Two novel terpyridine-based chromophores with donor-acceptor structural model containing modified triphenylamine moiety: Synthesis, crystal structures and two-photon absorption properties

Article abstract of DOI:10.1007/s11426-013-4940-7

Two novel terpyridine-based chromophores with D-A (D = donor, A = acceptor) structural model containing modified triphenylamine moiety (L ¹ and L ² ) have been conveniently synthesized via formylation and reduction in satisfactory yi

Full text of DOI:10.1007/s11426-013-4940-7

SCIENCE CHINA
Chemistry
doi: 10.1007/s11426-013-4940-7
•
ARTICLES •
January 2013 Vol.56 No.1: 1–10
doi: 10.1007/s11426-013-4940-7
Two novel terpyridine-based chromophores with donor-acceptor
structural model containing modified triphenylamine moiety:
Synthesis, crystal structures and two-photon
absorption properties
1
1
2
1
1
LIU Jie , ZHANG Qiong , DING HongJuan , ZHANG Jun , TAN JingYun ,
2
1*
1
1
WANG ChuanKui , WU JieYing , LI ShengLi , ZHOU HongPing ,
1
1,3*
YANG JiaXiang & TIAN YuPeng
1
Department of Chemistry, Key Laboratory of Functional Inorganic Material Chemistry of Anhui Province,
Anhui University, Hefei 230039, China
2
Department of Physics, Shandong Normal University, Jinan 250014, China
3
State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, China
Received May 15, 2013; accepted June 5, 2013
Two novel terpyridine-based chromophores with D-A (D = donor, A = acceptor) structural model containing modified tri-
1
2
phenylamine moiety (L and L ) have been conveniently synthesized via formylation and reduction in satisfactory yields, and
fully characterized. The single crystals of them were obtained and determined by X-ray diffraction analysis. The relationships
between structure and photophysical properties of the two chromophores were investigated both experimentally and theoreti-
cally. The measured maximum TPA cross-sections per molecular weight (max/MW) of the chromophores are 0.63 GM/(g mol)
1
2
(
L ) and 0.72 GM/(g mol) (L ), respectively, in DMF as a high polar solvent. The results indicate that the value of max/MW
could be well tuned by the intramolecular charge transfer (ICT), which could be realized by introducing additional elec-
tron-donor/acceptor groups.
terpyridine derivatives, photophysical properties, structure-property relationships, TD-DFT calculation, two-photon-
excited fluorescence
1
Introduction
[7, 14, 15], photodynamic therapy [16–18], two-photon
up-conversion lasing [19, 20] and optical power limiting
[
21–23].
Along with the aforementioned promising applications,
The two-photon absorption (TPA) process was theoretically
predicted by Maria Göppert-Mayer [1] in the 1931, and first
experimentally proved after the appearance of laser sources
in 1961 [2]. Since then, its practical significance has been
recognized by pioneering efforts. Significant advances have
been made in a great variety of potential applications in the
areas of three-dimensional (3D) optical storage [3–6], multi-
photon fluorescence imaging [7–13], 3D micro-fabrication
efforts are also focused on designing and synthesizing new
materials with striking TPA effect and large TPA cross-
section (TPA) values. Up to now, several strategies [2430]
have successfully been employed to achieve the aim, such
as enhancing the amount of branches, expanding the effec-
tive length of conjugation, improving ICT efficiency,
changing the strength of the donor and acceptor, and/or in-
creasing the planarity of the  center and so on. Although
*
Corresponding author (email: jywu1957@163.com; yptian@ahu.edu.cn)
©
Science China Press and Springer-Verlag Berlin Heidelberg 2013
chem.scichina.com www.springerlink.com

2
Liu J, et al. Sci China Chem January (2013) Vol.56 No.1
most organic molecules with strong TPA effect have been
synthesized, the reaction routes may be long, complex, and
inevitably the target compounds may be obtained in low
yields. Moreover, there exists another important problem
concerning comparison of nonlinear absorption efficiency
among disparate types of chromophores with different mo-
lecular weight, molecular volume, financial cost-scaling and
the number of effective electronic distribution for the bene-
fit of TPA effect, etc [31–33]. Therefore, it is challenging
for us to develop materials with large TPA which are based
on a relatively reasonable approach to scale NLO data, in
addition to facile synthesis and high yields.
mentally and theoretically.
2
Experimental
2
.1 Materials and apparatus
All chemicals were purchased as analytical grade and used
without further purification. The solvents were purified by
conventional methods. Mass spectrum was determined with
a Micro-mass GCT-MS (EI source). IR spectra were rec-
orded on NEXUS 870 (Nicolet) spectrophotometer in the
1
4000–400 cm region with samples prepared as KBr pellets.
1
13
Based on the aforementioned considerations, we de-
signed two novel D-A structural chromophores with tri-
phenylamine moiety as the electron donor (D) and
H- and C-NMR spectra were obtained on a Bruker
Avance 400 MHz spectrometer at 25 °C (TMS as internal
standard in NMR).
2
,2′:6′,2″-terpyridine, as the acceptor (A). The building
X-ray diffraction data of single crystals were collected on
a CCD diffractometer. The determination of unit cell pa-
blocks of triphenylamine and terpyridine always employed
to construct TPA chromophores [34, 35]. Apart from that,
we have other important reasons for the selection of the two
chromophores: (1) it is apparent that the route used is more
simpler, and higher yield can be achieved at almost every
step; (2) the properties of the chromophores (L and L pre-
sented in Figure 1) TPA will be relatively accurate com-
pared by TPA cross-section per molecular weight (max/MW)
owing to their almost approximate molecular volume and
production costs; (3) the subtle structural modifications only
appear at the terminal of the triphenylamine moiety in the
molecular skeleton, which will lead to increase of the TPA
across section values.
rameters and data collection were performed with Mo-K

radiation ( = 0.71073 Å). Unit cell dimensions were ob-
tained with least-squares refinements, and all structures
were solved by direct methods using SHELXS-97 [36]. The
other non-hydrogen atoms were located in successive dif-
ference Fourier syntheses. The final refinement was per-
1
2
formed by full-matrix least-squares methods with aniso-
2
tropic thermal parameters for non-hydrogen atoms on F
.
The hydrogen atoms were added theoretically riding on the
concerned atoms.
UV-vis absorption spectra were recorded on a UV-265
spectrophotometer. Fluorescence measurements were per-
formed at room temperature using a Hitachi F-7000 fluo-
rescence spectrophotometer. The fluorescence quantum
The two target chromophores were synthesized via
formylation and aldehyde group reduction starting from

