An attempt of molecular design and synthesis of 3,4′/4,3′-disubstituted benzylideneanilines with specified UV-Vis absorption maximum wavelength

Article abstract of DOI:10.1002/poc.3341

Thirty-one samples of 3,4′/4,3′-disubstituted benzylideneanilines (XBAY) with specified UV-Vis absorption maximum wavelength (λ_max) were designed and synthesized by applying the equation (Eqn (1)) which was abstracted from the UV-Vis absorption

Full text of DOI:10.1002/poc.3341

Research Article
Received: 7 June 2014,
Revised: 9 July 2014,
Accepted: 16 July 2014,
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI: 10.1002/poc.3341
An attempt of molecular design and synthesis
of 3,4′/4,3′-disubstituted benzylideneanilines
with specified UV–Vis absorption maximum
wavelength
Linyan Wanga,b,c, Chaotun Caob,c and Chenzhong Caob,c*
Thirty-one samples of 3,4′/4,3′-disubstituted benzylideneanilines (XBAY) with specified UV–Vis absorption maximum wave-
length (λmax) were designed and synthesized by applying the equation (Eqn (1)) which was abstracted from the UV–Vis ab-
sorption maximum wavelength energy (νmax = 1/λmax) of 4,4′-disubstituted benzylideneanilines. Then, the UV–Vis data (λmax
)
of the designed compounds were measured in anhydrous ethanol. The predicted UV–Vis data of designed compounds are in
agreement with the experimental ones, in which the mean absolute error is 2.9 nm. The results show that Eqn (1) is applicative
for the prediction of UV–Vis absorption λmax values of both 4,4′-disubstituted benzylideneanilines and 3,4′/4,3′-disubstituted
benzylideneanilines. For a same pair of groups (X and Y), one can at least get four disubstituted benzylideneaniline compounds
which have different λmax values. It perhaps provides a convenient method to design an optical material for benzylideneaniline
compounds. Copyright © 2014 John Wiley & Sons, Ltd.
Keywords: disubstituted benzylideneaniline; UV spectrum; molecular design; synthesis
In our previous research,[15–20] the excited-state substituent
constants have been proposed to quantify the influence of
INTRODUCTION
substituent on the UV–Vis absorption νmax values and were
applied successfully in quantifying the UV–Vis absorption νmax
values of compounds, such as XPh, XPhY, XPh(CH = CH)nPhY
(n = 0, 1, 2), XPhCH = NPhY and XPh(CH = CHPh)nY (n = 0, 1, 2).
Moreover, a general equation of quantifying the UV–Vis ab-
sorption νmax values of 4,4′-disubstituted benzylideneanilines
(XBAY) has been proposed,[15] which is rewritten as shown in
Eqn (1).
In recent years, optoelectronic materials have attracted extensive
attention as a new type of function material. In the field of opto-
electronic materials, the liquid crystal and nonlinear optical
(NLO) material are the hot topics and have been studied deeply,
which involve inorganic materials and organic materials.[1–3]
Compared with inorganic materials, organic materials have vaster
application prospects because their molecules are easy to be de-
signed and assembled. Some organic compounds containing
classical π conjugate system are applied well in many fields of op-
tical function materials due to their potential optoelectronic
properties.[4–7] The benzylideneanilines are a kind of typical com-
pounds that have π conjugate system; their polymers and coordi-
nation compounds are important optical functional compounds
and have been applied extensively in the fields of liquid crystal
and NLO material.[3,8–10] For example, Ramamurthi[11,12] et al.
have made many linear and nonlinear studies deeply about
the compounds of 4-bromo-4′-chloro benzylideneaniline and
4-bromo-4′-dimethylamino benzylideneaniline, and attained
meaningful results. The previous studies of benzylideneanilines
mostly focus on the synthesis, photoelectric performance
and quantitative molecular structure–performance relation-
ship.[10,13–15] As we know, luminescent materials and filters have
particularly a close connection to their UV–Vis absorption maxi-
mum wavelength energy; if a designed optoelectronic material
can be put into a practical application, its molecular UV–Vis ab-
sorption maximum wavelength energy (νmax) must be predicted
accurately in advance. Therefore, to design and synthesize a se-
ries of target compounds with the specified UV–Vis absorption
νmax ¼ 32119:79 ꢀ 718:51σðXÞ þ 1197:18σðYÞ ꢀ 1017:23Δσ2
X
ex
cc
ex2
cc
þ 1632:49
σ
ꢀ 229:53Δσ
(1)
* Correspondence to: Chenzhong Cao, School of Chemistry and Chemical Engi-
neering, Hunan University of Science and Technology, Xiangtan 411201, China.
