Styryl-extended Azopyrroles and their boron difluoride complexes: Synthesises, structures, spectra, and DFT calculation

Abstract

Three styryl-extended azopyrrole compounds (2–4) with different substituents (-H, -NO2, and -N(CH3)2) have been synthesized by Knoevenagel condensation reaction between azopyrrole and substituted benzaldehyde. Their BF2 complexes (5–7) were also synthesized. The planar structure of compound 3 was characterized by X-ray crystallographic study. Hirshfeld surface analysis reveals that van der Waals interactions and hydrogen-bonding are the dominant interactions in the crystal packing. All compounds have λmax absorption greatly red-shift even to deep-red light region (646 nm) due to the extended π-conjugation by styryl group and the introduction of BF2 group. The structures, frontier molecular orbitals (FMOs), energy gaps (ΔE) and UV–Vis spectra of these compounds were evaluated by DFT calculations. The results reveal that the styryl, electron donating and withdrawing groups, and BF2 group all can reduce the energy gap (ΔE) of the compounds, and finally cause their long-wavelength absorption.