Grafting perylenes to ZnO nanoparticles

Article abstract of DOI:10.1002/chem.201303416

A new prototype of dendritic perylenes suitable for the chemical functionalization of inorganic nanoparticles was synthesized and characterized. The bay-functionalized perylene core of these molecular architectures was coupled to a catechol moiety, which

Full text of DOI:10.1002/chem.201303416

DOI: 10.1002/chem.201303416
Full Paper
&
Functionalized Nanoparticles
Grafting Perylenes to ZnO Nanoparticles
Jçrg Schçnamsgruber, Lukas Zeininger, and Andreas Hirsch*[a]
Abstract: A new prototype of dendritic perylenes suitable
for the chemical functionalization of inorganic nanoparticles
was synthesized and characterized. The bay-functionalized
perylene core of these molecular architectures was coupled
to a catechol moiety, which serves as an anchor group for
the functionalization of metal oxides, in particular ZnO. To
increase the solubility of both the perylene and the targeted
hybrid nanostructures, a Newkome-type dendron bearing
nine positive charges was introduced. This charge was also
employed to stabilize the nanoparticles and further protect
them from Ostwald ripening through Coulombic repulsion.
ZnO quantum dots with an average diameter of 5 nm were
synthesized and functionalized with the perylene derivative.
Successful functionalization was clearly demonstrated by dy-
namic light scattering, zeta-potential measurements, ther-
mogravimetric analysis/MS, and UV/Vis and fluorescence
spectroscopy. The generated particle dispersions were stable
against agglomeration for more than eight weeks.
Introduction
ferent substituents in the imide position. By introducing polar
groups, even water-soluble perylene derivatives could be ob-
tained.[3–5] In recent years we have synthesized a family of such
polar, even amphiphilic, PDIs by integrating dendrons bearing
multiple negative and positive charges.[3,4,5a] Moreover, the
steric hindrance of the imide substituents can control self-ag-
gregation due to p–p stacking. The perylene moiety can be
substituted directly in the so-called bay region (1,6,7,12-posi-
tions)[6] and in the recently exploited ortho positions (2,5,8,11-
positions).[7] By introducing different substituents in these posi-
tions, electronic and optical properties can be tuned, and self-
aggregation can be hampered. In our study, another substitu-
tion pattern at PTCDA was also used. A benzimidazole-like
bridge was created by condensing an ortho-phenylenediamine
to the anhydride moiety of a perylene compound (Figure 1,
bottom).[8] The p system of perylene is extended along the
longer axis of the molecule. This evokes a bathochromic shift
in the absorption spectra, and solutions of such compounds
appear violet, blue, or green.
Perylene-3,4,9,10-tetracarboxylic acid diimides (bis-imides; PDI,
PBI; Figure 1) are widely investigated and used in scientific
studies.[1] They are also produced as excellent stable pigments
in the chemical industry. A well-known example is the deep
red dye Pigment Red 179 (Figure 1, PDI: R=methyl), which
was first reported in 1913.[2] As mother compound for PDIs,
perylene-3,4,9,10-tetracarboxylic acid dianhydride (PTCDA) is
used. Solubility can be controlled by synthesizing PDIs with dif-
Perylenes are also widely investigated in hybrid systems. Es-
pecially the generation of organic hybrid systems by linkage to
carbon allotropes such as C60, carbon nanotubes, and gra-
phene is well studied, among others by us.[9] We showed that
carbon nanotubes and graphene could be noncovalently func-
tionalized with amphiphilic PDI derivatives (through p–p inter-
action) to individualize, solubilize, and investigate them. For
generating mixed hybrid systems consisting of perylene linked
to inorganic metal oxides such as ZnO, TiO2, and indium tin
oxide, the perylene core must be covalently functionalized
with a suitable anchor group.
Figure 1. Perylene-3,4,9,10-tetracarboxylic acid diimide (PDI), perylene-
3,4,9,10-tetracarboxylic acid dianhydride (PTCDA), and benzimidazole deriva-
tive.
[a] J. Schçnamsgruber, L. Zeininger, Prof. Dr. A. Hirsch
Department of Chemistry and Pharmacy
Friedrich-Alexander Universitꢀt Erlangen-Nꢁrnberg
Institut fꢁr Organische Chemie
Zinc oxide quantum dots (QDs), as an established member
of aforementioned metal oxides family, have attracted consid-
erable attention owing to their promising electronic, optical,
and piezoelectric properties. ZnO is a direct-bandgap semicon-
ductor (3.37 eV) that absorbs in the near-UV region of the opti-
Henkestrasse 42, 91054 Erlangen (Germany)
Fax: (+49)9131-8526864
E-mail: andreas.hirsch@fau.de
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201303416.
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cal spectrum with a large free exciton binding energy of
60 meV at room temperature.[10] Meulenkamp et al.[11a] reported
in 1989 the synthesis and characterization of ZnO QDs. Since
then, many studies on their biological behavior and toxicity,[12]
physical properties,[13] and functionalization of the particle sur-
face,[14–16] which is the main topic of this report, were pub-
lished. Moreover, ZnO is an interesting material for thin solid
films with optoelectronic applications.[15a,17] In the functionali-
zation of inorganic nanoparticles, the colloidal stability of the
target systems must always be taken into account, which can
be achieved by means of charges on the surface of the
QDs.[15b]
lene core (B) by an imide bond and a small spacer unit. For
the functionalization step, self-aggregation of the compound
induced by p–p stacking should be minimized. Hence,
a 1,6,7,12-substituted (bay-functionalized) PTCDA derivative
was employed. The slight twisting of the perylene plane and
the sterically large substituents hamper close approach of the
molecules, in addition to the electrostatic hindrance provided
by the dendron. As anchoring group for ZnO binding, a cate-
chol unit was chosen, annulated directly to perylene through
an imidazole-like bridge (C). Catechol is well established as
a good anchor group to ZnO. We confirmed successful func-
tionalization using dynamic light scattering (DLS), zeta-poten-
tial measurements, thermogravimetric analysis (TGA), and UV/
Vis, fluorescence, and IR spectroscopy. The resulting perylene/
QD hybrid system was stable against aggregation and sedi-
mentation and showed electronic communication between
chromophore and semiconductor.
