Effect of substituents on the UV spectra of supermolecular system: Silver nanoparticles with bi-aryl Schiff bases containing hydroxyl

Article abstract of DOI:10.1002/poc.3910

Effect of substituents on the ultraviolet (UV) spectra of supermolecular system involving silver nanoparticles (AgNPs) and Schiff bases was investigated. AgNPs and 49 samples of model compounds (MC), bi-aryl Schiff bases containing hydroxyl (XBAY, involving 4-OHArCH?NArY, 2-OHArCH?NArY, XArCH?NAr-4′-OH, and XArCH?NAr-2′-OH), were synthesized. The size of AgNPs was characterized by transmission electron microscopy (TEM), and the UV absorption spectra of AgNPs, XBAYs, and MC-AgNPs mixed solutions were measured, respectively. The results show that (1) the size of AgNPs is larger in MC-AgNPs solutions than that in AgNPs solution due to the distribution of MC molecules on the surface of AgNPs; (2) the UV absorption wavelength of XBAYs changes in the action of AgNPs and their wavelength shift exists limitation between XBAY and MC-AgNPs solutions; and (3) the wavelength shift limit of MC-AgNPs (λ_WSL) is influenced by the substituents X and Y and the position of hydroxyl OH. The wavenumber Δν_WSL of λ_WSL can be quantified by employing the excited-state substituent constant σ^ex_CC and Hammett constant σ of substituents X and Y. Comparing with the 4-OH, the 4′-OH makes the Δν_WSL a red shift, whereas the 2′-OH, comparing with the 2-OH, makes the Δν_WSL a blue shift.

Full text of DOI:10.1002/poc.3910

Received: 24 August 2018
DOI: 10.1002/poc.3910
Revised: 6 October 2018
Accepted: 12 October 2018
R E S E A R C H A R T I C L E
Effect of substituents on the UV spectra of supermolecular
system: Silver nanoparticles with bi‐aryl Schiff bases
containing hydroxyl
Chao‐Tun Cao | Shimao Cheng | Jingyuan Zhang | Chenzhong Cao
Key Laboratory of Theoretical Organic
Abstract
Chemistry and Function Molecule,
Effect of substituents on the ultraviolet (UV) spectra of supermolecular system
involving silver nanoparticles (AgNPs) and Schiff bases was investigated.
AgNPs and 49 samples of model compounds (MC), bi‐aryl Schiff bases contain-
ing hydroxyl (XBAY, involving 4‐OHArCH¼NArY, 2‐OHArCH¼NArY,
XArCH¼NAr‐4′‐OH, and XArCH¼NAr‐2′‐OH), were synthesized. The size of
AgNPs was characterized by transmission electron microscopy (TEM), and
the UV absorption spectra of AgNPs, XBAYs, and MC‐AgNPs mixed solutions
were measured, respectively. The results show that (1) the size of AgNPs is
larger in MC‐AgNPs solutions than that in AgNPs solution due to the distribu-
tion of MC molecules on the surface of AgNPs; (2) the UV absorption wave-
length of XBAYs changes in the action of AgNPs and their wavelength shift
exists limitation between XBAY and MC‐AgNPs solutions; and (3) the wave-
length shift limit of MC‐AgNPs (λWSL) is influenced by the substituents X
and Y and the position of hydroxyl OH. The wavenumber ΔνWSL of λWSL can
Ministry of Education, Key Laboratory of
QSAR/QSPR of Hunan Provincial
University, School of Chemistry and
Chemical Engineering, Hunan University
of Science and Technology, Xiangtan,
China
Correspondence
Chenzhong Cao, Key Laboratory of
Theoretical Organic Chemistry and
Function Molecule, Ministry of Education,
Key Laboratory of QSAR/QSPR of Hunan
Provincial University, School of Chemistry
and Chemical Engineering, Hunan
University of Science and Technology,
Xiangtan 411201, China.
Email: czcao@hnust.edu.cn
Funding information
National Nature Science Foundation of
China, Grant/Award Number: 21672058
ex
be quantified by employing the excited‐state substituent constant σ and
CC
Hammett constant σ of substituents X and Y. Comparing with the 4‐OH, the
4′‐OH makes the ΔνWSL a red shift, whereas the 2′‐OH, comparing with the
2‐OH, makes the ΔνWSL a blue shift.
