Electrochromic π-Conjugated Copolymers Derived from Azulene, Fluorene, and Dialkyloxybenzothiadiazole

Abstract

A series of random π-conjugated copolymers P1, P2, and P3 were synthesised from 1,3-dibromoazulene, 4,7-dibromo-5,6-bis(dodecyloxy)benzo-2,1,3- thiadiazole, and 9,9-dioctylfluorene-2,7-bis(trimethyleneborate) via Suzuki coupling reactions. The copolymers P1-3 had molecular weights in the range of 17000-30900gmol-1 with polydispersity indexes of 1.45-2.03. Thermal analysis showed that the polymers P1-3 had good thermal stability with decomposition temperatures ranging from 341-363°C both in air and in nitrogen. Photoluminescence studies showed that polymer P1 and P2 are weakly fluorescent with low quantum yields of 0.013 and 0.0029 for P1 borne with 30% azulene and P2 borne with 50% azulene in the polymer backbone, respectively. P3 borne with 70% azulene resulted in complete quenching of fluorescence. The electrochemical band gaps for P1-3 are very close to their corresponding optical band gaps. Electrochromic study showed that three polymer thin films displayed the same colour change from yellowish green at the neutral and electrochemically-reduced state to greyish brown at the electrochemically-oxidised state. In particular, electrochromic contrasts of 17% and 13% for P2 and P3, respectively, were recorded in the near infrared region. © 2013 CSIRO.