1. Department of Chemistry, University of Manchester, Oxford Road, Manchester, M13 9PL UK
2. Dipartimento di Ingegneria dell'Informazione, Università di Pisa, Pisa 56122, Italy
3. The Molecular Foundry, Lawrence Berkeley National Laboratory Berkeley, Berkeley, CA, 94720, USA
4. Institute of Photonics, Vienna University of Technology, Vienna, 1040, Austria