Expanding the Knowledge of the Selective-Sensing Mechanism of Nitro Compounds by Luminescent Terbium Metal-Organic Frameworks through Multiconfigurational ab Initio Calculations

Theoretical investigation of naphthodithiophene diimide derivatives as fluorescent sensors for 2,4,6-trinitrophenol detection

CONTEXT

This study explored the geometry, aromaticity, electrostatic potential, and fluorescence sensing capability of N,N'-dimethyl naphthodithiophene diimide (C1-NDTI-S) and its derivatives (C1-NDFI-O and C1-NDPI-N), where thiophene rings were substituted with furan and pyrrole, respectively. Theoretical calculations revealed that C1-NDTI-S had the most negative adsorption energy for 2,4,6-trinitrophenol (TNP), and its electronic absorption spectrum and fluorescence spectrum decreased considerably upon TNP adsorption. Through FMO, hole-electron, independent gradient model, and energy decomposition analysis, it was revealed that the essence of fluorescence quenching is the intermolecular weak π-π interaction driving photo-induced electron transfer. Furthermore, C1-NDFI-O and C1-NDPI-N generated by modifying the structure of C1-NDTI-S have the potential to serve as more efficient fluorescent sensors for TNP detection. The fluorescence recovery times confirmed the suitability of the three compounds as fluorescence probes.

METHODS

In this study, the Gaussian 09 software package at B3LYP-D3(BJ)/6-311 +  + G** level was applied to optimize the structure, energy, and fluorescence recovery time. Multiwfn combined with VMD software package was used to analyze the aromaticity of compounds using LOL-π and HOMA, with a focus on the differences in aromaticity after thiophene was substituted with different rings. Using AMBER force field for energy decomposition analysis based on force field (EDA-FF), the weak intermolecular interaction components are decomposed. The independent gradient model analysis based on Hirshfeld partition analysis clearly demonstrates the π-π interactions between molecules, with the δginter parameter set to 0.005 a.u. Electron absorption spectroscopy, charge-transfer spectra spectroscopy, molecular interactions, and hole electron interactions were all completed with the help of Multifwn software.

Quantum chemical elucidation of the luminescence mechanism in a europium(III) co-doped UiO-66 chemosensor selective to mercury(II)

Lanthanide(III) ions can be incorporated into metal-organic frameworks (MOFs) to form Ln@MOFs through post-synthetic procedures. This makes the MOFs efficient luminescent chemical sensors for detecting trace amounts of heavy metals. In this report, a quantum chemical theoretical protocol has been carried out to elucidate the detection principle of the turn-off luminescence mechanism in a Eu@UiO-66(DPA)-type MOF selective to Hg2+ ions. UiO-66(DPA) is an iso-reticular MOF of UiO-66 constructed from the Zr6-cluster [Zr6(μ3-O)4(μ3-OH)4]12+ and the ligands 1,4-benzenedicarboxylate (BDC) and 2,6-pyridinedicarboxylate (DPA) as linkers. The sensitization and energy transfer (ET) in UiO-66(DPA) doped with Eu3+ were analyzed using multireference ab initio CASSCF/NEVPT2 methods and time-dependent density functional theory (TD-DFT). The cluster model used in the calculations comprises the Z6-cluster/BDC/DPA fragments with the DPA ligand coordinating to Eu3+ or Hg2+ ions. The proposed sensitization pathway involves intersystem crossing from S1(DPA) to T1(DPA), a plausible subsequent energy transfer from T1(DPA) to the 5D1 state of Eu3+, and then vibrational relaxation to the emissive 5D0 state. These results also suggest that the electronic states of the BDC ligand can be strengthened by the population of the T1 electronic states of the DPA antenna via ET. Periodic DFT calculations confirm the electronic state mixture of BDC and DPA linkers in the conduction bands, just above the electronic state of Eu3+ ions, which is in concordance with the proposed Eu3+ sensitization pathways. The assessed optical properties (absorption and emission) of Hg2+@UIO-66(DPA) explain the experimental behavior of this chemosensor when the Hg2+ ion replaces the Eu3+ ion and the luminescence diminishes.

