Dipolar state assisted aggregation induced optical behavior of push-pull Salen-type Schiff base (BIHyDE) in solution

Article abstract of DOI:10.1016/j.molstruc.2021.130140

Aggregation behavior of push-pull salen-type schiff base (BIHyDE) in different solvents at ground and excited state, has been investigated. At ground state, lower energy absorption band is suppressed during concentration dependent UV-Vis study in CHCl

Full text of DOI:10.1016/j.molstruc.2021.130140

Journal of Molecular Structure 1234 (2021) 130140
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Research paper
Dipolar state assisted aggregation induced optical behavior of
push-pull Salen-type Schiff base (BIHyDE) in solution
∗
Sumit Kumar Panja
Department of Chemistry, Uka Tarsadia University, Maliba Campus, Gopal Vidyanagar, Bardoli, Mahuva Road, Surat-394350, Gujrat, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Aggregation behavior of push-pull salen-type schiff base (BIHyDE) in different solvents at ground and
excited state, has been investigated. At ground state, lower energy absorption band is suppressed during
concentration dependent UV-Vis study in CHCl3 solution. The broadening of lower energy emission band
is observed during concentration dependent fluorescent study in CHCl3 solution. Interestingly, fluores-
cence life time of BIHyDE in solution is also altered during concentration dependent fluorescence study
in CHCl3 solvent. Similar aggregation is also observed at ground and excited state in ACN solvent. Dipolar
state and intermolecular dipolar interaction of BIHyDE molecule highly influence towards strong aggre-
gation process and orientation of molecule in solution. Ground state and excited state optical properties
are highly influenced by concentration of push-pull salen-type schiff base (BIHyDE) in different solvents.
Received 19 November 2020
Revised 8 February 2021
Accepted 20 February 2021
Available online 24 February 2021
Keywords:
Push-pull system
Aggregation
Dipolar state
Intermolecular interaction
Salen-type Schiff base
© 2021 Elsevier B.V. All rights reserved.
1. Introduction
useful as photosensitizers, [27] light-harvesting systems [26,28-
2
9] and nonlinear optical (NLO) materials. [30-31] H-type aggre-
Organic chromophores are a class of functional π-electron
rich systems, which have established themselves as attractive
molecules in modern organic electronics [1-5]. Due to tunable
optoelectronic properties of organic chromophores, these organic
chromophores are widely applied for designing light-emitting
diodes, [6-8] bioimaging probes, [9-10] and photoelectric emit-
ting devices, [11-13] particularly in the visible region. To design
efficient full-color emitting materials, the organic chromophores
are designed on the basis of underlying mechanisms, including
intramolecular charge-transfer (ICT), [14-15] twisted intramolecu-
lar charge-transfer (TICT), [16-17] excimer, [18] excited-state in-
tramolecular proton transfer (ESIPT), [19] and photoinduced elec-
tron transfer (PET) [20]. Above strategies provide useful informa-
tion to design novel and efficient full-color luminescent molecules.
In recent, push-pull organic molecules play a crucial role on aggre-
gation behavior and their application in organic electronics based
on ICT state [21-22].
gates display a blue-shifted absorption band with a low molar ex-
tinction coefficient [32-33] and nonfluorescent behavior [23-26].
The quenching properties of H-type aggregates have been theo-
retically explained through the coupled oscillator model [34-35].
H-aggregates have shown third order nonlinear susceptibility [36-
37] and used to measure the photocurrent in photovoltaic cells
[38]. Generally, H-type aggregated molecules are nonfluorescent
but remarkably large Stokes shift in fluorescent spectra in solu-
tion. [39] Nature of self-association is also influenced by structure
of organic chromophores, concentration, solvent polarity, pH, ionic
strength, and temperature [40-43].
Recently, Xiang et al. have reported that malonitrile-based salen
ligand can be used as a photoisomerization induced colorimetric
and fluorescent pH and Cu2 probes. [44] Previously, reported UV-
Vis spectra of push-pull Salen-Type Schiff Base (BIHyDE) has shown
different absorption properties with respect to molar extinction co-
efficient, which is totally different from our experimental results.
