1. Department of Chemistry and Centre for Materials Research, Queen Mary, University of London, Mile End Road, London E1 4NS, United Kingdom, Central Laser Facility, CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, United Kingdom, and Molecular Photonic Materials, van't Hoff Institute for Molecular Sciences, University of Amsterdam, Nieuwe Achtergracht 166, NL-1018 WV Amsterdam, The Netherlands