Star-shaped D-π-A molecules containing a 2,4,6-tri(thiophen-2-yl)-1,3,5- triazine unit: Synthesis and two-photon absorption properties

Article abstract of DOI:10.1002/ejoc.200900641

A series of new star-shaped donor-π-acceptor (D-π-A) mole-cules containing the 2,4,6-tri(thiophen-2-yl)-1,3,5-triazine unit were synthesized and characterized. The 1,3,5-triazine group, as a strong electron-accepting center, is connected to three electron

Full text of DOI:10.1002/ejoc.200900641

FULL PAPER
DOI: 10.1002/ejoc.200900641
Star-Shaped D-π-A Molecules Containing a 2,4,6-Tri(thiophen-2-yl)-1,3,5-
triazine Unit: Synthesis and Two-Photon Absorption Properties
Li Zou,[a] Zijun Liu,[a] Xiaobing Yan,[a] Yan Liu,[a] Yang Fu,[a] Jun Liu,[b] Zhenli Huang,*[b]
Xingguo Chen,*[a] and Jingui Qin[a]
Keywords: Photophysics / Nonlinear optics / Redox chemistry / Donor–acceptor systems / Nitrogen heterocycles
A series of new star-shaped donor-π-acceptor (D-π-A) mole-
cules containing the 2,4,6-tri(thiophen-2-yl)-1,3,5-triazine
unit were synthesized and characterized. The 1,3,5-triazine
group, as a strong electron-accepting center, is connected to
end group the optical properties can be modified. All com-
pounds exhibit two-photon absorption activity in the range
of 720–880 nm and show large two-photon absorption cross
sections that are closely related to the intramolecular charge
three electron-donating end groups through π-conjugated transfer and π-conjugated length of the molecule.
bridges. As a result of the coexistence of the electron ac-
ceptor and donor, these compounds show reversible or quasi-
reversible redox behavior. Through changing the peripheral
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
because of the good coplanarity of the conjugated system,
strong intramolecular charge-transfer (ICT), and additional
cooperative enhancement between the branches.[11] Many
studies have explored this design, developing triazine-con-
taining derivatives with large 2PA cross sections, and most
research has been done with the use of the 2,4,6-triphenyl-
1,3,5-triazine unit or related compounds.
Introduction
In the past decades much attention has been focused on
star-shaped octupolar molecules owing to their structural
symmetry and excellent optical and electronic properties.[1]
With well-defined structures, suitable conjugated length,
and good processibilities, they can be applied as promising
optoelectronic materials in many areas.[2]
However, little attention has been paid to 2,4,6-aromatic
heterocyclic substituted 1,3,5-triazine derivatives such as
2,4,6-tri(thiophen-2-yl)-1,3,5-triazine.[12] Structurally, the
thienyl group has richer π electron density than the phenyl
group and higher chemical and thermal stability than the
furan or pyrrole groups, so introducing a thienyl group into
the frame of 1,3,5-triazine-based conjugated compounds
may enrich the π electron density of the system and improve
the optoelectronic properties. This motivates us to design a
kind of star-shaped conjugated compound containing a
2,4,6-tri(thiophen-2-yl)-1,3,5-triazine unit. We wish to mod-
ify the photophysical properties of the compounds by
changing the acceptor–donor linkage and the electron-do-
nating strength of the end group. we also wish to obtain
some excellent 2PA materials and to further understand the
structure–property relationship.
Two-photon absorption (2PA) is a third-order nonlinear
optical process involving simultaneous absorption of two
low-energy photons to reach the high-energy excited state,
which can be applied in many areas including optical power
limiting,[3] two-photon upconversion lasing,[4] two-photon
fluorescence excitation microscopy,[5] 3D optical data stor-
age,[6] and photodynamic therapy.[7] Recently, much interest
has been focused on the design and synthesis of compounds
with large 2PA cross sections,[8] and experimental and theo-
retical research on the relationship between structure and
2PA properties have also been widely investigated.[9]
1,3,5-Triazine-based compounds show good optical and
electrical properties due to high electron affinity and sym-
metrical structure.[10] In particular, octupolar molecules
consisting of a strong triazine electron-accepting center and
an electron-donating end group linked through a π-conju-
gated bridge have been shown to be excellent 2PA materials,
Results and Discussion
[a] Department of Chemistry, Hubei Key Laboratory on Organic
and Polymeric Opto-Electronic Materials, Wuhan University,
Wuhan 430072, P. R. China
Synthesis and Characterization
E-mail: xgchen@whu.edu.cn
As shown in Scheme 1, 2,4,6-tris(thiophen-2-yl)triazine
(1) was synthesized by trimerization of thiophene-2-
carbonitrile in the presence of trifluoromethanesulfonic
acid.[13] Then, treatment of 1 with a threefold excess of N-
bromosuccinimide resulted in a mixture of 2,4-bis(5-bromo-
[b] Key Laboratory of Biomedical Photonics of Ministry of Educa-
tion, Huazhong University of Science and Technology,
Wuhan, 430074, P. R. China
E-mail: leo@mail.hust.edu.cn
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.200900641.