[45]
+
Further, aggregation behavior of organic chromophores can also
influence on optical properties and device applications. Depending
upon nature of molecular orientation, J-aggregate and H-aggregate
are formed in solution. The J-aggregate has shown a red-shifted
absorption compared to monomer band and enhanced fluores-
cence with a very small Stokes shift [23-26]. The J-aggregates are
For details and clear understanding of the photophysical be-
havior salen-type schiff Base molecule (BIHyDE, chart 1), we have
studied aggregation behaviors, intramolecular charge-transfer (ICT)
and excited-state proton transfer (ESIPT) moieties in solution us-
ing UV-vis, and fluorescence spectroscopy (steady state and time
resolved). Further, role of intramolecular interaction and nature of
aggregation at ground state and excited state in solution has been
investigated on the basis of experimental results.
∗
Corresponding author. Department of Chemistry, Uka Tarsadia University, Mal-
iba Campus, Gopal Vidyanagar, Bardoli, Mahuva Road, Surat-394350, Gujrat, India
https://doi.org/10.1016/j.molstruc.2021.130140
0
022-2860/© 2021 Elsevier B.V. All rights reserved.

S.K. Panja
Journal of Molecular Structure 1234 (2021) 130140
Chart 1. Structural Formula and Abbreviations of Investigated molecule.
2. Experimental section
2
.1. Chemicals and synthesis
All starting materials were procured from Sigma Aldrich
and are of analytical grade. Ultrapure water, acetonitrile, and
dichloromethane, ethanol, DMSO, and other solvents were pro-
cured from Sigma Aldrich. CDCl3 (Sigma-Aldrich) was used as re-
ceived for NMR studies.
Fig. 1. Normalized UV-Vis spectra of BIHyDE in different solvents.
2
.2. Synthesis and characterization of BIHyDE
(Horiba Jobin Yovon IBH Ltd.) using a nano LED light source at 340
nm, and the signals were collected at the magic angle (54.7°) po-
larization. The IRF of detector is (fwhm) = 750 ps. DAS6 software
was used to deconvolute the fluorescence decays. The relative con-
tribution of each component was obtained from the biexponential
fitting and finally expressed by the following equation.
Bn
an = ꢀ
Bi
B is the pre-exponential factor. The mean fluorescence lifetimes
i
for the decay curves were calculated from the decay times and the
relative contribution of the components using the following equa-
2
,3-diaminomaleonitrile (1 mmol) and 4-(diethylamino)-2-
hydroxybenzaldehyde (2.5 mmol) were taken in a round bottom
flask with catalytic amount of conc. H SO and was heated in
tion.
ꢀ
aiτi2
2
4
ꢀ
τꢁ = ꢀ
an oil bath at 60 ˚C for 3 hrs till the completion of the reaction.
After completion of the reaction, crude mixture was washed with
water (3 × 10 mL) followed by ethanol (3 × 10 mL), dried in high
vacuum to afford NMR pure product. State: Solid; Colour: Black;
aiτi
th
τi and ai are the fluorescence lifetime and its coefficient of the i
component, respectively.
MP.: 193 °C; Yield: 95 %; 1H-NMR (300MHz, CDCl ): δ (ppm) 11.64
3
(
s, 2H), 9.48 (s, 2H), 7.27 (s, 2H), 6.26 (d, J = 7.5 Hz, 2H), 6.06 (s,
3. Results and discussion
13
2
H), 3.41 (q, J = 7.0 Hz, 4H), 1.21 (t, J = 4.2 Hz, 6H); C-NMR (75
MHz, CDCl ): δ (ppm) 191.9, 164.3, 154.3, 135.3, 111.3, 104.3, 96.4,
3.1. Steady-state absorption and fluorescence measurements
3
4
4.0, 12.7.
The UV-Vis spectra of BIHyDE are recorded in different solvents
and presented in Fig. 1. From experimental absorption spectra, BI-
HyDE molecule exhibits three different absorption bands at 562
nm, 433 nm and 344 nm in ACN solvent respectively. The ab-
sorption bands at 562 nm and 433 nm are weak and broaden but
strong absorption band is observed at 344 nm in ACN. Intesity of
weak absorption band at 433 nmand 562 nm is altered depending
upon nature and polarity of solvents. Broaden lower energy ab-
sorption band (~562 nm) with low intensity is observed in polar
protic solvents. But in polar aprotic solvents, intesity of lower en-
ergy absorption (~562 nm) is relatively higher compared to polar
protic solvents. From UV-Vis studies, lower energy absorption band
is shifted from 549 nm (n-hexane) to 582 nm (DMSO) in solution
due to relative polarity of solvents. The shifting of lower energy
absorption band (549 nm to 582 nm) is due to enhancement of
solute-solvent interact from nonpolar to polar solvents (Fig. 1 and
Table 1). Intensity of lower energy absorption band also changes
from nonpolar to polar solvents. Relative intensity of lower absorp-
tion band is relatively higher in polar aprotic solvents compared to
polar protic solvents (Fig. 1).
