Charge, Spin and Structural Dynamics in Metal Based Molecular Complexes
Metal‑based molecular complexes are ubiquitous in the different area of Physics, Chemistry and Life Science. They are the main constituents of metalloproteins (e.g. Haem proteins) and of the dye-sensitized solar cells. They are also part of the family of bistable systems and of molecules undergoing magnetic changes under the effect of temperature, light or pressure, which are potential candidates for magnetic data storage devices. Recently they have been successfully used as sensitizers for organic light-emitting diodes (OLED), non-linear optical materials, luminescence-based sensors, and active components of electron- or energy-transfer assemblies.
In these systems, the metal to-ligand charge transfer (MLCT) singlet states, which absorb in the visible-UV, are the doorway states to long lasting charge separation and/or triplet or quintet states, with almost unitary yield. The former charge‑separated MLCT states provide a well localized electron, readily available for a variety of photophysical and photochemical processes; the latter states are photo‑switchable high‑spin states suitable for opto‑magnetic data‑storage devices. Note that several of these processes are also operative in metalloproteins.
It is therefore clear that understanding the structure and dynamics of electronic excited states of transition metal complexes is an important goal of current spectroscopic, photophysical, photochemical and theoretical research, both from the point of view both of fundamental science as from that of applications.
Our aim is to describe the ultrafast charge and spin dynamics in these systems, as well as their accompanying molecular structure changes. An important aspect of these studies in solution is the solvent response to the excitation of a large dipole (solvation dynamics). The specificity of our approach is the combination of several advanced ultrafast spectroscopic techniques: UV-Vis broadband ultrafast fluorescence up‑conversion techniques, UV-Vis broadband ultrafast transient absorption and picosecond and femtosecond X-ray Absorption Spectroscopy (XAS). The systems that have so far been investigated are Ruthenium, Iron, Iridium, Osmium, Platinum and Rhenium polypyridine and diimine complexes as well as bimetallic Platinum complexes.
A. El Nahhas, C. Consani, A. M. Blanco-Rodriguez, K. M. Lancaster and O. Braem et al. Ultrafast Excited-State Dynamics of Rhenium(I) Photosensitizers [Re(Cl)(CO)(3)(N,N)] and [Re(imidazole)(CO)(3)(N,N)](+): Diimine Effects. Inorganic Chemistry 50, p. 2932-2943, 2011.
R. M. van der Veen, A. Cannizzo, F. van Mourik, A. Vlcek and M. Chergui. Vibrational Relaxation and Intersystem Crossing of Binuclear Metal Complexes in Solution. Journal Of The American Chemical Society 133, p. 305-315, 2011.
A. Cannizzo, C. J. Milne, C. Consani, W. Gawelda and C. Bressler et al. Light-induced spin crossover in Fe(II)-based complexes: The full photocycle unraveled by ultrafast optical and X-ray spectroscopies. Coordination Chemistry Reviews, 254 p. 2677-2686, 2010.