Synthesis and characterization of subporphyrins with dendritic carbazole arms

Article abstract of DOI:10.1002/ejoc.200700981

A series of novel dendritic carbazole-functionalized subporphyrins, T(Cz-Gn)SubPs (n = 1-3), have been synthesized from pyridine-tri(pyrrol-1-yl) borane and the corresponding aldehydes. This study has demonstrated that intramolecular energy transfer from

Full text of DOI:10.1002/ejoc.200700981

FULL PAPER
DOI: 10.1002/ejoc.200700981
Synthesis and Characterization of Subporphyrins with Dendritic Carbazole
Arms
Tinghua Xu,[a] Ran Lu,*[a] Xingliang Liu,[a] Peng Chen,[a] Xianping Qiu,[a] and
Yingying Zhao[a]
Keywords: Subporphyrins / Carbazole / Dendrimers / Energy transfer / Light-harvesting antennas / Porphyrinoids
A series of novel dendritic carbazole-functionalized subpor-
phyrins, T(Cz-Gn)SubPs (n = 1–3), have been synthesized
from pyridine–tri(pyrrol-1-yl)borane and the corresponding
aldehydes. This study has demonstrated that intramolecular
energy transfer from the carbazole dendron to the subpor-
phyrin core occurs with a high efficiency which decreases
with increasing dendron generation, in accord with the
Förster mechanism of energy transfer. In addition, the carb-
azole dendron can lead to a blueshift of the absorption and
emission bands of the subporphyrin core. The light-harvest-
ing abilities of these compounds increase with increasing
generation. Meanwhile, these dendritic macromolecules
emit intense yellow-green light and may be good candidates
for photonic devices.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
sional structures which are constructed from an interior
core with a regular array of branching units. There has been
considerable interest in the incorporation of functional
units onto the exterior surface or into the interior of dendri-
mers. It is well known that a dendritic framework can affect
several functionalities by controlling the microenvironments
around the functional units.[6,7] In addition, carbazole is an
attractive molecule because of its intense luminescence, elec-
tron sufficiency, and potential for dendritic construc-
tion.[8–10] Therefore, novel dendrimers based on carbazole
as the repeating unit and the subporphyrin as the core may
exhibit fascinating photophysical and electronic properties.
To the best of our knowledge, there is no example of a
subporphyrin meso-linked to a rigid dendron. Herein, we
present the synthesis of a series of well-defined subporphyr-
ins with three dendritic carbazole arms (Scheme 1) and an
investigation of their photophysical properties.
Introduction
As an extended conjugated macrocyclic ring system,
ring-expanded porphyrins have been known for many years
and extensively studied on account of their unique proper-
ties and potential applications in two-photon absorption
and switches.[1] It is worth noting that the first ring-contrac-
ted porphyrin, subporphyrin, was prepared by Osuka and
co-workers under harsh reaction conditions as recently as
2006.[2] Subsequently, more versatile and facile synthetic
methods for the synthesis of meso-aryl-subporphyrins have
been developed by Kobayashi and Osuka and their co-
workers, but it is still a great challenge to introduce desired
functional groups such as dendritic substituents into sub-
porphyrins.[3] The subporphyrin features a 14π-electron aro-
matic core, but nonetheless adopts a nonplanar cone-
shaped conformation. It is also the porphyrinic counterpart
of subphthalocyanines whose optoelectronic properties can
be fine-tuned by varying their axial X ligands or by func-
tionalizing peripheral substituents.[2–4] Thus, it is possible
that the introduction of functional moieties as arms into the
subporphyrin core will provide some fantastic properties.
The synthesis of dendrimers, cascade molecules, and re-
lated hyper-branched systems, as well as their characteriza-
tion, is currently attracting great interest in the field of ma-
terials science.[5] Dendrimers are monodisperse, highly
branched macromolecules with well-defined three-dimen-
Results and Discussion
Synthesis of the Carbazole-Based Dendrons
The synthetic routes to the precursors of aldehydes 5, 8,
and 11 are shown in Scheme 2, Scheme 3, and Scheme 4.
To improve the solubility and stability of the molecules,
tert-butyl groups were introduced into the 3,6-positions of
the peripheral carbazoles in the dendrons. 3,6-Di-tert-butyl-
carbazole (4) was prepared in a yield of 54% by Friedel–
Crafts alkylation of carbazole by adaptation of a published
procedure.[11] The first-generation carbazole dendron 5
(Cz–G1–CHO) was obtained from compound 4 and p-
iodobenzaldehyde, catalyzed by Cu2O in N,N-dimethylacet-
amide (DMAc) at 170 °C for 20 h, by the Ullmann conden-
[a] State Key Laboratory of Supramolecular Structure and Materi-
als, College of Chemistry, Jilin University,
Changchun 130012, P. R. China
Fax: +86-431-88923907
E-mail: luran@mail.jlu.edu.cn
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
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FULL PAPER
Scheme 1. Molecular structures of T(Cz-Gn)SubPs 1–3.
