Tetraalkoxyphenanthrene-Fused Dehydroannulenes: Synthesis, Self-Assembly, and Electronic, Optical, and Electrochemical Properties

Dehydro[12]- and [18]annulene-Fused Ball-Shaped Ruthenium Complex Oligomers: Synthesis, Aromatic/Antiaromatic Effect, and Symmetry for Near-Infrared Optical Properties

The appropriate arrangement of near-infrared (NIR) chromophores allows for the modification of the peak wavelength in the NIR region and efficient use of NIR light. However, the preparation of novel NIR chromophores using simple procedures remains a formidable challenge. Herein, we report the synthesis of ball-shaped ruthenium complex oligomers. The metal complexes can be synthesized in a single step and interact strongly with NIR light. Alkyne-substituted low-symmetry ball-shaped ruthenium complexes were synthesized and subjected to Eglinton coupling to obtain dehydro[12] and [18]annulene-fused dimers and trimers. Fine-tuning of the reaction conditions led to the selective synthesis of the target oligomers. NMR spectroscopy confirmed that the 18π-aromatic and 12π-antiaromatic properties of the annulene influenced the ruthenium complex chromophore, and magnetic circular dichroism spectroscopy showed changes in the electronic structure of their excited state owing to molecular-symmetry differences. The absorption coefficient in the NIR region of the absorption spectra of the oligomers increased significantly, supporting the efficient use of light by oligomerization. The formation of oligomers using ball-shaped metal complexes is a simple and effective strategy for controlling NIR optical properties.

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

Norcorrole derivatives with 3,4,5-trialkoxyphenyl moieties at the meso 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 via 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.

Transforming Hetera-Buckybowls into Chiral Conjugated Polycycles Incorporating Epoxycyclooctadiene: a Two-Step Approach

Chiral π-conjugated polycycles have garnered increasing attention due to versatile applications in optoelectronic materials and biological sciences. In this study, we report the synthesis of chiral π-conjugated polycycles incorporating a chiral epoxycyclooctadiene moiety. Our synthetic strategy capitalizes on the novel reactions of hetera-buckybowl triselenasumanene (TSS) and is achieved in two-step manner. Firstly, the TSS is regio-selectively transformed into its ortho-quinone form. Subsequently, the nucleophilic addition reactions of TSS ortho-quinone by phenylethynides are metal ion-dependent. When utilizing (phenylethynyl)magnesium bromide as the nucleophile, two phenylethynyls are furnished onto the edged benzene ring of TSS. When the nucleophile is (phenylethynyl)lithium, a cascade of nucleophilic addition, intermolecular electron-transfer, ring-opening, and tetradehydro-Diels-Alder (TDDA) reactions occur sequentially in one-pot, ultimately affording chiral π-conjugated polycycles featuring the epoxycyclooctadiene moiety as an integral part of their backbones. This work represents a step forward in the synthesis of chiral π-conjugated polycycles using TSS as synthon.

Synthesis and Characterization of Silyl[n]acediynes (Linearly Fused Benzodehydro[12]annulenes): Utilizing Bulkiness of Silyl Groups to Improve Selectivity

[n]Acediynes have unique properties owing to their highly strained and extended π-electron system. We have previously reported the selective synthesis of a silyl[1]acediyne, i.e., silyldibenzotetradehydro[12]annulene, utilizing the bulkiness of the silyl groups to improve the selectivity of the reaction. Herein, we report the facile synthesis of high-order silyl[n]acediynes via Eglington coupling between silyldiethynylbenzene and silyltetraethynylbenzene. In fact, silyl[2]acediyne as well as silyl[1]acediyne can be isolated from the reaction mixture. Their structures were determined using X-ray crystallography and discussed with reference to our previous report, and their spectroscopic properties, including absorption, fluorescence, Raman, and IR spectra, were fully characterized with DFT calculations. A drastic redshift in their absorption and fluorescence spectra occurred with an increase in the order number n of the [n]acediynes. The antiaromaticities of the dehydro[12]annulene moieties at the center of the annulene ring in these silylacediynes were also evaluated using NICS values. The calculated values were small and positive, which confirmed the weak antiaromatic character of the rings.

Arylene-hexaynylene and -octaynylene macrocycles: extending the polyyne chains drives self-association by enhanced dispersion force

Tetraalkoxyphenanthrylene-hexaynylene and -octaynylene macrocycles, which represent the first examples of isolable arylene-alkynylene macrocycles (AAMs) that contain polyyne chains longer than tetrayne, were synthesized and their self-association behavior was examined. Extending the polyyne chain from diyne to tetrayne, hexayne, and octayne exponentially increased the self-association constant of the macrocycles.

Trithiazolyl-1,3,5-triazines bearing decyloxybenzene moieties: synthesis, photophysical and electrochemical properties, and self-assembly behavior

We synthesized the first members of trithiazolyl-1,3,5-triazines that combine attractive photophysical and self-assembling properties.

Effective stabilization of a planar phosphorus(iii) center embedded in a porphyrin-based fused aromatic skeleton

Planar phosphorus(iii) centers were effectively stabilized by structural constraint as well as aromatic stabilization in porphyrin-based fused π-conjugated frameworks.

