Investigation of photophysical properties of new branched compounds with triazine and benzimidazole units

Article abstract of DOI:10.1039/c4nj00360h

Three new acceptor-donor-acceptor branched compounds with triazine and benzimidazole units (M1, M2, and M3) were synthesized and characterized by infrared, hydrogen-1 nuclear magnetic resonance, carbon-13 nuclear magnetic resonance, mass spectrometry, and elemental analysis. Their photophysical properties were investigated including linear absorption, single-photon excited fluorescence, fluorescence quantum yield, two-photon absorption, and frequency up-converted fluorescence. When the number of branches increases, the spectral positions of the linear absorption and the single-photon excited fluorescence show red shifts, while the fluorescence quantum yields decrease. When the polarity of solvents increases, the spectral positions of the single-photon excited fluorescence and the Stokes shifts also show red shifts, while the fluorescence quantum yields of the two-branched compound (M2) and three-branched compound (M3) decrease. Under the excitation of an 800 nm laser with a pulse width of 80 fs, all these compounds emit intense green frequency up-converted fluorescence, and the two-photon absorption cross-sections are 210, 968, and 1613 GM for M1, M2, and M3, respectively. This result shows that significant enhancement of the two-photon absorption cross-section can be achieved by sufficient electronic coupling between the strong charge transfer acceptor-donor-acceptor quadrupolar branches through the s-triazine core. the Partner Organisations 2014.

Full text of DOI:10.1039/c4nj00360h

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Investigation of photophysical properties of
new branched compounds with triazine and
benzimidazole units
Cite this:DOI: 10.1039/c4nj00360h
Zhibin Cai,*a Mao Zhou,b Bo Li,c Ye Chen,c Fan Jina and Jiuqiang Huanga
Three new acceptor–donor–acceptor branched compounds with triazine and benzimidazole units (M1,
M2, and M3) were synthesized and characterized by infrared, hydrogen-1 nuclear magnetic resonance,
carbon-13 nuclear magnetic resonance, mass spectrometry, and elemental analysis. Their photophysical
properties were investigated including linear absorption, single-photon excited fluorescence, fluorescence
quantum yield, two-photon absorption, and frequency up-converted fluorescence. When the number of
branches increases, the spectral positions of the linear absorption and the single-photon excited fluorescence
show red shifts, while the fluorescence quantum yields decrease. When the polarity of solvents increases, the
spectral positions of the single-photon excited fluorescence and the Stokes shifts also show red shifts, while
the fluorescence quantum yields of the two-branched compound (M2) and three-branched compound (M3)
decrease. Under the excitation of an 800 nm laser with a pulse width of 80 fs, all these compounds emit
intense green frequency up-converted fluorescence, and the two-photon absorption cross-sections are 210,
968, and 1613 GM for M1, M2, and M3, respectively. This result shows that significant enhancement of the
two-photon absorption cross-section can be achieved by sufficient electronic coupling between the strong
charge transfer acceptor–donor–acceptor quadrupolar branches through the s-triazine core.
Received (in Montpellier, France)
11th March 2014,
Accepted 23rd April 2014
DOI: 10.1039/c4nj00360h
www.rsc.org/njc
and synthesized, some of which show significant enhancement
1. Introduction
of s.11 However, the known multi-branched TPA materials
The promising applications in many fields such as fluorescence normally consist of D–p–A dipolar molecules connected via a
imaging,1 fluorescent microscopy,2 three-dimensional optical common core.12 Little attention is paid to the incorporation of
data storage,3 three-dimensional microfabrication,4 frequency A–D–A/D–A–D quadrupolar molecules into the multi-branched
up-converted lasing,5 optical power limiting,6 and photo- structures. Thus such TPA materials remain largely untapped.
dynamic therapy7 have fuelled extensive research on two-
Several structural parameters of multi-branched compounds
photon absorption (TPA) materials. The development of efficient are expected to influence TPA properties, such as the nature of
TPA materials with large TPA cross-sections (s) in the near- the core and of the branches, as well as node and peripheral
infrared regions (700–1000 nm) has recently become one of the moieties. s-Triazine has two important properties that make it
most important subjects in material chemistry.
