Diarylmaleimide-based branched oligomers: Strong full-color emission in both solution and solid films

Article abstract of DOI:10.1039/c7ob02446k

Maleimide and benzene are employed as a dendron and a core, respectively, to construct two series of non-conjugate branched oligomers (B3G1 and B1G2) based on diarylmaleimide fluorophores by an alkylation reaction. Surface aryl groups are changed to tune

Full text of DOI:10.1039/c7ob02446k

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Takeharu Haino et al.
Solvent-induced emission of organogels based on tris(phenylisoxazolyl)
benzene
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Diarylmaleimide-based branched oligomers: strong full-color
emission in both solution and solid film
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
a
b
b
ab
Jingwei Wang, Rong Zheng, Huan Chen, Huimei Yao, Liyu Yan, Jie Wei, Zhenghuan Lin* and
b
Qidan Ling
DOI: 10.1039/x0xx00000x
Maleimide and benzene are employed as dendron and core, respectively, to construct two series of non-conjugate
branched oligomers (B3G1 and B1G2) based on diarylmaleimide fluorophores by alkylation reaction. Surface aryl groups
are changed to tune the emissive color of branched oligomers from blue (λem=480 nm) to red (λem=651 nm), realizing full-
color emission. The investigation on the photophysical properties of the oligomers indicates that they display intense
emission in both solution and solid film, due to the suppression of intramolecular rotation and intermolecular interaction.
Molecular simulation and natural transition orbitals analysis show the electron transition take place in the individual
arylmaleimide for the non-conjugate linkage of fluorophores in branched oligomers. It can avoid the unpredictability of
luminescent properties caused by the interaction of fluorophores. In addition, the good solubility, thermostability and
oxidative stability of the branched oligomers make them have huge potential in the solution-processable photonic
application. These results demonstrate such the design strategy of non-conjugate branched oligomers is a very efficient
and constructive method to get high-performance light-emitting materials in both solution and solid film.
www.rsc.org/
Therefore, the dual-state strong emission (DSE) in both solution and
solid is significant for a more comprehensive insight of organic
luminescence mechanisms and properties, as well as the practical
Introduction
Organic compounds with strong fluorescence have important
1
, 2
3, utilization. Just because of this, the DSE-active molecules have
applications in the fields of chemosensors and biological probes,
2
3-27
4
5-7
8,
9
received considerable attention in recent years.
photoelectronic devices,
and fluorescent bioimaging.
In addition, realizing full-color luminescence by regulation of the
photophysical properties of organic molecules is a hot topic for
Traditional organic fluorescent compounds with large aromatic
system display intense emission in dilute solution, but weak
fluorescence in the solid state for long exciton lifetime and
aggregation-caused quenching (ACQ) which results from the
2
7-31
wide applications in optoelectronic field.
Although
a
combination of several fluorophores with different emitting color,
such as blue, green and red, can obtain full-color emission, their
different stability and luminescent efficiency would cause a big
problem in the practical application. It is important to modify the
structure of one fluorophore to achieve tunable emission in both
solution and solid. Whereas, the luminescence of organic
compound is not as easy to be changed in the solid state as in
solution due to the huge effect of packing mode of molecules in
1
0-12
delocalization of exciton and strong π-π interactions.
The
luminescent process in solution offers a benefit of understanding
the emission properties at the molecular levels. However, the ACQ
effect badly impedes the practical applications of fluorescent
compounds in devices, like organic light-emitting diodes (OLEDs)
and organic lasers, etc. Since Tang and his co-workers reported
1
3, 14
solid-stated fluorescence of siloles and tetraphenylethylenes,
a
1
8, 32, 33
solid on the luminescent properties.
Consequently, it is a big
large numbers of organic compounds with aggregation-induced
emission (AIE) or aggregation-induced emission enhancement (AIEE)
challenge to design new compounds, especially DSE molecules, to
realize controllable and tunable fluorescence, even covering the
entire visible region.
1
5-22
have been developed.
Although AIE- and AIEE-active molecules
exhibit intense luminescence in aggregated states, they show non-
emission or weak emission in the solution for the non-radiative
relaxation of exciton mainly caused by the intramolecular rotation.
In this paper, we describe an unprecedented design to construct
full-color DSE-active materials by non-conjugately linking a kind of
fluorophore into a dendritic structure. The branched structure for
DSE molecules design has the following five advantages: (1) The
orderly 3D structure can restrain effectively the intermolecular
interaction and ACQ for spatial isolation effect, and consequently
improve solid-state emission. (2) The bulky dendritic structure can
suppress substantially the intramolecular rotation of fluorophore,
led to high quantum yield in solution. (3) The branched structure
makes the luminescent materials be of good solubility and film-
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forming ability, which are favorable for solution-processing
application. (4) There are many surface groups on the dendritic
structure, thus, it is easy to adjust the emitting color of molecules
Results and discussion
Design and Synthesis of branched oligomers
by changing these surface groups. (5) The non-conjugately linkage 3,4-Disubstituted arylmaleimide was chosen as fluorophore to
of dendron can keep the nature of fluorophore unchangeable in the design the branched oligomers for its flexible branched structure,
17, 27, 34, 35
branched molecules. Herein, two series of diarylmaleimide-based high quantum yield, and tunable emitting color.
These
branched oligomers (Fig. 1) with different surface groups were advantages render it be frequently used as a backbone to construct
3
4, 36-
designed and synthesized by employing benzene ring as core, and various multifunctional fluorescent materials applied to OLED,
4
0
41, 42
17, 18, 43
maleimide as branched units. The branched oligomers display
intense full-color emission in both solution and solid film.
anion sensing,
and data storage and process.
