Aggregation-Induced Emission and Sensing Characteristics of Triarylborane–Oligothiophene–Dicyanovinyl Triads

Article abstract of DOI:10.1002/chem.201603349

The design, synthesis and aggregation-induced emission properties of a new series of triarylborane–oligothiophene–dicyanovinyl (DCV) conjugates 4–6 (A–D–A’ type molecular configuration) are reported. The optical properties of 4–6 can be modulated by judiciously varying the number of thiophene units between electron deficient boryl and dicyanovinyl units. Compound 6 with terthiophene spacer showed highly red-shifted absorption and emission compared to 5 and 4 with bithiophene and monothiophene spacers, respectively. Compounds 5 and 6 show aggregation-induced emission enhancement in water/THF mixtures. Compounds 5 and 6 also showed solvent viscosity dependent emission characteristics. All the three compounds show distinct optical responses for small anions such as fluoride and cyanide. Filter paper strips coated with compounds 5 and 6 can detect F^?and CN^?in aqueous media with different colorimetric responses.

Full text of DOI:10.1002/chem.201603349

DOI: 10.1002/chem.201603349
Full Paper
&
Fluorescent Sensors |Hot Paper|
Aggregation-Induced Emission and Sensing Characteristics of
Triarylborane–Oligothiophene–Dicyanovinyl Triads
George Rajendra Kumar, Samir Kumar Sarkar, and Pakkirisamy Thilagar*[a]
Abstract: The design, synthesis and aggregation-induced
emission properties of a new series of triarylborane–oligo-
thiophene–dicyanovinyl (DCV) conjugates 4–6 (A–D–A’ type
molecular configuration) are reported. The optical properties
of 4–6 can be modulated by judiciously varying the number
of thiophene units between electron deficient boryl and di-
cyanovinyl units. Compound 6 with terthiophene spacer
showed highly red-shifted absorption and emission com-
pared to 5 and 4 with bithiophene and monothiophene
spacers, respectively. Compounds 5 and 6 show aggrega-
tion-induced emission enhancement in water/THF mixtures.
Compounds 5 and 6 also showed solvent viscosity depen-
dent emission characteristics. All the three compounds show
distinct optical responses for small anions such as fluoride
and cyanide. Filter paper strips coated with compounds 5
and 6 can detect Fꢀ and CNꢀ in aqueous media with differ-
ent colorimetric responses.
ics.[7] In this regard, seminal work has been carried out by Tang
and Parker.[6a–c] Recently, chemical modifications of AIE lumino-
gens with other functional units such as triarylborane, poly-
mers, crown ethers, peptides and metal complexes have also
been studied actively.[8] As a versatile fluorophore, triarylbor-
anes (TAB) have gained special attention for various purposes
for the last two decades.[9] Very recently, Chujo et al. and
others have developed tri- and tetra-coordinated boron based
AIE luminogens and utilized them for optoelectronic applica-
tions.[10]
Introduction
The design and synthesis of functional luminescent materials
have attracted a lot of attention due to their potential applica-
tions in the field of OLEDs (organic light-emitting diodes), bio-
logical and chemical diagnostic agents, security markers,
among others.[1] In the last two decades, several molecular sys-
tems with intriguing optical properties have been developed
by elegantly modulating the molecular conformations and
inter/intramolecular interactions.[2,3] Owing to their large
Stokes shifted luminescence characteristics, molecular systems
with donor–acceptor (D–A) architecture have been well ex-
ploited for developing several functional materials.[4] However,
often luminescence of D–A systems in the solid state is
quenched due to intermolecular dipole–dipole interactions in-
duced molecular aggregation. In the last decade molecule
with donor–acceptor–donor’ and acceptor–donor–acceptor’
(D–A–D’ and A–D–A’) architectures have been employed to cir-
cumvent the dipole–dipole interactions induced PL quenching
and subsequently to enhance the luminescence in the solid
state.[5]
Recently, we become interested in studying the structure–
property relationships of boron-containing luminogens.[11] As
part of the on-going program, we have studied the AIE proper-
ties of series of dyads composed of boron dipyrromethene–
naphthalimide (BODIPY–NPI) moieties.[12b,c] Initial studies involv-
ing systematic alterations of the NPI based molecules revealed
that a balance of intermolecular forces and molecular environ-
ment can be an effective recipe to impart AIE features in NPIs.
Later on, incorporation of NPI with boron containing dyes re-
sulted in broad emissive AIES-active (aggregation-induced
emission switching) materials and it was unveiled that, p–p in-
teractions can be either detrimental or beneficial depending
on the relative arrangements of neighbouring luminescent
units.[12] It occurred to us that incorporation of oligothiophene
between two different electron deficient receptors will result
in A–D–A’ types of luminogen. In addition, thiophene has
a lower resonance stabilization energy (29 kcalmolꢀ1) com-
pared to benzene (36 kcalmolꢀ1) and induce better electronic
communication between two receptor sites. Moreover, if the
receptors have different affinities for different anions, the re-
sulting A–D–A’ system can be utilised for selective detection of
more than one anion. Accordingly, we designed and synthe-
sised a series of boryl–p–spacer–DCV-based (DCV: dicyanovinyl
and p-spacer: oligothiophene) luminogens (4, 5, and 6) pos-
In recent years, aggregation-induced emission enhancement
(AIEE) has been the subject of several investigations, as most
of the optoelectronic applications require the luminogens to
be emissive in the solid state.[6] The concept of AIEE has
opened up new opportunities and perspectives for developing
functional luminescence materials that could find applications
in areas such as chemo-sensing, bio-imaging and optoelectron-
[a] G. R. Kumar, S. K. Sarkar, Prof. Dr. P. Thilagar
Inorganic and Physical Chemistry Department (IPC)
Indian Institute of Science (IISc), Bangalore 560012 (India)
E-mail: thilagar@ipc.iisc.ernet.in
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201603349.
Chem. Eur. J. 2016, 22, 1 – 12
1
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
sessing typical A–D–A’ architecture. The p-spacer length in
triads 4, 5, and 6 has been judiciously fine-tuned to impart
flexibility and effective electronic communication between the
two acceptors. Compounds 5 and 6 with longer spacers show
interesting AIE properties. Moreover, TAB and DCV units are
well known for their sensing abilities of fluoride and cyanide
ions.[13] Thus, the anion-sensing ability of the new triads 4, 5,
and 6 has also been evaluated.
Optical properties
Hexane solutions of compounds 4, 5, and 6 showed absorp-
tion maxima at 382, 434, and 468 nm, respectively (Figure 1).
These absorption peaks can be attributed to the combined in-
tramolecular charge transfer (ICT) transitions (thiophene to
DCV and thiophene to BMes2), and thiophene-based p!p*
transitions. Compounds 5 and 6 exhibit distinct boryl-based
p!pp* transitions at around 350 nm; the same for 4 is
merged with the lower energy band. Compound 6 (468 nm)
shows the most red-shifted absorption band followed by 5
(434 nm) and compound 4 (382 nm). This trend in the absorp-
tion features of 4, 5, and 6 clearly indicate that the bandgap is
highly depend on the length of the donor oligothiophene
unit.
Results and Discussion
Synthesis and characterisation
Compounds 1 and 2 were synthesized by selective borylation
of the respective bromoacetals (a for 1 and b for 2) and subse-
quent deprotection of aldehyde functional with 2N hydrochlo-
ric acid (Scheme 1). Compound 3 was obtained by a metal-
mediated (Pd(PPh3)4) cross-coupling reaction between “c” and
5-bromo-2-thiophenecarboxaldehyde in toluene.[14] Condensa-
tion of aldehydes (1–3) with malanonitrile in ethanol in the
presence of a catalytic amount of piperidine gave correspond-
ing compounds 4–6 (Scheme 2). All the compounds are char-
acterized by NMR, high-resolution mass spectrometric tech-
niques and CHN analysis. The appearance of a new singlet
peak (7.92 ppm for 4; 7.76 ppm for 5; 7.75 ppm for 6) confirms
the transformation of aldehyde functional groups into dicyano-
vinyl moieties. Due to the fast relaxation of the boron nucleus,
the peaks corresponding to the carbon attached to boron are
not observed in the 13C NMR spectra of compounds 4–6. From
HRMS analysis, it is clear that the molecular ion peaks corre-
spond to the respective sodium ion (Na+) adducts.
Figure 1. UV/Vis absorption (left) and photoluminescence (right) spectra of
4–6 in hexane under ambient conditions. Conc. 1ꢂ10ꢀ5 m, lex =382, 434 and
468 nm for 4, 5, and 6, respectively.
