Tunable AIEE fluorescence constructed from a triphenylamine luminogen containing quinoline-application in a reversible and tunable pH sensor

Article abstract of DOI:10.1039/c7cp03234j

Herein, tunable emissions in aggregation processes of triphenylamine derivatives (TPAQs) and their protonated cations, as well as protonated processes have been described. In this study, three triphenylamine-based compounds (TPAQs) were synthesized and their optical properties were investigated. Initially, the TPAQs displayed aggregation-induced emission enhancement (AIEE) properties via the restricted intramolecular charge transfer (ICT) state. Interestingly, the single-branched fluorophore (STPAQ) and its protonated cation emitted different color fluorescence in the solution and aggregation state. They emitted green fluorescence, which originated from the intramolecular charge transfer (ICT) state in a strong polar solvent, but the fluorescence bands turned blue, which was attributed to the LE state in the aggregated state. However, the cations of triple-branched fluorophores (TTPAQs) exhibited an inverse tunable emission process from bluish violet fluorescence of the LE state in a weak polar solvent (e.g., THF) to green fluorescence of the ICT state in the aggregated state. In a THF/water mixture solution (f_w = 10%), the STPAQ could switch its emission between blue and green in the pH range of 10.0-0.5. This phenomenon enabled STPAQ to serve as a fluorescent pH sensor in solution. In the powder state, double-branched fluorophores (DTPAQs) could be used as a fluorescent sensor for the detection of acidic and basic organic vapors in the solid state.

Full text of DOI:10.1039/c7cp03234j

View Article Online
View Journal
PCCP
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: M. Zhang, W.
Yang, T. Gong, W. Zhou and R. Xue, Phys. Chem. Chem. Phys., 2017, DOI: 10.1039/C7CP03234J.
Volume 18 Number
1
7
January 2016 Pages 1–636
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
PCCP
Physical Chemistry Chemical Physics
www.rsc.org/pccp
Accepted Manuscripts are published online shortly after
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 1463-9076
PERSPECTIVE
Darya Radziuk and Helmuth Möhwald
Ultrasonically treated liquid interfaces for progress in cleaning and
separation processes
rsc.li/pccp

Page 1 of 20
Physical Chemistry Chemical Physics
View Article Online
DOI: 10.1039/C7CP03234J
Tunable AIEE fluorescence constructed from triphenylamine
luminogen containing quinoline ꢀꢀꢀapplication to reversible and tunable
pH sensor
a
a
a
a
b
Mengmeng Zhang , Wen Yang , Tingfeng Gong , Weiqun Zhou *, Renyu Xue
a
School of Chemistry & Chemical Engineering and Material Science, Soochow University 199
Ren’ai Road, Suzhou, People’s Republic of China, 215123
b
School of Biology and Basic Medical Sciences, Soochow University 199 Ren’ai Road, Suzhou,
People’s Republic of China, 215123
*
Corresponding author. Tel.: +86 0512 65884827.
Eꢀmail address: wqzhou@suda.edu.cn (W. Zhou).
Abstract
It was described that the tunable emissions in aggregated processes of the triphenylamine
derivatives (TPAQs) and their protonated cations, as well as protonated processes. Three
triphenylamineꢀbased compounds (TPAQs) were synthesized and their optical properties were
investigated. Initially, TPAQs had aggregationꢀinduced emission enhancement (AIEE) properties
via the restricted intramolecular charge transfer (ICT) state. Interestingly, the single branch
fluorophore (STPAQ) and its protonated cation emitted the different color fluorescence when they
were in the solution and aggregated state. They emitted the green fluorescence, which originated
from intramolecular charge transfer (ICT) state in the strong polar solvent. But fluorescence bands
turned to the blue fluorescence, which was attributed to LE state in the aggregated state. However,
the cations of the triple branch fluorophores (TTPAQ) exhibited an inverse tunable emission
process from bluish violet fluorescence of the LE state in the weak polar solvent (THF) to the
green fluorescence of the ICT state in the aggregated state. In THF/water mixture solution
w
(f =10%), STPAQ could switch its emission between blue and green in the range of pH (10.0ꢀ0.5).
This phenomenon enabled STPAQ to serve as a fluorescent pH sensor in solution. In powder state,
double branch fluorophores (DTPAQ) could be used as a fluorescent sensor for detecting acidic
and basic organic vapors in solid state.
Introduction

Physical Chemistry Chemical Physics
Page 2 of 20
View Article Online
DOI: 10.1039/C7CP03234J
Fluorophores with a D–π–A system, due to their unique photochemical and intramolecular
[1–3]
charge transfer (ICT) properties , have been the subject of active research and widely applied in
[4–7]
[8ꢀ10]
[11–13]
organic lightꢀemitting diodes , fieldꢀeffect transistors
, nonlinear optics
, photovoltaic
[14–16]
[17–19]
devices
, biological fluorescent probes
and so on. The ICT proceeds with drastic
conformational changes, such as twisting at the bridge between electronꢀdonating and accepting
units in the excited state. Sometimes, the twisted intramolecular charge transfer (TICT) emission
[20ꢀ24]
can be observed
.The TICT emission is useful, especially for developing bioꢀsensing materials
due to the great affect on the intensity and the peak position of the TICT emission by
[25ꢀ32]
environmental factors, such as solvent polarity, temperature and viscosity
.
The discovery of the AIE phenomenon opens a new way to design and synthesize novel
[33]
luminescent molecules , which is wide class of propellerꢀshaped fluorophores that are
nonꢀemissive or weakly emissive in solution but become highly emissive in aggregated states. The
most popular AIE mechanism by experimental and theoretical investigations suggests at the single
[34]
molecular level restriction of intramolecular rotations (RIR) , intramolecular charge transfer
[35]
[36ꢀ38]
[39ꢀ40]
(
ICT) , twisted intramolecular charge transfer (TICT)
, restricted ICT
or cis−trans
[41]
isomerization
.
The triphenylamine (TPA) moiety has been employed as an activator for aggregationꢀinduced
emission and electronꢀdonor for intramolecular charge transfer (ICT) in the construction of
AIEꢀactive luminogens associated with its propellerꢀlike structure and excellent electronꢀdonating
[42–45]
[46]
characters
, which is explained by restriction of rotation , specific molecular packing, such
[47]
as herringbone stacking and intermolecular hydrogen bond interactions . Quinoline has been
used as an electronꢀacceptor group to construct luminogens. The present contribution reports a
distinctive approach for multiꢀbranched triphenylamine which was covalently linked to
triphenylamine centers to induce hindered rotation and the desired emission enhancement. The
molecular structure constructed by the control of intermolecular interactions and the
intramolecular charge transfer (ICT) effect, where the triphenylamine serves as the central donor
core, quinoline as the acceptor and imine conjugated chains serve as the πꢀbridge to extend the
conjugation length at the molecular level, have not yet been reported in the literature. The
triphenylamine derivatives of TPAQs luminogen (Scheme 1) display both remarkable

