Reversible mechanochromism and aggregation induced enhanced emission in phenothiazine substituted tetraphenylethylene

Article abstract of DOI:10.1039/c9nj03290h

Mono and tetra phenothiazine (PTZ) functionalized tetraphenylethylene (TPE) derivatives PTZTPE-1 and PTZTPE-4 were designed and synthesized by the Suzuki cross-coupling reactions between PTZ boronate ester and bromo TPEs. The PTZTPE-1 and PTZTPE-4 are hig

Full text of DOI:10.1039/c9nj03290h

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Reversible mechanochromism and aggregation induced enhanced emission in
phenothiazine substituted tetraphenylethylene
a
a
a*
Faizal Khan , Anupama Ekbote and Rajneesh Misra
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aDepartment of Chemistry, Indian Institute of Technology Indore,
Indore- 453552, India
*
Corresponding author
Email: rajneeshmisra@iiti.ac.in
Abstract
Mono and tetra phenothiazine (PTZ) functionalized tetraphenylethylene (TPE) derivatives
PTZTPE-1 and PTZTPE-4 were designed and synthesized by the Suzuki cross-coupling
reactions between PTZ boronate ester with bromo TPEs. The PTZTPE-1 and PTZTPE-4 are
highly emissive in solid state, which is crucial for a molecule to show mechanofluorochromism.
The strong donor ability of PTZ could affect the donor ability of TPE leading to changes in
electronic and photophysical properties of the target molecules. The number of PTZ moieties
attached to TPE could vary the twisting in the molecules, which could further affect the
mechanochromic properties. The photophysical, electrochemical, solvatochromic,
mechanochromic and AIE properties of PTZTPE-1 and PTZTPE-4 were studied. Both
PTZTPE-1 and PTZTPE-4 show significant mechanochromic behavior and comparable spectral
shift on grinding. The single crystal X-ray analysis of PTZTPE-1 reveals a twisted confirmation
of PTZ and TPE phenyl rings confirming strong AIE characteristics and reversible
mechanochromic behavior.
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Fig. 1. Chemical structures of PTZTPE-1 and PTZTPE-4.
Introduction
In recent years, research on organic luminogens exhibiting reversible solid state emission in
response to external stimuli has gained momentum[1,2] due to their fundamental importance and
potential application in sensors,[3] security inks, organic light emitting diodes,[4] fluorescent
switches, memory devices, optical recording, fluorescent bio-probes, and optoelectronic devices.[5-
9]
The compounds that show change in their solid state emission upon mechanical stimuli such as
grinding or scratching,[10,11] are known to show mechanofluorochromism (MFC).[12,13] The
reversible MFC behavior of these luminogens can be achieved by planarizing the twisted
confirmation or by subtle alternation of molecular packing.[14-17] The flexibility of donor and
acceptor moieties also affects the MFC behavior. Some other factors like molecular arrangement,
planarity, effective conjugation, interaction with the surrounding environment and position of
heavy atoms play a key role in regulating the MFC behaviour.[18,19] In general, organic dyes are
non-emissive in aggregated state due to the aggregation caused quenching (ACQ). This restricts
the use of such dyes as MFC materials.[20] The phenomena of aggregation induced emission (AIE)
results in materials with enhanced emission in aggregated state. Tetraphenylethylene (TPE) is one
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of the widely used AIEgen for design of solid state emissive molecules.[21-23] The non-planar
structure of TPE reduces π-π stacking in solid state and the restriction of intramolecular rotations
(RIR) results in enhanced emission in aggregated state.[24,25]
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TPE act as a weak electron donor and has been used in various D-A and D-A-D type
organic frameworks[26-28]. On the other hand, phenothiazine (PTZ) acts as a strong donor compared
to TPE due to the presence of electron rich S and N atoms and has been employed in various
material applications because of its low cost, easy and high yielding synthetic modifications. The
butterfly shaped structure of PTZ allows the molecule to be more twisted leading to higher
emission in solid state, making it suitable for MFC applications.[29,30]
Herein, we have designed and synthesized PTZ based TPE derivatives with an aim of
achieving high solid-state emission and good MFC behavior. The attachment of a strong donor to
a weak donor could tune the electronic properties of the molecular system. The strong electron
donating ability of PTZ could further affect the electron donating ability of TPE resulting in a
dipolar character in the molecules. The number of PTZ moieties attached to TPE is expected to
vary the twisting in the molecules which could further affect the mechanochromic properties.
