Fluorescent Dyes and PigmentsRAMI ISMAEL, Aralon GmbH, Heiligenroth, Germany HANSRUDOLF SCHWANDER, Ciba-Geigy AG, Basel, Switzerland PAUL HENDRIX, Radiant Color NV, Houthalen, Belgium 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. Introduction . . . . . . . . . . . . . . . . . 1 Naphthalimide Dyes. . . . . . . . . . . . 2 Coumarin Dyes . . . . . . . . . . . . . . . 3 Xanthene Dyes . . . . . . . . . . . . . . . 4 Thioxanthene and Benzoxanthene Dyes 7 Naphtholactam, Hydrazam Dyes and Homologues . . . . . . . . . . . . . . . . . 8 Azlactone Dyes . . . . . . . . . . . . . . . 9 Methine Dyes . . . . . . . . . . . . . . . . 9 Oxazine and Thiazine Dyes . . . . . . 10 Miscellaneous Fluorescent Dyes . . . 10 UV Fluorescent Chromophores with No or Low Body Color . . . . . . . . . . . 12 Special Uses . . . . . . . . . . . . . . . . 13 Daylight Fluorescent Pigments. . . . 15 1. Introduction Fluorescent dyes differ from normal dyes in their exceptional bright colors. This is the result of a combination of the reflexion of part of the incident light and emission of light by the dye. The major part of the light energy concentrates at selected wavelengths. Fluorescent dyes are used mainly as solvent, disperse, or reactive dyes (! Disperse Dyes, ! Reactive Dyes) in the coloring of textile fibers and plastics, in the production of inks and printing inks and, in combination with appropriate pigments, in the production of paints and lacquers. Fluorescent dyes are also employed as laser dyes (! Laser Dyes). Furthermore, daylight and UV light fluorescent dyes, mainly acid, basic, and solvent dyes, may be dissolved in a resin matrix or covalently bound to a resin or a polymer and then pulverized to form fluorescent pigments, suspensions, and emulsions (see Chap. 13 Daylight Fluorescent Pigments). Fluorescence occurs when molecules that have absorbed light and are in their lowest excited state S1 return to their ground state # 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 10.1002/14356007.a11_279.pub2 13.1. 13.1.1. 13.1.2. 13.1.3. 13.1.4. 13.1.5. 13.1.6. 13.2. 13.3. 13.4. Production . . . . . . . . . . . . . . . . . Dyes for Daylight Fluorescent Pigments. . . . . . . . . . . . . . . . . . . Pigment Matrices . . . . . . . . . . . . Formaldehyde-Free and SolventResistant Fluorescent Pigments. . . Sunlight Sensors . . . . . . . . . . . . . Fluorescent Modifications with Covalently Bound Dyes . . . . . . . . More-Not Resinated-Solid-State Fluorescent Pigments. . . . . . . . . . Quality Specifications of Fluorescent Pigments. . . . . . . . . . . . . . . . . . . Applications of Fluorescent Pigments Toxicology . . . . . . . . . . . . . . . . . 15 15 16 17 17 17 18 18 20 21 S0 and emit light (for a detailed discussion of fluorescence, see ! Dyes, General Survey). Some of the absorbed light energy also activates nuclear vibrations and is released as heat. Further energy is lost due to the conversion of the lowest excited state S1 to a triplet state T1 (intersystem crossing) and is not available for fluorescence. The quantum yield is a measure of the fluorescence efficiency of a compound, i. e., the proportion of the absorbed light energy that is emitted as fluorescent light. Fluorescent dyes absorb in the UVand visible region or solely in the visible region of the spectrum and emit light in the visible region of the spectrum at longer wavelengths than blue. Some of the fluorescent dyes emit in the infrared region and have found specific applications in laser writing and plastic welding applications. The fluorescent dyes treated in this article are distinguished from optical or fluorescent brighteners (! Optical Brighteners), which absorb in the invisible UV region and emit blue to blue-violet light,andfromtheUVsecuritydyes,whichabsorb in the invisible UV region and also emit at longer wavelength than blue but without having a so 2 Fluorescent Dyes and Pigments Figure 1. Reflectance spectra of colored surfaces a) Daylight fluorescent orange (ARACO 103 orange, ARALON GmbH, Germany); b) Theoretical white; c) Conventional orange (Pigment Orange 73); d) Theoretical black called “body color”. They appear colorless, unless they are exposedto a UV light.Reflectance spectra of various colored surfaces are shown in Figure 1. Furthermore, neither the abovementioned fluorescent infrared dyes are treated in this article, nor anti-stokes fluorescent dyes. Fluorescent dyes usually have rigid, extended p systems. Rigidity is of importance because it suppresses the release of energy due to activated nuclear vibrations. There are many examples explaining the importance of rigidity for showing fluorescence, like the fluorescent boradiazaindacene as compared with the nonfluorescent dipyrromethene (see above) or like the fluorescent fluorescein as compared with the nonfluorescent phenolphthalein. It is thought that the “floppiness” of a molecule allows more vibrational interactions which increase internal conversion rates of quenching fluorescent activity. Substituents such as heavy atoms (bromine or iodine) or nitro groups are detrimental to fluorescence because they favor intersystem crossing. Many dyes exhibit fluorescence, but to be of practical use, fluorescent dyes must satisfy certain requirements: they must produce a pure color dictated by their absorption and emission spectra, they must have a high molar extinction (high absorption), and most important, they must have a high quantum yield. These requirements are met by few dyes. A disadvantage shared by many fluorescent dyes is their poor lightfastness, but there are some exceptions. In this article some of the most important fluorescent dyes and their applications are described. For a general discussion of the properties of organic dyes and pigments, see ! Dyes, General Survey; ! Pigments, Organic. 