Push Pull Azo Chromophores Research Articles

Functionalized polymers with strong push-pull azo chromophores in side chain for optical application

In this paper, we show that the optical properties such as extinction coefficient, refractive index, optical conductivity and optical energy band gap of aminoazobenzene and pseudostilbene-type azobenzene polymers can be effectively manipulated by changing or adding various substituents in their polymeric system.We found that the absorption spectrum of aminoazobenzene polymer thin film is shifted to blue compared to pseudostilbene-type azobenzene polymer thin films. Therefore, the optical energy band gap for aminoazobenzene polymer thin film is higher than for pseudostilbene-type azobenzene polymers. We also noticed that the studied azo dyes polymer thin films exhibit high photoresponse proper for use in the optoelectronic applications.

Azo Polymer Microspheres with Photo‐Manipulated Surface and Topographic Structure

A methacrylate‐based copolymer containing side‐chain push–pull azo chromophores and adamantyl groups is synthesized and characterized by 1H NMR, DSC, thermal gravimetric analysis, gel permeation chromatography, and UV–vis. By exploiting its good solubility in a water‐immiscible solvent (dichloromethane), azo polymer microspheres are fabricated through the solution dispersion method. Surface relief structures are inscribed on the microsphere surfaces upon exposure to the interference pattern of laser beams at 532 nm. Meanwhile, the shape of the microspheres is stable upon the light irradiation, which is distinct from the submicron‐scale colloidal spheres of azo polymers. By using camphene as a porogen, microspheres with the well‐developed porous structures are prepared. For the first time, it is observed that pores on the azo polymer microspheres can be modified or even selectively closed upon irradiation with a linearly polarized laser beam. image

Epoxy-based azo polymer for photofabricating surface-relief quasi-crystal structures

A new epoxy-based azo polymer (BP-AZ-CSMB), which contained chiral-substituted push-pull azo chromophores, was synthesized by the post-polymerization azo-coupling reaction. This newly synthesized polymer was characterized by 1H NMR, FTIR, GPC, UV-Vis, DSC and TGA. When exposed to interference patterns of laser beam (532 nm, 100 mW cm−2), BP-AZ-CSMB showed ability to quickly form surface-relief-gratings. Due to this property, quasi-crystal surface relief structures were feasibly fabricated on the BP-AZ-CSMB films by using the dual-beam multiple exposure technique. The quasi-crystal structures with 6-, 8-, 10-, 12-, 36-, and 72-fold rotation symmetry were successfully photofabricated.

Photoinduced deformation behavior of a series of newly synthesized epoxy-based polymers bearing push–pull azo chromophores

A series of epoxy-based azo polymers was synthesized from a precursor polymer that was obtained by step-polymerization between 1,4-cyclohexanedimethanol diglycidyl ether and aniline. The azo polymers were prepared by post-polymerization azo-coupling reactions of the precursor polymer with several diazonium salts to introduce azo chromophores bearing different electron-withdrawing groups. Photoinduced colloid deformation and surface modulation were investigated by using self-assembled colloidal spheres and spin-coated films of the azo polymers upon irradiation with Ar+ laser. Rates of both colloid deformation and surface modulation showed a close correlation with the electron-withdrawing groups on the p-positions of the azobenzene moieties. The azo polymer bearing the carboxyl group as the electron-withdrawing substituent showed much faster rates for both the colloid deformation and surface modulation compared with the others in the series. For comparable cases, the photoinduced deformation rates were obviously faster for the newly synthesized polymer compared with an epoxy-based azo polymer reported before.

Synthesis, thermal and light absorption properties of push-pull azochromophores substituted with dendronizing phenyl and perfluorophenyl fragments

Synthesis, thermal and light absorption properties of push-pull azochromophores substituted with dendronizing phenyl and perfluorophenyl fragments

Photoresponsive behavior of two well-defined azo polymers with different electron-withdrawing groups on push–pull azo chromophores

Two well-defined methacrylate-based azo polymers bearing strong push–pull azo chromophores were synthesized by RAFT polymerization. The polymers contain cyano and carboxyl as electron-withdrawing groups at 4-positions of the azo chromophores. The polymers exhibited significantly different photoresponsive properties on all light-driven motion levels. When irradiated with a linearly polarized laser beam at 532 nm, the cyanoazobenzene-containing polymer showed rapid birefringence growth relative to that of the carboxylazobenzene-containing polymer. When the light was switched off, a much lower orientation decay was observed for the carboxylazobenzene-containing polymer compared with its counterpart. Upon irradiation with the interfering laser beams at these two wavelengths, surface-relief-grating amplitude formed on the film of the cyanoazobenzene-containing polymer and was substantially larger than that for the carboxyl substituted polymer. When the polymer films were irradiated with a homogenous laser beam at 488 and 532 nm, self-structured surface pattern was only detected for the cyanoazobenzene-containing polymer with the 532 nm light irradiation.