Taking this in consideration, we have synthesized two PTZ based derivatives of TPE, PTZTPE-
1
in which one PTZ unit is attached with TPE, and PTZTPE-4 in which four PTZ units are
attached with TPE. Both the derivatives are AIE active and mechanochromic in nature. The
photophysical, electrochemical, solvatochromic, mechanochromic and AIE properties of
PTZTPE-1 and PTZTPE-4 have been investigated.
Results and Discussions
Synthesis
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The combination of non-planar PTZ and the propeller shaped TPE in PTZTPE-1 and PTZTPE-
resulted in intense solid state emission. The compounds were synthesized by using Suzuki cross-
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coupling reactions between monobromo TPE (TPE-1Br) and tetrabromo TPE (TPE-4Br) with
boronate ester of phenothiazine (PTZ-Bpin). The synthetic route is outlined in Scheme 1. The
TPE-1Br and TPE-4Br were synthesized by the reported procedure.[31,32] The PTZ-Bpin was
synthesized by Miyaura borylation reaction between 3-bromo-10-propyl-10H-phenothiazine and
bis(pinacolato)diboron.[33] The detailed information about the synthesis of intermediates is given
in Scheme S1. The Suzuki cross-coupling reaction between TPE-1Br and TPE-4Br with boronate
ester of PTZ (PTZ-Bpin) yielded PTZTPE-1 and PTZTPE-4 in 69% and 75% yield respectively.
The synthesized compounds show good solubility in common organic solvents, such as
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dichloromethane, chloroform, tetrahydrofuran and toluene, and are well characterized by H-
NMR, 13C-NMR and HRMS techniques. The single crystal X-ray diffraction was done for
PTZTPE-1 crystals.
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Scheme 1. Synthetic scheme for PTZTPE-1 and PTZTPE-4.
Photophysical Properties
The electronic absorption and emission spectra (Fig. 2) for the compounds PTZTPE-1 and
PTZTPE-4 were recorded in THF and the corresponding data are listed in Table 1. The absorption
spectra of PTZTPE-1 shows peak at 274 nm and that of PTZTPE-4 shows peaks at 270 nm and
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10 nm corresponding to π-π* transitions. The PTZTPE-1 and PTZTPE-4 also show absorption
peaks at 323 nm and 355 nm, respectively. The peaks in longer wavelength region could be due to
the D-A character generated in the molecules. To further confirm this, we performed
solvatochromic studies. For PTZTPE-1, the study shows that the emission maxima value shifts
bathochromically on increasing polarity of the solvents while for PTZTPE-4, the emission
maxima value does not show much variation. These results suggested that the compound
PTZTPE-1 could have higher D-A character than PTZTPE-4.
The D-A character of PTZTPE-1 and PTZTPE-4 was further examined by DFT and TD-
DFT studies. The DFT study for PTZTPE-1 reveals that the HOMO is localized on PTZ moiety
while LUMO is localized on TPE moiety (Fig. 5). Since the electron density of HOMO and LUMO
is well separated in case of PTZTPE-1, and TD-DFT study reveals that the excitation is from
HOMO to LUMO, hence it can be concluded that D-A character is generated within the molecule
while for PTZTPE-4, the DFT and TD-DFT studies reveals that the electron density of HOMO
and LUMO is not separated (Fig. 5), hence PTZTPE-4 do not show a significant D-A character.
The emission spectra of PTZTPE-1 and PTZTPE-4 shows emission maxima at 539 nm and 574
nm respectively.
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Fig. 2. (a) Absorption and (b) normalized emission spectra of compounds PTZTPE-1 and
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PTZTPE-4 in THF solvent (2 x 10 M) (Excitation wavelength λ = 330 nm and 360 nm for
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PTZTPE-1 and PTZTPE-4 respectively).
Table 1. Photophysical and thermal properties of PTZTPE-1 and PTZTPE-4 recorded in dry
THF.
