Tandem diazonium salt electroreduction and click chemistry as a novel, efficient route for grafting macromolecules to gold surface

Bis-alkynylated oligoethyleneglycol (OEG) and a monopropargyl-functionalized perfluorinated ethylene glycol (FEG) were clicked to azide-functionalized gold surface (Au-N-3) at room temperature via the well known 1,3 cycloaddition click chemical reaction. The Au-N-3 substrate was obtained by nucleophilic attack of NaN3 on gold substrates modified by the electrochemical reduction of the BF4-, N-+(2)-C6H4-CH2Br diazonium salt. This electrochemical process yields aryl layer-modified gold of the type Au-C6H4-CH2Br (hereafter Au-Br). The untreated and modified gold plates were examined by XPS. PMIRRAS and contact angle measurements. XPS brought evidence for electrografting aryl layers by the detection of Br3d; azide functionalization by the increase of the N/Br atomic ratio; and click reaction of OEG with Au-N-3 by the increase of O/N ratio. In addition, the perfluorinated plate (Au-FEG) exhibited F1s and characteristic C1s peaks from -(CF2)(7)- chain and terminal CF3. Infra red spectroscopy (PMIRRAS) evidenced (i) grafting N-3 to Au-Br; (ii) characteristic stretching bands, from ethylene glycol units, C-O-C (1100-1300 cm(-1)); CF2 (1000-1100 cm(-1)) and CF3 (1100-1350 cm(-1)) from FEG grafts; and (iii) suppression of alkynyl bands from OEG and FEG after surface click chemistry. More importantly, PMIRRAS results support an important bridging of the bispropargyl oligoethylene glycol at the gold surface. Water drop contact angles were found to be 48.7 degrees and 83.0 degrees for Au-OEG and Au-FEG, respectively, therefore highlighting the control over the hydrophilic/hydrophobic character of the clicked substrate. This work shows that clicking macromolecules to grafted, diazonium salt-derived aryl layers is a novel, simple and valuable approach for designing robust, functional surface organic coatings. (C) 2009 Elsevier B.V. All rights reserved.