Alkylation
of maleimide with benzyl bromide is a common reaction employed
to synthesize arylmaleimide derivatives in a high yield. Thus,
benzene and maleimide were used as core and branched units,
respectively, to construct the non-conjugate branched oligomers by
alkylation. Different surface aryl groups (trifluoromethylbenzene,
benzene, bromobenzene, methoxylbenzene and benzylindole) were
utilized to adjust the emissive color of branched oligomers (Fig. 1).
The branched oligomers include three-branch-core and one-
generation ones (B3G1-F, B3G1-H, B3G1-B, B3G1-O and B3G1-N),
and one-branch-core and two-generation ones (B1G2-H, B1G2-O
and B1G2-N).
Synthetic route of the diarylmaleimide-based branched
oligomers is shown in Scheme 1. 3,4-Diphenylaleimides (M1-M4)
3
5
were obtained according to a reported procedure. B3G1-F, B3G1-
H, B3G1-B and B3G1-O were synthesized through a substitution
reaction of 3,4-diphenylaleimides (M1-M4) with 1,3,5-
tris(bromomethyl)benzene (core monomer) under strong alkaline
Fig. 1. Structure of B3G1 and B1G2 series denrimers.
Scheme 1 Synthetic route of branched oligomers.
2
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condition. The core monomer was replaced by monomer M6 to give
B1G2-H and B1G2-O. M6 was obtained by the same synthetic
reaction of M1-M4, followed by a substitution reaction of
benzylbromide and a bromination of NBS (Scheme S1). The
branched oligomers (B3G1-N and B1G2-N) containing
diindolylmaleimide fluorophore were prepared from 3,4-
diindolylmaleimide (M5) according to a similar synthetic route
(
Scheme 1). M5 was firstly turned into 3,4-diindolylmaleic
2
7
anhydride (M7) in 10% NaOH aqueous solution, and then
converted into monomer M9 through two-step reactions in a high
yield. The resulting B3G1-N and B1G2-N could be obtained through
the substitution reaction of M9 with M6 and 1,3,5-
tris(bromomethyl)benzene, respectively. It was found keeping the
reaction in the dark place was favorable to the synthesis of B3G1
and B1G2, due to the instability of core monomer. For the same
reason, the reaction have to be run in the temperature below 100
o
C, which, however, results in low yield of trisubstitued products
(
resulted molecules). Additionally, the synthesis of B3G1 and B1G2
with different surface aryl groups should choose different
alkali/solvent system. Otherwise, the resulted branched molecules
could not be obtained. For example, strong base NaH was needed
in the synthesis of B3G1-F with benzene as surface groups, while
2 3
the combination of weak base K CO and polar solvent acetone was
suitable for the synthesis of B3G1-N and B1G2-N with indole as
surface groups. The branched oligomers are soluble in common
solvents, such as toluene, dichloromethane, chloroform, THF, DMF,
etc.
Fig. 2 Absorption (a) and emission (b) spectra of oligomers in CHCl
3
solution, and their photographs (inset in b) taken under 365 nm UV
light. Branched oligomers in b arranged from left to right: B3G1-F,
B3G1-H, B1G2-H, B3G1-B, B3G1-O, B1G2-O, B3G1-N, and B1G2-N.
Photophysical properties in solution
Photophysical properties of the branched oligomers in chloroform
The effect of the peripheral aryl groups on emission of branched
oligomers is more significant than on their absorption. From the
emission spectra of branched oligomers shown in Fig. 2b, it was
found that they display substantial red shift with the increasing
electron-pushing ability of the aryl groups, resulting in a full-color
emission overlapping form blue of B3G1-F to red region of B1G2-N.
Relative to M2, M4 and M5, B1G2 type branched oligomers show
larger red-shift than B3G1 type ones (Fig. S2). It should be ascribed
to the space distribution of three fluorophores. Three
arylmaleimide equally disperse around the benzene core, while
they concentrate on one side of the core, which makes the
environmental polarity of fluorophore in B1G2 is larger than in
B3G1. To confirm the polar effect on the luminescent properties of
arylmaleimide fluorophores, their emission spectra in different
solvent were investigated (Fig. S3). These fluorophores indeed show
a red-shift of the emission band with the increasing polarity of
solvents. Experimental data of the photophysical properties of
branched oligomers and monomers are summarized in Table 1 and
Table S1, respectively.
(
10 uM) were investigated first. Fig. 2 gives their absorption and
emission spectra which are compared with the spectra of the
corresponding arylmaleimide monomers (M1-M5) in Fig. S1. Due to
the non-conjugated linkage between fluorophores (arylmaleimides),
branched oligomers display similar optic properties as their
corresponding monomers. There are mainly two absorption bands
between 250 nm and 600 nm in the absorption spectra of branched
oligomers (Fig. 2a). The first band before 325 nm is assigned to the
π-π* transition of separating maleimide or aryl units, while the
second band after 325 nm should be derived from the π-π*
transition involving both maleimide and aryl moieties. For B3G1-O,
B3G1-N, B1G2-O and B1G2-N, the second band companied by a
shoulder peak shows a red shift in solution. For example, maximum
absorption peak bathochromically shifts from 360 nm of B3G1-F to
4
82 nm of B3G1-N in chloroform. The red shift should be ascribed
to the strong electron-pushing ability of the surface aryl groups,
methoxylbenzene and indole, which cause an intramolecular charge
transition (ICT) from the aryl groups to maleimide.
