Synthesis and two-photon absorption properties of multi-branched styryl derivatives containing π-bond and σ-electron pair as bridge based on 1,3,5-triazine

Article abstract of DOI:10.1016/j.tet.2012.05.050

A series of new one, two, and three-branched two-photon absorption triazine derivatives with a π-bond and a σ-electron pair as a bridge have been synthesized and their photophysical properties have been systematically investigated. These chromophores showed obvious solvatochromic effects, i.e., significant bathochromic shifting of the emission spectra and larger Stokes shifts were observed in more polar solvents mainly due to intra-molecular charge transfer (ICT). The two-photon absorption (2PA) cross-section values were determined by the two-photon excited fluorescence (TPEF) measurements in DMF. This result further proved that a σ-electron pair as a bridge is an efficient way to transfer charge as well as a π bridge, and that their 2PA cross-section values (δ) increase with increasing branch number.

Full text of DOI:10.1016/j.tet.2012.05.050

Tetrahedron 68 (2012) 6569e6574
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and two-photon absorption properties of multi-branched styryl
derivatives containing
1,3,5-triazine
p
-bond and
s
-electron pair as bridge based on
,
a
a
a
a
Zheng Zheng a, Hong-ping Zhou a , Guo-yi Xu , Zhi-peng Yu , Xiao-fei Yang , Long-huai Cheng ,
*
Lin Kong a, Yan Feng a, Jie-ying Wu a, Yu-peng Tian a
,b,c
a Department of Chemistry, Anhui University and Key Laboratory of Functional Inorganic Materials Chemistry of Anhui Province, 230039 Hefei, PR China
b State Key Laboratory of Crystal Materials, Shandong University, 250100 Jinan, PR China
c State Key Laboratory of Coordination Chemistry, Nanjing University, 210093 Nanjing, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of new one, two, and three-branched two-photon absorption triazine derivatives with a p-bond
Received 15 March 2012
Received in revised form 8 May 2012
Accepted 15 May 2012
and a s-electron pair as a bridge have been synthesized and their photophysical properties have been
systematically investigated. These chromophores showed obvious solvatochromic effects, i.e., significant
bathochromic shifting of the emission spectra and larger Stokes shifts were observed in more polar
solvents mainly due to intra-molecular charge transfer (ICT). The two-photon absorption (2PA) cross-
section values were determined by the two-photon excited fluorescence (TPEF) measurements in
Available online 29 May 2012
Keywords:
DMF. This result further proved that a
s-electron pair as a bridge is an efficient way to transfer charge as
Triazine derivatives
Photophysical properties
Intra-molecular charge transfer
2PA cross section
well as a bridge, and that their 2PA cross-section values (
p
d
) increase with increasing branch number.
Ó 2012 Published by Elsevier Ltd.
s-Electron pair as bridge
1. Introduction
length, and planarity of the p
-center.2 For the multi-branched
molecules, which can significantly enhance 2PA cross sections be-
cause of the increase of chromophore density and the cooperative
enhancement effect among the chromophores.
