Study on synthesis and spectrum of novel styryl cyanine dyes with a carbazole bridged chain

Article abstract of DOI:10.1007/s10895-011-1014-0

Based on the frequently-used cyanine dye probe thiazole orange (TO), a novel kind of cyanine dye was designed and synthesized. Carbazole was inserted into the methylidyne structure of TO as a bridge to afford a kind of novel styryl cyanine dye with carbazole bridged chain. The dyes were characterized by HNMR and MS. The spectra of the novel dyes were also studied and the results showed that the fluorescent wavelength of novel carbzole dye shifted red for 100 nm, stock shift increased by 70 nm and the fluorescent intensity enhanced by 70 times compared to that of TO. When the novel dye was labeled by BSA, its fluorescent wavelength changed little and the intensity enhanced. It is indicated that it can be used as an excellent fluorescent probe in biological labeling. Springer Science+Business Media, LLC 2011.

Full text of DOI:10.1007/s10895-011-1014-0

J Fluoresc (2012) 22:807–814
DOI 10.1007/s10895-011-1014-0
ORIGINAL PAPER
Study on Synthesis and Spectrum of Novel Styryl Cyanine
Dyes with a Carbazole Bridged Chain
Xuening Fei & Yingchun Gu & Chao Li & Xu Yang
Received: 2 September 2011 /Accepted: 20 October 2011 /Published online: 23 November 2011
#
Springer Science+Business Media, LLC 2011
Abstract Based on the frequently-used cyanine dye probe
thiazole orange (TO), a novel kind of cyanine dye was
designed and synthesized. Carbazole was inserted into the
methylidyne structure of TO as a bridge to afford a kind of
novel styryl cyanine dye with carbazole bridged chain. The
dyes were characterized by HNMR and MS. The spectra of
the novel dyes were also studied and the results showed that
the fluorescent wavelength of novel carbzole dye shifted
red for 100 nm, stock shift increased by 70 nm and the
fluorescent intensity enhanced by 70 times compared to that
of TO. When the novel dye was labeled by BSA, its
fluorescent wavelength changed little and the intensity
enhanced. It is indicated that it can be used as an excellent
fluorescent probe in biological labeling.
Introduction
With the properties of electron rich system, carbazole and
its derivatives are widely used in the fields of dyes,
medicine, biology, photoelectricity and so on owing to
their advantages of large rigidity plan conjugated system,
aromatic structures with strong fluorescence and easily
being modified by the introduction of different kinds of
functions.
The indolocarbazole alkaloids are a kind of natural
products, a structurally rare, but biological activity class.
The indolocarbazole alkaloids are extremely interesting
owing to the wide range of biological activities including
antimicrobial, hypotensive, antifungal, and inhibition of
platelet aggregation. For example, Ellipticine is usually
used to treat thyroid carcinoma, breast cancer and renal
carcinoma.
.
.
Keywords Carbazole Bridge chain Novel styryl cyanine
.
.
dye Fluorescence Probe
NB-560 can inhibit the production of cancer cells. When
it was conjugated with DNA, indolocarbazole was embed-
ded into the two base pair of the double DNA and the
residues located in the spiral groove [1].
:
X. Fei Y. Gu
School of Chemical Engineering and Technology, TianJin
University,
Zeng et al. designed and synthesized 5-[2-(8-Hydroxy-
quinolin-2-yl)-vinyl]-2-methyl-quinolin-8-ol [2] .The stem
cell activity and antioxidation activity of the compound
were investigated. The results showed that the title
compound had a strong antioxidation activity and could
induce the proliferation of mesenchymal stem cell under a
low concentration condition. (E)-9-p-Tolyl-3-[2-(8-hy-
droxy-qui-nol-2-yl)vinyl]-carbazole and (E)-9-(p-Anisyl)-
3-[2-(8-hydroxy-qui-nol-2-yl)vinyl]-carbazole [3] were also
synthesized and the antioxidation activity and stem cell
Tianjin 300072, China
:
:
:
X. Fei Y. Gu C. Li X. Yang
Department of Material Science and Engineering, TianJin Institute
of Urban Construction,
Tianjin 300384, China
X. Fei (*)
Tianjin Institute of Urban Construction,
No.26 Jinjing Road, Xiqing District,
Tianjin, China
e-mail: xueningfei@126.coma

808
J Fluoresc (2012) 22:807–814
Fig. 1 Design of styryl cyanine
dye with carbazole on the bridge
chain
S
S
C
H
R N
R N
C
H
N
N
CH
N
OTs
OTs
CH
3
3
S
Br
N R
N
N
activity of the compounds were investigated too. Results
showed that one compound could induce effectively the
proliferation of mesenchymal stem cells under a low
concentration condition.
