Observation of the complex spectra for the supramolecular system involving silver nanoparticles-biaryl Schiff bases containing the nitro group

Article abstract of DOI:10.1002/poc.4059

A series of biaryl Schiff bases containing the nitro groups, 4-XArCH═NArNO₂-4′ (XBANO₂-4′) and 4-NO₂ArCH═NArY-4′ (4-NO₂BAY), were synthesized. Also, the fish sperm DNA (fsDNA) and silver nanoparticles (AgNPs) solutions were prepared. By mixing these compounds with fsDNA or AgNPs solution and determining the ultraviolet absorption spectra of the mixture solutions, an interesting phenomenon was found: a new absorption peak λ_max,lim appeared in the (XBANO₂-4′)-AgNPs solution, which was longer than the wavelength of λ_max of XBANO₂-4′ solution. The new absorption peak in the (XBANO₂-4′)-AgNPs solution was the complex spectrum originating from the electron transfer between XBANO₂-4′ and AgNPs. Whereas this phenomenon was not observed in the (4-NO₂BAY)-AgNPs solutions, a quantitative correlation analysis was carried out with the measured spectral data, and the results show that the wave number ν_max,lim of the λ_max,lim is mainly affected by the excited-state substituent constant (Formula presented.) rather than the ground Hammett constant σ of the X group. The redshift magnitude Δν_max,WSL, namely, Δν_max,WSL = (1/λ_max) ? (1/λ_max,lim), of the wavelength λ_max,lim is related to the highest occupied molecular orbital and lowest unoccupied molecular orbital of XBANO₂-4′. The discovery of this new phenomenon is helpful to understanding the interaction between AgNPs-organic compound supramolecular systems.

Full text of DOI:10.1002/poc.4059

Received: 11 November 2019
DOI: 10.1002/poc.4059
Revised: 22 January 2020
Accepted: 23 January 2020
R E S E A R C H A R T I C L E
Observation of the complex spectra for the supramolecular
system involving silver nanoparticles-biaryl Schiff bases
containing the nitro group
Chao-Tun Cao | Shi-Mao Cheng | Chenzhong Cao
Key Laboratory of Theoretical Organic
Abstract
Chemistry and Function Molecule,
Ministry of Education, Hunan Provincial
University Key Laboratory of
A
series of biaryl Schiff bases containing the nitro groups,
4-XArCH═NArNO2-40 (XBANO2-40) and 4-NO2ArCH═NArY-40 (4-NO2BAY),
were synthesized. Also, the fish sperm DNA (fsDNA) and silver nanoparticles
(AgNPs) solutions were prepared. By mixing these compounds with fsDNA or
AgNPs solution and determining the ultraviolet absorption spectra of the mix-
ture solutions, an interesting phenomenon was found: a new absorption peak
λmax,lim appeared in the (XBANO2-40)-AgNPs solution, which was longer than
the wavelength of λmax of XBANO2-40 solution. The new absorption peak in
the (XBANO2-40)-AgNPs solution was the complex spectrum originating from
the electron transfer between XBANO2-40 and AgNPs. Whereas this phenome-
non was not observed in the (4-NO2BAY)-AgNPs solutions, a quantitative cor-
relation analysis was carried out with the measured spectral data, and the
results show that the wave number νmax,lim of the λmax,lim is mainly affected by
QSAR/QSPR, 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, Hunan Provincial University
Key Laboratory of QSAR/QSPR, School of
Chemistry and Chemical Engineering,
Hunan University of Science and
Technology, Xiangtan 411201, China.
Email: czcao@hnust.edu.cn
ex
the excited-state substituent constant σ ðXÞ rather than the ground Hammett
CC
Funding information
National Nature Science Foundation of
China, Grant/Award Number: 21672058
constant σ of the X group. The redshift magnitude Δνmax,WSL, namely,
Δνmax,WSL = (1/λmax) − (1/λmax,lim), of the wavelength λmax,lim is related to the
highest occupied molecular orbital and lowest unoccupied molecular orbital of
XBANO2-40. The discovery of this new phenomenon is helpful to understand-
ing the interaction between AgNPs-organic compound supramolecular
systems.
