Hydrogen-bonding-induced electron transfer from triplet N,N-dialkyl-1-naphthylamines to benzophenone via triplet exciplexes

Article abstract of DOI:10.1021/jp9523940

Laser flash photolysis studies at 355-nm on the photoreactions of the benzophenone (BP) and N,N-dialkyl-1-naphthylamine, DANA (N,N-dimethyl-1-naphthylamine, DMNA, and N,N-diethyl-1-naphthylamine, DENA) system have been carried out with and without H₂O and methanol in acetonitrile (ACN) at 295 K. In the nanosecond time scale, triplet energy transfer from triplet BP (³BP*) to DANA occurs with the efficiency φ_TET (0.74 for DMNA and 0.61 for DENA) regardless of the presence of H₂O and methanol. After the formation of triplet DANA (³DANA*), the triplet exciplex ³(DANA...BP)* with weak charge-transfer character is produced with the equilibrium constant K₁ (10 M^-1 for DMNA and 9 M^-1 for DENA) between ³DANA* and BP. The mechanism for the formation of ³(DANA...BP)* is shown in Scheme 1. In the presence of H₂O and methanol, it is found that the intraexciplex electron transfer takes place to give the BP anion (BP^?-) and DANA cation (DANA^?+) radicals in the hydrogen-bonded triplet exciplex ³(DANA...BP)*_HB by H₂O or methanol. The mechanism for the production of DANA^?+ and BP^?- is proposed in Scheme 2. The equilibrium constants K₂ for the formation of ³(DANA...BP)*_HB with H₂O and methanol obtained are 0.55 and 0.45 M^-1 for DMNA, 0.50 and 0.40 M^-1 for DENA. The rate constants k_et for the intraexciplex electron transfer induced by hydrogen bonding are determined to be 2.5 × 10⁷ s^-1 for DMNA and 1.4 × 10⁷ s^-1 for DENA. It was revealed that the driving force for intraexciplex electron transfer is the negatively enlarged reduction potential of BP in ³(DANA...BP)*_HB due to the hydrogen bonding to the carbonyl group of BP in ³(DANA... BP)*.

Full text of DOI:10.1021/jp9523940

672
J. Phys. Chem. 1996, 100, 672-679
Hydrogen-Bonding-Induced Electron Transfer from Triplet N,N-Dialkyl-1-naphthylamines
to Benzophenone via Triplet Exciplexes1
Tatsuya Kiyota, Minoru Yamaji, and Haruo Shizuka*
Department of Chemistry, Gunma UniVersity, Kiryu, Gunma 376, Japan
ReceiVed: August 15, 1995; In Final Form: October 3, 1995X
Laser flash photolysis studies at 355-nm on the photoreactions of the benzophenone (BP) and N,N-dialkyl-
1-naphthylamine, DANA (N,N-dimethyl-1-naphthylamine, DMNA, and N,N-diethyl-1-naphthylamine, DENA)
system have been carried out with and without H2O and methanol in acetonitrile (ACN) at 295 K. In the
nanosecond time scale, triplet energy transfer from triplet BP (3BP*) to DANA occurs with the efficiency
φTET (0.74 for DMNA and 0.61 for DENA) regardless of the presence of H2O and methanol. After the
formation of triplet DANA (3DANA*), the triplet exciplex 3(DANA‚‚‚BP)* with weak charge-transfer character
3
is produced with the equilibrium constant K1 (10 M-1 for DMNA and 9 M-1 for DENA) between DANA*
3
and BP. The mechanism for the formation of (DANA‚‚‚BP)* is shown in Scheme 1. In the presence of
H2O and methanol, it is found that the intraexciplex electron transfer takes place to give the BP anion (BP•-)
3
and DANA cation (DANA•+) radicals in the hydrogen-bonded triplet exciplex (DANA‚‚‚BP)H*B by H2O or
methanol. The mechanism for the production of DANA•+ and BP•- is proposed in Scheme 2. The equilibrium
3
constants K2 for the formation of (DANA‚‚‚BP)H*B with H2O and methanol obtained are 0.55 and 0.45 M-1
for DMNA, 0.50 and 0.40 M-1 for DENA. The rate constants ket for the intraexciplex electron transfer
induced by hydrogen bonding are determined to be 2.5 × 107 s-1 for DMNA and 1.4 × 107 s-1 for DENA.
It was revealed that the driving force for intraexciplex electron transfer is the negatively enlarged reduction
potential of BP in 3(DANA‚‚‚BP)*HB due to the hydrogen bonding to the carbonyl group of BP in 3(DANA‚‚‚
BP)*.
Introduction
between triplet naphthalene derivatives and the ground-state
BP.24-31 It was shown that the triplet exciplexes had loose,
sandwich-like structures27 and weak charge-transfer character.24-31
It can be generalized that the triplet aromatic compounds
sensitized by BP would deactivate via triplet exciplexes.
As mentioned above, triplet energy transfer from triplet BP
to naphthalene derivatives occurred even in a mixed solvent of
ACN and water (4:1 v/v), as well as in ACN, producing triplet
naphthalene derivatives. However, exceptional results were
obtained in our preliminary work on N,N-dimethyl-1-naphthyl-
amine (DMNA). In ACN, triplet energy transfer from triplet
BP to DMNA produces triplet DMNA and the corresponding
triplet exciplex, whereas electron transfer took place during the
deactivation of triplet BP to yield the benzophenone anion and
DMNA cation radicals in ACN-H2O (4:1 v/v).32 It can be
predicted schematically that added water may play an important
role in altering the chemical interactions in the BP-DMNA
system in ACN.32 However, it has not been found yet whether
the triplet exciplex is involved in the reaction mechanism in
ACN-H2O (4:1 v/v) or not.
Since the first report on the triplet sensitization of naphthalene
by benzophenone in a rigid matrix by Terenin and Ermolaev,2
a large number of investigations on triplet energy transfer have
been carried out both theoretically3,4 and experimentally.5-21
However, little attention has been paid to the interactions of
triplet-sensitized compounds with the ground state of triplet-
energy donors until recently. We have been very interested in
the photochemical reactions and mechanism of triplet-sensitized
aromatic compounds, especially naphthalene derivatives with
benzophenone (BP) by means of nanosecond laser photolysis
techniques.22-32 When naphthylammonium ion22,25 and naph-
thol24,26 were employed as triplet energy acceptors from triplet
BP in acetonitrile (ACN) or a mixture of ACN and water (4:1
v/v) upon laser excitation at 355 nm, it was found by the
production of the benzophenone ketyl radical and the corre-
sponding naphthylamine cation and naphthoxy radicals that
hydrogen atom transfer occurred from triplet naphthylammo-
nium ion and naphthol to BP. Moreover, it was revealed by
kinetic treatment that the presence of protons in the employed
systems affected the rate of hydrogen atom transfer. In the case
of naphthylammonium ion, the rate was suppressed by protons25
but enhanced for naphthol.26 On the other hand, in the BP-
methoxynaphthalene system, electron transfer was found during
the decay of triplet methoxynaphthalene, resulting in the
production of the methoxynaphthalene cation and benzophenone
ketyl radicals only in the presence of protons in ACN-H2O
(4:1 v/v).23,28 The rate for electron transfer, in other words,
ionization of methoxynaphthalene increased with an increase
of the proton concentration. The reaction mechanism for the
hydrogen atom and electron-transfer processes, including the
proton effects, was explained in terms of triplet exciplexes
In the present paper, to clarify the solvent dependence of the
photochemical reactions of the BP-dialkylnaphthylamine sys-
tem, 355-nm laser flash photolysis was carried out at 295 K. It
was revealed that the radical ions were produced by electron
transfer induced by hydrogen bonding of H2O or methanol to
triplet exciplexes, and its reaction mechanism is discussed in
detail.
