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Triplet triplet absorption of biphenyl and related compounds
y&me
:
29, mimber 2
CHEMICAL
PHYSICS
LETTERS
15 Noiember
,’
: I I .,. T&ET
TRIPLET
.,
..
AB§OF+ON
‘,
:
:.
’ :
.,’
:OF 5IPHEN;L
D. LAVALETTE hstitut
1974
‘i’,;.; .L., ‘,,; :.
.‘.,.
du Radium.
,lND
RELATED
CO-MPOUNDS
and C. TETREAU
Biologic,
91405Or~ay.
Received 8 July 1974
Frarrce
..
Tripkt triplet absorption spectra ol biphenyl, carbszolc and phenanthre;e
have deen studied.in rigid glass at 77 K. are reported. A theoretical study has been performed using the Par&r-Parr-Pople appro+mation in order to support.the band assignments. Phenanthrene is shown to be &finitely not related to the other membxs qf the series. Triple;-triplet oscillator sircngths arc decreased in carbazolc, as cknparrd to biphenyl. This effect is discussed in terms of a possible dilution of the ground triplc?; in addition to the spectral dilution of the upper triplet states, as previous!y observed in derivatives of alternht m.olecules.
,&cilk~or
.-
strcng~s
kmd polarizations
1. Intioduction
the ground singlet or the first triplet state. However, configurations with four’open shells were retained only when occurring between the highest four bonding and the lowest four antibonding orbit&. All molecules were supposed to be planar. Available experimental evidence supports a planar geometry for triplet biphenyl [3]. The parameters used were: RC_C = R c_N = I .4 A;Z, : 3.25; 2, = 4.25;& = flcN = - 2.35 eV; Wpc = - 11.22 eV; WpN = - 28.16 eV; rcc =. lb-50 eV; YNN = 15.92 eV and ypq according to ref. [4] ..
In’s previous work, .the TT spectrum of ‘some aza.naphthalenes was shown to result from a moderate perturbation of the spectrum of the parent hydrocarbon naphthalene [ 1) _The interpretation of the perturbated spectruti was not only based on experiinen tai data but also required the help of an elementary cc$iguration analysis of the theoretical ?pectra- Greater difficulties can be expected however, when the number.of’n-electrons and cores changes in a given molecular series. For instance, the case of the structurally related molecules: biphcnyl, carbazole and. phenanthrene, which are so often compared in the literature; deserved a closer examination. The present study of the TT spectra of these molecules should give further evidence that the notion of parentage only holds to a limited extent.
2. Experimental
and theoretical
The results are presented in figs. 1-3 with inclusion. of W-spqctra and polarizations. TT polarized excitation specka were mqnitored on the TT bands carrying an arrow and the part of the UV spectrum selected for excitation in the TT polarization measurement is indicated by horizontal bars:Theoretical TT spectra were all shifted 4000 cm-’ to the red in order to obtain an easier comparison wit!1 experiment. The correspondence between the triplet polarizations and the symmetry of the triplet states is given in table I.
procedures
TT spectra were kmeasuied in EPA’at 77 K. Intensity and polarization measurements were performed adco;ding to the procedures already described [Z] . Theoretical TT spectra were computed in the Pzriser-ParrPople approximation,using @ound state SCF MO’s Configuration interaction was extende.d in principle to aDIsinglyexcited configuratiotis with iespect tq either 204
3. Results and assignments of triplet triplet spectra
1 3.1. B$hei~~l(& 1
.I)
Biphenjrl is the onli ,.
moiecile’in
.&hisseries for which ..‘,,
., . . .. ‘:,
‘_
;
‘.
..
Volume 29, number 2‘
. .
IS Novctmber I974
.’
‘_ CHEhlKCAL @HYSiCS LETTERS
:
+0.1 PI - 0.1
cr! N
a . Eo
hiC Fig. I. TT specirum of bipiiknyl. Singlet polarization bidden u-u transitions.
from ref, f6] _Theoretical
TT spqztrurn:
*‘transitions
witif<
0.01, o
fkr-
.
