Delayed Luminescence from Organic Compounds Induced by X

Chapter 34

Delayed Luminescence from Organic Compounds Induced by X-Radiation 1

Xingzhou Hu and G. David Mendenhall

Downloaded by CORNELL UNIV on September 30, 2016 | http://pubs.acs.org Publication Date: November 12, 1991 | doi: 10.1021/bk-1991-0475.ch034

Department of Chemistry, Michigan Technological University, Houghton, MI 49931

We have observed a delayed emission, ascribed to charge-recombination luminescence, up to 300 min after X-irradiation of simple and polymeric hydrocarbons. The emission was concentrated at red wavelengths (500600nm), and the initial intensities spanned four orders of magnitude. The decay of the emission could be represented adequately (r 0.98-1.00) in every case with a rate law At with 0.6

Φ


~Ί—

10

20

30

10

20

Ε Φ +·* η α> Φ >

2Η

Φ

J

0C

Q_ 30

Time, Min Figure 4. Luminescence decay of u n s t a b i l i z e d PP plaques Xi r r a d i a t e d 3.0 min. Top: samples a t 0°C., with one sample warmed to 30°C a f t e r 5.0 min. Bottom: samples a t 30°C., with one sample cooled to 0°C a f t e r 5.0 min.

Table 4.

Emission decay from X - i r r a d i a t e d poly(propylene) i n d i f f e r e n t atmospheres a

Atmosphere

A, p i n *

Air

1 0 1 1

045 998 012 02 ± 0 .02

0.5-25 0.6-27 1-28

avg

9.097 11.046 8.752 9.6 ± 1 .2

1 0 0 1

039 996 978 00 ± 0 03

1-28 1-28 1-29

avg

8.541 9.111 8.287 8.6 ± 0 4

0 0 0 0

880 885 926 90 ± 0 03

0.5-28 0.6-28 0.6-29

avg

8.433 10.131 7.446 8.7 ± 1 4

Ar

2 r > 0.996 f o r a l l cases. 10 rads/min.

t range, min

X - r a d i a t i o n 5min a t dose r a t e o f 2.71 χ

4

Clough and Shalaby; Radiation Effects on Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

34. HU & MENDENHALL

Delayed Luminescence Induced by X-Radiation

as large as i t was i n a i r . When argon replaced oxygen during the decay of luminescence from X - i r r a d i a t e d t h i n f i l m s of PE, there was l i t t l e e f f e c t on the luminescence i n t e n s i t y . From these r e s u l t s we i n f e r that a non-oxygen-dependent pathway was a major component of the observed luminescence.


In a l l of our X-ray studies the amount of r a d i a t i o n d i d not s i g n i f i c a n t l y change the nature of the sample as determined by other techniques. For instance, UV-visible spectra recorded before and a f t e r i r r a d i a t i o n , or immediately a f t e r i r r a d i a t i o n and a few hours l a t e r d i d not show any s i g n i f i c a n t differences, although we would expect differences to appear on longer standing. E f f e c t of 9.10-dibromoanthracene and fluorene. The anthracene (DBA) i s a well-known chemiluminescence enhancer but had an i r r e g u l a r e f f e c t on the short-term charge-recombination luminescence stimulated with X-rays (Table 5). At very high DBA loadings, we observed previously a 3-fold increase of luminescence compared with samples without DBA a f t e r long-term 7 - i r r a d i a t i o n s . ' The CL from poly(propylene) under other conditions, where reactions of peroxidic species predominate, was greatly enhanced by fluorescent a d d i t i v e s . 7

