Trichalcogenasumanene ortho-Quinones: Synthesis, Properties, and Transformation into Various Heteropolycycles

Radical Cation Salts of Hetera-Buckybowls: Polar Crystals, Negative Thermal Expansion and Phase Transition

Radical cation salts of π-conjugated polycycles are rich in physical properties. Herein, two kinds of hetera-buckybowls, ethoxy-substituted trithiasumanene (3SEt) and triselenasumanene (3SeEt), are synthesized as electron donors. Galvanostatic oxidation of them affords radical cation salts (3SEt)5 (TTFMPB)3 , (3SeEt)5 (TTFMPB)3 , (3SEt)4 PMA, and (3SeEt)4 PMA, where PMA is Keggin-type phosphomolybdate and TTFMPB is tetrakis[3,5-bis(trifluoromethyl)-phenyl]borate. In these salts, 3SEt/3SeEt are partially charged and show distinct conformation change with the site charge and counter anions. In TTFMPB salts, (TTFMPB)- forms hexagonal channels that accommodate the packing columns of 3SEt/3SeEt. In particular, (3SEt)5 (TTFMPB)3 adopts the R3c space group and is a polar crystal with the columns of 3SEt all in the up-bowl direction. The PMA salts of 3SEt/3SeEt are polar crystals (C2 space group) with 3SEt/3SeEt being planar and forming columnar stacks. (3SeEt)4 PMA shows a structural modulation below 200 K, namely, negative thermal expansion (NTE) of the unit cell volume and enlargement of the intermolecular distances between neighboring 3SeEt molecules. The four salts are semiconductors with an activation energy of 0.18-0.38 eV. The conductivity of (3SeEt)4 PMA shows a reversible transition upon cooling and heating, in accordance to the NTE structural modulation. This work paves the way toward conducting materials based on hetera-buckybowls.

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 of the C70 Fragment Buckybowl, Homosumanene, and Heterahomosumanenes via Ring-Expansion Reactions from Sumanenone

Bowl-shaped aromatic molecules, buckybowls, are attractive molecules because of the unique properties derived from their curved-π scaffolds. Doping heteroatoms into buckybowl frameworks is a powerful method to change their structural and electronical properties. Herein, we report the synthesis of C₇₀ fragment buckybowl, homosumanene, and heterahomosumanenes having a lactone moiety and a lactam moiety via three ring-expansion reactions using sumanenone as a common intermediate. X-ray diffraction analysis of the single crystals reveals their columnar packing structure with a shallow bowl-depth. The lactam moiety is readily derivatized to give azahomosumanene derivatives, nitrogen-doped analogues of homosumanene possessing a pyridine ring at the peripheral carbon. The synthetic application of the α-phenyl azahomosumanene as a cyclometalating ligand with platinum also revealed its utility for preparing a metal complex bearing a buckybowl ligand.

Recent Advances in Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds

This review surveys recent progress in the chemistry of polycyclic heteroaromatic molecules with a focus on structural diversity and synthetic methodology. The article covers literature published during the period of 2016-2020, providing an update to our first review of this topic (Chem. Rev. 2017, 117 (4), 3479-3716).

Synthesis and derivatization of hetera-buckybowls

Buckybowls have concave and convex surfaces with distinct π-electron cloud distribution, and consequently they show unique structural and electronic features as compared to planar aromatic polycycles. Doping the π-framework of buckybowls with heteroatoms is an efficient scheme to tailor inherent properties, because the nature of heteroatoms plays a pivotal role in the structural and electronic characteristics of the resulting hetera-buckybowls. The design, synthesis, and derivatization of hetera-buckybowls open an avenue for obtaining fascinating organic entities not only of fundamental importance but also of promising applications in optoelectronics. In this review, we summarize the advances in hetera-buckybowl chemistry, particularly the synthetic strategies toward these scaffolds.

