Versatile Open-Source Photoreactor Architecture for Photocatalysis across the Visible Spectrum

Article abstract of DOI:10.1021/acs.orglett.1c01910

Adoption of commercial photoreactors as standards for photocatalysis research could be limited by high cost. We report the development of the Wisconsin Photoreactor Platform (WPP), an open-source photoreactor architecture potentially suitable for general

Full text of DOI:10.1021/acs.orglett.1c01910

pubs.acs.org/OrgLett
Letter
Versatile Open-Source Photoreactor Architecture for Photocatalysis
Across the Visible Spectrum
Philip P. Lampkin, Blaise J. Thompson, and Samuel H. Gellman*
Cite This: Org. Lett. 2021, 23, 5277−5281
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ABSTRACT: Adoption of commercial photoreactors as standards for
photocatalysis research could be limited by high cost. We report the
development of the Wisconsin Photoreactor Platform (WPP), an open-
source photoreactor architecture potentially suitable for general adoption.
The WPP integrates inexpensive commercial components and common
high-intensity LEDs in a 3D-printed enclosure. Dimensions and features
of WPP reactors can be readily varied and configurations easily
reproduced. WPP performance is evaluated using literature trans-
formations driven by light of disparate wavelengths.
rigid enclosure and exchangeable, high-power photon sources to
improve reproducibility and reliability relative to ad hoc
experimental setups. However, the adoption of these reactors
as standards can be limited by their high cost. This problem is
compounded by the significant cost of acquiring multiple
proprietary photon sources when different emission profiles are
required.8
Here, we describe the Wisconsin Photoreactor Platform
(WPP), an economical source of high-performance photo-
reactors that can be easily fabricated, readily modified, and
precisely documented (Figure 1). This platform provides
reactors constructed from commercial components in a 3D-
printed enclosure. The WPP is designed around inexpensive
surface-mount LEDs as the light source. All design files are open-
source to maximize transferability. A specific reactor with
bespoke physical parameters can be fabricated by an
experimentalist with no prior experience in less than a day
(instructions in Supporting Information). The WPP is modular
and allows photoreactor capabilities to be expanded by use of a
well-established array of compatible electronic peripherals.
These factors combine to provide a versatile architecture that
could contribute to the standardization of photochemical
protocols and enhance the discovery and optimization of new
photochemical reactivity.
odern photocatalytic methods allow for formation of
1
Motherwise inaccessible products under mild conditions.
This capability has generated significant interest in the field of
visible-light photocatalysis2 and led many laboratories to explore
incorporation of photocatalysis into their work.
Photochemical transformations can be significantly affected
by small changes in experimental configuration.3 The number of
photons absorbed by the reaction mixture depends, in part, on
the intensity and emission profile of the light source as well as
the physical surroundings of the reaction vessel.4 These factors
make careful apparatus design and documentation essential for
reproducible photoreaction outcomes and reliable reaction
discovery.
Many approaches have been used to deliver photons to
reaction vessels, but no single, standardized approach has seen
widespread adoption to date.4 Operational variation can hinder
the reproduction of reported transformations, the description of
which may include only minimal characterization of light source
or documentation of experimental setup.4,5 Entry of new
researchers into this field and introduction of photoreactions
into the chemistry curriculum should be facilitated by
photoreactor platforms that enable accurate reproduction of
the apparatus employed in a published study, facilitate apparatus
customization for new applications in photocatalysis, and
streamline the documentation of apparatus modifications. The
work reported here is intended to achieve these goals.
Received: June 8, 2021
Published: June 23, 2021
Over the past few years, several commercial photoreactors
designed to address problems outlined above have been
reported.3,5,6 More recently, an open-access 3D-printed
enclosure for temperature-controlled photoreactions utilizing
expensive commercial light-emitting diode (LED) lamps was
detailed by Schiel and co-workers.7 These reactors integrate a
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A 3D-printed enclosure was designed to house a LED star and
multiple reaction vials (Figure 3A). As shown in Figure 1, this
Figure 1. Cutaway view of the Wisconsin Photoreactor Platform
architecture with labeled components. Estimated component cost is in
U.S. dollars as of June 2021.