Fluorene was expected to intercept f r e e - r a d i c a l s to give the 9-fluorenyl r a d i c a l . The reaction of t h i s r a d i c a l with oxygen, followed by subsequent termination r e a c t i o n , were expected to give some excited s i n g l e t fluorenone, which emits l i g h t with a high quantum e f f i c i e n c y . However, the presence of increasing fluorene lowered the i n t e n s i t y of the emission a f t e r X - i r r a d i a t i o n . Possibly the hydrocarbon acts as a trap f o r charge-carriers and depresses the generation of luminescent charge-pairs. Emission wavelengths. Since the emission under study here was rather weak, changed r a p i d l y i n the e a r l y stages, and required large sample areas, we d i d not attempt to use a conventional spectrometer for s p e c t r a l r e s o l u t i o n . We instead measured the f r a c t i o n of l i g h t from i r r a d i a t e d samples that passed through various c o l o r f i l t e r s (Figure 5, Table 6). The measured f r a c t i o n s w i l l d i f f e r from the true f r a c t i o n a l transmittance because of the s p e c t r a l response function of the detector, but p l o t s of the f r a c t i o n s against each other from d i f f e r e n t sources with the same instrument reveal whether the emission wavelengths are s i m i l a r or not. I f the spectra are i d e n t i c a l , the f r a c t i o n s p l o t t e d against each other w i l l f a l l on a diagonal l i n e , independent of the d e t a i l e d s p e c t r a l c h a r a c t e r i s t i c s of the emitter, color f i l t e r , or detector response function. From consideration of the data i n Table 6 and the response curve of the PM tube, which f a l l s r a p i d l y at longer wavelengths, we i n f e r that most of the l i g h t from X- anc 7 - i r r a d i a t e d samples l i e s between 500 and 600nm. This i s s t r i k i n g l y d i f f e r e n t from emission centered around 400-500 nm that i s c h a r a c t e r i s t i c of chemiluminescence from simple hydrocarbons and p o l y o l e f i n s . Thermoluminescence spectra from saturated hydrocarbons commonly d i s p l a y a bimodal d i s t r i b u t i o n with one peak around 500nm.


545


§46

RADIATION EFFECTS ON POLYMERS

Table

5.

Effect

of

DBA a n d F l u o r e n e

Additive,

wt%

A,

on Luminescence

from

X-irradiated

a

Poly(propylene)

m i n "

1

η

DBA:

0.010

3..64

±

0.03

1.. 0 8

+

0 .. 0 1

0.030

4,.00

±

0.30

1.. 0 6 +

0 .. 0 2

0.050

4. .6

0 .. 0 2

0.10

3..10

+ ±

± ± ± ±

0 ,. 0 4

±

1 .. 0 4

0.3 ±

1.. 0 2

0.05

0 .. 0 1

ane:

0.010

6 ,. 5

±

0.3

1 .. 0 8

0.030

5 .. 5

±

0.1

1 .. 0 6

0.050

3,.9

±

0.1

1 ,. 0 4

0.20

3,.2

±

0.1

0 ,. 9 9

Average

parameters

exposure

f o r

separately 0.94

±

3.0

f i t t e d

to

I

min.

Control

a n d showed

(average

-

0 .. 0 2 0 ,. 0 3 0 ,. 0 2

A t "

sample of

3

n

from

3

with

no

decays)

decays

after

DBA o r

A -

7.0

X-ray

fluorene ±

1.1

min"

0.06.


run ,

η


34.

HU & MENDENHALL

Delayed Luminescence Induced by X-Radiation

0

50

100

0

50

100

0

50

100

0

50

100

Figure 5. P l o t s of percentages of detected l i g h t from X- or 7 i r r a d i a t e d materials transmitted through various color f i l t e r s , a. PP with tetramethyldioxetane vs PP with BHN(80°C), b. PP, BHN vs PP, X-ray c. PE, X-ray, vs tetracosane, X-ray, d. Hexatriacontane, X-ray, vs PP, X-ray, e. PE, 7-ray vs PE, X-ray, f. TC ( d i s t i l l e d ) , X-ray vs TC (before d i s t i l l a t i o n ) , X-ray.