K E Y W O R D S
complex spectrum, para-nitrobiaryl Schiff base, silver nanoparticles, substituent electronic effect,
supramolecular system
1 | INTRODUCTION
glutathione glycopeptide (G-SH) was absorbed by AgNPs
to form the interfacial silver-thiolate shell and had strong
The formation of supramolecular systems involving silver
nanoparticles (AgNPs) and organic compounds causes
significant changes in the optical properties of organic
compounds.[1–5] The mechanism of optical properties
change attracted many researchers.[6–15] For example,
Ashenfelter et al[11] believed that the sulfhydryl (-SH) of
fluorescence. Wang et al[12] found that the adsorption of
the SH functional group of 4-mercaptopyridine (4-MPY)
by AgNPs enhanced Raman scattering. Francesko et al,
Liu et al, and Miao et al[13–15] designed functionalized
silver nanomaterials based on the changes of Raman
scattering spectra and redox potential of AgNPs-organic
J Phys Org Chem. 2020;e4059.
wileyonlinelibrary.com/journal/poc
© 2020 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/poc.4059

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CAO ET AL.
supramolecular system. The supramolecular systems
involving AgNPs-organic compounds have been widely
used in the detection of biological and organic sub-
stances, such as folic acid,[16] antibody[17] and RNA,[18]
glutathione, protein and growth factor,[19,20] and
mercaptoaniline.[21]
was measured by transmission electron microscopy
(TEM) (see Figure 1). The average size of AgNPs was
about 3.4 nm.
2.2 | Synthesis of MCs
Recently, our group[22] found that in the action of
AgNPs, the wavelength of the ultraviolet (UV) absorption
spectra of biaryl Schiff bases containing the hydroxyl
group shifted with the addition of AgNPs and finally
reached a limit value, which could be quantitatively cor-
related with the electronic effect constants of substitu-
ents. However, when we determined the UV spectra of
biaryl Schiff bases containing the nitro groups, such as
4-XArCH═NAr NO2-40 (XBANO2-40), in the action of
AgNPs, we observed a new phenomenon; that is, a new
absorption peak appeared at the longer wavelength of the
UV spectra of Schiff bases. We noted that the biaryl Schiff
bases molecules, in our previous works,[22] contained
bridging bond C═N, and also, some of them contained
hydroxyl group. No one of them contained nitro group. It
is not clear whether biaryl Schiff bases containing the
nitro groups have any special interaction with AgNPs.
Therefore, we want to investigate the UV spectra between
AgNPs and Schiff bases containing the nitro groups. In
view of this new phenomenon, this paper intends to get
meaningful results.
Model
compound
(MC)
4/40-NO2-disubstituted
benzylidene aniline p-XArCH═NArY-p (abbreviated as
p-XBAY-p) was synthesized by the method reported in
the literature (see Figure 2).[22–26] The crude products
were recrystallized with anhydrous ethanol, and the
1
purified MCs were characterized by H NMR. The NMR
spectra were recorded with a Bruker AV 500-MHz
spectrometer in CDCl3. The specific data and spectra are
available in Data S1.
2.3 | UV spectra of supramolecular
system
The MCs XBAYs were vacuum dried for a whole day
before measurements. The concentration of MC solution
2 | EXPERIMENTS
Fish sperm DNA (fsDNA) was purchased from Boao
Bio-Technology Co, Ltd (Shanghai, China). Other
chemicals were purchased from J&K Scientific Ltd. All
chemicals were of analytic grade and were used as it was
received without further purification.
2.1 | Preparation of fsDNA and AgNPs
FIGURE 1 Transmission electron microscopy diagram of
The preparation of fsDNA solution was as follows. First,
0.1 g of fsDNA was dissolved into 100.0 mL of double-
distilled water, and it was heated for 15 minutes in hot
water bath at 95ꢀC. Then, the reaction vessel was moved
immediately into ice water bath for being cooled rapidly
to 4ꢀC. A type of mixed single-strand DNA (ssDNA),
namely, the fsDNA solution of 1.0 gꢁL−1, was obtained.
