Photochromic behavior and mechanism of indole thiosemicarbazide derivates in amorphous powder, solution and nanofiber

Article abstract of DOI:10.1016/j.dyepig.2019.04.009

A series of Schiff bases containing the indole group were synthesized. The compound 2-[(1-methyl-1H-indol-3-yl)methylene] hydrazinecarbothioamide (4) exhibits excellent reversible photochromic properties both in solid?solid state and solution. Moreover, t

Full text of DOI:10.1016/j.dyepig.2019.04.009

Accepted Manuscript
Photochromic behavior and mechanism of indole thiosemicarbazide derivates in
amorphous powder, solution and nanofiber
Yuanyuan Che, Lang Liu, Jianzhang Zhao, Yuming Yu, Xianmei Zhao
PII:
S0143-7208(18)32633-0
https://doi.org/10.1016/j.dyepig.2019.04.009
DYPI 7464
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 30 November 2018
Revised Date: 3 April 2019
Accepted Date: 4 April 2019
Please cite this article as: Che Y, Liu L, Zhao J, Yu Y, Zhao X, Photochromic behavior and mechanism
of indole thiosemicarbazide derivates in amorphous powder, solution and nanofiber, Dyes and Pigments
(2019), doi: https://doi.org/10.1016/j.dyepig.2019.04.009.
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Graphical contents entry:
Photochromic behavior and mechanism of indole thiosemicarbazide derivates in
amorphous powder, solution and nanofibers
a
a
a, b, c
a,b
a
By Yuanyuan Che, Lang Liu,* Jianzhang Zhao,*
Yuming Yu, and Xianmei Zhao
Vi
s
Photochromic UV
A series of Schiff bases containing indole group were synthesized. Some of which exhibit reversible
photochromic properties in solid state. Moreover, the composited nanofibers show faster photochromic
rate and better fatigue resistant than in powder form. Their photochromic properties originate from the
intermolecular proton transfer, resulting in the isomerization between the thioketone−form and the
thioalcohol−form of the molecules, which is obvious different from that of classic Schiff bases such as
salicylal anils.
1

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Photochromic behavior and mechanism of indole
thiosemicarbazide derivates in amorphous powder,
solution and nanofiber
a
* a
* a, b, c
a,b
a
Yuanyuan Che, Lang Liu, Jianzhang Zhao,
Yuming Yu and Xianmei Zhao,
a
Key Laboratory of Energy Materials Chemistry, Ministry of Education, Institute of Applied
Chemistry, Xinjiang University, Urumqi 830046, Xinjiang, China.
E-mail: llyhs1973@sina.com; liulang@xju.edu.cn
b
School of Chemistry and Chemical Engineering, Xinjiang University, Urumqi 830046,
Xinjiang, China
c
State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of
Technology, E-208 West Campus, 2 Ling-Gong Road, Dalian 116024, P. R. China.
E-mail: zhaojzh@dlut.edu.cn
Abstract
A series of Schiff bases containing the indole group were synthesized. The compound 2-[(1-
methyl-1H-indol-3-yl)methylene] hydrazinecarbothioamide (4) exhibits excellent reversible
photochromic properties both in solid−solid state and solution. Moreover, the nanofiber
1

