9 research outputs found
Assembled Structures of Anion-Responsive π‑Systems Tunable by Alkyl/Perfluoroalkyl Segments in Peripheral Side Chains
Anion-responsive π-conjugated
molecules carrying semifluoroalkyl
chains were newly synthesized to examine the self-assembling features
and resulting electronic properties of these molecules and of ion-pairing
complexes formed when combined with a planar cation salt. Although
these compounds self-organize into columnar mesophases similar to
that of their hydrocarbon analog, in both the charge-free and charge-based
states, the fluorous moieties appended to the π-conjugated units
change the detailed phase-transition profiles and improve the thermal
stability of the ion-pairing complexes. The length of the fluoroalkyl
chains at the termini strongly affects the charge carrier mobility
through the one-dimensionally arranged π-conjugated motifs,
giving highly mobile charge carriers with extremely high intrinsic
mobility of 1.1 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> as a maximum value
Assembled Structures of Anion-Responsive π‑Systems Tunable by Alkyl/Perfluoroalkyl Segments in Peripheral Side Chains
Anion-responsive π-conjugated
molecules carrying semifluoroalkyl
chains were newly synthesized to examine the self-assembling features
and resulting electronic properties of these molecules and of ion-pairing
complexes formed when combined with a planar cation salt. Although
these compounds self-organize into columnar mesophases similar to
that of their hydrocarbon analog, in both the charge-free and charge-based
states, the fluorous moieties appended to the π-conjugated units
change the detailed phase-transition profiles and improve the thermal
stability of the ion-pairing complexes. The length of the fluoroalkyl
chains at the termini strongly affects the charge carrier mobility
through the one-dimensionally arranged π-conjugated motifs,
giving highly mobile charge carriers with extremely high intrinsic
mobility of 1.1 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> as a maximum value
Semiconducting Nanotubes by Intrachain Folding Following Macroscopic Assembly of a Naphthalene–Diimide (NDI) Appended Polyurethane
This
article describes a well-designed supramolecular assembly
of a classical polyurethane scaffold containing pendant n-type semiconducting
naphthalene–diimide (NDI) chromophores and consequences on
excited state dynamics and charge carrier mobilities. A polycondensation
reaction between hexamethylene–diisocyanate and a NDI-containing
diol in the presence of a chiral “mono-functional impurity”
produced the desired polymer (<b>P1</b>) with a predictable
degree of polymerization and end-capping by chiral units. In aliphatic
hydrocarbons, such as methylcyclohexane (MCH), <b>P1</b> adopts
a folded conformation with appreciably high thermal stability by intrachain
H-bonding among the urethane groups as established by solvent, concentration
and temperature-dependent FT-IR and <sup>1</sup>H NMR spectroscopy
and small angle XRD studies. Folded structure can be further ascertained
by the pronounced Cotton effect in MCH owing to the chiral induction
by the so-called “sergeant and soldiers” principle from
the asymmetric units located only at the chain ends. Intrachain folding
facilitates spatial organization of the pendant groups leading to
π–π interaction among the neighboring NDI chromophores
attached to the same polymer chain resulting in intense green emission
in MCH in sharp contrast to the blue-emitting unfolded polymer in
benign solvents such as CHCl<sub>3</sub> or THF. <b>P1</b> in
the folded state resembles the organization of classical bolaamphiphile
and thus adopts a polymersome-like spherical structure. Upon aging
macroscopic gelation can be observed owing to the fusion of these
discrete spherical assemblies generating micrometer long multiwall
nanotubes as noticed in HRTEM, AFM and fluorescence microscopy images.