Design and preparation of a multi-responsive Cd-based fluorescent coordination polymer for smart sensing of nitrobenzene and ornidazole

The improper utilization of nitrobenzene (NB) and ornidazole (ORN) has resulted in irreversible effects on the environment. By combining experimental investigation, density functional theory (DFT) calculations, and machine learning, an effective green strategy for detecting NB and ORN in aqueous solutions can be developed. In this study, a one-dimensional Cd-based coordination polymer (Cd-HCIA-3) was designed and synthesized using 5-((4-carboxybenzyl)oxy)isophthalic acid and rigid 2,2'-bipyridine under solvothermal reaction conditions. Cd-HCIA-3 exhibits excellent fluorescence properties and stability in aqueous solutions. DFT calculations were performed to predict the fluorescence sensing performance of Cd-HCIA-3, revealing that photoinduced electron transfer is the key mechanism for inducing fluorescence quenching in the presence of NB and ORN, with weak molecular interactions promoting electron transfer. Fluorescence sensing experiments were conducted to verify the DFT results, showing that Cd-HCIA-3 can selectively detect NB and ORN in aqueous solutions with limits of detection of 7.22 × 10-8 and 1.31 × 10-7 mol/L, respectively. This study's findings provide valuable insights into the design and synthesis of fluorescent coordination polymers for target analytes.

Fluorescence-quenching mechanisms of novel isomorphic Zn/Cd coordination polymers for selective nitrobenzene detection

Nitroaromatic compounds in aqueous undermine environmental sustainability and affect human health. The development of a fluorescent sensor capable of efficiently and selectively detecting trace amounts of nitroaromatic compounds presents a considerable challenge. This study introduced Zn/Cd isomeric coordination polymers (Zn-H2CIA-1/Cd-H2CIA-2), which are synthesized using 5-((4-carboxybenzyl)oxy)isophthalic acid (5-H3CIA) and 1,10-phenanthroline (Phen). The polymers have zero-dimensional discrete crystal structure with a six-coordinated scissor-like shape. The two coordination polymers can be used as fluorescent sensors for detecting nitrobenzene (NB) and demonstrated favorable sensitivity, with detection limits of 1.95 × 10-8 and 4.66 × 10-7 mol/L, respectively. Zn-H2CIA-1 exhibited stronger fluorescence and a more sensitive response to NB compared with Cd-H2CIA-2. To elucidate their fluorescence-quenching mechanisms, we analyzed Zn-H2CIA-1 by performing DFT and TD-DFT calculations. The pore structure, density of states, excitation energy, hole-electron distribution, and orbital composition were analyzed. The suitable size of pores in Zn-H2CIA-1 is the main reason for its high NB selectivity. Moreover, intermolecular π-π stacking interactions result in an orbital overlap between Zn-H2CIA-1 and NB, enabling the transfer of electrons from Zn-H2CIA-1 to NB. This electron transfer is identified as the fundamental cause of fluorescence quenching in Zn-H2CIA-1.

Photophysical characterization of tetrahydroxyphenyl porphyrin Zn(II) and V(IV) complexes: experimental and DFT study

Photodynamic therapy (PDT) is a promising technique for the treatment of various diseases. In this sense, the singlet oxygen quantum yield (Φ∆) is a physical-chemical property that allows to stablish the applicability of a potential photosensitizers (PS) as a drug for PDT. In the herein report, the Φ∆ of three photosensitizers was determined: metal-free tetrahydroxyphenyl porphyrin (THPP), THPP-Zn and the THPP-V metal complexes. Their biological application was also evaluated. Therefore, the in vitro study was carried out to assess their biological activity against Escherichia coli. The metal-porphyrin complexes exhibited highest activities against the bacterial strain Escherichia coli. at the highest concentration (175 μg/mL) and show better activity than the free base ligand (salts and blank solution). Results indicated a relation between Φ∆ and the inhibitory activity against Escherichia coli, thus, whereas higher is the Φ∆, higher is the inhibitory activity. The values of the Φ∆ and the inhibitory activity follows the tendency THPP-Zn > THPP > THPP-V. Furthermore, quantum chemical calculations allowed to gain deep insight into the electronic and optical properties of THPP-Zn macrocycle, which let to verify the most probable energy transfer pathway involved in the singlet oxygen generation.