Experimental Section
Benzophenone (BP) was purified twice by vacuum sublima-
tion. N,N-Dimethyl-1-naphthylamine (DMNA) from Tokyo
Kasei was purified by distillation in vacuo. N,N-Diethyl-1-
naphthylamine (DENA) was synthesized as follows: N-Ethyl-
1-naphthylamine was stirred with a small portion of H2SO4 in
X Abstract published in AdVance ACS Abstracts, December 1, 1995.
0022-3654/96/20100-0672$12.00/0 © 1996 American Chemical Society

Hydrogen-Bonding-Induced Electron Transfer
J. Phys. Chem., Vol. 100, No. 2, 1996 673
TABLE 1: Triplet Energies (ET), Molar Absorption
acetic anhydride for 2 h at room temperature. The solution was
poured into water, neutralized with NaHCO3, and extracted with
benzene. To a tetrahydorofuran (THF) solution of the product,
borane-THF solution was added dropwise, maintaining at 0
°C. After the solution was refluxed for 1 h and cooled to room
temperature, a 6 M HCl solution was added slowly to hydrolyze
the amine-borane complex. NaOH pellets were added to
saturate the aqueous phase, and the latter was extracted three
times with benzene. The product was purified by column
chromatography on silica gel with benzene. Furthermore,
vacuum distillation was carried out to give a colorless oil. The
product was identified to be DENA byNMR and mass spec-
troscopy.
Acetonitrile (ACN) was used as a solvent. ACN, methanol
(MeOH), and deionized water were purified by distillation. D2O
and methanol-d1 were used as supplied from Aldrich.
The concentration ranges of DMNA and DENA were (0-
1.5) × 10-3 and (0-1.0) × 10-3 M, respectively. BP was used
as a triplet sensitizer in the concentration range 0.01-0.2 M.
Under these experimental conditions, no contribution due to
direct excitation of DMNA and DENA at 355 nm to transient
absorption spectra was observed. All samples in quartz cells
with a 10-mm path length were degassed by freeze-pump-
thaw cycles on a high-vacuum line. The kinetic analysis for
the transient signal was carried out by the least-squares best-
fitting method within (5% errors. The third harmonics of a
nanosecond Nd3+:YAG laser (355 nm) from JK Lasers HY-
500 (pulse width 8 ns, laser power 40 mJ/pulse) was used for
sample excitation. For the direct excitation of DMNA and
DENA, a XeCl excimer laser (Lambda Physik Lasertechnik
Lextra 50) at 308 nm was equipped. The detection system for
transient absorption signals has been reported elsewhere.31
Laser photolysis was carried out at 295 K throughout this work.
The oxidation potential (Eox) of DMNA was cited from the
literature (0.75 V vs SCE in ACN).33 That of DENA was
estimated to be 0.75 V vs SCE by the CT absorption method34
with the use of 2,3,5,6-tetrachlorobenzoquinone (chloranil) in
ACN at 295 K.
Coefficients of the T-T Absorptions at Peak Wavelengths
(ꢀTλT), Quantum Yields for Intersystem Crossing (Φisc) and
Fluorescence (Φf), and Oxidation Potentials (Eox) of DMNA
and DENA
ꢀTλTb/M-1 cm-1
(λmax/nm)
a
ET /kcal
compd
mol-1
Φisc
Φfd
Eoxe/V
0.75f
0.75g
c
DMNA
DENA
54.0
51.0
5100 (550)
5500 (560)
0.35
0.64
0.23
0.18
a Determined from the 0-0 band of the phosphorescence spectrum
in methanol:ethanol (1:1 v/v) glass at 77 K. b Determined by the method
shown in ref 28. Errors within (5%. See text for details. c Determined
by the time-resolved thermal lensing method. Errors (0.02. See text
for details. d Errors (0.01. See text for details. e Versus SCE in ACN.
f Data from ref 33. g Determined by the CT absorption method. See
text for details.
Figure 1. (a) Time-resolved transient absorption spectra observed at
(1) 70, (2) 200, and (3) 480 ns after 355-nm laser pulsing in the BP
(1.0 × 10-2 M)-DMNA (4.0 × 10-4 M) system in ACN. (b) Reference
absorption spectra of 3BP* (solid) and 3DMNA* (broken). See text for
details.
The quantum yields (Φisc) for intersystem crossing of DMNA
and DENA in ACN at 295 K, determined by the time-resolved
thermal lensing method (TRTL),35 were 0.35 for DMNA and
0.64 for DENA. The fluorescence quantum yield (Φf) and
triplet energy (ET) are required for the determination of Φisc by
TRTL. The values of Φf for DMNA and DENA in ACN at
295 K were preliminarily determined to be 0.23 and 0.18,
respectively, by comparing with that of 1-naphthylamine in
cyclohexane (0.47).36 The ET values of DMNA and DENA
obtained were 54.0 and 51.0 kcal/mol, respectively, from the
0-0 bands of phosphorescence spectra in methanol:ethanol (1:1
v/v) glass at 77 K.
respectively. The transient absorption peaks at 520 nm observed
at 70 and 80 ns after laser pulsing in Figures 1a and 2a are
ascribable to the triplet-triplet (T-T) absorption spectrum of
BP in ACN.38 According to the first-order kinetics, the intensity
of the T-T absorption of BP decreases with increasing of new
transient absorption peaks at 550 and 560 nm with isosbestic
points at 540 and 545 nm, respectively, in Figures 1a and 2a.
The new absorption bands with their peaks at 550 and 560 nm
were assigned to the T-T absorption spectra of DMNA and
DENA, respectively, since they were the same as those observed
upon direct laser excitation of DMNA and DENA at 308 nm in
The molar absorption coefficients (ꢀTλT) of triplet DMNA
and DENA at the peak wavelength λ were 5100 M-1 cm-1 at
550 nm and 5500 M-1 cm-1 at 560 nm, respectively, by the
method reported previously.32
These data on DMNA and DENA are summarized in Table
1.