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FULL PAPER
thiophen-2-yl)-6-(thiophen-2-yl)-1,3,5-triazine and 2,4,6- MALDI-TOF mass spectrometry, and elemental analysis
tris(5-bromothiophen-2-yl)-1,3,5-triazine (2), which was (see the Experimental section and Supporting Information).
separated by column chromatography.[12d] Some other pre- They all showed good solubility in common organic sol-
cursors such as aromatic dioxaborolanes 3a–d[14] and aro- vents at room temperature and exhibited high thermal sta-
matic acetylene derivatives 4a–c[15] were prepared according bility with decomposition temperatures over 360 °C.
to literature procedures, in which different aromatic groups
were selected to tune the electron-donating ability of the
end group in the next synthesis of star-shaped conjugated
molecules.
One-Photon Physical Properties
Representative examples of the UV/Vis absorption of 5a–
d and 6a–c measured in CHCl3 at a concentration of
1.0ϫ10–5  are shown in Figure 1. The corresponding data
are collected in Table 1. Compared with 2,4,6-tris(thiophen-
2-yl)triazine, which has an absorption maximum at 314 nm
(Supporting Information, Figure S23), all of the com-
pounds show large redshifted absorption maximum in the
range of 390–440 nm as a result of π–π* transitions. The
order of UV/Vis absorption maximum (5a Ͼ 5bϾ 5d Ͼ
5c) corresponds to the same order of the electron-donating
strength of the end group: triphenylamine Ͼ 3-(N-alkylcarb-
azole) Ͼ 2-(N-alkylcarbazole) ≈ 2-(9,9-dialkylfluorene). A
similar absorption trend was also observed for 6a–c. It
should be noted that 5a and 6a exhibit nearly the same
absorption maximum (e.g.: 5a, 438 nm; 6a, 439 nm), al-
though 6a has larger conjugation length than 5a owing to
the introduction of a CϵC bond to connect the 2,4,6-tris-
(thiophen-2-yl)triazine core with the triphenylamine group.
This suggests that their UV/Vis absorption is mainly attrib-
uted to a strong ICT effect. For some other compounds
with the same core and same end group connected by a
different π-conjugation mode (such as 5b and 6b or 5c and
6c), they show a large different absorption maximum. For
example, the absorption maximum of 6b at 427 nm is red-
shifted by 12 nm relative to that of with 5b, as 6b has a
larger conjugation length than 5b. In addition, π-conjuga-
tion efficiency also exerts an influence on the absorption
spectra. The same electron-donating group at the 3- or 6-
position of the carbazole group in 5b has higher conjuga-
tion efficiency than the 2- or 7-position of the carbazole
group in 5d, so the absorption maximum of 5b at 415 nm
is redshifted by 12 nm relative to that of 5d at 403 nm.
Scheme 1. Synthetic routes for the precursors.
Scheme 2 shows the synthetic routes for the new star-
shaped molecules containing the 2,4,6-tri(thiophen-2-yl)-
1,3,5-triazine unit. Compounds 5a–d were obtained in very
high yield (Ͼ85%) by Suzuki coupling reaction[16] of 2 with
3a–d in the presence of Pd0 catalysts. Compounds 6a–c were
synthesized with high yield (Ͼ65%) through Sonogashira
coupling reaction[17] of 2 with 4a–c in the presence of
Pd(PPh3)4 and CuI. Their structures and purities were de-
termined by 1H NMR, 13C NMR, and FTIR spectroscopy,
Scheme 2. Synthetic routes for 5a–d and 6a–c.
