A novel NIR violanthrone derivative with high electron-deficiency: Effect of fluorescence on dicyanomethylene substitution

Article abstract of DOI:10.1007/s11458-010-0115-7

Near infrared (NIR) dyes attracted increasing interests in widely potential applications, such as fluorescent probe and living organism imaging, due to their low background signals from biomolecules, low light scattering and deep penetration, and low-cost excitation light sources. A novel NIR violanthrone derivative (VA-CN) with dicyanomethylene substitution was synthesized and fully characterized by ¹H NMR, ¹³C NMR, HRMS, and IR spectrometry. It is demonstrated that the original planar conformation of violanthrone ring (the nine fused benzene rings) becomes twisted and unsymmetrical upon the incorporation of two strong electron-withdrawing dicyanomethylene units. Photophysical, electrochemical performances as well as distinct solvatochromic effects were studied in detail. Considering the low reduction potential (-0. 56 V vs NHE), VA-CN could be considered as a good electron acceptor due to the strong electron deficiency resulted from dicyanomethylene group. A distinct increase in fluorescence was observed with 30-fold enhancement upon the addition of n-butyl amine. The reversible fluorescence "off-on" shows that VA-CN might be served as a promising fluorescent sensor for electron-rich amines.

Full text of DOI:10.1007/s11458-010-0115-7

Front. Chem. China 2010, 5(2): 200–207
DOI 10.1007/s11458-010-0115-7
RESEARCH ARTICLE
1
Introduction
Near infrared region (NIR) dyes have become an increasingly
interesting field in widely potential applications, such as
fluorescent probe and living organism imaging, due to their
low background signals from biomolecules, low light
scattering and deep penetration, and low-cost excitation
light sources [1–3]. Among NIR dyes, cyanine, squarylium,
and boron-dipyrromethene (BODIPY) dyes have been deeply
developed [4–12]. Meguellati et al. has reported an NIR
family of unsymmetrical imine-based trimethine and penta-
methine cyanine dye analogs that could form under reversible
and thermodynamically controlled conditions from building
blocks of non- or weakly emissive amine and aldehyde [4].
More recently, Umezawa et al. has successfully studied a
series of bright and color-tunable fluorescent dyes over a wide
range including NIR by introducing electron donors and
acceptors to BODIPY segment [1]. However, there is still
much room to develop various types of NIR dyes with high
molar extinction coefficients, longer emission wavelength,
and sharp and intense fluorescence with high chemical and
photo stabilities.
Violanthrone, a system fused with nine benzene rings, is a
well-known traditional anthraquinone vat dyestuff for cotton
coloration with high light fastness, high washing, and chlorine
bleaching. 16,17-dialkoxy violanthrone have been applied in
the area of NIR military and anti-counterfeiting techniques
because of its highly conjugated system. Recently, several
groups are engaged in its photochemical properties and
conductivity [13–16]. However, as an NIR fluorescent dye,
the emission peak of 16,17-dialkoxy violanthrone is located at
near 710 nm and not far from the visible red light region
A novel NIR violanthrone
derivative with high electron-
deficiency: effect of
fluorescence on
dicyanomethylene
substitution
1
,2
1
1
Bo LIU , Duo FAN , Qiong ZHANG ,
1
1
Yu CHEN and Weihong ZHU (✉)
Near infrared (NIR) dyes attracted increasing interests
in widely potential applications, such as fluorescent
probe and living organism imaging, due to their low
background signals from biomolecules, low light
scattering and deep penetration, and low-cost excitation
light sources. A novel NIR violanthrone derivative (VA-
CN) with dicyanomethylene substitution was synthe-
1
13
sized and fully characterized by H NMR, C NMR,
HRMS, and IR spectrometry. It is demonstrated that
the original planar conformation of violanthrone ring
(
the nine fused benzene rings) becomes twisted and
unsymmetrical upon the incorporation of two strong
electron-withdrawing dicyanomethylene units. Photo-
physical, electrochemical performances as well as
distinct solvatochromic effects were studied in detail.
Considering the low reduction potential ( – 0.56 V vs
NHE), VA-CN could be considered as a good electron
acceptor due to the strong electron deficiency resulted
from dicyanomethylene group. A distinct increase in
fluorescence was observed with 30-fold enhancement
upon the addition of n-butyl amine. The reversible
fluorescence “off-on” shows that VA-CN might be
served as a promising fluorescent sensor for electron-
rich amines.
