Kinetics of photoreduction of 9,10-phenanthrenequinone in the presence of amines and polymethylbenzenes

Article abstract of DOI:10.1007/s11172-005-0143-5

A study of the kinetics of photoreduction of 9,10-phenanthrenequinone in the presence of hydrogen donors (para-substituted N,N-dimethylanilines and polymethylbenzenes) showed that plots of the quantum yield of photoreduction (φ_H) and apparent reaction rate constant (k_H) vs. oxidation potential of hydrogen donors are extreme. In the presence of amines, k_H and φ_H increase, as a whole, whereas they decrease in the presence of polymethylbenzenes. In coordinates φ_H- ΔG_e (ΔG_e is the change in the free energy of electron transfer) for pairs quinone-H donor, φ_H increases with ΔG_e approaching to zero. For the amine series, this effect is mainly in the exothermic region of ΔG_e (ΔG_e < 0). For the series of polymethylbenzenes, this increase is observed in the endothermic region (ΔG_e > 0).

Full text of DOI:10.1007/s11172-005-0143-5

Russian Chemical Bulletin, International Edition, Vol. 53, No. 11, pp. 2485—2489, November, 2004
2485
Kinetics of photoreduction of 9,10ꢀphenanthrenequinone in the presence
of amines and polymethylbenzenes
M. P. Shurygina, S. A. Chesnokov, M. A. Lopatin, V. K. Cherkasov, and G. A. Abakumovꢀ
G. A. Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences,
49 ul. Tropinina, 603950 Nizhny Novgorod, Russian Federation.
Fax: +7 (831 2) 66 1497. Eꢀmail: cherkasov@imoc.sinn.ru
A study of the kinetics of photoreduction of 9,10ꢀphenanthrenequinone in the presence of
hydrogen donors (paraꢀsubstituted N,Nꢀdimethylanilines and polymethylbenzenes) showed
that plots of the quantum yield of photoreduction (ϕ ) and apparent reaction rate constant
H
(kH) vs. oxidation potential of hydrogen donors are extreme. In the presence of amines, kH and
ϕ
increase, as a whole, whereas they decrease in the presence of polymethylbenzenes. In
H
coordinates ϕ —∆Ge (∆Ge is the change in the free energy of electron transfer) for pairs
H
quinone—H donor, ϕH increases with ∆Ge approaching to zero. For the amine series, this effect
is mainly in the exothermic region of ∆Ge (∆Ge < 0). For the series of polymethylbenzenes, this
increase is observed in the endothermic region (∆Ge > 0).
Key words: 9,10ꢀphenanthrenequinone, hydrogen phototransfer, free energy of electron
transfer, N,Nꢀdimethylanilines, polymethylbenzenes.
Operation of various technical and biological photoꢀ
sensitive systems is based on the photoinduced electron
and hydrogen transfer involving carbonylꢀcontaining comꢀ
pounds.1,2 However, only few systematic studies of the
influence of the nature of reactants on the kinetics of
photoreduction reactions are known, and their results are
ambiguous. For instance, it has been found by the nanoꢀ
second laser photolysis technique for the kinetics of phoꢀ
toreduction of a series of pꢀbenzoquinones in the presꢀ
ence of 4ꢀphenylaniline3 that the rate constant of quinone
photoreduction kH decreases with an increase in the elecꢀ
tronꢀacceptor ability of the quinones. Similarly, for the
pꢀbenzoquinone—diphenylamine system,4 the calculated
kH values decrease with an increase in the reduction poꢀ
tential of the quinone in the duroquinone—pꢀcholoranil
series. At the same time, when the triplet state of
anthanthrone is quenched with anilines or phenols,5 kH inꢀ
creases with a decrease in the oxidation potential of amine
and phenol, and the logkH = f(E1/2(DH)) plots are linear in
both cases. As follows from these examples, the facilitaꢀ
tion of an electron transfer due to an enhancement of the
electronꢀwithdrawing3,4 or electronꢀreleasing5 properties
of reactants can change kH in opposite directions. A study
of the plots of the quantum yield (ϕH) of fluorenone phoꢀ
toreduction in the presence of a wide series of pꢀsubꢀ
stituted N,Nꢀdimethylanilines (from 4ꢀnitrileꢀN,Nꢀdiꢀ
methylaniline to N,N,N´,N´ꢀtetramethylꢀpꢀphenylenediꢀ
amine) showed6 that ϕH changed extremely with a change
in the electronꢀreleasing properties of the amine. A study
of the photoreduction of similar in structure oꢀbenzoꢀ
quinones in the presence of N,Nꢀdimethylanilines found7
that the plot of the apparent rate constant of photoreducꢀ
tion kH vs. halfꢀwave potential E1/2 of the polarographic
reduction of the quinones also has an extreme. Researchꢀ
ers are interested in studying the kinetics of photoreducꢀ
tion of other photoacceptors because of extreme plots of
ϕH or kH vs. redox characteristics of reactants in systems
containing fluorenone and oꢀbenzoquinones—N,Nꢀdiꢀ
methylanilines.
