Strongly fluorescent organogels and self-assembled nanostructures from pyrene coupled coumarin derivatives: Application in cell imaging

Article abstract of DOI:10.1039/c5tb00694e

Three different coumarin coupled pyrene derivatives with varying hydrophobic units (alkyl chains) have been synthesised and well characterized using NMR and mass spectral analysis. The gelation behaviour and self-aggregation properties of these compounds were studied relative to the molecular structure and solvent affinity. Among these derivatives, the one which is not having any hydrophobic tail displays efficient gelation in higher alcohols such as decanol and dodecanol. However the other derivatives having saturated and unsaturated hydrophobic tails form weak gel in different solvents. The morphology of gel was investigated by optical microscopy and high resolution transmission electron microscopy (HRTEM). The investigation of absorption and emission spectra of these compounds revealed that the photo-physical properties were significantly influenced by the self-assembly process in different solvents. The concentration dependent emission and ¹H NMR studies clearly suggest that the π-π stacking interaction and hydrogen bonding between carbonyl groups of coumarin coupled pyrene with the -OH group of solvent were the driving forces for the process of gelation and self-aggregation. Rheological investigation clearly demonstrates the flow behaviour and reversible nature of organogel under temperature and strain ramp up and ramp down experimental conditions. By getting clue from the self-assembly mechanism in different solvents, we derived nano-flakes from coumarin coupled pyrene derivatives and further explored their potential applications in the field of cell imaging. The size of the self-aggregated particles in the DMSO-water mixture has been identified using HRTEM and a zetasizer. The nanomaterials obtained via the self-assembly process were used for fibroblast and PC3 prostate cancer cell imaging applications. Further investigation reveals that these compounds suppress the proliferation of PC3 cells.

Full text of DOI:10.1039/c5tb00694e

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Journal Name
RSCPublishing
ARTICLE
Strongly fluorescent organogels and self-
assembled nanostructures from pyrene coupled
coumarin derivatives: Application in cell
imaging
Cite this: DOI: 10.1039/x0xx00000x
Received 00th January 2012,
Accepted 00th January 2012
Krishnamoorthy Lalitha, Subbiah Nagarajan*
DOI: 10.1039/x0xx00000x
Three different coumarin coupled pyrene with varying hydrophobic unit (alkyl chains) has been
synthesised and well characterized using NMR and mass spectral analysis. The gelation behaviour and
self-aggregation properties of these compounds were studied relative to the molecular structure and
solvent affinity. Among these derivatives, the one which is not having any hydrophobic tail displays
efficient gelation in higher alcohols such as decanol and dodecanol. However the other derivatives
having saturated and unsaturated hydrophobic tail forms weak gel in different solvents. The
morphology of gel was investigated by optical microscopy and High Resolution Transmission Electron
Microscopy (HRTEM). The investigation of absorption and emission spectra of these compounds
revealed that the photo-physical properties were significantly influenced by self-assembly process in
www.rsc.org/
different solvents. The concentration dependent emission and 1H NMR studies clearly suggest the
π-π
stacking interaction and hydrogen bonding between carbonyl groups of coumarin coupled pyrene with –
OH group of solvent were the driving force for the process of gelation and self-aggregation. Rheological
investigation clearly demonstrate the flow behaviour and reversible nature of organogel under
temperature and strain ramp up and ramp down experimental conditions. By getting clue from self-
assembly mechanism in different solvents, we derived nano flakes from coumarin coupled pyrene
derivatives and further explored its potential application in the field of cell imaging. The size of the self-
aggregated particles in DMSO-water mixture has been identified using HRTEM and zetasizer. The
nanomaterials obtained via self-assembly process have used for fibroblast and PC3 prostate cancer cell
imaging applications. Further investigation reveals that these compound supress the proliferation of
PC3 cells.
structures such as fibrils, tapes, rods and tubes are known as an
important class of soft materials.2,3 In particular, LMOGs based
Introduction
Supramolecular selfꢀassembly is one of the fundamental
techniques for the bottomꢀup fabrication of nanoscience. The
selfꢀassembly of small molecules to form diverse
supramolecular architectures via various nonꢀcovalent
on
πꢀconjugated organic compounds have drawn significant
interest due to their typical vantages such as diversity,
flexibility, and promising applications in optoelectronics, light
harvesting and energy materials.4 Moreover these fluorescent
gel systems show a remarkable variation in emission property
which might be due to the phase transition process renders
valuable information at molecular level selfꢀassembly. Most
frequently information on molecular level selfꢀassembly
renders opportunity to construct different nanostructures.
Recent past there are number of fluorescent organogel with
potential applications has been reported and same has been
reviewed in detail by Ajayaghosh and coꢀworkers.5 With the
intention of developing new fluorescent selfꢀassembled
interactions such as hydrogen bonding,
ꢀꢀꢀ interaction,
electrostatic and van der Waals interactions, hydrophilicꢀ
lipophilic balance (HLB) and other supramolecular weak forces
has attracted substantial interest.1 Selfꢀassembled materials hold
vast applications in the field of drug delivery, gene therapy,
tissue engineering, enzyme immobilization, wound healing,
water purification, biosensors and construction of novel nanoꢀ
or microscopic materials and devices.2 In this context low
molecular weight organic gels (LMOGs) formed by the
hierarchical assembly of gelators in a suitable solvent to
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VJieowuArrtnicalelONnlainme e
ARTICLE
DOI: 10.1039/C5TB00694E
materials we put our extensive synthetic efforts to obtain more A known quantity of gelator was mixed with appropriate
diverse pyreneꢀcoupled coumarin based ꢀgelator with various amount of solvent in a sealed test tube, and the system was
π
hydrophobic tails, which could be used for biomedical and heated to 90ꢀ120 ºC until the solid was dissolved. By this
biological research. The selfꢀassembled soft material i.e. gels procedure the solvent boiling point becomes higher than that
derived from πꢀgelators are called “πꢀgels”.5,6 ΠꢀGels derived under standard atmospheric pressure. The resulting solution
from naturally occurring fine chemical have received much was slowly allowed to cool to room temperature, and gelation
attention because of their wide range of applications. Coumarin, was visually observed by inverting the test tube. A gel sample
a class of benzopyrone derivative falls under such category and was obtained that exhibited no gravitational flow in inverted
has been used as an important pharmacophore for various tube is denoted as “G”. Instead of forming gel it remains as
diseases such as anticancer, antibacterial, antifungal, solution at the end of the tests is referred to as “S” (solution)
anticoagulant and antiꢀHIV agent.7 In continuation with our and it remain as precipitate, the system was denoted as “P”
ongoing research work in the field of selfꢀassembled materials, (precipitation). The system, in which the gelator is not soluble
herein we report a new class of πꢀgelator derived from even at the boiling point of the solvent, was called an insoluble
renewable plantꢀderived resource, cashew nut shell liquid, system (I).
