Density functional theory investigation of Eu(III) complexes with β-diketonates and phosphine oxides:: Model complexes of fluorescence compounds for ultraviolet LED devices

The density functional theory was employed to investigate Eu(III) complexes with three beta-diketonates and two phosphine oxides (complex M1: Eu(bdk)(3)(TPPO)(2), complex M2: Eu(bdk)(3)(TMPO)(2), and complex M3: Eu(bdk)(3)(TPPO)(TMPO)) deemed to be the model complexes of the fluorescence compounds for the ultraviolet LED devices we have recently developed. For each complex, two minimum energy points corresponding to two different optimized geometries (structures A and B) have been found, and the difference of the energy between two minimum energy points is found to be quite small (less than 1 kcal/mol). Vertical excitation energies and oscillator strengths for each complex at two optimized geometries have been obtained by the time-dependent density functional theory, and the character of the excited states has been investigated. For complex M3, the absorption edge is red-shifted, and the oscillator strengths are relatively large. The efficiency of intersystem crossing and energy transfer from the triplet excited state to the Eu(III) ion is considered by calculating Delta E-ISC (the energy difference between the first singlet excited state and the first triplet excited state) and Delta E-ET (the difference between the excitation energy of the complex for the first triplet excited state and the emission energy of the Eu(III) ion for D-5 to F-7).