Optical properties and electronic structure of Eu(III) complexes with HMPA and TPPO

• The absorption band in a region of 240–290 nm caused by the phenyl groups. • There is no visible excitation of the groups N(CH 3 ) 2 in Eu(hfac) 3 (HMPA) 2. • The absorption region of hfac compensated the disadvantages of the groups N(CH 3 ) 2 . • The main line maximum at 614 nm that forms the Eu 3+ luminescence. • The higher occupied MOs determined the structure HOMO-LUMO energy gap. Two adducts of Eu(III) tris-hexofluoroacetylacetonate with HMPA (OP(N(CH 3 ) 2 ) 3 , hexamethylphosphotriamide) and TPPO (OP(C 6 H 5 ) 3 , triphenylphosphine oxide) were studied by optical spectroscopy and quantum chemistry (DFT/TD-DFT). The structure of the higher occupied molecular orbitals (MO) of the two adducts determines differences in the position of the excitation band maximum of hfac ligands. According to the calculation data, all excited states are caused by the transition to 3 vacant π 4 * MOs of hfac ligands. Optical spectra of absorption, excitation and luminescence are obtained and interpreted. The peculiarity of the HOMO-LUMO structure, the low value of the energy gap, and the broadened absorption region of hfac ligands compensate the low absorbance ability of the groups N(CH 3 ) 2 in a region of 220–360 nm for the adduct Eu(hfac) 3 (HMPA) 2 , reducing the luminescence intensity by only 5–10% relative to the adduct of the Eu(III) complex with TPPO ligands.