Determining the excited-state substituent constants of furyl and thienyl groups

Article abstract of DOI:10.1002/poc.3799

Six series of styrene derivatives XCH═CHArY (total of 65) containing the styrene parent molecular skeleton were synthesized (here, Y is OMe, Me, H, F, Cl, CF₃, CN, and NO₂, and X is 2-furyl, 3-furyl, 2′-methyl-2-furyl, 2-thienyl, 3-thienyl, and 2′-methyl-2-theniyl). Their ultraviolet absorption spectra were measured in anhydrous ethanol, and their wavelength of absorption maximum λ_max was recorded. For the wavenumber ν_max (cm^?1, ν_max?=?1/λ_max) of the obtained λ_max, a quantitative correlation analysis was performed, and 6 excited-state substituent constants σ^ex_cc(p) of groups X were obtained by means of curve-fitting method. Taking the ν_max values of total 90 compounds of styrene derivatives as a data set (including 25 compounds from reference and 65 compounds of this work), a quantitative correlation analysis was performed, and the reliability of the obtained σ^ex_cc(p) was verified. In addition, 12 samples of disubstituted Schiff bases (XCH═NArY) involving the above groups X were synthesized, and their ν_max values were recorded. Using these 12 ν_max together with the 14 ν_max values of Schiff bases taken from reference (total of 26 compounds), it was further verified that the σ^ex_cc(p) values are reliable by means of quantitative correlation method.

Full text of DOI:10.1002/poc.3799

Received: 3 October 2017
DOI: 10.1002/poc.3799
Revised: 13 November 2017
Accepted: 16 November 2017
R E S E A R C H A R T I C L E
Determining the excited‐state substituent constants of furyl
and thienyl groups
Junyan Qu | Chao‐Tun Cao | Chenzhong Cao
Key Laboratory of Theoretical Organic
Abstract
Chemistry and Function Molecule,
Six series of styrene derivatives XCH═CHArY (total of 65) containing the sty-
rene parent molecular skeleton were synthesized (here, Y is OMe, Me, H, F,
Cl, CF3, CN, and NO2, and X is 2‐furyl, 3‐furyl, 2′‐methyl‐2‐furyl, 2‐thienyl, 3‐
thienyl, and 2′‐methyl‐2‐theniyl). Their ultraviolet absorption spectra were
measured in anhydrous ethanol, and their wavelength of absorption maximum
λmax was recorded. For the wavenumber νmax (cm−1, νmax = 1/λmax) of the
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, School of Chemistry and
Chemical Engineering, Hunan University
of Science and Technology, Xiangtan
411201, China.
obtained λmax, a quantitative correlation analysis was performed, and 6
ex
excited‐state substituent constants σ
of groups X were obtained by means
CCðpÞ
of curve‐fitting method. Taking the νmax values of total 90 compounds of sty-
Email: czcao@hnust.edu.cn
rene derivatives as a data set (including 25 compounds from reference and 65
compounds of this work), a quantitative correlation analysis was performed,
Funding information
National Natural Science Foundation of
China, Grant/Award Number: 21672058
ex
CCðpÞ
and the reliability of the obtained σ
was verified. In addition, 12 samples
of disubstituted Schiff bases (XCH═NArY) involving the above groups X were
synthesized, and their νmax values were recorded. Using these 12 νmax together
with the 14 νmax values of Schiff bases taken from reference (total of 26
ex
CCðpÞ
compounds), it was further verified that the σ
values are reliable by means
of quantitative correlation method.
KEYWORDS
excited‐state constant, furyl, styrene, thienyl, UV absorption spectrum
1 | INTRODUCTION
extensively studied because of its tunable luminescent
properties, and some of its derivatives show an interesting
phenomenon of aggregation‐induced emission,[10,11] that
is, molecules, under photoexcitation, are not emissive in
solution and are strongly luminescent in the solid
state.[12,13] Moreover, regioselective functionalization of
the thiophene rings in tetra(2‐thienyl)ethylene can lead
to the synthesis of a series of derivatives, which are suit-
able for investigating systematically their electronic,
photophysical, and electrochemical properties.[9]
The ultraviolet (UV)‐visible spectra of organic com-
pounds are associated with transitions between electronic
energy levels. Also, the energy of the wavelength of
absorption maximum λmax (nm) of a compound reflects
Substituted stilbenes XArCH═CHArY (XSBY), such as p/
m‐XC6H4CH═CHC6H4Y‐p/m (X, Y = OMe, Me, H, F, Cl,
CF3, CN, and NO2), are a typical conjugated organic
compound with 2 aryl groups attached to a vinylidene.[1]
It was widely used in medicines,[2–5] foods,[6] functional
materials,[7,8] and other fields due to their specific
structural features and characteristics. With the continu-
ous discovery of various activities and the extension
of application, stilbene compounds have attracted
extensive attention. For example, diphenylethylene,
dithienylethylene, and tetraphenylethylene show interest-
ing optical properties.[9] Tetraphenylethylene has been
J Phys Org Chem. 2018;e3799.
wileyonlinelibrary.com/journal/poc
Copyright © 2018 John Wiley & Sons, Ltd.