Sensitive fluorescent detection of phosmet and chlortetracycline in animal-derived food samples based on a water-stable Cd(II) chain-based zwitterionic metal-organic framework

The residues of pesticides and antibiotics have always been a major concern in agriculture and food safety. In order to provide a new method for the rapid detection of organophosphorus pesticides and antibiotics, a novel Cd(II) chain-based zwitterionic metal-organic framework MOF 1 with high sensitivity fluorescence sensing performance was successfully synthesized. A series of researches showed that the water- and pH-stable bifunctional MOF 1 has a great ability to detect phosmet (PSM) and chlortetracycline (CTC) in water through fluorescence quenching effect, with high detection sensitivity, low detection limits (0.0124 μM and 0.0131 μM), short response time (40 s) and reusability. Practical application results revealed that MOF 1 could detect PSM and CTC in milk, beef, chicken and egg samples, with satisfactory recoveries (95.2%-103.7%). As a novel fluorescence probe, MOF 1, is known the first case that can detect PSM in animal-derived samples, and the first dual-function material capable of detecting PSM and CTC. Mechanism studies displayed that competitive absorption and photoinduced electron transfer clearly authenticate the high quenching performance of the material.

Advance Progress on Luminescent Sensing of Nitroaromatics by Crystalline Lanthanide-Organic Complexes

Water environment pollution is becoming an increasingly serious issue due to industrial pollutants with the rapid development of modern industry. Among many pollutants, the toxic and explosive nitroaromatics are used extensively in the chemical industry, resulting in environmental pollution of soil and groundwater. Therefore, the detection of nitroaromatics is of great significance to environmental monitoring, citizen life and homeland security. Lanthanide-organic complexes with controllable structural features and excellent optical performance have been rationally designed and successfully prepared and used as lanthanide-based sensors for the detection of nitroaromatics. This review will focus on crystalline luminescent lanthanide-organic sensing materials with different dimensional structures, including the 0D discrete structure, 1D and 2D coordination polymers and the 3D framework. Large numbers of studies have shown that several nitroaromatics could be detected by crystalline lanthanide-organic-complex-based sensors, for instance, nitrobenzene (NB), nitrophenol (4-NP or 2-NP), trinitrophenol (TNP) and so on. The various fluorescence detection mechanisms were summarized and sorted out in the review, which might help researchers or readers to comprehensively understand the mechanism of the fluorescence detection of nitroaromatics and provide a theoretical basis for the rational design of new crystalline lanthanide-organic complex-based sensors.

Novel Lanthanide-Based Metal-Organic Framework Isomer as a Double Ratiometric Fluorescent Probe for Vanillymandelic Acid

The concentration of vanillymandelic acid (VMA) in urine is closely related with pheochromocytoma diagnosis. Thus, it is essential to develop more accurate and convenient fluorescence sensing strategies toward VMA. Until now, the design of double ratiometric detection methods for VMA was still in the unexplored stage. In this work, novel Ln³⁺-based metal-organic frameworks (QBA-Eu and QBA-Gd_0.875Eu_0.125) possessing dual emission peaks was fabricated successfully, which served as isomers of YNU-1 and exhibited more excellent water stability in fluorescence and structure than the ones of YNU-1. The formation of the complex between QBA ligands and VMA molecules via hydrogen bonds within QBA-Eu frameworks produced a new emission band centered at 450 nm and resulted in the decline of monomer emission intensity for QBA at 390 nm. Owing to the reduced energy gap [ΔE (S₁ - T₁)], the antenna effect was hampered and luminescence of Eu³⁺ ions also decreased. The developed double ratiometric (I_615nm/I_475nm, I_390nm/I_475nm) fluorescence sensors based on QBA-Eu and QBA-Gd_0.875Eu_0.125 possessed the advantages of fast response (4 min), low detection limits (0.58 and 0.51; 0.22 and 0.31 μM), and wide linear ranges (2-100 and 2-80 μM), which met the requirements of pheochromocytoma diagnosis. We also applied them to determine VMA in an artificial urine sample and diluted human urine sample and obtained satisfactory results. They will become prospective fluorescence sensing platforms for VMA.