1. Laboratory of Macromolecular Chemistry, UMR (CNRS) 5076, Ecole Nationale Supérieure de Chimie de Montpellier, 8 rue Ecole Normale, 34296 Montpellier Cedex 05, France, Department of Chemistry, University of Florida, PO Box 117200, Gainesville, Florida 32611-7200, and Department of Chemistry, Portland State University, Portland, Oregon 97207