Dendronized Perylenetetracarboxdiimides with Peripheral Triphenylamines for Intramolecular Energy and Electron Transfer

Article abstract of DOI:10.1002/chem.200304994

Novel perylene-3,4,9,10-tetracarboxdiimides (PDI) dyes functionalized with polyphenylene dendrimers attached at the bay region are reported. Derivatives of PDI bearing polyphenylene dendrimers up to the second generation, substituted with an increasing number of triphenylamine (TPA) moieties at the periphery, as well as a related nondendronized model compound were prepared. Intramolecular energy transfer was demonstrated by the observation of PDI emission on excitation of the triphenylamines, and electron transfer was detected by comparing photoluminescence quenching in solvents of different polarity.

Full text of DOI:10.1002/chem.200304994

FULL PAPER
Dendronized Perylenetetracarboxdiimides with Peripheral Triphenylamines
for Intramolecular Energy and Electron Transfer
Jianqiang Qu,[a] Neil G. Pschirer,[a] Daojun Liu,[b] Alina Stefan,[b]
Frans C. De Schryver,[b] and Klaus M¸llen*[a]
Abstract: Novel perylene-3,4,9,10-tet-
racarboxdiimides (PDI) dyes function-
alized with polyphenylene dendrimers
attached at the bay region are report-
ed. Derivatives of PDI bearing poly-
phenylene dendrimers up to the second
generation, substituted with an increas-
ing number of triphenylamine (TPA)
moieties at the periphery, as well as a
related nondendronized model com-
pound were prepared. Intramolecular
energy transfer was demonstrated by
the observation of PDI emission on ex-
citation of the triphenylamines, and
electron transfer was detected by com-
paring photoluminescence quenching
in solvents of different polarity.
Keywords: cycloaddition
dendrimers electron transfer
energy transfer ¥ perylenes
¥
¥
¥
Introduction
In recent years, there has been growing interest in under-
standing the photophysical and photochemical properties of
multicomponent dyads containing covalently linked electron
donors and acceptors, especially as an approach to artificial
photosynthesis.[1] Incorporation of rigid spacing units into
donor-linked acceptor molecular assemblies allows control
of the distance and angles between the donor and acceptor
sites, which govern the rate and efficiency of long-distance
photoinduced electron-transfer and charge-recombination
processes, which play important roles in potential applica-
tions such as photovoltaic and optoelectronic devices.[2]
Chromophores based on perylene-3,4,9,10-tetracarboxdi-
imides (PDI, 1) and derivatives thereof bearing substituents
in the 1,12- and 6,7-positions (the so-called bay regions) are
widely used as dyes and pigments in a variety of applications
due to their outstanding chemical, thermal, and photochemi-
cal stability,[3] for example, in paints, lacquers, reprographic
processes,[4] fluorescent solar collectors,[5] optical switches,[6]
and dye lasers.[7] The high electron mobilility[8] of PDI deriv-
atives was exploited by Friend, M¸llen et al.[9] in the fabrica-
tion of high-efficiency organic photovoltaic devices by using
a blend of electron-accepting PDI and a hole-accepting hex-
abenzocoronene. Gregg et al.[10] also reported solar cells
based on a polymer/PDI blend.
To investigate whether the large difference in forward and
backward electron-transfer rates in electron-donor/acceptor
composites is a molecular or materials property, we explored
photoinduced electron and energy transfer in molecular
dyads of electron donors covalently linked to PDI (accept-
or) through a rigid spacer. Redox-active triphenylamino
(TPA) groups, which are widely used as hole-transport (HT)
and electron-donor materials, were introduced into the bay
region of PDI. Since photoluminescence (PL) self-quench-
ing caused by aggregation,[11] can influence the investigation
of electron transfer from donor to acceptor, it would be ben-
eficial to encapsulate PDI within a ™protective∫ organic
matrix, effectively isolating the dye and preventing self-
quenching. Recently, we reported PDI derivatives bearing
highly soluble, three-dimensional, shape-persistent, thermal-
ly stable (>4508C), and photochemically stable polyphenyl-
ene dendrimers (PPD)[12] on the imide ring, which showed
no aggregation in solution and high photoluminescence effi-
ciency.[13] A polyphenylene dendrimer was therefore selected
[a] J. Qu, Dr. N. G. Pschirer, Prof. Dr. K. M¸llen
Max-Planck-Institute for Polymer Research
Ackermannweg 10
5128 Mainz (Germany)
Fax : (+49)6131-379100
E-mail: muellen@mpip-mainz.mpg.de
[b] D. Liu, Dr. A. Stefan, Prof. Dr. F. C. De Schryver
Laboratory for Photochemistry and Spectroscopy
Department of Chemistry, Katholieke Universiteit Leuven
(KULeuven) Celestijnenlaan 200F, 3001 Heverlee, (Belgium)
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DOI: 10.1002/chem.200304994
Chem. Eur. J. 2004, 10, 528 537

528 537
as spacer and rigid shell, with
the hole-transporting TPA moi-
eties located on the periphery
of the dendrimers. By using dif-
ferent solvents, it is possible to
address the effect of the polari-
ty of the medium on photoin-
duced charge separation and re-
combination.
Here we describe the synthe-
sis and characterization of tet-
rakis(4-ethynylphenoxy)peryle-
netetracarboxdiimide (5) as
core, and tetrakis[4-(diphenyl-
amino)phenoxy]perylenetetra-
carboxdiimide (12) as a non-
dendronized model compound.
