New quinacridone derivatives: Synthesis, photophysical and third-order nonlinear optical properties

Article abstract of DOI:10.1016/j.tet.2020.131057

A series of quinacridone third-order nonlinear optical chromophores containing phenyl, 4-methoxyphenyl and N,N-bis(4-methoxyphenyl)aniline groups were designed and synthesized. The optical properties, electrical properties, theoretical calculations and Z-Scan of the compounds were measured and analyzed to investigate the relationship between structure and third-order NLO properties. The experimental results showed that the introduction of electron-donating groups at the N-position of quinacridone decreases the energy gap (E_gap) between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the molecule, and promotes intramolecular charge transfer (ICT). Quinacridone derivatives containing N, N-bis (4-methoxyphenyl) aniline have good third-order nonlinear optical properties, with the nonlinear absorption coefficient (β) value of 1.4319 × 10^?13 and the second-order superpolarizability (γ) of 2.6849 × 10^?33 esu.

Full text of DOI:10.1016/j.tet.2020.131057

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New quinacridone derivatives: Synthesis, photophysical and third-order nonlinear
optical properties
Jianhong Jia, Dong Feng, Yangcheng Sha, Chunsong Zhou, Guanqiu Liang, Yuanbin
She
PII:
S0040-4020(20)30172-1
https://doi.org/10.1016/j.tet.2020.131057
TET 131057
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 2 January 2020
Revised Date: 7 February 2020
Accepted Date: 17 February 2020
Please cite this article as: Jia J, Feng D, Sha Y, Zhou C, Liang G, She Y, New quinacridone derivatives:
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New quinacridone derivatives: Synthesis, photophysical and
third-order nonlinear optical properties
Jianhong Jia∗, Dong Feng, Yangcheng Sha, Chunsong Zhou, Guanqiu Liang, Yuanbin She∗∗
College of Chemical Engineering, Zhejiang University of Technology, Hangzhou, 310032, PR
China
AbstractꢀA series of quinacridone third-order nonlinear optical chromophores containing
phenyl, 4-methoxyphenyl and N,N-bis(4-methoxyphenyl)aniline groups were designed and
synthesized. The optical properties, electrical properties, theoretical calculations and Z-Scan
of the compounds were measured and analyzed to investigate the relationship between
structure and third-order NLO properties. The experimental results showed that the
introduction of electron-donating groups at the N-position of quinacridone decreases the
energy gap (Egap) between the highest occupied molecular orbital (HOMO) and the lowest
unoccupied molecular orbital (LUMO) of the molecule, and promotes intramolecular charge
transfer (ICT). Quinacridone derivatives containing N, N-bis (4-methoxyphenyl) aniline have
good third-order nonlinear optical properties, with the nonlinear absorption coefficient (β)
value of 1.4319×10-13 and the second-order superpolarizability (γ) of 2.6849×10-33 esu .
Keywords: Third-order NLO; Quinacridone; Z-Scan technology; ICT
1

1.Introduction
In recent years, with the development of nonlinear optical materials in the fields of
microscopy[1], optical storage micromachining[2][3], three-dimensional data storage[4][5], optical
power limitation[6][7][8] and laser conversion[9], etc., the synthesis of new organic compounds
with superior third-order nonlinear optical properties has attracted people's attention. The
polarization of organic third-order nonlinear optical materials, originating from the
delocalization of π electrons in the main chain, showed strong photoelectric coupling
characteristics: the charge is easy to move, and the time required for the polarization of the
dielectric particles to generate electric dipoles is relatively short. Compounds containing large
π organic conjugated system [10][11][12][13] have good electrochemical properties, photochemical
properties[14][15], good mechanical and processing properties. In order to obtain a third-order
nonlinear optical material with a higher the second-order superpolarizability γ value, the
molecular structure need to be reasonably modified to give the molecules a large
delocalization, a large absorption wavelength, a small Egap, and a large molecular dipole
moment. Therefore, the organic conjugated compound containing the delocalized large π
structure may preferably be a third-order nonlinear optical material.
Quinacridone is a strong electron acceptor with a highly delocalized conjugated system.
When it is connected to an electron donating unit, it will lower Egap and promote ICT,
[ 16 ]
showing excellent NLO performance.
However, the rigid coplanar structure of
quinacridone increases the intermolecular π-π stacking, resulting in extremely poor solubility,
which reduces the third-order NLO performance.[17] Although the addition of different
2

