1198
J. Phys. Chem. 1981, 85, 1198-1202
Fluorescence Quenching of Solubilized Pyrene and Pyrene Derivatives by Metal Ions in SDS Micelles J. C. Dederen, M. Van der Auweraer, and F. C. De Schryver' Department of Chemistry, University of Leuven, Celestijnenkran200 F, B-3030 Heverlee, Belglum (Received: October 20, 1980; In Final Form: December 3 1, 1980)
A kinetic model describing the fluorescence quenching of micelle-solubilized probes including intermicellar quencher exchange is tested in detail with pyrene and pyrene derivatives as fluorescent probes, 10 metal ions as quenchers, and SDS as soap. The rate constants obtained are discussed,with emphasis on kqm,the micellar quenching rate constant. An empirical model and a theoretical model for the first-order micellar quenching rate constant are compared; both lead to excellent agreement with the experimental observations. Introduction In a preceding paper' we reported a detailed investigation of the quenching of 1-methylpyrene fluorescence by Cu2+in sodium dodecyl sulfate (SDS) micellar solutions. The results were analyzed in terms of a kinetic scheme published by Infelta et al. and Tachiya.2 This model proved to be unsatisfactory and had to be extended by an additional process: the direct exchange of quenchers between micelles. This process was already introduced in micellar electron-transfer kinetics3but remained unnoticed in fluorescence experiments. In this paper we present and discuss results obtained with various probe-quencher combinations using the extended kinetic model. The Model Scheme I lists the possible processes with exclusion of probe exchange between micellar and aqueous medium on the fluorescence time scale,4 where P, is a micelle containing one probe and n quenchers (asterisk superscript if excited); Mi is a micelle containing j quenchers; Q is a quencher (subscript a indicates aqueous; m, micellar, and t, total) (1) [Qtl = [&a1 + [&,I ko (s?) is the reverse fluorescence lifetime in the absence of quenchers. kq, (s-l) is the quenching rate constant, linearly dependent on the number of quenchers per micelle:2 kqm(n) = nkqm(1) (2) 12' (M-l s-l) is the quenchers adsorption rate constant. k(s-l) is the quenchers desorption rate constant, linearly dependent on the number of quenchers per micelle:2 k-(n) = nk-(1) (3) 12, (M-I s-l) is the rate constant for the direct quencher exchange between micelles, linearly dependent on the number of quenchers on the donating micelle: (4) k,(n or j ) = ( n or j)k,(l) One obtains eq 5 for the fluorescence decay after &pulse excitation: I ( t ) = A1 exp(-A2t - A3[1 - exp(-A4t)]) (5) (1) Dederen, J. C.; Van der Auweraer, M.; De Schryver, F. C. Chem. - - . -, 68. - -, 451-454. - - - - - -. -Phvr. T d t . 1979. (2)(a) Infelta, P.P.; Gratzel, M.; Thomas, J. K. J . Phys. Chem. 1974, 78,190-195. (b) Tachiya, M.Chem. Phys. Lett. 1975,33,289-292. (c) Infelta, P. P. Chem. Phys. Lett. 1979,61,88-91.(d) Yekta, A,; Aikawa, M.; Turro, N. J. Chem. Phys. Lett. 1979,63,543-548. (3)(a) Frank, A.J.;Gratzel, M.; Kozak, J. J. J.Am. Chem. SOC.1976, 98,3317-3321.(b) Henglein,A.; Proske, T. Ber. Bunsenges. Phys. Chem. 1978,82,471-476.( c ) Moroi, Y.;Braun, A. M.; Gratzel, M. J. Am. Chem. SOC.1979,101,567-572. (d) Moroi, Y.;Infelta, P. P.; Griltzel, M. J. Am. Chem. SOC.1979,101,573-579. (4)Almgren, M.; Grieser, F.; Thomas, J. K. J. Am. Chem. SOC.1979, 101,279-291. .-g-.
Scheme I process
P,*
+
P,
fluorescence
P,*
+
P,
quenching
Pn*
+
Qa
Pn+1*
quencher adsorption
Pn* + Qa + Pn-,* P,* + Mj + Pn+i* + Mj-1 P,* + Mj + Pn-i* + Mj+l
quencher desorption
+
quencher exchange
(supply1 quencher exchange
(removal)
j , n = 0 , 1 , 2, . . .
where A1 is the fluorescence intensity a t t = 0, I(0)
(7) A4 = k,,
+ It,[M] + k-
(8)
where [MI is the micellar concentration. If we assume a constant aggregation number ( N ) and critical micellar concentration (cmc), [MI is give?by [SDS] - cmc [MI = nr lvagg
(10) K = k + / k - = ~Qml/([Qa1[MI) Experimental Section All metal ions were obtained from Alfa-Ventron as their chloride salts (highest purity available) with exception of silver nitrate. (Nitrate is a weak quencher of pyrene in water and does not quench at all in anionic SDS micelles.) These salts were used as supplied. SDS (Merck, fur biochemische Zwecke) was recrystallized from P.A. methanol in the presence of activated charcoal. Pyrene (PO,Aldrich 99% +) and 1-methylpyrene ( P l , reduction of l-pyrenecarboxaldehyde Aldrich) were purified by high-pressure liquid chromatography. Solutions were prepared by transferring about 1 pL of a M stock solution of the fluorescent compound to a 10-mL volumetric flask and adding appropriate volumes of soap and quencher solutions and sonicating the mixture for 15 min in a warm bath (Martin Walther Sonamatic 150). All measuring samples were degassed by repeated freeze-pump-thaw cycles.
0022-3654/81/2085-1198$01.25/00 1981 American Chemical Society
The Journal of Physical Chemistry, Vol. 85, No. 9, 1981
Quenching of Pyrene Fluorescence in SDS Micelles
1199
TABLE I'
k', 109
k -9 105
ke,
l"s'
k 18?'
kqmChd,
d,,
107 A decay K S-I Nag b 0.415 1.84 1.6 5 85 1.6 5500 Eu3+ ,
