Publications by authors named "Ana de Bettencourt-Dias"

45 Publications

Solution structure of a europium-nicotianamine complex supports that phytosiderophores bind lanthanides.

Phys Chem Chem Phys 2021 Feb;23(7):4287-4299

Department of Chemical and Materials Engineering, University of Nevada, Reno, NV 89557, USA.

We report the solution structure of a europium-nicotianamine complex predicted from ab initio molecular dynamics simulations with density functional theory. Emission and excitation spectroscopy show that the Eu3+ coordination environment changes in the presence of nicotianamine, suggesting complex formation, such as what is seen for the Eu3+-nicotianamine complex structure predicted from computation. We modeled Eu3+-ligand complexes with explicit water molecules in periodic boxes, effectively simulating the solution phase. Our simulations consider possible chemical events (e.g. coordination bond formation, protonation state changes, charge transfers), as well as ligand flexibility and solvent rearrangements. Our computational approach correctly predicts the solution structure of a Eu3+-ethylenediaminetetraacetic acid complex within 0.05 Å of experimentally measured values, backing the fidelity of the predicted solution structure of the Eu3+-nicotianamine complex. Emission and excitation spectroscopy measurements were also performed on the well-known Eu3+-ethylenediaminetetraacetic acid complex to validate our experimental methods. The electronic structure of the Eu3+-nicotianamine complex is analyzed to describe the complexes in greater detail. Nicotianamine is a metabolic precursor of, and structurally very similar to, phytosiderophores, which are responsible for the uptake of metals in plants. Although knowledge that nicotianamine binds europium does not determine how plants uptake rare earths from the environment, it strongly supports that phytosiderophores bind lanthanides.
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http://dx.doi.org/10.1039/d0cp06150fDOI Listing
February 2021

New up-conversion luminescence in molecular cyano-substituted naphthylsalophen lanthanide(iii) complexes.

Chem Commun (Camb) 2021 Mar 15;57(20):2551-2554. Epub 2021 Feb 15.

Department of Chemistry, University of Nevada, Reno, Nevada 89557, USA.

A new naphthylsalophen and its 3 : 2 ligand-to-lanthanide sandwich-type complexes were isolated. When excited at 380 nm, the complexes display the characteristic metal-centred emission for Nd, Er and Yb. Upon 980 nm excitation, in mixed lanthanide and the Er complexes, Er-centred upconversion emission at 543 and 656 nm is observed, with power densities as low as 2.18 W cm.
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http://dx.doi.org/10.1039/d0cc08128kDOI Listing
March 2021

Effect of the aromatic substituent on the -position of pyridine-bis(oxazoline) sensitizers on the emission efficiency of their Eu and Tb complexes.

Dalton Trans 2020 Dec;49(48):17699-17708

Department of Chemistry, University of Nevada, Reno, NV 89557, USA.

Two efficient lanthanide ion sensitizers 2,6-bis(oxazoline)-4-phenyl-pyridine (PyboxPh, 1) and 2,6-bis(oxazoline)-4-thiophen-2-yl-pyridine (Pybox2Th, 2) were synthesized. 1 crystallizes in the monoclinic space group P21/c with cell parameters a = 16.3794(4) Å, b = 7.2856(2) Å, c = 11.7073(3) Å, β = 97.229(1)° and V = 1385.97(6) Å3. 2 crystallizes in the monoclinic space group P21/n with cell parameters a = 5.9472(2), b = 16.0747(6), c = 14.3716(5) Å, β = 93.503(1)° and V = 1371.35(8) Å3. Photophysical characterization of 1 shows that its triplet state energy is located at 22 250 cm-1 and efficient energy transfer is observed for EuIII and TbIII. Solutions of [Ln(PyboxPh)3]3+ in dichloromethane display an emission efficiency of 37.2% for Ln[double bond, length as m-dash]Eu and 24.0% for Ln[double bond, length as m-dash]Tb. The excited state lifetimes for EuIII and TbIII are 2.227 ms and 723 μs, respectively. The triplet state energy of 2 is located at 19 280 cm-1 and is therefore too low to efficiently sensitize TbIII emission. However, the sensitization of EuIII is effective, with an emission quantum yield of 14.5% and an excited state lifetime of 714 μs. This shows that the derivatization of the chelator is strongly influenced by the aromatic substituents on the para-position of the pyridine ring. New isostructural 1 : 1 complexes of PyboxPh with EuIII (3) and TbIII (4) were also isolated and crystallize in the triclinic space group P1[combining macron] with cell parameters a = 9.1845(2) Å, b = 10.3327(2) Å, c = 11.9654(2) Å, α = 98.419(1)°, β = 108.109(1)°, γ = 91.791(1)°, V = 1064.08(4) Å3 and a = 7.8052(1) Å, b = 11.8910(1) Å, c = 14.2668(2) Å, α = 72.557(1)°, β = 86.355(1)°, γ = 77.223(1)°, V = 1231.95(3) Å3, respectively.
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http://dx.doi.org/10.1039/d0dt03135fDOI Listing
December 2020

Full Visible Spectrum and White Light Emission with a Single, Input-Tunable Organic Fluorophore.

