Synthesis, Structures, and Properties of π-Extended Phosphindolizine Derivatives.

Dibenzo[b,g]phosphindolizine oxide and three types of benzo[e]naphthophosphindolizine oxides have been synthesized by the ring-closing metathesis of benzo[b]phosphole oxide and naphthophosphole oxides with two olefin tethers. Their molecular structures and properties were revealed by X-ray crystallographic analysis, UV-vis spectroscopy, and electrochemical analysis. The number and position of the benzene rings were found to alter the structural geometry and the HOMO/LUMO energy levels, and their effects were investigated by theoretical calculations. Among the phosphindolizine oxide derivatives investigated, only benzo[e]naphtho[2,3-b]phosphindolizine oxide with the naphthalene ring fused at 2,3-positions showed weak yellow fluorescence with a large Stokes shift.