Enhancement of Terbium(III)-Centered Luminescence by Tuning the Triplet Energy Level of Substituted Pyridylamino-4-R-Phenoxo Tripodal Ligands

Abstract

A series of luminescent phenoxo-bridged dinuclear TbIII complexes with tripodal ligands, 2,2′-[[(2-pyridinylmethyl)­imino]­di­(methylene)]-bis­(4-R-phenol), where R = CH3 (LCH3) (I), Cl (LCl) (II), CH3O (LCH3O) (III), COOCH3 (LCOOCH3) (IV), were prepared to probe the effect of para-substitution on the phenol ring of the ligand on the TbIII luminescence. For these TbIII complexes a complete suppression of the ligand-centered fluorescence is observed, which demonstrates an efficient ligand-to-metal energy transfer. Complex IV was found to be the one that shows the greater intensity of the emission at room temperature. The obtained quantum yields follow the trend IV > II ≫ I > III. The quantum yield for II and IV is approximately five times greater than those obtained for I and III, indicating that the LCl and LCOOCH3 are better sensitizers of the TbIII ions. These results were rationalized in terms of the variation of the energy gap between the triplet level (T1) of the ligand and the emissive 5D4 level of TbIII, due to the electron-acceptor or electron-donor properties of the substituents. The τav values are in the millisecond range for all the studied complexes and resulted independent of temperature. The Commission International d’Eclairage coordinates (CIE) for all complexes are in the green color region, being insensitive to the variation of temperature. Moreover, the color purity (CP) is ca. 90% for all complexes, being ca. 100% for IV. Thus, the introduction of electron-acceptor substituents on the ligand permitted us to improve the luminescent properties of the TbIII complexes.

Energy Transfer in Metal–Organic Frameworks for Fluorescence Sensing

“…Finally, the linker’s emission could be quenched completely, indicating efficient energy transfer from the linker to the metal center. 112 …”

Theoretical Modeling (Sparkle RM1 and PM7) and Crystal Structures of the Luminescent Dinuclear Sm(III) and Eu(III) Complexes of 6,6,7,7,8,8,8- Heptafluoro-2,2-dimethyl-3,5-octanedione and 2,3-Bis(2-pyridyl)pyrazine: Determination of Individual Spectroscopic Parameters for Two Unique Eu3+ Sites

“… 13 , 14 Luminescence can also be intensified by tuning the triplet state of the coordinating ligands to provide a suitable energy gap for effective energy transfer from the triplet state of the ligand to the emissive level of lanthanide ions. 15 Of the plethora of the ligands used as sensitizers, β-diketones are one of the most effective ligands 16 for the sensitization of the lanthanide ions since the β-diketone derivatives are easy to prepare, have greater stability, and present noticeable luminescence properties. 17 , 18 The fluorines in the fluorinated β-diketones also enhance the overall quantum yield by reducing the non-radiative decay occurring via high energy C–H/N–H vibrations by replacing them with lower energy C–F vibrations.…”

Thermal Dependence of the Luminescent Properties of Mononuclear TbIII Macrocyclic Complexes

“…924 cm À 1 . [17,24] The corresponding energy gap for the complexes with isothiocyanato ligands is 562 cm À 1 for TbL 1 NCS, 787 cm À 1 for TbL 2 NCS and 2559 cm À 1 for TbL 3 NCS. Table S5 summarizes the L* energies and ΔE[L*-5 D 4 ] values for all complexes.…”

“…For the quantum yield (Φ) measurements, a Quanta‐ϕ F‐3029 Integrating Sphere was coupled to the spectrofluorimeter, and the spectra were recorded at room temperature. The internal QY was calculated according to equation : [24] …”