LIGAND-CENTERED AND METAL-CENTERED INORGANIC EXCIPLEXES GENERATED BY EXCITED TRANSITION-METAL COMPLEXES

The photophysical and photochemical properties of two prominent groups of exciplexes generated by the excited transition metal complexes are discussed. The strong interaction between the excited tris-(alpha-dii mine) ruthenium(II) complex and the ground state silver ion results in both bimolecular and termolecular exciplexes. Since the stabilization originates from the overlap between the low-lying pi level of a coor dinated ligand and the empty 5s orbital of the silver ion, these excip lexes are called ligand-centered exciplexes (LCEs). In contrast, coord inatively unsaturated dicyanocuprate(I) in the excited state associate s with halide ions to create longer-lived, more highly luminescent met al-centered exciplexes (MCEs). The stepwise formation constants of exc iplexes and the thermodynamic parameters of the excited state equilibr ium determined by temperature-dependent measurements have been compare d and discussed. The kinetics and energetics of LCEs and MCEs strongly depend on the ionic strength and the solvent properties. Although the exciplex constituents of the two groups and their interaction have a rather different nature, some common behavior of these transition meta l complex exciplexes have been elucidated. (C) 1997 Elsevier Science S .A.