π-Extended 9b-Boraphenalenes: Synthesis, Structure, and Physical Properties.

Boraphenalenes, compounds in which one carbon atom in the phenalenyl skeleton is replaced with a boron atom, have attracted attention for their solid-state and electronic structures; however, the construction of boraphenalene skeletons remains challenging because of the lack of suitable methods. Through this study, we showed that the tandem borylative cyclization of C3-symmetric dehydrobenzo[12]annulenes produces a new class of fully fused boron-atom-embedded polycyclic hydrocarbons possessing a 9b-boraphenalene skeleton. The obtained compounds exhibited high electron-accepting characteristics, and their two-step redox process was reversible in the reductive region, involving interconversion of 9b-boraphenalene between Hückel aromaticity and antiaromaticity. Notably, the benzo[b]fluorene-fused derivative exhibited a stepwise single-crystal-to-single-crystal (SCSC) phase transition triggered by thermal annealing. Intermolecular electron coupling calculation of the crystal structures suggested a significant improvement of charge transporting ability associated with the SCSC phase transition. Moreover, adequate photoconductivity was observed for the single crystals before and after the SCSC phase transition through flash photolysis-time-resolved microwave conductivity.

Amplified spontaneous emission from a liquid crystalline phase: anisotropic property and active modulation.

Amplified spontaneous emission (ASE) is considered to be a primary indication of optical gain in active media without an external resonator. Molecular materials with ASE are expected to be one of the suitable light sources for specific applications such as optical coherent tomography owing to their low coherence and flexible tunability. Concentration quenching of emissive excited states has been a critical issue to boost the quantum efficiency of molecular materials in their condensed phases. The rod-like design of molecules with excited state intramolecular proton transfer (ESIPT) has been demonstrated to overcome this issue in highly-concentrated molecularly-doped systems, as represented by C4alkyne-HBT (2-(4-(1-hexynyl)-2-hydroxyphenyl)-benzothiazole). We designed an ESIPT molecule-doped liquid crystalline (LC) system for optical amplification via the ASE regime with its wide tunability of emission intensity. Detailed ASE behaviour and optical gain of a LC blend of C4alkyne-HBT and 4-pentyl-4'-cyano biphenyl (5CB) was evaluated to afford a maximum optical gain of 16.5 cm-1 with an estimated ASE threshold of optical pumping at 0.6-0.7 mJ cm-2. Although most ASE studies focus on homogeneous solutions, solids, or crystalline states, ASE from a soft-flexible LC phase is quite limited and advantageous for the design of an external optical resonator/cavity structure. Optical excitation parallel and perpendicular to the director resulted in the strong modulation of the ASE. By using the benefits of a LC phase, the ASE was actively modulated under the external electric field by the reorientation of the molecular dipole moment.

Synthesis of Closed-Heterohelicenes Interconvertible between Their Monomeric and Dimeric Forms.

Oxidative fusion reaction of cyclic heteroaromatic pentads consisting of pyrrole and thiophene gave closed-heterohelicene monomers and dimers depending on the oxidation conditions. Specifically, oxidation with [bis(trifluoroacetoxy)iodo]benzene (PIFA) gave closed-[7]helicene dimers connected at the ß-position of one of the pyrrole units with remarkably elongated C-C bonds of about 1.60 Å. Although this bond was intact against thermal and physical activations, homolytic bond dissociation took place in DMSO upon irradiation with UV light to give the corresponding monomers. Thus, interconversion between the closed-helicene monomer and dimer was achieved. The optically pure dimer was photo-dissociated into the monomers associated with a turn-on of circularly polarized luminescence (CPL).

Chiral Van Der Waals Superlattices for Enhanced Spin-Selective Transport and Spin-Dependent Electrocatalytic Performance.

