Formation of exciplexes in films of polyimides, polyamides, and polyquinazolones derived from aromatic and heteroaromatic diamines

Article abstract of DOI:10.1007/s11176-005-0471-z

The emission bands exchibited by films of polyimides derived from 1,3-bis(3,4-dicarboxyphenoxy)benzene dianhydride, hexafluoroisopropylidenedibenzene-3,3′,4,4′-tetracarboxylic dianhydride, and aromatic and heteroaromatic diamines, and also of polyamides and polyquinazolones derived from the same amines are exciplex bahnds. With polyamides, complexes in the ground state are formed. The fluorescence of the photoconductivity sensitizer Rhodamine 6G is quenched in films of these polymers by the exciplex mechanism. 2005 Pleiades Publishing, Inc.

Full text of DOI:10.1007/s11176-005-0471-z

Russian Journal of General Chemistry, Vol. 75, No. 10, 2005, pp. 1584 1593. Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 10, 2005,
pp. 1161 1170.
Original Russian Text Copyright
2005 by Rtishchev, Nosova, Solovskaya, Romashkova, Kudryavtsev.
Formation of Exciplexes in Films of Polyimides, Polyamides,
and Polyquinazolones Derived from Aromatic
and Heteroaromatic Diamines
N. I. Rtishchev*, G. I. Nosova**, N. A. Solovskaya**,
K. A. Romashkova**, and V. V. Kudryavtsev**
* St. Petersburg State Institute of Technology (Technical University), St. Petersburg, Russia
** Institute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg, Russia
Received October 28, 2004
Abstract The emission bands exchibited by films of polyimides derived from 1,3-bis(3,4-dicarboxyphen-
oxy)benzene dianhydride, hexafluoroisopropylidenedibenzene-3,3 ,4,4 -tetracarboxylic dianhydride, and
aromatic and heteroaromatic diamines, and also of polyamides and polyquinazolones derived from the same
amines are exciplex bahnds. With polyamides, complexes in the ground state are formed. The fluorescence of
the photoconductivity sensitizer Rhodamine 6G is quenched in films of these polymers by the exciplex
mechanism.
Aromatic polyimides [1], polyamides [2], and
poorly studied polyquinazolones [3] exhibit high heat
resistance, high optical transparency, and good dielec-
tric and film-forming properties; when modified with
functional photosensitive fragments, they can be used
in development of materials for optical technologies.
Photosensitive polymers are of considerable interest
from the viewpoint of their electronic, electrical,
photoelectric, luminescence, and photophysical prop-
erties [4 6].
is lower by two orders of magnitude [10].
The photoelectric properties of films are associated
with the excitation of the electronic systems of these
polymers. It is known that the major factor governing
the photoelectric properties of polyimide films is the
donor acceptor (DA) interaction in the polymer mole-
cule. The character and intensity of this interaction
depend on the structure of the repeating monomeric
unit, packing of the macrochains, and surrounding of
the arising complexes in the solid polyimide [6].
Polyimide macromolecules can be considered as DA
chains of the alternating structure [11] in which the
diimide fragment is the electron acceptor (A) and the
diamine residue, the electron donor (D). With strong
A (high electron affinity) and D (low ionization poten-
tial), the charge transfer is realized even in the ground
(S0) state, with the formation of intrachain complex 1
[Scheme 1, Eq. (1a)] and interchain complex 2
[Scheme 1, Eq. (1b)].
Previous studies revealed for the first time the high
(without doping with dyes) intrinsic photoconductiv-
ity in the visible range of polyimides and polyquin-
5
azolones (integral photosensitivity 2 10 2.5
4
1
10 cm2 J ) whose polymeric chains contain in the
diamine component of the repeating unit a quaternary
carbon atom with various substituents or diamines of
the heteroaromatic series [7 9]. The photoconductivity
of the polyamides prepared from the same diamines
Scheme 1.
h
h
a
f
(1a)
(1b)
AD
AD
A D+
(A D+)*
AD ,
h
AD
f
A
*D
h
A D
a
A D+
.
A D+
AD
AD
Simultaneously, along with the overall absorption
of D and A, a new long-wave band or shoulder ap-
pears in the electronic absorption spectrum, and the
polymer films become colored [12]; also, a broad
structureless fluorescence band appears. Its excitation
spectrum reproduces the shape of the new absorption
1070-3632/05/7510-1584 2005 Pleiades Publishing, Inc.

FORMATION OF EXCIPLEXES IN FILMS OF POLYIMIDES
1585
band. With a weak acceptor and/or donor, the electron
transfer in the photoexcited state with formation of
exciplexes becomes probable (Scheme 2).
ter to the emission bands of complexes 1 and 2.
The character of the exciplex may change depend-
ing on the surrounding. In particular, addition of cer-
tain dyes to polyimide films leads to sensitized photo-
generation of the charge carriers, accompanied by
quenching of the dye fluorescence. The sensitization
if due to formation of a nonfluorescent exciplex in-
volving the dye and D in the initial polymer [5, 13].
Scheme 2.
h
h
f
a
AD
AD*
(A D+)*
AD ,
(2a)
(2b)
AD
AD
a
AD
AD*
A
*D
h
h
AD
AD
f
.
