Synthesis and characterization of novel perylenediimide-cored dendrimer with fluorinated shell

Article abstract of DOI:10.1080/00397910903013754

A perylenediimide-based dendrimer, PDI-F, was designed and synthesized for application as red host emitter in nondoped organic light-emitting diodes. PDI-F was designed with perylenediimide as the luminescence core and pentafluorophenyl rings as the surface groups. The dendrimer molecule constructed in this way is bulky and nonplanar. PDI-F exhibits good solubility in common organic solvents and is suitable for wet methods such as spin coating to make thin films. All new compounds of the intermediates and the target dendrimer were characterized by 1H NMR, 13C NMR, mass spectrometry, and elemental analysis. In addition, the ultraviolet (UV) absorption and fluorescence (FL) of PDI-F were measured and discussed. To the best of our knowledge, this is the first report of dendrimer PDI-F.

Full text of DOI:10.1080/00397910903013754

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Synthesis and Characterization of Novel
Perylenediimide-Cored Dendrimer with
Fluorinated Shell
Huicai Ren a , Jiuyan Li b , Renjie Wang b , Qian Wang a & Di Liu a
a Department of Chemistry , Dalian University of Technology ,
Dalian, China
b State Key Laboratory of Fine Chemicals, Dalian University of
Technology , Dalian, China
Published online: 04 Feb 2010.
To cite this article: Huicai Ren , Jiuyan Li , Renjie Wang , Qian Wang & Di Liu (2010) Synthesis
and Characterization of Novel Perylenediimide-Cored Dendrimer with Fluorinated Shell, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
40:5, 759-765, DOI: 10.1080/00397910903013754
To link to this article: http://dx.doi.org/10.1080/00397910903013754
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Synthetic Communications1, 40: 759–765, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910903013754
SYNTHESIS AND CHARACTERIZATION OF NOVEL
PERYLENEDIIMIDE-CORED DENDRIMER WITH
FLUORINATED SHELL
Huicai Ren,1 Jiuyan Li,2 Renjie Wang,2 Qian Wang,1 and Di Liu1
1Department of Chemistry, Dalian University of Technology, Dalian, China
2State Key Laboratory of Fine Chemicals, Dalian University of Technology,
Dalian, China
A perylenediimide-based dendrimer, PDI-F, was designed and synthesized for application as
red host emitter in nondoped organic light-emitting diodes. PDI-F was designed with
perylenediimide as the luminescence core and pentafluorophenyl rings as the surface groups.
The dendrimer molecule constructed in this way is bulky and nonplanar. PDI-F exhibits good
solubility in common organic solvents and is suitable for wet methods such as spin coating
to make thin films. All new compounds of the intermediates and the target dendrimer were
characterized by 1H NMR, 13C NMR, mass spectrometry, and elemental analysis. In
addition, the ultraviolet (UV) absorption and fluorescence (FL) of PDI-F were measured
and discussed. To the best of our knowledge, this is the first report of dendrimer PDI-F.
Keywords: Dendrimer; fluorinated shell; perylenediimide
INTRODUCTION
Organic light-emitting diodes (OLEDs) are attracting more and more research
attention because of their practical applications in large-area flat-panel displays and
lighting.[1,2] Currently, the red-light-emitting materials and devices still lag behind
the green and blue components in both efficiency and stability and require further
improvements to match the criteria of full-color displays and white-light lighting.[3]
Recently, developing red host emitters for nondoped light-emitting diodes has
become a prevalent strategy to gain highly efficient red electroluminescence (EL).[4–9]
In this article, we designed and synthesized a novel red-emitting perylenedii-
mide dendrimer, PDI-F, with pentafluorophenyl peripheral groups (shown in
Fig. 1). Perylenediimide was selected as the luminescent core because of its red
fluorescence and high fluorescent quantum yield.[10] To prevent intermolecular
aggregation and concentration quenching, the bulky dendrons were introduced
into all four bay positions of the perylene ring to construct a nonplanar molecule.
Pentafluorophenyl rings were grafted to the dendrimer surface to function as the
electron-transporting moieties.
Received January 20, 2009.
Address correspondence to Di Liu, Department of Chemistry, Dalian University of Technology,
Dalian 116012, China. E-mail: liudi@dlut.edu.cn
759

