Manifestation of π–π Stacking Interactions in Luminescence Properties and Energy Transfer in Aromatically-Derived Tb, Eu and Gd Tris(pyrazolyl)borate Complexes

The three new complexes
TpPyLn­(CH3CO2)2(H2O) (Ln = Eu (1), Gd­(2), or Tb (3)) were prepared and characterized crystallographically.
In the crystal lattices of these complexes, separate molecules are
connected in infinite chains by π-stacking interactions. Complexes 1 and 3 display intense photoluminescence and
triboluminescence (red and green respectively), while compound 3 exhibits electroluminescence commencing at 9 V in an ITO/PVK/3/Al device (ITO = indium-tin oxide, PVK = poly­(N-vinylcarbazole)). A series of Eu/Tb-doped Gd compounds was prepared
by cocrystallization from mixtures of 1 and 2 or 2 and 3, respectively. It was shown
that π-stacking interactions are involved in increasing the
efficiency of energy transfer from the gadolinium complex to emitting
[TpPyEu]2+ or [TpPyTb]2+ centers, and this energy transfer occurs through hundreds of molecules,
resembling the process of energy harvesting in chloroplast stacks.