Light-induced Ligation of o-Quinodimethanes with Gated Fluorescence Self-reporting

Article abstract of DOI:10.1021/jacs.0c02002

We introduce a highly efficient photoligation system, affording a pro-fluorescent Diels-Alder product that, on demand, converts into an intensively fluorescent naphthalene via E1 elimination in the presence of catalytic amounts of acid. The Diels-Alder reaction of the photocaged diene (o-quinodimethane ether or thioether) with electron-deficient alkynes is induced by UV or visible light. In contrast to previously reported ligation techniques directly leading to fluorescent products, the fluorescence is turned on after the photoligation. Thus, the light absorption of the fluorophore does not undermine the photoligation via competitive absorption, and as a result, photobleaching or side reactions of the fluorophore are not observed. Critically, the gated generation of a fluorescent product allows for fluorometric determination of the conversion. We employ a simple synthesis strategy for heterobifunctional electron-deficient alkynes allowing for facile functionalization of payload molecules.

Full text of DOI:10.1021/jacs.0c02002

Subscriber access provided by University of Birmingham
Communication
Light Induced Ligation of o-Quinodimethanes
with Gated Fluorescence Self-Reporting
Florian Feist, Leona Lucas Rodrigues, Sarah L Walden, Tim W. Krappitz, Tim R. Dargaville,
Tanja Weil, Anja S. Goldmann, James P. Blinco, and Christopher Barner-Kowollik
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.0c02002 • Publication Date (Web): 15 Apr 2020
Downloaded from pubs.acs.org on April 15, 2020
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a service to the research community to expedite the dissemination
of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in
full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully
peer reviewed, but should not be considered the official version of record. They are citable by the
Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore,
the “Just Accepted” Web site may not include all articles that will be published in the journal. After
a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web
site and published as an ASAP article. Note that technical editing may introduce minor changes
to the manuscript text and/or graphics which could affect content, and all legal disclaimers and
ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or
consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 6
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
Light Induced Ligation of o-Quinodimethanes with Gated Fluores-
cence Self-Reporting
†
†
†
‡
Florian Feist,† §≠ Leona L. Rodrigues,† ≠ Sarah L. Walden, Tim W. Krappitz, Tim R. Dargaville,
‡
‡
‡
‡
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
§
†
†
†
‡
‡
‡
Tanja Weil, Anja S. Goldmann,* James P. Blinco,* and Christopher Barner-Kowollik*
† Centre for Materials Science, Queensland University of Technology, 2 George Street, Brisbane, QLD 4000 (Australia).
‡ School of Chemistry and Physics, Queensland University of Technology, 2 George Street, Brisbane, QLD 4000 (Australia).
§Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
≠ THESE AUTHORS CONTRIBUTED EQUALLY
ABSTRACT: We introduce a highly efficient photoligation system, affording a pro-fluorescent Diels-Alder product which on de-
mand converts into an intensively fluorescent naphthalene via E1-elimination in the presence of catalytic amounts of acid. The Diels-
Alder reaction of the photocaged diene (o-quinodimethane ether or thioether, o-QDMs) with electron deficient alkynes is induced by
UV or visible light. In contrast to previously reported ligation techniques directly leading to fluorescent products, the fluorescence is
turned on after the photoligation. Thus, the light absorption of the fluorophore does not undermine the photoligation via competitive
absorption and as a result, photobleaching or side reactions of the fluorophore are not observed. Critically, the gated generation of a
fluorescent product allows for fluorometric determination of the conversion. We employ a simple synthesis strategy for heterobifunc-
tional electron deficient alkynes allowing for facile functionalization of payload molecules.
