Synthesis, structures and photophysical properties of boron-fluorine derivatives based on pyridine/1,8-naphthyridine

Article abstract of DOI:10.1016/j.dyepig.2014.01.022

Three boron-fluorine complexes B1-B3 containing pyridine/1,8-naphthyridine were synthesized and structurally characterized. Compounds B1 and B2 exhibited strong fluorescence in solution and solid state. The solvent-dependent luminous properties and large

Full text of DOI:10.1016/j.dyepig.2014.01.022

Dyes and Pigments 105 (2014) 157e162
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis, structures and photophysical properties of boronefluorine
derivatives based on pyridine/1,8-naphthyridine
a
a
a
a,b,
*
Zhensheng Li , Xiaojun Lv , Yong Chen , Wen-Fu Fu
a
Key Laboratory of Photochemical Conversion and Optoelectronic Materials, CAS and HKU Joint Laboratory on New Materials,
Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, PR China
College of Chemistry and Engineering, Yunnan Normal University, Kunming 650092, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 November 2013
Received in revised form
Three boronefluorine complexes B1eB3 containing pyridine/1,8-naphthyridine were synthesized and
structurally characterized. Compounds B1 and B2 exhibited strong fluorescence in solution and solid state.
The solvent-dependent luminous properties and large Stokes shift in solution could be explained by
intramolecular charge transfer, which is confirmed by time-dependent density functional theory calcu-
13 January 2014
Accepted 24 January 2014
Available online 12 February 2014
lation. The absolute quantum yield of B1 in powder form reached 0.48 because of inhibiting planar
stacking. Single-crystal X-ray diffraction analyses of B1 and B2 revealed that weak intermolecular CeH/F
and H/ interactions hinder further stacking of dimers, consequently preventing aggregation-
p/p
p
p/p
Keywords:
Boronefluorine compound
induced quenching. Complex B3, composed of boronedipyrromethene and 1,8-naphthyridine fluo-
rophore, had potential applications as a pH ratiometric fluorescent sensor.
Ó 2014 Elsevier Ltd. All rights reserved.
1,8-Naphthyridine
Structures
Solid-state emission
Fluorescence quantum yield
pH sensor
1. Introduction
Naphthyridine derivatives are widely applied as biological
probes and assembled supramolecular systems because of its
Organoboron complexes are well known as one group of most
important fluorescent dyes because of their tunable emission
wavelengths [1e3] and high fluorescence quantum yields [4]. In
particular, boron dipyrromethene (BODIPY) derivatives have played
significant roles in many fields including fluorescent indicators [5],
energy-transfer cassettes [6], laser dyes [7], and photodynamic
therapy [8]. However, typical BODIPYs suffer from aggregation-
induced quenching (ACQ) caused by their small Stokes shift and
diverse coordination modes and multiple hydrogen-bonded self-
assembly ability [14,15]. However, BF core complexes based on 1,8-
naphthyridine unit have been little explored. Recently, we have
reported a series of emissive 1,8-naphthyridine-BF complexes that
exhibit diverse attractive photophysical properties [4,16,17]. Herein,
we synthesized three boron complexes B1eB3 containing pyridine/
1,8-naphthyridine, and their spectroscopic behaviors were inves-
tigated. Both B1 and B2 displayed strong emission in the solid state
2
2
tight
p
/p
packing in the solid state, which severely limits their
due to weak intermolecular CeH/F and H/p interactions.
applications as electroluminescence materials [9]. Generally, two
promising strategies are employed to avoid ACQ in solid state, that
is, aggregation-induced emission [10,11] and introduction of bulky
groups [12]. Although the methods are effective to enhance solid
emission, the energy of excited fluorophores will greatly exhaust
via nonradiative decay, resulting in low quantum yields in solution
Although B3 was not fluorescent in solid state, it exhibited pH-
dependent solution-emission spectra by protonation of naphthyr-
idine upon excitation at 330 nm, indicating that B3 could act as a
pH ratiometric fluorescent sensor.
2. Experimental section
[13]. Thus, it is still a challenge to obtain emissive BODIPY de-
rivatives both in solution and solid state.
2.1. Materials and instrumentations
*
Corresponding author. Key Laboratory of Photochemical Conversion and Op-
All starting materials were purchased commercially as reagent
toelectronic Materials, CAS and HKU Joint Laboratory on New Materials, Technical
Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, PR
China.
grade and used as received unless otherwise mentioned.
