1. Department
of Organic Chemistry, The Weizmann Institute of Science, 76100 Rehovot, Israel,
2. Department
of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208-3112, United States,
3. Department
of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208-3108, United States, and
4. Dipartimento
di Scienze Chimiche, Università di Catania, Catania 95125, Italy