Multicolored and durable electrochromism in water soluble naphthalene and perylene based diimides

Organic small molecules are advantageous in electrochromism as they exhibit high coloration efficiency, fast switching with vivid colors range at low potential range. However, the main problems in this type of electrochromes are film processing and dissolution of the compound during operation to restrict the durability. Herein, we have successfully synthesized two water soluble sulfonate group containing arylene diimides; NDI-cored NTSA and PDI-cored PRSA and comprehensively characterized by different spectroscopic techniques, morphological investigation and electrochemical characterizations, etc. Two diffusion controlled quasi-reversible redox waves are envisaged in both the compounds for stepwise reduction of neutral species to mono-anion radical and mono-anion radical to di-anion radical formation. Both NTSA and PRSA films show multichromic EC behavior in low potential range of +0.5 to -1.5 V with high optical contrast and high coloration efficiencies when measured in solution electrolytes. The durability test unveils the 80% retention of the optical contrast for NTSA, while 82% retention of the same for PRSA even after 800 cycles. The solid state ECD made of PRSA film also divulges the similar multi-chromic EC behavior. The results can provide a viable approach to design the high performance cathodically colored PDI and NDI ECMs as the potential candidate for energy-saving multi-colored smart window.