Towards multichromatic electrochromes from ambipolar conjugated azomethines

Article abstract of DOI:10.1039/c4nj00027g

A series of conjugated azomethines end-capped with phenylamides and consisting of different aromatic cores of varying π-donor strength were prepared. Their optical and electrochemical properties were investigated to assess the suitability of the azomethines as electrochromic materials. The azomethines were found to undergo both electrochemical oxidation and reduction in the window of -1.60 and +1.35 V vs. Ag/Ag⁺. The color of the ambipolar compounds could be dramatically changed when switched between their reduced, neutral, and oxidized states. The color of the different states was contingent on the π-donor strength of the central aromatic unit. The largest spectral difference of 350 nm between the reduced and oxidized states was observed when the central aromatic group was 3,4-ethylenedioxythiophene (EDOT). The colors detectable by the eye for this EDOT derivative were blue, red, and bleached for the reduced, neutral, and oxidized states, respectively. The multichromatic azomethine was used as an electrochromic layer in a functioning device. The proof-of-concept ambipolar electrochromic device could be repeatedly switched between its orange (neutral) and purple (reduced) states. The device could also be switched to its oxidized (bleached) state.

Full text of DOI:10.1039/c4nj00027g

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Towards multichromatic electrochromes from
ambipolar conjugated azomethines†
Cite this: New J. Chem., 2014,
38, 1668
Michael E. Mulholland,‡ Daminda Navarathne,‡§ Samim Khedri¶ and W. G. Skene*
A series of conjugated azomethines end-capped with phenylamides and consisting of different aromatic
cores of varying p-donor strength were prepared. Their optical and electrochemical properties were
investigated to assess the suitability of the azomethines as electrochromic materials. The azomethines
were found to undergo both electrochemical oxidation and reduction in the window of ꢀ1.60 and
+1.35 V vs. Ag/Ag+. The color of the ambipolar compounds could be dramatically changed when
switched between their reduced, neutral, and oxidized states. The color of the different states was
contingent on the p-donor strength of the central aromatic unit. The largest spectral difference of
350 nm between the reduced and oxidized states was observed when the central aromatic group was
3,4-ethylenedioxythiophene (EDOT). The colors detectable by the eye for this EDOT derivative were
blue, red, and bleached for the reduced, neutral, and oxidized states, respectively. The multichromatic
azomethine was used as an electrochromic layer in a functioning device. The proof-of-concept
ambipolar electrochromic device could be repeatedly switched between its orange (neutral) and purple
(reduced) states. The device could also be switched to its oxidized (bleached) state.
Received (in Montpellier, France)
6th January 2014,
Accepted 11th February 2014
DOI: 10.1039/c4nj00027g
www.rsc.org/njc
enhancing the optoelectronic properties of electrochromic
materials to span the entire visible spectrum. Focus has also
Introduction
In recent years, significant advances have been made in the been placed on improving device performance by extending
field of organic electronics in terms of materials properties.1 switching rates between their neutral and charged states, high
This has been spurred on in part by the unique combination of optical resolution, and high stability.21 Effort has also been
mechanical, flexibility, and processing advantages of organic focused on developing electrochromes having discrete colors
semiconductors over their traditional inorganic counter- for providing an extensive palette of colors that cover the full
parts.2,3 Such materials have successfully been used as active visible spectrum and extend into the near-infrared.18–34
layers in many electronic devices including photovoltaics,4–6
Most electrochromes undergo a single color change when
light-emitting diodes,7–14 and field effect transistors.15–17 switched between their neutral and charged states.18–35 Numer-
Organic electronics have also been expanded to electrochromic ous bichromatic electrochromes must therefore be assembled
devices that are used as smart windows of various dimensions to fabricate a working electrochromic device capable of multi-
and low-technological displays.18–34 Such devices take advan- ple colors.23 This process complicates device fabrication and
tage of the materials’ optical properties that reversibly change leads to color inhomogeneity and reduced device performance
when electrochemically switched between their neutral and in part due to the mismatched redox potentials of the different
charged states. To expand the applications portfolio of electro- electrochromes. Multichromatic materials are beneficial for
chromic devices, considerable effort has been dedicated to simplifying the fabrication of multicolored devices, but their
preparation is challenging.19,36,37 Ambipolar materials are
interesting multichromatic alternatives because they sustain
both an oxidation and reduction process, resulting in at least
three colors.
