WO2013171659A1

WO2013171659A1 - Electroluminescent compound comprising a metal-organic framework

Info

Publication number: WO2013171659A1
Application number: PCT/IB2013/053888
Authority: WO
Inventors: Frederik Kapteijn; Jorge Gascon; Hossein KHAJAVI; Patrick John BAESJOU; Abraham Rudolf Balkenende; Johan Hendrik KLOOTWIJK; Hendrik Adrianus Van Sprang
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2012-05-14
Filing date: 2013-05-13
Publication date: 2013-11-21
Also published as: WO2013171660A1

Abstract

The invention relates to an electroluminescent compound comprising a metal-organic framework. The metal-organic framework comprises metallic structural units linked by organic structural units. The electroluminescent compound further comprises a luminescent moiety that is comprised in at least a part of the organic structural units, and/or that resides in a pore of the metal-organic framework, and/or that is grafted to a coordinatively unsaturated metal site of the metal-organic framework. The electroluminescent compound can be used as basis for a light- generating layer of a light-emitting module.

Description

Electroluminescent compound comprising a metal-organic framework

FIELD OF THE INVENTION

The invention is directed to an electroluminescent compound, to a method for preparing the electroluminescent compound, to a light-emitting module comprising the electroluminescent compound, and to a light-emitting device comprising the light-emitting module.

BACKGROUND OF THE INVENTION

Electroluminescent device technology forms a major opportunity for advanced materials development impacting a large number of technology-based applications. These, for example, include flat panel displays which offer significant advantages over liquid crystal displays including much lower power requirements, improved definition, broader viewing angles and faster response times. The technology for electroluminescent devices offers the potential for lower cost lighting sources compared to incandescent lighting as well as fluorescent lighting applications.

Organic light-emitting diodes (OLEDs) based on electroluminescent organic molecules (also known as small molecule OLEDs or SMOLEDs) are being commercialized to replace liquid crystal displays based on lower power requirements, faster response times, better definition and also easier fabrication.

OLEDs may also be based on electroluminescent polymeric materials. Such OLEDs are also known as polymer light-emitting diodes or PLEDs. The use of

electroluminescent polymeric materials enables the manufacture of flexible OLEDs using roll-to-roll wet chemical processing techniques such as inkjet printing.

The potential for flexible OLEDs is considered to be large offering unique flat or contoured display panels. The development of PLEDs has focused on polymeric materials which exhibit electroluminescence. These materials are generally conjugated polymers, such as poly(phenylene vinylene), polyfluorenes, polyphenylenes, polythiophenes and

combinations of such structures.

Furthermore, a large number of low molecular weight compounds exists which exhibit fluorescence and electroluminescence. Some of these materials are commonly referred to as laser dyes. Many of these compounds have very high fluorescence and electroluminescence efficiencies. However, the properties desired for light-emitting devices are generally only observed in solution or at low levels of doping in electro-optical or electro-active polymers. In the solid state, these materials can crystallize and lack the mechanical integrity to be utilized in PLEDs or SMOLEDs. Additionally (and more importantly), their excellent fluorescence and electroluminescence properties are lost upon crystallization. These problems have been well documented in various reviews on the subjects of materials for light-emitting devices.

Some attempts have been made to combine different components in order to profit from the advantages of each component. For example, light-emitting devices have been proposed wherein a polymer matrix hosts an emitter guest material, such as a light-emitting dye or light-emitting polymer. Another example of the combination of different components is the use of organic/inorganic hybrid materials, such as hybrid nanocrystal PLEDs, for example as described by Colvin et al (Nature 1994, 370, 354-357).

A metal-organic framework is a compound that typically comprises an organic structure coordinated to at least one metal ion or cluster. Such metal-organic frameworks have been described in, for example, US-A-5 648 508 and EP-A-0 790 253. More recently, several reviews have been published on the topic. Cui et al (Chem. Rev. 2012, 112,

1126-1162) published a review article concerning luminescent functional metal-organic frameworks. These materials are said to be very promising as multifunctional luminescent materials, such as for applications in light-emitting and display devices. In this review article it is mentioned that it is theoretically feasible to incorporate nanoscale electroluminescent metal-organic frameworks between two conductors to provide an electroluminescent device. However, it is mentioned that the realization of such important functionality first requires the realization of electroluminescent metal-organic frameworks.