Herein, we report on the synthesis of perylene derivative 1,
which is suitable for the functionalization of ZnO nanoparticles
and simultaneously provides colloidal stability of resulting par-
ticle dispersions through Coulombic repulsions. Compound
1 is composed of three subunits (Figure 2). Subunit A of the
Results and Discussion
We first describe the synthesis and characterization of perylene
derivative 1 (Scheme 1). Preparation of the anchoring building
block started with veratrole (2), which was twofold nitrated
Scheme 1. Synthesis of protected catechol 6.
and subsequently deprotected with hydrobromic acid to
obtain 4,5-dinitrocatechol (3). Heating 3 with dichloro com-
pound 4 gave diphenylmethyl-protected catechol 5 in 52%
yield.[18] For condensation to the perylene anhydride, ortho-dia-
mino compound 6 was required. It was synthesized by reduc-
ing dinitro compound 5 with hydrogen at 50 bar in an auto-
clave with the aid of a Pd catalyst.
Figure 2. Cationic perylene compound 1 with a catechol as anchoring group
for ZnO QDs.
molecule is a second-generation dendrimer of the Newkome
type. The exterior branches carry quaternized pyridinium
groups, generating nine positive charges. This pattern was al-
ready used in our previous studies on the synthesis of water-
soluble PDIs. In this case, the dendron is intended to provide
solubility in alcohols, which are utilized as solvents for targeted
functionalization of the ZnO nanoparticles. Moreover, the ionic
dendron is expected to guarantee stability of the nanoparticles
in a colloidal dispersion due to electrostatic stabilization (Cou-
lombic repulsion). The dendron section is linked to the pery-
Perylene precursor 7, synthesized according to a literature
procedure,[19] was then condensed with protected catechol 6
at 1808C in quinoline to give mono-benzimidazolide
8
(Scheme 2). Formation of the undesired bis-benzimidazolide
was prevented by using an almost equimolar ratio of 7 and 6.
The Newkome-type dendron 9[3,4] was subsequently at-
tached to the perylene platform through a condensation reac-
tion with the remaining anhydride position of perylene 8 to
generate imide 10 (Scheme 3). Treating 10 with trifluoroacetic
acid (TFA) at 608C deprotected the carboxyl groups and the
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Table 1. Average diameters of the QDs measured by DLS and zeta poten-
tial measurements.
Unwashed
Washed
Functionalized
DLS diameter [nm]
zeta potential [mV]
5
5
25
À8.1Æ0.5
À16.8Æ1.0
+28.1Æ1.2
as the particle size did not change during the washing process,
a pronounced increase of the hydrodynamic diameter from 5
to 25 nm was observed after the addition of 1. The size distri-
bution of the washed and functionalized particles is shown in
Figure 3 (for details, see the Supporting Information). After
treatment with 1, only particles with an average diameter of
25 nm could be found. This could be explained not only by
bonding of perylene compound 1 to the surface of the nano-
particles, but also by the great influence of the cationic charg-
es at the periphery of the particles, which affect the solvate
shell of the QDs and thereby increase the hydrodynamic diam-
eter.
Scheme 2. Synthesis of protected perylene catechol 8.
catechol subunit to give 11. The cationic charges of 1 were in-
troduced by a ninefold amide coupling reaction with cationic
building block 12 in the presence of N,N’-dicyclohexylcarbodi-
imide (DCC) and N-hydroxybenzotriazole (HOBt) according to
a procedure that we reported earlier.[4]
The ZnO quantum dots were synthesized according to previ-
ous reports[11,14] by hydrolysis of zinc acetate. The average di-
ameter of the nanoparticles was determined to be 5 nm by
DLS and from the UV/Vis absorption spectra by means of an al-
gorithm.[20] For functionalization, equal volumes of a solution
of 1 in methanol (1ꢁ10À4 m) and ZnO QDs (washed and redis-
persed in methanol, ca. 10 wt%) were mixed and ultrasonicat-
ed for 15 min at room temperature. The resulting blue-green
solution remained stable for more than eight weeks until slight
precipitation occurred.
The zeta potential decreased during the washing process
from À8.1 to À16.8 mV, owing to removal of residual acetate
molecules in solution and at the surface of the particle,[11b]
which results in enhanced stability. For the functionalized QDs,
a zeta potential of +28.1 mV was measured. Values near to or
above 30 mV are regarded as an indication for a stable disper-
sion.[21] The particles gain stability due to the cationic charges
on the surface.
Table 1 lists particle sizes measured by DLS and zeta poten-
tials of the unwashed, washed, and functionalized QDs. Where-
For further characterization, UV/Vis absorption spectra of 1,
washed QDs, and functionalized QDs in methanol were record-
Scheme 3. Synthesis of target compound 1.
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Figure 3. Number size distribution of washed and functionalized ZnO nano-
particles, determined by algorithm from UV/Vis spectra and by DLS. The dif-
ference between the solid and dashed curves is due to the hydrodynamic
diameter, which is measured in DLS.
