Carrier Transport Switching of Ferroelectric BTBT Derivative.

Alkylamide-substituted [1]benzothieno[3,2-b][1]benzothiophene (BTBT) derivative of BTBT-NHCOC14H29 (1), which has ferroelectric N-H···O= hydrogen-bonding network of alkylamide group and two-dimensional (2D) electric structure of BTBT π-cores, was prepared to design the external electric field-responsive organic semiconductors. The short-chain derivative of BTBT-NHCOC3H7 (1') revealed the coexistence of a 2D electronic band structure based on the herringbone BTBT arrangement and the one-dimensional (1D) hydrogen-bonding chain. 1 formed a smectic E (SmE) liquid crystal phase above 412 K and showed ferroelectric hysteresis in the electric field-polarization (P-E) curves at 403-433 K. The remanent polarization (Pr) and coercive electric field (Ec) of 1 at 408 K, 0.1 Hz were 24.0 µC cm-2 and 5.54 V µm-1, respectively. By thermal annealing of thin-film 1 at 443 K, the molecular assembly structure of 1 changed from a monolayer to a bilayer structure with high crystallinity, resulting in conducting layers of BTBT parallel to the substrate surface. The organic field-effect transistor (OFET) device with thermally annealed thin-film 1 showed p-type semiconducting behavior with the hole mobility of 1.0 × 10-3 cm2 V-1 s-1. Furthermore, device 1 showed switching behavior of semiconducting properties by electric field poling and thermal annealing cycle. The electric field response of ferroelectrics modulated the molecular orientation and conduction properties of organic semiconductors, resulting in external electric field control of carrier transport properties.

Urea-Comprising Single Core Diketopyrrolopyrrole Derivatives: Exploring the Synthesis, Self-Assembly and Charge Transport Properties.

Supramolecular electronics exploits the distinctive features stemming from noncovalent interactions, guiding the self-assembly of molecules to craft materials endowed with customized electronic functionalities. Hydrogen-bonded materials, characterized by their capacity to establish dynamic and stable networks, introduce an extra dimension to the development of supramolecular electronic systems. This study presents a comparative analysis of two remarkably small semiconductors utilizing diketopyrrolopyrrole functionalized with urea units as hydrogen-bonding motifs, strategically positioned at opposing ends of the conjugated core. We show how the subtle distinction in functionalization not only influences morphology and self-assembly dynamics via hydrogen-bonding and π-π stacking formation, but also holds significant consequences for ultimate charge transport properties. Our observations into the interplay of noncovalent interactions provide valuable insights and strategic pathways for the design of novel materials with enhanced electronic characteristics.

Ferroelectric Organic Semiconductor: [1]Benzothieno[3,2-b][1]benzothiophene-Bearing Hydrogen-Bonding -CONHC14H29 Chain.

An alkylamide-substituted [1]benzothieno[3,2-b][1]benzothiophene (BTBT) derivative of BTBT-CONHC14H29 (1) and C8H17-BTBT-CONHC14H29 (2) were prepared to design the multifunctional organic materials, which can show both ferroelectric and semiconducting properties. Single-crystal X-ray structural analyses of short-chain (-CONHC3H7) derivatives revealed the coexistence of two-dimensional (2D) electronic band structures brought from a herringbone arrangement of the BTBT π core and the one-dimensional (1D) hydrogen-bonding chains of -CONHC3H7 chains. The thin films of 1 and 2 fabricated on the Si/SiO2 substrate surface have monolayer and bilayer structures, respectively, resulting in conducting layers parallel to the substrate surface, which is suitable for a channel layer of organic field-effect transistors (OFETs). The thin film of 1 indicated a hole mobility µFET = 2.4 × 10-5 cm2 V-1 s-1 and threshold voltage VTh = - 29 V, whereas that of 2 showed a µFET = 2.1 × 10-2 cm2 V-1 s-1 and threshold voltage VTh = -9.7 V. Both 1 and 2 formed the smectic E (SmE) phase above 410 and 369 K, respectively, where the existence of a hole transport pathway was confirmed in the SmE phase. The ferroelectric hysteresis behavior was observed in bulk 1 and 2 in the polarization-electric field (P-E) curves at the SmE phase. 1 showed the remanent polarization Pr = 2.3 µC cm-2 and coercive electric field Ec = 5.2 V µm-1, whereas the Pr and Ec of 2 were 3.4 µC cm-2 and 7.0 V µm-1 at the conditions of 453 K and 1 Hz. Introduction of alkylamide units into the BTBT π core has the potential to develop the external stimulus-responsive organic semiconductors brought from both ferroelectricity and semiconducting properties.