KEYWORDS
absorption wavelength shift, Schiff base, silver nanoparticles, substituent effect, ultraviolet absorption
spectra
1 | INTRODUCTION
OH, amino NH2, and mercapto SH could combine with
AgNPs and changed its wavelength of UV absorption
The optical properties of organic compounds can signifi-
cantly change in the action of silver nanoparticles
(AgNPs), such as enhancement of ultraviolet (UV) absorp-
tion and enhancement of Raman spectrum.[1–6] However,
it is still not clear how do the substituents affect the UV
spectra of organic compounds in the action of AgNPs.
Previous researches showed that an organic com-
pound with some functional groups such as hydroxyl
and intensity of Raman spectrum.[1–21] For example, the
AgNPs combining with mercapto SH of organic mole-
cules were widely used to detect selectively glutathione,[2]
monitor the onset of surface screening effects of plasma
resonance,[4] promote the cysteine‐functionalized AgNP
aggregates,[7] and investigate the photochromism of
azobenzenes.[9] The AgNPs combining with amino NH2
of organic molecules were widely investigated. Gill
J Phys Org Chem. 2018;e3910.
wileyonlinelibrary.com/journal/poc
© 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/poc.3910

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CAO ET AL.
et al.[3] studied on the simultaneous modification of fluo-
rescence intensity and lifetime of dye‐labeled DNA in the
presence of aggregated AgNPs. Su et al.,[13] Tang et al.,[15]
and Shahid et al.[18] employed AgNPs for the ultrasensi-
tive and multiplex DNA/miRNA detection, dyeing
natural protein fibers and silk functionalization. Also,
AgNPs received other applications, such as determination
of low‐activity hydrolases using Excited‐State Intramolec-
ular Proton‐Transfer (ESIPT) fluorescent indicators on
silver surfaces,[14] applications of the optical properties
of the silver clusters in the conformational studies of
human telomeric DNA,[17] and detection and removal of
rhodamine dyes by AgNPs.[1,6,10]
2.3 | Preparation of model compounds
According to our previous reports,[24–26] the substituted
aryl Schiff bases containing ortho/para hydroxyl
XArCH¼NArY (XBAYs) were synthesized with the
method as shown in Figure 1. These compounds were
purified by recrystallization in anhydrous alcohol and
1
were confirmed with H NMR and 13C NMR. The NMR
spectra were recorded with a Bruker AV 500 MHz spec-
trometer in DMSO (or CDCl3). The detailed data of the
synthesized compounds (2e, 2f, 2g, 2j, 3a, and 4a) are
available in the Supporting Information.
From the above reports, we think that if a series of
compounds with various substituents has a specific
functional group (eg, OH, NH2, or SH), how do the
UV spectra of these compounds change in the action
of AgNPs. It is a very interesting topic. In this paper,
we chose bi‐aryl Schiff bases containing hydroxyl
XArCH¼NArY as model compounds to investigate the
mentioned topic.
2.4 | Measurement of UV absorption
spectra
The model compounds XBAYs (MC) were vacuum dried
for a whole day before measurement. The concentration
of MC solution was 0.727mM, prepared by dissolving
MC in anhydrous ethanol (total volume 10 mL). The
MC solution and above AgNPs solution were employed
to measure the UV spectra. All UV spectra of the MC
solution, AgNPs solution, and MC‐AgNPs mixed solution
(supermolecular system) were recorded with a Shimadzu
UV‐2550 Spectrophotometer (Japan) at room tempera-
ture, scanning range 200 to 500 nm.
2 | EXPERIMENTAL SECTION
2.1 | Materials
Fish sperm DNA (fsDNA) was purchased from Boao Bio‐
Technology Co, Ltd (Shanghai, China). Silver nitrate
(AgNO3, 99%), sodium borohydride (NaBH4, >98.0%),
aromatic aldehydes (>98.0%), and aromatic amines
(>98.0%) were purchased from J&K Scientific Ltd. All
chemicals were of analytic grade and used as received
without further purification.
2.4.1 | UV spectra of model compounds
For each model compound, 50‐μL MC solution was
added into anhydrous ethanol in a sample cell (total
volume 3 mL). Then the UV spectrum of MC solution
was recorded. The peak of λmax (nm) and the peak next
to the λmax (expressed by the symbol “λ′max”) values
were collected and converted into corresponding wave-
number νmax (cm−1, νmax = 1/λmax) and ν′max (cm−1, ν′
2.2 | Preparation of AgNPs
= 1/λ′max) values.
max
In this work, 96 mL of fsDNA (1.0 g·L−1), 4 mL of AgNO3
(20.0mM) and 10 mL of NaBH4 (2.0mM) were employed
(total volume 110 mL) to prepare AgNPs solution accord-
ing to Long's method,[22,23] in which the fsDNA was used
as template in order to avoid the aggregation of AgNPs.