Figure 5. Fluorescence spectra of perylene compound 1 and ZnO nanoparti-
cles in MeOH. The asterisk indicates a peak due to direct scattering at the
excitation wavelength in the spectrometer.
revealed by DLS measurements is generated merely by func-
tionalization and not by any growth of ZnO.
Figure 5 shows the fluorescence spectra of 1 and washed
ZnO QDs. The perylene compound has a strong fluorescence
peak at 649 nm. The spectrum of the ZnO QDs shows the two
typical fluorescence bands: the exciton emission (bandgap
fluorescence) at 361 nm in the UV region and the broad, green
fluorescence band in the visible region, which appears with
much higher intensity at 525 nm.[16,22]
When the emission of the functionalized QDs was measured
with excitation at 330 nm (ZnO edge), the broad fluorescence
in the visible region appeared to be quenched almost com-
pletely (Figure 6). Only a very weak and broad peak with a max-
imum at 510 nm remained. This decrease can be attributed to
charge transfer (fluorescence resonance energy transfer, FRET)
between 1 and the QDs, because the radiation of free particles
is caused by excited electrons in the region of trapped holes
Figure 4. UV/Vis absorption spectra of functionalized ZnO nanoparticles and
references in MeOH.
ed (Figure 4). The spectrum of 1 shows a broad absorption
band at 588 nm. Broadening and bathochromic shifting of the
absorption bands compared to unsubstituted PBIs is caused by
bay substituents and enhancement of the p system by the
benzimidazole-bridged catechol. The absorption spectra of the
ZnO nanoparticles showed a typical absorption edge at
350 nm. In the spectrum of the functionalized nanoparticles,
both characteristic elements (absorption edge and perylene
bands) are combined. The only difference is a hypsochromic
shift of the perylene band to 582 nm, which can be attributed
to electronic interaction between QDs and 1. An effect of
growth of the ZnO particle during functionalization could be
excluded, because the ZnO edge in the spectrum of functional-
ized particles has the same slope and width as that of the ref-
erence. Any agglomeration would lead to increased absorption
beyond the bandgap absorption due to light-scattering effects.
Hence, the aforementioned increase in hydrodynamic diameter
Figure 6. Fluorescence spectra of functionalized nanoparticles. The asterisks
indicate peaks due to direct and second-order scattering at the excitation
wavelength in the spectrometer.
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on the surface of the QDs.[14,22] FRET should be possible owing
to the short distance between perylene and nanoparticle and
overlap of QD emission and perylene absorption.[23] The exci-
ton peak of the QDs in the UV region remains constant. The
perylene fluorescence (excitation at 600 nm) shows a maximum
fluorescence at 653 nm (dashed line). A slight bathochromic
shift of the maximum compared to free perylene 1 again indi-
cated interaction of the electronic states of perylene and ZnO.
Interchromophoric interaction, arising from densely functional-
ized particles, could also cause changes in absorption and fluo-
rescence spectra. To prevent this, a low concentration of 1 com-
pared to the number of QDs was used during the functionali-
zation step. Thus, the surface should be covered only sparsely.
To confirm that surface binding of cationic perylene 1 oc-
curred through the catechol anchor group and not just by
Coulombic interactions, we performed a reverse-phase (RP)
TLC experiment (Figure 7). Whereas a spot of 1 was eluted in
drons as 1, and a mixture of ZnO QDs with 13 were eluted at
the same time (Figure 7b and d). In contrast to the 1-function-
alized particles (Figure 7c), 13 could be eluted from the mix-
ture with ZnO (Figure 7d). Hence, the linkage of ZnO to
1 must be stronger than the Coulombic interaction with 13,
and this confirms covalent linkage of 1 through the catechol
anchor group.
Figure 9 shows TGA and TGA-MS curves of pure perylene 1,
washed ZnO QDs, and dried functionalized particles. Com-
pound 1 showed a significant weight loss of 60% from 220 to
Figure 9. TGA and TGA-MS curves of perylene 1, washed ZnO QDs, and
functionalized QDs. The ion currents belong to the TGA curve of the func-
tionalized QDs.
Figure 7. RP TLC plate (RP-18, eluent: THF/water 2/1). a) 1. b) 13. c) Func-
tionalized QDs. d) Mixture of 13 and QDs.
5008C. The washed ZnO particles showed an overall weight
loss of 15%, which conforms to the literature.[11b] The decrease
resulted from loss of weakly bound lithium acetate and, above
2508C, of covalently bound acetate molecules. The weight loss
of the functionalized particles is related to the aforementioned
processes. Moreover, the simultaneously measured mass spec-
tra showed ion current for three m/z values in the temperature
range of covalent weight loss. The ions with m/z=92, 120,
and 135, which are fragment ions of 1 (pyridinium head
group), gives evidence for successful functionalization of
the ZnO nanoparticles. Larger fragment ions of 1 could not be
observed.
a long band on the plate (Figure 7a), the functionalized parti-
cles stayed on the baseline (Figure 7c). Thus, complete func-
tionalization is shown, assuming that the particles are too
large to be eluted. In a reference experiment, cationic perylene
compound 13[4] (Figure 8), which bears the same cationic den-
Functionalization of ZnO particles deposited on a glass slide
was investigated. The glass slide was first spin-coated with a so-
lution of ZnO QDs and then annealed on a hot plate to dry
the surface. Subsequently, it was dipped in a solution of 1,
rinsed with methanol, and dried. Figure 10 shows the UV/Vis
absorption spectrum of the functionalized slide. The absorp-
tion band of the ZnO QDs could be detected at 350 nm, and
the maximum absorption of the perylene moiety appeared at
582 nm, as in the case of the particle solution. Thus, it could
be determined that 1 was directly bound to the nanoparticles,
because it could not be washed away by rinsing with metha-
nol. An equilibrium at the surface between adsorbed and free
perylene compound 1 was not observed. In this case, the ab-
sorption of 1 should have been decreased over several wash-
ing steps.
