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98 Acc. Chem. Res. 199 1,24 , 98-103Dye-Surfactant Interactions and Their Applications

ERMANNOARNI,*IERO AVARINO,nd GUIDOVISCARDIDipart im ento di Chimica Generale ed Organica App l ica ta, Universi td di Torino, Corso Mass imo D'Azegl io 48 , 10125 Torino, Italy

Received Apri l 5 , 1990 (Rev i sed Manuscr ip t Rece ived Novem ber 26, 1990)

During the first decades of th e 20th century, organicchemistry an d the che mis try of dyes and intermediatesdeveloped together an d could hardly be d ifferentiated.Later, the study of dyes, particularly color-structurerelationships, drew from structu ral and physical organicchemistry, including resonance theory, MO methods,and electronic spectra.T he principal a pplica tion of dyes is in the colorationof subs trate s, typically textiles. During the dyeingprocess, synthetic fibers require surfac tants or otherorganized assemblies such as micelles, vesicles, or layers.Such auxiliary agents will probably continue to be im-portant in the coloration of materials resulting fromcurrent a nd fu ture developments in fiber science andtechnology.T he application of binary dye-surfactant systems,together with an understanding of the interactionswithin them , is also relevan t to othe r scientific fields,including analytical chemistry, photography, lum ines-cence, and lasers. Of particular interes t are amp hiphilicdyes for which the concepts of color and surface-ac tiveproperties coexist within the same molecular frame-work.Dyeing Systems

For the coloration of polymeric substrates, three m aintechniques are employed. T he oldest and most widelyknown is the dyeing process which involves the transfe rof dyes by diffusion throu gh dy ebath s, adsor ption ontothe molecular surfaces of substrates, and f in d diffusionwithin the structure s of the subs trates. Covalent bondsmay be formed during th e transfer process. More re-cent techniques include the mass coloration (dope-dyeing) of synthetic polymers and th e printing of fabricswith print pastes. T he above processes need thepresence of auxiliaries to optimize the dy e uptak e byth e substra tes. Many of these auxiliaries have am -phiphilic structures.The physical chemistry of the dyeing process hasreceived muc h attentio n in th e last 40 years, and manytheories of dyeing have been proposed. Exp erime ntalmethods are mainly based (i) on the analysis of dyeuptake curves (the rate of dye transfer from t he b athinto the substrate) and (ii) on the analysis of dyeingisotherms (the position of the sorption-desorptionequilibrium a t infinite t ime). Th e state of the art inthis area is described in refs 1an d 2. Our work is aimed

Ermanno Ea r n i obtained his B.A. and Ph.D. at th e University of Turin,where he is currently Professo r of Dye Chemistry and Organic Applied Chem -istry. His research interests include synthesis of heterocyclic intermediatesand dyes and dye-surfactant interactions.Pier0 Savarino obtained hi s B.A. at the University of Turin, where he iscurrently Associate Professor of Industrial Chemistry. Hi s research interestsinclude dyeing mechanism s and spect rosc opic properties of intermed iates,dyes, and surfactants.Guido Viscardi obtained hi s B.A. at th e University of Turin, where h e iscurrently Researc h Fellow of Industrial Chemistry. Hi s research interestsinclude the synthesis of novel dyes and functionaiized surfactants and theirtechnical applications.0001-4842 I9 1 10124-0098$02.50O

at elucidating the complex interactions in th e terna rydye-fiber-surfactant system , with a view to optim izingthe tinctorial Th is Account describes someof our results with disperse, cationic, an d am phiphilicdyes.Seventy years ago disperse dyes were introdu ced forthe dyeing of cellulose secondary acetate and subse-quently were found to be advantageous for the colora-tion of other synthetic fibers. In particular, dispersedyes proved to be the principal class of dyes suitablefor the dyeing of polyester, the production of whichconsequently began to grow on a worldwide scale. T hestruc ture s of disperse dyes range from sim ple anthra -quinone derivatives 1 to more complex heterocyclicsystems 2. Th ey are sp aringly soluble in water (10-100

