Synthesis, one and two-photon optical properties of two asymmetrical and symmetrical carbazole derivatives containing quinoline ring

Article abstract of DOI:10.1016/j.molstruc.2013.07.042

The carbazole derivatives are suitable for two-photon absorption optical storage and photoluminescence material. Two carbazole derivatives, asymmetrical and symmetrical type molecules containing quinoline rings as electron acceptors and an N-ethylcarbazole group as electron donor, 9-ethyl-3-(2-quinolin)viny- carbazole (4) and 9-ethyl-3,6-bis(2-(quinolin)vinyl)-carbazole (5), had been synthesized by the Vilsmeier reaction of formylation and Knoevenagel condensation. The one-photon properties including absorption, fluorescence emission spectra, fluorescence quantum yields and fluorescence decay behaviors were investigated in N,N-dimethylformamide. Meanwhile, these compounds were theoretically surveyed by the density functional theory (DFT) and the time-dependent functional theory (TD-DFT). The two-photon excited fluorescence and two-photon absorption cross-sections were measured for the compounds by 120 fs pulse at 800 nm Ti: sapphire laser operating at 1 kHz repetition rate. The results showed that both of the two compounds 4 and 5 had higher fluorescence quantum yield (Φ) of 0.77 and 0.81 comparing with carbazole. Compounds 5 with symmetric π conjugated structure possessed longer fluorescence lifetime (τ) of 21.4 ns and larger two-photon absorption cross-sections (δ_TPA) of 364 × 10^-50 cm⁴ s/photon than those of compounds 4 with asymmetric π conjugated structure (τ = 10.03 ns and δ_TPA = 81 × 10^-50 cm⁴ s/photon). It was indicated that the one and two-photon optical properties of carbazole derivatives are influenced strongly by the symmetry and length of π conjugated structure.

Full text of DOI:10.1016/j.molstruc.2013.07.042

Journal of Molecular Structure 1051 (2013) 23–29
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, one and two-photon optical properties of two asymmetrical
and symmetrical carbazole derivatives containing quinoline ring
b
b
Liang Li a, Ping Wang b, Yichi Zhang b, Yiqun Wu a,b, , Zhimin Chen , Chunying He
⇑
a Shanghai Institutes of Optics and Fine Mechanics, Chinese Academy of Sciences, No. 390, Qinghe Road, Jiading District, Shanghai 201800, China
b Key Lab of Functional Inorganic Material Chemistry, Heilongjiang University, Ministry of Education, Harbin 150080, China
h i g h l i g h t s
ꢀ
ꢀ
ꢀ
ꢀ
Novel carbazole derivatives containing quinoline were synthesized.
Electronic transition of carbazole derivatives were theoretically studied by TD-DFT.
Long fluorescence lifetime of carbazole derivatives was obtained.
Two-photon absorption of compounds was measured by 120 fs pulse at 800 nm.
a r t i c l e i n f o
a b s t r a c t
Article history:
The carbazole derivatives are suitable for two-photon absorption optical storage and photoluminescence
material. Two carbazole derivatives, asymmetrical and symmetrical type molecules containing quinoline
rings as electron acceptors and an N-ethylcarbazole group as electron donor, 9-ethyl-3-(2-quinolin)viny-
carbazole (4) and 9-ethyl-3,6-bis(2-(quinolin)vinyl)-carbazole (5), had been synthesized by the Vilsmeier
reaction of formylation and Knoevenagel condensation. The one-photon properties including absorption,
fluorescence emission spectra, fluorescence quantum yields and fluorescence decay behaviors were
investigated in N,N-dimethylformamide. Meanwhile, these compounds were theoretically surveyed by
the density functional theory (DFT) and the time-dependent functional theory (TD-DFT). The two-photon
excited fluorescence and two-photon absorption cross-sections were measured for the compounds by
120 fs pulse at 800 nm Ti: sapphire laser operating at 1 kHz repetition rate. The results showed that both
Received 7 March 2013
Received in revised form 19 July 2013
Accepted 24 July 2013
Available online 31 July 2013
Keywords:
Carbazole derivatives
One and two-photon optical properties
Quinoline ring
of the two compounds 4 and 5 had higher fluorescence quantum yield (U) of 0.77 and 0.81 comparing
with carbazole. Compounds 5 with symmetric
p conjugated structure possessed longer fluorescence life-
time (
s
) of 21.4 ns and larger two-photon absorption cross-sections (dTPA) of 364 ꢁ 10ꢂ50 cm4 s/photon
than those of compounds 4 with asymmetric
p
conjugated structure (
s
= 10.03 ns and dTPA = 81 ꢁ 10ꢂ50
-
cm4 s/photon). It was indicated that the one and two-photon optical properties of carbazole derivatives
are influenced strongly by the symmetry and length of
p
conjugated structure.