(almost 40% ratio in the range of 650 – 700 nm), thus bringing
a very serious disturbance from the visible light region. With
this in mind, in this article we report a new type of NIR
fluorescent dye (VA-CN, Figure 1) based on violanthrone via
the incorporation of strong electron-withdrawing dicyano-
methylene unit. Interestingly, the original planar conformation
of violanthrone ring (the nine fused benzene rings) becomes
twisted and unsymmetrical upon the incorporation of two
strong electron-withdrawing dicyanomethylene units. Its
Keywords violanthrone derivative, dicyanomethylene fluorescent efficiency on dicyanomethylene substitution was
group, synthesis, NIR fluorescence
also discussed in detail.
2
Experimental
Received December 18, 2009; accepted March 15, 2010
1
. Key Laboratory for Advanced Materials and Institute of Fine
Chemicals, East China University of Science & Technology, Shanghai Violanthrone was commercially purchased and washed with
2
2
00237, China
methanol. Tetrabutylammonium hexafluorophosphoric was
purchased from Aldrich. All other chemicals and solvents
were obtained from Sinopharm Chemical Reagent Co., Ltd,
. College of Chemistry and Material Science, Hebei Normal University,
Shijiazhuang 050016, China
E-mail: whzhu@ecust.edu.cn
©
Higher Education Press and Springer-Verlag Berlin Heidelberg 2010

A novel NIR violanthrone derivative with high electron-deficiency: effect of fluorescence on dicyanomethylene substitution
201
Figure 1 Synthetic route of NIR fluorescence dyes VA-O and VA-CN.
China (reagent grade) and used as received. The synthesis of about 130°C and stirred for another 8 h and then cooled and
6,17-dihydroxy violanthrone (2) was performed according to poured into water (100 mL). The solid was filtered and
Ref. [17].
recrystallized with methanol and ethyl acetate, respectively.
1
1
13
H NMR and C NMR spectra were obtained by using a Compound VA-O was acquired as black solid (yield 12.5%).
1
Brucker AM-400 spectrometer. The mass spectra were con- H NMR (400 MHz, CDCl , ppm) d: 8.41 (d, J = 6.8 Hz, 2H),
3
ducted on a HP5989 mass spectrometer. UV-Vis spectra were 8.39 (d, J = 1.2 Hz, 2H), 8.28 (d, J = 8.0 Hz, 2H), 8.18 (d, J =
recorded on a Varian Cary 500 spectrophotometer, and fluor- 8.0 Hz, 2H), 8.10 (s, 2H), 7.76 (t, J = 7.2 Hz, 2H), 7.54 (t, J =
escence spectra on a Varian Cary Eclipse fluorescence spect- 7.6 Hz, 2H), 4.19 (t, 4H), 1.85 (m, 4H), 1.45 (m, 4H), 1.30 (m,
1
3
rophotometer. Cyclic voltammogram was determined with 16H), 0.85 (t, J = 6.8 Hz, 6H). C NMR (100 MHz, CDCl3,
Versastat II electrochemical workstation (Princeton Applied ppm) d: 182.4, 155.5, 135.2, 133.5, 132.8, 130.6, 128.5,
Research) using a platinum electrode as working electrode, a 128.3, 127.9, 127.0, 126.8, 126.4, 122.8, 122.0, 116.5, 112.5,
–1
platinum wire as counter electrode, and a Ag/AgCl electrode 69.1, 31.8, 29.8, 29.6, 29.3, 26.0, 22.7, 14.1. IR, n (cm ):
in saturated KCl solution as reference electrode. Tetrabutyl- 2925, 2851, 1740, 1380, 750.
–1
ammonium hexafluorophosphoric (0.1 mol$L ) was used as
supporting electrolyte, and ferrocene was used as internal 2.2 Synthesis of VA-CN
reference.
Compound VA-O (5.0 g, 4.9 mmol) and dicyanomethylene
1.5 g, 22.7 mmol) were added into acetic anhydride (30 mL).