fluorescent lifetime would prolong. If the conjugated
system was lengthened, the stability of probe would
decrease.
Recently, we studied on the synthesis and properties
of cyanine dye TO and its derivatives [18–21]. In order
to make the conjugated system lengthen without the
stability decrease, carbazole was inserted into the meth-
ylidyne structure of TO as a bridge to give a kind of novel
carbazole styryl cyanine dye with carbazole bridged
chain. With the introduction of carbazole, the stability of
the novel probes increased, fluorescent wavelength
shifted red, stock shift increased and the fluorescent
intensity was enhanced. The design of novel probe was
shown in Fig. 1.
Thiazole Orange (TO), an embedded cyanine dye, is
comprised of a benzothiazole ring covalently linked to a
quinoline via a monomethine bridge. It has been widely
used as an embedded cyanine dye for labeling nucleic
acids, which allows the detection of DNA and RNA in gels
by flow cytometry or microscopy [4]. Although the
fluorescence of free TO is extremely low in aqueous
solution, when bound to nucleic acids, the viscosity of the
dye’s local environment is markedly increased, resulting in
a drastic increase in fluorescence [5–8]. The large differ-
ence in fluorescence between free dye and nucleic acid-
bound dye suggests an excellent way to image, label and
detect cancer cells [9–17].
Materials and Methods
The fluorescent properties of dyes mainly depend on
their chemical structures, such as conjugate system,
coplanarity and riqidity. The longer the conjugate system
is, the stronger the fluorescent intensity and the fluorescent
emission wavelength would shift red, the background
disturbing of fluorescent probe would reduce and the
Materials and Instruments
Fluorescence spectra were scanned on a Cary Eclipse
fluorescence spectrophotometer (Varian,American). The
UV/Vis spectra were recorded on a Shimazu 2550
Scheme 1 Synthesis of carba-
CHO
zole bridge
DMF,POCl3
NaOH
EtBr
N
ClCH2CH2Cl
N
N
H
1
2
S
SH
N
S
NH2
DMF,POCl3
ClCH2CH2Cl
CHO
N
DMSO
N
N
3
4

J Fluoresc (2012) 22:807–814
809
Scheme 2 Synthesis of styryl
cyanine dye with carbazole on
the bridge chain
S
S
N
H
CHO
N
N
Br
N
R
+
Br
N R
EtOH
N
N
5
6a:R=CH2CH2COOH,
6b:R=CH2CH3,
6c:R=CH2(CH2)4COOH
6d:R=CH2Ph,
4
5a:R=CH2CH2COOH,
5b:R=CH2CH3,
5c:R=CH2(CH2)4COOH,
5d:R=CH2Ph
spectrophotometer (Jap.). American Mass spectral analyses
were obtained using an electrospray ionization (ESI) mass
spectrometer. HNMR spectra were recorded on a Bruker
(300 MHz or 400 MHz) spectrometer. Chemical shifts were
reported in parts per million (ppm) downfield from TMS
(tetramethylsilane), using D2O or DMSO-d6 as a solvent.
stirred for another 30 min and brought to room temperature
to react for 1 h. Compound 1(5.90 g, 30 mmol) of 1,2-
dichloroethane (15 mL) was added dropwise and then
stirred for 1 h, refluxed for 8 h and then cooled. When the
former work was up, the mixture was poured into cool
water and extracted with CH2Cl2 (3×10 mL). The organic
phase was washed with water, dried with anhydrous
MgSO4. The solvent was distilled off and the residue was
chromatographed over silica gel to give compound 2. Yield:
40%. m.p. 84–86°C.