In this work, we studied the kinetics of photoreducꢀ
tion of 9,10ꢀphenanthrenequinone in the presence of variꢀ
ous hydrogen donors: pꢀsubstituted N,Nꢀdimethylanilines
and polymethylbenzenes.
Experimental
Electronic absorption spectra were recorded on
Perkin—Elmer Lambdaꢀ25 and SFꢀ14 spectrophotometers in
benzene. NMR spectra were obtained on a Bruker DPXꢀ200
spectrometer.
9,10ꢀPhenanthrenequinone (1) (Aldrich) was recrystallized
from methanol. Toluene (2a) (Reakhim), 1,2ꢀdimethylbenzene
(oꢀxylene) (2b) (Reakhim), 1,4ꢀdimethylbenzene (pꢀxylene) (2c)
(Reakhim), 1,3,5ꢀtrimethylbenzene (mesitylene) (2d)
(Reakhim), 1,2,4,5ꢀtetramethylbenzene (durene) (2e)
(Reakhim), hexamethylbenzene (2f) (Aldrich), and benzene used
as solvent were purified according to standard procedures.8
N,N,N´,N’ꢀTetramethylꢀpꢀphenylenediamine (3a) (Fluka)
and 4ꢀnitrileꢀN,Nꢀdimethylaniline (3g) (Fluka) were purified
by double sublimation. 4ꢀMethylꢀN,Nꢀdimethylaniline (3c)
(Aldrich) and N,Nꢀdimethylaniline (3d) (Aldrich) were distilled.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2381—2385, November, 2004.
1066ꢀ5285/04/5311ꢀ2485 © 2004 Springer Science+Business Media, Inc.

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Shurygina et al.
4ꢀFormylꢀN,Nꢀdimethylaniline (3e) (Fluka) and 4ꢀbromoꢀN,Nꢀ
dimethylaniline (3f) (Aldrich) were recrystallized from hexane.
4ꢀMethoxyꢀN,Nꢀdimethylaniline (3b) was synthesized by a
known procedure.9
9ꢀHydroxyꢀ9ꢀ(3´,5´ꢀdimethylbenzyl)ꢀ10ꢀoxoꢀ9,10ꢀdihydroꢀ
phenanthrene was synthesized according to a previously described
procedure.10 1H NMR (CDCl3), δ: 2.19 (s, 6 H, CH3); 2.92,
3.00 (both d, 1 H each, CH2, J = 13 Hz); 3.99 (s, 1 H, OH); 6.43
(s, 2 H, CH(2´), CH(6´)); 6.81 (s, 1 H, CH(4´)); 7.38—7.95
(m, 8 Н, CH(1), CH(2), CH(3), CH(4), CH(5), CH(6),
CH(7), CH(8)).
A
1.5
1.2
0.9
0.6
0.3
9ꢀHydroxyꢀ9ꢀ[(NꢀphenylꢀNꢀmethyl)ꢀaminomethyl]ꢀ10ꢀoxoꢀ
9,10ꢀdihydrophenanthrene. 1H NMR (C6D6), δ: 2.55 (s, 3 H,
NCH3); 3.47 and 3.62 (both d, 1 H each, C(9)CH2N, J =
15 Hz); 4.53 (br.s, 1 H, ОН), signals of aromatic protons overꢀ
lap with the corresponding signals of the starting substances.