Llabres I Xamena et al (J. Phys. Chem. C 2007, 111, 80-85) discloses the use of metal-organic framework compound MOF-5 as component in an electroluminescence cell. MOF-5 has a three-dimensional structure consisting of zinc oxide structural units that are coordinated to benzene 1,4-dicarboxylate as organic structural units. In the

electroluminescence cell a uniform layer of 50 micrometers thickness comprising MOF-5 and DMF is sandwiched between a transparent ITO electrode and an aluminium counter electrode. When a square AC voltage is applied between the two electrodes,

electroluminescence from the cell can be observed, originating from the zinc oxide structural units.

Further to the above there remains a need for further electroluminescent materials, and improvements thereof, which are useful for being applied in light-emitting devices.

It is an object of the invention to address the aforementioned need and to provide an electroluminescent compound that can be used in a light-emitting module, which in turn can be incorporated in a light-emitting device. A further object of the invention is to provide a light-emitting module and a light-emitting device comprising the light-emitting module.

SUMMARY OF THE INVENTION

In a first aspect of the invention, the object is achieved by an electroluminescent compound comprising a metal-organic framework and a luminescent moiety, wherein the metal-organic framework comprises metallic structural units linked by organic structural units, and wherein the luminescent moiety is comprised in at least a part of the organic structural units, and/or resides in a pore of the metal-organic framework, and/or is grafted to a coordinatively unsaturated metal site of the metal-organic framework.

The luminescent moiety is chosen from the group consisting of inorganic compounds, inorganic-organic compounds such as metal-organic compounds, and organic compounds.

In the context of the present invention, the term "metal-organic framework" refers to a one-, two-, or three-dimensional coordination polymer including metallic structural units (sometimes also referred to as "inorganic connectors") and organic structural units (sometimes also referred to as "linkers"), wherein at least one of the metallic structural units is chemically bonded to at least one bi-, tri-or poly-dentate organic structural unit. It is noted that a "metallic structural unit" may refer to any structural unit comprising a metal or a metal oxide, and that an "organic structural unit" may also refer to a modified unit that contains an inorganic moiety coupled to an organic moiety.

In the context of the present invention, the term "luminescent moiety" refers to a moiety or compound which is capable of emitting light, for example by fluorescence or by phosphorescence, or by both. In the context of the present invention, the term "pore " refers to any kind of opening in the metal-organic framework that contributes to the framework's porosity.

In the context of the present invention, the term "metal-organic compound" refers to a compound comprising one or more metal ions surrounded by organic ligands. Such metal-organic compounds are sometimes also referred to as "coordination complexes" or "coordination compounds" .

The electroluminescent compound of the invention comprises a combination of a luminescent moiety and a structured support in the form of a metal-organic framework.

Compared to organic electroluminescent materials, electroluminescent compounds based on a metal-organic framework are more stable in that they are less sensitive towards oxygen and water.

Compared to known electroluminescent compounds based on a metal-organic framework, wherein the luminescent moiety is formed by the metallic structural units (see Llabres I Xamena et al), in the electroluminescent compound of the present invention the luminescent moiety is chemically combined with the organic structural units of the metal-organic framework, or it resides within pores of the metal-organic framework as a guest molecule, or it is grafted to the metallic structural units of the metal-organic framework, or any combination of these options. The aforementioned structural difference results in an increased versatility in that electroluminescence is independent on any solvents that may be present within the metal-organic framework. Furthermore, it results in an increased life time and in an increased efficiency.

The metal-organic framework comprised in the electroluminescent compound of the invention may comprise a single type of metallic structural unit, or different types of metallic structural units.

The metal-organic framework comprised in the electroluminescent compound of the invention may comprise a variety of metallic structural units. For example, at least part of the metallic structural units may comprise one or more elements selected from the group consisting of Al, Zn, Cu, Cr, In, Ga, Fe, Sc, Ti, V, Co, Ni, La, Ce, Pr, Nb, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No and Lr, such as one or more elements selected from the group consisting of Al, Zn, Ga, In, Fe, Cr and Sc, or one or more elements selected from the group consisting of Al, In, and Ga. When at least part of the metallic structural units comprise a rare earth element it is possible to tune the emission wavelength of the electroluminescent compound.

The metal-organic framework comprised in the electroluminescent compound of the invention may comprise a variety of organic structural units. For example, at least part of the organic structural units may comprise a moiety chosen from the group consisting of porphyrins, perylenes, and carboxylates. Examples of suitable carboxylates are

nitrogen-containing carboxylates such as pyridine-like moieties having one nitrogen atom (pyridines), two nitrogen atoms (imidazoles, bipyridines), three nitrogen atoms (triazoles) or more nitrogen atoms. Nitrogen-containing carboxylates may be used in combination with dicarboxylates and/or tricarboxylates. Further examples of suitable carboxylates are oxalic acid, malonic acid, succinic acid, glutaric acid, phthalic acid, isophthalic acid, terephthalic acid, citric acid, trimesic acid, and mixtures thereof.

