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

Abstract

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.