Dicyanostilbene-derived two-photon fluorescence dyes with large two-photon absorption cross sections

Article abstract of DOI:10.1016/j.molstruc.2011.08.016

Four dicyanostilbene-derived two-photon fluorescence (TPF) dyes were synthesized as the model compounds to systematically study the effect of the dicyano and the terminal substituent on the two-photon absorption (TPA). These four compounds (DSO, DCY, DTO and DPH) exhibit very large two-photon absorption cross sections (δ). DCY (A-π-A) with the terminal cyano group has especially high fluorescence quantum yield (0.71) and relatively large δ (1480 GM), while DPH (D-π-A) with the substitutedamino group at its terminus possesses the largest δ (2800 GM) and the longest emission wavelength (620 nm). The idealest terminal substituent should not be the alkoxy group but the substitutedamino group. This class of dicyanostilbene dyes possess small molecule size, large δ (830-2800 GM), long-wavelength emission (459-620 nm) and large Stokes shift (80-206 nm), and are ideal chromophores for TPF labels and probes.

Full text of DOI:10.1016/j.molstruc.2011.08.016

Journal of Molecular Structure 1006 (2011) 91–95
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Dicyanostilbene-derived two-photon fluorescence dyes with large
two-photon absorption cross sections
Chibao Huang a,b, Changhua Lin b, Anxiang Ren b, Nianfa Yang a,
⇑
a Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, College of Chemistry, Xiangtan University, Xiangtan 411105, China
b Department of Agricultural Engineering, Yingdong Bioengineering College, Shaoguan University, Shaoguan 512005, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 May 2011
Received in revised form 24 July 2011
Accepted 6 August 2011
Available online 25 August 2011
Four dicyanostilbene-derived two-photon fluorescence (TPF) dyes were synthesized as the model com-
pounds to systematically study the effect of the dicyano and the terminal substituent on the two-photon
absorption (TPA). These four compounds (DSO, DCY, DTO and DPH) exhibit very large two-photon
absorption cross sections (d). DCY (A–
p–A) with the terminal cyano group has especially high fluores-
cence quantum yield (0.71) and relatively large d (1480 GM), while DPH (D–
p–A) with the substituteda-
mino group at its terminus possesses the largest d (2800 GM) and the longest emission wavelength
(620 nm). The idealest terminal substituent should not be the alkoxy group but the substitutedamino
group. This class of dicyanostilbene dyes possess small molecule size, large d (830–2800 GM), long-wave-
length emission (459ꢀ620 nm) and large Stokes shift (80ꢀ206 nm), and are ideal chromophores for TPF
labels and probes.
Keywords:
Dicyanostilbene
Two-photon absorption cross section
Two-photon dye
Bioimaging
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
photonꢀ1 moleculeꢀ1), which is not large enough yet for biological
application. Higher values of d make it possible for lower dye con-
In recent years, two-photon excited fluorescence (TPF), which is
based on molecular two-photon absorption (TPA), has received
increasing attention for its various applications such as multipho-
ton fluorescence imaging and microscopy [1,2], microfabrication
[3–5], three-dimensional (3D) data-storage [6,7], optical power
limiting [8], up-converted lasing [9], photodynamic therapy
[10,11], and for the localized release of bio-active species [12].
Presently, this demand is being matched by rapid advances in
the design and synthesis of TPF dyes.
As a TPF dye for the functional materials, it must have high
molecular weight to ensure the strength, toughness and excellent
machinability of the material, whereas a TPF dye for bioimaging
should have small molecule size, low molecular weight and high
flexibility, which are indispensable to its good cell-permeability.
As is known to all, TPA cross section (d) of a dye mainly depends
centrations and laser power to meet the need for recording images,
which results in less background fluorescence from endogeneous
chromophores. This makes such chromophores interesting candi-
dates for molecular TPF labels and probes. The substitution of the
hydrogen atoms with the cyano groups on the aromatic ring can
dramatically boost the d value of molecules [15,16].
