Mixed-ligand bis(2,2'-bipyridine)ruthenium(II) complexes containing a hybrid donor-type P-N ligand of 8-(diphenylphosphino)quinoline (Ph2Pqn) or 2-(diphenylphosphino)pyridine (Ph2Ppy), [Ru(bpy)2(Ph2Pqn or Ph2Ppy)](PF6)2 (1 or 2; bpy = 2,2'-bipyridine), have been prepared. The X-ray crystal structure analyses of 1 and 2 revealed that Ph2Pqn and Ph2Ppy act as a bidentate ligand to form a five- and four-membered chelate ring, respectively. The four-membered chelate ring formed by Ph2Ppy has a very small bite angle (P(1)-Ru-N(1): 68.4(1)°), but the RuII(bpy)2 moiety in 2 has a typically strain-free structure. On the other hand, in the Ph2Pqn complex 1, one of the bpy planes is skewed remarkably from the Ru coordination plane due to an intramolecular steric interaction with a phenyl ring of Ph2Pqn. The redox potentials and the 1MLCT transition energies of the Ph2Pqn and Ph2Ppy complexes (1 and 2) were not so different from the averaged values of those of the corresponding 1,2-bis(diphenylphosphino)benzene (dppb) and 1,10-phenanthroline (phen) complexes, [Ru(bpy)2(dppb or phen)](PF6)2 (3 or 4). These facts indicate that the electronic asymmetry inherently present in Ph2Pqn and Ph2Ppy does not affect remarkably the ground state properties of the complexes. However, unlike complexes 2-4, the Ph2Pqn complex 1 in EtOH/MeOH (4:1) glass at 77 K exhibited a novel dual emission, giving a biexponential emission decay. The shorter-lived (τ = 10.8 μs) emission is attributable to the bpy-based 3MLCT emission, similar to the other RuII-polypyridine complexes, while the longer-lived (τ = 62.1 μs) emission can probably be assigned as arising from the quinoline-based 3(π-π*) excited state.
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