Transient absorption spectroscopy studies indicate formation of NDI
radical anions in the excited state both in unfolded and folded conformation
which contribute to their intrinsic electron transporting (n-type)
property, as revealed by flash-photolysis time-resolved microwave
conductivity (FP-TRMC). Significantly larger electron mobility and
longer lifetime of charge carriers were observed for the folded tubular
assembly than those for unfolded polymer, likely due to a better delocalization
of the charge-carriers in the integrated tubular assembly consisting
of stacked NDI arrays inside the multilayer wall
Donor/Acceptor Segregated π‑Stacking Arrays by Use of Shish-Kebab-Type Polymeric Backbones: Highly Conductive Discotic Blends of Phthalocyaninatopolysiloxanes and Perylenediimides
Construction of large-area electron
donor–acceptor (D–A)
interfaces and hole/electron pathways is important for photoconducting
and photovoltaic functions. Although blends of D- and A-type discotic
π-systems have a possibility to realize one-dimensional charge
carrier pathways as well as heterointerfaces, D–A segregated
structures are difficult to develop by self-assembly because they
are entropically unfavored structures. Here we report the use of shish-kebab-type
hole-transporting discotic columns fixed by a self-threading polysiloxane
chain and approach to such segregated nanostructures. Electron-donor/acceptor
blends of soluble phthalocyaninatopolysiloxanes (Poly-SiPcs)
and perylenedicarboximides (PDIs) were prepared, and their photoconductive
property was investigated. Although <b>Poly-SiPc1</b> shows
a photoinduced charge separation with <b>PDI1</b> analogous
to the corresponding monomeric phthalocyanines (<b>SiPc1</b> and <b>H</b><sub><b>2</b></sub><b>Pc1</b>), the <b>Poly-SiPc1</b>/<b>PDI1</b> system displays a remarkably
larger photoconductivity than <b>SiPc1/PDI1</b> and <b>H</b><sub><b>2</b></sub><b>Pc1</b>/<b>PDI1</b>, which
mostly results from the presence of hole-transporting pathways with
the mobility μ<sub>h,1D</sub> ∼ 0.1 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> in <b>Poly-SiPc1</b> along
the polysiloxane covalent bonds even upon mixing with <b>PDI1</b>. When π-stackable <b>PDI2</b> is used instead of <b>PDI1</b>, X-ray diffraction analysis disclosed obvious signs of
π-stacking periodicities for both Pc and PDI planes in the mixture,
indicating the presence of donor–acceptor segregated domains
of columnar structures. As a result, photoexcitation of <b>Poly-SiPc1</b>/<b>PDI2</b> generates highly mobile holes and electrons, leading
to the observation of a much larger conductivity
Ion-Based Materials Derived from Positively and Negatively Charged Chloride Complexes of π‑Conjugated Molecules
Oriented salts from planar charged
species were prepared by combining
positively and negatively charged receptor–anion complexes
with similar geometries using dicationic and electronically neutral
π-conjugated receptors. Phenylene- or pyrimidine-bridged bis(imidazolium)
dicationic anion receptors formed monocationic receptor–Cl<sup>–</sup> complexes that were accompanied by a free Cl<sup>–</sup>. This free Cl<sup>–</sup> was subsequently captured by pyrrole-based
neutral anion receptors to form negatively charged receptor–Cl<sup>–</sup> complexes. The ion pair of the resulting positively
and negatively charged planar receptor–Cl<sup>–</sup> complexes could produce a supramolecular octane gel, adopting a
lamellar self-organized structure in its xerogel state. On the other
hand, the solid-state ion pairs had hexagonal columnar mesophases,
which formed via alternate stacking of the positively and negatively
charged planar receptor–Cl<sup>–</sup> complexes. By
use of the flash-photolysis time-resolved microwave conductivity technique,
the one-dimensional charge-carrier transporting property, with a mobility
of 0.05 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, was determined for the newly prepared solid-state ion pairs
Propeller-Shaped Fused Oligothiophenes: A Remarkable Effect of the Topology of Sulfur Atoms on Columnar Stacking
Propeller-shaped regioisomers of
fused oligothiophenes <b>F9T</b><sub><b>endo</b></sub>, <b>F9T</b><sub><b>anti</b></sub>, and <b>F9T</b><sub><b>exo</b></sub> were successfully
synthesized. DFT calculations indicated that their core parts are
distorted from planarity due to intramolecular steric repulsions involving
large sulfur atoms. In contrast with soft crystalline <b>F9T</b><sub><b>anti</b></sub> and <b>F9T</b><sub><b>exo</b></sub>, <b>F9T</b><sub><b>endo</b></sub> self-assembles
into a hexagonal columnar liquid crystal (Col<sub>h</sub> LC), displaying
a clear X-ray diffraction (XRD) due to its stacked π-conjugated
core. In each LC column, well-organized intermolecular S–S
contacts are developed triple-helically along the columnar axis with
a helical pitch of 4.04 nm. Among LC semiconductors reported to date,
Col<sub>h</sub> LC <b>F9T</b><sub><b>endo</b></sub> displays
a top-class charge-carrier mobility (0.18 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>) with a distinct ambipolar character featuring
well-balanced hole and electron mobilities. A thin film, prepared
by mixing <b>F9T</b><sub><b>endo</b></sub> with soluble
fullerene PCBM, shows a photovoltaic response, when the fullerene
content is large enough to compensate a small absorptivity of <b>F9T</b><sub><b>endo</b></sub> for visible light
Optical and Structural Properties of ESIPT Inspired HBT–Fluorene Molecular Aggregates and Liquid Crystals
In bulk materials,
positional isomers not only help in understanding
how slight difference in molecular structure alters the crystal packing
and optical properties, but also play a key role in developing new
type of materials for functional applications. A detailed study on
the photophysical properties of fluorene–HBT positional isomers
in solution and in the solid state providing a molecular level understanding
of the factors which influence fluorescence behavior is reported.