Starting from this luminescent
core, first- and second-genera-
tion dendronized TPA-substi-
tuted PDI were prepared. We
report on their photophysical
properties in different solvents,
and we demonstrate that both
energy- and electron-transfer
reactions occur upon photoexci-
tation of TPA-PPD-PDI by
comparing the emission spectra
at different excitation wave-
lengths and photoluminescence
quantum yields in different
polar solvents. The degree of
discrimination between the
energy- and electron-transfer
processes strongly depends on
the polarity of the medium, and
Scheme 1. Synthesis of the core molecule 5: a) 4-Iodophenol, NMP, K2CO3, 808C, 15 h, 85%; b) trimethylsilyl-
ethyne, [PdCl2(PPh3)2], CuI, THF/Et3N, RT, 15 h, 91 %; c) nBu4NF, THF, RT, 30 min, 85%.
we demonstrate complete energy transfer in nonpolar sol-
vents.
raphy, and the desired product 4 is obtained in 91% yield as
a red solid. The tetraethynyl-substituted luminescent core
molecule 5 was obtained after cleavage of the trimethylsilyl
(TMS) groups with Bu4NF in distilled THF. The high solu-
bilities of 3, 4, and 5 in common organic solvents such as di-
chloromethane allows easy purification by column chroma-
tography and full characterization by standard spectroscopic
measurements.
Results and Discussion
Synthesis of tetrakis(4-ethynyl-p-phenoxy)perylenetetracar-
boxdiimide (5) as the core molecule: The synthesis of the lu-
minescent core 5 is shown in Scheme 1. It starts from tetra-
chloroperylenetetracarboxdiimide 2, which is readily availa-
ble on a gram scale.[14] Phenoxylation of 1 with an excess of
iodophenol in 1-methyl-2-pyrrolidone (NMP) gives tetra-
phenoxyperylenetetracarboxdiimide 3 with four iodo groups.
The iodo group was chosen as it is optimal for attachment
of an alkynyl group in the next step. The temperature of
phenoxylation, however, is important, as deiodonation
occurs if the reaction temperature is higher than 1008C; in
contrast, the yield decreases below 608C. The four iodo sub-
stituents were replaced by triisopropylsilylethynyl groups by
fourfold Hagihara Sonogashira coupling in high yield.[15]
The reaction was carried out in THF/NEt3 (3/1) at room
temperature with a [PdPdCl2(PPh3)2]/CuI catalyst system.
Base and catalyst are easily removed by column chromatog-
Synthesis of nondendronized model compound 12 and den-
drimers 7 and 8: The synthesis of model compound 1,6,7,12-
tetrakis[4-(diphenylamino)phenoxy]-N,N’-(2,6-diisopropyl-
phenyl)-perylene-3,4,9,10-tetracarboxdiimide (12) is shown
in Scheme 2. The four iodo substituents of 3 are easily re-
placed by diphenylamino groups in a fourfold Hartwig
Buchwald amination due to their high reactivity.[16] Quanti-
tative conversion was obtained when the reaction was car-
ried out in a glove box. The yield is significantly lower and a
deiodinated byproduct is formed if the reaction is performed
outside of the glove box due to the high reactivity of tri-tert-
butylphosphane.
The most important step of the dendrimer synthesis is the
Diels Alder cycloaddition, in which after extrusion of
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K. M¸llen et al.
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drimer 6a with eight TiPS-protected ethynyl groups. After
facile deprotection of 6a with Bu4NF, compound 6b was ob-
tained, which is easily purified by washing with methanol.
First-generation ethynyl-bearing dendrimer 6b was then
treated with 12 equivalents of 11 to give second-generation
dendritic chromophore
8 containing 16 triphenylamino
groups in a yield of 79% after column chromatography.
The functionalized dendritic structures 7 and 8, as well as
TiPS-protected first-generation dendrimer 6a and octa-
ethynyl-substituted unprotected first-generation dendrimer
6b, are all highly soluble in common solvents such as di-
chloromethane, toluene, and THF. Characterization by
Scheme 2. Synthesis of model compond 12: [Pd2(dba)3], tBu3P, tBuONa,
toluene, RT, 1 h, 98%.
1
MALDI-TOF mass spectrometry, elemental anaylsis, and H
and 13C NMR spectroscopy is therefore easily accomplished.
Experimentally determined and calculated m/z ratios agree
perfectly for 6a, 6b, 7, and 8 within the range of accuracy of
the instrument. The signals obtained for these macromole-
cules not only show the [M]+ peaks but also confirm their
monodispersity (see Experimental Section). Moreover,
MALDI-TOF MS measurements allow the detection of po-
tential growth imperfections resulting from ethynyl groups
that did not react during the Diels Alder reaction with
building blocks 9 and 11. Therefore, MALDI-TOF MS was
used both for the characterization of the monodisperse den-
dritic macromolecules described herein as well as for moni-
toring dendrimer growth, especially for the synthesis of
second-generation dendrimer 8, which requires a longer re-
action time. As an example, the MALDI-TOF spectrum of 8
(Figure 1) clearly demonstrates the monodispersity of this
compound.
carbon monoxide a new benzene ring is formed and penta-
phenylbenzene repeat units are obtained. The Diels Alder
cycloaddition requires an aromatic ethyne and a cyclopenta-
dienone derivative. The synthesis of 3,4-bis[4-(diphenylami-
no)phenyl]-2,5-diphenylcyclopenta-2,4-dienone (11) as func-
tional cyclopentadienone derivative is shown in Scheme 3. It
Characterization of dendrimers 7, 8 and their precursors
by 1H NMR spectroscopy was performed in tetrachloro-
ethane or dichloromethane due to their good solubility in
these solvents. Well-separated and assignable signals of non-
dendronized intermediates and the model compound 12
were obtained. The TiPS groups of 6a and the ethynyl pro-
tons of 6b are clearly assignable. Dendrimers 7 and 8 also
show well-separated signals (Figure 2) for the aromatic pery-
lene protons and for the aliphatic protons of the CH and
(CH3)2 groups on the imide structure. Most of the protons
of triphenylamino groups and dendrons are located together
between 6.4 and 7.2 ppm, but in the first generation, a single
peak for the dendron can be distinguished, which corre-
sponds to the only proton on the central benzene ring of the
pentaphenylbenzene unit (Figure 2). In addition, the intensi-
ty ratios between all separated peaks and the absorptions of
the aromatic region agree perfectly with the theoretically
expected values. All dendrimers should exhibit a high
degree of symmetry, but 13C NMR resonances of the poly-
phenylene dendrons could not be assigned completely be-
cause of the many overlapping signals, and some of the reso-
nances of the core carbon atoms are too weak to be detect-
ed for the second-generation dendrimer.