Page 3 of 20
Physical Chemistry Chemical Physics
View Article Online
DOI: 10.1039/C7CP03234J
solvatochromism and AIEE effect. These new observations indicate that the previously verified
mechanism of the restricted rotation in the aggregation state is not complete in this case.
Some of pH fluorescence probes based on protonation on heteroatomꢀcontaining groups such as
pyridinyl, quinolyl, amino and phenol were designed by a significant impact on the emission
[48ꢀ50]
intensity or color of chromophore
, which led to with these pHꢀsensitive groups. Indeed,
protonation–deprotonation is more readily realized and enjoys the advantages of reversibility, fast
reaction rate and nonꢀdestructive structural transformation. For application of optical data storage
(ODS), the dual/multiꢀchannel output mode intrinsic to fluorescence is more attractive due to
[51]
provide an extra signal for internal calibration and error correction . Based on the pHꢀresponsive
nature of the fluorophores, Hu etal have further developed both WORM and rewritable ODSes.
‘‘0’’ and ‘‘1’’ state of the encoded binary data, corresponding to the TICT and LE emission, can
[51]
be read easily using a spectrofluorophotometer . Moreover, a switchable module comprising
pendant pyridine groups, an amide linkage and a photoswitchable functionality (azobenzene) has
been designed by Singh etal. The module has been exploited for ternary/binary data storage with
nonꢀdestructive optical identity owing to its high photoꢀstability, excellent reversibility, and
[52]
chemicalꢀ/photoꢀswitchability . So, it is believed that fluorescence may be chosen as the next
generation of computerꢀreadable signals because of its scalability, correction capability and
potentially enhanced capacity. Herein we presented a new AIEE system with a reactive quinolyl
group and studied its switchable photoluminescence. It was expected to develop both rewritable
and write once readꢀmany (WORM) ODSes with single or dualꢀchannel outputs.
Results and discussion
Synthesis and structural characterization
Detailed synthetic procedures of the three compounds (STPAQ, DTPAQ and TTPAQ) are
displayed in Scheme 1 and structural characterization could be found at the experimental section
in (Fig. S1–S3).

Physical Chemistry Chemical Physics
Page 4 of 20
View Article Online
DOI: 10.1039/C7CP03234J
N
N
CHO
NH2
STPAQ
N
N
POCl
3
/DMF
N
C
2
H
5
OH/CH
3
COOH
NH2
N
N
N
N
POCl
3
/DMF
N
N
2 5 3
C H OH/CH COOH
1
N
N
N
N
OHC
CHO
DTPAQ
3
N
CHO
NH2
N
3
POCl /DMF
N
N
2 5 3
C H OH/CH COOH
N
TTPAQ
OHC
CHO
N
4
N
Scheme 1 The synthetic route of TPAQs
Optical properties
ICT is a relatively common phenomenon in molecules that consist of a D–A pair. Three
compounds have the same donor, triphenylamine and acceptor, quinoline and the difference of
them is only the number of branches. The UVꢀvisible and fluorescence spectra of the three
compounds in THF are depicted in Fig. S4(a). The low energy side of the absorption spectra was
dominated by a broad and structureless band at greater than or equal to 379 nm and underwent a
bathochromic shift for STPAQ, DTPAQ and TTPAQ due to the enhanced electronic coupling
[46]
between 5ꢀquinolinylimine and triphenylamine . Moreover, STPAQ also exhibited the second
distinctive band near 300 nm, which could be explained that the distortion between quinolyl and
4
ꢀdiphenylamineimine resulted in the decentralization of π electron clouds of the molecule. The
absorption band didn’t appear for both DTPAQ and TTPAQ due to multiꢀbranch coupling effects.
Absorption and PL spectra were also recorded in different polar solvents, such as nꢀhexane, THF,
CH Cl , acetonitrile and methanol (Fig. S4(bꢀd)). The maxima absorption and emission
2
2
wavelength, together with the fluorescence quantum yield (Φ ) in different polar solvents are listed
f
in Table 1. As shown in Table 1 and Fig. S4(bꢀd), the changes in the position of absorption bands
in the spectra were hardly observed, which indicated that the electronic structures in the ground

Page 5 of 20
Physical Chemistry Chemical Physics
View Article Online
DOI: 10.1039/C7CP03234J
state could be preserved from polarity changes. The bands were attributed to the local excited state
[53]
(
LE*) due to π−π* transitions on the triphenylamine moiety , as indicated by calculations (see
Fig. 1). The fluorescent emissions were displayed with the excited at 383, 403 and 400 nm for
STPAQ, DTPAQ and TTPAQ, respectively. The band redꢀshifted faintly with the increase of
branches for PL spectra, which was consistent with the first absorption peak in their UV curves.
Significant characteristics were revealed from the fluorescence spectra in the different solvents.
The emission bands shifted bathochromically with the increase of solvent polarity. Taken STPAQ
as example (Fig.S4(b)), the maximum emission at 436 nm in nꢀhexane shifted to 533 nm in
methanol. Similar solvent effects were also observed in PL spectra of DTPAQ and TTPAQ
(
Fig.S4(c) and Fig.S4(d)). In light of the moderate Stokes shifts of the emissions in nonꢀpolar
solvent (nꢀhexane), the ꢁλ were 57, 54 and 44 nm for STPAQ, DTPAQ and TTPAQ respectively,
which were arranged to the local excited (LE) state originating from π*ꢀπ transition of
triphenylamine. However, in polar solvent, such as methanol, the emission was governed by the
[54ꢀ55]
intramolecular charge transfer (ICT) state
. The emission, exhibiting large spectral shifts
across a wide range (Fig. S4(bꢀd)), showed the obvious charge transfer (CT) characteristics whose
[1]
transition dipole moments were strongly affected by solvent polarity . In polar solutions, the
emission clearly exhibited a positive solvatokinetic effect (Fig. S4(bꢀd)). That was, with increase
of solvent polarity, the emission red shifted together with a decrease of the relative intensity (see
Table 1). A Lippert–Mataga plot (Fig. S4(e)) of Stokes shift against the orientation polarizability
of the solvent gave a significant keen slope. And the Φ reduced with the increase of solvent
f
polarity (Table 1). In order to approve the ICT characteristic, the timeꢀresolved PL spectra of
TPAQs in THF were exhibited in Fig. S5. The fluorescence lifetime of pure THF was also tested.
The emissions had the longer fluorescence lifetime and were coincided with Lippert–Mataga plot.
All of characteristics implied the existance of the ICT state.
Table 1 Some photophysical data of three TPAQs and their protonated cations in pure solvents, aggregated states
and powder states
+
2+
3+
Solvent
nꢀhexane
THF
λmax (nm)
STPAQ
379
STPAQH
DTPAQ
397
DTPAQH
386
2
TTPAQ
400
TTPAQH
384
3
λa
366
λem
436
421
451
439
441
428
Φ
f
(%)
0.78
383
0.54
1.2
0.88
0.82
400
1.1
λ
a
355
403
374
378

