8 research outputs found
Conditional Extremes in Asymmetric Financial Markets
<p>The global financial crisis of 2007ā2009 revealed the great extent to which systemic risk can jeopardize the stability of the entire financial system. An effective methodology to quantify systemic risk is at the heart of the process of identifying the so-called systemically important financial institutions for regulatory purposes as well as to investigate key drivers of systemic contagion. The article proposes a method for dynamic forecasting of CoVaR, a popular measure of systemic risk. As a first step, we develop a semi-parametric framework using asymptotic results in the spirit of extreme value theory (EVT) to model the conditional probability distribution of a bivariate random vector given that one of the components takes on a large value, taking into account important features of financial data such as asymmetry and heavy tails. In the second step, we embed the proposed EVT method into a dynamic framework via a bivariate GARCH process. An empirical analysis is conducted to demonstrate and compare the performance of the proposed methodology relative to a very flexible fully parametric alternative.</p
Ī²āDiketiminate Germylene-Supported Pentafluorophenylcopper(I) and -silver(I) Complexes [LGe(Me)(CuC<sub>6</sub>F<sub>5</sub>)<sub><i>n</i></sub>]<sub>2</sub> (<i>n</i> = 1, 2), LGe[C(SiMe<sub>3</sub>)N<sub>2</sub>]AgC<sub>6</sub>F<sub>5</sub>, and {LGe[C(SiMe<sub>3</sub>)N<sub>2</sub>](AgC<sub>6</sub>F<sub>5</sub>)<sub>2</sub>}<sub>2</sub> (L = HC[C(Me)N-2,6ā<i>i</i>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>]<sub>2</sub>): Synthesis and Structural Characterization
Reactions of LGeMe (L = HCĀ[CĀ(Me)ĀN-2,6-<i>i</i>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>]<sub>2</sub>) with 0.25
or 0.5
equiv of (CuC<sub>6</sub>F<sub>5</sub>)<sub>4</sub> gave the products
[LGeĀ(Me)ĀCuC<sub>6</sub>F<sub>5</sub>]<sub>2</sub> (<b>1</b>)
and [LGeĀ(Me)Ā(CuC<sub>6</sub>F<sub>5</sub>)<sub>2</sub>]<sub>2</sub> (<b>2</b>), respectively. In situ formed <b>1</b> reacted
with 0.5 equiv of (CuC<sub>6</sub>F<sub>5</sub>)<sub>4</sub> to give <b>2</b> on the basis of NMR (<sup>1</sup>H and <sup>19</sup>F) spectral
measurements. Conversely, <b>2</b> was converted into <b>1</b> by treatment with 2 equiv of LGeMe. Reactions of LGeCĀ(SiMe<sub>3</sub>)ĀN<sub>2</sub> with 1 or 2 equiv of AgC<sub>6</sub>F<sub>5</sub>Ā·MeCN produced the corresponding compounds LGeĀ[CĀ(SiMe<sub>3</sub>)ĀN<sub>2</sub>]ĀAgC<sub>6</sub>F<sub>5</sub> (<b>3</b>) and
{LGeĀ[CĀ(SiMe<sub>3</sub>)ĀN<sub>2</sub>]Ā(AgC<sub>6</sub>F<sub>5</sub>)<sub>2</sub>}<sub>2</sub> (<b>4</b>). Similarly, <b>3</b> was converted into <b>4</b> by treatment with 1 equiv of AgC<sub>6</sub>F<sub>5</sub>Ā·MeCN and <b>4</b> converted into <b>3</b> by reaction with 2 equiv of LGeCĀ(SiMe<sub>3</sub>)ĀN<sub>2</sub>. X-ray crystallographic studies showed that <b>1</b> contains a rhombically bridged (CuC<sub>6</sub>F<sub>5</sub>)<sub>2</sub>, while <b>2</b> has a chain-structurally aggregated
(CuC<sub>6</sub>F<sub>5</sub>)<sub>4</sub>, both supported by LGeMe.
