1. Department of Physics and Astronomy, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH, U.K., Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, U.K., Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, F-38042 Grenoble Cedex 9, France, ISIS, Rutherford Appleton Laboratory, Didcot, OX11 0QX, U.K., and Cambridge Display Technology, Greenwich House, Greenwich Rise, Madingley Road, Cambridge, CB3 0TX, U.K.