Visible light-induced diastereoselective (E/Z)-photoisomerization equilibrium of
C=C benzofuran-3-one-hydantoin dyad
Oualid Talhi, Guido R. Lopes, Sergio M. Santos, Diana G. C. Pinto and Artur M. S. Silva*
QOPNA and CICECO Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
*Corresponding author. Tel: +351 234 370714; fax: +351 234 370084; e-mail: artur.silva@ua.pt
Electronic Supporting information
Table of Contents:
1.
Material
S3
2.
Synthesis, chromatographic separation and spectral characterization of
(E/Z)-5
S3
2.1. Synthesis of the intermediate (R/S)-1’,3’-Ditolylspiro[chroman-2,4'imidazolidine]-2',4,5'-trione 3
S3
2.2. Synthesis of the intermediate (2’R,5S)/(2’S,5R)-1’,3’-Ditolyl-5-(3-oxo-2,3dihydrobenzofuran-2-yl)imidazolidine-2,4-dione 4
S4
of
(E/Z)-1,3-Ditolyl-5-[3-oxobenzofuran-2(3H)2.3. Synthesis
ylidene]imidazolidine-2,4-dione (E/Z)-5
S5
2.4.
1
H NMR analysis, Thin Layer Chromatography and HPLC-UV separation
of (E/Z)-5
S5
Figure 1. Preparative thin layer chromatography separation of (E)-5 and
(Z)-5 diastereomers
S7
Figure 2. Analytical TLC control of pure (E)-5 and (Z)-5
S7
Figure 3. 1H NMR (CDCl3, 300 MHz) spectrum of the pure compound (Z)5
S8
Figure 4. 1H NMR (CDCl3, 300 MHz) spectrum of the pure compound (E)5
S8
Figure 5. 1H NMR (CDCl3, 300 MHz) of (E/Z)-5 1:3 mixture obtained
after the synthetic procedure
S9
Figure 6. HPLC separation of (E)-5 and (Z)-5
S9
2.5. UV absorption and determination of molar extinction coefficient of (E)-5
(Z)-5
S10
Figure 7. UV absorption of (E)-5 and (Z)-5 in chloroform
S10
Figure 8. Determination of εE and εZ for (E)-5 and (Z)-5 in chloroform
S10
S1
3.
4.
Study of photoisomeric equilibrium of (E/Z)-5
S10
Figure 9. Kinetic curves of (EZ)-photoisomerization in CH2Cl2 at 35°C
S12
Figure 10. Kinetic curves of (ZE)-photoisomerization in CH2Cl2 at 35°C
S12
Figure 11. Kinetic curves of (ZE)-photoisomerization in CH2Cl2 at
35°C – Study of the initial concentration [Z] 0 effects
S12
Figure 12. Kinetic curves of (ZE) photoisomerization at 35°C – Study of
solvent effects
S13
Figure 13. Kinetic curves of (ZE) photoisomerization in CHCl3 – Study
of temperature effects
S13
Computational studies on (E/Z)-5
S14
Figure 14. Superposition of the ground-state (S0) relaxed (E)- and (Z)-5
S14
isomers. The central imidazolidine rings have been aligned to allow for
better inspection of the structural differences between both isomers.
Figure 15. First excited-state (S1) energy conformations corresponding to
S14
the (E)- and (Z)-5 isomers (left and right, respectively), as calculated at the
LC-BLYP/cc-pVDZ level.
Figure 16. Superposition of the first excited-state (S1) relaxed (E)- and
(Z)-5 isomers
S15
Figure 17. Superposition of the (Z)-isomers optimized on the S0 (green)
S15
and S1 (orange) potential energy surfaces.
Figure 18. Superposition of the (E)-isomers optimized on the S0 (green)
and S1 (orange) potential energy surfaces.
