Novel amphipathic photoluminescent copolymers containing fluorene, pyridine and thiophene moieties: Synthesis, characterization and self-assembly

Article abstract of DOI:10.1016/j.polymer.2012.10.007

In order to investigate the explicit electro-optical properties and self-assembly variations of the photoluminescent polymer with sterically hindered side chains, two novel polymers (P0 and P1) based on fluorene, pyridine and thiophene moieties were successfully synthesized through Suzuki coupling reaction. The molecular structures of the polymers were fully characterized by ¹H NMR, ¹³C NMR, elemental analysis and gel-permeation chromatograph, respectively. The photophysical properties, energy band gap and self-assembly behaviors of polymer P0 and P1 were examined through UV-vis absorption, photoluminescent spectra, cyclic voltammetry, dynamic laser light scattering and transmission electron microscopy. The experimental results indicated that the polymers took on wide band gaps of 3.09 and 3.11 eV with blue-green emission in thin solid films. By combining supramolecular assembly nature of hydroxy, phenolic and pyridyl units with controlled micro-phase separation of well-defined amphipathic di-block copolymers, we have obtained stable vesicles from the fluorescent amphipathic polymers in aqueous solution. The size and morphology of the vesicles formed can be effectively tuned in a range of 1144 nm-291 nm. This work can serve as an excellent exploratory example for the fine self-assembly control principle in the amphipathic photoluminescent copolymer with sterically hindered side chains through the multiple weak interactions of the π-system.

Full text of DOI:10.1016/j.polymer.2012.10.007

Polymer 53 (2012) 5684e5690
Contents lists available at SciVerse ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Novel amphipathic photoluminescent copolymers containing fluorene, pyridine
and thiophene moieties: Synthesis, characterization and self-assembly
*
*
Hong-ji Jiang , Jin-long Zhang, Jian Sun, Wei Huang
Key Laboratory of Organic Electronics and Information Displays, Institute of Advanced Materials, Nanjing University of Posts and Telecommunications, Nanjing 210046, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 July 2012
Received in revised form
22 September 2012
Accepted 4 October 2012
Available online 11 October 2012
In order to investigate the explicit electro-optical properties and self-assembly variations of the pho-
toluminescent polymer with sterically hindered side chains, two novel polymers (P0 and P1) based on
fluorene, pyridine and thiophene moieties were successfully synthesized through Suzuki coupling
reaction. The molecular structures of the polymers were fully characterized by 1H NMR, 13C NMR,
elemental analysis and gel-permeation chromatograph, respectively. The photophysical properties,
energy band gap and self-assembly behaviors of polymer P0 and P1 were examined through UVevis
absorption, photoluminescent spectra, cyclic voltammetry, dynamic laser light scattering and trans-
mission electron microscopy. The experimental results indicated that the polymers took on wide band
gaps of 3.09 and 3.11 eV with blueegreen emission in thin solid films. By combining supramolecular
assembly nature of hydroxy, phenolic and pyridyl units with controlled micro-phase separation of well-
defined amphipathic di-block copolymers, we have obtained stable vesicles from the fluorescent
amphipathic polymers in aqueous solution. The size and morphology of the vesicles formed can be
effectively tuned in a range of 1144 nme291 nm. This work can serve as an excellent exploratory example
for the fine self-assembly control principle in the amphipathic photoluminescent copolymer with
Keywords:
Fluorene
Pyridine
Chromophore
sterically hindered side chains through the multiple weak interactions of the
p-system.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
while their branched counterparts with different molecular archi-
tecture are still rare now, and the star-shaped approach has been
generally regarded as an effective method for the design of amor-
phous optoelectronic materials [3e10]. One of the major advan-
tages of polyfluorene (PF) derivatives is that their electronic
properties can be tuned via the modification of the comonomer
block. The fluorene homopolymer has a large band gap (3.6 eV),
thus, the emission color of PF derivatives can be tuned over the
whole visible region by introducing small band gap comonomers
into the polymer backbone [11e19].
