Novel isoindigo-based conjugated polyelectrolytes: Synthesis and fluorescence quenching behavior with water-soluble poly(p-phenylenevinylene)s

Article abstract of DOI:10.1002/pola.27711

Two novel ID-based water-soluble conjugated polymers (+)-PIDPV and (-)-PIDPV were synthesized by Heck coupling reaction. These two polyelectrolytes are both consisted of isoindigo units and phenylenevinylene units. In the UV-vis absorption spectra, both (+)-PIDPV and (-)-PIDPV exhibit broad absorption bands that almost cover the whole visible region. Photophysical investigations reveal that the fluorescence of water-soluble PPV can be efficiently quenched by oppositely charged PIDPV at a very low concentration. Cationic PPV shows an efficient quenching effect with Κ_SV = 1.01 × 10⁶ M^-1 in the presence of (-)-PIDPV while the anionic PPV gives a lager quenching constant with Κ_SV = 1.71 × 10⁶ M^-1 in the presence of (+)-PIDPV. Furthermore, the blend films of water-soluble PPVs and oppositely charged PIDPV also exhibit excellent quenching effect. These properties suggest that (+)-PIDPV and (-)-PIDPV are promising materials in the application of ionic photoactive layer in the organic solar cells.

Full text of DOI:10.1002/pola.27711

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Novel Isoindigo-Based Conjugated Polyelectrolytes:
Synthesis and Fluorescence Quenching Behavior
with Water-Soluble Poly(p-Phenylenevinylene)s
Chun Kou, Xiaolong He, Xueyu Jiang, Yifeng Ni, Ling Liu, Changxin Huangfu, Kuan Liu
College of Science, Sichuan Agricultural University, Yaan 625014, People’s Republic of China
Correspondence to: K. Liu (E-mail: cosmicer@live.cn)
Received 13 January 2015; accepted 21 May 2015; published online 30 June 2015
DOI: 10.1002/pola.27711
ABSTRACT: Two novel ID-based water-soluble conjugated poly-
mers (1)-PIDPV and (2)-PIDPV were synthesized by Heck cou-
pling reaction. These two polyelectrolytes are both consisted
of isoindigo units and phenylenevinylene units. In the UV–vis
absorption spectra, both (1)-PIDPV and (2)-PIDPV exhibit
broad absorption bands that almost cover the whole visible
region. Photophysical investigations reveal that the fluores-
cence of water-soluble PPV can be efficiently quenched by
oppositely charged PIDPV at a very low concentration. Cationic
PPV shows an efficient quenching effect with KSV 5 1.01 3 106
M21 in the presence of (2)-PIDPV while the anionic PPV gives
a lager quenching constant with KSV 5 1.71 3 106 M21 in the
presence of (1)-PIDPV. Furthermore, the blend films of water-
soluble PPVs and oppositely charged PIDPV also exhibit excel-
lent quenching effect. These properties suggest that (1)-PIDPV
and (2)-PIDPV are promising materials in the application of
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KEYWORDS: isoindigo; conjugated polyelectrolytes; copolymer-
ization; synthesis; fluorescence quenching
damage to the underlying organic soluble active layer and
have environment-friendly processing capabilities. Further-
more, the ionic side groups of the polymers can induce large
interfacial dipoles to reduce the work-function of the cathode
and as a result the Voc of the device is increased and the
PCE is improved.19,20
INTRODUCTION Conjugated polyelectrolytes (CPEs) have
drawn a great deal of interest because of their excellent solu-
bility in water and other polar solvents which was achieved
by modification of the side chains with a set of ionic pend-
ants such as anionic carboxylates,1 phosphonates,2 sulfo-
nates,3,4 and cationic quaternary ammonium salts.5 With the
wonderful properties of strong and tunable absorption and
In the past few years, dye-based conjugated polymers have
attracted great attention and almost all of these polymers
exhibit excellent photoelectric properties due to their large
conjugated system.21 Isoindigo (ID) is a kind of indigoid
dyes as same as indigo and isatin, in which two indolin-2-
one units are connected by the central C@C bond in E con-
figuration and two intramolecular hydrogen bonds occur
between C@O and NAH groups.22,23 Investigation of the
medicinal properties of ID derivatives reveals that ID deriva-
tives such as 1-methylisoindigo (Meisoindigo) and 1-(tri-O-
acetylxylopyranosyl)-isoindigo (Natura) have a great anti-
cancer potency.24 Moreover, as same as other hydrogen-bond
dyes, IDs are always modified with alkyl groups via N-alkyla-
tion, which can break the hydrogen-bond network and
increase their solubility. Recently ID derivatives are used as
copolymerization units to form internal donor–acceptor (D–
A) structures in the synthesis of conjugated polymers due to
its strong electron-deficient lactam rings.25–27 Introduction
photoluminescence,
environment-friendly
processability,
water solubility, and aggregation phenomenon, CPEs have
been applied in a variety of photoelectric devices including
polymer light-emitting diodes (PLEDs),6–8 photovoltaic
cells,9,10 organic field effect transistors (OFETs),11,12 and
chemical and biological sensors.13,14 Conjugated polymers-
based bulk-heterojunction (BHJ) solar cells have been stud-
ied widely due to their advantages for fabrication of low-
cost, promising flexibility and processability but the low
power conversion efficiency (PCE) has always been the
essential drawback.15,16 Research on interface engineering17
demonstrates that the performance of the photovoltaic devi-
ces can be dramatically improved by introducing an interfa-
cial layer between the active layer and the metal electrode.
The inserted layer should be in ohmic contact to minimize
the contact resistant and maximize the open-circuit voltage
(Voc).18 It has been reported that CPEs are good candidates
for the interfacial layer material because they can prevent
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SCHEME 1 Synthetic routes of monomers and polymers.
of soluble ID unit into conjugated polymers can not only
optimize the electron structure but also lower the HOMO
energy levels and the band gaps, thus the polymers can har-
vest a large number of solar photon. Most of these polymers
exhibit broad absorption band in the visible region which
makes them become important components of active layers
in the organic solar cells.28 In 2010 the first ID-based conju-
gated polymer was blended with PC60BM to fabricate molec-
ular BHJ solar cells with PCE of 1.76%29 and now the
highest PCE of the ID-based organic solar cells is 8.2%.30 In
addition, the ID-based polymers are also used in organic
semiconductor memory devices where ID units act as
electron-trapping moieties to improve the on/off ratios and
in OFETs due to the relative high hole mobility of the
polymers.31
been realized by alkylation with sultone, which makes it pos-
sible to synthesize water-soluble ID derivatives. And the sul-
fonated ID electrolytes must be important parts in the
synthesis of anionic ID-based conjugated polyelectrolytes. On
the other hand, few cationic conjugated polyelectrolytes
were reported and almost all of these cationic polymers
were prepared by quaternization after the polymerrization.36
Completely charged cationic polyelectrolytes cannot be
obtained through this indirect method because not all of the
side groups of the polymers can be charged in this proce-
dure. Therefore, the direct strategy was designed and
achieved to afford the completely charged cationic polymers
in our work in which the cationic monomer was prepared
first via quaternization reaction followed by copolymerized
with oil-soluble ID to give the cationic polymers.
