Hetero-spiro compounds and their use as electroluminescence materials

Hetero-spiro compounds of the formula (I), ##STR1## where PA1 .PSI. is an element of the 4th main group of the Periodic Table with the exception of carbon, preferably Sn, Ge or Si, particularly preferably Ge or Si, and PA1 K.sup.1 and K.sup.2 are, independently of one another, conjugated systems, for use in electroluminescence devices. The compounds of the formula (I) have a good solubility in customary organic solvents, improved film-forming properties and a significantly reduced tendency to crystallize.

DESCRIPTION
 There is a great industrial need for large-area solid-state light sources
 for a series of applications, predominantly in the field of display
 elements, VDU technology and lighting engineering. The demands made of
 these light sources can at present not be completely satisfactorily met by
 any of the existing technologies.
 As an alternative to the conventional display elements, such as
 incandescent lamps, gas-discharge lamps and non-self-illuminating liquid
 crystal display elements, knowledge has existed for some time of
 electroluminescence (EL) materials and devices, such as light-emitting
 diodes (LEDs).
 Electroluminescence materials are materials which are capable of radiating
 light on application of an electric field. The physical model for
 describing this effect is based on the radiative recombination of
 electrons and electron gaps (holes). In light-emitting diodes, the charge
 carriers are injected via the cathode or anode into the
 electroluminescence material. Electroluminescence devices comprise a
 luminescence material as light-emitting layer. Electroluminescence
 materials and devices are generally described, for example, in Ullmann's
 Encyclopedia of Industrial Chemistry, Vol A9, 5th Ed. VCH Verlag 1987 and
 the literature cited therein. Apart from inorganic materials, such as
 ZnS/Mn or GaAs, organic compounds have also become known as EL materials.
 A description of EL devices comprising low molecular weight organic EL
 materials is given, for example, in U.S. Pat. No. 4,539,507.
 Disadvantages of these low molecular weight organic materials are, for
 example, the unsatisfactory film-forming properties and a pronounced
 tendency to crystallize.
 Recently, polymers have also been described as EL materials (see, for
 example, WO-A 90/13148). However, the light yield (quantum efficiency) of
 these materials is considerably lower than for low molecular weight
 compounds.
 It was desirable to find EL materials which have good light yields, at the
 same time can be processed into thin homogeneous films and have a low
 tendency to crystallize.
 It has now surprisingly been found that hetero-spiro compounds have
 excellent suitability as EL materials. Spiro compounds have at least one
 tetravalent Spiro atom which links two ring systems to one another. This
 is described in detail in Handbook of Chemistry and Physics, 62nd edition
 (1981-2), pp. C-23 to 25.
 Individual compounds of this type are described, for example, in U.S. Pat.
 No. 5,026,894, J. M. Tour et al., J. Am. Chem. Soc. 112 (1990) 5662 and J.
 M. Tour et al., Polym. Prepr. (1990) 408 as linkage elements for
 polymeric, organic semiconductors and have been proposed as materials for
 molecular electronics. However, possible use as EL materials cannot be
 derived therefrom.
 The invention accordingly provides for the use of hetero-spiro compounds of
 the formula (I),
 ##STR2##
 where
 .PSI. is an element of the 4th main group of the Periodic Table with the
 exception of carbon, preferably Sn, Ge or Si, particularly preferably Ge
 or Si, and
 K.sup.1 and K.sup.2 are, independently of one another, conjugated systems,
 in electroluminescence devices.
 Compounds of the formula (I) have good solubility in customary organic
 solvents, improved film-forming properties and a significantly reduced
 tendency to crystallize. This makes the production of electroluminescence
 devices easier and increases their life. The emission properties of the
 compounds used according to the invention can be adjusted across the
 entire range of the visible spectrum by selection of suitable
 substituents. In addition, the covalently bound arrangement of the two
 parts of the spiro compound allows a molecular structure such that certain
 properties can be set independently in the two halves of the molecule.
 Thus, one half can have, for example, charge transport or charge injection
 properties, while the other half has light-emitting properties. The
 spatial proximity of the two halves fixed by the covalent linkage is here
 favorable for energy transmission (see, for example, B. Liphardt, W.
 Luttke, Liebigs Ann. Chem. 1981, 1118).
 Preferred compounds of the formula (I) are hetero-spiro compounds of the
 formula (II),
 ##STR3##
 where the symbols and indices have the following meanings:
 gs:
 .PSI. is Si, Ge, Sn;
 D, E, F, G are identical or different and are --CR.sup.1 R.sup.2 --, --O--,
 --S--, --NR.sup.3 -- or a chemical bond;
 U, V are identical or different and are --CR.sup.1 R.sup.2 --, --O--,
 --S--, --NR.sup.3 --, --SiR.sup.1 R.sup.2 --, --SO.sub.2 --, --CO--,
 --CR.sup.4.dbd.CR.sup.5 -- or a chemical bond, with the proviso that
 either U or V is --CR.sup.1.dbd.CR.sup.2 -- or a chemical bond;
 T is --O--, --S--, --NR3--, --CR.sup.1 R.sup.2 --, --CH.dbd.N--,
 --CA.sup.5.dbd.CA.sup.6 --, --CH.dbd.CA.sup.7 --, preferably
 --CH.dbd.CH--;
 K, L, M, Q are identical or different, cyclic or acyclic hydrocarbon
 radicals which have conjugated electron systems and can also contain
 heteroatoms such as oxygen, nitrogen and/or sulfur;
 A.sup.1, A.sup.2, A.sup.3, A.sup.4 can be identical or different and have
 the same meanings as K, L, M, Q or are hydrogen, fluorine or a hydrocarbon
 radical having from 1 to 22, preferably from 1 to 15, carbon atoms which
 can also contain heteroatoms such as oxygen, nitrogen, silicon or
 fluorine; preferably a linear, branched and/or ring-containing alkyl,
 alkoxy, or alkyloxycarbonyl group, --CF.sub.3, --CN, --NO.sub.2,
 --NR.sup.6 R.sup.7, --Ar or --O--Ar;
 A.sup.6 is hydrogen
 A.sup.5 and A.sup.7 arc identical or different and are the values for B
 herein defined below with respect to formula (IV).
