Differential Sensing of Zn(II) and Cu(II) via Two Independent Mechanisms

Selective reduction of an anthracenone–quinoline imine derivative, <b>2</b>, using 1.0 equiv of NaBH₄ in 95% ethanol affords the corresponding anthracen-9-ol derivative, <b>3</b>, as confirmed by ¹H NMR, ¹³C NMR, ESI-MS, FTIR, and elemental analysis results. UV–vis and fluorescence data reveal dramatic spectroscopic changes in the presence of Zn­(II) and Cu­(II). Zinc­(II) coordination induces a 1,5-prototropic shift resulting in anthracene fluorophore formation via an imine–enamine tautomerization pathway. Copper­(II) induces a colorimetric change from pale yellow to orange-red and results in imine hydrolysis in the presence of water. Spectroscopic investigations of metal ion response, selectivity, stoichiometry, and competition studies all suggest the proposed mechanisms. ESI-MS analysis, FTIR, and single-crystal XRD further support the hydrolysis phenomenon. This is a rare case of a single sensor that can be used either as a chemosensor (reversibly in the case of Zn­(II)) or as a chemodosimeter (irreversibly in the case of Cu­(II)); however, the imine must contain a coordinating Lewis base, such as quinoline, to be active for Cu­(II)

Differential Sensing of Zn(II) and Cu(II) via Two Independent Mechanisms

Selective reduction of an anthracenone–quinoline imine derivative, <b>2</b>, using 1.0 equiv of NaBH₄ in 95% ethanol affords the corresponding anthracen-9-ol derivative, <b>3</b>, as confirmed by ¹H NMR, ¹³C NMR, ESI-MS, FTIR, and elemental analysis results. UV–vis and fluorescence data reveal dramatic spectroscopic changes in the presence of Zn­(II) and Cu­(II). Zinc­(II) coordination induces a 1,5-prototropic shift resulting in anthracene fluorophore formation via an imine–enamine tautomerization pathway. Copper­(II) induces a colorimetric change from pale yellow to orange-red and results in imine hydrolysis in the presence of water. Spectroscopic investigations of metal ion response, selectivity, stoichiometry, and competition studies all suggest the proposed mechanisms. ESI-MS analysis, FTIR, and single-crystal XRD further support the hydrolysis phenomenon. This is a rare case of a single sensor that can be used either as a chemosensor (reversibly in the case of Zn­(II)) or as a chemodosimeter (irreversibly in the case of Cu­(II)); however, the imine must contain a coordinating Lewis base, such as quinoline, to be active for Cu­(II)

Zinc(II) Mediated Imine–Enamine Tautomerization

Reduction of imine–anthracenone compounds selectively produces secondary alcohols leaving the external imine group unreacted. Addition of the Zn(II) ion induces a metal-mediated imine–enamine tautomerization reaction that is selective for Zn(II), a new fluorescence detection method not previously observed for this important cation

Zinc(II) Mediated Imine–Enamine Tautomerization

Reduction of imine–anthracenone compounds selectively produces secondary alcohols leaving the external imine group unreacted. Addition of the Zn(II) ion induces a metal-mediated imine–enamine tautomerization reaction that is selective for Zn(II), a new fluorescence detection method not previously observed for this important cation

Strengthening π–π Interactions While Suppressing C_sp2–H···π (T-Shaped) Interactions via Perfluoroalkylation: A Crystallographic and Computational Study That Supports the Beneficial Formation of 1‑D π–π Stacked Aromatic Materials

The design and synthesis of aromatic crystalline materials with controllable crystal structure packing is of particular interest in organic semiconductor and optoelectronic devices, where 1-D π–π stacked structures that enhance charge mobility are the most beneficial. We report here that the π–π interactions between aromatic molecules can be strengthened and the C_sp2–H···π (T–shape) interaction can be suppressed by perfluoroalkylation of corresponding aromatics. Both crystal structure data and ab initio calculations show that the π–π interaction is strengthened due to the electronic effects of perfluoroalkyl substituents, and the C_sp2–H···π interaction is suppressed by the steric effects of the perfluoroalkyl substituents. The C_sp3–F···F–C_sp3 attractive interactions between perfluoroalkyl chains further stabilize the crystal structures. We also found that C_sp3–F···π interaction can be eliminated if an optimal electron deficiency of the π system is tuned by adjusting the number of perfluoroalkyl substituents. The insight gained from this study is of particular interest in organic semiconductor research as well as the fields of molecular recognition, sensing, and design of enzyme inhibitors where π–π interactions are also important

