HYDROGEN-BONDED COMPLEXES OF AROMATIC CROWN-ETHERS WITH (9-ANTHRACENYL)METHYLAMMONIUM DERIVATIVES - SUPRAMOLECULAR PHOTOCHEMISTRY AND PHOTOPHYSICS - PH-CONTROLLABLE SUPRAMOLECULAR SWITCHING

The (9-anthracenyl)methylammonium and (9-anthracenyl)benzylammonium te trakis(hexafluorophosphate) salts give hydrogen-bonded complexes in CH 2Cl2 with aromatic crown ethers containing dibenzo (DB) or dinaphtho ( DN) units. The association constants vary from 3 x 10(3) to 1 x 10(6) M-1 in CH2Cl2, depending on the specific ammonium cation and crown eth er involved. In a number of cases, pseudorotaxane-like geometries for the complexes are demonstrated by (a) H-1 NMR spectroscopy in solution , (b) X-ray crystallography in the solid state, and (c) mass spectrome try in the gas phase. The results obtained by absorption, emission, an d excitation spectroscopy and excited lifetimes show that, as a conseq uence of the hydrogen bond driven recognition process, the anthracene chromophoric unit interacts with the aromatic units of the crown ether s. In the complexes involving the DB18C6, DB24C8, and DB30C10 macrocyc les, the interaction leads to the complete quenching of the fluorescen ce of the dialkoxybenzene moieties and parallels sensitization of the anthracene fluorescence. In the complexes of 1/5-DN38C10, both the cro wn and the anthracene fluorescence are completely quenched, most likel y by an energy-transfer cascade involving the triplet state of the dia lkoxynaphthalene moiety. In the complexes of 2/3-DN30C10, the interact ion between the anthracene moiety and the naphthalene rings of the cro wn 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 b y addition of CF3COOH or CF3SO3H to CH2Cl2 solutions containing crown ether and amine. The association process between DB24C8 and (9-anthrac enyl)benzylammonium salt can be reversed quantitatively upon addition of a suitable base and the complex can be formed again after treatment with acid.