A-π-D-π-A carbazole derivatives with remarkable solvatochromism and mechanoreponsive luminescence turn-on

Article abstract of DOI:10.1039/c7tc00559h

Two A-π-D-π-A molecules with a carbazole donor and a dicyanovinyl acceptor but differing in N-hexyl (h-CPDM) and N-isooctyl substituents (i-CPDM) were synthesized, and both of them presented remarkable dual properties of solvatochromism and mechanoresponsive luminescence (MRL) turn-on. The intrinsic intramolecular charge transfer (ICT) characteristic endowed both luminophors with a prominent solvatochromic effect, with emission color tuning from blue to orange-red by changing the solvent from nonpolar hexane to polar dimethyl sulfoxide. Meanwhile, the non-/weakly emissive original powders of h-CPDM and i-CPDM gave bright orange (610 nm) and yellow (596 nm) emission with the photoluminescence quantum yields increasing as high as 85-fold after being ground. Investigations revealed this mechanoresponsive luminescence turn-on could be ascribed to the disturbance of the π-π stacking interactions in the non-/weakly emissive J-aggregates by mechanical force. This work offers carbazole derivatives that can be used as sensitive fluorescent indicators for organic solvents and mechanical sensors.

Full text of DOI:10.1039/c7tc00559h

View Article Online
View Journal
Journal of
Materials Chemistry C
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: P. Wen, Z. Gao, R.
Zhang, A. Li, F. Zhang, J. Li, J. Xie, Y. Wu, M. Wu and K. Guo, J. Mater. Chem. C, 2017, DOI:
10.1039/C7TC00559H.
This is an Accepted Manuscript, which has been through the
Volume
4 Number 1 7 January 2016 Pages 1–224
Royal Society of Chemistry peer review process and has been
accepted for publication.
Journal of
Materials Chemistry C
Accepted Manuscripts are published online shortly after
Materials for optical, magnetic and electronic devices
www.rsc.org/MaterialsC
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 2050-7526
PAPER
~
Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
the Hofmeister effects
rsc.li/materials-c

Please do not adjust margins
Journal of Materials Chemistry C
Page 1 of 9
View Article Online
DOI: 10.1039/C7TC00559H
Journal Name
ARTICLE
A-π-D-π-A carbzazole derivatives with remarkable
solvatochromism and mechanoreponsive luminescence turn-on
Ping Wen,a Zhixiang Gao,b Rong Zhang,a Anran Li,c Fang Zhang,a Jie Li,* a Jingjuan Xie,a Yuezhen Wu,
a Min Wu,a KunPeng Guo* a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Two A-π-D-π-A molecules with carbazole donor and dicyanovinyl acceptor but differing in the N-hexyl (h-CPDM) and N-
isooctyl substitute (i-CPDM) were synthesized, and both of them presented remarkable dual properties of
solvatochromism and mechanoreponsive luminescence (MRL) turn-on. The intrinsic intramolecular charge transfer (ICT)
characteristic endowed both luminophors with prominent solvatochromic effect, with emission color tuning from blue to
orange-red by changing the solvent from nonpolar hexane to polar dimethyl sulfoxide. Meanwhile, the none/weakly
emissive original powders of h-CPDM and i-CPDM gave bright orange (610 nm) and yellow (596 nm) emission with
photoluminescence quantum yields increasing as high as 85-fold after being ground. Investigations revealed this
mechanoreponsive luminescence turn-on could be ascribed to the disturbance of the π-π stacking interactions in the
non/weakly emissive J-aggregates by the mechanical force. This work offers carbazole derivatives with applications as
sensitive fluorescent indicators for organic solvents and mechanical sensors.
www.rsc.org/
studied, which enabled us to understand the basic
mechanisms of MRL behavior. However, high-contrast MRL
luminescence on/off switching, especially luminescence turn-
Introduction
Organic compounds with molecules built up from alternating
electron-donating (D) and electron-accepting (A) segments
have attracted considerable attention by virtue of their wide
applications in the fields of fluorescence sensors,1 pH
indicators,2 viscosity probes,3 and mechanochromic materials.4
Among them, the A-π-D-π-A molecules are of particular
interest due to their symmetrical structure and balanced
dipole moment, which often exhibit intense fluorescence
resulting from the reduced dipole-dipole interactions.5 Owing
to their intrinsic intramolecular charge transfer (ICT) character,
these molecules are promising candidates for solvent polarity
detection because of the solvatochromic luminescence effect.6
However, highly sensitive detector molecules whose emitting
colors can be tuned in a wide range of wavelength with
intense luminescence distinguished by naked eyes are still
rare.7
on to meet the practical application, is difficult to be realized
for the traditional MRL materials. Recently, a few mechanical
force-induced luminescence turn-on systems based on
featured mechanisms have been reported. For example, by
breaking the donor-acceptor interaction after force stimuli, Pei
and co-workers reported
a blue luminescence turn-on
cocrystallized complex.9 Park and co-workers reported a shear-
induced blue luminescence on-off switching in stilbenic π-
dimer crystals by reversible [2+2] cycloaddition.10 Tian and co-
workers reported a force-induced cyan luminescence turn-on
compound based on mechanically switching intramolecular
charge transfer in molecular crystals.11 By mechanically
controlled photo-induced electron transfer in molecular
assemblies, Park and co-workers reported a force-induced
orange luminescence turn-on dicyanodistyrylbenzene based D-
A-D triad.12 Most of the reported responsive turn-on
luminescence was located in relative short wavelength region.
