A new series of luminescent heterometallic europium(III)–lutetium(III) terephthalate metal–organic frameworks, namely (EuxLu1−x)2bdc3·nH2O, was synthesized using a direct reaction in a water ...solution. At the Eu3+ concentration of 1–40 at %, the MOFs were formed as a binary mixture of the (EuxLu1−x)2bdc3 and (EuxLu1−x)2bdc3·4H2O crystalline phases, where the Ln2bdc3·4H2O crystalline phase was enriched by europium(III) ions. At an Eu3+ concentration of more than 40 at %, only one crystalline phase was formed: (EuxLu1−x)2bdc3·4H2O. All MOFs containing Eu3+ exhibited sensitization of bright Eu3+-centered luminescence upon the 280 nm excitation into a 1ππ* excited state of the terephthalate ion. The fine structure of the emission spectra of Eu3+ 5D0-7FJ (J = 0–4) significantly depended on the Eu3+ concentration. The luminescence quantum yield of Eu3+ was significantly larger for Eu-Lu terephthalates containing a low concentration of Eu3+ due to the absence of Eu-Eu energy migration and the presence of the Ln2bdc3 crystalline phase with a significantly smaller nonradiative decay rate compared to the Ln2bdc3·4H2O.
Fluorescent isocoumarin‐fused cycloalkynes, which are reactive in SPAAC and give fluorescent triazoles regardless of the azide nature, have been developed. The key structural feature that converts ...the non‐fluorescent cycloalkyne/triazole pair to its fluorescent counterpart is the pi‐acceptor group (COOMe, CN) at the C6 position of the isocoumarin ring. The design of the fluorescent cycloalkyne/triazole pairs is based on the theoretical study of the S1 state deactivation mechanism of the non‐fluorescent isocoumarin‐fused cycloalkyne IC9O using multi‐configurational ab initio and DFT methodologies. The calculations revealed that deactivation proceeds through the electrocyclic ring opening of the α‐pyrone cycle and is accompanied by a redistribution of electron density in the fused benzene ring. We proposed that the S1 excited state deactivation barrier could be increased by introducing a pi‐acceptor group into a position that is in direct conjugation with the formed C=O group and has a reduced electron density in the transition state. As a proof of concept, we designed and synthesized two fluorescent isocoumarin‐fused cycloalkynes IC9O‐COOMe and IC9O‐CN bearing pi‐acceptors at the C6 position. The importance of the nature of a pi‐acceptor group was shown by the example of much less fluorescent CF3‐substituted cycloalkyne IC9O‐CF3.
Fluorescent pairs of isocoumarin‐fused cycloalkynes IC9O‐COOMe and IC9O‐CN/1,2,3‐triazoles were developed. The basis for creating IC9O‐EWG is understanding the reason for the S1 state deactivation mechanism for their non‐fluorescent analog IC9O using multi‐configurational ab initio and DFT methodologies and eliminating this deactivation pathway through rational design.
Electrophile-promoted cyclizations of functionalized alkynes offer a useful tool for constructing halogen-substituted heterocycles primed for further derivatization. Preinstallation of an ...iodo-substituent at the alkyne prior to iodo-cyclization opens access to
ortho
di-iodinated heterocyclic precursors for the preparation of unsymmetrical heterocycle-fused enediynes. This general approach was used to prepare 2,3-diiodobenzothiophene, 2,3-diiodoindole, and 2,3-diiodobenzofuran, a useful family of substrates for systematic studies of the role of heteroatoms on the regioselectivity of cross-coupling reactions. Diiodobenzothiophene showed much higher regioselectivity for Sonogashira cross-coupling at C2 than diiodoindole and diiodobenzofuran. As a result, benzothiophene can be conveniently involved in a one-pot sequential coupling with two different alkynes, yielding unsymmetrical benzothiophene-fused enediynes. On the other hand, the Sonogashira reaction of diiodoindole and diiodobenzofuran formed considerable amounts of di-substituted enediynes in addition to the monoalkyne product by coupling at C2. Interestingly, no C3-monocoupling products were observed for all of the diiodides, suggesting that the incorporation of the 1
st
alkyne at C2 activates the C3 position for the 2
nd
coupling. Additional factors affecting regioselectivity were detected, discussed and connected, through computational analysis, to transmetalation being the rate-determining step for the Sonogashira reaction. Several enediynes synthesized showed cytotoxic activity, which is not associated with DNA strand breaks typical of natural enediyne antibiotics.