Self-assembly is a powerful and versatile method to construct
nanostructural materials. Self-assembled nanostructures obtained
from natural and synthetic amphipathic molecules serve as mimics
of biological membranes and enable the delivery of drugs, proteins,
genes, and imaging agents. Yet the precise molecular arrangements
demanded by these functions are difficult to achieve [20]. The unique
self-assembly properties of amphipathic block copolymers result
from the inherent immiscibility between different building blocks
and the competing thermodynamic effects [21]. Polymeric vesicles
formed from amphiphilic block copolymers have found a rich variety
of applications in nanotechnology as solubilizers and surface modi-
fiers as well as gene and drug delivery vehicles. For drug delivery
Highly soluble fluorene-based conjugated polymers are
considered as an outstanding class of blue light-emitting materials
due to their good thermal stability, high hole mobility, easy proc-
essability and high photoluminescent (PL) quantum yields in thin
solid films. During the past decade, a variety of copolymers derived
from 2,7-fluorenes and the comonomers have been actively
investigated, and the development of such copolymers has led to
the preparation of a series of fluorene-containing copolymers for
polymeric light-emitting diodes (PLEDs) [1,2]. It is believed that
most of these materials for electro-optical applications will benefit
a lot from a full investigation of electro-optical properties and the
nanostructures of the copolymer chain in different environments.
On the other hand, the most intensely studied fluorene-based
polymers are mainly linear conjugated
aggregate and end up with self-quenching of their luminescence,
p-systems, which tend to
* Corresponding authors. Tel./fax: þ86 2585866396.
E-mail addresses: iamhjjiang@njupt.edu.cn (H.J. Jiang), iamwhuang@
njupt.edu.cn, iamdirector@fudan.edu.cn (W. Huang).
0032-3861/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.polymer.2012.10.007

H.-j. Jiang et al. / Polymer 53 (2012) 5684e5690
5685
tracing, it makes strategic sense to combine the properties of drug
2.1.1. 2,7-Bis(trimethylene boronate)-9,9-dioctylfluorene (M0) [25],
delivery with optical labeling [22]. Hydrogen bonding has been
widely used for supramolecular assembly of small molecules and
polymers because of its molecularly specific and highly directional
characteristics [23]. Pyridine-based polymers remain a subject of
interest in the field of supramolecular chemistry due to their reactive
nitrogen heteroatom, and amphipathic small molecules can
hydrogen bond with one of the functional block of the copolymers,
leading to the formation of comb-like supramolecules with different
morphologies [24]. We have synthesized PL polymers containing
fluorene and 2,4,6-triphenyl pyridine moieties, and the effects of
noncoplanarmoleculararchitectureontheelectro-opticalproperties
of parent matrix were investigated [25]. However, the optoelectronic
variations of this kind of polymer in different self-assembly envi-
ronmentsstillhave notbeenstudied. Inthis paper, byintroducingthe
hydroxyl moieties and thiophene groups into the polymer backbone
containing pyridine to modulate the intermolecular interaction and
light-emitting wavelength, we report on the synthesis and charac-
terization of Poly(2,7-diyl-9,9-dioctylfluorene)-co-(6-(4-(2,6-bis(5-
thiophen-2-yl)pyridin-4-yl)phenoxy)hexyl accetate) (P0) and Poly
(2,7-diyl-9,9-dioctylfluorene)-co-(6-(4-(2,6-bis(5-thiophen-2-yl)
pyridin-4-yl)phenoxy)hexyl alcohol) (P1) with sterically hindered
side chains and unimolecular amphipathicity. The experimental
results indicated that the polymers took on wide band gaps of 3.09
and 3.11 eV with blueegreen emission in thin solid films. By
combining supramolecular assembly nature of hydroxy, phenolic
and pyridyl units with controlled micro-phase separation of well-
defined amphipathic di-block copolymer P1, we have obtained
stable vesicles of the fluorescent amphipathic polymers with size
ranging from 1144 nm to 291 nm in aqueous solution [26].
6-(4-(2,6-bis(5-bromo-thiophen-2-yl)pyridin-4-yl)phenoxy)hexyl
accetate (M1) [27,28]
A flask charged with a mixture of 6-(4-formylphenoxy)hexyl
acetate (0.67 g, 2.5 mmol), 1-(5-bromo-thiophen-2-yl)-ethanone (1 g,
5 mmol), ammonium acetate (2.54 g, 33.0 mmol) and acetic acid
(17 ml) were vigorously stirred, and was heated to reflux for 10 h.
