Synthesis and photophysical properties of tripod BODIPY dyes bearing mono-phenolic derivatives

Article abstract of DOI:10.1016/j.tet.2014.12.072

A series of new tripod boron dipyrromethene (BODIPY) dyes bearing mono-phenolic derivatives were synthesized and characterized. An optimized reaction condition for the synthesis of the bis-substituted intermediates was obtained. An unanticipated phenol-de

Full text of DOI:10.1016/j.tet.2014.12.072

Tetrahedron 71 (2015) 1304e1310
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and photophysical properties of tripod BODIPY dyes
bearing mono-phenolic derivatives
*
Jiahui Lu, Xin Qi , Tao Yue, Weiran Tang, Liping Ding
College of Material Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 August 2014
Received in revised form 8 December 2014
Accepted 21 December 2014
Available online 6 January 2015
A series of new tripod boron dipyrromethene (BODIPY) dyes bearing mono-phenolic derivatives were
synthesized and characterized. An optimized reaction condition for the synthesis of the bis-substituted
intermediates was obtained. An unanticipated phenol-dependent effect on the yields was found and
a hypothetic mechanism was proposed to elucidate the reactivity of the tripod dipyrromethene species
during the complexation step. The new dyes showed typical photophysical properties of the BODIPY
fluorophore.
Keywords:
Ó 2014 Elsevier Ltd. All rights reserved.
Boron dipyrromethene (BODIPY)
Tripod dipyrromethene
Cyanuric chloride
Phenol-dependent reactivity
1. Introduction
those based on photoinduced electron transfer (PET) principle, have
been formulated in this way.34e36 In this regard, a tripod BODIPY
Derivatives
of
4,4-difluoro-4-bora-3a,4a-diaza-s-indacene
structure, in which the meso aryl ring of the BODIPY core was
bridged with two groups via a 1,3,5-triazine unit, was reported
during recent years based on two kinds of synthetic pathways, i.e.,
the stepwise substitution of cyanuric chloride utilizing the
temperature-dependent reactivityof the threechlorine atoms when
treated with nucleophiles,37e39 and the condensation reactions
from 1,3,5-triazine-2,4-diamine derivatives.40,41 To the best of our
knowledge, however, only amine derivatives so far had been suc-
cessfully utilized to construct the tripod structure along with the
BODIPY unit. In order to exploit the scope of the possible nucleo-
philes and the synthetic routes of this tripod fluorescent structure,
we reported herein the synthesis and photophysical properties of
a series of new tripod BODIPY compounds bearing nucleophilic
phenolic derivatives via the stepwise substitution reactions.
(BODIPY) have attracted much attention as fluorescent dyes over the
past two decades because of high excitation coefficients, sharp ab-
sorption and emission spectra, high fluorescence quantum yields,
and high stability against light and chemical reactions.1,2 Thus, ex-
tensive studies have been reported for the application of BODIPY
dyes to fluorescent label,3e5 chemical sensor,6e8 solar energy con-
version,9e11 photodynamic therapy agent,12e14 and more recently,
antibacterial agent.15 Synthetic methods to access a variety of
BODIPY derivatives have also been developed including the direct
utilization of pyrrole derivatives,16e18 substitution on the pyrrole
moiety of the BODIPY frame,12,19,20 metal-catalyzed cross-
coupling,21e23 additioneelimination of the methyl group on the 3
and/or 5-position (so called Knoevenagel condensation reac-
tion),24e27 and the displacement of the fluorine atoms on 4-boron
recently reported.28e30 Another popular route to functionalize
BODIPY dyes is attributed to the substituents on the aryl ring located
at the 8-position of the BODIPY unit,31e33 where the orthogonal
geometry is adopted between the fluorophore and the meso aryl
ring. As the introduction of the selective groups at the meso position
usually cause little change of the BODIPY optical properties, more
attention can then be focused on the functionality and the chemical
property involved. Many interesting chemical sensors, particular
2. Results and discussion
2.1. Synthesis
The procedures for the synthesis of BODIPY derivatives 1e7
were outlined in Scheme 1. Along with 4-hydroxybenzaldehyde,
the compulsory aldehyde-functionality carrier, phenols 1ae7a
were used here as the nucleophiles instead of the amine derivatives
reported in previous protocol.37
The purification of the intermediates Xb would be the first
problem in designing the synthetic route of the bis-substitution of
the cyanuric chloride. Considering the much less difference of
* Corresponding author. Tel./fax: þ86 25 52112626; e-mail address: qixin@nuaa.
edu.cn (X. Qi).
http://dx.doi.org/10.1016/j.tet.2014.12.072
0040-4020/Ó 2014 Elsevier Ltd. All rights reserved.

J. Lu et al. / Tetrahedron 71 (2015) 1304e1310
1305
Scheme 1. Synthetic pathways for the target BODIPY dyes.
