Dithiazolo[5,4-b:4′,5′-d]phosphole: A Highly Luminescent Electron-Accepting Building Block

A family of highly emissive dithiazolo[5,4‐b:4′,5′‐d]phospholes has been designed and synthesized. The structures of two trivalent P species, as well as their corresponding P oxides, have been confirmed by X‐ray crystallography. The parent dithiazolo[5,4‐b:4′,5′‐d]phosphole oxide exhibits strong blue photoluminescence at λem=442 nm, with an excellent quantum yield efficiency of ϕPL=0.81. The photophysical properties of these compounds can be easily tuned by extension of the conjugation and modification of the phosphorus center. Compared with the established dithieno[3,2‐b:2′,3′‐d]phosphole system, the incorporation of electronegative nitrogen atoms leads to significantly lowered frontier orbital energy levels, as validated by both electrochemistry and theoretical calculations, thus suggesting that the dithiazolo[5,4‐b:4′,5′‐d]phospholes are valuable, air‐stable, n‐type conjugated materials. These new building blocks have been further applied to the construction of an extended oligomer with fluorene. Extension of the dithiazolophosphole core with triazole units through click reactions also provides a suitable N,N‐chelating moiety for metal binding and a representative molecular species was successfully used as a selective colorimetric and fluorescent sensor for CuII ions. Sliding down with a glow: Incorporation of nitrogen atoms into the dithienophosphole scaffold generates a new building block, dithiazolo[5,4‐b:4′,5′‐d]phosphole (see scheme), that combines intense luminescence with high electron affinity. A family of conjugated small molecules and a polymer based on this building block have been synthesized by a click reaction that also serves as a selective colorimetric and fluorescent sensor for CuII.