Novel homogeneous photocatalyst for oxygen to hydrogen peroxide reduction in aqueous media

Article abstract of DOI:10.1039/c9pp00206e

An isoquinolinium-pyrrole donor-acceptor dyad was found to exhibit photocatalytic activity in oxygen-to-peroxide photoreduction with oxalate as a sacrificial electron donor. The concentration of hydrogen peroxide was shown to reach a plateau of 0.57 mM. The screening of related pyridinium-pyrrole dyads showed the importance of the isoquinoline moiety in securing the photocatalytic activity.

Full text of DOI:10.1039/c9pp00206e

View Article Online
View Journal
Photochemical &
Photobiological
Sciences
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: D. A. Lukyanov, L.
D. Funt, A. S. Konev, A. Povolotskiy, A. A. Vereshchagin, O. Levin and A. F. Khlebnikov, Photochem.
Photobiol. Sci., 2019, DOI: 10.1039/C9PP00206E.
Volume 15 Number
3
March 2016 Pages 311–458
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Photochemical &
Photobiological
Sciences
An international journal
www.rsc.org/pps
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1474-905X
rsc.li/pps

Page 1 of 8
Photo Pc hl ee ams ei c da lo &n Po hto at do bj ui os tl o mg iac ra gl iSn c si ences
View Article Online
DOI: 10.1039/C9PP00206E
Journal Name
COMMUNICATION
Novel homogeneous photocatalyst for oxygen to hydrogen peroxide
reduction in aqueous media
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
a
Daniil A. Lukyanov, Liya D. Funt, Alexander S. Konev,* Alexey V. Povolotskiy, Anatoly A.
a
a
a
Vereshchagin, Oleg V. Levin and Alexander F. Khlebnikov
DOI: 10.1039/x0xx00000x
www.rsc.org/
An isoquinolinium-pyrrole donor-acceptor dyad was found to absorption of visible light by such inorganic photocatalysts has
exhibit photocatalytic activity in oxygen-to-peroxide limited their utilization for light harvesting. Dye
photoreduction with oxalate as a sacrificial electron donor. The sensibilization[
16]
[17,18]
or utilization of nanoparticles
can
concentration of hydrogen peroxide was shown to reach plateau increase the light absorption by such systems. Alternatively,
of 0.57 mM. The screening of related pyridinium-pyrrole dyads application of organic molecules as photocatalysts based on
showed the importance of isoquinoline moiety in securing the acridinium[
19–22]
or quinolinium
[23–28]
carcasses allows to
photocatalytic activity.
enhance catalyst efficiency by performing the reaction in the
homogenous mode in addition to the increased light
Environmental conservation fosters the search for energy
sources alternative to fossil fuel, the energy of sun irradiation
being most appealing among them.[
absorption. In particular, photocatalytic reduction of O
2
to
2 2
H O
using a mesitylacridinium donor-acceptor dyad I (Fig. 1)
1–3]
The natural way for
[21]
as a photocatalyst has been reported by Fukuzumi et al.
Environmentally friendly conversion of O to H requires
strong and “green” reductant. A perfect candidate seems to be
an oxalate ion due to its high reductive power (E = 0.475 V vs.
as the only by-
solar energy conversion, the photosynthesis, has low quantum
and mass efficiency. The charge separation state of the
photosystem II accumulates only 0.5 eV from the total photon
energy due to multiple energy losses during the cascade
charge separation.[ To increase the efficiency of solar energy
harvesting, extensive efforts have been devoted to the
development of artificial photocatalytic systems, which
accumulate the power of light in the energy of chemical bonds.
2
2 2
O
0
NHE), abundance in natural sources and CO
2
1,4]
[26–28]
product (eq. 1),
the last factor being the advantage over
[22,23]
conventional sacrificial electron donors such as aromatic
[20,21]
[19,29]
phenols,[23]
and polyaromatic hydrocarbons,
alcohols,
[30]
and amines.
[
1,5–7]
2
-
+
C
2
O
4
+ O
2
+2H = 2CO
2
+ H
2
O
2
(eq. 1)
Photoreduction of oxygen to hydrogen peroxide[5] is an
example of this approach, as hydrogen peroxide is one of the
most powerful and cheap oxidants used in chemical and
In our work, we explore pyrrolo-isoquinolinium and
[31]
[32]
pyrrolo-pyridinium dyads IIa-d and IIIa-d as a novel kind
of compact donor-acceptor system potentially able to
pharmaceutical industry. Oxidation processes involving H
are known to be selective, clean and green.[ In addition, H
2
O
O
2
2 2 2
photocatalyze the process of O to H O reduction with oxalate
8]
2
2
ions and compare their performance to mesitylacridinium I.
