Photoresponsive Amide-Based Derivatives of Azobenzene-4,4′-Dicarboxylic Acid—Experimental and Theoretical Studies

Abstract

Azobenzene derivatives are one of the most important molecular switches for biological and material science applications. Although these systems represent a well-known group of compounds, there remains a need to identify the factors influencing their photochemical properties in order to design azobenzene-based technologies in a rational way. In this contribution, we describe the synthesis and characterization of two novel amides (L1 and L2) containing photoresponsive azobenzene units. The photochemical properties of the obtained compounds were investigated in DMSO by UV-Vis spectrophotometry, as well as 1H NMR spectroscopy, and the obtained results were rationalized via Density Functional Theory (DFT) methods. After irradiation with UV light, both amides underwent trans to cis isomerization, yielding 40% and 22% of the cis isomer of L1 and L2 amides, respectively. Quantum yields of this process were determined as 6.19% and 2.79% for L1 and L2, respectively. The reverse reaction (i.e., cis to trans isomerization) could be achieved after thermal or visible light activation. The analysis of the theoretically determined equilibrium structure of the transition-state connecting cis and trans isomers on the reaction path indicated that the trans-cis interconversion is pursued via the flipping of the substituent, rather than its rotation around the N=N bond. The kinetics of thermal back-reaction and the effect of the presence of the selected ions on the half-life of the cis form were also investigated and discussed. In the case of L1, the presence of fluoride ions sped the thermal relaxation up, whereas the half-life time of cis-L2 was extended in the presence of tested ions.

Large Stimuli-Responsive Azobenzene Macrocycles as Functional Cavitands: Synthesis and Detection by NMR and MS Methods

“…It has been reported that the E-isomer absorption maximum for the azobenzene molecules lies in the range of 320-360 nm, whereas the largest absorption for the Z-isomer is usually located between 400 and 500 nm. [70][71][72][73] These maxima are observed in both the experimental and the theoretical spectra for 3b. The UV-Vis spectra for the sample 3b in Figure 4 are consistent with an experimental absorption pattern characteristic to a macrocycle that contains both the E and the Z conformers.…”