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Direct Chemical Evidence for Energy Transfer between Identical Molecules.

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[9] L. Radom, J . A. Pople, and W L. Mock, Tetrahedron Lett. 1972,
479.
[lo] L. M . Trefonas and R. Majeste, Tetrahedron 19, 929 (1963); A.
F. Cameron, K . K . Cheung, G . Ferguson, and J. M . Robertson, J. Chem.
SOC. B 1969, 559; M . R . St. Jaques, Dissertation, Los Angeles 1967.
1111 N . L. AIIinger and J. 7: Sprague, J. Amer. Chem. Soc. 94, 5734
( 1972).
1121 R. M . Gauin and Z . F. Wang, personal communication; .I.Amer.
Chem. SOC.95, 1425 (1973).
[l3J X-ray analysis of a heavy-atom derivative with a free double bond:
G. Ferguson and D. Hawley, personal communication.
[I41 P. Ganis, U . Lepore, and E . Martuscelli, J. Phys. Chem. 74, 2439
(1970).
[I51 J. Hase and A . Krebs, Z . Naturforsch. 26a, 1190 (1971).
1161 E . Heilbronner and V Hornung, unpublished work.
1171 J . R . Wiseman, H . F. Chan, and C. J. Aholn, J. Amer. Chem.
SOC.91, 2812 (1969).
Direct Chemical Evidence for Energy
Transfer between Identical Moleculed’*l
By Peter Lechtken and Nicholas J . Turro[*I
Energy transfer in the solid state, especially in crystals,
is a well-known and well-studied phenomenon[’]. However,
with the sole exception of some studies employing the
indirect technique of fluorescence depolarizationrZ1, there
exists little information in the literature concerning energy
transfer between identical molecules in fluid solution at
room temper~turer~~.
The difficulty in studying energy
transfer between identical molecules in fluid solution
resides in the absolute identity of the reactants and the
products [Reaction (111.
A*+A*A+A*
A*
+A
S (AA)*
CN
A
+ A*
-
Evidence for the occurrence of such an “energy hopping”
between identical molecules is of great interest for:
a) unraveling the question of whether e x c i m e r ~ [of~ ]ketones
exist [(AA)*; Reaction (2)];
b) providing a novel mechanism for “long range” energy
transfer;
c) understanding the factors which determine the duration
of electronic excitation in a molecule.
The ability of tetramethyl-l,2-dioxetane (1) to produce
high yields of excited singlet and triplet acetone upon
photoly~is[~]
provides a unique opportunity to demonstrate
electronic excitation transfer between identical molecules
by a direct chemical method of analysis. Indeed, ( I ) may
be considered as a stable, “masked” electronically excited
acetone molecule. Irradiation of ( I ) in deuterioacetone,
under conditions such that acetonef6] is not excited by
direct absorption of light (high pressure Hg lamp, 365 nm
line), effects the reaction scheme shown.
The acetone singlets and triplets generated from photolysis
of ( 1 ) were trapped with dicyanoethylene and diethoxyethylene, respectively, to give the corresponding oxetanes (2)
and (4)”’. Since the excitation energy must originally
reside on a [H,]-acetone (A-H,) molecule, one can determine the extent of energy transfer to [D,]-acetone (A-D,)
by simply measuring the ratio of ( 2 ) to (3) and/or ( 4 )
to (5) in the reaction products.
The analysis of the reaction mixture was executed by a
combination of gas chromatography and mass spectrometry. The relative amounts of (2) and ( 3 ) , or ( 4 ) and
( 5 ) , were determined from the intensities of the relevant
masses (Table 1).As standard controls, authentic mixtures
IhV
fcN
NC
.
IDJ-acetone
f 2)
+
(4)
Fig. I. Reaction scheme of energy transfer
(Even if some anisotropy were involved in the reaction,
say, initiated by excitation with polarized light, the rapid
rate of tumbling of molecules in fluid solution converts
the system into an isotropic one much faster than most
physical measurements can be made).
of (2) and (3) [or ( 4 ) and ( 5 ) ] were prepared and analyzed.