We viewed the photon source as the most important
component of the WPP. An ideal source would be limited to
the wavelength range necessary to drive an intended trans-
formation. Sources that emit light in a narrow wavelength range
minimize undesired heating and side reactions.9 Therefore, we
were drawn to single-color LEDs rather than broadly emitting
light sources, such as compact fluorescent lights (CFL) (Figure
2A). High-intensity LEDs with narrow emission profiles across
the visible range are available in inexpensive commercial
packages (Figure 2B,C). Access to defined but diverse photon
sources is important for new reaction discovery, as demon-
strated by recent reports of red and near-infrared (NIR) light
photocatalysts.10,11 Commercial high-intensity LEDs have seen
use in several recent studies of photocatalysis.12
Figure 3. (A) Assembled WPP device. (B) Single and multiple reaction
configurations of a WPP device fitted with a 4 mL vial holder and
reaction chamber module. (C) Illustration of WPP expandability using
optional driver boards.
enclosure is composed of a compact base, a reaction chamber,
and a vial holder. These three components fit together rigidly,
which ensures reproducibility of reaction vessel placement
relative to the photon source. Chambers and vial holders with
different physical parameters can be designed, printed, and
exchanged with one another, which allows the experimentalist to
use a variety of vessels. These designs can be documented in
research publications to facilitate transferability to other
laboratories. We provide printable modules for various common
reaction vessels and a light-blocking cover for WPP devices in
the Supporting Information.
The vial holders we have designed allow illumination of
several vials equally, for rapid screening of experimental
variables, or a single vial, for greatest light exposure (Figure
3B). The photoreactor incorporates a commercial aluminum
heatsink and low-profile computer fan to cool the LED and
reaction vessels. Standard lab stir plates can be used with the
small-footprint WPP architecture.
To support kinetics studies or screening of reaction
conditions, we designed a custom driver board to control
operation of multiple WPP devices simultaneously. Reactors
fitted with these boards can be connected in-series to a single
power source and control unit (Figure 3C). The control unit can
then “supervise” the light intensity and fan speed of each WPP
device via I2C, a commonly used protocol for communication
among digital integrated circuits.13 If extended functionality is
needed, any I2C-compatible peripherals could be connected to
the driver board for use with the WPP architecture. Many I2C-
compatible devices and sensors are commercially available,
including thermocouple adapters for temperature monitoring.14
For work not requiring such control and expandability, a
standard 1000 mA LED driver can be used. A simplified driver
board offering control over light intensity using only a
potentiometer is described in the Supporting Information.
Our intention is to make the WPP architecture suitable as an
open standard, with specific reactors easily producible by any
Figure 2. (A) Comparison of emission spectra of 450 nm Cree, Inc. XT-
E royal blue LED and ALZO Digital full spectrum CFL bulb. (B)
Industry-standard LED star mounted with 450 nm Cree, Inc. XT-E
LEDs. (C) Emission spectra of commercial LEDs purchased from
manufacturers Cree, Inc., Luxeon, and Inolux.
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Figure 4. Time studies of six literature photochemical reactions illustrating performance of the WPP platform relative to typical experimental setups.
All reactions were conducted in 4 mL vials with ∼1 to 2.5 mL of reaction volume. For exact conditions and procedures, see the Supporting Information.
Yields were determined by 1H or 19F NMR analysis of crude reaction mixtures using mesitylene or trifluorotoluene as an internal standard. (*) The
“WPP − 450 nm − Single Reaction” benchmark was conducted in a 4 °C refrigerator at 90% light intensity.
chemist. Toward that end, we have included our enclosure and
electronics design files as well as detailed component sourcing
and fabrication instructions in the Supporting Information. A
“living” online repository to which users can contribute custom
WPP modules is provided.15 3D printers and 3D-printing
services are readily available. We have found that the enclosure
can be fabricated using a variety of affordable 3D printers.
Commercial small-scale printed circuit board fabrication is
inexpensive and widely available. Our driver boards can be
assembled quickly without specialized tools. These features
should encourage adoption of the WPP.
reaction and multiple reaction configurations shown in Figure
3B was evaluated.
