Multi-addressable supramolecular gels based on linear amino acid and bisthienylcyclopentene

Article abstract of DOI:10.1002/poc.1253

1,2-Bisthienylperfluorocyclopentenes covalently linked to two aggregative side-arms derived from 11-aminoundecanoic acid have been designed to self-assemble leading to the formation of supramolecular gels which could be reversibly and independently reveal

Full text of DOI:10.1002/poc.1253

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 2007; 20: 888–893
Published online 17 September 2007 in Wiley InterScience
(www.interscience.wiley.com) DOI: 10.1002/poc.1253
Multi-addressable supramolecular gels based on linear
amino acid and bisthienylcyclopentene
Guillaume Sevez,1 Jiaan Gan,1 Jianfeng Pan,1 Xavier Sallenave,1 Annie Colin,2 Hassan Saadoui,2
3
4
1
*
Ahmed Saleh, Fritz Vo¨ gtle and Jean-Luc Pozzo
1
´
University Bordeaux1, UMR CNRS 5255, Institut des Sciences Moleculaires, F-33405 Talence, France
2Laboratoire du Futur, UMR Rhodia CNRS 5258, F-33608 Pessac, France
3Chemistry Department, Faculty of Science, University Assiut, 71516, Assiut, Egypt
4
´
´
Kekule Institu¨ t fu¨ r Organische Chemie und Biochemie, 53121, Bonn, Germany
Received 2 February 2007; revised 4 July 2007; accepted 12 July 2007
ABSTRACT: 1,2-Bisthienylperfluorocyclopentenes covalently linked to two aggregative side-arms derived from
11-aminoundecanoic acid have been designed to self-assemble leading to the formation of supramolecular gels which
could be reversibly and independently revealed or suppressed upon acidity, temperature changes and also light
irradiation. Copyright # 2007 John Wiley & Sons, Ltd.
Supplementary electronic material for this paper is available in Wiley InterScience at http://www.mrw.interscience.
wiley.com/suppmat/0894-3230/suppmat/
KEYWORDS: photochromism; self-assembly; gelation; photoswitchable; organogel
INTRODUCTION
induced. As diarylethene constitute a peculiar class of
molecular photoswitches that can undergo reversible
electrocyclization between their colourless ring-open and
coloured ring-closed forms when irradiated with appro-
priate wavelengths of light.6 Because of excellent fatigue
resistance, thermal stability in both isomeric forms,
solid-state photoreactivity and high photochemical
quantum yield, these molecules constitute obviously
powerful candidates to photoswitch in both directions
between sol and gel phases.7 Indeed, the photochromic
reactions of 1,2-bis-thienylcyclopentenes functionalized
with two amide groups have been reported to largely
influence the medium viscosity.8 Nevertheless incorp-
oration of diarylethene does not guarantee photoswitch-
able macroscopic phase transition as reported recently in
two very elegant studies. In fact these derivatives cova-
lently linked to a chiral moiety have been shown to
reversibly control supramolecular chirality switching
between different chiral aggregates in the gel phase,9 and
multi-switchable cholesterol-based gelators have been repor-
ted to be photochromic without any phase changes.10
Various compounds based on 11-aminoundecanoic acid,
hereafter denoted AUDA, have been shown to act as
potent organogelators or hydrogelators, furthermore the
presence of a sodium carboxylate has been exploited to
alter the self-assembling process and thus to largely
modify the gel formation upon acidic conditions.11 As an
attempt to obtain new functional organogelators with
multiple-switch applications, we have rationally designed
The reversible organo- and/or hydrogelation phenomenon
exhibited by low-molecular weight molecules (LMOGs)
is the subject of increasing attention.1 This class of
compounds is able to self-assemble into supramolecular
fibrous aggregates that in turn crosslink, thus entrapping
solvent molecules within three-dimensional networks.