2. Naphthalimide Dyes A very wide variety of naphthalimide dyes are known (! Naphthalimide Dyes and Pigments). brilliant greenish-yellow dyes with high quantum yields and high molar extinctions. which show exceptionally brilliant. C.8-naphthalimide is being increasingly used to dye wool and Nmethyl(4-methylamino)-3-sulfo-1. are usually intensely colored. 3.8-naphthalimide [54229-25-3] to dye polyamides. Different coumarin derivatives can be produced by Pechmann condensation of phenols with b-keto esters. C. Solvent Yellow 44 (2). which are useful for dyeing keratin fibers. Brilliant Sulfoflavin FF (1). Dyes derived from coumarin. greenishyellow fluorescent colors. They are moderately lightfast.8-naphthalic anhydride. especially for lightening of dark human hair [9].I.Fluorescent Dyes and Pigments Only a few important representative examples. The improvement in light stability due to the introduction of the N-cyclohexyl group is utilized in the synthesis of different light stabilizers of the hindered amine families. Compound 1 is prepared from p-toluidine and 4-amino-3-sulfo-1.or naphthalimidylamino-substituted thiol derivatives were developed as fluorescent dye compounds. CH3.I. Coumarin Dyes Many basic coumarin dyes found their applications as optical brighteners with intense fluorescence in the blue range. followed by the use of ammonia to substitute the chlorine atom with an amino group. 56205 [239130-2] serves as a dye for wool and polyamides [6]. New naphthalimido. X might be H or COO and R might be H. 56290 [247820-8] is used to dye plastics and is of some importance in the production of fluorescent pigments [7]. 4-Amino-3-sulfo-1.8-naphthalic anhydride [52173-68-9] which is obtained by sulfonating 4-amino-1. Similar water-soluble dyes are employed to dye silk and are used in fluorescent flaw detection.8-naphthalic anhydride with mxylidine. are discussed in this section. . The production of (2) involves the reaction of 4-chloro-1. 3 groups on both nitrogen atoms as shown in the structure below (4). 2H-1-benzopyran-2-one [91-64-5]. One more light-stable member of this dye family is a naphthalimide dye with cyclohexyl Many of these basic coumarins such as 7diethylamino-4-methylcoumarin (Coumarin 1) are applied also as laser dyes [11]. most of them show poor lightfastness. Compound 3 [23741-82-4] is a reactive dye which is employed to dye cellulose fibers [8]. The structure of some examples is given below. Heat can be supplied conventionally or by microwave irradiation [12]. or CF3 [10]. C. The eosines (bromine compounds) and erythrosines (iodine compounds). phloxine B. . and the imino group is replaced by oxygen. 4. 45350 Acid Yellow 73 [518-47-8] is the best known xanthene dye (! Triarylmethane and Diarylmethane Dyes). Rhodamine dyes (aminoxanthenes) are a very important class of xanthene dyes and are of considerable commercial importance.I. Eosin Y or Acid Red 87 [17372-87-1] is a tetrabromo derivative of fluorescein. their sulfonic acid derivatives are employed for dyeing polyamides.I. 45440 [632-68-8] are halogenated derivatives of fluorescein. Compound 16 is used as a disperse dye for polyesters and produces a brilliant red color of moderate lightfastness. Even a very dilute solution of this dye exhibits an intense yellowish-green fluorescence. Fluorescent coumarin dyes are used as disperse dyes for polyesters and polyamides. 45410 [1847287-2]. Substituted coumarins are successfully prepared in a one-pot synthesis catalyzed by silica gel-supported sulfuric acid under solvent-free conditions [20]. C. Coumarin dyes are among others obtained by reacting 2-hydroxy-4-dialkylaminobenzaldehyde with the nitrile (or acetate) derivative of a heterocycle as in the following example: The use of a nitrile derivative results in the introduction of an imino group at the 2-position of the coumarin ring. Hydrolysis occurs under the conditions employed for dyeing. it is red fluorescent and is available in cosmetic quality as D&C Red No. as in compound 7. Some important 7-diethylcoumarin dyes (compounds 8–15) are listed in Table 1. C. as in compound 16 [70546-257].I. which has a heterocyclic residue at the 3-position (6). 22. Xanthene Dyes Fluorescein (17). and Rose Bengal. and their cationic derivatives are used for dyeing polyacrylonitriles. Some of these dyes are important as laser dyes or are used in the production of fluorescent pigments (see Chap. A coumarine dye with orange red fluorescence and moderate light fastness is Solvent Red 197 [52372-39-1]. which is the 4-nitrile derivative of 10 [19]. 13). It is synthesized by reacting phthalic anhydride with resorcinol. yielding the corresponding coumarin derivative. The introduction of a nitrile group at the 4-position of the coumarin residue gives the dye an orange red or red color.4 Fluorescent Dyes and Pigments The most important fluorescent coumarin dyes are derivatives of 7-dialkylaminocoumarin. 7-Diethylcoumarin dyes [13–18] Constitution CAS registry number Color Use Reference yellow disperse dye a yellow for dyeing polyacrylonitrile. Basic Yellow 40) [38215-36-0] [34564-13-1] . fluorescent pigment a yellow disperse dye.I.Fluorescent Dyes and Pigments 5 Table 1. laser dye a yellow for dyeing polyamide b yellow disperse dye c [62143-26-4] yellow disperse dye d [28754-28-1] yellow disperse dye e [55470-53-6] orange for dyeing polyacrylonitrile f [27425-55-4] [12221-86-2] (C. I. Rhodamine 3 B (the ethyl ester of Rhodamine B). The product of the reaction of 3-diethylaminophenol with benzaldehyde-2.6 Fluorescent Dyes and Pigments They are intensely brilliant. . which is used to dye wool and polyamides. 