However, none of ID-based conjugated polyelectrolytes has
been reported yet. The ionic hydrogen bond dyes as water-
soluble 1,4-diketopyrrolo[3,4-c]pyrrole (DPP) derivatives
have been obtained by modified with carboxyl32 or sulfuric
acid ester33 on its N-alkyl side chain, but it gives a low yield
and an unsatisfied purity. Recently, the strategy to transform
such hydrogen-bond dyes as quinacridone34 and DPP35 into
water-soluble derivatives with high yield and purity has
Herein, we have successfully designed and synthesized two
kinds of novel conjugated polyelectrolytes: anionic PIDPV
((2)-PIDPV) and cationic PIDPV ((1)-PIDPV). First,
we accomplished the synthesis and the characterization of
two ionic monomers 6,6-dibromo-N,N-bis(4-sulfonylbutyl)-
isoindigo (Monomer 1) and 1,4-bis{3-(N,N,N-triethylammo-
nium)-1-oxapropyl}-2,5-divinyl-benzene dibromide (Mono-
mer 4). And then the two novel ionic compounds were
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according to the methods which reported in the referen-
ces.36,41 The chemical structures of (1)-PPV and (2)-PPV
are illustrated in Scheme 2.
Monomers’ Synthesis
6,6-Dibromo-N,N-Bis(4-Sulfonylbutyl)-Isoindigo ((2)-ID,
Monomer 1)
Under argon atmosphere, 6,6-dibromoisoindigo (0.6302 g,
1.5 mmol) and sodium hydride (0.096 g, 4 mmol) were
stirred in N,N-dimethyl-formamide (45 mL) and heated to 40
8C. Then 1,4-butane sultone (0.456 mL, 4.5 mmol) was
injected through a syringe. The mixture was stirred at 60 8C
for 11 h and then poured into ethanol (300 mL). The solu-
tion was filtered and the precipitate was dissolved in water.
The oil-soluble impurities were removed via filtration. The
solvent was evaporated under reduced pressure and the res-
idue was purified by recrystallization from potassium chlo-
ride solution (40 g/L) to give a brown solid. Finally the
crude product was dried under vacuum at 80 8C for 12 h to
give a dark brown solid. Yield: 0.4944 g, 44.8%. 1H NMR
(300 MHz, D2O, d): 8.39 (dd, J 5 29.2, 8.6 Hz, 2H), 7.11–6.75
(m, 4H), 3.40 (s, 4H), 2.98–2.72 (m, 4H), 1.95 – 1.36 (m,
8H). 13C NMR (75 MHz, DMSO-d6, d): 166.98, 145.86,
132.07, 130.80, 126.37, 124.49, 119.88, 111.87, 50.91, 26.20,
22.61. (The signal of the carbon of NACH2 is covered by the
heptet of DMSO-d6 in the range of 40.35–38.69 ppm). IR
(KBr): m 5 2933 (vs; mas(ACH2A)), 1698 (s; m(C@O)), 1594
(s), 1473 (s; m(ArC@C)), 1357 (vs; m(CAN)), 1178 (vs), 1042
(vs; m(sulfonate)), 726 cm21 (w, d(A (CH2)nA)). Anal. calcd.
for C24H24Br2N2Na2O8S2: C 39.15, H 3.01, N 3.80; found: C
39.06, H 2.94, N 3.77.
SCHEME 2 The chemical structures of (2)-PPV and (1)-PPV.
introduced into the backbone of (2)-PIDPV and (1)-PIDPV,
respectively, via Heck coupling reaction. As similar with
other ID-based conjugated polymers, (2)-PIDPV and (1)-
PIDPV also exhibit broad absorption bands in the visible
region but do not have fluorescence emission. Furthermore,
we also synthesized two water-soluble poly(p-phenylenevi-
nylene)s (PPVs): cationic PPV ((1)-PPV) and anionic PPV
((2)-PPV). Investigations of the optic properties of cationic
and anionic PPV with oppositely charged PIDPV were carried
out in the dilute aqueous solution and in the solid state. The
results show that the fluorescence of the water-soluble PPVs
was quenched with addition of the oppositely charged ID-
based polymers.
EXPERIMENTAL
FT-IR spectra were recorded on a Shimadzu FTIR-8400S IR
spectrometer. 1H NMR and 13C NMR measurements were
carried out on a Bruker Avance II-300MHz spectrometer
with tetramethylsilane as the internal reference. Elemental
analysis was performed on a CARLO ERBA 1106 elemental
analyzer. The UV–vis spectra were performed on a UNICO-
2102 UV–vis spectrophotometer. Photoluminescence (PL)
spectra were recorded on a Hitachi F-4600 luminescence
spectrophotometer.
6,6-Dibromo-N,N-Dibutyl-Isoindigo ((N)-ID, Monomer 2)
Under argon atmosphere, 6,6-dibromoisoindigo (0.8402 g, 2
mmol) and anhydrous potassium carbonate (1.6584 g, 12
mmol) was stirred in N,N-dimethylformamide (40 mL) for
30 minutes. Subsequently, n-butyl bromide was injected
through a syringe. The mixture was stirred at 100 8C for
15 h and then poured into water. The aqueous phase was
extracted with dichloromethane and the combined organic
layer was washed with brine and dried over anhydrous mag-
nesium sulfate. The solvent was evaporated under reduced
pressure. The product was purified by recrystallization from
dichloromethane/hexane (1/1) to give red needles. Yield:
6-bromooxindole, 6-bromoisatin, sodium hydride, 1,4-butane
sultone, anhydrous potassium carbonate, n-butyl bromide,
potassium tertbutoxide, poly(diallyldimethylammonium chlo-
ride) (PDDC), poly(sodium-p-styrenesulfonate) (PSS) were
obtained from domestic chemical companies. All the chemi-
cals were used as received. Toluene was distilled over
sodium with benzophenone as indicator. N,N-dimethylform-
amide was purified by distillation under vacuum.