which could selfꢀassemble into gel form and nano flakes form
in different solvents. Nowadays renewable resources have been
Gel-sol melting temperature (Tg).
vastly focused to establish and optimize efficient materials, Gel melting temperature was determined by flow of gel by test
biologically relevant molecules, and largeꢀscale production of tube inversion method. All gels obtained are thermally
fine chemicals.8 In the present report we have used cashew reversible. Above their gelation temperature, the gel phase
nutshell liquid (CNSL), an important byꢀproduct obtained from becomes solution phase, but could be returned to their original
the cashew nut industry.9 The major component of CNSL is a gel state upon cooling. Gel was prepared in a 5 mL glass vial as
bio based nonꢀisoprene lipid, cardanol which comprises a described above, the vial was immersed in the oilꢀbath ‘upside
mixture of phenolic lipids: 5% of 3ꢀ
n
ꢀpentadecylphenol (3ꢀ down’ and the vial is slowly heated. The temperature at which
,11 the gel melted down to solution was recorded as Gel melting
,14ꢀ temperature (Tg).
PDP), 50% of 3ꢀ(8 ꢀpentadecenyl)phenol, 16% of 3ꢀ(8
Z
Z
Zꢀ
pentadecadienyl)phenol
pentadecatrienyl)phenol.9
and
29%
of
3ꢀ(8Z,11Z
UV-Vis and Fluorescence measurements
UV/vis spectra were recorded on an Evolution 220 UV/visible
spectrophotometer (Thermo Scientific). The spectra were
recorded in the continuous mode between 200 and 700 nm,
with a wavelength increment of 1 nm and a bandwidth of 1 nm.
Experimental section
General materials and methods
All chemicals used for the synthesis of coumarin derivatives
3a-c) and fluorescent probes (5a-c) were purchased from
Emission
spectra were measured
on
a
JASCO
(
spectrofluorometer FPꢀ8200, by fixing the excitation value at
325 nm for dodecanol and DMSO. Selection of excitation value
is based on the absorbance maximum of probes in different
solvent. Samples for absorption and emission measurements
were contained in 1 cm X 1 cm quartz cuvette.
Sigma Aldrich, Merck, Alfa aesar and Avra chemicals and were
used without further purification. All solvents were dried and
freshly distilled before use. Solvents used for gelation studies
are of AR grade. Double distilled water was used for preparing
selfꢀassembled nanostructures. Column chromatography was
performed on Silica Gel (100ꢀ200 mesh) purchased from Avra
chemicals, INDIA. Fibroblast L929 cell line was purchased
from Sigma Aldrich and PC3 cells were obtained from National
Centre for Cell Science (NCCS), Pune, India.
Morphological analysis
Morphological analysis of gel formed by gelator was studied
using Carl Zeiss AXIO ScopeA1 fluorescent/phase contrast
microscope. A glass slide containing a small portion of gel was
mounted on Phase Contrast Microscope and the morphology of
gel was identified. Morphology of selfꢀassembled structure
such as gel and nano flakes were studied using JEOL JEM 2100
F FETEM.
Characterization
1H NMR and 13C NMR spectra were recorded on Bruker 300
MHz NMR Spectrometer at 298 K. The 1H and 13C NMR
chemical shifts were reported relative to TMS. Coupling
constants (J) are denoted in Hz and chemical shifts (δ) in ppm.
Molecular modelling studies
Proton multiplicity is assigned using the following
abbreviations: singlet (s), doublet (d), triplet (t), quartet (q),
multiplet (m). High resolution MS analyses were performed on
an Agilent 6520 QꢀTOF instrument by dissolving the solid
sample in methanol.
MM2 energy minimised diagram was performed using
ChemBio 3D Ultra 13. Red colour dotted line shows the
possible hydrogen bond formation.
X-Ray diffraction studies
Gelation method
A small portion of a wet gel sample formed by gelator in
decanol was transferred in a sample holder and coated like a
2 | J. Name., 2012, 00, 1-3
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Journal Name
Journal of Materials Chemistry B
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DOI: 10.1039/C5TB00694E
thin film. The XRD measurement was performed on XPertꢀ obtained as pale yellow liquid which darkens on further storage.
PRO Diffractometer system.
After a second distillation, mixture of cardanol monoꢀ, diꢀ and
triꢀene was obtained. Synthetic procedure for 3ꢀpentadecyl
phenol (hydrogenated cardanol), 1c is as follows: To the
Rheological measurements
The mechanical properties of gel were investigated with a stress solution of cardanol (10 mL) dissolved in dry methanol, 5%
controlled rheometer (Anton Paar 302 rheometer) equipped Pd/C was added slowly and the entire mixture was stirred in the
with a steelꢀcoated parallelꢀplate geometry (25 mm diameter). presence of H2 gas (1 atm) for 5h. After completion of reaction
The gap between two plates was 1 mm. The measurements as identified using TLC, the solution was filtered through a
were carried out at 23 ̊C. Firstly, amplitude sweep measurement celite bed to obtain crude 3ꢀpentadecyl phenol. The pure
was conducted, which provides the information about linear product was obtained by recrystallization process using hexane
viscoelastic range which is directly proportional to the as solvent.
mechanical strength of the gel sample. Secondly, the storage
modulus, G’ and the loss modulus, G” were monitored as
functions of frequency sweep from 0.1 to 300 rad sꢀ1.
Synthesis
General procedure for the o-formylation of substituted phenols
Cell proliferation assay
Dry paraformaldehyde (35 mmol) was added to a mixture of 3ꢀ
alkyl phenol (4 mmol), anhydrous MgCl2 (6 mmol) and
triethylamine (15 mmol) in acetonitrile (25 mL) and the
mixture was heated under reflux for about 12ꢀ15 h. After the
completion of the reaction as identified by using TLC, the
reaction mixture was cooled to room temperature and 5% aq.
HCl was added. The crude product was extracted with
ethylacetate, dried under Na2SO4 and purified using column
chromatography.