Society

American Chemical library 1155 16th St, N.W. Clough and Shalaby; Radiation Effects on Polymers

Washington, D.C. Society: 20038 Washington, DC, 1991. ACS Symposium Series; American Chemical

547

548


(0

H

U Ο I Β Χ

vo

JQ

co

CO

CM

σ\

vo

H

CM m

H en

(0 in

w

I


eu

>1 ΙΟ

, « ΗΗ

ω

Η

Os

m

©

I

χ χ

C ο u

^ ^

σ»

CM

H

CM

ο

VO

H

CO

«H

œ

σ*

00

CM

H

Ο

co

rH

CM m

in in

co

•

CM H

CM

•

H

• CM

Ο

•

CM

CM

I

Η

CM

CO

•

CM

co H

•

•Η ω (0

Φ •M rH •H

M

Ο Ο υ

I

Ο Ο H

CO

Ο

CO

•

m

•

CM

(H

>1

ο

υ

tjs

ι

vo

Ο Ο H

ιη œ

co

CM

œ

VO

Ο I Ο Η

VO œ

vo co

00

in

vo

CM

vo co

I

Ο

os

CO

Ο CM

ιΗ rH

CO

in

os

•

Η

•

•

ο

ο •M >1

φ υ c φ υ ω φ c

(0 Ρ

4

Ck

χ

•

Η

· in

-Ρ

CM ·Η (Ν

•Η 6

ω c (0

as 00

co Ο Ο Η

CO

r-*

in

co vo

Η œ

Ο

Η

Φ

rH

Η CM

Os

CO

u

U Ο

•Μ

Φ

Φ

U « Ο

R* + R H ---> R + H +

+

+

2

RH

+ 2

+

2

+2 Moreover, recombination of e" and a d i c a t i o n RH * would be required to generate an excited RH , which i s h i g h l y improbable on the time scale of our observations. The reaction of e" and R ~fo give R* would be s u f f i c i e n t l y exothermic to produce red l i g h t , although other modes of e x c i t a t i o n , such as fragmentation of a hot o l e f i n from n e u t r a l i z a t i o n of an o l e f i n cation r a d i c a l , are possible. Since cations do not u s u a l l y react with oxygen, we can also explain why samples under ambient conditions exposed to X-rays i n an i n e r t atmosphere show the same luminescence decay subsequently i n oxygen or argon, since the oxygen-sensitive r a d i c a l i s not formed u n t i l a f t e r luminescence has been emitted. Fluorescence emission at v i s i b l e wavelengths has i n f a c t been observed from benzylic r a d i c a l s and from trifluoromethyl r a d i c a l ( c f . PTFE). ,+


+

3 6

3 7

Since the putative r a d i c a l from the charge-recombination process In p a r a f f i n s can react with oxygen to i n i t i a t e autoxidation, the slow release and recombination of deeply-trapped electrons i n i r r a d i a t e d polymers may contribute to t h e i r c h a r a c t e r i s t i c delayed loss of p h y s i c a l properties. » Since the s e l f - r e a c t i o n s of peroxy r a d i c a l s so produced also can lead to chemiluminescence emission, the process i n turn may account f o r the minor, shortwavelength components of the l i g h t from X - i r r a d i a t e d materials i n t h i s study. Conclusions Our experiments show that charge-recombination luminescence from X-ray exposure i s an extremely widespread and e a s i l y measured property of organic compounds under ambient conditions provided that a s u f f i c i e n t l y large sample i s examined. The k i n e t i c s of the decay of the emission are consistent with some current theories of charge transport i n d i e l e c t r i c s . The s e n s i t i v i t y of the X-ray stimulated luminescence decay curves to sample p u r i t y and composition, and t h e i r r e l a t i v e i n s e n s i t i v i t y to atmosphere and temperature, i s behavior that i s e n t i r e l y s i m i l a r to charge-recombination luminescence we described e a r l i e r from a l i m i t e d set of polymer samples a f t e r s t i m u l a t i o n with incandescent l i g h t . The major difference i s that i n the present experiments the emission was observed from every s i n g l e sample that we i r r a d i a t e d . Since X-rays i n contrast to UV-visible photons, are absorbed by materials e n t i r e l y at the atomic l e v e l , the presence of molecular chromophores or impurities i s not necessary f o r chargeseparation to occur. I t i s apparent that e i t h e r charge-recombination luminescence or f r e e - r a d i c a l luminescence may predominate i n saturated organic materials exposed to i o n i z i n g r a d i a t i o n , depending on the time scale Clough and Shalaby; Radiation Effects on Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

