Synthesis, one- and two-photon properties of poly[9,10-bis(3,4-bis(2- ethylhexyl-oxy)phenyl)-2,6-anthracenevinylene-alt-N-octyl-3,6-/2, 7-carbazolevinylene]

Article abstract of DOI:10.1002/pola.23807

The synthesis, one- and two-photon absorption (TPA) and emission properties of two novel 2,6-anthracenevinylenebased copolymers, poly[9,10-bis(3,4-bis(2- ethylhexyloxy)phenyl)- 2,6-anthracenevinylene-alt-N-octyl-3,6-carbazolevinyl- ene] (P1) and poly[9,10

Full text of DOI:10.1002/pola.23807

Synthesis, One- and Two-Photon Properties of Poly[9,10-bis(3,4-bis(2-
ethylhexyl-oxy)phenyl)-2,6-anthracenevinylene-alt-N-octyl-3,6-/2,7-
carbazolevinylene]
HAICHANG ZHANG, ERQIAN GUO, XUEHENG ZHANG, WENJUN YANG
Key Laboratory of Rubber-Plastics (QUST), Ministry of Education, School of Polymer Science and Engineering,
Qingdao University of Science and Technology, 53-Zhengzhou Road, Qingdao 266042, People’s Republic of China
Received 22 September 2009; accepted 29 October 2009
DOI: 10.1002/pola.23807
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: The synthesis, one- and two-photon absorption (TPA)
and emission properties of two novel 2,6-anthracenevinylene-
based copolymers, poly[9,10-bis(3,4-bis(2-ethylhexyloxy)phenyl)-
2,6-anthracenevinylene-alt-N-octyl-3,6-carbazolevinyl-ene] (P1) and
poly[9,10-bis(3,4-bis(2-ethylhexyloxy)phenyl)-2,6-anthracenevinyl-
ene-alt-N-octyl-2,7-carbazolevinylene] (P2) were reported. The as-
synthesized polymers have the number-average molecular
weights of 1.56 ꢀ 104 for P1 and 1.85 ꢀ 104 g molꢁ1 for P2 and
are readily soluble in common organic solvents. They emit
strong bluish-green one- and two-photon excitation fluorescence
in dilute toluene solution (UP1 ¼ 0.85, UP2 ¼ 0.78, kem(P1) ¼ 491
nm, kem(P2) ¼ 483 nm). The maximal TPA cross-sections of P1
and P2 measured by the two-photon-induced fluorescence
method using femtosecond laser pulses in toluene are 840 and
490 GM per repeating unit, respectively, which are obviously
larger than that (210 GM) of poly[9,10-bis-(3,4-bis(2-ethylhexyloxy)
phenyl)-2,6-anthracenevinylene], indicating that the poly(2,6-anthra-
cenevinylene) derivatives with large TPA cross-sections can be
obtained by inserting electron-donating moieties into the polymer
C
V
backbone. 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym
Chem 48: 463–470, 2010
KEYWORDS: 2,6-anthracene-vinylene-based polymers; conju-
gated polymers; NLO; photophysics; two-photon absorption
INTRODUCTION Two-photon absorption (TPA) has become
of great interest in the photosciences owing to potential
applications in three-dimensional (3D) fluorescence imag-
ing,1 optical power limitation,2 lasing up-conversion,3 3D op-
tical data storage,4 3D micro-fabrication,5 and photodynamic
therapy.6 A variety of compounds exhibiting TPA properties,
including donor–acceptor–donor (D–A–D) type molecules,
donor–p–bridge–acceptor (D–p–A) type molecules, donor–p–
bridge–donor (D–p–D) type molecules, macrocycles, den-
drimers, polymers, and multibranched compounds have been
synthesized and their structure-property relationships have
been investigated.7 The results of these studies reveal that
TPA cross-sections (d) increases with the donor/acceptor
strength, conjugation length, molecular dimensionality, and
the planarity of the p-center.