Figure 8. Cationic PDI 13.
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Experimental Section
Materials and methods
The ZnO QDs were prepared according to procedures reported
earlier.[11,14] In brief, Zn(OAc)2 dihydrate (550 mg) was dissolved in
boiling ethanol (25 mL) and the solution cooled to 358C. LiOH
(60 mg) was dissolved in ethanol (25 mL) and the solution brought
to synthesis temperature, too. Then LiOH solution was added drop-
wise to zinc acetate solution with vigorous stirring. After 19 h of
aging at 358C, the ZnO nanoparticles were washed to remove by-
products by addition of n-heptane. White ZnO flocculates precipi-
tated. The supernatant was separated by centrifugation at
3500 rpm for 10 min. For characterization and functionalization the
ZnO QDs were redispersed in MeOH. Converting the absorption
spectra to the particle size distribution with an algorithm devel-
oped by Segets et al.[20] gave an average particle size of approxi-
mately 5 nm.
Figure 10. UV/Vis absorption spectra of functionalized ZnO nanoparticles on
an object slide.
The ZnO thin-layer films were generated by spin coating of object
slides with washed ZnO QDs (5 nm) in 0.1m ethanolic solution.
After spin coating for 60 s at 1200 rpm and then 5 min at
8000 rpm, the object slides were annealed at 908C on a hot plate
for 30 min. The resulting ZnO thin-layer films were stable against
washing and immersion in alcoholic solution for at least 48 h. For
functionalization the object slides were immersed in a methanolic
solution of perylene derivative 1 (6ꢁ10À10 m) for 40 min and subse-
quently dried on a hot plate (758C) for 10 min.
Conclusion
A
bay-functionalized perylene derivative was connected
through an imidazole-like bridge to a catechol anchor group
for binding to metal oxide surfaces. This construction motif
significantly extends the conjugated p system of the perylene
chromophore and, after functionalization, links the surface
atoms of the particle to the perylene core in a conjugative
manner. The particle dispersions showed pronounced stability
against agglomeration due to Coulombic repulsion provided
by the positive charges of the attached Newkome-type den-
drons of perylene derivative 1. The zeta potential of about
+30 mV clearly reflects the stability of the dispersions. Size
measurements by DLS confirmed functionalization of the parti-
cle surface, which resulted in an increase in hydrodynamic di-
ameter. Solutions of the perylene-functionalized ZnO nanopar-
ticles were also investigated by UV/Vis absorption and fluores-
cence measurements. Moreover, TGA-MS analysis proved that
1 is attached to the surface, due to the detection of character-
istic mass fragments of 1 generated by thermal cleavage reac-
tions and subsequent release from the surface into the gas
phase. To provide additional proof for the covalent binding of
1 to ZnO, an RP TLC experiment was carried out. Compound 1,
covalently bound to the nanoparticles, could not be eluted on
a TLC plate, whereas a comparable compound without an an-
choring group was easily eluted. Furthermore, ZnO nanoparti-
cles were deposited on glass slides by spin-coating and subse-
quently functionalized with 1. Here, the direct binding mode
of 1 to the surface was proven, because it was not possible to
remove 1 by washing. Such new prototypes of functionalized
nanoparticles open interesting possibilities for the construction
of optoelectronic devices by layer-by-layer deposition tech-
niques, especially alternating ligation with suitable negatively
charged counterparts. Investigations along these lines are cur-
rently under way.
4,5-Dinitrocatechol (3) was prepared from veratrole in two steps,
as reported earlier.[24] The tetrasubstituted perylene 7 was synthe-
sized according to a literature procedure.[8] Synthesis of dendrimer
9 and its precursors was described previously by us.[3,4] Preparation
of cationic building block 12 was reported before.[4] Quinoline was
freshly distilled, degassed with argon, and handled under inert at-
mosphere. DMF was used in HPLC grade. All other solvents and
chemicals were used as received. NMR spectra were recorded with
Bruker Avance 300 (300 MHz), Bruker Avance 400 (400 MHz), and
Jeol EX 400 (400 MHz) spectrometers. IR spectra were recorded on
a Bruker Tensor 27 (ATR or ZnSe plate) spectrometer. A Varian Cary
5000 was used for UV/Vis measurements. Fluorescence spectra
were obtained from a Shimadzu RF-5301 PC. Mass spectrometry
was carried out with a Shimadzu AXIMA Confidence (MALDI-TOF,
matrices: 2,5-dihydroxybenzoic acid (DHB), trans-2-[3-(4-tert-butyl-
phenyl)-2-methyl-2-propenylidene]malononitrile (DCTB)). High-reso-
lution mass spectrometry (HRMS) was performed on a Bruker mi-
croTOF II focus and a Bruker maXis 4G. For DLS measurements and
determination of the zeta potentials, a Zetasizer Nano series
ZEN3600 (Malvern Instruments) was used. The device uses a red
laser for measurements. Compound 1 also absorbs and emits light
in this region, but we observed no interaction between the laser
beam and 1, which could result in low-quality measurements. De-
tailed DLS studies on free compound 1 and functionalized QDs are
given in the Supporting Information. Solutions of 1 in methanol
showed DLS signals above 100 nm, which could result from surfac-
tantlike aggregation of the molecules. The centrifuge was a Her-
aeus Multifuge X1R (Thermo Scientific). The crystal structure of 5
(see Supporting Information) was obtained by a SuperNova Dual
Atlas (Mo, Agilent Technology GmbH). TGA and TGA-MS experi-
ments were carried out on a TGA/SDTA 851e (Mettler Toledo) and
a Skimmer STA 409 CD (Netzsch).