Suitable examples of the metal-organic framework comprised in the electroluminescent compound of the invention are those that are based on aluminium or aluminium carboxylates as metallic structural units, such as MIL-53, MIL-69, MIL-88, MIL-96, MIL- 100, MIL- 101 , and MIL- 110, wherein the acronym "MIL " refers to

"Materiaux de Vlnstitut Lavoisier" . Particularly suitable examples of the metal-organic framework comprised in the electroluminescent compound of the invention include MIL-53, MIL-69, MIL-88, and MIL-101.

From a practical point of view it is preferred that the metal-organic framework comprised in the electroluminescent compound of the invention is flexible, but it may also be rigid.

To prevent diffusion of the luminescent moiety out of the metal-organic framework, it is preferred that the luminescent moiety is chemically bonded to the metal-organic framework. Furthermore, by chemically binding luminescent moieties to the metal-organic framework it is possible to provide an electroluminescent compound with a higher content of luminescent moieties. Also, chemically binding moieties to the

metal-organic framework may result in an enhancement of luminescence through

conjugation.

In suitable examples of electroluminescent compounds wherein the luminescent moieties are chemically bonded to the organic structural units, the metal-organic framework comprises luminescent organic structural units that are the reaction product of (i) an organic structural unit provided with a functional group, and (ii) one or more luminescent moieties chosen from the group consisting of inorganic compounds, inorganic-organic compounds such as metal-organic compounds and organic compounds. Herein, the term "functional group " refers to its usual and ordinary meaning in organic chemistry, namely an

interconnected group of atoms that is responsible for a characteristic chemical reaction of the molecule to which the group is bonded. A functional group may comprise a leaving group.

The preparation of such luminescent organic structural units can be done by using various functional groups. For instance, the organic structural unit can be modified with one or more functional groups selected from the group consisting of amines, nitro groups, imines, pyridyls or derivatives thereof, haloformyls, haloalkyls, halogens including acyl halides such as acid chlorides. Good results have been achieved by modifying the organic structural unit with an amine functional group, but other functional groups may be used as well.

A functional group may be used to couple an inorganic compound, an inorganic-organic compound such as a metal-organic compound and/or an organic compound to an organic structural unit so as to produce a luminescent organic structural unit. The functional group may comprise a leaving group, which may be replaced with the inorganic compound, the inorganic-organic compound, or the organic compound.

Examples of inorganic compounds, inorganic-organic compounds, and organic compounds suitable for use as luminescent moiety are organic laser dyes and compounds that comprise a phosphorus atom, such as phosphine and phosphinates.

Examples of metal-organic compounds suitable for use as luminescent moiety are compounds that comprise silver, gold, a rare earth element such as a lanthanide, or a ferrocene.

When the luminescent moiety is chemically bonded to the organic structural units of the metal-organic framework, 50 % or more of the organic structural units may be functionalized with the luminescent moiety, such as 60 % or more or 70 % or more. For example, 70 % to 80 % or 70 % to 90 % of the organic structural units may be functionalized with a luminescent moiety. It may also be possible that substantially all of the organic structural units of the metal-organic framework have been functionalized with a luminescent moiety.

In an example of the electroluminescent compound of the invention, at least some of the organic structural units of the metal-organic framework have a functional group in the form of an amino group that is functionalized with a phthalic acid, such as an amino group functionalized with isophthalic acid, or an amino group functionahzed with terephthalic acid. It has been found that such functionalized amino groups can be readily reacted with a suitable luminescent moiety. Examples of resulting luminescent organic structural units are those of formula (I) and formula (II) below.

In formula (I), R can be hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an amino group, an alkoxy group, an aryloxy group, a heterocyclic oxy group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an acyloxy group, an acylamino group, an alkoxycarbonylamino group, an aryloxycarbonylamino group, a sulfonylamino group, a sulfamoyl group, a carbamoyl group, an alkylthio group, an arylthio group, a heterocyclic thio group or a heterocyclic group. R' can be the same as R" and can be a phenyl ring which may optionally be substituted.