a detailed theoretical study had.been performed already seem to be, no arguments at present for favounng he or the other assignment. .[.5]. The present polarization spectra confirm that the band at 27000 cm-l fj&, & 0.42) has the stie pokqization as the sin$et P band’and must be assigned t,o the ‘3.2: C&o/e (fig 21 0 _ ‘Ai * 3B;U trarkition (j& = 0.50). 11;ihe region of, the weaker bands [Sj (14000-24000 cm-l) one Y pqThe. pkuly resolved ‘IT spectmn’ of cnibazole shows iarization and one X poiarized tran~~tion,are found with .., two groups of bands cf&.‘= 0.24 and 0.06) polarized O-O bands located at 14600 and 20450 cm”, respec-along the X axis. *he assignment to the @xlated -two tively. There isonly one candidate state.foi the latter .‘ ,3A, c 3BZ transi?ions (#&,= = 0.2s and 0.09, respec-, : .: which has to be attributed to the sign forbidden tively) is straightfotiard. Beside the bathochromic shift and some lo&of structure, the lnost interesting ?A$‘+ 3B;U transition.. One forbidden 3JB& and,one .j ,, ,fmding is the huge reductio,ri of the osciktor strength very weakly &owed 3Bi, state (&& = 0.003), can . .‘ as compared to biphenyl. ..’ possibly contribute to the lowest TT transition. There _.
~.’
..‘
(,(
;
.‘
,.: _‘ ,:‘
.’ .‘ .
,,.,_ : ,,‘
.. :
.’
;‘
.’
.’ ,... ‘
::
.2d5
‘.
“
”
;‘
CHEMICAL~,PHYSIC$
LkiTERS,.’
,:
.I
‘15 November i974
.: 1,’
._ :
.~‘
., .,
.: .:
Fig.
2. TT spectrum
of carbazole.
1:3.3.';Phenn~~~,renelfig. 3) I. ., .: (,‘ : ... ‘ -‘. ,The,~tron~~~.~‘b~d of phenanthrene
Singlet.polarizationFromref. (71. : 4. Discussipn
(’
at 20200 .. .. Fig. 4,s’ho~s the c’orrelation of the eight most ~&IO&, :cm:: (f-& =.0.!5) has heen shown previously to be’ t&t orbit&. Ttie letters a, b, c; . . , shmd fo;.the orbit. long axis polaijzecj [8,:9] and obyiouijy corresponds als derived from’biphenyl’while the nukbkrs 1; 2,3, . , . “to~th’e ‘Ai G,~B$- Qansiti& +xMed &I 22000 cnirl ‘. are used fC)write eiectroriic configurations irrespective .‘ i witk1Jfc31~= 0.24. The mdre recently rep&ted weaker ’ of the’mcIecule_‘considered. Except for. the inversidn of ‘b~+r’$e red. [lo, l,:J have an dscillator~s~rengtk . orbitals a, b and al, b’, in phenanthrene a’good correfa-; ; ;f&.,=O.Oi and are found to be-equ,aIly k-polarized. ‘. tion wtis fn‘und: the $mmetq_ with respect t-0 the com_mdn Y axis is conserved gnd the coefficients on corre-. On&very weakly.aiibwed IfGc = 0.008) 3AT and &e : .’ sppjding iores a& of thd same oidkr of magnitude. ” %i,gn forbidden 3Af state.&re calcu:oted in *&isregion. J’hk’ prgnouncedvibratidna! structilre maj’perhags The’sinJet’k band correqbqding to configtirations .‘. : fwour: tj-&assignin&nt to the, sign forbidden 3Az +- 3 Bt,4 and ‘V:t’@ not affected by the orbital inversion. Its : greater in$&$y in c&bazoIe reflects the &ak-dawn’ ‘: which is $ti’ h ,a position to gain intensity from. the in-, .. .“‘ ..‘. +mse ‘ ?.,A; fTB$ at. 20’204 &I:‘.~ .-‘ : ,.: 1 .of t$e tign~selecti&~g_$e‘ [12}‘.‘in tl-iq nori-plteknt .’ :, :-. ., .I. _, ,_ ” ~,~&$I._ II .-._y%_j:;,..‘~ : 1’: .:,.Y.;.:‘,,,;
._ ,, ,.‘:.
;,
,,
. .:.:
,.,.,
,I .’
