Photochromism in a diarylethene derivative (1O) can be gated by a host-guest interaction where the thiazole orange groups are bound into the hydrophobic cavity of CB[8] in water. The closed-ring isomer (1C), which cannot be obtained freely in aqueous solution, survives even when the complex is dissociated by displacement from CB[8] by competition with 1-adamantanamine hydrochloride.