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Hydrogen-Bonded Complexes of Aromatic Crown Ethers with (9-Anthracenyl)methylammonium Derivatives. Supramolecular Photochemistry and Photophysics. pH-Controllable Supramolecular Switching†
journal contribution
posted on 1997-11-05, 00:00 authored 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. WilliamsThe (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.