addition of sieves. These data are shown in Figure 3. It is evident that 2-bromobutane was not adsorbed by 5-A sieves. The nonadsorption of secondary alkyl bromides was further confirmed by the exclusion of the reaction product of 11-tricosene with hydrogen bromide. Examination of Synthetic Blends. Because of the lack of pure olefins in the C M range, the impurities used to blend with 1-tetradecene were isolated from a commercial C14 alpha-olefin. The impurities were separated by contacting the alpha-olefin with 5-A Molecular Sieves for 18 hours a t the reflux temperature of 2,3-dimethylbutane. After removal of the solvent, the impurities were blended into API I-tetradecene. It can be seen from Table I1 t h a t there is good agreement between the actual normal alphaolefin content of the sample and the normal alpha-olefin determined by this method. Hydrobromination Analysis of Alpha-Olefin Samples. Table I11 is a comparison of the analysis of alphaolefin samples by the hydrobromination and infrared techniques (8). The samples that were analyzed were formed by an ethylene polymerization process. Since the olefins contain little if any
2-8ROMOBUTPNE
1
lSoPENTANE
ORE S I E V E S )
ACKNOWLEDGMENT
lLENE
2;.
employed; whereas, the infrared technique wiIl be in error to the e,utent of non-beta-branched alpha-olefin.
2-BROMOBUTANE
1
ISOPENTPNE
The author grat.efully acknowledges Robert E. Snyder for technical advice, Paul M. Brown for providing the gas chromatographic analysis, and Eleanor L. Saier for providing the infrared data. LITERATURE CITED
NAPHTHALENE
10 190
8
6
164
138
4 I12
2 86
0 TIME-MIN 60 TEMP-*C
Figure 3. Programmed chromatograms of 2-bromobutane and naphthalene in isopentane
non-beta-branched alpha-olefins, there is good agreement between the methods of analysis. I n the future, when normal alpha-olefins are prepared by other processed especially wax cracking, and nonbeta-branched alpha-olefins are present, the hydrobromination technique may be
(1) Barrer, R. M., J . Chem. SOC. Ann. Rept. X I Z , 44, (1944). (2) Kharasch, M. S., Hinckleng, J. A . , Jr. , J . Am. Chem. SOC. 56, 1212 (1934). (3) Kharasch, M. S., Mayo, F. R., Ibid., 55,2468 (1933). (4) Kharasch, M. S., McNab, M. C., Mayo, F. R., Ibid., p. 2531. (5) Kharasch, M. S., Potts, W. M., J . Org. Chem. 2, 195 (1937-8). (6) Nelson. K. H., Grimes, M. D., Heinrich, B. J'.,ANAL.CREM.29,1026 (1957). (7) O'Connor, J. G., Norris, M. S., Ibid., 32, 701 (1960). (8) Saier, E. L., Cousins, L. R., Basila, M. R., Zbid., 35, 2219 (1963). (9) Saier, E. L., Pozefky, A., Coggehall, N. D., Ibid., 26, 1258 (1954). (101 Schwartz. R. D.. Brasseaux. D. J.. Ibid., 29,1022 (i957j. RECEIVEDfor review July 19, 1963. Accepted August 26, 1963. Division of Petroleum Chemistry, 145 Meeting, ACS, Kew York, K. Y., September 1963.
Reflectance Fluorescence Spectra of Aromatic Compounds in Potassium Bromide Pellets B. L. VAN DUUREN and C. E. BARD1 Institute of Industrial Medicine, New York University Medical Center, New York, N. Y.
b The reflectance fluorescence excitation and emission spectra of solid aromatic compounds were measured in potassium bromide pellets in the concentration ranges 0.00002 to 0.2 mmole of compound per gram of potassium bromide. In some instances the fluorescence spectra were identical with those of solution spectra, whereas in others the maxima were shifted to longer wavelengths. For some hydrocarbons the appearance of the spectra was concentration-dependent. The fluorescence excitation and emission maxima of solid charge transfer complexes were also measured in potassium bromide pellets.
