Deciphering the photobehaviour of ensemble and single crystals of Zr-based ITQ MOF composites

[Display omitted] •Understanding the interactions that govern the photophysical behaviour of the composites of Nile Red and a 2D Zr-ITQ-HB MOF, and relevance of its surface and metal nature.•Energy transfer processes (0.34 ns) between neighbouring adsorbed NR molecules in the composites.•Intramolecular charge transfer reaction (0.6 ps) in the adsorbed NR molecules.•Emission of adsorbed NR aggregates (0.9 ns) and charge separated states (2.5 ns) of excited NR in the composites. Understanding the interactions that govern the photophysical behaviour of Metal-organic frameworks (MOFs) and their composites is paramount for their photochemical and photonic applications. In this work, we report on the photobehaviour of Nile Red (NR) adsorbed on the surface of 2D Zr-ITQ-HB (NR@Zr-ITQ-HB) MOF using ultrafast (fs-ns) and single-molecule fluorescence techniques. The results show the occurrence of energy transfer processes happening in 0.34 ns between neighbouring NR molecules, intramolecular charge transfer reaction (∼0.6 ps) and a vibrational cooling (10 ps) of the adsorbed dye. Time-resolved single-composite fluorescence microscopy experiments on different NR-loaded composites allowed to resolve the emission from adsorbed aggregates (0.9 ns) and from the charge separated state (2.5 ns) of excited NR. The different photobehaviour of NR adsorbed on ZrO2 nanoparticles indicates the relevance of the Zr-ITQ-HB MOFs surface to the observed photoinduced reactions in the composites. We discuss how the nature of both, the organic linkers and metal clusters in this kind of MOFs, affects the photodynamics of the composites. These results may help in designing MOFs "on demand" for their application in photons-based science and technology, like photocatalysis and lighting.