S2
S16
1. Material
Melting points were measured on Buchi B-540 equipment and are uncorrected. NMR spectra
were recorded on Bruker Avance 300 or 500 spectrometers (300.13 for 1H and 75.47 MHz for
C), with CDCl3 as solvent and the internal standard was TMS. Chemical shifts (δ) are
13
reported in ppm and coupling constants (J) in Hz, all are calculated using MESTRENOVA 8
(Free Trail License) analytical chemistry software suite for NMR, LC, GC and MS. The
signals are described as s (singlet), d (doublet), dd (doublet of doublet) and m (multiplet).
Unequivocal
13
C assignments were made with the aid of 2D HSQC, HMBC experiments
(delays for one bond and long-range JC/H couplings were optimized for 145 and 7 Hz,
respectively). Exact mass measurements were recorded on high resolution mass spectrometer
(HRMS) micrOTOF-Q and elemental analysis on Truspec 630-200-200 equipments. HPLC
analyses were performed on GILSON apparatus equipped with a Model 306 pump (Gilson,
Villiers-le-Bel, France), a manual injector (Rheodyne, Cotatica, USA), a Model 118 UV-Vis
detector (Gilson, Villiers-le-Bel, France). Chromatograms acquisition and peak area
calculations were processed using Gilson UniPoint Software. The determination of molar
extinction coefficient εE and εZ were performed on UV-visible absorption device type UV2501 PC Shimadzu spectrophotometer (Kyoto, Japan) using 1 cm pathlength and 1 ml quartz
cuvettes. For the synthesis of (E/Z)-5 we have used: chromone-2-carboxylic acid 1,
ditolylcarbodiimide 2 and 4-pyrrolidinopyridine (4-PPy) which all were purchased from
Sigma-Aldrich. All other chemicals and solvents (including HPLC grade solvent) used were
purchased from commercial sources. Preparative thin layer chromatography for (E/Z)-5
separation was performed with Merck silica gel 60 (70-230 mesh) plates (20 x 20 cm) and
compounds revelation was visually possible or could be done under UV-lamp. Analytical thin
layer chromatography for organic synthetic reactions and (E/Z)-photoisomerization
monitoring was realized on pre-coated Merck silica gel plates. Electric lamp type halogen
lamp (220-240 V, 50/60 Hz, Max 500 W) was used as a source of visible light irradiation to
study the kinetic of (E/Z)-photoisomerization.
2. Synthesis, chromatographic separation and spectral characterization of (E/Z)-5
2.1. Synthesis of the intermediate (R/S)-1’,3’-Ditolylspiro[chroman-2,4'-imidazolidine]2',4,5'-trione 3
Chromone-2-carboxylic acid 1 (2 g, 10.52 mmol) was added to a solution of
ditolylcarbodiimide 2 (10.52 mmol, 1 equiv) in dichloromethane (20 mL), followed by the
S3
addition of a catalytic amount of 4-PPy (0.52 mmol, 0.08 g, 0.05 equiv). The resulting
mixture was allowed to stirring overnight at room temperature. After that period, the solvent
was evaporated to dryness and the resulting resinous solid was directly recrystallized from
ethanol to
afford
(R/S)-1’,3’-Ditolylspiro[chroman-2,4'-imidazolidine]-2',4,5'-trione 3:
C25H20N2O4 (pale yellow solid, 3.80 g, yield 88 %, Mp = 182-183°C). 1H NMR (300.13 MHz,
CDCl3): δ = 2.33 and 2.35 (2s, 6H, 4”-CH3 and 4”’-CH3), 3.14 (3d, J = 16.9 Hz, 1H, H-3),
3.22 (d, J = 16.9 Hz, 1H, H-3), 6.98-7.09 (m, 2H, H-6, H-8), 7.18 and 7.23 (2d, J = 8.1 Hz,
4H, tolyl), 7.28 and 7.35 (2d, J = 8.4 Hz, 4H, tolyl), 7.44-7.53 (m, 1H, H-7), 7.76 (dd, J = 7.8,
1.7 Hz, 1H, H-5). 13C NMR (75.47 MHz, CDCl3): δ = 21.06 and 21.08 (4”-CH3 and 4”’-CH3),
41.1 (C-3), 89.2 (C-2), 117.4 (C-8), 119.8 (C-10), 122.4 (C-6), 125.5 and 128.4 (C-2” and C2”’), 126.2 (C-5), 127.9 and 129.5 (C-1” and C-1”’), 129.6 and 130.1 (C-3” and C-3”’), 136.3
(C-7), 138.4 and 139.1 (C-4” and C-4”’), 153.1 (C-2’), 158.0 (C-9), 167.1 (C-5’), 187.8 (C-4).
