Facile synthesis of gold nanoparticles using aggregates of pentacenequinone derivative and their catalytic activity for oxidative polymerization, homocoupling and reduction

Article abstract of DOI:10.1039/c4ra11116h

The fluorescent aggregates of pentacenequinone derivative 3 serve as reactors for the preparation of gold nanoparticles through irreversible oxidative polymerization to furnish pentacenequinone based mesoporous polyaniline derivative. Further, gold nanoparticles so generated also exhibit excellent catalytic activity for conversion of phenyl boronic acid to biphenyl and reduction of nitro aromatics to amino derivatives.

Full text of DOI:10.1039/c4ra11116h

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Facile synthesis of gold nanoparticles using
aggregates of pentacenequinone derivative and
their catalytic activity for oxidative polymerization,
homocoupling and reduction†
Cite this: RSC Adv., 2014, 4, 53795
*
Kamaldeep Sharma, Vandana Bhalla and Manoj Kumar
The fluorescent aggregates of pentacenequinone derivative 3 serve as reactors for the preparation of gold
nanoparticles through irreversible oxidative polymerization to furnish pentacenequinone based
mesoporous polyaniline derivative. Further, gold nanoparticles so generated also exhibit excellent
catalytic activity for conversion of phenyl boronic acid to biphenyl and reduction of nitro aromatics to
amino derivatives.
Received 24th September 2014
Accepted 13th October 2014
DOI: 10.1039/c4ra11116h
www.rsc.org/advances
preparation of AuNPs. To our pleasure, derivative 3 formed
uorescent aggregates in aqueous media and these aggregates
1. Introduction
served as reactors for the preparation of AuNPs without using
any reducing and stabilizing agents at room temperature.
Further, the gold nanoparticles so generated catalysed the
oxidative polymerization of pentacenequinone derivative 3
which resulted in the formation of pentacenequinone based
mesoporous polymeric material. The preparation of nitrogen
rich porous materials has attracted a lot of research interest due
to their potential applications in gas storage10 and as support
for many important catalysts.11 Interestingly, the nitrogen
adsorption and desorption studies of the polyaniline derivative
so obtained suggest that the material is mesoporous and was
found to have Brunauer–Emmett–Teller (BET) surface area and
adsorption average pore width of 5.0741 m2 gꢀ1 and 13.9 nm,
respectively. Earlier, small molecules/polymers having amino
groups have been used for preparation of gold nanoparticles12
and in case of o-phenylenediamine, gold catalyzed oxidative
polymerization of o-phenylenediamine monomers to poly(o-
phenylenediamine)13 has been observed. However, there is no
report regarding preparation of polymeric porous materials
utilizing gold catalyzed oxidative polymerization. Various
template based methods have been used for fabrication of
porous materials.14 However, most of these methods require
tedious post synthetic efforts for the removal of used template.15
In addition, removal of used template sometimes destroys the
porous materials.16 Thus, development of a simple and facile
method for the preparation of nitrogen rich porous material is
an area of great interest. In the present manuscript, we report a
simple and facile method for the preparation of AuNPs which
catalyse the oxidative polymerization of pentacenequinone
derivative 3. To the best of our knowledge, this is the rst report
where gold catalyzed oxidative polymerization has been carried
out for the preparation of pentacenequinone based mesoporous
Gold nanoparticles (AuNPs) as green catalysts have generated
great research interest in the frontiers between homogeneous
and heterogeneous catalysis.1 AuNPs and supported AuNPs
have been used to catalyze various chemical transformations in
organic synthesis such as photocatalytic hydroamination of
alkynes and alkenes,2 reduction of nitroaromatics3 and redox
reactions.4 Keeping in view the importance of AuNPs, various
methods such as seed mediated, chemical reduction, electro-
chemical, template based synthesis have been reported for the
preparation of AuNPs. Most of these methods involve the use of