Photocaged dienes based on o-methylbenzaldehydes (o-MBAs)
are frequently used in various applications, such as polymer net-
work formation1, single chain nanoparticle (SCNP) folding2,
3D-laser writing3 and many more, as they offer the attractive
feature of spatio-temporal control and serve as indispensable
tool in contemporary polymer and supramolecular chemistry.4-
7 A limitation of the ligation of o-MBAs and electron deficient
enes is the lack of a simple visual feedback that allows for mon-
itoring the reaction progress and selectivity in solution and on
surfaces.8 Many common photoinduced reactions, for instance
the nitrile imine tetrazole ene-reaction click reaction (NITEC),9
or the reaction of photocaged naphtoquinone-3-methides (o-
MQMs) with vinylethers10,11 form fluorescent products (pyra-
zoles, pyrazolines and naphtalenes, respectively). Despite this
advantage, the direct formation of reaction products that either
absorb in the same region or are red-shifted in their absorption
compared to their starting materials, represents a considerable
challenge. The competitive absorption of photons by the reac-
tion products, decreases the apparent quantum yield of the re-
action12 and potentially lead to secondary reactions or photo-
bleaching.13 In particular for the synthesis of materials such as
polymer conjugates,1 functionalized surfaces,14 microspheres,15
sequence-defined macromolecules16 or SCNPs,17 competitive
absorption presents a key challenge and limits the selectivity
and control over the reaction. Herein, we present a strategy us-
ing electron deficient alkynes as dienophiles forming pro-fluo-
rescent 1,4-dihydro-1-naphtholes. The naphtholes do not absorb
in the wavelength range where the respective o-MBAs are acti-
vated. After the completion of the photoreaction, highly fluo-
rescent naphthalenes are generated rapidly and quantitatively
by adding catalytic amounts of acid. The result is a photoreac-
tion that is not disturbed by competitive absorption and is read-
ily traceable by fluorescence spectroscopy due to the controlled
formation of the fluorophore.
Previous works18-22
EWG
EWG
R1
R1
R1
X
X
O
HO Ph
O
O
EWG
EWG
EWG
EWG
h
Ph
ν
ν
h
non fluorescent
X = O, S
This work
R1
EWG
R2
R1
R1
X
O
X
OH
R2
X
[H+]
ambient
R2
ν
h
EWG
non fluorescent
EWG
temperature
fluorescent
X = O, S
Scheme 1: (Top) Previous works using o-MBAs and electron deficient al-
kenes, or o-methylbenzophenones and alkynes.18-22 (Bottom) Approach to
fluorescent naphtalenes via non-fluorescent and blue-shifted 1,4-Dihydro-
1-naphtholes. EWG: electron withdrawing group.
The reaction of photocaged o-QDMs and electron deficient al-
kynes was first described by Porter and Tchir.23 Wallace and
coworkers investigated the reaction further and described the
isolation of the naphthalenes after reflux in xylene with yields
below 40%.18 Based on this pioneering work, the reaction of 2-
methyl benzophenones with alkynes was used frequently in
synthesis, for instance to obtain 3-aroylchromones, benzo[e]py-
rene bisimides and anthracene diimides using a vast excess of
alkynes, strong acids, aprotic solvents and elevated tempera-
tures.19-21 Therefore, all the above mentioned reactions are of
ACS Paragon Plus Environment

Journal of the American Chemical Society
limited use for the synthesis of advanced macromolecular ar-
Page 2 of 6
associated with the formation of C2. After on demand elimina-
tion, a new n-π* band at 345 nm and a fluorescence band at 420
nm was observed, corresponding to D2. The absorption spectra
impressively show that the intermediate C2 does not interfere
with the photoreaction as its absorption is shifted to shorter
wavelengths. As the stability of C2 was limited in ACN due to
the extremely rapid elimination, 13C and 2D-NMR spectra were
recorded in C6D6 where C2 was observed to be stable (see Sup-
porting Figs. S25-S26). The substrate scope for the reaction was
investigated using o-MBAs A1 and A2, which exhibit distinc-
tive absorption and reactivity and can be readily functional-
ized.7 Alkynes B1-B5 and diynes B6-B7 are model substrates
and functional analogues can be synthesized using different
strategies. Terminal alkynes similar to methyl propiolate B1
and phenylalkynes similar to B3 can be readily prepared using
propiolic acid or phenylpropiolic acid as precursors, respec-
tively. The synthesis of functional analogues of dimethyl acet-
ylenedicarboxylate (DMAD, B2) is considerably more diffi-
cult.25 4-oxo-2-butynoates B4 and B5 are readily accessible via
Cu(I) mediated sp-sp2 coupling of acid halides and propio-
lates.26, 27 Symmetric and non-symmetric diynes B6 and B7 can
be synthesized via different sp-sp coupling reactions and rear-
rangements.28 Hay coupling appeared most attractive as pro-
ceeds in the absence of reactive organometallic compounds.29
The synthesis and characterization of A2, B4-B7 are described
in the Supporting Information (Section 2.2-2.3). In Scheme 2,
the observed reaction products are depicted and summarized in
Table 1.