A series of experiments was performed in order to evaluate
the photocatalytic activity of compounds IIa-d and IIIa-d (Fig.
is believed to be useful green fuel able to produce electric
power in fuel electrochemical cells.[
9,10]
At present, hydrogen
peroxide is mainly produced by the costly, energy-consuming
and hazardous anthraquinone process,[ so the development
1
2
) for O reduction with oxalate as a sacrificial donor. A portion
11]
of each compound was dissolved in 8 mL of sodium oxalate
buffer (pH 4.5), the solutions obtained were irradiated by LED
light source with λmax = 415 nm and light emitting power of ca.
0
3
ted and the hydrogen peroxide content was evaluated im-
mediately using photometric titanyl oxalate technique and
iodometric technique[ to secure confident detection of H
2 2
of photocatalytic processes for H O synthesis would have a
positive environmental impact.
In the pioneering works in the field of photocatalysis,
.33 W while being maintained at 8 °C with air bubbling. After
h of continuous irradiation, a sample of solution was collec-
[
12,13]
[14,15]
mainly inorganic materials, such as TiO
2
and ZnO,
have been utilized as photocatalysts. However, poor
[
33]
34]
O .
2 2
a. Institute of Chemistry, Saint Petersburg University, 7/9 Universitetskaya nab., St.
Petersburg 199034, Russia, E-mail: a.konev@spbu.ru, a.khlebnikov@spbu.ru.
Electronic Supplementary Information (ESI) available: calibration curve for titanyl
Screening of the series IIa-d showed that only the pyrrole-
isoquinolinium dyad IIa possesses discernible photocatalytic
oxalate photometric analysis, UV-Vis spectra of compounds I-III, other data on activity. None of pyridinium-containing analogues shows any
electrochemical and photophysical study of IIa. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Photo Pc hl ee ams ei c da lo &n Po hto at do bj ui os tl o mg iac ra gl iSn c si ences
Page 2 of 8
Journal Name
COMMUNICATION
View Article Online
CO MDO
e
I: 10.1039/C9PP00206E
2
Mes ClO4
HN
HN
HN
Ph
Ph
Br
Ar
Ph
Br
O
Ar
N+
N+
N+
N+
Me
Ar = Ph
4
(a)
I, Mes = 2,4,6-(Me) C H
6 2
3
III
-MeOC H4 (b)
6
IIa
II, Ar = Ph
(b)
4
-BrC H4
(c)
6
4
-MeOC H4 (c)
4-NO C H (d)
6
2 6 4
4
-NO C H
(d)
2
6 4
Figure 1. Structures of compounds I, IIa-d, IIIa-d. Donor fragments are colored in blue, acceptor fragments in red.
photocatalytic activity. On the other hand, N- radiation without the catalyst, without the irradiation and the
methylisoquinolinium tetrafluoroborate has zero absorption irradiation under Ar atmosphere) produced any amount of
above 360 nm (SI, Fig. SI3), and the isoquinolinium fragment
2 2 2
H O , confirming it is the photocatalytic reduction of O with
by itself cannot thus account for the observed activity of IIa. direct involvement of IIa as a catalyst.
This lead us to conclusion that combination of pyrrole and
In accord with the reaction equation, the production of
depended on both pH of the medium and concentration
of oxalate ions. The pH screening showed that pH of 4.5
A series of control experiments was performed to establish resulted in the highest production of H (Fig. 2) measured
the necessity of each factor for H generation: the catalyst, after 3h of the reaction. At this pH, the concentration of H
the oxygen and the light. None of the control experiments (ir-
isoquinolinium fragments is necessary to provide the observed
2 2
H O
2
photocatalytic reduction of O to hydrogen peroxide.
2 2
O
O
2 2
2 2
O
produced in 3 h increased from 0.1 mM in 0.13 mM oxalate
buffer to 1 mM in 7 mM oxalate buffer. Further increase of
2 2
oxalate concentration did not affect the H O accumulation
rate (Fig. 2).
The time course of photocatalysis was recorded until the
persistent concentration of hydrogen peroxide was reached.
An array of 8 LEDs with overall light emitting power of ca. 2.64
W was used for these reactions to irradiate 0.1 mM solutions
of catalysts in oxalate buffer. In addition, each sample was
examined for catalyst degradation by monitoring the
absorbance of sample solution in near UV range. In order to
compare these results with the performance of the known
compound, the same experiment was carried out with 9-
mesityl-10-methylacridinium perchlorate I,
compound for photocatalytic oxygen reduction.[
a
21]
benchmark
Both compounds I and IIa demonstrate asymptotic curve
for hydrogen peroxide production, reaching plateau of ca. 0.4
mM and ca. 0.55 mM H
respectively (Fig. 3).
