Aggregation induced emission of diketopyrrolopyrrole (DPP) derivatives for highly fluorescent red films

Article abstract of DOI:10.1039/c8pp00403j

A large number of diketopyrrolopyrrole (DPP) compounds showing aggregation induced emission (AIE) have been reported in the past few years. However, although DPP compounds exhibited AIE and excellent luminescence properties, their luminescence properties in solid or film states were not much focused on. Here we synthesized and characterized a series of DPP compounds with triphenylamine (TPA) moieties to investigate the AIE properties in the solid film state depending on the functional groups (TPA, BTPA, and MTPA) attached to the TPA moieties. T2 and D2 thin films showed excellent fluorescence quantum yields of 31% and 26%, respectively, compared to an M2 thin film (9%). The restriction of an intramolecular rotation process could inhibit the aggregation induced quenching process and play a key role in achieving highly fluorescent molecules in the solid state.

Full text of DOI:10.1039/c8pp00403j

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Aggregation induced emission of
diketopyrrolopyrrole (DPP) derivatives for highly
Cite this: DOI: 10.1039/c8pp00403j
fluorescent red films†
a
a
a
a
Tae Gyu Hwang, Jeong Yun Kim, Jin Woong Namgoong, Jae Moon Lee,
a
a,b
a
Sim Bum Yuk, Se Hun Kim and Jae Pil Kim
*
A large number of diketopyrrolopyrrole (DPP) compounds showing aggregation induced emission (AIE)
have been reported in the past few years. However, although DPP compounds exhibited AIE and excellent
luminescence properties, their luminescence properties in solid or film states were not much focused on.
Here we synthesized and characterized a series of DPP compounds with triphenylamine (TPA) moieties to
investigate the AIE properties in the solid film state depending on the functional groups (TPA, BTPA, and
MTPA) attached to the TPA moieties. T2 and D2 thin films showed excellent fluorescence quantum yields
of 31% and 26%, respectively, compared to an M2 thin film (9%). The restriction of an intramolecular
rotation process could inhibit the aggregation induced quenching process and play a key role in achieving
highly fluorescent molecules in the solid state.
Received 14th September 2018,
Accepted 23rd November 2018
DOI: 10.1039/c8pp00403j
rsc.li/pps
functional groups capable of free rotation such as triphenyl-
1
. Introduction
1
5–18
amine (TPA) or tetraphenylethene (TPE)
However, the AIE
Recently, fluorescent π-conjugated organic materials have mechanism is difficult to elucidate because this effect is
become the subject of increasing research interest because of counter to classical concepts of photophysics. The most
their potential applications in organic light-emitting diodes common mechanisms for the AIE phenomenon include
1
–4
5
19,20
(
OLEDs),
agricultural photoconversion films, light harvest- restriction of intramolecular rotation (RIR),
restriction of
6
7
8–10
21
ing, optical storage, and chemosensing.
applications require fluorescent π-conjugated organic charge transfer (TICT),
Because such intramolecular charge transfer (ICT), twisted intramolecular
2
2
23
and J-aggregate formation.
materials to be in the solid state (or film state), excellent solid Although a theory that describes the AIE phenomenon univer-
state fluorescence quantum yields are required. However, sally has not yet been elucidated, considerable research is cur-
π-conjugated fluorescent organic molecules commonly exhibit rently underway to identify systems that exhibit AIE and
2
4,25
technical limitations owing to aggregation caused quenching develop industrial applications.
(
ACQ) resulting from π–π stacking interactions and dipole–
Diketopyrrolopyrrole (DPP) is a well-known π-conjugated
1
1,12
dipole interactions in the solid state.
Therefore, fluorescent organic dye that shows excellent fluorescence pro-
π-conjugated fluorescent organic molecules have poor solid perties. As DPP is an electron-deficient organic molecule, it
state fluorescence quantum yields. can be used as an electron acceptor (EA) for an electron donor
In 2001 and 2002, Tang and co-workers and Park and co- (ED) such as electron-rich TPA moieties. Therefore, it is poss-
workers first described the phenomenon of aggregation ible to form ED–EA π-conjugated structures with excellent fluo-
induced emission (AIE), in which enhanced emission is rescence and AIE properties by introducing free rotation moi-
1
3,14
26,27
observed in the aggregated state.
AIE has mainly been eties such as TPA and TPE into DPP.