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
desirable to employ molecules with a large TPA cross section. For
this requirement, research in both experimental and theoretical
ways for obtaining the structure–property relation has been
pushed forward [19–22]. In exploring strong TPA compounds,
Albota et al. had focused on symmetric intramolecular charge
transfer organic molecules and emphasized the importance of con-
jugation length, donor/acceptor strength, and molecular symmetry
[23]. Meanwhile, Reinhardt et al. had also respectively studied the
Two-photon absorption (TPA) is a phenomenon that involves
the excitation of a molecule by simultaneous absorption of two-
photons [1]. Therefore, two-photon absorption (TPA) holds a great
potential for a number of industrial and medical applications such
as optical power limiting [2–5], two-photon up-conversion lasing
[6,7], two-photon fluorescence excitation microscopy [8–12],
three-dimensional (3D) optical data storage and microfabrication
[13–18]. For all the applications mentioned above, it is highly
effects of the planarity of p-center, donor strength, and molecular
asymmetry on asymmetric intramolecular charge transfer ones
[24]. The available research results exhibited that the conjugation
length, donor–acceptor functionalities, conformation, orientation
of the molecule, the molecular dimensionality, molecular congre-
gating effects, etc. are significant factors to be considered in the
molecular design and synthesis [20,21].
⇑
Corresponding author at: Shanghai Institutes of Optics and Fine Mechanics,
Chinese Academy of Sciences, No. 390, Qinghe Road, Jiading District, Shanghai
201800, China. Tel.: +86 21 69918592/8087; fax: +86 21 69918562.
E-mail address: yqwu@siom.ac.cn (Y. Wu).
0022-2860/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2013.07.042

24
L. Li et al. / Journal of Molecular Structure 1051 (2013) 23–29
It is well known that carbazole is isoelectronic to diphenyl-
synthesized target compounds were identified by the measure-
ments of 1H NMR, IR and MS, and are in agreement with the chem-
ical structures shown in Scheme 1.
amine, but it has a planar structure and it can be imagined as the
bonded diphenylamine. The carbazole nucleus can be easily func-
tionalized at 3-, 6-, 9-positions and covalently linked to other
molecular groups [25]. Typical push–pull chromophores consist
2.2.2. Synthesis of 9-ethyl-3-(2-quinolin)viny-carbazole (4)
3-Formyl-9-ethyl-carbazole (1.784 g, 8 mmol) and 2-methyl-
quinoline (1.144 g, 8 mmol) were added in 50 ml acetic anhydride.
The reaction mixture was heated to 120 °C and refluxed for 36 h.
After the reaction, when cooled it to room temperature, the reac-
tion solution was poured into water, and adjusted its PH to neutral
with alkaline solution. Then it was extracted with dichloromethane
for three times to yield a rude sample. The product 4 was purified
through column chromatography on silica gel using ethyl acetate–
petroleum ether (1:4) as eluent.
9-ethyl-3-(2-quinolin)viny-carbazole (4), yield: 48.3%,
M.P.286 °C. kmax = 294 nm; 1H NMR(CDCl3): d(ppm) 1.3(t, 3H,
CH3), 4.5(m,2H, CH2), 7.2(m, 2H, CH@CH), 7.4–8.4(m, 13H, carba-
zole); IR(KBr): 2950, 2925, 1610, 1496, 1465, 1424, 1381, 1327,
1213, 966, 820 cmꢂ1; Anal. calcd(%) for C25H20N2: C, 86.21; H,
5.75; N, 8.04. Found: C, 85.67; H, 6.14; N, 8.19; LC–MS: m/z,
349.1(348.16) [M + 1].
