LAboratoire de Spectrochimie Infrarouge et Raman – UMR 8516
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Fundamental photophysics and photochemistry of photo-functional molecules and molecular assemblies

Participants : S. Aloïse , M. Barj , J. Berthet , G. Buntinx , S. Delbaere , O. Devos , V. De Waele , A. Idrissi , F.A. Miannay , O. Poizat , C. Ruckebusch , M. Sliwa

The development of innovative photoactive molecular materials for applications to opto-electronics, photonics/biophotonics, bioimagery, or photovoltaics is a fast-growing research field. The functionality of these complex materials cannot be controlled without a deep knowledge of the underlying photo-induced processes. Fundamental mechanistic photochemistry naturally meets a strong expectation from chemists involved in the design of novel photoactive materials. It is a key research focus of our activity, developed in close collaboration with a number of groups of chemists specialized in molecular engineering.

By investigating the reaction dynamics of photoactive molecules and materials on a wide range of time scales extending from femtoseconds to days, we are trying to gain a better understanding of the photoinduced processes responsible for the functionality of these photoactive systems. In particular, we look to identify the structural and physico-chemical parameters that govern the efficiency, specificity, and resistance to fatigue of the processes, at the molecular level but also at the material micro-scale level.

1. Mechanistic photochemistry and functionality at the molecular level

Current efforts focus on multifunctionnal photoswitchable organic systems (bi- or multi-photochromic compounds, photoactivable conductors, photo-controllable complexing agent for ion-release and ion-transport, multi-photon activable photoacid generators for 3d microlithography, nanohybrids for multiphoton absorption, …). Besides, some inorganic systems specifically designed for photocatalysis and solar energy conversion are also investigated.

Fig. 1. Photophysical reaction scheme of a linear donor-photosensitizer-acceptor triadic heteroleptic copper(I) complex optimized for an efficient stepwise photoinduced charge separation upon excitation of the copper(I) metal-to-ligand charge transfer (MLCT) excited state. The final charge-separated state has a 34 ns lifetime in acetonitrile and is formed with a quantum yield of 90% (collaboration CEISAM Nantes Univ., Refs. P 2011-61, P 2014-54).

Fig. 2. Excited-state dynamics of a new family of push-pull type light-emitting dyes determined by ultrafast time-resolved spectroscopy. In non-polar solvents and in the solid state the compounds are strongly fluorescent with band position widely tunable according to the nature of the electron acceptor substituent. In polar solvents, the fluorescent excited state is quenched by an ultrafast intramolecular charge-transfer process (collaboration CEISAM, Nantes Univ., Refs. P 2013-26, P 2013-33).

Fig. 3. Photophysics of the zwitterionic SBPa molecule designed for electronic conduction in the excited charge-transfer state, as inferred from ultrafast time-resolved spectroscopy in solution and advanced quantum chemistry calculations (collaboration Aoyama Gakuin Univ., Sagamihara, Japan, Ref. P 2011-38, P 2011-47, P 2012-5, P 2014-9).

Fig. 4. NMR spectroscopy demonstrates the feasibility of multiple commutation between 8 individually addressable molecular states in a novel hybrid molecular photoswitch based on a Dithienylethene Oxazolidine framework involving 3 coupled commutation functions (collaboration ISM Bordeaux, Ref. P 2014-46).

Fig. 5. Mechanism and dynamics of photo-controlled proton release by a two-photon activable photoacid generator for 3D microfabrication (collaboration IS2M, Haute-Alsace Univ., Mulhouse et LiPhy, Grenoble Alpes Univ., Ref. P 2015-14).

2. Mechanistic photochemistry and functionality of photoactive molecular materials

Fig.6. Photocontrolled luminescence switching in ZnO nanocristals grafted by photochromic dithienylethene molecules (collaboration Inst. Sci. Chim. Rennes, Ref. P 2014-59).

The work is centered on ultra-bright photo-luminescent nanomaterials for imaging/bio-imaging applications, nanohybrids for multiphoton excitation purposes, photo-actuators and photoswitch materials. From a fundamental point of view, we are particularly interested in the almost unexplored issue of reaction dynamics in organic and hybrid nanoparticles. For this purpose, a flagship project currently in progress is devoted to the development of ultrafast nanoscopy – i.e., time-resolved fluorescence spectroscopy with femtosecond time-resolution and nanometric spatial resolution – in order to be able to follow the photodynamics of single nanoparticles and to image the charge and energy transfer processes within each nanoparticle at the nanometric scale. In parallel, complementary chemometrics approaches are developped for the analysis of super-resolution fluorescence microscopy data and hyper-spectral imaging.

3. Dynamics of photoactive biosystems

A main objective is to understand the photoinduced phenomena that control the emission properties in emissive proteins, more particularly the bioluminescence of firefly and the emission of photo-switchable fluorescent proteins used as probes in super-resolution fluorescence microscopy.

Fig. 7. Applying an original single-molecule fluorescence imaging superresolution algorithm (SPIDER, Sparse Image DEconvolution and Reconstruction) to the watching of HEK cancer cells (Ref. P 2014-35).

Fig. 8. The analysis of UV-vis and IR spectra of oxyluciferin, the bioluminescent chromophore of firefly, by using multivariate curve resolution chemometrics approaches allowed us to spectrally identify the 6 chemical forms of this chromophore in solution and to determine the associated concentration profiles (collaboration New York Univ. Abu Dhabi and Technische Universität München, Ref. P 2013-41, P 2014-34).