A D+
In this connection, it seems urgent to study how
the structure of the monomeric unit (containing no
fragments with pronounced donor properties) affects
the polymer photophysics. In this study we examined
the luminescence characteristics of the synthesized
polyimides and polyquinazolones with various A and
D, and also, for comparison, of certain polyamides
that were not studied previously (I XXXI).
The fluorescence excitation spectrum of the exci-
plex reproduces the overall curve of absorption of D
and A, and the Stokes shift ( Ss) is abnormally high
1
(15000 20000 cm ) in contrast to the shift observed
1
with complexes 1 and 2 ( 6000 cm ) [6], although
the exciplex emission band itself is similar in charac-
Polyimides
O
O
O
O 3-C6H4-1 O
N R
N
O
n
I XII
4-C6H4C(Ph)2C6H4-4 (III), 4-C6H4CH(Ph)C6H4-4 (IV),
4-C H C(Me)(Ph)C H -4 (II),
R = 4-C6H4C(Me)2C6H4-4 (I),
6
4
6 4
4-C6H4O-4-C6H4C(Me)2C6H4-4-OC6H4-4 (V),
4-C6H4O-4-C6H4C(Me)(Ph)C6H4-4-OC6H4-4 (VI),
4-C6H4O-4-
O
N
(VIII), 3-C6H4 (IX),
C6H4-4 (XII).
C6H4C(Ph)2C6H4-4-OC6H4-4 (VII),
C6H4-4 (X),
3,5-C6H3
N
N
H
N
N
C6H4-4 (XI),
N
N
Ph
Me
O
O
N
C(CF3)2
N R
O
O
n
XIII XXIII
S
N
S
O
3-C6H4
(XV),
O
C6H4-3
(XIV),
3,5-C6H3
C6H4-4 (XIII),
R =
N
N
N N
O
(XIX),
3,5-C6H3CONH-4-C6H4
N
3,5-C6H3
C6H4-4 (XVII, XVIII),
Ph (XVI),
N
N N
O
N
C6H4-4 (XX, XXI),
C6H4-4 (XXII, XXIII).
N
H
N
H
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 10 2005

1586
RTISHCHEV et al.
Polyamides
[ NHRNHCOC6H4-4-OC6H4-4-C(O) ]n
,
XXIV XXVIII
N
N
N
O
C6H4-4 (XXIV),
C6H4-4 (XXV),
C6H4-4 (XXVI),
Ph (XXVIII).
R =
N
H
N
Ph
O
N
O
3,5-C6H3CONH-4-C6H4
(XXVII),
3,5-C6H3
N N
Polyquinazolones
N
N
Ph
Ph
CH2
N
N
R
CO
CO
n
XXIX XXXI
4-C6H4O-4-C6H4C(Me)2C6H4O-4-C6H4-4 (XXX),
C6H4-4 (XXXI).
R = 4-C6H4O-3-C6H4-1-OC6H4-4 (XXIX),
N
N
H
We estimated the capability of these polymers for
sensitized photogeneration of charge carriers from the
efficiency of quenching of the sensitizer fluorescence.
Taking into account the highest efficiency of laser
dyes [5], we chose Rhodamine 6G (Rh 6G).
fragment. In this case, one-component fluorescence is
1
observed with the band maximum at
18 103 cm
f
1
and Stokes shift of 22 103 cm ; on replacement
of the phenyl radical with the diphenyl oxide group
(polyimides V VII), an additional band appears with
1
20 103 cm . A similar pattern is observed upon
f
Luminescence properties of polymers. The spec-
tral characteristics of the polymers studied are given
in Table 1 and Figs. 1 3. The long-wave absorption
introducing into the diamine moiety various hetero-
cycles (e.g., 2-phenylbenzoxazole, 2,5-diphenyloxadi-
azole, polyimides XIII XXIII). For these substances,
the parameters of the short- and long-wave compo-
band of the polymers
is observed in the range
a
1
(40.4 29.6) 103 cm (248 338 nm) depending on
nents are
20 103 and (14 18) 103,
(12
f
Ss
14) 103 and (13 17) 103 cm , respectively. The
structure of the phthalimide (initially dianhydride)
component in the repeating unit of the polyimide
affects the position of the overall fluorescence band
insignificantly (cf. VIII and XIX, Table 1). However,
in going from I XII to XIII XXIII, the low-frequency
the structure of components A and D of the repeating
1
monomeric unit. Excitation in the range
always gave rise to a broad (
366 nm
1
7000 10000 cm )
1/2
1
fluorescence band in the range (26.0 12.0) 103 cm
with a very large Stokes shift. This shift depends on
the position of the bands of the components; the num-
ber of the bands (one to three) is determined by the
structure of the amine component of the repeating
unit. This is indicated by the results of measuring the
fluorescence excited with polarized light (Figs. 1 3).
1
maximum shifts bathoflorically by 500 cm , and the
Stokes shift of both components increases by 2100
1
and 2700 cm . In addition, the polyimides with benz-
imidazole substituents (polymers X XII) do not ex-
hibit the short-wave component, in contrast to poly-
imides XX XXIII.