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Table 1 Experimental data of photophysical properties of branched oligomers
b
-1
c
-1
λabs, (nm)
λem, (nm)
S / F
Φf, (%)
S / F
τ
, (ns)
kr, (ns )
knr, (ns )
a
S / F
S / F
S / F
S / F
B3G1-F
B3G1-H
B3G1-B
B3G1-O
B3G1-N
B1G2-H
B1G2-O
B1G2-N
360 / 369
362 / 368
379 / 383
412 / 421
482 / 488
376 / 377
404 / 414
479 / 483
482 / 481
508 / 507
541 / 541
574 / 571
605 / 606
524 / 518
580 / 575
651 / 640
42 / 65
86 / 54
64 / 65
63 / 60
24 / 28
67 / 66
37 / 35
20 / 10
10.34 / 10.64
17.97 / 10.84
13.91 / 3.70
12.11 / 5.76
7.19 / 2.74
16.18 / 8.41
12.75 / 6.77
6.23 / 2.46
0.041 / 0.061
0.048 / 0.050
0.046 / 0.176
0.052 / 0.104
0.033 / 0.102
0.041 / 0.078
0.029 / 0.052
0.032 / 0.041
0.056 / 0.033
0.008 / 0.042
0.026 / 0.095
0.031 / 0.069
0.106 / 0.263
0.020 / 0.043
0.049 / 0.096
0.128 / 0.366
a
b
c
r f f
S= Chloroform solution, F =Film. Radiative rate constant k = Φ /τ. Non-radiative rate constant knr = (1-Φ )/τ.
For the rigid structure, all of branched oligomers show higher electron density distribution of molecular orbitals of the
quantum yield than their corresponding arylmaleimide arylmaleimides is depicted in Fig. S6. The HOMO are mainly
monomers in solution. For example, of B3G1-F and B3G1-N is the populated on two symmetrically equivalent aryl rings, while the
double of their corresponding arylmaleimide fluorophores (M1 and LUMO is concentrated on the central maleimide moiety.
M5). The fluorescent lifetimes ( ) of branched oligomers were Localization degree of electrons is more significant with the
f
(Φ )
Φ
f
τ
measured using time-resolved single photon counting technique increase of electron-pushing ability of aryl group. This is an
and determined to be in the range of 6.23-17.97 ns in solution. indication of a charge transfer (CT) character for the maximum
However, the branched oligomers with same fluorophore, such as absorption band which is sensitive to the environmental polarity. It
B3G1-H and B1G2-H, B3G1-O and B1G2-O, B3G1-N and B1G2-N, is in agreement with the experimental result in the solution.
display similar lifetime in solution. It indicates that the
DFT-optimized geometry of branched molecules in ground state
photophysical properties of branched oligomers are closely related reveals that each fluorophore keeps similar twisted conformation as
to the arylmaleimide fluorophores. Time-resolved transient their corresponding arylmaleimide monomers (Fig. S7). The twisted
luminescence decay of branched oligomers in dilute solution is fluorophores linked by
plotted in Fig. S4. Consequently, their radiative rate constant ( oligomers present a screwier structure which is helpful to eliminate
and non-radiative rate constant ( nr) can be estimated from the the intermolecular interplay when aggregated in the condensed
formula and nr = (1- )/ , respectively (Table 1). High phase. TD-DFT calculated results of the first 6 singlet excited states
radiative rate constant of branched oligomers results in their high of branched oligomers are given in Table S3-S10. The calculated
a methylene group make branched
r
k )
k
k
r
=
Φ
f
/τ
k
f
Φ τ
quantum yield.
vertical absorption transition energy (S1) has much better
agreement with the experimental ones with an overestimation less
than 0.18 eV (Tabel 2). It was found that all of branched oligomers
Theory calculation
have degenerate excited states (S
1 2
and S for B1G2-O and B1G2-N,
Above experimental results suggest that each arylmaleimide in
branched oligomers behaves as an isolated fluorophore with little
electronic interaction between dendrons. To get insight into the
photophyscial properties of these arylmaleimides and branched
oligomers, including their ground-state and excited-state properties,
density functional theory (DFT) and time-dependent DFT (TD-DFT)
calculations were performed by using B3LYP and cam-6-31G (d) as
function and basis set, respectively. DFT-optimized geometry of the
five arylmaleimides (M1-M5) has a non-plannar conformation with
the twist angle between the maleimide ring and aryl ring at 22-46°
S
1
, S and S for other branched oligomers) due to same separated
2
3
fluorophores. It is difficult to visualize the location excitons and
possible electronic interactions within the branched oligomers for
the presence of such degenerate states and multiple orbital
transitions for each electronic transition. Consequently, natural
transition orbitals (NTOs) method was used to give a qualitative
description of an electronic excitation. From NTO pairs for the first
three excited singlet states of branched oligomers (Fig. 3, S8-S13),
note that all of electronic transition of degenerate states takes
place in the occupied and virtural obitals of individual fluorohphore,
corresponding to their HOMO and LUMO obitals (Fig. S6). It
indicates that there is no electronic communication between
(
Fig. S5). The computed vertical absorption properties from TD-DFT
given in Table S2 indicate that the first excited-state (S ) transition
1
occurs predominantly between HOMO and LUMO. The computed
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arylmaleimide fluorophores in branched oligomers, which makes isolated fluorophore.
branched oligomers behave similar photophysical properties as
Fig. 3 Natural transition orbital pairs for the first three excited singlet states of B3G1-H and B1G2-O.
