Ad esign for an effective molecular luminescent thermometerb ased on long-range electronic coupling in lanthanide coordination polymers is proposed. The coordination polymers are composed of lanthanide ions Eu III and Gd III ,t hree anionic ligands(hexafluoroacetylacetonate), and ac hrysene-based phosphine oxide bridges (6,12-bis(diphenylphosphoryl)chrysene). The zig-zago rientation of the single polymerc hains induces the formation of packed coordination structuresc ontaining multiple sites forC H-F intermolecular interactions, resulting in thermal stability above 350 8C. The electronic coupling is controlledb yc hanging the concentration of the Gd III ion in the Eu III-Gd III polymer.T he emission quantum yield and the maximum relative temperature sensitivity (S m)o fe mission lifetimesf or the Eu III-Gd III polymer (Eu:Gd = 1:1, F tot = 52 %, S m = 3.73 %K À1)w ere higher than those for the pure Eu III coordination polymer (F tot = 36 %, S m = 2.70 %K À1), respectively.E nhanced temperature sensing properties are causedb yc ontrol of long-range electronic coupling based on phosphine oxide with chrysene framework.

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In this review, we summarize the latest research progress in photophysics based on the π-4f charge transfer excited states of trivalent europium 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 π-4f mixing in HOMO and LUMO at the optimizedstructure in the ground state were calculated using DFT (LC-BLYP). The Eu-O distances and their π-4f mixed orbitals affect the energy level of LMCT states in Eu(III) complexes. The LMCT energy level of eight-coordinated Eu(III) complex was higher than that of sevencoordinated 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 5 D0→ 7 FJ 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.

Novel Eu­(III) coordination polymers with furan-based bridging ligands [Eu­(hfa)3(Cy)] n and [Eu­(hfa)3(Tol)] n (hfa: hexafluoroacetylacetonato, Cy: 2,5-bis­(dicyclohexylphosphoryl)­furan), Tol: 2,5-bis­(di-p-tolylphosphoryl)­furan) are reported. The rigidity of assembly steric structures was controlled by intermolecular interactions through the side groups in bridging ligands. They exhibited one of the best performances (thermal stability above 320 °C and external photoluminescence quantum yields of up to 71%) among reported lanthanide­(III) compounds. The triboluminescence activity was demonstrated to be dependent on the mechanical stability of the coordination polymers, which was proportional to the number of hydrogen atoms in the side groups. The second example of a large TL/PL spectral difference in [Tb,Eu­(hfa)3(Tol)] n also revealed discrete photophysical processes under the conditions of grinding and UV irradiation.

Luminescent lanthanide complexes containing effective photosensitizers are promising materials for use in displays and sensors. The photosensitizer design strategy has been studied for developing the lanthanide-based luminophores. Herein, we demonstrate a photosensitizer design using dinuclear luminescent lanthanide complex, which exhibits thermally-assisted photosensitized emission. The lanthanide complex comprised Tb(III) ions, six tetramethylheptanedionates, and phosphine oxide bridge containing a phenanthrene frameworks. The phenanthrene ligand and Tb(III) ions are the energy donor (photosensitizer) and acceptor (emission center) parts, respectively. The energy-donating level of the ligand (lowest excited triplet (T1) level = 19,850 cm−1) is lower than the emitting level of the Tb(III) ion (5D4 level = 20,500 cm−1). The long-lived T1 state of the energy-donating ligands promoted an efficient thermally-assisted photosensitized emission of the Tb(III) acceptor (5D4 level), resulting in a pure-green colored emission with a high photosensitized emission quantum yield (73%).

Soft-crystals are defined as flexible molecular solids with highly ordered structures and have attracted attention in molecular sensing materials based on external triggers and environments. Here, we show the soft-crystal copolymerization of green-luminescent Tb(III) and yellow-luminescent Dy(III) coordination centers. Soft-crystal polymerization is achieved via transformation of monomeric dinuclear complexes and polymeric structures with respect to coordination number and geometry. The structural transformation is characterized using single-crystal and powder X-ray diffraction. The connected Tb(III) crystal-Dy(III) crystal show photon energy transfer from the Dy(III) centre to the Tb(III) centre under blue light excitation (selective Dy(III) centre excitation: 460 ± 10 nm). The activation energy of the energy transfer is estimated using the temperature-dependent emission lifetimes and emission quantum yields, and time-dependent density functional theory (B3LYP) calculations. Luminescence-conductive polymers, photonic molecular trains, are successfully prepared via soft-crystal polymerization on crystal media with remarkable long-range energy migration.

Seven-coordinate Tb III complexes with strong luminescence and thermosensing properties are reported. Mononuclear [Tb(tmh) 3 (PEB)] [tmh: 2,2,6,6-tetramethyl-3,5-heptanedione, PEB: (diphenylphosphoryl)ethynyl]benzene and dinuclear [Tb 2 (tmh) 6 (m-BPEB)] [m-BPEB: 1,3-bis(diphenylphosphoryl)ethynyl]benzene were characterized by single-crystal X-ray analysis. The quantum yields of [Tb(tmh) 3 (PEB)] and [Tb 2 (tmh) 6 - [a]