Rose Bengal Immobilized on Supported Ionic-Liquid-like Phases: An Efficient Photocatalyst for Batch and Flow Processes

Article abstract of DOI:10.1002/cssc.201901533

The catalytic activity of Rose Bengal (RB) immobilized on supported ionic liquid (IL)-like phases was evaluated as a polymer-supported photocatalyst. In these systems, the polymer was designed to play a pivotal role. The polymeric backbone adequately modi

Full text of DOI:10.1002/cssc.201901533

Accepted Article
Title: Rose Bengal immobilized onto Supported Ionic Liquid-like
Phases: Efficient photocatalyst for batch and flow processes
Authors: Santiago Vicente Luis, David Valverde, Raul Porcar, Diana
Izquierdo, M. Isabel Burguete, and Eduardo Garcia-Verdugo
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ChemSusChem
10.1002/cssc.201901533
FULL PAPER
Rose Bengal immobilized onto Supported Ionic Liquid-like
Phases: Efficient photocatalyst for batch and flow processes
[
a]
[a]
[a]
[a]
[a]
David Valverde, Raul Porcar, Diana Izquierdo, M. Isabel Burguete, Eduardo Garcia-Verdugo*
[
a]
and Santiago V. Luis*
Abstract: The catalytic activity of Rose Bengal immobilized onto
supported ionic liquid-like phases has been evaluated as a polymer
supported photocatalyst. In these systems, the polymer is designed
to play a pivotal role. The polymeric backbone adequately modified
with ionic liquid-like moieties (Supported Ionic Liquid-Like Phases,
SILLPs) is not just an inert support for the dye but controls the
accessibility of reagents/substrates to the active sites and provides
specific microenvironments for the reaction. The structure of SILLPs
can be fine-tuned to adjust the catalytic efficiency of the RB−SILLP
composites achieving systems more active and stable than the
related systems in absence of IL-like units.
to processes performed in organic solvents like chloroform or
dichloromethane. To avoid the use of such non-polar VOC
solvents, the hydrophilic/hydrophobic balance of the support
should be fine-tuned increasing their compatibility with polar
solvents like water and alcohols.
Ionic Liquids (ILs) have been evaluated as alternative reaction
12-14
media for a wide range of catalytic processes,
and also
represent a simple and tunable alternative for the immobilization
and stabilization of photosensitizers, opening new avenues for
15-23
photocatalytic synthetic processes.
However, processes
involving homogenous ILs require the full recovery of the IL-
phase and the photosensitizer in a further step, which is not
always a simple task. The simplest solution is represented by
24
the use of supported ionic liquids (SILs). In the case of
polymers bearing IL-like fragments colantly atttached (Supported
Ioinic Liquid-Like Phases: SILLPs) the nature and loading of the
IL-like units influence the macroscopic properties of the
Introduction
Singlet oxygen is a powerful and versatile reagent that has been
applied for a wide range reaction of sequences in order to
25
material, but also plays an important role on the activity and
1
synthetize molecules with a certain degree of complexity. It can
stability of the immobilized catalytic species. Indeed, both the
polymer nature and the structural features of the IL-like units can
be considered as a green reagent, being generated in situ from
2
oxygen through irradiation with visible light of a photosensitizer.
26
be used to fine-tune their catalytic efficiency. Furthermore,
The use of singlet oxygen does not produce any waste or
SILPs based on solid-insoluble crosslinked polymers allow their
straightforward application for the development of continuous
3
residue, other than the photocatalyst, at the end of the process.
In this context, different approaches have designed for the
immobilization of photosensitizers into a different phase than
reactants and products, facilitating its recovery and reuse for
27
flow processes. In the search of new applications of SILLPs,
here we report the synthesis of polymeric materials modified
with IL-like units as suitable supports and solid media for
photocatalytic processes. The use of supported Rose Bengal,
immobilized on a variety of SILLPs, has been evaluated as a
photosensitizer for the photooxygenation of furoic acid as a well-
established benchmark reaction.
4,5
further catalytic cycles.
However, in some cases, this
immobilization can lead to a reduction of the photocatalytic
efficiency through the quenching of the excited states by the
polymeric matrix or by shortening the lifetime of the reactive
species. Therefore, an efficient support should provide a suitable
environment for the photocatalyst, providing site isolation to
prevent dye oligomerization and self-quenching, enhancing
quantum yields for singlet oxygen formation and dye
Results and Discussion
6
-8
photostability.
The support should also facilitate the
IL-like polymeric materials (PILs) were easily prepared by the
accessibility to the immobilized species of the reagents and
polymerization of monomers containing imidazolium fragments
9
substrates used in the selected solvents.
28-30
(
Scheme 1).
Different di-styrenic bisimidazolium monomers
Traditionally polymeric supported photocatalysts have been
based on hydrophobic matrices, which are hardly compatible
were obtained by alkylation of 1-(4-vinylbenzyl)-1H-imidazole
with different -bisbromoalkanes (n= 2, 4 and 6 for 1-3
respectively, Scheme SI.1). These crosslinking monomers were
co-polymerized with 2-hydroxyethyl methacrylate (4, HEMA)
using a 4:6 weight ratio, in presence of porogenic agents,
leading to a series of monolithic polymers (5-7). Materials
containing different monomer 2 : HEMA ratios were also
prepared (6a-c). Additionally, the imidazolium monomer 8,
obtained by alkylation of N-butylimidazole with p-chloromethyl
styrene, was co-polymerized with three different crosslinkers,
the divinylic momomer 2, trimethylolpropane trimethacrylate (9)
and N,N′-methylene-bis-acrylamide (10). Table 1 summarizes
1
0,11
with polar or aqueous environments,
limiting their application
[
a]
Professor, S. V. Luis and Dr. E. Garcia-Verdugo
Department of Inorganic and Organic Chemistry,
Supramolecular and Sustainable Chemistry Group, University
Jaume I, Avda Sos Baynat s/n, E-12071-Castellon. Spain. 1
E-mail: luiss@uji.es, cepeda@uji.es
Supporting information for this article is given via a link at the end
of the document.
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ChemSusChem
10.1002/cssc.201901533
FULL PAPER
the polymerization mixtures used for preparing all these
The immobilization of Rose Bengal (RB) was performed by
31
materials. All of them were obtained in excellent yields (>
5 %) and showed a good compatibility with polar solvents such
suspending the polymeric matrices (5-7 and 11-13) in
a
9
methanolic solution of RB. Eight different SILLPs, all of them
-2
as water and methanol. Thus, for instance, polymer 11 was able
to absorb 45.9 g of water / g of polymer and 24.6 g of MeOH / g
of polymer, while polymers 12 and 13, with higher crosslinking
degrees, showed lower absorption capacities (4.8 g water / g
and 3.4 g MeOH / g for polymer 12 or 5.7 g of water / g and 3.9
g of MeOH / g for polymer 13).
loaded with 3.92 x 10 mmol RB / g of polymer, were obtained
(15-22, Scheme 2). The total absence color of the solution
indicated the quantitative absorption of RB onto the polymeric
matrix. Furthermore, during the polymer washing no color loss
was detected and the analysis by UV-Vis at 557 nm of the
MeOH used did not show the presence in the washing solution
of any trace of leached RB.
Scheme 2. Immobilisation of RB on SILLPs. i) 1 mL of a 1000 ppm solution of
RB in MeOH for each 25 mg of polymer. RB loading 39.36 mol of RB / g.
In order to evaluate the photocatalytic efficiency of those RB-
SILLPs, the photooxygenation of 2-furoic acid 21 to butenolide
22 (5-hydroxy-5H-furan-2-one) was assayed as a benchmark
reaction (Scheme 3). A long list of applications of butenolide 22
can be found in the literature, being an important starting
substrate for the synthesis of insecticides, prostanoids, alkaloids,
3
2,33
etc.
The oxidation of 2-furoic acid (21) to 22 was carried out
o
Scheme 1. Synthesis of PILs by polymerization. i) 65 C, H
2
O, 1% AIBN. ii) 65
o
o
by irradiating (125 W Hg vapor lamp) a suspension of the
corresponding supported photocatalyst in a solution of 21. The
reactions were monitored by UV–vis following the bleaching of
the characteristic absorption band of 21 at 247 nm. Both
conversions and rate constants were used to analyze the
efficiency of the different polymeric photosensitizers.
C, MeOH/H
2
O (4:1), 1% AIBN. iii) 70 C, MeOH/H
2
O (5:1), 1% AIBN.
Table 1. Polymerization mixtures.
IL-
monomer
wt/wt)
co-
monomer
(wt/wt)
[
a]
Loading
[c]
Entry
SILLP
5
[b]
% IL
mmol/g
(
1
2
3
4
5
6
7
8
1 (0.4)
2 (0.8)
2 (0.5)
2 (0.4)
3 (0.4)
8 + 2(1)
8 (0.5)
8 (0.5)
4 (0.6)
1.24
68.9
92.3
80.6
73.0
74.1
100
6a
6b
6c
7
4 (0.2)
4 (0.5)
4 (0.6)
4 (0.6)
2 (0.1)
9 (0.5)
10 (0.5)
1.58
1.38
1.25
1.21
3.17
1,27
2.27
Scheme 3. Photocatalytic benchmark reaction: 50:1 substrate : photocatalyst
molar ratio (2% molar), room temperature. Irradiation: 125
pressure Hg vapor lamp for 120 min in open reaction test tubes equilibrated
with air. [21] = 9.6 mM in MeOH
11
12
13
W medium
35.1
62.0
Under these conditions, all the supported photocatalysts yielded
>
90 % conversions after 120 minutes. Essentially, a quantitative
[
H
a] AIBN 1% by weight of the polymerization mixture, porogen:
O/diethylenglycol (1:1 by weight) for 5, 6 and with a porogen :
monomeric mixture ratio of 75:40 by weight. Porogen for 11: H O, porogen
for 12: MeOH H O (4:1), porogen for 13: MeOH H O (5:1) with a porogen :
momeric mixture ratio of 4.5:1 by weight for 11, 2.5:1 by weight for 12 and
.5:1 by weight for 13. [b] Imidazolium unit loading calculated by elemental
analysis. [c] Percentage by weight of the IL-like units calculated as IL (%) =
mmol of imidazolium unit polymer) molecular weight of the
imidazolium salt fragment in the corresponding polymer x 10 .
selectivity for the transformation of 21 into 22 was observed in
all cases. It should be noted that no loss of the characteristic
coloration of the Rose Bengal was observed at the end of the
reaction in any of the cases studied. Small differences were
observed for the kinetic profiles of the tested systems showing,
regardless of loading and type of IL-like moieties, similar
catalytic efficiencies (Table 2, Fig. SI.1). In the same way, the
percentage and type of the crosslinker seems to have little
2
7
2
2
2
6
(
/
g
x
-
1
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ChemSusChem
10.1002/cssc.201901533
FULL PAPER
influence. Noteworthy, faster kinetics were observed for the
immobilized RB-SILLPs than for an RB solution and conversions
achieved after 120 min were always better than those for the
control experiment catalyzed by the disodium salt of RB (95-
higher RB loading (16c), while an irradiation time of 180 minutes
was required for the photocatalyst with the lowest RB-loading
(23c). The photocatalysts with intermediate loadings (23a and
23b) showed similar profiles of yield vs time (Fig SI.3) than 16c,
albeit their RB loadings were 2 and 10 times lower, respectively.
Thus, the highest TON and TOF50 values were obtained for 23c,
a polymer with a very low RB loading (0.2 µmol/g) with TON =
99% vs. 65-70%). The reuse of the photosensitizer 16c in
consecutive reaction cycles was also studied. This RB-SILLP
system was very stable, being reused for eight reaction cycles
without any decay in its photocatalytic activity (see Fig. SI.2).
-1
2867 (30 min) and TOF50 = 5213 h . These results suggest that
for the polymeric photosensitizer 16c (having the highest loading,
39.36 µmol of RB/g of SILLP) RB groups located near the
Table 2. Photooxydation of 21 by different RB-SILLPs obtained by
polymerisation.
surface of the polymer can act as a filter, absorbing the incident
radiation and preventing it from reaching the dye groups located
in more hindered sites ("screen effect"). This effect decreases
upon the reduction of the RB loading, increasing the catalytic
efficiency per dye unit. All the systems presented so far are
based in SILLPs obtained by copolymerization of the
corresponding IL-monomers (Scheme 1). In order to stablish the
effect of the polymer matrix on the behavior of the
-
4
Loading
mmol/g
[b]
Conv.
(%)
k 10
(s )
Entry
RB-SILLP
15
[a]
% IL
[c]
-1 [d]
1
1.24
68.9
92.3
80.6
73.0
74.1
100
35.1
62.0
-
99
97
90
98
99
98
99
98
70
4.51 ± 0.18
3.81 ± 0.06
3.29 ± 0.10
4.43 ± 0.09
4.2 ± 0.8
2
3
4
5
6
7
8
9
16a
16b
16c
17
1.58
1.38
1.25
1.21
3.17
1,27
2.27
-
photosensitizers,
a new series of gel type SILLPs were
synthesized (Scheme 4) by grafting IL-like units onto already
preformed polystyrene-divinylbenzene polymeric matrices (PS-
DVB, Merrifield gel-type resins). Three different SILLPs (25a-c)
were synthetized by modification of PS-DVB resins with different
loadings (1.1, 2.1 and 4.1 meq Cl / g, 24a-c, 1% DVB, gel-type,
18
5.4 ± 0.3
19
5.3 ± 0.3
200-400 mesh).
20
5.5 ± 0.19
3.25 ± 0.11
RB
[
a] Imidazolium units loading calculated by elemental analysis. [b]
Percentage by weight of the IL-like units calculated as IL (%) = (mmol of
imidazolium unit / g polymer) x Molecular weight of the imidazolium salt
-
1
fragment in the corresponding polymer x 10 . [c] Conversion for the photo-
oxidation of 21. [d] Rate constants for the photooxidation of 21 calculated
as the first-order rate constant for the initial period of the reaction.
Table 3. Effect of the RB loading onto SILLP 6c
-
4
[c]
µmol of
RB/g
k 10
(s )
TON
TOF50
(h )
Entry
RB-SILLP
16c
-1 [a]
[b]
-1
1
39.36
19.84
0.40
4.43 ± 0.09
4.65 ± 0.11
4.95 ± 0.07
1.93 ± 0.012
26
57
57
2
3
4
23a
23b
23c
114
527
Scheme 4. Synthesis of gel-type SILLPs and the corresponding RB
photocatalysts i) methylimidazole in DMF, 80 C, 14 hours. ii) 1 mL of a 1000
ppm solution of RB in MeOH for each 25 mg of polymer. RB loading 39.36
µmol of RB / g. iii) anion metathesis with the corresponding salt in MeOH.
o
289
2867
0.20
5213
The modification with methylimidazole took place quantitatively
with a significant change on the resin polarity. SILLPs 25a-c,
although based on a PS-DVB hydrophobic polymeric backbone,
showed a significant swelling in a polar solvent like MeOH, with
swellings of 40%, 59% and 84% (percentage of diameter
increase in methanol) for 25a, 25b and 25c respectively. RB
was quantitatively absorbed on polymers 25a-c and the resulting
RB-SILLPs (26a-c) were assayed for the model photooxidation
of furoic acid 21. Results obtained are summarized in Table 4
and Fig SI.4. The different kinetic profiles observed for these
systems suggest that the amount of IL-like units can be used to
fine-tune the catalytic behavior of the RB-SILLPs. For the
[
a] Rate constant for the photooxidation of 21 calculated as the first-order
rate constant for the initial period of the reaction. [b] TON calculated at 30
min. [c] TOF calculated at 50% of conversion.
Encouraged by these results, the effect of different variables
was evaluated in order to optimize the efficiency of the
immobilized system. In this way, the influence of the RB loading
on the SILLP was firstly examined. Variable amounts of RB were
absorbed onto the polymer 6c (39.36 to 0.20 µmol of RB / g of
SILLP, polymers 16c and 23a-b). Results obtained are
summarized in Table 3 and Fig. SI.3. A complete conversion of
2
1 was observed after 60 min of reaction for the catalyst with the
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ChemSusChem
10.1002/cssc.201901533
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polymers with a low loading of IL-like moieties (26a), the limited
swelling in MeOH can provide a less effective diffusion of
These results suggest that the IL-like units in the support allow a
fine-tuning of the photocatalytic efficiency of RB. This is
highlighted in Fig. 1, which shows a comparison of the RB-
SILLPs 16c and 26a with the commercially available RB grafted
onto PS-DVB (1% crosslinking, 0.1 mmol RB / g, 200-400 mesh,
31). RB immobilized on polymers containing IL-like units
(SILLPs) was clearly more active systems that when supported
on a polymer lacking such units, with the initial reaction rate
being ca. 7.5 times higher for RB-SILLPs.
reagents and oxygen through the polymer beads. In this regard,
1
a good diffusion is essential since
2
O is a short lived species
that might be quenched by the protic solvent before meeting the
substrate. Besides, a lower swelling can also produce local
photocatalyst aggregates (higher local concentration), which
would decrease the photochemical activity.
Table 4. Effect of the amount of IL-like units on the SILLPs.
[
a]
-4
Loading
(
[b]
k 10
(s )
Entry
Cat
26a
% IL
-1 [c]
mmol/g)
1
0.89
23
2.99 ± 0.03
7.90 ± 0.40
5.13 ± 0.08
2
3
26b
26c
1.92
2.99
45
70
100
a)
a)
80
6
0
0
-
-
0
,0
%(Cl )
Cl
[
a] Imidazolium units loading calculated by elemental analysis. [b] Percentage
by weight of the IL-like units calculated as IL (%) = (mmol of imidazolium unit /
polymer) Molecular weight of the imidazolium salt fragment in the
-
%(NT
TfO
-
f
)
-
-
-
0,5
1,0
1,5
2
4
g
x
-
-
-
1
%(
B
F
B
4
F4 )
corresponding polymer x 10 . [c] Rate constants for the photooxidation of 21
calculated as the first-order rate constant for the initial period of the reaction.
Cl
-
-
Ntf2
BF4
TfO
SbF6
2
%(TfO )
NTf
-
%(Sbf
SbF
-
6
6
20
0
)
0
500
1000
1500
2000
2500
3000
time (s)
0
20
40
60
80
100
120
time (min)
b )b )
SbF
SbF6
-
6
1
2
3
6c
6a
1
Tf OT f-O
B FB F4
-
4
NT
N
f
Tf2
-
2
ClC- l
,0000
0
0,0002
0,0004
0,0006
0,0008
Rate constant
Rate constant
Figure 2. a) Yield vs time profiles obtained for RB-SILLPs derived from 26a by
anion metathesis (27a-30a) for the oxidation 2-furoic acid with singlet oxygen
1
(
2 i 0 i 0
O ). Inset: ln(C/C )=kt for the initial period of the reaction, where C and C
are the concentrations of 21 at a certain time (t) and at t = 0, respectively.
Conditions: 50:1 substrate photocatalyst molar ratio (2% molar), room
Figure 1. Comparison of yield vs time profiles obtained for the oxidation 2-
1
:
furoic acid with singlet oxygen ( O
2
) in the presence of RB-SILLPs 16c and
temperature. Irradiation: 125W medium pressure Hg vapor lamp for 120 min in
open reaction test tubes equilibrated with air. [21] = 9.6 mM in MeOH. b) Effect
of the IL-like moieties counteranion on the rate constants.
2
6a and in the presence of commercial RB-PS-DVB 31. 50:1 substrate :
photocatalyst molar ratio (2% molar), room temperature. Irradiation: 125W
medium pressure Hg vapor lamp for 120 min in open reaction test tubes
equilibrated with air. [21] = 9.6 mM in MeOH. Squares: 16c. Dots: 26a.
-
4
-1
Triangles: 31 (Necker´s catalyst). Initial reaction rates: 6.19 ± 0.12 x 10 (s )
The nature of the anion can also be used to tune the properties
-
4
-1
-4
-1
34-36
for 16c; 6.40 ± 0.14 x 10 (s ) for 26a and 0.82 ± 0.02 x 10 (s ) for 31.
of catalytic units immobilized onto SILs.
Therefore, the effect
-
of the anion was evaluated by exchanging the Cl anion of the
-
-
-
-
RB-SILLP 26a by BF
4 2 6
, NTf , TfO and SbF (RB-SILLPs 27a-
The photocatalytic activity was clearly improved by the
enhanced swelling in MeOH for 26b. However, the further
increase in swelling for 26c is accompanied by some decrease
in activity. The much larger diameter of the polymeric beads for
3
0a, Scheme 4). ATR-FTIR and Raman spectroscopy were
2
5
used to follow the corresponding anion exchange, while diffuse
reflectance UV-vis spectroscopy was used to analyze the
presence of Rose Bengal. It has been reported that RB grafted
onto Merrifield resins display two high intensity absorption bands
located between 571 and 560 nm. The presence of a shoulder
at shorter wavelengths (ca. 530 nm) has been associated to the
formation dimers or aggregates in homogeneous and supported
2
6c when swollen, can hamper the efficient radiation absorption
by the RB units at the core of the particles. Accordingly, a
compromise between the loadings of both the photocatalyst and
the IL-like units must be reached to achieve the best catalytic
performance.
3
7
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3
8,39
40,41
RB esters.
RB-SILLPs displayed two broad bands at 566±3
at a wavelength not usable directly by the photosensitizer.
Thus, a QDs-SILLP (31) composite was easily obtained by
exposing SILLP 25a to solution of core–shell CdSe/ZnS QDs (50
and 523±4 nm, affected in position and intensity by the
counteranion present (Fig. SI.5 and Table SI.1) along with a
small shoulder below 500 nm. These changes highlight the very
different environment for the dye present in RB-SILLPs and that
is also affected by the nature of IL-like fragments counteranion.
Independently of the anion present, most photosensitizers
showed a similar activity (Fig. 2). Only 30a bearing SbF
anion, showed an increased reactivity in comparison with the
photosensitizers containing Cl , TfO , NTf and BF , which can
2 4
µg/mL in toluene). UV-Vis data indicated
a quantitative
immobilization of the QDs in the SILLP. Then, RB was
supported on the QDs-SILLP, affording the QDs-RB-SILLP
composite (32) with a loading of 60 µg of QDs / g and 39.36
µmol of RB / g of composite. As seen in Fig. 3, the use of the
composite 32 allowed the photooxidation to occur efficiently
when irradiating with blue UV-LEDs. Thus, at 15 minutes a 32%
conversion was obtained for the QDs-RB-SILLP 32, while only a
5 % yield was achieved with the related RB-SILLP 26a. This
suggests the existence of an effective Förster's Resonance
Energy Transfer (FRET) process leading to the indirect
excitation of the RB moiety when exciting the QD nanoparticle.
The overlapping between the emission of QDs and the
absorption of RB at the SILLP leads to population of the RB
triplet state and concomitantly to the efficient generation of
-
6
as the
-
-
-
-
be related to the low coordinating ability of this anion facilitating
a tighter interaction of RB with the IL-fragments.
All the above reactions were assayed with high-pressure Hg
lamps, which can be considered as the standard light source for
UV photochemical reactions. However, for this type of light
source, there is some mismatch between the light emitted and
the absorption frequency of the target molecular dye, which can
lead to reduction in efficiency, photocatalyst deactivation,
degradation of products and less selective processes. Therefore, singlet oxygen. Nevertheless, the process was less efficient that
the use of using simple LEDs, instead of the Hg lamp, was also
evaluated. UV-LEDs allow energy efficient, reliable, and simple
generation of almost monochromatic near-UV light, and allow a
straightforward building of cheap photochemical reactors. Figure
SI.6 shows the comparison of the results obtained from RB in
solution as well as with the RB-SILLP 27a, using the Hg lamp
and green UV-LEDs, for the photooxidation of 21. Comparable
results were obtained, especially regarding the initial rates,
although the Hg lamp, with a higher power, achieved slightly
higher final yields.
when irradiating directly 26a with green UV-LEDs (Fig. 3) even if
the initial rates were comparable.
Figure 4. Yield vs time on stream obtained for the photooxidation of 21. Dots:
-
1
-1
Necker catalyst at 0.1 mL min . Squares: 26a at 0.1 mL min . Triangles: 26a
-
1
at 0.05 mL min .
Continuous flow processes can help to increase the
sustainability of photocatalytic reactions as they present some
distinct advantages such as the easy separation of products and
the continuous reutilization of the photocatalyst in consecutive
cycles, avoiding downtime, and the consequent loss of
Figure 3. Yield vs time profiles obtained for the oxidation 2-furoic acid with
1
42
singlet oxygen ( O
2
). Conditions: 50:1 substrate : photocatalyst molar ratio (2%
productivity. Fig. SI.7 shows a schematic representation of the
molar), room temperature. Irradiation: Blue LED for 300 mim in open reaction
continuous flow reactor used to perform the photooxidation of
furoic acid. The system consists in a HPLC pump that feeds the
substrate to the reactor, which is a fluid bed reactor loaded with
RB-SILLP. A Hg lamp was used as the light source. The
behavior of 26a was compared with that of the commercially
test tubes equilibrated with air. [21] = 9.6 mM in MeOH. Squares: 26a. Dots:
-
4
-1
3
±
2 (QDs-RB-SILLP). Initial reaction rates: 1.32 ± 0.09 x 10 (s ) for 26a; 4.05
0.08 x 10 (s ) for 32.
-4 -1
1
0
available Necker catalyst (RB-PS-DVB). Figure 4 summarizes
Besides, the use of LEDs can open new avenues in the search
for more efficient photocatalytic processes. This is illustrated by
the combination of RB-SILLPs with a semiconductor quantum
dot (QD, i.e. CdSe), acting as a ‘light antenna’ to capture energy
-1
the results obtained. Using an initial flow rate of 0.1 mL min ,
the commercial catalyst provided a yield of ca. 25 %, which was
lower than the one achieved with 26a (ca. 45% yield).
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Furthermore, the commercial catalyst showed
deactivation after 200 min on continuous use, while the
performance of the RB-SILLP remained constant during at least
a
strong
copolymer resins (Merrifield peptide resin, 200-400 mesh, 1.2, 2.1 or 4.3
mmol / g Cl loading, 2 % cross-linked), methanol (MeOH, 99.9%,
Scharlau), bis(trifluoromethane) sulfonimide lithium salt (LiNTf , 99%,
2
Aldrich), acetone HPLC (99.9%, Scharlau) and other salts and solvents
were used as received.
-
8
7
hours. The yield with 26a could be further improved until ca.
0% by increasing the residence time through reducing the flow
-1
rate to 0.05 mL min . These results suggest that the continuous
flow photochemical generation of singlet oxygen can be
achieved by the simple immobilization RB onto SILLPs providing
a scalable, selective and high‐yielding platform, where the
oxidation proceeds using only light, air and catalytic amounts of
supported RB.
General characterization protocols: FT-IR spectra were obtained using
a spectrometer (JASCO FT/IR-6200) equipped with an ATR (MIRacle
-1
single-reflection ATR diamond/ZnSe) accessory at 4 cm resolution
-
1
(4000-600 cm spectral range). Raman spectra were obtained with a
NRS-3100 (Jasco) dispersive Raman spectrometer equipped with an
optical microscope and an air-cooled CCD detector (-65 ºC) using the
following conditions: 785 nm laser with a single monochromator, 600
−
1
l/mm grating, 0.2 mm slit, 12.75 cm
wavenumber of 1200 cm
resolution; with
a center
−
1
, a laser power of 90.1 mW and 10
Conclusions
accumulations of 5 s. Elemental analyses were obtained with a CHN
1
Euro EA 3000 instrument. H-NMR experiments were carried out using a
1
Rose Bengal immobilized onto SILs prepared by direct
copolymerization of imidazolium monomers or by grafting
imidazolium units on already performed polymers efficiently
promotes the photooxidation of furoic acid by generation of
singlet oxygen. The supported photocatalysts are equally active
under irradiation using an Hg lamp or, alternatively, under UV-
LEDs irradiation. The chemical and structural parameters of the
SILLPs can be easily fine-tuned to optimize the catalytic
efficiency of the RB-SILLPs. Adjusting the IL-like units loading
as well as the nature of the IL-counteranion has allowed
obtaining supported catalysts that are significantly more active
than related systems lacking the IL-like units, including
commercially available RB-PS-DVB systems. Furthermore, the
presence of these IL-like units facilitates the immobilization and
stabilization of QDs working as light antennas to increase the
light harvesting capacity at wavelengths not corresponding to
the optimal absorption of RB. Optimized RB-SILLPs showed a
remarkable stability and this has been used for developing an
Varian INOVA 500 ( H-NMR, 500 MHz) spectrometer. Chemical shifts
are given in delta (δ) values relative to TMS and the coupling constants
(
J) in Hertz (Hz). UV-Vis spectroscopy measurements were performed in
a Shimadzu UV2450 spectrophotometer (diffuse reflectance mode for
polymers) using an integrated sphere accessory and a light wavelength
range between 200 and 800 nm.
Synthetic protocols: Monomers 1-3 and 8 were obtained as shown in
43
Scheme SI.1 according to methods already reported in the literature.
Synthesis of 1-(4-vinylbenzyl)-1H-imidazole. NaHCO
mmol, 1.25 eq) was added to a mixture of imidazole (13.61 g, 199 mmol,
4 eq) in CH CN, then 1-(chloromethyl)-4-vinylbenzene (7.1 mL, 49.8
3
(5.25 g, 62.4
3
mmol, 1 eq) was added dropwise at RT. After the addition, the reaction
mixture was heated to 50 ºC and stirred for 20 h. The solvent was
removed in vacuum, and the remaining solution was extracted with
diethyl ether. The organic phase was washed with 2 M HCl (final pH = 4-
5
7
) 4 M NaOH was then added to the resulting aqueous phase until pH =
-8 (cloudy solution), and this solution was extracted with diethyl ether.
2 4
The obtained organic phase was dried over Na SO and the solvent was
removed in vacuum to afford the desired 1-(4-vinylbenzyl)-1H-imidazole
(6.55 g, 71 % yield).
efficient
continuous
mini-flow
photocatalytic
process
-
1
implemented for the photooxidation of 21, which demonstrated
to be a more active and stable system than the related one
using the commercial polymer where the photosensitizer is
grafted to a PS-DVB backbone in the absence of IL-like units.
These results open a new avenue for the combination of
advanced materials based on polymeric ionic liquids with
organic photo-dyes to develop more efficient and easier to use
photocatalytic systems.
FT-IR (cm ): 3005; 1570; 1505; 1408; 1320; 1285; 1231; 1017; 825; 745;
-
1
6
8
1
=
1
1
22. Raman (cm ): 3059; 1622; 1571; 1409; 1347; 1205; 1182; 1075;
1
3
31; 639. H NMR (CD OD, 500 MHz), δ (ppm): 5.08 (s, 2H), 5.27 (d, J =
0.9 Hz, 1H), 5.75, (d, J = 17.9 Hz, 1H), 6.66-6.71 (m, 1H), 6.88 (d, J
17.7 Hz, 2H), 7.08 (d, J = 9.5 Hz, 2H), 7.36 (d, J = 8.1 Hz, 2H), 7.53 (s,
3
H). C NMR (CD OD, 300 MHz) δ (ppm) 49.9, 115.2, 120.9, 127.1,
13
28.4, 129.4, 136.8, 137.3, 138.1. ESI/MS (m/z). [M+H] = 185.2.
General procedure for the synthesis of ionic monomers 1-3. 1-(4-
vinylbenzyl)-1H-imidazole (4.2 mmol), the appropriate dibromo-alkyl
3
spacer (2 mmol), and CH CN (10 mL) were loaded into a 25 mL two‐
necked flask. The mixture was heated to 80ꢀ°C for 24 h. The reaction
mixture was cooled down to RT and transferred to a 100 mL round‐
bottomed flask. The product was precipitated with Et O (50 mL) and
2
Experimental Section
sonicated for 10 min, and the white solid was then left to settle. The liquid
phase was removed carefully, and the washing procedure was repeated
Materials: All the reagents and solvents used were commercially
available. 4-vinylbenzyl chloride (p-chloromethylstyrene, 90%, Aldrich)
was purified over a column of basic aluminium oxide. 2,2′-Azobis(2-
methylpropionitrile) used as free radical initiator (AIBN, >98%, Aldrich),
N,N-dimethylformamide (DMF, 99.5%, Scharlau), 1-methylimidazole
twice with Et
2
O (2×50 mL). Finally, the white solid product was dried
under vacuum overnight.
3
3
,3′‐(Ethane‐1,2‐diyl)bis(1‐(4‐vinylbenzyl)‐1ꢀH‐imidazol‐
‐ium) chloride (1). Obtained as a white solid in 60% yield using the
(99%,
Aldrich),
1-butylimidazole
(98%,
Aldrich),
1-decyl-2-
former standard procedure.
methylimidazole (97% Aldrich), trimethylolpropane trimethacrylate
-1
FT-IR (cm ): 3053; 1558; 1416; 1341; 1156; 988; 908; 857; 795; 623.
(
(
technical grade, TMPTMA Aldrich), N,N ′ -methylenebis(acrylamide)
99% Aldrich), 4,5,6,7-tetrachloro-2′,4′,5′,7′-tetraiodofluorescein
-1
Raman (cm ): 1620, 1601, 1414, 1316, 1195, 1174, 1016, 828, 629, 291.
1
3
H-NMR (CD OD, 500 MHz) δ (ppm) 4.74 (s, 4H), 5.28 (d, J = 10.9 Hz,
disodium salt, Acid Red 94, Rose Bengal B sodium salt (Rose Bengal
sodium salt, 95%, Aldrich), polystyrene-bound Rose Bengal B (200-400
mesh, ~0.1 mmol / g, Aldrich), chloromethylated stryene/divinylbenzene
2
=
H), 5.41 (s, 4H), 5.84 (d, J = 17.7 Hz, 2H), 6.70-6.76 (m, 2H), 7.35 (d, J
18.1 Hz, 4H), 7.49 (d, J = 8.1 Hz, 4H), 7.72 (d, J = 7.9 Hz, 2H), 7.82 (d,
13
3
J = 7.9 Hz, 2H), 9.32 (s, 2H). C RMN (CD OD, 300 MHz) δ (ppm), 35.5,
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ChemSusChem
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FULL PAPER
-
1
5
3.0, 114.5, 122.9, 123.3, 127.0, 129.1, 133.5, 136.0, 139.1. ESI/MS
Polymer 11. FT-IR (cm ): 3382, 3133, 3058, 2959, 2928, 2870, 1630,
1613, 1560, 1513, 1453, 1425, 1359, 1326, 1155, 1117, 1020, 850, 825.
CHN analysis: %N (found): 8.9%, loading 3.17 mmol IL-like units / g of
polymer. %N (expected): 9,10% for 3.25 mmol IL-like units / g of polymer.
2+
(m/z) [M -2Br/2] = 198.2.
3
3
,3′‐(Butane‐1,4‐diyl)bis(1‐(4‐vinylbenzyl)‐1ꢀH‐imidazol‐
‐ium) chloride (2). Obtained as a white solid with 83% yield using the
-
1
former standard procedure.
FT-IR (cm ): 3143, 1561, 1459, 1156, 1009, 929, 860, 744, 627. Raman
Polymer 12. FT-IR (cm ): 3375, 2959, 2940, 2877, 1720, 1634, 1560,
1459, 1387, 1266, 1148, 1013, 973, 817, 756. CHN analysis: %N
(found): 3.6%, loading 1.27 mmol IL-like units / g of polymer. %N
(expected): 3.64% for 1.30 mmol IL-like units / g of polymer.
-
1
-
1
(
cm ): 1620, 1598, 1408, 1317, 1195, 1176, 1011, 825, 627, 315.
1
H-NMR (CD
3
OD, 500 MHz) δ (ppm) 1.95 (s, 4H), 4.30 (s, 4H), 5.28 (d, J
10.2 Hz, 2H), 5.30 (s, 4H), 5.82, (d, J =15.3 Hz, 2H), 6.70-6.75 (m, 2H),
.39 (d, J = 16.3 Hz, 4H), 7.48 (d, J = 7.6, 4H), 7.62 (d, J = 7.6 Hz, 2H),
-
1
=
7
7
Polymer 13. FT-IR (cm ): 3272, 3057, 2959, 2933, 2872, 1644, 1515,
1381, 1213, 1113, 816. CHN analysis: %N (found): 6.4%, loading 2.27
mmol IL-like units / g of polymer. %N (expected): 6.44% for 2.3 mmol IL-
like units / g of polymer.
13
3
.68 (d, J = 7.6 Hz, 2H), 9.28 (s, 2H). C RMN (CD OD, 300 MHz) δ
(ppm) 26.8, 30.1, 48.9, 52.4, 116.0, 123.3, 123.5, 127.4, 129.4, 134.9,
2+
1
3
3
36.6, 138.3. ESI/MS (m/z) [M -2Br/2] = 212.3.
,3′‐(Hexane‐1,6‐diyl)bis(1‐(4‐vinylbenzyl)‐1ꢀH‐imidazol‐
‐ium) chloride (3). Obtained as a white solid with 78% yield using the
Standard procedure for the preparation of polymers 15-20. 500 mg of
the corresponding SILLP (5-7 and 11-13) was suspended in 20 mL of a
solution of RB (1000 ppm in MeOH) and left under stirring for 24 h. Then
the polymer was filtered, washed with MeOH and dried in a vacuum oven
at 45 C. The absorption for RB at 557 nm was measured in the mother
liquor and in the washing liquid. In all cases the absorption corresponded
former standard procedure.
FT-IR (cm ): 3053, 1557, 1451, 1153, 922, 829, 740, 639. Raman (cm ):
-
1
-1
º
1
1
(
(
615, 1598, 1398, 1301, 1192, 1013, 818, 629, 599, 323. H-NMR
CD OD, 500 MHz) δ (ppm) 1.41 (s, 4H), 1.92 (s, 4H), 4.24 (s, 4H), 5.28
d, J = 10.1 Hz, 2H), 5.42 (s, 4H), 5.79 (d, J = 15.6 Hz, 2H), 6.71-6.75 (m,
-
3
3
with a quantitative uptake. RB loading: 3.98.10 mmol of RB / g polymer.
General synthesis of polymers 25a-c. The synthesis was performed as
44
2H), 7, 41 (d, J = 17.0 Hz, 4H), 7.50 (d, J = 8.2, 4H), 7.63 (d, J = 7.9 Hz,
already reported. A Merrifield resin (10 g, 24a-c) was introduced in a
round-bottomed flask (250 mL) then, the alkylimidazole (6 eq.) was
dissolved in DMF (100 mL) and introduced in the flask and the
suspension was refluxed for 14 hours. The NBP test was negative at the
end of this period confirming full conversion of chloromethyl groups.
The reaction was then filtered and the polymer was washed with DMF,
DMF : H O (1:1), THF and CH Cl and dried in a vacuum oven at 60 ºC.
Polymer 25a: FT-IR (cm ): 3419, 3141, 3060, 2922, 2848, 1567, 1616,
1510, 1449, 1332, 1159, 1022, 823, 761, 706, 661, 619. Raman (cm ):
1612, 1579, 1450, 1413, 1385, 1331, 1188, 1160, 1091, 1022, 1001, 831,
765, 716, 664, 642, 620, 411, 332. CHN analysis: %N (found): 2.5%,
loading 0.89 mmol IL-like units / g of polymer. %N (expected): 2.6% for
0.93 mmol IL-like units / g of polymer.
13
3
2H), 7.68 (d, J =7.8 Hz, 2H), 9.18 (s, 2H). C RMN (CD OD, 500 MHz) δ
(ppm) 25.8, 48.5, 112.1, 119.3, 119.6, 123.4, 123.5, 131.1, 132.7, 132.9,
2+
1
36.8, 138.3. ESI/MS (m/z) [M -2Br/2] = 226.3.
of 1-[(4-Ethenylphenyl)methyl]-3-butyl-imidazolium
chloride (8):ꢀ 1-butylimidazole (125 mmol) was dissolved in CH CN (30
45
Synthesis
3
mL) in a 100 mL round-bottom flask equipped with a stir bar. 4-
Chloromethylstyrene (19.5 mL, 139 mmol) was then added, and the
reaction was heated at 50 °C while stirring overnight. The reaction was
2
2
2
-
1
-
1
2
stopped after this time, and the reaction mixture was poured into Et O
(250 mL). The ionic product precipitated, and the mixture was placed in a
2
freezer for several hours. The Et O phase was decanted and the
resulting solid dried under vacuum lines at 40 °C overnight. Yield = 53.73
g, 82%. Characterization data were consistent with published values.
43
-1
Polymer 25b: FT-IR (cm ): 3023, 2924, 1561, 1450, 1160, 824, 762,
-
1
General procedure for the preparation of the polymers 5-7 and 11-13
by bulk polymerization. The polymerization mixture was prepared using
the corresponding composition of the monomeric mixture as shown in
Table 1 and different weight percentages (wt%) of the solvent mixture
used as the porogen an reported in the same table. The initiator, AIBN,
was 1% of the mass of the monomers. The mixture was vortexed,
sonicated and degassed until homogenous, then poured into a test tube
and placed in a hot bath at 70 °C for 24 hours. The resulting polymers
were washed in a Soxhlet (MeOH) to remove the unreacted starting
materials. The polymerization took place in all the cases with > 95% yield.
703, 661.4, 619, 548. Raman (cm ): 1605, 1406, 1325, 1181, 1015, 995,
824, 636, 614. CHN analysis: %N (found): 5.4%, loading 1.92 mmol IL-
like units / g of polymer. %N (expected): 5.9% for 2.1 mmol IL-like units /
g of polymer.
Polymer 25c: FT-IR (cm ): 3931, 3891, 3830, 3738, 3386, 3147, 3086,
2925, 1644, 1566, 1515, 1451, 1334, 1159, 824, 761, 706, 616. Raman
(cm ): 1615, 1455, 1415, 1387, 1332, 1192, 1092, 1024, 1004, 836, 769,
669, 646, 624, 414, 358, 270, 149. CHN analysis: %N (found): 10.6%,
loading 3.79 mmol IL-like units / g of polymer. %N (expected): 10.44% for
3.73 mmol IL-like units / g of polymer.
General procedure for the preparation of polymers 26a-c. 500 mg of
the corresponding SILLP (25a-c) was suspended in 20 mL of a solution
of RB (1000 ppm in MeOH) and left under stirring for 24 h. Then the
polymer was filtered, washed with MeOH and dried in a vacuum oven at
-
1
-
1
-
1
Polymer 5: FT-IR (cm ): 2943, 1721, 1563, 1456, 1392, 1271, 1157,
-
1
1
8
078, 1025, 848, 757. Raman (cm ): 1603, 1440, 1267, 1179, 1015, 956,
20, 593, 306. CHN analysis: %N (found): 3.4%, loading 1.24 mmol IL-
like units / g of polymer. %N (expected): 3.73% for 1.33 mmol IL-like
units / g of polymer.
Polymer 6a: FT-IR (cm ): 2945, 1720, 1564, 1457, 1389, 1155, 845, 760,
º
45 C. The absorption for RB at 557 nm was measured in the mother
liquors and in the washing liquid. In all cases the absorption
corresponded with a quantitative uptake. RB loading 3.98.10 mmol of
-
1
-
1
-3
623. Raman (cm ): 1603, 1440, 1179, 1014, 957, 821, 631, 594, 306.
CHN analysis: %N (found): 4.4%, loading 1.58 mmol IL-like units / g of
polymer. %N (expected): 4.54% for 1.62 mmol IL-like units / g of polymer.
Polymer 6b: CHN analysis: %N (found): 3.9%, loading 1.38 mmol IL-like
units / g of polymer. %N (expected): 3.90% for 1.4 mmol IL-like units / g
of polymer.
RB / g polymer.
General procedure for the preparation of polymers 27-30. 100 mg of
the corresponding SILLP (26a) was suspended in 12 mL of a MeOH :
H O mixture (10:1 v/v) containing an excess of the corresponding YX salt
2
and left under stirring for 24 h. Then the polymer was filtered, washed
with MeOH and dried in a vacuum oven at 45 C.
º
Polymer 6c: CHN analysis: %N (found): 3.5%, loading 1.25 mmol IL-like
units / g of polymer. %N (expected): 3.59% for 1.28 mmol IL-like units / g
of polymer.
-
1
4
Polymer 27: YX = NaBF . FT-IR (cm ): 3026, 2922, 1596, 1496, 1448,
-
1
1350, 1194, 1057, 756, 700, 613. Raman (cm ): 1592, 1439, 1317, 1174,
1145, 1020, 990, 784, 610, 397. CHN analysis: %N (found): 2.2%,
loading 0.77 mmol IL-like units / g of polymer. %N (expected): 2.25% for
0.80 mmol IL-like units / g of polymer.
-
1
Polymer 7: FT-IR (cm ): 2946, 1721, 1562, 1455, 1392, 1273, 1157,
-
1
1
1
076, 1022, 847, 757. Raman (cm ): 1604, 1440, 1411, 1322, 1179,
015, 822, 632, 595, 307. CHN analysis: %N (found): 3.4%, loading 1.21
-
1
mmol IL-like units / g of polymer. %N (expected): 3.47% for 1.24 mmol
IL-like units / g of polymer.
Polymer 28. YX = LiNTf
1350, 1194, 1057, 756, 700, 613. Raman (cm ): 1591, 1438 1317, 1172,
144, 1019, 990, 782, 730, 610, 395. CHN analysis: %N (found): 2.5%,
2
. FT-IR (cm ): 3026, 2922, 1596, 1496, 1448,
-
1
1
This article is protected by copyright. All rights reserved.

ChemSusChem
10.1002/cssc.201901533
FULL PAPER
loading 0.60 mmol IL-like units / g of polymer. %N (expected): 2.92% for
This research work was supported by the Spanish MINECO
0
.69 mmol IL-like units / g of polymer.
(
(
RTI2018-098233-B-C22)
PROMETEO/ 2016/071). D. V. thanks UNED (Costa Rica) for a
and
Generalitat
Valenciana
-
1
Polymer 29. YX = KTfO. FT-IR (cm ): 3026, 2922, 1596, 1452, 1267,
-
1
1159, 1026, 757, 700, 632, 544. Raman (cm ): 1592, 1483, 1174, 1145,
1020, 991, 783, 747, 611. CHN analysis: %N (found): 2.04%, loading
0.73 mmol IL-like units / g of polymer. %N (expected): 2.14% for 0.76
predoctoral fellowship. The technical support of the SCIC at the
Universitat Jaume I is acknowledged.
mmol IL-like units / g of polymer.
Polymer 30. YX = KSbF . FT-IR (cm ): 3026, 2922, 1596, 1487, 1450,
-
1
6
Keywords: photocatalysis • Ionic Liquids • Supported Ionic
Liquids • Rose Bengal • Flow Chemistry
-
1
1159, 757, 700, 653, 626, 545. Raman (cm ): 1591, 1439, 1317, 1174,
145, 1020, 991, 784, 611, 399. CHN analysis: %N (found): 2.0%,
1
loading 0.70 mmol IL-like units / g of polymer. %N (expected): 2.01% for
.72 mmol IL-like units / g of polymer.
Synthesis of polymer 32: To a suspension of SILLP 25a (250 mg) in
DMF (5 mL), 1.5 mL of a QDs solution in toluene (CdSe/ZnS, 510nm, 50
µg / mL) was added and the mixture left under stirring (300 rpm) and
protected from the light during 24 h. Then, the polymer was filtered,
[
[
[
1]
2]
3]
A. A. Ghogare, A. Greer, Chem. Rev. 2016, 116, 9994-10034.
A. Albini, M. Fagnoni, Green Chem. 2004, 6, 1-6
0
I. Pibiri, S. Buscemi, A. P. Piccionello, A. Pace, ChemPhotoChem 2018,
2
, 535-547.
J. Wahlen, D. E. De Vos, P. A. Jacobs, P. L. Alsters, Adv. Synth. Catal.
004, 346, 152-164.
D. Friedmann, A. Hakki, H. Kim, W. Choi, D.Bahnemann, Green Chem.
016, 18, 5391-5411.
Z. Xie, C. Wang, K. E. deKrafft, W. Lin, J. Am. Chem. Soc. 2011, 133,
056-2059.
[
4]
2
washed with DMF : H
dried under vacuum at 45 C. QDs loading: 0.3 mg QDs / g polymer.
00 mg of this resin (31) were suspended in a 1000 ppm solution of RB
2 2 2 2
O (1:1), H O, CH Cl and MeOH (5x5 mL) and
º
[5]
6]
2
1
[
in MeOH (4 mL) and left under stirring (300 rpm) and protected from the
2
light for 24 h. Afterwards, the polymer was filtered, washed with DMF :
º
[7]
[8]
S. Lacombe, T. Pigota, Catal. Sci. Technol. 2016, 6, 1571-1592.
L. Petrizza, M. Le Bechec, E. Decompte, H. El Hadri, S. Lacombe, M.
Save, Polym. Chem. 2019, Advance Article, 10.1039/C9PY00157C.
a) B. Altava, M. I. Burguete, E. García-Verdugo, S. V. Luis, Chem. Soc.
Rev. 2018, 47, 2722-2771. b) B. Altava, M. I. Burguete, E. García-
Verdugo, S. V. Luis, M. J. Vicent, J. A. Mayoral, React. Funct. Polym.
H
2
O (1:1), H
2
O, CH
2
Cl
2
and MeOH (5x5 mL) and vacuum dried at 45 C.
-
3
RB loading: 3.98.10 mmol of RB / g polymer.
[
9]
Standard protocol for the photooxidation of 2-furoic acid (21) to 5-
hydroxy-5H-furan-2-one. The corresponding photosensitizer was added
to 10 mL of a methanolic solution of 2-furoic acid (9.6 mM) in a test tube.
The heterogeneous mixture was kept under stirring and in equilibrium
with air. These test tubes were placed at 2 cm of a 0.1 M aqueous
solution of FeCl used as a filter for wavelengths lower than 450 nm and
3
irradiated with a 125-W medium-pressure Hg vapor lamp for at least 6 h.
The same experimental conditions were used in the dark in order to
2001, 48, 25-35.
[
[
10] J. Paczkowski, D. C. Neckers, Macromolecules 1985, 186, 1245-1253.
11] M. Suzuki, Y. Ohta, H. Nagae, T. Ichinohe, M. Kimura, K. Hanabusa, H.
Shirai, D. Wohrle, Chem. Commun. 2000, 213-214.
[
[
[
12] J. P. Hallett, T. Welton, Chem. Rev. 2011, 111, 3508-3576.
13] T. Welton, Biophysical Rev. 2018, 10, 691-706.
evaluate
a possible adsorption of the substrate into the polymer.
14] Y. Qiao, W. Ma, N. Theyssen, C. Chen, Z. Hou, Chem. Rev. 2017, 117,
Moreover, the following control experiments were carried out: (a)
irradiation in the absence of polymer and (b) irradiation of 2-furoic acid
with free Rose Bengal in solution (5 μM) as the photosensitizer. The
decreasing absorbance of 2-furoic acid was monitored by means of UV–
vis spectroscopy at 246 nm. For each measurement, 80 μL aliquots were
removed from the reaction mixture and diluted in 25 mL of the
appropriate solvent. The initial rate constants for each oxidation reaction
were calculated as first-order rate constants (k) as reported in the
6
881-6928.
[
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Entry for the Table of Contents
FULL PAPER
Polymers containing imidazolium
units are excellent and tunable
supports enhancing the stability and
activity of Rose Bengal as
David Valverde, Raul Porcar, Diana
Izquierdo, M. Isabel Burguete,
Eduardo Garcia-Verdugo* and
Santiago V. Luis*
O2
photooxidation catalyst under batch
and flow conditions.
Page No. – Page No.
Rose Bengal immobilized onto
Supported Ionic Liquid-like Phases:
Efficient photocatalyst for batch
and flow processes
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