Table 1
nucleophilic reactivity between the 4-hydroxybenzaldehyde and
Xa than that between 4-hydroxybenzaldehyde and amine de-
rivatives, a mixture would obviously be received when both the 4-
hydroxybenzaldehyde and Xa existed in the same reaction solution,
which was further complicated by the fact that the two substitution
steps must be conducted successively in one pot because of the
feature of the cyanuric chloride. It means that three possible kinds
of bis-substituted ethers, Xb, Y (the byproducts bearing two Xa
derivatives), and Z (the bis-aldehyde byproducts), would exist in
the reaction solution along with the excessive amount of phenols.
In this case, an optimized feed ratio and addition order were
adopted as follows: a less than stoichiometric amount of Xa was
introduced first and the introduction of 4-hydroxybenzaldehyde
was put in the second step. The profit from such an adjustment
lay in the fact that the phenols Xa would run out in first step and
have no opportunity to fulfill the second substitution to form Y,
which proved to be difficult to separate from Xb. Thus the kinds of
impurities formed in the reaction mixture would be minimized
after the 4-hydroxybenzaldehyde was subsequently added in the
same pot. Also, the Rf value of the bis-aldehyde byproduct Z from
the excess 4-hydroxybenzaldehyde and cyanuric chloride turned
out to be much lower than that of the target intermediates Xb,
leading to an easier separation via chromatography.
Furthermore, it was also found that the yields of the synthesis of
the tripod BODIPY dyes based on Xb were influenced by the struc-
tures of Xa when reacted at room temperature as reported.37 For the
phenols bearing the electron donating groups, such as methoxy and
methyl groups (1ae4a, Table 1), conventional yields (>30%) for the
corresponding BODIPY dyes were generally received, which were
good for the preparation of BODIPY dyes when aromatic aldehydes
were used as starting materials.1 And then the yields gradually de-
creased with the increasing electron deficiency of the phenols, and
an unanticipated low yield of around 5% for 2,4-dichlorophenol (7a)
Effects of temperatures and different phenolic derivatives Xa on the yields of dyes
Temp (ꢀC)
1a
2a
3a
4a
5a
6a
9.7
25.6
7a
4.8
25.5
25
w5
34
34.6
31.5
32.8
32.5
33.7
34.4
34.5
18.2
28.5
was observed. However, these yields were generally restored to
acceptable level (>24%) when lower reaction temperature (ca. 5 ꢀC)
was adopted, but no improvement was observed for the electron
rich phenols 1ae4a under the same conditions.
Obviously, the observed phenol-dependent change of the yields
was attributed to the different reactivity of the third chlorine atom
still attached to the triazine ring. If active enough, it might be dis-
placed during the process leading to some undesired byproducts.
Although it was understandable for the bis-substituted compounds
originating from the cyanuric chloride and phenolic derivatives to
behave somewhat higher reactivity compared to the ones from the
cyanuric chloride and amines, which were generally stable at am-
bient conditions,37,42,43 it was still beyond our expectations to ob-
serve the low yields at room temperature for 6a and 7a.
Considering the fact that both 7b and 7 survived from the workup
at ambient condition anyway, there should exist other factors
contributing to the generation of some kinds of more reactive
species during the condensation, oxidation, and complexation re-
actions. We then paid attention to the three structures relating to
the process (Scheme 2) and realized that it was the tripod dipyr-
romethenes (the oxidation products b) under basic conditions that
the triazine ring could be activated by a conjugated system formed
in situ with one pyrrole ring.
First, there wasn’t such kind of an elongated interaction between
triazine ring and pyrrole ring both in dipyrromethanes a where it
was interrupted by a sp3 hybridized methine, and in boron dipyr-
romethenes c where it was isolated by two planes perpendicular to

1306
J. Lu et al. / Tetrahedron 71 (2015) 1304e1310
Scheme 2. A proposed mechanism of the activated species.
each other in space.1,2 Second, there were two cases for dipyrro-
methenes b. Under acidic conditions, a geometry similar to the bo-
ron complex was preferred since the acidic pyrrolic proton could act
the same role as the boron atom did to fix the two pyrrole rings in
coplanar through a hydrogen bond. After the addition of excess base,
however, the hydrogen bond would be inhibited and the rigid co-
planarity of two pyrrole rings would disappear. Benefitting from the
free rotation of both the electron rich pyrrole ring and the meso
phenyl ring in this case, a partial coplanaritycould form between the
meso phenyl ring and the other pyrrole ring, giving rise to the for-
mation of the elongated conjugation between them. In this case, the
terminal pyrrole ring played an electron-withdrawing role since the
electronegative nitrogen atom on this pyrrole contributed only 1e to
the reaction mixture to provide nucleophiles under the basic con-
ditions, accounting for both the surprising low yields and the exis-
tence of many fluorescent bands with low Rf value on the
preparative TLC plates. Of course, addition of excess borontrifluoride
broke down the conjugation.
