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Quenching of the fluorescence of organic luminophores by oxygen in thin polymer films
Quenching of fluorescence of orgartic luminophores
1885
REFERENCES 1. E. F. CASASSA and Y. TAGAMI, Macromolecules 2: 14, 1969 2. A. A. GORBUNOV and A. M. SKVORTSOV, Vysokomol. soyed. A26: 2062, 1984 (Translated in Polymer Sci. 26: 10, 2306, 1984) 3. P. De GENNES, ldei skeilinga v fizike polimerov (Scaling Ideas in Polymer Physics), Mir, Moscow, 1982 4. M. DAOUD and P. de GENNES, J. Phys. 38: 85, 1977 5. P. R. GERBER and M. A. MOORE, Macromolecules 10: 476, 1977 6. A. A. GORBUNOV and A. M. SKVORTSOV, Vysokomol.osoyed. A22: 1137, 1980 (Translated in Polymer Sci. U.S.S.R. 22: 5, 1251, 1980)
Polymer Science U.S.S.R. Vol. 28, No. 8, pp. 1885-1891, 1986 Printed in Poland
0032-3950/86 $10.00+ .00 ~Ei 1987 Pergamon Journals Ltd.
QUENCHING OF THE FLUORESCENCE OF ORGANIC LUMINOPHORES BY OXYGEN IN THIN POLYMER FILMS* G. I. LASHKOV (dec.) and A. F. KAVTREV Vavilov State Optical Institute (Received 1 December 1984)
The anomalously high quenching of the luminescence of 9,10-bis-(phenylethynyl)-anthracene in thin flims of PMMA by oxygen at pressures 0-25 atm is due to the structural inhomogeneity of the objects and the migration of the energy of electron excitation over the molecules of the luminophore. Th.e apparatus of the theory of non-radiation energy transfer is used for the quantitative evaluation of the local mobility of oxygen in the regions of the polymer closest to the. luminophore. Comparison of the local and volume-average diffusion coefficients of oxygen determined from experiments on the quenching of fluorescence may be an effective express method for structural investigations of polymer films. THE pioneering w o r k o f Oster et al. [1, 2] revealing in synthetic p o l y m e r s at r o o m t e m p e r a t u r e the p h o s p h o r e s c e n c e o f the polyacenes a n d dyes was followed by a n u m b e r o f investigations in which the quenching o f p h o s p h o r e s c e n c e by oxygen was used to s t u d y its diffusion in p o l y m e r matrices [3-5]. I n this w o r k the l u m i n o p h o r e with a d e c a y time after luminescence in a n a e r o b i c conditions r T = 0 " I - I ' 0 sec was i n t r o d u c e d into the p o l y m e r d u r i n g its p r o d u c t i o n a n d either the value o f the p a r t i a l oxygen pressure at which the p h o s p h o r e s c e n c e o f the finely disperse p o l y m e r i c object is quenched by h a l f [5] o r the time o f m o v e m e n t o f the quenching front in the p o l y m e r b l o c k with p e n e t r a t i o n o f a t m s o p h e r i c oxygen f r o m the surface into the d e p t h was m e a s u r e d [3, 4].
* Vysokomol. soyed. A28: No. 8, 1692-1696, 1986.