The antiꢀproliferation activity was tested by MTS assay on
fibroblast L929 and PC3 cell line using the fluorescent dye,
yellow tetrazolium dye, which when treated with cells, form
purple coloured formazan product. The quantity of formazan is
presumably directly proportional to the number of viable cells
and is measured by using a spectrophotometer (1420ꢀ040
Victor 3 Multilabel Counter, PerkinElmer, USA) at 490 nm
dissolved in PBS buffer. Viable cells with active metabolism
convert MTT into a purple coloured formazan product. When
cells die, they lose the ability to convert MTT into formazan,
thus colour formation serves as a useful and convenient marker
of only the viable cells. Cells were seeded into 96ꢀwell plate
for 48 h prior treatment. They were then exposed to 40 µL of
different concentrations (20, 40, 80 and 250 µg/1000 µL) of
compounds, 5a-c in 0.1% DMSOꢀwater mixture and to control
(0.1% of DMSOꢀwater mixture). The relative viability was
expressed as a percentage of the control well that was treated
with the solvent 0.1% of DMSOꢀwater mixture only. Cell
viability (%) was estimated as a ratio of the absorbance of
treated cell (Nt) to absorbance of untreated cells (solvent) (Nu)
multiplied by 100.
Synthesis of cardanol-aldehyde (2b)
Dry paraformaldehyde (1.05 g, 35 mmol) was added to a
mixture of cardanol (1.21 g, 4 mmol), anhydrous MgCl2 (570
mg, 6 mmol) and triethylamine (2.1 mL, 15 mmol) in
acetonitrile (25 mL) and refluxed for 15h. After completion of
the reaction as identified by using TLC, the reaction mixture
was cooled to room temperature and 5% aq. HCl was added.
The crude product was extracted with ethylacetate, dried under
Na2SO4 and purified using column chromatography using silica
gel (hexaneꢀethylacetate, 98:2) to afford 2b as yellow liquid.
Yield = 88%.
1H NMR (300 MHz, CDCl3)
1.30 (m, 16H), 1.61ꢀ1.64 (m, 4H), 1.95ꢀ2.05 (m, 2H), 2.61 (t,
= 7.5 Hz, 2H), 6.80 (s, 1H), 6.83 (d, = 8.1 Hz, 1H), 7.44 (d,
δ: 0.88 (t, J = 6.9 Hz, 3H); 1.25ꢀ
J
J
Cell viability (%) = (Nt / Nu) x 100
J
Cell imaging/cell uptake studies
= 8.1 Hz, 1H), 9.83 (s, 1H), 11.05 (s, 1H). 13C NMR (75 MHz,
CDCl3) δ: 195.81, 161.81, 153.84, 130.49, 130.01, 129.76,
120.51, 118.86, 117.08, 36.45, 32.62, 32.59, 31.94, 31.86,
31.80, 30.66, 29.72, 29.67, 29.54, 29.45, 29.34, 29.30, 29.25,
29.21, 29.16, 29.01, 28.91, 18.86, 27.24, 27.17, 14.12.
The Cell imaging / Cell uptake study of our fluorescent
compounds 5a-c were tested on Fibroblast L929 and PC3 cell
lines. The cells were seeded into 6ꢀwell plate for 24 h prior
treatment. They were then exposed to 40 µL of 5a-c dissolved
in in 0.1% DMSOꢀPBS buffer mixture with the concentration
of 250 µg/1000 µL. After 4 h of exposure, the media were
drained and the cells were washed with PBS buffer for more
than 2 times. In order to differentiate the nucleus the Hoechst
stain was then added and incubated for 15 minutes. After 15
min incubation, the stain was drained and the cells were again
washed with PBS and subjected for imaging. The cells were
imaged using confocal microscope.
Synthesis of PDP-aldehyde, 2c
Dry paraformaldehyde (1.05 g, 35 mmol) was added to a
mixture of 3ꢀpentadecylphenol (1.22 g, 4 mmol), anhydrous
MgCl2 (570 mg, 6 mmol) and triethylamine (2.1 mL, 15 mmol)
in acetonitrile (25 mL) and the mixture was refluxed for 15h.
After completion of reaction as identified by TLC, the crude
product was extracted with ethylacetate, dried under Na2SO4
and purified using column chromatography (hexaneꢀ
ethylacetate, 96:4) to afford 2c as white solid. Yield = 92%; mp
= 53ꢀ56 ºC.
Distillation of Cardanol
CNSL was distilled at a temperature between 210 and 280 °C,
under a pressure of 2 to 8 mm Hg to get cardanol. Cardanol was
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DOI: 10.1039/C5TB00694E
1H NMR (300 MHz, CDCl3) δ: 0.88 (t,
J = 6.6 Hz, 3H), 1.25ꢀ (d, J = 15.6 Hz, 1H). HRMS (ESI+): m/z calcd for C28H16O3
1.59 (m, 26H), 2.61 (t,
= 9.3 Hz, 1H), 7.45 (d,
J
J
= 7.5 Hz, 2H), 6.80 (s, 1H), 6.85 (d,
= 7.8 Hz, 1H), 9.83 (s, 1H), 11.05 (s,
J
(MꢀH+2Li)+ = 413.1320; observed = 413.2647.
1H). 13C NMR (75 MHz, CDCl3) δ: 195.80, 161.81, 153.84,
Compound 5b
1
120.50, 118.85, 117.08, 36.45, 31.94, 30.67, 29.71, 29.68, Yellow solid; Yield = 74 %; mp – 126ꢀ128 ºC; H NMR (300
29.55, 29.45, 29.38, 29.25, 22.71, 14.13. MHz, CDCl3) : 0.81 (t, = 4.5 Hz, 3H), 1.20ꢀ1.26 (m, 14H),
General method for the synthesis of 3-acetyl-7-alkyl-2H- 1.51ꢀ1.60 (m, 8H), 1.9ꢀ1.96 (m, 2H), 2.67 (t, = 7.2 Hz, 2H),
chromen-2-one, 3a-c. 5.26ꢀ5.32 (m, 2H), 7.11 (d, = 7.8 Hz, 1H), 7.15 (s, 1H), 7.52
To the compound 2a-c (1 mmol) dissolved in ethanol, (d, = 7.8 Hz, 1H), 7.94ꢀ8.17 (m, 7H), 8.20 (d, = 15.6 Hz,
= 8.1 Hz, 1H), 8.54 (d, = 9.3 Hz, 1H), 8.59 (s,
= 15.6 Hz, 1H). 13C NMR (CDCl3, 75 MHz) δ:
δ
J
J
J
J
J
ethylacetoacetate (1.3 mmol), 0.3 mL of piperidine and 2ꢀ3 1H), 8.45 (d,
drops of glacial acetic acid were added. The mixture was 1H), 9.0 (d,
J
J
J
refluxed for 4 h. After the completion of the reaction as 184.82, 158.41, 154.15, 149.88, 139.66, 131.77, 129.92,
identified by TLC, the reaction mixture was cooled to room 129.34, 129.21, 128.41, 127.41, 127.32, 127.28, 126.06,
temperature and 20 ml of ice cold water was added. The crude 124.90, 124.73, 124.57, 124.39, 124.23, 123.82, 123.43,
product was extracted with chloroform and dried over 123.22, 122.64, 121.25, 115.10, 114.72, 34.99, 29.50, 28.41,
anhydrous Na2SO4 and purified using column chromatography 28.32, 29.02, 27.91, 27.70, 21.37, 12.83. HRMS (ES+): m/z
using silica gel. Detailed synthesis of compound 3a might be calcd for C43H45O3 (M+Na)+ = 632.3266; observed = 632.2545.