of a polar A–p–D system with a planar p-system end-capped by
a strong electron donor (D) and a strong electron acceptor (A). In
order to ensure intramolecular charge transfer (ICT) between the
donor (D = N-alkyl group etc.) and the acceptor (A = cyano group
etc.), double or triple bonds is the most common methods of link-
ing the
matic rings [26,27]. Carbazole moiety being a rigid structure with
donor-rigidised residue improves -electron delocalization
p-conjugated system between aromatic and hetero-aro-
a
p
resulting in better two-photon absorbing property [28]. Up to
now, many research groups have reported the structures, optical
and electronic properties of many carbazole derivatives because
of their excellent advantages of chemical, thermal and photochem-
ical stabilities as well as their ease adjustment of the electronic and
optical properties [29–35]. It is very important for the applications
of carbazole derivatives as optical materials to understand the rela-
tions between the optical properties and molecule structure, espe-
cially the effect of p-conjugated structure on the optical properties
of carbazole derivatives. In this paper, two carbazole derivatives,
asymmetrical and symmetrical type molecule containing quinoline
rings as electron acceptors and an N-ethylcarbazole group as elec-
tron donor, 9-ethyl-3-(2-quinolin)viny-carbazole and 9-ethyl-3,6-
bis (2-(quinolin)vinyl)-carbazole, have been synthesized by the
Vilsmeier reaction of formylation and Knoevenagel condensation.
Linear absorption spectra, one-photon excited fluorescence, fluo-
rescence quantum yields and fluorescence decay behaviors of the
compounds are investigated. Density functional theory (DFT) and
time-dependent functional theory (TD-DFT) are utilized to survey
theoretically the electron transition feature. The two-photon ex-
cited fluorescence of the compounds are studied by 120 fs pulse
at 800 nm Ti: sapphire laser operating at 1 kHz repetition rate
and two-photon absorption cross-section is measured. The effect
2.2.3. Synthesis of 9-ethyl-3,6-bis(2-(quinolin)vinyl)-carbazole (5)
3,6-dicarbaldehyde-9-ethyl-carbazole (2.008 g, 8 mmol) and 2-
methyl-quinoline (6.864 g, 48 mmol) were added in 100 ml acetic
anhydride. The reaction mixture was heated to 120 °C and refluxed
for 36 h. After the reaction, when cooled it to room temperature,
the reaction solution was poured into water, and adjusted its PH
to neutral with alkaline solution. Then it was extracted with
dichloromethane for three times to yield a rude sample. The prod-
uct 5 was purified through column chromatography on silica gel
using ethyl acetate–petroleum ether (1:6) as eluent.
9-ethyl-3,6-bis(2-(quinolin)vinyl)-carbazole (5), yield 43.1%.
M.P. 271 °C; kmax = 296 nm; 1H NMR(CDCl3): d(ppm) 1.5 (t, 3H,
CH3), 4.4(m, 2H, CH2), 7.2 (m, 4H, CH@CH), 7.4–8.4(m, 18H, carba-
zole); IR(KBr): 3037, 2955, 2929, 1589, 1501, 1483, 1426, 1381,
1312, 1232, 964, 819 cmꢂ1; Anal. calcd(%) for C36H27N3: C, 86.23;
H, 5.39; N, 8.38. Found: C, 85.46; H, 6.12; N,8 .42; LC–MS: m/z,
502.2(501.22) [M + 1].
of
p-conjugated structure containing quinoline rings as electron
acceptors and an N-ethylcarbazole group as electron donors on
the one and two-photon optical properties of the carbazole deriv-
atives is discussed as well.