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containing the compound 4 also shows excellent photochromic properties, which are better than
the amorphous powder of 4 itself. Based on the experiment results and theoretical calculation, we
confirm that the photochromic properties originates from the intermolecular proton transfer,
resulting in the isomerization of the thioketone−form and the thioalcohol−form in the
hydrazinecarbothioamide. This unique photochromic system is obviously different from that of
traditional Schiff bases, such as salicylideneanilines.
Keywords
: Photochromism, amorphous powder, nanofiber, Schiff bases, indole, intermolecular
proton transfer.
Introduction
Photochromic materials show various properties on both microscopic and macroscopic levels
upon the external stimulation and the photo-responses process may involve multiple photons and
1
-3
molecules. These materials also receive broad interests for their potential applications in
4
-9
5, 10
11
photoactive materials, such as optical switches, molecular sensors,
ophthalmic lenses,
1
2-15
16-18
19, 20
smart windows,
photochromic decorations,
and linear optical materials.
.
Organic photochromic materials have attracted significant attention for their structural
diversities and excellent fatigue resistance. So far, many efforts are focused on open/close ring
2
1,22
23-27
28-30
reactions in fulgides,
dithienylethenes,
spiropyrans or spiroxazines,
N=N cis-trans
3
1, 32
33,34.
isomerism in azobenzenes,
and enol/keto tautimerization in o-hydroxy Schiff bases.
Due
to their intrinsic properties, it is still a big challenge to improve the photochromic property, for
instance, most of the photochromic compounds only show excellent photochromic behaviors in
solution, not in the aggregated state, however, a single component with the solid−state
photochromism is more desired for practical application.
Jia and co-workers previously reported a series of pyrazolones with solid−state photochromic
behaviors, in which the pyrazolone is the essential moiety. The photochromic mechanism is
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attributed to the transition between the enol-form and the keto−form through the
inter/intramolecular proton transfer, which is independent of the C=N group of Schiff bases.
Moreover, the hydrogen bonds in the crystal structures for pyrazolones play an important role in
3
5-39
their photochromism.
. This series of compounds have been elegantly designed with an
emphasis on vaious substituents at 3− and/or 4−position of pyrazolones. However, majority of
these photochromic compounds exhibit the reversibility upon heating and show poor thermal
stability. And it has to be noteworthy that the excellent fatigue resistance and good thermal
stability are essential factors for the practical application. Thus, it’s desired to develop a new
photochromic system with excellent solid−state photochromic properties, which is different from
the traditional photochromic Schiff bases (pyrazolone derivatives) with the hydroxyl moieties.
Scheme 1. Structures of compounds.
Herein, a series of novel Schiff bases containing the indole group without the hydroxyl group
have been synthesized by a one-step condensation of indolealdehydes and thiosemicarbazides
(Scheme 1). Among these as−synthesized compounds, 2-(1H-indol-3-ylmethylene)-N-
phenylhydrazinecarbothioamide (3) and 2-[(1-Methyl-1H-indol-3-yl)methylene]
hydrazinecarbothioamide (4) exhibit good solid−state photochromic behaviors under alternating
irradiation of 365 nm light and visible light.
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Results and discussion
Solid−state photochromic properties
4
2
1
18min
08min
18min
Compound 1
Compound 2
Compound 3
2
1
1
3
53min
93min
03min
0min
0.6
0.4
0.2
1
.0
0.8
.6
0.4
.2
5
2
1
4
0
820 min
940 min
440 min
80 min
min
68min
42min
24min
14min
10min
0.8
0.6
0
44min
13min
7min
2min
0min
0.4
......
2min
0
0
0
.2
3
4
00
450
500
550
400 450 500 550 600
50 400 450 500 550
Wavelength(nm)
Wavelength(nm)
Wavelength(nm)
Figure 1. UV–vis diffuse reflectance spectra of the compounds 1-3 under the irradiation of 365
nm light for different time in solid−state.
The UV–vis diffuse reflectance spectra of the compounds 1-3 upon the irradiation of 365 nm
light are shown in Figure 1. Obviously, new bands appear at 380 nm to 500 nm for these
compounds 1 and 3 upon the 365 nm irradiation, in the range of 400 nm and 600 nm for the
compound 2. Their intensities increase with prolonging the irradiation time. After irradiating the
compounds 1, 2 and 3 for 253 min, 5820 min and 418 min, respectively, no further evolution is
observed, which indicates the attaining of the photo-stationary states (Figure 1). Meanwhile, the
white compounds changed into yellow (for the compounds 1 and 3) or yellow orange (for the
compound 2).
Moreover, we also investigate the photo-isomerization properties of the compounds 4-6 with
the methyl group at the N−position of the indole moiety. Figure S1 in the electronic
supplementary information (ESI) shows their UV−vis spectra. These compounds 4-6 have
similar properties as the compounds 1-3 under the irradiation of 365 nm light. The above result
indicates that all these compounds 1-6 exhibit photo-isomerization properties in solid−state.
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These colored amorphous powders are stable, and no de-coloration occurres even by heating at
1
00 °C. Moreover, they can be kept for a long time in the darkness at room temperature, which
indicates they have good thermal stabilities (Figure S2 in ESI). When these yellow compounds
-6 are exposed to visible light at room temperature, the colors of 1, 2, 5 and 6 do not change.
1
However, the yellow compounds 3 and 4 revert to the faint yellow with the decrease of the
absorption intensity in the range of 380~500 nm, but they are not fully recovered to the original
intensity of absorption bands (Figure 2). The above phenomenon indicates that the compounds 3
and 4 have solid−state photochromic properties. However, the other compounds have only
photo-isomerization properties and do not belong to the photochromic materials.
Compound 3
Compound 4
1.0
0.8
0.6
0.4
1
0
0
0
0
.0
.8
.6
.4
UV
visible
UV
visble
.2
3
0.2
350
50 400 450 500 550
400
450
500
550
Wavelength(nm)
Wavelength(nm)
Figure 2. UV−vis diffuse reflectance absorption spectra of the compounds 3 and 4: before (
)
and after ( ) the irradiation of 365 nm light, and after visible light at room temperature ( ).
The coloration–decoloration cycles under alternating irradiation of 365 nm light and visible
light are shown in Figure S3 in ESI. It is found that there is an obvious degradation after three
cycles for the compound 3. However, there is no obvious degradation of the compound 4 after
several cycles, which means that the compound 4 has good fatigue resistance. Compared to the
compounds 1-3 with the hydrogen atom at the N−position of the indole, the compounds 4-6 with
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the methyl group at the same position still have photo-isomerization properties, which indicates
that the H atom at the N−position of the indole does not participate in the photochromic process.
Photochromic mechanism
Figure 3. Hydrogen bond connection diagrams of the compounds 1 (a) and 2 (b).
In order to study the photochromic mechanism of these indole derivatives, we try to
grow single crystals of these compounds. Through various attempts, we only obtain the
single crystals of the compounds
solution for the compound and ethanol solution for the compound
Since the structures of these compounds are similar, we studied the photochromic
mechanism of these compounds by the analysis of the structures of and . The
crystallographic data, selected bond lengths and hydrogen bonds of the two compounds
1
and
2
by the slow evaporation of dimethyl formamide
1
2
in the darkness.
1
2
1
1
and
and
2
2
are displayed in Table S1-S3 in ESI, respectively. And the crystal structures of
are shown in Figure S4 in ESI. Based on the bond distances listed in Table S3, it is
S1 are 1.7021 (1) Å in and 1.6996(1) Å in , which
S single bond of 1.81 Å and the C=S double bond of 1.56 Å.
found that the bond lengths of C10
are between the C
−
1
2
4
0-42
−
Based on these results, we speculate that the sulfur in the thiosemicarbazide plays an
important role in the photochromic process. The hydrogen bond connection diagrams of
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the compounds
1
and
[N(1)−H(1)⋅⋅⋅S(1)],
N(3A)−H(3A)⋅⋅⋅S(1A)]) in the molecular structure of the compound 1, which [N(1)−H(1)⋅⋅⋅S(1)]
2
are shown in Figure 3. There are four intermolecular hydrogen bonds
(
[
[N(1A)−H(1AA)⋅⋅⋅S(1A),
[N(3)−H(3)⋅⋅⋅N(4A)]
and
and [N(1A)−H(1AA)⋅⋅⋅S(1A)] belong to the same hydrogen bond. Therefore, there are three
types of intermolecular hydrogen bonds. However, the molecular structure of the compound 2
contains only two types of intermolecular hydrogen bond, [N(1)−H(1)⋅⋅⋅S(1)] and
[
N(3)−H(3)⋅⋅⋅S(1)]. In the compound 2, the intermolecular hydrogen bond of
N(3)−H(3)⋅⋅⋅N(4A)] does not exist, which may be the methyl group at N4 increases the steric
[
hindrance between molecules. The photochromic mechanism of Schiff bases containing the
ortho−hydroxyl is the proton transfer from the hydroxyl group to the nitrogen atom in C=N
4
3
through an intramolecular hydrogen bond under photo-irradiation or heating. It has been
proved that the hydrogen bonds are effective to promote the proton transfer. For the
as−synthesized compounds, the intermolecular hydrogen bonds [N1−H1⋅⋅⋅S1] and [N3−H3⋅⋅⋅S1]
in their structures may play an essential role in the photochromic process. If the intermolecular
hydrogen bond [N1−H1⋅⋅⋅S1] participates in the photochromic reaction, when the H1 atom is
replaced by the methyl group, the formed compound should not have photochromic properties.
However, three compounds obtained by the incorporation of the methyl group at the N−position
of the indole still exhibit photochromic properties, which means that the intermolecular hydrogen
bond [N1−H1⋅⋅⋅S1] does not take part in the photochromic process and the intermolecular
hydrogen bond [N3−H3⋅⋅⋅S1] may be effective to promote the protons transfer. Therefore, the
photochromic mechanism may be that the H3 atom is transferred from N3 to S1 through the
hydrogen bond [N3−H3⋅⋅⋅S1] under the light irradiation, which leads to the isomerization of the
thioketone−form and the thioalcohol−form.
7