In presenting the results in Figures 4 and 5, we do not mean to
imply that the WPP is the best way to conduct any particular
photochemical reaction. Instead, we offer these data to suggest
that use of the WPP platform is likely to provide good results for
a wide range of photochemical transformations. In addition,
because the specifics of a WPP device can be easily varied and
documented, results achieved with this approach can be readily
reproduced in other laboratories. These features may be
particularly useful for researchers seeking to initiate studies in
this important field.
To establish the versatility and reliability of the WPP
architecture relative to typical experimental setups, we applied
this approach to six reactions from the recent photocatalysis
literature that are driven by light of disparate wavelengths.
Photoreaction apparatuses used for comparison were derived
from setups reported in the literature (see Supporting
Information). WPP device performance across both the single
The first “benchmark” process was the C−N cross-coupling of
4-bromobenzotrifluoride and morpholine via the photoexcita-
tion of nickel-amine complexes with ultraviolet A (UVA) light,
as described by Miyake et al. (Figure 4A).12a In both single- and
multiple-reaction configurations, a WPP device fitted with a 365
nm LED star decreased reaction time relative to a more
conventional apparatus fashioned from a commercial UV light
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trimethoxybenzene using the method reported by Li and co-
workers (Figure 4D).18 A WPP device with 450 nm LEDs
yielded product faster and in higher yield than did conventional
experimental setups involving a Kessil A160WE LED lamp, a
450 nm LED strip reactor, or a CFL bulb. Six reactions of this
type simultaneously carried out using a WPP device in the
multiple reaction configuration exhibited a consistent reaction
profile, indicating the reliability of the WPP architecture (Figure
S22). The same trend was observed when the protocol of
Stephenson et al. for trifluoromethylation of 2-acetyl-N-Boc-
pyrrole was evaluated (Figure 4E).19 Finally, the metal-
lophotoredox-catalyzed C−N cross-coupling of 4-bromobenzo-
trifluoride and morpholine of MacMillan et al. revealed a similar
trend (Figure 4F).20 Across all three blue-light reactions, both
WPP configurations offered superior performance relative to the
conventional experimental setups tested and similar perform-
ance to that reported for the photoreactor described by
MacMillan and co-workers (Figures S24−S26). In all cases,
yields obtained using a WPP device matched those achieved
with a commercial photoreactor.
As an additional test of architecture generality, we evaluated
WPP performance across a series of typical laboratory reaction
scales (Figure 5). Using the photocatalytic trifluoromethylation
of N-methyl-2-pyridone as a testbed, we conducted reactions at
0.1, 0.3, 1.0, and 2.0 mmol scale in a WPP device fitted with a
730 nm LED star. Enclosure modules for each scale were
designed to standardize reaction vessel placement across all
trials. In all cases, product was generated in ∼50% yield after 2 h.
Increases in reaction scale up to 20-fold relative to the initial 0.1
mmol trial reaction were accommodated without loss of
performance.
We have developed an open-source photoreactor platform
that enables rapid progress in cutting-edge photocatalysis
research and has a low barrier for adoption. The Wisconsin
Photoreactor Platform is inexpensive, adaptable, and highly
featured; therefore, the WPP should foster standardized
experimental protocols and reproducibility. We have demon-
strated the favorable performance of WPP devices across a series
of benchmark photoreactions using UVA, violet, NIR, and blue
light as well as in reaction scale-up. The WPP architecture meets
the need for a standardized approach to experimental apparatus
that is versatile, reliable, can be precisely documented and easily
reproduced, and is economically accessible to a broad
community of researchers.
Figure 5. Results of scale-up trials. Reactions conducted at indicated
scales using listed reaction vessel sizes over 2 hours. Yields were
determined by 19F NMR analysis of crude reaction mixtures using
trifluorotoluene as an internal standard.
curing chamber.16 With the WPP approach, reaction completion
was reached in 2 or 4 h with 96% yield for the single- or multiple-
reaction configuration, respectively, reproducing the yield
reported by Miyake. The UV chamber achieved only 53%
yield after 4 h of illumination.