HRMS (ESI+), m/z calcd for [C25H20N2O4+Na]+: 435.1321; found: 435.1309. Anal Calcd for
C25H20N2O4: C 72.80, H 4.89, N 6.79. Found: C 72.75, H 5.05, N 6.89%.
2.2. Synthesis
of
the
intermediate
(2’R,5S)/(2’S,5R)-1’,3’-Ditolyl-5-(3-oxo-2,3-
dihydrobenzofuran-2-yl)imidazolidine-2,4-dione 4
Sodium (10.52 mmol, 0.242 g) was added to ethanol (5 mL) and the resulting solution was
added dropwise (for 15 minutes) to a solution of the appropriate 1’,3’-ditolylspiro[chroman2,4'-imidazolidine]-2',4,5'-trione 3 (10.52 mmol) in ethanol (20 mL), placed in an ice-water
bath (0 °C). The reaction was left for 1 hour to reach room temperature under constant stirring.
After TLC monitoring, the ethanolic solution was poured in ice and water to be neutralized to
pH 7 with diluted hydrochloric acid. A yellowish white precipitate appeared which was then
purified
by
silica
gel
column
chromatography
using
a
(1:1)
of
light
petroleum:dichloromethane as eluent. The resulting pure compound were recrystallized from
ethanol
to
afford
(2’R,5S)/(2’S,5R)-1’,3’-Ditolyl-5-(3-oxo-2,3-dihydrobenzofuran-2-
yl)imidazolidine-2,4-dione 4: C25H20N2O4 (white solid, 2.74 g, yield 63 %, Mp = 181-183 °C).
1
H NMR (300.13 MHz, CDCl3): δ = 2.34 and 2.36 (2s, 6H, 4’’-CH3, 4’’’-CH3), 4.93 (d, J =
1.9 Hz, 1H, H-2’), 5.34 (d, J = 1.9 Hz, 1H, H-5), 7.00 (d, J = 8.5 Hz, 1H, H-7’), 7.06-7.13 (m,
1H, H-5’), 7.18-7.29 (2m, 6H, tolyl) and 7.36 (d, J = 8.4 Hz, 2H, tolyl), 7.55 (ddd, J = 8.5, 7.3,
1.5 Hz, 1H, H-6’), 7.69 (d, J = 7.7 Hz, 1H, H-4’). 13C NMR (75.47 MHz, CDCl3): δ = 20.92
and 21.15 (4”-CH3, 4”’-CH3), 62.1 (C-5), 80.6 (C-2’), 113.0 (C-7’), 121.5 (C-9’), 122.7 (C5’), 123.5 and 126.0 (C-2” and C-2”’), 124.3 (C-4’), 128.5 and 131.8 (C-1” and C-1”’), 129.7
and 129.9 (C-3” and C-3”’), 136.6 and 138.5 (C-4” and C-4”’), 138.1 (C-6’), 153.6 (C-2),
S4
166.2 (C-4), 172.6 (C-8’), 196.8 (C-3’). HRMS (ESI+), m/z calcd for [C25H20N2O4+Na]+:
435.1321; found: 435.1329.
