Exciplex formation between a pair of synthesized AIEgens leads to white light generation: A spectroscopic exploration

Article abstract of DOI:10.1039/d0nj02489a

Two compounds, namely 2-(1H-benzo[d]imidazol-2-yl)-6-methoxyphenol (BIMP) and (E)-ethyl 2-cyano-3-(pyren-3-yl)acrylate (ECPA), were synthesized and characterized. BIMP portrayed an interesting feature of aggregation promoted enhancement of excited state intramolecular proton transfer (ESIPT) in water. On the other hand, ECPA shows AIE emission in solution. Steady state spectroscopic studies revealed that the BIMP-ECPA ensemble in solution behaves as a white light emitter, where BIMP acts as a donor and ECPA as an acceptor. The mechanism operative behind the observed white light generation was revealed to be exciplex formation between BIMP and ECPA. The current report is the first example of white light generation from two synthesized AIEgens through exciplex formation and hence holds its own merit for a smart choice of synthesized compounds resulting in white light generation. This journal is

Full text of DOI:10.1039/d0nj02489a

View Article Online
View Journal
NJC
New Journal of Chemistry
Accepted Manuscript
A journal for new directions in chemistry
This article can be cited before page numbers have been issued, to do this please use: A. Bhattacharyya
and N. Guchhait, New J. Chem., 2020, DOI: 10.1039/D0NJ02489A.
Volume 42
This is an Accepted Manuscript, which has been through the
Number
6
21 March 2018
Pages 3963-4776
Royal Society of Chemistry peer review process and has been
accepted for publication.
NJC
New Journal of Chemistry
rsc.li/njc
A journal for new directions in chemistry
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
Information for Authors.
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 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 1144-2546
PAPER
Chechia Hu, Tzu-Jen Lin et al.
Yellowish and blue luminescent graphene oxide quantum dots
prepared via a microwave-assisted hydrothermal route using
H2O2 and KMnO4 as oxidizing agents
rsc.li/njc

Page 1 of 28
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
Exciplex Formation between a Pair of Synthesized AIEgens Leads to White Light
Generation: A Spectroscopic Exploration
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Arghyadeep Bhattacharyya and Nikhil Guchhait*
Department of Chemistry, University of Calcutta, 92, A.P.C. Road, Kolkata-700009, India
*Corresponding author. Tel.: +913323508386; fax: +913323519755.
E-mail address: nguchhait@yahoo.com (N. Guchhait).
Abstract: Two compounds, namely 2-(1H-benzo[d]imidazol-2-yl)-6-methoxyphenol (BIMP)
and (E)-ethyl 2-cyano-3-(pyren-3-yl) acrylate (ECPA) were synthesized and characterized.
BIMP portrayed the interesting feature of aggregation promoted enhancement of excited state
intramolecular proton transfer (ESIPT) process in water. On the other hand, ECPA shows AIE
emission in solution. Steady state spectroscopic studies revealed BIMP-ECPA ensemble in
solution behave as white light emitter, where BIMP acts as donor and ECPA as acceptor. The
mechanism operative behind the observed white light generation was revealed to be exciplex
formation between BIMP and ECPA. The current report is the first example of white light
generation from two synthesized AIEgens through exciplex formation and hence holds its own
merit for smart choice of synthesized compounds to result in white light generation.
1

New Journal of Chemistry
Page 2 of 28
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
Introduction
5
6
7
8
9
The seminal work by Tang et al1 in the discovery of aggregation induced emission (AIE)
phenomenon has opened up new avenues in the field of molecular recognition2, construction of
OLEDs3 as well as biological imaging agents4. Of late, several groups are engaged in designing
molecular probes where interesting excited state phenomena like excited state intramolecular
proton transfer (ESIPT), twisted intramolecular charge transfer (TICT) are present along with the
AIE phenomenon5. However, another practical application of immense importance concerning
AIE active probes is their ability to sensitize dye molecules, as reported by Liu et.al6, 7. The
sensitization of commercially available fluorescent dyes like Rhodamine B and Nile Red has
been achieved by AIE active Schiff bases by the mentioned group. In almost every case, the
mechanism operative behind the energy transfer or sensitization has been reported to be FRET6.
Hence, investigations of energy transfer, if any, between a pair of synthesized fluorophores
seemed to be an enticing problem to us. At this stage, we decided to check the properties of two
individual synthetic AIE active probes, namely 2-(1H-benzo[d]imidazol-2-yl)-6-methoxyphenol
(BIMP) and (E)-ethyl 2-cyano-3-(pyren-3-yl) acrylate (ECPA). BIMP was reported by Takagi
et al8 in a report concerning the relative efficacies of three methoxy substituted 2-
hydroxybenzimidazole derivatives. However, BIMP was neither subjected to rigorous
spectroscopic dissection, nor was the behavior of the same in aqueous medium discussed. Our
spectroscopic analyses proved that BIMP portrays the AIE promoted enhancement ESIPT
process. Such observations have been reported in different organic probes by McGrier as well as
Yu et al9, 10. Likewise for ECPA, Zhang et al exploited its emission properties to detect bisulfate
in food samples in 50% aqueous DMSO, without shedding any light on the spectroscopic
features of the same. Our analyses on ECPA revealed it to behave as an intramolecular charge
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2

