Inorganic Chemistry
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1
,4-benzoquinone (BQ), tetrachloro-1,4-benzoquinone (Cl Q), and
Product Analysis. Photodriven H evolution by hydroquinone
2
+ III
4
duroquinone (Me Q) were obtained commercially from Sigma-
derivatives (X-QH ) with Acr -Mes, Co (dmgH) pyCl, and H O
2 2 2
4
Aldrich Chemical Co., and tetrachlorohydroquinone (Cl QH ) and
was examined in a quartz cell (optical path length = 1.0 cm) using a
LED lamp (white light; 150 W) on a Hayashi WATCH-WORKS Co.
4
2
durohydroquinone (Me QH ) were obtained from Tokyo Chemical
4
2
+
Industry Co. 9-Mesityl-10-methylacridinium ion (Acr -Mes) was
prepared by the reaction of 10-methylacridone in dichloromethane
with mesitylmagnesium bromide, followed by the addition of
perchloric acid for hydrolysis and sodium hydroxide for neutralization,
LA-HDF158AS for irradiation at 298 K. H formed in the oxidation of
2
+
X-QH (1.0 mM) by an excited state of Acr -Mes (0.75 mM) with
2
III
Co (dmgH) pyCl (0.60 mM) and H O (2.0 M) in deaerated
2
2
CH CN after irradiation (white light) with a UV cut filter (λ > 420
3
3
6
and then purified by recrystallization from methanol/diethyl ether.
9
nm) from Sigma Koki Co. was identified by GC.
+
-Mesityl-10-methylacridinium (Acr -Mes) perchlorate. Anal. Calcd
QY Determination. The QY of photodriven H
2
evolution from
+
III
for C H ClNO ·0.15H O: C, 66.63; H, 5.42; N, 3.38. Found; C,
hydroquinone with Acr -Mes, Co (dmgH)
pyCl, and H O was
2
2
2
3
22
4
2
1
6
9
6.44; H, 5.22; N, 3.49. H NMR (300 MHz, CD CN): δ 8.16 (d, J =
determined under visible-light irradiation of monochromatized light
using a Xe lamp (300 W) on an ASAHI SPECTRA MAX-302 through
a band-pass filter transmitting (λ = 470 nm) at 298 K. Typically, the
3
.0 Hz, 2H), 7.93 (t, J = 9.0 Hz, 2H), 7.40 (s, 4H), 6.79 (s, 2H), 4.37
(
s, 3H), 2.02 (s, 3H), 1.25 (s, 6H). Tetrabutylammonium
hexafluorophosphate (TBAPF ) was obtained from Fluka Co.
amount of H produced during the photochemical reaction has been
2
6
Deuterated acetonitrile (CD CN or MeCN) was obtained from
time interval of 1 h (Figure S1c). The initial slope of the graph is
taken to determine the QY. The QY was estimated as QY (%) = R/I
3
Sigma-Aldrich Chemical Co. and used as received. Solvents, such as
acetonitrile (CH CN or MeCN) and water (H O), were dried
3
2
−
1
according to literature procedures and distilled under Ar prior to
× 100, where R (mol s ) is the initial rate of the H production rate
2
48
−1
use.
and I (einstein s ) is a coefficient based on the rate of the number of
incident photons absorbed by Acr -Mes per second. The total number
+
Instrumentation. The amount of evolved H was recorded by a
2
commercial gas chromatograph (Acme 6000 GC, Young Lin Ins.;
GC-2030, Shimadzu Ins.). Nanosecond time-resolved transient
absorption measurements were carried out using an Nd:YAG laser.
Measurements of nanosecond transient absorption spectra were
performed according to the following procedure: A mixture solution
in a quartz cell (1.0 cm × 1.0 cm) was excited by a Nd:YAG laser
of incident photons was determined using a standard actinometer as
follows. A quartz cell containing an aqueous solution (1.0 mL) of
III
potassium ferrioxalate (K
[Fe (C
O
2
)
4
], 0.15 M) was irradiated
3
3
using monochromatized light (λ = 470 nm) for 1, 2, and 3 min at 298
K, separately. At the end of the irradiation, a sodium acetate buffer
solution (2.0 mL) of phenanthroline was added to 1.0 mL of the
actinometer solution, and the solution was kept in the dark for 1 h.