Quantum yields of photoreduction of 9,10ꢀphenanthreneꢀ
quinone in the presence of polymethylbenzenes and pꢀsubstituted
N,Nꢀdimethylanilines were determined using a standard actiꢀ
nometer (potassium ferrioxalate). A benzene solution (4.4 mL)
containing 9,10ꢀphenanthrenequinone (1•10–3 mol L–1) and a
hydrogen donor (5•10–2 mol L–1) was deaerated, saturated with
argon, and placed in a quartz cell 1 cm thick. The solution was
irradiated with a monochromatic light of λ = 412 nm, which was
isolated from the full light flux of an KGMꢀ24ꢀ150 lamp using
an interference light filter no. 10. The intensity measurement of
the monochromatic light and experimental runs were carried
out according to a known procedure.2 The intensity of irradiaꢀ
tion with the monochromatic light λ = 412 nm was 1.53•10–9
Einstein s–1. Quantum yields were measured from a decrease in
the intensity of the absorption band of 9,10ꢀphenanthreneꢀ
quinone (λ = 410 nm, ε = 2200 L mol–1 cm–1).
Apparent rate constants of photoreduction of 9,10ꢀphenꢀ
anthrenequinone in the presence of pꢀsubstituted N,Nꢀdiꢀ
methylanilines and polymethylbenzenes were determined specꢀ
trophotometrically. A benzene solution (5 mL) containing
9,10ꢀphenanthrenequinone (4.2•10–4 mol L–1) and a hydrogen
donor (2.1•10–2 mol L–1) was deaerated, saturated with argon,
placed in a spectrophotometric cell 0.5 cm thick, and exposed at
a distance of 6 cm from the collimator of an illuminator with an
KGMꢀ24ꢀ150 lamp. The radiation with λ < 430 nm was isolated
from the light flux of the illuminator with an SSꢀ5 light filter.
Current concentrations of 9,10ꢀphenanthrenequinone were deꢀ
tected by a change in the intensity of the absorption band of
quinone (λ = 412 nm, ε = 2200 L mol–1 cm–1) according to the
Lambert—Bouger—Beer law. Under experimental conditions,
the photoreduction obeys a firstꢀorder kinetic equation in the
initial reaction step until a conversion of quinone of ∼30%. The
apparent rate constant of quinone photoreduction was deꢀ
termined from the slope ratio of the linear region of the
ln([A0]/[Aτ])—τ plot, where τ is the total time of irradiation of
the solution. The numerical value of the apparent rate constant
was averaged by three measurements with convergence of results
within 5%.
340
380
420
460
500
λ/nm
Fig. 1. Spectral changes upon irradiation with the light
λ < 430 nm at equal time intervals (40 s) of a solution of
9,10ꢀphenanthrenequinone (4.2•10–4 mol L–1) and mesitylene
(2.1•10–2 mol L–1) in benzene (deaerated solution was satuꢀ
rated with Ar, 298 K).
A
2.0
1.6
1.2
0.8
0.4
340
380
420
460
λ/nm
Fig. 2. Spectral changes upon irradiation with the light
λ < 430 nm at equal time intervals (40 s) of a solution of
9,10ꢀphenanthrenequinone (4.2•10–4 mol L–1) and N,Nꢀdiꢀ
methylaniline (2.1•10–2 mol L–1) in benzene (deaerated soluꢀ
tion was saturated with Ar, 298 K).
the color of solution due to the photoreduction of 1. The
changes in the spectral characteristics of 1 and 2d, as well
as 1 and 3a, in benzene upon irradiation with the light
λ < 430 nm at equal time intervals are presented in Figs. 1
and 2, respectively, as typical examples. It is seen that a
decrease in the absorption band intensity of the quinone
at 410 nm is accompanied by an increase in the absorꢀ
bance of the solutions in the UV spectral region, and
distinct isosbestic points are observed in both cases.