Furthermore, the unanticipated phenol-dependent reactivity of
the third chlorine in these tripod dipyrromethenes brought out
potential reactions to expand the synthetic diversity of the tripod
BODIPYs (Scheme 3). For the previous protocol, the third chlorine
atom must be displaced at high temperature to form the tri-
substituted aldehyde-containing intermediates before the con-
densation in order to construct the tri-substituted BODIPY struc-
ture (path a), and the introduced nucleophiles had to be stable
enough to survive from the subsequent TFA and DDQ conditions,
which obviously limited the utilization of the nucleophiles con-
taining acid-labile or oxidant-sensitive functional groups. For the
path b based on our proposal, however, this kind of limitation could
be eschewed as the third nucleophiles would be introduced after
the oxidation step. Also, the active spieces formed in situ allowed
the substitution to be performed at much low temperature. In-
vestigation dealing with this novel route is now on progress in our
group and the results will be submitted subsequently.
the
p system. Besides, the phenyl and triazine rings bridged by
a divalent oxygen atomwere in good coplanarity through, which the
electron effect of the substitutions could be transferred effectively.
Thus, combined with the relative electron deficiency from the
phenols (6a, 7a), the chlorine atom attached to triazine ring in the
corresponding dipyrromethenes might become reactive enough to
undergo some side reactions at room temperature. Meanwhile, as
the well-known complexity of the condensation between aldehyde
and pyrroles, there existed kinds of uncertain pyrrole derivatives in
Scheme 3. A novel synthetic route via the activated tripod dipyrromethenes.

J. Lu et al. / Tetrahedron 71 (2015) 1304e1310
1307
In brief, after a complete consumption of the phenolic de-
rivatives 1ae7a in the first step when reacted with 1.1 equiv of
cyanuric chloride in an ice-water bath, 1.4 equiv of 4-
hydroxybenzaldehyde was then added to bring the second sub-
stitution to the end point at room temperature. The intermediates
1be7b, isolated from column chromatography on silica gel with
a reproducible yield (ca. 70%), were then used to carry out the TFA-
catalyzed condensation with 2,4-dimethylpyrrole in anhydrous
THF at ambient temperature. After the subsequent oxidation by 2,3-
dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), anhydrous trie-
thylamine (TEA) and borontrifluoride etherate (BF3$OEt2) were
added at low temperature to fulfill the complexation. Conventional
purification operation on silica gel afforded the BODIPY dyes in
reasonable yields.
(C4eC9) rings are also planar with an average deviation of
ꢀ
0.0102 and 0.0106 A, respectively. The dihedral angle between the
pyrrole and the triazine rings is 41.97ꢀ. Part of the structure is dis-
ordered over two sites. Only one site is shown here for clarity.
2.3. Optical properties of dyes
The absorption spectra of dye 1 in several solvents were first
measured and a slight difference of lmax in different solvents (from
499nminMeOHto504nm inCHCl3)wasfound(Fig. 2). The difference
might be ascribed most likely to the effect of the refractive index of the
solvents used, where the refractive indexof MeOH was lower than that
of CHCl3.44 Similar cases were observed for other dyes (Table S1).
2.2. Structure characterization
All the new compounds were fully characterized by spectro-
scopic analyses (see Supplementary data). The 1H NMR spectrum
recorded for dye 2 (Fig. S4a), for example, displayed the distinctive
singlet peak at 5.99 ppm of the two protons at 2 and 6 positions on
the BODIPY framework. The peak at 2.56 ppm was assigned to the
two methyl groups at 3 and 5 positions. The peak at 1.37 ppm was
the two methyl groups at 1 and 7 positions. The pair of doublet
peaks at 7.19 and 7.03 ppm with a coupling constant of 8.0 Hz
corresponded to the typical para substitution of the 4-
methylphenyl group, and the peak at 2.34 ppm was the methyl
group on the same ring. The molecular ion peak at 559.1758 [Mþ] in
HRMS spectrum accompanied by a peak at 561.1779 [Mþ2]þ with
a relative intensity of 3:1 characterized the target dye structure
bearing one chlorine atom (Fig. S4c).
Fig. 2. Comparison of the absorption spectra of dye 1 in several solvents (colored solid
lines) and fluorescence spectrum of dye 1 in CH3CN (dotted line) at 298 K. Emission
spectrum recorded after excitation at 499 nm.
For its intermediate 2b, the 1H NMR (Fig. S3a) revealed the alde-
hyde groupat10.0 ppm. Thepairofdoubletpeaksat7.94and7.31ppm
with a coupling constant of 8.3 Hz and the pair of doublet peaks at 7.19
and 7.02 ppm with a coupling constant of 8.2 Hz represented the two
kinds of typical phenylene group, respectively. The singlet peak at
2.36 ppm was assigned to the methyl group. The presence of the al-
dehyde group was also confirmed via both 13C NMR (the absorption at
190.7 ppm) and IR (the strong absorption band at 1700 cmꢁ1). The
molecular ion peak at 341.8 [MþH]þ in MS spectrum accompanied by
a peak at 343.8 [MþHþ2]þ with a relative intensity of 3:1 proved the
existence of one chlorine atom in the molecule (Fig. S3c).