Correspondingly, <b>3</b> showed a terminally bound AgC<sub>6</sub>F<sub>5</sub> and <b>4</b> a chain-structurally aggregated
(AgC<sub>6</sub>F<sub>5</sub>)<sub>4</sub>, both supported by LGeCĀ(SiMe<sub>3</sub>)ĀN<sub>2</sub>. Photophysical studies proved that the GeāCu
metalāmetalloid donorāacceptor bonding persists in solutions
of <b>1</b> and <b>2</b> and GeāAg donorāacceptor
bonding in solutions of <b>3</b> and <b>4</b> as a result
of the clear migration of their emission bands compared to those of
the corresponding starting materials. Low-temperature (ā50
Ā°C) <sup>19</sup>F NMR spectral measurements detected dissociation
of <b>1</b>, <b>2</b>, and <b>4</b> by the aggregation
part of the CuC<sub>6</sub>F<sub>5</sub> or AgC<sub>6</sub>F<sub>5</sub> entities in solution. These results provide good support for pentafluorophenylcopperĀ(I)
or -silverĀ(I) species having Ī²-diketiminate germylene as a donor
because of its remarkably electronic and steric character
Ī²āDiketiminate Germylene-Supported Pentafluorophenylcopper(I) and -silver(I) Complexes [LGe(Me)(CuC<sub>6</sub>F<sub>5</sub>)<sub><i>n</i></sub>]<sub>2</sub> (<i>n</i> = 1, 2), LGe[C(SiMe<sub>3</sub>)N<sub>2</sub>]AgC<sub>6</sub>F<sub>5</sub>, and {LGe[C(SiMe<sub>3</sub>)N<sub>2</sub>](AgC<sub>6</sub>F<sub>5</sub>)<sub>2</sub>}<sub>2</sub> (L = HC[C(Me)N-2,6ā<i>i</i>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>]<sub>2</sub>): Synthesis and Structural Characterization
Reactions of LGeMe (L = HCĀ[CĀ(Me)ĀN-2,6-<i>i</i>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>]<sub>2</sub>) with 0.25
or 0.5
equiv of (CuC<sub>6</sub>F<sub>5</sub>)<sub>4</sub> gave the products
[LGeĀ(Me)ĀCuC<sub>6</sub>F<sub>5</sub>]<sub>2</sub> (<b>1</b>)
and [LGeĀ(Me)Ā(CuC<sub>6</sub>F<sub>5</sub>)<sub>2</sub>]<sub>2</sub> (<b>2</b>), respectively. In situ formed <b>1</b> reacted
with 0.5 equiv of (CuC<sub>6</sub>F<sub>5</sub>)<sub>4</sub> to give <b>2</b> on the basis of NMR (<sup>1</sup>H and <sup>19</sup>F) spectral
measurements. Conversely, <b>2</b> was converted into <b>1</b> by treatment with 2 equiv of LGeMe. Reactions of LGeCĀ(SiMe<sub>3</sub>)ĀN<sub>2</sub> with 1 or 2 equiv of AgC<sub>6</sub>F<sub>5</sub>Ā·MeCN produced the corresponding compounds LGeĀ[CĀ(SiMe<sub>3</sub>)ĀN<sub>2</sub>]ĀAgC<sub>6</sub>F<sub>5</sub> (<b>3</b>) and
{LGeĀ[CĀ(SiMe<sub>3</sub>)ĀN<sub>2</sub>]Ā(AgC<sub>6</sub>F<sub>5</sub>)<sub>2</sub>}<sub>2</sub> (<b>4</b>). Similarly, <b>3</b> was converted into <b>4</b> by treatment with 1 equiv of AgC<sub>6</sub>F<sub>5</sub>Ā·MeCN and <b>4</b> converted into <b>3</b> by reaction with 2 equiv of LGeCĀ(SiMe<sub>3</sub>)ĀN<sub>2</sub>. X-ray crystallographic studies showed that <b>1</b> contains a rhombically bridged (CuC<sub>6</sub>F<sub>5</sub>)<sub>2</sub>, while <b>2</b> has a chain-structurally aggregated
(CuC<sub>6</sub>F<sub>5</sub>)<sub>4</sub>, both supported by LGeMe.
