A DFT Analysis of Electronic, Reactivity, and NLO responses of a Reactive Orange Dye: the Role of Hartree-fock Exchange Corrections

An experimental and theoretical study based on DFT/TD-DFT approximations is presented to understand the nature of electronic excitations, reactivity, and NLO properties of reactive orange 16 dye (RO16), an azo chromophore widely used in textile and pharmacological industries. The results show that the solvent has a considerable influence on the electronic properties of the material. According to experimental results, the absorption spectrum is noticed by four intense transitions, which have been identified as $\pi\rightarrow\pi^*$ states using TD-DFT calculations. However, the TD-DFT results reveal a weak $n\rightarrow\pi^*$ in the low-lying spectral region. Continuum models of solvation indicate that these states suffer bathochromic and hypsochromic shifts, respectively. However, the expected blue shift for the absorption $n\rightarrow\pi^*$ is only described using long-range or dispersion-corrected DFT methods. RO16 is classified as a strong electrophilic system ($\omega > 1.5$ eV). From vacuum to solvent, the environment is active and changes the nucleophilic status from strong to moderate nucleophile ($2.0 \leq N \leq 3.0$ eV). The results also suggest that all electrical constants are strongly dependent on long-rang and Hartree-Fock exchange contributions, and the absence of these interactions gives results far from reality. In particular, the results for the NLO response show that the chromophore presents a potential application in this field, with a low refractive index, and first-hyperpolarizability ca. 214 times bigger than the value usually reported for urea ($\beta = 0.34 \times 10^{-30}$ esu), which is a standard NLO material. Concerning the solvent effects, the results indicate that $\beta_\textrm{total}$ increases ca. 180\% regarding the gas-phase value. The results suggest RO16 is a potential compound in NLO applications.

Bio-Inspired Soft Robotics: Tunable Photo-Actuation Behavior of Azo Chromophore Containing Liquid Crystalline Elastomers

Bio-inspiration relentlessly sparks the novel ideas to develop innovative soft robotic structures from smart materials. The conceptual soft robotic designs inspired by biomimetic routes have resulted in pioneering research contributions based on the understanding of the material selection and actuation properties. In an attempt to overcome the hazardous injuries, soft robotic systems are used subsequently to ensure safe human–robot interaction. In contrast to dielectric elastomer actuators, prolific efforts were made by understanding the photo-actuating properties of liquid crystalline elastomers (LCEs) containing azo-derivatives to construct mechanical structures and tiny portable robots for specific technological applications. The structure and material properties of these stimuli-responsive polymers can skillfully be controlled by light. In this short technical note, we highlight the potential high-tech importance and the photo-actuation behavior of some remarkable LCEs with azobenzene chromophores.

Metathesis Cyclopolymerization Triggered Self-Assembly of Azobenzene-Containing Nanostructure

Azobenzene (AB) units were successfully introduced into poly(1,6-heptadiyne)s in order to ensure smooth synthesis of double- and single-stranded poly(1,6-heptadiyne)s (P1 and P2) and simultaneously realize the self-assembly by Grubbs-III catalyst-mediated metathesis cyclopolymerization (CP) of AB-functionalized bis(1,6-heptadiyne) and 1,6-heptadiyne monomers (M1 and M2). Monomers and polymers were characterized by 1H NMR, mass spectroscopy, and GPC techniques. The double-stranded poly(1,6-heptadiyne)s exhibited a large scale of ordered ladder nanostructure. This result was attributed to the π−π attractions between end groups along the longitudinal axis of the polymers and van der Waals interactions between the neighboring polymeric backbones. While the Azo chromophore connected in the side chain of P2 induced conformation of micelles nanostructure during the CP process without any post-treatment. Furthermore, the photoisomerization of Azo units had an obviously different regulatory effect on the conjugated degree of the polymer backbone, especially for the single-stranded P2, which was attributed to the structural differences and the interaction between AB chromophores in the polymers.

Synthesis and Photoinduced Anisotropy of Polymers Containing Nunchaku-Like Unit with an Azobenzene and a Mesogen

A series of polymers containing nunchaku-like unit with an azo chromophore and a mesogen group was successfully prepared and photoinduced anisotropy of the obtained polymers was minutely investigated. Firstly, monomers containing nunchaku-like unit with an azo chromophore and a mesogen group linked by flexible group were synthesized. The structure of the monomers was confirmed via NMR COSY spectra. Subsequently, the obtained monomers were polymerized into corresponding polymers through RAFT polymerization. The prepared polymer samples were characterized through NMR, FTIR, gel permeation chromatography (GPC), and UV-vis testing while the thermal properties of the samples were investigated through differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA) measurements. The photoinduced isomerization of the polymers, which was researched in situ via measuring UV-vis spectra of the polymer solutions and spin-coated films under irradiation with 450 nm light or putting in darkness, demonstrated the rapid trans-cis-trans isomerization of the polymers. When irradiated with a linearly polarized light, significant photoinduced birefringence and dichroism were observed, suggesting photoinduced isomerization of azobenzene can drive orientation of mesogen in the system. This study blazes a way to design the optical materials with light-controllable birefringence and dichroism.