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Intersystem crossing yields in anthanthrene and perylene from photosensitised peroxidation
CHEMICAL
PHYSICS
LETTERS
1 (1967)
INTERSYSTEM AND PERYLENE
219-220.
NORTH -HOLLAND
PUBLISHING
COMP.ANY
, -AMSTERDAM
CROSSING YIELDS IN ANTHANTHRENE FROM PHOTOSIjNSITISED PEROXIDATION B. STEVENS and B. E. ALGAR
Department
of Chemistv.
The University
Received
of Sheffield.
England
1 July 1967
The quantum yields of anthanthrene and perylene sensitised phoioperoxidation of 9. lO-dimethyianthracene and 9,10-dimethyl-l, O-benzanthracene have been measured as a function of dissolved oxygen concentration in benzene solution. An analysis of the data in terms of the 021AR intermediate provides intersystern crossing yields for anthanthrene (0.23 * 0.04) and perylene (0.06 * 0.06); @ether with the respective quantum yields of fluorescence of 0.73 -L 0.06 and 0.89 f 0.06. these indicate that intemaI conversion does not contribute significantly to the overall relaxation of the lowest excited singlet states of these moIecuIcs_
It has previously been shown [l] that an analysis of the oxygen concentration dependence of the quantum yield yAoz of photoperoxidation of an aromatic hydrocarbon A can provide an estimate of the intersystem crossing yield YISC of the molecule A. In the presence of a sensitiser S, which absorbs the incident radiation but remains chemically unchanged, the proposed scheme is modified to : 1.
1s*
2.
is*_
3.
1s*-s
4.
5.
4
Stlzv
3s
3s
3s
+
02’
8.
3s
-I- or%-
s+
k6 << (k7”8)
o2
s+lo*n
02 = @q&5)
02
in v,hich case the quantum yield of photosensitised peroxidation of the substrate, YA02, is given by YAO22
k5°2 = *A kl+k2+k3 * k$8[J,IS&l;j
where &A = kgA/(kgA+klo) oxygen
4-s
7.
it is assumed that
If the intermediate
Is*+ 02-+%+ o2 1s* + 02’%i10+2
6.
is significant,
quenching
105
(1)
and VISC = l+/(kl+k2+k3). is produced.
of the sensitiser
(or
sofefy
by
substrlte)
triplet state, i.e. kg = k8 = 0 as in the case of naphthacene [ 11, eq. (1) reduces to
Quantum yields of peroxidation of 9, IO-dimethylanthracene DMA(3.3 x 10-4 AM)and of 9, Gl-dimethyl1,2-benzanthracene DMM(10-4 M), sensitised by anthanthrene and nervlene at 435.8 mcr . have been
B. STEVENS
220
and B. E. ALGAR Table 1 Quantum yields of intersystem crossing and of fluoressence yF in benzene at 25oC. yI8c Anthanthrene Perylene
0.23 * 0.04 0.06 f 0.06
YF 0.73 f 0.05 0.89 f 0.05
YISC
+yF
0.96 f 0.09 0.95 f 0.11
the combined limits of error the sum of both quantum yields is unity and it is concluded that internal conversion does not contribute significantly to the overall depopulation rate of the lowest errcited singlet state, i.e. k3 << (kl+kz) for these compounds. If the intermediate lo; were produced by oxygen quenching of both singlet and triplet states of the sensitiser, i.e. kq = b = 0, the appropriate reduction of eq. (1) would require that [l] yf~C = %ntercept/slope)
L Plot of quantum yield data in accordance with (2) for anthanthrene (0) and perylenc (0) sensitised peroxidation of DMA and for anthanthrene (A) and perylene (A) sensitised phoxidation of DMBA in benzene at 250C. Fig.
equation
The award of an S.R.C. maintenance grant is gratefully acknowledged (B.E.Algar).
as required by eq. (1) with kq = k8 = 0; (c) the intercept/slope ratio given by rf~C
= k&l++k3)
REFERENCES
is independent cf substrate and has the values tabulated for the different sensitisers. The
tabulated
values
of the quantum
which would exceed the limiting value of lYF = 0.32 for anthan~hrene as in the cane of naphthacene [ 1J. However in the absence of information concerning the triplet state energy of the former compound, process 5 may be restricted by energy requirements, as in the case of xanthene dyes [3].
yield
yF
of sensitiser fluorescence were measured under the same conditions relative to that of a solution of quinine bisulphate in 0.W H$Oq of the same optical density at the excitation frequency; within
[l] B. Stevens and B. E. AIgar,
Chem. Phys. Letters 1 (1967) 58. [2] cf. T. Wilson, J. Amer. Chem.Soc. 88 (1966) 28%; K. R. Kopechy and H. J. Reich, Canad. J. Chem. 43 (1965) 2265. [3] K. Gollnick and G. 0. Schenck. Pure and Applied Chem. 9 (1964) 507.