The molecular geometries of 4–6 are optimized using DFT
computational method. The aim is to understand their molecu-
lar and electronic structures (Figure 2). In all the cases, the di-
cyanovinyl unit and the neighbouring thiophene ring are in co-
planar arrangement. The boron centre in all the three com-
pounds adopts a perfect trigonal planar geometry. The boron–
carbon (mesothiophene) bond lengths in 5 (1.555 ꢁ), and 6
(1.551 ꢁ) are slightly shorter than the value noted for 4
(1.561 ꢁ). The dihedral angle between the planes of boron
(BC2) unit and DCV moiety gradually decreases as the thio-
phene chain length increases (for 4, 25.68; for 5, 11.48 and for
6, 78). The dihedral angle between the mesothiophene and
BC2 unit in 5 (18.58), or 6 (18.08) is significantly lower than the
value calculated for 4 (20.88). These results clearly indicate that
an increase in number of thiophenyl moiety between TAB and
DCV enhances the electronic communication between these
two acceptor units.
Scheme 1. Synthesis of compounds 1–3.
Upon photo-excitation at corresponding absorption maxima,
compound 4 showed a single emission peak with maxima at
around 461 nm, whereas structured emission bands were ob-
served for 5 and 6 (lmax; 481 nm for 5 and 527 nm for 6, re-
spectively; Figure 1). The energy of the emission peaks of 4, 5,
and 6 followed a similar trend as observed for absorption
spectra of these compounds. Compound 6 showed the most
red-shifted emission band followed by 5 and 4. Absolute fluo-
rescence quantum yield values clearly indicate that compound
6 (Ff =10.1%) is a better luminophore than 5 (FF =1.0%) and
Scheme 2. Synthesis of compounds 4–6.
Chem. Eur. J. 2016, 22, 1 – 12 www.chemeurj.org
&
&
2
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
Solvent polarity-dependent photophysical studies
To gain further insight into their optical features, the UV/Vis
absorption and fluorescence of 4, 5, and 6 were recorded in
solvents with different polarity (Figures 3 and 4). As the solvent
polarity was increased from hexane to DMSO, both absorption
and emission peaks of compounds 4, 5, and 6 were red-shifted
(Table 2). The bathochromic shift observed in the emission
Table 2. Photophysical properties of 4–6 in solvents of various polarities.
Cmpd Hexane
Toluene
CH2Cl2
DMSO
(labs/lem) [nm] (labs/lem) [nm] (labs/lem) [nm] (labs/lem) [nm]
4
5
6
382/461
434/481
468/527
387/494
443/495
478/555
388/535
447/508
486/586
394/–
448/516
487/606
Figure 2. Energy minimized geometries of 4 (top left), 5 (top right) and 6
(bottom) obtained from DFT (B3LYP as hybrid functional and 6-31G as basis
set) computational methods. Colour code; black=boron, grey=sulfur, light
grey=nitrogen.
spectra of compounds 4, 5, and 6 in polar solvents is signifi-
cantly higher compared to their respective absorption bands.
Thus, the excited state of these compounds is more polarized
than their corresponding ground state. As the polarity of the
solvent medium increases, fluorescence intensity of compound
4 gradually decreased with bathochromic shift. Compound 5
also showed significant Stokes shift in polar solvents, but the
intensity of the luminescence did not change with solvent po-
larity. Interestingly, as solvent polarity increased, the fluores-
cence intensity of 6 progressively increased with significant
bathochromic shift (Table 3).
4 (Ff =0.9%; Table 1). Time-resolved fluorescence studies were
carried out and radiative/non-radiative decay constant values
calculated using the following relationships. kr (radiative decay
constant)=Ff/t; knr (non-radiative decay constant)=(1ꢀFf)/t.
For 4 and 5, radiative and non-radiative decay pathways are
comparable whereas for 6, the radiative decay pathway is pre-
ferred. Thus, a higher fluorescence quantum yield is observed
for 6 compared to 4 and 5. The observed fluorescence quan-
tum yields of compounds 4–6 are significantly lower than the
values observed for TAB–amine–DCV systems reported inde-
pendently by Zhao et al.[15] and Thilagar and co-workers.[11g]
Quantum yields of 4 and 5 were not measurable in polar sol-
vents.
Table 3. Quantum yields of 6 in solvents of different polarities.
Table 1. Optical properties of 4–6 in hexane (1ꢂ10ꢀ5 m).
Hexane
10
Toluene
11
CH2Cl2
16
DMSO
18
Cmpd
labs
lem
Ff
t
kr
knr
FF [%]
[b]
[b]
[nm] [nm] [%][a] [lmax ns] [1ꢂ106 sꢀ1
]
[1ꢂ108 sꢀ1
]
4
5
6
382
434
468
461
481
527
0.9
1.0
10.1
3.8
4.4
4.1
2.4
2.3
24.6
2.6
2.2
2.1
Calculation of the excited-state dipole moment
[a] Absolute quantum yields are measured using integrating sphere.
[b] krꢀradiative decay constant, knrꢀnon-radiative decay constant [calcu-
lated using the relationship, kr =F/t and knr =(1ꢀF)/t].
Further, the change in dipole moment was calculated using
the Lippert–Mataga relationships from Stokes shift values ob-
served in various solvents for 4, 5, and 6 (Figure 5).[17] Changes
Figure 3. UV/Vis absorption spectra of 4 (left), 5 (middle), and 6 (right) in solvents (1ꢂ10ꢀ5 m) of different polarity.
Chem. Eur. J. 2016, 22, 1 – 12 www.chemeurj.org ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3
&
&
These are not the final page numbers! ÞÞ

Full Paper
Figure 4. Photoluminescence spectra of 4 (left), 5 (middle), and 6 (right) in solvents (1ꢂ10ꢀ5 m) of different polarity.
increased to 50 volume%. A sudden rise in emission maxima
(481 nm) was noted when the water fraction becomes 70%. At
fw %=90%, 5 showed a 14-fold increase in its emission intensi-
ty. These preliminary observations suggest that formation of
aggregated particles may be responsible for the observed fluo-
rescence enhancement. Under similar conditions, compound 6
behaves in a different way. The emission maximum at 567 nm
is red-shifted to 590 nm and no significant emission enhance-
ment was noted until the water fraction reached 60%. Emis-
sion enhancement was observed when the water fraction
reaches 70 volume%. A further increase in the water fraction
led to a decrease in emission intensity (fw %; 0%: 567 nm and
90%: 615 nm) with a red-shift. These results are slightly contra-
dictory with the previously reported TAB–TPE-based (TPE: tet-
raphenylethylene) AIE luminogens, for which only emission en-
hancement was observed.[10] The presence of the larger planar
terthiophene unit in 6 may impart more hydrophobic nature
and induce the formation of larger aggregates. As a result, the
emission intensity of 6 in higher water fractions decreases with
a red-shift. Compounds 5 and 6 are more flexible (structurally)
than 4. As a result, upon aggregation, rotational/vibrational
motions are minimized to a greater extent in 5 and 6 which
result in AIE enhancement. Being a poor luminescent material
with less possibilities of restricted structural reorganisation, the
probability of 4 to show AIE enhancement is much lower.
Figure 5. Lippert–Mataga plots for compounds 4–6. A linear relationship is
noted between Stokes shift and the solvent polarity parameter.
in dipole moments were calculated using the relationship de-
scribed in Equation (1):
Dꢀ1
n2ꢀ1
2Dm2
1
Df ¼
þ
Dv ¼
þconstant
hca3
2Dþ1 2n2þ1
in which D and n represent the dielectric constant and refrac-
tive index of the solvent, respectively. The term Dm is change
in dipole moment [Dm=mgꢀme; mg and me are the dipole mo-
ments in the ground and excited states, respectively], h is
Plank’s constant, c is velocity of light and a is the Onsagar
radius (Supporting Information, Table S1), which was obtained
from the optimized molecular structures in all the cases in the
absence of crystal structures. Compounds 4–6 show a linear re-
lationship between Dn and Df and from the slope of the plot,
the changes in dipole moments (Dm) were calculated to be
ꢁ19.7, ꢁ13.4, and ꢁ19.4 D for 4, 5, and 6, respectively. The
Dm for 4 and 6 is significantly larger than the value calculated
for 5. Hence, larger Stokes shifts are observed for 4 and 6 com-
pared to 5 in polar solvents.
Figure 6. Fluorescence spectra of 5 (left) and 6 (right) in various fractions of
THF/water mixtures.