1886
G . I . LASHKOVand A. F. KAVTREV
The known effect of quenching of fluorescence by oxygen was previously not regardeff as potentially possible in such investigations. In fact, the decay time of the fluorescent s t a t e o f organic molecules "¢s=10-6-10-9 sec is significantly lower than ~r and b y virtue of the slow course of the diffusion processes in polymers at a temperature below Tg negligible values of oxygen quenching might have been expected even at pressures P above atmospheric. Nevertheless, recently [6] heavy quenching of the fluorescence of compounds of t h e anthracene series with zs of the'order of units of nanosec was found in blocks of high molecular weight non-plasticized P M M A kept in an oxygen atmosphere at P = 1-100 atm. The present work seeks to demonstrate the possibility in principle of producing on the basis of the quenching of fluorescence in polymers highly effective thin film luminescent indicators for investigating the oxygen permeability of polymeric objects in the range 1-20 atm and higher. As luminophore we used 9,10-bis-(phenylethynyl)anthracene (A).* At room temperature the substance has a fluorescence decay time TS in PMMA measured by the photon count method and with a phase fluorometer (3.5--4)x 10 -9 sec and a quantum yield of fluorescence 0.8 _+0-1. The films were prepared by pouring onto a rotating glass surface solutions of the luminophore and polymer in toluene at a concentration of PMMA 10 grav. ~o. We used LPT-1 PMMA produced by the Plastpolimer Science-Production Association (MRTU 6-05-81'4-66). After pouring the films were dried in a thermostat at 60°C for 4 hr. The film thickness was measured with an MII-4 microinterferometer and was 0.5-15 lam. The absorption spectra were measured with the Perkin-Elmer 555 spectrophotometer. Tlae luminescence measurements were with a laboratory apparatus assembled from two MDR-2 monochromators, a lamp of the DKSL-1000 type with xenon filling, a FEU-79 and the V6-4 narrow band amplifier with the V9-2 phase detector. The time resolution of the measuring part was 1 sec. The apparatus was equipped with a cuvette for the optical measurements at the pressure 1-25 atm. The absorption spectra of the P M M A films did not change with variation in the concentration of A from 0.1 to 10 grav. ~ . Therefore, it was possible to use the published data on molar decimal absorption coefficients e in solutions of A presented in [7] (Fig. 1) to determine the molar content of A in the films by measuring the optical density and thickness d. Figure 1 presents the luminescence spectra measured on films with an optical density not exceeding 0.2 at the absorption maximum. The intensity of luminescence is reduced to an identical optical density at the wavelength of the exciting light 350 nm. From the results it follows that with increase in the concentration of the luminophore there is transformation typical of anthracene compounds [8] of monomer to eximer luminescence possibly accompanied by the formation of non-luminescing associates of A. Rise in the partial oxygen pressure above the polymeric object leads to quenching o f luminescence. The effectiveness of quenching 1/lo (I is the intensity of luminescence in absence of oxygen) depends on the working concentration of A in the polymer (Fig. 2). The abscissa in Fig. 2 gives the oxygen pressure values in the measuring cuvette. The * It was kindly made available by B. M, Krasovitskii.
Quenching of fluorescence of organic luminophores
1887
results were treated in the coordinates of the Stern-Folmer equation
/0
T-
1=
aKVo2,
(1)
where a is the coefficient of solubility of 02 in P M M A and K is the Stern-Folmer quenching constant. They are satisfactorily linearized for all the specimens studied in the range of the test pressues Po2 =0-20 atm.
E qO-OM't.[..cm-t 3
~V
//
~lh'~t~ "
/
[
ll/
/
~,~
/
0"5
~\-%-<, / ~ , ... ",¢,.~,0
~ i \y/ " ..: / \ \ ,\ \ \ "%~."~,. ~.~'¢~',. ~' ./~....." ~. ~.
0.25
II, t
I
4
J/.~,'.
: .... \
t
5
i ~ - .
i
6 ~,lO~ 217/7"/
Ft6. 1. Absorption spectrum (a) and the true spectrum (b) of the molecules of A in PMMA. Curves with numerals (content of the molecules A, gray. 7o) indicate the luminescence spectra. 2cxc~t=350 _+2 nm. In line with the published information [9] there are no grounds for assuming that in the tested pressure range the solubility of 02 in P M M A does not obey the Henry law. Then, in the dependence (1) the value K remains unchanged in the whole Po2 interval. This means that the quenching process may be described by using the theory of bimolecular quenching developed for liquid solutions [10] disregarding the instant interaction. Let us represent the dependence of K on the concentration of the luminophore (Fig. 3) and evaluate K by extrapolating the data to zero concentration of the luminophore. It will be seen that K increases by more than one order with change in ca to 0.27 mole/1. Now let us consider K for CA~0 K = f l z z s,
(2)
where/7 is the effectiveness of quenching on collision (in the liquid or singlet state "-"1); z is the number o f encounters per second.
1888
G.I.
LASHKOV and A. F. KAVTREV
At CA~0 only the quencher diffuses and therefore. 47rN A
z = 1000-r° D°2,
(3)
where ro is the distance of interaction equal to the sum of the van der Waals radii of the luminophore and quencher ,-- 5; NA is the Avogadro number; Do2 is the diffusion coefficient of oxygen.
