A Visible-Near Infrared Light Responsive Host-Guest Pair with Nanomolar Affinity in Water.

The discovery of stimuli-responsive high affinity host-guest pairs with potential applications under biological relevant con-ditions is a challenging goal. Herein we report a high-affinity 1:1 complex formed between cucurbit[8]uril and a water soluble photochromic diarylethene derivative. We found that confining the open isomer within the cavity of the receptor induces a red-shift in the absorption spectrum and leads to an enhancement of the photocyclization quantum yield from Φ = 0.04 to Φ = 0.32. This improvement in the photochemical performance enables quantitative photocyclization with visible light that together with the near-infrared light induced ring-opening reaction and the 100-fold selectivity for the closed isomer confirms this as an outstanding light-responsive affinity pair.