Diarylethenes were attached to the 5-position of 2'-deoxyuridine in order to yield three different photochromic nucleosides. All nucleosides were characterized with respect to their absorption and photochromic properties. Based on these results, the most promising photochromic DNA base modification was incorporated into representative oligonucleotides by using automated phosphoramidite chemistry. The switching of optical properties in DNA can be achieved selectively at 310 nm (forward) and 450 nm (backward); both wavelengths are outside the normal nucleic acid absorption range. Moreover, this nucleoside was proven to be photochemically stable and allows switching back and forth several times. These results open the way for the use of diarylethenes as photochromic compounds in DNA-based architectures.