Influence of the side-group at C=N bridging bond of bis-aryl Schiff bases on the wavelength of absorption maximum of ultraviolet absorption spectra

Article abstract of DOI:10.1002/poc.3550

The compounds N-(benzylidene)-anilines XArCH=NArY (XBAY), N-(phenyl-ethylene)-anilines XArC(CH₃)=NArY (XPEAY) and N-phenyl-α-phenylnitrones XArCH=N(O)ArY (XPNY) have bridging group CH=N, C(CH₃)=N and CH=N(O) respectively, in which the C(CH₃)=N has a side-group methyl CH₃ at carbon end and the CH=N(O) has a side-group O atom at nitrogen end. In this work, a series of XPEAY and XPNY were synthesized, and their longest wavelength maximum λ_max (nm) of ultraviolet absorption spectra were measured. Then the change regularity of the ν_max (cm^-1, ν_max=1/λ_max) of XPEAY and XPNY were investigated, and they were compared with that of XBAY (reported by ref.26). The results indicate: (1) There are no good linear relationships between the ν_max of XBAYs and XPEAYs or XPNYs. (2) In case of a same set of X-Y group couples, the distribution of λ_max of XPEAYs is larger than that of XPNYs. (3) The side-group CH₃ makes the effect of σ(X) larger than that of σ(Y) on the ν_max of XPEAYs, whereas the O atom makes the effect of σ(Y) larger than that of σ(X) on the ν_max of XPNYs. (4) The cross-interaction between X and Y has important effect on the all ν_max. However, the cross-interaction between CH₃ and X/Y has not important effect on the ν_max of XPEAY, and the cross-interaction between O and X/Y has not important effect on the ν_max of XPNY. Copyright

Full text of DOI:10.1002/poc.3550

Research Article
Received: 29 October 2015,
Revised: 11 January 2016,
Accepted: 04 February 2016,
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI: 10.1002/poc.3550
Influence of the side-group at C=N bridging
bond of bis-aryl Schiff bases on the
wavelength of absorption maximum of
ultraviolet absorption spectra
Qingqing Luoa, Chao-Tun Caoa, Zhongzhong Caoa and Chenzhong Caob*
The compounds N-(benzylidene)-anilines XArCH=NArY (XBAY), N-(phenyl-ethylene)-anilines XArC(CH3)=NArY (XPEAY) and
N-phenyl-α-phenylnitrones XArCH=N(O)ArY (XPNY) have bridging group CH=N, C(CH3)=N and CH=N(O) respectively, in
which the C(CH3)=N has a side-group methyl CH3 at carbon end and the CH=N(O) has a side-group O atom at nitrogen
end. In this work, a series of XPEAY and XPNY were synthesized, and their longest wavelength maximum λmax (nm) of ultra-
violet absorption spectra were measured. Then the change regularity of the νmax (cm-1, νmax=1/λmax) of XPEAY and XPNY
were investigated, and they were compared with that of XBAY (reported by ref.26). The results indicate: (1) There are no
good linear relationships between the νmax of XBAYs and XPEAYs or XPNYs. (2) In case of a same set of X-Y group couples,
the distribution of λmax of XPEAYs is larger than that of XPNYs. (3) The side-group CH3 makes the effect of σ(X) larger than
that of σ(Y) on the νmax of XPEAYs, whereas the O atom makes the effect of σ(Y) larger than that of σ(X) on the νmax of XPNYs.
(4) The cross-interaction between X and Y has important effect on the all νmax. However, the cross-interaction between CH3
and X/Y has not important effect on the νmax of XPEAY, and the cross-interaction between O and X/Y has not important effect
on the νmax of XPNY. Copyright © 2016 John Wiley & Sons, Ltd.
Keywords: cross-interaction effect; N-phenyl-α-phenylnitrone; N-(phenyl-ethylene)-aniline; side-group; Ultraviolet absorption spectra
XArCH=CHArY (abbreviated XSBY). Their research shows that
INTRODUCTION
the νmax of XSBYs can be quantified well by only employing
the σ parameter without Hammett constant σ.[25]
ex
cc
In recent years, optoelectronic materials have attracted extensive
attention as a new type of functional material.[1–9] Some organic
The correlations between the νmax of aryl-Schiff bases and sub-
stituent effects were also reported. Chen et al.[26] investigated
compounds, such as Schiff bases, which contains classical π con-
the substituent effects on the νmax of 4,4’-disubstituted
N-(benzylidene)-anilines p-XArCH=NArY-p (abbreviated p-
XBAY-p). Fang et al.[27–29] reported the substituent effects on
the νmax of extended benzylidene anilines and the effects of mo-
lecular conformation on the νmax of symmetrical Schiff bases.