Scheme 3. Synthesis of building block 11: [Pd2(dba)3], tBu3P, tBuONa,
toluene, RT, 1 h, 91%.
starts from dibromocyclopentadienone 10, prepared by basic
condensation.[12a] Cyclopentadienone derivative 11 was then
obtained in high yield by Buchwald coupling, as described
above for 12. 3,4-Bis[4-(triisopropylsilylethynyl)phenyl]-2,5-
diphenylcyclopenta-2,4-dienone (9) contains two dienophile
functions and can be regarded as an A2B branching reagent,
as the sterically demanding triisopropylsilyl (TiPS) groups
protect the two ethynyl groups. After completion of the
Diels Alder reaction with 9, the protecting groups can be
removed with Bu4NF to afford a first-generation dendrimer
with eight ethynyl groups as precursor for the second-gener-
ation dendrimer. In contrast, if the cyclopentadienone with
TPA functional groups 11 is used, triphenylamines can be at-
tached to the dendrimer at the periphery.
The syntheses of dendrimers 7 and 8 are shown in
Scheme 4. The first-generation dendrimer was formed by
Diels Alder reaction of core molecule 5 with a sixfold
excess of cyclopentadienone 11 in m-xylene at 1408C. Using
m-xylene as solvent has the advantage that the product is
easily isolated by precipitation with methanol. After filtra-
tion, the mixture of product 7 and excess 11 was obtained as
a dark red powder. Compound 7 was isolated by column
chromatography. To build up the second-generation den-
drimer, A2B building block 9 was employed. Diels Alder re-
action of core 5 with 9 afforded the first-generation den-
Visualization and simulation: The structure of the perylene
core was optimized by using the semiempirical PM3
method, and the dendrons decorated with TPAs from the
first and second generation were minimized separately by
using MM2 (MM+) force-field geometry optimization as
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Dendronized Perylenetetracarboxdiimides
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Scheme 4. Synthesis of first-generation dendrimer 7 and second-generation dendrimer 8: a) 6 equiv 11, m-xylene, 1408C, 15 h, 84%; b) i) 6 equiv 9,
m-xylene, 1408C, 15 h, 89%; ii) 16 equiv nBu4NF, THF, RT, 30 min, 80%; c) 12 equiv 11, m-xylene, 1508C, 48 h, 79%.
Figure 1. MALDI-TOF mass spectrum of second-generation dendrimer 8 (m/z: 8311 [M]+, dithranol matrix).
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shells with TPAs at the periph-
ery. The size of the compounds
increases with increasing den-
drimer generation; the diame-
ter is 3.7 nm for the first gener-
ation, and 5.3nm for the
second. Clearly, the perylene
core is shielded by the den-
drons, so that self-aggregation
of perylene units is prohibited.
The TPAs at the periphery
have various torsional angles
relative to PDI. In this case, the
simulation of the series of com-
pounds 12, 7,and 8 is a good ap-
proximation of the three-di-
mensional structures.
Steady-state spectroscopy: Den-
drimers 7 and 8 are soluble in
various solvents such as methyl-
cyclohexane, toluene, and THF.
Their absorption spectra in
Figure 2. 1H NMR spectrum of the first-generation dendrimer 7 at 300 K (500 MHz, CD2Cl4).
methylcyclohexane,
together
implemented in HyperChem 6.0
(Hypercube Inc.). Furthermore,
the whole dendritic system was
optimized by combining four
first- and second-generation
dendrons with the perylene
core and minimizing the whole
system. The nondendronized
model compound 12 was ob-
tained similarly by connecting
four TPAs with the minimized
perylene core and subsequent
geometry optimization of the
entire molecule. As shown in
Figure 3, the two naphthalene
rings of 12, 7, and 8 are strongly
twisted at the bay positions
with a torsional angle of around
288 between the two naphtha-
lene units, which is in good
agreement with the calculated
structure[13] and crystal struc-
ture of a similar molecule.[17] In
the simulated structure of
model compound 12, the phen-
oxy groups are nearly perpen-
dicular to the perylene ring.
The same considerations of tor-
sion angles hold for the den-
drimers
(not
shown
in
Figure 3). Molecular modeling
shows that dendrimers 7 and 8
are three-dimensional struc-
tures, and the chromophores
Figure 3. Visualization of nondendronized model compound 12 (top), first-generation dendrimer 7 (bottom
are surrounded by dendritic left), and second-generation dendrimer 8 (bottom right).
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Dendronized Perylenetetracarboxdiimides
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with those of dendrimers 7* and 8* (Figure 4)[18] with the
same PDI core but without the peripheral TPA groups as
model compounds for investigating optical properties of
additional peak between 400 and 460 nm corresponds to the
S0 S2 transition, for which the transition dipole moment is
along the short axis. The absorption between 300 and
380 nm is mainly due to the polyphenylene dendrons and
the TPA groups.[19] The difference in absorption in this
region between 7, 8 and 7*, 8* is due to the presence of
TPA. Figure 5 shows that the contribution of TPA to the ab-
sorption almost doubles with increasing generations, and
this reflects the corresponding change in the number of TPA
moieties at the dendrimer periphery.
The absorption and normalized emission spectra of den-
drimers 7 and 8 when excited at the PDI core, measured in
solvents of different polarity such as methylcyclohexane
(MCH, e=2.02[20]), toluene (TOL, e=2.38), and tetrahydro-
furan (THF, e=7.58), are shown in Figure 6. Both dendrim-
ers display similar absorption and emission bands, independ-
ent of the dendrimer generation or the solvent. However,
the absorption and normalized emission spectra exhibit
slight bathochromic shifts in polar solvents. The excitation
spectra are identical to the absorption spectra (not shown in
the figure).
The fluorescence quantum yields of dendrimers 7 and 8
(excited at 540 nm) and model compounds 7* and 8* were
Figure 4. Model compounds without the functional group: first-genera-
tion dendrimer 7* and second-generation dendrimer 8*.
dendrimers 7 and 8, are shown in Figure 5. The absorption
spectra of dendrimers 7 and 8 exhibit three absorption re-
gions. Between 480 and 600 nm the absorption reflects the
S0 S1 electronic transition of PDI along the long axis. An
Figure 5. Absorption spectra of the first-generation dendrimer 7 (g),
the second-generation dendrimer 8 (d), and their model compounds
7* (c) and 8* (b) in methylcyclohexane. The spectra are normalized
at the PDI absorption maximum.
