Synthesis and optical properties of a poly(2′,5′-dioctyloxy-4,4′,4″- terphenylenevinylene) with high content of (Z) vinylene units

Poly(2′,5′-dioctyloxy-4,4′,4″-terphenylenevinylene) with ( E ) configuration of the vinylene double bonds was prepared by Suzuki–Miyaura polymerization of ( E )-4,4′-dibromostilbene and 2,5-dioctyloxy-1,4-benzenediboronic acid. Attempts to extend this simple procedure to the synthesis of the polymer with ( Z ) configuration, starting from ( Z )-4,4′-dibromostilbene, were unsuccessful. However, the use of ( Z )-4,4′-diiodostilbene and a careful choice of Pd catalyst and experimental conditions, lead to a material with a >95/ Z )/( E ) ratio of vinylene units. The investigation of optical properties of both the ( E ) and ( Z ) polymers evidenced that ( Z ) linkages act as defects which reduce the effective conjugation length in the polymer backbone.