Effect of the acceptor moiety on the electrochemical and electrochromic properties of Donor-Acceptor-Donor polymer films

摘要

The aim of this work is to synthesize EC polymers having green or blue colour in the neutral state andtransparent oxidized state by using the D-A-D approach. Two different monomers,diphenylthienopyrazine (M1) and diphenylquinoxaline (M2) are synthesized. The monomers aresuccessfully electropolymerized to P1 and P2, respectively, by cyclic voltammetry on ITO substrates.The effect of the acceptor moiety on the electrochemical and electrochromic properties of the polymerfilms is investigated. Both polymers exhibit the characteristic redox couple due to theiroxidation/reduction at 0.95 V/0.62 V for P1 and at 1.05 V/0.35 V for P2; their doping/dedopingreaction is reversible. The two polymers have different optical properties; namely, the phenyl ring inthe acceptor unit (P2) caused hypsochromic shift. The acceptor moiety affects mainly the LUMO level;specifically, the LUMO level shifted to less negative values by replacing thiophene with phenyl. Theelectrochromic properties of the polymer films are strongly affected by the acceptor moiety. PolymerP1 changes its colour from green (neutral state), to grey (intermediate oxidised state), to transparentgrey/sky blue (oxidized state) and to lemon green (reduced state). Correspondingly, P2 starts fromroyal blue (neutral state), going to blue purple, grey-blue and light grey (intermediate oxidised states)and then to green (oxidized state); additionally, it became also oil green and light blue (reduced states).Both polymers are multi-coloured and were good candidates for application in electrochromic devices.