Dichloromethane was distilled over calcium hydride. The solvents
used for spectroscopic measurements were of HPLC grade. 2-(4,5-
E-mail address: fuwf@mail.ipc.ac.cn (W.-F. Fu).
http://dx.doi.org/10.1016/j.dyepig.2014.01.022
0143-7208/Ó 2014 Elsevier Ltd. All rights reserved.

158
Z. Li et al. / Dyes and Pigments 105 (2014) 157e162
diphenyl-1H-imidazol-2-yl)pyridine (L1) and 2-(pyridin-2-yl)-1H-
phenanthro[9,10-d]imidazole (L2) were synthesized according to
the literature methods [18]. 1,8-naphthyridine-2-carbaldehyde was
obtained by the previously reported procedure [19].
After 5 min, boron trifluoride etherate (2 mL,15.7 mmol) was added
dropwise. The solution was stirred overnight. The reaction was
quenched by adding water (20 mL) and the mixture was extracted
with CH
Na SO , and concentrated to dryness on a rotary evaporator. The
crude product was purified by silica gel column chromatography
2
Cl
2
(2 ꢀ 50 mL). The organic phase was dried by anhydrous
1
13
H and C spectra were recorded on a Bruker Avance 400
spectrometer in CDCl at room temperature. Electrospray Ionization
ESI) mass spectra were obtained on a Finnigan LCQ quadrupole ion
2
4
3
1
(
(CH
NMR (400 MHz, CDCl
8.09 (d, J ¼ 8.1 Hz,1H), 7.66e7.60 (m, 2H), 7.60e7.55 (m, 2H), 7.50 (t,
2
Cl
2
/EtOH, 20/1, v/v) to yield B1 as yellow solid (150 mg, 43%). H
trap mass spectrometer. UVeVis absorption spectra were recorded
using a Hitachi U-3010 spectrophotometer. Emission and excitation
spectra were obtained on a Hitachi F-4500 Fluorescence Spectro-
photometer. The fluorescence quantum yields in solution were
measured relative to quinine sulfate in 0.1 M sulfuric acid aqueous
3
) 8.45 (d, J ¼ 5.6 Hz, 1H), 8.24e8.16 (m, 1H),
13
J ¼ 6.2 Hz, 1H), 7.42e7.27 (m, 6H) ppm (Fig. S1); C NMR (101 MHz,
CDCl ) 145.88, 145.58, 145.17, 144.65, 141.30, 134.76, 134.47, 130.80,
3
128.76, 128.63, 128.38, 128.17, 127.32, 122.73, 117.67 ppm (Fig. S2).
þ
solution (
quantum yield was calculated by using Equation (1), where sub-
scripts std denotes standard, is quantum yield, I is the integrated
emission intensity, A is the absorbance, and n is the refractive index.
lex ¼ 345 nm,
F
F
¼ 0.546) at room temperature. The
ESI-MS m/z calcd. for C20
calcd. for C20 14BF
4.10; N, 12.22.
H14BF
2
N
3
(MþH) 346.1; found 346.2. Anal.
H
2 3
N : C, 69.63; H, 4.09; N,12.18; found: C, 69.57; H,
F
ꢀ
ꢁꢀ
ꢁꢀ
ꢁ
2
2.2.2. BF {2-(pyridin-2-yl)-1H-phenanthro[9,10-d]imidazole} (B2)
2
F
¼
F
Astd=Asample Isample=Istd nsample=nstd
(1)
The synthesis is analogous to B1 with L2 as the starting material.