J Am Chem Soc 2020 Nov 17. Epub 2020 Nov 17.

Department of Chemistry and Biochemistry, Ohio State University, Columbus, Ohio 43210, United States.

The blue emission of M2biQ can be tuned to specific wavelengths throughout the visible region by changing the identity of the cation it interacts with. These optical properties are observed in MeCN solution and the solid state. White light is obtained in MeCN by using either the proper ratio of zinc ions or acid. Thus, M2biQ acts as a nearly universal emitter (λ = 468-690 nm) with large Stokes shifts (116-306 nm, Δ = 7,042-11,823 cm). Full spectral profiles as well as quantum yields, lifetimes, and the crystal structures of key RGB and yellow emitters are reported. Emission wavelengths correlate with cationic radius, and TD-DFT calculations show that, for 1:1 complexes, the smaller the ion, the shorter the N-cation bond, and the greater the bathochromic emission shift.
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http://dx.doi.org/10.1021/jacs.0c08182DOI Listing
November 2020

Luminescence of Lanthanide Complexes with Perfluorinated Alkoxide Ligands.

Inorg Chem 2020 Jul 2;59(14):9807-9823. Epub 2020 Jul 2.

Department of Chemistry, Boston University, Boston, Massachusetts 02215, United States.

Four groups of rare-earth complexes, comprising 11 new compounds, with fluorinated O-donor ligands ([K(THF)][Ln(OCF)(THF)] (; Ln = Ce, Nd), [K](THF)[Ln(OCF)(THF)] (; Ln = Eu, Gd, Dy), [K(THF)][Ln(pin)(THF)] (; Ln = Ce, Nd), and [K(THF)][Ln(pin)(THF)] (; Ln = Eu, Gd, Dy, Y) have been synthesized and characterized. Single-crystal X-ray diffraction data were collected for all compounds except . Species , , and are uncommon examples of six-coordinate (Eu, Gd, Dy, and Y) and seven-coordinate (Ce and Nd) Ln centers in all-O-donor environments. Species , , , and are all luminescent (except where Ln = Gd and Y), with the solid-state emission of being exceptionally blue-shifted for a Ce complex. The emission spectra of the six Nd, Eu, and Dy complexes do not show large differences based on the ligand and are generally consistent with the well-known free-ion spectra. Time-dependent density functional theory results show that and undergo allowed 5f → 4d excitations, consistent with luminescence lifetime measurements in the nanosecond range. Eu-containing and , however, were found to have luminescence lifetimes in the millisecond range, indicating phosphorescence rather than fluorescence. The performance of a pair of multireference models for prediction of the Ln = Nd, Eu, and Dy absorption spectra was assessed. It was found that spectroscopy-oriented configuration interaction as applied to a simplified model in which the free-ion lanthanide was embedded in ligand-centered Löwdin point charges performed as well (Nd) or better (Eu and Dy) than canonical NEVPT2 calculations, when the ligand orbitals were included in the treatment.
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http://dx.doi.org/10.1021/acs.inorgchem.0c00782DOI Listing
July 2020

Luminescent lanthanide complexes with a pyridine-bis(carboxamide)-bithiophene sensitizer showing wavelength-dependent singlet oxygen generation.

Dalton Trans 2020 May 6;49(20):6661-6667. Epub 2020 May 6.

Department of Chemistry, University of Nevada, Reno, Nevada 89557, USA.

A new pyridine-bis(carboxamide)-based ligand with a bithiophene pendant, 2Tcbx, was synthesized. Its lanthanide ion (Ln) complexes, [Ln(2Tcbx)], were isolated and their photophysical properties were explored. Upon excitation at 360 nm, these complexes display emission in the near-infrared (NIR) with efficiencies of 0.69% for Ln = Yb, 0.20% for Ln = Nd, and 0.01% for Ln = Er, respectively. Concurrent O formation was seen for all complexes, with efficiencies of 19% for the Yb complex, 25% for the Nd complex, and 9% for the Er complex. When exciting at a longer wavelength, 435 nm, only Ln emission was observed and larger efficiencies of Ln-centered emission were obtained. The lack of O generation indicates that energy pathways involving different ligand conformations, which were investigated by transient absorption spectroscopy, are involved in the sensitization process, and enable the wavelength-dependent generation of O.
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http://dx.doi.org/10.1039/d0dt01034kDOI Listing
May 2020

Photocytotoxicity of Oligothienyl-Functionalized Chelates That Sensitize Ln Luminescence and Generate O.