The unique chemical and physical properties of these
materials have paved the way to fascinating nanostruc-
tured materials such as nanotubules of silica.2 However, it
remains a challenging task to design smart gels whose
formation could be simultaneously or alternatively
controlled by external stimuli such as heat, acidity,
electric fields and/or light. Of external changes, light has
the advantage of providing stimulus to specific chromo-
phores in the molecules by selective-wavelength irradia-
tion. In that connection, Zinic et al. recently reported an
irreversible photochemically induced gelation system
based on cis–trans photoisomerization of fumaride
derivatives.3 Anthracene-containing binary gelators4
and naphthopyran-based gelators5 have also been fruit-
fully designed as photoresponsive LMOGs, nevertheless
for both approaches the gels can only be transformed into
sol upon irradiation the back reaction being thermally
*Correspondence to: J.-L. Pozzo, University Bordeaux1, UMR CNRS
´
5255, Institut des Sciences Moleculaires, F-33405 Talence, France.
E-mail: jl.pozzo@ism.u-bordeaux1.fr
Copyright # 2007 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2007; 20: 888–893

MULTI-ADDRESSABLE SUPRAMOLECULAR GELS
889
Scheme 1. Rationally designed dithienylethenes substituted by two AUDA arms
photochromic organogelators based on bis-thienylper-
fluorocyclopentenes containing two AUDA aggregative
side-arms (Scheme 1).
obtained upon basic treatment could be considered as
supergelators.14 Indeed, the gel-to-sol phase transition
temperature of DMF gel using a 1% wt/v concentration of
2-Na (1.08 ꢀ 10ꢁ2 M) is as high as 120 8C, and millimolar
range of concentrations of the prepared organogelators is
efficient enough to gelify DMSO and DMF. For instance a
0.095% wt/v (10ꢁ3 M) 2-Na DMF gel melts at 30 8C. The
gels obtained are translucent and stable for months. These
outstanding gelling abilities are restricted to aprotic polar
solvents as these disodium salts can be dissolved in
various alcohols and water, and are totally insoluble in
apolar organic fluids. The minimum gelation concen-
trations for 1-Na and 2-Na are collected in Table 1 and the
gel-to-sol phase transition temperatures along concen-
tration variation are depicted on Fig. 1. 1-H and 2-H were
found to be very soluble in DMF and DMSO at ambient
temperature. Upon addition of sodium hydroxide, they
rapidly convert to the gel state which can in turn be
transformed into sol upon acidic addition. As the targeted
AUDA derivatives act as potent LMOG, this cycle can be
repeated several times before dilution will dramatically
change the macroscopic properties. Gels arising from
LMOGs are intrinsically thermoswitchable, here they
also respond to environmental variations of acidity by
reversibly transcripting the molecular modification to the
supramolecular level.
RESULTS AND DISCUSSION
In the present study, amide and urethane groups have been
selected as bridging units between the photoresponsive
and aggregative parts as these H-bonding groups do not
prevent the gel formation when sterically demanding
groups are connected to AUDA unit.10 A classic peptide-
coupling procedure using DCC, DMAP and methyl
11-aminoundecanoate was used to synthesize 1,2-bis[50-
(1000-carboxyldecylcarbamoyl)-20-methylthien-30-yl]
perfluorocyclopentene 1-H starting from the previously
described photochromic compound 5 bearing two carbo-
xylic functions,12 the resulting ester 6 being subsequently
saponified under mild conditions using lithium hydroxide
(Scheme 2). Diacid 2-H was synthesized in a three
step-procedure starting from 1,2-bis(5-formyl-2-
methylthien-3-yl)perfluorocyclopentene 7.13 This dialde-
hyde was reduced with sodium borohydride in corre-
sponding dihydroxymethyl derivative 8 which sub-
sequently condensed with an appropriate isocyanate to
yield a urethane derivative 9 which was converted by
saponification into 1,2-bis[5-(10-carboxydecylcarbamoy-
loxymethyl)-2-methylthien-3-yl] perfluorocyclopentene
2-H (Scheme 3). Compounds 1-H and 2-H were obtained,
respectively, in 18 and 57% overall yield.