Figure 1. UV/Vis spectra of 5a–d and 6a–c in CHCl3.
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Star-Shaped D-π-A Molecules Containing 2,4,6-tri(thiophen-2-yl)-1,3,5-triazine
Table 1. One-photon photophysical data of 5a–d and 6a–c.
solvent also influences the quantum yield (ΦF). Table 1 lists
the corresponding quantum yield of 5a–d and 6a–c in
CHCl3 and toluene, respectively. The corresponding ΦF
value of the compound in a nonpolar solvent such as tolu-
ene is larger than that in a polar solvent such as CHCl3.
Abs
Em
[a]
λmax
[nm]
λmax [nm]
ΦF
CHCl3 Toluene CHCl3 Toluene CHCl3 Toluene
5a
5b
5c
5d
6a
6b
6c
438
415
399
403
439
427
419
438
411
397
400
440
430
418
532
492
460
469
540
500
462
495
463
441
449
497
466
443
0.42
0.58
0.54
0.52
0.51
0.52
0.36
0.63
0.79
0.72
0.69
0.69
0.83
0.51
[a] The PL quantum yield (ΦF) was estimated with quinine bisulfate
(10–6  in 1  H2SO4) as a standard.
No photoluminescence of 2,4,6-tris(thiophen-2-yl)-1,2,3-
triazine was observed, but all the star-shaped molecules
based on the 2,4,6-tri(thiophen-2-yl)-1,3,5-triazine unit
show strong one-photon excited emission. The one-photon
excited photoluminescence (PL) spectra of 5a–d and 6a–c
in CHCl3 at a concentration of 1.0ϫ10–6  are shown in
Figure 2 and the data are summarized in Table 1. In the
same series, 5a–d show an emission maximum at 535, 494,
461, and 469 nm, respectively, which is also in agreement
with the order of electron-donating strength: tri-
phenylamine (5a) Ͼ 3-(N-alkylcarbazole) (5b) Ͼ 2-(N-alkyl-
carbazole) (5d) ≈ 2-(9,9-dialkylfluorene) (5c). Compounds
6a–c show a similar PL emission trend to 5a–c. Different
from UV/Vis absorption, 6a shows a more redshifted maxi-
mum emission than 5a as a result of the extension of conju-
gation by introduction of a CϵC bond.
Figure 3. UV/Vis absorption and PL spectra of 5a in different sol-
vents.
As expected, the introduction of the thienyl group into
triazine-based molecules can enrich the electron density for
this kind of new star-shaped molecule and influence their
photophysical properties. For example, the maximum ab-
sorption of 5a at 438 nm in THF is obviously redshifted in
comparison with the similar structural compounds such as
AF-450 consisting of a 1,3,5-triazine electron-accepting
center with three arms of an electron-donating di-
phenylamino group as well as a fluorene aromatic bridging
group,[11a] which showed absorption maximum at 415 nm
in THF. Also, the absorption maximum of 424 nm in THF
for TRZ-Ph-Tol (consisting of a 2,4,6-triphenyl-1,3,5-tri-
azine core and a diphenylamino derivative end group with
a thienyl bridge)[19] is less than that of 5a. Similarly, the
maximum absorption of 6a at 439 nm in CHCl3 is 11 nm
redshifted compared to that of T03 (428 nm in CHCl3),[11b]
although T03 contains a 2,4,6-triphenyl-1,3,5-triazine core
and a triphenylamine unit with an additional para electron-
donating methoxy group connected through a C=C bond
instead of the CϵC bond in 6a. Generally, a C=C bond
has better π-conjugation efficiency than a CϵC bond. This
indicates that introduction of a thienyl group strengthens
the π-electron density of the 1,3,5-triazine-based star-
shaped molecular system.
Figure 2. PL spectra of 5a–d and 6a–c in CHCl3.