conjugated polymers have become the targets of TPA inter-
est.10 However, in comparison with extensively studied small
molecular TPA chromophores, the conjugated polymers with
large d are still scarce at present.7,10–15 Although most typi-
cal conjugated polymers, such as ladder-type poly(p-phenyl-
ene),11 polyfluorene,12 poly(p-phenyleneethynylene),13 poly
[1,6-bis(3,6-dihexadecyl-N-carbazolyl)-2,4-hexadiyne],14 poly
(p-phenylenevinyl-ene)s,15 have been studied to show d >
10,000 GM per repeating unit in nanosecond laser pulses,
the d values measured by using nanosecond pulses are
roughly two to three orders of magnitude larger than those
measured by using femtosecond pulses because of the exis-
tence of excited state absorption in nanosecond laser excita-
tion.7(a),15(b) The real d for those traditional conjugated poly-
mers are rather low. Therefore, there is still a considerable
need for polymeric chromophores exhibiting large d in fem-
tosecond laser pulses.
In electronic, photonic, and optoelectronic fields, two types
of conjugated materials, small molecules and polymers, have
been used. For some practical applications, small molecular
materials have to be incorporated into the host polymer for
avoiding aggregation at high concentration,8,9 and their dis-
perse concentration in the host polymer matrix is limited by
the phase separation. Since the higher degrees of conjugation
could enhance d and the low aggregations could allow higher
concentration of the absorptive and fluorescent centers, the
Recently, to obtain the macromolecules with large d and
reduced aggregation, some hyperbranched polymers16 and
dendrimers17 containing TPA-active units have been synthe-
sized and shown the maximal d up to 600 GM per repeating
unit. Jen and coworkers have reported the synthesis and
metal ion sensing properties of poly[(2,5-bis(p-di-n-butylami-
nostyryl)benzene-1,4-diyl)-alt-(fluorene-2,7-diyl)] with d up
Correspondence to: W. Yang (E-mail: ywjph2004@qust.edu.cn)
C
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 463–470 (2010) 2009 Wiley Periodicals, Inc.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 1 Synthetic routes and
chemical structures of P1 and P2.
to 1000 GM.18 These results imply that the polymers exhibit-
ing large d could be constructed by employing molecular
chromophores with large d as building blocks or repeating
units. In this work, we design and synthesize two novel
donor-containing poly(2,6-anthracenevinylene)-based deriva-
tives (P1 and P2) by Wittig–Homer reaction between 9,10-
bis(3,4-bis(2-ethylhexyloxy)phenyl)-2,6-bis(diethylphosphoryl-
methyl)anthracene and N-octyl-3,6/2,7-diformylcarbazole
(Scheme 1). The incorporation of 2,7- and 3,6-carbazole can
endow polymer backbone with different donor strength and
conjugation length to investigate their one- and two-photon
properties. Although the donor-containing conjugated poly-
mers have been used in electroluminescence, photovoltaic
cell, photoluminescence, and thin film transistor,19 their TPA
properties have rarely been investigated. On the other hand,
to the best of our knowledge, although various anthracene-
based polymers and oligomers, such as poly(2,6-anthrylene),
poly(9,10-anthrylene), poly(9,10-anthracenevinylene), and
their derivatives, have been extensively reported,20 poly(2,6-
anthracenevinylene)s and 2,6-anthracenevinylene-containing
polymers are very scarce at present because of their syn-
thetic inaccessibility before.21 The 2,6 attachment of the vi-
nylene linkage on the anthryl ring could provide novel struc-
tures and properties such as the stronger fluorescence and
larger d compared with the 9,10 attachment under the D–p–
D motif.22 Very recently, we have developed a synthetic route
to high solubility and high-molecular weight of poly(9,10-di-
phenyl-2,6-anthracenevinylene)s.21(b,c) We now report the
synthesis of donor-containing poly(9,10-diphenyl-2,6-anthra-
cenevinylene)-based copolymers P1 and P2 and their large
TPA cross-sections in femtosecond laser pulses. For the sake
of comparison, poly[9,10-bis(3,4-bis(2-ethylhexyloxy)phenyl)-
2,6-anthracenevinylene] (PAV) is also included.