45160 Basic Red 1 [989-38-8].I. The first of the rhodamine compounds to be reported was Rhodamine B (18). and Rhodamine 6 G (19). approaching 100%. Rhodamine dyes are also one of the starting materials for the production of red fluorescent pigments. Its applications might be questioned in the upcoming years due to its high hazard potential [22]. The reaction of a coumarin dye with dicyanomethane produces 23. blue-red. Compound 22 is used as a reactive dye for dyeing cellulose fibers [26]. Dyes of this type have very high quantum yields. The alkyl groups on the nitrogen atoms of Sulforhodamine 101 (21) [60311-02-6] are less flexible than those of Sulforhodamine B (20) [25]. paper. C.I. The most important rhodamine dyes are synthesized by reacting 3-dialkylaminophenols with phthalic anhydride. and plastics. C. 45170 Basic Violet 10 [81-88-9] [21]. C. and as a laser dye. 45100 Acid Red 52 [3520-42-1] [24]. The carboxyl group of the product may then be esterified. which is used in fluorescent pigments.I.4-disulfonic acid is Sulforhodamine B (20). fluorescent dyes with very high molar extinctions and quantum yields and are used for coloring inks. Their sulfonated derivatives are used to dye wool and polyamides. C. and the molecule is thus more rigid. and are used as laser dyes. It is also employed in the production of fluorescent pigments. which can be considered as an azaxanthene dye [27]. have properties similar to those of 18 [23]. 45175 Basic Violet 11 [239063-8]. some of them are employed as laser dyes. as shown for Fluorescent Red GG (24). . It is used to impart a yellow color to polyesters [29] and is prepared by reacting benzo[k. sublimate-free disperse dye. The naturally occurring dye Iachnanthofluorone (28) [53766-48-6] is a red fluorescent xanthene derivative that is closely related to compounds 25–27 [33]. C. This compound is used as a disperse dye for polyesters.I. C.4-dicarboxylic anhydride with aminomethoxypropane. Somewhat better lightfastness is found for the purer version. Samaron Brilliant Yellow H 6 GL (25). These dyes are usually less brilliant than the coumarin dyes and the rhodamines. mineral oils. fats. 505700 [52372-36-8]. moderately lightfast. Thioxanthene and Benzoxanthene Dyes The color of fluorescent thioxanthene dyes ranges from yellow to red. It produces an intensely brilliant. is an Compound 26 [18014-08-9] can be employed as a disperse dye. If the latter is replaced by stearylamine. where an oxygen atom is present instead of the sulfur atom are called benzoxanthene dyes. Solvent Yellow 98. red color. 56235 Disperse Yellow 105 [14121-47-2]. Solvent Orange 63 [16294-75-0] [28]: Plastics can be colored red with compound 24 which has a good lightfastness. The thioxanthene ring system is produced by means of a Pschorr ring closure. Compounds 25 and 26 are also classified as naphthalimide dyes.I. 56238 [12671-74-8] is formed that is particularly useful for dyeing plastics in bulk. C. Disperse dye 27 [35763-62-3] and its isomer 27a give a very brilliant yellowish-red color having moderate lightfastness when applied to polyesters [32]. especially useful for coloring engineering plastics and is known as Solvent Red 196. 5. to impart a brilliant pink color to polyesters [31].I. with good lightfastness.Fluorescent Dyes and Pigments 7 intensely colored.l]thioxanthene-3.I. Structures as 25 or 26. Water-soluble homologues are mentioned in the literature [34]. but some of them show good lightfastness. C. lightfast. and waxes [30]. Naphtholactam. if n is 1. it is especially suitable for textile printing. Naphthostyril [13000-7] (the lactam of 1-aminonaphthalene-8carboxylic acid) reacts with a weakly basic aromatic or heterocyclic amine or with a reactive methylene group (e. Hydrazam Dyes and Homologues Naphtholactam dyes have colors ranging from yellow to red and are suitable for dyeing polyesters and. Polyesters can be dyed orange to red with a high degree of lightfastness by using dyes typified by compound 32 [39]. they show orange and red fluorescence.8 Fluorescent Dyes and Pigments 6. as shown below. Compound 29 [67880-03-9] is obtained if the reaction is performed with 2cyano-4-nitroaniline [36]. Structure 34. The disperse dye 30 [58470-74-9] gives a yellowish-red color with good lightfastness when applied to polyesters [37]. Compound 31 can be used to dye polyamides orange red with a high degree of lightfastness [38].. Although they show excellent lightfastness. their hue is blue and they fluoresce red or near infrared. typified by 33 [40]. If n is 0. polyamides [35]. in some cases. Very interesting homologues of this series with high absorption and quantum yields can be obtained by introducing the lactam functionality into the structure of perylene dyes. the coumarins. this compound produces a reddish-yellow color when used as a disperse dye with polyesters. shows the so-called hydrazam dyes. like naphthalenehydrazamimides and perylenehydrazamimides [41]. The R groups represent long alkyl chains.g. these dyes do neither have the high molar extinctions nor the quantum yields of. . for example. a barbituric acid derivative) in the presence of phosphoryl chloride in an inert solvent to yield naphtholactam dyes. Fluorescent Dyes and Pigments 9 polyacrylonitrile and acid-modified polyester fibers. the greenish-yellow disperse dyes (36) [25744-09-6] and (37) [51202-86-9] can be effectively used on polyesters.3. but with only moderate lightfastness [46]. Another methine dye (40) [23406-34-0] colors polyacrylonitrile a brilliant red. However. . lightfast. Methine Dyes Methine dyes (! Methine Dyes and Pigments) are cationic dyes that are used to color Dye 40 is formed by the condensation of 1. This product imparts a fluorescent. Although azlactone dyes of the donor-acceptor type (35) are very brilliant.3-trimethyl-2-methyleneindoline with 4(N-methyl-N-cyanoethylamino)benzaldehyde. Dye 38 is a fluorescent greenish-yellow [44] and is synthesized by condensation of 1. 