63 research outputs found
Naphthalenediimide-Benzothiadiazole Copolymer Semiconductors: Rational Molecular Design for Air-Stable Ambipolar Charge Transport
Rational
design of air-stable ambipolar polymeric semiconductors
was achieved by covalently connecting naphthalenediimide (NDI) units
with benzothiadiazole (BZ) through thiophene (T) linkers, namely, <b>PNDI-</b><i><b>mT</b></i><b>(BZ)</b><i><b>mT</b></i> (<i>m</i> = 1, 2), in which well-coplanar <i><b>mT</b></i><b>(BZ)</b><i><b>mT</b></i> moieties as a whole act as donors rather than acceptors reported
in previous studies. Decreasing the number of thiophene linkers from <i>m</i> = 2 to 1 lowers both LUMO and HOMO energy levels. As a
result, the carriers in organic thin film transistors (OTFTs) could
be switched from unipolar <i>p</i>-channel only to ambipolar
transport. In ambient conditions, <b>PNDI-</b><i><b>2T</b></i><b>(BZ)</b><i><b>2T</b></i> presents an average hole mobility of 0.07 Âą 0.02 cm<sup>2</sup> V<sup>â1</sup> s<sup>â1</sup>, while <b>PNDI-</b><i><b>T</b></i><b>(BZ)</b><i><b>T</b></i> exhibits balanced ambipolar charge transport in a bottom-gate/top-contact
device architecture, the average electron and hole mobilities was
0.05 Âą 0.02 (<i>Îź</i><sub>e</sub>) and 0.1 Âą
0.03 (<i>Îź</i><sub>h</sub>) cm<sup>2</sup> V<sup>â1</sup> s<sup>â1</sup>, respectively. Moreover, OTFTs based on both
polymer show good air-stability with negligible changes after stored
in ambient over 3 months
Solvatomechanical Bending of Organic Charge Transfer Cocrystal
We report here a new ternary solvated
(perylene-TCNB)¡2THF
cocrystal, which can transform into binary perylene-TCNB cocrystal
reversibly by successive desorption or absorption of THF solvent.
As a consequence, macroscopic mechanical bending would be realized
when repeated stimulation with THF solvent. The present results clearly
demonstrated that solvent induced mechanical bending is driven by
structural change at the molecular scale. Such solvatomechanical bending
behavior is clearly revealed for the first time
Solvatomechanical Bending of Organic Charge Transfer Cocrystal
We report here a new ternary solvated
(perylene-TCNB)¡2THF
cocrystal, which can transform into binary perylene-TCNB cocrystal
reversibly by successive desorption or absorption of THF solvent.
As a consequence, macroscopic mechanical bending would be realized
when repeated stimulation with THF solvent. The present results clearly
demonstrated that solvent induced mechanical bending is driven by
structural change at the molecular scale. Such solvatomechanical bending
behavior is clearly revealed for the first time
Substrate Effects in the Supramolecular Self-Assembly of 2,4,6-Tris(4-bromophenyl)-1,3,5-triazine on Graphite and Graphene
Two-dimensional
self-assembly of star-shaped 2,4,6-trisÂ(4-bromophenyl)-1,3,5-triazine
(BPT) molecule is investigated both on highly oriented pyrolytic graphite
(HOPG) and single-layer graphene (SLG) grown on a polycrystalline
Cu foil. Scanning tunneling microscopy (STM) reveals that this molecule
can form different self-assembling structures on these two different
surfaces. On the basis of high-resolution STM images, we find that
BPT molecules can form compact and loose assembly patterns with different
packing densities on HOPG surface and a porous structure with hexagonal-like
cavities on SLG surface. A combination of STM and density functional
theory calculations elucidates the interplay of moleculeâmolecule
and moleculeâsubstrate interactions on the assembling behavior
on both substrates
Solvatomechanical Bending of Organic Charge Transfer Cocrystal
We report here a new ternary solvated
(perylene-TCNB)¡2THF
cocrystal, which can transform into binary perylene-TCNB cocrystal
reversibly by successive desorption or absorption of THF solvent.
