Synthesis of Chain Type and Fused π-Conjugated Phosphole Derivatives

Phosphole has a low aromaticity and exhibits characteristic optical and electrochemical properties derived from the phosphorus-bridged 1,3-diene pi system. In addition, phosphole has an active lone pair at phosphorus. The most remarkable feature of the phosphole-based pi-systems is that their fundamental properties are tunable by chemical functionalizations at the phosphorus center. In this regard, phosphole-based pi-systems are now regarded as one of the future materials for use in optoelectronics. In this article, we would like to briefly summarize our recent results on the synthesis of novel pi-conjugated phosphole derivatives with representative examples, which contain phosphole-vinylene, phosphole-acetylene, phosphole-heterole, phosphole-benzene, phosphole-phosphole, benzo[c]phosphole, acenaphtho[c]phoshole, and diacenaphtho[b,d]phosphole skeletons. The target compounds were successfully prepared by two main approaches, titanacycle method and Stille coupling. Selected structural, optical, and electrochemical data for a few derivatives are also presented. The results described herein would give valuable information and guidelines for designing phosphole-based opto-electrochemical materials.