760
H. REN ET AL.
Figure 1. MALDI-TOF-MS (calcd. for C192H58F80N2O8 as 4038.29).
RESULTS AND DISCUSSION
Design and Synthesis
The dendrimer PDI-F was synthesized through the procedure described in
Scheme 1. To prevent intermolecular aggregation and concentration quenching, the
bulky dendrons were introduced through bisaryl ether structure into all four bay
positions of the perylene ring. The pentafluoropheneyl type dendron was formed by
Diels–Alder cycloaddition of tetrakis(pentafluoropheneyl)cyclopentadienone 6 to the
terminal ethynyl groups on the surface of the perylenediimide-based core 5.
Pentafluorophenyl rings were designed as the surface groups of the dendrimer because
of the strong electron-withdrawing nature and potential electron-transporting function.
The perylenediimide-containing core 5, bearing the light-emitting functional
group, and tetrakis(pentafluorophenyl)cyclopentadienone 6,[11–13] bearing electron-
transporting groups, are two important intermediates and were prepared through
several step reactions as shown in Scheme 1. The chemical structures of all intermedi-
1
ates were confirmed by H NMR and mass spectroscopy. Finally, the cycloaddition
of 5 and 6 in o-xylene at high temperature generated the target dendrimer PDI-F,
which is soluble in normal organic solvents and was purified by flash column chro-
matograph over silica gel with mixed petroleum ether and dichloromethane (3:2) as
eluent. The observation of [M þ H]þ peak at ca. m=z 4039 in matrix-assisted laser
desorption=ionization time-of-light (MALDI-TOF) mass spectra (shown in Fig. 1)
and 1H NMR, 13C NMR, and 19F NMR spectral data along with elementary analy-
sis unambiguously confirmed the chemical structure of the target dendrimer PDI-F.
Optical Properties
The normalized electronic absorption and fluorescence spectra of PDI-F
solution in dichloromethane and film spin coated on quartz substrate are shown
in Fig. 2. PDI-F exhibits absorption bands at 560, 523, and 440 nm in both solution
and film, which are associated with the p–pꢀ transition of the perylenediimide

PERYLENEDIIMIDE-CORED DENDRIMER
761
Scheme 1. Synthesis of dendrimer PDI-F. (a) Br2, H2SO4 (98 wt%); 4-iodophenol, NMP, K2CO3, 80 ꢁC
15 h, 80%; (b) trimethyl-silylethyne, [PdCI2(PPh3)2], CuI, THF=Et3N, rt, overnight, 85%; (c) n-Bu4NF,
THF, rt, overnight, 87%; (d) KI, NaCIO, aq.; (e) bromopentaflurobenzene, Mg, dry ether, reflux,
30 min, CoCI2, ꢂ20 ꢁC, overnight, 45%; (f) Co2(CO)8, o-xylene, rt, overnight; 195 ꢁC, 48 h, 54%; (g) 6,
o-xylene, reflux, 7 days, 81%.
Figure 2. Absorption and fluorescence spectra of PDI-F solutions in dichloromethane and films spin
coated on quartz substrates.

