Electric and steric hindrance effects of substituents on luminescence and force-stimuli response of cyanovinyl phenothiazine derivatives

Article abstract of DOI:10.1016/j.dyepig.2021.109296

Six cyanovinyl phenothiazine derivatives bearing substituents with different sizes, and electron-donating and -withdrawing abilities were designed and synthesized. The effect of substituents on photophysical properties in solution and solid states were sy

Full text of DOI:10.1016/j.dyepig.2021.109296

Dyes and Pigments 190 (2021) 109296
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: http://www.elsevier.com/locate/dyepig
Electric and steric hindrance effects of substituents on luminescence and
force-stimuli response of cyanovinyl phenothiazine derivatives
*
Tong Zhang, Yanning Han, Qiao Chen, Xinyu Chen, Pengchong Xue
Tianjin Key Laboratory of Structure and Performance for Functional Molecules, College of Chemistry, Tianjin Normal University, No. 393 Bin Shui West Road, Tianjin,
PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Six cyanovinyl phenothiazine derivatives bearing substituents with different sizes, and electron-donating and
Eletronic effect
Steric hindrance effect
Mechanochromism
Fluorescence
-
withdrawing abilities were designed and synthesized. The effect of substituents on photophysical properties in
solution and solid states were systematically investigated. The results suggested that electron-donating groups
almost did not influence absorption and emission properties in solutions because the distributions of molecular
3
HOMOs and LUMOs were independent of electron-donating groups. In contrast, trifluoromethyl (CF ) and cyano
Substituent
as electron-withdrawing units induced bathochromic shifts in both absorption and fluorescence spectra owing to
the decrease in LUMO energy levels. Furthermore, it was found that the photophysical properties in crystal states
strongly depended on the terminal substituent. Larger tert-butyl (t-butyl), methoxy and CF
smaller spectral shifts in relative to smaller groups after crystallization. Single crystal structures suggested both
CF and CN units lead a poor -stacking, but charge transfer existed in PCVCN crystals. J-type dimers were found
in PCVH and PCVN crystals. More interestingly, t-butyl, CF and methoxy moieties induced obvious color con-
3
groups resulted in
3
π
3
version and larger spectral shifts of 76 nm, 66 nm and 55 nm, respectively, under force stimuli. On the other
hand, the compounds with terminal hydrogen atom, naphthyl and cyano group possessed shifts of 46 nm, 34 nm
and 23 nm.
1
. Introduction
construct excellent MFC materials [23–25]. Phenothiazine can be
modified in its 3, 7, and 10 positions. Thus various mono-, di-, and
Organic small molecule materials that respond to external stimuli are
widely used in physical and chemical sensors [1], light-emitting diodes
2], and security [3]. Some these materials exhibit luminescent color
trisubstituted phenothiazine derivatives might be developed for MFC
molecules [26–29]. The results of previous studies suggest that pheno-
thiazine derivatives with MFC activity are always donor-acceptor
structures. A slight difference in molecular structure resulted in
diverse MFC behaviors.
[
change under mechanical force, which is a phenomenon called mecha-
nofluorochromism (MFC) [4]. Their luminescent colors and intensities
under mechanical forces, such as shear, grinding, crushing, friction, and
hydrostatic pressure, show a sharp conversion because of the variations
of intrinsic molecular structures or the intermolecular stacking type [5].
The introduction of many functional moieties as building blocks has
proven to be an efficient way to obtain MFC molecules, including
tetrephenylethene [6–8], 9,10-divinylanthracene [9–12], triphenyl-
amine [13,14], β-diketone boron [15–17], borondiiminates,
cyano-ethylene [18–20], and others. Pristine intermolecular in-
teractions can be easily destroyed by force, and then the photophysical
properties of solids change [21,22].
