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 cm² V^–1 s^–1 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 cm² V^–1 s^–1 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 ¹H 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 CHCl₃ 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>_<b>2</b><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>_<b>2</b><b>Pc1</b>/<b>PDI1</b>, which mostly results from the presence of hole-transporting pathways with the mobility μ_h,1D ∼ 0.1 cm² V^–1 s^–1 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^– complexes that were accompanied by a free Cl^–. This free Cl^– was subsequently captured by pyrrole-based neutral anion receptors to form negatively charged receptor–Cl^– complexes. The ion pair of the resulting positively and negatively charged planar receptor–Cl^– 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^– 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 cm² V^–1 s^–1, 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>_<b>endo</b>, <b>F9T</b>_<b>anti</b>, and <b>F9T</b>_<b>exo</b> 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>_<b>anti</b> and <b>F9T</b>_<b>exo</b>, <b>F9T</b>_<b>endo</b> self-assembles into a hexagonal columnar liquid crystal (Col_h 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_h LC <b>F9T</b>_<b>endo</b> displays a top-class charge-carrier mobility (0.18 cm² V^–1 s^–1) with a distinct ambipolar character featuring well-balanced hole and electron mobilities. A thin film, prepared by mixing <b>F9T</b>_<b>endo</b> with soluble fullerene PCBM, shows a photovoltaic response, when the fullerene content is large enough to compensate a small absorptivity of <b>F9T</b>_<b>endo</b> 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_f, 28–40%; <b>Ib</b> and <b>IIb</b> = Φ_f, 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^–1 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^–1. 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 (C₆₀) 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