 R.sup.1, R.sup.2, R.sup.3 are identical or different and are H or a
 hydrocarbon radical having from 1 to 12 carbon atoms, where R.sup.1 and
 R.sup.2 can together also form an unsubstituted or substituted ring;
 R.sup.4, R.sup.5 are identical or different and have the same meanings as
 R.sup.1, R.sup.2, R.sup.3 or are fluorine or --CF.sub.3 ;
 R.sup.6, R.sup.7 are identical or different and are H or a hydrocarbon
 radical having from 1 to 22 carbon atoms which can be aliphatic or
 aromatic, linear or branched and can also contain alicyclic elements,
 preferably methyl, ethyl, t-butyl, cyclohexyl, 3-methylphenyl; or R.sup.6
 and R.sup.7 together form a ring,
 ##STR4##
 Ar is an aromatic radical having up to 22 carbon atoms, preferably phenyl,
 biphenyl, 1-naphthyl, 2-naphthyl, 2-thienyl, 2-furanyl, where each of
 these aromatic radicals can be substituted by one or two groups R.sup.4,
 R.sup.5 ;
 Q and A.sup.1, K and A.sup.2, L and A.sup.3, M and A.sup.4 can,
 independently of one another, also each be joined together to form a ring
 which can be saturated, partially unsaturated or have maximum
 unsaturation, with a fused aromatic ring system preferably being present.
 Particular preference is given to hetero-spirobifluorene derivatives of the
 formula (III),
 ##STR5##
 where the symbols and indices have the following meanings:
 .PSI. is Si or Ge;
 K, L, M, Q, A are identical or different and are
 ##STR6##
 and A can also be identical or different and have the same meanings as R;
 R can be identical or different and have the same meanings as K, L, M, Q or
 is --H, a linear or branched alkyl, alkoxy or ester group having from 1 to
 22, preferably from 1 to 15, particularly preferably from 1 to 12, carbon
 atoms, --CN, --NO.sub.2, --NR.sup.2 R.sup.3, --Ar or --O--Ar;
 Ar is phenyl, biphenyl, 1-naphthyl, 2-naphthyl, 2-thienyl, 2-furanyl, where
 each of these groups can bear one or two radicals R,
 m, n, p are, independently of one another, identical or different and are
 0, 1, 2 or 3;
 X, y are identical or different and are CR, N;
 Z is --O--, --S--, --NR.sup.1 --, -CR.sup.1 R.sup.4 --, --CH.dbd.CH--,
 --CH.dbd.N--;
 R.sup.1, R.sup.4 can be identical or different and have the same meanings
 as R;
 R.sup.2, R.sup.3 are identical or different and are H, a linear or branched
 alkyl group having from 1 to 22 carbon atoms, --Ar, 3-methylphenyl.
 Preferred compounds of the formula (III) are those of the formulae
 (IIIa)-(IIIg)
 IlIa) K=L=M=Q and are selected from the group consisting of:
 ##STR7##
 R=C.sub.1 -C.sub.22 -alkyl, (CH.sub.2).sub.x --SO.sub.3.sup.- where x=2, 3
 or 4
 IIIb) K=M=H and Q=L and are selected from the group consisting of:
 ##STR8##
 IIIc) K=M and are selected from the group consisting of:
 ##STR9##
 R=C.sub.1 -C.sub.22 -alkyl, (CH.sub.2).sub.x --SO.sub.3.sup.- where x=2, 3
 or 4 and Q=L and are selected from the group consisting of:
 ##STR10##
 IIId) K=M and are selected from the group consisting of:
 ##STR11##
 and Q=L and are selected from the group consisting of:
 ##STR12##
 R=C.sub.1 -C.sub.22 -alkyl, (CH.sub.2).sub.x --SO.sub.3.sup.- where x=2, 3
 or 4
 IIIe) K=L=H and M=Q and are selected from the group consisting of:
 ##STR13##
 IIIf) K=L and are selected from the group consisting of:
 ##STR14##
 R=C.sub.1 -C.sub.22 -alkyl, (CH.sub.2).sub.x --SO.sub.3.sup.- where x=2, 3
 or 4 and M=Q and are selected from the group consisting of:
 ##STR15##
 IIIg) K=L and are selected from the group consisting of:
 ##STR16##
 and M =Q and are selected from the group consisting of:
 ##STR17##
 R=C.sub.1 -C.sub.22 -alkyl, (CH.sub.2).sub.x --SO.sub.3.sup.- where x=2, 3
 or 4
 particularly preferred compounds of the formula (III) are those of the
 formulae (IIIaa) to (IIIbd):
 (IIIaa) K=L=M=Q and are selected from the group consisting of:
 ##STR18##
 (Illab) K=M=H and Q=L and are selected from the group consisting of:
 ##STR19##
 (IIIac) K=M and are selected from the group consisting of:
 ##STR20##
 (IIIad) K=M and are selected from the group consisting of:
 ##STR21##
 (IlIba) K=L=M=Q and are selected from the group consisting of;
 ##STR22##
 (IIIbb) K=L=H and M=Q and are selected from the group consisting of:
 ##STR23##
 (IIIbc) K=L and are selected from the group consisting of:
 ##STR24##
 (IIIbd) K=L and are selected from the group consisting of:
 ##STR25##
 Very particularly preferred hetero-spiro compounds of the formula (III) are
 spirobi-9-silafluoreneg, such as 2,2',4,4',7,7'-hexakis (biphenylyl)
