Synthesis, photophysical and electrochemical properties of polyimides of tetraaryl imidazole

The new tetraaryl substituted imidazole-based diamines were designed and synthesized through Debus–Radziszewski imidazole synthesis, and characterized by FT-IR, 1H NMR spectroscopy and MASS spectroscopy. A series of new fluorescent polyimides (PI) were prepared by polymerization of the tetra substituted imidazole diamines with tetracarboxylic dianhydrides, such as pyromellitic dianhydride, naphthalene tetra carboxylic dianhydride and perylene tetra carboxylic dianhydride. These polymers were readily soluble in a variety of organic solvents and they also possess good thermal stability. The glass transition temperature of these polymers was in the range of 398–453 °C. The ultraviolet–visible absorption spectra showed that all of the polymers had absorption maxima around 344–521 nm with a fluorescence emission maxima around 420–531 nm. The electrochemical band gaps of PI-1, PI-2 and PI-3 copolymers are estimated to be 2.37, 2.17 and 2 eV, respectively. Similarly, the optical band gap of PI-1, PI-2 and PI-3 copolymers was found to be 3.15, 3.05, and 2.15 eV, respectively. These polymer exhibits fluorescence quantum yield of 0.65, 0.46, and 0.3% for PI-1, PI-2 and PI-3, respectively. The PIs also exhibited good flame retardant behavior.