When methanol solutions of 1-Na and 2-Na were
irradiated with 313 nm light absorption increased,
respectively, at 569 nm and 517 nm and reached by
3 min a photostationary state6 that consisted of a mixture
of ring-open and ring-closed forms, respectively, denoted
3-Na and 4-Na. When prolongated irradiation time (4 h)
were used, any further increase of closed forms was
detected, furthermore elucidation of 1H NMR spectrum of
Neutral dicarboxylic derivatives 1-H and 2-H failed to
gel any investigated fluids, on the contrary their
corresponding disodium salts 1-Na and 2-Na easily
Scheme 2. Synthetic route for 1-H and 1-Na
Copyright # 2007 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2007; 20: 888–893
DOI: 10.1002/poc

890
G. SEVEZ ET AL.
Scheme 3. Synthetic route for 2-H and 2-Na
Table 1. Minimum gel concentrationa at 30 8C
significant shift. When gels are irradiated, superimpo-
sable maxima have been found for DMSO and DMF, and
more interestingly this transformation is accompanied by
the gel-to-sol phase transition within 3 min. The absorp-
tion intensity of the photoinduced sols is noticeably lower
in comparison to expected values. This indicates that
some photochromic units are still embedded within small
remaining aggregates. In both solvents macroscopic
gelation could be photodisrupted. For further investi-
gation DMF was chosen because of the excellent stability
of the translucent gel and the minimum gelation
concentration (ca 1 mM). UV-irradiation (l > 530 nm)
of the photoinduced sols gave rise to the photocyclor-
eversion to reform 2-Na, which in turn gave birth to the
gel phase. This represents one of the rare examples of a
gel-to-sol phase transition that could be photoswitched in
both directions using appropriate wavelength (Scheme 5).
Pictures of the three steps of one cycle is depicted in
Fig. 2. Sequential alternating UV/Visible light irradiation
have been performed and resulting Tgel values have been
found to decrease as a function of number of cycles. This
phenomenon could not be ascribed neither to photo-
degradation, as the initial Tgel value was recovered by
simply heating and then cooling the uncoloured phase,
and nor to lowered photochemical electrocyclization
process efficiency as totally uncoloured gels are
reformed. Visible irradiation leads to a ring-opening
process which is only accompanied by a partial
reorganization of the network. Total reformation of a
three-dimensional network of numerous fibres that
composed a physical gel is usually thermally achieved
except for thixotropic gels.16 In that connection,
additional experiments based on mixing photochromic
gelators and simple-related compounds will be under-
taken in an attempt to overcome these limitations. This
macroscopic behaviour has also been characterized at the
supramolecular level using AFM technique. Non-
irradiated sample show the presence of numerous bundle
of fibrillar aggregates whereas the area irradiated through
a mask with UV light gave typical answer of solvents
(Fig. 3). This is an additional evidence that the molecular
event induces the supramolecular rearrangement of these
promising nanostructured materials.
Compounds
DMF
DMSO
1-Na
2-Na
1.45 (1.7)
0.95 (1)
7.58 (8.7)
6.56 (7.1)
aIn g Lꢁ1 (gelator/liquid); in parentheses in mM.
Figure 1. Tgel of disalt 2-Na as a function of organogelator
concentration: (^) in DMF; (*) in DMSO
the resulting mixture showed the presence of 2-Na, 4-Na
and a tricyclic by-product 10 (Scheme 4) in a 7:2:1
ratio.15 When diluted DMF and DMSO (0.2 mM)
solutions are exposed to UV-light, similar large absorp-
tion bands are obtained whose maxima do not exhibit any
Scheme 4. Tricyclic by-product 10
Copyright # 2007 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2007; 20: 888–893
DOI: 10.1002/poc

MULTI-ADDRESSABLE SUPRAMOLECULAR GELS
891
Scheme 5. Self-assembled supramolecular aggregates controlled by molecular changes induced by light and acidity
gels which may pave the way to new multi-responsive
sensor materials.
