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Mn(II)-based perovskite materials are being intensively explored for lighting applications; understanding the role of ligands regarding their photobehavior is fundamental for their development. Herein, we report on two Mn (II) bromide perovskites using monovalent (perovskite 1, P1) and bivalent (perovskite 2, P2) alkyl interlayer spacers. The perovskites were characterized with powder X-ray diffraction (PXRD), electron spin paramagnetic resonance (EPR), steady-state, and time-resolved emission spectroscopy. The EPR experiments suggest octahedral coordination in P1 and tetrahedral coordination for P2, while the PXRD results demonstrate the presence of a hydrated phase in P2 when exposed to ambient conditions. P1 exhibits an orange-red emission, while P2 shows a green photoluminescence, as a result of the different types of coordination of Mn(II) ions. Furthermore, the P2 photoluminescence quantum yield (26%) is significantly higher than that of P1 (3.6 %), which we explain in terms of different electron-phonon couplings and Mn-Mn interactions. The encapsulation of both perovskites into a PMMA film largely increases their stability against moisture, being more than 1000 h for P2. Upon increasing the temperature, the emission intensity of both perovskites decreases without a significant shift in the emission spectrum, which is explained in terms of an increase in the electron-phonon interactions. The photoluminescence decays fit two components in the microsecond regime—the shortest lifetime for hydrated phases and the longest one for non-hydrated phases. Our findings provide insights into the effects of linear mono- and bivalent organic interlayer spacer cations on the photophysics of these kinds of Mn (II)-based perovskites. The results will help in better designs of Mn(II)-perovskites, to increase their lighting performance.

Mixed-metal-organic frameworks (MMOFs) have emerged as promising photocatalyst candidates in multiple reactions. For instance, the doping of Zr-UiO-type MOFs with Ce atoms increases their photoactivity owing to a better overlap between the organic linker and Ce orbitals. However, it is not clear which is the ideal content of Ce to reach the optimal photocatalytic performance. Herein, a series of MMOFs isostructural to UiO-66 and with napthalene-2,6-dicarboxylate (NDC) as a linker were synthesized and characterized. The Ce content was varied from 0 to 100% and their corresponding structural, chemical, photodynamic, and photoresponse properties were investigated. Powder X-ray diffraction shows that when the content of Ce is 12% onward, in addition to the UiO-type structure, a second crystalline structure is cosynthesized (NDC-Ce). Steady-state and femtosecond (fs) to millisecond (ms) spectroscopy studies reveal the existence of two competing processes: a linker excimer formation and an ultrafast ligand-to-cluster charge transfer (LCCT) phenomenon from the organic linker to Zr/Ce metal clusters. The ultrafast (fs-regime) LCCT process leads to the formation of long-lived charge-separated states, which are more efficiently photoproduced when the content of Ce reaches 9%, suggesting that the related material would show the highest photoactivity. Photoaction spectroscopic measurements corroborate that the sample with 9% of Ce exhibits the maximum photocatalytic efficiency, which is reflected in a 20% increment in overall water splitting efficiency compared with the monometallic Zr-based MOF. The current study demonstrates the relationship between the photodynamical properties of the MMOFs and their photocatalytic performance, providing new findings and opening new ways for improving the design of new MOFs with enhanced photocatalytic activities.

Metal-organic frameworks (MOFs) have gained significant attention for their broad range of applications in a variety of scientific and technological fields. These materials are crystalline in nature and are formed through the self-assembly of metal ions or clusters with organic linkers via coordination bonds. Typically, MOFs adopt three-dimensional (3D) structures by assembling the subunits in all three spatial directions forming a relatively rigid network. However, in recent years, low-dimensional 2D-MOFs have garnered considerable interest due to their distinctive properties, particularly in gas adsorption/separation, sensing, catalysis, and chemical release applications. 2D-MOFs are created through the assembly of a single layer, resulting in sheet-like structures that provide larger active surface areas, thereby enhancing the diffusion of guest molecules. A notable example of this is the ITQ family of 2D-MOFs, which are formed through the assembly of 1D organic-inorganic structural subunits. The resulting mesoscopic lamellar structure of these MOFs favors interactions with organic molecules and hence improves the catalytic performance. Here, we provide a comprehensive overview of the available synthesis, structural characterization, physico-chemical properties, and specific catalytic performance of ITQ 2D MOF hybrid materials. We examine available strategies to obtain tuneable Lewis and Brønsted acid active sites from the 1D sub-domains as well as provide examples for the application of these MOFs in specific reactions. We also review studies on the effect of the nature of organic spacers as well as that of the metal clusters on the spectroscopic and photodynamical properties of composites formed by these MOFs as hosts with well-known organic fluorescent dyes (guests).

Controlling the composition, as well as the number and type of defects in metal-organic frameworks (MOFs) helps in the understanding of the interactions that govern their behaviours, and in consequence, their potential employment in a number of photonic applications. In this work, we report on the spectroscopy and photodynamics of two heterolinker (naphthalene-2,6-dicarboxylic acid, NDC, and 4-amino-8-cyanonaphthalene-2,6-dicarboxylic acid, NACDC) Zr-based MOFs that differ in the modulator used during the synthesis, thus leading to possible defects in the frameworks. We observed an inter-particle energy transfer (ET) that occurs from <10 to 160 ps in competition with an ultrafast intra-particle ET event from excited NDC to NACDC. In addition, due to the heterogeneity of the system, we found two different populations of the push-pull NACDC linker emitting from the charge transfer (CT) state. Single crystal fluorescence microscopy experiments further demostrated that the photobehavior of the studied MOFs is dominated by NACDC. Nanosecond (ns)-flash photolysis also revealed different photobehaviours related to the presence of defects, while the femtosecond (fs)-dynamics is independent of the modulators used for the MOFs’ synthesis. These results may help in engineering of MOFs for their application in photon-based science and technology and may lead to the construction of optoelectronic devices and better photocatalysts based on these materials.

[EN] 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 (similar to 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 photo induced 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.

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 ZrO 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.