Photomodulation of ultrastable host–guest complexes in water and their application in light-controlled steroid release

The cucurbit[8]uril (CB8) synthetic receptor is shown to form high-affinity host-guest complexes with dicationic dithienylethene (DTE) photoswitches in water. ITC experiments combined with computational studies suggest that the formation of the inclusion complexes is mainly driven by a combination of hydrophobic effects, ion-dipole, hydrogen- and chalcogen-bonding interactions. The binding affinities were observed to be much higher for the DTE closed isomers, reaching values in the picomolar range (up to 10¹¹ M⁻¹) while the open isomers display up to 10 000-fold lower affinities, setting ideal conditions for the development of robust photoswitchable host-guest complexes. The light-responsive affinity of these photoswitches toward CB8 was explored to control the encapsulation and release of nanomolar affinity steroids via competitive guest replacement.