Luminescent rare-earth-based MOFs as optical sensors

Abstract

Rare-earth-based metal-organic frameworks (ReMOFs) have emerged as an interesting family of compounds, for which new properties are increasingly being found. Based on the potential of ReMOFs, resulting from their optical properties, large numbers of investigations have been carried out during the last decade. Among these investigations, ReMOFs as optical sensors, using their luminescence properties, are increasingly becoming an attractive and useful topic of research. In this study, we have provided the basics of the luminescence behaviour of ReMOFs, various possible sensing mechanisms, and a summary of the uses of ReMOFs for the sensing of nitro explosives, cations, anions, small molecules, pH, and temperature.

Solvatochromism and Selective Sorption of Volatile Organic Solvents in Pyridylbenzoate Metal-Organic Frameworks

“…Additionally, the coexistence of inorganic (hydrophilic) and organic (hydrophobic) moieties in MOFs structure may offer control of their interaction with guest molecules [4]. Thus, MOFs are of interest for a wide range of applications such as gas sorption [4,7,16], storage [17], separation [18][19][20][21], and sensing [22][23][24][25]. The choice of organic linker is key to MOF properties.…”

“…This is a key feature for their selective sorption capacity [19,26]. The recognition of chemical information by an adsorbent MOF may be characterised by colour change known as chromism [27,28], or reversible change in structure size known as a breathing phenomenon [19,23]. The latter has been observed in both single ligand MOFs such as [Zn(34pba) 2 ] n as well as in a mixed ligand MOF [Cd(34pba)(44pba)] n ; where the channels react to stimuli caused by the temperature and size of the entering molecules such as alkyl alcohols, N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) [19,26].…”

Recent development of boronic acid-based fluorescent sensors

“…113 However, the molar extinction coefficient of the rare earth compound is relatively low, and the organic ligand needs to be sensitized by energy transfer. Based on this mechanism, Chang et al fabricated two lanthanide-based luminescent sensors 55 and 56.…”

Hexanuclear 3d − 4f metal–organic cages assembled from a carboxylic acid‐functionalized tris‐triazamacrocycle for highly selective fluorescent sensing of picric acid

“…It is known that at least two possible mechanisms may account for the fluorescence quenching of the electron‐rich sensors: photo‐induced electron transfer (PET) or fluorescence resonance energy transfer (FRET). The inability of nitroalkane and electron‐rich aromatic compounds on quenching the fluorescence emissions of 1 and 2 allows us to conjecture that the selective detection of NACs by two cages may be ascribed to the electron transfer from the excited‐state of the aromatic moiety inside the cage to the electron‐deficient NACs . Commonly, the electron‐deficient NACs with the lower LUMO (lowest unoccupied molecule orbital) energy level are more easy to accept the photo‐excited electron from the conduction band of the sensory material, thus leading to the greater quenching ability.…”

“…The inability of nitroalkane and electron-rich aromatic compounds on quenching the fluorescence emissions of 1 and 2 allows us to conjecture that the selective detection of NACs by two cages may be ascribed to the electron transfer from the excited-state of the aromatic moiety inside the cage to the electron-deficient NACs. [68][69][70] Commonly, the electron-deficient NACs with the lower LUMO (lowest unoccupied molecule orbital) energy level are more easy to accept the photo-excited electron from the conduction band of the sensory material, thus leading to the greater quenching ability. However, the observed consequence of the quenching efficiency is not fully coincident with the corresponding LUMO energies of the selected NACs, [71][72][73] implicating that the fluorescence quenching behavior is not controlled only by the PET mechanism.…”