 -9,9'-spirobi-9-silafluorene,2,2',4,4',7,7'-hexakis
 (terphenylyl)-9,9'-spirobi-9-silafluorene, and also the compounds shown in
 Table 1 in which the abbreviations G1 to G14 denote the following
 structural elements:
 ##STR26##
 ##STR27##
 TABLE 1
 Spirobi-9-silafluorene derivatives
 Compound K L M Q
 Spiro-1 G1 G1 G3 G3
 Spiro-2 G1 G1 G4 G4
 Spiro-3 G1 G1 G5 G5
 Spiro-4 G1 G1 G6 G6
 Spiro-5 G1 G1 G7 G7
 Spiro-6 G1 G1 G8 G8
 Spiro-7 G1 G1 G9 G9
 Spiro-8 G1 G1 G10 G10
 Spiro-9 G1 G1 G11 G11
 Spiro-10 G1 G1 G12 G12
 Spiro-11 G1 G1 G13 G13
 Spiro-12 G1 G1 G14 G14
 Spiro-13 G2 G2 G2 G2
 Spiro-14 G2 G2 G3 G3
 Spiro-15 G2 G2 G4 G4
 Spiro-16 G2 G2 G5 G5
 Spiro-17 G2 G2 G6 G6
 Spiro-18 G2 G2 G7 G7
 Spiro-19 G2 G2 G8 G8
 Spiro-20 G2 G2 G9 G9
 Spiro-21 G2 G2 G10 G10
 Spiro-22 G2 G2 G11 G11
 Spiro-23 G2 G2 G12 G12
 Spiro-24 G2 G2 G13 G13
 Spiro-25 G2 G2 G14 G14
 Spiro-26 G3 G3 G3 G3
 Spiro-27 G3 G3 G4 G4
 Spiro-28 G3 G3 G5 G5
 Spiro-29 G3 G3 G6 G6
 Spiro-30 G3 G3 G7 G7
 Spiro-31 G3 G3 G8 G8
 Spiro-32 G3 G3 G9 G9
 Spiro-33 G3 G3 G10 G10
 Spiro-34 G3 G3 G11 G11
 Spiro-35 G3 G3 G12 G12
 Spiro-36 G3 G3 G13 G13
 Spiro-37 G3 G3 G14 G14
 Spiro-38 G4 G4 G4 G4
 Spiro-39 G5 G5 G5 G5
 Spiro-40 G6 G6 G6 G6
 Spiro-41 G7 G7 G7 G7
 Spiro-42 G8 G8 G8 G8
 Spiro-43 G9 G9 G9 G9
 Spiro-44 G10 G10 G10 G10
 Spiro-45 G11 G11 G11 G11
 Spiro-46 G12 G12 G12 G12
 Spiro-47 G13 G13 G13 G13
 Spiro-48 G14 G14 G14 G14
 Spiro-49 H H G3 G3
 Spiro-50 H H G4 G4
 Spiro-51 H H G5 G5
 Spiro-52 H H G6 G6
 Spiro-53 H H G7 G7
 Spiro-54 H H G8 G8
 Spiro-55 H H G9 G9
 Spiro-56 H H G10 G10
 Spiro-57 H H G11 G11
 Spiro-58 H H G12 G12
 Spiro-59 H H G13 G13
 Spiro-60 H H G14 G14
 Spiro-61 G1 G3 G3 G1
 Spiro-62 G1 G4 G4 G1
 Spiro-63 G1 G5 G5 G1
 Spiro-64 G1 G6 G6 G1
 Spiro-65 G1 G7 G7 G1
 Spiro-66 G1 G8 G8 G1
 Spiro-67 G1 G9 G9 G1
 Spiro-68 G1 G10 G10 G1
 Spiro-69 G1 G11 G11 G1
 Spiro-70 G1 G12 G12 G1
 Spiro-71 G1 G13 G13 G1
 Spiro-72 G1 G14 G14 G1
 Spiro-73 G2 G4 G4 G2
 Spiro-74 G2 G5 G5 G2
 Spiro-75 G2 G6 G6 G2
 Spiro-76 G2 G7 G7 G2
 Spiro-77 G2 G8 G8 G2
 Spiro-78 G2 G9 G9 G2
 Spiro-79 G2 G10 G10 G2
 Spiro-80 G2 G11 G11 G2
 Spiro-81 G2 G12 G12 G2
 Spiro-82 G2 G13 G13 G2
 Spiro-83 G2 G14 G14 G2
 Spiro-84 G3 G4 G4 G3
 Spiro-85 G3 G5 G5 G3
 Spiro-86 G3 G6 G6 G3
 Spiro-87 G3 G7 G7 G3
 Spiro-88 G3 G8 G8 G3
 Spiro-89 G3 G9 G9 G3
 Spiro-90 G3 G10 G10 G3
 Spiro-91 G3 G11 G11 G3
 Spiro-92 G3 G12 G12 G3
 Spiro-93 G3 G13 G13 G3
 Spiro-94 G3 G14 G14 G3
 Spiro-95 H G3 G3 H
 Spiro-96 H G4 G4 H
 Spiro-97 H G5 G5 H
 Spiro-98 H G6 G6 H
 Spiro-99 H G7 G7 H
 Spiro-100 H G8 G8 H
 Spiro-101 H G9 G9 H
 Spiro-102 H G10 G10 H
 Spiro-103 H G11 G11 H
 Spiro-104 H G12 G12 H
 Spiro-105 H G13 G13 H
 Spiro-106 H G14 G14 H
 Some of the hetero-spiro compounds used according to the invention are
 known and some are new.
 The invention accordingly also provides Spiro compound of the formula (IV),
 ##STR28##
 where the symbols have the following meanings:
 .PSI. is Si, Ge or Sn;
 A, B, K, L, M, Q are identical or different and are
 ##STR29##
 and A, B can also be identical or different and each be a linear or
 branched alkyl, alkoxy or ester group having from 1 to 22 carbon atoms,
 --CN, --NO.sub.2 --Ar or --O--Ar;
 R is --H, a linear or branched alkyl, alkoxy or ester group having from 1
 to 22, preferably from 1 to 15, particularly preferably from 1 to 12,
 carbon atoms, --CN, --NO.sub.2, --NR.sup.2 R.sup.3, --Ar or --O--Ar;
 Ar is phenyl, biphenyl, 1-naphthyl, 2-ndphthyl, 2-thienyl, 2-furanyl, where
 each of these groups can bear one or two radicals R;
 m, n, p are, independently of one another, identical or different and are
 0, 1, 2 or 3;
 X, Y are identical or different ana are CR, nitrogen;
 Z is --O--, --S--, NR.sup.1 --CR.sup.1 R.sup.4 --, --CH.dbd.CH--,
 --CH.dbd.N--;
 R.sup.1, R.sup.4 can be identical or different and have the same meanings
 as R;
 R.sup.2, R.sup.3 are identical or different and are H, a linear or branched
 alkyl group having from 1 to 22 carbon atoms, --Ar or 3-methylphenyl.
 The spiro compounds of the invention or used according to the invention are
 prepared by literature methods known per se as are described in standard
 works on organic synthesis, e.g. Houben-Weyl, Methoden der Organischen
 Chemie, Georg-Thieme-Verlag, Stuttgart, in particular Volume 13/5, pp.
 30-87, and in the appropriate volumes of the series "The Chemistry of
 Heterocyclic Compounds" by A. Weissberger and E. C. Taylor (editors).