Aggregation-induced emission studies
To further elucidate the emission enhancement of 5 and 6 in
THF solution containing higher water fractions, time resolved
fluorescence studies of 5 and 6 are carried out (Figure 7 and
Fluorescence of 4, 5, and 6 in various fractions of THF/H2O
mixtures were studied (Figure 6). Compounds 5 and 6 show
aggregation-induced emission but not 4. In the case of 5, no
fluorescence change is observed until the water fraction (fw %)
Table S2, Supporting Information). Compound
5 exhibits
a single exponential fluorescence decay (t=5.9 ns) profile in
&
&
Chem. Eur. J. 2016, 22, 1 – 12
www.chemeurj.org
4
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
THF solution and a bi-exponential fluorescence decay (t1 =
6.8 ns, t2 =37.7 ns and tav =14.5 ns, see the Supporting Infor-
mation for more details) in THF containing 90% water by
volume. The mean fluorescence lifetime of 5 at fw =90% is sig-
nificantly higher than the fluorescence lifetime at fw =0%. In
the aggregated state, due to the restricted intramolecular rota-
tions of the thiophene units, a large number of molecules
prefer the radiative decay pathway. Thus, the average fluores-
cence lifetime is significantly increased with enhanced fluores-
cence intensity. As in the case of 5, 6 also exhibits a single ex-
ponential fluorescence decay profile in THF solution (t=4.4).
When the water fraction reached 70%, bi-exponential fluores-
cence decay (t1 =3.3 ns, t2 =14.2 ns and tav =4.06 ns) was ob-
served. The relative amplitude of t2 (14.2 ns) is very small (see
the Supporting Information for details). When the water frac-
tion reached 90%, the bi-exponential decay was mostly domi-
nated by t2 (tav =36.5 ns) and contribution from t1 decreased.
As discussed vide-supra, at higher water fractions (beyond
70%), aggregates increase in size and more of them are
formed. Upon aggregation, non-radiative decay pathways of 5
and 6 are significantly reduced. In true solution, structural reor-
ganisations facilitate rapid relaxation of the excited fluoro-
phores to the ground state via non-radiative pathways. Since
the structural reorganisation is prevented in aggregated form,
greater numbers of molecules prefers to relax from the excited
state via a radiative decay pathway and consequently fluores-
cence lifetime is increased. This is further supported by the
values of absolute quantum yields (Table 4). Both 5 and 6
show higher quantum yields in aggregated forms as compared
to their true solutions. The red-shift of the emission band in 6
during aggregation may be due to p–p stacking facilitated by
planar terthiophene–DCV unit.
gates in the presence of large fractions of water. In the case of
5, at fw =90%, 458 nm sized particles are formed. In the case
of 6, the aggregated particles grow bigger as the water frac-
tion increases (fw: 70%; 712 nm, fw: 80%; 825 nm). At 90%
water fraction, aggregated particle size becomes 955 nm. It is
evident that the reduced luminescence intensity of 6 in THF
solutions containing 80 and 90% water can be due to the for-
mation of bigger particles which may facilitate p–p stacking
between neighbouring molecules.
Solvent viscosity-dependent fluorescence studies
It is important to note that compounds 5 and 6 showed signif-
icant increase in the luminescence intensity in highly viscous
solvents. To gain further insight into the solvent viscosity-de-
pendent optical features of 4, 5, and 6, their optical signatures
were recorded in a highly viscous polar solvent, ethylene
glycol. Upon increasing the ethylene glycol fractions in metha-
nol solutions of 4, 5, and 6, the fluorescence intensity of 5 and
6 increased progressively (Figure 8), but no changes were ob-
served for 4. Compound 5 showed a three-fold increase of the
fluorescence intensity in viscous solvents, whereas 6 showed
a 1.4-fold increase. This type of viscosity-dependent fluores-
cence enhancement is well known for compounds with flexible
structures.[16] Since compounds 5 and 6 have long spacer they
may undergo structural reorganization in the excited state
which may partly deactivate the radiative decay of 5 and 6. In
viscous solvents, such structural reorganizations are restricted
due to the rigid environment and consequently the radiative
decay of 5 and 6 is facilitated.
Figure 8. Fluorescence spectra of 5 (left) and 6 (right) in various fractions of
Figure 7. Fluorescence decay profiles of compounds 5 (left) and 6 (right) in
methanol/glycerol mixtures.
THF and THF/water mixtures.
To determine whether the viscosity or solvent polarity con-
trols the optical dynamics of 5 and 6, their PL features were re-
corded in nonpolar viscous paraffin oil (Figure 9). As the paraf-
fin oil fractions increase in hexane solutions of 4, 5, and 6, the
fluorescence intensity of 5 and 6 increased gradually (2.3 times
for 5 and 1.4 times for 6) as observed in ethylene glycol. Com-
pound 4 showed no changes. Based on these results we con-
clude that viscosity plays a major role in determining the emis-
sion intensity of compounds 5 and 6. Photo-induced structural
dynamics of 5 and 6 could be controlled by increasing the vis-
cosity of the solvent medium. These observations confirm the
Table 4. Quantum yields of 5 and 6 in THF/water mixtures.
THF:H2O [%]
5 [FF %]
6 [FF %]
10:90
90:10
9
1.5
17
5.6
To understand the aggregation process, size-distribution of
aggregated particles formed is measured using dynamic light
scattering (Figures S21 and S22 in the Supporting Information).
The results showed that compounds 5 and 6 form nano-aggre-
Chem. Eur. J. 2016, 22, 1 – 12
www.chemeurj.org
5
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
Density functional theory studies
To understand the electronic structures of compounds 4–6,
DFT computational studies were performed using the B3LYP
functional and 6-31G(d) as basis set (Figure 11). The number of
thienyl units has a considerable impact on their molecular orbi-
tal localizations and electronic conjugation. In the case of 4,
the HOMO is localized on the p-orbital of the mesityl rings
whereas in the case of 5 and 6, it is delocalized over the bi-
thiophene and terthiophene rings, respectively, with a small
contribution from dicyanovinyl unit. In all the cases, LUMO is
delocalized over the dicyanovinyl unit, spacer (mono-, bi- and
terthiophene) and the empty orbital of the boron centre. The
energy of HOMO of 4, 5, and 6 steadily increase with increas-
ing donor oligothiophene length. Thus, HOMO–LUMO gap de-
creases effectively in 5 and 6. These observations corroborate
well with the experimental results.
Figure 9. Fluorescence spectra of 5 (left) and 6 (right) in various fractions of
hexane/paraffin mixtures.
involvement of restricted intramolecular motion in the process
of emission enhancement.
Solid-state emission characteristics
Although 5 and 6 show AIE characteristics, they are not fluo-
rescent in the solid state. To check whether a polymeric rigid
matrix can activate luminescence in the solid state, thin films
of 5 and 6 are made along with polymethylmethacrylate
(PMMA). PMMA and 5/6 were dissolved in THF and thin films
were made over a quartz plate by a drop-casting method
(Figure 10). Both the compounds showed intense lumines-
cence with considerable absolute quantum yields (5: lmax
=
517 nm, F=4.4% and 6: lmax =567 nm, F=11.4%). As ob-
served in solution state, compound 6 exhibits higher quantum
yield in PMMA matrix also. The rigid environment provided by
PMMA significantly reduces non-radiative decay channels and
enhances the emission efficiency. Maximum emission intensity
was observed when the weight percentage of compounds 5
and 6 are around 20%. Upon increasing the weight percent-
age of fluorophores beyond 20%, the fluorescence intensity
started to decrease. Probably at higher concentrations, 5 and 6
form short contacts between neighbouring molecules. As
a result, fluorescence decreases at higher weight percentages.
Figure 11. Calculated frontier molecular orbitals of 4–6 and the correspond-
ing energy levels by DFT method (B3LYP/6-31G, isovalue=0.04).
Anion binding studies
To evaluate the anion sensing abilities of 4–6, their photophys-
ical properties were examined in the presence of variety of
anions such cyanide, fluoride, chloride, bromide, iodide, nitrate,
and perchlorate (Figure S24, Supporting Information). The re-
sults indicate that compounds 4, 5, and 6 can selectively sense
small anions such as fluoride and cyanide.
