Binding ability of first and second generation/carbazolylphenyl dendrimers with Zn(ii) tetraphenylporphyrin core towards small heterocyclic substrates

Article abstract of DOI:10.1039/c3ra45660a

A study of complex formation of Zn(ii) tetraarylporphyrin dendrimers with carbazolylphenyl branches towards 1,4-diazabicyclo-[2.2.2]octane, pyridine, imidazole, N-methylimidazole and 1,2,3-triazole was carried out by spectrophotometric and ¹H NMR titration methods. It has been shown that the binding ability of the porphyrin receptors towards mono and bidentate N-containing substrates depends on the nature, number and generation of the branches. Bulky substituents are able either to significantly reduce the binding ability of the tetrapyrrolic cores due to the shielding of the porphyrin reaction centres, or to significantly increase it by forming intramolecular cavities for complementary binding of substrates. It has been determined that due to a good geometric match of the ligand's size with the size of the intramolecular cavities of the porphyrin receptors, and by the existence of additional hydrogen bonding and/or π-π interactions between the ligand and the triazole fragments of the porphyrin the Zn-tetraarylporphyrins with eight 4-carbazolylphenyl-1,2,3-triazole end groups of the first and the second generations could be used as effective receptors for imidazole, N-methylimidazole and 1,2,3-triazole. Taking into account the fact that binding is accompanied by a clear and easily identifiable response in the UV-Vis spectra of the reaction mixture, these metalloporphyrins could be considered as molecular optical sensing devices for small heterocyclic substrates.

Full text of DOI:10.1039/c3ra45660a

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PAPER
Binding ability of first and second generation/
carbazolylphenyl dendrimers with Zn(II)
tetraphenylporphyrin core towards small
heterocyclic substrates†
Cite this: RSC Adv., 2014, 4, 19703
Nguyen Tran Nguyen,a Galina M. Mamardashvili,b Olga M. Kulikova,b
c
b
a
*
*
Ivan G. Scheblykin, Nugzar Zh. Mamardashvili and Wim Dehaen
A study of complex formation of Zn(II) tetraarylporphyrin dendrimers with carbazolylphenyl branches
towards 1,4-diazabicyclo-[2.2.2]octane, pyridine, imidazole, N-methylimidazole and 1,2,3-triazole was
carried out by spectrophotometric and 1H NMR titration methods. It has been shown that the binding
ability of the porphyrin receptors towards mono and bidentate N-containing substrates depends on the
nature, number and generation of the branches. Bulky substituents are able either to significantly reduce
the binding ability of the tetrapyrrolic cores due to the shielding of the porphyrin reaction centres, or to
significantly increase it by forming intramolecular cavities for complementary binding of substrates. It has
been determined that due to a good geometric match of the ligand's size with the size of the
intramolecular cavities of the porphyrin receptors, and by the existence of additional hydrogen bonding
and/or p–p interactions between the ligand and the triazole fragments of the porphyrin the Zn-
tetraarylporphyrins with eight 4-carbazolylphenyl-1,2,3-triazole end groups of the first and the second
generations could be used as effective receptors for imidazole, N-methylimidazole and 1,2,3-triazole.
Taking into account the fact that binding is accompanied by a clear and easily identifiable response in
the UV-Vis spectra of the reaction mixture, these metalloporphyrins could be considered as molecular
optical sensing devices for small heterocyclic substrates.
Received 8th October 2013
Accepted 9th April 2014
DOI: 10.1039/c3ra45660a
www.rsc.org/advances
human hemoglobin in which the iron porphyrin (heme) is
surrounded by a globular protein (globin).9,10 In both cases, the
Introduction
xation of oxygen occurs as a result of its coordination at the
iron atom. It is assumed that a causal factor responsible for the
affinity of O2 to dendrimer porphyrins is the formation of
hydrogen bonds between oxygen molecules and the amide
groups of the branches' rst generation. The design and prop-
erties of “patched dendrimers” has been described,11 in which
different types of oligopeptide dendrons are asymmetrically
introduced on the Zn(II) porphyrin core. The “patch” gives the
porphyrin dendrimer an additional interface to bind with
another molecule or macromolecule. “patched dendrimers”
with porphyrin cores show molecular recognition phenomena
at the nanoscale, which provides good insight into the biolog-
ical molecular recognition performed by proteins and enzymes.
Porphyrin-based dendrimers are oen using as photofunc-
tional articial receptors, in which the strong photoabsorption
and intense uorescence signals of the porphyrin can respond
sensitively to substrate binding.12–17
Dendrimers are monodisperse macromolecules with highly
branched three-dimensional structures. Given the fact that the
size of dendrimeric macromolecules can be predicted and
controlled with a high accuracy they are oen called a new
generation of polymers and have a great future as polyfunc-
tional materials. The presence of channels and pores allows
them to encapsulate and/or activate small guest molecules,
including physiologically active ones.