EXPERIMENTAL
Materials
2,6-Dimethyl-9,10-bis(3,4-bis(2-ethylhexyloxy)phenyl)anthra-
cene (C), PAV, p-(N,N-dihexyl-amino)benzaldehyde were
available from previous works.21(c),22(a) N-Octyl-3,6-dibromo-
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ARTICLE
carbazole and N-octyl-2,7-dibromocarbazole were supplied
by professor Bo’s group.23 All the chemicals were purchased
from Aldrich Chemical Co. Toluene, benzene, and tetrahydro-
furan were distillate over metallic sodium before use. Other
solvents and reagents were analytical grade and were used
as received, unless otherwise claimed.
DMF was slowly added. The resulting mixture was stirred
1 h at ꢁ78 ꢂC and for 5 h at room temperature. After
quenching with water, the mixture was extracted with
dichloromethane and solvent was evaporated off. The crude
product was purified by column chromatography on silica
gel using ethyl acetate/hexane (1/10) as the eluent to afford
ꢂ
0.45 g of a yellow solid (yield: 64%), mp 102–104 C.
Measurements
1H NMR (300 MHz, CDCl3): d 10.13 (s, 2H), 8.66 (s, 2H),
8.08 (d, J ¼ 9.0 Hz, 2H), 7.54 (d, J ¼ 9.0 Hz, 2H), 4.38 (t, J ¼
7.5 Hz, 2H), 1.91 (m, 2H), 1.26 (m, 10H), 0.85 ppm (t, J ¼
6.0 Hz, 3H). 13C NMR (125 MHz, CDCl3): d 192.404, 141.723,
135.131, 126.851, 121.790, 121.405, 110.245, 43.614,
31.706, 29.690, 29.280, 29.111, 27.215, 22.556, 14.031. ELEM.
ANAL: Calcd (%) for C22H25NO2: C, 78.77; H, 7.51; N, 4.18; O,
9.54. Found: C, 78.66; H, 7.57; N, 4.24.
1H and 13C NMR spectra were recorded in CDCl3 on a JEOL
JNM-LA-300 (300 MHz) and 125-MHz AVANCE 500 (Bruker)
spectrometer, respectively. Molecular weights were deter-
mined using gel permeation chromatography (GPC, Waters
1515 HPLC) equipped with Styragel columns and using THF
as an eluent with polystyrene standards. The elemental anal-
ysis was performed on Perkin-Elmer 2400. The fluorescence
quantum yield Uf was determined in toluene at room tem-
perature by using quinine in 0.5 M H2SO4 as the reference.
UV–vis absorption spectra were obtained on a Cary500 spec-
trophotometer. Fluorescence measurements were carried out
on an Aminco Bowman series 2 luminescence spectrometer.
The absorption maximum of the compound was used as the
excitation wavelength for the PL measurement.
N-Octyl-2,7-diformylcarbazole (B)
Synthesized by the same procedure as described for N-octyl-
3,6-diformylcarbazole except that N-octyl-2,7-dibromocarba-
zole was used. A white solid of 0.39 g was obtained (yield:
ꢂ
56%), mp 131–133 C
The TPA cross-section of the compounds was measured with
the two-photon-induced fluorescence method by using the
femtosecond laser pulses as described.24 The excitation light
source was a mode-locked Ti:sapphire fs laser (Spectra-
Physics, Tsunami 3941, 700–910 nm, 80 MHz, <120 fs),
which was pumped by a compact cw prolite diode laser
(Spectra-physics, Millennia Pro 5S). The fluorescence signal
1H NMR (300 MHz, CDCl3): d 10.19 (s, 2H), 8.28 (d, J ¼ 9.0
Hz, 2H), 8.00 (s, 2H), 7.80 (d, J ¼ 9.0 Hz, 2H), 4.43 (t, J ¼
7.5 Hz, 2H), 1.91 (m, 2H), 1.27 (m, 10H), 0.85 ppm (t, J ¼
6.0 Hz, 3H). 13C NMR (125 MHz, CDCl3): d 191.499, 144.752,
129.609, 127.807, 124.251, 123.230, 109.760, 43.797,
31.684, 29.230, 29.073, 28.901, 27.176, 22.542, 14.024. ELEM.
