Visible-Light Excitable Europium(III) Complexes with 2,7-Positional Substituted Carbazole Group-Containing Ligands

Abstract

Two novel carbazole-based beta-diketones with 2- or 2,7-substituted groups in the carbazole ring, 2-(4'4'4'-trifluoro-1'3'-dioxobutyl)-carbazole (2-TFDBC) and 2,7-bis(4'4'4'-trifluoro-1''3'-dioxobutyl)-carbazole (2,7-BTFDBC), and their europium(III) ternary complexes Eu(2-TFDBC)(3)phen and Eu(2)(2,7-BTFDBC)(3)(phen)(2) were synthesized via a dexterously designed routine, where phen is 1,10-phenanthroline. The Eu(III) complexes were characterized by elementary analysis, IR and UV-visible absorption spectroscopy, thermogravimetric analysis (TGA), and photoluminescence (PL) measurements. TGA shows that the decomposition temperatures of the complexes are 361.4 and 367.3 degrees C, respectively. PL measurement results indicated that suitably expanded pi-conjugation in the complex molecules makes the excitation band redshift to the visible region, and both the Eu(III) complexes exhibit intense red emission under blue-light excitation. The triplet state energy levels of 2-TFDBC and 2,7-BTFDBC in the complexes are higher than that of the lowest excited level of Eu(3+) ion, (5)D(0), so the photoluminescence mechanism of the Eu(III) complexes was proposed as a ligand-sensitized luminescence process. All of the results indicate that Eu(2-TFDBC)(3)phen and Eu(2)(2,7-BTFDBC)(3)(phen)(2) are promising candidates as visible-light excitable red phosphor for luminescence applications.

Acridone‐Benzimidazole Ring‐Fused Ligands: A New Class of Sensitizers of Lanthanide Luminescence via Low‐Energy Excitation

“…A quantity of interest, when it comes to design ligands able to generate efficient antenna effects, is the sensitization efficiency η sens which can be deduced from two experimentally accessible parameters, the overall quantum yield Q L Ln (i.e. upon excitation in the ligand electronic levels) and the intrinsic quantum yield Q Ln Ln (i.e., upon direct f-f excitation); see Equation (4).…”

“…Nowadays, one of the growing challenges in the design of lanthanide luminescent devices is to extend the excitation wavelength from the UV into the visible range of the electro-magnetic spectrum. [4] Indeed, excitation with energetic UV radiation, especially below 340 nm, [5] suffers severe drawbacks in the field of bio-analysis, since it generates significant auto-fluorescence, causes cell damage, and requires the use of costly quartz optics. Presently, three different approaches are intensively explored with the aim of circumventing such undesired effect.…”

“…the absorbing d-block and the emissive lanthanide ion, that often reduces the efficiency of the energy transfer. Finally, it is also feasible to funnel energy through visible absorption bands (π-π* or intra-ligand charge transfer, ILCT) of purely organic chromophores such as fluorescein, [18] rhodamine, [19] 8-hydroxyquinoline, [20][21][22] carbazole- [4] or tetrazine-based [23] ligands, as well as boradiazaindacene dyes, [24] to name but a few examples. However, visible-absorbing organic chromophores with do- 3 [25] polyaminocarboxylates with one pendant arm bearing a sensitizing acridone group, [26,27] [Eu(fod) 3 (MK)] complex (MK = Michler's ketone, fod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-dione), [28] and [Eu(PHN) 3 (H 2 O)(DMF)]-PHN (HPHN = 9-hydroxyphenal-1-one), [29] only the ternary complex prepared by Zhang's group [25] displays remarkable photophysical properties; the overall quantum yield amounts to 52 % in toluene, this sizeable value being due to efficient energy transfer which, unusually, operates from a singlet state.…”

A novel europium(III)–imidazol–diketonate–phenanthroline complex as a red phosphor applied in LED

“…The synthesis routine of HIDTFBD is shown in Fig. 1 The europium(III) ternary complex was synthesized with a common method analogous to our earlier work [11] as shown in Fig. 2 (yield 61%).…”

An efficient bonding-type Eu-containing copolymer as red phosphor applied in LED

“…These results suggest that the coordination bonds formed between the Eu(III) ion and the ligands DBM and TOPO in the copolymer. [11], therefore improves the fluorescence efficiency, the coordination stability and the thermal stability [12][13][14] of the polymer, though it does not have obvious absorption in above 300 nm region.…”