1
0.5636 g, 53%. H NMR (300 MHz, CDCl3, d): 9.07 (d, J 5 8.6
Hz, 2H), 7.17 (dd, J 5 8.6, 1.8 Hz, 2H), 6.93 (d, J 5 1.6 Hz,
2H), 3.74 (t, J 5 7.3 Hz, 4H), 1.74–1.61 (m, 4H), 1.49–1.34
(m, 4H), 0.98 (t, J 5 7.3 Hz, 6H). 13C NMR (75 MHz, CDCl3,
d): 167.64, 145.67, 132.54, 131.15, 126.69, 125.07, 120.32,
111.24, 39.97, 29.39, 20.23, 13.74. IR (KBr): m 5 2961 (vs;
mas(ACH3, ACH2A)), 2868 (vs; ms(ACH3, ACH2A)), 1686 (s;
m(C@O)), 1594 (s), 1473 (s; m(ArC@C)), 1358 (vs; m(CAN)),
730 cm21 (w, d(A (CH2)nA)). Anal. calcd. for C24H24Br2N2O2:
C 54.16, H 4.54, N 5.26; found: C 54.01, H 4.52, N 5.16.
The synthetic routes of Monomers 1–4 and polymers (2)-
PIDPV and (1)-PIDPV are illustrated in Scheme 1. The Com-
pounds 1–7 were synthesized according the literatures: 6,6-
dibromoisoindigo (1),25 1,4-dibutyloxy-benzene (2),37 1,4-
bisbromomethyl-2,5-dibutyloxy-benzene (3),38 2,5-dibutyloxy-
1,4-xylylene-bis(triphenyl phosphonium bromide) (4),38 1,4-
bis{(N,N-diethyl-amino)-1-oxapropyl}c-benzene (5),39 1,4-bis-
{(N,N-diethylaminohydrochloride)-1-oxapropyl}-2,5-dichloro-
methane-benzene (6),39 {1,4-bis(4’-2-(N,N-diethylamino)e-
thoxy)-2,5-xylene}bis(triphenylphosphonium
chloride)
1,4-Divinyl-2,5-Dibutyloxy-Benzene ((N)-DVB, Monomer 3)
Under argon atmosphere, 1,4-xylylene-bis(triphenylphospho-
nium bromide)22,5-dibutyloxy (7.6601 g, 7.5 mmol),
dihydrochloride (7).40 The two water-soluble poly(p-phenyl-
enevinylene)s (1)-PPV and (2)-PPV were also prepared
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dichloromethane (100 mL) and formaldehyde aqueous
(30 mL) were stirred at 0 8C, then an aqueous solution of
NaOH (20 wt%, 65 mL) was added dropwise in 1 h and the
reaction mixture was stirred at room temperature for 24 h.
The organic phase was separated and the aqueous phase
was extracted with dichloromethane for three times. After
the combined organic layer was washed with brine and
water, the resulting solution was dried over anhydrous
sodium sulfate. Subsequently, the solvent was removed by
rotary evaporation and the residue was purified by recrystal-
lization from ethanol to give a pale-yellow crystal. Yield:
1.7658 g, 85.8%. 1H NMR (300 MHz, CDCl3, d): 7.13 – 7.01
(m, 2H), 6.99 (s, 2H) 5.72 (dd, J 5 17.7, 1.2 Hz, 2H), 5.25
(dd, J 5 11.1, 1.2 Hz, 2H), 3.97 (t, J 5 6.4 Hz, 4H), 1.86–1.71
(m, 4H), 1.58–1.45 (m, 4H), 0.98 (t, J 5 7.4 Hz, 6H). 13C NMR
(75 MHz, CDCl3, d): 150.57, 131.48, 127.08, 113.93, 110.37,
68.89, 31.50, 19.34, 13.87. IR (KBr): m 5 3105 (m; m(5C-H)),
m 5 2958 (vs; mas(-CH3, ACH2A)), 2870 (vs; ms(ACH3,
ACH2A)), 1674 (w; m(C@C)), 1622–1418 (s; m(ArC@C)), 1385
(s; d(ACH3)), 1307 (s; m(ACH3)), 1204 (vs; m(CAO)), 897 (s;
c(@CAH)), 738 cm21 (v; d(A (CH2)nA)). Anal. calcd. for
phine (0.0365 g, 0.12 mmol), triethylamine (2.5 mL) and
dimethylsulfoxide (5 mL) was stirred at 100 8C for 18 h. The
reaction solution was poured into the mixed solvent (etha-
nol/ethyl ether 5 1/1) and then filtered. The precipitate was
dissolved in dimethylsulfoxide and filtered by hydrophobic
filter membrane. The solution was poured into the mixed
solvent (ethanol/ethyl ether 5 1/1) and then filtered by
hydrophilic filter membrane again. Subsequently the residue
was redissolved in deionized water and the concentrated
solution was dialyzed against deionized water for 5 days
using a 4KD MWCO cellulose membrane (Spectra/Por Cellu-
lose Ester Membrane). Finally the solvent was removed by
rotary evaporation and the crude product was dried under
vacuum with P2O5 at 50 8C for 24 h to give a dark blue solid.
Yield: 0.2048 g, 46.6%. 1H NMR (300 MHz, DMSO-d6, d):
9.20–6.91 (m, 12H), 4.12 (d, J 5 31.6 Hz, 4H), 3.78 (s, 4H),
2.77–2.52 (m, 4H), 1.85–1.43 (m, 16H), 0.98 (dd, J 5 13.9,
6.5 Hz, 6H). IR (KBr): m 5 3120 (m; m(@CAH)), m 5 2954 (vs;
mas(ACH3, ACH2A)), 2869 (vs; ms(ACH3, ACH2A)), 1703 (vs;
m(C@O)), 1605–1490 (s; m(ArC@C)), 1419 (s; d(ACH3)), 1359
(vs; m(CAN)), 1202 (vs), 1103 (vs; m(sulfonate)), 995 cm21
(w; c(@CAH)).
C18H26O2: C 78.79, H 9.55; found: C 77.72, H 9.64.
1,4-Bis{3-(N,N,N-Triethylammonium)21-Oxapropyl}-
(1)-PIDPV
2,5-Divinyl-Benzene Dibromide ((1)-DVB, Monomer 4)
Under argon atmosphere, a mixture of 7 (3.0087 g, 3 mmol),
dichloromethane (50 mL) and formaldehyde aqueous solu-
tion (40 wt%, 15 mL) was stirred at 0 8C, and then an aque-
ous solution of NaOH (20 wt %, 28 mL) was added
dropwise in 1 h. After stirred for 24 h, the aqueous layer of
resulting solution was extracted with dichloromethane for
three times. The combined organic layer was washed with
water and dried with anhydrous sodium sulfate. The final
pale-yellow powder 8 was obtained after removing the sol-
vent by rotary evaporation and then transferred into a three-
necked flask. Under argon atmosphere, a mixture of bromo-
ethane (2 g) and acetone (10 mL) was added to the former
flask, which was stirred and heated to reflux for 2 days to
give a white precipitate. The solid was filtered, washed with
bromoethane and hot acetone repeatedly and finally dried
under vacuum to afford a white powder. Yield: 0.35 g, 21%.
