Herein we report evidence for a light-inducible DNAzyme. In so doing, we also disclose the synthesis and photochemical properties of a novel nucleoside:  8-(2-(4-imidazolyl)ethyl-1-thio)-2‘-deoxyriboadenosine (d1). The light sensitivity of (d1) was evaluated via an examination of the photoinduced reactivation of DNAzyme 8−17E from an inactive form that contained a single nucleotide (d1) modification. Restoration of DNAzyme activity results from a photoinduced reversion of (d1) to unmodified deoxyadenosine. Deuterium studies indicate that water is the source of hydrogen in the C8−H product and not the alkylthio group, suggesting that reversion of (1) to adenosine is not a consequence of simple homolysis of the C8−S bond but of an unprecedented photochemical conversion. This adenosine, which affords significant control of catalytic reactivation of a DNAzyme, may find general use in photodecaging other biological systems.