Very recently, our group reported two molecules with 2,5-
diphenylthiophene donor and 1,3-indandione acceptor
achieved red/near-infrared (NIR) MRL turn-on by mechanical
Similar to their applications as polarity sensor in solvents, ICT
molecules that exhibit mechanoreponsive luminescence (MRL)
characteristics in the solid state have drawn great attention
due to their potential applications in mechano-sensors, and
deformation detectors.8 To date, MRL materials displaying
luminescence dichromic behavior have been reported and
disturbing
their
non/weakly
emissive
metastable
nanostructures.13 However, developing controllable emission
off/on switching system is still challenging, and the
relationship between the molecular structure, intermolecular
interactions and emission properties are needed to be
disclosed.
*
In this work, two A-π-D-π-A carbazole derivatives using
dicyanovinyl groups as the electron-accepting moieties, but
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry C
Page 2 of 9
View Article Online
DOI: 10.1039/C7TC00559H
ARTICLE
Journal Name
Synthesis of 1h. 3, 6-Dibromo-carbazole (9.75 g, 30 mmol) and
bromohexane (5.94 g, 36 mmol) was dissolved in toluene (50
mL). The solution of KOH (4.5 g, 80 mmol) and tetrabutyl
ammonium bromide (TBAB) (976 mg, 3 mmol) in H2O (15 mL)
was added. Then the reaction mixture was stirred at 110 °C for
4 h. After cooling, the mixture was poured into H2O and
extracted with chloroform. The combined organic extracts
were dried over anhydrous MgSO4, filtered, and concentrated
under reduced pressure. 1h was recrystallized from ethyl ether
N
N
NC
NC
CN
CN
NC
NC
CN
CN
h-CPDM
i-CPDM
1
Scheme 1 Molecular structures of h-CPDM and i-CPDM.
to produce white crystals in an 89% yield. H NMR (600 MHz,
CDCl3) δ = 8.13 (d, J = 2.4 Hz, 2H), 7.54 (dd, J = 8.4, 1.8 Hz, 2H),
7.26 (d, J = 8.4 Hz, 2H), 4.23 (t, J = 7.2 Hz, 2H), 1.85 - 1.76 (m,
2H), 1.36 - 1.19 (m, 6H), 0.85 (t, J = 7.2 Hz, 3H).
differing in the N-hexyl (h-CPDM) and N-isooctyl substitute (i-
CPDM were designed and synthesized to address the
)
Synthesis of 1i. The procedure is similar to the synthesis of 1h
but using bromo-iso-octane instead of bromohexane.
Compound 1i was obtained as pale yellow oil by silica gel
problems identified above (Scheme 1). Due to their strong ICT
characteristics, these two compounds exhibited remarkable
solvatochromic effects, suggesting their applications in
solvents polarity detection. Moreover, their luminescence
properties in the solid state were highly dependent on the
molecular structure as well as the stability of the crystalline
phases in response to external force stimuli. For example,
upon grinding, the almost non-emissive solids demonstrated
stimuli-responsive fluorescence not only changing in colors
from red to orange (h-CPDM) and red to yellow (i-CPDM), but
also with absolute photoluminescence quantum yields (ΦFs)
raised as much as 85-fold. Based on these results, the
relationship between the molecular structure and the diversity
of luminescence behaviour, and the mechanism of MRL turn-
on in the solid state were investigated.
1
column chromatography (petroleum ether) in an 80% yield. H
NMR (600 MHz, CDCl3) δ = 8.13 (d, J = 1.8 Hz, 2H), 7.54 (dd, J =
8.7, 1.9 Hz, 2H), 7.22 (t, J = 5.8 Hz, 2H), 4.09 - 4.02 (m, 2H),
1.37 -1.15 (m, 9H), 0.86 (t, J = 7.5 Hz, 3H), 0.82 (t, J = 7.2 Hz,
3H).
Synthesis of 2h. Under a nitrogen atmosphere, 1h (4.12 g, 10
mmol), tetrakis(triphenylphosphine)palladium(0) (Pd(PPh3)4)
(576 mg, 0.5 mmol), K2CO3 (6.9 g, 50 mmol), 4-
(dihydroxyboryl)benzaldehyde (3.3 g, 22 mmol) and 1,2-glycol
dimethyl ether (200 mL) were added into a 500 mL three-
necked flask. The mixture was stirred at 100 °C for 24 h. After
cooling to room temperature, the mixture was poured into
H2O, extracted with chloroform and dried over anhydrous
MgSO4. After filtration and concentration under reduced
pressure, product 2h was obtained as yellow solid by silica gel
column chromatography (ethyl acetate: ethyl acetate= 1: 12 by
volume) in a 21% yield. 1H NMR (600 MHz, CDCl3) δ = 10.08 (s,
2H), 8.45 (d, J = 1.2 Hz, 2H), 8.01 (dt, J = 8.4, 1.8 Hz, 4H), 7.92
(dt, J = 8.4, 1.8 Hz, 4H), 7.81 (dd, J = 8.4, 1.8 Hz, 2H), 7.55 (d, J =
8.4 Hz, 2H), 4.38 (t, J = 7.2 Hz, 2H), 1.94 (m, 2H), 1.45 - 1.29 (m,
6H), 0.88 (t, J = 7.2 Hz, 3H).