1H NMR (300 MHz, D2O, d): 7.22 (s, 2H), 7.02 (dd, 2H), 5.85
(d, J 5 17.7 Hz, 2H), 5.41 (d, J 5 11.3 Hz, 2H), 4.53–4.43 (m,
4H), 3.81 – 3.72 (m, 4H), 3.46 (q, J 5 7.2 Hz, 12H), 1.35 (t,
J 5 7.2 Hz, 18H). 13C NMR (75 MHz, D2O, d): 149.09, 129.99,
127.06, 115.97, 109.97, 62.07, 55.31, 53.51, 6.81. IR (KBr):
m 5 3071 (m; m(@CAH)), m 5 2972 (vs; mas(ACH3, ACH2A)),
2883 (vs; ms(ACH3, ACH2A)), 1674 (w; m(C@C)), 1560–1462
(s; m(ArC@C)), 1353 (s; d(ACH3)), 1270 (s; m(ACH3)), 1213
(vs; m(CAO)), 875 cm21 (s; c(@CAH)). Anal. calcd. for
Under argon atmosphere,
a mixture of monomer 2
(0.2661 g, 0.5 mmol), monomer 4 (0.2892 g, 0.5 mmol), pal-
ladium(II) acetate (0.0068 g, 0.03 mmol), tri(O-toly)phos-
phine (0.0365 g, 0.12 mmol), triethylamine (5 mL), and
dimethylsulfoxide (20 mL) was stirred at 80 8C for 6 h. The
reaction solution was poured into the mixed solvent (ethyl
ether/acetone 5 5/4) and then filtered. The precipitate was
dissolved in H2O and then filtered by hydrophilic filter mem-
brane. The concentrated solution was dialyzed against deion-
ized water for 5 days using a 4KD MWCO cellulose mem-
brane (Spectra/Por Cellulose Ester Membrane). Finally the
solvent was removed by rotary evaporation and the crude
product was dried under vacuum with P2O5 at 50 8C for
24 h to give a dark blue solid. Yield: 0.1447 g, 29.6%. 1H
NMR (300 MHz, DMSO-d6, d): 9.10 (d, J 5 47.1 Hz, 2H),
7.88–6.89 (m, 10H), 4.49 (dd, J 5 57.9, 20.2 Hz, 4H), 3.99–
3.44 (m, 20H), 1.64 (d, J 5 27.1 Hz, 4H), 1.38 (s, 4H), 1.35 –
1.20 (m, 16H), 0.99 (d, J 5 22.9 Hz, 8H). IR (KBr): m 5 3048
(m; m(@CAH)), m 5 2954 (vs; mas(ACH3, ACH2A)), 2869 (vs;
ms(ACH3, ACH2A)), 1699 (vs; m(C@O)), 1605 (s), 1456 (s;
m(ArC@C)), 1419 (s; d(ACH3)), 1360 (vs; m(CAN)), 958 cm21
(w; c(@CAH)).
RESULTS AND DISCUSSION
Synthesis of Monomers and Polymers
Monomer 1 was obtained via N-alkylation reaction of 6,6-
dibromoisoindigo with 1,4-butane sultone, which is similar
to the synthesis of the sulfonated DPP derivatives. Here, ID
and DPP are both hydrogen-bond pigments with lactam rings
in their molecular structure, so they should exhibit the same
reactive site. In the procedure, 6,6-dibromoisoindigo was
alkylated under alkaline condition using sodium hydride as
the base and using anhydrous DMF as the solvent. DMF is
C26H46Br2N2O2: C 53.98, H 8.02, N 4.84; found: C 53.91, H
8.14, N 4.81.
Polymers’ Synthesis
(2)-PIDPV
Under argon atmosphere,
a mixture of monomer 1
(0.3682 g, 0.5 mmol), monomer 3 (0.1372 g, 0.5 mmol),
palladium(II) acetate (0.0068 g, 0.03 mmol), tri(O-toly)phos-
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FIGURE 1 FT-IR spectra of 6,6-dibromoisoindigo (a), (2)-ID (b),
FIGURE 2 FT-IR spectra of (2)-ID (a), (N)-DVB (b), and (2)-
and (N)-ID (c).
PIDPV (c).
the frequently used solvent in the synthesis of oil-soluble
derivatives of isoindigo. The use of the strong base sodium
hydride can accelerate the reaction rate and increase the
yield but the pyrrole rings of isoindigo may be destroyed in
this alkali environment, resulting in a variety of impurities
such as single substitution isoindigo and ring-open by-prod-
ucts. While the impurities mentioned above are hardly to be
removed thoroughly by filtration and recrystallization from
common organic solvents. Therefore, pure monomer 1 was
successfully obtained by recrystallization from potassium
chloride aqueous solution as same as the purification
method of water-soluble DPP derivative reported in our
previous work.35 Monomer 4 was prepared via a five-step
reaction, containing Williamson ether reaction, chloromethy-
lation, Ylide reaction, Wittig reaction, and quaternization. As
shown in Scheme 1, the product of the forth step was used
directly for the subsequent reaction without further purifica-
tion. And then after quaternization, the mixture was filtered
and the solid was washed to give the target product as a
white powder. At the same time, the triphenylphosphine
oxide which was characterized as the main by-products of
Wittig reaction was removed in the process of the purifica-
tion of monomer 4, because the triphenylphosphine oxide is
soluble in bromoethane and acetone but the target product
monomer 4 is not.
dialyzed against deionized water. The methods are similar to
the polymerization of DPP-based CPEs reported in our previ-
ous work.35 Water solubility of (1)-PIDPV, (2)-PIDPV, (1)-
PPV and (2)-PPV are around 11.8 mg mL21 ([repeat
unit]51.21 3 1022 M), 12.5 mg mL21 ([repeat unit] 5 1.42
3 1022 M), 120.7 mg mL21 ([repeat unit] 5 0.132 M) and
115.2 mg mL21 ([repeat unit] 5 0.159 M) at room tempera-
ture, respectively.
