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The fluorescence spectrum of the α-styryl radical, C6H5··CH2
Volume 12, number 4
CHEMICAL PHYSIiJS LETTERS
THE FLUORESCENCE
SPECTRUM OF THE &TYkYL
15 January
1972
RADICAL, C,H,d=CH,
B. BROCKLEHURST, J.S. ROBINSONi and D.N. TAWN Department
of CPtemistry, The University. Sheffield
S3 7HF, UK
Received2 November 1971 A green thermoluminescence
of-r-hadiatd
&WSY s~hti~ns
of phenol acetylene is ascribed to the fluorescence of the
crstyxyl radical.
Organic ions can be produced by r-radio!ysis and trapped in glassy alkane solutions at 77OK;on warming, they recombine, often producing luminescence of the solutes [I,23 . This thermoluminescence usually con-
sists of fluorescence and phosphorescence
of the
parent molecules; but emission
from radicals has also been observed; e.g., toluene,losing a hydrogen atom, gives benzyl fluorescence [3] and recently, the
a-methyl benzyl radical has been characterized as the emitter in styrene solutions, i.&, hydrogen atom addition occurs [4]. We report here similar observations on phenyl acetylene. The experimental methods have been described previously [S ] . Phenyl acetylene was purified by vapour-phase chromatcgraphy. The thermoluminescence of its solution in a 2: 1 mixture of methyl cyclohexane
and isopentane was first studied photo-electrically (low resolution). In addition to the fluorescence and phosphorescence of phenyl acetylene, a strong emission with a maximum at about 450 run was observed.
The relative intensities changed only slightly with concentration (range ICY3 to 5 X 1O-2 molar). This suggests that the emitter contains only one molecule ofthe solute: compare the behaviour of naphthalen! [5]. To obtain better resolution the thermoluminescence was photographed with a Hiiger E517 f/4 glass spectro-
graph (slit width 0.25 mm, bandwidth Spectra4
tubes containing
about
1 nm).
were irradiated with y-rays at 77OK to 200 krad (1.2 X lOI eV g-1) and allowed to warm up in front of the spectrograph slit, section by section, by raising them slowly out of liquid nitrogen. Similar experiments were made with toluene for comparison and the results are given jn table I. The bands were broad (about 5 nm). As well as the bands listed, phosphorescence bands of phenyl acetylene were found on the plates. The new bands were not produced by ultraviolet excitation either before y-irradiation, or after prolonged irradiation, warming and re-cooling, i.e., they are not due to the parent molecule, to an impurity or to a stable irradiation product. The new emission could be observed pitotoelectrically at very low doses (IO krad); this and the high viscosity of the sol.utions (even during warning) suggest that &e amount of chemical change occurring is very small. The electronic spectra ofa-styryl do not appear to have been reported previously. The ESR spectrum has been shown to be that of a n-radical [7], so its emission spectrum, should lie in the same region as those of benzyl and a-methyl be&. Table I shows that this is so. We therefore postulate that the emitter is formed by H-atom addition in the &position as in the case of styrene [4] , but we cannot rule out completely the addition of alkyi radicals derived from the solvent. Details
of the excitation process are not yet clear,
2 X 1O-2 molar solutions
l’he authors thank the Royal Society for an equipment grant and the Science Research Council for mair+nance
7 +%ent address: Kodak Limited, l&row,
6iO
Middlesex,UK.
D.N.T.:).
grants to two of them
(J.S.R. and
Yofume 12, number 4
IS ~anuasy 1972
CHE??ICAL PHYSICS LETTERS
T&le I Observed emission band maxima (cm-l) 20 110 s
19 760 hi
20 570
20 OS0
hf
S
19 660 W
20 540 M
Benzyla)
21630 S
21060 vs
Bentylb)
21580 S
21010
a-methyl-benzyic)
21600 S
21 000 S
20 000 S
a-sty&‘)
21 100 s
20 150 M
19 590
18 100
M
w
a> Ref. 161; Sotution in a 2:3 mixture of methyl
20 650 hf
VS
cycfohexanc
and isopmtme;
I? 000 W
‘i * *. *
only the strongest bands are quoted.
@This work: solution in a,2:1 rni~~ureof me&v1 euclohexzne ;urdisoaentane: band maxima. c) Ref. 141.
References
141 A. Deroukde, F. Kieffer, E. Migirdicyan and J. R&tr;t,
3. Chim. Phys 67 (1970) 193 11 [ 1j 3. Brockfehurst, Rad. Res. Rev. 2 (1970) 149. f2] F. Kieffer and hf. Magat, in: Actions chimiques et biofogiques des radiations, Vol. 14, ed. hf. Haissinsky
(Masso~, Paris, 1970) p. 13.5. [31 B. Brocklehurst, R.D. RusseIl and M.1. Swvadatti, Trans. Faraday Sot. 62 (1966) 1129.
fS1 B. Brocklehurst
and R.D. Russ&, Trans. Faraday Sot. 65 (1969) 2159. I6f L. Grajcar and S. Leach, Compt. Rend. Acad. Sci. (Paris) 252 [196X) 1014; J. Chirn. phys. 61 (f96$) 1513.
i71J rE. Bennett and J.A. How&r&C&m. Phys. Letters 9 (1971) 460.