3
ACN.39 The reference spectra of BP*, triplet DMNA and
3
DENA (3DMNA* and DENA*), are depicted in Figures 1b
and 2b, respectively. Consequently, the spectral changes in
Figures 1a and 2a demonstrate that the quenching of BP* by
3
DMNA and DENA is triplet energy transfer to produce
3
3DMNA* and DENA* in ACN, not electron transfer.
Results and Discussion
The values of the free energy change ∆GTET for triplet energy
transfer were estimated to be -15.2 (DMNA) and -18.2 kcal/
mol(DENA) from their triplet energies. On the other hand, the
free energy changes ∆Get for electron transfer from the
Triplet Energy Transfer and Exciplex Formation in ACN.
Triplet energy transfer from triplet BP (3BP*) to DMNA and
DENA is possible since the triplet energies of DMNA and
DENA (54.0 and 51.0 kcal/mol, respectively) are smaller than
that of BP (69.2 kcal/mol37). Figures 1a and 2a show the
transient absorption spectra observed after 355-nm laser pho-
tolysis in the BP (1.0 × 10-2 M)-DMNA (4.0 × 10-4 M) and
BP (1.0 × 10-2 M)-DENA (4.0 × 10-4 M) systems in ACN,
3
dialkylnaphthylamines, DANA (DMNA and DENA) to BP*
were estimated as -11.0 kcal/mol for both DMNA and DENA
(see eq 13). The values of ∆GTET are negatively large compared
to those of ∆Get. This fact may result because triplet energy
transfer takes place preferentially without electron transfer. Very

674 J. Phys. Chem., Vol. 100, No. 2, 1996
Kiyota et al.
3
denotes the initial concentration of BP* due to the formation
of 3BP* by laser pulsing, and [3DMNA* or 3DENA*]max
represents the maximum concentration of 3DMNA* or 3DENA*
3
produced by triplet energy transfer from BP* to DMNA and
DENA. [3BP*]max and [3DMNA* or 3DENA*]max can be
estimated by eqs 3 and 4, respectively, where OD520 is the initial
[3BP*]max ) OD520/ꢀTT
(3)
(4)
520
[3DMNA* or 3DENA*]max ) ODλ/ꢀTλT
absorbance at 520 nm due to the formation of 3BP*, ODλ is the
maximum absorbance for 3DMNA*and 3DENA* at a monitoring
wavelength λ (550 nm for DMNA and 560 nm for DENA) at
3
the end of triplet energy transfer from BP* to DMNA and
DENA, ꢀTT and ꢀTλT are the molar absorption coefficients of
520
3BP* at 520 nm, 3DMNA* at 550 nm and 3DENA* at 560 nm
TT
520
TT
550
TT
(ꢀ ) 6500 M-1 cm-1 38
,
ꢀ
) 5100 M-1 cm-1 and ꢀ
)
560
5500 M-1 cm-1, see Table 1), respectively. The values of φTET
for the BP-DMNA and -DENA systems in ACN were
experimentally determined to be 0.74 ((0.04) and 0.61 ((0.03),
respectively, with the use of eqs 2-4. The residual efficiencies
of 0.26 ()1-0.74) for DMNA and 0.39 ()1-0.61) for DENA
are considered to arise from the induced quenching of 3BP* by
DMNA and DENA. It is often reported that the induced
Figure 2. (a) Transient absorption spectra observed at (1) 80, (2) 200,
and (3) 530 ns after 355-nm laser pulsing in the BP (1.0 × 10-2 M)-
DENA (4.0 × 10-4 M) system in ACN. (b) Reference absorption spectra
3
3
of BP* (solid) and DENA* (broken). See text for details.
3
quenching of BP* by naphthalene derivatives competes with
triplet energy transfer.24-31,41
The rate constants for triplet energy transfer (kTET) and
induced-quenching (kIQ) are expressed by eqs 5 and 6, respec-
kTET ) φTETkq
(5)
(6)
kIQ ) kq - kTET
3
tively, since the quenching of BP* consists of both triplet
energy transfer and the induced-quenching processes. With the
use of eqs 5 and 6 and the obtained kq values, the values of
kTET and kIQ were, respectively, determined to be 7.3 × 109
and 2.6 × 109 M-1 s-1 for DMNA and 5.9 × 109 and 3.7 ×
109 M-1 s-1 for DENA. The values of kTET and kIQ, which are
close to the diffusion-controlled rate constant, indicate that both
triplet energy transfer and the induced quenching in the present
system in ACN occur in a collision process. Therefore, the
mechanism for the subjected triplet energy transfer can be
explained with that proposed by Dexter (the exchange mech-
anism).3
BP
obsd
Figure 3. Plots of the first-order decay rate (k ) of 3BP* as a
function of (a) [DMNA] obtained in the BP (1.0 × 10-2 M)-DMNA
and (b) [DENA] in the BP (1.0 × 10-2 M)-DENA system in ACN.
recently, it has been shown that in the 3BP* and 1-naphtholate
anion system the triplet energy transfer does not occur, but
electron transfer does, where the values of ∆GTET and ∆Get are
-12.5 and -15.6 kcal/mol, respectively.40
3
To elucidate the quenching mechanism of BP* by DMNA
BP
and DENA, the first-order decay rate (k ) of 3BP* was
It is known that triplet exciplexes between triplet-sensitized
naphthalene derivatives and BP are produced successively after
triplet energy transfer.24-31 Analogously, the triplet exciplex
obsd
measured and plotted as a function of [DMNA] and [DENA]
in parts a and b of Figure 3, respectively. Since plots gave
BP
obsd
formation between BP and 3DMNA* (or 3DENA*) was
straight lines, k
can be expressed by eq 1, where kB0 P and kq
ex
expected in the present system. The decay rates (k ) of
obsd
3
3DMNA* and DENA* were measured as a function of [BP]
BP
obsd
k
) kB0 P + kq[DMNA or DENA]
(1)
3
3
in ACN. After the formation of DMNA* and DENA* by
triplet sensitization, their absorption spectra decayed uniformly
according to the first-order kinetics. No residual absorbance
was observed in the range 350-750 nm after the depletion of
3
denote the rate constants for the decay of BP* in the absence
of DMNA or DENA and quenching of BP* by DMNA or
3
DENA, respectively. From the intercepts and slopes of the lines,
the values of kB0 P and kq were, respectively, determined to be
3.3 × 105 s-1 and 9.9 × 109 M-1 s-1 for DMNA and 3.3 × 105
s-1 and 9.6 × 109 M-1 s-1 for DENA. Since both values of kq
are close to that of a diffusion-controlled process, it can be said
ex
3DMNA* and DENA*. The plots of kobsd vs [BP] are shown
3
ex
obsd
in Figure 4. The value of k
increases with an increase of
[BP], but not linearly. Both plots for DMNA and DENA give
negative curvatures, which are evidence for the formation of
triplet exciplexes.24-31 Therefore, the mechanism for the triplet
exciplex formation in the present system can be accounted for
analogously by Scheme 1,24-31 where k0 and kex are the rate
3
that the quenching of BP* by DMNA and DENA occurs in a
diffusion process.
