Synthesis and characterization of photoactive azobenzene-based chromophores containing a bulky cholesteryl moiety

A Sulfhydryl Azobenzene-Modified Polyaniline/Silver Electrode and Its Photoswitching Electrochemical Performance

In this work, a sulfhydryl-functionalized azobenzene derivative (Azo) was synthesized and polyaniline/silver was modified (PANI/Ag) to make a nanocomposite (PANI/Ag/Azo). A series of characterization techniques like¹HNMR, UV-vis absorption spectra, Raman spectra, FT-IR, XRD, SEM, TEM, and TGA was employed to study Azo, PANI/Ag, and PANI/Ag/Azo. Electrochemical properties were measured by cyclic voltammetry (CV) and galvanostatic charging/discharging (GCD). CV showed that UV and blue light had hardly any effect on PANI/Ag. However, with the prolonged exposure time of UV light, the maximum CV current density of PANI/Ag/Azo rose from 1.24 to 2.72 A g^-1. Then, after 20 min of blue light irradiation, the maximum current density gradually recovered (from 2.72 to 1.26 A g^-1). The GCD also obtained similar results. After formula calculation, the specific capacitance of PANI/Ag/Azo also presented a reversible trend under the alternating irradiation of UV light and blue light. All the results show that PANI/Ag/Azo has a good photoelectric response, and its electrochemical performance can be reversibly adjusted by light. This result provides a new design idea for developing electrode materials with real-time electrochemical properties.

Thermally Stable Nitrothiacalixarene Chromophores: Conformational Study and Aggregation Behavior

Achieving high thermal stability and control of supramolecular organization of functional dyes in sensors and nonlinear optics remains a demanding task. This study was aimed at the evaluation of thermal behavior and Langmuir monolayer characteristics of topologically varied nitrothiacalixarene multichromophores and phenol monomers. A nitration/azo coupling alkylation synthetic route towards partially O-substituted nitrothiacalixarenes and 4-nitrophenylazo-thiacalixarenes was proposed and realized. Nuclear magnetic resonance (NMR) spectroscopy and X-ray diffractometry of disubstituted nitrothiacalix[4]arene revealed a rare 1,2-alternate conformation. A synchronous thermal analysis indicated higher decomposition temperatures of nitrothiacalixarene macrocycles as compared with monomers. Through surface pressure/potential-molecular area measurements, nitrothiacalixarenes were shown to form Langmuir monolayers at the air–water interface and, through atomic force microscopy (AFM) technique, Langmuir–Blodgett (LB) films on solid substrates. Reflection-absorption spectroscopy of monolayers and electronic absorption spectroscopy of LB films of nitrothiacalixarenes recorded a red-shifted band (290 nm) with a transition from chloroform, indicative of solvatochromism. Additionally, shoulder band at 360 nm was attributed to aggregation and supported by gas-phase density functional theory (DFT) calculations and dynamic light scattering (DLS) analysis in chloroform–methanol solvent in the case of monoalkylated calixarene 3. Excellent thermal stability and monolayer formation of nitrothiacalixarenes suggest their potential as functional dyes.

Cholesteric–azobenzene liquid crystalline copolymers: design, structure and thermally responsive optical properties

We report the synthesis of new functional cholesteric–azobenzene side-chain liquid crystalline copolymers and terpolymers, their temperature-responsive mesophase behavior, and stimuli responsive photonic properties from 400 nm to the near infra-red region of the electromagnetic spectra.

Structure-property relationships of symmetrical and asymmetrical azobenzene derivatives as gelators and their self-assemblies

Two different series of symmetrical and asymmetrical azobenzenes containing terminal cholesteryl/adamantyl derivatives (SAC/SAA and AAC) with varying spacer lengths (alkyl chains) have been developed. The gelation and aggregation of these derivatives were studied relative to structural motifs, spacer lengths, solvent affinity, temperatures and light conditions. Among these derivatives, the cholesteryl derivatives that have short alkyl chains (<3) act as efficient gelators in a variety of solvents. However, the cholesteryl derivatives with longer alkyl chains (11 spacer) and adamantyl derivatives did not possess this ability. Self-assembled fibrous structures were constructed by gelators with short alkyl chains (<3), while flower-like structures were constructed by gelators with moderately longer alkyl chains (3-6) at their respective critical gelation concentrations (CGCs) according to SEM (Scanning Electron Microscopy) and TEM (Transmission Electron Microscopy) analyses. In some cases, a partial/weak gel was observed in different solvents, which exhibited uniform spherical nanoparticles at CGCs. These nanoparticles were further entangled to form interconnected fibrous structures when the concentration was increased above the CGC (according to the SEM and TEM analyses). Secondary forces (van der Waals/H-bonding) and π-π stacking played important roles in the aggregation of both series in the solvents according to variable temperature (1)H-NMR analysis. The reversibility of sol-gel transitions by light was studied with respect to solvent affinity. This study revealed that reversible transitions were only observed in the non-polar solvents, as supported by the FTIR analysis of the gelators in the various solvents. The thermal and mesomorphic behaviors of the gelators by DSC (Differential Scanning Calorimetry) and POM (Polarized Optical Microscopy) analyses revealed that the chiral nematic (N*) and cholesteric mesophase (Ch*) were exhibited by only the short and longer alkyl chain cholesteryl derivatives, respectively. However, the cholesteryl derivative without a spacer (AAC0) did not exhibit any liquid crystalline phase but acted as an efficient gelator relative to the other gelators in this study.