Cao et al.[30] studied the effect of substituents on the νmax of
N-(4-substituted benzylidene) anilines and N-(4-substituted
benzylidene) cyclohexylamines. These studies of substituent ef-
jugate system are applied well in many fields of optical func-
tional materials due to their potential optoelectronic
properties.[10–12] Recently, Hasan Tanak[13,14] investigated the
energetic and structural properties of the Schiff base com-
pounds, 2-methyl-6-[2-(trifluoromethy)phenyliminomethyl]phenol
and (E)-2-[(2-chlorophenyl)iminomethyl]-4-trifluoromethoxyphenol.
Also, he calculated the optimized geometry, vibration spectra and
assignments, statistical thermodynamic parameters, electronic
absorption spectra and nonlinear optical properties by using
density functional theory. The calculated results are in agreement
with the experimental facts. His valuable works provide an
insight into the molecular properties of Schiff base compounds.
The aryl Schiff bases with a classic π-conjugated molecular
system have been employed in investigating the substituent
effects as an important parent-structure. The properties of parent-
structure can be easily influenced by the different factors including
chemical environment around and change of substituents in
molecules.
fects on the νmax of aryl-Schiff bases show that not only the
ex
cc
excited-state substituent parameter σ , but also Hammett con-
stant σ were employed in the quantitative correlations of the
ν
max. Wang[31] even made an attempt of molecular design and
synthesis of 3,4’/4,3’-disubstituted benzylidene anilines with
* Correspondence to: Chenzhong Cao, School of Chemistry and Chemical Engi-
neering, Hunan University of Science and Technology, Xiangtan 411201,China.
Email: czcao@hnust.edu.cn
Ultraviolet (UV) absorption spectra are usually used to study
the relationship between molecular structure and property (or
activity),[15–19] which is also an important method in the tests
of optical properties. Cao et al.[20–23] have successfully quantified
the UV absorption energy νmax (cm-1) of wavelength of absorp-
tion maximum λmax (nm) by applying the excited-state substitu-
a Q. Luo, C.-T. Cao, Z. Cao
Key Laboratory of Theoretical Organic Chemistry and Function Molecule, Min-
istry of Education, Key Laboratory of QSAR/QSPR of Hunan Provincial
University
b C. Cao
School of Chemistry and Chemical Engineering, Hunan University of Science
and Technology, Xiangtan 411201, China
[22–24]
ex
cc
ent parameter
σ
for the disubstituted stilbenes
J. Phys. Org. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.

Q. LUO ET AL.
specified λmax, on the basis of Chen’s report,[26] in which the pre-
dicted λmax values are in agreement with the experimental ones
for these designed compounds.
Japan), scanning range 200-500 nm, and scanning speed 10
nm/s in anhydrous ethanol. The spectrum of each target com-
pound was tested for three times (the absorption spectra of
XPNYs can be seen in the supporting information, the λmax
values of XPEAYs come from the Cao’s master thesis[35]), then
the mean value of λmax for each sample was employed in this
work, The λmax values of all target compounds were collected
and their λmax as well as νmax values (νmax=1/λmax) were listed
in Tables 1 and 2. The νmax values of XBAYs were employed from
Chen’s report.[26]
Comparing with the C=C non-polar bond in XSBY, there is
a polar C=N bridging group in the disubstituted benzy-
lideneanilines XArCH=NArY (abbreviated XBAY). By investigating
72 samples of XBAY, Chen et al.[26] proposed a penta-parameter
equation to quantify the νmax well. On the basis of the study on
XBAY, we come up with another two series of compounds: one is
the disubstituted N-(phenyl-ethylene)-anilines XArC(Me)=NArY
(abbreviated XPEAY) in which the H atom in CH=N is replaced
by a methyl CH3 (abbreviated Me); another is the disubstituted
N-phenyl-α-phenylnitrone XArCH=N(O)ArY (abbreviated XPNY)
in which an O atom is attached to the N in CH=N. The com-
pounds XPEAY and XPNY have C(Me)=N and CH=N(O) bridging
group carrying a side-group respectively, which are different
from the XBAY with a CH=N bridging group. What we want to
know is how their νmax are influenced by the substituents X
and Y, and what the differences of change regularities of the
νmax are for above mentioned three kinds of compounds. This
is an interesting topic and is worthy of being studied. For this
purpose, two series of compounds, XPEAYs and XPNYs were syn-
thesized, next, their wavelength of absorption maximum λmax
(nm) in the UV spectra were measured, and then, the correlations
between the νmax, (cm-1, νmax=1/λmax) and the substituent effects
of X and Y were carried out for the compounds XPEAYs and
XPNYs, also the different effect of substituents on the νmax of
the three kinds of compounds XBAY, XPEAY and XPNY were in-
vestigated in this work. Maybe it can provide us with a valuable
reference for designing and using these three kinds of com-
pounds as optical materials.[31]
EFFECT OF SUBSTITUENT ON THE νMAX OF
XPEAYS AND XPNYS
Chen[26] investigated the effects of substituents on the νmax of
XBAYs and obtained the correlation equation (1).
