Combined In Situ Illumination-NMR-UV/Vis Spectroscopy: A New Mechanistic Tool in Photochemistry

Article abstract of DOI:10.1002/anie.201801250

Synthetic applications in photochemistry are booming. Despite great progress in the development of new reactions, mechanistic investigations are still challenging. Therefore, we present a fully automated in situ combination of NMR spectroscopy, UV/Vis spectroscopy, and illumination to allow simultaneous and time-resolved detection of paramagnetic and diamagnetic species. This optical fiber-based setup enables the first acquisition of combined UV/Vis and NMR spectra in photocatalysis, as demonstrated on a conPET process. Furthermore, the broad applicability of combined UVNMR spectroscopy for light-induced processes is demonstrated on a structural and quantitative analysis of a photoswitch, including rate modulation and stabilization of transient species by temperature variation. Owing to the flexibility regarding the NMR hardware, temperature, and light sources, we expect wide-ranging applications of this setup in various research fields.

Full text of DOI:10.1002/anie.201801250

Angewandte
Communications
Chemie
International Edition: DOI: 10.1002/anie.201801250
German Edition: DOI: 10.1002/ange.201801250
Spectroscopic Methods
Combined In Situ Illumination-NMR-UV/Vis Spectroscopy: A New
Mechanistic Tool in Photochemistry
+
+
Andreas Seegerer , Philipp Nitschke , and Ruth M. Gschwind*
Abstract: Synthetic applications in photochemistry are boom-
ing. Despite great progress in the development of new
reactions, mechanistic investigations are still challenging.
Therefore, we present a fully automated in situ combination
of NMR spectroscopy, UV/Vis spectroscopy, and illumination
to allow simultaneous and time-resolved detection of para-
magnetic and diamagnetic species. This optical fiber-based
setup enables the first acquisition of combined UV/Vis and
NMR spectra in photocatalysis, as demonstrated on a conPET
process. Furthermore, the broad applicability of combined
UVNMR spectroscopy for light-induced processes is demon-
strated on a structural and quantitative analysis of a photo-
switch, including rate modulation and stabilization of transient
species by temperature variation. Owing to the flexibility
regarding the NMR hardware, temperature, and light sources,
we expect wide-ranging applications of this setup in various
research fields.
activation or deactivation of substrates or catalysts in photo-
catalysis.
[5]
However, besides the limited time resolution, NMR
spectroscopy faces the additional challenge that single-
electron transfer (SET) processes, which are typical for
photocatalysis, cause an interplay of paramagnetic and
diamagnetic species. Often, the lifetime of these paramag-
netic radical intermediates is so short that they do not even
affect the NMR spectra of the diamagnetic species. The
information on these transient radicals can often be accessed
only by photo-chemically induced dynamic nuclear polar-
ization (photo-CIDNP) through their diamagnetic recombi-
[
3b,6]
nation and disproportionation products.
In contrast,
stable long-lived radicals can impose severe challenges to
NMR spectroscopy. While in the case of several inorganic
complexes or proteins paramagnetic NMR spectroscopy can
[
7]
be successfully applied, it is usually not possible to detect
paramagnetic states of small organic molecules, such as those
used as photocatalysts in photochemistry. Furthermore, for
the stable radical states of photocatalysts, chemical exchange
often leads to severe line broadening even for the diamagnetic
P
hotocatalysis is one of the booming fields in organic
synthesis and has experienced a nearly exponential increase
in publications of synthetic strategies and applications during
[1]
[3b]
the last decades. Despite the high impact of new light-
induced transformations on synthesis, detailed insights into
photocatalytic mechanisms are still a real challenge. In
photochemistry, ultrafast UV/Vis spectroscopy is so far the
most commonly used method for detailed mechanistic studies,
owing to its capability to detect the initial photoexcited
states.