In addition, the solvatochromic behavior of the absorp-
tion and emission in different solvents was studied (Fig-
ure 3; Supporting Information, Figures S25–39). As an ex-
ample, Figure 3 describes the UV/Vis and PL spectra of 5a
Electrochemical Properties
The electrochemical behavior of 5a–d and 6a–c was in-
in different solvents. It was found that the polarity of the vestigated by using cyclic voltammetry (CV). The CV
solvent exerted little influence on the UV/Vis absorption. curves are shown in Figure 4 and the corresponding data
However, the bathochromism for the PL emission is obvi- are summarized in Table 2. Because of the coexistence of
ous as the polarity of the solvent increases. For example, the the strong electron-accepting center and the electron-donat-
emission maximum of 495 nm for 5a in toluene is shifted to ing end group, these star-shaped molecules show reversible
557 nm in dichloromethane. This phenomenon is similar to or quasireversible redox processes. Compounds consisting
some other star-shaped molecules.[18] The polarity of the of the same core and same end group (such as 5a and 6a,
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L. Zou, Z. Liu, X. Yan, Y. Liu, Y. Fu, J. Liu, Z. Huang, X. Chen, J. Qin
Table 2. Electrochemical properties and 2PA data of 5a–d and 6a–c.
FULL PAPER
Ered [V][a]
Eox [V][b]
LUMO [eV][c]
HOMO [eV][d]
σ2max [GM][e], λmax [nm]
5a
5b
5c
5d
6a
6b
6c
–1.93, –2.44
–2.01, –2.56, –2.72
–1.89, –2.35, –2.65
–2.41
–1.77, –2.21, –2.54
–1.84, –2.32
0.42
0.51
0.84
–2.87
–2.79
–2.91
–2.39
–3.03
–2.96
–3.02
–5.22
–5.31
–5.64
–5.14
–5.27
–5.22
–5.68
1233, 850
998, 750
839, 750
793, 750
1508, 850
1481, 750
879, 740
0.34, 0.68
0.47
0.42, 0.55
0.88
–1.78, –2.22, –2.52
[a] Estimated from the onset reduction potential. [b] Estimated from the onset oxidation potential. [c] Calculated with the formula ELUMO
/
+
+
eV = –e{Ered + [4.8 – E(Fc/Fc )]}. [d] Calculated with the formula EHOMO/eV = –e{Eox + [4.8 – E(Fc/Fc )]}. [e] 2PA cross sections, 1 GM
(Göppert–Mayer) = 10–50 cm4 sphoton–1, the experimental uncertainty on σmax is of the order of 10–15%.
5b and 6b, and 5c and 6c) show similar redox behaviors. surements. The 2PA spectra of the compounds in CHCl3
From the initial onset reduction potential and the initial are presented in Figure 5, and the data are summarized in
onset oxidation potential the HOMO and LUMO level Table 2.
were estimated according to a literature procedure.[20] As a
result of the strong electron-accepting ability of the triazine
unit, all compounds exhibit a low LUMO level. It is noted
that the band gap decreases as the electron-donating ability
of the end group increases in the same series.
Figure 5. Two-photon absorption spectra of 5a–d and 6a–c.
As shown in Figure 5, all the compounds display 2PA
activity in the range of 720–880 nm in CHCl3. In the same
series (i.e., 5a–d or 6a–c), as the electron-donating strength
of the end group increases, the maximum of the 2PA cross
Figure 4. CV measurement was performed in THF for the re-
section (σ2max) also obviously increases. This indicates that
strong 2PA activity is mainly attributed to large ICT effect
of the molecule. For example, the triphenylamine group ex-
hibits stronger electron-donating strength than the fluorene
and carbazole groups, so 6a and 5a with strong ICT show
much higher TPA cross section than any other related com-
pounds in the same series. In addition, it was found that
duction process (A) and for the oxidation process in CH2Cl2 (B).
Two-Photon Absorption Properties
The two-photon absorption of the star-shaped molecules
were measured by a two-photon-induced fluorescence tech-
nique in chloroform at a concentration of 5ϫ10–5 , and
the two-photon absorption cross section σ2 was calculated
by the following equation.[21]
6a has a larger σ2max value of 1508 GM than 5a (σ2max
=
1233 GM) because of the introduction of a CϵC bond to
link the 2,4,6-tris(thiophen-2-yl)triazine core with the tri-
phenylamine group, indicating that extended conjugation
also jointly influences the 2PA cross section. It should be
σ2s = σ2r(Fs/Fr)(Φr/Φs)(cr/cs)(nr/ns)
The subscripts s and r stand for the measured sample noted that 6a and 6b show comparable σ2max values al-
and reference molecule, respectively; F is the integrated though the triphenylamine group of 6a is more strongly
fluorescence intensity measured at the same power as the electron-donating than the N-alkylcarbazole group of 6b.