As a consequence, macroscopic mechanical bending would be realized
when repeated stimulation with THF solvent. The present results clearly
demonstrated that solvent induced mechanical bending is driven by
structural change at the molecular scale. Such solvatomechanical bending
behavior is clearly revealed for the first time
Synthesis of a Conjugated Polymer with Broad Absorption and Its Application in High-Performance Phototransistors
An amorphous copolymer (PBDTâBBT) of 4,8-bisÂ(2-thienyl)ÂbenzoÂ[1,2-<i>b</i>:4,5-<i>b</i>â˛]Âdithiophene and 5,5â˛-bibenzoÂ[<i>c</i>]Â[1,2,5]Âthiadiazole was synthesized by Stille coupling
polymerization. PBDTâBBT exhibited good solution processability,
excellent thermal stability with decomposition temperature of 437
°C, broad absorption (300â800 nm), deep HOMO
level (â5.7 eV), and LUMO level (â3.7 eV). The microstructure
order of PBDTâBBT thin films is not susceptible to thermal
annealing temperature (80â200 °C). Field-effect transistors
based on this polymer exhibited a charge-carrier mobility of 6 Ă
10<sup>â3</sup> cm<sup>2</sup> V<sup>â1</sup> s<sup>â1</sup>, threshold voltage of â1 V, and on/off current
ratio of 10<sup>6</sup> without any post-treatments. Thin film phototransistors
of PBDTâBBT exhibited a photoresponsivity of 3200 mA W<sup>â1</sup> and photocurrent/dark current ratio of 4 Ă 10<sup>5</sup>
Critical Content of Ultrahigh-Molecular-Weight Polyethylene To Induce the Highest Nucleation Rate for Isotactic Polypropylene in Blends
The influence of the addition of low amounts of ultrahigh-molecular-weight
polyethylene (UHMWPE) on the crystallization kinetics of isotactic
polypropylene (iPP) in iPP/UHMWPE blends has been investigated by
means of differential scanning calorimetry (DSC) and polarized optical
microscopy. During the nonisothermal crystallization process, the
primarily formed UHMWPE crystals serve as heterogeneous nucleating
agents for iPP nucleation, whereas during the isothermal crystallization
process, UHMWPE is in the molten state, iPP nucleation preferentially
occurs at the UHMWPE and iPP phase interfaces, and the spherulitic
growth rates are not obviously affected. It is particularly interesting
to find a critical UHMWPE content (2.5 wt %) in the blends to induce
the highest iPP nucleation rate; however, above the critical UHMWPE
content, the iPP nucleation rate slows because of aggregation of the
UHMWPE component. A delicately designed DSC measurement provides insight
into the nucleation mechanism of iPP at the interfaces between the
UHMWPE and iPP phase domains. It is proposed that the concentration
fluctuations generated from the unstable inhomogeneous phase interfaces
in the iPP/UHMWPE blends promote the formation of nuclei, which eventually
enhances the nucleation and overall crystallization rates of the iPP
component
Solution-Processed Flexible Organic Ferroelectric Phototransistor
In
this article, we demonstrate ferroelectric insulator, PÂ(VDF-TrFE),
can be integrated with red light sensitive polymeric semiconductor,
PÂ(DPP-TzBT), toward ferroelectric organic phototransistors (OPTs).