ANAL: Calcd (%) for C22H25NO2: C, 78.77; H, 7.51; N, 4.18; O,
9.54. Found: C, 78.71; H, 7.55; N, 4.21.
was recorded by
a spectrofluorometer (Ocean Optics,
USB2000). Samples were dissolved in toluene at concentra-
tions of 1.0 ꢀ 10ꢁ4 M in repeating unit and the two-photon
induced fluorescence intensity was measured at 700–900
nm by using fluorescein (1.1 ꢀ 10ꢁ4 M in water, pH ¼ 11)
as the reference, and the two-photon properties of fluores-
cein have been well characterized in the literature.25 The
intensities of the two-photon induced fluorescence spectra
of the reference and sample under the same measurement
conditions were determined and compared (input power
100 mW, which is among the linear dependence of fluores-
cence intensity on the square of the excitation intensity, Fig.
3). The TPA cross-section of sample ds, measured by using
the two-photon-induced fluorescence measurement tech-
2,6-Bis(diethylphosphorylmethyl)-9,10-bis(3,4-bis(2-ethyl-
hexyloxy)phenyl)anthracene (D)
A mixture of 2,6-dimethyl-9,10-bis(3,4-bis(2-ethylhexyloxy)-
phenyl)anthracene (C) (1.1 g, 1.3 mmol), NBS (0.52 g, 2.92
mmol), and benzoyl peroxide (27 mg, 0.11 mmol) in anhy-
drous benzene (40 mL) was refluxed for 4 h. The suspension
solid was filtered off and the solvent was removed by evapo-
ration under reduced pressure. The residue dried in vacuum
was added triethyl phosphate (30 mL) to be refluxed for
12 h. The excessive triethyl phosphate was distillated out by
reduced pressure and the residue was purified by column
chromatography on silica gel using ethyl acetate/CH2Cl2
(1:2) as the elueꢂnt to afford 0.88 g of white solid (yield:
61%), mp 61–63 C.
nique, can be calculated by using the equation: ds
¼
[(SsUrcr)/(SrUscs)]dr, where the subscripts s and r stand for
the sample and reference molecules, respectively.24 S is the
integral area of the two-photon fluorescence, U is the fluo-
rescence quantum yield, and c is the number density of the
molecules in solution. dr is the TPA cross-section of the ref-
erence molecule.
1H NMR (300 MHz, CDCl3): d 7.70 (d, J ¼ 9.0 Hz, 2H), 7.58
(d, J ¼ 3.0 Hz, 2H), 7.32 (d, J ¼ 9.0 Hz, 2H), 7.08 (dd, J ¼
9.0 Hz, 3.0 Hz, 2H), 6.93 (m, 4H), 3.99 (m, 12H), 3.83 (m,
4H), 3.20 (d, J ¼ 21 Hz, 4H), 1.86 (m, 2H), 1.77 (m, 2H),
1.28–1.70 (m, 32H), 1.20 (t, J ¼ 7.5 Hz, 12H), 0.88–1.05 ppm
(m, 24H). 13C NMR (125 MHz, CDCl3): d 150.329, 148.666,
131.486, 130.806, 130.276, 128.845, 128.658, 128.413,
123.164, 122.839, 116.539, 114.778, 112.546, 71.797,
71.582, 62.401, 39.436, 34.893, 33.782, 30.501, 29.054,
23.829, 23.023, 16.416, 14.048, 11.110. ELEM. ANAL: Calcd
(%) for C68H104O10P2: C, 71.42; H, 9.17; O, 13.99; P, 5.42.
Found: C, 71.38; H, 9.26.