become an ideal core: (1) with its ionization potential value of
Some strategies for molecular design have been proposed to 11.67 eV, it is more p-electron-deficient than other heterocyclic
improve s values. Among them, two general structural motifs rings; (2) unlike the benzene ring, connecting three large
are donor–bridge–acceptor (D–p–A) dipoles8 and acceptor– branches at the 2-, 4-, and 6-positions of a triazine will not
donor–acceptor (A–D–A)/donor–acceptor–donor (D–A–D) quad- create the steric interactions of the ortho-hydrogens. As a result,
rupoles.9 In 1999, Prasad and co-workers10 reported the discovery coplanarity is most probable with the ramification of extended
of non-additive enhancement of s in multi-branched structures electron delocalization between the triazine core and the
for the first time, which led to a new design strategy. Since then, a branches. Benzimidazole is an interesting aromatic hetero-
number of novel multi-branched compounds have been designed cycle, which possesses a p-conjugated electron system and
can act as an acceptor group. Its derivatives have received
increasing attention due to their distinctive linear and non-
linear optical properties and also due to their excellent thermal
stability. They are extensively used as second-order nonlinear
optical materials13 and fluorescent probes for recognizing
target molecules/ions.14
a College of Chemical Engineering, Zhejiang University of Technology, Hangzhou,
310014, P. R. China. E-mail: caizbmail@126.com
b Zhejiang Poly Pharmaceutical Co. Ltd., Hangzhou, 310009, P. R. China
c Key Laboratory of Polar Materials and Devices, Ministry of Education, East China
Normal University, Shanghai, 200241, P. R. China
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In this work, we designed and synthesized new one-
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As shown in Fig. 1 and listed in Table 1, there are two strong
branched, two-branched, and three-branched s-triazine deriva- absorption bands attributed to the solute molecules. The
tives (M1, M2 and M3), which have a strong electron-accepting absorption at about 343–352 nm is localized in styrene p–p*
triazine core and 1,4-phenylenedivinylene arms that feature transition, whereas the longer wavelength region absorption
peripheral electron-accepting benzimidazole. Two electron- (about 397–442 nm), namely the maximal linear absorption
donating methoxy groups are attached in the middle of the peak, can be assigned to an intramolecular charge transfer
arms in order to generate an A–D–A character. Their structures (ICT) transition. The absorption maxima (lambasx) of the com-
were characterized by IR, 1H NMR, 13C NMR, MS, and elemental pounds change slightly in different solvents, except in CHCl3.
analysis. The single- and two-photon related photophysical This suggests that there is a strong interaction between the lone
properties were investigated.
pair of electrons on the N atoms of the solute molecules and s*
(C–H) antibonding orbitals in CHCl3. In general, the extension
of the p-system exerts an important influence on the absorption
spectra. For example, the lambasx of M1 in THF is 421 nm, which is
red-shifted by 24 nm relative to that of MQ (397 nm), as M1 has
a longer conjugation length than MQ by the introduction of an
2. Results and discussion
2.1. Synthesis and characterization
The target compounds M1, M2, and M3 were synthesized
according to Scheme 1.
s-triazine unit and a vinyl group. In addition, for the com-
abs
max
pounds with the different number of branches, the l
2,4,6-Trimethyl-s-triazine (1) was prepared by trimerization
of ethyl acetimidate using glacial acetic acid as the catalyst. The
important intermediate aldehyde MQ containing a benzimida-
zole unit was reported here for the first time and was synthe-
sized by the condensation of 2-methyl-1H-benzimidazole with
2,5-dimethoxy-1,4-benzenedicarboxaldehyde (2). 2 was obtained
according to Sommelet’s procedure by reaction of 1,4-bis-
(bromomethyl)-2,5-dimethoxybenzene with hexamethylenetetra-
mine in chloroform, followed by hydrolysis in acetic acid.
Finally, the alkaline condensation reaction of 1 with MQ gave
the target compounds (M1, M2 and M3) in moderate yields. The
methyl group at the 2-, 4- or 6-position of the s-triazine ring can
be activated by the N atoms, which has the same high reactivity.
In order to improve the yield of one-branched (M1), two-
branched (M2), and three-branched (M3) products, respectively,
the key points of this condensation reaction are the molar ratio
of 1 to MQ and the feeding sequence of them.
increases from B423 nm to B433 nm and B438 nm when
going from M1 to M2 and M3. And their molar extinction
coefficients (e) also increase obviously. For example, the e in
THF increases from 7.54 ꢁ 104 molꢀ1 L cmꢀ1 of M1 to 17.81 ꢁ
104 molꢀ1 L cmꢀ1 of M2 and 25.51 ꢁ 104 molꢀ1 L cmꢀ1 of M3.
