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Pure Appl. Chem., 2006, Vol. 78, No. 12, pp. 2247-2259

On the way to supramolecular photochemistry at the single-molecule level

Christian Schäfer1, Björn Decker1, Matthias Letzel1, Francesca Novara1, Rainer Eckel2, Robert Ros2, Dario Anselmetti2 and Jochen Mattay1

1 Organic Chemistry I, Department of Chemistry, University of Bielefeld,P.O. Box 100131, 33501 Bielefeld, Germany
2 Applied Biophysics, Department of Physics, University of Bielefeld, P.O. Box 100131, 33501 Bielefeld, Germany

Abstract: Two examples of artificial supramolecular host-guest systems derived from resorc[4]arenes (calix[n]arenes based on resorcinol) and ammonium ions as guests have been studied by atomic force microscopy (AFM). For the first time, real single-molecule events have been determined for this type of supramolecular complexes and off-rates as well as molecular parameters of single-molecule aggregates such as the depths of the binding pocket (molecular length parameter) could be measured by applying the methods of dynamic force spectroscopy. In addition, this technique was also applied to differentiate between the two states (open and closed) of a photoswitchable resorc[4]arene-anthracene tweezer. An investigation of the exchange rates of various complexes in the gas phase by means of Fourier transform ion cyclotron resonance (FTICR) mass spectrometry confirmed the results of the AFM study.