is synthesized for surface Huisgen cycloaddition on metal oxides. Fourier-transformed infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy confirm the successful immobilization of the insulated azido scaffold on ZnO nanowire array surfaces. Owing to the highly independent immobilization, the scaffold allows rapid and complete conversion of the surface azido group in Huisgen cycloaddition reactions with ethynyl-terminated molecules, as confirmed by FT-IR spectroscopy monitoring. Cyclic voltammetry analysis of modified indium tin oxide substrates shows the positive effects of cyclic insulation toward suppression of intermolecular interaction between molecules introduced by the surface Huisgen cycloaddition reactions. The utility of the scaffold for heterogeneous catalysis is demonstrated in electrocatalytic selective O₂ reduction to H₂O₂ with cobalt(II) chlorin modified fluorine doped tin oxide electrode and photocatalytic H₂ generation with iridium(III) dye-sensitized Pt-loaded TiO₂ nanoparticle. These results highlight the potential of the insulated azido scaffold for a stepwise functionalization process, enabling precise and well-defined hybrid interfaces.