The degree of the fluorescence polarization (P) for
the majority of the films is not constant within the
band and, as a rule, changes stepwise, decreasing in
going to the red region. Thus, the overall emission
spectrum consists of several components differing in
P (from 36 to 2%, Table 2). Exceptions are polyimides
I IV containing diphenylmethane units in the amine
The contour and position of the overall fluores-
cence band of polyimides XIII XXIII are determined
by the structure of the heterocycle, position of the
2-phenylbenzazole group in the macromolecular chain
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 10 2005

FORMATION OF EXCIPLEXES IN FILMS OF POLYIMIDES
1587
Table 1. Spectral characteristics of polymer films
Table 2. Limiting degrees of fluorescence polarization for
polyimide, polyamide, and polyquinazolone films, P, %
3
3
Comp.
no.
10 ,
cm
10 ,
cm
(
334, 365 nm)
a
f
exc
/
x
1
1
Ss
ref
Comp.
no.
Comp.
Comp.
no.
P, %
P, %
P, %
I
II
III
IV
V
VI
VII
VIII
IX
40.5
40.5
40.4
40.5
43.0
43.0
43.0
34.0
40.8
31.3
31.2
32.2
32.0
32.5
34.0
32.4
32.4
32.8
31.8
32.2
32.0
32.0
32.0
29.6
30.4
29.8
17.8
18.0
17.8
18.0
22.7
22.5
22.6
22.5
1.2
1.3
1.3
1.5
1.6
1.1
2.0
2.1
2.0
1.9
2.1
2.8
3.1
1.5
0.8
7.4
1.5
no.
VIII
XIII
XIV
XVII 17, 10
XXI 36, 17
17, 3
12, 4
17, 3
XXII
XXIV 11, 8
XXV
XXVI
34, 23 XXVIII 17, 11
XXIX
XXX
XXXI
14, 21
28, 16
13, 6, 2
19.6 sh, 17.9 23.4, 25.1
20.0 sh, 17.9 23.0, 25.1
19.6 sh, 17.8 23.4, 25.2
20.1, 18.1
20.0, 18.3
17.8
13, 3
7, 5
XXVII 19, 11
13.9, 15.9
20.8, 22.5
13.5
X
XI
of the first maximum remains unchanged. Note that
the synthesis procedure mainly affects the position of
the second fluorescence maximum of the polyimides
containing imidazole structures. For example, when
the polyamido acid cyclization is performed in an
N-methylpyrrolidone solution (polyimide XXI), the
17.8
17.7
13.4
14.5
XII
XIII
XIV
XV
XVI
XVII
XVIII
XIX
XX
XXI
XXII
XXIII
XXIV
XXV
XXVI
19.6 sh, 17.3 12.4, 14.7
20.0 sh, 18.6 12.5, 13.9
19.1, 16.6 sh 14.9, 17.4
19.6 sh, 16.4 12.8, 16.0
19.6 sh, 17.3 12.8, 15.1
1
maximum is red-shifted by 1200 cm relative to the
same polymer prepared by chemical condensation of
the polyamido acid (polyimide XX, Table 1). The
emission spectra of polyimides I XXIII, recorded
from the films frozen to 77 K, are identical to the
spectra of the polymers in solution (CHCl3, dimethyl-
acetamide). The fluorescence excitation spectra re-
corded for some of them (Fig. 1, spectrum 2; Fig. 2a,
spectrum 2), irrespective of f, reproduce the shape of
the absorption curves, showing no new long-wave
maxima, except an ill-defined tail (Fig. 1, spectra
1 3) for polyimides VIII, IX, and XII. Assignment of
this absorption to complexes 1 or 2 (Scheme 1) seems
19.6 sh, 17.3 13.2, 15.5 16
20.0 sh, 18.6 11.8, 13.2
20.0 sh, 17.6 12.2, 14.6
20.0 sh, 16.4 12.0, 15.6
20.0 sh, 17.6 12.0, 14.4
20.0 sh, 17.2 12.0, 14.8
20.4, 19.4 sh
21.3, 18.0 sh
21.3, 18.0 sh
1.3
2.1
6.0
1.2
1.8
9.2, 10.2 46
9.1, 12.4
8.5, 11.8
6.0, 16.2
6.0, 13.8
12.4, 18.2
3.5
1.7
4.6
6.7
3.8
5.0
XXVII 34.6, 27.0 sh 21.0 sh, 18.4
XXVIII 33.1, 27.0 sh 20.8, 19.3
XXIX
XXX
35.7
35.0
32.2
23.3, 17.5
23.2, 19.0 sh 11.8, 16.0
23.3, 20.4,
18.5
improbable, because at varied
(313, 366, 406 nm)
the shape of the overall lumineexsccence band remains
constant.
XXXI
8.9, 11.8, 106
13.7
Taking into account the aforesaid and data from [6,
11, 14], we can assign the emission of the polymers
to the fluorescence of short-lived exciplexes formed
by Scheme 2 [Eqs. (2a), (2b)]. Participation of exci-
mers (or excited dimers) [15] seems doubtful because
of the positive value of P. It is known that, for an
excimer, P is negative [16]. At present, it is difficult
to identify the exciplexes formed in the polyimides.