 The preparation is carried out under reaction conditions which are known
 and suitable for the reactions specified. Use can here also be made of
 variants which are known per se and are not mentioned further here.
 Compounds of the formula (III) are obtained, for example, starting from
 bis(biphenyl-2,2'-diyl)silane(=9,9'-spirobi(9H-)silafluorene) (V) whose
 synthesis is described, for example, by H. Gilman, R. D. Gorsich, J. Am.
 Chem. Soc. 1958, 80, 3243.
 ##STR30##
 Compounds of the formula (IIIa) can be prepared, for example, starting with
 a tetralalgognation in the 2,2',7 and 7' positions of
 9,9'-spirobi-9-silafluorene and a subsequent substitution reaction, which
 are known from analogous C-spiro compounds (see, for example, U.S. Pat.
 No. 5,026,894). This can lead, for example via the corresponding cyano
 compounds, to aldehyde or carbqxylic acid functionality which is used, for
 example, for building up heterocycles.
 Compounds of the formula (IIIb) can be prepared, for example, by methods
 similar to those for compounds of the formula (Illa), with the
 stoichiometric ratios in the reaction being selected such that the 2,2' or
 7,7' positions are functionalized (see, for example, J. H. Weisburger, E.
 K. Weisburger, F. E. Ray, J. Am. Chem. Soc. 1959, 72, 4253; F. K.
 Sutcliffe, H. M. Shahidi, D. Paterson, J. Soc. Dyers Colour 1978, 94, 306
 ana G. Haas, V. Prelog, Helv. Chim. Acta 1969, 52, 1202).
 Compounds of the formulae (IIIc) and (IIId) can be prepared, for example,
 via a dibromination in the 7 and 7' positions of the
 2,2'-dicyano-9,9'-spirobi-9-silafluorene, which is synthesized in a manner
 similar to (IIIa), and subsequent reactions similar to those for compounds
 (IIIa).
 Compounds of the formulae (IIIe)-(IIIg) can be prepared, for example, by
 selection of suitable substituted starting compounds in building up the
 spirosilabifluorene, for example:
 ##STR31##
 In addition, the synthesis sequences such as nitration, reduction,
 diazotization and Sandmeyer reaction, with which those skilled in the art
 are familiar, are to be used. For the synthesis of the groups K, L, M, Q
 reference may be made, for example, to DE-A 23 44 732, 24 50 088, 24 29
 093, 25 02 904, 26 36 684, 27 01 591 and 27 52 975 for compounds
 containing 1,4-phenylene groups; DE-A 26 41 724 for compounds containing
 pyrimidine-2,5-diyl grqupri DE-A 40 26 223 and EP-A 0 391 203 for
 compounds containing pyridine-2,5-diyl groups; DE-A 32 31 462 for
 compounds containing pyridazine-3,6-diyl groups; N. Miyaura, T. Yanagi and
 A. Suzuki in Synthetic Communications 11 (1981) 513 to 519, DE-A-39 30
 663, M. J. Sharp, W. Cheng, V. Snieckus in Tetrahedron Letters 1987, 28,
 5093; G. W. Gray in J. Chem. Soc. Perkin Trans II, 1989, 2041 and Mol.
 Cryst. Liq. Cryst. 1989, 172, 165, Mol. Cryst. Liq. Cryst. 1991, 204, 43
 and 91; EP-A 0 449 015; WO 89/12039; WO 89/03821; EP-A 0 354 434 for the
 direct linking of aromatics and heteroaromatics.
 The preparation of disubstituted pyridines, disubstituted pyrazines,
 disubstituted pyrimidines and disubstituted pyridazines can be found, for
 example, in the appropriate volumes of the series "The Chemistry of
 Heterocyclic Compounds" by A. Weissberger and E. C. Taylor (editors).
 According to the invention, the spiro compounds of the formulae (I), (II)
 and (III) described are used as electroluminescence materials, i.e. they
 serve as active layer in an electroluminescence device. The invention
 accordingly also provides an electroluminescence material comprising one
 or more compounds of the formulae (I), (II) and/or (III). For the purposes
 of the invention, active layers are electroluminescence materials which
 are 30 capable of emitting light on application of an electric field
 (light-emitting layer), and also materials which improve the injection
 and/or the transport of the positive and/or negative charges (charge
 injection layers and charge transport layers).
 The invention accordingly also provides an electroluminescence device
 having one or more active layers comprising one or more compounds of the
 formulae (I), (II) and/or (III). The active layer can be, for example, a
 light-emitting layer and/or a transport layer and/or a charge injection
 layer. Emphasis should be given to the excellent hole-conducting
 properties of the materials of the invention, which can be used as d hole
 transport layer in, for example, photocopiers and laser printers. The
 general structure of such electroluminescence devices is described, for
 example, in U.S. Pat No. 4,539,507 and U.S. Pat No. 5,151,629.
 They usually comprise an electroluminescing layer between a cathode and an
 anode, with at least one of the electrodes being transparent. In addition,
 an electron injection and/or electron transport layer can be introduced
 between the electroluminescing layer and the cathode and/or a hole
 injection and/or hole transport layer can be introduced between the
 electroluminescing layer and the anode. Suitable cathodes are, for
 example, Ca, Mg, Al, In, Mg/Ag. Suitable anodes are, for example, Au or
 ITO (indium oxide/tin oxide on a transparent substrate, e.g. of glass or a
 transparent polymer).
 In operation, the cathode is placed at a negative potential compared with
 the anode, and electrodes from the cathode are thus injected into the
 electron injection layer/electron transport layer or directly into the
 light-emitting layer. At the same time, holes from the anode are injected
 into the hole injection layer/hole transport layer or directly into the
 light-emitting layer.
 The injected charge carriers move towards one another through the active
 layers under the action of the applied potential. This leads, at the
 interface between charge transport layer and light-emitting layer or
 within the light-emitting layer, to electron/hole pairs which recombine
 with emission of light.
 The color of the emitted light can be varied by means of the compound used
 as light-emitting layer, with express reference also being made to
 mixtures of the materials of the invention with one another and also with
 other materials, e.g. corresponding carbo-spiro compounds.
 Electroluminescence devices are used, for example, as self-illuminating
 display elements such as control lamps, alphanumeric displays, signs, and
 in optoelectronic couplers.