The main product of photoreduction of phenanthreneꢀ
quionone 1 in the presence of arenes 2 is the correspondꢀ
ing ketol,10 which was confirmed by the analysis of the
products of photointeraction of compounds 1 and 2d (see
Experimental). The NMR study of the products of reacꢀ
tion of 1 with 3d showed the formation of ketol 9ꢀhydroxyꢀ
Results and Discussion
The visible light irradiation of benzene solutions of
9,10ꢀphenanthrenequinone (1) and polymethylbenzenes
(2) or paraꢀsubstituted N,Nꢀdimethylanilines (3) changes

Photoreduction of 9,10ꢀphenanthrenequinone
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 11, November, 2004 2487
Table 1. Oxidation potentials of polymethylbenzenes 2 and
paraꢀsubstituted N,Nꢀdimethylanilines 3 (E1/2(DH/DH•+ ) and
)
experimental values of the quantum yield (ϕ ) and apparent
H
rate constant of photoreduction (kH) of 9,10ꢀphenanthreneꢀ
quinone 1 in the presence of the hydrogen donors
Hydrogen donor
E1/2(DH/DH /V
ϕ
kH•103/s–1
•+
)
H
2a
2b
2c
2d
2e
2f
2.28
1.87
1.86
1.85
1.59
1.46
1.12
0.86
0.84
0.71
0.65
0.49
0.16
0.03
0.10
0.15
0.14
0.34
0.43
0.70
0.41
0.63
0.53
0.41
~0
0.27
0.75
0.67
0.91
1.37
3.30
4.37
3.20
3.24
1.90
1.55
0.04
0.003
n = 1 (2a), 2 (2b, oꢀxylene), 2 (2c, pꢀxylene), 3 (2d, mesitylene),
4 (2e, durene), 6 (2f)
R = NMe2 (3a), OMe (3b), Me (3c), H (3d), C(O)H (3e),
Br (3f), CN (3g)
3g
3f
9ꢀ[(NꢀphenylꢀNꢀmethyl)aminomethyl]ꢀ10ꢀoxoꢀ9,10ꢀdiꢀ
hydrophenanthrene. Protons of the methylene group
linked with the asymmetric C(9) atom are nonequivalent.
In the NMR spectrum, the methylene group looks like an
AB multiplet with the center at 3.54 ppm and a spinꢀspin
coupling constant characteristic of geminal protons
of 15 Hz.
3e
3d
3c
3b
3a
~0
Note. Exposure conditions are given in the text, C6H6, 298 K.
For the photoreduction of 9,10ꢀphenanthrenequinone,
as in the case of other carbonylꢀcontaining comꢀ
pounds,2,11,12 the lowest excited triplet state is active
(quinone molecule transits to this state from the S(ππ*)
and S(nπ*) states).13 In the electronic absorption specꢀ
trum of 9,10ꢀphenanthrenequinone, the bands correꢀ
sponding to electron transitions S(π→π*) and S(n→π*)
have maxima at 410 and 510 nm.1 It is convenient to
monitor the reaction course by a decrease in the intensity
of the absorption band of 1 (λmax = 410 nm), whose molar
linear plots of E1/2(DH/DH ) vs Hammett σр constants for
•+
the substituents in an N,Nꢀdimethylaniline molecule.7
The oxidation potentials of polymethylbenzenes were obꢀ
tained by reducing the tabulated E1/2(DH/DH
to the potential against SCE in an 0.5 М solution of
NaClO4 in acetonitrile.
values14
•+
)
In Table 1, hydrogen donors are arranged in an order
of increasing their electronꢀdonor ability: from toluene to
hexamethylbenzene in the series of compounds 2 and
from pꢀnitrileꢀN,Nꢀdimethylaniline to N,N,N´,N´ꢀtetraꢀ
methylꢀpꢀphenylenediamine in the series of compounds 3.
For polymethylbenzenes, the ϕH and kH values increase
successively on going from toluene to hexamethylbenzene.
This can be caused by an increase in the number of hydroꢀ
gen atoms in molecules of compounds of the studied seꢀ
ries of H donors. For instance, the quantum yields of
photoreduction of 2,3,5,6ꢀtetrachloroꢀ1,4ꢀbenzoquinone
in the presence of 1ꢀmethylnaphthalene and 1,4ꢀdimethylꢀ
naphthalene differ by ~2 times.15 However, the ϕH and
kH values normalized to the number of hydrogen atoms in
a polymethylbenzene molecule also increase by 2.4 and
2 times on going from 2a to 2f, respectively. It is most
likely that for the reaction under study ϕH and kH depend
on both the number of hydrogen atoms in a hydrogen
donor molecule and its redox characteristics. When the
oxidation potential of compound 2 decreases, the effiꢀ
ciency of polymethylbenzenes as H donors increases.
In N,Nꢀdimethylanilines, on going from one amine to
another, the reaction center (dimethylamino group) reꢀ
mains unchanged, providing a more correct analysis of
the plots of ϕH and kH vs. electronꢀdonor ability of
amines 3. It follows from the data presented that a deꢀ
absorption coefficient in benzene is 2200 L mol–1 cm–1
.
