NOVELTY - New bichromophoric perylene and benzoperylene dyes consist of N-naphthalimidoalkyl-perylene-tetracarboxylic acid bis-imides (I) and N-naphthalimidoalkyl benzoperylene-hexacarboxylic acid tris-imides (II).    USE - The use of (I) and (II) is claimed: (A) as fluorescent dyes, specifically for machine-readable markings (especially alphanumeric prints or bar codes), in high sensitivity detection procedures or in scintillators; (B) as colorants (e.g. for paints, lacquers, paper or printing, writing, marking or coloring inks) or additives for other colorants for obtaining specific color nuances (especially luminous tones); (C) for frequency conversion of light, e.g. for converting short wavelength light into longer wavelength, visible light; (D) in display elements for numerous display, indication and marking purposes, e.g. passive display elements, indicators or traffic signals (e.g. traffic lights); (E) in fluorescent or other inks for ink-jet printers, especially water-resistant inks; (F) for decorative or artistic purposes; (G) for tracer purposes, e.g. in biochemistry, medicine, industry or science, the dye being bonded to substrates covalently or by auxiliarly bonding (e.g. hydrogen bonding, hydrophobic interaction or adsorption); (H) as fluorescent or other dyes in optical light collecting systems, in fluorescence activated displays, in cold light sources for inducing polymerization in plastics production, in material testing (e.g. in seiconductor production), for studying microstructures of integrated semiconductor components, in photoconductors, in photographic processes, in display, illumination or image conversion systems activated by electrons, ions or UV-radiation (e.g. in fluorescent displays, cathode ray tubes or fluorescent tubes), as components of integrated semiconductor circuits (optionally in combination with other semiconductors, e.g. in epitaxial form), in chemiluminescent systems (e.g. in chemiluminescent rods, luminescence immunoassays or other luminescent detection processes), as signal dyes (preferably for optical emphasis of characters, letters or other graphic symbols or characterization of labels or articles, using special optical imprints) or in dye lasers (specifically as fluorescent dyes for generating laser beams); (I) as Q-switch dyes in dye lasers; (J) as non-linear optical active components (e.g. for doubling or tripling laser light frequency); (K) for testing closed system seals; or (L) as rheology improver. An especially preferred application of (I) and (II) (not specifically covered in the claims) is in solar energy systems, as fluorescent dyes for light collector plates.    ADVANTAGE - (I) and (II) have a broad absorption spectrum (in particular absorbing a broadened spectrum of solar light); and good light fastness.    DETAILED DESCRIPTION - Bichromophoric perylene and benzoperylene dyes of formulae (I) and (II) are new.    R1-R 7 = H, halo or 1-37C n-alkyl, optionally (i) having 1-10 CH 2 units replaced by CO, O, S, Se, Te, CH=CH, N=CH, CH=N, CC, phenylene, pyridinylene, thienylene, naphthylene, mono- or diazanaphthylene, anthrylene and/or mono- or diazaanthrylene and/or (ii) substituted by 1-12 of halo, CN or 1-18C n-alkyl (optionally having 1-6 CH 2 units replaced by divalent groups as in (i) and optionally substituted by 1-12 of halo, CN or 1-18C alkyl (optionally having 1-6 CH 2 units replaced by divalent groups as in (i))); substituents in R 1-R 7 optionally have free valencies of methine groups or quaternary carbons bonded in pairs to complete rings (e.g. cyclohexane rings);    X = 1-12C n-alkyl (optionally having one or more CH 2 units replaced by divalent groups as in (i) above and optionally substituted as in (ii) above, pairs of substituents optionally also forming rings as defined for R 1-R 7 above).    INDEPENDENT CLAIMS are included for:    (1) the preparation of benzoperylene-bis-imides, by reacting an N-2,5-ditert. butyl-perylene-dicarboximide of formula (XII) with an N-(aliphatic substituted)-naphthalimide, suitably in presence of potassium or sodium tert. butylate and diazacyclononene (DBN) or diazacycloundecene (DBU); and    (2) the conversion of asymmetric N-substituted terrylene tetracarboxylic acid bis-imides containing an N-2,5-ditert. butyl substituent into the anhydride-carboximide using potassium hydroxide in tert. butyl alcohol.