Structural Transformable Coulomb Lattice of n-Type Semiconductors for Guest Sorption.

In recent years, highly designable organic porous materials have attracted considerable attention in the development of new types of molecular adsorption-desorption materials. The adsorption-desorption process also changes the electronic structure via the existence of guest molecules. Therefore, it is possible to change the physical property during the guest adsorption-desorption cycle using an appropriate chemical design of the host crystal lattice. As the development of n-type organic semiconductors has been limited, we focused on designing an n-type organic semiconductor material to control the host crystal lattice, electronic dimensionality, chemical stability, and high electron mobility using an ionic naphthalenediimide (NDI) derivative. Low symmetrical dianionic bis(benzene-m-sulfonate)-naphthalenediimide (m-BSNDI2-) forms various types of single-crystal (M+)2(m-BSNDI2-)·n(guest) with a combination of M+ = Na+, K+, Rb+, and guest = H2O, CH3OH. Four crystals of (K+)2(m-BSNDI2-)·n(H2O), (K+)2(m-BSNDI2-)·n(CH3OH), α-(K+)2(m-BSNDI2-), and ß-(K+)2(m-BSNDI2-) were transformable using the guest adsorption-desorption cycle. Two kinds of single-crystal (K+)2(m-BSNDI2-)·n(CH3OH) with n = 0 and 2.0 showed a single-crystal to single-crystal (SCSC) transformation through CH3OH desorption. On the contrary, five kinds of single crystals with n = 0, 3.0, 3.3, 4.75, and 5.5 were identified in the single-crystal X-ray structural analyses of (K+)2(m-BSNDI2-)·n(H2O). Systematic change of the ionic radii in (M+)2(m-BSNDI2-) modified the crystal lattice flexibility for the guest adsorption-desorption cycles.

Dendritic-Like Molecules Built on a Pillar[5]arene Core as Hole Transporting Materials for Perovskite Solar Cells.

Invited for the cover of this issue are the groups of S. Seki (Kyoto), G. Reginato (Sesto Fiorentino), J.-F. Nierengarten (Strasbourg), A. Abate (Berlin) and J. L. Delgado (San Sebastian). The image depicts an artistic view of a dendrimer-like hole transporting material at work in a perovskite solar cell. Read the full text of the article at 10.1002/chem.202101110.

Dendritic-Like Molecules Built on a Pillar[5]arene Core as Hole Transporting Materials for Perovskite Solar Cells.

Multi-branched molecules have recently demonstrated interesting behaviour as charge-transporting materials within the fields of perovskite solar cells (PSCs). For this reason, extended triarylamine dendrons have been grafted onto a pillar[5]arene core to generate dendrimer-like compounds, which have been used as hole-transporting materials (HTMs) for PSCs. The performances of the solar cells containing these novel compounds have been extensively investigated. Interestingly, a positive dendritic effect has been evidenced as the hole transporting properties are improved when going from the first to the second-generation compound. The stability of the devices based on the best performing pillar[5]arene material has been also evaluated in a high-throughput ageing setup for 500 h at high temperature. When compared to reference devices prepared from spiro-OMeTAD, the behaviour is similar. An analysis of the economic advantages arising from the use of the pillar[5]arene-based material revealed however that our pillar[5]arene-based material is cheaper than the reference.

Crystal Lattice Design of H2O-Tolerant n-Type Semiconducting Dianionic Naphthalenediimide Derivatives.