The Structure Characterizations of Monomers and
Polymers
Figure 1 shows the FT-IR spectra of 6,6-dibromoisoindigo
(a), (2)-ID (b) and (N)-ID (c). The absorption peak at
3136 cm21 in the Figure 1(a) which is attributed to the
NAH vibration disappears in Figure 1(b,c), indicating that
nitrogen hydrogen has been substituted completely in the
synthesis procedure of monomer 1 and 2. In addition, the
peak at 2933 cm21 in the Figure 1(b) is attributed to the
ACH2A vibration of sulfonylbutyl of (2)-ID and the peaks at
2961 and 2868 cm21 in the Figure 1(c) are, respectively,
The polymerization of the two polymers were both carried
out via Heck coupling reaction using Pd(OAc)2 as catalyst
and P(o-tolyl)3 as the corresponding ligand.42 Considering
the excellent solubility of monomer 1 and monomer 4 in
water and other polar solvents, the strong organic polar sol-
vent DMSO which is the common solvent to synthesize CPEs
in the Heck reaction was used. During the procedure of the
copolymerization, the conjugated length of (2)-PIDPV and
(1)-PIDPV which was detected by the UV–vis spectrum was
adjusted to be almost identical by controlling the polymer-
ization time. The polymers were collected by filtration after
precipitating in the mixed solvent (ethanol/ethyl ether 5 1/1
and ethyl ether/acetone 5 5/4), respectively, and purified by
FIGURE 3 FT-IR spectra of (N)-ID (a), (1)-DVB (b), and (1)-
PIDPV (c).
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FIGURE 4 1H NMR spectra of (2)-ID, (N)-DVB, and (2)-PIDPV.
attributed to the ACH3, ACH2A vibration of butyl of (N)-ID.
And the two peaks appear at 1178 and 1042 cm21 in Figure
1 (b) are attributed to the sulfonate. The results mentioned
above prove that the 6,6-dibromoisoindigo has been trans-
lated into (2)-ID and (N)-ID via N-alkylation.
Figure 2(a) and at 1202, 1103 cm21 in Figure 2(c) are
attributed to the sulfonate. While the peaks at 1358 and
1700 cm21 both appear in Figure 2(a,c) are due to the CAN
and C@O stretching vibration of isoindigo, respectively. All
these prove that the (2)-ID unit has been introduced into
the (2)-PIDPV. The absorption peaks at 3105 cm21 in Figure
2(b) and at 3120 cm21 in Figure 2(c) are attributed to the
CAH vibration of C@C double bond, demonstrating that the
Figure 2 shows the FT-IR spectra of (2)-ID (a), (N)-DVB (b)
and (2)-PIDPV (c). The peaks at 1178, 1042 cm21 in
FIGURE 5 1H NMR spectra of (N)-ID, (1)-DVB, and (1)-PIDPV.
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1
In the H NMR spectrum of (2)-PIDPV (Fig. 4), the presence
of the peaks at 4.12 ppm and 3.78 ppm which are respec-
tively attributed to OACH2 and NACH2 of (2)-PIDPV shows
the (2)-ID and (N)-DVB units have been introduced into the
main chain of (2)-PIDPV. These results can also be found in
the spectrum of (1)-PIDPV in Figure 5. Furthermore, the sig-
1
nal of SACH2 appears at 2.58 ppm in the H NMR spectrum
of (2)-PIDPV also proves that (2)-PIDPV was successfully
1
synthesized. In the H NMR spectrum of (1)-PIDPV, the peak
at 3.44 ppm is attributed to the hydrogen of NACH2 corre-
sponding to the signal appears at 3.46 ppm of (1)-DVB.
Moreover, the 1H NMR spectra of (1)-PIDPV and (2)-PIDPV
both show small signals in the region of 5–6 ppm which are
attributed to the terminal vinyl hydrogen of (1)-DVB and
(N)-DVB, respectively.43,44 All these results indicate that the
polymerizations of these two kinds of copolymers (2)-PIDPV
and (1)-PIDPV have been accomplished successfully by
using the synthetic methods shown in Scheme 1.
FIGURE 6 UV–vis spectra of (2)-ID (9.749 3 1025 M in DMSO),
(N)-DVB (1.058 3 1024 M in CH2Cl2), and (2)-PIDPV (5.255 3
1025 M in DMSO). [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
Figure 6 shows the UV–vis spectra of (2)-ID, (N)-DVB and
(2)-PIDPV while Figure 7 gives the UV–vis spectra of (N)-ID,
(1)-DVB and (1)-PIDPV. It has been found that the two
polymers and monomers of (2)-ID and (N)-ID have no fluo-
rescence emission, which is the same with other oil-soluble
ID derivatives and ID-based conjugated polymers.45 As
shown in this two figures, (2)-PIDPV and (1)-PIDPV give
broad absorption bands in the visible region. The absorption
peaks at 592 nm in the spectrum of (2)-PIDPV in Figure 6
and at 583 nm in the spectrum of (1)-PIDPV in Figure 7 are
associated with the p-p* transitions of the large p-conjugated
backbone of the two polymers, respectively. Moreover, com-
pared with the monomers, the absorption of (2)-PIDPV and
(1)-PIDPV both exhibit a remarkable red-shift due to their
long p-conjugated structures in the main chain.
vinylene structure in the main chain of (2)-PIDPV has been
obtained via Heck reaction. Similarly, the peak at 3071 cm21
in the Figure 3(b) which is attributed to the CAH vibration
of C@C double bond of (1)-DVB can also be observed in the
IR spectrum of (1)-PIDPV in Figure 3(c). Furthermore, the
C@O and CAN stretching vibration of isoindigo at 1686 and
1358 cm21, respectively, also have been characterized in Fig-
ure 3(c). These signals indicate that another conjugated poly-
electrolyte (1)-PIDPV has been obtained.
Figure 4 shows the 1H NMR spectra of (2)-ID, (N)-DVB and
(2)-PIDPV while Figure 5 gives the 1H NMR spectra of (N)-
ID, (1)-DVB and (1)-PIDPV. According to the spectra of (2)-
ID and (N)-ID, the peak at 2.86 ppm of (2)-ID in Figure 4 is
attributed to the hydrogen of SACH2, while the peak at 0.98
ppm of (N)-ID in Figure 5 is attributed to the methyl hydro-
gen. The signals of other structures of the two compounds
are basically the same. In the 1H NMR spectrum of (2)-ID,
the peak at 3.40 ppm is attributed to the hydrogen of
NACH2, and the signals in the region of 1.95 to 1.36 ppm
are due to the alkyl hydrogen in the middle of carbon chain
of sulfonylbutyl unit. The aromatic hydrogen of the bromo-
phenyl appears at 8.39 ppm and 7.11–6.75 ppm.
It is well-known that conjugated polyelectrolytes can aggre-
gate in its solution and that aggregated CPEs may be easily
In the 1H NMR spectrum of (N)-DVB in Figure 4, the singlet
at 6.99 ppm is attributed to the aromatic hydrogen of the
phenyl. The triplet at 7.05 ppm and doublets at 5.72, 5.25
ppm are attributed to the vinyl and terminal vinyl, respec-
tively. In addition, the hydrogen of O-CH2 appears at 3.97
ppm. In the 1H NMR spectrum of (1)-DVB in Figure 5, the
signals of those structures mentioned above are basically the
same as (N)-DVB. Furthermore, the peaks at 1.79 ppm, 1.50
ppm and the triplet at 0.98 ppm of (N)-DVB are due to the
hydrogen of butoxy unit. Compared with (N)-DVB, the signal
at 3.77 ppm with quartet at 3.46 ppm of (1)-DVB in the
Figure 5 is attributed to the hydrogen of NACH2 and the tri-
plet at 1.35 ppm is due to the methyl hydrogen.