By use of the attachment of two cyano groups to the single aro-
matic ring of a stilbene, a series of dicyanostilbene derivatives with
a considerably large d were synthesized by us. Meanwhile, this two-
cyano chromophore with the strong electron donor of a N,N0-disub-
stitutedamino group at its extremity has been successfully em-
ployed in the design of TPF probes for Hg2+ and Ag+ ions [17,18].
Herein we report a few more derivatives (Fig. 1) from this class of
dicyanostilbene dyes, and make a systematic study on their TPA
properties so as to further extend their application in bioimaging.
on the rigidity of its planar p-conjugated skeleton, which, in turn,
will inevitably weaken its cell-permeability. Therefore, for the pur-
pose of applying dyes in bioimaging, a balance needs to be struck
between increasing d and improving cell-permeability.
Stilbene derivatives are precisely such TPF dyes with small mol-
ecule size and moderately large d. Of a variety of donor–bridge–
2. Experimental
2.1. Materials and methods
NMR spectra were recorded on a VARIAN INOVA 400 MHz NMR
spectrometer. Mass spectral determinations were made on a ESI-
Q-TOF mass spectrometry (Micromass, UK). High resolution mass
acceptor (D–p–A) and donor–bridge–donor (D–p–D) stilbene deriv-
atives, the TPA properties were studied [13,14], and the values of
their
d
are approximately ꢁ400 GM (1 GM ꢂ 1 ꢃ 10ꢀ50 cm4 s
spectra measurements were performed on
a GC–TOF mass
spectrometry (Micromass, UK). Fluorescence measurements were
performed on a PTI-C-700 Felix and Time-Master system. Fluores-
cence quantum yields were measured using standard methods
⇑
Corresponding author. Fax: +86 731 58293833.
E-mail address: nfyang@xtu.edu.cn (N. Yang).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.08.016

92
C. Huang et al. / Journal of Molecular Structure 1006 (2011) 91–95
(d, J = 8.4 Hz, 2H), 2.42 (s, 3H), 1.36 (s, 3H). 13C NMR (CHCl3-d,
100 MHz) ppm: 160.00, 137.36, 131.82, 131.65, 130.26, 130.08,
129.89, 129.60, 128.28, 123.77, 123.71, 122.83, 114.32, 113.85,
55.35, 29.68.
Elemental analysis: calculated for C18H14N2O (MW 274.32):C
78.81%, H 5.14%, N 10.21%, O 5.83%; Found:C 78.93%, H 5.18%, N
10.18%, O 5.70%.
CN
OCH3
OCH3
OCH3
R
CN
H3C
NC
H3C
NC
DSO: R = OCH3
DCY: R = CN
DTO
S
CN
2.2.3. (E)-2-(4-cyanostyryl)-5-methylterephthalonitrile (DCY)
IR (KBr) cmꢀ1: 3082 (C@CAH), 2925 (CH3), 2238 (C„N), 1654
(ArAC@C), 1596 (aromatic C@C), 1514 (aromatic C@C), 957
(C@CAH), 805 (C@CAH), 668 (C@CAH).
N
H3C
NC
C8H17
DPH
HRMS (EI) m/z: 269.0951 (calcd for C18H11N3: 269.0953).
Yellow powder. Yield 66%; m.p. 263–265 °C; 1H NMR (400 MHz,
CDCl3) d: 8.03 (s, 1H), 7.71 (d, J = 8.4 Hz, 2H), 7.66 (d, J = 8.4 Hz,
2H), 7.65 (s, 1H), 7.45 (d, J = 16.0 Hz, 1H), 7.28 (d, J = 14.4 Hz, 1H),
2.61 (s, 3H). 13C NMR (CHCl3-d, 100 MHz) ppm: 141.91, 139.95,
137.91, 134.77, 133.09, 132.98, 132.93, 129.76, 127.86, 125.58,
118.69, 117.93, 116.46, 115.36, 112.68, 20.17.