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a
b
c
1
66
164
162
160
166
164
162
160
166
164
162
160
Electron binding energy (eV)
Electron binding energy (eV)
Electron binding energy (eV)
Figure 4. XPS spectra of S(2p) in the compound 4; (a) before the 365nm light irradiation; (b)
after the 365nm light irradiation; (c) after the irradiation of visible light for the colored powder. (
stands for A species
,
stands for B species.)
a
c
b
Scheme 2. Photochromic mechanism of the indole derivatives.
To verify the transformation from the thioketone−form to the thioalcohol−form under the
1
66
164
162
160
166
164
162
160
166
164
162
160
irradiation of 365 nm light, XPS spectra of the compound 4 before and after the irradiation of
Electron binding energy (eV)
Electron binding energy (eV)
Electron binding energy (eV)
3
65 nm light were studied, in which the S(2p) spectra are shown in Figure 4. Two peaks are
observed, the peak at 162.05 eV is the typical C=S bond, and the other one at 163.26 eV can be
4
4,45,46
ascribed to the C−S bond .
Before the irradiation of 365 nm light, the
thioketone−form/thioalcohol−form isomer ratio is 65 to 35, which is changed to 50 to 50 after
8

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the irradiation of 365 nm light. The proportion of the C−S increases while that of C=S decreases,
indicating that the thioketone−form has isomerized into the thioalcohol−form after the irradiation
of 365 nm light, as shown in the Scheme 2. After the irradiation with visible light, the
thioketone−form/thioalcohol−form isomer ratio is about 56 to 44 (Figure 4c). The result
indicates a slight decrease of C−S and increase of C=S. Based on the change trend of two species,
it can be inferred that the thioalcohol−form has isomerized to the thioketone−form after the
irradiation of visible light, but the reversibility is unsatisfactory.
In order to obtain the information of molecular structures during the photochromic process, the
IR spectra of the compound 4 before and after the irradiation of 365 nm light are measured (ESI,
−
1
−1
Figure S5). Before the irradiation with 365 nm light, the peaks at 3248 cm , 3096 cm and
−
1
47,48
3
073 cm for the original white compounds are attributed to the N−H stretching vibration.
−
1
After the irradiation with 365 nm light, the intensity of the peak at 3248 cm is decreased,
−1
−1
leading to the peaks at 3248 cm and 3261 cm combine into one broad peak in the overlapped
−1
−1
−1
region (3240-3270 cm ). At the same time, the peaks at 3096 cm and 3073 cm for the N−H
−
1
stretching vibration are disappeared. Moreover, a new peak appears at 1598 cm , which is
3
8, 39, 49, 50
assigned to the C=N stretching vibration.
. Based on the analysis of the Fourier
transform infrared spectra, we confirm that the photochromic mechanism is the isomerization of
the thioketone−form and the thioalcohol−form after the irradiation of 365 nm light. However, for
the IR spectra of the bleaching compound 4 after the irradiation with visible light, obvious
changes are not observed due to its incomplete recovery to the original structure.
In addition, according to the structures of the thioketone−form and the thioalcohol−form, their
absorption spectra are simulated by theoretical calculation (Figure S6). When the thioketone
transfer to the thioalcohol, the simulated absorption spectrum is red-shifted, which leads to the
9

