New emissive organic molecule based on pyrido[3,4-g]isoquinoline framework: Synthesis and fluorescence tuning as well as optical waveguide behavior

Article abstract of DOI:10.1016/j.tet.2013.02.041

In this paper we report the synthesis and crystal structures of emissive organic molecule (1a) based on pyrido[3,4-g]isoquinoline framework as well as its isomers 1b and 1c. The emission quantum yields decrease after transformation of pyridine moieties in 1a into the cyclic-amides in 1b and 1c. The fluorescent spectral results reveal that 1a, 1b, and 1c exhibit no AIE behavior. This is tentatively attributed to intramolecular weak C?H interactions, which may impede the intramolecular rotations based on the crystal structures of 1a and 1c. Interestingly, 1a, 1b, and 1c are emissive in the solid state, and among them 1a possesses the highest emission quantum yield (0.22). Moreover, the fluorescence of 1a in solution and solid state can be reversibly tuned by reactions with trifluoroacetic acid and triethylamine. Microarea PL studies reveal that microrods of 1a and these after exposure to HCl gas show typical waveguide behavior.

Full text of DOI:10.1016/j.tet.2013.02.041

Tetrahedron 69 (2013) 2687e2692
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
New emissive organic molecule based on pyrido[3,4-g]isoquinoline
framework: synthesis and fluorescence tuning as well as optical
waveguide behavior
*
Jianguo Wang, Guanxin Zhang , Zitong Liu, Xingui Gu, Yongli Yan, Chuang Zhang,
*
Zhenzhen Xu, Yongsheng Zhao, Hongbing Fu, Deqing Zhang
Beijing National Laboratory for Molecular Sciences, Organic Solids Laboratory and Photochemistry Laboratory, Institute of Chemistry,
Chinese Academy of Sciences, Beijing 100190, China
a r t i c l e i n f o
a b s t r a c t
Article history:
In this paper we report the synthesis and crystal structures of emissive organic molecule (1a) based on
pyrido[3,4-g]isoquinoline framework as well as its isomers 1b and 1c. The emission quantum yields
decrease after transformation of pyridine moieties in 1a into the cyclic-amides in 1b and 1c. The fluo-
rescent spectral results reveal that 1a, 1b, and 1c exhibit no AIE behavior. This is tentatively attributed to
intramolecular weak C/H interactions, which may impede the intramolecular rotations based on the
crystal structures of 1a and 1c. Interestingly, 1a, 1b, and 1c are emissive in the solid state, and among
them 1a possesses the highest emission quantum yield (0.22). Moreover, the fluorescence of 1a in so-
lution and solid state can be reversibly tuned by reactions with trifluoroacetic acid and triethylamine.
Microarea PL studies reveal that microrods of 1a and these after exposure to HCl gas show typical
waveguide behavior.
Received 16 November 2012
Received in revised form 3 January 2013
Accepted 4 February 2013
Available online 15 February 2013
Keywords:
Isoquinoline
Solid-state emission
Fluorescence tuning
Optical waveguide
Ó 2013 Published by Elsevier Ltd.
1. Introduction
determining the AIE feature of these molecules. Along this vein
many efforts have been taken to explore new molecular frameworks
Emissive organic molecules have been extensively studied for
sensing and molecular imaging for decades. Meanwhile, organic
molecules that exhibit strong emission in the solid states have re-
ceived increasing attention in recent years because of their potential
applications in optoelectronic devices such as optical waveguides,1,2
optically pumped lasers,3 and light-emitting diodes.4 However,
many luminophores are highly luminescent in solutions, but they
become weakly emissive in the solid states. This is usually ascribed
to the formation of detrimental species such as excimers and exci-
plexes in the solid states.5 In recent years, Tang and his co-workers
have reported that siloles,6 tetraphenylethylenes,7 and relevant
molecules show abnormal fluorescent behaviors; theyare weakly or
non-emissive in solution, but they become strongly emissive upon
formation of aggregation states and in the solid states.8 This ab-
normal fluorescent feature was referred to as AIE (aggregation-in-
duced emission). The structural features of siloles and tetraphenyl-
ethylenes include at least: (1) the molecules are not planar; (2) the
pi-components are connected with sigma-bonds. The internal ro-
tations around these sigma-bonds play a significant role in
exhibiting AIE behavior.7e11
In this paper, we report the synthesis and crystal structures of 1a
with pyrido[3,4-g]isoquinoline framework. The initial motivation of
this research is to invent new AIE molecules. Compound 1a entails
pi-components connected bysigma-bonds, thus theyare potentially
AIE molecules according to previous reports.8a,12 Unfortunately,
fluorescent spectral studies reveal that they do not show AIE feature.
