Electrosynthesis and Characterization of the Donor-Acceptor Type Multicolored Electrochromic Materials

Two novel monomer were synthesized via Stille cross coupling reaction. Electropolymerization of the monomers gave birth to the donor-acceptor type polymers: poly{10,13-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl) dibenzo[a,c]phenazine} (P1) and poly{10,13-bis(4-ethylthiophen-2-yl) dibenzo[a,c]phenazine} (P2). Cyclic voltammetry and UV-vis spectroscopy were used to study the electrochemical and optical properties of the polymer films. The surface morphologies of the polymer films were investigated by scanning electron microscopy (SEM). The slight structural modification of the two polymer films results in the variation of the optical and electronic properties. As shown in the studies, P1 film was green in the neutral state, and with the increment of the applied potentials, four different colors were observed (light green, greyish-green, grey and cadet blue). The P1 film had prominent high optical contrast (T%) of 74.8%, excellent response time of 0.6 s and good coloration efficiency (CE) of 285.8 cm(2)/C at 1600 nm. Electrochromic switching response for polymer film P1 at 470 nm, 790 nm was also monitored. The slight loss in percent transmittance contrast value at the three given wavelengths indicated the stable ability of the polymer film of P1. The colors of polymer film P2 in the neutral and oxidized state were greyish-blue and cadet green, respectively. The optical contrast (T%) of P2 film was found to be 64.5%, the response time was 2.4 s and the coloration efficiency (CE) was 316.7 cm(2)/C at the wavelength of 1340 nm. P2 film showed high stability at the wavelength of 1340 nm, but at 754 nm the stability was not satisfactory. Moreover, both of the two polymers exhibited low optical bandgap (E-g) (the E-g of P1 was 1.26 eV and the E-g of P2 was 1.54 eV). Both polymer films revealed obvious donor-acceptor behaviors, and they were not only n-dopable but also p-dopable.