Abstract
Two new donor–acceptor (D–A) type organic conjugated random copolymers were successfully synthesized by three-component Stille coupling polymerization of indolo[3,2-b]carbazole (ICZ), isoindigo (IID) and thiophene units, namely PITID-X (X = 1 and 2), with the controlled monomer feed ratios of 3:1:4 and 1:1:2, respectively. The strategy of incorporating different alkyl-branched donor/acceptor units and raw material feed ratios facilitated the improvement of optical properties, solubility, conjugated structure, and electrochromic performance. Cyclic voltammetry, UV-vis-NIR absorption spectra, kinetic and colorimetric measurements of the spray-coated films were recorded in the fabricated three-electrode cells. The results showed that PITID-2, whose optical/electrical properties were better than that of PITID-1, was the candidate electrochromic material due to low band gap of 1.58 eV accompanying the color changing from cyan (neutral state) to gray (oxidized state). The copolymer also illustrated fast bleaching/coloration response time of 2.04/0.33 and 1.35/1.50 s in a 4 s time interval, high coloration efficiency of 171.52 and 153.08 cm2 C−1 and stable optical contrast of 18% and 58% at the wavelength of 675 and 1600 nm, respectively.
Highlights
Π-conjugated organic polymers that have inherently remarkable electron or hole-transporting properties have been intensively investigated in optoelectronic materials for their huge potential application in various semiconductor devices, including electrochromic devices [1,2,3,4]
The well-matched donor and acceptor units are widely used in low-band-gap copolymers, which contributes to the significant improvement of intramolecular charge transfer ability and the enhancement of conjugated backbone length with higher onset absorption wavelength and absorption intensity [7,8,9]
The transmittance showed that several peaks were identified due to thedue asymmetrical stretching curves showed that similar severalcharacteristic similar characteristic peaks were identified to the asymmetrical vibration the skeletal of specific chemical bond/groups
Summary
Π-conjugated organic polymers that have inherently remarkable electron or hole-transporting properties have been intensively investigated in optoelectronic materials for their huge potential application in various semiconductor devices, including electrochromic devices [1,2,3,4]. Following the D–A strategy, energy band-gap levels, structural characteristics, and electrochromic properties can be adjusted by introducing different monomer units and side chains [5,6]. Our group and other researchers synthesized versatile ICZ derivatives to obtain functional conjugate structures and investigated their charge transporting, hole-transporting abilities and electrochromic properties in devices [20,21,22]. The nitrogen and oxygen atoms in the two lactam rings contribute to form intramolecular hydrogen bond and planar structure This can enhance the effective conjugation length and π–π interaction leading to a narrow energy band gap and high extinction coefficiency [24,25]. The cyclic voltammetry, absorption profiles, kinetic curves, and stability measurements were carried out to compare the corresponding electrochromic properties of the two copolymer films via UV-vis-NIR spectrophotometer, which was used in conjunction with electrochemical workstation
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