12 research outputs found
NCN Pincer–Pt Complexes Coordinated by (Nitronyl Nitroxide)-2-ide Radical Anion
New pincer–Pt complexes coordinated by (nitronyl
nitroxide)-2-ide
radical anion were prepared as stable compounds in high yields. The
structures of these Pt complexes and the oxidized complexes were unequivocally
determined by spectral and crystal structure analyses. The oxidation
potential of the nitronyl nitroxide moiety in these complexes was
shifted in the negative direction by ∼0.6 V as a result of
coordination to the PtÂ(II) atom
NCN Pincer–Pt Complexes Coordinated by (Nitronyl Nitroxide)-2-ide Radical Anion
New pincer–Pt complexes coordinated by (nitronyl
nitroxide)-2-ide
radical anion were prepared as stable compounds in high yields. The
structures of these Pt complexes and the oxidized complexes were unequivocally
determined by spectral and crystal structure analyses. The oxidation
potential of the nitronyl nitroxide moiety in these complexes was
shifted in the negative direction by ∼0.6 V as a result of
coordination to the PtÂ(II) atom
Trimeric Assembly of Dendritic Light-Harvesting Antenna with Two Kinds of Porphyrin Cores
A trimeric assembly of light-harvesting
antennas was prepared using
a copper-catalyzed Hüisgen 1,3-dipolar cycloaddition reaction
between a dendrimer having a zinc diethynyldiphenylporphyrin core
(ZnDEDPP) with two azide terminals and two equivalents of dendrimers
having a zinc tetraphenylporphyrin core (ZnTPP) with one ethynyl terminal.
The absorptions of the trimer appear in a longer-wavelength region
compared to monomeric references in toluene; however, there is almost
no shift in wavelength in 1,1,2,2-tetrachloroethane (TCE). Fluorescence
spectra of the trimer show that the singlet energy transfer from ZnTPP
to ZnDEDPP takes place more effectively in toluene than in TCE. These
absorption and fluorescence studies are compatible with solvent-dependent
conformation; the extended forms of the trimers are favored by solvation
in polar TCE, and the folded conformation is stabilized by the attractive
van der Waals and dipole–dipole interactions between the dendritic
chains in nonpolar toluene
2,11-Dibromo-13,14-dimesityl-5,8-dioxapentaphene: A Stable and Twisted Polycyclic System Containing the <i>o</i>‑Quinodimethane Skeleton
A stable <i>o</i>-quinodimethane
(<i>o</i>QDM)
derivative, 2,11-dibromo-13,14-dimesityl-5,8-dioxapentaphene (<b>3</b>) was synthesized, and its structure and properties were
investigated. The X-ray structural analysis showed a significantly
twisted π-framework and a clear bond-length alternation in the
central <i>o</i>QDM skeleton. Owing to the quinoidal conjugation, <b>3</b> exhibited a broad absorption band in the visible region
(up to 700 nm) and amphoteric redox behavior. Furthermore, radical
cation <b>3</b><sup>•+</sup> was isolated, and its electronic
structure was elucidated by spectroscopic measurements
Jonas Dryander to James Edward Smith
Believes Smith is right to include an index of the genera for "Flora Britannica" but that the English index should be at the end and approves of the title. [John] Sibthorp's plants have now been laid out in the herbarium
NCN Pincer–Pt Complexes Coordinated by (Nitronyl Nitroxide)-2-ide Radical Anion
New pincer–Pt complexes coordinated by (nitronyl
nitroxide)-2-ide
radical anion were prepared as stable compounds in high yields. The
structures of these Pt complexes and the oxidized complexes were unequivocally
determined by spectral and crystal structure analyses. The oxidation
potential of the nitronyl nitroxide moiety in these complexes was
shifted in the negative direction by ∼0.6 V as a result of
coordination to the PtÂ(II) atom
Construction of Snowflake-Shaped Dendritic Covalent Assemblies with Rigid Conjugated Networks
A convergent method for the construction of shape-persistent
nanoscale
assemblies with conjugated backbones was developed. The copper-free
Sonogashira coupling reaction was successfully applied to the formation
of multiple covalent connections between conjugated terminals (iodide
substituted aryl groups) of AB<sub>2</sub>-type outer components and
