Click reaction synthesis and photophysical studies of dendritic metalloporphyrins

Article abstract of DOI:10.1002/ejoc.201301158

Several dendritic zinc(II)-porphyrins bearing carbazole units at the terminals have been prepared through click reaction of azide-substituted Zn-porphyrin precursors and carbazole-based alkynes under [Cu(NCCH ₃)₄][PF₆] cat

Full text of DOI:10.1002/ejoc.201301158

FULL PAPER
DOI: 10.1002/ejoc.201301158
Click Reaction Synthesis and Photophysical Studies of Dendritic
Metalloporphyrins
Nguyen Tran Nguyen,[a] Johan Hofkens,[b] Ivan G. Scheblykin,[c] Mikalai Kruk,[d,e] and
Wim Dehaen*[a]
Keywords: Porphyrinoids / Dendrimers / Luminescence / Photochemistry / Fluorescence / Click chemistry
Several dendritic zinc(II)-porphyrins bearing carbazole units
at the terminals have been prepared through click reaction
of azide-substituted Zn-porphyrin precursors and carbazole-
based alkynes under [Cu(NCCH3)4][PF6] catalysis. This fam-
ily of new dendritic metalloporphyrins shows dual lumines-
cence from both the upper S2 and the lowest S1 singlet states.
The observed trends in the spectroscopic data and the photo-
physical properties of the dendrimers have been rationalized
in terms of the type of meso-spacer between the macrocycle
and dendritic shell. The key feature of the meso-spacer is
proposed to be the degree of hindrance towards aryl ring
rotation relative to the mean porphyrin plane. Based on the
observed differences in the S1ǞS0 fluorescence quantum
yield on going from four- to five-coordinate dendrimers, it
was shown that dendrimer architectures with all four meso-
aryl spacers sterically hindered, are most appropriate to mon-
itor processes related to axial ligation of the dendrimer core,
since they provide larger luminescence response differences
between the four-coordinate and five-coordinate forms. The
blue S2ǞS0 fluorescence quantum yield has been measured
and the observed trend has been rationalized in terms of the
S2ǞS1 energy gap law. No significant differences were ob-
served between the compounds either with different rota-
tional degree of freedom of the meso-spacers or with dif-
ferent ligation states of the dendrimer core.
cial for the structure and functional properties of designed
dendrimer molecules. Carbazole derivatives can be consid-
ered as promising dendron molecules that could be used to
prepare new functional dendrimers with a porphyrin core.[8]
Carbazole is an electron-rich conjugated system in which
the 3-, 6-, and 9-positions are the most reactive sites
towards electrophilic substitution.[9] Aryl substituents at the
9-position of the carbazole will result in a decrease in en-
ergy of the HOMO level[10] and so carbazole derivatives can
be used as host material in light-emitting devices.[11] Dif-
ferent approaches have been used to achieve high genera-
tion dendrimers,[7] with click chemistry (more specifically
the click reaction) being suggested as a reliable and useful
tool with which to achieve this goal. Thus, copper(I)-cata-
lyzed 1,3-dipolar cycloaddition of azides and terminal alk-
ynes is regioselective for the formation of 1,4-disubstituted
1,2,3-triazole products in high yields.[12] The 1,2,3-triazole
group has been considered a significantly π-conjugated
linker in intramolecular energy transfer (ET) processes.[13]
In the field of porphyrin chemistry, a series of triazole-
linked zinc(II)porphyrin-fullerenes was synthesized and
their photophysical properties were also reported.[13b,14]
Heterometallic, multiporphyrin dendrimers made by click
chemistry have shown rather efficient energy- and electron-
transfer reactions that can be used for solar energy conver-
sion.[15] The coordination of the nitrogen atoms of the tri-
azole rings to the Zn ions of the porphyrins, together with
π-π interactions between the zinc porphyrins bring about
Introduction
Porphyrin-based materials have been receiving consider-
able attention due to their numerous applications, with the
most important of them being in material chemistry,[1] cata-
lytic chemistry,[2] sensor design,[3] photodynamic therapy,[4]
and organic photovoltaics.[5] Dendritic encapsulation brings
to the core molecule new features and allows several of their
own properties to be either enhanced or suppressed.[6]
Therefore, the design of new dendritic porphyrins (which
can also be named as dendrimers with a porphyrin core)
with particular structure and properties is of considerable
interest,[7] and substantially extends the potential of por-
phyrin applications. The choice of the dendron type is cru-
[a] Molecular Design and Synthesis, Department of Chemistry,
KU Leuven,
Celestijnenlaan 200F, 3001 Leuven, Belgium
E-mail: wim.dehaen@chem.kuleuven.be
http://chem.kuleuven.be/en/research/mds/losa
[b] Molecular Imaging and Photonics, Department of Chemistry,
KU Leuven,
Celestijnenlaan 200F, 3001 Leuven, Belgium
[c] Lund University, Department of Chemical Physics,
P. O. Box 124, 22100 Lund, Sweden
[d] Belarussian State Technological University, Physics
Department,
Sverdlova str. 13a, 220050 Minsk, Belarus
[e] B. I. Stepanov Institute of Physics of National Academy of
Sciences,
Pr. Nezavisimosti 68, 220072 Minsk, Belarus
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201301158.
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Synthesis and Photophysical Studies of Dendritic Metalloporphyrins
dramatic changes in the conformation and photophysical
properties.[13a,13c,16] A smart porphyrin cage that was made
by click chemistry showed novel binding ability toward az-
ide anions.[17] To the best of our knowledge, there have been
no reports on the linkage of porphyrin and carbazole deriv-
atives through application of the click reaction. In this pa-
per, we report on the synthesis of a family of new dendritic
porphyrins through the click reaction starting from azido
porphyrins
and
carbazole-based
alkynes
under
[Cu(NCCH3)4][PF6] catalysis, and discuss the photophysical
properties of the target dendrimers.
Results and Discussion
Synthesis
The synthesis of 3,5-bis(azidomethyl)-2,4,6-trimethyl-
benzaldehyde (4) was based on the synthesis of mesital-
dehyde by treatment of aromatic compounds with di-
chloromethyl methyl ether in the presence of a Lewis acid
such as TiCl4.[18] However, reaction of the known 1,3-bis-
(bromomethyl)-2,4,6-trimethylbenzene (1)[19] and dichloro-
methyl methyl ether resulted in the formation of not only
3,5-bis(bromomethyl)-2,4,6-trimethylbenzaldehyde (2) but
also 3-bromomethyl-5-chloromethyl-2,4,6-trimethylbenz-
aldehyde (3), according to mass and 1H NMR spectroscopy
analyses. When purification by column chromatography
was carried out, these two aldehydes could not be obtained
in pure form. Therefore, this mixture of arylaldehydes was
treated with sodium azide to give 3,5-bis(azidomethyl)-
2,4,6-trimethylbenzaldehyde (4) in pure form (Scheme 1).
Scheme 2. Reagents and conditions: (i) 1. BF3·OEt2 (0.3 equiv.),
CH2Cl2, room temp., 1 h; 2. p-chloranil, reflux, 1 h.
as catalyst for the condensation between 4 and pyrrole, but
no porphyrin was obtained. Similarly, the reaction of mesit-
aldehyde and pyrrole in CH2Cl2 with either BF3·OEt2 or
TFA catalyst afforded no porphyrin. However, tetramesityl
porphyrin was obtained in 29–32% yield in the presence of
0.75% absolute ethanol in anhydrous CH2Cl2.[22]
With 0.3 equiv. BF3·OEt2 and 10 mm concentration of re-
actants, the synthesis of 9 in anhydrous CH2Cl2 containing
0.75% absolute ethanol was unsuccessful, and no porphyrin
appeared. Finally, when the amount of catalyst was in-
creased to 0.8 equiv., porphyrin 9 was obtained in a low but
reasonable yield of 9% (Scheme 3).
