In this paper, we report the interaction of the CB[7] molecular container with crown ether styryl and (bis)styryl dyes 1-6. The interaction of monostyryl dyes (1 and 2) with CB[7] results in the formation of 1:1 complexes where the CB[7] molecule is located on the region of the guest encompassing the pyridinium ring, C=C double bond, and a portion of the aryl ring of benzocrown ethers 1 and 2. For (bis)styryl dyes (3-5), the formation of two types of complexes with composition dye.CB[7].dye and CB[7].dye.CB[7] was confirmed by a combination of optical and electrospray ionization mass spectroscopy (ESI-MS) methods. In the case of (bis)styryl dye (6), both 2:1 and 1:1 compositions 6.CB[7].6 and CB[7].6 were formed. Complex formation is accompanied by substantial changes in the optical characteristics of the dyes and formation of long-lived excimer species. We tested the stimuli responsiveness of this system in response to metal ions. We find that the metal ions prefer to bind to the electrostatically negative ureidyl C=O portals of the CB[7] rather than with the crown ether moiety of the styryl dyes.

The combination of photoactive styryl(pyridinium) dyes and cucurbit[7]uril (CB[7]) in an integrated supramolecular system allowed us to design a novel high speed molecular machine based on the fully reversible shuttling motion of the dye inside the CB[7] host cavity. The driving force of this movement is the electrostatic potential change after the occurrence of intramolecular charge transfer in the excited state of the dye molecule that can be externally controlled by light. Steady-state and time-resolved optical spectroscopy as well as DFT calculations provided an unambiguous evidence for the ultrafast piston-like movement of the system between two states. The shuttling process occurs in the picosecond timescale and its bistability depends on the strength of the dye donor fragment.