-1
-1 a
λem (nm)a
Φfb
Compounds
λabs (nm), ε (Lmol cm )
Stokes shift
T (°C)
d
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PTZTPE-1
PTZTPE-4
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270 (24940), 310 (15470), 355
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(13090)
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Recorded in dry THF (2 x 10 M concentration). Fluorescence quantum yields were recorded using
quinine sulphate as a standard in 0.5 M H SO solution.
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Solvatochromism
The compounds PTZTPE-1 and PTZTPE-4 shows absorption maxima at 323 nm and 355 nm
respectively due to D-A character generated in the molecules.[34] To confirm this, we performed
solvatochromic study for both the compounds in a range of solvents from non-polar to polar
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(cyclohexane, toluene, chloroform, tetrahydrofuran, dichloromethane and N,N-
dimethylformamide (DMF))[35,36] and the corresponding data are listed in Table S1. The excited
state is generally more polar as compared to the ground state and hence polar solvents stabilize
excited state more than ground state, which results in decrease in the energy of excited state.
Hence, on increasing the polarity from cyclohexane to DMF for compound PTZTPE-1 and from
toluene to DMF for compound PTZTPE-4, bathochromic shift occurs in their emission spectra.
The absorption spectra were not much affected by changing the polarity of solvent reflecting the
presence of more polarized excited states. The compound PTZTPE-1 emitted sky-blue
fluorescence in nonpolar medium (cyclohexane) at 459 nm (Fig. 4). On increasing polarity, a
significant change from sky blue to green (in chloroform, 521 nm) and then to orange (in DMF,
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31 nm) takes place with an overall red shift of 172 nm. The tetra armed TPE i.e., PTZTPE-4 do
not show major changes in its λem value on increasing the polarity of the solvents from toluene
564 nm) to dichloromethane (579 nm) but a significant bathochromic shift occurs on moving from
dichloromethane to DMF of 105 nm.
(
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Fig. 3. Emission spectra of compounds PTZTPE-1 (a) and PTZTPE-4 (b) in solvents of different
polarity. (excitation wavelength for PTZTPE-1 and PTZTPE-4 is 330 nm and 360 nm
respectively).
Fig. 4. Photograph of compounds PTZTPE-1 and PTZTPE-4 in solvents of different polarity
(from left to right, cyclohexane to DMF) taken under 365 nm UV illumination.
Computational Analysis
In order to understand the geometry and the electronic structure of PTZTPE-1 and PTZTPE-4,
density functional theory (DFT) and time dependent density functional theory (TD-DFT)
calculations were performed using the Gaussian 09W program at B3LYP/6-31G(d,p) level.[39] The
geometry optimization was carried out in gas phase and the frontier molecular orbitals (FMOs) are
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displayed in Fig. 5. In both the compounds the electron density of LUMO energy level is mainly
located at TPE core. In case of PTZTPE-1 the electron density of HOMO energy level is centered
at PTZ moiety and in case of PTZTPE-4 it is located over the entire structure. The optimized
structure of both PTZTPE-1 and PTZTPE-4 reveals propeller shape of TPE. PTZTPE-4 contains
higher number of PTZ units which creates more twisting and hence it shows better
mechanochromic property as compared to PTZTPE-1. The HOMO-LUMO gap for PTZTPE-1
and PTZTPE-4 are 3.61 eV and 3.34 eV respectively. The HOMO and LUMO of PTZTPE-1 is
well separated that suggest donor-acceptor character of the molecule. The time dependent density
functional theory (TD-DFT) calculations were performed to understand the electronic transitions
in PTZTPE-1 and PTZTPE-4. The electronic transitions from TD-DFT calculation with
composition, assignment and oscillator strength are shown in Table S3.
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The optimized structure of PTZTPE-4 obtained from DFT calculation suggest that all the
four phenyl rings of TPE and PTZ are non-planar and oriented in four different directions in space
which may achieve molecular planarity on grinding causing extension in conjugation resulting in
good bathochromic shift. In case of PTZTPE-1, the higher order twisting is only one side and the
conversion of this twisted fragment to planar structure affects its conjugation to a little extent hence
less bathochromic shift occurs in its emission spectra.
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Fig. 5. Energy level diagram of PTZTPE-1 and PTZTPE-4.