4′-(4-(diphenylamino)phenyl)-2,2′:6′,2″-terpyridine, as illus-
yields ( ) were determined against the quinine sulfate
trated in Scheme 1. Their photophysical properties, such as
linear absorption, single- and two-photon excited fluores-
cence in various solvents, were systematically studied. Fur-
thermore, the connections between the structure and proper-
ties of the chromophores were investigated both experi-
standard. 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. With excitation at
the optimal excitation wavelength (ex-max), time-resolved
decay curves were performed on fluotime200 (Pico Quant)
using a time-correlated single-photon counting (TCSPC)
2 2
technique. SiO nanocrystals in H O sample were used as an
IRF reference for the lifetime reconvolution.
2
.2 Synthesis
2
.20.1 4′-(4-(4,4-Diphenylamino)-phenyl-2,2′:6′,2″-terpyridine
(L )
0
1
2
Figure 1 Molecules of dye L and dye L .
L was synthesized according to a previously reported
1
2
Scheme 1 Synthetic routes for two dyes L -L .

Liu J, et al. Sci China Chem January (2013) Vol.56 No.1
3
method [37].
for the desired yield. Using NaBH
4
as the reductive, the
2
final chromophore L was almost quantitatively achieved by
1
2
2
.2.2 4′-(4-(4-phenyl-4′-aldehydicphenyl) amino) phenyl-
,2′:6′,2″-terpyridine (L )
the reduction of L . In conclusion, the two novel dyes could
1
be conveniently synthesized in high yields.
At ice salt bath temperature, POCl (2.1 g, 13.7 mmol) was
3
added dropwise to a three-necked flask containing DMF
3
.2 Crystal structures
0
(
1.0 g, 13.7 mmol). After the frozen salt appeared, L (0.5 g,
1
3
mmol) dissolved in CHCl (50 mL) was added, and then
The crystallographic data, selected bond lengths and angles
0
1
2
refluxed for 24 h. After cooled to room temperature, the
mixture was poured into a large amount of ice water and
adjusted to pH = 8 using NaOH. After extracting with
for L , L and L are summarized in Table 1 and Table S1.
1
2
The crystal structures of L and L are shown in Figures 2
and 3, respectively. To illustrate the conformation of them,
parameters P1-P6 are presented in Table 2.
2 2 2 4
CH Cl , the mixture was dried over anhydrous Na SO and
evaporated to yield a yellow solid. The solid was purified by
silica gel chromatography column using petroleum/ethyl
3
.2.1 Similarities of their structures
1
acetate (5/1 V/V) as the eluent with 76% yield (0.40 g).
It can be seen that the terpyridyl group as an acceptor in L
1
2
0
H-NMR (400 MHz, CDCl
3
, TMS),  (ppm): 9.88 (s, 1H),
and L is coplanar like that of L , in which the dihedral an-
0
8
7
7

1
1
1
.99–8.87 (m, 6H), 8.15–8.05 (m, 4H), 7.77–7.75 (d, 2H),
.58–7.58 (d, 2H), 7.33–7.31 (d, 2H), 7.24–7.22 (m, 3H),
.16–7.14 (d, 2H). C-NMR (100 MHz, CDCl , TMS),
3
(ppm): 190.48, 156.13, 155.91, 152.97, 149.44, 149.06,
47.12, 146.01, 136.99, 134.61, 131.34, 129.87, 129.76,
28.65, 126.44, 125.76, 125.40, 123.90, 121.40, 120.36,
18.61. MS, m/z (%): 504.20 (100).
gles are given in Table 2. Another same structural unit in L ,
1
2
2
L and L is the triphenylamine as a donor. Due to the sp
1
3
0
1
2
Table 1 Crystal data collection and structure refinement of L , L and L
0
a)
1
2
Compound
Chemical formula
Formula weight
Crystal system
Space group
a(Å)
L
L
L
C
32
H
24
N
4
C
34
H
24
N
4
O
34 26 4
C H N O
476.57
504.57
Monoclinic
P2 /c
506.60
Orthorhombic
P2
2
.2.3
4′-(4-(4-phenyl-4′-hydroxymethyl phenyl) amino)
Triclinic
Pī
2
phenyl-2,2′:6′,2″-terpyridine (L )
1
1 1 1
2 2
1
9.298(5)
11.366(5)
12.783(5)
107.334(5)
98.911(5)
98.521(5)
1246.7(10)
2
14.493(5)
10.074(5)
18.050(5)
90.000(5)
101.068(5)
90.000(5)
2586.30(17)
4
14.899(5)
26.354(5)
7.292(5)
90.000(5)
90.000(5)
90.000(5)
2863(2)
4
Chromophore L (0.5 g, 1.0 mmol) was dissolved in 150
b(Å)
mL EtOH. Then 0.19 g (5.0 mmol) NaBH
ed as a solid. The reaction flask was placed in an oil bath at
0°C. The reaction was monitored by TLC. After the com-
4
was slowly add-
c(Å)
o