2
.3. NMR spectroscopy
1H and 13C-NMR spectra are recorded on NMR (Bruker) spec-
trometers operating at 300 and 75 MHz, respectively. Chemical
shifts (δ) are given in parts per million (ppm) using the residual
solvent peaks as reference relative to TMS. ‘J’ values are given in
Hz.
2
.4. Steady state UV-Vis and fluorescence measurement
Steady state UV-Vis and fluorescence spectral measurements
were measured in different solvents. The steady state absorption
spectra were recorded on Hitachi UV-vis U-3501 spectrophotome-
ter. The fluorescence spectra were recorded on a Perkin-Elmer LS55
fluorescence spectrophotometer equipped with a 10 mm quartz
cell and a thermostat bath.
2
.5. Time-resolved fluorescence measurement
Fluorescence lifetimes were measured from time-resolved in-
From our experimental results, it can be concluded that the di-
cyano group in BIHyDE plays an important role on electronic prop-
erty and solute-solvent interaction in solution. So, electronic and
tensity decay by the method of time-correlated single-photon
counting (TCSPC) technique by FluoroCube-01-NL spectrometer
2

S.K. Panja
Journal of Molecular Structure 1234 (2021) 130140
Table 1
Spectroscopic parameters from absorption and emis-
sion spectra.
Solvent
UV-Vis (λAbs
)
Fluorescence (λFl
)
max
max
n-hexane
THF
549 nm
550 nm
569 nm
562 nm
581 nm
566 nm
565 nm
581 nm
577 nm
604 nm
600 nm
611 nm
635 nm
608 nm
611 nm
620 nm
CHCl3
ACN
DMSO
THF
EtOH
H2O
Fig. 3. Normalized fluorescence spectra of BIHyDE in different solvents (λex =
530 nm).
Fig. 2. Effect of aq KOH on UV-Vis spectra of BIHyDE in ACN solvent.
solvatochromic properties of BIHyDE are significantly influenced by
the polarity of solvents at room temperature.
Further, alternation of optical properties of BIHyDE is also in-
vestigated in basic condition. For this purpose, diluted aq KOH so-
lution is added to ACN solvent containing BIHyDE (Fig. 2). From
UV-Vis spectra, it is observed that higher energy absorption band
at 344 nm is not shifted at all but spectral broadening is also ob-
served with increasing aq KOH concentration. Interesting factor is
that the lower energy absorption band (at 562 nm) is unaltered at
lower aq KOH concentration but prominent affect is observed at
higher concentration of aq KOH solution. At high conc of aq KOH
solution, the lower energy absorption band is shifted from 562 nm
to 595 nm in ACN (Fig. 2). The influence of KOH on optical behav-
ior in chloroform and DMSO solvents has been investigated and
similar results are also obtained.
Fig. 4. Concentration dependent UV-Vis spectra of BIHyDE in CHCl3 solvent.
Emission band from ICT state and ESIPT process may expect
from ICT state (Push-pull system) and keto-enol (ESIPT process)
but separately, emission band is not observed from ICT state and
ESIPT process. Single emission band is only observed for BIHyDE
in different solvents from fluorescence study.
3.2. Concentration dependent absorption and fluorescence
measurement
In presence of aq KOH, deprotonation of –OH group is taken
place and electron density of core benzene moiety is also en-
hanced, result the higher degree of dipolar state lowering the en-
ergy levels and enhanced the aggregation in solution.