Synthesis of Monomers
N-Octyl-3,6-diformylcarbazole (A)
1.6 mL of n-Butyllithium (2.85 M in hexane, 4.6 mmol) was
slowly added to a solution of N-octyl-3,6-dibromocarbazole
(0.92 g, 2.1 mmol) in anhydrous THF (20 mL) at ꢁ78 ꢂC
under nitrogen by using a syringe. The mixture was stirred
at that temperature for 1 h and then 1 mL of anhydrous
ANTHRACENEVINYLENE-BASED COPOLYMERS, ZHANG ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 1 One- and Two-Photon Properties of PAV, P1, and P2 in Toluene
c
Cpd
Mnꢄ10ꢁ4 (PDI)
kmax
kfl
Ud
kTPA
dmax
a
b
e
f
~
Dv
PAV
P1
P2
a
3.22 (3.37)
1.56 (2.04)
1.85 (2.71)
346, 446
496
491
483
2,210
2,100
2,180
0.50
0.85
0.78
790
800
810
210
840
490
353, 419, 445
354, 414, 437
d
e
The peak wavelength in the one-photon absorption spectra in nano-
meter (nm).
Fluorescence quantum yield.
Peak wavelength of the two-photon absorption spectra in nanometer
b
Peak wavelength of the one-photon fluorescence spectra in nanometer
(nm).
f
(nm).
The peak TPA cross-section in 10ꢁ50 cm4 s photonꢁ1 (GM).
c
Stokes shift in cmꢁ1
.
Polymerization
Poly[(9,10-bis(3,4-bis(2-ethylhexyloxy)phenyl)-2,6-
prepare N-octyl-3,6-diformyl-carbazole (A) and N-octyl-2,7-
diformylcarbazole (B), the corresponding dibromo-carbazoles
were treated with n-butyllithium in anhydrous THF and then
quenched by N,N-dimethylformamide. The radical-initiated bro-
mination of C with NBS in anhydrous benzene followed by the
treatment with P(OC2H5)3 to afford 2,6-bis(di-ethylphosphoryl-
methyl)-9,10-bis(3,4-bis(2-ethylhexyloxy)phenyl)anthracene (D).
All the intermediates were purified by column chromatography
anthracenevinylene)-alt-(9-oct-yl-carbazole-3,6-diyl)] (P1)
A solution of N-octyl-3,6-diformylcarbazole (A) (0.067 g,
0.20 mmol) and 2,6-bis(diethylphosphorylmethyl)-9,10-bis
(3,4-bis(2-ethylhexyloxy)phenyl)-anthracene (D) (0.225 g,
0.20 mmol) in anhydrous toluene (10 mL) was degassed and
ꢂ
then stirred for 5 min at 80 C under nitrogen. t-BuOK (0.11
1
g, 0.96 mmol) was added in portions and then stirred 3 h at
100 ꢂC. p-Dihexylaminobenzaldehyde (12 mg, 41 lmol) was
added and then reacted another 1 h. The mixture was
poured into 100 mL of methanol to precipitate the polymer.
The collected solid was dissolved into chloroform and fil-
tered through a short pad of silica gel column. The filtrate
was concentrated to ꢃ10 mL and precipitated into stirred
ethanol (50 mL). The formed precipitate was collected and
dried under vacuum to afford P1 as a yellow solid. 0.17 g
(yield: 72%).
on silica gel and characterized by H NMR and 13C NMR spec-
troscopy and elemental analysis. It has been shown that the
Wittig–Hornor route produces polymers of well-defined struc-
ture, which are practically all trans vinylene bonds and simplify
the structures.26 Therefore, the Wittig–Horner coupling
between 2,6-bis(diethylphosphorylmethyl)anthracene (D) and
the corresponding diformylcarbazole (A and B) was chosen to
synthesize the copolymers P1 and P2.
The as-synthesized P1 and P2 are readily soluble in common
organic solvents, such as toluene, chloroform, dichlorome-
thane, and tetrahydrofuran with the solubility > 20 mg
mLꢁ1. We attribute the good solubility of the polymers to
the presence of plenty of flexible side chains, which mini-
mize polymer interchain interactions. We employed GPC
using THF as the eluent and calibrating against polystyrene
standards to determine the molecular weight of the poly-
mers. P1 and P2 possess the number-average molecular
weights (Mn) of ꢃ1.56 ꢀ 104 and 1.85 ꢀ 104 g molꢁ1, and
the polydispersity indices of 2.04 and 2.71, respectively. The
average numbers of repeating units of the as-synthesized
polymers are estimated to be ꢃ13–15. Although the Mn val-
ues might be overestimated as observed in other conjugated
polymers,27 the as-synthesized polymers are readily film-
forming by spin-coating their solutions (the optoelectronic
properties in film states is under investigation).