Fig. 1. Molecular structures of DSO, DCY, DTO and DPH.
[19] on air-equilibrated samples at room temperature. Quinine
bisulfate in 0.05 mol Lꢀ1 H2SO4 (
= 0.546) was used as a reference
U
[19]. TPEF (two-photon-excited fluorescence) action cross-section
spectra were measured according to the experimental protocol
established by Xu and Webb [20], using a mode-locked Ti/sapphire
laser that delivers ꢁ80 fs pulses at 76 MHz. Fluorescein
(10ꢀ4 mol Lꢀ1 in 0.1 mol Lꢀ1 NaOH), whose TPEF action cross-sec-
tions are well-known [20], served as the reference. The quadratic
dependence of the fluorescence intensity on the excitation intensity
was verified for each data point, indicating that the measurements
were carried out in intensity regimes in which saturation or photo-
degradation does not occur. The measurements were performed at
room temperature on air-equilibrated solutions (10ꢀ5 mol Lꢀ1).
The experimental uncertainty on the absolute action cross-sections
determined by this method has been estimated to be 20% [20].
Absorption spectra were measured on a HP-8453 spectrophotome-
ter. Solvents were generally dried and distilled prior to use. Reac-
tions were monitored by thin-layer chromatography on Merck
silica gel 60 F254 precoated aluminum sheets. Column chromatogra-
Elemental analysis: calculated for C18H11N3 (MW 269.30):C
80.28%, H 4.12%, N 15.60%; Found:C 80.35%, H 4.14%, N 15.51%.
2.2.4. (E)-2-(3,4,5-trimethoxystyryl)-5-methylterephthalonitrile
(DTO)
IR (KBr) cmꢀ1: 3068 (C@CAH), 2977 (OCH3), 2924 (CH3), 2231
(C„N), 1650 (ArAC@C), 1593 (aromatic C@C), 1515 (aromatic
C@C), 1287 (CAO), 957 (C@CAH), 809 (C@CAH), 668 (C@CAH).
HRMS (EI) m/z: 334.1354 (calcd for C20H18N2O3: 334.1317).
Yellow powder. Yield 63%; m.p. 207–209 °C; 1H NMR (400 MHz,
CDCl3) d: 7.99 (s, 1H), 7.86 (s, 1H), 7.600 (s, 1H), 7.24 (d, J = 14.4 Hz,
1H), 6.70 (d, J = 16.4 Hz, 1H), 6.78 (s, 1H), 3.93 (s, 6H), 3.89 (s, 3H),
2.58 (s, 3H). 13C NMR (CHCl3-d, 100 MHz) ppm: 160.75, 139.80,
139.33, 135.64, 134.55, 134.29, 133.49, 130.16, 129.01, 128.76,
121.94, 119.65, 117.47, 116.62, 116.56, 114.47, 55.38, 55.24, 19.88.
Elemental analysis: calculated for C20H18N2O3 (MW 334.4):C
71.84%, H 5.43%, N 8.38%, O 14.35%; Found:C 71.89%, H 5.47%, N
8.37%, O 14.28%.
phy: Merck silica gel Si 60 (40–63 lm, 230–400 mesh). The
pH-dependent fluorescence studies were performed according to
the literature [21].
2.2. Synthesis
2.2.5. (E)-2-methyl-5-(2-(10-octylphenothiazin-3-yl)vinyl)
terephthalonitrile (DPH)
2.2.1. General procedure of the Wittig reaction to DSO, DCY, DTO and
DPH
IR (KBr) cmꢀ1: 3072 (C@CAH), 2974–2857 (saturated CAH),
2922 (CH3), 2238 (C„N), 1647 (ArAC@C), 1592 (aromatic C@C),
1511 (aromatic C@C), 1448 (CH3), 956 (C@CAH), 808 (C@CAH),
737 (n-octyl), 668 (C@CAH).