The final concentration of Ag is cAg = 0.727mM in the
AgNPs solution.
2.4.2 | UV spectrum of AgNPs solution
In a sample cell, 50‐μL AgNPs solution was added into
anhydrous ethanol (total volume 3 mL). Then the UV
spectrum of AgNPs solution was recorded.
FIGURE 1 Synthesis of model
compounds (1‐4 XBAYs, bi‐aryl Schiff
bases containing hydroxyl OH)

CAO ET AL.
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was about 6.3 nm. Figures 2 and 3 show that the size of
AgNPs in MC‐AgNPs solution is larger than that of
AgNPs in AgNPs solution. The size increase of AgNPs
in MC‐AgNPs may be due to the distribution of MC mol-
ecules on the surface of AgNPs. As regards the compound
1b, its molecular length is about 1.3 nm in the crystal
obtained by author (Scheme 1, CCDC No. 1868708; the
checkCIF can be seen in the Supporting Information);
thus, the average diameter of 1b‐AgNPs should be more
than 3.0 + 2 × 1.3 = 5.6 nm. It is consistent with the
measured results of Figure 3.
2.4.3 | UV spectra of MC‐AgNPs solutions
For each model compound, 50‐μL MC solution was
mixed with 50 × N μL AgNPs solution to form the MC‐
AgNPs solutions in anhydrous ethanol in a sample cell
(total volume 3 mL), where N = 1, 2, 3, …, indicating
the molar ratio 1:N of MC versus Ag (counted with cAg).
The MC‐AgNPs solutions were kept on for 0.5 hour in
avoiding light condition, and then their UV spectra were
recorded. The λmax,
and the next to λmax,
mix
mix
(expressed by the symbol “λ′max, mix”) values of these
MC‐AgNPs solutions were collected and converted into
corresponding νmax, mix and ν′max, mix values.
3.2 | UV spectra of MC and AgNPs
solution
3 | RESULTS AND DISCUSSION
3.1 | Size change of AgNPs
To observe the effect of concentration of MC and AgNPs
on the UV spectra, we recorded the UV spectra of 1b
and AgNPs in different concentrations, respectively, as
shown in Figure 4. It can be seen from Figure 4 that the
UV absorption wavelengths of 1b and AgNPs all do not
change in the concentrations of 1.0 × 10−5M to 10−4M
and only increase the absorbance as the concentrations
raise. The λmax of AgNPs is 263.4 nm (Figure 4, right).
The prepared AgNPs were characterized by transmission
electron microscopy (TEM). Figure 2 showed the TEM
and particle size distribution histogram, in which the
average diameter of AgNPs was about 3.0 nm. In order
to probe the size of AgNPs in MC‐AgNPs solutions, we
took 1b (4‐HOBA‐Me‐p) as an example. We added five
times AgNPs solution (molar ratio) into 1b (4‐HOBA‐
Me‐p) solution (forming 1b‐AgNPs mixed solution) and
kept on stirring the mixed solution for 0.5 hour. Then
we characterized the 1b‐AgNPs by TEM. Its TEM and
particle size distribution histogram were showed in
Figure 3. The average diameter of AgNPs in 1b‐AgNPs
3.3 | UV spectra of MC‐AgNPs solutions
It was observed that, in the process of adding AgNPs into
MC solution, the λmax of XBAY did not change, whereas
the λ′max, mix of XBAY was shifted. Take 1b, for example;
Figure 5 (left) showed that, in the 1b‐AgNPs (molar ratio
FIGURE 2 (left) Transmission electron microscopy and (right) particle size distribution diagram of silver nanoparticles (AgNPs) in AgNPs
solution

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CAO ET AL.
FIGURE 3 (left) Transmission electron microscopy and (right) particle size distribution diagram of silver nanoparticles (AgNPs) in 1b‐
AgNPs mixed solution (molar ratio 1b:Ag = 1:5)
example, the λ′max of 1b is 292.8 nm, and the λ′max, lim
of 1b‐AgNPs is 264.6 nm; therefore, the λWSL = λ′
− λ′max, lim = 292.8 − 264.6 = 28.2 nm for the 1b‐
max
AgNPs.
