No abstract

Azobenzene macrocycles are widely investigated as potential drug delivery systems and as part of molecular machines due to their photo-responsive properties. Herein, we synthesize a series of new azobenzene macrocycles, featuring up to eight switchable repeating units. We study the influence of different reaction conditions, base equivalents, concentration, reactant addition time and stirring time, on the formation of the macrocycles of different sizes, ranging from 10 to 40 aromatic rings in the macrocyclic architectures. High-resolution mass spectrometry and ion mobility (IM) mass spectrometry experiments and 1H and diffusion-ordered spectroscopy (DOSY) NMR are used to detect the presence of the macrocycles in gas phase and solution, respectively. While MS methods lead to the identification of the macrocycles, the differentiation between the different sizes of these macrocycles with DOSY NMR is limited. The responsiveness of the Z-to-E photo-switching of the smallest of the macrocycles, exhibiting 2 azobenzene units and in total 10 aromatic rings, separated with column chromatography, is studied with irradiation experiments, using both UV-Vis light and thermal excitation, and monitoring the sample with UV-Vis absorption and 1H NMR spectroscopy after the excitation. DFT calculations help shed light on the conformation of this isolated species.

Oxacalix[4]arene carboxylate binds, with different binding strengths, ammonium cations in methanol and forms complexes with amine molecules in the gas phase as characterized by NMR titration and drift tube IM-MS experiments and DFT calculations.