Also, dyes 1e7 showed the same absorption maximum in the
same kind of solvent, which was accordance with the phenomena
that groups at the meso position usually cause little change of the
BODIPY optical properties. We then turned our attention to the
determination of the intrinsic photophysical parameters of the
whole new dyes in acetonitrile or THF (Table 2). The molar ex-
tinction coefficients at lmax fluctuated around 70,000 Mꢁ1 cmꢁ1
,
while the relative lager one for dye 3 should be attributed to the
additional absorption from the naphthalene entity, which itself was
more conjugated than the corresponding phenyl groups in other
dyes. The emission maxima of all the molecules were in the range of
507e511 nm with respect to the solvent used, and a typical emis-
sion spectrum was also shown in Fig. 2. Small Stokes shifts
The X-ray crystal structure of dye 6 was shown in Fig. 1. The
pyrrole and the phenyl (C10eC15) rings are planar, with an average
ꢀ
deviation of 0.0827 and 0.0172 A, respectively. The dihedral angle
between these two rings is 80.41ꢀ. The triazine and the chlorophenyl
(
Dn¼316e394 cmꢁ1) and relatively high quantum yields between
0.46 and 0.65 were also received, which were in agreement with
those reported elsewhere for conventional meso-aryl-substituted
BODIPY dyes.
Table 2
Spectroscopic properties of the synthetic BODIPY dyes at 298 K
Dye
Solvents
labs
lem
3
(Mꢁ1 cmꢁ1
)
Stokes shifta
Ffb
(nm)
(nm)
(cmꢁ1
)
1
2
3
4
5
6
7
CH3CN
CH3CN
CH3CN
CH3CN
THF
499
499
499
499
501
501
501
507
508
507
509
511
511
511
74,500
63,600
100,600
81,680
79,100
62,600
72,300
316
355
316
394
390
390
390
0.51
0.46
0.48
0.64
0.44
0.65
0.40
THF
THF
a
Stokes shift: the difference in wavenumber between positions of the band
maxima of the absorption and emission spectra.
b
The relative fluorescence quantum efficiencies were determined in degassed
Fig. 1. X-ray crystal structure of dye 6.
solvents and fluorescein in 0.1 M NaOH (Ff¼0.85) was used as standard.45

1308
J. Lu et al. / Tetrahedron 71 (2015) 1304e1310
3. Conclusion
4.2. General procedure for the synthesis of intermediates
1be7b
In summary, a series of new tripod BODIPY dyes bearing mono-
phenolic derivatives have been successfully synthesized and fully
characterized by 1H NMR, 13C NMR, HRMS, and IR. Difference of
phenolic derivatives had little effect on the maximum absorption
and emission bands of these new dyes. The reaction conditions of
the successive bis-substitution of cyanuric chloride with two kinds
of phenols, such as the addition sequences and the feed ratios, were
studied and optimized based on the chemical properties of the
phenols. An unanticipated phenol-dependent difference of the
yields of the dyes was observed and a hypothetic mechanism was
proposed to elucidate the reactivity of the tripod dipyrromethene
species during the complexation step. According to the proposal,
the conjugate system generated in situ in basic solution should play
a key role in activating the chlorine atom still attached to the tri-
azine ring. Thus low reaction temperature was adopted to suppress
the reactivity of the species with electron deficient phenols and
reasonable yields (>24%) for those dyes were then received. These
results revealed potential novel synthetic pathway to construct
both the tripod BODIPYs containing acid- or oxidant-sensitive
groups and the third substitution at low temperature. Further ef-
forts are currently being devoted to the potential reactions of the
active chlorine atom in different tripod dipyrromethenes in order
to broaden the structure diversity and chemistry of the tripod
BODIPY dyes.
To a stirred solution of cyanuric chloride (368.8 mg, 2.0 mmol)
in methylene chloride (MC, 20 mL) in ice-water bath was added
dropwise a solution of phenolic derivative Xa (1.9 mmol) and
triethylamine (TEA, 0.31 mL, 2.2 mmol) in MC (10 mL) for 10 min.
After the addition, the mixture was stirred for another 20 min at
0e5 ꢀC until the complete consumption of Xa (monitored by TLC,
ethyl acetate/hexane¼1:8). A mixture of 4-hydroxybenzaldehyde
(270 mg, 2.2 mmol) and TEA (2.4 mmol, 0.34 mL) in MC (10 mL)
was added at the same temperature and the ice-water bath was
then removed. The solution was allowed to stir for additional 2 h at
room temperature to finish the second substitution reaction of
cyanuric chloride (monitored by TLC, ethyl acetate/hexane¼1:4).
Then, the reactant was passed through a silica gel column (w10 g)
and rinsed with eluant (ethyl acetate/hexane¼1:1, 80 mL). After
concentration under vacuum, the crude product was purified by
flash chromatography (ethyl acetate/hexane¼1:10) to afford the
tripod intermediates Xb.