A tellura-Baeyer-Villiger oxidation: one-step transformation of tellurophene into chiral tellurinate lactone

Baeyer-Villiger (BV) oxidation is a fundamental organic reaction, whereas the hetero-BV oxidation is uncharted. Herein, a tellura-BV oxidation is discovered. By oxidizing a tellurophene-embedded and electron-rich polycycle (1) with mCPBA or Oxone, an oxygen atom is inserted into the Te-C bond of the tellurophene to form tellurinate lactone mono-2. This reaction proceeds as follows: (i) 1 is oxidized to the tellurophene Te-oxide form (IM-1); (ii) IM-1 undergoes tellura-BV oxidation to give mono-2. Moreover, the hybrid trichalcogenasumanenes 7 and 8 are, respectively, converted to tellurinate lactones mono-9 and mono-10 under the same conditions, indicating that tellura-BV oxidation shows high chemoselectivity. Due to the strong secondary bonding interactions between the Te[double bond, length as m-dash]O groups on tellurinate lactones, mono-2, mono-9, and mono-10 are dimerized to form U-shaped polycycles 2, 9, and 10, respectively. Notably, mono-2, mono-9, mono-10, and their dimers show chirality. This work enables one-step transformation of tellurophene into tellurinate lactone and construction of intricate polycycles.

The copper-catalyzed synthesis of (Z)-2H-naphtho[1,8-bc]thiophenes with solid emission

In recent years, one of the main research interests of our group has been the construction of 6/5 π-systems through the regioselective conversion of parallel alkynes in naphthalene with the aim of exploiting potential fluorescent materials. Herein, the copper-catalyzed synthesis of polysubstituted (Z)-2H-naphtho[1,8-bc]thiophenes from 8-halo-1-ethynylnaphthalenes using potassium ethylxanthate as the sulfur source is reported. In this protocol, a series of thiophene-fused 6/5 π-system compounds was synthesized via copper-catalyzed Ullmann-type C(aryl)-S bond formation and the α-addition of an alkyne bond with high selectivity and in high yields. The synthesized polysubstituted (Z)-2H-naphtho[1,8-bc]thiophenes exhibited solid emission, which made them potential candidates for use in optoelectronic conjugated materials. By using DMSO/D2O (3 : 1) as the reaction solvent, the deuterated products could be obtained in good yields under standard conditions.

Elucidation of Diverse Solid-State Packing in a Family of Electron-Deficient Expanded Helicenes via Microcrystal Electron Diffraction (MicroED)*

Solid-state packing plays a defining role in the properties of a molecular organic material, but it is difficult to elucidate in the absence of single crystals that are suitable for X-ray diffraction. Herein, we demonstrate the coupling of divergent synthesis with microcrystal electron diffraction (MicroED) for rapid assessment of solid-state packing motifs, using a class of chiral nanocarbons-expanded helicenes-as a proof of concept. Two highly selective oxidative dearomatizations of a readily accessible helicene provided a divergent route to four electron-deficient analogues containing quinone or quinoxaline units. Crystallization efforts consistently yielded microcrystals that were unsuitable for single-crystal X-ray diffraction, but ideal for MicroED. This technique facilitated the elucidation of solid-state structures of all five compounds with <1.1 Å resolution. The otherwise-inaccessible data revealed a range of notable packing behaviors, including four different space groups, homochirality in a crystal for a helicene with an extremely low enantiomerization barrier, and nanometer scale cavities.

Synthesis of novel regioisomeric phenanthro[a]phenazine derivatives through the SNAr strategy and their self-assembly into columnar phases

Synthesis and characterization of novel discotic liquid crystalline regioisomers for optoelectronic applications.

Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

Since the first synthetic report in 2003 by Sakurai et al., sumanene (derived from the Indian 'Hindi as well as Sanskrit word' "Suman", which means "Sunflower"), a beautifully simple yet much effective bowl-shaped C 3-symmetric polycyclic aromatic hydrocarbon having three benzylic positions clipped between three phenyl rings in the triphenylene framework has attracted a tremendous attention of researchers worldwide. Therefore, since its first successful synthesis, a variety of functionalized sumanenes as well as heterosumanenes have been developed because of their unique physiochemical properties. For example, bowl-to-bowl inversion, bowl depth, facial selectivity, crystal packing, metal complexes, intermolecular charge transfer systems, cation-π complexation, electron conductivity, optical properties and so on. Keeping the importance of this beautiful scaffold in mind, we compiled all the synthetic routes available for the construction of sumanene and its heteroatom derivatives including Mehta's first unsuccessful effort up to the latest achievements. Our major goal to write this review article was to provide a quick summary of where the field has been, where it stands at present, and where it might be going in near future. Although several reviews have been published on sumanene chemistry dealing with different aspects but this is the first report that comprehensively describes the 'all-in-one' chemistry of the sumanene architecture since its invention to till date. We feel that this attractive review article will definitely help the scientific community working not only in the area of organic synthesis but also in materials science and technology.

