Design, synthesis, linear and nonlinear photophysical properties and biological imaging application of a novel Λ-type pyrimidine-based thiophene derivative

Article abstract of DOI:10.1016/j.molstruc.2014.04.058

A novel D-π-A-π-D type thiophene pyrimidine derivative, 2,2'-thiophene-4, 6-bis (4-N,N-diethylbenzene ethenyl) pyrimidine (L), was designed, synthesized via Knoevenagel and Suzuki coupling reactions, and fully characterized. The results of X-ray diffraction analysis revealed that single crystal of L belongs to P2₁2₁2₁ non-centrosymmetric space group, and the whole molecular skeleton exhibits a good coplanarity. Systematic photophysical properties were investigated for L. The connections between the properties and structure were explained relying on theoretical calculation. The thiophene pyrimidine derivative shows strong third-order nonlinear optical response and large two-photon absorption (2PA) cross section in high polar solvents. Finally, preliminary exploration in biological imaging also has been carried out, it shows a good biological application prospect.

Full text of DOI:10.1016/j.molstruc.2014.04.058

Accepted Manuscript
Design, synthesis, linear and nonlinear photophysical properties and biological
imaging application of a novel Λ-type pyrimidine-based thiophene derivative
Qiong Zhang, Junshan Luo, Lili Ye, Hui Wang, Bei Huang, Jun Zhang, Jieying
Wu, Shengyi Zhang, Yupeng Tian
PII:
S0022-2860(14)00425-6
DOI:
http://dx.doi.org/10.1016/j.molstruc.2014.04.058
MOLSTR 20565
Reference:
Journal of Molecular Structure
To appear in:
Received Date:
Revised Date:
Accepted Date:
12 February 2014
17 April 2014
17 April 2014
Please cite this article as: Q. Zhang, J. Luo, L. Ye, H. Wang, B. Huang, J. Zhang, J. Wu, S. Zhang, Y. Tian, Design,
synthesis, linear and nonlinear photophysical properties and biological imaging application of a novel Λ-type
pyrimidine-based thiophene derivative, Journal of Molecular Structure (2014), doi: http://dx.doi.org/10.1016/
j.molstruc.2014.04.058
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Design, synthesis, linear and nonlinear photophysical
properties and biological imaging application of a
novel Λ-type pyrimidine-based thiophene derivative
Qiong Zhang†a, Junshan Luo†a, Lili Ye†b, Hui Wanga, Bei Huang,b Jun Zhanga, Jieying
Wua*, Shengyi Zhanga, Yupeng Tiana*
a Department of Chemistry, Key Laboratory of Functional Inorganic Materials Chemistry of Anhui
Province, Anhui University, Hefei, 230039, P. R. China
b Department of Biology, Anhui University, Hefei 230039, P. R. China
†These authors contributed equally to this work.
∗Corresponding author Tel.: +86-551-65108151, Fax: +86-551-65107342, e-mail:
jywu1957@163.com; yptian@ahu.edu.cn)
Abstract
A novel D-π-A-π-D type thiophene pyrimidine derivative, 2,2’- thiophene-4, 6 -
bis (4-N, N-diethylbenzene ethenyl) pyrimidine (L), was designed, synthesized via
Knoevenagel and Suzuki coupling reactions, and fully characterized. The results of
X-ray diffraction analysis revealed that single crystal of L belongs to P212121
non-centrosymmetric space group, and the whole molecular skeleton exhibits a good
coplanarity. Systematic photophysical properties were investigated for L. The
connections between the properties and structure were explained relying on
theoretical calculation. The thiophene pyrimidine derivative shows strong third-order
nonlinear optical response and large two-photon absorption (2PA) cross section in
high polar solvents. Finally, preliminary exploration in biological imaging also has
been carried out, it shows a good biological application prospect.
Keywords: Thiophene pyrimidine derivative, Crystal structure, Two-photon
absorption, Biological imaging
1. Introduction
Design, synthesis and photophysical properties of novel organic molecules with
large two-photon absorption (2PA) cross sections have been received much attention
1

in the field of nonlinear optical materials [1-4] owing to the important applications,
such as two-photon microscopic imaging[5-7], optical data storage[8-10], 3D
microfabrication[11-13], up-converted stimulated emission[14] and photodynamic
therapy[15]. Previous works have revealed that molecules with electron-donor (D)
and electronic-withdrawing (A) groups linked by a π-conjugated bridge are endowed
with large 2PA cross sections. And then attention was devoted to multipolar molecular
model for the increase of the 2PA cross sections, like quadrupolar D-π-A-π-D
(A-π-D-π-A) and octupolar A-π-D or D-π-A structures. Recently, more interesting has
been focused on macromolecules[16-17], molecular aggregates[18-19], and metal
complexes[20-22]. However, the applications of 2PA materials put forward that apart
from the high 2PA cross sections, 2PA chromophores have to satisfy the various
specific requirements, such as excellent photostability, proper water solubility, and
good biocompatibility.
At present work, a novel thiophene pyrimidine derivative with D-π-A-π-D model
was designed, which was based on the considerations as follows. (1) Thiophene is a
chromophore with rich electronics, because of the good electron-donating,
electrochemical activity, environmental stability and workability[23-28]. Therefore,
thiophene was used as subtle modified unit attached to D-π-A-π-D molecular model,
which is different from previous design strategy. (2) Pyrimidine derivatives are also
with good biological activity. The pyrimidine ring is one of the four bases in DNA, so
itself has good biocompatibility and activity, and can easily be modified, therefore,
pyrimidine derivatives are widely used in anti-cancer[29], biological probes and other
pharmaceutical and biological fields[30-31]. Recently, J. G. Qin’s group, Z. L.
Huang’s and our group have reported pyrimidine derivatives for two-photon
absorption properties studies[32-35]. The results were confirmed that pyrimidine
derivatives can be tailored to be promising two-photon materials.
In this paper, 2,2’- thiophene-4, 6 - bis (4-N, N-diethylbenzene ethenyl)
pyrimidine (L) was focused on its synthesis, characterization, crystal structure and
photophysical properties combining with theoretical methods. Interestingly it was
found that D-π-A-π-D pyrimidine derivative with subtle modified by thiophene shows
2