/0_~
r
:1
iT
10
~2
1"0
i 0.5 0"5
5
tO
/5
~Pnz,atrn
FIG. 2. Quenching of fluorescence of A in PMMA by oxygen. Numerals in curves give content of A in grav. %. Let us determine Do2 in P M M A by measuring the kinetics of entry (or exit) of oxygen into the film (Fig. 4). Using the standard solution of the equation describing the diffusion o f a gas from a flat layer the results in Fig. 4 we determine Do2=5 × 10 -s cm2/sec. The absence of data on solubility er in specific films, however, prevents us from comparing the magnitude K measured and calculated from formula (2). Therefore, let us return to the dependence presented in Fig. 3. Increase in K with c A may be connected with the inclusion with rise in CA of the phenomenon of delocalization of excitation through non-radiation energy transfer between the A molecules. The process of quenching must be due to the superposing of material diffusion (oxygen in the polymer) and diffusion of excitation over A with the diffusion coefficient Dexci t. Then the formula (3) must be written in the form 4xNA
Z'
1000 r ° ( D ° ~ + D ~ i t )
(3a)
According to the theory developed in detail and repeatedly checked experimentally o f dipole-dipole inductive-resonance energy transfer [11, 12] the diffusion coefficient migration of excitation between molecules of the same type is determined by the rela-
Quenching of fluorescence of organic luminophores
1889
tion [12]
1 R~ Dexcit-- 3 s~4'
(4)
"~ / ~ A
where Ro is the critical distance of transfer of the energy of excitation between the molecules of A; /~A is the mean distance between them calculated as -
f4rc
\-lta
(5)
where rlA is the n u m b e r o f molecules of I p e r cm 3. ,~;o£m -1
].Ho
/
-----.
OOy l
]
14 [
I
i
0"1
1
i
8cm~gra~% I
_
02 CA,too~Oil
20 T [ m e , aec
40
Flo. 3 Fro. 4 Fio. 3. Quenching constant K as a function of the concentration of the luminophore. Flo. 4. Change in intensity of luminescence of a film of PMMA 12 /~m thick at cA= 1 gray. % in conditions of abrupt increase to 16 atm (descending curve) and of reduction (ascending curve) of pressure in the measuring cuvette. From the formula (4) and (5) it follows that /-~ ~excit~ ,.413 ~A , i.e. z' in expression (3a) and also K almost linearly (to the degree 1.33) rise with increase in CA. This occurs in the experiment at a relatively low concentration of A (Fig. 3) and allows use of linear extrapolation to determine K for CA~0. With increase in CA the magnitude K tends to saturation which is quite natural since the formation of eximer centres (Fig. 1) leads to localization of excitation on them and limitation of its mobility. The critical radius of transfer Ro (in cm) was determined by us from the formula [12]
R6=5.86xlO-25~ f f(v)e(v)dvv~,
(6)
where r/o is the quantum yield of luminescence of A in absence of transfer equal to 0.8; n is the refractive index of the polymer in the region of emission of luminescence ~ 1.5; is the spectral distribution of the fluorescence as a function of the wave
f(v)* *f(v)like r/o of the object containing A in an amount of0"l grav. % was measured by Ye. N.
Viktorova.
1890
G. I. LASHKOVand A. F. KAVTREV
number normalized to Sf(v)dv= 1; e(v) is the molar decimal coefficient of absorption; v is the wave number. Using the magnitude Ro calculated from formula (6) and equal to 0.38 x 10 -6 cm it is possible from relation (4) to evaluate Dex~i, for the initial experimental points o f the dependence in Fig. 3 (tangent to the experimental curve). Then by comparing the magnitudes K for CA~0 and in presence of transfer taking into account the relations (3) and (3a) one may evaluate the coefficient of oxygen diffusion manifest on quenching luminescence. Its value was 7 × 10 -s cm2/sec. A notable feature is the heavy divergence of the values of the diffusion coefficients of oxygen measured by the same method of quenching of fluorescence - from the time of filling the film with gas (5 × 10 -8 cm2.sec - 1) and from the dependence of quenching on the partial gas pressure over object (7 × 10-s cm2.sec - 1). The substantial structural heterogeneity of the polymer specimens investigated probably finds its reflexion in this difference. The luminophore on its dispersion in the polymer may be accomodated preferentially in the portions of the polymer with low local density of matter. If these portions have the dimensions r of the order of the diffusion shift in O2 in the time vs evaluated from the relation r = ~ / 6 - ~ then the local diffusion coefficient will differ from the volume-average. The volume-average diffusion coefficient is determined in experiments from the saturation of the polymer so that it is possible to determine the minimal size of the region of reduced local density r=\/6 x 5 x 10 -8 × 4 x 10 -9 ~,3.5 ~. Naturally, the longer the decay time r of the luminophore the less will the local diffusion coefficient differ from volume-average. Thus, the effect considered of quenching of fluorescence of organoluminophores in a polymer at raised oxygen pressure may be an express experimental method for investigating the structural heterogeneity of film polymer specimens. The anomalously high quenching of luminescence enhanced by the non-radiation transfer of the energy o f electron excitation of the molecules may be used to produce effective luminescent indicators for investigating the oxygen permeability of polymeric objects. The authors wish to express their sincere gratitude to V. L. Yermolayev for interest in the investigations and useful discussion of the paper.