1H NMR (300 MHz, CDCl3): d 8.31 (b, 2H), 8.04 (b, 2H), 7.73
(b, 4H), 7.45 (m, 2H), 7.32 (m, 2H), 7.18 (b, 6H), 7.04 (b,
4H), 4.31 (b, 2H), 3.95 (m, 8H), 1.95 (m, 6H), 1.27–1.61 (m,
42H), 0.91 ppm (m, 27H). ELEM. ANAL: Calcd (%) for
[C82H107NO4]n: C, 84.12; H, 9.21; N, 1.20, O, 5.47. Found: C,
84.83; H, 9.13; N, 1.17.
Poly[(9,10-bis(3,4-bis(2-ethylhexyloxy)phenyl)-2,6-
anthracenevinylene)-alt-(9-oct-yl-carbazole-2,7-diyl)] (P2)
Synthesized by the same procedure as described for P1
except that N-octyl-2,7-diformylcarbazole (B) was used. P2
was also a yellow solid. 0.15 g (yield: 64%).
1H NMR (500 MHz, CDCl3): d 8.16 (b, 2H), 7.96 (b, 2H), 7.77
(b, 4H), 7.48 (m, 3H), 7.31 (m, 3H), 7.15–7.25 (m, 6H), 7.02
(b, 2H), 4.38 (b, 2H), 3.92 (m, 8H), 1.91 (b, 6H), 1.25–1.60
(m, 42H), 0.93 ppm (m, 27H). ELEM. ANAL: Calcd (%) for
[C82H107NO4]n: C, 84.12; H, 9.21; N, 1.20, O, 5.47. Found: C,
83.84; H, 9.30; N, 1.22.
Linear Optical Properties of Polymer Solutions
The photophysical properties of P1 and P2 are investigated
in dilute toluene solutions. For the sake of comparison,
homopolymer PAV21(b) is also included. The normalized solu-
tion absorption and fluorescence spectra of P1, P2, and PAV
are depicted in Figures 1 and 2, respectively. The corre-
sponding photophysical data are summarized in Table 1. The
incorporation of carbazole unit into the polymer backbone
increases the relative intensities of the longest wavelength
absorption band (Fig. 1). Moreover, both the emission
RESULTS AND DISCUSSION
Synthesis and Characterization
The synthesis and chemical structures of the copolymers
P1 and P2 are shown in Scheme 1. N-Octyl-3,6-dibromocarba-
zole and N-octyl-2,7-dibromocarbazole are supplied by Bo’s
group.23 2,6-Dimethyl-9,10-bis(3,4-bis(2-ethylhexyloxy)phenyl)-
anthracene (C) and PAV are from a previous study.21(c) To
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FIGURE 1 UV–Vis absorption spectra of P1, P2, and PAV in tol-
uene solution. Concentration ¼ 1.0 ꢀ 10ꢁ4 mol Lꢁ1 in repeating
unit.
FIGURE 2 One-photon fluorescence spectra of P1, P2, and PAV
in toluene. Concentration ¼ 1.0 ꢀ 10ꢁ4 mol Lꢁ1 in repeating unit.
excited-state excitation.15 The polymer concentration is 1.0
spectra (kfl) and the longest wavelength absorption bands
ꢀ 10ꢁ4 mol Lꢁ1 in repeating unit.
(kabs) of P1 (kfl ¼ 491 nm, kabs ꢅ 433 nm) and P2 (kfl
¼
To confirm the occurrence of nonlinear absorption, the two-
photon excitation fluorescence of P1 and P2 were recorded
by changing the input laser powers (20–160 mW) under
800 nm, which falls within the strong linear (one-photon)
absorption band of these polymer solutions. These 2,6-
anthracenevinylene-based polymers have strong linear
absorption around 300–500 nm, but no absorption in the
spectral range of 550–1100 nm. If the polymer solutions are
irradiated with an 800 nm of laser pulses, there should not
be any one-photon absorption induced photoluminescence.
