Synthesis and optical properties of copolymers containing electron transporting 1,3,4-oxadiazole pendant groups

Abstract

Well-defined copolymer, P(3,6-EHCZ-alt-MPAOXD), containing a triarylamine and N-alkylcarbazole groups (as hole transport moieties with blue emission) in the main chain and a 1,3,4-oxadiazole pendant group (as an electron transporting moiety) was synthesized by Pd-catalyzed polycondensation of N-(2-ethylhexyl)-3,6-dibromo carbazole with 2-methylphenyl-5-(4-aminophenyl)-1,3,4-oxadiazole. For comparison, P(3,6-EHCZ-alt-AL) containing a triarylamine and a carbazole groups in the main chain was also prepared. P(3,6-EHCZ-alt-AL) exhibited lambda(max,UV) at 309 nm and lambda(max,PL) in the range of blue emission at 452 nm. However, P(3,6-EHCZ-alt-MPAOXD) exhibited lambda(max,UV) at 283 nm with a new peak at 359 nm, and red-shifted PL emission at 506 nm, possibly attributed to the extended conjugation by 1,3,4-oxadiazole pendant group. The electrochemical results revealed that incorporation of 1,3,4-oxadiazole group in the polymer side chain provided a closely matched HOMO energy levels with hole-injecting PEDOT layer, and reduced the band gap energy level