Estudo da formação e isolamento de heterocomplexos constituídos pela combinação entre 4,4’,4’’,4’’’- tetracarboxiftalocianina de ferro ou 4,4’,4’’,4’’’- tetrassulfoftalocianina de ferro e tetrakis (N-metil- 4-piridil) porfirina de ferro e aplicação em filmes LbL”
Resumo
The great
interest in supramolecular assemblies between porphyrins and phthalocyanines has
growing lately due to the enhancement on chemical and physical properties compared to
individual units. Ionic assemblies with metalloporphyrins and metallophthalocyanines
grafted with ionic substituents of opposite charges stand out due to favorable formation
and electronic density coupling between the macrocycles rings in a face-to-face array.
Most of the reports in the literature on these kinds of arrangements is limited to its solution
behavior. The main goal of this work were to synthesize and isolate heterocomplexes of
4,4’,4’’,4’’’-
irontetracarboxyphthalocyanine
(FeTcPc),
or
4,4’,4’’,4’’’-
irontetrasulfophthalocyanine
(FeTsPc),
with
irontetrakis(n-metil-4-pyridyl)porphyrin
(FeTMPyP). Three tetrapyrrolic macrocycles precursors were synthesized and
characterized, and the heterocomplex formation was investigated by spectroscopic
titration of FeTMPyP aqueous solution with FeTsPc or FeTcPc. The heterocomplex
stoichiometry
was
determined
by
Job’s
method.
The
stoichiometry
of
the
heterocomplexes was not affected by the substituents and dyads FeTsPc/FeTMPyP and
FeTcPc/FeTMPyP were obtained in both cases. For the first time, dyads were isolated
from solution, and characterized by infrared (IR) and ultraviolet-visible (UV-Vis)
spectroscopies, thermal analysis, and cyclic voltammetry. A significant change in the
macrocycles electronic levels were observed due to the electronic coupling in a face-to-
face arrangement. FeTsPc/FeTMPyP dyad presented an extensive orbital mixing, higher
than FeTcPc/FeTMPyP dyad. IR analysis showed an additional interaction through
coordination of bridged ligand between the metallic centers. Thermogravimetric analysis
of the heterocomplexes showed a different degradation profile of the macrocycles in each
dyad, which indicated that interaction between the macrocycles in each heterocomplex
might be different. Electrostatic Layer-by-Layer technique (LbL) was applied and thin films
of macrocycle precursors, mixed films (by intercalating precursor layers), and dyads were
obtained. FeTcPc, FeTsPc, and FeTMPyP macrocycles exhibited a linear transfer up to 48 bilayers. The mixed film between FeTsPc and FeTMPyP showed similar spectral
properties to FeTsPc/FeTMPyP dyad in solution indicating that similar macrocycles array
in the mixed films over the deposition. The cyclic voltammetry of the macrocycles and
dyads in solution showed that, in both cases, metallic centers electronic densities were
affected by dyad formation, but macrocyclic redox processes was more affected in
FeTcPc/FeTMPyP. The immobilization shifted the electrochemical redox process for
cathodic potentials. The results indicated that interaction between the macrocycles in the
dyads occur via two mechanisms, by ligand bridged interaction between the metallic
centers, and by electrostatic attraction of the peripheral substituents.