In general formula (II), R can be hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an amino group, an alkoxy group, an aryloxy group, a heterocyclic oxy group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an acyloxy group, an acylamino group, an alkoxycarbonylamino group, an

aryloxycarbonylamino group, a sulfonylamino group, a sulfamoyl group, a carbamoyl group, an alkylthio group, an arylthio group, a heterocyclic thio group or a heterocyclic group. R' can be the same as R" and can be a phenyl ring which may optionally be substituted. M' is a metal ion, for example a rare earth metal ion, such as a rare earth metal ion selected from the group consisting of yttrium, lanthanum, cerium, praseodymium, neodymium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. X¹, X², X³, X⁴, X⁵, and X⁶ can each independently be a halogen atom, such as fluorine, chlorine, or bromine. X¹, X², X³, X⁴, X⁵, and X⁶ can be the same.

In the electroluminescent compound of the invention the luminescent moiety may also reside in pores of the metal-organic framework. The luminescent moiety can, for example, be adsorbed to the inner surface of the metal-organic framework. The luminescent moiety can be intercalated after preparation of the metal-organic framework via known methods such as vapor deposition and/or adsorption and/or post-synthetic functionalization. It is also possible to prepare the metal-organic framework in the presence of a luminescent moiety which will then be incorporated (encapsulated or embedded) in the porous structure of the metal-organic framework.

Advantageously, the size restrictions imposed by the metal-organic framework prevent (or at least reduce) the formation of crystals of the luminescent moiety. Accordingly, luminescence quenching by crystal formation is significantly reduced and relatively high luminescence quantum yields are obtained. Additionally, the close proximity and regular organization of the luminescent moieties may lead to the occurrence of charge (electron) hopping mechanisms. Furthermore, luminescent moieties can be used that lack a reactive group thereby extending the range of possible luminescent moieties that can be used in the electroluminescent compound of the invention.

When the luminescent moiety resides in pores of the metal-organic framework, the latter may be loaded with the luminescent moiety to an extent of at least 0.8 luminescent moieties per organic structural unit of the metal-organic framework.

The metal-organic framework may have a one-dimensional porous structure (at least prior to functionalization). Luminescent moieties residing in the pores of such a one-dimensional porous metal-organic framework are highly ordered. The metal organic framework host can give rise to second-harmonic generation (also known as frequency doubling). In accordance with this phenomenon, a material is capable of generating photons with twice the frequency (half the wavelength) of incident photons. The metal-organic framework may also have a two-dimensional porous structure or a three-dimensional porous structure (at least prior to functionalization).

In the electroluminescent compound of the invention the luminescent moiety may be grafted to a coordinatively unsaturated metal of the metal-organic framework. When the metal-organic framework comprises metallic structural units with one or more coordinatively unsaturated metal sites, these sites can be occupied by a luminescent moiety.

The electroluminescent compound of the invention may be based on abundant elements which are not (or hardly) harmful for the environment, or poisonous. The electroluminescent compound of the invention may substantially consist of elements selected from the group consisting of hydrogen, oxygen, carbon, nitrogen, aluminium, and phosphorus.

The electroluminescent compound of the invention can be used as basis for an electroluminescent layer in a light-emitting device. For example, the electroluminescent compound of the invention may be blended with a matrix material to form a continuous phase, wherein the metal-organic framework is embedded as particles in the matrix material. Preferably, the matrix material is an at least partially transparent material. Depending on the intended application, the matrix material may comprise one or more compounds selected from the group consisting of polymers (such as electrically conductive polymers or electrically non-conductive polymers), amalgamate pastes, and liquid electrolytes.

The matrix material may comprise one or more electrically conductive polymers. Many different electrically conductive polymers are known in the art, for example polythiophenes, polyanilines, polycarbazoles, polypyrroles, and substituted derivatives thereof. As specific examples can be mentioned poly(3-butylthiophene-2,5-diyl (optionally with a phosphor-based dopant), poly(thiophene-2,5-diyl) which may optionally be bromine terminated, poly(3,4-ethylenedioxythiophene)-polystyrenesulphonate), poly(p-phenylene vinylene), polyaniline doped with BF₃, polyphenylene sulphide, conductive nylon, polyester urethane, and polyether urethane.

The matrix material may also comprise one or more non-conductive polymers.

Some examples thereof include epoxy resin without hardener and Nafion. Non-conductive polymers can be used in small scale electroluminescent devices. For example, a small scale device can be designed using point electrodes, which each are in direct contact with luminescent metal-organic framework crystals.

The matrix material may comprise a polymer that is doped with a dopant with the purpose of changing the electrically conductive properties of the matrix material.