The concentration dependent UV-Vis spectra of BIHyDE is
recorded in CHCl3 and presented in Fig. 4. From experimental ab-
sorption spectrum, BIHyDE has exhibited absorption bands at 344
nm (very strong), 433 nm (weak) and 562 nm (strong) in CHCl3
solvent. At very low concentration, intensity of absorption band at
562 nm is higher than absorption band at 344 nm. With increase
in concentration of BIHyDE, intensity of absorption band at 344 nm
is started dominating over the absoptionband at 562 nm in CHCl3
(Fig. 4). Others band at 433 nm is not altered significantly in same
absorption spectra (Fig. 4).
Further, steady state emission spectra of BIHyDE are recorded
in different solvents by exciting at 530 nm and shown in Fig. 3
and Table 1. Since BIHyDE contains both the intramolecular charge
transfer (ICT; Push-pull) and proton transfer moieties, there are the
possibilities of observing ICT, ESIPT and local emission (LE) bands.
But different emission processes like ICT state, ESIPT and LE bands
are suppressed by aggregated emission from concentration depen-
dent study.
Further, concentrattion dependent UV-Vis spectra of BIHyDE in
CHCl3 solvent is also normalized at 345 nm and presented in Fig. 5.
It is observed that lower energy absorption band at 569 nm is de-
creasing with increasing concentration of BIHyDE keeping the ab-
sorption band constant at 345 nm. From Fig. 4 and 5, it is clear that
the with increasing concentration of BIHyDE, change of absorp-
tion intensity is linear and it provides the aggregation behaviour
via lower energy state. This aggregation at lower energy state is to
be considered as J-type aggregation. So, BIHyDE shows the J-type
BIHyDE has shown strong emission peaks at 577 nm in n-
hexane (nonpolar) and at 635 nm in DMSO (polar) solvent (Fig. 3).
With increasing polarity of solvents, the nature of the emission
band shifted from 577 nm to 635 nm from n-hexane (nonpolar)
to DMSO (polar) solvent (Fig. 3). Remarkably, in every case, sin-
gle gaussian shaped fluorescence spectrum is observed for BIHyDE
molecule in polar and nonpolar solvents.
3

S.K. Panja
Journal of Molecular Structure 1234 (2021) 130140
Fig. 5. Normalized UV-Vis spectra of BIHyDE @ 345 nm in CHCl3 during concentra-
tion dependent Study.
Fig. 7. Concentration dependent life time decay profile of BIHyDE in CHCl3.
Table 2
Time resolved fluoresence parameters for BIHyDE in different sol-
vents.
Solvent
τ
1 (ns)
τ
2 (ns)
a1
a2
ꢀτꢁ (ns)
χ2
−
6
Concentration @2.4 × 10 (M)
CHCl3
EtOH
2.06
1.06
3.86
1.89
0.77
0.15
0.23
0.85
2.47
1.91
1.18
1.14
−
6
Concentration @4.8 × 10 (M)
CHCl3
EtOH
2.09
1.99
-
-
1
1
-
-
2.09
1.99
1.03
1.19
3
.3. Time-resolved fluorescence measurements
Fluorescence lifetimes have been measured to further investi-
gate the excited state behavior of BIHyDE in solution (Fig. 7 and
Table 2). All decay curves have been well fitted with mono and
biexponential decay pattern having acceptable χ2 values. Time-
resolved data are presented in Table 2. Time-resolved data reveals
that BIHyDE has shown mono and biexponential decay curves, de-
pending upon nature of solvent and its concentration. At very low
Fig. 6. Normalized concentration dependent fluorescence spectra of BIHyDE in
CHCl3.
−
6
aggregation in CHCl3 solvent. Similar aggregation is also observed
in polar aprotic slovents like ACN and DMSO solvent. The J-type
aggregation is observed due to presence of strong intermolecular
dipole-dipole interaction among molecules. Intermolecular dipole-
dipole interaction among molecules plays important role on de-
creasing absorbance at 569 nm (Fig. 5) but increasing absorbance
at 345 nm (normalized at 569 nm) with increasing concentration
of BIHyDE in solution.
concentration (2.4 × 10 (M)) in CHCl , biexponential decay com-
3
ponents is observed and the two species contribute different per-
−6
centage (23% and 77%). But at high concentration (@ 4.8 × 10
(M)) monoexponential decay components are observed and the
one species contributes 100% (Table 2). Similarly, at very low con-
−
6
centration (@2.4 × 10 (M)) in EtOH, biexponential decay compo-
nents is observed and the two species contribute in different per-
−6
centage (15% and 85%). But at high concentration (@ 4.8 × 10
Further, steady state fluorescence spectra of BIHyDE with differ-
ent concentration in CHCl3 are also measured and shown in Fig. 6.