Electrochemical Properties
The electrochemical properties of PTZTPE-1 and PTZTPE-4 were examined by cyclic
voltammetry (CV) and differential pulse voltammetry (DPV) analysis using 0.1M
tetrabutylammonium hexafluorophosphate (TBAF ) as supporting electrolyte and dry
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dichloromethane solvent at room temperature. Both the PTZTPE-1 and PTZTPE-4 shows
potential waves only in the positive range of their cyclic voltammograms (Fig. 6). The oxidation
process is reversible for both the compounds as shown by their voltammograms. Both the
PTZTPE-1 and PTZTPE-4 shows reversible oxidation potential at 0.55V corresponding to PTZ.
The incorporation of more PTZ moieties to PTZTPE-1 does not results in any change in the
oxidation potential of PTZTPE-4.
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Fig. 6 Cyclic voltammogram (CV) and differential pulse voltammogram (DPV) of compounds (a)
PTZTPE-1 and (b) PTZTPE-4 obtained using 0.1M TBAF as supporting electrolyte in dry
6
DCM solvent at room temperature.
Aggregation Induced Emission
The phenothiazine derivatives PTZTPE-1 and PTZTPE-4 contains tetraphenylethylene unit,
which is known for its AIE active behavior; therefore, AIE study was performed. Formation of
nano aggregates was initiated by progressive addition of water to the THF solution of PTZTPE-1
and PTZTPE-4, and the AIE characteristics of these systems were studied using fluorescence and
absorption spectroscopy (Fig. 7 and Fig. S2). Both the compounds are weakly emissive at lower
water percentage due to free rotation of phenyl rings of TPE moiety, which results in non-radiative
energy loss of the excited state. The formation of aggregates at higher water percentage restricts
the free rotation of the phenyl ring resulting in enhanced emission. The PTZTPE-1 and PTZTPE-
4 emit at 539 nm and 574 nm respectively in pure THF solution. Bathochromic shift occurs in the
emission spectra of PTZTPE-1 and PTZTPE-4 upto 60% and 50% water fraction respectively.
This behavior is due to stabilization of the charge transfer states due to increase in polarity. The
TPE derivative PTZTPE-1 exhibits AIE behavior after 70% and shows highest intensity peak at
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0% water fraction, whereas PTZTPE-4 exhibits AIE behavior after 50% and shows highest
intensity peak at 70% water fraction (Fig. 7b). From fluorescence studies it can be concluded that
the emission at lower water percentage is governed by ICT, however gradual increase in water
fraction resulted in the formation of aggregates. In PTZTPE-4, a slight drop in the emission
intensity was observed after 70% water fraction. This is due to the formation of the large-sized
aggregates, which decreases the effective dye concentration and hence less exposed to radiation as
0
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[37]
compared to smaller aggregates. . The AIE behavior was also studied using absorption
spectroscopy (Fig. S2). The absorption spectra for PTZTPE-1 reveals similar trend of absorption
bands up to 70% water fraction, above which there is scattering of light or the Mie effect was
observed.[38]
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Fig. 7. Emission spectra of compounds PTZTPE-1 (a) and PTZTPE-4 (b) in different THF- water
mixtures. (c) Plot of fluorescence intensity Vs. % of water fraction for the compounds PTZTPE-
-5
1 and PTZTPE-4 (2 x 10 M).
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Fig. 8. Photographs of compounds PTZTPE-1 (a) and PTZTPE-4 (b) in different THF- water
mixtures taken under 365 nm UV illumination.
Single Crystal X-ray Analysis
The crystals of PTZTPE-1 were obtained by slow evaporation of hexane in ethyl acetate. The
slow evaporation method in different solvents was used to obtain crystals for PTZTPE-4, however
the crystals obtained were not good enough for accurate structural elucidation. The crystal
structure of PTZTPE-1 was helpful to illustrate the aggregation induced emission and
mechanochromic properties. The PTZTPE-1 crystallize in the P2 /c space groups. The single
1
crystal structure of PTZTPE-1 (Fig. 9) reveals the propeller shape of TPE and butterfly shape of
phenothiazine. The phenothiazine and the phenyl ring of TPE do not lie in the same plane and has
a twisted confirmation with a torsion angle of 47.45°. Since the molecule is lacking planarity, in
the aggregated state it restricts the π–π stacking interaction which results in intense solid state
emission.
