Surface-confined monomers on electrode surfaces. 6. Adsorption and polymerization of 1,6-diisocyanohexane on Au and Pt

Thin films of 1,6-diisocyanohexane (DICH) can be formed on Au and Pt surfaces by immersion of clean substrates in 0.001-1.0 M solutions of DICH. Infrared transitions for both Au-bound and free isocyanide functionalities are observed after Au surfaces have been placed in methanolic solutions with DICH concentrations >0.001 M, indicating that some portion of the DICH layer is composed of molecules with only one of the isocyanide moieties bound to the Au surface. In addition, poly(DICH) layers are formed on Au as noted by the presence of imine bands in the reflection-absorption infrared (RAIR) spectra of such surfaces and the time-dependent nature of the band intensities of the imine and methylene modes. The resulting DICH-coated Pt and Au surfaces are effective transport barriers-substantially diminished redox responses of various solution probes are observed at such modified electrodes. In particular, the DICH films on Pt prevent 95% oxidation of the underlying metal surface. It is found that the remaining free isocyanide groups on the DICH-coated surfaces can be further polymerized (cross-linked) to various extents by exposure to oxygenated aqueous Ni2+ solutions, allowing for control of film permeability. These results point to the possible application of poly(DICH) films in the fields of chemical sensing and corrosion protection.