Page 3 of 28
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
7
8
9
transfer (ICT) probe and also showed aggregation induced emission in water. Interestingly,
BIMP and ECPA were found to generate white light in solution when mixed together and hence
their ensemble could be treated as a white light emitter. Furthermore, the detailed photophysical
survey revealed the underlying mechanism behind the white light generation to be an exciplex
formation between the two AIEgens. Although white light emitters have been reported by
various groups11-15, the use of two synthesized organic compounds as components in a white
light emitter has been reported by no other group according to our literature survey. Harnessing
exciplex formation to generate white light in solution is unique in itself, as FRET16 is almost
exclusively accounted for white light generation in various reports. The novelty also lies in the
fact that for the first time two emissive molecules are forming an exciplex to generate white light
in solution. Hence, the current report holds its own merit owing to the ludicrous photophysical
properties of two synthesized organic fluorophores as well as the rare phenomenon of white light
generation due to exciplex formation.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Experimental Section
Materials and methods
Ortho-vanillin, ethylene diamine, pyrene aldehyde were purchased from Sigma Aldrich and used
1
as received. H NMR spectra were recorded on a Bruker Advance 300 spectrometer, where
chemical shifts (δ in ppm) were determined with respect to Tetramethyl silane (TMS) as the
internal standard. Mass spectrometry was carried out in Waters Xevo G2-S Q TOF mass
spectrometer. DLS studies were carried out in Model DLS-nano ZS, Zetasizer, Nanoseries,
Malven Instrument capable of detecting particle size between 0.6 nm to 6.0 µM. For spectral
studies, UV grade solvents purchased from Spectrochem were used and double distilled water
3

New Journal of Chemistry
Page 4 of 28
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
7
8
9
was used throughout the spectroscopic investigations. Steady state electronic absorption and
fluorescence spectra were recorded on a Shimadzu UV–1900 spectrophotometer and Perkin
Elmer LS55 fluorimeter, respectively. Time resolved emission profile was recorded by Horiba
Delta Flex NL-fluorimeter. The goodness of fitting was judged using χ2 criteria30. The average
lifetime was calculated using standard procedures. The single crystal of compound BIMP was
mounted on a Bruker-AXS SMART APEX II diffractometer equipped with a graphite
monochromator and Mo Ka (l = 0.71073 Å) radiation. The crystal was placed 60 mm from the
CCD and 360 frames were measured with a counting time of 5 s. The structure was solved using
the Patterson method using SHELXS 97. Subsequent difference Fourier synthesis and least-
square refinement revealed the positions of the remaining non-hydrogen atoms. Non-hydrogen
atoms were refined with independent anisotropic displacement parameters. Hydrogen atoms
were placed in idealized positions and their displacement parameters were fixed to be 1.2 times
larger than those of the attached non-hydrogen atoms. Successful convergence was indicated by
the maximum shift/error of 0.001 for the last cycle of the least squares refinement. Absorption
corrections were carried out using SADABS program. All calculations were carried out using
SHELXS 97, PLATON 99, ORTEP-32 and WinGX system Ver-1.6417. For spectral studies,
stock solutions of BIMP and ECPA were prepared in spectroscopic grade acetonitrile and
DMOS respectively.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Synthetic procedure for 2-(1H-benzo[d]imidazol-2-yl)-6-methoxyphenol (BIMP)
To a stirred solution of 10 mmol ortho-vanillin in ethanol was added a 5 mL aqueous solution of
sodium bisulfate (11 mmol). The reaction mixture was stirred at room temperature for ~24 hours,
thereby forming a white precipitate (Scheme 1). The precipitate was filtered and washed with
ethanol. Then it was suspended in 15 mL DMF and 5 mL solution of 10 mmol ortho-
4

Page 5 of 28
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
7
8
9
phenylenediamine in DMF was added using a micropipette, giving an instant orange color. Then
the mixture was strongly heated a 120º C in an oil bath with stirring for 16 hours, when TLC
analysis showed completion of reaction. Then the reaction mixture was poured in ~100 mL of
ice-water mixture containing 2 gm of NaCl, resulting in yellowish solid. The solid was filtered
under suction and heated in 25 mL methanol. The hot solution was filtered and dried to give 2-
(1H-benzo[d]imidazol-2-yl)-6-methoxyphenol (BIMP) in 70% yield. The single crystals of
BIMP were obtained from slow evaporation of saturated acetonitrile solution. 1H NMR (DMSO-
d6, 298 K): 13.26 (s, 1H), 7.62 (d, 3H), 7.28 (s, 2H), 6.98 (d, 1H), 6.93-6.98 (m, 1H), 3.78 (s,
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
13
3H) C NMR (DMSO-d6, 298 K): 151.9, 148.6, 148.4, 122.9, 118.8, 117.7, 114.1, 112.6, 55.8
ESI-MS calculated for [M-H]+:241.2652, obtained: 241.2758.
Synthetic procedure for (E)-ethyl 2-cyano-3-(pyren-3-yl) acrylate (ECPA)
To a well stirred hot solution of 2mmol pyrene-1-carboxaldehyde in 10 mL ethanol 2.2 mmol of
ethyl cyanoacetate was added using a micropipette, followed by addition of ~2.5 mmol of fresh
piperidine using a micropipette (Scheme 1). The addition immediately resulted in orange
coloration of the reaction mixture. The reaction mixture was heated at 50º C for 6 hours, thereby
causing an orange precipitate in large amount. The reaction mixture was cooled and stirred for a
further period of 1 hour and filtered under suction and washed with ethanol, followed by air
1
drying to afford (E)-ethyl 2-cyano-3-(pyren-3-yl) acrylate (ECPA) in 90% yield. H NMR
13
(CDCl3, 298 K): 9.37 (s, 1H), 8.87 (s, 1H), 8.09-8.31 (m, 9H), 4.53 (s, 2H), 1.67 (s, 3H) C
NMR (CDCl3, 298 K): 162.8, 151.9, 134.6, 131.3, 130.9, 129.6, 127.2, 126.9, 126.7, 126.5,
126.1, 124.9, 124.5, 121.6, 62.7, 14.2 ESI-MS calculated for [M-H]+: 326.1181, obtained:
326.1171.
5