551


552

and conditions of examination. The d i f f e r e n t spectra from each source provide a natural way to separate t h e i r contributions and w i l l help us r e l a t e the l i g h t emission to polymer s t a b i l i t y . Acknowledgment


This work was generously supported by Himont USA, Inc. We also thank Dr. Y-S. Chao and Dr. S.M. Fernandez o f S c i e n t i f i c Research Associates, Inc., CT f o r carrying out the fluorescence measurement, and Drs. D.E. Mikkola and S.D. McDowell f o r assistance with the X - i r r a d i a t i o n s . References

1. 2. 3.

4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

Visiting Scientist from the Academia Sinica, Beijing, PRC. a. G.D. Mendenhall, Ang. Chem. Int. Ed. 1977, 16, 225-32. b. G.D. Mendenhall, Ang. Chem. Int. Ed. 1990, 29, 362-73. Visible CL: a. E.M.Y. Quinga and G.D. Mendenhall, J. Amer. Chem. Soc. 1986, 108, 474-8. b. X.C. Sheng and G.D. Mendenhall, 198th American Chemical Society Meeting, Miami Beach, FL, September, 1989, Abstract Org-109. c. S.-H. Lee and G.D. Mendenhall, J. Amer. Chem. Soc. 1988, 110, 4318-23. IR CL: a. Q. Niu and G.D. Mendenhall, J. Amer. Chem. Soc. 1990, 112, 1656-7. b. S.H. Lee, Q. Niu, X.C. Sheng, and G.D. Mendenhall, Photochem. Photobiol., 1989, 50, 251. Proprietary work for Exxon Chemical Co, 1978; see reference 25. K.R. Flaherty, W.M. Lee, and G.D. Mendenhall, J. Polym. Sci.: Polym. Lett. 1984, 22, 665-7 G. D. Mendenhall, H. Byun, and J. E. Cooke, in "Advances in Polyolefins", R. B. Seymour and T. Cheng, eds., Plenum Press, NY, 1987, pp. 405-434. G.D. Mendenhall, H.K. Agarwal and J.M. Cooke, T.S. Dziemianowicz, in Polymer Stabilization and Degradation, ACS Symp. Ser. 280, 1985, pp 373-85. X. Hu, G.D. Mendenhall, and R. Becker, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 1990, 31(2), 323-4. G.D. Mendenhall, S.X. Liang, and Ε. H-T. Chen, J. Org. Chem. 1990, 55, 3697. C.A. Ogle, S.W. Martin, M.P. Dziobak, M.W. Urban and G.D. Mendenhall, J. Org. Chem. 1983, 48, 3728. G.D. Mendenhall, Tetrahedron Lett. 1983, 24, 451-2. X. Guo and G.D. Mendenhall, Chem. Phys. Lett. 1988, 152, 14650. a. H. Fricke and S. Morse, Phil. Mag. 1929, 7, 129-141. b. Radiation Dosimetry, Vol II, F.H. Attix, W.C. Roesch, ed., Academic Press, N.Y., 1966, pp. 167-97. Handbook of Spectroscopy, Vol. I, J.W. Robinson, ed., CRC Press, Inc., Cleveland, 1974, p. 181 and p. 237. A.K. Jonscher and A. dePolignac, J.Phys.C.:Solid State Phys.,1984,17, 6493-6519. G.D. Mendenhall and H.K. Agarwal, J. Appl. Poly. Sci. 1987, 33, 1259 and references therein. S.W.S. McKeever, "Thermoluminescence of Solids", Cambridge University Press, New York, 1985. Clough and Shalaby; Radiation Effects on Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

34.HU&MENDENHALLDelayedLuminescenceInducedbyX-Radiation553

19. 20. 21.


