- Email: [email protected]
Reaction of chemical acceptors with singlet oxygen produced by direct laser excitation
REACTION
OF
CHEMfcAr,
PRODUCED
ACCEPTORS
BY DIRECT
The out>& of the $d-YAG kzsvr :li 10% nm tics vxtltin the z Ag + v *- xi absorpt ion txtxi of the osvgen molecule. We wish to rqmrt here cliroct generation of lA oxygen in solution by cscitation of dissolved oxygen with the 35 Watt n~ultimoclc C.W. output from a Hoiobeam Type 250 laser. Hgh oxygen pressures, up to 140 atm. are required since the absorption intensity is proportional to the square of the oxygen concentrntion { 11. Given sufficient osygen absorption the high laser power available generates enough la to react with added chemical accrptors at a high rate. _Acccptor decay was detccled by measurement of the acceptor rit)sortx~~e during the rour~c. of Insur irradiation. Laser scatter interference vjtth the absorb;tncc measurerncMs was c~iimin:~tctl by the use of suitnble filters.
LASER
WITIf
SISGLET
EXCfTATfOS
OXYGES
Volume
7. number
CHEMICAL PEIYSICS LETTERS
~1
Reaction
rates
15 November
1970
Table 1 with ‘A oxygen in l,l,Z-trichiorotrifiuoroethane
Relative Acceptor ---
_...----_ --.. _______-_--_-_.-9,10-diphen~lanthracene
kl AA (WC-‘) +I) --------4----P-7 x 10 39’7
tctrnphenylc~c
SO0
4 x 1o-3
5 x IO 2 x 1,::
lopentrldiennne
rulmenc
522
l,:S-dimeth!:lfuran
822 b)
1 .:~-tiiphen~Iisobenzof~~r~n . -
-II0
--_-_. ---.-
.-.-_-..-- -- .--
--. -
Laser
(k@QIQl)
reactivity Photosensitized 4 ---.-__
1
i
7 8 W
20
7 X 10-2 -. --
100
II 12 C) 120
--__
a) In p.vridine from ref.[Z]. h) Xe:tsured 3s inhibition of rubrem?
C) 13~ compxisnn
oxnlation. with tetramethylethylene in ref. f31.
of its mated at ‘r- 3 mole litre -I by comparison absorption with that of the gas at the same pressure. The solvent concentration is 9 mole litre -1 so that if the solvent quenching rate is low relative to that of 02 then oxygen quenching will be the dominant process. The 1A quenching rate by geseoics oxygen at low pressures is reported as 1.3 x 10~ Iitre mole-l set-1 141 and so we may estimate a W~ZZ~I?IW?I vaiue for h~[Qi of 4 X 163 set-l. This would give kA’S ranging from 4 X x 105 litre mole-l see-1 for S,lO-diphenylanthracene to 4 r i07 litre mole-1 see-1 for I ,3 -diphenyliso5enzofuran. The absolute rate constant (quenching plus reaction) for 2,5 - dimethylfuran in the gas phase has recently been reported as 1.4x 1.06 litre mole-1 see-l [S]. From the present work a minimum total quenching rate of 8 x 106 litre mole-l set-1 is calculated for solution which appears to be somewhat higher than the gas phase value. Evans [6] has previously reported direct photophysical generation of La by He-Pu’e laser excitation (632.8 nm) of the oxygen dimol absorption band. We find that the Nd-YAG laser confers two important advantages: If The laser power is at least one thousand
476
times higher than that available from the He& laser, and thus a higher IA production rate is possible; 2) The possibility exists that some acceptors may have weak absorptions in the Visible red SO that the He-Ne laser may cause some direct acceptor excitation. The risk of this is much
reduced laser.
with the 1065 nm output of the Nd-YAG
This work was supported in part from the Research Corporation.
RR FERENC
ES
111I. H. C. Matheson t2j
T.WiIsm,
by a grant
and J. Lee, J.Am.Chcm.Soc.sS
unpublished
dntn.
(19615) 26%. 131 R.Iliggins, C.S.Foote l nd II. Chcng. in: O?cnJ:~r~tr:! of organic compounds. Vol.3 (Americ:m Chemietll Society, Washington, 1968) p. 11X2. [J] R.P.Wage, in: Advances in photochemistry, Yol. i, eds.J.Eu’.Pitts. G.S.Hammond tend W.A.Xoyes Jr. (Intersciencc, sew York, IDGL)) p.311. [Sj W. S.Gleason, A. D. Hrondbcnt, E. Whittle and J. S. Pi:ts, J.Am.Chem.Soc.92 (1970) ZOGS. [(if D.F.Evnns, Chcm.Commun.(l9G9) 367.
