Synthesis, characterization, spectral property, Hirshfeld surface analysis and TD/DFT calculations of 2, 6-disubstituted benzobisoxazoles

An effective and clean aerobic oxidative method for the synthesis of 2,6-disubstituted benzobisoxazole using the free radical catalysis was obtained. 2, 6-Di(pyridin-4-yl)-benzo[1,2-d:4,5-d']bisoxazole was synthesized and characterized by 1H and 13C NMR spectroscopy, elemental analysis, UV–vis and emission spectroscopy, as well as by single-crystal X-ray crystallography. In the crystal structure, a self-assembled two-dimensional (2-D) layer supramolecular frameworks is formed with the help of intermolecular hydrogen bonds and π···π stacking interactions. On the basis of experimental results, a plausible reaction mechanism of 2,2′-disubstituted benzoxdiazoles with 4-methoxy-TEMPO as the catalyst is proposed. To obtain more insights into the structure and bonding, DFT calculations were performed. The obtained calculation results were compared with the X-ray diffraction data. The electronic transitions and spectral features of 5a and 5b were discussed by TD-DFT calculations. In addition, the noncovalent interactions among compounds have been also analyzed using Hirshfeld surface analysis.