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Electron Transfer from an Excited Electron Donor in the Triplet State to an Acceptor Molecule.

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[l] K. Dimroth and W. Stiide, Angew. Chem. 80, 966 (1968);
Angew. Chem. internat. Edit. 7, 881 (1968).
[2] K. Dimroth, N . Gr&& H . Perst, and F. W. Steuber, Angew.
Chem. 79, 58 (1967); Angew. Chem. internat. Edit. 6, 85 (1967).
[3] K. Dimroth, N . Greif, W. Stade, and F. W. Steuber, Angew.
Chem. 79, 725 (1967); Angew. Chem. internat. Edit. 6,711 (1967).
[4] (1. Thewalt, Angew. Chem. 81, 783 (1969); Angew. Chem.
internat. Edit. 8, 770 (1969).
Electron Transfer from an Excited Electron Donor
in the Triplet State to an Acceptor Molecule
By G . Briegleb and H. Scliuster[*]
We have investigated the influence of electron donor-acceptor
(EDA) complex formation on the triplet-triplet (TT) absorppossibilities of electron transition (energy level scheme, see
tion spectrum of the electron donors (D) naphthalene (f)
Figure). Comparison of the observed and estimated Gm*
and phenanthrene (2) in complexes with the electron accepvalues shows that G C T ~ does not correspond to the measured
tors (A) tetrachlorophthalic anhydride (3) and pyromellitic
CT*-absorption bands. No distinction can be made between
dianhydride ( 4 ) .The TT absorption spectra were recorded in
GCT; and GCT:
within the limits of accuracy of estimation.
n-propyl ether,glass at T = 96 to 118°K by flash spectroA superposition of both transitions is conceivable, thus
photometryrll. The triplet state of ( 1 ) and ( 2 ) in the cornproviding a possible explanation inter aliu for a diffuse
plex IDA/ with (3) or ( 4 ) was excited by irradiation within
broadening of the CT* band in the case of the phenanthrene
the frequency of the charge transfer (CT) absorption bands
complex ( 2 1 4 3 ) .
ria the singlet excited state lD-'A-\: of the complex with
Received: July 28, 1969
[Z 72 IEl
German version: Angew. Chem. 81, 790 (1969)
subsequent "intersystem crossing" energy transfer
+ ID+A[. This excitation mechanism was possible since the
[*I Prof. Dr. G. Briegleb and Dr. H. Schuster
condition Epj+A-jz > FD;AI. or in the case of complexes
Institut f u r Physikalische Chemie der Universitat
with donor-triplet excimers ED..jD+d.-Ix > ~ D D ~ A I ,
87 Wurzburg, Markusstrasse 9-11 (Germany)
was fulfilled. The triplet state had to be excited via the C T
[ l ] H . T. Witt, R . Moraw, and A. Miiller, 2. physik. Chem. N . F.
singlet state in order to prevent a triplet excitation of the free
20,193 (1959); G. Porter, Angew. Chem. 73,7 (1961); in A . Weissdonor molecules not bonded in the complex.
berger: Technique of Organic Chemistry. Interscience, New York
The TT absorption spectra of complexed ( 1 ) and (2) in the
1963, Vol. VI11/2, p. 1055; J . S. Brinen, J. chem. Physics 49, 586
frequency range 20 t o 25 Y lo3 crn-1 exhibit characteristic
changes compared t o the TT absorption spectra of the free
[ 2 ] G. Briegleb and H . Schuster, Chem. Physics Letters 4 , 51
donors ( I ) and (2) 121. The triplet lifetime is also reduced by
complex formation, i.e. the probability of the T + So transiI31 hVcTf "_ hvcT - ED(S0 TI) ;JWX; 2 hvcTj f E A ( S 1 7 S 2 ) ;
tion is increased. The TT spectrum of complexed triplet exhvCT5 2 hvCTT f ED+ + D+*; for further details see: G. Brregleb
cimers of (f) and (2) was measured at slightly higher
and H . Schuster, Z. Naturforsch. a, to be published.
temperatures (106-113 OK) and/or in the presence of an excess of donor. It was also possible to detect the excimers in
the phosphorescence spectrum by irradiation within the
frequency of the CT band at T = 100 t o 120'K and in the
N-Halogenoimidosulfur Difluorides
presence of an excess of the donor [21.
and N,N'-Dihalogenosulfur Diimides
The ionization energy of the triplet excited donor bonded in
the complex lD+AI is reduced by the energy required for
T1 + SO excitation. Hence CT* absorption bands corresponding to transition of an electron f r o m the rriplet excited donor
to an unoccupied energy level of the acceptor in frequency
ranges of relatively long wavelength could be expected. We
first found CT* bands of this kind in complexes IDFA[ of
triplet excited ( I ) and (2) with ( 3 ) and ( 4 ) after the population of IDFA1 had been increased by flash excitation in the
frequency range of the C T bands of the complexes IDA1 in
the ground state in solutions in n-propyl ether glass at 96 to
By K . Seppelt and W. Sundermeyer[*I
N-Halogenoimidosulfur difluorides (2) have previously been
prepared by reaction of halogens with N-fluoroformylimidosulfur difluoriderll, FC(O)NSFz, in the presence of cesium
fluoride or by reaction of halogens with bis(difluorosu1fur(1v)imido)mercury 121, Hg(NSF&.
We have recently investigated the cleavage of N-halogenobis(trimethylsily1)amines( I ) with non-metallic halides 131 and have
found a further route to compounds (2) by reaction of ( I )
(X = CI, Br) with sulfur tetrafluoride.
The experimentally determined C T * frequencies of the CT*
band maxima are given in the Table, as are the CT* freGcT;,
and G C T ~ for a transition of the DT
quencies GcT!,
electron 1 or 2 of theT1-excited donor to various energy
levels of the acceptor calculated (31 assuming the various
Angew. Chem. internat. Edit.
GCT; [a]
C C T [a]
1 Vol. 8 (1969) 1 No. 10
X-N[Si(CH3)312 iSF4
(lb), X
+ 2 (CH3)jSiF
GCT; [a]
77 1
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acceptor, transfer, molecules, donor, triple, electro, state, excited
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