Electrochemical and electrochromic properties of arylene diimide dyes with N-phenylphenothiazine units

Five arylene diimides containing N -phenylphenothiazine or N -phenyl-3,7-di- tert -butylphenothiazine units as N -substituents, coded as PTZ-PMDI , PTZ-NTDI , tBuPTZ-PMDI , tBuPTZ-NTDI and tBuPTZ-PTDI , were synthesized from condensation of N -(4-aminophenyl)phenothiazine and N -(4-aminophenyl)-3,7-di- tert -butylphenothiazine with pyromellitic dianhydride ( PMDA ), naphthalene-1,4,5,8-tetracarboxylic dianhydride ( NTDA ) and perylene-3,4,9,10-tetracarboxylic dianhydride ( PTDA ), respectively. Incorporation of tert -butyl substituents on the PTZ active sites reduces the oxidation potential and increases the redox stability and solubility of the PTZ-diimides. PTZ-PMDI and PTZ-NTDI without tert -butyl substituents on the PTZ units are insoluble in suitable organic solvents , therefore the characterization of their electrochemical and electrochromic properties is unavailable. All the tBuPTZ-diimide compounds were electrochemically active and underwent reversible oxidation and quasi-reversible reduction as evidenced by cyclic voltammetry studies. These diimide compounds changed colors when they were reduced and oxidized, demonstrating their multi-electrochromic properties. The tBuPTZ-diimides gave a colored state of pink and red upon electro-oxidation, together with a low onset bias of 0.6 V and good switching stabilities. The electrochromic devices using these diimides as electroactive compounds were constructed and their electrochromic performance was studied. • Redox-active arylene diimide dyes with N -phenylphenothiazine have been synthesized. • The diimide dyes showed ambipolar redox and electrochromic properties. • The diimides exhibited high optical contrast, coloration efficiency, and cycling stability.