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Massimiliano Lanzi

Associate Professor

Department of Industrial Chemistry "Toso Montanari"

Academic discipline: CHIM/04 Industrial Chemistry

Research

Keywords: NLO (non linear optic) hybrid solar cells supramolecular architecture SHG (second harmonic generation) PPF (post-polymerization functionalization)

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.

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