Visible-light photoresponsivity of a 4-(dimethylamino)azobenzene unit incorporated into single-stranded DNA: Demonstration of a large spectral change accompanying isomerization in DMSO and detection of rapid (Z)-to-(E) isomerization in aqueous solution

We demonstrate significant visible-light photoresponsivity in a synthesized oligonucleotide containing a built-in pseudonucleotide possessing a 4-(dimethylarnino)azobenzene (4-DMAzo) side chain. In dry DMSO as solvent, two clearly distinguishable spectra corresponding to the (E) and (Z) forms of the 4-DMAzo moiety tethered to the oligonucleotide were recorded with a conventional spectrophotometer before and after irradiation with 420 nm wavelength light, which induced (E)-to-(Z) isomerization. In addition, (Z)-to-(E) isomerization was accelerated by irradiation with either visible (λ = 550 nm) or UV (λ = 350 nm) light, demonstrating reversible photoresponsivity of the pseudo-ohgonucleotide. In aqueous solutions the (Z)-to-(E) thermal isomerization of the photoresponsive pseudo-ohgonucleotide was very rapid and was only detectable by laser flash photolysis.