These give a clear indication of a certain coupling between the
branches, resulting in charge redistribution and extended
p-delocalization.
As shown in Fig. 2 and listed in Table 1, all these com-
pounds emit SPEF between 400 and 650 nm under the excita-
tion at their maximum absorption wavelengths. In contrast to
the absorption properties, the SPEF maxima (lSPEF
max ) exhibit
solvent polarity dependencies. The empirical parameter ET(30)
has been used fairly effectively to describe solvent polarity,
whose values of THF, CHCl3, CH2Cl2, and CH3CN are 37.4, 39.1,
40.7, and 45.6, respectively.15 Upon increasing solvent polarity,
SPEF
max
both the l
and the Stokes shift (Dv) show regular red shifts.
The elemental analyses of three target compounds (M1, M2
and M3) and the important intermediate (MQ) were in agree-
ment with their molecular formulae and all of them gave well-
defined 1H and 13C NMR spectra. The (E)-configurations of the
C–C double bonds were certified by the coupling constants
3J(H,H) = 16.0–16.6 Hz for the olefinic AB spin systems. The
strong band between 1505 and 1529 cmꢀ1 in the FT-IR spectra
was assigned to the skeleton vibration absorption of the s-triazine
ring. The characteristic absorption peaks around 3380, 1625, and
1211 (1040) cmꢀ1 indicated the existence of N–H, CQC, and C–O–
C, respectively. In the ESI-MS spectrum of M3, the signals of
[M + H]+, [M + 2H]2+, and [M + 3H]3+ were detected. In the case of
M2, the signals of [M + H]+ and [M + 2H]2+ were detected. In the
case of M1, only the signal of [M + H]+ was detected. This may be
due to the fact that imidazole is a relatively strong base.
A reasonable explanation is that the change in the energy
positions of the ground state S0 and the excited state S1 is
related to their dipole moments. In this case, the dipole
moment of S1 may be larger than that of S0, S1 is more lowered
than S0 by the polarity of the solvent, resulting in the reduction
of the energy gap between S0 and S1. Compared with MQ, the
SPEF
max
l
and the maximum SPEF intensity (ISmPaExF) of M1 increase
consistently and significantly. For example, in THF solution,
SPEF
the l
of M1 at 483 nm is red-shifted by 42 nm relative to that
max
SPEF
of MQ at 441 nm, and the I
increases with the ratio of
max
1.0 : 5.8 (MQ : M1). This can be attributed to the longer con-
jugation length and the stronger electron-accepting ability of
s-triazine with respect to that of the formyl group. The compar-
SPEF
ison among M1, M2, and M3 indicates that both the l
and
max
SPEF
the I
increase as the branch number increases, which
max
implies the large extension of p-delocalization resulting from
the cooperative effect between the branches. The fluorescence
2.2. Linear absorption and single-photon excited fluorescence
The linear optical properties of the target compounds (M1, M2 quantum yields (F) in different solvents are measured with a
and M3) and the intermediate (MQ) in various solvents are 0.1 mol Lꢀ1 sodium hydroxide solution of fluorescein (F =
listed in Table 1. Their UV-visible absorption and single-photon 0.916) as reference. The F of M1 is very high and is more than
excited fluorescence (SPEF) spectra in THF are shown in three times that of MQ, suggesting that the architecture of M1
Fig. 1 and 2.
helps suppress the nonradiative decay pathways. The F of MQ
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Scheme 1 Synthesis of the target compounds (M1, M2 and M3).
(0.25–0.30) and M1 (0.86–0.92) do not vary significantly in leads to the decrease of F,17 so the results here also evidenced
different solvents, whereas the F of M2 and M3 decrease with the enhancement of the TICT effect when the number of
increasing solvent polarity. Especially, the F dramatically branches increases.
decreases to 0.03 for M2 and 0.01 for M3 in highly polar
By comparing the linear photophysical data in Table 1, we
max , Dv, and
CH3CN. Another noteworthy observation is that the F of the can find that the linear spectral behaviors (lambasx, lSPEF
one-branched, two-branched, and three-branched compounds F) of M2 are closer to those of M3, while more different from
can be sequenced as M3 o M2 o M1. Normally, the twisted those of M1. These imply that the electronic structure of M2 is
intramolecular charge transfer (TICT) process in a molecule more similar to M3, rather than to M1.