New Journal of Chemistry
Page 6 of 28
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
Results and discussions
5
6
7
8
9
Compounds BIMP and ECPA were synthesized as shown in Scheme 1. The detailed
characterization has been provided in the Supporting Information (ESI, Fig. S1-S6). The single
crystal of BIMP (CCDC Number: 1974402) was obtained to explore the effects of H-bonding
and stacking in the solid state. The ORTEP diagram of BIMP at 50% probability is provided in
Figure S7. BIMP shows both intramolecular and intermolecular hydrogen bonding feature (Fig.
1a). The phenolic -OH proton of BIMP undergoes a hydrogen bonding with N1.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
SO3Na
H
N
CHOH
NH2
NH2
DMF
NaHSO3, Ethanol
24 hrs stirring, rt
CHO
OH
reflux, 16 hrs
N
OH
O
OH
O
O
2-(1H-benzo[d]imidazol-2-yl)-6-
methoxyphenol (BIMP)
H
CHO
CO2Et
CN
piperidine
ethanol, stirring, rt
CN
CO2Et
(E)-ethyl 2-cyano-3-(pyren-3-yl)acrylate (ECPA)
Scheme 1. Synthetic routes of BIMP and ECPA.
Similarly, the amine proton H6 undergoes H-bonding with phenolic -OH proton. Due to this
hydrogen bonding, an extended hydrogen bonded network is obtained (Fig. 1b). BIMP also
undergoes non-classical hydrogen bonding with the aromatic proton (H5) and methoxy O atom
(Fig. 1a). A similar extended network is formed by this non-classical hydrogen bonding (Fig.
1b). The preliminary spectroscopic investigations of the two compounds were started by
6

Page 7 of 28
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
7
8
9
recording the absorption profiles of the two compounds in various solvents (Fig. 2a, Table 1).
BIMP showed two distinct bands at ~300 and ~320 nm in all solvents studied. The two bands
could be transition to two electronic states or ground state two forms of BIMP as was reported
for the parent compound 2-(2’-hydroxyphenyl)benzimidazole (HBI) by Dogra et al18. Adding
Tetrabutylammonium hydroxide as a source of base to the acetonitrile solution of BIMP, a new
band was generated ~380 nm (ESI, Fig. S8a), indicating anion formation (anion of HBI is
reported to appear at ~347 nm18 in the absorption spectrum). Upon exciting BIMP at the
aforesaid wavelengths, dual emission was observed in both cases (Fig. 2b, ESI Fig. S9 for
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
a)
b)
Fig. 1 (a) Hydrogen bonding interactions in BIMP. (b) Classical and Non classical hydrogen
bonded network in BIMP.
7

New Journal of Chemistry
Page 8 of 28
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
7
8
9
profiles of BIMP when excited at 300 nm). The short wavelength emission band at ~370 nm was
assigned to be due to the local or enol emission (LE) of BIMP, whereas the long wavelength
band at ~480 nm was assigned to be keto form or ESIPT emission (PT) of BIMP as reported by
Takagi et al8. Similar spectral observation was reported for its parent compound 2-(2’-
hydroxyphenyl) benzimidazole18. Further support of the long wavelength band to be the ESIPT
band of the keto-form was obtained upon adding base to an acetonitrile solution of BIMP
whereupon the long wavelength band disappeared and a new emission band was obtained at
~440 nm (ESI, Figure S8b) for the anion (emission of anion of HBI is reported to be at ~410
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fig. 2 (a) Normalized Absorption profile of BIMP (10 µM) in various solvents. (b) Emission
profiles of BIMP (5 µM) in various solvents (ex=320 nm). (c) Normalized Absorption profiles
8