large two-photon absorption (2PA) cross sections in the near infrared region and high
polar solvents. Furthermore, the potential application in biological imaging was
carried out.
2. Experimental
2.1. Materials and instrumental measurement
All chemicals were commercially available and the solvents were purified by
1
conventional methods before using them. H-NMR and 13C-NMR spectra was
recorded with a Bruker AV400M NMR spectrometer with TMS as the internal
standard, coupling constants J are given in Hertz. Mass spectrum was determined with
a Micromass GCT-MS (EI source). Fourier transform infrared (FT-IR) spectra were
recorded in on a SHIMADZU IRPrestige-21 spectrophotometer in the range of
400-4000 cm-1 with samples prepared as KBr pellets. Absorption spectra were
obtained on a UV-265 spectrophotometer. Fluorescence measurements were
performed using a Hitachi F-7000 fluorescence spectrophotometer. Elemental analysis
was performed on Perkin-Elmer 240 instrument. Single-crystal X-ray diffraction
measurements were carried out on a Bruker Smart 1000 CCD diffractometer equipped
with a graphite crystal monochromator situated in the incident beam for data
collection at room temperature. The determination of unit cell parameters and data
collections were performed with Mo-Kα radiation (λ = 0.71073 Å). Unit cell
dimensions were obtained with least-squares refinements, and all structures were
solved by direct methods using SHELXS-97. The final refinement was performed by
full-matrix least-squares methods with anisotropic thermal parameters for
non-hydrogen atoms on F2. The hydrogen atoms were added theoretically and riding
on the concerned atoms.
2.2 Measurements
(1) The fluorescence quantum yield of chromophores is very difficult to measured
directly under practical conditions, other special auxiliary instruments and methods
are needed. The accurate measurement of the quantum yield of the chromophore is
therefore frequently used in the actual experiment as reference [36], and then the
3

unknown chromophore was measured according to their absorption and fluorescence
quantum yield. The following is the quantum yield formula [37]:
2
F
ns
nr
s
Ar
As
∫
∫
Φs = Φr
2
F
r
The sign of s and r respectively represent the sample and reference samples, A is the
absorbance at the wavelength of excitation, n is the refractive index of the solvent, Φr
is fluorescence quantum yield of reference samples.
Due to the inactivation process, including radiative transition and non-radiative
transition excited molecule fluorescence quantum yield can be defined as follows:
Φr=kr/(kr+ knr)
The kr is the rate constant of fluorescence emission, knr is the sum of rate constant
of non-radiative in transition process, it depends on the competition results of the
fluorescence emission process and the non-radiative in transition process.
The chromophores absorb energy after excitation, undergoing a series of
transformation, and then returned to the radiative transition ground state and emit
fluorescence. When the excitation is stopped, the fluorescence intensity of the
molecule started to decline, the time of the drops when excited with the maximum
intensity to 1/e required is known as the fluorescence lifetime, and its formula is:
τ=1/(kr+ knr)
As above, the kr is the rate constant of fluorescence emission, knr is the sum of rate
constant of non-radiative in transition process.
(2) TPEF spectra were measured using femtosecond laser pulse and Ti: sapphire
system (680–1080 nm, 80 MHz, 140 fs, Chameleon II) as the light source. All
measurements were carried out in air at room temperature. 2PA cross sections were
measured using two-photon-induced fluorescence measurement technique. The 2PA
cross sections (δ) are determined by comparing their TPEF to that of fluorescein in
solvents, according to the following equation[38]
Φref cref nref
F
δ = δref
Φ
c
n Fref
Here, the subscripts ref stands for the reference molecule. δ is the 2PA cross-section
4

value, c is the concentration of solution, n is the refractive index of the solution, F is
the TPEF integral intensities of the solution emitted at the exciting wavelength, and Φ
is the fluorescence quantum yield. The δref value of reference was taken from the
literature [39a].
The 2PA spectra of the chromophores were determined in the wavelength range
(700–900 nm) by investigating their two-photon-excited fluorescence (TPEF) in
different solvents with a concentration of 2.0×10-4 mol/L.
2.3. Synthesis
The title chromophore L was synthesized according to Scheme 1.
Scheme 1. Synthesis route of the title chromophore L
2.3.4. Preparation of chromophore 2-thienyl-4,6-bis(4-N,N-ethylaminostyryl)
pyrimidine (L)
1.91 g (15 mmol) 2 - thiophene boronic acid and a small amount of Pd (PPh3)4
were added into the solution of 6.07 g (11mmol) chromophore 1[39b], 16 mL
triethylamine and 60 mL DMF under the atmosphere of N2, the reaction mixture was
stirred for 3h at the temperature of 130 ºC. The mixture was extracted with
dichloromethane and the organic layer was collected. The organic layer was dried
over anhydrous MgSO4 and filtered. The organic solvent was completely removed by
rotary evaporation. The crude product was purified by chromatography on a silica gel
with ethyl acetate/petroleum mixture (1:16 v/v) as the eluent. Yellow solid was
collected, Yield:4.47g(80%). 1H-NMR (CDCl3, 400MHz) δ = 1.2 (t, 12H, J = 6.8Hz)，
5

δ = 3.4 (q, 8H, J = 6.4 Hz)，δ = 6.69 (d, 4H, J = 8 Hz), δ = 7.51(d, 4H, J = 8 Hz), δ =
6.46-6.86 (d, 2H, J = 16 Hz), δ = 7.84-7.88 (d, 2H, J = 16 Hz) δ = 7.02 (s, 1H). δ =
13
7.15-7.17 (t, 1H, J = 8 Hz ) δ = 8.12 (s, 1H). C-NMR (CD3COCD3, 150MHz) δ:
12.93, 44.94, 112.37113.42, 121.35, 123.90, 128.72, 129.08, 130.02, 130.29, 137.82,
145.88, 149.66,161.39, 164.45. IR (KBr, cm-1) selected bands: 3035(s), 2967(s),
2925(m), 1602(s), 1521(s), 1496(s), 1433(s), 1401(s), 1353(s), 1301(s), 1268(s),
1226(s), 1183(s), 1149(s), 1075(s), 1034(s), 977(s), 885(m), 800(s) , 706(s), 675(m),
642(s). Calcd for C32H36N4S (508.72): C, 75.55 H, 7.13 N, 11.01. found: C, 75.58 H,
7.11 N, 10.99 MS, m/z (%): 508.26([M+], 100%).
3. Results and Discussion
3. 1. Crystal structure description
Single crystal of chromophore L suitable for X-ray diffraction analysis was
obtained by slow evaporation of the solution of the chromophore L in CH2Cl2 and
acetonitrile solution at room temperature for several days. The crystal structure of
chromophore L was shown in Fig. 1. Selected bond lengths and angles were listed in
Table 1 and 2, respectively. The crystal of the chromophore L belongs to the P212121
space group. As shown in Fig. 1, the C=C double bonds in the molecule is in a trans
1
configuration in accordance with the results of H-NMR spectra. Fig. 2 shows the
bent molecule from the side view of the crystal structure. The dihedral angle between
the thiophene ring and the pyrimidine ring is 3.75°. The other dihedral angles between
two benzene rings and pyrimidine ring are 22.03° and 17.12°, respectively, so that the
whole molecule displays a good planarity favoring the electron delocalization in the
molecule. As the listed bond length in Table 2, several bond lengths are intermediate,
such as C(15)-C(21) [1.484 Å], C(21=C(22) [1.320 Å], C(22)-C(23) [1.462 Å],
C(12)-C(13) [1.461 Å], C(12)=C(11) [1.324 Å], C(11)-C(8) [1.447 Å], C(17)-S(1)
[1.704 Å], showing that there is a high degree of electron delocalization containing
thiophene and pyrimidine rings in the molecule, which should lead to good optical
properties.
6