Because consecutive photoinduced electron transfer
[
8]
(conPET) processes (Figure 1) recently emerged as a hot
topic to address the activation of strong bonds and higher
redox potentials, detailed mechanistic investigations are
highly demanded in the photocatalysis community. In
conPET processes, long-lived radical anions (usually elusive
to NMR spectroscopy) are the central key intermediates
generated by PET utilizing a sacrificial electron donor D. A
second photoexcitation of this radical anion leads to a photo-
[
2]
states. We and other groups have recently shown that NMR
spectroscopy can provide essential mechanistic information
on photochemical and photocatalytic processes, despite its
[
3]
insensitivity and poor time resolution, by providing quanti-
tative reaction profiles of reactants, products, and intermedi-
ates. Complementary to ultrafast UV/Vis, mechanistic fea-
tures downstream from the initial photoexcitation, such as
[8,9]
excited state with reduction potentials of up to À2.4 V. This
provides an elegant way to increase the scope for metal-free
photoredox catalysis under mild conditions using commer-
cially available organic photocatalysts.
[
3b]
single- versus two-electron transfer processes,
proton
transfer pathways, or multiple concurrent reaction mecha-
To extend the scope of high-resolution NMR spectro-
scopic investigations in photocatalysis with stable radicals,
a combined NMR and UV/Vis spectroscopic tool would be
[3a]
nisms, can be elucidated by NMR spectroscopy. Further-
more, owing to its high-resolution spectra, NMR spectroscopy
provides detailed structural information about intermolecular
[4]
interactions and aggregation, revealing key information of
[
+]
[+]
[
*] A. Seegerer, P. Nitschke, Prof. Dr. R. M. Gschwind
Institute of Organic Chemistry, University of Regensburg
Universitꢀtsstrasse 31, 93053 Regensburg (Germany)
E-mail: ruth.gschwind@chemie.uni-regensburg.de
+
[
] These authors contributed equally to this work.
Supporting information, including experimental details, and the
ORCID identification number(s) for the author(s) of this article can
be found under:
Figure 1. Schematic of a consecutive photoinduced electron transfer
(conPET) process. D=sacrificial electron donor, Q=quenching
[
8c]
https://doi.org/10.1002/anie.201801250.
substrate.
Angew. Chem. Int. Ed. 2018, 57, 1 – 6
ꢀ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!

Angewandte
Communications
Chemie
[
10]
ideal.
However, reaction profiles of photocatalytic pro-
cesses featuring longer reaction times of up to several hours
or even days impose severe challenges for separated setups.
While separated setups can have matching experimental
conditions such as temperature and concentration, an exact
match of light absorption/intensity, which depend on the
geometry and positioning of light source and reaction vessel
as well as parameters such as convection/diffusion properties,
is best realized by using an in situ combination.
In addition to photocatalysis, an in situ setup combining
UV/Vis, NMR, and illumination would show a broad applic-
ability in the field of photoswitches and molecular
[
11]
machines. Herein, such a setup provides direct, quantitative
correlations between absorbance and structure of switching
[
12]
states and can be used to track full conversion cycles.
For static equilibria, Tolstoy et al. introduced an in situ
combination of UV/Vis and high-resolution solution NMR
spectroscopy (UVNMR) in 2009 to achieve absolute com-
[13]
parability of both methods. However, this setup cannot be
applied for dynamic, light-induced (photo) chemical process-
es because of the hampered diffusion caused by a reflector
between bulk solution for NMR spectroscopy and an aliquot
for UV/Vis spectroscopy. Furthermore, an additional light
source for illumination is missing and the NMR probe has to
be drilled to guide optical fibers to the tip of the NMR tube.
Therefore, in this paper we describe a fully automated
triple combination of in situ illumination and UV/Vis and
NMR spectroscopy. The potential of this setup is demon-
strated by acquisition of combined UVNMR reaction profiles
of a light-induced conPET process and a photoswitchable
spiropyran.
Figure 2. A) Schematic of UVNMR-illumination setup. B) Close-up of
the illumination fiber and the reflection dip probe inside the NMR
tube. C) Photos of the setup including the outer amberized NMR tube,
PTFE reflector, screw cap, and coaxial insert with both optical fibers
inside, (dis)assembled with/without light.
