Preparation, Characterization And Performance Of Photoresponsive Poly (Arylene Ether)s Containing Azobenzene

Polymers containing azobenzene units in main chains or as pendant groups along the backbone have been attracting a great deal of attention because of their potential applications in optical data storage, optical switches, and electro-optical modulators. Azo-polymers have many attractive features, especially their unique reversible photoisomerization and the anisotropy of the azobenzene chromophores. The photoisomerization can cause significant changes in the bulk properties, surface properties and polarity of the polymers. In recent years, azobenzene chromophores have been introduced into some high-Tg aromatic polymers such as azo-PI and azo-PU because this strategy is helpful to improve the stability of azobenzene chromophores for optical storage applications. Poly(arylene ether)s (PAEs) are high-performance thermoplastics well known for their excellent thermal, mechanical, and environmental stabilities. These materials can be used in a wide range of demanding applications from aerospace to microelectronics. Functionalized poly(arylene ether)s have received much attention due to their potential applications in proton-exchange membranes, light-emitting materials, and optical materials.In this work, we designed and synthesized a series of photoresponsive azo-poly(arylene ether)s by direct copolymerization or post-functionalization. Their trans-cis isomerization and optical properties were investigated. The detailed researches were summarized as the following:(1) A series of di-azobenzene functionalized poly(arylene ether)s were successfully synthesized via a nucleophilic substitution polycondensation reaction. These polymers exhibit good solubility and thermal stability. Upon irradiation with 360 nm UV light, all polymers exhibited obvious photoisomerization behavior in DMF solution due to the existence of azobenzene groups. The rate constants of the photoisomerization of copolymers were 0.0210, 0.0253, and 0.0309 s^-1 for 3b, 3c, and 3d, respectively. Copolymer 3b shows the lowest trans-to-cis photoisomerization rate due to the steric hindrance of the polymer chain configuration. Upon irradiation with a 532 nm Nd:YAG laser beam, copolymers presented large photoinduced birefringence with a remnant value greater than 85% of the saturation value, and no fatigue phenomena were observed after several cycles of inscription–erasure–inscription sequences. The photoinduced birefringence of copolymers has a strong dependence on temperature: at the beginning, the birefringence value increases with temperature until reaches its'maximum, and then decreases. Therefore the birefringence value can be controlled effectively by varying temperatures.(2) In order to improve the stability of photoinduced birefringence, a series of azobenzene functionalized poly(arylene ether)s with high glass transition temperature were successfully synthesized via post-functonalizaton reaction. These polymers exhibit high glass transition temperature (T_g>199 oC), good thermal stability (T_d5 > 384 oC) and homogeneous photoisomerization behaviors. These azo-polymers presented large, high-quality, photoinduced birefringence with a remnant value up to 94%, indicating the excellent stability of the photoinduced orientation. This stability is mainly attributed to the rigidity of aromatic structures of polymers, which suppress the relaxation process of the photoalignment. Furthermore, multiple writing/erasing experiments indicate that the azo-polymers have potential applications in reversible optical storage.(3) Generally, the flexibility of polymer chains is helpful for the motion of azobenzene groups and increasing the growth rates of birefringence. Therefore, we prepared novel poly(arylene ether)s with flexible azobenzene pendants by classical esterification with DCC and DMAP as catalyst at room temperature. Low reaction temperature and weak basic reaction medium can give a mild condition to avoid side-reaction of azo-polymer. These polymers exhibit good solubility, thermal stability and homogeneous photoisomerization behaviors. The most important is that the introduction of flexible segments between azobenzene groups and aromatic main chains greatly increases the growth rates of birefringence.(4) Patterning organic luminescent molecules with ordered micro/nanoscopic features has attracted much attention for their applications in photonics, optoelectronics, fullcolor displays, and other related areas. Dip-pen nanolithography (DPN), inkjet printing, shadow mask patterning and other methods are commonly used to achieve these color patterns. However, most of them require dedicated equipments and involve multiple steps. Herein, we prepared poly(arylene ether)s containing both azobenzene and rare earth luminescent groups to achieve color patterns. The carboxyl-containing azo-PAEs were used as macromolecular ligands. Using europium (Eu³⁺) or terbium (Tb³⁺) as the central ion and 1,10-phenanthroline (Phen) as co-ligand, a series of novel rare earth coordination polymers were prepared. IR measurements indicate that both the oxygen atoms of carboxyl groups of azo-PAEs and the nitrogen atoms of 1,10-phenanthroline were coordinated with rare earth ions. XRD measurements indicate the rare earth ions have been distributed homogeneously within the polymer matrix due to the formation of coordination bonds between rare earth ions and the carboxyl groups of azo-PAEs. By exposing rare earth polymers films to an interference pattern of laser beams (355 nm) at modest intensity, stable and blight fluorescent surface relief gratings (SRGs) can be formed. Furthermore, we fabricated designable and various fluorescent two-dimensional micropatterns by combination of the fluorescent azobenzene-containing materials and femtosecond laser direct writing technique. It is notable that the patterns are erasable and the color of patterns can be tailored easily by tuning the central ion.