Correspondingly, <b>3</b> showed a terminally bound AgC<sub>6</sub>F<sub>5</sub> and <b>4</b> a chain-structurally aggregated
(AgC<sub>6</sub>F<sub>5</sub>)<sub>4</sub>, both supported by LGeCĀ(SiMe<sub>3</sub>)ĀN<sub>2</sub>. Photophysical studies proved that the GeāCu
metalāmetalloid donorāacceptor bonding persists in solutions
of <b>1</b> and <b>2</b> and GeāAg donorāacceptor
bonding in solutions of <b>3</b> and <b>4</b> as a result
of the clear migration of their emission bands compared to those of
the corresponding starting materials. Low-temperature (ā50
Ā°C) <sup>19</sup>F NMR spectral measurements detected dissociation
of <b>1</b>, <b>2</b>, and <b>4</b> by the aggregation
part of the CuC<sub>6</sub>F<sub>5</sub> or AgC<sub>6</sub>F<sub>5</sub> entities in solution. These results provide good support for pentafluorophenylcopperĀ(I)
or -silverĀ(I) species having Ī²-diketiminate germylene as a donor
because of its remarkably electronic and steric character
Reactivity Studies of (Phenylethynyl)germylene LGeCī¼CPh (L = HC[C(Me)N-2,6ā<i>i</i>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>]<sub>2</sub>) toward Pentafluorophenylcopper(I), -silver(I), and -gold(I) Complexes
Reactions of (phenylethynyl)Āgermylene LGeCī¼CPh
(L = HCĀ[CĀ(Me)ĀN-2,6-<i>i</i>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>]<sub>2</sub>)
with 0.25 equiv of (CuC<sub>6</sub>F<sub>5</sub>)<sub>4</sub>, 1 equiv
of AgC<sub>6</sub>F<sub>5</sub>Ā·MeCN, and 1 equiv of AuC<sub>6</sub>F<sub>5</sub>Ā·SC<sub>4</sub>H<sub>8</sub>, respectively,
yielded LGeĀ(Cī¼CPh)ĀCuC<sub>6</sub>F<sub>5</sub> (<b>1</b>), [(LGeCī¼CPh)<sub>2</sub>Ag]<sup>+</sup>[AgĀ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>]<sup>ā</sup> (<b>2</b>),
and LGeĀ(Cī¼CPh)ĀAuC<sub>6</sub>F<sub>5</sub> (<b>3</b>).
Complexes <b>1</b>ā<b>3</b> were characterized
by IR and NMR spectroscopy and X-ray crystallography. Compound <b>1</b> shows a bonding pattern of the CuC<sub>6</sub>F<sub>5</sub> entity by both the phenylethynyl Cī¼C linkage and the L ligand
backbone of the Ī³-C atom, while <b>3</b> exhibits a bonding
mode of the AuC<sub>6</sub>F<sub>5</sub> entity at the germylene center.
Compound <b>2</b> is an ionic derivative featuring the GeāAg
donorāacceptor bond formed under redistribution of the AgC<sub>6</sub>F<sub>5</sub> entity. Further reactions of <b>1</b> with
(CuC<sub>6</sub>F<sub>5</sub>)<sub>4</sub>, AgC<sub>6</sub>F<sub>5</sub>Ā·MeCN, and AuC<sub>6</sub>F<sub>5</sub>Ā·SC<sub>4</sub>H<sub>8</sub> afforded the complexes LGeĀ(Cī¼CPh)Ā(CuC<sub>6</sub>F<sub>5</sub>)Ā(MC<sub>6</sub>F<sub>5</sub>) (M = Cu (<b>4</b>), Ag
(<b>5</b>), Au (<b>6</b>)). Compounds <b>4</b>ā<b>6</b> were characterized by IR and NMR spectroscopy, and <b>5</b> and <b>6</b> were further investigated by X-ray crystallography.
