A Photophysical Study of Sensitization-Initiated Electron Transfer: Insights into the Mechanism of Photoredox Activity

Article abstract of DOI:10.1002/anie.201916359

The development of photocatalytic reactions has provided many novel opportunities to expand the scope of synthetic organic chemistry. In parallel with progress towards uncovering new reactivity, there is consensus that efforts focused on providing detaile

Full text of DOI:10.1002/anie.201916359

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Accepted Article
Title: A Photophysical Study of Sensitization-Initiated Electron
Transfer: Insights into the Mechanism of Photoredox Activity
Authors: Max Coles, Gina Quach, Jonathon Beves, and Evan Guy
Moore
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10.1002/anie.201916359
Angewandte Chemie International Edition
COMMUNICATION
A Photophysical Study of Sensitization-Initiated Electron
Transfer: Insights into the Mechanism of Photoredox Activity
Max S. Coles,[a] Gina Quach,[a] Jonathon E. Beves,[b] and Evan G. Moore*[a]
Abstract: The development of photocatalytic reactions has provided
many novel opportunities to expand the scope of synthetic organic
chemistry. In parallel with progress towards uncovering new reactivity,
there is consensus that efforts focused on providing detailed
mechanistic insight in order to uncover underlying excited-state
reactions are essential to maximise formation of desired products.
With this in mind, we have investigated the recently reported
Sensitization-Initiated Electron Transfer (SenI-ET) reaction for C-H
arylation of activated aryl halides. Using a variety of techniques, and
in particular nanosecond transient absorption spectroscopy, we are
able to distinguish several characteristic signals from the excited state
species involved in the reaction, and subsequent kinetic analysis
under various conditions has facilitated a detailed insight into the likely
reaction mechanism.
In the reported catalytic cycle,[2] a key feature proposed was a
single electron transfer (SET) reaction from DIPEA to the excited
Scheme 1. Catalytic C-H arylation of an activated aryl bromide in the presence
of [Ru(bpy)3]2+ and pyrene as light harvesting and redox active components.
PAH acceptor, ostensibly in its triplet state, Pyr (T1). Shortly
afterwards, some uncertainty in this mechanism was noted,[3]
since the reaction between these two components;
With the advent of transition metal photoredox catalysis, many
organic reactions previously considered to be unfeasible, due to
high activation energies or poorly activated substrates, can now
be proposed as viable synthetic pathways.[1] Inspired by
photosynthetic reaction mechanisms, where light harvesting and
subsequent redox reactions are decoupled, the König group
recently reported[2] conditions for highly efficient C-H arylation of
activated aryl bromides, as shown in Scheme 1. In this reaction,
C-C bond formation under mild conditions was achieved by
exploiting two different components to absorb light and then
undertake subsequent redox reactions. Specifically, by using
[Ru(bpy)3]2+ as a strong visible light harvesting unit in the
presence of a polycyclic aromatic hydrocarbon (PAH) such as
pyrene, with the addition of Hünig's base (DIPEA) as an electron
donor, formation of the highly reactive pyrene radical anion (Pyr•–)
was proposed. Upon one electron reduction, subsequent
fragmentation of the aryl halide yields the (hetero)aryl radical,
*Pyr (T1) + DIPEA  Pyr•– + DIPEA+
(1)
should be highly endergonic (ca. -1.0 V vs SCE). As a possible
alternative, a mechanism involving Triplet-Triplet Annihilation
(TTA) to form an excited singlet state, Pyr (S1), was proposed,[3]
for which subsequent SET to form the radical anion;
*Pyr (S1) + DIPEA  Pyr•– + DIPEA+
(2)
is more thermodynamically reasonable (ca. +2.1 V vs SCE).[3] It
was also suggested that direct observation of the radical anion
using time resolved absorption spectroscopy, as well as its power
and/or concentration dependence, may yield further insight into
the reaction mechanism.
Inspired by these reports, herein we discuss our investigation of
this reaction using nanosecond transient absorption spectroscopy
(ns-TA). This technique has been recognised[4] as being useful for
the identification of important reaction intermediates.[5] In
particular, the [Ru(bpy)3]2+ complex has distinct and easily
recognizable ns-TA features. For example, in addition to the
ground state bleach (GSB) signal centered at around 450 nm, the
3MLCT excited state of this complex, which is rapidly formed
(<100 fs) after photoexcitation, has an additional excited state
absorption (ESA) signal in the visible region at ca. 370 and
>500 nm, corresponding to newly formed ligand localized (bpy
radical) and charge transfer (LMCT) absorption bands.[6] Similarly,
the excited state singlet *Pyr (S1), triplet state *Pyr (T1), and
radical anion (Pyr•–) of the pyrene chromophore have well-known
and characteristic ESA features at ca. 470, 520 and 495 nm
respectively.[7]
which can combine with
a
trapping reagent such as
N-methylpyrrole to yield the product after oxidation.
