4 research outputs found
Carbon Cationic Relay via Superelectrophiles: Synthesis of Spiro‑diazafluorenes
Superelectrophilic-initiated
carbon cationic relay reactions of
diazafluorenones with phenols were developed to provide strategically
novel and atom-economic access to spirodiazafluorenes via tandem Friedel–Crafts
reaction, nucleophilic addition, and intramolecular cyclization sequences.
A range of spirodiazafluorenes that are difficult to synthesize with
traditional protocols has been constructed successfully in middle
to high yields using this method
Structure–Property Study on Two New D–A Type Materials Comprising Pyridazine Moiety and the OLED Application as Host
In
this paper, two new pyridazine based donor–acceptor type
materials, i.e., 3CzPyaPy: 9,9′-(3-(6-(9H-carbazol-9-yl)Âpyridazin-3-yl)Âpyridine-2,6-diyl)ÂbisÂ(9H-carbazole)
and 4CzPyPyaPy: 3,6-bisÂ(2,6-diÂ(9H-carbazol-9-yl)Âpyridin-3-yl)Âpyridazine,
were synthesized with high yields. These two materials exhibited strong
absorption/emission with high molar extinction coefficients and moderate
photoluminescence quantum yield. The glass transition temperature
of 3CzPyaPy was detected to be as high as 131 °C, showing its
high thermal stability. Although the absorption energies and oxidation/reduction
behaviors of the two materials were similar, the emission from 4CzPyPyaPy
with longer effective-conjugation length presented hypsochromic shift
both in films and in dilute solutions, contradicting to the common
sense. The single crystal structure study disclosed their different
space stretching and packing: 3CzPyaPy was twisted in larger angles
and adopted dimerlike packing, while 4CzPyPyaPy showed smaller torsion
angles and exhibited slipped herringbone packing. The dimerlike packing
in 3CzPyaPy is responsible for its bathochromic shift of emission
in solid state, while its unsymmetrical molecular structure accounts
for that in solution. We believe that the unsymmetrical molecular
structure of 3CzPyaPy is partially responsible for its high thermal-stability
and also responsible for its HOMO dispersion which renders it slightly
more difficult to oxidize. 3CzPyaPy was proved to be a bipolar-transport
material and when served as a phosphor host, a green phosphorescent
device achieved maximum efficiencies of 54.0 cd A<sup>–1</sup>, 42.4 lm W<sup>–1</sup>, and 17.7%, which are among the best
with nonoptimized device structure, demonstrating its great potential
for optoelectronic application. Furthermore, the new synthesized pyridazine
derivatives and the corresponding structural and molecular-packing
influences on material properties give a new insight into molecule
tailoring
Organic Nanosynthesis of Ancient Windmill-like Window Gridarenes at Molecular Scale
We
focus on another kind of square-type unit nanogrids with starlike divergent extensibility.
As a result, square windmill-like nanogrid <b>WG4</b>
have been successfully synthesized by two different kinds of fluorene-based nanosynthons,
namely I-shape nanosynthon and L-shape nanosynthon synthesis method. Besides <b>WG4</b>, triangle and hexagon windmill-like
nanogrids (<b>WG3</b> and <b>WG5</b>) are also obtained via one-pot nanosynthesis of I-shape nanosynthon with <b>WG3</b>
as the main product. For the L-shape nanosynthon synthetic method, the
cyclization process possesses higher selectivity, resulting to an excellent yield
for <b>WG</b>4. In addition, two
stereoisomers of the triangle nanogrids, <i>cis-trans</i>-<b>WG3</b> and <i>cis-cis-</i><b>WG3</b>, were
separated and characterized from the single-crystal X-ray diffraction and <sup>1</sup>H
NMR analyses for getting insight into the configuration of the triangle nanogrids
with the skeleton planarization for the <i>trans</i>-configuration
and deplanarization for the <i>cis</i>-configuration
Steric-Hindrance-Functionalized Polydiarylfluorenes: Conformational Behavior, Stabilized Blue Electroluminescence, and Efficient Amplified Spontaneous Emission
Control
of the hierarchical molecular organization of polydiarylfluorenes
by synthetic strategies is significant for optimizing photophysical
properties as well as the performance of light-emitting devices. Herein,
for the suppression of molecular aggregation and enhancement of luminescence
efficiency, a series of steric units were introduced into polydiarylfluorenes
by copolymerization, with the aim of integrating the advantages of
the steric-hindrance effect and of the β-phase. Optical and
Raman spectroscopies revealed a β-phase conformation for a polymer
copolymerized with spiroÂ[fluorene-9,9′-xanthene] (SFX), with
photoluminescence (PL) peaks at 454, 482, and 517 nm. Moreover, the
morphological stability and electroluminescence (EL) stability were
also improved without compromising the performance of the polymer
light-emitting diodes (PLEDs). Furthermore, three steric-hindrance-functionalized
copolymers showed significantly decreased thresholds for amplified
spontaneous emission (<i>E</i><sub>th</sub><sup>ASE</sup>) and enhanced stability following thermal annealing treatment. These
results indicate that steric-hindrance functionalization is a superior
approach to improve the overall stability and optoelectronic properties
for blue-light-emitting π-conjugated polymers