Scheme 2. Synthesis of Cz–G1–CHO (5) and Cz–G2–CHO (8).
sation reaction in a yield of 75%.[7k,8b,8c,10] The second-gen-
eration carbazole dendron 8 (Cz–G2–CHO) was synthe-
sized from compound 7 and p-iodobenzaldehyde under sim-
ilar conditions in a yield of 72%, while compound 7 was
synthesized from compounds 4 and 6 through an Ullmann
coupling reaction followed by cleavage of the N–Ts bond
under basic conditions (70%, two steps).[7k,8b,8c,10] The first
synthetic route we chose for the preparation of the third-
generation carbazole dendron 11 (Cz–G3–CHO) is shown
in Scheme 3. The iodination of compound 9, which was ob-
tained from the Ullmann condensation reaction of carb-
azole and p-iodobenzaldehyde, was pursued to give com-
pound 10.[10c] Compound 11 was obtained in a low yield
(10%) through the Ullmann condensation reaction of com-
pounds 10 and 7 at 190 °C for 24 h. To explain the low yield
it was proposed that the aldehyde groups were partially oxi-
dized by Cu2O under the experimental conditions and
would have been completely oxidized above 190 °C for 24 h.
If the temperature was lowered or the reaction time short-
ened the amount of mono adduct, whose solubility and po- Scheme 3. Synthesis of Cz–G3–CHO (11).
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Synthesis of Subporphyrins with Dendritic Carbazole Arms
larity are similar to those of the double adduct, would be tube could avoid oxidation at a higher temperature.[10]
increased. Therefore, another synthetic route was designed Compound 12 was treated with KOH in mixed solvents to
and amended to improve the yield and simplify the purifica- remove the Ts group and the resulting product was con-
tion of 11 (Scheme 4). The Ullmann condensation reaction densed with p-iodobenzaldehyde at 180 °C for 20 h to give
between compound 6 and 7 was carried out at 200 °C for the third-generation carbazole dendron 11 which was
60 h to obtain compound 12, which was recrystallized from recrystallized from EtOH/THF (4:1, v/v) in a yield of 70%
EtOH/THF (1:1, v/v) twice to give a yield of 65%. Com- after chromatography using petroleum ether/CH2Cl2 (1:2,
pound 12 was previously synthesized in a yield of only 14% v/v) as the eluent.
due to the lower reactivity and easier oxidation of the larger
carbazole oligomers.[8b] It was found that the use of a sealed
Synthesis of the Dendrimers
The synthetic routes to the dendritic subporphyrins 1–3
are outlined in Scheme 5. First, we tried the Adler reaction
conditions which are effective for the preparation of meso-
aryl-subporphyrins[3a–3c] but failed in this application. The
reason for this might be that more time is required for the
reaction between pyridine–tri(pyrrol-1-yl)borane (13) and
the large-volume aldehyde (in this case the dendritic alde-
hyde),[12] but also a major side-reaction involving the acid-
promoted scrambling of 13 under such harsh condition
takes place, suppressing the formation of the dendritic sub-
porphyrins. Osuka and co-workers presented another
method for the synthesis of subporphyrins which involved
a one-pot two-step reaction under milder conditions.[3b] Ac-
cordingly, 13 and 3 equivs. of Cz–G1–CHO (5) were con-
densed in the presence of trifluoroacetic acid (TFA) at 0 °C
under N2 for 2 h in order to avoid the acid-promoted
scrambling. During the reaction process the color of the
mixture changed from light-yellow to deep-red.[13] After be-
ing quenched with pyridine, the reaction mixture was re-
fluxed in o-dichlorobenzene for 1 h to complete the air-oxi-
dation. Dendrimer 1 was obtained in only 2% yield after a
Scheme 4. Improved synthetic route to Cz–G3–CHO (11).
tedious purification procedure based on multiple column
Scheme 5. Synthesis of T(Cz-Gn)SubPs 1–3.
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chromatography steps. Dendrimers 2 and 3 were similarly very likely drop by several orders of magnitude if the trans-
synthesized from Cz–G2–CHO (8) and Cz–G3–CHO (11) fer takes place in a single hop, so energy transfer in the
in yields of 2.2 and 1.4%, respectively. With increasing gen- large dendritic subporphyrins may occur in several steps.