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Table 1 Linear and nonlinear optical properties of the target compounds (M1, M2 and M3) and the intermediate (MQ)
abs a
max
SPEF b
max
TPEF e
Compound
Solvent
l
(nm)
l
(nm)
Dvc (cmꢀ1
)
Fd
l
max
(nm)
s f (GM)
s/MWg
MQ
THF
397
402
399
397
441
458
459
460
2513
3042
3276
3450
0.25
0.27
0.30
0.28
443, 461
479, 492
485, 496
497
101
0.328 (0.6)
CHCl3
CH2Cl2
CH3CN
M1
M2
THF
421
428
422
420
483
493
497
500
3049
3081
3576
3810
0.92
0.86
0.90
0.87
210
968
0.508 (1.0)
1.377 (2.7)
1.624 (3.2)
CHCl3
CH2Cl2
CH3CN
THF
431
439
433
431
490
501
503
505
2794
2819
3214
3400
0.46
0.31
0.17
0.03
CHCl3
CH2Cl2
CH3CN
M3
THF
435
442
438
436
493
504
506
508
2705
2783
3068
3251
0.38
0.23
0.12
0.01
1613
CHCl3
CH2Cl2
CH3CN
a
b
Maximum linear absorption wavelength, c = 1 ꢁ 10ꢀ5 mol Lꢀ1
.
Maximum single-photon excited fluorescence wavelength, c = 1 ꢁ 10ꢀ7 mol Lꢀ1
.
c
d
e
f
Stokes shift. Fluorescence quantum yield. Maximum two-photon excited fluorescence wavelength, c = 1 ꢁ 10ꢀ5 mol Lꢀ1
.
Two-photon
absorption cross-section, 1 GM = 1 ꢁ 10ꢀ50 cm4 s photonꢀ1
.
Reduced TPA cross-section, i.e., a two-photon absorption cross-section divided by the
g
molecular weight. The numbers in parentheses are relative values.
2.3. Two-photon properties
The two-photon excited fluorescence (TPEF) spectra of the
target compounds (M1, M2 and M3) and the intermediate
(MQ) in THF are shown in Fig. 3. The corresponding nonlinear
optical properties are listed in Table 1. Upon excitation of
800 nm laser pulses with a pulse width of 80 fs, MQ emits blue
frequency up-converted fluorescence with two maximum emis-
sion peaks at 443 and 461 nm, while the target compounds emit
intense green frequency up-converted fluorescence with the
TPEF
max
maximum TPEF wavelength (l
) at 479 and 492 nm
(shoulder) for M1, 485 (shoulder) and 496 nm for M2, and
497 nm for M3. M1, M2, and M3 also show shoulder emission
bands at B514 nm. These observations indicate the existence
of more than one emitting state. The dominant state here
should not be the locally excited state but the ICT state.
Fig. 1 UV-visible absorption spectra of the target compounds (M1, M2
and M3) and the intermediate (MQ) in THF (c = 1 ꢁ 10ꢀ5 mol Lꢀ1).
SPEF
TPEF
Compared with the l
in THF, the corresponding l
is
max
max
Fig. 2 SPEF spectra of the target compounds (M1, M2 and M3) and the
intermediate (MQ) in THF (c = 1 ꢁ 10ꢀ7 mol Lꢀ1).
Fig. 3 TPEF spectra of the target compounds (M1, M2 and M3) and the
intermediate (MQ) in THF (c = 1 ꢁ 10ꢀ5 mol Lꢀ1).
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Fig. 4 TPEF spectra of the target compounds (M1, M2 and M3) and the intermediate (MQ) in THF under different laser excitation intensities
(c = 1 ꢁ 10ꢀ5 mol Lꢀ1). Insets are the TPEF intensities versus the square of the laser excitation intensities.
bathochromically shifted. This can be attributed to the reab- we selected fluorescein in 0.1 mol Lꢀ1 sodium hydroxide
sorption effect, since the SPEF spectra in the short wavelength (c = 1 ꢁ 10ꢀ5 mol Lꢀ1) as the reference (s = 36 GM18).
sides and the linear absorption spectra in the long wavelength
sides overlap.