Two-photon absorption (2PA) is a third-order non-linear optical
process involving simultaneous absorption of two photons to reach
the excited state. Fluorescent molecules with large 2PA cross-
sections have attracted a great deal of attention due to their su-
perior photophysical properties and various applications in 3D
optical data storage, bioimaging, optical limiting, photodynamic
therapy, and microfabrication.1 Most of these applications are
based on the fluorescence properties of the two-photon excited
molecule. So the significant issue is how to synthesize the materials
with large 2PA cross section. There are several efficient design
strategies put forward to enhance the 2PA cross section of the
Previous studies show that many octupolar compounds based
on a triazine core and electron-donating substituents have been
reported to exhibit large 2PA cross-sections.3 1,3,5-Triazine-based
compounds show good optical and electrical properties due to their
high electron affinity and symmetrical structure.4 Structurally, N,N-
diethylaniline can enhance the extent of electron delocalization
and ability to donate electrons of the 2PA compound. Until now,
most of the studies about the two-photon materials employed C]C
bonds as the linkage to combine a 1,3,5-triazine core with an
electron-donating end group while little attention has been paid to
the alteration of the acceptoredonor linkage. Recently, spectral,
and photophysical characteristics of some N-triazinyl derivatives
have been reported,5 but 2PA and applications of such materials are
studied rarely. Wang et al.6 reported a new 2PA-active compound
employing a nitrogen atom as the linkage to combine a 1,3,5-
molecular, such as the
donor and acceptor symmetrically or asymmetrically to form
DeAeD, De eA, De eD, De eA structures, macrocycles, den-
p-conjugated was employed to connect
p
p
p
drimers, polymers, and multi-branched molecules. Furthermore,
several other studies on structureeproperty relationship reveal
that the 2PA cross section increase with the D/A strength, chain
triazine core with styrylpyridyl groups. A
s-electron pair as
a bridge can be used to not only extend the molecular conjugated
system and promote solubility, but also to avoid the aggregation-
* Corresponding author. Tel.: þ86 551 5108151; fax: þ86 551 5107342; e-mail
induced fluorescence quenching of the strong
pep stacking
address: zhpzhp@263.net (H.p. Zhou).
0040-4020/$ e see front matter Ó 2012 Published by Elsevier Ltd.
doi:10.1016/j.tet.2012.05.050

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Z. Zheng et al. / Tetrahedron 68 (2012) 6569e6574
interaction in these large flat
a series of new compounds containing a 1,3,5-triazine unit and
investigate their structureeproperty relationships.
p
-systems. This motivates us to design
and the one-photon excited fluorescence data of T1eT3 are re-
stricted to DMF. Linear absorption and fluorescence spectra of
T1eT3 are shown in Figs. 1 and 2.
In view of the above advantages we have strategically designed
and presented a similar one-step method to prepare one-, two-
branched compounds (T1, T2) and pullepush type octupolar tri-
azine molecule (T3) by changing the ratio of RNH2 and 2,4,6-
trichloro-1,3,5-triazine. Their linear photophysical characteriza-
tion was performed in different organic solvents and 2PA properties
were investigated by means of two-photon fluorescence spectros-
copy. Then their structureeproperty relations will be discussed on
the molecular basis.
As shown in Fig. 1, compounds T1eT3 exhibit one major ab-
sorption bands: the peak at about 370 nm is of charge-transfer
character. The fluorescence deviation in solution can be attrib-
uted to the interaction of the solute with the local molecular en-
vironment including solvent molecules and other surrounding
solute molecules. For each of the three compounds, the OPEF peak
position lmax showed an increasing tendency as the solvent polarity
increased except in DMF. The Stokes shift also showed mono-
tonically increasing tendency with the increase of solvent polarity
except in DMF. On the other hand, the quantum yields (F) of T1eT3
decreased consistently and significantly as the polarity of solvent
increases except in DMF, and were especially highly quenched in
acetonitrile (Fig. 1). These can be explained by the stronger solute/
solvent interaction at the excited state comparing with that at the
ground state, which indicates that the increasing polarity of the
excited state increases. The energy level can be lowered greatly by
increasing dipoleedipole interaction between the solute and sol-
vent. However, a slight blue shift in absorption of T1eT3 is ob-
served in low polar solvents, while the absorption peaks are found
to be red shifted in high polar solvents, such as acetonitrile and
DMF. It may have great changes in the molecular geometry of ex-
cited states before fluorescence emission.
2. Results and discussion
2.1. Synthesis
Synthetic routes of these series of compounds T1eT3 and their
intermediates are depicted in Scheme 1. Diethylamine, 4-fluoro-
benzaldehyde, and cyanuric chloride are available commercially.
