A new class of high T_g and organosoluble aromatic poly(amine-1,3,4-oxadiazole)s containing donor and acceptor moieties for blue-light-emitting materials

A new naphthylamine-derived aromatic dicarboxylic acid, 1-[N,N-di(4-carboxyphenyl)amino]-naphthalene (2), was successfully synthesized by the sodium hydride-mediated condensation of 1-aminonaphthalene with 4-fluorobenzonitrile, followed by the alkaline hydrolysis of the intermediate dicyano compound 1, Four poly(amine-hydrazide)s were prepared from the polycondensation reactions of the dicarboxylic acid 2 and 4,4′- dicarboxytriphenylamine (2′) with terephthalic dihydrazide (TPH) and isophthalic dihydrazide (IPH), respectively, via the Yamazaki phosphorylation reaction. The poly(amine-hydrazide)s were readily soluble in many common organic solvents and could be solution cast into transparent and flexible films with good mechanical properties. These hydrazide polymers had glass-transition temperatures (T_g) in the range of 182-230°C and could be thermally cyclodehydrated into the corresponding oxadiazole polymers in the range of 300-400°C. The resulting poly(amine-1,3,4-oxadiazole)s had useful levels of thermal stability associated with high T_g (263-277°C), 10% weight-loss temperatures in excess of 500°C, and char yield at 800°C in nitrogen higher than 54%. These polymers exhibited maximum UV-vis absorption at 344-391 and 352-391 nm in NMP solution and solid-state films, respectively. Their photoluminescence spectra in NMP solution showed maximum bands around 495-529 and 457-476 nm in the green and blue region for TPH and IPH series, respectively. The poly(amine-hydrazide) (I-IPH) derived from diacid 2 and IPH showed a blue photoluminescence at 457 nm with full-width at half-maximum (fwhm) of 85 nm and exhibited a 34% quantum yield in NMP solution. Blue electroluminescence characteristics were observed from the poly(amine-1,3,4- oxadiazole)s of III-IPH and III-TPH. Cyclic voltammograms of the poly(amine-hydrazide) films cast onto an indium-tin oxide (ITO)-coated glass substrate exhibited one oxidation redox couples (E_onset) at 1.11 V vs Ag/AgCl in dry acetonitrile solution, and revealed electrochromic characteristics with a color change from colorless to green at applied potentials switched between 0 and 1.6 V. The present study suggests that novel poly(amine-hydrazide)s and poly(amine-1,3,4-oxadiazole)s have a great potential as new blue-emitting materials with hole-transporting and electrochromic characteristics.