Table 2 Experimental absorption transition energies (
E
) and
Photophysical properties in films
Calculated absorption photophysics with electronic excitation
Photophysical properties of the branched oligomers in solid film
were investigated next. The films were obtained by spin-coating
their chloroform solution (10 mg/mL) at the speed of 1000 r/s. The
absorption and emission spectra of branched oligomers are shown
in Fig. S14 and Fig. 4a, respectively. For a comparison, the spectra
properties of monomers (M1-M5) in solid were determined and
shown in Fig. S15, as well as the relevant data summarized in Table
S1. As mentioned above, the absorption and emission spectra of
dendimers in solution exhibit similar characteristic as that of their
corresponding monomers, due to the non-conjugated linkage
between diarylmaleimides in branched oligomers. However, the
discrepancy of absorption wavelength (λabs) of branched oligomers
between solution and films is obviously smaller than that of
monomers, resulted from the specific dendric structure that can
effectively inhibit the intermolecular interaction. For instance, the
maximum λabs of M2 bathochromically shift 22 nm from 361 nm in
solution to 383 nm in films. The red-shift was found to be 6 nm for
energies (
E
) and oscillator strength (
Exptl
f) of arylmaleimides
Calcd
E
, eV (
f)
E, eV
S1
S2
S3
B3G1-F
B3G1-H
B3G1-B
B3G1-O
B3G1-N
B1G2-H
B1G2-O
B1G2-N
3.44
3.44
3.27
3.01
2.57
3.30
3.07
2.59
3.52 (0.17)
3.45 (0.14)
3.36 (0.22)
3.16 (0.20)
2.75 (0.15)
3.40 (0.21)
3.13 (0.16)
2.67 (0.24)
3.55 (0.28)
3.47 (0.23)
3.39 (0.33)
3.17 (0.32)
2.77 (0.24)
3.43 (0.09)
3.13 (0.28)
2.69 (0.15)
3.57 (0.10)
3.49 (0.11)
3.41 (0.16)
3.20 (0.19)
2.88 (0.17)
3.43 (0.25)
3.38 (0.26)
3.34 (0.18)
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B3G1-H, and 1 nm for B1G2-H. The same situation was found in the Thermal and electrochemical properties
emission spectra of branched oligomers in solid film. For instance,
Thermal properties of polymers were investigated by
thermogravimetric analysis (TGA) under a nitrogen atmosphere at a
the difference of maximum λem between solution and solid is more
than 10 nm for M1, M3 and M5, but less than 3 nm for B3G1-F,
B3G1-B and B3G1-N. Like in solution, branched oligomers in solid
film exhibit full-color emission ranging from blue (481 nm) to red
o
scan speed of 10 C/min. From the TGA plots shown in Fig. 5, it can
be found that most of branched oligomers exhibit excellent thermal
o
properties with the decomposed temperature (T
d
) above 400 C,
(
640 nm).
except for B3G1-O. However, the 5% weight-loss temperature (T5%
)
o
of B3G1-O, B3G1-N, B1G2-O and B1G2-N was found at 277 C, 282
o
o
o
C, 212 C and 272 C, respectively (Table S11), which is lower than
that of other branched oligomers. It should be related to the
deprivation of peripheral methoxy or benzyl groups in B3G1-O,
B1G2-O, B3G1-N and B1G2-N in high temperature. In general, the
thermal stability of the branched oligomers is good enough to meet
their application need for devices.
Fig. 5 TGA curves (upper) of branched oligomers and their CV curves
(
bottom) in solid film.
Fig. 4 Emission (a) spectra and transient fluorescence decays (b) of
branched oligomers in solid film.
Electrochemical properties of the branched oligomers were
measured by cyclic voltammetry
in a 0.1 M n-Bu NPF solution in acetonitrile with Ag/AgCl as
（CV）at a scan rate of 100 mV/s
Although the spectra properties of branched oligomers mainly
depend on optic transition of the individual arylmaleimide
fluorophores, their quantum yield very differs from the
corresponding monomers. For the weak intermolecular interaction,
branched oligomers in films show high emission efficiency and
radiative rate constant. Φf of branched oligomers in solid film
matches that in solution. Especially for B3G1-F, B3G1-B and B3G1-N,
their Φf in film exceeds that in solution. It was found that the Φf of
most of the monormers in solid is lower than that in solution for
strong intermolecular interactions, such as π-π stacking and dipole-
dipole interaction. In particular, M5 shows strong ACQ feature. In
the case of branched oligomers, the separation and protection of
fluorophores in dendric structure make them be of high emission
efficiency in both solution and solids. Time-resolved transient
luminescence decay of branched oligomers in solid film is plotted in
Fig. 4b. After fitting the curves, their fluorescent lifetime was found
to ranges from 2.46 ns to 10.84 ns, which is smaller than in solution.
B3G1-H, B3G1-O and B3G1-N show similar lifetime as B1G2-H,
B1G2-O and B1G2-N, respectively, for the same fluorophore.
4
6
reference electrode. The CV data and reduction curves of branched
oligomers are given in Table S11 and Fig. 5, respectively. All of
branched oligomers demonstrate mostly reversible reduction scan
with similar reduction wave at about -0.70 V for their common
electron-deficient unit, maleimide ring. The recorded CV curves
+
were calibrated using a ferrocene/ferrocenium (Fc/Fc ) redox
couple (4.8 eV below the vacuum level) as an external standard. The
+
E
1/2 of the Fc/Fc redox couple was found to be 0.40 V vs the Ag
quasireference electrode. As a result, the LUMO and HOMO energy
levels of the branched oligomers can be estimated using the the
onset
empirical equation ELUMO = -(Ered
ELUMO
+ 4.40) eV and EHOMO = -
opt
onset
opt
Eg , where Ered
and Eg stand for the onset potentials of
reduction and optical band gap, respectively. The LUMO levels of
the branched oligomers lie around -3.70 eV, while their HOMO
levels locate in the range of -5.90 ~ -6.69 eV for the different
electron-pushing groups in the fluorophore (Fig. 6). The fact that all
of branched oligomers have oxidation potentials larger than 5.9 eV
6
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suggests their stability at ambient conditions. These results will Molecular Simulations
guide the application of the oligomers in photoelectric devices.