Synthesis
1,2-Diphenylmethylenedioxy-4,5-dinitrobenzene (5): 4,5-Dinitro-
catechol (2.150 g, 10.74 mmol) was mixed with a,a-dichlorodiphe-
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nylmethane (2.546 g, 10.74 mmol), and the reaction mixture
heated to 1708C in a preheated oil bath under a steady flow of ni-
trogen. Orange foaming was observed. After 30 min the reaction
was completed and the mixture was cooled to room temperature.
The crude product was recrystallized from hot ethanol to give 5 as
light yellow crystals (2.049 g, 5.62 mmol, 52%). H NMR (300 MHz,
RT, CDCl3): d=7.35 (s, 2H, CH), 7.43 (m, 6H, CH), 7.52 ppm (m, 4H,
CH); 13C NMR (75 MHz, RT, CDCl3): d=105.1 (CH), 122.4 (C), 126.0,
0.118 mmol, 0.3 equiv) and imidazole (1070 mg, 15.720 mmol,
40 equiv) were heated to 1008C for 2 h. After cooling down to
room temperature the mixture was dissolved in CHCl3 and purified
by column chromatography (CHCl3/MeOH 200/1). 10 was obtained
as
a
dark green solid (135 mg, 0.048 mmol, 12%). 1H NMR
1
(400 MHz, RT, CDCl3): d=1.21 (m, 2H, CH2), 1.28 (m, 36H, CH3), 1.39
(s, 27H, CH3), 1.39 (s, 81H, CH3), 1.64 (m, 4H, CH2), 1.91 (m, 24H,
CH2), 2.16 (m, 26H, CH2), 4.08 (t, J=7.3 Hz, 2H, CH2), 6.05 (m, 4H,
NH), 6.81 (m, 8H, CH), 7.24 (m, 8H, CH and 1H, CH), 7.34 (m, 6H,
CH), 7.58 (m, 4H, CH), 7.98 (s, 1H, CH), 8.16, 8.18, 8.37, 8.38 ppm (s,
4H, perylene-H); 13C NMR (100.5 MHz, RT, CDCl3): d=25.4, 26.9
(CH2), 28.0 (CH3), 29.7, 29.8 (CH2), 31.4 (CH3), 31.7, 31.9 (CH2), 34.3
(C), 37.1 (CH2), 57.4, 80.5 (C), 96.8, 99.7 (CH), 115.6, 117.8, 118.4,
118.5, 119.0 (perylene-C), 119.3, 119.4, 119.4, 119.5 (CH), 119.7,
119.9, 120.2, 120.3, 120.8, 121.2, 121.8, 121.8, 122.0, 122.8, 122.9
(perylene-C), 126.3, 126.6, 126.7, 126.8, 128.4, 129.3 (CH), 132.2,
133.6, 139.2, 139.9 (perylene-C), 146.7, 146.8 (CH), 147.0 (perylene-
C), 147.3, 147.4 152.9, 153.0, 153.1, 153.4, 155.7, 155.9, 156.1, 156.1,
~
128.6, 130.2 (CH) 137.6, 138.9, 150.1 ppm (C); IR (ATR): nmax =624,
637, 669, 697, 725, 753, 766, 794, 816, 70, 918, 938, 1016, 1034,
1077, 1158, 1176, 1213, 1258, 1279, 1306, 1323, 1333, 1352, 1377,
1447, 1471, 1496, 1525, 1544, 1576, 1593, 1633, 1652, 3069, 3276,
3465 cmÀ1; MS (MALDI-TOF, DCTB): m/z=365 [M+H]+.
1,2-Diphenylmethylenedioxy-4,5-diaminobenzene (6): Com-
pound 5 (1.244 g, 3.42 mmol) was dissolved in ethyl acetate
(50 mL). After addition of 100 mg of catalyst (20% Pd(OH)2 on char-
coal), the mixture was hydrogenated in an autoclave at 50 bar H2
pressure for 16 h. The catalyst was filtered off by using Celite as
filter aid. The solvent was evaporated and the resulting solid was
dried under vacuum to afford light yellow 6 (1.007 g, 3.31 mmol,
~
159.9, 163.4 (C), 172.8, 172.9, 173.2 ppm (COO); IR (ZnSe): nmax
=
849, 1018, 1153, 1215, 1291, 1367, 1459, 1508, 1542, 1590, 1656,
1698, 1732, 2362, 2854, 2925, 3356 cmÀ1; UV/Vis (CH2Cl2): l=377,
449, 585, 625 nm; fluorescence (CH2Cl2): l=675 nm; MS (MALDI-
TOF, DCTB): m/z=2788 [M]+; HRMS (ESI-TOF, acetonitrile/methanol)
1
97%). H NMR (300 MHz, RT, CDCl3): d=3.16 (brs, 4H, NH2), 6.36 (s,
2H, CH), 7.33 (m, 6H, CH), 7.53 ppm (m, 4H, CH); 13C NMR (75 MHz,
RT, CDCl3): d=99.6 (CH), 115.9 (C), 126.4, 128.1, 128.8 (CH) 140.6,
found: m/z=1416.2497; calcd: 1416.2467 [M+2Na]2+
.
~
140.7 ppm (C); IR (ATR): nmax =624,637, 669, 696, 725, 753, 795,
816, 870, 918, 938, 1016, 1034, 1077, 1176, 1214, 1257, 1279, 1306,
1324, 1334, 1353, 1377, 1447, 1471, 1496, 1525, 1544, 1576, 1594,
1633, 1652, 3069, 3277, 3466 cmÀ1; MS (MALDI-TOF, DCTB): m/z=
304 [M]+; HRMS (ESI-TOF, acetonitrile/methylene chloride) found:
m/z=304.12061; calcd: 304.12063 [M]+.
