Transmissive-to-Black Electrochromic Devices Based on Cross-Linkable Tetraphenylethene-Diphenylamine Derivatives

Abstract

Transmissive-to-black switching organic electrochromic device based on a cross-linkable, symmetric diphenylamine derivative with a tetraphenylethene core is reported. The tetraphenylethene-diphenylamine derivative, TPOSt with thermally cross-linkable styrene end groups and the model derivative, TPOMe were synthesized as a mixture of cis- and trans- isomers by Buchwald-Hartwig amination reactions. Cross-linked films of TPOSt on ITO showed a reversible, two-electron redox peak at 0.69 V vs Ag/AgCl corresponding to the formation of TPOSt dications which exhibited an absorption spectra spanning the entire visible region and extending up to 1100 nm. Further, the electrochromic switching between a highly transmissive, light yellow colored neutral state (L*= 97, a*= -5, b*= 16) and a black coloured oxidized state (L*= 41, a*= 2, b*= 8) with high optical contrasts (up to 50%ΔT) and reasonably low switching times (<10 s) were demonstrated over 1500 cycles using a simple electrochromic device design [FTO/EC layer/ ...