Tuning the absorption spectra and nonlinear optical properties of D‐π‐A azobenzene derivatives by changing the dipole moment and conjugation length: a theoretical study

The optical properties of several azobenzene derivatives were modulated by varying the dipole moments and conjugation lengths of the D‐π‐A systems. The relationship between the structure and absorption spectrum and polarizability was studied in the gas phase, THF and MeOH solutions, respectively, by using the density functional theory. The calculated absorption spectra and second‐order polarizabilities are in good agreement with the available experimental observations. In comparison with the D‐π‐A monomer, the H‐shaped D‐π‐A dimer almost doubles the dipole moments and hence increases the second‐order polarizabilities, without a significant shift in the maximum absorption bands. The addition of another azobenzol group between electron‐donating and ‐accepting groups increases the second‐order polarizabilities by 4–6 times, but leads to an evident red‐shift of about 65–80 nm in spectra. The relative second‐order polarizability of the halogen‐substituted derivatives is in the sequence of ? CF₃ > ? F > ? Cl > ? Br, without obvious substituent effects on the optical transparency. The D‐π‐A chromophores with the strong electron‐donating (amino) and ‐accepting (acetyl) substituent present the larger second‐order polarizabilities, at the cost of about 20 nm red‐shift of the maximum absorption lengths relative to the halogen‐substituted species. It is also demonstrated that both the linear and nonlinear optical properties augment with the increase in solvent polarity, accompanied by a red‐shift in the wavelengths of maximum absorption by about 18 and 23 nm, respectively, in THF and MeOH solutions. The changes in optical properties upon the structural modifications are further rationalized by the electronic structures of various H‐shaped dimers. Copyright © 2010 John Wiley & Sons, Ltd.     

Modification of Nucleic Acids by Azobenzene Derivatives and Their Applications in Biotechnology and Nanotechnology

Azobenzene has been widely used as a photoregulator due to its reversible photoisomerization, large structural change between E and Z isomers, high photoisomerization yield, and high chemical stability. On the other hand, some azobenzene derivatives can be used as universal quenchers for many fluorophores. Nucleic acid is a good candidate to be modified because it is not only the template of gene expression but also widely used for building well‐organized nanostructures and nanodevices. Because the size and polarity distribution of the azobenzene molecule is similar to a nucleobase pair, the introduction of azobenzene into nucleic acids has been shown to be an ingenious molecular design for constructing light‐switching biosystems or light‐driven nanomachines. Here we review recent advances in azobenzene‐modified nucleic acids and their applications for artificial regulation of gene expression and enzymatic reactions, construction of photoresponsive nanostructures and nanodevices, molecular beacons, as well as obtaining structural information using the introduced azobenzene as an internal probe. In particular, nucleic acids bearing multiple azobenzenes can be used as a novel artificial nanomaterial with merits of high sequence specificity, regular duplex structure, and high photoregulation efficiency. The combination of functional groups with biomolecules may further advance the development of chemical biotechnology and biomolecular engineering.     

Reversed‐Phase High‐Performance Liquid Chromatographic Separation and Determination of 4‐Amino‐azobenzene‐4′,5‐disulfonic Acid and Related Products in Industrial Wastewater Effluents

A simple and rapid reversed‐phase high‐performance liquid chromatographic method for the separation and determination of 4‐amino‐azobenzene‐4′,5‐disulfonic acid (AABDS) and its process‐related impurities was developed. The separation was achieved on a μ‐Bondapak C₁₈ column using 0.15 M ammonium sulfate‐acetonitrile (55:45) (v/v) as eluent. A UV‐visible spectrophotometric detector fixed at 386 nm was used both for detection and quantitation. The method was used not only for quality assurance but also for process development and wastewater management of AABDS.     

New Azobenzene Dye Colorimetric and Ratiometric Chemosensors for Mercury(Ⅱ)Ion

A new series of azobenzene dyes, which possessed colorimetric and ratiometric recognition to Hg²⁺ based on the mechanism of internal charge transfer (ICT), was developed and characterized. The molecules involving azo and imino functional groups can coordinate with Hg²⁺ to result in a large blue shift from 453 to 363 nm corresponding to a notable color change from orange to pale yellow in aqueous methanol solution (H₂O/CH₃OH=1/4, V/V), which can be applied to naked eye detection of Hg²⁺. The sensitivity, selectivity and binding mode of the sensors to Hg²⁺ were investigated by UV‐Vis spectroscopy.     

3-溴-4-丁氧基-4′-硝基偶氮苯三阶非线性光学性能的研究

采用Z扫描技术对一种新的偶氮苯类化合物的三阶非线性光学系数进行了测量。实验结果的分析表明,该化合物具有较大的三阶非线性极化率;其三阶非线性主要来源于强的π电子离域性。     

偶氮侧链聚合物液晶的光学性质及其光存储应用

有机聚合物是一类非重要的非线性光学材料，它在光通信和高密度光存储等高技术领域中有良好的应用前景，文章介绍了偶氮侧链聚合物液晶的光学性质及其在光存储领域中的应用。     

Photoresponsive Formation of an Intermolecular Minimal G‐Quadruplex Motif

The ability of three different bifunctional azobenzene linkers to enable the photoreversible formation of a defined intermolecular two‐tetrad G‐quadruplex upon UV/Vis irradiation was investigated. Circular dichroism and NMR spectroscopic data showed the formation of G‐quadruplexes with K⁺ ions at room temperature in all three cases with the corresponding azobenzene linker in an E conformation. However, only the para–para‐substituted azobenzene derivative enables photoswitching between a nonpolymorphic, stacked, tetramolecular G‐quadruplex and an unstructured state after E–Z isomerization.     

How Photoisomerization Drives Peptide Folding and Unfolding: Insights from QM/MM and MM Dynamics Simulations

Photoswitchable azobenzene cross‐linkers can control the folding and unfolding of peptides by photoisomerization and can thus regulate peptide affinities and enzyme activities. Using quantum mechanics/molecular mechanics (QM/MM) methods and classical MM force fields, we report the first molecular dynamics simulations of the photoinduced folding and unfolding processes in the azobenzene cross‐linked FK‐11 peptide. We find that the interactions between the peptide and the azobenzene cross‐linker are crucial for controlling the evolution of the secondary structure of the peptide and responsible for accelerating the folding and unfolding events. They also modify the photoisomerization mechanism of the azobenzene cross‐linker compared with the situation in vacuo or in solution.     

Volume generation towards dynamic surface morphing in liquid crystal polymer networks

ABSTRACT

Thin coatings based on liquid crystal networks (LCNs) modified with azobenzene moieties are able to create dynamic surface topographies in the micrometre range by exposure with UV light. The surface corrugations can be erased and restored by switching ‘off’ and ‘on’ the UV illumination. Various configurations were presented. The formation of the protrusions was proven to be induced mainly by excessive volume formation when the order in the LCNs is reduced. It is suggested that this extra volume formation can be further enhanced by stimulating the oscillatory dynamics of trans-cis and cis-trans isomerisation. Therefore, dual-wavelength exposure not only exciting the trans state of azobenzene by 365 nm UV light but simultaneously also the cis state by 455 nm blue light was shown to enhance the effect.