Theory calculations were carried out with the Gaussian 09 program.
Geometry at ground state was optimized with the density
functional theory (DFT) using the B3LYP functional and 6–31G*
basis set. The vertical excited energies were calculated with the
time–dependent density functional theory (TD-DFT) at CAM-B3LYP/
6
–31G*.
Synthesis of compound M9
,4-Bisindoylmaleic anhydride (M7) (800 mg, 2.4 mmol) was mixed
with NaH (168 mg, 7 mmol) in dried THF (23 ml) under a nitrogen
atmosphere, and the solution was stirred at 0 for 45 minutes. To
3
℃
the mixture was added benzyl bromide (1.2 mL, 10 mmol), the
reaction mixture was kept stirring at reflux under argon for 10 h,
and cooled to room temperature. The reaction was diluted with
ethyl acetate and successively washed with 1 M dilute hydrochloric
acid, water and brine. It was then dehydrated over anhydrous
Fig. 6 HOMO and LUMO energy levels for branched oligomers in
solid film.
MgSO and dried in vacuo to give the crude product of 3,4-bis-(N-
4
benzylindolyl) maleic anhydride (M8) which was used without
further purification.
Experimental
3,4-Bis-(N-benzylindolyl) maleic anhydride (600 mg, 1.18 mmol),
Materials and Measurements
anhydrous ammonium acetate (2.270 mg, 29.5 mmol) and
anhydrous methanol (60 mL) was added to hydrothermal synthesis
All the reagents and solvents used in the experiments were
obtained from commercial suppliers and used as received without
further purification, unless otherwise noted. Thin layer
chromatography was performed on G254 silica gel plates of
Qingdao Haiyang Chemical. Column chromatography was
conducted on Yantai Huanghai brand silica gel (200-300 mesh).
Diarylmaleimides M1, M2, M3, M4 and M7 were synthesized
reactor. The reaction was allowed to put into an oven at 100
℃
overnight, and cooled to room temperature. The reaction was
extracted with ethyl acetate. The organic phase was washed with
brine. It was then dehydrated over anhydrous MgSO . After
4
removing the solvent, the crude product was purified by column
chromatography with ethyl acetate/petroleum ether (1:4) as the
1
2
7, 35
eluant, affording compound M9 in 95% yield. H NMR (400 MHz,
according to a previously reported method.
CDCl ) δ 7.73 (d,
J
= 3.4 Hz, 2H), 7.58 (s, 1H),7.37–7.27 (m, 6H), 7.21
3
Low temperature reaction was performed on a Yuhua DFY-5/80
reactive bath. High-resolution MALDI-TOF mass spectra were
recorded on a Bruker microflex LRF spectrometer. NMR spectra
(
d,
J
= 8.3 Hz, 2H), 7.15–7.09 (m, 4H), 7.03 (d, = 20.4, 13.2,4.5 Hz,
J
1
3
4
1
H), 6.76–6.71 (m, 2H), 5.35 (s, 4H). C NMR (100 MHz, DMSO) δ
73.25, 138.11, 136.25, 132.68, 129.03, 128.10, 127.90, 127.31,
3
were measured in d-CDCl or d-DMSO on a Bruker Ascend 400 FT-
1
13
126.66, 122.32, 121.53, 120.04, 111.04, 105.80, 49.85.
NMR spectrometer. H and C chemical shifts were quoted relative
to the internal standard tetramethylsilane. UV-vis spectra were
obtained on a Shimadzu UV-2600 spectrophotometer. The PL
Synthesis of compound B3G1-F
spectra were probed on a Shimadzu RF-5301PC fluorescence M1 (517 mg, 1.35 mmol) and NaH (39 mg, 1.62 mmol) were placed
spectrophotometer. Fluorescence lifetime and absolute quantum in a 25 mL flask. 8 mL of dry THF was injected into flask under a
yield values of solution and solid were measured using an nitrogen atmosphere at 0
℃ and was vigorously stirred for 40 min.
Edinburgh Instruments FLS920 Fluorescence Spectrometer with a 6- Then, 1,3,5-tris(bromomethyl)benzene (80 mg, 0.224 mmol) in dry
inch integrating sphere. Thermo gravimetric analysis (TGA) was THF (2 mL) was added to the reaction mixture, which was heated to
−1
measured by a Mettler 851e with a heating rate of 10 °C min
refluxed for 12 h. After the reaction mixture was cooled to room
under flowing nitrogen. Cyclic voltammetry (CV) was performed on temperature, it was added 1M dilute hydrochloric acid and
a CHI600D electro-chemical analyzer in anhydrous THF containing extracted with ethyl acetate. The organic phase was washed with
tetra-n-butyl-ammonium hexafluorophosphate (TBAPF6, 0.1 M) as brine, and then dehydrated over anhydrous MgSO . After removing
4
supporting electrolyte at 298 K. A conventional three electrode cell the solvent, the crude product was purified by column
was used with a platinum working electrode and a platinum wire as chromatography with DCM /petroleum ether (1:2) as the eluant,
1
the counter electrode. The Pt working electrode was routinely affording light blue solids of B3G1-F. Yield: 41%. H NMR (400 MHz,
polished with a polishing alumina suspension and rinsed with CDCl ) δ 7.58 (d, J = 8.3 Hz, 13H), 7.52 (d, J = 8.2 Hz, 11H), 7.45 (s,
3
1
3
acetone before use. The measured potentials were recorded with 3H), 4.82 (s, 6H). C NMR (100 MHz, CDCl ) δ 169.37, 137.23,
3
respect to Ag/AgCl reference electrode. All electrochemical 136.34, 132.31, 131.98, 131.42, 130.24, 128.28, 125.70, 41.85.