Previous studies suggested that mono-substituted D- -A phenothia-
π
zine derivatives in the 3-position possess excellent response to force
stimuli. However, systematical investigation on how the substituents
close to electron-withdrawing (EW) units regulate intrinsic electron
transition, intermolecular interaction, and force-induced spectral shifts
is still missing [30–35]. Therefore, we designed six compounds with
D-
electron-donating (ED) group plays a donor role, 1,4-divinylphenyl unit
is the -bridge, and EW cyano is an acceptor, thereby ensuring that these
π-A structure. As shown in Scheme 1, phenothiazine as
π
compounds contribute to MFC activity [36–40]. Furthermore, to inves-
tigate how substituents close to cyano as acceptor group affect molecular
internal photophysical properties, modified phenyl and naphthyl groups
Phenothiazine is a strong electron-rich compound with, a butterfly-
like conformation. It has been used as an efficient building block to
*
Corresponding author.
E-mail addresses: xuepengchong@126.com, hxxyxpc@tjnu.edu.cn (P. Xue).
https://doi.org/10.1016/j.dyepig.2021.109296
Received 21 September 2020; Received in revised form 26 February 2021; Accepted 5 March 2021
Available online 23 March 2021
0
143-7208/© 2021 Elsevier Ltd. All rights reserved.

T. Zhang et al.
Dyes and Pigments 190 (2021) 109296
were introduced. Methoxy and t-butyl acted as ED units, CF
3
and cyano
and S2. Obtained energy levels are consistent with those from electro-
chemical measurements. Theory calculation also confirmed that only
additional EW groups could obviously affect the energy levels and then
result in red-shifted absorption bands. The results also suggest that
electron transitions ascribed to longest absorption wavelength were
mainly rooted in the transitions from corresponding HOMOs to LUMOs.
The distributions of all HOMOs were identical and they mainly distrib-
uted on phenothiazine, adjacent double bond, and phenyl ring (Fig. 2
and S2). This result explained why all compounds had similar and high
HOMO energy levels [43–46]. Furthermore, the densities of LUMO at
phenothiazine moieties for all compounds sharply decreased. Moreover,
LUMOs of molecules without additional EW substituents almost located
at two double bonds, the central phenyl rings, and the central cyano
units. The densities at terminal methoxy, t-butyl, and another phenyl
ring of naphthalene were very low. Therefore, their similarity in terms of
are the EW group. The results indicate that electronic effect of sub-
stituents may influence molecular electronic transition, but only
electron-withdrawing units strongly impact the absorption and fluo-
rescence spectra in solutions. On the other hand, the substituents play an
important role on regulating molecular MFC properties in the solids
states. Methoxy, t-butyl, trifluoromethyl as large groups support more
obvious color contrast under force stimuli.
2
. Results and discussion
2
.1. Synthesis
Scheme 2 shows their synthesis routes. First, phenothiazine reacted
with ethyl bromide in the presence of NaH to get 1, which is further
converted to 2 by a Vilsmier reaction. A Wittig reaction produced 3.
Compound 4 was obtained through a Heck coupling reaction of 3 and 4-
bromobenzaldehyde. The target compounds were easily obtained by a
condensation reaction with the help of basic catalysts.
3
LUMO energy levels to PCVH was easily understood. In contrast, CF and
cyano remarkably increased the densities of LUMOs in the terminal
phenyl ring, and LUMOs partially distributed at terminal EW units too,
thereby successfully reducing the LUMO energy levels and the corre-
sponding energy gaps [47–49].
As shown above, light excitation led to the transitions from HOMOs
and LUMOs for all compounds, and then, intramolecular charge transfer
2
.2. Photophysical properties in solution
would occur after light excitation, illustrating their intrinsic D- -A
π
These compounds have poor solubilities in cyclohexane, but are
characteristic. Solvent-dependent absorption and fluorescence spectra
were measured to further prove it. They had moderate fluorescence
soluble in common solvents, such DCM, THF, toluene, DMF and DMSO.