T
fluorescence spectra of dilute solutions of aromatic hydrocarbons have in recent years been investigated extensively (17') and are often used in analytical work (18). However, comparatively few studies have been carried out on the fluorefcence characteristics ocaromatic hydrocarbons in solid form. HE
2198
ANALYTICAL CHEMISTRY
The fluorescence of solids has been studied using powdered crystalline materials (13, 1 4 ,single crystals (18, 16), microcrystalline suspensions (6), and microcrystalline deposits on glass plates (2). In the present work the fluorescence of solid aromatic hydrocarbons was investigated in potassium bromide pellets. The pellet technique was first developed for infrared absorption spectrometry and it is noF widely used for this purpose. More recently pellets were also used for ultraviolet and visible absorption spectrometry (IO,19). The reflectance fluorescence method was developed for the examination of weak charge transfer complexes of biological interest. Such application will be described elsewhere. In the course of this work a number of observations were made on the fluorescence of solids and these are examined in this report. The method also offers the obvious advantage that absorption, fluorescence, and infrared spectra can be measured on the same sample.
EXPERIMENTAL
Purification of Aromatic Compounds. All compounds used in this
work were purified by one or more of the following procedures: column chromatography, crystallization, and vacuum sublimation. Purity was established by melting points, ultraviolet absorption spectra, and the absence of other fluorescent compounds as shown by thin-layer chromatography on silica gel plates ( 1 ) (solvent: cyclohexane-benzene, 1:1). Preparation of Periflanthene [Diindeno (1,2,3-cd:1',2 ',3'-1m) p e r y l e n e ] . This hydrocarbon was prepared by selfcondensation of fluoranthene with sodium amide in xylene ( 7 ) . The compound was purified by vacuum sublimation t o give red crystals (m. p. > 360" C.). Anal. Calcd. for CSHM: C, 95.97; H, 4.03. Found: C, 96.08; H, 4.03. 1,3,5-Trinitrobenzene. Commercial grade material (K & K Laboratories, Jamaica, N. Y.) was purified by repeated crystallization from 957, ethyl alcohol (m.p. 123-5" C.).
I:4
b Figure 2. Fluorescence emission spectra of dibenz(a,h)anthracene
.. . .. .
1 0.2 mmole per gram KBr. Primary filter 7 - 5 4 . Secondary filter 3-75. Excitation at 3 0 0 mp -2 Same as 1 but at 0.0002 mmole per gram KBr DBA in cyclohexane soh3- tion, 0.004 mmole per liter
-
Figure 1. Sample area for measurement of fluorescence of aromatic hydrocarbons in KBr pellets
RFI
1.
Sample area of Farrand spectrofluorometer Sample hcllder KBr pellet 4. Slit 5. Monochromatic exciting light 6. Fluorescence emitted 7. Secondary filter 2. 3.
Solvents. T h e solJent used in t h e measurement of solution spectra was spectroscopic grade cyclohexane (Matheson, Coleman and Bell, East Rutherford, N. J.). I1ithe preparation of pellets fluorometric grade benzene (Hartman-Leddon Co., Philadelphia, Pa.) was used. Potassium bromide. Infrared quality potassium bromide (Harshaw Chemical Co., Cleveland, Olio) was used for t h e preparation of pellcts. Fluorescence Instrumentation.
d
Farrand automatic recording spectrofluorometer (Farrand Optical Co., Inc., New York, N. Y.) equipped with a high intensity 150-watt i c . xenon arc (Hanovia Lamp Division, Newark, N. J.) was used. Slit widths were Table 1.