It is accepted that the s is proportional to the imaginary part
of the third-order polarizability,19 and if the frequency (w) is
As shown in Fig. 1, all of the compounds have absorption neglected, the third-order polarizability, g, can be expressed as
cut-offs below 500 nm, indicating that there will be no linear the eqn (2):20,21
absorption when the laser source of 800 nm is used for TPA
Mge2Dmge
2
2
02
gxxxx ¼ 24
ꢀ 24
4 þ
(2)
X
Mge
Mge Mee
2
applications. Their TPEF spectra in THF under different laser
excitation intensities are displayed in Fig. 4. The fluorescence
intensities show quadratic dependences on the laser excitation
3
3
0
Ege
Ege
Ege Ege
e0
intensities, suggesting that the up-converted fluorescence emis- Therefore, the s value depends predominantly on the transition
sions originate from the TPA process. dipole moment between the ground state and the first excited
The s is obtained by comparing the TPEF intensity of the state (Mge), the transition energy between the ground state and
sample with that of a reference compound using the following the first excited state (Ege), and the dipole moment difference
eqn (1):18
between the ground state and the first excited state (Dmge).
The s of M1 is 210 GM, which is twice as large as that of MQ
(101 GM). The s-triazine acceptor and elongation of the con-
jugation pathway make M1 have stronger ICT and a higher
degree of electron delocalization, thus Ege decreases and Mge
Fs fr nr cr
Fr fs ns cs
ss ¼
sr
(1)
where the subscripts s and r denote the sample and the increases. From eqn (2), the smaller Ege and larger Mge is, the
reference compound. F and F represent the TPEF integral higher the g will be, finally leading to the increase of the s
intensity and the SPEF quantum yield. n and c are the refractive value. The s increases significantly as the number of branches
index and the concentration of the solution. In this work, increases from 1 to 2 and 3. The ratio of s is 1.0 : 4.6 : 7.7
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(M1 : M2 : M3), which is greatly larger than that between the
The linear absorption spectra were measured on a Shimadzu
branch numbers (1 : 2 : 3). The reduced TPA cross-section UV-2550 UV-visible spectrophotometer. The SPEF spectra mea-
(s/MW), which is most useful with regards to material selection surements were performed using a RF-5301PC fluorescence
when the maximal number density of a chromophore is spectrophotometer with the maximum absorption wavelengths
required, also varies in a proportion of 1.0 : 2.7 : 3.2. This as the excitation wavelengths. The fluorescence quantum yields
dramatic enhancement of M2 and M3 should be attributed to were determined using fluorescein in 0.1 mol Lꢀ1 sodium
the sufficient electronic coupling between the branches.22 Their hydroxide as the standard. The TPEF spectra were measured
individual branches, which have a A–D–A quadrupolar charac- using a femtosecond Ti:Sapphire laser (Micra + RegA9000,
ter, can not only lead to strong intra-branch charge transfer, but Conherent) as the pump source with a pulse width of 80 fs, a
also facilitate inter-branch electronic communication through repetition rate of 250 kz, and a central wavelength of 800 nm.
the s-triazine core. It should be noted that the two-photon
4.2. Synthesis
excitation studies were performed at one wavelength (800 nm)
owing to the limit of our laser apparatus. A further enhance-
4-[(1E)-2-(1H-Benzimidazol-2-yl)ethenyl]-2,5-dimethoxybenz-
ment of the s value should be expected at the optimal excitation aldehyde (MQ). A mixture of 2-methyl-1H-benzimidazole (1.32 g,
wavelength.