Fig. 1a and Table 1 show the absorption spectra and peak data. Four
compounds without additional EW groups had nearly the same ab-
sorption peaks (ca. 410 nm). EW groups induced red-shifted absorption
F
quantum yields in cyclohexane (Φ , Table 1). The maximal emission
peak of PCVTF was at 544 nm, and a red-shifted emission band with a
peak of 559 nm was observed for PCVCN. Other compounds had similar
emission bands, and the emission peaks were nearly identical and at
about 515 nm. Fluorescence lifetimes were measured too. As shown in
Fig. S3, the compounds without additional EW groups have similar
fluorescence lifetimes, and the fluorescence PCVTF and PCVCN decay
slowly and have longer lifetimes, which further imply EW groups have
significant influence on molecular photophysical properties. When these
compounds were dissolved in xylene and dichloromethane (DCM), their
absorption spectra possessed small red shifts relative to those in cyclo-
hexane (Fig. S4, Table S2). However, their fluorescence spectra showed
obvious red shifts in polar solvents (Fig. S5) and fluorescence quantum
yields obviously decrease (Table S3). The linear relationship between
emission energies and solvent polarities emerged (Fig. S5). In addition,
visible emission bands in highly polar DMSO and DMF were not
observed. These results indicated the existence of larger polar excited
bands. For instance, the maximum absorption peak of PCVTF with CF
3
was at 426 nm, and cyano as the stronger EW group resulted in the
longest absorption wavelength of 436 nm.
To further elucidate the difference in absorption spectra, electro-
chemical measurements were performed in dichloromethane [41,42].
As shown in Fig. S1, all compounds had similar couple reversible redox
peaks within the range of 0.5–1.7 V. Their HOMO energy levels were
determined through comparison with an external redox reference. The
results listed in Table 1 indicate their high and similar HOMO energy
levels. Four compounds without additional EW groups possessed similar
LUMO energy levels of about 2.15 eV. Moreover, the EW groups
decreased the LUMO energy levels of PCVTF and PCVCN. PCVCN had a
lowest LUMO energy level. These results clearly showed that only the
EW groups regulated molecular LUMO energy levels, and that the dif-
ference in their absorption spectra was due to the decrease in LUMO
energy levels. Methoxy and t-butyl as donor have weak effect on LUMO
energy levels.
molecules after excitation, and further confirmed the D-
50].
By observing optimized conformations (Fig. 2a), phenothiazine units
in all compounds were found to be V-shaped. The steric hindrance
π-A structure
[
Quantum chemical calculations were further used as reliable means
to investigate the substituent’s effect. The results were listed in Tables S1
Scheme 1. Molecular structures of six compounds.
2

T. Zhang et al.
Dyes and Pigments 190 (2021) 109296
Scheme 2. Synthesis route of six compounds.
ꢀ 5
Fig. 1. (a) Absorption and (b) emission spectra of six compounds in cyclohexane (10 M).
between the
α
-H of naphthalene and the H atom of the double bond
PCVMO, PCVTB, and PCVTF had small shifts in their absorption bands.
For instance, blue-shifts of 4 and 6 nm were observed for PCVMO and
PCVTB, respectively, and PCVTF possessed a red-shift of 8 nm. In
contrast, red-shifts of PCVCN, PCVH, and PCVN absorption spectra were
larger and more than 13 nm. In particular, the first absorption peak of
PCVCN was located at 461 nm, indicating the largest red-shift of 25 nm
◦
induced a large twist angle of 50.6 in PCVN. Moreover, the volumes of
substituents differed, and then, they will affect the intermolecular
packing in solid state. So, we anticipated that all compounds would
respond to the force stimuli and that substituents may regulate their
luminescent and responsive behaviors in solid states.
(
Fig. 3c) [51–53]. Red-shifted absorption band made the as-synthesized
PCVCN crystals deep red.
