Electronic Structure of Eu(III) Adducts with OP(C6H5)3 and OP[NMe2]3

Ultraviolet photoelectron spectroscopy in the gas phase (UPS, HeI), X-ray photoelectron spectroscopy in the condensed phase (XPS, MgKα), and quantum chemical methods (DFT) are used to study the adducts of Eu(III) tris-hexafluoroacetylacetonate with two molecules of four-coordinated phosphorus, namely HMPA (OP[N(CH3)2]3) and TPPO (OP(C6H5)3). Spectral bands of valence and core levels are interpreted using energy calculations and localization of Kohn-Sham orbitals. It is shown that TPPO and HMPA molecules influence the electronic structure of the complexes; positions and localizations of molecular orbitals are determined, the nature of bonding between Eu(III) and three chelate ligands and two neutral molecules is established. The differences in positions and compositions of occupied and vacant orbitals participating in energy transfer under excitation are shown. It is estimated that the bonding energy between Eu(hfac)3 and the two molecules is 10.91 eV for OP(C6H5)3, 12.62 eV for OP[NMe2]3, and 24.9 eV for SP[NMe2]3. It is shown how the differences between the energies and localizations of HOMOs of neutral molecules affect the structure, localization of adducts by the frontier molecular orbital (MO) and HOMO-LUMO gaps and how these differences determine the parameters of “antenna” ligand effects and the relative quantum yield of the luminescence of the adduct.