Ruthenium−Terpyridine Complexes with Multiple Ethynylpyrenyl or Ethynyltoluyl Subunits: X-ray Structure, Redox, and Spectroscopic Properties

Several heteroleptic and homoleptic ruthenium−terpyridine complexes bearing two and four ethynylpyrenyl or
ethynyltoluyl residues have been prepared from complexes carrying reactive bromo functions. Cross-coupling promoted
by low-valent palladium(0) on these preformed complexes has advantageously been used to prepare the target
complexes. The structure of a bis-terpyridine complex carrying four ethynylpyrenyl subunits was determined by
single-crystal X-ray diffraction, showing a distorted octahedral geometry around the metal center, with the
ethynylpyrenyl fragment being slightly tilted (about 5°) from the terpyridine plane. The molecular packing is
characterized by intermolecular π···π interaction within dimers. The counteranions and the solvent molecules are
entrapped in well-defined channels spanning along the a-axis. The complexes are redox active with a Ru oxidation
overlapping the pyrene oxidation and two well-defined ligand-centered reduction processes. Pyrene reduction is
irreversible and strongly cathodic. The new multichromophoric complexes are luminescent both in solution and in
rigid matrix at 77 K, with room-temperature lifetimes and quantum yields significantly larger than those of [Ru(terpy)2]2+.
At room temperature, the toluyl-substituted complexes are triplet metal-to-ligand charge-transfer (3MLCT) emitters,
whereas for the pyrene-grafted complexes pyrene-centered emission is observed. For the latter complexes, the
energy gap, ΔTT, between higher 3MLCT levels and lower ligand-centered (3ππ*, 3LC) levels is in the 640−730
cm-1 range, which results in the interstate dynamics at the basis of the observed luminescent behavior. At 77 K,
for the pyrene-grafted complexes, the emission reveals features that are tentatively ascribed to intraligand interactions
involving the pyrene and terpyridine units.