 The invention is illustrated by the examples without being restricted
 thereto.

EXAMPLES
 Example 1
 2,2'-Dilithiobiphenyl
 26 ml of a solution of 28 mmol of n-BuLi in absolute diethyl ether (ether)
 were added dropwise over a period of 5 minutes to an ice-cooled,
 vigorously stirred solution of 4.0 g (12.9 mmol) of 2,2'-dibromobiphenyl
 in 40 ml of ether and the mixture was subsequently stirred for 5 hours at
 room temperature.
 Example 2
 Bis(biphenyl-2,2'-diyl)silane (9,9'-spirobi-9-silafluorene)
 A solution of 24 mmol of 2,2'-dilithiobiphenyl in 70 ml of ether prepared
 as described in Example 1 was added dropwise over a period of one hour to
 a vigorously stirred solution of 1.87 g (11 mmol) of silicon tetrachloride
 in 30 ml of ether. The mixture was stirred for a further 1.5 hours at room
 temperature and was refluxed for 3 hours. 50 ml of benzene were
 subsequently added and the mixture was refluxed for a further 2 hours.
 After shaking with 100 ml of water, the organic phase is dried over
 magnesium sulfate and filtered, the major part of the ether was distilled
 off on a rotary evaporator. From the cooled solution, 1.45 g of crude
 product laving a melting point of from 222 to 225.degree. C. were
 isolated. After evaporation, the filtrate gave a further 0.6 g of product
 (total yield 56%). Crystallization from ethanol gave a melting point of
 227.degree. C. Elemental analysis:

% C H Si
 calc. 86.72 4.85 8.44
 found 86.86 4.98 8.33
 The remarkably high stability of this compound is shown by the boiling
 point of 460.degree. C., which is reached without visible decomposition.
 Example 3
 Bis(biphenyl-2,2'-diyl)germane (9,9'-spirobi-9-germafluorene)
 A solution of 50 mmol of 2,2'-dilithiobiphenyl prepared in 140 ml of ether,
 as described in Example 1, was reacted as described in Example 2 with 5.35
 g (25 mmol) of germanium tetrachloride. After work-up and
 recrystallization from ethyl acetate, 2.77 g (29%) of product were
 obtained. White prisms, melting point 245.degree. C., boiling point
 470.degree. C. without decomposition. Elemental analysis:

% Ge
 calc. 19.23
 found 18.88
 Example 4
 Biphenyl-2,2'-diylsilicon dichloride
 78 mmol of 2,2'-dilithiobiphenyl prepared in 230 ml of ether, as described
 in Example 1, were reacted as described in Example 2 with 252 g (1.48 mol,
 i.e. 18-fold excess) of silicon tetrachloride. After distilling off the
 excess SiCl.sub.4 and working-up, 3.5 g of a solid product were obtained
 and after recrystallization from ethyl acetate this gave 2.89 g (22 %) of
 bis(biphenyl-2,2'-diyl) silane as described in Example 2. The combined
 mother liquors were evaporated and the remaining oil was distilled at 0.01
 mbar, with a small amount of biphenyl going over as initial fraction and
 7.41 g (38%) of biphenyl-2,2'-diylsilicon dichloride going over as main
 fraction at from 108 to 110.degree. C.

% Cl Si
 calc. 28.3 11.33
 found 26.5 10.75
 Example 5
 10,10-Biphenyl-2,2'-diylphenoxasilin
 A solution of 120 mmol of 2,2'-dilithiodiphenyl ether in 180 ml of THF,
 prepared as described by H. Gilman, W. J. Trepka, J. Org. Chem. 27, 1418
 (1962), was added to a solution of 37.7 g (150 mmol) of
 biphenyl-2,2'-diylsilicon dichloride in 200 ml of THF, prepared as
 described in Example 4. The mixture was stirred for 12 hours at 20.degree.
 C., hydrolyzed using a mixture of ice and sulfuric acid and the aqueous
 phase was extracted with ether. After distillating work-up at .ltoreq.0.05
 mm, the main fraction going over at 150.degree. C. was recrystallized from
 ethanol: 12.5 g (30%).
 Example 6
 Bis(bibenzyl-2,2'-diyl)silane
 A solution of 2.1 ml (20 mmol) of silicon tetrachloride in 50 ml of THF was
 added dropwise to a solution of 2,2'-dilithiobibenzyl which had previously
 been prepared from 15 g (40 uirol) of 2,2'-dibromobibenzyl and 97 mmol of
 a 1.7 molar solution of n-butyllithium in a hexane fraction. The mixture
 was refluxed for 1 hour and worked-up as in Example 5. 5.0 g of a
 solidifying oil went over at a pressure of 0.05 mm between 125 and
 210.degree. C., and after being recrystallized twice this gave 1.0 g (12%)
 of bis(bibenzyl-2,2'-diyl)silane having a melting point of 175.degree. C.
 Elemental analysis:

% C H
 calc. 86.60 6.19
 found 86.21 6.05
 Example 7
 Bis(stilbene-2,2'-diyl)silane from
 bis(.alpha.,.alpha.'(.beta.')-dibromobibenzyl-2,2'-diyl)silane
 A slurry of 1.94 g (5 mmol) of bis(bibenzyl-2,2'-diyl)silane, prepared as
 described in Example 6, and 1.78 g (10 mmol) of N-bromosuccinimide in 100
 ml of tetrachloromethane were heated to boiling under irradiation with a
 300 W incandescent tungsten lamp. The succinimide formed was filtered off
 with suction, the filtrate was evaporated to dryness on a rotary
 evaporator, the residue was taken up in 15 ml of toluene and admixed with
 2 ml of 2-dimethylaminoethanol. The mixture was stirred for 48 hours and
 then heated to boiling for 6 hours. The toluene was removed in vacuo, the
 residue was admixed with 50 ml of 5% strength by weight sodium hydroxide
 solution and shaken with ether. After drying over magnesium sulfate, the
 ether was evaporated and the residue was purified by chromatography in
 toluene/cyclohexane on 30 g of silica gel.