According with the literature, porphyrin-based dendrimers
are of great interest.1–8 It was found that Fe(II) porphyrins con-
taining polyethylenglycol branches have
a much higher
(1500 times) constant of reversible binding of O2 compared with
aMolecular Design and Synthesis, Department of Chemistry, KU Leuven,
Celestijnenlaan 200F, B-3001 Leuven, Belgium. E-mail: wim.dehaen@chem.
kuleuven.be; Fax: +32 16 327990; Tel: +32 16 3 27439
bCoordination Chemistry of Macrocyclic Compounds, G.A. Krestov Institute of Solution
Chemistry of Russian Academy of Sciences, Akademicheskaya St.1, 153045 Ivanovo,
Russia
cLund University, Department of Chemical Physics, P.O. Box 124, 22100, Lund, Sweden
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c3ra45660a
This paper investigates the binding ability of Zn-tetraary-
lporphyrins with different number [two (ZnD1-G1, ZnD4-G1,
ZnD7-G2), four (ZnD2-G1, ZnD5-G1, ZnD8-G2) and eight (ZnD3-
G1, ZnD6-G1, ZnD9-G2)] and generation [the rst (ZnD1-G1,
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ZnD2-G1, ZnD3-G1, ZnD4-G1, ZnD5-G1, ZnD6-G1) and the
second (ZnD7-G2, ZnD8-G2, ZnD9-G2)] of carbazolylphenyl
branches towards 1,4-diazabicyclo-[2.2.2]octane (L1), pyridine
(L2), imidazole (L3), N-methylimidazole (L4) and 1,2,3-triazole
(L5) in toluene. The dendrimers also differ by the nature of
bridging spacers [oxygen (ZnD1-G1, ZnD2-G1, ZnD3-G1) and
1,2,3-triazole (ZnD4-G1, ZnD5-G1, ZnD6-G1, ZnD7-G2, ZnD8-
G2, ZnD9-G2)] connecting the tetraarylporphyrin core and car-
bazolylphenyl fragments. Zn(II) tetraphenylporphin (ZnTPP)
was taken as the object of comparison. The compounds ZnD4-
G1, ZnD5-G1, ZnD6-G1, ZnD7-G2, ZnD8-G2, ZnD9-G2 were
previously synthesized18 as new uorescent switches and pho-
toactive devices for detection of substrates of different nature.
Result and discussion
Synthesis
Scheme 2 Dendrimers H2D1-G1 (7), H2D2-G1 (8), H2D3-G1 (9).
The synthesis of dendrimers H2D1-G1, H2D2-G1 and H2D3-G1
was based on Lindsey method starting from 5-mesityldipyrro-
methane19 or pyrrole and carbazole-based aldehydes.
with 0.3 equivalent of BF3$OEt2. Similarly, 5,10,15,20-tetrakis[4-
(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenoxy)me-thylphenyl]
porphyrin (8) was obtained in 15% when arylaldehyde (3) was
reacted with pyrrole under the same conditions that were used
to make dendrimer (7). The synthesis of 5,10,15,20-tetrakis[3,5-
bis((4-(3,6-di-tert-butyl-9H-carbazol-9-yl)-phenoxy)methyl)-2,4,6-
trimethylphenyl] porphyrin (9) was unsuccessful when using
the procedure that applied for making dendrimer (7). In the
presence of 0.75% absolute ethanol in dry CH2Cl2, the tetra-
substituted porphyrin (9) was obtained in 5%. The increase in
the amount of Lewis acid catalyst from 0.3 to 0.8 equivalent as
well as the condensation time between (6) and pyrrole did not
lead to any change in the yield of dendrimer (9). The low yield of
making dendrimer (9) was due to the sterically hindered methyl
groups at 2 and 6 positions and bulky groups at 3 and 5 posi-
tions of compound (6). Dendrimers (7), (8) and (9) were then
metallated in CHCl3 to obtain ZnD1-G1, ZnD2-G1 and ZnD3-G1
in quantitative yield.
The nucleophilic substitution reaction of 4-(3,6-di-tert-butyl-
9H-carbazol-9-yl)phenol (1)20 and 4-bromomethylbenzaldehyde
(2)21 in DMF resulted in the formation of 4-[(4-(3,6-di-tert-butyl-
9H-carbazol-9-yl)phenoxy)methyl]benzaldehyde (3) (Scheme 1).
Similarly, the mixture of arylaldehydes consisting of 3,5-bis(-
bromomethyl)-2,4,6-trimethylbenzaldehyde (4) and 3-bromo-
methyl-5-chloromethyl-2,4,6-trimethylbenzaldehyde (5)18 was
reacted with (1) and 3,5-bis[(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)-
phenoxy)methyl]-2,4,6-trimethylbenzaldehyde (6) was obtained
(Scheme 1) in pure form aer column chromatography
purication.
The condensation between arylaldehyde (3) and 5-mesi-
tyldipyrromethane19 was carried out in dry CH2Cl2 and the
presence of a Lewis acid catalyst BF3$OEt2 at room temperature.
