Synthesis, optical, electrochemical, and thermal studies on triazole-based dendrimers with diphenylamine as surface group

Article abstract of DOI:10.1016/j.tetlet.2010.07.130

Fréchet-type dendrimers with hole-transporting diphenylamine as surface group and electron-transporting triazole moiety as building block have been synthesized by convergent synthetic strategy through 'click chemistry' methodology. First generation dendri

Full text of DOI:10.1016/j.tetlet.2010.07.130

Tetrahedron Letters 51 (2010) 5167–5172
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis, optical, electrochemical, and thermal studies on triazole-based
dendrimers with diphenylamine as surface group
*
Perumal Rajakumar , Chinnadurai Satheeshkumar, Sebastian Raja
Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai 600 025, Tamil Nadu, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Fréchet-type dendrimers with hole-transporting diphenylamine as surface group and electron-transport-
ing triazole moiety as building block have been synthesized by convergent synthetic strategy through
‘click chemistry’ methodology. First generation dendrimer exhibits longer relaxation time, higher quan-
tum yield in the fluorescence spectrum, and better thermal stability than the zero and second generation
dendrimers. CV studies showed irreversible reduction potential and the formation of radical cation due to
diphenylamine moiety.
Received 27 May 2010
Revised 16 July 2010
Accepted 22 July 2010
Available online 29 July 2010
Keywords:
Dendrimers
Diphenylamine
1,2,3-Triazole
Click
Ó 2010 Elsevier Ltd. All rights reserved.
Alkynes
Azides
Synthetic aspects of dendrimers with unique physical and
chemical properties are receiving high momentum during recent
times.1–3 Dendritic molecules with varied functionalities allow
their use in diverse applications including light harvesting,4 drug
delivery,5 biomedical,6 catalysis,7 and material applications.8 Click
chemistry9,10 refers to the facile, efficient, selective, and versatile
chemical transformation to synthesize triazole system through
copper(I)-catalyzed addition of azide to alkyne (CuAAC).11 The syn-
thesis of dendrimers through click chemistry offers three advanta-
ges (i) azides and alkynes are clicked together and no protection
and deprotection protocols are needed, (ii) 1,2,3-triazole moiety
is a good ligand for metal ions and also a proton transport facilita-
tor and, (iii) gives high yield of the dendrimers with stereoselectiv-
ity on the triazole branching unit. Recently, click chemistry12
approach has been used for the synthesis of dendrimers13 with
chalcone and carbohydrate moiety at the periphery.
Diphenyalamine-based dendrimers play an indispensable role
in the field of organic light emitting devices (OLEDs),14 field effect
transistors (FETS)15, and dye-sensitized solar cells (DSSCs).16,17
Diphenylamine derivatives have been used for the synthesis of
materials for electroluminescence,18 liquid crystalline,19 electro-
lyte additive,20 and for biological applications.21 Incorporation of
triazole unit into diphenylamine-based dendrimer system would
alter the physico-chemical behaviors and also would find applica-
tions in the field of material science and biology.22
In continuation of our studies on dendrimers, we have investi-
gated the photophysical, electrochemical, and thermal properties
of diphenylamine-based triazole dendrimer 1, 2, and 3 (Fig. 1).
The dendrimers were obtained by a simple convergent route via
click chemistry.
Dendrimers 1, 2, and 3 have diphenylamine as surface group
and hence can loose an electron easily and can generate the hole.
By cascade process the triazole branching units can transfer one
of their electrons to the hole of the diphenylamine group and
hence the whole molecule can function as hole-transporting sys-
tem. Dendrons 5, 9, and 11 were synthesized in good yields as
shown in Schemes 1–3. The reaction of 1.0 equiv of diphenylamine
4 with 1.25 equiv of propargyl bromide in the presence of NaH in
dry DMF for 4 h afforded the dendron 523 in 68% yield (Scheme 1).
In order to synthesize the first generation alkyne-dendron 9,
3,5-bis(azidomethyl)phenol 7 was used as a building block, which
in turn was obtained in 74% yield by the treatment of 1.0 equiv of
3,5-bis(bromomethyl)phenyl acetate 624 with 2.1 equiv of NaN3 in
DMF at room temperature for 48 h followed by deacylation using
ethanolic KOH at reflux for 2 h. The structure of the compound 7
was characterized from spectral and analytical data.