Chemistry 2020 Sep 18;26(52):12060-12066. Epub 2020 Aug 18.

Department of Chemistry, University of Nevada, Reno, Reno, NV, 89557, USA.

Three new compounds containing a heptadentate lanthanide (Ln ) ion chelator functionalized with oligothiophenes, nThept(COOH) (n=1, 2, or 3), were isolated. Their Ln complexes not only display the characteristic metal-centered emission in the visible or near-infrared (NIR) but also generate singlet oxygen ( O ). Luminescence efficiencies (ϕ ) for [Eu1Thept(COO) ] and [Eu2Thept(COO) ] are ϕ =3 % and 0.5 % in TRIS buffer and 33 % and 3 % in 95 % ethanol, respectively. 3Thept(COO) does not sensitize Eu emission due to its low-lying triplet state. Near infra-red (NIR) luminescence is observed for all NIR-emitting Ln and ligands with efficiencies of ϕ =0.002 %, 0.005 % and 0.04 % for [YbnThept(COO) ] (n=1, 2, or 3), and ϕ =0.0007 %, 0.002 % and 0.02 % for [NdnThept(COO) ] (n=1, 2, or 3) in TRIS buffer. In 95 % ethanol, quantum yields of NIR luminescence increase and are ϕ =0.5 %, 0.31 % and 0.05 % for [YbnThept(COO) ] (n=1, 2, or 3), and ϕ =0.40 %, 0.45 % and 0.12 % for [NdnThept(COO) ] (n=1, 2, or 3). All complexes are capable of generating O in 95 % ethanol with ϕ efficiencies which range from 2 % to 29 %. These complexes are toxic to HeLa cells when irradiated with UV light (λ =365 nm) for two minutes. IC values for the Ln complexes are in the range 15.2-16.2 μm; the most potent compound is [Nd2Thept(COO) ] . The cell death mechanisms are further explored using an Annexin V-propidium iodide assay which suggests that cell death occurs through both apoptosis and necrosis.
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http://dx.doi.org/10.1002/chem.202001568DOI Listing
September 2020

Wavelength-Dependent Singlet Oxygen Generation in Luminescent Lanthanide Complexes with a Pyridine-Bis(Carboxamide)-Terthiophene Sensitizer.

Chemistry 2020 Jun 19;26(32):7274-7280. Epub 2020 May 19.

Department of Chemistry, University of Nevada, Reno, Reno, NV, 89557, USA.

Lanthanide ion (Ln ) complexes, [Ln(3Tcbx) ] (Ln =Yb , Nd , Er ) are isolated with a new pyridine-bis(carboxamide)-based ligand with a 2,2':5',2''-terthiophene pendant (3TCbx), and their resulting photophysical properties are explored. Upon excitation of the complexes at 490 nm, only Ln emission is observed with efficiencies of 0.29 % at 976 nm for Ln =Yb and 0.16 % at 1053 nm for Ln =Nd . Er emission is observed but weak. Upon excitation at 400 nm, concurrent O formation is seen, with efficiencies of 11 % for the Yb and Nd complexes and 13 % for the Er complex. Owing to the concurrent generation of O , as expected, the efficiency of metal-centered emission decreases to 0.02 % for Yb and 0.05 % for Nd . The ability to control O generation through the excitation wavelength indicates that the incorporation of 2,2':5',2''-terthiophene results in access to multiple sensitization pathways. These energy pathways are unraveled through transient absorption spectroscopy.
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http://dx.doi.org/10.1002/chem.202000587DOI Listing
June 2020

Luminescent Carbazole-Based Eu and Yb Complexes with a High Two-Photon Absorption Cross-Section Enable Viscosity Sensing in the Visible and Near IR with One- and Two-Photon Excitation.

Inorg Chem 2020 Mar 13;59(5):3193-3199. Epub 2020 Feb 13.

Department of Chemistry, University of Nevada, Reno, Nevada 89557, United States.

The newly synthesized Eu and Yb complexes with the new carbazole-based ligands CPAD and CPAP display the characteristic long-lived metal-centered emission upon one- and two-photon excitation. The Eu complexes show the expected narrow emission bands in the red region, with emission lifetimes between 0.382 and 1.464 ms and quantum yields between 2.7% and 35.8%, while the Yb complexes show the expected emission in the NIR region, with emission lifetimes between 0.52 and 37.86 μs and quantum yields between 0.028% and 1.12%. Two-photon absorption cross sections (σ) as high as 857 GM were measured for the two ligands. The complexes showed a strong dependence of the one- and two-photon sensitized emission intensity on solvent viscosity in the range of 0.5-200 cP in the visible and NIR region.
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http://dx.doi.org/10.1021/acs.inorgchem.9b03561DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065274PMC
March 2020

Anion-π and H-Bonding Interactions Supporting Encapsulation of [Ln(NO)] (Ln = Nd, Er) with a Triazine-Based Ligand.