The intermediate 1 and aldehyde 2 were synthesized efficiently
according to the literature.7,8 Compound 3 was produced by the
Wittig reaction between the Wittig reagent and the corresponding
aldehyde in the solid phase with t-BuOK as base.9 Compound 4 was
prepared by the hydrazine hydrate reduction method in the pres-
ence of Pd/C catalyst in ethanol medium.10 The targeted com-
pounds (T1eT3) were obtained by the palladium-catalyzed CeN
coupling strategy.11
As listed in Table 1 and Fig. 2, from T1 to T3, the one-photon
absorption maxima in DMF show regular red shifts as the
branch number increases and the spectral intensities also vary
regularly, the absorption coefficients (
consistently and significantly as the branch number increases.
Note that the
of T1eT3 are of the order of 104 and they in-
3 max) of the maxima increase
3
max
crease in the ratios 1.0:1.9:3.0 with the number of chromophores.
These can be assigned to the extended -delocalization and
p
a certain coupling between the branches in T2 and T3. The en-
hancement can be more clearly seen by revealing the reduced
molar absorbance
the molecular weight. The
1.0:1.2:1.4 for T1eT3. This means that the unit molecular weight
leads to larger by incorporating more branches into the
central triazine ring.
3 max/MW, which is defined as
3
divided by
max
3 max/MW values increase with a ratio of
3
max
The OPEF maxima were obtained at their maxima excitation
wavelengths in DMF. From T1 to T3, OPEF spectra show slight blue
shifts as the branch number increases. These blue shifts may be
because N,N-diethylaniline serves as an electron donor, 1,3,5-
triazine as an electron acceptor and styryl as a chromophore in
these compounds. The ICT state of molecules with DepeA struc-
tures has a high photoluminescence (PL) emission ability; hence,
the single peak in the PL emission spectra manifests that the state
responsible for the PL emission is not the localized excited state but
the ICT state. Thus, the different dipole moments of the ICT state
and the ground state lead to the shift in PL spectra.3c Note that the
fluorescence quantum yields (F) of T1eT3 reduce with the ratios of
3.8:2.6:1.0 as the branch number increases. This indicates that
these chromophores employed the nitrogen atom as the linkage
allowing internal rotation in the monomer form in organic solvents,
whereby the fluorescence was reduced. This can be ascribed to the
partial conjugation structure resulting from the delocalization of
the lone pair electrons on nitrogen.
Scheme 1. Synthetic routes to target compounds T1eT3.
2.2. One-photon absorption and emission properties
2.3. Two-photon properties
The photophysical data of T1eT3 are listed in Table 1. The one-
photon absorption (OPA) and one-photon excited fluorescence
(OPEF) were measured in five solvents of different polarities at
The two-photon excited fluorescence spectra (TPEF) of three
compounds in DMF were recorded at their maximum excitation
wavelength with a pulse duration of 140 fs under 500 mw (milli-
a
concentration c¼1ꢀ10ꢁ5 mol Lꢁ1
.
To further investigate the
watt). The TPEF data of T1eT3 are described in Table
1
spectra relationship of the compounds, the one-photon absorption
(c¼1ꢀ10ꢁ3 mol Lꢁ1).

Z. Zheng et al. / Tetrahedron 68 (2012) 6569e6574
6571
Table 1
The linear and two-photon absorption properties of T1eT3
max/MWc
lmax
Dne
Ff
lmax
sh
s
/MWi
a
b
d
g
Solvents
lmax
3
3
max
T1
T2
T3
Benzene
THF
Ethanol
Acetonitrile
DMF
Benzene
THF
Ethanol
Acetonitrile
DMF
Benzene
THF
Ethanol
Acetonitrile
DMF
375
373
370
371
373
376
373
370
370
375
374
373
364
371
377
4.69
4.32
4.40
3.12
3.82(1.0)
7.75
8.75
8.55
4.83
7.26(1.9)
9.42
11.30
7.86
8.76
11.26(3.0)
428
440
442
453
453
428
442
442
454
452
425
436
440
450
451
3302
4082
4403
4879
4735
3231
4185
4403
5001
4543
3209
3874
4745
4732
4352
0.138
0.096
0.037
0.013
0.069(3.8)
0.104
0.042
0.016
0.008
0.047(2.6)
0.100
0.063
0.023
0.014
0.0092(1.0)
0.0113(1.2)
0.0129(1.4)
481
484
488
1014(1.0)
1810(1.8)
2597(2.6)
2.45(1.0)
2.81(1.1)
2.97(1.2)
0.018(1.0)
a
Absorption peak position in nm (1ꢀ10ꢁ5 mol Lꢁ1).
