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Luminescence and ODMR of a diacetylene single crystal
Journal of Luminescence 18/19 (1979) 482—486 © North-Holland Publishing Company
LUMINESCENCE AND ODMR OF A D’ACETYLENE SINGLE CRYSTAL H. EICHELE and M. SCHWOERER Universitat Bayreuth, Phvsikalisches Institut, Postfach 3008, D 8580 Bayreuth, Fed. Rep. Germany
and J.U. VON SCHUTZ Physikalisches Institut. Teil 3. Universitdt Stuttgart, D-7000 Stuttgart 80, Fed. Rep. Germany
Carbazolyl substituted diacetylene crystals in their monomeric form have been investigated by luminescence and ODMR spectroscopy. The phosphorescence spectrum originates from four trap triplet states. Their depths (23, 71. 224 and 369cm ), their fine-structure parameters (0.097 /13/ <0.1002 cm 0.0068
1. Introduction Solid state polymerization of diacetylene monomer crystals yields macroscopic polymeric single crystals. Therefore high polymers can be investigated without the complication of unknown structural disorder. Contrasting to the properties of chromophore substituted saturated polymers [1] fully polymerized diacetylene crystals do not luminesce in the visible and uv-region. However partially polymerized. defective and monomeric diacetylenes show luminescence [2, 3]. In order to understand this quenching by polymerization, first the luminescence properties of diacetylenes in their monomeric form have to be investigated. We studied several differently substituted diacetylene monomer crystals [4]. Here we report the phosphorescence and ODMR-results of a carbazolyl-substituted diacetylene (DCH) stacked in the crystal as shown in fig.
2. Luminescence spectra UV-excitation (A 310 nm) yields fluorescence and phosphorescence. The phosphorescence spectrum is composed of four series denoted by a, b, c and d. A list of the observed vibronic frequencies may be found in ref. [51. Fig. 2 shows the temperature dependencies of the intensities and phosphores482
H. Eichele et al/Luminescence and ODMR of a diacetylene single crystal
C NC~C
c~cNN ~
cCN ~
~C~N
7 c~
N.
~
~ S
•..~
C
~
N’~~~C “~-~
C~CN c .~
483
c C
\
N
C
c
N
c
C
/C\
~ ~ ~ ~c_c_N._N.-_._-~._C C
C~C
~
,N
~
C~C....c ~“c C
Fig. 1. Stacking of the carbazolyl substituted diacetylene molecules in the crystal.
cence lifetimes of the 0—0-transitions a—d. Below certain temperatures the intensities as well as the life-times are constant. Above these temperature values both, the intensities and the lifetimes, decrease rapidly. This behaviour has been analyzed using the model of triplet exciton trapping discussed by GUttler et al. [61yielding the trap depths 23, 71, 224 and 369cm ‘.According to this model the fit of the theoretical curves to the lifetime-plots (fig. 2) indicate the existence of a triplet exciton band above the trap states [7].
3. ODMR results Adiabatic and transient ODMR experiments reveal the triplet character of the trap states. Their zero field splitting parameters and sublevel decay rate constants are tabulated in table 1. The complete kinetic schemes resulting from the analysis of the transient ODMR-experiments [7] are shown in fig. 3. As can be seen from this figure the traps differ in their kinetic behaviour.
4. Discussion Monomeric DCH-crystals show phosphorescence of four triplet traps which are populated by a triplet exciton band. This band is formed by the interaction of the substituents. Because the fine-structure parameters of the traps are very similar to those of carbazol traps in the neat crystal [8], the triplet wavefunction is constricted to the substituent. The different kinetic properties of the traps indicate different local symmetries. Because the DCH-phosphorescence is quite insensitive to crystal doping [9] the traps are probably due to lattice distortions.
I
/
Trap
t22/.
f
I m
I
~~0O
10
/ A
/
A
A
/
I 0.15
Lu 7’cm Trapb ~
I
c~
/ /
.~ /
0 0
/
a
I
Trap a
23cm
m
5
Temperature/K
I
4
a)
~2
N
U a)
~ -
\..
Trap a
Tra~b
\
4 4 4 Temperature/ K
...,
10
—~
.
_________________
~
Temperature/K
1~
._J
~2
E
a)
a) N
a)
~
ft
~
Trap d
20
Temperature/ K
10
_________________
~
Temperature/K
i
Trapc
_____________________
.~2
a) N iiiA
~
16
—2
E
N a)
1~
U ±~_+~_+_ (fl4
Fig. 2. Temperature dependence of the phosphorescence intensities (left) and lifetimes of trap a d (right).
0 005 01 0,2 025 Reciprocal Temperature—_~.
$
J_
~
0. (I, 0
? ?
P ~
~
a)
o
a)~a
U C
359cm~~
C ~0I
Trapd
4 ~~pO
Is
~
>~
I
4.020
30
\~\
20
‘S 0
‘S
a
a’ 0
a
a a
a
‘S
a
‘S
‘2 03
01
~opcZ
Trap a
1
02
3
01 02 03
no
Trap d
~
Trap b
Fig. 3. Kinetic schemes of the trap states in DCH monomer crystals. The lengths of the arrows correspond to the rate (constants). The relative steady state populations are drawn in diagrams on the left of each level scheme. Curved arrows: total sublevel decay rate constants, straight arrows: population rates and relative radiative decay rate constants.