To enable combined, time-resolved UVNMR reaction
profiles, an absolute time control of UV/Vis, NMR measure-
ments, and illumination is required. Therefore, the NMR
console was used as the central time control unit. It directly
addresses the illumination device (LED transistor) and the
UV/Vis spectrometer through TTL signals (Figure 2A),
implemented as events in modified NMR pulse sequences
(see Supporting Information). For a UV/Vis measurement,
the UV/Vis spectrometer forwards the TTL signal of the
NMR console to a D-Hal-light source to control its shutter,
that is, the emitted light hits the sample exclusively during the
Our new optical fiber-based UVNMR-illumination setup
combines a UV/Vis-reflection dip probe (Avantes) with our
[14]
in situ LED-illumination device inside an NMR spectrom-
eter (Figure 2A). The optical fiber for illumination (with
a sandblasted tip) and the reflection dip probe for UV/Vis
measurements are placed together inside a coaxial quartz
glass insert within an amberized NMR tube. The optical fiber
for illumination and the reflection dip probe (Figure 2B)
were used for guiding the light of the LED illumination device
and the deuterium-halogen (D-Hal)-lamp directly into the
NMR tube and to detect the reflected light. A PTFE insert
inside the NMR tube acts as reflector (Figure 2B). Owing to
an outer diameter of the coaxial quartz glass insert of 3 mm
and an inner diameter of 4 mm of the outer NMR tube, an
active layer of 1 mm is given in the range of the NMR radio
frequency (RF) coils (Figure 2B). To ensure homogeneity of
the solution by diffusion, the distance between the tip of the
insert and the PTFE reflector was set to approximately 1 mm
[15]
UV/Vis measurement.
To demonstrate the power of our UVNMR-illumination
setup combined in situ UV/Vis and NMR reaction profiles of
a conPET process are presented. In this process, light
(450 nm) transforms the photocatalyst N,N-bis(2,6-diisopro-
pylphenyl)-perylene-3,4,9,10-bisdicarboximide (PDI) into the
À
stable radical anion PDIC in presence of an electron donor D
À
(in this case, NEt ). A second photoexcitation of PDIC is
3
proposed to allow for a reduction of aryl halides such as 4-
bromo-benzaldehyde Ald-Br to the corresponding aryl Ald
[
8a]
(Figures 1 and 3A,B and the Supporting Information). In
this reaction, PDI shows extreme line broadening effects in
the NMR spectra (Figure 3C). Even prior to illumination, all
signals of PDI are significantly broadened most probably
owing to an exchange with an electron donor acceptor
(
path length of approximately 2 mm). To adjust the path
length, a customized screw cap was developed (Figure 2C, for
details see the Supporting Information), which connects the
NMR tube and the insert tightly, so that even air-sensitive
samples and (photo) reactions can be analyzed. The whole
setup is portable, fully remote-controlled, and applicable to
every conventional solution NMR spectrometer without any
alteration. This allows for an extremely flexible application
regarding the NMR setup (probe, field, temperature) adapted
to the individual problems.
complex between NEt and PDI with the typical distance-
3
[3b]
dependent line broadening of radicals. The protons H and
4
H (Figure 3C, see the Supporting Information) attached to
5
the central perylene core nearly vanished, H and H are
1
2
broadened, and even proton H of the isopropyl group on PDI
3
[
16]
are slightly affected. In contrast, without illumination the
2
www.angewandte.org
ꢀ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2018, 57, 1 – 6
These are not the final page numbers!

Angewandte
Communications
Chemie
feasible. Studies towards an absolute quantification are in
progress.
Thus, the UV/Vis data provides important, time-resolved
information about reactants invisible to NMR spectroscopy,
enabling a semiquantitative reaction profile for the evolution
À
of PDIC . Complementary to the UV/Vis spectra, simulta-
neously recorded NMR spectra give full quantitative and
structural insight into participating diamagnetic reactants and
[
17]
reaction/decomposition products (Figure 3E).
With this in situ combination of NMR and UV/Vis
spectroscopy and illumination, complete reaction profiles of
the whole progress of a reaction including paramagnetic and
diamagnetic species can be obtained and important interac-
tions as well as structural details can be investigated. This
enables totally new possibilities to elucidate reaction mech-
anisms in photocatalysis. Further studies about this contro-
versial mechanism are in progress.
Photoswitches are another promising field of applications
for the in situ combination of NMR and UV/Vis spectroscopy
and illumination. In our previous study about photoswitch-
able spiropyrans, deviations between the quantitative data of
UV/Vis and NMR spectroscopy were found, demonstrating
the importance of identical light intensities and reaction
[
18]
vessels in separated setups. To demonstrate the advantages
of our UVNMR-illumination setup with only one illumina-
tion device and a common reaction vessel, a spectroscopic
analysis of a similar photoswitchable spiropyran is presented.