Dianionic bis(propionate)-naphthalenediimide (PCNDI2-) formed simple 2:1 cation-anion salts of (M+)2(PCNDI2-)·(H2O)n (M+ = Li+, Na+, K+, Rb+, and Cs+), which exhibited reversible H2O adsorption-desorption behavior because of the presence of their electrostatically binding crystal lattices. The maximum H2O adsorption amounts (n) for M+ = Li+, Na+, K+, Rb+, and Cs+ were 0.25, 6.0, 4.0, 6.0, and 2.0, respectively, whereas the reversible gate-opening (gate-closing) H2O adsorption-desorption isotherms were observed at 273 and 298 K, except for M+ = Li+. High ionic conductivities of around 10-4-10-5 S cm-1 were observed in M+ = Na+ and K+ salts, whereas short-range thermal fluctuations occurred in large cations of M+ = Rb+ and Cs+. The change in the electrostatic lattice energy for M+ = Na+ and K+ salts during the H2O adsorption-desorption cycles was significantly larger than those for M+ = Rb+ and Cs+. Therefore, the Na+ and K+ salts had a considerably flexible electrostatic crystal lattice with a large amplitude of lattice modulation during the H2O sorption cycle. In contrast, the lattice modulation for M+ = Rb+ and Cs+ salts involved a low magnitude of ion displacements, forming a relatively rigid cation-anion electrostatic crystal lattice. The flash-photolysis time-resolved microwave conductivity and transition absorption spectroscopy results revealed the high electron mobility of H2O-adsorbed thin films, wherein the crystallized H2O molecules did not act as electron-trapping sites. The values of electron mobility increased in the order of Cs+ ≈ Rb+ > K+ > Na+ > Li+.

Switching of Electron and Ion Conductions by Reversible H2O Sorption in n-Type Organic Semiconductors.

Polar H2O molecules generally act as trapping sites and suppress the electron mobility of n-type organic semiconductors, making chemical design of H2O-tolerant and responsive n-type semiconductors an important step toward multifunctional electron-ion coupling devices. The introduction of effective electrostatic interactions between potassium ions (K+) and carboxylate (-COO-) anions into the electron-transporting naphthalenediimide π-framework enables the design of high-performance H2O-tolerant n-type semiconductors with a reversible H2O adsorption-desorption ability, where the electron mobility and K+ ionic conductivity were coupled with the reversible H2O sorption behavior. The reversible H2O adsorption into the crystals enhanced the electron mobility from 0.04 to 0.28 cm2 V-1 s-1, whereas the K+ ionic conductivity decreased from 3.4 × 10-5 to 4.7 × 10-7 S cm-1. Because this reversible electron-ion conducting switch is responsive to H2O sorption behavior, it is a strong candidate for H2O gating carrier transport systems.

Impact of Chirality on Hydrogen-Bonded Supramolecular Assemblies and Photoconductivity of Diketopyrrolopyrrole Derivatives.

Hydrogen bonds can efficiently guide the self-assembly of organic materials, enabling to tune the properties of the aggregation processes. In the case of π-conjugated materials, several parameters such as temperature, concentration and solvent can be used to modify the aggregation state while tuning the optoelectronic properties. Chirality can be included within the impacting parameters due to the differences in molecular packing. Here, chiral and achiral thiophene-capped diketopyrrolopyrrole derivatives were designed and synthesized containing amide bonds, with the aim to study the interplay between chiral assemblies and their stabilization through hydrogen-bonding. Differences in aggregation properties were observed with spectroscopy and microscopy, and a contactless microwave-based technique was used to study their intrinsic charge carrier mobility. The positive role of hydrogen-bonding has been highlighted and the differences between chiral and achiral compounds have been elucidated.

Intermolecular cascaded π-conjugation channels for electron delivery powering CO2 photoreduction.

Photoreduction of CO2 to fuels offers a promising strategy for managing the global carbon balance using renewable solar energy. But the decisive process of oriented photogenerated electron delivery presents a considerable challenge. Here, we report the construction of intermolecular cascaded π-conjugation channels for powering CO2 photoreduction by modifying both intramolecular and intermolecular conjugation of conjugated polymers (CPs). This coordination of dual conjugation is firstly proved by theoretical calculations and transient spectroscopies, showcasing alkynyl-removed CPs blocking the delocalization of electrons and in turn delivering the localized electrons through the intermolecular cascaded channels to active sites. Therefore, the optimized CPs (N-CP-D) exhibiting CO evolution activity of 2247 µmol g-1 h-1 and revealing a remarkable enhancement of 138-times compared to unmodified CPs (N-CP-A).