Fig. 1 ORTEP structure of chromophore L with atomic labeling scheme(with 50%
thermal ellipsoid probability). All hydrogen atoms and solvent molecules are omitted
for clarity
Fig. 2 Side view of crystal structure of chromophore L
Table 1. Crystal data and structure refinement for chromophore L
Empirical formula
Formula weight
C32 H36N4S
508.72
Crystal system, space group
Volume
Orthorhombic, P212121
3509(3) Å3
Unit cell dimensions deg.
a = 8.514(4) Å b = 18.233(9) Å c =
22.030(10) Å
Final R indices [I>2σ(I)]
R indices (all data)
R1 = 0.0875, wR2 = 0.2332
R1 = 0.1681, wR2 = 0.2801
1.047
Goodness-of-fit on F2
Table 2. Selected bond lengths [Å] and angles [°] for chromophore L
Bond lengths [Å] angles [°]
C(8)-C(11)
C(11)-C(12)
1.447(7)
1.324(6)
C(12)-C(11)-C(8)
C(11)-C(12)-C(13)
128.6(5)
123.3(5)
7

C(12)-C(13)
C(15)-C(21)
C(21)-C(22)
C(22)-C(23)
C(13)-N(2)
C(16)-N(2)
C(17)-S(1)
C(20)-S(1)
1.461(7)
1.484(7)
1.320(7)
1.462(7)
1.358(6)
1.332(6)
1.704(6)
1.686(8)
N(2)-C(13)-C(12)
C(15)-N(1)-C(16)
C(20)-S(1)-C(17)
C(22)-C(21)-C(15)
C(21)-C(22)-C(23)
C(14)-C(13)-C(12)
C(14)-C(15)-C(21)
N(1)-C(15)-C(21)
118.0(4)
115.0(4)
88.4(4)
123.8(5)
126.5(5)
122.4(5)
119.9(5)
117.6(5)
3.2. Linear absorption, TD-DFT studies and single-photon-excited fluorescence
The linear absorption spectra and the single-photon excited fluorescence spectra of
the chromophore L in different solvents (c=1×10–5 mol·L–1) were shown in Fig. 3 (a).
The corresponding spectral data were summarized in Table 3. The chromophore L
shows a strong absorption in the UV-vis region. The maximum bands of the linear
absorption spectra locate between 400 to 450 nm. With the increasing of solvent
polarity, the maximum linear absorption bands exhibit a slight red-shift, due to that
the excitation state is more stable than the ground state in polar solvents, suggesting
that a significant charge rearragement takes place when excited, which is consistent
with multidimensional intramolecular charge transfer (MDICT) occurring between the
core and the branches.
In order to investigate the photophysical properties of L, especially the influence of
the extended the π-conjugate system in the ground state and the excited state energy
redistribution, density functional theory calculations (DFT) of L are carried out. As
shown in Fig. 4, the electron cloud is distributed uniformly in the ground state, and
obviously transferring from single branch over the whole molecule. In the excited
state, however, the electron-cloud of L transferred from the whole molecule to the
thiophene unit, which indicates the charge transition (CT) in the excited state. Besides,
the electron-cloud of L are around the centre-part in the excited-state (Fig. 2b), which
caused the central parts to possess a relatively high energy. The effect may induce the
8

molecules to be twisted in the excited-state. As the result, the molecule is partial
conjugation in the ground state. After excited, the electrons are concentrated on the
center-core instead of their branch, which leads the V-shape molecule further to be
twisted. As shown in Table 3, the lowest-energy excitation band of L (λ : 456.95 nm )
is assigned as the intramolecular charge transfer (ICT) transition [π → π*] due to the
HOMO(H)
→
LUMO(L) transition. It is obviously that the strong
electron-withdrawing pyrimidine unit has no obvious effect on increasing ICT. The
transition in the high- energy absorption region is 323.09 nm mainly due to the H →
L+2 transition [π → π*]. Therefore, it is inferred that the oscillator strength of the
low-energy absorption bands of L is larger than those of the high-energy bands.
Basically, the calculated singlet-singlet transitions in L are in reasonable agreement
with the experimental λab in the two major absorption bands observed.
The single-photon excited fluorescence spectra (SPEF) of chromophore L in six
solvents of different polarities at a concentration c=1×10-5 mol·L-1 are collected in
Table 4 and Fig. 3 (a) including the fluorescence quantum yields and lifetimes (Fig.
5). Upon increasing the solvent polarity, the fluorescence maxima of chromophore L
show remarkable bathochromic shifts and the Stokes shifts also show a tendency to
monotonically increase. This can be explained by the fact that the excited state may
possess a higher polarity than the ground state, for solvatochromism is associated with
a lowering of the energy levels. An increased dipole–dipole interaction between the
solute and solvent leads to a lowering of the energy level. To be noticed, the
introducing of the thienyl unit will increase the electron-donating effect. Meanwhile,
the slight blue-shift of L in THF can be explained as the non-radiative transition of L,
with the result that the molecule has lower symmetry and poorer complanation which
leads to the broken of the rotating of the C-C bond.[40] As shown in Fig. 3 (b), L
shows a more sensitivity to five solvents, which exhibit potential application for the
development of efficient sensors for the detection of volatile organic compounds
(VOCs).
9

Fig. 3 Linear absorption and Single-photon excited fluorescence spectra of
chromophore L in different solvents (C = 1×10-5 mol·L-1)
Table 3 Photophysical properties of chromophore L in different solvents
Configuration
λmax(n.m) f(a.u) E/eV
Composition
Character
136(H) →
137(L)( 0.66040)
HOMO→LUMO
456.95
323.09
1.2574 2.7678
0.3382 3.8375
π→π*
136(H) →
139(L+2)(0.59537)
→LUMO+
HOMO
2
π→π*
10