The reaction of the bisazide 7 with acetylenic-dendron 5 under
click reaction conditions gave the dendron 8 in 79% yield. The
hydroxyl dendron 8 was also characterized from IR, 1H NMR, 13C
NMR, and EI-MS spectra. Further, the hydroxyl dendron 8 under-
goes O-alkylation with propargyl bromide in the presence of
K2CO3 in DMF at 60 °C to afford first generation acetylenic-dendron
925 in 82% yield (Scheme 2). The absorption band at 3259 cmÀ1 in
* Corresponding author. Tel.: +91 44 22202810; fax: +91 44 22300488.
E-mail address: perumalrajakumar@gmail.com (P. Rajakumar).
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.07.130

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P. Rajakumar et al. / Tetrahedron Letters 51 (2010) 5167–5172
N
N
N
N
N
N
N
N
O
N
N
N
N
N
N
N
N
N
N
N
N
N
O
N
N
N
H3C
CH3
N
N
N
H3C
CH3
N
N
N
N
N
N
CH3
N
CH3
N
N
O
N
N
N
N
N
N
N
N
1
N
2
N
N
N
N
N
N
N
N
N
N
O
N
N
N
N
N
N
N
N
N
N
N
N
N
N
O
N
N
N
N
N
N
N
O
N
N
O
N
N
N
O
H3C
CH3
N
N
N
N
N
N
N
CH3
N
N
N
N
N
O
N
N
O
N
O
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
O
N
N
N
N
N
N
N
N
N
3
Figure 1. Moelcular structure of dendrimers 1, 2 and 3.
IR spectrum showed the presence of acetylenic unit. In the 1H NMR
spectrum of dendron 9, the acetylenic protons appeared as a triplet
at d 2.33 (J = 2.1 Hz) and O-methylene protons appeared as a dou-
blet at d 4.49 (J = 2.1 Hz). The N-methylene and benzylic protons
appeared as singlets at d 5.06 and 5.34, respectively, in addition
to the aromatic protons. In 13C NMR spectrum, dendron 926
displayed four sharp peaks at d 48.6, 53.5, 55.9, and 76.3 for
acetylenic, benzylic, N-methylene, and O-methylene carbons,

P. Rajakumar et al. / Tetrahedron Letters 51 (2010) 5167–5172
5169
1
2
i
i
H
N
N3
N
5
9
i
H3C
CH3
N3
4
5
N3 CH3
Scheme 1. Reagents and conditions: (i) Propargyl bromide, NaH, DMF, room
12
temperature.
11
i
respectively. The triazole carbon appeared at d 122.2 in addition to
10 aromatic carbons. Further the mass spectrum (EI-MS) of com-
pound 9 showed the molecular ion peak at m/z 656.2.
3
Similarly, the reaction of 1.0 equiv of phenolic azide 7 with
2.1 equiv of first generation dendron 9 under click reaction condi-
tion as mentioned earlier afforded second generation phenolic
dendron 10 in 86% yield (Scheme 3). The 1H NMR spectrum of
dendron 10 displayed singlets at d 4.98, d 5.01, d 5.23, and d 5.28
for N-methylene and O-methylene protons and two sharp singlets
appeared at d 7.40 and 7.51 for –CH– protons of triazole in addition
to aromatic protons. The 13C NMR spectrum of dendron 10 dis-
played four signals at d 48.2, d 53.5, d 53.7, and d 61.7 for N-meth-
ylene and O-methylene carbons and the –CH– carbon of triazole
moiety appeared at d 120.9 and d 123.0 in addition to aromatic car-
bons. The structure of compound 10 was also confirmed by the
appearance of molecular ion peak at m/z 1540.7 [M++Na] in the
mass spectrum (MALDI-TOF). Further, 1.0 equiv of second genera-
Scheme 4. Reagents and conditions: (i) CuSO4Á5H2O (5 mol %), Na ascorbate
(10 mol %), THF/H2O (1:1), rt, 12 h, 1, 83%; 2, 85%; 3, 71%.
tion phenolic dendron 10 when treated with 1.25 equiv of propar-
gyl bromide in the presence of K2CO3 in DMF at 60 °C for 24 h gave
the second generation alkyne-dendron 11 in 73% yield (Scheme 3).
The 1H NMR spectrum of dendron 11 showed a triplet at d 2.45
(J = 2.1 Hz) for acetylenic proton, a doublet at d 4.57 (J = 2.1 Hz) for
O-methylene protons adjacent to the acetylenic unit, and the two
different types of triazole –CH– protons appeared as singlets at d
7.35 and d 7.56, respectively in addition to the aromatic protons.
