Synthesis and properties of thieno[2,3-d:5,4-d’]bisthiazoles and their oxidized derivatives: Thionyl chloride as a sulfurative ring-fusing reagent towards thiophene-based ring-fused heteroaromatic compounds

Heteroarene-Fused Benzo[b]arsoles: Structure, Photophysical Properties, and Effects of the Bridging Element

Heteroarene-fused heteroles have attracted considerable attention owing to their unique electronic and photophysical properties. The bridging element plays a crucial role in determining the electronic characteristics of the resulting π-conjugated molecules. In this study, we synthesized a series of heteroarene-fused benzo[b]arsoles and investigated their structures and photophysical properties. All the synthesized arsoles exhibited phosphorescence at 77 K, whereas arsole oxide did not. The phosphorescence intensities of the pnictogen-containing heteroles (phosphorus and arsenic) were significantly higher than those of the tetrel-containing heteroles (silicon and germanium). This trend was analyzed through theoretical calculations, focusing on the energy levels of the excited singlet and triplet states as well as the spin-orbit coupling matrix elements. Furthermore, the indole-fused benzoarsole oxide exhibited a mechanically induced emission color change. The removal of crystalline water triggered a change in the molecular packing that reduced the excimer emission.

Synthesis and Characterization of a Cyclic Trimer of a Chiral Spirosilabifluorene

A chiral shape-persistent macrocyclic compound (Si-[3]), designed by the C/Si substitution in the spiro-atom of spirobifluorene in the cyclic trimer (C-[3]), has been successfully synthesized in this study. The C/Si substitution made the spiro-conjugation and energy levels of HOMO and LUMO decrease. Due to the silicon substitution, the macrocyclic compound Si-[3] was able to be degraded by fluoride ions, but its reaction rate was slower than that of the unsubstituted spirosilabifluorene, showing the chemical stability of Si-[3]. Furthermore, the chiroptical properties of Si-[3] with D3-symmetric macrocyclic structure were investigated, and (P,P,P)-Si-[3] showed a high emission quantum yield (Φf=80 %) and moderate dissymmetry factor of circularly polarized luminescence (CPL) (glum,exp=-1.2×10-3). According to the time-dependent density-functional theory (TD-DFT) calculations using polarizable continuum model (PCM), the bright CPL from Si-[3] was explained by a planarization of one bisilafluorenyl moiety at the excited state, which is responsible for the almost fully-allowed radiative transition with a short emission lifetime of τf=1.89 ns.

Facile synthesis of dibenzothiophene S-oxides from sulfinate esters

An efficient method to prepare dibenzothiophene S-oxides is disclosed. Suzuki-Miyaura cross-coupling of 2-bromoaryl sulfinate esters with arylboronic acids selectively at the bromo group followed by electrophilic cyclization of the resulting sulfinate ester moiety provides diverse dibenzothiophene S-oxides. Further transformations including Pummerer-type C-H propargylation and aryne reactions realize to synthesize highly functionalized dibenzothiophene derivatives.

Synthesis and stereochemistry of chiral aza-boraspirobifluorenes with tetrahedral boron-stereogenic centers

We have synthesized chiral aza-boraspirobifluorenes and evaluated their structural and photophysical properties.