Hydrogen-Bonded Complexes of Aromatic Crown Ethers with (9-Anthracenyl)methylammonium Derivatives. Supramolecular Photochemistry and Photophysics. pH-Controllable Supramolecular Switching†
journal contributionposted on 05.11.1997, 00:00 by Peter R. Ashton, Roberto Ballardini, Vincenzo Balzani, Marcos Gómez-López, Simon E. Lawrence, M. Victoria Martínez-Díaz, Marco Montalti, Arianna Piersanti, Luca Prodi, J. Fraser Stoddart, David J. Williams
The (9-anthracenyl)methylammonium and (9-anthracenyl)benzylammonium tetrakis(hexafluorophosphate) salts give hydrogen-bonded complexes in CH2Cl2 with aromatic crown ethers containing dibenzo (DB) or dinaphtho (DN) units. The association constants vary from 3 × 103 to 1 × 106 M-1 in CH2Cl2, depending on the specific ammonium cation and crown ether involved. In a number of cases, pseudorotaxane-like geometries for the complexes are demonstrated by (a) 1H NMR spectroscopy in solution, (b) X-ray crystallography in the solid state, and (c) mass spectrometry in the gas phase. The results obtained by absorption, emission, and excitation spectroscopy and excited lifetimes show that, as a consequence of the hydrogen bond driven recognition process, the anthracene chromophoric unit interacts with the aromatic units of the crown ethers. In the complexes involving the DB18C6, DB24C8, and DB30C10 macrocycles, the interaction leads to the complete quenching of the fluorescence of the dialkoxybenzene moieties and parallels sensitization of the anthracene fluorescence. In the complexes of 1/5-DN38C10, both the crown and the anthracene fluorescence are completely quenched, most likely by an energy-transfer cascade involving the triplet state of the dialkoxynaphthalene moiety. In the complexes of 2/3-DN30C10, the interaction between the anthracene moiety and the naphthalene rings of the crown ether is relatively strong, as indicated by the perturbation of the absorption bands, the disappearance of the fluorescence bands of the naphthalene- and anthracene-type chromophoric units, and the appearance of a new, broad fluorescence band. The complexes can also be formed by addition of CF3COOH or CF3SO3H to CH2Cl2 solutions containing crown ether and amine. The association process between DB24C8 and (9-anthracenyl)benzylammonium salt can be reversed quantitatively upon addition of a suitable base and the complex can be formed again after treatment with acid.