Synthesis and characterization of a cyano-substituted electroluminescent polymer with well-defined conjugation length

Abstract

A novel copolymer, poly[1,6-hexanedioxy-1,4-phenylene-1,2-ethenylene-(2,5-dicyano-1,4- phenylene)-1,2-ethenylene-1,4-phenylene] (HCN-PPV), with alternating conjugated and non-conjugated blocks is synthesized by the Wittig reaction. The conjugated block containing one unit of 2,5-dicyano-1,4-phenylene vinylene is linked to a flexible linear hexyl chain spacer by an ether group in the backbone. The polymer is soluble in common organic solvents such as CHCl3 and CH2Cl2. The number average molecular weight (Mn) is 2517 with a polydispersity index of 1.75. The optical bandgap of HCN-PPV is 2.48 eV. λmax of the PL spectrum of the polymer film sample lies at 533 nm, corresponding to green light emission. The polymer also shows good thermal stability with a decomposition temperature of 304 °C under air atmosphere. Cyclic voltammetric investigation of the polymer reveals a reversible n-doping process and an irreversible p-doping process. The onset for the n-doping process occurs at -1.48 V (vs. SCE), while the onset for the p-doping process occurs at 1.19 V (vs. SCE). The results imply that HCN-PPV is an n-dope type electroluminescent polymer.