Fig. 4 Molecular orbital energy diagram for chromophore L
Table 4 Excitation energies (E), corresponding wavelengths (λ), oscillator
strengths (f) and major contribution for chromophore L
UV
λab
FL
λem
Stoke’s
10-8kr 10-8knr
logεmax
Solvents
Φ
shift(cm-1)
/s-1
/s-1
(nm)
(nm)
C6H6
CH2Cl2
THF
432
445
437
440
440
448
4.73
4.78
4.75
4.80
4.72
4.79
490
534
520
556
554
554
0.94
0.71
0.73
0.12
0.13
0.19
2740
3745
3652
4742
4677
4271
13.06
3.06
6.03
1.93
0.89
1.17
0.83
1.25
2.23
14.19
5.96
5.00
CH3CH2OH
CH3CN
DMF
11

Fig. 5 Time-resolved fluorescence decay profiles of chromophore L in different
solvents
3.3. Lippert-Mataga plots
As described above, the fluorescence spectra showed large Stokes shifts depending
on the solvent polarity. Further, significant solvatochromism is observed suggesting a
large change in dipole moment between ground and emissive excited states. The
Lippert-Mataga equation is the most widely used to evaluate the dipole moment
changes of the dyes with photoexcitation:[41a,b]
2∆f
4πε0ꢀca3
(µe − µg )2 + b
(1)
∆ν =
ε −1
n2 −1
(2)
∆f =
−
2ε +1 2n2 +1
in which ∆ν = νabs - νem stands for Stokes shift, νabs and νem are absorption and
emission (cm-1), ꢀ is the Planck’s constant, c is the velocity of light in vacuum, a is
the Onsager radius and b is a constant. ∆f is the orientation polarizability, µe and µg
are the dipole moments of the emissive and ground states, respectively and ε0 is the
permittivity of the vacuum. (µe-µg)2 is proportional to the slope of the Lippert -Mataga
12

plot.
Plots of the Stokes shifts as a function of the solvent polarity factor ∆f are shown in
Fig. 5. Only the data involving the aprotic solvents are shown because application of
this analysis with solvents where specific solute-solvent interactions are present is not
appropriate. As shown in Fig. 5, the Lippert-Mataga plot of L gave large slop which
infers larger dipole moment changes for L with photoexcitation. The slope of the
best-fit line is related to the dipole moment change between the ground and excited
states (µe-µg). The slope of L is -12318 cm-1. So the values of µe-µg were calculated as
18.68 D for dye L (eq 1). The large value of L indicates that the molecule in the
excited state has an extremely polar structure, corresponding with their linear and
nonlinear optical properties [41c].
According to the Lippert -Mataga plot, the excited-state has a larger dipolar
moment than the ground-state due to the charge redistribution, which is probably
derived from the relaxation of the initially formed Franck-Condon excited state.[41d]
Besides, the large dipole moment value of L (18.68 D) suggests that the ICT effect
may contribute to the synergistic electron donating ability of the
N,N-ethylaminostyryl group. The points of L in DMF are deviate from linearity,
indicating that the red-shift in DMF was contributed to the influence of the solvent
polarity[41e] as well as the great deviation from linearity of L is easier to combine
with proton, which is coincided with the large red-shift and the obviously reduce of
intensity in DMF.
3.3. Time resolved measurements
Time-resolved fluorescence measurements were performed and the detailed data of
the fluorescence decay curves of L are listed in Table 5. The experimental errors are
estimated to be 10% from sample concentrations and instruments. The lifetime of L
in six solvents is obtained by monitoring at the monomer emission. The decay
behavior of L is in a double-exponential manner in the solution obtained by
monitoring at the monomer emission. The lifetime of L is almost from the
contribution of the longer lifetime species. As shown in Table 5, the weighted mean
lifetime of L in THF (2.19 ns) is much longer than that of CH3CH2OH (0.74 ns),
13

CH3CN (1.20 ns), DMF (1.25 ns) and C6H6 (1.49 ns). This may be attributed to the
larger delocalization of the lone pair of electrons on S and N atom from L, leading to
a larger molecular stabilization effect for the excited state in THF. The long lifetime
indicates the existence of new aggregation species or excitonic couplings. [42a]
Additionally, the fluorescence lifetimes of L in solution was calculated by
multiplying the corresponding quantum yield on natural lifetime, which can be easily
calculated from the known Strickler-Berg equation (eqn. (1)) [42b] A calculated
fluorescence lifetime of 2.10 ns in CH2Cl2 was obtained, which is in excellent
agreement with the experimental value (2.14 ns) and further validate the experimental
time-resolved technique.
~
~
~
I(ν )dν
1
ε(ν )
∫
= 2.88×10−9 n2
~
dν
(1)
∫
~
−3
~ ~
~
τ 0
ν
I(ν )ν dν
∫
in which n is the refractive index, I is the fluorescence emission, ε is the extinction
~
coefficient, and
is the wave-number.
ν
The natural radiative lifetime τ0 and the fluorescence lifetime τ are related through
the quantum yield Φ by
τ
Φ =
(2)
τ 0
Interestingly, a short component had a decay lifetime of 0.24 ns (the corresponding
amplitude is 40.24%), and the following component had 1.07 ns (A = 59.76%) in
ethanol. The analysis revealed that there were two kinds of components in the excited
state and each component had its inherent FL lifetime [43]. However, the emission
spectrum showed only one peak. In the case of this point, the intense of the other band
should overlap the existing band or it appeared as a shoulder on the spectrum [44].
The lifetimes of L in THF is almost 3-fold than that of ethanol, and the rates of the
radiative (kr = Φ/τ) decay have been reduced almost by 3-fold, indicating that the
inducing of N, N-ethylaminostryryl group may greatly increased the ICT strength and
reduced the energy of the excited-state. Besides, the lifetime of L in CH2Cl2 is much
longer than that of in ethanol and CH3CN, indicating a much stable excited-state of L
14