b
c
d
e
f
Maximum molar absorbance in 104 molꢁ1 L cmꢁ1
.
The reduced 3 max, i.e., the value of 3 max divided by the molecular weight, the numbers in parentheses are relative values by assigning that of T1 as 1.
Peak position of SPEF in nm (1.0ꢀ10ꢁ5 mol Lꢁ1), excited at the absorption maximum.
Stokes shift in cmꢁ1
.
Quantum yields determined by using coumarin 307 (1.0ꢀ10ꢁ5 mol Lꢁ1) as the standard.
TPEF peak position in nm pumped by femtosecond laser pulses at 500 mw at their maximum excitation wavelength.
2PA cross section in GM.
g
h
i
Reduced cross section, i.e., 2PA cross section divided by molecular weight. The numbers in parentheses are relative values.
Two-photon fluorescence spectra of T1eT3 in DMF pumped by
wavelength can be attributed to the TPEF mechanism. As shown in
Fig. 3d, all the three compounds display 2PA activity in the range of
680e780 nm in DMF.
femtosecond laser pulses under different pumped powers at their
maximum excitation wavelengths are presented in Fig. 3aec. The
insets show logarithmic plots of the fluorescence integral versus
pumped powers with a slope of 1.94, 1.96, and 1.96 when the input
laser power is increasing, suggesting a two-photon excitation
mechanism. As no linear absorption was observed in the range from
500 nm to 2000 nm, the emission excited by 730e740 nm laser
It can be seen from Table 1 that the fluorescence peak wave-
lengths are obviously red-shifted by 28e37 nm compared to those
of OPEF in DMF, which can be explained by the reabsorption effect.
For one-photon induced emission measurements, we used dilute
solutions (1ꢀ10ꢁ5 mol Lꢁ1), thus the reabsorption of the fluores-
cence within the samples is negligible. In the case of two-photon
excitation, concentrated solutions (1ꢀ10ꢁ3 mol Lꢁ1) were used.
Since the 730e740 nm laser beam can pass through the whole
solution without linear depletion, the fluorescence emission is not
only from the surface layer, but also from inside the solution
sample. As a result, the reabsorption of the shorter wavelength
fluorescence by the concentrated sample can no longer be
neglected. The short wavelength side of the two-photon fluores-
cence was reabsorbed by the solution and red-shifts of the fluo-
rescence spectra were readily observed.12
As shown in Fig. 4, the intensities of TPEF of T1eT3 exhibit the
sequence of T3<T1<T2. These similarities between TPEF and OPEF
indicate that both the emissions for a given compound are from the
Fig. 1. Linear absorption and fluorescence of T1eT3 in five organic solvents of different
Fig. 2. OPA spectra (left) and OPEF spectra (right) of T1eT3 in DMF with a concen-
polarities with a concentration of 1ꢀ10ꢁ5 mol Lꢁ1
.
tration of 1ꢀ10ꢁ5 mol Lꢁ1
.

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Z. Zheng et al. / Tetrahedron 68 (2012) 6569e6574
Moreover, these well-conjugated structures allow sufficient elec-
tronic coupling between the branches, which has also been ex-
perimentally confirmed by the above-mentioned linear and non-
linear photophysical data.
