Visible-light photocontrol of (E)/(Z) isomerization of the 4-(dimethylamino)azobenzene pseudo-nucleotide unit incorporated into an oligonucleotide and DNA hybridization in aqueous media

We demonstrate significant photoresponsivity in aqueous media to visible light of pseudo-oligonucleotides possessing 4-(dimethylamino)azobenzene (4-DMAzo) side chains. The spectrum of the 4-DMAzo moiety during 436 nm light irradiation at pH >9 was clearly different from that of the all (E)-form, indicating the presence of the (Z)-form. Thermal (Z)-to-(E) recovery isomerization was faster at pH 9 (kZ-E = ∼101 s-1) than at pH 11; however, addition of 50% ethanol significantly slowed the thermal recovery isomerization at pH 9 (kZ-E = ∼2 s-1) and increased the magnitude of the spectral changes. Significant photoregulation of DNA hybridization by visible light was demonstrated under this condition.