Experimental
Materials and characterization
All reagents and solvents were purchased from J&K Chemical
and used without purification. NMR spectra measurements
were carried out at a Bruker NMR 600 spectrometer. MALDI-
TOF mass spectrometric measurements were performed on a
Waters MALDI Micro MX mass spectrometer, with 2,5-
dihydroxy benzoic acid (DHB) as the matrix. Elemental analysis
was run on a Vario EL III Elemental Analyzer. UV-Vis spectra
Synthesis of 2i. The procedure is similar to the synthesis of 2h
but using 1i instead of 1h. Compound 2i as yellow solid was
obtained by silica gel column chromatography (ethyl acetate:
were recorded on
a
HTIACH U-3900 Spectrometer.
1
ethyl acetate= 1: 12 by volume) in a 41% yield. H NMR (600
Photoluminescent (PL) spectra were recorded on a HORIBA
FluoroMax-4 spectrometer. The fluorescence quantum yields
of the compounds in solutions were measured by comparing a
standard (quinine sulfate in 1 N H2SO4 aqueous solution, ΦF =
0.56). The absolute fluorescence quantum yields of the solids
were measured on a HORIBA FluoroMax-4 spectrometer using
an integrating sphere. The transient photoluminescence decay
profiles of the solids were recorded using an Edinburgh
Instrument FLS980 spectrometer equipped with an EPL-375
picosecond pulsed diode laser. Differential scanning
calorimetry (DSC) experiments were recorded on a NETZSCH
DSC 204 instrument at a scanning rate of 5 K min-1. Powder X-
ray diffraction measurements were performed on a Bruker X-
ray diffractometer.
MHz, CDCl3) δ = 10.08 (s, 2H), 8.447 (d, J = 1.8 Hz, 2H), 7.93 (dt,
J = 7.8, 1.2 Hz, 4H), 7.971 (dt, J = 7.8, 1.2 Hz, 4H), 7.803 (dd, J =
8.4, 1.2 Hz, 2H), 7.517 (d, J = 4.2 Hz, 2H), 4.250 (t, J = 7.2 Hz,
2H), 1.436 - 1.254 (m, 9H), 0.958 (t, J = 7.2 Hz, 3H), 0.884 (t, J =
7.2 Hz, 3H).
Synthesis of h-CPDM. 2h (459 mg, 1 mmol) was dissolved in
absolute ethyl alcohol (25 mL) and tetrahydrofuran (15 mL)
and stirred for 30 min at 75 °C. Then malononitrile (145 mg,
2.2 mmol) was added into the solution. After stirred for
additional 8 h, the precipitate was filtered and dried. The
crude product was recrystallized from ethyl ether to afford h-
1
CPDM as orange-red solid in a 64% yield. H NMR (600 MHz,
CDCl3) δ = 8.45 (d, J = 1.2 Hz, 2H), 8.04 (d, J = 8.4 Hz, 4H, 7.91
(d, J = 8.4, 4H), 7.82 (dd, J = 8.4, 1.2 Hz, 2H), 7.79 (s, 2H), 7.55
(d, J = 9.0 Hz, 2H), 4.38 (t, J = 7.2 Hz, 2H), 1.27-1.46 (m, 8H),
0.88 (t, J = 7.2 Hz, 3H). 13C NMR (151 MHz, CDCl3) δ = 159.17,
Synthesis
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry C
Page 3 of 9
View Article Online
DOI: 10.1039/C7TC00559H
Journal Name
ARTICLE
H
N
N
(HO)2B
CHO
N
NC
CN
N
Br
THF, C2H5OH
TBAB, KOH
H2O, Toluene
Br
Br
Pd(PPh3)4, K2CO3
DME, H2O
Br
Br
NC
NC
CN
OHC
CHO
2h
1h
h-CPDM
CN
H
N
N
(HO)2B
CHO
N
Br
NC
CN
N
THF, C2H5OH
TBAB, KOH
H2O, Toluene
Br
Br
Pd(PPh3)4, K2CO3
DME, H2O
Br
Br
NC
NC
CN
2i
1i
OHC
CHO
i-CPDM
CN
Scheme 2 Synthesis of h-CPDM and i-CPDM.
148.08, 141.45, 131.60, 130.32, 129.11, 127.79, 125.66, 123.61, two compounds in various solvents exhibited one
119.41, 114.13, 113.05, 109.86, 81.09, 77.28, 77.03, 76.77, characteristic absorption band in the range of 414-431 nm (Fig.
43.56, 31.54, 29.02, 26.96, 22.54, 14.01. MS (MALDI-TOF, m/z): 1). Meanwhile, both of the two compounds showed similar
710.4 [M + matrix]+, 558.4 [M]+. Anal. Calcd for C38H29N5: C, absorption maxima and profiles in solutions, indicating a small
82.14; H, 5.26; N, 12.6. Found: C, 82.02; H, 5.16; N, 12.53.
change of dipole moment at the ground state in different
Synthesis of i-CPDM. The procedure is similar to the synthesis solvents.15 On the contrary, the emission spectra of h-CPDM
of h-CPDM but using 2i instead of 2h. Compound i-CPDM was and i-CPDM showed strong solvent polarity dependence (Fig.
afforded as red solid by recrystallization in a 34% yield. 1H 2a and 2b). As illustrated in Table 1, the emission bands were
NMR (600 MHz, CDCl3) δ = 8.45 (d,
8.4, 2.4 Hz, 4H), 7.91 (dt, = 9.0, 1.8 Hz, 4H), 7.82 (dd,
1.8 Hz, 2H), 7.79 (s, 2H), 7.53 (d, = 8.4 Hz, 2H), 1.46 - 1.27 (m, hexane to polar DMSO, respectively, which was typical ICT
9H), 0.96 (t, = 7.2 Hz, 3H), 0.88 (t,
= 7.2 Hz, 3H). 13C NMR effect. It was noted that such large solvatochromic shifts of 49
J
= 7.8 Hz, 2H), 8.03 (dt,
J
=
bathochromic shifted from 457 nm to 606 nm and from 451nm
J
J
= 8.4, to 619 nm as increasing the solvent polarity from nonpolar
J
J
J
(151 MHz, CDCl3) δ = 159.19, 148.07, 141.91, 131.61, 130.29, nm (h-CPDM) and 68 nm (i-CPDM) led to distinct fluorescence
129.13, 127.79, 125.63, 123.57, 119.36, 114.14, 113.05, 110.14, colors covering from blue to orange-red, which could be
81.11, 76.89, 76.77, 47.83, 39.53, 31.02, 28.81, 25.62, 24.42, clearly distinguished by naked eyes under a 365 UV lamp (Fig.