762
H. REN ET AL.
core.[13] The pentafluorophenyl peripheral groups are transparent in the visible-light
region. Upon photoexcitation at 523 nm, PDI-F exhibits red fluorescence in dichlor-
omethane solution with the emission peak at 605 nm and two shoulders at 640 and
700 nm. The fluorescent quantum yield of PDI-F in dilute ethanol was measured as
cal. 0.81 using Rhodamine B in ethanol (U ¼ 0.90) as standard. The fluorescence
spectrum of PDI-F film has features similar to that of solution, but slightly
blue-shifted by 3 nm compared to the solution. Another change is that the emission
intensity of 640- and 700-nm bands increased in film, which is favorable for gener-
ating saturated red emission. The absence of any long-wavelength emission band
excludes the possibility of intermolecular aggregates or excimer formation even in
solid film, which should benefit from the hindrance of intermolecular stacking by
the nonplanar molecular conformation.
EXPERIMENTAL
Materials and Instruments
All the chemicals for the synthesis are of analytical grade and were used as
received without further purification. 1H NMR, 13C NMR, and 19F NMR spectra were
recorded on a Varian Inova spectrometer (400MHz); chemical shifts were referenced
to tetramethylsilane (TMS) and fluorobenzene respectively. Mass spectra (MS) were
recorded on a Micromass Q-Tof (Micromass, Wythenshawe, U.K.) mass spectrometer
for electrospray ionization (ESI)–MS and a Bruker Biflex III mass spectrometer
for MALDI-TOF-MS. Elemental analyses were carried out on a Carlo-Erba 1106
elemental analyzer. Absorption and fluorescence spectra were recorded with a
ultraviolet–visible (UV-vis) spectrophotometer (Perkin-Elmer Lambda 35) and a
fluorospectrophotometer (Perkin-Elmer Luminescence LS50B), respectively.
Synthesis of Compounds
1,6,7,12-Tetrabromoperylene-3,4,9,10-tetracarboxylic acid bisanhydride
(1). A mixture of perylene-3,4,9,10-tetracarboxylic acid bisanhydride (10 g,
25 mmol) and 200 mL of 98 wt% sulfuric acid was stirred at room temperature for
12 h. The mixture was then heated to 85 ꢁC, and 0.31 g I2 (1.2 mmol) was added. Sub-
sequently, 5 mL (15.595 g, 195 mmol) Br2 was added dropwise over 12 h, and the
reaction mixture was heated for 24 h at 85 ꢁC. Then 0.31 g I2 (1.2 mmol) was added,
and the reaction temperature was raised to 110 ꢁC. Five mL (15.595 g, 195 mmol) Br2
were added dropwise over 12 h, and the reaction mixture was heated for an
additional 80 h at 110 ꢁC. After being cooled to room temperature, the excess bro-
mine was removed by saturated solution of NaHSO3. The resultant precipitate
was washed with a large amount of water until the filtrate became neutral. The solid
residue was dried in a vacuum at 120 ꢁC for 8 h to give 18 g (90%) of a red-brown
powder. The crude product was used directly in a later reaction without further
purification because of its insolubility in organic solvents.
N0-(2,6-Diisopropylphenyl)-1,6,7,12-tetrabromoperylene-3,4,9,10-tetra-
carboxylic acid bisimide (2). 2,6-Diisopropylaniline (2.0 g, 11.3 mmol) was added
to a mixture of 2.0 g (2.8 mmol) 1,6,7,12-tetrabromoperylene-3,4,9,10-tetracarboxylic