Translated by A. CROZY REFERENCES
1. 2. 3. 4. 5.
G. OSTER, N. GEACINTOV and A. U. KHAN, Nature 196: 4859, 1089, 1962 G. OSTER, N. CEACINTOV and Th. CASSEN, Acta Phys. Polonica 26: 489, 1964 S. CZARNECKI and M. KRYSZEWSKI, J. Polymer Sci. AI: 3067, 1963 E. I. HORMATS and F. C. UNTERLEITNER, J. Phys. Chem. 69: 3677, 1965 I. A. ZAKHAROV, T. V. SHAKINA and V. B. ALESKOVSKII, Zh. prikl, spektroskop. 12: 703, 1970 6. A. P. POPOV, G. I. LASHKOV, A. S. CHERKASOV, O. B. RATNER, B. M. KRASOVITSKII and V. M. SHERSHUKOV, Optika i Spektroskop. 58: 941, 1985 7. I. B. BERLMAN, Handbook Fluorescence Spectra of Aromatic Molecules. Second Edition, p. 469, Acad. Press, N.Y.-L, 1971
Thermodynamic flexibility of macromolecules with double bonds in main chain
1891
8. A. S. CHERKASOV, Molekulyarnaya fotonika (Molecular Photonics). p. 244, Nauka, Leningrad, 1970 9. S. A. REITLINGER, Pronitsayemost' polimernykh materialov (Permeability of Polymer Materials), p. 269, Khimiya, Moscow, 1977 10. A. WELLER, Phys. Chem. 13: 335, 1957 11. V. L. YERMOLAYEV, Ye. N. BODUNOV, Ye. B. SVESHNIKOVA and T. A. SHAKHVERDOV, Bezyzluchadtel'nyi perenos energii elektronnogo vozbuzhdeniya (Non-Radiation Transfer of the Energy of Electron Excitation). Nauka, Lcningrad, 1977 12. V. M. AGRANOVICH and M. D. GALANIN, P,:rcnos enc;gii elcktronnogo vozbuzhdeniya v kondensirovannykh sredakh (Transfer of the Energy of Electron Excitation in Condensed Media). p. 64, Nauka, Moscow, 1978
Polymer ScienceU.S.S.R.Vol. 28, No. 8, pp. 1891-1901, 1986 Printed in Poland
0032 3950/86 $10.004-.00 © 1987 PergamonJournals Ltd.
STUDY OF THE THERMODYNAMIC FLEXIBILITY OF MACROMOLECULES WITH DOUBLE BONDS IN THE MAIN CHAIN. CONTINUUM MODEL* A. L..RABINOVICH, V. G. DASHEVSKII (dec.) and P. O. RIPATTI Nesmeyanov Institute of Organo-Element Compounds, U.S.S.R. Academy of Sciences (Received 1 December 1984)
The computer simulation method is used to make a comparative analysis of the equilibrium flexibility of the polymers of 1,4-cis- and 1,4-trans polybutadiene, poly-eis and poly-trans propenylene and also the unperturbed characteristics of oligomers containing double bonds in the main chain. The calculations are based on the assumption of a continuous spectrum of conformations. The persistent length and characteristic ratio of the trans polyenes are greater than of the cis and increase with rise in the trans polyenes in the content of the trans double bonds but fall with increase in the content cff the cis ones in the cis polyenes. As compared with the conditions of free rotation the cis polyenes are less flexible than the trans. Increase in the number of double bonds in the oligomer chains leads to fall in the mea~a distances between ends, their squares and the squares of the radii of inertia and also the moduli of the temperature coefficients. With displacement of the double bonds from the ends to the middle of the molecule reduction in the geometric dimensions of the chain is observed. THEORETICAL analysis o f the equilibrium flexibility o f p o l y m e r chains c o n t a i n i n g d o u b l e bonds and investigation o f the u n p e r t u r b e d characteristics o f p o l y u n s a t u r a t e d oligomers are o f considerable interest as they allow one to study the r e l a t i o n between the local an d global properties o f the molecule3 with wide p r a c t i c a l applications. The present * Vysokomot. soyed. A28: No. 8, 1697-1705, 1986.