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The crystal packing diagram of PTZTPE-1 (Fig. S5 and Fig. S6) shows only C–H…π
interaction which make them loosely packed and hence sensitive to grinding thereby showing
mechanochromism. The molecules of PTZTPE-1 are held together via mutual C(25)–H(25)…π
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(red centroid-C1–C2–C3–C4–C5–C6, 3.572 Å) interaction. The other intermolecular C–H…π
interactions that exists in PTZTPE-1 are C(32)–H(32)…π (yellow centroid-C1–C2–C3–C4–C5–
C6, 3.767 A), C(32)–H(32)…π (blue centroid-C1–C2–C3–C4–C5–C6, 3.569 Å) (Fig. S5).
Fig. 9. (a) Single crystal structure of PTZTPE-1 (b) Packing diagram of PTZTPE-1 (Antiparallel
arrangement).
Mechanochromism
The TPE derivatives PTZTPE-1 and PTZTPE-4 are expected to show mechanoresponsive
change in their solid state emission because of the propeller shape and AIE nature of TPE and
nonplanar structure of PTZ. It was assumed that number of PTZ moieties may vary the extent of
mechanochromism. Higher number of PTZ moieties are expected to create more twisting in their
structures. Both the PTZTPE-1 and PTZTPE-4 were grinded mechanically with mortar and pestle
and their mechanochromic behavior was investigated using solid state emission spectroscopy. The
corresponding data are listed in Table 2. The pristine form of PTZTPE-1 exhibits blue emission
at 475 nm. Grinding of PTZTPE-1 bathochromically shifts the emission wavelength from 475 nm
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to 519 nm (Fig. 10a). The fumigation of the grinded form of PTZTPE-1 using dichloromethane
for 7—10 minutes reverted the emission to 478 nm. The tetra armed compound PTZTPE-4
exhibits good mechanochromic behavior and its pristine form shows a bright cyan colored
emission at 498 nm (Fig. 10b). The grinded form displays yellow fluorescence at 545 nm. On
fumigation with dichloromethane, the emission returns to 509 nm. The shift in solid state emission
generated due to mechanical grinding for PTZTPE-1 and PTZTPE-4 is 44 nm and 47 nm
respectively. To check the phase transformation from pristine to ground state associated to the
reversible mechanochromic behavior, powder X-ray diffraction (PXRD) technique was used. The
PXRD pattern for the pristine form of compound PTZTPE-4 exhibited sharp diffraction peaks
due to its crystalline nature (Fig. S3). The grinded state for the same compound exhibited broad
diffused peaks which confirms the amorphous nature of the compound. On fumigation, the broad
diffused peaks transform into sharp diffraction peaks which indicates the reversible crystalline
nature of the compound. The pristine form of compound PTZTPE-1 is also crystalline as shown
by its PXRD pattern (Fig. S3). The grinded form of PTZTPE-1 exhibited broad diffused peaks
which on fuming transform into sharp diffraction peaks suggesting reversible crystalline nature of
PTZTPE-1. The reversible mechanochromic behavior of compounds PTZTPE-1 and PTZTPE-
1
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can be explained based on morphology change from crystalline to amorphous and this change is
due to modification of molecular arrangement on grinding. The absolute quantum yield of pristine,
grinded and fumed form of PTZTPE-1 is 0.23, 0.24 and 0.08 respectively. The absolute quantum
yield of pristine, grinded and fumed form of PTZTPE-4 is 0.22, 0.23 and 0.34 respectively.
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Table 2. Solid state emission maxima of compounds PTZTPE-1 and PTZTPE-4.
Emission
λpristine (nm)
λground (nm)
λfumed (nm)
Λλ (nm)a
Compounds
0
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PTZTPE-1
PTZTPE-4
475
498
519
545
478
509
44
47
aGrinding-induced spectral shift, [Λλ = λground –λpristine
]
Fig. 10. Solid state emission spectra of compounds PTZTPE-1 (a) and PTZTPE-4 (b) in pristine,
grinded and fumed forms. Photographs (inset) taken under UV illumination.