´
´
´
Laboratoire de caracterisation photophysique des materiaux conjugues,
´
´
´
Departement de chimie, Universite de Montreal, CP 6128, Centre-ville, Montreal,
QC, Canada. E-mail: w.skene@umontreal.ca
Few ambipolar electrochromes are known and those that are
† Electronic supplementary information (ESI) available: Including, NMR, absor-
bance, and spectroelectrochemical spectra and cyclic voltammograms. See DOI: reported have mostly been polymers.32–34 While polymer elec-
10.1039/c4nj00027g
trochromes have many mechanical and opto-electronic advan-
tages, they can suffer from inconsistent properties. This is in
part due to batch-to-batch variations in molecular weights and
‡ Contributed equally.
§ Current address: Cytec Industries Inc., 1937 West Main Street, Stamford CT
06902, USA.
their high polydispersities. These cause variances in the redox
potentials and color reproducibility. These shortcomings can
´
¶ Current address: Faculty of Pharmacy, Universite Laval, Quebec, Quebec,
Canada.
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spacers was believed to provide a cathodic character to the
compounds. Therefore, incorporating an amide moiety into
azomethines was expected to afford desired ambipolar proper-
ties. Bearing this in mind, 1A–C were targeted because of their
expected anodic and cathodic behavior that would result in
color switching when oxidized and reduced. A terminal phenyl
was chosen because it was expected not to significantly alter the
optical properties of the neutral state. This is of importance
because the effect of the central aryl electron donating segment
on the electrochemical properties, in addition to the absor-
bance of the neutral, reduced, and oxidized states could be
accurately assessed. The added advantage of the phenyl amide
is that the reduced state should absorb in the visible region.
The collective properties would yield insight into the tune-
ability of the optical and electrochemical properties by altering
the central aromatic group. The thiophene derivative (1A) was
selected for benchmarking the effect of the p-donating strength
Chart 1 Ambipolar azomethines prepared and examined for multi-
chromaticity.
be overcome with oligomers that can be isolated in high purity of the central moiety on the optical and electrochemical proper-
and that have concise structures. Accurate structure–property ties. Increasing the electron donating effect of the central
studies are also more readily possible with oligomers than their moiety should counterbalance the electron withdrawing effect
polymeric counterparts. Taking this into consideration con- of the azomethines and esters of 4 (Scheme 1), while reducing
comitant with their easy preparation and purification, ambi- the HOMO–LUMO energy gap. This is in contrast to the poor
polar electrochromic oligomers offer significant advantages donating strength of fluorene, where the properties of 1C
over their polymer counterparts.
should be significantly different than 1A and 1B.38
To assess the suitability of ambipolar oligomers as viable
The precursor 4 can be selectively condensed with aryl
electrochromes, three azomethine derivatives were prepared dialdehydes to afford mono-adduct derivatives of 3.30 The
and evaluated. The thiophene-based azomethines 1A–C terminal amines of these amide-free derivatives can further
(Chart 1) were targeted because of their well-established anodic react. This route was not preferred for preparing 1A–C because
electrochromic behavior.28,29,31 They are further interesting as the reaction conditions were expected to promote component
possible ambipolar materials because of the electron with- exchange rather than the desired condensation.27 Instead, 4
drawing character of the azomethine bond that gives rise to a was condensed with benzoyl chloride in the presence of
cathodic behavior. Most azomethine derivatives however have triethylamine at room temperature to afford 3 (Scheme 1).
high reduction potentials that preclude their usefulness as The latter was selectively formed over the double condensed
functional materials. Moreover, the cathodic pathway of azo- product owing to the reduced reactivity of the amine once it is
methines usually reduces the heteroatomic bond instead of conjugated with an electron withdrawing group.39 3 was then
producing a visibly detectable reduced state. A significant color reacted with the selected dialdehydes in EtOH and catalytic
difference between the neutral and reduced states is beneficial trifluoroacetic acid (TFA) to afford the desired 1A–C in 60–80%
for high color contrast and is a desired property of electro- yields. The resulting compounds were brightly colored solids.
chromic devices. This is in contrast to azomethine reduction The color of each compound correlated well with the donor
that destroys the conjugation, resulting in irreversible decolora- strength of the central moiety. The electron rich EDOT 1C
tion. Amides were therefore incorporated into the conjugated was red, 1A was orange, and the fluorene derivative 1C was
azomethines for desired cathodic color switching with 1A–C. colored yellow.