Perylene compound 11: Compound 10 (135 mg, 0.048 mmol) was
dissolved in 5 mL of trifluoroacetic acid (TFA) and the solution was
heated to 608C for 2 h. TFA was distilled off on a rotary evaporator
and the residue was suspended in toluene and the solvent evapo-
rated again. The procedure of distilling toluene was repeated three
times to fully remove the TFA by codistillation. The crude dark
solid was dissolved in a small amount of THF and precipitated with
pentane. After two additional reprecipitation steps, 10 was filtered
off and dried in vacuum to obtain a dark green solid (100 mg,
Perylene compound 8: 1,6,7,12-Tetrakis(4-tert-butylphenoxy)pery-
lene-3,4:9,10-tetracarboxylic
acid
dianhydride
(1000 mg,
1.015 mmol, 1.0 equiv), 6 (309 mg, 1.015 mmol, 1.0 equiv), and zinc
chloride (166 mg, 1.218 mmol, 1.2 equiv) were dissolved in 10 mL
of degassed and freshly distilled quinoline. The mixture was stirred
at 1808C for 4 h under argon atmosphere. After cooling to room
temperature quinoline was distilled off with a kugelrohr. The dark
residue was dissolved in 25 mL of dichloromethane, washed with
water, and dried over MgSO4. The solvent was removed under re-
duced pressure and the crude product was purified by column
chromatography (dichloromethane/hexane 1/1). After evaporation
of the solvent, 8 was obtained as a dark green solid (493 mg,
1
0.048 mmol, 98%). H NMR (400 MHz, RT, CDCl3 +[D]TFA): d=1.29
(m, 48H, CH3), 1.32 (m, 2H, CH2), 1.64 (m, 4H, CH2), 2.12 (m, 26H,
CH2), 2.40 (m, 24H, CH2), 4.10 (m, 2H, CH2), 6.50 (m, 4H NH), 7.32
(m, 9H, CH), 8.20, 8.22, 8.23, 8.48, 8.57 (s, 5H, CH); 13C NMR
(100.5 MHz, RT, CDCl3 +[D]TFA): d=28.1, 29.0 (CH2), 28.0 (CH3), 31.0
(CH3), 31.7, 31.9 (CH2), 34.4 (C), 36.5 (CH2), 59.2 (C), 99.3, 102.8 (CH),
117.9, 119.3, 119.7, 122.5 (perylene-C), 127.3 (CH), 131.7 (perylene-
C), 149.0 (CH), 147.0 (perylene-C), 152.3 (C), 176.5 (COO),
1
~
180.3 ppm (COOH); IR (ATR): nmax =611, 703, 720, 748, 800, 834,
0.393 mmol, 39%). H NMR (300 MHz, RT, CDCl3): d=1.30 (m, 36H,
878, 892, 918, 989, 1014, 1034, 1093, 1173, 1284, 1346, 1407, 1457,
1505, 1543, 1587, 1655, 1694, 1980, 2049, 2162, 2322, 2954, 3064,
3306 cmÀ1; UV/Vis (THF): l=377, 437, 583, 610 nm; fluorescence
(THF): l=655 nm; MS (MALDI-TOF, DHB): m/z=2120 [M]+, 2143
[M+Na]+.
CH3), 6.84 (m, 8H, CH), 7.17 (s, 1H, CH), 7.23 (m, 8H, CH), 7.32 (m,
6H, CH), 7.55 (m, 4H, CH), 7.90 (s, 1H, CH), 7.95, 8.13, 8.16,
8.37 ppm (s, 4H, perylene-H); 13C NMR (100.5 MHz, RT, CDCl3’): d=
31.4, 31.4, 31.4, 31.5 (CH3), 34.3, 34.3, 34.3, 34.4 (C), 96.7, 96.8, 99.7,
99.8 (CH), 114.8, 115.4, 117.3, 117.8, 117.8, 118.2, 118.2, 118.3, 118.7
(perylene-C), 119.0, 119.1, 119.2, 119.3, 119.4, 119.4, 119.5, 119.5
(CH), 120.0, 121.1, 121.2, 121.3, 121.6, 121.7, 121.9, 122.1, 122.2,
122.4, 123.0, 123.4 (perylene-C), 126.2, 126.3, 126.4, 126.6, 126.7,
126.7, 126.8, 126.8, 126.8, 126.9, 126.9, 128.3, 129.2 (CH), 132.3,
132.8, 132.8, 133.9, 139.1, 139.1, 139.8, 139.9, 143.3 (perylene-C),
146.8, 146.9, 147.0, 147.2, 147.3, 147.4, 147.6, 147.7, 147.8, 152.6,
152.6, 152.9, 153.1, 153.2, 153.4, 153.4, 153.5, 155.5, 155.6, 155.8,
155.9, 156.0, 156.2, 156.3, 156.7, 159.6, 159.9, 160.1, 160.2 ppm (C);
Perylene compound 1: Compound 11 (50 mg, 0.024 mmol,
1 equiv) and HOBt (58 mg, 0.432 mmol, 18 equiv) were dissolved in
3 mL of DMF under N2 atmosphere and the solution cooled to 08C.