Physical Chemistry Chemical Physics
Page 6 of 20
View Article Online
DOI: 10.1039/C7CP03234J
λ
em
465
0.79
385
502
0.42
379
513
0.15
383
533
0.12
466
0.38
363
510
0.16
350
526
0.12
466
0.94
406
489
0.67
399
504
0.32
403
516
0.17
439
0.47
382
465
0.32
374
496
0.13
477
0.72
400
490
0.32
398
503
0.24
400
513
0.10
440
0.8
Φ
f
(%)
λ
a
383
453
0.52
371
466
0.3
Carrene
Acetonitrile
Methanol
λ
em
Φ
f
(%)
λ
a
λem
(%)
Φ
f
λ
a
λ
em
Φ
f
(%)
λ
a
395
465
5.07
355
464
387
490
389
460
0.06
381
492
29.3
383
502
0.57
λem
(%)
Aggregated
Powder
Φ
f
0.028
15.01
I/I
0
(fw(%)) 6.8(90%) 0.1(92%) 18.1(90%)
(%) 4.54 0.04 17.5
0.16(92%)
0.11
40.7(80%) 0.71(95%)
27.56 0.34
Φ
f
+
a
In aggregated state, all of data were obtained in THF/water solution except for λ and λem of STPAQ (methanol/water) and STPAQH
(
acetonitrile/water)
In an effort to understand the electron transition processes, electron distribution of three TPAQs
were obtained by optimizing single molecular stable structures at both the ground and the first
excited states using DFT and TDꢀDFT methods (B3LYP/6ꢀ31G(d)). The configurations,
molecular orbital amplitude plots of HOMO and LUMO and their corresponding energy levels of
three TPAQs are depicted in Fig. 1. The orbital distribution of HOMOꢀ1 is also showed in Fig. 1
to realize the property of the second transition. In the ground states, the electron clouds of all of
HOMOꢀ1, HOMO and LUMO levels were nearly distributed homogeneously, confirming the
absence of the ICT process, which was consistent with UV spectra. The excited energies both
HOMO→LUMO and HOMOꢀ1→LUMO decreased with the increase of the branches, which
corresponded to the bathochromic shift of the UV absorption due to the enhanced electronic
coupling between 5ꢀquinolinylimine and triphenylamine. The frontier molecular orbital
distribution in the first excited states showed the explicit ICT feature, suggesting a typical the
excited ICT process. Taking STPAQ as an example, the first emission transition from LUMO to
HOMO processed a electron transfer from quinolyl to triphenylamineimine. The calculational
transition energy (2.40ev) corresponded to the emission energy in acetonitrile (2.41ev (513 nm,

Page 7 of 20
Physical Chemistry Chemical Physics
View Article Online
DOI: 10.1039/C7CP03234J
Table 1)). The second emission transition from LUMO to HOMOꢀ1 hadn’t obvious ICT
characteristic, which was arranged to π*→π transition. And the transition energy (2.77ev)
corresponded to the emission energy in nꢀhexane (2.84ev (436 nm, Table 1)). For DTPAQ and
TTPAQ, the decentralization distribution were more distinct due to the enhanced electronic
coupling between 5ꢀquinolinylimine and triphenylamine. The transition energies both ꢁELUMO
HOMOꢀ1 reduced for all of TPAQs, but, the reduced latitude of ꢁELUMO
was larger than that of ꢁELUMO HOMO. So, the energy difference of two transitions decreased with
→
HOMO and ꢁELUMO
→
→
HOMOꢀ1
→
the increase of the branch numbers, which coincided with emission spectra.
In consideration of the fluorophores, the twisted intramolecular charge transfer (TICT) model
proposed by Grabowski etal can be more suitable for these molecular system. In all fluorophores,
the diphenylamineimine and quinolyl aren’t in the same plane due to the CꢀN single bond
connected to quinoline twists. The high twist of the CꢀN bond brings to the TICT. The dihedral
angles between quinolyl and diphenylamineimine in single molecule ground, the first excited state
of three TPAQs together with the single crystal of STPAQ are listed in Table 2. First of all, as for
o
STPAQ, the dihedral angle of 80.1 in the first excited state is larger than that in the ground state
o
(
59.9 ). In the subvertical dihedral angles in first excited state, the electron distribution is more
decentralized than that in the ground state , which implies the large distortion conformation in the
excited state will be benefit to the formation of ICT. And the subvertical dihedral angles in first
excited state implied that the ICT state of the luminogens was favorite to the distortion of the
conformation. Electron clouds distribution of the frontier molecular orbital (Fig. 1) supports it.
The electron transition processes a distortion from LUMO (population in quinolyl) to HOMO
(population in triphenylamine). The dihedral angles in the first excited state of DTPAQ and
TTPAQ are less than that of STPAQ and almost consistent with that in the ground state. The less
distortion conformations of the dihedral angles displayed less ICT. So, the slopes in Lippert–
Mataga plot were less than that of STPAQ.
The molecular structure of cisꢀSTPAQ was optimized in the ground and the first excited state
by DFT and TDꢀDFT methods at the level of B3LYP/6ꢀ31G(d) to explore the probability of the
isomerization fluorescence of cisꢀtrans isomers in the excited state. Both configurations were
displayed in Fig. S6. In the ground state, although diphenylphenylimine was nearly perpendicular
o
to the quinoline, the dihedral of CꢀC=NꢀC (Fig. S6) was ꢀ7.3 , closed to the same plane. But, the