Scheme 1. Reagents and conditions: (i) NaN3, CH3COCH3/H2O
(4:1), reflux, overnight.
The synthesis of 5,15-bis(2,4,6-trimethylphenyl)-10,20-
bis(4-azidomethylphenyl) porphyrin (7) was based on the
Lindsey method starting from 5-mesityldipyrromethane (5)
[20]
and 4-(azidomethyl)benzaldehyde (6).[21] Porphyrin
5,10,15,20-tetrakis(4-azidomethylphenyl)porphyrin (8),[17]
was prepared from 4-(azidomethyl)benzaldehyde (6)[21] and
pyrrole (Scheme 2).
Scheme 3. Reagents and conditions: (i) 1. BF3·OEt2 (0.8 equiv.), ab-
solute C2H5OH in CH2Cl2 (0.75%), room temp., 1 h; 2. p-chloranil,
reflux, 1 h.
With a concentration of starting materials of 10 mm in
anhydrous CH2Cl2, the yield of 7 reached 40% with
0.3 equiv. BF3·OEt2 (see the Supporting Information,
In the Ullmann coupling, the rate-determining step is the
Table S1). When the conditions optimized for the synthesis loss of halide from the aryl halide stage, and the order of
of 7 were applied to make 5,10,15,20-tetrakis(3,5-bis(azido- reactivity of aryl halides is well-known (Ar-I Ͼ Ar-Br Ͼ
methyl)-2,4,6-trimethylphenyl)porphyrin (9), no target com- Ar-Cl ϾϾ Ar-F).[23] Based on the Ullmann N-arylation of
pound was obtained. In further attempts to prepare the de- carbazoles and aryl halides, a low yielding (27%) synthesis
sired compound 9, trifluoroacetic acid (TFA) was also tried of 1-bromo-3,5-bis[3,6-bis(tert-butyl)carbazol-9-yl]benzene
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N. T. Nguyen, J. Hofkens, I. G. Scheblykin, M. Kruk, W. Dehaen
FULL PAPER
(10) by condensation of 1,3,5-tribromobenzene and 3,6-di-
tert-butyl-9H-carbazole was reported.[24] Goodbrand and
Hu demonstrated that the addition of 1,10-phenanthroline
as the copper-binding ligand accelerated the traditional
Ullmann condensation catalyzed by CuI.[23b] Furthermore,
the reaction of aryl bromides and carbazole in the presence
of 1,10-phenanthroline was also reported in good yields,
ranging from 42 to 52%.[11b,11c] Thus, the yield of 10 in-
creased from 27 to 40% when 1,10-phenanthroline was
added to the reaction mixture and N,N-dimethylformamide
(DMF) was used as solvent. The Sonogashira reaction was
then carried out under catalysis of CuI and [PPh3]2PdCl2
between 10 and trimethylsilylacetylene to protected
3,5-biscarbazole phenylacetylene (11). Compound 11 was
then deprotected to give 1-ethynyl-3,5-bis[3,6-bis(tert-
butyl)carbazol-9-yl]benzene (12) in good yield (Scheme 4).
The copper(I)-catalyzed azide-alkyne cycloaddition
(CuAAC reaction or click reaction) is considered a very re-
liable reaction that can be carried out in a variety of sol-
vents, with various sources of CuI catalyst.[12a,15c,25] To es-
tablish a suitable procedure for the synthesis of dendrimers
Scheme 4. Reagents and conditions: (i) CuI, 1,10-phenanthroline,
K2CO3, DMF, 160 °C, overnight; (ii) [P(Ph)3]2PdCl2, CuI, THF,
Et3N, 65 °C, overnight; (iii) K2CO3, CH2Cl2, CH3OH, room temp.,
overnight.
Scheme 5. Synthesis of dendrimers A–F. Reagents and conditions: terminal alkyne (4–16 equiv.), [Cu(NCCH3)4][PF6] (0.2–0.8 equiv.),
Et3N (2 drops), THF, 60 °C, 4 h.
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Synthesis and Photophysical Studies of Dendritic Metalloporphyrins
through click reaction, porphyrin 7 was treated with 3,6-di- efficient upon going from D to E and then to F dendrimer
tert-butyl-9-(4-ethynylphenyl)carbazole[10b,26]
in
tetra- is due to an increase in the number of carbazoles attached
hydrofuran (THF) under [Cu(NCCH3)4][PF6] catalysis. to the porphyrin (Figure 1, inset), and essentially the same
However, these conditions led to the formation of a non- trend is also observed for the A–C series of dendrimers (not
fluorescent copper(II)-porphyrin core dendrimer, according shown).
to TLC and mass spectrometric analysis. To avoid this, free-
base porphyrins 7, 8,[15b,17] and 9 were initially metallated
to afford zinc(II)-porphyrins in quantitative yield, then the
click reaction was conducted to generate dendrimers A–F
in good yield. There was no observable Zn/Cu exchange
under the reaction conditions. Dendrimers A–C were ob-
tained from the reaction of zinc(II)-porphyrin (7), zinc(II)-
porphyrin (8),[17] and zinc(II)-porphyrin (9), respectively,
with 3,6-di-tert-butyl-9-(4-ethynylphenyl)carbazole.[10b,26]
Similarly, dendrimers D–F were obtained from the reaction
of zinc(II)-porphyrins and 1-ethynyl-3,5-bis[3,6-bis(tert-bu-
tyl)carbazol-9-yl]benzene (12). To avoid side-product for-
mation, zinc(II)-porphyrins were treated with a large excess
of terminal alkynes so that all azido groups were trans-
formed into the 1,2,3-triazole linker. Dendrimers A, B, D
and E were isolated in acceptable yield (90%), whereas den-
Figure 1. Absorption spectra of dendrimers D–F in the UV range
drimers C and F were obtained in yields of 30 and 26%,
respectively, due to difficulties during chromatographic pu-
rification (Scheme 5).
measured for equimolar concentrations of four-coordinate Zn-por-
phyrin core in CH2Cl2. Inset shows the carbazole band extinction
coefficient at 345 nm as a function of the number of attached car-
bazoles per porphyrin.
The formation of target dendrimers was evidenced by
mass spectrometry (MALDI-TOF) and NMR spec-
In the near-UV and visible ranges, the absorption profile
is due to the porphyrin core. These dendrimer spectra retain
all the main features of the “parent” Zn-tetra-aryl-por-
1
troscopy. H NMR spectra clearly show that the initial sig-
nals corresponding to the α-methylene protons of the azido
groups of the azido porphyrins at 4.7 ppm disappeared
completely and a new methylene peak developed at 5.8 ppm
that was diagnostic for the formation of triazole groups (see
the Supporting Information). Gel permeation chromatog-
raphy (GPC) showed that the dendrimers obtained were
pure and monodisperse [polydispersity index (PDI) = 1; see
the Supporting Information]. FTIR analysis indicated com-
plete disappearance of the azide bond (2080 cm–1) in den-
drimers A–F (see the Supporting Information).
phyrin
core
and
(Zn-5,10,15,20-tetraphenyl-porphyrin
Zn-5,10,15,20-tetrakis(2,4,6-trimeth-
(ZnTPP)[27]
ylphenyl)-porphyrin (ZnTMesP)[22,28]) (Tables 1 and 2).
