Preparation and Photophysical Properties of All-trans Acceptor-π-Donor (Acceptor) Compounds Possessing Obvious Solvatochromic Effects

Article abstract of DOI:10.1071/CH17021

A series of all-trans acceptor-π-donor (acceptor) compounds (BAQ, SFQ, BLQ, and XJQ) were conveniently synthesised and characterised by infrared, nuclear magnetic resonance, mass spectrometry, and elemental analysis. Their photophysical properties, including linear absorption, one-photon excited fluorescence, two-photon absorption, and two-photon excited fluorescence, were systematically investigated. All the compounds show obvious solvatochromic effects, such as significant bathochromic shifts of the emission spectra and larger Stokes shifts in more polar solvents. Under excitation from a femtosecond Ti:sapphire laser with a pulse width of 140 fs, they all exhibit strong two-photon excited fluorescence, and the two-photon absorption cross-sections in THF are 851 (BAQ), 216 (SFQ), 561 (BLQ), and 447 (XJQ) GM respectively. A combination of density functional theory (DFT) and time-dependent density functional theory (TDDFT) approaches was used to investigate the relationships between the structures and the photophysical properties of these compounds. The results show that they may have a potential application as polarity-sensitive two-photon fluorescent probes.

Full text of DOI:10.1071/CH17021

CSIRO PUBLISHING
Aust. J. Chem.
Full Paper
http://dx.doi.org/10.1071/CH17021
Preparation and Photophysical Properties of All-trans
Acceptor–p-Donor (Acceptor) Compounds Possessing
Obvious Solvatochromic Effects
A
A C
,
A
B
B
Yu-Lu Pan, Zhi-Bin Cai,
Li Bai, Sheng-Li Li, and Yu-Peng Tian
A
College of Chemical Engineering, Zhejiang University of Technology,
Hangzhou 310014, China.
B
Department of Chemistry, Anhui Province Key Laboratory of Functional
Inorganic Materials, Anhui University, Hefei 230039, China.
C
Corresponding author. Email: caizbmail@126.com
A series of all-trans acceptor–p-donor (acceptor) compounds (BAQ, SFQ, BLQ, and XJQ) were conveniently synthesised
and characterised by infrared, nuclear magnetic resonance, mass spectrometry, and elemental analysis. Their photophysical
properties, including linear absorption, one-photon excited fluorescence, two-photon absorption, and two-photon excited
fluorescence, were systematically investigated. All the compounds show obvious solvatochromic effects, such as
significant bathochromic shifts of the emission spectra and larger Stokes shifts in more polar solvents. Under excitation
from a femtosecond Ti : sapphire laser with a pulse width of 140 fs, they all exhibit strong two-photon excited fluorescence,
and the two-photon absorption cross-sections in THF are 851 (BAQ), 216 (SFQ), 561 (BLQ), and 447 (XJQ) GM
respectively. A combination of density functional theory (DFT) and time-dependent density functional theory (TDDFT)
approaches was used to investigate the relationships between the structures and the photophysical properties of these
compounds. The results show that they may have a potential application as polarity-sensitive two-photon fluorescent
probes.
Manuscript received: 9 January 2017.
Manuscript accepted: 24 April 2017.
24 May 2017.
Published online:
Introduction
electron-transport channel, which can greatly facilitate the
charge transfer between the donor and the acceptor.[16,17]
Increasing the number of styrene moieties and the trans-
configuration of the carbon–carbon double bond may improve
the quantum efficiency of the p*–p electronic transition, and
thus enhance the fluorescence emission.[18,19] Triphenylamine
has special propeller starburst molecular structure; pyrrole and
thiophene are closed circular 6p-electron conjugated systems.
Owing to their high electron-donating ability, electrochemical
activity, and environmental stability, they have been widely
used in opto- and electro-active materials.[20–24] The formyl
group consists of a carbonyl group joined by a single bond to a
hydrogen atom, which is rarely chosen as the electron acceptor
in TPA materials. However, we have previously reported the
TPA behaviour of a series of new compounds with a formyl
group.[25,26] The results reveal that formyl has a correspond-
ingly strong electron-withdrawing ability and is beneficial in
intramolecular charge transfer (ICT).
Two-photon absorption (TPA), which is defined as the simul-
taneous absorption of a pair of photons during the excitation of a
molecule, was first predicted by Go¨ppert-Mayer.[1] Molecules
with large TPA cross-sections (s) have potential significant
applications in many fields, such as two-photon fluorescence
microscopy,[2,3] optical limiting,[4–6] three-dimensional optical
data storage,[7–9] and photodynamic therapy.[10–12] Recently,
two-photon fluorescent (TPF) probes have attracted consider-
able interest because of their high spatial resolution, deep pen-
etration, low photodamage, low phototoxicity, and reduced
photobleaching.[13–15] Conventional fluorescent molecules such
as rhodamine, fluorescein, and cyanine dyes usually exhibit a
small s (s , 100 GM; 1 GM¼ 1 ꢀ 10ꢁ50 cm4 s photonꢁ1), which
restricts their application as TPF probes. Thus, the development
of efficient fluorescent molecules with a large s is clearly
necessary.
