Photophysical properties of a supramolecular interlocked conjugate

The binding behavior between a rigid, pi-accepting aromatic polycycle (ADIQ.2PF(6)) and an electron-donating crown ether (CE(10)) is reported in acetonitrile solution. In CH3CN at low concentration of crown ether, the binding data are consistent with formation of a 1:1 complex in which the ADIQ-2PF(6) residue is partially encapsulated by the crown ether (K-1 perpendicular toapproximate to 500 dm(3) mol(-1)). As the mole fraction of crown ether increases, mass spectrometry indicates formation of a molecular aggregate in which two crown ethers are bound to a single ADIQ.2PF(6) entity in the form of a [3]pseudorotaxane. Molecular modeling and NMR spectroscopic studies indicate that the crown ether fits loosely on the end of the polycycle without significant penetration along the molecular axis. Binding causes extinction of fluorescence from the polycycle, allowing estimation of the second binding constant (K-2 approximate to 400 dm(3) mol(-1)) and results in the appearance of a charge-transfer absorption band in the visible region. Illumination into this absorption band promotes formation of an intimate radical ion pair with a time constant of ca. 3 ps. Subsequent charge recombination occurs with a lifetime of ca. 25 ps and results in greatly enhanced population of the triplet excited state localized on the polycycle. There is little or no separation of the radical ion pair into solvated ions.