Nevertheless, minor changes could be seen in the spectra,
which deserve to be discussed in detail. These subtle
changes reveal the structure-property relationships of the
new dendrimers and allow an understanding of how the
optical properties of such dendrimers may be tuned in the
desired direction. The studied dendrimers differ in the type
of porphyrin core molecule, having either phenyl groups
with low steric hindrance or strongly sterically hindered
mesityl groups in the meso-positions. Two other structural
differences relate to the position of the dendrons attached
to the aryl ring (para- or meta-position) and the structure
Photophysical Properties
Absorption Spectra
In the UV range, the absorption of the carbazole den- of the dendrons themselves. They allow the steric bulk of
drons dominate (Figure 1). The peak position of the carba- the dendritic shell for dendrimers A–F to be adjusted.
zole absorption bands remains unchanged in both the A–C
All the dendrimers have the porphyrin core chelated with
and D–F series of dendrimers (λ0,0CZ = 346.5 and 345.0 nm, Zn2+, thus axial ligation with oxygen- or nitrogen-contain-
respectively). The increase in carbazole band extinction co- ing Lewis bases is expected to take place under appropriate
Table 1. Spectral data for the studied compounds with the four-coordinate form of the Zn-porphyrin core. Solvent is CH2Cl2.
ΔλStokes [cm–1]
abs
abs
fl
fl
λ0,0 [nm]
λ1,0 [nm]
A0,0/A1,0
λ0,0 [nm]
λ0,1 [nm]
F0,0/F0,1
A
587.5
586.0
588.5
587.5
586.5
588.5
585.5
586.0
549.0
548.0
552.0
548.5
548.5
552.0
547.5
549.0
0.160
0.220
0.120
0.155
0.200
0.105
0.170
0.090
595.5
596.0
594.5
595.5
596.5
594.5
595.0
594.0
645.5
645.5
647.0
645.0
645.5
647.0
645.0
646.5
0.450
0.510
0.225
0.450
0.510
0.215
0.480
0.240
228
287
171
228
285
171
272
230
B
C
D
E
F
ZnTPP
ZnTMesP
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N. T. Nguyen, J. Hofkens, I. G. Scheblykin, M. Kruk, W. Dehaen
Table 2. Spectral data for the studied compounds with the five-coordinate form of the Zn-porphyrin core. Solvents are THF or pyridine.
FULL PAPER
abs
abs
fl
fl
λ0,0 [nm]
λ1,0 [nm]
A0,0/A1,0
λ0,0 [nm]
λ0,1 [nm]
F0,0/F0,1
ΔλStokes [cm–1]
A-THF
596.0
596.0
598.5
596.0
596.0
598.5
605.5
594.5
603.5
595.5
557.0
557.0
560.5
557.0
557.0
560.5
567.0
555.5
563.5
558.5
0.320
0.400
0.280
0.300
0.390
0.285
0.410
0.325
0.520
0.260
601.5
603.0
601.5
601.5
603.0
601.5
610.0
600.0
610.0
598.0
654.5
655.0
657.5
654.5
655.0
657.5
666.5
653.0
664.0
654.0
0.800
0.900
0.585
0.815
0.890
0.600
0.800
0.790
1.095
0.510
154
196
83
154
196
83
122
154
177
71
B-THF
C-THF
D-THF
E-THF
F-THF
F-Pyridine
ZnTPP-THF
ZnTPP-Pyridine
ZnTMesP-THF
conditions. Ligand binding studies were undertaken by us drance induced by two ortho-methyl groups, and it is ap-
recently.[16] It was found that dendritic encapsulation does proximately 60–70° in the case of phenyl substitution be-
not prevent Zn2+-porphyrin ligation, and the equilibrium cause relatively little steric interaction occurs.[31] In the den-
constants K for the binding of different ligands was mea- drimers, these features give rise to substantial differences in
sured. The core porphyrins have a planar conformation of the A0,0/A1,0 ratio between compounds B and E (both hav-
the macrocycle in the four-coordinate (unligated) form, and ing all four unhindered spacers) from one side, and C and
a dome-type nonplanar distortion is observed for the F (both having all four hindered spacers) from the other.
ligated forms.[29] Interactions of the dendritic shell with the
Table 3 indicates the Soret band maxima for all the
porphyrin core would depend on the conformational state studied dendrimers. It can be seen that the spectral shift of
of the porphyrin. Therefore, it seems reasonable to analyze the Soret bands follow the same trend for both ligated (in
the spectroscopic data for the four- and five-coordinate den- THF) and nonligated (in CH2Cl2) dendrimers. The energy
drimer core separately (Tables 1 and 2, respectively).
of the B band (Soret) can be fitted as a linear function of
The formation of dendrimers results in small long-wave- the Q band energy in both sets of data. This fact indicates
length shifts of the absorption bands (compounds B and E that the effects of both dendritic encapsulation and axial
compared to parent ZnTPP, or compounds C and F com- ligation can be monitored with either the Q- or B-band re-
pared to parent ZnTMesP). These changes take place gions without any loss of information. The mean difference
simultaneously with changes in the ratio of the intensities between the B- and Q-band energies for all the studied den-
of the pure electronic band to the vibronic band in both drimers is 6700Ϯ90 cm–1, which is in excellent agreement
absorbance (A0,0/A1,0) and fluorescence (F0,0/F0,1) spectra with the data reported for the series of metallocomplexes of
(Table 1). The A0,0/A1,0 value is related to the ratio of the TPP.[30a]
transition dipole moments of these transitions. On the other
hand, this ratio is proportional to the square of the energy
Table 3. Soret band maxima for the studied compounds in CH2Cl2
difference between the two one-electron configurations:
and THF.
1
A
0,0/A1,0 ≈ [1E(a2u, eg) – E(a1u, eg)]2, and is used as a mea-
λB [nm]
sure of the energy mismatch between the highest occupied
molecular orbitals (HOMOs) a2u and a1u (D4h symmetry
notation).[30] Both the long wavelength band shift and in-
crease in the A0,0/A1,0 ratio are likely to result from electron
density transferring from the dendrons to the macrocycle.
This leads to a slight increase in the electron density at the
meso-carbon atoms of the porphyrin, thus increasing the
energy of the a2u MO. The more separated in energy a2u
and a1u orbitals are, the higher the absorption of the 0,0
transition is.[30]
CH2Cl2
THF
A
B
C
D
E
F
420.0
420.0
423.5
420.0
420.0
423.5
424.5
424.5
428.5
424.5
425.0
428.5
The gradual spectral evolution in the meso-substituted
A similar trend was also observed when the spectroscopic porphyrin-indolocarbazole conjugates when the substitu-
data for all dendrimers studied (in both four- and five-coor- tion pattern changes in the series as B4, AB3, ABAB,
dinate forms of porphyrin core) were compared. A simple AABB, A3B (A = indolocarbazole fragment attached via
rationale for such a behavior lies in the relationship of the phenyl spacer, B = mesityl) has been explained recently.[32]
spectral pattern and the type of the nearest aryl ring to By applying this approach to the case under consideration,
the meso-carbon spacer. The A0,0/A1,0 value is different for the relationship between the spectral pattern and the type of
parent ZnTPP and ZnTMesP porphyrins and may be re- the nearest aryl ring to the meso-carbon spacer is revealed
lated to the position of the aryl ring relative to the mean (Figure 2). The ground state absorption spectrum of den-
macrocycle plane, which modulates the strength of the elec- drimers with the same type of dendrons depends on the
tronic communication between them. In the case of mesityl meso-spacer type, with the phenyl spacer allowing the high-
substitution, the dihedral angle θ is 90° due to steric hin- est absorptivity of the 0,0 transition band, and the mesityl
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Synthesis and Photophysical Studies of Dendritic Metalloporphyrins
spacer the lowest. The reverse is true for the 1,0 band posi- based on the ΔλStokes value behavior in dendrimers, the in-
tion (Tables 1 and 2).
fluence of the dendritic shell on the intrinsic conforma-
tional flexibility of the porphyrin core could be estimated.