3. Conclusion
We have reported one-step syntheses of a series of multi-
branched two-photon absorbing triazine derivatives by changing
the ratio of RNH2 and 2,4,6-trichloro-1,3,5-triazine. The studies
further demonstrated that having a
efficient way to transfer charge as well as a
s
-electron pair as bridge is an
bridge to induce
p
a large 2PA cross section. Among the three compounds, T3 was
found to exhibit a large 2PA across section values (2597 GM) as
measured by the two-photon induced fluorescence methods. We
believe that the design method and fabrication strategy are po-
tentially applicable to the derivatization of analogous two-photon
absorption chromophores.
Fig. 3. (a)e(c) 2PF spectra of T1eT3 in DMF pumped by femtosecond laser pulses under
different pumped powers at their maximum excitation wavelength, insert contains the
logarithmic plots of the fluorescence integral of chromophores versus different excita-
tion intensities. (d) Two-photon absorption cross sections of T1eT3 in DMF versus ex-
citation wavelengths of identical energy of 0.5 w (experimental uncertainties: 10%).
4. Experimental section
4.1. General experimental methods
Chemicals were purchased and used as received. Every solvent
was purified as conventional methods beforehand. IR spectra were
recorded with a Nicolet FT-IR NEXUS 870 spectrometer (KBr discs)
in the 4000e400 cmꢁ1 region. 1H and 13C NMR spectra were
recorded on a 400 or 500 MHz NMR instrument using CDCl3 or
(CD3)2CO as solvent. Chemical shifts were reported in parts per
million (ppm) relative to internal TMS (0 ppm) and coupling con-
stants in hertz. Splitting patterns were described as singlet (s),
doublet (d), triplet (t), quartet (q), or multiplet (m). Mass spectra
were obtained on a Micromass GCT-MS Spectrometer, and ESI-MS
spectra were obtain on a Finnigan LCQ Spectrometer. MALDI-TOF
mass spectra were recorded on a time-of-flight (TOF) mass spec-
trometer using a 337 nm nitrogen laser with alpha-cyano-4-
hydroxycinnamic acid as matrix.
4.2. Optical measurements
The one-photon absorption (OPA) spectra were recorded on
a UV-265 spectrophotometer. The one-photon excited fluorescence
(OPEF) spectra measurements were performed using a Hitachi F-
7000 fluorescence spectrophotometer. OPA and OPEF of T1eT3
were measured in five organic solvents of different polarities with
the concentration of 1.0ꢀ10ꢁ5 mol Lꢁ1. The quartz cuvettes used are
Fig. 4. The two-photon fluorescence spectra of T1eT3 in DMF (c¼1ꢀ10ꢁ3 mol Lꢁ1
)
pumped by femtosecond laser pulses at 500 mw at their maximum excitation
wavelength.
same excited state, though their initial FrankeCondon states may
be different. The difference between TPEF and OPEF is mainly
during the excitation process: two-photon absorption versus
single-photon absorption. It can be seen from Table 1, the 2PA
of 1 cm path length. The fluorescence quantum yields (F) were
determined by using coumarin 307 as the reference according to
the literature method.13 Quantum yields were corrected as follows:
ꢀ
ꢁ
rh2s Ds
sh2r Dr
cross-section values (
1.0:1.8:2.6 as the branch number increases in the series of T1eT3.
The reduced 2PA cross section /MW, which is defined as divided
s) increases obviously with the ratios of
A
A
Fs
¼
Fr
s
s
by the molecular weight, varies in a proportion of 1.0:1.1:1.2. This
means that the unit molecular weight enables enhanced 2PA cross-
section values as the branch number increases. This leads to the
indication of some interactions between branches in the molecule,
thus resulting in charge redistribution and extended delocalization.
Consequently, the enhancement effect works in both linear and
non-linear 2PA processes for compounds T1eT3.