( )
8
o
( )
pletion of the reaction, the solvent was removed under re-
duced pressure. The solid was recrystallized from EtOH.
o
( )
3
V(Å )
2
After filtration and drying under vacuum, L was obtained
Z
1
as a slightly yellow solid. Yield 91.6% (0.46 g). H-NMR
R
1
, wR
2
(I2(I))
(all data)
0.0428, 0.0980 0.0391, 0.0925 0.0481, 0.0943
0.0676, 0.1159 0.0601, 0.1059 0.0861, 0.1123
(
400 MHz, CDCl , TMS),  (ppm): 8.74–8.67 (m, 4H),
R
1
, wR
2
3
2
8
7
5
.69–8.67 (d, 2H), 7.92–7.88 (t, 2H), 7.82–7.80 (d, 2H),
Goodness-of-fit on F
0.970
0.994
0.983
.38–7.35 (m, 2H), 7.32–7.29 (m, 4H), 7.20–7.15 (m, 6H),
a) Crystal data cited from the Ref. [30].
1
3
3
.29 (s, 1H), 4.67 (s, 2H). C-NMR (100 MHz, CDCl ,
TMS),  (ppm): 156.23, 155.70,149.76, 148.97, 148.71,
1
1
1
47.29, 146.93, 137.02, 135.80, 131.85, 129.41, 128.37,
28.18, 124.85, 124.71, 123.81, 123.50, 123.16, 121.43,
18.39, 65.05. MS, m/z (%): 506.40 (100).
3
Results and discussion
3
.1 Synthesis
1
The synthetic route toward the D-A target ligands (L and
2
0
L ) is depicted in Scheme 1. L was obtained by the
Ullmann condensation according to the previously reported
1
method. Through the Vilsmeier-Haack reaction, L was
synthesized with the 76% yield. Owing to the influence of
the electron withdrawal and space baffle existing in the
0
chromophore L , it is necessary to increase the reactant ratio
0
1
for L , DMF and POCl
3
, and to prolong the reaction time
Figure 2 Crystal structure of L (hydrogen atoms are omitted for clarity).

4
Liu J, et al. Sci China Chem January (2013) Vol.56 No.1
0
that, the dihedral angle of P6 decreases from 64.82° (L ) to
,0
1
3
1.00° (L ).
Compared with L ,
–CH OH), a weaker electron-donor group (EDG), is intro-
1
a
hydroxymethyl substituent
(
2
2
duced to the triphenylamine moiety in L . Interestingly, the
subtle modification also leads to several differences as fol-
lows. (1) It is found that the crystal system and space group
2
of L are orthorhombic and P2
1
2
1
2
1
, respectively. (2) The
bond length of C(31)–C(34) (1.50 Å) is slightly longer than
1
3
that of C(31)–C(34) in L , which may result from the sp
hybrid of C atom in the –CH OH unit. (3) The dihedral an-
gle of P6,0 increases to 53.59°, due to the plane of P ′ with-
out well delocalization with the adjacent N atom, which is
2
0
1
1
3
1.00° in L . (4) The bond length of N(4)–C(28) in L is
2
shorter than that in L .
3
.3 Linear absorption and single-photon exited fluo-
rescence (SPEF)
2
Figure 3 Crystal structure of L (hydrogen atoms are omitted for clarity).
3
.3.1 Linear absorption properties
0
1
0
1
2 a)
Table 2 Conformational parameters for L , L and L
The photophysical data of the three chromophores (L , L
and L ) are summarized in Table 3. The linear absorption of
2
0
1
2
Compound
L
L
L
the chromophores in seven different solvents with the con-
P
P
P
P
P
P
6,0
6,1
6,2
2,3
3,4
3,5
64.82°
49.36°
29.47°
32.50°
4.16°
31.00°
50.17°
40.02°
36.74°
6.44°
53.59°
26.43°
35.23°
25.91°
4.95°
centration of 1.0×10 mol L is shown in Figures 4 and S1,
5
1
respectively.
0
From those absorption spectra, it is apparent that L and
2
1
L exhibit dual bands in the 270–450 nm range, while L
6.79°
11.48°
5.38°
displays three bands in the same region. The longer wave-
length band at about 350–370 nm is attributed to ICT transi-
a) P6,0 represens the dihedral angles between P
6
and P
0
, and so on.
*
tion or → transition of the whole molecule for the
0
1
2
chromophores L , L and L , while the shorter wavelength
band near 290 nm is attributed to the absorption of the tri-1
phenylamine moiety. Additionally, a shoulder band of L
also appeared at about 335 nm, which is consistent with the
crystal structural feature above. This band is assigned to the
hybrid of the central nitrogen atom of triphenylamine moi-
ety, the nitrogen and its three adjacent carbon atoms are
approximately coplanar (named as the P6 plane), with the
sum of the three C–N–C angles (360.0°) and almost the
same C–N bond length. However, the three phenyl ring
planes are arranged in a propeller-like fashion owing to
space repulsion among the phenyl rings, thus avoiding
molecule aggregation, and resulting in a highly soluble
amorphousness.
*
π orbital electron of the aldehyde group transition to the π
orbit of the whole molecule because the values of the max-
imum molar extinction coefficient (max) are all more than
4
−1
−1
2.0×10 mol L cm in different selected solvents. As
shown in Figures 4 and S1, little solvatochromism was ob-
served by increasing the solvent polarity, indicating that the
little difference in dipoles between the ground and excited
state of the chromophores was observed in spite of periph-
eral solvents’ polarity. Another feature is that the maximum
0
-2
3
.2.2 Differences between the crystal structures of L
0
1
Compared with the crystal structures between L and L ,
there is an aldehyde group (–CHO), a medium electron
withdrawing group (EWG), attached to the triphenylamine
1
2
absorption bands of L and L are red-shifted by 12 nm and
1
0
moiety in L , resulting in their structural changes, presented
3 nm, respectively, relative to that of L at 356 nm in ethyl
in Tables 1, 2 and S1. The differences between them are
concluded as follows. (1) They belong to two crystal sys-
tems, triclinic and monoclinic, and two space groups, Pī and
acetate solvent. The results reveal that introducing different
units to the triphenylamine group can influence the elec-
tron-donating ability of it. Furthermore, the different elec-
tron-donating ability may influence the bandgap of the in-
tramolecular charge-transfer of the chromophores as well,
which will result in different linear absorption properties.
These findings can also be supported by theory calculations
as follows.
1
P2 /c. (2) The –CHO unit is well conjugated with the phe-
nyl ring (P0) with the bond length of C(31)–C(34): 1.47 Å,
which is between the normal C=C double bond (1.34 Å) and
C–C single bond (1.54 Å) showing that there is a partially
1
delocalized -electron system in L molecule. Apart from