2.3. Synthesis of (E/Z)-1,3-Ditolyl-5-[3-oxobenzofuran-2(3H)-ylidene]imidazolidine-2,4-dione
(E/Z)-5
Iodine (0.068 g dissolved in 1 mL of DMSO) was added to a solution of the appropriate
1,3-ditolyl-5-(3-oxo-2,3-dihydrobenzofuran-2-yl)imidazolidine-2,4-dione 4 (5.26 mmol) in
DMSO (3 mL) and the reaction mixture was refluxed under nitrogen flow and shielded from
intense light for 30 minutes. After TLC analysis which indicates de formation of two
compounds, the reaction solution was poured into ice (10 g) and water (20 mL). An intense
yellow precipitate appeared which was filtrated and washed with water. The obtained solid
was taken in dichloromethane (150 mL) and washed with a saturated solution of sodium
thiosulfate (2 x 150 ml) after solvent removal; the crude resinous product is then
recrystallized from ethanol to afford 83 % of (E/Z)-5 isomeric mixture.
2.4. 1H NMR analysis, thin-layer chromatography and HPLC-UV separation of (E/Z)-5
After filtration and recuperating the dried yellow mixture of (E/Z)-5, it is then dissolved in of
dichloromethane (10 mL) to be deposited on preparative TLC silica plates (10 plates) and
subsequently the two (E/Z)-5 isomers were separated and isolated using dichloromethane as
eluent for 40 minutes procedure (Figure 1), being (E)-5 the first compound eluted and
recrystallized from ethanol, while (Z)-5 was recrystallized from toluene. The purity of the (E)5 and (Z)-5 compounds was controlled by analytical TLC using CH2Cl2 as eluent (Figure 2,
TLC plate on left) and confirmed by elemental analysis. It is strongly recommended to work
away from intense light during this phase of chromatographic separation since these
compounds are photosensitive and can proceed with the (E/Z)-photoisomerization
interconversion very rapidly. We have also monitored this photoisomeric reaction using
analytical TLC (Figure 2, TLC plate on right). The two isomers (E)-5 and (Z)-5 were jointly
obtained in a 1:3 ratio after the synthetic procedure as evaluated by NMR proton integration
(Figure 3-5) and confirmed by HPLC analysis (Figure 6). The photoisomerization
phenomenon could also be monitored by 1H NMR to measure the (E/Z)-ratio after visible
light irradiation for a known period of time (as indicted in the results).
(Z)-1,3-Ditolyl-5-[3-oxobenzofuran-2(3H)-ylidene]imidazolidine-2,4-dione
(Z)-5:
C25H18N2O4 (yellow solid, 1.35 g, yield 62 %, Mp = 232 °C). 1H NMR (300.13 MHz, CDCl3):
S5
δ = 2.39 and 2.47 (2s, 6H, H-4”-CH3 and 4”’-CH3,), 6.74 (dd, J = 8.9, 0.6 Hz, 1H, H-7’), 7.137.20 (m, 1H, H-5’), 7.24-7.29 (2m, 6H, tolyl) and 7.40 (d, J = 8.4 Hz, 2H, tolyl), 7.46-7.54 (m,
1H, H-6’), 7.74-7.77 (m, 1H, H-4’).
13
C NMR (75.47 MHz, CDCl3): δ = 21.1 and 21.2 (4”-
CH3 and 4”’-CH3), 112.4 (C-7’), 119.7 (C-5), 121.7 (C-9’), 123.9 (C-5’), 124.7 (C-4’), 125.9
and 127.6 (C-2” and C-2”’), 128.3 and 131.4 (C-1” and C-1”’), 129.3 and 129.7 (C-3” and C3”’), 136.40 (C-2’), 136.43 (C-6’), 138.5 and 138.9 (C-4” and C-4”’),152.8 (C-2), 158.3 (C-4),
163.9 (C-8’), 180.5 (C-3’). HRMS (ESI+), m/z calcd for [C25H18N2O4+Na]+: 433.1164; found:
433.1171. Anal Calcd for C25H18N2O4: C 73.16, H 4.42, N 6.83. Found: C 73.23, H 4.52, N
6.70%.
