A cerium-based metal–organic framework (MOF; 1) with a UiO-66 (UiO: University of Oslo) framework topology was synthesized solvothermally by employing 3,4-dimethylthieno[2,3-b]thiophene-2,5-dicarboxylic acid as a ligand. The MOF was thoroughly characterized by X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction, infrared spectroscopy, and thermogravimetric and N₂ sorption analyses. The activated material (1′) retained its structural integrity in water, acetic acid and 1 M HCl solution. XPS investigation reveals the presence of both Ce(III) and Ce(IV) ions in 1. Owing to the presence of mixed-valence cerium ions, 1′ was able to oxidize the chromogenic peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) or 2,2′-azinobis(3-ethylbenzothizoline-6-sulfonic acid) (AzBTS) in the absence of an external oxidizing agent. Thus, it showed inherent oxidase-like catalytic properties. Inspired by the excellent oxidase-mimicking activity of 1′, a protocol was developed for the rapid colorimetric sensing of biothiols in NaAc buffer (0.2 M, pH = 4). The sensing ability of 1′ towards cysteine was also demonstrated in human blood plasma. Furthermore, the redox-active cerium ions enabled 1′ to exhibit excellent heterogeneous catalytic performance in aerobic oxidation catalysis of thiol compounds. The material is reusable (both as a sensor and as a catalyst), low-cost and highly stable, which renders it a promising candidate for the monitoring of biothiols in immunoassays and medical diagnosis as well as for industrial oxidation catalysis.

The new, dimethyl-functionalized Ce(IV)-based UiO-66 (UiO = University of Oslo) metal–organic framework (MOF) material Ce-UiO-66-(CH₃)₂ (1) was successfully synthesized under solvothermal conditions (100 °C, 15 min) by employing ammonium cerium(IV) nitrate and the 2,5-dimethyl-1,4-benzenedicarboxylate (H₂BDC-(CH₃)₂) ligand in a DMF/H₂O (DMF = N,N-dimethyl formamide) mixture. The phase purity of the as-synthesized and thermally activated form (1′) of the compound was confirmed by a combination of X-ray powder diffraction (XRPD) analysis, Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric (TG) analysis. As verified by the thermogravimetric analysis, the compound is thermally stable up to 300 °C in air atmosphere. Based on the XRPD measurements, the material retains its crystallinity after treatment with water, methanol, acetic acid and 1 M HCl. As confirmed by the gas sorption experiments, the compound shows significant microporosity towards N₂ (BET surface area = 845 m² g⁻¹) and CO₂ (adsorption capacity = 34 cm³ g⁻¹ at 0 °C and 1 bar). The catalytic activity of 1′ has been studied in the oxidation of styrene and cyclohexene using tert-butylhydroperoxide (TBHP) as the terminal oxidant. The catalyst is reusable for four cycles with no significant drop in its activity which is further confirmed by a hot filtration experiment.

The synthesis of four isoreticular, water-stable Zr(IV) metal–organic frameworks (MOFs) was conducted under solvothermal conditions by using thienothiophene-based ligands. The MOFs were fully characterized by XRPD analyses, FT-IR spectroscopy and TG analyses. The ligands were systematically modified with methyl and phenyl groups for tuning the fluorescence and hydrophobic behaviour of the MOFs. The photophysical properties of free ligands and the corresponding MOFs were investigated by steady-state as well as time-resolved fluorescence experiments. The MOFs containing π-electron rich, conjugated thieno[3,2-b]thiophene units were employed for the sensing of metal ions. All the MOFs displayed high selectivity and sensitivity towards the sensing of biologically important Fe³⁺ ions in pure aqueous medium through the fluorescence quenching mechanism. Detailed experimental investigations suggest that the transfer of electrons from the electron-rich frameworks to the half-filled 3d orbitals of Fe³⁺ ions results in fluorescence quenching. Surprisingly, the electron acceptor methyl viologen (MV²⁺) ions exhibited a reverse trend in the quenching efficiency compared to the Fe³⁺ ions. Both the steric and electronic effects of the attached functional groups can be proposed to play determining roles in the fluorescence quenching mechanism. All the MOFs showed high photostability and reusability, which are beneficial for the long-term real-world detection of Fe³⁺ ions. Interestingly, the MOFs can be utilized to construct molecular logic gates for the efficient discrimination between Fe³⁺ and Fe²⁺ ions.

An overview of recent development of optical chemosensors for detecting volatile aldehydes, covering the sensing mechanisms based on colorimetric, fluorometric, etc., or dual modes, in correlation with the materials design and structure optimization.