4.2.1. 4-(4-Chloro-6-(2,4-dimethylphenoxy)-1,3,5-triazin-2-yloxy)
benzaldehyde (1b). Yield 77.4%, white solid. Mp 126.4e127.7 ꢀC. 1H
NMR (300 MHz, CDCl3):
d
9.95 (s, 1H), 7.88 (d, J¼8.4 Hz, 2H), 7.31 (d,
J¼8.4 Hz, 2H), 7.31 (d, J¼8.6 Hz, 2H), 7.01 (s,1H), 6.98 (d, J¼8.4 Hz,1H),
6.91 (d, J¼8.1 Hz, 1H), 2.27 (s, 3H), 2.10 (s, 3H); 13C NMR (100 MHz,
CDCl3): d 190.8,174.0,172.5,171.9,155.6,147.8,136.5,134.5132.1,131.4,
129.3,127.8,122.2,120.8, 20.9,16.1; IR (KBr, cmꢁ1):
n 3014, 2918, 2852,
4. Experimental section
1678, 1597, 1514, 1380, 1282, 1213, 1153, 1010, 853, 605; HRMS (ESI):
356.0796 ([MþH]þ), calcd for C18H14ClN3O3: 356.0802 ([MþH]þ).
4.1. General materials and methods
4.2.2. 4-(4-Chloro-6-(p-tolyloxy)-1,3,5-triazin-2-yloxy)benzaldehyde
Unless otherwise noted, materials were obtained from com-
mercial suppliers and used without further purification. All air
and moisture sensitive reactions were carried out under nitro-
gen atmosphere in oven-dried glassware. Anhydrous THF was
freshly distilled over sodium and benzophenone ketyl under
nitrogen before use. Triethylamine was dried over molecular
sieve before use. 1H and 13C NMR spectra were recorded using
Bruker ARX-300 or AVANCED 400 spectrometer. Chemical shifts
were given in parts per million (ppm) and coupling constants (J)
in hertz (Hz). Mass spectra were obtained using Bruker micrO-
TOF Q II or Bruker ultrafleXtreme MALDI-TOF/TOF spectrometer.
Infrared spectra were measured on a Nexus670 infrared spec-
trophotometer (Thermonicolet). Absorption spectra were ob-
tained on UV1800 spectrometer (Shimadzu). Fluorescence
emission spectra were recorded using Cary Eclipse spectro-
fluorophotometer (Varian). Both excitation and emission slit
widths were 2.5 nm. The fluorescence quantum yields were
measured in degassed solvents at 25 ꢀC by a relative method
using fluorescein (Ff¼0.85 in 0.1 M NaOH) as the standard.45 The
following equation was used to calculate the relative fluores-
cence quantum yield:
(2b). Yield 72.0%, white solid. Mp 147.2e148.9 ꢀC. 1H NMR
(400 MHz, CDCl3):
J¼8.3 Hz, 2H), 7.19 (d, J¼8.2 Hz, 2H), 7.02 (d, J¼8.2 Hz, 2H), 2.36 (s,
3H); 13C NMR (100 MHz, CDCl3):
190.7, 173.8, 172.6, 171.8, 155.5,
149.0, 136.4, 134.5, 131.4, 130.2, 122.1, 120.7, 20.9; IR (KBr, cmꢁ1):
d
10.02 (s, 1H), 7.95 (d, J¼8.3 Hz, 2H), 7.34 (d,
d
n
3030, 2920, 2860, 1700, 1560, 1500, 1450, 1370, 1290, 1240, 1190,
1010, 953, 605; MS (ESI): 341.8 ([MþH]þ), calcd for C17H12ClN3O3:
342.0 ([MþH]þ).
4.2.3. 4-(4-Chloro-6-(naphthalen-1-yloxy)-1,3,5-triazin-2-yloxy)
benzaldehyde (3b). Yield 76.2%, white solid. Mp 127.5e128.6 ꢀC. 1H
NMR (400 MHz, CDCl3):
d
9.95 (s, 1H), 7.90 (d, J¼7.9 Hz, 1H), 7.78 (t,
J¼8.3 Hz, 4H), 7.59e7.48 (m, 2H), 7.45 (t, J¼7.9 Hz, 1H), 7.25 (d,
J¼7.2 Hz, 1H), 7.18 (d, J¼8.4 Hz, 2H); 13C NMR (100 MHz, CDCl3):
d
190.7, 174.2, 173.0, 171.9, 155.5, 147.2, 134.7, 134.4, 131.2, 128.2,
126.9, 126.8, 126.2, 125.4, 122.0, 121.0, 117.6; IR (KBr, cmꢁ1):
n 3061,
2833, 2796, 2732, 1699, 1547, 1499, 1439, 1356, 1294, 1217, 1157,
1093, 945, 896; MS (ESI): 377.8 ([MþH]þ), calcd for C20H12ClN3O3:
378.1 ([MþH]þ).
