Electrochemically assisted grafting of asymmetric alkynyl(aryl)iodonium salts on glassy carbon with focus on the alkynyl/aryl grafting ratio

摘要

Glassy carbon (GC) surfaces are functionalized exploiting the electrochemical reduction of asymmetric iodonium salts of the general formula [4-Z-C_6H_4-I~+-C≡C(CH_2)4Cl, Z = NO_2, Br, F, H, or CH_3]. The range of Z groups was selected aiming to examine the C_(aryl)-I bond energy as a function of the "electron withdrawing/ electron donating" ability of the Z-group, with the ultimate purpose of controlling the alkynyl/ aryl grafting ratio. The electroreduction mechanism and the characteristics of the grafted surface are studied by means of cyclic voltammetry and X-ray photoelectron spectroscopy. It is shown that the alkynyl/ aryl grafting ratio decreases with the increasing electron withdrawing nature of Z, which induces a weakening of the C_(aryl)-I bond. Ab initio DFT vertical electron affinities (EA_v) allowed to rationalize the electroreduction potentials of both the bulk and surface functionalised redox couples. Moreover, the alkynyl/ aryl grafting ratio is assessed, at a molecular level, on the basis of ab initio DFT potential energy surfaces.