(E)-1,3-Ditolyl-5-[3-oxobenzofuran-2(3H)-ylidene]imidazolidine-2,4-dione
(E)-5:
C25H18N2O4 (yellow solid, 0.46 g, yield 21 %, Mp = 208-210 °C). 1H NMR (300.13 MHz,
CDCl3): δ = 2.42 and 2.45 (2s, 6H, 4”-CH3 and 4”’-CH3), 7.15-7.21 (m, 1H, H-5’), 7.28-7.35
and 7.37-7.42 (2m, 9H, H-7’ and tolyl), 7.58-7.68 (m, 2H, H-6’, H-4’). 13C NMR (75.47 MHz,
CDCl3): δ = 21.2 and 21.3 (4”-CH3 and 4”’-CH3), 112.4 (C-7’), 118.8 (C-5), 121.8 (C-9’),
124.0 (C-5’), 124.8 (C-4’), 126.0 and 127.7 (C-2” and C-2”’), 128.3 and 131.5 (C-1” and C1”’), 129.3 and 129.7 (C-3” and C-3”’), 136.5 (C-6’), 137.0 (C-2’), 138.6 and 139.0 (C-4” and
C-4”’), 152.9 (C-2), 164.0 (C-8’), 180.6 (C-4), 191.3 (C-3’). HRMS (ESI+), m/z calcd for
[C25H18N2O4+Na]+: 433.1164; found: 433.1171. Anal Calcd for C25H18N2O4: C 73.16, H 4.42,
N 6.83. Found: C 73.45, H 4.45, N 6.76 %.
UV
Visible
Figure 1. Preparative thin layer chromatography separation of (E)-5 (above) and (Z)-5 (below)
diastereomers: Silica plates are showing the results of the preparative TLC experiments in
CH2Cl2 after 40 min of experience, both of the clearly separated isomers can be revealed
under UV (see on left) or visible light (see on right).
S6
Figure 2. Analytical TLC control of pure (E)-5 and (Z)-5: The TLC plate on left indicate (E)5 and (Z)-5 pure compounds after chromatographic separation and the initial (E/Z) 1:3
mixture obtained after the synthetic procedure. In the TLC plate on right, we have used the
isolated pure isomers (E)-5 and (Z)-5 (at t = 0, before visible light exposure) as references to
analyze them after visible light irradiation (using electric room lighting) of about 30 to 40 min.
S7
1''
7' 8' 1'
6'
O
5'
Tolyl protons
4'
9'
5
3' 2'
4
O O
N
3
O
2
1'''
H-7’
H-5’
H-4’
1
N
p-CH3
H-6’
Figure 3. 1H NMR (CDCl3, 300 MHz) spectrum of the pure compound (Z)-5.
7'
6'
5'
1'
8' O
3' 2'
4'
9'
O
O
5
4 3 1'''
N
2
N1 O
1''
Tolyl protons
H-7’
H-4’ H-6’
H-5’
p-CH3
Figure 4. 1H NMR (CDCl3, 300 MHz) spectrum of the pure compound (E)-5.
S8
— (Z)-5
— (E)-5
Tolyl protons
H-7’
p-CH3
H-4’
H-4’ H-6’
Figure 5. 1H NMR (CDCl3, 300 MHz) of (E/Z)-5 1:3 mixture obtained after the synthetic
procedure.
Figure 6. HPLC separation of (E)-5 (10.4 min) and (Z)-5 (14.5 min): The HPLC separation of
(E)-5 and (Z)-5 was done on normal phase (silica gel) at 25°C using a Waters Spherisorb S5W
column (particle size 5 µm, 200 mm × 4.6 mm i.d., Milford, USA). The mobile phase used
was hexane/THF [isocratic mode, 80:20 (v/v)] at a flow rate of 1.0 mL/min. The UV detector
was set at 254 nm. An injection of 50 µL of 0.5 gL-1 concentrated sample in chloroform
(mixture of (E/Z)-5 obtained after the organic synthetic procedure) was used.
