10 research outputs found
Dual-band low profile antennas for body-centric communications
No full textDual-band operation is highly desirable for wearable devices that need to connect with a range of wireless systems. We present a series of microstrip-line fed, dual-band compact patch antennas designed to operate in the common 2.45 GHz and 5.8 GHz bands for body-centric communications. All of the designs are low-profile and, with further study, may be suitably implemented in flexible or fabric materials. Our best performance was obtained with a shorted parasitic patch element close to a rectangular patch operating at the TM10 mode. This design, with an overall height of less than ¿/24, had a radiation efficiency of 91% at 2.45 GHz and 95% at 5.8 GHz in free space. When placed 2 mm above a muscle tissue phantom at 2.45 GHz, an efficiency of 52% and a 2:1 impedance bandwidth of 95 MHz was obtained. The bandwidth at the 5.8 GHz band was 400 MHz in free space
Unsymmetric Pentacene- and Pentacenequinone-Fused Porphyrins: Understanding the Effect of Cross- and Linear-Conjugation
No full textUnsymmetric pentacenequinone-fused (cross-conjugated)
and pentacene-fused
(linear-conjugated) porphyrins were designed and synthesized. The
cross-conjugated (AM1–AM3) and linear-conjugated (AM5–AM7) porphyrins displayed strikingly different sets of
optical and electronic properties, both of which are unusual and nontypical
of porphyrins. MCD, DFT, and TDDFT calculations suggest that multiple
charge transfer states exist in both π-conjugated systems, which
contributes to the complex absorption and MCD spectra of these molecular
systems. The general Gouterman’s four-orbital model used to
explain porphyrin spectroscopy led to contradicting theoretical and
experimental data, and is thus not applicable for these molecular
systems. The “2 + 4” and “3 + 3” active
spaces have been deduced and have proven effective to interpret the
absorption and MCD spectra of the pentacenequinone-fused (cross-conjugated)
and pentacene-fused (linear-conjugated) porphyrins, respectively.
Spectroelectrochemistry of AM5–AM7 revealed broad and
intense IR absorptions in the range of 1500–2500 nm, illustrating
the exceptional ability of these pentacene-fused systems to accommodate
positive charges. A pronounced metal effect was observed for pentacene-fused
porphyrins. While pentacene-fused Ni(II) porphyrin (AM6) demonstrated an abnormal ability to stabilize pentacene
with a half-life of >28.3 days, the half-life of the free base
and
Zn(II) counterparts were normal, similar to those of pentacene analogues.
This work provides important and useful information on guiding new
material designs
Unsymmetric Pentacene- and Pentacenequinone-Fused Porphyrins: Understanding the Effect of Cross- and Linear-Conjugation
No full textUnsymmetric pentacenequinone-fused (cross-conjugated)
and pentacene-fused
(linear-conjugated) porphyrins were designed and synthesized. The
cross-conjugated (AM1–AM3) and linear-conjugated (AM5–AM7) porphyrins displayed strikingly different sets of
optical and electronic properties, both of which are unusual and nontypical
of porphyrins. MCD, DFT, and TDDFT calculations suggest that multiple
charge transfer states exist in both π-conjugated systems, which
contributes to the complex absorption and MCD spectra of these molecular
systems. The general Gouterman’s four-orbital model used to
explain porphyrin spectroscopy led to contradicting theoretical and
experimental data, and is thus not applicable for these molecular
systems. The “2 + 4” and “3 + 3” active
spaces have been deduced and have proven effective to interpret the
absorption and MCD spectra of the pentacenequinone-fused (cross-conjugated)
and pentacene-fused (linear-conjugated) porphyrins, respectively.
Spectroelectrochemistry of AM5–AM7 revealed broad and
intense IR absorptions in the range of 1500–2500 nm, illustrating
the exceptional ability of these pentacene-fused systems to accommodate
positive charges. A pronounced metal effect was observed for pentacene-fused
porphyrins. While pentacene-fused Ni(II) porphyrin (AM6) demonstrated an abnormal ability to stabilize pentacene
with a half-life of >28.3 days, the half-life of the free base
and
Zn(II) counterparts were normal, similar to those of pentacene analogues.
