During the past three decades semiconducting pi-conjugated molecules and polymers have attracted a strong interest in laboratories worldwide. These materials may combine the processability and/or mechanical properties of polymers with the electrical and optical properties of functional organic molecules. In particular the use of these materials in light-emitting diodes, field-effect transistors, photovoltaic cells, and other opto-electronic devices has motivated the development of synthesis and processing methods of conjugated polymer materials with unique properties.
In our IMO-IMOMEC laboratories, a lot of effort has been put on the development of novel synthetic approach to high molecular weight, low defect content poly(arylene vinylene) derivatives. Precursor routes were designed and developed allowing the processability of the final conjugated polymers whatever the chemical structure of the derivative: sulfinyl and dithiocarbamate precursor routes. Using those precursor methods, several interesting PPV derivatives were synthesized and evaluated: MDMO-PPV, PEO-PPV, 3D-poly(triptycene vinylene), etc.
Among a variety of materials platforms, poly(arylene ethynylene) (PAE) derivatives have attracted the attention of a large number of researchers. Many PAEs have been reported to date, and this family of conjugated polymers has established itself as an important class of materials with interesting optical and electronic properties. Our IMO-IMOMEC group has a specific interest in this family of polymers towards chemo-sensor applications and more specifically towards explosive detection.
Poly(3-alkylthiophene)s are used as benchmark p-type materials in heterojunction photovoltaic (PV) devices. Semiconductor performance of these polymers can be degraded by residual catalyst impurities, defects in polymer chain regiospecificity, and low molecular weight of the polymers. Our IMO-IMOMEC goal is the design and synthesis of novel derivatives not commercially available with consistently high purity, regioregularity, and molecular weight using Rieke and GRIMM chemistries. The choice and the functionalization of the side-chains allow us to explore effects of polymer architecture on device performances and lifetime. The high mobility and broad light absorption make them attractive materials for organic transistor and photovoltaic applications.
Low band gap polymers
Beside PTVs already presented, Polyisothianaphthene (PITN) is a low band gap polymer with a strong quinoïd character having a band gap value around 1-1.2 eV and based on isothianaphthene which is a thiophene ring with a fused benzene ring in the 3 and 4 positions.
The chemical synthesis of PITN is based mainly on cationic oxidative polymerisation. A non-oxidative thermal polymerization was reported by IMO-IMOMEC towards a soluble derivative a few years ago. Only low device efficiencies are reported so far from such polymer, most likely due to its poor solubility properties and therefore thin film quality.
Pi-conjugated oligomers and small molecules
Among others, n-type pi-conjugated molecules are of great interest and our work focus on the design and development of n-type and ambipolar semiconductor molecules targeting high-mobility and stability as well as the solubility/processing towards transistors applications.
Another point of interest lays in the development of molecules of acceptor/donor type (A-D-SH and/or D-A-SH) towards self-assembling monolayers (SAM) useful for electronic switching and memory devices.
Another topic deals with the design and the synthesis of specific porphyrinoid chromophores (porphyrins, corroles, expanded porphyrins, subporphyrins) and their incorporation in larger superstructures towards optoelectronic applications.