1
2
3
4
5
6
7
8
chitectures including acid or heat sensitive structures in partic-
ular for bioconjugates. Bioorthogonal reactions require an ex-
ceptional level of chemical selectivity and mild reaction condi-
tions resulting in minimal interference with existing functional
groups in biomolecules.24 Furthermore, no heterobifunctional
(non-symmetric) alkyne substrates have been reported for this
reaction, rendering the synthesis of modular linker molecules
unexplored. To overcome the limitations described above, we
exploit the high driving force towards aromatization of 1,4-di-
hydro-1-naphtholes (DHNPs). We establish which substrates
allow for efficient reaction under mild reaction conditions at
concentrations suitable for polymer post-functionalization or
bioligation (0.5 mmol L-1 to 50 mmol L-1). Furthermore, we es-
tablished synthesis strategies for heterobifunctional alkynes
linkers. Initially, o-MBA (A125, 1.00 eq., 50 mmol L-1) and the
electron deficient acetylenedicarboxylic acid dimethylester
(DMAD, B2, 1.05 eq, 52.5 mmol L-1) are irradiated with a
385 nm LED in deuterated acetonitrile after deoxygenation.
The formation of the intermediate DHNP (C2) was observed
via 1H-NMR (Figure 1). Upon exposure to air and therefore for-
mation of carbonic acid by absorption of CO2, the naphthalene
D2 was formed quantitatively within four hours via E1-elimi-
nation. Additionally, the conversion was directly followed by
the disappearance of the UV-Vis n-π* band at 320 nm of o-
MBA and the appearance of a new absorption band at 280 nm
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
O
A1 + B2
2
1
2
O
3
5
A1
1
4
O
O
4
3
O
5
B2
O
C2
D2
385 nm CH3CN-d3
2
O
O
O
H
1
4
OH
5,3
O
2'
1
2'
2
O
H
3
5
C2
4
H+
O
O
2
O
1
1
O
4,5
O
2
3
3
5
D2
4
10
9
8
7
6
5
4
3
2
δ / ppm
Figure 1 (Left) 1H-NMR spectra of the reaction between o-MBA A1 and B2 to form cycloadduct C2 under irradiation with 385 nm
LED (LED-emission spectrum refer to supporting Fig. S69) and E1-Elimination to D2 with assigned resonances. (Right) UV-VIS
absorption and fluorescence emission spectra of the reaction mixture (black line), after up to 20 minutes of irradiation with 385 nm
in the quartz cuvette (black to red line) and after addition of 10 mmol% p-TsOH and up to 12 minutes (red to blue line). For detailed
analytical information for all compounds depicted in Fig. 1 refer to supporting Figs. S25, 26, 29, 30, 57, and 67.
ACS Paragon Plus Environment

Page 3 of 6
Journal of the American Chemical Society
Table 1: Batch photoligation experiments using o-MBAs A1, A2 (5 mmol
If an alkyne with reduced reactivity is present, a fraction of o-
MBA A is converted to benzocyclobutane E upon irradiation.
This side-reaction was previously described when we studied
the photoinduced [4+4]-cycloaddition of o-MBAs.30
L-1, 1.00 eq.) and alkynes B1-B5 (5.5 mmol L-1, 1.10 eq.) or diynes B6-B7
(5.5 mmol L-1, 1.10 eq.), irradiation time (t), YD isolated yield. D/E: ratio of
the desired Diels-Alder adduct vs. the 4π electrocyclization (refer to
Scheme 2). D/D’ ratio of regioisomers.