2
.3. Response to mechanical force
To obtain insights into the differences in absorption spectral shift,
their single crystals were tested for growth. Unfortunately, only four
good single crystals were obtained. The data of single crystals are listed
in Table S5. PCVMO and PCVTB formed very thin lamellar crystals in
different solvents or mixed solvents, and then their intermolecular
Fig. 3a shows the photos of pristine crystals under natural and UV
lights. PCVTB is yellow, PCVMO, PCVH, PCVN, and PCVTF are orange
and PCVCN is deep red. Moreover, the changes of their first absorption
peaks also differed in solid state. As shown in Fig. S4 and Table S4,
3

T. Zhang et al.
Dyes and Pigments 190 (2021) 109296
Table 1
molecules emerges in their crystals because of their small spectral shift
after crystallization [54]. Thus, terminal substituents may act as effec-
Photophysical data of six compounds.
tive building block to regulate the intermolecular
phase.
π
-stacking in crystal
Compound
λ
abs
λ
em
Lifetime
(ns)
HOMO
LUMO
E
g
b
c
d
e
(
nm,
ε
,
(nm)
(Φ
(eV)
(eV)
(eV)
4
a
1
0 )
F
)
As shown above, the substituent strongly impacted the intermolec-
ular -stacking, and then, substituent-controlled emission spectra were
PCVMO
PCVTB
PCVH
410
1.23)
409
1.12)
411
1.45)
410
1.35)
426
1.02)
436
0.89)
518
2.57
2.46
2.51
2.53
2.94
3.14
ꢀ 4.78
ꢀ 4.77
ꢀ 4.77
ꢀ 4.81
ꢀ 4.82
ꢀ 4.82
ꢀ 2.23
ꢀ 2.22
ꢀ 2.22
ꢀ 2.27
ꢀ 2.37
ꢀ 2.44
2.55
2.55
2.55
2.54
2.45
2.38
π
(
(0.43)
514
expected. As shown in Fig. 3a, PCVTB emitted strong green fluorescence.
Its emission band was wide, the maximum was at 539 nm (Fig. 3b,
(
(0.51)
516
Table S4), and it had the largest Φ
rescence and an emission wavelength of 563 nm. The emission
maximum of PCVTF with a large CF group was located at 577 nm.
PCVH and PCVN had similar emission maxima. PCVCN in crystal has a
longest emission wavelength of 657 nm and a smallest Φ . Fig. 3c show
F
of 0.72. PCVMO had yellow fluo-
(
(0.46)
515
PCVN
3
(
(0.51)
544
PCVTF
PCVCN
F
(
(0.41)
559
the spectral shifts from cyclohexane to crystals. The result clearly in-
dicates that the fluorescent shifts in solid state have the same trend as
that of the absorption spectra [55]. For instance, a smallest shift of 25
nm was observed while PCVTB formed crystals. PCVH and PCVN
red-shifted their fluorescence maxima by more than 66 nm. The largest
shift of 98 nm appeared, while the substituent was smallest and linear
(
(0.32)
a
Maximal absorption peak in cyclohexane.
Maximal emission peak in cyclohexane.
b
c
Electrochemical method was used to obtain the HOMO energy levels by
comparing with an external reference in DCM.
d
The LUMO energy level was estimated by the equation: ELUMO = EHOMO
+
cyano group although -stacking is weak in its crystals. Longest emission
π
Eg.
e
wavelength of PCVCN crystals may be from the intermolecular charge
transfer emission [56]. The absorption and fluorescent changes in solids
state suggested that the photophysical properties of this series of com-
pounds were strongly regulated by the substituents because of different
g
E is energy gap and was determined from the edge of the absorption band in
DCM.
stacking in crystal phase are still unknown. Fig. 4 show the intermo-
lecular stacking of PCVH, PCVN, PCVTF, and PCVCN. Crystal PCVTF
π
-stacking in crystal. Because the MFC behavior of a compound signifi-
cantly depends on the intermolecular interaction in solid state, the
substituent-regulated response to force stimuli was anticipated.