However, 1a shows relatively strong emission, which can be tuned
by exposure to HCl. Moreover, microrods of 1a display optical
waveguide behavior.
2. Results and discussion
2.1. Synthesis and characterization
The synthesis of 1a, 1b, and 1c started from compound 2, which
was transformed into 313 after reaction with NH2OH. Compound 3
was allowed to react with (AcO)2O to yield 414 quantitatively. The
Rh-catalyzed oxidative coupling reaction between compound 4 and
1,2-diphenylethyne led to compound 5. Reaction of 5 with 1-
bromohexane in the presence of NaH yielded the O-alkylation
product 1a in 41% yield after separation with column chromatog-
raphy. Besides 1a the N-alkylation products 1b and 1c were also
* Corresponding authors. Tel.: þ86 10 6263 9355; fax: þ86 10 6256 2693; e-mail
address: dqzhang@iccac.ac.cn (D. Zhang).
0040-4020/$ e see front matter Ó 2013 Published by Elsevier Ltd.
http://dx.doi.org/10.1016/j.tet.2013.02.041

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J. Wang et al. / Tetrahedron 69 (2013) 2687e2692
obtained in 30 and 27% yields, respectively (see Scheme 1). The
chemical structures of 1a, 1b, and 1c were confirmed by NMR, MS,
IR, and element analysis data (see Experimental section). Moreover,
crystal structures of 1a and 1c were determined (see below).
C5eC6 and C12eC13 bonds. Fig. S1 depicts the intermolecular
packing and interactions for 1a. There are no intermolecular piepi
interactions, but multiple intermolecular short C/H contacts are
available.
O
O
O
O
OH
O
N
O
N
O
H
ii
iii
H
i
NH
H
H
O
N
N
O
HO
HN
O
O
O
O
O
2
4
3
5
OC6H13
N
O
O
C6H13
C6H13
N
iv
N
N
N
+
N
+
C6H13
OC6H13
OC6H13
O
1a
1b
1c
Scheme 1. The chemical structure and synthetic approach for compounds 1a, 1b, and 1c: (i) hydroxylamine hydrochloride, NaOH, H2O/CH3OH, rt, 2 h, 95%; (ii) (AcO)2O, CH2Cl2,
quantitatively; (iii) 1,2-diphenylethyne, [RhCp
Cl2]2, CsOAc, CH3OH, 60 ꢀC, 16 h; (iv) NaH, DMF, 80 ꢀC, overnight.
*
2.2. Crystal structures
The molecular structure of 1c is not only non-planar, but also
non-central symmetric. The four phenyl rings are out of the central
framework, which is not fully planar. Intramolecular short in-
The crystallographic data of 1a and 1c were provided in Table S1.
Fig. 1 shows the molecular structures of 1a and 1c. The bond
lengths and angles of 1a and 1c are in normal region. The molecular
structure of 1a is central symmetric. The pi-components of 1a are
not coplanar, but the central framework pyrido[3,4-g]isoquinoline
is almost planar; the phenyl rings C13eC14eC15eC16eC17eC18
and C6eC7eC8eC9eC10eC11 form dihedral angles of 46.68ꢀ and
66.26ꢀ with the central framework. The distances of C11/H14 and
ꢀ
ꢀ
teratomic contacts C13eH20 (3.015 A), C20eH13 (3.292 A),
ꢀ
ꢀ
ꢀ
C7eH20 (3.091 A), C44eH41 (3.287 A), C41eH44 (3.045 A), and
ꢀ
C35eH44 (3.131 A) exist within 1c; thus, it is also expected that
these weak intramolecular interactions are not favorable for the
rotations around C7eC8, C14eC15, C35eC36, and C42eC43 bonds.
