Triphenylmethane based-polyimines with multiple switching characteristics triggered by pH, photoirradiation and electrical current

Pursuing smart multifunctional materials development, novel polyimines containing various receptor groups were synthesized and fully characterized towards halochromic, electrochromic, and cis-trans photo-isomerization responses. To this aim, a novel triphenylmethane diamine carrying the photochromic receptor was prepared and used in polycondensation with aromatic or heteroaromatic dialdehydes. Structural, molecular weights, thermal, optical, and electrochemical characteristics were evaluated to accomplish the basic characterization. In addition, the density functional theory (DFT) was involved to calculate the optimized geometry and electronic structure of polyimines. The variation of the polymer backbone structure was significantly affected by the exocyclic bond angle and resulted in the modulation of the (opto)electronic properties. The switching characteristics induced by the environmental pH were surveyed by protonation with HCl vapors in the solid state, by means of UV–Vis spectroscopy, when planarity and donor-acceptor strength experienced important changes. At the action of the electrical current, all polyimines revealed electrochromic characteristics in the solid state, both during oxidation or reduction, with the color switch from original yellowish to light/dark orange or brown. These polymers further experienced fast trans-cis photoisomerization switches of the azo moiety anchored on the TPM core with high efficiency, up to 94 %, in solution, and good stability and reversibility, even in the solid state. The multifunctional behavior demonstrated by the present polyimines can be exploited in various (opto)electronic applications, including electrochromic devices and chemical sensors.