The blend of matrix material and electroluminescent compound may comprise 2

% to 70 % of the metal-organic framework based on the total volume of the blend, such as 4 % to 40 %, for example 5 % to 30 %, or 5 % to 25 %.

The blend of matrix material and electroluminescent compound may comprise two or more electroluminescent compounds, each of the electroluminescent compounds having a different emission spectrum, wherein the different emission spectra may be partly overlapping. By selecting different emission spectra, the overall emission spectrum of the blend can be tuned to the specific needs of the user.

The blend of matrix material and electroluminescent compound may comprise further components such as conventional additives including dopants, and charge transport compounds (such as solid or liquid electrolytes). Furthermore, laser dyes may be included as optional additives for changing or tuning the wavelength of the emitted light, wherein the laser dye can be physically separate from the electroluminescent compound. An example of a laser dye that may be used for this purpose is Coumarin 540A.

In a second aspect of the invention, the object is achieved by a method for preparing the electroluminescent compound according to the first aspect of the invention, wherein the method comprises the steps of (i) preparing a metal-organic framework using an organic structural unit with a functional group, and (ii) reacting the functional group with one or more luminescent moieties. These two steps can be performed in any order.

The preparation of metal-organic frameworks is well-known in the art (see, for example, Rowsell et al, Microporous and Mesoporous Materials 2004, 73, 3-14). Typically, the preparation of a metal-organic framework involves heating a mixture containing inorganic salts and organic compounds in a specific solvent such as DMF at a specific temperature such as in the range of 60 degrees Celsius to 120 degrees Celsius, for several hours to two days. Alternative preparations of metal-organic frameworks include

mechano-chemical grinding, electrochemical synthesis, sonochemical synthesis, and microwave-assisted synthesis. In mechano-chemical grinding, a mixture of organic compounds and metal salts is ground together in a mechanical ball mill to yield the metal-organic framework. The advantage of this method is that no organic solvents are required. In electrochemical synthesis the metal element is provided by one of the electrodes and no salt residues are included in the metal-organic framework. In general lower temperatures are required than in solvo-thermal synthesis, and continuous production is feasible. Sonochemical synthesis has the advantage of leading to homogeneous nucleation and short crystallization time. Microwave-assisted synthesis makes use of microwaves to produce nanosized crystals. Microwave-assisted synthesis allows synthesis of high-quality metal-organic frameworks at short reaction times.

Providing an organic structural unit with a functional group is well known in the art of organic chemistry. It is also possible to prepare the functionalized metal-organic framework by using a compound that already has a functional group as starting material for the organic structural unit.

Step (i) of the method of the invention typically involves a preparation of a metal-organic framework using an organic structural unit that already comprises a functional group. Alternatively, the functional group may be introduced after having prepared the metal-organic framework.

An alternative method for preparing the electroluminescent composition of the first aspect of invention comprises the steps of (i) preparing a metal-organic framework using an organic structural unit; and (ii) adsorbing a luminescent moiety at the internal surface of the metal-organic framework. The luminescent moiety may also be adsorbed to one of the building blocks before it is used to prepare a metal-organic framework.

In accordance with this alternative method, the luminescent moiety is not chemically bonded to the metal-organic framework, but instead adsorbed to the surface of the framework structure, preferably to the internal surface of pores of the framework structure. Adsorption can, for instance, be performed from the gas phase, or from solution.

Electroluminescent compounds according to the first aspect of the invention, wherein the luminescent moiety is grafted to coordinatively unsaturated metal sites in the metal-organic framework, can for example be prepared by impregnation, such as by dry impregnation (also known as incipient wetness or pore volume impregnation) using an amount of solution equal to the pore volume, or by wet impregnation, using an excess of solution volume. They can also be prepared by chemical vapor deposition or atomic layer deposition methodologies. In a third aspect of the invention, the object is achieved by a light-emitting module comprising a light- generating layer, and first and second electrodes between which a voltage can be applied to generate an electric field in at least a part of the light- generating layer, wherein the light- generating layer comprises the electroluminescent compound according to the first aspect of the invention.

Any conventional electrode materials can be used, such as aluminium electrodes.

The light-emitting module may further comprise an auxiliary layer that is located between the light- generating layer and at least one of the first and second electrodes. An example of such an auxiliary layer is a dielectric layer, which can prevent direct interaction between the light- generating layer and the at least one of the first and second electrodes.