As shown in Fig. S1, multiple intermolecular short C/H contacts
exist within crystal of 1c, but there are no intermolecular piepi
interactions.
ꢀ
ꢀ
C14/H11 are 3.063 A and 3.425 A, respectively; these weak
intramolecular interactions may impede the rotations around
2.3. Emissive properties in solutions and solid states
Compounds 1a, 1b, and 1c show absorptions around 355, 405,
and 425 nm as shown in Fig. S2. Table 1 lists the absorption maxima
of 1a, 1b, and 1c. Compared to those of 1b and 1c, the absorption
spectrum of 1a is slightly red-shifted. In comparison, they all show
Table 1
The photophysical properties of 1a, 1b, and 1c
c
a
a
Compounds Absorption Fluorescence lmax
Flb
Fs
h
sl
i
hssi
lmax (nm)
(nm) (lex¼360 nm)
(ns) (ns)
1a
1b
1c
278, 362
266, 356
258, 354
447, 470
472, 472
469, 469
0.25
0.098 0.07
0.092 0.033 1.43 0.948
0.22
5.16 7.867
2.35 2.139
a
An apparent decay time constant h
s
i was determined by using the relation h i ¼
s
P
P
n
n
i ¼ 1 ai ꢁ si
=
i ¼ 1 ai (n¼1e3), where si and ai, respectively, represent the in-
dividual exponential decay time constant and the corresponding preexponential
factor,
sl is solution state fluorescence lifetime,
s
s is solid-state fluorescence lifetime.
Fl represents the respective solution fluorescence quantum efficiency, which
b
was measured using quinine in 1 N H2SO4 aqueous solution as the reference
(
F
¼0.55, lex¼346 nm).
c
Fs represents the respective solid-state fluorescence quantum efficiency, which
was measured with calibrated integrating sphere.
emissions around 447 and 470 nm (see Fig. 2A). The emission
quantum yields of 1a, 1b, and 1c in solution were measured. As
listed in Table 1, 1a is the most strongly emissive with the emission
quantum yield of 0.25. It is interesting to note that the emission
quantum yields decrease by gradual transformation of pyridine ring
in 1a into the cyclic-amides in 1b and 1c. The fluorescence lifetimes
of 1a, 1b, and 1c in solution were also measured (see Table 1). They
Fig. 1. Molecular structures of 1a (up) and 1c (below); the hydrogen atoms have been
omitted for clarity.

J. Wang et al. / Tetrahedron 69 (2013) 2687e2692
2689
shifted from 470 to 555 nm after addition of 20 equiv of TFA. Such
fluorescence change can be detected with naked-eye as illustrated
in inset of Fig. 3, where the photos of the solutions of 1a under UV
light irradiation were displayed in the absence and presence of TFA.
Simultaneously, the absorption spectrum of 1a is changed upon
addition of TFA; the absorptions at 356, 405, and 426 nm are
gradually reduced and a new absorption tail till 500 nm emerges
(see Fig. S3). The fluorescence responsiveness of 1a toward TFA is
likely due to the protonation of pyridine moieties in 1a. Moreover,
the fluorescence of 1a can be restored by further addition of trie-
thylamine as shown in Fig. 4. Therefore, the fluorescence of 1a in
solution can be reversibly tuned by addition of acid and base.
Fig. 2. (A) Fluorescence spectra of compounds 1a, 1b, and 1c (1.0ꢁ10ꢂ5 M) in CH2Cl2
(excited at 360 nm); (B) fluorescence spectra of compounds 1a, 1b, and 1c in the solid
state (excited at 360 nm).
are all in nanosecond region. As expected, 1a shows the longest
fluorescence lifetime (5.16 ns).
The fluorescence spectra of 1a, 1b, and 1c in THF were also
measured after addition of different amounts of water. Un-
fortunately, no obvious fluorescence enhancement was observed
for 1a, 1b, and 1c. Thus, 1a, 1b, and 1c do not exhibit AIE behavior.