The enhanced electron withdrawing character of the amide was
expected to work in concert with the azomethine for color
Electrochemical properties
switching mediated by electrochemical reduction without sacri- Electrochemical measurements of the azomethines were done to
ficing the color change upon oxidization. The multichromati- determine both the oxidation (Eox) and reduction potentials
city of the amide-azomethine derivatives 1A–C having both (Ered). A potential of oxidation contingent on the central aryl unit
electrochemical oxidation and reduction contingent on struc- was observed for the compounds as seen in Fig. 1 and Table 1. 1B
ture are herein presented.
had the less positive potential of oxidation as expected owing to
the strong electron donating EDOT moiety. Meanwhile, 1C had
the most positive Eox as a result of the reduced p-donor strength
of the fluorene relative to its thiophene counterparts. A pseudo-
reversible oxidation was observed for 1B, whereas the oxidation
processes of 1A and 1C were irreversible. The pseudo-reversible
Results and discussion
Synthesis
Azomethines are known for their anodic electrochromic behavior. behavior was assigned based on the appearance of the reverse
Conjugating the terminal acceptor amides with the azomethine wave at increasing scan rates (see Fig. S14, ESI†). The different
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Scheme 1 Synthetic scheme for the preparation of amide-azomethine derivatives 1A–C: (i) Et3N, THF, r.t. and (ii) TFA (cat.), EtOH, r.t. to reflux.
paramount for determining the number of electrons involved in
the electrochemical process, quantification was instead deter-
mined from the Randles–Sevcik equation.41 Using equimolar
ferrocene as the internal reference and assuming the same
diffusion coefficient for ferrocene and 1A–C, all the compounds
were found to undergo a one-electron transfer, as derived from
the linear correlation of current vs. (scan rate)1/2 plots (ESI†).
The cathodic process was also investigated given it was a
desired property. As expected, 1A–C could be reduced within
the operating window of the solvent. This is contrast to the
amide-free derivatives of 1A–C whose reduction is often buried
in the solvent reduction peak. Similar to what was observed
with the oxidation, the reduction potentials were contingent on
the central aromatic unit. The difference in reduction poten-
tials is from the different donor strength of the aryl group that
counteracts the electron withdrawing effect of the azomethines.
This is supported by the Ered of 1B that is 150 mV more positive
than 1C. The reduction process of both 1A and 1B was found to
involve one-electron. The differences in the potential of
reduction were corroborated by DFT theoretical calculations.
The gas phase LUMO energy values calculated from the ground
state optimized geometries were found to increase by 0.2 eV
when progressing from 1A to 1C (see ESI†). Experimentally, the
reduction of 1C could not be accurately determined because of
its close proximity to the solvent reduction peak. This aside, the
electrochemical measurements confirm that the amide-
azomethine derivatives undergo both oxidation and reduction
processes and they are ambipolar.
Fig. 1 Cyclic voltammograms of 1A (black), 1B (red), and 1C (blue) with
0.1 M TBAPF6 at a scan rate of 100 mV sꢀ1 with equimolar ferrocene used
as an internal reference. The reversible redox couple at ca. 450 mV
corresponds to the internal reference.
Table 1 Absorbance of the azomethines in their different states measured
in dichloromethane
b
lmax (nm)
Compound Eoxa (V) Ereda (V) Neutral
Oxidizedc,e
Reducedd,e
1A
1B
1C
1.20
1.05
1.35
ꢀ1.50 480 (Yellow) 300 (Colorless) 500 (Blue)
ꢀ1.45 500 (Orange) 310 (Colorless) 640 (Blue)
ꢀ1.60 430 (Yellow) 330 (Colorless) 540 (Orange)
Optical properties
Values reported are peak potentials relative to Ag/Ag+. Measured in
a
b
The absorbance of 1A–C in the neutral, oxidized and reduced
forms were investigated to further evaluate them as ambipolar
electrochromes. The corresponding spectra of the azomethines
in their different states are seen in Fig. 2 along with the
degassed dichloromethane. Applied potential of 2.0 V vs. Ag/Ag+.
c
Applied potential of ꢀ2.0 V vs. Ag/Ag+. Values in parentheses refers
d
e
to the color detected by the eye as per Table 2.
behavior of 1B is courtesy of the 3,4-disubstitution that increases lmax values and CIE coordinates found in Tables 1 and 2,
the stability of oxidized intermediate and reduces its propensity respectively. As seen with the electrochemical measurements,
to cross-couple via known means.40 Since a reversible behavior is the absorbance maximum of the neutral states of 1A–1C was
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Table 2 CIE Lab color coordinates of the azomethine derivatives in
different statesa
L*
Compound
State
a*
b*
1A
1A
1A
1B
1B
1B
1C
1C
1C
Neutral
96
86
99
87
69
90
93
76
101
14
4.9
0.6
26
ꢀ14
ꢀ0.005
ꢀ4.6
43
48
11
4.4
26
ꢀ27
2.4
52
Reduced
Oxidized
Neutral
Reduced
Oxidized
Neutral
Reduced
Oxidized
11
5.3
ꢀ0.9
a
Measured in dichloromethane.
whereas 1C was 60 nm hypsochromically shifted. The absorbance
shifts are from the different p-donor strengths of the central
aromatic units.