This work provides important and useful information on guiding new
material designs
Unsymmetric Pentacene- and Pentacenequinone-Fused Porphyrins: Understanding the Effect of Cross- and Linear-Conjugation
No full textUnsymmetric pentacenequinone-fused (cross-conjugated)
and pentacene-fused
(linear-conjugated) porphyrins were designed and synthesized. The
cross-conjugated (AM1–AM3) and linear-conjugated (AM5–AM7) porphyrins displayed strikingly different sets of
optical and electronic properties, both of which are unusual and nontypical
of porphyrins. MCD, DFT, and TDDFT calculations suggest that multiple
charge transfer states exist in both π-conjugated systems, which
contributes to the complex absorption and MCD spectra of these molecular
systems. The general Gouterman’s four-orbital model used to
explain porphyrin spectroscopy led to contradicting theoretical and
experimental data, and is thus not applicable for these molecular
systems. The “2 + 4” and “3 + 3” active
spaces have been deduced and have proven effective to interpret the
absorption and MCD spectra of the pentacenequinone-fused (cross-conjugated)
and pentacene-fused (linear-conjugated) porphyrins, respectively.
Spectroelectrochemistry of AM5–AM7 revealed broad and
intense IR absorptions in the range of 1500–2500 nm, illustrating
the exceptional ability of these pentacene-fused systems to accommodate
positive charges. A pronounced metal effect was observed for pentacene-fused
porphyrins. While pentacene-fused Ni(II) porphyrin (AM6) demonstrated an abnormal ability to stabilize pentacene
with a half-life of >28.3 days, the half-life of the free base
and
Zn(II) counterparts were normal, similar to those of pentacene analogues.
This work provides important and useful information on guiding new
material designs
New Insight into an Old Problem: Analysis, Interpretation, and Theoretical Modeling of the Absorption and Magnetic Circular Dichroism Spectra of Monomeric and Dimeric Zinc Phthalocyanine Cation Radical
No full textThe
chemically or spectroelectrochemically generated formation and aggregation
of zinc(II) tetra-tert-butylphthalocyanine cation
radical [ZnPctBu]+•, which was highly
soluble in common organic solvents, were investigated using UV−vis
and magnetic circular dichroism (MCD) spectroscopies with an emphasis
on the influence of the axial ligand on the fingerprint (∼500
nm) and NIR (720∼1000 nm) spectral envelopes. MCD spectroscopy
is suggestive that the NIR band at ∼1000 nm observed for the
antiferromagnetically coupled cation radical dimer, [ZnPctBu]22+, has no degeneracy, the monomer–dimeric
equilibrium is temperature dependent, and higher degree aggregates
can be formed at specific conditions. Sixteen different exchange-correlation
functionals were tested to accurately predict the energies, intensities,
and profiles of the UV–vis and MCD spectra of the phthalocyanine
cation radical monomer and dimer. It was found that the M05 exchange-correlation
functional (along with several other functionals that include 27–42%
of Hartree–Fock exchange) provided an excellent agreement (∼0.1
eV for the degenerate excited states observed by MCD spectroscopy)
between theory and experiment for the phthalocyanine cation-radical
monomer and dimer. Not only did time-dependent density functional
theory (TDDFT) calculations with M05 exchange-correlation functional
correctly predict the nondegenerate NIR charge-transfer band at ∼1000
nm, all degenerate excited states, monomer and dimer energies, and
oscillator strengths, but also they correctly described the nature
of the experimentally observed at ∼500 nm MCD B-term (fingerprint band) detected for both the monomeric and dimeric
phthalocyanine cation radicals. The TDDFT data explain the similarities
in the UV–vis and MCD spectra of the monomeric and dimeric
species observed between the UV and fingerprint spectral envelopes
as well as correctly predicted the antiferromagnetic coupling between
the two singly oxidized phthalocyanine macrocycles in the dimer
Resolving a Half-Century-Long Controversy between (Magneto)optical and EPR Spectra of Single-Electron-Reduced [PcFe]<sup>−</sup>, [PcFeL]<sup>−</sup>, and [PcFeX]<sup>2–</sup> Complexes: Story of a Double Flip
No full textThe reduction of iron(II) phthalocyanine
(Pc(2−)FeII) or its bisaxially coordinated complexes
results in the formation
of the purple/red [PcFe]−, [PcFeL]−, and [PcFeX]2– (L is neutral and X is anionic
ligand) species. The X-ray structure of the [K(DME)4][PcFe]
complex exhibits a square-planar [PcFe]− anion. 1H NMR spectra of the reduced species have one or two phthalocyanine
broad peaks between 15 and 17 ppm. Solution magnetic moments are consistent
with the presence of a single unpaired electron. A solid-state Mössbauer
spectrum of [K(DME)4][PcFe] is consistent with an early
report [Taube, R. Pure Appl.