sample
std
1
The product wasobtained asa brownyellowsolid. Yield:30%. H NMR
(
8
400 MHz, CDCl
3
) 8.69 (dd, J ¼ 19.1, 8.9 Hz, 3H), 8.59 (d, J ¼ 5.3 Hz,1H),
Solid-state fluorescence quantumyields were measured using an
.47 (d, J ¼ 7.9 Hz,1H), 8.25 (d, J ¼ 5.9 Hz, 2H), 7.76e7.62 (m, 4H), 7.58
integrating sphere F-3018 (HORIBA JOBIN YVON) equipped to the
Spex 1681 Flurolog-2 Model F111 spectrophotometer. The pH
measurements were performed utilizing a Mettler-Toledo FE20K pH
meter. Single crystals of B1 and B2 suitable for X-ray diffractionwere
grown by slow evaporation of solutions of the samples in CHCl
diffraction data were collected on a Rigaku R-AXIS RAPID IP X-Ray
diffractometer using a graphite monochromator with MoK radia-
tion (
¼ 0.071073 nm) at 293 K. The structures were solved by direct
methods and refined by full-matrix least-squares methods on all F
data (SHELX-97). CCDC-855326 (B2) contains the supplementary
crystallographic data for this paper [20]. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
13
(s,1H) ppm (Fig. S3); C NMR (101MHz,CDCl
3
)146.31,144.80,143.53,
141.74, 129.72, 128.86, 127.63, 127.46, 127.29, 126.61, 125.94, 123.74,
1
23.69,123.63,123.49,123.30,122.63,118.78 ppm (Fig. S4); ESI-MS m/
þ
z calcd. for C20
12BF
H
12BF
2
N
3
(MþH) 344.1; found 344.2. Anal. calcd. for
3
. The
C
20
H
N
2 3
: C, 70.03; H, 3.52; N, 12.25; found: C, 70.10; H, 3.55; N,
12.20.
a
l
2.2.3. 8-(1,8-naphthypridine)-1,3,5,7-tetramethyl-4,4-
2
difluoroboradiazaindacene (B3)
,8-Naphthyridine-2-carbaldehyde (370 mg, 2.3 mmol) was
dissolved in dry CH Cl (200 mL). 2,4-Dimethylpyrrole (456 mg,
.8 mmol) and one drop of trifluoroacetic acid were added under N
1
2
2
4
2
atmosphere. The mixture was stirred at room temperature in the
dark for 3 h. After oxidation with 2,3-dichloro-5,6-dicyano-p-ben-
zoquinone (DDQ) (1.01 g, 2.3 mmol), triethylamine (TEA) (4 mL)
2
.2. Synthetic procedures
3 2
and BF $Et O (5 mL) were added dropwise to the mixture. The
Synthetic procedures of B1eB3 were depicted in Scheme 1.
reaction solution was stirred for another 3 h, and the brown
mixture was washed with water and brine, dried over anhydrous
magnesium sulfate and concentrated at reduced pressure. The
crude product was purified by silica-gel column chromatography
2
(
2
.2.1. Synthesis of BF {2-(4,5-diphenyl-1H-imidazol-2-yl)pyridine}
B1)
At room temperature, triethylamine (2 mL) was added to a stir-
redmixture of L1 (297 mg,1.0 mmol) in dry CH Cl (30 mL) under N
(petroleum/EtOAc ¼ 10:1, v/v) to yield B3 as red solid, 130 mg, yield
1
2
2
2
.
15%. H NMR (400 MHz, CDCl
3
)
d
9.24 (d, J ¼ 2.3 Hz, 1H), 8.38 (d,
Scheme 1. Synthetic procedures and chemical structures of B1eB3.

Z. Li et al. / Dyes and Pigments 105 (2014) 157e162
159
J ¼ 8.2 Hz, 1H), 8.32 (dd, J ¼ 8.2, 1.8 Hz, 1H), 7.67e7.60 (m, 2H), 5.98
was typical for the BODIPY dyes, attributed to the 0e0 vibrational
band of the S eS transition, while the latter were associated with
1,8-naphthyridine unit [14].
(
s, 2H), 2.58 (s, 6H), 1.23 (s, 6H) ppm (Fig. S5). ESI-MS m/z calcd. for
0
1
þ
C
C
21
H19BF
19BF
2
2
N
N
4
(MþH)
377.1; found 377.2. Anal. calcd. for
21
H
4
: C, 67.06; H, 5.09; N, 14.90; found: C, 67.13; H, 5.06; N,
3
The solution emission maxima of B1 and B2 in CHCl were
1
3
3
4.95.
located at 520 nm and 522 nm, respectively. The Stokes shift of B1
was up to 106 nm, which was 14 nm larger than that of B2. And the
. Result and discussion
fluorescence quantum yield of B1 (
F
¼ 0.23) was a little lower than
that of B2 (
F
¼ 0.30). The results were not surprising because the
.1. Single X-ray crystallography
phenyl rings of B1 appended to the imidazole ring could rotate
around the CeC bond, which reduced the energy of the excited
state even though the rotation was limited by steric hindrance.
However, this did not occur in the fused ring system in B2. The
Stokes shift of B3 was only 15e18 nm in solution, which was usual
for 8-substituted BODIPY derivatives (Fig. 3).