nitrogen-containing electron donors to the benzene ring of the quinacridone structure has been
studied[18], the introduction of different electron donors at their N-position has not been
studied, and we expect such designs to have better performance. Thus, a different electron
donor can be inserted at the N-position of the quinacridone to form a donor-acceptor-donor
(D-A-D) chromophore. The relationship between D, π and A has been studied by Filip Bureš
et al.[19], but the relationship between our quinacridone derivatives and third-order nonlinear
optical properties has not been verified. This system is not only expected to change the planar
structure of the quinacridone core, but also to increase the degree of conjugation of π
electrons.[20][21]
.
In this paper, we designed and synthesized a series of quinacridone-based derivatives by
coupling bromobenzene, p-methoxybromobenzene, 4-bromo-N,N-bis (4-methoxyphenyl)
aniline with the parent quinacridone molecule (Scheme 1). Structurally, the quinacridone core
tends to be planar[17][18], however, after the introduction of the electron donating groups, all
compounds have core distortion and improved solubilities. In addition, the effects of different
structures of quinacridone derivatives on optical properties, electrochemical properties and
third-order nonlinear optical properties were discussed, and further verified using
semi-empirical (ZINDO)[22][23] and density functional theory (DFT)[24][25]
.
2. Experimental section
2.1. Materials
Unless otherwise indicated, all chemicals, solvents and starting materials are used as
purchased without further purification.
3

2.2. Instruments
The 1H nuclear magnetic-resonance (1H MNR) spectra was recorded on a Varian XL-200
spectrometer with tetramethylsilane (TMS) (Bruker, SwissConfederation) as the internal
standard. MS spectra were recorded on an AB SCIEX 5800 MALDI TOF/TOF™. The
melting points were obtained using a Microscopic digital melting point instrument X-4
(Beijng tech, China) under N2 at a heating rate of 10 ·min-1. The Ultraviolet-visible (UV-vis)
absorption spectra of the synthesized compounds were recorded on a UV-1800 UV-visible
spectrophotometer (Shimadzu, Japan) with a quartz cuvette (path length 1 cm). The
fluorescence spectra were obtained with a RF-6000 PC (Shimadzu, Japan). Cyclic
voltammetry(CV) was performed on an IVIUM V63126 instrument (Ivium Technologies,
Netherlands) with a scan rate of 100 mV·s−1. A three-electrode configuration was used for the
measurements, with a platinum disk as the working electrode, a platinum wire as the counter
electrode, and an Ag/Ag+ electrode as the reference electrode.
2.3. Synthesis
2.3.1. 5,12-Biphenyl-5,12-dihydroquinolino[2,3-b]acridine-7,14-dione (1)
5,12-Dihydroquinolino[2,3-b]acridine-7,14-dione (0.20 g,0.064 mmol), cesium carbonate
(0.83 g, 0.26 mmol), CuI (0.012 g, 0.006 mmol), iodobenzeneand (0.52 g, 0.26 mmol), and
2,2,6,6-tetramethylheptane-3,5-dione (0.024 g, 0.012 mmol) were placed in a 50 mL
three-neck flask, purged with three nitrogen/vacuum cycles, and under nitrogen atmosphere
added N,N-dimethylformamide (DMF) 20 mL. The mixture was heated at reflux for 24 h and
then cooled to room temperature. The resulting mixture was poured into saturated 50 mL salt
water and filtered. The crude product was purified by column chromatography eluting with
4