Physical Chemistry Chemical Physics
Page 8 of 20
View Article Online
DOI: 10.1039/C7CP03234J
o
dihedral (Fig. S6) of structure in the first excited state was ꢀ93.3 due to the twist of the NꢀC single
bond connected with diphenylphenylimine and quinoline. The subvertical configuration of
cisꢀSTPAQ in the first excited state was similar to that of transꢀSTPAQ in the first excited state.
The energy of cisꢀSTPAQ was only higher 0.09ev than that of transꢀisomer. Thus, these imine
systems couldn’t emit a weak fluorescence originated from the cisꢀtrans isomerization in the
excited state.
Fig. 1 The configurations, the frontier molecular orbital and the energy levels of STPAQ, DTPAQ and TTPAQ in
the ground state and the first excited state obtained by DFT and TDꢀDFT calculations
Table 2 The dihedral angles between phenylimine and quinolyl of TPAQs and their cations, obtained by DFT and
TDꢀDFT calculations (Ground and the first excited state) and XRD determination (Crystal)
o
Dihedral angle( )
State
Ground state
The first
excited
STPAQ DTPAQ TTPAQ
59.9
59.2
58.1
neutral
cation
80.1
53.3
54.0
crystal
41.3
56.2
Ground state
The first
excited
40.1
58.9
40.2
54.1
8
9.2
Aggregated and tunable fluorescence effects of TPAQs

Page 9 of 20
Physical Chemistry Chemical Physics
View Article Online
DOI: 10.1039/C7CP03234J
The AIE properties of these fluorophores were assessed by a typical experiment, which was
done by dissolving each fluorophore in a good solvent (THF) and then adding high proportion of
bad solvent (water). The formation of aggregates can also be confirmed by the changes of UVꢀVis
spectra (Fig. S7(aꢀc)) in THF/water mixtures with various water volume fractions (f
w
). And the
levelledꢀoff tails appeared in the visible region of the UV spectra when f was equal to 80% or
w
more, indicating that the aggregates were probably at nanoscale sizes. As expected, the
precipitated aggregates were more emissive than their solutions (Fig. 2(a–d)). For STPAQ,
aggregated and tunable PL effects from green emission in solvent to blue in aggregated completed
simultaneously with the addition of water. Only adding 10% water, the blue PL at 465 nm (Fig.
ꢀ
5
ꢀ1
2
(a)) in pure THF (5×10 mol·L ) reduced remarkably, due to the increase of the solvent
polarity, which could be caused by the ICT effect. From f =20% to 70%, the emission appeared
the large bathochromic shift. When f was added up to 70%, the emission shifted to green, and the
w
w
maximum emission wavelength was at 526 nm, which was dominated by the TICT state. Continue
diluting THF solution to 80% aqueous mixture, the PL intensity at 526 nm increased continuously.
Simultaneously, a blue fluorescence peak appeared in the left shoulder of the fluorescence, and the
maximum emission wavelength was at 465nm, which was dictated by the LE state. Afterwards,
the TICT fluorescence reduced gradually and disappeared finally with the formation of
aggregation state and the blue LE fluorescence increased gradually until the unchanged.
Obviously, the dual fluorescence of the supposed AIE (from TICT and LE state) can’t be entirely
used to explain just in a proton mixture solution. Before the AIE formation, there is hydrogen
bond (HB) interaction of the water hydrogen with the amine group of TPA. The specific
interaction will decrease the electron releasing ability of such fragment and hence also the TICT
formation, favoring the emission back from the LE.

Physical Chemistry Chemical Physics
Page 10 of 20
View Article Online
DOI: 10.1039/C7CP03234J
Fig. 2 Fluorescence spectra of in solution (pure good solvent) and aggregation state of TPAQs. Solvent mixture for
STPAQ in THF/water (a), in methanol/water (b), DTPAQ (c) and TTPAQ (d) in THF/water. Insets in the upper
right corner are fluorescence microꢀimagings (b (STPAQ), c (DTPAQ) and d (TTPAQ)) at the excited wavelength
of 365nm and the upper centre is fluorescence imaging (b) of STPAQ under UV light with the wavelength of
3
65nm.
[36]
The fluorescence annihilation at 526 nm could be explained by restricted ICT mechanism
.
The single crystal of STPAQ was obtained by a slow solution diffusion method, and its molecular
conformation and packing manners were investigated by using single crystal Xꢀray diffraction.
The crystallographic data was deposited by Cambridge crystallographic data, CCDC number was
[46]
1
536071. The ORTEP diagram was shown in Fig. 3(a). Similar to triphenylamine derivatives
,
STPAQ also adopted a twisted conformation in the crystals. The propellerꢀshaped triphenylamine
group could cause the steric hindrance effect to hinder the tight intermolecular packing. The
o
dihedral angle between quinolyl and triphenylamineimine (Table 2) was 41.3 and less than that
o
(
59.9 ) in single molecule obtained by DFT calculation, which generated the reduced TICT in
crystal and resulted in the annihilation of TICT fluorescence at 526 nm. Furthermore, the reducing
torsional angle predicated the enhancement of πꢀconjugation. So, the blue LE emission at 465 nm
was observed. Moreover, the intermolecular interactions in the crystals restricted intramolecular
rotations, fixed the molecular conformation and strengthened LE fluorescence. Along the long and
short axes of the molecular backbone, the twisted molecules adopted headꢀtoꢀtail and slipped
faceꢀtoꢀface packing, respectively in Fig. 3(b). The schiff base chains of two molecules formed a
herringbone dimer stacking by a weak interaction C···C (3.372 Å, Fig. 3(b)). Adjacent molecules
packed in headꢀtoꢀtail Jꢀstacking together by two C···H interactions (2.883 Å and 2.705 Å). The
threeꢀatomic interactions, C···H···C (2.356 Å, 2.854 Å) brought in a parallel Hꢀstacking (Fig.
3
(b)), which resulted in a weak AIEE of LE fluorescence (Table 1 and Fig .2).