excitation beam; Φ is the fluorescence quantum yield; c is The possible reason is that the coplanarity of N-alkylcarb-
the number density of the molecules in the solution; n is the azole group is higher than that of the triphenylamine group.
refractive index of solution. The σr term is the 2PA cross This suggests that the strategy through increasing electron-
section of the reference molecule. Here fluorescein was cho- donating strength of the end group and extending the con-
sen as the reference molecule.[22] The compounds are stable jugation length of the system is an effective approach for
under these conditions and no obvious change was ob- enhancing 2PA cross section of 2,4,6-tri(thiophen-2-yl)-
served in the UV/Vis spectra after completing the TPA mea- 1,3,5-triazine-based star-shaped molecules.
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Star-Shaped D-π-A Molecules Containing 2,4,6-tri(thiophen-2-yl)-1,3,5-triazine
(d, 3 H), 7.17(d, 3 H) ppm. MS (EI): m/z = 565.0. C15H6N3S3Br3
(564.14): calcd. C 31.94, H 1.07, N 7.45, S 17.05; found C 32.42,
H 1.38, N 7.62, S 16.46.
Conclusions
A series of new star-shaped molecules containing the
2,4,6-tri(thiophen-2-yl)-1,3,5-triazine unit was synthesized
through two kinds of classical Pd-catalyzed coupling reac-
tions. The synthetic method is convenient and the yields are
very high. An electrochemical study indicates that all the
compounds exhibit reversible or quasireversible redox be-
havior as a result of the donor–acceptor system of the tri-
azine center and the peripheral moieties. Photophysical
measurements indicate that introduction of a thienyl group
can enrich the electron density of the system, and a change
in the end group can modify the optical properties. Prelimi-
nary studies show that these molecules have very large 2PA
cross sections. The feasible synthetic routes and large 2PA
cross sections of these new star-shaped molecules suggest
that the introduction of a combination of a π-electron-rich
thienyl group and a CϵC bond into the triazine-based sys-
tem is an efficient strategy to design new star-shaped conju-
gated molecules with excellent 2PA properties.
General Procedure for the Preparation of 5a–d: Compound 2
(1 equiv.), dioxaborolane 3a–d (3.3 equiv.), Pd(PPh3)4 (2 mol-%),
and K2CO3 (10 equiv.) were dissolved in THF/H2O (8 mL/2 mL)
under an argon atmosphere. The reaction mixture was stirred at
65 °C for 30 h, and then CHCl3 (50 mL) was added, and the mix-
ture was washed with water (2ϫ50 mL). The organic layer was
dried with anhydrous MgSO4 and concentrated under vacuum. The
residue was purified by flash chromatography (petroleum ether/
CHCl3).
5a: Compound 2 (85 mg, 0.15 mmol), 3a (183 mg, 0.50 mmol),
Pd(PPh3)4 (5 mg), and K2CO3 (0.683 g, 5 mmol). Orange solid
(150 mg, 92%) was obtained by flash chromatography (petroleum
ether/CHCl3, 1:1). Decomposition temperature (Td) 368 °C. IR
(KBr): ν = 3028.4, 2964.1, 2919.1, 2848.3, 1589.9, 1536.9, 1494.2,
˜
1441.5, 1371.6, 1318.7, 1267.8, 1182.3, 1039.1, 798.5, 694.0 cm–1.
1H NMR (300 MHz, CDCl3): δ = 8.23 (d, 3 H), 7.60 (d, 6 H), 7.33
(t, 6 H), 7.29 (d, 9 H), 7.16 (d, 12 H), 7.10–7.08 (m, 12 H) ppm.
13C NMR (75 MHz, CDCl3): δ = 166.2, 145.0, 147.2, 146.2, 138.3,
131.7, 128.4, 126.6, 125.9, 123.8, 122.4, 122.0 ppm. MS (MALDI-
TOF): m/z = 1057.1. C69H48N6S3 (1057.35): calcd. C 78.38, H 4.58,
N 7.95; found C 78.08, H 4.70, N 7.64.