Protein-directed crystalline 2D fullerene assemblies.

Water soluble 2D crystalline monolayers of fullerenes grow on planar assemblies of engineered consensus tetratricopeptide repeat proteins. Designed fullerene-coordinating tyrosine clamps on the protein introduce specific fullerene binding sites, which facilitate fullerene nucleation. Through reciprocal interactions between the components, the hybrid material assembles into two-dimensional 2 nm thick structures with crystalline order, that conduct photo-generated charges. Thus, the protein-fullerene hybrid material is a demonstration of the developments toward functional materials with protein-based precision control of functional elements.

Systematic Synthesis of Tetrathia[8]circulenes: The Influence of Peripheral Substituents on the Structures and Properties in Solution and Solid States.

We developed the diversity-oriented approach for the synthesis of tetrathia[8]circulenes with a variety of peripheral substituents. Iridium-catalyzed direct C-H borylation of tetrathienylene provided 1,4,7,10-tetraboryltetrathienylene as a major product. 1,4,7,10-Tetraboryltetrathienylene served as an a key intermediate to achieve the selective synthesis of octasubstituted or tetrasubstituted tetrathia[8]circulenes via rhodium-catalyzed annulation with symmetric internal alkynes or sequential Sonogashira-Hagihara coupling and base-promoted intramolecular cyclization. A variety of substituents were installed at the peripheral positions of tetrathia[8]circulenes systematically. The self-assembling behavior of tetrathia[8]circulenes was investigated using 1H NMR and AFM measurements. The number and the chain length of alkyl groups exerted a significant influence on the aggregation ability and the crystal packing structures of tetrathia[8]circulenes in both solution and solid states. We also found that the molecular arrangement of the self-assembled tetrathia[8]circulene molecules affected the hole mobility assessed by the FP-TRMC method.

Helical Pore Alignment on Cylindrical Carbon.

Interest in chiral substances has mainly focused on the substances themselves, but not on the accompanying space, especially regarding the pore alignment. As a method to form both the chiral substance and the accompanying space, cylindrical self-assembly of uniform polystyrene nanoparticles with fructose is carried out in the presence of both carbon and sodium alginate, which is followed by heat treatment in an inert atmosphere. The carbonization generates fructose-derived honeycomb-like carbon walls with helically aligned nanopores left after the polystyrene decomposition. The diffuse reflectance circular dichroism measurements give peaks with opposite signs for the d- and l-fructose-derived cylindrical carbons. Circularly polarized light sensitivity in transient photoconductivity is confirmed apparently in the carbon-based helical structures. This sensitivity as well as straightforward formation of composites with another component to give helicity shows potential applications of the helically aligned pores.

Ion-Pairing Assemblies Comprising Anion Complexes of π-Extended Anion-Responsive Molecules.

Anion-responsive molecules comprising phenanthropyrrole rings were synthesized by oxidative coupling. Spectroscopic and theoretical examinations revealed the effects of the π-extended structures. In the solid state as ion-pairing assemblies, Cl- complexes of π-extended derivatives formed stacked structures composed of Cl- complexes themselves and those formed with countercations using extended π-moieties. Aliphatic anion-responsive molecules and their Cl- complexes, as ion pairs with the triazatriangulenium cation, provided hexagonal columnar structures with liquid-crystalline mesophases.

Two-step template method for synthesis of axis-length-controlled porphyrin-containing hollow structures.

π-Conjugated porphyrin-containing hollow structures with defined axis-length were successfully synthesized by a two-step template method, i.e., template-assisted cyclization and oligomerization. During the oligomerization, templates played important roles in controlling the reaction rates and the axis lengths. The hollow structures exhibited an extended effective π-conjugation because of the high coplanarity between porphyrins.

Peripherally Cyanated Subphthalocyanines as Potential n-Type Organic Semiconductors.