Previously, some
reported for π-conjugated fluorescent organic materials with highly emissive π-conjugated AIE-DPPs in the solid state were
1
6,17
reported.
In this study, in order to investigate the lumine-
scence properties of DPP depending on the TPA moieties and
to further expand previous research studies for highly emissive
AIE-DPPs in the solid state, a series of DPP compounds con-
taining three different TPA moieties (TPA, BTPA, and MTPA)
with different donating abilities were designed and syn-
thesized (Scheme 1). The photophysical properties of these
compounds were changed in both non-aggregated states
a
Lab. of Organic Photo-functional Materials, Department of Materials Science and
Engineering, Seoul National University, Seoul 08826, Republic of Korea.
E-mail: Jaepil@snu.ac.kr
b
EM Development Team, ChemE Inc., 199, Techno 2-ro, Yuseong-gu, Daejeon 34025,
Republic of Korea
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
c8pp00403j
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Scheme 1 Synthetic route for target compounds.
(in pure tetrahydrofuran (THF)) and aggregated states (in THF/ and M2, which contained TPA moieties, show AIE, but D6C, as
water mixtures) depending on the TPA moiety introduced into a control without TPA moieties, shows ACQ.
DPP. In addition, thin films of the DPP compounds in poly
(methyl methacrylate) (PMMA) were fabricated to observe the
2.2 Photophysical properties in the solution
AIE phenomenon in the solid film state. The relationship
between the photophysical properties and the shapes of the
aggregates formed on the surface of the thin films was ana-
lyzed using field emission scanning electron microscopy
The UV–vis absorption and photoluminescence (PL) emission
spectra of the DPP compounds in a pure THF solution at a
concentration of 1 × 10− M are shown in Fig. 1, and the
associated photophysical parameters are summarized in
Table 1. As shown in Fig. 1a and Table 1, the maximum wave-
length of absorption (λabs. max) of D6C is 476 nm, whereas T2,
D2, and M2 exhibited bathochromic shifts with λmax values of
5
(FE-SEM).
5
03, 504, and 513 nm, respectively. As depicted in Fig. 1 and
Fig. 2, for T2, D2, and M2, the low energy band at around
00 nm originates from an ICT process, whereas the high
2
. Results and discussion
2
.1 Design and synthesis
5
We designed and synthesized a series of DPP compounds energy band at around 400–440 nm is attributed to the n–π*
incorporating TPA moieties with different donating abilities transition of the TPA moieties. Increasing the donating power
following the general Suzuki coupling reactions described in of the TPA moieties introduced into DPP (MTPA > BTPA > TPA)
the literature (Scheme 1). However, palladium catalysts were resulted in a larger bathochromic shift of the maximum wave-
used 3–10 times more than that reported in the literature to length of absorption. Fig. 1b shows the fluorescence emission
1
5,16
achieve desirable yields.
spectra of the DPP compounds. As shown in Fig. 1b and
Compounds T2, D2, and M2 were readily synthesized from Table 1, the maximum wavelength of fluorescence (λem. max) of
D6C in high yields via Suzuki coupling reactions with TPA-BO, D6C is 557 nm, whereas T2, D2, and M2 exhibit bathochromic
BTPA-BO, and MTPA-BO. Characterization of the target com- shifts, with λem. max values of 590, 602, and 625 nm, respect-
pounds by nuclear magnetic resonance (NMR) spectroscopy, ively. As the donating power of the TPA moieties increased
mass spectrometry, and elemental analysis confirmed their (MTPA > BTPA > TPA), the bathochromic shift of the
theoretical molecular structures. It is assumed that T2, D2, maximum wavelength of fluorescence became larger. The fluo-
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Fig. 1 (a) Absorption and (b) PL spectra of D6C, T2, D2, and M2 in THF at a concentration of 1 × 10− mol L−1
5
.
Table 1 Photophysical data for D6C, T2, D2, and M2 in THF
Table 2 Solubilities of D6C, T2, D2, and M2 at room temperature
Absorption Emission
Stokes
shift
(nm)
D6C
T2
D2
M2
a
a
a,b
a,b,c
d
3
max
λ
abs. max
λ
em. max
Φ
f
Compound (L mol cm−1
−1
)
(nm)
(nm)
(%)
THF
CHCl
++++
++++
++
++
+
+
+++
+++
3
D6C
T2
D2
21 700
30 000
42 200
50 500
476
503
504
513
557
590
602
625
67
71
68
2
81
87
98
++++: >5.0 × 10 mg L ; +++: 5.0 × 10 –1.0 × 10 mg L−1; ++: 5.0 ×
4
−1
4
5
3
4
−1
2
3
−1
10 –5.0 × 10 mg L ; +: 5.0 × 10 –5.0 × 10 mg L .
