S1
Supporting information
Controlling azobenzene photoswitching through combined ortho-
fluorination and –amination
Zafar Ahmed+, Antti Siiskonen+, Matti Virkki, Arri Priimagi*
Laboratory of Chemistry and Bioengineering, Tampere University of Technology, P.O. Box
541, FI-33101 Tampere, Finland.
E-mail: [email protected]
ORCID IDs:
Zafar Ahmed: 0000-0002-4737-6238
Antti Siiskonen: 0000-0003-3718-2031
Matti Virkki: 0000-0003-1340-9297
Arri Priimagi: 0000-0002-5945-9671
Electronic Supplementary Material (ESI) for ChemComm.This journal is © The Royal Society of Chemistry 2017
S2
Table of Contents:
1. The structures of the synthesized compounds 1 – 9 S3
2. General methods S3 – S4
3. Synthetic procedures S3 – S7
4. Computational studies S8 – S18
5. NMR spectra for compounds S19 – S30
6. Mass spectra for compounds S31 – S35
7. Photoisomerization studies S35 – S44
8. References S45
S3
1. The structures of the synthesized compounds 1 – 9
2. General Methods
All commercially available reagents and solvents were purchased either from Sigma Aldrich
Co. or from VWR and were used without further purifications unless otherwise mentioned.
Purification of the products was carried out either by column chromatography on Silica gel 60
(Merck) mesh size 40-63 µm or on preparative TLC plates (Merck) coated with neutral
aluminium oxide 60 F254. NMR spectra were recorded using Varian Mercury 300 MHz
spectrometer using TMS as internal standard. HRMS measurements were done with Waters
LCT Premier XE ESI-TOF bench top mass spectrometer. Lock-mass correction (leucine
enkephaline as reference compound), centering and calibration were applied to the raw data to
obtain accurate mass. UV-visible absorption spectra were recorded using quartz cuvettes on an
S4
Agilent Cary 60 spectrophotometer equipped with an Ocean Optics qpod 2e Peltier-
thermostated cell holder (temperature accuracy ± 0.1 °C). Photoexcitation experiments were
conducted using a Prior Lumen 1600 light source with multiple choices for narrow-band LEDs
at different wavelengths. The photoexcitation wavelengths were chosen for each compound
near an absorption maximum.
3. Synthesis
(E)-1-(2-fluoro-4-methoxyphenyl)-2-(4-methoxyphenyl)diazene (1):
To a solution of 3-fluorophenol (3 mmol, 236 mg) and 4-methoxyphenyldiazonium
tetrafluoroborate (3.3 mmol, 732 mg) in MeCN (7.5 mL) was added K2CO3 (12 mmol, 1.65 g)
at room temperature. The reaction mixture turned reddish-brown. After 30 min, another portion
of K2CO3 (3.0 mmol, 414 mg) and methyl iodide (6 mmol, 360 uL) were added and the mixture
was stirred overnight at room temperature. The reaction mixture was diluted with ethyl acetate,
filtered through Celite and concentrated on rotary evaporator. The crude was purified by
column chromatography on silica gel using 20% ethyl acetate/hexane to yield compound 1
(600 mg, 77%) as orange-yellow solid. 1H NMR (300 MHz, CDCl3, TMS): δ = 7.90 (d, J =
9.09 Hz, 2H), 7.80-7.74 (m, 1H), 6.99 (d, J = 9.09 Hz, 2H), 6.79-6.73 (m, 2H), 3.89 (s, 3H),
3.87 (s, 3H). 13C NMR (75 MHz, CDCl3, TMS): δ = 162.76, 161.86, 160.99 (d, J = 246.02 Hz),
147.29, 134.98 (d, J = 7.19 Hz), 124.65, 118.49 (d, J = 1.66 Hz), 114.16, 110.67 (d, J = 2.76
Hz), 101.84 (d, J = 23.77 Hz), 55.82, 55.55. 19F NMR (282 MHz, CDCl3): δ = -122.34 (m).
MS (ESI-TOF): m/z calcd for C14H13FN2O2: 261.1101; found: 261.1039 [M+H]+.
(E)-1,2-bis(2-fluoro-4-methoxyphenyl)diazene (2):
Compound 2 was prepared following a reported procedure.[1] A mixture of 2-fluoroaniline
(3.61 mmol, 510 mg), freshly ground KMnO4 (1.80 g) and FeSO4·7H2O (1.80 g) in DCM (36
mL) was refluxed overnight. After cooling to the room temperature, the reaction mixture was
filtered through Celite, dried over MgSO4 and concentrated under reduced pressure. The crude
residue was purified by column chromatography using 20% ethyl acetate/hexane to give the
desired symmetrical azobenzene 3 (350 mg, 35%) as an orange/red solid. 1H NMR (300 MHz,
CDCl3, TMS): δ = 7.84-7.78(m, 2H), 6.79-6.73 (m, 4H), 3.88 (s, 3H). 13C NMR (75 MHz,
CDCl3, TMS): δ = 163.31 (d, J = 9.40 Hz), 161.50 (d, J = 256.52 Hz), 135.49 (d, J = 7.19 Hz),
118.95 (d, J = 2.21 Hz), 111.01 (d, J = 2.77 Hz), 102.04 (d, J = 23.77 Hz), 56.10. 19F NMR
S5
(282 MHz, CDCl3): δ = -122.07 (m). MS (ESI-TOF): m/z calcd for C14H12F2N2O2: 279.0943;
found: 279.0945 [M+H]+.