Page 11 of 20
Physical Chemistry Chemical Physics
View Article Online
DOI: 10.1039/C7CP03234J
(
a)
(
b)
Fig. 3 The ORTEP diagram (a) and some intermolecular interactions (b) in the crystal of STPAQ
To obtain a clear tunable PL effect of STPAQ, AIE effect was investigated in a polar solvent,
methanol, then adding high proportion of water, which was displayed in Fig. 2(b). STPAQ emitted
a green weak TICT fluorescence (λmax =533 nm) in pure methanol. However, the blue local
fluorescence was observed in aggregation state. The fluorescence imaging in the inserted left
picture of Fig. 2(b) displayed the color difference in both pure methanol and aggregation state
under 365 nm UV light. Fluorescence microscopy image at the excited of 365 nm in the inserted
right picture of Fig. 2(b) displayed a strong blue emission light.
Compared with STPAQ, for DTPAQ and TTPAQ, the weak TICT state resulted in the
hypsochromic shift of TICT emission. Additionally, the enhanced πꢀconjugation led to the
bathochromic shift of the LE emission. Both TICT and LE states closed to each other, double
emissions phenomenon disappeared. Thus, the tunable fluorescence wasn’t obvious. The emission
wavelength in THF at 466 nm (DTPAQ) and 477 nm (TTPAQ) only turned to 490 nm (DTPAQ)
and 492nm (TTPAQ) in aggregated state. But, the aggregations of DTPAQ and TTPAQ
effectively blocked the TICT process and enhanced AIE effect. AIE effect (I/I ) increased from
0
6
.8ꢀfold (STPAQ) to 18.1 (DTPAQ) and 40.7 (TTPAQ). Fluorescence microscopy images at the
excited of 365 nm are displayed in the inserted right pictures of Fig. 2 (c (DTPAQ) and d
TTPAQ)).
To better understand the AIE mechanisms, SEM images of their aggregates were studied (Fig.
(
S8). As shown in Fig. S8, three compounds showed spheroidal (STPAQ), cubic block (DTPAQ)
and column (TTPAQ) like nanoꢀaggregates with diameters in the range of 100–400 nm,
respectively. All of fluorescence microꢀimages supported the nanoꢀmicroꢀstructures with SEM.
Tunable fluorescence effect of the cations
The formation of the cations and the reversibility of protonation and deprotonation are
displayed in Scheme S1.The cations were achieved in acidified THF by adding trifluoroacetic acid

Physical Chemistry Chemical Physics
Page 12 of 20
View Article Online
DOI: 10.1039/C7CP03234J
1
(
TFA) to complete protonation of TPAQs monitored by H NMR (Fig. S9). The quinoline protons
(
a and b) changed after protonation because of the transformation of the quinoline in STPAQ to an
+
1
electronꢀdeficient quinolinium unit in STPAQH . The H NMR spectra restored fully when an
excess of triethylamine (TEA) was injected into the solution, which indicated that the
transformation between TPAQs and their cations were completely reversible. Theoretically, the
cations of TPAQs should have the strong ICT effect due to the absence of electron of cations.
Investigation of ICT effect was carried out by determining photophysical properties in the
different polarity solvents, which are displayed in Fig. S10. The fluorescence emissions of three
cations in pure THF (Fig. S10(a)) showed the hypsochromic shift of the fluorescence bands with
the increase of branches. When the solvent polarity changed from nꢀhexane to acetonitrile, the
changes in the position of absorption bands in the spectra were hardly observed (Fig. S10(bꢀd)),
which further showed that the unchanged electronic structures in the ground state from polarity
changes. But the changes were revealed from the fluorescence spectra. It was a pity that all cations
didn’t emit fluorescence in methanol, which could be attributed to the intermolecular charge
transfer between the cations and methanol molecule or the intermolecular hydrogen bond
f
interactions. Similar to the neutral molecules, the bathochromic shift and reduced Φ (Table 1) of
the emission bands were observed with the increase of the solvent polarity. For the cation of
STPAQ, Lippert–Mataga plot (Fig. S10(e)) gave a more steep slope than that of neutral molecule,
which implied the existance of the stronger ICT state.
To further obtain insights into the structureꢀphotophysical properties relationship, the stable
single molecular structure of cation of STPAQ was optimized by DFT and TDꢀ DFT method at the
ground and the first excited state. Frontier molecular orbitals of three cations are depicted in Fig. 4.
o
The dihedral angle between quinolyl and triphenylamineimine was 89.2 (Table 2) in the molecule
+
o
of STPAQH , closed to perpendicular and larger than that in neutral state (59.9 ). So, the TICT
model was also suitable for the cation system. The more distorted molecules were, the stronger
TICT fluorescence emitted in polar solvent. Additionally, because of the increase of distortion of
the molecules, the cations reduced electronic coupling between quinolyl and triphenylamineimine
and resulted in the less extended πꢀconjugation length on the long axis of the molecule. It was
result that the local fluorescence bands of the cations hypsochromic shifted with the increase of
the branches in THF. From Table 2, the dihedral angles between triphenylamineimine and

Page 13 of 20
Physical Chemistry Chemical Physics
View Article Online
DOI: 10.1039/C7CP03234J
quinolyl of the cations of DTPAQ and TTPAQ were nearly the same as that of neutral molecules,
which resulted in a consistent slopes of Lippert–Mataga plot with neutral molecules.
+
2+
3+
Fig. 4 Frontier molecular orbitals of STPAQH , DTPAQH
2
and TTPAQH
3
in the ground state and the first
excited state from left to right
We studied the AIE phenomenon of the three cations. The UV absorption spectra in various
THF/water solutions are displayed in Fig. S11(aꢀc). The changes in the UV spectra with varying
water volume fractions could confirm the formation of aggregates of cations. Meanwhile,
leveledꢀoff tails appeared in the visible region when the f
that the aggregates were probably of nanoscale sizes. AIE effect of cations is depicted in Fig.
(aꢀd). All of cations didn’t exhibit AIE. The fluorescence intensity of three cations in the
w
was equal to 90% or more, indicating
5
aggregated state was less than that of the neutral molecules. I/I
0
were 0.1 (STPAQ), 0.16 (DTPAQ)
+
and 0.71 (TTPAQ). From Fig. 5(a), the maximum emission at 466 nm of STPAQH dominated by
the LE state in THF shifted red with the addition of water, which was governed by TICT state.
+
When STPAQH was aggregated, TICT state was restrained, and displayed back a weak LE
fluorescence (464 nm). Tunable fluorescence effect was investigated in a polar solvent,
acetonitrile and then adding high proportion of water, which was displayed in Fig. 5(b). A green
ꢀ5
ꢀ1
TICT fluorescence (λmax =526 nm) in pure acetonitrile (5×10 mol·L ) transformed gradually into
the blue local fluorescence in aggregation state. The fluorescence imaging under 365 nm UV light
displayed in the inserted pictures of Fig. 5(b) gave an obvious color difference.
Tunable fluorescence appearance of the cation of TTPAQ was different from that of STPAQ
+
and STPAQH . The cations of TTPAQ displayed a strong bluish violet fluorescence at 422 nm in
pure THF. Only adding 10% water, the fluorescence at 422 nm disappeared immediately and

