* Corresponding authors

^a Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9746 AG Groningen, The Netherlands
E-mail: b.l.feringa@rug.nl, stefano.crespi@kemi.uu.se

^b Faculty of Engineering and Natural Sciences, Tampere University, FI-33101 Tampere, Finland

^c European Laboratory for Non Linear Spectroscopy (LENS), via N. Carrara 1, 50019 Sesto Fiorentino, Italy

^d ICCOM-CNR, via Madonna del Piano 10, 50019 Sesto Fiorentino, FI, Italy

^e Van't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, The Netherlands

^f Institute for Molecules and Materials, FELIX Laboratory, Radboud University, Toernooiveld 7c, 6525 ED, Nijmegen, The Netherlands

^g Department of Chemistry, Ångström Laboratory, Uppsala University, Box 523, 751 20 Uppsala, Sweden