8 research outputs found
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 NaBH<sub>4</sub> in 95% ethanol affords
the corresponding anthracen-9-ol derivative, <b>3</b>, as confirmed
by <sup>1</sup>H NMR, <sup>13</sup>C 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 NaBH<sub>4</sub> in 95% ethanol affords
the corresponding anthracen-9-ol derivative, <b>3</b>, as confirmed
by <sup>1</sup>H NMR, <sup>13</sup>C 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<sub>sp2</sub>–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<sub>sp2</sub>–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<sub>sp2</sub>–H···π interaction
is suppressed by the steric effects of the perfluoroalkyl substituents.
The C<sub>sp3</sub>–F···F–C<sub>sp3</sub> attractive interactions between perfluoroalkyl chains further stabilize
the crystal structures. We also found that C<sub>sp3</sub>–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)<sub>3</sub>LnCl<sub>6</sub> Crystals as Models for the Coordination Environment of LnCl<sub>3</sub> (Ln = Sm, Eu, Dy, Er, Yb) in 1‑Butyl-3-methylimidazolium Chloride Ionic-Liquid Solution
A series of (BMI)<sub>3</sub>LnCl<sub>6</sub> (Ln = Sm, Eu, Dy, Er, Yb) crystals was prepared from solutions
of LnCl<sub>3</sub> 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>2<sub>1</sub>/<i>c</i> and
four formula units per unit cell. The first coordination sphere of
Ln<sup>3+</sup> consists of six Cl<sup>–</sup> anions forming
a slightly distorted octahedral LnCl<sub>6</sub><sup>3–</sup> center. The second coordination sphere is composed of nine BMI<sup>+</sup> cations. The emission spectra and luminescence lifetimes
of both (BMI)<sub>3</sub>LnCl<sub>6</sub> crystals and LnCl<sub>3</sub> in BMICl solution were measured. The spectroscopic similarities
suggest that crystalline (BMI)<sub>3</sub>LnCl<sub>6</sub> provides
a good model of the Ln<sup>3+</sup> coordination environment in BMICl
solution
(BMI)<sub>3</sub>LnCl<sub>6</sub> Crystals as Models for the Coordination Environment of LnCl<sub>3</sub> (Ln = Sm, Eu, Dy, Er, Yb) in 1‑Butyl-3-methylimidazolium Chloride Ionic-Liquid Solution
A series of (BMI)<sub>3</sub>LnCl<sub>6</sub> (Ln = Sm, Eu, Dy, Er, Yb) crystals was prepared from solutions
of LnCl<sub>3</sub> 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>2<sub>1</sub>/<i>c</i> and
four formula units per unit cell. The first coordination sphere of
Ln<sup>3+</sup> consists of six Cl<sup>–</sup> anions forming
a slightly distorted octahedral LnCl<sub>6</sub><sup>3–</sup> center. The second coordination sphere is composed of nine BMI<sup>+</sup> cations. The emission spectra and luminescence lifetimes
of both (BMI)<sub>3</sub>LnCl<sub>6</sub> crystals and LnCl<sub>3</sub> in BMICl solution were measured. The spectroscopic similarities
suggest that crystalline (BMI)<sub>3</sub>LnCl<sub>6</sub> provides
a good model of the Ln<sup>3+</sup> coordination environment in BMICl
solution