The preparation of AgNPs was carried out according
to the methods of our previous work.[22] That is, AgNO3
was reduced by NaBH4, and fsDNA was used as
stabilizer. The final concentrations employed were
c (ssDNA) = 0.87 gꢁL−1 for fsDNA and cAg = 0.727 mM
for Ag in the AgNPs solution. The size of AgNPs solution
AgNP solution (taken from[22]). AgNP, silver nanoparticle
FIGURE 2 The synthetic route of XBANO2-40 and 4-NO2BAY
molecules

CAO ET AL.
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was 0.727 mM, prepared by dissolving MC in anhydrous
ethanol. The UV spectrum of MC solution (total volume
was 3 mL; concentration was 1.21 × 10−5 M) was
recorded with a ShimadzuUV-1800 spectrophotometer
(Japan) at room temperature, and the λmax (nm) was
obtained. For each compound-AgNPs (MC-AgNPs) sys-
tem, firstly, 5 μL of MC solution was added to a set of
graduated tubes; the AgNPs solution was subsequently
added into the MC solutions, making the MC:Ag molar
ratio to be 1:N (N = 0, 1, 2, ..., 9), and then, the volume
was adjusted to 3 mL with anhydrous ethanol. The
MC-AgNPs solutions were kept on for 1 hour in avoiding
light condition, and then, their UV spectra were
recorded. The peaks of λmax,mix of the mixing system
(MC-AgNPs) were recorded. When the absorption wave-
length did not change any more, the solution's peak of
λmax,mix was taken as the limit wavelength, expressed as
λmax,lim. The measured data were listed in Table 1.
fsDNA and AgNPs solutions did not shift in the above
concentration range, yet their absorbance intensities
changed for each case.
The UV spectrum of fsDNA had
a peak at
λmax = 262.0 nm, whereas that of AgNPs had two peaks,
one at 263.8 nm and the other at 430.4 nm (λmax). The
former belonged to fsDNA, and the latter was caused by
AgNPs. Figure 3 is the comparison of UV spectra of
fsDNA with AgNPs solutions; there are no absorption
peaks in the range of 320 to 400 nm for both fsDNA and
AgNPs.
(the absorbance of A and B, from bottom to top, is
5, 10, 20, 40, 80, and 160 μL of fsDNA and AgNPs in
3 mL of anhydrous ethanol, respectively). AgNP, silver
nanoparticle; fsDND, fish sperm DNA; UV, ultraviolet
3.2 | Comparison of UV spectra of MC
with MC-AgNPs solutions
3 | RESULTS AND DISCUSSION
In order to investigate the shift of λmax of 4-NO2BAY and
XBANO2-40 in the presence of AgNPs, we recorded the
UV absorption under different ratios of MC:Ag. An inter-
esting phenomenon was observed when the AgNPs solu-
tion was mixed with the MC solution.
3.1 | Comparison of UV spectra of fsDNA
with AgNPs solutions
In order to investigate the variation of UV spectra of
fsDNA and AgNPs solutions, we determined the UV
spectra of fsDNA and AgNPs solutions with different
concentrations (total volume was 3 mL, in which the
volumes of fsDNA and AgNPs were going from 5 to
160 μL, respectively). It was shown that the UV spectra of
As regarding the (4-NO2BAY)-AgNPs solutions, the
absorption peak of the original 4-NO2BAY solution was
shifted, but there was no new absorption peak in the
direction of longer wavelength of its λmax. For example,
the λmax of 4-NO2BANMe2-40 (Figure 4) was 442.3 nm.
After it was mixed with the AgNPs solution, no new
TABLE 1 . The λmax, λmax,lim, and Δνmax,WSL values of MC-AgNPs, and the substituent constants of X and Y groups
a
a
c
ex
ex
No.