In the case of a four-coordinate porphyrin core, the ΔλStokes
values remain practically unchanged for dendrimers B and
E (“ZnTPP-like”), but a decrease of the Stokes shift was
shown in the case of “ZnTMesP-like” dendrimers C and F
(Table 4). A substantial decrease in the ΔλStokes value takes
place upon ligation in both parent porphyrins and dendri-
mers. About the same reduction of ca. 100 cm–1 is found
for both ZnTPP porphyrin and dendrimers B and E, indi-
cating that the dendrimer/core interactions do not alter the
intrinsic conformational changes occurring upon the axial
ligation. Axial ligation of sterically hindered ZnTMesP
leads to about a threefold decrease in the ΔλStokes value
down to ca. 80 cm–1, irrespective of the type of ligand. One
can suggest that ZnTMesP-L possesses a quite rigid molec-
ular conformation. In the case of “ZnTMesP-like” ligated
dendrimers C-THF and F-THF, the same value of the
Stokes shift is found. This means that neither ligand free
(in CH2Cl2) nor ligated (in THF) porphyrin core undergoes
noticeable restrictions from the dendritic shell to adopt a
dome-type conformation. A slightly higher value was mea-
sured for F-Pyr dendrimer, but the differences were too
small for unambiguous interpretation.
Figure 2. Correlation between the A0,0/A1,0 ratio and the number
of sterically hindered spacers in the studied compounds with the
four-coordinate form of the Zn-porphyrin core (closed circles, A–
F), and with the five-coordinate form of the Zn-porphyrin core
(open circles, A-THF–F-THF).
In the case of a pure electronic substitution effect, the
A
0,0/A1,0 ratio is known to be reciprocal to the energy of
the 0,0 band for tetra-aryl-porphyrins.[30,33] Since, for such
1
1
porphyrins, the relation E(a2u, eg) Ͻ E(a1u, eg) holds, de-
crease in the energy of the one-electron configuration simul-
taneously leads to larger splitting 1E(a2u, eg) – 1E(a1u, eg).[33]
Therefore, when dome-type nonplanar distortions are in-
duced (the degree of which depends on the ligand basicity,
i.e., pyridine induces higher nonplanar distortions com-
pared with THF[34]) in going from four- to five-coordinate
compounds, a long-wavelength shift of the absorption spec-
trum takes place. There is no linear correlation over the
whole set of data (Figure 3) since the ligands have their own
electronic contribution.
Table 4. Stokes shift values for four- and five-coordinate forms of
the Zn-porphyrin core of dendrimers A–F.
Compound
ΔλStokes
Compound
ΔλStokes
[cm–1]
[cm–1]
A
B
C
D
E
F
228
287
171
228
285
171
A-THF
154
196
83
154
196
83
122
154
177
71
B-THF
C-THF
D-THF
E-THF
F-THF
F-Pyridine
ZnTPP-THF
ZnTPP-Pyridine
ZnTMesP-THF
ZnTMesP-Pyridine
ZnTPP
272
230
ZnTMesP
82
Luminescent Properties
All the studied dendrimers are luminescent molecules
possessing dual emission (Figure 4): the S1ǞS0 fluorescence
and the fluorescence from higher excited states, namely,
S2ǞS0 fluorescence, which is frequently also named blue
fluorescence.[36] Thus, the dendrimers provide a dual red
and blue luminescent response.
The S1ǞS0 and S2ǞS0 fluorescence differ in their life-
times. Whereas the S1 state lifetime was found to be around
2 ns (Table 5), the S2 state lifetime for Zn-tetraarylporphyr-
ins was three orders of magnitude shorter, i.e., 1.5–
3 ps.[36,37] As a result of such a short lifetime, blue S2ǞS0
Figure 3. Correlation between the long-wavelength (0,0) band
maximum in the absorption spectra and the A0,0/A1,0 ratio for den-
drimers with four sterically hindered spacers.
abs
fl
The Stokes shift ΔλStokes = λ0,0 – λ0,0 can be consid- fluorescence should be practically insensitive to the slow
ered as an estimate of the conformational flexibility/degree conformational dynamics in dendrimers. The main photo-
of freedom for tetrapyrrolic compounds.[34,35] Therefore, physical parameters for the lowest singlet S1 state of the
Eur. J. Org. Chem. 2014, 1766–1777
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N. T. Nguyen, J. Hofkens, I. G. Scheblykin, M. Kruk, W. Dehaen
FULL PAPER
Formation of a five-coordinate dendrimer core (L =
THF) brings about changes in the kfl and knr rate constants.
The kfl value decreases slightly for dendrimers C and F, and
remains about the same for dendrimers B and E. It is inter-
esting to note that the value of the emission rate constant
kfl for “ZnTPP-like” and “ZnTMesP-like” dendrimers is
roughly the same as for the parent core porphyrins after
ligation with THF. Radiationless deactivation rate constant
knr undergoes minor changes in all cases, except for a de-
crease in dendrimers A and D. All these changes lead to a
decrease in the fluorescence quantum yield of dendrimers
C and F, and an increase in Φfl for dendrimers A and D.
An increase in both kfl and knr rate constants is observed
when the core of dendrimer F is ligated with pyridine. As a
result, the fluorescence quantum yield Φfl slightly decreases,
since the probability of radiationless deactivation increases.
Ligation with pyridine is found to lead to very similar fluo-
rescence quantum yields in all the studied compounds. It
could be suggested that internal radiationless conversion
may account for the increase in the knr value upon the for-
mation of axially ligated compounds upon the formation of
a dome type nonplanar conformer, since intersystem cross-
ing is expected to be barely affected.[34a]
Figure 4. Total luminescence spectra of compounds D-THF–F-
THF (spectra of porphyrins A-THF–C-THF are not shown, since
compounds A and D, B and E, C and F are spectrally undistin-
guishable in pairs, see Tables 1, 2, 3, and 4, and 6). The blue S2ǞS0
fluorescence spectra (λexc = 400 nm for all the compounds, with the
exception of F-Pyr, where λexc = 410 nm; λem = 415–550 nm) are
normalized for the intensity of the electronic (0,0) band, and the
red S1ǞS0 fluorescence spectra (λexc = 545 nm; λem = 550–740 nm)
are normalized for the intensity of the vibronic (0,1) band. Spectra
measured in CH2Cl2 are shown in the Supporting Information.