3
The efficiency (φTET) for triplet energy transfer from BP*
3
3
constants for the decay processes of DANA* and (DANA‚‚‚
BP)* to the ground state (DANA abbreviated for dialkylnaph-
thylamine represents DMNA or DENA), respectively, k1 and
k-1 are the rate constants for the association and dissociation
to DMNA and DENA can be defined by eq 2, where [3BP*]max
φTET ) [3DMNA* or 3DENA*]max/[3BP*]max
(2)

Hydrogen-Bonding-Induced Electron Transfer
J. Phys. Chem., Vol. 100, No. 2, 1996 675
ex
3
Figure 4. Plots of the first-order decay rate (kobsd) of DMNA* (b)
3
and DENA* (O) vs [BP] obtained by 355-nm laser photolysis in the
BP-DMNA (1.5 × 10-3 M) and -DENA (1.0 × 10-3 M) system in
ACN. The solid curves were calculated by eq 7. See text for details.
SCHEME 1
Figure 5. (a) Transient absorption spectra observed at (1) 70, (2) 160,
(3) 280, and (4) 550 ns after 355-nm laser pulsing in the BP (1.0 ×
10-2 M)-DMNA (4.0 × 10-4 M) system in ACN-H2O (4:1 v/v). (b)
Reference absorption spectra for BP•- (solid) and DMNA•+ (broken).
See text for details.
TABLE 2: Rate Constants and Efficiencies for Quenching
3
of BP* by DMNA and DENA in ACNa
b
b,c
b,d
kq /
kTET
/
kIQ /
compd
109 M-1 s-1
φTET
109 M-1 s-1
109 M-1 s-1
DMNA
DENA
9.9
9.6
0.74e
0.61f
7.3
5.9
2.6
3.7
a See text for details. b Errors within (5%. c Determined by eq 5.
d Determined by eq 6. e Errors (0.04. f Errors (0.03.
TABLE 3: Kinetic Parameters for the Triplet Exciplex
Formationa,b
compd
k0 /104 s-1
c
kex/106 s-1
K1/M-1
DMNA
DENA
3.0
7.5
2.5
3.4
10
9
a Errors within (5%. b In ACN at 295 K. c Determined by direct
laser excitation at 308 nm.
3
of (DANA‚‚‚BP)*, respectively, and K1 ()k1/k-1) denotes an
Figure 6. (a) Transient absorption spectra observed at (1) 80, (2) 180,
(3) 330, and (4) 800 ns after 355-nm laser pulsing in the BP (1.0 ×
10-2 M)-DENA (4.0 × 10-4 M) system in ACN-H2O (4:1 v/v). (b)
Reference absorption spectra for BP•- (solid) and DENA•+ (broken).
See text for details.
3
3
equilibrium constant between DANA* + BP and (DANA‚‚‚
BP)*. According to Scheme 1, k
ex
obsd
can be expressed by eq 7.
k0 + kexK1[BP]
1 + K1[BP]
ex
obsd
k
)
(7)
DENA in ACN-H2O (4:1 v/v) was quite different from that in
ACN. Figures 5a and 6a show the transient absorption spectra
observed after 355-nm laser photolysis in the BP (1.0 × 10-2
M)-DMNA (4.0 × 10-4 M) and BP (1.0 × 10-2 M)-DENA
(4.0 × 10-4 M) system in ACN-H2O (4:1 v/v), respectively.
The absorption bands at 520 nm obtained at 70 and 80 ns in
Figures 5a and 6a are due to 3BP*.38 The T-T absorption band
of BP decreases according to the first-order kinetics with
increasing of new peaks at 375, 435, and 630 nm with isosbestic
points around 450 and 550 nm in both Figures 5a and 6a. The
former two peaks are ascribable to the corresponding cation
radicals of DMNA and DENA (DMNA•+ 32 and DENA•+ 42),
while the latter one can be assigned to be the absorption
spectrum of the benzophenone anion radical (BP•-).32 The
reference absorption spectra of BP•-, DMNA•+, and DENA•+
are depicted in Figures 5b and 6b. The transient absorption
The values of k0 were obtained to be 3.0 × 104 s-1 for DMNA
and 7.5 × 104 s-1 for DENA by direct excitation at 308 nm in
ACN. When eq 7 was applied to the experimental values of
ex
obsd
k
by the least-squares method, the values of kex and K1
were, respectively, best-fitted to be 2.5 × 106 s-1 and 10 M-1
for DMNA and 3.4 × 106 s-1 and 9 M-1 for DENA. The solid
curves in Figure 4 were drawn with the use of eq 7 and the
best-fitted values of kex and K1. The kinetic parameters obtained
are listed in Table 3. Since the relation of k0 , kexK1[BP] exists
in the range 0.01 M e [BP] e 0.2 M, it is concluded that
3DANA* produced from triplet energy transfer by 3BP* mainly
3
deactivates via the triplet exciplex (DANA‚‚‚BP)* according
to Scheme 1.
Radical Ion Formation in a Mixed Solvent of ACN and
H2O (4:1 v/v). The quenching process of 3BP* by DMNA and

676 J. Phys. Chem., Vol. 100, No. 2, 1996
Kiyota et al.
TABLE 4: Molar Absorption Coefficients of BP•-,
DMNA•+, and DENA•+ in ACN-H2O (4:1 v/v) at 295 Ka
wavelength/nm
BP•- b
DMNA•+ b
DENA•+ c
375
435
630
650
1600
300
5000
5400
6500
4200
2300
2400
6700
4300
2400
2500
a In units of M-1 cm-1 b Data from ref 32. c Determined by the same
.
method for DMNA•+ shown in ref 32.
spectra at 550 and 800 ns in Figures 5a and 6a were reproduced
by the superpositions of those of BP•- and the corresponding
cation radical with a 1:1 concentration ratio. Therefore, the
spectral changes in Figures 5a and 6a demonstrate that after
the depletion of 3BP*, BP•-, and DMNA•+ (or DENA•+) were
produced in the BP-DMNA and -DENA systems in ACN-
H2O (4:1 v/v) by electron transfer.
The efficiency (φrad) for the formation of BP•- and cation
3
radicals against the disappearance of BP* was quantified as
follows. Since the concentration of BP•- produced was found
to be the same as that of the countercation radical, φrad was
defined by eq 8, where [BP•-]max and [DMNA•+ or DENA•+]max
Figure 7. (a) Transient absorption spectra observed with the delay
time (1) 200 ns, (2) 520 ns, and (3) 1.2 µs after 355-nm laser pulsing
in the BP (1.0 × 10-2 M)-DMNA (1.5 × 10-3 M) system with H2O
(1.0 M) in ACN. (b) Transient absorption spectra observed at (1) 240
ns, (2) 400 ns, and (3) 1.0 µs after 355-nm laser pulsing in the BP (1.0
× 10-2 M)-DENA (1.0 × 10-3 M) system with H2O (4.5 M) in ACN.
