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Imidazo[1,2-a]pyridine derivatives have excellent potential for chelation with transition metal ions. Two new imidazo[1,2-a]pyridine-8-carboxylates were synthesized and characterized by 1H NMR, 13C NMR, HRMS, and single crystal-XRD techniques. Methyl carboxylate (probe 1) turns on fluorescence upon coordination with Zn2+, while sodium carboxylate (probe 2) turns off its fluorescence upon coordination with Co2+ or Cu2+ ions present in aqueous acetonitrile medium. 13C NMR study revealed that the change in metal ion specific binding was due to the involvement of carboxylate anion in complex formation with Co2+ or Cu2+ ions. The carboxylate anion at 8-position also enhanced the sensitivity of detection of probe 2 by an order of magnitude (detection limits: 3.804 × 10–7 M, probe 1/Zn2+; 0.420 × 10–7 M, probe 2/Co2+ and 0.304 × 10–7 M, probe 2/Cu2+). The detection limits of probes 1 and 2 comply well with the World Health Organization (WHO) and US Environmental Protection Agency (US-EPA) guidelines for detection of heavy metal ions present in drinking water and ground water. Both the probes form a 1:1 complex with Zn2+, Co2+ or Cu2+, and the stoichiometry was verified by Job plot and ESI-mass analysis. The sensing mechanism is explained using 13C NMR experiments, ESI-mass analytical data and theoretical DFT calculations. The suitability of probes 1 and 2 for on-site detection and quantitative determination of Zn2+, Co2+ and Cu2+ ions present in biological, environmental and industrial samples is demonstrated. In addition, both 1 and 2 are used for detection of intracellular contamination of Zn2+, Co2+ or Cu2+ ions in onion epidermal cells. [ABSTRACT FROM AUTHOR]

Density functional theoretical calculations predicted non‐coplanar twisted geometry for two new imidazo[1,2‐a]pyridine derivatives, Imp and ImBt. Analysis of single‐crystal of Imp asserted the non‐coplanar twisted geometry, which is implicated in aggregation induced emission (AIE) of small aromatic molecules. Universal quenching by water was observed in aqueous THF solutions of Imp and ImBt, but they showed AIE effect when the water content was more than 80 %. Non‐fluorescent solutions of Imp and ImBt in THF‐water (7 : 3 v/v) mixture turned fluorescent on addition of specific metal ions prompting their potential to be explored for turn‐on sensor applications. While ImBt showed AIE response to Cd2+, Hg2+ and Al3+, Imp displayed AIE effect only to Cd2+ ions, under identical conditions. Absence of interference from common metal ions (including Hg2+ and Al3+) led to selective formation of Imp‐CdCl2 (1 : 1) complex, which offered the limit of detection of Cd2+ to be 19.2 μM. The observed selectivity for Cd2+ permitted the use of Imp in the imaging of live Rhizoctonia oryze contaminated with Cd2+ ions. [ABSTRACT FROM AUTHOR]

We report a triazole appended imidazopyridine based chemosensor (probe 1) for sequential detection of Cu2+ and CN− ions using fluorometry. Probe 1 is fluorescent in aqueous acetonitrile (H2O‐CH3CN, 1:1, v/v) when common metal ions are present, but the fluorescence is quenched when Cu2+ is present. The binding mechanism, quantitative determination and the mode of interaction of Cu2+ with probe 1 are explained using fluorescence spectroscopy, electrospray ionization mass spectrometry and Density Functional Theory (DFT) calculations. The observed detection limit for Cu2+ is found to be (18.17×10−6 M) and it is comparable with those reported for other Cu2+ chemosensors. Further, the 1–Cu2+ complex formation is found to be reversible, and this property has been successfully exploited for the quantitative determination of CN− ions in aqueous acetonitrile. Addition of CN– leads to a complete recovery of fluorescence from 1–Cu2+ complex, permitting the real time detection with the lower limit of detection of CN− being 33.57×10−6 M. The observed experimental results are supported by DFT calculations. A possible application of 1–Cu2+ in fluorescence imaging of Rhizoctonia solani mycelia cells, contaminated with CN− ions, is also represented. [ABSTRACT FROM AUTHOR]

In the title imidazo[1,2-a]pyridine derivatives, N-tert-butyl-2-(4-meth­oxy­phen­yl)-5-methyl­imidazo[1,2-a]pyridin-3-amine, C19H23N3O, (I), and N-tert-butyl-2-[4-(di­methyl­amino)­phen­yl]imidazo[1,2-a]pyridin-3-amine, C19H24N4, (II), the 4-meth­oxy­phenyl ring in (I) and the 4-(di­methyl­amino)­phenyl ring in (II) are inclined to the respective imidazole rings by 26.69 (9) and 31.35 (10)°. In the crystal of (I), mol­ecules are linked by N—H· · ·N hydrogen bonds, forming chains propagating along the [001] direction. The chains are linked by C—H· · ·π inter­actions, forming layers parallel to the (010) plane. In (II), the crystal packing also features N—H· · ·N hydrogen bonds, which together with C—H· · ·N hydrogen bonds link mol­ecules to form chains propagating along the c-axis direction. The chains are linked by C—H· · ·π inter­actions to form layers parallel to the (100) plane. Inversion-related layers are linked by offset π–π inter­actions [inter­centroid distance = 3.577 (1) Å]. The inter­molecular inter­actions of both compounds were analyzed using Hirshfeld surface analysis and two-dimensional fingerprint plots. [ABSTRACT FROM AUTHOR]