@::@H OH1

2mg/L) and therefore require the presence of a dis-persing agent, which enhances their solubility.12 Th eseagen ts work by producing energy barriers which main-tain dispersions in their metastable condition, thusavoiding the coalescence of dispersed pa rt i~ 1e s. l~t isstill a ma tter of de bate by which mechanism the dyeis released from the micellar pseudophase to effectsorption by the fiber, i.e., whether via direct contactbetween micelles an d fiber surface or via adsorp tion ofsingle molecules from th e continuous aqueous phase.A technically important interaction of surfactant sys-tems with dyes is repres ented by t he m illing of dyes to(1 ) Zollinger, H. Color Chem istry; VCH: Weinhein, 1987.(2 ) Johnson, A. The Theory of Coloration of Te xtiles; Society of Dyers(3 ) Bami, E.;Savarino, P.; Di M odica, G.; Carpignano, R.; Papa, S. S.;(4 ) Barni, E.; Savarino, P.; Carpignano, R.; Larovere, R.; Giraudo, G.( 5 ) Carpignano, R.; Savarino, P.;Barni, E.; Clementi, S.; Giulietti, G.(6) Savarino, P.; Viscardi, G.; Barni, E.; Pelizzetti, E.; Pramauro, E.;(7 ) Savarino, P.; Viscardi, G.; Barni, E.; Carpignano, R. Dyes Pigm.(8) Savarino, P.; Barni, E.; Viscardi, G.; Carpignano, R.; Di M odica,(9 ) Savarino, P.; Barni, E. ; Viscardi, G.; Carpignano, R.; Anselmi, U.(IO) Savarino, P.; Carpignano, R.; Viscardi, G.; Barni, E.; Ferrero, G.(11)Savarino, P.; V iscardi, G.; Carpignano, R.; Bami, E. Colloids Surf.(12) Jones, F. J.SOC.Dyers Colour. 1984, 100, 6 .(13) Rosen, M. J. CHEMTECH 1985, 292.

and Colourists: Bradford, 1989.Giraudo, G. Dyes Pigm. 1984,5, 15 .Dyes Pigm. 1985, 6, 83.Dyes Pigm. 1985,6, 189.Minero, C. Ann. Chim. (Rome) 1987, 77, 285.1988, 9, 295.G. J. SOC.Dyers Colour. 1988, 104, 125.A n n . Chim. (Rome) 1988, 78, 179.Ann. Chim. (Rome) 1988, 78, 381.1989, 35, 251.

0 1991 American Chem ical Societv

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Dye-Surfactant Interactionsproduce suitable subm icron-size particle^.'^ For furtherinformation on the charac teristics of disperse dyes, ontheir use, and on the role of surfactant additives indyeing processes, see refs 1,2, and 15-19.We have proposed the use of double-tailed surfac-tants and sonication to set up d yebaths for the dyeingof polyester fabr ics with disperse dye 3.20 Th is dye was

d y n ec m-70

60

50

40

Ace. Chem. Res., Vol.24, N o. 4, 1991 99---

--

CI

CI CH33

designed by chemom etric procedures for its excellentfastness qualities, including lightfastness.21 A seriesof co mp arative test s using cationic, anionic, and non-ionic single- and doub le-tailed additives were carriedout with th e dye a nd th e additives simultaneously so-nicated in the bath. Th e best results from the pointof view of both bath exhaustion and uniformity ofcoloration were obtained with very low concentrationsof DDDAC (didodecyldimethylammonium chloride).T he use of doub le-tailed cationic sur facta nts as ad-ditives in d yeing processes was also shown to be suc-cessful in th e dyeing of polyacrylon itrile with cationicdyes. Typically dyes having high affinity an d low mi-gration properties ca n p roduce superficial saturation ofthe anionic sites (sulfonate, sulfate, carboxylate) andan unequal d istribution of th e dye on the substrate.Hence colorless cations, which com pete with the dyesfor the anionic sites, are currently added.22 Fur ther-more, in a wide comparative test with C.I. Basic Red18 4, the use of DDDAC as additive exhibited by far thebest retarding and leveling proper tie^.^^ We stress theL I