We may only assume the presence of several local
centers in the polymer molecule, required for the exci-
plex formation. Since a change in the dipole orienta-
(backbone or pendant chain), and procedure of the
polymer synthesis. Replacement of the thiazole core
(polyimides XIII, XIV) with the oxazole core (XVII,
XIX) only weakly affects of both maxima (18600,
f
1
17300 cm , Table 1) and their intensity, irrespective
of the position of the heterocycle in the molecular
chain, whereas introduction of the benzimidazole ring
(polyimide XX) considerably enhances the intensity
of the first band. In the polymer containing the oxa-
diazole ring (polyimides XV, XVI),
of the low-
tion in the S1 state is restricted by the lifetime
,
f
s
frequency component is minimal in this series of
this quantity and P vary in the same direction. There-
fore, we can state that the red component in the
emission spectra of the polyimides with the maximum
1
polymers, 16 103 cm . In going from polyimides
XIII and XVII with the 2-phenylbenzazole group in
the backbone to polyimides XIV and XIX with the
same group in the pendant chain, the second maxi-
1
in the range (18.0 16.4) 103 cm (Table 1), whose
degree of polarization is the lowest (Table 2; Figs. 1,
2a), is the most short-lived.
1
mum is blue-shifted (by 1300 cm ), and the position
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 10 2005

1588
RTISHCHEV et al.
, nm
400
300
500
600 700
0.8
0.4
80
If,
A
arb. units
3
3
1
2
1
1
P
0.2
40
2
0.1
1
4
0
42
38
34
30
26
10 , cm
22
18
14
3
1
Fig. 1. Long-wave absorption (left) and fluorescence (right) band of films (295 K) of polyimides (1) VIII, (2) IX, and (3) XII
(
(
313, 366 nm); (4) fluorescence of Rh 6G in polymethacrylate (
546 nm); (1 ) fluorescence excitation spectrum
334 nm) of polyimide VIII.
exc
exc
450, 550 nm) and (1 ) fluorescence polarization spectrum (
f
exc
, nm
400
300
500
600
If,
A
arb. units
(a)
1
80
0.8
1
P
2
2
0.2
0.4
1
40
0.1
1
2
0
0
1
(b)
P
80
0.8
1
2
4
2
4
3
0.2
2
0.4
0
40
0
0.1
1
37
33
29
25
21
17
3
1
10 , cm
Fig. 2. Spectral characteristics (295 K) of (a) polyimide films and (b) polyamides and 5-amino-2-(4-aminophenyl)benzoxazole
in chloroform. Absorption (left) and fluorescence (right) spectra: (a) polyimides (1) XVII and (2) XIX; (b) polyamides
(1) XXVI (
313, 366 nm) and (2, 3) XXVII (
313 and 366 nm, respectively); (4) 5-amino-2-(4-aminophenyl)benz-
exc
exc
oxazole (
365 nm). Fluorescence polarization spectra: (a) polyimides (1 ) XVII and (2 ) XIX (
334 nm); (b) poly-
exc
exc
amides (1 ) XXVI and (2 ) XXVII (
366 nm); (1 ) excitation spectrum of polyimide XVII ( 540 nm).
exc
f
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 10 2005

FORMATION OF EXCIPLEXES IN FILMS OF POLYIMIDES
, nm
1589
300
400
500
600
If,
A
arb. units
1
0.8
2
80
2
3
P
30
40 20
10
1
1
0.4
0
2
0
37
33
29
25
10 , cm
21
17
3
1
Fig. 3. Absorption and luminescence of films of (1) polyquinazolone XXIX, (2) polyquinazolone XXXI, and (3) 5-amino-2-
(4-aminophenyl)benzimidazole in dimethylacetamide. , nm: (1) 313 and (2, 3) 366. Fluorescence polarization spectra of
polyquinazolones (1 ) XXIX ( 334 nm) and (2 ) XXXI (
exc
366 nm).
exc
exc
In the case of polyamides containing the same
diamine fragments as polyimides XIII XXIII (poly-
mers XXIV XXVIII, Table 1), we also observed two
fluorescence bands, one of which was shifted hypso-
florically relative to the corresponding component in
lar to that of the starting amine can be realized in the
case of formation of the intermolecular hydrogen bond
NH OC, decreasing the electron-withdrawing effect
of the carbonyl group in the polyamide macromole-
cule. Broadening of the emission band from the long-
wave side is caused by the presence of a weak red
component (a shoulder at about 18000 cm ; appar-
ently, exciplex emission). The fact that the position
and shape of the fluorescence band are independent of
the spectrum of the polyimide:
(20 21) 103 and
f
1
(18 19) 103 cm ;
(6 9) 103 and (10 16)
1
Ss
1
103 cm . Considerably smaller
of the blue
Ss
component is apparently due to a different nature of
the emission center. A strong influence on the lumi-
nescence characteristics of the polyamide is exerted
by the position of the 2-phenylbenzazole fragment:
in the backbone or pendant chain of the macromole-
cule. Figure 2 shows the spectral characteristics of
(a) polyimides and (b) polyamides that were prepared
from the same diamines containing the 2-phenylbenz-
oxazole fragment in the backbone (XVII, XXVI) and
pendant chain (XIX, XXVII). In the series XVII
(313, 366 nm) indicates that complexes 1 and 2
exc
are not formed, or that the probability of their forma-
tion is low. The polyamide containing the heterocycle
in the pendant chain (polymer XXVII), like its analog
XXVI, exhibits two-component fluorescence, but, in
contrast to XXVI, its major component is the exciplex
1
emission at 18400 cm , and the short-wave com-
1
ponent is minor (shoulder at 21000 cm ). The ab-
sorption spectrum of XVII contains, along with the
1
XIX, the absorption maximum ( ) is slightly red-
a
major maximum at 34600 cm characterizing the
1
shifted (by 600 cm ), and the general shape of the
absorption of 2-phenylbenzoxazole, also a long-wave
emission band does not change; only a high-frequency
1
shoulder at
27000 cm , significantly overlapping
1
a
shift of the red component (by 1300 cm ) is ob-
with the high-frequency component of the fluores-
cence; the relative intensity of the high-frequency
served (see above; Fig. 2a, spectra 1, 2).