Then p-chloranil was used as oxidant and the reaction mixture
was reuxed for 1 hour. The starting materials' concentration
was optimized at 10 mM in CH2Cl2, the yield of 5,15-bis(2,4,6-
trimethylphenyl)-10,20-bis[4-(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)-
phenoxy)methylphenyl] porphyrin (7) (Scheme 2) reached 34%
Dendrimers ZnD4-G1, ZnD5-G1, ZnD6-G1, ZnD7-G2, ZnD8-
G2, ZnD9-G2 (Scheme 3) were synthesized via the copper(I)-
catalyzed azide–alkyne cycloaddition (CuAAC reaction or click
reaction) in THF solvent under [Cu(NCCH3)4][PF6] catalysis.18
Binding ability
The strength of axial binding of electron donating ligands (L) on
Zn(II) porphyrins (ZnP) depends on the degree of aromaticity of
the tetrapyrrolic macrocycle.22,23 The aromaticity of the tetra-
pyrrolic macrocycle is higher, the more strongly a zinc cation is
connected with the macrocycle nitrogen atoms. The reasons of
decreasing of the tetrapyrrolic macrocycle aromaticity can be
both the electronic inuence of the substituents, and a spatial
factor causing distortion of the planar structure of the tetra-
pyrrolic macrocycle, especially due to unsymmetrical substitu-
tion with bulky substituents.
Next to distortion of the planar structure of the tetrapyrrolic
macrocycle, bulky substituents can also create steric hindrance
Scheme 1 Synthesis of carbazole-based aldehydes.
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leads to an increase in the stability constants of the 1 : 1
complexes between the dendrimers (ZnD1-G1, ZnD2-G1, ZnD7-
G2, ZnD8-G2) and monodentate ligands L2–L5 as compared
with the similar complexes of ZnTPP (Fig. S2 and Table 1)
(ESI†). This could be explained by distortion of the planar
structure of the tetrapyrrolic macrocycle due to substitution
with bulky groups.
The decreasing of the binding ability of the para-substituted
porphyrins with two (ZnD4-G1) and four (ZnD5-G1) 4-(4-(3,6-
bis(t-butyl)carbazol-9-ylphenyl)-1,2,3-triazole) branches of the
rst generation as compared with the corresponding complexes
of ZnTPP with L2–L524 probably is the result of shielding of the
metalloporphyrin central zinc cation by one of the carbazolyl-
phenyl fragments. The optimized structures of the dendrimers
ZnD1-G1, ZnD4-G1 and ZnD7-G2 are given as an example of the
validation of provided assumption on Fig. S3 (ESI†). Tetra-
substituted dendrimers ZnD2-G1, ZnD5-G1 and ZnD8-G2 are
characterized by the same features.
It should be noted that meta-octasubstitution of the tetra-
pyrrolic core phenyl groups by eight 4-(4-(3,6-bis(t-butyl)carba-
zol-9-ylphenyl)-1,2,3-triazole branches of the rst (ZnD6-G1)
and the second (ZnD9-G2) generations leads to an increase in
the stability constants of the 1 : 1 complexes between the den-
drimers and the monodentate ligands L2–L5 as compared with
the similar complexes of ZnTPP and para-substituted den-
drimers ZnD1-G1, ZnD2-G1, ZnD3-G1, ZnD4-G1, ZnD5-G1,
ZnD7-G2, ZnD8-G2.24 As could be seen from Table 1, among the
complexes of ZnD6-G1 with L2–L524 the complex between ZnD6-
G1 and L4 has the highest stability constant. This could be
explained by a good geometric match of the ligand size to the
size of the intramolecular cavities of the porphyrinic receptor.
The decrease in the value of the binding constant of the
complexes between ZnD9-G2 and L4 in comparison with the
similar complexes of the dendrimer with L3 testies that beside
a good geometric match between host–guest molecules the
formation of additional hydrogen bonding interactions
between the L3 and the triazole fragments of ZnD9-G2 may be
possible.
Scheme 3 Structures of dendrimers ZnD4-G1, ZnD5-G1, ZnD6-G1,
ZnD7-G2, ZnD8-G2, ZnD9-G2.
to the ligands axial coordination due to shielding of the met-
alloporphyrin reaction center from both sides or a single side of
the molecule. On the other hand, highly branched bulky
substituents may form intramolecular binding cavities for
effective binding of guest molecules.
Axial coordination of L1–L5 (Scheme 4) to ZnP is accompa-
nied by a characteristic red shi of the absorption bands in the
UV-Vis spectra of the system ZnP–L and a high eld shi of the
ligand protons signals in the 1H NMR spectra of the corre-
sponding complexes. It should be noted that upon complexa-
tion of ZnP with monodentate ligands L2–L5, over a wide
concentration range of the ligands (CL ¼ 1 ꢀ 10ꢁ7 to 8 ꢀ
10ꢁ2 M), changes in the UV-Vis spectra of the reaction mixture
occur with the formation of one family of spectral curves with
one set of isosbestic points. The titration curve has one step,
which indicates the formation of a single type of complexes in a
ratio of 1 : 1. The details of the spectrophotometric and 1H NMR
titration are described in the preliminary communication.24 The
changes in the UV-Vis spectra of the system ZnD3-G1–L3 and
the corresponding binding isotherms are depicted on Fig. S1 as
an example (ESI†).