νmaxðXBAYÞ ¼ 32120 ꢀ 718:51σðXÞ þ 1197:18σðYÞ
ex
ex2
ꢀ1017:23Δσ2 þ 1632:49∑σ ꢀ 229:53Δσ
cc
cc
(1)
Where σ is Hammett constant, Δσ2 is the substituent specific
cross-interaction effect expressed with Hammett constant be-
tween X and Y,[36] that is Δσ2=[σ(X)-σ(Y)]2={[σF(X)+σR(X)]- [σF(Y)
+σR(Y)]}2; ∑σcecx is the sum of excited-state substituent constants
ex
ex
ex2
σ ðXÞ of X and σ ðYÞ of Y; Δσ
is the substituent specific
cc
cc
cc
cross-interaction effect expressed with excited-state substituent
ꢀ
ꢁ
2
ex2
cc
ex
cc
ex
cc
constants between X and Y, namely Δσ ¼ σ ðXÞ ꢀ σ ðYÞ
.
The parent molecular skeletons of XPEAY and XPNY are similar
to that of XBAY, whether the change regularities of νmax of
XPEAYs and XPNYs are also in keeping with that of XBAYs or
not. Thus we plotted the experimental νmax of XBAYs against that
of corresponding XPEAYs (e.g., p-MeBAF-p versus p-MePEAF-p)
and that of corresponding XPNYs (e.g., p-MeBAF-p versus p-
MePNF-p) respectively, and obtained Figure 1.
EXPERIMENTAL SECTIONS
Materials prepared
In this work, the XPNY and XPEAY were synthesized according to
the reports of Liu[32] and Barluenga[33] as shown in scheme 1. All
the compounds were characterized by 1H NMR, in which the
confirmation of XPEAYs were carried out by employing the
method of our previous work.[34]
It can be observed in Figure 1 that the νmax of XBAYs versus
XPEAYs and XBAYs versus XPNYs all have no good correlation.
It implies that the factors affecting the νmax of XPEAYs and XPNYs
are different from these of XBAYs. In order to probe their differ-
ences, we still employed the 5 parameters in equation (1) to cor-
relate the νmax of XPEAYs and XPNYs, and got the equations (2)
and (3), respectively.
Date preparation.
The products were vacuum dried for a whole day before mea-
surement. Their spectra were recorded by UV-2550 (SHIMADZU,
νmaxðXPEAYÞ ¼ 31142 ꢀ 2439:43σðXÞ þ 2464:05σðYÞ ꢀ 308:60Δσ2
(2)
ex
cc
ex2
cc
þ1090:09∑σ þ 288:99Δσ
R ¼ 0:9880; S ¼ 317:96; F ¼ 344:86; n ¼ 48
νmaxðXPNYÞ ¼ 31781 þ 86:41σðXÞ ꢀ 1123:55σðYÞ ꢀ 461:32Δσ2
(3)
ex
cc
ex2
cc
þ2029:93∑σ ꢀ 583:96Δσ
R ¼ 0:9893; S ¼ 241:31; F ¼ 431:48; n ¼ 53
In which, R is the correlation coefficient, S is the standard de-
viation, and F is the Fisher ratio, n is the date-points of regression
equation respectively. The correlations of equations (2) and (3)
show that the parameters of equation (1) can also be used to
quantify the νmax of XPEAYs and XPNYs, but their contributions
Scheme 1. The synthesis of samples of (a) XPNYs and (b) XPEAYs
wileyonlinelibrary.com/journal/poc
Copyright © 2016 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. (2016)

EFFECT OF SIDE-GROUP ON UV OF ARYL SCHIFF BASES
Table 1. The wavelength of absorption maximum λmax(nm) and its wavenumber νmax(cm-1) of UV spectrum for XPEAYs and the
substituent constants values σF, σR and σeccx for groups X and Y
ex
σ (X)b
ex
σ (Y)b
c
d
e
No.
X
Y
σF(X) a
σF(Y)a
σR(X)a
σR(Y)a
λmax exp.
νmax exp.