Organophosphorus(iii) compounds usually take on stable pyramidal structures with a large inversion barrier of 30–35 kcal mol^–1. In contrast, diphenylphosphine-fused Ni(ii) porphyrin, where the phosphorus atom is directly attached at the meso-position and embedded in a rigid skeleton, exhibits a considerably planarized phosphorus center. Here we report the synthesis of a mesityl-substituted Ni(ii) porphyrin analogue, 6, which allowed an evaluation of the inversion barrier (ΔG‡203) by variable temperature ¹H NMR spectroscopy which showed it to be exceptionally small, at 14.0 kcal mol^–1. The observed small inversion barrier has been attributed to conformational constraint imposed by the fused structure. In addition, it was thought that the planar transition state is stabilized by the Ni(ii) porphyrin network that allows the contribution of a 22π-aromatic circuit involving phosphorus lone-pair electrons. Along this postulate, we attempted to engineer diarylphosphine-fused porphyrins with smaller inversion barriers by replacing the fused benzene rings with five-membered heterocyclic rings such as thiophene, benzothiophene, benzofuran, indole, benzothiophene 1,1-dioxide, and thiophene 1,1-dioxide. In that order, the aromatic character of the heterocycle decreases, which leads to increasing contribution of the 22π-aromatic circuit. Actually, the inversion barrier of the phosphorus center becomes smaller in this order and reaches 8.7 kcal mol^–1 for thiophene 1,1-dioxide-fused Ni(ii) porphyrin 15, supporting the postulate.

Tetraalkoxyphenanthrene-Fused Thiadiazoloquinoxalines: Synthesis, Electronic, Optical, and Electrochemical Properties, and Self-Assembly

π-Extended thiadiazoloquinoxaline (TQ) derivatives 1a,b-3a,b, in which a tetraalkoxyphenanthrene moiety is annulated with the TQ core and benzene rings are incorporated via the ethynylene spacer, were synthesized. They display absorption bands reaching into 750 nm and possess the electron-affinity comparable to [60]fullerene. The CF₃- and OMe-substituents on the benzene rings have moderate effects on modulation of the HOMO and LUMO levels. Tetraalkoxyphenanthrene-fused TQs 1a,b-3a,b aggregate in the solid state and assemble in solution through π-π stacking interactions. The self-assembly of 1a,b-3a,b into 1D superstructures was confirmed, and the difference in the alkoxy groups and the solvents for self-assembly proved to change their morphology. Comparison of the properties of 1a and those of reference compounds 4 and 5 clarified the effects of both the fusion of the phenanthrene moiety and the introduction of ethynylene spacers on the properties.

Facile Synthesis of Polycyclic Pentalenes with Enhanced Hückel Antiaromaticity

Pentalenes represent highly reactive Hückel antiaromatics with 8π electrons. Usually, pentalenes are stabilized by incorporation of two benzene rings in a fused fashion. In dibenzo[a,e]pentalenes, however, the high aromaticity of the fused benzene rings compromises the inherent antiaromaticity of the pentalene core. Herein, we disclose that this forfeited antiaromaticity can be restored by fusing four additional aromatic rings onto the peripheral positions of dibenzo[a,e]pentalenes. Such polycyclic pentalenes were prepared by successive transannular cyclizations via in situ-generated tetrakisdehydro[16]annulenes. The thus obtained compounds showed intriguing properties, for example, characteristic absorptions in the visible-to-near-infrared (NIR) region and low reduction potentials. These results hence afford a design principle to produce highly antiaromatic yet stable pentalenes. The antiaromaticity of the pentalene core can be widely tuned via the degree of aromaticity of the peripherally fused rings.

3D and 2D supramolecular assemblies and thermotropic behaviour of a carbo-benzenic mesogen

A carbo-benzenic mesogen gives rise to a tubular-columnar discotic liquid crystal at 115 °C, the rectangular arrangement of which is identical in STM images on an HOPG surface.

Benzo- and Naphthopentalenes: Syntheses, Structures, and Properties

Benzo- and naphthopentalene derivatives were synthesized, and the effects of structural variations on their antiaromaticity and optoelectronic and electrochemical properties were examined experimentally and theoretically in detail. The results unveiled that with increasing the bond order of the carbon-carbon bond ([5,6] junction) shared by the pentalene and aromatic moieties, the 8π antiaromatic character of pentalene is enhanced and the HOMO-LUMO gap is decreased, which accompanies both the elevation of the HOMO level and the lowering of the LUMO level. The ethynylene units between the pentalene skeleton and the phenyl groups proved to extend π-conjugation sufficiently.

Synthesis and Characterization of Dirhenadehydro[12]annulenes

The 12-membered-ring metallacycles [mer-Re{≡CCH=C(R)C≡C-}Cl(PMe2 Ph)3 )]2 (R=CMe3 , 1-adamantyl), which are organometallic analogues of antiaromatic octadehydro[12]annulene, are prepared by heating the methyl carbyne complexes mer-Re{≡CCH=C(R)C≡CH}(CH3 )Cl(PMe2 Ph)3 . An intermolecular σ-bond metathesis between the Re-CH3 bond and the acetylenic C-H bond is proposed for their formation.