eration of the dendron, the volume of the aldehydes became Hence, the larger transfer distance in this dendritic system
larger, and the reaction time was lengthened to 6 and 12 h is significant because it introduces more energy-transfer
for the condensation reactions of 13 with Cz–G2–CHO (8) steps. Furthermore, the emission intensity of the subpor-
and Cz–G3–CHO (11), respectively. Since the dendritic sub- phyrin core increases from 1 to 3 under excitation at
porphyrins in B–OH forms were strongly adsorbed by silica 299 nm. This can be explained by the fact that the growing
gel, the pure products were obtained by column chromatog- number of carbazoles in the higher generation dendrimers
raphy once on silica gel and twice on alumina. All the den- results in increasing absorption. All the dendritic subpor-
dritic subporphyrins are readily soluble in many common phyrins 1–3 exhibit strong fluorescence emission. The fluo-
organic solvents including petroleum ether, CH2Cl2, chloro- rescence quantum yields were determined by using quinine
form, THF, and toluene. All the new compounds were char- sulfate as a standard and the ΦF values for 1–3 in CHCl3
acterized unambiguously by FT-IR, 1H and 13C NMR, are 0.154, 0.136, and 0.110 (Table 1), respectively, similar to
C,H,N elemental analyses, and MALDI-TOF mass spec- that of the meso-phenylsubporphyrin.[3a]
trometry (see the electronic supporting information).
Optical Properties of the T(Cz-Gn)SubPs
Figure 1 shows the UV/Vis absorption spectra of com-
pounds 1–3. Several absorption bands in the visible region
are observed, including two Q-bands in the range of 450–
530 nm together with a Soret band at around 380 nm and
others in the UV region (250–350 nm) due to the carbazole
units. The absorbance of the carbazole units is clearly pro-
portional to their increased number in each generation
which indirectly reflects the structural flawlessness of the
as-synthesized dendrimers. Compared with the meso-phen-
Figure 1. UV/Vis absorption spectra (normalized at the Soret
ylsubporphyrin, the Soret bands of the dendritic subpor-
phyrins 1–3 are redshifted from 373 to 390, 381, and
380 nm, respectively.[3a] Significantly, the Soret bands of 1–
3 are blueshifted with increasing generation of the dendron
(Table 1). This may be due to the larger volume of carb-
azole dendron in compounds 2 and 3 which can enlarge the
dihedral angle and weaken the degree of conjugation be-
tween the subporphyrin ring and the carbazole dendrons.[3b]
Similarly, the emission bands of the dendrimers in dilute
bands) of 1–3 in CHCl3.
Table 1. Photophysical data for T(Cz-Gn)SubPs 1–3 in CHCl3.
max
max[a]
[c]
Dendrimers
λ
[nm]
λ
[nm] ΦET[b] [%] ΦF
abs
em
T(Cz-G1)SubP (1) 298, 353, 390, 471, 498
T(Cz-G2)SubP (2) 299, 353, 381, 468, 494
T(Cz-G3)SubP (3) 299, 351, 380, 465, 492
556
545
537
82
77
60
0.154
0.136
0.110
solution are also blueshifted with increasing generation un- [a] Excited at 299 nm. [b] Energy-transfer efficiency (ΦET) was cal-
culated by comparing the absorption and excitation spectra of the
der excitation of the subporphyrin core, for example, the
dendrimers by monitoring the emission of the subporphyrin core.
emission bands of 1–3 appear at 556, 545, and 537 nm,
[c] The fluorescence quantum yields were determined against qui-
nine sulfate in 0.1  H2SO4 (ΦF = 0.546, λ = 366 nm) as the stan-
respectively (Figure 2 and Table 1).[3a] The emission of the
carbazole units at around 420 nm was significantly weak-
ened when 1–3 were selectively excited at 299 nm, whereas
a strong emission ascribed to the subporphyrin cores was
observed (Figure 3) which indicates effective intramolecular
energy transfer from the carbazole units to the subporphy-
rin core. The efficiency of the energy transfer (ΦET) can be
estimated by comparing the absorption and excitation spec-
tra of the dendron units.[14] The ΦET values of 1–3 are 82,
77, and 60%, respectively (see Figures S1–S3 and Table 1).
Clearly, the energy-transfer efficiency decreases with in-
creasing generation of the dendrimers. This trend can be
ascribed, in the context of the Förster mechanism of energy
transfer, to the influence of the distance between the donor
and the acceptor, the overlap integral between the carb-
azole-based dendrons and the subporphyrin core.[6a] With
dard.
Figure 2. Normalized emission spectra of 1–3 in CHCl3 (λex
=
an increase in energy-transfer distance, the efficiency would 390 nm for 1, λex = 381 nm for 2 and 3).
