Photoinduced orientation and cooperative motion of three epoxy-based azo polymers

Abstract

In this work, photoinduced orientation of three epoxy-based polymers bearing different type azo chromophores was studied. The epoxy-based azo polymers were synthesized through post-polymerization azo-coupling reactions based on an epoxy-based precursor polymer (BP-AN), which was synthesized by the step polymerization between bisphenol-A diglycidyl ether and aniline. The chromophore orientation and cooperative motion of the main-chain groups were studied by birefringence characterization, polarized infrared spectroscopy, and two-dimensional (2D)-IR correlation spectroscopy (COS). The results show that the orientation behavior of the epoxy-based azo polymers is closely related with the electronwithdrawing groups on the azo chromophores. The azo polymer BP-AZ-CN, which contains azo chromophores with cyano as the electron-withdrawing group, shows the fastest birefringence growth rate. The azo polymer BP-AZ-CA, containing carboxyl as the electron-withdrawing group, possesses high birefringence residual value and the highest saturated orientation degree in the series. Cooperative motion between azobenzene moieties and non-photochromic polymer backbone was revealed by polarized FTIR and 2D-IR COS. The photoinduced anisotropy is a result of the orientation of both azo chromophore and polymer main-chain. The understanding of the structure-property relationships can be used to develop materials with better performance for data storage and other applications.

Liquid-crystalline compounds containing both a strong push–pull azo chromophore and a cholesteryl unit as photoresponsive molecular glass materials

“…[2,4,5,33,36,[38][39][40] In contrast to the typical decay relaxation, no birefringence decrease is observed for CA-Chol and CN-Chol after switching off the irradiating light (Figure 4). [2,4,5,33,36,[38][39][40] In contrast to the typical decay relaxation, no birefringence decrease is observed for CA-Chol and CN-Chol after switching off the irradiating light (Figure 4).…”

“…R-Chol (R=CA, CN or NT) shows both the properties of glassy materials and liquid crystal (LC) depending on the temperature. 36 The liquid crystal textures of R-Chol (R = CA, CN or NT) observed with POM are given in Figure S3 (ESI). After glass transition, the materials enter the liquid crystalline phase as indicated by POM and XRD.…”

“…Before the excitation laser was switched on, no transmittance of the probing laser beam can be detected by the photodiode, because the sample placed between the crossed polarizers is isotropic. [31,32,36,38] It reflects the influence of the electron-withdrawing groups on the photoinduced orientation ability at the molecular level. As homeotropical alignment is typical in smectic LC, the predominant orientational direction of the mesogenic groups could be perpendicular to the substrate surface.…”

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

“…For main-chain azo polymers, it has been reported that photoinduced changes tend to be most pronounced for macromolecules that possess conformationally restricted geometries, because steric and electronic perturbations caused by local azobenzene isomerization can be more efficiently transmitted throughout the linkages [52,53]. Our previous study has indicated that the photoinduced orientation degree of a BP-based azo polymer bearing the carboxylic groups on chromophores is much higher than those of other polymers without the COOH groups in the series [54]. The study also revealed a more significant cooperative orientational motion of the azo chromophores and polymer main-chain groups for this polymer due to the hydrogen-bonding of the COOH groups.…”

Epoxy‐Based Azopolymers with Enhanced Photoresponsive Properties Obtained by Cationic Homopolymerization

“…Epoxy networks are intensively used in a wide range of technological applications due to their excellent thermal and mechanical properties . Currently, there are few published studies on the development of photoresponsive azo‐modified epoxy networks with different optical properties . We have previously reported the synthesis and characterization of azo‐modified epoxy systems obtained by different polymer growth mechanisms: step growth polymerization, by epoxy‐amine and epoxy‐isocyanate reactions, and anionic homopolymerization initiated by different amines .…”