The 13C NMR spectrum of dendron 11 displayed the acetylenic
and O-methylene carbons at d 48.4, 53.3, 53.7, 55.9, 61.7, 76.6,
OH
O
OR
iv
N
N
N
N
iii
N
N
N
N
N
N
N
N
E
E
N
N
N
N
6, R = COCH3
E = CH2Br
8
9
i
ii
7, R = H
E = CH2N3
Scheme 2. Reagents and conditions: (i) NaN3, DMF, room temperature, 48 h; (ii) EtOH, KOH, reflux, 2 h; (iii) 5 (2.1 equiv), CuSO4Á5H2O (5 mol %), Na ascorbate, (10 mol %),
THF/H2O (1:1), rt, 79%, 12 h, (iv) propargyl bromide, K2CO3, DMF, 60 °C, 24 h, 82%.
O
OH
N
N
N
N
i
N
N
N
N
N
N
N
N
ii
7
O
N
O
N
O
N
O
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
10
11
Scheme 3. Reagents and conditions: (i) 9 (2.1 equiv), CuSO4Á5H2O (5 mol %), Na ascorbate (10 mol %), THF/H2O (1:1, v/v), rt, 86%, 12 h; (ii) propargyl bromide, K2CO3 DMF,
60 °C, 24 h, 73%.

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P. Rajakumar et al. / Tetrahedron Letters 51 (2010) 5167–5172
Figure 2. MALDI-TOF-MS spectra of dendrimer 1 (A), 2 (B) and 3 (C).
and 77.5 and the triazole –CH– carbons at d 120.6 and 123.4. The
appearance of molecular ion peak at m/z 1556 in mass spectrum
(FAB-MS) further confirmed the structure of the dendrimer 11.27
Synthesis of diphenylamine-based triazole dendrimers 1, 2, and
3 through 1,3-dipolar cycloaddition of alkynes 5, 9, and 11 with
the azide 1212 via click chemistry28 is summarized in Scheme 4.
The reaction of 1.0 equiv of triazide 12 with 3.3 equiv dendritic
arm 5, 9, and 11 in the presence of CuSO4Á5H2O (5 mol %) and so-
dium ascorbate (10 mol %) in a mixture of THF/water (1:1) afforded
the dendrimers 1, 2, and 3 in 83%, 85%, and 71% yields, respectively
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
2
1
3
(Scheme 4). The structure of the dendrimers 1,29 30, and 331 was
2
completely characterized from spectral and analytical data. Figure
2 shows the MALDI-TOF MS spectrum of dendrimer 1, 2, and 3.
The absorption and emission spectra of dendrimers 1, 2, and 3
were recorded in DMSO (1 Â 10À5 M) at room temperature and
the values are summarized in Table 1. Dendrimers 1, 2, and 3 exhi-
bit strong absorption bands in the range of 291–293 nm. The incor-
poration of more number of triazole moiety with diphenylamine as
surface group may cause the resulting molecules to be less copla-
nar. Furthermore, as the number of diphenylamine chromophores
increases from zero to first, then to second generation, the molar
extinction coefficient also increases at the constant concentration
of dendrimers 1, 2, and 3 which indicates that the amount of light
absorbed by the dendritic antenna increases with the increase in
the generation.32
300
320
340
360
380
400
420
440
460
wavelength (nm)
Figure 3. Emission spectrum of dendrimers 1, 2 and 3.
dendrimers due to the valency effect. However, in dendrimer 3
extensive steric crowding suppresses the valency effect of the
diphenylamine surface group and hence the quantum yield de-
creases. In dendrimer 3, steric factor and valency effect35 act in
the opposite direction and the valency effect is suppressed by ex-
cess crowding of the surface and branching units. Alternatively, a
better solute-solvent interaction for the compound with increasing
charge transfer may also decrease the quantum yield.36
In order to understand the nature of the excited state, life time
measurements of the dendrimers 1, 2, and 3 were recorded using
IBH, TCSPC technique on excitation at 365 nm in DMSO as solvent.
