Tuning the optical properties of flurophore-hexylcarbazole organic nanoribbons with dispersed inorganic nanocrystals (AgNCs)

Article abstract of DOI:10.1039/c0jm00004c

A carbazole derivative (3-(2,2-dicyanovinyl)-9-hexylcarbazole, abbreviated as L) has been designed, synthesized and used to prepare a novel organic-inorganic nanohybrid consisting of silver nanocrystals (Ag NCs) uniformly dispersed on the surface of L nanoribbons. Detailed characterizations have been performed. The results reveal that L couples with Ag NCs through a π-conjugated unit, which results in a significant red-shift of the fluorescence (FL), an obvious increase of FL lifetime and enhanced Raman scattering.

Full text of DOI:10.1039/c0jm00004c

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Tuning the optical properties of flurophore-hexylcarbazole organic
nanoribbons with dispersed inorganic nanocrystals (AgNCs)†
Lin Kong,a Jiaxiang Yang,ab Xiaopeng Hao,b Hongping Zhou,a Jieying Wu,a Fuying Hao,a Lin Li,a
a
Shengyi Zhang, Baokang Jin, Xutang Tao, Minhua Jiang and Yupeng Tian
a
b
b
abc
*
Received 12th January 2010, Accepted 8th June 2010
DOI: 10.1039/c0jm00004c
A carbazole derivative (3-(2,2-dicyanovinyl)-9-hexylcarbazole, abbreviated as L) has been designed,
synthesized and used to prepare a novel organic–inorganic nanohybrid consisting of silver nanocrystals
(Ag NCs) uniformly dispersed on the surface of L nanoribbons. Detailed characterizations have
been performed. The results reveal that L couples with Ag NCs through a p-conjugated unit, which
results in a significant red-shift of the fluorescence (FL), an obvious increase of FL lifetime and
enhanced Raman scattering.
Silver, a common noble metal, receives much attention
Introduction
because of its unique optical, electrical, mechanical and chemical
properties,8 which can be used in many fields, such as catalysis,9
medical devices,10 bioanalysis11 and surface enhanced Raman
scattering (SERS).12 As is known, the organic components in Ag
NCs-containg hybrids mostly involve thiols, carboxylates,
amides, imidazoles, indoles and hydroxyls.13–16 Ag-based hybrids
involving carbazole derivative are scarcely reported. In this
study, we are interested in obtaining nanohybrids from carbazole
derivatives and silver as a strategy for preparing new optical
materials in which the metal and the fluorophore could act
synergistically.5a,17
One trend in nanomaterial research is to generate multi-
functionality by bringing nanostructures with different proper-
ties into one system.1 In addition, interactions between inorganic
NCs and organic molecules can bring about new physical
properties, such as enhancing or tuning the optical properties.2
To this end, decoration of organic nanostructures with metal or
semiconductor nanoparticles may prove to be an attractive route
to organic–inorganic hybrid nanomaterials.1c In this field, the
conjugation of inorganic species allows property improvement of
a considerable number of organic materials, including carbon
nanotubes and conductive polymers.3 However, to the best of
our knowledge, the feasibility of this modification has not been
reported for carbazole-based nanostructures yet.
Considering all the aspects above, we first rationally designed
and successfully synthesized a carbazole derivative (3-(2,2-
dicyanovinyl)-9-hexylcarbazole) (L), in which the carbazole
group was employed as electron-donor unit, the dicyano group
as an electron-acceptor unit, and the hexyl group as a flexible
chain to increase the solubility of the compound. Therefore,
carbazole and dicyano units were linked by a vinyl bond to form
a novel organo-soluble D-p-A molecule. L can self-assemble into
nanotubes, nanofibres and nanowires by changing the processing
solvent. Then, it was coupled with Ag NCs through a modified
polyol process. We found that the prepared organic–inorganic
nanohybrid consisted of silver nanocrystals (Ag NCs) uniformly
dispersed on the surface of the L nanoribbons, and the coupling
brought about a significant fluorescence red–shift, obviously
prolonged FL lifetime and enhanced Ramam scattering. The
study opens the possibility of utilizing the hybrid nanomaterials
for a multitude of potential applications, such as chemical
sensing and organo–electronic device fabrication.
