From thiophene to Sulflower

Theoretical study on the structures, electronic properties, and aromaticity of thia[4]circulenes

The structures, electronic properties, and aromaticity of a series of thia[4]circulenes are predicted using quantum chemical calculations.

Quadruply BN-Fused Tetrathia[8]circulenes with Flexible Frameworks: Synthesis, Structures and Properties

Quadruply BN-fused tetrathia[8]circulenes were synthesized through four-fold electrophilic borylation. The single-crystal X-ray diffraction analysis revealed that the BN-fused tetrathia[8]circulene with peripheral phenyl groups exhibits crystal polymorphism, in which the circulene core adopts both planar and saddle conformations in the solid state. The experimental and theoretical studies revealed that the weaker aromaticity of azaborine compared with benzene renders the flexibility of the BN-fused tetrathia[8]circulenes.

Enthalpically and Entropically Favorable Self-Assembly: Synthesis of C4h -Symmetric Tetraazatetrathia[8]circulenes by Regioselective Introduction of Pyridine Rings

Self-assembly of π-conjugated molecules in solution generally occurs owing to either an enthalpic or an entropic gain; however, designing π-conjugated systems that simultaneously exhibit enthalpically and entropically favorable self-assembly behavior is challenging. Herein, the self-assembly behavior of tetraazatetrathia[8]circulenes is disclosed, which is driven by both enthalpy and entropy. Single-crystal X-ray diffraction analysis demonstrated that molecules of these tetraazatetrathia[8]circulenes form face-to-face stacked dimers with a 1D columnar structure owing to the circularly arranged dipole moments. Importantly, concentration- and temperature-dependent ¹ H NMR spectra revealed that the formation of self-assemblies of tetraazatetrathia[8]circulenes in chloroform and methanol is favored by both enthalpic and entropic factors. The unique association behavior is due to the presence of sp² -hybridized nitrogen atoms, which weakly coordinate to the hydrogen atoms of these solvents and reduce the π-electron density of the circulene cores.

Aggregation-Induced Emission in Tetrathia[8]circulene Octaoxides via Restriction of the Dynamic Motion of their Negatively Curved π-Frameworks

Curved polycyclic aromatic hydrocarbons exhibit intriguing properties, but their flexible and dynamic nature is often considered to be unfavorable for achieving excellent emission properties. In this study, we prepared tetrathia[8]circulene octaoxides that adopt a negatively curved conformation. We found that these molecules exhibit aggregation-induced emission (AIE) that originates from the restriction of the dynamic motion of their saddle-shaped π-frameworks in the solid and aggregated states.

Chelated Fischer carbene complexes of annulated thiophenes: synthesis, structure and electrochemistry

Two (thieno[3,2-b]thiophene) and three annulated thiophenes (dithieno[2,3-b;3',2'-d]thiophene and dithieno[3,2-b;2',3'-d]thiophene) were employed as building blocks to synthesize linear or semi-circular chelated mononuclear biscarbene and dinuclear tetracarbene complexes. The electronic properties of the annulated thienylene chelated carbene complexes were investigated by cyclic voltammetry experiments and compared to non-chelated Fischer-type monocarbene complexes. Density functional theory (DFT) calculations were used to assign the redox events and to probe the extent of electron delocalisation as well as the possibility of electronic (intramolecular metal-metal) communication as a result of intervalence. The differences of these electronic properties in the conjugated chelated carbene complexes are compared to chelated carbene compounds without a linear conjugated pathway.

Hetero[8]circulenes: synthetic progress and intrinsic properties

Synthetic route for hetero[8]circulenes are classified into the annulative construction of eight-membered ring and the peripheral ring fusion of eight-membered ring. Post-transformation enables the tuning of structural features and electronic nature.

Aromaticity and photophysics of tetrasila- and tetragerma-annelated tetrathienylenes as new representatives of the hetero[8]circulene family

The electronic structure, absorption and emission spectra, aromaticity and photophysical behavior of the recently synthesized tetrasilatetrathia[8]circulene and tetragermatetrathia[8]circulene compounds have been studied computationally.

Metalcarbonyl analogues of annelated cyclooctatetraene and cyclodecapentaene derivatives with a planar core cycle: a quantum chemical study

With the help of DFT calculations the possibility of stabilizing non-standard flat conformations of cyclooctatetraene and cyclodecapentaene by equatorially located metalcarbonyl substituents has been predicted. Structures and stabilities of a new family of metalcarbonyl Cr(CO)5, Fe(CO)4, Ni(CO)3, Ti(CO)4, and Ni(CO)2 cyclooctatetraene and cyclodecapentaene derivatives have been studied. All cyclooctatetraene derivatives, except the Ti(CO)4 derivative, have planar structures and are characterized by the pronounced anti-aromaticity of the core cycle. In the case of cyclodecapentaene complexes, the planar structures are formed by only Fe(CO)4 and Ni(CO)3 derivatives. Stabilization of non-standard planar forms is caused by both sterically enforced flattening of the core cycles and their π-interactions with metalcarbonyl moieties.

Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds: Synthetic Routes, Properties, and Applications

Two-dimensionally extended, polycyclic heteroaromatic molecules (heterocyclic nanographenes) are a highly versatile class of organic materials, applicable as functional chromophores and organic semiconductors. In this Review, we discuss the rich chemistry of large heteroaromatics, focusing on their synthesis, electronic properties, and applications in materials science. This Review summarizes the historical development and current state of the art in this rapidly expanding field of research, which has become one of the key exploration areas of modern heterocyclic chemistry.

Diversity-oriented synthesis of tetrathia[8]circulenes by sequential C–H borylation and annulation

We have succeeded in the diversity-oriented synthesis of tetrathia[8]circulenes by sequential C–H borylation and annulation from cyclic tetrathiophene.

Quantum-mechanical calculations on molecular substructures involved in nanosystems

In this review article, four ideas are discussed: (a) aromaticity of fullerenes patched with flowers of 6-and 8-membered rings, optimized at the HF and DFT levels of theory, in terms of HOMA and NICS criteria; (b) polybenzene networks, from construction to energetic and vibrational spectra computations; (c) quantum-mechanical calculations on the repeat units of various P-type crystal networks and (d) construction and stability evaluation, at DFTB level of theory, of some exotic allotropes of diamond D5, involved in hyper-graphenes. The overall conclusion was that several of the yet hypothetical molecular nanostructures herein described are serious candidates to the status of real molecules.

Impact of heterocirculene molecular symmetry upon two-dimensional crystallization

Despite the development of crystal engineering, it remains a great challenge to predict the crystal structure even for the simplest molecules, and a clear link between molecular and crystal symmetry is missing in general. Here we demonstrate that the two-dimensional (2D) crystallization of heterocirculenes on a Au(111) surface is greatly affected by the molecular symmetry. By means of ultrahigh vacuum scanning tunneling microscopy, we observe a variety of 2D crystalline structures in the coverage range from submonolayer to monolayer for D_8h-symmetric sulflower (C₁₆S₈), whereas D_4h-symmetric selenosulflower (C₁₆S₄Se₄) forms square and rectangular lattices at submonolayer and monolayer coverages, respectively. No long-range ordered structure is observed for C_1h-symmetric selenosulflower (C₁₆S₅Se₃) self-assembling at submonolayer coverage. Such different self-assembly behaviors for the heterocirculenes with reduced molecular symmetries derive from the tendency toward close packing and the molecular symmetry retention in 2D crystallization due to van der Waals interactions.