Novel polyamides with pendant p-phenylenediamine and α-/β-substituted naphthalene: synthesis, characteristics, and effects of substitution sites on electro-switchable optical behaviors

Abstract

Recently, electro-switchable optical materials have attracted much attention for their promising applications in optoelectronic devices and biological analysis. The structures of active optical moieties are dominant for the resulting performance, which raises the requirement of studying their structure-property relationship. In this study, two p-phenylenediamine–based polyamides (α-HPA and β-HPA) containing α-/β-substituted pendant naphthalene were designed and synthesized to investigate the effect of two substitution sites of naphthalene on their thermal, optical, electrochemical, electrochromic, and electrofluorochromic behaviors. Quantum chemical calculations were carried out to help the analysis of the experimental results. The as-prepared polyamides both exhibited excellent solubility, thermal stabilities (no weight loss before 300 °C in air), and optical switching stability (500 cycles). Because of the more twisted conformation and stronger charge transfer effect between diphenylamine and α-substituted naphthalene, the α-HPA exhibited higher glass transition temperature, higher coloration efficiency, weaker fluorescence quantum efficiency, red-shifted emission wavelength, and rapider switching speed than the β-HPA. This study not only presents a deep understanding of substitution sites of fluorophores on the electro-switchable optical behaviors but also demonstrates the tailorability of the electrochromic/electrofluorochromic characteristics through fine structure adjustment, paving a pathway for further development of high-performance electrochromic/electrofluorochromic materials.