In the light-emitting module the first and second electrodes may both be provided at the same side of the light-generating layer. The light- generating layer may also be sandwiched between the first and second electrodes, wherein one of the electrodes is at least partially transparent. Transparent conductive oxides such as tin-doped indium oxide (also known as ITO) can be used as transparent electrode materials. Alternatively, the

light-generating layer may be sandwiched between the first and second electrodes, wherein the second electrode is located at an edge of the light- generating layer.

The light- generating layer of the light-emitting module may have a layer thickness in the range of 5 micrometers to 100 micrometers, such as in the range of 10 micrometers to 80 micrometers or in the range of 20 micrometers to 50 micrometers.

The light-emitting module of the invention may comprise additional layers, such as charge injection layers and charge transfer layers.

The light-emitting module of the invention may be prepared by a wet chemical process wherein a blend comprising the electroluminescent compound is applied as a paste.

The light-emitting module may be incorporated in a light-emitting device, together with a controller for applying a voltage between the first and second electrodes. Preferably, the controller is arranged to apply an AC voltage, for example an AC voltage having a frequency in a range between 100 Hz and 10,000 Hz. The lower limit of this frequency range is chosen to avoid flicker, and the upper limit to make optimal use of charge generation processes in the light-emitting module. The AC voltage preferably has a waveform wherein the transition between minimum to maximum takes place in a relatively short period of time, because it has been experimentally determined that for such waveforms the light-emitting device has the best performance. Examples of such preferred waveforms are a square wave, a triangle wave, and a pulsed wave. The AC voltage may consist of negative or positive voltages only, by applying a DC bias on the AC signal. This has the advantage that only one type of amplifier can be used.

The light-emitting device of the invention may be used in various applications, such as lighting applications, photovoltaic applications, and photocatalytic applications.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the photoluminescence spectrum of a metal-oxide framework that has been functionalized in accordance with the invention, as compared to the

photoluminescence spectrum of the non-functionalized metal-oxide framework.

Figure 2 schematically shows a preparation of a light-emitting module comprising an electroluminescent compound according to the invention.

Figures 3(a) and 3(b) show the photoluminescence and electroluminescence spectra, respectively, of a light-emitting device according to the invention.

Figures 4(a) and 4(b) show photographs of a light-emitting device according to the invention when switched off and on, respectively.

Figures 5(a) to 5(c) schematically show several layouts that are possible for light-emitting modules according to the invention.

It is noted that these figures are diagrammatic and not drawn to scale. For the sake of clarity and convenience, relative dimensions and proportions of parts of these figures may have been shown exaggerated or reduced in size.

DETAILED DESCRIPTION OF THE EMBODIMENTS

To prepare an electroluminescent compound according to the present invention, amino MIL-53 (Al) was used as metal-organic framework for the introduction of diphenyl phosphine oxide, which was chemically anchored at the amines to the terephthalic acid of the metal-organic framework.

The post-functionalization of the amino MIL-53 (Al) changed many aspects of the metal-organic framework structure. From high-quality X-ray diffraction patterns it was observed that the metal-organic framework lattices were permanently expanded to accommodate the organo-phosphines that were introduced. More significant, electronic changes occur through this functionalization, causing a shift and enhancement of light emission, brought about by visible light illumination.

Figure 1 illustrates the response of phosphinated amino MIL-53 (Al) to excitation with radiation of 400 nm, as compared to a non-functionalized amino MIL-53 (Al). The color of the emitted light of the phosphinated amino MIL-53 (Al) is a light blue with maximum emission at a wavelength of 466 nm, while the non-functionalized amino MIL-53 (Al) has significantly lower emission intensity with a maximum emission at a wavelength of 616 nm.

A similar emission response can be observed by using the phosphine oxide functionalized amino MIL-53 (Al) as electroluminescent compound in a light- generating layer of a light-emitting module, and by applying a sufficient potential difference to the light-generating layer. AC potential differences with peak-to-peak voltages in the range of 30 V to 600 V AC have been explored.

An example of a preparation of a light-emitting module by a wet chemical process is schematically shown in Figure 2.

In Figure 2(a) first and second electrodes 201 and 202, respectively, are provided by cutting a sheet of a suitable electrode material such as aluminium in two pieces. In Figure 2(b) the first and second electrodes 201 and 202 are both attached on a non-conductive epoxy support 203. In Figure 2(c) the epoxy support 203 with the first and second electrodes 201 and 202 is secured on the work surface by using chemically inert tape 204, such as Scotch tape obtainable from 3M. It is advisable that an antistatic agent such as antistatic foam cleanser is applied to the work surface prior to use. In Figure 2(d) a blend 205 is applied as a paste onto the first and second electrodes 201 and 202 using a doctor blade technique such that the blend 205 at least bridges the first electrode 201 with the second electrode 202. The blend 205 has been prepared by mixing phosphine amino MIL-53 (Al) and

poly(thiophene-2,5-diyl) (CAS No. 25233-34-5) in chloroform in a weight ratio of 1:4.