:‘ ._ ‘
1‘
.‘
Volume
29, number 2
CHEhIICAL PHYSICS LETTERS
,I.S November
1974
0.1 P a .l
,
x-y+ x+r+
I Y+Y-
I
a(r)
,i3cm-1
P(X)
1
-
Fig. 3. IT
spectrum’of phenanthienedIe.,
molecule, as compared to phenanthrene. This band is hidden in biphenyl [6]. In contrast, configuration Vi’, whkh gives rise both to the singlet P band and to’the first triplet state, invalves orbit& b, b’ for phenanthrene instead of orbitals a, a’ for biphenyl and carbazole. Since orbit& a and b have quite distinct nodal characteristics, trjplet phenanthrene is expected to exhibii different properties, a fact reflected by ZFS and spin density measurements [13, 141. A further consequence of the orbital inversion is that any sing!y excited configuration with respect to the first triplet in phenanthrene corresponds to a doubly excited configuration in biphenyl and carbazole, which therefore will have no optical TT transition in comm,on with ‘.‘.
phenanthrene. It Follows from these simple argtments that phenanthrene cannot be considered as a model for the isoelectronic carbazole molecule. Table 1 gives a limited development of the upper triplet sthtes involved in TT absorption. One striking feature in the spectrum of carbazole ;~as the intej!sity decrease in comparison to biphenyl. The weak red bands of biphen;ll are missing;.unless they are shifted below 10000 crnW1, this fact suggests that spectral dilutkn has reduced their intensity below’the,detection limit [ 1] , ’ Spectral dilution is responsible for the shoulder observed at 20000 cm-l incarbazole. In this process, part of the infensity of,the ‘Ai’+ 313;U transition is .-trans.ferred to another Ai state (&e = 0.006) calcui lated at-30000 cm-l in biphenyl (fig. l), which is con.,.
.. .’
x
:
: 205
Voltime 29, number.2 :
‘-
.CHEMICALPHYS:CS LETTERS ‘.
,.
..‘..
‘. 4’
,” . .
:
,3’
.’
/2’.
:
1’
;.
d’
___--
C’ b’.
__----‘-,.Y..-------______ . .
-: ;
_..-._
+7
,---___&_ -
--hy__
a
.’ 2 :
.
.
., -:.
__c------_.-.-._, ‘- ----PEY._eI ..
: ._ A
F&.4. A-nombering
. .
__-_----0
__-y---
d
‘.
4
._ _.._+-~---_~~:,_.- i’ _.,-_~_______----.-.-.--
_._
‘2
3;. _’
_,
. ,’
‘y.. ‘_.-.-.,
”
.,
‘,
,.
-..
.’
.
.’
.;
-.I-.-.A :
,‘*...
___---,--
a’
.,
-____.
13 November 1974
.
;
.’
. ., :
*
,c,
P
of orbit& used fcr defining ccnrigtirations. B, C,.and P.= xbital correlation for biphenyl, carb~azole and phe-
nanthrenc
:
:. : .Biphenyl
.’ polar&ion
x
‘.,
.-.
p-clarization I’
.’
Table 1
..
Carbazolk
Phenantbrene
A;
AI
A; ..
B;g,
.Bz
B; ..
first triplet
&U
BZ
B;
TI
0.79 v:’ + 0.35 vz”
0.70 Vi’ + 0.48 -L-;’
0.82 vi’ + 0.36 v:’
T,
0.68 I,$ + 0.68 Y”4
0.65 Vi’ + 0.61 b<’
0.65 i:’ + 0.65 Vi’
.,:
..
7 I,.’
side&y lowered,in carbazole. The overall oscillator strength can therefore be eetiniated tof= 0.30 for carbazole against f = Cl:42 for the corresponding tran.‘sition.of biphenyl. A check of +&orbital transition r-no ments showed- a variation &about 5% only. Table 1 suggests an.dternative mechariikn affecting the ground tripjer. Since configuration Vi’ is mainly responsible ,for the,trans’ition,moment towards the upper triplets, -its sn-rallerweight in carbazole should 1ead.to.a reduc: tion of the ‘oscillator strength in the ratio of the’ squared coefficidntC Assuming identical orbital transition mo- 1 ..ments; this. reduction amounts to 1129, which is,com:” par?b!e”to the experimental ratio: fiB)/fiC) = l.4. This ’ “crude therefore.points to a situation where, : .ar&r+nt .. .’ ., ,i .,,,
::q : _,.,
.’
”
,..::
;
: .. z: ; :. .:: .-.,.;-’ : .’
,.
.. ”
‘, ,.