Experimental Section
5b: Compound 2 (68 mg, 0.12 mmol), 3b (182 mg, 0.40 mmol),
Pd(PPh3)4 (5 mg), and K2CO3 (0.546 g, 4 mmol). Orange solid
(141 mg, 88%) was obtained by flash chromatography (petroleum
Reagents and Instruments: 2,4,6-Tri(thiophen-2-yl)-1,3,5-triazine (1)
was obtained by a literature procedure.[13] Dioxaborolanes 3a–d[14]
and ethynyl derivatives 4a–c[15] were prepared as described in the
literatures. Tetrahydrofuran (THF) was dried with and distilled
from K/Na alloy under an atmosphere of dry argon. Triethylamine
(TEA) was dried with and distilled from KOH and oxygen was
removed before use. All the other reagents and solvents were used
as commercially purchased without further purification. 1H and
13C NMR spectroscopy was conducted with a Varian Mercury 300
spectrometer using tetramethylsilane (TMS, δ = 0 ppm) as internal
standard. Fourier transform infrared (FTIR) spectra were recorded
with a Perkin-Elmer-2 spectrometer in the region 4000–400 cm–1.
UV/Vis spectra were obtained by using a Schimadzu UV-2550 spec-
trometer. Fluorescent spectra were obtained by using a Hitachi F-
4500 spectrometer. Mass spectra (EI) were recorded with a VJ-
ZAB-3F mass spectrometer. Elemental analysis was performed
with a Carloerba-1106 microelemental analyzer. Thermal analysis
was performed with a Netzsch STA449C thermal analyzer at a
ether/CHCl , 2:3). T 466 °C. IR (KBr): ν = 2921.7, 2849.3, 1536.8,
˜
3
d
1506.8, 1433.5, 1372.5, 1150.8, 1040.4, 794.4, 745.2, 563.5 cm–1. 1H
NMR (300 MHz, CDCl3): δ = 8.47 (d, 3 H), 8.31 (t, 3 H), 8.20 (d,
3 H), 7.87 (d, 3 H), 7.49 (m, 6 H), 7.42 (d, 6 H), 7.30 (d, 3 H), 4.30
(t, 6 H), 1.89 (t, 6 H), 1.36–1.25 (br., 54 H), 0.88 (t, 9 H) ppm. 13C
NMR (75 MHz, CDCl3): δ = 167.5, 152.8, 141.2, 140.8, 139.3,
133.0, 126.23, 125.4, 124.4, 123.5, 123.3, 123.1, 120.9, 119.5, 118.3,
109.2, 43.4, 32.2, 29.8, 29.6, 29.2, 27.5, 22.9, 14.4 ppm. MS
(MALDI-TOF): m/z = 1326.5. C87H102N6S3 (1327.98): calcd. C
78.69, H 7.74, N 6.33; found C 78.16, H 7.72, N 6.61.
5c: Compound 2 (68 mg, 0.12 mmol), 3c (182 mg, 0.40 mmol),
Pd(PPh3)4 (5 mg), and K2CO3 (0.546 g, 4 mmol). Greenish yellow
solid (130 mg, 94%) was obtained by flash chromatography (petro-
leum ether/CHCl3, 3:1). Td 390 °C. IR (KBr): ν = 2925.6, 2852.2,
˜
1535.9, 1504.6, 1460.9, 1374.0, 1044.2, 801.7, 560.3 cm–1. 1H NMR
(300 MHz, CDCl3): δ = 8.35 (d, 3 H), 7.76 (d, 12 H), 7.53 (d, 3 H),
7.37 (m, 9 H), 2.06 (m, 12 H), 1.08 (br. m, 36 H), 0.78 (t, 18 H),
0.68 (br., 12 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 167.7,
152.2, 152.0, 151.3, 142.2, 140.7, 140.0, 133.1, 133.0, 127.7, 127.2,
125.4, 124.4, 123.2, 120.7, 120.4, 120.2, 55.5, 40.7, 31.7, 29.9, 24.0,
22.8, 14.3 ppm. MS (MALDI-TOF): m/z = 1324.8. C90H105N3S3
(1325.01): calcd. C 81.58, H 7.99, N 3.17; found C 81.65, H 7.98,
N 3.18.
