Synthesis of new luminescent supramolecular assemblies from fluorenyl porphyrins and polypyridyl isocyanurate-based spacers

Article abstract of DOI:10.1016/j.tet.2011.10.081

Two new dendrimeric supramolecular assemblies bearing twelve and twenty-four fluorenyl peripheral donor groups surrounding an organic core have been prepared and studied. These assemblies are composed of three zinc porphyrins possessing each four (ZnTFP)

Full text of DOI:10.1016/j.tet.2011.10.081

Tetrahedron 68 (2012) 98e105
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of new luminescent supramolecular assemblies from fluorenyl
porphyrins and polypyridyl isocyanurate-based spacers
a
b
a
a
c
ꢀ ꢀ
Samuel Drouet , Areej Merhi , Gilles Argouarch , Frederic Paul , Olivier Mongin ,
Mireille Blanchard-Desce c, Christine O. Paul-Roth a
Sciences Chimiques de Rennes, SCR-UMR CNRS 6226, Universite de Rennes 1, 35042 Rennes Cedex, Universite Europeenne de Bretagne, France
,b,
*
a
ꢀ
ꢀ
ꢀ
b
c
ꢀ
ꢀ
ꢀ
Institut National des Sciences Appliquees, INSA-SCR, 35043 Rennes Cedex, Universite Europeenne de Bretagne, France
ꢀ
ꢀ
ꢀ
ꢀ
Chimie et Photonique Moleculaires UMR CNRS 6510, Universite de Rennes 1, 35042 Rennes Cedex, Universite Europeenne de Bretagne, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Two new dendrimeric supramolecular assemblies bearing twelve and twenty-four fluorenyl peripheral
donor groups surrounding an organic core have been prepared and studied. These assemblies are
composed of three zinc porphyrins possessing each four (ZnTFP) and eight fluorenyl chromophores
(ZnOOFP) linked together by a central tris-pyridyl organic ligand. Due to efficient energy transfer be-
tween the fluorenyl arms, which act as antennas, and the Zn centres, which act as emitters; these as-
semblies behave as red emitters after selective UV or visible irradiation. The kinetic stability of these
supramolecular assemblies and its impact on their photophysical properties are discussed.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 7 October 2011
Accepted 24 October 2011
Available online 29 October 2011
Keywords:
Fluorescence
Porphyrins
Fluorene
Light-harvesting
Supramolecular assemblies
Red emission
1. Introduction
the fact that 1 exhibits good red chromaticity and enhanced emis-
sion efficiency, it is now interesting to incorporate the corre-
Porphyrin systems present wide potential applications in dif-
ferent fields, such as, for instance, light-harvesting, Organic Light
Emitting Diodes (OLEDs) or switches. For efficient solar energy
harvesting, several chromophores are needed in order to collect
light from the entire solar spectrum.1 In this connection, the pho-
tosynthetic light-harvesting systems (I and II) consist of well or-
ganized porphyrin antennas in sophisticated three-dimensional
structures.2 As in nature, construction of multichromophoric sys-
tems is important to ensure maximum use of solar energy. Thus, the
ability to design and construct (super- or supra-) molecular archi-
tectures in which the energy flow can be controlled constitutes
a great (and timely) challenge.
We have previously reported the synthesis of porphyrins pos-
sessing several fluorenyl arms and focused on their photophysical
properties,3e5 along with their possible use in OLEDs.6 Notably,
a high fluorescence quantum yield (24%) was evidenced for 1,
demonstrating the good capacity of the fluorenyl units to enhance
quantum yields by increasing the radiative deactivation process. By
sponding zinc complex 3 and the related zinc porphyrin 4 in
oligomeric assemblies and to study their luminescence.
Arrays containing different kinds of dyes can be engineered in
several ways: either by using covalent bonds or by self-assembly. On
the one hand, star-shaped trimer structures in which the porphyrin
building blocks are connected covalently by a purely organic spacer
have been largely studied. In 1999, Osuka synthesized a model of
benzene connected in the 1,3 and 5 positions to three zinc por-
phyrins.7 Other triangular spacers have been employed with the
same 1,3,5 topology.8 Subsequently, a series of arrays containing
three, four and six tetraphenylporphyrin (TPP) units were synthe-
sized.9 For covalently bonded star-shaped pentamers, the use of
(phenylethynyl)benzene spacers connected at the meso position of
a central porphyrin unit has also been made by Lindsey and co-
workers.10 Recently, Sanders reported a large scale synthesis of tri-
podal porphyrin arrays: in these assemblies, the three zinc por-
phyrins are covalently linked byan alkyne bridge to a tripodal unit.11
On the other hand, supramolecular approaches offer an alternative
way to assemble the nano-objects in a desired manner, like in the
photosynthetic light-harvesting complexes. An interesting ap-
proach for mimicking these complicated systems is to design small-
sized chromophores, which can self-organize into light-harvesting
architectures. Supramolecular synthetic methods12 have
* Corresponding author. Tel.: þ33 (0)2 23 23 63 72; fax: þ33 (0)2 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 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.10.081