Page 9 of 28
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
of ECPA (6 µM) in various solvents. (d) Emission profiles of ECPA (4 µM) in various solvents
(ex=405 nm). (For solvent abbreviations, please refer to Tables 1 and 2).
7
8
9
nm17). The existence of enol emission in non-polar solvent like heptane indicates the stabilization
of the same by intramolecular hydrogen bonding between the phenolic –OH proton and the
methoxy oxygen or nitrogen of imidazole unit. Interestingly, the PT band was found to
experience gradual blue shifting upon moving from non-polar to protic solvents (Table 1). This
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table 1 Steady state absorption and emission spectral parameters of BIMP in different solvents
absmax(nm)
300, 320
300, 320
300, 320
305, 325
300, 327
300, 320
300, 320
emmax(nm)
364, 490
370, 482
370, 478
375, 480
365, 486
365, 475
-, 475
PT
Solvent (abbreviation used in text)
n-heptane (Heptane)
Chloroform (CHCl3)
Acetonitrile (ACN)
Dimethylsulfoxide (DMSO)
methanol (MeOH)
Isopropanol (iPrOH)
Water
0.043
0.060
0.052
0.075
0.121
0.567
0.784
could be due to donation of charge from the –NH moiety of BIMP to the keto form. This
donation is favoured in case of poor solvating non-polar solvents. But good solvation by dipolar
or hydrogen bonding interactions arrests the donation of charge, thereby affecting blue shift in
9

New Journal of Chemistry
Page 10 of 28
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
7
8
9
the emission spectrum. A single band at ~475 nm was observed when excited at either 300 or
320 nm (Fig. 2b) in water. This could be the consequence of any of four reasons: i) only ESIPT,
ii) water assisted ESIPT or iii) AIE or iv) AIE through ESIPT19. However, the second possibility
was ruled out after comparing the solid state emission spectra of BIMP (Fig. 3a). Since the solid
state emission spectra as well as that in water were totally in accordance, it could be stated that in
aqueous phase BIMP behaves similarly to that in solid state, a condition considered necessary
for a compound to be considered AIE active20. This was better understood from the color of
solutions of BIMP under UV chamber and comparing them with that of the solid state (Fig. 3b).
However, BIMP showed blue color (color of solid state under UV light) in acetonitrile also other
than water. This primarily indicated formation of aggregates in acetonitrile too. However,
concentration increment experiments denied the possibility of aggregate formation in acetonitrile
(Fig. 4a). Gradual increment in concentration of BIMP caused quenching of both bands, an
outcome of the well known aggregation caused quenching (ACQ)20. However, addition of BIMP
in water (Fig. 4b) caused gradual increment in the emission intensity, indicating aggregate
formation in water as well as restriction of intramolecular rotation (RIR) which usually causing
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
21
deactivation through non-radiative processes . Furthermore, if the spectrum in acetonitrile be
observed, both bands are present, signifying sufficient solvation of BIMP by acetonitrile.
However, a single emission band in water ensured aggregate formation reinforces ESIPT
process, as in solid state only ESIPT is favoured for 2-hydroxybenzothaizole and
benzimidazoles22. A perusal of the quantum yield values of BIMP in various solvents indicates
the aggregate formation in water (Table 1). The quantum yield value is much higher in polar
protic solvents as compared to non polar solvents. This could be due to two factors: a) the higher
dielectric constant provided by this solvent stabilizes the excited state of the compounds and (b)
10

Page 11 of 28
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
7
8
9
the effect of viscosity. Most convincing proof of aggregate formation exclusively in water was
obtained from Dynamic Light Scattering (DLS) experiment (ESI, Fig. S10a & b). The particle
size of BIMP in acetonitrile was 174.0 nm, whereas the same in water was 342.0 nm. The
approximately doubled value of hydrodynamic radius could assure the aggregate formation in
water23. Followed by the steady state spectral studies, the excited state lifetime of BIMP was
measured in various solvents and monitored at both the LE and PT bands (Fig. 4a, 4b, Table 2)
using an available pulsed laser diode excitation source of 320 nm wavelength. When monitored
at the LE wavelength (370 nm), BIMP showed exclusive monoexponential decay having
lifetime in the order of a few nanoseconds. Addition of base to acetonitrile solution of BIMP
generated a long component having lifetime of 3.45 ns, which was identified as the anion
lifetime of BIMP. When monitored at the PT emission (~475 nm), mono exponential decay was
observed in non-polar solvents like heptane and chloroform. However, biexponential decay was
observed in acetonitrile and methanol. The longer lifetime component with very small
contribution in those solvents correlated with the lifetime of the locally excited enol form. But,
the larger component with faster lifetime corresponds to the PT form observed in these polar
solvents as reported earlier24. The monoexponential decay for both the decays in polar solvents
DMSO and isopropanol may reflect the cumulative effect of viscosity as well as hydrogen
bonding25. In water, an exceptionally long lifetime component of 5.64 ns was observed with a
contribution of 71%. The very high lifetime was an outcome of BIMP forming aggregates in
aqueous medium. The shorter component of 1.78 ns could be due to the anion of BIMP in
equilibrium with the aggregated form of BIMP in water. The crystal packing of BIMP also
supported the aggregate formation. As was seen in Fig. 1c, BIMP was found to form hydrogen
bonded network. Such a network could be easily formed in poor polar solvent heptane as
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
11

