- Email: [email protected]
Electrogeneration of triplet states of intramolecular anthracene-amine systems
Volume
70, number
CHEMICAL
3
PHYSICS
ELECTROGENERATION
OF TRIPLET STATES
OF INTRAMOLECULAR
ANTHRACENE-AMINE
R ZIEBIG
SYSTEMS
and F. FXAGST
Seknon Clemie, Humboldt-Umverslt~t, Recewed
29 November
DDR-104 BerLn, GDR
1979
In the electron trancfer bctwcen the catlon ralcals Ah D+or A systems and the amon ralcals B-of some heterocychc IS formed tnplet state of the anthraccne moiety 3A h D or 3AMD molecular tnplet e~c~plews 3A%‘J or 3(A%+) and 3(B-D3 A or
cene-anune
1. Introduction In the reaction between electrogenerated anion radrcak A- and cation radicals Dt , the formation of excited smglet states ‘A* or ID*, triplet states 3A or 3D, and exciplexes ‘(A-D+)* , is found, If the compounds A and D fulfl the electrochemical and spectroscopic conditions for electrochemiluminescence (ECL) [I-31. This is not the case for N-p-tolylphthalinude (NT’PI) as anion radical precursor and some N-N-dimethylaniline denvatives D as cation radical precursors. Therefore, the electron transfer between NTPI- and D+ in tetrahydrofuran (THE) occurs without luminescence. However, If an anthracene derivatiye is hnked to the anune by a himethylene group (compounds AMD), the emissron OH mtramolecular anthracene-amine excrplex l(A-D+)* as well as of the anthracene moiety r A*M D is detected in THF and the partrcipatron of triplet states 3AM D or 3(Aq+) m the ECL p recess IS made probable from a magnetrc field effect on the ECL intensity and from energy-transfer experiments [4] _ Dt + NTPI-:
no em&on;
AM Dt + NTF%: t (A%+)* The mechanism, 544
15 March 1980
LETTERS
in THF formation
and SAM
D or ‘(A-D+)
by which anthracene
of 1A* M D, . is exerted
al-
MD+of the amme moiety of four mtramolecular anthraand carbonyl compounds In acetomtrde/toluene, the As mtermedlates m thrs process, mtramolecular and mter3(B-D+$-A are discussed
though it IS not du-ectly invoIved m the electron fer reaction, is not yet clear. Therefore, the ECL compounds Ia-Id was studred in mixed systems a series of anion radical precursors B- and in the ence of triplet quenchers Q.
transof with pres-
IJCH3
Ian = 1, R = CeH5; Icn=3,R=CHa;
Ibn=3,R=H. Idn=3,R=C6Hs.
In order to favour the formation of the triplet uct 3AM D, a polar solvent (acetonitriIe/toluene was chosen for these experiments.
prod1 : 1)
2. Experimental The preparation and purification of the l-amino3-anthryI-(P)-propanes Ib-Id were described elsewhere [S] .9-(N-methyI-N-p-anisyl-amino)-methyI1O-phenylanthracene Ia (m.p. 169OC) was prepared from 9-bromomethyl-lo-phenylanthracene and Nmethylq-anisidine and identified by C,H,N-analysis, mass spectroscopy (M+ = 403) and IUMR spectros-
Volume 70, number 3
CHEMICAL
PHYSICS
copy. The other compounds used in mixed ECL and energy-transfer experiments were purchased or prepared and purified according to literature procedures. All measurements were carried out in a 0.1 M solution of tetran-butylammonium perchlorate in a 1 : 1 acetonitnle/toluene mixture (TBAP/AN/TOL). The addition of toluene was necessary because some of the compounds were not sufficiently soluble m pure acetonitnle. The ECL was generated at a rotating ring-disc electrode (RRDE, o = 3 14 s- *) usmg cells, electrodes and apparatus as described in a previous paper 161. As reference electrodes, saturated aqueous calomel electrodes (SCE) were apphed. Au potentials given in this paper refer to this electrode. The apparatus used for the measurement of the ECL spectra and for the investigations in a magnetic field were also described previously [7,8]. AU measurements were carried out under a nitrogen atmosphere.