2.3. One-photon optical properties measurements
2. Experimental
The linear absorption spectra were measured in DMF at a con-
centration of c = 1.0 ꢁ 10ꢂ5 mol/dm3, in which the solvent influ-
ence was not included. The linear absorption spectra of the
compounds were obtained by a Perkin Elmer Lambda 900UV/Vis/
NIR (SanJose, California, USA) spectrophotometer. One-photon
fluorescence spectra were measured at room temperature. Fluores-
cence decay curves were recorded with the lifetime combined sin-
gle-photon counting technique using a commercially available
Edinburgh Instruments, model LS-55 spectrometer equipped with
a 375 nm picosecond pulse diode laser made in Britain. The fluo-
rescence quantum yield Uv ¼ ðAs ꢁ F ꢁ n2 ꢁ UsÞ=ðA ꢁ Fs ꢁ n2Þ
2.1. Instrumentation
1H NMR spectra were recorded in CDCl3 on a Bruker AVANCE-
300 MHz NMR instrument using TMS as internal standard. IR spec-
tra were recorded using Perkin Elmer FT-IR System. The spectra of
the solid compounds were performed in the form of KBr pellets.
Mass spectra were obtained with a Bruker Agilent 6890-5973 MAL-
DI-TOF mass spectrometer. Elemental analyses were performed
using a PE2400 elemental analyzer. Melting points were deter-
mined on xꢂ5 melting point detector.
v
v
v
s
where A denotes the absorbance at the excitation wavelength, F
means the area under the fluorescence curve and n is the refraction
2.2. Synthesis
index. Subscripts s and
unknown quantum yield, respectively. Rhodamine B in ethanol at
25 °C ( = 0.9) was made as the standard.
v refer to the standard and to the sample of
2.2.1. Synthesis of materials
U
The synthetic route is outlined in Scheme 1. Carbazole was hal-
ogenated by bromobutane in alkaline condition. Compound 2 and
3 were synthesized by the Vilsmeier reaction of formylation from
9-alkyl-carbazole. 9-ethyl-3-(2-(quinolin-2-yl) vinyl)-carbazole
(4) and 9-butyl-3,6-bis(2-(quinolin)vinyl)-carbazole (5) were
synthesized using knoevenagel condensation. 9-ethyl-carbazole
(1), 9-ethyl-3-formyl-carbazole (2) and 3,6-diformacy-9-ethyl-car-
bazole (3) were synthesized by the reported procedure [36]. The
2.4. Two-photon fluorescence measurements
In order to explore the TPA properties of the target compounds,
we use two-photon excited fluorescence method to measure the
TPA cross section by laser [37,38]. The experimental setup is
shown in Fig. 1. The two-photon fluorescence spectra of the com-
pounds are investigated by a 120-fs 800-nm pulse Ti: sapphire

L. Li et al. / Journal of Molecular Structure 1051 (2013) 23–29
25
Scheme 1. The synthetic route of the target compounds.
to research singlet–singlet electronic transition for these
molecules.
3. Results and discussion
3.1. One-photon absorption and fluorescence emission spectra
The one-photon absorption and emission spectra of carbazole, 4
and 5 in DMF are shown in Fig. 2. The
peaks of the carbazole derivatives 4 and 5 locate at 360 nm and
p ?
p⁄ character absorption
Fig. 1. Experimental setup for two-photon exited fluorescence.
femto-second laser operating at 1 kHz repetition rate in the DMF at
a concentration of 1.0 ꢁ 10ꢂ3 mol/dm3. The fluorescence spectra
are recorded by a 16-bit CCD (Jobin–Yvon, Horiba, France) that
mounted at the output of the monochromator.
2.5. Computational procedures
All calculations are performed using Gaussian 03 W. The geom-
etry optimizations of the electronic ground state are carried out at
the density functional theory (DFT) level [37,38] with the hybrid
Becke, three-parameter, Lee–Yang–Parr (B3LYP) exchange correla-
tion functional [39,40], and the split-valence 6-31G⁄ basis set [41].
DFT/B3LYP/6-31G⁄ has been reported to be an accurate formalism
for calculating the structural properties of many molecular sys-
tems [36,42]. Time-dependent functional theory (TD-DFT) is used
Fig. 2. (a–c) are linear absorption of carbazole, 4 and 5 in DMF (d0 = 1.0 ꢁ 10ꢂ5
-
mol dmꢂ3); (d–f) are fluorescence intensity of carbazole,
4 and 5 in DMF
(d0 = 1.0 ꢁ 10ꢂ5 mol dmꢂ3).