The mixture was stirred and refluxed for 6 h, then cooled and
poured into hot water (100 mL). The solid was filtered and
washed with ethanol (200 mL). After recrystallized with ethyl
acetate, the dark green product was further purified by column
The geometrical, electronic, and optical properties of VA-O
and VA-CN were calculated using Gaussian 03 program
package [18]. The molecular structures were optimized using
hybrid B3LYP exchange-correlation functional and the all-
electron 6–31 g (d) double-x plus polarization basis set [19].
For the excited state calculation, we employed the 6–31 + g
(
chromatography on silica using CH Cl /petroleum ether 4∶1
(
d) double-x plus polarization and diffuse basis set. The
2
2
(
1
v/v) as elute. VA-CN was obtained as green solid (yield
ground-state geometries have been optimized in both vacuum
and solution by a standard force-minimization procedure.
Solvation effects were evaluated by means of polarizable
continuum model [20].
1
1.3%). H NMR (400 MHz, CDCl , ppm) d: 8.60 (d, J =
3
7
8
8
.6 Hz, 2H), 8.48 (d, J = 7.6 Hz, 1H), 8.42 (d, J = 8.4 Hz, 1H),
.38 (d, J = 8.4 Hz, 2H), 8.32 (d, J = 8.4 Hz, 1H), 8.28 (d, J =
.4 Hz, 1H), 8.23 (s, 1H), 8.18 (s, 1H), 7.84 (t, J = 7.2 Hz,
2
.1 Synthesis of 16,17-dioctyloxyviolanthrone (VA-O)
1H), 7.78 (t, J = 7.6 Hz, 1H), 7.67 (t, J = 7.6 Hz, 1H), 7.55 (t, J
7.2 Hz, 1H), 4.31 (t, 4H), 1.95–1.87 (m, 4H), 1.45 (t, J =
a mixture of 16,17-dihydroxyviolanthrone (5.0 g, 7.2 Hz, 4H), 1.29 (m, 16H), 0.85 (m, 6H). C NMR
=
1
3
To
0
.01 mol) and potassium carbonate (10.3 g, 0.075 mol) in (100 MHz, CDCl , ppm) d: 182.7, 182.5, 160.1, 156.3,
3
DMF (35 mL) heated to 120°C, 1-bromooctane (13.9 g, 156.0, 135.3, 135.0, 133.9, 133.1, 132.9, 132.8, 132.5, 130.7,
0
.05 mol) was added during 3 h. The reactant was heated to 130.5, 129.0, 128.5, 128.2, 128.0, 127.9, 127.6, 127.5, 127.3,
Frontiers of Chemistry in China Vol. 5, No. 2, 2010

2
02
Bo LIU, Duo FAN, Qiong ZHANG, Yu CHEN and Weihong ZHU
1
13
1
1
6
2
27.2, 126.6, 125.5, 124.0, 123.3, 123.1, 122.9, 122.8, 122.3, characterized by H NMR, C NMR, HRMS, and IR
21.4, 120.3, 117.0, 116.8, 116.5, 116.2, 113.1, 112.6, 112.2, spectra.
9.5, 31.8, 29.9, 29.5, 29.3, 26.2, 22.6, 14.1. IR, n (cm ):
–1
1
As a comparison of the H NMR spectra between VA-O and
925, 2851, 2210, 1380, 750. FAB-MS: calc. for VA-CN (Figure 2), there is no obvious difference between the
+
í
signals of saturated hydrogen atoms (Hh – H , H – H )
o
h
í
[
C H O N + Na ]: 831.3675, found: 831.3660.
5
6
48
2
2
o
since the long tail n-octyl group is not near to the p-
delocalization system. While the dicyanomethylene unit is
introduced into VA-O, the enhancement of electron-with-
drawing capability makes the molecular polarity of VA-CN
higher in electron distribution, thus resulting in an obvious
change in chemical shift for aromatic hydrogens. As expected,
the chemical shifts corresponding to H – H in the parent
ring of VA-O are located at 8.41, 8.28, 8.39, 7.54, 7.76, 8.18
and 8.10 ppm, respectively, presenting a relatively good
symmetry. However, with respect to VA-O, all signals
3
Results and discussion
3
.1 Synthesis
Violanthrone, used as starting material, shows poor solubility
in most organic solvents due to its relatively strong rigidity
and polarity. While long alkoxy substitutents on the bay of
violanthrone were introduced, its solubility can be improved
significantly [17]. Therefore, compound violanthrone was
oxidized into 16,17-dihydroxy violanthrone and two long tail
n-octyloxy groups were then incorporated through William-
son reaction (Figure 1). The resulted compound VA-O can be
dissolved in common organic solvents, such as CH Cl ,
a
g
corresponding to the parent ring hydrogen in VA-CN shift
î
to downfield and are split. The chemical shifts of and H –
a
î
H
in VA-CN were 8.60, 8.48, 8.38, 8.32, 8.23, 7.84,
g
í í
.67 ppm (for H – H ) and 8.60, 8.42, 8.38, 8.28, 8.18, 7.78,
a g
7
7
2
2
î
î
.55 ppm (for H – H ), respectively. Moreover, two split
a
g
toluene, CCl , ethyl acetate (EA), THF, and DMF.