This is probably due to the intramolecular weak interactions (see
above), which may impede the rotations around the sigma-bonds
(C5eC6 and C12eC13 in 1a, C7eC8, C14eC15, C35eC36, and
C42eC43 in 1c) even in solution.
The fluorescence spectra of 1a, 1b, and 1c in the solid state were
also measured (see Fig. 2B). Compared to those in solution, the
fluorescence spectra of 1a, 1b, and 1c in the solid state are slightly
red-shifted. For instance, the emission maximum of 1a is shifted
from 447 to 470 nm in solution to 473 and 505 nm, respectively, in
the solid state. The emission quantum yields and fluorescence
lifetimes of 1a, 1b, and 1c in the solid state were also measured and
listed in Table 1. Compounds 1a,1b, and 1c are comparably emissive
in the solid state as the respective solutions of 1a, 1b, and 1c. This
agrees well with the observation that their average fluorescence
lifetimes in the solid state are also relatively long (see Table 1). The
following structural features may attribute to the relatively strong
fluorescence of 1a, 1b, and 1c in the solid state: (1) molecules of 1a,
1b, and 1c are non-planar, thus intermolecular piepi interactions
are not favorable (see Fig. S1); (2) intermolecular multiple C/H
interactions will reduce the non-radiative pathways to enhance the
emission efficiency.
Fig. 4. Fluorescence spectra of CH2Cl2 solution of 1a (1.0ꢁ10ꢂ3 M): (a) 1a only, (b)
1aþTFA (20.0 equiv), (c) 1aþTFA (20.0 equiv)þtriethylamine (20.0 equiv); the excita-
tion wavelength was 360 nm.
The fluorescence of 1a in the solid state also shows re-
sponsiveness toward acid. Fig. 5A depicts the variation of the
fluorescence spectrum of 1a upon exposure to HCl gas of different
concentrations. Similarly, the solid fluorescence intensity becomes
weak and red-shifted by increasing the concentration of HCl gas.
The emission color of 1a in the solid state is changed from blue to
green after exposure to HCl gas (320,000 ppm) as illustrated in
Fig. 5B and C, where PL (photo-luminescence) images after expo-
sure 1a to HCl gas (320,000 ppm) for 5 min are displayed. However,
the fluorescence of 1a in the solid state can be restored by just
letting the solid of 1a that was treated with HCl gas in air for
30 min.
2.4. Tuning the fluorescence of 1a by addition of acid and
base
Interestingly, the fluorescence of 1a can be tuned by addition of
acid. As depicted in Fig. 3, the fluorescence of 1a becomes gradually
weak and red-shifted after addition of different amounts of tri-
fluoroacetic acid (TFA). For instance, the emission intensity at
470 nm is reduced by ca. 1500 folds, and the emission maximum is
Fig. 5. (A): Solid-state fluorescence spectra of 1a upon exposure to different concen-
trations of HCl gas for 5.0 min. (B) and (C): PL images of 1a before (B) and after (C)
exposure to HCl gas (320,000 ppm) for 5.0 min.
2.5. Waveguide behavior of microrods of 1a
The microrods of 1a, which were prepared by evaporation of the
solution of 1a in CH2Cl2/MeOH (v/v, 5:1), were excited with a fo-
cused laser down to the diffraction limit at different local positions
along the length of the microrods. Fig. 6A depicts the microarea PL
(photoluminescence) microscopic images for microrods of 1a. In-
terestingly, blue-green emission was detected from both ends of
the microrods of 1a irrespective of the excitation position. In
Fig. 3. Fluorescence spectra of 1a (1.0ꢁ10ꢂ3 M) in CH2Cl2 after addition of different
amounts of TFA (0e20.0 equiv) with lex.¼438 nm; inset shows the photos of CH2Cl2
solution of 1a (1.0ꢁ10ꢂ3 M) in the absence or presence of TFA under UV light (365 nm)
irradiation.

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J. Wang et al. / Tetrahedron 69 (2013) 2687e2692
the propagation distance as depicted in the inset of Fig. 6D. Simi-
larly, the optical loss coefficient at 473 nm was estimated to be
35.11 dB/mm.