23.04, 14.04, 10.92. MS (MALDI-TOF, m/z): 738.4 [M + matrix]+, 2c and2d). The ΦFs of the compounds increased with solvent
586.4 [M]+. Anal. Calcd for C40H33N5: C, 82.3; H, 5.7; N, 12.00.
Found: C, 82.15; H, 5.62; N, 12.23
Result and discussion
Synthesis
The target CPDM homologues were synthesized according to
literatures by a three-step procedure as depicted in Scheme
2.14 Compounds 1h and 1i were synthesized by the alkylation Fig.
1 UV-vis absorption spectra of (a) h-CPDM and (b) i-CPDM in various
solvents (10-5 M).
reaction of 3,6-dibromo-carbazole with bromohexane and
bromo-iso-octane, respectively. 2h and 2i were obtained by
Suzuki reaction of 4-formylphenylboronic acid with 1h and 1i
,
respectively. Finally, h-CPDM and i-CPDM were synthesized by
Knoevenagel condensation reaction of malononitrile with 2h
and 2i, respectively. The chemical structures of h-CPDM and i-
CPDM were fully characterized by 1H NMR, 13C NMR, mass
spectrometry and elemental analysis. Both h-CPDM and i-
CPDM are soluble in common organic solvents such as CHCl3,
CH2Cl2 and THF, but insoluble in methanol and water.
Photophysical properties
UV-Vis absorption and photoluminescence properties of h-
CPDM and i-CPDM were studied in solvents with different
polarities as shown in Fig. 1 and Fig. 2, and the corresponding
data were illustrated in Table 1. The absorption spectra of the
Fig. 2 PL spectra of (a) h-CPDM and (b) i-CPDM in various solvents (10-5 M). Photograph
of (c) h-CPDM and (d) i-CPDM in various solvents under irradiation at 365 nm.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry C
Page 4 of 9
View Article Online
DOI: 10.1039/C7TC00559H
ARTICLE
Journal Name
polarity just in the primary region, and decreased in the very permanent dipole moments of the excited state and the
strong polar solvents, producing a distinct maximum. This up- ground state, respectively. The letter ε0 is the permittivity of
down phenomenon has been observed in some compounds the vacuum,
ε is the static dielectric constant of the solvent, n
with ICT characteristics.16 From hexane to THF, the increased is the refractive index, and ∆ƒ is the orientation polarizability.
ΦF of “negative solvation effect” can be ascribed to the Fig. 3 showed the plots of the Stokes shifts (∆ν) versus
reduction of “the proximity effect” of π-π* and n-π* transition orientational polarizability (∆ƒ). According to the Lippert-
and the “conformation change” of the molecule with the Mataga equation, the slope of the best-fit line was related to
increased solvent polarity.16 With a further increase of the the dipole moment change between the ground state and the
solvent polarity from THF to DMSO, the decreased ΦF of excited state (μe-μg). The values were calculated to be 15224
“positive solvation effect” is attributed to the domination of and 17100 for h-CPDM and i-CPDM, respectively. Comparing
the ICT process. The two competing mechanisms resulted in to some typical molecules that show ICT fluorescence, these
the observed maximum fluorescence quantum yields of 29.0% results indicate a large dipole moment change between the
and 33.6% for h-CPDM and i-CPDM in THF, respectively.
excited state and the ground state.18 In other words, when the
charges transfer from the electron-donating carbazole unit to
the electron-withdrawing dicyanovinyl units in a more polar
solvent, the dipole moment is increased in the excited state.
As a result, the polarized excited state is stabilized to adapt to
the enhanced dipole moment through the relocation of the
polar solvent molecules, resulting in lowered energy and the
red-shifted PL maximum.11 Thus, h- CPDM and i-CPDM whose
ICT states are highly sensitive to the solvent polarity may be
applied to the development of efficient chemical sensors for
the detection of volatile organic compounds.
To better evaluate the effects of solvents on the emission
features, the relationship between the solvent polarity
parameter and the Stokes shift according to the Lippert–
Mataga equation was investigated.17
In which ∆ν stands for the Stokes shift, νa and νe represent the
maximum absorption and emission wavenumbers (cm-1),
Theoretical calculation
respectively. The letter
h is Planck’s constant, c is the speed of
The ICT characteristics of the compounds are further
supported by the density functional theory (DFT) calculation
results. As can be seen in Fig. 4a, for both of the molecules, the
highest occupied molecular orbitals (HOMOs) are mainly
localized on the central carbazole core with sizeable
distribution on the two phenyl rings, whereas the lowest
unoccupied molecular orbitals (LUMOs) are mostly
distributed on the dicyanovinyl units as well as the phenyl
rings. Thus, the spatial separation between the HOMO and
LUMO indicated a typical ICT effect between the electron-
donating moiety and the electron-withdrawing moieties.19
Additionally, it was found that both h-CPDM and i-CPDM
molecules adopted moderately twisted conformations, but
they were different in the symmetry of the skeletons.