Since the λ′max, mix of 1b‐AgNPs solutions shifts rap-
idly at the molar ratio of 1b:Ag being from 1:0 to 1:2,
we performed a detailed investigation for the λ′max, mix
SCHEME 1 The molecular conformation of 1b in crystal
(molecular length is about 1.3 nm)
change. The result was showed in Figure 6. In order to
investigate whether Figure 6 is a peak of the simple
sum of the λmax peak of AgNPs and the λ′max peak of
MC or not, we added simply the UV spectra of AgNPs
into that of 1b by means of employing diverse molar
ratios of 1b:Ag and got their calculated UV spectra. Then,
from the calculated UV spectra, we extracted the calcu-
lated λ′max, mix peak. The experimental λ′max, mix values
of 1b‐AgNPs solutions and the calculated λ′max, mix values
of the simple sum of the AgNPs and 1b were all presented
in Figure 7.
5:2) solution, (1) the λmax of 1b did not change (that is,
the λmax of 1b was equal to the λmax, mix of 1b‐AgNPs)
and only the absorbance of the λmax reduced, (2) whereas
the λ′max of 1b shifted (λ′max > λ′max, mix) and the absor-
bance of the λ′max increased and (3) the λmax of AgNPs
solution disappeared. Figure 5 (right) showed that the λ′
of 1b‐AgNPs solution changed rapidly from the
max, mix
molar ratio of 1b:Ag being 1:0 to 1:2. However, the λ′
did no longer change in case of the molar ratio
Figure 6 indicates that the wavelength of λ′max, mix
changes continuously with the adding AgNPs into 1b
solution. Figure 7 shows that the wavelength of λ′max,
max, mix
of 1b:Ag being more than 1:5. Thus, we take this λ′max,
mix as limit wavelength λ′max, lim and take the wavelength
interval between the λ′max of MC and the λ′max, lim of MC‐
AgNPs solution as the wavelength shift limit of MC‐
AgNPs (λWSL), namely, λWSL = λ′max − λ′max, lim. For
decreases rapidly at the beginning addition of AgNPs
mix
and then decreases slowly with the continuous adding
AgNPs, and also, the experimental λ′max, mix of 1b‐AgNPs
FIGURE 4 The UV absorption spectra of 1b (left) and silver nanoparticles (AgNPs) (right) in different concentrations

CAO ET AL.
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FIGURE 5 (left) The UV absorption spectra of 1b (4‐OHBA‐Me‐p), silver nanoparticles (AgNPs), and 1b‐AgNPs (5:2) solution, and (right)
1b‐AgNPs solution at different molar ratio of 1b:Ag (bottom 1:0 to top 1:7)
FIGURE 6 The wavelength shift
process of 1b‐AgNPs solutions at equal
absorbance (molar ratios of 1b:Ag are 1:0
to 1:2). AgNPs, silver nanoparticles
FIGURE 7 Plot of λ′max, mix versus the
molar ratios of 1b:Ag. (The ● indicates the
experimental λ′max, mix of 1b‐AgNPs
solutions; the Δ indicates the calculated λ′
of simple sum of the AgNPs and
max, mix
1b). AgNPs, silver nanoparticles
decreases rapider than the calculated λ′max,
of the
molar ratio and their limit wavelength λ′max,
were
lim
mix
simple sum of the AgNPs and 1b, which means that there
is an interaction between MC molecules and AgNPs.
In this paper, 49 samples of MC solutions were
employed to mix with the AgNPs solution at different
recorded. Then their wavelength shift limits (λWSL) of
MC‐AgNPs solutions were obtained from the couples of
λ′max of MC and λ′max, lim of MC‐AgNPs solution. The λ′
max of MC solution and λWSL of MC‐AgNPs solution were

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CAO ET AL.
listed in Tables 1 and 2, respectively, in which the λWSL
values were listed in descending order (large to small).
The wavelength changing from the λ′max of MC solu-
tion to the λ′max, lim of MC‐AgNPs solution may be due to
the formation of aggregates between MC and AgNPs.
According to the reports of literature,[2,3,8,13,19,34] the
surface of nanoparticles can be combined with O, S, and
N atoms of organic molecules to form a nanoparticle
whose surface links many organic molecules (that is,
nanoparticle‐organic molecule complexes, NOC). For
these XBAY molecules used in this work, they have
hydroxyl OH and bridging bond CH¼N, and their O
and N atoms can combine with AgNPs. Perhaps, these
interactions between MC molecules and AgNPs can be
illustrated with Figure 8. Therefore, we assume that there
are Nx free MC molecules in the original MC solution.