4
peaks with equal integrity in VA-CN are observed. For
Meanwhile, it is necessary to increase the bipolarity
between donor and acceptor for the sake of red-shift in the
absorption maxima to near infrared area. As is well known,
cyano group is a kind of very strong electron-acceptor that is
broadly applied in many intramolecular charge-transferring
example, in the compound VA-O, H is a sharp single peak,
g
representing two symmetric hydrogen atoms. In VA-CN, two
í
î
single peaks with equal integrity correspond to Hg and H ,
g
í
thus indicating that the chemical environment of Hg is
î
(
ICT) systems [21–23]. Therefore, four cyano groups (two different from Hg . In the case of VA-CN, the split for such
strong electron-withdrawing dicyanomethylene unit) were aromatic hydrogens in NMR signals obviously indicates that
incorporated into carbonyl groups through Knoevenagel the original planar conformation of violanthrone ring (the nine
reaction (VA-CN, Figure 1). Notably, since the carbonyl fused benzene rings) becomes twisted and unsymmetrical
groups in the violanthrone system are much less reactive due upon the incorporation of two strong electron-withdrawing
to the large conjugation system of violanthrone, the target dicyanomethylene unit.
compound could not be obtained through most traditional
To gain insight into the twisted conformation, the optimized
Knoevenagel reaction conditions [24]. Finally, we success- ground state geometries of VA-O and VA-CN were calculated
fully synthesized VA-CN via using acetic anhydride as both using Gaussian 03 program. Optimized structures of VA-O
solvent and catalyst. Its chemical structure was fully and VA-CN are shown in Figure 3, and characteristic
1
Figure 2 Comparison of H NMR spectra between VA-O and VA-CN
Frontiers of Chemistry in China Vol. 5, No. 2, 2010

A novel NIR violanthrone derivative with high electron-deficiency: effect of fluorescence on dicyanomethylene substitution
203
Figure 3 Optimized ground state geometries of VA-O and VA-CN calculated using B3LYP/6-31G (d) in gas.
parameters of dihedral angles are presented in Table 1. It is complicated than that of VA-O (as shown in Experimental
clear that the nine fused benzene rings in compound VA-O section).
were nearly in the same plane. The distortion between two
planes consist of B1–B4 and B6–B9 is characterized by can be further evidenced by IR spectra (Figure 4). Strong
For VA-CN, the incorporation of dicyanomethylene groups
–1
dihedral angles labeled with Ð2-3-3¢-2¢ (31.81°) and Ð8-9- peaks at 2925 and 2851 cm represent the saturated C-H
¢-8¢ (0.90°). The distortion is mainly attributed to the steric symmetric and asymmetric flex oscillation, respectively. Due
9
effect of methoxy substitution. Actually, the two methoxy to similar frequency of flex oscillation and low resolution,
groups are tilted out of these two planes, with Ð1-2-3-3¢ only two vibration peaks were observed in the spectra.
–1
(
13.07°) and Ð1¢-2¢-3¢-3 (13.04°). In the case of VA-CN, Meanwhile, a weak vibration peak at 750 cm correspondes
the introduction of the more bulky dicyanomethylene to the characteristically vibrational oscillation of (CH ) . In
2
n
–1
groups leads to even more fiercely twisted ground state VA-O, the peak at 1740 cm is the characteristic peak of
geometry. This could be evidenced from the larger dihedral carbonyl groups. Notably, after substituted with dicyano-
–1
angles of Ð4-5-6-7 (34.23°), Ð4¢-5¢-6¢-7¢ (34.21°) and Ð2- methylene units, the peak at 1740 cm disappeared whereas a
–
1
3
-3¢-2¢ (33.57°) in VA-CN (Table 1). Consequently, the sharp and strong peak at the wavenumber of 2209 cm
benzene rings B1¢, B2¢, B3¢ and B4¢ are no longer in the
same plane, neither are the rings B6¢, B7¢, B8¢ and B9¢.
