Chromic

Reversible four-color electrochromism triggered by the electrochemical multi-step redox of Cr-based metallo-supramolecular polymers

Takefumi Yoshida, Yoshikazu Ninomiya and Masayoshi Higuchi

Four colors electrochromism (yellow, magenta, blue, and navy) has been achieved in Cr(III)-based metallo-supramolecular polymers (polyCr), which was synthesized by complexation of Cr ion and 1,4-di[[2,2':6',2''-terpyridin]-4'-yl]benzene (L). The polymer structure was determined by X-ray absorption fine structure (XAFS) measurement and X-ray photoelectron spectroscopy (XPS). Molecular weight of polyCr was calculated as 3.2 ×107 Da by right angle light scattering (RALS). The EXAFS fitting indicated that the bond distances of Cr–N are 2.020 and 2.208 Å, respectively. A firm of polyCr shows multi-color electrochromism (EC) or absorption: sharp peak at 380 nm at 0 V vs. Ag/Ag+(yellow), sharp peak at 510 nm and broad peak at 800 nm at –0.6 V vs. Ag/Ag+(magenta), broad peak at 610 nm and among 700-900 nm at –1.2 V vs. Ag/Ag+(blue), broad peak among 450-900 nm at –1.8 V vs. Ag/Ag+ (navy).The transmittances change (DT), the switching times for coloring and bleaching (Tc, Tb) and the coloration efficiency (hc,hb): [DT, (Tc, Tb), (hc,hb)] were [39.2% , (5.56 s, 1.39 s), (169 cm2/C, 230 cm2/C)] at 510 nm among –0.6 and 0.2 V vs. Ag/Ag+, [67.0%, (6.93s, 2.52 s), (138 cm2/C, 172 cm2/C)] at 610 nm among –1.2 and 0.2 V vs. Ag/Ag+, [86.1%, (6.80 s, 3.03 s), (167 cm2/C, 134 cm2/C)] at 780 nm among –1.8 and 0.2 V vs. Ag/Ag+, respectively, during the cycles. The durability expreimental indicates that polyCr shows EC property at least 100 cycles.