4.2.4. 4-(4-Chloro-6-(4-methoxyphenoxy)-1,3,5-triazin-2-yloxy)
benzaldehyde (4b). Yield 70.0%, white solid. Mp 124.5e124.9 ꢀC. 1H
FfðxÞ
¼
FfðsÞðAx A ÞðI I Þðn n Þ2
=
=
=
x s
s
x
s
NMR (400 MHz, CDCl3):
(d, J¼7.7 Hz, 2H), 7.06 (d, J¼7.9 Hz, 2H), 6.89 (d, J¼8.0 Hz, 2H), 3.80
(s, 3H); 13C NMR (100 MHz, CDCl3):
190.7, 173.9, 172.8, 171.8, 157.8,
155.6, 144.7, 134.5, 131.4, 122.2, 121.9, 114.7, 55.6, 29.7. IR (KBr,
d
10.01 (s, 1H), 7.94 (d, J¼7.6 Hz, 2H), 7.33
where A stands for the absorbance (in the range of 0.015e0.07) at
the excitation wavelength, I is the integrated area under the
emission spectra, n is the refractive index of the solvents (at 25 ꢀC)
used in measurements, and the subscripts s and x represent stan-
dard and test sample, respectively. X-ray crystallographic data were
d
cmꢁ1):
n 3062, 2916, 2837, 1693, 1600, 1556, 1503, 1445, 1360, 1294,
1203, 1028, 945, 806; MS (ESI): 357.8 ([MþH]þ), calcd for
collected on a Bruker D8 Quest CMOS diffractometer equipped with
C
17H12ClN3O4: 358.1 ([MþH]þ).
ꢀ
a Mo K
a
radiation (
l
¼0.71073 A) at 293 K, using a
u scan mode
with an increment of 1ꢀ. CCDC 1037951 contains the supplementary
crystallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
4.2.5. 4-(4-Chloro-6-phenoxy-1,3,5-triazin-2-yloxy)benzaldehyde
(5b). Yield 73.2%, white solid. Mp 164.1e165.9 ꢀC. 1H NMR
(400 MHz, CDCl3)
J¼7.6 Hz, 2H), 7.32 (d, J¼8.0 Hz, 2H), 7.29 (t, J¼9.2 Hz, 1H), 7.14 (d,
d
10.01 (s, 1H), 7.94 (d, J¼8.0 Hz, 2H), 7.41 (t,

J. Lu et al. / Tetrahedron 71 (2015) 1304e1310
1309
J¼7.6 Hz, 2H); 13C NMR (100 MHz, CDCl3)
d
190.7, 173.9, 172.4, 171.8,
13C NMR (100 MHz, CDCl3):
d
173.8, 172.6, 172.1, 155.8, 151.7, 149.1,
155.5, 151.2, 134.5, 131.4, 129.7, 126.7, 122.1, 121.1. IR (KBr, cmꢁ1):
n
143.1, 140.2, 136.4, 133.2, 131.3, 130.2, 129.4, 122.3, 121.4, 120.7, 21.0,
3068, 2960, 2916, 2849, 2790, 1724, 1597, 1556, 1516, 1363, 1304,
14.6, 14.5; IR (KBr, cmꢁ1):
n
2968, 2928, 2856, 1552, 1506, 1444,
1194, 1080, 976, 806; MS (ESI): 327.8 ([MþH]þ), calcd for
1360, 1304, 1190, 1156, 1076, 985, 808; HRMS (MALDI-TOF/TOF):
559.1759 (Mþ), calcd for C29H25BClF2N5O2: 559.1758 (Mþ).
C
16H10ClN3O3: 328.0 ([MþH]þ).
4.2.6. 4-(4-Chloro-6-(4-chlorophenoxy)-1,3,5-triazin-2-yloxy)benz-
4.3.3. 4,4-Difluoro-8-(4-(4-chloro-6-(naphthalen-1-yloxy)-1,3,5-
triazin-2-yloxy)phenyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-in-
dancene (3). Yield 33.7%, red sticky oil. 1H NMR (400 MHz, CDCl3):
aldehyde (6b). Yield 69.6%, white solid. Mp 148.6e149.4 ꢀC. 1H
NMR (400 MHz, CDCl3)
d
10.03 (s,1H), 7.96 (d, J¼8.6 Hz, 2H), 7.37 (d,
J¼8.8 Hz, 2H), 7.34 (d, J¼8.5 Hz, 2H), 7.10 (d, J¼8.8 Hz, 2H); 13C NMR
d
7.90 (d, J¼7.9 Hz, 1H), 7.82 (d, J¼7.9 Hz, 1H), 7.77 (d, J¼8.3 Hz, 1H),
(100 MHz, CDCl3)
d
190.7, 174.0, 172.3, 172.2, 155.5, 149.6, 134.6,
7.58e7.51 (m, 2H), 7.46 (t, J¼7.9 Hz, 1H), 7.28 (d, J¼7.5 Hz, 1H), 7.13
(d, J¼8.6 Hz, 2H), 7.10 (d, J¼8.6 Hz, 2H), 5.98 (s, 2H), 2.56 (s, 6H),1.25
132.2, 131.2, 129.9, 122.6, 122.2; IR (KBr, cmꢁ1):
n 3040, 2920, 2850,
2730, 1700, 1560, 1530, 1500, 1450, 1370, 1290, 1240, 1190, 1070,
953, 806; HRMS (ESI): 362.0096 ([MþH]þ), calcd for C16H9Cl2N3O3:
362.0099 ([MþH]þ).
