Synthesis and characterization of ortho bromo-methoxy aminoazobenzene derivatives

Aminoazobenzene derivatives with four ortho substituents with respect to the NN double bond are a relatively unexplored class of azo compounds that show promise for use as photoswitches in biology. Tetra-ortho methoxy aminoazobenzenes, in particular, can form azonium ions under physiological conditions and exhibit red-light photoswitching. Here, we report the synthesis and characterization of two ortho bromo-methoxy aminoazobenzene derivatives. These compounds form red light absorbing azonium ions but only under very acidic conditions (pH <1). While the low pKa makes the azonium form unsuitable, the neutral versions of these compounds undergo trans-to-cis photoisomerization with blue-green light and exhibit slow (τ½ ~10 min) thermal reversion and so may find applications under physiological conditions.