43]. orange color to polyacrylonitrile. 7.3-trimethylindoline-2-ylidene acetaldehyde [84-33-3] (Fischer base aldehyde) with 3phenyl-2-pyrazoline [936-47-0]. They possess excellent coloring power and lightfastness [42.3.3-trimethyl-2-(3-chloro-1-propylidene)indoline [45].3. Azlactone Dyes Azlactones are formed by condensation of benzoylglycine (hippuric acid) with an aromatic aldehyde in the presence of acetic anhydride and sodium acetate. Dye 39 is formed by coupling diazotized ptoluidine to 1. 8. they are not lightfast. Compound 46 is a fluorescent. spectrum. Both steps are carried out in the same reaction vessel. Its maximum absorption is shifted to longer wavelengths in comparison with stilbene systems due to its more extensive conjugation. Oxazine and Thiazine Dyes Oxazine dyes (! Azine Dyes). are employed as laser dyes [48].. is synthesized by replacing the bromine atom of 4-bromo-6aminoanthrapyrimidine with an octadecylamino residue. dye 42. C. are used predominantly to color polyacrylonitrile greenish-blue [47].g. can be regarded as an optical brightener (! Optical Brighteners) which absorbs light in the visible region of the Compound 45 is a brilliant. 51004 [63589-47-9]. fluorescent. Miscellaneous Fluorescent Dyes Diphenyl Brilliant Flavine 7 GFF (44). dye 43 imparts a fluorescent. sublimation-fast color with especially good lightfastness. Some dioxazines are also fluorescent dyes. exhibit fluorescence at long wavelengths from 650 to 680 nm and are also used as laser dyes. yellowish-red color to polyamides [49]. yellowish-green dye and is suitable for dyeing fats and oils [30]. e. can be prepared by acylation of 1aminoanthraquinone with acetic anhydride.I.I. 10. It is used as a direct dye for coloring cellulose fibers greenish-yellow. C. disperse dye that can be used to dye polyesters. Thiazine dyes. including 41.I. followed by condensation with anthranilic acid and zinc chloride at 100–110 C. C. such as Basic Blue 3 (41). 70150 [2228118-1] [51]. followed by acylation with butyric chloride. it produces a greenish-yellow.I. Disperse Yellow 77 (45). Some of these dyes. Direct Yellow 96 [61725-08-4] [50]. C.10 Fluorescent Dyes and Pigments 9. . 68410 [6871-92-7]. a derivative of anthraquinone [52]. Fluorol 242 (46). some fluorescent in the infrared region. which is attended by fluorescence quenching. 59040 [6358-69-6]. C. 11). see structure 51. No. lightfast dye [53]. Unsymmetrical substitution is also known for both regions. They dissolve in the plastic material producing lightfast. It is used to color thermoplastic materials yellow in bulk and is suitable for material testing (see Chap. In other extended core perylenes.I. O-aryl replaced with H) or have small substituents at the N atoms combined with substituted O-aryl groups. C. showing pyrene structure. heat-resistant fluorescent colors [60]. 59]. However. Similar persistent fluorescence of perylenediimide dyes is caused by steric inhibition of aggregation [58. 11 industrial applications like data storage and energy transfer. They produce extremely lightfast. The O-aryl substituents prohibit the general tendency of aggregation of perylene diimide dyes.I. is not fluorescent. 59075 [2744-505]. Perylenediimide dyes with O-aryl substituents in the bay region [57] are technically important as colorants for engineering plastics. 12). The reported dyes either exhibit branched alkyl chains with no substituents in the bay region (R ¼ H. methyl. Interesting fluorescent homologues of perylene diimide dyes. Structure 50 shows terylene diimides (n ¼ 2) and quaterylene diimides (n ¼ 3) [55]. is a heat-resistant. were developed for novel The vat dye Thioindigo Red B (52).I. ethyl. 8). is often used in applications like text markers and is also available in cosmetic grade (D&C Green No.Fluorescent Dyes and Pigments Solvent Green 5 (47). A is representing different aromatic core extensions of the known perylene structures [56]. this substance and its derivatives can be used conveniently in the bulk dyeing of plastics. red colors and are suitable for the production of fluorescent collectors (see Chap. C. 73300 [522-75-8]. Perylenetetracarboxylic acid diarylimide derivatives typified by 49 [54] are used in the bulk dyeing of plastics (! Naphthalimide Dyes). Asymmetrical thioindigo derivatives are . Solvent Green 7 or Pyranine (48). 6-tris(N-dimethylamino)pyrimidine yields Azo Orange (58). In addition to the presence of single chromophores in fluorescent molecules many compounds were synthesized. C. The formation of 59 from 58 illustrates that the stiffening of a molecular structure can convert a nonfluorescent azo dye into a fluorescent system. UV Fluorescent Chromophores with No or Low Body Color Dyes. triades. but is converted to the yellow fluorescent dye 59 [38432-19-8] by treatment with acid [67]. hyperbranched polymers. are of high interest for security applications. dendrimers.12 Fluorescent Dyes and Pigments suggested as especially suitable for the bulk dyeing of polyesters [61]. diades. when long alkyl chains or alkyl-substituted phenyl groups are attached to the DPP core. The major amount of these dyes remains unpublished for good reasons. For a detailed study of the fluorescence of indigoid dyes see [62] and for syntheses and examinations of different Oxindigos (53) see [63. and self-assembling structures. Azo coupling of 5-nitro-2-aminoindazole to 2. 