02 03
01
00
C.,
‘S ~0
a ‘S (S
0
a
a a.
‘S
a 0
‘S 0 ‘S
‘S
0
486
H. Eichele ef al./ Luminescence and ODMR of a diacetvlene single crystal Table I Fine structure parameters and depopulation rate constants. 13 and E are the absolute zero field splitting parameters. k, (i x, y, z) are the total sublevel decay constants D (cm
F (cm
Trap depth (cm ‘1 5]
~0.00007
~0.00007
a
23
0.10021
0.00971
h
71
c d
224 3(9
trap
‘)
0.09838 1)09728
(/3) k~ (s ‘)
‘)
(/3) (
0 I 46~~
(/3) k I)
0.07
0.27
0.00684
~0.08
0 4—0.29(a)
0.05
0.01054 0 00877
0.0~ ~0 30
0.04 0 31
0 07
(a): Estimated from the condition k(4.2 K) (/3): Uncertainty approximately I S~.
~(k,
+
k
+
k
This is reasonable because DCH monomer undergoes a phase transition at 142 K, which partially destroys the crystal [9].
Acknowledgements We thank V. Enkelmann, G. Schleier and 6. Wegner for the crystals and the projection of the crystal structure. W. Goldacker, D. Schweitzer and H. Zim mermann kindly supplied their manuscript prior to publication.
References (I] W. Klöpffer and H. Bauser. 7. Phys. Chem 101 (1976) 25. [21 H. Eichele and M. Schwoerer, Phys. Stat. Sol. (a) 43 (1977) 465. 13] D. Bloor, D.N. Batchelder and F.H. Preston, Phys. Stat. So!. (a) 40(1977) 279. [4] The crystals were supplied by G. Sch!eier and R. Tieke from the ‘lnstitut fur Makromolekulare Chemie”. Prof. G. Wegner in Freiburg. Fed. Rep. Germany [S[ V. Enkelmann. G Schleier. G. Wegner. H. Eichele and M. Schwoerer. Chem. Phys I elI ~2 (1977)314. 161 W. GQttler. J.U. von Schütz and H.C. Wolf. Chem. Phys. 24 (1977) 1S9. 171 H. Eichele, M. Schwoerer and J.U. von SchOtz. Chem. Phys. Lett.. in press. [8] W. Goldacker. D. Schweitzer and H Zimmermann. to he published 19] H. Elchele. Thesis. Universitat Bayreuth (1978).
LUMINESCENCE AND ODMR OF A D’ACETYLENE SINGLE CRYSTAL H. EICHELE and M. SCHWOERER Universitat Bayreuth, Phvsikalisches Institut, Postfach 3008, D 8580 Bayreuth, Fed. Rep. Germany
and J.U. VON SCHUTZ Physikalisches Institut. Teil 3. Universitdt Stuttgart, D-7000 Stuttgart 80, Fed. Rep. Germany
Carbazolyl substituted diacetylene crystals in their monomeric form have been investigated by luminescence and ODMR spectroscopy. The phosphorescence spectrum originates from four trap triplet states. Their depths (23, 71. 224 and 369cm ), their fine-structure parameters (0.097 /13/ <0.1002 cm 0.0068
1. Introduction Solid state polymerization of diacetylene monomer crystals yields macroscopic polymeric single crystals. Therefore high polymers can be investigated without the complication of unknown structural disorder. Contrasting to the properties of chromophore substituted saturated polymers [1] fully polymerized diacetylene crystals do not luminesce in the visible and uv-region. However partially polymerized. defective and monomeric diacetylenes show luminescence [2, 3]. In order to understand this quenching by polymerization, first the luminescence properties of diacetylenes in their monomeric form have to be investigated. We studied several differently substituted diacetylene monomer crystals [4]. Here we report the phosphorescence and ODMR-results of a carbazolyl-substituted diacetylene (DCH) stacked in the crystal as shown in fig.
2. Luminescence spectra UV-excitation (A 310 nm) yields fluorescence and phosphorescence. The phosphorescence spectrum is composed of four series denoted by a, b, c and d. A list of the observed vibronic frequencies may be found in ref. [51. Fig. 2 shows the temperature dependencies of the intensities and phosphores482
H. Eichele et al/Luminescence and ODMR of a diacetylene single crystal
C NC~C
c~cNN ~
cCN ~
~C~N
7 c~
N.
~
~ S
•..~
C
~
N’~~~C “~-~
C~CN c .~
483
c C
\
N
C
c
N
c
C
/C\
~ ~ ~ ~c_c_N._N.-_._-~._C C
C~C
~
,N
~
C~C....c ~“c C
Fig. 1. Stacking of the carbazolyl substituted diacetylene molecules in the crystal.
cence lifetimes of the 0—0-transitions a—d. Below certain temperatures the intensities as well as the life-times are constant. Above these temperature values both, the intensities and the lifetimes, decrease rapidly. This behaviour has been analyzed using the model of triplet exciton trapping discussed by GUttler et al. [61yielding the trap depths 23, 71, 224 and 369cm ‘.According to this model the fit of the theoretical curves to the lifetime-plots (fig. 2) indicate the existence of a triplet exciton band above the trap states [7].