Figure 6. Normalized absorption and emission spectra (excitation at
530 nm) of the first-generation dendrimer 7 (A) and the second-genera-
tion dendrimer 8 (B) in methylcyclohexane (c), toluene (b) and
THF (g).
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Table 1. Photoluminescence quantum yield (FPL) in polar and nonpolar
solvents at room temperature (reference chromophore: Cresyl Violet, ex-
citation at 540 nm)
Solvent
7
8
7*
8*
methylcyclohexane
toluene
THF
0.77
0.14
0.001
0.830.96
0.55
0.02
0.93
0.92
0.77
0.91
0.76
measured in different solvents with cresyl violet as reference
and are listed in Table 1.[21] The presence of TPA at the pe-
riphery of dendronized perylenetetracarboxdiimides dramat-
ically quenches the fluorescence of the PDI core in polar
solvents such as THF. The fluorescence quenching can be
explained by efficient intramolecular electron transfer in-
duced by excitation of the electron acceptor PDI. To obtain
experimental proof of this phenomenon, femtosecond transi-
ent absorption spectroscopy is presently being performed on
these systems, and preliminary results indicate the presence
of a broad absorption band above 700 nm that belongs to
the anion of perylenetetracarboxdiimide. A full account of
these results will be published elsewhere. In nonpolar sol-
vents such as methylcyclohexane, only a slight decrease in
quantum yield (540 nm excitation wavelength) was observed
for dendrimer 8 relative to model compound 8*, and this in-
dicates an absence or very low efficiency of intramolecular
electron transfer. Earlier reports on intramolecular electron
transfer in donor spacer acceptor dyads also demonstrated
the dependence of the rate of electron transfer on the die-
lectric constant of the solvent.[22] The intramolecular elec-
tron transfer efficiency is also dependent on the dendrimer
generation (or the average distance between the electron
donor and acceptor), as can be clearly seen in Table 1. Par-
ticularly in the case of toluene, an appreciable difference
was observed for the quantum yields of dendrimers 7 and 8,
while 7* and 8* have the same quantum yield. For the first-
generation dendrimer 7, in which the distance between the
electron donor and the electron acceptor is shorter, more ef-
ficient intramolecular electron transfer was observed, even
in methylcyclohexane.
Figure 7. Fluorescence emission spectra of the first-generation dendrimer
7 (A) and the second-generation dendrimer 8 (B) in methylcyclohexane
(c), toluene (a) and THF (g). The spectra are normalized to the
same absorbance at the excitation wavelength 360 nm. The emission
spectra (d) of dendrimers 7 and
8 in methylcyclohexane excited
around the PDI absorption maximum at the same absorbance are also
shown.
To investigate the possibility that energy transfer com-
petes with electron transfer in these systems, 7 and 8 were
also excited in the same solvents at 360 nm. The excitation
wavelength of 360 nm was chosen on the basis of the ab-
sorption spectra in Figure 5, so that TPA can be selectively
excited. The fluorescence emission spectra of dendrimers 7
and 8 in different solvents, normalized to the same optical
density at 360 nm, are shown in Figure 7. Interestingly, the
excitation of TPA in both 7 and 8 gives rise to a strong emis-
sion from the PDI core and no TPA emission in nonpolar
methylcyclohexane. Compared to the emission intensity of 7
and 8 excited at 567 nm in methylcyclohexane (direct exci-
tion of the PDI core), a decrease to 65% was observed
when they are excited at 360 nm for identical optical density
(Figure 7). The values of the quantum yield also decrease in
the same ratio when 7 and 8 are excited at the same wave-
length (Table 2).
Table 2. Fluorescence quantum yield at room temperature (reference
compounds: perylene for 7 and 8, excitation 360 nm; quinine sulfite for
TPA, excitation 290 nm).
Solvent
7
8
TPA
methylcyclohexane
toluene
0.46
0.06
0.54
0.22
0.13
0.105
nent of 42 ps. This component does not appear in the analy-
sis of the decay histograms obtained by excitation at 543nm
(direct excitation of PDI chromophore) of the same com-
pound in the same solvent. All of these data point to a very
efficient energy transfer process followed by electron trans-
fer in methylcyclohexane. The higher rate of electron trans-
fer for 7 and 8 in methylcyclohexane with excitation at
360 nm can be understood by the more exothermic process
at this excitation wavelength. The negligible fluorescence
emission from the PDI core observed in THF solution from
Time-resolved measurements on 8 excited at 360 nm in
methylcyclohexane indicate the presence of a rise compo-
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Dendronized Perylenetetracarboxdiimides
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(300 mL) at 808C in a 500 mL flask in the presence of powdered anhy-
drous K2CO3 (2.5 g, 18 mmol) under argon. The temperature was kept at
808C overnight. The reaction mixture was cooled to room temperature
and poured into hydrochloric acid (800 mL, 2n). The precipitated prod-
uct was filtered under suction, washed three times with water (100 mL),
and dried at 758C under vacuum. The crude product was purified by
column chromography (eluent: CH2Cl2, Rf =0.95) to give red solid 3
(7.9 g, 85%). M.p. 381.48C; 1H NMR (250 MHz, C2D2Cl4, 300 K): d=
8.12 (s, 4H), 7.54 (d, J=8.7 Hz, 8H), 7.36 (t, J=8.0 Hz, 2H), 7.20 (d, J=
8.0 Hz, 4H), 6.68 (d, J=8.8 Hz, 8H), 2.59 (m, 4H), 1.04 ppm (d, J=
6.7 Hz, 24H); 13C NMR (60 MHz, C2D2Cl4, 300 K): d=164.5 (C=O),
156.5, 156.3, 146.6, 140.3, 134.3, 131.4, 130.6, 125.2, 124.2, 123.1, 121.9,
121.8, 121.6, 89.5 (CI), 30.2 (CH isopropyl), 25.4 ppm (CH3 isopropyl);
IR (KBr): n˜ =2960, 2867, 2361, 2336, 1706, 1671, 1592, 1508, 1478, 1408,
1339, 1310, 1281, 1201, 1006, 873, 673, 526 cmÀ1; UV/Vis (chloroform):
lmax (e)=573 (51824), 536 (32471), 455 nm (19630mÀ1 cmÀ1); photolumi-
nescence spectrum (chloroform): lmax =610 nm; FD MS (8 kV): m/z:
1581.7 (100%) [M]+ (calcd 1582.3); elemental analysis (%) calcd for
C72H54I4N2O8: C 54.63, H 3.44, N 1.77; found: C 54.25, H 3.71, N 1.63.
both 7 and 8 indicates the dominance of electron transfer.