Molecule h-CPDM possessed almost symmetrical structure
with the dihedral angles between the substituted phenyl ring
and the central carbazole unit 34.4°/34.5°, while i-CPDM was
less symmetrical, and the corresponding dihedral angles
were34.2°/34.9° (Fig 4b). The geometry parameters of the
light in vacuum, a is the Onsager radius. μe and μg are the
Table 1 Photophysical properties of the compounds in various solvents.
λAbs
λPL
Stokes shift
(cm-1)
ΦF
Compound
Solvent
∆f
(nm)
(nm)
(%)
h-CPDM
Hexane
Toluene
THF
0
415
427
423
420
418
430
423
428
422
416
417
427
457
504
550
598
602
606
451
493
556
599
617
619
2215
3578
5459
7087
7312
6754
1468
3080
5711
7344
7773
7264
10.9
12.7
29.0
1.3
0.012
0.21
0.28
0.29
0.26
0
Acetone
Acetonitrile
DMSO
0.34
0.32
15.0
20.9
33.6
4.3
i-CPDM
Hexane
Toluene
THF
0.012
0.21
0.28
0.29
0.26
Acetone
Acetonitrile
DMSO
0.67
0.55
Fig. 3 Fluorescence Stokes shifts as a function of orientational polarizability ∆f in
various solvents
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry C
Page 5 of 9
View Article Online
DOI: 10.1039/C7TC00559H
Journal Name
ARTICLE
The PL spectra of
h
-CPDM and
i
-CPDM in THF/water
Fig. 4 (a) HOMO and LUMO spatial distributions and (b) geometrically optimized 3D
molecular models in the ground/excited state from the side view of h-CPDM and i-
CPDM by TD-DFT B3LYP/6-31G(d) calculation.
excited states were calculated by means of the time-
dependent density functional theory (TD-DFT). Upon excitation,
the corresponding dihedral angles were decreased to
27.5°/29.0° and 28.0°/29.1° for h-CPDM and i-CPDM
respectively. Furthermore, the C-C distance between the
phenyl ring and the central carbazole unit was declined by 0.01
Å going from the optimized ground state to the excited state
for both of the molecules. These changes of molecular
geometry in the excited state led to large Stokes shift,20 as
verified by the experimental results.
Fig. 5 UV-Vis absorption spectra of (a) h-CPDM and (b) i-CPDM, and fluorescence
spectra of (c) h-CPDM and (d) i-CPDM (10-5 M) in THF/water mixtures with different
water fractions. The effect of water fractions on the maximum emission intensity of (e)
h-CPDM and (f) i-CPDM.
mixtures and the effect of fw on the emission intensity were
shown in Fig. 5c-5f. h-CPDM and i-CPDM exhibited strongest
yellow fluorescence in pure THF peaking at 550 and 556 nm,
respectively. When the water fraction was increased, the
fluorescence maximums showed apparent redshift with a
dramatic decrease in the intensity. This aggregation-caused
emission quenching (ACQ) effect may be attributable to the
the unfavorable π-π interactions between the molecules in the
On the other hand, comparing with the organic fluorophores
with planar or rigid twisted conformation,21 this moderately
twisted skeleton may exhibit fantastic luminescent behaviors,
for example, mechanoresponsive properties in the solid
state.22 Moreover, the linear and branched N-alkyl
substituents afforded different steric hindrance, which would
be expected to play an important role in tuning the
intermolecular interactions or the stability of the crystalline
phases in their aggregated state, and as a result influenced the
corresponding luminescence.
J
-aggregates.13
Mechanoresponsive luminescence properties
To evaluate the possible MRL characteristics of h-CPDM and i-
CPDM, their luminescence behaviors in the solid states were
studied under mechanical stimuli. As shown in Fig. 6 and
Table2, the original powders of h-CPDM and i-CPDM obtained
from the evaporation of the CH2Cl2 solvent emitted very weak
red and orange-red light at 678 nm (ΦF = 0.9%) and 661 nm
Aggregation-caused emission quenching
To investigate the fluorescence behaviors of h-CPDM and i-
CPDM in aggregated states, the UV-vis absorption and PL
spectra in THF/water mixtures with different fraction of water
(fw) were studied (Fig. 5). When the fw was up to 80 and 90%,
the absorption spectra exhibited significant changes and
leveled-off tails clearly appeared in long-wavelength region
(Fig 5a and 5b). This can be ascribed to the well-known Mie
scattering caused by nanosized particles, which indicates that
h-CPDM and i-CPDM molecules aggregate in high water
fractions.8a,23 The red-shifts of λAbs to 438 nm and 430 nm for
h-CPDM and i-CPDM when fw reaches 90% indicate that J-
aggregations may occur.13,24
Fig. 6 Fluorescence spectra of the original and the ground samples of (a) h-CPDM
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry C
Page 6 of 9
View Article Online
DOI: 10.1039/C7TC00559H
ARTICLE
Journal Name
and (b) i-CPDM. Photographs of (c) h-CPDM and (d) i-CPDM before and after
grinding take under a 365 nm UV lamp.