M2
112
a
× 10−5 M concentration of the compounds in pure THF solution.
1
b
c
The absorption
λmax was used as the excitation wavelength. THF solution. Consequently, it is assumed that T2 and D2 had
Fluorescence quantum yields were obtained using an integrating
lower energy dissipation via rotation of TPA moieties than M2.
d
sphere.
λem. max − λabs. max.
2.3 Solubility and planarity
The solubilities of the synthesized DPP compounds in THF
rescence quantum yields (Φ ) of D6C, T2, D2, and M2 in pure and CHCl3 (CF) are shown in Table 2. The solubilities were
f
THF solutions (Table 1) were determined to be 67%, 71%, found to be high in both THF and CF, decreasing in the order
6
8%, and 2%, respectively, using an integrating sphere. of D6C > M2 > T2 > D2. In T2 and D2, π–π stacking interactions
Although most of the AIE luminophores showed poor fluo- are strengthened owing to the increased planarity achieved by
1
3–15,26–28
rescence quantum yields in dilute solutions,
T2 and introducing bulky aromatic substituents at the Br positions of
D2 exhibited noticeable fluorescence quantum yields in pure the D6C structure. Therefore, the solubilities of T2 and D2 are
Fig. 2 Electron density distributions of the frontier molecular orbitals of D6C, T2, D2, and M2.
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2
9
lower than that of D6C. In contrast, M2 exhibited higher 2.5 AIE characteristics in THF/H
solubility than T2 and D2 because M2 had a branched
2
O mixtures
To examine the optical behavior of the synthesized DPP com-
pounds in the aggregated states, different amounts of water,
which is a poor solvent for luminophores, were added to the
pure THF solutions to induce aggregation. Fig. 3 and 4 show
the absorption spectra and PL spectra with the corresponding
optical images of the DPP compounds in THF/water mixtures
methoxy substituent at the para positions of TPA inhibiting
intermolecular π–π stacking in M2 compared to T2 and
1
2,30
D2.
2
.4 Computational analysis
w
The electronic structures of DPP compounds, and the HOMO with water fractions (ƒ ) of 0%–90%. The optical images of PL
and LUMO of each compound were analyzed by computational were obtained under illumination of a 365 nm UV lamp. As
calculations (DFT/B3LYP/6-31G, Gaussian 09 program shown in Fig. S1,† the optical properties of the mixtures were
package) to investigate the relationship between the photo- analyzed after sonicating for an hour to disperse the precipi-
physical properties. The HOMOs, LUMOs, and electron density tated molecules. Fig. 5 shows the plot of I (the PL intensity in
distributions of the frontier molecular orbitals for the opti- the THF/water mixture)/I
mized structures of the DPP compounds are shown in Fig. 2. water fractions of the DPP compounds.
The calculated band gaps of D6C, T2, D2, and M2 (2.77, 2.5,
The concentration of each compound was maintained at
.48, and 2.45 eV, respectively) increased in the order of 1 × 10− mol L in aqueous mixtures. As shown in Fig. 3, the
(the PL intensity in pure THF) versus
0
4
−1
2
M2 < D2 < T2 < D6C. T2, D2, and M2 showed separated elec- absorption tails of T2, D2, and M2 in the THF/water mixture
tron cloud distributions between the HOMO and the LUMO, were extended into the long wavelength region (600–700 nm)
whereas it seemed similar between the HOMO and LUMO of with increasing water fractions. According to the literature, the
D6C. Notably, the LUMOs of T2, D2, and M2 had higher elec- extended absorptions indicate the formation of aggregates of
tron densities in the DPP core than the HOMOs because the the nanoparticles in the presence of water, and the level-off
electron-rich TPA moieties functioned as EDs, whereas the tails in the visible region are attributed to the Mie scattering
3
1
electron-deficient DPP core functioned as an EA. Therefore, it caused by the nanosized particles. As shown in the PL
seemed evident that DPP compounds with TPA moieties had spectra in Fig. 4b–d, substitution of TPA moieties at the Br
more ICT characteristics between the ED and the EA than the positions of D6C affected the optical properties. In the pure
one without TPA moieties. These results suggest that expand- THF solution, D6C showed strong yellowish green light, T2
ing the π-conjugation system of DPP with electron donating and D2 showed strong orange light, and M2 was nearly non-
moieties induced separation between the HOMO and the luminescent. The PL intensity of D6C was not changed signifi-
LUMO. As shown in Fig. 1, the absorption and PL spectra of cantly from ƒ
T2, D2, and M2 exhibited bathochromic shifts relative to those decrease dramatically from ƒ
of D6C.