A solution of DCC (89 mg, 0.432 mmol, 18 equiv) in 1 mL of DMF
was added and the solution stirred at 08C. 12 (472 mg,
1.728 mmol, 72 equiv) in 1 mL of DMF was added dropwise and
the mixture was stirred for 48 h at room temperature. DMF was
distilled off under reduced pressure and the residue was dissolved
in a small amount of methanol. A red solid was precipitated by ad-
dition of a larger quantity of acetone. The suspension was centri-
fuged and the precipitation repeated twice. After drying in
vacuum, 1 was obtained as a dark blue solid (36 mg, 0.009 mmol,
~
IR (ATR): nmax =613, 641, 696, 727, 746, 765, 796, 828, 849, 888, 949,
977, 1014, 1043, 1091, 1110, 1137, 1171, 1209, 1281, 1341, 1377,
1408, 1457, 1497, 1548, 1588, 1697, 1739, 1768, 1980, 2049, 2361,
2586 2867, 2958, 3059 cmÀ1; UV/Vis (CH2Cl2): l=450, 632 nm; fluo-
rescence (CH2Cl2): l=694 nm; HRMS (ESI-TOF, acetonitrile/methyl-
ene chloride) found: m/z=1252.494061; calcd: 1252.486848 [M]+.
1
38%). H NMR (400 MHz, RT, CD3OD): d=1.26 (m, 81H, CH3), 1.40
(m, 40H, CH3 +CH2), 1.95, 2.20 (m, 74H, CH2), 3.23 (m, 18H, CH2),
4.62 (m, 18H, CH2), 7.26 (m, 8H, CH), 7.67 (m, 8H, CH), 8.12 (m,
18H, CH), 8.93 ppm (m, 18H, CH), perylene protons could not be
Perylene compound 10: Compound
8 (493 mg, 0.393 mmol,
1.0 equiv), 9 (610 mg, 0.393 mmol, 1.0 equiv), zinc acetate (26 mg,
Chem. Eur. J. 2014, 20, 2529 – 2536
www.chemeurj.org
2535
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
observed due to line broadening; 13C NMR (100.5 MHz, RT, CD3OD):
d=30.5, 32.3 (CH3), 35.4, 36.9 (qC tBu), 37.7, 55.0, 59.1, 59.9 (CH2),
118.1–132.6 (br, per-C), 126.9, 145.9 (py-CH), 172.9 (py-C),
182.0 ppm (COO), not all signals could be observed due to line
Schmidt, F. Hauke, A. Hirsch, Adv. Mater. 2010, 22, 5483–5487; C. Oels-
ner, C. D. Schmidt, F. Hauke, M. Prato, A. Hirsch, D. M. Guldi, J. Am.
Chem. Soc. 2011, 133, 4580–4586; C. Backes, C. D. Schmidt, F. Hauke, A.
Hirsch, Chem. Asian J. 2011, 6, 438–444; D. Wrobel, K. Lewandowska,
Opt. Mater. 2011, 33, 1424–1428; C. Backes, F. Hauke, A. Hirsch, Adv.
Mater. 2011, 23, 2588–2601; A. Hirsch, J. M. Englert, F. Hauke, Acc.
Chem. Res. 2013, 46, 87–96.
~
broadening; IR (ATR): nmax =622, 658, 800, 813, 836, 877, 891, 962,
1015, 1041, 1113, 1152, 1175, 1214, 1281, 1341, 1396, 1457, 1506,
1556, 1643, 1691, 1980, 2015, 2148, 2162, 2321, 2360, 2960, 3056,
3274 cmÀ1; UV/Vis (MeOH): l=396, 448, 588 nm; fluorescence
(MeOH): l=648 nm.
ˇ
[10] ꢄ. ꢅzgꢂr, Ya. I. Alivov, C. Liu, A. Teke, M. H. Reshchikov, S. Dogan, V. Av-
rutin, S.-J. Cho, H. MorkoÅ, J. Appl. Phys. 2005, 98, 041301; A. Janotti,
C. G. van de Walle, Rep. Prog. Phys. 2009, 72, 126501.
[11] a) E. A. Meulenkamp, J. Phys. Chem. B 1998, 102, 7764–7769; b) R. Marc-
zak, D. Segets, M. Voigt, W. Peukert, Adv. Powder Technol. 2010, 21, 41–
49.
[12] N. Jones, B. Ray, K. T. Ranjit, A. C. Manna, FEMS Microbiol. Lett. 2008, 279,
71–76; D. Lin, B. Xing, Environ. Sci. Technol. 2008, 42, 5580–5585; B. C.
Heng, X. Zhao, S. Xiong, K. W. Ng, F. Y.-C. Boey, J. S.-C. Loo, Food Chem.
Toxicol. 2010, 48, 1762–1766.
[13] N. S. Pesika, Z. Hu, K. J. Stebe, P. C. Searson, J. Phys. Chem. B 2002, 106,
6985–6990; D. Segets, R. Marczak, S. Schꢆfer, C. Paula, J.-F. Gnichwitz,
A. Hirsch, W. Peukert, ACS Nano 2011, 6, 4658–4669; C. He, T. Sasaki, Y.
Shimizu, N. Koshizaki, Appl. Surf. Sci. 2008, 254, 2196–2202.
[14] R. Marczak, F. Werner, J.-F. Gnichwitz, A. Hirsch, D. M. Guldi, W. Peukert,
J. Phys. Chem. C 2009, 113, 4669–4678.
[15] a) F. Werner, J.-F. Gnichwitz, R. Marczak, E. Palomares, W. Peukert, A.
Hirsch, F. Werner, J. Phys. Chem. B 2010, 114, 14671–14678; b) J.-F.
Gnichwitz, R. Marczak, F. Werner, N. Lang, N. Jux, D. M. Guldi, W. Peu-
kert, A. Hirsch, J. Am. Chem. Soc. 2010, 132, 17910–17920; c) E. Tang, G.