New Journal of Chemistry
Page 12 of 28
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
7
8
9
hydrogen bonding shall be favored. Hence, the long lifetime component in heptane could be
explained. In water the hydrogen bonding interactions shall be ruptured. However, BIMP shall
still form aggregates via non-classical H-bonding interactions as shown in Figure 1d. Thus,
detailed photophysical survey of BIMP supports the possibility of aggregate formation in water.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fig. 3 (a) Solid state emission profile of BIMP (inset: color of BIMP under ambient light (left)
and UV light (right)). (b) Color of BIMP (20 µM) in (from left): n-Heptane, Chloroform,
acetonitrile, dimethylsulfoxide, methanol, isopropanol and water. (c) Color of ECPA (15 µM) in
(from left): n-Heptane, Chloroform, acetonitrile, dimethylsulfoxide, methanol, isopropanol and
water. (d) Solid state emission profile of ECPA (inset: color of ECPA under ambient light (left)
and UV light (right).
12

Page 13 of 28
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fig. 4(a) Emission spectra with increasing concentration of BIMP in acetonitrile. (b)
Concentration increment of BIMP in water, (c) Effect of increasing water content on the
emission profile of ECPA (4 µM).
13

New Journal of Chemistry
Page 14 of 28
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
Table 2 Excited State Lifetime parameters of BIMP in various solvents, BIMP + base in
5
6
acetonitrile
7
8
9
λmon(nm)/Solvents(species)
360/n-Heptane (BIMP)
490/n-Heptane (BIMP)
364/chloroform (BIMP)
483/ chloroform (BIMP)
370/acetonitrile (BIMP)
478/acetonitrile (BIMP)
375/dimethylsulfoxide (BIMP)
480/dimethylsulfoxide (BIMP)
365/methanol (BIMP)
τ1 (ns)/α1 (%) τ2 (ns)/α2 (%) χ2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1.22/100
0.85/79
-
1.05
0.97
1.12
1.04
1.06
1.07
1.17
1.21
1.09
0.93
0.92
1.15
1.19
1.09
5.94/21
0.98/100
0.73/100
1.87/100
0.30/98.163
0.85/100
2.29/100
0.61/98
-
-
-
1.83/2
-
-
486/methanol (BIMP)
2.23/100
1.82/100
1.78/28
-
365/isopropanol (BIMP)
475/isopropanol (BIMP)
475/water (BIMP)
2.03/2
-
3.45/100
-
440/acetonitrile(BIMP+base)
5.64/72
-
Following BIMP, thorough photo physical characterization of ECPA was conducted (Fig. 2c,
Table 3). A 6 µM solution of ECPA showed prominent absorption band between ~400-430 nm
depending on the solvent polarity as shown in Table 3 and a high energy band at ~300 nm. The
structured nature of bands was due to the pyrene nucleus26 in ECPA. The broadening of the tail
14

Page 15 of 28
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
7
8
9
in aqueous medium could be an outcome of the well known Mie Scattering27.The red shift of the
absorption maxima compared to the unsubstituted pyrene could be accounted for as an outcome
of the introduction of ethyl cyanoacetate moiety, thereby increasing chromophoric stabilization.
The low energy band was assigned to be due to S0→S1 transition whereas the high energy band
could be due to some higher order transition. The emission profiles (Fig. 2d, Table 3) of ECPA
exhibited structured bands at ~450 nm and a hump at ~510 nm in n-heptane. Since pyrene
monomer in solution is associated with structured bands28, the high energy band was assigned to
be due to the pyrene moiety in ECPA. However, with increment in polarity, the emission
maxima underwent a red shift (Table 3). The red shift in emission maxima could be due to
different extent of stabilization of the locally excited state compared to the ground state or a
possible intramolecular charge transfer (ICT) from pyrene nucleus to the ethyl cyanoacetate unit
in ECPA. Such an ICT could be possible due to the unique property of the pyrene nucleus that
can serve as source or sink for negative charge depending on the substitution29. However, with
introduction of protic solvents, the emission maxima underwent a blue shift, indicating the effect
difference in relative stabilization of the states30. Interestingly, in aqueous solution, ECPA
showed strong emission band at ~620 nm and a small band at ~475 nm. To understand the origin
of the red shifted band in water, color of solutions under UV light were compared to that in the
solid state (Fig. 2). The exact correspondence of the red color of ECPA in solid state with that in
water indicated at aggregate formation in water. Approaching in a similar manner to BIMP, the
DLS profiles of ECPA were recorded in acetonitrile and water (ESI, Fig. S11a, b). The
hydrodynamic radius underwent an increment of 1.5 times in water compared to acetonitrile.
Followed by DLS, effect of increasing percentage of water in a binary mixture of acetonitrile and
water on the emission spectrum of ECPA was observed (Fig. 3). The quantum yield value of
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
15

New Journal of Chemistry
Page 16 of 28
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
7
8
9
ECPA was higher in water than any other solvent, indicating aggregate formation (Table 3).
After 80% water content, the emission profile consisted of a band at ~615 nm. Recalling that
solid state emission profile of ECPA also consisted of a single band at ~620 nm, it could thus be
concluded that like BIMP, ECPA behaves similarly in water as well as in solid state. The above
observations thus established ECPA as an AIE active molecule. At this juncture, it is worthwhile
to note that although AIE effect is observed for both ECPA and BIMP in water as evidenced
from emission studies, DLS studies indicate that substantial aggregates are formed in acetonitrile
for both compounds. However, these aggregates do not lead to emission increment. Rather ACQ
is operative in organic solvents. The photophysical studies of ECPA were concluded by
recording the excited state lifetime in various solvents using a 405 nm LASER source (Fig. 5).
The decay profiles of ECPA consisted of very fast components
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
16