resulting in MRL luminescence turn-on. Comparing with the
liner N-hexyl group of h-CPDM
,
Fig. 7 Time-resolved fluorescence spectra of (a) h-CPDM and (b) i-CPDM in
original and ground state. λex = 375 nm
Fig. 8 XRD patterns of the original and the ground sample of (a) h-CPDM and (b)
i-CPDM
(
ΦF = 0.3%), respectively, which can be regarded as the
-aggregates.13
the branched N-isooctyl substituent of i-CPDM induced larger
steric hindrance, which lowered the phase stability of the
original powders and suppressed the adverse intermolecular
interactions more effectively. So, we suppose that a more
random molecular packing were responsible for the more
significant enhancement of ΦF value for i-CPDM after being
ground.
fluorescent “off” states due to the formed
J
Upon grinding with a pestle, the ground samples showed
luminescence not only in dramactially enhanced intensity, but
also with obvious blue-shift. For h-CPDM, the blue-shift value
was 68 nm, and the ΦF value was increased by 9.7-fold. In the
case of i-CPDM, the fluorescent peak was blue-shifted for 65
nm, while the ΦF value was enlarged by as much as 85-fold
respect to that of the original powders. Thus, both h-CPDM
and i-CPDM exhibited remarkable MRL turn-on behaviors.
The time-resolved emission-decay behaviors of the samples in
original and ground states were investigated to obtain further
information of the MRL turn-on. The fluorescence lifetimes of
h-CPDM and i-CPDM became longer after being ground (Fig. 7
and Table 2), indicating that phase transition might exist
during the grinding treatment.24 Moreover, the radiative rate
constants (krs) of the ground samples were much larger than
the original ones, which should be attributable to the
activation of radiative pathways in the molecular arrangement
of the ground states.
The phase changes in the aggregated states of h-CPDM and
i-CPDM were further confirmed by the DSC analysis (Fig. 9).
There was an endothermic peak at 220 °C (ΔH 49.9 J/g) for h-
CPDM and 222 °C (ΔH 44.3 J/g) for i-CPDM corresponding to
the melting point, respectively. After being ground, exothermic
peaks were appeared at 145 °C (ΔH 36.8 J/g) for h-CPDM and
123 °C (ΔH 32.2 J/g) for i-CPDM, respectively, indicating that
the ground samples were in a metastable state. Thus, the DFT
calculation, combined with the XRD patterns and the DSC
results well demonstrated that the MRL turn-on was derived
from disturbing the molecular packing in the non/weakly
emissive J-aggregates of the moderately twisted molecules in
the π-π stacking directions.
To determine the mechanism of the MRL turn-on, X-ray
diffraction measurement was carried out for each sample (Fig.
8). For the original powders of h-CPDM, there were two sharp
diffraction peaks in the small-angle region at 5.93° and 11.74°
Conclusions
with the
being ground, these two peaks moved to 8.31° and 15.16°,
resulting in decreased -spacings of 10.63 Å and 5.84 Å,
d-spacings of 14.83 Å and 7.53 Å, respectively. After
In summary, two novel A-π-D-π-A molecules with carbazole
donor and dicyanovinyl acceptor but differing in N-hexyl
substitute (h-CPDM) and N-isooctyl substitute (i-CPDM) were
designed and synthesized. Both luminophors showed
remarkable solvatochromic effects: the emission color tuned in
a wide wavelength region from blue to orange-red with the
increase of the solvent polarity. Interestingly, the original
powders of h-CPDM and i-CPDM based on ACQ effect
exhibited MRL turn-on characteristics. XRD and DSC
characterizations revealed that the MRL turn-on mechanism
d
respectively. Meanwhile, two peaks in the wide-angle region
were considerably weakened or diminished: the peaks at 21.85°
and 25.67° with the d-spacings of 4.06 and 3.47 Å, which were
probably caused by the ordered packing of the hexyl chains
through the van der Waals interactions and the π-π stacking of
the aromatic rings, respectively.25 This result indicated that the
grinding treatment decreased the intermolecular distance, and
impaired the ordered arrangement of the hexyl chains and the
was ascribed to the disturbance of the π-π interactions in J-
π-π stacking interactions in J-aggregates, which brought out
aggregates of the moderately twisted molecules. The ground
the enhanced intensity as well as the blue-shift of the
fluorescence. Similar to h-CPDM, the original powders of i-
CPDM also exhibited a well-ordered microcrystalline structure.
The peaks at 8.27° and 15.07° with the d-spacings of 10.68 Å
and 5.87 Å could be indexed to the intermolecular distances.
After being ground, these two diffraction peaks were
disappeared, and the peak for π-π stacking (25.52°, 3.49 Å)
was weakened obviously. The result suggested that most of
the π-π stacking was disturbed to random molecular packing,
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry C
Page 7 of 9
View Article Online
DOI: 10.1039/C7TC00559H
Journal Name
ARTICLE
Fig. 9 DSC curves of the original and ground samples for (a) h-CPDM and (b) i-
CPDM
Table 2. Photophysical properties of the solids in original and ground state
Compound
Original sample
Ground sample
λPL (nm)
ΦF (%)
τ (ns)
kr (ns-1)
knr (ns-1)
λPL (nm)
ΦF (%)
τ (ns)
kr (ns-1)
knr (ns-1)
h-CPDM
i-CPDM
678
661
0.9
0.3
6.37
1.37
0.0014
0.0022
0.156
0.728
610
596
8.7
6.83
1.45
0.012
0.177
0.134
0.513
25.6
Acta. A., 2016, 172, 58-64.(c) J. Q. Tong, Y. J. Wang, J. Mei, J.