in CH2Cl2. The extensive the π-system will increase both the kr and knr, which mainly
because of the photoisomerization and enhanced the excited-state energy level.
Except for the tunable fluorescence and decreased FL lifetime, the exciton-plasmon
interactions and energy transfer between L also resulted in dramatically optimization
on NLO activity, such as 2PA and TPEF.
3.3 Third-order nonlinear optical susceptibility:
Through the open- and close- Z-scan method [45], the sign and magnitude of the
second and third-order nonlinear optical (NLO) susceptibility of L was measured,
including the nonlinear refractive index (γ), nonlinear absorption coefficient (β), 2PA
cross section (δ) and third-order nonlinear optical susceptibility (χ(3)). For the
experiments, the pulse length was 140 fs, the repetition rate was kept at 10 Hz, and
the average laser power was 36 mW. The results were shown in Fig. 7. The
nonlinearity parameters for L was extracted and summarized in Table 6.
3.3.1 Open aperture Z-scan measurement:
Nonlinear absorption coefficient β was measured by open aperture Z-scan
technique. For the open aperture, the normalized transmittance as a function of the
position along the z axis can be written as formula (2)
[−q(z)]m
∞
βI0Leff
[1+(z / z0 )2 ]α
, where
(2)
Tz =
q(z) =
∑
m=0 (m +1)3/2
2
where z was the distance of the sample and beam focus, z0 = πω0 /λ was the diffraction
length of the beam with ω0 the spot size at focus, I0 was the intensity of the light at
focus, Leff was the effective length of the sample, α was the linear absorption
coefficient at the wavelength used [46]. The molecular TPA cross-section (δ) could be
determined by using the following relationship
δ = hυβ×10-3/NAd,
(3)
where h was the Planck’s constant, υ was the frequency of input intensity, NA was the
Avogadro constant, and d was the concentration of the sample.
Detailed experiments revealed that the 2PA cross sections changed over the excitation
15

wavelengths from 680 to 900 nm. Thus, by tuning the pump wavelengths
incrementally from 680 to 900 nm while keeping the input power fixed and then
recording the Z-scan intensity, the 2PA spectra were obtained which were shown in
Fig. 8. The best excitation wavelength (λ=780 nm) was slightly shorter than twice that
of the corresponding linear absorption maximum (448 for L in DMF). Based on the
equation (2) and (3), β of L was 0.4499 cm/GW, and δ was 18998 GM. However, we
should point out that there is still an observed difference in the absolute values of
two-photon cross sections (σ) obtained from the two techniques. The Z-scan method
yields σ directly from the experimental measurement, while the two-photon
fluorescence technique results in a quantity, two-photon excited action cross-section
(TPEACS), which is simply the product of absolute σ and the single-photon
fluorescence quantum efficiency. Thus, the δ values obtained by the Z-scan method
could be overestimated compared to those obtained by the two-photon excited
fluorescence method due to that no influence of fluorescence quantum yield was
considered in the measurement.[47]
The nonlinear refraction indexes of L were determined by the close aperture Z-scan
technique. The resulting data and fitted curve are shown in Fig. 9. The effective
third-order NLO susceptibility χ(3) of the sample can be calculated by the following
equations:[48]
−4
2
2
Reχ (3) =10 n0ε0c γ /π Im χ (3) = 10−2 n02ε0c2βλ / 4π 2
2
χ(3)
and
= )
(Reχ(3) )2 + (Imχ(3)
,
where ε0 is the vacuum permittivity, c is the light velocity in vacuum and n0 is the
linear refractive index of DMF. In this case, the third-order nonlinear refractive index
γ can be derived from the equations: [49]
∆Tpv = 0.406(1 − S)0.25 | ∆φ |
,
∆φ = KLeff γI0
In both equations, ∆Tpv is the difference between the peak and the valley of the
normalized transmission, S is the fraction of the transmitted beam through the
aperture, and ∆Φ is the on-axis phase shift, where ∆Tpv = 1.04 (L), K = 2π/λ. And then
the obtained γ and χ (3) are listed in Table 6.
From Table 6, it was observed that the values of third-order nonlinear optical
16

susceptibility of L versus the polarity of the different solvent show a nonmonotonic
dependence. We note here that L exhibit strong refractive index (γ ) and the real part
of the third-order nonlinear optical susceptibility (Re(χ(3)) in DCM. The drastic
solvatochromism can be explained by the effect that there is only two reactive
hydrogen atom in DCM due to the strong electron-withdrawing ability of the other
chlorine substituents. The possibility of forming hydrogen bonds between the solvent
(DCM) and solute molecules may further lower the excitation energy level.[51] To
our knowledge, this phenomenon has been scarcely reported up to now, and there
have been few theoretical studies to address the solvent effect.
Considering the high 2PA cross section and remarkable value of χ (3) due to highly
delocalized π-electronic configuration and large intrinsic polarizability, the
chromophore L could be a good candidate for third-order NLO materials. L belongs
to the D–π–A analogue since the N, N-ethylaminostryryl part possesses very strong
electron-donating character. Combining with pyrimidine enhances the
electron-acceptor character, converting L to a moderate polarized D–π–A unit going
forward ICT process which makes L having a strong third-order nonlinear optical
responses.
17

Fig. 6 The open and closed aperture Z-scan data of L in DMF. The filled squares
represent the experimental data and the solid curve is the theoretical data.
3.4. Two-photon absorption (TPA) and two-photon excited fluorescence (TPEF):
The previous experiments revealed that chromophore L has no linear absorption in
the range of 700-1000 nm, so if chromophore L is excited by light in the wavelength
range of 700-1000nm, it is impossible to produce single-photon excited up-converted
fluorescence. The logarithmic plots of the fluorescence integral versus input power
have slope of 2.10 as the input laser power is increased, suggesting a two-photon
excitation mechanism. As shown in Fig. 7, chromophore L displays 2PA activity in
the range of 720–880 nm in DMF. It can be seen from Table 3 that the fluorescence
peak wavelengths of chromophore L are evidently red-shift by 20 nm in comparison
with those of SPEF in DMF, which can be explained by the reabsorption effect. These
similarities between TPEF and SPEF indicate that both of the emissions for a given
dye are from the same excited state, though their initial Frank–Condon states may be
different[50].
The 2PA cross sections of chromophore L in different solvents (Fig. 8) show that
the largest 2PA cross sections of chromophore L in various solvents are all located at
840nm, and chromophore L has the largest 2PA cross section in acetonitrile
(2010GM), also very large value in DMF (1473GM) at the wavelength of 840nm.
Obviously, the polarity of the solvent and the excitation wavelength has significant
18

influence on the two-photon absorption cross section. Comparing to the previous
chromophores derived from pyrimidine[34, 52], small changes in the structure may
have important implications in terms of molecular engineering for specific
applications, because the 2PA properties (in terms of cross sections, position of the
maximum, and bandwidth), as well as the one photon and the photoluminescence
characteristics can be affected considerably. Thus, it becomes possible to optimize the
transparency/2PA efficiency and the fluorescence/2PA efficiency trade-off. With these
findings, the novel chromophore L bearing the pyrimidine group as a
electron-acceptor, N, N-diethylamino groups as donors, as well as modified with
thiophene unit exhibits much larger two-photon cross sections located the near IR
region in high polar solvent, which promote us to further study its potential
application in bioimaging.
Fig. 7 The two-photon excited fluorescence spectra of chromophore L (Excitation
wavelength at 800nm, energy of 300mW, C = 2.0 × 10-4 mol·L-1) in different solvents.
Insert Fig.: Output fluorescence ( Iout ) vs. the square of input laser ( Iin ) for
chromophore L.
19