The emergence of the chiral-induced spin-selectivity (CISS) effect offers a new avenue for chiral organic molecules to autonomously manipulate spin configurations, thereby opening up possibilities in spintronics and spin-dependent electrochemical applications. Despite extensive exploration of various chiral systems as spin filters, one often encounters challenges in achieving simultaneously high conductivity and high spin polarization (SP). In this study, a promising chiral van der Waals superlattice, specifically the chiral TiS2 crystal, is synthesized via electrochemical intercalation of chiral molecules into a metallic TiS2 single crystal. Multiple tunneling processes within the highly ordered chiral layered structure of chiral TiS2 superlattices result in an exceptionally high SP exceeding 90%. This remarkable observation of significantly high SP within the linear transport regime is unprecedented. Furthermore, the chiral TiS2 electrode exhibits enhanced catalytic activity for oxygen evolution reaction (OER) due to its remarkable spin-selectivity for triplet oxygen evolution. The OER performance of chiral TiS2 superlattice crystals presented here exhibits superior characteristics to previously reported chiral MoS2 catalysts, with an approximately tenfold increase in current density. The combination of metallic conductivity and high SP sets the stage for the development of a new generation of CISS materials, enabling a wide range of electron spin-based applications.

Two-Step Synthesis of B2 N2 -Doped Polycyclic Aromatic Hydrocarbon Containing Pentagonal and Heptagonal Rings with Long-Lived Delayed Fluorescence.

Pentagon-heptagon embedded polycyclic aromatic hydrocarbons (PAHs) have aroused increasing attention in recent years due to their unique physicochemical properties. Here, for the first time, this report demonstrates a facile method for the synthesis of a novel B2 N2 -doped PAH (BN-2) containing two pairs of pentagonal and heptagonal rings in only two steps. In the solid state of BN-2, two different conformations, including saddle-shaped and up-down geometries, are observed. Through a combined spectroscopic and calculation study, the excited-state dynamics of BN-2 is well-investigated in this current work. The resultant pentagon-heptagon embedded B2 N2 -doped BN-2 displays both prompt fluorescence and long-lived delayed fluorescence components at room temperature, with the triplet excited-state lifetime in the microsecond time region (τ = 19 µs). The triplet-triplet annihilation is assigned as the mechanism for the observed long-lived delayed fluorescence. Computational analyses attributed this observation to the small energy separation between the singlet and triplet excited states, facilitating the intersystem crossing (ISC) process which is further validated by the ultrafast spectroscopic measurements.

Activation of AMP-activated protein kinase (AMPK) through inhibiting interaction with prohibitins.

5'-Adenosine monophosphate-activated protein kinase (AMPK) is a potential therapeutic target for various medical conditions. We here identify a small-molecule compound (RX-375) that activates AMPK and inhibits fatty acid synthesis in cultured human hepatocytes. RX-375 does not bind to AMPK but interacts with prohibitins (PHB1 and PHB2), which were found to form a complex with AMPK. RX-375 induced dissociation of this complex, and PHBs knockdown resulted in AMPK activation, in the cultured cells. Administration of RX-375 to obese mice activated AMPK and ameliorated steatosis in the liver. High-throughput screening based on disruption of the AMPK-PHB interaction identified a second small-molecule compound that activates AMPK, confirming the importance of this interaction in the regulation of AMPK. Our results thus indicate that PHBs are previously unrecognized negative regulators of AMPK, and that compounds that prevent the AMPK-PHB interaction constitute a class of AMPK activator.

Constitutional isomerism of the linkages in donor-acceptor covalent organic frameworks and its impact on photocatalysis.

When new covalent organic frameworks (COFs) are designed, the main efforts are typically focused on selecting specific building blocks with certain geometries and properties to control the structure and function of the final COFs. The nature of the linkage (imine, boroxine, vinyl, etc.) between these building blocks naturally also defines their properties. However, besides the linkage type, the orientation, i.e., the constitutional isomerism of these linkages, has rarely been considered so far as an essential aspect. In this work, three pairs of constitutionally isomeric imine-linked donor-acceptor (D-A) COFs are synthesized, which are different in the orientation of the imine bonds (D-C=N-A (DCNA) and D-N=C-A (DNCA)). The constitutional isomers show substantial differences in their photophysical properties and consequently in their photocatalytic performance. Indeed, all DCNA COFs show enhanced photocatalytic H2 evolution performance than the corresponding DNCA COFs. Besides the imine COFs shown here, it can be concluded that the proposed concept of constitutional isomerism of linkages in COFs is quite universal and should be considered when designing and tuning the properties of COFs.