1
2
3
4
5
6
7
8
9
Importantly, the ratio of Diels-Alder product C/C’ and 4π elec-
trocyclization product E is concentration dependent (unimolec-
ular vs. bimolecular reaction). Furthermore, regioisomers C/C’
or D/D’ can be formed in the case of non-symmetric alkynes.
No o-MBA Alkyne Solvent t [min] D/E YD
D/D’
1
2
3
4
5
7
6
8
9
A1
A1
A1
A1
A2
A2
A2
A1
A1
B1
B1
B2
B2
B1
B2
B2
B3
B4
B4
B5
B5
B4
B4
B5
B5
B6
B7
ACN
Toluene 15
ACN 20
20
32:68 25% 100:0
76:24 71% 100:0
n.d. 96% --
R1
R1
X
OH
X
R2
R2
[H+]
X = O, S
R1
X
B
CO2Me
Toluene 15
Toluene 30
n.d. 97% --
CO2Me
CO2Me
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
C
D
R2
R1
O
5:95 --
13:87 --
100:0
--
R1
R1
ν
h
X
OH
X
ACN
30
A
X
CO2Me
[H+]
R2
CO2Me
R2
ν
h
OH
Toluene 30
Toluene 30
91:9 89% --
-- 0% --
E
C'
D'
ACN
Toluene 20
ACN 20
Toluene 15
ACN 40
Toluene 20
ACN 40
30
n.d. 98% 70:30
n.d. 97% 65:35
n.d. 95% 92:8
n.d. 96% 87:13
97:3 94%a 66:34
99:1 96%a 54:46
n.d. 94%a 93:7
n.d. 86%a 76:24
n.d. 96% 99:1
55:45 49% n.d.
Scheme 2: Light induced reaction pathways of o-MBAs A in the presence
of electron deficient alkynes B to form 1,4-dihydro-1-naphtholes C via
Diels-Alder reaction or 1-hydroxybenzocyclobutanes E via [4π] electrocy-
clization. 1,4-dihydro-1-naphtholes C can be converted quantitatively to
napthalenes D with catalytic amounts of acid.
10 A1
11 A1
12 A1
13 A2
14 A2
15 A2
16 A2
17 A1
18 A1
The experiments summarized in Table 1 were conducted in a
batch reactor (setup described in supporting Fig. S1) to facilitate
isolation and characterization via NMR spectroscopy and
LCMS (supporting Figs. S27-55 and Figs. S56-S66). The two
solvents, acetonitrile and toluene, were chosen to determine the
influence of the dipole moment on the reaction. By comparing
entry 1 and 2 or 3 and 4, it can be concluded that the ligation
reactions of both o-MBAs with alkynes is more efficient in tol-
uene. The more electron rich B3 and to a lesser extent B1 ex-
hibit low reactivity and therefore result in the formation of ben-
zocyclobutanes (see entries 1, 2, 5, 8). The same result can be
observed comparing diynes B6 and B7 (entry 15, 16). o-MBA
A1 is more reactive than o-MBA A2 resulting in a lower extent
of benzocyclobutane formation (comparison of entries 3 and 7).
In general, 4-oxo-2-butynoates B4 and B5 showed the highest
reactivity and no 4π-electrocyclization was observed as a result.
The regioselectivity (ratio of C/C’ and D/D’) is influenced by
the steric hindrance and the electronic properties. For the sub-
strate combination A2 and B4 as well as A2 and B5, the result-
ing products D8, D8’, D9 and D9’ were separated and their
structure elucidated via 2D-NMR spectroscopy. In addition, the
reaction quantum yields for the reaction of A1, A2 and B4 were
determined employing a monochromatic light source (refer to
supporting Figs. S87-90). Whereas A1 shows a minor depend-
ence on the solvent dipole moment (ΦR,ACN: 0.68 ± 0.02 vs.
