The research is devoted to the development of new synthetic
techniques leading to the obtainment of new intermediates and
monomers bearing suitably tailored functional groups. In
particular, the synthesized molecules will be the starting
point for the preparation of inherently conducting polymers, mainly
based on thiophenic repeating units, so to conjugate
the lightness, workability, flexibility and structural
versatility typical of macromolecular derivatives with the peculiar
features (NLO activity, LC behavior, electrical conductivity)
imparted by the monomer functional groups. The main features of the
prepared side-chain functionalized thiophenic homopolymers,
copolymers or oligomers will be the solubility in a wide range of
organic solvents, the self-assembly capability and the possibility
to be prepared through cost-effective and high-yield chemical
procedures using, when possible, the most environmental-friendly
solvents and reagents.
The aim of this applied research theme is to synthesize and
characterize a number of new thiophenic monomers 3-substituted with
alkylic, phenyl/phenoxy alkylic and/or functional groups able to
reduce the rotational freedom of the deriving polymer, to enhance
the planarity of the polymeric backbone with positive effects on
the electrical and electrooptical properties of the resulting
materials.
The side chains might also contain electron-donor groups, so to
enrich the electronic density of the polythiophenic backbone.
Stilbenic or azobenzenic chromophoric units (Chr) will be
eventually added to thiophenic moieties in monomers or polymers to
generate highly dipolar nonsymmetrical electronic structures,
suitable for getting highly active NLO materials. The synthesis
will point also to the achievement of high solubilities in common
organic solvents since this could make the characterization, the
workability and the filmability of these polymers easier; in case
of low solubility we could improve it by means of copolymerization
of functionalized thiophenic units with thiophenic monomers
3-substituted with long and flexible alkylic side chains (internal
plasticizers) and the control of the chromophore density along the
backbone chain could also allow a tuning of the NLO properties of
the final material. Further modifications on the copolymers
structure will include the insertion of alkylic chains
omega-functionalized with strongly interacting polar groups on the
polymeric backbone, so as to improve the versatility of this kind
of material. In particular, the intention is to introduce different
groups (COOH, NH2, NR2, CN, SH, SR) to enhance the ability of the
polymer to complex some metal ions or to increase the electrostatic
interactions among the lateral chains to obtain a self-assembling
material or, at least, to reduce the conformational disorder of the
thiophenic backbone improving its mean conjugation length, thus
favoring its electronic properties extending the solitonic or, if
doped, polaronic or bipolaronic domain walls. This contrivance is
in fact strategical for the preparation of high-efficiency
photovoltaic organic solar cells..
Particular attention will be made on the polymerization
reactions conditions: polymers could be prepared preliminarly by
direct oxidative polymerization of the monomers via iron
trichloride and subsequently by a regiochemically controlled
coupling polymerization.
Moreover, if the monomers were incompatible with the above-stated
procedures, a post-polymerization functionalization of precursor
polymers with high solubility and structural versatility (i.e.
poly(w-bromoalkyl)thiophenes) could be used. Comparisons will be
made among products obtained with the different polymerization
techniques, with the aim to get a better insight on the course of
the polymerization reaction and on oxidation potentials of the
functionalized thiophenes, Finally, the obtained results will be
compared with the ones reported in the literature, especially
regarding polythiophenes obtained with a configurational ordered
structure by the organometallic polycondensations of some
thiophenic functionalized monomer strategically derivatized on the
2,5 positions with different groups and reciprocally
reactive.
A number of techniques will be used to characterize the compounds
both in solution and in the solid state. The structural
characterizations will ensue from FTIR spectral analysis especially
in the regions defining the substitued positions of the thiophene
ring, the functional groups in the lateral chains and the actual
conformations. The effective achievement of the desired structures
and, in the case of polymers, the reliableness of high
regioregularities, will be confirmed by detailed examinations of 1H- and 13C-NMR spectra. The performing features of the materials will be
analyzed by thermal analysis (DSC, DTA and TGA), X-ray diffraction,
UV-Vis techniques in solution and in film at different temperatures
and electrical and photoconductivity.
