Reducing polyazomethine to poly(N-phenylbenzylamine) with near infrared electrochromic, fluorescence and photovoltaic properties

Abstract

A novel series of solution-processable near-infrared (NIR) electrochromic aromatic poly(N-phenylbenzylamines) (RPAMs) have been synthesized by the reduction of polyazomethines (PAMs). The RPAMs were characterized by FT-IR and ¹H NMR spectroscopy. Thermogravimetric analysis (TGA) showed that all the RPAMs were stable, with 5% weight losses recorded above 353 °C in nitrogen atmosphere. All the polymers are readily soluble in common organic solvents such as CHCl₃, THF, DMF and DMAc. The RPAMs exhibit a strong blue-green fluorescence with a maximum at 415–514 nm, and the fluorescence quantum yield of RPAM-a in THF is about 18%. The PL intensity and color of the RPAMs changed depending on the value of pH. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of these polymers were determined in the range of −4.51–−5.03 and −1.58–−2.33 eV (vs. the vacuum level) by cyclic voltammetry method consistent with the results of quantum chemical calculation. The polymer films revealed excellent stability of the electrochromic characteristics, with a color change from neutral pale yellowish to a purple doped form at applied potentials ranging from 0.0 to 1.5 V. The RPAMs showed a typical photovoltaic response and the SEM images implied the RPAM would be inclined to self assemble into ball particles.