By slow evaporation of the samples in CHCl
3
, only single crystals
of B1 and B2 suitable for X-ray diffraction analysis were obtained.
Both compounds were crystallized in space group P2 /c. As shown
in Fig. 1, B1 and B2 had similar crystal structures, exhibiting a
1
slightly distorted tetrahedral geometry around boron atoms. The
bond lengths of B1eN1 and B1eN2 were 1.616(2) and 1.539(2) A in
Interestingly, both the absorption and emission spectra of B1
and B2 were solvent-dependent (Fig. 4 and Fig. S6). With solvent
polarity increasing, the lowest-energy absorption bands were
marked blue-shift. For example, the absorption peak of B2 was
observed at 447 nm in hexane, while the corresponding peak
appeared at 403 nm in acetonitrile. Similar behaviors were also
observed for compound B1. The observed negative solvatochrom-
ism indicates that the energy level of the ground state decreases
more significantly than that of excited state with increasing solvent
polarity, making energy gap larger. The solvent-dependent behav-
ꢀ
the structure of B1, respectively, and these corresponding bond
ꢀ
lengths for B2 were 1.611(4) and 1.541(4) A. The coordination of
boron with nitrogen atoms forced the related imidazole and pyri-
dine rings in both structures to lie in a plane. In B1, because of the
steric hindrance among the aromatic rings, the dihedral angles
ꢁ
between imidazoleepyridine plane and two phenyl rings were 7.1
ꢁ
and 37.5 , respectively. In contrast, the two terminal phenyl rings in
B2 were fused together with imidazole moiety to form as a phe-
nanthro[9,10-d]-imidazole group, the whole molecular were
0 1
iors indicated the S eS absorption bands with intramolecular
charge transfer (ICT) characteristics [21].
ꢀ
therefore highly planar with a small average deviation of 0.0295 A.
Both compounds contain conjugated aromatic system, thus they
Diphenyl-imidazole or phenanthro-imidazole substituents as
could form dimers by
were further extended along crystallographic b axis through weak
CeH/F and H/ contacts instead of interactions (Fig. 2). In
the structure of B1, the stacking area decreased due to steric
hindrance caused by two lateral twisted phenyl rings. For B2, the
CHCl molecule interacts with the host molecule by way of CeH/N
hydrogen bond.
p
/
p
interactions. Furthermore, the dimers
2
electron-donating groups, along with a BF core and pyridine
electron-deficient moieties, resulted in a “pushepull” system [17].
Photoexcitation of such a system would generate large dipolar
moments affected significantly by environmental polarity. In
addition, Emission spectra of B1 and B2 measured in polar solvents
displayed bathochromic shifts with low fluorescence yields [22]
and increased Stokes shifts in polar solvent, which further
confirmed the ICT mechanism. The spectra of B2 contained well-
resolved vibrational structure (Fig. 4) in hexane, which dis-
appeared gradually with increasing solvent polarity as the vibration
was restrained by polar molecules.
p
p/p
p
/p
3
3.2. Spectroscopic properties
The spectral properties of B1eB3 in various solvents and solid
state were examined. The data were summarized in Table 1. B1 and
B2 exhibited multiple absorption bands in CHCl , and the lowest-
energy absorption maxima at 414 nm for B1 and 430 nm for B2
were attributed to S eS transition. In comparison with that of B1,
the lower-energy absorption of B2 is ascribed to the enlarged
conjunction system lowering the transition energy (Fig. 3). The
molar absorption coefficient for B2 was much larger than that of B1,
because the twisted phenyl rings of B1 did not facilitate electrons
transition. Compound B3 exhibited an intense absorption band at
Compounds B1 and B2 were highly fluorescent in solid state. By
an integrating sphere, the absolute fluorescent quantum yields for
B1 and B2 in powder form were estimated to be 0.48 and 0.21,
respectively. B1 exhibited more intense solid-state fluorescence
than B2 due to the unfused phenyl rings considerably decreasing
stacking area, which was confirmed by X-ray single crystal analysis.
Notably, the maximum emission wavelengths of B1 and B2 had no
obvious difference whatever in solution and in solid powder, which
indicated the fused phenyl rings have less effect on the emission
spectra than fused thiophene system [23]. As expected, B3 did not
3
0
1
p-
5
3
09 nm and moderate absorptions at 338 nm in CHCl . The former
Fig. 1. Crystal structures of B1 (a) and B2 (b).

