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Photoemissive and Photostable Host - Guest MOF for Energy Applications

Photoemissive and photostable host-guest MOF for energy applications [2016]


Porous crystalline MOFs offer long-range ordering and well defined void spaces, thereby enabling nano-caging of guest molecules to achieve unconventional opto-electronic properties. We have recently demonstrated that host-guest non-covalent interaction can be utilised to yield exciting photonic MOF systems, useful for lighting, sensing and electronic applications. Using an in-situ guest trapping strategy, we have achieved nano-caging of a bulky emissive metal complex guest (ZnQ – an OLED emitter) within the internal large voids of the zeolitic imidazolate framework-8 (ZIF-8) hosts. We have characterized their photoluminescence characteristics by means of spectroscopic techniques, which are substantiated by density functional (DFT) simulations to understand the possible electronic pathways arising from donor-acceptor energy transfer mechanisms. We discovered that, the extensive host-guest intermolecular interactions caused by spatial nano-confinement of ZnQ in ZIF-8 pores led to a strong red-shifted emission spectra evidenced in the encapsulated hybrid crystals. This translates into a warmer color rendering potentially useful for LED lighting applications. Another striking result concerns, the major improvement observed in the photophysical stability of the luminescent guest species upon caging inside ZIF-8 pores. We established that, the nanoscale cavity of MOF could act as a protective vessel thus shielding light-sensitive fluorophores against rapid photochemical decomposition processes. It is envisaged that the host-guest nano-confinement methodology presented in this work may be extended to the vast family of MOF systems available in the literature.