Synthesis and characterization of bis(4-amino-2-bromo-6-methoxy)azobenzene derivatives

David Martínez-López; Amirhossein Babalhavaeji; Diego Sampedro; G Andrew Woolley

doi:10.3762/bjoc.15.296

Synthesis and characterization of bis(4-amino-2-bromo-6-methoxy)azobenzene derivatives

Beilstein J Org Chem. 2019 Dec 30:15:3000-3008. doi: 10.3762/bjoc.15.296. eCollection 2019.

Authors

David Martínez-López¹, Amirhossein Babalhavaeji², Diego Sampedro¹, G Andrew Woolley²

Affiliations

¹ Departamento de Química, Universidad de La Rioja, Centro de Investigación en Síntesis Química (CISQ), Madre de Dios, 53, 26006 Logroño, Spain.
² Department of Chemistry, University of Toronto, 80 St. George St., Toronto, M5S 3H6, Canada.

Abstract

Aminoazobenzene derivatives with four ortho substituents with respect to the N-N double bond are a relatively unexplored class of azo compounds that show promise for use as photoswitches in biology. Tetra-ortho-methoxy-substituted aminoazobenzene compounds in particular can form azonium ions under physiological conditions and exhibit red-light photoswitching. Here, we report the synthesis and characterization of two bis(4-amino-2-bromo-6-methoxy)azobenzene derivatives. These compounds form red-light-absorbing azonium ions, but only under very acidic conditions (pH < 1). While the low pK _a makes the azonium form unsuitable, the neutral versions of these compounds undergo trans-to-cis photoisomerization with blue-green light and exhibit slow (τ_1/2 ≈ 10 min) thermal reversion and so may find applications under physiological conditions.

Keywords: azobenzene; azonium; molecular switches; ortho substitution; photoisomerization; photoswitch; visible light.

Grants and funding

We are grateful to the Natural Sciences and Engineering Research Council of Canada and MINECO/FEDER (CTQ2017-87372-P) for financial support. D. M.-L. thanks the U. de La Rioja for a fellowship.