S9
2.5. UV absorption and determination of molar extinction coefficient of (E)-5 and (Z)-5
Under strict lightless conditions 4.26 × 10−2, 2.13 x 10-2 and 1.07 × 10−2 mM solutions were
prepared in chloroform using the pure isolated (Z)-5 synthesized as described earlier. The
solutions were immediately subjected to UV-visible absorption measurement using 1 cm
pathlength and 1 ml quartz cuvettes (Figure 7). The same procedure was done with the pure
(E)-5 with the following concentrations: 3.66 × 10−2, 1.83 × 10−2 and 9.15 x 10-3 mM.
Absorbance at λmax = 254 nm of each solution was recorded. The plots between absorbance
and solution concentration were then constructed leading to the molar extinction coefficients
εE = 12.922 and εZ = 13.397 mM-1 of compounds (E)-5 and (Z)-5 in chloroform, respectively
(Figure 8).
1,0
Abs
0,8
(Z)-DTBI
(Z)-5
0,6
(E)-5
(E)-DTBI
0,4
0,2
0,0
250
350
450
Wavelenght (nm)
Figure 7. UV absorption of (E)-5 and (Z)-5 in chloroform.
0,6
Abs (254 nm)
Abs (254 nm)
0,6
0,4
Abs = 12,922 [E]
R² = 0,9975
0,2
0,4
Abs = 13,397 [Z]
R² = 0,9983
0,2
0,0
0,0
0,00
0,01
0,02
0,03
0,00
0,04
0,02
0,04
0,06
[Z] (mM)
[E] (mM)
Figure 8. Determination of εE and εZ for (E)-5 and (Z)-5 in chloroform.
3. Study of photoisomeric equilibrium of (E/Z)-5
We designed homogeneous isotherm systems at various temperatures to study the (E/Z)photoisomeric equilibrium using an electric lamp as visible light source providing the same
photo-intensity during the whole period of study. The electric lamp is place at a fixed distance
S10
(20 cm) from the reaction vial which is sealed with a rubber stopper (to avoid solvent
evaporation) and equipped with a stirring system and thermometer to measure the internal
solution temperature. The designed reactor is placed in a dark chamber making sure that the
system is away from any other external visible light sources.
HPLC analyses were done by injecting samples of 50 µL collected by mean of graduated
syringe through the rubber stopper. At the beginning of the HPLC monitoring, freshly
prepared standards of a known initial concentration [E]0 and [Z]0 of (E)-5 and (Z)-5 solutions
in the used solvent of reaction (conserved under strict lightless conditions in closed cuvettes
of 1 cm3 volume at room temperature) were immediately subjected to HPLC analyses before
they were placed under the above described visible light irradiation system. After appropriate
visible light exposure time (as indicated in the results), each solution was measured by HPLC
analysis to determine [E]t and [Z]t until the (E/Z)-photoisomeric equilibrium is achieved
(when we arrive to stationary phase of the same limit concentration value), thus, [E]e and [Z]e
are known. Various isotherms were studied, at 35°C due to the electric lamp heating, at 60°C
using water bath and at –20°C using cryostat; all temperatures of the solutions were precisely
controlled using thermometer placed directly inside the vial through the rubber stopper. In
addition, the (E/Z)-photoisomeric study was performed in diverse solvent system (as indicated
in the results). During all the HPLC monitoring for the kinetic study of (E/Z)photoisomerization, the conditions are set up as follows: normal phase (silica gel) at 25 °C
using a Waters Spherisorb S5W column (particle size 5 µm, 200 mm × 4.6 mm i.d., Milford,
USA); mobile phase used was Hexane/THF (isocratic mode, 80:20 (v/v)) at a flow rate of 1.0
ml/min; UV detector was set at 254 nm (see chromatogram in Figure 6).
