The Synthesis and Properties of Ladder-Type π-Conjugated Compounds with Pyrrole and Phosphole Rings.

The phosphole ring is known as a useful building block for constructing π-conjugated organic materials. Here, we report ladder-type benzophospholo[3,2-]indole (BPI) derivatives where the phosphole and the pyrrole rings are directly fused. Compounds - with different aryl groups on the phosphorous center were successfully synthesized, and the solid-state structure of was confirmed using X-ray crystallographic analysis. The BPIs exhibit relatively high fluorescence quantum yield (Φ 0.50-0.72) and demonstrate a larger Stokes shift compared with a series of benzophospholo[3,2-]benzoheteroles. The benzophospholo[3,2-]carbazole derivative , which possesses a benzene ring between the phosphole and the pyrrole rings of the BPI, was also synthesized, and its solid-state structure was confirmed using X-ray crystallographic analysis. Compound was found to show a smaller Stokes shift compared with the BPI.