.,
in additi,Dn to the dilution of the upper level, some dilution of the ground level is also taking place. This complication was absent in the case of the azanaphthalenes [ I]. The, “leakage” of Vi”seems to result from.the
proximity of Vc,twhich is considerably lower in carbazole (0.7’6 eV) than in biphenyl(1.89 ev), because of the removal of the orbital degeneracy in carbazole. :
Refeien :es
;, 1..
D. +va$tte and F. Pcradejqrdi, Cbem. Phys. Letters 20 (1973) 379. [2] D. I;av.arette,.J.‘C$m. Phyk 66 (196$ 1853, 1860. ., .’ ‘, [I] C..l:eueap,
; ., ;_ ;_._ :: ,- .:. -,
;.] ., ‘,‘, .’
‘. :
.“, ._, _,
]
:, :
:
S?lume
29, number 2
CHEVlCAL
PHYSICS LETTERS,
‘,
L5 November
1974
‘_ [3] J. Mispeltcr, Chem. Phys. Letters 10 (1971) 539. [4] K. Nishimoto and N. Mataga, 2. Physik. Chem. (Frank.: furt/Main) 12 (i957) 335. IS] Y. hfeybr, R. Astier and J.&f. Leclercq, Chbm. Phys. Letters4 (1970)557. ‘. (61 G. Hohineicher, F. Dorr, N. hlika and S. Schneider, Be;. Bunsen&es. Physik. ChCm. 72 (19681.1144. ]7 ] S.C. Chakravorty tid SC. Ganguly,‘J. Chem..Phys. 52 (1970) 2760, (81 h1.A. El-Sayed and T. Pailopoulos, J. Chem. Phys..39 (1963) a34.
[9,j b; Lavalette, Chem. Phys. Letters‘: (1969) 67. [lo]-B.R. He&y and %I. Rasha, J.‘Chem. Phys. 47 (1967) 3319. [ 11j M.W. Windsor and J.R, Novak, in: The triplet stare, ed. A.B. Zahlan (Cambridg Univ. Press, London. 1967) p. 229. ‘, [12] R. Pariser, J. Chem. Phys. 24,(L956) 250. [13 J S. Siegel and H.S. Judeikis, J. Phys. Che,m. 70 (1966) .2201. _.. [ 141 J. Mispelter, J.Ph. Grivet, !.I. Baiwir and J.hI. Lhosti. ibiol. Phys. 24 (1972) 205.
.
:
29, mimber 2
CHEMICAL
PHYSICS
LETTERS
15 Noiember
,’
: I I .,. T&ET
TRIPLET
.,
..
AB§OF+ON
‘,
:
:.
’ :
.,’
:OF 5IPHEN;L
D. LAVALETTE hstitut
1974
‘i’,;.; .L., ‘,,; :.
.‘.,.
du Radium.
,lND
RELATED
CO-MPOUNDS
and C. TETREAU
Biologic,
91405Or~ay.
Received 8 July 1974
Frarrce
..
Tripkt triplet absorption spectra ol biphenyl, carbszolc and phenanthre;e
have deen studied.in rigid glass at 77 K. are reported. A theoretical study has been performed using the Par&r-Parr-Pople appro+mation in order to support.the band assignments. Phenanthrene is shown to be &finitely not related to the other membxs qf the series. Triple;-triplet oscillator sircngths arc decreased in carbazolc, as cknparrd to biphenyl. This effect is discussed in terms of a possible dilution of the ground triplc?; in addition to the spectral dilution of the upper triplet states, as previous!y observed in derivatives of alternht m.olecules.
,&cilk~or
.-
strcng~s
kmd polarizations
1. Intioduction
the ground singlet or the first triplet state. However, configurations with four’open shells were retained only when occurring between the highest four bonding and the lowest four antibonding orbit&. All molecules were supposed to be planar. Available experimental evidence supports a planar geometry for triplet biphenyl [3]. The parameters used were: RC_C = R c_N = I .4 A;Z, : 3.25; 2, = 4.25;& = flcN = - 2.35 eV; Wpc = - 11.22 eV; WpN = - 28.16 eV; rcc =. lb-50 eV; YNN = 15.92 eV and ypq according to ref. [4] ..
In’s previous work, .the TT spectrum of ‘some aza.naphthalenes was shown to result from a moderate perturbation of the spectrum of the parent hydrocarbon naphthalene [ 1) _The interpretation of the perturbated spectruti was not only based on experiinen tai data but also required the help of an elementary cc$iguration analysis of the theoretical ?pectra- Greater difficulties can be expected however, when the number.of’n-electrons and cores changes in a given molecular series. For instance, the case of the structurally related molecules: biphcnyl, carbazole and. phenanthrene, which are so often compared in the literature; deserved a closer examination. The present study of the TT spectra of these molecules should give further evidence that the notion of parentage only holds to a limited extent.