After the completion of the reaction monitored by thin-layer chro-
matography, it was cooled to room temperature. Upon cooling to room
temperature, a precipitate was filtered, washed with water three
times and dried to afford the product. It was purified by column
chromatography on silica gel eluting with petroleum ether/chloroform
(3:1) to give a yellowsolid of M1 (0.79 g, 5.51 mmol) in a yield of 50%.1H
NMR (400 MHz, CDCl3):
4.06 (s, 2H), 4.08e4.14 (s, 2H), 6.94e7.08 (m, 4H), 7.31e7.42 (m, 2H),
7.50e7.65 (m, 4H); 13C NMR (100 MHz, CDCl3):
21.1, 25.9, 28.6, 29.2,
d 1.12e1.63 (s, 8H), 1.96e2.01 (s, 3H), 3.96e
d
76.3, 77.2,112.8,114.6,114.9,124.2,128.1,130.2,130.4,149.8,150.9,171.4;
MS(MALDI-TOF): Calcd for C27H25Br2NO3S2 m/z (%) ¼ 652.87 (100.0),
Found ¼ 652.43 (100.0). Elementary analysis of C27H25Br2NO3S2
(652.87): Calcd. C 51.03, H 3.97, N 2.20; Found C 50.92, H 3.82, N 2.39.
All of the polymerizations were carried out by palladium(0)-
catalyzed Suzuki coupling reactions with equivalently molar ratio
of the diboronic ester monomer to the dibromo monomers under
dry nitrogen protection. A typical procedure for the polymerization
of the alternating copolymer P0 is given below. P1 was synthesized
according to documented procedures by the reaction of P0 with
sodium hydrate in THF with a yield of 90% [29].
P0: A mixture of monomer M0 (0.77 g,1.37 mmol), monomer M1
(0.87 g, 1.37 mmol), alq336 and catalytic amount of Pd(PPh3)4 were
added to a degassed mixture of toluene (20 mL) and Na2CO3 aqueous
solution (2.0 M, 4.0 mL). The mixture was vigorously stirred at 90 ꢀC
for 72 h under nitrogen atmosphere. After the routine Suzuki end-
capping reaction of 1-bromobenzene and phenyl boronic acid in
turn, 50 mL toluene was added, and the organic layer was separated
and washed with brine for drying over anhydrous MgSO4. The
residue was filtered with a short column chromatography on silica
gel with toluene as eluent to yield a light yellow solution. Upon part
of solvent being evaporated off, the concentrated solution was
dropped slowly into a solution of methanol while being well stirred.
The obtained organic precipitate was collected on a filter, washed by
methanol followed by soxhlet extraction with acetone for 48 h to
removetheoligomersandcatalystresidue. Therecoveredyield of the
2. Experimental
2.1. Materials and instruments
Fluorene, n-butyl-lithium, 2,7-dibromo-fluorene, 6-(4-formyl-
phenoxy)hexyl acetate, 1-(5-bromo-thiophen-2-yl)-ethanone, tri-
isopropyl borate, and tetrakis(triphenylphosphine) palladium(0)
(Pd(PPh3)4) were purchased from Acros Organics and used without
further purification. Tetrahydrofuran (THF) and toluene were
distilled over sodium/benzophenone under nitrogen atmosphere.
The other common solvents were purified according to their stan-
dard methods.
yellow solid was 68%.1H NMR (400 MHz, CDCl3):
d 0.53e1.78 (broad,
All NMR spectra were recorded on a Varian Mercury plus 400 at
22 ꢀC. Tetramethylsilane was used as internal reference for all
the compounds. Gel-permeation chromatography (GPC) results
were obtained with Shimadzu LC-VP system with polystyrenes as
the standard and THF as the eluent. Elemental analysis was per-
formed on a CHNS-O (Elementar Co.). The UVevis absorption and
PL emission spectra were recorded on Shimadzu UV-3150 and
RF-5300PC spectrometers, respectively. The molecular masses of
intermediates were determined by Shimadzu Matrix assistant
laser desorption/ionization time-of-flight mass spectrometry
(MALDI-TOF-MASS). Cyclic voltammetry (CV) was performed on an
Autolab Pgstat30 potentiostat/galvanostat system (Ecochemie,
Netherlands). The experiments were carried out on glass carbon
electrode in acetonitrile solution containing 0.1 M tetrabuty-
lammonium hexafluorophospate (TBAPF6) using a Pt wire as
counter electrode and a Ag/AgNO3 (0.1 M) electrode as reference
electrode at a scan rate of 100 mV sꢁ1 at room temperature.
