Exciplexes are short-lived, heterodimeric "excited complexes"' that are stable in the electronic excited state while dissociative in the electronic ground state. Their formation can be considered as the association between an excited monomer * M and a second monomer N in the ground state, as depicted by the following rea School of Chemistry, The University of Melbourne, Parkville, Australia. ; Tel: +61-(0)3-8344 6784; E-mail: lars.goerigk@unimelb.edu.au.