160
Z. Li et al. / Dyes and Pigments 105 (2014) 157e162
Fig. 2. Weak intermolecular interactions in B1 (a) and B2 (b).
Table 1
Spectroscopic properties of B1eB3 in various solvent and in solid state.
naphthyridine moiety in B3 increased with an isobestic point at
00 nm, whereas the main absorption band attributed to BODIPY
3
Dyes
Media
labs/nm
3
max
lem/nm
Stokes
shift/nm
F
F
core did not show obvious changes. Upon excitation at 330 nm, B3
exhibited two main emission bands at 521 nm and 365 nm in
3
ꢂ1
ꢂ1
(dm mol cm )
B1
Hexane
428
408
414
391
393
e
14,600
14,200
15,000
13,500
12,100
e
510
528
520
525
543
509
507
526
522
531
527
502
524
522
527
521
516
82
120
106
134
150
e
0.22
0.15
0.23
0.12
0.10
0.48
0.95
0.32
0.30
0.14
0.08
0.21
0.08
0.06
0.07
0.16
0.04
3 2
CH OH/H O (1:1 v/v) (Fig. 5, Figs. S7 and S8). The former was
CH
2
Cl
2
typical fluorescence for the BODIPY dyes, and the latter was asso-
CHCl
3
þ
ciated with 1,8-naphyridine unit. Addition of H to B3 in CH
3
OH/
CH
CH
3
3
OH
CN
2
H O solution, the intensity of emission peak at 521 nm decreased
while the one at 365 nm increased significantly when the 1,8-
naphthyridine unit was protonated. The results revealed that the
oxidative photoinduced electron transfer from the excited BODIPY
to the electron-deficient 1,8-naphthyridine unit, resulting in fluo-
rescence from BODIPY quenching [27,28]. The ration of the fluo-
rescent intensities at 365 nm and 521 nm (I365/I521) increased from
0.05 to 4.50. The results indicate that B3 can be considered as a
ratiometric pH sensor.
Solid
Hexane
B2
B3
447
421
430
404
403
e
15,500
19,600
21,000
20,000
20,000
e
67
105
92
127
124
e
CH
2
Cl
2
CHCl
3
CH
CH
3
3
OH
CN
Solid
Hexane
506
506
509
503
501
44,600
60,000
55,000
55,800
55,200
18
16
16
18
CH
2
Cl
2
CHCl
3
CH
CH
3
3
OH
CN
15
3.4. Time-dependent density functional theory calculations
To gain further insight into the observed spectroscopic behavior
of B1 and B2, time-dependent density functional theorycalculations
were performed on the dyes using the Gaussian 09 package [29]. The
geometrical structures for the ground and lowest singlet excited
states of the compounds were optimized at the TD-CAM-B3LYP/6-
31-G(d) level [30]. The character of singly occupied orbitals of the
display any fluorescence in the solid state possibly due to
interaction [24].
p/p
3.3. pH dependent fluorescence
S
0
/ S
of B1 and B2 both originated from a
4,5-diphenyl-imidazol or phenanthro[9,10-d]imidazole unit to a p*
1
transitions of B1 and B2 wereshownin Fig. 6. The transitions
It has been previously reported that the fluorescence of BF
2
-core
p
orbital mainly localized on a
compounds could be tuned by protonation of imidazole/pyridine
25,26]. Unfortunately, the presented compounds B1 and B2 were
unstable in the low pH value media due to the imidazole was
[
orbital localized on the pyridine moiety. The electron redistribution
resulted in the considerable dipole moment changes of ꢂ9.12 D for
B1 and ꢂ9.19 D for B2 along the x direction (from the left benzene
protonated. In the range of pH values 2.1e4.9, the absorbance of
3
Fig. 3. Absorption (a) and emission (b) spectra of B1eB3 in CHCl .

Z. Li et al. / Dyes and Pigments 105 (2014) 157e162
161
Fig. 4. The Absorption (a) and emission (b) spectra of compound B2 in different organic solvent and solid state.
Fig. 5. The effects of pH values on the absorption (a) and emission (b) spectra of B3 (5
m
M,
l
ex ¼ 330 nm).
ring to the pyridine unit). This indicated that an efficient intra-
molecular charge transfer process could be responsible for large
Stoke shifts and solvatochromism of these compounds. The vertical
excitation energies in the gas phase were calculated to be 373 nm for
B1 and 380 nm for B2, which is a slight blue shift compared with the
experimental absorption spectra in solution. However, the calcu-
lated trends of both complexes were in good agreement with those
obtained experimentally.