26
L. Li et al. / Journal of Molecular Structure 1051 (2013) 23–29
372 nm, respectively. The kabsmax of the two compounds present an
n ? p⁄ character at 294 nm and 296 nm and display a slight
red-shift compared with the maximum absorption peaks of carba-
zole (at 282 nm). Meanwhile, compared to the asymmetric struc-
ture of compounds 4, the conjugation length of compounds 5 is
increased by modified quinoline ring on the 3, 6- of the bilateral
carbazole unit and the 372 nm absorption peaks (kabs) of com-
pounds 5 happen red-shifted 12 nm because of its disubstituted
at 3, 6-position to form a symmetry A–p–D–p–A type structure.
Furthermore, the absorption spectra of the compounds show that
there is no linear absorption in the range of 450–900 nm, which
would be a wide window for investigating the two-photon optical
properties.
In Fig. 2, c and d show the fluorescence emission spectra of sam-
ples 4 and 5 in the DMF at a concentration of 1.0 ꢁ 10ꢂ5 mol dmꢂ3
respectively. The kexcmax and kflu, as well as the fluorescence quan-
tum yields of 4 and 5 in DMF are shown in Table 1. The kflu fluor-
escence wavelengths of 4 and 5 are at 484 and 492 nm, locating the
blue–green spectral range. They are greatly red-shifted more than
124 nm compared with the kflu fluorescence wavelengths of carba-
zole (at 368 nm). It is found that absorption and fluorescence spec-
Fig. 3. The fluorescence decay curve of carbazole, compounds 4 and 5 in DMF.
(Carbazole) > 3.461 eV (Compound 4) > 3.287 eV (Compound 5),
which indicate that introducing quinoline ring on the 3,6-of the
bilateral carbazole unit is more favorable for the stability of molec-
ular systems.
tra have nearly mirror-image profiles. From Table 1, the
4 and 5 correspond to 91, and 94, respectively. The fluorescence
quantum yields of the compounds 4 and 5 are 0.77 and 0.81 in
the DMF, which are equivalent to 6.4 and 6.8 times that of carba-
zole (0.12). Fluorescence quantum yields can be greatly en-
hanced by introducing quinoline ring on the position of 3 or 3, 6
of the carbazole unit to increase the -conjugation length. The
DkStokes of
U
To aid the interpretation of our experimental results, we have
carried out a theoretical study to determine the equilibrium geom-
etry of the molecules, as well as to predict their electronic transi-
tions, either related to one-photon absorption. All the theoretical
computations for singlet–singlet electronic transition are carried
out within the DFT framework. TD-DFT has been assumed at vac-
uum conditions to calculate the absorption spectrum. The theoret-
ical results for one-photon absorption (OPA) of compound 4 and 5
are displayed in Table 3, which include transitions energies (E),
oscillator strengths (f) and main configurations. From Table 3, it
is observed that the first electronic transition via theoretical calcu-
lation for compound 4 occurs at 365 nm, which is almost consis-
tent experimental result (kab = 360 nm), seen in Fig. 2. Analysis of
the molecular orbitals of compound 4 indicates that the main exci-
tation from the highest occupied molecular orbital (HOMO) to the
U
p
fluorescence decay behaviors of compound 4 and 5 in DMF are re-
corded. The fluorescence decay curves of compounds are shown in
Fig. 3. The fluorescence lifetime (
that both of these two carbazole derivatives 4 and 5 have long
fluorescence lifetime ( ) of 10.03 ns and 21.4 ns, which are much
longer than that of carbazole (6.66 ns). Because of the longer
conjugation length, fluorescence lifetime ( ) of compound 5 with
s) is given in Table 1. It is found
s
p
-
s
symmetrical structure is as twice long as that of compound 4 with
asymmetrical.
lowest unoccupied molecular orbital (LUMO) has a
ter. On the other hand, the theoretical electronic transition
(kab = 370 nm, f = 0.575) for compound 5 allow
p⁄ transition,
p ?
p⁄ charac-
3.2. Frontier molecular orbitals
p
?