FIGURE 7 UV–vis spectra of (N)-ID (4.379 3 1025 M in CH2Cl2),
(1)-DVB (1.057 3 1024 M in DMSO) and (1)-PIDPV (9.654 3
1025 M in DMSO). [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
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PPV in bromoethane, and the neutral PPV was synthesized
by Gilch reaction. However, the synthesis of completely
charged cationic PPV can not be achieved because the low
boiling point of bromoethane prevents the nucleophilic sub-
stitution reaction from being carried out at elevated temper-
ature, which results in an incompletely quaternization. Most
of the PPVs can exhibit strong fluorescence emission and the
fluorescence can be effectively quenched by different
quenchers, which provides a potential for PPVs to apply as
materials in the chemical and biological sensors. Further-
more, the first observed quenching effect in CPEs was in the
investigation of the fluorescence quenching of MPS-PPV by
methyl viologen (MV21).50 We have mentioned that ID is an
excellent electron-withdrawing group which suggests that
the two ID-based CPEs (1)-PIDPV and (2)-PIDPV have the
ability of accepting electrons. Here, the fluorescence quench-
ing effects of PPV/PIDPV complexes were investigated to
reveal the interactions between PPV and oppositely charged
PIDPV.
FIGURE 8 UV–vis spectra of (1)-PPV in aqueous solution under
different concentration of (2)-PIDPV. [Color figure can be
viewed in the online issue, which is available at wileyonlineli-
brary.com.]
Fluorescence Quenching Mechanisms
Two standard mechanisms51 are used to explain the fluores-
cence quenching effect: (1) static quenching (a) which is due
to the formation of fluorophore/quencher complexes in the
ground state; (2) dynamic quenching (b) which results from
the random collision between the fluorophore and quencher,
so the dynamic quenching is also called collisional quench-
ing. Static and dynamic quenching can be distinguished by
absorbed on the chromatography column, so it is difficult to
get precise molecular weight information of CPEs from gel
permeation chromatography (GPC). The key reason is that it
is very hard to find a suitable solvent to meet the requests
of the measurement. Furthermore, owing to the aggregation
phenomenon of CPEs, light scattering which is the common
technique to measure the molecular weight as same as GPC
is not available, too.46 In this paper, the two CPEs (2)-PIDPV
and (1)-PIDPV were dialyzed against deionized water using
a 4KD MWCO cellulose membrane, which is the same with
the method reported in our previous work.35 This approach
can not only remove impurities but also ensure that the
molecular weight of (2)-PIDPV and (1)-PIDPV are more
than 4000 (at least four constitutional repeating units).
Although we can only get a general result in this way, but it
is enough to prove that the polymerization of the two CPEs
has been completed successfully and to satisfy the require-
ment of photophysics measurement.
Ka
hm
ꢁ
ƒ!
F1Q ꢀ ½F; Qꢀ
½F ; Qꢀ ! F1Q
(1)
(2)
kq
ꢁ
ƒ!
F 1Q
F1Q
the absorption spectra of the fluorophore. No changes of
the absorption spectra can be observed in the dynamic
quenching because it only affects the excited states of the
fluorophore. However, in the static quenching the formation
of ground-state complex will exhibit different absorption
behavior and result in perturbation of the absorption
spectra.51,52
Fluorescence Quenching Investigation of PPV/PIDPV
Complexes
Poly(p-phenylenevinylene) (PPV) has been used as the elec-
tron donor in the polymer solar cells and as the active layer
in light emitting diodes (LEDs) due to its excellent process-
ability and favorable electronic and spectroscopic properties
in the past years. Poly[2-methoxy-5-(2-ethyl)hexoxy-1,4-phe-
nylenevinylene] (MEH-PPV) is the first conjugated polymer
to use in the BHJ solar cells47 and double layers organic
solar cells,48 and now it has become a kind of typical elec-
tron donor materials. Furthermore, the negatively charged
PPV such as poly(5-methoxy-2-(3-sulfopropoxy)21,4-phenyl-
enevinylene) (MPS-PPV)49 was obtained by modified with
sulfonyl chloride groups and it created a brand new research
field of novel synthetic method and frontier applications for
conjugated polyelectrolytes. Compared with MPS-PPV, the
cationic PPV was prepared by quaternization of the neutral
As shown in the equations (a) and (b), F* is an excited-state
fluorophore, Q is a quencher, rq is the bimolecular quenching
rate constant and Ka is the association constant for formation
of the ground-state complex [F, Q].
And both quenching mechanisms can be quantitatively
described by the Stern–Volmer equation:
I0=I511KSV ½Qꢀ
where I0 and I are the fluorescence intensities of the system
in the absence and presence of the quencher, respectively,
and KSV is the Stern–Volmer quenching constant. I0/I versus
[Q] is expected to give a linear plot according to the Stern–
Volmer equation.
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FIGURE 11 Stern–Volmer plot for the fluorescence quenching
of (1)-PPV under different concentration of (2)-PIDPV. [Color
figure can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
FIGURE 9 UV–vis spectra of (2)-PPV in aqueous solution under
different concentration of (1)-PIDPV. [Color figure can be
viewed in the online issue, which is available at wileyonlineli-
brary.com.]
Fluorescence Quenching of PPV
As shown in Scheme 2, the level of the quarternization of
(1)-PPV is determined to be 50% which is a rough estimate
according the NMR and the value is the same with the result
in our previous work.36 Investigations of the optic properties
of (1)-PPV/(2)-PIDPV and (2)-PPV/(1)-PIDPV complexes
in the aqueous solution were carried out. As shown in Figure
8, with addition of (2)-PIDPV, the absorption of (1)-PPV at
386 nm is overlapped with the absorption of (2)-PIDPV at
370 nm leading to an increase of absorbance at 380 nm. The
new absorption at 580 nm appearing in the spectra is attrib-
uted to the (2)-PIDPV. (2)-PPV gives a similar phenomenon
in Figure 9 in the presence of (1)-PIDPV. These properties
indicate that interaction between PPVs and the oppositely
charged PIDPV does not exist in the ground state and the
absorbance of the PPVs just exhibits a linear superposition
with increasing concentration of the oppositely charged
PIDPV. Furthermore, according to the absorption spectra of
PPVs, it can be concluded that dynamic quenching is the
leading factor of the quenching mechanism between PPVs
and oppositely charged PIDPV.