1
Synthesis
Synthesis of 3-Benzothiazole-6-Formyl Carbazole(4)
3-benzothiazole-6-formyl Carbazole was synthesized by
alkylation, formylation, ring closing reaction and formylation
from carbazole (Scheme 1).
Synthesis of 3-benzothiazole-N-ethyl carbazole (compound 3)
A mixture of compound 2 (1.20 g, 5.40 mmol) , amino-
thiopheno (0.70 g, 5.60 mmol) and DMSO (10 mL) was kept
at 195°C for 3 h under an atmosphere of nitrogen and then
cooled, poured into cool water and filtered. The filtrate was
washed with water and acetone to give compound 3. Yield:
Synthesis of N-ethyl carbazole (compound 1) A mixture of
25 mL DMSO, NaOH (1.30 g, 33 mol) and carbazole (5 g,
30 mol) in a 100 mL flask was stirred at room temperature
for 1 h. Bromoethane (3.60 g, 33 mol) was added dropwise
over 45 min into the mixture. After that, the mixture was
stirred for another 6 h. The mixture was poured into cool
water to precipitate the white crude product. The N-ethyl
carbazole compound 1 was then filtered, washed and dried
under vacuum. Yield: 85%, m.p. 68–70°C.
1
78%, m.p. 142–145°C. HNMR (400 MHz,CDCl3)δ: 1.45–
1.49 (t, J=7.20 Hz, 3H), 4.37–4.43(m, 2H), 7.28–7.38(m,
2H), 7.43–7.54(m, 4H), 7.91(d, J=8.00 Hz, 1H), 8.08(d, J=
8.00 Hz, 1H), 8.21(d, J=7.60 Hz, 2H), 8.86(s, 1H). ESI-MS
(m/z): 329.9 [M++1].
3-benzothiazole-6-formyl-N-ethyl carbazole (compound 4)
The synthetic method was similar to that of compound 2.
Yield: 35%, m.p. 171–173°C. 1HNMR(400 MHz,CDCl3) δ:
1.43–1.46: (t, J=7.20z, 3H), 4.35–4.40(m, 2H), 7.30–7.34
(t, J=7.20 Hz, 1H), 7.42–7.48(m, 3H), 7.86(d, J=8.00 Hz,
1H), 7.99–8.04(t, J=9.20 Hz, 2H), 8.22(d, J=8.40 Hz, 1H),
Synthesis of 3-formyl-N-ethyl carbazole (compound 2) To a
stirred solution of DMF (15 mL) in a 100 mL flask under
ice-cold condition, POCl3 (7.70 g, 50 mmol) was added
dropwise. When the addition was over, the reaction was
Fig. 2 (a) Fluorescent spectra
(a)
(b)
of 6a with different concentra-
80
tions, (b) Fluorescent intensities
of 6a with different concentrations
80
5
10
25
70
60
50
40
30
20
10
0
c
10-4 mol/L
70
60
50
40
30
20
10
0
20
1.3
y=22.807x+6.7719
R2=0.9815
0.6
0.3
0.2
500 550 600 650 700 750 800 850
Wavelength(nm)
0
5
10
15
20
C 10-4mol/L)

810
J Fluoresc (2012) 22:807–814
Fig. 3 (a) Fluorescent spectra
of 6a at different pH, (b) Fluo-
rescent intensities of 6a with the
change of pH
(a)
(b)
250
200
150
100
50
250
200
150
100
50
pH=1
pH=2
pH=4
pH=7
pH=8
pH=10
pH=12
0
500
550
600
650
700
750
800
0
2
4
6
8
10
12
pH
Wavelength(nm)
8.64(s, 1H), 8.82(s, 1H), 10.06(s, 1H). ESI-MS (m/z):
357.8[M++1].
(0.12 g, 0.42 mmol) in 20 mL CH2CH3OH were added to
a 100 mL flask, followed by catalytic piperdine (1–3
drop). The resulting mixture was allowed to be refluxed
and stirred for 12 h. When it was cooled to room
temperature, CH3COOH was added and stirred for 2 h.
Aether was added to give a red solid. The crude product
was filtered, washed and the residue was chromatographed
over silica gel to give compound 6.
Synthesis of Compounds 5a-5d
The compounds 5a-5d were synthesized according to
literature methods [18].