In this case, the colorless 1’,3’-dihydro-1’,3’,3’-trimethyl-6-
Figure 3. A) Photocatalytic reduction of 4-bromo-benzaldehyde Ald-Br
to benzaldehyde Ald through a PDI-catalyzed conPET process. B) H
spectra of the reaction mixture, before and after illumination (450 nm)
[
8a]
1
nitrospiro[2H-1-benzo-pyran-2,2’-(2H)-indole]
1
can be
switched to its open, purple, zwitterionic state 2 (Figure 4A)
showing Ald-Br and Ald at 313 K in [D ]DMF. C) Line broadening and
7
by irradiation with UV light (365 nm) inside the NMR
vanishing of the PDI proton signals (red) upon illumination because of
[11a]
spectrometer at 300 K in [D ]THF.
The in situ-recorded
À
À
8
exchange with PDIC . D) Conversion of PDI into PDIC monitored by
UV/Vis spectrum (Figure 4B) shows new absorption maxima
at 533 and 575 nm with continuous illumination. Comple-
mentarily, the NMR spectrum (Figure 4C) gives immediate
information about the quantity of the opened spiropyran 2
in situ UV/Vis spectroscopy. E) Combined NMR and UV/Vis reaction
profiles allow for in situ kinetic information of both paramagnetic
À
(
PDIC ) and diamagnetic reactants (Ald-Br, Ald) in photocatalysis.
(21% after 2 min). However, upon switching off the light, 2
vanishes within circa 24 s in the NMR spectrum (t1/2 (300 K) =
17.4 s determined by UV/Vis spectroscopy), which prevents
a detailed structural study by NMR spectroscopy at 300 K
(Figure 4D and the Supporting Information).
By cooling the sample inside the NMR spectrometer to
180 K, without changing any other parameter of the setup, the
thermal back-reaction rate was reduced significantly (Fig-
ure 4E and the Supporting Information). This enables more
time-consuming NMR experiments to investigate both spe-
cies without degradation products (see Supporting Informa-
tion).
UV/Vis spectra show only small absorption bands of PDICÀ
Figure 3D; Supporting Information). This hints that in
(
specific cases, NMR spectroscopy might be very sensitive
for the detection of electron donor–acceptor complexes.
Immediately after turning on the light, the NMR proton
signals of the PDI core (H , H ) vanish completely. The other
4
5
NMR proton signals of PDI are only detectable for seconds or
minutes. However, even in the case of detection within the
first minutes, for example, of H , the severe line broadening
3
prevents any reliable quantification of both diamagnetic
photocatalyst and paramagnetic intermediate (Figure 3C).
UV/Vis spectroscopy shows its power for the detection of
Structural information about the preferred configuration
and conformation can be essential to understand different
binding properties of the isomers of photo switchable
stable radicals. After a few minutes of illumination at 450 nm,
the absorption maxima of PDICÀ (698 and 794 nm)
[8a]
rise,
molecules, for example, in biochemical applications. Fur-
[19]
while the absorbance of PDI (455 and 482 nm) steadily
decreases (Figure 3D). Besides its advantages in eliminating
all previously described common issues associated with
reaction conditions in separated setups, this study also reveals
a general application of this combined UVNMR-illumination
setup. In the case of UV/Vis detectable intermediates/
reactants, a relative quantification over time by UV/Vis is
thermore, the time-dependent conversion of different isomers
can be tracked online by NMR and/or UV/Vis spectroscopy
to show the active species present during a reaction. In
general the low-temperature applicability of the setup enables
temperature-dependent rate modulation and stabilization to
detect unstable intermediates by NMR and UV/Vis spectros-
copy. In addition, combinations of UVNMR with advanced
Angew. Chem. Int. Ed. 2018, 57, 1 – 6
ꢀ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3
These are not the final page numbers!

Angewandte
Communications
Chemie
Acknowledgements
We would like to thank the German Science Foundation
DFG) (GRK 1626, Chemical Photocatalysis) and European
(
Research Council (ERC-CoG 614182-IonPairsAtCatalysis)
for financial support, Dr. H. Bartling for helpful discussions,
and Peter Braun for an initial theoretical draft to combine
in situ NMR and UV/Vis spectroscopy and illumination.
Conflict of interest
The authors declare no conflict of interest.