Liu J, et al. Sci China Chem January (2013) Vol.56 No.1
5
0
1
2
Table 3 Single-photon-related photophysical properties of L , L and L in several different solvents
a)
b)
c)
d)
e)
f)
g)
h)
Compds
Solvents

max (max
)

max
v

f
 (ns)
1.98
2.82
3.23
2.70
4.83
2.59
5.19
k
r
k
nr
0
L
C
6
H
6
288(3.74) 360(2.75)
287(3.92) 358(2.98)
286(3.75) 356(2.86)
288(3.64) 357(2.65)
286(4.02) 351(3.03)
285(3.72) 358(2.73)
287(3.33) 359(2.59)
430
466
447
448
491
499
485
4522
6474
5719
5711
7882
7432
7006
0.65
0.48
0.60
0.70
0.29
0.17
0.46
3.28
1.70
1.86
2.59
0.61
0.65
0.90
1.77
1.83
1.24
1.11
1.46
3.21
1.03
CH
CH
2
Cl
2
3
COOEt
THF
CH CN
3
EtOH
DMF
1
278(2.91) 335(2.62)
L
C
6
H
6
452
507
466
464
514
496
496
4758
6872
5715
5475
7499
6866
6720
0.33
0.15
0.26
0.31
0.03
0.01
0.12
2.25
3.04
3.84
2.30
2.92
0.15
3.38
1.46
0.48
0.68
1.33
0.11
0.33
0.36
2.98
2.81
1.92
3.02
3.31
66.34
2.60
3
72(3.50)
82(2.85) 332(2.66)
76(2.93)
80(2.88) 338(2.92)
68(3.66)
78(2.93) 338(2.80)
70(3.66)
80(2.91) 335(2.70)
71(3.59)
84(2.81) 332(2.46)
70(3.59)
77(2.92) 338(2.64)
72(3.41)
2
2
2
2
2
2
CH
2
3
Cl
2
3
CH
COOEt
3
THF
CH CN
3
3
3
EtOH
DMF
3
3
2
L
C
CH
CH
THF
CH CN
EtOH
DMF
6
H
6
292(2.69) 362(2.07)
293(2.84) 361(2.17)
291(3.37) 359(2.69)
290(2.74) 360(2.09)
288(2.73) 358(2.16)
289(2.96) 362(2.20)
292(2.69) 364(2.04)

438
470
456
457
499
506
496
4793
6424
5618
5896
7432
7785
7311
0.95
0.58
0.52
0.72
0.20
0.13
0.44
2.16
2.97
3.49
2.93
5.09
2.16
5.61
1
4.40
1.97
1.50
2.44
0.40
0.58
0.78
0.23
1.40
1.36
0.97
1.56
4.05
1.00
2
Cl
2
3
COOEt
3
5
1
4
1
a) Peak position of the largest absorption band in nm (1.0×10 mol L ); b) maximum molar absorbance in 10 mol L cm ; c) peak position of SPEF,
exited at the absorption maximum; d) stokes shift in cm ; e) quantum yields determined by using quinine sulfate as standard; f) the fitted fluorescence life-
time; g) the rate constant of a radiative process (1.0×10 s ); h) the cumulative rate constant of a non-radiative process (1.0×10 s ).

1
8
1
8
1
0
1
2
1
2
Figure 4 Linear absorption and SPEF spectra of L , L and L in ethyl
acetate with a concentration of 1.0×10 mol L .
Figure 5 Representation of calculated Kohn-Sham orbitals of L and L
(TD-DFT/B3LYP).

5
1
Table 4 Calculated linear absorption properties (nm), excitation energy
3
.3.2 TD-DFT computational studies
1
2
(
eV), oscillator strengths and major contribution for L and L
It is well known that electronic excitation from the HOMO
to the LUMO produces the first singlet excited state. Thus,
TD-DFT computational studies at the B3LYP level basis set
Compound  (nm) E (eV) Composition
f
1
2
L
L
364.14
345.58
3.81
4.06
4.70
0.6337 132→133 (H→L)(0.67365)
0.2109 132→135 (H→L+2)(0.65386)
0.1904 132→136 (H→L+3)(0.41562)
1
2
were also carried out for L and L using the G03 software
38]. Figure 5 gives straight-forward representations of the
2
90.40
381.36
95.03
[
3.63
4.80
0.4036 133→134 (H→L)(0.67841)
0.2124 132→134 (H1→L)( 0.57483)
electron density distribution for them, and the energies and
compositions of some frontier orbitals are listed in Table 4.
2

6
Liu J, et al. Sci China Chem January (2013) Vol.56 No.1
According to the calculated results, it is easily confirmed
that the substituent –CHO in L is involved in the whole
electronic delocalization process. One of the bands is at
45.58 nm, HOMO to LUMO+2, consistent with the ex-
phores present remarkable bathochromic shifts with in-
creasing polarity of the solvents. The maximum emission
1
0
wavelength of L is shifted by 55 nm from 430 nm in ben-
1
3
zene to 485 nm in DMF, while that of L is shifted by 44
2
perimental results that a shoulder band appears in the linear
nm from 452 nm in benzene to 496 nm in DMF, that of L
1
absorption band of the chromophore L . The other two tran-
is shifted by 58 nm (438 nm in benzene and 496 nm in
DMF). This suggests that the fluorescent exited state (de-
fined as the first exited state, S1) of the molecule should
possess larger dipole moment than that of the ground state.
The dipole-dipolar interactions between the solute and sol-
vent increase, leading to a more significant energy level
decrease for the exited state [39]. Besides, the Stokes’ shift
was also calculated (Table 3), which can further demon-
strate the influence of the solvent on fluorescence.
sition bands exist at the position of 364.14 nm and 290.40
nm, respectively. The former band assigned as ICT with
lower energy is derived from the transition of HOMO→
LUMO. The latter, at shorter wavelengths, may be related to
the absorption of the triphenylamine moiety, corresponding
to the composition of HOMO to LUMO+3.
1
2
2
Compared with L , the –CH OH unit in L has seldom
contribution to the electron density distribution, although
the absorption spectra of the investigated chromophores
show similar features. There exist only two transition bands
The fluorescence quantum yields (
f
), listed in Table 3,
were measured by using quinine sulfate as the standard [40].
2
02
based on the theoretical calculation for L . The lower ener-
The fluorescence quantum yields of L
change signifi-
gy excitation band at 381.36 nm is mainly assigned as ICT,
which originates from the HOMO→LUMO transition. In-
terestingly, this band position is nearly 17 nm red-shifted
cantly with different polar solvents. Higher  values are
f
obtained in non-polar solvents with the highest  values
f
2
0
observed in C H . The order of  values is L (0.95) > L
(0.65) > L (0.33) in the benzene solution. It implies that the
6
6
f
1
1
compared with that of L . The result can be not only rea-
sonably explained by TD-DFT calculations of the lowest
excited state energy (HOMO→LUMO), but also be power-
fully confirmed by the experimental linear absorption spec-
introduction of the group –CH OH helps to decrease the
nonradiative decay pathways, and enhance the fluorescence
quantum yields. However, the –CHO group has the opposite
2
1
2
tra of chromophores, L and L . The remaining band (
=
effect to that of the –CH
deduction, the rate constants for radiative (kr)
2
OH. To further confirming this
and nonradia-
max
2
95.03 nm, f = 0.21) is ascribed to local transition of the
tive (knr) decays were calculated with reference to the
triphenylamine moiety as a result of the HOMO–1 →
LUMO transition.
Method A (Supporting Information). From the Table 3, the
2
value k
r
of L in benzene is apparently higher than that of
3.3.3 Single-photon excited fluorescence (SPEF)
the other chromophores.
The single-photon excited fluorescence (SPEF) spectra were
measured in the same concentrations in seven different or-
ganic solvents as those of the linear absorption spectra at
their maximum excitation wavelengths. The SPEF spectra
3.4 Two-photon excited fluorescence (TPEF) and the-
oretical calculation of TPA cross sections (δ)
2
0,1
of L and L are shown in Figures 6 and S2, respectively.
3.4.1 Two-photon excited fluorescence (TPEF)
0
–2
Related photophysical data of L , including fluorescence
quantum yields ( ), non/radiative rate constant (k , k ),
As shown in Figure 4, there is no linear absorption in the
02
f
r
nr
range 600–880 nm for L , indicating that there are no en-
ergy levels corresponding to one electron transition in the
spectral range. Therefore, upon excitation from 600 to 880
nm, it is impossible to produce single-photon excited

Stokes’ shift and fluorescence lifetimes ( ) (Figures 7 and
S3) are collected in Table 3.
The figures show that SPEF spectra of all the chromo-
2
5
1
Figure 6 (a) Single-photon excited fluorescence of L in seven selected solvents with a concentration of 1.0×10 mol L ; (b) fluorescence emission pho-
tographs of L in seven selected solvents.
2

Liu J, et al. Sci China Chem January (2013) Vol.56 No.1
7
with a slope of 2.12, 2.03 and 2.12, respectively, when the
input laser power is increasing, suggesting a two-phonon
02
excitation mechanism for the three molecules L
.
From Figures 11(a) and S6, at the optimal excited wave-
length, for example, it can be found that the TPEF spectra
of the chromophores in four different solvents present posi-
tive solvatochromism, the same trend as the one-photon
fluorescence. The phenomenon may be contributed to the
similarly vibronic structures in the TPEF and SPEF spectra
of the chromophores [42]. It can be found that the highest
intensity of the TPEF exists in the high polar solvent DMF,
2
especially for that of L . Figure 11(b) shows the TPEF of
0
2
L
at the excited wavelength in DMF solution. The inten-
2
0
sities of TPEF of the three are in the sequence of L > L >
1
L . Based on the principle, the smaller the energy gap is, the
2
Figure 7 Time-resolved fluorescence curves of L in seven selected
solvents.
higher the possibility of the two-photon excitation is. The
sequence is in complete consistency with DFT calculation,
which is 3.63 eV (L ), 3.75 eV (L ), and 3.81 eV (L ) about
2
0
1
the energy gap of the three chromophores, respectively.
up-converted fluorescence [41].
0−2
TPA cross sections () of L (Figure S7) have been
obtained in four different polar solvents using the Method
B given in Supporting Information. Figure 12 shows the
TPA cross-section per molecular weight (max/MW) of the
chromophores in DMF. The maximum max/MW values at
While keeping the input power at the intensity of 500
mW, we recorded the TPEF intensities, which were meas-
ured by tuning the pump wavelength increment at 10 nm
from 690 to 850 nm, and the TPEF spectra were obtained
(
Figures 8 and S4). Figures 9, 10 and S5 show the logarith-
0
mic plots of the fluorescence integral versus pumped powers
the excitation wavelength are 0.53 GM/(g mol) (L ), 0.63
1
2
Figure 8 Two-photon fluorescence spectra of L and L in DMF pumped by femtosecond laser pulses at 500 mW at different excitation wavelengths.
1
3
1
Figure 9 (a) TPEF spectra of L under different pumped powers at 710 nm, with c = 1.0×10 mol L in DMF; (b) output fluorescence (Iout) vs. the square
of input laser power (Iin) for L .
1

8
Liu J, et al. Sci China Chem January (2013) Vol.56 No.1
2
3
1
Figure 10 (a) TPEF spectra of L under different pumped powers at 760 nm, with c = 1.0×10 mol L in DMF; (b) output fluorescence (Iout) vs. the
2
square of input laser power (Iin) for L .
2
3
1
Figure 11 (a) Two-photon fluorescence spectra of L in different solvents with the same concentration of 1.010 mol L in em = 760 nm; (b)
0
−2
3
1
two-photon fluorescence spectra of L in DMF (1.010 mol L ) at excited wavelength.
3
.4.2 Theoretical calculation of TPA cross sections ()
To obtain more information about relationships between the
structure and TPA properties, theoretical calculation of TPA
cross sections () was performed on equilibrium geometries
1
2
of molecules (L and L ) using the DALTON 2011 pro-
gram [43] in gas phase optimized by Gaussian package [38]
at the hybrid density functional theory (DFT/B3LYP) level
with 6-31G* basis set. The TPA cross section, which can be
directly compared with the experimental results, is defined
as the following equation:
2
5
0
2
4
 a   g()
1
tp


tp
(1)
5c0
f

02
Figure 12 TPA cross-section per molecular weight (/MW) of L in
In this equation, a is the Bohr radius, c is the speed of
0
0
DMF vs. excitation wavelengths of identical energy of 500 mW.
light,  is the fine structure constant,  is the photon fre-
quency of the incident light, and g() denotes the spectral
line profile, which is assumed to be a  function here, and f
is the lifetime broadening of the final state, which is com-
1
2
GM/(g mol) (L ) and 0.72 GM/(g mol) (L ), respectively.
L has the largest max/MW value, indicating that the
2
–
CH
2
OH group has been involved in the conjugated system
monly assumed to be 0.1 eV [44].  is written as follows
tp
of the molecule to some extent and provides some electrons
to the whole system, which may increase the ICT. However,
the substituent –CHO of L , due to its medium electron
[45],
*
*
*
tp

[F S S  GS S  H S S ] (2)
  

1

withdrawing, may decrease the ICT efficiency. Therefore,
L has a lower max/MW value than that of L .
Here F, G, and H are coefficients dependent on the po-
larization of the light. S is the TPA transition matrix ele-
1
2

Liu J, et al. Sci China Chem January (2013) Vol.56 No.1
9
ment. For the absorption of two photons with the same fre-
section may be obtained by subtle modification rather than
extending conjugated length over complicated organic syn-
thesis.
quency  /2, it can be written as [46],
f

0|μ |ii | μ |f  0|μ |ii|μ |f 
α
β
β
α
S ＝
αβ i
＋
(3)



ω－ω/2
ω－ω/2
i f
i
f

This work was financially supported by the National Natural Science
Foundation of China (21071001, 51142011, 21271004, 21201005 and
Here 
i
and 
f
are the excitation frequency of the inter-
mediate state |i and final state |f, respectively, ,   (x, y,
z), and the summation goes over all the intermediate states
including the ground state |0 and the final state |f.
2
1271003), Ministry of Education Funded Projects Focus on returned
overseas scholar and Program for New Century Excellent Talents in Uni-
versity (China).
0
The nonlinear optical data of the three chromophores (L ,
1
2
L and L ) in gas phase are listed in Table 5, from which the
calculated optical properties depending on the different
geometries can be observed readily. The largest TPA cross
Appendix A. Supplementary data
CCDC 85415 and 90578 contain the supplementary crys-
0
1
1
2
section of the molecules is 262.77 for L , 265.38 for L , and
tallographic data for L and L , respectively. These data can
be obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB21EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.
cam.ac.uk.
2
50
4
2
85.64 GM for L (1 GM = 10 cm s/photon). It is ap-
parent that the theoretical calculation is consistent with the
2
1
0
experimental result trend (L > L > L ) shown in Figures
2 and S7.
1

50
4
Table 5 Two-photon absorption cross-section tp (1 GM = 10 cm
s/photon) of the three lowest exited states with the excitation energy E (eV)
and the corresponding wavelength tp (nm) in the gas phase
1
2
3
Göppert-Mayer M. Über elementarakte mit zwei Quantensprüngen.
Ann Phys (Leipzig), 1931, 9: 273–294
Kaiser W, Garrett CGB. Two-photon excitation in CaF
2
+
2
:Eu . Phys
0
a)
L
E
3.39
3.40
4.01
4.14
4.19
4.28
Rev Lett, 1961: 229–231

tp
729.53 727.38 616.73 597.37 590.24 577.83
Cumpston BH, Ananthavel SP, Barlow S, Dyer DL, Ehrlich JE,
Erskine LL, Heikal AA, Kuebler SM, Lee IYS, Dianne MM, Qin JQ,
Röckel H, Rumi M, Wu XL, Marder SR, Perry JW. Two-photon
polymerization initiators for three-dimensional optical data storage
and microfabrication. Nature, 1999, 398: 51–54

tp
262.77
3.46
0.04
3.62
0.19
3.76
18.33
3.85
23.54
4.09
0.00
4.23

1
L
L
E

tp
714.77 683.18 657.74 642.36 604.67 584.66

tp
265.38
0.39
127.22
0.29
7.49
0.14
4
5
Yuan WF, Sun L, Tang HH, Wen YQ, Jiang GY, Huang WH, Jiang

L, Song YL, Tian H, Zhu DB.
A novel thermally stable
2
E
3.25
3.41
3.99
4.12
4.15
4.28
spironaphthoxazine and its application in rewritable high density
optical data storage. Adv Mater, 2005, 17: 156–160

tp
760.96 725.25 619.82 600.27 595.93 577.83
285.64 0.04 0.13 39.93 19.81 0.03
a) The data of two-photon absorption cross-section δtp cited from the
Ref. [30].

tp
Li L, Tian YP, Yang JX, Sun PP, Wu JY, Zhou HP, Zhang SY, Jin
BK, Xing XJ, Wang CK, Li M, Cheng GH, Tang HH, Huang WH,
Tao XT, Jiang MH. Facile synthesis and systematic investigations of
a series of novel bent-shaped two-photon absorption chromophores
based on pyrimidine. Chem Asian J, 2009, 4: 668-680;
6
7
Yanez CO, Andrade CD, Yao S, Luchita G, Bondar MV, Belfield KD.
Photosensitive polymeric materials for two-photon 3D WORM
optical data storage systems. J Am Chem Soc, 2009, 1: 2219–2229
Zhou WH, Kuebler SM, Braun KL, Yu TY, Cammack JK, Ober CK,
Perry JW, Marder SR. An efficient two-photon-generated photoacid
applied to positive-tone 3D microfabrication. Science, 2002, 296:
4
Conclusion
1
Two novel D-A triphenylamino terpyridine derivatives (L
2
and L ) were facilely synthesized via formylation and re-
duction. Based on the experimental and theoretical investi-
gation, the structure–property relationships were established.
The two chromophores showed apparent positive solvato-
chromism in various solvents mainly due to the ICT. Be-
cause of their almost approximate molecular volume and
production costs, the TPA cross-section per molecular
weight (max/MW) was selected to compare NLO data. In
high polar solvent DMF, the max/MW of the chromophores
1
106–1109
8
Kim HM, Cho BR. Two-photon probes for intracellular free metal
ions, acidic vesicles, and lipid rafts in live tissues. Acc Chem Res,
2
009, 42: 863–872
9
0
Berezin MY, Achilefu S. Fluorescence lifetime measurements and
biological imaging. Chem Rev, 2010, 110: 2641–2684
Kim MK, Lim CS, Hong JT, Han JH, Jang HY, Kim HM, Cho BR.
Sodium-ion-selective two-photon fluorescent probe for in vivo imag-
ing. Angew Chem Int Ed, 2010, 49: 364–367
1
1
1
1
2
Lee JH, Lim CS, Tian YS, Han JH, Cho BR. A two-photon
fluorescent probe for thiols in live cells and tissues. J Am Chem Soc,
1
2
is 0.63 GM/(g mol) (L ) and 0.72 GM/(g mol) (L ), respec-
tively. Furthermore, it was readily found that the EDG,
2
010, 132: 1216–1217
Wang XC, Tian XH, Zhang Q, Sun PP, Wu JY, Zhou HP, Jin BK,
Yang JX, Zhang SY, Wang CK, Tao XT, Jiang MH, Tian YP.
Assembly, two-photon absorption, and bioimaging of living cells of a
cuprous cluster. Chem Mater, 2012, 24: 954–961
Zheng Z, Yu ZP, Yang MD, Jin F, Zhang Q, Zhou Hp, Wu JY, Tian
YP. Substituent group variations directing the molecular packing,
electronic structure, and aggregation-induced emission property of
–
CH OH can increase the ICT, which had the same direc-
2
tion of charge transfer in the whole molecule. However,
compared with the –CH OH, the EWG, –CHO had almost
contrary effect, leading to decrease of the ICT. Therefore,
the findings also implied that relatively large TPA cross
2
1
3