Carbazole derivatives, as is well known, bear a rigid conju-
gated plane and exhibit good hole and electron transporting
properties. Their charge transporting hybrids can generate free
carriers in the visible region through the photo-carrier generation
process.4 In many cases, carbazole groups can be employed as
electron-donors, and be linked with an electron-acceptor group
to form D-p-A type molecules (D ¼ donor, A ¼ acceptor), which
is regarded as an ideal candidate for nonlinear optical materials.5
In addition, electron transfer or electron separation between the
carbazole group and the acceptor group renders this class of
compounds as highly anisotropic structures. Consequently, the
crystallization tends to occur preferentially along the direction of
the D–A dipole–dipole interaction.6 Recently, our group7 has
synthesized a number of carbazole derivatives with linear and
nonlinear optical properties.
Experimental section
aDepartment of Chemistry, Anhui University and Key laboratory of
Inorganic Materials Chemistry of Anhui Province, Hefei, 230039, China.
E-mail: yptian@ahu.edu.cn
Synthesis of L
bThe State Key Laboratory of Crystal Materials, Shandong University,
Na2CO3 (1.06 g, 0.01 mol), dicyanomethane (1.1 mL, 0.02 mol)
and b-cyclodextrin (b-CD) were dissolved in 100 mL distilled
water. The above solution was added drop-wise into a 5 mL
ethanol solution of N-hexylcarbazole-3-aldehyde (2.57 g,
0.01 mol, see ESI†), and then stirred at room temperature for
36 h under a N2 atmosphere. The reaction was monitored by
Jinan, 250100, P. R. China
cThe State Key Laboratory of Coordination Chemistry, Nanjing
University, Nanjing, 210093, P. R. China
† Electronic supplementary information (ESI) available: Further
synthesis details, Figs S1–8, Table S1 and a movie of the coupling
process. See DOI: 10.1039/c0jm00004c
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undisturbed overnight for precipitation. The precipitate was
filtered and washed five times with high-purity water to remove
excessive PVP, EG and other inorganic residue, then dried under
vacuum at 50 ꢁC for 10 h to obtain a grey-black solid. The solid
was dispersed into high-purity water (1.0 mg mLꢀ1) for TEM,
SEM, UV-vis, fluorescence, and time-resolved analysis.
Pure Ag NCs were prepared by the same process in the absence
of L.
Characterization
The X-ray diffraction (XRD) patterns were recorded on
a
MXP18AHF diffractometer using Cu ꢁ Ka radiation
ꢁ
ꢀ
(l ¼ 1.54056 A) in the 2q range from 10 to 70 . The morphol-
ogies were obtained on a field-emission scanning electron
microscope (FESEM, Hitachi S-4800) and a transmission elec-
tron microscope (TEM, JEM-2100). The Raman spectra were
recorded with a Labram-HR spectrometer using the 785 nm line
of the Ar ion for excitation. UV-vis absorption spectra were
obtained on a LKB Biochem (Shimadzu UV-265) in the wave-
length range 300–600 nm. Fluorescence spectra were measured at
room temperature using a Hitachi F-3500 spectrometer. The
time-resolved fluorescence decay was performed on an Edin-
burgh FLS920 spectrofluorometer with a 450 W Xe lamp as the
excitation source. 5.0 ꢂ 10ꢀ6 mol Lꢀ1 fluorescein in 0.1 mol Lꢀ1
NaOH aquatic solution was used as the standard. A reconvo-
lution fit of the decay profiles was made with F900 analysis
software to get the lifetime value.