6a (400 MHz, DMSO-d6) δ: 1.35(m, 3H), 2.68–2.73
(m,2H), 4.44–4.45(m, 2H), 5.05–5.06(m, 2H), 7.40–
7.43(m, 3H), 7.51–7.58(m, 6H), 7.73–7.76(m, 2H),
7.96(d, J=7.60 Hz, 2H), 8.11(d, J=7.20 Hz, 2H),
8.28(s, 1H), 8.48(s, 1H), 8.92(d, H=9.60 Hz,1H),
10.17(s, COOH). ESI-MS (m/z): 554.3[M+], 555.4
[M++1].
6b (300 MHz, CD3OD) δ1.38–1.43(t, J=7.05 Hz,
3H), 1.58–1.63(t, J=7.20 Hz, 3H), 4.21–4.28(m, 2H),
4.65–4.72(m, 2H), 7.17–7.27(m, 2H), 7.31–7.42(m,
3H), 7.66(d, J=9.90 Hz,4H), 7.79–7.94(m, 4H), 8.04
(d, J=8.70 Hz, 1H), 8.28(s, 1H), 8.45(s, 1H), :8.63–
8.71(m, 2H). ESI-MS (m/z): 510.3[M+], 511.4
[M++1].
5a (400 MHz, CDCl3) δ: 1.82(t, J=7.20 Hz, 2H), 3.04
(s, 3H), 5.45–5.50(m, 2H), 7.98–8.05(m, 2H), 8.21–
8.25(t, J=7.80 Hz, 1H), 8.39(d, J=8.40 Hz, 1H), 8.45
(d, J=9.20 Hz, 1H), 10.52(d, J=6.00 Hz, 1H). ESI-MS
(m/z): 216.1[M+], 217.1 [M++1].
5b (400 MHz, CDCl3) δ: 1.23(t, J=5.25 Hz, 3H), 3.04
(s, 3H), 5.46–5.51(m, 2H), 7.99–8.07(m, 2H), 8.21–
8.34(t, J=7.60 Hz, 1H), 8.38–8.423(t, J=9.80 Hz, 2H),
10.58(d, J=5.60Hz, 1H). ESI-MS (m/z): 172.0[M+],
173.1 [M++1].
5c (400 MHz, CD3OD) δ: 1.39–1.44(m, 2H), 1.52–
1.57(m, 2H), 1.92–1.97(m, 2H), 2.19–2.23(t,
J=9.60 Hz, 2H), 3.01(s, 3H), 5.00–5.05(m, 2H),
8.05–8.09(t, J=8.00 Hz, 2H), 8.40(d, J=11.60 Hz,
1H), 8.59(d, J=11.2 Hz, 1H), 8.60(d, J=11.6 Hz, 1H),
9.57(d, J=8.00 Hz, 1H). ESI-MS(m/z): 258.1[M+], 259.1
[M++1].
6c (300 MHz, DMSO-d6) δ: 1.17–1.20(m, 5H),
1.52–1.56(m, 2H), 1.94–1.96(m, 2H), 2.07–2.13(m,
5d (400HMz,CDCl3) δ: 3.03(s, 3H), 6.68(s, 2H), 7.28
(d, J=7.60 Hz, 3H ), 7.41(d, J=9.60 Hz, 2H), 7.89–
7.93(t,J=8.20 Hz, 1H ), 8.04–8.10(m ,2H), 8.32(d,
J=9.60 Hz, 1H), 8.52(d, J=9.60 Hz, 1H), 10.56(d,
J=6.80 Hz,1H). ESI-MS (m/z): 234.0[M+], 235.1
[M++1].
400
CH2Cl2 (621.01,372.75)
350
300
250
DMSO (651.01,87.57)
200
150
100
50
CH3COCH3 (648.98,40.62)
CH3OH (641.01,37.70)
Syntehsis of the Title Compounds 6a-6d
0
The compound 6a-6d was obtained by Knoecenaget
condensation (Scheme 2).
