Photoconductivity Switching in Semiconducting Two-Dimensional Crystals via Molecular Tetris.

Two-dimensional organic materials are mainly constructed by using orthogonal anisotropic connectivity of covalent bonding and π-π stacking. The noncovalent connectivity between building blocks is presumed to be too delicate to stabilize the two-dimensional (2D) layers. Contrary to this assumption, we constructed graphite-like 2D layered material by utilizing pure noncovalent connectivity, i.

Electrically conductive charge-segregated pseudo-polymorphs comprising highly planar expanded π-electronic cations.

Independently stacked positively and negatively charged π-electronic systems in charge-segregated columnar structures are desired for electronic properties derived from their electron-deficient and -rich assembling states, respectively. An expanded π-electronic cation, benzoporphyrin Au complex, was synthesized as the component of ion pairs in combination with counteranions. In contrast to benzoporphyrin, which is known for its insolubility in organic solvents, the ion pairs with bulky anions in this study are soluble in common organic solvents.

Radical Cation of Tris(Triarylamine) Connected through 1,2,3-Benzenetriyl Bridge: A Three-Redox-Center Organic Mixed-Valence System.

To explore intramolecular charge-transfer (ICT) pathways in three-redox-center organic mixed-valence (MV) radical cation, a tris(triarylamine) (TTA), in which three triarylamine (TA) redox-active centers are connected in a side-by-side fashion via 1,2,3-benzenetriyl bridging unit, has been newly synthesized. The MV state of the TTA radical cation has been investigated by a combination of experimental and theoretical methods, and the ICT pathway between three redox-active centers has been revealed. The intervalence CT (IVCT) band analysis gave an electronic coupling value comparable to the ortho-phenylene-bridged bis(triarylamine) radical cation.

Diruthenium(II,II) Complex Assemblies Showing Electrical Conduction via π-Stacked 2-Pyrenecarboxylate Moiety.

Through-space electrical conduction in paddlewheel-type homovalent dinuclear complexes remains poorly understood, despite the numerous reports on these complexes. Herein, the electrical conduction of new Ru(II,II) complexes with 2-pyrenecarboxylate (pyrCOO) ligands, [Ru(pyrCOO)X] ⋅ n(X) (where X=DMF (Ru-DMF), NMP (Ru-NMP), DMA (Ru-DMA)), was investigated. The dimensionality of π-stacking interactions between discrete molecules in Ru-DMA is higher (two-dimensional) than in Ru-DMF and Ru-NMP (stair-like one-dimensional).

Charge-Segregated Ion-Pairing Assemblies Comprising Dipolar π-Electronic Cations.

Two pentamethine dyes with nearly identical structures but slightly different dipole moments were prepared as ion pairs. The ion pairs provided charge-segregated assemblies stabilized by dipole-dipole interactions between the positively charged π-electronic systems. The stacking structure of the bromo-substituted pentamethine cation was more stabilized by a larger dipole moment, as suggested by energy decomposition analysis.

Impact of Double-π-Bridge on Bis(Triarylamine)-Based Organic Mixed-Valence System: A Case Study of Diaza[1.1](4,4")ortho-Terphenylophane Radical Cation.

A bis(triarylamine) (BTA) radical cation, bridged by two o-terphenylene moieties, was prepared and characterized to explore the impact of the double-π-bridge on the intramolecular charge/spin transfer process in the 2-site organic mixed-valence (MV) compound. Spectroscopic analyses on optically and thermally assisted intervalence charge-transfer (IVCT) processes revealed that the doubly π-bridging enhanced the charge delocalization between two nitrogen redox-active centers, whereas the electronic coupling was not so strengthened, in comparison with the singly π-bridging reference compound.

Boosting Photoconductivity by Increasing the Structural Complexity of Multivariate Covalent Organic Frameworks.

The assessment of the photoconductivity of Donor-Acceptor (D-A) ordered bulk heterojunctions is gaining attention for the development of innovative organic semiconductors in optoelectronics. Here, the synthesis of pyrene-based (D) Covalent Organic Frameworks, achieve through a multivariate reaction involving two distinct acceptors is reported (A). The products are characterized using powder x-ray diffraction, N sorption isotherms, electronic microscopy, and in silico calculations, among other techniques.

Synthesis of substituent-free dioxadiaza[8]circulene to investigate intermolecular interactions and photophysical properties.

Peripherally unsubstituted dioxadiaza[8]circulene, as the first example of structurally identified pristine hetero[8]circulene, was synthesized by the substituent detachment reactions. The solid-state structures and photophysical properties were analysed to elucidate intermolecular interactions. Herzberg-Teller type emission was considered to explain the optical behavior.

Responsive Chirality: Tailoring Supramolecular Assemblies with External Stimuli as Future Platforms for Electronic/Spintronic Materials.

Supramolecular chirality is the major branch of supramolecular chemistry, which not only plays important roles in biological processes but also in synthetically designed aggregated systems. To understand the complex processing of biological systems, the only way is to design supramolecular chiral ensembles that mimic natural biomolecules such as Deoxyribonucleic acid (DNA), Ribonucleic acid (RNA), amino acids, etc. In addition, chiral systems and self-assemblies as molecular motifs with breaking spatial inversion symmetry have been regarded as key substances in electronics and spintronics as well as in fundamental chemistry and physics.

Electron Transport over 2D Molecular Materials and Assemblies.