reported elsewhere.
1
Compound 5c
= 6.3 Hz, 3H), 1.14ꢀ1.24 (m, 16H), Yellow solid; Yield = 82%; mp – 158ꢀ160ºC; H NMR (300
1.56ꢀ1.60 (m, 4H), 1.90ꢀ1.96 (m, 2H), 2.65 (t, = 8.1 Hz, 2H), MHz, CDCl3) δ: 0.88 (t, = 6.3 Hz, 3H), 1.20ꢀ1.50 (m, 24H),
2.65 (s, 3H), 4.88ꢀ4.9 (m, 1H), 5.25ꢀ5.34 (m, 1H), 7.09 (d, 1.65ꢀ1.69 (m, 2H), 2.74 (t,
7.5 Hz, 1H), 7.1 (s, 1H), 7.47 (d, = 8.1 Hz, 1H), 8.43 (s, 1H). 1H), 7.23 (s, 1H), 7.60 (d,
Compound 3b: Yellow liquid; Yield = 82 %; H NMR (300
MHz, CDCl3) : 0.80 (t,
1
δ
J
J
J
J
=
J
J
= 7.5 Hz, 2H), 7.19 (d,
= 7.8 Hz, 1H), 8.02ꢀ8.16 (m, 3H),
= 15.6 Hz, 1H), 8.54 (d, = 8.1
= 9.3 Hz, 1H), 8.68 (s, 1H), 9.07 (d, = 15.6
J = 7.8 Hz,
J
13C NMR (75 MHz, CDCl3) δ: 194.54, 158.52, 154.58, 150.44, 8.19ꢀ8.25 (m, 4H), 8.20 (d,
J
J
J
146.54, 128.97, 128.66, 124.64, 122.21, 115.09, 49.72, 44.25, Hz, 1H), 8.62 (d,
J
35.30, 30.9, 30.7, 29.81, 29.55, 28.68, 28.49, 28.34, 28.28, Hz, 1H). 13C NMR (CDCl3, 75 MHz) δ: 184.73, 18.25, 154.00,
28.11, 28.04, 27.96, 27.81, 27.28, 26.19, 26.11, 21.67, 21.63, 149.77, 146.78, 139.54, 131.60, 129.75, 129.16, 129.05,
14.16.
Compound 3c:White solid; Yield = 89 %; 1H NMR (300 MHz, 124.38, 124.24, 124.10, 123.63, 123.39, 123.26, 123.06,
CDCl3) δ: 0.85 ( t, = 7.2 Hz, 3H), 1.18ꢀ1.32 (m, 24H), 1.59ꢀ 122.53, 121.08, 114.94, 112.59, 30.40, 28.17, 28.13, 28.01,
1.67 (m, 2H), 2.71 (s, 3H), 2.72 (t, = 6.9 Hz, 2H), 6.90ꢀ7.14 27.90, 27.84, 27.69, 21.17, 12.60. HRMS (ES+): m/z calcd for
(d, = 8.1 Hz, 1H), 7.17 (s, 1H), 7.54 (d,
= 7.8 Hz, 1H), 8.5 C43H47O3 (M+Na)+ = 634.3439; observed = 634.5325.
128.25, 127.24, 127.14, 127.11, 125.88, 124.71, 124.54,
J
J
J
J
(s, 1H). 13C NMR (75 MHz, CDCl3) δ: 194.99, 158.96, 154.99,
150.88, 146.96, 129.35, 125.05, 122.62, 115.52, 115.49, 35.71,
21.29, 30.22, 20.97, 29.06, 29.02, 28.99, 28.89, 28.78, 28.73,
22.06, 13.49.
Results and discussion
Synthesis
Pyrene coupled coumarin derivatives that were designed for
selfꢀassembly studies are shown in Scheme 1. By complying
electrophilic aromatic substitution reaction on phenol, we have
Synthesis of coumarin coupled pyrene derivatives (5a-c)
General procedure
synthesized both cardanolꢀaldehyde 2b and PDPꢀaldehyde 2c
.
To a solution of 3ꢀacetyl coumarin (1 mmol) dissolved in 10
mL of nꢀbutanol, 1ꢀpyrenecarboxyaldehyde (1.3 mmol), 3 drops
of glacial acetic acid and 0.3 mL of piperidine was added and
The Knoevenagel reaction of compounds 2a-c with ethyl
acetoacetate under optimized reaction condition led to the
formation of desired 3ꢀacetylcoumarins 3a-c in good yields. πꢀ
Gelators 5a-c has been synthesized in good yields by aldol
the contents were refluxed at 120 ̊C for 12 h. After completion
of reaction as identified by TLC, the solvent was removed
under vacuum. The residue thus obtained was triturated with
10ml of ethanol until the formation of fine precipitate. The
precipitate was then filtered off and crystallized from methanol
or ethanol.
condensation of 3a-c with 1ꢀpyrenecarboxaldehyde
4 (Scheme
1). Here we have synthesised and completely characterized
three different compounds with varying hydrophobicity and
same has been utilized for selfꢀassembly studies.
