A. El-ghayoury et al., Intramolecular triplet energy transfer in metal polypyridine complexes bearing ethynylated aromatic groups, J PHYS CH A, 104(7), 2000, pp. 1512-1523
A series of polytopic ligands has been synthesized in which a central,aroma
tic hydrocarbon (1, 4-phenylene, 1,4-naphthalene, or 9,10-anthracene) is li
nked to 2,2'-bipyridine (bpy) or 2,2':6',2 "-terpyridine (terpy) units via
ethynylene bonds and the coordination sites have been capped with one or tw
o metal [M = Ru(II) or Os(II)] residues. The phenylene connector has little
effect on the photophysical properties of the terminal metal complexes, ex
cept in the case of "Ru(terpy)" where the tripler lifetime is prolonged rel
ative to the parent complex. An exceptionally long tripler lifetime (tau(T)
= 475 ns) is found fur the corresponding binuclear Ru(terpy)-based complex
built around the naphthalene-derived connector, although the lowest-energy
tripler state is associated with the metal complex. Reversible intramolecu
lar triplet energy transfer occurs between the reactants in the "Ru(bpy)"-c
ontaining systems assembled from the naphthalene-based connector, with the
lowest-energy tripler state being of naphthalene-like character. The photop
hysical propel-ties of the corresponding "Os(bpy)" fragments remain relativ
ely unaffected upon replacing phenylene with naphthalene. Fast tripler ener
gy transfer occurs from the Ru(bpy) fragments to the central anthracene uni
t, the latter lying at much lower energy, but reversible triplet energy tra
nsfer is found with the Os(bpy) units linked to anthracene. The various rat
e constants for electron exchange are considered in terms of current theory
to estimate a value for the matrix element (V-DA approximate to 8 cm(-1)).
Tripler energy transfer from the Ru(bpy) fragments to anthracene falls wel
l within the Marcus inverted region.