Spectroelectrochemistry was done to evaluate the absor-
bance of the oxidation and reduction states. This was done by
increasing the applied potentials by ꢁ0.1 V and measuring the
resulting absorbance spectrum. The three azomethines under-
went significant color changes when both oxidized and
reduced. For example, the absorbance in the 400–550 nm
region of 1A decreased when oxidized with a concurrent
increase in the absorbance in the 250–300 nm range. The
400–500 nm absorbance similarly decreased when reduced,
but a broad peak from 550–700 nm appeared. In terms of
colors discernable by a user, the neutral form was orange, the
reduced state was blue, and the color bleached when oxidized.
The color changes associated with the different redox states are
seen in the inset of Fig. 2.
1B underwent similar spectral changes. The red color of its
neutral state was bleached with electrochemical oxidization.
This is evident in Fig. 2 where the absorbance at 500 nm
decreases with the simultaneous emergence of a peak around
310 nm when 1B is oxidized. In contrast, the reduced form of
1B was deep blue in color owing to the emergence of a peak
around 550–700 nm. Given the weak yellow color of its neutral
state, the visible color changes of 1C were less pronounced than
1A and 1B. Nonetheless, the color of 1C was bleached when it
was oxidized and it turned orange when it was reduced. The
collective spectroelectrochemical data confirm the ambipolar
character and multichromaticity of the azomethines. The ambi-
polar color change is further seen in the spectroelectrochem-
istry of 1B in Fig. 3. This compound was examined in more
detail because it showed the best optical transitions amongst
the compounds studied. Spectral changes were observed when
applying a potential of +1.0 V vs. Ag/Ag+. No spectral changes
were observed when increasing the potential above 1.8 V.
Similarly, spectral changes were observed for the reduced state
of 1B with applied potentials beginning at ꢀ0.7 V.
Fig. 2 Absorbance spectra of the neutral (black), oxidized (blue), and
reduced (red) forms of 1A (A), 1B (B), and 1C (C). Inset: photographs of
the honeycomb working electrode of the oxidized (left), neutral (middle),
and reduced (right) states.
Electrochromic devices
Since the EDOT derivative 1B showed well defined color changes
contingent on the central aryl unit. Taking 1A as a benchmark, in addition to desired oxidation and reduction processes, this
the absorbance of 1B was bathochromically shifted by 50 nm, azomethine was chosen to fabricate an electrochromic device.
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switching rates can be from the slow diffusion of the large
bulky TBAPF6 electrolyte and associated conformational
changes of the electrochrome.42,43 Reversible switching
between the neutral and reduced states was possible. However,
the neutral and oxidized states could be switched three times
before color degradation occurred (see ESI†). The limited duty
cycle is in part from mixing of the electrochrome with the
electrolytic gel, leading to short circuiting. This aside, the
proof-of-concept device confirms that three-color states are
possible with amide-azomethines when electrochemically
switched between their neutral, oxidized, and reduced states.
Conclusion
Three conjugated electronic push–pull azomethines were prepared
using aromatic cores of varying p-donor strength in addition to end-
capping with electron withdrawing amides. Their absorbance was
contingent on the donor strength of the central aromatic unit. The
three azomethines showed ambipolar electrochromic behavior with
three distinct colored states being observed when switched between
their neutral, oxidized, and reduced states. The EDOT derivative
showed significant color changes when electrochemically oxidized
and reduced, spanning 350 nm across the visible spectrum. These
color transitions were easily detected by the eye and are suitable
optical properties for display purposes. The suitability of the amide-
azomethines for electrochromic materials preparation was demon-
strated with a working electrochromic device that was prepared
from the EDOT derivative. This proof-of-concept study successfully
demonstrated that ambipolar azomethines capable of sustaining
both oxidation and reduction can successively be used as electro-
chromic materials. It further illustrated the advantages of amide
containing conjugated azomethines for achieving ambipolar proper-
ties. The knowledge gained will be used to prepare a new generation
of multichromatic materials having different amides. This provides
the means to tune the reduction potential and color, ultimately
providing the means to tailor the optical and electrochemical
properties of electrochromic devices.