1 of 10
https://doi.org/10.1002/poc.3799

2 of 10
QU ET AL.
its gap between the highest occupied molecular orbital
(HOMO) and the lowest unoccupied molecular orbital
(LUMO). For an organic compound, the gap between
HOMO and LUMO is related with its fluorescence, and
the energy levels of HOMO and LUMO are related with
its oxidation potential and reduction potential. For the
development of optical materials, it is a basic theoretical
topic that how molecular structure affects the molecular
optical properties. As we know, substituents have an
important effect on the molecular optical properties for
these compounds with same parent molecule. Thus, it is
a very interesting topic that how substituent effects affect
quantitatively the optical properties of organic com-
pounds. Hammett[14] constant σ[15–17] was first used for
chemists using substituent parameters to quantify the
optical properties of organic compounds. However,
research results showed little successful case. Later, Jiang
et al[18] proposed a spin‐delocalization effect constant and
combined with Hammett constant to correlate the optical
properties of some organic compounds, in which the cor-
2 | EXPERIMENTAL SECTIONS
2.1 | Synthesis of 1‐furyl/thienyl‐2‐aryl
ethylene
The target compounds were synthesized by Wittig‐Horner
reaction,[29] and their molecular structures were charac-
1
terized by nuclear magnetic resonance spectrum (The H
NMR and 13C NMR chemical shift data and spectra can
be seen in supporting information). Their E‐isomers were
obtained by means of chromatographic column separa-
tion and confirmed by the absorption frequencies of out‐
of‐plane deformation of group ‐HC═CH‐ in infrared spec-
1
1
tra and the magnitude of H─ H coupling constant in
nuclear magnetic resonance. The synthetic route was
shown in Figure 1. 3/4‐substituted benzyl chloride
(15 mmol) and triethyl phosphite (15 mmol) were mixed
in a 100 mL flask and continuously stirred for 4 hours at
reflux temperature. After cooling to room temperature
without separating intermediate product, furaldehyde/
thiophenecarboxaldehyde (12 mmol) and tetrahydrofuran
(THF, 20 mL) were added in successively, and then NaH
(45 mmol) was added in slowly under ice water bath con-
ditions. The reaction mixture was heated to reflux for
1 hour. After reaction, the reaction mixture was cooled
to room temperature and poured into a beaker containing
80 mL of ice water with constant stirring. If there is imme-
diately precipitated solids, the solids was collected by filter
and then recrystallized in anhydrous ethanol. If not, the
reaction mixture was extracted with ethyl acetate, and
then solids were precipitated successively by evaporating
solvent.
relation was much improved. In 2008, Cao et al[19] pro-
ex
CC
posed an excited‐state substituent constant
σ
to
express the effect of substituents on the properties of com-
ex
CC
pounds at excited state, and then we used the σ to cor-
relate quantitatively the UV absorption spectra and
reduction potential of substituted benzene, substituted
stilbene, and Schiff bases.[20–26] We observed that the
ex
CC
UV absorption spectra were mainly affected by the σ
for the substituted benzene and substituted stilbene com-
pounds, while the UV absorption spectra of Schiff bases
ex
CC
were affected by both substituents σ and σ.
The constant σCexC, proposed by Cao,[19] provides a con-
venience for investigating quantitatively optical properties
of organic compounds, but, up to now, there are only a
2.2 | Determination of UV absorption
spectrum
ex
CC
few number of substituents being determined the σ
values, which cannot far meet the needs of investigation
and application. Above situation is due to the difficulties
of the synthesis of organic compounds and the establish-
ment of model equations. Therefore, if we want to
Take anhydrous ethanol as solvent, the target compounds
were dissolved (about 2.0 g·L−1), and all solutions were
prepared freshly. Their UV absorption spectrum was
recorded by UV‐1800 (SHIMADZU, Japan), scanning
range 200 to 500 nm. Take anhydrous ethanol as
ex
CC
increase σ values of certain groups, we have to do more
experiments.[21,27,28] As we know, furyl and thienyl are
common optically active groups and appear more fre-
quently in organic compounds, and the extraction of their
ex
CC
σ
is an important work for the study of optical mate-
rials. Because there is difficult to synthesize compounds
with the molecular skeleton of XArCH═CHArY (X = 2‐
furyl, 3‐furyl, 2′‐methyl‐2‐furyl, 2‐thienyl, 3‐thienyl, and
2′‐methyl‐2‐thienyl), we design and synthesize the series
of target compounds (XCH═CHArY) and measure their
longest wavelength maximum λmax (nm) of UV absorp-
ex
CCðpÞ
tion spectra and try to determine the σ
of furyl and
thienyl by means of curve‐fitting method.