Polyamide XXVI exhibits a broad, weakly struc-
fluorescence band grows with an increase in
from
313 to 366 nm (Fig. 2b, spectra 2, 3). Tehxics fact
suggests that polymer XXVII can form, along with
exciplexes (Scheme 2), also complexes 1 and 2
(Scheme 1). Presumably, the role of acceptor A in the
charge transfer is played by the benzoylamide or ben-
zoyldiphenyl oxide group of the polymer.
1
tured luminescence band with
21300 cm , asym-
f
metric to the long-wave absorption band with
29800 cm (Fig. 2b, spectra 1). Taking into accounat
1
the overlap of both bands and similarity of their char-
acteristics to those of the starting diamine, 5-amino-
2-(4-aminophenyl)benzoxazole (Fig. 2b, spectra 4),
we can assign the observed emission primarily to an
intramolecular transition with a significant contribu-
tion of the charge transfer from the amine nitrogen
atom to the heterocyclic core [17]. The structure simi-
Polyamides XXIV, XXV, and XXVIII behave sim-
ilarly, showing well-defined exciplex fluorescence
(Table 1).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 10 2005

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RTISHCHEV et al.
Polyquinazolones XXIX XXXI have a broad struc- pair, which is followed by formation of free charge
tureless long-wave absorption band apparently includ- carriers (Scheme 3).
ing several * and n * transitions. Replace-
ment of bis(1,3-phenoxy)benzene (polymer XXIX)
with 2-phenylbenzimidazole (XXXI) leads to a low-
Scheme 3.
h
1
a
D
frequency shift of the band maximum by 3500 cm
S
S*
S
(S D+)* (S D+)
S + D+
1
h
and of the red edge by 2400 cm (Fig. 3, spectra 1,
f
2). Taking into account the short-wave absorption of
1
the heterocyclic fragment ( 33000 cm ) [18], we can
assume appearance of a new la
* transition in-
The fluorescence quenching increases in going to
films of polymers containing heterocyclic structures
in the diamine component of the repeating unit; the
process is the most intense with the benzimidazole
component. This result is consistent with our previous
data on the sensitized photoconductivity [7 10]: On
introducing Rhodamine 6G into films of the benzimi-
dazole polyimide, the photoconductivity increased by
an order of magnitude compared to the other poly-
mers.
volving the amine nitrogen atom of the quinazolone
ring and the system of substituent R. Such a transi-
tion may be realized in other polyquinazolones also.
Significant overlap of the first (short-wave) fluores-
cence band of XXXI (23300 cm ) with the long-
wave absorption band suggests that the first band is
1
an autonomous molecular
*
transition with a
significant contribution of charge transfer, similar in
nature to the corresponding transition in 5(6)-amino-
2(4-aminophenyl)benzimidazole molecules [19] with
1
To summarize the results obtained, we can make
the following conclusions. We confirmed our previous
assumption [11] that all aromatic polyimides form
exciplexes in films. Complexes of this type are also
formed by heterocyclic polyimides and by polyamides
and other polymers in which the AD interaction is
realized. The relative lifetime of the exciplexes can be
estimated from the degree of polarization of the film
luminescence within the given band. Polyamides de-
rived from 2-phenylbenzazole derivatives as di-
amine components can form, along with exciplexes,
also various complexes in the ground state.
4500 cm (Fig. 3, spectra 2, 3). The other two
Ss
components in the fluorescence spectrum of this poly-
1
mer (20400 and 18500 cm ) are due, apparently, to
the exciplex emission, like both bands in the spectra
of XXIX and XXX (Table 1; Fig. 1, spectrum 1).
Quenching of photosensitizer luminescence. The
majority of polymers (Table 1) do not quench the
fluorescence of Rhodamine 6G dye or quench it
weakly:
/
= 1 2 {
and
are the quantum
ref
ref
efficiencies ofxthe sensitizer fluorexscence in an inert
reference polymer [poly(methyl methacrylate)] and in
the given polymer, respectively}. The other polymers
can be subdivided into two groups with respect to
EXPERIMENTAL
ref/ :
/
= 3 7: XIII < XXV < XXIX <
x
ref
x
1
XXVII < XXX < XXI < XXVIII < XVII;
16 106: XVIII < XXIV < XXXI.