Physical Chemistry Chemical Physics
Page 14 of 20
View Article Online
DOI: 10.1039/C7CP03234J
exhibited a broad strong green fluorescence band at 513 nm which was attributed to the TICT state.
Afterwards, the PL decreased with the increase of water until 60% aqueous mixture. Adding water
continuously, the PL enhanced slowly and up to invariablenes and showed an ICT fluorescence.
The cations of TTPAQ presented the more deficiency electrons of three positive charge cation
system than that of TTPAQ, which resulted in the strong interactions between cations and anions
in the aggregated state. So, the cations displayed ICT fluorescence. The fluorescence imaging
under 365 nm UV light displayed in the inserted pictures of Fig. 5(d) gave an obvious color
difference.
Fig. S8 displays SEM images of the three cations. In the SEM images, all nanoparticles were in
spherical shape with an average size of around 100ꢀ200 nm. This result gives direct evidence of
molecular aggregation, which is consistent with UV determination.
Fig. 5 Fluorescence spectra of in solution (pure good solvent) and aggregation state of three cations. Solvent
mixture for the cations of STPAQ in THF/water (a), in acetonitrile/water (b), DTPAQ (c) and TTPAQ (d) in
THF/water. The insets are fluorescence imagings under UV light with the wavelength of 365nm.
pH sensing and tunable fluorescence effect
w
UV and fluorescence titrations in THF/water (f =10%) are displayed in Fig. 6. Some

Page 15 of 20
Physical Chemistry Chemical Physics
View Article Online
DOI: 10.1039/C7CP03234J
photophysical data of three TPAQs in different pH (THF/water, V/V=9/1) are listed in Table 3.
The UV spectra remained almost unchanged from pH=5.0 to pH=10.0. Above pH =5.0, the
maximum absorption appeared at 386 nm (STPAQ), 403 nm (DTPAQ) and 400 nm (TTPAQ).
When pH<5.0, the absorption shifted blue gradually and until the invariableness of the new
absorption at 357 nm (STPAQ), 374 nm (DTPAQ) and 370 nm (TTPAQ) finally with pH
decreasing. The fluorescence titration was almost similar to UV titration. The fluorescence
emission of STPAQ remained almost unchanged from pH=5.0 to pH=10.0. From pH=5.0 to 0.5,
the emission at 435 nm disappeared and a new emission in lower energy at about 498 nm appeared.
At pH=2.0, the new emission was up to the maximum, and the I/I was 19.6. It indicated that
0
STPAQ molecules accomplished the protonated process.
Fig. 6 UV and fluorescence titrations of STPAQ (a), DTPAQ (b) and TTPAQ (c) in THF/water solution (V/V=9/1)
The fluorescence titrations of DTPAQ and TTPAQ were similar to that of STPAQ. From Table
3
5
, the values of I/I enhanced with the increase of branches and the I/I were 22.1 (DTPAQ) and
0 0
2.1 (TTPAQ), which illustrated the sensibility of pH increased with the increase of branches.
Here, it was attributed to multiꢀbranches TICT cooperating effect.
w
Tunable fluorescence was observed to STPAQ in THF/water solution (f =10%) with the pH
decrease. STPAQ displayed a blue weak LE fluorescence at 435 nm between pH=6 to 10.
However, when pH=5, the green ICT emission (λmax =498 nm) was observed and stronger than the

Physical Chemistry Chemical Physics
Page 16 of 20
View Article Online
DOI: 10.1039/C7CP03234J
former. And when pH <4, the green strong ICT emission increased and covered the LE
fluorescence. It further indicated that TICT state of the cation was stronger than that STPAQ. The
fluorescence imaging under 365 nm UV light displayed in the inserted pictures of Fig. 6(a) gave
an obvious color difference.
Table 3 Some photophysical data of three TPAQs in different pH (THF/water, V/V=9/1)
Maximum Wavelength
λ
a
(nm)
λ
em (nm)
pH<3
STPAQ
357
386
498
435
19.6
493
460
22.1
488
463
52.1
pH>4
I/I
DTPAQ
I/I
0
pH<3
pH>5
374
403
0
pH<3
pH>5
370
400
TTPAQ
I/I0
Application
The luminescent materials responsive to acid/alkali might be more attractive because a
switchable (or tunable) emission was readily obtained based on the repeated protonation and
deprotonation process. Taken DTPAQ as an example, because of the reversible emission of
DTPAQ by repeated deprotonation and protonation, we can use DTPAQ to determine volatile
organic compounds with high acidity and basicity. A thinꢀlayer of chromatography (TLC) plate
was used as solid support. The dyeꢀloaded plate emitted a faint yellow light due to the partial
2
+
transformation of DTPAQ to DTPAQH
2
by the weak acidity of the silica gel (Fig. 7 top (left)).
After fuming with TFA vapors, the dye spot turned orange and emitted weak blue fluorescence
under UV lamp (365 nm). However, the luminous point converted back to its pale yellow state and
bluish green emissive neutral form (right) when treated with TEA vapors. The switch between the
bluish green and blue states can be repeated many times without fatigue by alternately fuming
with TEA and TFA vapors as the process is nonꢀdestructive in nature.

Page 17 of 20
Physical Chemistry Chemical Physics
View Article Online
DOI: 10.1039/C7CP03234J
Fig. 7 Photos of DTPAQ spots on a TLC plate before (left) and after fuming with (central) TFA and (right) TEA
vapors under normal room lighting (RL) (top) and UV illumination (365 nm) (bottom).
Conclusions
In this paper, three triphenylamineꢀbased compounds (TPAQs), namely STPAQ, DTPAQ and
TTPAQ, were designed and synthesized. In light of the existance of ICT state, AIE properties
were investigated by using a good strong polar (methanol or acetonitrile) or weak polar solvent
(THF), and a bad solvent (water). The AIEE effect enhanced with the increase of the quinolyl
branches. Tunable emission phenomena were observed accompanied with AIEE effect. The
fluorescence emission of both neutral and cation of STPAQ turned from green originated from
TICT state in polar solvent (methanol and acetonitrile) to blue attributed to LE state in aggregated
state due to restrained TICT. The cation of TTPAQ emitted the fluorescence from bluish violet
(
LE) in weak polar solvent (THF), to green (ICT) in aggregated state due to the large absence of
3
+
electrons of TTPAQH
3
and cationꢀanion interactions in crystal. TPAQs emission can be
reversibly switched by repeated protonation and deprotonation, indicates TPAQs can work as a
fluorescent pH sensor in 10% water solution and a chemosensor for detecting volatile organic
compounds with high acidity and basicity. The results of this study also provide valuable
information for the future design of new fluorescent probes, whose lightꢀemitting behaviors can be
readily tuned by simply varying the environmental conditions.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (No. 51079094),
the Natural Science Foundation of Jiangsu Province (No. BK2010215), and the Natural science
fund for colleges and universities in Jiangsu Province (No. 16KJD150002). The Project was