3. Results
and discussion
The ECL was generated at a rotatmg platinum ring-disc electrode (RRDE) in 0.1 M TBAP/AN/TOL contairung 10-S M of one of the compounds Ia-Id and of the other components involved in the experiments. In most cases the cations were generated at the disc electrode and the anions at the ring electrode. In control experiments no significant change of the results was found in the reverse case. The voltammetric half-wave potentials, triplet energies and singlet energies of the compounds are given in table 1. As a suitable anion radical precursor B, N+tolylphthalimide (NTPI) is used in most of these experiments. Deviating from the results in THF [4J, in no case could any emission be detected within the sensitivlty linuts of the instruments if NTPI- and the cation radicals of Ia-Id, AA D+ or AMDt , are produced at the RRDE. Obviously, the formation of exciplexes found in THF for this reaction is ineffective in the more polar solvent AN/TOL. However, if perylene (PER) is added to the AADt/NTPIor AMDf/ NTPI- systems, the sensitized perylene spectrum is observed (fg. 1, curve 4). It can be seen from the comparison between the luminescence-potential curves (fig. 1, curves 2 and 3) and the voltammogram (curve 1) that the emission unambiguously originates
15 March 1980
LETTERS
Table 1 Anodic and cathodic half-wave potenti&, tiplet energies and singlet energies of the compounds investigated COmpound a)
E% (V versus SCE) b)
q”pz (V versus SCE) b)
la Ib
+0.62 +0.54 +0.55 +0.54 >+1.7 +1.05
-1.93 -1.98 -2.01 -1.97 -1.40 -1.67
IC
Id NTPI PER
ET C) (ev)
ES (ev)
I.80 1.81 1.80 1.80 d) 1.56
3.08 3.15 3.15 3.08 d) 28
a) Abbreviations see text. b) Anodlc half-wave potentials in acetonitrile and cathodic half-wave potentials in DMF [S]. c) In the case of la-Id the triplet energes of 9methylanthracene, S,ZO-dunethylanthracene and 9-phenylanthracene are given. d) Values un~~nown
from the reaction between the cation radical of the amine moiety (q2 = +0.54 V) and the anion radical of NTPI (E$2 = -1.40 V). Above +l .O V (oxidation of PER and the anthracene moiety) the anode reaction becomes irreversible [S] and the intensity decreases. The increase in intensity at the anodic wave of PER (EF2 = - 1.67 V) should rather be due to an enhanced formation of NTPIT by the homogeneous
Ld.
.. .
I
.
1
.
.
.
.
.
.
Fig. 1. Voltammogram at the rotating disc electrode (curve I, w = 78 s-l), dependence of the ECL intensity on the potew bal of the disc electrode Es at the RRDE (curve 2, ER = +0.85 V and curve 3, ER = - I.60 V) and ECL spectmm (curve 4, not corrected for reabsorption) of a solution co* taining Id, NTPI and PER (concentrations loo3 M) in 0.Z M TEMP/AN/TOL
545
CHEMICAL
Volume 70, number 3
PHYSICS
15 March 1980
LETTERS
reaction between PER- and NTPI than to the direct excitation of PER. The Iuminescence of the AAD?/ NTPI- system was about 20 times more intense than in the case of the AM Dt/NTPIsystems, between which no srgmficant difference in intensny was found. In a magnetic field of 5 kG an increase rn intensity of 17-2 1% was found. This indicates the partrcipation of trrplet states. In general, for a triplet mechanism a magnetrc field effect of S-30% is expected
AMD-e+AMDf
[S,91Energeticahy, neither the tnplet state 3NTPI nor that of the amine moiety AA3D or AM3D can primarily be formed in the electron transfer [see eq. (14) below] _ Although both tnplet energies are not known, they can be estimated to be higher than 2.5 eV (NTPI) and 2.9 eV (N,N-drmethylq-anisidine) from other ECL experiments [l I ] and from the values of related compounds. This exceeds by far the reaction enthalpy of the electron transfer, which is about 1.9 eV accordurg to eq. (14). From the same reason also the excited singlet states ~NTPI*, rA*M D and AM ID* can be excluded. Three drfferent interpretations of the sensitized perylene emission are possible: (i) An energy transfer from the reaction center of the electron transfer to the neighbouring anthracene moiety leads to the direct formation of ;AAD or 3AM D. Such an energy transfer should be more effective for AAD than for AM D and would explain the differences 111the sensitized ECL mtensities. Subsequently 3A*D or 3AM D is quenched by PER and 3PER is transformed mto the ertuttmg smglet state by triplet-tnplet anmhdation.
