Read e-book online Azo Polymers: Synthesis, Functions and Applications PDF

By Xiaogong Wang

ISBN-10: 3662534223

ISBN-13: 9783662534229

ISBN-10: 366253424X

ISBN-13: 9783662534243

This e-book explores practical polymers containing fragrant azo chromophores in side-chain, main-chain and different elements in their buildings, referred to as azo polymers and which proportion universal photoresponsive houses. It makes a speciality of the molecular structure of azo polymers, the artificial equipment and their most crucial services, akin to photoinduced birefringence and dichroism, surface-relief-grating (SRG) formation, and light-driven deformation of liquid crystal elastomers. It combines a normal survey of the topic and in-depth discussions of every subject, together with various illustrations, figures, and pictures. supplying a stability among an creation to the middle innovations and a photograph of sizzling and rising subject matters, it truly is of curiosity to graduate scholars and researchers operating during this and comparable fields.

Xiaogong Wang is a Professor on the division of Chemical Engineering, Tsinghua collage, China.

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Extra resources for Azo Polymers: Synthesis, Functions and Applications

Example text

Cis photoisomerization is considerably slowed down in the liquid compared to the gas phase, while the cis ! trans process is barely affected by the environment [77]. This difference has been attributed to the significant hindrance of the steric neighbor interactions to the reorientation of the phenyl rings. In a separate study, the photoisomerization of azobenzene in vacuum and various solvents has been studied by a modified molecular dynamic simulation adopting an ab initio torsion–inversion force field [78].

The early-stage exploration of the timeresolved spectroscopic studies on the photoisomerization mechanism can be traced back to the reports of emission from excited states of azobenzene [52, 53]. In that stage, the results obtained from the time-resolved spectroscopy supported the dualpathway mechanism proposed by Rau et al. [54–57]. Femtosecond time-resolved UV–vis absorption spectroscopy has been used to study the photoisomerization dynamics [55]. A short-lived transient absorption is observed at 370–450 nm, which is assigned to the absorption related to the S2 (π, π*) excited state of trans-azobenzene.

However, the approximation is invalid near degeneracies where potential energy surface cross. In this case, a small change in nuclear geometry will cause a large change in the electronic wave function [1]. In a PES representation, trans and cis isomers are shown as some minimum energy points on the ground energy surface separated by energy barriers. The trans– cis isomerization through intermediate structures is shown by a representative point moving on the PESs. The isomerization processes involve the PESs of the ground state S0 and few singlet and triplet excited states such as S1, S2, T1, and T2.

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Azo Polymers: Synthesis, Functions and Applications by Xiaogong Wang


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