J Am Chem Soc 2019 09 17;141(38):15102-15110. Epub 2019 Sep 17.

Department of Chemistry , University of Nevada , Reno , Nevada 89557-0216 , United States.

Reaction of Nd and Er nitrate salts with a 1,3,5-tris(dipicolylamine)-triazine () ligand yielded two unprecedented examples of [Ln(NO)] (Ln = Nd, Er) moieties completely encapsulated by the ligands. They are found in the two new complexes, [(H)][(Nd(NO))]·2CHCN (), and the related [(H)][(Er(NO))]·3CHCN·2HO (). The structures of the complexes are similar and they crystallize in the triclinic -1 space group with = 12.1630(3), = 12.2694(3), = 17.6357(5) Å, = 2611.10(12) Å, and = 14.3372(4), = 17.1271(4), = 25.2207(7) Å, = 5934.7(3) Å, respectively. Anion-π interactions, which are reported here for the first time for Ln ion complexes, hydrogen bonding interactions and π-π stacking support the formation of the encapsulated species. Evidence of the protonated ligand in and was found through isolation of (H)(NO). Finally, the pH-dependent ability of the ligand to extract La and nitrate ions from aqueous into toluene solution is demonstrated.
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http://dx.doi.org/10.1021/jacs.9b05566DOI Listing
September 2019

Secondary-Sphere Chlorolanthanide(III) Complexes with a 1,3,5-Triazine-Based Ligand Supported by Anion-π, π-π, and Hydrogen-Bonding Interactions.

Inorg Chem 2020 Jan 11;59(1):151-160. Epub 2019 Sep 11.

Department of Chemistry , University of Nevada , Reno , Nevada 89557-0216 , United States.

2,4,6-Dipicolylamine-functionalized 1,3,5-triazine (dpat) was isolated. When reacted with LaCl, compound [(LaCl)(Hdpat)][HO] () formed, which crystallized in the monoclinic 2/ space group with parameters = 11.47 Å, = 19.22 Å, = 20.98 Å, = 4652.02 Å, and β = 90.53°. When reacted with NdCl, the complex [NdCl(HO)(Hdpat)][Cl](MeOH) () crystallized in the monoclinic 2/ space group with unit cell parameters = 20.05 Å, = 12.81 Å, = 20.64 Å, = 5004.40 Å, and β = 110.20°. In both cases, the dpat ligand forms a bowl-shaped cavity that partially envelops the Ln-containing central unit, which is anionic in and neutral in . The formation of these outer-sphere complexes is supported by secondary interactions, including π-π stacking, hydrogen bonding, and anion-π between the chlorolanthanide(III) fragment and the electron-deficient 1,3,5-triazine ring. Evidence of protonation of the pyridine rings in dpat was substantiated through the isolation of [Hdpat][Cl] (). This compound crystallized in the monoclinic 2/ space group with parameters = 11.93 Å, = 20.22 Å, = 15.28 Å, = 3664.97 Å, and β = 94.35°. Four pyridine rings are pairwise protonated in . dpat showed a moderate ability to extract La from an aqueous to an organic phase, indicating its potential, through judicious manipulation of secondary-sphere interactions, as the starting point for efficient extractants for Ln ions.
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http://dx.doi.org/10.1021/acs.inorgchem.9b01804DOI Listing
January 2020

O Generating Luminescent Lanthanide Complexes with 1,8-Naphthalimide-Based Sensitizers.

Inorg Chem 2019 Oct 10;58(19):13471-13480. Epub 2019 Sep 10.

Department of Chemistry , University of Nevada , Reno , Nevada 89557 , United States.

Lanthanide ion (Ln) complexes with two new 1,8-naphthalimide-based ligands, and , were isolated, and their photophysical properties were explored. Upon excitation at 335 nm, and sensitize visible and near-infrared emitting Ln ions (Ln = Eu, Nd, and Yb) and generate singlet oxygen (O). The quantum yields of Eu luminescence for [Eu()] and [Eu()] are 16.7% and 8.3%, respectively, with O generation efficiencies of 41% and 59%, respectively. The efficiencies of O generation for the NIR emitting complexes [Ln()] are 59% and 56%, respectively, and those for [Ln()] (Ln = Nd, Yb) are 64% and 61%, respectively. In an oxygen-free environment, the quantum yields of Eu luminescence for [Eu()] and [Eu()] increase to 20% and 18%, respectively.
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http://dx.doi.org/10.1021/acs.inorgchem.9b02431DOI Listing
October 2019

Estimating the Individual Spectroscopic Properties of Three Unique Eu Sites in a Coordination Polymer.

