Basis of a presentation given at Materials Discussion No. 4, 11–14 September 2001, Grasmere, UK.
Electronic supplementary information (ESI) available: experimental details and spectroscopic data for compounds 4b, 5b, 8b, 9b, 14b, 15b, 21b, 29, 30, 31, 33, 34, 35, 36 and 38. See http://www.rsc.org/suppdata/jm/b1/b102988f/