Novel soluble polyazomethines with pendant carbazole and triphenylamine derivatives: preparation, characterization, and optical, electrochemical and electrochromic properties

Abstract

Two series of novel polyazomethines (PAMs) P1–P5, Pa–Pe with an M_n of 1522–7879 g mol⁻¹ were prepared via the direct polycondensation from N,N-Bis(4-aminophenyl)-4-N′-carbazolyl-1,4- phenylenediamine, and N,N-Bis (4-aminophenyl)-N′,N′-di-phenyl-1,4-phenylenediamine with various dicarboxaldehyde such as phthaldialdehyde, 1,3-isophthalaldehyde, terephthalaldehyde, 4,4′-diformyltriphenylamine, 3,5-thiophenedialdehyde. All the polymers were amorphous with good solubility in many organic solvents, such as CHCl₃, tetrahydrofuran (THF), N-methyl-2-pyrrolidinone (NMP) and N,N-dimethylacetamide (DMAc), and could be solution-cast into polymer films. All polymers displayed outstanding thermal stabilities, i.e. 20% wt loss in excess of 470 °C under nitrogen. A hybrid density functional theory (DFT) method was used to calculate the optimized geometry and electronic structure of PAMs. The variation of the backbone ring significantly affected the dihedral angles and resulted in the variation of electronic properties. The HOMO and LUMO energy levels of these polymers calculated by electrochemistry and absorption spectra were in the range 4.687–5.189 and 2.366–2.989 eV below the vacuum level, respectively. Our study demonstrated the backbone ring can tune the electronic properties of conjugated PAMs effectively. All obtained PAMs revealed stability of electrochromic characteristics, changing color from original yellowish to red or violet or blue. And multiple reversible colours states were observed upon chemical doping. The properties prove that the polyazomethines are multipurpose materials which will be used in hole-transporting, electrochromic and chemical sensor applications in the near future.