Inorg Chem 2018 Dec 28;57(24):15421-15429. Epub 2018 Nov 28.

Institute of Chemistry , University of Campinas , 13083-970 São Paulo , Brazil.

We isolated a coordination polymer with the formula [Eu(3,5-dcba)(HO)(dmf)]·2dmf, with three unique Eu coordination sites in the asymmetric unit, with the Eu ions bridged by 3,5-dichlorobenzoato (3,5-dcba) ligands. The coordination polymer crystallized in the triclinic space group P1̅ with unit cell dimensions a = 12.4899(15), b = 16.326(2), and c = 25.059(3) Å, α = 84.271(3)°, β = 84.832(3)°, and γ = 68.585(3)° and V = 4725.2(10) Å. The characteristic D → F ( J = 0-4) Eu transitions were observed upon ligand-centered excitation. Emission lifetimes of 0.825 ± 0.085 and 1.586 ± 0.057 ms were observed and were attributed to the sites with coordination of water or dimethylformamide (dmf) molecules to each ion, respectively. Through a combination of spectroscopy and calculations, we determined the photophysical properties of each unique Eu site. Energy-transfer rates ligand → Eu were determined for each unique site using the overlapped polyhedra method. The rates depend on the coordinated water molecules and the different donor-acceptor distances. The two sites without coordinated water molecules and shortest donor-acceptor distance display the fastest energy-transfer rate ligand → Eu, whereas the site with coordinated water molecules and longest donor-acceptor distance displays the slowest energy-transfer rate. Donor-acceptor distances were estimated computationally and were confirmed by calculating the frontier orbitals in the asymmetric units of the polymer using density functional theory.
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http://dx.doi.org/10.1021/acs.inorgchem.8b02720DOI Listing
December 2018

Synthesis, Structure, Photophysical Properties, and Photostability of Benzodipyrenes.

Chemistry 2019 Jan 20;25(6):1441-1445. Epub 2018 Dec 20.

Department of Chemistry, University of Nevada, Reno, 1664 N. Virginia St., Reno, NV, 89557, USA.

This work explores the syntheses, structures, photophysical properties, and photostability of benzodipyrenes (BDPs). BDPs were synthesized through an InCl -AgNTf -catalyzed, four-fold alkyne benzannulation reaction. The structures of BDP 4 a and its corresponding endoperoxide product were unambiguously confirmed by X-ray crystallography. The BDPs reported here can also be recognized as peri- and cata-benzannulated pentacenes with a non-functionalized central ring. Unlike the previous reported pentacene-based polycyclic aromatic hydrocarbons, the absorbances of the BDPs were blueshifted by ca. 40 nm relative to pentacene, even after extension of π-conjugation. The newly synthesized BDP products exhibit relatively good stability with half-lives as high as 4612 min in THF.
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http://dx.doi.org/10.1002/chem.201805248DOI Listing
January 2019

Mn Doped AIZS/ZnS Nanocrystals: Synthesis and Optical Properties.

J Alloys Compd 2017 Nov 28;725:1077-1083. Epub 2017 Jul 28.

Department of Electrical and Biomedical Engineering, University of Nevada Reno, NV, USA.

In this work, Mn doped AIZS/ZnS (Mn:AIZS/ZnS) nanocrystals (NCs) have been synthesized in an approach using heat-up and drop-wise addition of precursors. On the basis of the characterization of these doped NCs on their optical properties and materials, it is found that: (1) as more Mn atoms are doped into NCs, the doped NCs present photoluminescence (PL) red-shift and quantum yield quenching; (2) the doped NCs possess a short PL lifetime in tens of microseconds and a long PL lifetime in hundreds of microseconds, and the short lived PL is more dominant than the long lived one; and (3) the doped NCs present a reversible PL thermal quenching in a range from room temperature to 170°C. Possible PL mechanisms of these NCs were discussed by analyzing their time-resolved PL spectra and thermal stability.
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http://dx.doi.org/10.1016/j.jallcom.2017.07.262DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5724564PMC
November 2017

ZnS Nanoparticles Sensitize Luminescence of Capping-Ligand-Bound Lanthanide Ions.

Inorg Chem 2017 Mar 27;56(6):3260-3268. Epub 2017 Feb 27.

Department of Chemistry, University of Nevada , Reno, Nevada 89557, United States.

