Photo-controllable cytotoxicity in cell culture using a diarylethene photoswitch

For diarylethene (DAE) derivatives, whose dark cytotoxicity varies greatly depending on their isomerization state, we observe that the non-toxic open-ring isomer taken up by cells is converted to a toxic closed-ring isomer after only 10 seconds of UV light irradiation. This enables these derivatives to cause pronounced cell death after 1 day. Furthermore, when the closed-ring isomer is detoxified by opening the ring with green light irradiation after several intervals, cell damage increases with the period that DAE remains in the closed-ring state. The timescale at which the closed-ring isomer triggers the onset of cytotoxicity is considered in conjunction with the intercalation properties of DAE into DNA, and we also discuss the application of photonic molecular machines as a new technology for the control of biosystems.