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colour change. However, the absorption intensity is different because of the mixed
thioketone−form and thioalcohol−form in the photostationary state of the compound 4 under the
irradiation of 365 nm light. The above results indicate that the theoretical calculation matches
well with the experimental absorption spectra of the thioketone−form and the thioalcohol−form.
Photochromic properties of nanofiber
Among all the as−synthesized compounds, the compound 4 exhibits excellent photochromic
property. In order to exploit its application, the PVP−4 nanofiber is prepared by the
electrospinning. As shown in Figure 5, the nanofibers of PVP−4 have a smooth surface and an
average diameter of 40 nm. The absorption spectra of the PVP−4 nanofiber under the irradiation
of 365 nm light and visible light are shown in Figure 6a, 6b. The nanofiber has the similar
photochromic property as the amorphous powder of the compound 4. Furthermore, the PVP−4
nanofiber can reach the photo-stationary state after 365 nm light irradiation for 21 min, which is
much faster than that of the amorphous powder (143 min). The first-order rate constant
k
is 0.22
−1
−1
min , which is much bigger than that (
k = 0.02 min ) of the amorphous powder (Figure S7 in
ESI). The result shows that reducing the size of 4 to nanoscale can largely improve the rate of the
photochromic reaction. When the colored PVP−4 nanofiber is exposed to visible light for 62 min
at room temperature, the yellow color reverts to the faint yellow, accompanying with the
decrease of the absorption intensity in the range of 380~450 nm, but they are not fully recovered
to the original intensity of absorption bands (Figure 6b). The reversibility of the PVP−4
nanofiber is shown in Figure 6c. Except for the memory of the first cycle, there is no degradation
after 10 cycles. The above results indicate that the PVP−4 nanofiber has a faster photochromic
kinetics and better fatigue resistance than the compound 4 in amorphous powder.
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Figure 5. SEM image of the PVP−4 nanofiber sample.
a
1min
c
b
0
0
0
0
0
0
.9
.8
.7
.6
.5
.4
1.2
1.0
0.8
0.6
0.4
1.2
1.0
0.8
0.6
0.4
2
1
.....
7min
.
2
0
min
min
visble
UV
3
00 350 400 450 500
Wavelength(nm)
300 350 400 450
Wavelength(nm)
0
2
4
6
8
10
Number of cycles
Figure 6. UV−vis spectra of the PVP−4 nanofiber upon the irradiation of 365 nm at different
times (a), UV−vis spectra of the PVP−4 nanofiber: before ( ) and after ( ) irradiation of
65 nm light, and after visible light at room temperature ( ) (b), photochromic cycles of the
PVP−4 nanofiber under alternating irradiation of 365 nm light and visible light (c)
3
In order to verify that the photochromic mechanism of the nanofiber sample, the XPS spectra
of S(2p) in the PVP−4 nanofiber before and after the irradiation with 365 nm light is shown in
Figure S8. These peaks are divided into two peaks, in which the peak at 162.02 eV is the typical
C=S bond, and the other one at 163.35 eV can be ascribed to the C−S bond. The ratio of the
thioketone-form/thioalcohol-form isomer is 67 to 33 for the nanofiber before the irradiation with
3
65 nm light, which is changed to 57 to 43 after the irradiation with 365 nm light. The
11

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population of the thioalcohol−form increases along with a decrease of the thioketone−form after
the irradiation with 365 nm light. These data indicate that the thioketone−form has isomerized
into the thioalcohol−form after the irradiation with 365 nm light. In addition, the IR spectra of
the nanofiber before and after the irradiation with 365 nm light are shown in Figure S9.
−1
After the irradiation with 365 nm light, the peak at 2977 cm is disappeared which is
−1
assigned to the peak of the N
shifted. However, other changes were not observed due to the lower amount of the
photochromic compound in the nanofiber sample Based on XPS and IR analyses of the
−H stretching vibration, and the peak at 1665 cm is red-
.
nanofiber sample, we conclude that the photochromic mechanism of the nanofiber is same to the
amorphous powder.
Photoisomerization properties in solution
The time-dependent absorption spectra of the compound 4 in tetrahydrofuran and
dichloromethane upon the irradiation of the 365 nm light are shown in Figure 7. The absorption
of the compound 4 appear at 334 nm in tetrahydrofuran and at 335 nm in dichloromethane,
respectively. Upon the 365 nm light irradiation, the maximum absorption bands at 298~375 nm
decrease while the absorption band at 250~298 nm increase, with an isosbestic point at 298 nm
in tetrahydrofuran and dichloromethane. After 80 s and 60 s of the 365 nm light irradiation, there
is no more evolution in the spectra for the compound 4 in tetrahydrofuran and dichloromethane.
When ceasing the 365 nm light irradiation, these systems can recover to their initial state in the
darkness. Figure 8 shows the time-dependent absorption spectra of the colored compound 4 in
tetrahydrofuran and dichloromethane in the darkness at room temperature. It can be seen that the
two systems have completely recovered to their initial state in the darkness for about 120 min
(tetrahydrofuran) and 47 min (dichloromethane) at room temperature. These results indicate that
12

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the compound 4 exhibits photochromic performance in solution.
0.5
0.4
0.3
0.2
0.1
0.0
a
UV 80s
UV 40s
UV 20s
UV 0s
b
0
0
0
.4
.3
.2
UV 60s
UV 30s
UV 10s
UV 0s
0.1
0
.0
250 300 350 400
Wavelength(nm)
2
50 300 350 400 450
Wavelength(nm)
−5
-1
Figure 7. Absorption spectra of 4 (1.0×10 mol L ) in tetrahydrofuran (a) and dichloromethane
b) upon the irradiation of 365 nm light. (UV: stands for under the irradiation of 365 nm light).
(
0
0
0
0
0
0
.5
.4
.3
.2
.1
.0
A 120min
A 60min
A 30min
A 13min
A 5min
A 47min
A 37min
A 27min
A 17min
A 8min
a
b
0
.4
0.3
.2
0.1
.0
A 2min
UV 80s
A 3min
UV 1min
0
0
2
50 300 350 400 450
250 300 350 400 450
Wavelength(nm)
Wavelength(nm)
−5
-1
Figure 8. Absorption spectra of the colored compound 4 (1.0×10 mol L ) in tetrahydrofuran (a)
and dichloromethane (b) in the darkness at room temperature. (A stands for in the darkness).
The time−dependent absorption spectra of other compounds in tetrahydrofuran and
dichloromethane upon the 365 nm light irradiation are shown in Figure S10-S14. It can be seen
that the absorption of these compounds with –CH
3 2
or –Ph on R will develop a new band at
3
75~440 nm in tetrahydrofuran and dichloromethane which may be attributed to the n−π*
13