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Thermogravimetric Analysis
Thermal stability is one of the important characteristics for a molecule to be utilized in
optoelectronic applications. The thermal properties of PTZTPE-1 and PTZTPE-4 were evaluated
by thermogravimetric analysis. The thermal decomposition temperatures were found to be 365 °C
and 425 °C for PTZTPE-1 and PTZTPE-4 at 5% weight loss respectively. The TGA plot is shown
in Fig. S4 and the corresponding data are listed in Table 1.
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Conclusion
Two phenothiazine based tetraphenylethylene derivatives were designed and synthesized by
keeping in mind that phenothiazine will results in more twisting to the target structures and their
structural, photophysical, aggregation induced emission (AIE) and mechanochromic properties
were evaluated. Both the mono and tetra substituted TPE (PTZTPE-1 and PTZTPE-4) shows
nearly equal spectral shift in response to mechanical stimuli. The PXRD studies shows that color
change is associated with the morphology change from amorphous state to the crystalline state.
Both the compounds are emissive in solid state and display AIE characteristics. The PTZTPE-4
do not show significant D-A character while the PTZTPE-1 exhibit D-A character which is
confirmed by solvatochromic and TD-DFT studies. The compounds can act as smart materials that
change color in response to a mechanical stimulus hence the work will be helpful in the
development of mechanoresponsive organic materials.
Experimental Section
General Methods
Chemicals were used as received unless otherwise indicated. All oxygen or moisture sensitive
1
13
reactions were performed under nitrogen/argon atmosphere. H NMR (400 MHz) and C NMR
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(
100 MHz) spectra were recorded on a Bruker 400 MHz FT-NMR spectrometer at room
1
temperature. H NMR chemical shifts are reported in parts per million (ppm) relative to the solvent
residual peak (CDCl , 7.26 ppm). Multiplicities are given as s (singlet), d (doublet), t (triplet) and
3
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m (multiplet) and the coupling constants, J, are given in hertz. C NMR chemical shifts are
reported relative to the solvent residual peak (CDCl , 77.0 ppm). Thermogravimetric analysis was
3
performed on the Mettler Toledo thermal analysis system. UV−visible absorption spectra were
recorded on a Perkin-Elmer Lamba 35 instrument. Emission spectra were taken in a Fluoromax-
4
C, S/n.1579D-1417-FM Fluorescence software Ver 3.8.0.60. The relative quantum yields in
solution were calculated using Quinine sulphate in 0.5 M H SO as standard. The quantum yields
2
4
in solid state were measured using K-sphere Integrating sphere. The excitation and emission slits
were 3/3 nm for the emission measurements and 3/3 for solid quantum yield measurements. All
the measurements were done at 25 °C. HRMS were recorded with an Agilent 6545A Q-TOF mass
spectrometer and on a Bruker-Daltonics micrOTOF-Q II mass spectrometer. The voltammograms
were recorded on a CHI620D electrochemical analyzer in dichloromethane solvent and 0.1 M
TBAF as the supporting electrolyte. The electrodes used were glassy carbon as a working
6
electrode, Pt wire as a counter electrode and SCE as a reference electrode. Single crystal X-ray
data for compounds PTZTPE-1 and PTZTPE-4 were collected on a Bruker D8 VENTURE
diffractometer equipped with CMOS Photon 100 detector and Mo-Kα (λ = 0.71073 Å) radiation
was used.
Synthesis and characterization of PTZTPE-1 : A mixture of TPE-1Br (0.4 g, 0.97 mmol), 10-
propyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-10H-phenothiazine (PTZ-Bpin) (0.53 g,
1
.45 mmol) (PTZ-Bpin), Pd(PPh ) (0.055 g, 0.05 mmol), and potassium carbonate (0.403 g, 2.91
3 4
mmol) was dissolved in THF/ethanol/water (9/3/1 v/v/v) and heated to reflux for 12 h under
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nitrogen atmosphere. The reaction mixture was cooled to room temperature and poured into water.