Synthesis of 3,4-benzocoumarin using violet light and the
vitamin photocatalysis strategy detailed by Gilmour et al. was
examined next (Figure 4B).12b Using a standard 400 nm LED
strip reactor, based on the design of Stephenson et al.,17 we
obtained <5% yield after 8 h of continuous illumination. In
contrast, a WPP device with a 395 nm light source provided 75%
yield across single- and multiple-reaction configurations after 8
h, matching the literature yield and indicating the robust
performance of the WPP architecture in this transformation.
The single-reaction configuration achieved 72% yield after only
2 h.
Inspired by the recent report of Rovis et al. on the
development of NIR photocatalysts,11 we examined their Os-
photocatalyzed trifluoromethylation of N-methyl-2-pyridone
using a WPP device with a 730 nm LED star (Figure 4C). Both
WPP configurations provided faster product formation than did
a 630 nm LED strip photoreactor, despite stronger absorption of
the Os(tpy)2(PF6)2 photocatalyst at 630 nm.11 The trifluor-
omethylated product was generated in 48% yield with both WPP
configurations after 2 h of illumination, while the LED strip
reactor provided 35% yield. The yield obtained using a WPP
device closely agreed with the yield reported by Rovis and co-
workers.11
We note that the comparison setups we used for the reactions
in Figure 4A−C are not the specialized setups described in the
original reports. Our goal in this work is to show that the WPP is
effective across a range of photoreactions rather than to
determine whether this architecture provides the best possible
way to conduct any particular photoreaction.
ASSOCIATED CONTENT
* Supporting Information
■
sı
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.1c01910.
Photon source characterization data, experimental details,
and NMR spectra (PDF)
Wisconsin Photoreactor Platform apparatus fabrication
and operation instructions (PDF)
Wisconsin Photoreactor Platform project repository at
time of publication (ZIP)
AUTHOR INFORMATION
Corresponding Author
■
We explored reactor efficacy with three blue light photo-
reactions previously used by MacMillan et al. to benchmark a
commercial photoreactor.3 We first tested our platform’s
performance in catalyzing the trifluoromethylation of 1,3,5-
Samuel H. Gellman − Department of Chemistry, University of
Wisconsin, Madison, Wisconsin 53706, United States;
orcid.org/0000-0001-5617-0058; Email: gellman@
chem.wisc.edu
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Authors
pubs.acs.org/OrgLett
Letter
redox- and Photoelectrochemical Synthesis. ChemPhotoChem. 2021, 5
(5), 431−437.
Philip P. Lampkin − Department of Chemistry, University of
Wisconsin, Madison, Wisconsin 53706, United States;
orcid.org/0000-0002-6908-9619
Blaise J. Thompson − Department of Chemistry, University of
Wisconsin, Madison, Wisconsin 53706, United States;
orcid.org/0000-0002-3845-824X
(8) The Penn PhD Photoreactor MK 2, the precursor of which was
reported in ref 3, is available with a 450 nm light source from Sigma
Aldrich Millipore for $4910 USD as of 2021. Photon sources emitting
420 or 365 nm light are sold separately for $752 USD each. See:
https://www.sigmaaldrich.com/catalog/product/sial/z744035.
(9) Protti, S.; Ravelli, D.; Fagnoni, M. Wavelength Dependence and
Wavelength Selectivity in Photochemical Reactions. Photochem.
Photobiol. Sci. 2019, 18 (9), 2094−2101.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.orglett.1c01910
(10) (a) Mei, L.; Veleta, J. M.; Gianetti, T. L. Helical Carbenium Ion:
A Versatile Organic Photoredox Catalyst for Red-Light-Mediated
Reactions. J. Am. Chem. Soc. 2020, 142 (28), 12056−12061. (b) Bilger,
J. B.; Kerzig, C.; Larsen, C. B.; Wenger, O. S. A Photorobust Mo(0)
Complex Mimicking [Os(2,2′-Bipyridine)3]2+and Its Application in
Red-to-Blue Upconversion. J. Am. Chem. Soc. 2021, 143 (3), 1651−
1663.