/
=
x
ref
The H NMR spectra were recorded on a Bruker
AC-200 spectrometer (200 MHz) in DMSO-d6 rela-
tive to the solvent signal. The absorption spectra were
measured on a Specord M-40 spectrophotometer. The
apparatus and procedure of the luminescence measure-
ments were described elsewhere [21]. The lumines-
cence of films was measured in the frontal mode, and
that of solutions, at an angle of 90 . In low-tempera-
ture (77 K) measurements, the polymer solution in
chloroform was applied as a thin layer on the front
wall of a cylindrical quartz cell; after thorough drying
at 40 50 C, the resulting film was frozen. The polari-
zation measurements were performed using film pola-
roids. The degree of the fluorescence polarization P
was determined as follows:
Minor changes in the optical parameters of the dye
in the films (absorption, 542 5 nm; fluorescence,
560 575 nm) are apparently due to the macro- and
a
f
microeffects of the polymer matrix.
It is known that the sensitizer luminescence can be
quenched either by nonradiative energy transfer and
by electron transfer [5, 13]. In the first case, the nec-
essary condition is the overlap of the fluorescence
spectrum of the dye (S) with the absorption spectrum
of the polymer (complexes 1 and 2). As follows from
Figs. 1 3, this condition is not met: The energy defi-
1
ciency is 4000 9000 cm . A reasonable alternative
is an exciplex mechanism [13, 20] involving inter-
action of the excited sensitizer (S) molecule with the
donor fragment (D) of the polymer chain. A nonfluo-
rescing or weakly fluorescing exciplex is presumably
formed; it subsequently transforms into a radical ion
P = [I||
I /(T /100)]/[I|| + I /(T /100)],
where I|| and I are the intensities of the fluorescence
components (at a given frequency ) parallel and per-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 10 2005

FORMATION OF EXCIPLEXES IN FILMS OF POLYIMIDES
1591
pindicular to the polarized excitation beam, respec-
tively; T is the transmission by the monochromator-
analyzer of the perpendicular component, which was
determined in a separate experiment [22].
precipitate was filtered off, washed with water, and
recrystallized from aqueous DMF; yield 11.8 g (90%),
mp 215 216 C. The dinitro compound was reduced
with SnCl2 7H2O in concentrated HCl at 90 100 C
for 2 3 h. The isolated diamine was sublimed in a
The optical sensitizer of the photoconductivity,
Rhodamine 6G dye, was introduced both in each film
of the polymer and into an inert reference polymer,
poly(methyl methacrylate).
vacuum (2 mm Hg) at 210 C; yield 7.5 g (80%),
1
mp 228 229 C. H NMR spectrum (DMSO-d6),
,
ppm: 5.06 s (4H, NH2), 6.03 s (1H), 6.69 s (2H),
7.33 7.38 m (2H), 7.69 7.72 m (2H).
The fluorescence quenching was measured at an
excitation wavelength of 546 nm and was calculated
by the formula
2-(3,5-Diaminophenyl)benzothiazole was prepared
similarly to 2-(3,5-diaminophenyl)benzoxazole, start-
ing from 3,5-dinitrobenzoyl chloride and 2-aminothio-
1
phenol; yield 69%, mp 192 193 C (subl.). H NMR
/
= Iref(100
x
Tx)/Ix(100
Tref),
ref
spectrum (DMSO-d6), , ppm: 5.06 s (4H, NH2),
6.02 s (1H), 6.65 s (2H), 7.31 7.58 m (2H), 7.89
8.13 m (2H).
where
and
are the quantum efficiencies of the
dye fluorreefscence xin the standard and given polymers,
respectively; Iref and Ix are the fluorescence intensities
in the band maximum ( 560 575 nm); and Tref and
Tx are the transmissions of the corresponding films at
546 nm (70 90%). The relative measurement error
was 20%.
3,5-Diamino-N-[4-(5-phenyloxadiazol-2-yl)phen-
yl]benzamide was prepared similarly to 2,5-bis(3-
aminophenyl)oxadiazole, starting from 3,5-dinitroben-
zoyl chloride and 2-(4-aminophenyl)-5-phenyloxadi-
azole (synthesized from 4-nitrobenzoyl chloride and
benzhydrazide); yield 67%, mp 244 245 C (from
N-Methylpyrrolidone and N,N -dimethylacetamide
were dried over CaH2 and vacuum-distilled.
acetone DMF). 1H NMR spectrum (DMSO-d6),
,
ppm: 4.96 s (4H, NH2), 6.04 s (1H), 6.34 s (2H),
7.63 7.65 m (3H), 7.99 8.14 m (6H), 10.27 s (1H,
NHCO).
1,3-Bis(3,4-dicarboxyphenoxy)benzene dianhydride
and hexafluoroisopropylidenebisbenzene-3,3 ,4,4 -tet-
racarboxylic acid dianhydride were heated in a vacu-
um at 170 200 C to convert the hydrolyzed species
into the anhydride. 6,6 -Methylenebis(2-phenyl-3,1-
benzoxadiazin-4-one) was prepared according to [3].
