Phenylthiophene-Containing Poly(2,5-dithienylpyrrole)s as Potential Anodic Layers for High-Contrast Electrochromic Devices

Abstract

A new phenylthiophene-containing 2,5-dithienylpyrrole derivative, namely 2,5-di(thiophen-2-yl)-1-(4-(thiophen-2-yl)phenyl)-pyrrole (DTTPP), was synthesized and its corresponding homopolymer (PDTTPP) and copolymers (P(DTTPP-co-DTP (dithieno[3,2-b:2’,3’-d]pyrrole)) and P(DTTPP-co-DTC (3,6-di(2-thienyl)carbazole))) were prepared using electrochemical polymerization. Spectroelectrochemical studies showed that the PDTTPP film was yellowish-green, bluish purple, and deep bluish violet in neutral, oxidized, and highly oxidized states, respectively. The P(DTTPP-co-DTP) film exhibited a conspicuous color transition between five colors (orange brown at 0 V, coffee at 0.8 V, bluish gray at 1.0 V, bluish purple at 1.2 V, and deep bluish violet at 1.4 V). The maximum optical contrast (ΔTmax) of the PDTTPP, P(DTTPP-co-DTP), and P(DTTPP-co-DTC) films were estimated as 36.7% at 970 nm, 63.5% at 1216 nm, and 46.2% at 932 nm, respectively, and the coloration efficiency (η) of the PDTTPP and P(DTTPP-co-DTP) films were determined as 303.84 cm2 C−1 at 970 nm and 260.65 cm2 C−1 at 1216 nm, respectively, in an ionic liquid solution. A dual type PDTTPP/PProDOT-Et2 (poly(3,3-diethyl-3,4-dihydro-2H-thieno[3,4–b][1,4]dioxepine)) electrochromic device (ECD) attained a high ΔTmax (43.5%) and a high coloration efficiency (895.53 cm2 C−1) at 594 nm, whereas a P(DTTPP-co-DTP)/PProDOT-Et2 ECD realized a high ΔTmax (52.4%) at 592 nm and satisfactory long-term cycling stability and open circuit memory.