O
2 2
concentration for catalysts I and IIa
2 2
The stationary conditions of H O
production when the
rate of formation is equal to the rate of decomposition might
be one of the reasons for the asymptotic behavior of the
process. However, hydrogen peroxide is known to be stable at
temperatures below 14 °C.[
14]
Consistent with this, no
decomposition of
experiment on irradiation of H
the oxalate buffer used in the experiments on photochemical
generation of H . Also, experiments on photogeneration of
H O in solutions with pre-added aliquot of H O (0.4, 0.8, 1.3
H
2
O
2
was observed in the control
2 2
O
solution with 415 nm LED in
2 2
O
Figure 2. The pH (top, 67 mM oxalate solution) and [C
.5) dependence of concentration of H
irradiation (λ 415 nm) in the presence of compound IIa. (Air bubbling through the
2
O
4
2-] (bottom, red squares, pH
2
2
2 2
4
2
O
2
in the reaction medium after 3h of and 3.1 mM) show continuous grow of H O concentration.
2 2
These results refute the hypothesis about reaching the
stationary conditions of hydrogen peroxide formation.
aqueous reaction medium at 8°C.) Blue circles show conversion of oxalate ions to H
2 2
O .
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 2
Please do not adjust margins

Page 3 of 8
Photo Pc hl ee ams ei c da lo &n Po hto at do bj ui os tl o mg iac ra gl iSn c si ences
Journal Name
COMMUNICATION
View Article Online
DOI: 10.1039/C9PP00206E
Figure 4. Time courses of catalyst degradation for the experiments using compounds I
(
c 0.1 mM)(top) and IIa (c 0.1 mM) (bottom).
Figure 3. Time courses of H
°C) of air-bubbled oxalate aqueous solution (67 mM) using compounds IIa (c 0.1 mM)
top) and I (c 0.1 mM) (bottom). Fits of the experimental data are shown as solid lines.
2 2
O production for the experiments on irradiation (λ 415 nm,
8
(
0
푘1퐶푐푎푡
1 ― 푒 ― 푘2푡
)
[
퐻 푂2]
=
(
2
(eq. 3)
푘2
An alternative cause for the asymptotic behavior might be the
Fitting of the experimental data according to eq. 3 gives
decomposition of the catalyst during the process. Indeed, the effective rate constants for H O generation, k , and
2
2
1
almost complete depletion of the catalyst absorption bands catalyst decomposition, k , respectively for the processes
2
was observed in the case of compound I within first 7 minutes catalyzed by the catalysts I and IIa (Table 1). Extrapolation of
of the reaction (Fig. 4, top). During twice the same time period, the H O concentration to the infinity according to eq. 3
2
2
0
no changes were observed in the absorption spectrum of defines the asymptotic limit as k1C /k to give 0.38 mM for
cat
2
compound IIa (Fig. 4, bottom). However, longer exposition compound I and 0.58 mM for compound IIa. So, despite the
showed evolution of the absorption spectrum of the reaction lower rate of H O generation, compound IIa allows to reach
2
2
medium, two new bands appearing at ca. 380 and ca. 420 nm. the higher concentrations of H O due to the higher stability of
2
2
The new bands steadily grew during the first 100 min of the compound IIa under the experimental conditions.
reaction. Subsequent overall fading of the absorption is most
To get insight on the mechanism of photocatalytic
probably due to continuous degradation of the catalyst.
hydrogen peroxide formation by IIa, we performed a series of
In view of the observed instability of the catalysts, the electrochemical and spectroscopic studies.
kinetics of the hydrogen peroxide production are best
In cyclic voltammetry (CV) studies, compound IIa shows
described by eq. 1, where the reduction of O to H occurs one reduction and one oxidation peak (Fig. 5). Exploring CV
with effective rate constant k at the catalyst exponentially dependence on the potential sweep rate shows that the peak
decaying with rate constant k . The effective rate constant k
2
2 2
O
1
2
1
potentials stabilize at sweep rates of 50 mV/s at ca. 0 and –1.6
(permanent V (vs. TEMPOL/TEMPOL ) for oxidation and reduction of IIa
+
takes into account that the concentrations of O
air flow) and H (buffer solution) are constant.
2
+
respectively. In view of the low dependence of the peak poten-
푑
[
퐻2푂2
]
푘 퐶 푒 ― 푘2푡
0
2 2
Table 1. The rate constants for the H O photogeneration by use of catalysts Ia and II.
=
(eq. 2)
1
푐푎푡
푑푡
Catalyst
I
IIa
k
, s-1
k
, s-1
1 2
k , mM
C0cat/k
1
2
Solution of the differential equation 2 under boundary
condition of [H ] = 0 at t = 0 gives the expression for the
time evolution of the H concentration (eq. 3).
