Conformation of azo-bridge in 3,3′-dinitro-2,2′-azobipyridine and its 4,4′(or 5,5′ or 6,6′)-dimethyl-derivatives: Vibrational studies and DFT quantum chemical calculations

•Four azobipyridines were synthesized.•Based on the DFT modeling the structures of these compounds were proposed.•The vibrational characteristics of the azo-bond were reported.•The role of substitution position of the methyl group was discussed.

Syntheses of 3,3′-dinitro-2,2′-azobipyridine and 4,4′ (or 5,5′ or 6,6′)-dimethyl-3,3′-dinitro-2,2′-azobipyridine have been described. Molecular structures of these compounds have been determined and compared, to the basic compound, azobipyridine, reported by us earlier. The conformation of the azo-bond and other structural data are discussed in terms of substitution place of methyl chromophore. Fourier transform IR and Raman spectra of these compounds have been measured and analysed. The 6-311G (2d,2p) basis set with the B3LYP functional have been used to discuss the space conformation and dynamics of the studied compounds.

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