Thermally-assisted photosensitized emission in a trivalent terbium complex.

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%).

Long-Range LMCT Coupling in EuIII Coordination Polymers for an Effective Molecular Luminescent Thermometer*.

A design for an effective molecular luminescent thermometer based on long-range electronic coupling in lanthanide coordination polymers is proposed. The coordination polymers are composed of lanthanide ions EuIII and GdIII , three anionic ligands (hexafluoroacetylacetonate), and a chrysene-based phosphine oxide bridges (6,12-bis(diphenylphosphoryl)chrysene). The zig-zag orientation of the single polymer chains induces the formation of packed coordination structures containing multiple sites for CH-F intermolecular interactions, resulting in thermal stability above 350 °C. The electronic coupling is controlled by changing the concentration of the GdIII ion in the EuIII -GdIII polymer. The emission quantum yield and the maximum relative temperature sensitivity (Sm ) of emission lifetimes for the EuIII -GdIII polymer (Eu:Gd=1:1, Φtot =52 %, Sm =3.73 % K-1 ) were higher than those for the pure EuIII coordination polymer (Φtot =36 %, Sm =2.70 % K-1 ), respectively. Enhanced temperature sensing properties are caused by control of long-range electronic coupling based on phosphine oxide with chrysene framework.

The Role of π-f Orbital Interactions in Eu(III) Complexes for an Effective Molecular Luminescent Thermometer.

Luminescent Eu(III) complexes with a ligand-to-metal charge transfer (LMCT) state were demonstrated for the development of a molecular thermometer. The Eu(III) complex was composed of three anionic ligands (hfa: hexafluoroacetylacetonate) and a phosphine oxide derivative containing a chrysene framework (diphenylphosphorylchrysene (DPCO)). The chrysene framework induced a rigid coordination structure via intermolecular interactions, resulting in a high thermal stability (decomposition point: 280 °C). The Eu(III) complex also exhibited an extremely high molar absorption coefficient (490000 cm-1 M-1), high intrinsic emission quantum yields (73%), and temperature-dependent energy migration between ligands and Eu(III) ion. The characteristic energy migration system was explained by the presence of the LMCT state based on π-f orbital interactions.

First demonstration of the π-f orbital interaction depending on the coordination geometry in Eu(iii) luminophores.

Herein, the π-f orbital interaction depending on the coordination geometry in the Eu(iii) complex is demonstrated. Thermal analysis and computational calculations showed the phase transition of the Eu(iii) complex based on the change in the coordination geometry. A red-shifted LMCT band and radiative rate changes associated with the phase transition were found in the Eu(iii) complex.

First aggregation-induced emission of a Tb(iii) luminophore based on modulation of ligand-ligand charge transfer bands.

Herein the aggregation-induced emission (AIE) of a Tb(iii) complex is reported for the first time. The Tb(iii) complex is composed of three anionic ligands (acac: acetylacetonate) and one large hetero-π-conjugated neutral ligand (dpq: dipyrido[3,2-f:2',3'-h]quinoxaline). The formation of a crystalline J-aggregate of the Tb(iii) complex (CJ-Tb(iii)) was characterized by X-ray crystal structure analysis and absorption spectra. A crystalline H-aggregate (CH-Tb(iii)) was also prepared using the ligand steric effect (tmh: 2,2,6,6-tetramethyl-3,5-heptanedionate). The emission and AIE properties of CJ-Tb(iii) were evaluated using emission spectra, lifetime, and quantum yields, whereas CH-Tb(iii) did not emit photons. Density functional theory calculations predict that the AIE originates from the modulation of ligand-to-ligand charge transfer bands through J-aggregation.