Ketols have light yellow color.10 For instance, the elecꢀ
tronic absorption spectrum of the product of the reaction
of compounds 1 and 2d (9ꢀhydroxyꢀ9ꢀ(3´,5´ꢀdimethylꢀ
benzyl)ꢀ10ꢀoxoꢀ9,10ꢀdihydrophenanthrene) in benzene
contains an unresolved band in the visible region with the
red boundary at 500 nm. The molar absorption coefficient
of this absorption band at λ = 410 nm is equal to
12 L mol–1 cm–1. This value is two orders of magnitude
lower than the molar absorption coefficient of 9,10ꢀphenꢀ
anthrenequinone, which makes it possible to study specꢀ
trophotometrically the kinetics of photoreduction of
phenanthrenequinone 1 in the presence of polymethylꢀ
benzenes 2 and 3 from a decrease in the absorption band
of 1 at λmax = 410 nm.
The photoreduction of phenanthrenequinone 1 in the
presence of compounds 2 and 3 was studied using irradiaꢀ
tion of reactant solutions with the light λ < 430 nm (see
Experimental). The oxidation potentials of H donors and
the quantum yields and apparent rate constants of phoꢀ
toreduction of 1 in the presence of 2a—f and 3a—g for
each pair of reactants are presented in Table 1 (oxidaꢀ
tion potentials of dimethylanilines 3a—d,g against satuꢀ
rated calomel electrode were taken from Ref. 14). The
E1/2(DH/DH ) value for compound 3e was calculated from
•+

2488
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 11, November, 2004
Shurygina et al.
crease in the oxidation potential E1/2(DH/DH
of amine
and its analogs, viz., oꢀ and pꢀquinones, including 1).
This indicates that the hydrogen phototransfer reacꢀ
tion involving these photoacceptors proceeds through
the photoinduced electron transfer from DH to 3A* to
form intermediate radical ion products. Direct proofs
for the stepwise character of the photoreduction were
obtained from the picosecond photolysis study of the
"classical" system benzophenone—N,Nꢀdimethylaniline
(BP—DMA).21,22 This mechanism of hydrogen transfer
for the photoreduction of carbonylꢀcontaining compounds
was proposed and discussed in earlier studies.6,15,18,19,23
It seems reasonable to consider a relation between the
kinetic parameters of photoreduction and ∆Ge due to the
presence of an electron transfer step. The ∆Ge value inꢀ
cludes the energy of the excited state of a photoacceptor
E00 and redox characteristics of a photoacceptor and
H donor24,25
•+
)
is accompanied by a decrease in the ϕH and kH values.
The ϕH value for 3f, which is lower than the expected
value likely due to the influence of the Br atom on
the lifetime of an excited complex between reactant
molecules, does not obey the monotonic plot ϕH
f(E1/2(DH/DH )). As whole, the plots ϕH
=
=
a
•+
f(E1/2(DH/DH ) and k = f(E1/2(DH/DH ) are Sꢀlike.
•+
•+
)
H
)
For E1/2(DH/DH ) < 0.5 V and E1/2(DH/DH ) > 0.8 V, the
•+
•+
ϕH and kH values are minimum and maximum, reꢀ
spectively, and they change sharply in the interval
0.5
<
E1/2(DH/DH
< 0.8 V. The plots ϕH =
•+
)
f(E1/2(DH/DH ) and k = f(E1/2(DH/DH ) are close for
•+
•+
)
)
H
both systems 1—2 and 1—3, which makes it possible to
use both experimentally determined parameters ϕH and
kH to describe the kinetic relations of 9,10ꢀphenanthreneꢀ
quinone photoreduction.
If ϕH is considered as a function of E1/2(DH/DH
ignoring differences in the nature of H donors, then
the resulting experimental data form, as a whole, a
,
•+
)
∆Ge = –∆E00 – E1/2(A /A) + E1/2(DH/DH
–
•+
)
•–
– T∆Se + 0.13 eV,
(1)
waveꢀlike relation ϕH = f(E1/2(DH/DH ). The plots
•+
)
where ∆E00 is the energy of the triplet 0→0 transition of
ϕH = f(E1/2(DH/DH ) are inverse in two regions of
•+
)
the lowest excited state of a carbonylꢀcontaining comꢀ
values of the oxidation potentials of H donors. At
pound, E1/2(A
is the redox potential of an acceptor,
•–
/A)
E1/2(DH/DH
< +1.12 V the quantum yield of photoreꢀ
•+
)
and ∆Se is the entropy change upon the formation of a
chargeꢀtransfer complex (contact radical ion pair). The
following characteristics of 9,10ꢀphenanthrenequinone
were used for the calculation of ∆Ge: ∆E00 = 2.12 eV,26
duction of 1 increases with an increase in E1/2(DH/DH
,
•+
)
and at E1/2(DH/DH
> +1.46 V ϕH decreases. For the
•+
)
systems of reactants 1—2 and 1—3, the change in the
character of the ϕH = f(E1/2(DH/DH ) plot coincides
•+
)
E1/2(A /A) = –0.66 eV,14 and T∆Se ≈ –0.23 eV obtained24
•–
with a change in the nature of the H donor and can
be explained by this fact. At the same time, for the
fluorenone—3 system, this change is observed within
the series of N,Nꢀdimethylanilines in an interval of
for quenching excited states of aromatic hydrocarbons in
the presence of N,Nꢀdiethylaniline.