-2
-3
-4
2.3(2)·10
7.0(4) ·10
6.1(6) ·10
1.2(1) ·10
0.38
0.58
O
2 2
-4
2 2
O
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Photo Pc hl ee ams ei c da lo &n Po hto at do bj ui os tl o mg iac ra gl iSn c si ences
Page 4 of 8
COMMUNICATION
Journal Name
tials on the potential sweep rates, the redox processes
corresponding to these redox waves can be considered
electrochemically reversible and can be used to estimate the
formal electrode potentials. Taking the slowest (10 mV/s)
View Article Online
DOI: 10.1039/C9PP00206E
+
–
potential sweep data for IIa/IIa and IIa/IIa redox couples
corrected for 28 mV of polarization potential (–0.032 and
–
1.586 V respectively) as the closest assessments of the formal
o
potentials, and considering formal potential E vs. SHE for
TEMPO/TEMPO reference couple of 0.750 V, one can
estimate E vs. SHE values for IIa/IIa and IIa/IIa redox couples
+
o
+
–
to comprise 0.718 and –0.836 V respectively. So, in view of the
o
E values for other possible redox couples in the explored
system, both reduction of IIa by oxalate ion and oxidation of
IIa by molecular oxygen with formation of H
O
2 2
are
thermodynamically forbidden under standard conditions.
+
–
o
O
2
+ 2H +2e = H
2
O
2
E = 0.695 V
+
–
o
2 2 2 2
Figure 6. Electrode potential vs. H O concentration diagram, pH 4.5, pO 3.6, pCO 4.9,
H
2
O
2
+ 2H + 2e = 2H
2
O
E = 1.76 V
2
-
1.2. Red area shows the range of [IIa]/[IIa+] ratio corresponding to
2 4
pC O
+
–
o
2
CO
2
+ 2H +2e = H
2
C
2
O
4
E = –0.345 V
+
thermodynamically allowed oxidation of IIa to IIa upon reduction of O
area shows the range of [IIa ]/[IIa] ratio corresponding to thermodynamically allowed
reduction of IIa to IIa upon oxidation of C O to CO .
2 4 2
2
to H
2
O
2
. Violet
–
–
o
Br
2
+ 2e = 2Br
E = 1.096 V
-
+
–
o
-
2-
IIa + e = IIa
E = 0.718 V
–
–
o
IIa + e = IIa
E = -0.836 V
However, these processes become thermodynamically data, we suppose the shoulder at 400 nm in the UV spectrum
allowed under non-standard conditions for certain ratios of of IIa to be a charge transfer band due to the intramolecular
the oxidized and reduced forms of IIa and H
O
2 2
(Fig. 6). That charge transfer process from pyrrole to isoquinoline moiety.
means, catalytic cycle involving transformations of
a
TD DFT study of compound IIa testifies further to this
compound IIa is thermodynamically allowed. Under these hypothesis. According to DFT (B3LYP/6-31+G(d,p)) calculations,
circumstances, the absence of the notable reaction in the dark HOMO of IIa is localized on the diphenyl-pyrrole fragment,
shows that the role of light is to provide energy necessary to while LUMO is localized on the isoquinolinium moiety (Fig. 8).
overcome the activation barrier endowing thus compound IIa TD DFT modelling (PCM, water) predicts the lowest electro-
1
1
with the properties of photocatalyst.
nically excited state of IIa to have configuration HOMO LUMO
The UV-vis absorbance spectrum of compound IIa shows (>99% contribution of HOMOLUMO transition to the
strong absorption in near UV region (max 335 nm) with smaller formation of the state). The predicted energy of the state (2.57
shoulder at 400 nm extending to 490 nm (Fig. 7). Comparison eV/483 nm) and the low oscillator strength (0.0271) match
to the model methyl isoquinolinium compound shows the 335 well to the observed picture in the UV-Vis spectrum.
nm band to be due to absorption of the isoquinolinium
fragment. Isoquinolinium compounds are reported to form 300–400 nm have peak at 445 nm with notable shoulder at
Emission spectra of compound IIa excited at the range
3
5
36
intermolecular charge transfer complexes or charge shift
465 nm (Fig. 7). This two-peak pattern finds reflection in the
exciplexes with aromatic hydrocarbons, showing charge excitation spectrum (450 nm emission), most probably being
3
5
transfer absorption band at 392–415 nm or charge shift due to the vibronic structure of the CT absorption band
3
6
exciplex emission band at ca. 440–580 nm . In view of these
(compound IIa has strong absorption at 1607, 1489 and 1393
-1
cm ). At excitation with 390–400 nm light, the emission band
is contaminated with the Raman scattering of water, but the
two-peaks pattern remains at excitations with wavelengths
shorter than 360 nm, where the Raman scattering band of wa-
ter is shifted below 400 nm (Fig. 7, excitation at 340 nm).
