Double-Electrochromic Coordination Polymer Network Films

Formation and characteristic properties of organized double-electrochromic films consisting of electrochromic poly(4-(2,2':6,2″-terpyridyl)phenyliminofluorene) (P-1)-zinc ion complexes and electrochromic anions are reported. The anions are 2,2'-azino-bis(3-ethylbenzo-thiazoline-6-sulfonate) (ABTS) and poly((4-sulfonatophenyl)iminofluorene) (P-2). The films were prepared upon multiple sequential adsorption of P-1 and the zinc salts of ABTS and P-2 on solid supports using coordinative interactions between the Zn ions and the terpyridine (tpy) ligands. The ABTS and P-2 ions are incorporated in the films via electrostatic forces neutralizing the charge of the complexed divalent zinc (Zn(2+)) ions. The optical, electrochemical, and electrochromic properties of the films are described. Films consisting of the Zn ion complex of P-1 and ABTS are yellow in the neutral state and change their color to brownish gray and finally blue, if anodically oxidized at ∼640 mV vs FOC. Films containing the Zn ion complex of P-1, with P-2 as a counterion, are yellow in the neutral state and change color to dark red and finally blue, if anodically oxidized at ∼450 mV vs FOC. Compared with previously reported films of the Zn ion complex of P-1 with nonelectroactive hexafluorophosphate as the counterion, the new films exhibit faster response times, as well as higher contrast, and the colors in the oxidized state are modified. The films are stable under ambient conditions and might be useful as active layers in electrochromic devices.