The structure of symmetric azoazoles according to ab initio computations

Abstract We present a structural study of a family of azo compounds—azo derivatives of azoles (azoazoles, Az1–N=N–Az2)—focusing on the thirty-nine symmetric members (Az1 = Az2), ranging from pyrrole to pentazole. These compounds can act as photoswitches, meaning they can reversibly interconvert between two isomeric forms upon exposure to light. The calculated geometries are compared with experimental structures available in the Cambridge Structural Database. Rotation around the Az–N single bond gives rise to three conformers (A, B, and C), which exhibit various noncovalent interactions analyzed using the Quantum Theory of Atoms-in-Molecules (QTAIM) and Noncovalent Interaction (NCI) approaches. Finally, three spectroscopic properties—electronic, vibrational, and especially NMR—are compared with experimental data and critically evaluated against calculated values.