Considering their practical applications as probes, the design
of new TPA materials must combine enhanced s with a high
fluorescence quantum yield (F) and low excitation energy to
decrease photodamage. Herein, we selected styrene as the
p-bridge, triphenylamine (or 1-methylpyrrole, or thiophene)
as the electron donor (D) and the formyl (or nitro) as the electron
acceptor (A) to design four all-trans A-p-D (or A-p-A0) com-
pounds (BAQ, SFQ, BLQ, and XJQ) (Fig. 1). Styrene is a good
The four target compounds are all-trans conjugated aromatic
aldehydes. These kinds of compounds are usually synthesised
using fairly complicated routes including six to nine reaction
steps.[27–32] The routes are so long that they significantly decrease
overall efficiency. In the present paper, a simple, mild, and
efficient three-step synthetic method has been adopted, which
comprises the following reactions: Arbuzov reaction, solvent-free
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B
Y.-L. Pan et al.
styrene with triethyl phosphite. Then, LSZ was subjected to the
solvent-free HWE reaction with different aromatic aldehydes to
furnish the desired trans-alkenes 3a–3d. The HWE reaction is
the reaction of stabilised phosphonate carbanions with carbonyl
compounds to produce predominantly trans-alkenes. Herein,
more attention has been paid to the HWE reaction under solvent-
free conditions instead of in organic solvents owing to its
environmental and economic benefits. Finally, the target com-
pounds BAQ, SFQ, BLQ, and XJQ were synthesised from
3a–3d via the Mizoroki–Heck reaction. The Mizoroki–Heck
reaction has been proved to be a powerful method for C=C bond
formation in organic synthesis.
N
OHC
BAQ
S
1
In the H NMR spectra, the chemical shifts (d) of 3a–3d
OHC
at 6.72–6.77 ppm (J1 17.6–17.7, J2 10.9–11.1 Hz, 1H), 5.76–
5.91 ppm (J 17.5–17.9 Hz, 1H), and 5.24–5.32 ppm (J 10.8–
11.3 Hz, 1H) correspond to the hydrogens attached to the terminal
carbon–carbon double bonds. Doublets with coupling constants of
J ¼ 16.1–16.5 Hz were observed for the target compounds, which
is consistent with the expected all-trans configurations. The peaks
at 9.98–10.00 ppm are characteristic of the formyl groups. In the
Fourier-transform (FT)-IR spectra, the strong bands between 1692
and 1697 cmꢁ1 were assigned to the stretching vibration of
the carbonyl group. The characteristic absorption peaks at
,1587–1595 and 957–965 cmꢁ1 indicate the presence of the
trans configuration at the carbon–carbon double bonds. Mass
spectrometry was used to further verify the structures of the target
compounds. The measured values (m/z [M þ H]þ 478.1, 317.2,
314.3, 356.4) agree well with calculated ones.
SFQ
N
Me
OHC
BLQ
NO2
OHC
Linear Absorption and TDDFT Computational Studies
XJQ
The optical characteristics of the target compounds BAQ, SFQ,
BLQ, and XJQ in solvents with different polarities are sum-
marised in Table 1. The corresponding linear absorption spectra
are shown in Fig. 2.
Fig. 1. Molecular structures of the target compounds BAQ, SFQ, BLQ,
and XJQ.
As depicted in Fig. 2, one can see that XJQ exhibits one
absorption band, BAQ and SFQ show two obvious absorption
bands, whereas one of the two absorption bands of BLQ
degenerates into a shoulder. The high-energy bands centred at
,310 nm are attributed to the p–p* transition of the terminal
electron donors (triphenylamine, thiophene, pyrrole). The low-
energy bands located at 376–412 nm originate from an ICT
process. Their maximum absorption peaks (lambasx) change slightly
(#7 nm) with increase in solvent polarity from toluene (TOL) to
CH3CN, revealing that the surrounding solvent molecules have
Horner–Wadsworth–Emmons (HWE) reaction, and Mizoroki–
Heck reaction. Both the yield and the trans-stereoselectivity are
satisfactory.
These target compounds were fully characterised and gave
well-defined NMR, IR, and mass spectrometry spectra corre-
sponding to their expected molecular structures. Their linear and
non-linear photophysical properties were systematically inves-
tigated in various solvents. The experimental studies of the
compounds were computationally supplemented by density
functional theory (DFT) and time-dependent density functional
theory (TDDFT) to provide deep insight into their structure–
property relationships. Interestingly, it was found that all the
compounds investigated exhibit pronounced positive polarity-
dependent solvatochromic effects and correspondingly large s
values. Therefore, their potential application as polarity-sensi-
tive TPF probes can be proposed.
little influence on the transition energy of the target compounds.
abs
Compared with SFQ, BLQ, and XJQ, the l
of BAQ is
max
obviously red-shifted; this is due to the fact that the triphenyla-
mine donor can significantly extend the p-conjugated system.
The maximum molar absorption coefficients (emax) of the A-p-A0
compound XJQ are larger than those of the A-p-D compounds
(BAQ, SFQ, and BLQ), which implies that the nitro acceptor
improves the light-absorbing ability of the entire molecule.
To further analyse the assignment of transitions in the
absorption spectra, TDDFT calculations using Gaussian 09
and B3LYP/6–31G* basis sets were performed on the target
compounds. The compositions of some frontier orbitals are
listed in Table S1 (Supplementary Material).
