Color-tunable organic composite nanoparticles based on perylene tetracarboxylic-diimides and a silicon-cored fluoranthene derivate

Article abstract of DOI:10.1039/c3tc31097c

Well-defined organic composite nanoparticles were prepared from perylene bisimide dye and silicon-cored fluoranthene derivate molecules. The composite nanoparticles exhibited good stability and thermal properties. The fluorescence emission of the perylene bisimide dye can be efficiently enhanced in composite nanoparticles based on efficient Foester resonant energy transfer. The composite nanoparticles exhibited tunable emission colors from blue to red by changing the concentration of the perylene bisimide dye. White-light emission with CIE coordinates (0.327, 0.339) was obtained as a good candidate for applications in white optoelectronic devices.

Full text of DOI:10.1039/c3tc31097c

Journal of
Materials Chemistry C
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Color-tunable organic composite nanoparticles based
on perylene tetracarboxylic-diimides and a silicon-cored
fluoranthene derivate
Cite this: J. Mater. Chem. C, 2013, 1,
5367
*
Hua Wang, Huanling Xie, Yan Liang, Linglong Feng, Xiyuan Cheng, Haifeng Lu
and Shengyu Feng
*
Well-defined organic composite nanoparticles were prepared from perylene bisimide dye and silicon-cored
fluoranthene derivate molecules. The composite nanoparticles exhibited good stability and thermal
properties. The fluorescence emission of the perylene bisimide dye can be efficiently enhanced in
Received 8th June 2013
Accepted 9th July 2013
¨
composite nanoparticles based on efficient Foster resonant energy transfer. The composite
nanoparticles exhibited tunable emission colors from blue to red by changing the concentration of the
perylene bisimide dye. White-light emission with CIE coordinates (0.327, 0.339) was obtained as a good
candidate for applications in white optoelectronic devices.
DOI: 10.1039/c3tc31097c
www.rsc.org/MaterialsC
stacking to increase uorescence. In contrast to this, when
small amounts of PTCDI molecules are embedded in composite
Introduction
Organic nanoparticles based on small organic molecules have
gained increasing attention over the last few years because of
their fascinating optoelectronic properties and promising
applications in optics and electronics elds.1–9 The vast number
of organic molecules available and the exibility of nanoparticle
preparation have facilitated investigations on a series of organic
nanoparticles with specic functionalities and applications.2–11
Among these organic nanoparticles, binary composite organic
nanoparticles have shown great potential in optical and elec-
tronic applications because of their multi-functionalities and
enhanced performance.6,8,12,13 Such nanoparticles combine the
available properties of their parent constituents. Furthermore,
energy transfers caused by interactions between the molecules
of two compounds may generate new properties to meet current
and future demands.14,15
Perylene tetracarboxylic diimides (PTCDIs) are fascinating
uorescent materials with high uorescence quantum yields as
well as high photo and thermal stabilities. PTCDIs have long
been used in various optoelectronic elds.16–19 However, solid-
state PTCDIs tend to form aggregates that result in uorescence
quenching because of attractive dipole–dipole interactions and
effective intermolecular p–p stacking interactions.20 Therefore,
developing solid-state PTCDI molecules with efficient emission
is necessary.21 The usual method was the side-chain modica-
tion reactions with bulky, steric groups that may distort the p–p
nanoparticles, the scattering of these molecules prevents
attractive dipole–dipole interactions and intermolecular p–p
stacking interactions among the particles thereby achieving
high uorescence. Such binary systems may generate new
optical functionalities based on energy transfer from the matrix
to the PTCDI. In this work, N,N-dicyclohexyl-perylene-3,4,9,10-
tetracarboxylic acid bisimide (CH-PTCDI), a PTCDI derived
from simple modication, was selected for the preparation of
organic composite nanoparticles to verify our hypothesis.
Selection of the proper molecules to be used as a matrix is a
crucial issue in forming this efficient binary system. First, the
matrix material should have unique molecular structures that
can prevent the excimer or exciplex formation, which would
cause red-shiing in the solid state.22,23 In addition, these
molecules should have good thermal properties for higher
stability and longer lifetime of the composite nanoparticles and
devices, such as thermal stability and high glass transition
temperature.24,25 Silicon-cored compounds have been proved to
be appropriate optoelectric materials.26–29 Given their tetrahe-
dral environment, the units attached to the central Si atom are
signicantly twisted against each other resulting in a non-
coplanar structure. The non-planar structure can provide steric
hindrance that prevents the close-packing of the molecules
thereby effectively suppressing molecular recrystallization and
interactions between p-systems and causing a red shi in the
solid state. In this paper, a new silicon-cored uoranthene
derivate named bis(7,10-diphenyl-uoranthene)methyl-phenyl-
silane (BFMPS) with efficient solid-state blue emission was
designed and synthesized as a matrix. BFMPS exhibited good
thermal stability and high glass transition temperature. A series
Key Laboratory of Special Functional Aggregated Materials, Ministry of Education,
School of Chemistry and Chemical Engineering, Shandong University, Jinan,
250100, People's Republic of China. E-mail: fsy@sdu.edu.cn; Fax: +86-531-
88564464; Tel: +86-531-88364866
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of organic composite nanoparticles with different CH-PTCDI CH), 2.60 (m, 4H, CH2), 1.93 (d, 4H, CH2), 1.80 (d, 6H, CH2),
contents were prepared based on CH-PTCDI and BFMPS. To the 1.28–1.53 (m, 6H, CH2).