With respect to our system, the nitrogen atom as the linkage
was adopted to combine a 1,3,5-triazine core with substituents to
provide a large 2PA cross sections (1014 GM, 1810 GM, 2597 GM),
which indicates the lone pair electrons on the amino nitrogen atom
of T1eT3 may have delocalized onto the conjugated system of the
molecule and it may increase intra-molecular charge transfer.
where the s and r indices designate the sample and reference
samples, respectively, A is the absorbance at lexc is the average
,
h
refractive index of the appropriate solution, and D is the integrated
area under the corrected emission spectrum.14
Two-photon absorption (2PA) cross-sections (d) of the samples
were obtained by two-photon excited fluorescence (TPEF)
method15 at femtosecond laser pulse and Ti: sapphire system
(680e1080 nm, 80 MHz, 140 fs) as the light source. The sample was
dissolved in different solvents at
a
concentration of
1.0ꢀ10ꢁ3 mol Lꢁ1. The intensities of TPEF spectra of the reference
and the sample were determined at their excitation wavelength.
Thus, 2PA cross section (d) of samples was determined by the
equation:

Z. Zheng et al. / Tetrahedron 68 (2012) 6569e6574
6573
(d, J¼16.4 Hz, 1H), 6.71 (d, J¼8.8 Hz, 2H), 3.43 (q, J¼7.1 Hz, 4H), 1.16
(t, J¼7.0 Hz, 6H); 13C NMR (100 MHz, CDCl3)
d
168.4, 164.2, 147.4,
Fref cref nref
F
d
¼
dref
F
c
n Fref
137.1, 133.9, 128.2, 126.4, 124.5, 123.0, 121.8, 111.8, 44.1, 13.0; HRMS
(GCT-MS): found 413.1177. C21H21Cl2N5 requires 413.1174.
where the ref subscripts stand for the reference molecule (here
fluorescein in aqueous solution at concentration of
4.3.6. Preparation of T2. A suspension of 0.14 g (0.75 mmol) of
cyanuric chloride, 0.58 g(4.5 mmol)ofDIPEAdissolvedin 5 mLofdry
THF was added into a round-bottom flask equipped with a magnetic
stirrer in an ice-bath, and a solution of 0.2 g (0.75 mmol) of 4 dis-
solved in 10 mL dry THF was added dropwise and stirred at room
temperature for 1 h. Then the reaction mixture was refluxed at 70 ꢂC
for 8 h. Another molar amount of 4 (0.2 g, 0.75 mmol) was added
dropwise into the preceding reaction system. The reaction was
refluxed and monitored by TLC. After the completion of the reaction,
appropriate amount of CH2Cl2 was added and the solution was
washed with water. The organic phase was dried with anhydrous
MgSO4, filtered, concentrated, and recrystallized with ethanol to give
0.13 g of yellow solid. Yield: 27.5%. Mp: >300 ꢂC; IR (KBr, cmꢁ1) 3421,
3017, 2969, 2928, 1601, 1570, 1501, 1373, 1264, 1188, 1076, 960, 825,
1.0ꢀ10ꢁ3 mol Lꢁ1 was used as reference).
d is the 2PA cross-
sectional value, c is the concentration of the solution, n is the re-
fractive index of the solution, F is the TPEF integral intensities of the
solution emitted at the exciting wavelength, and
F is the fluores-
cence quantum yield. The dref value of reference was taken from the
literature.16
4.3. General procedure for the preparation of T1eT3
4.3.1. 4-Nitro-benzyl-triphenylphosphonium bromide (1). 4-Nitro-
benzyl-triphenylphosphonium bromide was prepared referring the
literature.7
4.3.2. 4-Diethylaminobenzaldehyde
(2a). 4-Diethylaminobenzal-
797; 1H NMR (400 Hz, (CD3)2CO)
d
9.09 (s, 2H), 7.75 (d, J¼7.2 Hz, 4H),
dehyde was prepared referring the literature.8
7.53 (d, J¼7.6 Hz, 4H), 7.41 (d, J¼8.8 Hz, 4H), 7.15 (d, J¼16.4 Hz, 2H),
6.93 (d, J¼16.0 Hz, 2H), 6.72 (d, J¼8.8 Hz, 4H), 3.43 (q, J¼7.1 Hz, 8H),
4.3.3. Preparation of 3. Compound 3 was prepared referring the
literature.9 1.67 g 3 was obtained as a dark red flaky solid. Yield:
31.3%. Mp: 162e164 ꢂC; IR (KBr, cmꢁ1) 2977, 2925, 1603, 1578, 1520,
1503, 1378, 1329, 1103, 969, 749, 687; 1H NMR (400 Hz, (CD3)2CO)
1.17 (t, J¼7.0 Hz,12H); 13C NMR (100 MHz, CDCl3)
d 168.5,164.2,147.4,
137.2, 133.9, 128.2, 126.4, 124.5, 123.0, 121.8, 111.9, 44.1, 13.0; HRMS
(MSI): found 644.5000. C39H43ClN7 requires 644.3268.