The typical procedure for 6a-6d was: aldehyde 4
(0.10 g, 0.28 mmol) in 30 mL CH2CH3OH and salt 5
500 550 600 650 700 750 800 850 900
Wavelength(nm)
Fig. 4 Fluorescent spectra of 6a in different solvents

J Fluoresc (2012) 22:807–814
811
80
70
60
50
40
30
20
10
0
6a(642.02,76.50)
naget condensation to afford C = C and the title styryl
cyanine dye with carbazole bridged chain obtained.
6b(640.00,48.81)
Spectral Properties of Cyanine Dye Probe
to with Carbazole Bridged Chain
6d(648.36,21.19)
Effect of Concentration on the Fluorescence
Concentration was a factor exerting effect on the fluores-
cence. In this paper, the fluorescent spectra of a series 6a
samples in CH3OH were scanned at 500 nm. The
concentrations of 6a were geminated from 0.2×10−4 mol/L
to 20×10−4 mol/L.
500
600
700
800
Wavelength(nm)
Fig. 5 Fluorescent spectra of styryl cyanine dye with carbazole bridge
chain
The fluorescent spectra were shown in Fig. 2. Peak
characteristics of fluorescence and the maximum emission
wavelength of samples with different concentrations were
of little difference. The florescence intensity increased with
the increasing of concentration between 0.2×10−4 mol/L–
2.5×10−4 mol/L, but decreased when the concentration
exceeded 5×10−4 mol/L. With the increasing of the
concentration, the absorbent excited quantum number
increased and the emissive quantum number increased
too, leading to the enhancement of the fluorescent intensity
of the fluorescent compound. When the fluorescent inten-
sity enhanced to the maximum, it decreased, which may
result from fluorescence self-quenching.
2H), 4.52–4.54(m, 2H), 4.91–4.93(m, 2H), 7.39–7.44
(t, J=7.35 Hz, 1H), 7.50–7.55(t, J=7.50 Hz, 1H),
7.75–7.83(m, 2H), 8.00–8.01(m, 3H), 8.11(d,
8.10 Hz,1H), 8.17–8.23(m, 2H), 8.37(s, 2H), 8.48(d,
J=8.70 Hz, 2H), 8.99(s, 1H), 9.11(d, J=10.5 Hz, 2H),
9.35(s, 1H). ESI-MS (m/z):596.4[M+], 597.5[M++1].
6d (400 MHz, DMSO-d6) δ: 1.12–1.08(t,
J=7.20 Hz,3H), 3.84–3.90(m, 2H), 5.54(s, 2H), 6.76–
6.83(m, 3H), 6.87–6.91(m, 4H), 6.94(d,
J=8.40 Hz, 1H), 7.03(d, J=8.80 Hz, 1H), 7.23–7.36
(m, 4H), 7.42–7.45(t, J=7.80 Hz, 1H), 7.50–7.56(m,
3H), 7.66(d, J=8.80 Hz, 1H), 7.73(d, J=6.40 Hz, 1H),
8.25(s, 1H), 8.10(s, 1H), 8.32(d, J=8.80 Hz, 1H), 8.54
(d, J=6.80 Hz, 1H). ESI-MS (m/z): 572.2[M+], 573.2
[M++1].
ph Effect on the Fluorescence of 6a
Although the fluorescent properties of compounds
depend on the chemical molecular structure, environ-
mental factors where the molecules were in can also
affect the fluorescence.
Results and Discussion
Five 6a solutions of 1×10−4 mol/L) in CH3OH were
prepared, and then the pH were adjusted from 1 to 12
respectively by addition of dilute HCl or NaOH. Because of
the addition quantity were small, the changes of total
volume could be ignored. The fluorescent spectra of five 6a
solutions excited at 500 nm were shown in Fig. 3.