[*] Prof. N. J. Turro
Department of Chemistry, Columbia University
New York, N. Y. 10027 (USA)
Dr. P. Lechtken
Institut fur Organische Chemie I der Universitat
Erlangen-Numberg
852 Erlangen, Henkestrasse 42 (Germany)
We gratefully acknowledge the support of the DAAD through
a NATO Fellowship and through the Air Force Office of Scientific
Research (AFOSR-70-1848) and the National Science Foundation (NSFGP-26602X).
Fragment X = H, D
Table I. Mass numbers for analysis of deuterium contents [8]
cx3co
cx3cocx,
(CX,),CCHCN
(CX3),CCHOC2H,
( M - IS)
(2)
(3)
Oxetane
(4)
43
58
(5)
43
58
81
46
64
86
-
-
100
106
121
124
-
-
-
46
64
-
[**I
314
Analysis of the oxetanes from addition of singlet acetone
to dicyanoethylene revealed 5 & 2% deuteriooxetane (3)
A n g m . Chum. inturnat
Edlr
/ Vol. 12 ( 1 9 7 3 ) / No. 4
in the total oxetane mixture, while the corresponding deuterated oxetane ( 5 ) from addition of triplet acetone to
diethoxyethylene accounted for 10+5% of the total oxetane mixture.
leads to the followApplication of Stern-Volmer
ing rate constants for energy transfer:
third main Group have so far been unknown. We here
report the first synthesis of a boracyclosilane.
It is known that octaphenylcyclotetrasilane[21reacts with
lithium with ring fission to 1,4-dilithiooctaphenyltetrasilane ( I )I3]:
N~/K
4 Ph,SiCl,
k:
ki
Singlet-Singlet:
Triplet-Triplet:
3.5 x 10' mol-' S K '
= 2.8 x 10' mol- ' s - '
=
Thus, within the experimental error of f50%, the two
energy transfer rate constants are equal and about three
orders of magnitude smaller than the value for diffusion
in acetone (z5 x lo9 mol- ' s- ').
The number of energy hopping events, (DHOP,depends on
the ratio of the rates of hopping to the sum of all deactivation rates (Yk,,).
In uure acetone at room temuerature
,( [ A ] = l 4 ~ , x k f , = 0 . 6 109s-',
~
x k i = 2 x 105s-')1'01
the singlet makes only one hop per lifetime, while the
triplet makes about 14 hops per lifetime.
.I
1
Received: November 13, 1972 [Z 769 IE]
German version: Angew. Chem. 85. 300 (1973)
[l] G . C. Niemnnn and G . W Robinson, J . Chem. Phys. 37, 2150 (1962).
Concerning its importance for photodegradation as well as photosyntheses see: R . F . Cozzens and R. B. Fox, J. Chem. Phys. 50, 1532 (1969).
S. P. McGlynn, L . Azarruya, 7: Azumi, F. Watson, and A . Armstrong,
L . Augenstein, R . Mason, and B. Rosenberg: Physical Processes in Radiation Biology. Academic Press, New York 1964, p. 93. References to
energy transfer in ketone polymers can be found in: F . J . Golemba
and J. E. Guillei, Macromolecules 5 , 212 (1972).
121 7h. Forsrer . Fluoreszenz organischer Verbindungen, 1st Edit. Vandenhoeck und Ruprecht, Gottingen 1951, pp. 172ff.
[3] P . 1. Wagner, J . Amer. Chem. SOC.88, 5672 (1966); R . F . B o r h a n
and D. R. Kearns, J. Amer. Chem. SOC.88, 3467 (1966).
[4] Arguments for as well as against the existence of an acetone excimer
can be found in: M . O'Sullican and A. C. Testa. J. Amer. Chem. SOC.
90, 6245 (1968); 92, 5842 (1970); N . C. Yang, W Eisenhnrdr, and J .
Libmann, J. Amer. Chem. SOC.94, 4030 (1972).
[5] N . J. Turro and P. Lechrken, Pure Appl. Chem. 33, 363 (1973).
[6] Identical, simultaneously irradiated samples without dioxetane
showed no oxetane formation.
[7] J . C . Dalton, P. A. W i e d e , and N . J . Turro, J . Amer. Chem. SOC.
92, 1318 (1970); M . Niemczyck and N . J . Turro, unpublished.
[S] None of the oxetanes shows a molecular ion even at an ionization
energy of only IOeV.