best of our knowledge, this study is the rst to report the use of
silicon-based material in the formation of composite nano-
particles. The resulting organic composite nanoparticles
showed high uorescence and color-tunable properties. Highly
efficient energy transfer from BFMPS to CH-PTCDI was also
observed. Moreover, even small amounts of CH-PTCDI mole-
cules signicantly changed the optoelectronic properties of the
composite nanoparticles. Interestingly, white light emission,
which has potential application in optoelectronic devices, was
achieved when the appropriate content of CH-PTCDI was
adopted.
Preparation of organic composite nanoparticles
Organic composite nanoparticles were prepared using a simple
reprecipitation method. In a typical preparation, 100 mL of a
DMF solution of CH-PTCDI/BFMPS of different ratios (BFMPS
concentration, 1.0 Â 10À3 M; CH-PTCDI/BFMPS ratio ranged
from 0.05% to 10%) was rapidly injected into 10 mL of deion-
ized water under vigorous stirring at room temperature. The
organic composite nanoparticles were then obtained and
measurements were taken.
Results and discussion
Tunable uorescence emission of the organic composite
Experimental section
Preparation of BFMPS
nanoparticles
The molecular structure of BFMPS is shown in Scheme 1. BFMPS
was synthesized via a simple Diels–Alder reaction. In a sealed
stainless steel reactor, 7,9-diphenyl-cyclopenta[a]acenaphthylen-
8-one (5.30 g, 15 mmol) and diethynylmethylphenylsilane (1.70 g,
10 mmol) were dissolved in 30 mL of xylene. The reaction was run
The absorption of CH-PTCDI showed good overlap with the
emission spectrum of BFMPS in the range of 400 nm to 550 nm
(Fig. 1), thus allowing the occurrence of energy transfer. The
uorescence spectra of the composite nanoparticles with
different CH-PTCDI/BFMPS ratios are shown in Fig. 2(a). Pure
CH-PTCDI nanoparticles were nearly non-uorescent, which
can be attributed to the intermolecular p–p interactions
between the conjugated planes of CH-PTCDI. Pure BFMPS
nanoparticles showed one peak with a maximum wavelength at
452 nm, which can be assigned to its blue light emission. The
maximum uorescence emission of pure BFMPS nanoparticles
at 452 nm had no obvious red shi compared with that in the
solution at 448 nm. This result can be attributed to the tetra-
hedral structure with a Si atom which effectively reduced the
intermolecular p–p interactions. All of the composite nano-
particles exhibited two peaks: one peak at 449 nm without a
shi was assigned to the emission of BFMPS and another peak
that shied from 553 nm to 622 nm with increasing CH-PTCDI
content was attributed to the emission of CH-PTCDI. The
BFMPS emission decreased rapidly whereas the CH-
PTCDI emission increased gradually, with increasing CH-PTCDI
content in the composite nanoparticles. When the CH-PTCDI
content was 10%, the BFMPS emission was almost completely
ꢀ
for 20 h at 230 C under a N2 atmosphere. The xylene was then
removed in a vacuum, and the product was puried by silica gel
column chromatography. A yellow solid powder was obtained
with a yield of 40%. 1H NMR (DMSO, 400 MHz, ppm): d 0.35
(s, 3H), 6.34 (d, 2H), 7.17 (t, 4H), 7.23–7.32 (m, 12H), 7.38–7.49
(m, 13H), 7.58 (d, 4H), 7.70 (d, 2H), 7.77 (d, 2H). 13C NMR (CDCl3,
100 MHz, ppm): d À0.85 (Si–CH3), 123.19, 123.29, 126.33, 126.88,
127.49, 127.55, 127.57, 127.61, 127.68, 128.16, 128.18, 128.53,
128.81, 129.19, 129.71, 129.98, 130.17, 132.89, 135.43, 136.14,
136.19, 136.80, 137.42, 137.60, 137.98, 138.62, 141.11, 143.77. 29Si
NMR (CDCl3, 80 MHz, ppm): d À8.42. Anal. calcd for C63H42Si: C
91.49%, H 5.12%; found: C 91.36%, H 5.18%. MALDI-TOF (m/z):
calcd 826.31; found 826.39.