22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35.

36. 37. 38. 39.

a. A. Charlesby and R.H. Partridge, Proc. Roy. Soc. 1963, 17087; 188-206. b. I. Boustead and A. Charlesby, Proc. Roy. Soc. London 1970, A316, 291-302. a. B. Ries, G. Schonherr, H. Bassler and M. Silver, Phil. Mag. 1984, B49, 259. b. F. Stolzenburg, B. Ries and H. Bassler, Ber. Bunsenges. Physik. Chem. 1987, 91, 853. G. Sawa, M. Ieda and K. Kitagawa, Elect. Lett. 1974, 10, 4951. P. J. Wunsche,Macromol.Sci.-Phys. 1984, B23, 65-84. eg. a. M.G. Alonso-Amigo and S. Schlick, Macromolecules, 1987, 20, 795-801. b. R.F. Becker, D.J. Carlsson, J.M. Cooke and S. Chmela, Polym. Degrad. Stab. 1988, 22, 313-323. G. D. Mendenhall, H. Byun, and J. E. Cooke, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 1985, 26, 376-7. G.E. Ashby, J. Poly. Sci. 1961, 50, 99. B.J. Kelsall and L. Andrews, J. Phys. Chem. 1984, 88, 2723-9. a. A. Markiewicz and R.J. Fleming, J. Polym. Sci. B: Polym. Physics, 1986, 24, 1713-24. b. A. Markiewicz and R.J. Fleming, J. Phys. D. Appl. Phys. 1988, 21, 349-55. C.S. Woo, A.P. D'Silva, V. A. Fassel, and G.J. Oestreich, Environ. Sci. Tech., 1978, 12, 173-4. Z.A. Kadir, F. Yoshii, K. Makuuchi, and I. Ishigaki, Polymer 1989, 30, 1425-32. See also ref. 15. J.T. Randall and M.H.F. Wilkins, Proc. Roy. Soc. (London) 1945, 184, 390-407. a. Reference 14b, p. 100. b. W. Lefik, A. Plonka, and J. J. Kroh, Radioanal. Nucl. Chem. 1986, 101, 267-73. a. P.W. Klymko and R. J. Kopelman, Chem. Phys. 1983, 87, 75. b. L.A. Dissado, Chem. Phys. Lett. 1986, 124, 206-210. W.H. Hamill, J. Phys. Chem. 1978, 82, 2073-7. a. K. Toriyama, N. Keichi and M.J. Iwasaki, Am. Chem. Soc. 1987, 109, 4496-4500. b. D.W. Werst and A.D. Trifunac, J. Phys. Chem. 1988, 92, 1093-1103. c. A.D. Trifunac, D.W. Werst and L.T. Percy,Radiat.Phys. Chem 1989, 34, 547-552. From ΔΗ f(t-Bu ) = 167 kcal/mole, ΔH (t-Bu˙) = 8.4 kcal/mole, . andε(PP)=2 we calculate e + t-Bu ---> t-Bu˙ + 79kcal/mole corresponding to 362nm. b. H.M. Rosenstock, K. Draxl, B.W. Steiner, J.T. Herron, J. Phys Chem. Ref. Data, 6, Suppl 1, 1977. c. S.W. Benson, "Thermochemical Kinetics", 2nd ed., John Wiley and Sons, NY, 1976, p. 299. B.B. Craig and M.F. Sonnenschein, J. Lumin. 1989, 43, 227. R. Hermann,Radiat.Phys. Chem. 1989, 34, 369-74. T.S. Dunn and J.L. Williams, J. Indus. Irrad. Tech., 1983, 1, 33. The X-ray absorption spectra of polymers withC.,H,Oatoms only are very similar: M. Przybylski, M. Stamm, R. Zietz, J. Physique, 1987, 48, 1351-6 +

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f

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1991


Delayed Luminescence from Organic Compounds Induced by X

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