However, we have observed the strong fluorescence emission
from the polymer solutions under different laser intensities.
Figure 3 presents that the output fluorescence intensity of
483 nm, kabs ꢅ 426 nm) are hypsochromatically shifted to
some extent compared with that of PAV (kfl ¼ 496 nm, kabs
ꢅ 446 nm) (Figs. 1 and 2). This implies that the insertion of
3,6- and 2,7-carbazole into PAV backbone has shortened the
effective conjugation length of the corresponding polymer.
On the other hand, although P1 and P2 have the similar
shape of absorption spectra and almost same absorption
onset, the lower energy absorption bands of P1 and P2 are
located at the different wavelength regions (Fig. 1), which is
consistent with their different PL spectra that P1 shows less
blue-shift PL spectrum than P2. The different hypsochromic
shift of the absorption and emission spectra for P1 and P2
indicates that the optical properties of these conjugated
materials are highly dependent on both the nature of the
active building blocks and the way in which they are linked.
It is well known that, in comparison between 3,6- and 2,7-
carbazole, 3,6-carbazole has a stronger electron-donating
ability and 2,7-carbazole has a better conjugation-extending
ability. To this 2,6-anthracenevinylene-based system, the con-
tribution to the spectral blue-shift from the conjugation-
extension of 2,7-carbazole is over that from the strong donor
strength of 3,6-carbazole. The PL spectra of P1, P2, and PAV
are less resolved and reflect the lack of intrachain ordering
that is due to the twist structure between phenyl and
anthryl ring and plenty of flexible side chains and the kink-
like carbazole segments (especially for 3,6-carbazole).28 P1
and P2 emit strong bluish-green fluorescence with the PL
quantum yields (Uf) of 0.85 and 0.78, respectively, measured
relative to quinine (Uf ¼ 0.50 in 0.5 M H2SO4).29 These two
Uf values are significantly higher than that of PAV (Table 1).
FIGURE 3 The dependence of output fluorescence intensity of
polymers P1 and P2 in toluene on the input laser power under
the excited wavelength of 800 nm. The inset is the linear de-
pendence of logarithmic output fluorescence intensity (up-
conversion signal) on logarithmic input laser power. Concentration
¼ 1.0 ꢀ 10ꢁ4 mol Lꢁ1 in repeating unit.
Two-Photon Optical Properties of Polymer Solutions
We used two-photon-induced fluorescence measurement
technique to investigate the two-photon properties of the
three polymers. The femtosecond laser pulses (120 fs) were
employed for avoiding possible complications due to the
ANTHRACENEVINYLENE-BASED COPOLYMERS, ZHANG ET AL.
467

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
(repeating units). It is also interesting to note that PAV itself
shows appreciable TPA cross-section (210 GM), which is
large among poly(arylenevinylene)s reported in literatures in
FIGURE 4 Two-photon excitation spectra of P1, P2, and PAV in
toluene under the excitation power of 100 mW. Concentration
¼ 1.0 ꢀ 10ꢁ4 mol Lꢁ1 in repeating unit.
P1 and P2 solutions is nonlinearly increased with the input
laser power. The plot of logarithmic output fluorescence in-
tensity versus logarithmic input laser power gives a power-
law dependence of exponent 2.07–2.13 (the inset of Fig. 3),
which is indicative of a two-photon excitation process. As
predicted,7 there is a good spectral overlap between the one-
and two-photon excitation fluorescence for both P1 and P2
(Fig. 5, vide post), indicating that the fluorescence emission
occurs from the same excited states, regardless of the mode
of excitation.