For BAQ, SFQ, and BLQ, the low-energy bands (calculated
at 387, 390, and 417 nm) were assigned to the ICT transition due
to HOMO - LUMO. The high-energy bands (calculated at 321,
322, and 327 nm) mainly due to the HOMO - LUMO þ 1,
HOMO - LUMO þ 1, and HOMO ꢁ 1 - LUMO respectively
Results and Discussion
Synthesis and Characterisation
Among the four target compounds, BLQ, SFQ, and XJQ are
new. BAQ was synthesised by McNulty[31] and Dubinina[32]
using a seven-step or nine-step synthetic route where Wittig
reaction was repeatedly used. Herein, we presented a three-step
method to readily prepare the target compounds in moderate
yields. The synthetic routes are depicted in Scheme 1.
[(4-Ethenylphenyl)methyl]phosphonic acid diethyl ester
(LSZ) was obtained by Arbuzov reaction of 4-(chloromethyl)

Photophysical Properties of All-trans A-p-D (A0) Compounds
C
O
OEt
OEt
Cl
P
P(OEt)3
1
LSZ
N
DMF
N
CHO
N
POCl3
3a
3b
2a
S
CHO
CHO
S
LSZ
2b
N
DMF
N
Me
N
POCl3
Me
Me
3c
3d
2c
NO2
CHO
O2N
2d
N
OHC
OHC
OHC
OHC
BAQ
S
N
OHC
Br
SFQ
BLQ
XJQ
Pd(OAc)2, (o-MeC6H4)3P
Me
NO2
Scheme 1. Synthesis of the target compounds BAQ, SFQ, BLQ, and XJQ.
were assigned to the p–p* transition of triphenylamine (or
thiophene, or pyrrole). In addition, XJQ exhibits one absorption
band (calculated at 368 nm) originating from HOMO - LUMO
þ 1, which corresponds to the ICT transition. Thus, the results
from the theoretical calculations are consistent with their exper-
imental absorption spectra.
solvents are shown in Fig. 3. Insets are the fluorescence pho-
tographs and chromaticity coordinates diagram. The corre-
sponding data are listed in Table 1.
In comparison with the absorption spectra, the one-photon
emission spectra display a strong solvatochromic response to
solvent polarity. It can be clearly seen from Table 1 and Fig. 3
OPEF
max
that the OPEF maxima (l
) of the target compounds show
One-Photon Excited Fluorescence and Solvatochromic
Properties
remarkable bathochromic shifts as the solvent polarity increases
following the order: TOL , THF , CH2Cl2 , CH3CN. The
solvatochromic behaviour is closely related to the terminal
electron donor (or acceptor). From TOL to CH3CN, the lmOPaxEF
The one-photon excited fluorescence (OPEF) spectra of the
target compounds BAQ, SFQ, BLQ, and XJQ in different

D
Y.-L. Pan et al.
Table 1. Photophysical properties of the target compounds BAQ, SFQ, BLQ, and XJQ in different solvents
A [nm]
10ꢁ4 eB [molꢁ1 L cmꢁ1
]
l
C [nm]
DvD [cmꢁ1
]
jE
l
F [nm]
TPEF
max
sG [GM]
abs
max
OPEF
max
Compound
Solvent
l
BAQ
Toluene
THF
412
407
410
406
383
376
383
382
401
404
401
397
389
387
394
394
2.36
2.25
1.76
2.85
2.71
3.74
2.94
3.80
2.01
4.63
2.59
3.38
3.79
4.76
3.79
6.26
490
3864
6388
6722
7087
4604
5719
6189
7722
3339
6471
7144
7552
4830
6037
7032
7836
0.55
0.31
0.17
0.02
0.46
0.27
0.23
0.16
0.33
0.26
0.12
0.02
0.14
0.18
0.15
0.03
525
545
851
550
566
570
465
479
502
514
463
547
562
567
479
505
545
570
577
CH2Cl2
CH3CN
Toluene
THF
SFQ
BLQ
XJQ
502
518
83
216
CH2Cl2
CH3CN
Toluene
THF
525
577
309
561
CH2Cl2
CH3CN
Toluene
THF
546
554
223
447
CH2Cl2
CH3CN
AMaximum linear absorption wavelength, c ¼ 1 ꢀ 10ꢁ5 mol Lꢁ1
.
BMaximum molar absorption coefficient.
CMaximum one-photon excited fluorescence wavelength, c ¼ 1 ꢀ 10ꢁ6 mol Lꢁ1
.
DStokes shift.
EFluorescence quantum yield, measured using quinine sulfate in 0.5 mol Lꢁ1 sulfuric acid as the standard (F ¼ 0.546[33]).
The experimental error is estimated to be 10–15 %.
FMaximum two-photon excited fluorescence wavelength, c ¼ 1 ꢀ 10ꢁ3 mol Lꢁ1
.
GTwo-photon absorption cross-section. The experimental error is estimated to be 10–15 %.
(c) 0.5
0.4
(a)
0.3
0.2
0.1
0
TOL
THF
TOL
THF
CH2Cl2
CH3CN
CH2Cl2
CH3CN
0.3
0.2
0.1
0
300
400
500
600
300
400
500
600
Wavelength [nm]
Wavelength [nm]
(b)
(d)
0.4
0.3
0.2
0.1
0
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
TOL
THF
CH2Cl2
CH3CN
TOL
THF
CH2Cl2
CH3CN
300
400
500
600
300
400
500
600
Wavelength [nm]
Wavelength [nm]
Fig. 2. Linear absorption spectra of the target compounds in different solvents with a concentration of 1 ꢀ 10ꢁ5 mol Lꢁ1: (a) BAQ; (b) SFQ; (c) BLQ; and
(d) XJQ.