reducing agents, stabilizing agents and shape directing addi-
tives.5 Further, the yield of AuNPs formed by these methods is
also low. On the other hand, wet chemical method gives the
high yield of metal nanoparticles of various shapes with control
over their size and morphology,6 but this method suffers from
the limitations of requiring longer reaction time and high
temperature.7 Thus, development of a simple and facile method
for the preparation of AuNPs with high catalytic efficiency
remains a challenge. Recently, we reported pentacenequinone
derivatives having nitrile groups.8 The uorescent aggregates of
these derivatives served as reactors for the preparation of gold
nanoprisms and gold nanospheres. In continuation of this
work, we now designed and synthesized symmetrically
substituted pentacenequinone derivative
3 having amino
groups at the periphery. We envisaged that aggregates of
derivative 3 may exhibit affinity towards gold ions due to the
presence of amino groups9 and will serve as reactors for the
Department of Chemistry, UGC Sponsored-Centre for Advanced Studies-I, Guru Nanak
Dev University, Amritsar-143005, Punjab, India. E-mail: vanmanan@yahoo.co.in; Fax:
+91 (0)183 2258820; Tel: +91 (0)183 22588029 ext. 3202
† Electronic supplementary information (ESI) available: Optical and spectroscopic
data of derivatives 3. See DOI: 10.1039/c4ra11116h
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material. In addition, the AuNPs show good catalytic activity for which the formation of AuNPs takes place. Solution of these NPs
the homocoupling of phenylboronic acid under aerobic condi- was used as such for the catalytic reactions.
tions and reduction of nitroaromatics to amino derivatives. The
catalytic activity of these NPs is better/comparable to reported
systems in literature (see Table S1–S3 in ESI†).
3. Results and discussion
Pentacenequinone derivative 3 was synthesized by Suzuki-
Miyaura coupling of 2,3,9,10-tetrabromopentacene 6,13-dione
2. Experimental section
2.1. Materials
1 17 with aniline boronic ester 2 18 (Scheme 1). The structure of
derivative 3 was conrmed from its spectroscopic and analytical
data. 1H NMR spectrum of derivative 3 showed three singlets at
All reagents were purchased from Aldrich and were used
without further purication. THF was dried over sodium and
5.14, 8.15 and 8.86 ppm, two doublets at 6.49 and 6.92 ppm
benzophenone and kept over molecular sieves overnight before
corresponding to the NH2 and aromatic protons, repectively
use. Silica gel (60–120 mesh) was used for column
(Fig. S18 in ESI†). The mass spectrum of derivative 3 showed a
parent ion peak at m/z 674.1713 (M + 2)+ (Fig. S19 in ESI†). These
chromatography.
spectroscopic data corroborate the structure
compound.
3 for this
2.2. Instruments
The UV-vis spectrum of derivative 3 in THF exhibits two
absorption bands at 287 and 415 nm, respectively. On addi-
tion of water (#60% volume fractions) to the THF solution of
derivative 3, the absorption band at 415 is blue shied to
396 nm and level-off tail is observed in the visible region
(Fig. 1A). The absorption studies suggest the formation of
aggregates in the aqueous media. On the other hand, in the
uorescence spectrum, aggregates of derivative 3 in H2O/THF
(6 : 4) exhibit two emission bands at 373 and 477 nm (Fig. S2
in ESI†) which result from locally excited state and intra-
molecular charge transfer state, respectively.19 The scanning
electron microscopy (SEM) image of derivative 3 in the
solvent mixture of H2O/THF (6 : 4) shows the presence of
irregular shaped aggregates (Fig. 1B). The aggregates formed
were visibly transparent and stable at room temperature for
several weeks.
The presence of amino groups at the periphery of the
derivative 3 prompted us to investigate its sensing behaviour
toward different metal ions by UV-vis and uorescence
spectroscopy. The UV-vis studies of aggregates of derivative
3 (10 mM) in H2O/THF (6 : 4) mixture were carried out toward
different metal ions such as Au3+, Ag+, Ni2+, Cu2+, Cd2+, Hg2+,
Fe2+, Zn2+, Pb2+, Fe3+, Co2+, Na+, K+, Li+, Cr3+ ions as their
perchlorate/chloride/or both perchlorate and chloride salts.