Interestingly, the emission at 350–400 nm (Fig. 7, bottom, red
dot line), which corresponds to the fluorescence of the
max
isoquinolinium moiety (Fig. 7, bottom,  = 375 nm) is rather
low. This is most probably due to the fluorescence quenching
of the isoquinolinium fragment via the electron transfer from
the pyrrole moiety, resulting in population of the CT state.
The lifetime of 450 nm CT emission band in IIa in the
absence of oxalate ions and oxygen comprises 5.2 ns, giving
the rate constant for radiative relaxation to the ground state
Figure 5. CVA of compound IIa (c 1 mM in DMF/LiClO
sweep rate υ. Inset: dependence of oxidation (red dots) and reduction (blue dots)
potential peaks on υ. Potentials are given vs. TEMPOL/TEMPOL in the same medium.
4
(0.1 M)) at variable potential kfl=0.2·10
9
s
-1. Both the nanosecond time domain for the
emission and the independence of the decay constant on the
presence of oxygen testify to the singlet nature of the CT ex-
+
4
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 8
Photo Pc hl ee ams ei c da lo &n Po hto at do bj ui os tl o mg iac ra gl iSn c si ences
Journal Name
COMMUNICATION
View Article Online
DOI: 10.1039/C9PP00206E
Figure 8. HOMO (left) and LUMO (right) of compound IIa according to DFT (B3LYP/6-
1+G(d,p)) calculations.
3
implying involvement of a dynamic process to fluorescence
quenching. In accord with this, Stern-Volmer plot for
fluorescence intensity has non-linear character, while Stern-
Volmer plot for fluorescence lifetime has linear character.
Linear fit of the latter allowed to determine the rate constant
of bimolecular fluorescence quenching with oxalate kred to
9
-1
-1
comprise 2.5·10 M ·sec (Fig. 10).
Based on these data, the following mechanism for the
photocatalytic activity of compound IIa for reduction of oxygen
to hydrogen peroxide can be proposed (Fig. 11). Compound IIa
is excited to a singlet electronically excited state upon
irradiation with 420 nm light. The electronically excited state
can undergo radiative relaxation to the ground state with
9
-1
constant rate of 0.2·10 s or accept an electron from oxalate
9
ion via electron transfer process with rate constant of 2.5·10
-1
-1
M ·sec . The reduced species of IIa is oxidized by molecular
oxygen recovering IIa and leading to superoxide radical-anion,
which eventually gives hydrogen peroxide.
In a set of compounds IIIa-d, the rise of absorbance at 400
nm was also noticed during photocatalytic experiment, and it
was initially attributed to peroxotitanyl species. However, time
courses of the abovementioned reactions showed a constant
absorbance at 400 nm starting from t = 0 sec point. Further
analysis of the samples by iodometric technique did not detect
2 2
any H O contained. Finally, addition of titanyl solution to the
samples of compounds IIIa-d without irradiation caused an im-
mediate rise of absorbance at 400 nm. These facts lead us to
conclusion that the rise of absorbance at 400 nm observed in
Figure 7. Top: 3D plot of excitation/emission spectra of compound IIa. Region covered
with white pattern corresponds to the Raman scattering of water (3000–3700 cm-1
band). Middle and bottom: excitation (red short dash line, em = 450 nm), emission (red
solid line, ex = 400 nm, red dot line, ex = 340 nm) and absorption (red short dash dot
line) spectra of compound IIa (c 0.01 mM (emission) and 0.22 mM (absorption) in
water) vs. absorption (blue short dot line), excitation (blue dash line, em = 375 nm)
and emission (blue dash dot dot line, ex = 320 nm) spectra of N-methylisoquinolinium
tetrafluoroborate (IQ, c 0.1 mM (absorption) and 0.01 mM (emission) in water).
cited state. Additional conformation is the absence of the
singlet oxygen fluorescence at 1270 nm for the studied system.
Unlike oxygen, oxalate ions demonstrate obvious
quenching effect on the fluorescence of IIa. Both the fluore-
sence intensity (SI, Figs. SI15, SI16) and fluorescence lifetime
Figure 9. Dependence of fluorescence lifetime of compound IIa (aqueous solution, c
0
.01 mM) on concentration of oxalate ions. Inset: kinetic trace for fluorescence at 465
(Fig. 9) depend strongly on the concentration of oxalate ions,
nm (excitation at 390 nm).
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Photo Pc hl ee ams ei c da lo &n Po hto at do bj ui os tl o mg iac ra gl iSn c si ences
Page 6 of 8
COMMUNICATION
Journal Name
Conflicts of interest
View Article Online
DOI: 10.1039/C9PP00206E
There are no conflicts of interest to declare.
