Preparation And Performance Of Azobenzene-containing Poly(Arylene Ether)s And Their Rare Earth Complexes

In recent years, polymers containing azobenzene units (azo-polymers) have attractedconsiderable attention owing to their potential application in optical data storage, opticalswitching and nonlinear optical materials. Because of the unique reversiblephotoisomerization and photoinduced anisotropy of the azobenzene chromophores,azo-polymers can show a variety of photoresponsive variations, such as photoinduced phasetransition, photoinduced surface-relief-gratings (SRGs), and photoinduced birefringence.Recently, the introduction of azobenzene chromophores to some high-Tgaromatic polymers isattractive, because this strategy is helpful to improve the stability of azobene chromophoresfor optical storage application. Poly(aryl ether)s (PAEs) are a family of high-performanceengineering thermoplastics with excellent thermal, mechanical and electrical properties.Functionalized poly(aryl ether)s have been widely studied as proton exchange membranes(PEMs), light emitting materials and optical materials.In this work, we designed and synthesized a series of azobenzene monomers, which hadbeen introduced into poly(arylene ether)s by nucleophilic substitution polycondensationreaction or grafting reaction. Their trans-cis isomerization and optical properties wereinvestigated. We also synthesized a series of rare earth Eu3+complexes usingazobenzene-containing poly(arylene ether)s as macromolecular ligands, and theirphotoresponsive behavior and fluorescence properties were also investigated. The detailedresearches were summarized as the following: (1) A series of poly(arylene ether)s containing mono/bis-azobenzene moieties in the sidechain were successfully synthesized via a nucleophilic substitution polycondensationreaction. These polymers exhibit good thermal stability. Upon irradiation with a532nm Nd:YAG laser beam, the poly(arylene ether)s with bis-azobenzene pendantsshowed larger photoinduced birefringence intensity and better stability of thephotoinduced orientation than the poly(arylene ether)s with mono-azobenzenependants. The photoinduced birefringence of the PAEs with bis-azobenzene pendantsshowed a dependence on temperature: at the beginning, the birefringence valueincreased with temperature until reached its’ maximum, and then decreased. Byexposing their spin-coating films to an interference pattern of laser beam, tpoly(arylene ether)s with bis-azobenzene pendants could be used for fabrication ofsurface relief gratings (SRGs).(2) A series of azobenzene-containing side-chain poly(arylene ether)s with variousspacer lengths (2,6or12methylene units) were successfully synthesized via anucleophilic substitution grafting reaction between poly(ether sulfone)s withhydroxylphenyl side groups and azobenzene monomers AZOi. These azo-polymersshow good thermal stability with glass transition temperatures and5%weight-losstemperatures above119oC and347oC, respectively. The results ofphotoisomerization experiments indicated that the polymer with longer spacerscorrespond to higher photoisomerization rates. Upon irradiation with a532nmneodymium doped yttrium aluminum garnet (Nd:YAG) laser beam, they presentedremnant values of birefringence larger than82%of the saturation value ofbirefringence, indicating the good stability of the photoinduced orientation. Nofatigue phenomena have been observed after several cycles ofinscription–erasure–inscription sequences.(3) Poly(arylene ether)s containing azobenzene chromophores and carboxyl groups inthe side chain was synthesized via a nucleophilic substitution grafting reaction. Thecarboxyl-containing azo-PAE was used as macromolecular ligands. Using europium (Eu3+) as the central ion and1,10-phenanthroline (Phen) as co-ligand, a novel rareearth coordination polymer was prepared. The introduction of rare ions decreased thephotoisomerization rates. Upon irradiation with a532nm neodymium doped yttriumaluminum garnet (Nd:YAG) laser beam, the rare earth coordination polymer showedbetter stability of the photoinduced orientation and less value of photoinducedbirefringence than the carboxyl-containing azo-PAE.(4) A series of novel rare earth Eu3+coordination polymers were prepared by usingmain-chain azobenzene-containing poly(arylene ether)s as macromolecular ligand，and1,10-phenanthroline and DMF as co-ligands. The main-chainazobenzene-containing poly(arylene ether)s was synthesized via a nucleophilicsubstitution polycondensation reaction. The rare earth complexes were confirmed bymeans of IR and WAXD. The UV–vis spectra of the lanthanide complexes usingmain-chain phenylazo naphthalen poly(aryl ether)s as macromolecular showed thatthe absorption wavelength of the azobenzene chromophore was separated from theexcitation and emission wavelengths of the lanthanide ions. By exposing the films ofthe lanthanide complexes to an interference pattern laser beam, surface relief gratings(SRGs) could be formed on the films. Under the excitation, fluorescent patterns ofthe SRGs could be observed by the measurement of fluorescence microscopy.