1885
REFERENCES 1. E. F. CASASSA and Y. TAGAMI, Macromolecules 2: 14, 1969 2. A. A. GORBUNOV and A. M. SKVORTSOV, Vysokomol. soyed. A26: 2062, 1984 (Translated in Polymer Sci. 26: 10, 2306, 1984) 3. P. De GENNES, ldei skeilinga v fizike polimerov (Scaling Ideas in Polymer Physics), Mir, Moscow, 1982 4. M. DAOUD and P. de GENNES, J. Phys. 38: 85, 1977 5. P. R. GERBER and M. A. MOORE, Macromolecules 10: 476, 1977 6. A. A. GORBUNOV and A. M. SKVORTSOV, Vysokomol.osoyed. A22: 1137, 1980 (Translated in Polymer Sci. U.S.S.R. 22: 5, 1251, 1980)
Polymer Science U.S.S.R. Vol. 28, No. 8, pp. 1885-1891, 1986 Printed in Poland
0032-3950/86 $10.00+ .00 ~Ei 1987 Pergamon Journals Ltd.
QUENCHING OF THE FLUORESCENCE OF ORGANIC LUMINOPHORES BY OXYGEN IN THIN POLYMER FILMS* G. I. LASHKOV (dec.) and A. F. KAVTREV Vavilov State Optical Institute (Received 1 December 1984)
The anomalously high quenching of the luminescence of 9,10-bis-(phenylethynyl)-anthracene in thin flims of PMMA by oxygen at pressures 0-25 atm is due to the structural inhomogeneity of the objects and the migration of the energy of electron excitation over the molecules of the luminophore. Th.e apparatus of the theory of non-radiation energy transfer is used for the quantitative evaluation of the local mobility of oxygen in the regions of the polymer closest to the. luminophore. Comparison of the local and volume-average diffusion coefficients of oxygen determined from experiments on the quenching of fluorescence may be an effective express method for structural investigations of polymer films. THE pioneering w o r k o f Oster et al. [1, 2] revealing in synthetic p o l y m e r s at r o o m t e m p e r a t u r e the p h o s p h o r e s c e n c e o f the polyacenes a n d dyes was followed by a n u m b e r o f investigations in which the quenching o f p h o s p h o r e s c e n c e by oxygen was used to s t u d y its diffusion in p o l y m e r matrices [3-5]. I n this w o r k the l u m i n o p h o r e with a d e c a y time after luminescence in a n a e r o b i c conditions r T = 0 " I - I ' 0 sec was i n t r o d u c e d into the p o l y m e r d u r i n g its p r o d u c t i o n a n d either the value o f the p a r t i a l oxygen pressure at which the p h o s p h o r e s c e n c e o f the finely disperse p o l y m e r i c object is quenched by h a l f [5] o r the time o f m o v e m e n t o f the quenching front in the p o l y m e r b l o c k with p e n e t r a t i o n o f a t m s o p h e r i c oxygen f r o m the surface into the d e p t h was m e a s u r e d [3, 4].
* Vysokomol. soyed. A28: No. 8, 1692-1696, 1986.