Acknowledgements
This work was supported by Saint Petersburg State University
grant no. 12.40.1427.2017). Research was carried out with the
(
support of the Research park of St. Petersburg State University
Magnetic Resonance Research Center, Chemical Analysis and
Materials Research Center, Center for Optical and Laser Mate-
rials Research, Educational Resource Center of Chemistry and
Resource center "Computer center of Saint Petersburg State
University"
.
Figure 10. Stern-Volmer plot for fluorescence kinetics of compound IIa (water, c 0.01
mM) at variable concentrations of oxalate ions.
Notes and references
‡
UV-Vis spectra were recorded on Shimadzu UV-1700 and UV-
this case is caused by the formation of complexes of 1800 spectrometers. Deionized water was obtained from Merck
compounds IIIa-d with the titanium reagent used.
Millipore Simplicity purification system. Argon gas of 99,998%
purity was used. Oxalate buffer with pH 4.5 was prepared by
2 2 4 2 2 4
dissolution of 2 g of H C O and 6 g of Na C O in 1 L of
deionized water. Solutions with pH of 2.5, 6.5, 8.5 and 10.5 were
Conclusions
2 4
prepared by acidification of the initial buffer with 1 M H SO or
basification with 10% (w/w) NaOH until the required pH was
In a series of novel pyridinium- and isoquinolinium-pyrrole
donor-acceptor dyads, isoquinolinium-pyrrole dyad IIa was
shown to exhibit the photocatalytic activity in oxygen to
peroxide reduction with catalytic performance comparable to
the reference mesitylacridinium compound. While affording
reached. Inorganic chemicals were purchased from local
suppliers. Compounds I,[ IIa-d,
35]
[31]
IIIa-d
[32]
were synthesized
according to previously reported methods.
Photocatalytic experiments were performed in the self-made
photoreactor. The irradiation source was made from HPL-
H O
2 2
concentration plateau similar to the reference compound H44TU1BA-V2 LED mounted on an efficient radiator and fed by
0.58 mM and 0.38 mM, respectively), dyad IIa shows better LC-125/500-A AC/DC inverter. The reaction vessel was mounted
stability under the catalysis conditions. Most probable mecha- in the way so that all 60° light cone lies within the transparent
(
bottom of the vessel. The vessel was cooled by water jacket with
° C water circulating inside and the mean temperature inside
nism of the photocatalytic activity of dyad IIa includes electron
transfer from oxalate ion to electronically excited molecule of
the photocatalyst. Unlike isoquinolinium-pyrrole dyad,
pyridinium-pyrrole dyads do not show photocatalytic activity.
8
the reaction vessel was monitored by thermometer. Air bubbling
was performed using an air pump connected through the syringe
needle.
The H
ml) of the reaction mixture were collected, 2.5 ml of H
v/v) was added to each sample (W and R), then saturated
TiO(KC solution (2 ml) was added to the W sample, and fi-
nally both samples were diluted to 15 ml by deionized water.
Then the UV spectra of R vs deionized water and W vs R were
recorded immediately in the range of 350-450 nm. The
absorbance at 400 nm was used to quantify the hydrogen
peroxide content using the calibration plot recorded in the 4-80
µg sample content range.
2
O
2
content was determined as follows: two aliquots (2
C2O42-
2
SO (1:17
4
kred
2
CO2
2 4 2
O )
1
*
e-
Ph
N
NH
Ph
Ph
N
NH
Ph
kfl
Photoluminescence spectra and luminescence kinetic curves
were measured on Horiba Fluorolog-3 spectrometer. The study
of luminescent properties was carried out at a concentration of
h
k1
420 nm
O2
+
0
.01 mM, at which the optical density did not exceed 0.1 at the
H2O2
excitation wavelength for all samples. Luminescence kinetic
curves were excited by LEDs with pulse duration of about 1 ns
and measured with the Time-Correlated Single Photon Counting
technic.
Ph
N
HO2
O2
HO2
NH
Ph
Geometry optimization of IIa was performed with the B3LYP
density functional method and 6-31+G(d,p) basis set with PCM
solvation model for water. Stationary point on the potential-
energy surface was characterized by evaluating the Hessian
Figure 11. Proposed mechanism for reduction of
photocatalyzed by compound IIa.
O
2 2 2
to H O with oxalate
6
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 8
Photo Pc hl ee ams ei c da lo &n Po hto at do bj ui os tl o mg iac ra gl iSn c si ences
Journal Name
COMMUNICATION
Selective Radical Coupling Using 9-Mesityl-10-
DOI: 10.1039/C9PP00206E
Photocatalyst. J. Am. Chem. Soc. 2004, 126, 15999–16006.
eigenvalues. Calculations of the excited states were performed
using TD DFT method at the same level of theory.