(s, 6H); 13C NMR (100 MHz, CDCl3):
d 174.1, 173.0, 172.0, 155.8, 151.5,
147.3,143.1,140.1,134.8,133.0,131.3,129.2,128.3,126.9,126.8,126.7,
126.2, 125.4, 122.0, 121.4, 121.0, 117.6, 14.6, 14.5; IR (KBr, cmꢁ1):
n
2970, 2940, 2860, 1600, 1580, 1540, 1500, 1380, 1310, 1260, 1210,
985, 810; HRMS (MALDI-TOF/TOF): 595.1762 (Mþ), calcd for
4.2.7. 4-(4-Chloro-6-(2,4-dichlorophenoxy)-1,3,5-triazin-2-yloxy)
benzaldehyde (7b). Yield 71.3%, white solid. Mp 120.8e122.0 ꢀC. 1H
C
32H25BClF2N5O2: 595.1758 (Mþ).
NMR (400 MHz, CDCl3)
d
10.02 (s, 1H), 7.95 (d, J¼8.4 Hz, 2H), 7.47 (d,
J¼2.2 Hz, 1H), 7.33 (d, J¼8.4 Hz, 2H), 7.29 (dd, J¼8.7, 2.2 Hz, 1H), 7.13
4.3.4. 4,4-Difluoro-8-(4-(4-chloro-6-(4-methoxyphenoxy)-1,3,5-
triazin-2-yloxy) phenyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-
indancene (4). Yield 34.0%, red sticky oil. 1H NMR (400 MHz,
(d, J¼8.7 Hz, 1H); 13C NMR (100 MHz, CDCl3):
d 190.6, 174.3, 171.8,
155.6, 146.0, 134.7, 132.9, 131.4, 130.5, 128.4, 123.9, 122.1; IR (KBr,
cmꢁ1):
n
3086, 2835, 2796, 2739, 1701, 1583, 1549, 1473, 1439, 1359,
CDCl3):
2H), 6.00 (s, 2H), 3.79 (s, 3H), 2.56 (s, 6H), 1.38 (s, 6H); 13C NMR
(100 MHz, CDCl3): 173.8, 172.8, 172.1, 157.8, 155.9, 151.8, 144.8,
143.1, 140.2, 133.2, 131.4, 129.4, 122.3, 121.9, 121.5, 114.6, 55.6, 14.6,
14.5; IR (KBr, cmꢁ1):
3057, 2968, 2920, 2841, 1547, 1504, 1442,
d
7.36e7.26 (m, 4H), 7.08 (d, J¼8.8 Hz, 2H), 6.90 (d, J¼8.9 Hz,
1298,1213,1157,1095, 952, 812; MS (ESI): 395.6 ([MþH]þ), calcd for
C
16H8Cl3N3O3: 396.0 ([MþH]þ).
d
4.3. General procedure for the synthesis of dyes 1e7
n
1360,1304,1194,1072, 982, 810; HRMS (MALDI-TOF/TOF): 575.1699
(Mþ), calcd for C29H25BClF2N5O3: 575.1707 (Mþ).
To a stirred solution of pre-dried Xb (0.5 mmol) and 2,4-
dimethylpyrrole (98 mg, 1.03 mmol) in dry THF (10 mL) was added
a catalytic amount of F3CCOOH under N2 at room temperature. After
stirring for 2 h, a mixture of pre-dried 2,3-dichloro-5,6-dicyano-1,4-
benzoquinone (114 mg, 0.5 mmol) in dry THF (10 mL) was added
dropwise for 10 min and the reactant solution was stirred further for
1 h. The mixture was passed through an Al2O3 column (w20 g) and
further eluted by MC/MeOH (40:1) to get a dark brown solution.
After concentration with aspirator, the residue was dried under
vacuum overnight and was then dissolved in anhydrous THF (10 mL)
in an ice-water bath. Dry TEA (1.2 mL) was added, followed by
dropwise addition of BF3$OEt2 (1.5 mL) for 15 min. The ice-water
bath was removed and the reaction mixture was allowed to stir
overnight. H2O (30 mL) was then added to quench the reaction, and
the organic solvent was removed under reduced pressure. The res-
idue was then extracted with MC (3ꢂ20 mL), washed with brine
(2ꢂ30 mL) and H2O (30 mL), dried over anhydrous Na2SO4. The
solvent was evaporated by water aspirator and the residue was first
separated by flash chromatography on silica gel column (MC/
hexane¼2:5), followed by preparative TLC purification (MC/
hexane¼1:5) for the brown-yellow elution to afford target dyes X.