Among various metal ions tested, nanoaggregates of derivative 3
show selective response towards Au3+ ions (Fig. S3 and S4 in
ESI†). Upon addition of Au3+ ions (200 equiv.) to the solution of
derivative 3 in mixed aqueous media (H2O/THF, 6/4), a new
absorption band is observed at 560 nm which suggests the
formation of AuNPs (inset Fig. 2A).20 The intensity of this band
increases with time and the rate constant21 for the formation of
AuNPs was found to be 7.18 ꢂ 10ꢀ5 sꢀ1 (see pS12 in ESI†).22 On
the other hand, complete quenching in uorescence intensity
UV-vis spectra were recorded on a SHIMADZU UV-2450 spec-
trophotometer, with a quartz cuvette (path length, 1 cm). The
cell holder was thermostatted at 25 ꢁC. The uorescence spectra
were recorded with a SHIMADZU 5301 PC spectrouorimeter.
Scanning electron microscope (SEM) images were obtained with
a eld-emission scanning electron microscope (SEM CARL
ZEISS SUPRA 55). TEM images were recorded from Trans-
mission Electron Microscope (TEM)-HITACHI. Elemental anal-
ysis (C, H, N) was performed on a Flash EA 1112 CHNS-O
1
analyzer (Thermo Electron Corp.). H NMR was recorded on a
JEOL-FT NMR-AL 300 MHz spectrophotometer using CDCl3 and
DMSO-d6 as solvent and tetramethylsilane SiMe4 as internal
standards. UV-vis studies were performed in THF and H2O/THF
mixture. Data are reported as follows: chemical shis in ppm
(d), multiplicity (s ¼ singlet, d ¼ doublet, br ¼ broad singlet m ¼
multiplet), coupling constants
interpretation.
J (Hz), integration, and
2.3. Synthesis
Compound 3. To a solution of 1 (0.5 g, 0.808 mmol) and 2
(0.780 g, 3.56 mmol) in 1,4-dioxane (20 ml) were added K2CO3
(0.891 g, 6.464 mmol), distilled H2O (2.1 ml) and [PdCl2(PPh3)2]
(0.170 g, 0.242 mmol) under N2 atmosphere and the reaction
mixture was reuxed overnight. The 1,4-dioxane was then
removed under vacuum and the residue so obtained was treated
with water, extracted with dichloromethane and dried over
anhydrous Na2SO4. The organic layer was evaporated to dryness
under reduced pressure and residue so obtained was puried by
column chromatography using 95 : 5 (chloroform : MeOH) as
an eluent to give 0.163 g (30%) of compound 3 as dark brown
1
solid; mp. >260ꢁ C; H NMR (300 MHz, DMSO d6): d ¼ 5.14 [s,
8H, NH2], 6.49 [d, 8H, J ¼ 6.0 ArH], 6.92 [d, 8H, J ¼ 6.0 ArH], 8.15
[s, 4H, ArH], 8.86 [s, 4H, ArH], TOF MS ES+: 674.1713 (M + 2)+;
elemental analysis: calcd. for C46H32N4O2: C 82.12; H 4.79; N
8.33; found: C 82.08; H 4.76; N 8.29. Due to poor solubility of
compound 3 in common organic solvents, its 13C NMR spec-
trum could not be recorded.
Synthesis of AuNPs. To a 3 ml solution of compound
3 (10 mM) in H2O/THF (6 : 4, v/v) was added 0.1 M AuCl3 (60 mL).
The reaction was stirred at room temperature for 2 min during Scheme 1 Synthesis of pentacenequinone derivative 3.
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Fig. 3 TEM images of aqueous gold solution of derivative 3 showing
presence of bundles of nanofibres and spherical gold nanoparticles.
Scale bar (A) and (B) 100 nm.
Fig. 1 (A) UV-vis spectra of derivative 3 (10 mM) showing the variation
of absorption intensity in THF and 60% H2O/THF mixture (B) SEM
image of derivative 3 in H2O/THF (6 : 4) mixture showing irregular
shaped aggregates; scale bar 200 nm.