E-mail: czcao@hnust.edu.cn
a L. Wang
School of Chemistry and Chemical Engineering, Central South University,
Changsha 410083, China
b L. Wang, C. Cao, C. Cao
School of Chemistry and Chemical Engineering, Hunan University of Science
and Technology, Xiangtan 411201, China
c L. Wang, C. Cao, C. Cao
Key Laboratory of Theoretical Organic Chemistry and Function Molecule
(Hunan University of Science and Technology), Ministry of Education, Hunan
Provincial University Key Laboratory of QSAR/QSPR, Hunan University of
Science and Technology, Xiangtan 411201, China
ν
max values is a key and an important work for getting the opto-
electronic materials with the desired performance.
J. Phys. Org. Chem. 2014
Copyright © 2014 John Wiley & Sons, Ltd.

L. WANG, C. CAO AND C. CAO
In Eqn (1): σ is the Hammett constant;
MOLECULAR DESIGN
ex
CC
σ
is the excited-state substituent constant;
Equation (1) was extracted from the UV–Vis absorption νmax
values of 72 samples of 4,4′-disubstituted benzylideneanilines,
2
Δσ2 ¼ ½σðXÞ ꢀ σðYÞꢁ ;
ex
CC
together with the corresponding σ and σ constants of para-
substituents.[15] Also, its accuracy of predicting UV–Vis absorption
νmax values of 4,4′-disubstitued benzylideneanilines has been
X
ex
ex
ex
σ
¼ σ ðXÞ þ σ ðYÞ;
CC
CC
CC
ꢀ
ꢁ
ex 2
CC
ex
ex
CC
2
Δσ
¼ σ ðXÞ ꢀ σ ðYÞ
CC
It can be seen that the UV–Vis absorption νmax values of com-
ex
CC
pounds XBAY can be calculated only known of the σ and σ
constants.[17,18,21] Therefore, we try to employ Eqn (1) to design
benzylideneanilines with the given UV–Vis absorption νmax
values. First, to calculate the UV–Vis absorption νmax values of ti-
tled compounds, then to synthesis these compounds and deter-
mine their UV–Vis absorption λmax values (λmax =1/νmax). In this
work, a meaningful result was attained by comparing the pre-
dicted values and the experimental ones.
Scheme 1. The synthesis of samples of XBAYs
Table 1. The predicted UV–Vis absorption maximum wavelength energy (νmax) and substituent constants values for the designed
compounds
a
a
σ(X)b
σ(Y)b
ν )
max.pred.(cmꢀ1 c
ex
CC
ex
CC
No.
X
Y
σ
ðXÞ
σ
ðYÞ
1
2
3
4
5
6
7
8
m-F
m-F
m-F
m-F
m-Br
m-Br
m-Br
m-Br
p-Me2N
p-MeO
p-Me
p-Cl
p-Me2N
p-MeO
p-Me
p-F
0.02
0.02
0.02
0.02
ꢀ0.03
ꢀ0.03
ꢀ0.03
ꢀ0.03
ꢀ0.03
0.10
ꢀ1.81
ꢀ0.50
ꢀ0.17
ꢀ0.22
ꢀ1.81
ꢀ0.50
ꢀ0.17
0.06
ꢀ0.22
ꢀ1.81
ꢀ0.03
ꢀ0.03
ꢀ0.03
ꢀ0.03
ꢀ0.03
ꢀ0.03
0.02
0.34
0.34
0.34
0.34
0.39
0.39
0.39
0.39
0.39
ꢀ0.83
ꢀ0.27
ꢀ0.17
0.23
ꢀ0.83
ꢀ0.27
ꢀ0.17
0.06
25 799
30 328
31 154
31 799
25 601
30 157
30 986
31 848
31 672
26 493
28 314
31 273
31 363
31 023
29 725
28 483
28 040
31 497
32 131
32 010
30 719
29 567
27 938
31 422
32 059
31 979
30 744
29 614
28 313
30 366