FIGURE 1 Synthesis of samples of compounds XCH═CHArY

QU ET AL.
3 of 10
TABLE 1 The wavelength of absorption maximum λmax (nm) and its wavenumber νmax (cm−1) of ultraviolet absorption spectrum for
ex
CC
XCH═CHArY and the substituent constants values σ and σ for groups X and Y
b
b
c
d
ex
No.
X
Y
σ(Y)a
σ
(p)(X)a
σ
ðYÞ
σeCxCðpÞðXÞ
λmax, exp
vmax, exp
CC
1
H
p‐F
0.06
0.00
0.06
0.00
0.00
246.0
40 650
2
H
H
0.00
0.31
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
247.2
249.0
250.0
251.0
251.0
252.0
254.6
257.0
258.5
260.0
261.0
263.1
263.5
274.5
282.0
294.0
307.8
311.2
312.0
307.4
312.1
320.5
285.0
390.0
324.1
318.7
316.0
316.5
321.7
322.5
336.9
317.0
316.6
319.7
293.2
290.0
288.1
278.8
292.1
40 453
40 161
40 000
39 841
39 841
39 683
39 277
38 911
38 685
38 462
38 314
38 008
37 951
36 430
35 461
34 014
32 485
32 133
32 055
32 536
32 044
31 204
35 087
25 641
30 855
31 377
31 646
31 596
31 085
31 008
29 682
31 546
31 586
31 279
34 106
34 483
34 710
35 868
34 235
3
H
p‐Me(CO)O
p‐SiMe3
p‐Me
p‐t‐Bu
p‐Cl
−0.08
−0.13
−0.17
−0.17
−0.22
−0.33
−0.43
−0.50
−0.56
−0.60
−0.69
−0.70
−1.13
−1.40
−1.81
0.00
4
H
−0.07
−0.17
−0.20
0.23
0.00
5
H
0.00
6
H
0.00
7
H
0.00
8
H
p‐Br
0.23
0.00
9
H
p‐MeSO2
p‐OMe
p‐I
0.72
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
H
−0.27
0.18
0.00
H
0.00
H
p‐MeSO
p‐COOMe
p‐CN
p‐COMe
p‐SMe
p‐NMe2
H
0.49
0.00
H
0.45
0.00
H
0.66
0.00
H
0.50
0.00
H
0.00
0.00
H
−0.83
0.00
0.00
Ph
−0.01
−0.01
−0.01
−0.01
−0.01
−0.01
0.42
−0.86
−0.86
−0.86
−0.86
−0.86
−0.86
−1.09
−1.09
−0.97
−0.97
−0.97
−0.97
−0.97
−0.97
−0.97
−0.97
−0.97
−0.97
−0.46
−0.46
−0.46
−0.46
−0.46
Ph
p‐Me
p‐Et
−0.17
−0.15
0.06
−0.17
−0.13
0.06
Ph
Ph
p‐F
Ph
p‐Cl
0.23
−0.22
−0.70
0.00
Ph
p‐CN
H
0.66
CHO
CHO
2‐furyl
2‐furyl
2‐furyl
2‐furyl
2‐furyl
2‐furyl
2‐furyl
2‐furyl
2‐furyl
2‐furyl
3‐furyl
3‐furyl
3‐furyl
3‐furyl
3‐furyl
0.00
p‐NMe2
p‐OMe
p‐Me
H
−0.83
−0.27
−0.17
0.00
0.42
−1.81
−0.50
−0.17
0.00
0.02
0.02
0.02
p‐F
0.06
0.02
0.06
p‐Cl
0.23
0.02
−0.22
−0.12
−0.70
−0.03
0.02
p‐CF3
p‐CN
m‐Me
m‐Cl
m‐CN
p‐OMe
p‐Me
H
0.54
0.02
0.66
0.02
−0.07
0.37
0.02
0.02
0.56
0.02
0.56
−0.27
−0.17
0.00
−0.08
−0.08
−0.08
−0.08
−0.08
−0.50
−0.17
0.00
p‐F
0.06
0.06
p‐Cl
0.23
−0.22
(Continues)

4 of 10
QU ET AL.