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transition. At the same time, a fast decrease of the maximum absorption band at 300~375nm is
due to the π−π* transition upon the 365 nm light irradiation. The other five compounds except
the compound 1 can recover to their initial state in the darkness. The above phenomenon
indicates that these compounds exhibit the photoisomerization in their tetrahydrofuran and
dichloromethane solution, respectively.
Conclusions
Novel hydrazinecarbothioamide derivatives bearing the indole group have been prepared.
Under the alternating irradiation with UV and visible light, some of them exhibit reversible
photochromic property not only in solution but also in solid−state, and they also exhibit good
fatigue resistant. Based on these results of singlet crystal structure, XPS, IR and theoretical
calculations, the photochromic mechanism in solid−state is ascribed to the isomerization between
the thioketone−form and the thioalcohol−form via the intermolecular proton transfer. More
significantly, the PVP-4 nanofiber shows faster photochromic rate and better fatigue resistance
than the compound 4 in the amorphous powder, which indicates the potential practical
application of this material. These novel compounds shed light on the development of new
photochromic materials.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (21362037,
5
1672235), National “Ten Thousand People Plan”(2017), Xinjiang “Tianshan Elite Plan” (2017),
the Program for Changjiang Scholars and Innovative Research Team in the University of
14

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Ministry of Education of China (IRT1081), and the Doctoral Innovation Program of Xinjiang
University (XJUBSCX-2016010).
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3
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5
Irie, M. Photochromism: memories and switches-introduction. Chem. Rev. 2000, 100, 1683.
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8
Helmy, S.; Leibfarth, F. A.; Oh, S.; Poelma, J. E.; Hawker, C. J.; Read, d. A. J. Photoswitching using visible light: a new
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16

ACCEPTED MANUSCRIPT
Electronic Supplementary Information for:
Photochromic behavior and mechanism of indole thiosemicarbazide derivates
in amorphous powder, and solution and nanofibers
a
* a
* a, b, c
a,b
a
Yuanyuan Che, Lang Liu, Jianzhang Zhao,
Yuming Yu and Xianmei Zhao,
a
Key Laboratory of Energy Materials Chemistry, Ministry of Education, Institute of
Applied Chemistry, Xinjiang University, Urumqi 830046, Xinjiang, China.
E-mail: llyhs1973@sina.com, liulang@xju.edu.cn
b
School of Chemistry and Chemical Engineering, Xinjiang University, Urumqi 830046,
Xinjiang, China
c
.
State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian
University of Technology, E-208 West Campus, 2 Ling-Gong Road, Dalian 116024, P. R.
China.
E-mail: zhaojzh@dlut.edu.cn
1
. Materials and characterization
Indole-3-carboxaldehyde, 1-methyl-indole-3-carboxaldehyde, thiosemicarbazide, 4-methyl-3-
thiosemicarbazide, 4-phenyl-3-thiosemicarbazide and polyvinylpyrrolidone (PVP) were
purchased from JK Company. All other reagents were commercially available with AR grade and
used without further purification.
The UV–vis spectra of powder were measured on a Hitachi UV-3010H spectrometer with
an integrating sphere accessory. A 12 W lamp in ZF-8 ultraviolet analysis instrument was used as
the light source for irradiation of samples, the reflective filter size is 50 mm, the distance
between the sample and the light source is 15 cm. Melting point was measured with a TECH XT-
1
5
melting point apparatus without correction. H NMR was carried out on an INOVA-400 NMR
Spectrometer with DMSO-d6 as the solvent and TMS as an internal standard. HR MS spectra
were made on an Ultimate 3000/Q-Exactive. The elemental analyses were made on vario EL III.
17

ACCEPTED MANUSCRIPT
Fourier transform infrared spectra(FT-IR) were obtained on a Bruker Vertex-70 with the
attachment of diffuse reflection for amorphous powder and total reflection for nanofibers. The X-
ray single crystal diffraction data were collected on Rigaku R-AXIS SPIDER with an imaging
plate system and a graphite monochromatism MoKα radiation (λ = 0.71073 Å). The intensity
was measured by -scans. Cell constants and the orientation matrix for data collection were
ω
obtained by least-squares refinement of the diffraction data. The structure was solved by the
2
direct methods and refined by the full-matrix least-squares techniques on F using the
SHELXTL-97 software package. All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms bond to the carbon atoms were placed in calculated positions and refined as
riding mode and other atoms were located in different Fourier maps and refinement cycles.
CCDC 1877290 for the compound 1 and CCDC 1877289 for the compound 2 contained the
supplementary crystallographic data for this paper. X-ray photoelectron spectroscopy (XPS)
results were collected by using a Thermo ESCALAB 250 instrument using monochromatic Al X-
ray resource. Theoretically calculations were performed using the Gaussian 09 program. The
electrospinning setup was purchased from Beijing Ucalery Technology Development Co., Ltd.
The morphology of products was observed by sanning electron microcopy (SEM) on a hitachi S-
4
800 scanning electron microscope with an acceleration voltage of 5 kV.
18