2,6-Bis(diethylamide)-4-oxo(3-thiopropane)pyridine (BDP) and 2,6-bis(methyl ester)-4-oxo(3-thiopropane)pyridine (BMP) were synthesized. These compounds chelated Ln ions and sensitized their emission. The 3:1 complexes of BDP displayed efficiencies of 18% and 12% for Eu and Tb, respectively. The analogous complexes of BMP had efficiencies of 23% and 18% for Eu and Tb, respectively. Both BDP and BMP were used to cap ZnS nanoparticles (NPs) in a one-pot synthesis, and then Ln ions were added, resulting in systems with metal ions at the surface of the capped NPs. Photoexcitation of the Eu and Tb systems through NPs capped with these two ligands, with the carboxylato derivative of BMP [dicarboxylato-4-oxo(3-thiopropane)pyridine] and the nonchromophore 3-mercaptopropionate, resulted in sensitized Ln-centered emission. The Eu-containing systems displayed higher efficiencies in the range 0.04-0.23% than the corresponding Tb-containing systems with efficiencies in the range 0.01-0.15%. The NPs capped with BDP were the exception; in this case, efficiencies of 0.36% and 0.79% for Eu and Tb, respectively, were observed.
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http://dx.doi.org/10.1021/acs.inorgchem.6b02638DOI Listing
March 2017

Estimating the Donor-Acceptor Distance To Tune the Emission Efficiency of Luminescent Lanthanide Compounds.

Inorg Chem 2017 Jan 22;56(2):709-712. Epub 2016 Dec 22.

Institute of Chemistry, University of Campinas , Campinas, São Paulo, Brazil.

The influence of the donor-acceptor distance R on the photophysical properties, including the emission quantum yield, of two europium complexes with the same coordination number, and thus similar microsymmetries, was investigated by spectroscopic and computational methods. K[Eu(dipicCbz)] was synthesized using the new ligand dipicCbz and its photophysical properties compared to Cs[Eu(dipic)]. We found that a 50% increase in R from 4.1 to 6.5 Å results in a substantial decrease in the emission efficiency from 24 to 1.8%.
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http://dx.doi.org/10.1021/acs.inorgchem.6b02637DOI Listing
January 2017

Luminescence and Nonlinear Optical Properties in Copper(I) Halide Extended Networks.

Inorg Chem 2016 Nov 13;55(21):11408-11417. Epub 2016 Oct 13.

Georgetown University , Department of Chemistry, 3700 O Street NW, Washington, D.C. 20057, United States.

The syntheses, structures, and luminescence properties of a series of copper(I) halide coordination polymers, prepared with mono- and bidentate N-heteroaromatic ligands, are reported. These metal-organic coordination networks form [CuIL] for bidentate ligands (where L = pyrazine (1), quinazoline (2)) and [CuIL] for monodentate ligands (where L = 3-benzoylpyridine (3) and 4-benzoylpyridine(4)). Both sets of compounds exhibit a double-stranded stair-CuI-polymer, or "ladder" structure with the ligand coordinating to the metal in a bidentate (bridging two stairs) or monodentate mode. The copper bromide analogues for the bidentate ligands were also targeted, [CuBrL] for L = pyrazine (5) with the same stair structure, as well as compositions of [CuBr(L)] for L = pyrazine (6) and quinazoline (7), which have a different structure type, where the -Cu-Br- forms a single-stranded "zigzag" chain. These copper halide polymers were found to be luminescent at room temperature, with emission peaks ranging from ∼550 to 680 nm with small shifts at low temperature. The structure (stair or chain), the halide (I or Br), as well as the ligand play an important role in determining the position and intensity of emission. Lifetime measurements at room and low temperatures confirm the presence of thermally activated delayed fluorescence, or singlet harvesting for compounds 1, 2, and 7. We also investigated the nonlinear optical properties and found that, of this series, [CuBr(quinazoline)] shows a very strong second harmonic generating response that is ∼150 times greater than that of α-SiO.
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http://dx.doi.org/10.1021/acs.inorgchem.6b01879DOI Listing
November 2016

Ligand Design for Luminescent Lanthanide-Containing Metallopolymers.

Inorg Chem 2016 Oct 2;55(20):9954-9963. Epub 2016 Aug 2.

Department of Chemistry, University of Nevada, Reno , Reno, Nevada 89557, United States.

The isolation of emissive materials with lanthanide ions is a topic of interest for imaging, display, and sensing applications, and it requires tuning of the electronics of the systems, such that, during the process of sensitization of the metal-centered luminescence, energy transfer from the sensitizer to the lanthanide ion is efficient and the resulting materials have the characteristics required for a given application. We discuss here our group's work in controlling the singlet- and triplet-state energies of sensitizing ligands through the choice of functional groups on the pyridine rings chelating to the lanthanide ions and show how we achieved progressively higher emission efficiencies. We describe targeted functionalization that led to highly emissive systems in solution and in the solid state and to new metallopolymers with norbornene or dicyclopentadiene-based backbones and pyridinebis(oxazoline) pendants, which display red Eu-based, green Tb-based, and, for the first time, blue Tm-based emission.
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http://dx.doi.org/10.1021/acs.inorgchem.6b00946DOI Listing
October 2016

Pyrenes, Peropyrenes, and Teropyrenes: Synthesis, Structures, and Photophysical Properties.