νmax.cal.
cc
cc
1
2
3
4
5
6
7
8
p-OMe
p-OMe
p-OMe
p-OMe
p-OMe
p-Me
p-Me
p-Me
p-Me
H
H
H
p-Cl
p-Cl
p-Cl
p-Cl
p-Cl
p-Cl
p-F
p-F
p-F
p-F
p-F
p-F
p-F
p-CF3
p-CF3
p-CF3
p-CF3
p-CF3
p-CF3
p-NO2
p-NO2
p-NO2
p-NO2
p-NO2
p-NO2
m-Cl
m-Cl
m-Cl
p-Cl
p-NMe2
p-OMe
p-Me
p-Cl
0.29
0.29
0.29
0.29
0.29
0.01
0.01
0.01
0.01
0.00
0.00
0.00
0.42
0.42
0.42
0.42
0.42
0.42
0.45
0.45
0.45
0.45
0.45
0.45
0.45
0.38
0.38
0.38
0.38
0.38
0.38
0.65
0.65
0.65
0.65
0.65
0.65
0.37
0.37
0.37
0.42
0.45
0.65
0.42
0.45
0.65
0.00
0.45
0.15
0.29
0.01
0.42
0.45
0.15
0.29
0.45
0.51
0.29
0.00
0.45
0.15
0.29
0.01
0.42
0.45
0.51
0.15
0.29
0.01
0.00
0.42
0.45
0.51
0.15
0.29
0.01
0.00
0.42
0.45
0.15
0.29
0.01
0.00
0.42
0.45
0.29
0.01
0.45
-0.07
-0.07
-0.07
0.34
0.34
0.34
0.56
0.56
-0.56
-0.56
-0.56
-0.56
-0.56
-0.18
-0.18
-0.18
-0.18
0.00
0.00
0.00
-0.19
-0.19
-0.19
-0.19
-0.19
-0.19
-0.39
-0.39
-0.39
-0.39
-0.39
-0.39
-0.39
0.16
0.16
0.16
0.16
0.16
0.16
0.13
0.13
0.13
0.13
0.13
0.13
0.00
0.00
0.00
-0.19
-0.39
0.13
-0.19
-0.39
0.13
0.00
-0.39
-0.98
-0.56
-0.18
-0.19
-0.39
-0.98
-0.56
-0.39
0.15
-0.50
-0.50
-0.50
-0.50
-0.50
-0.17
-0.17
-0.17
-0.17
0.00
-1.81
-0.50
-0.17
-0.22
0.06
-1.81
-0.50
0.06
356.00
330.00
320.00
316.00
316.00
359.50
337.70
321.05
313.73
330.00
324.65
323.89
373.89
342.20
332.60
327.95
327.00
315.06
361.65
337.66
329.05
322.00
322.75
320.82
313.52
385.93
351.46
340.83
335.01
335.65
336.33
432.75
380.95
363.60
351.45
354.30
353.35
349.00
334.10
329.50
330.90
323.75
354.95
320.95
317.61
344.25
301.45
295.25
28090
30303
31250
31646
31646
27816
29612
31148
31875
30303
30802
30875
26746
29223
30066
30492
30581
31740
27651
29616
30391
31056
30984
31170
31896
25911
28453
29340
29850
29793
29733
23108
26250
27503
28454
28225
28301
28653
29931
30349
30221
30888
28173
31158
31485
29049
33173
33870
27637
30046
30680
31528
31526
27996
30190
31584
32103
29982
31142
31355
26707
29077
29689
30668
30568
31214
27809
29908
30456
31061
31402
31275
31980
25922
28323
28935
29608
29994
29846
23264
26543
27370
28172
28459
28455
29003
29578
30446
30119
30853
27912
31214
31897
29173
33126
33047
p-F
p-NMe2
p-OMe
p-F
p-CN
p-OMe
H
9
-0.70
-0.50
0.00
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
-0.56
0.00
0.00
0.00
p-F
-0.39
-0.98
-0.56
-0.18
-0.19
-0.39
0.15
-0.98
-0.56
-0.18
0.00
-0.19
-0.39
0.15
-0.98
-0.56
-0.18
0.00
-0.19
-0.39
-0.98
-0.56
-0.18
0.00
-0.19
-0.39
-0.56
-0.18
-0.39
0.00
0.06
p-NMe2
p-OMe
p-Me
p-Cl
-0.22
-0.22
-0.22
-0.22
-0.22
-0.22
0.06
0.06
0.06
0.06
0.06
-1.81
-0.50
-0.17
-0.22
0.06
-0.70
-1.81
-0.50
-0.17
0.00
p-F
p-CN
p-NMe2
p-OMe
p-Me
H
p-Cl
p-F
-0.22
0.06
0.06
0.06
p-CN
p-NMe2
p-OMe
p-Me
H
p-Cl
p-F
p-NMe2
p-OMe
p-Me
H
-0.70
-1.81
-0.50
-0.17
0.00
-0.22
0.06
-1.81
-0.50
-0.17
0.00
-0.22
0.06
-0.50
-0.17
0.06
-0.03
-0.03
-0.03
0.02
-0.12
-0.12
-0.12
-0.12
-0.12
-0.12
-1.17
-1.17
-1.17
-1.17
-1.17
-1.17
0.02
p-Cl
p-F
p-OMe
p-Me
p-F
m -Me
m -Me
m -Me
m -F
m -F
m -F
m -CN
m -CN
0.02
0.02
-0.22
0.06
-1.17
-0.22
0.06
-1.17
0.00
0.06
p-F
p-NO2
p-Cl
p-F
p-NO2
H
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.02
0.02
0.56
0.56
p-F
aThe values were taken from Reference.[25]
bThe values were taken from Reference.[22]
cThe values were obtained by this work, which were presented in Cao’s master thesis[35] and were not yet published.
dνmax exp=1/λmax exp
.
eCalculated values with Eqn(2).