Polyimides I XVII, XIX, XX, and XXIII. A stoi-
chiometric amount of the starting dianhydride was
added to a solution of appropriate diamine in N-meth-
ylpyrrolidone. The viscous solution of the initially
formed polyamido acid (25 wt %) was stirred for 8 h
at room temperature and then diluted to a concentra-
tion of 5 8 wt %. After that, the imidizing mixture
consisting of acetic anhydride and pyridine (volume
ratio 2 : 1) was added in a fivefold excess relative to
the polyimide monomeric units. Triethylamine (vol-
ume ratio to pyridine 1 : 10) was added to prevent
formation of the isoimide. After stirring for 10 h, the
solution was heated at 60 C for 2 h and slowly poured
into methanol; the precipitate thus formed was filtered
off, washed with methanol, and vacuum-dried at 60 C.
Diamines of the diphenylmethane series were pre-
pared according to [1], and the heterocyclic diamines
(starting compounds for preparing polyimides XI
XIII, XVII, and XX), according to [23 25].
2,5-Bis(3-aminophenyl)oxadiazole was prepared
by the reaction of 3-nitrobenzoyl chloride with hydra-
zine hydrate in N,N -dimethylacetamide, followed by
the cyclization of the resulting dinitro compound in
thionyl chloride and reduction of the product in DMF
on Raney nickel in the presence of hydrazine hydrate;
yield 72%, mp 248 248.5 C (from dioxane). 1H NMR
spectrum (DMSO-d6), , ppm: 5.50 s (4H, NH2),
6.78 6.81 m (2H), 7.18 7.30 m (2H).
Polyimides XVIII, XXI, and XXII. Cyclodehydra-
tion of the intermediate polyamido acid was per-
formed in a mixture of N-methylpyrrolidone with
toluene at 170 C (the released water was removed by
continuous azeotropic distillation). The resulting poly-
imides had high softening points, were soluble in
amides and, in some cases, in chlorinated solvents,
and form strong transparent films when applied onto
substrates.
2-(3,5-Diaminophenyl)benzoxazole. To a solution
of 5.45 g of 2-aminophenol in 60 ml of N,N -dimeth-
ylacetamide, cooled to 15 C, we added 11.54 g of
3,5-dinitrobenzoyl chloride. Then the mixture was
stirred for 1 h at 0 C and 2 h at 20 C. To the resulting
solution we added 9.05 g of p-toluenesulfonic acid
and 40 ml of p-xylene; the cyclization of the resulting
dinitro compound was performed at 160 C for 6 h,
with continuous removal of the released water. The
Polyamides XXIV XXVIII. To a 15 wt % solution
of appropriate diamine in N,N -dimethylacetamide,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 10 2005

1592
RTISHCHEV et al.
cooled to 10 C, we added with stirring 4,4 -bis(chlo-
rocarbonyl)diphenyl oxide. After stirring for 20 min,
the mixture was warmed up to 20 C, and the stirring
was continued for an additional 2 h. The released HCl
was scavenged with propylene oxide. The polymer
concentration was brought to 10 wt %, the viscous
solution was poured into water, and the precipitate
thus formed was washed with two portions of ethanol
and vacuum-dried at 60 C.
4. Fizicheskaya khimiya: Sovremennye problemy (Phys-
ical Chemistry: Modern Problems), Kolotyr-
kin, Ya.M., Ed., Moscow: Khimiya, 1987, p. 165.
5. Rumyantsev, B.M., Berendyaev, V.I., Vasilenko, N.A.,
Malengo, S.V., and Kotov, B.V., Vysokomol. Soedin.,
Ser. A, 1997, vol. 39, no. 4, p. 720.
6. Hasegawa, M. and Horie, K., Prog. Polym. Sci., 2001,
vol. 26, no. 1, p. 259.
7. Aleksandrova, E.L., Nosova, G.I., Solovskaya, N.A.,
Romashkova, K.A., Luk’yashina, V.A., Konozob-
ko, E.V., and Kudryavtsev, V.V., Fiz. Tekh. Poluprov.,
2004, vol. 38, no. 6, p. 678.
Polyquinazolones XXIX XXXI. To a solution of
appropriate diamine in m-cresol, we added a stoichio-
metric amount of 6,6 -methylenebis(2-phenyl-3,1-
benzoxazin-4-one) at 20 C (25 wt % monomers) and
P2O5 as dehydrating agent (70 mol % relative to the
diamine). The oil bath temperature was raised to
150 C over a period of 1 h, the mixture was stirred at
this temperature for 2 h, after which it was further
heated to 180 C over a period of 1 h and stirred at this
temperature for an additional 6 h. The cooled viscous
solution of the polymer was poured into ethanol, and
the precipitate thus formed was washed. After drying,
the polymer was dissolved in N,N -dimethylacet-
amide. The solution was filtered and again poured into
ethanol; the precipitate thus formed was washed with
ethanol. Polyquinazolones were dried in a vacuum at
a temperature gradually raised from 60 to 100 C.