Photophysical Properties of All-trans A-p-D (A0) Compounds
E
(a)
(c)
300
250
200
150
100
50
300
TOL
THF
CH2Cl2
TOL
THF
CH2Cl2
CH3CN
250
200
150
100
50
CH3CN
0
0
300
400
500
600
700
300
400
500
600
700
Wavelength [nm]
Wavelength [nm]
(b)
(d)
250
200
150
100
50
200
150
100
50
TOL
THF
CH2Cl2
CH3CN
TOL
THF
CH2Cl2
CH3CN
0
0
300
400
500
600
700
300
400
500
600
700
Wavelength [nm]
Wavelength [nm]
Fig. 3. One-photon excited fluorescence spectra of the target compounds in different solvents with a concentration of 1 ꢀ 10ꢁ6 mol Lꢁ1: (a) BAQ; (b) SFQ;
(c) BLQ; and (d) XJQ. Insets are the fluorescence photographs and chromaticity coordinate diagrams.
8500
ranges from 490 to 570 nm for BAQ, from 465 to 514 nm for
BAQ
SFQ
BLQ
8000
7500
7000
6500
6000
5500
5000
4500
4000
3500
3000
SFQ, from 463 to 567 nm for BLQ, and from 479 to 570 nm for
XJQ. One can see that the fluorescence colours change signifi-
cantly in different solvents. BLQ is particularly sensitive to the
OPEF
XJQ
polarity of the solvents. Its l
the fluorescence changes from the blue region to the orange
is red-shifted by 104 nm, and
max
region. The Stokes shifts (Dv) exhibit the same solvent polarity
. These can be explained by the fact
OPEF
max
dependencies as the l
that the excited state may possess higher polarity than the
ground state; the increased dipole–dipole interaction between
the solute and solvent leads to a lowering of the energy level,
which is accompanied by the positive solvatochromism.[34]
The Lippert–Mataga equation can be used to estimate the
dipole moment changes (me – mg) of the compounds with
photoexcitation,[35] as follows:
BAQ y ꢁ 11590x ꢂ 3858
y ꢁ 7141x ꢂ 4480
BLQ y ꢁ 15111x ꢂ 3314
SFQ
XJQ y ꢁ 9910x ꢂ 4589
0.05 0.10
0.15
0.20
0.25
0.30
0
0.35
Orientation polarisability Δf
2Df
2
Fig. 4. Lippert–Mataga plots of the target compounds BAQ, SFQ, BLQ,
and XJQ.
Dv ¼
ðme ꢁ mgÞ þ constant
ð1Þ
ð2Þ
4pe0hca3
dielectric constant, and n is the refractive index. (me – mg)2 is
proportional to the slope of the Lippert–Mataga plot.
From the plots of Dn versus Df (Fig. 4), we find that the slopes
of the fit line for the target compounds are 11590 (BAQ), 7141
(SFQ), 15111 (BLQ), and 9910 (XJQ) cmꢁ1 respectively.
Considering the slopes and the Onsager radii together, the
me – mg values may be arrange in the sequence BAQ . BLQ .
XJQ . SFQ. The me – mg value is an important factor that affects
the TPA properties.
e ꢁ 1
n2 ꢁ 1
Df ¼
ꢁ
2e þ 1 2n2 þ 1
in which Dv ¼ vabs – vem represents the Stokes shift, vabs and vem
are the absorption and the emission frequency (cmꢁ1); h is
Planck’s constant, c is the velocity of light in vacuum, a is the
Onsager radius, e0 is the permittivity of the vacuum, me and mg
are the dipole moments of the excited state and the ground
state respectively; Df is the orientation polarisability, e is the

F
Y.-L. Pan et al.
830 nm
850 nm
810 nm
870 nm
790 nm
890 nm
770 nm
690 nm
730 nm
750 nm
710 nm
910 nm
930 nm
950 nm
(a)
500
400
300
200
The values of F were determined using quinine sulfate in
0.5 mol Lꢁ1 sulfuric acid as the standard (F ¼ 0.546[33]). The
value of F was obtained as follows:
Ar ns2 Fs
As nr2 Fr
Fs ¼ Fr
ð3Þ
where the subscripts s and r designate the sample and the
reference respectively; A is the absorbance at the excitation
wavelength, n is the refractive index of the relevant solution, and
F is the integrated area under the corrected emission spectrum.
As shown in Table 1, with increasing solvent polarity, the F of
XJQ variesslightlyexceptinhighly polar CH3CN, whereas the F
of BAQ, SFQ, and BLQ decreases monotonically and obviously.
