METAL-BASED REVERSE INTERRUPT0RS WITH PHOTOMODULATED LUMINESCENCE AND NLO ACTIVITY: FROM FUNDAMENTALS TO MOLECULAR MATERIALS – COMET

Photonic devices that incorporate photochromic molecules represent the future of digital optical storage where the recording of information is accomplished with light. In a rewritable optically memory, all functions, read, write and erase, are to be controlled by light energy. Different kinds of signal outputs can be used for optical storage including refractive index, luminescence, electric conductance, magnetic couplings…Among these various modes, photoswitching luminescence or/and NLO is very promising and significant work based on fluorescent changes of organic optical switches as non destructive read-out, has thus been developed. More recently, a metal-organic approach has been developed and a few examples of photochromic unit-containing metal complexes have been designed and synthesized. The use of metal complexes offers several advantages: additional excited states, tunability of excited state energies, high luminescence quantum yield. Recently, our group has reported the first exemple of an efficient ON/OFF photoswitching of the NLO response of metal-containing chromophores. The objectives of the project are to develop new organometallic photochromic systems with high luminescence efficiency, high NLO activity, high signal-to-noise ratio, high sensitivity, and high activity in solid film. For this purpose, we will develop luminescent and NLO active metal-based "reverse interruptors", featuring functionalized cyclometallated (C^N)- phenylpyridine Ir and Pt complexes, and bipyridine metal (Ru, Zn) complexes, the luminescence and the NLO activity of which will be photomodulated by a DTE unit. These complexes represent attractive candidates as dipolar and octupolar NLO-phores as far as they display ILCT (IntraLigand charge-transfer) or MLCT (MLCT: Metal-to-Ligand Charge-Transfer) transitions. We propose as "reverse interruptors" non centro-symmetric chromophores in which an electron-accepting pyridine fragment A and an electron-donating group D are placed on the same thienyl ring of a photochromic DTE unit. The conjugated pathway from D to A is effective when the DTE is in its open form. The photoisomerization process of the open DTE unit into its closed form would allow the modulation of the emission and NLO properties of the organic and metallo-organic chromophores. Finally, we propose to covalently graft the photochromic component onto the polymer by using the atom transfer radical polymerization (ATRP) which has emerged as an excellent technique for the synthesis of well-defined polymers with a narrow molecular weight distribution. The switching properties, the modulation of the luminescence and NLO activity, of these new molecular systems will be investigated in solution as well as on polymer films. The synthetic methodologies of these metallic systems will be based on our experience of bipyridyl and phenylpyridyl metal complexes. Our group in Rennes has also a great expertise in the elaboration of metallo NLO-phores. The photochemical and photoswitching studies of the ligands and the corresponding metal complexes will be performed by the group of K. Nakatani (PPSM, ENS Cachan, partner 2) to characterize all the molecular interruptors. Photophysical studies will be developed with partner 2 and in collaboration with Dr J. A. Gareth Williams (University of Durham, UK). Computational studies (DFT and TD-DFT) will be performed by Pr A. Boucekkine (Rennes) in order to rationalize the experimental optical results. NLO studies will be carried out by Prof. I. Ledoux (LPQM, ENS Cachan, partner 3). The molecular NLO activities will be measured by using either the EFISH technique for the dipolar species, or the harmonic light scattering technique (HLS) for the octupolar chromophores. This project will allow the achievement of innovative dual metal-based systems.