@I) Formation of an intermolecular triplet exciplex and subsequent energy transfer to PER or to the anthracene moiety. ‘llus triplet exciplex could also be a transition state of mechanism (I).
AAD-e+AADt
,
B+e+B:, AADf
(1) (2)
+B-+3Af’D+B,
(3)
3AAD -I- PER + AAD + 3PER ,
(4)
2 3PER + ‘PER*
(5)
+ PER,
1PER* --f PER + hu .
(6)
(u) Formation of an rntramolecular triplet excrplex, which either 1s quenched by PER or is transformed lnro 3AAD and 3AMD, respectively. 546
,
(7)
B+e+B-, AAADt
(2) + Jj- + 3(A?+)
+B ,
3(rD+)+PER+AMD+3PER, 3 (m+)
AMD:
+3AMD.
(8) (9) (IO)
-I- Br + 3(B-D+wA,
(11)
3(B-D+vA-+B+3AMD,
(12)
PER + 3(B-D+jM
(13)
A +3PER+AMD+B.
Further evidence about the triplet state prrmarily formed in this process should be given from energetic considerations. In the electron transfer an excited state can be formed only IF its energy is lower than or equal to the reaction enthalpy AH, whrch can be estimated from the polarographic half-wave potentials
D-31
TAS=O.l
eV.
(14)
In a series of experunents wrth Id, NTPI was replaced by other compounds B, the half-wave potentials of which differ in a stepwise manner, and the sensrtized ECL intensity of PER IS measured. The results are shown in fig. 2a. The luminescence of PER is observed only if the difference ETi$(AM D) E$(B) exceeds 1.8 eV, suggesting that the triplet energy of the unknown intermediate is between 1.8 and 1.9 eV. The same result was obtained in a second series of experiments with Ic and NTPI, in which PER was replaced by some other tnplet energy acceptors Q w&h different trrplet energies (fig. 2b). only for ET(Q) f 1.8 eV couId the sensitized ECL spectrum of Q be measured,whereas for ET(Q) > 1.8 eV no ECL is observed. Therefore, the tnplet energy of the anthracene moiety (1.80 to 1.82 eV) seems to be the critical energy for the ECL of the AhDt/Br/Q and AM Dt/
Volume
70, number
CHEMICAL
3
b)
Cl) IO-
t
.-
.
iz =z
, -10
:
.. ::
_g
s
y
7 E = z
=
2 3 lt L .--. . ’ 18 22 I.& E,%UdI - E;:% 6 I , V -
energy to the anthracene moiety without any intermediate step seems unlikely. On the other hand, it cannot he decided to what extent an intramolecular triplet exciplex, which could also have an energy of 1.8 eV, participates in this process.
-05
Acknowledgement
.5
0
15 March 1980
.
06
05-
PHYSICS LETTERS
6 .
.
. 16
a
’ 18
a
.-20
E,(Q)
ev
-
18
’ 0 22
Fig. 2. Sensihzed ECL mtenslty of Q m 0.1 M TBAP/AN/TOL at the RRDE, not corrected for the dependence of the photomultipher response on the wavelength. Concentrations of all components 10s3 M. (a) Dependence on the difference between the oxidation half-wave potential of Id and the reduction ha&wave potentials of some anion radical precursors B. Compounds B/Q- (1) anthraquinonelrubrene, (2) benzile/ PER, (3) I&bls-@-benzoyIvinyl)-benzene/PER, (4) fluorenonel PER, (5) N-phenyl-naphthakmide/PER, (6) NTPI/PER, (7) pmethoxybenzophenone/l,3di_p-blphenyiyl+phenyl-2pyrazolme. (b) Dependence on the tnplet energy of the emitter Q for Ic/NTPI. Compounds Q: (1) PER, (2) 1,3,4,7tetraphenyhsobenzofuran, (3) 9,IO-d1q-biphenylylanthracene, (4) 9,1Odlphenylanthracene, (5) 9,IO&methylanthracene, (6) 9-methylanthracene, (7) I-p-blphenylyl-3,5-diphenyl-2pyrazohne, (8) pyrene.
