327,427 research outputs found
Bis-Spiro-Oxetane and Bis-Spiro-Tetrahydrofuran Pyrroline Nitroxide Radicals: Synthesis and Electron Spin Relaxation Studies
No full textSynthesis of bis-spiro-oxetane and
bis-spiro-tetrahydrofuran pyrroline
nitroxide radicals relies on the Mitsunobu reaction-mediated double
cyclizations of N-Boc protected pyrroline tetraols.
Structures of the nitroxide radicals are supported by X-ray crystallography.
In a trehalose/sucrose matrix at room temperature, the bis-spiro-oxetane
nitroxide radical possesses electron spin coherence time, Tm ≈ 0.7 μs. The observed enhanced Tm is most likely associated with strong hydrogen
bonding of oxetane moieties to the trehalose/sucrose matrix
Governor Spiro T. Agnew's press conference and signing of the Convention Bill and Miscegenation Bill, March 15, 1967
No full textGovernor Spiro T. Agnew's press conference on pay increases for executive employees, changes to the Maryland correctional system, the harbor tunnel, and crime rates, March 15, 1967. In addition, Governor Spiro T. Agnew makes a speech on the signing of the Convention Bill, which outlines the procedures for a new Maryland constitution to be written. Governor John Tawes and William S. James also speak on the passing of the bill. Lastly, Governor Spiro T. Agnew makes a statement before signing the Miscegenation Bill, which removed restrictions on inter-racial marriages
Spiro-Linked Ter-, Penta-, and Heptafluorenes as Novel Amorphous Materials for Blue Light Emission
No full textA series of spiro-linked oligofluorenes were synthesized that exhibit blue emission with
photoluminescence quantum yields in some cases exceeding 0.50 in neat spin-coated films.
Differential scanning calorimetry revealed highly variable glass transition temperatures. A
longer conjugation length is desired for better stability against thermally activated
crystallization, and a shorter pendant is desired for a higher glass transition temperature
at a given conjugation length. In contrast to poly(2,7-(9,9-di-n-octylfluorene)), prolonged
heating of spiro-oligo(fluorene) films resulted in no changes in morphology, emissive color,
and photoluminescence quantum yield. The propensity of spiro-oligo(fluorene)s to thermally
activated crystallization was rationalized with molecular shapes predicted by molecular
mechanics simulations
Spiro-Fluorene-Containing Cyclic Olefin Polymers
No full textFor application to optical polymer materials with a high
refractive
index and low birefringence as well as high thermal stability and
low hygroscopicity, we have performed the ring-opening metathesis
(co)polymerization (ROMP, ROMCP) of fluorene-based norbornene (NB)
monomers, spiro[fluorene-9,4′-tricyclo[5.2.1.02,6]dec-8-en] (endo-1 and exo-1) and subsequent hydrogenation to produce spiro-fluorene-containing
cyclic olefin polymers. The living ROMP and the kinetics of the ROMCP
with NB were investigated. A series of hydrogenated endo- and exo-isomeric polymers, H-poly(1) and H-poly(1-co-NB), with random,
gradient, and block sequences, were synthesized and characterized.
They are highly soluble in common organic solvents due to their large
fractional free volume, as indicated by broad X-ray diffraction patterns.
The glass-transition temperatures (Tg)
of H-poly(1-co-NB) significantly increased
with the content of 1 up to 273 °C [H-poly(endo-1)]. The endo-isomeric
polymers exhibited significantly higher Tg values and slightly lower solubility than their exo-counterparts, probably because of the slightly smaller fractional
free volume of the endo-isomers. The refractive indexes
of H-poly(1)s are as high as 1.61, and the stress-optical
coefficients in the rubbery state (CR)
of H-poly(1-co-NB) are less than zero.
