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Improving electrochromic properties via copolymerization

Taskin, Asli Tuba
Balan, Abidin
Udum, Yasemin Arslan
Toppare, Levent Kamil
Copolymers of 5,8-di(1H-pyrrol-2-yl)-2,3-di(thiophen-2-yl) quinoxaline (PTQ) in the presence of 2,2'-bis(3,4-ethylenedioxythiophene) (BiEDOT) and 4,7-bis(2,3-dihydrothieno[3,4-b][1,4] dioxin-5-yl)-2-dodecyl-2H-benzo[1,2,3] triazole (BEBT) were synthesized via the potentiodynamic method in a tetrabutylammonium perchlorate/dichloromethane (TBAP/DCM) (0.1 M) solvent-electrolyte couple. P(PTQ-co-BiEDOT) reveals an oxidation potential at +0.45 V and a reduction potential at -0.2 V (figure 1(a)), whereas the homopolymer, P(PTQ) has an oxidation potential of +0.55 V and a reduction potential of +0.1 V. Spectroelectrochemical behaviors and the switching ability of copolymers were investigated by ultraviolet-visible (UV-vis) spectroscopy and cyclic voltammetry. The spectroelectrochemical behaviors of the P(PTQ-co-BiEDOT) and P(PTQ-co-BEBT) in comparison to the homopolymer revealed solid evidence of copolymerization based upon the differences in the spectral signatures. P(PTQ-co-BEBT) reveals 80% optical contrast at 1450 nm whereas the homopolymer achieves only 66% at 1460 nm. Coloration efficiency of P(PTQ-co-BEBT) was found to be 132 cm(2) C(-1) compared to 116 cm(2) C(-1) of the homopolymer at 100% full switch in the visible region. Switching times of the polymers were evaluated by kinetic studies upon measuring the per cent transmittance (%T) at the maximum contrast point. P(PTQ-co-BEBT) switches between the two extreme states in 0.5 s compared to 1.2 s for the homopolymer.