The authors thank Dr. H.-J. Hamann and Dr, W. Jugelt for the support of these investigations and for helpful discussions of the results.
References
[ 21 [3] [4] [S] [6] 17 ] [ 81
B-/Q systems. From
this reason, the most probable mechanism is the formation of 3 AAD or SAM D via an instable intermolecular triplet exciplex 3(B-D”$ A or 3 (B-D+* A [reactions (11) and (1211, the lifetime of which is too short for an intermolecular ener-
gy transfer to Q. The direct transfer of the reaction
Faulkner and A.J. Bard, Electroanalytical chemistry, VoL 10, ed. A.J. Bard (Dekker, New York, 1976)_ L.R Faulkner, Intern. Rev. SCI. Phys. Chem. Ser. 2 9 (1976) 213. F. Pragst, 2. Chem 18 (1978) 41. R Zleblg. %-.I. Hamann, IV. Jugelt and F. Ragst, J_ Luminescence, to be published K-J. Hamann, F. Pragst and W. Jugelt, J. Prakt. Chea 318 (1976) 369. R Zlebig, F. Pragst and W. Jugelt, Z. Physik Chem (Leipzig) 259 (1978) 1009. F. Pragst, R Zlebrg, J. Kunze, IV. Jugelt and ICL Krause, Z. Physik. Chem. (Leipzig) 257 (1976) 465. F. Ragst, G. Fabian, R. Ziebig, D. Schmidt and IV. Jugelt, Chem. Phys. Letters 36 (1975) 630. LR Faulkner, H. Tachrkawa and A.J. Bard, J. Am, Chem. Sot. 94 (1972) 691. R. Ziebig and F. Pragsf 2. physik. Chem (Leipzig) 260 (1979) 748. F. Pragst, R. Ziebrg and E. Boche, J. Luminescence 21 (1979) 21.
[ 11 LR
[9] [IO] [ 1 I]
547
70, number
CHEMICAL
3
PHYSICS
ELECTROGENERATION
OF TRIPLET STATES
OF INTRAMOLECULAR
ANTHRACENE-AMINE
R ZIEBIG
SYSTEMS
and F. FXAGST
Seknon Clemie, Humboldt-Umverslt~t, Recewed
29 November
DDR-104 BerLn, GDR
1979
In the electron trancfer bctwcen the catlon ralcals Ah D+or A systems and the amon ralcals B-of some heterocychc IS formed tnplet state of the anthraccne moiety 3A h D or 3AMD molecular tnplet e~c~plews 3A%‘J or 3(A%+) and 3(B-D3 A or
cene-anune
1. Introduction In the reaction between electrogenerated anion radrcak A- and cation radicals Dt , the formation of excited smglet states ‘A* or ID*, triplet states 3A or 3D, and exciplexes ‘(A-D+)* , is found, If the compounds A and D fulfl the electrochemical and spectroscopic conditions for electrochemiluminescence (ECL) [I-31. This is not the case for N-p-tolylphthalinude (NT’PI) as anion radical precursor and some N-N-dimethylaniline denvatives D as cation radical precursors. Therefore, the electron transfer between NTPI- and D+ in tetrahydrofuran (THE) occurs without luminescence. However, If an anthracene derivatiye is hnked to the anune by a himethylene group (compounds AMD), the emissron OH mtramolecular anthracene-amine excrplex l(A-D+)* as well as of the anthracene moiety r A*M D is detected in THF and the partrcipatron of triplet states 3AM D or 3(Aq+) m the ECL p recess IS made probable from a magnetrc field effect on the ECL intensity and from energy-transfer experiments [4] _ Dt + NTPI-:
no em&on;
AM Dt + NTF%: t (A%+)* The mechanism, 544
15 March 1980
LETTERS
in THF formation
and SAM
D or ‘(A-D+)
by which anthracene
of 1A* M D, . is exerted
al-
MD+of the amme moiety of four mtramolecular anthraand carbonyl compounds In acetomtrde/toluene, the As mtermedlates m thrs process, mtramolecular and mter3(B-D+$-A are discussed
though it IS not du-ectly invoIved m the electron fer reaction, is not yet clear. Therefore, the ECL compounds Ia-Id was studred in mixed systems a series of anion radical precursors B- and in the ence of triplet quenchers Q.
transof with pres-
IJCH3
Ian = 1, R = CeH5; Icn=3,R=CHa;
Ibn=3,R=H. Idn=3,R=C6Hs.
