Fully organic electroactive monomers for electrochromic behaviors having high coloration efficiency and long cycle stability towards flexible Solid-State electrochromic device

Constructing an electrochromic material with high switching stability as well as energy-saving property is really challenging with respect to the practical application which mainly depends on the lower response time, higher switching stabilities and higher colouration efficiencies. Herein, we have reported the design and synthesis of electroactive triphenylamine end capped to central pyromellitic dianhydride, naphthalenetetracarboxylic dianhydride, perylenetetracarboxylic dianhydride based three donor - acceptor - donor type monomers which are subsequently electropolymerized on conductive glass surface to have polymers which are subsequently explored by extensive cyclic voltammetry studies. Density functional theory (DFT) studies disclose that HOMO is localized solely on triphenylamine unit which accounts for the electropolymerization process upon oxidation. Besides, TD-DFT calculations unveil the responsible electronic transitions for electrochromism in the polymers. Three polymers exhibit the reversible multiple colour changes of colourless to brown to deep blue in the anodic region by applying voltage 0 to 1 to 1.2 V and also colourless to deep pink in the cathodic region (voltage window of 0 to −2 V) with attractive response times, optical contrast, switching stabilities, and coloration efficiencies. These polymers can be switched upto 10,000 cycles with the colouration efficiency 800 cm2/C in the anodic process and 600 cycles for the cathodic process in a three electrodes configuration. These values, to the best of our knowledge, are not reported for triphenylamine based fully organic electrochromic material till now. Finally, Solid-state devices made of three polymers have demonstrated the electrochromism operated at a potential range of 0 to 2.5 V. Among them, the large area (5 × 5 cm2) of device coated with naphthalenetetracarboxylic diimide is electrochemically stable for 4000 switching cycles, suggesting its suitability as a potential electrochromic material for next-generation flexible EC display application.