φrad ) [BP•-]max/[3BP*]max
)
[DMNA•+ or DENA•+]max/[3BP*]max (8)
are the maximum concentrations of the produced BP•- and
DMNA•+ (or DENA•+).
Here, the values of [BP•-] max and [DMNA•+ or DENA•+]max
were given by eq 9, where OD630 denotes the maximum
alternation of reactions between ACN and ACN-H2O (4:1 v/v)
was expected to originate in water molecules. To make clear
the effect of H2O on the photochemical reaction in the BP-
DANA system in ACN, laser photolysis in ACN with various
concentration of H2O was carried out.
[BP•-]max ) [DMNA•+ or DENA•+]max
)
OD630/(ꢀ•- + ꢀ6•+30) (9)
630
Parts a and b of Figure 7 show the transient absorption spectra
observed after 355-nm laser photolysis in the BP (1.0 × 10-2
M)-DMNA (1.5 × 10-3 M)-H2O (1.0 M) and -DENA (1.0
× 10-3 M)-H2O (4.5 M) systems in ACN, respectively. The
transient absorption bands at 550 and 560 nm obtained at 200
and 240 ns after laser pulsing, respectively, in parts a and b of
Figure 7 were produced from rapid triplet energy transfer by
3BP*. These bands at 550 and 560 nm are ascribed to the T-T
absorption spectra of DMNA and DENA, respectively. With
decreasing of the absorption bands of 3DMNA* and 3DENA*,
new absorption peaks at 375, 435, and 630 nm appear in both
parts a and b of Figure 7 at 1.2 and 1.0 µs after laser pulsing
with isosbestic points, respectively. These new bands at 375
and 630 nm are ascribable to the superpositions of the absorption
spectra of BP•- and the corresponding cation radials (DMNA•+
or DENA•+) with a 1:1 concentration ratio (see the reference
spectra in Figures 5b and 6b). The formation rate for BP•-
plus DMNA•+ (or DENA•+) at 630 nm was the same as the
decay rate of 3DMNA* (1.0 × 106 s-1) at 550 nm or 3DENA*
(2.7 × 106 s-1) at 560 nm. Therefore, the spectral changes in
Figure 7a,b show that in wet ACN BP•- and DMNA•+ (or
absorbance at 630 nm due to the formation of BP•- and
DMNA•+ (or DENA•+), ꢀ6•-30 and ꢀ•+ represent, respectively,
630
the molar absorption coefficients of BP•- and DMNA•+ (or
DENA•+) at 630 nm (see Table 4). The value of [3BP*] was
estimated by eq 3. From eqs 3, 8, and 9, the values of φrad in
ACN-H2O (4:1 v/v) were determined to be 0.77 ((0.04) for
the BP-DMNA and 0.63 ((0.03) for the BP-DENA systems.
3
The quenching rate constants of BP* in the BP-DMNA
and-DENA systems in ACN-H2O (4:1 v/v) were determined
BP
by plotting the decay rate (k ) of 3BP* as a function of
obsd
BP
obsd
[DMNA] and [DENA]. Since plots of k
gave a straight line
BP
obsd
against [DMNA] and [DENA], k
can be expressed by eq 1.
From the intercept and slope of the line, the values of kB0 P and
kq were determined to be 3.3 × 105 s-1 and 9.5 × 109 M-1 s-1
for DMNA and 3.3 × 105 s-1 and 9.5 × 109 M-1 s-1 for DENA,
respectively. Since both values of kq in ACN-H2O (4:1 v/v)
were close to those of a diffusion-controlled process, the
quenching of 3BP* by DMNA and DENA proceeded in a
diffusion process as well as in ACN, where triplet energy
transfer and the exciplex formation were observed. However,
no formation of 3DMNA* or 3DENA* was observed in ACN-
H2O (4:1 v/v), but formation of the radical ions was observed.
There must be the solvent dependence or effect of added H2O
(whose concentration is estimated to be ca. 11 M in ACN-
H2O (4:1 v/v)) on interactions in the present system. It is
revealed in the next section that the radical ion formation, i.e.,
electron transfer, takes place via triplet exciplexes.
3
DENA•+) are not produced with a depletion of BP*, but with
a decay of 3DMNA* (or 3DENA*) sensitized by 3BP*. When
methanol (MeOH) was added ([MeOH] ) 3 M) in the BP-
DMNA and -DENA systems in ACN instead of H2O, the
production of BP•- and DMNA•+ (or DENA•+) was also
3
3
observed with the disappearance of DMNA* (or DENA*)
produced by the sensitization of 3BP*. Since the radical
formation of BP•- and DMNA•+ (or DENA•+) was induced by
the addition of a little amount of H2O or MeOH to ACN, the
photochemical process in the BP-DANA system was not so
affected by the dielectric constant of solvent. Therefore, it
seems that the hydroxy group of H2O and MeOH offers a
Electron Transfer Induced by Hydrogen Bonding in
Triplet Exciplexes. The addition of H2O (ACN:H2O ) 4:1
v/v) to the BP-DANA system in ACN led to the formation of
the radical ions, but only triplet energy transfer and formation
of triplet exciplex took place in the absence of H2O. The drastic

Hydrogen-Bonding-Induced Electron Transfer
J. Phys. Chem., Vol. 100, No. 2, 1996 677
Figure 8. Plots of the first-order formation rate (koRbsd) of BP•- and DANA•+ as a function of [BP] obtained in the BP-DMNA (1.5 × 10-3 M) with
(a) [H2O] ) 0 (O), 1.0 (4), 2.0 (0), and 3.0 M (b), and (b) [MeOH] ) 0 (O), 0.8 (4), 1.6 (0), and 3.1 M (b), and BP-DENA (1.0 × 10-3 M)
with (c) [H2O] ) 0 (O), 2 (4), 4 (0), and 7.5 M (b), and (d) [MeOH] ) 0 (O), 2 (4), 4 (0), and 7.5 M (b) in ACN. The solid curves were
calculated by eq 10. See text for details.