Selective Fluorescence Sensing of Copper(II) and Water via Competing Imine Hydrolysis and Alcohol Oxidation Pathways Sensitive to Water Content in Aqueous Acetonitrile Mixtures

Addition of hydrazines to a 1,8-disubstituted anthraquinone macrocycle containing a polyether ring produces site-selective imination, where hydrazone formation produces the more sterically hindered adduct. Reduction of the remaining carbonyl group to a secondary alcohol followed by addition of copper­(II) ion causes intense yellow fluorescence to occur, which is selective for this metal cation and allows this system to be used as a fluorescence sensor. In the presence of water, a green-fluorescent intermediate appears, which slowly decomposes to produce the original starting anthraquinone. The addition of a large amount of water radically changes the reaction pathway. In this case, oxidation of the secondary alcohol is kinetically faster than hydrolysis of the hydrazone, although the same anthraquinone product is ultimately produced. Stern–Volmer data suggest that dioxygen quenches the green emission through both dynamic and static mechanisms; the static ground-state effect is most likely due to association of oxygen with the copper-bound fluorescent intermediate

(BMI)₃LnCl₆ Crystals as Models for the Coordination Environment of LnCl₃ (Ln = Sm, Eu, Dy, Er, Yb) in 1‑Butyl-3-methylimidazolium Chloride Ionic-Liquid Solution

A series of (BMI)₃LnCl₆ (Ln = Sm, Eu, Dy, Er, Yb) crystals was prepared from solutions of LnCl₃ dissolved in the ionic liquid, 1-butyl-3-methylimidazolium chloride (BMICl). Crystals with Ln = 5% Sm + 95% Gd and with Ln = 5% Dy + 95% Gd were also grown to assess the importance of cross-relaxation in the Sm and Dy samples. The crystals are isostructural, with monoclinic space group <i>P</i>2₁/<i>c</i> and four formula units per unit cell. The first coordination sphere of Ln³⁺ consists of six Cl^– anions forming a slightly distorted octahedral LnCl₆^3– center. The second coordination sphere is composed of nine BMI⁺ cations. The emission spectra and luminescence lifetimes of both (BMI)₃LnCl₆ crystals and LnCl₃ in BMICl solution were measured. The spectroscopic similarities suggest that crystalline (BMI)₃LnCl₆ provides a good model of the Ln³⁺ coordination environment in BMICl solution

(BMI)₃LnCl₆ Crystals as Models for the Coordination Environment of LnCl₃ (Ln = Sm, Eu, Dy, Er, Yb) in 1‑Butyl-3-methylimidazolium Chloride Ionic-Liquid Solution

A series of (BMI)₃LnCl₆ (Ln = Sm, Eu, Dy, Er, Yb) crystals was prepared from solutions of LnCl₃ dissolved in the ionic liquid, 1-butyl-3-methylimidazolium chloride (BMICl). Crystals with Ln = 5% Sm + 95% Gd and with Ln = 5% Dy + 95% Gd were also grown to assess the importance of cross-relaxation in the Sm and Dy samples. The crystals are isostructural, with monoclinic space group <i>P</i>2₁/<i>c</i> and four formula units per unit cell. The first coordination sphere of Ln³⁺ consists of six Cl^– anions forming a slightly distorted octahedral LnCl₆^3– center. The second coordination sphere is composed of nine BMI⁺ cations. The emission spectra and luminescence lifetimes of both (BMI)₃LnCl₆ crystals and LnCl₃ in BMICl solution were measured. The spectroscopic similarities suggest that crystalline (BMI)₃LnCl₆ provides a good model of the Ln³⁺ coordination environment in BMICl solution