1. School of Chemistry and Molecular Sciences University of Sussex, Brighton BN1 9QJ, UK Institute for Polymers and Organic Solids and Materials Research Laboratory, University of California, Santa Barbara, California 93106 IBM Research Division, Zurich Research Laboratory 8803 Rüschlikon, Switzerland; Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy European Synchrotron Radiation Facility, B.P. 220 F-38043 Grenoble, France, and Université de Lausanne, Institut de Cristallographie CH-1015...