The fluorescence decay fits as bi-exponential with life time s1 and
Dendrimers 1, 2, and 3 showed strong fluorescence between
350 and 373 nm and the emission maxima at 373 nm was ob-
served for the dendrimer
3 (Fig. 3). A red-shift maxima
(kem = 373 nm) was observed for second generation dendrimer 3
when compared to those of the corresponding zero and first gener-
ation dendrimers 1 and 2 due to the increase in the number of do-
nor amine surface group, which is also called the valency effect in
dendrimers. The increase in the number of triazole moiety in the
dendrimers might perturb the coplanarity altering the fluorescence
nature of the dendrimers.
s
2 as 2.97 and 8.72; 2.97 and 10.2; 2.86, and 9.66 ns for dendrimers
1, 2, and 3, respectively (Table 2).
The fluorescence decay (Fig. 4) of dendrimer 2 shows a longer
relaxation time s2 than for the dendrimer 1 and 3 and the ampli-
tude A1 is comparatively greater than A2 for all the dendrimers.
However, A1 for dendrimer 3 is greater than for dendrimer 1 and
2. Excessive crowding in dendrimer 3 dominates and hence the
Further, the fluorescence quantum yields (Uf) of dendrimers 1,
2, and 3 were measured in DMSO using tryptophan33 as the stan-
dard. The quantum yields of dendrimers 1, 2, and 3 are found to
be 0.16, 0.19, and 0.17, respectively. In general, increase in the
number of diphenylamime moiety might lead to increase in the
fluorescence quantum efficiency.34 Hence, dendrimer 3 could be
expected to show the higher quantum efficiency among all the
lifetime (s2) and relative amplitude (A2) are found to be less. The
presence of more number of triazole and diphenylamine surface
Table 1
Table 2
Absorption, emission and thermal data of dendrimers 1, 2 and 3
Lifetime relaxation and amplitude of dendrimers 1, 2 and 3
Dendrimers kabs max (nm)
e
(mol/L)
kem max (nm) UF
Tdecg (°C)
Dendrimers
Analysis
Life time (ns)
Amplitude (%)
1
2
3
291
293
293
8.44 Â 104 350, 364
1.35 Â 105 351, 364
1.87 Â 105 360, 373
0.16 390
0.19 522
0.17 481
s1
s2
A1
A2
1
2
3
Bi-exponential
Bi-exponential
Bi-exponential
2.97
2.97
2.86
8.72
10.2
9.66
92.98
70.20
96.93
07.02
29.80
03.07
g
Determined by thermal gravimetric analyzer with a heating rate of 10 °C/min
under N2.

P. Rajakumar et al. / Tetrahedron Letters 51 (2010) 5167–5172
5171
of the dendrimers in the presence of 0.1 M of Bu4NPF6 as a support-
ing electrolyte was used in all the experiments. All solutions were
purged with purified N2 gas for about 10 min before carrying out
the CV studies. The cyclic voltammogram was recorded from 2.0
to À1.6 against Ag/AgCl reference electrode. We have observed
an irreversible cyclic voltammetry response in both anodic and
cathodic side for all the three dendrimers. The resulting peak po-
tential and peak current values are given in Table 3.
During the anodic scan there is a possibility for the formation of
carbocation due to the loss of single electron from the diphenyl-
amine molecules. On the other hand, there is an irreversible reduc-
tion peak at about À1.3 V due to the reduction of diphenylamine
molecule. A similar oxidation peak potential +1.0 V versus Ag/AgCl
for diphenylamine was noted in the literature.37 This indicates the
formation of radical cation and the reaction mechanism for the
electron transfer process is shown in Scheme 5.
The oxidation peak potential values for 1 and 3 are almost sim-
ilar whereas for dendrimer 2 the peak potential is less positive than
the others. From the CV (Fig. 5) it is clear that on increasing the
number of diphenylamine group in the periphery, the oxidation
potential abruptly decreases which could be due to the intramolec-
ular interactions within diphenylamine moiety. Recent studies
have shown that there is no redox reaction for triazole group pres-
ent in ferrocene monolayer assembly, which was generated by
click reaction between azidoundecanethiol and ferrocenepropy-
none.38 Hence, the present study confirms that the redox process
is purely due to single electron transfer reaction on the diphenyl-
amine moiety.
Figure 4. Fluorescence decay of dendrimers 1, 2 and 3.