After adding AgNPs into MC solution, each piece of
AgNPs can adsorb x MC molecules on its surface to form
an NOC, namely, AgNPs‐MCx. As the AgNPs are added
continuously into the MC solution, the AgNPs‐MCx num-
ber increase gradually; thus, the free MC molecules in the
solution decrease gradually, and at last, the AgNPs‐MCx
solution forms. It can be expected that the λ′max, lim of
MC‐AgNPs solution should be the UV absorption
TABLE 1 The λ′max (nm) of MC, λWSL (nm) of MC‐AgNPs, ΔνWSL (cm−1), and substituent effect constants of groups X and Y for XBAYs (1
and 3)
a
c
c
d
σ(X)b
σ(Y)b
σ
ðXÞ
σ
ðYÞ
I(4′‐OH)
ex
CC
ex
CC
No.
Compound
λ′max
λWSL
ΔνWSL
1h
1i
4‐HOBA‐OMe‐m
4‐HOBA‐Me‐m
4‐HOBA‐H‐p
294.4
294.4
294.8
292.2
295.0
294.0
292.8
292.8
290.6
287.0
286.6
287.2
286.8
285.6
297.6
281.2
276.2
272.4
268.8
269.4
268.4
267.2
269.8
266.4
266.6
264.4
30.8
30.8
29.6
29.4
29.2
29.0
28.6
28.2
25.6
23.4
22.6
22.6
21.8
21.4
36.2
15.6
15.6
10.4
8.2
−3969
−3969
−3786
−3829
−3724
−3722
−3697
−3640
−3324
−3093
−2987
−2974
−2868
−2836
−4639
−2089
−2167
−1457
−1171
−1136
−1115
−1007
−958
−0.37
−0.37
−0.37
−0.37
−0.37
−0.37
−0.37
−0.37
−0.37
−0.37
−0.37
−0.37
−0.37
−0.37
−0.83
−0.27
0.66
0.12
−0.07
0.00
−0.19
−0.19
−0.19
−0.19
−0.19
−0.19
−0.19
−0.19
−0.19
−0.19
−0.19
−0.19
−0.19
−0.19
−1.81
−0.50
−0.70
−0.33
−0.03
−0.22
0.10
0.10
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
−0.03
0.00
1c
1g
1j
4‐HOBA‐CF3‐p
4‐HOBA‐F‐m
0.54
−0.12
0.02
0.34
1m
1n
1b
1l
4‐HOBA‐CF3‐m
4‐HOBA‐CN‐m
4‐HOBA‐Me‐p
4‐HOBA‐Br‐m
4‐HOBA‐Br‐p
4‐HOBA‐Cl‐p
0.43
0.09
0.56
0.56
−0.17
0.39
−0.17
−0.03
−0.33
−0.22
−0.50
0.06
1f
0.23
1e
1a
1d
1k
3a
3b
3g
3f
0.23
4‐HOBA‐OMe‐p
4‐HOBA‐F‐p
−0.27
0.06
4‐HOBA‐Cl‐m
p‐NMe2BA‐4′‐OH
p‐OMeBA‐4′‐OH
p‐CNBA‐4′‐OH
p‐BrBA‐4′‐OH
m‐BrBA‐4′‐OH
p‐ClBA‐4′‐OH
m‐OMeBA‐4′‐OH
m‐MeBA‐4′‐OH
p‐MeBA‐4′‐OH
m‐FBA‐4′‐OH
m‐ClBA‐4′‐OH
p‐HBA‐4′‐OH
0.37
0.02
−0.37
−0.37
−0.37
−0.37
−0.37
−0.37
−0.37
−0.37
−0.37
−0.37
−0.37
−0.37
−0.19
−0.19
−0.19
−0.19
−0.19
−0.19
−0.19
−0.19
−0.19
−0.19
−0.19
−0.19
0.23
3l
0.39
3e
3h
3i
8.0
0.23
7.8
0.12
7.0
−0.07
−0.17
0.34
−0.03
−0.17
0.02
3c
3j
6.8
6.0
−865
3k
3d
5.4
−775
0.37
0.02
3.6
−522
0.00
0.00
aΔνWSL = 1/λ′max − 1/λ′max, lim
.
bThe values were taken from Hansh et al.[27]
cThe values were taken from previous studies.[28–33]
dIndicator variable of 4′‐OH.

CAO ET AL.