The presence of peaks of Au, C, O and N in energy disper-
sive X-ray (EDX) spectrum of resulting solution (Fig. S10 in
ESI†) conrmed the presence of organic compound and
AuNPs.13
To get insight into the mechanism of formation of AuNPs
and polyaniline material, we slowly evaporated the solution of
aggregates of derivative 3 containing AuNPs. Aer several days,
precipitates were observed. The X-ray diffraction (XRD) analysis
of the resulting precipitates showed the broad peak centered at
Bragg angle (2q/degree) ꢃ24ꢁ which may be attributed to
amorphous polyaniline polymer.13 Further, four diffraction
peaks were observed at 37.82, 44.08, 64.28, and 77.24ꢁ which
may be assigned to 111, 200, 220 and 311 faces of a Au crystal,
respectively (Fig. S11 in ESI†). These four peaks showed the
characteristic pattern of face-centered cubic (fcc) gold (0).23
Next, the precipitates were washed several times with THF. The
1H NMR spectrum of the residue so obtained aer evaporation
of THF exhibits three sharp peaks at 6.93, 7.05 and 7.14 ppm
corresponding to –NH2 and –NH– groups24 of polyaniline
derivative (see pS21 in ESI†). Thus, 1H NMR study supports the
formation of pentacenequinone based polyaniline derivative.
The SEM images of resulting residue show presence of entan-
gled nanorods with network structure (Fig. 4A–C).
The porous structure of polyaniline was characterized by
atomic force microscopy (AFM) through non-contact measure-
ments. The topography images of polyaniline (Fig. 5) show
porous surface.
The porosity parameters of polyaniline were studied by using
nitrogen adsorption and desorption measurements to deter-
mine the pore size and specic surface area of the polymeric
material (Fig. 6).
Fig. 2 (A) UV-vis spectra of derivative 3 (10 mM) upon addition of Au3+
ions (200 equiv.) and at different time intervals in H2O/THF (6/4) inset:
UV-vis spectra in range 450–700 nm taken at different time
intervals showing band at 560 nm. (B) Fluorescence spectra of deriv-
ative 3 (10 mM) upon addition of Au3+ ions in H2O/THF (6/4); buffered
with HEPES, pH ¼ 7.0. lex. ¼ 287 nm.
was observed upon addition of Au3+ ions (0–200 equiv.) to the
solution of derivative 3 (H2O/THF, 6/4) (Fig. 2B). This quenching
in uorescence emission is attributed to binding of Au3+ ions
with nanoaggregates of derivative 3. The changes in the
absorption spectra suggest interaction of gold ions with the
amino groups of aggregates of derivative 3 and their subsequent
reduction to zero valent gold atoms.
The detection limit for Au3+ ions was found to be 70 nM
(70 ꢂ 10ꢀ9 M). The calculated Stern–Volmer constant of nano-
aggregates of derivative 3 for Au3+ ions was found to be 1.63 ꢂ
103 Mꢀ1 (Fig. S6 in ESI†). Under the same conditions as used for
Au3+ ions, we tested the binding behaviour of aggregates of
derivative 3 toward other metal ions such as Au3+, Ag+, Ni2+,
Cu2+, Cd2+, Hg2+, Fe2+, Zn2+, Pb2+, Fe3+, Co2+, Na+, K+, Li+, Cr3+
ions (Fig. S7 and S8 in ESI†) but no signicant change in uo-
rescence intensity of aggregates of derivative 3 was observed
(Fig. S9 in ESI†).
The TEM images of solution of derivative 3 in the presence of
gold ions show the presence of bundles of nanobres and
spherical AuNPs (Fig. 3A and B).
Fig. 4 SEM images of pentacenequinone based polyaniline obtained
after oxidative polymerization of derivative 3. Scale bar (A) 1 mm (B) and
(C) 200 nm.
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Scheme 2 Schematic diagram to illustrate the probable reaction
mechanism for the formation of polyaniline.