Scheme 1 The synthetic route to L
TLC to ensure complete reaction. Then, the reaction mixture was
extracted with 500 mL of CH2Cl2 and the organic layer was
washed three times with distilled water, and then dried over
anhydrous magnesium sulfate overnight. The solvent was
removed with a rotary evaporator. The residue was then
recrystallized from ethanol to obtain 3.17 g yellow needle
crystals (yield 97%). 1H NMR (400 MHz, CDCl3) d (ppm): 8.66
(d, J ¼ 2.0 Hz, 1 H), 8.17 (d, J ¼ 8.0 Hz, 1 H), 8.13 (d, J ¼ 8.8 Hz,
1 H), 7.88 (s, 1 H), 7.59 (t, J ¼ 8.0 Hz, 1 H), 7.51 (s, 1 H), 7.48
(s, 1 H), 7.38 (t, J ¼ 7.6 Hz, 1 H), 4.36 (t, J ¼ 7.2 Hz, 2 H), 1.95–
1.88 (m, J ¼ 7.2 Hz, 2 H), 1.43–1.28 (m, 6 H), 0.89 (t, J ¼ 7.2 Hz,
3 H). 13C NMR (100 MHz, CDCl3) d 13.94, 22.48, 26.86, 28.90,
31.46, 43.60, 109.67, 109.71, 114.18, 115.13, 120.97, 121.02,
122.36, 122.58, 123.73, 125.15, 127.37, 128.56, 141.24, 143.93,
160.13. FT-IR (KBr cmꢀ1): n ¼ 2219 (m), 2976 (w), 1566 (m),
1396 (s), 1236 (w). Anal. calcd for C22H21N3: C, 80.70%; H,
6.46%; N, 12.83%. Found: C, 81.45%; H, 6.02%; N, 12.47%. MS
(EI) m/z (%): 327.17 (M, 40), 256.07 (M–C5H11, 100).
Results and discussion
Synthesis of L
The new organic compound with a dicyano unit was obtained via
a Knoevenagel reaction between N-hexylcarbazole-3-aldehyde
and dicyanomethane. Interestingly, the yield is up to 97% with
the assistance of b-CD in aqueous solution. a-CD and g-CD are
used to investigate the effect of cavity size, and the yields are
almost the same as that of b-CD. Other phase transfer catalysts,
such as 18-crown-6, alkyl ammonium salts, laurylsulfonic acid
sodium salt and so on, are also used instead of b-CD, respec-
tively, but the yields are very low. Considering the structure of
b-CD, which has a hydrophilic shell and a hydrophobic cavity,19
it acts as a ‘‘micro-reactor’’ providing enough space for the
reaction between N-hexylcarbazole-3-aldehyde and dicyano-
methane inside the cavity. The water molecules can depart from
the cavity to complete the reaction. After reaction, L is obtained
by the removal of the b-CD molecules through washing with
distilled water. b-CD can be recovered and reused without loss of
activity.
Preparation of L nanostructures
The organic nanostructures were prepared using a recrystalliza-
tion method.18 In typical experiments, L was recrystallized by
microwave irradiation (464 W, SanleWr650) in benzene, tetra-
hydrofuran, ethanol or ethylene glycol (EG). In the cooling
process, the samples were left undisturbed to stabilize the
nanostructures. The products were filtered and then dispersed
into high-purity water for SEM and fluorescence studies.
Preparation of the L–Ag hybrid
Effect of the solvent on the aggregation of L
The hybrid materials were produced using a modified polyol
process. In detail, AgNO3 (9.0 mg, 0.05 mmol) and poly(vinyl
pyrrolidone) (PVP-K30, 40 mg) were dissolved in 10 mL of EG,
then L (16.3 mg, 0.05 mmol) was added, followed by microwave
heating for 2 min. During the process, the transparent solution
gradually changed from light yellow to deep brown. Then, the
solution was cooled to room temperature naturally and kept
In the present work, L nanostructures are simply prepared in
several solvents with no addition of any surfactant, template or
catalyst. L is a typical D-p-A type molecule, in which both the
donor and the acceptor group make the molecules aggregate
along one direction to form one-dimensional nanostructures.20
FESEM and TEM images of L self-assembly aggregation from
different solvents are shown in Fig. 1. The slovent-induced
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of L–solvent are stronger than those of L–L, when L molecules
dissolve into the solvent, resulting in particles with a smaller size.