11. Compound 59 can be used as a disperse dye to impart a lightfast. was also recommended for the bulk dyeing of plastics. Compound 58 is not fluorescent. 73095 [6417-51-2] [66]. This dye is synthesized by the acylation of indigo with phenylacetyl chloride and ring closure. to concentrate all the harvested light and to convert it into a red or near infrared emission [68–71]. which utilize single chromophores as monomers to create a wide range of light-emitting oligomers. The naphthyridine dione dye Ciba Lake Red B (57). 64].4. polymers. Diketopyrrolopyrrole (DPP. 54) pigments like Pigment Orange 73 or Pigment Red 254 lose their pigment character. A variety of representative fluorescent dyes of this group was synthesized and is utilized in industrial applications. A comprehensive report on fluorescent diketopyrrolopyrroles can be found in [65]. it produces red fluorescent shades. yellow color to polyesters. Some of them include dyes of different absorption wavelengths and can be tuned in order to absorb the light from short wavelength regions.I. which have their hue only under UV-light. Still the general principle of those dyes is a high Stokes’ shift between the . but does not include their use as laser dyes [73] (! Laser Dyes). although they themselves do not fluoresce. of the orange fluorescent perylene dyes without any substituents in the bay region. 59]. emitting afterwards blue. which are colored with a fluorescent dye. Fluorescent Collectors. Silver ions can be titrated in this way. Aggregation problems e. amino acids. Fluorescent probes permit measurement of various parameters in cellular systems. can be detected at a concentration of 2 ng/ mL [77]. In precipitation titrations. e. Special Uses The general uses of fluorescent dyes as colorants for fibers and plastics have been described in the preceding sections. poly(methyl methacrylate). for example. have been encountered by the introduction of bulky groups at the nitrogen atoms [58. orange. The advantage of using solar collectors in combination with solar cells is of importance when daylight is diffuse like in the winter period in middle Europe. which is then concentrated and collected by total internal reflection and released from the thin surfaces at the edges of the sheets. Daylight fluorescent pigments are treated in Chapter 13. Derivatizing Reagents. aniline..g.g. where X might be O. Material Testing. and lipids) can be converted into their fluorescent derivatives with a suitable reagent. Rose Bengal).g. for example. Fluorescent Probes. or NH [72]. Thiols. S. green. Indicators. typified by 49 have proved to be most useful for this 13 purpose. Fluorescent dyes. Photochemistry. Fluorescent collectors consist of highly transparent plastic sheets. Another class of fluorescent indicators consists of water-soluble compounds whose fluorescence changes at the end point. Exposure of the sheets to diffuse sunlight produces fluorescent light. such as 4-methyl-7hydroxycoumarin (66) [90-33-5] (pKa ¼ 7. Substances that are normally very difficult to detect (amines. and red. Fluorescent dyes are used as indicators in analytical titrations (! Indicator Reagents). Examples of such reagents are given in Table 2 (compounds 61–65). peptides. 12. using fluorescein (17) or Rhodamine 6 G (19) as an indicator. The derivative is then separated by means of TLC or HPLC and its fluorescence is measured. yellow. . carboxylic acids. Detection sensitivity is very high. The collected light energy can be used to produce electricity by means of solar cells (! Solar Technology) [76]. e.Fluorescent Dyes and Pigments absorption wavelength and the fluorescence wavelength. Daylight Fluorescent Pigments. This chapter describes special applications of fluorescent dyes.. in particular xanthene dyes (e. the pH can be measured by treating thin tissue sections with a fluorescent pH indicator. are used as sensitizers in photochemistry [74]. Dyes showing perylene diimide structures. can be titrated with organic mercury compounds using fluorescein as an indicator. The principle of solar collectors is not new. the first plates were mentioned in 1969 [75]. A variety of fluorescent dyes. Solvent Green 5 (47). enabling the absorption and activation of the molecule under UV light. These indicators permit the titration of turbid or colored solutions. For example.. Interesting benzazole derivatives showing such properties are shown in structure 60.6) [78]. sugars.g. the fluorescent dye is adsorbed to the surface of the precipitate and undergoes a clearly recognizable change in fluorescence at the end point. Compounds 64 and 65 are particularly interesting fluorogenic compounds because they produce intensely fluorescent derivatives. are used in the testing of materials to detect microflaws in the surfaces of metals. and 2hydroxy-3-naphthoic acid (67) [92-70-6]. Reagents used to synthesize fluorescent derivatives for chemical analyses Name CAS registry number Naphthyl isocyanate (61) [86-84-0] alcohols and amines 1-Dimethyl-5-naphthalene-sulfonyl chloride (dansyl chloride) (62) [605-65-2] amines and phenols Fluorescein isothiocyanate (FITC) (63) [27022-45-3] amines. For example. Test strips coated with fluorescent probes have attained considerable importance in medical diagnostics [81]. and proteins 1. and sulfates of highly fluorescent phenols with pKa values between 6 and 9 such as 4-methyl-7-hydroxycoumarin (66). OPTA) (64) [643-79-8] primary amines N-4-(2-benzimidazoyl) phenylmaleimide (BIPM) (65) [27030-97-3] thiols Other fluorescent probes are used to determine the partial pressure of oxygen. such as thiamine [80]. fluorescein (17). phosphates. amino. Fluorescence-based immunoassays have also been developed (! Diagnostic Reagents). viscosity. Interference caused by the addition of foreign fluorescent probes can often be avoided by exploiting the intrinsic fluorescence of many natural products. [79]. etc.2-Benzenedicarboxaldehyde (o-phthalic anhydride.14 Fluorescent Dyes and Pigments Table 2. the membrane potential. theophylline in serum may be determined by this method. . Suitable substrates are provided by the carboxylic acid esters. Enzyme activity can be measured by allowing enzymes to act on a substrate to produce an intensely fluorescent product. Structural formula Derivatized compounds Enzyme Substrates. acids. the redox status. the degree of lipophilicity. or ordinary pigments (e. Dyes generally are soluble in the application medium. glucose and galactose) are important in determining the activity of enzymes that cleave sugars. Covalent bonding between perylene chromophores and the guest silicon-based carrier results in right robust and finely dispersed emitting particles [86–88]. Esters formed from compound 66 and longchain fatty acids are commercially available and are suitable for measuring the activity of carboxyl esterases. Daylight Fluorescent Pigments 13. 15 fluorescent pigments consist of finely divided resin particles that contain daylight fluorescent dyes. the time interval between light absorption and emission is very short (108 s). Z0 substituents are alkyl chains with most preferably 16 to 20 carbon atoms.g. consistent of silicon-based sol/gel glass as an inorganic carrier. Since compound 67 fluoresces very intensely at 460 nm. Inorganic. the rate at which the intensity of fluorescence increases can be used to measure enzyme activity (direct continuous kinetic assay) [82].1. polyol esters. In structure 68. or with phosphorescent pigments. Their luminosity and brilliance make them particularly useful if intense or long-distance visibility is needed. The matrix has a high affinity for the dye. while pigments are practically insoluble.1. Production Most daylight fluorescent pigments are composed of one or more fluorescent dyes and a solid dye-carrying substrate or matrix. 13. see also ! Pigments.g. Most daylight Daylight fluorescent pigments are mainly applied due to their peerless brightness. Fluorescent toners or fluorescent melting pigments have a distinct solubility. As a rule. and motor oil [83]. Dyes Pigments for Daylight Fluorescent Pigments and dyes are distinguished from each other by their solubility in the application medium. thereby protecting it from environmental hazards. and the fluorescence persists only in the presence of an exciting light source. polyalkylene glycols. End of the 1990s more advanced mechanically resistant structures have been prepared. These pigments should not be confused with UV fluorescent pigments. . Oil Fluorescent Markers Naphthalimide dyes with long alkyl chains found technical importance due to their solubility in a variety of organic compounds such as mineral oil.Fluorescent Dyes and Pigments The glycosidic ethers of these phenols formed with a variety of sugars (e. which continue to emit light in the dark. but they are not solubilized by solvents in the final application and have a very low or negligible migration. The palmitic acid ester of compound 67 exhibits very weak fluorescence at 400 nm and is cleaved to palmitate and 67 by the enzyme lipase. a variety of other markers emitting at longer wavelengths have been synthesized as lipophilic fluorescent dyes. UV absorbers. which only fluoresce under UV light. either to obtain optimal brightness or in combination with conventional pigments in order to brighten applications with conventional colors. Beside the greenish yellow fluorescent naphthalimide markers.1. More advanced molecules of this category of naphthalimide dyes are reported in [84]. Daylight fluorescent pigments absorb UV and visible light from daylight and reemit it at a higher wavelength as visible radiation. phthalocyanines or titanium dioxide) are sometimes also included. but selected grades of polymers are usually used as matrices. 13. General. 1... Fluorescent pigments can be prepared by adsorbing fluorescent dyes onto the surface of fine silica gel particles [85]. the Z. Optical brighteners. Table 4.1 to 10 wt %. As a result. a liquid resin [92] or a molten wax [93]. Mixtures of fluorescent dyes very often emit light at a higher intensity than that produced by the separate dyes. which is emitted additionally to the normal reflection of not Table 3.2. the visibility is up to three times higher than that of a comparable conventional – not fluorescent – hue. This results in the formation of spherical pigment particles. Crystalline polyester resins suitable for producing fluorescent pigments [97] are called “melting fluorescent pigments” and are mainly used for coloring olefins. and the physical or chemical bonding between the utilized dyes and the resins.5 wt %. Further reaction yields a highly cross-linked. Examples of pigment reflectance at different wavelengths are listed in Table 4. 