First, PCVMO as an example was discussed. The as-synthesized or-
ange solid of PCVMO emitted yellow fluorescence, but the ground solid
was orange and had red fluorescence. The maximal emission peak of
ground solid was at 618 nm (Fig. 5a, Table 2), indicating a bathochromic
shift of 55 nm. Grinding also promoted a red-shift of 30 nm in the ab-
sorption spectra (Fig. S4a). Such a large change in absorption spectra
belongs to an orthorhombic system with Pca2
a triclinic system with P-1 space group, whereas the crystal systems of
PCVH and PCVN are monoclinic and have the same P2 /c space group.
1
space group, PCVCN has
1
In crystal, two PCVH molecules stacked together in antiparallel way and
form a J-type dimer with a short interplanar distance of 3.37 Å. Such
stacking is consistent with a redshift of 15 nm of absorption spectra. In
PCVN crystal, an antiparallel J-type dimer was observed too. The
interplanar distance is 3.69 Å. So, a large red-shift in absorption spectra
relative to its cyclohexane solution is rational. In PCVTF crystal, one-
dimensional twisted J-aggregate was found. Although the interplanar
distance is short (3.45 Å), the overlap between two molecules is very
small (Fig. 4c, right). Therefore, only a small red-shift of 8 nm was
observed for PCVTF. PCVCN molecules form a twisted 1D J-aggregate
too, in which the interplanar distance is 3.33 Å, but the overlap between
two molecules is also small. In addition, it was found that there was
overlapping region between phenothiazine and acceptor (Fig. 4d). So, a
charge transfer may exist and should be responsible for large red shift in
absorption spectra. Although the specific stacking in PCVMO and PCVTB
is unknown, it is possible that small overlap or loose stacking between
suggested the obvious conversion in intermolecular
π
-stacking and that
grinding induced the enhanced interaction between chromophores.
π-π
In addition, the absorption and emission spectra could be restored, while
the ground solids were fumed by saturated vapors of THF, xylene, ethyl
◦
acetate, and DCM, or thermal annealing at 100 C for 10 min. The
restored solids could turn into powder with red fluorescence too. Such
conversion might be repeated many times, implying the reversibility of
1
the MFC process (Fig. S7). After several cycles, the H NMR spectrum of
the solid was the same as that of pristine solid, indicating that force
stimuli did not destroy molecular chemical structure. Thus, the excellent
response of PCVMO to force stimuli can be ascribed to the force-induced
conversion of intermolecular packing [57].
Fig. 2. (a) Optimized configuration, and (b) HOMO and LUMO energy levels obtained from electrochemical results, and corresponding visual HOMO (bottom) and
LUMO (top).
4

T. Zhang et al.
Dyes and Pigments 190 (2021) 109296
Fig. 3. (a) Photos of as-synthesized crystals under (top) natural and (bottom) 365 nm light, (b) corresponding fluorescence spectra and (c) the shifts of spectral
maxima comparing with those in cyclohexane solutions.
Mechanical force always destroys the ordered stacking of crystals.
Powder XRD patterns were used to investigate the force-induced phase
transition. As shown in Fig. 6a, the as-synthesized PCVMO solids had
strong diffraction peaks, indicating an ordered stacking or crystal phase.
After grinding, these diffraction peaks almost disappeared. This finding
suggests that mechanical grinding damaged the pristine molecular
stacking and resulted in an amorphous state. Moreover, the diffraction
peaks emerged again while the ground solids were fumed by solvent
vapors. The locations of peaks were the same as those of pristine solids,
which was the evidence of the recovery of pristine ordered stacking.