TABLE 1 (Continued)
b
b
c
d
ex
No.
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
X
Y
σ(Y)a
0.54
σ
(p)(X)a
σ
ðYÞ
σeCxCðpÞðXÞ
−0.46
−0.46
−0.46
−0.46
−0.46
−0.46
−1.25
−1.25
−1.25
−1.25
−1.09
−1.09
−1.09
−1.09
−1.09
−1.09
−1.09
−1.09
−1.09
−1.09
−1.09
−1.09
−1.09
−0.66
−0.66
−0.66
−0.66
−0.66
−0.66
−0.66
−0.66
−0.66
−0.66
−0.66
−0.66
−0.66
−0.66
−1.08
−1.08
−1.08
λmax, exp
298.8
316.1
282.5
289.1
293.0
293.8
330.1
334.0
345.0
331.7
332.9
326.4
323.5
322.3
328.3
327.0
340.8
371.0
323.6
323.3
326.0
324.8
324.6
306.0
294.7
293.0
291.6
297.6
307.0
321.2
297.4
297.2
300.3
298.3
296.1
298.7
297.0
337.7
332.0
328.6
vmax, exp
CC
3‐furyl
p‐CF3
p‐CN
m‐Me
m‐F
−0.08
−0.08
−0.08
−0.08
−0.08
−0.08
0.13
−0.12
−0.70
−0.03
0.02
33 467
31 636
35 398
34 590
34 130
34 037
30 294
29 940
28 986
30 148
30 039
30 637
30 912
31 027
30 460
30 581
29 343
26 954
30 902
30 931
30 675
30 788
30 807
32 680
33 933
34 130
34 294
33 602
32 573
31 133
33 625
33 647
33 300
33 523
33 772
33 478
33 670
29 612
30 120
30 432
3‐furyl
0.66
3‐furyl
−0.07
0.34
3‐furyl
3‐furyl
m‐Cl
m‐CN
p‐Cl
0.37
0.02
3‐furyl
0.56
0.56
2′‐methyl‐2‐furyl
2′‐methyl‐2‐furyl
2′‐methyl‐2‐furyl
2′‐methyl‐2‐furyl
2‐thienyl
0.23
−0.22
−0.12
−0.70
0.56
p‐CF3
p‐CN
m‐CN
p‐OMe
p‐Me
H
0.54
0.13
0.66
0.13
0.56
0.13
−0.27
−0.17
0.00
0.05
−0.50
−0.17
0.00
2‐thienyl
0.05
2‐thienyl
0.05
2‐thienyl
p‐F
0.06
0.05
0.06
2‐thienyl
p‐Cl
0.23
0.05
−0.22
−0.12
−0.70
−1.17
−0.03
0.02
2‐thienyl
p‐CF3
p‐CN
p‐NO2
m‐Me
m‐F
0.54
0.05
2‐thienyl
0.66
0.05
2‐thienyl
0.78
0.05
2‐thienyl
−0.07
0.34
0.05
2‐thienyl
0.05
2‐thienyl
m‐Cl
m‐CF3
m‐CN
p‐OMe
p‐Me
H
0.37
0.05
0.02
2‐thienyl
0.43
0.05
0.09
2‐thienyl
0.56
0.05
0.56
3‐thienyl
−0.27
−0.17
0.00
−0.02
−0.02
−0.02
−0.02
−0.02
−0.02
−0.02
−0.02
−0.02
−0.02
−0.02
−0.02
−0.02
−0.02
0.01
−0.50
−0.17
0.00
3‐thienyl
3‐thienyl
3‐thienyl
p‐F
0.06
0.06
3‐thienyl
p‐Cl
0.23
−0.22
−0.12
−0.70
0.10
3‐thienyl
p‐CF3
p‐CN
m‐OMe
m‐Me
m‐F
0.54
3‐thienyl
0.66
3‐thienyl
0.12
3‐thienyl
−0.07
0.34
−0.03
0.02
3‐thienyl
3‐thienyl
m‐Cl
m‐CF3
m‐CN
m‐NO2
p‐OMe
p‐Me
H
0.37
0.02
3‐thienyl
0.43
0.09
3‐thienyl
0.56
0.56
3‐thienyl
0.71
0.66
2′‐methyl‐2‐thienyl
2′‐methyl‐2‐thienyl
2′‐methyl‐2‐thienyl
−0.27
−0.17
0.00
−0.50
−0.17
0.00
0.01
0.01
(Continues)

QU ET AL.