1886
G . I . LASHKOVand A. F. KAVTREV
The known effect of quenching of fluorescence by oxygen was previously not regardeff as potentially possible in such investigations. In fact, the decay time of the fluorescent s t a t e o f organic molecules "¢s=10-6-10-9 sec is significantly lower than ~r and b y virtue of the slow course of the diffusion processes in polymers at a temperature below Tg negligible values of oxygen quenching might have been expected even at pressures P above atmospheric. Nevertheless, recently [6] heavy quenching of the fluorescence of compounds of t h e anthracene series with zs of the'order of units of nanosec was found in blocks of high molecular weight non-plasticized P M M A kept in an oxygen atmosphere at P = 1-100 atm. The present work seeks to demonstrate the possibility in principle of producing on the basis of the quenching of fluorescence in polymers highly effective thin film luminescent indicators for investigating the oxygen permeability of polymeric objects in the range 1-20 atm and higher. As luminophore we used 9,10-bis-(phenylethynyl)anthracene (A).* At room temperature the substance has a fluorescence decay time TS in PMMA measured by the photon count method and with a phase fluorometer (3.5--4)x 10 -9 sec and a quantum yield of fluorescence 0.8 _+0-1. The films were prepared by pouring onto a rotating glass surface solutions of the luminophore and polymer in toluene at a concentration of PMMA 10 grav. ~o. We used LPT-1 PMMA produced by the Plastpolimer Science-Production Association (MRTU 6-05-81'4-66). After pouring the films were dried in a thermostat at 60°C for 4 hr. The film thickness was measured with an MII-4 microinterferometer and was 0.5-15 lam. The absorption spectra were measured with the Perkin-Elmer 555 spectrophotometer. Tlae luminescence measurements were with a laboratory apparatus assembled from two MDR-2 monochromators, a lamp of the DKSL-1000 type with xenon filling, a FEU-79 and the V6-4 narrow band amplifier with the V9-2 phase detector. The time resolution of the measuring part was 1 sec. The apparatus was equipped with a cuvette for the optical measurements at the pressure 1-25 atm. The absorption spectra of the P M M A films did not change with variation in the concentration of A from 0.1 to 10 grav. ~ . Therefore, it was possible to use the published data on molar decimal absorption coefficients e in solutions of A presented in [7] (Fig. 1) to determine the molar content of A in the films by measuring the optical density and thickness d. Figure 1 presents the luminescence spectra measured on films with an optical density not exceeding 0.2 at the absorption maximum. The intensity of luminescence is reduced to an identical optical density at the wavelength of the exciting light 350 nm. From the results it follows that with increase in the concentration of the luminophore there is transformation typical of anthracene compounds [8] of monomer to eximer luminescence possibly accompanied by the formation of non-luminescing associates of A. Rise in the partial oxygen pressure above the polymeric object leads to quenching o f luminescence. The effectiveness of quenching 1/lo (I is the intensity of luminescence in absence of oxygen) depends on the working concentration of A in the polymer (Fig. 2). The abscissa in Fig. 2 gives the oxygen pressure values in the measuring cuvette. The * It was kindly made available by B. M, Krasovitskii.
Quenching of fluorescence of organic luminophores
1887
results were treated in the coordinates of the Stern-Folmer equation
/0
T-
1=
aKVo2,
(1)
where a is the coefficient of solubility of 02 in P M M A and K is the Stern-Folmer quenching constant. They are satisfactorily linearized for all the specimens studied in the range of the test pressues Po2 =0-20 atm.
E qO-OM't.[..cm-t 3
~V
//
~lh'~t~ "
/
[
ll/
/
~,~
/
0"5
~\-%-<, / ~ , ... ",¢,.~,0
~ i \y/ " ..: / \ \ ,\ \ \ "%~."~,. ~.~'¢~',. ~' ./~....." ~. ~.
0.25
II, t
I
4
J/.~,'.
: .... \
t
5
i ~ - .
i
6 ~,lO~ 217/7"/
Ft6. 1. Absorption spectrum (a) and the true spectrum (b) of the molecules of A in PMMA. Curves with numerals (content of the molecules A, gray. 7o) indicate the luminescence spectra. 2cxc~t=350 _+2 nm. In line with the published information [9] there are no grounds for assuming that in the tested pressure range the solubility of 02 in P M M A does not obey the Henry law. Then, in the dependence (1) the value K remains unchanged in the whole Po2 interval. This means that the quenching process may be described by using the theory of bimolecular quenching developed for liquid solutions [10] disregarding the instant interaction. Let us represent the dependence of K on the concentration of the luminophore (Fig. 3) and evaluate K by extrapolating the data to zero concentration of the luminophore. It will be seen that K increases by more than one order with change in ca to 0.27 mole/1. Now let us consider K for CA~0 K = f l z z s,
(2)
where/7 is the effectiveness of quenching on collision (in the liquid or singlet state "-"1); z is the number o f encounters per second.
1888
G.I.
LASHKOV and A. F. KAVTREV
At CA~0 only the quencher diffuses and therefore. 47rN A
z = 1000-r° D°2,
(3)
where ro is the distance of interaction equal to the sum of the van der Waals radii of the luminophore and quencher ,-- 5; NA is the Avogadro number; Do2 is the diffusion coefficient of oxygen.