Compound 5a
1
Yellow solid; Yield = 77 %; mp – 212ꢀ214 ºC; H NMR (300
MHz, CDCl3)
1H), 7.79 (t,
= 6.6 Hz, 1H), 8.15 (t,
(d, = 8.4 Hz, 1H), 8.67 (d,
δ
: 7.47 (t,
= 7.5 Hz, 1H), 7.78 (d,
= 7.5 Hz, 1H), 8.24ꢀ8.41 (m, 6H), 8.59
= 9.3 Hz, 1H), 8.79 (s, 1H), 8.89
J
= 7.5 Hz, 1H), 7.54 (d,
J = 8.1 Hz,
J
J
= 9.0 Hz, 1H), 8.0 (d, J
J
J
J
4 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C5TB00694E
Table 1. Solvents/vegetable oils used for gelation studies
Observation (CGC % wt/v)#
S. No
Solvent/vegetable oils
5a
5b
5c
1
Ethanol
P
P
P
2
nꢀButanol
PG
PG
P
3
Octanol
G (1.3)
G (1.3)
P
4
Decanol
G (0.28)
G (1.3)
P
6
Dodecanol
Toluene
G (0.4)
G (1.0)
G (4.0)
7
S
S
S
I
S
S
8
Benzene
S
S
9
1,2ꢀDichlorobenzene
Chloroform
Hazelnut oil
Olive oil
S
S
Scheme 1. Synthesis of pyrene coupled coumarin derivatives 5a-c
.
10
11
12
13
14
15
I
I
S
S
PG
S
S
G (1.3)
P
G (1.3)
P
Gelation studies
Heavy paraffin oil
Light paraffin oil
Sesame oil
S
S
S
PG
PG
PG
Supramolecular gelation is a process in which a pool of solvent
molecules immobilized within highly entangled fibrous
network obtained by the selfꢀassembly of gelator.10 Pyrene
based low molecular weight organogelators (LMOG) are
having a tendency to gelate solvents by using weak bonding
mechanism.11 Pyrene coupled coumarin, 5a act as an excellent
supramolecular gelator. Selfꢀassembly of such an efficient
gelator through nonꢀcovalent interactions into fibrillar
aggregate that could immobilize the solvent molecule by
capillary force to form a gel. Gelation ability of the gelator in
aromatic solvents, alcohols and vegetable oils were summarized
# S = solution; P = precipitate; I = insoluble; G = gel; PG = partial gel.
Critical Gelation Concentration (CGC) is presented in parenthesis [% (w/v)]
Morphological analysis
Organogel: Morphology of gels were examined by using optical
microscopy and HRTEM. Optical microscopy image of
organogel obtained from 5a in dodecanol is shown in Figure 1.
All the structure clearly explains the formation of entangled
thin fiber and twisted fiberꢀlike structures with the dimension
ranging between 100ꢀ200 nm (Figure 1). Figure 1a and b
represents the optical microscopy image of gel formed by
compound 5a in dodecanol under white light. The inset in
figure 1b clearly depicts the formation of helical nano fibers.
The fluorescence nature of selfꢀassembled supramolecular
structure has been identified by optical microscopy under
fluorescence light. Figure 1c and 1d explains the fluorescence
character of selfꢀassembled fibres and twisted fibres. In order to
have the further insight of gel, we have performed HRTEM
analysis (Figure 1e and f). It should be remarked that width of
the fiber or twisted fiber is higher than the molecular dimension
of gelator 5a. This result clearly depict that several gelator
molecule selfꢀassemble to form supramolecular architecture.
in Table 1. It is evident from table 1 that πꢀGelators 5a and 5b
exhibit excellent organogelation ability, showing critical
gelation concentrations (CGCs) of 0.28 and 1.0 % (wt/v)
respectively in higher alcohols such as decanol and dodecanol
respectively. These gels were melted upon heating and form gel
on cooling, hence they fall under the category of
thermoreversible gel. In fact organogel formed by 5a and 5b
experience a gel to sol transition upon heatingꢀcooling cycles
(Tg = 65 ̊C). Tg increases with increase in concentration of
gelator until it reaches the saturation point. Compound 5c did
not form gel in any of the tested solvent because of its enhanced
hydrophobicity. Further detailed gelation test clearly shows that
compound 5a-5c do not form gel in any of the aromatic
solvents tested and form stable gel in long chain alcohols and
vegetable oils. Increasing the lipophilicity of the pyrene
coupled coumarin derivatives by introducing unsaturated and
saturated alkyl chain decreases the gelation ability.
Morphology and properties of the
assembly mechanism of
π
ꢀgel resembles the selfꢀ
π
ꢀconjugated
molecule.5
Morphological studies reveals the formation of uniformly
entangled fibrillar structure due to the hierarchical fashion of
selfꢀassembly of pyrene coupled coumarin derivative in highly
crossꢀlinked three dimensional supramolecular polymeric
structure to form gel. Pictures of gel prepared in various
solvents such as decanol, dodecanol and hazelnut oil under day
light and UV light is shown in Figure 1g & 1h.
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been extended to other compounds 5b and 5c also. Average
size of nano flakes formed by 5a-c in DMSOꢀwater mixture
(1X10ꢀ3M solution) at lower concentration ranges between 10ꢀ
100 nm (Figure 2).
Figure 2. (a) Self-assembly of 5a in DMSO-water (1:1 ratio; 1X10-3M solution) (b-
e) HRTEM images of the self-assembly of 5a, 5b and 5c in DMSO-water mixture
respectively.
1H NMR studies
The supramolecular interaction of 5a has been inferred by
1
NMR spectral analysis. From H NMR under the influence of
different solvent, dilution and at different temperature could
reveal both Hꢀbonding and also the interaction between the
aromatic moieties
(
π
ꢀ
π
interaction). Solvent and or
concentration dependent NMR studies for gelator 5a has been
performed to probe the driving force for the selfꢀassembly
process (Figure 3).
Figure 1. (a-d) Optical microscopy image of gel, 5a in dodecanol (0.28 % wt/v) [(a
& b) under white light (inset show the formation of twisted fibers); (c & d) under
fluorescence light]; (e & f) HRTEM images of gel, 5a in dodecanol; (g & h)
Pictures of gel under day light and UV light respectively [left-5a in decanol,
middle-5b in hazelnut oil and right-5a in dodecanol]
Selfꢀassembled nano flakes: Since pyrene coupled coumarin, 5a
selfꢀassemble to form gel in long chain alcohols, we were more
interested in look on the selfꢀassembly behaviour of gelator 5a
in water. Selfꢀassembled nano flakes were prepared by
refluxing the calculated amount gelator 5a dissolved in 1:1 ratio
of DMSOꢀwater mixture followed by cooling at room
temperature. On heating gelator 5a got completely dissolved in
solvent mixture and selfꢀassembly has been induced by keeping
the mixture undisturbed at room temperature. This resultant
solution has been considered as stock solution and could be
further diluted for cell imaging application. HRTEM analysis
clearly depict the formation of nano flakes. This studies has
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Figure 3. 1H NMR spectra (aromatic region alone) of the compound, 5a; (a) in
DMSO-d6; (b) in DMSO-d6 + dodecanol (1:1 ratio); (c) in DMSO-d6 + dodecanol
(1:2 ratio).