(11) Ravetz, B. D.; Tay, N. E. S.; Joe, C. L.; Sezen-Edmonds, M.;
Schmidt, M. A.; Tan, Y.; Janey, J. M.; Eastgate, M. D.; Rovis, T.
Development of a Platform for Near-Infrared Photoredox Catalysis.
ACS Cent. Sci. 2020, 6 (11), 2053−2059.
(12) The following references describe using high-intensity
commercial LEDs in custom experimental setups for photocatalysis
research: (a) Lim, C. H.; Kudisch, M.; Liu, B.; Miyake, G. M. C-N
Cross-Coupling via Photoexcitation of Nickel-Amine Complexes. J.
Am. Chem. Soc. 2018, 140 (24), 7667−7673. (b) Morack, T.;
Metternich, J. B.; Gilmour, R. Vitamin Catalysis: Direct, Photocatalytic
Synthesis of Benzocoumarins via (−)-Riboflavin-Mediated Electron
Transfer. Org. Lett. 2018, 20 (5), 1316−1319. (c) Bosque, I.; Bach, T.
3-Acetoxyquinuclidine as Catalyst in Electron Donor-Acceptor
Complex-Mediated Reactions Triggered by Visible Light. ACS Catal.
2019, 9 (10), 9103−9109. (d) Elliott, L. D.; Kayal, S.; George, M. W.;
Booker-Milburn, K. Rational Design of Triplet Sensitizers for the
Transfer of Excited State Photochemistry from UV to Visible. J. Am.
Chem. Soc. 2020, 142 (35), 14947−14956.
(13) Prabhu, G. R. D.; Urban, P. L. Elevating Chemistry Research with
a Modern Electronics Toolkit. Chem. Rev. 2020, 120 (17), 9482−9553.
(14) I2C-compatible peripherals are available from vendors:
(a) https://www.sparkfun.com/. (b) https://www.adafruit.com.
(c) https://www.seeedstudio.com/.
(15) Users of the WPP can contribute custom modules, electronics
and other designs to the WPP repository for others to use. See https://
github.com/uw-madison-chem-shops/wisconsin-photoreactor.
(16) Aung, T.; Liberko, C. A. Bringing Photochemistry to the Masses:
A Simple, Effective, and Inexpensive Photoreactor, Right out of the Box.
J. Chem. Educ. 2014, 91 (6), 939−942.
(17) Douglas, J. J.; Albright, H.; Sevrin, M. J.; Cole, K. P.; Stephenson,
C. R. J. A Visible-Light-Mediated Radical Smiles Rearrangement and Its
Application to the Synthesis of a Difluoro-Substituted Spirocyclic ORL-
1 Antagonist. Angew. Chem., Int. Ed. 2015, 54 (49), 14898−14902.
(18) Li, L.; Mu, X.; Liu, W.; Wang, Y.; Mi, Z.; Li, C. J. Simple and
Clean Photoinduced Aromatic Trifluoromethylation Reaction. J. Am.
Chem. Soc. 2016, 138 (18), 5809−5812.
(19) Beatty, J. W.; Douglas, J. J.; Miller, R.; McAtee, R. C.; Cole, K. P.;
Stephenson, C. R. J. Photochemical Perfluoroalkylation with Pyridine
N-Oxides: Mechanistic Insights and Performance on a Kilogram Scale.
Chem. 2016, 1 (3), 456−472.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank Professors Tehshik Yoon and AJ Boydston of UW-
Madison for helpful discussions. We are grateful to Dr. Ilia A.
Guzei (UW-Madison) for photography assistance, the Weix and
Stahl laboratories (UW-Madison) for sharing reagents, and the
Goldsmith group (UW-Madison) for use of a spectrometer. We
thank Sebastian Thompson (UW-Madison) for help fabricating
custom LED stars, UW-Madison organic chemistry lab teaching
staff for donation of a UV chamber, and Martin Csanaki (Opel
Szentgotthárd Kft.) for provision of a computer fan model. This
research was supported in part by the U.S. National Science
Foundation (CHE-1904940). Spectroscopic instrumentation
was supported by the UW-Madison Instructional Laboratory
Modernization Award and NIH Grant No. 1S10 OD020022-1.
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