Synthesis, electrochromic, halochromic and electro-optical properties of polyazomethines with a carbazole core and triarylamine units serving as functional groups

Abstract

A series of aromatic polyazomethines (PAMs) were prepared via direct polycondensation from 9-(2-ethylhexyl)-carbazole-3,6-dicarboxaldehyde and six different types of diamine containing triarylamines. The PAMs displayed good solubility in many organic solvents, such as tetrahydrofuran (THF), chloroform (CHCl₃) and N,N-dimethylformamide (DMF) which was beneficial for polymer film formation via spin coating, and exhibited outstanding thermal stability. These PAMs exhibited blue-green photoluminescence around 405–520 nm with a quantum yield of up to 48% in a dichloromethane (CH₂Cl₂) solution. They exhibited halochromic properties with a color change from yellow to red, accompanied by fluorescence quenching after HCl-doping. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the PAMs were determined from cyclic voltammograms to be −5.01 to −4.88 eV and −2.15 to −2.11 eV, respectively. The PAMs films not only had good electrochromic properties with high coloration efficiency, but also generated photovoltage and photocurrent under simulated solar radiation.