Therefore, a reversible phase transformation between crystalline and
amorphous state happened during grinding and fuming [58]. In other
emission wavelength emerged in the pristine PCVN crystals owing to
strong interaction, which resulted in a small bathochromic shift of
π-π
34 nm after grinding. The emission maximum of ground PCVH was
located at 625 nm, which led to a moderate shift of 46 nm. The fluo-
rescence maximum of PCVTF shifted from 576 nm to 644 nm under force
stimuli, meaning a large bathochromic shift of 68 nm. The emission
color changed from orange to deep red, accompanied by a red-shift of
27 nm in the absorption spectra. The maximal fluorescence peak of
PCVCN was at 680 nm after grinding, implying a red-shift of 23 nm. A
smallest shift of 9 nm in the absorption spectra was observed. As a result,
the larger the shift in absorption spectra was, the more obvious the
fluorescence change was. By comparing spectral shifts after crystalli-
zation and grinding, the substituent-dependent MFC in this series of
compounds was found to be related to substituent-regulated intermo-
works, mechanical force enhances intermolecular
π
- interaction, which
π
reduced the energy gap of transition from excited molecule to a ground
one; then, red-shifted fluorescence appeared.
lecular stacking. In pristine crystals, OCH
lead to weak interaction and loose stacking, and then, short fluo-
rescence wavelengths appear. While their crystals are damaged and
changed into amorphous state by force, interactions are more
3 3
, CF , t-butyl with large sizes
The responses of other compounds to force were investigated and
compared. As expected, they all exhibited MFC behaviors. Their powder
XRD patterns implied that five compounds showed the phase transitions
between crystal and amorphous states during the grinding-fuming cycle
π-π
π-π
strongly altered. As a result, large bathochromic shifts were observed. In
the case of PCVCN, because of the existence strong intermolecular
(
Fig. 6). Their spectral changes and data are shown in Fig. 5 and S6 and
Table 2. Red shifts in their absorption and fluorescence could be found
after grinding, and the spectra were recovered by fuming. Spectral
changes could be repeated many times, indicating reversible MFC pro-
cess. However, spectral shift magnitudes differed and strongly relied on
their terminal substituents. The ground solids of PCVMO, PCVTB, and
PCVN had similar absorption and emission maxima, suggesting similar
transition energy gaps. Their photoluminescent behaviors strongly
depended on substituents in pristine crystal phases, so the spectral shifts
after grinding also exhibited substituent-dependence. For example,
PCVTB with the largest t-butyl group possessed the largest spectral shifts
in the absorption (36 nm) and emission (76 nm) spectra. A longer
charge transfer, mechanical force only slightly changed the
action, leading to a small spectral shift.
π
- inter-
π
3. Conclusion
Substituents of different sizes and various electronic effects were
introduced into a D- -A phenothiazine derivative to investigate the in-
π
fluences of substituent effects on molecular intrinsic photophysical
properties in solution and solid state, as well as the response to force
stimuli. The results suggested that ED groups have weak influence on
electron transitions in solutions, but large ED groups led to short
5

T. Zhang et al.
Dyes and Pigments 190 (2021) 109296
Fig. 4. Intermolecular stacking of (a) PCVH, (b) PCVN, (c) PCVTF and (d) PCVCN. Left and right figures are in front and top views, respectively.
emission wavelength in pristine crystals. EW groups induced red-shifted
fluorescence in solutions. Single crystals suggest that CF and CN units
could prevent molecules from forming large overlapping in the crystal
using an integrating sphere, respectively. The absorption spectra were
obtained by a reflection model. C, H, and N elemental analyses were
performed on a PerkinElmer 240C elemental analyzer. XRD patterns
were obtained on a Bruker D8 Advance X-ray diffraction instrument
3
π
state, and PCVH and PCVN form J-type dimers. All compounds exhibited
MFC and the substituents could regulate their MFC properties. Obvious
spectral shift and sharp color conversion could be observed in com-
equipped with graphite-mono-chromatized CuK
α
radiation (λ = 1.5418
◦
ꢀ 1
◦
Å), by employing a scanning rate of 0.0261 s in the 2θ range from 5
◦
pounds with OCH
3
, CF
3
, and t-butyl moieties. A largest fluorescent
to 30 . Cyclic voltammetry was employed on an electrochemistry work
ꢀ 1
spectral shift of 76 nm appeared while the crystals of PCVTB with t-butyl
group were ground. This work helped elucidate how to utilize sub-
stituents to regulate molecular response to force and contributed to the
development of more excellent and colorful MFC materials.