3. ODMR results Adiabatic and transient ODMR experiments reveal the triplet character of the trap states. Their zero field splitting parameters and sublevel decay rate constants are tabulated in table 1. The complete kinetic schemes resulting from the analysis of the transient ODMR-experiments [7] are shown in fig. 3. As can be seen from this figure the traps differ in their kinetic behaviour.
4. Discussion Monomeric DCH-crystals show phosphorescence of four triplet traps which are populated by a triplet exciton band. This band is formed by the interaction of the substituents. Because the fine-structure parameters of the traps are very similar to those of carbazol traps in the neat crystal [8], the triplet wavefunction is constricted to the substituent. The different kinetic properties of the traps indicate different local symmetries. Because the DCH-phosphorescence is quite insensitive to crystal doping [9] the traps are probably due to lattice distortions.
I
/
Trap
t22/.
f
I m
I
~~0O
10
/ A
/
A
A
/
I 0.15
Lu 7’cm Trapb ~
I
c~
/ /
.~ /
0 0
/
a
I
Trap a
23cm
m
5
Temperature/K
I
4
a)
~2
N
U a)
~ -
\..
Trap a
Tra~b
\
4 4 4 Temperature/ K
...,
10
—~
.
_________________
~
Temperature/K
1~
._J
~2
E
a)
a) N
a)
~
ft
~
Trap d
20
Temperature/ K
10
_________________
~
Temperature/K
i
Trapc
_____________________
.~2
a) N iiiA
~
16
—2
E
N a)
1~
U ±~_+~_+_ (fl4
Fig. 2. Temperature dependence of the phosphorescence intensities (left) and lifetimes of trap a d (right).
0 005 01 0,2 025 Reciprocal Temperature—_~.
$
J_
~
0. (I, 0
? ?
P ~
~
a)
o
a)~a
U C
359cm~~
C ~0I
Trapd
4 ~~pO
Is
~
>~
I
4.020
30
\~\
20
‘S 0
‘S
a
a’ 0
a
a a
a
‘S
a
‘S
‘2 03
01
~opcZ
Trap a
1
02
3
01 02 03
no
Trap d
~
Trap b
Fig. 3. Kinetic schemes of the trap states in DCH monomer crystals. The lengths of the arrows correspond to the rate (constants). The relative steady state populations are drawn in diagrams on the left of each level scheme. Curved arrows: total sublevel decay rate constants, straight arrows: population rates and relative radiative decay rate constants.
02 03
01
00
C.,
‘S ~0
a ‘S (S
0
a
a a.
‘S
a 0
‘S 0 ‘S
‘S
0
486
H. Eichele ef al./ Luminescence and ODMR of a diacetvlene single crystal Table I Fine structure parameters and depopulation rate constants. 13 and E are the absolute zero field splitting parameters. k, (i x, y, z) are the total sublevel decay constants D (cm
F (cm
Trap depth (cm ‘1 5]
~0.00007
~0.00007
a
23
0.10021
0.00971
h
71
c d
224 3(9
trap
‘)
0.09838 1)09728
(/3) k~ (s ‘)
‘)
(/3) (
0 I 46~~
(/3) k I)
0.07
0.27
0.00684
~0.08
0 4—0.29(a)
0.05
0.01054 0 00877
0.0~ ~0 30
0.04 0 31
0 07
(a): Estimated from the condition k(4.2 K) (/3): Uncertainty approximately I S~.
~(k,
+
k
+
k
This is reasonable because DCH monomer undergoes a phase transition at 142 K, which partially destroys the crystal [9].
Acknowledgements We thank V. Enkelmann, G. Schleier and 6. Wegner for the crystals and the projection of the crystal structure. W. Goldacker, D. Schweitzer and H. Zim mermann kindly supplied their manuscript prior to publication.
References (I] W. Klöpffer and H. Bauser. 7. Phys. Chem 101 (1976) 25. [21 H. Eichele and M. Schwoerer, Phys. Stat. Sol. (a) 43 (1977) 465. 13] D. Bloor, D.N. Batchelder and F.H. Preston, Phys. Stat. So!. (a) 40(1977) 279. [4] The crystals were supplied by G. Sch!eier and R. Tieke from the ‘lnstitut fur Makromolekulare Chemie”. Prof. G. Wegner in Freiburg. Fed. Rep. Germany [S[ V. Enkelmann. G Schleier. G. Wegner. H. Eichele and M. Schwoerer. Chem. Phys I elI ~2 (1977)314. 161 W. GQttler. J.U. von Schütz and H.C. Wolf. Chem. Phys. 24 (1977) 1S9. 171 H. Eichele, M. Schwoerer and J.U. von SchOtz. Chem. Phys. Lett.. in press. [8] W. Goldacker. D. Schweitzer and H Zimmermann. to he published 19] H. Elchele. Thesis. Universitat Bayreuth (1978).