ACCEPTED MANUSCRIPT
2
. Synthesis and characterization of indole derivatives.
Synthesis
of
2-(1H-indol-3-ylmethylene)
hydrazinecarbothioamide
(1).
Thiosemicarbazide (0.273 g, 3 mmol) and glacial acetic acid(0.5 mL) were added into an
ethanol solution (25 mL) of indole-3-carboxaldehyde (1.355 g, 3mmol), and the mixture
was stirred and refluxed for 40 min at 80 °С. After that, the mixture was cooled to room
temperature and a large quantity of faint yellow precipitation occurred. The precipitation
was collected by the filtration, which was recrystallized from ethanol, obtaining the white
amorphous powder. Other compounds can be readily prepared with the same method as
the compound 1.
2-(1H-indol-3-ylmethylene)hydrazinecarbothioamide (1): Yield 69.12 %; m.p. 201.9-
1
2
03.5
℃
; H NMR (400 MHz, DMSO-d6, TMS):
δ
11.60 (s, 1H, NH), 11.18 (s, 1H,
NH), 8.30 (s, 1H, CH), 8.22 (d, J = 7.8 Hz, 1H, ArH), 8.02 (s, 1H, NH ), 7.81 (d, J = 2.8
2
2
Hz, 1H, ArH), 7.43 (s, 1H, NH ), 7.41 (s, 1H, ArH), 7.24 – 7.16 (m, 1H, ArH), 7.15 –
+
7
.08 (m, 1H, ArH). HRMS: Calcd ([
Elemental analysis: (C10
%) C, 54.95; H, 4.33; N, 25.09; S, 14.40.
C
10
H
10
N
4
S
] ), m/z = 219.0626; found, m/z = 219.0699.
10 4
H N S) Calcd. (%) C, 55.02; H, 4.62; N, 25.67; S, 14.69. Found
(
2-(1H-indol-3-ylmethylene)-N-methylhydrazinecarbothioamide (2): Yield 74.96 %;
1
m.p. 205-207.4
℃
; H NMR (400 MHz, DMSO-d6, TMS):
δ
11.60 (s, 1H，NH), 11.18
(
s, 1H, NH), 8.31 (s, 1H, CH), 8.29 (d, J = 7.7 Hz, 1H, CH), 7.92 (q, J = 4.4 Hz, 1H, NH),
7.81 (d, J = 2.8 Hz, 1H, ArH), 7.43 (d, J = 7.9 Hz, 1H, ArH), 7.18 (dtd, J = 14.8, 7.1, 1.2
Hz, 2H, ArH), 3.09 (d, J = 4.6 Hz, 3H, CH ). HRMS: Calcd ([C H N S]+), m/z =
3
11 12
4
2
12 4
33.0777; found, m/z = 233.0855. Elemental analysis: (C11H N S) Calcd. (%) C, 56.87; H,
5.21; N, 24.12; S, 13.80. Found (%) C, 56.86; H, 5.051; N, 23.68; S, 13.66.
2-(1H-indol-3-ylmethylene)-N-phenylhydrazinecarbothioamide (3): Yield 81.37 %;
1
m.p. 197.3-198.6
℃
; H NMR (400 MHz, DMSO-d6, TMS):
δ
11.69 (s, 1H, NH), 11.61
(
s, 1H, NH), 9.62 (s, 1H, NH), 8.42 (s, 1H, CH), 8.24 (d, J = 7.7 Hz, 1H, CH), 7.92 (d, J =
19

ACCEPTED MANUSCRIPT
2
.8 Hz, 1H, ArH), 7.66 (dd, J = 8.5, 1.0 Hz, 2H, ArH), 7.45 (d, J = 7.8 Hz, 1H, ArH), 7.42
7.34 (m, 2H, Ph-H), 7.24 – 7.11 (m, 3H, Ph-H). HRMS: Calcd ([C H N S]+), m/z =
–
16
14
4
2
95.0939; found, m/z = 295.1012. Elemental analysis: (C H N S) Calcd. (%) C, 65.28; H,
16 14 4
4.79; N, 19.03; S, 10.89. Found (%) C, 64.78; H, 4.79; N, 18.65; S, 10.95.
2-[(1-Methyl-1H-indol-3-yl) methylene] hydrazinecarbothioamide (4): Yield 73.18 %;
1
m.p. 196.0.7-197.9
℃
; H NMR (400 MHz, DMSO-
d
6
, TMS):
), 7.80 (s, 1H, ArH), 7.48 (d,
J = 8.2 Hz, 1H, ArH), 7.43 (s, 1H, NH ), 7.27 (ddd, J = 8.2, 7.1, 1.2 Hz, 1H, ArH), 7.17
δ11.16 (s, 1H, NH), 8.28
(
s, 1H, CH), 8.25 (d, J = 7.8 Hz, 1H, ArH), 8.04 (s, 1H, NH
2
2
(
ddd, J = 8.0, 7.1, 1.0 Hz, 1H, ArH), 3.81 (s, 3H,CH ). HRMS: Calcd ([C H N S]+), m/z
3 11 12 4
=
233.0783; found, m/z = 233.0855. Elemental analysis: (C H N S) Calcd. (%) C, 56.87;
11 12 4
H, 5.21; N, 24.12; S, 13.80. Found (%) C, 56.90; H, 5.056; N, 23.67; S, 13.67.
2-[(1-Methyl-1H-indol-3-yl) methylene]-N-methylhydrazinecarbothioamide (5): Yield
1
7
6.29 %; m.p. 217.1-218.6
℃
; H NMR (400 MHz, DMSO-d6, TMS):
δ
11.16 (s, 1H,
NH), 8.30 (d, J = 7.8 Hz, 1H, ArH), 8.28 (s, 1H, NH), 7.92 (d, J = 4.6 Hz, 1H, NH), 7.78
s, 1H, ArH), 7.47 (d, J = 8.1 Hz, 1H, ArH), 7.29 – 7.25 (m, 1H, ArH), 7.22 – 7.17 (m,
H, ArH), 3.80 (s, 3H, CH ), 3.08 (d, J = 4.6 Hz, 3H, CH ). HRMS: Calcd ([ ]+),
m/z = 247.0939; found, m/z = 247.1012. Elemental analysis: (C H N S) Calcd. (%) C,
(
1
3
3
12 14 4
C H N S
12
14
4
5
8.51; H, 5.73; N, 22.74; S, 13.02. Found (%) C, 58.47; H, 5.259; N, 22.31; S, 12.84.
2-[(1-Methyl-1H-indol-3-yl) methylene]-N-phenylhydrazinecarbothio- amide(6): Yield
1
8
0.16 % ; m.p. 196.2-197.3
℃
; H NMR (400 MHz, DMSO-d6, TMS):
δ
11.58 (s, 1H,
NH), 9.62 (s, 1H, NH), 8.39 (s, 1H, CH), 8.26 (d, J = 7.9 Hz, 1H), 7.90 (s, 1H), 7.65 (d, J
7.9 Hz, 2H), 7.51 (d, J = 8.1 Hz, 1H), 7.38 (t, J = 7.8 Hz, 2H), 7.27 (dd, J = 11.2, 4.1
Hz, 1H), 7.24 – 7.15 (m, 2H), 3.83 (s, 3H, CH ). HRMS: Calcd ([ ]+), m/z =
09.1096; found, m/z = 309.1168. Elemental analysis: (C17 S) Calcd. (%) C, 66.21; H,
.23; N, 18.17; S, 10.40. Found (%) C, 65.91; H, 5.542; N, 17.88; S, 10.12.
=
3
17 16 4
C H N S
3
5
16 4
H N
20