Upon fluoride binding, the intensity of the respective ab-
sorption bands of 4, 5, and 6 decrease and concomitantly
a new absorption band appears in the longer wavelength
region (Figure 12). The new absorption band observed for 5·Fꢀ
(526 nm) and 6·Fꢀ (572 nm) are significantly red-shifted com-
pared to the band observed for 4·Fꢀ (424 nm). Since the new
absorption bands observed for 5·Fꢀ (526 nm) and 6·Fꢀ
(572 nm) fall in the visible region of the electromagnetic spec-
trum, a distinct colour change could be observed by the naked
eye. Thus, compounds 5 and 6 are potential colorimetric
sensor for selective detection of fluoride ions.
Figure 10. Photoluminescence spectra of thin films made up of 5 (left) and
6 (right) in PMMA (20%w/w). Inset shows photographic images taken under
the UV lamp (colour images are given in Supporting Information).
On the other hand, compound 4 does not show any fluores-
cence in the solid state even after mixing with PMMA. The ob-
served solid-state quantum yields are lower than the values
noted for TAB–TPE derivatives.[10]
The fluoride-binding event was also monitored by 1H and
19F NMR titrations (Figure S25, Supporting Information). The
&
&
Chem. Eur. J. 2016, 22, 1 – 12
www.chemeurj.org
6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
Figure 13. Changes in photoluminescence spectra of 4 (top left,
lex =380 nm), 5 (top right, lex =430 nm) and 6 (bottom, lex =460 nm; conc.
1ꢂ10ꢀ5 m) in the presence of TBAF (2 mL=0.1 equiv) in THF.
Figure 12. Changes in UV/Vis absorption spectra of 4 (top left), 5 (top right),
and 6 (bottom; conc. 1ꢂ10ꢀ5 m) in the presence of TBAF (2 mL=0.1 equiv)
in THF.
CDCl3 solution 5 was mixed with 10 equivalents of tetrabutyl-
Since compound 5 exhibits ratiometric fluorescence response
(the peak at 501 nm decreases and the peak at 608 nm in-
creases) for fluoride binding, this molecule can be used as self-
calibrating fluorescence probe for fluoride ions. The change in
absorption and fluorescence features of 4, 5, and 6 stops after
the addition of one equivalent of fluoride ions confirming the
formation of 1:1 fluoride adducts.
1
ammonium fluoride (TBAF) and changes in H and 19F resonan-
1
ces were monitored. In H NMR, the proton region correspond-
ing to the mesityl proton showed a complex NMR pattern but
no changes in the DCV proton signal was observed. Only, 19F
signal corresponding to the Ar3B·Fꢀ moiety was observed in
19F NMR. Based on these results one can conclude that the
fluoride binds only to the boron centre and does not interact
with the DCV unit. These results are in-line with the previous
reports on similar molecules.[11f,g] Having confirmed the forma-
tion of monofluoride complexes of 4 and 5 and 6, computa-
tional studies[18–20] were carried out with the objective of un-
derstanding the origin of new absorption bands for 4·Fꢀ, 5·Fꢀ
and 6·Fꢀ (Figure S27, Supporting Information). The HOMO of
4·Fꢀis localized on one of the two mesityl moieties of Ar3B·Fꢀ
fragment. In contrast, the HOMO of 5·Fꢀ and 6·Fꢀ is delocal-
ized over the entire Ar3B·Fꢀ fragment in both the complexes.
The LUMOs of 4·Fꢀ, 5·Fꢀ, and 6·Fꢀ are delocalized over the
DCV and thiophenyl spacers. Furthermore, the HOMO!LUMO
bandgap of fluoride complexes decreased significantly com-
pared to their respective free Lewis acids 4, 5, and 6. From
these results we conclude that the new absorption band ob-
served for fluoride complexes 4·Fꢀ, 5·Fꢀ and 6·Fꢀ arises from
intramolecular charge transfer from in situ generated electron-
rich borate donor (Ar3B·Fꢀ) to the electron-deficient DCV ac-
ceptor. These results are in line with our earlier report on fluo-
ride binding studies of TAB–BTH–BODIPY triad.[11b]
Upon addition of tetrabutyl ammonium cyanide ions, the
absorption of 4 gradually decreases with 31 nm bathochromic
shift. In the presence of 1 equivalent of cyanide, the absorption
peaks of 5 and 6 decrease and a new absorption band appears
in the longer wavelength region (Figure 14). Upon addition of
second equivalent of cyanide, the newly formed absorption
peaks at longer wavelength region disappear; subsequently
the solution of 5 and 6 become colourless. These colour
changes can be seen by the naked eye. Hence, compounds 5
and 6 can be used as a colorimetric sensor for cyanide ions.
To rationalize the cyanide binding process, NMR titrations
were carried out (Figure S26, Supporting Information). In gen-
The fluoride-binding event was also studied using fluores-
cence spectrometry (Figure 13). When excited at 380 nm, the
fluorescence intensity of compound 4 decreases steadily as the
concentration of TBAF increases. Under similar conditions,
upon excitation at 430 nm the intensity of emission peak at
501 nm for 5 gradually decrease and a new emission peak pro-
gressively appears at 608 nm. In the case of 6, the fluoride
binding considerably increases the intensity of the fluores-
cence with 17 nm bathochromic shift. These results clearly in-
dicate that the fluoride complexes 5·Fꢀ and 6·Fꢀ are better lu-
minophores than their corresponding free Lewis acids 5 and 6.
Figure 14. Changes in UV/Vis absorption spectra of 4 (top left), 5 (top right),
and 6 (bottom; 1ꢂ10ꢀ5 m) in presence of TBACN (2 mL=0.1 equiv) in THF.
Chem. Eur. J. 2016, 22, 1 – 12
www.chemeurj.org
7
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
eral, the hydrogen atom attached to the electrophilic carbon
centre of dicyanovinyl group resonates at around 7–8 ppm in
1
the H NMR spectrum and upon cyanide coordination under-
goes an upfield shift to around 4–5 ppm.[21] Compounds 5 and
6 exhibit a singlet peak at 7.75 ppm corresponding to the di-
cyanovinyl unit. The addition of one equivalent of cyanide ions
to 5 resulted in the formation of complex multiple peaks at ar-
omatic region and two singlet peaks at 4.4 and 4.5 ppm. The
formation of these peaks along with the coexistence of anoth-
er singlet at 7.75 ppm indicates that cyanide ions bind with
both the receptor sites simultaneously (Scheme 3). After the
addition of two equivalents of cyanide ions, the spectrum
shows only one singlet peak at around 4.4 ppm indicating that
both the receptor sites are completely saturated. Thus, the
complex NMR pattern observed for a 1:1 mixture of cyanide
and probe 5 can be attributed to the presence of multiple spe-
cies at this stage of titrations. These results are in accordance
with our previous reports on TAB–DCV based cyanide recep-
tors.
Figure 15. Changes in photoluminescence spectra of 4 (top left), 5 (top
right) and 6 (bottom; 1ꢂ10ꢀ5 m) in the presence of TBACN (2 mL=0.1 equiv)
in THF.
As observed for fluoride binding, the cyanide binding also
quenches the luminescence of compound 4 at 382 nm. In the
case of 5 and 6, the cyanide binding exhibited complex lumi-
nescence characteristics (Figure 15). In the presence of one
equivalent of cyanide, the fluorescence intensity of both 5 and
6 increased with significant red-shift. When an additional
equivalent of cyanide was added, the intensity of the lumines-
cence decreased with considerable blue-shift. The spectral
changes observed for 4, 5, and 6 stop upon addition of two
equivalents of cyanide. These results clearly indicate that two
equivalents of cyanide saturate both the receptors in 4, 5, and
6 and generate [4·(CN)2]2ꢀ, [5·(CN)2]2ꢀ, and [6·(CN)2]2ꢀ, respec-
tively. Significant residual fluorescence observed for cyanide
complexes [5·(CN)2]2ꢀ and [6·(CN)2]2ꢀ suggest that these com-
plexes are better luminophores than the corresponding com-
pounds 5 and 6.
Table 5. Binding constants.[a]
4
5
6
K (Fꢀ) [105 mꢀ1
K (CNꢀ) [105 mꢀ1
]
0.21
1.33
0.53
0.86
3.58
0.10
]
[a] Binding constants are calculated from UV/Vis absorption titrations by
plotting (1ꢀI/I0)/[Anion] against I/I0.For 4, 5, and 6. In the case of K (CNꢀ),
the values correspond to average for binding at two different receptor
sites.
tion wavelengths of 381, 434, and 468 nm are chosen for 4, 5,
and 6, respectively for calculating the binding constants
(Table 5).