91]. % Blue Green Lemon Orange Red Magenta 455 520 535 605 615 625 75 115 169 225 203 171 . which solidifies when cooled and is then pulverized to give a fine pigment powder [90. the dye. nm Reflectance. Since their market introduction. The concentrations of the dyes in the matrix range from ca. older generations of fluorescent pigments showed different disadvantages [89]. fluorescent pigments have always been stir-in pigments. and violet dyes. Many dyes exhibit daylight fluorescence. The fluorescence quenching and migration of the dyes out of the carrier are much more difficult to influence and to control at high dye concentrations. This is due to the conversion of a portion of the absorbed light to light at the hue-wavelength. Sensitized fluorescence is one of the basic principles used in the production of fluorescent pigments and occurs when a portion of the excitation energy of one dye is transferred to a second dye with similar electron energy levels. Other matrices are based on benzoguanamine–formaldehyde resins which are prepared by emulsion polymerization in an aqueous phase [94]. For further details of bulk and emulsion polymerization. a theoretical white surface reflects a maximum of 100% of the incident light (practically around 97%). Germany) at 25% in acrylic resin at a film thickness of 12 mm Color Maximum emission wavelength. 13. Red fluorescent xanthene dyes exhibit the highest emission intensity at a concentration of ca. The pigments may also be prepared by emulsion polymerization. Pigment Matrices Most fluorescent pigments are based on toluenesulfonamide–melamine–formaldehyde resins that are prepared by bulk polymerization. orange. Despite this main advantage.1. Spectrophotometric parameters of daylight fluorescent pigments of the ARACO 10 series (ARALON GmbH. pink. the most important are listed in Table 3. and magenta shades are obtained by mixing yellow. this is due to sensitized fluorescence. pink. The pigment performance depends on the resin (major impact). 0. Pigments based on polyamide [95] and polyester matrices [96] show high heat resistance. At specific wavelengths. As can been seen in Figure 1. daylight fluorescent pigments reflect more light than a white surface does at that wavelength. and the interaction. see ! Polymerization Processes. Yellow naphthalimide dyes may be added at a concentration of up to 10 wt % without causing appreciable quenching.16 Fluorescent Dyes and Pigments 99% of current fluorescent pigments are solid solutions of fluorescent dyes in resins. whereas daylight fluorescent pigments can show a total reflection of over 220 % at the hue-wavelength. 0. for instance. colored resin. Dyes for daylight fluorescent pigments Pigment CAS registry number Color Solvent Yellow 44 (2) Solvent Yellow 160 : 1 Basic Yellow 40 Basic Violet 10 (18) Basic Red 1 (19) Acid Red 52 (20) [2478-20-8] [61902-43-0] [12221-86-2] [81-88-9] [989-38-8] [3520-42-1] yellow greenish-yellow greenish-yellow pink pink pink absorbed parts of the illuminating light. in which the colored precondensate is further reacted after being mixed at high speed into. but very few are useful for making pigments. The fluorescent dyes are added at different stages of the polymerization process. Bright fluorescent yellow. The second dye is thus excited (sensitized) and fluoresces. red. Radiation-Curing Systems. many similar carriers were utilized. 17 bound dyes is overwhelming. Sunlight Sensors A range of fluorescent pigments was developed which fade at a controllable rapid rate in response to light exposure. Recent developments are based on thermoset polyesteramide chemistry.3. Chap. Paint Systems. Acrylic-based fluorescent nanoparticles were prepared by modifying different dyes. formaldehyde-free fluorescent pigments have been developed mainly for coloring olefins [103].10-tetracarboxylic diimides and their polymerization in acrylic resins is reported in [107]. Potential applications range from ensuring that fluorescent safety materials have retained their high visibility to the production of temporary ‘self-erasing’ markings [105]. Fluorescent Modifications with Covalently Bound Dyes The number of novel syntheses of fluorescent particles and preparations based on covalently Figure 2. paints. Fluorescent dyes used in cross-linked polymer particles [106] . cosmetic and noncosmetic grades of solvent resistant.1. arising especially at high temperatures. mainly perylene dyes with ethane groups. PVC. 3. For this purpose. rubbers. 13.4. 2) are reported in [106]. These formaldehyde-free pigments overcome the problem of formaldehyde out-gassing. Due to their low or absent migration in PVC and PU. PU. 7. Formaldehyde-Free and SolventResistant Fluorescent Pigments Initially. formaldehyde-free pigments were developed [104]. Beside the above-mentioned polyester resins [97]. and compounds containing hydroxyl groups [101] have also been used as pigment matrices.Fluorescent Dyes and Pigments For radiation-curable fluorescent ink bases see [98] ! Paints and Coatings. urethane resins derived from isocyanates. Cross-linked polymer particles containing fluorescent dyes (Fig. The synthesis of polymerizable perylene3. looking on the amount of submitted patents and publications. which polymerize into the acrylic matrix through radical polymerization [102]. Advanced fluorescent plastic colorants with very low plateout allow longer production runs on the injection molders [99]. They can be used to produce light exposure or fading indicators which can be easily read with the naked eye. they need to be heat-resistant. Claimed is a fluorescent pigment containing a polymer matrix based on PMMA and an apolar fluorescent dye of the coumarin or perylene series.1. Possible applications are plastic safety materials.5. 13.4. which deal with this subject.9. but high solvent resistance is not required.1. 