Excitation at 360 nm of 7 and 8 in toluene results in exten-
sive quenching of electron transfer in 7 and enhanced elec-
tron transfer in 8, which is also proved by the lower quan-
tum yield compared with the values obtained on excitation
at 540 nm (Tables 1 and ). Since we have multiple donors
and only one acceptor, and different distances between the
donors and the acceptor, detailed quantitative analysis at
the ensemble level of this system is not feasible. At the
single-molecule level, however, compound 8 could be ana-
lyzed in a polystyrene matrix and showed, for a fraction of
molecules, forward and backward electron transfer.[23]
Conclusion
1,6,7,12-Tetrakis[4-(trimethylsilylethynyl)phenoxy-N,N’-(2,6-diisopropyl-
We have presented the synthesis of polyphenylene dendron-
ized perylenetetracarboxdiimides bearing peripheral triphe-
nylamino groups. Due to the shape-persistent properties of
polyphenylene dendrons, the distance between the PDI core
and TPA is well defined. Intramolecular electron and
energy transfer in these donor spacer acceptor systems was
confirmed by steady-state spectroscopy by exciting the ac-
ceptor and the donor in solvents with various polarities.
While intramolecular energy transfer dominates in nonpolar
solvents, intramolecular electron transfer suppresses energy
transfer efficiently and becomes the dominant process in
polar solvents. Furthermore, intramolecular electron transfer
becomes more significant with decreasing dendrimer genera-
tion, that is, with shorter distance between TPA donor and
PDI acceptor.
phenyl)perylene-3,4,9,10-tetracarboxdiimide (4): Compound
3 (5.0 g,
3.1 mmol) was dissolved in a degassed mixture of triethylamine (50 mL)
and absolute THF (150 mL) under argon. [PdCl2(PPh3)2] (180 mg, 2
mol%), CuI (240 mg, 10 mol%), and PPh3 were then added under a flow
of argon. After the flask was sealed with a septum, trimethylsilylethyne
(1.80 g, 18.6 mmol) was injected. The reaction mixture was stirred at
room temperature overnight, and then poured into an equal volume of
dichloromethane and filtered. Hydrochloric acid (6m) was carefully
added to the filtrate until the aqueous phase became slightly acidic
(pH<5). Then the organic phase was removed, washed twice with distil-
led water, extracted with a saturated solution of ammonium chloride,
washed again several times with distilled water, and dried over magnesi-
um sulfate. The solvent was removed under reduced pressure, and the
crude product purified by column chromatography on silica gel to afford
4 (4.2 g, 91%). M.p. >4008C; 1H NMR (250 MHz, C2D2Cl4, 300 K): d=
8.06 (s, 4H), 7.38 (m, 10H), 7.20 (t, J=8.0 Hz, 2H), 6.85 (d, J=8.5 Hz,
8H), 2.58 (m, 4H), 1.04 (d, J=6.7 Hz, 24H), 0.16 ppm (s, 48H);
13C NMR (60 MHz, C2D2Cl4, 300 K): d=163.4 (C=O), 156.0, 155.7, 146.3,
134.1, 133.3, 131.2, 129.9, 124.4, 123.6, 121.4, 121.3, 121.2, 120.0, 119.9,
104.3, 94.7, 29.5, 24.1, 0.0 ppm (CH3Si); IR (KBr): n˜ =2960, 2361, 2159,
1708, 1674, 1591, 1498, 1405, 1339, 1280, 1205, 864, 759, 546 cmÀ1; UV/Vis
Experimental Section
(chloroform):
lmax
(e)=574
(45278),
536
(28290),
458 nm
(18907mÀ1 cmÀ1); photoluminescence spectrum (chloroform): lmax
=
608 nm (excitation 540 nm); FD MS (8 kV): m/z: 1462.5 (100%) [M]+
(calcd 1464.0); elemental analysis (%) calcd for C92H90N2O8Si4: 75.47, H
6.20, N 1.91; found: C 75.08, H 6.36, N 1.84.
Materials: THF (Fluka) was distilled over sodium/benzophenone. Bu4NF
(Fluka), [PdPdCl2(PPh3)2] (Strem), trimethylsilylethyne (Aldrich), cop-
per(i) iodide, p-iodophenol (Avocado), m-xylene (Aldrich), sodium tert-
butyloxide (Aldrich), tBu3P (Aldrich), [Pd2(dba)3] (Aldrich, dba=diben-
zylideneacetone) were used as obtained from commercial sources.
Column chromatography was performed with dichloromethane (chroma-
solv, Riedel) or toluene on silica gel (Geduran Si60, Merck). All yields
are for isolated compounds.
1,6,7,12-Tetrakis(4-ethynylphenoxy)-N,N’-(2,6-diisopropylphenyl)pery-
lene-3,4,9,10-tetracarboxdiimide (5): Compound 4 (1.0 g, 0.68 mmol) was
dissolved in THF (50 mL) under argon. A solution of nBuNF (1.7 g,
5.4 mmol) in THF was added by injection. The mixture was stirred for
30 min at room temperature. The solution was diluted with dichlorome-
thane (200 mL) and then extracted with hydrochloric acid (100 mL, 6m).
