Unconventional Conjugated Polymers Derived from a Common Set of trans-Enediyne Monomers

Abstract

This account describes our recent efforts in the design and synthesis of several series of unconventional conjugated polymers derived from a common set of trans-enediyne (tEDY) monomers. The journey started with a failed attempt, through acyclic diene metathesis of triene monomers, to prepare soluble polyacetylenes (PAs) having cross-conjugated side-groups on alternate double bonds along the main chain. At this seemingly dead end of the project, we found that the tEDY intermediates leading to triene monomers could undergo alkyne metathesis to generate soluble polydiacetylenes (PDAs). Such acyclic enediyne metathesis represents the first example of a solution synthesis of PDAs, in contrast to the conventional topochemical methods. By applying Glaser–Hay-type reaction conditions with selected tEDY monomers, polytriacetylenes were smoothly obtained; these possessed aromatic units directly attached to the polymer main chains, which significantly affected the electronic properties of the polymers. Furthermore, through hydroboration of the tEDY monomers, ‘boron-doped’ polyacetylenes (BDPAs) were prepared that can be considered as PAs with every fourth double bond replaced with a boron atom. These BDPAs represent the first boron main-chain conjugated polymers lacking aromatic units along the backbone, potentially enhancing electronic delocalization along the main chain.