Fluorescence Quenching Investigation of Methyl Red Adsorption on Aluminum-Based Metal–Organic Frameworks

Abstract

The adsorption of methyl red (MR) isomers (ortho, meta, and para) on metal-organic frameworks (MOFs) was investigated by using a fluorescence quenching technique. All three MR isomers were found to quench the fluorescence of MOFs effectively. Nonlinear fluorescence quenching trends were observed in Stern-Volmer plots. A modified nonlinear Stern-Volmer equation with the concepts of multiple adsorption sites, adsorption strength, and quencher accessibility was successfully adopted to fit the fluorescence quenching data. The fitted parameters were correlated with the structural properties of MRs and MOFs. The order of quenching efficiency was found to be m-MR > p-MR > o-MR for all MOFs. This indicates that MR molecules not only adsorb via carboxylate-metal bonding but also adsorb through π-π interactions between the aromatic rings of MR and linker molecules in MOFs. The position of the carboxylate group in MRs and the structure of the linkers in MOFs are the key factors affecting the fluorescence quenching efficiency.

Exploring the “Goldilocks Zone” of Semiconducting Polymer Photocatalysts by Donor–Acceptor Interactions

“…Conversely, exposure to vapours of electron deficient arenes, such as nitrobenzene, leads to fluorescence quenching because excited electrons are being depleted (Figure S60 in the Supporting Information) . The position of absorption maxima of individual SNPs did not change significantly upon VOC adsorption, indicating that the electronic structure of the ground state remained unchanged, and hence, pointing towards (weak) physisorption of VOCs . Most noteworthy, the changes in fluorescence are systematically lower for SNPs with an aryl spacer between the D–A moieties (all SNPs‐2 ), and higher for those without (all SNPs‐1 ) (Figure S61 in the Supporting Information).…”

“…[22] Theposition of absorption maxima of individual SNPs did not change significantly upon VOCadsorption, indicating that the electronic structure of the ground state remained unchanged, and hence,p ointing towards (weak) physisorption of VOCs. [23] Most noteworthy,t he changes in fluorescence are systematically lower for SNPs with an aryl spacer between the D-A moieties (all SNPs-2), and higher for those without (all SNPs-1)( Figure S61 in the Supporting Information). The relative changes of fluorescence are independent of guest accessible surface area.…”

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“…The positive deviation at a high concentration of the quencher could be attributed to the simultaneous presence of dynamic (collisional) and static quenching. 34,35 Chen et al 36 have developed a general nonlinear SV model based on the Sips adsorption isotherm model 37 to describe the uorescence quenching with nonlinear trends that could be written as the following equation:…”

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“…Quenching plots of I0/I allow for an estimated rate of quenching to be determined and indicate simply whether multiple quenching processes are operating. 26 The plots for the five analytes are shown in Figure S7. The quenching plots for MJ3' upon exposure to TNT, 2,4-DNT, PETN and RDX are all linear, and this implies that only one type of quenching process is operative in these cases.…”