3. Conclusion
A new emissive organic molecule (1a) based on pyrido[3,4-g]
isoquinoline framework as well as its isomers 1b and 1c are re-
ported. The emission quantum yields decrease after transformation
of pyridine moieties in 1a into the cyclic-amides in 1b and 1c.
Compounds 1a, 1b, and 1c exhibit no AIE behavior. This may be due
to intramolecular weak C/H interactions, which may impede the
intramolecular rotations based on the crystal structures of 1a and
1c. Interestingly, 1a, 1b, and 1c are emissive in the solid state, and
among them 1a possesses the highest emission quantum yield
(0.22). Moreover, the fluorescence of 1a in solution and solid
state can be reversibly tuned by reactions with acid and base.
Microarea PL studies reveal that microrods of 1a show typical
waveguide behavior with blue-green emission at the ends of
microrods, and these microrods after exposure to HCl gas also ex-
hibit optical waveguide property with green emission at the ends of
microrods.
Fig. 6. Bright-field and microarea PL images of compound 1a, by exciting the microrod
from different positions, (A) before and (B) after exposure to HCl gas; spatially resolved
PL spectra of outcoupled light at a distance of a, b, c, d, e, f, and g (curves from bottom
to top) from the tip of a single microrod, recorded by focused 351 nm laser excitation,
(C) before exposure to HCl gas, (D) after exposure to HCl gas; the insets show the
variation plot of the fluorescence intensities at 472 and 473 nm versus the propagation
distance.
4. Experimental section
4.1. General method
All chemical materials were purchased from Alfa Aesar, Sigma-
general, the emission of light can only be observed at the local area
of the excited position. The appearance of the outcoupling light at
the ends of each microrod of 1a is a typical characteristic of
waveguide behavior.
eAldrich or TCI for direct use. The water used was purified by
Millipore filtration system. Melting points were measured with
1
Buchi B540. H NMR and 13C NMR were collected on Bruker Avance
€
400-MHz spectrometer. MALDI-TOF mass spectra were recorded
with BEFLEX III spectrometer. Absorption spectra were recorded on
UVeviseNIR spectrophotometer (UV-3600, Shimadzu spectrome-
ter). Steady-state fluorescence spectra were recorded with Hitachi
(F-4500) spectrophotometers at 25 ꢀC. The IR spectra were mea-
sured on the IR spectrometer (TENSOR-27). PL images were recor-
ded with Olympus research inverted system microscope (FV1000-
IX81, Tokyo, Japan) equipped with a charge couple device (CCD,
Olympus DP71, Tokyo, Japan) camera; the excitation source is a Hg
lamp equipped with a band-pass filter (330e380 nm). All photo-
graphs were recorded on a Canon digital camera.
The spatially resolved PL spectra were measured in order to gain
further insight into the light waveguide behavior within microrods
of 1a. Fig. 6C shows the collected PL spectra at the end of a single
microrod of 1a under the excitations at different positions (labeled
as a, b, c, d, e, f, and g). The emission spectra upon excitation at
different positions kept almost unaltered. But, the emission in-
tensity at the microrod-ends decreased upon increasing the prop-
agation distance. As depicted in the inset of Fig. 6C, the emission
intensity at 472 nm of the outcoupled light decreased almost ex-
ponentially with the propagation distance. Note that the emission
intensities of the excited points do not change substantially with
the position along the microrods. Thus, the inset of Fig. 6C can also
represent the variation of intensity ratio of incident and outcoupled
light versus the propagation distance. By fitting the data of inset of
Fig. 6C according to the reported procedure,15 the optical loss co-
efficient at 472 nm for microrods of 1a was estimated to be
20.91 dB/mm. Based on the fact that the collected PL spectra at the
end of a single microrod of 1a under the excitations at different
positions are almost the same, self-absorption may not contribute
largely to the optical loss during the light propagation. Thus, it is
assumed that the substrate effect and Rayleigh scattering may in-
duce the optical loss observed for microrod of 1a, according to
previous studies.1,2,16
4.2. Crystal structural analysis
Crystals of 1a and 1c were grown by slow evaporation from the
dichloromethane/methanol mixed solution. All single crystals data
were collected on Rigaku Saturn diffractometer with CCD area
detector. All calculations were performed using the SHELXL97 and
crystal structure crystallographic software packages. Crystallo-
graphic data (excluding structure factors) for the structure(s) re-
ported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no.
