Phosphorus and Silicon Heteroles for the Engineering of Molecular Conjugated Materials with Optoelectronic Functions – PSICO

Pi-Conjugated oligomers and polymers based on a planar backbone of sp2-bonded carbon atoms have attracted increasing interest in recent years owing to their potential application for electronic devices. For example, light-emitting diodes (OLED)s for display based on polymer technology are commercialized since 2002. However, research in this field is still needed especially toward the development of optimized materials for white-LEDs (WOLED)s. This type of devices is of tremendous interest since they can potentially replace traditional incandescent white light sources generating enormous energy saving. The aim of this project is the development of novel conjugated materials using organophosphorus and organosilyl building blocks which have been rarely investigated for such purpose. Two approaches are envisaged to obtain a white emission: the doping of a blue-emitting matrix with an orange-red emitter (approach A), and the design of derivatives able to form emissive aggregates (excimers or clusters) in the solid state (approach B). The performances of the molecular materials are mainly determined by the chemical structure of the conjugated chains and by the interchain interactions. Hence, in order to further improve the performances of these materials, it is necessary to tune their physical properties (HOMO-LUMO gap, emission efficiency, RedOx potential…) at the molecular level and to control the morphology of the material. The first aim of this proposal is to prepare novel conjugated frameworks of enhanced performance for the tailoring of (WOLED)s via the incorporation of phosphorus and silicon heteroles in the backbone of pi-conjugated systems. These synthons have been selected since they possess electronic properties that differ notably from those of commonly used building blocks (thiophene, pyrrole…). We want to exploit their vanishing aromatic character and unique type of endocyclic conjugation (hyperconjugation between the dienic moiety and the heteratomic moiety) to obtain molecular materials with low HOMO-LUMO gap and high electronic affinity. The use of phosphole and silole building blocks will allow interesting structural diversification using the versatile reactivity of these heteroatoms. Heavy metal complexes (Ir, Pt…) bearing phosphole- and silole-chromophores will be prepared with the aim to obtain efficient triplet emitters (phosphorescent dyes) due to the expected strong spin-orbit coupling. The photophysical and electrochemical properties of all new derivatives, including the transition metal complexes, will be elucidated both in solution and solid state. Then, the best compounds will be used as materials for the development of (WOLED)s. The intimate physical mechanism of charge injection and transport will be investigated. In order to obtained optimized (WOLED)s, the grafting of P- and Si-chromophores bearing Si(OR)3 groups on inorganic surfaces such as ITO will also be investigated. The direct grafting should favour electron-transfer processes and sol-gel polycondensation involving the Si(OR)3 groups should afford amorphous materials. This complementary and interdisciplinary approach is expected to provide some specifications for the optimization of advanced materials for these optoelectronic applications. This proposal is mainly centred on the synthesis of novel P- and Si-molecular materials and the study of their electronic properties. The target application is the engineering of advanced (WOLED)s structure. This integrated scheme going from chemical synthesis to the engineering of devices is one of the key points of this proposal.