heating rate of 20 °Cmin–1 in argon with
a flow rate of
50 cm3 min–1 for thermogravimetric analysis (TGA). A mode-
locked Ti:sapphire laser (Mai Tai, Spectra-Physics Inc., USA) was
used as the excitation source. The average output power, pulse
width, and repetition rate were 0.5 W, 100 fs, and 80 MHz, respec-
tively. After passing through a Pockel cell (350–80 LA BK, Conop-
tics Inc., USA) that was used to control the power of the laser, the
laser was focused on the cell (polished on all sides) by a focusing
lens (f = 6 cm). The emission light was collected by an objective
lens (Olympus, Japan) and then was focused by another objective
lens on a fiber Spectrometer (HR2000, Ocean Optics Inc., USA),
which was used to record the fluorescent spectra. Fluorescein in
water was chosen as the reference standard.
5d: Compound 2 (68 mg, 0.12 mmol), 3d (160 mg, 0.40 mmol),
Pd(PPh3)4 (5 mg), and K2CO3 (0.546 g, 4 mmol). Greenish yellow
solid (132 mg, 93%) was obtained by flash chromatography (petro-
leum ether/CHCl3, 1:1). Td 483 °C. IR (KBr): ν = 2921.2, 2849.4,
˜
1536.8, 1506.8, 1433.5, 1372.5, 1150.8, 1040.4, 794.4, 745.2,
1
2,4,6-Tris(5-bromothiophen-2-yl)-1,3,5-triazine (2): To a solution of
1 (0.98 g, 3 mmol) in DMF (20 mL) was added an excess amount
of NBS (2.14 g, 12 mmol) in potions. The reaction was stirred at
room temperature for at least 3 d. The mixture was poured into
H2O (500 mL), and the precipitate was filtered off. The product
was obtained by chromatography (petroleum ether) to afford a
563.5 cm–1. H NMR (300 MHz, CDCl3): δ = 8.34 (d, 3 H), 8.11
(t, 6 H), 7.74 (s, 3 H), 7.66 (d, 3 H), 7.54 (d, 3 H), 7.49 (d, 3 H),
7.42 (d, 3 H), 7.28 (d, 3 H), 4.22 (m, 6 H), 2.13 (m, 3 H), 1.52–
1.25 (br. m, 24 H), 1.00–0.90 (br. m, 18 H) ppm. 13C NMR
(75 MHz, CDCl3): δ = 167.5, 152.6, 141.9, 141.46, 140.2, 132.9,
131.6, 126.2, 124.3, 123.4, 122.8, 120.9, 120.6, 119.3, 117.7, 109.4,
106.5, 47.4, 39.7, 31.3, 29.1, 24.8, 23.3, 14.4, 11.2 ppm. MS
1
white solid (0.87 g, 51%). H NMR (300 MHz, CDCl3): δ = 7.96
Eur. J. Org. Chem. 2009, 5587–5593
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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5591

L. Zou, Z. Liu, X. Yan, Y. Liu, Y. Fu, J. Liu, Z. Huang, X. Chen, J. Qin
FULL PAPER
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(MALDI-TOF): m/z = 1159.2. C75H78N6S3 (1159.66): calcd. C
77.68, H 6.78, N 7.25; found C 77.49, H 6.79, N 7.35.
General Procedure for the Preparation of 6a–c: Compound 2
(1 equiv.), ethynyl derivative 4a–c (3.3 equiv.), Pd(PPh3)4 (2 mol-%),
CuI (2 mol-%), and PPh3 (2 mol-%) were dissolved in THF/TEA
(10 mL/1 mL) under an argon atmosphere. The reaction mixture
was stirred at 45 °C for 3 d. The solvent was removed under vac-
uum. The crude residue was purified by flash chromatography (pe-
troleum ether/CHCl3).