Two molecules <b>Ia</b> and <b>IIa</b> were synthesized
by Suzuki coupling reaction and their photophysical properties were
compared to positional isomers <b>Ib</b> and <b>IIb</b>. Crystal structure analyses and density functional theory (DFT)
computation studies were performed to understand structure–properties
relation and the results reveal that changing substitution pattern
has a marked influence on their packing modes and luminescence properties.
Strong noncovalent interactions (π–π) in the solid
state hamper the excited state intramolecular proton transfer (ESIPT)
process which causes fluorescence quenching in the solid state (<b>Ia</b> and <b>IIa</b> = Φ<sub>f</sub>, 28–40%; <b>Ib</b> and <b>IIb</b> = Φ<sub>f</sub>, 55–67%).
Compounds show solvent–responsive and aggregation induced emission
(AIE) properties. Bent structures of <b>Ia</b> with double and
symmetric substitution of ESIPT motifs exhibit particularly unique
condensed phase upon heating, confirmed as a nematic liquid crystalline
phase, and this is the first report on the ESIPT and AIE active liquid
crystalline materials with a banana-shaped molecule
Pressure Modulation of Backbone Conformation and Intermolecular Distance of Conjugated Polymers Toward Understanding the Dynamism of π‑Figuration of their Conjugated System
Continuous
tuning of the backbone conformation and interchain distance
of a π-conjugated polymer is an essential prerequisite to unveil
the inherent electrical and optical features of organic electronics.
To this end, applying pressure in a hydrostatic medium or diamond
anvil cell is a facile approach without the need for side-chain synthetic
engineering. We report the development of high-pressure, time-resolved
microwave conductivity (HP-TRMC) and evaluation of transient photoconductivity
in the regioregular poly(3-hexylthiophene) (P3HT) film and its bulk
heterojunction blend with methanofullerene (PCBM). X-ray diffraction
experiments under high pressure were performed to detail the pressure
dependence of π-stacking and interlamellar distances in P3HT
crystallites and PCBM aggregates. The HP-TRMC results were further
correlated with high-pressure Raman spectroscopy and density functional
theory calculation. The increased HP-TRMC conductivity of P3HT under
pressure was found to be relevant to the planarity of the backbone
conformation and intramolecular hole mobility. The effects of pressure
on the backbone planarity are estimated to be ∼0.3 kJ mol<sup>–1</sup> based on the compressibility derived from the X-ray
diffraction under high pressure, suggesting the high enough energy
to cause modulation of the planarity in terms of the Landau-de Gennes
free energy of isolated P3HT chains as 0.23 kJ mol<sup>–1</sup>. In contrast, the P3HT:PCBM blend showed a simple decrease in photoconductivity
irrespective of the identical compressive behavior of P3HT. A mechanistic
insight into the interplay of intra- and intermolecular mobilities
is a key to tailoring the dynamic π-figuration associated with
electrical properties, which may lead to the use of HP-TRMC for exploring
divergent π-conjugated materials at the desired molecular arrangement
and conformation
Topologically Directed Assemblies of Semiconducting Sphere–Rod Conjugates
Spontaneous organizations
of designed elements with explicit shape
and symmetry are essential for developing useful structures and materials.
We report the topologically directed assemblies of four categories
(a total of 24) of sphere–rod conjugates, composed of a sphere-like
fullerene (C<sub>60</sub>) derivative and a rod-like oligofluorene(s)
(OF), both of which are promising organic semiconductor materials.
Although the packing of either spheres or rods has been well-studied,
conjugates having both shapes substantially enrich resultant assembled
structures. Mandated by their shapes and topologies, directed assemblies
of these conjugates result not only in diverse unconventional semiconducting
supramolecular lattices with controlled domain sizes but also in tunable
charge transport properties of the resulting structures. These results
demonstrate the importance of persistent molecular topology on hierarchically
assembled structures and their final properties