Diethyl-2,5-dicyano-4-methylbenzylphosphonate (5) and the
aldehyde (6, 7, or 10, 1 equiv) were suspended in about freshly dis-
tilled THF (about 50 mL), then NaH (1.2 1.5 equiv) in THF was
added dropwise, with stirring. This procedure was carried out in
an ice-bath. The mixture was continuously stirred at room temper-
ature for a further 20 h, then poured into distilled water (200 mL).
The pH value was adjusted to 7.0 by addition of 0.1 M hydrochloric
acid. The product was extracted twice with CH2Cl2, and the organic
layer was dried overnight over anhydrous MgSO4. The solvent was
removed with a rotary evaporator to give the crude product. In or-
der to get the desired trans compound, the crude product was
isomerized by dissolving in toluene and refluxing with trace
amounts of iodine for 4 h [14]. After removing the solvent, the res-
idue was purified by column chromatography on silica gel using
dichloromethane–petroleum ether (1:4) as eluent.
HRMS (EI) m/z: 477.2234 (calcd for C31H31N3S: 477.2239).
Yellow powder. Yield 58%; m.p. 238–240 °C; 1H NMR (400 MHz,
CDCl3) d: 7.96 (s, 1H), 7.57 (s, 1H), 7.32 (s, 2H), 7.14 (m, 4H), 6.85
(m, 2H), 3.87 (s, 2H), 2.57 (s, 3H), 1.81 (m, 2H), 1.44 (m, 2H), 1.28
(m, 8H), 0.87 (t, J1 = 6.0 Hz, J2 = 7.2 Hz, 3H). 13C NMR (CHCl3-d,
100 MHz) ppm: 146.26, 144.44, 141.55, 140.91, 139.85, 139.14,
134.31, 133.75, 130.80, 129.88, 129.07, 127.46, 127.34, 126.72,
125.81, 124.08, 122.77, 119.85, 117.46, 116.54, 115.51, 114.31,
47.73, 45.68, 44.81, 31.71, 29.17, 26.89, 22.58, 19.88, 14.01.
Elemental analysis: calculated for C31H31N3S (MW 477.66):C
77.95%, H 6.54%, N 8.80%, S 6.71%; Found:C 78.07%, H 6.59%, N
8.71%, S 6.63%.
2.2.2. (E)-2-(4-methoxystyryl)-5-methylterephthalonitrile (DSO)
IR (KBr) cmꢀ1: 3075 (C@CAH), 2974 (OCH3), 2923 (CH3), 2220
(C„N), 1630 (ArAC@C), 1598 (aromatic C@C), 1519 (aromatic
C@C), 1281 (CAO), 952 (C@CAH), 804 (C@CAH), 668 (C@CAH).
HRMS (EI) m/z: 274.1100 (calcd for C18H14N2O: 274.1106).
Light yellow powder. Yield 82%; m.p. 212–214 °C; 1H NMR
(CHCl3-d, 400 MHz) ppm: 7.10 (s, 1H), 6.92 (s, 1H), 6.43 (d,
J = 8.4 Hz, 2H), 6.19 (d, J = 16 Hz, 1H), 6.01 (d, J = 16 Hz, 2H), 5.84
3. Results and discussion
3.1. Design and synthesis of DSO, DCY, DTO and DPH
2,5-Dibromo-p-xylene (2) [22], 2,5-dimethyl-terephthalonitrile
(3) [22], 2-bromomethyl-5-methylterephthalonitrile (4) [18], 1-
diethylphosphorylmethyl-4-methyl-2,5-dicyanobenzene (5) [18],
10-n-octylphenothiazine (9) [23], and 10-n-octylphenothiazine-3-

C. Huang et al. / Journal of Molecular Structure 1006 (2011) 91–95
93
Br
CN
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
Br2 , CH2Cl2
CuCN, DMF
reflux, 24 h
Abs(DSO)
OF(DSO)
TF(DSO)
Abs(DTO)
OF(DTO)
TF(DTO)
0~20 °C, 24 h
Br
NC
1
2
3
CN
CN
P(OEt)3
reflux, 24 h
NBS, CCl4
80 °C, 3 h
H3C
NC
H3C
NC
O
Br
P
(OEt)2
5
4
200
300
400
500
600
700
NaH, THF
0 °C, 12 h
CN
Wavelength / nm
R
R
H3C
NC
Fig. 2. One-photon absorption, and one- and two-photon emission spectra of DSO
and DTO (1 M) in CH2Cl2.