The organic layer was extracted with dichloromethane and the combined organic layers were
washed with saturated brine solution and water and dried over anhydrous sodium sulfate. After
filtration and solvent evaporation, the residue was purified by silica-gel column chromatography
1
1
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using hexane/dichloromethane (2/3 v/v) as eluent. Light green solid of PTZTPE-1 was obtained
1
in 69% yield (0.383 g). H-NMR (400 MHz, CDCl 25 °C): δ 7.33 (d, J=1Hz, 1H), 7.31 (d, J=1Hz,
3,
1
H), 7.28 (s, 1H), 7.02-7.16 (m, 20H), 6.90 (t, J=2Hz, 1H), 6.86 (s, 1H), 6.84 (s, 1H), 3.82 (t,
1
3
J=2Hz, 2H), 1.83 (m, J=2Hz, 2H), 1.01 (t, J=2Hz, 3H). C-NMR (100 MHz, CDCl , 25 °C): δ
3
1
45.09, 143.80, 143.74, 142.39, 141.02, 140.54, 137.68, 134.86, 131.78, 131.43, 131.36, 127.76,
127.69, 127.63, 126.47, 125.56, 125.12, 124.44, 122.37, 115.45, 115.34, 49.20, 20.12, 11.35 ppm.
+
HRMS: m/z 571.2328 (M , calcd 571.2329).
Synthesis and characterization of PTZTPE-4 : A mixture of TPE-4Br (0.4 g, 0.62 mmol), 10-
propyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-10H-phenothiazine (PTZ-Bpin) (1.13 g,
3
.7 mmol), Pd(PPh ) (0.11 g, 0.1 mmol), and potassium carbonate (1.02 g, 7.4 mmol) was
3 4
dissolved in THF/ethanol/water (9/3/1 v/v/v) and heated to reflux for 36 h under nitrogen
atmosphere. The reaction mixture was cooled to room temperature and poured into water. The
organic layer was extracted with dichloromethane and the combined organic layers were washed
with saturated brine solution and water and dried over anhydrous sodium sulfate. After filtration
and solvent evaporation, the residue was purified by silica-gel column chromatography using
hexane/dichloromethane (2/3 v/v) as eluent. Light green solid of PTZTPE-4 was obtained in 75%
1
yield (0.596 g). H-NMR (400 MHz, CDCl 25 °C): δ 7.36 (m, 8H), 7.34 (s, 4H), 7.32 (s, 4H),
3
,
7
.18 (s, 1H), 7.14 (m, 15H), 6.92 (t, J=2Hz, 4H), 6.89 (d, J=1Hz, 4H), 6.87 (d, J=1Hz, 4H), 3.84
1
3
(t, J=2Hz, 8H), 1.86 (m, J=2Hz, 8H), 1.03 (t, J=2Hz, 12H). C-NMR (100 MHz, CDCl , 25 °C):
3
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δ 145.11, 144.36, 142.50, 140.30, 137.82, 134.87, 131.92, 127.43, 127.19, 125.62, 125.56, 125.15,
24.52, 122.33, 115.46, 115.32, 49.22, 20.14, 11.32 ppm. HRMS: m/z 1289.4654 (M+H, calcd
1
1289.4634).
0
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ASSOCIATED CONTENT
Supporting Information
Synthetic route for intermediates, Absorption spectra in solvatochromic and AIE study, PXRD
patterns, TG curves, crystal structural data, NMR spectra, HRMS, Electrochemical data, DFT and
TD-DFT calculations.
■
AUTHOR INFORMATION
Corresponding Authors
Email: rajneeshmisra@iiti.ac.in
Conflicts of Interest
No conflicts of interest to declare.
Acknowledgements
We acknowledge the support by Department of Science and Technology (DST-SERI) (Project No.
(DST/TMD/SERI/D05(C)), Indian National Science Academy (INSA) Project No.
INSA(SP/YSP/139/2017/229), New Delhi and Council of Scientific and Industrial Research
(
Project No. CSIR 01(2934)/18/EMR-II), New Delhi, Science and Engineering Research Board
SERB Project) (Project No. CRG/2018/000032). We thank Prof. Sangit Kumar, IISER Bhopal
(
and Dr. Shaikh M. Mobin, IIT Indore for their help and guidance. We also thank the Sophisticated
Instrumentation Centre (SIC), Indian Institute of Technology (IIT) Indore. F. K. thanks Council of
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Scientific and Industrial Research (CSIR) for fellowship. A.E. thanks Indian Institute of
Technology (IIT) Indore for fellowship.
Keywords:
Mechanochromism,
Aggregation
Induced
Emission,
Phenothiazine,
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0
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Tetraphenylethylene, AIEgens.
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