rescence quenching can be explained by the ACQ phenom-
w
= 0% to 60%. However, the intensity began to
= 70% to 90%. This fluo-
w
w
Fig. 3 Absorption spectra of (a) D6C, (b) T2, (c) D2, and (d) M2 in THF/water mixtures with different water fractions (ƒ ).
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w
Fig. 4 Optical images and PL spectra of (a) D6C, (b) T2, (c) D2, and (d) M2 in THF/water mixtures with different water fractions (ƒ ).
0 w
Fig. 5 Plot of I (the PL intensity in the THF/water mixture)/I (the PL intensity in pure THF) versus the water fractions (ƒ ) of (a) D6C, (b) T2, (c) D2,
and (d) M2.
enon, which is typical of organic fluorescent molecules. In Fig. 3b and S2b,† with the formation of aggregates at ƒ
contrast, T2, D2, and M2 showed different fluorescence behav- 50%, the emission of T2 also increased. As shown in Fig. 5b,
ior in the aggregated state. As shown in Fig. 4b, with gradual the maximum intensity of PL was 1.1-fold higher at ƒ = 80%
addition of water to the THF solution, the emission of T2 than that in the pure THF solution. In addition, small dual
rapidly weakened when ƒw ≤ 40%. However, as shown in peaks at 590–610 nm and 620–640 nm are observed at ƒw
w
≥
w
=
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5
0% and 60%. This phenomenon could be related to the irreg- caused via the RIR process of the TPA moiety through the for-
ular formation of aggregated nanoparticles. As shown in mation of aggregates. Interestingly, both T2 and D2 showed
Fig. S1b,† because T2 aggregated abruptly, it was irregularly poor fluorescence in aqueous mixtures with low water frac-
aggregated inside the nanoparticles. Therefore, T2 precipitated tions. It is assumed that because the high polarity of water
from the aqueous mixtures at ƒw = 50% and 60%, and certain caused an intramolecular charge separation of DPP com-
different emissions could be observed from the dispersion of pounds, the energy of the first singlet excited state was lowered
precipitated irregular aggregates. The changes in the PL and thereby alleviated the transition of the molecule into other
spectra of the DPP compounds in THF/water mixtures were states such as the triplet state with corresponding fluorescence
3
3
also related to the solvent effect. TICT is caused by the twisting quenching. As shown in Fig. 3d, 4d, and S1d,† the emissions
of a single bond between the ED and EA as the solvent polarity of M2 aqueous mixtures rapidly enhanced with the formation
2
7
increases, achieved here by adding water to THF solution.
of aggregates at ƒw ≥ 40%. The maximum PL intensity was
= 60% than that in the pure THF
The DPP core functioned as an EA, and the TPA moieties func- about 600-fold higher at ƒ
w
tioned as EDs. Consequently, the former peak (590–610 nm) of solution. Also, intensive dual peaks at 570–600 nm and
T2 is assigned to a local excited state (LE), and the latter one 610–650 nm are observed from ƒw = 40% to 60%. The newly
(620 nm–640 nm) could be related to the TICT state, which is arisen former peak (570–600 nm) of M2 could be related to the
shown in the longer wavelength region in an equilibrium state aggregation state originating from the irregularly formed
at ƒw = 50% and 60%. The PL intensity of mixtures with high aggregated nanoparticles, and the latter one (610 nm–650 nm)
water fractions at ƒ = 70% and 80% was enhanced compared is assigned as the TICT state from ƒ = 40% to 60%. However,
w w
to the intensity of pure THF solution due to the increased RIR the aggregation state disappeared from 70% to 90%. The net
process. At ƒ = 90%, the net outcome PL intensity was slightly outcome PL intensity of M2 aqueous mixtures from ƒw = 70%
w
w
decreased, and the spectrum of the mixture shifted to a longer to 90% decreased compared to that at ƒ = 50% and 60% but
wavelength region. This may be related to the TICT state orig- still showed AIE properties. The above results indicated that
inating from the high solvent polarity due to the high water the luminescence properties of DPP compounds could be
fraction. Thus, the measured luminescence properties of T2 changed depending on the degree of aggregation with the
aqueous mixtures showed no regularity at high water fractions. corresponding water fractions in THF/water mixtures. In
As shown in Fig. 4c, the emission of D2 also weakened rapidly addition, the RIR process by TPA moieties plays an important
3
4
until ƒ
the formation of aggregates at ƒ
also increased. As shown in Fig. 5c, the maximum intensity of
PL was about 1.6-fold higher at ƒ = 60% than that in the pure DPP compound/PMMA thin films were fabricated to observe
THF solution. In addition, dual peaks at 590–610 nm and the AIE properties of the DPP compounds while minimizing
20–640 nm are observed at ƒ = 50% and 60%. This phenom- the solvent effects. The surface properties of the fabricated
w
≤ 30%. However, as shown in Fig. 3c and S2c,† with role in the emission behavior of the aggregated molecules.