The emission rate constant kfl and radiationless deactiva-
compounds studied are listed in Table 5. All of them reveal tion rate constant knr behavior can be rationalized in terms
differences between the four- and five-coordinate forms of of the degree of steric hindrance induced by meso-aryl spa-
the Zn-porphyrin core. Therefore, we performed the analy- cers, as done above when analyzing the ground-state ab-
sis for the four-coordinate core dendrimers first and then sorption spectra. Two correlation plots are presented in Fig-
compared these values with those for the ligated dendri- ure 5. The “ZnTPP-like” dendrimers B and E do not show
mers. The emission rate constant kfl increased upon forma- substantial differences in either kfl or knr values when going
tion of dendrimers compared with the parent core por- from the four- to five-coordinate dendrimer core. Dendri-
phyrins. Thus, the kfl value in dendrimers C and F is about mers A and D, which follow the trans-Ph2-Mes2 pattern in
30% higher than those of ZnTMesP, and the kfl value in architecture, maintain approximately the same kfl value, but
dendrimers B and E is about 20% higher than the parent the knr value reduces substantially upon dendrimer core lig-
ZnTPP. In addition, the radiationless rate constant knr re- ation. Finally, in “ZnTMesP-like” dendrimers C and F, the
mains practically unchanged upon dendrimer formation radiationless deactivation probability knr does not undergo
(see Table 5). As a result, the fluorescence quantum yield large changes, but their kfl values decrease remarkably upon
Φfl increases noticeably in dendrimers, reaching 0.038–0.043 ligand attachment. Therefore, the fluorescence quantum
compared to 0.032–0.033 for the parent core porphyrins. yield Φfl remains about the same in dendrimers B and E,
Dendrimers A and D show intermediate kfl and knr values, slightly increases in dendrimers A and D, and decreases no-
which also leads to an increase in the fluorescence quantum ticeably in dendrimers C and F. Thus, one can suggest that
yield Φfl of the same order of magnitude as those of dendri- dendrimer architectures with all four meso-aryl spacers pro-
mers B and E. Thus, the S1ǞS0 fluorescence response viding a degree of steric hindrance are most appropriate to
quantum yield is maximal in dendrimers C and F.
monitor the processes related to the axial ligation of the
Table 5. Luminescent properties for the S1 state of dendrimers A–F.
Four-coordinate core
τfl [ns]
Five-coordinate core[a]
τfl [ns]
Φfl ϫ102
kfl, 107 s–1
knr, 108 s–1
Φfl ϫ102
kfl, 107 s–1
knr, 108 s–1
A
3.8
3.8
3.9
3.8
3.8
4.3
3.3
3.2
1.98
1.67
2.30
1.99
1.70
2.36
1.75
2.33
1.92
2.28
1.70
1.91
2.24
1.82
1.89
1.37
4.86
5.76
4.18
4.83
5.66
4.06
5.53
4.15
4.0
3.7
3.7
4.3
3.9
3.6/3.4
3.3/3.2
3.6/3.3
2.33
1.68
2.44
2.25
1.72
2.46/1.96
1.54/1.81
2.42/1.92
1.79
2.20
1.52
1.91
2.27
1.46/1.74
2.14/1.77
1.49/1.72
4.11
5.73
3.95
4.25
5.59
3.92/4.93
6.28/5.35
3.98/5.04
B
C
D
E
F
ZnTPP
ZnTMesP
[a] Data for L = THF and L = Pyr are given in the nominator and denominator, respectively.
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Synthesis and Photophysical Studies of Dendritic Metalloporphyrins
dendrimer core, since they provide larger luminescence re- absorption spectrum. There is a long-wavelength shift on
sponse differences between the four- and five-coordinate going from compounds that have the dendrimer core ligated
dendrimer core (Table 6).
with THF to those with pyridine as a ligand. The fluores-
cence quantum yields Φfl are of the same order of magni-
B
tude in the four studied dendrimers A-THF, B-THF, D-
B
THF, and E-THF. However, there is a small decrease in Φfl
for “ZnTMesP-like” dendrimers C-THF and F-THF. The
B
Φfl value decreases further upon ligation of dendrimer F
with pyridine.
The quantum yield of the blue S2ǞS0 fluorescence de-
pends on the competition between the radiationless internal
S2ǞS1 conversion and the S2ǞS0 radiative transition rate
constants.[36] The radiationless internal S2ǞS1 conversion is
much higher than the S2ǞS0 radiative transition rate and
this results in a very low blue fluorescence quantum yield
ΦflB. Therefore, to a good approximation, ΦflB can be taken
as the simple ratio kfl(S2ǞS0)/kIC(S2ǞS1). For the TPP
metallocomplexes, the internal conversion rate kIC(S2ǞS1)
is known to be reciprocal to the energy gap ΔE(S2–S1).[38]
The plot of the ΦflB value as a function of the S2–S1 energy
gap (Figure 6) demonstrates a good linear correlation in the
series consisting of the parent ZnTPP and ZnTMesP por-
phyrins (both four-coordinate and ligated with THF and
pyridine) and the ligated dendrimers A-THF–F-THF, and
F-Pyr. Such a correlation may be explained by changes in
the internal conversion rate constant kIC(S2ǞS1) due to
variation of the energy gap ΔE(S2–S1), whereas the radiative
transition rate constant kfl(S2ǞS0) remains about the same.
It is worthwhile to note that essentially the same behavior
is observed for both four- and five-coordinate (with THF
and pyridine) compounds. The differences in the rotational
degree of freedom for meso-substituents/dendrons in the
ZnTPP and “ZnTPP-like” dendrimers B and E, the
ZnTMesP and “ZnTMesP-like” dendrimers C and F, and
the trans-Ph2-Mes2 pattern dendrimers A and D, also have
no noticeable influence on either the internal conversion
rate kIC(S2ǞS1) or radiative transition rate kfl(S2ǞS0).
Figure 5. Correlation between the rate constant of emissive (kfl,
upper panel) and total radiationless (knr, lower panel) deactivation
of lowest singlet S1 state and the number of sterically hindered
spacers in the studied compounds with the four-coordinate form
of the Zn-porphyrin core (closed symbols, A–F), and with the five-
coordinate form of the Zn-porphyrin core (open symbols, A-THF–
F-THF).
Table 6. Luminescent properties for the S2 state of dendrimers
A–F.
fl
fl
λ0,0 [nm]
λ0,1 [nm]
ΦflB ϫ103
A-THF
431.0
432.0
432.5
431.0
432.0
432.5
440.5
427.0
430.0
439.0
427.5
428.0
438.0
454.0
455.0
455.5
454.0
455.0
455.5
466.5
–
454.0
472.0
–
455.0
472.0
0.92
1.11
0.78
1.10
1.09
0.79
0.41
1.25
1.10
0.60
0.85
1.31
0.53
B-THF
C-THF
D-THF
E-THF
F-THF
F-Pyr
ZnTPP
ZnTPP-THF
ZnTPP-Pyridine
ZnTMesP
ZnTMesP-THF
ZnTMesP-Pyridine
Parameters of the blue S2ǞS0 fluorescence for the
studied compounds are presented in Table 5. The positions
of the blue fluorescence spectrum follow the trend for the and parent porphyrins.
Figure 6. Correlation between the blue S2ǞS0 fluorescence quan-
tum yield Φfl and the energy gap ΔE(S2–S1) for dendrimers A–F
B
Eur. J. Org. Chem. 2014, 1766–1777
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1773

N. T. Nguyen, J. Hofkens, I. G. Scheblykin, M. Kruk, W. Dehaen
FULL PAPER
beam. The fluorescence was spectrally resolved by a monochroma-
tor (Sciencetech 9030, 6 mm bandwidth), and detected by a micro-
channel plate photomultiplier tube (MCP-PMT, R3809U, Hamam-
atsu). A time-correlated Single Photon Timing PC module (SPC
830, Becker & Hickl) was used to obtain the fluorescence decay
histogram in 4096 channels. The decays were recorded with 10,000
counts in the peak channel, in time windows of 25 ns correspond-
ing to 6.1 ps/channel and analyzed globally with a time-resolved
fluorescence analysis (TRFA) software. The full-width at half-
maximum (FWHM) of the IRF was typically in the order of 32 ps.