O
5
l
DSO: R = OCH3
DCY: R = CN
6
82 % (DSO)
66 % (DCY)
Abs(DCY)
OF(DCY)
TF(DCY)
Abs(DPH)
OF(DPH)
TF(DPH)
1.0
1.0
0.8
0.6
0.4
0.2
0.0
OCH3
OCH3
OCH3
CN
OCH3
OCH3
OCH3
5
0.8
0.6
0.4
0.2
0.0
H3C
O
NaH, THF
63 %
NC
DTO
7
S
S
N
POCl3
DMF
CH3(CH2)7Br
DMSO
N
H
CH2Cl2
(CH2)7CH3
8
9
200
300
400
500
600
700
800
S
S
Wavelength / nm
CHO
CN
5
N
Fig. 3. One-photon absorption, and one- and two-photon emission spectra of DCY
H3C
NC
C8H17
N
and DPH (1 lM) in CH2Cl2.
NaH, THF
58 %
(CH2)7CH3
DPH
10
Table 1
Photophysical properties of four dyes.
Scheme 1. Synthetic procedures of DSO, DCY, DTO and DPH.
Ud
kmax
dmax
sg
bh
a
b
c
(2)e
f
Dyes
kmax
kfl
4mST
DSO
DTO
DCY
DPH
328
358
312
414
459
479
392
620
131
121
80
0.294
0.320
0.710
0.030
620
700
660
780
830
0.36
0.49
0.68
1.45
1.2
1.5
2.2
4.1
carbaldehyde (10) [23] were synthesized according to literature
procedures. DSO, DCY, DTO and DPH (Scheme 1) were obtained
in modest yield by condensation between 5 and aldehydes 6, 7
and 10, respectively.
1050
1480
2800
206
Absorption maximum with lowest energy in nm, c = 10ꢀ5 M.
Emission maximum in nm, c = 10ꢀ6 M.
Stokes shift in nm.
a
b
c
3.2. One-photon absorption and fluorescence spectra
Relative to quinine sulfate 10ꢀ6 M in 0.05 mol Lꢀ1 H2SO4; estimated error, 10%
d
of the given values.
e
Two-photon excitation maximum in nm.
One-photon absorption and fluorescence spectra of DSO, DCY,
DTO and DPH in CH2Cl2 solution are depicted in Figs. 2 and 3.
The results indicate that the maximum absorption wavelengths
(kmax) of DSO, DCY, DTO and DPH increase with a stronger donor
(Table 1), indicating that a stronger donor is more beneficial to ex-
f
The peak TPA cross-sections in 10ꢀ50 cm4 s/photon (GM); estimated error, 20%
of the given values.
g
Fluorescence lifetime in ns.
Two-photon absorption coefficient in cm/GW.