View Article Online
methylacridinium Ion as an Effective Electron-Transfer
2
2
1 H. Kotani, K. Ohkubo and S. Fukuzumi, Formation of
hydrogen peroxide from coal tar as hydrogen sources using
1
I. McConnell, G. Li and G. W. Brudvig, Energy Conversion in
Natural and Artificial Photosynthesis. Chem. Biol. 2010, 17,
9
-mesityl-10-methylacridinium ion as an effective
4
34–447.
photocatalyst. Appl. Catal. B Environ. 2008, 77, 317–324.
2 K. Ohkubo, K. Mizushima, R. Iwata, K. Souma, N. Suzuki and
S. Fukuzumi, Simultaneous production of p-tolualdehyde and
hydrogen peroxide in photocatalytic oxygenation of p-xylene
and reduction of oxygen with 9-mesityl-10-methylacridinium
ion derivatives. Chem. Commun. 2010, 46, 601–603.
2
3
C. F. Shih, T. Zhang, J. Li and C. Bai, Powering the Future with
Liquid Sunshine. Joule 2018, 2, 1925–1949.
Y. Lee, C. Park, N. Balaji, Y.-J. Lee and V. A. Dao,
High-efficiency Silicon Solar Cells: A Review. Isr. J. Chem.
2
015, 55, 1050–1063.
4
K. Satoh, Isolation and Properties of the Photosystem II
Reaction Center A2, in Photosynthetic Reaction Center, J.
Deisenhofer, J.R. Norris, Eds., Academic Press: San Diego,
2
3 K. Ohkubo, T. Kobayashi and S. Fukuzumi, Direct
Oxygenation of Benzene to Phenol Using Quinolinium Ions as
Homogeneous Photocatalysts. Angew. Chemie - Int. Ed.
1
993.
2
011, 50, 8652–8655.
5
6
7
S. Fukuzumi, Artificial photosynthesis for production of
hydrogen peroxide and its fuel cells. Biochim. Biophys. Acta -
Bioenerg. 2016, 1857, 604–611.
2
2
4 K. Ohkubo, T. Kobayashi and S. Fukuzumi, Photocatalytic
alkoxylation of benzene with 3-cyano-1-methylquinolinium
ion. Opt. Express 2012, 20, A360.
H. Imahori, Y. Mori and Y. Matano, Nanostructured artificial
photosynthesis. J. Photochem. Photobiol. C Photochem. Rev.
5 K. Ohkubo, A. Fujimoto and S. Fukuzumi, Photocatalytic
Monofluorination of Benzene by Fluoride via Photoinduced
Electron Transfer with 3‑Cyano-1-methylquinolinium. J.
Phys. Chem. A 2013, 117, 10719–10725.
6 Y. Yamada, A. Nomura, T. Miyahigashi and S. Fukuzumi,
Photocatalytic production of hydrogen peroxide by two-
electron reduction of dioxygen with carbon-neutral oxalate
using a 2-phenyl-4-(1-naphthyl)quinolinium ion as a robust
photocatalyst. Chem. Commun. 2012, 48, 8329–8331.
7 Y. Yamada, A. Nomura, T. Miyahigashi, K. Ohkubo and S.
Fukuzumi, Acetate Induced Enhancement of Photocatalytic
Hydrogen Peroxide Production from Oxalic Acid and
Dioxygen. J. Phys. Chem. A 2013, 117, 3751–3760.
2
003, 4, 51–83.
T. Bottari, G. Trukhina, O. Ince and M. Torres, Towards
artificial photosynthesis: Supramolecular, donor–acceptor,
porphyrin- and phthalocyanine/carbon nanostructure
ensembles. Coord. Chem. Rev. 2012, 256, 2453–2477.
R. Ciriminna, L. Albanese, F. Meneguzzo and M. Pagliaro,
Hydrogen Peroxide: A Key Chemical for Today’s Sustainable
Development. ChemSusChem 2016, 9, 3374–3381.
2
8
2
2
9
1
R. S. Disselkamp, Energy Storage using Aqueous Hydrogen
Peroxide. Energy&Fuels 2008, 22, 2771–2774.
0 S. Fukuzumi and Y. Yamada, Hydrogen Peroxide used as a
Solar Fuel in One-Compartment Fuel Cells. ChemElectroChem
8 Y. Yamada, A. Nomura, K. Ohkubo, T. Suenobu and S.
Fukuzumi, The long-lived electron transfer state of the 2-
phenyl-4-(1-naphthyl)quinolinium ion incorporated into na-
nosized mesoporous silica–alumina acting as a robust photo-
catalyst in water. Chem. Commun. 2013, 49, 5132–5134.
9 G. Xu, Y. Liang and F. Chen, Continuously photocatalytic
2
016, 3, 1978–1989.