Figure 9. Plots of the first-order formation rate (koRbsd) of BP•- and DANA•+ vs [H2O] obtained in the (a) DMNA (1.5 × 10-3 M)-BP (0.01 (O),
0.05 (4), and 0.1 M (0)) and (b) DENA (1.0 × 10-2 M)-BP (0.01 (O), 0.05 (4), and 0.12 M (0)) systems, and vs [MeOH] in the (c) DMNA (1.5
× 10-3 M)-BP (0.01 (O), 0.025 (4) and 0.05 M (0)) and (d) DENA (1.0 × 10-3 M)-BP (0.01 (O), 0.05 (4), and 0.12 M (0)) in ACN. The solid
curves were calculated by eq 10. See text for details.
clue for solving the mechanism for electron transfer from
most probable interaction of H2O and MeOH was hydrogen
bonding to triplet exciplexes since triplet exciplexes have weak
charge-transfer structure.24-31
3
3DMNA* (or DENA*) to BP in ACN.
To elucidate the mechanism for formation of BP•- and
DANA•+ induced by H2O or MeOH, the kinetic elucidation of
the rate of radical formation was carried out in the presence of
various [ROH] (ROH denotes H2O or MeOH). The rate
(kRobsd) for the formation of BP•- and DMNA•+ (or DENA•+) at
various [BP] and [ROH] was measured at 630 nm. Both BP•-
and DMNA•+ (or DENA•+) were formed according to the first-
order kinetics. Figures 8 and 9 show the plots of kRobsd vs [BP]
and vs [ROH] in the BP-DMNA (1.5 × 10-3 M) and -DENA
(1.0 × 10-3 M) systems with various [ROH] and [BP] in ACN,
respectively. The value of kRobsd increases nonlinearly with an
increase of [BP] or [ROH]. It is known that the negative
curvature of kRobsd against [BP] and [ROH] is evidence for the
formation of triplet exciplexes between triplet naphthalene
derivatives and BP24-31 and indicates that the triplet exciplexes
interacting with ROH are precursors for BP•- and DMNA•+
(or DENA•+) in the present system. It was presumed that the
By the analogy of the proposed reaction mechanism for triplet
exciplexes previously,24-31 the mechanism for the production
of radical ions can be explained by Scheme 2, where 3(DANA‚‚‚
3
3
BP)* , (DANA‚‚‚BP)*HB, and (DANA•+ + BP•-) denote the
triplet exciplex between 3DANA* and BP, the hydrogen-bonded
triplet exciplex by ROH (H2O or MeOH), and the triplet radical
pair of BP•- and DANA•+, respectively. Here k0, kex, and kHB
represent the rate constants for the decay processes of 3DANA*,
3
3(DANA‚‚‚BP)*, and (DANA‚‚‚BP)H*B, to the ground state,
respectively, ket the rate constant of electron transfer in
3(DANA‚‚‚BP)H*B, k1 and k-1 the rate constants for the associa-
3
tion and dissociation of (DANA‚‚‚BP)*, respectively, k2 and
k-2 the rate constants for the association and dissociation of
3(DANA‚‚‚BP)*HB, respectively, K1 ()k1/k-1) and K2 ()k2/k-2
)
the corresponding equilibrium constants. The triplet radical pair
3(DANA•+ + BP•-) rapidly dissociates into DANA•+ and

678 J. Phys. Chem., Vol. 100, No. 2, 1996
Kiyota et al.
SCHEME 2
tives to the BP site, since little change in the T-T absorption
spectra is observed between triplet exciplexes and free triplet
naphthalene derivatives.24-31 Thus, in the present system, it is
conceivable that the lone-pair electrons of the carbonyl group
3
of BP in (DANA‚‚‚BP)* will be donated to ROH to form the
hydrogen bonding. Subsequently, the charge density on the
3
carbonyl group of BP in (DANA‚‚‚BP)*HB is considered to be
3
reduced compared with that of BP in (DANA‚‚‚BP)*. As a
result, the electron affinity of BP in 3(DANA‚‚‚BP)H*B increases
to achieve intraexciplex electron transfer.
According to Scheme 2, the formation of radical ions during
the decay of 3BP* in ACN-H2O (4:1 v/v) in Figures 5a and 6a
was interpreted as follows. The rates (kRobsd) for the formation
of radicals were evaluated by eq 10 to be 9.1 × 106 s-1 for the
BP (0.01 M)-DMNA (4 × 10-4 M) system and 4.6 × 106 s-1
for the BP (0.01 M)-DENA (4 × 10-4 M) system in the
presence of [H2O] ) 11.1 M in ACN with the use of the
determined values of k0, kex, K1, k3, and K2 in Tables 3 and 5.
TABLE 5: Kinetic Parameters for Hydrogen-Bonded
Triplet Exciplexesa
compd
ROH
K2/M-1
k3 /107 s-1
b
DMNA
H2O
MeOH
H2O
0.55
0.45
0.50
0.40
2.5
2.4
1.4
1.3
BP
3
On the other hand, the rates for the decay (kobsd) of BP* by
DMNA and DENA were estimated to be 4.3 × 106 s-1 at
[DMNA] ) 4.0 × 10-4 M and 4.3 × 106 s-1 at [DENA] ) 4.0
× 10-4 M by use of eq 1 and the values of k0BP and kq obtained
DENA
MeOH
a In ACN at 295 K. Errors within (5%. b k3 = ket. See text for
details.
in ACN. The calculated values of kRobsd and kBP indicate that
obsd
the values of kRobsd are larger than those of kBP ; in other words,
BP•-, escaping from the solvent cage without geminate recom-
bination due to the triplet spin multiplicity. On the assumptions
that (1) the equilibria among 3DANA* + BP, 3(DANA‚‚‚BP)*,
and 3(DANA‚‚‚BP)H*B are established quickly enough before the
relaxation of these three transient species and (2) the T-T
absorption spectra of 3(DANA‚‚‚BP)* and 3(DANA‚‚‚BP)H*B are
obsd
the rate-determining step for the radical ion formation in ACN-
H2O (4:1 v/v) was the quenching process of 3BP*. In fact, the
BP
obsd
calculated rates of k
were in agreement with those observed
(4.1 × 106 s-1 for DMNA and DENA) in ACN-H2O (4:1 v/v)
within experimental error ((5%). It turned out that in ACN-
H2O (4:1 v/v), as soon as 3DMNA* and 3DENA* were formed
from triplet energy transfer by 3BP*, electron transfer in
3(DANA‚‚‚BP)H*B occurred.
3
similar to that of DANA*, the decay rate for these triplet
intermediates, kRobsd, i.e., the formation rate for BP•- and
DANA•+, can be expressed by eq 10, where k3 ) ket + kHB
.