ACCEPTED MANUSCRIPT
4
. Synthesis of nanofibers
PVP-4 nanofiber: 1 g of PVP (10 wt. %) and 100 mg (1 wt. %) of the compound 4 were
dissolved in dimethyl sulfoxideat at room temperature for the electrospinning. The solution was
supplied through a 5 mL plastic syringe attached to a capillary tip with an inner diameter of 0.2
mm and then electrospun onto aluminum foil using a point to plate assembly. The electrical
potential (10 kV), solution flow rate (0.6 mL/h) and capillary tip to collector plate distance (20
cm) were adjusted for the stable electrospinning. Samples were dried to remove the residual
solvent in a vacuum oven at room temperature for one day.
5
. Solid−state photochromic properties.
1
.0
1
1
0
0
0
0
.2 Compound 4
1.5
1.0
Compound 6
Compound 5
1650min
1
1
8
6
5
4
3
2
1
0
43min
20min
0min
0min
0min
0min
0min
0min
0min
min
1
9
3
1
9
6
320min
00min
30min
50min
0min
.0
.8
.6
.4
.2
0.8
0.6
3
510min
1650min
00min
150min
min
9
0min
0
.4
0.2
400
0
0
.5
.0
9min
min
4
0min
0
400
450
500
400
500
600
500
600
700
Wavelength(nm)
Wavelength (nm)
Wavelength(nm)
21

ACCEPTED MANUSCRIPT
Figure S1. UV–vis spectra of the compounds 4-6 upon the irradiation of 365 nm at different times in
solid−state at room temperature.
Figure S1 shows UV-vis spectra of these compounds 4, 5 and 6. Just like these compounds 1-
3
, under the irradiation of 365 nm light, a new band appeared between 380 nm and 480 nm for
the compound 4 and between 400 nm and 650 nm for these compounds 5 and 6. The intensity is
increased with prolonging the irradiation time. Consequently, after the irradiation for 143 min,
2
7.5 h and 58 h, these photostationary states of 4, 5 and 6 are reached, respectively.
1
1
0
0
.5
.0
.5
1.5
1.0
0.5
0.0
a
b
1
1
.....
4 day
3 day
14 day
3 day
1
.....
.
.
1
0
day
1
0
day
.0
3
00 400 500 600 700
Wavelength(nm)
300 400 500 600 700
Wavelength(nm)
Figure S2. UV–vis spectra of the colored compounds 3 (a) and 4 (b) in the darkness at different times at room
temperature.
visible
visible
a
b
0.8
0.6
0.4
0.2
0.8
0.6
0.4
0.2
UV
UV
0
1
2
3
4
5
0
1
2
3
4
5
Number of cycles
Number of cycles
Figure S3. Coloration-decoloration cycles of the compounds 3 (a) and 4 (b).
22

ACCEPTED MANUSCRIPT
6
. Crystal data
Table S1. Crystal data for 1 and 2.
Compound
1
2
Empirical formula
Formula weight
Wavelength
C H N S
218.28
0.71073 Å
C H N S
232.31
0.71073 Å
10
10
4
11 12 4
Crystal system,
space group
Triclinic
P-1
Monoclinic
P2(1)/c
a = 7.1935 (4) Å
b =11.1738 (6) Å
c = 13.5713 (8) Å
α =68.8070 (10) º
β = 85.1670 (10) º
γ = 82.4710 (10) º
a = 13.3949 (9) Å
b = 5.1353 (4) Å
c = 16.0927 (11) Å
α = 90 º
β = 101.4360 (10) º
γ = 90 º
Unit cell dimensions
3
3
Volume
1007.50 (10) Å
1084.99(13) Å
Z
4
4
3
3
Calculated density
Absorption coefficient
F(000)
1.439 g / cm
0.290 mm
456
1.422 g / cm
0.274 mm
488
-1
-1
Index ranges
9
≤
h
≤
9, -14
16
≤
k
≤
11,
-17
20
8808
≤
h
≤
16, -6
≤
k
≤
6, -20
≤
l
-
17 <= l
≤
≤
Reflections collected
Independent reflections
Goodness-of-fit on F^2
8618
4390 [R(int) = 0.0103]
1.038
2447 [R(int) = 0.0142]
1.052
Data / restraints / parameters 4390 / 0 / 271
2447 / 4 / 146
Final R indices [I>2sigma(I)]
R indices (all data)
R = 0.0320, wR = 0.0801
R = 0.0302, wR = 0.0789
1
2
1
2
R
1
= 0.0368, wR
2
= 0.0841
R
1
= 0.0335, wR
2
= 0.0816
23