Moreover, since the available reducing power of the pyrene
radical anion (-2.1 V vs SCE) is significantly greater than that of
the *[Ru(bpy)3]2+ (3MLCT) excited state oxidation potential
(-0.81 V vs SCE) and the one electron reduced [Ru(bpy)3]+
complex (-1.33 V vs SCE), the reaction of less reactive aryl
halides was also facilitated. This allowed the synthetic scope of
this reaction to be expanded to include a variety of aryl chlorides
(and pseudohalides) which were similarly activated towards
carbon–carbon (and carbon–heteroatom) bond-forming reactions.
The reaction conditions initially reported by König could not be
used for the purposes of the current study, as this would yield
solutions too optically dense for ns-TA analysis. As a result, it was
necessary to first benchmark the observed organic reactivity upon
10-fold dilution of the reaction components, which we have
undertaken using 1H NMR and GC-MS analysis. The
corresponding reaction conditions and characterisation data are
given in the Supporting Information (see Experimental Details and
[a]
[b]
School of Chemistry and Molecular Biosciences, The University of
Queensland, Brisbane, QLD, 4072, Australia
E-mail: egmoore@uq.edu.au
School of Chemistry, University of New South Wales, Sydney, NSW,
2052, Australia
Supporting information for this article is given via a link at the end of
the document.
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10.1002/anie.201916359
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Table 1. Summary of excited state lifetime data determined by global fitting of
ns-TA data under a variety of initial reaction conditions.
Fig. S1 and S2), which showed the desired reaction product is
formed, albeit in a lower yield of ca. 55 %. These results provide
confidence that our spectroscopic measurements are applicable
to the catalytic reaction.
[Pyrene]
(mM)
[DIPEA]
(mM)
*[Ru(bpy)3]2+
(3MLCT)
1 (ns)
*Pyr
(T1)
2 (s)
[Ru(bpy)3]+
3 (s)
Entry[a]
Having confirmed the SenI-ET reaction was productive under our
diluted reaction conditions, we next sought to investigate the
kinetic behavior of the various photogenerated species likely to
be present using ns-TA spectroscopy, by employing differing
initial concentrations of pyrene and DIPEA. As a starting point, the
ns-TA spectra of [Ru(bpy)3]2+ measured in degassed DMSO were
collected (see Fig. S3, Supp. Info.), yielding features described
earlier corresponding to the GSB and ESA signals of the 3MLCT
1
2
3
4
0
0
0
0
0
1043.3
± 4.0
N/A
N/A
N/A
N/A
N/A
0.5
1.0
2.0
809.3
± 5.1
13.6
± 0.4
720.0
± 4.2
12.3
± 0.2
623.5
± 4.4
11.8
± 0.2
excited state. Global analysis of this data yielded
a
monoexponential lifetime of 1.04 ± 0.01 sec.
5
6
7
0
0
0
14
28
56
831.9
± 5.3
N/A
N/A
N/A
38.1
± 2.6
Measurements in the presence of differing initial concentrations
of pyrene (see Fig. S4-S6, Supp. Info.) revealed quenching of the
*[Ru(bpy)3]2+ (3MLCT) excited state lifetime as expected (see
Table 1, entries 2-4). This allowed the dynamic Stern-Volmer
quenching constant (Ksv) for the intramolecular reaction between
the *[Ru(bpy)3]2+ (3MLCT) excited state and pyrene to be
established (see Fig. S7, Supp. Info.), yielding a bimolecular
quenching rate constant for Triplet-Triplet-Energy-Transfer
(TTET) of kTTET = 3.09  108 M-1 s-1. Also evident in the ns-TA data
was the slow appearance of ESA signals at ca. 420 and 520 nm
(see Fig. S4-S6, Supp. Info.) which, by comparison to literature,[7b]
could be unambiguously attributed to the formation of *Pyr (T1) via
the TTET mechanism, which then decays on a ca. 10-15 sec
timescale.