Angew Chem Int Ed Engl 2016 08 26;55(35):10427-30. Epub 2016 Jul 26.

Department of Chemistry, University of Nevada, Reno, 1664 N. Virginia St., Reno, NV, 89557, USA.

The design of a relatively simple and efficient method to extend the π-conjugation of readily available aromatics in one-dimension is of significant value. In this paper, pyrenes, peropyrenes, and teropyrenes were synthesized through a double or quadruple benzannulation reaction of alkynes promoted by Brønsted acid. This novel method does not involve cyclodehydrogenation (oxidative aryl-aryl coupling) to arrive at the newly incorporated large arene moieties. All of the target compounds were synthesized in moderate to good yields and were fully characterized with the structures unambiguously confirmed by X-ray crystallography. As expected, photophysical characterization clearly shows increasing red-shifts as a function of extended conjugation within the fused ring systems.
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http://dx.doi.org/10.1002/anie.201604741DOI Listing
August 2016

Cadmium and Zinc Alloyed Cu-In-S Nanocrystals and Their Optical Properties.

J Nanopart Res 2013 Nov;15(11)

Department of Chemistry, University of Nevada, Reno, NV, USA.

Cadmium (Cd) and zinc (Zn) alloyed copper-indium-sulfide (Cu-In-S or CIS) nanocrystals (NCs) in several nanometers were prepared using thermal decomposition methods, and the effects of Cd and Zn on optical properties, including the tuning of NC photoluminescence (PL) wavelength and quantum yield (QY), were investigated. It was found that incorporation of Cd into CIS enhances the peak QY of NCs whereas zinc alloying diminishes the peak. In contrast with Zn alloying, Cd alloying does not result in a pronounced luminescence blue shift. The further PL decay study suggests that Cd alloying reduces surface or intrinsic defects whereas alloying with Zn increases the overall number of defects.
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http://dx.doi.org/10.1007/s11051-013-2056-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3881318PMC
November 2013

Turning on lanthanide luminescence via nanoencapsulation.

Inorg Chem 2013 Jun 21;52(11):6311-8. Epub 2013 May 21.

Department of Chemistry and Physics, Armstrong Atlantic State University, 11935 Abercorn Street, Savannah, Georgia 31419, USA.

Encapsulation of macrocyclic europium(III) chelates by discrete, monodisperse SiO2 nanoparticles (NPs) has been carried out, and the resulting significant enhancement of metal-derived luminescence has been studied to rationalize this dramatic effect. The tetraiminodiphenolate motif chosen for this study is easily synthesized and incorporated into the NP matrix under ambient conditions. The free complex exhibits primarily weak ligand-derived emission at room temperature, typical for these compounds, and displays intense metal-centered luminescence from the europium only when cooled to 77 K. Upon encapsulation by the NPs, however, europium-derived luminescence is visibly "turned on" at room temperature, yielding strong emission peaks characteristic of europium(III) with a corresponding enhancement factor of 6 × 10(6). The similar ligand singlet and triplet excited-state energies determined for the free complex (20820 and 17670 cm(-1), respectively) versus the encapsulated complex (20620 and 17730 cm(-1)) indicate that encapsulation does not affect the energy levels of the ligand appreciably. Instead, a detailed analysis of the metal-centered emission and ligand singlet and triplet emission bands for the free and encapsulated complexes reveals that the enhanced metal emission is due to the rigid environment afforded by the silica NP matrix affecting vibrationally mediated energy transfer. Further, the metal-centered emission lifetimes in methanol versus deuterated methanol indicate a decrease in the number of coordinated solvent molecules upon encapsulation, changing from an average of 3.3 to 2.1 bound methanol molecules and reducing the known quenching effect on europium-centered luminescence due to nearby OH vibrations.
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http://dx.doi.org/10.1021/ic3022722DOI Listing
June 2013

Synthesis, lanthanide coordination chemistry, and liquid-liquid extraction performance of CMPO-decorated pyridine and pyridine N-oxide platforms.

Inorg Chem 2013 Mar 5;52(6):3063-83. Epub 2013 Mar 5.

Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA.