w
≥ 40%, the emission of D2
2.6 Fabrication of DPP compound/PMMA thin films
w
6
w
enon could also be related to the irregular formation of aggre- thin films were investigated through FE-SEM. As shown in
gated nanoparticles. As shown in S1c,† irregular aggregates of Fig. 6, the thicknesses of the thin films formed on quartz
D2 precipitated from the aqueous mixtures from ƒw = 30% to plates were measured by FE-SEM. The fabricated films had a
6
w
0% and showed opaque dispersion from ƒ = 70% to 90%. In thickness of about 11 µm to minimize the effects caused by
addition, the dual peaks at 550–590 nm and 600–630 nm were the differences in thicknesses. Fig. 7 shows the FE-SEM
observed for the aqueous mixture from ƒw = 40% to 90% are images of the surfaces of the thin films. As shown in Fig. 7a,
shown in Fig. 3c. In contrast to T2, an intense former peak the surface of the D6C/PMMA thin film was uniform with
(
550–590 nm) of D2 could be related to the aggregation state, agglomerated particles of about 20–30 nm size. However, as
and the latter one (600 nm–625 nm) is assigned to an LE state shown in Fig. 7b–d, the surfaces of the T2/PMMA, D2/PMMA,
from ƒ = 40% to 90%. The environment inside the irregularly and M2/PMMA thin films were not uniform, and the agglomer-
w
formed aggregated nanoparticles is less polar than the ated particles were bulkier than those in the D6C/PMMA thin
medium outside, which explains why the aggregate emission film. The differences observed in the surface images of these
3
2
state is blue-shifted from that of the LE state. The enhance- DPP compound/PMMA thin films were related to the solubility
ment of the net outcome PL intensities at ƒ ≥ 40% was and planarity of the DPP compounds, as described earlier.
w
Fig. 6 FE-SEM images of the cross-sections of DPP compound/PMMA thin films: (a) D6C, (b) T2, (c) D2, and (d) M2.
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Fig. 7 FE-SEM images of the surface of DPP compound/PMMA thin films: (a) D6C, (b) T2, (c) D2, and (d) M2.
Fig. 8 (a) Absorption and (b) PL spectra of D6C, T2, D2, and M2 in PMMA films.
Consequently, D6C showed relatively uniform aggregation in Table 3 Photophysical data for D6C, T2, D2, and M2 in PMMA films
the thin film owing to its relatively low planarity. In contrast,
T2, D2, and M2 were non-uniformly aggregated in the polymer
matrix due to their higher planarity than D6C.
a,b,c
d
Absorption
Emission
Φ
f
Stokes shift
(nm)
a
a,b
Compound
λabs. max (nm)
λ
em. max
(nm) (%)
D6C
T2
D2
480
508
509
517
574
614
611
640
11
31
26
9
94
106
102
123
2
.7 Photophysical properties of DPP compound/PMMA thin
M2
films
a
5
mol% of the compounds in a PMMA thin film coated on a quartz
b
The normalized absorption and emission spectra, photo-
physical data, and optical images of the thin films are depicted
plate. The absorption λmax was used as the excitation wavelength.