The dendrimers ZnD6-G1, ZnD9-G2 can be seen as a “picket-
fence” porphyrins with intramolecular cavities formed by the 4-
carbazolylphenyl-1,2,3-triazole end groups emanating from
both sides of the porphyrin core (Fig. S4) (ESI†).24
It was found that para-substitution of the tetrapyrrolic core
phenyl groups by two (ZnD1-G1) or four (ZnD2-G1) 4-(4-(3,6-
bis(t-butyl)carbazol-9-ylphenyl)-oxy) fragments and by two
(ZnD7-G2) or four (ZnD8-G2) 4-(4-(3,6-bis(t-butyl)carbazol-9-
ylphenyl)-1,2,3-triazole) branches of the second generation
Table 1 Stability constants of 1 : 1 complexes (Kassoc 1, Mꢁ1) between
ZnP and monodentate ligands L2–L5 in toluene, CZnP z 1.1 ꢀ 10ꢁ5 M
L2
L3
L4
L5
ZnTPP
5800
26460
39550
86 900
79 500
186 300
5050
480
8030
11 090
87 700
90
240
660 000
9050
15 100
810 500
ZnD1-G1
ZnD2-G1
ZnD3-G1
ZnD4-G1
ZnD5-G1
ZnD6-G1
ZnD7-G2
ZnD8-G2
ZnD9-G2
24 180
26 400
30 500
1200
120 800
118 050
250 000
7250
11 700
545 600
70 400
80 250
600 500
3900
8500
110 000
30 530
25 000
115 000
782 500
43 000
61 800
360 000
Scheme 4 Structures of ligands L1–L5.
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Table 2 The stability constants of 1 : 1 and 2 : 1 complexes of ZnP with
bidentate ligand L1 in toluene at 25 ꢂC, CZnP z 1.5 ꢀ 10ꢁ5 Ma
On the other hand, the meta-octasubstituted dendrimer
ZnD3-G1 can not form similar intramolecular cavities for the
ligand due to the lack of 1,2,3-triazole bridging fragments
between tetrapyrrolic core and carbazolylphenyl branches. This
is the reason why the binding ability of ZnD3-G1 towards L2–L5
is much less in comparison with ZnD6-G1,24 ZnD9-G2 and it is
comparable while signicantly higher than the corresponding
values for ZnD1-G1, ZnD2-G1 (Table 1). The dependence of the
stability constants of octa-substituted dendrimers ZnD3-G1,
ZnD6-G1, ZnD9-G2 with L2–L5 on the nature of small N-con-
taining organic molecules is summarized in Fig. 1.
In line with our interests in the supramolecular chemistry of
porphyrins,25–28 we also investigated the binding ability of ZnD1-
G1, ZnD2-G1, ZnD3-G1, ZnD4-G1, ZnD5-G1, ZnD6-G1, ZnD7-G2,
ZnD8-G2, ZnD9-G224 towards the bidentate ligand L1. It is well
known that upon interaction of ZnP with bifunctional nitrogen
containing ligands formation of the complexes in a ratio of
either 1 : 1 or 2 : 1 is possible.29–31 Spatially distorted porphyrins
or porphyrins with bulky substituents do not form complexes
with L1 in a ratio of 2 : 1.
2 : 1 complexes,
1 : 1 complexes,
Kassoc 2, (Mꢁ2
)
Kassoc 1, (Mꢁ1
)
ZnTPP
5.0 ꢀ 109
6.0 ꢀ 109
6.0 ꢀ 109
4.0 ꢀ 1010
1.7 ꢀ 108
1.3 ꢀ 109
—
1.9 ꢀ 105
2.1 ꢀ 105
2.2 ꢀ 105
2.1 ꢀ 105
2.3 ꢀ 104
9.7 ꢀ 104
1.3 ꢀ 106
2.1 ꢀ 105
2.9 ꢀ 105
7.4 ꢀ 105
ZnD1-G1
ZnD2-G1
ZnD3-G1
ZnD4-G1
ZnD5-G1
ZnD6-G1
ZnD7-G2
ZnD8-G2
ZnD9-G2
7.0 ꢀ 109
8.0 ꢀ 109
—
a
The error in determining the stability constants was 5–7% (for 1 : 1
complexes) and 10% (for 2 : 1 complexes).
stages. The changes in the UV-Vis spectra of the system ZnD3-
G1–L1 in toluene are depicted in Fig. 2 as an example.
The study of complex formation of dendrimers with two
(ZnD1-G1, ZnD4-G1, ZnD7-G2) and four (ZnD2-G1, ZnD5-G1,
ZnD8-G2) branches and the octa-substituted dendrimer ZnD3-
G1 without 1,2,3-triazole bridging groups between the tetra-
pyrrolic core and the carbazolylphenyl fragments with L1, using
the method of spectrophotometric titration, showed that these
processes, similarly to the system ZnP–L1, proceed in two
There are two families of spectral curves with two sets of
isosbestic points in the UV-Vis spectra of the system. Each of
them is characterized by its own step in the corresponding
titration curves (Fig. S5 and S6) (ESI†). Existence of two steps in
the complexation also is conrmed by the graphical depen-
dence of lg[(A0 ꢁ Ai)/(Ai ꢁ Ak)] from lg CL for the system. The
1
splitting of the ligand non-equivalent proton signal in the H
NMR spectrum of the complex formed at the high concentra-
tions of the ligand according with the literature25–28 indicates
the formation of a 1 : 1 complex. One signal of the ligand
equivalent protons in the spectrum of the complex at lower
concentrations of the ligand reveals the formation of the 2 : 1
complex between ZnD3-G1 and L1.