station (CHI 604) at room temperature at a scan rate of 50 mV s . The
working electrode was a Pt disc, a Pt wire was used as the auxiliary
electrode, and reference electrode was Ag/AgCl electrode. Tetrabuty-
lammonium tetrafluoroborate (0.1 M) in dry DCM was used as the
+
supporting electrolyte. The ferrocenium/ferrocene (F
c
/F
c
) redox couple
4
. Experimental section
was used as an external potential reference. The HOMO energy levels
were obtained by comparing the oxidation half-wave potentials with an
+
4
.1. Measurements and instruments
external reference (F
c
/F
c
, ꢀ 4.8 eV relative to vacuum). Geometrical
optimization was performed by density functional theory (DFT) calcu-
lations at B3LYP/6-31G(d) level with the Gaussian 09 W program
package. Electronic transition data were obtained by the TD/DFT-CAM-
b3lyp/6-31G(d) calculations based on the configurations at ground
state.
1H and 13C NMR spectra were recorded using a Bruker Avance 400
3 6
MHz spectrometer at 400 MHz and 100 MHz in CDCl and DMSO‑d .
UV–Vis spectra were obtained on a Mapada UV-1800pc spectropho-
tometer. Fluorescence emission spectra were obtained on a Hitachi F-
4
700 fluorescence spectrophotometer. The fluorescence quantum yields
Single crystal X-ray diffraction experiments were carried on in a
Bruker SMART APEX II CCD-based diffractometer with graphite
of solutions and solids were measured by comparing to a standard and
6

T. Zhang et al.
Dyes and Pigments 190 (2021) 109296
Fig. 5. Fluorescence spectra of (a) PCVMO, (b) PCVTB, (c) PCVH, (d) PCVN, (e) PCVTF and (f) PCVCN under different states. Insets are the photos of solids under
65 nm light.
3
monochromatized Cu K
α
radiation (λ = 1.54184 Å) using the ϕꢀ
ω
scan
Table 2
technique at room temperature. Multiscan absorption corrections were
applied with the SADABS program. CCDC 2053199 2053200, 2053201
and 2053202 contains the supplementary crystallographic data.
Compounds 1, 2, 3 and 4 were prepared based on the reported
procedure [59].
Absorption and fluorescence data of six compounds before and after mechanical
force stimuli.
λ
abs (nm)
Δλabs (nm)
λ
em (nm)
Δλem (nm)
pristine
ground
pristine
ground
4
.1.5.4-((Z)-1-cyano-2-(4-((E)-2-(10-ethyl-10H-phenothiazin-3-yl)
PCVMO
PCVTB
PCVH
406
403
426
423
434
461
436
439
437
433
461
470
30
36
11
10
27
9
563
539
581
583
576
657
618
615
625
617
644
680
55
76
46
34
68
23
vinyl)phenyl)vinyl)benzonitrile (PCVCN).
Compound 4 (0.2 g, 0.56 mmol), 4-cyanoacetonitrile (0.08 g, 0.56
mmol) were dispersed in EtOH (25 mL). The mixture was heated to
reflux and then pyrrolidine (0.1 mL) was added. After 2 h, the solution
was cooled to room temperature, and a large amount of deep red solids
PCVN
PCVTF
PCVCN
7

T. Zhang et al.
Dyes and Pigments 190 (2021) 109296
Fig. 6. Powder XRD patterns of (a) PCVMO, (b) PCVTB, (c) PCVH, (d) PCVN, (e) PCVTF, and (f) PCVCN in different states.
appeared. Rude product was obtained after filtration and washing with
DMSO‑d
6
) δ 145.16, 144.12, 143.73, 140.49, 138.47, 133.05, 131.92,
ethanol. Pure product was achieved by column chromatography (silica
131.14, 130.10, 129.78, 127.69, 127.02, 126.73, 126.45, 125.70,
124.72, 123.11, 122.54, 122.22, 118.43, 117.59, 115.47, 115.41,
111.21, 107.43, 41.24, 12.57. Elemental Analysis: C, 79.80; H, 4.81; N,
8.72; found: C, 79.70; H, 4.89; N, 8.70.