Page 17 of 28
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fig. 5 (a) Decay profiles of BIMP in various solvents monitored at LE. (b) Decay profiles of
BIMP in various solvents monitored at PT. (c) Decay profiles of ECPA in various solvents.
Table 3 Steady State spectral parameters of ECPA in various solvents
absmax(nm)
emmax(nm)

Solvent (abbreviation used
in text)
n-heptane (Heptane)
Chloroform (CHCl3)
Acetonitrile (ACN)
293, 305, 387, 411, 433
263, 309, 392, 435
305, 385, 419
451, 473, 511
495, - , -
0.012
0.015
0.013
508, - , -
17

New Journal of Chemistry
Page 18 of 28
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
7
8
9
Dimethylsulfoxide (DMSO)
Methanol (MeOH)
Isopropanol (iPrOH)
Water
308, 390, 427
515, - , -
512, - , -
500, - , -
475, - , 612
0.025
305, 388, 424
307, 390, 433
313, 396, 437
0.032
0.045
0.685
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
beyond the instrumental resolution to provide any fitting in all solvents. The very fast
components of the decay profiles were the consequence non-radiative decay through the flexible
bonds24 in ECPA. However, for water, the decay was triexponential in nature when monitored at
615 nm. The lifetime values were ~3.6 ns (23%), 11.95 ns (72%) and 0.4 ns (5%). The
component having the longest lifetime was thus assigned to be due to aggregates of ECPA in
water. The component having lifetime of 3.6 ns was assigned to be due to monomer of pyrene
co-existing with the aggregate and the fast component was probably due to some solvated form
of ECPA with water molecules. Having explored the photophysical characteristics of both the
compounds under consideration, it was investigated whether any energy transfer was possible
between the two molecules. The rationale behind considering the possibility of an energy transfer
between the two molecules was the appreciable overlap of the emission profile of BIMP with the
absorption profile of ECPA (ESI, Fig. S12). This suggested that BIMP can act as a photon
donor and ECPA as an acceptor31.
18

Page 19 of 28
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fig. 6 (a) Normalized emission spectra of BIMP (ex=320 nm), ECPA (ex=405 nm) and their
mixture (ex=320 nm), (b) Titration of BIMP (10 µM) with increasing amount of ECPA
(ex=330 nm) (0 µM to 10 µM) (inset middle) white light generated from ECPA and BIMP
mixture, (c) Decay profiles of BIMP-ECPA ensemble when monitored at 470 nm, (d) Decay
profiles of BIMP-ECPA ensemble when monitored at 625 nm. For all the spectra the solvent
used was water.
Upon adding ECPA (0 µM to 10 µM) to an aqueous solution of BIMP, the emission band for
BIMP was reduced to a hump along with generation of a red shifted band at ~500 nm was
formed and was accompanied by a band at ~625 nm (Fig. 6a & b). The decrement of the band at
~470 nm as well as the concomitant increment of the band at ~620 nm was accompanied by an
19

New Journal of Chemistry
Page 20 of 28
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
isoemissive point, indicating equilibrium. Thus, the emission profile of BIMP-ECPA ensemble
5
6
consisted of bands at ~470 nm, 500 nm as well as ~625 nm.
7
8
9
Table 4 Excited State Lifetime parameters of BIMP-ECPA when monitored at 470 nm
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Species
τ1 (ns)/α1 (%) τ2 (ns)/α2 (%) χ2
BIMP+2.0 µM ECPA
BIMP+5.0 µM ECPA
BIMP+10.0 µM ECPA
BIMP+20.0 µM ECPA
1.43/19.8
1.34/22.3
1.27/21.4
1.23/21.0
4.80/81.2
4.45/77.7
4.42/78.6
4.30/79
1.20
1.09
1.13
1.00
This indicated that the emission profile encompassed the entire range of the visible light
spectrum. To verify this, color of the solution of BIMP-ECPA was observed under UV-light
(Fig. 6b inset). Interestingly, the color of the solution was white under UV-light. The white light
generation could also be rationalized from the titration profile of BIMP with ECPA (Fig. 6b),
where the bands at 470 nm, 500 nm and 625 nm were having almost same intensity values. This
striking observation of white light generation was further analyzed to find out the underlying
process responsible behind this observation. The most important spectral feature of the BIMP-
ECPA ensemble was that the individual emission wavelengths of the two constituents each
underwent a red shift. This red shift in the emission maximum was first indication of a possible
exciplex formation between BIMP and ECPA as a very well known exciplex pair pyrene-
dimethylaniline is also reported to be associated with a red shifted band upon exciplex
formation32. Furthermore, the decrement of intensity of the emission profile of BIMP-ECPA
ensemble was in agreement of the observation of decrement of emission quantum yield upon
20