Compounds <b>4</b>ā<b>6</b> all show an additional
bonding of the respective MC<sub>6</sub>F<sub>5</sub> moiety at the
germylene center of <b>1</b>. These studies reveal a multiple
donor reactivity of LGeCī¼CPh. The slightly different Lewis
acidic properties of the congeneric pentafluorophenylcopperĀ(I), -silverĀ(I),
and -goldĀ(I) complexes as acceptors are thus disclosed
Reactivity Studies of (Phenylethynyl)germylene LGeCī¼CPh (L = HC[C(Me)N-2,6ā<i>i</i>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>]<sub>2</sub>) toward Pentafluorophenylcopper(I), -silver(I), and -gold(I) Complexes
Reactions of (phenylethynyl)Āgermylene LGeCī¼CPh
(L = HCĀ[CĀ(Me)ĀN-2,6-<i>i</i>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>]<sub>2</sub>)
with 0.25 equiv of (CuC<sub>6</sub>F<sub>5</sub>)<sub>4</sub>, 1 equiv
of AgC<sub>6</sub>F<sub>5</sub>Ā·MeCN, and 1 equiv of AuC<sub>6</sub>F<sub>5</sub>Ā·SC<sub>4</sub>H<sub>8</sub>, respectively,
yielded LGeĀ(Cī¼CPh)ĀCuC<sub>6</sub>F<sub>5</sub> (<b>1</b>), [(LGeCī¼CPh)<sub>2</sub>Ag]<sup>+</sup>[AgĀ(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>]<sup>ā</sup> (<b>2</b>),
and LGeĀ(Cī¼CPh)ĀAuC<sub>6</sub>F<sub>5</sub> (<b>3</b>).
Complexes <b>1</b>ā<b>3</b> were characterized
by IR and NMR spectroscopy and X-ray crystallography. Compound <b>1</b> shows a bonding pattern of the CuC<sub>6</sub>F<sub>5</sub> entity by both the phenylethynyl Cī¼C linkage and the L ligand
backbone of the Ī³-C atom, while <b>3</b> exhibits a bonding
mode of the AuC<sub>6</sub>F<sub>5</sub> entity at the germylene center.
Compound <b>2</b> is an ionic derivative featuring the GeāAg
donorāacceptor bond formed under redistribution of the AgC<sub>6</sub>F<sub>5</sub> entity. Further reactions of <b>1</b> with
(CuC<sub>6</sub>F<sub>5</sub>)<sub>4</sub>, AgC<sub>6</sub>F<sub>5</sub>Ā·MeCN, and AuC<sub>6</sub>F<sub>5</sub>Ā·SC<sub>4</sub>H<sub>8</sub> afforded the complexes LGeĀ(Cī¼CPh)Ā(CuC<sub>6</sub>F<sub>5</sub>)Ā(MC<sub>6</sub>F<sub>5</sub>) (M = Cu (<b>4</b>), Ag
(<b>5</b>), Au (<b>6</b>)). Compounds <b>4</b>ā<b>6</b> were characterized by IR and NMR spectroscopy, and <b>5</b> and <b>6</b> were further investigated by X-ray crystallography.