On the contrary, if the interactions of L–L are stronger, L
molecules tend to aggregate, resulting in particles with a larger
size. Furthermore, several peaks at the diffraction angles
(10–25ꢁ) in the XRD patterns give the evidence that the
arrangement of L molecules should be ordered in the aligned
nanofibres and nanohybrid (Fig. 2b and c).
Fluorescence properties of L with different morphologies
The fluorescence properties of L nanostructures have been
studied at room temperature under identical experimental
conditions and the results are shown in Fig. S1.† The
dilute benzene solution of L shows a blue emission at 452 nm
(Fig. S1a†), while it centers at about 510 nm in solid state
(Fig. S1f†). However, one-dimensional nanostructures with
different morphologies exhibit obviously different emission
spectral profiles (Fig. S1b–e†). Compared with that of dilute
solution, the maximal emission spectra of the nanostructures
from benzene, THF and EtOH exhibit red-shifts of 28 nm, 30 nm
and 48 nm from 452 nm to 480 nm (Fig. S1b†), 482 nm
(Fig. S1c†) and 505 nm (Fig. S1d†), respectively. When EG is
used as solvent, the emission spectrum centers at about 508 nm
(Fig. S1e†), which is very close to 510 nm in the solid state. This
phenomenon should be attributed to interactions between
neighboring molecules.23 Nanomaterials with different
morphologies are promising candidates to exhibit different
optical properties due to different methods of molecular
stacking.24
Fig. 1 The morphologies of L from different solvents: (a) benzene, (b)
EtOH, (c) THF (insert: a typical TEM image with an open-ended
structure), (d) EG.
Formation of L–Ag hybrids
After detailed investigation on free L aggregation, the hybrid-
ization from L and Ag was further studied, as follows. EG is
chosen as the solvent in the preparation because the morphology
obtained from it is more regular than those obtained from the
others. The L–Ag hybrid is prepared by heating the EG solution
containing L, AgNO3 and PVP. During the process, the assembly
of L and the formation of Ag NCs occur simultaneously. The
XRD pattern (Fig. 2c), EDX analysis (ESI, Fig. S2†) and XPS
analysis (Fig. S3†) of the hybrid confirm the existence of both Ag
and L. For the hybrid, the morphology of L changes from
aligned nanofibres to random nanoribbons, which are tens of
nanometres thick, micrometres wide, and tens of micrometres
long, indicating that L is greatly affected during this process. On
the other hand, Ag NCs were found to deposit in a near mono-
disperse manner on the surface of L nanoribbons with an average
diameter of about 55 ꢃ 8 nm (Fig. 3b), which is slightly smaller
Fig. 2 XRD patterns of samples prepared by microwave treatment with
EG (10 mL) solution containing: (a) AgNO3 (0.5 mmol), PVP (0.04 g),
MW heating for 2 min, (b) AgNO3 (0.5 mmol), L (0.5 mmol), PVP
(0.04 g), MW heating for 2 min, (c) L (0.5 mmol), MW heating for 2 min.
morphological change of L is remarkable. The product from
benzene (Fig. 1a) consists of nanofibres with lengths of hundreds
of micrometres. Nanorods are observed in ethanol with lengths
and diameters of micrometres and hundreds of nanometres,
respectively (Fig. 1b). The main product is nanotubes in THF
(Fig. 1c). L molecules in EG solution self-assemble into aligned
nanofibres (Fig. 1d), with lengths and diameters of tens of
micrometres and hundreds of nanometres, respectively. This
solvent-based morphology variation can be attributed to the
different intensity of noncovalent intermolecular interactions
between L–L and L–solvent.6,21 It is known that different
dominant intermolecular interactions, such as H-bonds, p–p
interactions and van der Waals force etc., are responsible for the
formation of organic nano- and submicro-structures with
different shapes.22 The noncovalent intermolecular interactions
Fig. 3 SEM micrographs of (a) Ag NCs, (b) L–Ag hybrids.