Physical Chemistry Chemical Physics
Page 18 of 20
View Article Online
DOI: 10.1039/C7CP03234J
funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.
Reference
1
2
3
Z. R. Grabowski and K. Rotkiewicz, Chem. Rev., 2003, 103, 3899ꢀ4031.
Y. Zhu, S. Guang, X. Su, H. Xu and D. Xu, Dyes Pigm., 2013, 97, 175ꢀ183.
W. Z. Yuan, Y. Y. Gong, S. M. Chen, X. Y. Shen, J. W. Y. Lam, P. Lu, Y. W. Lu, Z. M. Wang,
R. R. Hu, N. Xie, H. S. Kwok, Y. M. Zhang, J. Z. Sun and B. Z. Tang, Chem. Mater., 2012, 24,
1518ꢀ1528.
4
5
A. J. Heeger, Chem. Soc. Rev., 2010, 39, 2354ꢀ2371.
R. H. Friend, R. W. Gymer, A. B. Holmes, J. H. Burroughes, R. N. Marks, C. Taliani, D. D.
Bradley, S. D. Dos, J. L. Bredas, M. Logdlund and W. R. Salaneck, Nature, 1999, 397,
121ꢀ128.
6
7
8
Y. Shirota, J. Mater. Chem., 2005, 15, 75ꢀ93.
K. R. Justin Thomas, J. T. Lin, Y. T. Tao and C. H. Chuen, Chem. Mater., 2004, 16, 5437ꢀ5444.
T. Lei, Y. Cao, Y. L. Fan, C. J. Liu, S. C. Yuan and J. Pei, J. Am. Chem. Soc., 2011, 133,
6099ꢀ6101.
9
1
1
1
P. T. Wu, F. S. Kim and S. A. Jenekhe, Chem. Mater., 2011, 23, 4618ꢀ4624.
0 F. S. Kim, X. G. Guo, M. D. Watson and S. A. Jenekhe, Adv. Mater., 2010, 22, 478ꢀ482.
1 G. S. He, L. S. Tan, Q. Zheng and P. N. Prasad, Chem. Rev., 2008, 108, 1245ꢀ1330.
2 P. L. Wu, X. J. Feng, H. L. Tam, M. S. Wong and K. W. Cheah, J. Am. Chem. Soc., 2009, 131,
886ꢀ887.
1
1
1
1
1
3 E. Maǒas, G. Marcelo, S. Pinto, T. Can˜eque, A. M. Cuadro, J. J. Vaquero and J. M. G.
Martinho, Chem. Commun., 2011, 47, 7374ꢀ7376.
4 A. Mishra, C. Uhrich, E. Reinold, M. Pfeiffer and P. Ba¨uerle, Adv. Energy Mater., 2011, 1,
2
65ꢀ273.
5 H. X. Zhou, L. Q. Yang, S. C. Price, K. J. Knight and W. You, Angew. Chem., 2010, 122,
164ꢀ8167.
8
6 X. Zhang, J. W. Shim, S. P. Tiwari, Q. Zhang, J. E. Norton, P. T. Wu, S. Barlow, S. A. Jenekhe,
B. Kippelen, J. L. Bre′das and S. R. Marder, J. Mater. Chem., 2011, 21, 4971ꢀ4982.
7 F. Qian, C. Zhang, Y. Zhang, W. He, X. Gao, P. Hu and Z. Guo, J. Am. Chem. Soc., 2009, 131,
1460ꢀ1468.
18 E. Kim and S. B. Park, Chem. – Asian J., 2009, 4, 1646ꢀ1658.
19 P. Y. Gu, C. J. Lu, Z. J. Hu, N. J. Li, T. T. Zhao, Q. F. Xu, Q. H. Xu, J. D. Zhang and J. M. Lu,
J. Mater. Chem. C., 2013, 1, 2599ꢀ2606.
20 E. Lippert, W. Lgder, H. Boss in Advances in Molecular Spectroscopy (Ed.: A. Marngini),
Pergamon Press, Oxford, 1962, p. 443.
21 A. Siemiarczuk, Z. R. Grabowski, A. Krlwczyn´ ski, M. Asher, M. Ottolenghi, Chem. Phys.
Lett., 1977, 51, 315ꢀ320.
22 Z. R. Grabowski, K. Rotkiewicz and A. Siemiarczuk, J. Lumin., 1979, 18ꢀ19, Part 1, 420ꢀ424.
23 J. Wu, W. Liu, J. Ge, H. Zhang and P. Wang, Chem. Soc. Rev., 2011, 40, 3483ꢀ3495.
24 K. Hamasaki, H. Ikeda, A. Nakamura, A. Ueno, F. Toda, I. Suzuki and T. Osa, J. Am. Chem.
Soc., 1993, 115, 5035ꢀ5040.
25 S. Sasaki, S. Suzuki, W. M. C. Sameera, K. Igawa, K. Morokuma and G. Konishi, J. Am.