Keywords: conPET · NMR spectroscopy · photochemistry ·
photoswitches · UV/Vis spectroscopy
[
1] a) M. Majek, A. Jacobi von Wangelin, Acc. Chem. Res. 2016, 49,
316 – 2327; b) I. Ghosh, L. Marzo, A. Das, R. Shaikh, B. Kçnig,
2
Acc. Chem. Res. 2016, 49, 1566 – 1577; c) M. A. Garcia-Garibay,
J. Am. Chem. Soc. 2012, 134, 8289 – 8292; d) J. M. R. Naraya-
nam, C. R. J. Stephenson, Chem. Soc. Rev. 2011, 40, 102 – 113;
e) K. Zeitler, Angew. Chem. Int. Ed. 2009, 48, 9785 – 9789;
Angew. Chem. 2009, 121, 9969 – 9974; f) N. A. Romero, D. A.
Nicewicz, Chem. Rev. 2016, 116, 10075 – 10166; g) B. Kçnig, Eur.
J. Org. Chem. 2017, 1979 – 1981.
Figure 4. A) Equilibrium of spiropyran 1 and 2. Upon excitation of
with a 365 nm LED, 1 switches into its open, colored form 2. The
1
photoswitch process can be detected by UV/Vis spectroscopy, while
NMR spectroscopy unambiguously confirms the structure of the open
form 2. B) Absorption spectra under the influence of light (365 nm).
C) Corresponding NMR spectra showing new signals of 2 after
illumination at 300 K. D) UV/Vis spectra of the thermal back reaction
of 2 to 1 at 300 K once the light is turned off. E) UV/Vis spectra of 2 at
[
2] a) Y. Zhang, J. Kubicki, M. S. Platz, J. Am. Chem. Soc. 2009, 131,
1
3602 – 13603; b) U. Megerle, M. Wenninger, R.-J. Kutta, R.
Lechner, B. Kçnig, B. Dick, E. Riedle, Phys. Chem. Chem. Phys.
011, 13, 8869 – 8880; c) J. Wang, G. Burdzinski, J. Kubicki, M. S.
1
80 K; the thermal back reaction is extremely slow, which enables
2
a full investigation without the need of continuous illumination.
PSS=photo stationary state.
Platz, J. Am. Chem. Soc. 2008, 130, 11195 – 11209; d) P. K.
Verma, F. Koch, A. Steinbacher, P. Nuernberger, T. Brixner, J.
Am. Chem. Soc. 2014, 136, 14981 – 14989; e) E. Riedle, M. K.
Roos, S. Thallmair, C. F. Sailer, N. Krebs, B. P. Fingerhut, R.
de Vivie-Riedle, Chem. Phys. Lett. 2017, 683, 128 – 134; f) J. Xue,
H. L. Luk, S. V. Eswaran, C. M. Hadad, M. S. Platz, J. Phys.
Chem. A 2012, 116, 5325 – 5336.
NMR techniques like DOSY to investigate aggregates or
complexes are feasible.
To summarize, in this study we present a fully automated
triple combination of in situ high-resolution NMR and UV/
Vis spectroscopy and illumination in a new optical fiber-based
setup. By merging two very important methods in the field of
mechanistic investigations, it is now possible to monitor and
quantify paramagnetic and diamagnetic species simultane-
ously and in a time-resolved manner during a light-induced
photochemical transformation by NMR and UV/Vis spec-
troscopy. Besides the elimination of all common issues related
to the use of separated systems, like concentration and
temperature, the setup circumvents all deviations in terms of
light intensity, reaction vessel, convection, and diffusion. Its
applicability in a wide temperature range opens the oppor-
tunity to modulate the reaction rate of ongoing reactions or
switching cycles to stabilize transient intermediates or con-
formers. Overall, the combined triple setup that includes
high-resolution NMR and UV/Vis spectroscopy and illumi-
nation with different wavelengths will allow for detailed
mechanistic and structural investigations in various research
fields.
[
3] a) H. Bartling, A. Eisenhofer, B. Kçnig, R. M. Gschwind, J. Am.
Chem. Soc. 2016, 138, 11860 – 11871; b) C. Feldmeier, H.
Bartling, K. Magerl, R. M. Gschwind, Angew. Chem. Int. Ed.
