A double plug-socket system capable of molecular keypad locks through controllable photooxidation.

Two robust divalent complexes have been successfully constructed by using complementary rigid spacers (anthracene vs. 1,4,5,8-naphthalenediimide (NDI)) and two pairs of [24]crown-8 ethers and secondary dialkylammonium functionalities as binding motifs. It was demonstrated that properly selected, rigid spacers are more efficient than flexible ones for achieving strong multivalent association. This is presumably due to the preorganization of the rigid spacers, the cooperation between charge-transfer interactions of rigid spacers, and the complexation of the binding motifs. Furthermore, the intermolecular photoinduced electron transfer (PET) between rigid spacers in these robust complexes could be switched on and off by modulating their complexation through acid-base reactions, which is reminiscent of a plug-socket system capable of electron transfer. In addition, the self-sensitized photooxidation of the divalent host with anthracene as a spacer can be completely inhibited after complexation with the divalent guests that contain NDI as spacers. This process could also be understood by invoking intermolecular PET and could be turned on and off through acid-base reactions. The photophysical and photochemical properties of these robust complexes have been interpreted as molecular keypad locks with alarm systems. Thus, a double plug-socket system and molecular keypad locks were successfully integrated inside robust multivalent systems and then the normal molecular devices were endowed with logic functions.