2. Experimental
and theoretical
The results are presented in figs. 1-3 with inclusion. of W-spqctra and polarizations. TT polarized excitation specka were mqnitored on the TT bands carrying an arrow and the part of the UV spectrum selected for excitation in the TT polarization measurement is indicated by horizontal bars:Theoretical TT spectra were all shifted 4000 cm-’ to the red in order to obtain an easier comparison wit!1 experiment. The correspondence between the triplet polarizations and the symmetry of the triplet states is given in table I.
procedures
TT spectra were kmeasuied in EPA’at 77 K. Intensity and polarization measurements were performed adco;ding to the procedures already described [Z] . Theoretical TT spectra were computed in the Pzriser-ParrPople approximation,using @ound state SCF MO’s Configuration interaction was extende.d in principle to aDIsinglyexcited configuratiotis with iespect tq either 204
3. Results and assignments of triplet triplet spectra
1 3.1. B$hei~~l(& 1
.I)
Biphenjrl is the onli ,.
moiecile’in
.&hisseries for which ..‘,,
., . . .. ‘:,
‘_
;
‘.
..
Volume 29, number 2‘
. .
IS Novctmber I974
.’
‘_ CHEhlKCAL @HYSiCS LETTERS
:
+0.1 PI - 0.1
cr! N
a . Eo
hiC Fig. I. TT specirum of bipiiknyl. Singlet polarization bidden u-u transitions.
from ref, f6] _Theoretical
TT spqztrurn:
*‘transitions
witif<
0.01, o
fkr-
.
a detailed theoretical study had.been performed already seem to be, no arguments at present for favounng he or the other assignment. .[.5]. The present polarization spectra confirm that the band at 27000 cm-l fj&, & 0.42) has the stie pokqization as the sin$et P band’and must be assigned t,o the ‘3.2: C&o/e (fig 21 0 _ ‘Ai * 3B;U trarkition (j& = 0.50). 11;ihe region of, the weaker bands [Sj (14000-24000 cm-l) one Y pqThe. pkuly resolved ‘IT spectmn’ of cnibazole shows iarization and one X poiarized tran~~tion,are found with .., two groups of bands cf&.‘= 0.24 and 0.06) polarized O-O bands located at 14600 and 20450 cm”, respec-along the X axis. *he assignment to the @xlated -two tively. There isonly one candidate state.foi the latter .‘ ,3A, c 3BZ transi?ions (#&,= = 0.2s and 0.09, respec-, : .: which has to be attributed to the sign forbidden tively) is straightfotiard. Beside the bathochromic shift and some lo&of structure, the lnost interesting ?A$‘+ 3B;U transition.. One forbidden 3JB& and,one .j ,, ,fmding is the huge reductio,ri of the osciktor strength very weakly &owed 3Bi, state (&& = 0.003), can . .‘ as compared to biphenyl. ..’ possibly contribute to the lowest TT transition. There _.
~.’
..‘
(,(
;
.‘
,.: _‘ ,:‘
.’ .‘ .
,,.,_ : ,,‘
.. :
.’
;‘
.’
.’ ,... ‘
::
.2d5
‘.
“
”
;‘
CHEMICAL~,PHYSIC$
LkiTERS,.’
,:
.I
‘15 November i974
.: 1,’
._ :
.~‘
., .,
.: .:
Fig.
2. TT spectrum
of carbazole.