Fluorescence quantum yields were obtained using an integrating
in Fig. 8, Table 3, and Fig. 9, respectively. The spectra were nor- sphere.
malized to ensure the reliability of the data because of the lack
of uniformity in the thin films. The absorption and emission
c
d
λem. max − λabs. max.
spectra of the thin films tended to exhibit bathochromic shifts and 4 nm, respectively, relative to those in the pure THF solu-
compared with those in the solution. The absorbance spectra tion. The PL spectra of D6C, T2, D2, and M2 also bathochromi-
of D6C, T2, D2, and M2 bathochromically shifted by 4, 5, 5, cally shifted by 17, 24, 9, and 15 nm, respectively, relative to
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4. Experimental section
4.1 General
TPA-BO, BTPA-Pre, and MTPA-Pre were purchased from Tokyo
Chemical Industry. PMMA with a number-average molecular
weight (M ) of 350 000 was purchased from Aldrich and was
n
used as received. All other chemicals were purchased from
commercial suppliers and used as received without further
purification. The intermediates 3,6-bis(4-bromophenyl)-2,5-
dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DPPH), 4-[bis(biphenyl-
Fig. 9 Optical images of D6C/PMMA, T2/PMMA, D2/PMMA, and M2/
PMMA films.
those in the pure THF solutions. The fluorescence quantum
yields of the D6C, T2, D2, and M2 thin films were 11%, 31%,
4-yl)amino]phenylboronic acid (BTPA-BO), and 4-(bis(4-meth-
oxyphenyl)amino)phenylboronic acid (MTPA-BO) were syn-
2
6%, and 9%, respectively.
1
5,36,37
thesized efficiently according to literature procedures.
The fluorescence quantum yield of M2 in the film state
1
Transparent glass substrates were provided by NTP, Inc.
and C NMR spectra were recorded on a Bruker Avance III 500
spectrometer at 500 MHz in CHCl -d or dichloromethane-d
H
(9%) exhibited a 4.3-fold enhancement compared with that in
1
3
the pure THF solution (2%) through the AIE process. However,
although T2 and D2 exhibited AIE properties in THF/water
mixtures, they showed decreased quantum yield in the thin
films compared to the values in the pure THF solutions. In
general, when fluorescent organic molecules form planar
aggregates, π–π stacking and intermolecular interactions
3
with tetramethylsilane (TMS) as an internal standard.
Elemental analysis was performed with a Thermo Scientific
Flash EA 1112 elemental analyzer. Matrix-assisted laser desorp-
tion/ionization time-of-flight (MALDI-TOF) mass spectra were
recorded on an Applied Biosystems Voyager-DE STR
Biospectrometry Workstation using cyano-4-hydroxycinnamic
acid (CHCA) as a matrix. UV–vis absorption spectra were
recorded using a PerkinElmer Lambda 25 spectrophotometer.
PL spectra and absolute fluorescence quantum yields were
obtained using PerkinElmer LS 55 and Jasco International
FP-8500ST spectrofluorometers, respectively. FE-SEM images
were acquired using a Zeiss MERLIN Compact field emission
scanning electron microscope; Pt was coated on the samples
using a JEOL MSC-101 sputter coater for 40 s at a current
strength of 40 mA to avoid charging of the surface. Density
functional theory (DFT) calculations were performed with the
Gaussian 09 program package using the 6-31G(d,p) Pople basis
set for all elements and the conventional B3LYP exchange cor-
relation function.
3
5
increase, which may cause ACQ. As shown in Fig. 7b and c,
the surface images of T2 and D2 showed more bulky and
planar forms than D6C because of increased planarity.
Consequently, more π–π stackings and intermolecular inter-
actions may arise in the thin films of T2 and D2 than D6C.
However, the fluorescence quantum yields of T2 (31%) and D2
(26%) in the film state were 2.3–2.8-fold that in a thin film of
D6C (control, 11%) and 2.97–3.63-fold that in a thin film of
M2. It is because obviously the AIE process originates from the
RIR process of the TPA moieties and inhibits the ACQ process
in a trade-off relationship. Therefore, it is clear that T2 and D2
had AIE characteristics in the film state and their fluorescence
quantum yields in the solid state (thin film) were much higher
than that of M2.