Preparation of CH-PTCDI
CH-PTCDI was synthesized according to
a
published
method.30,31 Perylene-3,4,9,10-tetracarboxylic acid bisimide (1 g,
1.8 mmol) and 20 mL of cyclohexane were mixed in a 100 mL
three-necked ask with stirring. The mixture was then heated to
reux for 24 h under a N2 atmosphere. Aer cooling to room
temperature, the precipitate was obtained by ltration and
sequentially washed with 5% (w/w) NaOH, water, and ethanol.
The product was further puried by silica column chromatog-
raphy, and a red solid was obtained with a yield of 91%. 1H NMR
(CDCl3, 400 MHz, ppm): d 8.63 (m, 8H, perylene), 5.07 (m, 2H,
Fig. 1 Absorption (dashed) and fluorescence emission (solid) spectra of BFMPS
(blue) and CH-PTCDI (orange) in the CH2Cl2 solution.
Scheme 1 Molecular structures of BFMPS and CH-PTCDI.
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Fig. 3 Emission colors of composite nanoparticles in the CIE 1931 chromaticity
diagram. The contents of CH-PTCDI and the CIE color coordinates: (1) 0%, (0.160,
0.178); (2) 0.05%, (0.208, 0.226); (3) 0.1%, (0.253, 0.271); (4) 0.2%, (0.327,
0.339); (5) 1%, (0.438, 0.401); (6) 2%, (0.503, 0.411); (7) 10%, (0.546, 0.381).
Fig. 2 (a) Fluorescence emission spectra of composite organic nanoparticles
(excitation at 370 nm). (b) Fluorescence emissions of composite organic nano-
particles taken under a UV lamp (365 nm). The concentrations of CH-PTCDI: (A)
0%; (B) 0.05%; (C) 0.1%; (D) 0.2%; (E) 1%; (F) 2% and (G) 10%.
standard white light emission and may be a good candidate for
the white light-emitting devices.
Morphology of the organic composite nanoparticles
The sizes and shapes of the composite nanoparticles were
determined. The representative transmission electron micro-
scope (TEM) image of nanoparticles with 0.2% CH-PTCDI
content is shown in Fig. 4(a). The composite nanoparticles were
approximately spherical with sizes ranging from 50 nm to
60 nm. The formation of the composite nanoparticles may be
attributed to the hydrophobic and p–p interactions that
induced the aggregation of BFMPS and CH-PTCDI.6 Fig. 4(b)
shows the uorescence microscopic images of the composite
nanoparticles with 0.2% CH-PTCDI content. The nanoparticles
exhibited similar emission colors aer being dropped onto a
glass slide. This nding indicates that the CH-PTCDI molecules
were embedded into the BFMPS nanoparticles, and are well
distributed in the composite nanoparticles during the repreci-
pitation process. Moreover, the prepared composite nano-
particles exhibited color-tunable emission colors in the solid
state. Thus, they are suitable to be applied in organic light-
emitting devices.
quenched. This observation indicates the occurrence of
complete energy transfer from BFMPS to CH-PTCDI. Fig. 2(b)
clearly shows that the uorescence of the composite nano-
particles changed in color from blue to red as the CH-PTCDI
concentration increased. In contrast to the related reports,
these binary composite nanoparticles exhibited a much wider
color-tunable range.8 The uorescence quantum yields of the
composite nanoparticles were further measured according to a
published reference, and all of the composite nanoparticles
with different concentrations of CH-PTCDI showed efficient
uorescence emission (Table 1).32
The CIE color coordinates were calculated from the emission
spectra as shown in a CIE chromaticity diagram in Fig. 3. The
emission colors of the composite nanoparticles can be tuned
from blue (0.160, 0.178) to red (0.546, 0.381) by controlling the
CH-PTCDI concentration. White light emission was obtained
when the CH-PTCDI concentration was 0.2% and the CIE color
coordinates (x, y) were (0.327, 0.339). It was very close to the
Enhancement of CH-PTCDI uorescence emission and energy
transfer in composite nanoparticles
Table 1 The fluorescence quantum yields of the composite nanoparticles with
different contents of CH-PTCDI
Fig. 2(a) shows that the CH-PTCDI emission exhibited a red
shi from 553 nm to 622 nm, and that the intensity of this
emission decreased when the CH-PTCDI content in the
composite nanoparticles was higher than 1%. This phenom-
enon can be attributed to the aggregation of the CH-PTCDI
Content of CH-PTCDI 0% 0.05% 0.1% 0.2% 1%
2% 10%
Quantum yields 9.8% 8.9% 9.9% 13.1% 12.4% 7.2% 4.3%
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Fig. 5 (a) Excitation spectra of composite nanoparticles with CH-PTCDI molar
concentrations of 0%, 0.05%, 0.1%, 0.2%, 1%, 2%, and 10%. (Detecting wave-
length: 0%, 449 nm; 0.05%, 553 nm; 0.1%, 559 nm; 0.2%, 563 nm; 1%, 569 nm;
2%, 573 nm; 10%, 622 nm.) (b) Fluorescence emission spectrum of a nanoparticle
suspension with a CH-PTCDI content of 0.2%.