1
X
Y
σ
ðXÞ
σ
ðYÞ
σR(X)b σR(Y)b σF(X)b σF(Y)b λmax
λmax,lim Δνmax,WSL
εd
CC
CC
p-NMe2
p-NO2 −1.81
p-NO2 −0.50
p-NO2 −0.17
−1.17
−1.17
−1.17
−1.17
−1.17
−1.17
−1.81
−0.50
−0.17
0.06
−0.98
−0.56
−0.18
−0.39
−0.19
0.15
0.13
0.13
0.15
0.29
0.01
0.45
0.42
0.51
0.65
0.65
0.65
0.65
0.65
0.65
0.65
0.65
0.65
0.65
0.65
0.65
0.15
0.29
0.01
0.45
0.42
0.51
389.2 405.6
1039
2867
4245
3550
3663
4406
16 500
2
p-OMe
p-Me
346.4 384.6
331.8 386.2
338.4 384.6
334.8 381.6
333.1 390.4
442.3
30 300
38 200
37 300
35 100
21 800
3
0.13
4
p-F
p-NO2
0.06
0.13
5
p-Cl
p-NO2 −0.22
p-NO2 −0.70
0.13
6
p-CN
p-NO2
p-NO2
p-NO2
p-NO2
p-NO2
p-NO2
0.13
7
p-NMe2 −1.17
p-OMe −1.17
p-Me −1.17
p-F −1.17
0.13
−0.98
−0.56
−0.18
−0.39
−0.19
0.15
8
0.13
371.8
9
0.13
353.8
10
11
12
0.13
340.3
p-Cl −1.17
p-CN −1.17
−0.22
−0.70
0.13
345.0
0.13
349.2
Abbreviations: AgNP, silver nanoparticle; MC, model compound.
aThe values were taken from Hansch et al.[27]
bThe values were taken from Cao et al, Qu et al, and Zhu et al.[28–30]
cIt was calculated with the expression: Δνmax,WSL = 1/λmax − 1/λmax.lim
.
dThe molar extinction coefficient of the λmax,lim, which was calculated on the basis of MC concentration.

4 of 8
CAO ET AL.
FIGURE 3 The UV spectra of (A) fsDNA and (B) AgNPs in various concentrations
FIGURE 5 The UV spectra of AgNPs, 4-MeBANO2-40, and
FIGURE 4 The UV spectra of AgNPs, 4-NO2BANMe2-40, and
(4-NO2BANMe2-40)-AgNPs (mole ratio, MC:Ag = 1:9). AgNP, silver
nanoparticle; MC, model compound; UV, ultraviolet
(4-MeBANO2-40)-AgNPs (the arrow “!” indicates the peak shifting
of 4-MeBANO2-40 to (4-MeBANO2-40)-AgNPs, which was studied in
this work). AgNP, silver nanoparticle; UV, ultraviolet
absorption peak appeared in the direction of longer than
442.3 nm.
Figure 6 is the UV absorption at equal absorbance for
(4-MeBANO2-40)-AgNPs, where 331.8 nm was the λmax of
4-MeBANO2-40 and 386.2 nm was the λmax,lim of
(4-MeBANO2-40)-AgNPs supramolecular system. Its
Δλ = 386.2 − 331.8 = 54.4 nm. The absorption peak at
However, in (XBANO2-40)-AgNPs solutions, besides
the original absorption peaks of XBANO2-40 shift, a new
absorption peak of λmax,lim appeared in the direction of
longer wavelength of its λmax, and the original λmax peak
disappeared. In the XBANO2-40 solutions, with the addi-
tion of AgNPs solution, the λmax of XBANO2-40 moved to
the longer wave direction (redshift). When the molar
ratio of Ag to XBANO2-40 reached to 9:1, the wavelength
did no longer move. This indicated that the MC mole-
cules were basically complexed with AgNPs and under-
went intermolecular charge (electron) transfer to produce
UV absorption. That is, in case the molar ratio of Ag to
MC was above 9:1, the longest wavelength of UV
absorption was the absorption peak of MC-AgNPs
complex spectrum. Here, we employed the λmax,lim to
express the wavelength of the absorption peak and
the Δλ = λmax,lim − λmax to express the displacement
(redshift) of the wavelength. Take 4-MeBANO2-40, for
example, Figure 5 is the peak shifting from the UV of
4-MeBANO2-40 to that of (4-MeBANO2-40)-AgNPs.
FIGURE 6 The detailed wavelength shift process of
(4-MeBANO2-40)-AgNPs solution at equal absorbance. (From left to
right, the mole ratio of MC:Ag was 1:0, 2:1, 1:1, 1:2, 1:3, 1:4, 1:5,
1:6, 1:7, 1:8, and 1:9, respectively). AgNP, silver nanoparticle; MC,
model compound

CAO ET AL.
5 of 8
386.2 nm was a new absorption peak, which was not
observed in the UV spectrum of 4-MeBANO2-40 or AgNPs
solution, respectively. Moreover, when the molar ratio of
Ag to 4-MeBANO2-40 reached to 9:1, the absorption
intensity (absorbance) of the peak of 386.2 nm did not
increase. It could be reasonably explained that the con-
centration of MC-AgNPs supramolecular complex in
MC-AgNPs supramolecular solution depended on the
original concentration of MC in the system, rather
than excess AgNPs. When all 4-MeBANO2-40 molecules
were complexed with the AgNPs, the absorbance
of (4-MeBANO2-40)-AgNPs supramolecular system
remained unchanged.
From Table 1, it could be concluded that the
minimum redshift of compounds 1-6 was 16 nm
(4-Me2NBANO2-40) and the maximum was 57 nm
(4-CNBANO2-40), and the redshift was very obvious. It is
noteworthy that the λmax,lim of (XBANO2-40)-AgNPs com-
plex spectra has no linear relationship with the λmax of
XBANO2-40 UV absorption.
The detailed peak shift process for all MC-AgNPs
solutions (nos 1-12 of Table 1) can be seen in Data S1.
We want to know whether the λmax shifting of
XBANO2-40 originates from the interaction of fsDNA or
AgNPs. Thus, we mixed the XBANO2-40 and fsDNA to
form the (XBANO2-40)-fsDNA solution then recorded the
UV spectra of (XBANO2-40)-fsDNA solutions under dif-
ferent volume ratios. It was observed that there was no
λmax shifting of XBANO2-40 in the (XBANO2-40)-fsDNA
solution. For example, Figure 7 is the UV spectra of
fsDNA, 4-MeBANO2-40, and (4-MeBANO2-4’)-fsDNA
solutions, where the λmax of 4-Me-BANO2-40 did not
change as the addition of the fsDNA solution. The above
experimental results indicated that the λmax shifting of
X-BANO2-40 was originated indeed from the action of
AgNPs rather than the action of fsDNA.
The above experimental facts showed that the λmax of
XBANO2-40 appeared redshift in the (XBANO2-40)-AgNPs
supramolecular system, whereas the λmax of 4-NO2BAY
did not appear redshift in the (4-NO2BAY)-AgNPs sys-
tem. It means that the λmax redshift in MC-AgNPs depend
on the position of nitro group attached to the biaryl Schiff
base molecule.
Do other compounds with strong electron-
withdrawing groups (such as 4-CNBAY-40 and
4-XBACN-40) have similar behavior? Recently, we stud-
ied on the UV spectra of supramolecular system
involving 38 samples of (p-XBAY-p) excluding OH,
NH2, and SH groups, in which both 4-CNBAY-40 and
4-XBACN-40 all did not appear λmax redshift in the
action of AgNPs.[31] It implies that the λmax redshift is
the specific behavior of XBANO2-40 in the action of
AgNPs.
3.3 | Quantitative correlation of
supramolecular complex spectra of MC-
AgNPs
According to our previous report,[32,33] the νmax (cm−1
,
νmax = 1/λmax) of Schiff bases could be quantitatively cor-
related with Hammett constant σ and the excited-state
ex
CC
substituent constant σ . For compounds 1-6 in Table 1,
the λmax,lim was converted to νmax,lim. Because the substit-
uent parameters of substituent NO2 in molecules
4-XBANO2-40 is fixed, we correlated quantitatively these
ex
CC
νmax,lim values with the substituent parameters σ ðXÞ ,
σR(X), and σF(X) of the substituents X, respectively. The
results indicated that the correlations between νmax,lim
and σR(X) or σF(X) all were bad, and the correlation
ex
CC
between νmax,lim and σ ðXÞ was good, as shown in
Equation (1). It could be seen that the complex spectra of
(XBANO2-40)-AgNPs supramolecular system were mainly
ex
CC
affected by the excited-state substituent constant σ ðXÞ
of the X group but not by the Hammett constant σ of the
ex
X group. Positive σ ðXÞ value makes νmax,lim increase
CC
ex
CC
and λmax,lim shorten; negative σ ðXÞ value makes
νmax,lim decrease and λmax,lim lengthen.
vmax,lim = 26 168:66 + 790:88σeCxCðXÞ
ð1Þ
R = 0:9445,S = 205:68,F = 33:08,n = 6:
In order to investigate the factor of affecting the wave-
length redshift in going from the λmax of MC to the
λmax,lim of (XBANO2-40)-AgNPs, we used Δνmax,WSL to
express the difference of wavenumber between them;
that is, Δνmax,WSL = (1/λmax) − (1/λmax,lim). It is an inter-
esting topic that what is the factor of dominating the
FIGURE 7 The UV spectra of fsDNA (0:10),4-MeBANO2-40
(8:0), and (4-MeBANO2-40)-fsDNA solutions under different volume
ratios (from MC:fsDNA = 8:20 to 8:100 μL). fsDNA, fish sperm
DNA; MC, model compound; UV, ultraviolet

6 of 8
CAO ET AL.
Δνmax,WSL. We think it may be related to the molecular
frontier orbital of both MC and AgNPs. Here, we
employed the HOMOMC and HOMOAgNPs to express the
highest occupied molecular orbital (HOMO) of MC and
AgNPs respectively and the LUMOMC and LUMOAgNPs
for the lowest unoccupied molecular orbital (LUMO) of
them, respectively. Dewar et al[34] and Pysh et al[35] ever
pointed out that the charge transfer spectra of
π-complexes were resulted from the charge transfer, in
which the electron transfer is going from the HOMO of
donor to the LUMO of acceptor. According to this view,
we think that the λmax,lim should be originated in the
electron transfer from the HOMOAgNPs to the LUMOMC
or from the HOMOMC to the LUMOAgNPs. Thus, the
Δνmax,WSL may be expressed as Equation (2).
From Equation (2), we can see that what the λmax of
XBANO2-40 appears redshift in (XBANO2-40)-AgNPs
should have proper energy of LUMOMC and HOMOMC
(lower energy of LUMOMC and higher energy of
HOMOMC). In the XBANO2-40 molecule, because of the
strong electron-withdrawing effect of both the nitro
group and the bridge bond CH═N, the π electrons flow
strongly from the aldehyde aryl to the aminoaryl when
the X group is electron-donating group. it is favorable for
the positive charges distributing on the aldehyde aryl
(decreasing the energy of LUMOMC, or increasing elec-
tron acceptability), which makes the aldehyde aryl ring
more receptive to the electron transfer from HOMOAgNPs
.
Also, it is favorable for the negative charges distributing
on the nitro group (increasing electron donor capability
of oxygen anion O−), which makes the nitro group of MC
easier transfer the electron to the LUMOAgNPs. Figure 8 is
the diagram of the π electron transfer in the MC mole-
cules. The above analysis can be confirmed by the reduc-
tion potential ERed of compound XBAY. It was known
that the reduction potentials of organic compounds
depend on the energy of the LUMO. On the basis of the
quantitative equation of reduction potential of XBAY,
reported by Luo et al[36] (formula 6, herein) and Cao
et al,[37] we calculated the reduction potentials ERed of
compounds 1-6 in Table 1 and got the ERed values,
−2.101, −1.988, −1.978, −1.898, −1.789, and −1.538 V,
respectively. It indicates that the LUMO energy of
4-NMe2BANO2-40 is lower than that of 4-CNBANO2-40,
and the former is easier to accept electron transfer from
HOMOAgNPs than the latter does. Figure 9 was obtained
ÂÀ
Á
À
ÁÃ
Δνmax,WSL = k LUMOMC −HOMOAgNPs + LUMOAgNPs −HOMOMC
:
ð2Þ
Here, k is coefficient. Equation (2) also can be rewritten
as Equation (3).
Â
À
ÁÃ
Δνmax,WSL = k ðLUMOMC −HOMOMCÞ + LUMOAgNPs −HOMOAgNPs
:
ð3Þ
Since the LUMOAgNPs and HOMOAgNPs of AgNPs are
fixed, the item (LUMOAgNPs − HOMOAgNPs) is a constant.
The item (LUMOMC − HOMOMC) is indeed the energy of
λmax of MC, which can be expressed as the νmax. Thus,
Equation (3) may be expressed as Equation (4).
Δνmax,WSL = a + bðLUMOMC −HOMOMCÞ = a + bνmax
,
ð4Þ
FIGURE 8 The π electron transfer of molecules XBANO2-40
(the arrow “!” indicates the direction of π electron transfer)
where a is constant and b is coefficient. Equation (4)
indicates that the Δνmax,WSL can be correlated with the
LUMOMC and HOMOMC of MC. Therefore, we used the
νmax values of compounds 1-6 in Table 1 to correlate
their Δνmax,WSL of (XBANO2-40)-AgNPs, and obtained
Equation (5).
Δνmax,WSL = −17 329 + 0:710593νmax
ð5Þ
R = 0:9755,S = 303:34,F = 78:7,n = 6:
Equation (5) has good correlation, which shows that
Δνmax,WSL is affected by the νmax of XBANO2-40. The
larger νmax of XBANO2-40 will result in a greater
Δνmax,WSL of (XBANO2-40)-AgNPs and a greater redshift
from the λmax of MC to the λmax,lim of MC-AgNPs.
FIGURE 9 Plot of the calculated Δνmax.WSL,cal with
Equation (5) versus the experimental Δνmax,WSL,exp values

CAO ET AL.
7 of 8
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values of Δνmax.WSL of Equation (5). We can see, from
Figure 9, that the calculated values are in good agree-
ment with the experimental values.
The experimental results of this work show that the
absorption peak of 4-NO2BAY is not longer than the λmax
wavelength of 4-NO2BAY in the action of AgNPs, which
indicates that there is no electron transfer between
4-NO2BAY and AgNPs. The reason is still unclear and
needs further study.
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By studying the UV spectra of a series of biaryl Schiff
bases containing the strong electron- withdrawing group
(NO2) to strong electron-donating group (NMe2) and
AgNPs, we can get the following conclusions:
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ated between the nitro-containing biaryl Schiff base
and the AgNPs, which is related to the position of the
nitro group attached to.
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3. The compound XBANO2-40 produces intermolecular
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fsDNA. Its longest wavelength λmax,lim has a quantita-
tive relationship with the substituent constant of the
X substituent. Compared with the λmax of XBANO2-40,
the redshift Δλ of intermolecular complex spectrum
λmax,lim is related to the highest occupied molecular
orbital HOMOMC and lowest unoccupied molecular
orbital LUMOMC of MC.
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supramolecular systems involving AgNP-substituted
N-(phenyl-ethylene)-anilines[38] and AgNPs-biaryl
Schiff bases containing hydroxyl.[22] The discovery of
this new phenomenon is conducive to understanding
the interaction between AgNPs-organic compound
supramolecular systems.
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A.
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ACKNOWLEDGMENT
[20] H. Li, M. Wang, C. Z. Wang, W. Li, W. B. Qiang, D. K. Xu,
Anal. Chem. 2013, 85(9), 4492.
Authors is very grateful to the National Nature Science
Foundation of China (21672058).
[21] L. W. Nien, M. H. Chien, B. K. Chao, A. J. Chen, J. H. Li,
J. Phys. Chem. C 2016, 120(6), 3448.
ORCID
[22] C.-T. Cao, S. M. Cheng, J. Y. Zhang, C. Z. Cao, J. Phys. Org.
Chem. 2019, 32(3), e3910. https://doi.org/10.1002/poc.3910
[23] C. T. Cao, Y. K. Bi, C. Z. Cao, Spectrochim. Acta A 2016,
163, 96.
Chenzhong Cao https://orcid.org/0000-0001-5224-7716
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SUPPORTING INFORMATION
Additional supporting information may be found online
in the Supporting Information section at the end of this
article.
How to cite this article: Cao C-T, Cheng S-M,
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supramolecular system involving silver
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