 Example 8
 3,3',5,5'-Tetraphenyl-9,9'-spiro-9H-bi-9-silafluorene from
 tetrakis(biphenylyl-4)silane
 10.8 g (46.3 mmol) of 4-bromobiphenyl together with 1.95 g (11.6 mol) of
 silicon tetrachloride were dissolved in 100 ml of absolute ether and
 subsequently treated with 2.5 g (110 mmol) of sodium. The mixture was
 heated to reflux and then stirred for a further 4 hours at room
 temperature until the metal had dissolved. After removal of the ether, the
 residue was extracted with toluene in a Soxhlet apparatus: 6.7 g (90%),
 mp. 281.degree. C. from xylene.
 5.4 g (10 mmol) of tetrakis(biphenylyl-4)silane were dissolved in 200 ml of
 1,2-dichlorobenzene and, while passing nitrogen through the solution, was
 admixed in portions with 6.5 g (40 mmol) of iron(III) chloride. The
 mixture was heated to boiling over a period of 3 hours. When HCl could no
 longer be detected as NH.sub.4 Cl in the off-gas, the mixture was
 evaporated on a rotary evaporator, the residue was digested a number of
 times with 5% strength by weight hydrochloric acid and the residue was
 recrystallized from xylene with addition of 1 g of silica gel: 2.7 g
 (51%).
 Example 9
 2,2'-Dinitro-9,9'-spiro-9-silabifluorene
 3.16 g (13 mmol) of Cu(NO.sub.3).sub.2.3 H.sub.2 O are taken up at room
 temperature using 20 ml of acetic anhydride and stirred. After a few
 minutes, the internal temperature rises to about 40-45.degree. C. with the
 blue suspension becoming turbid. 2 g (6 mmol) of
 9-sila-9,9'-spirobifluorene are subsequently added and stirring is
 continued at 40.degree. C. After 4 hours at 40.degree. C., the reaction is
 complete. During the reaction, the color of the suspension changed to
 turquoise. It is carefully stirred into about 100 ml of water and shaken
 with chloroform. After evaporating the organic phase on a rotary
 evaporator and dialoguing the residue in a little chloroform, the solution
 is precipitated with 100 ml of hexane: 2 g of colorless product (79%).
 2,2',7,7'-Tetranitro-9,9'-spiro-9-silabifluorene can be obtained as main
 product by a similar route using a different stoichiometry.
 Example 10
 2,2'-Diamino-9,9'-spiro-9-silabifluorene
 A mixture of 4.0 g of dinitrospiro-9-silabifluorene and 4.0 g of iron
 powder were refluxed in 100 ml of ethanol while 15 ml of concentrated
 hydrochloric acid were added dropwise over a period of 30 minutes. After
 refluxing for a further 30 minutes, excess iron was filtered off. The
 green filtrate was added to a solution of 400 ml of water, 15 ml of
 concentrated NH.sub.4 OH solution and 20 g of sodium potassium tartrate.
 The white diamine was filtered off from the dark green solution of the
 iron complex. The diamine was purified by dissolving it in dilute
 hydrochloric acid, stirring at room temperature with activated carbon
 (Darco) and filtration. The filtered solution was neutralized dropwise
 with NH.sub.4 OH solution while stirring mechanically (precision glass
 stirrer) and the precipitated product was filtered off with suction. This
 gave 3.3 g of white 2,2'-diamino-9,9'-spiro-9-silabifluorene which was
 recrystallized from ethanol.
 2,2',7,7'-Tetraamino-9,9'-spiro-9-silabifluorene can be obtained as main
 product by a similar method using a different stoichiometry.
 Example 11
 2,2'-Dibromo-9,9'-spiro-9-silabifluorene
 2.0 g (5.5 mmol) of 2,2'-diamino-9,9'-spiro-9-silabifluorene are dissolved
 in 20 ml of water and 5 ml of concentrated hydrobromic acid, cooled to
 about 0.degree. C. and slowly admixed with a solution of 0.8 g of
 NaNO.sub.2 in about 5 ml of water while maintaining this temperature. The
 mixture is stirred at this temperature for about 30 mins, and the solution
 of the resulting bisdiazonium salt is poured into an ice-cooled solution
 of 1 g of CuBr in 10 ml of HBr. The resulting solution is stirred at
 100.degree. C., with gas evolution occurring and the product formed being
 precipitated as a white deposit. After gas evolution has ended, the
 product is filtered off with suction, washed with NaRCO.sub.3 solution
 until neutral and washed with water until free of salts. The product is
 subsequently reprecipitated from chloroform/hexane: 1.8 g of colorless
 powder (66%).
 2,2',7,71-Tetrabromo-9,9'-gpiro-9-silabifluorene can be obtained as main
 product from 2,2',7,7'-tetraamino-9,9'spiro-9-silabifluorene by a similar
 route using a different stoichiometry.
 Example 12
 9,9'-Spiro-9-silabifluorene-2,2'-dicarboxylic acid from
 2,2'-dibromo-9,9'-spiro-9-silabifluorene via
 2,2'-dicyano-9,9'-spiro-9-silabifluorene
 1.18 g (2.4 mmol) of 2,2'-dibromo-9,9'-spiro-9-silabifluorene, as described
 in Example 11, and 0.54 g of CuCN were refluxed for 6 hours in 5 ml of
 DMF. The brown mixture obtained was poured into a mixture of 3 g of
 FeCl.sub.3 (hydrated) and 1.5 ml of concentrated hydrochloric acid in 20
 ml of water. The mixture was maintained at from 60 to 70.degree. C. for 30
 minutes to destroy the Cu complex.
 The hot aqueous solution was extracted twice with toluene. The organic
 phases were then washed with dilute hydrochloric acid, water and 10%
 strength by weight aqueous NaOH. The organic phase was filtered and
 evaporated. The yellow residue obtained was recrystallized from methanol.
 This gave 0.64 g (70%) of 2,2'-dicyano-9,9'-spiro-9-silabifluorene as
 slightly yellowish crystals (melting range from 230 to 260.degree. C.).
 3.82 g (10 mmol) of 2,2'-dicyano-9,9'-spiro-9-silabifluorene were refluxed
 for 6 hours with 30 ml of 30% strength by weight NaOH and 40 ml of
 ethanol. The disodium salt of the spirosilabifluorenedicarboxylic acid
 precipitated as a yellow solid which was filtered off and heated in 25%
 strength by weight aqueous HCl to isolate the free acid. The
 spirosilabifluorenedicarboxylic acid was recrystallized from glacial
 acetic acid. This gave 2.52 g (60%) of white crystals (mp. &gt;360.degree.