1
EA/CH2Cl2 (1/200), yielding the product 1 as a orange solid (0.16 g, 54%), m.p. >400 . H
NMR (500 MHz ,CDCl3) δ 8.55 (s, 1H), 8.25 (s, 1H), 7.88-7.79 (m, 4H), 7.78-7.71 (m, 1H),
13
7.51-7.41 (m, 3H), 7.02 (d, J = 8.8 Hz, 1H). C NMR (126 MHz, CDCl3) δ 179.18, 144.32,
137.80, 137.68, 136.35, 131.69, 130.80, 129.37, 127.39, 124.76, 123.00, 119.43, 117.52,
+
115.88, 115.62, 113.35, 111.08. HRMS (ESI) m/z calcd for C32H21N2O2 (M+H)+ 465.15975,
found 465.15945.
2.3.2. 5,12-Bis(4-methoxyphenyl)-5,12-dihydroquinolino[2,3-b]acridine-7,14-dione
(2)
The synthetic procedure was basically the same as that of 1, except that compound
iodobenzene was replaced with 4-bromoanisole (0.60 g, 0.26 mmol), N,N-dimethylformamide
was replaced by N,N- dimethylacetamide, and the reaction time was extended to 48 h. The
crude product was purified by column chromatography eluting with EA/CH2Cl2 (1/40),
yielding the product 2 as an orange solid (0.21 g, 62%), m.p. >400 °C. 1H NMR (500 MHz,
CDCl3) δ 8.58 - 8.34 (m, 1H), 8.21- 8.13 (m, 1H), 7.73-7.60 (m, 1H), 7.40-7.23 (m, 6H), 6.98
(d, J = 8.8 Hz, 1H), 4.04 (s, 4H). 13C NMR (126 MHz, CDCl3) δ 179.23, 179.23, 160.67,
144.43, 144.43, 137.99, 137.40, 135.41, 130.59, 130.59, 130.38, 127.34, 124.99, 122.23,
+
119.78, 117.34, 116.67, 116.61, 115.69. HRMS (ESI) m/z calcd for C34H25N2O4 (M+H)+
525.18088, found 525.18088.
5

2.3.2. 4-Bromo-N,N-bis(4-methoxyphenyl)aniline (T-1)
4-Bromoaniline (2.00 g, 11.63 mmol), p-iodoanisole (8.16 g, 34.87 mmol), KOH (5.22 g,
93.05 mmol), CuCl (0.12 g, 1.16 mmol), and 1,10-phenanthroline monohydrate (0.42 g, 2.33
mmol) were placed in a 100 mL three-neck flask, purged with three nitrogen/vacuum cycles,
and under nitrogen atmosphere added methylbenzene 40 mL. The mixture was heated at
reflux for 24 h and then cooled to room temperature. The solvent was removed by distillation
under reduced pressure. The crude product was purified by column chromatography eluting
with PE/CH2Cl2 (4/1), yielding the product T-1 as a light yellow solid (3.98 g, 89%), 1H NMR
(500 MHz, CDCl3) δ 7.26-7.23 (m, 1H), 7.04 (d, J = 9.0 Hz, 1H), 6.86-6.77 (m, 1H), 3.81 (s,
2H).
2.3.3
5,12-Bis(4-(bis(4-methoxyphenyl)amino)phenyl)-5,12-dihydroquinolino[2,3-b]acridine-7,14-
dioneꢁ3ꢂ
The synthetic procedure was basically the same as that of 1, except that compound
iodobenzene was replaced with 4-bromo-N,N-bis(4-methoxyphenyl)aniline (0.980 g, 0.260
mmol), N,N-dimethylformamide was replaced by N,N- dimethylacetamide, and the reaction
time was extended to 48 h. The crude product was purified by column chromatography
eluting with EA/CH2Cl2 (1/40), yielding the product 3 as an orange solid (0.22 g, 60%),
m.p. >400℃.1H NMR (500 MHz, CDCl3) δ 8.52 (dd, J = 8.1, 1.5 Hz, 1H), 8.27 (s, 1H), 7.58
(ddd, J = 8.6, 6.9, 1.6 Hz, 1H), 7.35-7.28 (m, 5H), 7.29-7.22 (m, 1H), 7.18-7.13 (m, 4H),
13
7.03-6.98 (m, 1H), 6.98 (s, 5H), 3.91-3.80 (m, 7H). C NMR (126 MHz, CDCl3) δ 179.58,
6

159.56, 159.22, 149.77, 146.99, 144.60, 138.08, 135.83, 129.90, 129.76, 129.65, 127.48,
125.86, 125.15, 124.45, 123.14, 122.56, 119.76, 117.60, 116.01, 115.71, 113.44. HRMS (ESI)
m/z calcd for C60H46N4O6 (M+H)+ 919.34, found 919.3471.
+
3. Results and discussion
3.1. Synthesis and characterization
The synthetic routes for the compounds 1, 2 and 3 are shown in Scheme 1. Among them,
1, 2 and 3 are new compounds. Synthesis of quinacridone derivatives starting from a
commercially available quinacridone precursor, three target compounds were obtained by
Ullmann coupling reaction in which the target compounds 2 and 3 were reacted in
N,N-dimethylformamide solvent for 24 hours. The yield was only 15%, but the solvent was
changed to N,N-dimethylacetamide, and the reaction time was extended to 48 hours to obtain
a yield of 60%. All of target compounds were fully characterized by NMR and
High-resolution mass spectrometry.
O
O
Br
KOH, CuCl, Toulene
I
N
＋
NH2
1,10-phenanthroline monohydrate
O
Br
R
N
O
O
H
N
Cs2CO3, CuI, DMF
R
＋
Br
N
R
2,2,6,6-tetramethylheptane-3,5-dione
N
H
O
O
O
O
2:
1:
R=
R=
3:
R=
N
O
Scheme 1 The synthesis procedure of the quinacridone derivatives
7