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Fig. 4 A schematic representation of the creation of the L–Ag hybrid:
(a) L clusters, (b) incipient L fibres, (c) aggregation of L fibres (upper) and
silver adsorption (lower), (d) typical SEM images of L nanofibres (upper)
and L–Ag hybrids (lower). Insert: the schematic diagram of L assembly.
Fig. 5 UV-vis spectra of (a) L nanofibres, (b) Ag NCs and (c) L–Ag
hybrids.
at 289 and 325 nm correspond to transition of the carbazole
group. The peak at 420 nm corresponds to the p–p* transition of
the L molecule. While the peak at 450 nm can be regarded as the
surface plasmon resonance (SPR) band of the Ag NCs with
a slight red-shift from that of pure Ag NCs (Fig. 5b). This red
shift might arise from the interactions between the newly
produced organic nanoribbons and Ag NCs in situ. The high
dielectric constant of the organic moiety as matrix will lower the
Plasmon frequency. For L–Ag hybrids and pure Ag NCs, wide
SPR bands are not symmetric. Such an optical feature is eluci-
dated based on a broadened size distribution,26 which is consis-
tent with the results of SEM analysis.
than the 65 ꢃ 5 nm Ag NC produced in the absence of L
(Fig. 3a). The aggregation of Ag NCs on the surface of L may
induce the broadened size distribution.
During the process, Ag+ may interact with L when they are
mixed at the very beginning,25 therefore, L serves as a shape-
directing agent to guide the subsequent growth of the Ag NCs,
besides PVP. The reduced Ag at these sites can serve as nuclei for
further growth. In hot EG solution during MW heating, L is
dissolved and Ag NCs are dispersed uniformly in the solution.
When the solution cools naturally, some of the L molecules are
precipitated, which drives Ag NCs to precipitate along with
them. As a result, Ag NCs eventually disperse on the surface of
the L nanoribbons. More interestingly, the diameter of the Ag
NCs dispersed on the surface of L nanoribbons changes little
when reaction conditions change, including reaction time and the
concentration of AgNO3 (see the ESI†). The only change is the
number of Ag NCs clinging to the ribbons. The results reveal that
L molecules play an important role in determining the Ag NCs’
size.
The fluorescence spectrum of L fibres displays a clear emission
peak at 508 nm (Fig. 6a), which is attributed to the typical
HOMO–LUMO transition of the L.7b When L couples with Ag
NCs, the emission is partially quenched and a new band at
590 nm appears (Fig. 6b). The as-prepared samples are chemi-
cally stable for at least one year under ambient conditions
without any observable changes in the UV-vis absorption or
Based on the results mentioned above, the formation
process of the novel hybrid is presented in Fig. 4. L molecules can
self-assemble into one-dimensional structures due to weak
interactions between neighboring molecules. When AgNO3 is
introduced during the aggregation process, the assembly of L and
the formation of Ag NCs occur simultaneously and affect each
other. Lastly, nanohybrids consisting of Ag NCs uniformly
dispersed on L nanoribbons appear.
Optical properties of the L–Ag hybrids
In this study, an important goal beyond synthesis of the hybrids
is to investigate the optical properties. Indeed, when the hybrids
form, one observes a decrease of the emission of L and the
appearance of a new emission band.