The optimized geometry of the ground is obtained and shown in
Fig. 4. It is showed that the optimized structure possesses a good
planarity conjugated system, in which one- or two-quinolone ring
are linked from 3 or 3, 6 of cabazole unit. The planarity is its impor-
tant structure property, which is directly related to the conjugation
corresponding now to HOMOꢂ1 ? LUMO+1 transition, which is
almost in good agreement with the 372 nm obtained in the exper-
imental results (in Fig. 2). The remaining calculated transitions
present low oscillator strength and cannot be observed in the
linear absorption spectrum.
of
p bond system. The nature and energies of the HOMO and LUMO
of the compounds, which play an important role in the photo lumi-
nescence properties of the compounds, are investigated at the DFT/
B3LY/6-31G⁄ level. The isodensity surface plots of HOMO and
LUMO are shown in Fig. 5. The HOMOs of the compounds are delo-
calized among the whole molecules and the distributions of the
LUMO appear to be different for the two molecules. Table 2 lists
the calculated HOMO and LUMO energies. The increase in the
conjugated length makes the HOMO energies higher, the LUMO
energies lower, and the energy gaps narrower [36]. From Table 2,
it can be known that the increase of the conjugation length also
results in the decrease of energy gaps (4E): 4.798 eV
3.3. Two-photon absorption properties
Based on the two-photon (TPA) excited fluorescence method of
studying TPA property, the intensity If of fluorescence induced by
two-photon excitation determined by laser intensity I0 and the to-
tal number of molecules N is given by the following equation [37]:
If ¼ CI2N
ð1Þ
0
where C is a constant. Pulsed intensities at the geometric focal point
are calculated using the following equation:
Table 1
Absorption, excitation and fluorescence spectra data of carbazole, 4 and 5 in DMF.
Sample
kabs (nm)
kexcmax (nm)
kflu (nm)
D
kStokes (nm)
U
s (ns)
Carbazole
4
5
282, 332a
294, 360
296, 372
294a
393
398
368a
484
492
74a
91
94
0.12a
0.77
0.81
6.66
10.03
21.40
a
The data are from Ref. [36].

L. Li et al. / Journal of Molecular Structure 1051 (2013) 23–29
27
Fig. 4. The optimized geometry of the ground state of the compound 4 and 5.
Fig. 5. Plots of HOMO and LUMO of 4 and 5 by DFT//B3LYP/6-31G⁄.
laser pulse at 800 nm using different input power. To make sure
that the collected light signal is not from other absorption mecha-
nisms, but from the fluorescence after TPA, we adjust the input
power and record the intensity dependence of the fluorescence.
Meanwhile, the logarithm of the fluorescence intensity as the ver-
tical axis is plotted with the logarithm of input power as the ab-
scissa, shown in the insert. The slopes of the line are 1.94 and
1.96, respectively, which confirm that TPA is the main excitation
mechanism of the intense fluorescence emission at the femtosec-
ond regime.
From Fig. 6 to know, the shape of the two-photon fluorescence
emission spectra is identical with the shape of one-photon fluores-
cence emission spectra. And the two-photon fluorescence emission
wavelengths of 4 and 5 possess a maximum at 480 nm and
482 nm. This result demonstrates that the two-photon and the
one-photon fluorescence processes take place from the same final
excited state. Moreover, the two-photon-induced fluorescence
method is adopted to explore TPA cross sections. To study the
TPA cross-section dTPA of the two carbazole derivatives, we employ
fluorescein (dissolved in water, pH = 11) as the standard
Table 2
Negative of the HOMO (ꢂ
e
HOMO) and LUMO (ꢂ
eHOMO (eV)
eLUMO) energies, calculated by TD-DFT.
Molecule
ꢂ
ꢂeLUMO (eV)
4E
Cabazolea
4
5
5.4427
5.0558
5.0177
0.6444
1.5948
1.7300
4.798
3.461
3.287
a
The data from Ref [36].
2
p
ðN:A:Þ
I0ðtÞ ¼
PðtÞ
ð2Þ
k2
where N.A. = n sinh, h is the half-angle of collection for the lens, I0
means the intensity at the geometric focal point, and P refers to
the incident power. So, using the formula If ¼ CI2N for dealing with
0
logarithms, the linear relation between the logarithm of the fluores-
cence intensity and of input power can be attained; the slope of the
line should be 2 to confirm whether the process has a TPA
mechanism.