3.2. Photophysical properties
3.2.1. Ultraviolet-visible absorption spectroscopy
To reveal the effect of different electron-donating groups on the charge transfer
absorption properties of the three compounds, the UV-visible spectra of the three compounds
were measured in CH2Cl2, as shown in Figure 1. The data are summarized in Table 1 below.
The Figure 1 shows the ultraviolet absorption range of the target compound at 220-650nm,
where the absorption at 450-550 nm is the characteristic absorption band of quinacridone.
From Figure 1 two prominent characteristic absorption bands can be observed. One of
the characteristic absorption bands lies between 220-320 nm, which is attributed to the n-π*
transition of the electrons on the heterocyclic ring and the π-π* transition of the molecule.
Another characteristic absorption band is between 450-550 nm, which is generated by the
transfer of electrons from the donor (N-R) in the molecule to the acceptor (C=O). The
stronger the electron-donating ability of the group introduced in quinacridone, the stronger the
[26]
electron-transporting ability inside the molecule, which in turn causes red shift.
The
maximum absorption peaks of compounds 1 to 3 are located at 509 nm, 511 nm, and 515 nm.
Compared with the maximum absorption peak of compound 1, the maximum absorption
peaks of 2 and 3 are red-shifted by 2 nm and 6 nm, respectively. This is due to the higher
electron-donating properties of p-methoxyphenyl and N, N-bis (4-methoxyphenyl) aniline
introduced in 2 and 3.
8

Figure 1. UV-vis absorption spectra of the quinacridone derivatives in the dilute
solution (1 × 10-5 M in CH2Cl2)
Table 1. The photophysical data of the quinacridone derivatives
Stokes shift
b
Compound
λmax (nm)
λonseta (nm)
ΦPL
λem (nm)
(nm)
291,476,509
318,481,511
292,485,515
529
539
541
0.98
0.81
-
522
562
-
137
1
2
3
177
-
a The lowest-energy absorption edge of the absorption spectra. b Tested in CH2Cl2 solution, calculation
methods and standards in Reference [27].
3.2.2. Fluorescence spectrum
Figure 2 shows the fluorescence spectrum (concentration of 2 x 10-6 M) of a D-A-D type
quinacridone derivative in toluene and CH2Cl2 using an excitation wavelength of λ = 475 nm.
Fluorescence data are shown in Table 1 and Table 2. Compound 1, 2 solution was
9

yellow-green, while compound 3 shown orange-red color. Among the tested compounds, 1 is
a planar structure, which is beneficial to the occurrence of radiation transition, so its
fluorescence quantum yield (ΦPL) in toluene and CH2Cl2 is as high as 0.94 and 0.98. A
substance with high fluorescence efficiency, the molecules of which are mostly in a planar
configuration and have a certain rigidity[28]. However, compound 3 due to the introduction of
the N,N-bis(4-methoxyphenyl)aniline group, the spatial structure of the entire molecule is
distorted, resulting in a greatly reduced ΦPL (0.35) in toluene and fluorescence quenching in
CH2Cl2. The emission peak position of compound 2 is significantly red-shifted compared to 1,
but the luminous efficiency in toluene and CH2Cl2 is lower ΦPL of 0.75 and 0.85, probably
due to ICT and the competing non-radiative process with fluorescence due to -OCH3 groups,
which facilitates the absorption of energy from the compound to high energy orbit.
Figure 2. Fluorescence spectra of the quinacridone derivatives in the dilute solution (a:
the test solvent is toluene, b: the test solvent is CH2Cl2).
10

