Immobilization of Ethynyl-π-Extended Electron Acceptors with Amino-Terminated SAMs by Catalyst-Free Click Reaction

Surface modification of SiO₂ using a catalyst-free quantitative reaction between an amine and an ethynyl-π-extended naphthalenediimide was investigated. A post-reaction method, in which the catalyst-free reaction was performed at the surface after the formation of amino-terminated self-assembled monolayers (SAMs), resulted in dense, uniform modification of the SiO₂ surface with the naphthalenediimide molecules. Both X-ray reflectivity and angle-resolved X-ray photoemission spectroscopy showed consistent results for the layer thickness and density. In contrast, a pre-reaction method, in which an amino-silane and the ethynyl-π-extended naphthalenediimide reacted first and then formed a SAM, afforded a sparse SAM on the SiO₂ surface, probably due to the steric hindrance of the naphthalenediimide moieties. The in situ decoration of the SiO₂ surface by a catalyst-free quantitative reaction offers a facile route for modifying surface properties with various π-conjugated molecules suitable for many applications.