2514
G. OSTER,G. K. Ostrmi, AND G. I ~ R G
Vol. 66
EXTREMELY LOIL’G-LIVED INTERMEDIATES IN PHOTOCHEMICAL REACTIONS OF DYES IN NON-VISCOUS MEDIA’s2 B Y GERALDOSTER, GISELAKALLMANN
OSTER, AND
GERHART &RG3
Department of Chemistry, Polytechnic Institute of Brooklyn, Brooklyn, N . Y . Receined M a y 26, 1962
Halogenated fluorescein dyes in the presence of tertiary amines are photochemically dehalogenated by visible light. With longer wave lengths of illumination iodine atoms may be removed but chlorines remain. Dechlorination takes place with shorter wave lengths. Selective dehalogenation also can take place using white light when properly chosen amines are present. I n all case8 an unstable yellow intermediate with a lifetime of the order of seconds is formed. It is postulated that the intermediate is a semiquinone which decomposes spontaneously to yield dark-stable partially dehalogenated species. through a chromous chloride solution. Nitric oxide (Matheson Co.) was purified with sulfuric acid and potassium hydroxide solutions according to the method of Moser.7 Procedures.-Photochemical conversion of the dyes was accomplished by illuminating with visible light from a shde containing a 500-watt tungsten lamp (General mild reducing agent such as allyl thiourea. We projector Electric CZX) and a glass filter (Corning 3-73) which rehave extended this work recently using various moves light of wave lengths shorter than about 400 mp. secondary and, particularly, tertiary amines as Provision was made to both dellerate and stir the solutions by electron donors for the light excited dyes. It has passing nitrogen through the samples. To obtain oxygenconditions, the solutions were flushed with nitrogen for been found previously with thiazine dyes that these free 15 min. prior to and during the irradiation. amines participate in photochemical reactions to When a continuous recording of transmittance versus time give the leuco thiazine.‘j With the halogenated was required, the light passing through the sample was fluoresceins, however, certain of the amines also filtered with a propriate glass and interference filters and output of t i e detector (Type 2A-L6 Hoffman Electronics cause a photodehalogenation. These reactions the Corp. silicon photovoltaic cell) registered on a Varian Asare selective as to which halogen atoms are re- sociates Type G-10 recorder. moved from the light-excited dye molecules. In Transient phenomena were studied with two different seta the course of these studies we further noted that in of apparatus. For studies at 550 mp with rose bengal (FlIdCL), the dye chosen for most of these studies, the continuthe early stages of the photodehalogenation there ously recording apparatus described above was employed. is some reversibility in the dark and that the reac- This apparatus also included sliding mechanisms for quickly tion involves the formation of yellow intermediates interposing or removing filters placed before or after the sample. After a brief (3 sec. or less) strong illumination having a lifetime of the order of seconds. white light the analyzing filters ( i . e . , filters between the It is the purpose of the present paper to describe with sample and the detector) were removed and an identical set the process of photodehalogenation, to identify of filters was interposed between the light source and the the stable products produced, and to try to estab- sample. I n this way the dark recovery of the species produced during the strong illumination could be recorded. lish the identity of the intermediate. The other apparatus, a single-beam recording monochromator, consisting of a Bausch and Lomb grating monochroExperimental Materials.-The dyes (fluorescein, 2’,7’-dichlorofluore,s- mator with an RCA 1P21 multiplier phototube as the deteccein, 4’,5’-dibromofluorescein, 4’,5’-diiodofluorescein, 2 ,- tor and a Leeds and Northrup Speedomax recorder, has been 4’~5’,7’-tetrabromofluorescein, 2’,4‘,5‘,7‘-tetraiodofluores- described elsewhere.8 Here the transient species was cein, 2’,4’,5’,7‘-tetrabromo-3,4,5,6-tetrachlorofluorescein,measured at a variety of wave lengths. The procedure was 2’,4’,5’,7’-tetraiodo-3,4,5,6-tetrachlororfluorescein)were ob- to interpose, after a brief strong illumination, neutral density tained either from Eastman Kodak Go. Organic Chemicals filters between the light source and the sample, and to record or from Allied Chemical and Dye Corporation. Hereafter, at each wave length the time-course of the decay of the these dyes are referred to as F1, FlCle, FlBrr, FlI2, FlBr4, transient species. The same arrangement was employed to Fl14, FlBrrCla, and FlIdCL, respectively. The dyes were em- measure the dark recovery a t various wave lengths. All light sources and recorders were operated through ployed as the sodium salts. Those dyes obtained from Eastman (reagent grade FlClz and FlL, practical F1 and FlBrS) voltage stabilizers (Sola Electric Co. transformers). The were available only in the acid form so that in these cmes spectra of stable species were determined in a Cary Model 11 the sodium salt was prepared. The remaining dyes from recording spectrophotometer with 1 cm. path length cells. The pK values of the dyes were obtained by the usual Allied were histological grade. Triethanolamine and nitrilotriacetic acid were Eastman technique of plotting the optical density of the dyes at apReagent grade. Ethylenediaminetetraacetic acid, disodium propriate wave lengths as a function of pH and reading the salt, was Dow Chemical Co. reagent grade. Anhydrous pK from the inflection point of the resulting sigmoidal curve. Chromatographic Rr values were obtained by a descending N,N,N’.N’-tetramethylethylenediaminewas obtained from method using Whatman No. 1 paper with 88% ammonia, Ames Laboratories, South Norwalk, Conn. Oxygen, helium, and prepurified nitrogen were obtained ethanol, and water in the proportion of 5 : 10:85 by v ~ l u m e . ~ Electrophoretic mobilities were determined on a Research from Airco. The nitrogen was purified further by passing it Specialties Model E-800-2B paper electrophoresis apparatus. Whatman No. 1 paper wm employed and the determination ( 1 ) Supported by the United States Air Force through the Air was carried out in 0.1 M phosphate buffer a t pH 8.0 with an Force Cambridge Research Laboratories under Contract No. AF applied potential of 250 volts.
Introduction Previous work in our L a b ~ r a t o r y has ~ . ~ demonstrated that fluorescein and its halogenated derivatives undergo photofading in the presence of a
lQ(604)-8056. (2) Taken in part from the dissertation of Cerhart Karg to be suhmitted to the Faculty of the Polytechnic Institute of Brooklyn in partial fulfillment of the requirements for the degree of Doctor of Philosophy. ( 3 ) National Science Foundation Predootoral Fellow. 1958-1961. (4) C. Oster and A. H. Adelman, J. A m . Chem. Soc., 7 8 , 913 (1958). ( 5 ) A. H. Adelman and G. Oster, (bid..78, 3977 (1933). ( G ) G. Oster and N. Wotherspoon, zbid., 79, 4836 (1937).
Results The values of absorption maxima, pK’s, Rt numbers, and electrophoret,ic mobilities of the (7) L. hfoser, Z . ona2. Chem., 6 0 , 401 ( 1 9 1 1 ) . ( 8 ) N. Wotherspoon and G. Oster, J. A m . Chem. Suc.. 79, 3992 (1957). (9) I
