Hybrid thin films containing N,N′-bis(2-phosphonoethyl)-1,4,5,8-naphthalenediimide
(PNDI)
and zinc cations (PNDI/Zn films) were built on silicon and indium
tin oxide (ITO) substrates by a simple layer-by-layer deposition process.
Silicon substrates primed with a layer of phosphonate groups were
immersed alternately into zinc nitrate and PNDI aqueous solutions,
yielding PNDI/Zn films containing up to 40 layers. ITO substrates,
on the other hand, were used without priming, and the deposition sequence
began with a PNDI layer. All film growth steps were conducted at room
temperature, using aqueous solutions, thus assuring an environmentally
clean process. The PNDI/Zn films were studied by X-ray reflectivity
and grazing angle X-ray diffraction, using synchrotron radiation source.
The films were constituted by crystallites, containing zinc phosphonate
layers oriented nearly parallel to the substrate. PNDI/Zn films on
ITO were reduced to stable free radicals, which were observed by UV–visible
spectroscopy. Moreover, PNDI/Zn bulk materials with structural analogy
with the films were produced.