Linear relationships were noted between (1ꢀI/I0)/[Xꢀ] and I/I0
in which I0, I and [Xꢀ] are initial absorbance value, absorbance
value after each addition of anion source, and concentration of
fluoride/cyanide, respectively (Figures S13–S15, Supporting In-
formation). The slope obtained from the fitted linear line di-
rectly gave the value of the binding constants. Compound 6
exhibited the highest binding affinity towards fluoride ions,
whereas 4 exhibits highest binding affinity towards cyanide
ions. Anion binding constant values for 4–6 are comparable to
those obtained for TAB–amine–DCV[11f] based probes.
Binding constants
The fluoride and cyanide binding constants of 4, 5, and 6 were
calculated using the absorption titration data. Stock solutions
(1.0ꢂ10ꢀ5 m) of receptors (4–6) and TBAF/TBACN (1ꢂ10ꢀ3 m) in
tetrahydrofuran (THF) were prepared. A stock solution (2 mL)
of receptor was placed in a screw-capped quartz cell of 1 cm
width and fluoride/cyanide was added in an incremental fash-
ion. After a constant interval of time, their corresponding ab-
sorption spectra were recorded at 298 K. Each titration was re-
peated at least three times to get consistent values. Absorp-
To find out the sensitivity of the probes 4–6 towards fluoride
and cyanide ions, detection limits are calculated by adopting
the procedures reported elsewhere[22] using the formula 3s/k,
s; standard deviations, k; slope of the linear fitting (emission
Scheme 3. Possible species formed during the cyanide titration of 5; predicted using 1H NMR studies.
Chem. Eur. J. 2016, 22, 1 – 12 www.chemeurj.org
&
&
8
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
intensity vs. [Xꢀ], Supporting Information). The fluoride detec-
tion limits for compounds 4, 5, and 6 were found to be 2.02,
1.52, and 2.82 ppm, respectively. In the case of cyanide ion, the
detection limits were found to be 2.0, 0.2 and 0.16 ppm for 4,
5, and 6, respectively. Detection limit values indicate that the
reported probes are able to sense Fꢀ/CNꢀ from the medium
even in ppm range indicating higher sensitivity. Compound 5
exhibits lowest detection limit for fluoride ions whereas 6 ex-
hibits lowest detection for cyanide ions (see the Supporting In-
formation for more details).
Conclusions
A new series of TAB–thiophene–DCV (A–D–A’) conjugates 4, 5,
and 6 was synthesized. It was found that, increasing the
number of thiophene rings between the two acceptor sites
can facilitate increased electronic conjugation between the
two acceptors with significant reduction of band gap between
frontier molecular orbitals. Interestingly, compounds 5 and 6
with longer p-spacers showed higher fluorescence in polar sol-
vents, which is quite rarely observed for fluorophores with
donor–acceptor configurations. The fluorescence quantum
yield of 5 and 6 can be modulated by viscosity of the solvent
medium. Compounds 5 and 6 exhibit aggregation-induced
emission and strong luminescence in the solid state in a poly-
meric matrix. DLS measurement confirms formation of aggre-
gated particles is responsible for the enhanced luminescence
of 5 and 6 in poor solvents. Since reorganisation of the molec-
ular structure is restricted in a rigid environment, non-radiative
decay channels are minimized to a significant extent. Com-
pounds 4–6 exhibit selective response towards fluoride and cy-
anide ions. Importantly, 5 and 6 show different colorimetric re-
sponse towards the interfering anions fluoride and cyanide
ions. Compound 5 showed fluorescence ratiometric response
towards fluoride ions and can be used as a self-calibrating fluo-
ride indicator. Test strips made up of probes 5 and 6 have po-
tential application in identifying fluoride and cyanide ions in
aqueous medium with different colorimetric responses.
Reversible anion binding behaviour is an essential character-
istic for the probes to be utilized in multiple numbers of times.
Hence, the reversibility of fluoride binding in 4, 5, and 6 were
examined by using an external reagent (BF3·OEt2) to remove
fluoride ions from the fluoride bound species (4·Fꢀ, 5·Fꢀ, and
6·Fꢀ). Addition of BF3·OEt2 (4ꢂ10ꢀ2 m, 2 mL) to solutions of
fluoride bound species resulted in nearly complete restoration
of the luminescence probes 4, 5, and 6 (Supporting Informa-
tion) indicating that 4–6 can be regenerated after utilizing for
fluoride ion detection.
Test-strip method for aqueous fluoride and cyanide ion de-
tection
The selective and visual colorimetric responses of 5 and 6 to-
wards fluoride and cyanide provided an opportunity to devel-
op low-cost test strips for practical applications. These test
strips are made by coating the solutions of 5 and 6 on filter
paper strips. When these strips were dipped into water conta-
minated with fluoride and cyanide ions (0.1m solution), the
colour changed completely (Figure 16). These results clearly
demonstrate the potential practical applications of 5 and 6 to
detect fluoride and cyanide in water by a simple test-dip
method.
Experimental Section
Materials and methods
All moisture-sensitive reactions were carried out under an atmos-
phere of purified nitrogen using standard Schlenk techniques. THF
was distilled over sodium prior to use. HPLC grade solvents were
used for absorption and emission spectroscopic measurements. All
the UV/Vis absorption, fluorescence and NMR titrations were car-
ried out at room temperature in freshly distilled solvents. Electronic
absorption spectra were recorded on a PerkinElmer LAMBDA 750
UV/visible spectrophotometer. Fluorescence emission and excita-
tion spectra were recorded on a Horiba JOBIN YVON Fluoromax-4
spectrometer. DFT calculations were performed using standard
computational methods and basis sets as incorporated in the
Gaussian 09 software package. Dimesitylborylbithiophene aldehyde
(2) was synthesized following previously reported methods.[11b]
Synthetic procedures
Synthesis of 1: 5-Bromo-2-thiophenecarboxaldehyde (1.25 mL,
10.47 mmol) and triethylorthoformate (1.9 mL, 12.56 mmol) were
dissolved in ethanol (30 mL). A catalytic amount of dil. HCl was
added and the reaction mixture was heated under reflux for 6 h.
Evaporation of all the volatiles gave the protected aldehyde “a”
(2.6 g; 93.86% yield) which was used for next step without any fur-
ther purification. To a solution of “a” (2 g, 7.54 mmol) in THF, nBuLi
(1.6m in hexane, 5.19 mL, 8.30 mmol) was added dropwise under
a N2 atmosphere at ꢀ788C and the reaction mixture was stirred at
this temperature for 60 min. BFMes2 (2.43 g, 9.05 mmol) was
added. The reaction mixture allowed to attain room temperature
and stirring was continued for another 12 h. The reaction was
Figure 16. Photographs of THF solutions of 5 and 6 in presence/absence of
fluoride and cyanide under day light (top). Test strips coated with probes 5
and 6 and their colorimetric response towards Fꢀ and CNꢀ in water (0.1m).
Chem. Eur. J. 2016, 22, 1 – 12
www.chemeurj.org
9
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
quenched with 2 N HCl. The reaction mixture was extracted with
ethyl acetate. The combined organic layer was washed with water,
dried under Na2SO4 and concentrated under reduced pressure to
afford a crude product. Analytically pure product was obtained by
column chromatography over silica gel using 5% ethyl acetate in
hexane as eluent. Yield: 1.5 g (55.14%) as an off-white solid.
1H NMR (400 MHz, CDCl3, TMS): d=9.99 (s, 1H), 7.81 (d, J=4 Hz,
2H), 7.45 (d, J=4 Hz, 2H), 6.84 (s, 4H), 2.31 (s, 6H), 2.07 ppm (s,
12H).
Acknowledgements
P.T. thanks the Department of Science and Technology (DST),
New Delhi, for the financial support. G.R.K. thanks the UGC,
New Delhi and SKS thanks IISc for research fellowships.
Keywords: aggregation-induced emission enhancement
anion discriminators · fluorescence · sensors · triarylborane
·
Synthesis of 3: 5-Bromo-2-thiophenecarboxaldehyde (0.21 mL,
1.73 mmol) and c (1 g, 1.73 mmol) were taken in a two-necked
flask under nitrogen atmosphere in toluene. The resultant solution
was degassed for 30 min to remove all the dissolved oxygen, sub-
sequently a catalytic amount of Pd(PPh3)4 (0.09 g, 0.05 mmol) was
added. The reaction mixture was heated under reflux condition for
12 h. All the volatiles are evaporated completely and the product
was extracted with ethyl acetate and purified by column chroma-
tography over silica gel using 50% ethyl acetate in hexane eluent.
