Synthesis and Characterization of Photoactive Methyl 4-Bromo-3-((2,6-Difluorophenyl)diazenyl) Benzoate


The synthesis and structure of a novel ortho-fluoroazobenzene, methyl 4-bromo-3-((2,6-difluorophenyl)diazenyl) benzoate is described. The title molecule crystallizes in the centrocemetric space group P-1 with two rotomer molecules of the title compound in the asymmetric unit. The position of ortho-fluoro azo rings differ between the two rotomers with one molecule having a rotation angle of 4.4° and the other molecule having a rotation angle of 76.9° with respect to the methyl 4-bromobenzoate. Due to the tight packing the pure molecule was not seen to be photoactive. However, in solution the absorption bands in the visible region show a separation of about 20 nm as expected for o-fluoroazobenzene. A comparison to related and previously published co-crystals of substituted azobenzenes are presented.

Graphic Abstract

The structure of a novel ortho-fluoroazobenzene, methyl 4-bromo-3-((2,6-difluorophenyl)diazenyl) benzoate reveals the presence of two crystallographically unique rotomers in the lattice, and although the molecule is photoactive in solution, the close-packed lattice appears to inhibit photo-induced structural reorganization in the crystalline state.

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We would like to thank Travis Mitchell for helpful discussions.


Funding for this research was provided by: National Science Foundation, Directorate for Mathematical and Physical Sciences (Award No. DMR-2003932)

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Correspondence to Jason B. Benedict.

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Sylvester, E.D., Benedict, J.B. Synthesis and Characterization of Photoactive Methyl 4-Bromo-3-((2,6-Difluorophenyl)diazenyl) Benzoate. J Chem Crystallogr (2021).

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  • Crystal structure
  • Photochrome
  • Ortho-fluoroazobenzene
  • Azobenzene
  • Twisted-confirmation