Synthesis and Characterization of Novel 2-Alkyl-1,3,4-Oxadiazoles Containing a Phenylazo Group

An efficient method for the synthesis of novel phenylazo-containing moieties is described. The derivatives of 5-(4-(phenyldiazenyl)phenyl)-1,3,4-oxadiazole, substituted at position 2 of the heterocyclic scaffold with alkyl groups of different chain lengths, were prepared. The titled compounds were obtained using the appropriate 4-(5-alkyl-1,3,4-oxadiazol-2-yl)anilines, which were directed to diazotization and subsequently coupled to phenol, resorcinol, and N,N-dimethylaniline. Additionally, we report a mild and effective procedure for the preparation of 4-(5-alkyl-1,3,4-oxadiazol-2-yl)anilines via the selective reduction of the corresponding 2-alkyl-5-(4-nitrophenyl)-1,3,4-oxadiazoles using sodium borohydride-tin(II) chloride dihydrate as the reducing system. The chemical structures of the prepared compounds were confirmed by 1H- and 13C-NMR, IR, and UV-Vis spectroscopy.

Organoboron based photochromic gelator

A series of tetra-coordinate boron-peptide conjugates has been reported. The incorporation of a photochromic organoboron unit into the gelator endows photoactivity to the supramolecular gels. While the structural transformation of the gelator upon UV irradiation minimally impacts the formed self-assembled structures, it indeed influences their rheological properties.

Morphology-Mediated Photoresponsive and Fluorescence Behaviors of Azobenzene-Containing Block Copolymers

We investigated the relationship between the self-assembled morphology of poly( tert-butyl acrylate)- block-poly(6-[4-(4'-methoxyphenylazo)phenoxy]hexyl methacrylate) (P tBA- b-PAzoMA) block copolymers and their photoresponsive and fluorescence behaviors. The morphology of P tBA- b-PAzoMA copolymers was manipulated by dissolving them in mixed dimethylformamide (DMF)/hexanol solvents. When P tBA- b-PAzoMA was dissolved in DMF-rich (neutral) solvents, a favorable interaction between the DMF molecules and both blocks resulted in a random-coiled conformation. The unconfined morphology facilitated the formation of both nonassociated and head-to-head organized azobenzene mesogens, which promoted fluorescence emission. When hexanol, a P tBA-selective solvent, was added to DMF, the solvency of P tBA- b-PAzoMA worsened, leading to its assembly into micelles, with PAzoMA in the micelle core. The confinement of azobenzene moieties in the micelle core hindered their trans-to- cis photoisomerization, thereby considerably decreasing the kinetics of photoisomerization and the population of cis isomers. Additionally, a nanoconfined geometry resulted in compactly packed chromophores, causing fluorescence loss. When P tBA- b-PAzoMA was exposed to UV light, the increased number of cis isomers hampered the closely packed mesogens, resulting in a substantial enhancement of fluorescence emission. When the mole fraction of the PAzoMA block was increased, P tBA- b-PAzoMA formed clusters, causing the slow kinetics of photoisomerization and fluorescence quenching.

A Natural Glycyrrhizic Acid-Tailored Light-Responsive Gelator

The construction of stimuli-responsive materials by using naturally occurring molecules as building blocks has received increasing attention owing to their bioavailability, biocompatibility, and biodegradability. Herein, a symmetrical azobenzene-functionalized natural glycyrrhizic acid (trans-GAG) was synthesized and could form stable supramolecular gels in DMSO/H₂ O and MeOH/H₂ O. Owing to trans-cis isomerization, this gel exhibited typical light-responsive behavior that led to a reversible gel-sol transition accompanied by a variation in morphology and rheology. Additionally, this trans-GAG gel displayed a distinct injectable self-healing property and outstanding biocompatibility. This work provides a simple yet rational strategy to fabricate stimuli-responsive materials from naturally occurring, eco-friendly molecules.

Photoresponsive behavior and switchable nonlinear optical properties of Langmuir-Blodgett film based on azobenzene derivatives

Here, we present the investigations of photo-isomerization behavior and the nonlinear optical properties of azobenzene derivative LB films. The few-layer LB films of AOB-t4 and BNB-t4 exhibit positive nonlinear refraction and two-photon absorption properties as revealed by picosecond Z-scan. The increased conjugation by introducing an oxadiazole group improves the photo-isomerization rate and the nonlinear optical properties, due to a weaker intermolecular interaction and the formation of J-aggregates within AOB-t4 LB film. The third-order susceptibility of cis-AOB-t4 9-layer LB film reaches 1.866 × 10^-9 esu and the two-photon absorption coefficient is on the order of 10^-8 m/W. Interestingly, the 15-layer AOB-t4 LB film shows negative nonlinear refraction and saturable absorption. Taken together, we have demonstrated the switchable nonlinear optical absorption and refraction properties of AOB-t4 LB film with changing film thickness, which is of significance for nonlinear optics and photonics applications.

E–Z isomerization of the –CN– bond in anthracene-based acylhydrazone derivatives under visible light

The E–Z isomerizations of the –CN– group upon visible light irradiation induced the photoresponsive behaviour of AHP-mB8.