Intermolecular energy transfer between phenanthrene and lanthanide ions in aqueous micellar solution

Abstract

The direction and mechanism of energy transfer between phenanthrene and tris(dipicolinato)lanthanide(III)[Ln(pdc)^3– ₃, Ln = Dy, Eu, Tb] anions in aqueous cetyltrimethylammonium micellar solution is shown to depend on the relative energies of the aromatic triplet states and the lanthanide excited states. For the terbium complex, the transfer occurs from the ⁵D₄ excited state to the coexcited phenanthrene lowest triplet (T₁) thereby exciting the phenanthrene to a higher triplet T₂, whereas for Eu(pdc)^3– ₃ and Dy(pdc)^3– ₃ the energy transfer is from the aromatic triplet T₁ to the ground state of the lanthanide complex. In each case the involvement of the triplet state has been demonstrated by triplet–triplet adsorption spectroscopy, and the behaviour of the lanthanide excited states observed from their luminescence kinetics. Oxygen quenching studies confirm the proposed mechanisms.