 C., IR band at 1685 cm.sup.-1, C.dbd.O).
 Example 13
 9,9'-Spiro-9-silabifluorene-2,2',7,7'-tetracarboxylic acid was prepared in
 a similar manner from 2,2',7,7'-tetrabromo-9,9'-spiro-9-silabifluorene.
 Example 14
 2,2'-Bis(bromomethyl)-9,9'-spiro-9-silabifluorene from
 9,9'-spiro-9-silabifluorene 2,2'-dicarboxylic acid via
 2,2'-bis(hydroxymethyl)-9,9'-spiro-9-silabifluorene using a method similar
 to that of V. Prelog, D. Bedekovicc, Helv. Chim. Acta 1979, 62, 2285
 At room temperature, 10 g of a 70% strength by weight solution of sodium
 dihydrobis (2-methoxyethoxy) aluminate (Fluka) in toluene were slowly
 added dropwise to a suspension of 2.08 g (5 mmol) of 2,2'-dicarboxy-9,9'-
 spiro-9-silabifluorene-2,2'-dicarboxylic acid in 20 ml of toluene. After
 refluxing for 2 hours, during which time the carboxylic acid dissolved,
 the excess reducing agent was decomposed at 10.degree. C. using water, the
 mixture was acidified with concentrated hydrochloric acid and shaken with
 chloroform.
 The organic phase which had been washed with water and dried over magnesium
 sulfate was evaporated and the residue was recrystallized from benzene.
 This gave 1.7 g of 9,9'-spiro-9-silabifluorene-2,2'-dimethanol
 (mp.&gt;250.degree. C.). 92 g of a 33% strength by weight aqueous solution
 of hydrogen bromide in glacial acetic acid were added dropwise to a
 solution of 14 g of 9,9'-spiro-9-silabifluorene-2,2'-dimethanol in 400 ml
 of toluene and the mixture was refluxed for 7 hours. It was then admixed
 with 200 ml of water and the organic phase was washed with water, dried
 over magnesium sulfate and evaporated. Chromatography on silica gel using
 toluene gives 11 g of 2,2'-bis(bromomethyl)-9,9'-spiro-9-silabifluorene as
 colorless platelets.
 Example 15
 A solution of 0.4 g of 9,9'-spiro-9-silabifluorene-2,2'-dimethanol, as
 described in Example 14, in 15 ml of toluene was admixed with 5 g of
 chromium(VI) oxide on graphite (Seloxcette, Alpha Inorganics) and refluxed
 for 48 hours under nitrogen. The mixture was then filtered with suction
 through a sintered glass filter and the filtrate was evaporated.
 Chromatography on silica gel using chloroform and crystallization from
 methylene chloride/ether gave 150 mg of
 9,9'-spiro-9-silabifluorene-2,2'-dicarbaldehyde (mp.&gt;300.degree. C.)
 and 200 mg of 2'-hydroxymethyl-9,9'-spiro-9-silabifluorene-2-carbaldehyde
 (mp.&gt;260.degree. C.).
 Example 16
 2,2'-Bis(benzofuran-2-yl)-9,9'-spiro-9-silabifluorene using a method
 similar to that of W. Sahm, E. Schinzel, P. Jurges, Liebigs Ann. Chem.
 1974, 523.
 2.7 g (22 mmol) of salicylaldehyde and 5.4 g (10 mmol) of
 2,2'-bis(bromomethyl)-9,9'-spiro-9-silabifluorene, as described in Example
 14, were dissolved at room temperature in 15 ml of DMF and admixed with
 0.9 g (22.5 mmol) of pulverized NaOH and a spatula tip of KI. The mixture
 was heated to boiling and stirred for 1 hour at the boiling temperature.
 After cooling, the reaction solution was admixed with a mixture of 0.5 ml
 of concentrated hydrochloric acid, 7 ml of water and 7 ml of methanol.
 Stirring was continued for 1 hour at room temperature, the crystalline
 reaction product was filtered off with suction, washed first with cold
 methanol, then with water and dried in vacuo at 60.degree. C. This gave
 4.6 g (79%) of the bigbenzylphenyl ether. 6.0 g (10 mmol) of the
 bisbenzylphenyl ether were admixed in 10 ml of toluene with 2.1 g (22.5
 mmol) of freshly distilled aniline. A spatula tip of p-toluenesulfonic
 acid was added and the mixture was boiled attached to a water separator
 until water no longer separated (from about 3 to 5 hours). On cooling the
 reaction mixture, the corresponding bisbenzylidenephenylamine
 crystallized. It was filtered off with suction, washed with methanol and
 dried in vacuo at 60.degree. C. It can be further purified by
 recrystallization from DMF. 7.5 g (10 mmol) of the
 bisbenzylidenaphenylamine and 0.62 9 (11 mmol) of KOH are introduced under
 nitrogen into 30 ml of DMF. The mixture is subsequently heated at
 100.degree. C. for 4 hours while stirring. After cooling to room
 temperature, the precipitate was filtered off and washed with a little DMF
 and water. After drying at 600C in a vacuum drying oven, the 2,2'-bis
 (benzofuran-2-yl) -9,9'-spiro-9-silabifluorene was purified by
 recrystallization from methyl benzoate.
 Example 17
 2,2',7,7'-Tetrakis(benzofuran-2-yl)-9,9'-spiro-9-silabifluorere
 was prepared using a method similar to Example 1 with an appropriately
 changed stoichiometry.
 Example 18
 2,2',7,7'-Tetraphenyl-9,9'-spiro-9-silabifluorene
 5.1 g (7.9 mmol) of 2,2',7,7'-tetrabromo-9,9'-spiro-9-silabifluorere 3.86 g
 (31.6 mmol) of phenylboronic acid, 331.5 mg (1.264 mmol) of
 triphenyiphosphine and 70.9 mg (O.316 minol) of palladium acetate were
 slurried in a mixture of 65 ml of toluene and 40 ml of aqueous sodium
 carbonate solution (2M). The mixture was refluxed for 24 hours while
 stirring vigorously. After cooling to room temperature, it was filtered
 with suction, the solid washed with water and dried at 50.degree. C. in
 vacuo. This gave 2.4 g of product. The filtrate was extracted with 50 ml
 of toluene and the dried organic phase was evaporated to dryness. This
 gave a further 1.42 g of product. Total yield: 3.82 g (76%)
 Example 19
 2,2',7,7'-Tetrakis(biphenyl-4-yl)-9,9'-spiro-9-silabifluorene
 5.1 g (7.9 mool) of 2,2',7,7'-Tetrabromospiro-9-silabifluorene, 6.57 g
 (33.2 mmol) Of biphanylylboronic acid, 331.5 mg (1.264 mmcol) of
 triphenylphosphine and 70.9 mg (0.316 mmol) of palladium acetate were
 slurried in a mixture of 65 ml of toluene and 40 ml of aqueous sodium
 carbonate solution (2M). The mixture was refluxed for 24 hours while
 stirring vigorously. After cooling to room temperature, it was filtered
 with suction, the solid was washed with water and dried at 50.degree. C.
 in vacuo. Yield: 5.87 g (79%).