PERYLENEDIIMIDE-CORED DENDRIMER
763
acid bisanhydride and 40 mL propionic acid under an N2 atmosphere; the reaction
mixture was stirred and heated at 140 ꢁC for 10 h. After being cooled to room
temperature, the solvent was removed by rotary evaporation, and the crude product
was purified by silica-gel column chromatography (eluent: petroleum ether–
dichloromethane ¼ 1:1 v=v) to yield perylene bisimide product as a red-brown solid
1
(2.38 g, 85%). H NMR (CD2Cl2, 400 MHz): 8.95 (s, 4H), 7.56 (t, J ¼ 8.0 Hz, 2H),
7.41 (d, J ¼ 8.0 Hz, 4H), 2.75 (m, 4H), 0.89 (d, J ¼ 5.2 Hz, 24H).
1,6,7,12-Tetrakis(4-iodophenoxy)-N,N0-(2,6-diisopropylphenyl)perylene-3,
4,9,10-tetracarboxdiimide (3). Tetrabromoperylenetetracarboxdiimide (2.0 g,
1.95 mmol) was stirred with p-iodophenol (2.57 g, 11.7 mmol) in 1-methyl-2-pyrrili-
done (NMP) (100 ml) at 80 ꢁC in a 250-ml flask in the presence of powdered anhy-
drous K2CO3 (0.82 g, 5.9 mmol) under an N2 atmosphere overnight. Then the
reaction mixture was cooled to room temperature and poured into hydrochloric acid
(300 ml, 2 N). The precipitated product was filtered under suction, washed three times
with water (100 mL), and dried at 75 ꢁC under vacuum. The crude product was
purified by column chromography (eluent: petroleum ether=dichloromethane ¼ 1:2
1
v=v) to give a red solid (2.47 g, 80%). H NMR (CD2Cl2, 400 MHz): 8.12 (s, 4H),
7.54 (d, J ¼ 8.8 Hz, 8H), 7.38 (t, J ¼ 8.0 Hz, 2H), 7.22 (d, J ¼ 8.0 Hz, 4H), 6.68 (d,
J ¼ 8.8 Hz, 8H), 2.58 (m, 4H), 1.02 (d, J ¼ 8.0 Hz, 24H). Field desorption ionization
mass spectrometry (FD-MS): m=z: 1584.8 (100%) [M]þ (calcd. 1584).
1,6,7,12-Tetrakis[4-(trimethylsilylethynyl)phenoxy-N,N0-(2,6-diisopro-
pylphenyl)perylene-3,4,9,10-tetracarboxdiimide (4). Compound
3
(1.0 g,
0.63 mmol) was dissolved in a degassed mixture of triethylamine (20 mL) and
absolute THF (10 mL) under N2. [PdCl2(PPh3)2] (90 mg, 5 mol%), CuI (60 mg,
0.315 mmol), and PPh3 (89 mg, 0.34 mmol) were then added under a flow of N2.
After the flask was sealed with a septum, trimethylsilylethyne (0.45 ml) was injected.
The reaction mixture was stirred at room temperature overnight and then poured
into an equal volume of dichloromethane and filtered. The solvent was removed,
and the crude product was purified by column chromatography on silica gel (eluent:
1
petroleum ether=dichloromethane ¼ 3:2 v=v) to afford 4 (0.77 g, 85%). H NMR
(CD2Cl2, 400 MHz): 8.12 (s, 4H), 7.39 (t, J ¼ 8.0 Hz, 2H), 7.34 (d, J ¼ 8.0 Hz, 8H),
6.83 (d, J ¼ 8.0 Hz, 8H), 2.60 (m, 4H), 1.01 (d, J ¼ 6.8 Hz, 24H), 0.15 (s, 48H). FD
MS: m=z: 1462.5 (100%) [M]þ (calcd. 1464).
1,6,7,12-Tetrakis(4-ethynylphenoxy)-N,N0-(2,6-diisopropylphenyl)perylene-
3,4,9,10-tetracarboxdiimide (5). Compound 4 (50 mg, 0.034 mmol) and NH4F
(10.1 mg, 0.27 mmol) were dissolved in THF (5 mL) under N2. A solution of n-Bu4-
NF (1.3 mg, 0.005 mmol) in THF was added by injection. The mixture was stirred at
room temperature overnight. Then the solvents were removed in vacuum, and the
crude product was purified by column chromatography on silica gel (eluent: pet-
1
roleum ether=dichloromethane ¼ 1:2 v=v) to give a red solid 5 (35 mg, 87%). H
NMR (CD2Cl2, 250 MHz): 8.15 (s, 4H), 7.38 (d, J ¼ 7.5 Hz, 8 H), 7.25 (t, 2H),
6.87 (d, J ¼ 7.5 Hz, 8H), 3.05 (s, 4H), 2.59 (m, 4H), 1.02 (d, J ¼ 7 Hz, 24H). FD
MS: m=z: 1176 (100%) [M þ H]þ (calcd. 1175.0).
Tetrakis(pentafluorophenyl)cyclopentadienone (6). To a 100-mL round-
bottom flask charged with Co2(CO)8 (1.5 g, 4.5 mmol) and decafluoro-tolane