5 of 10
TABLE 1 (Continued)
b
b
c
d
σ(Y)a
0.06
0.23
0.54
0.66
0.78
0.34
0.37
0.43
0.56
0.71
σ
(p)(X)a
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
σ
ðYÞ
σeCxCðpÞðXÞ
−1.08
−1.08
−1.08
−1.08
−1.08
−1.08
−1.08
−1.08
−1.08
−1.08
λmax, exp
327.7
335.3
336.1
350.3
384.8
330.5
332.9
332.7
335.6
332.7
vmax, exp
ex
No.
81
82
83
84
85
86
87
88
89
90
X
Y
CC
2′‐methyl‐2‐thienyl
2′‐methyl‐2‐thienyl
2′‐methyl‐2‐thienyl
2′‐methyl‐2‐thienyl
2′‐methyl‐2‐thienyl
2′‐methyl‐2‐thienyl
2′‐methyl‐2‐thienyl
2′‐methyl‐2‐thienyl
2′‐methyl‐2‐thienyl
2′‐methyl‐2‐thienyl
p‐F
0.06
30 516
29 824
29 753
28 547
25 988
30 257
30 039
30 057
29 797
30 057
p‐Cl
−0.22
−0.12
−0.70
−1.17
0.02
p‐CF3
p‐CN
p‐NO2
m‐F
m‐Cl
m‐CF3
m‐CN
m‐NO2
0.02
0.09
0.56
0.66
aThe values were taken from Hansh et al.[30]
bThe values were taken from Cao et al.[19]
cThe λmax, exp of nos. 1‐17 was taken from Jiang et al.[31] the λmax, exp of nos. 18‐23 was taken from Cao et al.[32] the λmax,exp of nos. 24‐25 was taken from Jiang.[33]
the λmax, exp of nos. 26‐90 was obtained by this work.
dνmax, exp = 1/λmax, exp
.
reference, the spectrum of each target compound was
standard deviation, F is the Fisher ratio, and n is the date
points of the regression equation. Equation 1 has a good
correlation. However, it should be noted that molecular
skeleton of the target compounds is XCH═CHArY, and
its parent molecule is styrene (CH2═CHPh), which is dif-
tested for 3 times, and the mean value of λmax was used
for each sample. The λmax and νmax (cm−1, νmax = 1/λmax
)
values of all target compounds were collected and listed in
Table 1 (The UV spectra can be seen in supporting
information).
ferent from that of XSBY or XArY. Thus, Equation 1 is no
ex
CCðpÞ
longer suitable for fitting the σ
values of groups X in
ex
3 | DETERMINING THE σ
CCðpÞ
the compounds XCH═CHArY. To investigate the change
regularity of the νmax of XCH = CHArY, we collected
the νmax values of 25 samples of compound XCH═CHArY
(X = H, Ph, CHO) (Table 1, nos. 1‐25, reported by previ-
ous studies[31–33]) and performed a regression analysis
for these νmax values against the substituent constants
and obtained Equation 2.
VALUES OF FURYL AND THIENYL
Cao et al[21,34] investigated systematically the νmax of UV
absorption for stilbene compounds (XSBY) and
established a correlation equation. Recently, we[28] fur-
ther synthesized 7 series of stilbene compounds and col-
lected the νmax values of disubstituted benzene (XArY)
and XSBY and got the νmax values of total 225 compounds.
Then we correlated the νmax with 3 parameters (σ(XY),
σeCxC, and νmax,parent) and obtained Equation 1.
vmax ¼ 40448:92 þ 8:38σðYÞ þ 13230:48σðpÞðXÞ
ex
þ 3556:31σ ðYÞ
CC
þ 9186:48σeCxCðpÞðXÞ−5132:97Δσ2
ex
þ 2084:59σ ðXYÞ;
(2)
CC
νmax ¼ 9267:131 þ 1468:417σðXYÞ
ex
R ¼ 0:9999; S ¼ 36:83; F ¼ 44990:97; n ¼ 25;
þ 0:069∑σ vmax;parent þ 0:712vmax;parent
;
(1)
CC
ex
where σ ðXYÞ is the cross‐interaction effect expressed
CC
ex
ex
CC
with
σ
between X and Y, that is,
σ
ðXYÞ =
R ¼ 0:9946; S ¼ 355:22; F ¼ 6814:17; n ¼ 225;
CC
2
ex
ex
σ
ðXÞ × σ ðYÞ, and Δσ is the substituent specific
CC
CCðpÞ
where σ(XY) is the cross‐interaction effect expressed with
σ between X and Y, that is, σ(XY) = σ(X)·σ(Y) and νmax,
cross‐interaction effect expressed with Hammett con-
stant between X and Y, that is, Δσ2 = [σ(Y) − σ(p)(X)]2.