Therefore, the chemical environment between aromatic
í
í
î
î
protons (H – H and H – H ) becomes different so as to
a
g
a
g
1
present different chemical shifts in H NMR (Figure 2).
Based on the same reason, the carbon signals in C NMR of
VA-CN are also unsymmetrical, and become much more
1
3
Table 1 Important dihedral angle parameters optimized ground state
geometries of VA-O and VA-CN calculated with B3LYP/6-31G (d) in gas
dihedral angles
Ð1-2-3-3¢
VA-O
13.07°
13.04°
31.81°
11.78°
0.90°
VA-CN
11.12°
11.14°
33.57°
12.04°
34.23°
34.21°
Ð1¢-2¢-3¢-3
Ð2-3-3¢-2’
Ð8-9-9¢-8’
Ð4-5-6-7
Ð4¢-5¢-6¢-7¢
0.90°
Figure 4 IR spectra of VA-O and VA-CN.
Frontiers of Chemistry in China Vol. 5, No. 2, 2010

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04
Bo LIU, Duo FAN, Qiong ZHANG, Yu CHEN and Weihong ZHU
appeared. The new peak corresponds to the characteristic peak longer redshift. For the purpose of increasing the ICT effect
of cyano groups in VA-CN. Obviously, two carbonyl groups and of shifting the emission wavelength, the higher electron-
in VA-O have successfully substituted by the two dicyano- deficient dicyanomethylene groups are incorporated. As
methylene units.
expected, in consistent with the above red-shift in absorption,
the emission peak of VA-CN moves to the longer wavelength
at 771 nm (Figure 5). However, the emission peak of VA-CN
becomes unexpectedly quenched. With respect to VA-O, the
observed fluorescence is decreased by roughly 2 orders of
magnitude upon the substitution with highly electron-
deficient dicyanomethylene groups. Obviously, the serious
fluorescence quenching of VA-CN may be resulted from the
existence of non-radiative competion before the radiative
emission processes [25]. As mentioned above, the conforma-
tion of nine fused benzene rings changes from the original
planar (VA-O) to the twisted and unsymmetrical (VA-CN)
upon the incorporation of dicyanomethylene unit, which
might also play a role in the fluorescence quenching.
3
.2 Photophysical properties of VA-O and VA-CN
The absorption and emission spectra of VA-O and VA-CN
in CH Cl are shown in Figure 5. The reference compound
2
2
of VA-O exhibits three absorption peaks at 262, 395 and
48 nm. The lmax at 648 nm is attributed to the
6
intramolecular charge transfer (ICT) band of the violan-
throne backbone, which is heavily effected by the charge
transfer from n-octyloxy groups to carbonyl groups in
the violanthrone backbone. Compared with VA-O, when
carbonyl groups are substituted with dicyanomethylene
groups, a red-shifted absorption peak of VA-CN is observed
at 701 nm with higher molar extinction coefficient (4.69 Â
To further explain the effect of ICT and large red-shift
4
–1
–1
1
0 L$mol $cm ).
between labs and l , the solvatochromism was investigated
em
in detail (Figures 6–8). With an increase in the solvent
polarity, VA-O presents a 46 nm red-shift from 629 nm in
CCl to 675 nm in DMF (Figure 6), and VA-CN red shifts by
4
2
7 nm from 679 nm in CCl to 706 nm in DMF (Figure 7).
4
Correspondingly, the solvatochromism in the emission band
of VA-O was observed to shift from 681 nm in CCl to 723 nm
4
in DMF (Figure 8). With increasing solvent polarity, the
molecule becomes high polarization, thus enlarging the dipole
moments and resulting in red-shift in both absorption and
emission spectra. The higher the polarity of solvents, the
lower the energy of relaxed states, which was arisen from the
larger red-shift in the emission spectra for VA-O [26].
However, the solvent polarity does not present significant
influence on molar extinction coefficients.