CCDC: 905697 for 1a and 905698 for 1c.
As discussed above, the blue-green emission of 1a in the solid
state is changed to green emission upon exposure to HCl gas. In-
terestingly, microrods of 1a after treatment with HCl gas also show
typical optical waveguide behavior. As shown in Fig. 6B, where the
microarea PL microscopic images of the microrod of 1a after ex-
posure to HCl gas (320,000 ppm) were displayed, green lumines-
cence spots at both tips and relatively weaker emission from the
bodies of the microrod were detected. Fig. 6D shows the collected
PL spectra at the end of a single microrod of 1a after exposure to HCl
gas under the excitations at different positions (labeled as a, b, c, d,
e, and f). Again, the fluorescence intensity decreased by prolonging
4.3. Photophysical studies
Fluorescence quantum efficiencies of 1a, 1b, and 1c in the solids
states were recorded on FLSP 920 fluorescence spectroscopy with
a calibrated integrating sphere system. Fluorescence lifetimes of 1a,
1b, and 1c (both the solution state and the solid state) were mea-
sured based on the time-resolved PL experiments, which were
made with a regenerative amplified Ti:sapphire laser (Spectra-
Physics, Spitfire) at 400 nm. The PL spectra were recorded with
a streak camera (C5680, Hamamatsu Photonics) attached to a pol-
ychromator (Chromex, Hamamatsu Photonics), for which the

J. Wang et al. / Tetrahedron 69 (2013) 2687e2692
2691
temporal and spectral resolutions of the detector are w10 ps and
2 nm, respectively. All the spectroscopic measurements were car-
ried out at room temperature.
MALDI-TOF: 684.4 [M]þ. Anal. Calcd for C48H48N2O2: C, 84.17; H,
7.06; N, 4.09. Found: C, 83.95; H, 7.03; N, 4.13.
4.5.2.3. Compound 1c. Yield 27%; mp 309.0e310.2 ꢀC; nFTIR (KBr)
4.4. Optical waveguide measurements
3059, 2954, 2929, 2856, 1641, 1588, 1492, 1442, 1370, 1345, 1326,
1299, 1074, 698 cmꢂ1; 1H NMR (400 MHz, CDCl3):
d (ppm) 8.40 (s,
To measure the microarea PL spectra of single microrod, the
microrods dispersed on a glass cover-slip were excited with an UV
2H), 7.23e7.15 (m,16H), 7.10 (d, J¼6.7 Hz, 4H), 3.77 (d, J¼7.8 Hz, 4H),
1.56 (s, 4H), 1.19e0.99 (m, 12H), 0.76 (t, J¼7.1 Hz, 6H). 13C NMR
laser (
l¼351 nm, Beamlok, Spectra-physics). The excitation laser
(100 MHz, CDCl3): d (ppm) 161.98, 140.87, 136.14, 134.75, 134.67,
was filtered with a band-pass filter (330e380 nm), then focused to
excite the microrod with an objective (50ꢁ, N.A.¼0.80). After
passing through a narrow band filter (LD01-405, Semrock), the
excitation laser was focused on the sample by the same objective
131.48, 130.34, 128.21, 128.13, 127.86, 127.01, 125.84, 119.45, 46.53,
31.00, 28.50, 26.47, 22.35, 13.89. MALDI-TOF: 684.5 [M] þ. Anal.
Calcd for C48H48N2O2: C, 84.17; H, 7.06; N, 4.09. Found: C, 84.13; H,
6.76; N, 4.13.
and the spot size was less than 2 mm. The collected microarea PL
emission was filtered by a long-pass filter (BA420), and coupled to
a grating spectrometer (Acton, SP-2358) with matched ProEm:
512B EMCCD camera (Princeton Instruments).
Acknowledgements
The present research was financially supported by Chinese
Academy of Sciences, NSFC, and State Key Basic Research Program.