The plot ϕH = f(∆Ge) is presented in Fig. 3. The
∆Ge value varies from –0.96 eV to +1.17 eV. Reaction
pairs 1—3 exist in the endothermic region of ∆Ge values,
E1/2(DH/DH
from +0.16 to +1.12 V;6 the plot of ϕH vs.
•+
)
E1/2(DH/DH
is extreme with
a
maximum at
•+
)
E1/2(DH/DH
= +0.65 V (3c). A similar curve kH
=
•+
)
ϕ
H
f(E1/2(DH/DH ) was obtained for the photoreduction of
•+
)
2,3,5,6ꢀtetrachloroꢀ1,4ꢀbenzoquinone in the presence
of 2: with an increase in E1/2(DH/DH ) from +1.46 V (2f)
to +1.85 V (2d), kH increase, whereas further they deꢀ
crease sharply on going to xylenes and toluene,16 and the
•+
0.6
0.4
0.2
1
2
maximum of kH corresponds to E1/2(DH/DH ) ≈ +1.85 V.
•+
Thus, the plots of ϕH and/or kH vs. E1/2(DH/DH
for
•+
)
9,10ꢀphenanthrenequinone, fluorenone, and 2,3,5,6ꢀtetꢀ
rachloroꢀ1,4ꢀbenzoquinone are extreme. The position of
the maximum is determined by the photoacceptor nature.
For 9,10ꢀphenanthrenequinone, it lies at E1/2(DH/DH
+1.12 V; for fluorenone, in a region of E1/2(DH/DH
≈
≈
•+
)
•+
)
+0.65 V; for 2,3,5,6ꢀtetrachloroꢀ1,4ꢀbenzoquinone, in a
region of E1/2(DH/DH ) ≈ +1.85 V.
•+
As found by numerous studies, carbonylꢀcontaining
compounds are characterized, on the one hand, by effiꢀ
cient photoreduction and, on the other hand, by the
"Rehm—Weller dependence" 17 between the logarithm of
the quenching rate constant of 3А* and the free energy of
electron transfer logkq = f(∆Ge)18—20 (A is benzoquinone
–0.8
–0.4
0
0.4
0.8
∆Ge/eV
Fig. 3. Quantum yield (ϕ ) of photoreduction of 9,10ꢀphenꢀ
H
anthrenequinone in the presence of N,Nꢀdimethylanilines (1)
and polymethylbenzenes (2) as a function of the free energy of
electron transfer (∆Ge) (irradiation with the light λ = 412 nm,
benzene, 298 K).

Photoreduction of 9,10ꢀphenanthrenequinone
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 11, November, 2004 2489
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A WileyꢀIntercience Publication John Wiley and Sons, New
York—London—Sydney—Toronto, 1972.
9. C. Weigand and G. Hilgetag, Organisch chemische
Experimentierkunst, Verlag, Leipzig, 1964.
while the exothermic region contains reaction pairs 1—2.
As ∆Ge increases (i.e., on going from negative to posiꢀ
tive ∆Ge), the ϕH values increase, reach a maximum at
∆Ge = +0.01 eV (reactant pair 1—3f), and then decrease
(system 1—2).