ConspectusTwo-dimensional (2D) molecular materials, in which the major interactions are confined in 2D planes with contrasted force fields acting in between the planes, have been key electronic functional materials since the past decade. Even without referring to the functionals of graphene-based systems, 2D electronic conjugated systems are expected to show extrawide dynamic ranges in electronic density of states (DOS) tuning, effective electron mass, electron mobility, and conductivity. A major advantage of 2D electronic systems is their compatibility with the ubiquitous electronic devices designed using planar structures, such as transistors and memories, which is associated with the utility of 2D active materials.

An n-type semiconducting diazaporphyrin-based hydrogen-bonded organic framework.

Significant effort has been devoted to the development of materials that combine high electrical conductivity and permanent porosity. This paper discloses a diazaporphyrin-based hydrogen-bonded organic framework (HOF) with porosity and n-type semiconductivity. A 5,15-diazaporphyrin Ni(ii) complex with carboxyphenyl groups at the positions afforded a HOF due to hydrogen-bonding interactions between the carboxy groups and -nitrogen atoms.

Impacts of heteroatom substitution on the excited state dynamics of π-extended helicenes.

Benzo-annulated aza[9]helicene ([9]AH) and thia[9]helicene ([9]TH) were prepared as novel π-extended heterohelicenes. [9]TH showed a quite short fluorescence lifetime of ∼0.3 ns and intense phosphorescence at low temperature that were attributed to its larger spin-orbit coupling and faster intersystem crossing between pseudo-degenerate S and triplet states.

Ultrafine Spatial Modulation of Diazapyrene-Based Two-Dimensional Conjugated Covalent Organic Frameworks.

Tailormade bottom-up synthesis of covalent organic frameworks (COFs) from various functional building blocks offer not only tunable topology and pore size but also multidimensional properties. High crystallinity is one of the prerequisites for their structures and associated physicochemical properties. Among different π-conjugated motifs for constructing COFs, pyrene-based tetragonal structures are effective in achieving highly ordered and crystalline states.

Sulfur-Bridged Cationic Diazulenomethenes: Formation of Charge-Segregated Assembly with High Charge-Carrier Mobility.

Sulfur-bridged cationic diazulenomethenes were synthesized and exhibited high stability even under basic conditions due to the delocalization of positive charge over the whole π-conjugated skeleton. As a result of the effective delocalization and the absence of orthogonally oriented bulky substituents, the cationic π-conjugated skeletons formed a π-stacked array with short interfacial distances. A derivative with SbF as a counter anion formed a charge-segregated assembly in the crystalline state, rather than the generally favored charge-by-charge arrangement of oppositely charged species based on electrostatic interactions.

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 -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.

Norcorroles as antiaromatic π-electronic systems that form dimension-controlled assemblies.

Norcorrole derivatives with 3,4,5-trialkoxyphenyl moieties at the positions were synthesized to form various stacking assemblies in single crystals and thermotropic liquid crystals (LCs) depending on aliphatic chain lengths. Triple-decker stacking structures were formed the interactions between the antiaromatic systems formed for the butoxy and dodecyloxy derivatives in the single-crystal and LC states, respectively. In particular, the LC state exhibited discotic columnar structures comprising triple deckers to exhibit high electric conductivity, as supported by molecular dynamics simulations.

Substitution-pattern- and counteranion-dependent ion-pairing assemblies of heteroporphyrin-based π-electronic cations.

Metal complexation and peripheral modifications of thiaporphyrins have been investigated for preparing polarized π-electronic cations with anion-dependent ion-pairing assembling modes, including charge-segregated structures exhibiting electric conductive properties.

Carrier Transport Switching of Ferroelectric BTBT Derivative.

Alkylamide-substituted [1]benzothieno[3,2-][1]benzothiophene () derivative of -NHCOCH (), which has ferroelectric N-H···O= hydrogen-bonding network of alkylamide group and two-dimensional (2D) electric structure of π-cores, was prepared to design the external electric field-responsive organic semiconductors. The short-chain derivative of NHCOCH () revealed the coexistence of a 2D electronic band structure based on the herringbone arrangement and the one-dimensional (1D) hydrogen-bonding chain. formed a smectic E (SmE) liquid crystal phase above 412 K and showed ferroelectric hysteresis in the electric field-polarization (-) curves at 403-433 K.

Benzannulated Double Aza[9]helicenes: Synthesis, Structures, and (Chir)optical Properties.

A benzannulated double aza[9]helicene 1 was successfully synthesized via a one-pot oxidative fusion reaction. 1 was derivatized to N-alkylated double aza[9]helicene 1-Et and 1-Bu, whose structures were determined by X-ray diffraction analysis. 1-Et and 1-Bu exhibited red-shifted absorption and fluorescence spectra compared to single aza[9]helicene.

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.

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

An alkylamide-substituted [1]benzothieno[3,2-][1]benzothiophene () derivative of -CONHCH () and CH--CONHCH () 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 (-CONHCH) derivatives revealed the coexistence of two-dimensional (2D) electronic band structures brought from a herringbone arrangement of the π core and the one-dimensional (1D) hydrogen-bonding chains of -CONHCH chains. The thin films of and fabricated on the Si/SiO 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).

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.

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 β-position of one of the pyrrole units with remarkably elongated C-C bonds of about 1.60 Å.

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 TiS crystal, is synthesized via electrochemical intercalation of chiral molecules into a metallic TiS single crystal.