Table 3
The electrochemical parameters obtained for the dendrimers 1, 2 and 3 in DMF at
26 °C
Dendrimers
Epa (mV)
Epc (mV)
1
2
3
1.30
1.37
1.13
À0.83
À1.11
À0.85
In conclusion, a highly efficient synthesis of triazole-based den-
drimers 1, 2, and 3 with diphenylamine as surface group has been
achieved in excellent yields. All the dendrimers synthesized were
thoroughly characterized from spectral and analytical data and
all the dendrimers exhibit UV absorption at 291–293 nm and emis-
sion at 350–373 nm. Dendrimer 2 exhibits higher quantum yield,
longer relaxation time in the fluorescence spectrum, and better
thermal stability than dendrimers 1 and 3, and in CV studies, den-
drimer 2 showed multi-reduction wave potentials with large posi-
tive value than the dendrimer 1 and 3. The antioxidant properties
of the other similar dendrimers are underway.
groups with less steric interaction makes dendrimer 2 as a better
fluorescence-sensing material than dendrimers 1 and 3.
All the dendrimers showed good thermal stability as deter-
mined by thermo gravimetric analysis. However, dendrimer 2
exhibited higher thermal stability with decomposition tempera-
ture (Tdec) 522 °C (Table 1) than dendrimer 1 and 3. The excess
crowding in dendrimer 3 slightly decreased its thermal stability.
The electrochemical behavior of diphenylamine-terminated
dendrimers has been investigated using cyclic voltammetry tech-
nique. A single compartment cell containing 0.1 mM concentration
e-
N
R
H
N
R
N
R
-
R = Dendrimer
Scheme 5. Formation of radical cation in diphenylamine moiety.
3
1
2
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
Potential Vs Ag/Agcl
Potential Vs Ag/Agcl
Potential Vs Ag/Agcl
Figure 5. Cyclic voltammograms of dendrimers 1, 2 and 3 in DMF (1 Â 10À5 M) presence of Bu4NPF6 (0.1 M) at 50 mV/s scan rate.

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P. Rajakumar et al. / Tetrahedron Letters 51 (2010) 5167–5172
25. General procedure for the synthesis of alkyne dendrons: A mixture of phenolic
Acknowledgments
dendron (1.1 mmol), propargyl bromide (1.2 mmol) and K2CO3 (0.3 g,
2.1 mmol) in dry DMF (10 mL) was stirred at 60 °C for 10 h. The reaction
mixture was then extracted with CHCl3 (2 Â 100 mL) washed with water
(100 mL), dried (Na2SO4) and concentrated in vacuo and the resulting crude
product was purified by column chromatography (SiO2) using CHCl3/MeOH
(99:1) as the eluent.
Authors thank the University Grant Commission (UGC), New
Delhi for financial assistance and the DST-FIST for providing NMR
spectral facility to the department and C.S. thank the National Cen-
ter for Ultra Fast Processes, the University of Madras for fluores-
cence studies, and Dr. K. Pandian, Department of Inorganic
chemistry, University of Madras for fruitful discussions on CV
studies.
26. Dendron 9: Yield 0.67 g (82%). 1H NMR (300 MHz, CDCl3): d = 2.33 (t, J = 2.1 Hz,
1H); 4.49 (d, J = 2.1 Hz, 2H); 5.06 (s, 4H), 5.34 (s, 4H); 6.54 (s, 1H); 6.62 (s, 2H);
6.93 (t, J = 7.5 Hz, 4H); 7.05 (d, J = 8.1 Hz, 8 H); 7.22 (t, J = 7.5 Hz, 8H); 7.26 (s,
2H). 13C NMR (75 MHz, CDCl3): d = 48.6, 53.5, 55.9, 76.3, 77.6, 114.1, 119.6,
120.9, 121.9, 122.2, 129.4, 137.2, 146.3, 147.4, 158.4. MS (EI) m/z = 656.2 [M+].
Elemental Anal. Calcd for C41H36N8O: C, 74.98; H, 5.52; N, 17.06. Found: C,
74.87; H, 5.43; N, 17.13.
References and notes
27. Dendron 11: Yield 0.85 g (73%); mp 95–98 °C (dec); 1H NMR (300 MHz, CDCl3):
d = 2.45 (t, J = 2.1 Hz, 1H); 4.57 (d, J = 2.1 Hz, 2H); 4.97 (s, 4H); 5.04 (s, 8H); 5.29
(s, 8H); 5.43 (s, 4H); 6.49 (s, 2H); 6.63 (s, 4H); 6.82 (s, 3H); 6.89 (t, J = 7.2 Hz,
8H); 7.04 (d, J = 8.4 Hz, 16H); 7.19 (t, J = 7.8 Hz, 16H); 7.35 (s, 4H); 7.56 (s, 2H).