10 mmol), 2 (1.94 g, 10 mmol), acetic anhydride (3 mL), and
acetic acid (1.5 mL) was heated under reflux for 6 h, then cooled
to room temperature. After concentrated hydrochloric acid
(15 mL) was added, the mixture was filtered. The filtrate was
neutralized with 30% aqueous sodium hydroxide solution
3. Conclusions
The combination of an s-triazine core (acceptor), methoxy (30 mL) and gave a precipitate. The precipitate was purified by
groups (donor), and benzimidazole end-groups (acceptor) with column chromatography on silica gel using petroleum ether/
1,4-phenylenedivinylene p-bridges has resulted in a new type of ethyl acetate (10 : 1) as an eluent to give yellow needle crystals
acceptor–donor–acceptor branched compounds. They were suc- (2.32 g, 75.3%). M.p. 145–147 1C; 1H NMR (500 MHz, DMSO-d6):
cessfully synthesized and characterized by infrared, hydrogen-1 d 12.77 (s, 1H), 10.35 (s, 1H), 7.92 (d, J = 16.5 Hz, 1H), 7.62 (d, J =
nuclear magnetic resonance, carbon-13 nuclear magnetic reso- 7.5 Hz, 1H), 7.59 (s, 1H), 7.54 (d, J = 16.5 Hz, 1H), 7.49 (d, J =
nance, mass spectrometry, and elemental analysis. Their linear 7.5 Hz, 1H), 7.31 (s, 1H), 7.18–7.23 (m, 2H), 3.99 (s, 3H), 3.92
and nonlinear photophysical properties were investigated. (s, 3H); FT-IR (KBr): v 3264, 3055, 2953, 2868, 1664, 1604, 1473,
Under an 800 nm laser irradiation with a pulse width of 1413, 1213, 1127, 1040, 971, 882, 733, 694 cmꢀ1; ESI-MS: m/z (%):
80 fs, the three-branched compound M3 exhibits the strongest 308.8 (100) [M + H]+; elemental analysis calcd (%) for C18H16N2O3:
two-photon excited fluorescence and the largest two-photon C 70.12, H 5.23, N 9.09; found C 70.45, H 5.29, N 9.35.
absorption cross-section value of 1613 GM, which is higher
2-[(1E)-2-[2,5-Dimethoxy-4-[(1E)-2-(4,6-dimethyl-1,3,5-triazin-
than the reported two-photon absorption cross-section values 2-yl)ethenyl]phenyl]ethenyl]-1H-benzimidazole (M1). To a mix-
of many donor–p–acceptor three-branched compounds with an ture of 1 (0.55 g, 4.5 mmol), potassium hydroxide (0.3 g), and
s-triazine core.23 This result shows that significant enhance- methonal (30 mL) was added a solution of MQ (0.92 g, 3 mmol)
ment of the two-photon absorption cross-section can be in methanol (30 mL) dropwise. The reaction mixture was
achieved by sufficient electronic coupling between the strong refluxed for 20 h and then the solvent was removed. The residue
charge transfer acceptor–donor–acceptor quadrupolar branches was purified by column chromatography on silica gel using
through the s-triazine core.
petroleum ether/ethyl acetate (8 : 1) as an eluent to give a
orange-yellow crystalline powder (0.63 g, 50.8%). M.p. 276–
278 1C; 1H NMR (500 MHz, DMSO-d6): d 12.70 (s, 1H), 8.44
(d, J = 16.1 Hz, 1H), 7.92 (d, J = 16.6 Hz, 1H), 7.60 (d, J = 7.3 Hz,
1H), 7.54 (s, 1H), 7.48 (d, J = 7.3 Hz, 1H), 7.45 (s, 1H), 7.43 (d, J =
16.6 Hz, 1H), 7.34 (d, J = 16.1 Hz, 1H), 7.17–7.22 (m, 2H), 3.98
4. Experimental
4.1. Materials and instruments
2,4,6-Trimethyl-s-triazine (1)24 and 2,5-dimethoxy-1,4-benzene- (s, 6H), 2.56 (s, 6H); 13C NMR (500 MHz, DMSO-d6): d 175.5,
dicarboxaldehyde (2)25 were synthesized according to the litera- 170.6, 152.2, 151.4, 151.2, 135.4, 128.3, 127.3, 126.3, 124.4,
ture procedures. Other materials were commercially available 122.0, 119.5, 111.0, 109.9, 56.3, 56.2, 25.1; FT-IR (KBr): v 3388,
and were used without further purification.
