New naphthalene diimide-based compounds containing triarylamine units and imine linkages: Thermal, optical and electrochemical properties

Two novel poly(azomethinenaphthaleneimide)s (poly(AZ-NI)s) and azomethine-naphthalene diimide (AZ-NI) consisting of electron-donating triarylamine with imine linkages and electron-accepting naphthalene diimide moieties were prepared via condensation of N,N′-bis(4-amino-2,3,5,6-tetramethylphenyl)naphthalene-1,4,5,8-dicarboxyimide (DANDI) with 4-formyltriphenylamine, 4,4′-diformyltriphenylamine and 4,4′,4″-triformyltriphenylamine. The thermal degradation kinetics of obtained compounds was studied by TGA. The activation energy (Ea) of thermal decomposition process was estimated by the first order Coats–Redfern equation and was in the range 115.1–266.7 kJ/mol. Poly(AZ-NI)s and AZ-NI exhibited useful levels of thermal stability, their 5% weight-loss temperatures were above 350 °C. Optical properties of the prepared compounds were investigated by UV–vis and photoluminescence (PL) measurements. The obtained alternating donor–acceptor compounds emitted mainly blue light. The electrochemical behavior of poly(AZ-NI)s, AZ-NI and DANDI was studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). As calculated from CV, the electrochemical energy band gap (Eg) of the linear polymer was equal to 1.15 eV, but the Eg of the branched one was lower: 1.06 eV, whereas the Eg of AZ-NI and DANDI was 1.32 and 0.47 eV, respectively. For the first time, to the best of our knowledge, polynaphthaleneimides with triphenylamine units and azomethine linkages have been described in this article.