4.5. Synthesis and characterization
Supplementary data
4.5.1. Synthesis of compound 5. Compound 4 (1.0 g, 3.57 mmol),1,2-
diphenylethyne (1.39 g, 7.85 mmol), [Cp RhCl2]2 (110 mg, 5 mol %),
*
Absorption spectra, fluorescence lifetime fitting curves, crystals
data and 1H and 13C NMR spectra, for 1a, 1b or 1c. Supplementary
data associated with this article can be found in the online version,
at http://dx.doi.org/10.1016/j.tet.2013.02.041.
and CsOAc (2.05 g, 10.7 mmol) were added to a round bottom flask.
Then, MeOH (30 mL) was added. The reaction mixture was stirred
at 60 ꢀC for 16 h. Afterward, the mixture was filtered, and the solid
was washed with water and CH2Cl2.The residue was dried under
reduced pressure to afford compound 5 as a light-yellow solid,
which was used for the next step without further purification for its
poor solubility; MS (MALDI-TOF): 517 (MþHþ), 539 (MþNaþ).
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4.5.2.1. Compound 1a. Yield: 41%; mp 231.2e232 ꢀC; nFTIR (KBr)
3054, 2956, 2926, 2855, 1591, 1573, 1537, 1423, 1339, 1300, 1211,
1147, 1072, 909, 701 cmꢂ1; 1H NMR (400 MHz, CDCl3):
d (ppm) 8.60
(2H, s), 7.47e7.38 (10H, m), 7.34e7.32 (4H, m), 7.21e7.18 (6H, m),
4.57 (4H, t, J¼6.4 Hz), 1.82e1.78 (4H, m), 1.46e1.43 (4H, m),
1.35e1.33 (8H, m), 0.92 (6H, t, J¼6.8 Hz). 13C NMR (100 MHz, CDCl3):
5. (a) Friend, R. H.; Gymer, R. W.; Holms, A. B.; Burroughes, J. H.; Marks, R. N.;
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d
(ppm) 159.60, 145.40, 140.55, 137.78, 135.44, 131.75, 130.44,
128.42, 127.46, 127.18, 127.06, 124.49, 121.77, 120.51, 66.45, 31.63,
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N, 4.09.
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4.5.2.2. Compound 1b. Yield 30%; mp 204.9e205.6 ꢀC; nFTIR
(KBr) 3054, 2954, 2925, 2856, 1648, 1612, 1593, 1558, 1428, 1341,
1320, 1299, 1229, 1030, 701 cmꢂ1 1H NMR (400 MHz, CDCl3)
;
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Tian, H. Chem.dEur. J. 2011, 17, 2647; (d) Jiang, Y. H.; Wang, Y. C.; Hua, J. L.; Tang,
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d
(ppm) 8.86 (s,1H), 8.11 (s,1H), 7.45e7.34 (m, 5H), 7.29 (d, J¼7.8 Hz,
2H), 7.25e7.12 (m, 13H), 4.52 (t, J¼6.2 Hz, 2H), 3.80 (t, J¼6.2 Hz, 2H),
1.81e1.71 (m, 2H), 1.59 (s, 2H), 1.37 (s, 2H), 1.33e1.23 (m, 4H),
1.19e1.10 (m, 2H), 1.07 (d, J¼2.8 Hz, 4H), 0.89 (t, J¼6.4 Hz, 3H), 0.77
(t, J¼7.1 Hz, 3H). 13C NMR (100 MHz, CDCl3)
d (ppm) 162.30, 159.34,
146.19, 140.59 9, 140.45, 137.46, 136.49, 135.98, 134.76, 134.17,
131.67, 131.57, 130.39, 128.63, 128.24, 127.94, 127.90, 127.43, 127.32,
127.04, 126.87, 126.37, 125.02, 121.35, 120.97, 119.21, 66.32, 46.45,
31.56, 31.04, 28.80, 28.56, 26.49, 25.86, 22.64, 22.37, 14.10, 13.91.

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However, the results indicated that the yield of 1a was not enhanced when LDA
or n-BuLi was applied under the same reaction conditions. Compounds 1a, 1b,
and 1c were obtained in 25, 20, and 12% yields, respectively, when n-BuLi was
used as the base. Similarly, 1a, 1b, and 1c were yielded in 35, 28, and 20% yields,
respectively, when LDA was applied.
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