Here, according to the treatment of Cao et al,[32] the
Δσ2 = 0 for the X being H and Ph. Equation 2 shows a
is the wavenumber of the parent molecular of stil-
parent
ex
bene or benzene. ∑σ is the sum of excited‐state substit-
CC
ex
CC
ex
CC
uent constants of X and Y, that is, ∑σ = σ ðXÞ +
good correlation. Thus, we use Equation 2 as the origi-
ex
CC
ex
CCðpÞ
σ
ðYÞ, in which R is the correlation coefficient, S is the
nal reference equation to simulate the σ
values of

6 of 10
QU ET AL.
ex
CCðpÞ
TABLE 2 The σ
values of para‐furyl and para‐thienyl groups
Substituent
2‐furyl
−0.97
3‐furyl
−0.46
2′‐methyl‐2‐furyl
−1.25
2‐thienyl
−1.09
3‐thienyl
−0.66
2′‐methyl‐2‐thienyl
−1.08
ex
σ
CCðpÞ
FIGURE 3 Plot of the calculated λmax, cal by Equation 4 versus the
experimental λmax, exp for the 26 compounds of Table 3
FIGURE 2 Plot of the calculated νmax, cal by Equation 3 versus the
experimental ones of XCH═CHArY
TABLE 3 Calculated and experimental λmax (nm) and νmax (cm−1) values of compounds XCH═NArY
a
a
b
b
c
No.
X
Y1
Y2
λmax, cal
νmax, cal
λmax, exp
νmax, exp
Δλmax
1
C6H5
p‐NMe2
378.6
26 411
376.2
26 580
2.4
2
C6H5
p‐OMe
p‐Me
p‐H
331.9
320.0
313.1
314.4
317.1
309.2
320.5
321.4
316.1
316.7
315.8
313.1
315.8
320.6
309.5
299.4
340.7
328.2
316.9
328.7
344.3
331.5
319.9
332.0
314.5
30 131
31 252
31 934
31 802
31 532
32 341
31 202
31 119
31 631
31 573
31 661
31 940
31 667
31 189
32 311
33 399
29 350
30 472
31 560
30 422
29 048
30 169
31 258
30 119
31 797
332.1
317.8
309.8
310.0
313.4
313.1
316.1
320.8
314.0
313.5
314.3
314.6
313.5
325.0
311.8
301.2
341.8
331.8
315.0
326.7
346.0
333.6
325.7
335.6
317.2
30 113
31 464
32 276
32 257
31 910
31 942
31 634
31 172
31 847
31 898
31 817
31 786
31 898
30 769
32 072
33 201
29 257
30 139
31 746
30 609
28 902
29 976
30 703
29 797
31 526
−0.2
2.2
3
C6H5
4
C6H5
3.3
5
C6H5
p‐F
4.4
6
C6H5
p‐Cl
3.8
7
C6H5
p‐CF3
p‐CN
p‐Me
p‐Me
p‐Me
p‐Me
p‐Cl
−3.9
4.4
8
C6H5
9
C6H5
m‐Me
m‐F
0.6
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
C6H5
2.1
C6H5
m‐Br
m‐Cl
m‐Cl
m‐Me
3.2
C6H5
1.5
C6H5
−1.5
2.3
C6H5
m‐Me
p‐OMe
p‐Me
p‐CF3
p‐OMe
p‐Me
p‐CF3
p‐CN
p‐OMe
p‐Me
p‐CF3
p‐CN
p‐OMe
3‐thienyl
3‐thienyl
3‐thienyl
2‐thienyl
2‐thienyl
2‐thienyl
2‐thienyl
2′‐methyl‐2‐thienyl
2′‐methyl‐2‐thienyl
2′‐methyl‐2‐thienyl
2′‐methyl‐2‐thienyl
3‐furyl
−4.4
−2.3
−1.8
−1.1
−3.6
1.9
2.0
−1.7
−2.1
−5.8
−3.6
−2.7
aThe νmax, cal values was calculated by Equation 4. λmax, cal = 1/νmax, cal
bThe λmax, exp of nos. 1‐8 was taken from Chen et al.[35] the λmax, exp of nos. 9‐14 was taken from Wang et al.[22] The rest of λmax, exp was obtained by this work.
cΔλmax = λmax, cal − λmax, exp
.
.

QU ET AL.