four conjugated terminals (acetylenic bonds) of an inner A<sub>4</sub>-type core dendrimer. The conjugated networks in the starting components
are expanded during the assembly process to afford nanoscale dendritic
conjugated networks of the type A<sub>4</sub>(AB<sub>2</sub>)<sub>4</sub>, which have a porphyrin core, and longer (3.9 or 4.5 nm)
and shorter (1.6 nm) conjugated chains. Fluorescence measurements
revealed that singlet energy is effectively transferred in the assemblies
from peripheral benzyl ether units and conjugated chains to the free
base porphyrin core
Synthesis and Higher-Order Structure of Linear Dendrimeric Assemblies
A series of linear covalent assemblies
of dendrimers with conjugated
backbones were synthesized by means of an iterative divergent and
convergent method in which copper-catalyzed acetylene–azide
cycloaddition reactions were used to form flexible linkages. UV–vis
and fluorescence spectra indicate that dendrimeric assemblies have
a strong propensity to adopt folded conformations in which conjugated
backbones adopt planar conformations. The folded conformation is stabilized
by strong attractive van der Waals and dipole–dipole interactions
between the dendrimers
Magnetic Control of the Charge-Separated State Lifetime Realized by Covalent Attachment of a Platinum Complex
Dynamics of the photogenerated charge-separated
(CS) state is studied for a newly synthesized molecular triad, in
which the donor (D) dimethoxytriphenylamine, 1,3-bisÂ(2-pyridylimino)Âisoindolate
platinum (BPIPt), and the acceptor (A) naphthaldiimide are linked
with a triethynylbenzene unit (BPIPt–DA). Photoexcitation of
BPIPt gives rise to generation of a long-lived (∼4 μs)
CS state BPIPt–D<sup>+</sup>A<sup>–</sup>, of which
the lifetime is considerably increased by an applied magnetic field
of 270 mT. The positive magnetic field effect (MFE) is in contrast
to the negative MFE for the reference DA molecule, which indicates
successful switching of the initial spin state of the CS state from
singlet to triplet. Simulations of the MFE and time-resolved electron
paramagnetic resonance show that spin-selective charge recombination
and spin relaxation are unaffected by attachment of BPIPt. The minimum
impact of heavy atom substitution on the electronic and magnetic properties
has been realized by the small electronic coupling mediated by the
rigid <i>meta</i>-triethynylbenzene
Very Long-Lived Photoinduced Charge-Separated States of Triphenylamine–Naphthalenediimide Dyads in Polymer Matrices
Photoinduced
electron transfer was studied in dyads (<b>dyad1</b> and <b>dyad2</b>) containing triphenylamine (MTA) and naphthalenediimide
(MNDI) linked with oligoÂ(phenyleneÂethynylene) dispersed in rigid
polymer matrices of polystyrene (PS), polyÂ(vinyl chloride), and polyÂ(methyl
methacrylate). Photoexcitation of these dyads yielded long-lived charge-separated
(CS) states involving MTA<sup>+</sup> and MNDI<sup><b>–</b></sup>. The quantum yields of charge separation in <b>dyad1</b> and <b>dyad2</b> were approximately 0.4 and 0.3, respectively,
in the polymer matrices. The CS lifetime for <b>dyad2</b> in
PS was longer (400 ms) than those in polyÂ(vinyl chloride) (120 ms)
and polyÂ(methyl methacrylate) (65 ms) at 298 K. In addition, CS state
had a very long lifetime of 5.4 s in glassy toluene at 100 K. Below
glass transition temperatures, polymer side chain motions with various
relaxation rates should affect the charge recombination processes.
The energy gap (Δ<i>G</i>) and outer-sphere reorganization
energy (λ) in the charge recombination process were estimated
using a slow-frequency component for dielectric constants. By use
of Δ<i>G</i> and λ values, the matrix dependence
of the CS lifetimes was successfully rationalized based on Marcus
theory, and the charge recombination process in PS with low polarity
and high polarizability should be in a deeper inverted region than
the other polymer matrices. It also suggested that the rigidity of
the polymer effectively suppressed intramolecular motions promoting
the charge recombination process