1. Ingénierie et Architectures Macromoléculaires, Institut Charles Gerhardt, Ecole Nationale Supérieure de Chimie de Montpellier (UMR 5253-CNRS), 8, rue de l'Ecole Normale, 34296 Montpellier Cedex 1, France, Department of Chemistry, University of Florida, P.O. Box 117200, Gainesville, Florida 32611-7200, and Department of Chemistry, Portland State University, Portland, Oregon 97207