The UV-vis absorption spectra show that the L–Ag hybrids
exhibit four major absorption peaks at 289 nm, 325 nm, 420 nm
(a shoulder peak) and 450 nm (Fig. 5c). The former three peaks
are very similar to that of pure L nanofibres (Fig. 5a). The peaks
Fig. 6 Fluorescence spectra at room temperature of (a) L nanofibres, (b)
L–Ag hybrids. Inset: photos of L nanofibres (left) and L–Ag hybrids
(right) under 365 nm UV light.
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fluorescence emission. It is also noted that such an emission
feature is observed only for the hybrids formed in situ, but not for
the physically mixed Ag NCs and L nanofibres, from which only
L fluorescence emission is observed.
Several explanations have been proposed to understand the
new band emergence: (a) the electricmagnetic coupling effect
between the two components leads to new fluorophore formation
of L–Ag hybrids. The band at 590 nm is the inherent fluorescent
emission of L–Ag hybrids; (b) the formation of a new D–A
system27 at the interface, in which L can provide electrons, while
the Ag+ existing on the surface of the Ag NCs can serve as an
electron acceptor. Thus a new D–A system is generated at the
interface, with electron redistribution being a fundamental effect.
In these two possible mechanisms, upon Ag coupling, the
internal charge transfer (ICT) within the L platform changes,
which then promotes a change in the emission wavelength.28
However, the interface between L and Ag NCs in the physical
mixture decreases sharply, as shown in Fig. S1,† which cannot
bring about such strong interactions between them; (c) The band
edge of Ag NCs should match the excited-state potential of L,29
including the lowest unoccupied molecular orbital (LUMO) of
the L molecule (the ‘‘conduction band’’ of the single-molecule
semiconductor) and the highest occupied molecular orbital
(HOMO) (the ‘‘valence band’’ of L fibre). So the photogenerated
electrons will be distributed between L and Ag NCs provided
that they are in close contact.30 This factor also determines the
particle size of Ag NCs in the nanohybrids because an optimum
particle size should exist to balance the appropriate bandgap.29
Therefore, it can be concluded that the new fluorescence band
may be derived from the interactions between L and either Ag+
on the surface of Ag NCs or directly with Ag NCs or a combi-
nation of both. Thus, the fluorescence emission may be influ-
enced by the ratio of L to Ag in the hybrids and the size of surface
area contacting the two components. The work is being further
explored.
Fig. 8 A comparison of the NRS and SERS spectra of: (a) L nanofibres,
(b) physically mixed L nanofibres and Ag NCs and (c) L–Ag hybrids.
is significantly shorter than the 10.84 ns of the L–Ag hybrids. The
L–Ag hybrid seems to provide a stable environment for the
excited state. The increase in s1 accompanying Ag adsorption on
L suggests that the coupling of L accentuates the yield of electron
decay, which is responsible for slower decay, thereby resulting in
a longer average decay time.31 Although L has a higher degree of
aggregation in the hybrid than that in the nanofibres, and the
aggregation is also one of the reasons for the change in the FL
lifetime, but it can’t lead to such a great value. This result further
confirms the existence of a new fluorophore system, as discussed
previously.