4
.2 Syntheses of compounds
,6-Bis(4-bromophenyl)-2,5-dihexyl-2,5-dihydropyrrolo-3,4-
A series of diketopyrrolopyrrole compounds incorporating cpyrrole-1,4-dione (D6C). solution of DPPH (6 g,
3
. Conclusions
3
A
three different triphenylamine moieties were synthesized, and 13.52 mmol) in N-methyl-2-pyrrolidone (NMP) (70 mL) was
their photophysical properties were analyzed in pure THF stirred at room temperature under a nitrogen atmosphere.
solutions, THF/water mixtures, and thin films. All the diketo- After stirring for 2 h, potassium tert-butoxide (t-BuOK) (4.83 g,
pyrrolopyrrole compounds with triphenylamine moieties 43.04 mmol) was added dropwise. After stirring for 2 h, 1-iodo-
showed different red emissions with aggregation induced hexane (17.320 g, 81.67 mmol) was added dropwise. The
emission characteristics. The difference in the luminescence resulting solution was stirred for another 2 h at 45 °C and then
properties of the prepared diketopyrrolopyrrole compounds cooled to room temperature. The reaction mixture was directly
was attributed to the different functional groups attached to evaporated at 180 °C using a vacuum rotary evaporator with an
the triphenylamine moieties, and the fluorescence quantum oil bath. The crude product was purified by column chromato-
2 2
yields of solid thin films of diketopyrrolopyrrole were graphy using CH Cl as the eluent to obtain bright orange crys-
1
changed as 9%, 26%, and 31%. Consequently, this work pro- tals of D6C (4.63 g, 56% yield). H NMR (500 MHz, CDCl ), δ
3
vided some insight into tuning the triphenylamine moieties (ppm): 7.62–7.67 (m, 8H), 3.69–3.72 (t, J = 7.75 Hz, 4H),
for obtaining highly emissive diketopyrrolopyrrole com- 1.52–1.55 (t, J = 7 Hz, 4H), 1.17–1.24 (m, 12H), 0.81–0.84 (t, J =
1
3
pounds in the solid film state. Therefore, diketopyrrolo- 7 Hz, 6H). C NMR (125 MHz, CDCl ), δ (ppm): 162.59,
3
pyrrole with optimal triphenylamine moieties could also 147.63, 132.39, 130.28, 127.11, 126.00, 110.07, 42.02, 31.37,
become excellent solid state emissive materials by aggrega- 29.54, 26.53, 22.63, 14.12. MALDI-TOF MS: m/z 615.00 (100%,
+
tion induced emission.
M + H ). Elemental analysis: calcd for C H Br N O : C,
3
0
34
2 2 2
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5
8.65; H, 5.58; Br, 26.01; N, 4.56; O, 5.21. Found: C, 58.62; H, 79.07; H, 6.64; N, 5.27; O, 9.03. Found: C, 79.05; H, 6.74; N,
.57; N, 4.54; O, 5.24. 5.26; O, 8.98.
,6-Bis(4′-(diphenylamino)-1,1′-biphenyl-4-yl)-2,5-dihexyl-2,5-
dihydropyrrolo-3,4-c-pyrrole-1,4-dione (T2). mixture of
Pd(PPh3)4 (100 mg, 0.091 mmol), D6C (0.28 g, 0.46 mmol), The solubility properties of the synthesized compounds in
and TPA-BO (0.40 g, 1.38 mmol) in dry THF (40 mL) was THF and CHCl were examined to observe the planarity of the
5
3
4.3 Investigation of solubility
A
3
stirred for 30 min at room temperature under a nitrogen atmo- compounds. The prepared compounds were added to the sol-
sphere. After increasing the temperature of the mixture to vents at various concentrations, and the solutions were soni-
6
2 3
0 °C, an aqueous solution of K CO (3.65 M, 5 mL) was added cated for 5 min using an ultrasonic cleaner ME6500E. The
dropwise and the resulting mixture was maintained at this solutions were left to stand for 24 h at room temperature and
temperature for 12 h. The reaction mixture was then poured checked for precipitation to determine the solubility of the
2
9
into water and extracted with CH
layers were dried over anhydrous MgSO
to dryness. The crude product was purified by column chrom-
atography using CH Cl : hexane (3 : 1, v/v) as the eluent to According to literature procedures, PMMA thin films doped
obtain red crystals of T2 (0.35 g, 80% yield). H NMR with the synthesized compounds were prepared on quartz
2
Cl2. The combined organic synthesized compounds.