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Synthesis of Subporphyrins with Dendritic Carbazole Arms
(2.6 g, 11.2 mmol), Cu2O (2.8 g, 19.4 mmol), and DMAc (8 mL)
were added sequentially to a sealed tube under nitrogen and heated
at 170 °C in an oil bath for 20 h. Then the mixture was cooled to
room temperature and filtered. The filtrate was poured into H2O
(300 mL) and stirred for 20 min. The solid was collected by fil-
tration and recrystallized from petroleum ether to give 3.1 g (75%)
of a light-yellow solid, m.p. 159.0–160.0 °C. IR (KBr): ν = 3049.1,
˜
2962.3, 2902.5, 2865.8, 2732.8, 1699.1, 1600.7, 1512.0, 1471.5,
1369.3, 1324.9, 1296.0, 1263.2, 1234.3, 1205.4, 1161.0, 1103.1,
1035.6, 885.2, 810.0, 727.1 cm–1. The strong peak at 1699.1 cm–1 is
the νs of the C=O moiety. 1H NMR (CDCl3, 500 MHz): δ = 10.11
(s, 1 H, -CHO), 8.32 (s, 2 H, Ar-H), 8.19 (d, J = 8.5 Hz, 2 H, Ar-
H), 7.90 (d, J = 8.5 Hz, 2 H, Ar-H), 7.52 (d, J = 9.0 Hz, 2 H, Ar-
H), 7.46 (d, J = 9.0 Hz, 2 H, Ar-H), 1.42 (s, 18 H, -CH3) ppm (see
Figures S9 and S10). 13C NMR (CDCl3, 125 MHz): δ = 191.0,
143.9, 138.4, 134.1, 131.3, 126.2, 124.1, 116.5, 109.3, 34.8, 31.9 ppm
(see Figure S25). MS: calcd. 383.5; found 384.3 [M+ + H].
C27H29NO (383.53): calcd. C 84.55, H 7.62, N 3.65; found C 84.50,
H 7.75, N 3.61.
Figure 3. Emission spectra of 1 µ 1–3 in CHCl3 (λex = 299 nm).
Conclusion
Versatile synthetic routes to subporphyrins with dendritic
carbazole arms T(Cz-Gn)SubPs 1–3 by one-pot two-step re-
actions from pyridine–tri(pyrrol-1-yl)borane and the corre-
sponding aldehydes have been explored. A rigorous and te-
dious purification procedure based on multiple chromatog-
raphy steps is required to obtain 1–3. The intramolecular
4-[3,6-Bis(3,6-di-tert-butyl-9H-carbazol-9-yl)-9H-carbazol-9-yl]benz-
aldehyde (8): 3,6-Di-tert-butyl-9-[3-(3,6-di-tert-butyl-9H-carbazol-
9-yl)-9H-carbazol-6-yl]-9H-carbazole (7) (4.1 g, 5.7 mmol), 4-iodo-
benzaldehyde (1.8 g, 7.8 mmol), Cu2O (1.8 g, 12.5 mmol), and
energy transfer from the carbazole dendron to the subpor- DMAc (10 mL) were added sequentially to a sealed tube under
nitrogen and heated at 170 °C in an oil bath for 20 h. Then the
mixture was cooled to room temperature and filtered. The filtrate
was poured into H2O (400 mL) and stirred for 20 min. The solid
was collected by filtration and purified by chromatography (silica
gel, petroleum ether/ethyl acetate, 20:1, v/v) to give 4.0 g of a light-
yellow solid which was further recrystallized from EtOH/THF (4:1,
v/v) to give 3.4 g (72%) of a light-yellow solid, m.p. Ͼ250 °C. IR
phyrin core occurs with a high efficiency, which decreases
with increasing generation of the dendron, in accord with
the Förster mechanism of energy transfer. In addition, the
light-harvesting abilities of these compounds increase with
increasing generation. The energy transfer in the large den-
dritic subporphyrins occurs in several transfer steps. The
carbazole dendron can significantly influence the absorp-
tion and emission bands of the subporphyrin core, which
are blueshifted with increasing generation of the dendron.
(KBr): ν = 3051.0, 2962.3, 2902.5, 2865.8, 2738.6, 1701.0, 1600.7,
˜
1490.8, 1365.4, 1324.9, 1297.9, 1263.2, 1236.2, 1203.4, 1161.0,
1105.1, 879.4, 810.0 cm–1. The strong peak at 1701.0 cm–1 is the νs
1
Meanwhile, these dendritic macromolecules emit intense of the C=O moiety. H NMR (CDCl3, 500 MHz): δ = 10.19 (s, 1
H, -CHO), 8.24 (d, J = 8.0 Hz, 4 H, Ar-H), 8.16 (s, 4 H, Ar-H),
7.97 (d, J = 8.0 Hz, 2 H, Ar-H), 7.72 (d, J = 8.5 Hz, 2 H, Ar-H),
7.64 (d, J = 10.5 Hz, 2 H, Ar-H), 7.45 (d, J = 8.5 Hz, 4 H, Ar-H),
7.33 (d, J = 10.5 Hz, 4 H, Ar-H), 1.40 (s, 36 H, -CH3) ppm (see
Figures S13 and S14). 13C NMR (CDCl3, 125 MHz): δ = 190.8,
142.8, 142.7, 140.0, 139.6, 135.2, 131.7, 131.6, 127.0, 126.2, 124.6,
123.6, 123.2, 119.4, 116.3, 111.1, 109.0, 34.7, 32.0 ppm (see Fig-
ure S26). MS (MALDI-TOF): calcd. 826.1; found 825.6 (see Fig-
ure S4). C59H59N3O (826.12): calcd. C 85.78, H 7.20, N 5.09; found
C 85.80, H 7.31, N 5.20.
yellow-green light and may be good candidates for photonic
devices.