The 1H NMR spectra of compound 5a shows clearly
concentration
dependent
features.
Resonance
signal
corresponding to the aromatic protons displayed a downfield
shift with the increase in the concentration of gelator solvent.
In nonꢀgelling solvent (DMSOꢀd6) aromatic protons showed
signals between 7.45ꢀ8.90 ppm. Upon increasing the
concentration of gelling solvent, these protons experience
downfield shift and appears in between 7.85ꢀ9.60 ppm (Figure
Figure 4. (a) SAXD data for gel prepared by 5a in decanol and (b) proposed self-
assembly mechanism.
Absorbance and emission studies
3). It is well known phenomenon that the existence of
stacking in ꢀconjugated system shifts the aromatic protons
more towards downfield. Thus the magnitude of stacking in
5a increases with increase in the concentration of gelling
solvent.
πꢀπ
As discussed previously,
πꢀconjugated fluorescent gel have
π
attained more interest because of its potential applications
especially in electronic and medical fields.5,13 Accompanying
the intention of studying the potential application in the field of
medicine we have performed spectroscopic investigation on
fluorescent organogel. The absorption spectrum of compound
5a in different solvents such as acetonitrile, DMSO and
dodecanol is shown in figure 5a. In acetonitrile solvent,
compound 5a show three bands centred at 307, 392 and 427
nm, which are assigned to unꢀaggregated form of coumarin and
pyrene unit. The peak observed at 307 nm experience red shift
and appeared at 352 nm by changing the solvent to DMSO.
This red shift may be due to weak interaction of DMSO with
coumarin core of 5a. Absorption spectra of compound 5a in
dodecanol, a gelling solvent show red shift in all these peaks
centred at 324 and 448 nm, which is due to molecular
aggregation involving the formation of hydrogen bonding
πꢀπ
XRD studies
XꢀRay diffraction (XRD) experiment was employed to acquire
an additional information about molecular packing of selfꢀ
assembled 5a in the gel state. Figure 4 shows the small angle
XRD pattern of gel prepared from decanol. Small angle XRD
of the gel provides a Bragg’s reflection at 2.3 nm obtained from
the packing of decanol due to the van der Waals interactions in
gel network. The peak observed at 1.75 nm articulates
coumarin coupled pyrene moiety. Bragg’s reflection at 1.27 nm
and 1.06 nm attributed to hydrogen bonded decanol with the
carbonyl groups of pyreneꢀcoupled coumarin derivative, 5a
(Figure 4a). This reflections are approximately equal to the
molecular length of 5a and hydrogen bonded decanol, which
was confirmed by molecular modelling studies using energy
minimized calculations. In addition XRD spectra of this gel
show peak with position in the ratio of 1:2:3 suggest the
existence of lamellar structure. Peaks appear at 0.37ꢀ0.48 nm
between carbonyl carbons coumarin moiety and dodecanol, πꢀπ
stacking of pyrene (Figure 5a). Molecular selfꢀassembly of 5a
in higher alcohol has been clearly identified using UVꢀvis.
Since gelator 5a forms nano flakes in DMSOꢀwater mixture, we
intended to perform UV titration of compound 5a dissolved in
DMSO (1X10ꢀ5 M) with PBS buffer solution. Absorbance band
for 5a in DMSO solvent observed at 427 nm gradually
are assignable to the (001) aspect of πꢀπ stacking of aromatic
units.12 Based on the results obtained by NMR studies and
XRD, we propose mechanism for the formation of selfꢀ
assembled molecular gel (Figure 4b).
decreases with sequential addition of 100ꢀL of PBS buffer
solution. The addition of PBS buffer to 5a dissolved in DMSO
resulted in the formation of selfꢀassembled nano flakes (Figure
5a). The absorption spectra shift may take place either by solute
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solvent interaction or soluteꢀsolute interaction induced by selfꢀ piecemeal addition of 100
ꢀL of PBS buffer. In aggregated
assembly or via chemical process such as charge transfer, state, the emission spectrum covers a broad range of visible
proton transfer, etc. ꢀConjugated molecule 5a display higher spectral range and exhibit vibronic coupling maximum at 414
molar extinction coefficient in the solvents tested clearly and 576 nm. The formation of selfꢀassembled nano flake like
indicate the involvement of * and nꢀ * transitions. Right structure has been identified by the drastic increase in emission
π
π
ꢀ
π
π
after investigating the selfꢀassembly features of 5a to form gel intensity with a red shift (Figure 5c). We have also determined
and nano flakes using UVꢀvis spectroscopy, we have evaluated the fluorescence quantum yields of 5a-c in different solvents
the fluorescence property. Under selfꢀassembled state we could (1X10ꢀ5M). A very low fluorescence quantum yield ranging
observe the intense fluorescence which stimulated us to further from 9ꢀ12 % has been observed for compound 5aꢀc in DMSOꢀ
explore the emission property of compound 5a-c under PBS buffer (1:1 ratio), which could be due to the selfꢀ
different experimental conditions. Emission spectra of aggregation process. Quantum yields of 73% was observed in
compound 5a-c displayed substitution dependence emission DMSO solvent alone. Similarly selfꢀassembly of 5b and 5c was
behaviour i.e. substitution on coumarin moiety slightly also identified by using UV and fluorescence studies (Figure 5d
influence the emission property. Compound 5a in dodecanol and 5e). Fluorescence of selfꢀassembled system was not
can selfꢀassemble to form gel. In selfꢀassembled state, emission quenched even in extreme pH conditions (pH 4 & 10), and thus
spectrum of 5a in dodecanol shows three peaks centred at 389, this system can be applied for cell imaging application under
409 and 554 nm. Disꢀassembly has been induced by gradual physiologically important conditions at various pH values.
