Electroluminescence coordination polymers

On the other hand, lanthanide ions are well known for their unique optical properties. These properties are extensively used in numerous fields such as laser amplifiers (Adam, 2002 Kuriki et al., 2002) or electroluminescent materials (Kido and Okamoto, 2002) for instance. Coordination polymers could be veiy interesting as far as optical properties are concerned. Indeed they are transparent and the rare earth ions distribution can be perfectly controlled by an appropriate choice of the ligand while in plastic or glasses they are generally statistically dispersed. The prerequisites of such coordination polymers exhibiting optical properties are obviously the following the material must be thermally rather stable, solvent molecules must be avoided and the inter-metallic distances must be carefully adjusted in order to allow the best efficiency for the targeted application. 

This concept was extended by Che et al. for a series of terpyridine containing chromophores [88]. The respective zinc coordination polymers obtained thereby were investigated by optical spectroscopy, NMR and viscosimetry. These coordination polymers exhibit fluorescence ranging from violet to yellow and two such polymeric compoxmds coifld be successfully incorporated into an electroluminescent device. Whereas in polymer 33 the green fluorescence originates from the fluorene unit located between the tpy ligands, the blue fluorescence in polymer 34 stems from the 4 -phenyl-substituted tpy ligand itself, so that in the latter case tpy acts as both the structural and the functional unit. 

Spiro-FPAl/TPBI/Bphen Cs/Al. A very low operating voltage of 3.4 V at luminance of 1000 cd/m2 was obtained, which is the lowest value reported for either small-molecule or polymer blue electroluminescent devices. Pure blue color with CIE coordinates (0.14, 0.14) have been measured with very high current (4.5 cd/A) and quantum efficiencies (3.0% at 100 cd/m2 at 3.15 V) [245]. In another paper, Spiro-FPA2 (126) was used as a host material with an OLED device structure of ITO/CuPc/NPD/spiro-FPA2 l%TBP/Alq3/LiF that produces a high luminescent efficiency of 4.9 cd/A [246]. 

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. 

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