+
measurements were carried out under atmospheric pressure of MALDI MASS m/z [M+Na+H] calcd 1293.2058, found 1293.6165.
nitrogen.
Synthesis of compound B3G1-H
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Journal Name
M2 (0.8 g, 3.2 mmol), 1,3,5-tris(bromomethyl)benzene (141 mg, 0.4 M9 (317 mg, 0.624 mmol), 1,3,5-tris(bromomethyl)benzene (35 mg,
mmol) and potassium tert-butylate (2.17 g, 19.2 mmol) were placed 0.098 mmol) and potassium carbonate (129 mg, 0.936 mmol) were
in a 10 mL flask. 6 mL of dry DMF was injected into flask under a placed in a 25 mL flask. 6 mL of acetone was injected into flask
nitrogen atmosphere at 90 ℃ and was vigorously stirred for 24 h. under nitrogen atmosphere and was vigorously stirred for 12 h at
After the reaction mixture was cooled to room temperature, the 90 ℃. After the reaction mixture was cooled to room temperature.
reaction was extracted with ethyl acetate. The organic phase was The reaction mixture was extracted with ethyl acetate, and washed
washed with brine. It was then dehydrated over anhydrous MgSO
4
.
4
with brine. It was then dehydrated over anhydrous MgSO . After
After removing the solvent, the crude product was purified by removing the solvent, the crude product was purified by column
column chromatography with DCM/petroleum ether (1:2) as the chromatography with ethyl acetate/petroleum ether (1:4) as the
1
1
eluant, affording green solids of compound B3G1-H. Yield: 48%. H eluant, affording red solids of compound B3G1-N. Yield: 48%. H
NMR (400 MHz, CDCl ) δ 7.36 (d, J = 8.0 Hz, 13H), 7.27 (t, J = 7.3 Hz, NMR (400 MHz, DMSO) δ 7.93 (s, 6H), 7.28 (tt, J = 14.1, 7.7 Hz,
3
1
3
7
1
4
8
3
H), 7.24 – 7.17 (m, 13H), 4.72 (s, 6H). C NMR (100 MHz, CDCl ) δ 27H), 7.13 (d, J = 7.1 Hz,12H), 6.93 (t, J = 7.7 Hz, 6H), 6.84 (d, J = 8.0
1
3
69.50, 136.63, 135.49, 129.12, 128.88, 127.81, 127.64, 127.27, Hz, 6H), 6.53 (t, J = 7.6 Hz, 6H), 5.36 (s,12H), 4.77 (s, 6H). C NMR
+
0.80. MALDI MASS m/z [M+Na+H] calcd 885.2815, found (100 MHz, DMSO) δ 171.68, 138.63, 137.88, 136.24, 132.99, 129.00,
85.0221.
127.90, 127.33, 126.49, 126.18, 122.39, 121.72, 120.17, 111.09,
+
1
05.71, 49.85, 41.61. MALDI MASS m/z [M+H] calcd 1637.6422,
found 1638.1194.
Synthesis of compound B3G1-B
M3 (1 g, 2.47 mmol), 1,3,5-tris(bromomethyl)benzene (150 mg,
Synthesis of compound B1G2-H and B1G2-O
0.42 mmol) were placed in a 50 mL flask. 5 mL of dry DMF was
injected into flask under a nitrogen atmosphere. Then, a fresh M2 or M4 (1.14 mmol) and NaH (32 mg, 1.33 mmol) were placed in
sodium methoxide solution made from sodium (87 mg, 3.8 mmol) a 25 mL flask. 6 mL of dry THF was injected into flask under a
and methanol (15 mL) was added to the reaction mixture at 0 ℃ nitrogen atmosphere at 0 ℃ and was vigorously stirred for 40 min.
and vigorously stirred for 40 min, which was heated to 100 ℃ for Then, M6 (100 mg, 0.19 mmol) in dry THF (2 mL) was added to the
12 h. After the reaction mixture was cooled to room temperature reaction mixture, which was heated to refluxed for 12 h. After the
and added 1 M HCl aqueous solution, it was extracted with ethyl reaction mixture was cooled to room temperature and added 1 M
acetate. The organic phase was washed with brine, and then HCl aqueous solution, it was extracted with ethyl acetate. The
dehydrated over anhydrous MgSO
crude product was purified by column chromatography with DCM anhydrous MgSO
petroleum ether (1:5) as the eluant, affording green solids of was purified by column chromatography with ethyl
4
. After removing the solvent, the organic phase was washed with brine. It was then dehydrated over
4
. After removing the solvent, the crude product
/
1
compound B3G1-B. Yield: 37%. H NMR (400 MHz, DMSO) δ 7.61 – acetate/petroleum ether (1:4) as the eluant, affording green or
1
3
7
.55 (m, 12H), 7.27 (dd, J = 10.0, 8.1Hz, 15H), 4.72 (s, 6H). C NMR yellow solids of compound B1G2-H or B1G2-O.
1
(100 MHz, CDCl
3
) δ 169.72, 137.29, 135.42, 132.04, 131.33, 128.12, B1G2-H. Green solids. Yield: 36%. H NMR (400 MHz, CDCl
3
) δ 7.53 –
27.09, 124.87, 41.68. MALDI MASS m/z [M+K] calcd 1373.7045, 7.28 (m, 33H), 4.80 (d, J = 7.8 Hz, 6H). C NMR (100 MHz, CDCl ) δ
170.37, 138.22, 136.35, 136.28, 135.76, 130.55, 130.22, 129.91,
+
13
1
3
found 1373.1160.