h
tend
overlap with the large
kmax for 4 could be because the substitutedamino group delocalizes
the -orbital more efficiently than the other groups, which results
p
-conjugated system because the p-electron of the donor can
p-electron in the aromatic ring. The largest
order DCY, DSO, DTO and DPH, indicating that a stronger donor
is more beneficial to intramolecular charge transfer (ICT) in the ex-
cited state, which contributes to a larger twisted angle. The larger
the twisted angle, the lower the energy of the excited state, hence
p
in a larger conjugated skeleton. Compared to DSO, DTO and DPH,
DCY showed the smallest kmax of 312 nm. Most importantly, unlike
the emission wavelength will be larger. The Stokes shifts (4mST
)
DSO, DTO and DPH with a D–
p
–A architecture, DCY is the A–
p
–A
range from 80 to 206 nm, indicating that the energy of the emitting
states are significantly lower than the Franck–Condon singlet
states. The kfl of DPH shows the greatest bathochromic shift and
thus the largest Stokes shift in comparison to DSO, DCY and DTO,
indicating that the donor stabilizes the lowest excited state more
than the ground state (Table 1). This could be explained if the
architecture.
Compared with the absorption spectra, a similar result was
observed in the fluorescence spectra except that the substituent
effect was larger. The emissive maximum wavelengths (kfl) of four
dyes increase with increasing electron-donating capacity in the

94
C. Huang et al. / Journal of Molecular Structure 1006 (2011) 91–95
two-photon allowed states are close to the lowest excited states.
As discussed above, the donor stabilizes the latter more than the
ground state to diminish the energy gap between the ground-
and two-photon allowed states. This would predict a higher fluo-
rescence quantum yield, because the smaller the energy gap is,
the higher the probability of the excitation will be. On the other
hand, the Stokes shift decreased from DSO to DTO, probably be-
cause two methoxy groups on the side chain of DTO must share
the cyano group acceptor to diminish the excited-state charge
transfer. Most of the compounds are considerably fluorescent and
the fluorescence quantum yields are close to 0.3, and even high
up to 0.71 for DCY. The much lower quantum yield for DPH may
be due to the sulfur atom in the phenothiazine moiety, which
may facilitate the nonradiative pathways. TPF spectra are almost
identical with OPF spectra.
2800
2400
2000
1600
1200
800
DSO
DTO
DCY
DPH
δ
400
520 560 600 640 680 720 760 800 840
Wavelength / nm
Fig. 4. Two-photon-induced fluorescence spectra for DSO, DCY, DTO and DPH
(10
lM) in CH2Cl2 solution (with experimental error ꢁ 20%).
3.3. Two-photon absorption cross-section and the two-photon-
induced fluorescence excitation spectra
1.4
The two-photon absorption cross-section ds was measured by
using the two-photon-induced fluorescence measurement tech-
nique with the following equation,
DSO
DTO
DCY
DPH
1.2
1.0
Ss
Sr
g
g
rUrCr
sUsCs
ds ¼
dr
ð1Þ
0.8
0.6
0.4
0.2
0.0
where the subscripts s and r stand for the sample and reference
molecules, respectively [24]. The intensity of the signal collected
by a PMT detector was denoted as S.
g is the fluorescence quantum
yield. is the overall fluorescence collection efficiency of the exper-
U
imental apparatus. The number density of the molecules in solution
was denoted as C. dr is the TPA cross-section of the reference
molecule.
0
2
4
6
8
10
12
Input intensity / GW.cm-2
Fig. 4 shows the two-photon-induced fluorescence excitation
spectra of DSO, DTO, DCY and DPH. It can be seen that a two-pho-
ton-induced fluorescence excitation spectrum is similar to the cor-
responding to one-photon absorption (OPA) spectrum, and the
Fig. 5. Dependences of the transmitted intensities of DSO, DCY, DTO and DPH
(10 M, in CH2Cl2) on the incident intensities.
l
maximum TPA wavelength (kmax(2)) is approximately double kmax
.
Although, among these four dyes, the kmax, kfl, and 4mST of DCY
The values of the maximum d (dmax) remarkably increase in the or-
der DSO, DTO, DCY and DPH. DCY with the A– –A architecture
exhibits rather large d relative to DSO and DTO of D– –D type,
(2)
are all the smallest, its kmax value exceeds that of DSO (Table
p
1), indicating the molecular planar rigidity enables kmax(2) to batho-
p
chromically shift.
which attributes to the conjugation or the orbital coupling be-
tween the terminal cyano group and the aromatic ring system.