Page 21 of 28
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
7
8
9
exciplex formation in aqueous medium by Cosa et al33. The determination of quantum yield of
the ECPA-BIMP ensemble also indicated exciplex formation. The standard for measuring
quantum yield was chosen to be Coumarin 15334. The quantum yield for both the bands at ~470
nm (0.784 to 0.025) and ~625 nm (0.685 to 0.032) underwent a decrement in the ensemble.
However, the band at 500 nm underwent had a quantum yield of 0.02. The excited state lifetime
values were recorded for BIMP-ECPA ensemble (Fig. 6). The lifetime of BIMP underwent
gradual decrement upon addition of ECPA (Fig. 6, Table 3). However, the lifetime of ECPA
underwent a dramatic reduction in the ensemble when monitored at 625 nm. This could be
explained upon considering the fact that even unsubstituted pyrene undergoes considerable
decrement in lifetime upon exciplex formation with dimethylaniline. Furthermore, the decrement
in lifetime is markedly observed in polar solvents as reported by Schryver et al35. The final
evidence behind exciplex formation was provided by recording the excitation spectra of the
ensemble at ~470 nm as well as ~625 nm. Resemblance of the UV spectra of the components
with the excitation spectra confirmed no ground state association occurs between the two
compounds considered (ESI, Fig. S13). Hence, it was proved that formation of exciplex was the
driving reason behind generation of white light in a mixture of BIMP and ECPA. The white
light generation phenomenon was also evidenced by constructing CIE chromacity diagrams for
ECPA-BIMP mixture in water (ESI, Fig. S14). The coordinates of pure white light is (0.33,
0.33). For the mixture, the CIE coordinates were (0.35, 0.38). Thus, the CIE coordinates closely
reiterate the white light generation in water for ECPA-BIMP mixture. Our results were in close
agreement to that reported by Das et al in a similar report involving white light emission from
fluorophore36. The role of water as the proper choice of solvent was also explored. Firstly, water
is a common bad solvent for both these compounds. Hence, the blue and red fluorogens form
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
21

New Journal of Chemistry
Page 22 of 28
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
7
8
9
exciplex to generate white light in water. In other good solvents the titration yielded blue and
green light respectively, thereby the efficacy of water as the medium for white light generation
was understood (Fig. 7). In the solid state, no white light generation was observed even after
mixing them intimately in powdered form using mortar pestle. Thus, the polar environment of
water provides the necessary dielectric for the exciplex to form, which is otherwise absent in the
solid state. It is noteworthy to mention here that the possibility of simultaneous excitation of both
molecules was also considered. ECPA when excited at 320 nm showed very poor emission
intensity. Hence, the ratiometric nature of the titration profile between ECPA and BIMP was
due to exciplex formation and not due to simultaneous excitation. To have an idea of the excited
state processes leading to the exciplex formation a qualitative description. When both ECPA and
BIMP are mixed together in solvent, at first maximum BIMP molecules are excited as the
excitation wavelength is closer to the UV-Vis absorption maxima of BIMP. Then release of
photon of wavelength ~460 nm prompts excitation of ECPA molecules, whereupon the
complexation of the two species occur, leading to a very fast lived exciplex, whose emission
profile encompasses the visible region.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
22

Page 23 of 28
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fig. 7 (a) Titration of BIMP(10 µM) with ECPA (0 µM to 10 µM) in acetonitrile (inset: color
of BIMP-ECPA mixture under UV light); (b) Titration of BIMP(10 µM) with ECPA (0 µM to
10 µM)in chloroform (inset: color of BIMP-ECPA mixture under UV light). In both cases,
ex=330 nm.
Conclusions
The detailed photophysical survey of two synthesized AIE active probes BIMP and ECPA was
conducted. AIE occurs through ESIPT in case of BIMP whereas ECPA, also behaves as an AIE
active probe in non-aqueous medium. An aqueous solution of the two compounds generated
white light visible through the naked eye under UV light. Photophysical investigation of the
white light generation revealed the rare phenomenon of exciplex formation was responsible
behind the observation. We believe that our current report shall be useful in designing of donor
acceptor pairs for designing of white light emission pairs for OLED applications.
23

New Journal of Chemistry
Page 24 of 28
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
Acknowledgement
5
6
7
8
9
AB and SCM would like to acknowledge CSIR and UGC for their fellowship. NG thanks DST,
India (Project No. EMR/2016/004788) and CSIR, India (01(2920)18/EMR-II) for financial
support. The authors would like to thank Professor Dilip Kumar Maity, University of Calcutta
for providing instrumental facility for emission measurements and DLS studies.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
References
1 Y. Chen, J. W. Y. Lam, R. T. K. Kwok, B. Liu, B. Z. Tang, Mater. Horiz., 2019, 6, 428-433.
2 S. B. Roy, K. K. Rajak, J. Photochem. Photobiol. A 2017, 332, 505-514.
3 Y. Wang, Y. Liao, C. P. Cabry, D. Zhou, G. Xie, Z. Qu, D. W. Bruce, W. Zhu, J. Mater. Chem.
C, 2017, 5, 3999-4008.
4 Q. Chen, C. Jia, Y. Zhang, W. Du, Y. Wang, Y. Huang, Q. Yang, Q. Zhang, J. Mater. Chem.
B, 2017, 5, 7736-7742.
5 V. S. Padalkar, D. Sakamaki, K. Kuwada, N. Tohnai, T. Akutagawa, K. I. Sakai, S. Seki, RSC
Adv., 2016, 6, 26941-26949.
6 J. Chai, Y. Wu, B. Yang, B. Liu, J. Mater. Chem. C, 2018, 6, 4057-4064.
7 J. Yang, J. Chai, B. Yang, B. Liu, Spectrochim. Acta Part A., 2019, 211, 272–279.
8 K. Takagi, Y. Yamada, R. Fukuda, M. Ehara, D. Takeuchi, New J. Chem. 2018, 42, 5923-
5928.
24

