Triphenylamine based redox-active, fluorescent polyamides: synthesis and photophysics

Abstract

An electroactive series of polyamides was synthesized from 4,4′-diamino-4′′-phenoxy triphenylamine (1), 4,4′-diamino-4′′-benzyloxy triphenylamine (2) and terephthaloyl or isophthaloyl chloride. The FTIR (Fourier Transform Infrared) spectral characterization and solubility test of the subsequent polyamides (PA I-IV), UV-vis, photoluminescence spectral analysis (PL) and cyclic voltammetry were utilized to assess photophysical and electrochemical properties of the materials. The oxidative-thermal stability of the polyamides as judged by thermogravimetric analysis was found to be in the range 438-532 °C with the char yield more than 53% at 800 °C. Introduction of aryloxy triphenylamine units along with polymer backbone flexibility improved the organosolubility of the synthesized polyamides (PA I-IV). The appreciable organosolubility of the (PA I-IV) is enough to be used in coating applications such as inkjet printing. Bluish green light emission from our synthesized materials upon excitation at 375 nm is credited to the triphenylamine linked amide-based polymer chain. Both pendent phenoxy and benzyloxy groups at para position in (PA I-IV) have also elevated the HOMO energy levels and hence lowered the onset oxidation potential. Additionally, the computational analysis was also conducted to get optimized ground-state geometry by DFT method (B3LYP) with 6-31G basis set. The 3-dimensional distributions of both HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) of the polymers were obtained. The computational data of the polymers also augmented the experimental data suggesting their future use as redox-active materials.