In order to favour the formation of the triplet uct 3AM D, a polar solvent (acetonitriIe/toluene was chosen for these experiments.
prod1 : 1)
2. Experimental The preparation and purification of the l-amino3-anthryI-(P)-propanes Ib-Id were described elsewhere [S] .9-(N-methyI-N-p-anisyl-amino)-methyI1O-phenylanthracene Ia (m.p. 169OC) was prepared from 9-bromomethyl-lo-phenylanthracene and Nmethylq-anisidine and identified by C,H,N-analysis, mass spectroscopy (M+ = 403) and IUMR spectros-
Volume 70, number 3
CHEMICAL
PHYSICS
copy. The other compounds used in mixed ECL and energy-transfer experiments were purchased or prepared and purified according to literature procedures. All measurements were carried out in a 0.1 M solution of tetran-butylammonium perchlorate in a 1 : 1 acetonitnle/toluene mixture (TBAP/AN/TOL). The addition of toluene was necessary because some of the compounds were not sufficiently soluble m pure acetonitnle. The ECL was generated at a rotating ring-disc electrode (RRDE, o = 3 14 s- *) usmg cells, electrodes and apparatus as described in a previous paper 161. As reference electrodes, saturated aqueous calomel electrodes (SCE) were apphed. Au potentials given in this paper refer to this electrode. The apparatus used for the measurement of the ECL spectra and for the investigations in a magnetic field were also described previously [7,8]. AU measurements were carried out under a nitrogen atmosphere.
3. Results
and discussion
The ECL was generated at a rotatmg platinum ring-disc electrode (RRDE) in 0.1 M TBAP/AN/TOL contairung 10-S M of one of the compounds Ia-Id and of the other components involved in the experiments. In most cases the cations were generated at the disc electrode and the anions at the ring electrode. In control experiments no significant change of the results was found in the reverse case. The voltammetric half-wave potentials, triplet energies and singlet energies of the compounds are given in table 1. As a suitable anion radical precursor B, N+tolylphthalimide (NTPI) is used in most of these experiments. Deviating from the results in THF [4J, in no case could any emission be detected within the sensitivlty linuts of the instruments if NTPI- and the cation radicals of Ia-Id, AA D+ or AMDt , are produced at the RRDE. Obviously, the formation of exciplexes found in THF for this reaction is ineffective in the more polar solvent AN/TOL. However, if perylene (PER) is added to the AADt/NTPIor AMDf/ NTPI- systems, the sensitized perylene spectrum is observed (fg. 1, curve 4). It can be seen from the comparison between the luminescence-potential curves (fig. 1, curves 2 and 3) and the voltammogram (curve 1) that the emission unambiguously originates
15 March 1980
LETTERS
Table 1 Anodic and cathodic half-wave potenti&, tiplet energies and singlet energies of the compounds investigated COmpound a)
E% (V versus SCE) b)
q”pz (V versus SCE) b)
la Ib
+0.62 +0.54 +0.55 +0.54 >+1.7 +1.05
-1.93 -1.98 -2.01 -1.97 -1.40 -1.67
IC
Id NTPI PER
ET C) (ev)
ES (ev)
I.80 1.81 1.80 1.80 d) 1.56
3.08 3.15 3.15 3.08 d) 28
a) Abbreviations see text. b) Anodlc half-wave potentials in acetonitrile and cathodic half-wave potentials in DMF [S]. c) In the case of la-Id the triplet energes of 9methylanthracene, S,ZO-dunethylanthracene and 9-phenylanthracene are given. d) Values un~~nown
from the reaction between the cation radical of the amine moiety (q2 = +0.54 V) and the anion radical of NTPI (E$2 = -1.40 V). Above +l .O V (oxidation of PER and the anthracene moiety) the anode reaction becomes irreversible [S] and the intensity decreases. The increase in intensity at the anodic wave of PER (EF2 = - 1.67 V) should rather be due to an enhanced formation of NTPIT by the homogeneous
Ld.