Hybrid Chiral MoS2 Layers for Spin-Polarized Charge Transport and Spin-Dependent Electrocatalytic Applications.

The chiral-induced spin selectivity effect enables the application of chiral organic materials for spintronics and spin-dependent electrochemical applications. It is demonstrated on various chiral monolayers, in which their conversion efficiency is limited. On the other hand, relatively high spin polarization (SP) is observed on bulk chiral materials; however, their poor electronic conductivities limit their application. Here, the design of chiral MoS2 with a high SP and high conductivity is reported. Chirality is introduced to the MoS2 layers through the intercalation of methylbenzylamine molecules. This design approach activates multiple tunneling channels in the chiral layers, which results in an SP as high as 75%. Furthermore, the spin selectivity suppresses the production of H2 O2 by-product and promotes the formation of ground state O2 molecules during the oxygen evolution reaction. These potentially improve the catalytic activity of chiral MoS2 . The synergistic effect is demonstrated as an interplay of the high SP and the high catalytic activity of the MoS2 layer on the performance of the chiral MoS2 for spin-dependent electrocatalysis. This novel approach employed here paves way for the development of other novel chiral systems for spintronics and spin-dependent electrochemical applications.

A Supramolecular Polymer Constituted of Antiaromatic NiII Norcorroles.

For the creation of next-generation organic electronic materials, the integration of π-systems has recently become a central theme. Such functional materials can be assembled by supramolecular polymerization when aromatic π-systems are used as monomers, and the properties of the resulting supramolecular polymer strongly depend on the electronic structure of the monomers. Here, we demonstrate the construction of a supramolecular polymer consisting of an antiaromatic π-system as the monomer. An amide-functionalized NiII norcorrole derivative formed a one-dimensional supramolecular polymer through π-π stacking and hydrogen-bonding interactions, ensuring the persistency of the conducting pathway against thermal perturbation, which results in higher charge mobility along the tightly bound linear aggregates than that of the aromatic analogue composed of ZnII porphyrins.

Antiaromatic 1,5-Diaza-s-indacenes.

s-Indacene is a classical non-alternant hydrocarbon that contains 12 π-electrons in a cyclic π-conjugation system. Herein, we report its nitrogen-doped analogue, 1,5-diaza-s-indacene. 1,5-Diaza-s-indacenes were readily prepared from commercially available 2,5-dichlorobenzene-1,4-diamine through a two-step transformation consisting of a palladium-catalyzed Larock cyclization with diaryl acetylenes followed by hydrogen abstraction. The thus obtained 1,5-diaza-s-indacenes exhibited distinct antiaromaticity, as manifested in clear bond-length alternation, a forbidden HOMO-LUMO transition, and a paratropic ring current. As compared to the parent s-indacene, the 1,5-diaza-s-indacenes showed higher electron-accepting ability owing to the presence of imine-type nitrogen atoms. The 1,5-diaza-s-indacene core is effectively conjugated with the peripheral aryl groups, which enables fine-tuning of the absorption spectra and redox properties. The two possible localized forms of 1,5-diaza-s-indacene were compared in terms of their energetic aspects.

Interplay of structural dynamics and electronic effects in an engineered assembly of pentacene in a metal-organic framework.

Charge carrier mobility is an important figure of merit to evaluate organic semiconductor (OSC) materials. In aggregated OSCs, this quantity is determined by inter-chromophoric electronic and vibrational coupling. These key parameters sensitively depend on structural properties, including the density of defects. We have employed a new type of crystalline assembly strategy to engineer the arrangement of the OSC pentacene in a structure not realized as crystals to date. Our approach is based on metal-organic frameworks (MOFs), in which suitably substituted pentacenes act as ditopic linkers and assemble into highly ordered π-stacks with long-range order. Layer-by-layer fabrication of the MOF yields arrays of electronically coupled pentacene chains, running parallel to the substrate surface. Detailed photophysical studies reveal strong, anisotropic inter-pentacene electronic coupling, leading to efficient charge delocalization. Despite a high degree of structural order and pronounced dispersion of the 1D-bands for the static arrangement, our experimental results demonstrate hopping-like charge transport with an activation energy of 64 meV dominating the band transport over a wide range of temperatures. A thorough combined quantum mechanical and molecular dynamics investigation identifies frustrated localized rotations of the pentacene cores as the reason for the breakdown of band transport and paves the way for a crystal engineering strategy of molecular OSCs that independently varies the arrangement of the molecular cores and their vibrational degrees of freedom.