2015, 54, 1347 – 1351; Angew. Chem. 2015, 127, 1363 – 1367;
c) M. V. Gomez, A. Juan, F. Jimꢀnez-Mꢁrquez, A. de la Hoz,
A. H. Velders, Anal. Chem. 2018, 90, 1542 – 1546; d) D. M.
Schultz, F. Lꢀvesque, D. A. DiRocco, M. Reibarkh, Y. Ji, L. A.
Joyce, J. F. Dropinski, H. Sheng, B. D. Sherry, I. W. Davies,
Angew. Chem. Int. Ed. 2017, 56, 15274 – 15278; Angew. Chem.
2017, 129, 15476 – 15480; e) N. Mallo, P. T. Brown, H. Iranma-
nesh, T. S. C. MacDonald, M. J. Teusner, J. B. Harper, G. E. Ball,
J. E. Beves, Chem. Commun. 2016, 52, 13576 – 13579; f) J. Kind,
L. Kaltschnee, M. Leyendecker, C. M. Thiele, Chem. Commun.
ˇ
2
016, 52, 12506 – 12509; g) E. Prochꢁzkovꢁ, L. Cechovꢁ, J. Kind,
Z. Janeba, C. M. Thiele, M. Dra cˇ ꢂnsk y´ , Chem. Eur. J. 2018, 24,
92 – 498; h) A. Bahamonde, P. Melchiorre, J. Am. Chem. Soc.
4
2016, 138, 8019 – 8030; i) A. Mills, C. OꢃRourke, J. Org. Chem.
2015, 80, 10342 – 10345.
[
4] a) A. Seegerer, J. Hioe, M. M. Hammer, F. Morana, P. J. W.
Fuchs, R. M. Gschwind, J. Am. Chem. Soc. 2016, 138, 9864 –
9
873; b) N. Sorgenfrei, J. Hioe, J. Greindl, K. Rothermel, F.
Morana, N. Lokesh, R. M. Gschwind, J. Am. Chem. Soc. 2016,
38, 16345 – 16354; c) J. Greindl, J. Hioe, N. Sorgenfrei, F.
Morana, R. M. Gschwind, J. Am. Chem. Soc. 2016, 138, 15965 –
5971.
1
1
4
www.angewandte.org
ꢀ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2018, 57, 1 – 6
These are not the final page numbers!

Angewandte
Communications
Chemie
[
[
[
5] a) K. Chen, N. Berg, R. Gschwind, B. Kçnig, J. Am. Chem. Soc.
[11] a) J. Piard, J. Chem. Educ. 2014, 91, 2105 – 2111; b) J.-P. Sauvage,
2017, 139, 18444 – 18447; b) J. Dadovꢁ, S. Kꢄmmel, C. Feldmeier,
Angew. Chem. Int. Ed. 2017, 56, 11080 – 11093; Angew. Chem.
2017, 129, 11228 – 11242; c) C. Cheng, J. F. Stoddart, ChemPhys-
Chem 2016, 17, 1780 – 1793; d) B. L. Feringa, R. A. van Delden,
N. Koumura, E. M. Geertsema, Chem. Rev. 2000, 100, 1789 –
1816.
J. Cibulkovꢁ, R. Pa zˇ out, J. Maixner, R. M. Gschwind, B. Kçnig,
R. Cibulka, Chem. Eur. J. 2013, 19, 1066 – 1075; c) A. Eisenhofer,
J. Hioe, R. M. Gschwind, B. Kçnig, Eur. J. Org. Chem. 2017,
2194 – 2204.
6] a) R. Kaptein, J. Chem. Soc. D 1971, 732 – 733; b) M. Goez,
Annual Reports on NMR Spectroscopy, Elsevier, Amsterdam
[12] Combination of illumination and in situ UVNMR in the field of
photoswitches was already described by Gaeva et al. However,
detailed information about the setup is missing: E. B. Gaeva, V.
Pimienta, S. Delbaere, A. V. Metelitsa, N. A. Voloshin, V. I.
Minkin, G. Vermeersch, J. C. Micheau, J. Photochem. Photobiol.
A 2007, 191, 114 – 121.
[13] a) P. M. Tolstoy, B. Koeppe, G. S. Denisov, H.-H. Limbach,
Angew. Chem. Int. Ed. 2009, 48, 5745 – 5747; Angew. Chem. 2009,
121, 5855 – 5858; b) B. Koeppe, P. M. Tolstoy, H. H. Limbach, J.