Dynamic laser light scattering (DLLS) were obtained with Broo-
khaven system. Transmission electron microscopy (TEM) was ob-
tained with Hitachi HT7700. Fourier transform infrared (FT-IR)
spectra were recorded with a Shimadzu IR Affinity-1 spectrometer
from KBr pellets.
42),1.96e2.01 (s, 3H), 3.95e4.23 (broad, 4H), 6.96e7.16 (broad, 2H),
7.35e7.57 (broad, 2H), 7.61e7.98 (broad, 12H), 13C NMR (100 MHz,
CDCl3): d 14.02, 21.13, 25.96, 29.67, 31.46, 40.36, 55.23, 62.93, 64.48,
68.04, 112.83, 114.61, 119.98, 120.19, 124.23, 126.16, 127.20, 128.17,
130.41, 133.36, 140.01, 143.52, 147.15, 149.83, 152.35, 160.15, 171.4;
Elementary analysis of (C56H65NO3S2)n (863.44)n, Calcd. C 77.82, H
7.58, N 1.62; Found: C 77.24, H 7.29, N 1.31.
P1: 1H NMR (400 MHz, CDCl3):
d 0.53e1.78 (broad, 43), 3.52e
3.78 (broad, 2H), 3.95e4.23 (broad, 2H), 6.96e7.16 (broad, 2H),
7.35e7.57 (broad, 2H), 7.61e7.98 (broad, 12H). 13C NMR (100 MHz,
CDCl3):
d 14.02, 21.13, 23.84, 25.96, 28.63, 29.67, 31.46, 40.36,
112.83, 114.61, 119.98, 121.51, 124.23, 126.16, 127.20, 128.17, 130.22,
130.41, 140.01, 140.52, 149.83, 150.95,171.29; Elementary analysis of
(C54H63NO2S2)n (821.43)n, Calcd. C 78.88, H 7.72, N 1.70; Found: C
78.01, H 7.98, N 2.29.
3. Results and discussion
3.1. Synthesis and characterization of the polymers
Polymer P0 was prepared via the Suzuki coupling method by
using M0 and M1 at a feed ratio of 1:1 (Scheme 2). The synthetic

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H.-j. Jiang et al. / Polymer 53 (2012) 5684e5690
OC6H12OCOCH3
OC6H12OCOCH3
O
NH4CO3
+
2
Br
CH3COOH
S
S
S
N
Br
Br
O
M1
Scheme 1. The chemical route to synthesize the target monomer M1.
route to the chosen new monomer M1 is depicted in Scheme 1,
according to a previously reported methodology through an alter-
native liquid phase synthetic pathway of 6-(4-formylphenoxy)hexyl
acetate and 1-(5-bromo-thiophen-2-yl)-ethanone with a relatively
high yield [30,31]. Polymer P0 was finally end-capped with benzene
to improve their thermal and photophysical stabilities. The chemical
structures of resulting monomers, polymer P0 and P1 have been
well identified via 1H NMR, 13C NMR, GPC against standard poly-
styrene, elemental analysis, MALDI-TOF mass spectra and FT-IR
spectra, respectively. Polymer P0 was completely soluble in
common organic solvents, such as chloroform, toluene, and ethyl
acetate and so on. The numbereaverage molar mass and weighte
average molar mass of polymer P0 were 7500 and 10,600 with
a polydispersity distribution index of 1.41 (mono-modal). The FT-IR
spectra of P0 thin solid film (Fig. 1) showed the characteristic peaks
at 1215 cmꢁ1, which is due to eCeOe asymmetric stretching con-
nected with pyridine rings. The peak at 2975 cmꢁ1 and 2925 cmꢁ1
can be assigned to the stretching of eCeH in aromatic fluorene
segments. The group peaks at 1740 cmꢁ1 can be assigned to eC]O
stretching in acetate [31], which has disappeared in the FT-IR spectra
of polymer P1. The frequency doubling peaks from 1500 cmꢁ1 to
1830 cmꢁ1 and bending vibration at 750 cmꢁ1 validate the aromatic
structure of polymer P1. The stretching vibration of eOeH of poly-
mer P1 is not very obvious, and the stretching vibrating intensity of
eC]Ne in pyridine of polymer P1 at 2290 cmꢁ1 has decreased
when compared with that of polymer P0, which may be caused by
the potential intermolecular interaction of hydroxy and pyridine
rings in polymer P1. To further characterize the chemical structures
of polymer P0 and P1, we have recorded the NMR spectra of polymer
P0 and P1. The chemical shift of hydrogen in methylene near ethyl
acetate has changed from 4.02 ppm to 3.64 ppm on account of the
different chemical environments, and the conversion rate of poly-
mer P0 to P1 can be determined to be 92% according to the peak area
ratio of methylene attached to the oxygen of phenol derivatives to
that of alcohol from NMR spectra (S4 and S6 in Supporting
Information). The FT-IR and NMR spectra verified the chemical
structures of polymer P0 and P1. In addition, the elemental analysis
results were well consistent with the calculated ones.