The TPA cross-sections (d) are determined under 100 mW of
input laser power (which falls within the power range of
two-photon excitation) as a function of excitation wavelength
(700–900 nm). The two-photon excitation spectra for P1, P2,
and PAV were depicted in Figure 4. The relevant spectro-
scopic parameters were summarized in Table 1. It can be
seen that all polymers exhibited broad TPA bands with the
maximal TPA cross-sections (dmax) around 800 nm. The max-
imal TPA cross-sections (dmax) of P1, P2, and PAV were 840,
490, and 210 GM per repeating unit, respectively. PAV shows
the smallest TPA cross-sections among these three polymers
although the degree of conjugation along polymer backbone
for PAV is the best. This can be ascribed to the absent donor
substituent across the 2,6-anthracenevinylene unit. Compar-
ing between 3,6- and 2,7-linkages of carbazole, 3,6-carbazole
is a stronger electron-donating moiety and a weaker conjuga-
tion-extending block, but P1 exhibits obviously larger dmax
value than P2, which indicates that, at least in this system,
the incorporation of strong electron-donating moieties into
the polymer backbone to form D–p–D motif is more effective
in enhancing TPA cross-sections than the extension of conju-
gation length. Nevertheless, the d values of P1 and P2 are
fairly large and obviously higher than that of the linear and
hyperbranched conjugated polymers reported in literatures
in terms of femtosecond laser pulses,11–17 implying that
polymers with large TPA cross-sections can be obtained by
employing effective TPA chromophores as the building blocks
FIGURE 5 Normalized one-photon absorption (OPA) and fluo-
rescence (OPEF), two-photon excitation (TPA) and fluorescence
(TPEF) spectra of P1, P2, and PAV in toluene. The two-photon
excitation spectra are plotted against kTPA/2 (twice the photon
energy).
468
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ARTICLE
terms of femtosecond pulses.15 This might be due to that the
large and planar p-center is favor of the increase of TPA
cross-sections.7 A reasonable comparison among poly(aryle-
nevinylene)s still requires investigation since the measure-
ment of TPA cross-sections is complicated and is interfered
with many factors.
3 He, G. S.; Zhao, C. F.; Bhawalkar, J. D.; Prasad, P. N. Appl Phys Lett
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Maughon, D.; Qin, J.; Rockel, H.; Rumi, M.; Wu, X. L.; Marder, S. R.;
Perry, J. W. Nature 1999, 398, 51–54.
5 Zhou, W.; Kuebler, S. M.; Braun, K. L.; Yu, T.; Cammack, J. K.; Ober, C.
The normalized one-photon absorption, fluorescence, and the
two-photon fluorescence and excitation spectra for these
polymer solutions were depicted in Figure 5. The two-pho-
ton allowed state (kTPA/2, twice the photon energy) of PAV,
P1, and P2 were all located at shorter wavelengths than the
longest wavelength absorption bands (the lowest energy
absorption maxima). This is consistent with the prediction
that the two-photon allowed states for quadrupoles are at a
higher energy than the Franck–Condon states (one-photon
allowed states).30
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CONCLUSIONS
We have synthesized two novel donor-containing 2,6-anthra-
cenevinylene-based copolymers by the Wittig–Hornor cou-
pling between 9,10-bis(3,4-bis(2-ethylhexyloxy)-phenyl)-2,6-
bis(diethylphosphorylmethyl)anthracene and N-octyl-3,6-
diformyl-carbazole (P1) and N-octyl-2,7-diformylcarbazole
(P2), and their TPA cross-sections (dTPA) are measured by
the two-photon induced fluorescence method using femto-
second pulses. P1 and P2 have high-molecular weights (Mn
¼ 1.6–1.8 ꢀ 104) and high-fluorescence quantum yields (Uf
¼ 0.85–0.78). They exhibit strong TPA properties and the
maximal dTPA of P1 and P2 are 840 GM and 490 GM per
repeating unit, respectively. These dTPA values are obviously
higher than that (210 GM) of their reference polymer, PAV,
indicating that the incorporation of strong electron-donating
moieties into the polymer backbone to form D–p–D repeat-
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sion of conjugation length. Polymers with large dTPA can be
obtained by employing effective TPA chromophores as the
repeating units.
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This work was supported by NSFC of China (No. 50573036),
Qingdao Agency of Science and Technology (05-1-JC-90), and
Open Project of State Key Laboratory of Supramolecular Struc-
ture and Materials (SKLSSM200707). The authors thank Pingp-
ing Sun (Qingdao University of Science and Technology,
Qingdao, 266042, China) for the measurement of TPA
properties.
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