2-(1H-diazol-2-ylmethylene)indane-1-ones and 2-(1H-diazol-2-ylmethylene)-1H-indene-1,3(2H)-diones: Photoisomerization and hydrogen-bonding-induced association

The products of condensation of 2-imidazolyl-, 4-imidazolyl-, 3-pyrazolylcarbaldehydes with indan-1-one 1–3 and 1H-indene-1,3(2H)-dione 4–6 were synthesized. The E-isomers of 1–3 undergo UV-induced isomerization to the Z-isomers stabilized by intramolecular NH⋯OC hydrogen bond with the pyrrolic-type NH group. Theoretical analysis of all isomers, tautomers and rotamers showed that the degree of conjugation between the diazolyl group and the CO group decreases in the order 1 > 2>3. Spectroscopic study of 1–6 performed before and after UV irradiation allowed to conclude on the nature of the associates formed. A remarkably different association of the 2- and 4-imidazolyl derivatives 4 and 5 was revealed by X-ray and confirmed theoretically, leading to the formation of the chelate rings closed by NH⋯OC hydrogen bond in 4 or by N–H … Npyridinic hydrogen bond in 5. Both chelate rings include two bifurcate H-bonds with bifurcation on the carbonyl oxygen and the pyrrolic NH hydrogen. [Display omitted] •2-Azolylmethylidene 1-indanones and -1,3-indandiones were synthesized.•The titled compounds were studied by the IR, UV, NMR spectroscopy, X-ray analysis and theoretical calculations.•The E/Z isomerization, tautomerization, H-bonding and self-association depend on the heterocycle and the isomer structure.