The quality of the fits was judged by the fit parameters χ2 (Ͻ 1.2),
Zχ2 (Ͻ 3) and the Durbin Watson parameter (1.8ϽDWϽ2.2) as
well as by visual inspection of the residuals and autocorrelation
function.
Conclusions
The spectral luminescent properties of the family of Zn-
porphyrin core dendrimers with triazole-linked carbazole
dendrons have been studied. The dual emission of the den-
drimers in the blue and red regions has been observed and
characterized in detail. It was found that the spectral prop-
erties of new dendrimers retain the main features of the
parent core porphyrins. The observed trends in the spectro-
scopic data and photophysical properties of the dendrimers
have been rationalized in terms of the type of meso-spacer
between the macrocycle and dendritic shell. The key feature
of the meso-spacer is expected to be the degree of hindrance
for aryl ring rotation relative to the mean porphyrin plane.
Based on the observed differences in the S1ǞS0 fluores-
cence quantum yield upon going from four- to five-coordi-
nate dendrimers, the mesityl-like dendrimer architecture is
The absorbance and fluorescence measurements were conducted
in standard rectangular cells (1ϫ1 cm, Hellma) in air-equilibrated
solutions at 293Ϯ2 K. Deoxygenated solutions were used for mea-
surements of the fluorescence quantum yield and lifetime. Deoxy-
expected to be optimal for sensor design due to the largest genation of the solutions was performed by argon bubbling for
20 min immediately before measurements. The fluorescence quan-
tum yield Φfl was determined by using standard sample methods,
with the Zn-5,10,15,20-tetraphenylporphyrin (Zn-TPP) taken as a
changes in the luminescent signal upon porphyrin core
ligation. The blue S2ǞS0 fluorescence quantum yield values
for dendrimers can be rationalized in terms of the S2ǞS1
energy gap law.
standard sample (Φ0 = 0.033).
fl
3,5-Bis(azidomethyl)-2,4,6-trimethylbenzaldehyde (4): Yellow oil. 1H
NMR (300 MHz, CDCl3, 25 °C, TMS): δ = 10.62 (s, 1 H, CHO),
4.50 (s, 4 H, 2ϫ CH2), 2.54 (s, 6 H, 2ϫ CH3), 2.49 (s, 3 H,
CH3) ppm. 13C NMR (75 MHz, CDCl3, 25 °C, TMS): δ = 195.31
(CHO), 142.24 (C-Ar), 139.15 (2ϫ C-Ar), 134.16 (C-Ar), 131.62
(2ϫ C-Ar), 48.11 (2ϫ CH2), 16.90 (CH3), 15.98 (2ϫ CH3) ppm.
HRMS (EI): m/z calcd. for C12H14N6O 258.1229; found 232.1110
[MH+ – N2].
Experimental Section
General Experimental Methods: NMR spectra were acquired with
Bruker Avance 300 MHz, Bruker AMX 400 MHz or Bruker Av-
ance II+ 600 MHz spectrometers, and chemical shifts (δ) are re-
ported in parts per million (ppm) referenced to tetramethylsilane
(TMS) or the internal (NMR) solvent signals. Mass spectra were
recorded with a HP5989A apparatus (CI and EI, 70 eV ionization
energy) with an Apollo 300 data system or with a Thermo Finnigan
LCQ Advantage apparatus (ESI). Exact mass measurements were
acquired with a Kratos MS50TC instrument (performed in the EI
mode at a resolution of 10000). Melting points (not corrected) were
determined with 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 purification. Gel permeation chromatog-
raphy (GPC) was used to determine the polydispersity index (PDI)
of all dendrimers A–F; a Shimadzu 10A apparatus was used with
a Plgel 5 μm mixed-D column and all measurements were per-
formed in THF as eluent against polystyrene standards. Infrared
spectra were recorded with an Alpha FTIR spectrometer. MALDI-
TOF mass spectrometry was carried out with a Bruker Daltonics –
ultraflex II & ultraflex II TOF/TOF using the matrix 2,5-dihydrox-
ylbenzoic acid for all samples.
1-[(Trimethylsilyl)ethynyl]-3,5-bis[3,6-bis(tert-butyl)carbazol-9-yl]-
benzene (11): White solid; m.p. 320–322 °C. 1H NMR (300 MHz,
4
CDCl3, 25 °C, TMS): δ = 8.13 (d, JH,H = 0.93 Hz, 4 H, Ar-H),
4
4
7.75 (d, JH,H = 1.71 Hz, 1 H, Ar-H), 7.73 (d, JH,H = 1.71 Hz, 2
4
3
H, Ar-H), 7.49 (dd, JH,H = 1.71, JH,H = 8.67 Hz, 4 H, Ar-H),
7.45 (d, 3JH,H = 8.46 Hz, 4 H, Ar-H), 1.46 (s, 36 H, tert-butyl), 0.27
(s, 9 H) ppm. 13C NMR (75 MHz, CDCl3, 25 °C, TMS): δ =
128.24, 124.85, 123.99, 116.54, 109.29 (CH-Ar), 143.56, 139.91,
138.92, 126.46, 123.81 (C-Ar), 103.35, 97.03 (CϵC), 34.91 (C, tert-
butyl), 32.13 (CH3, tert-butyl) ppm. MALDI-TOF: m/z calcd. for
C51H60N2Si [M+] 728.45; found 728.29.
1-Ethynyl-3,5-bis[3,6-bis(tert-butyl)carbazol-9-yl]benzene (12):
White solid; m.p. Ͼ 350 °C. 1H NMR (300 MHz, CDCl3, 25 °C,
TMS): δ = 8.14 (s, 4 H, H-carbazole), 7.80 (s, 1 H, Ar-H), 7.76 (s,
2 H, Ar-H), 7.47 (ddd, 8 H, H-carbazole), 3.21 (s, 1 H, CϵCH),
1.46 (s, 36 H, tert-butyl) ppm. 13C NMR (75 MHz, CDCl3, 25 °C,
TMS): δ = 128.13, 124.92, 123.89, 116.40, 109.12 (CH-Ar), 143.52,
139.93, 138.71, 125.22, 123.72 (C-Ar), 82.10, 79.35 (CϵC), 34.75
(C, tert-butyl), 31.97, 32.13 (CH3, tert-butyl) ppm. HRMS (EI): m/z
calcd. for C48H52N2 656.4130; found 656.4120.