745.9
± 7.6
32.0
± 2.6
584.8
± 5.2
26.3
± 1.2
8
9
1.0
0.5
1.0
14
28
28
676.5
± 9.2
5.8
± 0.4
37.0
± 4.5
636.0
± 5.8
3.6
± 0.3
29.0
± 2.7
10
610.2
± 7.1
3.9
± 0.2
25.2
± 4.9
11[b]
1.0
28
576.0
± 4.7
4.4
± 0.2
25.8
± 2.1
[a] All samples contain 0.2 mM [Ru(bpy)3]Cl2 as the photocatalyst in degassed
DMSO. [b] Measurement conducted in the presence of 20 mM
2-bromobenzonitrile and 200 mM N-methylpyrrole.
*[Ru(bpy)3]2+ (3MLCT) + Pyr  [Ru(bpy)3]2+ + *Pyr (T1)
(3)
[Ru(bpy)3]+ complex, which was identified by comparison to the
literature.[8]
From the corresponding kinetic fits, a decrease in the *Pyr (T1)
lifetime upon increasing concentrations of pyrene was also found
(see Table 1, entries 2-4), which we rationalised by the presence
of Triplet-Triplet-Annihilation (TTA) under these conditions.
The resulting 3MLCT lifetimes are also summarized (see Table 1,
entries 5-7), and Stern-Volmer analysis as before (see Fig. S12,
Supp. Info.) allowed Ksv and hence the bimolecular SET
quenching rate with DIPEA as the electron donor to be evaluated
as kSET = 1.31  107 M-1 s-1. A decrease in the lifetime of the
[Ru(bpy)3]+ complex upon increasing DIPEA concentrations is
ascribed to an increase in the rate of non-geminate charge
recombination due to elevated DIPEA+ concentrations.[9]
*Pyr (T1) + *Pyr (T1)  *Pyr (S1) + Pyr
(4)
Indeed, the occurrence of TTA was also confirmed using Time
Correlated Single Photon Counting (TCSPC) fluorescence
lifetimes techniques (see Fig. S8, Supp. Info.). Specifically, the
3MLCT emission of the [Ru(bpy)3]2+ complex monitored at 620 nm
after 450 nm excitation yielded a ca. 690 ns decay time, which
showed excellent agreement with an observed rise in anti-stokes
upconverted *Pyr (S1) fluorescence at 390 nm. This signal
subsequently decayed on the sec timescale, providing definitive
evidence for the presence of TTA.
[Ru(bpy)3]+ + DIPEA+  [Ru(bpy)3]2+ + DIPEA
(6)
The photophysical behavior of the [Ru(bpy)3]2+ complex in the
presence of differing concentrations of both pyrene and DIPEA
was then investigated (see Fig. S3-S15, Supp. Info.). The kinetic
data is summarized (see Table 1, entries 3, 6, 8-10) and an
example of the observed ns-TA spectra at various time delays,
together with results from global fitting analysis is shown in Fig. 1.
Cursory inspection of the ns-TA data obtained in this case reveals
the presence of ESA signals which can be attributed to the initially
formed 3MLCT excited state, together with other evolving ESA
signals from both *Pyr (T1) and the one-electron reduced
[Ru(bpy)3]+ complex. By fitting the kinetic decay profile to a three
exponential model, the results from global analysis allows the
differing spectral features of *[Ru(bpy)3]2+ (3MLCT), *Pyr (T1) and
the [Ru(bpy)3]+ to be more clearly resolved in the corresponding
Decay Associated Difference Spectra (DADS) shown in Fig. 1c.
Concurrently, the behavior of [Ru(bpy)3]2+ in the presence of
varying initial concentrations of DIPEA was also investigated (see
Fig. S9-S11, Supp. Info.). As was the case with pyrene, significant
quenching of the *[Ru(bpy)3]2+ (3MLCT) excited state lifetime was
observed, which in this case can be attributed to reductive
quenching of the metal complex in the presence of the amine
electron donor.