S. Drouet et al. / Tetrahedron 68 (2012) 98e105
99
developed rapidly and porphyrins proved particularly useful for the
design of robust architectures because of their rigid framework.13
One-, two-, and three-dimensional materials are now routinely ac-
cessible bysynthetic strategies based on hierarchical organization of
porphyrins. Thus, porphyrins are very useful not only as active
molecular components for light-harvesting antenna systems, but
also as rigid building blocks for the construction of variety of func-
tional devices.14
New tris-pyridyl spacer 7. This new isocyanurate-based ligand
was obtained in one step from the corresponding triyne 8,15 and 4-
bromopyridine (9) following a Sonogashira coupling protocol in
DMF (Scheme 2). After purification, 7 is obtained as a beige solid in
51% yield. This new ligand was also fully characterized by usual
means. Its high symmetry allows monitoring the progress of the
catalytical coupling reaction, in a straightforward way, by 1H NMR.
Supramolecular assemblies 5 and 6. To a solution of 3 equiv of 3 or
4 in CH2Cl2,1 equiv of tris-pyridyl ligand 7 is added (Scheme 3). After
1 h, the desired porphyrin trimers 5 or 6 can be isolated, as deep
violet powders. These new products were characterized by usual
solution spectroscopies (NMR, UVevis and IR) and microanalysis,
but proved too fragile to be characterized by mass spectrometry,
since only the constitutive fragments were detected by LSI-MS.
Ligation of pyridyl rings to zinc porphyrins is intrinsically weak
(association constant, ca. 1ꢁ103 Mꢂ1) and relatively labile; thus, in
solution, coordination oligomers are generally in equilibrium with
the monomers.19 For these supramolecular systems, stability in
(dilute) solution is therefore a key question. The stability of the
supramolecular assemblies 5 and 6 in CH2Cl2 solution was thus
checked by a combination of 1H NMR, UVevis absorption and
spectrofluorimetric measurements.
In the present contribution, the synthesis of the desired por-
phyrin trimer is based on the pyridine-to-metal coordination. Thus,
porphyrins are connected by dative bonds to a new kind of organic
bridge having three pyridine sites pointing at 120ꢀ from each
other.15 This bridge consists of an original tripodal ligand (7), which
was synthesized in a straightforward way from a readily available
tris-alkynyl isocyanurate precursor, independently developed by
some of us.15 Such a ligand is expected to exhibit a better trans-
parency in the near UV and visible range, and therefore to impart
a higher photostability to the supramolecular assembly than related
1,3,5-phenylene based derivatives. Two different porphyrins were
used to test this approach: (i) the known monomeric zinc porphyrin
3 bearing four fluorenyl units rigidly held on the meso positions and
(ii) a new zinc porphyrin mentioned above (4), bearing eight pen-
dant fluorenyl units more flexibly connected to the same positions
via methylene linkers. Following the synthesis of these new building
blocks, we will describe the self-assembly and characterization of
the desired porphyrin oligomers 5 and 6, respectively. Finally, the
photophysical studies of the building blocks and related super-
molecular systems will be reported and discussed.
The 1H NMR signals obtained in deuterated chloroform for zinc
complexes 3 and 4 are fine and well resolved. A clear difference in
shift is observed for the bridging tripodal ligand 7 when free and in
the corresponding assemblies 5 and 6 (Figs. 1 and 2). The latter is
induced by axial coordination of 7 to zinc porphyrin units. In both
cases, HeH polarization transfer studies (COSY) allowed to assign
the various signals detected, the integration of the signals revealed
that adducts 5 and 6 have the correct stoichiometry.
2. Results and discussion
2.1. Synthesis
For example, the 1H NMR spectrum of 5 reveals the two 1H res-
onances of the pyridine units, HA and HB, significantly upfield of
their positions in 7, as expected for protons located within the
shielding cone of a porphyrin (Fig. 2).19,20 This effect decreases
gradually as the proton distance from the shielding macrocycles
increases, with Dd¼ꢂ3.0 and Dd¼ꢂ0.8 for HA and HB, respectively.
These signals are also broader and less resolved, in line with the
highly fluxional nature of the ligand at ambient temperature. In
addition, we can notice that all the twelve peripheral protons on the
porphyrin meso-fluorene arms are equivalent. Similar statements
hold for the larger assembly 6, except that HA is not observed at
25 ꢀC, in reason of its strong fluxionality.
Zinc porphyrins 3 and 4. The meso-tetrafluorenylporphyrin free
base 1 was prepared as previously reported,16 while the synthesis
of the dendrimeric free base 217 is based on the condensation re-
ꢀ
action reported by Frechet. The metallation of these porphyrin
monomers by zinc acetate proceeds in dichloromethane at reflux,18
to give the corresponding zinc porphyrins 35 and 4, in 87% and 81%
yield, respectively (Scheme 1). The new complex 4 was fully char-
acterized by means of NMR spectroscopy, microanalysis and high
resolution mass spectrometry.
N
Zn(CH3CO2)2,2H2O
CH2Cl2,
N
H
H
N
N
N
Zn
N
N
N
Reflux /2h
TFP
(1)
ZnTFP
(3)
Yield 87%
O
O
O
O
O
O
O
O
N
O
N
H
H
Zn(CH3CO2)2,2H2O
N
N
O
N
N
Zn
N
N
O
O
CH2Cl2, MeOH
Reflux /2h
O
O
O
O
OOFP
(2)
ZnOOFP
(4)
Yield 81%
Scheme 1. Synthesis of zinc complexes 3 and 4.