Chem.1974, 38, 427−438]. The solid-state EPR spectrum
of the [PcFe]− anion is close to that recorded by
Konarev et al. [Dalton Trans.2012, 41, 13841−13847]. Solution EPR spectra of reduced species
have axial symmetry (g⊥ ∼
2.08–2.17 and g|| ∼ 1.95–1.96)
and correlate well with spectra reported by Lever and Wilshire in
1978 [Inorg. Chem.1978, 17, 1145−1151]. The UV–vis spectra of pentacoordinated
[PcFeL]− and [PcFeX]2– anions
consist of the characteristic bands around 810, 690, and 515 nm. These
bands correlate well with the set of MCD pseudo A-terms and resemble transitions in the [Pc(3−)M]− and [Pc(3−)ML]− compounds. The UV–vis
and MCD spectra of [PcFeL]− and [PcFeX]2– complexes are in stark contrast to the crystallographically characterized
reference [Pc(2−)CoI]− anion,
which is EPR silent, has a regular diamagnetic 1H NMR spectrum,
and has an intense Q-band at 699 nm, which correlates well with the
strong MCD A-term. The DFT and TDDFT calculations
are suggestive of the iron(II) center in a (dxy)2(dxz,yz)3(dz2)1 (s = 1) electronic configuration
that is antiferromagnetically coupled with the one-electron-reduced
Pc(3−) ligand (i.e., [Pc(3−)FeII]−, [Pc(3−)FeIIL]−, and [Pc(3−)FeIIX]2–). The calculated EPR, Mössbauer,
and UV–vis spectra of [PcFe]−, [PcFeL]−, and [PcFeX]2– complexes are in
excellent agreement with the experimental data, thus resolving the
controversy between axial s = 1/2 like EPR and Pc(3−)-like
UV–vis spectra of these compounds
Role of MCD and Mössbauer Spectroscopy in the Explanation of the Properties of a Highly Soluble (μ-Oxo)bis[tetra(<i>tert</i>-butyl)(phthalocyaninato)iron(III)] Complex, Its Pyridine Adduct, and Redox Forms Oxidized under Anaerobic Conditions in Non-Coordinating Solvents
No full textSolid-state Mössbauer spectra of a highly soluble
(μ-oxo)bis[tetra(tert-butyl)(phthalocyaninato)iron(III)]
complex 1 ((PctBuFe)2O) consist of
two doublets that represent bent geometry in μ-oxo(1) (1a, ΔEQ = 0.43 mm/s, T = 10 K) and linear geometry in μ-oxo(2) (1b, ΔEQ = 1.40 mm/s, T = 10 K) isomers with the ratio between two isomers depending on
the purification method. Both isomers were found to be diamagnetic
and transform entirely to the 1a isomer in solution.
The room- and low-temperature magnetic circular dichroism (MCD) spectra
of 1a μ-oxo(1) show one Faraday A- and one B-term
between 670 and 720 nm, which correlate with the 690 nm band and 709
nm shoulder observed in the UV–vis spectrum of this compound.