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Figure S4. Single crystal structures of the compounds 1 (a) and 2 (b), the ellipsoid represents 50%
displacement of atoms.
Table 2. Hydrogen bonds for 1 and 2 (Å and º).
1
D−H...A
N(1)−H(1)..S(1)
d(D−H)
0.86
d(H...A)
2.63
d(D...A)
3.3941
3.3374
2.6402
3.2891
3.3938
2.693
<(DHA)
148
N(1A)−H(1AA)..S(1A) 0.86
N(4A)−H(4AA)..N(2A) 0.86
N(3)−H(3)..N(4A)
N(3A)−H(3A)..S(1A)
N(4)−H(4A)..N(2)
2.54
155
2.29
105
0.86
0.86
0.86
2.44
168
2.55
166
2.35
104
2
D−H...A
d(D−H)
0.86
d(H...A)
d(D...A)
<(DHA)
N(1)−H(1)..S(1)
N(3)−H(3)..S(1)
N(4)−H(4)..N(2)
2.57
2.71
2.22
3.4254
3.3762
2.6079
173
135
107
0.86
0.86
Table 3. Selected bond lengths (Å) of 1 and 2.
1
S(1)-C(10)
N(1)-C(8)
N(2)-C(9)
N(4)-C(10)
C(2)-C(3)
C(3)-C(4)
1.7021(14)
1.3785(19)
1.2870(19)
1.3294(19)
1.4417(19)
1.398(2)
N(1)-C(1)
N(2)-N(3)
N(3)-C(10)
C(1)-C(2)
C(2)-C(9)
1.3647(19)
1.3848(16)
1.3349(19)
1.376(2)
1.4375(19)
1.4134(19)
1.404(2)
C(3)-C(8)
C(5)-C(6)
C(4)-C(5)
1.388(2)
C(6)-C(7)
1.381(2)
C(7)-C(8)
1.393(2)
S(1A)-C(10A)
N(1A)-C(8A)
N(2A)-C(9A)
N(4A)-C(10A)
C(2A)-C(3A)
C(3A)-C(4A)
C(4A)-C(5A)
C(6A)-C(7A)
1.6942(14)
1.3793(19)
1.2875(18)
1.3372(19)
1.4423(19)
1.399(2)
N(1A)-C(1A)
N(2A)-N(3A)
N(3A)-C(10A)
C(1A)-C(2A)
C(2A)-C(9A)
C(3A)-C(8A)
C(5A)-C(6A)
C(7A)-C(8A)
1.3522(18)
1.3889(16)
1.3370(18)
1.3800(19)
1.4342(19)
1.4136(19)
1.405(2)
1.385(2)
1.382(2)
1.392(2)
2
S(1)-C(10)
N(1)-C(8)
N(2)-C(9)
N(4)-C(10)
C(1)-C(2)
C(2)-C(9)
C(3)-C(8)
C(5)-C(6)
C(7)-C(8)
1.6996(13)
1.3784(19)
1.2865(17)
1.3309(17)
1.3817(18)
1.4401(18)
1.4173(18)
1.403(2)
N(1)-C(1)
N(2)-N(3)
N(3)-C(10)
N(4)-C(11)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(6)-C(7)
1.3584(18)
1.3837(14)
1.3473(17)
1.4510(18)
1.4467(18)
1.4004(19)
1.3844(19)
1.381(2)
1.394(2)
24

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7
. Photochromic properties of amorphous powder
α
β
γ
a
3
500
3000
2500
2000
1500
1000
-
1
Wavelength (cm )
-
1
3
1073 cm
-
α
3
096 cm
α
β
-
1
3
261 cm
β
-
1
3
049 cm
γ
-
1
-1
3248 cm
3049cm
-
1
1
598 cm
-
1
γ
3073 cm
-
1
b
c
1400
3046 cm
3
600 3400 3200 3000 2800
1700
1600
Wavelength (cm )
1500-1
-
1
Wavelength (cm )
−
1
Figure S5. IR spectra of the compound 4 (a); the magnified IR spectra between 3600 and 2800 cm (b),
−1
between 1700 and 1400 cm (c). (α:before the irradiation of 365nm light; β: after the irradiation of 365nm
light; γ: after the irradiation of visible light for the colored form.)
.
25

ACCEPTED MANUSCRIPT
thioalcohol-form
thioketone-form
1.0
0.8
0.6
0.4
0.2
0.0
2
00 300 400 500 600 700
Wavelength (nm)
Figure S6. Simulated UV-vis absorption spectra of the thioketone-form and thioalcohol-form for the
compound 4 by the b3lyp/6-311++g (d, p).
Quantum chemical calculations are performed on the molecular geometry of the
thioketone-form and the thioalcohol-form for the compound 4. The electronic absorption
spectra of each molecule is systematically simulated by time-dependent DFT (TD-DFT)
method from the optimized structure at the same level. The molecular geometry is
designed based on the crystal structure of the compound 1, which is directly taken from
the X-ray diffraction experimental results without any constraints. The ground-state
geometry of each molecule is fully optimized by using the density functional theory
(
DFT) calculations with a hybrid functional B3LYP (Becke's three parameter hybrid
1, 2
functional using the LYP correlation functional) at 6-311++G(d,p) basis set level, and
these calculations are carried out with the Gaussian 09 packages.
26

ACCEPTED MANUSCRIPT
8
. Photochromic properties of nanofibers
ι
3
2
1
0
0
4
powder
PVP-4 nanofibers
50 100 150
Time (min)
0
Figure S7: First-order kinetic plots for the photoisomerization reaction of amorphous powder (blue dash line)
and nanofibers(red solid line) for the compound 4 induced by 365nm light at room temperature.
The corresponding first-order rate constant of the compound
determined by fitting the experimental data to the following equation: kt = ln[(A∞-
)/(A -A )]. Where k is the first-order rate constant, and A , A , and A are the observed
absorbance at the beginning, end, and time t, respectively. The absorbance is collected at
4 and its fiber is
A
0
∞
t
0
∞
t
the wavelength of 420 nm for the amorphous powder and 410 nm for the PVP−4
nanofibers, where the maximum of the optical density.
a
b
1
66
164
162
160
166
164
162
160
Electron binding energy (eV)
Electron binding energy (eV)
27

ACCEPTED MANUSCRIPT
Figure S8. XPS spectra of S(2p) in the PVP−4 nanofibers before (a) and after (b) the 365nm light irradiation. (
stands for A species,
stands for B species.)
a
α
β
3500
3000
2500
Wavelength (cm )
2000
1500
1000
-
1
-1
-1
2
950 cm
b
1665 cm
1669 cm
c
-
1
-1
2
977 cm
α
-1
2918 cm
α
-
1
2950 cm
-1
2
875 cm
β
β
3
200
3000
2800
2600
1600 1400 1200 1000 800
-
1
-
1
Wavelength (cm )
Wavelength (cm )
−
1
Figure S9. IR spectra of the PVP−4 nanofibers(a); the magnified IR spectra between 3000 and 2600 cm (b),
−
1
between 1730 and 800 cm (c). (α:before the irradiation of 365nm light; β: after the irradiation of 365nm light)
28