(E)-1-(2,6-difluoro-4-methoxyphenyl)-2-(4-methoxyphenyl)diazene (3):
Compound 3 was prepared by following the similar procedure used for the synthesis of 1. To
a solution of 3,5-difluorophenol (2 mmol, 262 mg) and 4-methoxyphenyldiazonium
tetrafluoroborate (2.2 mmol, 488 mg) in MeCN (5 mL) was added K2CO3 (8 mmol, 1.10 g) at
room temperature. The reaction mixture turned reddish-brown. After 30 min, another portion
of K2CO3 (2.0 mmol, 276 mg) and methyl iodide (4 mmol, 240 uL) were added and the mixture
was stirred overnight at room temperature. The reaction mixture was diluted with ethyl acetate,
filtered through Celite and concentrated on rotary evaporator. The crude was purified by
column chromatography on silica gel using 20% ethyl acetate/hexane to yield compound 2
(445 mg, 84%) as orange-yellow solid. 1H NMR (300 MHz, CDCl3, TMS): δ = 7.90 (d, J =
9.00 Hz, 2H) , 7.00 (d, J = 9.00 Hz, 2H), 6.58 (d, J = 9.00 Hz, 2H), 3.90 (s, 3H), 3.86 (s, 3H). 13C NMR (75 MHz, CDCl3, TMS): δ = 162.26, 160.86 (t, J = 13.52 Hz), 157. 20 (dd, J =
257.87, 7.73 Hz), 147.93, 124.56, 114.16, 98.95 (d, J = 2.90 Hz), 98.60 (d, J = 1.93 Hz), 56.00,
55.58. 19F NMR (282 MHz, CDCl3): δ = -118.73 (m). MS (ESI-TOF): m/z calcd for
C14H12F2N2O2: 279.0928; found: 279.0945 [M+H]+.
(E)-1-(5-methoxy-2-((4-methoxyphenyl)diazenyl)phenyl)pyrrolidine (4):
A mixture of compound 1 (0.115 mmol, 30 mg) and pyrrolidine (2 mL) was stirred at room
temperature for 6 hours. The reaction mixture was diluted with ethyl acetate (20 mL). The
organic phase was washed with water (3×), dried over Na2SO4 and concentrated. The crude
was purified over silica gel using ethyl acetate/hexane (20%) as eluent to yield compound 4
(32 mg, 90%) as dark orange solid.1H NMR (300 MHz, CDCl3, TMS): δ = 7.80 (d, J = 9.00
Hz, 1H), 7.75 (d, J = 9.00 Hz, 2H), 6.99 (d, J = 9.00 Hz, 2H), 6.34-6.29 (m, 2H), 3.88 (s, 3H),
3.86 (s, 3H), 3.70-3.26 (m, 4H), 2.03-1.99 (m, 4H). 13C NMR (75 MHz, CDCl3, TMS): δ =
162.52, 160.22, 148.28, 147.86, 135.54, 123.76, 118.22, 114.06, 103.50, 99.39, 55.49, 55.27,
52.42, 25.93. MS (ESI-TOF): m/z calcd for C18H21N3O2: 312.1716; found: 312.1712 [M+H]+.
(E)-1-(5-methoxy-2-((4-methoxyphenyl)diazenyl)phenyl)piperidine (5):
A mixture of compound 1 (0.096 mmol, 25 mg) and pyrrolidine (2 mL) was stirred at 55 ˚C
for 20 hours. The reaction mixture was cooled to room temperature and diluted with ethyl
acetate (20 mL). The organic phase was washed with water (3×), dried over Na2SO4 and
S6
concentrated. The crude product was purified over silica gel using ethyl acetate/hexane (20%)
as eluent to yield compounds 5 (30 mg, 96 %) as dark orange solid. 1H NMR (300 MHz, CDCl3,
TMS): δ = 7.90 (d, J = 9.00 Hz, 2H) , 7.69 (d, J = 6.00 Hz, 1H), 7.00 (d, J = 9.00 Hz, 2H),
6.59-6.52 (m, 2H), 3.89 (s, 3H), 3.86 (s, 3H), 3.23-3.19 (m, 4H), 1.87-1.79 (m, 4H), 1.68-1.60
(m, 2H). 13C NMR (75 MHz, CDCl3, TMS): δ = 162.65, 161.41, 153.23, 147.79, 139.26,
124.56, 118.28, 114.36, 106.57, 104.50, 55.76, 55.63, 54.74, 26.59, 24.63. MS (ESI-TOF): m/z
calcd for C19H23N3O2: 326.1848; found: 326.1869 [M+H]+.
(E)-1-(2-((2-fluoro-4-methoxyphenyl)diazenyl)-5-methoxyphenyl)pyrrolidine (6): A
mixture of compound 2 (0.089 mmol, 25 mg) and pyrrolidine (2 mL) were stirred at room
temperature for 20 hours. The reaction mixture was diluted with ethyl acetate (20 mL). The
organic phase was washed with water (3×), dried over Na2SO4 and concentrated. The crude
was purified over silica gel using ethyl acetate/hexane (20%) as eluent to yield compound 6
(24 mg, 81 %) and 7 (5 mg, 15%) as dark orange solids respectively. 1H NMR (300 MHz,
CDCl3, TMS): δ = 7.85 (d, J = 9.00 Hz, 1H), 7.58-7.52 (m, 1H), 6.78-6.70 (m, 2H), 6.32-6.25
(m, 2H), 3.85 (s, 6H), 3.69-3.64 (m, 4H), 2.03-1.98 (m, 4H). 13C NMR (75 MHz, CDCl3, TMS):
δ = 163.13, 161.29 (d, J = 10.50 Hz), 160.42 (d, J = 252.66 Hz), 148.78, 136.21, 136.05 (d, J =
6.63 Hz), 118.90, 118.80 (d, J = 2.76 Hz), 110.70 (d, J = 3.32 Hz), 104.14, 102.08 (d, J = 23.77
Hz), 99.44, 56.00, 55.52, 52.70, 26.17. 19F NMR (282 MHz, CDCl3): δ = -123.17 (m). MS
(ESI-TOF): m/z calcd for C18H20FN3O2: 330.1602; found: 330.1618 [M+H]+.