ΦR,toluene: 0.78 ± 0.03), the reaction quantum yield of A2 is
Toluene 20
Toluene 30
Toluene 30
a) combined yield after regioisomer separation
Most fluorophores depicted in Figure 2 do not have structural
analogues reported in literature, therefore the fluorescence
quantum yields were determined (refer to supporting Fig. S71).
The emission wavelength of the naphthyl thioethers are in gen-
eral higher than their naphthylether analogues (fluorescence
spectra of D1-D11 see supporting Figs. S72-S82). In addition,
the photostability of the formed fluorophores was studied. D1,
D2, D7 and D10 were irradiated under conditions similar to the
photoligation (5 mmol L-1, ACN-d3, 385 nm LED and 365 nm
LED respectively, NMR spectra see supporting Figs. S51-S55).
D1, D2 and D7 showed high photostability, whereas D10 was
completely converted to various unknown products. This result
underlines the advantage of the formation of a non-absorbing
intermediate during the photoreaction, avoiding subsequent re-
action or photobleaching.
highly solvent dependent (ΦR,ACN: 0.011 ± 0.001 vs. ΦR,toluene
:
0.14 ± 0.01)
O
CO2Me
MeO2C
B2
CO2Me
Ph
CO2Me
O
CO2Me
CO2Me
O
S
H
CH3
A1
A2
B1
B3
B4
MeO2C
CO2Me
Ph
O
B6
O
B5 Ph
MeO2C
B7
Scheme 3: Overview of the o-MBAs A1, A2 and the alkynes B1-7 utilized
in the batch reactions.
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 4 of 6
Bu
O
O
O
O
O
O
S
O
O
O
1. BuLi, -78 °C
2. LiBr, BF3*Et2O
-50 °C
HO
+
OH
TsOH
H
O
1
O
O
4
O
O
O
O
+
O
O
2
3
O
OH
L2
60 °C, 3 d
O
THF
HO
OH
O
O
D1 λΕmax: 411 nm
D2 λΕmax: 403 nm
D4 λΕ
max: 448 nm
L1
: 0.72 ± 0.04
Φ
3
Φf
Φ
f: 0.54 ± 0.03
f: 0.37 ± 0.0
4
5
6
7
Bu
Bu
O
O
O
O
S
O
S
O
O
Scheme 4: Synthesized linkers L1, L2 exhibiting terminal OH groups for
further functionalization (characterization supporting Figs. S17-S20).
Ph
Ph
O
O
O
O
O
O
O
λΕmax: 426 nm
λΕmax: 456 nm
λΕ
Φ
λΕ
Φ
In conclusion, we pioneer a light induced ligation system for o-
MBAs that allows for gated fluorescence response. The self-re-
porting can be triggered quantitatively under very mild condi-
tions, allowing for fluorometric evaluation of the ligation reac-
tion. With the most suitable alkynoate substrates, we designed
a linker molecule that can be attached to payload molecules and
demonstrated that the reaction can be carried out in aqueous
media using visible light. We envisage that this technique will
open new possibilities in biological applications and advanced
material synthesis.
D6
D7
D8
max: 486 nm
D9
max: 471 nm
8
Φ
04
Φ
04
2
5
f: 0.32 ± 0.0
f: 0.02 ± 0.0
f: 0.02 ± 0.0
f: 0.18 ± 0.0
9
Bu
Bu
O
O
O
O
S
O
S
O
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
O
O
O
O
O
O
O
O
Ph
λΕmax: 456 nm
Ph
max: 487 nm
λΕmax: 426 nm
λΕ
λΕ
D9'
max: 451 nm
D6'
D7'
D8'
Φ
04
Φ
04
Φ
3
Φ
2
f: 0.15 ± 0.0
f: 0.02 ± 0.0
f: 0.02 ± 0.0
f: 0.18 ± 0.0
O
Ph
O
CO2Me
O
O
O
O
λΕmax: 421 nm
λΕmax: 411 nm
D11
D10
Φ
7
Φ
6
f: 0.64 ± 0.0
f: 0.60 ± 0.0
ASSOCIATED CONTENT
Supporting Information
Materials, Instrumentation, Synthetic procedures, Supporting
Spectroscopic Data. The Supporting Information is available free
of charge on the ACS Publications website.