These low birefringences and large fractional free volumes are derived
from the bulky spiro-fluorene moiety oriented vertically to the polymer
main chain
Vice President Spiro T. Agnew's speech at the American Farm Bureau Inc. (AFBI) meeting, Washington, D.C., circa December 1969
No full textVice President Spiro T. Agnew's speech at the American Farm Bureau Inc. (AFBI) meeting in the International Ballroom at the Washington Hilton Hotel, Washington, D.C., circa December 1969. Vice President Agnew speaks on Senator Albert Gore, Sr.'s amendment on farm subsidies, and addresses how the federal government will help solve the many problems farmers face
Spiro-Bifluorene-Cored Dopant-Free Conjugated Polymeric Hole-Transporting Materials Containing Passivation Parts for Inverted Perovskite Solar Cells
No full textTwo spiro-bifluorene-based dopant-free HTMs (X22 and
X23) have
been synthesized by facilely condensing spiro-bifluorene diamine with
3,4-ethylenedioxythiophene (EDOT)-5,7-dicarbonyl dichloride and 2,3,5,6-tetrafluoro-terephthaloyl
dichloride, respectively. In the X22 molecule, lone pairs of electrons
on the sulfur (S) and oxygen (O) functional groups interact with the
perovskite materials. The hole mobility (μh) of X22
(3.9 × 10–4 cm2 V–1 S1–) is more than twice that of X23 (1.4 ×
10–4 cm2 V–1 S1–). The conductivity (σ0) of X22 is
2.73 × 10–4 S cm–1, which
is also higher than that of X23 (2.39 × 10–4 S cm–1). The EDOT moiety benefits the contact
angle of CH3NH3PbI3 precursor solutions
on HTMs as low as 24°. The X22-based device with an indium-doped
tin oxide/hole transport material (HTM)/CH3NH3PbI3/phenyl-C61-butyric acid methyl ester (PC61BM)/bathocuproine/Ag structure achieves a power conversion
efficiency (PCE) of 19.18%. The PCE of the device based on X23 containing
fluorine is 18.70%, and the contact angle between HTM and the perovskite
precursor solution is 32°. The X22- and X23-based devices at
ambient temperature (≈25 °C) in N2 retain 86%
and 79% of the initial PCE after 150 days. The effect of S, O, and
F heteroatoms plays an important role in the side chain modification
of HTMs, improving defect passivation in HTM/CH3NH3PbI3 interfaces by multiple functional groups
Eversive Maps of Bounded Convex Domains in â„‚n+1
No full textA duality principle, relating the geometry of the Kobayashi metric with the CR geometry of the boundaries of smoothly bounded, strongly convex domains in â„‚n+1, is established. A characterization of the holomorphic Jacobi vector fields of those domains is also given
Construction, Characterization, and Properties of Poly(iminofuran-spiro-oxindole)s through Catalyst-Free Multicomponent Spiropolymerization of Diisocyanides, Activated Alkynes, and Bis-isatins
No full textSpiropolymers built from monomers without spirocyclic
structures
have garnered significant academic interest and hold substantial technological
value. However, their construction still remains a challenging project,
primarily due to limited polymerization methods. Herein, we introduce
a novel multicomponent spiropolymerization for synthesizing poly(iminofuran-spiro-oxindole)s
from diisocyanides, activated alkynes, and bis-isatins without the
use of catalyst, even under mild conditions. The common natural product
isatin, a vital feedstock in the dye industry and pharmaceutical fields,
has been elegantly and rationally employed to construct spiropolymers.
The resultant spiropolymers demonstrate favorable solubility, excellent
thermal stability, satisfactory isolated yields (up to 92.6%), and
high molecular weights (up to 56800 g/mol). The experimental data
and theoretical calculations reveal that only the carbonyl group located
at position 3 of isatin is involved in the formation of spiropolymers.
Notably, despite lacking conventional fluorophores, the prepared poly(iminofuran-spiro-oxindole)
displays both clusterization-triggered emission and aggregation-enhanced
emission properties. Intriguingly, the photoluminescence can be quenched
by both ferrous and ferric ions efficiently in an organic solution
and only ferric ions exclusively in an organic/water mixture. It is
highly anticipated that this instructive work will open a new avenue
of spiropolymer construction and contribute to expanding diverse applications
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