A Hexanuclear Cadmium Metal–Organic Framework Exhibiting Dual Mechanisms to Trigger a Fluorescence‐Quenching Response toward Iron(III) Ions

Abstract

A hexanuclear CdII metal–organic framework (1) based on 4‐(1H‐pyrazole‐4‐carboxamido)benzoic acid (H2L) and featuring a three‐dimensional microporous framework was synthesized. Notably, 1 shows a unique fluorescence‐quenching response toward Fe3+ ions with high selectivity and sensitivity (Stern–Volmer constant KSV = 2.07 × 104 m–1). The response is attributable to the coaction of absorption competition and energy‐transfer (ET) mechanism. Furthermore, spectral analysis indicates that the energy‐transfer mechanism makes the dominant contribution to the fluorescence quenching of 1.

Novel Multifunctional Zn Metal–Organic Framework Fluorescent Probe Demonstrating Unique Sensitivity and Selectivity for Detection of PA and Fe3+ Ions in Water Solution

“…The quenching efficiency between PA and 1 can be quantitatively calculated using the Stern−Volmer (S−V) equation: (I 0 /I) = 1 + K SV [Q], where I 0 and I is the emission intensity of 1 before and after addition of PA, respectively, K sv is quenching constant, and [Q] is the concentration of PA. As shown in Figure 4b, the S−V plot displays linear relation at a low concentration of PA, while it shows upward bending trend at high concentration of PA, which can be attributed to the self-absorption between MOFs and analytes. At low concentration, K SV is up to 7.8 × 10 4 M −1 , which was comparable to the previous reported MOF for detection of PA. 16,28,29 Meanwhile, the limit of detection was further calculated according to the corresponding the data. As shown in Figure S13, the value of detection limit is up to 2.56 × 10 −6 M, suggesting that 1 can act as an excellent sensor to detect PA with high selectivity and sensitivity in aqueous solution.…”

Highly Sensitive Detection of Iron Ions in Aqueous Solutions Using Fluorescent Chitosan Nanoparticles Functionalized by Rhodamine B

“…Chitosan is the only natural alkaline polysaccharide obtained from partial deacetylation of chitin, which is antibacterial, biocompatible, and renewable. , Chitosan is hydrophilic and has a large number of hydroxyl and amino groups, allowing it to strongly interact with metal ions while providing the sites for numerous attractive chemical modifications. , Especially, there are plenty of N and O in chitosan chains, which are hard bases, and iron ions are hard acids. According to the soft and hard acid–base theory, , iron ions are easily combined with O and N. Therefore, the introduction of more N and O elements can greatly improve the ability of fluorescent probes to identify and detect iron ions when preparing fluorescent probes. − Thus, the combination of chitosan and fluorescent small molecules may be an effective method for preparing fluorescent probes for the detection of Fe 3+ in aqueous solutions with high sensitivity and selectivity.…”

A novel fluorescence phenomenon caused by amine induced ion-exchange between Cd2+ and Fe3+ ions

“…For ion detection, analyzing the change of fluorescence is a immediate and effective method. There are mainly five kinds of detection mechanisms: the collapse of the framework, 12 the ion-exchange between the targeted ions and central metal ions of MOFs, 13 the resonance energy transfer, 14 the absorption competition, 15 and the weak interaction between metal ions and the heteroatom within the organic ligands. 16 Of course different mechanisms can also exist in the same detection process.…”

“… 16 Of course different mechanisms can also exist in the same detection process. 15 Since lots of MOFs have the fluorescence excitation or emission wavelength which overlaps with the ultraviolet absorption wavelength range of iron ions, these complexes are often used to detect iron ions with the mechanism of absorption competition and resonance energy transfer. 15,17 However, the detection of iron ions with the mechanism of ion-exchange is rarely reported up to now, especially caused by inducing group.…”

“… 15 Since lots of MOFs have the fluorescence excitation or emission wavelength which overlaps with the ultraviolet absorption wavelength range of iron ions, these complexes are often used to detect iron ions with the mechanism of absorption competition and resonance energy transfer. 15,17 However, the detection of iron ions with the mechanism of ion-exchange is rarely reported up to now, especially caused by inducing group. In addition, the quenching process of iron ions by most metal–organic frameworks rarely contains any peak shifts or enhances, as is the case with the quenching process of reference complex 2 herein (Fig.…”