In the spectra of the five solutions, the fluorescent
intensities of samples in acid medium were stronger than
the others. The fluorescent intensities decreased with the
pH added and decreased obviously in the basic medium
with a red shift of the fluorescent wavelength. As an
organic weak acid, its fluorescent intensity was affected by
Synthesis
In order to enhance the fluorescent intensity, increase the
Stock shift and increase the stability of TO, carbazole was
inserted into the methylidyne structure of TO as a bridge to
give a kind of novel carbazole styryl cyanine dye with
carbazole bridged chain. First, 3-substituted of carbazole
was formylated, reacted with aminothiopheno to afford 3-
benzothiazoleN-ethyl carbazole, which was formylated to
give 3-benzothiazole-6-formyl-N-ethyl carbazole. The for-
myl reacted with active methylene compounds by Knoece-
Table 1 Degradation curve of cyanine 6a and 6b
Time/h
0
2
4
6
8
10
12
Rate of decline
Fluorescent intensity
6a
6b
34.50
34.60
33.05
31.20
32.80
30.01
32.01
29.36
31.73
29.17
31.36
29.03
31.01
28.20
10.38%
18.50%

812
J Fluoresc (2012) 22:807–814
Table 2 Physical constants of
solvents and the max absorption
wavelengths of 6a
Sovlent
Dielectric Constant
refractive index (n)
f(n)*
λ
max(nm)
R*10−3(cm−1
)
CH3OH
32.6
20.7
24.3
9.1
1.329
1.358
1.361
1.424
1.443
1.445
0.1690
0.1801
0.1812
0.2033
0.2092
0.2102
479.00
480.00
485.00
493.00
493.50
495.00
2.0876
2.0833
2.0619
2.0284
2.0263
2.0202
CH3COCH3
CH3CH2OH
CH2Cl2
CHCl3
5.5
CH2ClCH2Cl
10.45
pH obviously, that’s because they were different in
electronic configuration under different pH values.
12 h. The fluorescent intensities of 6a and 6b weakened
only a little in the process, which indicated that the
photoreduction stabilities of 6a and 6b were good.
Solvent Effect on the Fluorescent Property of 6a
Solvent Effect on the UV–vis Spectra of 6a
Solution obviously affects on the fluorescent properties.
The fluorescent spectra of 6a in different solutions were
shown in Fig. 4.
The UV–vis spectra of 6a in different solvent with same
concentration were scanned and the results were shown in
Table 2.
Solvent affected the UV–vis spectra of 6a. The absorp-
tion wavelength was longer with the refractive index
increased. In CH3OH, the absorption wavelength was
479 nm and 495 nm in CH2ClCH2Cl, which shifted red
of 16 nm.
In order to investigate if the physical constants of
solution affected the maximum absorption wavelength,
the r=1/λmax was calculated by f(n) = (n2-1)/(2n2+1)
from the measured λmax. The line of Bayliss f(n) was
calculated by equation f(n) = (n2-1)/(2n2+1). The rela-
tionship between r and Bayliss function f(n) was shown in
Fig. 6.
The maximum fluorescent emission wavelength shifted
red with the solvent polarity added. The maximum
emission wavelength in DMSO was at 651 nm, which
shifted 13 nm, 7 nm and 12 nm compared to those in
CH3OH, CH3COCH3 and CH2Cl2 respectively. It may
because that when the dye molecule is excited, the
electronic excited state has bigger polarity than the ground
state. The increased polarity makes the electronic excited
state much more stable than the ground state, resulting in
the red shift of wavelength.
Substitutional Groups on Quinoline Side Chain Effect
on the Fluorescent Properties of Carbazole Styryl Dyes
There was some relativity between r and Bayliss
function f (n). The relativity was satisfying from the data
R2=0.9518. It indicated that shift of absorption peak
depend on the refractive index of the solvent used. The
maximum absorption wavelength became longer with the
increase of n value.
Fluorescent properties of styryl dyes with carbazole bridged
chain could also be affected by substitutional groups on
quinoline side chain. In this paper, the fluorescent spectra
of 6a, 6b, 6d with the same concentration in CH3OH were
obtained and shown in Fig. 5
The maximum emission wavelengths of the dyes were at
about 640 nm. The maximum emission wavelengths of 6d
with benzyl group on on quinoline side chain shifted 8 nm
compared to that of 6b. The fluorescent intensity of 6a was
the strongest while that of 6d was the weakest.
2.10
2.09
2.08
y=-1.6834x+2.3745
R2 =0.9473
2.07
2.06
2.05
2.04
2.03
2.02
2.01
Photoreduction Stability
6a and 6b with the same concentration of 2.5×10−5 mol /L
were prepared and irradiated by 250 w high-pressure
mercury lamp at a distance of 10 cm. The fluorescence
intensities were measured per 2 h and the data were shown
in Table 1.
