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
E-mail: