EIJI FUJIMORI
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Two Phosphorescences and Electron Transfer in Dye-Disulfhydryl Compound Complex
by Eiji Fujimori Photobiology Section, Energetics Branch, Space Physics Laboratory, A i r Force Cambridge Research Laboratories, Bedford. Massachusetts (Received October 1, 1964)
Mercaptoethanol and dimercaptopropanol form a complex with a cationic dye. Two dyes interacting with two SH groups in the complex with dimercaptopropanol exhibit two different absorptions and two different phosphorescences. Each one of them, present at a shorter wave length, corresponds to an absorption and a phosphorescence of the complex with mercaptoethanol. The dye-dimercaptopropanol coniplex is more photosensitive than the dye-mercaptoethanol complex. A phototropism observed in the former complex is based on an electron transfer.
Introduction
Materials and Methods
In previous studies,*-3 phototropic behavior of various dye-sulfhydryl conipound coniplexes was investigated. This phototropism was due to a photocheniical reduction of the dye by sulfhydryl compounds in these complexes. Triplet formation of the conjugated dye molecule was shown to be enhanced and this enhancement of triplet state was considered to be induced by a charge-transfer process with the sulfur. Considering characteristics of absorption, fluorescence, and phosphorescence of these complexes, the sulfhydryl Compounds studied so far could be divided into two classes. The first one shows an absorption peak at 520 t n M with a considerable quenching of fluorescence. Proteins containing sulfhydryl group, SOdiuni hydrosulfide, and glutathione belong to this class.2 The second not only absorbs in a shorter wave length region than 520 nib (showing two maxima in some cases), but also fluoresces. A phosphorescence also shifts to a shorter wave length. Thioglycolic acid and cysteine are assigned to the second group.S A further investigation has been extended to a diSulfhydryl compound and has led to a new complex which has characteristics of both the first and second type : two different phosphorescences and two different absorptions. A light-induced electron transfer related to the phototropism of this complex has also been studied.
The yellow dye (Figure l ) , a derivative of 3’,6’dichlorofluoran, was prepared in the same method as reported previously. Mercaptoethanol and dimercaptopropanol (California Corp. for Biochemical Research) were used without further purification. All absorption spectra were determined on a Cary Model 14 spectrophotometer. In order to prevent the further oxidation of sulfhydryl compounds by air in an dkaline medium, a cell was filled with a solution immediately after mixing and closed with a stopper. Fluorescence, phosphorescence, and their action spectra were measured by means of an Aniinco-Keirs spectrophosphorimeter. For the determination of phosphorescence and its action spectra, solutions containing 50% glycerol were used a t liquid nitrogen temperature. Photovoltaic changes were measured by a Kintel digital voltmeter, Model 456B, with readout Model 473A. The cell consisted of a platinum electrode with a saturated calomel electrode as reference. Sitrogen gas was passed through the solution. Electron spin resonance absorption was determined by a Varian V-4502 equipped with 100-kc. field modulation. Ir-
The Journal nf Physical Chemtstry
(1) E. Fujimori, Bull. Chem. SOC.J a p a n , 28, 334 (1955).
(2) E.Fujimori, S a t u r e , 201, 1183 (1964). (3) E.Fujimori, to be published.
Two PHOSPHORESCENCES IN DYE-DISULFHYDRYL COMPOUND COMPLEX
D+
-
94 1
Q-coo-
Figure 1. Dye-dimercaptopropanol complex.
0.6
6
Figure 3. Formation of dye-dimercaptopropanol complex followed by the change of absorption spectra; 0.1 M dimercaptopropanol, 2.5 X M dye, and 1 N NaOH: (1) 20 min. after mixing; (2) 2 hr.; (3) 5 hr.; (4) 24 hr.
0.4 a
6
t
0.2
0
300
400
500
X ( mp) Figure 2. Formation of dye-mercaptoethanol complex followed by the change of absorption spectra; 0.1 M mercaptoethanol, 3.1 x 1 0 + M dye, and 1 N NaOH: (1) 2 min. after mixing; (2) 1 hr.; (3) 2 hr.; (4) 4 hr.; (5) 6 hr.; (6) 24 hr. 3 0 0 4 0 0
radiation was made a t a distance of 10 cm. by a 1-kw. tungsten projection lamp.