/0_~
r
:1
iT
10
~2
1"0
i 0.5 0"5
5
tO
/5
~Pnz,atrn
FIG. 2. Quenching of fluorescence of A in PMMA by oxygen. Numerals in curves give content of A in grav. %. Let us determine Do2 in P M M A by measuring the kinetics of entry (or exit) of oxygen into the film (Fig. 4). Using the standard solution of the equation describing the diffusion o f a gas from a flat layer the results in Fig. 4 we determine Do2=5 × 10 -s cm2/sec. The absence of data on solubility er in specific films, however, prevents us from comparing the magnitude K measured and calculated from formula (2). Therefore, let us return to the dependence presented in Fig. 3. Increase in K with c A may be connected with the inclusion with rise in CA of the phenomenon of delocalization of excitation through non-radiation energy transfer between the A molecules. The process of quenching must be due to the superposing of material diffusion (oxygen in the polymer) and diffusion of excitation over A with the diffusion coefficient Dexci t. Then the formula (3) must be written in the form 4xNA
Z'
1000 r ° ( D ° ~ + D ~ i t )
(3a)
According to the theory developed in detail and repeatedly checked experimentally o f dipole-dipole inductive-resonance energy transfer [11, 12] the diffusion coefficient migration of excitation between molecules of the same type is determined by the rela-
Quenching of fluorescence of organic luminophores
1889
tion [12]
1 R~ Dexcit-- 3 s~4'
(4)
"~ / ~ A
where Ro is the critical distance of transfer of the energy of excitation between the molecules of A; /~A is the mean distance between them calculated as -
f4rc
\-lta
(5)
where rlA is the n u m b e r o f molecules of I p e r cm 3. ,~;o£m -1
].Ho
/
-----.
OOy l
]
14 [
I
i
0"1
1
i
8cm~gra~% I
_
02 CA,too~Oil
20 T [ m e , aec
40
Flo. 3 Fro. 4 Fio. 3. Quenching constant K as a function of the concentration of the luminophore. Flo. 4. Change in intensity of luminescence of a film of PMMA 12 /~m thick at cA= 1 gray. % in conditions of abrupt increase to 16 atm (descending curve) and of reduction (ascending curve) of pressure in the measuring cuvette. From the formula (4) and (5) it follows that /-~ ~excit~ ,.413 ~A , i.e. z' in expression (3a) and also K almost linearly (to the degree 1.33) rise with increase in CA. This occurs in the experiment at a relatively low concentration of A (Fig. 3) and allows use of linear extrapolation to determine K for CA~0. With increase in CA the magnitude K tends to saturation which is quite natural since the formation of eximer centres (Fig. 1) leads to localization of excitation on them and limitation of its mobility. The critical radius of transfer Ro (in cm) was determined by us from the formula [12]
R6=5.86xlO-25~ f f(v)e(v)dvv~,
(6)
where r/o is the quantum yield of luminescence of A in absence of transfer equal to 0.8; n is the refractive index of the polymer in the region of emission of luminescence ~ 1.5; is the spectral distribution of the fluorescence as a function of the wave
f(v)* *f(v)like r/o of the object containing A in an amount of0"l grav. % was measured by Ye. N.
Viktorova.
1890
G. I. LASHKOVand A. F. KAVTREV
number normalized to Sf(v)dv= 1; e(v) is the molar decimal coefficient of absorption; v is the wave number. Using the magnitude Ro calculated from formula (6) and equal to 0.38 x 10 -6 cm it is possible from relation (4) to evaluate Dex~i, for the initial experimental points o f the dependence in Fig. 3 (tangent to the experimental curve). Then by comparing the magnitudes K for CA~0 and in presence of transfer taking into account the relations (3) and (3a) one may evaluate the coefficient of oxygen diffusion manifest on quenching luminescence. Its value was 7 × 10 -s cm2/sec. A notable feature is the heavy divergence of the values of the diffusion coefficients of oxygen measured by the same method of quenching of fluorescence - from the time of filling the film with gas (5 × 10 -8 cm2.sec - 1) and from the dependence of quenching on the partial gas pressure over object (7 × 10-s cm2.sec - 1). The substantial structural heterogeneity of the polymer specimens investigated probably finds its reflexion in this difference. The luminophore on its dispersion in the polymer may be accomodated preferentially in the portions of the polymer with low local density of matter. If these portions have the dimensions r of the order of the diffusion shift in O2 in the time vs evaluated from the relation r = ~ / 6 - ~ then the local diffusion coefficient will differ from the volume-average. The volume-average diffusion coefficient is determined in experiments from the saturation of the polymer so that it is possible to determine the minimal size of the region of reduced local density r=\/6 x 5 x 10 -8 × 4 x 10 -9 ~,3.5 ~. Naturally, the longer the decay time r of the luminophore the less will the local diffusion coefficient differ from volume-average. Thus, the effect considered of quenching of fluorescence of organoluminophores in a polymer at raised oxygen pressure may be an express experimental method for investigating the structural heterogeneity of film polymer specimens. The anomalously high quenching of luminescence enhanced by the non-radiation transfer of the energy o f electron excitation of the molecules may be used to produce effective luminescent indicators for investigating the oxygen permeability of polymeric objects. The authors wish to express their sincere gratitude to V. L. Yermolayev for interest in the investigations and useful discussion of the paper.