Experimental Section
Ether and benzene were freshly distilled from sodium and benzo-
phenone. Pyrrole was distilled from sodium and pyridine was dis-
tilled from CaH2. N,N-Dimethylacetamide (DMAc) was dried with
P2O5. Other chemicals were used as received. 3,6-Di-tert-butyl-9H-
carbazole (4),[11] 3,6-diiodo-9-tosyl-9H-carbazole (6),[10c] and com-
pound 7[7l,8c] were prepared according to the literature. Tri(pyrrol-
1-yl)borane was prepared from LiBH4 and pyrrole by the reported
procedure and was converted into pyridine–tri(pyrrol-1-yl)borane
(13) by treatment with dry pyridine under N2.[12] 1H and 13C NMR
spectra were recorded with a Mercury plus spectrometer at 500 and
125 MHz, respectively, using CDCl3 as solvent in all cases. UV/Vis
spectra were determined with a Shimadzu UV-1601PC spectropho-
tometer. Photoluminescence (PL) spectra were recorded with a Shi-
madzu RF-5301 Luminescence spectrometer. IR spectra were mea-
sured using a Nicolet-360 FT-IR spectrometer by incorporating
samples in KBr disks. Mass spectra were performed with an Ag-
ilent 1100 and AXIMA CFR MALDI-TOF (matrix-assisted laser
desorption ionization time-of-flight) mass spectrometers (COM-
PACT). C,H,N elemental analyses were measured with a Perkin-
Elmer 240C elemental analyzer.
4-(9H-Carbazol-9-yl)benzaldehyde
(9):
Carbazole
(3.34 g,
20 mmol), 4-iodobenzaldehyde (5.0 g, 21.6 mmol), Cu2O (4.0 g,
27.8 mmol), and DMAc (15 mL) were added sequentially to a se-
aled tube under nitrogen and heated at 160 °C in an oil bath for
20 h. Then the mixture was cooled to room temperature and fil-
tered. The filtrate was poured into H2O (300 mL) and stirred for
20 min. The solid was collected by filtration and recrystallized from
EtOH to give 4.1 g (76%) of a light-yellow solid, m.p. 156.0–
158.0 °C. IR (KBr): ν = 3049.1, 2821.5, 2732.8, 1702.9, 1596.8,
˜
1512.0, 1450.3, 1361.6, 1336.5, 1317.2, 1226.6, 1209.2, 1161.0,
1103.1, 829.3, 750.2 cm–1. The strong peak at 1702.9 cm–1 is the νs
1
of the C=O moiety. H NMR (CDCl3, 500 MHz): δ = 10.14 (s, 1
H, -CHO), 8.29 (d, J = 8.0 Hz, 2 H, Ar-H), 8.22 (d, J = 8.0 Hz, 2
H, Ar-H), 7.92 (d, J = 8.5 Hz, 2 H, Ar-H), 7.54 (d, J = 8.5 Hz, 2
H, Ar-H), 7.49 (t, J = 14.5 Hz, 2 H, Ar-H), 7.36 (t, J = 14.5 Hz, 2
H, Ar-H) ppm (see Figure S11). 13C NMR (CDCl3, 125 MHz): δ =
191.0, 143.3, 140.0, 134.6, 131.3, 126.7, 126.2, 124.0, 120.8, 120.5,
109.7 ppm (see Figure S27). MS: calcd. 271.3; found 272.5 [M +
4-(3,6-Di-tert-butyl-9H-carbazol-9-yl)benzaldehyde (5): 3,6-Di-tert-
butyl-9H-carbazole (4) (2.79 g, 10 mmol), 4-iodobenzaldehyde
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H]+. C19H13NO (271.31): calcd. C 84.11, H 4.83, N 5.16; found C
84.14, H 4.75, N 5.20.
125 MHz): δ = 142.6, 140.8, 140.1, 138.2, 133.6, 131.1, 130.2, 127.4,
127.1, 126.8, 126.1, 124.0, 123.6, 123.1, 119.5, 116.7, 116.2, 110.9,
109.0, 34.7, 32.0 ppm (see Figure S30). C123H121N7O2S (1761.39):
calcd. C 83.87, H 6.92, N 5.57; found C 83.68, H 6.97, N 5.55.