7 of 10
ex
TABLE 4 Excited‐state constant values σ (σeCxCðmÞ, σeCxCðpÞ) and Hammett constant values σ (σm, σp) for meta‐ and para‐substituents
CC
a
b
a
b
ex
ex
ex
ex
No.
Substituent
σ
σ
No.
Substituent
σ
σ
CCðmÞ
CCðpÞ
CCðmÞ
CCðpÞ
(σm)c
(σp)c
(σm)c
(σp)c
1
NH2
−0.88
23
CN
0.56
−0.70
(0.66)
−1.13
(0.50)
−0.13
(−0.66)
−0.19
(−0.37)
−0.82
(0.15)
−1.09
(0.42)
−1.31
(0.56)
2
OH
0.47
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
MeCO
SiMe3
t‐Bu
(0.12)
3
SH
(−0.07)
−0.17
(−0.20)
−0.43
(0.72)
−0.60
(0.49)
−0.17
(−0.17)
−0.69
(0.45)
−0.08
(0.31)
−1.40
(0.00)
−0.12
(0.54)
−0.34
4
CHO
5
NEt2
MeSO2
MeSO
Me
6
H
0.00
0.00
(0.00)
0.66
(0.00)
−1.17
(0.78)
−1.13
(−0.04)
−1.06
(−0.61)
−1.05
(0.23)
−0.39
(0.60)
−0.70
(0.45)
−0.92
7
NO2
−0.03
(0.71)
0.08
(−0.07)
8
CHCH2
COOMe
OCOMe
SMe
(0.06)
9
NHEt
10
11
12
13
14
15
16
17
18
19
20
CCH
0.18
(0.21)
SO2NH2
CF3
0.09
(0.43)
COOH
c‐Propanyl
CONH2
Ph
CF═CF2
−0.61
(0.36)
C(Me)═CH2
−0.98
(0.05)
−0.17
0.01
−0.86
(−0.01)
−1.81
(−0.83)
−1.52
(−0.03)
−0.97
(0.02)
(0.06)
0.17
CH(OH)CH2COOPr
NMe2
PhO
(−0.16)
0.00
CH(OH)CH2CCH
−0.15
(0.25)
Et
−0.06
−0.13
(−0.15)
−0.50
(−0.27)
0.06
2‐furyl
3‐furyl
2‐thienyl
3‐thienyl
(−0.07)
0.10
OMe
F
−0.46
(−0.08)
−1.09
(0.05)
(0.12)
0.02
(0.34)
0.02
(0.06)
−0.22
(0.23)
Cl
−0.66
(−0.02)
(0.37)
(Continues)

8 of 10
QU ET AL.
TABLE 4 (Continued)
a
b
a
b
ex
CCðmÞ
ex
CCðpÞ
ex
CCðmÞ
ex
CCðpÞ
No.
Substituent
σ
σ
No.
Substituent
σ
σ
21
Br
−0.03
(0.39)
0.05
−0.33
(0.23)
−0.56
(0.18)
43
2′‐methyl‐2‐furyl
−1.25
(0.13)
−1.08
(0.01)
22
I
44
2′‐methyl‐2‐thienyl
(0.35)
a
ex
ex
σ
is the excited‐state substituent constant of meta‐substituent. The σ
values of OMe, Me, F, Cl, CF3, and CN were taken from Cao et al.[21] The σex
CCðmÞ
CCðmÞ
CCðmÞ
values of OH were taken from Zhou et al.[27] The σex
b
values of NO2, I, CHCH2, Ph, Et, NMe2, and CCH were taken from Zhu et al.[28]
CCðmÞ
ex
ex
CCðpÞ
σ
is the excited‐state substituent constant of para‐substituent. The σ
values of 2‐furyl, 3‐furyl, 2′‐methyl‐2‐furyl, 2‐thienyl, 3‐thienyl, and 2′‐methyl‐2‐
CCðpÞ
values was taken from Cao et al.[19]
ex
CCðpÞ
theniyl were obtained by this work, and the rest of σ
cσm and σp are Hammett constants of meta‐ and para‐substituents, respectively. Their values were taken from Hansh et al.[30]
ex
furyl and thienyl. Take the determining σ
of group
experimental values νmax, exp. We converted the calculated
max, cal to λmax, cal and observed that the average absolute
error between the calculated wavelength and the experi-
ex
mental ones was only 2.2 nm. It indicates that the σ
CCðpÞ
CCðpÞ
ν
2‐furyl for an example, the νmax values of compounds
(Table 1, nos. 26‐35) have been measured in anhydrous
ethanol. In Equation 2, the values of νmax, σ(p)(X), σ(Y),
and σ ðYÞ all are known, while the σex
value of
values of furyl and thienyl (Table 2) are reliable.