Iodocyclization of Ar-iodoacetylenes yields 2,3-diiodoheteroindene substrates for C2-regioselective Sonogashira cross-couplings. The high selectivity observed for diiodobenzothiophene allows the one-pot synthesis of unsymmetrical enediynes.
β-NaYF4:Eu3+ microparticles co-doped with Gd3+ ions were obtained by hydrothermal synthesis at 180 °C using citric acid as a stabilizing agent. All synthesized materials have a β-NaYF4 crystalline ...phase, where the unit cell volume increases upon the addition of Eu3+ and Gd3+ ions. The particles have a hexagonal prism shape and a size of 40–714 nm, where Eu3+ and Gd3+ doping results in size reduction. Upon 393 nm excitation, phosphors exhibit distinct emission peaks centered at 591, 615, and 695 nm and a weak band at 650 nm attributed to 5D0–7FJ transitions (J = 1–4). The optimum Eu3+ doping concentration was found to be 30% in the NaYF4 host. Concentration quenching was realized through dipole–dipole interactions. Kinetic measurements showed a gradual decline of the 5D0 lifetime from 6.7 ms to 2.2 ms along with an increase in Eu3+ doping concentration. Co-doping of the small Gd3+ number led to an increase of emission intensity and 5D0 lifetime. The effects of Eu3+ doping and Gd3+ co-doping on radiative and nonradiative decay rates were studied using 4f–4f intensity theory.
β-NaYF4 microcrystals co-doped with Yb3+, Er3+/Tm3+, and Gd3+ ions were synthesized via a hydrothermal method using rare-earth chlorides as the precursors. The SEM and XRD data show that the doped ...β-NaYF4 form uniform hexagonal prisms with an approximate size of 600–800 nm. The partial substitution of Y by Gd results in size reduction of microcrystals. Upconversion luminescence spectra of microcrystals upon 980 nm excitation contain characteristic intra-configurational ff bands of Er3+/Tm3+ ions. An addition of Gd3+ ions leads to a significant enhancement of upconversion luminescence intensity with maxima at 5 mol % of dopant.
The luminescent coarse-, micro- and nanocrystalline europium(III) terephthalate tetrahydrate (Eu2bdc3·4H2O) metal-organic frameworks were synthesized by the ultrasound-assisted wet-chemical method. ...Electron micrographs show that the europium(III) terephthalate microparticles are 7 μm long leaf-like plates. According to the dynamic light scattering technique, the average size of the Eu2bdc3·4H2O nanoparticles is equal to about 8 ± 2 nm. Thereby, the reported Eu2bdc3·4H2O nanoparticles are the smallest nanosized rare-earth-based MOF crystals, to the best of our knowledge. The synthesized materials demonstrate red emission due to the 5D0–7FJ transitions of Eu3+ upon 250 nm excitation into 1ππ* state of the terephthalate ion. Size reduction results in broadened emission bands, an increase in the non-radiative rate constants and a decrease in both the quantum efficiency of the 5D0 level and Eu3+ and the luminescence quantum yields. Cu2+, Cr3+, and Fe3+ ions efficiently and selectively quench the luminescence of nanocrystalline europium(III) terephthalate, which makes it a prospective material for luminescent probes to monitor these ions in waste and drinking water.
A new series of luminescent heterometallic europium(III)–lutetium(III) terephthalate metal–organic frameworks, namely (Eusub.x Lusub.1−x )sub.2 bdcsub.3 ·nHsub.2 O, was synthesized using a direct ...reaction in a water solution. At the Eusup.3+ concentration of 1–40 at %, the MOFs were formed as a binary mixture of the (Eusub.x Lusub.1−x )sub.2 bdcsub.3 and (Eusub.x Lusub.1−x )sub.2 bdcsub.3 ·4Hsub.2 O crystalline phases, where the Lnsub.2 bdcsub.3 ·4Hsub.2 O crystalline phase was enriched by europium(III) ions. At an Eusup.3+ concentration of more than 40 at %, only one crystalline phase was formed: (Eusub.x Lusub.1−x )sub.2 bdcsub.3 ·4Hsub.2 O. All MOFs containing Eusup.3+ exhibited sensitization of bright Eusup.3+ -centered luminescence upon the 280 nm excitation into a sup.1 ππ* excited state of the terephthalate ion. The fine structure of the emission spectra of Eusup.3+ 5 Dsub.0 -sup.7 Fsub.J (J = 0–4) significantly depended on the Eusup.3+ concentration. The luminescence quantum yield of Eusup.3+ was significantly larger for Eu-Lu terephthalates containing a low concentration of Eusup.3+ due to the absence of Eu-Eu energy migration and the presence of the Lnsub.2 bdcsub.3 crystalline phase with a significantly smaller nonradiative decay rate compared to the Lnsub.2 bdcsub.3 ·4Hsub.2 O.