Raman scattering analysis
There are several functional groups in L that can interact with
silver in the hybrid, such as a carbazole ring, a vinyl bond and
a C^N group. To further investigate which one is the ‘‘hot spot’’,
Raman spectral experiments are carried out. It is known that
SERS is a common technique for analyzing the adsorption of
molecules on the surfaces of metallic NCs, mainly those of Ag
and Au, by considering the relative intensities and the frequency
shifts of the bands with respect to the corresponding Raman
bands of the free molecule. This technique is based mainly on the
enormous enhancement of the electromagnetic field occurring in
the vicinity of the metallic nanoparticles.32
Time-resolved measurement
To further study the spectral features of the hybrid, time-resolved
fluorescence decay profile measurements were carried out. The
fluorescence decay of L in solution (1.0 ꢂ 10ꢀ3 mol Lꢀ1) is too
fast to measure as well as that of the Ag NCs. The decay profiles
of L nanofibres and L–Ag hybrids are shown in Fig. 7. Table S1
(ESI†) contains pertinent fitting parameters obtained for each
decay curve. The FL lifetime of the L nanofibres is 0.20 ns, which
The Raman spectra of L and the L–Ag hybrids are given in
Fig. 8. The spectra clearly indicate that the Raman scattering of
L in the L–Ag hybrids (Fig. 8c) is significantly enhanced,
compared to that of pure L nanofibres (Fig. 8a). Besides the
enhancement, several differences between the spectra can also be
seen. The bands at 1560 cmꢀ1, 1470 cmꢀ1 and 1322 cmꢀ1 in NRS
are attributed to the ring breathing of the benzene ring, the C]C
stretching vibration and the d (CH) band, respectively.33 After
coupling with Ag NCs, the band at 1560 cmꢀ1 red-shifts to
1574 cmꢀ1 by 14 cmꢀ1. Also, the FWHM (full width at half-
maximum) of the band broadens from 12 to 40 cmꢀ1 upon
coupling. The band at 1470 cmꢀ1 red-shifts by 21 cmꢀ1 with the
FWHM broadening from 5 cmꢀ1 to 20 cmꢀ1 and the band at
1322 cmꢀ1 red-shifts by 10 cmꢀ1 with the FWHM broadening
Fig. 7 The normalized fluorescence lifetimes at lex 370 nm: (a) L
nanofibres (lem ¼ 508 nm) and (b) L–Ag hybrids (lem ¼ 590 nm).
5.0 ꢂ 10ꢀ6 mol Lꢀ1 fluorescein in 0.1 mol Lꢀ1 NaOH aquatic solution was
used as the standard (green line).
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from 9 cmꢀ1 to 60 cmꢀ1. At the same time, it is also observed that
the band at 2222 cmꢀ1 in NRS attributed to the n(C^N)
stretching vibration33b does not change. The results reveal that
the couple interaction between L and Ag NCs takes place
through the p configuration unit. The large enhancement factors
may be due to the coupling of the localized surface plasmon
(LSP) of Ag NCs and the enhanced electromagnetic field inten-
sity localized at the interface.34 The shift is strongly attracted to
the coupling between L and Ag NCs. The weak interactions
further influence the electronic distribution of L, which accounts
for the changes observed in the SERS spectra35 and the fluores-
cence band.
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The Raman spectrum of physically mixed L nanofibres and Ag
NCs is also shown in Fig. 8b. No stretching frequency change is
observed, suggesting that the two components in the physical
mixture cannot lead to such strong interactions between them.
The results are consistent with the observations of fluorescent
experiments.
Conclusions
14 A. S. Kumbhar and G. Chumanov, Chem. Mater., 2009, 21,
2835.
In summary, we have combined two exciting research objects, Ag
NCs and a functional organic semiconductor (L), to form a new
hybrid nanomaterial. The morphologies were characterzied by
SEM and TEM. Ag NCs are uniformly dispersed on the surface
of L nanoribbons. L couples with Ag NCs via a p-conjugated
unit. The subsequent weak interactions between them lead to
a significant red-shift of fluorescence, an obvious increase of the
FL lifetime and enhanced Raman scattering. The newly-formed
nanohybrid can optimize the optical properties and also open up
the possibility of utilizing the nanohybrid for a multitude of
applications in bio- and chemical sensing and nanoelectronics,
such as ultra sensitive detection of molecular coupling, imaging,
and localized activation of photochemical processes.
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This research was supported by the National Natural Science
Foundation of China (20771001, 50703001, 20775001, 20875001
and 50873001), the Natural Science Foundation of Education
Department of Anhui Province (KJ2010A30) and Foundation
for Scientific Innovation Team of Anhui Province
(2006KJ007TD).
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