It should be noted that complex formation of dendrimers
ZnD6-G1,24 ZnD9-G2 with L1 in toluene proceeds in a single step
with the formation of only 1 : 1 complexes. Probably, the pres-
ence of the bulky branches in the rst and second generations
prevents two-center coordination of L1. The stability constants
of the considered complexes are presented in Table 2.
Conclusions
Fig. 1 Stability constants of ZnTPP and octa-substituted dendrimers
with L2–L5 in toluene, 25 ꢂC.
Thus, the study of complex formation of Zn(II) tetraar-
ylporphyrins with carbazolylphenyl branches by spectrophoto-
metric and 1H NMR titration methods showed that their
binding ability towards mono and bidentate N-containing
organic molecules depends on the nature, number and gener-
ation of the branches. Bulky substituents are able either to
signicantly reduce the binding ability of the tetrapyrrolic cores
due to the shielding of the porphyrin reaction centers, or
signicantly increase it by forming of intramolecular cavities for
complementary binding of substrates. By varying the number of
the branches and the number of their generation, it is possible
to develop intramolecular cavities of different shapes for
selective binding of guest molecules by a good geometric match
of the ligand size to the size of the cavities, and by a existence of
Fig. 2 The changes in the UV-Vis spectra of the system ZnD3-G1–L1
in toluene at 20 ꢂC, CZnD3-G1 ¼ 0 to 1.0 ꢀ 10ꢁ4 M.
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additional p–p and/or hydrogen bonding interactions between optical density of the solution at a given wavelength at a given
the ligand and the triazole fragments of the porphyrin. These concentration.
metalloporphyrins could be considered as a molecular optical
Synthesis of 4-[(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phe-
sensing device for small heterocyclic substrates due to a clear noxy)methyl]benzaldehyde (3). 4-Bromomethylbenzaldehyde
and easily identiable response in the UV-Vis spectra of the (2) (200 mg, 1.1 mmol, 1 equiv.) and 4-(3,6-di-tert-butyl-9H-car-
reaction mixture.
bazol-9-yl)phenol (1) were stirred in DMF (10 ml) for a few
minutes. Then K2CO3 was added and the reaction was con-
ducted at 80 ꢂC overnight under N2 atmosphere. Crude product
was puried by column chromatography (silica, eluent CH2Cl2–
Experimental
General experimental methods
heptane 2 : 1) to obtain (3) (366 mg, 73%) as a white solid. M.p.
1
ꢂ
ꢂ
190–192 C. H NMR (300 MHz, CDCl3, 25 C, TMS): d ¼ 10.05
(s, 1H, CHO), 8.13 (s, 2H, H-carbazole), 7.95 (d, 3JH,H ¼ 7.92, 2H,
H-Ar), 7.66 (d, 3JH,H ¼ 7.89, 2H, H-Ar), 7.44 (d, 3JH,H ¼ 8.67, 4H,
H-Ar), 7.25 (d, 3JH,H ¼ 8.49, 2H, H-Ar), 7.14 (d, 3JH,H ¼ 8.64, 2H,
H-Ar), 1.45 ppm (s, 18H, tert-butyl). 13C NMR (75 MHz, CDCl3,
25 ꢂC, TMS): d ¼ 191.86, 130.14, 128.34, 127.58, 123.53, 116.21,
115.88, 109.03 (CH-Ar), 157.25, 143.69, 142.60, 139.63, 136.09,
131.48, 123.08 ppm (C-Ar), 69.57 (CH2), 34.71 (C, tert-butyl),
32.02 ppm (CH3, tert-butyl). HRMS (EI): m/z calcd for
NMR spectra were acquired on commercial instruments (Bruker
Avance 300 MHz, Bruker AMX 400 MHz or Bruker Avance II+
600 MHz) and chemical shis (d) are reported in parts per
million (ppm) referenced to tetramethylsilane (TMS) or the
internal (NMR) solvent signals. Mass spectra were run using a
HP5989A apparatus (CI and EI, 70 eV ionisation energy) with
Apollo 300 data system or a Thermo Finnigan LCQ advantage
apparatus (ESI). Exact mass measurements were acquired on a
Kratos MS50TC instrument (performed in the EI mode at a
resolution of 10 000). Melting points (not corrected) were
determined using a Reichert Thermovar apparatus. For column
chromatography, 70–230 mesh silica 60 (E. M. Merck) was used
as the stationary phase. Chemicals received from commercial
sources were used without further purication. MALDI-TOF
mass spectrometry was carried out on Bruker Daltonics –
ultraex II & ultraex II TOF/TOF using the matrix 2,5-dihy-
droxylbenzoic acid for all samples.
Spectroscopic methods and instrumentation. 1,4-Dia-
zabicyclo-[2.2.2]octane (L1), pyridine (L2), imidazole (L3),
N-methylimidazole (L4) and 1,2,3-triazole (L5) from Sigma-
Aldrich were used without further purication. 1H NMR spectra
were recorded on a Bruker VC-500 (500.17 MHz) in CDCl3 using
TMS as the internal standard. UV-Vis spectra of the porphyrins
and their evolution upon addition of the ligands were measured
on a Carry 100 spectrophotometer.
C
34H35NO2: 489.27 [M+]; found 489.26 [M+].