CHEMICAL PHYSIiJS LETTERS
THE FLUORESCENCE
SPECTRUM OF THE &TYkYL
15 January
1972
RADICAL, C,H,d=CH,
B. BROCKLEHURST, J.S. ROBINSONi and D.N. TAWN Department
of CPtemistry, The University. Sheffield
S3 7HF, UK
Received2 November 1971 A green thermoluminescence
of-r-hadiatd
&WSY s~hti~ns
of phenol acetylene is ascribed to the fluorescence of the
crstyxyl radical.
Organic ions can be produced by r-radio!ysis and trapped in glassy alkane solutions at 77OK;on warming, they recombine, often producing luminescence of the solutes [I,23 . This thermoluminescence usually con-
sists of fluorescence and phosphorescence
of the
parent molecules; but emission
from radicals has also been observed; e.g., toluene,losing a hydrogen atom, gives benzyl fluorescence [3] and recently, the
a-methyl benzyl radical has been characterized as the emitter in styrene solutions, i.&, hydrogen atom addition occurs [4]. We report here similar observations on phenyl acetylene. The experimental methods have been described previously [S ] . Phenyl acetylene was purified by vapour-phase chromatcgraphy. The thermoluminescence of its solution in a 2: 1 mixture of methyl cyclohexane
and isopentane was first studied photo-electrically (low resolution). In addition to the fluorescence and phosphorescence of phenyl acetylene, a strong emission with a maximum at about 450 run was observed.
The relative intensities changed only slightly with concentration (range ICY3 to 5 X 1O-2 molar). This suggests that the emitter contains only one molecule ofthe solute: compare the behaviour of naphthalen! [5]. To obtain better resolution the thermoluminescence was photographed with a Hiiger E517 f/4 glass spectro-
graph (slit width 0.25 mm, bandwidth Spectra4
tubes containing
about
1 nm).
were irradiated with y-rays at 77OK to 200 krad (1.2 X lOI eV g-1) and allowed to warm up in front of the spectrograph slit, section by section, by raising them slowly out of liquid nitrogen. Similar experiments were made with toluene for comparison and the results are given jn table I. The bands were broad (about 5 nm). As well as the bands listed, phosphorescence bands of phenyl acetylene were found on the plates. The new bands were not produced by ultraviolet excitation either before y-irradiation, or after prolonged irradiation, warming and re-cooling, i.e., they are not due to the parent molecule, to an impurity or to a stable irradiation product. The new emission could be observed pitotoelectrically at very low doses (IO krad); this and the high viscosity of the sol.utions (even during warning) suggest that &e amount of chemical change occurring is very small. The electronic spectra ofa-styryl do not appear to have been reported previously. The ESR spectrum has been shown to be that of a n-radical [7], so its emission spectrum, should lie in the same region as those of benzyl and a-methyl be&. Table I shows that this is so. We therefore postulate that the emitter is formed by H-atom addition in the &position as in the case of styrene [4] , but we cannot rule out completely the addition of alkyi radicals derived from the solvent. Details
of the excitation process are not yet clear,
2 X 1O-2 molar solutions
l’he authors thank the Royal Society for an equipment grant and the Science Research Council for mair+nance
7 +%ent address: Kodak Limited, l&row,
6iO
Middlesex,UK.
D.N.T.:).
grants to two of them
(J.S.R. and
Yofume 12, number 4
IS ~anuasy 1972
CHE??ICAL PHYSICS LETTERS
T&le I Observed emission band maxima (cm-l) 20 110 s
19 760 hi
20 570
20 OS0
hf
S
19 660 W
20 540 M
Benzyla)
21630 S
21060 vs
Bentylb)
21580 S
21010
a-methyl-benzyic)
21600 S
21 000 S
20 000 S
a-sty&‘)
21 100 s
20 150 M
19 590
18 100
M
w
a> Ref. 161; Sotution in a 2:3 mixture of methyl
20 650 hf
VS
cycfohexanc
and isopmtme;
I? 000 W
‘i * *. *
only the strongest bands are quoted.
@This work: solution in a,2:1 rni~~ureof me&v1 euclohexzne ;urdisoaentane: band maxima. c) Ref. 141.
References
141 A. Deroukde, F. Kieffer, E. Migirdicyan and J. R&tr;t,
3. Chim. Phys 67 (1970) 193 11 [ 1j 3. Brockfehurst, Rad. Res. Rev. 2 (1970) 149. f2] F. Kieffer and hf. Magat, in: Actions chimiques et biofogiques des radiations, Vol. 14, ed. hf. Haissinsky
(Masso~, Paris, 1970) p. 13.5. [31 B. Brocklehurst, R.D. RusseIl and M.1. Swvadatti, Trans. Faraday Sot. 62 (1966) 1129.
fS1 B. Brocklehurst
and R.D. Russ&, Trans. Faraday Sot. 65 (1969) 2159. I6f L. Grajcar and S. Leach, Compt. Rend. Acad. Sci. (Paris) 252 [196X) 1014; J. Chirn. phys. 61 (f96$) 1513.
i71J rE. Bennett and J.A. How&r&C&m. Phys. Letters 9 (1971) 460.