764
H. REN ET AL.
(1.5 g, 4.4 mmol), o-xylene (25 ml) was injected by syringe under N2 atmosphere.
After rigorously degassing by freeze–pump–thaw, the reaction solution was stirred
at room temperature overnight and then heated to reflux under N2 for 48 h. O-xylene
was removed under vacuum, and the crude product was dissolved into 200 mL
dichloromethane and passed through a 1-cm high neutral Al2O3 pad. Recrystalliza-
tion from dichloromethane gave a red powder (0.87 g, 54%). Mp ¼ 231.5–232 ꢁC. MS
(FD): m=z: 744.8 (Mþ). 19F NMR (CD2Cl2): d ¼ ꢂ136.88 to ꢂ136.91 (d), ꢂ137.09 to
ꢂ137.13 (d), ꢂ147.50 to ꢂ147.59 (t), ꢂ149.68 to ꢂ149.77 (t), ꢂ158.34 to ꢂ158.42
(m), ꢂ160.01 to ꢂ160.08 (m).
Target dendrimer PDI-F. A solution of 108 mg (0.09192 mmol) 5 and 548 mg
(0.7354mmol) 6 in 15ml o-xylene was stirred and refluxed for 7 days under an atmos-
phere of dry nitrogen. After cooling to room temperature, the solvent was evaporated
under reduced pressure. The crude product was purified by flash-column chromato-
graphy over silica gel with mixed petroleum ether and dichloromethane (3:2 v=v) as elu-
1
ent to give 300 mg pure product as red powder. Yield 81%, mp 413ꢁC. H NMR
(CD2Cl2, 250 MHz): 8.17 (s, 4H), 7.78 (s, 4H), 7.44 (t, J ¼ 8.0 Hz, 2H), 7.26–7.23 (d,
13
J ¼ 7.5 Hz, 4H), 7.05 (d, J ¼ 8.5 Hz, 8H), 6.77 (d, J ¼ 8.5 Hz, 8H), 2.66 (m, 4H), 1.03
ꢁ
=
(d, J ¼ 7.5 Hz, 24H). C NMR (600MHz, CD2Cl2, 25 C): d ¼ 163.4 (C O), 156.6,
155.8, 146.3, 145.6, 143.2, 141.0, 139.0, 136.3, 135.4, 134.8 134.2, 132.7, 131.2, 130.8,
130.0, 129.2 (d), 127.1, 124.5, 124.0, 122.0, 121.7, 120.2, 113.1, 111.5, 29.6 (CH, isopro-
pyl), 24.1 (CH3, isopropyl). 19F NMR (CD2Cl2, 500 MHz): d ¼ ꢂ136.932 to ꢂ138.826
(m), ꢂ148.818 to ꢂ149.007 (d), ꢂ149.628 (s), ꢂ150.527 (s), ꢂ158.745 to ꢂ159.332 (m).
MS (MALDI-TOF): m=z: 4039 [M þ H]þ(calcd. 4038). Elemental analysis calcd. (%)
for C192H58F80N2O8: C, 57.07; H, 1.45; N, 0.69. Found: C, 57.01; H, 1.38; N, 0.73.
CONCLUSIONS
In conclusion, we synthesized and characterized a novel perylenediimide-cored
first generation dendrimer PDI-F, which is a promising candidate for application in
organic light-emitting diodes, especially for nondoped red-light-emitting diodes.
Sixteen pentafluorophenyl rings were grafted as the shell of the bulky nonplanar
molecule. Modification to the chemical structure of dendrimers for high fluorescent
quantum yield and more saturated red fluorescence is in progress in our laboratory.
ACKNOWLEDGMENTS
We gratefully acknowledge the National Natural Science Foundation of China
(Project Nos. 20704002, 20602004, and U0634003), the Program for Changjiang
Scholars and Innovation Research Team in University (IRT0711), and the NKBRSF
(2009CB220009) for financial support of this work.
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