CH-PTCDI. The energy transfer from BFMPS to CH-PTCDI
further enhanced the uorescence emission of CH-PTCDI.
Meanwhile, the energy transfer quenched BFMPS emission and
enhanced CH-PTCDI as the CH-PTCDI content increased. Based
on the variation of emission intensity proportion between
BFMPS and CH-PTCDI, the composite nanoparticle exhibited
tunable emission colors. Therefore, these results can suffi-
ciently verify our hypothesis. This strategy will enhance the
application of the PTCDI derivate in optoelectric devices.
The energy transfer mechanism in these organic composite
nanoparticles was detected and investigated. No uorescence was
observed when the nanoparticle was excited at 449 nm. Thus, the
possibility of radiative energy transfer from BFMPS to CH-PTCDI
can be excluded. The decay of the emission from BFMPS was
measured to further identify the energy transfer mechanism. As
shown in Table 2, the lifetime of BFMPS became shorter with
increased CH-PTCDI content. For example, the lifetime of BFMPS
without CH-PTCDI was about 9.44 ns, and then decreased to
Fig. 4 TEM (a) and fluorescence microscopy (b) images of the composite
nanoparticle with CH-PTCDI content of 0.2%.
molecules in the composite nanoparticles with increasing
CH-PTCDI concentration.6 The excitation spectra of the
composite nanoparticles with different CH-PTCDI concentra-
tions were obtained from 553 nm to 622 nm [Fig. 5(a)]. The
excitation spectra of the composite nanoparticles were similar
to that of pure BFMPS, indicating that the CH-PTCDI emission
energy originated from BFMPS when the composite nano-
particles were irradiated at 370 nm. The uorescence spectra
with the different excitation wavelengths of the composite
nanoparticles at 0.2% are shown in Fig. 5(b). When the nano-
particle was excited at 284 nm and 370 nm, the emission
intensities of CH-PTCDI at 559 nm were 187 times and 76 times
higher than that at 505 nm, which was irradiated directly to
CH-PTCDI. This phenomenon indicates the efficient antenna
effect of BFMPS to CH-PTCDI which may be considered as
further evidence of efficient energy transfer.6,8 In contrast to the
non-uorescence property of pure CH-PTCDI, uorescence
emission of CH-PTCDI molecules in the composite nano-
particles was observed at the excitation wavelength of
Table 2 The fluorescence lifetimes of the composite nanoparticles with different
contents of CH-PTCDI
Concentration of CH-PTCDI/%
0%
9.44
0.05%
6.57
0.1%
5.91
0.2%
5.11
1%
2.49
2%
1.63
10%
0.95
s (ns)
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0.95 ns with the concentration of CH-PTCDI (10%). Based on the
above-mentioned data, the energy transfer phenomenon in the
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nanoparticles were further measured. BFMPS and CH-PTCDI
exhibited decomposition temperatures (corresponding to 5%
weight loss) as high as 420 and 417 ꢀC. This result clearly
showed that the two parent component molecules had good
thermal stability. Therefore, this binary composite system
based on BFMPS and CH-PTCDI is an excellent system with
good thermal stability, which is a desirable feature for the
stability of composite nanoparticles in devices. The decompo-
sition temperatures (corresponding to 5% weight loss) of the
composite nanoparticles with 0.2% CH-PTCDI content was 421
ꢀC indicating that these novel composite nanoparticles had
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temperatures and glass transition temperature were observed
ꢀ
for BFMPS at 286 C and 220 ꢀC, respectively. The high glass
transition temperature and melting temperature of BFMPS can
prevent the molecular recrystallization in composite nano-
particles which subsequently leads to the good stability and
lifetime of the composite nanoparticles in devices. The uo-
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Novel and well-dened organic composite nanoparticles were
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¨
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Acknowledgements
This work was nancially supported by the National Natural
Science Foundation of China (no. 21274080 and 21204043), the
Key Natural Science Foundation of Shandong Province of China
(no. ZR2011BZ001 and ZR2009BZ006) and the Doctor Station
Foundation of Chinese Education Department (no. 200603086).
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