0 1
Fig. 6. The singly occupied molecular orbitals of the S / S transitions of compounds B1 and B2.

162
Z. Li et al. / Dyes and Pigments 105 (2014) 157e162
4
. Conclusions
[10] Yang Y, Su X, Carroll CN, Aprahamian I. Aggregation-induced emission in BF
hydrazone (BODIHY) complexes. Chem Sci 2012;3:610e3.
11] Zhang ZY, Xu B, Su JH, Shen LP, Xie YS, Tian H. Color-tunable solid-state
2
-
[
In summary, we have developed a series of BF
2
core complexes
0
emission of 2,2 -biindenyl-based. Angew Chem Int Ed 2011;50:11654e7.
containing pyridine/naphthyridine with intense solid-state fluo-
rescence. The ICT process leads to large Stokes shifts and solvent-
dependent photophysical properties for B1 and B2. The intense
solid emissions of B1 and B2 indicate that the weak intermolecular
interactions could inhibit aggregation-induced quenching, which is
instructive for developing solid-state luminescent materials. B3
does not show similar spectroscopic behaviors, but it displays about
[12] Lu H, Wang Q, Gai L, Li Z, Deng Y, Xiao X, et al. Tuning the solid-state lumi-
nescence of BODIPY derivatives with bulky arylsilyl groups: synthesis and
spectroscopic properties. Chem Eur J 2012;18:7852e61.
[
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[
13] Kubota Y, Tanaka S, Funabiki K, Matsui M. Synthesis and fluorescence prop-
erties of thiazole-boron complexes bearing a -ketoiminate ligand. Org Lett
012;14:4682e5.
b
2
14] Chen Y, Fu WF, Li JL, Zhao XJ, Ou XM. Conformation impact on spectral
II
properties of bis(5,7-dimethyl-1,8-naphthyridin-2-yl)amine and its Zn
complex. New J Chem 2007;31:1785e8.
15] de Greef TF, Ercolani G, Ligthart GBWL, Meijer EW, Sijbesma RP. Influence of
selectivity on the supramolecular polymerization of AB-type polymers
capable of both A/A and A/B interactions. J Am Chem Soc 2008;130:13755e
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9
3 2
0-fold fluorescence ratio change upon protonated in CH OH/H O,
which indicates that the compound could serve as a pH ratiometric
fluorescent sensor.
[16] Quan L, Chen Y, Lv XJ, Fu WF. Aggregation-induced photoluminescent changes
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Acknowledgments
[
17] Wu YY, Chen Y, Gou GZ, Mu WH, Lv XJ, Du ML, et al. Large stokes shift induced
2
by intramolcular charge transfer in N,O-chelated naphthyridine-BF com-
This work was financially supported by the Ministry of Science
and Technology (2013CB834804, 2012DFH40090). We thank the
Natural Science Foundation of China (NSFC Grant Nos. 21071123,
plexes. Org Lett 2012;14:5226e9.
18] Eseola AO, Zhang M, Xiang JF, Zuo W, Li Y, Woods JAO, et al. Synthesis and
characterization of nickel(II) complexes bearing 2-(imidazol-2-yl)pyridines or
[
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21273257 and U1137606), and CAS-Croucher Funding Scheme for
norbornene. Inorg Chim Acta 2010;363:1970e8.
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dicarboxaldehyde into novel 2,7-dimenthylimine derivatives. J Heterocycl
Chem 2002;39:829e32.
[20] The main work of the article has been completed in 2011. In 2012, the authors
became aware of a report where compound B1 was prepared by Mao M,
Xiao S, Li J, Zou Y, Zhang R, Pan J, et al. Solid-emissive boron-fluorine de-
rivatives with large Stokes shift Tetrahedron 2012;68:5037e41. In present
work, the effect of fused phenyl rings on spectral characteristics of B1 and B2
are fully compared.
Joint Laboratories, Yunnan Key Project (2010CC007) and Program
for Changjiang Scholars and Innovative Research Team in Univer-
sity (IRT0979) for financial support.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.dyepig.2014.01.022.
[
21] Zhang JC, Wang DY. Modern photochemistry. Beijing: Industry Press Journal;
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