Figure 2: Isolated products from the photoligation experiments summa-
rized in Table 1, including fluorescence emission maxima and fluorescence
quantum yields.
As reported earlier, o-MBA thioaldehydes such as A2 are per-
forming reasonably well in protic solvents including solvent
mixtures containing water.7 The compatibility with aqueous so-
lutions is crucial for applications involving biomolecules. Sur-
prisingly, we found that the reaction of A2 in ACN:H2O mix-
tures results in the decrease of 4π electrocyclization compared
to pure acetonitrile (refer to Table 2). Although, longer reaction
times due to the previously reported decrease in the quantum
yield of the photoreaction were required.31 In addition, from the
ACN:H2O reaction mixture we performed the elimination reac-
tion in a buffer solution at pH 4.2 and monitored the reaction
progress via fluorescence spectroscopy (refer to supporting Fig.
S8). The fact that the elimination takes place at ambient tem-
perature in aqueous solution without the addition of a catalyst
is especially important considering potential biological applica-
tions.
AUTHOR INFORMATION
Corresponding Authors
christopher.barnerkowollik@qut.edu.au
a.goldmann@qut.edu.au
j.blinco@qut.edu.au
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
C.B.-K. acknowledges funding from the Australian Research
Council (ARC) in the form of a Laureate Fellowship enabling his
photochemical research program as well as key support from the
Queensland University of Technology (QUT). C.B.-K., J. B. and S.
L. W. acknowledge support via an ARC Discovery project targeted
at red-shifting photoligation chemistry. F. F. and L. R. gratefully
acknowledge QUT for PhD Fellowships. T. K. gratefully acknowl-
edges funding by the Leopoldina Fellowship Program, German Na-
tional Academy of Sciences Leopoldina (LPDS 2017-05). T.D. is
supported by the ARC Future Fellowship scheme (FT150100408).
This work was enabled by use of the Central Analytical Research
Facility hosted by the Institute for Future Environments at QUT. T.
W. acknowledges support from the European Research Council
(ERC) via a Synergy Grant (319130-BioQ).
Table 2: Batch photoligation experiments in ACN:H2O (75:25 v/v) using
o-MBA A2 (5 mmol L-1, 1.00 eq.)and alkyne B2 or B4 (5.5 mmol L-1, 1.10
eq.) LED-irradiation wavelengths (λmax), irradiation time (t), YD isolated
yield. D/E: ratio of the desired Diels-Alder adduct vs. the 4π electrocycliza-
tion (see Scheme 2). D/D’ ratio of regioisomers.
No o-MBA Alkyne λmax[nm] t [min] RD/E YD
D/D’
98:2 95% --
1
2
3
A2
A2
A2
B2
B2
B4
385
415
415
150
360
360
86:14 75% --
100:0 98% 82:18
REFERENCES
1.
Kaupp, M.; Hiltebrandt, K.; Trouillet, V.; Mueller, P.;
In order to use the herein established reactions, it is essential to
have access to functional alkyne-linkers. Importantly, alkyno-
ates are reactive towards many nucleophiles. Therefore, we de-
signed two linkers (L1, L2) that can be attached to substrates
using well-established ligation methods, such as esterification.
L1 is prepared via esterification of propiolic acid, whereas L2
is accessible by ring opening of ε-caprolactone with methyl pro-
piolate following a literature protocol.32
Quick, A. S.; Wegener, M.; Barner-Kowollik, C., Wavelength
selective polymer network formation of end-functional star
polymers. Chem. Commun. 2016, 52 (9), 1975-1978.
2.
Claus, T. K.; Zhang, J.; Martin, L.; Hartlieb, M.; Mutlu,
H.; Perrier, S.; Delaittre, G.; Barner-Kowollik, C., Stepwise Light-
Induced Dual Compaction of Single-Chain Nanoparticles.
Macromol. Rapid Commun. 2017, 38 (16), 1700264.
3.