The organic phase was removed, washed with distilled water (100 mL),
and dried over magnesium sulfate. The solvents were removed in
vacuum, and the crude product was purified by column chromatography
on silica gel (eluent: CH2Cl2, Rf =0.90) to give red solid 5 (677 mg,
1
Physical and analytical methods: H and 13C NMR spectra were recorded
on Bruker AMX 250 and AC 300 spectrometers by using the residual
proton signals of the solvent or the carbon signal of the deuterated sol-
vent as the internal standard. Chemical shifts are reported in parts per
million. IR spectra were obtained on a Nicolet FT-IR 320. For 13C j-
modulated spin-echo NMR measurements, the abbreviations q and t rep-
resent quaternary C atoms and CH2, and CH3 and CH groups, respective-
ly. FD mass spectra were performed with a VG-Instruments ZAB 2-SE-
FDP. MALDI-TOF mass spectra were measured with a Bruker Reflex II
with THF and dithranol as matrix (molar ratio dithranol/sample 250/1).
The mass peaks with the lowest isotopic mass are reported. UV/Vis ab-
sorption spectra were recorded on a Perkin Elmer Lambda 9 spectropho-
tometer, and photoluminescence spectra on a SPEX Fluorolog 2 spec-
trometer. The correction for the wavelength-dependent intensity of the
excitation source was performed by using the rhodamine quantum coun-
ter. The elemental analyses were carried out by the Microanalytical Lab-
oratory of the Universit‰t Mainz (Germany).
1
85%). M.p. >4008C; H NMR (300 MHz, THF, 300 K): d=8.24 (s, 4H),
7.45 (d, J=8.8 Hz, 8H), 7.38 (t, J=8.0 Hz, 2H), 7.26 (d, J=8.8 Hz, 8H),
3.54 (s, 4H), 2.73 (m, 4H; CH isopropyl), 1.09 ppm (d, 24H, J=6.8 Hz;
CH3 isopropyl); 13C NMR (75 MHz, THF, 300 K): d=163.8 (C=O), 157.3,
156.6, 147.1, 135.2, 134.4, 132.3, 130.4, 125.1, 124.8, 122.3, 122.1, 122.0,
120.8, 120.3, 83.8 (C ethynyl), 79.3 (CH ethynyl), 30.4 (CH isopropyl),
24.7 ppm (CH3 isopropyl); IR (KBr): n˜ =3296, 3073, 2963, 2923, 2871,
2361, 2336, 1708, 1672, 1591, 1497, 1407, 1338, 1308, 1281, 1205, 876, 671,
554 cmÀ1
; UV/Vis (chloroform): lmax (e)=573 (51358), 536 (32653),
455 nm (20179mÀ1 cmÀ1); photoluminescence spectrum (chloroform):
lmax =600 nm (excitation 540 nm); FD MS (8 kV): m/z: 1175 (100%)
[M]+ (calcd 1175.0); elemental analysis (%) calcd for C80H58N2O8, 81.75,
H 4.97, N 2.38; found: C 80.80, H 4.89, N 2.19.
1,6,7,12-Tetrakis(4-iodophenoxy)-N,N’-(2,6-diisopropylphenyl)perylene-
3,4,9,10-tetracarboxdiimide (3): Tetrachloroperylenetetracarboxdiimide 2
(5.0 g, 5.9 mmol) was stirred with p-iodophenol (8.0 g, 36 mmol) in NMP
First-generation dendrimer bearing 8 triisopropylsilylethynyl groups (6a):
A mixture of 5 (200 mg, 0.17 mmol) and 9 (720 mg, 1.0 mmol) in m-
535
Chem. Eur. J. 2004, 10, 528 537
www.chemeurj.org
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

K. M¸llen et al.
FULL PAPER
xylene (5 mL) was stirred at 1408C for 15 h under argon. The cooled re-
action mixture was added to 100 mL of methanol. The precipitated prod-
uct was filtered under suction and reprecipitated several times in metha-
nol until the red color of 9 disappeared. Finally, the product was dried
under vacuum and purified by column chromatography on silica gel
(eluent: CH2Cl2 Rf =0.95) to give red solid 6a (610 mg, 89%). M.p. >
4008C; 1H NMR (250 MHz, CD2Cl2, 300 K): d=8.11 (s, 4H), 7.49 (s,
4H), 7.35 (t, J=7.9 Hz, 2H), 7.22 (d, J=8.4 Hz, 4H), 7.8 6.65 (m,
116H), 2.63(m, 4H), 1.18 (s, J=6.7 Hz, 24H; TiPS CH isopropyl),
1.00 ppm (m, 168H); 13C NMR (75 MHz, C2C2Cl4, 300 K): d=163.4 (q,
C=O), 156.1 (q), 154.0 (q), 145.7 (q), 141.5 (q), 141.0 (q), 140.8(q), 140.6
(q), 140.3 (q), 140.2 (q), 139.7 (q), 139.2 (q), 138.6 (q), 138.1 (q), 133.1
(q), 132.8(t), 131.5 (t), 131.2 (t), 130.9 (t), 130.2 (t), 129.8 (t), 129.5 (t),
128.8 (t), 128.5 (t), 128.1 (t), 127.4 (t), 126.6 (t), 126.4 (t), 122.9 (q), 120.9
(q), 120.8 (q), 120.5 (q), 119.5 (t), 107.5 (q), 90.5 (q), 29.3(t; CH isopro-
pyl), 24.5 (p; CH3 isopropyl), 18.9 (p; SiCH3 isopropyl), 11.6 ppm (t; Si-
CH isopropyl); IR (KBr): n˜ =3031, 2941, 2892, 2864, 2362, 2152, 1709,
1675, 1591, 1501, 1462, 1404, 1336, 1306, 1279, 1206, 1171, 1105, 1072,
1015, 994, 916, 881, 836, 759, 672, 562 cmÀ1; UV/Vis (chloroform): lmax
(e)=584 (45287), 543(27428), 466 nm (21325 mÀ1 cmÀ1); photolumines-
cence spectrum (chloroform): lmax =610 nm (excitation 540 nm);
MALDI-TOF MS: m/z: 4041 (100%) [M]+ (calcd 4044); elemental anal-
ysis (%) calcd for C280H298N2O8Si8: 83.16, H 7.43, N 0.69; found: C 82.47,
H 7.07, N 0.64.