Results The reaction of mercaptoethanol with the dye was followed by the change of absorption spectra with time. As illustrated in Figure 2, the complex between the dye and mercaptoethanol, CH2(SD)-CH20H, showed an absorption peak at 490 mp with a shoulder a t 465 mp. The complex between dimercaptopropanol and the dye, CH~(SD)-CH(SD)-CHZOH (Figure 1) resulted in another shoulder at 520 mp in addition to the absorption bands produced by the dye-mercaptoethanol complex (Figure 3). Both complexes exhibit the same green fluorescence. Fluorescence spectra and action spectra for this fluorescence are shown in Figures 4 and 5. In the complex with mercaptoethanol, an excitation at 490 mp caused the fluorescence band to appear at 515 mp and a phosphorescence band a t 600 mp (1 and 3 in Figure 4). The same excitation at 490 mp of the dimercapto-
500
€52
m
X (mp) Figure 4. Fluorescence, phosphorescence, and their action spectra of dye-mercaptoethanol complex; 0.1 M mercaptoethanol, 6.25 X M dye, and 1 N NaOH: (1) fluorescence spectrum (excitation a t 470 m p ) ; (2) action spectrum (fluorescence a t 515 mp); (3) phosphorescence spectrum (excitation a t 490 mp); (4) action spectrum (phosphorescence a t 600 mp).
propanol complex brought forth a new phosphorescence at 645 mp as a shoulder, as well as the same fluorescence at 515 mp and the phosphorescence at 600 mp (1 and 3 in Figure 5). Exciting this complex at 520 mp did give rise only to the phosphorescence a t 645 mp (5 in Figure 5). As is obvious from 4 and 6 in Figure 5, action spectra for these two phosphorescences at 600 and 650 mp are clearly different, showing a peak a t 490 mp for the 600 mp phosphorescence and a peak at 520 mp for the 650 mp phosphorescence. These peaks correspond to the main peak and its shoulder of the absorption spectrum (4 in Figure 3). These results Volume 69,Number S March 1966
EIJI FUJIMORI
942
82-0.72 c 0
> k
5 0.7
z
w n -J
f 0.68 0 300
400
5w
600
X(mpLL) Figure 5. Fluorescence, phosphorescence, and their action spectra of dye-dimercaptopropanol complex: 0.1 M M, dye and 1 N dimercaptopropanol, 2.5 X NaOH: (1) fluorescence spect-rum (excitation a t 490 mp); (2) action spectrum (fluorescence at 510 mp); (3) phosphorescence spectrum (excitation a t 490 mp); (4)action spectrum (phosphorescence a t 600 m&); (5) phosphorescence spectrum (excitation a t 520 mp); (6) action spectrum (phosphorescence a t 650 mp).
20
0
700
40
Figure 6. Change of optical density and electron spin resonance in darkness of irradiated dye-dimercaptopropanol complex ; 0.1 M dimercaptopropanol, 2.5 X M dye, and 1 N NaOH.
- 0.3
~
OFF
OFF
- 0.4 prove the existence of two separate species which can absorb and phosphoresce at two different wave lengths. The dye-mercaptoethanol complex showed no noticeable photobleaching when irradiated with light, while the dye-dimercaptopropanol coniplex bleached in light and regenerated rapidly within a few minutes in darkness. The regeneration reaction after 10 min. of irradiation is apparent in the change of optical density at 490 nip (see Figure 6). A photo-induced electron spin resonance absorption similar to that found in complexes with other sulfhydryl compounds2, was also detected. The decay of this light-induced electron spiri resonance signal in darkness can also be seen in Figure 6. A negative change of the oxidationreduction potential was greater in the dimercaptopropanol coniplex than in the mercaptoethanol complex (Figure 7). This could be expected since the former complex was noticeably photobleached, thus producing the electron spin resonance signal. A recovery of the oxidation-reduction potential in darkness was as quick as the regeneration of a photobleached state and the decay of the dectron spin resonance.