PHYSICS
LETTERS
1 (1967)
INTERSYSTEM AND PERYLENE
219-220.
NORTH -HOLLAND
PUBLISHING
COMP.ANY
, -AMSTERDAM
CROSSING YIELDS IN ANTHANTHRENE FROM PHOTOSIjNSITISED PEROXIDATION B. STEVENS and B. E. ALGAR
Department
of Chemistv.
The University
Received
of Sheffield.
England
1 July 1967
The quantum yields of anthanthrene and perylene sensitised phoioperoxidation of 9. lO-dimethyianthracene and 9,10-dimethyl-l, O-benzanthracene have been measured as a function of dissolved oxygen concentration in benzene solution. An analysis of the data in terms of the 021AR intermediate provides intersystern crossing yields for anthanthrene (0.23 * 0.04) and perylene (0.06 * 0.06); @ether with the respective quantum yields of fluorescence of 0.73 -L 0.06 and 0.89 f 0.06. these indicate that intemaI conversion does not contribute significantly to the overall relaxation of the lowest excited singlet states of these moIecuIcs_
It has previously been shown [l] that an analysis of the oxygen concentration dependence of the quantum yield yAoz of photoperoxidation of an aromatic hydrocarbon A can provide an estimate of the intersystem crossing yield YISC of the molecule A. In the presence of a sensitiser S, which absorbs the incident radiation but remains chemically unchanged, the proposed scheme is modified to : 1.
1s*
2.
is*_
3.
1s*-s
4.
5.
4
Stlzv
3s
3s
3s
+
02’
8.
3s
-I- or%-
s+
k6 << (k7”8)
o2
s+lo*n
02 = @q&5)
02
in v,hich case the quantum yield of photosensitised peroxidation of the substrate, YA02, is given by YAO22
k5°2 = *A kl+k2+k3 * k$8[J,IS&l;j
where &A = kgA/(kgA+klo) oxygen
4-s
7.
it is assumed that
If the intermediate
Is*+ 02-+%+ o2 1s* + 02’%i10+2
6.
is significant,
quenching
105
(1)
and VISC = l+/(kl+k2+k3). is produced.
of the sensitiser
(or
sofefy
by
substrlte)
triplet state, i.e. kg = k8 = 0 as in the case of naphthacene [ 11, eq. (1) reduces to
Quantum yields of peroxidation of 9, IO-dimethylanthracene DMA(3.3 x 10-4 AM)and of 9, Gl-dimethyl1,2-benzanthracene DMM(10-4 M), sensitised by anthanthrene and nervlene at 435.8 mcr . have been
B. STEVENS
220
and B. E. ALGAR Table 1 Quantum yields of intersystem crossing and of fluoressence yF in benzene at 25oC. yI8c Anthanthrene Perylene
0.23 * 0.04 0.06 f 0.06
YF 0.73 f 0.05 0.89 f 0.05
YISC
+yF
0.96 f 0.09 0.95 f 0.11
the combined limits of error the sum of both quantum yields is unity and it is concluded that internal conversion does not contribute significantly to the overall depopulation rate of the lowest errcited singlet state, i.e. k3 << (kl+kz) for these compounds. If the intermediate lo; were produced by oxygen quenching of both singlet and triplet states of the sensitiser, i.e. kq = b = 0, the appropriate reduction of eq. (1) would require that [l] yf~C = %ntercept/slope)
L Plot of quantum yield data in accordance with (2) for anthanthrene (0) and perylenc (0) sensitised peroxidation of DMA and for anthanthrene (A) and perylene (A) sensitised phoxidation of DMBA in benzene at 250C. Fig.
equation
The award of an S.R.C. maintenance grant is gratefully acknowledged (B.E.Algar).
as required by eq. (1) with kq = k8 = 0; (c) the intercept/slope ratio given by rf~C
= k&l++k3)
REFERENCES
is independent cf substrate and has the values tabulated for the different sensitisers. The
tabulated
values
of the quantum
which would exceed the limiting value of lYF = 0.32 for anthan~hrene as in the cane of naphthacene [ 1J. However in the absence of information concerning the triplet state energy of the former compound, process 5 may be restricted by energy requirements, as in the case of xanthene dyes [3].
yield
yF
of sensitiser fluorescence were measured under the same conditions relative to that of a solution of quinine bisulphate in 0.W H$Oq of the same optical density at the excitation frequency; within
[l] B. Stevens and B. E. AIgar,
Chem. Phys. Letters 1 (1967) 58. [2] cf. T. Wilson, J. Amer. Chem.Soc. 88 (1966) 28%; K. R. Kopechy and H. J. Reich, Canad. J. Chem. 43 (1965) 2265. [3] K. Gollnick and G. 0. Schenck. Pure and Applied Chem. 9 (1964) 507.