Compound Naphthalene Anthracene Phenanthrene
adjusted according to requirements. The pellets were examined with proper choices of glass color filters (Corning Glass Works, Corning, K.Y.) and were also compared with spectra obtained without filters. A 1P28 multiplier phototube was used for all measurements. Solution spectra were measured in a quartz fluorescence cell (10 X 10 x 50 mm.). Potassium bromide pellet spectra were measured using potassium bromide disks, 0.7 to 1.0 mm. thick, 13.0 mm. in diameter, which were prepared with an evacuable potassium bromide die. The die is the same as that used for infrared spectrometry (Research and Industrial Instrument Co., London, England). The pellet was placed on a black nonfluorescent
,', 400
I 450
'Le
--
530
5
I
Wavelength, rnp
metal holder, the same as that used for the examination of paper chromatogram strips (Farrand Optical Co.). The positioning of the pellet with respect to incident light and fluorescence emitted is shown in Figure 1. The pellet is positioned a t an angle of 30' n-ith respect to the incident beam. This angle is preferable to the 45' angle. in that specularly reflected incident light will be greater a t the 45' angle. With the arrangement shown here the
Fluorescence Emission Spectra of Solid Aromatic Compounds
Concn., Filtersa mmole/g. KBr Primary Secondary 0 02-0 2 0 05 0.00002
r -
/-a4 1-64
0-54 3-75
0.00002-0.2
7-51
1-64
Excitation wavelength, m p
Emission maxima, mp
Emission maxima reported, mp
315 375
340 348b 425, 447, 475(sh), 515(eh), 427, 445. 470, 505(sh),c 550(sh) 448, 475, 535, 5 7 3
3i0
390,405,430,455
See text
388, 408, 433, 460,c385, 415, 434, 460, 485* 417, 440, 462* 410,430, 463, 491b 475b 4751 497. 520. 547(shY
Chrysene Fluorene Pyrene Fluoranthene Benzo(a)pyrene
0.00002-0.02 7-54 3-75 300 405,425,450 0.00002-0 .02 7-54 0-5 1 315 405, 428,452, 475 0.02-0.002 1-64 3-75 370 463, 485(sh) 0.00002-0 02 1-64 3-i5 385 438(sh), 460,495(sh) 0 02 7-54 3-75 360 480, 505(sh) 0.00002 7-54 0-51 360 387; 405; 425, 450, 485(sh) Dibenz(a,h)anthracene 0 2 7.54 0.52 375 428, 450, 470, 505(sh) 424, 452, 472, 505, 54.Y 0.00002 See Figure 2 Perylene 0 0002-0 05 7-59 3-70 3i5 535(sh), 568 579b Benzo(g,h,i)fluoran0.2 1-64 3-75 395 465,487 ... thene 0.00002 1-64 3-75 395 425, 452,465,487,520 Periflanthened 0.001 ... 3-69 410 590, 620(sh) ... Tricy cloquinazolinee 0.01 7-39 3-72 355 530, 565 ... a Color glass filters (Corning Glass Works). Other filter combinations can in. some instances be used. (12).
e D-
Measurements mad€,on an energy-recording spectrofluorometer (14) by D. T. Palumbo, Sylvania Electric Products, Inc., Towanda,
sa. a
Synthesis described under Experimental. Obtained from R . W. Balddn, Cancer Research Department, The University, Nottingham, England. ~
_ _ _ _ _ _ _ _ _ _ _ _ ~
VOL. 35, NO. 13, DECEMBER 1963
2199
I
385 463 478
Wavelength, m i
Figure 3.