Figure 10 shows the photoluminescence (PL) spectra of (1)-
PPV in the presence of (2)-PIDPV which was measured with
excitation wavelength at 440 nm. Figure 11 gives the Stern–
Volmer plot for the fluorescence quenching of (1)-PPV by
(2)-PIDPV with detection wavelength at 528 nm. It is
obvious that the PL intensity of (1)-PPV is quenched effec-
tively with addition of (2)-PIDPV (0–10 3 1027 M with
repeat units) to the dilute solution of (1)-PPV (c 5 5 3
1025 M with repeat units). As shown in Figure 11, the
Stern–Volmer plot for fluorescence quenching of (1)-PPV is
linear with KSV 5 1.01 3 106 M21 for the concentration of
(2)-PIDPV in the range of 0–6 3 1027 M. The results show
that the fluorescence emission of (1)-PPV is quenched effec-
tively by the (2)-PIDPV at a very low concentration, which
suggests that (1)-PPV exhibits a very high sensitivity to the
oppositely charged quencher (2)-PIDPV. With the increasing
concentration of (2)-PIDPV, the Stern–Volmer plot has a
tendency to be curved upward and this phenomenon indi-
cates that besides dynamic quenching some other processes
are involved in the quenching behavior of (1)-PPV/(2)-
PIDPV system, including static quenching,53 ion-pair complex
formation between the PPV and the quencher, interchain
exciton diffusion in the complex of (1)-PPV/(2)-PIDPV,54
chromophore aggregation and variation with varying concen-
tration of quencher.55
FIGURE 10 PL spectra of (1)-PPV in aqueous solution under
different concentration of (2)-PIDPV. [Color figure can be
viewed in the online issue, which is available at wileyonlineli-
brary.com.]
Herein, we display a model to explain the fluorescence
quenching mechanism between PPV and oppositely charged
PIDPV. As shown in Figure 12, ID and DVB segments are,
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FIGURE 12 The assumed model of the fluorescence behavior of (1)-PPV/(2)-PIDPV complexes. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
respectively, stand for isoindigo unit and 1,4-divinyl-benzene
unit while PPV and PIDPV segments are, respectively, repre-
sent the backbone of poly(p-phenylenevinylene) and ID-
based conjugated polymer synthesized in this article. At such
a low concentration of c 5 5 3 1025 M with repeat units,
the (1)-PPV aggregates very weakly in the aqueous solution
and thus exhibits strong fluorescence emission, but when the
(2)-PIDPV was added into its dilute solution, ion-pair com-
plexes of (1)-PPV and the quencher (2)-PIDPV were
induced to be formed by Coulombic attraction between the
ionic units. Upon absorption of light, the excitions can trans-
fer from the fluorophore (1)-PPV to the quencher (2)-
PIDPV due to the excellent electron accepting properties of
the isoindigo in the main chain of (2)-PIDPV. Therefore, the
fluorescence of (1)-PPV was efficiently quenched in the
presence of (2)-PIDPV, and the ultrafast interchain transfer
of the excitions within the fluorophore-quencher system
results in a large KSV value.
The optical spectra of (2)-PPV shows similar properties
with (1)-PPV. Figure 13 gives the photoluminescence (PL)
spectra of (2)-PPV in the presence of (1)-PIDPV which was
measured with excitation wavelength at 370 nm. Figure 14
gives the Stern–Volmer plot for the fluorescence quenching
between (2)-PPV and (1)-PIDPV with detection wavelength
at 502 nm. Addition of (1)-PIDPV (0–10 3 1027 M with
repeat units) into the dilute solution of (2)-PPV (c 5 5 3
1025 M with repeat units) results in an efficient fluorescence
FIGURE 13 PL spectra of (2)-PPV in aqueous solution under
different concentration of (1)-PIDPV. [Color figure can be
viewed in the online issue, which is available at wileyonlineli-
brary.com.]
FIGURE 14 Stern–Volmer plot for the fluorescence quenching
of (2)-PPV under different concentration of (1)-PIDPV. [Color
figure can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
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FIGURE 17 PL spectra of (2)-PPV in aqueous solution under
different concentration of PDDC. [Color figure can be viewed in
the online issue, which is available at wileyonlinelibrary.com.]
FIGURE 15 UV–vis spectra of (2)-PPV in aqueous solution
under different concentration of PDDC. [Color figure can be
viewed in the online issue, which is available at wileyonlineli-
brary.com.]
(PDDC) and of (1)-PPV in the presence of poly(sodium-p-
styrenesulfonate) (PSS). PDDC and PSS are cationic and ani-
onic polymers respectively, and they are two conventional
polyelectrolytes but not conjugated polymers.
quenching of (2)-PPV at a low concentration. As shown in
Figure 14, the Stern–Volmer plot for the fluorescence
quenching of (2)-PPV shows
K
a linear response with
SV 5 1.71 3 106 M21 for the concentration of (1)-PIDPV in
the range of 0–6 3 1027 M and it tends to be curved
upward with the increasing concentration of (1)-PIDPV. The
mechanisms of this quenching effect of (2)-PPV is similar
with (1)-PPV. The research on the fluorescence quenching of
PPVs/CPEs complexes using CPE as the quencher provides a
possibility to research on the quenching effect between the
oppositely charged polymers.
As shown in Figure 15, unconspicuous changes are observed
in the UV–vis spectra of (2)-PPV with addition of PDDC. Fig-
ure 16 gives a similar phenomenon of (1)-PPV in the pres-
ence of PSS. Figure 17 shows the PL spectra of (2)-PPV in
the presence of PDDC which was measured with excitation
wavelength at 370 nm and Figure 18 gives the PL spectra of
(1)-PPV in the presence of PSS which was measured with
excitation wavelength at 440 nm. It is obvious that the fluo-
rescence of (2)-PPV is violently quenched by PDDC while
the fluorescence of (1)-PPV exhibits an insignificant
enhancement with addition of PSS. The results may be
caused by the different charge density of the two conven-
tional polymers. According to the report, the charge density
To further study the interactions between PPVs and polyelec-
trolytes, we also investigate the optic properties of (2)-PPV
in the presence of poly(diallyldimethylammonium chloride)
FIGURE 16 UV–vis spectra of (1)-PPV in aqueous solution
under different concentration of PSS. [Color figure can be
viewed in the online issue, which is available at wileyonlineli-
brary.com.]
FIGURE 18 PL spectra of (1)-PPV in aqueous solution under
different concentration of PSS. [Color figure can be viewed in
the online issue, which is available at wileyonlinelibrary.com.]