Spectroscopic Methods and Instrumentation: UV/Vis spectra were
recorded with a Perkin–Elmer Lambda 20 or Cary Varian spectro-
photometer. The fluorescence spectra and fluorescence excitation
spectra were measured with an SFL-1211 spectrofluorimeter (JSC
Solar). The fluorescence decay kinetics were measured with an in-
house constructed single-photon counting spectrometer (KU
Leuven). The OPA, pumped with a mode-locked Ti:sapphire laser
(Tsunami, Spectra Physics), was used as excitation source. The lin-
early polarized excitation light was rotated to a vertical direction
by the use of a Berek compensator (New Focus) in combination
with a polarization filter and directed onto the sample. The emis-
sion spectra were collected at 90° with respect to the incident light
and guided through a polarization filter that was set at the magic
angle (54.7°) with respect to the polarization of the excitation
5,15-Bis(2,4,6-trimethylphenyl)-10,20-bis(4-azidomethylphenyl)-
porphyrin (7): Purple solid. 1H NMR (300 MHz, CDCl3, 25 °C,
TMS): δ = 8.76 (d, 3JH,H = 4.53 Hz, 4 H, H-pyrrole), 8.69 (d, 3JH,H
3
= 4.71 Hz, 4 H, H-pyrrole), 8.23 (d, JH,H = 7.71 Hz, 4 H, Ar-H),
7.67 (d, 3JH,H = 7.89 Hz, 4 H, Ar-H), 7.27 (s, 4 H, H-mesityl), 4.68
(s, 4 H, 2ϫ CH2), 2.61 (s, 6 H, 2ϫ CH3), 1.83 (s, 12 H, 4ϫ CH3),
–2.61 (s, 2 H, 2ϫ NH) ppm. 13C NMR (75 MHz, CDCl3, 25 °C,
TMS): δ = 134.83, 127.77, 126.49 (CH-Ar), 142.07, 139.37, 138.35,
137.77, 118.60, 118.48 (C-Ar), 54.87 (CH2), 21.62 (4ϫ CH3), 21.45
(2ϫ CH3) ppm. MALDI-TOF: m/z calcd. for C52H44N10 808.375;
found 808.145.
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Synthesis and Photophysical Studies of Dendritic Metalloporphyrins
5,10,15,20-Tetrakis{[3,5-bis(azidomethyl)-2,4,6-trimethyl]-
(s, 144 H, tert-butyl) ppm. 13C NMR (100 MHz, CDCl3, 25 °C,
TMS): δ = 131.34, 127.14, 126.92, 123.76, 119.46, 116.29, 109.16
phenyl}porphyrin (9): Purple solid. 1H NMR (300 MHz, CDCl3,
25 °C, TMS): δ = 8.56 (s, 8 H, H-pyrrole), 4.72 (s, 16 H, 8ϫ CH2), (CH-Ar), 149.85, 147.05, 143.15, 141.79, 141.20, 138.98, 138.50,
2.78 (s, 12 H, 4ϫ CH3), 1.93 (s, 24 H, 8ϫ CH3), –2.38 (s, 2 H, 2ϫ 138.08, 129.17, 129.05, 123.48, 118.96 (C-Ar), 49.36 (CH2), 34.72
NH) ppm. 13C NMR (75 MHz, CDCl3, 25 °C, TMS): δ = 140.24, (C, tert-butyl), 31.99 (CH3, tert-butyl), 19.75 (CH3), 16.40
140.12, 138.10, 129.85, 118.36 (C-Ar), 49.14 (CH2), 19.49 (2 ϫ (CH3) ppm. MALDI-TOF: m/z calcd. for C288H292N36Zn:
CH3), 16.54 (CH3) ppm. MALDI-TOF: m/z calcd. for C64H62N28
1222.571; found 1222.561.
4318.324 [M+]; found 4320.7 [M + 2H+]. Polydispersity index (PDI)
= 1.037.
ZnII-5,15-bis(2,4,6-trimethylphenyl)-10,20-bis(4-azidomethyl-
Dendrimer D: Purple solid. 1H NMR (400 MHz, CDCl3, 25 °C,
TMS): δ = 8.79 (d, 3JH,H = 4.68 Hz, 4 H, H-pyrrole), 8.74 (d, 3JH,H
phenyl)porphyrin: Purple solid. 1H NMR (300 MHz, [D8]THF,
3
3
25 °C, TMS): δ = 8.76 (d, JH,H = 4.71 Hz, 4 H, H-pyrrole), 8.65
= 4.28 Hz, 4 H, H-pyrrole), 8.22 (d, JH,H = 7.68 Hz, 4 H, Ar-H),
3
3
4
(d, JH,H = 4.71 Hz, 4 H, H-pyrrole), 8.21 (d, JH,H = 7.89 Hz, 4
8.19 (d, JH,H = 2.12 Hz, 4 H, Ar-H), 8.16 (s, 8 H, H-carbazole),
3
3
H, Ar-H), 7.72 (d, JH,H = 7.92 Hz, 4 H, Ar-H), 7.28 (s, 4 H, H-
8.06 (s, 2 H), 7.80 (s, 2 H), 7.60 (d, JH,H = 7.28 Hz, 4 H, Ar-H),
7.55 (d, 3JH,H = 8.52 Hz, 8 H, H-carbazole), 7.50 (dd, 4JH,H = 1.28,
mesityl), 4.75 (s, 4 H, 2ϫ CH2), 2.59 (s, 6 H, 2ϫ CH3), 1.84 (s, 12
H, 4ϫ CH3) ppm. 13C NMR (75 MHz, [D8]THF, 25 °C, TMS): δ
= 135.58, 132.63, 130.82, 128.47, 126.97 (CH-Ar), 150.75, 150.64,
144.31, 140.65, 139.85, 138.07, 136.04, 120.25, 119.39 (C-Ar), 55.34
(CH2), 21.94 (4ϫ CH3), 21.56 (2ϫ CH3) ppm. MALDI-TOF: m/z
calcd. for C52H42N10Zn 870.29; found 870.22.
ZnII-5,10,15,20-tetrakis{[3,5-bis(azidomethyl)-2,4,6-trimethyl]-
phenyl}porphyrin: Purple solid. 1H NMR (300 MHz, [D8]THF,
25 °C, TMS): δ = 8.56 (s, 8 H, H-pyrrole), 4.79 (s, 16 H, 8ϫ CH2),
2.80 (s, 12 H, 4ϫ CH3), 1.94 (s, 24 H, 8ϫ CH3) ppm. 13C NMR
(75 MHz, [D8]THF, 25 °C, TMS): δ = 150.63, 142.57, 140.67,
138.61, 130.98, 119.57 (C-Ar), 131.48 (CH-pyrrole), 49.81 (CH2),
19.62 (2ϫ CH3), 16.52 (CH3) ppm. MALDI-TOF: m/z calcd. for
C64H60N28Zn 1284.484; found 1285.497 [M + H+].
3
4JH,H = 0.84, JH,H = 8.74 Hz, 8 H, H-carbazole), 7.24 (s, 4 H, H-
mesityl), 5.83 (s, 4 H, CH2), 2.61 (s, 6 H, 2ϫ CH3), 1.78 (s, 12 H,
4 ϫ CH3), 1.47 (s, 72 H, tert-butyl) ppm. 13C NMR (100 MHz,
CDCl3, 25 °C, TMS): δ = 135.08, 132.15, 130.98, 127.71, 126.08,
123.93, 123.72, 122.11, 120.47, 116.40, 109.34 (CH-Ar), 150.04,
149.86, 147.22, 143.56, 143.37, 140.41, 139.18, 138.97, 138.90,
137.50, 133.98, 133.70, 119.54, 119.14 (C-Ar), 54.33 (CH2), 34.79
(C, tert-butyl), 32.03 (CH3, tert-butyl), 21.62 (CH3), 21.47
(CH3) ppm. MALDI-TOF: m/z calcd. for C148H146N14Zn
2183.114; found 2183.223. Polydispersity index (PDI) = 1.028.