CH, X-4

reciprocal beneficial effect ob tained by th e utilizationof tech niques from other scientific areas, such as useof ultrasonics and the evaluation of the effects of sur-fac tan t s wi th t ri st imulus co l~ r i m e t ry .~ ~In our studies on amphiphilic dyes, we have inves-tigated th e behavior of some model azo dyes. Am phi-(14) Colour Ter ms and D efinitions; Society of Dyers and Colourists:Bradford, 1988.(15) Dawson, J. F. Reu. Prog. Color. Relat. To p. 1978, 9, 25.(16) D atyner, A. Surfa ctants in Tex tile Processing; Marcel Dekker:New York, 1983.(17) H allas, G. In Developments in the Chemistry and Technology ofOrganic Dyes; Griffiths, J., Ed.; Blackwell Scientific Pub lications: Ox-ford, 1984.(18) Dawson, J. F. Reu. Prog. Color. Relat. T o p . 1984, 14 , 90.(19) Trotman, E. R.Dyeing and Chemical Technology of TextileFibres; Charles Griffin: High Wycombe, 1984.(20) Barni, E.; arpignano, R. ; Di Modica, G.; Savarino, P.; Viscardi,G . J.Dispersion Sci. Technol. 1988, 9, 75.(21) Carpignano,R.; avarino, P. ; Barni, E.; Di M odica, G.; Papa, S.S. J. SOC.Dyers Colour. 1985, 101, 270.(22) Beckmann, W. In The Dyeing of Synthetic-Polymer and AcetateFibres; Nunn, D. M., Ed.; The Dyers Company Publication Trust:Bradford, 1979 Chapter 5.(23) Barni, E.; Savarino, P .; Viscardi, G.; Cargnino, F .; Ferrero, G .;Levis, M. J. Dispersion Sci. Technol. 1988, 9, 309.(24) Billmeyer, F. W., Jr.; Saltzman, M. Principles of Color Tech-nology; Wiley: New York, 1981; p 62.

Y I I

I I I I I I I I I-5 - 4 - 3 - 2 L o g[CI

Figure 1. Surface tension data: (*) dye 5; (*) dy e 6; (A) ye 7;( 0 ) ye 8.

5 10 '5 C, . io5) mole/LFigu re 2. Dyeing isotherm of dye 8: temperature 100 O C ; pH4.8.philic structures are characterized by the presence ofboth hydrophob ic and hydrophilic moieties. Dyes 5-7contain bo th sulfonic and carboxylic groups, whereasthe latter a re absent in dye 8. They are soluble and

COOH

N'HCOR5: R =C3H76: R =C7Hl,7: R =Cl,H23

NHCOR8, R =C7HIb

self-micellizing, as can be observed by plotting theirsurface .tension versus co ncentration (Figure 1).6Theiry efficiency and effecti~eness '~epend on thechain length and th e hydrophilic character of th e polargroups. Th e dyeing isotherms (Figure 2, dy e 8, as anexamp le) show an asym ptotic shape and can be evalu-ated with the Langmuir equation. Th e mechanism ofthis dyeing process is an exchange between dye anionsand fiber gegenions (X-). The maximum acid dye-binding capacity is determined by the number of basicgroups present in the polyamide (see Chapter 11 in ref1). A large number of experiments led us to somegeneralizations abo ut the op timal operative conditions:(a) dyeing tem perature should not be very high (ca. 80"C); (b) long chains are preferred; (c) low pH values

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100 Ace. Chem. Res., Vol. 24 , No. 4, 1991enhance th e dye uptake in the fiber (positive sites areincreased, whereas th e ionization of th e carboxyl groupsis depressed); and (d) the carboxyl group of the dyeseems to participate in the dye-substrate interaction,depending on pH and temperature.Amphiphilic Dyes

In a retrospective look a t am phiphilic dyes, Carbolandyes are of special interest. The ir production evolvedin the 1930s to m eet th e dyeing requirem ents of woolfibers. The se dyes, e.g., Carbolan C rimson B (C.I. AcidRed 138) (9), are simple water-soluble azo dyes intoC I ~ H ~ S @ N = N ~ O ,HCOCH3

S03Na0 0Na3OS9

which a hydrophobic group has been introduced. Theseprovide hydrophobic interactions, thereby preventingdesorption from the fiber and yielding adequate fast-ness to washing.% T he pioneering work on amp hiphilicazo dyes was done by H. E. Fierz-David and W. Kus-ter,26who synthesized a series of dyes of formula 10,with th e alkyl chain R1 covering the full range C1to C19and one or two hydrophilic groups. T he ability of dyes

Barni et al.

NHCOR,IO: R, =CH3 t o C19H39R2 =H, COOHR3 =H, S03HR4=H, S03H

to lower the surface tension of water was system aticallymeasured.Am phiphilic dyes play an im portan t role in classicalcolor photography. In the dye-forming processes,suitable dye precursors (couplers) 11-13 are incorpo-

COOH

\COOH11

12rated in the photographic layers containing the chro-mogenic reaction with th e oxidized developer (e.g., thequinone diiminium ion 14), yielding th e final dye (e.g.,dye 15 with coupler 12). Th e dyes formed w ith 11,12,and 13 are yellow, mage nta, an d cyan, respectively, asrequired for the subtractive color process. T he dyeprecursors have been made nondiffusing in swollen

(25) Meybeck, J.; Galafassi, P. Appl. Polym. Symp. 1971, 18 , 463.(26) Fierz-David, H. E.; Kuster,K. Helu. Chim. ct a 1939, 22 , 82.

H36c17'C-CHXII I

Q ISO3H

12 14RI

AvO3H15

gelatin of the photographic layer by the attachment ofballasting CI7or C18. Th e corresp ondin g loss of solu-bility in th e aqueous gelatinous emulsion is compen-sated by the p resence of sulfonic (or carboxylic) groups.'Cyanine Dyes

If a polyene chain contains at th e extrem e positionsan electron donor and an electron acceptor, the re-sulting chromogen is called polymethine. In cyaninedyes both the donor a nd th e acceptor moieties containa t least one nitrogen atom , which is usually present ina heterocyclic ring. For a more detailed classificationof cyanines and for recent,tr end s in their main app li-cations as sensitizing dyes in p hotography, see ref 27and C hapters 3 an d 14 in ref 1. We have prepared andinvestigated several series of cy anine dyes28-32ontain-ing tuned alkyl chains as described below.T he interaction of organized assemblies with hydro-phobic cyanines has a beneficial effect on the deag-gregation of dyes. Figure 3 shows the spec tra of dye 16,which displays a very broad abso rption in water d ue toth e formation of complex aggregates. T he use of so-

C16H33 C16H3316

nication does not improve th e deaggregation. Inmethanol th e dye is supposed to be in its monomericform. T he spectrum resulting from the addition ofDODAC (dioctadecyldimethylammonium chloride)vesicles to th e aqueous m edium gives evidence for th emarked deaggregation afforded by the organized sur-factant.Surfactan ts have been found to have a n interestingeffect on the pho tostability of dyes. Figure 4 illustrates

(27) Ficken, G. Chem. Ind. (London) 1989,672.(28) Barni, E.; Savarino, P.; Pelizzetti, E.; Rothenberger, G. Helu.(29) Barni, E.; Savarino, P.; Viscardi, G.; Pelizzetti, E. J . Heterocycl.(30) Barni, E.; Savarino, P.;Pelizzetti, E. Nouu. J. Chim. 1983,7,711.(31)Barni, E.; Savarino, P.; Larovere, R.; Viscardi, G.; Pelizzetti, E.(32) Barni, E.; Savarino, P.;Viscardi, G.; Pelizzetti, E. J. Heterocycl.

Chim. ct a 1981,64, 1943.Chem. 1983.20.23.J . Heterocycl. Chem. 1986,23, 209.Chem. 1985,22, 1727.

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Dye-Surfactant Interactions.Ti4

12 -

10 -

6 -

Figure 3. Electronic absorption spectra of cyanine 16: (-) inmethanol (1X lod M) ; (---) in water (2 X loa M) ; (-.-) in water(2 X M) after sonication; (*) in the presence of DODAC (5x IO4 M). Th e water samples contained 5% methanol to enhancethe solubility of the dye.1

I 'II I I I I 1 1 15 10 15 20 25 t [mi"]Figure 4. Bleaching of cyanine 17 irradiated at h 2 300 nm: (I)in water-methanol (5% v/v); (11)with SDS 1.6 X lo-* M; (111)with DODAC (3.4 X M).the bleaching curves of dye 17 under continuous irra-diation with a high-pressure mercury lamp. Whereas

C16H3317

th e aqueous solution decolorized in a very short tim e,the presence of anion ic micelles (sodium dodecyl sulfate,SDS) an d, more ben eficially, of c ationic vesicles (DO-DAC), enhanced the ph otostability by a t least 2 ordersof magnitude.A peculiar feature of amphiphilic cyanine dyes isrepresented by the buildup of layers of dyes accordingto th e technique first developed by I. Langmuir and K.B l ~ d g e t t . ~ ~he basic principles and the potentialityof LB films have been recently o utlined in Accounts.34Recently new sophisticated techniques have been in-troduced for a more complete and reliable characteri-zation of LB o rganized molecular assemblies. A recent

(33)Blodgett, K. B.; Langmuir, I. Phys. Reu. 1937, 1 , 980.(34)Arnett, E. M.; Harvey, N. G.; Rose, P. L. Acc. Chem. Res. 1989,22, 31.