Fig. 5 Topographical AFM-images of the surface of polyaniline of
derivative 3 showing presence of pores.
We also investigated the catalytic activity of the AuNPs so
generated in the aqueous media for the homocoupling of
phenylboronic acid under aerobic conditions (See pS7 in ESI†).
We were pleased to know that in comparison to reported
systems, AuNPs of derivative 3 exhibit better/comparable
catalytic activity for the homocoupling of phenylboronic acid
under aerobic conditions (See pS4 in ESI†). In a toluene/H2O
(2 : 1) mixture, the yield of biphenyl and phenol in the prod-
ucts was found to be 80% and 20%, respectively. Further, we
also investigated the reduction of p-nitroaniline and p-nitro-
phenol to p-phenylenediamine and p-aminophenol in the
presence of AuNPs using NaBH4 (see pS8 in ESI†). Addition of
catalytic amount of gold nanoparticles solution 5 mL (10 nmol)
generated by aggregates of derivative 3 to the solution of
p-nitroaniline and p-nitrophenol results in complete reduction
of p-nitroaniline and p-nitrophenol to p-phenylenediamine
and p-aminophenol in 18 minutes and 8 minutes respectively
(Fig. 7A and B).
Fig. 6 Nitrogen adsorption and desorption curve of polyaniline of
derivative 3 at 295 K.
The reaction was monitored by UV-vis spectroscopy and the
calculated rate constants21 for the catalytic reduction of p-
nitroaniline and p-nitrophenol by gold nanoparticles of deriv-
The Brunauer–Emmett–Teller (BET) study shows presence
of pores of size 13.9 nm with B.E.T surface area of 5.074
(m2 gꢀ1). The negative values of the adsorbed quantity reveal
that tubular polyaniline structure has almost no micropores.25
The nitrogen adsorption and desorption data at 275 K is given
in Table 1.
atives 3 were found to be 4.53 ꢂ 10ꢀ3 sꢀ1 and 8.85 ꢂ 10ꢀ3 sꢀ1
,
respectively (see pS18 in ESI†). A blank experiment was carried
out for the reduction of p-nitroaniline and p-nitrophenol with
We also carried out UV-vis studies of derivative 3 towards
Au3+ ions in pure THF. However, absorption spectrum does not
indicate formation of nanoparticles (Fig. S12 in ESI†). These
studies suggest the importance of water in the preparation of
AuNPs. We propose that upon addition of Au3+ ions to the
solution of aggregates of 3, the gold ions enter the network of
interconnected channels, interact with amino groups and get
reduced. Thus, aggregates of derivative 3 function as reducing
agent as well as stabilizing agent for the preparation of AuNPs.26
Further, the AuNPs so generated catalyze the oxidative poly-
merization of derivative 3, hence, polyaniline of derivative 3 was
obtained (Scheme 2).
Fig. 7 UV-vis spectra for the reduction of (A) p-nitroaniline and (B) p-
nitrophenol by adding NaBH4 aqueous solution using gold nano-
particles of derivative 3 as catalyst.
Table 1 Surface area, pore size, pore volume, and N2 adsorbed for polyaniline material
BET surface
area (m2 gꢀ1
Langmuir surface
Pore volume
(cm3 gꢀ1
Adsorption average
pore width (nm)
Volume of N2 adsorbed
cm3 gꢀ1
Material
)
area (m2 gꢀ1
)
)
Polyaniline
5.0741
20.2870
0.053714
13.9
3.33
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We designed and synthesized symmetrically substituted
pentacenequinone derivative 3 which forms aggregates in
aqueous media. These aggregates serve as reactors for prep-
aration of AuNPs. AuNPs so generated act as catalyst for
preparation of mesoporous polyaniline derivative. In addi-
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homocoupling reaction of phenylboronic acid in aerobic
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Acknowledgements
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Potential for Excellence” (UPE) project. K. D. S is thankful to
DST-PURSE for fellowship. We are thankful to Shahi Imam Reja
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