Photo-induced isomerization in ruthenium nitrosyl complexes Ru-NO / Ru-ON commutation


Photo-induced isomerization in ruthenium nitrosyl complexes Ru-NO / Ru-ON commutation

Obtaining materials with an atom or molecule that can be switched into two distinct states can generate storage capacities comparable to those of the DNA molecule, i.e. of the order of a terabyte/cm3. The choice of photochromic systems was made in favor of ruthenium complexes with a nitrosyl ligand for which two metastable states (MS1, MS2) resulting from the presence of the ruthenium-nitrosyl bond can be observed. Structural studies have shown different conformations of the Ru-NO unit depending on the state concerned.

[RuIINO] → [RuII(ON)]

Among complexes prepared in the group, [Ru(NO)Cl(py)4](PF6)2.1/2H2O exhibit remarkable quasi-complete commutation properties at the solid state (coll. M. Buron-Lecointe).

Figure 1 : trans (NO,Cl)-[Ru(py)4(Cl)NO](PF6)2.1/2H2O : molecular commutation GS/MS1 on single crystals.

Many systems derived from this reference complex have been synthesized and characterized. The main questions that have arisen concern the mechanisms involved. The strong tripartite interaction between experimentalists (LCC team, M. Buron-Lecointe team, IPR, Rennes) and theorists (M. Boggio-Pasqua team, LCPQ, Toulouse) has been decisive.

Optical and structural measurements on the ground state, but also on the excited states, have made it possible to propose a mechanism by sequential absorption of two photons. Without the absorption of the second photon, the system would remain on MS2, considered as non-dissociative, without any possible transition to the MS1 state. On the other hand, the computational study showed an extremely favorable situation with exaltation of the intensity of the transitions for MS2 and collapse for MS1. Irradiation in this ideal zone then allows a complete switch from GS to MS1.

Figure 2 : trans (NO,Cl)-[Ru(py)4(Cl)NO](PF6)2.1/2H2O: possible electronic mechanisms by sequential absorption of two photons (a). Absorption spectra in the ground state and in MS1 and MS2 metastable states obtained by TD-DFT calculations (b)

Figure 3 : Xerogel of trans (NO,Cl)-[Ru(py)4(Cl)NO](PF6)2)

These molecular systems were embedded in transparent polymer or silica matrices to obtain objects of controlled sizes.


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