Ubiquitous organic molecule-based free-standing nanowires with ultra-high aspect ratios.

The critical dimension of semiconductor devices is approaching the single-nm regime, and a variety of practical devices of this scale are targeted for production. Planar structures of nano-devices are still the center of fabrication techniques, which limit further integration of devices into a chip. Extension into 3D space is a promising strategy for future; however, the surface interaction in 3D nanospace make it hard to integrate nanostructures with ultrahigh aspect ratios. Here we report a unique technique using high-energy charged particles to produce free-standing 1D organic nanostructures with high aspect ratios over 100 and controlled number density. Along the straight trajectory of particles penetrating the films of various sublimable organic molecules, 1D nanowires were formed with approximately 10~15 nm thickness and controlled length. An all-dry process was developed to isolate the nanowires, and planar or coaxial heterojunction structures were built into the nanowires. Electrical and structural functions of the developed standing nanowire arrays were investigated, demonstrating the potential of the present ultrathin organic nanowire systems.

Extended conjugation of ESIPT-type dopants in nematic liquid crystalline phase for enhancing fluorescence efficiency and anisotropy.

Organic compounds capable of excited-state intramolecular proton transfer (ESIPT) show fluorescence with a large Stokes shift and serve as solid-state emitters, luminescent dopants, and fluorescence-based sensing materials. Fluorescence of ESIPT molecules is usually increased in the solid state, but is weak in solvents due to the accelerated non-radiative decays by rotational motions of a part of the molecular core in these environments. Here we report, using a representative ESIPT motif 2-(2-hydroxyphenyl)benzothiazole (HBT), the extended-conjugation strategy of keeping sufficient fluorescence efficiency both in the solid state and in organic media. The introduction of an alkyl-terminated phenylene-ethynylene group into the HBT molecule dramatically enhances the fluorescence quantum yield from 0.01 to 0.20 in toluene and from 0.07 to 0.32 in a representative room-temperature nematic liquid crystal, 4-pentyl-4'-cyano biphenyl (5CB). The newly-synthesized CnP-C[triple bond, length as m-dash]C-HBT (n = 5 or 8) serves as a fluorescent dopant in 5CB and exhibits anisotropic fluorescence with the order parameter of 0.48, where the luminescence is controlled by the applied electric-field. The enhanced emission efficiency is rationalized by the larger height of energy barrier for the ESIPT process due to the introduction of phenylene-ethynylene groups.

Noncovalent Functionalization of Few-Layered Antimonene with Fullerene Clusters and Photoinduced Charge Separation in the Composite.

Few-layered antimonene (FLSb) nanosheets were noncovalently functionalized with fullerene C60 clusters by quick addition of a poor solvent (i.e., acetonitrile) into a mixed dispersion of FLSb and C60 in a good solvent (i.e., toluene). In a flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurement, the FLSb-C60 composite, (FLSb+C60 )m , showed a rapid rise in transient conductivity, whereas no conductivity signal was observed in the single components, FLSb and C60 . This demonstrated the occurrence of photoinduced charge separation between FLSb and C60 in (FLSb+C60 )m . Furthermore, a photoelectrochemical device with an electrophoretically deposited (FLSb+C60 )m film exhibited an enhanced efficiency of photocurrent generation, compared to those of the single-components, FLSb and C60 , due to the photoinduced charge separation between FLSb and C60 . This work provides a promising approach for fabrication of antimonene-organic molecule composites and paves the way for their application in optoelectronics.

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.

Rod-like transition first or chain aggregation first? ordered aggregation of rod-like poly(p-phenyleneethynylene) chains in solution.