1
Dendrimer E: Purple solid. H NMR (600 MHz, CDCl3, 25 °C,
4
TMS): δ = 8.85 (s, 8 H, H-pyrrole), 8.20 (d, JH,H = 1.62 Hz, 8 H,
3
Ar-H), 8.17 (d, JH,H = 7.74 Hz, 8 H, Ar-H), 8.15 (s, 16 H, H-
3
Dendrimer A: Purple solid. 1H NMR (600 MHz, CDCl3, 25 °C,
TMS): δ = 8.84 (d, 3JH,H = 4.44 Hz, 4 H, H-pyrrole), 8.78 (d, 3JH,H
carbazole), 8.08 (s, 4 H), 7.79 (s, 4 H), 7.58 (d, JH,H = 7.68 Hz, 8
3
H, Ar-H), 7.54 (d, JH,H = 8.22 Hz, 16 H, H-carbazole), 7.48 (dd,
4
3
4JH,H = 1.68, JH,H = 1.62, JH,H = 8.25 Hz, 16 H, H-carbazole),
5.83 (br s, 8 H, CH2), 1.44 (s, 144 H, tert-butyl) ppm. 13C NMR
(150 MHz, CDCl3, 25 °C, TMS): δ = 135.04, 132.05, 125.95,
123.87, 123.80, 121.98, 120.61, 116.38, 109.27 (CH-Ar), 150.01,
147.15, 143.34, 143.22, 140.35, 138.86, 133.87, 123.67, 120.24 (C-
Ar), 54.18 (CH2), 34.74 (C, tert-butyl), 31.98 (CH3, tert-butyl) ppm.
MALDI-TOF: m/z calcd. for C240H240N24Zn 3521.880 [M+],
3493.880 [M – 28]; found 3522.791 [M + H+], 3495 [M – 28 + 2H+].
Polydispersity index (PDI) = 1.028.
3
= 4.38 Hz, 4 H, H-pyrrole), 8.27 (d, JH,H = 7.68 Hz, 4 H, Ar-H),
3
8.15 (s, 4 H, H-carbazole), 8.10 (d, JH,H = 8.28 Hz, 4 H, Ar-H),
8.08 (s, 2 H, H-triazole), 7.68 (d, 3JH,H = 8.28 Hz, 4 H, Ar-H), 7.66
3
3
(d, JH,H = 8.22 Hz, 4 H, Ar-H), 7.48 (d, JH,H = 7.14 Hz, 4 H,
3
Ar-H), 7.40 (d, JH,H = 8.28 Hz, 4 H, Ar-H), 7.27 (s, 4 H, H-mes-
ityl), 5.96 (s, 4 H, 2ϫ CH2), 2.62 (s, 6 H, 2ϫ CH3), 1.81 (s, 12 H,
4 ϫ CH3), 1.47 (s, 36 H, tert-butyl) ppm. 13C NMR (150 MHz,
CDCl3, 25 °C, TMS): δ = 135.11, 132.15, 131.04, 127.73, 127.23,
127.12, 126.16, 123.70, 119.93, 116.30, 109.27 (CH-Ar), 150.12,
149.93, 147.92, 143.55, 143.07, 139.24, 139.22, 138.89, 138.21,
137.62, 133.98, 129.29, 119.64, 119.22 (C-Ar), 54.40 (CH2), 34.77
(C, tert-butyl), 32.04 (CH3, tert-butyl), 21.62 (CH3), 21.46
(CH3) ppm. MALDI-TOF: m/z calcd. for C108H100N12Zn 1628.748
[M+], 1600.748 [M – 28]; found 1629.629 [M + H+], 1600.714 [M –
28]. Polydispersity index (PDI) = 1.024.
Dendrimer F: Purple solid. 1H NMR (300 MHz, CDCl3, 25 °C,
TMS): δ = 8.56 (br s, 8 H, H-pyrrole), 8.12 (s, 48 H, 32 H-carba-
zole, 16 H-phenyl), 7.90 (br s, 8 H, H-triazole/H-phenyl), 7.74 (br
3
s, 8 H, H-phenyl/H-triazole), 7.47 (d, JH,H = 8.46 Hz, 32 H, H-
3
carbazole), 7.40 (d, JH,H = 8.31 Hz, 32 H, H-carbazole), 5.79 (br
s, 16 H, 8ϫ CH2), 2.75 (br s, 12 H, 4ϫ CH3), 1.93 (br s, 24 H, 8ϫ
CH3), 1.39 (s, 288 H, tert-butyl) ppm. 13C NMR (100 MHz,
CDCl3, 25 °C, TMS): δ = 149.82, 146.47, 143.50, 143.38, 141.62,
141.32, 140.37, 138.88, 138.74, 138.60, 138.31, 133.93, 131.55,
129.07, 123.88, 123.70, 122.02, 120.17, 118.87, 116.41, 109.26,
108.95 (C-Ar), 49.75 (CH2), 34.73 (C, tert-butyl), 31.97 (CH3, tert-
butyl), 20.01 (CH3), 17.00 (CH3) ppm. MALDI-TOF: m/z calcd.
for C448H476N44Zn 6542.28 [M+], 6514.28 [M – 28]; found 6542.23
[M+], 6513.37 [M – H+ – 28]. Polydispersity index (PDI) = 1.030.
1
Dendrimer B: Purple solid. H NMR (400 MHz, CDCl3, 25 °C,
TMS): δ = 8.85 (s, 8 H, H-pyrrole), 8.13 (s, 16 H, Ar-H), 7.73 (s, 4
H, H-triazole), 7.68 (d, 3JH,H = 7.04 Hz, 8 H, Ar-H), 7.50 (d, 3JH,H
3
= 8.2 Hz, 8 H, Ar-H), 7.41 (d, JH,H = 8.24 Hz, 16 H, Ar-H), 7.30
3
(d, JH,H = 8.6 Hz, 8 H, Ar-H), 5.62 (s, 8 H, 2ϫ CH2), 1.43 (s, 72
H, tert-butyl) ppm. 13C NMR (100 MHz, CDCl3, 25 °C, TMS): δ
= 150.08, 147.43, 143.56, 143.09, 139.07, 138.04, 135.05, 133.86,
131.96, 128.67, 127.06, 126.89, 125.82, 123.69, 123.50, 120.16,
119.97, 116.31, 109.22 (C and CH-Ar), 54.03 (CH2), 34.73 (C, tert-
butyl), 32.01 (CH3, tert-butyl) ppm. MALDI-TOF: m/z calcd. for
C160H148N20Zn 2413.148 [M+], 2385.148 [M – 28]; found 2415.042
[M + 2H+], 2385.120 [M – 28]. Polydispersity index (PDI) = 1.015.
Supporting Information (see footnote on the first page of this arti-
cle): Experimental procedures, NMR, FTIR, mass spectra of new
compounds, gel permeation chromatography (GPC) of porphyrins,
absorption and luminescence spectra of porphyrins.
Dendrimer C: Purple solid. 1H NMR (400 MHz, CDCl3, 25 °C,
TMS): δ = 8.70 (sbr, 8 H, H-pyrrole), 8.13 (s, 16 H, H-carbazole),
3
Acknowledgments
8.01 (d, JH,H = 7.04 Hz, 16 H, Ar-H), 7.72 (s, 8 H, H-triazole),
3
3
7.56 (d, JH,H = 8.24 Hz, 16 H, Ar-H), 7.38 (d, JH,H = 7.04 Hz,
16 H, Ar-H), 7.31 (d, 3JH,H = 8.6 Hz, 16 H, Ar-H), 5.69 (sbr, 16 H, This work was supported by a FP-7 grant from the EC for Re-
CH2), 2.50 (sbr, 12 H, 4ϫ CH3), 1.90 (sbr, 24 H, 8ϫ CH3), 1.42 ppm search, Technological Development and Demonstration Activities
Eur. J. Org. Chem. 2014, 1766–1777
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1775

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Received: August 1, 2013
Published Online: February 11, 2014
Eur. J. Org. Chem. 2014, 1766–1777
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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