Translated by A. CROZY REFERENCES
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G. OSTER, N. GEACINTOV and A. U. KHAN, Nature 196: 4859, 1089, 1962 G. OSTER, N. CEACINTOV and Th. CASSEN, Acta Phys. Polonica 26: 489, 1964 S. CZARNECKI and M. KRYSZEWSKI, J. Polymer Sci. AI: 3067, 1963 E. I. HORMATS and F. C. UNTERLEITNER, J. Phys. Chem. 69: 3677, 1965 I. A. ZAKHAROV, T. V. SHAKINA and V. B. ALESKOVSKII, Zh. prikl, spektroskop. 12: 703, 1970 6. A. P. POPOV, G. I. LASHKOV, A. S. CHERKASOV, O. B. RATNER, B. M. KRASOVITSKII and V. M. SHERSHUKOV, Optika i Spektroskop. 58: 941, 1985 7. I. B. BERLMAN, Handbook Fluorescence Spectra of Aromatic Molecules. Second Edition, p. 469, Acad. Press, N.Y.-L, 1971
Thermodynamic flexibility of macromolecules with double bonds in main chain
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8. A. S. CHERKASOV, Molekulyarnaya fotonika (Molecular Photonics). p. 244, Nauka, Leningrad, 1970 9. S. A. REITLINGER, Pronitsayemost' polimernykh materialov (Permeability of Polymer Materials), p. 269, Khimiya, Moscow, 1977 10. A. WELLER, Phys. Chem. 13: 335, 1957 11. V. L. YERMOLAYEV, Ye. N. BODUNOV, Ye. B. SVESHNIKOVA and T. A. SHAKHVERDOV, Bezyzluchadtel'nyi perenos energii elektronnogo vozbuzhdeniya (Non-Radiation Transfer of the Energy of Electron Excitation). Nauka, Lcningrad, 1977 12. V. M. AGRANOVICH and M. D. GALANIN, P,:rcnos enc;gii elcktronnogo vozbuzhdeniya v kondensirovannykh sredakh (Transfer of the Energy of Electron Excitation in Condensed Media). p. 64, Nauka, Moscow, 1978
Polymer ScienceU.S.S.R.Vol. 28, No. 8, pp. 1891-1901, 1986 Printed in Poland
0032 3950/86 $10.004-.00 © 1987 PergamonJournals Ltd.
STUDY OF THE THERMODYNAMIC FLEXIBILITY OF MACROMOLECULES WITH DOUBLE BONDS IN THE MAIN CHAIN. CONTINUUM MODEL* A. L..RABINOVICH, V. G. DASHEVSKII (dec.) and P. O. RIPATTI Nesmeyanov Institute of Organo-Element Compounds, U.S.S.R. Academy of Sciences (Received 1 December 1984)
The computer simulation method is used to make a comparative analysis of the equilibrium flexibility of the polymers of 1,4-cis- and 1,4-trans polybutadiene, poly-eis and poly-trans propenylene and also the unperturbed characteristics of oligomers containing double bonds in the main chain. The calculations are based on the assumption of a continuous spectrum of conformations. The persistent length and characteristic ratio of the trans polyenes are greater than of the cis and increase with rise in the trans polyenes in the content of the trans double bonds but fall with increase in the content cff the cis ones in the cis polyenes. As compared with the conditions of free rotation the cis polyenes are less flexible than the trans. Increase in the number of double bonds in the oligomer chains leads to fall in the mea~a distances between ends, their squares and the squares of the radii of inertia and also the moduli of the temperature coefficients. With displacement of the double bonds from the ends to the middle of the molecule reduction in the geometric dimensions of the chain is observed. THEORETICAL analysis o f the equilibrium flexibility o f p o l y m e r chains c o n t a i n i n g d o u b l e bonds and investigation o f the u n p e r t u r b e d characteristics o f p o l y u n s a t u r a t e d oligomers are o f considerable interest as they allow one to study the r e l a t i o n between the local an d global properties o f the molecule3 with wide p r a c t i c a l applications. The present * Vysokomot. soyed. A28: No. 8, 1697-1705, 1986.