1
gel, CH
2
Cl
2
/petroleum ether (V/V = 1:5). Yield: 71%. H NMR (400
MHz, DMSO‑d
6
) δ 8.23 (s, 1H), 8.02–7.95 (m, 6 H), 7.75 (d, J = 8.0 Hz,
H), 7.45 (m, 2 H), 7.35 (d, J = 16.0 Hz 1 H), 7.25–7.19 (m, 2 H), 7.15
d, J = 8.0 Hz 1H), 7.03 (d, J = 8.0 Hz 2H), 6.95 (t, J = 8.0 Hz 1H), 3.94
2
(
(
4.1.6.(Z)-3-(4-((E)-2-(10-ethyl-10H-phenothiazin-3-yl)vinyl)
phenyl)-2-(4-(trifluoromethyl)phenyl)acrylonitrile (PCVTF).
1
3
q, J = 8.0 Hz, 2 H), 1.32 (t, J = 6.0 Hz, 3 H). C NMR (101 MHz,
8

T. Zhang et al.
Dyes and Pigments 190 (2021) 109296
PCVTF was obtained through the similar procedure to that of
PCVCN. Bu NOH was used as catalyst.
Yield: 68%. H NMR (400 MHz, DMSO‑d
Declaration of competing interest
4
1
6
) δ 8.21 (s, 1H), 8.02–7.99
To the best of our knowledge, the named authors have no conflict of
interest, financial or otherwise.
(
m, 4H), 7.90 (d, J = 8.0 Hz, 2H), 7.75 (d, J = 8.0 Hz, 2H), 7.46–7.44 (m,
2
1
8
1
1
1
1
H),7.35 (d, J = 16.0 Hz, 1H), 7.25–7.19 (m, 2H), 7.15 (d, J = 8.0 Hz,
H), 7.035 (d, J = 12.0 Hz, 2H), 6.95 (t, J = 8.0 Hz, 1H), 3.945 (q, J =
Acknowledgement
1
3
.0 Hz, 2H), 1.32 (t, J = 6.0 Hz, 3H). C NMR (101 MHz, DMSO‑d ) δ
6
44.69, 144.10, 143.74, 140.31, 138.00, 132.00, 131.17, 129.99,
29.66, 127.70, 127.02, 126.68, 126.49, 126.10, 126.06, 125.73,
25.36, 124.72, 123.12, 122.54, 122.23, 119.99, 117.78, 115.47,
07.58, 41.23, 12.57. Elemental Analysis: C, 73.26; H, 4.42; N, 5.34;
This work was supported by the Scientific Research Foundation of
Tianjin Normal University (Grant No. 5RL151), the Foundation of
Development Program of Future Expert in Tianjin Normal University
(WLQR201804) and the Science &Technology Development Fund of
Tianjin Education Commission for Higher Education (2018ZD12).
found: C, 73.31; H, 4.32; N, 5.24.
.1.7.(Z)-3-(4-((E)-2-(10-ethyl-10H-phenothiazin-3-yl)vinyl)
4
phenyl)-2-phenylacrylonitrile (PCVH).
Appendix A. Supplementary data
PCVH was obtained through the similar procedure to that of PCVCN.
Bu
4
NOH was used as catalyst.
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.dyepig.2021.109296.
1
Yield: 94%. H NMR (400 MHz, DMSO‑d
6
) δ 8.03 (s, 1H), 7.97 (d, J
=
8.0 Hz, 2H), 7.79–7.71 (m, 4H), 7.55–7.51 (m, 2H), 7.47–7.43 (m,
3
1
H), 7.32 (d, J = 16.0 Hz, 1H), 7.23–7.19 (m, 2H), 7.15 (d, J = 8.0 Hz
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