This ferroelectricity-modulated phototransistor possesses different
nonvolatile and tunable dark current states due to PÂ(VDF-TrFE)âs
remnant polarization. As a result, the OPT is endowed with a tunable
dark current level ranging from 1 nA to 100 nA. Once the OPT is programmed
or electrically polarized, its photo-to-dark (signal-to-noise) ratio
can be âflexibleâ during photodetection process, without
gate bias application. This kind of organic ferroelectric phototransistor
has great potential in detecting wide ranges of light signals with
good linearity. Moreover, its tuning mechanism discussed in this work
can be helpful to understand the operation mechanism of organic phototransistor
(OPT). It can be promising for novel photodetection application in
plastic electronic devices
Graphene Oxide as a Monoatomic Blocking Layer
Monolayer graphene oxide (mGO) is shown to effectively protect molecular thin films from reorganization and function as an atomically thin barrier for vapor-deposited Ti/Al metal top electrodes. Fragile organic LangmuirâBlodgett (LB) films of C<sub>22</sub> fatty acid cadmium salts (cadmium(II) behenate) were covered by a compressed mosaic LB film of mGO flakes. These hybrid LB films were examined with atomic force microscopy (AFM) and X-ray reflectivity, both with and without the metal top electrodes. While the AFM enabled surface and morphology analysis, the X-ray reflectivity allowed for a detailed structural depth profiling of the organic film and mGO layer below the metal top layers. The structure of the mGO-protected LB films was found to be perfectly preserved; in contrast, it has previously been shown that metal deposition completely destroys the first two LB layers of unprotected films. This study provides clear evidence of the efficient protection offered by a single atomic layer of GO
Unveiling Secrets of Overcoming the âHeteroatom Problemâ in Palladium-Catalyzed Aerobic CâH Functionalization of Heterocycles: A DFT Mechanistic Study
Directed
CâH functionalization of heterocycles through an
exocyclic directing group (DG) is challenging due to the interference
of the endocyclic heteroatom(s). Recently, the âheteroatom
problemâ was circumvented with the development of the protection-free
Pd-catalyzed aerobic CâH functionalization of heterocycles
guided by an exocyclic CONHOMe DG. We herein provide DFT mechanistic
insights to facilitate the expansion of the strategy. The transformation
proceeds as follows. First, the Pd<sub>2</sub>(dba)<sub>3</sub> precursor
interacts with <i>t</i>-BuNC (L, one of the substrates)
and O<sub>2</sub> to form the L<sub>2</sub>PdÂ(II)-Ρ<sup>2</sup>-O<sub>2</sub> peroxopalladiumÂ(II) species that can selectively oxidize <i>N</i>-methoxy amide (e.g., PyCONHOMe) substrate, giving an active
L<sub>2</sub>PdÂ(II)ÂX<sub>2</sub> (X = PyCONOMe) species and releasing
H<sub>2</sub>O<sub>2</sub>. After <i>t</i>-BuNC ligand migratory
insertion followed by a 1,3-acyl migration and association with another <i>t</i>-BuNC, L<sub>2</sub>PdÂ(II)ÂX<sub>2</sub> converts to a more
stable C-amidinyl L<sub>2</sub>PdÂ(II)ÂXXⲠ(XⲠ= PyCONÂ(<i>t</i>-Bu)ÂCîťNOMe) species. Finally, L<sub>2</sub>PdÂ(II)ÂXXâ˛
undergoes CâH activation and CâC reductive elimination,
affording the product. The CâH activation is the rate-determining
step. The success of the strategy has three origins: (i) the <i>N</i>-methoxy amide DG can be easily oxidized <i>in situ</i> to generate the active L<sub>2</sub>PdÂ(II)ÂX<sub>2</sub> species
via the oxidase pathway, thus preventing the destructive oxygenase
pathway leading to stable <i>t</i>-BuNCO or the O-bridged
dimeric PdÂ(II) species. The methoxy group in this amide DG greatly
facilitates the oxidase pathway, and the tautomerization of <i>N</i>-methoxy amide to its imidic acid tautomer makes the oxidation
of the substrate even easier. (ii) The X group in L<sub>2</sub>PdÂ(II)ÂX<sub>2</sub> can serve as an internal base to promote the CâH activation
via CMD (concerted metalation-deprotonation) mechanism. (iii) The
strong coordination ability of <i>t</i>-BuNC substrate/ligand
suppresses the conventional cyclopalladation pathway enabled by the
coordination of an endocyclic heteroatom to the Pd-center
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