1
4
8
28.96, 128.86, 128.77, 128.70, 128.58, 128.53, 128.10, 127.89,
+
2.05, 41.65. MALDI MASS m/z [M+Na+H] calcd 885.2815, found
Synthesis of compound B3G1-O
85.2761.
M4 (507 mg, 1.64 mmol) and NaH (45 mg, 1.968 mmol) were placed
in a 25 mL flask. 8 mL of dry THF was injected into flask under a
nitrogen atmosphere at 0 ℃ and was vigorously stirred for 40 min.
Then, 1,3,5-tris(bromomethyl)benzene (60 mg, 0.164 mmol) in dry
THF (2 mL) was added to the reaction mixture, which was heated to
refluxed for 12 h. After the reaction mixture was cooled to room
temperature and added 1 M HCl aqueous solution, it was extracted
with ethyl acetate. The organic phase was washed with brine, and
1
B1G2-O. Green solids. Yield: 33%. H NMR (400 MHz, CDCl
3
) δ 7.49
–
13
7.20 (m, 22H), 6.79 (d, J = 8.7 Hz, 7H), 4.70 (s, 6H), 3.75 (s, 12H).
3
C NMR (100 MHz, CDCl ) δ 170.90, 170.36, 160.76, 138.42, 136.38,
1
1
35.74, 134.14, 131.47, 130.92, 130.18, 128.88, 128.69, 128.00,
27.87, 121.24, 114.11, 55.31, 42.04, 41.49. MALDI MASS m/z
+
[
M+Na+H] calcd 1005.3237, found 1005.2536.
Synthesis of compound B1G2-N
4
then dehydrated over anhydrous MgSO . After removing the
solvent, the crude product was purified by column chromatography M9 (510 mg, 1 mmol), M6 (106 mg, 0.2 mmol) and potassium
with DCM/petroleum ether (3:1) as the eluant, affording yellow carbonate (207 mg, 1.5 mmol) were placed in a 25 mL flask. 8 mL of
1
solids of compound B3G1-F. Yield: 38%. H NMR (400 MHz, CDCl
3
) δ dry acetone was injected into flask under a nitrogen atmosphere
7
.37 (t, J = 8.5 Hz, 12H), 7.32 (s, 3H), 6.73 (d, J = 8.8 Hz, 12H), 4.68 and was vigorously stirred for 12 h at reflux. After the reaction
1
3
(s, 6H), 3.75 (s, 18H). C NMR (100 MHz, CDCl
3
) δ 170.82, 160.60, mixture was cooled to room temperature, it was extracted with
1
37.53, 134.21, 131.51, 127.84, 121.40, 113.99, 55.24, 41.48. ethyl acetate. The organic phase was washed with brine. It was then
+
MALDI MASS m/z [M+H] calcd 1042.3551, found 1041.9077.
dehydrated over anhydrous MgSO . After removing the solvent, the
4
crude product was purified by plate chromatography with ethyl
acetate/petroleum ether (1:4) as the eluant, affording red solids of
Synthesis of compound B3G1-N
1
compound B1G2-N. Yield: 31%. H NMR (400 MHz, CDCl
3
) δ 7.72 (s,
4
H), 7.42 (s, 10H), 7.27 (dd, J = 13.8, 6.7 Hz, 15H), 7.19 (d, J = 8.2 Hz,
8
| J. Name., 2012, 00, 1-3
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Or gP al en ai sc e&d Bo i on mo to al ed cj uu ls at r mC ha re gmi ni ss try
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DOI: 10.1039/C7OB02446K
Journal Name
ARTICLE
4
=
2
1
1
1
1
H), 7.10 (d, J = 7.1 Hz, 8H), 7.01 (dd, J = 17.1, 8.0 Hz, 8H), 6.72 (t, J
4
5
6
7
8
9
1
1
J. Xu, J. Pan, X. Jiang, C. Qin, L. Zeng, H. Zhang and J. F.
Zhang, Biosens. Bioelectron., 2016, 77, 725-732.
7.5 Hz, 4H), 5.36 – 5.22 (m, 8H), 4.83 (d, J = 19.1 Hz, 4H), 4.75 (s,
1
3
A. J. C. Kuehne and M. C. Gather, Chem. Rev., 2016, 116
,
,
3
H). C NMR (100 MHz, CDCl ) δ 171.93, 170.40, 138.85, 136.59,
12823-12864.
M. Y. Wong and E. Zysman-Colman, Adv. Mater., 2017, 29
1605444.
36.44, 136.36, 135.75, 132.07,130.17, 128.86, 128.73, 128.67,
27.86, 127.09, 126.83, 126.44, 122.42, 122.28, 120.20, 109.99,
+
06.42, 50.57, 41.99, 41.50. MALDI MASS m/z [M+Na] calcd
Z. Yang, Z. Mao, Z. Xie, Y. Zhang, S. Liu, J. Zhao, J. Xu, Z. Chi
and M. P. Aldred, Chem. Soc. Rev., 2017, 46, 915-1016.
J.-T. Hou, W. X. Ren, K. Li, J. Seo, A. Sharma, X.-Q. Yu and J.
S. Kim, Chem. Soc. Rev., 2017, 46, 2076-2090.
041.5084, found 1041.8810.
P. Reineck and B. C. Gibson, Adv. Opt. Mater., 2017,
6.
Y.-X. Li, M.-P. Pang, Z.-W. Zhang, G.-B. Li and G.-X. Sun, RSC
Adv., 2013, , 14950-14953.
X. L. Xu, F. W. Lin, W. Xu, J. Wu and Z. K. Xu, Chem. Eur. J.,
015, 21, 984-987.
