A new mode of luminescence in lanthanide oxalates metal–organic frameworks

Abstract

Two lanthanide metal–organic frameworks [Ln-MOFs, Ln = Eu(III), Tb(III)] composed of oxalic acid and Ln building units were hydrothermally synthesized and fully characterized by powder X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscope, and energy-dispersive X-ray spectroscopy. Furthermore, their magnetic susceptibility measurements were obtained using SQUID based vibrating sample magnetometer (MPMS 3, Quantum Design). Both Ln-MOFs exhibited highly efficient luminescent property. Solid-state photoluminescence (PL) measurements revealed phosphorescence emission bands of Eu-MOF and Tb-MOF centered at 618 nm (red emission) and 550 nm (green emission) upon excitation at 396 nm and 285 nm, respectively. Eu-MOF and Tb-MOF displayed a phosphorescence quantum yield of 53% and 40%, respectively. Time-resolved PL analyses showed very long lifetime values, at 600 and 1065 ± 1 µs for Eu-MOF and Tb-MOF, respectively. Calculations performed by density functional theory indicated a charge transfer form metal centres to the ligand which was in good agreement with the experimental studies. Therefore, this new mode of highly photoluminescent MOF materials is studied for the first time which paves the way for better understanding of these systems for potential applications.

Construction of Highly Luminescent Lanthanide Coordination Polymers and Their Visualization for Luminescence Sensing

“…This problem is resolved by the “sensitization” of organic ligands, a process known as the “antenna effect.” − , However, most organic ligands are not fully sensitized, resulting in low quantum yields of Ln 3+ ions. In addition, due to the low luminescence efficiency of Sm 3+ and the high excited-state energy levels of Dy 3+ , Eu 3+ and Tb 3+ are still the most studied for emission in the visible region, − so that the characteristic emission of Sm 3+ - and Dy 3+ -based coordination polymers is still limited and needs to be urgently developed.…”

Photochromic Ln-MOFs: A Platform for Metal-Photoswitch Cooperativity

“…In particular, integration of photochromic molecules within Ln-MOFs is a promising approach to probe possible interactions between lanthanide-based metal centers and light-responsive components, which could be used to tune the optical and electronic properties of the bulk material with high spatiotemporal control using light as a noninvasive stimulus. − In this direction, incorporation of azo compounds in Ln-MOFs is an attractive strategy since photoresponsive azobenzene derivatives integrated in bulk materials have already been applied as, for example, actuators due to significant changes in their molecular conformations, polarity, and light absorption upon their photoisomerization. − Further, azobenzene derivatives have been used to control liquid crystal domains or photophysical properties of nonlinear optical materials and sensors − due to their long thermal half-lives, large extinction coefficients, high photoisomerization quantum yields, and fatigue resistance. − While there are several reports on azobenzene inclusion within MOFs, there are very few reports on metal­(III)-based photochromic MOFs containing azobenzene (e.g., MIL-101, MIL-53, MIL-68, and MIL-58 derivatives), and besides that, the majority of these materials possess photoinactive linkers in combination with d 0 and d 10 metal centers. − Further, there are currently no reports in the literature that combine both X-ray diffraction data and photophysical measurements to evaluate how the integration of photochromic azobenzene moieties in Ce-, Nd-, or Pr-MOFs could be leveraged to tailor the photoisomerization behavior of the azobenzene unit. Therefore, a fundamental understanding of how azobenzene derivatives may be employed for tailoring optical and electronic properties of materials containing lanthanide-based metal centers is extremely limited, and the literature reports are scarce. − In this direction, studies that combine photophysical measurements with X-ray crystallographic analysis of photoswitch-lanthanide interactions are an important first step toward understanding how photochromic molecules can be used to enhance the performance of lanthanide-based materials by offering precise control over the photophysical profile of such metal–organic materials, which defines and broadens the scope of their applications. − As a result, such studies could lay the foundation for the next generation of optoelectronic devices including logic gates, multilevel anticounterfeiting technologies, and information encryption systems, as well as materials for high-speed data processing …”

Lanthanide(iii) (Er/Ho) coordination polymers for a photocatalytic CO2 cycloaddition reaction

“…19 Materials incorporating molecular and solid-state properties will exhibit attractive chemical or physical properties. As an example, the emission characteristics of solidstate Ln materials 34 and the solubility 35 characteristics of molecular compounds would be the perfect association of molecular 36 and solid-state physical features in lanthanide chemistry. 37 Herein, we use 4-aminobenzoic acid (whose deprotonated form is 4-aminobenzoate or 4-ABA) to synthesize two new isostructural lanthanide carboxylates crystallizing in 1D ribbons.…”

“…19 Materials incorporating molecular and solid-state properties will exhibit attractive chemical or physical properties. As an example, the emission characteristics of solid-state Ln materials 34 and the solubility 35 characteristics of molecular compounds would be the perfect association of molecular 36 and solid-state physical features in lanthanide chemistry. 37…”