The two-photon fluorescence spectra of samples 4 and 5 in the
DMF are shown in Fig. 6a and b. They pumped by a femtosecond
(UFlu = 0.92) and the value of its TPA cross-section obtain from
Table 3
Electronic transition data obtained by TD-DFT (kab) for 4 and 5 at the B3LYP/6-31 G⁄ optimized geometry.
Molecule
Electronic transitions
Transitions energy (eV)
kab (nm)
Exp.akab (nm)
f
Main configurations
4
5
S
S
0 ? S1
0 ? S3
3.45
2.17
365
370
360
372
0.748
0.575
HOMO ? LUMO
HOMOꢂ1 ? LUMO+1
0.6320
0.5614
a
Exp. is experimental result.

28
L. Li et al. / Journal of Molecular Structure 1051 (2013) 23–29
Fig. 6. Two-photon fluorescence for samples 4 (a) and 5 (b) in DMF pumped by femtosecond laser pulse at 800 nm using different input power; The linear graphs are the
logarithm of integrate fluorescence signal of 4 (c) and 5 (d) versus logarithm of the input intensity. The black squared dots are the measured fluorescence data and the solid
line is a linear fit.
Ref. [38], dflu = (38.0 9.7) ꢁ 10ꢂ50 cm4 s/photon. Because the dif-
ference of the refractive index of water (1.333) and the DMF
(1.4296) is small, it is neglected in the calculation. The TPA
cross-section for the sample is defined as follows:
because of it great potential for application in TPA materials. Two
carbazole compounds were synthesized by the Vilsmeier reaction
of formylation and Knoevenagel condensation. The one and two-
photon absorption properties were reported in this paper. The
OPA properties of carbazole derivatives with quinoline were mea-
sured including UV–Vis spectra, fluorescence spectra and fluores-
cence decay behaviors. The fluorescence quantum yields (0.77
and 0.81) and fluorescence lifetime (10.03 ns and 21.4 ns) of com-
pound 4 and compound 5 were bigger than those of carbazole,
(0.12 and 6.66 ns). The TPA properties of carbazole derivatives
were studied using the TPA fluorescence method with 800 nm
femtosecond pulses laser. Meanwhile, the compound 5 exhibited
large two-photon cross-sections, 364 ꢁ 10ꢂ50 cm4 s/photon, with
Uflu Fsample
Usample Fflu
dsample
¼
dflu
ð3Þ
The fluorescence quantum yield of sample has been provided
from its single-photon fluorescence spectrum, shown in Table 1.
The following are derived: d4 = 81 ꢁ 10ꢂ50 cm4 s/photon; d5 -
= 364 ꢁ 10ꢂ50 cm4 s/photon, which reveal that the TPA cross-sec-
tion of compound 5 is more than 4 times that of compound 4.
The results demonstrate that the TPA cross-sections d of carbazole
derivatives are improved by bilateral substitution of quinoline on
the 3- and 6-position of carbazole derivatives. Meanwhile, com-
pared with dTPA of other 9-ethyl-carbazole derivatives, the dTPA of
9-ethyl-3,6-bis(2-(quinolin)vinyl)-carbazole (compound 5) is
much larger than that of 9-ethyl-3,6-bisstyryl-carbazole
(dTPA = 115 ꢁ 10ꢂ50 cm4 s/photon) [36], which implies that if the
strong acceptor quinolone group is substituted on the carbazole
unit and the conjugation length is extended via the addition of a
double bond between the quinolone acceptor and carbazole bridge,
the TPA cross section is increased greatly.
800 nm laser excitation. Owing to the increase of the
p-conjuga-
tion length by connecting quinoline rings from 3- and 6- of carba-
zole, the fluorescence decay behaviors and TPA cross-section
values of the carbazole derivatives were enhanced. Based on the
OPA and TPA properties, the compound may be a promising candi-
date material for the application in TPA three-dimension optical
data storage, organic electro-luminescent and two-photon nano/
micro-structure fabrication. The investigation on optical data stor-
age of application is progressing in our laboratory, and the results
will be released in the future.
4. Conclusion
Acknowledgements
In this paper, experimental and theoretical investigation on the
asymmetric-type and symmetric-type carbazole were performed
This work was partially financially supported by the National
Natural Science Foundation of China (61137002) and the Research

L. Li et al. / Journal of Molecular Structure 1051 (2013) 23–29
29
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