1:3.3.';Phenn~~~,renelfig. 3) I. ., .: (,‘ : ... ‘ -‘. ,The,~tron~~~.~‘b~d of phenanthrene
Singlet.polarizationFromref. (71. : 4. Discussipn
(’
at 20200 .. .. Fig. 4,s’ho~s the c’orrelation of the eight most ~&IO&, :cm:: (f-& =.0.!5) has heen shown previously to be’ t&t orbit&. Ttie letters a, b, c; . . , shmd fo;.the orbit. long axis polaijzecj [8,:9] and obyiouijy corresponds als derived from’biphenyl’while the nukbkrs 1; 2,3, . , . “to~th’e ‘Ai G,~B$- Qansiti& +xMed &I 22000 cnirl ‘. are used fC)write eiectroriic configurations irrespective .‘ i witk1Jfc31~= 0.24. The mdre recently rep&ted weaker ’ of the’mcIecule_‘considered. Except for. the inversidn of ‘b~+r’$e red. [lo, l,:J have an dscillator~s~rengtk . orbitals a, b and al, b’, in phenanthrene a’good correfa-; ; ;f&.,=O.Oi and are found to be-equ,aIly k-polarized. ‘. tion wtis fn‘und: the $mmetq_ with respect t-0 the com_mdn Y axis is conserved gnd the coefficients on corre-. On&very weakly.aiibwed IfGc = 0.008) 3AT and &e : .’ sppjding iores a& of thd same oidkr of magnitude. ” %i,gn forbidden 3Af state.&re calcu:oted in *&isregion. J’hk’ prgnouncedvibratidna! structilre maj’perhags The’sinJet’k band correqbqding to configtirations .‘. : fwour: tj-&assignin&nt to the, sign forbidden 3Az +- 3 Bt,4 and ‘V:t’@ not affected by the orbital inversion. Its : greater in$&$y in c&bazoIe reflects the &ak-dawn’ ‘: which is $ti’ h ,a position to gain intensity from. the in-, .. .“‘ ..‘. +mse ‘ ?.,A; fTB$ at. 20’204 &I:‘.~ .-‘ : ,.: 1 .of t$e tign~selecti&~g_$e‘ [12}‘.‘in tl-iq nori-plteknt .’ :, :-. ., .I. _, ,_ ” ~,~&$I._ II .-._y%_j:;,..‘~ : 1’: .:,.Y.;.:‘,,,;
._ ,, ,.‘:.
;,
,,
. .:.:
,.,.,
,I .’
:‘ ._ ‘
1‘
.‘
Volume
29, number 2
CHEhIICAL PHYSICS LETTERS
,I.S November
1974
0.1 P a .l
,
x-y+ x+r+
I Y+Y-
I
a(r)
,i3cm-1
P(X)
1
-
Fig. 3. IT
spectrum’of phenanthienedIe.,
molecule, as compared to phenanthrene. This band is hidden in biphenyl [6]. In contrast, configuration Vi’, whkh gives rise both to the singlet P band and to’the first triplet state, invalves orbit& b, b’ for phenanthrene instead of orbitals a, a’ for biphenyl and carbazole. Since orbit& a and b have quite distinct nodal characteristics, trjplet phenanthrene is expected to exhibii different properties, a fact reflected by ZFS and spin density measurements [13, 141. A further consequence of the orbital inversion is that any sing!y excited configuration with respect to the first triplet in phenanthrene corresponds to a doubly excited configuration in biphenyl and carbazole, which therefore will have no optical TT transition in comm,on with ‘.‘.
phenanthrene. It Follows from these simple argtments that phenanthrene cannot be considered as a model for the isoelectronic carbazole molecule. Table 1 gives a limited development of the upper triplet sthtes involved in TT absorption. One striking feature in the spectrum of carbazole ;~as the intej!sity decrease in comparison to biphenyl. The weak red bands of biphen;ll are missing;.unless they are shifted below 10000 crnW1, this fact suggests that spectral dilutkn has reduced their intensity below’the,detection limit [ 1] , ’ Spectral dilution is responsible for the shoulder observed at 20000 cm-l incarbazole. In this process, part of the infensity of,the ‘Ai’+ 313;U transition is .-trans.ferred to another Ai state (&e = 0.006) calcui lated at-30000 cm-l in biphenyl (fig. l), which is con.,.
.. .’
x
:
: 205
Voltime 29, number.2 :
‘-
.CHEMICALPHYS:CS LETTERS ‘.
,.
..‘..
‘. 4’
,” . .
:
,3’
.’
/2’.
:
1’
;.
d’
___--
C’ b’.
__----‘-,.Y..-------______ . .
-: ;
_..-._
+7
,---___&_ -
--hy__
a
.’ 2 :
.
.
., -:.
__c------_.-.-._, ‘- ----PEY._eI ..
: ._ A
F&.4. A-nombering
. .
__-_----0
__-y---
d
‘.
4
._ _.._+-~---_~~:,_.- i’ _.,-_~_______----.-.-.--
_._
‘2
3;. _’
_,
. ,’
‘y.. ‘_.-.-.,
”
.,
‘,
,.