29 143
9
m-Br
p-Cl
0.23
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
m-MeO
p-Me2N
p-MeO
p-Cl
p-CF3
p-CN
p-NO2
p-Me2N
p-MeO
p-Me
p-Cl
p-Me2N
m-Me
m-Me
m-Me
m-Me
m-Me
m-Me
m-F
m-F
m-F
m-F
m-F
m-F
m-Br
m-Br
m-Br
m-Br
m-Br
m-Br
0.12
ꢀ0.83
ꢀ0.07
ꢀ0.07
ꢀ0.07
ꢀ0.07
ꢀ0.07
ꢀ0.07
0.34
0.34
0.34
0.34
0.34
0.34
0.39
0.39
0.39
0.39
0.39
0.39
0.12
ꢀ1.81
ꢀ0.50
ꢀ0.22
ꢀ0.12
ꢀ0.70
ꢀ1.17
ꢀ1.81
ꢀ0.50
ꢀ0.17
ꢀ0.22
ꢀ0.70
ꢀ1.17
ꢀ1.81
ꢀ0.50
ꢀ0.17
ꢀ0.22
ꢀ0.70
ꢀ1.17
ꢀ1.81
ꢀ0.70
ꢀ1.17
ꢀ0.83
ꢀ0.27
0.23
0.54
0.66
0.78
ꢀ0.83
ꢀ0.27
ꢀ0.17
0.23
0.66
0.78
ꢀ0.83
ꢀ0.27
ꢀ0.17
0.23
0.66
0.78
0.02
0.02
0.02
0.02
p-CN
p-NO2
p-Me2N
p-MeO
p-Me
p-Cl
0.02
ꢀ0.03
ꢀ0.03
ꢀ0.03
ꢀ0.03
ꢀ0.03
ꢀ0.03
0.10
p-CN
p-NO2
p-Me2N
p-CN
m-MeO
m-MeO
m-MeO
ꢀ0.83
0.10
0.10
0.66
0.12
0.12
p-NO2
0.78
a
ex
CC
ex
CC
ex
CC
For p- or m-substituent, the σ is the σ ðpÞ or σ ðmÞ, respectively.
bFor p- or m-substituent, the σ is the σp or σm, respectively.
cνmax = 1/λmax
.
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MOLECULAR DESIGN OF SCHIFF BASE WITH SPECIFIED UV ABSORPTION WAVELENGTH
Table 2. The predicted UV–Vis data and experimental ones of the designed compounds
No.
X
Y
λ
max.pred.(nm)a
ν
max.pred.(cmꢀ1 a
)
λ
max.expt.(nm)b
ν )
max.expt.(cmꢀ1 b
1
2
3
4
5
6
7
8
m-F
m-F
m-F
m-F
m-Br
m-Br
m-Br
m-Br
p-Me2N
p-MeO
p-Me
p-Cl
p-Me2N
p-MeO
p-Me
p-F
387.6
329.7
321.0
314.5
390.6
331.6
322.7
314.0
315.7
377.5
353.2
319.8
318.9
322.3
336.4
351.1
356.6
317.5
311.2
312.4
325.5
338.2
357.9
318.3
311.9
312.7
325.3
337.7
353.2
329.3
343.1
25 799
30 328
31 154
31 799
25 601
30 157
30 986
31 848
31 672
26 493
28 314
31 273
31 363
31 023
29 725
28 483
28 040
31 497
32 131
32 010
30 719
29 567
27 938
31 422
32 059
31 979
30 744
29 614
28 313
30 366
29 143
385.4
337.0
321.3
314.4
388.5
338.6
323.4
312.2
317.2
379.5
356.9
314.8
316.2
321.2
330.5
349.5
349.9
318.4
313.4
310.5
323.6
340.3
360.5
315.2
312.3
321.5
327.5
339.4
353.3
335.2
348.4
25 946
29 676
31 128
31 809
25 739
29 531
30 921
32 033
31 528
26 350
28 020
31 765
31 631
31 135
30 254
28 609
28 582
31 410
31 906
32 205
30 907
29 388
27 738
31 722
32 017
31 103
30 532
29 465
28 301
29 830
28 702
9
m-Br
p-Cl
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
m-MeO
p-Me2N
p-MeO
p-Cl
p-CF3
p-CN
p-NO2
p-Me2N
p-MeO
p-Me
p-Cl
p-Me2N
m-Me
m-Me
m-Me
m-Me
m-Me
m-Me
m-F
m-F
m-F
m-F
m-F
m-F
m-Br
m-Br
m-Br
m-Br
m-Br
m-Br
p-CN
p-NO2
p-Me2N
p-MeO
p-Me
p-Cl
p-CN
p-NO2
p-Me2N
p-CN
m-MeO
m-MeO
m-MeO
p-NO2
aλmax.pred is the predicted UV–Vis absorption maximum wavelength of the target compounds, νmax.pred. = 1/λmax.pred
bλmax.expt. is the experimental UV–Vis absorption maximum wavelength of the target compounds, νmax.expt. = 1/λmax.expt.
.
.
of 3,4′/4,3′-disubstituted benzylideneanilines
by using Eqn (1). Compared with the molecular
structure of 4,4′-disubstituted benzylidenea-
nilines, we think, the 3,4′/4,3′-disubstituted
benzylideneanilines should have different
UV–Vis absorption νmax values. Therefore,
if we can design some 3,4′/4,3′-disubstituted
benzylideneanilines, we will get some com-
pounds with different UV–Vis νmax values from
the corresponding 4,4′-disubstituted benzylide-
neanilines. In this work, the Hammett constants
σ (para/meta-substituent) and the excited-state
substituent constantsσeCxC (para/meta-substituent)
are employed, and then we use Eqn (1) to pre-
Figure 1. The plot of the predicted UV–Vis absorption maximum wavelengths (λmax) versus
the experimental ones for the compounds of Table 2
ex
ccðmÞ
Table 3. The absolute error distribution
verified. At that time, there were no σ
values of meta-
substituent so that the prediction of UV–Vis absorption νmax
values of the meta-substituted benzylideneanilines couldn’t be
Range of absolute errors
in nm
Number of compounds
from Table 2
0–3.0
3.1–6.0
6.1–9.0
carried out. Recently, Cao[18] et al. proposed excited-state substitu-
22
5
4
ex
ccðmÞ
ent constants σ
values for several meta-substituents, which
makes it possible to calculate the UV–Vis absorption νmax values
J. Phys. Org. Chem. 2014
Copyright © 2014 John Wiley & Sons, Ltd.
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L. WANG, C. CAO AND C. CAO
values are in range of 22 612 to 32 444 cmꢀ1
,
that is λmax from 442.2 to 308.2 nm (the gap
is 134 nm).
Combining the 31 samples of this work in
Table 2 and the 72 samples of 4,4′-disubstitued
benzylideneanilines reported by Chen[15] into
one data set (103 samples of compounds), we
plot their predicted wavelength (λmax.pred.) versus
the experimental ones (λmax.expt.), and got Fig. 2.
As seen from Fig. 2, the UV–Vis absorption
λmax values of the designed 3,4′/4,3′-disubsti-
tuted benzylideneanilines in this work fall on
the trend line of the UV–Vis absorption λmax
values of 4,4′-disubstituted benzylideneanilines
accurately. It means that Eqn (1) is feasible to
Figure 2. Plot of the predicted wavelength versus the experimental ones of 103 samples of
XBAY (the symbol ‘ο’ represents the 31 samples of this work, and the ‘Δ’ represents the 72 sam-
ples of 4,4′-disubstituted benzylideneanilines in reference [15])
Table 4. The difference of UV–Vis absorption maximum wavelength (λmax) for some pairs of molecules
No.
1
X
Y
λ
max.expt.(nm)
No.
3
X
Y
λ
max.expt.(nm)
p-F
m-F
p-Me
p-Me
317.4
321.3
311.3
313.4
370.0
379.5
359.7
353.3
p-F
m-F
p-Me2N
p-Me2N
p-F
m-F
p-MeO
p-MeO
p-Me2N
p-Me2N
p-F
374.6
385.4
356.7
349.9
330.1
337.0
314.9
318.4
p-Me
p-Me
p-MeO
m-MeO
p-Me2N
p-Me2N
p-F
m-F
m-F
2
p-Me2N
p-Me2N
p-MeO
m-MeO
4
p-MeO
p-MeO
p-F
m-F
dict the UV–Vis absorption νmax values of the 3,4′/4,3′-disubsti-
tuted benzylideneanilines, including 31 samples of target
compounds in all, as shown in Scheme 1. The substituents in
the designed benzylideneanilines are of electron-withdrawing
substituents (e.g. NO2, CN) and electron-donating substituents
(e.g. NMe2, OMe). The predicted UV–Vis absorption νmax values
of target compounds were listed in Table 1.
make a molecule design of 3,4′/4,3′-disubstituted benzylide-
neanilines with specified UV–Vis absorption λmax values.