Synthesis of Tellurium-Containing π-Extended Aromatics with Room-Temperature Phosphorescence

A synthesis of tellurium-embedded π-extended aromatics from tellurium powder and readily available cyclic diaryliodonium salts has been developed. The versatility of this method has been demonstrated by the synthesis of various functionalized dibenzotellurophenes (DBTe's), a ladder-type π-system, and a heterosumanene. These compounds demonstrated good air/moisture stability and high thermal stability. Remarkably, many DBTe's exhibited interesting tunable room-temperature phosphorescence (RTP) in the solid state.

A "Phase Separation" Molecular Design Strategy Towards Large-Area 2D Molecular Crystals

2D molecular crystals (2DMCs) have attracted considerable attention because of their unique optoelectronic properties and potential applications. Taking advantage of the solution processability of organic semiconductors, solution self-assembly is considered an effective way to grow large-area 2DMCs. However, this route is largely blocked because a precise molecular design towards 2DMCs is missing and little is known about the relationship between 2D solution self-assembly and molecular structure. A "phase separation" molecular design strategy towards 2DMCs is proposed and layer-by-layer growth of millimeter-sized monolayer or few-layer 2DMCs is realized. High-performance organic phototransistors are constructed based on the 2DMCs with unprecedented photosensitivity (2.58 × 10⁷ ), high responsivity (1.91 × 10⁴ A W^-1 ), and high detectivity (4.93 × 10¹⁵ Jones). This "phase separation" molecular design strategy provides a guide for the design and synthesis of novel organic semiconductors that self-assemble into large-area 2DMCs for advanced organic (opto)electronics.

Doping Sumanene with Both Chalcogens and Phosphorus(V): One-Step Synthesis, Coordination, and Selective Response Toward AgI

Heterasumanenes 4-6 containing chalcogen (S, Se, and Te) and phosphorus atoms have been synthesized in a one-pot reaction from trichalcogenasumanenes 1-3 by replacing one chalcogen atom with a P=S unit. The P=S unit makes 4-6 almost planar and shrinks the HOMO-LUMO gap as compared to 1-3. The bonding between Ag⁺ and S atom on P=S brings about a distinct change to the optical properties of 4-6; 4 in particular shows a selective fluorescence response toward Ag⁺ with LOD of 0.21 μm. Compounds 4-6 form complexes with AgNO₃ to be (4)₂ ⋅AgNO₃ , (5)₂ ⋅AgNO₃ , and (6)₂ ⋅(AgNO₃ )₃ . In complexes, the coordination between Ag⁺ and P=S is observed, which leads to shrinkage of C-P and C-X (X=S, Se, Te) bond lengths. As a result, 4, 5, and 6 are all bowl-shaped in complexes with bowl-depths reaching to 0.66 Å, 0.42 Å, and 0.40 Å, respectively. There are Ag-Te dative bonds between Ag⁺ and Te atom on telluorophene in (6)₂ ⋅(AgNO₃ )₃ .

Trichalcogenasumanenes containing various chalcogen atoms: synthesis, structure, properties, and chemical reactivity

Trichalcogenasumanenes containing two kinds of chalcogen are synthesized. The majority chalcogen governs the optical properties and the heavier chalcogen governs the chemical reactivity.

Opening two benzene rings on trichalcogenasumanenes toward high performance organic optical-limiting materials

Two flanking benzene rings on trichalcogenasumanenes (1a/1b) were opened upon oxidation, and the successive ring reconstruction afforded donor-acceptor type polycycles containing diimide units (3a/3b). 3a and 3b show excellent optical-limiting properties superior to C60.

Biconcave and Convex-Concave Tribenzotriquinacene Dimers

A new chiral tribenzotriquinacene bearing an ortho-bromoaniline nucleus was synthesized and optically resolved. The individual enantiomers, the absolute configuration of which was confirmed by single-crystal X-ray structure analysis, were stereoselectively converted into the same pyrazine-fused syn-bis-TBTQ derivative by chirality-assisted Buchwald-Hartwig amination. The corresponding diastereomeric anti-dimer was obtained alongside the syn-dimer from the racemic sample under similar reaction conditions. X-ray structure analysis of the dimers confirmed the mutual biconcave and convex-concave configuration of their TBTQ moieties and the preservation of the orthogonal orientation of the indane wings within each of them.