4
and then evaporated
4.4 Fabrication of thin films
2
2
1
(
500 MHz, CD Cl ), δ (ppm): 7.88–7.89 (m, 4H), 7.73–7.75 (m, plates by the doctor blade technique using CHCl3 solutions
2 2
4
7
1
H), 7.55–7.57 (m, 4H), 7.26–7.30 (m, 8H), 7.11–7.14 (m, 12H), with a fixed PMMA concentration of 5 wt% showing optimal
.04–7.07 (m, 4H), 3.78 (t, J = 7.5 Hz, 4H), 1.56–1.62 (m, 4H), coatability. The synthesized compounds were added to PMMA/
1
3
.19–1.26 (m, 12H), 0.83 (d, J = 7 Hz, 6H). C NMR (125 MHz, CHCl solutions at a concentration of 3 mol% relative to the
3
2 2
CD Cl ), δ (ppm): 163.13, 148.62, 148.23, 148.03, 143.56, quantity of PMMA monomer units. More than 3 mol% concen-
1
1
33.77, 129.91, 129.84, 128.30, 127.22, 127.14, 125.35, 123.90, trations were out of the detection limit of UV and PL analyzing
23.79, 110.40, 42.39, 31.82, 29.93, 26.91, 23.05, 14.31. equipment. The cast films were dried under vacuum for 24 h
+
38
MALDI-TOF MS: m/z 943.7 (100%, M ). Elemental analysis: at 80 °C.
calcd for C66 : C, 84.04; H, 6.63; N, 5.94; O, 3.39.
Found: C, 84.04; H, 6.62; N, 5.97; O, 3.38.
62 4 2
H N O
3
,6-Bis(4′-(di(1,1′-biphenyl-4-yl)amino)-1,1′-biphenyl-4-yl)- Conflicts of interest
2
,5-dihexyl-2,5-dihydropyrrolo-3,4-c-pyrrole-1,4-dione
Compound D2 was prepared according to a procedure similar
to that for T2, using BTPA-BO (0.61 g, 1.38 mmol) instead of
TPA-BO to produce red crystals of D2 (0.47 g, 82% yield). H
NMR (500 MHz, CD Cl ), δ (ppm): 7.89–7.91 (d, J = 8.5 Hz,
(D2).
The authors declare no competing financial interest.
1
Acknowledgements
2
2
4
7
7
H), 7.76–7.78 (d, J = 8.5 Hz, 4H), 7.59–7.63 (m, 12H),
This work was supported by the Technology Innovation
Program (No. 10052798) funded by the Ministry of Trade,
Industry & Energy (MI, Korea) and the Institute of Planning
and Evaluation for Technology in Food, Agriculture, Forestry
and Fisheries (IPET) through the Advanced Production
Technology Development Program, funded by the Ministry of
Agriculture, Food and Rural Affairs (MAFRA) (117017-3).
.54–7.57 (m, 8H), 7.41–7.44 (m, 8H), 7.29–7.33 (m, 4H),
1
3
.22–7.25 (m, 12H), 3.74–3.80 (m, 4H), 0.80–1.60 (m, 22H).
), δ (ppm): 163.10, 148.22, 147.89,
46.80, 143.38, 140.74, 136.23, 134.02, 129.48, 128.99, 128.21,
C
NMR (125 MHz, CDCl
3
1
1
4
28.13, 127.19, 127.04, 126.94, 126.75, 124.99, 124.09, 110.03,
2.36, 31.46, 29.90, 29.69, 29.58, 26.65, 22.69. Elemental ana-
lysis: calcd for C90
Found: C, 86.08; H, 6.44; N, 4.42; O, 3.12.
,6-Bis(4′-(bis(4-methoxyphenyl)amino)-1,1′-biphenyl-4-yl)-
,5-dihexyl-2,5-dihydropyrrolo-3,4-cpyrrole-1,4-dione (M2).
78 4 2
H N O : C, 86.64; H, 6.30; N, 4.49; O, 2.56.
3
Notes and references
2
Compound M2 was prepared according to a procedure similar
to that for T2, using MTPA-BO (0.48 g, 1.38 mmol) instead of
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blue thermally activated delayed fluorescence molecules
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crystals of M2 (0.34 g, 70% yield). H NMR (500 MHz, CDCl
δ (ppm): 7.88–7.90 (d, J = 8.5 Hz, 4H), 7.69–7.71 (d, J = 8.5 Hz,
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.79–3.82 (m, 16H), 0.82–1.69 (m, 22H). C NMR (125 MHz,
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40.72, 131.43, 129.42, 127.76, 127.14, 126.71, 126.30,
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7
0
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