Considering the existence of an electron donor at one end and an
electron acceptor at the other end, the latter response is likely due
to the ‘twisted intramolecular charge transfer’ (TICT) effect.[36]
The three compounds BAQ, SFQ, and BLQ undergo strong ICT
from the donor to the acceptor in the excited state, which is
accompanied by a twist around the bond joining the donor and the
acceptor. The F values of XJQ are significantly smaller than
those of the other three compounds (BAQ, SFQ, and BLQ). As
we know, the nitro group mostly acts as a fluorescence quencher
owing to its non-radiative transfer, which consumes the excited
energy by strong vibration of the group.[37,38]
100
0
450
500
550
600
650
700
Wavelength [nm]
(b)
1200
1000
800
600
400
200
0
5.2
5.0
4.8
4.6
4.4
4.2
300 mW
400 mW
500 mW
600 mW
700 mW
800 mW
Experimental data
Fitted results
Slope – 2.02
2.4 2.5 2.6 2.7 2.8 2.9 3.0
log/in
Two-Photon Properties
480
520
560
600
640
680
The non-linear optical properties of the target compounds BAQ,
SFQ, BLQ, and XJQ are listed in Table 1. Representative two-
photon excited fluorescence (TPEF) spectra of BAQ in THF are
shown in Fig. 5.
Wavelength [nm]
Fig. 5. (a) Two-photon excited fluorescence spectra of BAQ in THF
pumped by femtosecond laser pulses at 500 mW under different excitation
wavelengths. (b) Two-photon excited fluorescence spectra of BAQ in THF
at 830 nm under different input power levels. Inset is the logarithmic plot
of the output fluorescence integral (Iout) of BAQ versus the input laser
power (Iin).
As observed from Fig. 2, in the wavelength range
500–1000 nm, there is no linear absorption for the four target
compounds. During the test, on excitation from 690 to 950 nm,
laser-induced fluorescence appeared, which can be ascribed to
frequency up-converted TPEF. The inset in Fig. 5b shows a
log–log plot of the excited fluorescence signal versus the laser
power; the slope value is 2.02 for BAQ. It provides direct
evidencefor the quadratic dependence ofthe excited fluorescence
intensity on the input laser power, suggesting a two-photon
excitation mechanism. The other compounds (SFQ, BLQ, and
XJQ) also proved to have the same excitation mechanism.
It can be seen from Table 1 that the peak wavelengths of
TPEF are clearly red-shifted by 27–67 nm compared with those
of OPEF in THF and TOL, which was attributed to the fluores-
cence reabsorption effect within the solutions.[39] The similari-
ties between TPEF and OPEF indicate that both of the emissions
for the given compounds are from the same excited state.
The s values of the target compounds were measured using
the two-photon induced fluorescence method. A femtosecond
Ti : sapphire laser system (680–1080 nm, 80 MHz, 140 fs) was
used as the light source. The incident average power of 500 mW
was adjusted with a Glan prism. Then, the fluorescent emission
was collected and recorded on an Ocean Optics USB 4000-FLG
spectrofluorometer. The samples were dissolved in different
solvents with a concentration of 1 ꢀ 10ꢁ3 mol Lꢁ1. The s values
were determined with the following equation:
the fluorescence quantum yield; n and c are the refractive index
and the concentration of the solution. In the present work, we
selected fluorescein in 0.1 mol Lꢁ1 sodium hydroxide (c ¼ 1 ꢀ
10ꢁ3 mol Lꢁ1) as the reference; the s value of the reference was
taken from the literature.[40]
The s values of the target compounds in THF and TOL in the
690–950 nm region are displayed in Fig. 6. The experiments
reveal that from 690 to 950 nm, the s values are dependent on the
excitation wavelength. The optimal excitation wavelengths in
THF and TOL are both at 830 nm (BAQ, BLQ) and 770 nm
(SFQ, XJQ). The maximum s values in THF (TOL) were
calculated to be 851 (545) GM for BAQ, 216 (83) GM for
SFQ, 561 (309) GM for BLQ, and 447 (223) GM for XJQ
respectively. All of the target compounds have larger a s in THF
than in TOL and follow the sequence BAQ . BLQ . XJQ .
SFQ in both solvents.
In order to investigate the influence of different electron
donors (or acceptors) on the s of the target compounds, DFT
calculations were performed using the Gaussian 09 program and
B3LYP 6-31G basis sets were used for the calculations. Their
optimised structures are depicted in Fig. S1 (Supplementary
Material). The energy levels and the electron cloud distributions
of the frontier molecular orbitals are shown in Fig. 7. The
HOMO and LUMO diagrams clearly show that the typical
ICT processes have happened to all four target compounds. As
for the three A-p-D compounds (BAQ, SFQ, and BLQ), most of
Fs Fr nr cr
Fr Fs ns cs
ss ¼
sr
ð4Þ
where the subscripts s and r denote the sample and the reference
respectively; F and F represent the TPEF integral intensity and

Photophysical Properties of All-trans A-p-D (A0) Compounds
G
(a) 900
800
700
600
500
400
300
200
100
0
Experimental
BAQ
SFQ
BLQ
XJQ
Materials and Methods
DMF and Et3N were dried and distilled before use. All the other
chemicals and solvents were purchased as reagent grade and
used without further purification. Melting points were measured
on an X-4 micromelting point apparatus without correction.
1H NMR spectra were recorded using a Bruker Avance III 500
spectrometer in CDCl3 or [D6]DMSO solvent with tetra-
methylsilane (TMS) as an internal standard. FT-IR spectra were
recorded on a Thermo Nicolet 6700 spectrometer using KBr
pellets. Mass spectra were recorded on a Thermo LCQ TM Deca
XP plus ion-trap mass spectrometer by electrospray ionization
mass spectrometry (ESI-MS). Elemental analyses were deter-
mined with a Thermo Finnigan Flash EA 1112 apparatus.