The cyano group contains the carbon–carbon triple bond (C„C)
3.4. Optical limiting and two-photon absorption coefficient
whose
p-orbital can overlap with the large
p-electron in aromatic
ring, further extending
p
-conjugated system and increasing the
The optical limiting experiments of DSO, DTO, DCY and DPH
were performed at picosecond laser pumping. Fig. 5 shows the
transmitted intensity as a function of the incident intensity for a
molecular planar rigidity, which will enable a large increase in d.
Four dyes all exhibit rather large d, especially DPH, and even
high up to 2800 GM (Table 1), which is almost larger one order
of magnitude than that of the other stilbene derivatives containing
no two-cyano. Therefore, the attachment of two cyano groups to
the single aromatic ring of stilbene can dramatically boost the d va-
lue of molecules. In addition, the terminal strong electron-donating
substituent such as the substitutedamino group in DPH is able to
greatly increase d value. However, the alkoxy group is not satisfac-
tory candidate. For instance, the value of even DTO with three
methoxy groups is less than half that of DPH. Hence, an ideal stil-
bene-derived dye should be such a push–pull chromophore with
the strong electron donor of the substitutedamino group at its
extremity and the strong electron acceptor of two cyano groups
on its single aromatic ring. The interaction between the amino
group and the cyano groups can significantly improve ICT and in-
crease the stationary dipole moment upon excitation, which dras-
tically boosts the d value of the fluorophore.
dye (CH2Cl2, 10 lM) in a 5 mm cell. Each datum was an average
of 10 laser shots. We also determined the transmittance of the pure
CH2Cl2 solvent in the same 5 mm cell in order to eliminate the
influences from the solvent and the cell walls. By fitting the exper-
imental curve of transmitted intensity versus input intensity on
the two-photon absorption assumption, the TPA coefficient (b) of
a dye can be obtained (Table 1), and the b value increases with
increasing d. Similarly, their fluorescence lifetime also increases
as d increases. The experimental data shown in Fig. 5 indicate that
the optical limiting behavior of these four dyes is dominated
mainly by TPA.
4. Conclusion
In summary, we have demonstrated the effectiveness of stil-
bene derivatives with two cyano groups in the single aromatic ring
which can contribute to a very large d. The cyano group is not only
(2)
Their kmax values evidently increase in the order DSO, DCY,
DTO and DPH, rather than in the order DCY, DSO, DTO and DPH.

C. Huang et al. / Journal of Molecular Structure 1006 (2011) 91–95
95
[3] C.N. LaFratta, J.T. Fourkas, T. Baldacchini, R.A. Farrer, Angew. Chem. 119 (33)
(2007) 6352.
[4] S.-J. Jhaveri, J.-D. McMullen, R. Sijbesma, L.-S. Tan, W. Zipfel, C.-K. Ober, Chem.
Mater. 21 (10) (2009) 2003.
[5] S.-H. Park, D.-Y. Yang, K.-S. Lee, Laser Photon. Rev. 3 (1–2) (2009) 1.
[6] K.D. Belfield, K.J. Schafer, Chem. Mater. 14 (9) (2002) 3656.
[7] C.O. Yanez, C.D. Andrade, S. Yao, G. Luchita, M.V. Bondar, K.D. Belfield, ACS
Appl. Mater. Interfaces 1 (2009).
[8] S.L. Oliveira, D.S. Correa, L. Misoguti, C.J.L. Constantino, R.F. Aroca, S.C. Zilio, C.R.
Mendonca, Adv. Mater. 17 (15) (2005) 1890.
[9] T.-C. Lin, S.-J. Chung, K.S. Kim, X. Wang, G.S. He, J. Swiatkiewicz, H.E. Pudavar,
P.N. Prasad, Adv. Polym. Sci. 161 (2003) 157.