Fig. 3 Spectroelectrochemistry of 1B as a function of applied potential:
(A) 0 to 1.8 V and (B) 0 to ꢀ1.3 V vs. Ag/Ag+.
Experimental section
General procedures
All chemicals and reagents were obtained from commercial
sources unless otherwise stated. Anhydrous and degassed
solvents were obtained from an activated alumina solvent
purification system. CDCl3 was repeatedly passed over a plug
of activated basic alumina to remove undesired acid contami-
nants. The 1H NMR and 13C NMR were completed on a
400 MHz spectrometer. All NMR data was referenced to the
chloroform signal and peak multiplicity was reported as fol-
lows: s = singlet d = doublet, t = triplet, q = quartet, p = pentet,
tt = triplet of triplets, m = multiplet and br = broad.
Fig. 4 Electrochromic device of 1B in the neutral (left) and reduced (right)
states.
This was done to demonstrate the multichromaticity of the ambi-
polar azomethine. The proof-of-concept device using 1B as the
electrochromic layer changed colors similar to what was observed
in solution. As seen in Fig. 4, the functioning electrochromic device
switched from orange to blue when reduced. The switching rates
were slow with this device with the cathodic color change occurred
Absorbance and spectroelectrochemistry
on the order of minutes. Subsequent oxidation of the reduced state Measurements were done on a Cary UV-vis-NIR absorbance
to the original neutral form occurred within seconds. The different spectrophotometer. Electrochemical redox potentials were
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measured on a multichannel potentiostat. Solutions of each dissolved in absolute ethanol (20 mL) followed by the addition
compound were made by dissolving them in anhydrous of a few drops of TFA. The reaction mixture was stirred over-
dichloromethane with 0.1 M NBu4PF6. A 1 mm thick platinum night at room temperature under nitrogen for 1A and 1B. For
wire mesh was used as the working electrode with a platinum 1C, the reaction mixture was refluxed overnight under nitrogen.
wire auxiliary electrode and silver wire reference electrode. The resulting precipitated solids (60–80% yield) were filtered
Measurements were done at 0.1 V intervals.
and washed with copious amounts of cold ethanol to remove
any by-products and unreacted starting materials. The products
were not purified further and they were air dried.
Electrochemistry
Cyclic voltammetry measurements were done on a multi-
Tetraethyl-5,50-((1E,10E)-(thiophene-2,5-diylbis(methanyl-
channel potentiostat. Compounds were dissolved in dichloro- ylidene))bis(azanylylidene))bis(2-benzamidothiophene-3,4-
methane with 0.1 M NBu4PF6. A platinum electrode was used as dicarboxylate) (1A). 1H-NMR (CDCl3): d = 12.25 (s, 2H), 8.49
the working electrode with a platinum wire as the auxiliary (s, 2H), 8.01 (d, 4H, 7.2 Hz), 7.62 (t, 2H, 7.4 Hz), 7.55 (m, 4H),
electrode. The reference electrode was a silver wire electrode. 7.43 (s, 2H), 4.46 (q, 4H,7.1 Hz), 4.38 (q, 4H, 7.1 Hz), 1.49 (t, 6H,
Oligomers solutions (0.1 mM) were prepared with an equimolar 7.1 Hz), 1.39 (t, 6H, 7.1 Hz) 13C-NMR (CDCl3): d = 165.4, 165.2,
amount of ferrocene as an internal reference (Epa = 0.435 V vs. 164.1, 155.2, 146.2, 142.1, 133.3, 132.7, 131.7, 129.3, 127.8, 61.9,
SCE).44 Eox and Ered measurements were done at 100 mV sꢀ1
.
61.8, 14.7, 14.2. HR-MS(+) calcd for [C40H36N4O10S3 + H]+:
829.1666, found: 829.1647.