10
Liu J, et al. Sci China Chem January (2013) Vol.56 No.1
isophorone derivatives. J Org Chem, 2013, 78: 3222–3234
LaFratta CN, Fourkas JT, Baldacchini T, Farrer RA. Multiphoton
fabrication. Angew Chem Int Ed, 2007, 46: 6238–6258
Zhao C, Burchardt M, Brinkhoff T, Beardsley C, Simon M, Wittstock
G. Microfabrication of patterns of adherent marine bacterium
Phaeobacter inhibens using soft lithography and scanning probe
lithography. Langmuir, 2010, 26: 8641–8647
cost-scaling and comparison of two-photon absorption effieciency in
disparate molecules (organometallic complexes for nonlinear optics.
48.)––A response to “comment on ‘organometallic complexes for
nonlinear optics. 45. Dispersion of the third-order nonlinear optical
properties of triphenylamine-cored alkynylruthenium dendrimers.’
Increasing the nonlinear response by two orders of magnitude.” Adv
Mater, 2011, 23: 1433–1435
1
1
4
5
1
6
Kim S, Ohulchanskyy TY, Pudavar HE, Pandey RK, Prasad PN.
Organically modified silica nanoparticles co-encapsulating photo-
sensitizing drug and aggregation-enhanced two-photon absorbing
fluorescent dye aggregates for two-photon photodynamic therapy. J
Am Chem Soc, 2007, 129: 2669–2675
Balaz M, Collins HA, Dahlstedt E, Anderson HL. Synthesis of
hydrophilic conjugated porphyrin dimmers for one-photon and
two-photon photodynamic therapy at NIR wavelengths. Org Biomol
Chem, 2009, 7: 874–888
Gallavardin T, Chloe Armagnat, Maury O, Baldeck PL, Lindgren M,
Monnereau C, Andraud C. An improved singlet oxygen sensitizer
with two-photon absorption and emission in the biological transparency
window as a result of ground state symmetry-breaking. Chem
Commun, 2012, 48: 1689–1691
32 Roberts RL, Schwich T, Corkery TC, P.Cifuentes M, A.Green K,
Farmer JD, Low PJ, Marder TB, Samoc M, Humphrey MG.
Organometallic complexes for nonlinear optics. 45. Dispersion of the
third-order nonlinear optical properties of triphenylamine-cored al-
kynylruthenium dendrimers. Adv Mater, 2009, 21: 2318–2322
33 Varnavski O, Yan X-Z, Mongin O, Blanchard-Desce M, Goodson T.
Strongly interacting organic conjugated dendrimers with enhanced
two-photon absorption. J Phys Chem C, 2007, 111: 149–162
34 Ning ZJ, Tian H. Triarylamine: A promising core unit for efficient
photovoltaic materials. Chem Commun, 2009, 45: 5483–5495
35 Cremer J, Briehn CA. Novel highly fluorescent triphenylamine-based
oligothiophenes. Chem Mater, 2007, 19: 4155–4165
1
1
7
8
36 Sheldrick GM. SHELXTLV 5.1 software reference manual. Madison:
BrukerAXS, Inc. 1997
1
9
Abbotto A, Beverina L, Bozio R, Bradamante S, Ferrante C, Pagani
GA, Signorini R. Push-pull organic chromophores for frequency
up-converted lasing. Adv Mater, 2000, 12: 1953–1967
Tian H, Feng YL. Next step of photochromic switches? J Mater
Chem, 2008, 18: 1617–1622
37 Qiu DF, Zhao Q, Bao XY, Liu KC, Wang HW, Guo YC, Zhang LF,
Zeng JL, Wang H. Electropolymerization and characterization of an
alternatively conjugated donor-acceptor metallopolymer: Poly-
2
+
2
2
0
1
[Ru(4′-(4-(Diphenylamino)phenyl)-2,2′:6′,2″-terpyridine)
Chem Commun, 2011, 14: 296–299
2
] . Inorg
Lin TC, He GS, Prasad PN, Tan LS. Degenerate nonlinear absorption
and optical power limiting properties of asymmetrically substitute-
dstilbenoid chromophores. J Mater Chem, 2004, 14: 982–991
Li SL, Wu JY, Tian YP, Tang YW, Jiang MH, Fun HK,
Chantrapromma S. Preparation, characterization, two-photon
absorptio and optical limiting properties of a novel metal complex
containing carbazole. Opt Mater, 2006, 28: 897–903
Lin TC, Huang YJ, Chen YF, Hu CL. Two-photon absorption and
effective broadband optical power limiting properties of a multi-
branched chromophore containing 2,3-diarylquinoxalinyl moieties as
the electron-pulling units. Tetrahedron, 2010, 66: 1375–1382
Mongin O, Porrès L, Katan C, Pons T, Mertz J, Mireille B-D.
Synthesis and two-photon absorption of highly soluble three-
branched fluorenylene-vinylene derivatives. Tetrahedron Lett, 2003,
38 Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE, Robb MA,
Cheeseman JR, Jr. JAM, Vreven T, Kudin KN, Burant JC, Millam
JM, Iyengar SS, Tomasi J, Barone V, Mennucci B, Cossi M,
Scalmani G, Rega N, Petersson GA, Nakatsuji H, Hada M, Ehara M,
Toyota K, Fukuda R, Hasegawa J, Ishida M, Nakajima T, Honda Y,
Kitao O, Nakai H, Klene M, Li X, Knox JE, Hratchian HP, Cross JB,
Adamo C, Jaramillo J, Gomperts R, Stratmann RE, Yazyev O, Austin
AJ, Cammi R, Pomelli C, Ochterski JW, Ayala PY, Morokuma K,
A.Voth G, Salvador P, Dannenberg JJ, Zakrzewski VG, Dapprich S,
Daniels AD, Strain MC, Farkas O, Malick DK, D.Rabuck A,
Raghavachari K, Foresman JB, Ortiz JV, Q.Cui, Baboul AG, Clifford
S, Cioslowski J, Stefanov BB, Liu G, Liashenko A, Piskorz P,
Komaromi I, Martin RL, Fox DJ, Keith T, Al-Laham MA, Peng CY,
Nanayakkara A, Challacombe M, Gill PMW, Johnson B, Chen W,
Wong MW, Gonzalez C, Pople JA. Gaussian03, Revision B. 04,
Wallingford: Gaussian, Inc., CT, 2004
39 Woo HY, Liu B, Kohler B, Korystov D, Mikhailovsky A, Bazan GC.
Solvent effects on the two-photon absorption of distyrylbenzene
chromophores. J Am Chem Soc, 2005, 127: 14721–14729
40 Zheng Z, Zhang Q, Yu ZP, Yang MD, Zhou HP, Wu JY, Tian YP.
Four new two-photon absorbing imidazo[4,5-f]1,10-phenanthroline
derivatives dyes with different dipole moment orientation based on
different group: Synthesis, optical characterization and bioimaging. J
Mater Chem C, 2013, 1: 822–830
41 Kong L, Yang JX, Zhou HP, Li SL, Hao FY, Zhang Q, Tu YL, WU J,
Xue ZM, Tian YP. Synthesis, photophysical properties and TD-DFT
calculation of four two-photon absorbing triphenylamine derivatives.
Sci Chi Chem, 2013, 56: 106–116
42 Hu ZJ, Zhang RL, Sun PP, Li L, Wu JY, Yang JX, Tian YP, Wang
CK. Three asymmetrical conjugated D--D′ sulfur-containing
chromophores with a focus on two-photon absorption. Aust J Chem,
2011, 64: 174–179
43 DALTON. A molecular electronic structure program. Release Dalton.
http://daltonprogram.org/.2011
44 Strickler JH, Webb WW. Three-dimensional optical data storage in
refractive media by two-photon point excitation. Optics Letters, 1991,
16: 1780–1782
2
2
2
2
3
4
4
4: 8121–8125
2
5
Grabowski ZR, Rotkiewicz K. Structural changes accompanying
intramolecular electron transfer: Focus on twisted intramolecular
charge-transfer states and structures. Chem Rev, 2003, 103: 3839–4031
Beverina L, Fu J, Leclercq A, Zojer E, Pacher P, Barlow S, Stryland
EWV, Hagan DJ, Brédas J-L, Marder SR. Two-photon absorption at
telecommunications wavelengths in a dipolar chromophore with a
pyrrole auxiliary donor and thiazole auxiliary acceptor. J Am Chem
Soc, 2005, 127: 7282–7283
Tian YP, Li L, Zhang JZ, Yang JX, Zhou HP, Wu J, Sun PP, Tao LM,
Guo YH, Wang CK, Xing H, Huang WH, Tao XT, Jiang MH.
Investigations and facile synthesis of a series of novel multi-
functional two-photon absorption materials. J Mater Chem, 2007, 17:
2
2
2
6
7
8
3
646–3654
Li L, Yang JX, Wang CX, Hu ZJ, Tian YP, Li J, Wang CK, Li M,
Cheng GH, Tang HH, Huang WH, Tao XT, Jiang MH.
Multi-carbazole derivatives for two-photon absorption data storage:
Synthesis, optical properties and theoretical calculation. Sci Chi
Chem, 2010, 53: 884–890
Shao JJ, Guan ZP, Yan YL, Jiao CJ, Xu QH, Chi C. Synthesis and
characterizations of star-shaped octupolar triazatruxenes-based two-
photon absorption chromophores. J Org Chem, 2011, 76: 780–790
Liu B, Zhang Q, Ding HJ, Hu GJ, Du YJ, Wang CK, Wu JY, Li SL,
Zhou HP, Yang JX, Tian YP. Synthesis, crystal structures and
two-photon absorption properties of a series of terpyridine-based
chromophores. Dyes Pigm, 2012, 95: 149–160
2
3
9
0
45 Cammi R, Cossi M, Tomasi J. Analytical derivatives for molecular
solutes. III. Hartree-Fock static polarizability and hyperpolarizabilities
in the polarizable continuum model. J Chem Phys, 1996, 104: 4611–4620
46 Shen YR. The Principles Of Nonlinear Optics. New York: Wiley,
1984
3
1
Schwich T, Cifuentes MP, Gugger PA, Samoc M, Humphrey MG.
Electronic, molecular weight, molecular volume, and financial