.. .
I
.
1
.
.
.
.
.
.
Fig. 1. Voltammogram at the rotating disc electrode (curve I, w = 78 s-l), dependence of the ECL intensity on the potew bal of the disc electrode Es at the RRDE (curve 2, ER = +0.85 V and curve 3, ER = - I.60 V) and ECL spectmm (curve 4, not corrected for reabsorption) of a solution co* taining Id, NTPI and PER (concentrations loo3 M) in 0.Z M TEMP/AN/TOL
545
CHEMICAL
Volume 70, number 3
PHYSICS
15 March 1980
LETTERS
reaction between PER- and NTPI than to the direct excitation of PER. The Iuminescence of the AAD?/ NTPI- system was about 20 times more intense than in the case of the AM Dt/NTPIsystems, between which no srgmficant difference in intensny was found. In a magnetic field of 5 kG an increase rn intensity of 17-2 1% was found. This indicates the partrcipation of trrplet states. In general, for a triplet mechanism a magnetrc field effect of S-30% is expected
AMD-e+AMDf
[S,91Energeticahy, neither the tnplet state 3NTPI nor that of the amine moiety AA3D or AM3D can primarily be formed in the electron transfer [see eq. (14) below] _ Although both tnplet energies are not known, they can be estimated to be higher than 2.5 eV (NTPI) and 2.9 eV (N,N-drmethylq-anisidine) from other ECL experiments [l I ] and from the values of related compounds. This exceeds by far the reaction enthalpy of the electron transfer, which is about 1.9 eV accordurg to eq. (14). From the same reason also the excited singlet states ~NTPI*, rA*M D and AM ID* can be excluded. Three drfferent interpretations of the sensitized perylene emission are possible: (i) An energy transfer from the reaction center of the electron transfer to the neighbouring anthracene moiety leads to the direct formation of ;AAD or 3AM D. Such an energy transfer should be more effective for AAD than for AM D and would explain the differences 111the sensitized ECL mtensities. Subsequently 3A*D or 3AM D is quenched by PER and 3PER is transformed mto the ertuttmg smglet state by triplet-tnplet anmhdation.
@I) Formation of an intermolecular triplet exciplex and subsequent energy transfer to PER or to the anthracene moiety. ‘llus triplet exciplex could also be a transition state of mechanism (I).
AAD-e+AADt
,
B+e+B:, AADf
(1) (2)
+B-+3Af’D+B,
(3)
3AAD -I- PER + AAD + 3PER ,
(4)
2 3PER + ‘PER*
(5)
+ PER,
1PER* --f PER + hu .
(6)
(u) Formation of an rntramolecular triplet excrplex, which either 1s quenched by PER or is transformed lnro 3AAD and 3AMD, respectively. 546
,
(7)
B+e+B-, AAADt
(2) + Jj- + 3(A?+)
+B ,
3(rD+)+PER+AMD+3PER, 3 (m+)
AMD:
+3AMD.
(8) (9) (IO)
-I- Br + 3(B-D+wA,
(11)
3(B-D+vA-+B+3AMD,
(12)
PER + 3(B-D+jM
(13)
A +3PER+AMD+B.
Further evidence about the triplet state prrmarily formed in this process should be given from energetic considerations. In the electron transfer an excited state can be formed only IF its energy is lower than or equal to the reaction enthalpy AH, whrch can be estimated from the polarographic half-wave potentials
D-31
TAS=O.l
eV.
