Divalent lanthanide metal complexes

Details Divalent lanthanide metal complexes Divalent lanthanide metal complexes

2001-07-31

2002-12-10

Nazario-Gonzalez, Porfirio (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C548S109000, C534S015000, C313S503000, C313S506000, C428S690000, C428S917000

Reexamination Certificate

active

06492526

ABSTRACT:

This invention relates to divalent lanthanide metal complexes, to processes for their preparation and to light emitting devices containing the complexes.
Flat panel displays are the critical enabling technology for many current applications, including laptop computers and “head up” displays, as they offer several potential advantages over conventional cathode ray tube displays, including compactness and low power consumption.
Currently, the flat panel display market is dominated by liquid crystal technology, but these materials suffer several drawbacks including small operational viewing angles, poor image contrast and high power consumption. As an alternative technology for flat panel displays, electroluminescent (EL) displays using semiconducting organic polymers offer the potential of lower cost, improved viewing angles, better contrast and lower power consumption. However, these materials often have broad emission profiles, resulting in poor chromaticity and reduced device efficiency.
Typically, a flat panel device is a multilayer assembly of structurally important films consisting of a transparent electrode, insulation, phosphor and metal electrode. All are important materials in device fabrication, but the single most important element in the development of a multi-colour electroluminescent device is the phosphor.
It is known that organometallic complexes can be used as phosphors in electroluminescent devices. For example, U.S. Pat. No. 5,552,547 describes complexes of aluminium, gallium and indium in which one of the ligands acts as a “built-in” fluorescent dye. The colour of the light which is emitted from the complex is determined by the ligand which acts as the dye.
Lanthanide-based materials are gaining popularity as phosphors for thin film devices, as they offer several potential advantages over other light emitting species: such as narrow emission linewidths, the potential for device structures with efficiencies greater than 25% and excellent Commission Internationale de I'Eclairage (CIE) colourmap coordinates. To date, two distinct types of lanthanide metal based phosphors have been reported in the literature; those based upon solid-state inorganic matrices doped with small amounts of the lanthanide ion and molecular coordination complexes. Conventional inorganic thin film EL devices are based upon solid-state phosphors and this group of materials are amongst the most extensively studied of all EL devices in the literature. Unfortunately, these solid-state devices, often based on doped II-VI materials, require large driving voltages and this has hampered their development in portable thin film displays, although there are reports of adequately functioning thin film structures. Recently, several groups of workers have recognised the potential of molecular organometallic phosphors to incorporate the processing and manufacturing advantages of organic materials with the emissive properties of the solid-state materials and reports of the use of lanthanide coordination complexes as hybrid materials are becoming increasingly common. To date these devices have been based almost exclusively upon trivalent europium (red emitting) and terbium (green emitting) complexes with bidentate oxygen donor ligands such as benzoylbenzoate and acetylacetonate derivatives.
M. A. Pavier et al., Thin Solid Films, 284-285 (1996) 644-647, describe electroluminescence from dysprosium- and neodymium-containing Langmuir-Blodgett films. The metal is in the trivalent state in the complexes and the ligand used is a pyrazolone-based molecule in which the binding to the metal by the ligand occurs via a beta-diketonate-type arrangement.
The trivalent europium complex with phenanthroline and thenoyltrifluoroacetone is disclosed in Sano et al,
Jpn. J. Appl. Phys
., vol.34 (1995), p. 1883-1887 and Campos et al in
J. Appl. Phys
., vol.80, no.12 (1996), p. 7144-7150. Both Sano et al and Campos et al teach the use of the complexes to provide red light in electroluminescent devices. Like the complexes disclosed by Pavier et al, it is the beta-diketonate part of the ligand which binds to the metal.
The synthesis and structure of bis(tris(3,5-dimethtylpyrazolyl)borate)samarium (II) is described by Takats et al in
Organometallics
1993, 12, 4286-4288. However, there is no mention of the light emitting properties of the compound, only its structure and that of its reaction product with azobenzene. The syntheses and structures of the compounds bis[hydrotris(3-tert.butyl-5-methylpyrazolyl) borato]samarium and bis[hydrotris(3-tert.butyl-5-methylpyrazolyl) borato]ytterbium are described by Zhang et al. in New J. Chem. 1995. 19. 573-585. Certain bis- and mono-hydrotris(pyrazolyl)borate complexes of samarium and ytterbium are also described by J. Takats, J. Alloys and Compounds 249 (1997) 52-55.
Light emitting devices containing lanthanide (III) complexes are described in WO 98/06242. Trispyrazolylborate complexes of non-lanthanide metals are also mentioned but only as electron transporting hosts for phosphors. There is no mention of the use of trispyrazolylborate complexes as phosphors, of complexes of these ligands with lanthanide metal ions or of lanthanide (II) complexes at all.
One of the problems associated with the optical emissions from the trivalent lanthanide metal ions is that they are dominated by the relatively weak spin forbidden f—f transitions. Also, the wavelength of the emission from these transitions is generally independent of the ligand in the complex and is therefore difficult to tune by altering the nature of the ligand. The present invention solves these problems by providing a new class of lanthanide metal complexes for use as phosphors in light emitting devices in which the lanthanide metal is in the +2 oxidation state i.e., it is divalent.
Accordingly, the present invention provides a light emitting device comprising a complex containing a divalent lanthanide metal cation complexed with from one to three polydentate ligands.
Unlike the emissions from the trivalent lanthanide metal ions, emissions from the metal in the divalent state may arise from both inter-shell transitions between the 4f
6
5d
1
excited state and the 4f
7
ground state and charge transfer (CT) transitions, both of which are quantum mechanically allowed and therefore potentially very efficient. Furthermore, unlike the f—f transition of trivalent species, the wavelength of the emission is ligand-dependent and, therefore, potentially tunable. Emission linewidths are also broadened since the transition is affected by differences in metal-ligand bond lengths between the ground and excited states of the molecule.
Preferably, each ligand in the complexes of the invention comprises one or more pyrazolyl groups, optionally substituted and optionally fused with a substituted or unsubstituted, heterocyclic or carbocyclic, aromatic or non-aromatic, ring system, and one of the nitrogen atoms of the pyrazolyl groups forms a coordinate bond to the metal. More preferably, each ligand is a trispyrazolylborate anion, the pyrazolyl groups each being optionally substituted and optionally fused with a substituted or unsubstituted, heterocyclic or carbocyclic, aromatic or non-aromatic, ring system, optionally substituted at the boron atom.
Suitable complexes for use in the invention are desirably those having the formula (I):
[(Z(L)
3
)
p
M]A
q
  (I)
wherein
Z is a carbon atom or R
1
—B fragment
p is 1 or 2
q is 2-p
A is a counterion
R
1
is: (i) hydrogen, aryl or aralkyl each optionally substituted with from one to five halogen or C
1
to C
6
alkyl groups; or (ii) C
1
to C
6
alkyl, C
2
to C
6
alkenyl or C
2
to C
6
alkynyl each optionally substituted with one or more halogen atoms
each L is covalently bound to Z and is independently selected from a group of the formula (II) or (III)
in which R
2
, R
3
and R
4
are independently selected from: (i) halogen, cyano, nitro, sulphono, amino, C
1
to C
6
alkylamino, C
1
to C
6
alkylamido, carboxyl, C
1
to C
6
alkyloxycarbonyl, hydr

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