Fluorescence emission spectra of pyrene
-1
-2 3-
--
0.2 mmole per liter in cyclohexane 20 mrnoles per liter in cyclohexane 0.0025 mmole per gram KBr
incident beam covers the entire area of the]-pellet. Dibenz(a,h)anthracene in cyclohexane and quinine sulfate in water were used to calibrate the spectrofluorometer for intenqity (16'). All spectra were measured a t room temperature. Ultraviolet Absorption Instrumentation. These spectra were obtained with a Beckman DU spectrophotometer equipped with an automatic recording unit (Process and Instruments Co., Brooklyn, X. Y.)using 10 X 10 X 50 mm. quartz cells. Preparation of Pellets. T h e pure hydrocarbon or heterocyclic, in M eights ranging from 1 to 10 mg., mas crushed and miyed in an agar mortar with 200 mg. of potassium bromide. Smaller amounts of hydrocarbons, 1 fig. to 1 mg., were added to 200 mg. of potassium bromide as aliquots of dilute solutions of the hydrocarbons in benzene folloa ed by freeze drying. The pellets nere prepared directly from these mixtures. For the preparation of trinitrobenzene compleses the donor and acceptor in equimolar proportion; (0.01 mmole of each) nere dissolved in benzene (1 ml.) and added to 200 mg. of potassium bromide. Benzene \\a3 removed in a high vacuum, the residue was crushed and mixed, and pellets were prepared as described above. RESULTS AND DISCUSSION
The fluorescence spectra obtained with 13 solid aromatic compounds in potassium bromide pellets are given in Table I. Concentration Effects and Sensitivity. K i t h i n the range of concentration examined the following hydrocarbons did not show changes in 2200
ANALYTICAL CHEMISTRY
fluorescence emission spectra with change in concentration: naphthalene, chrysene, fluorene, fluoranthene, and perylene. However, anthracene, phenanthrene, benzo (a)pyrene , dibenz(a,h)anthracene, and benzo(g,h,i)fluoranthene exhibit concentration effects similar to the quenching and reabsorption phenomena encountered with solution spectra (16). Anthracene shows at 0.00002 mmole per gram of potassium bromide a new peak a t 405 mp, whereas the other peaks shonn in the table become weaker peaks or shoulders on the 405-mp peak. Bowen and Lawley (6) measured the fluorescence of microcrystalline suspensions of anthracene. They found that the shorter wavelength maxima, a t 405 and 425 mp, become more intense as the anthracene particle size decreases; a t the smallest particle size examined, the spectrum is similar to that of anthracene in solution. The present findings with anthracene pellets and concentration dependence parallel Bowen and Lam ley's (6) finding with particle size. Phenanthrene shows the same series of peaks throughout the concentration range examined, but at high dilution (0.00002 mmole per gram of potassium bromide) the 390-mp peak, which is a shoulder a t higher concentrations, becomes the most intense peak. Benzo(a)pyrene shows a notable concentration dependence. At high concentration (0.02 mmole per gram of potassium bromide) it shows a single maximum a t 480 mp with a shoulder at 505 mp. A t high dilution the series of shorter wavelength
maxima appear. Concentration dependence in the case of dibenz(a,h)anthracene is illustrated in Figure 2. Concentration effects were not examined for periflanthene and tricycloquinazoline. The fluorescence of solid hydrocarbons in pellets could be recorded without difficulty in most instances at concentrations as low as 0.00001 mmole per gram of potassium bromide, with the proper choice of filters. The order of fluorescence intensity for anthracene, fluorene, fluoranthene, benzo(a)pyrene, chrysene, and dibenz(a,h)anthracene, all a t concentrations of 0.00002 mmole per gram of potassium bromide, is the same as that of a dilute solution of dibenziqh) anthracene containing 4 X mmole per nil. of cyclohexane. Concentration-fluorescence intensity relationships were not examined. Comparison with Solution Spectra. Xaphthalene. pyrene, fluoranthene, and tricycloquinazoline show the same emission spectra in potassium bromide pellets and in solution. The pyrene pellet fluorescence spectrum corresponds to that of a concentrated solution (20 mmoles per liter) of pyrene in cyclohexane (Figure 3). This is expected, since pyrene is known to undergo excited state dimerization in concentrated solution (11). Benzo(a)pyrene and dibenz(a,h)anthracene show the same maxima in pellet spectra at low concentrations and in solutions in cyclohexane, This identity in solid and solution spectra is shown in Figure 2 for dibenz(a,h)anthracene. The solid and solution spectra (16) are different for : anthracene] phenanthrene, chrysene, fluorene, perylene, and benzo(g,h,i)fluoranthene. I n all these cases there is a shift to longer wavelength in going from the solution to the solid spectrum. The excited state dimerization of pyrene and other hydrocarbons in concentrated solutions was discussed recently by Birks and Christophorou 13, 4). They point out that emissions occurring a t longer wavelengths in concentrated .elutions and in solids are due to dimer formation. Excitation Spectra of Solids. Most of the hydrocarbons examined showed useful excitation spectra. T h e fluorescence excitation and emission spectra of fluorene are given in Figure 4. Fluoranthene. which shows the same emission spectra in the solid and in solution, exhibits a shift to longer wavelength in the excitation spectrum of the solid compared to a solution (Figure 5). However, a t 1011-concentration (0.00002 mmole per gram of potassium bromide) the major excitation peak occurs a t 355 mg corresponding to the solution excitation spectrum (curve 2, Figure 5). Benzo(a)pyrene shows, a t lorn concentrations, excitation maxima a t 365 and
~
Excitation
~~
~~
Emission
Excitation
E ni 5 s ion
I I
RFI J
RF I
350
400
450
500
Wavelength, r n l
Figure 4. fluorene
Fluorescence spectra of KBr pellet of
0.00002 mniole per gram KBr. Primary filter 7-54. Secondary filter 0.51. Excitation with emission a t 410 m k Emission with excitation a t 3 1 5 m p
390
1
400
350
450
400
450
500
51
l"/aVelength, rrp
Figure 5.