4-(3,6-Diiodo-9H-carbazol-9-yl)benzaldehyde (10): Compound
9
(3.0 g, 11.1 mmol) was dissolved in refluxing acetic acid (75 mL).
The solution was cooled to 80 °C, KI (2.48 g, 14.9 mmol) and KIO3
(1.8 g, 8.4 mmol) were added, and the system was maintained at
80 °C for another 5 h. After that, the mixture was cooled to room
temperature, filtered, and then the collected solid was poured into
5% NaHSO3 (200 mL) to remove I2 and KIO3. The solid was col-
lected by filtration and recrystallized from THF to give 4.8 g (82%)
Improved Procedure for the Synthesis of Compound 11: Compound
12 (3.0 g, 1.7 mmol) was dissolved in THF (20 mL), DMSO
(10 mL), and H2O (2 mL), and then KOH (2.0 g, 35.7 mmol) was
added. The mixture was refluxed for 4 h (monitored by TLC), co-
oled to room temperature, neutralized by HCl, and then poured
into water to give the tosyl-deprotected product of 12 as a white
solid in a quantitative yield. Then the obtained products (2.7 g,
1.7 mmol), 4-iodobenzaldehyde (1.0 g, 4.3 mmol), Cu2O (1.3 g,
9.0 mmol), and DMAc (10 mL) were added sequentially to a sealed
tube under nitrogen and heated at 180 °C in oil bath for 20 h. Then
of a light-yellow solid, m.p. Ͼ250 °C. IR (KBr): ν = 3056.8, 2833.1,
˜
2740.5, 1699.1, 1596.8, 1508.1, 1465.7, 1425.2, 1359.6, 1313.4,
1274.8, 1224.6, 1207.3, 1161.0, 1018.3, 865.9, 829.3, 796.5 cm–1.
The strong peak at 1699.1 cm–1 is the νs of the C=O moiety. 1H
NMR (CDCl3, 500 MHz): δ = 10.14 (s, 1 H, -CHO), 8.76 (s, 2 H, the mixture was cooled to room temperature and filtered. The fil-
Ar-H), 8.21 (d, J = 8.0 Hz, 2 H, Ar-H), 7.90 (d, J = 8.0 Hz, 2 H,
Ar-H), 7.77 (d, J = 8.5 Hz, 2 H, Ar-H), 7.35 (d, J = 8.5 Hz, 2 H,
trate was poured into H2O (400 mL) and stirred for 20 min. The
solid was collected by filtration, purified by chromatography (silica
Ar-H) ppm (see Figure S12). 13C NMR (CDCl3, 125 MHz): δ = gel, petroleum ether/CH2Cl2, 1:2, v/v), and recrystallized from
190.7, 142.2, 139.4, 135.3, 134.5, 131.5, 129.6, 126.9, 125.0, 111.8,
83.8 ppm (see Figure S28). MS: calcd. 523.1; found 523.8 [M +
H]+. C19H11I2NO (523.11): calcd. C 43.62, H 2.12, N 2.68; found
C 43.40, H 2.26, N 2.72.
EtOH/THF (4:1, v/v) to give 2.0 g (70%) of a light-yellow solid.
The characterization data was the same as those listed above.
meso-Tris(Cz-G1)subporphyrin (1): Cz–G1–CHO (5) (1.2 g,
3.13 mmol) was added to a suspension of pyridine–tri(pyrrol-1-yl)-
borane (13) (300 mg, 1.04 mmol) in 1,2-dichlorobenzene (45 mL)
and the mixture was cooled to 0 °C in an ice bath. After the drop-
wise addition of trifluoroacetic acid (0.085 mL, 1.10 mmol)
through a syringe, the mixture immediately turned from light-yel-
low to deep-red and was stirred for 2 h at 0 °C under N2. Then the
acid was quenched with pyridine (0.1 mL) and the resulting solu-
tion was heated at reflux for 1 h. The solvent was removed by dis-
tilling the mixture. The resulting black tar was purified by
chromatography (silica gel, CH2Cl2 as an eluent) to afford crude 1.