Excess blend 205 and excess epoxy support 203 may be removed, together with the chemically inert tape 204, before drying and removing any remaining solvent to create a light-generating layer of about 38 micrometers thickness. In Figure 2(e) first and second contacts 206 and 207, respectively, are provided for applying a voltage between the first and second electrodes 201 and 202 to create an electric field in at least a part of the

light-generating layer. The resulting light-emitting module 200 may then be sealed (for example by lamination) for optimal protection against environmental influences. It is noted that in the light-emitting module 200 the first and second electrodes 201 and 202 are provided on the same side of the light- generating layer that has been formed from the blend 205.

Figure 3 illustrates the emission response of a device comprising the phosphine oxide functionalized amino MIL-53 (Al) as electroluminescent compound. In Figure 3(a) the photoluminescence upon excitation with radiation of 375 nm is compared to the

electroluminescence upon applying an AC voltage of 10 V at a frequency of approximately 60 Hz. In Figure 3(b) the electroluminescence upon applying an AC voltage of 10 V is compared to the electroluminescence upon applying an AC voltage of 260 V, both at a frequency of approximately 60 Hz. No significant differences can be observed up to 500 nm, after which the relative intensity of the AC electroluminescence seems to fluctuate slightly.

It was found that the device lifetime is increased if during the first operation the voltage is slowly increased to the desired long-term operating voltage, which during the lifetime of the device is preferably not exceeded.

Applying AC voltage resulted in light emission starting at about 10 V. Up to 260

V and 600 V have been tested while exposed to a non-inert atmosphere.

The emission of the light was homogeneous over the entire surface. No dark area was seen at the separation line between the two electrode surfaces.

Figure 4 shows photographs of the device when switched off (Figure 4(a)), i.e. when no voltage is applied, and of the same device when a voltage is applied and the device is emitting light (Figure 4(b)).

Device efficiency was determined using an Ulbricht integrating sphere to count the photon emission rate and using the wavelength distribution, the emitted energy relative to the electrical energy input (product of current and voltage) amounted to about 1 %.

A light-emitting module may be obtained by sandwiching a layer comprising the electroluminescent compound of the invention between two electrodes. Alternative device layouts may be based on other electrode configurations. Several of these other electrode configurations are shown in Figure 5.

In Figure 5(a), first and second electrodes 811 and 812, respectively, are present on carrier substrate 813. The first and second electrodes 811 and 812 each have the form of a strip, and they are located at opposite sides of the carrier substrate 813.

A light- generating layer 814 is provided on top of the first and second electrodes 811 and 812. Each of the first and second electrodes 811 and 812 is confined to an edge of the light- generating layer 814.

In Figure 5(b), first and second electrodes 821 and 822, respectively, are present on carrier substrate 823. The first and second electrodes 821 and 822 are formed as interdigitated electrodes, each electrode having an outer "supply" part and inner "digit" parts. A light- generating layer 824 is provided on top of the first and second electrodes 821 and 822.

In Figures 5(a) and 5(b) electrodes are present on only one side of the light-generating layer 814 or 824. Although for practical purposes it is preferred to have both electrodes on the carrier substrate 813 or 823, for each of the layouts shown in Figures 5(a) and 2(b) the second electrode 812 or 822 may also be provided on top of the light- generating layer 814 or 824.

In Figure 5(c) first electrode 831 is present on carrier substrate 833, and has the form of a plane. Light- generating layer 834 is provided on top of the first electrode 831. Second electrode 832 is provided on top of the light-generating layer 834, wherein the second electrode 832 has the form of a frame, and wherein the perimeters of the plane and the frame are substantially aligned with each other. It is noted that the layout of Figure 5(c) is shown in an exploded view for the sake of clarity. In this Figure 5(c), first and second electrodes 831 and 832 are provided on opposite sides of the light-generating layer 834. The second electrode 832 is confined to an edge of the light- generating layer 834, leaving a central part of the light- generating layer 834 exposed.

Figure 5(d), also in exploded view for the sake of clarity, shows a layout that is comparable to that of Figure 5(c) but now the first electrode 841 also has the shape of a frame, similar to the second electrode 842. The perimeters of the two frames are substantially aligned with each other. First and second electrodes 841 and 842 are provided on opposite sides of the light- generating layer 844, and both are confined to an edge of the

light-generating layer, leaving a central part of the light- generating layer 844 exposed.

