1. Department of Chemistry Carnegie Mellon University Pittsburgh PA 15213 USA
2. Department of Chemistry University of Pittsburgh Pittsburgh PA 15260 USA
3. Department of Chemistry Dalhousie University Halifax Nova Scotia B3H 4R2 Canada
4. Center for Functional Nanomaterials Brookhaven National Laboratory Upton NY 11973 USA
5. Present address: Department of Physics Graduate Center City University of New York New York NY 10016 USA
6. Photonics Initiative Advanced Science Research Center City University of New York New York NY 10031 USA