(E)-1,2-bis(4-methoxy-2-(pyrrolidin-1-yl)phenyl)diazene (7): A mixture of compound 3
(0.071 mmol, 20 mg) and pyrrolidine (2 mL) was stirred at 55 ˚C for 20 hours. The reaction
mixture was cooled to room temperature and diluted with ethyl acetate (20 mL). The organic
phase was washed with water (3×), dried over Na2SO4 and concentrated. The crude product
was purified over silica gel using ethyl acetate/hexane (20%) as eluent to yield compounds 6
(6 mg, 21 %) and 7 (20 mg, 74%) as dark orange solids. Compound 7: 1H NMR (300 MHz,
CDCl3, TMS): δ = 7.59 (d, J = 9.68 Hz, 2H), 6.34-6.30 (m, 4H), 3.85 (s, 6H), 3.69-3.65 (m,
8H), 2.02-1.98 (m, 8H). 13C NMR (75 MHz, CDCl3, TMS): δ = 161.56, 148.01, 136.71, 118.41,
103.15, 100.00, 55.50, 52.70, 26.16. MS (ESI-TOF): m/z calcd for C22H28N4O2: 381.2296;
found: 381.2291[M+H]+.
(E)-1,1'-(5-methoxy-2-((4-methoxyphenyl)diazenyl)-1,3-phenylene)dipyrrolidine (8): A
mixture of compound 3 (0.093 mmol, 26 mg) and pyrrolidine (2 mL) was stirred at room
temperature for 6 hours. The reaction mixture was diluted with ethyl acetate (20 mL). The
S7
organic phase was washed with water (3×), dried over Na2SO4 and concentrated. The crude
was purified over silica gel using ethyl acetate/hexane (20%) as eluent to yield compound 8
(10 mg, 28%) as dark orange solid. The compound 6 was very labile as degradation was already
observed during purification and characterization.1H NMR (300 MHz, CDCl3, TMS): δ = 7.65
(d, J = 8.78 Hz, 2H), 6.5 (d, J = 8.78 Hz, 2H), 5.81 (s, 2H), 3.86 (s, 3H), 3.84 (s, 3H), 3.40-
3.35 (m, 8H), 1.94-190 (m, 8H). 13C NMR (75 MHz, CDCl3, TMS): δ = 162.38, 159.19,
148.87, 148.40, 122.61, 113.97, 113. 86, 88.97 (d, J = 4.61 Hz), 55.52-55.03 (m), 52.42, 25.82.
MS (ESI-TOF): m/z calcd for C22H28N4O2: 381.2263; found: 381.2291[M+H]+.
(E)-1-(3-fluoro-5-methoxy-2-((4-methoxyphenyl)diazenyl)phenyl)pyrrolidine (9):
To a solution of compound 3 (0.2 mmol, 53 mg) in MeCN (2 mL) was added pyrrolidine (1
mmol, 80 uL) dropwise at room temperature. After 2.5 h, the reaction mixture was diluted with
EtOAc (25 mL), washed with saturated NaHCO3 (15 mL), dried over Na2SO4, filtered and
evaporated. The crude was purified over silica gel using 5% ethyl acetate/toluene as eluent to
yield compound 9 (61 mg, 92%) as an orange solid. 1H NMR (300 MHz, CDCl3, TMS): δ =
7.78 (d, J = 9.00 Hz, 2H), 6.99 (d, J = 9.00 Hz, 2H), 6.13-6.03 (m, 2H), 3.88 (s. 3H), 3.82 (s,
3H), 3.51-3.47 (m, 4H), 1.96-1.91 (m, 4H). 13C NMR (75 MHz, CDCl3, TMS): δ = 161.06,
160.61 (d, J = 14.49 Hz), 154.30 (d, J = 256.90), 148.16, 148.09, 148.07 (m), 125.66 (d, J =
7.73 Hz), 123.76, 114.13, 114.04, 95.55 (d, J = 1.93 Hz), 91.39, 91.06, 55.55-55.37 (m), 52.47,
25.82. 19F NMR (282 MHz, CDCl3): δ = -122.05 (m). MS (ESI-TOF): m/z calcd for
C18H20FN3O2: 330.1635; found: 330.1618 [M+H]+.
S8
4. Computational studies
All the calculations were performed with Gaussian 16 Revision A.03 (Gaussian Inc.,
Wallingford CT). The B3LYP/6-31+G(d,p) method was used and the calculations were
performed in acetonitrile using the polarizable continuum model (PCM). Default values were
used for other parameters. A frequency calculation was performed after each geometry
optimization to conform that the obtained conformation was a true minimum (i.e. no imaginary
frequencies) or a transition state (one imaginary frequency). Intrinsic reaction coordinate (IRC)
runs were used to verify that the obtained transition states lead to starting materials and
products.
The density functional theory calculations, used to gain further insight into the reaction
mechanism and selectivity, revealed that the azo group could act either as a base or as a
hydrogen-bond acceptor, thereby leading to two different reaction mechanisms (see below).
Reaction of 1 with piperidine and that of 3 and 9 with pyrrolidine proceeds via three-step
mechanism. The initial transition state leads to an intermediate with the proton still attached to
the amine nitrogen. This proton migrates to the azo group and cleavage of fluorine in the final
step affords the desired product. Compounds 1, 2 and 6 react with pyrrolidine via a one-step
mechanism where the initial transition state directly leads to the final product and the azo group
acts only as a hydrogen-bond acceptor, not as a base. In both mechanisms, the attack by amine
is the rate-determining step. The selectivity can be explained by comparing the energy barriers
for that step (Table S1). As expected, the electron-withdrawing fluorine in 3 clearly decreases
the energy barrier, or increases the reaction rate. The second amination of the resulting product
(9 à 8) is much slower, presumably due to steric hindrance and the electron-donating effect
of the pyrrolidine substituent. A fluorine on the opposite ring, as in 2, does not have a
significant effect on the energy barrier. However, the presence of an amine on the opposite
ring, as in 6, increases the energy barrier significantly, presumably due to steric effects.