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TABLE 2 The λ′max (nm) of MC, λWSL (nm) of MC‐AgNPs, ΔνWSL (cm−1), and substituent effect constants of groups X and Y for XBAYs (2
and 4)
σ(X)b
σ(Y)b
σ
ðXÞ
σ
ðYÞ
I(2′‐OH)
a
c
c
d
ex
CC
ex
CC
No.
Compound
λ′max
λWSL
ΔνWSL
2h
2g
2m
2k
2e
2i
2‐HOBA‐CN‐p
2‐HOBA‐CF3‐p
2‐HOBA‐CN‐m
2‐HOBA‐Br‐m
2‐HOBA‐Cl‐p
280.2
271.6
274.2
271.6
271.2
271.6
269.6
271.4
270.6
270.6
268.8
269.8
268.8
285.2
276.2
269.4
269.8
263.0
264.0
264.0
260.6
261.8
257.6
14.8
11.4
10.0
8.4
−1990
−1613
−1380
−1175
−1150
−1117
−1105
−1062
−924
−924
−820
−786
−705
−2587
−2197
−1165
−1074
−350
−289
−173
147
−0.38
−0.38
−0.38
−0.38
−0.38
−0.38
−0.38
−0.38
−0.38
−0.38
−0.38
−0.38
−0.38
−0.27
0.66
0.66
0.54
−0.10
−0.10
−0.10
−0.10
−0.10
−0.10
−0.10
−0.10
−0.10
−0.10
−0.10
−0.10
−0.10
−0.50
−0.70
−0.22
−0.17
0.00
−0.70
−0.12
0.56
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
0.56
0.39
−0.03
−0.22
0.02
8.2
0.23
2‐HOBA‐F‐m
8.0
0.34
2f
2‐HOBA‐Br‐p
7.8
0.23
−0.33
0.09
2l
2‐HOBA‐CF3‐m
2‐HOBA‐OCH3‐p
2‐HOBA‐Cl‐m
2‐HOBA‐H‐p
7.6
0.43
2a
2j
6.6
−0.27
0.37
−0.50
0.02
6.6
2c
2d
2b
4a
4e
4d
4b
4c
4h
4g
4f
5.8
0.00
0.00
2‐HOBA‐F‐p
5.6
0.06
0.06
2‐HOBA‐CH3‐p
p‐OMe‐BA‐2′‐OH
p‐CN‐BA‐2′‐OH
p‐Cl‐BA‐2′‐OH
p‐Me‐BA‐2′‐OH
p‐H‐BA‐2′‐OH
m‐Br‐BA‐2′‐OH
m‐Cl‐BA2′‐OH
m‐F‐BA‐2′‐OH
m‐CF3‐BA‐2′‐OH
m‐CN‐BA‐2′‐OH
5.0
−0.17
−0.38
−0.38
−0.38
−0.38
−0.38
−0.38
−0.38
−0.38
−0.38
−0.38
−0.17
−0.10
−0.10
−0.10
−0.10
−0.10
−0.10
−0.10
−0.10
−0.10
−0.10
19.6
15.8
8.2
0.23
7.6
−0.17
0.00
2.4
2.0
0.39
−0.03
0.02
1.2
0.37
−1.0
−1.4
−5.4
0.34
0.02
4i
203
0.43
0.09
4j
797
0.56
0.56
aΔνWSL = 1/λ′max − 1/λ′max, lim
.
bThe values were taken from Hansh et al.[27]
cThe values were taken from previous studies.[28–33]
dIndicator variable of 2′‐OH.
wavelength of AgNPs‐MCx (neither the λ′max of XBAY
nor the λmax of AgNPs), which is close to but not equal
to the λmax of AgNPs (263.4 nm). In fact, the experimental
λ′max, lim of MC‐AgNPs solutions in Tables 1 and 2 are all
in the range of 260.0 to 266.0 nm, which coincide with
the above expectations.
others have wavelength red shift. Figures 9 and 10 indi-
cate the change of λWSL values. These λWSL values are
dominated by the location of hydroxyl OH and the type
of substituents in MC molecules.
