Dithieno[3,2-b:2',3'-d]arsoles have been synthesized via a safe and easy synthetic procedure, in which volatile arsenic intermediates are excluded. The obtained dithienoarsole derivatives were stable in the ambient atmosphere, unlike their phosphorus analogues, dithienophospholes. The Suzuki-Miyaura coupling reaction is applicable for structural modification and expansion of the π-conjugated system, and carried out the polymerization of the compounds. Dithienoarsoles showed an intense emission not only in solution but also in the solid state, and their molecular packing was analyzed by X-ray crystallography. The main-chain type dithienoarsole polymer formed a luminescent film. This work has demonstrated that dithienoarsole is a promising building block for luminescent materials.

A synthetic method to obtain an arsole-containing π-conjugated polymer by the post-transformation of the organotitanium polymer titanacyclopentadiene-2,5-diyl unit with an arsenic-containing building block is described. The UV/Vis absorption maximum and onset of the polymer were observed at 517 nm and 612 nm, respectively. The polymer exhibits orange photoluminescence with an emission maximum (E ) of 600 nm and the quantum yield (Φ) of 0.05. The polymer proved to exhibit a quasi-reversible redox behavior in its cyclic voltammetric (CV) analysis. The energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were estimated to be -5.43 and -3.24 eV, respectively, from the onsets for oxidation and reduction signals in the CV analysis. Further chemical modification of the arsole unit in the π-conjugated polymer by complexation of gold(I) chloride occurred smoothly resulting in the bathochromic shift of the UV/Vis absorption and lowering of the LUMO energy level.

2,5-Diarylarsoles were easily synthesized from nonvolatile arsenic precursors. Diiodoarsine was generated in situ and reacted with titanacyclopentadienes to give 2,5-diarylarsoles. The structures and optical properties were studied in comparison with those of 2,5-diarylphosphole. It was found that the arsoles were much more stable in the air than the phosphole. Single crystal X-ray diffraction revealed the arsenic atoms adopted a trigonal pyramidal structure, reflecting on the s-character of the lone pair. The obtained 2,5-diarylarsoles and 2,5-diarylphosphole showed intense emission in solutions and solid state. In addition, the optical properties were controlled by transition-metal coordination.

We experimentally demonstrated the intrinsic nature of arsoles as promising functional heteroles. A series of 2,5-diarylarsoles are easily and safely prepared through the procedure in which non-volatile arsenic intermediates are employed to overcome the synthetic barrier due to the concern of volatility of the arsenic precursors used in conventional methods. A Pd-catalyzed Suzuki-Miyaura coupling reaction can be applied to the obtained arsoles for fine molecular design, unlikely to phospholes. It was demonstrated that the optical and electronic properties, i.e. emission colors, quantum yields, and energy levels of the frontier orbitals, are similar to those of phospholes, as conventional theoretical studies have predicted. Furthermore, it was found that arsoles showed mechanochromic properties.