addition of dodecanol, the intensity of peak observed at 409 nm From these result, we resolve that at higher concentration, 5a
got increased and peak centred at 554 nm showed blue shift. and 5b selfꢀassemble to form gel in decanol and dodecanol, and
The observed significant blue shift of fluorescence maxima is at lower concentration compounds 5a-c selfꢀassemble to form
mainly due to disꢀassembly of selfꢀassembled structure attained nanostructures such as nanoꢀsheet and nanoꢀflakes in DMSOꢀ
by titrating against dodecanol. (Figure 5b). Fluorescence water (1:1 mixture). Since bioꢀapplications of organogels were
emission spectra of 5a was also measured in DMSO to look decently researched in the literature, we aimed to explore the
insight the effect of solvent. Compound 5a in DMSO shows possible application of selfꢀassembled material i.e. nano flakes
three intense peaks at 397, 409 and 478 nm, which is different in cell imaging applications.
from the peaks observed for dodecanol. The molecular
aggregation of 5a dissolved in DMSO was induced by
Figure 5. (a) UV-Vis spectra of 5a in different solvents (1X10-5 M), dotted line represents the UV titration of 5a in DMSO with PBS buffer; (b) Emission spectra of 5a in
dodecanol and its response with respect to dilution, inset shows the plot of emission intensity vs concentration; (c) Fluorescence titration of 5a in DMSO with PBS
buffer and its corresponding plot of wavelength vs concentration; (d & e) Emission spectra of 5b and 5c in dodecanol respectively and its response with respect to
dilution. In titration experiments, direction of arrow show the response of absorption and emission intensity with piecemeal addition of 100
solvent. 2 mL of initial volume of solution (1X10-5M) was taken for titration experiments.
ꢀL of corresponding
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material behaves in a nonꢀlinear fashion.14 Figure 6b shows a
strain sweep of organogel prepared by compound 5a in
Rheological studies
The elastic behaviour and flow characteristics of an organogel dodecanol. With gradual increase in strain, G
were determined by measuring rheology.14 In frequency sweep constant and at a certain point gradual drop was observed and
experiment the variation of storage modulus (G ) and loss cross over occurs between G and G′′, the point at which the
modulus (G′′) were monitored as a function of applied cross over occurs is considered as critical strain ( c) of a gel.
frequency at a constant strain of 0.1% at room temperature by The c for organogel was found to be 2.73 (G’=G”=490.7 Pa)
using organogel prepared from compound 5a in dodecanol at a (Figure 6b). Below c (G’>G’’) gel behaves like a rigid solid,
′ and G′′ remains
′
′
γ
γ
γ
concentration of 0.5% wt/v. Constant strain has been fixed by and this result clearly depict the formation of highly structured
performing amplitude sweep. G’ represents the ability of material, which could be disturbed by increasing the strain
deformed gel to restore its original geometry and G’’ represents above γc, eventually become fluidꢀlike. Continuous temperature
tendency of gel to flow. For nonꢀviscous liquid, G’ = 0 and for ramp up and ramp down experiment clearly depict the stability
solids G’’ = 0. In viscoelastic material like gels, throughout the of gel and hold back both structural and mechanical property
entire range of frequency sweep, the value of G′ was found to even at elevated temperatures for more than three cycles
be more than that of G′′ (Figure 6a). G’and G’’ exhibited a very (Figure 6c). Strain experiment demonstrate the exceptional
little frequency dependency with an increase in applied angular mechanical behaviour of these gels which has been identified
frequency. Thus viscoꢀelastic deportment of gel was by simultaneously applying high and low magnitude of strain
independent of frequency sweep, and this result suggesting that such as 100% and 0.1 % respectively. Under 100 % strain, both
it possess good tolerance to external forces (Figure 6a). For G’ and G’’ values were apparently decreased because of the
organogel, at an angular frequency 0.1 rad/s, G’ in the order of broken network structure and recovery of G’ and G’’ was
magnitude 11 times greater than G’’. The rheological behaviour observed within 1ꢀ5 seconds by decline in strain to 0.1%. This
of a viscoelastic soft material is independent of strain up to a result clearly arguing the reversible nature of gel and fast
critical strain level (γc) and beyond γc, G′ start decline and the recovery of the mechanical property (Figure 6d).
Figure 6. (a and b) Angular frequency and strain amplitude dependence of G′ and G′′ of organogel, 5a; (c) Response of storage (G’) and loss modulus (G’’) of organogel
with respect to temperature. Ramp up and ramp down temperature is 25-to-45ºC; (d) Time course change of G’ and G’’ of organogel in step strain condition 100%
strain (4.5 min) and 0.1% strain (4.5 min) were applied alternatively. Concentration of SSG and MSSG: 0.5 wt/v% in dodecanol.
solvent. The fluorescent nano flakes thus derived has been
potentially used for cell imaging applications. Yao et. al. in his
Cell imaging studies
The study on the effect of solvent in selfꢀassembly process review clearly discussed the significance of combination of
indicates that coumarin coupled pyrene derivatives can slowly fluorescence and nanomaterials.15 The recent development and
assemble into fluorescent gel and nano flakes in different innovation of fluorescent nanoparticles with unique optical
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properties establish a new map for fluorescence imaging and fibroblast L929 cells and PC3 human prostate cancer cells.
sensing applications both in vitro and in vivo 15
The use of Medium has been prepared by dissolving 250µg of compound
.
organic fluorescent molecules possess more advantage of being 5a-c in 1000µL of solvent (0.1% DMSOꢀwater mixture).
much brighter and more stable than the fluorescent proteins. In Concentration of medium is as follows: 5a: 0.6X10ꢀ3M, 5b: 0.4
addition the position of organic fluorescent molecules could be X10ꢀ3M and 5c: 0.4 X10ꢀ3M. At first we have studied the time
determined in precision than the fluorescent proteins. Most of dependent internalization of selfꢀassembled nano flake formed
applications such as in vitro and in vivo labelling in cells, by 5a
. Figure 7 clearly explains the internalization of selfꢀ
tissues, and organisms, proteomic and genomic studies, disease assembled nanoparticle at different intervals such as 1 min, 5
diagnostics, pharmaceutical screening, drug delivery, min, 10 min and 2 h respectively. Then for further detailed
assembled molecular control, protein purification, biological investigation, cells were incubated with medium containing 5a-
therapeutics, and medical imaging, sensing in cancer research,
and selective tumor targeting rely on fluorescence traced using Laser Confocal Scanning Microscopy (LCSM).
spectroscopy.16 Fluorescence imaging is one of the sensitive The green fluorescence arising from selfꢀassembled
c for 24 h. After incubation period, cellular localization was
π
ꢀ
and most informative analytical techniques in modern research. conjugated derivatives 5a-c were clearly observed in the
Selfꢀassembled nano flakes of 5a-c formed in DMSOꢀwater cytoplasm and perinuclear region of the cells. In compound 5a-
mixture could be potentially used for live cell imaging
c
, substituent at 7th position of coumarin moiety directly
application. These nano particles of size between 10ꢀ100 nm influence the fluorescence intensity. Compound 5a is not
are in the same range of dimension such as proteins, antibodies, having any substituent at coumarin core possesses more
membrane receptors, etc. These interesting characteristics, fluorescent character, whereas the other derivatives 5b and 5c
linked with their high surface to volume ratio impressed us to are have alkyl substituent exert comparatively less fluorescence
proceed further in this field. For our studies we have chosen property (Figure 8).