Mueller, P.; Zieger, M. M.; Richter, B.; Quick, A. S.;
Fischer, J.; Mueller, J. B.; Zhou, L.; Nienhaus, G. U.; Bastmeyer,
ACS Paragon Plus Environment

Page 5 of 6
Journal of the American Chemical Society
M.; Barner-Kowollik, C.; Wegener, M., Molecular Switch for Sub-
19.
Sammes, P. G.; Wallace, T. W., Photochemical
Diffraction Laser Lithography by Photoenol Intermediate-State
Cis–Trans Isomerization. ACS Nano 2017, 11 (6), 6396-6403.
reactions. Part V. Photoinduced cyclisations of 3-aroylchromones.
J. Chem. Soc., Perkin Trans. 1 1975, (19), 1845-1849.
1
2
3
4
5
6
7
8
4.
Tasdelen, M. A.; Kiskan, B.; Yagci, Y., Externally
20.
Ilhan, F.; Tyson, D. S.; Meador, M. A., Phenacenes from
stimulated click reactions for macromolecular syntheses. Prog.
Polym. Sci. 2016, 52, 19-78.
Diels−Alder Trapping of Photogenerated o-Xylylenols:ꢀ
Phenanthrenes and Benzo[e]pyrene Bisimide. Org. Lett. 2006, 8
(4), 577-580.
5.
Biological Applications. Top. Curr. Chem. 2016, 374 (1).
6. Aubert, S.; Bezagu, M.; Spivey, A. C.; Arseniyadis, S.,
Herner, A.; Lin, Q., Photo-Triggered Click Chemistry for
21.
Tyson, D. S.; Carbaugh, A. D.; Ilhan, F.; Santos-Pérez,
J.; Meador, M. A., Novel Anthracene Diimide Fluorescent Sensor.
Chem. Mater. 2008, 20 (21), 6595-6596.
Spatial and temporal control of chemical processes. Nat. Rev.
Chem. 2019, 3 (12), 706-722.
22.
Mateos, J.; Cherubini-Celli, A.;
Carofiglio, T.;
9
7.
Feist, F.; Menzel, J. P.; Weil, T.; Blinco, J. P.; Barner-
Bonchio, M.; Marino, N.; Companyó, X.; Dell’Amico, L., A
microfluidic photoreactor enables 2-methylbenzophenone light-
driven reactions with superior performance. Chem. Commun. 2018,
54 (50), 6820-6823.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Kowollik, C., Visible Light-Induced Ligation via o-
Quinodimethane Thioethers. J. Am. Chem. Soc. 2018, 140 (37),
11848-11854.
8.
Li, J.; Kong, H.; Huang, L.; Cheng, B.; Qin, K.; Zheng,
23.
Porter, G.; Tchir, M. F., Photoenolization of Ortho-
M.; Yan, Z.; Zhang, Y., Visible Light-Initiated Bioorthogonal
Photoclick Cycloaddition. J. Am. Chem. Soc. 2018, 140 (44),
14542-14546.
Substituted Benzophenones by Flash Photolysis. J. Phys. Chem. A
1971, (23), 3772-3777.
24.
McKay, Craig S.; Finn, M. G., Click Chemistry in
9.
Ramil, C. P.; Lin, Q., Photoclick chemistry: a fluorogenic
Complex Mixtures: Bioorthogonal Bioconjugation. Chemistry &
Biology 2014, 21 (9), 1075-1101.
light-triggered in vivo ligation reaction. Curr. Opin. Chem. Biol.
2014, 21, 89-95.
25.
Sultan, N.; Thomas, C.; Blanco, L.; Deloisy, S.,
10.
Arumugam, S.; Popik, V. V., Light-induced hetero-
Preparation of unsymmetrical dialkyl acetylenedicarboxylates and
related esters by enzymatic transesterification. Tetrahedron Lett.
2011, 52 (27), 3443-3446.
Diels-Alder cycloaddition: a facile and selective photoclick
reaction. J. Am. Chem. Soc. 2011, 133 (14), 5573-9.
11.
Arumugam, S.; Popik, V. V., Photochemical Generation
26.
