LUMINESCENT MOFS ARCHITECTURES FOR RADIOACTIVE GAS DETECTION AND ENGINEERING LARGE STOKES SHIFT

The precise spatial assembly of chromophores inside MOF allows for the rational fabrication of photonic materials with unique photophysical properties. We propose an innovative radioactive gas detector based on highly porous luminescent MOFs.[1] Hf-based MOFs containing diphenyl anthracene (DPA) moieties display high porosity (SBET = 2550 m2 g-1), fast and reversible adsorption of noble gases (proven by combined experimental adsorption and simulation methods) and high photoluminescence and scintillating properties. After exposure to radioactive gases, Hf-DPA displays fast and bright scintillation sensitized by the decay of the radioactive nuclei that allows for their effective detection at ultra-low concentrations. Indeed, 85Kr isotope was detected even at activity as low as 0.3 kBq⋅m3, below the minimum value declared for commercial devices, strongly supporting the development of MOFbased scintillators for radioactive gas detection. Fast composite scintillators were engineered by embedding nanocrystalline Zr-MOFs containing highly luminescent DPA moieties in a continuous polymer matrix.[2] The hybrid bulk scintillators display good light yield, fast time response and an ultrafast scintillation rise time of ~ 50 ps, making them promising materials for time resolved applications. Moreover, nanocrystalline hetero-ligand Zr-based MOFs with high luminescent quantum yield and large Stokes shift emission were engineered by coassembly donor and acceptor chromophores, diphenyl anthracene (DPA) and diphenyl tetracene (DPT) moieties, respectively, to generate reabsorption-free emitters with potential applications in bioimaging, solar luminescent concentrators and bulk scintillators.[3] The two luminescent ligands, with similar molecular length and topology, were homogeneously inserted inside the MOF nanocrystals as proven by 129Xe hyperpolarized NMR experiments. The overlap between the emission frequency of DPA molecule and the absorption spectrum of DPT, and the precise spatial arrangement of neighbor chromophores promote fast energy diffusion and effective energy transfer inside the MOF nanocrystals, generating large Stokes shift emission (ΔE ~ 6000 cm−1) with fluorescence quantum yield of ~ 0.6. The remarkable photophysical properties of these large Stokes shift emitters stimulate the preparation of fast emitting composite scintillators with negligible reabsorption and benchmark performance comparable to commercial materials. References [1] M. Orfano, J.Perego et al. Nature Photonics 2023, in press. [2] J. Perego, et al. Nature Photonics 2021, 15, 393-400. [3] J. Perego, et al. Nature Communications 2022, 13, 3504.