Synthesis of 3,5-bis[(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)-
phenoxy)methyl]-2,4,6-trimethylbenzaldehyde (6). The mixture
of arylaldehydes (180 mg), consisting of 3,5-bis(bromomethyl)-
2,4,6-trimethylbenzaldehyde (4) and 3-bromomethyl-5-chlor-
omethyl-2,4,6-trimethylbenzaldehyde (5), and carbazole-based
phenol (1) were dissolved in DMF (10 ml) and the mixture was
stirred at room temperature for a few minutes. Subsequently,
K2CO3 (148 mg, 1.08 mmol) and a catalytic amount of 18-crown-
6 (26.4 mg, 0.1 mmol) were added and the reaction was carried
ꢂ
out at 80 C overnight under N2 atmosphere. Purication was
conducted via a silica column (CH2Cl2–heptane1.5 : 1) to obtain
1
(6) (390 mg) as a white solid. M.p. 268–270 ꢂC. H NMR (300
MHz, CDCl3, 25 ꢂC, TMS): d ¼ 10.72 (s, 1H, CHO), 8.14 (s, 4H, H-
carbazole), 7.48 (m, 8H, H-carbazole), 7.29 (d, 3JH,H ¼ 8.64, 4H,
3
H-Ar), 7.21 (d, JH,H ¼ 8.67, 4H, H-Ar), 5.22 (s, 4H, CH2), 2.66
(s, 6H, 2 ꢀ CH3), 2.62 (s, 3H, CH3), 1.46 ppm (s, 36H, tert-butyl).
13C NMR (75 MHz, CDCl3, 25 ꢂC, TMS): d ¼ 195.33 (CHO),
128.34, 123.51, 116.21, 115.64, 109.05 (CH-Ar), 157.76, 143.63,
142.60, 140.26, 139.68, 134.01, 132.51, 131.42, 123.09 (C-Ar),
64.48 (CH2), 34.72 (C, tert-butyl), 32.04 (CH3, tert-butyl), 16.58
(CH3), 15.89 ppm (CH3). MALDI-TOF: m/z calcd for C64H70N2O3:
914.54 [M+]; found 914.53 [M+].
Synthesis of 5,15-bis(2,4,6-trimethylphenyl)-10,20-bis[4-(4-
(3,6-di-tert-butyl-9H-carbazol-9-yl)phenoxy)methylphenyl]
porphyrin (7). Arylaldehyde (3) (100 mg, 0.20 mmol, 1 equiv.)
and 5-mesityldipyrromethane (54 mg, 0.20 mmol, 1 equiv.) were
dissolved in dry CH2Cl2 (20 ml) and the solution was purged
with N2 for a few minutes. Then BF3$OEt2 (7.5 ml, 0.06 mmol,
0.3 equiv.), in dry CH2Cl2 (1 ml), was added dropwise and the
resulting solution was stirred at room temperature for 1 hour
under N2 atmosphere. Subsequently, p-chloranil (100 mg,
0.41 mmol, 2 equiv.) was added in powder form and the mixture
was heated at reux for 1 hour. The solvent was evaporated and
The UV-visible absorption spectral studies reveal red shif-
ted Soret and visible bands upon addition of the ligands to a
solution of the investigated receptor porphyrins conrming
that the N-containing entity of the ligands binds to the Zn-
cation of the coordination centre of the tetrapyrrolic
macrocycle.
The stability constants of the metalloporphyrin complexes
with the ligands in ratio of 1 : 1 (Kassoc 1) and 2 : 1 (Kassoc 2) were
calculated according with the literature17 based on spectro-
photometric data at two wavelengths (decreasing and
increasing) using the following relationships:
ꢀ
ꢁ
½A ꢁ Bꢃ
½Aꢃ½Bꢃ
DAi;l DAo;l
1
2
Kassoc 1
¼
¼ 1=½Bꢃ
; Mꢁ1
DAo;l DAi;l
1
2
ꢀ
ꢁ
½A ꢁ B ꢁ Aꢃ
DAi;l DAo;l
1 2
Kassoc 2
¼
¼ 1=½Aꢃ½Bꢃ
; Mꢁ2
2
DA
DA
i;l2
½Aꢃ ½Bꢃ
o;l1
where, l1 is the decreasing wavelength, l2 is the increasing then purication was carried out with column chromatography.
wavelength, [A] is the Zn-porphyrin concentration, [B] is the The rst ash column (silica, eluent CH2Cl2) was to remove
ligand concentration, DAo is the maximal change of the optical dark pigments and the second one (silicagel, CH2Cl2–heptane
density at the given wavelength, DAi – is the change of the 1 : 1.5) was to separate the different porphyrin fractions. Pure
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1
product (51 mg, 34%) was obtained as a purple solid. H NMR was washed three times with distilled water. The organic layer
(300 MHz, CDCl3, 25 ꢂC, TMS): d ¼ 8.84 (d, 3JH,H ¼ 4.71, 4H, H- was dried over MgSO4 and the solvent was evaporated under
pyrrole), 8.71 (d, 3JH,H ¼ 4.5, 4H, H-pyrrole), 8.29 (d, 3JH,H ¼ 7.71, vacuum to obtain Zn(II)-porphyrin in pure form in quantitative
4H, H-Ar), 8.17 (s, 4H, H-carbazole), 7.87 (d, 3JH,H ¼ 7.74, 4H, H- yield.