Fig. 8 Two-photon absorption cross sections of chromophore L in different solvents
vs excitation wavelengths of identical energy of 300mW, C = 2×10-4 mol·L-1)
2.4. Cell image and cytotoxicity assay
Considering the dyes’ application in TPEF imaging, an MTT assay was performed
to ascertain the cytotoxic effect of chromophore L against HepG2 cells over a 24 h
period. Cytotoxicity is a potential side effect of the dyes that must be controlled when
dealing with living cells or tissues. Fig. 9 shows the cell viability for HepG2 cells
treated with chromophore L at different concentrations for 24 h. The results clearly
indicated that HepG2 cells incubated with concentration of 5 mM of chromophore L
remained 80% viable after 24 h of feeding time, demonstrating the superior
biocompatibility of chromophore L. In addition, it was found that a high
concentration only leads to a gradual decrease of viable cells as shown in Fig. 9. As a
result, cytotoxicity tests definitely indicate that low-micromolar concentrations of
chromophore L have small toxic effects on living cells over a period of 24 h, and L
has great potential for further biological studies.
As pyrimidine group has relatively low toxicity toward live cells, chromophore L
was picked out which exhibit high quantum yield, large 2PA cross-section and long
fluorescent lifetime. Fluorescent images of confocal microscopy and two-photon
20

microscopy of HepG2 cells labeled with chromophore L were captured. Chromophore
L was first dissolved in DMSO to 2mM, then diluted by PBS (phosphate buffer
solution) to 40 µM. HepG2 cells incubated with 40 µM of chromophore L, in growth
media at 37 οC, 5% CO2 for 2 h, then washed by PBS and directly moved to confocal
laser scanning microscopy without fixation.
Our initial confocal microscopy studies reveal that chromophore L with functions
as a luminescent cellular DNA stain for HepG2 cells being successfully taken up by
live cells and clearly emerges from cellular cytoplasm (Fig. 10(a) and (b)); we
presume that the luminescence from punctuate bright dots outside the nuclei region is
because of the aggregation of the complex inside the cell cytosol. This result
demonstrates that the observed cell cytosol uptake must be due to the presence of the
intact chromophore L. To further demonstrate the potential applications of
chromophore L for two photon microscopy (TPM) imaging in living cells, HepG2
cells were cultured and stained with chromophore L. The results showed that
chromophore L is clearly capable of detecting the cytoplasm section in HepG2 cells
(Fig. 10(c)).
Fig. 9 MTT assay of HepG2 cells treated with chromophore L at different
concentrations for 24 h.
21

Fig. 10 (a) Bright-field image of HepG2 cells. (b)One-photon image of HepG2 cells
incubated with 10 µM chromophore L after 20 min of incubation, washed by PBS
buffer. λex = 330 nm (emission wavelength from 579-670 nm). (c) Two-photon
image of HepG2 cells incubated with 10 µM chromophore L after 30 min of
incubation, washed by PBS buffer. λex = 760 nm (emission wavelength from
539-590nm). (d) The overlay of (a) to (c). Scale bars represent 10 µm.
4. Conclusion
This systematic study of the simple preparation, absorption, photoluminescence,
two-photon-absorption properties, including two- photon fluorescence, two-photon
absorption cross section (δ), two-photon absorption coefficient (β), nonlinear
refractive index (γ) and third-order nonlinear optical susceptibility χ(3), crystal
structures, and theoretical calculation on a novel bent-shaped pyrimidine
chromophore L were carried out, which allowed us to draw structure-property
relationships for both spectral tuning and amplification of the molecular 2PA in the
NIR spectral range. An increased dipole-dipole interaction between the solute and
solvent molecules resulted in red-shift of absorption and photoluminescence. The
strong couple effects further brought about energy transfer in the whole molecule,
which also resulted in quenching of fluorescence and reduced FL lifetime.
Low-micromolar concentrations of L were tested showing no obvious toxic effect in
imaging HepG2 cells. Moreover, 2PFM bioimaging was also demonstrated that L
offered good biological effect due to its excellent biocompatibility and low toxicity.
The advantages make the L to be fluorogenic detection, two-photon absorption
molecule being capable of sensing activities. Further work will focus on the extension
of this novel strategy to the imaging of other classes of pyrimidine. We are however
22

enthusiastic that, in future, class and specific small molecule probes based on L may
be discovered.
Acknowledgments
This work was supported by a grant for the National Natural Science Foundation
of China (21271004, 21071001, 51372003, 21201005, 21275006), the Natural
Science Foundation of Anhui Province (1208085MB22). Ministry of Education of
China Funded Projects Focus on returned overseas scholar.
References
[1] G.S. He, L.S. Tan, Q.D. Zheng, P. N. Prasad. Chem. Rev. 108 (2008) 1245.
[2] P.C. Ray. Chem. Rev. 110 (2010) 5332.
[3] S. Ellinger, K.R. Graham, P. Shi, R.T. Farley, T.T. Steckler, R.N. Brookins, et al.
Chem. Mater. 23 (2011) 3805.
[4] S.Sumalekshmy, C.J. Fahrni, Chem. Mater. 23 (2011) 483.
[5] Y.M. Yang, Q. Zhao, W. Feng, F.Y. Li. Chem. Rev. 113 (2013) 192.
[6] K.T. Yong, J. Qian, I. Roy, H.H. Lee, E.J. Bergey, K.M. Tramposch. Nano. Lett. 7
(2007) 761.
[7] C. Coenjarts, O. Garci′a, L. Llauger, J. Palfreyman, A.L. Vinette, J.C. Scaiano. J.
Am. Chem. Soc. 125 (2003) 620.
[8] C.O. Yanez, C.D. Andrade, S. Yao, G. Luchita, M.V. Bondar. Appl. Mater.
Interfaces. 1 (2009) 2219.
[9] C.C. Corredor, Z.L. Huang, K.D. Belfield, A.R. Morales, M.V. Bondar. Chem.
Mater. 19 (2007) 5165.
[10] A.S. Dvornikov, E.P. Walker, P.M. Rentzepis. J. Phys. Chem. 113 (2009) 13633.
[11] S.J. Jhaveri, J.D. McMullen, R. Sijbesma, L.S. Tan, W. Zipfel , C.K. Ober. Chem.
Mater. 21 (2009) 2003.
[12] W.H.Zhou, S.M. Kuebler, K.L. Braun, T.Y. Yu, J.K. Cammack, C.K. Ober, J.W.
Perry, S.R. Marder. Science. 296 (2002) 1106.
[13] X. Zhong, M.L. Zheng, X.Z. Dong, W.Q. Chen, F. Jin, Z.S. Zhao and X.M. Duan.
Soft. Matter. 7 (2011) 10353.
23