Acc. Chem. Res., Vol. 24, N o. 4, 991 10 1article35 nvestigates in dept h t he correlations of phasediagrams a nd crystallization behavior with the opticalproperties of a mixture of a single-tailed cyanine dye18-stearic acid (cosurfac tant) mixture. This charac-

I ' ICiaH37 CH318

terization employed a variety of methods includingpressure-area isotherms, fluorim etry, absorp tion mea-surem ents, electron d iffraction, and fluorescence mi-croscopy. In particular, the last techniqu e permits adirect observation of th e lateral structu re formation inmonolayers, e.g., during phase transitions.Th e hydrophobic tails of am phiphilic cyanine dyesare usually hydrocarbon chains. Recently struc turalmodification of th e tails has been used t o obtain newinformation on the intermolecular interaction betweenthe hyd rophobic moieties. For exam ple, M. Ma tsumotoand co-workers have substituted th e chains in thesymmetrical dye 19 with the so-called "mesogenicunits", which contain phenylcyclohexyl groups (dye20).36 This substitution results in larger anisotropic

C5H11 C 5H ll20polarizability of th e mesogenic groups. This leads tostronger interaction between the hydrophobic partsbecause of the increased dispersion force and the in-troduction of a permanent dipole. Interesting data havebeen obtained on cluster formation at the air-waterinterface, on in-plane spectral anisotropy of LB filmswith cad mium icosanoate, and co nsequently, on t he flow

orientation of the crystallites a t th e air-water interfaceduring th e deposition process.Analytical Applications

In the presence of dyes (chromophoric reagents) orof colored binary com plexes (sensitized system s), sur -factants have contributed to th e development of newspectrophotometric and fluorimetric methods for t hedeterm ination of micro amou nts of metal ions, anions,(35) Duschl, C.; Kemper, D.; Frey, W.; Meller, P.;Ringsdorf,H.; Knoll,W. J. Phys. Chem. 1989,93,4587.(36) Matsumoto, M.; ekiguchi, T.; Tanaka, H.; Tanaka, M.; Naka-mura, T.; Tachibana, H.; Manda, E.; Kawabata, Y.; ugi, M. J . Phys .Chem. 1989, 3, 877.

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102 Acc. Chem. Res. , Vol. 24, No. 4, 1991N2

Fe (111) f r e ey-1Barni et al.

Sur fac tant m o n o m e r t p t ETE NTATE

Chelate complexFe (111) boundto the m ice l le

MAGNETIC STIRRING TABLE

PERMEATEFigure 5. Scheme of t he micellar-enhanced ultrafiltration device.and biological compounds. Thes e methods are mainlybased on the dramatic microenvironmental changesexperienced by the chromophore (or lumophore) in theorganized media. A review on dye-surfactant interac-tions, with particular attention to connections withanalytical chemistry, has been made by M. E. DiazGarcia and A. S a n ~ - M e d e l . ~ ~fur the r review of or-ganized assemblies in analytical chemiluminescencespectroscopy has been recen tly published.38Analytical problems also include chemical separa tionprocedures. In this respect, dye-surfactant associationsappear to be useful. Micellar extractions and micel-lar-enha nced ultrafiltration have been investigated inth e separatio n of iron(II1) using nonionic su rfact ant/amp hiphilic ligand mixed aggregates. In ref 39 de-scriptions of the techniques and of the experimentalresul ts obta ined by using tuned-chain [ (a lkyl-carbonyl)amino]salicylic acids as ligands are reported.Ligands 21-25 are the dye precursors of the am phiphilicdyes 5-7.40 Figure 5 depicts the scheme of th e mi-