The linear absorption spectra were recorded on a Shimadzu
UV-2550 UV–visible spectrophotometer. The OPEF spectra
were recorded using an RF-5301PC fluorescence spectropho-
tometer with the maximum absorption wavelengths as the
excitation wavelengths. F was determined using quinine sulfate
in 0.5 mol Lꢁ1 sulfuric acid as the standard.
680 700 720 740 760 780 800 820 840 860 880 900 920 940 960
Wavelength [nm]
(b)
600
BAQ
SFQ
BLQ
XJQ
500
400
300
200
100
0
[(4-Ethenylphenyl)methyl]phosphonic Acid Diethyl
Ester (LSZ)
LSZ wasprepared via the methodinreference[41]. Yield:90.6 %.
4-[(1E)-2-(4-Ethenylphenyl)ethenyl]-N,
N-diphenylbenzenamine (3a)
4-(Diphenylamino)benzaldehyde (15 mmol, 4.10 g), LSZ
(10 mmol, 2.54 g), tBuOK (20 mmol, 2.24 g) and 7-mm stainless
steel balls were placed in a grinding jar. The grinding jar was
placed in a planetary ball-mill and stirred at 550 rotations per
minute for 2 h at room temperature. The mixture became sticky
and 60 mL CH2Cl2 was added to the jar, then the reaction
mixture was washed twice with 200 mL water. The resulting
organic layer was dried over MgSO4 and concentrated under
vacuum. The residue was isolated by silica-gel column chro-
matography (light petroleum/ethyl acetate 10 : 1 v/v) to afford
light-yellow needle crystals. Yield 2.99 g; 80.2 %, mp 192–
1938C. dH ([D6]DMSO, 500 MHz) 7.55 (d, J 8.3, 2H), 7.52 (d, J
8.7, 2H), 7.47 (d, J 8.3, 2H), 7.33 (dd, J1 8.3, J2 7.6, 4H), 7.22 (d,
J 16.4, 1H), 7.12 (d, J 16.4, 1H), 7.08 (t, J 7.4, 2H), 7.05 (dd, J1
8.5, J2 0.9, 4H), 6.96 (d, J 8.6, 2H), 6.73 (dd, J1 17.7, J2 11.0,
1H), 5.85 (d, J 17.9, 1H), 5.26 (d, J 11.3, 1H). vmax (KBr)/cmꢁ1
3025, 1588, 1512, 1493, 1334, 1282, 1176, 970, 839, 753, 696,
533. m/z (ESI-MS) 374.4 [M þ H]þ. Anal Calc. for C28H23N: C
90.04, H 6.21, N 3.75; found C 90.16, H 6.23, N 3.79 %.
680 700 720 740 760 780 800 820 840 860 880 900 920 940 960
Wavelength [nm]
Fig. 6. Two-photon absorption cross-sections of the target compounds
BLQ, SFQ, BAQ, and XJQ in (a) THF; and (b) TOL in the 690–950 nm
regions.
the electron clouds of the HOMO are distributed on the triphe-
nylamine (or thiophene, or pyrrole) donor and the styrene
p-bridge, whereas in the LUMO, the electron cloud density
localised on the donors decreases (especially for BAQ), and the
electron cloud density on the terminal formyl acceptor increases
significantly. For the A-p-A0 compound (XJQ), the electron
transfer is from the formyl group to the more strongly electron-
withdrawing nitro group. The calculated HOMO–LUMO
energy gaps (DE) are 2.64 (BAQ), 3.01 (SFQ), 2.83 (BLQ),
and 2.85 (XJQ) eV respectively. The s value shows a positive
correlation with me – mg, but negative correlation with DE. It is
noted that the s values follow the sequence BAQ . BLQ .
XJQ . SFQ, which is consistent with the calculated results of
DE and me – mg.
2-[(1E)-2-(4-Ethenylphenyl)ethenyl]thiophene (3b)
The synthesis of this compound was similar to 3a. Off-white
flaky crystals. Yield 76.6 %, mp 129–1318C. dH (CDCl3,
500 MHz) 7.45 (d, J 8.4, 2H), 7.41 (d, J 8.4, 2H), 7.25 (d, J 16.1,
1H), 7.21 (d, J 5.1, 1H), 7.09 (d, J 3.4, 1H), 7.02 (dd, J1 5.1, J2
3.5, 1H), 6.93 (d, J 16.1, 1H), 6.73 (dd, J1 17.6, J2 10.9, 1H), 5.79
(dd, J1 17.5, J2 0.6, 1H), 5.27 (dd, J1 10.8, J2 0.6, 1H). vmax
(KBr)/cmꢁ1 3067, 1622, 1505, 1406, 1228, 1178, 960, 832, 691,
515. m/z (ESI-MS) 213.1 [M þ H]þ. Anal Calc. for C14H12S: C
79.20, H 5.70; found C 79.38, H 5.82 %.
Conclusions
In the present work, a series of all-trans A-p-D (A0) compounds
BAQ, SFQ, BLQ, and XJQ were easily synthesised using a
three-step reaction route. Their linear absorption, one-photon
excited fluorescence, two-photon absorption, and two-photon
excited fluorescence were systematically investigated in various
solvents. All the compounds show obvious solvatochromic
effects and correspondingly large s values. They may have a
potential application as polarity-sensitive TPF probes.
2-[(1E)-2-(4-Ethenylphenyl)ethenyl]-1-methyl-1H-pyrrole (3c)
The synthesis of this compound was similar to 3a. Yellow
crystalline powder. Yield 73.8 %, mp 74–768C. dH (CDCl3,

H
Y.-L. Pan et al.
0
BAQ
SFQ
BLQ
XJQ
LUMO ꢂ 1: ꢀ1.39 eV
ꢀ1
LUMO ꢂ 1: ꢀ1.60 eV
LUMO ꢂ 1: ꢀ2.45 eV
ꢀ2
LUMO: ꢀ2.21 eV
HOMO: ꢀ5.04 eV
LUMO: ꢀ2.28 eV
LUMO: ꢀ2.39 eV
ꢀ3
ꢀ4
ꢀ5
LUMO: ꢀ3.06 eV
HOMO: ꢀ4.92 eV
HOMO: ꢀ5.40 eV
ꢀ6
ꢀ7
HOMO: ꢀ5.91 eV
HOMO ꢀ 1: ꢀ6.09 eV
Fig. 7. Energy levels and electron cloud distributions of the frontier molecular orbitals.
500 MHz) 7.43 (d, J 8.4, 2H), 7.39 (d, J 8.4, 2H), 6.98 (d, J 16.2,
1H), 6.86 (d, J 16.1, 1H), 6.72 (dd, J1 17.6, J2 10.9, 1H), 6.66
(t, J 2.0, 1H), 6.51 (dd, J1 3.7, J2 1.4, 1H), 6.17 (t, J 3.2, 1H), 5.76
(d, J 17.7, 1H), 5.24 (d, J 11.0, 1H). vmax (KBr)/cmꢁ1 3026,
2941, 2816, 1698, 1667, 1624, 1598, 1470, 1425, 1300, 1060,
958, 821, 712. m/z (ESI-MS) 210.3 [M þ H]þ. Anal Calc. for
C15H15N: C 86.08, H 7.22, N 6.69; found C 86.24, H 7.37,
N 6.84 %.
146.87, 143.24, 138.47, 137.51, 136.72, 135.52, 134.98, 131.66,
130.02, 129.61, 128.37, 127.73, 127.37, 126.94, 126.69, 126.34,
124.22, 123.35, 122.89. vmax (KBr)/cmꢁ1 3024, 1696, 1587,
1510, 1491, 1330, 1284, 1168, 965, 833, 752, 696, 546. m/z
(ESI-MS) 478.1 [M þ H]þ. Anal Calc. for C35H27NO: C 88.02,
H 5.70, N 2.93; found C 88.17, H 5.85, N 3.21 %.
2-[(1E)-2-[4-[(1E)-2-(4-Formylphenyl)ethenyl]phenyl]
ethenyl]thiophene (SFQ)
1-Ethenyl-4-[(1E)-2-(4-nitrophenyl)ethenyl]benzene (3d)
The synthesis of this compound was similar to BAQ. Yellow
crystalline powder. Yield 64.8 %, mp 220–2228C. dH ([D6]
DMSO, 500 MHz) 9.99 (s, 1H), 7.92 (d, J 8.3, 2H), 7.84 (d, J 8.3,
2H), 7.67 (d, J 8.4, 2H), 7.63 (d, J 8.4, 2H), 7.53 (d, J 16.2, 1H),
7.50 (d, J 16.4, 1H), 7.49 (d, J 5.1, 1H), 7.41 (d, J 16.4, 1H), 7.25
(d, J 3.4, 1H), 7.09 (dd, J1 5.1, J2 3.5, 1H), 6.98 (d, J 16.2, 1H). dC
([D6]DMSO, 125 MHz) 192.33, 143.18, 142.32, 136.79,
135.80, 135.00, 131.56, 130.17, 130.01, 128.02, 127.91, 127.37,
127.18, 126.95, 126.71, 125.54, 122.33. vmax (KBr)/cmꢁ1 3022,
1697, 1621, 1593, 1421, 1211, 1166, 958, 832, 706, 541. m/z
(ESI-MS) 317.2 [M þ H]þ. Anal Calc. for C21H16OS: C 79.71,
H 5.10; found C 79.94, H 5.28 %.
The synthesis of this compound was similar to 3a. Yellow
crystalline powder. Yield 75.4 %, mp 173–1758C. dH ([D6]
DMSO, 500 MHz) 8.25 (d, J 8.8, 2H), 7.88 (d, J 8.8, 2H), 7.68 (d,
J 8.2, 2H), 7.55 (d, J 16.5, 1H), 7.53 (d, J 8.2, 2H), 7.45 (d, J 16.5,
1H), 6.77 (dd, J1 17.7, J2 11.1, 1H), 5.91 (d, J 17.7, 1H), 5.32
(d, J 11.1, 1H). vmax (KBr)/cmꢁ1 3022, 1589, 1510, 1337, 1107,
974, 848, 516. m/z (ESI-MS) 252.2 [M þ H]þ. Anal Calc. for
C16H13NO2: C 76.48, H 5.21, N 5.57; found C 76.69, H 5.43,
N 5.74 %.