[10] M. Velusamy, J.-Y. Shen, J.-T. Lin, Y.-C. Lin, C.-C. Hsieh, C.-H. Lai, C.-W. Lai, M.-L.
Ho, Y.-H. Chen, P.-T. Chou, J.-K. Hsiao, Adv. Funct. Mater. 19 (15) (2009) 2388.
[11] C.-F. Peter, Acc. Chem. Res. 41 (2) (2008) 190.
the best terminal substituent for the fluorescence quantum yield
but also good for increasing d, while the terminal substitutedamino
group is the most advantageous for TPA and the bathochromic shift
of the emission wavelength. The alkoxy group is the unsatisfactory
candidate as the terminal group. Hence an ideal dicyanostilbene
dye should contain the terminal substitutedamino group. This class
of dicyanostilbene dyes possess small molecule size, large d (830–
2800 GM), long-wavelength emission (459ꢀ620 nm) and large
Stokes shift (80ꢀ206 nm), and are ideal chromophores for TPF la-
bels and probes.
Acknowledgment
[12] G.C.R. Ellis-Davies, Nat. Methods 4 (2007) 619.
[13] J.E. Ehrlich, X.L. Wu, I.-Y.S. Lee, Z.-Y. Hu, H. Röckel, S.R. Marder, J.W. Perry, Opt.
Lett. 22 (24) (1997) 1843.
[14] Z. Liu, Q. Fang, D. Wang, D. Cao, G. Xue, W. Yu, H. Lei, Chem. Eur. J. 9 (2003)
5074.
[15] W.J. Yang, D.Y. Kim, C.H. Kim, M.Y. Jeong, S.K. Lee, S.J. Jeon, B.R. Cho, Org. Lett. 6
(9) (2004) 1389.
Financial supports from China Postdoctoral Science Foundation
funded project (No. 20100471224) and Guangdong Natural Science
Foundation (S2011040000536) is deeply acknowledged.
[16] S.J.K. Pond, M. Rumi, M.D. Levin, T.C. Parker, D. Beljonne, M.W. Day, J.-L. Brédas,
S.R. Marder, J.W. Perry, J. Phys. Chem. A 106 (2002) 11470.
[17] C. Huang, A. Ren, C. Feng, N. Yang, Sens. Actuators B: Chem. 151 (1) (2010) 236.
[18] C. Huang, J. Fan, X. Peng, Z. Lin, B. Guo, A. Ren, J. Cui, S. Sun, J. Photochem.
Photobiol. A 199 (2008) 144.
[19] D.F. Eaton, J. Photochem. Photobiol. B 2 (1988) 523.
[20] C. Xu, W.W. Webb, J. Opt. Soc. Am. B 13 (1996) 481.
[21] S.C. Burdette, G.K. Walkup, B. Spingler, R.Y. Tsien, S.J. Lippard, J. Am. Chem. Soc.
123 (2001) 7831.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2011.08.016.
References
[22] H. Huang, Q. He, H. Lin, F. Bai, Z. Sun, Q. Li, Polym. Adv. Technol. 15 (2004) 84.
[23] Y. Zou, W. Wu, G. Sang, Y. Yang, Y. Liu, Y. Li, Macromolecules 40 (2007) 7231.
[24] S.J.K. Pond, O. Tsutsumi, M. Rumi, O. Kwon, E. Zojer, J.L. Brédas, S.R. Marder,
J.W. Perry, J. Am. Chem. Soc. 126 (30) (2004) 9291.
[1] H.M. Kim, C. Jung, B.R. Kim, S.-Y. Jung, J.H. Hong, Y.-G. Ko, K.J. Lee, B.R. Cho,
Angew. Chem. Int. Ed. 46 (2007) 3460.
[2] M.K. Kim, C.S. Lim, J.T. Hong, J.H. Han, H.-Y. Jang, H.M. Kim, B.R. Cho, Angew.
Chem. Int. Ed. 49 (2010) 364.