Fluorescence spectra of fluoranthene
10.01 mmole per gram KBr. Primary filter 1-64. Secondary filter 3 - 7 5 . Excitation with emission at 4 6 0 mp. Emission with excitation at 3 8 5 m p 2.. 0.07mmole per liter in cyclohexane. Excitation with emission at 4 4 0 mp. Emission with excitation at 3 6 0 mp
. . ..
385 mp which agree with the ultraviolet absorption and fluores :ence excitation maxima of dilute solut ons. Similarly, dibenz(a,h)anthracene shows, a t low concentration, excitation maxima a t 297 and 325 mp with a shoulder a t 340 rnw corresponding t o the excitation and absorption spectra of solutions (16). Single-Crystal and Powder Spectra.
Sangster and Irvine (I$ reported on the fluorescence spectra oi a number of aromatic hydrocarbons as single crystals. The values taken from their work, and shown in Table I, were read from their published curves and will therefore be approximate. The general nature of their spectra is in agreement with that found in th3 present work. The other reported va ues were measured on an energy-rectording spectrofluorometer with powdered materials. The instrument used for this purpose and the method have been described in detail (14). These results are in agreement with the measurements made on pellets in the present work with a different instrument. The fluorescence excitation and emission spectra obtained with powdered phenanthrene a t room temperature are shown in Figure 6 for comparison with that obtained with the pellet, given in Figure 7 . Schmillen (IS) and Sponer (16) recently reported on the luminescence of solid aromatic h:ydrocarbons as polycrystalline powder:; and as single crystals. Energy transfer is of importance in the examination of the fluorescence of mixtures of solids and was examined for chrysen1:-perylene mixtures ( I S ) . These and other related
I
390
3M
340
360
380
380
400
j
I
OM
440
460
Wavelength, n p
Figure 6.
Fluorescence spectra of powdered phenanthrene
Measured with constant energy instrument (Perkin-Elmer Corp.) (9). Emission with excitation at 3 4 0 m p
VOL. 35, NO. 13, DECEMBER 1 9 6 3
2201
(8, IO). I n cases where reported values are available, they are in good agreement with results obtained on pellets, but there are some shifts in the emission maxima. The pellet method is also expected to be useful in the examination of weak charge transfer complexes, which may not be observed in dilute solutions (6, 9).
Emission
Excitation
ACKNOWLEDGMENT
The authors are indebted to D. T. Palumbo, Sylvania Electric Products, Inc., Towanda, Pa., for kindly esamining the fluorescence spectra of several powdered hydrocarbons with a PerliinElmer Model No. 195 constant energy spectrofluorometer and to R. W. Baldwin, Cancer Research Department, The University, Nottingham, England, for kindly supplying a sample of tricycloquinazoline. Periflanthene was synthesized by J. A. Bilbao, formerly of these laboratories.