Table 2. Fluorescence date of the quinacridone derivatives in toluene solvent.
Compound
λabs (nm)
λem (nm)
ΦPL
509
511
515
513
516
524
0.94
0.75
0.35
1
2
3
Figure 3 shows the fluorescence emission spectra of three compounds in different polar
solvents. The fluorescence emission spectra of the compounds 1 and 2 are not affected by the
polarity of the solvent, but the emission peak of the solvent in the solvent toluene showed a
slight blue shift. For compound 3, it shows fluorescence quenching or slight fluorescence in
common solvents (such as dichloromethane, DMSO, chloroform, acetonitrile, etc.). This is
because the introduction of N, N-bis (4-methoxyphenyl) aniline group destroys the planar
configuration of the molecule[28], resulting in a non-radiative transition of the excited state.
Compound 3 has fluorescence in toluene, mainly because the toluene solvent inhibits the
non-radiative transition of the molecule.
11

2
1
3
Figure 3. Fluorescence spectra of the quinacridone derivatives in various solvents .
3.3. Electrochemical properties
In order to further investigate the effect of substituent changes on the molecular
properties of the target compound, electrochemical analysis was performed by cyclic
voltammetry. Using a standard three-electrode system (with platinum carbon as the working
electrode, platinum wire as the auxiliary electrode, Ag/AgCl electrode as the reference
electrode, and ferrocene as the internal standard) as the electrolytic cell, tetrabutylammonium
hexafluorophosphate (TBAPF6) is a supporting electrolyte. The sample to be tested and the
electrolyte are dissolved in dichloromethane, wherein the TBAPF6 concentration is 0.1 M and
-3
the concentration of the analyte is 1 × 10 M, and the scanning speed is 100 mV/s. The
cyclic voltammetry curves of the three target compounds are shown in Figure 4, and the
specific data are listed in Table 3. When calculating the HOMO and LUMO energy levels of
12

the compounds, the initial oxidation potential is obtained according to the cyclic voltammetry
curve of the organic compounds, and the HOMO energy level is calculated. The LUMO
energy level is added by the HOMO value plus the band gap. The Egap[29]value is available,
and the data is shown in Table 3.
It can be seen from Table 3 that the HOMO / LUMO energy levels can calculated to be
-6.198/-3.854 eV, -6.101/-3.800 eV, -5.804/-3.512 eV for 1, 2 and 3 respectively. The
introduction of an electron donor can reduce the oxidation initiation potential of the molecule,
increase the HOMO level, facilitate the injection of holes, and increase the hole mobility of
the material [30].When the N-position of quinacridone introduces a strong electron-donating
N,N-bis(4-methoxyphenyl)aniline group, the HOMO level is significantly improved, and the
Egap between HOMO and LUMO is lowered, making electrons more prone to transition,
which is beneficial to ICT.
Table 3. CV data of the quinacridone derivatives.
Electrochemical (eV)
ꢁꢆ
Compound
ꢀ
(V)
Egap a (eV)
ꢁꢂꢃꢄꢅ
HOMOb
-6.198
-6.101
-5.804
LUMOc
-3.854
-3.800
-3.512
1.098
2.344
2.301
2.292
1
2
3
1.001
0.704
a Band gap estimated from λonset, Egap = 1240/λonset
.
b EHOMO = -(Eꢁꢁꢂꢆꢃꢄꢅ +5.1) eV. c ELUMO = Eꢁꢁꢂꢆꢃꢄꢅ + Egap
.
13

Figure 4. CV curves of the quinacridone derivatives are measured in CH2Cl2.
3.4. Nonlinear optical properties
In order to study the relationship between the structure of the compound and the
third-order nonlinear optical properties, the Z-scan curve of the three target compounds (1~3)
at 1030 nm was tested by Z-scan technique[31]
.
The sample was firstly prepared into a chloroform solution at a concentration of 1
mg/mL and placed in a sample cell having a thickness of 2 mm. The laser pulse energy used
in the experiment was 0.4 uJ[32], the wavelength was 1030 nm, the pulse width was 190 fs, and
the focal length was 250 mm. Similarly, the solvent chloroform was also measured under the
same experimental conditions and found to have no nonlinear absorption, so the effect of the
nonlinear optical effect of the solvent on the test can be ignored.
The closed-cell curve of the target compound 1~3 are shown in Figure 5. As can be seen
14

from the figure, the closed-loop curve shows a large peak-to-valley structure, indicating that
the nonlinear refractive index n2[33] of the compound is greater than zero, for self-focusing
phenomenon.
The opening curve of the target compound 1~3 are shown in Figure 6. The opening
curve of the compound 1~3 are valley-like, so these compounds are all anti-saturation
absorption. The χ(3) and γ of the compound 1~3 were calculated by the calculation method in
Reference[34]. The specific data is shown in Table 4.
Figure 5. Normalized close-aperture Z-scan curves of the quinacridone derivatives
solutions. The open circles and solid lines represent the experimental data and
theoretical fitting curves, respectively
15