R!HN&oo21 , R =CH,22 , R =CBH,23 , R =C7H1524 , R =CgH1g25 , R =CllH23

cellar-enhanced ultrafiltratio n device. Th e amphiphilicligand ( dye) forms a c helate complex with Fe3+ whichis formally uncharged. Th e latter, in tur n, is stronglybound w ithin t he host micelle made u p by a nonionicor a cationic surfactant. T h e successive removal ofthese aggregates from th e feed solution is achieved byusing an ultrafiltrating membrane having a pore sizesmall enough to reject the micelles. Figure 6 graphicallyillustrates some experimental data .Cationic micelles function better than nonionic mi-celles in the effective removal of th e complexes. Indeed,the same sepa ration efficiency obtained in working witha dy e having a Cll chain in nonionic micelles is achieved(37)Diaz Garcia, M. E.; Sanz-Medel, A. Talanta 1986, 3, 255.(38)Hinze, W. L.; rinivasan, N.; Smi th, T. K.; Igarashi, S.;Hoshino,H. In Multidimensional Luminescence; Warner, I. M., Mc Goun, L. B.,Eds.; JAI Press: Greenwich, CT, 1990;Chapter 8.(39) ramauro, E.; elizzetti, E. Trends Anal . Chem. 1988,7,260.(40) arni et al., manuscript in preparation.

Figure 6. Micellar-enhanced ultrafiltration performances indifferent surfacta nt systems ; nC =number of carbon atoms inR in dyes 5-7: ( 0 ) onionic surfactant CI2Es; *) cationic sur-factant, hexadecyltrimethylammonium nitr ate (HTA N). M em-brane: Spectra-Por C, cutoff molecular weight 10000 daltons;I =0.1 M NaNO,; [HNO,] =0.002; [ligand] =1 X lo-,; [sur-factant] =2 x @; [iron(III)]=1 x lo4.by using th e more soluble C7 erivative in hexadecyl-trimethylamm onium nitrate (H TAN ). Moreover, theuse of a cationic surfa ctan t introdu ces more selectivityin the separatio n, due to th e electrostatic repulsion ofuncomplexed cations which remain in t he aqueous bulkphase. Micellar-mediated techniques afford novelseparation procedures whose advantages include lowcosts, low toxicity of th e aqu eous sur facta nts relativeto organic solvents, and low alteration or denaturationof biomolecules.Miscellaneous

Subjec ts in the area of dye-surfactant interaction sare impressively diverse. Rela ted article s reviewed byChemical Abstr acts during the 1980s are distributedover 20 out of 80 sections. Th ese sections includeSurface-active gents, Dyes ,and Surface chemistry,colloids, as well as Imm unoche mistry , Woodprodu cts, and Energy technology. Clearly there iswide interest in dye-surfactant pairing. He re we de-scribe some selected examples, reporting only a fewreferences from which f urth er bibliography can be de-duced.A high-contrast rapid-processing photographic ma-terial with a su ppo rt and hyd rophilic colloid layers hasbeen proposed. T he silver halide emulsion layer con-tains AgX grains th at are spectrally sensitized withsuitable merocyanines an d a fluorocarbon ~ ur fa c t an t . ~ ~More recently, an analogou s ma terial has been claimedas suitable for laser exposure.42 T he above examplesillustrate applications th at exploit the interactions be-tween sensitizing dyes an d fluorine containing surfac-tants.Dyes in surfactant systems can also function as lu -minescence probes for the investigation of th e str uctu reand dynamics of organ ized molecu la r a~sembl ie s .~~Drastic changes are shown in th e spec tral properties ofdyes when the latter interact with micelles or bilayermem branes (vesicles and lamellae) set u p w ith bioma-terials (lecithin) or with synthetic surfactant^.^^^^^^^^Several examples of this application follow. (1)T h ehighly fluorescent and solvatochormic hydrolysisproduct of the cationic dye C.I. Basic Blue 12 (Nile Blue

(41) anyu, T.; Yorozudo, H. (Konica Co.) Jpn. Kokai Tokkyo KohoJ P 62,265,651 7,265,651; hem. Abstr. 1988, 08, 213837~.(42) no, K. (Konica Co.) Eur. Pat. Appl. EP 318,936; hem. Abstr.1990, 12 , 14201j.(43) urro, N. . Chem. Abstr. 1987, 06, 3345h.(44) endler, J. H. Chem. Br. 1984, 098.(45) Fendler, J. H.; Tundo, P. Acc. Chem. Res. 1984, 7, .