OF
CHEMfcAr,
PRODUCED
ACCEPTORS
BY DIRECT
The out>& of the $d-YAG kzsvr :li 10% nm tics vxtltin the z Ag + v *- xi absorpt ion txtxi of the osvgen molecule. We wish to rqmrt here cliroct generation of lA oxygen in solution by cscitation of dissolved oxygen with the 35 Watt n~ultimoclc C.W. output from a Hoiobeam Type 250 laser. Hgh oxygen pressures, up to 140 atm. are required since the absorption intensity is proportional to the square of the oxygen concentrntion { 11. Given sufficient osygen absorption the high laser power available generates enough la to react with added chemical accrptors at a high rate. _Acccptor decay was detccled by measurement of the acceptor rit)sortx~~e during the rour~c. of Insur irradiation. Laser scatter interference vjtth the absorb;tncc measurerncMs was c~iimin:~tctl by the use of suitnble filters.
LASER
WITIf
SISGLET
EXCfTATfOS
OXYGES
Volume
7. number
CHEMICAL PEIYSICS LETTERS
~1
Reaction
rates
15 November
1970
Table 1 with ‘A oxygen in l,l,Z-trichiorotrifiuoroethane
Relative Acceptor ---
_...----_ --.. _______-_--_-_.-9,10-diphen~lanthracene
kl AA (WC-‘) +I) --------4----P-7 x 10 39’7
tctrnphenylc~c
SO0
4 x 1o-3
5 x IO 2 x 1,::
lopentrldiennne
rulmenc
522
l,:S-dimeth!:lfuran
822 b)
1 .:~-tiiphen~Iisobenzof~~r~n . -
-II0
--_-_. ---.-
.-.-_-..-- -- .--
--. -
Laser
(k@QIQl)
reactivity Photosensitized 4 ---.-__
1
i
7 8 W
20
7 X 10-2 -. --
100
II 12 C) 120
--__
a) In p.vridine from ref.[Z]. h) Xe:tsured 3s inhibition of rubrem?
C) 13~ compxisnn
oxnlation. with tetramethylethylene in ref. f31.
of its mated at ‘r- 3 mole litre -I by comparison absorption with that of the gas at the same pressure. The solvent concentration is 9 mole litre -1 so that if the solvent quenching rate is low relative to that of 02 then oxygen quenching will be the dominant process. The 1A quenching rate by geseoics oxygen at low pressures is reported as 1.3 x 10~ Iitre mole-l set-1 141 and so we may estimate a W~ZZ~I?IW?I vaiue for h~[Qi of 4 X 163 set-l. This would give kA’S ranging from 4 X x 105 litre mole-l see-1 for S,lO-diphenylanthracene to 4 r i07 litre mole-1 see-1 for I ,3 -diphenyliso5enzofuran. The absolute rate constant (quenching plus reaction) for 2,5 - dimethylfuran in the gas phase has recently been reported as 1.4x 1.06 litre mole-1 see-l [S]. From the present work a minimum total quenching rate of 8 x 106 litre mole-l set-1 is calculated for solution which appears to be somewhat higher than the gas phase value. Evans [6] has previously reported direct photophysical generation of La by He-Pu’e laser excitation (632.8 nm) of the oxygen dimol absorption band. We find that the Nd-YAG laser confers two important advantages: If The laser power is at least one thousand
476
times higher than that available from the He& laser, and thus a higher IA production rate is possible; 2) The possibility exists that some acceptors may have weak absorptions in the Visible red SO that the He-Ne laser may cause some direct acceptor excitation. The risk of this is much
reduced laser.
with the 1065 nm output of the Nd-YAG
This work was supported in part from the Research Corporation.
RR FERENC
ES
111I. H. C. Matheson t2j
T.WiIsm,
by a grant
and J. Lee, J.Am.Chcm.Soc.sS
unpublished
dntn.
(19615) 26%. 131 R.Iliggins, C.S.Foote l nd II. Chcng. in: O?cnJ:~r~tr:! of organic compounds. Vol.3 (Americ:m Chemietll Society, Washington, 1968) p. 11X2. [J] R.P.Wage, in: Advances in photochemistry, Yol. i, eds.J.Eu’.Pitts. G.S.Hammond tend W.A.Xoyes Jr. (Intersciencc, sew York, IDGL)) p.311. [Sj W. S.Gleason, A. D. Hrondbcnt, E. Whittle and J. S. Pi:ts, J.Am.Chem.Soc.92 (1970) ZOGS. [(if D.F.Evnns, Chcm.Commun.(l9G9) 367.