2 2
Figure 5 Absorption spectra of VA-O and VA-CN in CH Cl (1.0
–5
–1
 10 mol$L ). Inset: emission spectra of VA-O (  1) and VA-
CN ( Â 10).
As is known, the reference carbonyl-containing compound
VA-O is a NIR fluorescent chromophore with an emission
located at 716 nm and a Stokes-shift (58 nm) in CH Cl
2
2
(
Figure 5), resulting from the possible ICT transition from n-
octyloxy group (electron donor) to carbonyl group (electron
acceptor) in the violanthrone backbone. As a NIR fluorescent
dye, the emission peak of VA-O is located at 716 nm, which is
not far from the visible red light region. Actually, for the
purpose of applications in military and anti-counterfeiting,
there is a very serious problem in the emission spectra of VA-
O from the visible light region, almost 40% in the range of
Figure 6 Normalized absorption spectra of VA-O in a variety of
6
50 – 700 nm (Figure 5). Generally, the higher ICT effect, the
solvents.
Frontiers of Chemistry in China Vol. 5, No. 2, 2010

A novel NIR violanthrone derivative with high electron-deficiency: effect of fluorescence on dicyanomethylene substitution
205
Figure 7 Normalized emission spectra of VA-O in a variety of
solvents (excitation at lmax).
2
Figure 9 Cyclic voltammograms of VA-O and VA-CN in CH Cl
(1.0 Â 10 mol$L ).
2
–3
–1
from the dicyanomethylene group. It is the ICT effect of
stronger electron-withdrawing dicyanomethylene unit that
decreases the LUMO energetic stabilization from the stronger
electron-withdrawing capability of dicyanomethylene group
with respect to carbonyl group, resulting in a band gap
contraction from 1.82 eV (VA-O) to 1.50 eV (VA-CN).
Obviously, the analysis of redox potentials reveals the
importance of carbonyl and dicyanomethylene groups in
modulating the frontier molecular orbital of VA-O and VA-
CN with good reversibility (redox stability).
We also calculated the solvent effect on the electronic
property of compound VA-CN by hybrid density functional
*
theory with 6–31G basis set as implemented in the Gaussian
03 program [17]. As seen in Table 2, both LUMO and HOMO
are destabilized upon the increase of polarity. The decrease of
the band gap, which is due to the bathochromic solvent effect,
is observed since the HOMO destabilization is the major
effect. This trend is in good agreement with experiments.
Figure 8 Normalized absorption spectra of VA-CN in a variety of
solvents.
3
.3 Electrochemical properties of VA-O and VA-CN
Table 2 Calculated HOMO, LUMO, and band gap (HOMO and
LUMO gaps) of VA-CN
To investigate the redox properties, cyclic voltammetry
measurements were performed in CH Cl at a scan rate of
vacuum
– 3.5242
– 5.3541
1.8299
CCl
4
DMF
2
2
LUMO (eV)
HOMO (eV)
Band gap (eV)
– 3.4822
– 5.2678
1.7856
– 3.4558
– 5.1881
1.7323
–1
1
00 mV$s using Pt as working electrode, Ag/AgCl as
reference electrode, Pt wire as counter electrode, and
ferrocene as the internal standard. The cyclic voltammograms
of VA-O and VA-CN were shown in Figure 9. Both VA-O and
VA-CN shows two reversible oxidation peaks at potentials of 3.4 Interaction of VA-CN with electron-rich amine
.09, 1.49 Vand 1.10, 1.49 V vs NHE, respectively, which are
1
assigned as the oxidation of violanthrone backbone. Besides, Considering the low reduction potential ( – 0.56 V vs NHE),
VA-O presents a single reversible reduction peak at – 0.96 V VA-CN might be considered as a good electron acceptor
vs NHE, which can be attributed as the reduction of carbonyl because of the stronger electron deficiency resulted from
groups into the quinonoidal dianion [27]. Comparing with dicyanomethylene group. We attempted to utilize amine as
VA-O, the reduction potential of VA-CN was shifted to potential donor to get further insight into the binding with VA-
–
0.56 V vs NHE due to stronger electron deficiency resulted CN. Upon titrating with n-butyl amine, the absorption spectra
Frontiers of Chemistry in China Vol. 5, No. 2, 2010

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06
Bo LIU, Duo FAN, Qiong ZHANG, Yu CHEN and Weihong ZHU
of VA-CN shows an obvious decrease at the peak of 701 nm
and an increase at the peak of 633 nm with a distinct isosbestic
point at 654 nm (Figure 10). Due to the low reduction
potential, it is possible to expect that the system of VA-CN
with strong electron-deficient cyano groups could bind with
lone pair electrons of amine and thus could result in a possible
intermolecular charge transfer band (located at 633 nm). After
binding with amines, the original intramolecular charge
transfer band becomes decreased, thus resulting in the
absorption peak (lmax) blue-shifted by 68 nm from 701 to
6
33 nm. Moreover, the absorption can be recovered to the
original state while equivalent acetic acid was added. In order
to further avoid the interference of hydrogen bond, appro-
priate amount methanol was added into the solvent followed
by n-butyl amine. Same change in the absorption blue-shift is
kept. Therefore, possible hydrogen bonding might be ruled
out.