and purified by column chromatography on silica gel (eluent: toluene,
Rf =0.75) to give 8 (320 mg, 79%). M.p.: 317.28C; 1H NMR (250 MHz,
CD2Cl2, 300 K): d=8.15 (s, 4H), 7.50 (s, 4H), 7.46 (s, 4H), 7.44 (s, 4H),
7.33 (t, J=7.8 Hz, 2H), 7.18 6.49 (m, 396H), 2.70 (m, 4H), 1.11 ppm (d,
J=6.8 Hz, 24H); 13C NMR (60 MHz, CD2Cl2, 300 K): d=163.6 (q, C=
O), 156.0 (q), 154.3(q), 148.1 (q), 148.1 (q), 146.3(q), 145.7 (q), 145.3
(q), 142.1 (q), 142.0 (q), 141.6 (q), 141.2 (q), 141.0 (q), 140.6 (q), 140.4
(q), 140.3 (q), 140.2 (q), 139.6 (q), 139.4 (q), 139.2 (q), 138.9 (q), 138.5
(q), 138.2 (q), 136.2 (q), 135.6 (q), 132.9 (t), 132.0 (t), 131.8 (t), 131.4 (t),
130.3 (t), 129.4 (t), 129.3 (t), 127.9 (t), 127.2 (t), 126.6 (t), 125.8 (t), 123.9
(t), 123.7 (t), 123.6 (t), 123.3 (q), 122.6 (t), 122.5 (t), 121.3 (q), 120.8 (q),
29.4 (t; CH isopropyl), 24.1 ppm (p; CH3 isopropyl); IR (KBr): n˜ =3031,
2963, 2923, 2361, 1707, 1673, 1591, 1494, 1448, 1405, 1334, 1311, 1278,
1205, 1172, 1075, 1022, 878, 751, 697, 554, 510cmÀ1; UV/Vis (chloroform):
lmax (e)=583(36771), 543(21992), 468 nm (17286 mÀ1 cmÀ1); photolumi-
nescence spectrum (chloroform) lmax =607 nm (excitation 540 nm);
MALDI-TOF MS: m/z: 8311 (100%) [M]+ (calcd 8313); elemental anal-
ysis (%) calcd for C624H442N18O8: C 90.08, H 5.35, N 3.03; found: C 89.56,
H 5.43, N 2.79.
3,4-Bis[4-(N,N’-diphenylamino)phenyl]-2,5-diphenylcyclopenta-2,4-dien-
one (11): Dibromocyclopentadienone 10 (2.2 g, 4.0 mmol), diphenylamine
(1.8 g, 8.0 mmol), [Pd2(dba)3] (73mg), and tBuONa (1.15 g, 12.0 mmol)
were added to a 50 mL Schlenk flask in a glove box. Toluene (30 mL)
was poured into the flask to dissolve the mixture, and tri-tert-butylphos-
phane toluene solution (1.2 mL, 20 mgmLÀ1, prepared from pure tri-tert-
butylphosphane and distilled toluene in the glove box) was added by in-
jection. The mixture was stirred at room temperature for 1 h under
argon. Then the solution was filtered under suction, and the filtrate ex-
tracted with water (500 mL). The organic phase was dried under vacuum
to give a dark crude product. The product 11 (2.6 g, 99%) was purified
by column chromography on silical gel (eluent: CH2Cl2, Rf =0.95). M.p.
273.38C; 1H NMR (250 MHz, CD2Cl2, 300 K): d=7.18 (m, 18H), 7.00 (m,
12H), 6.74 ppm (m, 8H); 13C NMR (60 MHz, CD2Cl2, 300 K): d=200.5
(C=O), 154.6, 148.4, 147.5, 131.9, 131.0, 130.5, 129.7, 128.2, 127.5, 126.7,
125.3, 124.9, 123.9, 121.5 ppm; IR (KBr): n˜ =3031, 2362, 1701, 1588, 1488,
First-generation dendrimer bearing 8 ethynyl groups (6b): Trialkylsilyl
derivative 6a (600 mg, 0.15 mmol) was dissolved in THF (20 mL) under
argon. A solution of nBu4F in THF (750 mg, 2.4 mmol, 1.0m) was inject-
ed slowly into the flask. The mixture was stirred for 30 min at room tem-
perature. After most of the THF was removed under vacuum to give a
red solid, methanol (100 mL) was added to the solution to give a precipi-
tate, which was collected by filtration and washed three times with meth-
anol (100 mL). The product 6b was dried under vacuum (340 mg, 80%).
1
M.p. >4008C; H NMR (250 MHz, CD2Cl2, 300 K): d=8.13(s, 4H), 7.58
(s, 4H), 7.93(t, J=7.8 Hz, 2H), 7.32 (d, J=8.5 Hz, 4H), 7.14 6.65 (m,
88H), 3.03 (s, 4H), 3.01 (s, 4H), 2.68 (m, 4H), 1.09 ppm (d, J=6.6 Hz,
24H); 13C NMR (75 MHz, C2D2Cl4, 300 K): d=163.4 (q, C=O), 156.1 (q),
154.1 (q), 145.6 (q), 141.3(q), 141.0 (q), 140.9 (q), 140.7 (q), 140.2 (q),
139.6 (q), 139.1 (q), 138.4 (q), 138.0 (q), 133.1 (q), 131.7 (t), 131.3 (t),
131.0 (t), 130.6 (q), 130.2 (t), 128.1 (t), 127.6 (t), 126.8(t), 126.2 (t), 122.9
(q), 120.9 (q), 120.4 (q), 119.5 (t), 119.2 (q), 118.8 (q), 84.4 (q), 77.5 (q),
1442, 1355, 1277, 1176, 1111, 1077, 1025, 894, 840, 752, 696, 618, 561cmÀ1
;
FD MS (8 kV): m/z: 718.2 (100%) [M]+ (calcd 718.8); elemental analysis
(%) calcd for C53H38N2O: C 88.55, H5.33, N 3.90; found: C 88.53, H 5.24,
N 3.88.