Discussion The complex of the dye with mercaptoethanol containing hydroxy group as a substituent absorbs, fluoresces, and phosphoresces atr the shortest wave length among complexes studied so far. Other sulfhydryl compounds, containing carboxyl group or aniino group, form complexes which have a main absorption in the range 495-505 nip, fluorescence in the The Journal of Physical Chemistry
60
TIME (SECONDS]
-0.6 0
1
I
IO
I
I
I
20 TIME (MINUTES)
I
1
30
Figure 7 . Photovoltaic change of the complexes: X, 0.1 M mercaptoethanol, 5 X M 'dye, and 1 N NaOH; 0, 0.1 M dimercaptopropanol, IO-* M dye, and 1 iV NaOH.
range 530-535 nip, and phosphorescence at 615620 mp. A complex with sulfhydryl proteins absorbs at 520 nip and phosphoresces at 650 nip. Such a variety of spectral characteristics is known in charge-transfer complexes between the same electron acceptor and a number of electron donors. This charge-transfer interaction possibly induces the forniation of triplet state, which gives a triplet emission, phosphorescence. The coniplex with diinercaptopropanol exhibits not only the same absorption, fluorescence, and phosphorescence as in the one with niercaptoethanol, but also another series of absorption and phosphorescence which is siniilar to those found in the coniplex with proteins and sodium hydrosulfide. These two different absorptions and phosphorescences possibly originate from two separate dye niolecules : one interacting with a sulfur a t a middle carbon and
THEPHOTOCHEMISTRY OF METHYLISOPROPYL KETOKE
the other associating with another sulfur at a terminal carbon. It should be pointed out that energy transfer would be possible froni the middle dye molecule fluorescing at 510 mk to the terminal dye molecule absorbing at 520 nip. Less photosensitivity is found in the mercaptoethanol complex than in the dimercaptopropanol complex. The phototropism is related to a lightinduced electron transfer which is evidenced by the change of photovoltaic effect and electron spin resonance absorption. This indicates that the two sulfurs
943
interacting with the same dye molecules differ in the capability of charge transfer. The fact that the same conjugated molecules associating with sulfhydryl groups in a different environment show different spectral and photochemical characteristics would be significant for the function of SH groups in energetics of biological systems.
Acknowledgments. The author wishes to thank Miss Maria Tavla and Mrs. Frances Pearlmutter for their valuable assistance.
The Photochemistry of Methyl Isopropyl Ketone'"
by A. Zahra and W. Albert Noyes, Jr.lb Department of Chemistry, The University of Rochester, Rochester, New York
(Received October 8, 1964)
The photochemistry of methyl isopropyl ketone (3-methyl-2-butanone) is contrasted with that of 2-pentanone since the former, as distinguished from the latter, may not undergo a Norrish Type I1 reaction. The main reactions are those one would expect from photochemical dissociation into radicals but there is also almost certainly some direct dissociation into acetaldehyde and propylene by a process designated by Norrish as Type 111. By the addition of oxygen and of biacetyl it is possible to show that a triplet state as well as a singlet state must be considered in any detailed mechanism of the photochemistry of this ketone. Some suggestions are made as to the role each one plays. Analyses were performed for carbon monoxide, methane, ethane, propylene, and propane. The propylene always exceeds the propane so that these two gases are not formed solely by disproportionation of isopropyl radicals.
The photochemistry of simple ketones leads to a dissociation into radicals2 and the over-all yields may be discussed in terms of the reactions of the radicals formed in primary and in secondary processes. However when one of the groups attached to the carbonyl group has y carbon atoms with attached hydrogen atoms there may be another type of reaction which is nonfree-radical in character and which leads directly to the formation of a methyl ketone and an olefin. This type of reaction was first discovered by Norrish and Appleyard3 and it has become known as a Norrish Type I1 reaction. It was suggested4 that a six-mem-
bered ring formed by internal hydrogen bonding might permit the parent molecule to dissociate directly into acetone and the olefin. Strong evidence that this is (1) (a) This work was supported in part by a grant from the Office
of Aerospace Research, Office of Scientific Research, U. S. Air Force. A. Z. is also indebted to the American Friends of the Middle East, Inc., and to the Mission Department, United Arab Republic, through the U.A.R. Education Bureau in Washington, (b) T o whom inquiries should be addressed a t : Department of Chemistry, University of Texas, Austin, Texas.
D. C. for fellowships.
(2) For a review, see W. A. Noyes, J r . , G. B. Porter, and J. E. Jolley, Chem. Rea., 5 6 , 49 (1966). (3) R . G. W. Norrish and M . E. S. Appleyard, J . Chem. Soc., 874 (1934).
Volume 60, Number 9
March 1066