ex
CC
CCðpÞ
group 2‐furyl must be a fixed value in the compounds
ex
2‐furyl‐CH═CHArY. Further, the method of curve fitting
4.2 | Application of σ
in correlating
CCðpÞ
ex
was used to simulate the most appropriate σ
value
CCðpÞ
the λmax of disubstituted Schiff bases
Further, to test the availability ofσeCxCðpÞ, we synthesized 12
of 2‐furyl. With above stated way, we obtained 6 para‐
ex
CCðpÞ
substituent constants σ
values of X groups including
samples of disubstituted Schiff bases (XCH═NArY) and
measured their λmax of UV absorption in anhydrous etha-
nol (Table 3, nos. 15‐26). In addition, we also collected the
νmax values of 14 samples of 3′/4′‐disubstituted Schiff
bases (PhCH═NArY) (Table 3, nos. 1‐14, reported by
Wang et al[22] and Chen et al[35]). A regression analysis
of the νmax values of the 26 compounds was made against
the substituent constants, and Equation 4 was obtained.
2‐furyl, 3‐furyl, 2′‐methyl‐2‐furyl, 2‐thienyl, 3‐thienyl,
and 2′‐methyl‐2‐theniyl for the E‐isomers X‐
CH═CHArY, as shown in Table 2.
4 | RESULT DISCUSSION
ex
4.1 | Verifying the reliability of σ
CCðpÞ
ex
CCðpÞ
To verify the reliability of σ
in Table 2, we correlated
νmax ¼ 36961:71 þ 9003:04σ ðXÞ þ 988:20ΣσFðYÞ (4)
ðpÞ
quantitatively the νmax of all 90 compounds in Table 1
þ1809:35ΣσRðYÞ þ 2153:54∑σeCxCðYÞ
ex
CCðpÞ
ex
CC
with σ
ðXÞ, σ ðYÞ, and σ and then obtained Equa-
tion 3.
þ5741:26σeCxCðpÞðXÞ;
vmax ¼ 40278:6 þ 320:99σðYÞ þ 12041:65σðpÞðXÞ
(3)
R ¼ 0:9770; S ¼ 327:68; F ¼ 83:99; n ¼ 26;
þ3325:01σ ðYÞ þ 9002:15σeCxCðpÞðXÞ−4431:1Δσ2
ex
CC
ex
þ1881:91σ ðXYÞ;
in which ΣσF(Y) and ΣσR(Y) are the sum of induced
and conjugated effect constants of groups Y at the aniline
ring, respectively, that is, ΣσF(Y) = σF(Y1) + σF(Y2) and
ΣσR(Y) = σR(Y1) + σR(Y2), and ∑σeCxCðYÞ is the sum of
excited‐state substituent constants of groups Y, that is,
CC
R ¼ 0:9963; S ¼ 302:90; F ¼ 1878:39; n ¼ 90:
The correlation of Equation 3 is very good. Therefore,
we recommend Equation 3 to express the change regular-
ity of the νmax of compounds XCH═CHArY. To observe
the calculation results of Equation 3 more intuitively, we
plotted the calculated values against the experimental
ones (see Figure 2).
ex
CC
ex
∑σ ðYÞ = σ ðY1Þ + σeCxCðY2Þ. We converted the calcu-
CC
lated νmax, cal of Equation 4 to λmax, cal and listed the λmax
and νmax values in Table 3. It indicates that the average
absolute error between the calculated wavelength values
and the experimental ones of the 26 compounds was only
2.6 nm, which is within the experimental error range.
As seen from Figure 2, the calculated values νmax, cal
by Equation
3
are in good agreement with the
Figure 3 is the plot of calculated λmax,
values by
cal

QU ET AL.
9 of 10
provide convenience for the study of the optical properties
and the molecular design of optical materials for those
organic conjugated compounds containing furyl and
thienyl.
ACKNOWLEDGEMENT
The work was supported by the National Natural Science
Foundation of China (21672058).
ORCID
Chenzhong Cao http://orcid.org/0000-0001-5224-7716
FIGURE 4 Plot of excited‐state substituent constants (σeCxC) versus
Hammett constants (σ)
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CCðpÞ
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SUPPORTING INFORMATION
Additional Supporting Information may be found online
in the supporting information tab for this article.
How to cite this article: Qu J, Cao C‐T, Cao C.
Determining the excited‐state substituent constants
of furyl and thienyl groups. J Phys Org Chem. 2018;
e3799. https://doi.org/10.1002/poc.3799
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