Further chromatography (alumina, from CH2Cl2 to CH2Cl2/ethyl
acetate, 1:20, v/v as eluent) twice gave 1 as a brown-orange solid
4-{3,6-Bis[3,6-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)-9H-carbazol-
9-yl]-9H-carbazol-9-yl}benzaldehyde (11): 3,6-Di-tert-butyl-9-[3-
(3,6-di-tert-butyl-9H-carbazol-9-yl)-9H-carbazol-6-yl]-9H-carb-
azole (7) (5.0 g, 6.9 mmol), 4-(3,6-diiodo-9H-carbazol-9-yl)benzal-
dehyde (10) (1.5 g, 2.9 mmol), Cu2O (2.1 g, 14.6 mmol), and DMAc
(20 mL) were added sequentially to a sealed tube under nitrogen
and heated at 190 °C in oil bath for 24 h. Then the mixture was
cooled to room temperature and filtered. The filtrate was poured
into H2O (400 mL) and stirred for 20 min. The solid was collected
by filtration and was purified by chromatography (silica gel, petro-
leum ether/CH2Cl2, 1:2, v/v) to give 1.9 g of a white solid which
was further recrystallized three times from EtOH/THF (2:1, v/v) to
1
(28 mg, 2.0%). H NMR (CDCl3, 500 MHz): δ = 8.34–8.32 (d, 12
give 0.5 g (10%) of a white solid, m.p. Ͼ250 °C. IR (KBr): ν = H, Ar-H), 8.22 (s, 6 H, β-H), 7.96 (d, J = 7.0 Hz, 6 H, Ar-H), 7.67
˜
3047.1, 2960.3, 2902.5, 2865.8, 1704.8, 1600.7, 1490.8, 1363.5, (d, J = 8.5 Hz, 6 H, Ar-H), 7.57 (d, J = 8.5 Hz, 6 H, Ar-H), 1.52
1323.0, 1296.0, 1263.2, 1232.4, 1162.9, 1033.7, 877.5, 810.0 cm–1.
(s, 54 H, -CH3), –2.53 (s, 1 H, -OH) ppm (see Figures S19 and S20).
The strong peak at 1704.8 cm–1 is the νs of the C=O moiety. 1H
13C NMR (CDCl3, 125 MHz): δ = 143.2, 140.4, 139.1, 138.2, 135.6,
NMR (CDCl3, 500 MHz): δ = 10.23 (s, 1 H, -CHO), 8.56 (s, 2 H, 134.3, 130.5, 126.7, 123.8, 122.6, 119.8, 116.4, 109.4, 34.8, 32.0 ppm
Ar-H), 8.32–8.27 (m, 6 H, Ar-H), 8.15 (s, 8 H, Ar-H), 8.04 (d, J =
8.0 Hz, 2 H, Ar-H), 7.87 (s, 4 H, Ar-H), 7.65–7.60 (m, 8 H, Ar-H),
7.44 (d, J = 8.5 Hz, 8 H, Ar-H), 7.33 (d, J = 8.5 Hz, 8 H, Ar-H),
1.45 (s, 72 H, -CH3) ppm (see Figures S15 and S16). 13C NMR
(CDCl3, 125 MHz): (see Figure S29). MS (MALDI-TOF): calcd.
1711.3; found 1712.3 (see Figure S5). C123H119N7O (1711.31):
calcd. C 86.33, H 7.01, N 5.73; found C 86.17, H 6.92, N 5.81.
(see Figure S31). MS (MALDI-TOF): calcd. 1302.6 [M – OH]+;
found 1302.5 [M – OH]+ (see Figure S6). C93H91BN6O (1319.57):
calcd. C 84.65, H 6.95, N 6.37; found C 84.36, H 7.03, N 6.44.
meso-Tris(Cz-G2)subporphyrin (2): Cz–G2–CHO (8) (1.7 g,
2.06 mmol) was added to a suspension of pyridine–tri(pyrrol-1-yl)-
borane (13) (200 mg, 0.70 mmol) in 1,2-dichlorobenzene (30 mL)
and the mixture was cooled to 0 °C in an ice bath. After the drop-
wise addition of trifluoroacetic acid (0.056 mL, 0.73 mmol)
through a syringe, the solution was stirred for 6 h at 0 °C in the
dark under N2. The mixture slowly turned from light-yellow to
3,6-Bis[3,6-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)-9H-carbazol-9-
yl]-9-tosyl–9H-carbazole (12): 3,6-Di-tert-butyl-9-[3-(3,6-di-tert-bu-
tyl-9H-carbazol-9-yl)-9H-carbazol-6-yl]-9H-carbazole (7) (5.0 g,
6.9 mmol), 3,6-diiodo-9-tosyl-9H-carbazole (6) (1.7 g, 2.9 mmol), deep-red. The acid was quenched with pyridine (0.07 mL) and the
Cu2O (2.1 g, 14.6 mmol), and DMAc (20 mL) were added sequen-
tially to a sealed tube under nitrogen and heated at 200 °C in an
oil bath for 60 h. Then the mixture was cooled to room temperature
and filtered. The filtrate was poured into H2O (400 mL) and stirred
for 20 min. The solid was collected by filtration and recrystallized
resulting solution was heated at reflux. After 1 h the solvent was
removed by distillation from the mixture. The resulting black tar