The λWSL values of Tables 1 and 2 show that, on the
whole, the λWSL values of 1 and 3 (containing 4/4′‐OH)
are larger than that of 2 and 4 (containing 2/2′‐OH). In
the series of compounds 1 and 3, the most λWSL value is
of 3a (p‐NMe2BA‐OH‐4′), up to 36.2 (nm). It should be
noted that the positive λWSL value indicates a blue shift
and negative λWSL value is a red shift. In Tables 1 and
2, some of the MC‐AgNPs solutions have lager λWSL value
and the others have smaller λWSL value. Some of the MC‐
AgNPs solutions have wavelength blue shift, and the
3.4 | Effect of substituent on the
wavelength shift limit λWSL
To quantify the effect of substituent on the UV spectra of
organic compounds, author's group[28–33] proposed
excited‐state substituent constant σeCxC. Using the σ con-
stant together with Hammett electronic effect constant
σ,[27] the wavenumbers νmax of the λmax were well corre-
lated for these conjugated compounds involving
substituted stilbenes and benzenes,[25,30–33,35–38] styrene
ex
CC

8 of 11
CAO ET AL.
For the XBAYs (1 and 3)‐AgNPs,
Δ νWSL ¼ −2574:05 þ 1327:857σRðXÞ
þ 1975:339σFðYÞ
ex
ex
þ 1387:344σ ðXÞ−550:787σ ðYÞ − 722:466Δσ2
CC
CC
þ 1233:244I
4′‐OH
ð
Þ
R ¼ 0:9845; S ¼ 256:8; F ¼ 99:87; n ¼ 26
(1)
FIGURE 8 Diagram of MC molecules interacting with silver
nanoparticles (AgNPs) in the process of adding AgNPs into MC
solution (where Nx, (N − 1)x, (N − 2)x, …, and N are the number of
free MC molecules and x is the number of MC molecules
distributing on the surface of AgNPs)
For the XBAYs (2 and 4)‐AgNPs,
Δ νWSL ¼ 334:8966 þ 1834:212σðXÞ
ex
þ2666:438σ ðXÞ
CC
À
Á
2
ex
ex
CC
þ423:5608σ ðYÞ−794:64Δσ2 −907:115Δ σ
CC
− 696:894I
2′‐OH
ð
Þ
(2)
derivatives,[28,32] aryl Schiff bases,[39–52] and disubstituted
R ¼ 0:9812; S ¼ 175:7; F ¼ 68:78; n ¼ 23
pyrimidines.[53] Here, we also employed the excited‐state
ex
CC
substituent constant σ and Hammett electronic effect
constant σ to quantify the ΔνWSL of MC‐AgNPs solutions.
After optimizing, we obtained the regression equation (1)
and equation (2), respectively.
where R is the correlation coefficient, S is the standard
deviation, F is the Fisher ratio, and n is the date points
of the regression equation, respectively.
FIGURE 9 The λWSL value of XBAYs (1
and 3)‐AgNPs mixed solutions (the
number of MC is in Table 1). AgNPs, silver
nanoparticles
FIGURE 10 The λWSL value of XBAYs
(2 and 4)‐AgNPs mixed solutions (the
number of MC is in Table 2). AgNPs, silver
nanoparticles

CAO ET AL.
9 of 11
FIGURE 11 The λWSL (nm) of 1 (blue)
and 3 (red) for the couples of X and Y
(X = Y)
FIGURE 12 The λWSL (nm) of 2 (blue)
and 4 (red) for the couples of X and Y
(X = Y)
FIGURE 13 (left) Plot of calculated ΔνWSL, cal versus experimental ΔνWSL, exp of MC‐silver nanoparticles (AgNPs) solutions for the XBAYs
in Table 1 (O) and Table 2 (Δ) and (right) plot of calculated λWSL, cal versus experimental λWSL, exp of MC‐AgNPs solutions for the XBAYs in
Tables 1 and 2

10 of 11
CAO ET AL.
In Equations 1 and 2, the meanings of parameters are
as follows:
is, comparing with the 4‐OH, the 4′‐OH results in a red
shift of ΔνWSL, whereas, comparing with the 2‐OH, the
2′‐OH results in a blue shift of ΔνWSL
.
As regards the effect of position of X or Y group on the
λWSL of XBAYs, there are two kinds of cases: One is the
series of 1 and 3, and the other is the series of 2 and 4.
In the former case, the compounds 1 have larger λWSL
than 3 in case of substituent X(m/p) = Y(m/p), as shown
in Figure 11, whereas in the latter, the compounds 2 have
generally smaller λWSL than 4 in case of X(p) = Y(p), and
in contrast, the compounds 2 have larger λWSL than 4 in
case of X(m) = Y(m), as shown in Figure 12.