Wang, A. J. Qin, J. Z. Sun, B. Z. Tang, Chem. Eur. J., 2014, 20
4661-4670. (d) X. Y. Shen, Y. J. Wang, E. G. Zhao, W. Z. Yuan,
Y. Liu, P. Lu, A. J. Qin, Y. G. Ma, J. Z. Sun and B. Z. Tang, J.
Phys. Chem. C., 2013, 117, 7334-7347.
(a) A. Belay, E. Libnedengel, H. K. Kima and Y. H. Hwanga,
Luminescence, 2016, 15, 133-152. (b) J. P. Bridhkotia, R.
Gahlauta, H. C. Joshib, S. Panta, J. Lumin.. 2011, 131, 1869-
1873. (c) Y. Q Tan, Q. Zhang, J. C. Yua, X. Zhao, Y. P. Tian, Y. J.
Cui, X. P Hao, Y. Yang and G. D. Qian, Dyes Pigments., 2013,
97, 58–64. (d) S. M. Ji, J. Yang, Q. Yang, S. S. Liu, M. D. Chen
and J. Z. Zhao, J. Org. Chem., 2009, 74, 4855-65.
i-CPDM samples displayed more remarkable ФF value increase,
which could be attributed a more random packing of the
molecules caused by the larger steric hindrance of the N-
isooctyl chain. This work would provide a new strategy for
developing dual functional luminophors with solvatochromism
and mechanical-induced emission turn-on behaviors.
,
7
Acknowledgements
This work was financially supported by the National Natural
Science Foundation of China (61605138 and 21303117), the
Qualified Personnel Foundation of Taiyuan University of
Technology (QPFT) (No: tyutrc-201255a), and the Shanxi
Provincial Key Innovative Research Team in Science and
Technology (201513002-10).
8
9
(a) V. K. Chandraa, B. P. Chandrab, J. Lumin., 2012, 132, 858–
869. (b) X. Q. Zhang, Z. G. Chi, Y. Zhang, S. W. Liu, J. R. Xu,
ChemInform, 2013,
J. Luo, L. Y. Li, Y. Song and J. Pei, Chem. Eur. J., 2011, 17
10515 10519.
10 J. W. Chung, Y. You, H. S. Huh, B. K. An, S. J. Yoon, S. H. Kim,
S. W. Lee and S. Y. Park, J. Am. Chem. Soc., 2009, 131
8163 8172.
1, 3376-3390.
,
–
,
–
11 Q. K. Qi, J. Y. Qian, X. Tan, J. B. Zhang, L. J. Wang, B. Xu, B.
Zou and W. J. Tian, Adv. Funct. Mater., 2015, 25, 4005–4010.
12 (a) M. S. Kwon, J. Gierschner, S. J. Yoon and S. Y. Park, Adv.
Mater., 2012, 24, 5487–5492. (b) M. S. Kwon, J. Gierschner,
Notes and references
1
(a) J. Sim, H. Lee, K. Song, S. Biswas, A. Sharma, G. D. Sharma
and J. Ko, J. Mater. Chem. C., 2016, , 3508-3516. (b) J. J.
4
J. Seo and S. Y. Park, J. Mater. Chem. C., 2014, 2, 2552–2557.
Bryant, Y. Zhang, B. D. Lindner, E. A. Davey, A. L. Appleton, X.
Qian and U. H. Bunz, J. Organ. Chem., 2012, 77, 7479-7486.
(c) A. Kumar, V. Kumar, U. Diwan and K. K. Upadhyay,
Sensors. Actuat. B-Chem., 2013, 176, 420-427. (d) I. A.
Karpenko, Y. Niko, V. P. Yakubovskyi, A. O. Gerasov, D.
Bonnet, Y. P. Kovtun and A. S. Klymchenko, J. Mater. Chem. C,
2016, 4, 3002–3009.
N. K. Lifshin, L. Albertazzi, M. Bendikov, P. S. Baran and D
Shabat, J. Am. Chem. Soc., 2012, 134, 20412-20420.
13 K. P. Guo, F. Zhang, S. Guo, K. Li, X. Q. Lu, J. Li, H. Wang, J.
Cheng and Q. Zhao, Chem. Commun., 2017, 53, 1309-1312.
14 (a) K. P. Guo, Z. X. Gao, J. Cheng, Y. Shao, X. Q. Lu, H. Wang,
Dyes Pigments., 2015, 115, 166-171. (b) K. P. Guo, K. Yan, X.
Lu, Y. Qiu, Z. Liu, J. Sun, F. Yan, W. Guo, S. Yang, Org. Lett..
2012, 14, 2214-2217. (c) A. Yassin, T. Rousseau, P. Leriche, A.
Cravino and J. Roncali, Sol. Energ. Mat. Sol. C., 2011, 95, 462-
468.
2
3
4
15 Y. J. Chen, Y. Ling , L. Ding , C. L. Xiang and G. Zhou, J. Mater.
Chem. C., 2016, 4, 8496-8505.
16 (a) P. Wang and S. Wu, J. Lumin., 1994, 62, 33-39. (b) W.A. Jr.
Siebrand and M.Z. Zgierski, J. Chem. Phys., 1980, 72, 1641-
1644.
M. A. Haidekker, T. P. Brady, D. Lichlyter and E. A.
Theodorakis, Bioorg. Chem., 2005, 33, 415-425.
(a) Y. Z. Liu, Y. X. Lei, M. C. Liu, F. Li, H. P. Xiao, J. X. Chen, X.
B. Huang, W. X. Gao, H. Y. Wu and Y. X. Cheng, J. Mater.
Chem. C., 2016, 4, 5970-5980. (b) C. D. Dou, L. Han, S. S.
