Complexes terbium

Terbium complexes reported for electroluminescence can be separated mainly into two classes terbium carboxylates and P-diketone complexes. Terbium carboxylates have good luminescence but they are difficult to use as efficient emission materials in OLEDs due to their multi-coordination mode and consequent formation of inorganic polymers with poor solubility or volatility. For these reasons, in this section we will focus on use of the newly developed f)-diketonate terbium complexes in OLEDs. 

Similar to the europium complexes, the terbium complexes used as good emitters in OLEDs also need to have high photoluminescent efficiencies, good carrier transporting properties, and sufficiently good thermal stability for small molecule materials to form a film by thermal evaporation in vacuum. 

After a systematic study of the terbium pyrazolonate complexes, we demonstrated that Tb(ip-PMP)3(TPPO)2 (compound 36) had very good electron transport properties and the recombination zone was confined mainly to the TPD layer, while Tb(ip-PMP)3(H20)(Et0H) (compound 37) showed only a hole-transport property and the recombination zone was confined mainly to the AIQ layer (Eigure 11.24). To adjust the carrier-transport properties and make the recombination zone easily confined to the terbium complex layer, we synthesized 

The results revealed that holes and electrons were more easily confined to this complex by constructing a proper device configuration. To prevent the hole from entering the AIQ layer, a 20 nm layer of hole blocking material, BCP, was inserted between complex 38 and AIQ in the device with configuration ITO/TPD (20 nm)/complex 38 (50 nm)/BCP (20 nm)/AlQ 

Complex Singlet energy level/eV Triplet energy level/eV 

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Terbium, tris(2,2,6,6-tetramethyf-3,5-heptanedione)-photosubstitution, 1,408 Terbium complexes f5-diketones, 3, 1081... 

Hildebrandt N, Charbonniere LJ, Lohmannsroben HG (2007) Time-resolved analysis of a highly sensitive forster resonance energy transfer immunoassay using terbium complexes as donors and quantum dots as acceptors. J Biomed Biotechnol 2007 79169... 

Lanthanide ions have been used as DEFRET acceptors in split probes for DNA sequence such as shown in Figure 15.137 When using europium and terbium complexes, the choice of chromo-phores is rather restricted, owing to the high-energy emissive states associated with these ions (vide supra). In this case, the donor chromophore is a salicylic acid unit appended to an... 

L. Huang, H. Tian, F. Li, D. Gao, Y. Huang, and C. Huang, Blue organic electroluminescent devices based on a distyrylarylene derivatives as emitting layer and a terbium complex as electrontransporting layer, J. Luminescence, 97 55-59 (2002). 

The related bis(pyrazolyl)borate ligand [L5]- forms 10-coordinate complexes of the type [Ln(L5)2(N03)]. The terbium complex in particular has promising luminescence characteristics, with a lifetime of 2.6 ms and quantum yield of 0.36 in methanol (49). However, the complexes are not stable in water. 

An attempt to synthesize binuclear complexes led to the development of the back-to-back ligand [L7]2-. The lanthanide coordination environment of the resultant [ ( )2 2( 7)] complexes is the same as that in the parent mononuclear [L4]- complexes, as shown in Pig. 7. Despite the possibility of displacement of the nitrate anions by solvent molecules, a reasonable lifetime (0.9 ms) and quantum yield (0.13) is recorded for aqueous solutions of the terbium complex (49). 

Recently, a series of derivative ligands, [L19]4-—[L23]4-, has been reported (32,62), where the acetophenone chromophore in [L18]4- is replaced by a dipyrazolylpyridine chromophore. These form lanthanide complexes that are stable in aqueous solution, and which possess very promising photophysical attributes. The europium and terbium complexes of all these ligands have long lifetimes (1.3-1.4 ms for europium and 2.3-2.8 ms for terbium) in water that are largely unchanged by solvent deuteration, indicating the effective exclusion of solvent from the primary coordination sphere. 

A closely related ligand is [L41]3- where one side of the cyclen ring is replaced by a pyridyl group (72). In addition to the high quantum yield of the terbium complex ( = 0.51), the complex exhibits in vivo and in vitro tissue selectivity, allowing it to be used for imaging of adenocarcinoma cells. 

High quantum yields and long lifetimes have been reported for a series of calixcrowns with appended bipyridyl chromophores, such as L48 (82). Photophysical studies in acetonitrile gave lifetimes of 0.95-1.38 and 1.83-1.93 ms, and quantum yields of 0.18 0.32 and 0.32-0.39 for europium and terbium complexes, respectively. 

M. A. Fotopoulou and P. C. Ioannou, Post-Column Terbium Complexation and Sensitized Fluorescence for the Determination of Norepinephrine, Epinephrine and Dopamine Using High-Performance Liquid Chromatography, Anal. Chim. Acta 2002,462, 179. 

In most of the europium complexes the fluorescence is due to the last effect. The intramolecular energy transfer within europium and terbium complexes was first observed by Weissman [630] in 1942, and subsequently investigated by many other workers. 

Pandya, S., Yu, J. H., Parker, D., Engineering emissive europium and terbium complexes for molecular imaging and sensing. 

Parker, D., Senanayake, P. K., Williams, J. A. G., Luminescent sensors for pH, p0(2), halide and hydroxide ions using phenanthridine as a photosensitiser in macrocyclic europium and terbium complexes. J. Chem. Soc., Perkin Trans. 21998, 2129-2139. 

Parker and Williams recently reported NAND logic action in the terbium complex 16.[S8] The delayed emission of the lanthanide ion is switched off when H+ and 02 are present simultaneously. Protonation of the phenanthridine side chain causes its triplet excited state to approach theTb(m) 5D4 excited state energetically. This leads to equilibration of these two excited states and sharing of their properties. Thus, the metal-centered state displays the 02 sensitivity usually only found in organic triplets. 

The same technique was used for the preparation of europium and terbium complexes Ln(N03)3 2L (L = bipy, 1,10-phen, and diphenylguanidine) [701e], However, the preparative possibilities of (3.277) are still unclear because, in the majority of experiments, the yields of final products are limited. 

Figure 7.3 Terbium complexes with their ligands and coordination type. 1 is dendritic, whereas 2 and 3 both contain a methoxy substituent group in the ligand and form one-dimensional chains.

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