[9] N . J . Turrot Molecular Photochemistry, 2nd Ed. W. A. Benjamin,
New York 1967, pp. 92R
[lo] A. M . Halpern and W R . Ware, J. Chem. Phys. 54, 1271 (1971),
and own measurements.
Boracyclopentasilane,a New Type of
Heterocyclic Silane
THF-
Ph,Si-SiPh,
~i
Ph,Si-SiPh,
THF
I
I
Ph,Si-SiPh,
I
Ph,Si
I
SiPh,
We have been able to isolate this Li compound (1) as
tetrahydrofuran adduct; it had previously been obtained
only in solution and used therein for manifold reactions.
Metalating ring cleavage in a little tetrahydrofuran leads
to Ph,Si4Li2 .2 T H F being precipitated as yellowish-red,
small crystals which can be recrystallized from cyclohexane: m. p. 121-123 "C (uncorr. in a sealed tube). 'H-NMR
(in C6D6):Ph multiplet at 3.25-2.08 ppm, two T H F multiplets at 8.78 (THF in C6D, 8.47) and 6.68 (6.64) ppm.
The compound IS very sensitive to oxygen and hydrolysis.
First attempts to convert (1) by dichloro(pheny1)borane
into nonaphenylboracyclopentasilane failed; we obtained
only polymeric products. However, analogously to the
work of Noth et u / . ~ ~ who
I
raised the electron density
of a Si-B bond by dimethylamino-substitution, thus stabilizing it, it proved possible to cyclize ( 1 ) to 1-(dimethylamino)-2,2,3,3,4,4,5,5-octaphenyl1-boracyclopentasilane
(2) by means of dichloro(dimethy1amino)borane:
The boracyclosilane (2) forms small white crystals, has
an unusually low density, and is very sensitive to oxygen
and hydrolysis; it is slightly soluble in benzene, .toluene
or xylene, still less so in cyclohexane and insoluble in
pentane or ether. M.p. 261-263°C (uncorr. in a sedled
tube).
The 'H-NMR spectrum (in ChD6;TMS standard) shows
a singlet for the methyl-protons at 7.08 ppm and a phenyl
multiplet at 3.16-2.17 ppm in the proportions 1 : 6.9 (calc.
1 : 6.7). In the IR spectrum the phenyl and dimethylamino
vibrations are at their usual frequencies, but the vB-N
at 1392 cm- lies remarkably low. In the Raman spectrum
vB-N appears at 1394cm-' and a further band at
541 cm- ' which is presumably to be considered as a symmetrical ring vibration. The UV spectrum, compared with
those of other heterocycles of the type Si4X (with X=Si.
Ge, N, P, 0 or S), gives a band at the particularly long-wave
position 330 nm (E = 1700).
Experimental
Solutions of (Ph2Si),Liz.2THF (0.044 mol) in T H F
(180ml) and of Me,NBCI, (0.044 mol) in benzene (250ml)
By Edwin Hengge and Dieter Wolferr''
Only a few heterocyclic silanes with cumuIated Si-Si
bonds are known''' and most of them contain, as hetero
atoms, elements of the fourth, fifth and sixth main Group.
Analogous cyclosilane derivatives with elements of the
See, inrrr aiia. E . Hengge and U . B2-ichcy, Monatsh. Chem. 97.
1309 (1966); C'. M'unnagur and 0.Brandsrurfer, ihid. 94, 1090 (1963);
97, 1352 (1966); Angew. Chem. 75, 345 (1963); Angew. Chem. internat.
Edit. 2, 263 (1963); M . Kicmada e f a/.. Kogyo Kagaku Zasshi 66, 637
(1963); Chem. Abstr 1963. 15303.
[*] Prof. Dr E. Hengge and DiplLIng. D. Wolfer
Anorganisch-chemisches Institut der Technischen Hochschule
A-8010 Graz, Stremayrgasse 16 (Austria)
[2] f . S. Kipping and I . E. Sands, J . Chem. Soc. 1921, 830, 848.
[3] A . W P. Jurcie, H . J . S . Winkler. D. J . Pererson, and H . Gilinun,
J. Amer. Chem. Soc. 83. 1921 (1961).
[4] H . Nijth and C . Hijllerer. Chem. Ber. YY, 2197 (1966).
[I]
315
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