Syntheses for a set of new ligands containing one or two carbamoylmethylphosphine oxide (CMPO) fragments appended to pyridine and pyridine N-oxide platforms are described. Molecular mechanics analyses for gas phase lanthanide-ligand interactions for the pyridine N-oxides indicate that the trifunctional NOPOCO molecules, 2-{[Ph2P(O)][C(O)NEt2]C(H)}C5H4NO (7) and 2-{[Ph2P(O)][C(O)NEt2]CHCH2}C5H4NO (8), and pentafunctional NOPOP'O'COC'O' molecules, 2,6-{[Ph2P(O)][C(O)NEt2]C(H)}2C5H3NO (9) and 2,6-{[Ph2P(O)][C(O)NEt2]CHCH2}2C5H3NO (10), should be able to adopt, with minimal strain, tridentate and pentadentate chelate structures, respectively. As a test of these predictions, selected lanthanide coordination chemistry of the N-oxide derivatives was explored. Crystal structure analyses reveal the formation of a tridentate NOPOCO chelate structure for a 1:1 Pr(III) complex containing 7 while 8 adopts a mixed bidentate/bridging monodentate POCO/NO binding mode with Pr(III). Tridentate and tetradentate chelate structures are obtained for several 1:1 complexes of 9 while a pentadentate chelate structure is observed with 10. Emission spectroscopy for one complex, [Eu(9)(NO3)3], in methanol, shows that the Eu(III) ion resides in a low-symmetry site. Lifetime measurements for methanol and deuterated methanol solutions indicate the presence of four methanol molecules in the inner coordination sphere of the metal ion, in addition to the ligand, with the nitrate anions most likely dissociated. The solvent extraction performance of 7-10 in 1,2-dichloroethane for Eu(III) and Am(III) in nitric acid solutions was analyzed and compared with the performance of 2,6-bis(di-n-octylphosphinoylmethyl)pyridine N-oxide (TONOPOP'O') and n-octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (OPhDiBCMPO) measured under identical conditions.
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http://dx.doi.org/10.1021/ic3025342DOI Listing
March 2013

Unusual nitro-coordination of europium(III) and terbium(III) with pyridinyl ligands.

Dalton Trans 2012 Aug;41(36):11212-8

Department of Chemistry, University of Nevada, Reno, Reno, Nevada, USA.

A new ligand family based on picoline, bipyridine and terpyridine containing a nitro moiety has been synthesized and its coordination and sensitization ability for lanthanide ions has been studied. Three new complexes were characterized by X-ray single crystal diffraction and all three show uncommon coordination of the nitro moiety to the lanthanide ion. 5cTb, a terpyridine-nitro derivative with Tb(NO(3))(3), crystallizes in the orthorhombic space group Pbca with a = 15.125(3), b = 13.776(3), c = 18.716(4) Å, and V = 3899.8(13) Å(3) and is isostructural with its Eu(III) analog (5cEu) with cell parameters a = 15.1341(4), b = 13.7070(4), c = 18.8277(5) Å. 6Eu, a tripodal amine with a nitro-derivatized pyridine with Eu(CF(3)SO(3))(3), crystallizes in the triclinic space group P1 with a = 11.067(2), b = 11.633(2), c = 12.772(3) Å, α = 110.94(3), β = 97.49(3), γ = 91.42(3)° and V = 1518.1(5) Å(3). Finally, ligand 5a, a bipyridine-nitro derivative, crystallizes in the orthorhombic space group P2(1)/n with a = 3.7128(3), b = 11.7806(8), c = 19.9856(14) Å, β = 92.925(2)° and V = 873.01(11) Å(3). All four ligands show sensitization of Eu(III) and Tb(III) luminescence.
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http://dx.doi.org/10.1039/c2dt31308aDOI Listing
August 2012

A water-soluble Pybox derivative and its highly luminescent lanthanide ion complexes.

J Am Chem Soc 2012 Apr 13;134(16):6987-94. Epub 2012 Apr 13.

Department of Chemistry, University of Nevada, Reno, Nevada 89557, USA.

A new water-soluble Pybox ligand, 1, has been synthesized and found to crystallize in the monoclinic P2(1)/n space group with unit cell parameters a = 6.0936(1) Å, b = 20.5265(4) Å, c = 12.0548(2) Å, and β = 90.614(1)°. In the crystal, a water molecule is bound through hydrogen-bonding interactions to the nitrogen atoms of the oxazoline rings. This ligand was used to complex a variety of lanthanide ions, opening up new avenues for luminescence and catalysis in aqueous environment. These complexes are highly luminescent in aqueous solutions, in acetonitrile, and in the solid state. Aqueous quantum yields are high at 30.4% for Eu(III), 26.4% for Tb(III), 0.32% for Yb(III), and 0.11% for Nd(III). Er(III) did not luminesce in water, but an emission efficiency of 0.20% could be measured in D(2)O. Aqueous emission lifetimes were also determined for the visible emitting lanthanide ions and are 1.61 ms for Eu(III) and 1.78 ms for Tb(III). Comparing emission lifetimes in deuterated and nondeuterated water indicates that no water molecules are coordinated to the metal ion. Speciation studies show that three species form successively in solution and the log β values are 5.3, 9.6, and 13.8 for Eu(III) and 5.3, 9.2, and 12.7 for Tb(III) for 1:1, 2:1, and 3:1 ligand to metal ratios, respectively.
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http://dx.doi.org/10.1021/ja209572mDOI Listing
April 2012