Unravelling Why and to What Extent the Topology of Similar Ce‐Based MOFs Conditions their Photodynamic: Relevance to Photocatalysis and Photonics

• Published in: Advanced science 2019-10, Vol.6 (19), p.1901020-n/a
• Main Authors: Caballero‐Mancebo, Elena, Cohen, Boiko, Smolders, Simon, De Vos, Dirk E., Douhal, Abderrazzak
• Format: Article
• Language: English
• Subjects: Defects; excimers; Experiments; intramolecular charge transfer; Lasers; ligand metal cluster charge transfer (LCCT); metal–organic frameworks (MOFs); Photocatalysis; photodynamics; Scanning electron microscopy; Single crystals
• ISSN: 2198-3844; 2198-3844
• DOI: 10.1002/advs.201901020

Metal–organic frameworks (MOFs) are emerging materials for luminescent and photochemical applications. Armed with femto to millisecond spectroscopies, and fluorescence microscopy, the photobehaviors of two Ce‐based MOFs are unravelled: Ce‐NU‐1000 and Ce‐CAU‐24‐TBAPy. It is observed that both MOFs show ligand‐to‐cluster charge transfer reactions in ≈100 and ≈70 fs for Ce‐NU‐1000 and Ce‐CAU‐24‐TBAPy, respectively. The formed charge separated states, resulting in electron and hole generation, recombine in different times for each MOF, being longer in Ce‐CAU‐24‐TBAPy: 1.59 and 13.43 µs than in Ce‐NU‐1000: 0.64 and 4.91 µs. The linkers in both MOFs also undergo a very fast intramolecular charge transfer reaction in ≈160 fs. Furthermore, the Ce‐NU‐1000 MOF reveals excimer formation in 50 ps, and lifetime of ≈14 ns. The lack of this interlinkers event in Ce‐CAU‐24‐TBAPy arises from topological restriction and demonstrates the structural differences between the two frameworks. Single‐crystal fluorescence microscopy of Ce‐CAU‐24‐TBAPy shows the presence of a random distribution of defects along the whole crystal, and their impact on the observed photobehavior. These findings reflect the effect of linkers topology and metal clusters orientations on the outcome of electronic excitation of reticular structure, key to their applicability in different fields of science and technology, such as photocatalysis and photonics. Linkers topology and metal cluster orientations in metal–organic frameworks play a key role in their behavior. Armed with ultrafast spectroscopy and microscopy, the photobehaviors of Ce‐NU‐1000 and Ce‐CAU‐24‐TBAPy, involving ligand‐to‐cluster charge transfer, electron‐hole recombination, excimer formation, and intramolecular charge transfer reactions, unravel the structural differences between the two frameworks, key to their applicability, for example, in photocatalysis and photonics.