1. Department of Physics; Freie Universität Berlin; Arnimallee 14 14195 Berlin Germany
2. Chemistry Division; Brookhaven National Laboratory; Upton NY 11973-5000 USA
3. Department of Chemistry; KTH Royal Institute of Technology; Stockholm 10044 Sweden
4. State Key Laboratory of Fine Chemicals; DUT-KTH Joint Education and Research Centre on Molecular Devices; Dalian University of Technology (DUT); Dalian 116024 PR China