(14)
In a series of experunents wrth Id, NTPI was replaced by other compounds B, the half-wave potentials of which differ in a stepwise manner, and the sensrtized ECL intensity of PER IS measured. The results are shown in fig. 2a. The luminescence of PER is observed only if the difference ETi$(AM D) E$(B) exceeds 1.8 eV, suggesting that the triplet energy of the unknown intermediate is between 1.8 and 1.9 eV. The same result was obtained in a second series of experiments with Ic and NTPI, in which PER was replaced by some other tnplet energy acceptors Q w&h different trrplet energies (fig. 2b). only for ET(Q) f 1.8 eV couId the sensitized ECL spectrum of Q be measured,whereas for ET(Q) > 1.8 eV no ECL is observed. Therefore, the tnplet energy of the anthracene moiety (1.80 to 1.82 eV) seems to be the critical energy for the ECL of the AhDt/Br/Q and AM Dt/
Volume
70, number
CHEMICAL
3
b)
Cl) IO-
t
.-
.
iz =z
, -10
:
.. ::
_g
s
y
7 E = z
=
2 3 lt L .--. . ’ 18 22 I.& E,%UdI - E;:% 6 I , V -
energy to the anthracene moiety without any intermediate step seems unlikely. On the other hand, it cannot he decided to what extent an intramolecular triplet exciplex, which could also have an energy of 1.8 eV, participates in this process.
-05
Acknowledgement
.5
0
15 March 1980
.
06
05-
PHYSICS LETTERS
6 .
.
. 16
a
’ 18
a
.-20
E,(Q)
ev
-
18
’ 0 22
Fig. 2. Sensihzed ECL mtenslty of Q m 0.1 M TBAP/AN/TOL at the RRDE, not corrected for the dependence of the photomultipher response on the wavelength. Concentrations of all components 10s3 M. (a) Dependence on the difference between the oxidation half-wave potential of Id and the reduction ha&wave potentials of some anion radical precursors B. Compounds B/Q- (1) anthraquinonelrubrene, (2) benzile/ PER, (3) I&bls-@-benzoyIvinyl)-benzene/PER, (4) fluorenonel PER, (5) N-phenyl-naphthakmide/PER, (6) NTPI/PER, (7) pmethoxybenzophenone/l,3di_p-blphenyiyl+phenyl-2pyrazolme. (b) Dependence on the tnplet energy of the emitter Q for Ic/NTPI. Compounds Q: (1) PER, (2) 1,3,4,7tetraphenyhsobenzofuran, (3) 9,IO-d1q-biphenylylanthracene, (4) 9,1Odlphenylanthracene, (5) 9,IO&methylanthracene, (6) 9-methylanthracene, (7) I-p-blphenylyl-3,5-diphenyl-2pyrazohne, (8) pyrene.
The authors thank Dr. H.-J. Hamann and Dr, W. Jugelt for the support of these investigations and for helpful discussions of the results.
References
[ 21 [3] [4] [S] [6] 17 ] [ 81
B-/Q systems. From
this reason, the most probable mechanism is the formation of 3 AAD or SAM D via an instable intermolecular triplet exciplex 3(B-D”$ A or 3 (B-D+* A [reactions (11) and (1211, the lifetime of which is too short for an intermolecular ener-
gy transfer to Q. The direct transfer of the reaction
Faulkner and A.J. Bard, Electroanalytical chemistry, VoL 10, ed. A.J. Bard (Dekker, New York, 1976)_ L.R Faulkner, Intern. Rev. SCI. Phys. Chem. Ser. 2 9 (1976) 213. F. Pragst, 2. Chem 18 (1978) 41. R Zleblg. %-.I. Hamann, IV. Jugelt and F. Ragst, J_ Luminescence, to be published K-J. Hamann, F. Pragst and W. Jugelt, J. Prakt. Chea 318 (1976) 369. R Zlebig, F. Pragst and W. Jugelt, Z. Physik Chem (Leipzig) 259 (1978) 1009. F. Pragst, R Zlebrg, J. Kunze, IV. Jugelt and ICL Krause, Z. Physik. Chem. (Leipzig) 257 (1976) 465. F. Ragst, G. Fabian, R. Ziebig, D. Schmidt and IV. Jugelt, Chem. Phys. Letters 36 (1975) 630. LR Faulkner, H. Tachrkawa and A.J. Bard, J. Am, Chem. Sot. 94 (1972) 691. R. Ziebig and F. Pragsf 2. physik. Chem (Leipzig) 260 (1979) 748. F. Pragst, R. Ziebrg and E. Boche, J. Luminescence 21 (1979) 21.
[ 11 LR
[9] [IO] [ 1 I]
547