Yield: 0.8 g (88%; straw-yellow solid). 1H NMR (400 MHz, CDCl3):
d=9.86 (s, 1H), 7.67 (d, J=4 Hz, 1H), 7.37 (d, J=4 Hz, 1H), 7.34 (d,
J=4 Hz, 1H), 7.27 (d, J=4 Hz, 1H), 7.23 (d, J=4 Hz, 1H), 7.21 (d,
J=4 Hz, 1H), 6.85 (s, 4H), 2.32 (s, 6H), 2.15 ppm (s, 12H).
[1] a) J. H. Schçn, H. Meng, Z. Bao, Nature 2001, 413, 713–716; b) J. Kido,
Y. Okamoto, Chem. Rev. 2002, 102, 2357–2368; c) Y. L. Tung, P. C. Wu,
C. S. Liu, Y. Chi, K. K. Yu, Y. H. Hu, P. T. Chou, S. M. Peng, G. H. Lee, Y. Tao,
A. J. Carty, C. F. Shu, F. I. Wu, Organometallics 2004, 23, 3745–3748;
d) S. C. Lo, P. L. Burn, Chem. Rev. 2007, 107, 1097–1116; e) Q. Zhao, C.
Huanga, F. Li, Chem. Soc. Rev. 2011, 40, 2508–2524; f) G. Crivat, J. W. Tar-
aska, Trend. Biotechnol. 2012, 30, 8–16; g) F. Steiner, S. Bange, J. Vogel-
sang, J. M. Lupton, J. Phys. Chem. Lett. 2015, 6, 999–1004; h) Y. Chen, R.
Guan, C. Zhang, J. Huang, L. Ji, H. Chao, Coord. Chem. Rev. 2016, 310,
16–40.
[2] a) G. Zhang, J. Lu, M. Sabat, C. L. Fraser, J. Am. Chem. Soc. 2010, 132,
2160–2162; b) O. Bolton, K. Lee, H. J. Kim, K. Y. Lin, J. K. Kim, Nat. Chem.
ˇ
ˇ
2011, 3, 205–207; c) P. Galer, R. C. Korosec, M. V. Vidmar, B. J. Sket, J.
Am. Chem. Soc. 2014, 136, 7383–7394; d) Y. Gong, Y. Zhang, W. Z. Yuan,
J. Z. Sun, Y. Zhang, J. Phys. Chem. C 2014, 118, 10998–11005; e) S. Mu-
kherjee, P. Thilagar, Chem. Commun. 2015, 51, 10988–11003; f) C. Botta,
S. Benedini, L. Carlucci, A. Forni, D. Marinotto, A. Nitti, D. Pasini, S. Righ-
ettoce, E. Cariati, J. Mater. Chem. C. 2016, 4, 2979–2989.
Synthesis of 4: Malanonitrile (19 mL, 0.191 mmol),
1 (0.1 g,
0.277 mmol) and a catalytic amount of piperidine were dissolved
in ethanol (25 mL) under stirring. The progress of the reaction was
monitored by TLC. After complete consumption of compound 1,
all the volatiles were removed and the resultant crude product was
purified by column chromatography over silica gel (eluent:
hexane/ethyl acetate 96:4) to obtain the analytically pure com-
pound. Yield: 15 mg (13%), off-white solid. 1H NMR (400 MHz,
CDCl3): d=7.92 (d, J=4 Hz, 1H), 7.82 (s, 1H), 7.44 (d, J=4 Hz, 1H),
6.84 (s, 4H), 2.31 (s, 6H), 2.06 ppm (s, 12H); 13C NMR (100 MHz,
CDCl3): d=156.11, 152.82, 141.73, 140.11, 139.65, 129.03, 115.48,
114.40, 23.89, 21.77 ppm; ESI-MS calcd: C26H25BN2S (M+Na+)
431.1724; found 431.1767; elemental analysis calcd (%) for
C26H25BN2S: C, 76.47; H, 6.17; N, 2.65; found: C, 76.82; H, 6.08; N,
2.48.
[3] a) Y. Li, G. Vamvounis, S. Holdcroft, Chem. Mater. 2002, 14, 1424–1429;
b) Y. Yamaguchi, Y. Matsubara, T. Ochi, T. Wakamiya, Z. Yoshida, J. Am.
Chem. Soc. 2008, 130, 13867–13869; c) Y. Niko, S. Kawauchi, S. Otsu, K.
Tokumaru, G. Konishi, J. Org. Chem. 2013, 78, 3196–3207.
[4] a) S. Priyadarshy, M. J. Therien, D. N. Beratan, J. Am. Chem. Soc. 1996,
118, 1504–1510; b) S. A. Jenekhe, L. Lu, M. M. Alam, Macromolecules
2001, 34, 7315–7324; c) J. S. Yang, S. Y. Chiou, K. L. Liau, J. Am. Chem.
Soc. 2002, 124, 2518–2527; d) X. Sun, Y. Liu, X. Xu, C. Yang, G. Yu, S.
Chen, Z. Zhao, W. Qiu, Y. Li, D. Zhu, J. Phys. Chem. B 2005, 109, 10786–
10792; e) H. Meier, Angew. Chem. Int. Ed. 2005, 44, 2482–2506; Angew.
Chem. 2005, 117, 2536–2561; f) S. Haid, M. Marszalek, A. Mishra, M. Wie-
lopolski, J. Teuscher, J. E. Moser, R. H. Baker, S. M. Zakeeruddin, M. Grꢃt-
zel, P. Bꢃuerle, Adv. Funct. Mater. 2012, 22, 1291–1302; g) D. Su, J. Oh,
S. C. Lee, J. M. Lim, S. Sahu, X. Yu, D. Kim, Y. T. Chang, Chem. Sci. 2014,
5, 4812–4818; h) H. Chen, W. Lin, W. Jiang, B. Dong, H. Cuia, Y. Tang,
Chem. Commun. 2015, 51, 6968–6971;i) S. Sasaki, G. P. C. Drummen, G.
Konishi, J. Mater. Chem. C 2016, 4, 2731–2743.
Synthesis of 5: Compound 5 was synthesized following a similar
procedure as that for 4. The quantities involved and characteriza-
tion data are as follows. 2 (0.1 g, 0.226 mmol), malanonitrile (15 mL,
0.226 mmol), piperidine (catalytic amount), Yield: 0.035 g in 31.5%
as a reddish-black powder. 1H NMR (400 MHz, CDCl3): d=7.76 (s,
1H), 7.62 (d, J=4 Hz, 1H), 7.51 (d, J=4 Hz, 1H), 7.39 (d, J=4 Hz,
1H), 7.33 (d, J=4 Hz, 1H), 6.84 (s, 4H), 2.31 (s, 6H), 2.12 ppm (s,
12H); 13C NMR (100 MHz, CDCl3): d=153.67, 150.60, 149.23, 146.63,
141.49, 141.34, 140.29, 139.65, 134.91, 129.28, 128.83, 126.18,
114.51, 113.70, 23.91, 21.71 ppm; ESI-MS calcd: C30H27BN2S2 (M+
Na+) 513.1601; found 513.1604; elemental analysis calcd (%) for
C30H27BN2S2: C, 73.46; H, 5.55; N, 5.71; found: C, 73.31; H, 5.75; N,
5.78.
[5] a) K. R. Justin Thomas, J. T. Lin, M. Velusamy, Y. T. Tao, C. H. Chuen, Adv.
Funct. Mater. 2004, 14, 83–90; b) G. Qian, B. Dai, M. Luo, D. Yu, J. Zhan,
Z. Zhang, D. Ma, Z. Y. Wang, Chem. Mater. 2008, 20, 6208–6216; c) E.
Ramachandran, R. Dhamodharan, J. Mater. Chem. C 2015, 3, 8642–
8648.
[6] a) J. Luo, Z. Xie, J. W. Y. Lam, L. Cheng, H. Chen, C. Qiu, H. S. Kwok, X.
Zhan, Y. Liu, D. Zhu, B. Z. Tang, Chem. Commun. 2001, 1740–1741;
b) B. K. An, S. K. Kwon, S. D. Jung, S. Y. Park, J. Am. Chem. Soc. 2002, 124,
14410–144154; c) J. Chen, C. C. W. Law, J. W. Y. Lam, Y. Dong, S. M. F. Lo,
I. D. Williams, D. Zhu, B. Z. Tang, Chem. Mater. 2003, 15, 1535–1546;
d) S. J. Lim, B. K. An, S. D. Jung, M. A. Chung, S. Y. Park, Angew. Chem.