J. Phys. Org. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/poc

Q. LUO ET AL.
wileyonlinelibrary.com/journal/poc
Copyright © 2016 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. (2016)

EFFECT OF SIDE-GROUP ON UV OF ARYL SCHIFF BASES
J. Phys. Org. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/poc

Q. LUO ET AL.
Figure 1. Plot of the νmax.exp of XBAYs vs that of XPEAYs, and the νmax.exp of XBAYs vs that of XPNYs a: XBAYs vs XPEAYs (38 couples); b: XBAYs vs XPNYs
(38 couples)
are different from that to the νmax of XBAYs. For purpose of com-
parison, the coefficients in front of each parameter of equations
(1), (2) and (3) were all collected in Table 3.
These experimental facts can be used to design UV absorption
materials, from which we can employ these three kinds of com-
pounds, XBAYs, XPEAFYs and XPNYs to obtain a series of mate-
rials with more distribution of λmax in UV spectra. For examples,
when X=MeO, F, Cl, CF3 and NO2, Y=Cl (Table 4), the λmax is from
313.6 (FBACl) to 360.2 nm (NO2PNCl), in which their λmax gap is
46.6 nm, and in case of the same set of X groups and Y=Me (Ta-
ble 4), their λmax gap is 48.4 nm between NO2PEAMe and FPNMe.
It can be observed in Table 3 that: (i) In compound XPEAYs, the
parameters σ(X), σ(Y), Δσ2 and ∑σcecx have similar effect on the νmax
as they do in XBAYs, whereas the Δσeccx2 item has an opposite ac-
2
ex
cc
tion as it does in XBAYs. (ii) In XPNYs, the effect of Δσ , ∑σ and
ex2
Δσ
on the νmax have a similar effect as they do in XBAYs,
cc
whereas the σ(X) and σ(Y) have opposite action as they do in
XBAYs. It is to say that the introduction of a side-group to the
C=N bridging bond in XBAYs will lead to a different change reg-
ularity of the νmax for XPEAYs and XPNYs.
The action of side-group
For the parameters in equations (1), (2) and (3), their relative con-
tributions (Ψr) and fraction contributions (Ψf) can be calculated
by equations (4) and (5),[37,38] and the calculated results were
listed in Table 5.
RESULT DISCUSSION
―
The change of λmax in XBAY, XPEAY and XPNY
ψr ¼ mi X i
(4)
The intercepts of equations (1), (2) and (3) are 32120, 31142 and
31781 cm-1, which correspond to the λmax values 311.33, 321.11
and 314.66 nm of the parent molecules HBAH, HPEAH and HPNH
respectively. It shows that the side-group Me at the carbon end
and O atom at the nitrogen end of C=N bond all increase the
wavelength of λmax for the parent molecules. However this incre-
ment is not a constant between XBAYs and XPEAYs or XPNYs
due to the different coefficients in front of parameters in equa-
tions (1), (2) and (3). In general, the λmax(XPNY) and λmax(XPEAY)
are longer than that of λmax(XBAY) in case that the molecules of
XPNYs, XPEAYs and XBAYs carry a same couple of X-Y groups,
which can be seen in Table 4.
An interesting phenomenon has been observed from Table 4
that if keep Y group fixed and change X group, the variation of
λmax is least for XBAY, namely Δλmax(XBAY) < Δλmax(XPNY), and
Δλmax(XBAY) < Δλmax(XPEAY). Whereas the Δλmax(XBAY) is larg-
est in case of X group fixed and Y group changing, that is,
Δλmax(XBAY) > Δλmax(XPNY), and Δλmax(XBAY) > Δλmax(XPEAY).
ꢂ
ꢂ
ꢂ
ꢂ
R2 ψ
ꢂ
ðiÞꢂ
r
ꢂ
ꢂ
ψfðiÞ
¼
ꢁ100%
(5)
X
ꢂ
ꢂ
ꢂ
ψ
ðiÞꢂ
r
i
Where the mi and Xi are the coefficient and the average value
of the parameters and the R is the correlation coefficients of the
equations, respectively. The sum is over the parameters in the
equations.
Table 5 shows that among the 5 parameters in equations (1),
(2) and (3), which correspond to the compounds XBAYs, XPEAYs
and XPNYs, the item ∑σ made the most contribution, and the
total contribution of excited-state substituent constant (items
∑σ and Δσeccx2) is more than 50% for these three kinds of com-
ex
cc
ex
cc
pounds. It is interesting that the introduction of the side-group
CH3 makes the effect of σ(X) larger than that of σ(Y) on the νmax
Table 3. The coefficients in front of the parameters in equations (1), (2) and (3)
Equation
compound
coefficient
Δσ2
∑σ
Δσ
ex
cc
ex2
cc
σ(X)
σ(Y)
(1)
(2)
(3)
XBAY
XPEAY
XPNY
-718.51
-2439.43
86.41
1197.18
2464.05
-1123.55
-1017.23
-308.60
-461.32
1632.49
1090.09
2029.93
-229.53
288.99
-583.96
wileyonlinelibrary.com/journal/poc
Copyright © 2016 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. (2016)

EFFECT OF SIDE-GROUP ON UV OF ARYL SCHIFF BASES
Table 4. Some examples of λmax(nm) of XBAY, XPEAY and XPNY with same couple of X-Y groups
X
Y
XBAYa
XPEAYb
XPNYb
X
Y
XBAYa
XPEAYb
XPNYb
F
Cl
Cl
313.6
317.4
318.8
319.9
345.0
31.4
317.4
319.9
321.9
326.5
353.8
36.4
310.0
310.3
311.3
313.8
314.9
340.3
30.3
322.8
328.0
316.0
335.7
354.3
38.3
329.1
320.0
332.6
340.8
363.6
43.6
323.9
320.8
321.1
327.0
316.0
354.3
38.3
318.7
324.6
337.2
320.5
360.2
41.5
315.2
331.3
320.7
318.3
358.1
42.9
314.1
314.7
319.7
320.7
331.4
355.1
41.0
MeO
F
Cl
Me
MeO
314.9
318.8
319.9
331.5
16.6
313.8
315.2
317.4
321.9
337.9
24.1
339.1
340.3
345.0
353.8
14.7
316.0
316.0
320.0
330.0
14.0
327.0
327.0
328.0
332.6
342.2
15.2
351.5
353.4
354.3
363.6
12.1
331.4
337.2
331.3
334.3
5.9
320.7
321.9
324.6
320.7
325.3
4.6
355.7
355.1
360.2
358.1
5.1
MeO
CF3
NO2
Δλmax
F
MeO
Cl
CF3
NO2
Δλmax
H
F
Me
Cl
MeO
NO2
Δλmax
Δλmax
Cl
F
H
Cl
Me
MeO
Me
Δλmax
NO2
H
F
Cl
F
Me
Δλmax
aThe values of νmax were taken from Reference.[26]
bThe values of λmax were measured in this work.
2
ex
Table 5. The relative and fraction contribution (Ψr and Ψf ) of σ(X), σ(Y), Δσ , ∑σeccx and Δσ 2 in equations (1), (2) and (3).
cc
ex
ex2
Δσ
Compound
XBAY
Equation
(1)
variable
σ(X)
σ(Y)
Δσ2
∑σ
cc
cc
Ψr
Ψf (%)
Ψr
Ψf (%)
Ψr
Ψf (%)
-89.82
3.71
-559.04
32.46
13.11
0.81
32.93
1.37
-134.50
7.81
-114.43
7.08
-440.97
18.16
-110.56
6.42
-103.24
6.38
-1650.61
67.93
-723.77
42.03
-1124.12
69.50
-155.58
4.41
153.15
8.89
228.07
14.10
XPEAY
XPNY
(2)
(3)
of XPEAYs, whereas the introduction of an O atom makes the ef-
fect of σ(Y) larger than that of σ(X) on the νmax of XPNYs.
Attentions should be paied to the substituent specific cross-
interaction effects between X and Y groups, namely Δσ2 and
and X or Y have important contribution to the νmax of XPNYs.
Thus we put the corresponding items, ω2=[σ(Me)-σ(X)]2= [-0.17-
σ(X)]2 and χ2=[σ(Me)-σ(Y)]2=[-0.17-σ(Y)]2 into equation (2), and
put items γ2= [σ(Oꢀ)-σ(X)]2=[-0.81-σ(X)]2 and β2=[σ(Oꢀ)-σ(Y)]2=[-
0.81-σ(Y)]2 into the equation (3), then carried out the regression
analysis respectively. The obtained results showed that the con-
tributions of cross-interactions ω2 and χ2 to the νmax of XPEAYs
are so little that can be ignored, and so do the contributions of
γ2 and β2 to the νmax of XPNYs.
ex2
Δσ items also play an important role in quantifying the νmax
cc
for all three kinds of compounds, XBAYs, XPEAYs and XPNYs.
What we want to know is whether the cross-interactions be-
tween the Me and X or Y have important contribution to the νmax
of XPEAYs, and whether the cross-interactions between the Oꢀ
Figure 2. Plot of the calculated wavenumbers versus the experimental ones for XPEAY in Table 1 and XPNY in Table 2 (the symbols ‘o’ and ‘Δ’ repre-
sent the XPEAY and XPNY respectively)
J. Phys. Org. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/poc

Q. LUO ET AL.
Figure 2 is the plot of the calculated wavenumbers νmax, cal.
versus the experimental ones νmax, exp. for XPEAYs and XPNYs.
It can be seen in Figure 2 that the calculated wavenumbers are
in good agreement with the experimental values for XPEAYs
and XPNYs, and the distribution of νmax of XPEAYs in Table 1 is
wider than that of XPNYs in Table 2.
Acknowledgements
The work was supported by the National Natural Science Foun-
dation of China (No. 21272063), Scientific Research Fund of
Hunan Provincial Education Department (No.14C0466) and the
Natural Science Foundation of Hunan (No. 14JJ3112).
We noted that, in case of a set of same X-Y group couples, the
XPEAYs has more distribution of νmax than XPNYs has. For a cal-
culation example, the biggest νmax is 33870 cm-1 (p-FPEACN-m)
(corresponding to λmax 295.25 nm) and the least νmax is 23108
cm-1 (p-NO2PEANMe2-p) (corresponding to λmax 432.75 nm) for
the 48 samples of XPEAYs in Table 1, and its gap (Δλmax) of λmax
is 137.50 nm. If these X-Y group couples in XPEAYs are attached
to the XPNYs, we can calculate their corresponding νmax with
equation (3). The obtained results are as the following: the big-
gest νmax is 32154 cm-1 (λmax 311.00 nm) of p-FPNCN-m, and
the least νmax is 25297 cm-1 (λmax 395.31 nm) of p-NO2PNNMe2-
p, in which the gap (Δλmax) of λmax is only 84.31 nm, and is much
less than that of XPEAYs. Here we also calculated the νmax of 72
samples of XBAY reported by Chen[26] with equations (2) and (3)
respectively, and obtained the gap (Δλmax) 123.46 nm and
101.55 nm respectively. It also shows that the side-group Me at
carbon end increases the distribution of λmax. Maybe, this differ-
ence is due to the interaction between the polarity of C=N bond
and the electron donating effect of the side-group. Because the
C=N bond is a polar double bond, the electronegativity of N
atom is bigger than that of C atom, the π-electron density is
transferred along the C to N, and the Me is an electron-donating
group. Thus, when the electron-donating group Me connects
with the carbon atom end of C=N, its electron donating effect
is in agreement with the transfer direction of the π-electron den-
sity of C=N. Whereas, for the O atom at the nitrogen atom end of
C=N, its unshared p electron pairs will transfer electron density
to the N of C=N, which is opposite to the transfer direction of
the π-electron density of C=N. As a result, the Me group is more
effective than O atom to promote the conjugate effect in the in-
terested molecules. That is to say, if there are a same set of X-Y
group couples in hand, one expect to get a set of compounds
with more distribution of λmax, it is better to employ the XPEAYs
rather than the XPNYs molecule series.
REFERENCES
[1] X. B. Sun, Y. Q. Liu, X. J. Xu, J. Phys, Chem B. 2005, 109, 10786–10792.
[2] M. Elbing, G. C. Bazan, Angew Chem Int Ed. 2008, 47, 834–838.
[3] A. Rajendran, T. Tsuchiya, S. Hirata, J. Phys, Chem A. 2012, 116,
12153–12162.
[4] H. L. Zhong, E. J. Xu, D. L. Zeng, J. P. Du, J. Sun, S. J. Ren, B. Jiang, Q.
Fang, Org Lett. 2008, 10, 709–712.
[5] D. M. Sun, Z. J. Ren, M. R. Bryce, S. K. Yan, J. Mater, Chem C. 2015, 3,
9496–9508.
[6] M. G. Han, Y. Tian, Z. Yuan, L. Zhu, B. W. Ma, Angew Chem Int Ed.
2014, 53, 10908–10912.
[7] C. K. Zhou, Y. Tian, Z. Yuan, M. G. Han, J. M. Wang, L. Zhu, M. S.
Tameh, C. Huang, B. W. Ma, Angew Chem Int Ed. 2015, 54,
9591–9595.
[8] L. C. Chen, K. C. Zhang, C. Q. Tang, Q. D. Zheng, Y. Xiao, J. Org, Chem.
2015, 80(3), 1871–1877.
[9] Z. Yuan, Y. Shu, Y. Tian, Y. Xin, B. W. Ma, Chem Commun. 2015, 51,
16385–16388.
[10] Y. Jia, J. B. Li, Chem Rev. 2015, 115, 1597–1621.
[11] L. Vukovic, C. F. Burmeister, P. Kral, J Phys Chem Lett. 2013, 4,
1005–1011.
