Synthesis, crystal structures and solvent dependent cis-trans conversion of 2-(4-hydroxylphenyl)-azopyrrole

Two 2-(4-hydroxylphenyl)-azopyrrole compounds, 1 (N-H) and 2 (N-Me), have been synthesized and characterized by X-ray crystallography. The slight change of the substituent on pyrrole N atom can drastically tune the properties of azopyrrole. Compound 1 self-assembled into pillar structure through N-H...O and O-H...N hydrogen bonds, whereas, compound 2 self-assembled into double-strand helical structure through O-H...N hydrogen bond and formed tube structure by crystal packing. The UV-Vis spectra studies revealed that the cistrans conversion rate of compound 2 is solvent dependent, which is promoted by the protic solvent and polar solvent. The structure, stability and molecular orbital of different conformers of 1 and 2 were studied by DFT calculation.

Automated summary

Two 2-(4-hydroxylphenyl)-azopyrrole compounds were synthesized and characterized. The properties of azopyrrole can be drastically tuned by slight changes in the substituent on the pyrrole N atom. Compound 1 self-assembled into a pillar structure through hydrogen bonds, while compound 2 formed a double-strand helical and tube structure. UV-Vis spectra studies showed that the cistrans conversion rate of compound 2 is solvent dependent, with protic and polar solvents promoting the conversion.