13. Nonplasticized poly(vinyl chloride) and its copolymers [100]. The matrix is a cross-linked poly(meth) acrylate prepared by suspension polymerization. and printing inks. 3) are reported in [108]. fluorescent chromophores are reported.9.I. pigment properties. especially light stability and heat stability might differ within the same group. with bright yellow color. Lyotropic polyamide carboxylic acid esters with perylene dyes units in the main chain are shown in Figure 4 [110].18 Fluorescent Dyes and Pigments Figure 3.6. 13. The chemical structure of a mesoionic molecule [113]. 13. Special series are available for most applications to satisfy the specific requirements of processing techniques and formulations. and solid-state fluorescence is shown in Figure 6. 48052 [2387-03-3] shown in Figure 5 [111]. One example is the well-known Pigment Yellow 101. Sometimes. and heat differ within the various groups. Other modifications of Pigment Yellow 101 were synthesized and examined [112]. Quality Specifications of Fluorescent Pigments Daylight fluorescent pigments are offered in a series of colors with carriers having often the same basic structure. The novel functionalized perylenetetracarboxylic acid diimides and the use of the colored and/or fluorescent polymers (Fig. A novel and interesting solid-state fluorescent perylene pigment with strong orange red fluorescence is shown in Figure 7 [114]. which lose part of their substituents upon heating. C.10-tetracarboxylic acid diimides are used as initiators and/or coreactants for polymerization reactions. which are strong enough for industrial applications. Example of polymeric colorant [108] Functionalized perylene-3.4. The chromophores were bonded to the polymer following the newly developed shear approach and imidized after orientation. light. . solubility. resistance to solvents. Heat is applied to decrease their solubility and restoring their pigment properties in some carriers [116]. More-Not Resinated-Solid-State Fluorescent Pigments Very few pure crystalline pigments have daylight fluorescent properties. Series showing low efflorescence or migration of the low-molecular-mass fraction of the resin and no efflorescence or low migration of the dyes are preferred. Properties as color strength. particle size.1. In addition to the above-mentioned variations of solid-state fluorescent pigments. Novel liquid-crystalline poly phenylene ether (PPE)–naphthalene copolymers display blue solid-state fluorescence [109]. Switchablesolid-statefluorescenceisdepicted by fluorenone-based host compounds [115]. Important factors in recent years concern safety issues. While long alkyl chains are known from previous studies to increase the solubility of the perylene chromophores attended by a decrease of the pigment character of the molecules.2. short alkyl chains support the pigmentary character. Polymers with solid-state fluorescence [110] Fluorescent Dyes and Pigments 19 .Figure 4. safety clothing. Fluorescent pigments are generally fine powders with a particle size of 2–10 mm. Chemical structure of Pigment Yellow 101 Figure 6. and Using more sophisticated coating systems with special layers in addition to the UV absorbing one Long light stability to indoor light exposure is generally given. Mesoionic fluorescent organic yellow pigment [113] Adding UV absorbers Using higher pigment concentration Increasing the thickness of the application Using a top coat. They are easily dispersed in commonly used binders. For offset printing or stationary applications.g. especially for the highquality grades on the market. marker-pens. and rapid identification are important. and especially sport shoes has been noticed. Since the 2000s. Due to their nature. Typical applications are the marking of danger areas. resin vehicles. Novel solid-state fluorescent perylene pigment [114] The right choice and development of the suitable matrix for the utilized dye and application is the major quality distinction between different available grades on the market. and textiles). detergent packaging. As UV-responsive colors. consumer goods. sport clothes. ambulances. fluorescent pigments have always been stir-in pigments. security. in entertainment decorations and in automating processes. Light stability problems are countered in the final application via: Figure 5. aircrafts. a white undercoat is recommended for optimal brightness results. submicron dispersions are available [117]. The wide demand for daylight fluorescent pigments has resulted in the development of special products for printing. As a result of their striking visual impact. Applications of Fluorescent Pigments Figure 7. coating. traffic signs and cones. safety jackets. and symbols on slow-moving vehicles. nail varnish. almost all available grades do not require further grinding in the final application. . which includes UV absorbers. daylight fluorescent pigments are used to enhance a wide range of products (e. Fluorescent pigments are used where safety. high visibility. and food contact applications. cosmetic. painting. 13. as well as for publicity and advertising. coated papers. face and body painting. the correct choice of the right pigment for the right application is crucial and requests a high qualified technical communication on all sides of the supply chain. Cosmetic grades have found their applications in traditional cosmetic articles like lip sticks. naval vessels and buoys. and polymers. just mixing is sufficient to obtain homogeneity and finely dispersed preparations. packaging.3. these pigments are employed in the coding and tracing of documents. High control of the production parameters and all influencing parameters are required in order to guarantee consistent quality and avoid application problems. a very wide utilization in toys. 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