Zirconium alkylbisphosphonates are prepared by treating
a derivatized substrate alternately with solutions of Zr4+ and a bisphosphonic acid.
We report here the preparation of
electroactive and photoactive metal phosphonate thin films, containing
neutral and cationic
organic groups. Electronic spectroscopy, ellipsometry, atomic
force microscopy, and electron
probe microanalysis were used to characterize the structure and
composition of these thin
films. An N,N‘-dialkylphenylenediamine
bisphosphonate (1,4-bis(4-phosphonobutylamino)benzene) gives uniform lamellar thin films, with low root-mean-square
roughness. The
stoichiometry of this film is low in Zr relative to other zirconium
bisphosphonate films [i.e.,
Zr0.75(bisphosphonate)]. Bisphosphonic acids
with cationic organic groups (e.g.,
H2O3PCH2CH2−(4,4‘-bipyridinium)−CH2CH2PO3H2)
do not follow the typical layered growth motif but
instead form crystallites on the substrate surface. Lamellar
growth in films prepared with
neutral bisphosphonic acids can be perturbed by adding ammonium ions to
the bisphosphonic
acid growth solutions, leading to the growth of large crystallites.
Electrochemical studies
were carried out on crystallite films of viologen bisphosphonate based
materials, grown on
both gold foil and Sn[Sb]O
x
-coated glass
substrates. The estimated reduction potential for
viologen in these films (−0.83 V) is independent of film thickness
but shows kinetic limitations
that are directly related to film thickness. The E°
of the viologen moiety in ZrPV(X) films
is 150 mV more negative than that of dimethylviologen in solution or in
other thin films.
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