(DE19645063-A1)      Optical brighteners are claimed which contain one or more spiro compounds of formula (I) where K1 and K2 = conjugated systems; and Q = C, Si, Ge, Sn or Pb.    Also claimed is an optical brightener which has (a) a fluorescence quantum yield of 40 (especially 50)% or more as a solid; and (b) a drop in room temperature emission maximum at 380-750 nm of no more than 25% after a 1 thick layer on a quartz substrate has been heated at 250C for 30 minutes at 1 mbar or below in an inert atmosphere.    USE -   Claimed use of any of these optical brighteners is as a transformation material for UV in increasing the efficiency of solar cells.    The compounds may also be used for a wide variety of purposes including UV filters; addition to high molecular materials including those derived from unsaturated compounds (e.g. polyolefins, acrylic compounds), ring-opened products (e.g. polyamides of polycaprolactam type), polycondensation products (e.g. polyesters, polyamides, polycarbonates), polyaddition products (e.g. polyurethanes, epoxide resins) or semi-synthetic materials; in various formed products (e.g profiles, plates, films, coverings); in powders, in dye baths or printing pastes; in fibres and textiles; in emulsions, dispersions and paper. The compounds may be used as scintillators, for various photographic purposes including electrophotographic reproduction or supersensitising, for the brightening of photographic layers. They may also be used in washing powder/liquid compositions.    ADVANTAGE -   The brighteners have high heat and light stability. They are soluble in polar solvents.    (EP935691-A1)      Optical brighteners are claimed which contain one or more spiro compounds of formula (I) where K1 and K2 = conjugated systems; and Q = C, Si, Ge, Sn or Pb.    Also claimed is an optical brightener which has (a) a fluorescence quantum yield of 40 (especially 50)% or more as a solid; and (b) a drop in room temperature emission maximum at 380-750 nm of no more than 25% after a 1 thick layer on a quartz substrate has been heated at 250C for 30 minutes at 1 mbar or below in an inert atmosphere.    USE -   Claimed use of any of these optical brighteners is as a transformation material for UV in increasing the efficiency of solar cells.    The compounds may also be used for a wide variety of purposes including UV filters; addition to high molecular materials including those derived from unsaturated compounds (e.g. polyolefins, acrylic compounds), ring-opened products (e.g. polyamides of polycaprolactam type), polycondensation products (e.g. polyesters, polyamides, polycarbonates), polyaddition products (e.g. polyurethanes, epoxide resins) or semi-synthetic materials; in various formed products (e.g profiles, plates, films, coverings); in powders, in dye baths or printing pastes; in fibres and textiles; in emulsions, dispersions and paper. The compounds may be used as scintillators, for various photographic purposes including electrophotographic reproduction or supersensitising, for the brightening of photographic layers. They may also be used in washing powder/liquid compositions.    ADVANTAGE -   The brighteners have high heat and light stability. They are soluble in polar solvents.    (CN1235651-A)      Optical brighteners are claimed which contain one or more spiro compounds of formula (I) where K1 and K2 = conjugated systems; and Q = C, Si, Ge, Sn or Pb.    Also claimed is an optical brightener which has (a) a fluorescence quantum yield of 40 (especially 50)% or more as a solid; and (b) a drop in room temperature emission maximum at 380-750 nm of no more than 25% after a 1 thick layer on a quartz substrate has been heated at 250C for 30 minutes at 1 mbar or below in an inert atmosphere.    USE -   Claimed use of any of these optical brighteners is as a transformation material for UV in increasing the efficiency of solar cells.    The compounds may also be used for a wide variety of purposes including UV filters; addition to high molecular materials including those derived from unsaturated compounds (e.g. polyolefins, acrylic compounds), ring-opened products (e.g. polyamides of polycaprolactam type), polycondensation products (e.g. polyesters, polyamides, polycarbonates), polyaddition products (e.g. polyurethanes, epoxide resins) or semi-synthetic materials; in various formed products (e.g profiles, plates, films, coverings); in powders, in dye baths or printing pastes; in fibres and textiles; in emulsions, dispersions and paper. The compounds may be used as scintillators, for various photographic purposes including electrophotographic reproduction or supersensitising, for the brightening of photographic layers. They may also be used in washing powder/liquid compositions.    ADVANTAGE -   The brighteners have high heat and light stability. They are soluble in polar solvents.    (US6187224-B1)      Optical brighteners are claimed which contain one or more spiro compounds of formula (I) where K1 and K2 = conjugated systems; and Q = C, Si, Ge, Sn or Pb.    Also claimed is an optical brightener which has (a) a fluorescence quantum yield of 40 (especially 50)% or more as a solid; and (b) a drop in room temperature emission maximum at 380-750 nm of no more than 25% after a 1 thick layer on a quartz substrate has been heated at 250C for 30 minutes at 1 mbar or below in an inert atmosphere.    USE -   Claimed use of any of these optical brighteners is as a transformation material for UV in increasing the efficiency of solar cells.    The compounds may also be used for a wide variety of purposes including UV filters; addition to high molecular materials including those derived from unsaturated compounds (e.g. polyolefins, acrylic compounds), ring-opened products (e.g. polyamides of polycaprolactam type), polycondensation products (e.g. polyesters, polyamides, polycarbonates), polyaddition products (e.g. polyurethanes, epoxide resins) or semi-synthetic materials; in various formed products (e.g profiles, plates, films, coverings); in powders, in dye baths or printing pastes; in fibres and textiles; in emulsions, dispersions and paper. The compounds may be used as scintillators, for various photographic purposes including electrophotographic reproduction or supersensitising, for the brightening of photographic layers. They may also be used in washing powder/liquid compositions.    ADVANTAGE -   The brighteners have high heat and light stability. They are soluble in polar solvents.    (JP2001503795-W)      Optical brighteners are claimed which contain one or more spiro compounds of formula (I) where K1 and K2 = conjugated systems; and Q = C, Si, Ge, Sn or Pb.    Also claimed is an optical brightener which has (a) a fluorescence quantum yield of 40 (especially 50)% or more as a solid; and (b) a drop in room temperature emission maximum at 380-750 nm of no more than 25% after a 1 thick layer on a quartz substrate has been heated at 250C for 30 minutes at 1 mbar or below in an inert atmosphere.    USE -   Claimed use of any of these optical brighteners is as a transformation material for UV in increasing the efficiency of solar cells.    The compounds may also be used for a wide variety of purposes including UV filters; addition to high molecular materials including those derived from unsaturated compounds (e.g. polyolefins, acrylic compounds), ring-opened products (e.g. polyamides of polycaprolactam type), polycondensation products (e.g. polyesters, polyamides, polycarbonates), polyaddition products (e.g. polyurethanes, epoxide resins) or semi-synthetic materials; in various formed products (e.g profiles, plates, films, coverings); in powders, in dye baths or printing pastes; in fibres and textiles; in emulsions, dispersions and paper. The compounds may be used as scintillators, for various photographic purposes including electrophotographic reproduction or supersensitising, for the brightening of photographic layers. They may also be used in washing powder/liquid compositions.    ADVANTAGE -   The brighteners have high heat and light stability. They are soluble in polar solvents.