[14] J.J. Jasieniak, I. Fortunati, S. Gardin, R. Signorini, R. Bozio, A. Martucci and P.
Mulvaney. Adv. Mater. 20 (2008) 69.
[15] L. Beverina, M. Crippa, M. Landenna, R. Ruffo, P. Salice, F. Silvestri, S. Versari,
A. Villa, L. Ciaffoni, E. Collini, C. Ferrante, S. Bradamante, C.M. Mari, R. Bozio
and G.A. Pagani. J. Am. Chem. Soc. 130 (2008) 1894.
[16] J.A. Bilbrey, S.K. Sontag, N.E. Huddleston, W.D. Allen and J. Locklin. ACS.
Macro. Lett. 1 (2012) 995.
[17] Q.Q. Shi, W.Q. Chen, J.F. Xiang, X.M. Duan, X.W. Zhan. Macromolecules. 44
(2011) 3759.
[18] Z.P. Yu , Y.Y. Duan, L.H. Cheng, Z.L. Han, Z. Zheng, H.P. Zhou, J.Y. Wu and Y.P.
Tian. J. Mater. Chem. 22 (2012) 16927.
[19] R.R. Hu, J.L. Maldonado, M. Rodriguez, C. Deng, C.K.W. Jim, J.W.Y. Lam,
M.M.F. Yuen, G. Ramos-Ortiz and B.Z. Tang. J. Mater. Chem. 22 (2012) 232.
[20] Y.H. Gao, J.Y. Wu, Y.M. Li, P.P. Sun, H.P. Zhou, J.X. Yang, S.Y. Zhang, B.K. Jin
and Y.P. Tian. J. Am. Chem. Soc. 131 (2009) 5208.
[21] D.M. Li, X.H. Tian, G.J. Hu, Q. Zhang, P. Wang, P.P. Sun, H.P. Zhou, X.M. Meng,
J.X. Yang, J.Y. Wu, B.K. Jin, S.Y. Zhang, X.T. Tao and Y.P. Tian. Inorg. Chem. 50
(2011) 7997.
[22] X.C. Wang, X.H. Tian, Q. Zhang, P.P. Sun, J.Y. Wu, H.P. Zhou, B.K. Jin, J.X.
Yang, S.Y. Zhang, C.K. Wang, X.T. Tao, M.H. Jiang and Y.P. Tian. Chem. Mater.
24 (2012) 954.
[23] D.J. Schipper, K. Fagnou. Chem. Mater. 23 (2011) 1594.
[24] F. Terzi, L. Pasquali, M. Montecchi, S. Nannarone, A. Viinikanoja, T. Aäritalo, M.
Salomäki, J. Lukkari, B. Doyle and R. Seeber. J. Phys. Chem. 115 (2011) 17836.
[25] S.V. Rocha and N.S. Finney. J. Org. Chem. 78 (2013), 11255.
[26] A.B. Nepomnyashchii, R.J. Ono, D.M. Lyons, J.L. Sessler, C.W. Bielawski, A.J.
Bard. J. Phys. Chem. Lett. 3 (2012) 2035.
[27] P. Hammarström, R. Simon, S. Nyström, P. Konradsson, A. Åslund and P.R.
Nilsson . Biochemistry. 49 (2010) 6838.
[28] A. Mishra, C.Q. Ma, P. Bäuerle. Chem. Rev. 109 (2009) 1141.
24

[29] L. Krudenier, C.W. Chung, Z.J. Cheng, J. Liddle, K.H. Che. Nature. 488 (2012)
404.
[30] A. Rustighi, M.A. Tessari, F. Vascotto, R. Sgarra, V. Giancotti and G. Manfioletti.
Biochemistry. 41 (2002) 1229.
[31] Y. Tanaka, S. Oda, H. Yamaguchi, Y.C. Kondo, C. Kojima and A. Ono. J. Am.
Chem. Soc. 129 (2007) 244.
[32] B. Liu, H.L. Zhang, J. Liu, Y.D. Zhao, Q.M. Luo, Z.L. Huang. J. Mater. Chem.
17 (2007) 2921.
[33] B. Liu, H.L. Zhang, J.Liu, Y.D. Zhao, Q.M. Luo, Z.L. Huang. Tetrahedron.
Letters. 48 (2007) 5958.
[34] L.Li, Y.P. Tian, J.X. Yang, P.P. Sun, J.Y. Wu, H.P. Zhou, S.Y. Zhang, B.K. Jin, X.J.
Xing, C.K. Wang, M. Li, G.H. Cheng, H.H. Tang, W.H. Huang, X.T. Tao and
M.H. Jiang. Chem. Asian. J. 4 (2009) 668.
[35] K. Zhao, Y. Luo. J. Phys. Chem. B. 114 (2010) 13167.
[36] J.N. Demasa, G.A. Crosby. J. Phys. Chem. 75 (1971) 991.
[37] J. Olmsted. J. Phys. Chem. 83 (1979) 2581.
[38] R. Signorini, C. Ferrante, D. Pedron, M. Zerbetto, E. Cecchetto, M. Slaviero, I.
Fortunati, E. Collini, R. Bozio, A. Abbotto, L. Beverina and G.A. Pagani. J. Phys.
Chem. A. 112 (2008) 4224.
[39] (a) O. Varnavski, T. Goodson III, L. Sukhomlinov, R. Twieget. J. Phys. Chem. B.
108 (2004) 10484. (b) C. Tang, Q. Zhang, D.D. Li, J. Zhang, P.F. Shi, S.L.Li,
J.Y. Wu and Y.P. Tian. Dyes and Pigments. 99 (2013) 20.
[40] X.M. Wang, F. Jin, Z.G. Chen, S.Q. Liu, X.H. Wang, X.M. Duan, X.T. Tao and
M.H. Jiang. J. Phys. Chem. C. 115 (2011) 776.
[41] (a) S.A. Patel, M.Cozzuol, J.M. Hales, C.I. Richards, M. Sartin, J.C. Hsiang, T. Vosch, J. W.
Perry and R.M. Dickson. J. Phys. Chem. C. 113 (2009) 20264. (b) S.M. Ji, J. Yang, Q. Yang,
S.S. Liu, M.D. Chen, J.Z. Zhao. J. Org. Chem. 74 (2009) 4855. (c) M. Irie, K. Sayo. Solvent
J. Phys. Chem. 96 (1992) 7671. (d) W.Z. Yuan, Y.Y. Gong, S.M. Chen, X.Y. Shen, J.W.Y.
Lam, P. Lu, Y.W. Lu, Z.M. Wang, R.R. Hu, N. Xie, H.S. Kwok, Y.M. Zhang, J.Z. Sun and
B.Z. Tang. Chem. Mater. 24 (2012) 1518. (e) A.W. White, R. Almassy, A.H. Calvert, N.J.
25