Int. Ed. 2004, 43, 6346–6350; Angew. Chem. 2004, 116, 6506–6510;
e) S. J. Lim, B. K. An, S. Y. Park, Macromolecules 2005, 38, 6236–6239;
f) Q. Zeng, Z. Li, Y. Dong, C. Di, A. Qin, Y. Hong, L. Ji, Z. Zhu, C. K. W. Jim,
G. Yu, Q. Li, Z. Li, Y. Liu, J. Qin, B. Z. Tang, Chem. Commun. 2007, 70–72;
g) Y. Hong, J. W. Y. Lam, B. Z. Tang, Chem. Commun. 2009, 4332–4353;
h) R. Hu, E. Lager, A. A. Aguilar, J. Liu, J. W. Y. Lam, H. H. Y. Sung, I. D. Wil-
liams, Y. Zhong, K. S. Wong, E. P. Cabrera, B. Z. Tang, J. Phys. Chem. C
2009, 113, 15845–15853; i) Z. Zhao, B. Hea, B. Z. Tang, Chem. Sci. 2015,
6, 5347–5364; j) F. Bu, R. Duan, Y. Xie, Y. Yi, Q. Peng, R. Hu, A. Qin, Z.
Zhao, B. Z. Tang, Angew. Chem. Int. Ed. 2015, 54, 14492–14497; Angew.
Chem. 2015, 127, 14700–14705; k) J. Freudenberg, F. Rominger, U. H. F.
Bunz, Chem. Eur. J. 2015, 21, 16749–16753; l) M. Han, Y. Takeoka, T. Seki,
J. Mater. Chem. C 2015, 3, 4093–4098; m) M. Huang, R. Yu, K. Xu, S. Ye,
Synthesis of 6: Compound 6 was synthesized following a similar
procedure as that for 4 and 5. The quantities involved and charac-
terization data are as follows. 3 (0.1 g, 0.191 mmol), malanonitrile
(12 mL, 0.191 mmol), piperidine (catalytic amount), yield: 80 mg in
73% as reddish-black powder. 1H NMR (400 MHz, CDCl3): d=7.75
(s, 1H), 7.62 (d, J=4 Hz, 1H), 7.37 (d, J=4 Hz, 1H), 7.35 (m, 2H),
7.24 (m, J=4 Hz, 2H), 6.84 (s, 4H), 2.31 (s, 6H), 2.14 ppm (s, 12H);
13C NMR (100 MHz, CDCl3): d=150.40, 149.10, 148.39, 141.81,
141.31, 140.73, 140.51, 139.30, 135.20, 134.13, 128.72, 128.65,
127.20, 126.62, 125.08, 115.65, 113.85 ppm; ESI-MS calcd:
C34H29BN2S3 (M+Na+) 595.1478; found 595.1812; elemental analy-
sis calcd (%) for C34H29BN2S3: C, 71.32; H, 5.10; N, 4.89; found: C,
71.20; H, 5.13; N, 4.75.
&
&
Chem. Eur. J. 2016, 22, 1 – 12
www.chemeurj.org
10
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
S. Kuang, X. Zhu, Y. Wan, Chem. Sci. 2016, 7, 4485–4491; n) B. Xu, W. Li,
J. He, S. Wu, Q. Zhu, Z. Yang, Y. C. Wu, Y. Zhang, C. Jin, P. Y. Lu, Z. Chi, S.
Liu, J. Xua, M. R. Bryce, Chem. Sci. 2016, 7, 5307–5312.
[11] a) C. A. Swamy, P. S. Mukherjee, P. Thilagar, J. Mater. Chem. C 2013, 1,
4691–4698; b) S. K. Sarkar, P. Thilagar, Chem. Commun. 2013, 49, 8558–
8560; c) P. C. A. Swamy, S. Mukherjee, P. Thilagar, Chem. Commun. 2013,
49, 993–995; d) P. Sudhakar, S. Mukherjee, P. Thilagar, Organometallics
2013, 32, 3129–3133; e) C. A. Swamy, P. S. Mukherjee, P. Thilagar, Inorg.
Chem. 2014, 53, 4813–4823; f) G. R. Kumar, P. Thilagar, Dalton Trans.
2014, 43, 7200–7207; g) G. R. Kumar, S. K. Sarkar, P. Thilagar, Phys. Chem.
Chem. Phys. 2015, 17, 30424–30432; h) S. K. Sarkar, G. R. Kumar, P. Thila-
gar, Chem. Commun. 2016, 52, 4175–4178.
[12] a) S. Mukherjee, P. Thilagar, Chem. Commun. 2013, 49, 7292–7294; b) S.
Mukherjee, P. Thilagar, Chem. Eur. J. 2014, 20, 8012–8023; c) S. Mukher-
jee, P. Thilagar, Chem. Eur. J. 2014, 20, 9052–9062; d) S. Mukherjee, P.
Thilagar, Phys. Chem. Chem. Phys. 2014, 16, 20866–20877.
[7] a) D. Ding, K. Li, B. Liu, B. Z. Tang, Acc. Chem. Res. 2013, 46, 2441–2453;
b) C. T. Leung, Y. Hong, S. Chen, E. Zhao, J. W. Y. Lam, B. Z. Tang, J. Am.
Chem. Soc. 2013, 135, 62–65; c) C. Zhang, S. Jin, S. Li, X. Xue, J. Liu, Y.
Huang, Y. Jiang, W. Chen, G. Zou, X. J. Liang, ACS Appl. Mater. Interfaces
2014, 6, 5212–5220; d) X. J. Feng, J. Peng, Z. Xu, R. Fang, H. Zhang, X.
Xu, L. Li, J. Gao, M. S. Wong, ACS Appl. Mater. Interfaces 2015, 7, 28156–
28165; e) E. Zhao, Y. Chen, H. Wang, S. Chen, J. W. Y. Lam, C. W. T. Leung,
Y. Hong, B. Z. Tang, ACS Appl. Mater. Interfaces 2015, 7, 7180–7188; f) J.
Mei, N. L. C. Leung, R. T. K. Kwok, J. W. Y. Lam, B. Z. Tang, Chem. Rev.
2015, 115, 11718–11940; g) L. Hu, Y. Duan, Z. Xu, J. Yuan, Y. Dong, T.
Han, J. Mater. Chem. C 2016, 4, 5334–5341.
[13] a) S. Yamaguchi, S. Akiyama, K. Tamao, J. Am. Chem. Soc. 2001, 123,
11372–11375; b) T. W. Hudnall, Y. M. Kim, M. W. P. Bebbington, D. Bouris-
sou, F. Gabbai, J. Am. Chem. Soc. 2008, 130, 10890–10891; c) G. Zhou,
C. L. Ho, W. Y. Wong, Q. Wang, D. Ma, L. Wang, Z. Lin, T. B. Marder, A.
Beeby, Adv. Funct. Mater. 2008, 18, 499–511; d) T. W. Hudnall, C. W. Chiu,
F. P. Gabba¨ı, Acc. Chem. Res. 2009, 42, 388–397; e) C. R. Wade, A. E. J.
Broomsgrove, S. Aldridge, F. P. Gabbaı, Chem. Rev. 2010, 110, 3958–
3984; f) Z. M. Hudson, C. Sun, M. G. Helander, H. Amarne, Z. H. Lu, S.
Wang, Adv. Funct. Mater. 2010, 20, 3426–3439; g) Y. Kim, H. S. Huh, M.
Lee, I. L. Lenov, H. Zhao, F. P. Gabbai, Chem. Eur. J. 2011, 17, 2057–2062;
h) C. Sun, Z. M. Hudson, M. G. Helander, Z. H. Lu, S. Wang, Organometal-
lics 2011, 30, 5552–5555; i) Z. M. Hudson, C. Sun, M. G. Helander, Y. L.
Chang, Z. H. Lu, S. Wang, J. Am. Chem. Soc. 2012, 134, 13930–13933;
j) B. Chen, Y. Ding, X. Li, W. Zhu, J. P. Hill, K. Ariga, Y. Xie, Chem.
Commun. 2013, 49, 10136–10138; k) W. Lin, Q. Tan, H. Liang, K. Y.
Zhang, S. Liu, R. Jiang, R. Hu, W. Xu, Q. Zhao, W. Huang, J. Mater. Chem.
C 2015, 3, 1883–1887; l) K. Suzuki, S. Kubo, K. Shizu, T. Fukushima, A.
Wakamiya, Y. Murata, C. Adachi, H. Kaji, Angew. Chem. Int. Ed. 2015, 54,
15231–15235; Angew. Chem. 2015, 127, 15446–15450; m) P. Puneet, R.
Vedarajan, N. Matsumi, Polym. Chem. 2016, 7, 4182–4187.
