1. IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120; Department of Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts 01003; Departments of Chemistry, Materials and the Materials Research Laboratory, University of California, Santa Barbara, California 93106; and Department of Chemistry and the Skaggs Institute for Chemical Biology, The Scripps Research Institute, BCC-315 10550 N. Torrey Pines Road, La Jolla, California 92037