*[Ru(bpy)3]2+ (3MLCT) + DIPEA  [Ru(bpy)3]+ + DIPEA+
(5)
The photoproducts of this SET reaction are photoreduced
[Ru(bpy)3]+ and DIPEA+. Accordingly, the appearance of the
ns-TA spectrum clearly evolves over time towards that of the
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3, 8, 10). Given the reaction of [Ru(bpy)3]2+ and DIPEA in isolation
was shown to form the one electron reduced [Ru(bpy)3]+ complex,
these two results strongly implicate an excited state reaction
between these two photoproducts. Taking the available
thermodynamic data and photocatalytic behavior into
consideration, our ns-TA results are consistent with formation of
the highly reactive pyrene radical anion (Pyr•–) via an excited state
intermolecular electron transfer reaction between these two
products, which we can summarize as;
(a)
5
0
t = 0
t =5 ns
t = 1 ns
t = 50 ns
t = 500 ns
t = 1 s
t = 5 s
t = 50 s
t = 250 s
t = 250 ns
t = 750 ns
t = 2 s
t = 10 s
t = 100 s
-5x10-3
Pyr (T1) + [Ru(bpy)3]+  Pyr•– + [Ru(bpy)3]2+
(7)
400
500
600
700
800
wavelength / nm
Notably, this reaction is expected to be highly exergonic (ca.
+1.23 V vs SCE) and is one of the reaction pathways proposed[10]
by König involving photochemically and/or photoredox generated
reactive intermediates that may be present in the reaction mixture
under catalytic conditions.
(b)
5
0
In order to revisit the possibility of a TTA mediated pathway for
Pyr•– radical anion generation, we have undertaken similar
TCSPC lifetime measurements using the [Ru(bpy)3]2+ complex in
the presence of both pyrene and DIPEA. In this case we also
observed evidence for TTA. However the intensity of the
upconverted *Pyr (S1) fluorescence was reduced to less than 5 %
of that observed in the absence of DIPEA (see Fig. S16, Supp.
Info). The decrease in upconverted *Pyr (S1) fluorescence can be
potentially attributed to SET quenching in the presence of DIPEA,
which is thermodynamically favourable (eqn 2), and results in
formation of the Pyr•– radical anion via the TTA mechanism.
Alternatively, the bimolecular quenching of *Pyr (T1) with
concomitantly formed [Ru(bpy)3]+ (eqn 7) would decrease the
*Pyr (T1) excited state population available to undergo the TTA
process, and similarly result in the observed decreased in
upconverted *Pyr (S1) fluorescence.
-5x10-3
380 nm
420 nm
470 nm
520 nm
650 nm
0.001
0.01
0.1
1
10
100
time delay / sec
(c)
5
0
Global Fit A1
Global Fit A2
Global Fit A3
-5x10-3
tau1 = 0.61 sec
tau2 = 3.9 sec
tau3 = 25.2 sec
In order distinguish between these two possibilities, we have
sought to estimate the relative contributions of TTA compared to
SenI-ET quenching of the *Pyr (T1) excited state. Using a
modified Stern-Volmer approach, and the concentration
dependent decrease in *Pyr (T1) lifetime, we estimate the rate of
bimolecular Triplet-Triplet-Annihilation as kTTA = 1.341010 M-1 s-1
(see Fig. S17, Supp. Info.). The rate constant for bimolecular
SenI-ET quenching was evaluated via the concentration
dependent decrease in *Pyr (T1) lifetime as a function of
[Ru(bpy)3]+ (kSenI-ET = 2.21011 M-1 s-1, see Fig. S18, Supp. Info.),
and the latter is approximately an order of magnitude faster than
kTTA. Using these rate constants, we are able to estimate the
proportion of the *Pyr (T1) excited state which will be quenched
via the TTA compared to SenI-ET pathways (see Section 14,
Supp. Info.). The results of these calculations reveal the vast
majority of *Pyr (T1) will be consumed by the SenI-ET mechanism,
with only a minor proportion (ca. <5%) of *Pyr (T1) diverted
towards TTA and other non-radiative processes. This is fully
consistent with the >95% decrease in upconverted *Pyr (S1)
fluorescence observed experimentally by TCSPC methods.
Accordingly, it appears that the TTA pathway is effectively shut-
down in the presence of the one electron reduced [Ru(bpy)3]+
complex, and the SenI-ET reaction is the primary source of Pyr•–
radical anions involved in the subsequent organic photocatalysis
reactions.
400
500
600
700
800
wavelength / nm
Figure 1. (a) Observed ns-TA spectra (ex = 450 nm) at various time delays for
a solution of 0.2 mM [Ru(bpy)3]2+, 1.0 mM Pyrene, and 28 mM DIPEA in
degassed DMSO (b) Corresponding decay kinetics at selected wavelengths and
(c) global fitting analysis showing Decay Associated Difference Spectra (DADS).