Figure 11 Emission intensity at 712 nm of VA-CN with various
–
5
–1
equivalence of n-butyl amine in CH
2
Cl
2
(1.0 Â 10 mol$L ).
dicyanomethylene units, the original planar conformation of
violanthrone ring becomes twisted and unsymmetrical. It is
demonstrated that VA-CN could be considered as a good
electron acceptor due to its stronge electron deficiency
resulted from the dicyanomethylene group. A distinct increase
in fluorescence was observed with 30-fold upon the addition
of n-butyl amine. The reversible fluorescence “off-on” shows
that VA-CN might be served as a promising fluorescent sensor
for electron-rich amines.
Acknowledgements The work was financially supported by the
National Natural Science Foundation of China, Program for New
Century Excellent Talents in University (Grant No. NCET-06-0418),
the “Dawn” Program of Shanghai Education Commission, China
(Grant No. 07SG34), and Research Fund for the Doctoral Program of
Higher Education of China (Grant No. 200802510011).
Figure 10 UV-Vis spectra of VA-CN with various equivalent of
–
5
–1
n-butyl amine in CH
2
Cl
2
(1.0 Â 10 mol$L ).
Weihong ZHU received his B.S. degree in
Department of Chemistry from Nanjing Nor-
mal University (Nanjing, China) in 1992, and
obtained his M.S. degree in organic chemistry
from Nankai University (Tianjin, China) in
More interestingly, a distinctive increase of fluorescence
excited at the isosbestic point of 654 nm was found upon the
addition of various equivalent of n-butyl amine (Figure 11).
The fluorescence intensity was increased by nearly 30 folds.
Also, the fluorescence “off-on” is reversible. While the
addition of acetic acid, the fluorescence intensity decreases
accordingly, which was indicative of the possible interaction
between the deficient center of VA-CN and lone-pair electrons
of amine. It shows that VA-CN might be served as a promising
fluorescent sensor for electron-rich amines.
1
995. He studied applied chemistry under the
direction of Professor He Tian at the Institute
of Fine Chemicals of East China University of
Science & Technology, and received his Ph.D.
degree in 1999. He worked in the field of chemical modification of
carbon nanotubes with Dr. Nobutsugu Minami in National Institute
of Advanced Industrial Science and Technology (AIST Central 5),
Tsukuba, Japan as a postdoctoral researcher from 2001 to 2003, and
worked in the field of chemical modification with N@C60 with Prof.
Akasaka in Tsukuba University, Japan as a visiting professor from
4
Conclusions
2
004 to 2005. He became a full professor in 2004 and deputy director
in 2006. His current research interests include the syntheses of novel
functional organic or copolymer dyes and dendrimers. He is a co-
inventor of 17 Chinese invention patents (6 authorized) and has
A novel NIR dye VA-CN was synthesized and fully
characterized by H NMR, HRMS, and IR spectra. Upon
1
the incorporation of two strong electron-withdrawing published more than 70 papers in international journals. He has
Frontiers of Chemistry in China Vol. 5, No. 2, 2010

A novel NIR violanthrone derivative with high electron-deficiency: effect of fluorescence on dicyanomethylene substitution
207
received several awards, including the Author of National Excellent 13. Hansongnern, K.; Chooto, P.; Amornpitoksuk, P., Int. J.