Page 25 of 28
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
9 P. Jagadesan, T. Whittemore, T. Beirl, C. Turro, P. L. McGrier, Chem. Eur. J., 2017, 23, 917 –
5
6
925.
7
8
9
10 J. C. Qin, B. D. Wang, Z. Y. Yang, K. C. Yu, Sens. Actuator. B-Chem., 2016, 224, 892-898.
11 J. Kido, M. Kimura, K. Nagai, Science., 1995, 267, 1332–1334.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
12 Y. Sun, N. C. Giebink, H. Kanno, B. Ma, M. E. Thompson, S. R. Forrest, Nature, 2006, 440,
908-912.
13 S. Y. Lee, T. Yasuda, Y. S. Yang, Q. Zhang, C. Adachi, Angew. Chem., Int. Ed., 2014, 53,
6402–6406.
14 K. V. Rao, K. K. Datta, M. Eswaramoorthy and S. J. George, Adv. Mater., 2013, 25, 1713–
1718.
15 S. Reineke, F. Lindner, G. Schwartz, N. Seidler, K. Walzer, B. Lüssem and K. Leo, Nature,
2009, 459, 234–238.
16 C. Curutchet, B. Mennucci, Chem. Rev., 2017, 117, 294–343.
17 (a) SAINT, version 6.02; SADABS, version 2.03, Bruker AXS Inc, Madison, WI, 2002;
(b) Sheldrick, G. M.; SHELXS 97, Program for Structure Solution, University of Göttingen,
Germany, 1997;
(c) Sheldrick, G. M.; SHELXL 97, Program for Crystal Structure Refinement, University of
Göttingen, Germany, 1997.
18 H. K. Sinha, S. K. Dogra, Chem. Phy., 1986, 102, 337-347.
25

New Journal of Chemistry
Page 26 of 28
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
19 L. Macdonald, J. Wang, N. Alexander, H. Li, T. Liu, Y. Pang, J. Phys. Chem. B, 2016, 120,
5
6
766−772.
7
8
9
20 J. Mei, N. L. C. Leung, R. T. K. Kwok, J. C. Y. Lam, B. Z. Tang, Chem. Rev. 2015, 115,
11718-11940.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
21 Y. Hong, J. W. Y. Lam, B. Z. Tang, Chem. Commun., 2009, 4332-4353.
22 V. S. Padalkar, S. Seki, Chem. Soc. Rev., 2016, 45, 169-202.
23 A. Sen Gupta, K. Paul, V. Luxami, Sens. Actuator. B-Chem., 2017, 246, 653-661.
24 C. C. Hsieh, C. M. Jiang, P. T. Chou, Acc. Chem. Res., 2010, 43, 1364-1374.
25 S. C. Makhal, A. Bhattacharyya, S. Ghosh, N. Guchhait, J. Photochem. Photobiol. A, 2018,
365, 67-76.
26 S. Ghosh , A. A. Masum, A. Ganguly, M. A. Alam, M. M. Islam and N. Guchhait, RSC
Adv., 2016, 6, 93335-93342.
27 H. Auweter, H. Haberkorn, W. Heckmann, D. Horn, E. Luddecke, J. Rieger and H. Weiss,
Angew. Chem., Int. Ed., 1999, 38, 2188–2191.
28 D. M. J. Sena, H. O. Pastore and F. B. Pessine, Phys Chem Chem Phys., 2009, 11, 7219-7294.
29 U. Diwan, V. Kumar, R. K. Mishra, N. K. Rana, B. Koch, M. K. Singh and K. K. Upadhyay,
Anal. Chim. Acta, 2016, 929, 39-48.
30 F. A. S. Chipem, A. Mishra, G. Krishnamoorthy, Phys. Chem. Chem. Phys., 2012, 14, 8775-
8790.
26

Page 27 of 28
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
31 J. R. Lakowicz, Principles of Fluorescence Spectroscopy (third Ed.) Springer, New York,
2006.
7
8
9
32 L. Arnaut, S. Formosinho and H. Burrows, Transition between Electronic States, in Chemical
Kinetics: From Molecular Structure to Chemical Reactivity. Elsevier Publishing Company, 2007,
385-435.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
33 C. D. Borsarelli, J. J. Cosa and C. M. Previtali, Langmuir., 1992, 8, 1070-1075.
34 A. M. Brouwer, Pure Appl. Chem., 2011, 83, 2213–2228.
35 J. P. Palmans, M. V. D. Auweraer, A. M. Swinnen and F. C. D. Schryver, J. Am. Chem. Soc.,
1984, 106, 7721-7728.
36. S. Samanta, U. Manna and G. Das, New J. Chem., 2017,41, 1064-1072.
27

New Journal of Chemistry
Page 28 of 28
View Article Online
DOI: 10.1039/D0NJ02489A
1
2
3
4
5
6
7
8
9
TOC
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Compounds BIMP and ECPA show aggregation promoted ESIPT and AIE emission,
respectively. BIMP-ECPA ensemble behaves as white light emitter through exciplex formation.
28