3050, 2931, 2831, 1629, 1529, 1412, 1374, 1214, 1042, 977, 849,
Melting points were measured on an X-4 micromelting point 749 cmꢀ1; ESI-MS: m/z (%): 414.1 (100) [M + H]+; HRESI-MS
apparatus without correction. 1H and 13C NMR spectra were calcd for C24H24N5O2 [M + H]+: 414.1930; found: 414.1921;
collected on a Bruker AVANCE III 500 apparatus, with TMS as elemental analysis calcd (%) for C24H23N5O2: C 69.72, H 5.61,
internal standard and DMSO-d6 as solvent. FT-IR spectra were N 16.94; found: C 69.97, H 5.65, N 17.13.
recorded on a Thermo Nicolet 6700 spectrometer using KBr
2,20-[(6-Methyl-1,3,5-triazine-2,4-diyl)bis[(1E)-2,1-ethenediyl(2,5-
pellets. Mass spectra were recorded on a Therm LCQ TM Deca dimethoxy-4,1-phenylene)-(1E)-2,1-ethenediyl]]bis-1H-benzimidazole
XP plus ion trap mass spectrometry instrument. Elemental (M2). This compound was synthesized using a procedure similar to
analyses were conducted on a Thermo Finnigan Flash EA that described for M1 except that the molar ratio between MQ and 1
1112 apparatus.
was changed to 2.5 : 1. Orange-red crystalline powder. Yield 43.2%.
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M.p. 228–230 1C; 1H NMR (500 MHz, DMSO-d6): d 12.72 (s, 2H), 8.50
(d, J = 16.1 Hz, 2H), 7.93 (d, J = 16.5 Hz, 2H), 7.61 (d, J = 7.6 Hz, 2H),
7.58 (s, 2H), 7.49 (d, J = 7.7 Hz, 2H), 7.47 (s, 2H), 7.45 (d, J = 16.6 Hz,
2H), 7.40 (d, J = 16.0 Hz, 2H), 7.16–7.23 (m, 4H), 4.00 (s, 12H), 2.63
(s, 3H); 13C NMR (500 MHz, DMSO-d6): d 175.7, 170.9, 152.3, 151.4,
151.1, 135.3, 128.4, 127.3, 126.6, 124.5, 122.1, 119.4, 111.0, 109.9,
56.3, 56.2, 25.4; FT-IR (KBr): v 3371, 3040, 2932, 2832, 1625, 1520,
1410, 1369, 1211, 1040, 978, 852, 743 cmꢀ1; ESI-MS: m/z (%): 704.5
(100) [M + H]+, 352.9 (30) [M + 2H]2+; HRESI-MS calcd for
C42H38N7O4 [M + H]+: 704.2985; found: 704.3012; elemental analysis
calcd (%) for C42H37N7O4: C 71.68, H 5.30, N 13.93; found: C 71.89,
H 5.47, N 14.08.
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dimethoxy-4,1-phenylene)-(1E)-2,1-ethenediyl]]tris-1H-benzimidazole
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that described for M1 except that the molar ratio between MQ
and 1 was changed to 6 : 1 and 1 was added to MQ instead of the
latter being added to the former. Red crystalline powder. Yield
37.6%. M.p. 270–272 1C; 1H NMR (500 MHz, DMSO-d6): d 12.72
(s, 3H), 8.58 (d, J = 16.0 Hz, 3H), 7.95 (d, J = 16.5 Hz, 3H), 7.61
(d, J = 7.6 Hz, 3H), 7.58 (s, 3H), 7.49 (d, J = 7.5 Hz, 3H), 7.47
(s, 3H), 7.45 (d, J = 16.6 Hz, 3H), 7.40 (d, J = 16.0 Hz, 3H), 7.18–
7.21 (m, 6H), 4.04 (s, 18H); 13C NMR (500 MHz, DMSO-d6): d
171.0, 152.3, 151.5, 151.2, 135.3, 128.4, 127.4, 126.8, 124.6, 122.1,
119.6, 110.9, 110.0, 56.4, 56.3; FT-IR (KBr): v 3381, 3056, 2931,
2835, 1622, 1505, 1409, 1373, 1210, 1040, 975, 852, 742 cmꢀ1
;
ESI-MS: m/z (%): 994.4 (60) [M + H]+, 497.9 (100) [M + 2H]2+, 332.5
(50) [M + 3H]3+; HRESI-MS calcd for C60H52N9O6 [M + H]+:
994.4041; found: 994.4013; elemental analysis calcd (%) for
C60H51N9O6: C 72.49, H 5.17, N 12.68; found: C 72.68, H 5.24,
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