[14] S. Ma, H. Zhang, N. Zhao, Y. Cheng, M. Wang, Y. Shena, G. Tu, J. Mater.
Chem. A 2015, 3, 12139–12144.
[15] C. Wang, J. Jia, W. N. Zhang, H. Y. Zhang, C. H. Zhao, Chem. Eur. J. 2014,
20, 16590–16601.
[16] a) G. Oster, Y. Nishijlx, J. Am. Chem. Soc. 1956, 78, 1581–1584; b) S. Shar-
afy, K. A. Muszkat, J. Am. Chem. Soc. 1971, 93, 4119–4125.
[17] E. Sakuda, Y. Ando, A. Ito, N. Kitamura, J. Phys. Chem. A 2010, 114,
9144–9150.
[18] a) A. D. Becke, J. Chem. Phys. 1993, 98, 5648–5652; b) Gaussian 09, Revi-
sion A.02, 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. Peters-
son, 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. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J.
Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Nor-
mand, 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. Moroku-
ma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dap-
prich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski,
D. J. Fox, Gaussian, Inc., Wallingford CT, 2009.
[8] a) D. Chen, J. Zhan, M. Zhang, J. Zhang, J. Tao, D. Tang, A. Shen, H. Qiua,
S. Yin, Polym. Chem. 2015, 6, 25–29; b) A. Han, H. Wang, R. T. K. Kwok,
S. Ji, J. Li, D. Kong, B. Z. Tang, B. Liu, Z. Yang, D. Ding, Anal. Chem. 2016,
88, 3872–3878; c) Y. X. Zhu, Z. W. Wei, M. Pan, H. P. Wang, J. Y. Zhanga,
C. Y. Su, Dalton Trans. 2016, 45, 943–950.
[9] a) T. Noda, Y. Shirota, J. Am. Chem. Soc. 1998, 120, 9714–9715; b) S. Ya-
maguchi, T. Shirasaka, T. Tamao, Org. Lett. 2000, 2, 4129–4132; c) C. D.
Entwistle, T. B. Marder, Angew. Chem. Int. Ed. 2002, 41, 2927–2931;
Angew. Chem. 2002, 114, 3051–3056; d) A. Sundararaman, K. Venkata-
subbaiah, M. Victor, L. N. Zakharov, A. L. Rheingold, F. Jakle, J. Am.
Chem. Soc. 2006, 128, 16554–16565; e) T. Agou, J. Kobayashi, T. Kawa-
shima, Chem. Eur. J. 2007, 13, 8051–8060; f) U. Megerle, F. Selmaier, C.
Lambert, E. Riedlea, S. Lochbrunnerc, Phys. Chem. Chem. Phys. 2008, 10,
6245–6251; g) Z. M. Hudson, S. Wang, Acc. Chem. Res. 2009, 42, 1584–
1596; h) G. L. Fu, H. Y. Zhang, Y. Q. Yan, C. H. Zhao, J. Org. Chem. 2012,
77, 1983–1990; i) M. Steeger, C. Lambert, Chem. Eur. J. 2012, 18, 11937–
11948; j) L. Chen, Y. Jiang, H. Nie, R. Hu, H. S. Kwok, F. Huang, A. Qin, Z.
Zhao, B. Z. Tang, ACS Appl. Mater. Interfaces 2014, 6, 17215–17225; k) C.
Reus, F. Guo, A. John, M. Winhold, H. W. Lerner, F. Jꢃkle, M. Wagner,
Macromolecules 2014, 47, 3727–3235; l) T. Kushida, A. Shuto, M. Yoshio,
T. Kato, S. Yamaguchi, Angew. Chem. Int. Ed. 2015, 54, 6922–6925;
Angew. Chem. 2015, 127, 7026–7029; m) L. Ji, R. M. Edkins, L. J. Sewell,
A. Beeby, A. S. Batsanov, K. Fucke, M. Drafz, J. A. K. Howard, O. Moutou-
net, F. Ibersiene, A. Boucekkine, E. Furet, Z. Liu, J. F. Halet, C. Katan, T. B.
Marder, Chem. Eur. J. 2014, 20, 13618–13635; n) X. Yin, J. Chen, R. A. La-
lancette, T. B. Marder, F. Jakle, Angew. Chem. Int. Ed. 2014, 53, 9761–
9765; Angew. Chem. 2014, 126, 9919–9923; o) A. G. Bonn, O. S. Wenger,
J. Org. Chem. 2015, 80, 4097–4107; p) Z. Zhang, R. Edkins, J. Nitsch, K.
Fucke, A. Eichhorn, A. Steffen, Y. Wang, T. B. Marder, Chem. Eur. J. 2015,
21, 177–190; q) K. Schickedanz, T. Trageser, M. Bolte, H. W. Lerner, M.
Wagner, Chem. Commun. 2015, 51, 15808–15810; r) V. M. Hertz, H. W.
Lerner, M. Wagner, Org. Lett. 2015, 17, 5240–5243; s) P. Joshi, R. Vedara-
jan, N. Matsumi, Chem. Commun. 2015, 51, 15035–15038; t) X. Yin, F.
Guo, R. A. Lalancette, F. Jꢃkle, Macromolecules 2016, 49, 537–546; u) Y.
Ren, F. Jꢃkle, Dalton Trans. 2016, 45, 13996–14007.
[10] a) W. Z. Yuan, S. Chen, J. W. Y. Lam, C. Deng, P. Lu, H. H. Y. Sung, I. D. Wil-
liams, H. S. Kwok, Y. Zhang, B. Z. Tang, Chem. Commun. 2011, 47,
11216–11218; b) R. Yoshii, A. Hirose, K. Tanaka, Y. Chujo, Chem. Eur. J.
2014, 20, 8320–8324; c) R. Yoshii, A. Hirose, K. Tanaka, Y. Chujo, J. Am.
Chem. Soc. 2014, 136, 18131–18139; d) M. Tominaga, H. Naito, Y. Mori-
saki, Y. Chujo, New J. Chem. 2014, 38, 5686–56980; e) R. Yoshii, K.
Tanaka, Y. Chujo, Macromolecules 2014, 47, 2268–2278; f) K. Tanaka, Y.
Chujo, NPG Asia Materials 2015, 7, e223; g) L. Chen, G. Lin, H. Peng, H.
Nie, Z. Zhuang, P. Shen, S. Ding, D. Huang, R. Hu, S. Chen, F. Huang, A.
Qin, Z. Zhao, B. Z. Tang, J. Mater. Chem. C 2016, 4, 5241–5247; h) S. Li,
Y. Shang, L. Wang, R. T. K. Kwokb, B. Z. Tang, J. Mater. Chem. C 2016, 4,
5363–5369; i) H. Shi, D. Xin, X. Gu, P. Zhang, H. Peng, S. Chen, G. Lin, Z.
Zhao, B. Z. Tang, J. Mater. Chem. C 2016, 4, 1228–1237; j) T. Butler, W. A.
Morris, J. S. Kosicka, C. L. Fraser, ACS Appl. Mater. Interfaces 2016, 8,
1242–1251.
[19] A. D. Becke, Phys. Rev. A 1988, 38, 3098–3100.
[20] C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785–789.
[21] W. C. Lin, S. K. Fang, J. W. Hu, H. Y. Tsai, K. Y. Chen, Anal. Chem. 2014, 86,
4648–4652.
[22] A. Shrivastava, V. B. Gupta, Chron. Young Sci. 2011, 2, 21–25.
Received: July 14, 2016
Published online on && &&, 0000
Chem. Eur. J. 2016, 22, 1 – 12
www.chemeurj.org
11
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
FULL PAPER
Hazard detectors: The design and syn-
thesis of a series of triarylborane–oligo-
thiophene–dicyanovinyl triads 4–6 (A–
D–A’) is reported (see figure). The opti-
cal properties of 4–6 were elegantly
modulated by judiciously varying the
number of thiophenyl spacer between
the acceptors. Compounds 5 and 6 are
AIE active and also exhibit significant lu-
minescence in a PMMA matrix. Filter
paper strips coated with compounds 5
and 6 can detect Fꢀ and CNꢀ in aque-
ous media with different colorimetric re-
sponses.
&
Fluorescent Sensors
G. R. Kumar, S. K. Sarkar, P. Thilagar*
&& – &&
Aggregation-Induced Emission and
Sensing Characteristics of
Triarylborane–Oligothiophene–
Dicyanovinyl Triads
&
&
Chem. Eur. J. 2016, 22, 1 – 12
www.chemeurj.org
12
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!