13C NMR (75 MHz, CDCl3): d = 48.4, 53.3, 53.7, 55.9, 61.7, 76.4, 77.5, 114.1,
114.8, 119.3, 120.6, 120.9, 121.9, 122.7, 123.4, 129.9, 137.1, 137.2, 143.5, 146.0,
147.3, 158.5, 158.9. MS (FAB): m/z = 1556 [M+]. Elemental Anal. Calcd for
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28. General procedure for Cu-catalyzed Huisgen click reaction: A mixture of azide
(0.32 mmol), alkyne (1.04 mmol), CuSO4.5H2O (5 mol %), and sodium ascorbate
(10 mol %) in a mixture of THF/H2O (1:1, v/v, 20 mL) was stirred for 12 h at
room temperature. The residue obtained after evaporation of the solvent was
washed thoroughly with water and dissolved in CHCl3 (150 mL). The organic
layer was separated, washed with brine (1 Â 150 mL), dried (anhydrous
Na2SO4), and evaporated to give the crude triazole, which was purified by
column chromatography (SiO2) using the eluent as mentioned under each
compound.
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29. Dendrimer 1: Yield 0.75 g (83%); mp 158–160 °C. 1H NMR (300 MHz, CDCl3):
d = 2.14 (s, 9H); 5.02 (s, 6H); 5.43 (s, 6H); 6.92 (t, J = 7.2 Hz, 6H); 7.02 (d,
J = 8.1 Hz, 12H); 7.20 (t, J = 7.5 Hz, 12H); 7.25 (s, 3H). 13C NMR (75 MHz,
CDCl3): d = 16.5, 48.3, 48.9, 121.0, 121.6, 121.7, 129.3, 130.4, 139.5, 145.6,
147.5. MS (MALDI-TOF): m/z = 907.2 [M+], 946.12 [M+K+]. Elemental Anal.
Calcd for C57H54N12: C, 75.47; H, 6.00; N, 18.53. Found: C, 75.56; H, 6.14; N,
18.64.
30. Dendrimer 2: Yield 0.5 g (85%); mp 103–106 °C. 1H NMR (300 MHz, CDCl3):
d = 2.37 (s, 9H); 4.92 (s, 6H); 5.02 (s, 12H); 5.25 (s, 12H); 5.61 (s, 6H); 6.47 (s,
3H); 6.61 (s, 6H); 6.88 (t, J = 7.2 Hz, 12H); 7.02 (d, J = 7.8 Hz, 24H); 7.18 (t,
J = 7.8 Hz, 24H); 7.33 (s, 6H); 7.44 (s, 3H). 13C NMR (75 MHz, CDCl3): d = 16.8,
48.4, 49.1, 53.5, 61.8, 114.1, 119.2, 120.9, 121.9, 122.7, 122.8, 129.4, 130.6,
137.2, 139.9, 143.1, 146.1, 147.3, 158.9. MS (MALDI-TOF): m/z = 2254.9 [M+],
2279.5 [M+Na+]. Elemental Anal. Calcd for C135H123N33O3: C, 71.88; H, 5.50; N,
20.49. Found: C, 71.95; H, 5.59; N, 20.57.
31. Dendrimer 3: Yield 0.19 g (71%); mp 102–104 °C. 1H NMR (300 MHz, CDCl3):
d = 2.22 (s, 9H); 4.84 (s, 12H); 4.91 (s, 24H); 5.15 (s, 24H); 5.26 (s, 18H); 5.46 (s,
6H); 6.36 (s, 9H); 6.51 (s, 18H); 6.69–7.20 (m, 120H); 7.35 (s, 12H); 7.48 (s, 9H).
13C NMR (75 MHz, CDCl3): d = 15.8, 28.7, 47.3, 52.3, 52.5, 60.6, 112.9, 113.6,
116.8, 119.1, 119.9, 120.7, 121.5, 122.0, 122.6, 128.3, 129.6, 136.2, 136.3, 138.8,
142.4, 145.3, 146.4, 157.9. MS (MALDI-TOF): m/z = 4991.4 [M+K+]. Elemental
Anal. Calcd for C291H261N75O9: C, 70.57; H, 5.31; N, 21.21. Found: C, 70.69; H,
5.28; N, 21.16.
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