d
8.19 (d, J¼8.8 Hz, 2H), 7.75 (d, J¼8.8 Hz, 2H), 7.50 (d, J¼9.2 Hz, 2H),
4.3.7. Preparation of T3. A suspension of 0.057 g (0.31 mmol) of
cyanuric chloride, 0.247 g (0.93 mmol) of intermediate 4, 0.130 g
(1.24 mmol) of anhydrous Na2CO3, and 30 mL of DMF under ni-
trogen was added into a three-necked flask equipped with a mag-
netic stirrer, a reflux condenser, and a nitrogen input tube. The
reaction mixture was heated to 140 ꢂC for 0.5 h and then 0.05 g
(5 mol %) Pd(PPh3)4 was added. The reaction mixture was refluxed
about 30 h and monitored by TLC. Then appropriate amount of
CH2Cl2 was added and the solution was washed with water. The
organic phase was dried with anhydrous MgSO4, filtered, and
concentrated. The gray product was purified by column chroma-
tography with petroleum (bp 60e90 ꢂC)/ethyl acetate (5:1 by vol-
ume) as eluent to yield 0.11 g of yellow solid. Yield: 41.4%. Mp:
>300 ꢂC; IR (KBr, cmꢁ1) 3390, 3018, 2968, 2927, 1603, 1519, 1488,
1412, 1374, 1265, 1186, 1076, 959, 823; 1H NMR (400 Hz, CDCl3)
7.41 (d, J¼16.0 Hz, 1H), 7.08 (d, J¼16.0 Hz, 1H), 6.73 (d, J¼9.2 Hz,
2H), 3.45 (q, J¼7.1 Hz, 4H), 1.17 (t, J¼7.2 Hz, 6H); 13C NMR (100 MHz,
CDCl3) d 148.3, 145.8, 145.2, 133.8, 133.1, 132.2, 132.0, 131.94, 131.92,
128.7, 128.6, 128.4, 126.0, 124.2, 123.3, 120.9, 111.5, 44.4, 12.6; HRMS
(GCT-MS): found 296.1505. C18H20N2O2 requires 296.1525.
4.3.4. Preparation of 4. A solution of 1.85 g (6.2 mmol) of 3 dis-
solved in 40 mL ethanol was added into a round-bottom flask
equipped with a magnetic stirrer and heated at 80 ꢂC. Then 1.25 g of
Pd/C catalyst was added into the preceding reaction system and
a solution of 7.4 g of 85% hydrazine hydrate was added dropwise for
about 0.5 h. The reaction was monitored by TLC. After the com-
pletion of the reaction, the mixture was filtered immediately, stir-
red by slowly adding appropriate amount of water and filtered
under vacuum to give 1.35 g of white solid. Yield: 82.0%. Mp:
109e110 ꢂC; IR (KBr, cmꢁ1) 3450, 3364, 3016, 2967, 2967, 1609,
1520, 1463, 1371, 1356, 1261, 1195, 1151, 962, 824; 1H NMR (400 Hz,
d
7.56 (d, J¼8.4 Hz, 6H), 7.44 (d, J¼8.0 Hz, 6H), 7.40 (d, J¼8.4 Hz, 6H),
7.50 (d, J¼16.4 Hz, 3H), 6.90 (d, J¼16.4 Hz, 3H), 6.68 (d, J¼8.4 Hz,
6H), 3.40 (q, J¼7.1 Hz, 12H), 1.20 (t, J¼7.0 Hz, 18H); 13C NMR
(CD3)2CO)
d
7.32 (d, J¼8.4 Hz, 2H), 7.24 (d, J¼8.4 Hz, 2H), 6.82 (s,
(100 MHz, CDCl3) d 164.2, 147.2, 137.1, 133.5, 127.8, 127.7, 126.4,
2H), 6.67 (d, J¼8.8 Hz, 2H), 4.66 (s, 2H), 3.39 (q, J¼7.1 Hz, 4H),1.14 (t,
125.1, 123.5, 120.9, 111.8, 44.4, 12.7; MALDI-TOF: found 873.4152.
