Rationally designed multiple hydroxyl-group-based chemosensors L1–L4 containing arene-based fluorophores are presented for the selective detection of Al3+ and Ga3+ ions. Changes in the absorption and emission spectra of L1–L4 in ethanol were easily observable upon the addition of Al3+ and Ga3+ ions. Competitive binding studies, detection limits, and binding constants illustrate significant sensing abilities of these chemosensors with L4, showing the best results. The interaction of Al3+/Ga3+ ions with chemosensor L4 was investigated by fluorescence lifetime measurements, whereas Job’s plot, high-resolution mass spectrometry, and 1H NMR spectral titrations substantiated the stoichiometry between L4 and Al3+/Ga3+ ions. The solution-generated [L-M3+] species further detected pyrophosphate ion (PPi) by exhibiting emission enhancement and a visible color change. The binding of Al3+/Ga3+ ions with chemosensor L4 was further supported by density functional theory studies. Reversibility for the detection of Al3+/Ga3+ ions was achieved by utilizing a suitable proton source. The multiionic response, reversibility, and optical visualization of the present chemosensors make them ideal for practical applications for real samples, which have been illustrated by paper-strip as well as polystyrene film-based detection.

In the present study, an ecofriendly and zero-cost approach has been demonstrated for the preparation of carbon quantum dots by one-pot hydrothermal treatment of leaf extracts of neem (Azadirachta indica). The as-synthesized neem carbon quantum dots (N-CQDs) exhibited high fluorescent quantum yields (QYs) up to 27.2%. Moreover, N-CQDs also act with a peroxidase-like-mimetic activity toward the oxidation of peroxidase substrate 3,3′,5,5′-tetramethyl­benzidine (TMB) in association with hydrogen peroxide (H2O2). Further, the kinetics of peroxidase-like catalytic activity follows the Michaelis–Menten and ping-pong pathway. In addition, the H2O2 sensitive TMB oxidation motivated the colorimetric detection of H2O2 which showed linearity from 0.1 to 0.5 mmol/L with a detection limit (LOD) of 0.035 mmol/L. Furthermore, the blue colors of oxidized TMB (ox-TMB) were selectively reduced in native TMB with ascorbic acid (AA) without any interference of other reducing agents. The linear range of AA detection was lying between 5 and 40 μM with a LOD up to 1.773 μM. The practicability assay of the proposed sensing system toward the detection of AA was also investigated in real sample analysis such as common fruits which showed good sensitivity to the presence of AA. Therefore, this convenient, ecofriendly, and cost-effective peroxidase-based sensing system opens a new platform for analysis of AA in real samples and in complex biological systems.

This work reports three heterometallic coordination polymers (HCPs), namely, [{(1′) 2 Zn 8 Na 24), originated from a common Co 3+ based metalloligand 1 offering eight arylcarboxylic acid groups where 1′ and 1″ respectively contribute eight and six anionic carboxylate groups. The crystal structure analyses display three-dimensional nature of all three HCPs wherein metalloligands are connected through secondary metals. Detailed topological analyses illustrate that the metalloligands function as the nodes that are connected to secondary building units (SBUs) composed of Zn 2+ , Cd 2+ , and Mn 2+ ions coordinated by the arylcarboxylate groups. All three HCPs effectively function as the heterogeneous catalysts for the Lewis acid assisted Knoevenagel condensation reactions of assorted aldehydes with three different active methylene compounds.

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On–off–on detection of Hg2+ and GSH using green-synthesized CQDs from T. indica leaves for the first time.

Pyridine-2,6-dicarboxamide based scaffolds with appended naphthyl groups act as fluorescent probes for the selective detection of Pd2+ ions in aqueous medium and have applications as paper-strip sensors, as polystyrene films, and in cell imaging.