The (EZ) and (ZE) photoisomeric equilibrium kinetics which are indicated in the
manuscript are all graphically represented in this supporting material section (Figure 9-13).
The plot of the negative natural logarithm of X versus time indicates the pseudo-first order
kinetics of the equilibrium processes. The slope of the best-fit line yields the rate constants (ke
+ kz).
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4,00
100
3,50
80
3,00
2,50
Z
40
ln (X)
(%)
60
2,00
ln (x) = 0,0297 t
R² = 0,9916
1,50
E
1,00
20
0,50
0,00
0
0
100
200
300
0
400
20
40
Time (min)
60
80
100
120
Time (min)
Figure 9. Kinetic curves of (EZ)-photoisomerization in CH2Cl2 at 35°C ([E]0 = 0.5 g.L-1).
100
4,00
3,50
80
3,00
2,50
Z
40
ln (X)
(%)
60
2,00
ln (X) = 0,0315 t
R² = 0,9949
1,50
E
1,00
20
0,50
0,00
0
0
100
200
300
0
400
20
40
60
80
100
120
Time (min)
Time (min)
Figure 10. Kinetic curves of (ZE)-photoisomerization in CH2Cl2 at 35°C ([Z]0 = 0.5 g.L-1).
25
5,00
4,50
20
ln (X) = 0,0585 t
R² = 0,9915
4,00
3,50
3,00
1.0
1.0g/L
gL-1
10
ln (X)
E(%)
15
0.5g/L
gL-1
0.5
ln (X) = 0,0315 t
R² = 0,9949
2,50
2,00
1,50
1,00
5
0,50
0,00
0
0
100
200
300
0
400
20
40
60
80
100
120
Time (min)
Time (min)
Figure 11. Kinetic curves of (ZE)-photoisomerization (Z)-5 in CH2Cl2 at 35°C – study of
the initial concentration [Z]0 effects.
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35
4,00
30
3,50
3,00
20
ECHCl3
15
ECH2Cl2
ln (X) = 0,077 t
R² = 0,9946
2,50
ln (X)
E(%)
25
ln (X) = 0,0315 t
R² = 0,9949
2,00
1,50
10
1,00
5
0,50
0,00
0
0
100
200
300
0
400
20
40
Time (min)
60
80
100
120
Time (min)
Figure 12. Kinetic curves of (ZE)-photoisomerization (Z)-5 at 35°C ([Z]0 = 0.5 g.L-1) –
study of solvent effects
35
4,00
30
3,50
ln (X) = 0,077 t
R² = 0,9946
3,00
25
20
35 °C
15
- 20 °C
ln (X)
E(%)
2,50
ln (X) = 0,0426 t
R² = 0,9912
2,00
1,50
60 °C
10
ln (X) = 0,0614 t
R² = 0,9924
1,00
0,50
5
0,00
0
0
100
200
300
0
400
20
40
60
80
Time (min)
Time (min)
Figure 13. Kinetic curves of (ZE)-photoisomerization (E/Z)-5 in CHCl3 ([Z]0 = 0.5 g.L-1) –
study of temperature effects
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4. Computational studies on (E/Z)-5
Figure 14. Superposition of the ground-state (S0) relaxed (E)-5 and (Z)-5 isomers. The
central imidazolidine rings have been aligned to allow for better inspection of the structural
differences between both isomers.
Figure 15. First excited-state (S1) energy conformations corresponding to the (E)-5 and (Z)-5
isomers (left and right, respectively), as calculated at the LC-BLYP/cc-pVDZ level.
Figure 16. Superposition of the first excited-state (S1) relaxed (E)-5 and (Z)-5 isomers
(details as in Figure 14).
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Figure 17. Superposition of the (Z)-isomers optimized on the S0 (green) and S1 (orange)
potential energy surfaces.
Figure 18. Superposition of the (E)-isomers optimized on the S0 (green) and S1 (orange)
potential energy surfaces.
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