-..
.’
.
.’
.;
-.I-.-.A :
,‘*...
___---,--
a’
.,
-____.
13 November 1974
.
;
.’
. ., :
*
,c,
P
of orbit& used fcr defining ccnrigtirations. B, C,.and P.= xbital correlation for biphenyl, carb~azole and phe-
nanthrenc
:
:. : .Biphenyl
.’ polar&ion
x
‘.,
.-.
p-clarization I’
.’
Table 1
..
Carbazolk
Phenantbrene
A;
AI
A; ..
B;g,
.Bz
B; ..
first triplet
&U
BZ
B;
TI
0.79 v:’ + 0.35 vz”
0.70 Vi’ + 0.48 -L-;’
0.82 vi’ + 0.36 v:’
T,
0.68 I,$ + 0.68 Y”4
0.65 Vi’ + 0.61 b<’
0.65 i:’ + 0.65 Vi’
.,:
..
7 I,.’
side&y lowered,in carbazole. The overall oscillator strength can therefore be eetiniated tof= 0.30 for carbazole against f = Cl:42 for the corresponding tran.‘sition.of biphenyl. A check of +&orbital transition r-no ments showed- a variation &about 5% only. Table 1 suggests an.dternative mechariikn affecting the ground tripjer. Since configuration Vi’ is mainly responsible ,for the,trans’ition,moment towards the upper triplets, -its sn-rallerweight in carbazole should 1ead.to.a reduc: tion of the ‘oscillator strength in the ratio of the’ squared coefficidntC Assuming identical orbital transition mo- 1 ..ments; this. reduction amounts to 1129, which is,com:” par?b!e”to the experimental ratio: fiB)/fiC) = l.4. This ’ “crude therefore.points to a situation where, : .ar&r+nt .. .’ ., ,i .,,,
::q : _,.,
.’
”
,..::
;
: .. z: ; :. .:: .-.,.;-’ : .’
,.
.. ”
‘, ,.
.,
in additi,Dn to the dilution of the upper level, some dilution of the ground level is also taking place. This complication was absent in the case of the azanaphthalenes [ I]. The, “leakage” of Vi”seems to result from.the
proximity of Vc,twhich is considerably lower in carbazole (0.7’6 eV) than in biphenyl(1.89 ev), because of the removal of the orbital degeneracy in carbazole. :
Refeien :es
;, 1..
D. +va$tte and F. Pcradejqrdi, Cbem. Phys. Letters 20 (1973) 379. [2] D. I;av.arette,.J.‘C$m. Phyk 66 (196$ 1853, 1860. ., .’ ‘, [I] C..l:eueap,
; ., ;_ ;_._ :: ,- .:. -,
;.] ., ‘,‘, .’
‘. :
.“, ._, _,
]
:, :
:
S?lume
29, number 2
CHEVlCAL
PHYSICS LETTERS,
‘,
L5 November
1974
‘_ [3] J. Mispeltcr, Chem. Phys. Letters 10 (1971) 539. [4] K. Nishimoto and N. Mataga, 2. Physik. Chem. (Frank.: furt/Main) 12 (i957) 335. IS] Y. hfeybr, R. Astier and J.&f. Leclercq, Chbm. Phys. Letters4 (1970)557. ‘. (61 G. Hohineicher, F. Dorr, N. hlika and S. Schneider, Be;. Bunsen&es. Physik. ChCm. 72 (19681.1144. ]7 ] S.C. Chakravorty tid SC. Ganguly,‘J. Chem..Phys. 52 (1970) 2760, (81 h1.A. El-Sayed and T. Pailopoulos, J. Chem. Phys..39 (1963) a34.
[9,j b; Lavalette, Chem. Phys. Letters‘: (1969) 67. [lo]-B.R. He&y and %I. Rasha, J.‘Chem. Phys. 47 (1967) 3319. [ 11j M.W. Windsor and J.R, Novak, in: The triplet stare, ed. A.B. Zahlan (Cambridg Univ. Press, London. 1967) p. 229. ‘, [12] R. Pariser, J. Chem. Phys. 24,(L956) 250. [13 J S. Siegel and H.S. Judeikis, J. Phys. Che,m. 70 (1966) .2201. _.. [ 141 J. Mispelter, J.Ph. Grivet, !.I. Baiwir and J.hI. Lhosti. ibiol. Phys. 24 (1972) 205.
.