Novel luminescent and electrochromic polyhydrazides and polyoxadiazoles bearing pyrenylamine moieties

Abstract

New aromatic polyhydrazides bearing redox-active pyrenylamine unit were prepared from the polycondensation reactions of N,N-di(4-carboxyphenyl)-1-aminopyrene with terephthalic dihydrazide (TPH) and isophthalic dihydrazide (IPH), respectively, via the phosphorylation reaction. These two hydrazide polymers could be further cyclodehydrated into the corresponding oxadiazole polymers in the range of 300–400 °C in the solid state. The resulting poly(1,3,4-oxdiazole)s had high glass-transition temperatures (298–304 °C) and high thermal stability (10% weight-loss temperature in excess of 520 °C). The dilute solutions of all the hydrazide and oxadiazole polymers showed a medium to high fluorescence with emission maxima around 457–545 nm in the blue to yellowish-green region. The polymer films revealed one redox couples upon electrochemical oxidation, together with interesting electrochromic behaviors: color changes from pale yellow neutral state to pale green oxidized states. Additionally, cyclic voltammetry studies of the oxadiazole polymers also showed reduction processes accompanied by strong color changes from pale yellow to orange, red or deep blue due to the formation of radical anions of the oxadiazole and pyrene units.