According to Scheme 2, the efficiency (φet) for electron
transfer induced by ROH in 3(DANA‚‚‚BP)H*B has a relationship
with those for the formation of BP•- and DANA•+ (φrad) and
triplet energy transfer from 3BP* to DANA (φΤΕΤ) as follows:
k0 + kexK1[BP] + k3K1K2[ROH][BP]
kRobsd
)
(10)
1 + K1[BP] + K1K2[ROH][BP]
The values of K2 and k3 were evaluated by the least-squares
method of best-fitting to the experimental values of kRobsd with
the use of eq 10, k0, kex, and K1 (see Table 3). The best-fitted
values of K2 and k3 are listed in Table 5. The solid curves in
Figures 8 and 9 were drawn by use of the kinetic parameters
(k0, kex, K1, k3, and K2) and eq 10. Under the experimental
condition, the relation of k3K1K2[ROH][BP] . k0 and kexK1[BP]
exists. Therefore, 3DANA* and 3(DANA‚‚‚BP)*, which equili-
brate with 3(DANA‚‚‚BP)H*B, mainly deactivate via 3(DANA‚‚‚
φrad ) φetφTET
(11)
The values of φΤΕΤ (0.74 for DMNA and 0.61 for DENA) and
φrad (0.77 for DMNA and 0.63 for DENA in ACN-H2O (4:1
v/v)) were determined above. With the use of eq 11, the φet
value was calculated to be unity within the experimental error
((5%). On the other hand, according to Scheme 2, the value
of φet can be given by eq 12. Since the φet value was determined
BP)* according to Scheme 2. The K2 values (0.55 M-1 for
HB
φet ) ket/(ket + kHB) ) ket/k3
(12)
DMNA and 0.50 M-1 for DENA) by H2O are slightly larger
than those (0.45 M-1 for DMNA and 0.40 M-1 for DENA) by
MeOH. The difference in K2 values between MeOH and H2O
may originate from the hydrogen bonding ability related to the
pKa values43 of MeOH (16)44 and H2O (14).44
to be unity, it was found that the value of ket was equal to that
of k3. On the other hand, the k3 value determined for H2O was
almost the same as that for MeOH in both DMNA and DENA
systems within experimental errors ((5%). Thus, the rate
constant, ket, for intraexciplex electron transfer induced by
hydrogen bonding is revealed to be independent of hydrogen-
bonding molecules (2.5 × 107 s-1 for DMNA and 1.4 × 107
s-1 for DENA). Moreover, the former is twice as large as the
latter. The difference in ket values may arise from the free
energy change (∆Get) for electron transfer. ∆Get is expressed
by eq 13, where Eox and Ered are the oxidation potentials of
Recently, it has been reported that the intermolecular electron
transfer takes place upon excitation of a hydrogen bonded
donor-acceptor complex in the ground state.45-47 It was
proposed that electron transfer was induced by the proton
movement on the hydrogen bond.45-47 We examined the isotope
effect on electron transfer in the present system by use of D2O
and methanol-d1. Since little isotope effect on the kinetic
parameters was observed within experimental error ((5%), it
was suggested that the electron-transfer mechanism in the
present system is different from that in the intermolecular
hydrogen-bonded donor-acceptor complex in the ground state.
From the viewpoint of the electronic structure of triplet
exciplexes, the mechanism for the present electron transfer can
be explained as follows. It is known that triplet exciplexes have
weak charge-transfer character from triplet naphthalene deriva-
∆Get ) 23.06(Eox - Ered) - ET - PC (in kcal/mol) (13)
DMNA and DENA (0.75 V vs SCE, see Table 1) and reduction
potential of BP (-1.83 V vs SCE in ACN),48 respectively, ET
and PC are the triplet energy of the reactive state for electron
transfer and the Coulombic potential in ACN (1.4 kcal/mol),49
respectively. The ET values were used with those of 3DMNA*

Hydrogen-Bonding-Induced Electron Transfer
J. Phys. Chem., Vol. 100, No. 2, 1996 679
and 3DENA* (54.0 and 51.0 kcal/mol, respectively, see Table1).
The ∆Get values were calculated to be 4.1 kcal/mol for DMNA
and 7.1 kcal/mol for DENA by eq 13. These positive values
of ∆Get usually predict little probability of electron transfer.
However, electron transfer assisted by hydrogen bonding was
observed in the present system. As mentioned above, the charge
(11) (a) Bensasson, R.; Land, E. J. Trans. Faraday Soc. 1971, 67, 1904.
(b) Amand, B.; Bensasson, R. Chem. Phys. Lett. 1975, 34, 44.
(12) Kobashi, H.; Morita, T.; Mataga, N. Chem. Phys. Lett. 1973, 20,
376.
(13) Strambini, G. B.; Galley, W. C. J. Chem. Phys. 1975, 63, 3467.
(14) Anderson Jr., R. W.; Hochstrasser, R. M.; Lutz, H.; Scott, G. W.
J. Chem. Phys. 1974, 61, 2500.
(15) Gessner, F.; Scaiano, J. C. J. Am. Chem. Soc. 1985, 107, 7206.
(16) Closs, G. L.; Piotrowiak, P.; MacInnis, J. M.; Fleming, G. R. J.
Am. Chem. Soc. 1988, 110, 2652.
(17) Engel, P. S.; Horsey, D. W.; Scholz, J. N.; Karatsu, T.; Kitamura,
H. J. Phys. Chem. 1992, 96, 7524.
(18) Haggquist, G. W.; Katayama, H.; Tsuchida, A.; Ito, S.; Yamamoto,
M. J. Phys. Chem. 1993, 97, 9270.
(19) (a) Wilson, T.; Frye, S.; Halpern, A. M. J. Am. Chem. Soc. 1984,
106, 3600. (b) Indig, G. C.; Catalani, L. H.; Wilson, T. J. Phys. Chem.
1992, 96, 8967.
(20) Birks, J. B. Photophysics of Aromatic Molecules; Wiley: New York,
1970.
3
density on the carbonyl group of BP in (DANA‚‚‚BP)* is
considered to be reduced upon hydrogen bonding of ROH.
3
Consequently, the electron affinity of BP in (DANA‚‚‚BP)H*B
3
should increase compared with that of BP in (DANA‚‚‚BP)*.
In addition, the radical ions formed are stabilized by solvation
of ROH (H2O or MeOH), resulting in a decrease of ∆Get. This
intraexciplex electron transfer may be interpreted by a thermo-
neutral or a slightly endothermic process.
(21) Turro, N. J. Molecular Photochemistry; Benjamin/Cummings:
Menlo Park, CA, 1978.
Concluding Remarks
(22) Shizuka, H.; Fukushima, M. Chem. Phys. Lett. 1983, 101, 598.
(23) Shizuka, H.; Hagiwara, H.; Satoh, H.; Fukushima, M. J. Chem.
Soc., Chem. Commun. 1985, 1454.
(24) Shizuka, H.; Hagiwara, H.; Fukushima, M. J. Am. Chem. Soc. 1985,
107, 7816.
(25) Kohno, S.; Hoshino, M.; Shizuka, H. J. Phys. Chem. 1991, 95,
5489.
(26) Kaneko, S.; Yamaji, M.; Hoshino, M.; Shizuka, H. J. Phys. Chem.
1992, 96, 8028.
(27) Sekiguchi, T.; Yamaji, M.; Tatemitsu, H; Sakata, Y.; Shizuka, H.