4.3.5. 4,4-Difluoro-8-(4-(4-chloro-6-phenoxy-1,3,5-triazin-2-yloxy)
phenyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indancene
(5). Yield 28.5%, red sticky oil. 1H NMR (400 MHz, CDCl3)
d
7.42 (t,
J¼7.9 Hz, 2H), 7.32e7.29 (m, 5H), 7.16 (d, J¼7.9 Hz, 2H), 6.00 (s, 2H),
2.56 (s, 6H), 1.38 (s, 6H); 13C NMR (100 MHz, CDCl3):
173.4, 172.4,
171.9,155.9,151.6,151.3,143.0,140.0,133.2,130.0,129.2,126.6,122.3,
121.1,14.6, 14.5; IR (KBr, cmꢁ1):
3057, 2961, 2920, 2861, 1593, 1553,
d
n
1443, 1359, 1300, 1196, 1155, 1074, 974, 808; HRMS (MALDI-TOF/
TOF): 545.1595 (Mþ), calcd for C28H23BClF2N5O2: 545.1601 (Mþ).
4.3.6. 4,4-Difluoro-8-(4-(4-chloro-6-(4-chlorophenoxy)-1,3,5-
triazin-2-yloxy) phenyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-
indancene (6). Yield 25.6%, dark red solid. Mp 183.0e184.5 ꢀC. 1H
NMR (400 MHz, CDCl3)
7.12 (d, J¼8.9 Hz, 2H), 6.00 (s, 2H), 2.56 (s, 6H), 1.39 (s, 6H); IR (KBr,
cmꢁ1):
3101, 3065, 2968, 2918, 2851, 1591, 1557, 1439, 1356, 1263,
1196, 1157, 1084, 970, 806, 735; 13C NMR (100 MHz, CDCl3)
173.9,
d
7.38 (d, J¼8.9 Hz, 2H), 7.35e7.27 (m, 4H),
n
d
172.1, 155.8, 151.6, 149.6, 143.0, 140.0, 133.5, 132.1, 131.3, 130.1, 129.7,
122.7, 122.3, 121.4, 14.5; HRMS (MALDI-TOF/TOF): 579.1202 (Mþ),
calcd for C28H22BCl2F2N5O2: 579.1212 (Mþ).
4.3.1. 4,4-Difluoro-8-(4-(4-chloro-6-(2,4-dimethylphenyloxy)-1,3,5-
triazin-2-yloxy)phenyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-in-
dancene (1). Yield 34.6%, orange-red solid. Mp 257.2e258.6 ꢀC. 1H
4.3.7. 4,4-Difluoro-8-(4-(4-chloro-6-(2,4-dichlorophenoxy)-1,3,5-
triazin-2-yloxy)phenyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-in-
dancene (7). Yield 25.5%, red sticky oil. 1H NMR (400 MHz, CDCl3)
NMR (300 MHz, CDCl3)
J¼8.3 Hz,1H), 6.94 (d, J¼8.2 Hz,1H), 5.99 (s, 2H), 2.56 (s, 6H), 2.30 (s,
3H), 2.14 (s, 3H), 1.38 (s, 6H); 13C NMR (100 MHz, CDCl3):
173.9,
172.5, 172.2, 155.9, 151.7, 147.8, 143.1, 140.2, 136.4, 133.2, 132.1, 131.4,
129.3,127.7,122.3,121.4, 120.8, 20.9,16.1,14.6,14.5; IR (KBr, cmꢁ1):
d 7.31e7.22 (m, 4H), 7.05 (s, 1H), 7.01 (d,
d
7.48 (d, J¼2.3 Hz, 1H), 7.36e7.27 (m, 5H), 7.17 (d, J¼8.7 Hz, 1H),
6.00 (s, 2H), 2.56 (s, 6H), 1.38 (s, 6H); 13C NMR (100 MHz, CDCl3):
174.0, 172.2, 171.7, 155.9, 151.6, 146.1, 143.0, 140.1, 133.4, 132.9,
131.3,129.5, 128.4, 127.6, 124.0, 122.2, 121.5, 14.6, 14.5; IR (KBr,
cmꢁ1):
3101, 3055, 2961, 2918, 2853, 1554, 1441, 1358, 1298, 1261,
d
d
n
2962, 2922,1548,1504,1442,1359,1296,1190, 981, 808; HRMS (ESI):
n
574.1968 ([MþH]þ), calcd for C30H27BClF2N5O2: 574.1992 ([MþH]þ).
1190, 1155, 1083, 982, 806, 735; HRMS (MALDI-TOF/TOF): 613.0831
(Mþ), calcd for C28H21BCl3F2N5O2: 613.0822 (Mþ).
4.3.2. 4,4-Difluoro-8-(4-(4-chloro-6-(p-tolyloxy)-1,3,5-triazin-2-
yloxy)phenyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indancene
(2). Yield 32.1%, range-red solid. Mp 203.1e204.9 ꢀC. 1H NMR
Acknowledgements
(400 MHz, CDCl3):
(d, J¼8.0 Hz, 2H), 5.99 (s, 2H), 2.56 (s, 6H), 2.34 (s, 3H), 1.37 (s, 6H);
d
7.32e7.26 (m, 4H), 7.19 (d, J¼8.0 Hz, 2H), 7.03
This research was financially supported by startup funding from
Naning University of Aeronautics and Astronautics, and the

1310
J. Lu et al. / Tetrahedron 71 (2015) 1304e1310
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