0.17
0.18
0.19
f(n)
0.20
0.21
The fluorescent intensities of 6a and 6b were declined by
only 10.38% and 18.50% respectively after irradiated for
Fig. 6 Curve of f (n) with absorption wave number of 6a in different
solvents

J Fluoresc (2012) 22:807–814
813
Table 3 Data of carzabole
styryl cyanine dye and TO
Dye
Excition wavelength (nm)
Emission wavelength (nm)
Stocks shift(nm)
Intensity (a.u.)
TO
6a
480
500
547
638
67
0.77
138
44.94
Properties Compared with TO
stock solution to afford TO-BSA and carbazole styryl dye-
BSA respectively and the fluorescent spectra were shown in
Fig. 7.
The fluorescent intensity of TO enhanced and the
wavelength shifted blue after labeled by BSA compared
to that of TO. Under the same concentration, the fluorescent
intensity of carbazole styryl dyes enhanced and the
wavelength shifted little, exhibiting preferable fluorescent
stability.
In order to compare the fluorescent properties of dye 6a
and TO, the solutions of them with the same concen-
tration were prepared and scanned at 480 nm. The data
results were shown in Table 3. The fluorescent wave-
length of 6a shifted red of 91 nm compared to that of TO
and Stocks shift increased 71 nm. When 6a was used in
biological chemical, overlap between the excitation and
emission wavelength could be reduced and the back-
ground interference could be decreased, leading to the
resolution improvement.
Conclusion
In comparison with the structure of TO, the novel
carbazole styryl dyes has extended conjugated system.
The π electrons are excited easier, resulting that the
fluorescent intensity enhances and the wavelength shifts
red. The novel carbazole styryl dyes also has large rigidity
plan, which make the reciprocity and conjugation of π
electrons increase. Consequently, the wavelength of the
novel carbazole styryl dyes shifted red to near the near-
infrared region, the fluorescent intensity enhanced and the
Stocks shift increased. The novel dyes have the better
performance than TO, which can be used as an excellent
cyanine dye probe in biological labeling.
Based on the structure of the excellent cyanine dye TO,
carbazole was inserted into the methylidyne structure of TO as
a bridge to afford a series novel carbazole styryl cyanine dyes.
The compounds were characterized by HNMR and MS.
Fluorescent results showed that the fluorescent wave-
length of novel carbzole styryl cyanine dye shifted red of
100 nm compared to that of TO, stock shift increased
80 nm ,the fluorescent intensity enhanced by 70 times and
the photoreduction stability was excellent. The novel
carbazole styryl cyanine dye kept the same conjugated
plane structure of its precursors TO and the embedded
fluorescent properties. When the novel dye was labeled by
BSA, its fluorescent wavelength changed little and the
intensity enhanced.
Fluorescent Properties of Carbazole Styryl Dyes Labeled
by BSA
The novel carbazole styryl cyanine dye has the excellent
fluorescent properties, for the fluorescent wavelength
shifted red, intensity enhanced and Stock shift increased.
The fluorescent owned better performance than TO,
therefore, it can be used as an excellent cyanine dye probe
in biological labeling.
25 mg BSA was dissolved in 0.05 mol/L Tris–HCl buffer
(pH=7.7) as a stock solution. TO and carbazole styryl dyes
solutions in CH3OH with the same concentration of 1×
10−4 mol/L were prepared as standard solutions respective-
ly. 5 mL of standard solution was diluted to 15 mL by BSA
Fig. 7 Fluorescent spectra of
(a)
(b)
carbazole styryl cyanine dye
4.5
labeled by BSA and TO labeled
by BSA
30
6a-BSA
4.0
25
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
TO-BSA
6a
20
15
TO
10
5
0
500
550
600
650
700
750
550 600 650 700 750 800 850
Wavelength(nm)
Wavelength(nm)

814
J Fluoresc (2012) 22:807–814
Acknowledgements This work was financially supported by the
National Natural Science Foundation of China (No. 21072147,
51178289), Key Project of Science and Technology Committee of
Tianjin (10JCYBJC10500). The work in the article also supported by
Technology Development Foundation Plan Project of Tianjin Colleges
(No. 20100503).
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