J. Phys. Chem. 1993, 97, 7003.
(28) Yamaji, M.; Sekiguchi, T.; Hoshino, M.; Shizuka, H. J. Phys. Chem.
1992, 96, 9353.
(29) Shizuka, H.; Yamaji, M. Proc. Indian Acad. Sci. (Chem. Sci.) 1993,
105, 747.
(30) Yamaji, M.; Tamura, K.; Shizuka, H. J. Chem. Soc., Faraday Trans.
1994, 90. 533.
(31) Yamaji, M.; Aihara, Y.; Itoh, T.; Tobita, S.; Shizuka, H. J. Phys.
Chem. 1994, 98, 7014.
(32) Yamaji, M.; Kiyota, T.; Shizuka, H. Chem. Phys. Lett. 1994, 226,
199.
(33) Zweig, A.; Maurer, A. H.; Roberts, B. G. J. Org. Chem. 1967, 32,
1322.
(34) Chen, E. C. M.; Wentworth, W. E. J. Chem. Phys. 1975, 63, 3183.
(35) (a) Yanagidate, M.; Takayama, K.; Takeuchi, M.; Nishimura, J.;
Shizuka, H. J. Phys. Chem. 1993, 97, 8881. (b) Suzuki, T.; Kajii, Y.;
Shibuya, K.; Obi, K. Res. Chem. Intermediates 1991, 15, 261; Chem. Phys.
1992, 161, 447.
By means of laser flash photolysis techniques at 355 nm, the
photochemical reactions of the BP-dialkylnaphthylamine sys-
tem in ACN at 295 K with and without H2O or MeOH are
revealed as follows:
(1) Regardless of the presence of H2O or MeOH, the triplet
exciplex 3(DANA‚‚‚BP)* between 3DANA* and BP is formed
after triplet energy transfer from 3BP* to DANA. In the
presence of H2O or MeOH, the intraexciplex electron transfer
takes place effectively in the hydrogen bonded exciplex,
3(DANA‚‚‚BP)H*B to give DANA•+ and BP•-. The mechanism
for the production of DANA•+ + BP•- is shown in Scheme 2.
(2) The equilibrium constants K2 for the formation of
3(DANA‚‚‚BP)H*B with H2O and MeOH obtained are 0.55 and
0.45 M-1 for DMNA and 0.50 and 0.40 M-1 for DENA,
respectively. The rate constants ket for the intraexciplex electron
transfer induced by hydrogen bonding by both H2O and MeOH
are determined to be 2.5 × 107 s-1 for DMNA and 1.4 × 107
s-1 for DENA.
(3) According to our interpretation, electron transfer in
3(DANA‚‚‚BP)H*B occurs due to an increase in electron affinity
3
of BP in (DANA‚‚‚BP)* by hydrogen bonding.
(36) Meech, S. R.; O’Connor, D. V.; Phillips, D. J. Chem. Soc., Faraday
Trans. 2 1983, 79, 1563.
(37) Murov, S. L.; Carmichael, I.; Hug, G. L. Handbook of Photochem-
istry, 2nd ed.; Marcel Dekker: New York, 1993.
(38) Bensasson, R. V.; Gramain, J. C. J. Chem. Soc., Faraday Trans. 1
1980, 76, 1801.
(39) The transient absorption spectra observed after direct laser excitation
of DMNA and DENA at 308 nm (XeCl excimer laser) in ACN decayed
uniformly in the range 350-750 nm and were quenched effectively by
dissolved oxygen.
(40) Yamaji, M.; Kiyota, T.; Kimura, S.; Shizuka, H. Chem. Phys. Lett.
1995, 237, 419.
(41) Yamaji, M.; Tanaka, T.; Shizuka, H. Chem. Phys. Lett. 1993, 202,
191.
(42) The molar absorption coefficient and absorption spectrum of
DENA•+ were determined by the same method obtained those of DMNA•+
in ref 32.
(43) Cramer, L. E.; Spears, K. G. J. Am. Chem. Soc. 1978, 100, 221.
(44) Isaacs, N. S. Physical Organic Chemistry; John Wiley & Sons,
Inc.: New York, 1987; p 211.
Acknowledgment. This work was supported by a Grant-
in-Aid on Priority-Area-Research: Photoreaction Dynamics
(06239101) from the Ministry of Education, Science and Culture
of Japan. The authors thank Mr. K. Shima for his assistance
with the synthesis of DENA.
References and Notes
(1) (a) This paper is dedicated to the late Professor Paul de Mayo,
FRS, of the University of Western Ontario in memory of his contribution
to the development of photochemistry. (b)This work was presented at the
XVth IUPAC Symposium on Photochemistry, July, 1994, Prague, Czech
Republic.
(2) Terenin, A.; Ermolaev, V. Trans. Faraday Soc. 1956, 52, 1042.
(3) Dexter, D. L. J. Phys. Chem. 1953, 21, 836.
(4) Inokuti, M.; Hirayama, F. J. Chem. Phys. 1965, 42, 1978.
(5) (a) Porter, G.; Wilkinson, F. Proc. R. Soc. (London) 1961, A264,
1. (b) Wilkinson, F. AdV. Photochem. 1964, 3, 241.
(6) Moore, W. M ; Ketchum, M. J. Am. Chem. Soc. 1962, 84, 1368.
(7) (a) Lamola, A. A.; Leermarkers, P. A.; Byers, G. W.; Hammond,
G. S. J. Am. Chem. Soc. 1965, 87, 2322. (b) Herkstroeter, W. G.; Jones, L.
B.; Hammond, G. S. J. Am. Chem. Soc. 1966, 88, 4777.
(8) Smaller, B.; Avery, E. C.; Remko, J. R. J. Chem. Phys. 1965, 43,
922.
(9) (a) Wagner, P. J. J. Am. Chem. Soc. 1967, 89, 5715. (b) Wagner,
P. J.; Kochever, I. J. Am. Chem. Soc. 1968, 90, 2232. (c) Wagner, P. J.;
McGrath, J. M.; Zepp, R. G. J. Am. Chem. Soc. 1972, 94, 6883.
(10) Sandros, K. Acta. Chem. Scand. 1969, 23, 2815.
(45) Miyasaka, H.; Tabata, A.; Kamada, K.; Mataga, N. J. Am. Chem.
Soc. 1993, 115, 7335.
(46) Tanaka, H.; Nishimoto, K. J. Phys. Chem. 1984, 88, 1052.
(47) Turro, C.; Chang, C. K.; Leroi, G. E.; Cukier, R. I.; Nocera, D. G.
J. Am. Chem. Soc. 1992, 114, 4013.
(48) Wagner, P. J.; Truman, R. .; Punchlaski, A. E.; Wake, R. J. Am.
Chem. Soc. 1986, 108, 7727.
(49) Weller, A. Z. Phys. Chem. (Munich) 1982, 133, 93.
JP9523940