The σ is Hammett electronic effect constant of X
or Y substituent in molecule XBAY; the σ(X) and
σ(Y) indicate the σ value of X and Y, respectively;
the σF and σR stand for the field/inductive effect
and resonance effect, respectively, where
σF + σR = σ for the interested group X (or Y).
The Δσ2 is the substituent specific cross‐
interaction effect expressed with Hammett
constant σ between X and Y, that is,
Figure 13 is the plot of calculated ΔνWSL, cal and λWSL,
cal with Equations 1 and 2 versus the experimental ΔνWSL,
Δσ2 = [σ(X) − σ(Y)]2.
ex
CC
The σ is the excited‐state substituent constant
and λWSL, exp of Tables 1 and 2, respectively, which
exp
of X or Y substituent in molecule XBAY; the
shows that the calculated ΔνWSL, cal and λWSL, cal values
are in agreement with the experimental ΔνWSL, exp and
λWSL, exp ones.
ex
ex
ex
σ
ðXÞ and σ ðYÞ indicate the σ value of X
CC
CC
CC
and Y, respectively.
À
Á
2
ex
The Δ σ
is the substituent specific cross‐
CC
interaction effect expressed with excited‐state
substituent constant σ between X and Y, that
4 | CONCLUSION
ex
CC
À
Á
2
2
ex
CC
ex
CC
ex
CC
is, Δ σ
= [σ ðXÞ − σ ðYÞ] .
Experimental results show that the UV absorption wave-
length of bi‐aryl Schiff bases containing hydroxyl (4/4′‐
OH and 2/2′‐OH) changes in the action of AgNPs. The
absorption wavelength exists a limitation, and these
wavelength shift limits (λWSL) of MC‐AgNPs solutions
(supermolecular system) are influenced by substituents
X and Y and the position of the hydroxyl OH. The wave-
number ΔνWSL of wavelength shift limit can be quantified
The I(4′‐OH) is the indicator variable, when the
molecule contains 4′‐OH, I4′‐OH = 1, otherwise,
I4′‐OH = 0.
The I(2′‐OH) is the indicator variable, when the
molecule contains 2′‐OH, I2′‐OH = 1, otherwise,
I2′‐OH = 0.
ex
CC
by employing the excited‐state substituent constant σ
and Hammett electronic effect constant σ of X and Y
substituents. Comparing with the 4‐OH, the 4′‐OH makes
the ΔνWSL a red shift, and comparing with the 2‐OH, the
2′‐OH makes the ΔνWSL a blue shift.
In addition, we also observed that bi‐aryl Schiff bases
without hydroxyl had different UV absorption behavior
in the action of AgNPs. We will report these results in
our subsequent paper.
The results of Equations 1 and 2 show that the ΔνWSL of
MC‐AgNPs solutions can be quantified by employing the
ex
excited‐state substituent constant σ and Hammett elec-
CC
tronic effect constant σ of substituents X and Y. However,
there are some difference of the factors affecting the ΔνWSL
of MC‐AgNPs solutions for the XBAYs containing 4/4′‐OH
(1 and 3) versus those containing 2/2′‐OH (2 and 4). It can
be seen from the coefficients in front of the parameters of
Equations 1 and 2 that (1) the positive σR(X), σF(Y), and
ex
σ
σ
ðXÞ result in a red shift of ΔνWSL, and the positive
CC
ex
ACKNOWLEDGEMENT
2
ðYÞ and Δσ result in a blue shift of ΔνWSL for the 1
CC
The work was supported by the National Nature Science
Foundation of China (21672058).
ex
CC
and 3 XBAYs and (2) the positive σ(X), σ ðXÞ, and
σ
ðYÞ result in a red shift of ΔνWSL, and the positive Δσ2
ex
CC
À
Á
2
ex
and Δ σ
result in a blue shift of ΔνWSL for the 2 and
CC
ORCID
4 XBAYs. In the solutions of (1 and 3)‐AgNPs, the effect
ofΔ σex 2 on the ΔνWSL can be ignored, whereas the effect
of σ(Y) on the ΔνWSL can be ignored in the solutions of
(2 and 4)‐AgNPs. In addition, the coefficients in front of
the indicator variables show that the effect of 4′‐OH on
the ΔνWSL is different from that of 4‐OH; also, the effect
of 2′‐OH on the ΔνWSL is different from that of 2‐OH. That
À
Á
Chenzhong Cao http://orcid.org/0000-0001-5224-7716
CC
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How to cite this article: Cao C‐T, Cheng S,
Zhang J, Cao C. Effect of substituents on the UV
spectra of supermolecular system: Silver
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