4-[(1E)-2-[4-[(1E)-2-[4-(Diphenylamino)phenyl]ethenyl]
phenyl]ethenyl]benzaldehyde (BAQ)
2-[(1E)-2-[4-[(1E)-2-(4-Formylphenyl)ethenyl]phenyl]
ethenyl]-1-methyl-1H-pyrrole (BLQ)
3a (1 mmol, 0.37 g), 4-bromobenzaldehyde (1 mmol, 0.18 g), Pd
(OAc)2 (0.03 mmol, 0.007 g), tri-o-tolylphosphine (0.13 mmol,
0.04 g), and anhydrous DMF/Et3N were added to a three-necked
flask equipped with a magnetic stirrer, a reflux condenser, and a
nitrogen input tube. The mixture was stirred under N2 at 1208C
for 20 h. After cooling, the resulting mixture was poured into the
ice water and filtered. The crude product was purified by silica-
gel column chromatography (light petroleum/ethyl acetate
12 : 1 v/v) to give an orange-yellow crystalline powder. Yield:
0.34 g, 71.3 %, mp 232–2348C. dH ([D6]DMSO, 500 MHz) 9.98
(s, 1H), 7.91 (d, J 8.1, 2H), 7.83 (d, J 8.1, 2H), 7.66 (d, J 8.2, 2H),
7.61 (d, J 8.2, 2H), 7.53 (d, J 8.4, 2H), 7.50 (d, J 16.5, 1H), 7.39
(d, J 16.5, 1H), 7.33 (t, J 7.7, 4H), 7.27 (d, J 16.3, 1H), 7.14
(d, J 16.3, 1H), 7.08 (t, J 7.5, 2H), 7.05 (d, J 7.9, 4H), 6.96
(d, J 8.3, 2H). dC ([D6]DMSO, 125 MHz) 192.32, 146.92,
The synthesis of this compound was similar to BAQ. Orange-
yellow crystalline powder. Yield 56.7 %, mp 189–1918C. dH
([D6]DMSO, 500 MHz) 9.99 (s, 1H), 7.92 (d, J 8.3, 2H), 7.84 (d,
J 8.3, 2H), 7.64 (d, J 8.4, 2H), 7.60 (d, J 8.4, 2H), 7.50 (d, J 16.5,
1H), 7.38 (d, J 16.5, 1H), 7.24 (d, J 16.2, 1H), 6.90 (d, J 16.2,
1H), 6.81 (t, J 2.0, 1H), 6.51 (dd, J1 3.7, J2 1.6, 1H), 6.05 (t, J 3.1,
1H). dC ([D6]DMSO, 125 MHz) 192.33, 143.32, 138.03,
134.90, 134.86, 131.76, 131.36, 130.01, 127.30, 126.87, 126.52,
126.23, 124.26, 123.96, 118.01, 108.06, 106.84, 33.69. vmax
(KBr)/cmꢁ1 3024, 2945, 2820, 1692, 1624, 1588, 1480, 1414,
1304, 1165, 1059, 957, 825, 716. m/z (ESI-MS) 314.3 [M þ H]þ.
Anal Calc. for C22H19NO: C 84.31, H 6.11, N 4.47; found C
84.41, H 6.25, N 4.57 %.

Photophysical Properties of All-trans A-p-D (A0) Compounds
I
4-[(1E)-2-[4-[(1E)-2-(4-Nitrophenyl)ethenyl]phenyl]
ethenyl]benzaldehyde (XJQ)
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Yu, X. Q. Yu, M. H. Jiang, J. Mol. Struct. 2007, 839, 50. doi:10.1016/
J.MOLSTRUC.2006.10.044
The synthesis of this compound was similar to BAQ. Yellow
crystalline powder. Yield 68.1 %, mp 238–2408C. dH ([D6]
DMSO, 500 MHz) 10.00 (s, 1H), 8.26 (d, J 8.8, 2H), 7.93 (d, J
8.3, 2H), 7.89 (d, J 8.8, 2H), 7.85 (d, J 8.3, 2H), 7.74 (s, 4H), 7.58
(d, J 16.4, 1H), 7.53 (d, J 16.6, 1H), 7.49 (d, J 16.6, 1H), 7.45 (d,
J 16.4, 1H). dC ([D6]DMSO, 125 MHz) 192.38, 146.19, 144.00,
143.05, 136.90, 136.34, 135.11, 132.76, 131.42, 130.03, 127.79,
127.61, 127.43, 127.29, 127.05, 126.65, 124.05. vmax (KBr)/
cmꢁ1 3056, 1693, 1595, 1512, 1339, 1107, 964, 806, 541. m/z
(ESI-MS) 356.4 [M þ H]þ. Anal Calc. for C23H17NO3: C 77.73,
H 4.82, N 3.94; found C 77.89, H 4.91, N 4.25 %.
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Supplementary Material
Properties and spectra of target compounds BAQ, SFQ, BLQ,
and XJQ are available in the Supplementary Material.
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Acknowledgements
We are grateful for financial support from the Natural Science Foundation of
Zhejiang province, China, (grant No. LY15B030006) and the National
Natural Science Foundation of China (grant no. 21103151).
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