This DADS data allowed the excited state lifetimes for each
species with differing initial reaction conditions to be readily
analyzed. For example, the initially formed MLCT excited state
3
for a given *[Ru(bpy)3]2+ complex can undergo either TTET or
SET when both pyrene and DIPEA are present in solution,
depending on the collisional reaction partner, and the DADS show
these two processes occur in tandem. The quenching of the
resulting *[Ru(bpy)3]2+ (3MLCT) excited state lifetime is
summative, as expected, and is in agreement with the previous
individually evaluated Ksv constants, allowing the contribution of
each process to also be estimated.
More importantly, the evaluated lifetime data reveals a clear
decrease in lifetime of the photoreduced [Ru(bpy)3]+ complex with
increasing initial concentration of pyrene (see Table 1, entries
6, 9, 10). Similarly, the *Pyr (T1) lifetime is strongly quenched as
a function of the initial DIPEA concentration (see Table 1, entries
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Lastly, with the catalytic reaction in mind, we undertook a final
ns-TA measurement (see Fig. S19, Supp. Info) using catalytically
relevant concentrations of [Ru(bpy)3]2+, pyrene and DIPEA in the
presence of 2-bromobenzonitrile and N-methylpyrrole (see Table
1, entry 11). The resulting fit of kinetic parameters for *Pyr (T1)
and the [Ru(bpy)3]+ complex are within experimental error of those
in the absence of organic substrates, indicating a lack of
interaction between these components. Interestingly, the
*[Ru(bpy)3]2+ (3MLCT) excited state lifetime is reduced by ca. 30
ns in the presence of 2-bromobenzonitrile and N-methylpyrrole,
proposed mechanism also agrees with recently published
results[12] wherein an analogous photoredox reaction was
proposed to mediate the Birch reduction of several different
arenes. This work demonstrates that not only the primary
photoredox reaction, but also the possibility of secondary
reactions between components can be involved in catalytic
processes, and should be considered when organic photoredox
mechanisms are proposed.
Experimental Section
suggesting it may play an additional role as
a potential
General. [Ru(bpy)3]Cl2·6H2O (bpy = 2,2’-bipyridine), pyrene, N,N-
diisopropylethylamine (DIPEA), N-methylpyrrole, 2-bromobenzonitrile and
d6-DMSO were obtained from Sigma Aldrich and were used as received.
HPLC grade DMSO was obtained from Fisher Scientific and was dried
over 3 Å molecular sieves prior to use.
photooxidant of the C-H arylated product. The possibility of
*[Ru(bpy)3]2+ (3MLCT) being involved in formation of the final
product was also by suggested10 by König, although further
experiments using different concentrations of organic substrate
would be required to confirm this step. It is unfortunate we were
not able to directly observe formation of the pyrene radical anion
(Pyr•–) using ns-TA spectroscopy, despite its well-known[7c] and
intense ESA signal at 495 nm. However, this may be rationalized
if the rate of Pyr•– formation from the two precursors as shown in
eqn. 7 is slow, compared to its consumption. In this context, we
note the reverse electron transfer reaction to form the pyrene
ground state;
Physical Methods. 1H NMR spectra in d6-DMSO were recorded using a
Bruker Avance 500 MHz spectrometer, and were referenced to the
residual solvent peak at 2.50 ppm. GC-MS was performed on a Shimadzu
QP-2010 equipped with a capillary column (length: 30 m; diam.: 0.25 mm;
film: 0.1 μM), using He as the carrier gas. For Transient Absorption (ns-TA)
measurements, a broadband pump-probe spectrometer (EOS, Ultrafast
Systems, LLC) was used, while for time-resolved emission measurements,
a time-resolved fluorescence spectrometer (Halcyone, Ultrafast Systems,
LLC) was utilised, operating in Time Correlated Single Photon Counting
(TCSPC) mode. In both cases, an amplified laser system (Spitfire ACE,
Spectra Physics) was the excitation source, delivering ca. 100 fs laser
pulses at 800 nm with a 1 kHz repetition rate, which were then coupled to
an OPA system (Topas Prime, Light Conversion), to deliver excitation
pulses tuned to 450 nm. Samples for spectroscopic measurements were
degassed by three consecutive freeze-pump-thaw cycles, had an
absorbance of ca. 0.4 over the 2 mm path length used, and were stirred
mechanically during each measurement. Resulting spectrophotometric
data was processed using Igor Pro (Wavemetrics, Version 6.1.1.2).