Ar), 7.56 (d, 3JH,H ¼ 8.46, 4H, H-Ar), 7.49 (d, 3JH,H ¼ 8.64, 4H, H-
Dendrimer ZnD1-G1. 1H NMR (300 MHz, CDCl3, 25 ꢂC, TMS):
Ar), 7.36 (m, 8H, H-Ar), 7.29 (s, 4H, H-mesityl), 5.50 (s, 4H, 2 ꢀ d ¼ 8.93 (d, 3JH,H ¼ 4.71 Hz, 4H, H-pyrrole), 8.80 (d, 3JH,H ¼ 4.71
3
CH2), 2.63 (s, 6H, 2 ꢀ CH3), 1.85 (s, 12H, 4 ꢀ CH3), 1.48 (s, 36H, Hz, 4H, H-pyrrole), 8.30 (d, JH,H ¼ 7.92 Hz, 4H, H-Ar), 8.17 (d,
tert-butyl), ꢁ2.59 ppm (s, 2H, 2 ꢀ NH). 13C NMR (75 MHz, 4JH,H ¼ 1.5 Hz, 4H, H-carbazole), 7.86 (d, 3JH,H ¼ 7.92 Hz, 4H, H-
CDCl3, 25 ꢂC, TMS): d ¼ 134.77, 128.40, 127.78, 125.94, 123.54, Ar), 7.56 (d, 3JH,H ¼ 8.85 Hz, 4H, H-Ar), 7.49 (dd, 3JH,H ¼ 8.67 Hz,
116.20, 116.04, 109.12 (CH-Ar), 157.88, 142.56, 141.88, 139.75, 4JH,H ¼ 1.71 Hz, 4H, H-Ar), 7.35 (dd, 3JH,H ¼ 8.85 Hz, 4JH,H ¼ 2.46
139.39, 138.40, 137.76, 136.16, 131.31, 123.10, 118.86, 118.42 (C- Hz, 8H, H-Ar), 7.28 (s, 4H, H-mesityl), 5.48 (s, 4H, CH2), 2.63 (s,
Ar), 70.50 (CH2), 34.74 (C, tert-butyl), 32.06 (CH3, tert-butyl), 6H, CH3), 1.84 (s, 12H, CH3), 1.48 ppm (s, 36H, tert-butyl). 13C
21.65 (CH3), 21.48 ppm (CH3). MALDI-TOF: m/z calcd for NMR (75 MHz, CDCl3, 25 ꢂC, TMS): d ¼ 134.68, 132.33, 130.85,
C
104H100N6O2: 1465.94 [M+]; found 1465.84 [M+].
128.38, 127.68, 125.80, 123.55, 116.20, 116.06, 109.14 (CH-Ar),
Synthesis of 5,10,15,20-tetrakis[4-(4-(3,6-di-tert-butyl-9H- 157.89, 150.04, 149.98, 142.68, 142.56, 139.75, 139.24, 138.99,
carbazol-9-yl)phenoxy)methylphenyl] porphyrin (8). Compound 137.49, 135.87, 131.29, 123.10, 119.78, 119.39 (C-Ar), 70.57
(3) was reacted with pyrrole under BF3$OEt2 catalysis using the (CH2), 34.74 ppm (C, tert-butyl). MALDI-TOF: m/z calcd for
procedure that was applied for the synthesis of dendrimer D1
(7). Crude product was puried by column chromatography
C
104H98N6O2Zn: 1527.71 [M+]; found 1527.78 [M+].
Dendrimer ZnD2-G1. 1H NMR (300 MHz, CDCl3, 25 ꢂC, TMS):
3
(silica, CH2Cl2–heptane 1 : 1) to get pure compound (15%) as a d ¼ 9.03 (s, 8H, H-pyrrole), 8.30 (d, JH,H ¼ 7.71 Hz, 8H, H-Ar),
1
purple solid. H NMR (300 MHz, CDCl3, 25 C, TMS): d ¼ 8.92 8.17 (d, 4JH,H ¼ 1.29 Hz, 8H, H-carbazole), 7.88 (d, 3JH,H ¼ 7.92
ꢂ
(s, 8H, H-pyrrole), 8.28 (d, 3JH,H ¼ 7.71 Hz, 8H, H-Ar), 8.17 (s, 8H, Hz, 8H, H-Ar), 7.56 (d, 3JH,H ¼ 8.67 Hz, 8H, H-Ar), 7.49 (dd, 3JH,H
H-carbazole), 7.86 (d, 3JH,H ¼ 7.71 Hz, 8H, H-Ar), 7.55 (d, 3JH,H
¼
¼ 8.67 Hz, 4JH,H ¼ 1.68 Hz, 8H, H-Ar), 7.35 (dd, 3JH,H ¼ 8.64 Hz,
8.46 Hz, 8H, H-Ar), 7.49 (d, JH,H ¼ 8.67 Hz, 8H, H-Ar), 7.35 4JH,H ¼ 2.46 Hz, 16H, H-Ar), 5.48 (s, 8H, CH2), 1.48 (s, 72H, tert-
3
(d, JH,H ¼ 8.64 Hz, 16H, H-Ar), 5.45 (s, 8H, CH2), 1.48 (s, 72H, butyl). 13C NMR (75 MHz, CDCl3, 25 ꢂC, TMS): d ¼ 134.70,
3
tert-butyl), ꢁ2.70 ppm (s, 2H, 2 ꢀ NH). 13C NMR (75 MHz, 132.13, 128.38, 125.87, 123.54, 116.21, 116.03, 109.12 (CH-Ar),
CDCl3, 25 ꢂC, TMS): d ¼ 134.83, 128.38, 125.98, 123.55, 116.21, 157.89, 150.24, 142.65, 142.57, 139.75, 136.02, 131.31, 123.11,
116.00, 109.12 (CH-Ar), 157.86, 142.57, 141.95, 139.73, 136.27, 120.80 (C-Ar), 70.54 (CH2), 34.73 (C, tert-butyl), 32.05 (CH3, tert-
131.31, 123.10, 119.82 (C-Ar), 70.42 (CH2), 34.73 (C, tert-butyl), butyl). MALDI-TOF: m/z calcd for C152H144N8O4Zn: 2210.06 [M+];
32.05 (CH3, tert-butyl). MALDI-TOF: m/z calcd for C152H146N8O4: found 2210.28 [M+].