The rod-like configuration of conjugated polymer chains with its low energetic disorder is the key to utilizing the backbone as a highly electrically-conductive wire. An energetic disorder that is higher than 0.1 eV, coupled with vibronic modes of the chains, leads to the localization of charges. Herein, we have tracked precisely the rod-like transition of poly(p-phenyleneethynylene) (PPE) chains as a function of temperature in diluted solutions, and shown a steep increase in persistence length at 230 K. The resulting rod-like configuration of the PPE chains with its extended electronic conjugation exhibited an extremely small energetic disorder of ∼70 meV, and was stabilized by subsequent polymer aggregate formation.

Highly Miscible Hybrid Liquid-Crystal Systems Containing Fluorescent Excited-State Intramolecular Proton Transfer Molecules.

Doping of luminescent molecules in a nematic liquid-crystal (LC) host is a convenient approach to develop light-emitting LC displays that would be a promising alternative to conventional LC displays. The requirements for the luminescent guest molecules include high miscibility in the host LC, high-order parameters in the host LC media to show anisotropic luminescence, lack of self-absorption, transparency in the visible region, and a large photoluminescence quantum yield independent of its concentration. To address these issues, here, we newly synthesize a highly miscible and fluorescent excited-state intramolecular proton transfer molecule, C4-C≡C-HBT, based on 2-(2-hydroxyphenyl)benzothiazole (HBT). This compound is highly miscible in a conventional room-temperature nematic LC 4-pentyl-4'-cyano biphenyl (5CB) up to 14 wt % (∼12 mol %) and exhibits a large photoluminescence quantum yield of ΦFL = 0.32 in the 5CB host, both of which were achieved by the introduction of an alkynyl group into the HBT core. C4-C≡C-HBT possesses a high-order parameter of S = 0.46 in 5CB, and the C4-C≡C-HBT/5CB mixtures show anisotropic fluorescence whose intensity is controlled by the applied electric field. A patterned image is demonstrated, which is not visible under an ambient environment but is readable upon UV illumination, relying on the orientational differences of ordered C4-C≡C-HBT molecules.

Landscape of Charge Carrier Transport in Doped Poly(3-hexylthiophene): Noncontact Approach Using Ternary Combined Dielectric, Paramagnetic, and Optical Spectroscopies.

We report on a comprehensive measurement system for mobility and energy states of charge carriers in matter under dynamic chemical doping. The temporal evolution of the iodine doping process of poly(3-hexylthiophene) (P3HT) was monitored directly through electron paramagnetic resonance (EPR) and optical absorption spectroscopy, as well as differential electrical conductivity by the microwave conductivity measurement. The increase in conductivity was observed after the EPR intensity reached a maximum and declined thereafter, and the conductivity finally reached ∼80 S cm-1. The carrier species changed from a paramagnetic polaron with an estimated mobility of µP+ ≈ 2 × 10-3 cm2 V-1 s-1 to an antiferromagnetic polaron pair with µPP+ ≈ 0.6 cm2 V-1 s-1. The technique presented here can be a ubiquitous method for rapid and direct observation of charge carrier mobility and energy states in p-type semiconducting materials as a completely noncontact, experimental, and quantitative technique.

Hash-Mark-Shaped Azaacene Tetramers with Axial Chirality.

The tetramers of azapentacene derivatives with unique hash mark (#)-shaped structures were prepared in a quite facile manner. The #-shaped tetramers are optically active due to possessing extended biaryl skeletons, and the structure of the tetramer composed of four dihydrodiazapentacene (DHDAP) units (1) was investigated as the first example of this kind of molecule. The tetramer 1 showed characteristic chiroptical properties reflecting its orthogonally arranged quadruple DHDAP moieties, as well as redox activity. The solution of enantiopure 1 exhibited intense circularly polarized luminescence (CPL) with a dissymmetry factor of 2.5 × 10-3. The absolute configuration of the enantiomers of 1 was experimentally determined by X-ray crystal analysis for the dication salt of the enantiomer of 1 with SbCl6- counterions. The solutions of enantiopure 12+·2[SbCl6-] also showed NIR circular dichroism (CD) spectra over the entire range from visible to 1100 nm, enabling the modulation of the chiroptical properties by redox stimuli.