Pyr•– + [Ru(bpy)3]2+  Pyr + [Ru(bpy)3]+
(8)
is also exergonic (ca. +0.77 V vs SCE), and we would expect this
reaction to also be accelerated by Coulombic effects.[11]
Considering all of the available spectroscopic evidence, we
propose the catalytic reaction mechanism shown in Fig. 2.
Synthesis of 2-(1-methyl-1H-pyrrol-2-yl)benzonitrile. In a 5 mL, 1 cm
quartz degassing cuvette equipped with
a magnetic stirrer bar,
2-bromobenzonitrile (0.1 mmol, 1.0 eqv), [Ru(bpy)3]Cl2·6H2O (0.001 mmol,
0.01 eqv, 1 mol %), pyrene (0.005 mmol, 0.05 eqv, 5 mol %), DIPEA (0.14
mmol, 1.4 eqv) and N-methylpyrrole (1 mmol, 10 eqv) were dissolved in 5
mL of dry d6-DMSO. This solution was subjected to three freeze pump
thaw cycles and was then backfilled with argon. The reaction mixture was
irradiated at 450 nm using a monochromated Xenon arc lamp with an
average power of ca. 50 mW for 18 hours. The crude reaction mixture was
first analysed by 1H NMR and GC-MS, and was then transferred to a
separating funnel, where water (20 mL) and brine (5 mL) were added. The
mixture was extracted with ethyl acetate (3 x 15 mL), and the combined
organic layers were dried over anhydrous MgSO4, filtered and then
concentrated under vacuum. The crude product was purified using flash
chromatography on silica with 3:1 (v/v) hexanes/ethyl acetate as the eluent
(ca. 55% yield by NMR). 1H NMR (500 MHz, d6-DMSO) δ 7.91 (ddd, J =
7.8, 1.4, 0.6 Hz, 1H), 7.74 (ddd, J = 7.9, 7.5, 1.4 Hz, 1H), 7.58 (ddd, J =
7.9, 1.2, 0.6 Hz, 1H), 7.53 (td, J = 7.7, 1.2 Hz, 1H), 6.97 (ddd, J = 2.7, 1.8,
0.4 Hz, 1H), 6.31 (dd, J = 3.7, 1.8 Hz, 1H), 6.14 (dd, J = 3.6, 2.7 Hz, 1H),
3.57 (d, J = 0.3 Hz, 3H). GC-MS (EI) m/z calc’d for C12H10N2: 182.08;
Found: 182.90 [M+H]+.
Figure 2. Proposed SenI-ET mechanism showing formation of both *Pyr (T1)
and [Ru(bpy)3]+ by visible light absorption, and subsequent formation of Pyr•–
which initiates the observed C-H arylation reaction.
In this mechanism, competing energy and electron transfer
reactions using [Ru(bpy)3]2+ as a common light harvesting unit
results in the formation of both *Pyr (T1) and the one-electron
reduced [Ru(bpy)3]+ complex, with DIPEA acting as the electron
source. These excited state and one-electron reduced species
are sufficiently long-lived (ca. 10-40 sec) in solution, facilitating
their bimolecular reaction to form the Pyr•– radical anion, which is
able to reduce aryl halides leading to the observed C-H arylation
products. Interestingly, the process we describe is indeed a two-
photon process, as proposed by Ceroni,[3] since one photon each
is required to generate the *Pyr (T1) and photoreduced [Ru(bpy)3]+
complex, but operates via a very different pathway to TTA. Our
Acknowledgements
Financial support by the Australian Research Council (ARC-
DP160100870) is gratefully acknowledged.
Keywords: SenI-ET • photoredox • catalysis • mechanism
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10.1002/anie.201916359
Angewandte Chemie International Edition
COMMUNICATION
Entry for the Table of Contents
COMMUNICATION
Sensitization Initiated Electron
Transfer (SenI-ET) for
Max S. Coles, Gina Quach, Jonathon
E. Beves, and Evan G. Moore*
photocatalysis has been
Page No. – Page No.
investigated under various reaction
conditions using nanosecond
transient absorption (ns-TA)
spectroscopy. By characterising the
kinetic behaviour of the different
excited state species involved, a
detailed insight into the reaction
mechanism has been obtained.
A Photophysical Study of
Sensitization-Initiated Electron
Transfer: Insights into the
Mechanism of Photoredox Activity
This article is protected by copyright. All rights reserved.