All-electron relativistic computations on the low-lying electronic states, bond length, and vibrational frequency of CeF diatomic molecule with spin-orbit coupling effects

Ab initio all-electron computations have been carried out for Ce+ and CeF, including the electron correlation, scalar relativistic, and spin-orbit coupling effects in a quantitative manner. First, the n-electron valence state second-order multireference perturbation theory (NEVPT2) and spin-orbit configuration interaction (SOCI) based on the state-averaged restricted active space multiconfigurational self-consistent field (SA-RASSCF) and state-averaged complete active space multiconfigurational self-consistent field (SA-CASSCF) wavefunctions have been applied to evaluations of the low-lying energy levels of Ce+ with [Xe]4f(1)5d(1)6s(1) and [Xe]4f(1)5d(2) configurations, to test the accuracy of several all-electron relativistic basis sets. It is shown that the mixing of quartet and doublet states is essential to reproduce the excitation energies. Then, SA-RASSCF(CASSCF)/NEVPT2+SOCI computations with the Sapporo(-DKH3)-2012-QZP basis set were carried out to determine the energy levels of the low-lying electronic states of CeF. The calculated excitation energies, bond length, and vibrational frequency are shown to be in good agreement with the available experimental data. (c) 2018 Wiley Periodicals, Inc

All-electron relativistic spin-orbit multireference computation to elucidate the ground state of CeH

The all-electron relativistic spin-orbit multiconfiguration/multireference computations with the Sapporo basis sets were carried out to elucidate the characters of the low-lying quasi-degenerate electronic states for the CeH diatomic molecule. The present computations predict the ground state of CeH to be a pure quartet state of 4f(1)5d(1)(5d(sigma)-H-1s)(2)6s(1) configuration (omega = 3.5). The first excited state (omega = 2.5) shows a doublet dominant of 4f(1)(5d(sigma)-H-1s)(2)6s(2) configuration at a short bond length while it changes to a quartet dominant at a long bond length. The Ce-H stretching fundamental frequency was calculated to be 1345 cm(-1) in the ground state, which is in good agreement with the experimental value, 1271 cm(-1), measured by a matrix-isolation technique

Practical electronic ground-and excited-state calculation method for lanthanide complexes based on frozen core potential approximation to 4f electrons

A practical electronic ground- and excited-state calculation method for lanthanide complexes is proposed by introducing frozen core potential (FCP) approximation to 4f electrons of a lanthanide atom ion (Ln(3+)). Based on the fact that the FCP method is formally equivalent to the elongation method, the 4f-frozen FCP calculations of Ln(3+) complexes were successfully performed using the elongation method implemented in GAMESS quantum chemistry program. By comparing the 4f-frozen FCP calculation results of several lanthanide complexes with the results of the standard calculations, it was confirmed that the excitation energies by these calculations are comparable. Also, the SCF convergence and stability were significantly improved by the FCP approximation. We further propose a method to relax the rotational degrees of freedom for the frozen 4f orbitals. This relaxation slightly improves the accuracy of the excitation energies for f-f transitions

Seven-Coordinate Luminophores: Brilliant Luminescence of Lanthanide Complexes with C-3v Geometrical Structures

Enhanced luminescence properties of mononuclear lanthanide complexes with asymmetric seven-coordination structures are reported for the first time. The lanthanide complexes are composed of a lanthanide ion (Eu-III or Tb-III), three tetramethyl heptanedionato ligands, and one triphenylphosphine oxide ligand. The coordination geometries of the lanthanide complexes have been evaluated by using single-crystal X-ray analyses and shape-measurement calculations. The complexes are categorized to be seven-coordinate monocapped octahedral structures (point group C-3v). The seven-coordinate lanthanide complexes show high intrinsic emission quantum yields, extra-large radiative rate constants, and unexpected small nonradiative rate constants. The brilliant luminescence properties have been elucidated in terms of the asymmetric coordination geometry and small vibrational quanta related to thermal relaxation

Coordination Geometrical Effect on Ligand-to-Metal Charge Transfer-Dependent Energy Transfer Processes of Luminescent Eu(III) Complexes

Photophysical properties of europium (Eu(III)) complexes are affected by ligand-to-metal charge transfer (LMCT) states. Two luminescent Eu(III) complexes with three tetramethylheptadionates (tmh) and pyridine (py), [Eu(tmh)(3)(py)(1)] (seven-coordinated monocapped-octahedral structure) and [Eu(tmh)(3)(py)(2)] (eight-coordinated square antiprismatic structure), were synthesized for geometrical-induced LMCT level control. Distances between Eu(III) and oxygen atoms of tmh ligands were estimated using single-crystal X-ray analyses. The contribution percentages of pi-4f mixing in HOMO and LUMO at the optimized structure in the ground state were calculated using DFT (LC-BLYP). The Eu-O distances and their pi-4f mixed orbitals affect the energy level of LMCT states in Eu(III) complexes. The LMCT energy level of an eight-coordinated Eu(III) complex was higher than that of a seven-coordinated Eu(III) complex. The energy transfer processes between LMCT and Eu(III) ion were investigated using temperature-dependent and time-resolved emission lifetime measurements of D-5(0) -> F-7(J) transitions of Eu(III) ions. In this study, the LMCT-dependent energy transfer processes of seven- and eight-coordinated Eu(III) complexes are demonstrated for the first time

Effective Photosensitization in Excited-State Equilibrium: Brilliant Luminescence of Tb-III Coordination Polymers Through Ancillary Ligand Modifications

Molecular photosensitizers provide efficient light-absorbing abilities for photo-functional materials. Herein, effective photosensitization in excited-state equilibrium is demonstrated using five Tb-III coordination polymers. The coordination polymers are composed of Tb-III ions (emission center), hexafluoroacetylacetonato (photosensitizer ligands), and phosphine oxide-based bridges (ancillary ligands). The two types of ligand combinations induces a rigid coordination structure via intermolecular interactions, resulting in high thermal stability (with decomposition temperatures above 300 degrees C). Excited-triplet-state lifetimes of photosensitizer ligands (tau=120-1320 mu s) are strongly dependent on the structure of the ancillary ligands. The photosensitizer with a long excited-triplet-state lifetime (tau >= 1120 mu s) controls the excited state equilibrium between the photosensitizer and Tb-III, allowing the construction of Tb-III coordination polymer with high Tb-III emission quantum yield (>= 70 %)