Curtin, R.J. Griffin, Z. Hostomsky, K. Maegley, D.R. Newell, S. Srinivasan and B.T. Golding.
J. Med. Chem. 43 (2000) 4084.
[42] (a) Z. Zheng, Z.P. Yu, M.D. Yang, F. Jin, Q. Zhang, H.P. Zhou, J.Y. Wu and Y.P. Tian. J. Org.
Chem. 78 (2013) 3222. (b) S.J. Strickler, R.A. Berg. J. Chem. Phys. 37 (1962) 814.
[43] S. Murphy, L.B. Huang, P.V. Kamat. J. Phys. Chem. C. 115 (2011) 22761.
[44] L. Kong, J.X. Yang, H.P. Zhou, S.L. Li, F.Y. Hao, Q. Zhang, Y.L. Tu, J.Y. Wu,
Z.M. Xue and Y.P. Tian. Sci. China. Chem. 56 (2013) 106.
[45] D.M. Li, Q.Z. Wang, J.Y. Wu, Y.H. Kan, Y.P. Tian, H.P. Zhou, J.X. Yang, X.T.
Tao and M.H. Jiang. Dalton. Trans. 40 (2011) 8170.
[46] T. Geethakrishnan, P.K. Palanisamy. Opt. Commun. 270 (2007) 424.
[47] Z.Q. Ji, Y.J. Li, T.M. Pritchett, N.S. Makarov, J.E. Haley, Z.J. Li, M. Drobizhev,
A. Rebane and W.F. Sun. Chem. Eur. J. 17 (2011) 2479.
[48] (a) J.F. Ge, Y.T. Lu, R. Sun, J. Zhang, Q.F. Xu, N.J. Li, Y.L. Song, J.M. Lu. Dyes
and Pigments 91 (2011) 489; (b) J. Mattu, T.G. Johansson, W.J. Leach. Phys. Chem.
C. 111 (2007) 6868.
[49] (a) T. Xia, D.J. Hagan, M. Sheik-Bahae, E.W. Van Stryland. Opt. Lett. 19 (1994)
317; (b) I.L. Bolotin, D.J. Asunskis, A.M. Jawaid, Y.M. Liu, P.T. Snee, L. Hanley. J.
Phys. Chem. C. 114 (2010) 16257.
[50] Z. Zheng, Q. Zhang, Z.P. Yu, M.D. Yang, H.P. Zhou, J.Y. Wu and Y.P. Tian. J.
Mater. Chem. C. 1(2013) 822.
[51] Y.X. Yan, H.H. Fan, Y.H. Guo, C.K. Lam, H. Huang , Y.H. Sun, L. Tian, C.K.
Wang, Y.P. Tian, H.Z. Wang and X.M. Chen. Materials Chemistry and Physics 101
(2007) 329.
[52] (a) L. Li, Y.P. Tian, J.X. Yang, P.P. Sun, L. Kong, J.Y. Wu, H.P. Zhou, S.Y. Zhang,
B.K. Jin, X.T. Tao and M.H. Jiang. Chem. Commun. 46 (2010) 1673. (b) Z.J. Liu, T.
Chen , B. Liu , Z.L. Huang, T. Huang, S.Y. Li, Y.X. Xu and J.G. Qin. J. Mater. Chem.
17 (2007) 4685. (c) D.G. Chen, C.Zhong, X.H. Dong, Z.H. Liu, J.G. Qin. J. Mater.
Chem. 22 (2012) 4343.
26

Table 5. Fluorescence quantum yield and fluorescence lifetime of L in five solvents.
λdeta (nm)
<τ>d(ns)
1.49
c
c
solvents
τ 1b (ns)
0.69
A
1
τ 2b (ns)
1.56
A
2
χ2
7.74
6.63
92.26
93.37
97.02
59.76
78.89
74.19
1.00
1.03
1.01
1.17
1.21
1.28
C6H6
CH2Cl2
THF
490
534
520
556
554
554
1.00
2.18
2.10
1.03
2.98
2.22
2.19
0.24
40.24
21.11
25.81
1.07
0.74
CH3CH2OH
CH3CN
DMF
0.34
1.44
1.20
0.39
1.55
1.25
aDetection wavelength. bFluorescence lifetime. cFractional contribution. dWeighted
mean lifetime.
Table 6. Third-order NLO data for L in five solvents.
L
C6H6
0.449
18998
3.79
DCM
0.451
19125
9.15
THF
0.455
19082
8.47
EtOH CH3CN
DMF
β (cm GW-1)
σ (GM)
0.451
19252
3.15
0.452
19082
6.86
0.449
18998
6.69
γ (10-16 m2 W-1)
Re(χ(3))
1.97
4.75
4.40
1.63
3.56
3.47
(10-14esu)
Im(χ(3))
1.45
1.45
1.47
1.45
1.46
1.45
(10-8esu)
χ
(3) (10-8esu)
1.45
1.45
1.47
1.45
1.46
1.45
β:nonlinear absorption coefficient. σ:2PA cross-section. γ:an effective third-order nonlinear
refractive index. Re(χ(3)) :Nonlinear polarizability of real component. Im(χ(3)) :Nonlinear
polarizability of imaginary part. χ(3):the effective third-order NLO susceptibility.
27

Highlights
A novel D-π-A-π-D type thiophene pyrimidine derivative (L) was obtained.
The single crystal of L belongs to P212121 non-centrosymmetric space group, which
exhibits a good coplanarity.
L shows strong third-order nonlinear optical response and its preliminary exploration
in biological imaging has been carried out.
28

Graphic Abstract
29