Dendrimeri a base fenilenica e poliareni iperramificati funzionalizzati con gruppi trasportatori di lacune e di elettroni per applicazioni in optoelettronica

Responsabili di progetto

Umberto Giovanella, Irina Khotina

Accordo

RUSSIA - RAS old - Russian Academy of Sciences old

Bando

CNR/RAS 2011-2013

Dipartimento

Progettazione Molecolare

Area tematica

Scienze chimiche e tecnologie dei materiali

Stato del progetto

Nuovo

Proposta di ricerca

Among the organic light-emitting materials, the high molecular weight compounds are of the greatest interest, since they can form films mechanically and thermally more stable with respect to the low molecular weight organic compounds.
The solution-processability, solid-state ordering, efficient electroluminescence, color stability, and high charge-carrier mobility are interconnected key factors for designing low-cost optoelectronic devices. The synthesis of hyperbranched polymer is proposed to match up these factors.
The aim of the project is the design and synthesis new monomers, oligomeric model compounds, dendrimers, and polymers containing electron-donor or electron-acceptor groups linked to new phenylene branched structures to be used in optoelectronics and photonic devices. The electro-optical characterization of the compounds will be used to define the structure / properties relationships  and give a feedback to improve the materials.
The phenylene dendrimers, containing 1,3,5-triphenylsubstituted benzene ring as a core and branched phenylene periphery, revealing effective electroluminescence, will be synthesized in the project. New hyperbranched polyphenylenes chemical defects free, soluble in organic solvents and having in the periphery  groups as dioctylfluorene, triphenylamine, thiophene, phenotiazine, for the realization of either electron, or hole conductivity will also be synthesized. In this connection, 1,3,5-tri(4-bromophenyl)benzene and 1,3,5-tri(4-bromodiphenyl)benzene will be synthesized in gram quantities by cyclocondensation of 4-bromoacetophenone or 4-bromo-4'-acetyldiphenylene. The former  compounds are the precursors for the synthesis of dendrimers of the second and subsequent generations, as well as polymers. They will also be used to produce pinacolborate derivatives to carry out the polymer and model reactions by the Suzuki method. The Suzuki polycondensation reaction to give hyperbranched olygophenylenes will be held on the basis of monomer tribromides or triiodides, and pinacolborate derivative as the comonomers, in the presence of a palladium catalyst. By varying the ratio of comonomers molecular weight of the produced hyperbranched structures, similar to dendrimers, could be controlled.
Optical characteristics of the systems will be studied according to this ratio. If bromine- (or iodine-) containing monomer is taken in excess, the terminal groups will always be an halide, and they could be turned into  phenyl groups or other un-reactive ones, by adding at the end of the reaction the excess of phenylboronic acid or pinacolborate derivative of thiophene, fluorene, phenotiazine. For lengthening of phenylene arms of the branched structures, the polycondensation of trifunctional with difunctional monomers will be carried out and to equalibrate the functionality, monofunctional monomer will be added simultaneously. Dendrimers with peripheral groups of thiophene, phenotiazine, substituted fluorene will be synthesized as well.
The branched individual compounds will be synthesized to assess the effect of a number of p-substituted benzene rings in the system, as well as the influence of the peripheral groups on the emission and other optical properties of phenylene branched structures.
The absorption and photoluminescence (PL) spectra together with PL quantum yield (PL-QY) measurements will be carried out. Moreover, the mobility of electrons and holes will be determined and prototypes of electroluminescent devices will be prepared and characterized. 
The materials proposed in this project, are supposed to approach the properties of inorganic analogues, i.e. high quantum yield and rate of charge transfer, photo-stability, and energy gap tunability, etc.
Finally, the possibility to prepare, by exploiting the different solubility of the materials,  multi-layered devices with layers with different electro-optical behaviour will be evaluated.
The cohesion of skills in chemical design and synthesis of the group of Dr. Khotina at Institute of Organoelement Compounds and the experience of ISMAC optoelectronic group (Giovanella, Dr. Destri, Dr. Botta) in spectroscopic characterization and OLED preparation and characterization is well documented by several joint publications.

Obiettivi della ricerca

The aim of this research project is the design, synthesis and electro-optical characterization of new semiconductor materials based on conjugated hyperbranched polymers for optoelectronics and photonic. In the last decade, polymer semiconductor materials have been intensively studied and successfully emerged as an alternative to inorganic materials in many electronic devices such as organic light-emitting diodes (OLEDs).
The dendrimer approach is proposed to synthesize new hyperbranched polyphenylenes or phenylene dendrimers. In fact, the branched structures improve the solubility (ease of processing) and impart a supramolecular organization suitable to prevent aggregation of macromolecules in solid-state and, consequently, luminescence quenching. Moreover, the insertion of electron-acceptor and electron-donor functional groups will address electronic properties in terms of high charge-carrier mobility (carrier balance).
The  study of the relationship between conjugated dendrimers or branched polymers structure and their optical activity is an important issue of the project and of fundamental importance for designing new organic materials with desired properties suitable for optoelectronic applications. HOMO and LUMO energy levels, electrons and holes conductivity, absorption and photoluminescence spectra, photoluminescence quantum yield and electroluminescence quantum efficiency will be measured.

Ultimo aggiornamento: 22/05/2025