Tuning gas adsorption in photoresponsive and spin crossover metal-organic frameworks

Orateur : Roberta POLONI (SIMaP, CNRS, Univ. Grenoble Alpes)

Metal-organic frameworks (MOFs) are attracting much attention in recent years for their potential use in gas separation, for example as physical adsorbents of carbon dioxide from a flue gas. Usually, temperature is increased to release CO2 from the material. But a few recent studies have demonstrated that an efficient capture-and-release process can be obtained upon light excitation in azobenzene- functionalized photoactive MOFs [1,2]. By combining DFT calculations and classical Monte Carlo methods, we recently demonstrated that in these MOFs, the notable change in gas uptake upon light irradiation, is due to the blocking of the strongly adsorbing metal sites upon isomerization of the azo groups from trans to cis [3]. Interestingly, our study suggests a large fraction of cis at the photostationary state. A large optical absorption band separation of the first and second excited states between trans and cis within the MOF could support this hypothesis. In order to address this point, we have computed the optical absorption spectra of these MOFs and their ligands using different computational approaches : periodic and embedded GW/BSE calculations as wavefunction-based CASSCF/CASPT2. In the final part of the talk I will present some ongoing computational studies on a Fe-based coordination polymer that we believe could exhibit large difference affinity for CO2 or similar gases upon spin transition.

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