Reactivity of the nitro-group of a p-conjugated polymer upon the interface formation with chromium: a photoelectron spectroscopy investigation

X-ray photoelectron spectroscopy was used in order to investigate the interface formation between chromium and thin films of a newly synthesised p-conjugated polymer P PA-pNO2PA.; the investigated material is a block copolymer consisting of phenylacetylene PA. and para-nitro phenylacetylene pNO2PA. units w– CH5C–R.n– CH5C–RX .m–xN ; R5C6H5, RX5C6H4NO24. Chromium was evaporated stepwise in situ onto the polymer surface and the XPS spectra of the substrate polymer and of the metal overlayer were studied as a function of increasing chromium thickness. In the early stages of the interface formation, chromium was found to interact mainly with the nitrogen atoms of the –NO2 groups, that are reduced to nitride-like species; the N–O bond is broken, as evidenced by the modifications occurring in the N1s and O1s spectra. The changes in the C1s spectra upon increasing metal deposition suggest the formation of a chromium–arene p-complex at low chromium coverage and of carbide-like species at higher chromium thickness. q1999 Elsevier Science B.V. All rights reserved