Device fabrication
Tetraethyl-5,50-((1E,10E)-((2,3-dihydrothieno[3,4-b][1,4]dioxine-
A film of 1B was deposited on an ITO coated glass substrate by 5,7-diyl)bis(methanylylidene))bis(azanylylidene))bis(2-benzamido-
spray-coating a 1 mg mLꢀ1 solution of 1B in dichloromethane thiophene-3,4-dicarboxylate) (1B). 1H-NMR (CDCl3): d = 12.24
on a 10 cm2 area. A UV-curable gel electrolyte was then (s, 2H), 8.54 (s, 2H), 8.01 (m, 4H), 7.63 (m, 2H), 7.55 (m, 4H),
deposited on a separate ITO plate in a square region defined 4.34–4.47 (m, 12H), 1.48 (t, J = 7.1 Hz), 1.38 (t, J = 7.1 Hz). 13C-NMR
by a taped section.30 The two plates were then placed onto each (CDCl3): d = 165.5, 165.2, 164.1, 145.8, 145.7, 144.5, 143.2, 133.2,
other and then compressed together. These were then irra- 129.3, 127.7, 127.1, 121.9, 110.1, 65.3, 61.8, 61.7, 14.6, 14.1. HR-
diated with UV light of 350 nm for 10 min. The finished device MS(+) calcd for [C42H38N4O12S3 + H]+: 887.1721, found: 887.1701.
was connected to an electrochemical workstation using copper
tapes and switched between neutral and charged states.
Tetraethyl-5,50-((1E,10E)-((9,9-dihexyl-9H-fluorene-2,7-diyl)bis-
(methanylylidene))bis(azanylylidene))bis(2-benzamidothiophene-
3,4-dicarboxylate) (1C). 1H-NMR (CDCl3): d = 12.25 (s, 2H), 8.54
(s, 2H), 8.04 (m, 4H), 7.84 (s, 2H), 7.80 (s, 4H), 7.63 (m, 2H), 7.56
Synthesis
2A was commercially available while 2B, 2C, and 4 were (m, 4H), 4.50 (q, 4H, J = 7.1 Hz), 4.40 (q, 4H, J = 7.1 Hz), 1.51
prepared according to previously reported methods.45–49
(t, 6H, J = 7.1 Hz), 1.40 (t, 6H, J = 7.1 Hz), 1.00–1.15 (m, 10H),
Diethyl-2-amino-5-benzamidothiophene-3,4-dicarboxylate (3). 0.76 (t, 6H, J = 7.2 Hz). 13C-NMR (CDCl3): d = 165.8, 165.3, 164.2,
In a 250 mL one-neck round bottom flask equipped with a stir 157.1, 152.4, 145.8, 143.9, 143.1, 135.6, 133.2, 131.9, 129.3,
bar, 4 (1.0 g, 3.87 mmol) was dissolved in THF (100 mL) and 129.1, 127.8, 127.0, 122.9, 120.8, 109.9, 61.8, 61.7, 55.4,
triethyl amine (1.35 mL, 9.66 mmol). To this was added benzoyl 40.5, 31.7, 23.9, 22.7, 14.7, 14.2, 14.1. HR-MS(+) calcd for
chloride (0.45 mL, 3.87 mmol) and the reaction mixture was [C61H66N4O10S2 + H]+: 1079.4293, found: 1079.4276.
stirred at room temperature under nitrogen overnight. The
solvent was evaporated under vacuum to remove most of
the THF, after which dichloromethane (100 mL) was added.
The solution was washed with a sodium bicarbonate solution
Acknowledgements
followed by brine. The organic phase was extracted, dried with Financial support from the Natural Sciences and Engineering
magnesium sulfate, and then filtered. The resulting crude Research Council of Canada is acknowledged for Discovery,
product was purified by column chromatography using a 1 : 1 Strategic Research, Idea to Innovation, and Research Tools and
mixture of ethyl acetate : hexane as the eluent. The title com- Instrument grants. Canadian Foundation for Innovation is also
1
pound was isolated as a yellow solid in 50–60% yield. H-NMR acknowledged for additional equipment and infrastructure.
(CDCl3): d = 11.45 (s, 1H), 7.94 (m, 2H), 7.59 (m, 1H), 7.52 (m, The Center for Self-Assembled Chemical Structures is also
2H), 5.50 (s, 2H), 4.35 (q, 2H, J = 7.2 Hz), 4.29 (q, 2H, J = 7.2 Hz) acknowledged. S.K. thanks NSERC for an undergraduate
1.36 (t, 3H, J = 7.2 Hz), 1.34 (t, 3H, J = 7.2 Hz). 13C-NMR (CDCl3): scholarship.
d = 166.2, 165.4, 163.8, 154.6, 135.6, 132.9, 132.0, 129.1, 127.5,
110.2, 102.1, 61.2, 60.4, 14.6, 14.4. HR-MS(+) calcd for
[C17H18N2O5S + H]+: 363.1009, found: 363.1015.
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