17 (a) S. Sasaki, G. P. C. Drummen, G.-i. Konishi, J. Mater. Chem.
C, 2016, 4, 2731–2743. (b) J. Zhang, J. Li, W. H. Chen, D.
Zhao, H. Y. Zhang and Y. Wang, J. Phys. Chem. Lett.. 2011,
666-670. (c) Z. H. Guo, Z. X. Jin, J. Y. Wang and J. Pei, Chem.
Commun.. 2014, 50, 6088-6090.
F. Dumur, N. Gautier, N. G. Planas, Y. Sahin, E. Levillain, N.
Mercier and P. Hudhomme, J. Org. Chem., 2004, 69, 2164-
2177.
(a) S. Kothavale, N. Sekar, Dyes Pigments., 2017, 136, 31-45.
(b) D. Babusca , C. Morosanu , D. O. Dorohoi, Spectrochim.
2
,
Zheng, J. S. Yu, H. Wang, B. Xu, Tetrahedron Lett.. 2016, 57
2044–2048.
,
5
6
18 (a) M. Tanaka, M. Muraoka, Y. Matsui, E. Ohta, A. Sakai, T.
Ogaki, Y. Yoshimoto and H. Ikeda, ChemPhotoChem, In press
DOI: 10.1002/cptc.201600028. (b) J. Q. Tong, Y. J. Wang, J.
Mei, J. Wang, A. J. Qin, J. Z. Sun, B. Z. Tang. Chem. Eur. J.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry C
Page 8 of 9
View Article Online
DOI: 10.1039/C7TC00559H
ARTICLE
Journal Name
2014, 20, 4661 – 4670. (c) Y. Niko, S. Sasaki, K. Narushima, D.
K. Sharma, M. Vacha and G.-i. Konishi, J. Org. Chem. 2015, 80
10794–10805.
,
19 X. Lu, Q. Feng, T. Lan, G. Zhou and Z.-S. Wang, Chem. Mater.,
2012, 24, 3179–3187.
20 G.Haberhauer, R. Gleiter, C. Burkhart, Chem. Eur. J. 2016, 22
971–978.
,
21 (a) Q. S. Zhang, J. Li, K. Shizu, S. P. Huang, S. Hirata, H.
Miyazaki and C. Adachi, J. Am. Chem. Soc., 2012, 134, 14706-
14709. (b) G. Mhes, H. Nomura, Q. S. Zhang, T. Nakagawa
and C. Adachi, Angew. Chem. Int. Ed., 2012, 51, 11311–
11315.
22 (a) B. J. Xu, Z. G. Chi, J. Y. Zhang, X. Q. Zhang, H. Y. Li, X. F. Li,
S. W. Liu, Y. Zhang and J. R. Xu, Chem. Asian. J., 2011, 6,
1470–1478. (b) Y. Q. Cao, Y. Xi, X. Y. Teng, Y. Li, X. L. Yan, L. G.
Chen, Dyes Pigments. 2017, 137, 75-83.
23 N. R. Vanier and C. H. Hung. US, US 8486364 B2. 2013.
24 (a) E. Ando, J. Miyazaki, K. Morimoto, Thin Solid Films. 1985,
133, 21–28. (b) S. K. Samanta, S. Bhattacharya, Chem.
Commun., 2012, 49, 1425-1427.
25 (a) C. Ma, X. Zhang, Y. Yang, Z. Ma, L. Yang, Y. Wu, H. Liu, X.
Jia, Y. Wei, J. Mater. Chem. C., 2016, 4, 4786-4791. (b) X.
Zhang, Z. Ma, Y. Yang, X. Zhang, Z. Chi, S. Liu, J. Xu, X. Jia, Y.
Wei, Tetrahedron, 2014, 70, 924-929. (c) P. Xue, J. Sun, P.
Chen, P. Gong, B. Yao, Z. Zhang, C. Qian, R. Lu, J. Mater.
Chem. C., 2015,
26 (a) J. Li, W. Zhou, J. Yang, X. Lang, P. Huang, J. Colloid. Interf.
Sci., 2013, 395, 99 103. (b) L. Zang, Y. Che and J. S. Moore,
3, 4086-4092.
–
ChemInform, 2009, 41, 1596-1608. (c) B. C. Englert, M. D.
Smith, K. I. Hardcastle and U. H. F. Bunz, Macromolecules,
2004, 37, 8212-8221.
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 9 of 9
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C7TC00559H
AꢀπꢀDꢀπꢀA carbzazole derivatives with remarkable solvatochromism
and mechanoreponsive luminescence turnꢀon
Ping Wen,a Zhixiang Gao,b Rong Zhang,a Anran Li,c Fang Zhang,a Jie Li,* a Jingjuan
Xie,a Yuezhen Wu, a Min Wu,a KunPeng Guo* a
a
Ministry of Education Key Laboratory of Interface Science and Engineering in Advanced
Materials, Research Center of Advanced Materials Science and Technology, Taiyuan University of
Technology, Taiyuan, 030024, China. E-mail: lijie01@tyut.edu.cn, guokunpeng@tyut.edu.cn
b
School of Physics and Electronic Science, Shanxi Datong University, Datong 037009, P. R.
China.
c School of Chemistry and Environment, Beihang University, Beijing, P. R. China
∗ Corresponding author.
Table of Contents
Two AꢀπꢀDꢀπꢀA carbzazole derivatives differing in the Nꢀhexyl and Nꢀisooctyl
substitute were developed. They exhibited prominent solvatochromic effect and
luminescence turnꢀon characteristics upon mechanical force stimuli.