S9
Transition states:
The transition states were located using the command “opt(ts,calcfc)” and the starting geometry
for the calculations were chosen by running a constrained geometry scan and varying the
relevant interatomic distance (Figure S1). The geometry with the highest energy was chosen as
the starting geometry. The scan A was used to locate the starting geometry for the first reaction
step, B for the proton transfer step and C for the fluorine cleavage step.
Figure S1. Constrained geometry scans. The interatomic distance that is varied is marked with
r(x-x).
N
NF
N H
r(C-N)
N
N-
F N+H
r(N-H)
N
HN
F Nr(C-F)
A B
C
Table S1. The amination reaction energy barriers (∆E) and changes in free energies (∆G) for the transition states (in kcal mol-1) (B3LYP/6-31+G(d,p)) in acetonitrile (PCM).
Reaction ∆E[a] ∆E relative to 1 à 4
∆G[a] ∆G relative to 1 à 4
1 à 4 17.0 0 32.9 0 1 à 5 24.1 7.1 39.3 6.4
2 à 6 17.3 0.3 33.2 0.3 6 à 7 22.6 5.6 36.6 3.7 3 à 9 15.2 -1.8 30.9 -2.0 9 à 8 20.1 3.1 34.4 1.5 [a] Relative to the sum of starting materials
S10
One-step vs three-step mechanism:
The proposed one-step (starting material à product) and three-step reaction (starting material
à intermediate 1 à intermediate 2 à product) mechanisms are shown in Figure S2.
Figure S2. Proposed reaction mechanisms of the amination reaction.
In the one-step mechanism, the first transition state leads directly to the final product by
fluorine cleavage. In that case, the azo group functions as a coordinating group via a hydrogen
bond, not as a base.
In the three-step mechanism, the first transition state leads to the intermediate 1 where the
proton is still attached to pyrrolidine. The proton is then transferred to the azo group via another
transition state with a very low energy barrier. The fluorine cleavage then proceeds via a third
transition state, which also has a low energy barrier. Finally, the azo group is (presumably)
deprotonated by excess pyrrolidine to afford the final product (that step was not modelled)
N
N
F NH
N
N-
F N+
N
N
N
C-F cleavage
H
protontransfer
N
HN
F N
1) C-F cleavage2) proton removal
rate-determining transition state intermediate 1
intermediate 2final product
S11
Transition states and intermediates for the amination of 1-3, 6 and 9:
Reaction 1 à 4: The amination reaction of compound 1 with pyrrolidine proceeds in one-step.
The transition state geometry is shown in Figure S3. The IRC run from that transition state led
to a geometry similar to intermediate 1 but the subsequent geometry optimization led to the
final product, not intermediate 1. The transition state for the proton transfer could be located
by starting the constrained geometry optimization from the intermediate 2 (not from the
intermediate 1 as for other compounds) but the IRC run backwards from that transition state,
which should lead to the intermediate 1, leads to the final product. This odd behavior might be
explained by a bifurcated transition state but that idea was not further studied.
Figure S3. Reaction 1 à 4: transition state geometry.
Reaction 1 à 5: The amination reaction of 1 with piperidine proceeds in three steps. The
transition state for the first step is shown in Figure S4 and the energy barrier is +24.1 kcal/mol.
The intermediate 1 is shown in Figure S5 and the energy is +13.0 kcal/mol compared to the
starting materials. The transition state for the proton transfer is shown in Figure S6 and the
energy is +8.1 kcal/mol. The intermediate 2 is shown in Figure S7 and the energy is +6.2
kcal/mol compared to the starting materials. The transition state for the final step, or the
fluorine cleavage is shown in Figure S8 and the energy barrier is +4.1 kcal/mol.
S12
Figure S4. Reaction 1 à 5: transition state geometry for the first step.
Figure S5. Reaction 1 à 5: optimized geometry of the intermediate 1.
Figure S6. Reaction 1 à 5: transition state geometry for the proton transfer step.
S13
Figure S7. Reaction 1 à 5: optimized geometry of the intermediate 2.
Figure S8. Reaction 1 à 5: transition state geometry for the fluorine cleavage step.
Reaction 2 à 6: The amination reaction of 2 proceeds in one step. The transition state is shown
in Figure S9 and the energy barrier for that step is +17.0 kcal/mol. The IRC run forward of this
transition state leads directly to the final product by cleavage of the fluorine and without the
transfer of the proton. Therefore, in this case the azo group acts only as a hydrogen bond
acceptor, not as a base.
S14
Figure S9. Reaction 2 à 6: transition state geometry.
Reaction 6 à 7: The amination reaction of 6 proceeds in one-step. The transition state is shown
in Figure S10 the energy barrier is +22.6 kcal/mol. The IRC run forward of that transition state
leads directly to the final product without the proton transfer. Therefore, in this case the azo
group acts only as a hydrogen bond acceptor, not as a base.
Figure S10. Reaction 6 à 7: transition state geometry.
S15
Reaction 3 à 9: The amination reaction of 3 proceeds in three steps. The transition state for
the first step is shown in Figure S11 and the energy barrier is 15.2 kcal/mol. The intermediate
1 is shown in Figure S12 and the energy is +9.1 kcal/mol compared to starting materials. The
transition state for the proton transfer step is shown in Figure S13 and the energy barrier is only
2.4 kcal/mol. The intermediate 2 is shown in Figure S14 and the energy is +3.9 kcal/mol
compared to the starting materials. The transition state for the final step, or fluorine cleavage,
is shown in Figure S15. The energy barrier for that step is 4.7 kcal/mol.