RFI
LITERATURE CITED
(1) Bekersky, I., ANAL.CHEM.35, 261
(1963). (2) Birks, J. B., Cameron, A. J. W., Proc. Roy. SOC.249A, 297 (1959).
1 400 Wavelength, mp 1
450
500
(3) Birks, J. B., Christophorou, L. G., Nature 196,33 (1962). (4) Ibid., 197, 1064 (1963). (5) Booth, J., Boyland, E., Orr, S. F. D., J . Chent. SOC.1954, 598. (6) Bowen, E. J., Lawley, P. D., Nature 164, 572 (1949). (7) Braun, J., von, Manz, G., Ber. 70,1603
5 0
Figure 7. Fluorescence spectra of phenanthrene in potassium bromide pellet 0.02 mmole per gram KBr. Primary filter 1-64. Secondary filter 3-75. Excitation with emission a t 410 m p Emission with excitation ot 370 rnb Spectrofluorometer (Farrand Optical Co.)
(1937). ( 8 ) Czekalla, J., Briegleb, G., Herre, W., 2.Elektrochem. 63, 712 (1959).
(9) DeSantis, F., Giglio, E., Liquori, A. M., Ripamonti, A,, Nature 191, 900
studies indicate the difficulties involved in the measurement of the fluorescence of solids, since minute traces of impurities readily influence the appearance of solid fluorescence spectra. However, with the powerful methods of purification and establishment of purity of materials, such as thin-layer chromatography, this difficulty can be readily overcome. Fluorescence of Charge Transfer Complexes. Czekalla, Briegleb, and
Herre (8) have measured the absorption and fluorescence maxima of frozen dilute solutions of the charge transfer complexes formed between aromatic hydrocarbons and several strong acceptors, including 1,3,5-trinitrobenzene. In the present work the reflectance fluorescence excitation and emission maxima of several trinitrobenzene complexes with aromatic hydrocarbons were examined. Some of these maxima are given in Table I1 together with the reported values
( 1961 ). (10) Dexar, M. J. S.,Lepley, A . R., J . Am. Chem. SOC.83, 4560 (1961). (11) Forster, T., Kasper, K., 2. Elektrochem. 59, 976 (1955). (12) Sangster, R. C., Irvine, J. W., J . Chem. Ph s 24, 670 (1956). 3) Schmilyen, A. , “Luminescence of Organic and Inorganic Materials,” p. 30, H. Kallmann and G. M. Spruch,
eds., Wiley, Kew York and London,
1962. 4) Slavin,
W., Mooney, R. W., Palumbo, D. T., J . O p t . SOC.Am. 51, 93
(1961). 5) Sponer, H., “Luminescence of Organic and Inorganic Materials,” p. 143,
H. Kallmann, and G. M.Spruch, eds., Wiley, New York and London, 1962. (16) Van Duuren, R. L., ANAL.CHEM.32, Table II. Absorption and Fluorescence of Solid benzene Complexes (MP)
Hydrocarbon Naphthalene Anthracene Phenanthrene P rene FYuoranthene 4 KBr pellet.
2202
Solutions a t Absorption 377 463 3 73 422 (10)”
...
ANALYTICAL CHEMISTRY
- 190” C. (8) Emission 513 610 52 1
*.. ...
KBr Dellete at room temperature Excitation Emission 375 462 373 460 360
530 570 530 560 530
1436 (1960). (17) Van Duuren, B. L., Chem. Revs. 63, 325 (1963). (18) White, C. E., Weissler, A., ASAL. CHEM.34, 81R (1962). (19) Wyman, G. X IJ . Opt. SOC.Am. 45, 965 (1955).
RECEIVED for review July 1, 1963. hccepted August 23, 1963. The spectrofluorometer used in this work was purchased through a field investigation grant, No. CS-9577 from the Public Health Service, National Institutes of Health of the U. S. Department of Health, Education and Welfare, National Cancer Institute. Work sup orted by grant C5946 from tile National Eancer Institute, ~ a t i o n aInst ~ itutes of Health, Public Ilealth Ser\.icc,.