−1
(
Continuum SLII-10, 4−6 ns fwhm, λ = 355 nm, 80 mJ pulse , 10
ex
Hz). The photodynamics were monitored by continuous exposure to
a Xe lamp for the visible region and a halogen lamp for the near-IR
region as a probe light and a photomultiplier tube (Hamamatsu 2949)
as a detector. The kinetic traces at the appropriate wavelengths were
assembled from the time-resolved spectral data. UV−vis spectra were
recorded on a Hewlett-Packard 8453 diode-array spectrophotometer
equipped with a UNISOKU Scientific Instruments USP-203A
cryostat. X-band EPR spectra were recorded at 77 K using a JEOL
X-band spectrometer (JES-FA100). The experimental parameters for
EPR measurements by JES-FA100 were as follows: microwave
frequency = 9.028 GHz, microwave power = 1.0 mW, modulation
amplitude = 1.0 mT, modulation frequency = 100 kHz, and time
Then, the solution was diluted by half using H
O (i.e., 1.0 mL of the
2
solution and 1.0 mL of H O). The absorbance at 510 nm due to
2
2
+
−1
−1
[Fe(phen)
] (ε = 11050 M cm at λmax = 510 nm) was measured
3
to determine the total number of incident photons using the QY for
32
photodecomposition of ferrioxalate (Φ = 0.92 at 468 nm) to be 1.43
−
9
−1
2+
× 10 einstein s [rate of formation of [Fe(phen) ] after dilution
3
−
3
−7
−1
= 1.22 × 10 (slope of an inset)/11050 (ε) = 1.10 × 10 M s and
rate of formation of [Fe(phen)
2
+
−7
]
before dilution = 1.10 × 10
M
3
−
1
−3
−9
−1
s
× (2 × 10 L) × 6 (dilution factor) = 1.32 × 10 mol s ; I =
−
9
−1
−9
−1
1
.32 × 10 mol s /0.92 = 1.43 × 10 einstein s ]. The QY was
determined to be 10% from the amount of H produced during the
2
1
(
(
(
1
Figure S1c) measured by a standard method using an actinometer
constant = 0.03 s. H NMR spectra were measured with Bruker model
III
32
K [Fe (C O ) ]) under photoirradiation (λ = 470 nm) at 298 K
AVANCE III 400 FT-NMR digital spectrometer. Electrochemical
measurements were performed on a CHI630B electrochemical
analyzer in a deaerated MeCN solution containing 0.10 M nBu NPF
3
see Figure S1b), where the photon flux was determined to be 1.43 ×
−
9
−1
0
einstein s .
4
6
(
TBAPF ) as a supporting electrolyte at 298 K. A conventional three-
6
electrode cell was used with a Pt working electrode (surface area of
0
ASSOCIATED CONTENT
sı Supporting Information
■
2
.3 mm ), a Pt wire counter electrode, and an Ag/Ag(NO ) (0.010
3
*
M) reference electrode. The Pt working electrode (BAS) was
routinely polished with a BAS polishing alumina suspension and
rinsed with MeCN before use. The measured potentials were
+
recorded with respect to an Ag/Ag reference electrode. All potentials
Figures S1−S14 for the QY, TON, and stability of the
catalysts, UV−vis absorption, transient absorption, and
+
(
vs Ag/Ag ) were converted to values versus saturated calomel
47
electrode by adding 0.29 V.
EPR spectral changes for photocatalytic H evolution,
2
Kinetic Studies. Typically, photoinduced ET from X-QH to the
2
•+
+
3
•
•+
and cyclic voltammograms of the reactants (PDF)
Mes moiety of the ET state of Acr -Mes [ (Acr -Mes )] and ET
from Acr -Mes to Co (dmgH) pyCl were examined by monitoring
•
III
2
nanosecond time-resolved transient spectral changes. The kinetic
traces were assembled, monitoring the decay at 500 nm due to the
Mes moiety of (Acr -Mes ) (0.10 mM) with various concen-
Corresponding Authors
■
•+
3
•
•+
trations of X-QH (0−8.0 mM) in deaerated MeCN. First-order rate
Wonwoo Nam − Department of Chemistry and Nano Science,
Ewha Womans University, Seoul 03760, Korea; School of
2
constants were determined under pseudo-first-order conditions by
fitting the changes in transient absorbance for the decay of the peak at
•
•+
3
•
5
00 nm due to the excited Acr -Mes in ET from X-QH to (Acr -
2
•+
Mes ) in deaerated MeCN at 298 K. Monitoring the decay at 520
•
3
•
•+
nm due to the Acr moiety of (Acr -Mes ) (0.10 mM) with various
III
Shunichi Fukuzumi − Department of Chemistry and Nano
Science, Ewha Womans University, Seoul 03760, Korea; Faculty
concentrations of Co (dmgH) pyCl (0−0.60 mM) in deaerated
MeCN. First-order rate constants were determined under pseudo-
2
first-order conditions by fitting the changes in transient absorbance
•
•
for the decay of the peak at 520 nm due to Acr -Mes in ET from Acr -
III
Mes to Co (dmgH) pyCl in deaerated MeCN at 298 K.
2
F
Inorg. Chem. XXXX, XXX, XXX−XXX