1
1
1
1
1
1
1 G. Goor, J. Glenneberg and S. Jacobi, Hydrogen Peroxide, in
Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH,
2
000.
2 G. Irick, Determination of the Photocatalytic Activities of
Titanium Dioxides and Other White Pigments. J. Appl. Polym.
Sci. 1972, 16, 2387–2395.
2
3
production of H
ethylanthraquinone as photocatalyst. J. Mol. Catal. A Chem.
016, 420, 66–72.
2 2
O with high concentrations using 2-
3 J. R. Harbour, J. Tromp and M. L. Hair, Photogeneration of
2
2
hydrogen peroxide in aqueous TiO dispersions. Can. J.
0 H. Görner, Photoinduced oxygen uptake for 9,10-
anthraquinone in air-saturated aqueous acetonitrile in the
presence of formate, alcohols, ascorbic acid or amines.
Photochem. Photobiol. Sci. 2006, 5, 1052–1058.
Chem. 1985, 63, 204–208.
4 M. C. Markham and K. J. Laidler, A kinetic study of photo-
oxidations on the surface of zinc oxide in aqueous
suspensions. J. Phys. Chem. 1953, 57, 363–369.
3
3
1 A. F. Khlebnikov, M. V. Golovkina, M. S. Novikov and D. S.
Yufit, A Novel Strategy for the Synthesis of 3-(N-
5 T. R. Rubin, J. G. Calvert, G. T. Rankin and W. MacNevin,
Photochemical Synthesis of Hydrogen Peroxide at Zinc Oxide
Surfaces. J. Am. Chem. Soc. 1953, 75, 2850–2853.
Heteryl)pyrrole Derivatives. Org. Lett. 2012, 14, 3768–3771.
2 L. D. Funt, M. S. Novikov, G. L. Starova and A. F. Khlebnikov,
Synthesis and properties of new heterocyclic betaines: 4-
Aryl-5-(methoxycarbonyl)-2-oxo-3-(pyridin-1-ium-1-yl)-2,3-
dihydro-1H-pyrrol-3-ides. Tetrahedron 2018, 74, 2466–2474.
3 R. M. Sellers, Spectrophotometric Determination of
Hydrogen Peroxide Using Potassium Titanium(IV) Oxalate.
Analyst 1980, 105, 950–954.
6 A. P. Hong, D. W. Bahnemann and M. R. Hoffmann, Cobalt(II)
Tetrasulfophthalocyanine on Titanium Dioxide: A New
Efficient Electron Relay for the Photocatalytic Formation and
Depletion of Hydrogen Peroxide in Aqueous Suspensions. J.
Phys. Chem. 1987, 91, 2109–2117.
7 C. Wang, X. Zhang, B. Yuan, Y. Wang, P. Sun, D. Wang, Y. Wei
and Y. Liu, Multi-heterojunction photocatalysts based on
3
WO nanorods: Structural design and optimization for
enhanced photocatalytic activity under visible light. Chem.
Eng. J. 2014, 237, 29–37.
8 H. Il Kim, O. S. Kwon, S. Kim, W. Choi and J. H. Kim,
Harnessing low energy photons (635 nm) for the production
3
3
3
1
4 S. B. Brown, P. Jones and A. Suggett, Iron(lll) complex
interference in the iodometric determination of hydrogen
peroxide. Anal. Chim. Acta 1968, 43, 343–346.
5 J. Nasielski and E. Vander Donckt, Propriété physico-
chimiques de composés à caractère aromatique IX. Mise en
évidence de complexes de transfert de charge entre des
dérivés N-méthylés monoaza-aromatiques et des hydro-
carbures aromatiques. Theor. Chim. Acta, 1964, 2, 22–28.
6 J. P. Dinnocenzo, P. B. Merkel and S. Farid, Cationic (charge
shift) exciplexes. J. Phys. Chem. A 2017, 121, 7903−7909.
K. Ohkubo, S. Fukuzumi and D. A. Nicewicz, 9-Mesityl-10-
methylacridinium Perchlorate, in Encyclopedia of Reagents
for Organic Synthesis, John Wiley&Sons, 2001.
1
1
2
2 2
of H O using upconversion nanohybrid photocatalysts.
Energy Environ. Sci. 2016, 9, 1063–1073.
9 K. Ohkubo, K. Suga and S. Fukuzumi, Solvent-free selective
photocatalytic oxidation of benzyl alcohol to benzaldehyde
by molecular oxygen using 9-phenyl-10-methylacridinium.
Chem. Commun. 2006, 2018–2020.
0 H. Kotani, K. Ohkubo and S. Fukuzumi, Photocatalytic
Oxygenation of Anthracenes and Olefins with Dioxygen via
3
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Photochemical & Photobiological Sciences
Page 8 of 8
View Article Online
DOI: 10.1039/C9PP00206E