Remote-control photocycloreversion of dithienylethene driven by strong push–pull azo chromophores

In this communication, a novel photochromic molecular switch DTE-2(Azo-CN) containing both dithienylethene and push-pull azo chromophores was synthesized. The push-pull azo chromophores can significantly accelerate the ring opening of the C-C bond of DTE closed isomer when irradiated with light far away from the maximum absorption band of the DTE closed isomer.

Photoresponsive diblock copolymers bearing strong push–pull azo chromophores and mesogenic biphenyl groups

Abstract A series of diblock copolymers bearing strong push–pull azo chromophores and mesogenic biphenyl groups in the respective blocks was synthesized by reversible addition fragmentation chain transfer polymerization through two successive polymerization steps. All the diblock copolymers with different ratios of the block lengths exhibited photoinduced birefringence behavior similar to a corresponding azo homopolymer. After switching off the irradiation light, the birefringence relaxation of the diblock copolymers was found to be much smaller compared with that of the azo homopolymer, which is a very attractive advantage for photo-storage applications. On the other hand, the surface-relief-grating formation observable for azo homopolymer could not be detected for the diblock copolymers. The results indicate that the photoresponsive properties of the azo polymer block are closely related with the phase-separated structure of the diblock copolymers and can be further optimized to meet the requirement for specific applications.

Photoresponsive diblock copolymers bearing strong push–pull azo chromophores and cholesteryl groups

A series of diblock copolymers bearing strong push–pull azo chromophores and cholesteryl groups on the respective blocks was synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization. The liquid crystal phase structure, microphase-separated morphology, and photoresponsive properties of the block copolymers were investigated by using DSC, POM, AFM, XRD and laser irradiation. The results show that the cholesteryl block (PChEMA) forms smectic-A mesophase and the morphology depends on the length of the azo block (PAzoCN). When the azo block is short, such as PChEMA50-b-PAzoCN7, no microphase separation can be identified. For PChEMA50-b-PAzoCN28, PAzoCN appears as the hexagonal-packed nanocylinders embedded in the PChEMA matrix. When the azo block length further increases, the block copolymer PChEMA50-b-PAzoCN73 forms microphase-separated lamellae. The microphase separation shows no obvious restraint on the photoinduced orientation of the azo chromophores, but micron-scale mass transport of the photoresponsive PAzoCN block is inhibited by the phase confinement.

Amphiphilic block copolymers bearing strong push–pull azo chromophores: Synthesis, micelle formation and photoinduced shape deformation

In this work, a series of amphiphilic diblock copolymers bearing strong push–pull type azo chromophores was synthesized through post-polymerization azo-coupling reaction scheme. The copolymers (P(CNAZOm-b-MAAn)), composed of 2-(N-ethyl-N-(4-(4′-cyanophenylazo)-phenyl)amino)ethyl methacrylate (CNAZO) and methacrylic acid (MAA) blocks, were obtained through four-step reactions. Firstly, precursor diblock copolymers (P(EMAm-b-tBMAn)) were obtained through sequential two-stage ATRP reactions of 2-(N-ethyl-N-phenylamino)ethyl methacrylate (EMA) and tert-butyl methacrylate (tBMA). Then, 4-amino-4′-cyanoazobenzene chromophores were introduced by azo-coupling reaction of P(EMAm-b-tBMAn) with diazonium salt of 4-aminobenzonitrile. Finally, P(CNAZOm-b-MAAn) was obtained through selective hydrolysis of the tert-butyl ester linkages in the tBMA blocks. Three block copolymers with the same CNAZO block length (m=100) and different MAA block lengths (n=5, 13, 23) were prepared by this method. The polymer and copolymers prepared in the process were characterized by GPC, 1H NMR, UV–vis, DSC and TGA measurements. Results show that P(CNAZOm-b-MAAn) forms spherical micellar aggregates by gradually increasing the water content in THF/H2O mixtures. The diameters of the spherical aggregates are related to the composition of the block copolymers and the water-adding rate. The block copolymer with larger molecular weight of the hydrophilic MAA block forms the aggregates with the smaller average size. The increase of the water-adding rate also shows an effect to reduce the diameters. Upon irradiation with a linearly polarized Ar+ laser beam, the spherical aggregates can be elongated in the light polarization direction. The deformation degree shows an almost linear dependence on the light irradiation time in the testing period. The deformed aggregates can recover the original spherical shape after thermal annealing at a temperature above Tg of the block copolymer.

Synthesis of 5-nitropyridin-2-ylazo push-pull derivatives

A practical method has been devised for the synthesis of previously unknown push-pull azochromophores with 5-nitropyridin-2-yl acceptor moiety from 2-amino-5-nitro-1-oxypyridine.