Wang, Y.; Hoye, T. R., Isomerizations of Propargyl 3-
and the Reactivity of o-Naphthoquinone Methides in Aqueous
Solutions. J. Am. Chem. Soc. 2009, 131 (33), 11892-11899.
Acylpropiolates via Reactive Allenes. Org. Lett. 2018, 20 (15),
4425-4429.
12.
Menzel, J. P.; Noble, B. B.; Lauer, A.; Coote, M. L.;
27.
Huynh, T. N. T.; Retailleau, P.; Denhez, C.; Nguyen,
Blinco, J. P.; Barner-Kowollik, C., Wavelength Dependence of
Light-Induced Cycloadditions. J. Am. Chem. Soc. 2017, 139 (44),
15812-15820.
K. P. P.; Guillaume, D., Regioselective synthesis of 3,4,5-
trisubstituted 2-aminofurans. Organic & Biomolecular Chemistry
2014, 12 (28), 5098-5101.
13.
Uno, K.; Bossi, M. L.; Irie, M.; Belov, V. N.; Hell, S.
28.
derivations. Tetrahedron Lett. 2014, 55 (17), 2763-2772.
29. Lai, B.; Bai, R.; Gu, Y., Lignosulfonate/Dicationic Ionic
Shi, W.; Lei, A., 1,3-Diyne chemistry: synthesis and
W., Reversibly Photoswitchable Fluorescent Diarylethenes
Resistant against Photobleaching in Aqueous Solutions. J. Am.
Chem. Soc. 2019, 141 (41), 16471-16478.
Liquid Composite as a Task-Specific Catalyst Support for Enabling
Efficient Synthesis of Unsymmetrical 1,3-Diynes with A Low
Substrate Ratio. ACS Sustain. Chem. Eng. 2018, 6 (12), 17076-
17086.
14.
Chatterjee, D. K.; Gnanasammandhan, M. K.; Zhang, Y.,
Small Upconverting Fluorescent Nanoparticles for Biomedical
Applications. Small 2010, 6 (24), 2781-2795.
15.
Hooker, J. P.; Delafresnaye, L.; Barner, L.; Barner-
30.
Hooker, J. P.; Feist, F.; Delafresnaye, L.; Barner, L.;
Kowollik, C., With polymer photoclicks to fluorescent
microspheres. Mater. Horiz. 2019, 6 (2), 356-363.
Barner-Kowollik, C., Precisely Controlled Microsphere Design via
Visible-Light Cross-Linking of Functional Prepolymers. Adv.
Funct. Mater. 2019, 0 (0), 1905399.
16.
Konrad, W.; Fengler, C.; Putwa, S.; Barner-Kowollik,
C., Protection-Group-Free Synthesis of Sequence-Defined
Macromolecules via Precision λ-Orthogonal Photochemistry.
Angew. Chem. Int. Ed. 2019, 58 (21), 7133-7137.
31.
Menzel, J. P.; Feist, F.; Tuten, B.; Weil, T.; Blinco, J. P.;
Barner-Kowollik, C., Light-Controlled Orthogonal Covalent Bond
Formation at Two Different Wavelengths. Angew. Chem. Int. Ed.
2019, 58 (22), 7470-7474.
17.
Heiler, C.; Offenloch, J. T.; Blasco, E.; Barner-Kowollik,
C., Photochemically Induced Folding of Single Chain Polymer
Nanoparticles in Water. ACS Macro Lett. 2017, 6 (1), 56-61.
32.
Grant, T. N.; Benson, C. L.; West, F. G., Ring Expansion
of Lactones and Lactams via Propiolate 1-Carbon Intercalation.
Org. Lett. 2008, 10 (18), 3985-3988.
18.
Arnold, B. J.; Mellows, S. M.; Sammes, P. G.; Wallace,
T. W., Photochemical reactions. Part II. Cycloaddition reactions
with photoenols from 2-methylbenzaldehyde and related systems.
J. Chem. Soc., Perkin Trans. 1 1974, (0), 401-409.
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 6 of 6
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
6
ACS Paragon Plus Environment