Figure 7. LCSM images of fibroblast L929 incubated with nano flake derived from 5a. (a-e) Internalization of nanoparticle at 0 – 120 minute respectively; (f) 3D view of
internalization of nanoparticle at 1 min. In figure 7a-e, top left: blue colour from Hoechst strain used to differentiate nucleus; Top middle: green fluorescence from
cytoplasm and perinuclear region of the cells by fluorescent nanoparticle; bottom middle: combined view of blue and green colour fluorescence from nucleus, and
cytoplasm and perinuclear region of the cells. Increase on intensity of green fluorescence in fibroblast L929 cells with respect to time is from self-fluorescent
conjugated nano flakes derived from 5a 18
π-
.
It is interesting to note that among 5b and 5c, 5b shows mechanism regulates how cells interact with their environment
comparatively more fluorescent character. From this result one and it involves four different mechanisms such as Clathrinꢀ
could say fluorescence intensity decreases with increase in mediated endocytosis, caveolae mediated endocytosis,
hydrophobicity of
πꢀconjugated systems (Figure 8). macropinocytosis and phagocytosis. Inhibitors such as sucrose
Nanoparticles/nano flakes prepared by selfꢀassembly process and chlorpromazine, blocking agents of clathrinꢀcoated pit
from 5a-c were uniformly located into the cytoplasm of the formation had no significant effect on cellular uptake and
cells. The increase in incubation time enhance the uptake of filipin, an inhibitor of caveolaeꢀassociated endocytosis) also
fluorescent nano flakes. Endocytosis is the internalization of had no significant inhibition effect on the nanoparticle uptake.
extracellular material via membranous vesicles.17 Endocytic Nocodazole, an inhibitor of macropinocytosis inhibited the
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uptake of nanoparticle up to 60%. These results suggested that uptake
macropinocytosis and phagocytosis are the prominent cell
pathway
for
selfꢀassembled
nanoparticles.18
Figure 8. LCSM images of (a) fibroblast incubated with 5a; (b) fibroblast incubated with 5b; (c) fibroblast incubated with 5c; (d-f) PC3 prostate cancer cells incubated
with 5a-c for 24h respectively. In figure 8a-f, top left: blue colour from Hoechst strain used to differentiate nucleus; top right: green fluorescence from and cytoplasm
and perinuclear region of the cells fluorescent nanoparticle; bottom right: combined view of blue and green colour fluorescence from nucleus, and cytoplasm and
perinuclear region of the cells. Rupture of cell membrane and overflow of cytoplasm could be directly identified from figure 8d-f 18
We didn’t observe any cell damage in fibroblast L929 on
treatment with nano flakes, which entails the low cytotoxicity
of nanoflakes in fibroblast. Cytotoxicity assay on both
fibroblast and PC3 cells also supports the results obtained from
LCSM. Treatment of PC3 cells with selfꢀassembled nano flakes
heads to the cell death in PC3 cells by inhibiting Wnt/βꢀcatenin
pathway, which has been identified based on cell membrane
rupture and the overflow of cytoplasm (Figure 8dꢀf). Coumarin
based antiꢀcancer drug, decursin inhibits Wnt/βꢀcatenin
Figure 9. Graphical representation of (a) cell viability of fibroblast and PC3 cells
when exposed to 250µg/1000µL of compound 5a-c. (b) Cell viability of PC3 cells
when exposed to increasing concentration of 5a-c (20-80µg/1000µL). In
fibroblast % of cell viability was around 95-98%
pathway and cellular proliferation.19 Cell proliferation or cell
viability are good indicants of cell death. In order check the
toxicity of compounds 5a-c, we have examined cell viability
towards fibroblast and PC3 cells. Fibroblast incubated with
different concentrations of 5a-c experience low cytotoxicity.
Incubation of PC3 cells with different concentrations of 5a-c
show considerable cytotoxic effect (Figure 9). These selfꢀ
fluorescent probes could be potentially used for optical
diagnosis and treatment for prostate cancer.
Conclusions
By utilizing aldol condensation as key step, a new class of
pyrene coupled coumarin derivatives were successfully
synthesised. Molecular structure of these compounds were
completely characterized using NMR and mass spectral
analysis. We have reported the formation of transparent
fluorescent organogel with CGC of 0.28
supramolecular selfꢀassembly through hydrogen bonding and
stacking of pyrene units. Morphology of organogel was
% wt/v via
π
ꢀ
π
investigated by optical microscopy and HRTEM. The
concentration dependent absorbance and emission studies and
1H NMR analysis reveal that hydrogen bonding between the
carbonyl groups of 5a and long chain alcohols, and
πꢀπ
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VJieowuArrtnicalelONnlainme e
DOI: 10.1039/C5TB00694E
stacking interactions were the driving force for the process of
selfꢀaggregation and gel formation. Optical property of
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We thank Department of Science and Technology (IFAꢀCHꢀ04
and #SB/FT/CSꢀ024/2013), India and Board of Research in
Nuclear Science (#37(1)/20/47/2014), Department of Atomic
Energy, India for financial support.
ACS Nano, 2011,
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This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 13

Journal of Materials Chemistry B
Page 14 of 14
View Article Online
DOI: 10.1039/C5TB00694E
Abstract
The present work reports facile synthesis of pyrene coupled coumarin derivatives which
could form self-assembled molecular gel in long chain alcohols and nano flakes in aqueous
medium. The morphology and physical properties of the organogel and nanoparticles were
studied by HRTEM, absorbance and emission studies. Mechanical strength and reversible
nature of organogel has been extensively studied using rheology. The nanomaterials
obtained via self-assembly process could be potentially used in fluorescence imaging
applications.