was purified by chromatography (silica gel, CH2Cl2 as an eluent)
to afford crude 2. Further chromatography (alumina, from CH2Cl2/
petroleum ether, 1:1, to CH2Cl2/petroleum ether, 3:1, v/v as eluent)
twice gave 2 as a brown-orange solid (40 mg, 2.2%). 1H NMR
twice from EtOH/THF (4:1, v/v) to give 3.4 g (65%) of a white
1
solid, m.p. Ͼ250 °C. H NMR (CDCl3, 500 MHz): δ = 8.75 (d, J (CDCl3, 500 MHz): δ = 8.50 (m, 6 H, Ar-H), 8.44 (s, 6 H, Ar-H),
= 8.5 Hz, 2 H, Ar-H), 8.36 (s, 2 H, Ar-H), 8.25 (s, 4 H, Ar-H), 8.15 8.33 (s, 6 H, Ar-H), 8.18 (s, 18 H, Ar-H and β-H), 7.97 (d, J =
(s, 8 H, Ar-H), 8.03 (d, J = 8.0 Hz, 2 H, Ar-H), 7.95 (d, J = 8.5 Hz, 8.5 Hz, 6 H, Ar-H), 7.74 (d, J = 8.5 Hz, 6 H, Ar-H), 7.48 (d, J =
2 H, Ar-H), 7.60 (s, 8 H, Ar-H), 7.44 (d, J = 8.0 Hz, 8 H, Ar-H),
7.38–7.32 (m, 10 H, Ar-H), 2.43 (s, 3 H, -CH3), 1.45 (s, 72 H,
8.5 Hz, 12 H, Ar-H), 7.40 (d, J = 8.5 Hz, 12 H, Ar-H), 1.48 (s,
108 H, -CH3) ppm (see Figures S21 and S22). 13C NMR (CDCl3,
-CH3) ppm (see Figures S17 and S18). 13C NMR (CDCl3, 125 MHz): δ = 142.6, 140.5, 140.3, 140.1, 137.4, 136.8, 134.7, 131.3,
1070
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Eur. J. Org. Chem. 2008, 1065–1071

Synthesis of Subporphyrins with Dendritic Carbazole Arms
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C189H181BN12O (2647.35): calcd. C 85.75, H 6.89, N 6.35; found C
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borane (13) (100 mg, 0.35 mmol) in 1,2-dichlorobenzene (35 mL)
and the mixture was cooled to 0 °C in an ice bath. After the drop-
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a syringe, the solution was stirred at 0 °C for 12 h and stirred at
room temperature for 2 h in the dark under N2. The mixture turned
from light-yellow to deep-red very slowly. The acid was quenched
with pyridine (0.05 mL) and the resulting solution was heated at
reflux. After 1 h the solvent was removed by distillation from the
mixture. The resulting black tar was purified by chromatography
(silica gel, toluene as eluent) to afford crude 3. Further chromatog-
raphy (alumina, from toluene to CH2Cl2/petroleum ether, 1:1, v/v
1
as eluent) twice gave 3 as a brown-orange solid (26 mg, 1.4%). H
NMR (CDCl3, 500 MHz): δ = 8.64 (s, 6 H, Ar-H), 8.59 (s, 6 H,
Ar-H), 8.52 (s, 6 H, Ar-H), 8.30 (s, 12 H, Ar-H), 8.16 (s, 24 H, Ar-
H), 7.97 (d, J = 8.0 Hz, 6 H, Ar-H), 7.71 (d, J = 8.0 Hz, 18 H, Ar-
H), 7.64 (d, J = 8.0 Hz, 12 H, Ar-H), 7.53 (s, 6 H, β-H), 7.45 (d,
J = 8.5 Hz, 24 H, Ar-H), 7.36 (d, J = 8.5 Hz, 24 H, Ar-H), 1.47 (s,
216 H, -CH3) ppm (see Figures S23 and S24). 13C NMR (CDCl3,
125 MHz): δ = 142.6, 141.3, 141.1, 140.6, 140.2, 135.0, 132.5, 132.3,
130.9, 130.4, 128.8, 126.6, 126.1, 124.5, 123.8, 123.5, 123.1, 120.2,
119.5, 116.2, 111.9, 111.0, 109.1, 34.7, 32.0 ppm (see Figure S33).
MS (MALDI-TOF): calcd. 5281.9 [M – OH]+; found 5279.1 [M –
OH]+ (see Figure S8). C381H361BN24O (5302.91): calcd. C 86.29, H
6.86, N 6.34; found C 86.02, H 7.22, N 6.17.
[7]
Supporting Information (see also the footnote on the first page of
1
this article): H and 13C NMR spectra of all new compounds and
MALDI-TOF MS spectra of compounds 1–3, 8, and 11.
Acknowledgments
This work was financially supported by the National Natural Sci-
ence Foundation of China (NNSFC), (No. 20574027) and the Pro-
gram for New Century Excellent Talents in University (NCET).
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Received: October 17, 2007
Published Online: December 12, 2007
Eur. J. Org. Chem. 2008, 1065–1071
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1071