Compounds <b>4</b>ā<b>6</b> all show an additional
bonding of the respective MC<sub>6</sub>F<sub>5</sub> moiety at the
germylene center of <b>1</b>. These studies reveal a multiple
donor reactivity of LGeCī¼CPh. The slightly different Lewis
acidic properties of the congeneric pentafluorophenylcopperĀ(I), -silverĀ(I),
and -goldĀ(I) complexes as acceptors are thus disclosed
Determining the Conformational Landscape of Ļ and Ļ Coupling Using <i>para</i>-Phenylene and āAviramāRatnerā Bridges
The
torsional dependence of donorābridgeāacceptor
(DāBāA) electronic coupling matrix elements (<i><b>H</b></i><sub><i><b>DA</b></i></sub>, determined from the magnetic exchange coupling, <i><b>J</b></i>) involving a spin S<sub>D</sub> = 1/2 metal semiquinone
(Zn-<b>SQ</b>) donor and a spin S<sub>A</sub> = 1/2 nitronylnitroxide
(<b>NN</b>) acceptor mediated by the Ļ/Ļ-systems
of <i>para</i>-phenylene and methyl-substituted <i>para</i>-phenylene bridges and by the Ļ-system of a bicyclo[2.2.2]Āoctane
(<b>BCO</b>) bridge are presented and discussed. The positions
of methyl group(s) on the phenylene bridge allow for an experimentally
determined evaluation of conformationally dependent (Ļ) and
conformationally independent (Ļ) contributions to the electronic
and magnetic exchange couplings in these DāBāA biradicals
at parity of D and A. The trend in the experimental magnetic exchange
couplings are well described by CASSCF calculations. The torsional
dependence of the pairwise exchange interactions are further illuminated
in three-dimensional, āRamachandran-typeā plots that
relate DāB and BāA torsions to both electronic and exchange
couplings. Analysis of the magnetic data shows large variations in
magnetic exchange (<i><b>J</b></i> ā 1ā175
cm<sup>ā1</sup>) and electronic coupling (<i><b>H</b></i><sub><i><b>DA</b></i></sub> ā 450ā6000
cm<sup>ā1</sup>) as a function of bridge conformation relative
to the donor and acceptor. This has allowed for an experimental determination
of both the Ļ- and Ļ-orbital contributions to the exchange
and electronic couplings
Determining the Conformational Landscape of Ļ and Ļ Coupling Using <i>para</i>-Phenylene and āAviramāRatnerā Bridges
The
torsional dependence of donorābridgeāacceptor
(DāBāA) electronic coupling matrix elements (<i><b>H</b></i><sub><i><b>DA</b></i></sub>, determined from the magnetic exchange coupling, <i><b>J</b></i>) involving a spin S<sub>D</sub> = 1/2 metal semiquinone
(Zn-<b>SQ</b>) donor and a spin S<sub>A</sub> = 1/2 nitronylnitroxide
(<b>NN</b>) acceptor mediated by the Ļ/Ļ-systems
of <i>para</i>-phenylene and methyl-substituted <i>para</i>-phenylene bridges and by the Ļ-system of a bicyclo[2.2.2]Āoctane
(<b>BCO</b>) bridge are presented and discussed. The positions
of methyl group(s) on the phenylene bridge allow for an experimentally
determined evaluation of conformationally dependent (Ļ) and
conformationally independent (Ļ) contributions to the electronic
and magnetic exchange couplings in these DāBāA biradicals
at parity of D and A. The trend in the experimental magnetic exchange
couplings are well described by CASSCF calculations. The torsional
dependence of the pairwise exchange interactions are further illuminated
in three-dimensional, āRamachandran-typeā plots that
relate DāB and BāA torsions to both electronic and exchange
couplings. Analysis of the magnetic data shows large variations in
magnetic exchange (<i><b>J</b></i> ā 1ā175
cm<sup>ā1</sup>) and electronic coupling (<i><b>H</b></i><sub><i><b>DA</b></i></sub> ā 450ā6000
cm<sup>ā1</sup>) as a function of bridge conformation relative
to the donor and acceptor. This has allowed for an experimental determination
of both the Ļ- and Ļ-orbital contributions to the exchange
and electronic couplings
Water-Soluble Polythiophene for Two-Photon Excitation Fluorescence Imaging and Photodynamic Therapy of Cancer
Positively
charged water-soluble polythiophene (<b>PT0</b>) that could
self-assemble into nanoparticles in pure water solution was designed
and synthesized. <b>PT0</b> exhibited high photostabilities
and pH stabilities, excellent biocompatibility, strong <sup>1</sup>O<sub>2</sub> generation capability, and large two-photon absorption
cross sections. Moreover, we showed that the fluorescence of <b>PT0</b> was unaffected by the interference of biomolecules and
metal ions. As an example application, <b>PT0</b> was demonstrated
to be capable of simultaneous cell imaging and photodynamic therapy
under either one-photon or two-photon excitation modes