In Figure 5(e) light- generating layer 854 is provided on carrier substrate 853. First and second electrodes 851 and 852, respectively, are provided against opposite side walls of the light- generating layer 854. Although both electrodes are shown to fully cover the entire width of the light- generating layer 854, this does not have to be the case and the light-generating layer 854 may also extend above and/or below the two electrodes. The device layouts shown in Figures 5(c) to 5(e) may be used in a photoframe device. For example, for the layout of Figure 5(c) the second electrode 832 can be comprised in the frame and electrically isolated from the first electrode 831 that is provided on the backplane of the photoframe device.

In each of the layouts shown in Figure 5, the light- generating layers 814, 824, 834, 844 and 854 will show homogeneous emission of light upon application of a voltage between the first and second electrodes. All these layouts have the advantage that there is no need for a transparent electrode because the viewing side of the light- generating layer is completely (in Figures 5(a), 5(b) and 5(e)) or almost completely (in Figures 5(c) and 5(d)) unobstructed by an electrode surface.

Although the layouts shown in Figure 5 have symmetric electrode configurations, also asymmetric electrode configurations may be used, all being capable of providing a homogeneous emission without a relation to the relative sizes of the electrode areas.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. Electroluminescent compound comprising a metal-organic framework and a luminescent moiety, wherein the metal-organic framework comprises metallic structural units linked by organic structural units, and wherein the luminescent moiety:

(i) is comprised in at least a part of the organic structural units, and/or

(ii) resides in a pore of the metal-organic framework, and/or

(iii) is grafted to a coordinatively unsaturated metal site of the metal-organic framework.

2. The electroluminescent compound according to claim 1, wherein each organic structural unit comprising a luminescent moiety is a product of a reaction between an organic structural unit provided with a functional group, and the luminescent moiety.

3. The electroluminescent compound according to any of the previous claims, wherein each organic structural unit is a porphyrin, a perylene, or a carboxylate.

4. The electroluminescent compound according to any of the previous claims, wherein the luminescent moiety comprises one or more compounds selected from the group consisting of rare earth metal complexes, phenyl-based phosphines, phosphine oxides, substituted phosphines containing hydrogen, alkyls, alkenyls, alkynyls, aryls, amines, alkoxides, aryloxides, heterocyclic oxides, acyls, alkoxycarbonyls, aryloxycarbonyls, acyloxides, acylamines, alkoxycarbonylamines, aryloxycarbonylamines, sulfonylamines, sulfamoyls, carbamoyls, alkylthiols, arylthiols, and heterocyclic thiols.

5. The electroluminescent compound according to any of the previous claims, wherein the metal organic framework is a phosphine oxide functionalized amino

metal-organic framework or a phosphinated amino metal-organic framework.

6. The electroluminescent compound according to any of the previous claims, wherein the metal organic framework has a one-dimensional porous structure, a

two-dimensional porous structure, or a three-dimensional porous structure.

7. Method for manufacturing the electroluminescent compound according to any of claims 1 to 6, comprising the steps of:

- preparing the metal-organic framework using organic structural units with functional groups, and

- reacting the functional groups with the luminescent moiety.

8. Method for manufacturing the electroluminescent compound according to any of claims 1 to 6, comprising the steps of:

- preparing the metal-organic framework, and

- adsorbing the luminescent moiety at the internal surface of the metal-organic framework.

9. Light-emitting module comprising a light- generating layer, and first and second electrodes between which a voltage can be applied to generate an electric field in at least a part of the light- generating layer, wherein the light- generating layer comprises the electroluminescent compound according to any of claims 1 to 6.

10. Light-emitting module according to claim 9, wherein the first and second electrodes are both provided at the same side of the light- generating layer.

11. Light emitting module according to claim 9, wherein the first and second electrodes are provided at opposite sides of the light-generating layer, and wherein the second electrode is located at an edge of the light- generating layer.

12. Light-emitting device comprising the light-emitting module according to any of claims 9 to 11, and a controller for applying the voltage between the first and second electrodes, wherein the voltage is an AC voltage.

13. Light-emitting device according to claim 12, wherein the AC voltage has a waveform choses from the group consisting of square waves, triangle waves, and pulsed waves..

14. Light-emitting device according to claim 12 or 13, wherein the AC voltage has frequency in a range between 100 Hz and 10,000 Hz.