Electrochemical and optical properties of novel terthienyl based azobenzene, coumarine and fluorescein containing polymers: Multicolored electrochromic polymers

Three electroactive terthienyl based monomers, namely 1-phenyl-2-[4-(2,2′:5′,2″-terthien-3′-ylmethoxy)phenyl]diazene (TTAz), 4-(2,2′:5′,2″-terthien-3′-ylmethoxy)-2H-chromen-2-one (TTCo) and methyl 2-[3-oxo-6-(2,2′:5′,2″-terthien-3′-ylmethoxy)-3H-xanthen-9-yl] benzoate (TTFlo), were synthesized with good yields and their conducting polymers were electrochemically prepared on ITO electrode surfaces. The effect of chromophore type on electrochemical and optical properties of the polymers was investigated using cyclic voltammetry and spectroelectrochemical techniques in detail. Results revealed that type of chromophore group greatly influences the electronic and optoelectronic behaviors of electrochromic materials. It was observed that PTTAz, PTTCo and PTTFlo also exhibited multicolored electrochromism at their neutral and oxidized states. Electrochromic switching studies indicated that PTTAz (28% at 500 nm, 25% at 770 nm and 64% at 1220 nm) and PTTCo (25% at 475 nm, 32% at 740 nm and 63% at 1200 nm) have higher optical contrasts (ΔT%) with longer switching times than those of PTTFlo (16% at 496 nm and 50% at 1280 nm) in both visible and NIR regions. Comparing with PTTFlo film, PTTAz and PTTCo polymer films showed more reasonable switching stabilities. Besides, the optical band gaps were calculated from the onset of π-π* transition in polymer's neutral states, as 1.65 eV, 1.80 eV and 1.78 eV for PTTAz, PTTCo and PTTFlo, respectively.