UV–vis and MCD spectra of 1a are almost independent
of the temperature. Both 1a and 1b are diamagnetic
between room temperature and 4 K. Electrochemical experiments show
up to three oxidations and up to four reduction processes in 1a. Its oxidation under spectroelectrochemical or chemical
(in the absence of oxygen-containing oxidants) conditions in non-coordinating
solvents results in the formation of broad NIR bands around 1195 nm
(first oxidation) and 1264 nm (second oxidation). The MCD spectra
of the redox-active species show a Faraday B-term signal with negative
amplitude in this region and are very different from those in the
monomeric PctBu(1−)FeIIIX2 complexes 5X (X = Cl– or CF3CO2–). The pyridine
adduct of 1a ((PyPctBuFe)2O; 2Py) is paramagnetic (μB =
2.19, g = 2.11, and J = −6.1
cm–1) and has a major peak at 627 nm of its UV–vis
spectrum, which is associated with a MCD pseudo A-term. Density functional
theory (DFT) and time-dependent DFT (TDDFT) calculations, along with
the exciton coupling theory, were used to explain the unusually red-shifted
intense transitions in 1a as well as the H-aggregate-like
spectra of the pyridine adduct 2Py
Application of Levers EL Parameter Scale toward Fe(II)/Fe(III) versus Pc(2-)/Pc(1) Oxidation Process Crossover Point in Axially Coordinated Iron(II) Phthalocyanine Complexes
No full textThe electronic structures and, particularly,
the nature of the
HOMO in a series of PcFeL2, PcFeL′L″, and
[PcFeX2]2– complexes (Pc = phthalocyaninato(2-)
ligand; L = NH3, n-BuNH2, imidazole
(Im), pyridine (Py), PMe3, PBu3, t-BuNC, P(OBu)3, and DMSO; L′ = CO; L″ =
NH3 or n-BuNH2; X = NCO–, NCS–, CN–, imidazolate
(Im–), or 1,2,4-triazolate(Tz–)) were probed by electrochemical, spectroelectrochemical, and chemical
oxidation as well as theoretical (density functional theory, DFT)
studies. In general, energies of the metal-centered occupied orbitals
in various six-coordinate iron phthalocyanine complexes correlate
well with Lever Electrochemical Parameter EL and intercross the phthalocyanine-centered a1u orbital in several compounds with moderate-to-strong
π-accepting axial ligands. In these cases, an oxidation of the
phthalocyanine macrocycle (Pc(2-)/Pc(1-)) rather than the central
metal ion (Fe(II)/Fe(III)) was theoretically predicted and experimentally
confirmed
Reconstrucción de una teoría politológica, el Sufragio Activo Meritocrático
No full textA non-formal reconstruction of the theory of the meritocratic active suffrage is presented, which proposes the plural vote in local communities based on political merit, according to the prosociality of local political participation. The method is based on structuralist metatheory, adapted to the analysis of human science theories. The intratheoretical and intertheoreticalor networks of the theory were reconstructed, and a critique of it was made based on its adjustment to the social context. It is concluded that the analyzed theory is well founded, although it deserves adequate development for its operationalization and application.Se presenta una reconstrucción no formal de la teoría del Sufragio Activo Meritocrático, el cual consiste en la propuesta del voto plural en comunidades locales, con base en el mérito político, según la prosocialidad de la participación política local. El método se basa en la metateoría estructuralista, adaptada al análisis de teorías de ciencias humanas. Se reconstruyeron la red intrateórica e interteórica de la teoría, y se efectuó una crítica a ésta sobre la base de su ajuste al contexto social. Se concluye que la teoría analizada está bien fundamentada, aunque amerita de desarrollo adecuado para su operacionalización y aplicación
Reconstrucción de una teoría politológica, el Sufragio Activo Meritocrático
No full textA non-formal reconstruction of the theory of the meritocratic active suffrage is presented, which proposes the plural vote in local communities based on political merit, according to the prosociality of local political participation. The method is based on structuralist metatheory, adapted to the analysis of human science theories. The intratheoretical and intertheoreticalor networks of the theory were reconstructed, and a critique of it was made based on its adjustment to the social context. It is concluded that the analyzed theory is well founded, although it deserves adequate development for its operationalization and application.Se presenta una reconstrucción no formal de la teoría del Sufragio Activo Meritocrático, el cual consiste en la propuesta del voto plural en comunidades locales, con base en el mérito político, según la prosocialidad de la participación política local. El método se basa en la metateoría estructuralista, adaptada al análisis de teorías de ciencias humanas. Se reconstruyeron la red intrateórica e interteórica de la teoría, y se efectuó una crítica a ésta sobre la base de su ajuste al contexto social. Se concluye que la teoría analizada está bien fundamentada, aunque amerita de desarrollo adecuado para su operacionalización y aplicación