Doctoral Dissertation of PR China (2001), Ninth Fok Yingtong’s
Photoenergy 1999, 1, 143–145
Young Scholar (2004), Enlisted in New Century Outstanding Talent 14. Inokuchi, H., Org. Electron. 2006, 7, 62–76
Support Program (2006).
1
5. Cabanillas-Gonzalez, J.; Yeates, S.; Bradley, D. D. C., Synth.
Met. 2003, 139, 637–641
1
1
6. Seybold, G.; Wagenblast, G., Dyes Pigments 1989, 11, 303–317
References
7. Rauhut, M. M.; Roberts, B. G.; Maulding, D. R.; Bergmark, W.;
Coleman, R., J. Org. Chem. 1975, 40, 330–335
8. Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala, P. Y.;
Chen, W.; Wong, M. W.; Andres, J. L.; Replogle, E. S.; et al.,
Gaussian 03, revision C.01, Gaussian, Inc.: Pittsburgh, PA,
2004
1. Umezawa, K.; Nakamura, Y.; Makino, H.; Citterio, D.; Suzuki,
1
K., J. Am. Chem. Soc. 2008, 130, 1550–1551
2. Weissleder, R., Nat. Biotechnol. 2001, 19, 316–317
3. Tang, B.; Cui, L. J.; Xu, K. H.; Tong, L. L.; Yang, G. W.; An, L.
G., ChemBioChem 2008, 9, 1159–1164
19. Becke, A. D., J. Chem. Phys. 1993, 98, 5648–5652
4
5
6
. Meguellati, K.; Spichty, M.; Ladame, S., Org. Lett. 2009, 11, 20. Ditchfield, R.; Herhe, W. J.; Pople, J. A., J. Chem. Phys. 1971,
123–1126
54, 724–728
. Lee, H.; Mason, J. C.; Achilefu, S., J. Org. Chem. 2008, 73, 21. Isborn, C. M.; Leclercq, A.; Vila, F. D.; Dalton, L. R.; Brédas, J.
1
723–725
L.; Eichinger, B. E.; Robinson, B. H., J. Phys. Chem. A 2007,
111, 1319–1327
. Geiger, T.; Kuster, S.; Yum, J. H.; Moon, S. J.; Nazeeruddin, M.
K.; Grätzel, M.; Nüesch, F., Adv. Funct. Mater. 2009, 19, 2720– 22. Liu, B.; Zhu, W. H.; Zhang, Q.; Wu, W. J.; Xu, M.; Ning, Z. J.;
727
Xie, Y. S.; Tian, H., Chem. Commun. 2009, 1766–1768
. Dilek, G.; Akkaya, E. U., Tetrahedron Lett. 2000, 41, 3721– 23. Mishra, A.; Fischer, M. K. R.; Bäuerle, P., Angew. Chem. Int. Ed.
724
2009, 48, 2474–2499
. Yagi, S.; Ohta, T.; Akagi, N.; Nakazumi, H., Dyes Pigments 24. Suzuki, T.; Ichioka, K.; Higuchi, H.; Kawai, H.; Fujiwara, K.;
2
7
8
9
3
2
008, 77, 525–536
. Bae, J. S.; Gwon, S. Y.; Son, Y. A.; Kim, S. H., Dyes Pigments
009, 83, 324–327
0. Loudet, A.; Burgess, K., Chem. Rev. 2007, 107, 4891–4932
Ohkita, M.; Tsuji, T.; Takahashi, Y., J. Org. Chem. 2005, 70,
5592–5598
2
25. Fabian, J.; Nakazumi, H.; Matsuoka, M., Chem. Rev. 1992, 92,
1197–1226
1
1
1. Wang, Y. W.; Yu, M. X.; Yu, Y. H.; Bai, Z. P.; Shen, Z.; Li, F. Y.; 26. Valeur, R., Molecular Fluorescence: Principles and Applica-
You, X. Z., Tetrahedron Lett. 2009, 50, 6169–6172
tions; Wiley-VCH: Verlag GmbH, 2001, p 200–225
2. Tian, M.; Peng, X.; Feng, F.; Meng, S.; Fan, J.; Sun, S., Dyes 27. Jacob, J.; Sax, S.; Piok, T.; List, E. J. W.; Grimsdale, A. C.;
Pigments 2009, 81, 58–62
Müllen, K., J. Am. Chem. Soc. 2004, 126, 6987–6995
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