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Dye-Surfactant InteractionsA, a biological stain ) is a useful probe of th e surfa ctan tphase of a C7H16-Aereosol OT- H20 reverse micellarsystem with th e total luminescence spectroscopy (TLS)technique.a (2) Liphoph ilic, solvatochromic dye probeshave contributed to th e spectroscopic determination ofthe effective dielectric constants of the interfacial regionof several ionic and nonionic micelles.47 (3 ) T h e dam-age of h ea t stress (followed by suble thal recovery) onthe permeability barrier of the outer membrane ofEscherichia coli cells has been ev aluated by using thefluorescent dye N-phenyl-l-naphthylamine.48 4)Acolor reaction between 3,4,5,6-tetrachlorogallein-Mo(V1) complex in a Tri ton X 405-poly(vinyl alcohol)micellar medium and human serum albumin has re-sulted a highly sensitive method for it s d e t e r m i n a t i ~ n . ~ ~( 5 ) T he entrapping of dyes and drugs and their solu-bilization, stabilization, and release into a surroundingenvironment have been studied in photosensitivephospholipid vesicles,% n soy bean phosphatidylcholineoligolamellar liposomes an d pota to mitochondria:l inlysolecithin micelles and lecithin liposomal mem-and in carboxyfluorescein-loadedvesicles.53 Incontrast, one group has concluded tha t cyanine dyes didnot prove to be suitable probes for sensing th e plasmamembrane potential in yeasts.54Rhodamine 6G (26) is by far th e most used dye fordye lasers. Several hund reds of dyes have been em-+ .H E , C ~ W J ~ ~ ~ ~ N H C ~ H S

Ace. Chem . Res., Vol. 24, N o. 4, 1991 103ployed, allowing operation to occur over a wide spec tralrange (250-1300 nm) with a continuous tunability. Th edyes must have high photochemical stability andfluorescence qua ntum yield. Sur facta nt systems haverecently been combined with dyes. Binary solventsmade up by surfactants are able to solubilize dyemolecules (two to three molecules for each micelle),result ing in a stable colloidal suspension which increasesthe lasing efficiency and the th ermal stability of the dyesolution.55Concluding Remarks and Future Opportunities

In the 1970s progress in th e developmen t of textiledyes appeared to come to a relative standstill. All fiberswere readily dyed in a w ide chromatic range and withexcellent performances. Furthermore, caution pervadedthe produc tion an d the indiscrim inate use of dyes be-cause of the ir possible toxicity, particularly induced byprecursors such a s aromatic am ines.At the beginning of the 199Os, we witness a livelychange in th e situation. Hum ans definitely prefer acolored world, as evidenced by a w orld consumption ofdyes in 1988 of 600 kilotons. Produ ction strategies mu stbe adap ted to environmental requirements, includingthe use of renewable raw materials. T he recent de-velopment of m aterials science presumably will bringout novel substrates which, in tur n, will demand noveldyes an d auxiliaries.For nonconventional, high-technology, specializedapplications of dyes, the demand has increased dra-matically in recent years, and th e dye-surfactant com-bination represents one of the most vital areas oftechnical research and development.In conclusion, it is interesting to note that until recentyears the stud ies of analytical chem ists, physical chem-ists, physicists, biologists, pharmacologists, etc. de-pended on structu res available commercially or by oc-casional contacts. More recently, the use of tailor-madedyes and surfactants has been spreading, an d conse-quently, dialogue with syn thetic chemists has becomecloser. Th is symbiotic and interdisciplinary trend ofresearch offers the best opportunities for the future.

0c00c2H56(46) Sahyun, M. R. V. J.Phys. Chem. 1988,92, 6028.(47) Warr, G. G.; Evans, D. F. Langmuir 1988,4,217.(48) Tsuchido, T.; Aoki, I.; Takan o, M. J. Gen.Microbiol. 1989,135,(49) Fujita, Y.; Mori, I.; Fujita, K.; Nakahashi, Y.; Nakanishi, T. Ya -(50) Tirrell, David A. U S . US 4,833,061; Chem. Abs tr . 1990, 112,

1941.kugaku Zasshi 1987,107,640.14279r.._~(51) Dodin, G .;Dupont, J. J. hys. Chem. 1987,91,6322.(52) Nakagaki, M.; Komatsu, H.; Handa, T. Chem. Pharm. Bull. 1986,

(53) Liu, Z. Y.; Solow, R.; Hu, V. W. Biochim. Biophys. Acta 1988,945,34, 4486.253. (55) Moran, M. B.; Marrs, C. D. Statutory Invent. Regist. US 483;Chem.Abstr. 1988, 109, 180100h.54 ) Wolk, U.; Hoefer, M. Biochem. Int . 1987, 14, 501.