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 (k(Z)(-E) = approximately 10(1) s(-1)) than at pH 11; however, addition of 50% ethanol significantly slowed the thermal recovery isomerization at pH 9 (k(Z)(-E) = approximately 2 s(-1)) and increased the magnitude of the spectral changes. Significant photoregulation of DNA hybridization by visible light was demonstrated under this condition.