Figure S11. Reaction 3 à 9: transition state geometry for the first step.
Figure S12. Reaction 3 à 9: optimized geometry of the intermediate 1.
S16
Figure S13. Reaction 3 à 9: transition state geometry for the proton transfer step.
Figure S14. Reaction 3 à 9: optimized geometry of the intermediate 2.
Figure S15. Reaction 3 à 9: transition state geometry for the fluorine cleavage step.
S17
Reaction 9 à 8: The amination reaction of 9 proceeds in three steps. The transition state for
the first step is shown in Figure S16 and the energy barrier is +20.1 kcal/mol. The intermediate
1 is shown in Figure S17 and the energy is +13.6 kcal/mol compared to the starting materials.
The transition state for the proton transfer is shown in Figure S18 and the energy barrier is only
+1.2 kcal/mol. The intermediate 1 is shown in Figure S19 and the energy is +6.0 kcal/mol
compared to the starting materials. The transition state for the final step, or the fluorine
cleavage, is shown in Figure S20 and the energy barrier is only +1.9 kcal/mol.
Figure S16. Reaction 9 à 8: transition state geometry for the first step.
Figure S17. Reaction 9 à 8: optimized geometry of the intermediate 1.
S18
Figure S18. Reaction 9 à 8: transition state geometry for the proton transfer step.
Figure S19. Reaction 9 à 8: optimized geometry of the intermediate 2.
Figure S20. Reaction 9 à 8: transition state geometry for the fluorine cleavage step.
S19
5. NMR spectra
Compound 1
Chemical Shift (ppm)8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0
Nor
mal
ized
Inte
nsity
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
2.90
2.18
2.36
1.00
2.12
7.92 7.
897.
787.
74
7.26
7.01
6.98
6.78
6.76 6.
74 6.74
3.89
3.87
Chemical Shift (ppm)168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24
Nor
mal
ized
Inte
nsity
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
162.
7616
1.86
159.
36
147.
29
135.
0313
4.94
124.
65
118.
48
114.
1611
0.69
110.
65
102.
0010
1.69
77.4
377
.00
76.5
8
55.8
255
.55
S20
Compound 2
Chemical Shift (ppm)-32 -40 -48 -56 -64 -72 -80 -88 -96 -104 -112 -120 -128 -136 -144 -152 -160 -168 -176
Nor
mal
ized
Inte
nsity
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
-122
.34
-122
.38
Chemical Shift (ppm)-122.1 -122.2 -122.3 -122.4 -122.5 -122.6
-122
.31
-122
.34
-122
.35
-122
.38
Chemical Shift (ppm)9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0
Nor
mal
ized
Inte
nsity
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
6.02
4.32
2.00
7.84
7.81
7.78
7.26 6.
796.
786.
746.
73
3.88
S21
Chemical Shift (ppm)176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24
Nor
mal
ized
Inte
nsity
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.416
3.38 163.
25
159.
84
135.
5413
5.44
122.
79
118.
94
110.
9911
0.16
102.
5010
2.20
101.
89
77.6
677
.25
76.8
2
56.1
0
Chemical Shift (ppm)-32 -40 -48 -56 -64 -72 -80 -88 -96 -104 -112 -120 -128 -136 -144 -152 -160 -168 -176 -184 -192 -200 -208
Nor
mal
ized
Inte
nsity
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
-122
.06
Chemical Shift (ppm)-121.5 -122.0
-122
.03
-122
.06
-122
.11
S22
Compound 3
Chemical Shift (ppm)8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0
Nor
mal
ized
Inte
nsity
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
3.20
1.96
2.13
2.00
7.92
7.89
7.27
7.02 6.
99
6.61
6.60
6.57
6.56
3.90
3.86
S23
Compound 4
Chemical Shift (ppm)8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0
Nor
mal
ized
Inte
nsity
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
4.22
4.15
6.00
1.95
1.92
2.81
*
*
7.82 7.79
7.77
7.74
7.27 7.
016.
98
6.34 6.
33 6.30 6.
296.
29
3.88
3.86
3.70
3.68
3.67 3.
66
2.03
2.01
2.00
1.99
S24
Compound 5
Chemical Shift (ppm)176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24
Nor
mal
ized
Inte
nsity
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.416
2.52
160.
22
148.
2814
7.86
135.
54
123.
76
118.
22
114.
06
103.
50 99.3
9
77.4
377
.00
76.5
7
55.4
952
.42 25
.93
Chemical Shift (ppm)8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0
Abso
lute
Inte
nsity
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
8.6
4.4
6.2
2.3
2.2
1.0
2.1
7.92 7.89
7.70
7.68
7.27
7.02
6.99
6.59 6.
596.
566.
55 6.53
6.52
3.89
3.86
3.23 3.21
3.19
1.87 1.
85 1.83
1.81
1.79
1.68 1.
661.
641.
60
S25
Compound 6
Chemical Shift (ppm)168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24
Abso
lute
Inte
nsity
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.816
2.65
161.
41
153.
23
147.
79
139.
26
124.
56
118.
2811
4.36
106.
5710
4.50
77.6
977
.26
76.8
4
55.7
6 55.6
354
.74
26.5
924
.63
Chemical Shift (ppm)8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0
Nor
mal
ized
Inte
nsity
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
4.50
4.53
6.46
2.33
2.26
1.12
1.00
*
7.87
7.84
7.58 7.
557.
557.
53 7.52 7.26
6.78 6.77
6.73
6.73
6.32 6.32 6.29 6.
266.
25
3.85
3.69
3.66
3.64
2.03 2.01
2.00
1.99
1.98
S26
Chemical Shift (ppm)176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24
Nor
mal
ized
Inte
nsity
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.716
3.13
162.
