Infrared study of intercomponent interactions in a switchable hydrogen-bonded rotaxane.
The macrocycle in rotaxane 1 is preferentially hydrogen bonded to the succinamide station in the neutral form, but can be moved to the naphthalimide station by one-electron reduction of the latter. The hydrogen bonding between the amide NH groups of the macrocycle and the C double bond O groups in the binding stations in the thread was studied with IR spectroscopy in different solvents in both states. In addition, the solvent effect on the vibrational frequencies was analyzed; a correlation with the solvent acceptor number (AN) was observed. The conformational switching upon reduction could be detected by monitoring the hydrogen-bond-induced shifts of the nu(CO) frequencies of the C double bond O groups of the succinamide and the reduced naphthalimide stations. The macrocycle was found to shield the encapsulated station from the solvent: wavenumbers of nu(CO) bands of the C double bond O groups residing inside the macrocycle cavity remain unaffected by the solvent polarity.
Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Nieuwe Achtergracht 129, 1018 WS Amsterdam, The Netherlands.
Dhiredj C
DC
Jagesar
Frantisek
F
Hartl
Wybren Jan
WJ
Buma
Albert M
AM
Brouwer