The maximum absorption in solution and thin solid film undergoes
a red shift in the turn of polymer P0 and P1. The other unique
feature of the two polymers is that the width of ultraviolet
absorption curve in solution is wider than that of thin solid films,
and these results are markedly different from our previous results
of similar polymers [25]. The specific mechanism is not clear at this
stage. A possible interpretation may be the potential hydrogen
bond interactions between hydroxy and pyridine of polymer P1
and unique state of aggregation in thin solid film caused by non
linear conjugated structures of polymer P0 and P1. However, as
calculated from the absorption onsets in THF solution and thin solid
film, the optical band gaps of the two polymers in solution and thin
solid film are 3.11 eV and 3.09 eV, which indicates that the optical
band gap and maximum UVevis absorption have been affected by
the different features of the polymers and the PL emission band in
solution is rarely associated with the size and number of the
substituents, the resulted torsion angle and the relative movement
of the phenyl rings. In order to evaluate the fine difference in light-
emitting ability of polymer P0 and P1, the absolute PL quantum
yields of polymer P0 and P1 in THF solution were determined in
integrated sphere at room temperature. It was interesting to notice
that the absolute PL quantum efficiency was as high as 51% for P1
and 44% for P0. The absolute PL quantum efficiency of P1 was
relatively higher than that of P0, and the potential hydrogen
bonding between the hydroxyl moieties and THF or pyridyl units
may contribute to this value.
3.3. Electrochemical properties
In order to find further information about the conjugated
structures of polymer P0 and P1, we employed CV to probe the
HOMO and LUMO energy levels of polymer P0 and P1 thin solid
films. The HOMO and LUMO energy levels and the energy band
gaps (EgCV) of the polymer thin solid films were calculated according
to the following equations [32].
LUMO ¼ ꢁeðEred þ 4:71ÞðeVÞ; HOMO
¼ ꢁeðEox þ 4:71ÞðeVÞ; EgCV ¼ eðEox ꢁ EredÞðeVÞ
3.2. Photophysical properties
The oxidation and reduction potentials derived from the onset
of electrochemical potential are summarized in Table 2, and Fig. 3
illustrates the CV curves in detail. Polymer P0 exhibits an irre-
versible oxidation during the first CV scan, which is probably due to
the irreversibility of one single two electron transfer or can be due
to a much more negative potential for the second reduction step in
unsymmetrical dipyridine blocks of pyridine unit [33]. In conju-
gated polymers, the maximum wavelengths of UVevis absorption
and PL emission are determined by the band gap of material. The
The photophysical properties of polymer P0 and P1 were
investigated both in dilute THF solution and thin solid films. The
absorption and PL emission datas of the polymers are summarized
in Fig. 2 and Table 1. As shown in Fig. 2, the absorption spectra of the
polymer solutions and thin solid films shows peaks locating in the
range from 390 to 430 nm, which can be attributed to the most
prominent pep* transitions derived from the polymer backbones.