1116
1.36
161.
2215
8.73 14
8.78
136.
2113
6.10
136.
01
118.
9011
8.82
110.
72
104.
1410
2.24
101.
9399
.44
77.6
977
.26
76.8
4
56.0
055
.52
52.7
0
26.1
7
Chemical Shift (ppm)-40 -48 -56 -64 -72 -80 -88 -96 -104 -112 -120 -128 -136 -144 -152 -160 -168 -176 -184
Nor
mal
ized
Inte
nsity
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
-123
.17
Chemical Shift (ppm)-122.7 -122.8 -122.9 -123.0 -123.1 -123.2 -123.3 -123.4
-123
.14
-123
.17
-123
.18
-123
.21
S27
Compound 7
Chemical Shift (ppm)8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0
Nor
mal
ized
Inte
nsity
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
8.09
8.16
5.80
4.16
2.04
7.61 7.57
7.27 6.
346.
336.
326.
326.
30
6.30
3.85
3.69
3.67
3.66
3.65 2.
02 2.01
2.00
1.99
1.98
Chemical Shift (ppm)176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24
Nor
mal
ized
Inte
nsity
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
161.
56
148.
01
136.
71
118.
41
103.
1510
0.00
77.6
977
.26
76.8
4
55.5
052
.70
26.1
6
S28
Compound 8
Chemical Shift (ppm)8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0
Nor
mal
ized
Inte
nsity
0
0.5
1.0
1.5
2.0
2.5
3.0
8.83
8.28
6.28
2.00
2.39
1.98
7.66 7.
63
7.27
6.97
6.94
5.81
3.86
3.84
3.38
1.92
Chemical Shift (ppm)176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24
Abso
lute
Inte
nsity
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
162.
3815
9.19
148.
8714
8.40
122.
61
113.
9711
3.86
89.0
088
.94
77.4
377
.00
76.5
7
55.6
155
.52
55.4
255
.33
52.4
2
25.8
2
S29
Compound 9
Chemical Shift (ppm)8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0
Nor
mal
ized
Inte
nsity
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
4.24
4.40
3.29
2.09
2.14
2.00
*
**
7.80
7.78
7.27
7.01
6.98
6.13
6.12
6.10
6.09
6.08
3.88
3.82
3.51
3.49
3.47
1.96 1.
941.
941.
931.
91
Chemical Shift (ppm)176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24
Nor
mal
ized
Inte
nsity
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
161.
0616
0.71
160.
5115
6.01
152.
60
148.
0914
8.07
125.
7112
5.61
123.
76
114.
13 114.
04 95.5
7
91.3
991
.06
77.4
277
.00
76.5
8
55.4
955
.45
55.3
752
.47
25.8
2
S30
Chemical Shift (ppm)0 -8 -16 -24 -32 -40 -48 -56 -64 -72 -80 -88 -96 -104 -112 -120 -128 -136 -144 -152 -160 -168 -176
Nor
mal
ized
Inte
nsity
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
2.1
-122
.05
Chemical Shift (ppm)-121.6 -121.7 -121.8 -121.9 -122.0 -122.1 -122.2 -122.3
-122
.00
-122
.05
-122
.06
S31
6. Mass spectra
Compound 1
Compound 2
clf/MeOH
m/z220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400 410 420 430 440
%
0
100
%
0
100
%
0
100ZA234 (0.036) Is (1.00,1.00) C14H13FN2O2 1: TOF MS ES+
8.45e12261.1039
262.1071
263.1097
ZA234 1 (0.036) AM (Cen,4, 80.00, Ar,12000.0,557.28,1.00,LS 5); Sm (SG, 2x10.00) 1: TOF MS ES+ 1.10e3261.1101
254.0310222.0036
246.0629223.9997 317.0345265.9420 310.1271282.0288
268.0480 303.0202368.0481
324.0178343.0614 364.0937
413.2720372.1847 399.1189 442.2786435.2975
ZA234 1 (0.036) 1: TOF MS ES+ 181261.1093
254.0303222.0066
223.9941246.0888
310.1251265.9374282.0272 289.0379
317.0270368.0401
323.0434 343.0522 364.9349413.2704399.1173372.1736 442.2660436.2876
M o le c u la r F o rm u la : C 1 4 H 1 3 F N 2 O 2
F o rm u la W e ig h t : 2 6 0 .2 6 3 6 2 3 2
NN
F
O
O
MeCN
m/z245 250 255 260 265 270 275 280 285 290 295 300 305 310 315 320 325 330 335 340 345 350 355
%
0
100
%
0
100
%
0
100ZA275 (0.036) Is (1.00,1.00) C14H12F2N2O2 1: TOF MS ES+
8.45e12279.0945
280.0976
281.1003
ZA275 1 (0.036) AM (Cen,4, 80.00, Ar,9000.0,556.28,1.00,LS 5); Sm (SG, 2x10.00) 1: TOF MS ES+ 4.33e3279.0943
249.9836 278.0867264.0720252.1654
280.0981307.2113
281.1047290.2179 295.0949 345.1162309.2214 324.2441 339.1974331.3290 348.2432
ZA275 1 (0.036) 1: TOF MS ES+ 468279.0849
249.9777 278.0779280.0937
307.2015 345.0993
NN
F
O
OF
S32
Compound 3
Compound 4
MeCN
m/z240 245 250 255 260 265 270 275 280 285 290 295 300 305 310 315 320 325 330
%
0
100
%
0
100
%
0
100ASB11 (0.036) Is (1.00,1.00) C14H12F2N2O2 1: TOF MS ES+
8.45e12279.0945
280.0976
281.1003
ASB11 1 (0.036) AM (Cen,4, 80.00, Ar,9000.0,556.28,1.00,LS 5); Sm (SG, 2x10.00) 1: TOF MS ES+ 3.45e3279.0928
249.9827242.0846 244.1017
278.0872250.9865 271.1785259.1624 269.2132
307.2077
280.0964306.2469295.0898281.0977 293.1075
308.2126324.2432322.1458 326.2859
ASB11 1 (0.036) 1: TOF MS ES+ 429279.0858
249.9743242.0764 278.0744
307.2071280.0901
295.0716 306.2524308.2097
324.2444
Acc=6ppmM+1
NN
F
FO
O
Molecular Formula: C14H12F2N2O2Formula Weight: 278.2540864
clf/MeOH
m/z220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400 410 420 430
%
0
100
%
0
100
%
0
100ZA265 (0.036) Is (1.00,1.00) C18H21N3O2 1: TOF MS ES+
8.04e12312.1712
313.1743
314.1770
ZA265 1 (0.036) AM (Cen,4, 80.00, Ar,9000.0,557.28,1.00,LS 5); Sm (SG, 2x10.00) 1: TOF MS ES+ 992312.1716
310.1558286.1060277.0990
245.0783229.1418 264.1200 309.1312287.1109
313.1740
342.1730319.1981 335.1404 393.2122349.1909 375.1766 413.2870 419.3087
429.1893
ZA265 1 (0.036) 1: TOF MS ES+ 189312.1928
286.1246277.1192
245.0990229.1564 264.1389
310.1762
287.1281 309.1518
313.1942
342.2062318.2061
M o le c u la r F o rm u la : C 1 8 H 2 1 N 3 O 2F o rm u la W e ig h t : 3 1 1 .3 7 8 2 4
N N
O
O N
Acc= 1ppm
S33
Compound 5
Compound 6
Clf/MeOH
m/z290 295 300 305 310 315 320 325 330 335 340 345 350 355 360 365 370 375 380 385
%
0
100
%
0
100
%
0
100ZA277 (0.035) Is (1.00,1.00) C19H23N3O2 1: TOF MS ES+
7.95e12326.1869
327.1899
328.1927
ZA277 1 (0.035) AM (Cen,4, 80.00, Ar,9000.0,556.28,1.00,LS 5); Sm (SG, 2x10.00) 1: TOF MS ES+ 1.08e4326.1848
321.2269307.1975301.1507288.1534 299.1776 309.1317
327.1895
331.1748 371.3142349.1720345.2306337.2610 363.2352361.2171 377.2458 381.3541
ZA277 1 (0.035) 1: TOF MS ES+ 794326.1691
321.2230
327.1782
331.1676371.3090348.1612
M o le c u la r F o rm u la : C 1 9 H 2 3 N 3 O 2
F o rm u la W e ig h t : 3 2 5 .4 0 4 8 2
NN
MeO
OMeN
MeCN
m/z290 295 300 305 310 315 320 325 330 335 340 345 350 355 360 365 370 375 380 385
%
0
100
%
0
100
%
0
100ZA276A (0.036) Is (1.00,1.00) C18H20FN3O2 1: TOF MS ES+
8.04e12330.1618
331.1649
332.1676
ZA276A 1 (0.036) AM (Cen,4, 80.00, Ar,9000.0,556.28,1.00,LS 5); Sm (SG, 2x10.00) 1: TOF MS ES+ 948330.1602
287.2561324.2926307.2074296.2562 298.2738 312.2993 321.2316
331.1637
371.3190332.1831 339.3206 369.1751345.1310 358.2137 377.3009 381.3698386.2821
ZA276A 1 (0.036) 1: TOF MS ES+ 117330.1590
287.2509324.2860307.2061296.2537 302.1763 315.2912
331.1646
331.1791 371.3164 377.3059
M+1Acc=4ppm
NN
O
OFN
Molecular Formula: C18H20FN3O2
Formula Weight: 329.3687032
S34
Compound 7
Compound 8
clf/MeOH
m/z364 366 368 370 372 374 376 378 380 382 384 386 388 390 392 394 396 398 400 402 404 406 408
%
0
100
%
0
100
%
0
100ZA279B_gud (0.035) Is (1.00,1.00) C22H28N4O2 1: TOF MS ES+
7.66e12381.2291
382.2321
383.2350
ZA279B_gud 1 (0.035) AM (Cen,4, 80.00, Ar,9000.0,556.28,1.00,LS 5); Sm (SG, 2x10.00) 1: TOF MS ES+ 1.59e3381.2296
369.3534367.3615365.3331
371.3198 380.2259377.3341
391.2870382.2340
383.3621 385.3471389.2996
392.2890397.3808 399.3410
407.4001403.3289
ZA279B_gud 1 (0.035) 1: TOF MS ES+ 162381.2191
369.3272367.3517363.3158
371.3182 380.2174377.3387
391.2816382.2272
383.3713 385.3167387.3711
392.2872
395.2381 397.3874399.3362 405.3496
M+1Acc=1ppm
NN
O
ON
N
Molecular Formula: C22H28N4O2Formula Weight: 380.48332
clf/MeOH
m/z300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 600 620 640 660 680 700 720 740
%
0
100
%
0
100
%
0
100ZA268 (0.036) Is (1.00,1.00) C22H28N4O2 1: TOF MS ES+
7.66e12381.2291
382.2321
383.2350
ZA268 1 (0.036) AM (Cen,4, 80.00, Ar,9000.0,557.28,1.00,LS 5); Sm (SG, 2x10.00) 1: TOF MS ES+ 1.01e3381.2263
379.2121
312.2051 338.3428 377.0651
382.2325
419.3192383.2344 427.3800 663.4522513.1722499.1591451.0456 553.2651 634.3146562.0737 597.1015 741.1951679.4380
716.7794
ZA268 1 (0.036) 1: TOF MS ES+ 150381.2479
379.2407
312.2321 339.3747
382.2612
419.3506386.0681 513.2025427.4142 499.1942 663.5166 741.2533
N N
O
O N
N
Molecular Formula: C22H28N4O2Formula Weight: 380.48332
S35
Compound 9
7. Photoisomerization studies
UV–visible absorption spectra were recorded using 1 cm quartz cuvettes on an Agilent
Cary 60 spectrophotometer equipped with an Ocean Optics qpod 2e Peltier-thermostated
cell holder (temperature accuracy ± 0.1 °C). Photoexcitation experiments were performed
using a Prior Lumen 1600 light source with multiple choices for narrow-band LEDs at
different wavelengths. The photoexcitation wavelength was chosen for each compound
near an absorption maximum. The power density was about 250 mW cm-2 and the samples
were illuminated for 30–90 seconds until a photostationary state was reached. All
measurements were done in spectrophotometric grade acetonitrile.
The measurements for compounds 1–3, 5 and 9 were carried out at 50, 60 and 70 ºC due to
their cis-lifetimes being impractically long for a direct measurement at 25 ºC. UV–visible
spectra were measured with time intervals chosen such that around ten points are measured
while the absorbance is seen to return by at least 80 % towards the dark-adapted value after
photoexcitation. The cis-isomer decay was studied by observing the absorbance at a
wavelength chosen on the long-wavelength edge (about 80 % of maximum absorption) of
MeCN
m/z305 310 315 320 325 330 335 340 345 350 355 360 365 370
%
0
100
%
0
100
%
0
100ASB113 (0.035) Is (1.00,1.00) C18H20FN3O2 1: TOF MS ES+
8.04e12330.1618
331.1649
332.1676
ASB113 1 (0.035) AM (Cen,4, 80.00, Ar,9000.0,556.28,1.00,LS 5); Sm (SG, 2x10.00) 1: TOF MS ES+ 900330.1635
307.2117
308.2158 329.1577324.2821321.2005311.0998
331.1674
368.1563365.2000332.1688 341.1922 353.3596348.2394346.1365 362.1669371.3200
ASB113 1 (0.035) 1: TOF MS ES+ 109330.1530
307.2001
308.2073329.1441325.2767321.1808315.2852314.1493
331.1634
365.1916332.1513353.3755337.9683 341.1815 362.1640 368.1354
NN
FO
ON
S36
the longest-wavelength absorption peak clearly visible in the trans-rich absorption
spectrum.
Single exponential fits where performed to determine the cis lifetime at each temperature.
The fitting equation2 was −(𝐴$%& − 𝐴')×𝑒+,- + 𝐴$%&, where 𝐴$%& is the absorbance after
infinite time i.e. absorbance in dark, 𝐴' is the absorbance at the beginning of cis decay, i.e.
absorbance at photostationary state, k it the cis-decay rate constant and t is time. The
parameters 𝐴$%&, 𝐴' and 𝑘 were used as free parameters in the fits. The cis-lifetimes were
then calculated as 𝜏 = 2, where necessary. The natural logarithm of 𝑘 was calculated at
each temperature and plotted as a function of inverse temperature. From these Arrhenius
plots, the cis-lifetimes at 25 ºC were extracted by linear fitting and extrapolation. Error
estimates were extracted from the Arrhenius plots by calculating the maximum and
minimum values for the lifetimes given by the error limits of the Arrhenius plot
extrapolation. The error estimate given is the maximum minus minimum divided by two.
Compounds 4, 6 and 7 were measured at 25 ºC. The values reported for compounds 6 and
7 were measured at the same time of the year. Repetition of the measurement after a few
months for 6 and 7 gave notably shorter lifetime values from same synthetic batch. This
variation might be due to moisture and a varying humidity level at different times of the
year. Compounds 4 and 7 were studied by continuously monitoring the absorbance at a
selected wavelength and compound 6 by measuring the absorption spectrum with chosen
intervals. A Single exponential function mathematically identical to the one used for
compounds 1–3, 5 and 9 was used to determine the cis lifetimes directly from these
measurements and the standard error given by fitting was used for the error estimate.
S37
Figure S21. Thermal cis-to-trans isomerization of compound 1 at 70°C.
Figure S22. Arrhenius plot of compound 1.
S38
Figure S23. Thermal cis-to-trans isomerization of compound 2 at 70°C.
Figure S24. Arrhenius plot of compound 2.
S39
Figure S25. Thermal cis-to-trans isomerization of compound 3 at 60°C.
Figure S26. Arrhenius plot of compound 3.
S40
Figure S27. Cis-lifetime for compound 4 in kinetic mode at 25°C.
Figure S28. Back and forth switching cycles of 4 using 435 and 595 nm wavelengths.
S41
Figure S29. Thermal cis-to-trans isomerization of compound 5 at 60°C.
Figure S30. Arrhenius plot of compound 5.
S42
Figure S31. Thermal cis-to-trans isomerization of compound 6 at 25°C.
Figure S32. Cis-lifetime calculation for compound 6.
S43
Figure S33. Cis-lifetime study for compound 7 in kinetic mode at 25°C.
Figure S34. Thermal cis-to-trans isomerization of compound 9 at 70°C.
S44
Figure S35. Arrhenius plot of compound 9.
Figure S36. Back and forth switching cycles of 9 using 405 and 595 nm wavelengths.
S45
Figure S37. 1HNMR spectra of compound 9 (expanded methoxy regions) before (a) and after
(b) irradiation with 405 nm. Integration of methoxy protons indicates > 80% trans-cis
conversion.
8. References [1] C.Knie,M.Utecht,F.Zhao,H.Kulla,S.Kovalenko,A.M.Brouwer,P.Saalfrank,S.Hecht,
D.Bleger,Chem.-Eur.J.2014,20,16492.
[2]M.Poutanen,O.Ikkala,A.Priimagi,Macromolecules2016,49,4095.