The fluorescence maxima of BIHyDE at 600 nm is remained unal-
(M)), monoexponential decay components are observed and the
one species contributes 100% (ESI-Fig. 2: Table 2).
When monitoring life time at very low concentation, significant
contribution arises from monomer of BIHyDE but at higher con-
centration, significant contribution comes from aggregated form of
BIHyDE due to presence of the intermolecular H-bonding interac-
tion and dipolar-dipolar interactions.
tered with different concentration of BIHyDE in CHCl . But emis-
3
sion band broadening is observed even at very low concentration
(
~10 6 (M)) and indicates that strong intermolecular interaction is
−
present at excited state of BIHyDE in CHCl3 (Fig. 6 and Figure S2).
From concentration dependent fluorescence spectra, it is clear
that the emission is only appeared from J-type aggregated BIHyDE.
J-type aggregated BIHyDE has shown unique lower energy emis-
sion band during concentration dependent fluorescence study. Ex-
cited state aggregation is occurred even at lower energy compared
Here, value of τ1 and τ2 has been changed significantly with
variation of solvents and concentration of solute. It is observed
that τ1 always predominates over τ2 in polar protic and aprotic
solvents. But τ1 component fully is dominated by concentration of
BIHyDE in polar aprotic and protic solvents. Polar aprotic solvent
influences the life time of BIHyDE significantly. At lower to higher
concentarion of BIHyDE in polar aprotic solvents, the life time is
decreased and shows the change from biexpontial to monoexpo-
nential decay profile (Fig. 7 and Table 2). Overall, average fluores-
cence life time (τav) is also altered depending upon concentration
of BIHyDE in solution. Change of average life time from 1.91 ns to
1.99 ns is observed in EtOH during change of concentration from
to nonaggregated form of BIHyDE molecule in CHCl . In presence
3
of strong intermolecular dipole-dipole interaction among BIHyDE
molecules, J-type aggregation is observed in CHCl3 solution. Sim-
ilar observation is also observed in ACN solvent (Figure S2). In-
termolecular dipole-dipole interaction among molecules plays im-
portant role on broadening the fluorescence spectra (normalized at
6
00 nm) with increasing concentration (Fig. 6).
4

S.K. Panja
Journal of Molecular Structure 1234 (2021) 130140
Fig. 8. Schematic presentation of aggregation of BIHyDE in solvent.
2
.4x10-6 (M) to 4.8x10-6 (M). At similar concentration range, and
tion may highly influence towards strong aggregation process and
orientation of molecule in solution. The π-electron of benzene ring
may take part an important role on J-type aggregation process at
ground state and excited state. Aggregation is observed at ground
and excited state in polar protic and aprotic solvents. Detailed ag-
gregation mechanism is under process and will be helpful for wide
application in material chemistry.
average life time is also altered from 2.47 ns to 2.09 ns in CHCl3.
Therefore, we conclude that at lower concentation (2.4x10-6 M)
in polar aprotic and protic solvents, there is significant contribu-
tion of monomer (~23%) and aggregate (~77%) form of BIHyDE.
Where as, at higher concentation (4.8x10-6 M) in polar aprotic and
protic solvents, only aggregate form (100%) of BIHyDE contributes.
It is clear that H-bonding solvents can influence the photophys-
ical properies of BIHyDE in solution. Intermolecular H-bonding in-
teraction and dipolar-dipolar interactions may enhance the non-
radiative path and responsible for shorter fluorescence life time.
At very low concentration, monomer is observed in polar aprotic
solvents to polar protic solvent. But at higher concentration, only
molecular aggregate is formed and observed in both polar protic
and aprotic solvents.
Declaration of Competing Interest
None.
Acknowledgment
SKP acknowledges to Department of Chemistry for providing
infrastructure and instrument facilities at Uka Tarsadia University,
Surat-394350, Gujrat, India.
From these observations, it is clear that at lower concetration
of BIHyDE, absorption and emission are solely occurred from non-
aggregate (monomer) species but at relatively higher concentra-
tion, different absorption and emission are observed from aggre-
gated species of BIHyDE in solution. Intermolecular dipolar state
assisted aggregation is taking place in solution. Schematic concen-
tration dependent aggregation and optical properties of BIHyDE in
solution has been presented in Fig. 8.
Supplementary materials
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.2021.130140.
References
4. Conclusion
[1] T.J.J. Müller, U.H.F. Bunz, Functional organic materials: Syntheses, strategies,
and applications, Ed., Wiley VHC, Weinheim, 2007.
Aggregation behavior of push-pull salen-type schiff base (BI-
[
2] S. Reineke, T. C. Rosenow, B. Lüssem, K. Leo, Improved high-brightness ef-
ficiency of phosphorescent organic LEDs comprising emitter molecules with
small permanent dipole moments, Adv. Mater. 22 (2010) 3189–3193.
HyDE) at ground and excited state, has been investigated in differ-
ent solvents. At ground state, lower energy band is suppressed in
concentration dependent UV-Vis spectra but emission band broad-
ening is observed in concentration dependent fluorescence spec-
tra in solution. Interestingly, fluorescence life time of BIHyDE is
also altered during concentration dependent fluorescence study in
solution. From time resolved fluorescence spectra, it is observed
that average life time is altered depending upon concentration of
BIHyDE. With increasing concentration, average fluorescence life
time is decreased. At low concentration (< 2.4 × 10− M), aver-
age life time is contributed from monomer but at higher concen-
tration (> 4.8 × 10−6 M), average fluorescence life time is con-
tributed from only J-type aggregated molecule. The variation of
average life time with concentration indicates that non-radiative
process plays important role on supramolecular self-assemble pro-
cess in solvents. Dipolar state and intermolecular dipolar interac-
[3] L. Maggini, D. Bonifazi, Hierarchised luminescent organic architectures: design,
synthesis, self-assembly, self-organisation and functions, Chem. Soc. Rev. 41
(2012) 211–241.
[4] M. Zhu, C. Yang, Blue fluorescent emitters: design tactics and applications in
organic light-emitting diodes, Chem. Soc. Rev. 42 (2013) 4963–4976.
[5] C. Fan, L. Zhu, T. Liu, B. Jiang, D. Ma, J. Qin, C. Yang, Using an organic molecule
with low triplet energy as a host in a highly efficient blue electrophosphores-
cent device, Angew. Chem., Int. Ed. 53 (2014) 2147–2151.
[6] J. Kido, Y. Okamoto, Organo lanthanide metal complexes for electroluminescent
materials, Chem. Rev. 102 (2002) 2357–2368.
6
[7] I. D. W. Samuel, G. A. Turnbull, Organic semiconductor lasers, Chem. Rev. 107
2007) 1272–1295.
(
[
8] A. C. Grimsdale, K. Leok Chan, R. E. Martin, P. G. Jokisz, A. B. Holmes, Synthesis
of light-emitting conjugated polymers for applications in electroluminescent
devices, Chem. Rev. 109 (2009) 897–1091.
[
9] A.S. Stender, K. Marchuk, C. Liu, S. Sander, M.W. Meyer, E. A. Smith, B. Neu-
pane, G. Wang, J. Li, J. -X. Cheng, B. Huang, N. Fang, Single cell optical imaging
and spectroscopy, Chem. Rev. 113 (2013) 2469–2527.
5

S.K. Panja
Journal of Molecular Structure 1234 (2021) 130140
[
10] X.H. Wang, Z.Q. Guo, S.Q. Zhu, Y.J. Liu, P. Shi, H. Tian, W.H. Zhu, Rational de-
sign of novel near-infrared fluorescent DCM derivatives and their application
in bioimaging, J. Mater. Chem. B 4 (2016) 4683–4689.
[27] K. Hunger, W. Bauer, T. Clausen, M. Filosa, R. Pedrazzi, A. G. Puntener, E. Ross,
in: Industrial dye: Chemistry, properties, applications, ed., K. Hunger, Wi-
ley-VCH, Weinheim, 2003, pp. 427–542. Ch. 5.
[
11] R. Zhang, Y. Zhao, T.F. Zhang, L. Xu, Z.H. Ni, A series of short axially sym-
metrically 1,3,6,8-tetrasubstituted pyrene-based green and blue emitters with
[28] D. M. Eisele, J. Knoester, S. Kirstein, J. P. Rabe, D. A. Vanden Bout, Uniform ex-
citon fluorescence from individual molecular nanotubes immobilized on solid
substrates, Nat. Nanotechnol. 4 (2009) 658–663.
4-tert-butylphenyl and arylamine attachments, Dyes Pigm 130 (2016) 106–
1
15.
[29] B. J. Walker, V. Bulovic, M. G. Bawendi, Quantum dot/J-aggregate blended films
for light harvesting and energy transfer, Nano Lett. 10 (2010) 3995–3999.
[30] J. Knoester, Collective nonlinear optical properties of disordered J-aggregates,
Adv. Mater. 7 (1995) 500–502.
[
12] S.Y. Lee, T. Yasuda, Y.S. Yang, Q. S. Zhang, C. Adachi, Luminous Butterflies,
Butterflies luminous: Efficient exciton harvesting by benzophenone derivatives
for full-color delayed fluorescence OLEDs, Angew. Chem., Int. Ed. 53 (2014)
6
402–6406.
[31] E. Collini, C. Ferrante, R. Bozio, A. Lodi, G. Ponterini, Large third-order nonlin-
ear optical response of porphyrin J-aggregates oriented in self-assembled thin
films, J. Mater. Chem. 16 (2006) 1573–1578.
[
13] D. Dimic, M. Petkovic, Control of a photoswitching chelator by metal Ions: DFT,
NBO, and QTAIM analysis, Int. J. Quantum Chem. 116 (2016) 27–34.
[
14] X. Shen, Y. Wang, E. Zhao, W. Yuan, Y. Liu, P. Lu, A. Qin, Y. Ma, J. Sun, B.
Z. Tang, Effects of substitution with donor–acceptor groups on the properties
of tetraphenylethene trimer: Aggregation-induced emission, solvatochromism,
and mechanochromism, J. Phys. Chem. C 117 (2013) 7334–7347.
[32] O. -K. Kim, J. Je, G. Jernigan, L. Buckley, D. Whitten, Super-helix formation
induced by cyanine J-aggregates onto random-coil carboxymethyl amylose as
template, J. Am. Chem. Soc. 128 (2006) 510–516.
[33] V. Kumar, G.A. Baker, S. Pandey, Ionic liquid-controlled J- versus H-aggregation
of cyanine dyes, Chem. Commun. 47 (47) (2011) 4730–4732.
[
15] V. Xue, W. Liu, X. Qiu, Y. Gao, W. Yang, Remarkable isomeric effects on opti-
cal and optoelectronic properties of N-phenylcarbazole-capped 9,10-divinylan-
thracenes, J. Phys. Chem. C 118 (2014) 18668–18675.
[34] T. Forster, Energy migration and fluorescence, J. Biomed. Opt. 17 (2012)
011002-10.
[
16] L.M. Zhu, J.C. Xu, Z. Sun, B.Q. Fu, C.Q. Qin, L.T. Zeng, X.C. Hu, A twisted in-
tramolecular charge transfer probe for rapid and specific detection of trace
biological SO2 derivatives and bio-imaging applications, Chem. Commun. 51
[35] M. Kasha, H.R. Rawls, M.A. El-Bayoumi, The exciton model in molecular spec-
troscopy, Pure Appl. Chem. 11 (1965) 371–395.
[36] Z. Xu, W. Lu, P.W. Bohn, Electronic Resonance and Local Field Effects on the
Nonlinear Optical Activity of H-Aggregate-Forming Stilbazolium Amphiphiles,
J. Phys. Chem. 99 (1995) 7154–7159.
(2015) 1154–1156.
[
17] N. B. Teran, G. S. He, A. Baev, Y. R. Shi, M. T. Swihart, P. N. Prasad, T. J. Marks,
J. R. Reynolds, Twisted thiophene-based chromophores with enhanced in-
tramolecular charge transfer for cooperative amplification of third-order op-
tical nonlinearity, J. Am. Chem. Soc. 138 (2016) 6975–6984.
18] H. Saigusa, E. C. Lim, Excimer formation in van der Waals dimers and clusters
of aromatic molecules, Acc. Chem. Res. 29 (1996) 171–178.
[37] H. Zhou, T. Watanabe, A. Mito, I. Honma, K. Asai, K. Ishigure, Encapsula-
tion of
3
H
aggregates in silica film with high nonlinear optical coefficient
−8
(χ =3.0×10
esu) by a simple sol–gel method, Mater. Lett. 57 (2002)
[
589–593.
[38] K. Saito, H-aggregate formation in squarylium Langmuir-Blodgett films, J. Phys.
Chem. B 105 (2001) 4235–4238.
[
19] C. C. Hsieh, C.M. Jiang, P. T. Chou, Recent experimental advances on excited-s-
tate intramolecular proton coupled electron transfer reaction, Acc. Chem. Res.
[39] N. Ryu, Y. Okazaki, E. Pouget, M. Takafuji, S. Nagaoka, H. Ihara, R. Oda, Fluo-
rescence emission originated from the H-aggregated cyanine dye with chiral
gemini surfactant assemblies having a narrow absorption band and a remark-
ably large Stokes shift, Chem. Commun. 53 (2017) 8870–8873.
[40] Y. Wang, Resonant third-order optical nonlinearity of molecular aggregates
with low-dimensional excitons, J. Opt. Soc. Am. B 8 (1991) 981–985.
[41] B. Becker, J. Clapper, K.R. Harkins, J. A. Olson, Situ screening assay for cell vi-
ability using a dimeric cyanine nucleic acid stain, Anal. Biochem. 221 (1994)
78–84.
[42] S. Das, P. V. Kamat, Can H-Aggregates serve as light-harvesting antennae?
triplet−triplet energy transfer between excited aggregates and monomer thio-
nine in aersol-OT solutions, J. Phys. Chem. B 103 (1999) 209–215.
[43] F. Meng, K. Chen, H. Tian, L. Zuppiroli, F. Nuesch, Cyanine dye acting both as
donor and acceptor in heterojunction photovoltaic devices, Appl. Phys. Lett. 82
(2003) 3788–3791.
43 (2010) 1364–1374.
[
20] L. Levi, T.J.J. Müller, Multicomponent syntheses of functional chromophores,
Chem. Soc. Rev. 45 (2016) 2825–2846.
[
21] D. M. Khramov, C. W. Bielawski, Donor-acceptor triazenes: Synthesis, charac-
terization, and study of their electronic and thermal Properties, J. Org. Chem.
72 (2007) 9407–9417.
[
[
[
22] L.E. McNamara, N. Liyanage, A. Peddapuram, J. S. Murphy, J. H. Delcamp, N.
I. Hammer, Donor–acceptor–donor thienopyrazines via Pd-catalyzed C–H acti-
vation as NIR fluorescent materials, J. Org. Chem. 81 (2016) 32–42.
23] S. Gadde, E. K. Batchelor, J.P. Weiss, Y. Ling, A. E. Kaifer, Control of H- and
J-aggregate formation via host−guest complexation using cucurbituril hosts, J.
Am. Chem. Soc. 130 (2008) 17114–17119.
24] Y. Xu, P. Xue, D. Xu, X. Zhang, X. Liu, H. Zhou, J. Jia, X. Yang, F. Wang, R. Lu,
Multicolor fluorescent switches in gel systems controlled by alkoxyl chain and
solvent, Org. Biomol. Chem. 8 (2010) 4289–4296.
[44] J. Cheng, Y. Zhang, X. Ma, X. Zhou, H. Xiang, Colorimetric and fluorescent
pH and Cu2 probes induced by photoisomerization of a malenonitrile-based
+
[25] N. Ryu, H. Hachisako, Enhanced fluorescence of loosely packed dye aggregates,
Chem. Lett. 44 (2015) 211–213.
Salen ligand, Chem Commun 49 (2013) 11491.
[
26] F. Wurthner, T. E. Kaisera, C. R. Saha-Moller, J-aggregates: From serendipitous
discovery to supramolecular engineering of functional dye materials, Angew.
Chem., Int. Ed. 50 (2011) 3376–3410.
[45] J. Cheng, K. Wei, X. Ma, X. Zhou, H. Xiang, Synthesis and photophysical
properties of colorful salen-type schiff bases, J. Phys. Chem.
16552–16563.
C 117 (2013)
6