H.-j. Jiang et al. / Polymer 53 (2012) 5684e5690
5687
Br
Br
N
S
S
O
O
B
B
+
O
O
C H
17
C H
8
8
17
M0
OC H OCOCH
3
6
12
C H
17
C H
8
17
8
N
S
n
S
o
Pd(PPh ) , 90 C, 72 h
3 4
2M Na CO , Toluene
2 3
P0
OC H OCOCH
3
6
12
C H
17
C H
8
8
17
N
S
n
S
NaOH, THF, 3h,
Room Temperature
P1
OC H OH
6
12
Scheme 2. The synthetic route of polymer P0 and P1.
factors that influence the band gap of polymer are conjugated
length, solid-state intermolecular ordering and the presence of
electron-withdrawing or -donating moieties. Therefore, by modi-
fying one or more of these properties, polymers with controlled
band gaps and thus, specific optical and electrical characteristics
can be synthesized. In this regard, we can control the effective
conjugated length, which is dependent upon the torsion angle
between the repeating units along the polymer backbone, by
choosing sterically hindered units along the polymer backbone or
by introducing bulky side chains to twist the units out of plane.
Generally, when electron-withdrawing substituents are attached to
gap is 3.23 eV, which are not significantly changed from those of
polymer P1. However, these values are considerably changed from
those of PF [34], which validates that the star-shaped fragments of
2,4,6-trithiophenylpyridine can greatly alter the energy levels of
polymer P0 and P1 thin solid films and the introduction of V-
shaped 2,4,6-trithiophenylpyridine certainly distorts the linear
conjugated structure of PF thin solid film. Further analysis of the
structures of polymers will allow us to clearly understand how the
structure feature affects the electro-optical performance of conju-
gated material for device optimization.
the conjugated molecules, the electron density in the
p-system of
3.4. Self-assembly properties
the conjugated molecule will be decreased. Consequently, the
molecule will be stabilized and the oxidation potential will be
increased in turn, corresponding to a shift of the HOMO energy
level to lower energy. The HOMO and LUMO energy levels of
polymer P0 are ꢁ5.81 and ꢁ2.58 eV, and the corresponding band
As its amphipathic nature, polymer P1 was solvated in a mixed
solvent of THF/water in different volume ratios and concentrations.
P1-0 stands for a P1 solution of THF/water in a volume ratio of 4/1
and a concentration of 0.2 mg mLꢁ1. P1-1: 3/2 and 0.2 mg mLꢁ1
;

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H.-j. Jiang et al. / Polymer 53 (2012) 5684e5690
Table 1
UVevis absorption and PL emission spectral datas of polymer P0 and P1 in solution
and thin solid films.
THF
Film
abs
em=ex
abs
em=ex
l
l
Egopt
Qpl(%)d
l
l
Egopt
max
max
max
max
(nm)a
(nm)b
(eV)c
(nm)a
(nm)b
(eV)c
P1
P0
P1
398
429
458(398)
483(429)
3.00
3.02
44
51
404
412
497(404)
500(412)
3.11
3.09
a
Maximum absorption wavelength.
Maximum emission and excitation wavelength.
Optical band gap determined from the UVevis absorption onset.
Absolute PL quantum efficiency in THF solution.
b
c
d
P1-2: 3/2 and 0.1 mg mLꢁ1; P1-3: 2/3 and 0.2 mg mLꢁ1. The
resulting solution was characterized by DLLS, which is a noninva-
sive method of analyzing aggregates in solution. In briefly, no
obvious granules are observed in the P1-0 solution, and the solu-
tion is still in a transparent state (S8 in Supporting Information).
After addition of water, the solution of P1-1, P1-2 and P1-3 change
immediately into a white milky suspension, which validates that
the polymer backbone are really amphipathic in nature. As shown
in Fig. 4, the mean diameters of the vesicles of polymer P1 in P1-1,
P1-2 and P1-3 solution are 1144 nm, 455 nm and 291 nm under
different solvent conditions. As the water content is increased and
the concentration of the polymer solution is decreased, the mean
diameters of the vesicles of polymer P1 in solution are also
decreased, and the change of water content has a more pronounced
effects on the size of the vesicle than concentration of the polymer
solution, which indicates the different mechanism for the vesicles
under different water environments. The hydroxy and pyridine
moieties in the mainchain of polymer P1 are hydrophilic groups in
nature, and in a suitable microenvironment, there are inevitably
P0
500
1000 1500 2000 2500 3000 3500 4000
-1
Wave Number(cm )
Fig. 1. The FT-IR spectra of polymer P0 and P1 thin solid films.