 Example 20
 Synthesis of 2,2',7,7'-tetrakis(biphenyl-4-yl)-9,9'-spiro-9-silabifluorene
 In a 250 ml two-neck flask fitted with reflux condenser and precision glass
 stirrer, 5.5 g of 2,2',7,7'-tetrabromospiro-9-silabifluorene, 7.2 g of
 4-biphenylylboronic acid and 400 mg of
 tetrakis(triphenylphosphine)palladium(0) were slurried in a mixture of 100
 ml of toluene and 50 ml of potassium carbonate solution. The mixture was
 refluxed for 8 hours under a blanket of protective gas while stirring with
 a precision glass stirrer. After cooling, the product was filtered off
 with suction, the precipitate was washed with water and dried. In the
 filtrate, the toluene phase was separated off and the aqueous phase was
 shaken once with chloroform. The combined organic phases were dried over
 sodium sulfate and evaporated, thus giving a second fractional of the
 product. The two product fractions were combined (8 g) and dissolved in
 chloroform. The chloroform solution was boiled with activated carbon and
 filtered through a short column containing silica gel. Evaporation and
 recrystallization from chloroform/pentane gave colorless crystals which
 fluoresced blue under UV illumination. Melting point: 408.degree. C.
 (DSC).
 .sup.1 H-NMR (CDC.sub.3, ppm): 7.14 (d, J=1.53 Hz, 4 H); 7.75 (dd, J=7.93,
 1.53 Hz, 4 H); 8.01 (d, J=7.93 Hz, 4 H); 7.34 (dd, J=7.32, 1.37 Hz, 4 H);
 7.42 (t, J=7.32 Hz, 8 H); 7.Sf (24 H).
 Example 21
 Synthesis of
 2,2'-bis[(5(p-t-butylphenyl)-1,3,4-oxadiazol-2-yl]9,9'-spiro-9-silabifluor
 ene from 9,9'-spiro-9-silabifluorene-2,2'-dicarboxylic chloride and
 5-(4-butylphenyl)tetrazole
 21a) Synthesis of 5-(4-t-butylphenyl)tetrazole
 In a 250 ml round-bottom flask fitted with reflux condenser, 4.9 g of
 p-t-butylbenzonitrile, 3.82 g of lithium chloride and 5.85 g of sodium
 azide and 8.2 g of triethylammonium bromide in 100 ml of DMF were heated
 at 120.degree. C. for 8 hours. After cooling to room temperature, 100 ml
 of water were added and the mixture was admixed in an ice bath with dilute
 hydrochloric acid until no further precipitate was formed. The mixture was
 filtered with suction, the precipitate was washed with water and dried.
 Recrystallization from ethanol/water gave 4.4 g of colorless crystals.
 21b) 9,9'-Spiro-9-silabifluorene-2,2'-dicarboxylic chloride
 In a 100 ml round-bottom flask fitted with reflux condenser and drying
 tube, 2.1 g (5 mmol) of 9,9'-spiro-9-silabifluorene-2,2'-dicarboxylic
 acid, as described in Example 12, were refluxed for 4 hours with 20 ml of
 (freshly distilled) thionyl chloride and 3 drops of DMF. After cooling,
 the reflux condenser was replaced by a distillation bridge and excess
 thionyl chloride was distilled off in vacuo. 40 ml of petroleum ether
 (boiling point: 30.degree.-60.degree. C.) were added to the residue and
 distilled off, leaving the crystalline acid chloride.
 21c)
 2,2'-Bis[(5-(p-t-butylphenyl)-1,3,4-oxadiazol-2yl]9,9'-spiro-9-silabifluor
 ene
 2.0 g (11 mmol) of 5-(4-t-butylphenyl)tetrazol dissolved in 20 ml of
 anhydrous pyridine were added as described in Example 21.b to the acid
 chloride and the mixture was refluxed for 2 hours under protective gas.
 After cooling, the mixture was poured into 200 ml of water and allowed to
 stand for 2 hours. The precipitated oxidiazole derivative was filtered off
 with suction, washed with water and dried in vacuo. It was subsequently
 chromatographed on silica gel using chloroform/ethyl acetate (99:1) and
 recrystallized from chloroform/pentane. This gave 2.3 g of colorless
 crystals.
 Example 22
 2,2',7,7'-Tetrakis(biphenyl)-4-yl)-9,9'-spiro-9-silabifluorene, as
 described in Example 19, was dissolved in chloroform (30 mg/ml) and
 applied by means of spin coating (1,000 rpm) to a glass support coated
 with 30 indium/tin oxide (ITO), with a homogeneous, transparent film being
 formed. An electrode of Mg/Ag (80/20) was applied to this film by vacuum
 deposition. On application of an electric potential between the ITO
 electrode and the metal electrode, with the metal electrode having a
 negative potential compared with the ITO electrode, a blue
 electroluminescence was observed.
 Example 23
 As described in Example 22, further test specimens were produced by vacuum
 deposition onto an ITO layer (30 Ohm), with the following parameters being
 obtained:
 thickness of the
 2,2',7,7'-tetrakis(biphenyl-4-yl)-9,9'-spiro-9-silabifluorene layer
 a.sub.1 =60 nm,
 thickness of the aluminum tris(8-oxyquinoline) layer: b.sub.1 =20 nm,
 thickness of the Al+Mg (3%) layer: c.sub.1 =135 nm,
 analogous test specimen: a.sub.2 =60 nm, b.sub.2 =0 nm, a.sub.3 =41 nm,
 b.sub.3 =150 nm.
 All three test specimens showed blue electroluminescence.