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FIGURE 19 The assumed model of the fluorescence behavior of (1)-PPV/PSS complexes. [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
of PDDC is calculated to be 6.19 mmol/g (meg/g) which is
higher than PSS. As a result, the electronic attraction
between (2)-PPV and PDDC is much stronger than the
attraction force between (1)-PPV and PSS so that the forma-
tion of (2)-PPV/PDDC complexes by ion pairing is very tight
and the fluorescence of (2)-PPV is drastically quenched.56,57
PSS are induced by electrostatic attraction of the ionic side
groups and as a result the distance of the main chains of
(1)-PPV is increased slightly. Finally, the exciton transfer
between the main chains is avoided by the inserted PSS
chains and the self-quenching of (1)-PPV is inhibited to a
certain extent. Thus, the PL spectrum of (1)-PPV shows a
weak fluorescence enhancement in the presence of PSS.
Two assumed models are displayed here to illustrate the
interactions between the water-soluble PPVs and the oppo-
sitely charged conventional polymers. The model of (1)-
PPV/PSS complexes is shown in Figure 19 where PSS and
PPV segmers are, respectively, stand for poly(sodium-p-styre-
nesulfonate) and the backbone of poly(p-phenylenevinylene).
When PSS was added into the dilute aqueous solution of
(1)-PPV, the formation of complexes between (1)-PPV and
Moreover, the model of (2)-PPV/PDDC complexes is dis-
played in Figure 20 where PDDC and PPV segmers are
respectively stand for poly(diallyldimethylammonium chlo-
ride) and the backbone of poly(p-phenylenevinylene). We
have mentioned that PPV only aggregates weakly in the
aqueous solution with a low concentration thus exhibits
strong fluorescence emission. When PDDC is added,
FIGURE 20 The assumed model of the fluorescence behavior of (2)-PPV/PDDC complexes. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
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FIGURE 23 UV–vis spectra of (2)-PPV, (1)-PIDPV films and
their blend film ((2)-PPV/(1)-PIDPV 5 1/1, c/c [repeat unit], on
quartz substrate). [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
FIGURE 21 UV–vis spectra of (1)-PPV, (2)-PIDPV films and
their blend film ((1)-PPV/(2)-PIDPV 5 1/1, c/c [repeat unit], on
quartz substrate). [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
respectively, show the UV–vis and PL spectra of (1)-PPV,
(2)-PIDPV films and their blend film ((1)-PPV/(2)-
PIDPV 5 1/1, c/c [repeat unit]). It is obviously that the fluo-
rescence of (1)-PPV is completely quenched in the presence
of (2)-PIDPV in the solid state while the UV–vis spectrum of
the blend film just show a superposition of (1)-PPV and
(2)-PIDPV, which proves that the interaction between the
two oppositely charged polymers does not exist in the
ground state. (2)-PPV and (1)-PIDPV give a similar result as
shown in Figures 23 and 24. The fluorescence emission of
(2)-PPV is almost completely quenched with addition of
(1)-PIDPV in the solid state while the UV–vis spectrum of
the blend film show a superposition of (2)-PPV and (1)-
PIDPV. The phenomena mentioned above indicate the photo-
induced electron transfer and exciton diffusion between the
complexes of (2)-PPV and PDDC are formed due to the elec-
trostatic attraction between the ionic units and the attraction
force is very strong because of the high charge density of
PDDC. Driven by the strong attraction the two polymers
twist tightly so that the complexes may form a colloid in the
aqueous solution. In the circumstances the solution is not a
real solution but a colloidal solution, therefore, the fluores-
cence of (2)-PPV is almost quenched completely.58 The
results indicate that the fluorescence quenching effect of
(2)-PPV/PDDC complexes is completely different from the
quenching mechanism of the PPV-PIDPV system which is
governed by the standard quenching mechanisms.
Furthermore, we have also investigated the optic properties
of the polymers in the solid state. Figures 21 and 22,
FIGURE 22 PL spectra of (1)-PPV film and the blend film of
(1)-PPV and (2)-PIDPV ((1)-PPV/(2)-PIDPV 5 1/1, c/c [repeat
unit], on quartz substrate). [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
FIGURE 24 PL spectra of (2)-PPV film and the blend film of
(2)-PPV and (1)-PIDPV ((2)-PPV/(1)-PIDPV 5 1/1, c/c [repeat
unit], on quartz substrate). [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
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chains of oppositely charged PPVs and PIDPV.59 These prop-
erties suggest that (1)-PIDPV and (2)-PIDPV can be used as
the active matrix in the construction of CPE-based photovol-
taic cells.
10 V. Tamilavan, K. H. Roh, R. Agneeswari, D. Y. Lee, S. Cho,
Y. Jin, S. H. Park, M. H. Hyun, J. Polym. Sci., Part A: Polym.
Chem. 2014, 52, 3564–3574.
11 J. H. Seo, A. Gutacker, B. Walker, S. Cho, A. Garcia, R.
Yang, T.-Q. Nguyen, A. J. Heeger, G. C. Bazan, J. Am. Chem.
Soc. 2009, 131, 18220–18221.
CONCLUSIONS
12 K. Manoli, M. M. Patrikoussakis, M. Magliulo, L. M. Dumitru,
M. Y. Mulla, L. Sabbatini, L. Torsi, Org. Electron. 2014, 15,
2372–2380.
Two novel ID-based conjugated polyelectrolytes (1)-PIDPV
and (2)-PIDPV were synthesized and characterized, and they
both have favorable coverage of the visible light region. The
fluorescence of water-soluble PPV can be quenched by the
oppositely charged PIDPV at a very low concentration. (1)-
PPV shows an efficient quenching effect with KSV 5 1.01 3
106 M21 in the presence of (2)-PIDPV while (2)-PPV gives
a lager quenching constant with KSV 5 1.71 3 106 M21 in
the presence of (1)-PIDPV. The Stern–Volmer plot of the two
PPVs both are curved upward. In the absorption spectra,
PPVs only exhibit a linear superstition with addition of the
oppositely charged PIDPV, which suggests that dynamic
quenching process is dominant in the mechanisms of the
quenching effect. Two conventional polyelectrolytes PDDC
and PSS were also used to investigate the fluorescence
quenching between PPV and polyelectrolytes. The results
show great difference with PPV/PIDPV complexes. The fluo-
rescence of (2)-PPV is strongly quenched by PDDC while
(1)-PPV exhibits a weak enhancement with addition of PSS.
Moreover, in the solid state the fluorescence of the water-
soluble PPVs is also effectively quenched by the oppositely
charged PIDPV. The excellent optic properties which (2)-
PIDPV and (1)-PIDPV exhibit suggest that the two polymers
can become important materials in the fabrication of ionic
double layers solar cells.
13 J. You, T. Park, J. Kim, J. S. Heo, H.-S. Kim, H. O. Kim, E.
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