Pi-conjugated phosphasilenes stabilized by fused-ring bulky groups.

Pi-conjugated phosphasilenes with a variety of aryl substituents on the silicon atom have been synthesized by the use of a 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl (Eind) group. X-ray structural analysis shows the highly coplanar pi-framework stabilized by the perpendicularly fixed Eind groups. The strong pi-pi* absorptions have been observed, demonstrating the extension of pi-conjugation over the skeleton. The DFT calculations indicate that the LUMO involves the substantial contribution of the 3p(pi)*(Si-P)-2p(pi)*(carbon pi-electron system) conjugation. The electrochemical properties of the phosphasilens are also presented.