It has previously been shown7 that for the fluoreꢀ
none—3 system ∆Ge changes from –0.44 eV to +0.53 eV;
the plot ϕH = f(∆Ge) is also extreme, and the ϕH maxiꢀ
mum is observed at ∆Ge = +0.06 eV. For the system
2,3,5,6ꢀtetrachloroꢀ1,4ꢀbenzoquinone—2, ∆Ge varies
from –0.30 to +0.52 eV; with an increase in ∆Ge, the kH
values increase, reach a maximum at ∆Ge = +0.09 eV, and
then decrease.16 A similar result was obtained7 for the
photoreduction of a series of eight similar in structure
oꢀbenzoquinones in the presence of N,Nꢀdimethylanilines
3d, 3e, and 3f. In this case, the redox characteristics of
both photoacceptors and H donors changed. Three exꢀ
10. K. Maruyama, K. Ono, and J. Osugi, Bull. Chem. Soc. Jpn,
1972, 45, 847.
treme plots kH = f(E1/2(A /A)) were obtained, and on
11. J. A. Barltrop and J. D. Coyle, Excited States in Organic
Chemistry, John Wiley and Sons, London—New York—
Sydney—Toronto, 1975.
12. S. Patai, The Chemistry of the Quinonoid Compounds, John
Wiley and Sons, Chichester—New York—Brisbane—
Toronto—Singapore, 1988, 2, 878 pp.
13. D. N. Shigorin, L. Sh. Tushishvili, A. A. Shcheglova, and
N. S. Dokunikhin, Zh. Fiz. Khim., 1971, 45, 511 [J. Phys.
Chem. USSR, 1971, 45 (Engl. Transl.)].
•–
going to coordinates kH = f(∆Ge) they ran into one plot
with a maximum at ∆Ge = +0.09 eV. A comparison of the
obtained data shows that for all reaction systems under
study the maximum values of ϕH and/or kH correspond to
pairs of reactants, whose ∆Ge is close to zero. On going
from zero to the endothermic or exothermic region of
∆Ge, the ϕH and/or kH values decrease.
Thus, the study of the kinetics of 9,10ꢀphenanthreneꢀ
quinone photoreduction in the presence of hydrogen doꢀ
nors (pꢀsubstituted N,Nꢀdimethylanilines and polymethylꢀ
benzenes) showed that the quantum yield of photoreducꢀ
tion and apparent reaction rate constant exhibit an exꢀ
treme change with an increase in the oxidation potential
of hydrogen donors. In the presence of amines, the ϕH
and kH values increase as a whole, while they decrease in
the presence of polymethylbenzenes. In the coordinates
ϕH—∆Ge (change in the free energy of electron transfer),
for pairs quinone—Н donor, ϕH increases as the ∆Ge valꢀ
ues approach to zero in both cases: this occurs in the
exothermic region of ∆Ge (∆Ge < 0) for the series of amines
and in the endothermic region (∆Ge > 0) for the polyꢀ
methylbenzene series.
14. Ch. K. Mann and K. K. Barnes, Elektrochemical Reactions in
Nonaqueous Systems, Marcel Decker, Inc., New York, 1970.
15. G. Jones, W. A. Haney, and X. T. Phan, J. Am. Chem. Soc.,
1988, 110, 1923.
16. S. A. Chesnokov, G. A. Abakumov, V. K. Cherkasov, and
M. P. Shurygina, Dokl. Akad. Nauk, 2002, 385, 780 [Dokl.
Chem., 2002 (Engl. Transl.)].
17. D. Rehm and A. Weller, Ber. Bunsenges. Phys. Chem., 1969,
73, 834.
18. S. G. Cohen, A. Parola, and G. H. Parsons, Chem. Rev.,
1973, 73, 141.
19. P. P. Levin and V. A. Kuzmin, Usp. Khim., 1987, 56, 527
[Russ. Chem. Rev., 1987, 56 (Engl. Transl.)].
20. S. Fukuzumi, S. Itoh, T. Komori, T. Suenobu, A. Ishida,
M. Fujitsuka, and O. Ito, J. Am. Chem. Soc., 2000, 122, 8435.
21. H. Miyasaka, K. Morita, K. Kamada, and N. Mataga, Bull.
Chem. Soc. Jpn, 1990, 63, 3385.
22. K. S. Peters, A. Cashin, and P. Timbers, J. Am. Chem. Soc.,
2000, 122, 107.
23. S. Arimitsu, H. Masuhara, N. Mataga, and H. Tsubomura,
J. Phys. Chem., 1975, 79, 1255.
This work was financially supported by the Foundaꢀ
tion of the President of the Russian Federation (Grant
NShꢀ1649.2003.3).
24. H. Knibbe, D. Rehm, and A. Weller, Ber. Bunsenges. Phys.
Chem., 1969, 73, 839.
References
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2. Einführung in die photochemie, Ed. G. O. Bekker, VEB
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Received June 30, 2004