5, 1-
Conclusions
2
0
1
An effective design method was presented to construct highly
efficient fluorescent materials in both solution and solid film, by
non-conjugately linking fluorophores into the branched oligomers.
3
2
According to the method, two series of branched oligomers, 12 L. Zong, Y. Xie, C. Wang, J.-R. Li, Q. Li and Z. Li, Chem.
Commun., 2016, 52, 11496-11499.
Y. Dong, J. W. Y. Lam, A. Qin, J. Liu, Z. Li and B. Z. Tang,
Appl. Phys. Lett., 2007, 91, 011111.
J. Luo, Z. Xie, J. W. Lam, L. Cheng, H. Chen, C. Qiu, H. S.
Kwok, X. Zhan, Y. Liu and D. Zhu, Chem. Commun., 2001,
1740-1741.
including three-branch-core and one-generation ones (B3G1-F,
B3G1-H, B3G1-B, B3G1-O and B3G1-N), and one-branch-core and
two-generation ones (B1G2-H, B1G2-O and B1G2-N), were
synthesized by employing diarylmaleimide as fluorophore. Surface
aryl groups were changed to tune the luminescent color of
branched oligomers. In order of electron-pushing ability, they are
trifluoromethylbenzene (B3G1-F), benzene (B3G1-H and B1G2-H),
bromobenzene (B3G1-B), methoxylbenzene (B3G1-O and B1G2-O)
and benzylindole (B3G1-N and B1G2-N). The emissive wavelength
1
1
3
4
1
1
5
6
Y. Liu, Y. Lei, F. Li, J. Chen, M. Liu, X. Huang, W. Gao, H. Wu,
J. Ding and Y. Cheng, J. Mater. Chem. C, 2016,
870.
P. Mazumdar, D. Das, G. P. Sahoo, G. Salgado-Morán and
4, 2862-
2
A. Misra, Phys. Chem. Chem. Phys., 2015, 17, 3343-3354.
of branched oligomers bathochromically shift from 480 nm of 17 X. Mei, K. Wei, G. Wen, Z. Liu, Z. Lin, Z. Zhou, L. Huang, E.
Yang and Q. Ling, Dyes Pigm., 2016, 133, 345-353.
X. Mei, G. Wen, J. Wang, H. Yao, Y. Zhao, Z. Lin and Q. Ling,
J. Mater. Chem. C, 2015, 3, 7267-7271.
X. Wang, Y. Wu, Q. Liu, Z. Li, H. Yan, C. Ji, J. Duan and Z. Liu,
Chem. Commun., 2015, 51, 784-787.
B3G1-F to 651 nm of B1G2-N with the increasing electron-pushing
ability of surface groups. Theory calculation shows that the optic
properties of branched oligomers basically depend on the
electronic transition of individual fluorophore. There are no
1
1
8
9
interactions between the fluorophores in branched oligomers for 20 Z. Xie, C. Chen, S. Xu, J. Li, Y. Zhang, S. Liu, J. Xu and Z. Chi,
Angew. Chem. Int. Ed., 2015, 54, 7181-7184.
B. Xu, J. He, Y. Mu, Q. Zhu, S. Wu, Y. Wang, Y. Zhang, C. Jin,
C. Lo and Z. Chi, Chem. Sci., 2015, 6, 3236-3241.
S. Xu, T. Liu, Y. Mu, Y. F. Wang, Z. Chi, C. C. Lo, S. Liu, Y.
their non-conjugated structure. However, the emissive intensity of
branched oligomers in both solution and solid film has been greatly
improved, relative to arylmaleimide fluorophores. The good
solubility, chemical stability, and thermostability of the branched
oligomers make them have huge potential in the solution-
processable photonic application.
2
2
1
2
Zhang, A. Lien and J. Xu, Angew. Chem. Int. Ed., 2015, 54
874-878.
,
2
2
2
2
2
2
2
3
4
5
6
7
8
9
A. S. Abd-El-Aziz, C. Agatemor, N. Etkin and B. Wagner,
Macromol. Rapid Commun., 2016, 37, 1235-1241.
G. Chen, W. Li, T. Zhou, Q. Peng, D. Zhai, H. Li, W. Z. Yuan,
Y. Zhang and B. Z. Tang, Adv. Mater., 2015, 27, 4496-4501.
M. Huang, R. Yu, K. Xu, S. Ye, S. Kuang, X. Zhu and Y. Wan,
Chem. Sci., 2016, 7, 4485-4491.
M. Li, Y. Niu, X. Zhu, Q. Peng, H.-Y. Lu, A. Xia and C.-F. Chen,
Chem. Commun., 2014, 50, 2993-2995.
X. Mei, J. Wang, Z. Zhou, S. Wu, L. Huang, Z. Lin and Q. Ling,
Conflicts of interest
There are no conflicts of interest to declare.
Acknowledgements
J. Mater. Chem. C, 2017,
H. Chen, Y. Tang, H. Shang, X. Kong, R. Guo and W. Lin, J.
Mater. Chem. B, 2017, , 2436-2444.
J. Han, J. You, X. Li, P. Duan and M. Liu, Adv. Mater., 2017,
, 1606503.
30 H. Tachibana, N. Aizawa, Y. Hidaka and T. Yasuda, Acs
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X. Wei, L. Bu, X. Li, H. Agren and Y. Xie, Dyes Pigm., 2017,
36, 480-487.
5, 2135-2141.
This work was supported by the National Natural Science
Foundation of China (21374017, 21401023 and 21574021), the
Natural Science Foundation of Fujian Province (2017J01684),
and Educational Commission of Fujian Province (JA14068).
5
29
4
3
3
1
2
1
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