Page 19 of 20
Physical Chemistry Chemical Physics
View Article Online
DOI: 10.1039/C7CP03234J
Chem. Soc., 2016, 138, 8194ꢀ8206.
26 N. P. F. Barthes, I. A. Karpenko, D. Dziuba, M. Spadafora, J. Auffret, A. P. Demchenko, Y.
Mely, R. Benhida, B. Y. Michel and A. Burger, RSC Adv., 2015, 5, 33536ꢀ33545.
27 A. Okamoto, K. Tainaka, K. Nishiza and I. Saito, J. Am. Chem. Soc., 2005, 127, 13128ꢀ13129.
28 A. Suzuki, N. Nemoto, I. Saito and Y. Saito, Org. Biomol. Chem., 2014, 12, 660ꢀ666.
29 J. Feng, K. Tian, D. Hu, S. Wang, S. Li, Y. Zeng, Y. Li and G. Yang, Angew.Chem., Int. Ed.
2
011, 50, 8072ꢀ8076; Angew. Chem., 2011, 123, 8222ꢀ8226.
0 H. Dong, Y. Wei, W. Zhang, C. Wei, C. Zhang, J. Yao and Y. S. Zhao, J. Am. Chem. Soc.,
016, 138, 1118ꢀ1121.
1 Y. Wei, H. Dong, C. Wei, W. Zhang, Y. Yan and Y. S. Zhao, Adv. Mater., 2016, 28,
424ꢀ7429.
3
3
2
7
3
2 H. Dong, C. Zhang, J. Yao and Y. S. Zhao, Chem. Asian J., 2016, 11, 2656ꢀ2661.
3 J. D. Luo, Z. L. Xie, J. W. Y. Lam, L. Cheng, H. Y. Chen, C. F. Qiu, H. S. Kwok, X. W. Zhan,
Y. Q. Liu, D. B. Zhu and B. Z. Tang, Chem. Commun., 2001, 1740ꢀ1741.
4 Y. Hong, J. W. Y. Lam and B. Z. Tang, Chem. Commun., 2009, 4332ꢀ4353.
5 P. Y. Gu, C. J. Lu, F. L. Ye, J. F. Ge, Q. F. Xu, Z. J. Hu, N. J. Li and J. M. Lu, Chem.
Commun., 2012, 48, 10234ꢀ10236.
3
3
3
3
3
3
3
4
4
4
6 B. R. Gao, H. Y. Wang, Y. W. Hao, L. M. Fu, H. H. Fang, Y. Jiang, L. Wang, Q. D. Chen, H.
Xia and L. Y. Pan, J. Phys. Chem. B., 2009, 114, 128ꢀ134.
7 M. Cai, Z. Gao, X. Zhou, X. Wang, S. Chen, Y. Zhao, Y. Qian, N. Shi, B. Mi and L. Xie, Phys.
Chem. Chem. Phys., 2012, 14, 5289ꢀ5296.
8 H. Naito, K. Nishino, Y. Morisaki, K. Tanaka and Y. Chujo, Angew. Chem., Int. Ed. 2017, 56,
2
54ꢀ259.
9 Z. Q. Liang, X. M. Wang, G. L. Dai, Ch. Q. Ye, Y. Y. Zhou and X. T. Tao, New J. Chem.,
015, 39, 8874ꢀ8880.
2
0 Z. Q. Yan, Z. Y. Yang, H. Wang, A. W. Li, L. P. Wang, H. Yang, B. R. Gao, Spectrochimica
Acta Part A., 2011, 78, 1640ꢀ1645.
1 Z. Xie, B. Yang, F. Li, G. Cheng, L. Liu, G. Yang, H. Xu, L. Ye, M. Hanif and S. Liu, J. Am.
Chem. Soc., 2005, 127, 14152ꢀ14153.
2 J. Mei, Y. Hong, J. W. Y. Lam, A. Qin, Y. Tang and B. Tang, Adv. Mater., 2014, 26,
5429ꢀ5479.
43 L. Zhang, Y. T. Chen and J. Z. Jiang, Dyes Pigm., 2016, 124, 110ꢀ119.
44 Y. Tao, Q. Wang, Y. Shang, C. Yang, L. Ao, J. Qin, D. Ma and Z. Shuai, Chem. Commun.,
2009, 77.
4
4
5 B. Liu, Q. Zhang, H. J. Ding, J. Y. Wu and Y. P. Tian, Dyes Pigm., 2012, 95, 149ꢀ160.
6 C. C. Li, W. Yang, W. Q. Zhou,* M. M. Zhang, R. Y. Xue, M. Y. Li and Z. Q. Cheng, New J.
Chem., 2016, 40, 8837.
47 W. Yang, C. C. Li, M. M. Zhang, W. Q. Zhou,* R. Y. Xue, H. L. Liu and Y. Y. Li, Phys.
Chem. Chem. Phys., 2016, 18, 28052.
48 X. F. Ma, J. H. Cheng, J. Y. Liu, X. G. Zhou and H. F. Xiang, New J. Chem., 2015, 39,
492ꢀ500.
4
9 Z. Y. Yang, W. Qin, J. W. Y. Lam, S. J. Chen, H. Y. Sung, I. D. Williams and B. Z. Tang,
Chem Sci., 2013, 4, 3725ꢀ3730.
50 X. D. Yang, Y. Gao, Z. B. Huang, X. H. Chen, Z. Y. Ke, P. L. Zhao, Y. C. Yan, R. Y. Liu and

Physical Chemistry Chemical Physics
Page 20 of 20
View Article Online
DOI: 10.1039/C7CP03234J
J. Q. Qu, Mater. Sci. Eng., C, 2015, 52, 97ꢀ102.
1 L. Y. Hu, Y. A. Duan, Z. Z. Xu, J. Yuan, Y. P. Dong and T. Y. Han, J. Mater. Chem. C., 2016,
, 5334ꢀ5341.
2 A. K. Singh, P. K. Yadav, N. Kumari, R. Nagarajan and L. Mishra, J. Mater. Chem. C., 2015, 3,
2123ꢀ12129.
5
5
5
5
5
4
1
3 M. Aydemir, G. Haykır, F. Türksoy, S. Gümüꢂ, F. B. Dias and A. P. Monkman, Phys. Chem.
Chem. Phys., 2015, 17, 25572ꢀ25582.
4 L. O. Pålsson, C. S. Wang, A. S. Batsanov, S. M. King, A. Beeby, A. P. Monkman and M. R.
Bryce, Chem. Eur. J., 2010, 16, 1470ꢀ1479.
5 D. Fan, Y. P. Yi, Z. D. Li, W. J. Liu, Q. Peng and Z. G. Shuai, J. Phys. Chem. A., 2015, 119,
5233ꢀ5240.
56 X. F. Zhang, Y. K. Zhang, L. M. Liu, J Lumin., 2014, 145, 448ꢀ453.
57 S. A. Svarovsky, R. H. Simoyi and S. V. Makarov, J. Phys. Chem. B., 2001, 105, 12634.
5
5
6
8 A. D. Becke, J. Chem. Phys., 1993, 98, 5648.
9 A. D. Becke, J. Chem. Phys., 1992, 96, 2155.
0 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G.
Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P.
Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T.
Vreven, J. E. Montgomery, J. A. Peralta Jr, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K.
N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C.
Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B.
Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J.
Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski,
G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas, J. B.
Foresman, J. V. Ortiz, J. Cioslowski and D. J. Fox, Gaussian 09, Gaussian, Inc, Wallingford,
CT, 2009.