UV in THF Solution
UV in Thin Solid Film
PL in THF Solution
PL in Thin Solid Film
a
1.0
0.8
0.6
0.4
0.2
0.0
Table 2
Electrochemical datas of polymer P0 and P1 thin solid films.
Reductiona
Oxidationa
LUMO/HOMO (eV)
EgCV (eV)c
Epa/Epc (V)b
Epc/Epa (V)b
P0
P1
e/ꢁ2.76
e/ꢁ2.92
1.54/e
1.62/e
ꢁ2.58/ꢁ5.81
ꢁ2.60/ꢁ5.73
3.23
3.13
a
Determined by CV for polymer thin solid films coated on glassy carbon
300
350
400
450
500
550
600
electrode.
b
Epa and Epc stood for anodic peak potentials and cathodic peak potentials,
respectively.
Wavelength (nm)
c
Electrochemical band gap obtained by CV.
UV in THF Solution
UV in Thin Solid Film
PL in THF Solution
PL in Thin Solid Film
b
1.0
0.8
0.6
0.4
0.2
0.0
350
400
450
500
550
600
650
700
Wavelength (nm)
Fig. 2. Normalized UVevis absorption and PL emission spectra of polymer P0(a) and
P1(b) in THF solution and thin solid films.
Fig. 3. CV curves of polymer P0 and P1 thin solid films.

H.-j. Jiang et al. / Polymer 53 (2012) 5684e5690
5689
Fig. 4. TEM micrograph and numbereaverage hydrodynamic size of the vesicles obtained of polymer P1 in THF/water (v/v and mg mLꢁ1). (a, b, P1-1), (c, d, P1-2) and (e, f, g, P1-3).
some hydrogen bonding interactions between them. In the present
solution concentration and with the decrease of the concentration,
the number of molecules participating in the formation of stable
vesicles is decreased, which will reduce the size of the vesicle.
When the solution volume ratio is changed from 3/2 to 2/3, the
mean diameter of the vesicles is changed from 1144 nm to 291 nm,
which may be caused by the orientation of the hydrophilic group in
the mainchain. In order to prove this hypothesis and to investigate
the correlation between the assemblies in solution and a dried
sample on the substrate, the morphologies of the aggregates were
examined by TEM. As shown in Fig. 4, the vesicles of polymer P1 in
P1-1, P1-2 and P1-3 dried sample are sill in the spherical shape
with mean diameters in the range from 80 nm to 500 nm. As the
evaporation of polymer droplet at room temperature is a complex

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and uncontrollable process, the polydispersion of particle diameter
is not very uniform. The size and morphology of the formed vesicle
are strongly correlated with volume ratios and concentrations of
the mixed solution. To further probe the photophysical properties
of the formed vesicles, we have tried to investigate the UVevis
absorption and PL emission properties of luminescent particles in
dispersion liquid, but the intensities of absorption and PL emission
have exceeded the upper limit of instruments, and the relative
intense fluorescence from vesicles of polymer P1 endow them with
wide potential applications in chemical and biological sensors.
Interestingly, the vesicles of polymer P1 are changed from a fluffy
solid to nuclear-shell structure in the turn of P1-1, P1-2 and P1-3,
and there is an obvious coexistence of fluffy solid and nuclear-shell
structures in P1-3 (Fig. 4-g), which strongly validate the hypothesis
obtained from the DLLS characterization. It is expected that with
further increase of water volume, nuclear-shell structured vesicles
with different thickness and chemical composition will be formed.
This result is markedly different from double-layer hollow vesicles
formed by the flexible mainchain and amphipathic polymers [35].
The specific mechanism is now studied, and we will report our
results in the due course.
Appendix A. Supporting information
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.polymer.2012.10.007.
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In summary, two novel polymers based on fluorene, pyridine
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were successfully synthesized through the Suzuki coupling reac-
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The photophysical properties, energy band gaps and self-assembly
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Acknowledgments
This work was financially supported by the Major Research
Program from the State Ministry of Science and Technology
(2009CB930600 and 2012CB933301), the Ministry of Education of
China (IRT1148), the Priority Academic Program Development of
Jiangsu Higher Education Institutions, the Natural Science Foun-
dation of the Jiangsu Higher Education Institutions of China
(10KJB150012) and Nanjing University of Posts and Telecommuni-
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