Photocontrol of Polar Aromatic Interactions by a Bis-Hemithioindigo Based Helical Receptor.

The first example of a bis-hemithioindigo (bis-HTI)-based molecular receptor was realized. Its folding and selective binding affinity for aromatic guest molecules can be precisely controlled by visible light and heat. The thermodynamically stable state of the bis-HTI is the s-shaped planar Z,Z-configuration. After irradiation with 420 nm light only the E,Z-configuration is formed in a highly selective photoisomerization. The E,Z-isomer adopts a helical conformation because of the implementation of repulsive steric interactions. The E,Z-configured helix is able to recognize electron-poor aromatic guests exclusively through polar aromatic interactions and also distinguishes between regioisomers. After heating, the Z,Z-configuration is completely restored and the aromatic guest molecule is efficiently released.