1. Contribution from the Departments of Chemistry and Materials, Institute for Polymers and Organic Solids, University of California, Santa Barbara, California 93106, Laboratoire de Photonique Quantique et Moléculaire−UMR CNRS 8537, Ecole Normale Supérieure de Cachan, 61 Avenue du Président Wilson, 94235 Cachan Cedex, France, and Department of Chemistry, University of Rochester, Rochester, New York 14627