[12] F. S. Santos, T. M. H. Costa, V. Stefani, J. Phys, Chem A. 2011, 115,
13390–13398.
[13] H. Tanak, J. Mole, Struct: Theochem. 2010, 950, 5–12.
[14] H. Tanak, J. Phys, Chem A. 2011, 115, 13865–13876.
[15] M. Guillaume, B. Champagne, J. Phys, Chem A. 2006, 110(48),
13007–13013.
[16] X. K. Jiang, G. Z. Ji, D. Z. Wang, J Phys Org Chem. 1995, 8, 781–790.
[17] H. P. Jia, S. X. Liu, L. Sanguinet, J Org Chem. 2009, 74, 5727.
[18] Z. Yuan, Q. Tang, K. Sreenath, J. T. Simmons, A. H. Younes, D. E. Jiang,
L. Zhu, Photochem Photobiol. 2015, 91, 586–598.
[19] J. Megow, T. Körzdörfer, T. Renger, M. Sparenberg, S. Blumstengel, F.
Henneberger, V. May, J. Phys, Chem C. 2015, 119(10), 5747–5751.
[20] C. Z. Cao, G. F. Chen, Y. X. Wu, Sci China Chem. 2011, 54(11),
1735–1744.
[21] G. F. Chen, C. Z. Cao, J. Phys, Org Chem. 2010, 23(8), 776–782.
[22] C. Z. Cao, G. F. Chen, Z. Q. Yin, J Phys Org Chem. 2008, 21, 808–815.
[23] C. Z. Cao, B. Sheng, G. F. Chen, J Phys Org Chem. 2012, 25, 1315–1320.
[24] C. Z. Cao, Y. X. Wu, Sci China Chem. 2013, 56(7), 883–910.
[25] C. Hansch, A. Leo, R. W. Taft, Chem Rev. 1991, 91, 165–169.
[26] G. F. Chen, C. Z. Cao, B. T. Lu, B. Sheng, J Phys Org Chem. 2012, 25,
327–333.
[27] Z. J. Fang, C. Z. Cao, J Mole Struct. 2013, 1036, 447–451.
[28] Z. J. Fang, C. Z. Cao, Spectrochim. Acta Part A. 2013, 111, 62–67.
[29] Z. J. Fang, C. Z. Cao, J Mole Struct. 2014, 1063, 307–312.
[30] C. T. Cao, B. Y. Wei, C. Z. Cao, Acta Phys-Chim Sin. 2015, 31(2),
204–210.
CONCLUSIONS
From the above investigation, we can get the following conclu-
sions. After the side-groups Me and O atom were introduced to
the C=N bridging bond of the disubstituted aryl Schiff base
XBAY, the XPEAY and XPNY compounds were formed. However
there is no linear relationship between the νmax of XBAYs and
XPEAYs or XPNYs. There are different change regularities of νmax
for the three kinds of compounds, XBAYs, XPEAYs and XPNYs. In
case of a same set of X-Y group couples, the distribution of λmax
of XPEAYs with the C(Me)=N bridging group is larger than that of
XPNYs with CH=N(O) bridging group, which is due to the Me be-
ing at the carbon end of C=N and its electron donating effect be-
ing in agreement with the transfer direction of π-electron density
of C=N. The contributions of cross-interactions between the Me
and X or Y to the νmax of XPEAYs are so little that can be ignored,
and so do the contributions of cross-interactions between the
Oꢀ and X or Y to the νmax of XPNYs. Maybe the results of this
work can provide a theoretical refference for designing those op-
tical materials involving aryl-Schiff base molecules.
[31] L. Y. Wang, C. T. Cao, C. Z. Cao, J. Phys, Org Chem. 2014, 27(10),
818–822.
[32] S. J. Liu, Y. H. Wang, Green Chem. 2009, 11, 1397–1400.
[33] J. Barluenga, A. Jiménez-Aquino, F. Aznar, C. Valde´s, J Am Chem Soc.
2009, 131(11), 403–4041.
[34] Z. Z. Cao, C. T. Cao, C. Z. Cao, J Phys Org Chem. 2015, 28, 564–569.
[35] Z. Z. Cao, [D]. XiangTan: Hunan university of Science and technol-
ogy: master thesis, 2015.
[36] C. Z. Cao, B. T. Lu, G. F. Chen, J Phys Org Chem. 2011, 24, 335–341.
[37] D. E. Needham, I. C. Wei, P. G. Seybold, J Am Chem Soc. 1988, 110,
4186–4194.
[38] F. Liu, Y. Liang, C. Cao, N. Zhou, Talanta. 2007, 72, 1307–1315.
SUPPORTING INFORMATION
Additional supporting information can be found in the online
version of this article at the publisher’s website.
wileyonlinelibrary.com/journal/poc
Copyright © 2016 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. (2016)