Figure 6. Normalized open-aperture Z-scan curves of the quinacridone derivatives
solutions. The open circles and solid lines represent the experimental data and
theoretical fitting curves, respectively.
According to the data in Table 4, the third-order nonlinear performance exhibited by this
series of compounds is roughly the same as the expected value of the initial design of the
compound, and the nonlinear absorption coefficient ꢁβꢂwere between 1.3271~1.4319×10-13
esu. The third-order nonlinear polarizability χ(3) were between 5.5418~6.9312×10-12 esu, and
the second-order hyperpolarizability (γ) were between 1.5457~2.6849× 10-33 esu. The γ values
of 1,5-diaminopurine[35] and sulfonation in the naphthalimide derivatives[36] reported in the
literature are 5.1271×10-34 esu, 3.1541×10-34 esu. And the highest of our synthesis 3 can
reach 2.6849× 10-33 esu, the reason for the above phenomenon is attributed to the fused
16

heterocyclic structure of quinacridone, especially because the molecule contains electrons and
these structures have a carbonyl group (C= O) of the withdrawal group and electron-inducing
groups (N-R), and these structures have higher electron transport capabilities and electron
delocalization. For the convenience of comparison, the opening curve of 1~3 are placed in the
same picture as shown in Figure 7. The depth of the opening is from 3 > 2 > 1. As can be
seen from Table 4, the γ value of 3 (γ = 2.6849 × 10-33 esu) is increased by 1.74 times than the
γ value of 1 (1.54570 × 10-33 esu). 3 exhibits better third-order nonlinear performance, which
is attributed to the stronger chargeability of the N,N-bis(4-methoxyphenyl)aniline group,
which
enhances
the
HOMO
level.
As
a
strong
electron
donor,
N,N-bis(4-methoxyphenyl)aniline group has stronger power supply than phenyl and
methoxyphenyl groups, and promotes ICT, which is also very beneficial for improving the
third-order nonlinear performance of materials.
Table 4. Third-order NLO parameters of the quinacridone derivatives in CHCl3
β (m/W)
×10-13
n2 (m2/W) χ(3) R(esu) χ(3) I(esu)
χ(3) (esu)
×10-12
γ (esu)
×10-33
Compound
×10-17
×10-13
×10-12
1.3271
1.3764
1.4319
1.1742
9.5482
5.4589
5.5418
6.0252
6.9312
1.5457
1.8842
2.6849
1
2
3
1.1728
1.1586
9.7538
9.2370
5.9457
6.8694
17

Figure 7. Normalized open-aperture Z-scan curves of the quinacridone derivatives
3.5. Theoretical calculation
To further explained the relationship between the molecular structure and properties of
the synthesized target compounds, we performed a DFT calculation. The structural
optimization of the three target compounds synthesized were shown in Figure 8. The structure
of the compound was simulated by Gaussian. The quinacridone derivatives 1 and 2 have good
molecular planarity. Due to the large steric hindrance of the N,N-bis(4-methoxyphenyl)aniline
group and the quinacridone precursor, the 3 molecular structure forms a certain distortion,
which weakens the strong π-π stacking between molecules, so 3 has better solubility.
18

2
1
3
Figure 8. Optimized geometries of the quinacridone derivatives
at the B3LYP/6-31G(d) level.
Generally, for organic third-order nonlinear optical materials with excellent performance,
HOMO is mostly located in the donor region, and LUMO is located in the acceptor portion,
which is more beneficial to the transport of molecules from the donor to the acceptor, while
the molecular energy charge transfer is often associated with third-order nonlinear
performance of organic materials. The DFT theoretical calculationsꢁFigure 9ꢂ shown that
for the compounds 1 and 2, both the LUMO and HOMO orbitals fall on the quinacridone
parent ring. While compound 3 introduces a N,N-bis(4-methoxyphenyl)aniline group as a
donor at the N-position of the quinacridone, the LUMO orbital mainly falls on the
quinacridone
parent
ring,
and
the
HOMO
orbital
falls
on
the
N,N-bis(4-methoxyphenyl)aniline group. Compound 3 has a significant improvement in the
HOMO level of the introduction of the benzene ring (1) at the N-position of the quinacridone.
19