β-NaYF
4
:Eu
3+
microparticles co-doped with Gd
3+
ions were obtained by hydrothermal synthesis at 180 °C using citric acid as a stabilizing agent. All synthesized materials have a β-NaYF
4
...crystalline phase, where the unit cell volume increases upon the addition of Eu
3+
and Gd
3+
ions. The particles have a hexagonal prism shape and a size of 40-714 nm, where Eu
3+
and Gd
3+
doping results in size reduction. Upon 393 nm excitation, phosphors exhibit distinct emission peaks centered at 591, 615, and 695 nm and a weak band at 650 nm attributed to
5
D
0
-
7
F
J
transitions (
J
= 1-4). The optimum Eu
3+
doping concentration was found to be 30% in the NaYF
4
host. Concentration quenching was realized through dipole-dipole interactions. Kinetic measurements showed a gradual decline of the
5
D
0
lifetime from 6.7 ms to 2.2 ms along with an increase in Eu
3+
doping concentration. Co-doping of the small Gd
3+
number led to an increase of emission intensity and
5
D
0
lifetime. The effects of Eu
3+
doping and Gd
3+
co-doping on radiative and nonradiative decay rates were studied using 4f-4f intensity theory.
Eu
3+
and Gd
3+
doping results in the size reduction of β-NaYF
4
: Eu
3+
, Gd
3+
microparticles; Gd
3+
co-doping enhances the luminescence intensity.
β-NaYF
4
:Eu
3+
microparticles co-doped with Gd
3+
ions were obtained by hydrothermal synthesis at 180 °C using citric acid as a stabilizing agent. All synthesized materials have a β-NaYF
4
...crystalline phase, where the unit cell volume increases upon the addition of Eu
3+
and Gd
3+
ions. The particles have a hexagonal prism shape and a size of 40–714 nm, where Eu
3+
and Gd
3+
doping results in size reduction. Upon 393 nm excitation, phosphors exhibit distinct emission peaks centered at 591, 615, and 695 nm and a weak band at 650 nm attributed to
5
D
0
–
7
F
J
transitions (
J
= 1–4). The optimum Eu
3+
doping concentration was found to be 30% in the NaYF
4
host. Concentration quenching was realized through dipole–dipole interactions. Kinetic measurements showed a gradual decline of the
5
D
0
lifetime from 6.7 ms to 2.2 ms along with an increase in Eu
3+
doping concentration. Co-doping of the small Gd
3+
number led to an increase of emission intensity and
5
D
0
lifetime. The effects of Eu
3+
doping and Gd
3+
co-doping on radiative and nonradiative decay rates were studied using 4f–4f intensity theory.
Shape-specific copper oxide nanostructures have attracted increasing attention due to their widespread applications in energy conversion, sensing, and catalysis. Advancing our understanding of ...structure, composition, and surface chemistry transformations in shaped copper oxide nanomaterials during changes in copper oxidation state is instrumental from both applications and preparative nanochemistry standpoints. Here, we report the study of structural and compositional evolution of amorphous copper (II) hydroxide nanoparticles under hydrazine reduction conditions that resulted in the formation of crystalline Cu2O and composite Cu2O-N2H4 branched particles. The structure of the latter was influenced by the solvent medium. We showed that hydrazine, while being a common reducing agent in nanochemistry, can not only reduce the metal ions but also coordinate to them as a bidentate ligand and thereby integrate within the lattice of a particle. In addition to shape and composition transformation of individual particles, concurrent interparticle attachment and ensemble shape evolution were induced by depleting surface stabilization of individual nanoparticles. Not only does this study provide a facile synthetic method for several copper (I) oxide structures, it also demonstrates the complex behavior of a reducing agent with multidentate coordinating ability in nanoparticle synthesis.
PDF