C57H63N9 requires 873.5206.
J¼7.2 Hz, 6H); 13C NMR (125 MHz, CDCl3)
d 147.0,145.4,129.4,129.2,
127.5, 127.3, 125.6, 124.2, 115.5, 112.0, 44.7, 12.8; HRMS (GCT-MS):
found 266.1777. C18H22N2 requires 266.1783.
4.3.5. Preparation of T1. A suspension of 0.14 g (0.75 mmol) of
cyanuric chloride, 0.22 g (1.5 mmol) of anhydrous K2CO3 dissolved
in 5 mL of dry THF was added into a round-bottom flask equipped
with a magnetic stirrer in the ice bath, and a solution of 0.2 g
(0.75 mmol) of 4 dissolved in 10 mL dry THF was added dropwise
and stirred at room temperature for 1 h. Then the mixture was
refluxed at 70 ꢂC for 8 h. The reaction was monitored by TLC. After
the completion of the reaction, appropriate amount of CH2Cl2 was
added with stirring and the solution was washed three times with
water. The organic phase was obtained after removing the aqueous
phase. Then it was dried with anhydrous MgSO4, filtered, concen-
trated, and recrystallized with ethanol to give 0.15 g of yellow solid.
Yield: 49.0%. Mp: >300 ꢂC; IR (KBr, cmꢁ1) 3421, 3017, 2969, 2928,
1601, 1570, 1518, 1501, 1373, 1265, 1151, 1188, 1076, 961, 825, 797; 1H
Acknowledgements
This work was supported by Program for New Century Excellent
Talents in University (China), Doctoral Program Foundation of
Ministry of Education of China (20113401110004), Science and
Technological Fund of Anhui Province for Outstanding Youth
(10040606Y22), National Natural Science Foundation of China
(21071001, 51142011, 21102001, and 21101001), Natural Science
Foundation of Education Committee of Anhui Province
(KJ2012A024, KJ2010A030), the 211 Project of Anhui University, the
Team for Scientific Innovation Foundation of Anhui Province
(2006KJ007TD), Ministry of Education Funded Projects Focus on
Returned Overseas Scholar, and Anhui University Student In-
novative Experiment Plan (XJ103575023, KYXL201100337). Thank
Lingxia Zheng of Department of Physics and Materials Science of
City University of Hong Kong for her help in writing the paper.
NMR (400 Hz, (CD3)2CO)
d
9.91 (s, 1H), 7.71 (d, J¼8.4 Hz, 2H), 7.58
(d, J¼8.8 Hz, 2H), 7.43 (d, J¼8.8 Hz, 2H), 7.13 (d, J¼16.4 Hz, 1H), 6.96

6574
Z. Zheng et al. / Tetrahedron 68 (2012) 6569e6574
4. (a) Inomata, H.; Goushi, K.; Masuko, T.; Konno, T.; Imai, T.; Sasabe, H.; Brown, J.
Supplementary data
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Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.tet.2012.03.055. These data in-
clude MOL files and InChiKeys of the most important compounds
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