8. Aleksandrova, E.L., Nosova, G.I., Romashkova, K.A.,
Galaktionova, E.F., and Kudryavtsev, V.V., Opt. Zh.,
2002, vol. 69, no. 10, p. 10.
9. Aleksandrova, E.L., Solovskaya, N.A., Nosova, G.I.,
Romashkova, K.A., Luk’yashina, V.A., and Kudryav-
tsev, V.V., Abstracts of Papers, III Mezhdunarodnaya
konferentsiya Amorfnye i mikrokristallicheskie polu-
provodniki (III Int. Conf. Amorphous and Micro-
crystalline Semiconductors ), St. Petersburg, 2002,
p. 103.
10. Nosova, G.I., Aleksandrova, E.L., Solovskaya, N.A.,
Romashkova, K.A., Gofman, I.V., Luk’yashina, V.A.,
Zhukova, E.V., and Kudryavtsev, V.V., Vysokomol.
Soedin., Ser. A, 2005, vol. 47, no. 9.
Films were applied onto glass supports by centri-
fugation from a 2% solution of a polymer in chloro-
form or N,N -dimethylacetamide. The coating was
dried at 60 C and then at 80 100 C in a vacuum to
constant weight. The polymer layer thickness was
1 2 m. If necessary, Rhodamine 6G (chemically
pure grade) was added into the initial polymer solu-
tion in an amount of 1 wt % relative to the polymer.
11. Kotov, B.V., Zh. Fiz. Khim., 1988, vol. 62, no. 10,
p. 2709.
12. Lamskaya, E.V. and Kotov, B.V., Dokl. Akad. Nauk
SSSR, 1987, vol. 296, no. 6, p. 1397.
13. Rumyantsev, B.M., Berendyaev, V.I., and Kotov, B.V.,
Vysokomol. Soedin., Ser. A, 1998, vol. 40, no. 11,
p. 1787.
14. Kapustin, G.V., Rumyantsev, B.M., Pebalk, D.V., and
Kotov, B.V., Vysokomol. Soedin., Ser. A, 1996,
vol. 38, no. 8, p. 1343.
ACKNOWLEDGMENTS
The study was financially supported by the Presi-
dent of the Russian Federation (project no. NSh-
1824.2003.3).
15. Guillet, J., Polymer Photophysics and Photochemistry:
An Introduction to the Study of Photoprocesses in
Macromolecules, New York: Cambridge Univ. Press,
1985.
REFERENCES
16. Ghosh, A.S., Gupta, D., and Basi, S., J. Photochem.,
1975, vol. 4, no. 3, p. 227.
1. Bessonov, M.I., Koton, M.M., Kudryavtsev, V.V.,
17. Rtishchev, N.I., Lebedeva, G.K., Kvitko, I.Ya., and
El’tsov, A.V., Zh. Obshch. Khim., 1988, vol. 58,
no. 9, p. 2148.
and Laius, L.A., Poliimidy
klass termostoikikh
polimerov (Polyimides: a Class of Heat-Resistant
Polymers), Leningrad: Nauka, 1983.
18. Cernani, A. and Passerini, R., J. Chem. Soc., 1954,
p. 2261; Lostovskii, I.Ya., Pushkina, L.N., and Ma-
zalov, S.P., Zh. Obshch. Khim., 1962, vol. 32, no. 11,
p. 2617.
2. Sokolov, L.B., Termostoikie aromaticheskie poliamidy
(Heat-Resistant Aromatic Polyamides), Moscow:
Khimiya, 1975.
3. Kulota, S., Moriwaki, T., Ando, T., Eton, S., and
Fukami, A., J. Polym. Sci., Polym. Chem. Ed., 1986,
vol. 24, no. 9, p. 2047.
19. Rtishchev, N.I., Kvitko, I.Ya., Nagorskaya, L.P., and
El’tsov, A.V., Zh. Obshch. Khim., 1993, vol. 63, no. 2,
p. 429.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 10 2005

FORMATION OF EXCIPLEXES IN FILMS OF POLYIMIDES
1593
20. Rumyantsev, B.M., Balabanov, E.I., Semenova, L.V.,
Yudina, G.I., and Mel’nichuk, L.A., Usp. Nauchn.
Fotogr., 1984, vol. 22, p. 161.
Applications to Photochemistry and Analytical
Chemistry, Amsterdam: Elsevier, 1968.
23. Preston, J., De Winter, W.E., and Hofferbert, W.L.,
J. Heterocyclic Chem., 1969, vol. 6, no. 1, p. 119.
24. Kym, O., Chem. Ber., 1899, vol. 32, no. 9, p. 2178.
25. Smolenkova, L.A., Rudaya, L.I., Kvitko, I.Ya., and
21. Rtishchev, N.I., El’tsov, A.V., Kvitko, I.Ya., and
Alam, L.B., Zh. Obshch. Khim., 1980, vol. 50, no. 9,
p. 2070.
El’tsov,
A.V.,
USSR Inventor’s Certificate
22. Parker, C.A., Photoluminescence of Solutions. With
no. 486018, 1973, Buyll. Izobret., 1976, no. 36.
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