A series of peripherally dicyano-, tricyano-, and tetracyano-substituted subphthalocyanines (SubPcs) have been prepared through microwave-assisted, palladium-mediated cyanation of iodinated precursors. The introduction of π-accepting cyano groups in the macrocycle clearly influences its electronic and redox properties, which are dependent on the number and relative position of these substituents. Additional functionalization of the periphery of SubPcs with electron-donating or -withdrawing groups allows for a further fine-tuning of their features, leading to intensely absorbing, strongly electron-accepting panchromatic dyes with low-lying LUMO energy levels. Flash-photolysis time-resolved microwave conductivity measurements on vapor-deposited films demonstrate that some of these novel SubPc derivatives display remarkable intrinsic charge-carrier mobilities that are comparable to or larger than those of other known well-performing acceptor SubPcs; thus confirming their potential as n-type organic semiconductors for application in the fabrication of photovoltaic devices.

Preparation, Electronic and Liquid Crystalline Properties of Electron-Accepting Azaacene Derivatives.

A series of electron-accepting azaacene-type materials 1-4 with different kinds and degrees of intermolecular interactions were synthesized. Simple modification of the terminal substituents significantly modulated the photophysical and electrochemical properties. The degree of weak intermolecular interaction determined the emergence of a liquid crystalline (LC) phase for each compound. Dipole-dipole interaction, π-π interaction, and van der Waals interaction all contributed to stabilize the LC phase of 1 and 2. The introduction of strong hydrogen bonding interaction enabled the formation of a highly ordered LC phase in 4. Charge-transport properties of 1, 2, and 4 were also investigated.

Supramolecular Chirality Issues in Unorthodox Naphthalene Diimide Gelators.

Herein, the self-assembly of a few 1,3-dihydroxyl functionalized naphthalene diimide (NDI) derivatives has been reported with particular emphasis on the impact of chirality on gelation and the effect of self-assembly on charge-carrier mobility. A nonconventional gelator (R)-NDI, devoid of any long alkyl chains, exhibited spontaneous gelation in tetra-chloroethylene (TCE). Based on X-ray crystallography and powder X-ray diffraction studies, it was established that a ladder-like hydrogen-bonded chain formation between the 1,3-dihydroxyl group leads to the fibrillar structures with preferential helicity. Likewise the (S)-isomer also exhibited identical gelation and mesoscopic structure but produced fibrils with the opposite handedness. Intriguingly, an equimolar mixture of the (R)- and (S)-isomers did not show any gelation ability, rather a macroscopic precipitation was observed and, in sharp contrast to the individual isomers, the morphology of the mixture showed ill-defined near spherical agglomerates. Differential scanning calorimetry (DSC) studies revealed an identical crystallization peak for the supramolecular polymer produced from the enantiopure gelators ((R)- or (S)-isomer), which was absent in their equimolar mixture. However, mixtures of the two isomers with enantiomeric excess retrieved the gelation ability and preferential helicity demonstrating that chiral amplification is operative in the present system through the so-called "majority rule" effect. Chirality induction was also realized by the "sergeant and soldier" principle in the supramolecular assembly of an achiral NDI gelator in the presence of either the (R)- or (S)-isomer as the chiral dopant. However, the strong helical bias induced by the chiral gelator was found to be opposite in nature compared to that found in the self-assembly of the pure chiral gelator that has been rarely reported in the literature. Flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements indicated the strong positive impact of the gelation on the electrical conductivity.

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.

Regio- and Stereoselective Synthesis of Triarylalkene-Capped Rotaxanes via Palladium-Catalyzed Tandem Sonogashira/Hydroaryl Reaction of Terminal Alkynes.

Triarylalkene-capped conjugated rotaxanes were synthesized via a palladium-catalyzed tandem Sonogashira/hydroaryl reaction between aryl halides and terminal alkynes bearing two permethylated α-cyclodextrins (PM α-CDs) with high regioselectivity because of the insulation effect of the PM α-CDs. Moreover, sequential Sonogashira coupling and hydroarylation reactions using different aryl substrates afforded a regio- and stereoselective trisubstituted alkene as a single product. This new class of rotaxane-forming reactions can be used to increase the diversity of rotaxane skeletons, and thereby the material functionalities of rotaxanes.