New azomethine-phthalic diimides: Synthesis and thermal, optical and electrochemical characterization

Abstract A new diamine with phthalic diimide moiety, i.e. N,N′-bis(4-amino-2,3,5,6-tetramethylphenyl)phthalene-1,4-dicarboxyimide was synthesized and applied for condensation with 4-(4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-heptadecafluoroundecyloxy)benzaldehyde and 4-octadecyloxybenzaldehyde, which resulted in two new azomethine-phthalic diimides (AZ-PDIs). Thermal, optical and electrochemical properties of AZ-PDIs were discussed in relation to their analogous containing instead of five-membered six-membered imide rings (AZ-NDIs) described in our previous work. The phase behavior of AZ-PDIs examined by differential scanning calorimetry (DSC) and polarized optical microscopy (POM) confirms their liquid crystalline properties in wide range of temperatures. AZ-PDIs do not show decomposition below 400 °C as was found based on thermogravimetric analyses (TGA). Optical properties of the prepared compounds were investigated by UV–vis and photoluminescence (PL) measurements. Azomethine-phthalic diimides emitted blue light with emission maximum ( λ em ) at ca. 446–492 nm contrary to azomethine-naphthalene diimides which emitted green light and λ em was at 536 and 540 nm. The obtained compounds are electrochemically active and undergo reversible reduction and oxidation as evidenced by differential pulse voltammetry (DPV). The azomethine-phthalic diimides exhibited low electrochemical band gap ca. 1.68 eV being promising for optoelectronic applications.