This indicated that N,N-bis(4-methoxyphenyl)aniline group has a stronger electron donating
ability than the phenyl ring. By introducing a N,N-bis(4-methoxyphenyl)aniline group as a
donor at the N-position of quinacridone, the HOMO level of 3 is increased the most, so the
compound 3 Egap(3.0064 eV) is the smallest (the theoretical calculation data is shown in Table
5. Therefore, the introduction of a strong electron donating N,N-bis(4-methoxyphenyl)aniline
group facilitates ICT and exhibits better third-order nonlinear optical performance.
Comparing the CV HOMO/LUMO level, we can find that the value of the CV test is
inconsistent with the theoretically calculated value. However, the decrease trend of
compounds 1 to 3 is consistent, so theoretical calculations have a good guiding value for the
design of compounds.
Jakob Wudarczyk and Klaus Müllen et al. found that the enhancement of the molecular
dipole moment can also reflect the enhancement of third-order nonlinear optical
performance[37]. In the molecular design, it was found through theoretical calculation that N,
N-bis(4-methoxyphenyl)aniline group also played a role in improving the molecular dipole
moment (see Table 5). A quinacridone derivative in which the N-position is substituted by a
phenyl ring has
a
molecular dipole moment of 0.0012 debye. Once
a
N,N-bis(4-methoxyphenyl)aniline group is introduced, the molecular dipole moment can be
increased to 0.5655 debye. The second-order hyperpolarizability (γ) of the third-order
nonlinear optical material is theoretically calculated in combination with the semi-empirical
ZINDO method. Theoretical calculations and experimental data are not numerically identical,
because the calculations are data obtained without solvents and gases. However, the trend of
nonlinear performance of the compounds presented by the data is completely consistent, that
20

is, the γ value: 3>2>1. From the theoretical calculation data, it can be found that the low Egap
and the large dipole moment are favorable for the third-order nonlinear optical performance.
This may be due to the introduction of the N,N-bis(4-methoxyphenyl)aniline group, which
causes distortion of the entire molecular structure, thereby reducing the π-π accumulation
between the molecules, and making the electron flow in the molecule smoother.
Figure 9. DFT-calculated frontier molecular orbitals of the quinacridone derivatives
Table 5. DFT-calculated (B3LYP/6-31G G(d)*) HOMO and LUMO energiesꢃdipole
moment, Second-order hyperpolarizability.
21

dipole
moment
(Debye)
γ (esu)
×10-33
HOMO
LUMO
Egap (eV)
Compd.
ꢁeVꢂ
ꢁeVꢂ
-5.1337
-4.9955
-4.8216
-1.9722
3.1615
3.1060
3.0064
0.0012
0.0010
0.5655
0.2606
0.3026
0.8995
1
2
3
-1.8895
-1.8152
4.Conclusions
In summary, we have reported three quinacridone derivatives with D-A-D push-pull
structure synthesized and characterized by UV, FL, NMR and HRMS spectroscopy.
Theoretical and experimental studies have shown that the introduction of
a
N,N-bis(4-methoxyphenyl)aniline donor group at the N-position of quinacridone significantly
enhances the HOMO level and reduces Egap, which facilitates charge transfer within the
molecule. The third-order NLO properties exhibited are the best among all chromophores.
The third-order NLO magnetic susceptibility (χ(3)) of the compound is 6.9312×10-12 esu, while
the second-order hyperpolarizability of the molecule γ is 2.6849×10-33 esu. The chromophore
3 exhibits significant third-order NLO performance, which is in line with our structural design
strategy. The results have clearly shown that quinacridone derivatives have great potential
applications in third-order nonlinear optical materials.
Acknowledgements
This work was supported by Yinglin Song from the College of Physical, Optoelectronics and
Energy in Soochow University for the Z-scan experiment and helpful discussions. We are
22

thankful for the financial support from the National Natural Science Foundation of
China (Grant no. 21452001).
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New quinacridone derivatives: Synthesis, photophysical and
third-order nonlinear optical properties
•
•
A series of new D-A-D structure quinacridone derivatives have been synthesized.
The N-position electron-substituted quinacridone exhibited good third-order
NLO.
•
N, N-bis (4-methoxyphenyl) aniline group will enhance third-order NLO
response.

Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered
as potential competing interests: