The synthesis and aggregation-induced near-infrared emission of terrylenediimide-tetraphenylethene dyads

Article abstract of DOI:10.1039/c6cc01187j

We design and synthesize terrylenediimide-tetraphenylethene dyads, which exhibit featured aggregation-induced near-infrared fluorescence with a maximum emission wavelength of up to 800 nm.

Full text of DOI:10.1039/c6cc01187j

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Synthesis and Aggregation-Induced Near-Infrared Emission of
Terrylenediimide-Tetraphenylethene Dyads†
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
a
b
c
Nuo-Hua Xie, Chong Li, * Jun-Xia Liu, Wen-Liang Gong, Ben Zhong Tang,* Guigen Li,* and
a,c
Ming-Qiang Zhu*
DOI: 10.1039/x0xx00000x
www.rsc.org/
We design and synthesize terrylenediimide-tetraphenylethene advantage of the attractive properties of TPE and since it can
dyads, which exhibit featured aggregation-induced near-infrared be easily modified as a molecular building block, it would be
fluorescence with maximum emission wavelength up to 800 nm.
desirable to design terrylenediimide-tetraphenylethene
conjugates (TDI-TPEs) enabling condensed state enhanced
near-infrared emission. Recently, aggregation induced near-
infrared emission materials aroused great attentions due to
Perylenediimides and terrylenediimides have been used as
long-wavelength (red or near-infrared) emissive molecules in
organic optoelectronics and biosensing because of their high
1
5
their good prospect in optoelectronic and biological areas.
1
,2
efficient emission in dilute organic solution. However, their
applications have been limited because the strong aggregation
tendency of planar perylenediimides and terrylenediimides in
concentrated solution or in solid state causes dramatic
Although several works in literatures have reported AIE
luminogens with far red/near-infrared emission, their
maximum emission peaks were usually located below 700nm
or only part of their emission spectra was spread into the NIR
3
1
3,16-18
fluorescence quenching. Although they emit intensely in
range.
Besides, many of them rely on an elaborate design
9,20
1
dilute solutions, their light emissions are often quenched when
they are fabricated into solid films due to compact aggregate
formation, resulting in distinct drop of luminescence
and complex synthesis.
Here we integrate TDI and AIE-
active TPE into a single molecule by covalently binding one TDI
and four TPE molecules. We designed two styles of covalent
binding: one is π-conjugated (TDI-4TPE) while another is O-
bridged non-conjugated (TDI-O-4TPE). By this way, TDI as a
typical aggregation-induced quenching (ACQ) fluorophore was
converted to NIR-AIE luminogens exhibiting characteristic
aggregation-induced enhanced near-infrared fluorescence
with maximum emission wavelength up to 800 nm which has
not have been reported before to the best of our knowledge.
4
efficiency. They are also highly susceptible to concentration
quenching and become either weakly emissive or even not
5
emissive at all in solid state. The limitation can promisingly be
broken by introducing aggregation induced emission (AIE). AIE
6
was discovered in 2001, and within the last few years a great
deal of effort has been undertaken to study this
7
-8
9
phenomenon.
tetraphenylethene,
fluorescence quenching in the solution, contrary to it solid
state, which shows enhanced luminescence.
AIE-active materials such as silole and
1
0
are chromophores that exhibit
O
N
O
Tetraphenylethene (TPE) was selected as an ideal fluorophore
due to its large Stokes' shifted fluorescence as well as
B(OH)2
TDI-4TPE
1
1
O
N
O
enhanced fluorescence in solid state than in solution.
Previous investigations indicate that PDI-TPE conjugates show
TPE-B(OH)
2
O
N
O
Br
Br
Br
Br
1
2-14
their typical aggregation-induced red emission.
Taking
O
N
O
O
N
O
O
O
O
O
OH
TDI-O-4TPE
TDI-4Br
TPE-OH
O
N
O
Scheme 1 Synthetic route to TDI-4TPE and TDI-O-4TPE conjugates
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calculations of TDI-4TPE and TDI-O-4TPE were carried out to
understand their geometries and electronic structures at the
molecular level. The optimized geometries of TDI-4TPE and
TDI-O-4TPE are shown in Fig. 1a and 1b, respectively. Both TDI-
4
TPE and TDI-O-4TPE embrace twisted conformations along
the backbone compared with planar structure of TDI (Fig. S2,
ESI†). The computerized energy gap (Eg) of TPE, TDI, TDI-4Br,
TDI-4TPE and TDI-O-4TPE are 4.12, 1.98, 2.01, 1.79 and 1.87eV,
respectively. The twisting angles between the naphthalene
units in central terrylene plane are 21.66° for TDI-4TPE while
that of TDI-O-4TPE is 16.17°. The dihedral angles between the
two outermost naphthalene units are 54.18° in TDI-4TPE.
Evidently, strong torsion between naphthalene units in TDI-
4
TPE results from the steric effect and electron conjugation of
adjacent TPEs. Such propeller-like, non-planar conformations
of these two molecules, especially for TDI-4TPE, would
severely impede the π−π stacking interactions between
terrylene units in the aggregate state. In terms of the
electronic structures, the lowest unoccupied molecular orbitals
(LUMO) of TDI-4TPE is dominated by the orbitals from the TDI
core, while the electron cloud of the highest occupied
molecular orbitals (HOMO) is stretched to TPE units. The
HOMO−LUMO distribuꢀon indicates that TDI-4TPE possesses
an intrinsic intramolecular charge transfer (ICT) character. In
comparison, the LUMO and HOMO of TDI-O-4TPE are not
apparently influenced by introduction of four TPE units.
Fig. 1 HOMO and LUMO energy levels of (a) TDI-4TPE and (b) TDI-O-4TPE.
Molecular orbital amplitude plots of HOMO and LUMO energy levels calculated
g
using B3LYP/6-31G (d) basis set in Gaussian 09program. E (energy gap) = LUMO -
HOMO.
The synthetic procedures of TDI-4TPE and TDI-O-4TPE are
shown in Scheme 1. TDI-4TPE was synthesized by Suzuki cross-
coupling of TDI-4Br with TPE-B(OH)
by nucleophilic substitution of TPE-OH with TDI-4Br in the
presence of K CO . TDI-4TPE and TDI-O-4TPE were produced
2
. TDI-O-4TPE was prepared
2
3
with practical yields, and exhibit good solubility in common
solvents. The detailed synthetic procedures are depicted in
electronic supplementary information (ESI†). The final
1
13
products were fully characterized by H NMR
MALDI-TOF HPLC (Fig. S1, ESI†) element analysis and
correspond well with their expected structures (See the ESI†).
、 C NMR、
、
、
TDI-4TPE and TDI-O-4TPE have donor-acceptor (D–A) Fig. 2 Optical properties in organic solvents. (a) Absorption and (b) Fluorescence
spectra of TDI-4TPE. (c) Absorption and (d) Fluorescence spectra of TDI-O-4TPE.
structures, which contain elementary units of electron-
(
e) and (f) are the fluorescence decay curves of TDI-4TPE and TDI-O-4TPE
donating TPE and electron-accepting TDI. The only difference respectively. For the steady-state spectra, the excitation wavelength is 600nm.
-
3
The solutions were prepared by injecting of 25 μL DCM solution (1 × 10 M ) into
.5 mL different organic solvents. Each the organic solvent contains 1% DCM.
Especially, the dye molecules are aggregated as nanoparticles in poor solvents
such as hexane, methanol and DMF. For the transient state fluorescence spectra,
the excitation wavelength is 340 nm and the maximum emission wavelengths
of TDI-4TPE and TDI-O-4TPE is that there is charge transfer
from TPEs to TDI due to the electron conjugation between TDI
and TPEs in TDI-4TPE while that of TDI-O-4TPE has been
isolated by O-bridges. Density functional theory (DFT)
2
2
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were monitored. The instrument response function (IRF) is about 100 ps. The
concentrations for all the solutions are 1 × 10 M.
candidate for visible-light transmissive materials with NIR
absorption and emission activities which is exactly a NIR
fluorescent probe for in vivo imaging.
-
5
0
.25
.20
2.0x10
1.5x10
1.0x10
5.0x10
5
5
5
4
a
b
0
.1mg/mL
0
0.1mg/mL
.5mg/ml
1mg/mL
0.5mg/mL
1mg/mL
0
.
e
u
c
n
a
0.15
0.10
(
y
b
r
i
o
s
s
n
b
A
t
n
0
.05
.00
0
0.0
3
00
400
500
600
700
800
800
800
650
650
650
700
750
800
850
850
850
Wavelength (nm)
Wavelength (nm)
0
.08
.06
c
d2x10
4
0
0.1mg/mL
0.5mg/ml
1mg/mL
0.1mg/mL
0.5mg/mL
1mg/mL
.
e
c
.
n
a
(
a
y
b
r
0.04
0.02
i
4
1x10
o
s
s
n
b
A
t
e
n
0
0.00
Fig. 3 Optical properties of TDI-4TPE and TDI-O-4TPE in hexane/DCM binary solvents
with different hexane fractions (by volume %). (a) Absorption and (b) fluorescence
spectra of TDI-4TPE (c) Absorption and (d) fluorescence spectra of TDI-O-4TPE. The
300
400
500
600
700
700
750
800
Wavelength (nm)
Wavelength (nm)
e0.09
f
3x10
5
5
5
0
.1mg/mL
0.5mg/mL
1mg/mL
-
5
0.1mg/mL
0.5mg/mL
1mg/mL
concentrations are all 1.0 x 10 M.The excitation wavelength is 600nm.
.
e
u
c
2x10
1x10
n
(
a
y
i
o
s
s
n
We investigated the optical properties of TDI-4TPE and TDI-
O-4TPE in various organic solvents. The corresponding UV-Vis
absorption and emission spectra are presented in Fig. 2. The
absorption spectra of TDI-4TPE and TDI-O-4TPE in
dichloromethane (DCM) are peaked at ~731 and ~697 nm,
respectively, indicative of a longer conjugation length of TDI-
b
A
t
e
0
.03
.00
n
0
0
300
400
500
600
700
700
750
800
Wavelength (nm)
Wavelength (nm)
Fig. 4 Optical properties in polystyrene (PS) film. (a) Absorption spectra of TDI. (b)
Emission spectra of TDI. (c) Absorption spectra of TDI- 4TPE. (d) Emission spectra of
TDI- 4TPE. (e) Absorption spectra of TDI-O-4TPE. (f) Emission spectra of TDI-O-4TPE.
4
TPE due to the integration of four TPEs (Fig. 2a and 2c). The Excitation wavelength: 620 nm. The Polystyrene (PS) film samples were prepared by
spin coating of chloroform solution containing PS polymer (100 mg/mL) and dyes (0.1
decreases of the absorbance of TDI-O-4TPE in DMF and
methanol are attributed to the poor solubility of high
hydrophobic molecules in strong polar solvents. The molar
mg/mL, 0.5 mg/mL, 1 mg/mL, respectively) onto clean quartz plates.
4
−1
−1
The AIE properties of TDI-4TPE and TDI-O-4TPF were
investigated in DCM/hexane binary solvents (Fig. 4) as well as
THF/water ones (Fig. S3, ESI†). The absorption spectra of TDI-
absorptivity of TDI-4TPE (6.46 × 10 M cm ) is similar to that
4
of TDI-O-4TPE (7.27 × 10 M cm ).
−1
−1
TDI-4TPE and TDI-O-4TPE have considerable fluorescence
quantum yields (QYs) in low polar solvents while relatively
lowin polar solvent (Table S1).Their fluorescence lifetimes (Fig.
4
TPE do not show much change with an increase of hexane
fraction (Fig. 3a). However, the PL intensity of TDI-4TPE in
DCM/hexane is dramatically enhanced as the hexane fraction
increase from 10% to 99% (Fig. 3b). For TDI-O-4TPE, the
absorbance are fluctuating in a small range when the hexane
fraction is between 0-70% and decrease dramatically when the
hexane fraction increases to 80%, which is attributed to the
poor solubility of TDI-O-4TPE in hexane (Fig. 3c). The
photoluminescence (PL) intensity of TDI-O-4TPE exhibits a
gradual increase as the hexane fraction in DCM/hexane
increases to 70% followed by a drop when hexane is up to 80%,
which is probably attributed to the precipitation of TDI-O-TPE
from hexane due to the decrease of solubility of TDI-O-TPE in
hexane (Fig. 3d). However, their PL intensities decrease with
2e and 2f, Table S2) decrease as the polarity increase
indicating that the non-radiative transitions process are
strengthened and thus the emission become weak. Both λabs
and λem exhibit considerable redshifts as the solvents varying
from weak polar solvent to strong polar solvent. The maximum
fluorescence emission peaks (λem) of TDI-4TPE and TDI-O-4TPE
in DCM are present at 797 nm and 718 nm respectively which
fall in typical first NIR window (Fig. 2b and 2d). As shown in Fig.
2b (insert picture), the fluorescence of TDI-4TPE is not
observable in naked eyes, even in n-hexane and cyclohexane
because TDI-4TPE completely emits no visible fluorescence but
strong NIR fluorescence. In comparison, the “red-edge”
fluorescence of TDI-O-4TPE can be seen in naked eyes under
increasing water fraction in THF/water (Fig. S3 and S4, ESI†).
TDI-4TPE and TDI-O-4TPE exhibit similar AIE characteristics in
DCM/hexane although they do not show AIE in THF/water,
3
65nm irradiation.
TDI-O-4TPE shows noticeable visible light to far-red
1
2
which are similar to PDI-TPE reported previously.
absorption and red light to NIR emission. In comparison, the
absorption and emission spectra as well as the photos of TDI-
Since TDI-O-4TPE and TDI-4TPE display AIE-active far-red
and NIR activity, their optical properties in polymer matrix
have been investigated. The preliminary comparison of the
emission spectra of solid powders of TDI, TDI-4Br, TDI-4TPE
and TDI-O-4TPE indicates that TDI-4TPE and TDI-O-4TPE emit
strong fluorescence while the emission intensities of TDI and
4TPE demonstrate that TDI-4TPE shows weak visible light
absorption with a little “red-edge” and totally no visible light
emission. Alternately, TDI-4TPE shows strong NIR absorption
and NIR emission. This indicates that TDI-4TPE is a promising
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4Br-TDI are much weaker (Fig. S4, ESI†). It is noteworthy first NIR window. Especially, the maximum emission peak of
that TDI-4TPE and TDI-O-4TPE do not show evident fluorescent TDI-4TPE is up to 800 nm. The absorptions at far-red to near-IR
quenching in the solid state due to aggregation-caused region of TDI-4TPE and TDI-O-4TPE are promising in
broadening of photo-responsive spectra in solar cells.
Moreover, their NIR emission features are desirable in NIR
sensing and deep tissue imaging. The further investigation
1
.0
.8
about the NIR absorbers and emitters of TDI-TPEs is underway.
These novel AIE-active NIR emitters will become a promising
role in NIR OLED and in vivo bioimaging.
TDI
TDI-4TPE
TDI-O-4TPE
This work was supported by the National Basic Research
Program (973) of China (2015CB755602 and 2013CB922104)
and the National Science Foundation of China (NSFC 21474034
and 21174045). We also thank Analytical and Testing Center of
Huazhong University of Science and Technology and the
Center of Micro-Fabrication and Characterization (CMFC) of
WNLO for use of their facilities.
4-dicyanomethylene-2-methyl-
0
6-(4-dimethylaminostyryl)-4H-pyran
0
400
800
1200
1600
Time (s)
Fig 5 The fluorescence intensity of dyes in PS film under persistent 302 nm UV light
irradiation. The monitored emission wavelength: TDI, 670nm; TDI-O-4TPE, 700nm; TDI-
Notes and references
4
6
TPE, 780nm; (d) 4-dicyanomethylene-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran,
30nm.
1
2
3
4
5
6
S. K. Yang, X. Shi, S. Park, S. Doganay, T. Ha and S. C.
Zimmerman, J. Am. Chem. Soc. 2011, 133, 9964-9967.
C. Jung, B. K. Müller, D. C. Lamb, F. Nolde, K. Müllen and C.
Bräuchle, J. Am. Chem. Soc. 2006, 128, 5283-5291.
Z.Xu, B. He, J. Shen, W. Yang and M. Yin, Chem. Commun.
quenching. The absorption spectra of TDI, TDI-4TPE and TDI-O-
TPE in PS films indicate a great linear increase of absorbance
4
2
013, 49, 3646-3648.
Y. Huang, J. Wang and Z. Wei, Chem. Commun. 2014, 50
at different content in solid PS films (Fig. 4a, 4c and 4e). In the
emission spectra, it is observed that the emission intensity of
TDI at 0.5 mg/ml is only 1.5-2 times of that of TDI at 0.1 mg/ml
,
8343-8345.
W. Wang, L.-S. Li, G. Helms, H.-H. Zhou and A. D. Q. Li, J. Am.
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(Fig. 4b). Even the first emission intensity of TDI at 1 mg/ml
becomes lower than that at 0.5 mg/ml, which indicates that
strong aggregation-causing fluorescence quenching at high
concentration. In comparison, the emission intensity of TDI-
7
8
9
Y. Hong, J. W. Y. Lam and B. Z. Tang, Chem. Soc. Rev. 2011,
4
0
, 5361-5388.
Y. Hong, J. W. Y. Lam and B. Z. Tang, Chem. Commun. 2009,
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4
TPE and TDI-O-4TPE increase gradually with the increase of
concentration in PS films (Fig. 4d and 4f). The discernible
difference between TDI and their TPE derivatives indicates that
the aggregation-caused quenching can be efficiently inhibited,
4
B. Z. Tang, X. Zhan, G. Yu, P. P. S. Lee, Y. Liu and D. Zhu, J.
Mater. Chem. 2001, 11, 2974-2978.
even reversed by introduction of TPE groups. The emission 10 M. P. Aldred, C. Li, G.-F. Zhang, W.-L. Gong, A. D. Q. Li, Y. Dai,
D. Ma and M.-Q. Zhu, J. Mater. Chem. 2012, 22, 7515-7528.
wavelength of TDI-O-4TPE is 695 nm, longer than that of TDI at
1
1
1 M. P. Aldred, C. Li and M.-Q. Zhu, Chem. Eur. J. 2012, 18
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2 M. P. Aldred, G.-F. Zhang, C. Li, G. Chen, T. Chen and M.-Q.
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,
665 nm while the maximum emission of TDI-4TPE even shifts
1
to 780 nm, which can act as typical NIR emitters. The
maximum emission wavelength exhibits ascending redshifts in
1
order of TDI, TDI-O-4TPE and TDI-4TPE, indicating the electron 13 Q. Zhao, S. Zhang, Y. Liu, J. Mei, S. Chen, P. Lu, A. Qin, Y. Ma,
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and conjugation effect gradually increases.
1
1
4 Y. J. Wang, Z. Li, J. Tong, X. Y. Shen, A. Qin, J. Z. Sun and B. Z.
Tang, J. Mater. Chem. C 2015, , 3559-3568.
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Organic fluorescent dyes have been faced the challenge of
photostability. Here we compare the emission intensity change
of TDI, TDI-4TPE, TDI-O-4TPE and a commercial dye 4-
dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-
pyran upon 600 nm visible light (Fig. S5, ESI†) and 302 nm UV
irradiation (Fig. 5). It was observed that the emission intensity
of TDI, TDI-4TPE and TDI-O-4TPE keep constant even increase
while the commercial dye exhibit serious photobleaching.
3
,
4494-4562
16 X. Y. Shen, W. Z. Yuan, Y. Liu, Q. L. Zhao, P. Lu, Y. G. Ma, I. D.
Williams, A. J. Qin, J. Z. Sun and B. Z. Tang, J. Phys. Chem. C
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7 K. Li, W. Qin, D. Ding, N. Tomczak, J. L. Geng, R. R. Liu, J. Z.
Liu, X. H. Zhang, H. W. Liu, B. Liu and B. Z. Tang, Sci. Rep.
2013, 3, 1150.
1
Specifically, upon 302 nm irradiation, TDI, TDI-4TPE and TDI-O- 18 W. Qin, K. Li, G. X. Feng, M. Li, Z. Y. Yang, B. Liu and B. Z.
Tang, Adv. Funct. Mater. 2014, 24, 635-643.
4
TPE exhibit great photostability (Fig. S6, ESI†), implying a
1
2
9 J. L. Geng, K. Li, W. Qin, L. Ma, G. G. Gurzadyan, B. Z. Tang
and B. Liu, Small 2013, , 11, 2012-2019
0 H. G. Lu, Y. D. Zheng, X. W. Zhao, L. J. Wang, S. Q. Ma, X. Q.
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potential application in ambient environment single-molecule
spectroscopy.
9
In conclusion, we have designed and synthesized two typical
TPE-decorated TDI dyads, which exhibit strong aggregation-
induced enhanced emission with excellent photostability in the
4
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