New cardo silylated poly(azomethine)s containing 9,9′-diphenylfluorene units as materials with Brønsted acid-dependent fluorescence

Aromatic poly(azomethine)s have been studied due to their attractive properties such as high thermal stability, semiconducting behavior and the ability to coordinate species with their imine units (CN). In this paper, the synthesis and characterization of two novel silylated poly(azomethine)s containing cardo units are reported. These materials were highly soluble in organic solvents such as chloroform and m-cresol and were thermally stable, and PAzMC1 exhibited a high glass transition temperature value (287 °C), while that for PAzMC2 was not observed. UV–visible spectrophotometry revealed absorption bands related to the aromatic backbone of both PAzMCs, 300–285 nm in tetrahydrofuran and 310–301 nm in dimethylsulfoxide, and bands attributed to the conjugated imine unit at around 350 nm. In order to investigate the phenomenon of the emission of fluorescence promoted by dopant agents with regard to potential optoelectronic applications, the materials were doped with H₂SO₄ and their optical and electrochemical properties investigated. Thus, the absorption band of the imine group was suppressed due to the nitrogen atoms being protonated. Fluorescence spectroscopy analysis developed in dilute solutions of polymers showed no emission from the undoped polymers, whereas the acid-doped species emitted fluorescence in the UV and violet regions (322 nm). Cyclic voltammetry measurements were carried out and HOMO–LUMO energies were estimated. This study provides a starting point for the development of new poly(azomethine)s with doping-dependent emission.