Correspondence
Johannes A.A.A.W. Elemans and Roeland J.M. Nolte, Radboud University, Institute for Molecules and Materials, Heyendaalseweg 135, 6525 AJ Nijmegen, the Netherlands,
Ben L. Feringa, University of Groningen, Stratingh Institute for Chemistry, Nijenborgh 4, 9747 AG Groningen, the Netherlands
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