2148.84 [M+]; found 2148.30 [M+].
Dendrimer ZnD3-G1. 1H NMR (600 MHz, CDCl3, 25 ꢂC, TMS):
Synthesis of 5,10,15,20-tetrakis[3,5-bis((4-(3,6-di-tert-butyl-9H- d ¼ 8.88 (sbr, 8H, H-pyrrole), 8.12 (s, 16H, H-pyrrole), 7.50 (d,
carbazol-9-yl)phenoxy)methyl)-2,4,6-trimethylphenyl] porphyrin 3JH,H ¼ 8.1 Hz, 16H, H-Ar), 7.40 (d, 3JH,H ¼ 8.82 Hz, 16H, H-Ar),
3
(9). 3,5-Bis[(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenoxy)methyl]- 7.32 (sbr, 16H, H-Ar), 7.27 (d, JH,H ¼ 8.82 Hz, 16H, H-Ar), 5.48
2,4,6-trimethylbenzaldehyde (6) (200 mg, 0.21 mmol, 1 equiv.) (sbr, 16H, CH2), 2.95 (s, 12H, CH3), 2.05 (sbr, 24H, CH3), 1.43 (s,
13
ꢂ
and pyrrole (15 ml, 0.21 mmol, 1 equiv.) were dissolved in CH2Cl2 144H, tert-butyl). C NMR (100 MHz, CDCl3, 25 C, TMS): d ¼
(22 ml) and absolute ethanol (164 ml). The solution was purged 128.34, 123.47, 116.17, 115.79, 109.09 (CH-Ar), 158.20, 150.08,
with N2 for 15 minutes. The reaction was carried out following 142.55, 140.72, 139.73, 131.44, 131.25, 130.80, 123.09, (C-Ar),
the procedure described above using BF3$OEt2 (0.3 equiv.). Crude 65.94 (CH2), 34.68 (C, tert-butyl), 32.01 (CH3, tert-butyl), 19.27
product was puried by column chromatography (silica, CH2Cl2– (CH3), 16.30 ppm (CH3). MALDI-TOF: m/z calcd for
heptane 1 : 1) to get pure compound (10 mg, 5%) as a purple
solid. 1H NMR (600 MHz, CDCl3, 25 ꢂC, TMS): d ¼ 8.82 (sbr, 8H, H-
pyrrole), 8.10 (s, 16H, H-carbazole), 7.48 (sbr, 16H, H-Ar), 7.39 (d,
3JH,H ¼ 7.74 Hz, 16H, H-Ar), 7.32 (sbr, 16H, H-Ar), 7.25 (s, 16H, H-
C
272H284N12O8Zn: 3912.15 [M+]; found 3912.26 [M+].
Acknowledgements
Ar), 5.46 (sbr, 16H, CH2), 2.93 (s, 12H, CH3), 2.05 (sbr, 24H, CH3), This work was supported by a FP-7 grant from the EC for
1.41 ppm (s, 144H, tert-butyl). 13C NMR (100 MHz, CDCl3, 25 ꢂC, Research, Technological Development and Demonstration
TMS): d ¼ 158.15, 144.97, 142.55, 140.91, 140.16, 139.72, 131.27, Activities, “Dendrimers for Photonic Devices” IRSES-PEOPLE-
130.96, 128.35, 123.47, 123.07, 116.16, 115.77, 109.08 (C, CH-Ar), 2009-247260-DphotoD, under the “International Research Staff
65.86 (CH2), 34.68 (C, tert-butyl), 32.00 (CH3, tert-butyl), 19.32 Exchange Scheme”. Nguyen Tran Nguyen thanks Ministry of
(CH3), 16.33 ppm (CH3). MALDI-TOF: m/z calcd for Education and Training, Vietnam International Education
C
272H286N12O8: 3851.26 [M+]; found 3851.58 [M+].
Development (VIED) for nancial support during his Ph.D in KU
Leuven, Belgium.
General procedure for synthesis of zinc(II) porphyrin
Notes and references
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added to a ask of 25 ml containing CHCl3 (10 ml) and the
solution was heated at reux for 4 hours. The resulting mixture
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RSC Adv., 2014, 4, 19703–19709 | 19709