EXPERIMENTAL
Photochromic measurements (UV-visible) were per-
formed in methanol, DMF and DMSO solution of
spectrometric grade (Aldrich) at 20 8C. The analysis
cell (optical pathlength 1 cm) was placed in a thermo-
stated copper block with magnetic stirring inside the
sample chamber of a Beckman-DU-7500-diode-array
spectrometer. Flash column chromatography was per-
formed on silica gel (Merck 40–63 mm). Melting points
were determined on an Electrothermal Eng. Ltd melting
point apparatus and are uncorrected. H and 13C NMR
1
Figure 2. Photocontrolled Gel-to-sol phase transition of
2-Na DMF gel/4-Na sol. (Left: 2-Na before irradiation,
middle: 4-Na sol and right: photoregenerated 2-Na DMF gel)
spectra were determined on a Bruker AC 250 NMR
spectrometer with CDCl3 or DMSO-d6 as a solvent and
TMS as an internal standard (d ¼ 0 ppm). UV-visible
measurements were performed using a Hitachi U-3300
spectrophotometer. FT-IR measurements were performed
using a Perkin Elmer Paragon 1000 instrument. Mass
spectra were recorded on a VG AutoSpec apparatus using
electronic impact at 70 eV. MALDI-MS spectra were
CONCLUSION
In conclusion, we demonstrated that acid- and photo-
responsive organogelators can be readily obtained from
the combination of a P-type photochromic dithieny-
lethene and a versatile aggregative unit derived from a
synthetic amino acid. As expected, the multi-addressable
molecular switches operate at supramolecular scale, the
phase changes among gel and sol being independently
driven by acidity, light and temperature. Of particular
interest for organogelator material science are such smart
recorded in the positive mode by using
a
2,5-dihydroxy-benzoic acid in dioxane as matrix.
Microanalyses were determined in the microanalytical
laboratory at the CNRS, Vernaison. AFM was performed
using Tapping Mode (Nanoscope IIa, Digital Instruments,
Inc.) with a pyramidal Si3N4 tip.
Figure 3. AFM height images of native (left) and partially irradiated (on top) with 313 nm UV light 2-Na DMF gel (right)
Copyright # 2007 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2007; 20: 888–893
DOI: 10.1002/poc

892
G. SEVEZ ET AL.
PREPARATION OF COMPOUNDS
solution. The mixture was stirred at room temperature for
2 h. Then the solvent was removed under vacuum. The
product was washed with dichloromethane and diethyl
ether and dried to yield 54 mg of the disodium salt (1-Na)
in 96% yield as a white solid. 9: mp 232.3(decom.) 8C.
1H NMR (CD3OD, 250 MHz) d 7.74 (s, 2H), 3.32 (m,
4H), 2.14 (t, J ¼ 7.5 Hz, 4H), 1.92 (s, 6H), 1.70–1.50 (m,
8H), 1.40–1.20 (m, 24H); 19F NMR (CDCl3, 200 MHz) d
ꢁ112.0, ꢁ133.8; FT-IR (KBr-cast): 3315, 2925, 2853,
1628, 1564, 1442, 1420, 1339, 1304, 1275, 1194, 1141,
1113, 1052, 987.
1,2-Bis{5(-[10((-(methoxycarbonyl)-
decylcarbamoyl]-2(-methylthien-3(-
yl}perfluorocy-clopentene (6)
A mixture of (5) (500 mg, 1.1 mmol) and triethylamine
(1.0 g, 9.9 mmol) were dissolved in 30 ml dry THF under
nitrogen atmosphere. Then DMAP (50 mg, 0.4 mmol) and
DCC (600 mg, 3 mmol) were added. The mixture was
stirred at room temperature overnight. N,N-dicyclo-
hexylurea was collected by filtration, and the filtrate
was concentrated under reduced pressure. The residue
was then chromatographed on silica gel with dichlor-
omethane/ethyl acetate (10:1) as eluent to afford 364 mg
of 1,2-bis{50-[1000-(methoxycarbonyl)-decylcarbamoyl]-
20-methylthien-30-yl}perfluorocyclopentene (6) in 35%
yield. 6: mp 113.3–115.7 8C. 1H NMR (CDCl3, 300 MHz)
d 7.40 (s, 2H), 5.98 (s, 2H), 3.66 (s, 6H), 2.05 (q, J ¼ 6.4,
7.1 Hz, 4H), 2.30 (t, J ¼ 7.5 Hz, 4H), 1.91 (s, 6H),
1.65–1.50 (m, 8H), 1.40–1.20 (m, 24H); 13C NMR
(CDCl3, 300 MHz) d 173.4, 159.9, 145.2, 136.8, 126.0,
124.0, 50.4, 39.2, 33.1, 28.6, 28.4, 28.3, 28.2(2C), 28.1,
25.9, 23.9, 13.8; 19F NMR (CDCl3, 200 MHz) d ꢁ110.3,
ꢁ132.0; MALDI-MS. m/z 873.2 [MþNaþ].