Am. Chem. Soc. 2011, 133, 7897 – 7908.
2009, pp. 77 – 147; c) “Hyperpolarization Methods NMR Spec-
troscopy”: M. Goez, Topics in Current Chemistry, Springer,
Heidelberg 2012, pp. 1 – 32; d) I. Kuprov, M. Goez, P. A. Abbott,
P. J. Hore, Rev. Sci. Instrum. 2005, 76, 084103.
7] a) M. Enders in Modeling of Molecular Properties (Ed.: P.
Comba), Wiley-VCH, Weinheim, 2011, pp. 49 – 63; b) I. Bertini,
C. Luchinat, G. Parigi, R. Pierattelli, ChemBioChem 2005, 6,
1536 – 1549; c) I. Bertini, C. Luchinat, G. Parigi, E. Ravera,
NMR of Paramagnetic Molecules: Applications to Metallobio-
molecules and Models, Elsevier B.V., Amsterdam, 2017; d) F. H.
Kçhler, Encyclopedia of Magnetic Resonance, Wiley, Chichester,
[14] C. Feldmeier, H. Bartling, E. Riedle, R. M. Gschwind, J. Magn.
Reson. 2013, 232, 39 – 44.
[15] During the UV/Vis measurements the light of the illumination
fiber is turned off by the NMR console (pulse program).
[16] The methine proton of the isopropyl group is under one of the
DMF solvent signals and hence not further discussed.
[17] Owing to the charge-transfer complex formation even without
light, which causes severe line broadening of all PDI signals in
NMR spectra, a quantitative analysis could not be performed.
[18] C. Wolff, J. Kind, H. Schenderlein, H. Bartling, C. Feldmeier,
R. M. Gschwind, M. Biesalski, C. M. Thiele, Magn. Reson.
Chem. 2016, 54, 485 – 491.
2011; e) F. Rastrelli, A. Bagno, Chem. Eur. J. 2009, 15, 7990 –
8004.
[
8] a) I. Ghosh, T. Ghosh, J. I. Bardagi, B. Kçnig, Science 2014, 346,
25 – 728; b) L. Zeng, T. Liu, C. He, D. Shi, F. Zhang, C. Duan, J.
7
Am. Chem. Soc. 2016, 138, 3958 – 3961; c) I. Ghosh, B. Kçnig,
Angew. Chem. Int. Ed. 2016, 55, 7676 – 7679; Angew. Chem.
2016, 128, 7806 – 7810; d) M. Neumeier, D. Sampedro, M. Majek,
V. de la Pena OꢃShea, A. Jacobi von Wangelin, R. Pꢀrez-Ruiz,
Chem. Eur. J. 2017, 23, 1 – 5.
[
9] a) A. Graml, I. Ghosh, B. Kçnig, J. Org. Chem. 2017, 82, 3552 –
[19] A. A. Beharry, G. A. Woolley, Chem. Soc. Rev. 2011, 40, 4422 –
4437.
3
5
560; b) M. Poznik, B. Kçnig, React. Chem. Eng. 2016, 1, 494 –
00.
[
10] Recently a laser/EPR/low resolution NMR combination was
introduced to investigate photo-induced DNP on the solvent,
a potential combination of radicals, diamagnetic species and
light in solution. G. Liu, S.-H.- Liou, N. Enkin, I. Tkach, M.
Bennati, Phys. Chem. Chem. Phys. 2017, 19, 31823 – 31829.
Manuscript received: January 30, 2018
Version of record online: && &&, &&&&
Angew. Chem. Int. Ed. 2018, 57, 1 – 6
ꢀ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

Angewandte
Communications
Chemie
Communications
Spectroscopic Methods
In situ illumination-NMR-UV/Vis spec-
troscopy is presented as a tool to inves-
tigate light-induced processes by provid-
ing quantitative, time resolved, structural,
and mechanistic information. The inves-
tigations show a light-triggered conPET
process and temperature-dependent rate
modulation of a photoswitch.
A. Seegerer, P. Nitschke,
R. M. Gschwind*
&&&& — &&&&
Combined In Situ Illumination-NMR-UV/
Vis Spectroscopy: A New Mechanistic
Tool in Photochemistry
6
www.angewandte.org
ꢀ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2018, 57, 1 – 6
These are not the final page numbers!