2 COMPUTATIONAL METHODS

The geometry optimization of mesogenic Eu(III) complexes in the ground state was performed by the DFT method using the Prirоdа 06 software.[28,29] According to our previous studies[8,9,11,27,30] we used generalized gradient approximation with the Perdew-Burke-Ernzerhof (PBЕ) exchange-correlation functional.[31] Relativistic basis sets rL11 for Eu(III) and rL1 for other atoms within the scalar relativistic approximation were used.[32] These sets are analogues of the cc-pVDZ and cc-pCVDZ double-zeta basis sets of Dunning, respectively.[33] Calculations were performed for isolated molecules without symmetry constraints. Optimization ended when the gradient value reached 3∙10­6 eV/Å, the SCF convergence accuracy was set to 3∙10­5 eV.
The types of coordination polyhedra were determined using the SHAPE software.[34-36] This program uses sets of points of continuous shape which correspond to the positions of atoms in optimized geometries of molecules and determines polyhedra by the smallest deviations of these sets from the vertices of ideal reference polyhedra.
Experimental IR spectra were observed for pressed thin tablets of Eu(III) complexes with potassium bromide on ALPHA FT-IR spectrometer (Bruker) with a spectral of range 375-7500 cm-1 and resolution 4 cm-1. The vibrational modes of the IR spectra were calculated by the DFT method and PBE0 functional, as well as the NMR chemical shifts with the gauge-independent atomic orbital method. Experimental chemical shifts were taken from other publications.[8,9,30,37]
TDDFT method with various density functionals was unable to separately localize triplet excitation on each of the ligands in the studied Eu(III) complexes during the optimization of the excited state structures. The obtained excited states were intraligand or delocalized. Unlike density functional-based methods, configuration interaction singles method (CIS) correctly predicted excitation localization on separate ligands. Therefore, in this work the triplet excited state structures were optimized by the CIS method using the Firefly v. 8 software which is partially based on the GAMESS code.[38,39] For Eu(III) ions the scalar quasirelativistic 4f-in-core pseudopotential ECP52MWB with the associated valence basis set was used,[40,41] for other atoms - 6-31G(d,p). Then TDDFT/PBE0 method was applied for CIS optimized geometries to calculate the values of triplet excited states. Empirical dispersion correction (DFT-D version 4 with Becke-Johnson damping)[42] was used to improve the long-range behavior of DFT.
To determine the experimental values of the triplet excited states, we used the phosphorescence spectra of gadolinium(III) (Gd(III)) complexes with the corresponding ligands which are characterized by a clear phosphorescence band of ligands.[8,43,44]
In order to evaluate the emission efficiency of the studied Eu(III) complexes, the intramolecular energy transfer rates from the triplet levels of ligands to the resonance levels of Eu(III) were calculated according to the procedure described in [45, 46]. The theoretical values of quantum yields were compared to the previously obtained experimental absolute quantum yields.[47]
The structure-topological software package ToposPro V. 5.3.3.4 was used for the analysis of Voronoi-Dirichlet polyhedra (VDP) after optimization of the ground and excited state structures.[48]