Cheng, X. Ma, X. Pang, Q. Zhao, Appl. Surf. Sci. 2006, 252, 5227–5232.
[16] S. Chen, U. Nickel, X. Ren, J. Colloid Interface Sci. 1995, 176, 286–292; E.
Vaishnavi, R. Renganathan, Bull. Mater. Sci. 2012, 35, 1173–1179.
[17] H. Faber, M. Klaumꢂnzer, M. Voigt, D. Galli, B. F. Vieweg, W. Peukert, E.
Spiecker, M. Halik, Nanoscale 2011, 3, 897–899.
Acknowledgements
The authors thank Doris Segets (Peukert group, LFG Erlangen)
for calculating the particle size distribution from the UV/Vis ab-
sorption spectra. We thank the Cluster of Excellence EAM and
the State of Bavaria “Solar Technologies Go Hybrid” for finan-
cial support.
Keywords: dendrimers
polycations · quantum dots
· dyes/pigments · nanoparticles ·
[1] C. Huang, S. Barlow, S. R. Marder, J. Org. Chem. 2011, 76, 2386–2407; F.
Wꢂrthner, Chem. Commun. 2004, 1564–1579; C. Li, H. Wonneberger,
Adv. Mater. 2012, 24, 613–636.
[2] M. Kardos, German Patent, DE 276956, 1913.
[3] C. D. Schmidt, C. Bçttcher, A. Hirsch, Eur. J. Org. Chem. 2007, 5497–
5505.
[4] J. Schçnamsgruber, B. Schade, R. Kirschbaum, J. Li, W. Bauer, Ch. Bçttch-
er, Th. Drewello, A. Hirsch, Eur. J. Org. Chem. 2012, 6179–6186.
[5] a) C. D. Schmidt, C. Bçttcher, A. Hirsch, Eur. J. Org. Chem. 2009, 5337–
5349; b) T. Tang, J. Qu, K. Mꢂllen, S. E. Webber, Langmuir 2006, 22,
7610–7616; K. Peneva, G. Mihov, A. Herrmann, N. Zarrabi, M. Bçrsch,
T. M. Duncan, K. Mꢂllen, J. Am. Chem. Soc. 2008, 130, 5398–5399; S.
Rehm, V. Stepanenko, X. Zhang, T. H. Rehm, F. Wꢂrthner, Chem. Eur. J.
2010, 16, 3372–3382; T. Heek, C. Fasting, C. Rest, X. Zhang, F. Wꢂrthner,
R. Haag, Chem. Commun. 2010, 46, 1884–1886; B. Gao, H. Li, H. Liu, L.
Zhang, Q. Bai, X. Ba, Chem. Commun. 2011, 47, 3894–3896.
[6] M. Queste, C. Cadiou, B. Pagoaga, L. Giraudet, N. Hoffmann, New J.
Chem. 2010, 34, 2537–2545.
[18] G. Iacazio, C. Pꢃrrisol, B. Faure, J. Microbiol. Methods 2000, 42, 209–214.
[19] D. Dotcheva, M. Klapper, K. Mꢂllen, Macromol. Chem. Phys. 1994, 195,
1905–1911.
[20] D. Segets, J. Gradl, R. K. Taylor, V. Vassilev, W. Peukert, ACS Nano 2009, 3,
1703–1710.
[21] R. Greenwood, K. Kendall, J. Eur. Ceram. Soc. 1999, 19, 479–488; D.
Hanaor, M. Michelazzi, C. Leonelli, C. C. Sorrell, J. Eur. Ceram. Soc. 2012,
32, 235–244.
[22] D. W. Bahnemann, C. Kormann, M. R. Hoffmann, J. Phys. Chem. 1987, 91,
3789–3798; P. V. Kamat, B. Patrick, J. Phys. Chem. 1992, 96, 6829–6834.
[23] L. Wang, R. Yan, Z. Huo, L. Wang, J. Zeng, J. Bao, X. Wang, Q. Peng, Y. Li,
Angew. Chem. 2005, 117, 6208–6211; Angew. Chem. Int. Ed. 2005, 44,
6054–6057; X. Chen, M.-C. Estꢃvez, Z. Zhu, Y.-F. Huang, Y. Chen, L.
Wang, W. Tan, Anal. Chem. 2009, 81, 7009–7014.
[7] S. Nakazono, S. Easwaramoorthi, D. Kim, H. Shinokubo, A. Osuka, Org.
Lett. 2009, 11, 5426–5429; S. Nakazono, Y. Imazaki, H. Yoo, J. Yang, T.
Sasamori, N. Tokitoh, T. Cedric, H. Kageyama, D. Kim, H. Shinokubo, A.
Osuka, Chem. Eur. J. 2009, 15, 7530–7533.
[24] L. Perrin, P. Hudhomme, Eur. J. Org. Chem. 2011, 5427–5440.
[8] T. Maki, H. Hashimoto, Bull. Chem. Soc. Jpn. 1952, 25, 411–413; J. Fort-
age, M. Sꢃvarac, C. Houarner-Rassin, Y. Pellegrin, E. Blart, F. Odobel, J.
Photochem. Photobiol. A 2008, 197, 156–169.
Received: August 30, 2013
Revised: December 1, 2013
[9] J. Hua, F. Meng, F. Ding, F. Li, H. Tian, J. Mater. Chem. 2004, 14, 1849–
1853; N. V. Kozhemyakina, J. M. Englert, G. Yang, E. Spiecker, C. D.
Published online on February 2, 2014
Chem. Eur. J. 2014, 20, 2529 – 2536
www.chemeurj.org
2536
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim