Linear porphyrin dimers with fluorenyl arms linked by an ethynyl bridge

Article abstract of DOI:10.1016/j.tet.2013.06.019

A series of porphyrin monomers bearing fluorenyl donor groups is presented; successively, compounds 10, 11, 12, and 13 bearing three fluorenyl groups. Starting from these building blocks, the synthesis of new porphyrin ethynyl-linked dimers 7 and 8, beari

Full text of DOI:10.1016/j.tet.2013.06.019

Tetrahedron 69 (2013) 7112e7124
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Linear porphyrin dimers with fluorenyl arms linked by an ethynyl
bridge
,
,b,
*
Areej Merhi a b, Samuel Drouet a, Nicolas Kerisit a, Christine O. Paul-Roth a
a
ꢀ
Institut de Sciences Chimiques de Rennes, ISCR e UMR CNRS 6226, Universite de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France
Institut National des Sciences Appliquees, INSA e ISCR, 35043 Rennes Cedex, France
b
ꢀ
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of porphyrin monomers bearing fluorenyl donor groups is presented; successively, compounds
10, 11, 12, and 13 bearing three fluorenyl groups. Starting from these building blocks, the synthesis of new
porphyrin ethynyl-linked dimers 7 and 8, bearing in totally six peripheral fluorenyl arms is attempted.
Dimers are obtained by coupling two porphyrin monomers, using a palladium catalyst, by a rigid bridge.
Luminescence studies of new dimers 7 and 8 are presented. We can then compare the detailed lumi-
nescence properties of these dimers with former porphyrin monomer possessing four fluorenyl arms TFP
(2), which is the precursor model of this work, to porphyrin dendrimers bearing various numbers of
fluorenyl arms (3 and 4) and finally to corresponding supramolecular assemblies (5 and 6).
Ó 2013 Elsevier Ltd. All rights reserved.
Received 14 May 2013
Accepted 5 June 2013
Available online 13 June 2013
Keywords:
Porphyrins
Fluorene
Dimer
Luminescence
Quantum yield
1. Introduction
the porphyrins are directly connected by a single bond, usually be-
tween the meso positions, have been prepared by Smith’s group,
Assemblies of porphyrins have shown interesting properties for
the fabrication of electronic devices, optical, and for the conversion
of solar energy. For efficient solar energy harvesting, several chro-
mophores are needed in order to collect light from the entire solar
spectrum.1 In this connection, the photosynthetic light-harvesting
systems (I and II) consist of well-organized porphyrin antennas in
sophisticated three-dimensional structures.2 As in nature, con-
struction of multi-chromophore systems is important to ensure
maximum use of solar energy. Thus, the ability to design and con-
struct molecular architectures in which the energy flow can be
controlled constitutes a great challenge. One approach is to use
porphyrins as building blocks and to assemble them by different
coupling methods. There are many ways to link porphyrins together,
for example, for one of the first assemblies; the ester bond was used
in 1976 by Anton3 to synthesis diporphyrins and triporphyrins.
These compounds were studied for the energy and electrons
transfer in biological processes. In 1983, Milgrom published the
synthesis of a broad assembly of porphyrins, linked by ether bond, to
study the properties of light collection.4 Many assemblies in which
these systems allow electronic interactions between coupled por-
phyrins.5 Therien et al. published the synthesis of porphyrins dimer
linked in meso position by a triple bond as a model for light col-
lecting antenna.6 Later, the synthesis of dimers and trimers linked
by an ethynyl bond in different positions like the mesoemeso,
mesoeb and beb, was proposed to study the influence on the
properties of absorption and emission.7 Lindsey’s research group
has developed methods for the preparation of a wide variety of
assemblies of porphyrins linked by alkyneearyl bond; they studied
their potential as light collector. This approach was used to form
linear porphyrin like dimers and trimers,8,9 we will now consider
this type of linear rigid ethynyl bridge.
On our side, we have previously reported the synthesis of por-
phyrin possessing four fluorenyl arms directly connected at the
meso positions (TFP, compound 2).10e13 More recently, a complete
family of relevant porphyrins was studied in collaboration with
Williams.14 Surprisingly, TFP exhibited a remarkably high quantum
yield (24%), compared to the reference TPP, demonstrating the
capacity of the fluorenyl units to enhance quantum yields. We next
tested the corresponding platinum(II) complex in the fabrication of
red Organic Light Emitting Diodes (OLEDs) obtained by vapor dif-
fusion deposition15,16 or spin coating.17 Then, to exploit this effi-
ciency, a series of porphyrin dendrimers (generations G1 and G2)
bearing these fluorenyl dendrons, was prepared, namely: 3 and 4
(Fig. 1). However, the synthesis of a higher generation porphyrin
* Corresponding author. Tel.: þ33 02 23 23 63 72; fax: þ33 02 23 23 56 37; e-mail
addresses: christine.paul@univ-rennes1.fr, christine.paul@insa-rennes.fr (C.O.
Paul-Roth).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.06.019

A. Merhi et al. / Tetrahedron 69 (2013) 7112e7124
7113
CH2
O
CH2
O
CH2
O
CH2
N
H
O
TPP
N
H
N
N
Compound 1
O
O
H2C
H2C
O
O
H2C
H2C
OOFP
Compound 3
TFP
Compound 2
O
O
O
O
O
H2C
O
O
CH2
O
O
CH2
O
O
H2C
O
N
H
N
H
N
N
O
O
H2C
O
CH2
O
O
O
O
H2C
O
H2C
O
O
O
O
SOFP
Compound 4
Assembly 5
Assembly 6
HN
N
N
N
N
N
M
NH
N
M= Zn Dimer 7
M= 2H Dimer 8
Fig. 1. Compounds 1, 2, 3, 4, 5, 6, 7, and 8.

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A. Merhi et al. / Tetrahedron 69 (2013) 7112e7124
(G3) failed, most likely the so called ‘starburst limit effect’ was
reached.18 Also, supramolecular assemblies 5 and 6, using these
efficient building blocks have been prepared and studied by our
group (Fig. 1).17
a phenyleC^Cephenyl bridge, another, with also three fluorenyl
units in the meso positions, with one activable iodo group to link
with a rigid bridge. The synthesis strategy is based on the coupling
of two A3B porphyrins; one metalized, and another free, for an
easier separation. This biporphyrin-connection is made by
a Sonogashira coupling, under conditions optimized by Lindsey.8,9
First, we will describe the synthesis of prepared aldehyde 9
and then in more details, the synthesis of the new intermediate
porphyrins 10, 11, 12, and 13, possessing one anchoring point. In
a second time, the previous intermediate porphyrins 12 and 13 are
connected to obtain the dimer zinc complex porphyrins 7 and by
demetalation: to obtain free base dimer 8. Preliminary photo-
physical results are reported; in this case, six efficient antenna
are connected by direct meso connection to the porphyrin
macrocycles.
Another way to exploit highly efficient fluorenyl-based anten-
nae with systems like TFP will be proposed in this report. After
consideration of all these examples of assemblies, and knowing the
capacity of fluorenyl arms to absorb light, the idea is to synthesize
dimers of porphyrins as a model for the effect of light collecting
antenna, substituted by six fluorenyls units in the meso position. In
addition, we have seen that when the fluorenyl units were directly
connected at the meso position like in TFP, there was a high fluo-
rescence quantum yield. The preparation of a new assemblies of
fluorenyleporphyrins linked by alkyneearyl bond8,9 will be con-
sidered and by this approach, we will form linear porphyrin dimers.
The bond will be formed by coupling a porphyrin with an iodo
group and another with a terminal alkyne function, catalyzed by
a palladium complex, studied in different conditions. However, in
this respect, the synthesis of new monomers is required. To this
aim, new building blocks with three peripheral fluorenyl groups
and one anchoring point are described (10, 11, 12, and 13).
Photophysical results concerning new linear porphyrin dimers
free and zinc complex are reported and compared to previous data
for monomer TFP,19 secondly to the porphyrin dendrimers bearing
fluorenyl dendrons, namely: 3 and 4 (generation G1 and G2)18,20,21
and finally to the corresponding supramolecular assemblies using
these efficient building blocks 5 and 6.17
It should be noted that in the conditions used, the non-
substituted fluorenyl arm is stable but alkyl chains have often
been introduced on the position-9 of the fluorenyl units to increase
their solubility.22
2.1.2. Synthesis of 4-((trimethylsilyl) ethynyl)benzaldehyde 9. This
synthesis is done in one step by Sonogashira coupling. In more
details, the aldehyde 9 is prepared by coupling between 4-
bromobenzaldehyde and (trimethylsilyl) ethynyl in the presence
of a palladium catalyst, a cocatalyst (copper/iodide), and a base
(triethylamine) in THF.23 The aldehyde 9 is obtained as a white
powder with a yield of 92% (Scheme 1).
Pd(PPh ) Cl
3 2
2
CuI, NEt
3
CHO
TMS
Br
CHO
TMS
H
THF
9
92 %
Scheme 1. Synthesis of compound 9 (4-((trimethylsilyl)ethynyl) benzaldehyde).
2. Results and discussion
2.1. Synthesis
2.1.3. Synthesis and characterization of porphyrin 10, possessing
three fluorenyl arms. Theprotectedfree-baseporphyrinA3B(10), was
prepared from two aldehydes: the fluorenylcarbaldehyde (commer-
cial) and previous prepared; 4-((trimethylsilyl)ethynyl)benzaldehyde
9. The synthesis of porphyrin 10 is made by the method of Lindsey: it
consists of mixed condensation between two different aldehydes and
pyrrole (Scheme 2). Three equivalents of fluorenylcarbaldehyde and
1 equiv of benzaldehyde 9, prepared in advance, are reacted with
2.1.1. Objectives. The aim of this work consist of the synthesis
of porphyrin dimer starting from two types of porphyrins:
one substituted at three positions by meso fluorenyl units and
an acetylenic group on purpose to future ethynyl-link by
CHO
1) BF3.OEt2 cat.
NH
N
N
2) p-chloranil
TMS
N
H
HN
CHO
CHCl3
TMS
15 %
9
10
Scheme 2. Synthesis of porphyrin 10.

A. Merhi et al. / Tetrahedron 69 (2013) 7112e7124
7115
4 equiv of pyrrole. The reaction takes place in chloroform, at room
temperature, catalyzed by the Lewis acid BF3$OEt2. After 3 h of re-
action, adding 3 equiv of p-chloranil in order to oxidize the por-
phyrinogen formed, the reaction mixture is refluxed for 1 h. After
neutralization of the acid catalyst with triethylamine, the solvent is
evaporated. Porphyrin 10 is isolated as a purple solid from other re-
action products (polymers as well as mono fluorenyl, di fluorenyl,
etc.) by chromatography on silica gel with a yield of 15%, and was
fully characterized.
directly from the organic layer. The zinc complex 12 is obtained as
a dark red powder with a yield 97%. New zinc complex porphyrin 12
was fully characterized; the hydrogen and carbon atom-labeling
Scheme is shown in Fig. 2.
2.1.6. Synthesis and characterization of porphyrin-free base 13, pos-
sessing three fluorenyl arms. The second type porphyrin is prepared
in one step, according to the method of Lindsey and consists
of mixed condensation between two aldehydes and pyrrole
(Scheme 5). Three equivalents of fluorenylcarbaldehyde and
1 equiv of 4-iodobenzaldehyde for 4 equiv of pyrrole are reacted.
The reaction takes place in chloroform at room temperature, cat-
alyzed by the Lewis acid: BF3$OEt2. After 3 h of reaction, 3 equiv of
oxidant; p-chloranil are added and the reaction mixture was
refluxed for 1 h. After neutralization of the acid catalyst by trie-
thylamine, the solvent is evaporated. Porphyrin 13 is isolated as
a violet powder, from other reaction products (polymers as well as
mono fluorenyl, tri fluorenyl, etc.) by several successive chroma-
tographies on silica gel, with a yield of 8%. New intermediate por-
2.1.4. Preparation and characterization of deprotected porphyrin 11,
possessing three fluorenyl arms. The porphyrin 10 is then basified to
give the free-base porphyrin 11: with the deprotected acetylenic
function (Scheme 3). This deprotection step of 10 involves the ac-
tion of a base: potassium carbonate in a mixture of solvent (DCM/
methanol) at room temperature. Deprotected porphyrin 11 was
obtained as a dark red-violet powder with a yield of 98%, and was
fully characterized; the hydrogen and carbon atom-labeling
Scheme is shown in Fig. 2.
NH
N
N
NH
N
N
K2CO3
H
TMS
HN
HN
CH2Cl2/MeOH
98 %
10
11
Scheme 3. Synthesis of porphyrin 11.
H
H
H
H
H
H
H '
H
H
H '
9
H
H
9
H
H
H
9
H
9
H
8
H
H
8
H
H
H
A
H
H
B
A
B
1
1
HN
N
N
N
N
N
N
H
I
7
H
7
M
H
Cb' Cb
NH
H
5
H
H
6
3
H
H
H
H
4
6
3
H
B
B
H
A
4
5
A
H
H
H
H
H
H
H
M = 2H Compound 11
M = Zn Compound 12
Compound 13
Fig. 2. Hydrogen and carbon atom-labeling for porphyrins 11, 12 and for iodo porphyrin-intermediate 13.
2.1.5. Preparation and characterization of the zinc porphyrin complex
12. The free base porphyrin 11 is then metalated in a (DCM/
methanol) mixture at room temperature, in the presence of 5 equiv
of zinc acetate, Zn(CH3CO2)2$2H2O under inert atmosphere, to give
the zinc porphyrin complex 12 (Scheme 4). The reaction progress
was monitored by UVevisible spectroscopy or by TLC, spotting
phyrin 13 was fully characterized; the hydrogen and carbon atom-
labeling Scheme is shown in Fig. 2.
2.1.7. Synthesis and characterization of the dimer possessing six flu-
orenyl arms 7. The dimer 7 consists of a covalently linked assembly
of two porphyrins, one metalated by zinc: 12 and free-base 13,

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A. Merhi et al. / Tetrahedron 69 (2013) 7112e7124
NH
N
N
N
N
N
N
Zn(CH3CO2)2.2H2O
H
Zn
H
HN
CH2Cl2/MeOH
97 %
11
12
Scheme 4. Synthesis of zinc porphyrin complex 12.
1) BF3.OEt2 cat.
CHO
NH
N
N
2) p-chloranil
I
HN
CHCl3
N
H
I
CHO
8 %
13
Scheme 5. Synthesis of iodo porphyrin-intermediate 13.
separated by a rigid phenylephenyl triple bond bridge. This new
dimer possesses in totally six fluorenyl groups directly connected
in meso position, this should exalt the luminescence of the
compound.
First, the reaction is performed by adding a slightly excess of
zinc complex porphyrin 12 to 1 equiv of free base iodo-porphyrin
13 in a mixture of (THF/triethylamine) (5/1) in the presence of
Pd(0) catalyst and a large excess of triphenylarsine (AsPh3) as li-
gand (Scheme 6a). In these conditions the yield is very low (5%) and
it was difficult to isolate dimer 7.
In more details, to a solution of a slightly excess of zinc complex
porphyrin 12, and 1 equiv of 13, 0.3 equiv of the Pd(0) catalyst is
added: Pd2(dibenzylidene acetone)3$CHCl3 (Pd2(dba)3). Then, fi-
nally, 2.4 equiv of AsPh3 in freshly distillate THF and triethylamine
(5/1 mixture), were added. This solution was stirred for 72 h at
35 ꢀC under argon. Then, the reaction mixture was cooled at room
temperature, filtered, and evaporated to dryness. These conditions
optimized by Lindsey8,9 are preferred to standard conditions for
Sonogashira coupling involving copper iodide, in order to avoid any
risk of porphyrin copper formation. The residue was purified by
two successive column chromatographies on silica gel, using (DCM/
heptane) as an eluent and is purified by precipitation (heptane),
affording the desired product 7, as a dark red powder with a yield of
5%. In these conditions two by-products were isolated: compounds
14 and 15 (Scheme 6b).
tri(o-tolyl)phosphine (P(o-tol)3) was tried. In these different con-
ditions, a reasonable yield could be reached.
In more details, the reaction is now performed by adding 1 equiv
of zinc complex porphyrin 12 and 1 equiv of free base iodo-
porphyrin 13 in a mixture of (toluene/triethylamine) (5/1) in the
presence of 0.3 equiv of Pd(0) catalyst and an excess of P(o-tol)3 as
ligand (Scheme 6a). The reaction mixture was stirred for 24 h at
35 ꢀC under argon. In these conditions, the yield is acceptable (25%)
and it is possible, after two chromatographies and precipitation in
heptane to isolate dimer 7 pure, as a dark red powder. The con-
nection was confirmed by matrix-assisted laser desorption ioni-
zation time-of-flight mass spectrometry (MALDI-TOF MS) and
UVevisible spectrometry. This new compound 7 is very soluble in
most organic solvents and can be purified by precipitation (Et2O,
heptane). Compound 7 was fully characterized by usual solution
spectroscopies (NMR, mass spectrometry) and microanalysis. For
clarity by NMR, the hydrogen and carbon atom-labeling scheme is
shown in Fig. 3.
2.1.8. Synthesis and characterization of the free dimer possessing six
fluorenyl arms 8. This new free dimer 8 was obtained from the
mono zinc complex 7 by acidic treatments with a Bronsted acid, like
trifluoroacetic acid (TFA), the dark red DCM solution turns imme-
diately green. The reaction mixture was stirred and controlled by
UVevisible spectrometry to be sure the entire zinc complex is
eliminated, to obtain the totally free and protonated porphyrin
dimer. Finally, sodium carbonate was added to neutralize acid and
To avoid formation of former by-products and to optimize
the yield, a different ligand as AsPh3 for the palladium catalyst:

A. Merhi et al. / Tetrahedron 69 (2013) 7112e7124
7117
(a)
Catalyst:
Tris(dibenzylideneacetone)dipalladium(0)
Pd2(dba)3
NH
N
N
N
N
N
N
I
H
Zn
HN
b/ P(o-tol)3
a/AsPh3
13
12
THF/NEt3
(5:1)
Toluene/NEt3
(5:1)
OR
Tris(phenyl)arsine
5 %
25 %
Tris(o-tolyl)phosphine
HN
N
N
N
N
N
Zn
NH
N
+ by products 14 and 15
Dimer 7
(b)
NH
N
N
N
N
As
Zn
N
HN
N
15
14
Scheme 6. (a) Synthesis of dimer 7. (b) By-products 14 and 15.
to get a red solution, to obtain the free, not protonated porphyrin
dimer 8. Then, the residue was purified by column chromatography
on silica gel using DCM to obtain neutral 8. This free dimer 8 was
characterized by NMR, UVevisible and mass spectrometry.
4.2 ppm, are the CH2 protons of the three fluorenyl groups. In the
region between 7.5 and 8.5 ppm resonate the aromatic protons
(fluorenyl and phenyl). Concerning the meso substituents of the
porphyrin: we can notice that all the seven protons on the three
fluorenyl arms are equivalent, and in expected position: 8.38 (s,
3H); 8.25 (d, 3H); 8.17 (d, 3H); 8.06 (d, 3H); 7.70 (d, 3H), 7.52 (m,
3H) and 7.44 (m, 3H). At low field; around 9 ppm, there are three
signals, a singlet integrating for four protons and an AB system; two
doublets, for two protons each, they are all assigned to the protons
2.2. NMR studies
The 1H NMR signals obtained in deuterated chloroform for
porphyrins 10, 11, 12, 13, and finally 7 and 8, were carried out at
room temperature, are fine and well resolved.
pyrrole-
b which, being located outside the shielding cone, are
highly deshielded.
2.2.1. 1H NMR characterization of compound 10 and 11. At high field,
around ꢁ3 ppm, we observe the two protons carried by the ni-
trogen atoms in the heart of the porphyrin, this observed shift is
due to be in the shielding cone of the porphyrin macrocycle. At
For these two intermediate compounds 10 and 11, there is only
a clear difference for the protons of the methyl trimethylsilyl group
(0.4 ppm) and for the acetylenic function at 3.3 ppm. The other
proton signals are quiet similar.

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A. Merhi et al. / Tetrahedron 69 (2013) 7112e7124
H
H
H
H
H
H9'
H9''
H
C10
C11
HN
H
H
H8'
H6'
C9
N
HA'
HB
HA
HB'
C '
9
H1'
N
N
N
N
C14
C15
C16
C "
C ''
8
C "
5
C6
C5
C4
9
C "
4
C '
2
H7'
Cb' Cb
Zn
NH
C1
N
H3'
HA'
H4' H5'
HB'
HB
HA
C19
C20
H
H
H
H
H
H
H
H
Dimer 7
Fig. 3. Hydrogen and carbon atom-labeling for new dimer 7.
2.2.2. 1H NMR characterization of compound 12. For this zinc
complex and for the precursor 11, there is only a clear difference for
the protons carried by the nitrogen atoms in the heart of the por-
phyrin; around ꢁ3 ppm, these protons are not observed for the zinc
complex 12. The other proton signals are quiet similar.
a peripheral iodo group showing the shift for the b pyrrolic protons
as indicated by the arrows. In this region, in both cases a singlet
(integrating for 4H) at 9.02 and 8.92 ppm, respectively, and an AB
system (integrating for 4H) are obtained. A small difference in shift
0
0
is also observed for the four protons (HA and HB ) in the phenyl
group; two doublets are observed, for zinc complex 12:
7.89 ppm and for the corresponding free base-iodo 13, at
7.96 ppm. The other proton signals are quiet similar and we can
notice that all the seven peripheral protons on the three fluorenyl
arms are equivalent for 12 and 13, and in expected positions: 8.4
d
¼8.17;
2.2.3. 1H NMR characterization of compound 13. 1H NMR charac-
terization of compound 13 is similar to free porphyrins 10 and 11.
In Fig. 4, we can observe the 1H NMR studies (in CDCl3) of zinc
complex 12 (on the top), in comparison to free base 13 possessing
d
¼8.15;
Fig. 4. 1H NMR studies (in CDCl3) of dimer 7 (with a CH2Cl2 pic), in comparison to zinc porphyrin complex 12 (on the top) and for iodo porphyrin-intermediate 13 showing the shift
as indicated by the arrows.

A. Merhi et al. / Tetrahedron 69 (2013) 7112e7124
7119
(H1), 8.3 (H4), 8.1 (H3), 8.0 (H5), 7.7 (H8), 7.5 (H6), 7.4 (H7). Con-
range: located at 554 nm and 595 nm (Fig. 5c and Table 1). An
additional broad band is also observed in UV range, which corre-
0
cerning the CH2 group of the fluorenyl (H9 and H9 ): they are
equivalent and in both monomers, we observe
d
¼4.20 ppm.
sponds to pep* absorption of the fluorenyl chromophores. This UV
absorption, at 273 nm, is weaker for the zinc complex 12 then
reference TFP (2), due to the smaller number (three vs four) of
fluorenyl groups.
For porphyrin dimer, compound 7dIt shows the presence of
a Soret band at 428 nm and four bands, which are located at 513 nm
(Qy(0, 1), very weak), 555 nm (Qy(0, 0), strong), 597 nm (Qx(0, 1),
strong) and 643 nm (Qx(0, 0), weak), corresponding to the super-
position of visible absorption of free base porphyrin (H2Por) and
zinc complex (ZnPor). In addition, there is a wide band at 281 nm
corresponding to the absorption of the six fluorenyls arms (Table 1).
2.2.4. 1H NMR characterization of dimer compound 7. One can note
on Fig. 4, the disappearance of the singlet corresponding to the
acetylenic proton at 3.30 ppm of the precursor zinc porphyrin
complex 12. For 7, at high field, we could not observe the two
protons carried by the nitrogen atoms of the porphyrin-free base in
the dimer. At 4.2 ppm, there is a singlet for the 12 protons of the
CH2 protons of the six fluorenyl groups. In the region between 7.5
and 8.5 ppm resonate the aromatic protons (fluorenyl and phenyl),
meso substituents of the porphyrin: we can notice that all the seven
protons on the six fluorenyl arms are approximately equivalent.
They are in expected positions in comparison to the monomers:
8.42 (s, 6H); 8.29 (m, 6H); 8.18 (m, 6H); 8.06 (d, 6H); 7.71 (d, 6H);
7.54 (t, 6H) and 7.43 (t, 6H). Around 9 ppm, there are five signals
2.3.2. Electronic spectra of titration. The formation of free dimer 8
by adding TFA to zinc complex 7 was followed by UVevisible
spectrophotometry (Fig. 5b). During this titration, the Soret band,
initially at 428 nm, for dimer 7, is red shifted to 461 nm, because of
protonation and consequently loss of encapsulated zinc.
assigned to the protons pyrrole-b: 9.09 (s, 4H), 9.07 (d, 2H), 9.05 (s,
4H), 9.04 (s, 4H), 9.02 (d, 2H). Three of these signals are singlet
integrating for four protons each and two signals are an AB system
integrating in totally for four protons, due to the symmetry of this
molecule.
In most cases, concerning protonation of a porphyrin monomer,
because of small difference between stability constant (K3 and K4)
due to cooperative protonation, only two forms are observed by
spectral methods:27 the neutral free base H2Por and the dication
2.2.5. 1H NMR characterization of free dimer compound 8. Now at
high field, we could observe the four protons carried by the nitro-
gen atoms of the two porphyrin-free bases in the dimer as a singlet
at ꢁ2.70. At 4.22 ppm, there is a singlet for the 12 protons of the
CH2 protons of the six fluorenyl groups. As before, in the region
between 7.4 and 8.9 ppm resonate the aromatic protons (fluorenyl
and phenyl) meso substituents of the porphyrin: we can notice that
all the seven protons on the six fluorenyl arms are equivalent, and
in expected positions in comparison to the monomers: 8.32 (s, 6H);
8.18 (m, 6H); 8.08 (m, 6H); 7.98 (d, 6H); 7.68 (d, 6H); 7.52 (t, 6H) and
7.43 (t, 6H). Around 8.9 ppm, there is a large signal for the 16
H4Por2D
:
K3
K4
H2Por
Free base
H3Por+
H4Por2+
Monocation
Dication
In our work, dissolution of dimer 7 writed ZnPoreH2Por be-
cause composed of a zinc complex (ZnPor) and a free base (H2Por)
in neutral DCM solution results in a UVevisible spectrum with
a maximum absorbance at 428 nm, the evolution of visible spectra
by protonation (adding regular small quantities of TFA) of starting
ZnPoreH2Por is shown in Fig. 5b. By adding TFA we have:
protons pyrrole-b.
2.3. Photophysical properties
½ZnPoreH2Porꢂ/½ZnPoreH4Porꢂ2þ/½H4PoreH4Porꢂ4þ
2.3.1. Electronic spectra. The recording of the UVevisible absorp-
tion spectra of the porphyrins 10, 11, 12, 13, and finally 7, 8, was
carried out at room temperature in DCM. For these compounds,
measurements at different concentrations were performed; a more
concentrated solution is used to display the Q bands and a less
concentrated to the Soret band of porphyrin. The UVevisible
spectra of free porphyrin 10, 11, and 13 exhibit an intense Soret
band with a maximum absorption similar around 424 nm and four
Q bands characteristic of a porphyrin free base, which are located at
519, 555, and 593 and at 649 nm. In addition, there is a wide band
around 275 nm corresponding to the absorption of fluorenyl arms,
In our case, the dication form [ZnPoreH4Por]2D is not observed,
probably due to the small difference between stability constant,
only the neutral form [ZnPoreH2Por] and the tetra-protonated
form [H4PoreH4Por]4D are observed by UVevisible.
The evolution of these spectra for both protonation steps has
been followed by UVevisible to understand the process, so we
observe an isosbestic point at 432 nm; illustrating the formation of
a distinct species: [H4PoreH4Por]4D. For this tetracation porphyrin
dimer, we observe the presence of a band at 461 nm and large band,
which is located at 684 nm corresponding to the superposition of
visible absorption of two similar protonated porphyrins.27 No
evolution of the spectrum is observed if more acid is added. Then,
we neutralize this tetracation [H4PoreH4Por]4D, by adding NEt3:
the pep* absorption in the UV range is clearly apparent but absent
for TPP (1), see Fig. 5a. For compound 2, the four fluorenyl arms
absorb in the UV range with a maximum absorption peak at
272 nm, while for free bases 10, 11, and 13 possessing only three
arms, the absorption is weaker with a maximum at 275 nm. At
425 nm is the B(0,0) band (Soret band), slightly red shifted com-
pared to 417 nm for TPP (1), approximately as much as for TFP (2)
(426 nm). This tendency in red shifting is observed as well for the
four Q bands.
The Zn(II) porphyrin complexes exhibit characteristic change in
the electronic spectra compared to the free-base porphyrins. The
absorption spectra of Zn(II) porphyrins display a single Q band
absorption, which is a combination of the Qx and Qy bands due to
the D4h symmetry of metal porphyrins, instead of the D2h symmetry
of free base porphyrins, with two discernible sub-bands (Q(0,1) and
Q(0,0))24e26. Thus, the zinc complex 12 exhibit an intense Soret
band at 426 nm, together with two weak Q-bands in the visible
½H4PoreH4Porꢂ4þ/½H2PoreH2Porꢂ
The evolution of visible spectra by basifying is shown in Fig. 5b.
Deprotonation occurred on titration with NEt3, transforming the
[H4PoreH4Por]4D into the free base, so absorbance at 462 nm
disappeared and an isosbestic point at 432 nm, is again observed.
We can notice that the original spectrum of dimer 7, is not restored
because of the irreversible loss of encapsulated zinc but no partial
degradation is observed. A new form is obtained corresponding to
the neutral species [H2PoreH2Por] named free dimer 8.
For free base porphyrin dimer 8dIt shows the presence of
a Soret band at 426 nm: this band is slightly blue shifted compared

7120
A. Merhi et al. / Tetrahedron 69 (2013) 7112e7124
1,1
(a)
(b)
1,1
1
Reference compound TPP (1)
Dimer 7
0,9
0,7
0,5
0,3
0,1
-0,1
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0
Reference compound TFP (2)
OOFP (3)
+ 1 TFA
+ 2 TFA
SOFP (4)
+ 3 TFA
Dimer 8
+ 4 TFA
Dimer free and zinc (7)
+ 5 TFA
Dimer 8 protonnated
Dimer 8 neutral
-0,1
240
230
330
430
530
Wavelength (nm)
630
730
340
440
540
640
740
Wavelength (nm)
(c)
0,95
0,7
Dimer 8
Iodo compound 13
Free alcyne 11
Zn complex alcyne 12
0,45
0,2
-0,05
240
340
440
Wavelength (nm)
540
640
Fig. 5. a/Absorption spectra of TPP (red), TFP (pink), OOFP (dark blue), SOFP (green) and new dimers 7 (orange), 8 (violet) in DCM at room temperature. All the spectra are
normalized to the spectrum of the reference TPP at 417 nm (concentration w2.0ꢃ10ꢁ6 M). b/Formation of free dimer 8 by protonation of zinc complex 7. c/Absorption spectra of
precursors 11, 12, 13, and new dimer 8 in DCM at room temperature.
to 428 nm for dimer 7, due to the loss of zinc. This tendency in blue
shifting is not observed for the Q bands; they are slightly red shifted
compared to dimer 7, and the relative intensities are different. They
are located at 521 nm (Qy(0, 1); strong), 557 nm (Qy(0, 0); strong),
595 nm (Qx(0, 1); strong) and 650 nm (Qx(0, 0); weak), corre-
sponding typically to visible absorption of a free porphyrin.
In addition, there is exaltation in UV absorption: a wide band at
268 nm corresponding to the absorption of the six fluorenyls arms
is observed. We can notice in Fig. 5a, that in this conjugated system
possessing six fluorenyl arms and two porphyrin macrocycles, the
antenna absorption is stronger for dimer 8, then for TFP possessing
four arms per porphyrin heart. In Fig. 5c the UVevisible absorption
of monomers 11, 12, and 13 are compared to the absorption of free
dimer 8. The profiles of parents monomers 11, 12 (except Q bands),
and 13 are quiet similar.
2.3.3. Emission spectroscopy. Generally, the emission spectra of
porphyrin zinc complexes consist of three sub-bands assigned to
a vibronic progression from a Q state: the band near 720 nm
assigned as Q(2,0) is very weak and appears often as an extended
tail on the Q(1,0) band. The strongest emission band Q(0,0) is
typically around 600 nm and the second peak; Q(1,0) at w 650 nm,
due to the metal coordination.13
The fluorescence spectra at 25 ꢀC of the zinc(II) complex 12, after
excitation in the Soret band (or B(0,0) band) reveals a strong red
fluorescence with a peak maximum Q(0,0) at 607 nm and a second
peak, Q(1,0) at 655 nm (Fig. 6a). We can notice that the band near
720 nm assigned as Q(2,0), does not appear for this complex.
For comparison, the emission spectrum of free iodo compound
13 is also reported. After excitation in the Soret band, a strong red
emission at 663 nm, assigned as Q(1,0), and a weaker shoulder at

A. Merhi et al. / Tetrahedron 69 (2013) 7112e7124
7121
Table 1
after excitation in the Soret band, a weak emission at 600 nm,
a strong red emission at 657 nm and a weaker shoulder at 720 nm
are observed.
Photophysical properties of the fluorenyl porphyrins 1, 2, 3, and 4 in dilute CH2Cl2
solution at 298 K, and of dimers 7 and 8, zinc complex 12 and free base 11, 13, under
the same conditions for comparison
In conclusion for this compound 7, we clearly identify the free
base part and the zinc complex part of the non-symmetrical dimer
molecule [ZnPoreH2Por]. In the opposite for demetalated dimer 8,
of type [H2PoreH2Por], possessing two similar free base moieties
H2Por, we observe as expected, two peaks: at 657 (Q(1,0)) and
720 nm (Q(2,0)).
Porphyrin
lmax/nma lmax/nmb lmax/nm Q bands lem/nm
UV band Soret band
Ffc
TPP (1)
TFP (2)
OOFP (3)
SOFP (4)
Free 11
Zn (12)
Iodo (13)
Dimer (7)
d
417
426
423
423
425
426
424
428
426
513, 548, 589, 646 650, 714
519, 557, 593, 649 661, 725
516, 551, 592, 653 656, 721
517, 552, 590, 647 656, 721
518, 555, 594, 649 657, 700
0.12
0.24
0.13
0.14
0.21
0.07
0.05
272
263
270
275
273
275
281
554, 595
607, 655
2.3.4. Energy transfer. The efficiency of energy transfer from fluo-
renyl donors toward porphyrin acceptor will be discussed. Excita-
tion of dimers 7 and 8 in the fluorenyl antennae results in the red
emission of porphyrins with a max at 657 nm in both cases. Ef-
fectively, the blue fluorenyl emission is partly quenched for dimer 7,
almost completely quenched for free dimer 8, and red emission is
seen predominantly from the porphyrin (Fig. 6b and c). We have to
notice that, when excited directly at 425 nm, dimers 7 and 8 show
a strong red emission in comparison to the indirect excitation at
280 nm. But this is not evidence of inefficient energy transfer but of
a more complex process.28
519, 555, 593, 649 663, 728
513, 555, 597, 643 600, 657, 720 0.05
521, 557, 595, 650 657, 720 0.17
Free dimer (8) 268
a
Wavelengths of the absorption maxima in the UV region (200e400 nm range).
b
Wavelengths of the absorption maxima in the Soret or
(400e450 nm range).
B band region
c
Fluorescence quantum yields using TPP in DCM as standard, following excita-
tion into the Soret bands.
728 nm, assigned as Q(2,0) are observed (Fig. 6a). That means that
by emission spectroscopy, we should be able to clearly identify the
free base moiety H2Por and the zinc complex moiety ZnPor of the
dimer molecule [ZnPoreH2Por]. Concerning, dimer 7, effectively;
The excitation spectrum of compound 7 around 657 nm (Fig. 6d)
reveals that the strong emission from the Soret state is populated
(a)
(b)
Dimer 7
280 nm
Zn 12
425 nm
Free 11
Zn
Iodo 13
Free Dimer 8
6
Fluorenyls (7)
300
400
500
Wavelength (nm)
600
700
800
500
550
600
650
700
750
800
Wavelength (nm)
(c)
(d)
Dimer 7
280 nm
Free Dimer 8
425 nm
Excitation of Free Dimer 8
Excitation of mono Zinc Dimer 7
6
Fluorenyls (8)
300
400
500 600
Wavelength (nm)
700
800
240
340
440
Wavelength (nm)
540
640
740
Fig. 6. a/Emission spectra of monomers 11, 12, and 13 compared to dimers 7 and 8 in DCM at room temperature. All the spectra are normalized to the spectrum of dimer 7 at 657 nm
(concentration w2.0 10ꢁ6 M). b/Fluorescence spectra of 7 in DCM at room temperature under single photon excitation conditions. A partial quenching of the donor emission is
observed upon excitation of 7 at 280 nm (blue), resulting in a significant porphyrin emission from 7, compared to direct emission of 7 at 425 nm (red). c/Fluorescence spectra of 8 in
DCM at room temperature under single photon excitation conditions. A partial quenching of the donor emission is observed upon excitation of 8 at 280 nm (blue), resulting in
a significant porphyrin emission from 8, compared to direct emission of 7 at 425 nm (red). d/Photoluminescence spectra of dimer 7 (plain red) and 8 (plain blue) in CH2Cl2 solution
(w1.0 10ꢁ6 M), at 25 ꢀC, the emission spectra were cut above 800 nm. Excitation spectra of compounds 7 (dashed red) and 8 (dashed blue) at 650 nm.

7122
A. Merhi et al. / Tetrahedron 69 (2013) 7112e7124
when the fluorenyl band is excited. This indicates that excitation
over all the 200e650 nm region leads to the population of the
fluorescent excited states of the porphyrin, as the fluorene ab-
sorption becomes apparent under such excitation conditions. For
comparison, the corresponding excitation spectrum of free dimer 8
is also shown in Fig. 6d, and we can see an enhancement in the UV
region due to the fluorenyl arms for the latter.
new dimers, still in the idea of increasing the number of antennae
around the heart porphyrin for light collection.
4. Experimental section
4.1. General procedures
Thus for these compounds 7 and 8, the luminescence can be
modulated in a large range of excitation wavelengths from UV to
red, to finally obtain the desired red emission.
All reactions were performed under argon and were magneti-
cally stirred. Solvents were distilled from appropriate drying agent
prior to use, DCM and CHCl3 from CaH2 and THF was distilled using
sodium/benzophenone system. The rest of the solvents used
were of HPLC grade. Commercially available reagents were used
without further purification unless otherwise stated. Pyrrole
and 2-fluorenecarboxaldehyde were purchased from Aldrich and
were used as received. References TFP¼tetrafluorenylporphyrin,
TPP¼tetraphenylporphyrin.
2.3.5. Fluorescence quantum yields. The fluorescence quantum
yields of these compounds were next determined by comparing
with a calibration standard of compound 1 (TPP) in degassed tol-
uene solution presenting a fluorescence quantum yield of 0.12,29
preferentially to a benzene solution with a fluorescence quantum
yield of 0.13.30 [In this latter case, different refractive indices of the
solvents used in the standard and sample must be corrected.31 In
consequence the correction made for the difference in refractive
indices of solvents is in this case not necessary.] The quantum yield
was calculated from the following equation:
1H NMR and 13C NMR in CDCl3 were recorded using Bruker 200
DPX, 300 DPX, and 500 DPX spectrometers. The chemical shifts are
referenced to internal TMS. The assignments were performed by 2D
NMR experiments: COSY (Correlation Spectroscopy), HMBC (Het-
eronuclear Multiple Bond Correlation), and HMQC (Heteronuclear
Multiple Quantum Coherence). UV spectra were recorded on UVI-
KON XL from Biotek instruments. PL emission was recorded on
a Photon Technology International (PTI) apparatus coupled on an
814 Photomultiplier Detection System, Lamp Power Supply 220B
and MD-5020. Steady-state fluorescence measurements were per-
formed at room temperature on dilute solutions (ca. 10ꢁ6 M) using
an Edinburgh Instruments (FLS 920) spectrometer working in
photon-counting mode, equipped with a calibrated quantum
counter for excitation correction. Fluorescence quantum yields
Fs
¼
FTPP ꢃ ðFs=FTPPÞ ꢃ ðATPP=AsÞ ꢃ ðnTPP=nsÞ2
In the above expression, Fs is the fluorescent quantum yield
of the new compound, F is the integration of the emission in-
tensities, n is the index of refraction of the solution, and A is the
absorbance of the solution at the exciting wavelength. The sub-
scripts TPP and s denote the reference (TPP) and unknown sam-
ples, respectively.32
Values of quantum yield obtained in degassed toluene, of free
ligands 1, 2, 3, and 4 are reported in Table 1. Compounds 3 and 4
present a luminescence quantum yield (13 and 14%, respectively),
which is similar to that of the reference 1 (12%). We showed earlier
that increasing the number of dendrons does have any significant
influence on the quantum yield. As a result, a system in which
a 5,10,15,20-tetraphenylporphyrin is linked, via ether bridges, to 8
or 16 fluorenyl donor moieties in position 3 and 5, presents the
same luminescence efficiency as the parent TPP compound.20,28 For
these reasons dimer with direct connection of fluorenyl on meso
position was proposed.
For free dimer 8: a conjugated system possessing six fluorenyl
arms and two free porphyrin macrocycles, a high luminescence
quantum yield (17%) is obtained in non-degassed DCM, higher than
previous none conjugated dendrimers; with 8 or 16 fluorenyl arms
(compounds 3 and 4, respectively) and as the reference TPP com-
pound (1), but not as high as the parent compound TFP (2).
The corresponding zinc complexes, monomer 12 and dimer 7
have low luminescence quantum yield (around 5e7%), which is
relatively high for zinc complexes, higher than reference compound
ZnTPP (3.3%) and similar to the parent compound ZnTFP (5%).13
were measured using standard methods; TPP in DCM (
lex¼417 nm) was used as a reference. The reported fluorescence
quantum yields are within ꢄ10%.
F
¼0.12 at
4.2. Synthesis of monomers
4.2.1. Synthesis of 4-((trimethylsilyl)ethynyl)benzaldehyde 9 (was
described earlier.23) Trimethylsilylacetylene (5 mL, 4.03 g,
41.0 mmol) was added to a solution of 4-bromobenzaldehyde
(5.00 g, 27.0 mmol), Pd(PPh3)2Cl2 (50 mg, 0.07 mmol), and CuI
(25 mg, 0.13 mmol) in distilled THF (40 mL) under argon. Then,
triethylamine (6.5 mL) was added and the reaction mixture was
heated at 40 ꢀC overnight. The solvent was evaporated under re-
duced pressure. The obtained residue was extracted in DCM,
washed in water, dried with MgSO4, and then taken into dryness.
The solid was then purified by column chromatography on silica gel
using a mixture of heptane/DCM (1:1) as eluent. The compound 9
was obtained as a pale yellow solid to yield 5.04 g (92%). 1H NMR
(400 MHz, CDCl3, d in ppm): 10.01 (s, 1H, CHO), 7.83 (d, 2H, Hphenyl,
3JHH¼7.6 Hz), 7.62 (d, 2H, Hphenyl
(CH3)3Si).
,
3JHH¼7.2 Hz), 0.29 (s, 9H,
3. Conclusions and outlook
4.2.2. Synthesis of 5,10,15-(trifluorenyl)-20-(4-((trimethylsilyl)ethy-
nyl)phenyl) porphyrin 10. 2-Fluorenylcarboxylaldehyde (3.00 g,
15.4 mmol), 4-(trimethylsilyl)ethynyl benzaldehyde (1.00 g,
5.0 mmol), and pyrrole (1.4 mL, 20.0 mmol) were added to distilled
chloroform (1.5 L) in a double necked round bottom flask under
argon. The flask was covered with aluminum foil since the reaction
is light sensitive at this stage. Boron trifluoride diethyl etherate,
In summary, a series of highly luminescent intermediate por-
phyrins bearing three fluorenyl groups was presented, successively,
compounds 10, 11, 12, and 13. Starting from these building blocks,
new linear dimers 7 and 8, bearing in totally six peripheral fluo-
renyl arms were synthesized and fully characterized. We compared
the luminescence properties of these new dimers with the refer-
ence TPP (1), porphyrin dendrimers (3 and 4), but also with TFP (2),
which was the promising precursor model of this work.
Perspectives may be changing the bridge connecting the two
porphyrins of the assembly to optimize the luminescence, and
eventually extend this work to corresponding trimers synthesis.
We can also consider grafting dendrons at the periphery of these
BF3$OEt2 (560 mL) was added, and the reaction was kept at room
temperature for 3 h. Then, 3 equiv of p-chloranil (3.78 g, 15.4 mmol)
were added and the solution was heated to reflux (light protection
was removed). After 1 h, the solution was cooled to room tem-
perature. Two pipettes of triethylamine were added to neutralize
the reaction mixture. Solvent was evaporated and the residue was
filtered over silica with heptane/DCM (65:35) and then (45:55). The

A. Merhi et al. / Tetrahedron 69 (2013) 7112e7124
7123
solid obtained was subjected to a second column chromatography
of silica using the eluent heptane/DCM (70:30). The expected
compound 10 was obtained as a purple solid to yield 756 mg (15%).
428 (316), 554 (11), 596 (3). Anal. Calcd for C67H40N4Zn$CH3OH: C,
81.80, H, 4.44, N, 5.61, found C, 81.22, H, 4.75, N, 5.18. MALDI-TOF
MS: calcd for C67H40N4Zn: 965.25444 [MH]þ, found: 965.90810
[MH]þ. MS (ESI): calcd for C67H40N4Zn: 987.24421 [MNa]þ, found:
987.2432 [MNa]þ.
New intermediate porphyrin 10 was fully characterized. 1H NMR
3
(400 MHz, CDCl3,
d
in ppm): 8.92 (d, 2H, JHH¼5.0 Hz, Hb-pyrrolic),
3
8.91 (s, 4H, Hb-pyrrolic), 8.82 (d, 2H, JHH¼4.4 Hz, Hb-pyrrolic), 8.38 (s,
3
3H, Hfluorenyl, H1), 8.25 (d, 3H, JHH¼7.6 Hz, Hfluorenyl, H4), 8.17 (m,
4.2.5. Synthesis of 5,10,15-(trifluorenyl)-20-(4-iodophenyl)porphyrin
13. A solution of 4-iodobenzaldehyde (1.00 g, 4.3 mmol),
2-fluorenecarboxaldehyde (2.52 g, 12.9 mmol), and pyrrole
(1.18 mL, 17.2 mmol) in distilled chloroform (1.5 L) was placed in
a two necked flask under argon. The chloroform solution was
degassed by argon bubbling for 20 min. The flask was covered with
aluminum foil since the reaction is light sensitive at this stage.
5H, 2Hphenyl and 3Hfluorenyl, H3), 8.06 (d, 3H, 3JHH¼8.0 Hz, Hfluorenyl
,
3
3
H5), 7.87 (d, 2H, JHH¼8.4 Hz, Hphenyl), 7.70 (d, 3H, JHH¼7.2 Hz,
H
fluorenyl, H8), 7.52 (m, 3H, Hfluorenyl, H6), 7.44 (m, 3H, Hfluorenyl, H7),
4.20 (s, 6H, 3CH2-fluorenyl), 0.37 (s, 9H, Si(CH3)3), ꢁ2.61 (broad s, 2H,
NH). Anal. Calcd for C70H50N4Si$0.5CHCl3: C, 81.82, H, 4.92, N, 5.14,
found: C, 81.88, H, 6.06; N, 4.71. MALDI-TOF MS calcd for
C70H50N4Si: 975.38047 [MH]þ, found: 975.43900 [MH]þ.
Boron trifluoride diethyl etherate, BF3$OEt2 (690
mL) was added
with a syringe. The solution was stirred for 3 h at room tempera-
ture. Then, the oxidant, p-chloranil (3.44 g, 14 mmol) was added,
and the reaction mixture was refluxed for 1 h (light protection was
removed). After neutralization of the acid catalyst by adding two
pipettes of triethylamine, the solvent was removed. The resulting
black solid was purified by two column chromatographies (column
1: CH2Cl2/heptane 1:1, and then column 2: CH2Cl2/heptane 1:4)
affording 330 mg (8%) of the desired porphyrin 13 as a purple solid.
The new intermediate porphyrin 13 was fully characterized; the
hydrogen and carbon atom-labeling scheme for this monomer is
4.2.3. Synthesis of 5,10,15-(trifluorenyl)-20-(4-ethynylphenyl)por-
phyrin 11. Potassium carbonate (145 mg, 1.05 mmol) was added to
a solution of porphyrin 10 (200 mg, 0.21 mmol) in distilled DCM
(36 mL) and methanol (12 mL) under argon. The reaction mixture
was stirred at room temperature for 47 h. Then solvent was evap-
orated under reduced pressure. The obtained residue was extracted
in dichloromethane, washed with 10% (v/v) aqueous solution of
sodium hydrogen carbonate, dried with MgSO4, and then taken into
dryness. The solid obtained was filtered over silica with DCM as an
eluent. The deprotected porphyrin 11 was obtained as a purple
powder to yield 187 mg (98%). This new intermediate porphyrin 11
shown in Fig. 2. 1H NMR (400 MHz, CDCl3,
d in ppm): 8.94 (d, 2H,
3JHH¼5.0 Hz, Hb-pyrrolic), 8.92 (s, 4H, Hb-pyrrolic), 8.84 (d, 2H,
was fully characterized. 1H NMR (400 MHz, CDCl3,
d in ppm): 8.94
3JHH¼4.4 Hz, Hb-pyrrolic), 8.39 (s, 3H, Hfluorenyl, H1), 8.24 (d, 3H,
3
(d, 2H, JHH¼5.0 Hz, Hb-pyrrolic), 8.92 (s, 4H, Hb-pyrrolic), 8.84 (d, 2H,
3JHH¼4.4 Hz, Hb-pyrrolic), 8.39 (s, 3H, Hfluorenyl, H1), 8.25 (d, 3H,
3JHH¼7.6 Hz, Hfluorenyl, H4), 8.17 (m, 5H, 2Hphenyl and 3Hfluorenyl, H3),
3JHH¼8.0 Hz, Hfluorenyl, H4), 8.15 (m, 5H, 2Hphenyl, HA and 3Hfluorenyl
,
H3), 8.05 (d, 3H, 3JHH¼7.6 Hz, Hfluorenyl, H5), 7.96 (d, 2H, 3JHH¼7.6 Hz,
3
Hphenyl, HB), 7.70 (d, 3H, JHH¼7.2 Hz, Hfluorenyl, H8), 7.52 (m, 3H,
3
3
8.06 (d, 3H, JHH¼7.6 Hz, Hfluorenyl, H5), 7.89 (d, 2H, JHH¼8.0 Hz,
Hfluorenyl, H6), 7.44 (m, 3H, Hfluorenyl, H7), 4.20 (s, 6H, 3CH2-fluorenyl),
3
Hphenyl), 7.70 (d, 3H, JHH¼7.2 Hz, Hfluorenyl, H8), 7.53 (m, 3H, Hfluor-
ꢁ2.60 (s, 2H, NH). Rf on silica plate using DCM/heptane (60:40):
0.48. UVevis (lmax, (ε, 10ꢁ3 Mꢁ1 cmꢁ1), CH2Cl2, nm): 275 (34), 424
(287), 519 (11), 556 (5), 593 (1.5), 649 (1.6). Anal. Calcd for
C65H41IN4$0.5CH2Cl2: C, 75.11, H, 4.04, N, 5.35, found: C, 74.60, H,
4.40, N, 5.17. MALDI-TOF MS: calcd for C65H41IN4: 1027.22737
[MNa]þ, found 1027.22640 [MNa]þ and 1005.24542 [MH]þ, found
1005.24460 [MH]þ.
enyl, H6), 7.44 (m, 3H, Hfluorenyl, H7), 4.21 (s, 6H, 3CH2-fluorenyl), 3.31 (s,
1H, CalkyneeH), ꢁ2.65 (broad s, 2H, NH). Rf on silica plate using
DCM/heptane (60:40): 0.46. FT-IR (n, KBr, cmꢁ1): 2106 (C^C).
UVevis (lmax, (ε, 10ꢁ3 Mꢁ1 cmꢁ1), CH2Cl2, nm): 275 (83), 425 (624),
519 (24), 556 (14), 593 (4.7), 649 (4.9). Anal. Calcd for
C67H42N4$CH3OH: C, 87.34, H, 4.96, N, 5.99, found: C, 87.51, H, 5.08,
N, 5.70. MALDI-TOF MS: calcd for C67H42N4: 903.34877 [MH]þ,
found: 903.3400 [MH]þ. MS (ESI): calcd for C67H42N4: 925.33072
[MNa]þ, 903.34877 [MH]þ, found: 925.3305 [MNa]þ, 903.3471
[MH]þ.
4.3. Synthesis of dimers 7 and 8
4.3.1. Synthesis of dimer
7 using AsPh3 as a catalytical li-
gand. A solution of 12, zinc(II)-5,10,15-(trifluorenyl)-20-(4-
ethynylphenyl)porphyrinato (52 mg, 0.053 mmol), free base 13,
5,10,15-(trifluorenyl)-20-(4-iodophenyl)porphyrin (50 mg, 0.050
mmol), Pd2(dba)3$CHCl3 (16 mg, 0.015 mmol), and AsPh3 (37 mg,
0.12 mmol) was prepared in 18 mL of freshly distilled THF under
argon. Then, triethylamine (3.5 mL) was added to this solution. This
reaction mixture was stirred for 72 h at 35 ꢀC under argon. Then, it
was cooled at room temperature, filtered, and evaporated to dry-
ness. The residue was purified by column chromatography on silica
gel using DCM/heptane (1:1) as eluent then increasing the pro-
portion of DCM till 100% affording the product 7, as a dark red
impure powder with a yield of around 5%. Two side products; 14
and 15 were isolated and characterized as shown below (see Sec-
tion 4.4.).
4.2.4. Synthesis of Zn(II)-5,10,15-(trifluorenyl)-20-(4-ethynylphenyl)
porphyrinato 12. Zn(CH3CO2)2$2H2O (220 mg, 1.0 mmol) was
added to a solution of porphyrin 11 (185 mg, 0.2 mmol) in distilled
DCM (127 mL) and methanol (63 mL) under argon. The reaction
mixture was stirred during 24 h at room temperature. The reaction
progress was monitored by UVevisible spectroscopy and by TLC,
spotting directly from the organic layer. Solvent was evaporated
under reduced pressure. The obtained residue was extracted in
dichloromethane, washed with 10% (v/v) aqueous solution of so-
dium hydrogen carbonate, dried with MgSO4, and then taken into
dryness. The solid obtained was filtered over silica with DCM as an
eluent. The metalated porphyrin 12 was obtained as a purple solid
to yield 188 mg (97%). The new zinc porphyrin complex, 12 was
fully characterized; the hydrogen and carbon atom-labeling
scheme for this monomer is shown in Fig. 2. 1H NMR (400 MHz,
4.3.2. Synthesis of dimer 7 using P(o-tol)3 as a catalytical li-
gand. A solution of 1 equiv of 12, zinc(II)-5,10,15-(trifluorenyl)-20-
(4-ethynylphenyl)porphyrinato (48 mg, 0.05 mmol), 1 equiv of free
base 13, 5,10,15-(trifluorenyl)-20-(4-iodophenyl)porphyrin (50 mg,
0.05 mmol), Pd2(dba)3$CHCl3 (7.8 mg, 0.007 mmol), and P(o-tol)3
(18 mg, 0.06 mmol) in 18 mL of freshly distilled toluene was pre-
pared under argon. Finally, triethylamine (3.5 mL) was added to this
solution. The reaction mixture was stirred for 24 h at 35 ꢀC under
argon. Then, it was cooled at room temperature, filtered, and
3
CDCl3,
d
in ppm): 9.04 (d, 2H, JHH¼5.0 Hz, Hb-pyrrolic), 9.02 (s, 4H,
Hb-pyrrolic), 8.93 (d, 2H, 3JHH¼4.4 Hz, Hb-pyrrolic), 8.39 (s, 3H, Hfluorenyl
,
H1), 8.25 (d, 3H, 3JHH¼8.0 Hz, Hfluorenyl, H4), 8.17 (m, 5H, 2Hphenyl and
3
3Hfluorenyl: H3), 8.05 (d, 3H, JHH¼7.2 Hz, Hfluorenyl, H5), 7.89 (d, 2H,
3JHH¼8.0 Hz, Hphenyl), 7.69 (d, 3H, JHH¼7.6 Hz, Hfluorenyl, H8), 7.53
3
(m, 3H, Hfluorenyl, H6), 7.44 (m, 3H, Hfluorenyl, H7), 4.20 (s, 6H, 3CH2-
fluorenyl), 3.30 (s, 1H, CalkyneeH). FT-IR (n, KBr, cmꢁ1): 2106 (C^C).
UVevis (lmax, (ε, 10ꢁ3 Mꢁ1 cmꢁ1), CH2Cl2, nm): 273 (36), 303 (19),

7124
A. Merhi et al. / Tetrahedron 69 (2013) 7112e7124
evaporated to dryness. The residue was purified twice by column
chromatography on silica gel using DCM/heptane (1:1) as eluent
then increasing the proportion of DCM. Product 7 was isolated as
a dark red powder when DCM/heptane (3:1) were used. Then, the
obtained product was precipitated in heptane to afford 7 as a pure
product with 25% yield. The reaction was followed by MALDI-TOF
MS as well as by NMR. This new compound 7 is very soluble in
most organic solvents and can be purified by precipitation (DCM/
heptane). Compound 7 behaved well on silica gel chromatography
and was fully characterized by usual solution spectroscopies (NMR,
mass spectrometry) and microanalysis; the hydrogen and carbon
atom-labeling scheme for this monomer is shown in Fig. 3. 1H NMR
by-product 14 was isolated as a purple solid and characterized by
proton NMR and Mass. 1H NMR (400 MHz, CDCl3,
d
in ppm): 9.01 (d,
3
2H, JHH¼4.8 Hz, Hb-pyrrolic), 9.00 (s, 4H, Hb-pyrrolic), 8.95 (d, 2H,
3JHH¼4.8 Hz, Hb-pyrrolic), 8.38 (s, 3H, Hfluorenyl, H1), 8.22 (m, 5H,
2Hphenyl and 3Hfluorenyl, H4), 8.14e8.11 (m, 3H, Hfluorenyl, H3),
3
8.05e8.02 (m, 3H, Hfluorenyl, H5), 7.92 (d, 2H, JHH¼8.0 Hz, Hphenyl),
7.69e7.66 (m, 5H, 2Hphenyl and 3Hfluorenyl, H8), 7.54e7.50 (m,
3Hfluorenyl, H6), 7.44e7.40 (m, 5H, 2Hphenyl and 3Hfluorenyl, H7), 4.18
(s, 6H, 3CH2-fluorenyl). MALDI-TOF MS: calcd for C73H44N4Zn:
1043.54742 [MH]þ, found 1043.0360 [MH]þ.
4.4.2. Compound 5,10,15-(trifluorenyl)-20-(4-phenyl-(diphenyl-ar-
sine))porphyrin 15. Among the obtained fractions from the column
chromatography, the arsine porphyrin 15 was obtained in a purple
solid, always mixed with non-reacted iodo compound 13 or dimer
7. This by-product 15 was characterized by Mass: MALDI-TOF MS:
calcd for C77H51AsN4: 1108.17740 [MH]þ; found 1108.04600 [MH]þ.
(500 MHz, CDCl3,
d in ppm): 9.09 (s, 4H, Hb-pyrrolic), 9.07 (d,
3JHH¼5.7 Hz, 2H, Hb-pyrrolic), 9.05 (s, 4H, Hb-pyrrolic), 9.04 (s, 4H, Hb
-
3
pyrrolic), 9.02 (d, JHH¼5.6 Hz, 2H, Hb-pyrrolic), 8.42 (s, 6H, Hfluorenyl
,
0
0
H1 ), 8.35 (m, 2H, Hphenyl), 8.29 (m, 6H, Hfluorenyl, H4 ), 8.26 (m, 2H,
3
0
Hphenyl), 8.18 (m, 6H, Hfluorenyl, H3 ), 8.06 (d, 6H, JHH¼7.8 Hz,
3
0
H
fluorenyl, H5 ), 8.05 (m, 2H, Hphenyl), 7.71 (d, 6H, JHH¼7.6 Hz,
3
0
0
H
fluorenyl, H8 ), 7.54 (t, 6H, JHH¼6.9 Hz, Hfluorenyl, H6 ), 7.43 (t, 6H,
Acknowledgements
3
0
JHH¼6.5 Hz, Hfluorenyl, H7 ), 7.42 (m, 2H, Hphenyl), 4.22 (s, 12H, 6CH2-
fluorenyl). 13C NMR (CDCl3): 150.4 (m, Cq, C1-4-6-9-11-14-16-19),143.7 (Cq,
The authors are grateful to Dr. S. Sinbandhit (CRMPO) for the
technical assistance and helpful discussions for NMR. The authors
are grateful to Region Bretagne for ARED grant for A.M., MRT for
PhD grant concerning S.D. Partial Funding for the project was ob-
00
00
00
00
C9 ), 141.7 (Cq, C4 ), 141.6 (Cq, C8 ), 141.5 (Cq, C5 ), 134.7 (CB), 134.5
0
0
(CA), 134.0 (Cq, C2 ), 133.4 (C4 ), 132.1 (m, CH, C2-3-7-8-12-13-17-18),
0
0
0
0
0
0
131.3 (C1 ), 130.0 (CB ), 127.0 (C6 and C7 ), 126.8 (CA ), 125.2 (C8 ),
0
0
0
121.6 (m, Cq, C5-10-15-20), 120.2 (C5 ), 117.8 (C3 ), 37.1 (C9 ). Rf on silica
lmax, (ε,
ꢀ
ꢀ
tained from the ‘Universite Europeenne de Bretagne’ (UEB) and
from FEDER by an EPT grant in the ‘MITTSI’ program from RTR
BRESMAT.
plate using DCM/heptane (60:40): 0.36. UVevis
(
10ꢁ3 Mꢁ1 cmꢁ1), CH2Cl2, nm): 281 (150), 428 (479), 513 (10), 555
(37), 597 (16), 643 (w). Anal. Calcd for C132H80N8Zn$3CH2Cl2: C,
77.27, H, 4.13, N, 5.34, found: C, 77.31, H, 4.82, N, 5.02. MALDI-TOF
MS: calcd for C132H80N8Zn: 1841.57974 [MH]þ, found 1841.18810
[MH]þ.
References and notes
1. Wasielewski, M. R. J. Org. Chem. 2006, 71, 5051.
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4. Milgrom, L. R. J. Chem. Soc., Perkin Trans. 1 1983, .
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6. Lin, V. S.-Y.; Di Magno, S. G.; Therien, J. M. Science 1994, 264, 1105.
7. Lin, V. S.-Y.; Therien, J. M. Chem.dEur. J. 1995, 1, 645.
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8941.
9. Wagner, R. W.; Johnson, T. E.; Li, F.; Lindsey, J. S. J. Org. Chem. 1995, 60, 5266.
10. Paul-Roth, C.; Rault-Berthelot, J.; Simonneaux, G. Tetrahedron 2004, 60, 12169.
11. Poriel, C.; Ferrand, Y.; Le Maux, P.; Paul-Roth, C.; Simonneaux, G.; Rault-Ber-
thelot, J. J. Electroanal. Chem. 2005, 583, 92.
12. Paul-Roth, C. O.; Simonneaux, G. Tetrahedron Lett. 2006, 47, 3275.
13. Paul-Roth, C. O.; Simonneaux, G. C. R. Acad. Sci., Ser. IIb: Chim. 2006, 9, 1277.
14. Paul-Roth, C.; Williams, G.; Letessier, J.; Simonneaux, G. Tetrahedron Lett. 2007,
48, 4317.
4.3.3. Synthesis of free dimer 8. This new dimer 8 was obtained
from the mono zinc complex 7 by acidic treatments. To a solution of
1 equiv of dimer 7 (10 mg, 0.005 mmol), in 5 mL of freshly distilled
DCM under argon, was added trifluoroacetic acid in large excess
(TFA, 0.05 mL, 75 mg, 0.66 mmol). Immediately, the dark red DCM
solution turned green. The reaction mixture was stirred for 30 min
at room temperature and was controlled by UVevisible spec-
trometry to be sure that zinc was entirely eliminated from the
porphyrin macrocycle, to obtain the totally free and protonated
porphyrin dimer. Finally, potassium carbonate was added to
neutralize this dark green solution, to obtain the free, but
nonprotonated porphyrin dimer 8. The red solution was stirred for
30 min at room temperature. Then, the residue was filtrated on
silica gel using DCM as eluent to afford neutral 8, as a pure product:
15. Drouet, S.; Paul-Roth, C. O.; Fattori, V.; Cocchi, M.; Williams, J. A. G. New J. Chem.
2011, 35, 438.
a dark red powder with 95% yield. 1H NMR (500 MHz, CDCl3
ppm): 8.94 (m, 16H, Hb-pyrrolic), 8.62 (m, 4H, Hphenyl), 8.32 (s, 6H,
d in
16. Ren, X.; Ren, A.; Feng, J.; Sun, C. J. Photochem. Photobiol., A 2009, 203, 92.
17. Drouet, S.; Merhi, A.; Argouarch, G.; Paul, F.; Mongin, O.; Blanchard-Desce, M.;
Paul-Roth, C. O. Tetrahedron 2012, 68, 98.
18. Merhi, A.; Drouet, S.; Kerisit, N.; Paul-Roth, C. O. Tetrahedron 2012, 68, 7901.
19. Paul-Roth, C.; Rault-Berthelot, J.; Simonneaux, G.; Poriel, C.; Abdalilah, M.;
Letessier, J. J. Electroanal. Chem. 2006, 597, 19.
20. Drouet, S.; Paul-Roth, C.; Simonneaux, G. Tetrahedron 2009, 65, 2975.
21. Drouet, S.; Paul-Roth, C. O. Tetrahedron 2009, 65, 10693.
22. Li, B.; Li, J.; Fu, Y.; Bo, Z. J. Am. Chem. Soc. 2004, 126, 3430.
23. Austin, W. B.; Bilow, N.; Kelleghan, W. J.; Lau, K. S. Y. J. Org. Chem. 1981, 46, 2280.
24. Gouterman, M. The Porphyrins; Academic: New York, NY, 1978; vol. 324.
25. Gouterman, M. J. Mol. Spectrosc. 1961, 6, 138.
26. Austin, E.; Gouterman, M. Bioinorg. Chem. 1978, 9, 281.
27. Falk, J. E. Porphyrins and Metalloporphyrins; Elsevier: Amsterdam, The Nether-
lands, 1964.
H
fluorenyl, H1), 8.18 (m, 6H, Hfluorenyl, H4), 8.08 (m, 6H, Hfluorenyl, H3),
7.98 (d, 6H, 3JHH¼7.8 Hz, Hfluorenyl, H5), 7.78 (m, 4H, Hphenyl), 7.68 (d,
3
3
6H, JHH¼7.6 Hz, Hfluorenyl, H8), 7.52 (t, 6H, JHH¼6.9 Hz, Hfluorenyl
,
3
H6), 7.43 (t, 6H, JHH¼6.5 Hz, Hfluorenyl, H7), 4.22 (s, 12H, 6CH2-
fluorenyl), ꢁ2.70 (4H, NH).
UVevis (lmax, (ε, 10ꢁ3 Mꢁ1 cmꢁ1), CH2Cl2, nm): compound 8 as
a tetracation [H4PoreH4Por]4D: 268e280, 461, 681; compound 8
as a double free base [H2PoreH2Por]: 268 (181), 426 (522), 521
(26), 557 (15), 595 (5), 650 (4). MALDI-TOF MS: calcd for C132H82N8:
1779.66624 [MH]þ, found 1778.95120 [MH]þ.
28. Drouet, S.; Ballut, S.; Rault-Berthelot, J.; Turban, P.; Paul-Roth, C. Thin Solid Films
2009, 517, 5474.
4.4. Characterization of by-products 14 and 15
29. Owens, J. W.; Smith, R.; Robinson, R.; Robins, M. Inorg. Chim. Acta 1998, 279,
226.
30. Zang, X. H.; Xie, Z. Y.; Wu, F. P.; Zhou, L. L.; Wong, O. Y.; Lee, C. S.; Kwong, H. L.;
Lee, S. T.; Wu, S. K. Chem. Phys. Lett. 2003, 382, 561.
31. Quimby, D. J.; Longo, F. R. J. Am. Chem. Soc. 1975, 97, 5111.
32. Demas, J. N.; Crosby, G. A. J. Phys. Chem. 1971, 75, 991.
4.4.1. Complex Zn(II)-5,10,15-(trifluorenyl)-20-(4-phenylethynyl-
phenyl)porphyrinato 14. The porphyrin 14 was obtained pure as
a first fraction of the column when using DCM/heptane (1:1). This