[2]
[3]
6a: Compound 2 (56 mg, 0.1 mmol), 4a (89 mg, 0.33 mmol),
Pd(PPh3)4 (5 mg), CuI (2 mg), and PPh3 (2 mg). Orange solid
(98 mg, 88%) was obtained by flash chromatography (petroleum
ether/CHCl , 2:1). T 366 °C. IR (KBr): ν = 2922.3, 2194.5, 1590.6,
˜
3
d
1498.2, 1443.9, 1371.5, 1319.1, 1278.1, 1021.5, 798.4, 695.1,
1
584.9 cm–1. H NMR (300 MHz, CDCl3): δ = 8.14 (d, 3 H), 7.38
[4]
[5]
(d, 6 H), 7.31–7.26 (m, 18 H), 7.13 (d, 12 H), 7.08 (d, 3 H), 7.01
(d, 6 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 167.1, 148.7, 147.2,
141.6, 132.8, 131.9, 130.8, 129.7, 125.5, 124.1, 122.0, 115.0, 97.0,
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82.4 ppm. MS (MALDI-TOF): m/z
= 1129.0. C75H48N6S3
(1129.42): calcd. C 79.76, H 4.28, N 7.44; found C 79.27, H 4.41,
N 7.08.
6b: Compound 2 (77 mg, 0.14 mmol), 4b (162 mg, 0.45 mmol),
Pd(PPh3)4 (5 mg), CuI (2 mg), and PPh3 (2 mg). Yellow solid
(120 mg, 64%) was obtained by flash chromatography (petroleum
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ether/CHCl , 1:1). T 449 °C. IR (KBr): ν = 2920.9, 2192.2, 1596.5,
˜
3
d
1501.2, 1478.3, 1439.1, 1374.2, 1349.4, 1247.2, 1021.44, 799.4,
1
743.8, 567.3 cm–1. H NMR (300 MHz, CDCl3): δ = 8.33 (s, 3 H),
8.19 (d, 3 H), 8.12 (d, 3 H), 7.66 (d, 3 H), 7.50 (t, 3 H), 7.43 (d, 6
H), 7.37 (t, 3 H), 7.27 (d, 3 H), 4.31 (t, 6 H), 1.88 (br., 6 H), 1.34–
1.24 (br. m, 54 H), 0.87 (br., 9 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 167.0, 141.4, 141.0, 140.6, 132.5, 131.8, 131.1, 129.4,
126.4, 124.4, 123.1, 122.6, 120.8, 119.7, 112.6, 109.2, 109.1, 98.3,
81.6, 43.4, 32.1, 29.8, 29.8, 29.7, 29.6, 29.6, 29.2, 27.5, 22.9,
14.4 ppm. MS (MALDI-TOF): m/z
= 1399.4. C93H102N6S3
(1400.04): calcd. C 79.78, H 7.34, N 6.00; found C 79.92, H 7.61,
N 6.11.
6c: Compound 2 (77 mg, 0.14 mmol), 4c (161 mg, 0.45 mmol),
Pd(PPh3)4 (5 mg), CuI (2 mg), and PPh3 (2 mg). Greenish yellow
solid (141 mg, 74%) was obtained by flash chromatography (petro-
leum ether/CHCl3, 4:1). Td 421 °C. IR (KBr): ν = 2924.6, 2851.0,
˜
2196.2, 1504.9, 1457.8, 1372.1, 1025.5, 800.7, 738.2, 582.9 cm–1. 1H
NMR (300 MHz, CDCl3): δ = 8.20 (d, 3 H), 7.72 (d, 6 H), 7.55 (d,
6 H), 7.38 (d, 3 H), 7.35 (s, 9 H), 1.99 (t, 12 H), 1.14–1.06 (br. m,
36 H), 0.77 (t, 18 H), 0.63 (br., 12 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 167.2, 151.4, 151.1, 142.4, 142.0, 140.5, 133.1, 132.0,
130.9, 130.6, 128.0, 127.2, 126.2, 123.2, 120.8, 120.4, 120.0, 97.8,
83.1, 55.5, 40.6, 31.8, 30.0, 24.0, 22.9, 14.3 ppm. MS (MALDI-
TOF): m/z = 1396.1. C96H105N3S3 (1397.08): calcd. C 82.53, H
7.58, N 3.01; found C 82.77, H 7.98, N 2.81.
[9]
Supporting Information (see footnote on the first page of this arti-
1
cle): H NMR, 13C NMR, IR, and mass spectra; one-photon ab-
sorption and emission spectra in different solvents.
Acknowledgments
This work was financially supported by the National Natural Sci-
ence Foundation of China (No. 20774071).
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Received: June 12, 2009
Published Online: September 23, 2009
Eur. J. Org. Chem. 2009, 5587–5593
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5593