Further, comparing the designed 3,4′/4,3′-disubstituted
benzylideneaniline molecules with the corresponding 4,4′-
disubstitued benzylideneaniline molecules, their difference of
UV–Vis maximum wavelength (λmax.expt.) can be observed. Some
pairs of molecules were listed in Table 4. The results of Table 4
show us that one can use a pair of groups (X and Y) to design di-
substituted benzylideneanilines with different λmax values, for ex-
ample, Me2N and MeO, the λmax values are four cases (353.3,
359.7, 370.0 and 379.5 nm) as they are in p- or m-position respec-
tively, in which the Δλmax is about 26 nm. For the pair of F and
Me2N, the Δλmax is about 35 nm. Generally, the Δλmax increases
as the |σ(X) ꢀ σ(Y)| value increases. It provides us a convenient
method to obtain the disubstituted benzylideneanilines which
have different λmax values in optical materials.
RESULTS AND DISCUSSIONS
The predicted UV–Vis absorption νmax values of 31 samples in
Table 1 are in range of 25 601 to 32 131 cmꢀ1, that is λmax from
390.6 to 311.2 nm. In order to test the reliability of the predicted
values, these 31 designed samples of Table 1 were synthesized,
and also their UV–Vis absorption maximum wavelengths (λmax.expt
)
in ethanol were determined, which were listed in Table 2.
Using the predicted UV–Vis absorption νmax values, we can
calculate their corresponding UV–Vis absorption λmax values
CONCLUSIONS
(λmax = 1/νmax). Figure 1 is the plot of λmax.pred. versus λmax.expt.
.
Table 2 and Fig. 1 show that the predicted values (λmax.pred.
)
The model Eqn (1) derived from 4,4′-disubstituted benzylide-
neanilines is also suitable for predicting the UV–Vis absorption νmax
values of 3,4′/4,3′-disubstituted benzylideneanilines. The predicted
wavelength values accord with the experimental ones well despite
the UV–Vis absorption λmax values of the interested compounds
distribute in a large range. Equation (1) is of great theoretical signif-
icance in guiding the design and synthesis of optoelectronic mate-
rial which contains aromatic Schiff base molecules. And for the
disubstituted benzylideneanilines with a same pair of groups
(X and Y), we can attain the molecules with different UV–Vis ab-
sorption λmax values just as the position of the substituents
changes, and their Δλmax increases as the |σ(X) ꢀ σ(Y)| value
are in agreement with the experimental values (λmax.expt.). The
mean absolute error between the predicted values and the ex-
perimental ones is 2.9 nm.
Among the absolute errors, the minimum is 0.1 nm, and the
maximum is 8.8 nm. The absolute error distribution can be seen
in Table 3. Although the absolute errors of several compounds
are somewhat large, the predicted data and the experimental
data coincide well as a whole.
In our reported work,[15] the UV–Vis absorption νmax values of
72 samples of 4,4′-disubstitued benzylideneanilines were used to
establish the model Eqn (1), in which the UV–Vis absorption νmax
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J. Phys. Org. Chem. 2014

MOLECULAR DESIGN OF SCHIFF BASE WITH SPECIFIED UV ABSORPTION WAVELENGTH
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The substituted benzylideneanilines were all synthesized with
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327.
1
rified with anhydrous alcohol and were confirmed with H-NMR
and 13C-NMR. All UV–Vis spectra of the target compounds were
measured in anhydrous ethanol, and the obtained absorption
νmax values were listed in Table 2. The detailed data of the syn-
thesized compounds are available in the Supporting Information.
Acknowledgements
[16] C. Z. Cao, G. F. Chen, Y. X. Wu, Sci China Chem 2011, 54(11), 1735.
[17] C. Z. Cao, G. F. Chen, Z. Q. Yin, J Phys Org Chem 2008, 21(9), 808.
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[19] G. F. Chen, C. Z. Cao, J Phys Org Chem 2010, 23, 776.
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[21] C. Hansch, A. Leo, R. Taft, Chem Rev 1991, 91(2), 165.
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The project was supported by the National Natural Science
Foundation of China (no. 21272063) and the Natural Science
Foundation of Hunan (no. 14JJ3112).
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