1,2-Bis(5(-hydroxylmethyl-2(-
methylthien-3(-yl)perfluorocyclopentene (8)
To a solution of 7 (100 mg, 0.24 mmol) in 20 ml
ice-cooled methanol, NaBH4 (18 mg, 0.48 mmol) was
added. The mixture was stirred for 2 h, ice water was then
added to quench the reaction and the product was
extracted with dichloromethane and dried over Na2SO4.
Removal of the solvent gave a light red crude product
which was subsequently purified by flash column
chromatography with 10:1 dichloromethane/methanol
as eluent to afford 94 mg of 1,2- bis(50-hydroxylmethyl-
20-methylthien-30-yl)perfluorocyclopentene (9) in 95%
yield as a white powder. 9: mp 132.7–133.7 8C. (reference
mp: 125–128 8C) 1H NMR (CDCl3, 250 MHz) d 6.95 (s,
2H), 4.75 (s, 4H), 1.88 (s, 6H); 13C NMR (DMSO-d6,
300 MHz) d 149.7, 145.2, 127.7, 127.3, 62.5, 18.5; 19F
NMR (CDCl3, 200 MHz) d ꢁ110.2, ꢁ132.0; MALDI-
MS. m/z 474 [Mþ2Naþ]. Anal. Calcd for C17H14F6O2S2:
C, 47.66; H, 3.29. Found: C, 47.67; H, 3.37.
1,2-Bis[5(-(10((-carboxy-decylcarbamoyl)-
2(-methylthien-3(-yl]perfluorocyclopentene
(1-H)
Ester (6) (115 mg, 0.13 mmol) was dissolved in 15 ml
ethanol and then was added to a solution of lithium
hydroxide (37 mg, 1.54 mmol) in 10 ml water. The mixture
was stirred at room temperature overnight. The solution
was acidified to pH 5 with 1N hydrochloride solution and
stirred for 2 h. The product was extracted with dichlor-
omethane and dried over Na2SO4 and evaporated in
vacuum to yield a light red residue which was subsequently
purified by flash column chromatography with 10%
methanol in ethyl acetate to afford 56mg of 1,2-bis[50-
(1000-carboxy-decylcarbamoyl)-20-methylthien-30-yl]
perfluorocyclopentene (1-H) in 52% yield as a light
yellow viscous oil. 1-H: 1H NMR (DMSO-d6, 300 MHz) d
11.99 (br, 2H), 8.62 (s, 2H), 7.83 (s, 2H), 3.20 (m, 4H),
2.21 (m, 4H), 1.87 (s, 6H), 1.55–1.40 (m, 8H), 1.35–1.10
(m, 24H); 13C NMR (DMSO-d6, 300 MHz) d 174.4, 159.9,
146.0, 138.9, 126.6, 124.1, 54.8, 33.6, 28.9 (2C), 28.8,
28.7 (2C), 28.5, 26.4, 24.4, 14.2; 19F NMR (DMSO-d6,
200 MHz) d ꢁ109.8, ꢁ131.5; MALDI-MS. m/z 845.5
[MþNaþ].
1,2-Bis{5(-[10((-(methoxycarbonyl)-
decylcarbamoyloxymethyl]-2(-methylthien-
3(-yl}perfluorocyclopentene (9)
A mixture of 8 (0.52 g, 1.2 mmol) and triethylamine
(1.0 g, 9.9 mmol) were dissolved in 20 ml dry THF under
nitrogen atmosphere. Methyl 11-isocyanatoundecanoate
(2.3 g, 9.5 mmol) was added and the reaction mixture was
refluxed for 24 h. The solvent was evaporated to give a
light red oil residue. The residue was dissolved in 20 ml
dichloromethane, then 50 ml of water was added and the
mixture was stirred overnight. The water layer was
extracted with dichloromethane. The combined organic
layer was dried over Na2SO4 and concentrated.
The product was then chromatographed on flash column
with 0.5% methanol in dichloromethane as eluent
to afford 864 mg of 1,2-bis{50-[1000-(methoxycarbonyl)-
decylcarbamoyloxymethyl]-20-methylthien-30-yl}per-
1,2-Bis[5(-(10((-carboxy-decylcarbamoyl)-2(-
methylthien-3(-yl]perfluorocyclopentene
disodium salt (1-Na)
1
fluorocyclopentene (9) in 85% yield. H NMR (CDCl3,
250 MHz) d 7.00 (s, 2H), 5.12 (s, 4H), 4.75 (m, 2H), 3.67
(s, 6H), 3.17 (m, 4H), 2.30 (t, J ¼ 7.6 Hz, 4H), 1.85 (s,
6H), 1.64–1.40 (m, 8H), 1.35–1.2 (m, 24H); 13C NMR
Diacid 1-H (53 mg, 0.064 mmol) dissolved in 5 ml
methanol was added to 129 mg of a 1N sodium hydroxide
Copyright # 2007 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2007; 20: 888–893
DOI: 10.1002/poc

MULTI-ADDRESSABLE SUPRAMOLECULAR GELS
1
893
(CDCl3, 400 MHz) d 174.6, 155.2, 143.4, 137.4, 127.6,
124.6, 60.8, 51.7, 41.4, 34.3, 30.2, 29.7, 29.6, 29.5(2C),
29.4, 26.9, 25.2, 14.6; 19F NMR (CDCl3, 200 MHz) d
ꢁ110.3, ꢁ132.1; MALDI-MS. m/z 933.4 [MþNaþ].
Anal. Calcd for C43H60F6N2O8S2: C, 56.69; H, 6.64; N,
3.07. Found: C, 57.10; H, 6.92; N, 3.23.
(decom.). H NMR (CD3OD, 300 MHz) d 7.08 (s, 2H),
5.14 (s, 4H), 3.09 (m, 4H), 2.15 (t, J ¼ 6.3 Hz, 4H), 1.86
(s, 6H), 1.70–1.40 (m, 8H), 1.40–1.20 (m, 24H); FT-IR
(KBr-cast): 3341, 2919, 2840, 1698, 1565, 1462, 1442,
1417, 1339, 1270, 1191, 1157, 1137, 1113, 1049, 985.
Anal. Calcd for C41H54F6N2Na2O8S2: C, 53.12; H, 5.87;
N, 3.02; Na, 4.96. Found: C, 52.94; H, 6.03; N, 2.98; Na,
4.64.
1,2-Bis[5(-(10((-carboxy-
decylcarbamoyloxymethyl)-2(-methylthien-
3(-yl]perfluoro-cyclopentene (2-H)
Acknowledgements
Ester 9 (674 mg, 0.74 mmol) was dissolved in 35 ml
ethanol, and then was added to a solution of lithium
hydroxide (700 mg, 29.2 mmol) in 25 ml water. The
mixture was stirred at room temperature overnight. The
solution was acidified to pH 5 with 1N hydrochloride
solution and stirred for 2 h. The product was extracted
with dichloromethane and dried over Na2SO4 and
evaporated in vacuum to yield a light red residue which
was subsequently purified by flash column chromatog-
raphy with 4% methanol in dichloromethane to afford
460 mg of 1,2-bis[50-(1000-carboxy-decylcarbamoyloxy-
methyl)-20-methylthien-30-yl]perfluorocyclopentene (2-H)
This collaborative work was realized within the frame-
work COST D11 Action that is deeply acknowledged.
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1
istic H NMR data d (CH3) 2.66 and 2.68, d (CH2O) 4.97 and d
(CH-thienyl) 6.52 ppm.
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Copyright # 2007 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2007; 20: 888–893
DOI: 10.1002/poc