1,6,7,12-Tetrakis[4-(N,N’-diphenylamino)phenoxy]-N,N’-(2,6-diisopropyl-
phenyl)perylene-3,4,9,10-tetracarboxdiimide (12): Compound 3 (500 mg,
0.32 mmol), diphenylamine (20 mg, 1.3 mmol), [Pd2(dba)3] (12 mg), and
tBuONa (180 mg, 2.0 mmol) were added to a 25 mL Schlenk flask in the
glove box. Toluene (10 mL) was injected into the flask to dissolve the
mixture. Tri-tert-butylphosphane in toluene (0.2 mL, 20 mgmLÀ1) was
then injected into the flask in the glove box. The mixture was stirred at
room temperature for 4 h under argon. After 1 h, the solution was fil-
tered under suction and the filtrate extracted with water (100 mL). The
organic phase was dried under vacuum to obtain a purple crude product,
which was purified by column chromography (eluent: CH2Cl2, Rf =0.90)
to give 12 (501 mg, 91%). M.p.: 234.68C; 1H NMR (250 MHz, CD2Cl2,
300 K): d=8.26 (s, 4H), 7.42 (t, J=7.9 Hz, 2H), 7.24 (d, J=8.8 Hz, 4H),
7.15 (t, J=8.2 Hz, 16H), 7.01 6.83(d, J=8.8 Hz, 40H), 2.64 (m, 4H),
1.04 ppm (d, J=6.8 Hz, 24H); 13C NMR (60 MHz, CD2Cl2, 300 K): d=
163.7 (C=O), 156.3, 150.9, 148.1, 146.4, 145.0, 133.6, 131.5, 129.7, 125.2,
124.6, 124.4, 123.3, 123.1, 121.0, 120.7, 120.5, 29.4 (CH isopropyl),
24.1 ppm (CH3 isopropyl); IR (KBr): n˜ =2962, 2361, 1706, 1673, 1589,
1493, 1405, 1335, 1309, 1275, 1202, 874, 752, 696, 511 cmÀ1; UV/Vis
29.3(t; CH isopropyl), 24.5 ppm (p; CH isopropyl); IR (KBr): n˜ =3294,
3
3030, 2963, 2927, 2869, 2361, 2336, 2106, 1708, 1673, 1591, 1501, 1440,
1404, 1336, 1307, 1279, 1205, 1170, 1105, 1016, 842, 700, 651, 558 cmÀ1
;
UV/Vis (chloroform): lmax (e)=583(51645), 543(1312)3, 462 nm
(24006mÀ1 cmÀ1); photoluminescence spectrum (chloroform): lmax
=
610 nm (excitation 540 nm); MALDI-TOF MS: m/z: 2793(100%) [ M]+
(calcd 2793); elemental analysis (%) calcd for C208H138N2O8: 89.44, H
4.98, N 1.00; found: C 88.45, H 5.06, 0.91.
First-generation dendrimer bearing 8 diphenylamino groups (7): As for
6a, 5 (100 mg, 0.085 mmol) and 11 (370 mg, 0.51 mmol) gave 9 (300 mg,
84%). M.p.: 292.58C; 1H NMR (250 MHz, C2D2Cl4, 300 K): d=8.15 (s,
4H), 7.54 (s, 4H), 7.35 (t, J=7.8 Hz, 2H), 7.21 6.59 (m, 172H), 2.61 (m,
4H), 1.05 ppm (d, J=6.7 Hz, 24H); 13C NMR (60 MHz, CD2Cl2, 300 K):
d=163.5 (q, C=O), 156.2 (q), 154.0 (q), 147.9(q), 147.9 (q), 145.7 (q),
145.3(q), 145.0 (q), 141.9 (q), 141.7 (q), 140.9 (q), 140.3(q), 139.6(q),
139.4 (q), 139.3 (q), 138.4 (q), 136.0 (q), 135.4 (q), 133.2 (q), 132.8 (t),
131.8(t), 131.3 (t), 130.7 (q), 130.4 (t), 129.3 (t), 127.8 (t), 127.3 (t), 126.5
(t), 125.9 (t), 124.2 (t), 123.8 (t), 123,5 (t), 123.0 (q), 122.5 (t), 122.3 (t),
121.1 (t), 121.0 (q), 120.4 (q), 119.5 (t), 29.3(t; CH isopropyl), 24.4 ppm
(p; CH3 isopropyl); IR (KBr): n˜ =3027, 2962, 2361, 1707, 1672, 1509,
1493, 1439, 1403, 1322, 1275, 1203, 1173, 1107, 1074, 1022, 839, 751, 696,
664, 562, 509cmÀ1; UV/Vis (chloroform): lmax (e)=584 (45777), 543
(28197), 457 nm (21092mÀ1 cmÀ1); photoluminescence spectrum (chloro-
form) lmax =607 nm (excitation 540 nm); MALDI-TOF MS: m/z: 3935
(100%) [M]+ (calcd 3935); elemental analysis (%) calcd for
(chloroform):
lmax
(e)=595
(25268),
537
(23696),
437 nm
(13332mÀ1 cmÀ1); FD MS (8 kV): m/z: 1747.8 (100%) [M]+ (calcd
1748.0); elemental analysis (%) calcd for C120H94N6O8: C 82.45, H 5.427,
N 4.81; found: C 82.40, H 5.43, N 4.81.
C
288H210N10O8: C 87.82, H 5.37, N 3.56; found: C 86.89, H 5.06, N 3.44.
Acknowledgement
Second-generation dendrimer bearing 8 N,N’-diphenylamino groups (8):
A mixture of 6b (150 mg, 0.050 mmol) and 11 (460 mg, 0.65 mmol) in m-
xylene (5 mL) was stirred at 1508C for 48 h under argon. The cooled re-
action mixture was added to methanol (100 mL). The precipitated prod-
uct was filtered under suction. The product 8 was dried under vacuum
This research was supported by the Max-Planck Society, the TMR Euro-
pean Research Program through the SISITOMAS project, the Volkswa-
gen Stiftung, the Bundesministerium f¸r Bildung and Forschung, and by
536
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 528 537

Dendronized Perylenetetracarboxdiimides
528 537
the BASF AG. The FWO and DWTC through IAP-V-03are thanked for
financial support.
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