100
S. Drouet et al. / Tetrahedron 68 (2012) 98e105
N
N
O
N
O
N
N
N
N
N
N.HCl
PdCl2(PPh3)2 / CuI
DMF / NEt3 / 70°C
+
O
O
O
O
Br
(excess)
7
(51 %)
9
8
N
Scheme 2. Synthesis of ligand 7.
2.2. Photophysical properties
absorption of the fluorene chromophores. This UV absorption is
stronger for the zinc complex 4 due to the larger number (eight vs
four) of fluorene groups in the meso arms.
The free tris-pyridine ligand 7 in CH2Cl2 displays two bands:
a strong one at 285 nm and a weak one at 302 nm (Fig. 3a and Table
1). Upon apical binding of a pyridyl ligand to a zinc porphyrin, a red
shift of 2e10 nm of the characteristic absorptions observed for the
free porphyrin is expected, due to the stabilisation of the corre-
sponding excited-states in the pyridyl-Zn adduct.19 Actually, these
2.2.1. Electronic spectra. 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)).21e23 Thus, the zinc complexes 3 and 4
exhibit an intense B band (Soret band), together with two weak Q-
bands in the visible range (Fig. 3 and Table 1). An additional broad
band is also observed in UV range, which corresponds to
pe
p*
red shifts are observed for both 5 (Fig. 3b) and 6 (see
N
N
N
N
N
N
CH Cl , 1h
2
2
O
N
O
O
N
Zn
N
N
3
N
+
N
N
O
N
O
O
25 °C
N
N
N
N
N
N
N
N
N
N
N
N
N
N
5
3
7
(91 %)
O
O
O
O
N
O
N
N
N
O
O
N
N
O
O
O
O
O
N
2+
O
3
CH Cl , 1h
Zn
N
2
2
O
N
O
O
N
N
N
N
O
+
O
O
O
O
N
O
O
O
O
25 °C
O
O
O
N
N
N
N
N
O
N
N
O
O
N
N
N
N
O
N
O
O
O
O
O
N
N
O
4
6
7
(96 %)
Scheme 3. Synthesis of supramolecular assemblies 5 and 6.

S. Drouet et al. / Tetrahedron 68 (2012) 98e105
101
H6'
N
H5'
C6'
C5'
H7'
C7'
H4'
C5''
C4'
H2
H3
C4
C8'
C4''
C9''
H3'
C8''
C3'
H8'
C2 C3
C9'
C2'
H9'
H9''
C1'
C1
D
C20
C19
C5
C6
N
O
N
O
O
H1'
HD
HC
C18
C17
C7
C8
N
N
Zn2+
N
N
HB
C16
C15
C9
HA
N
C10
N
N
D
C14
C11
D
7
C13 C12
3
H6'
H5'
C5'
C5''
C6'
H7'
H4'
C3'
C7'
C8'
C4'
C4''
C9''
H3'
C8''
C9'
H
8'
C2'
H9'
H9''
C1'
CH
O
HH
HB
H1'
HH'
H5'
C5' C6'
C5''
H6'
C7'
C8'
H8'
H4'
C4'
H2
H3
HE
H3'
CD
CE
CB
CA
C2 C3
H7'
C3'
C2'
C4''
C9''
C1
C20
C4
CD
C8''
C9'
D
C5
C6
CB
N
O
C1'
CH
C19
HB
H
9'
C18
C17
C7
C8
H9''
Zn2+
H
HH'
1'
HH
N
N
C16
C9
N
14
C10
C15
D
C
C11
D
C13 C12
4
Fig. 1. Hydrogen and carbon atom-labelling for the porphyrin complexes 3, 4 and ligand 7.
Supplementary data S1), but only at relatively high concentrations
(10ꢂ3 M). At lower concentrations, due to the labile coordination of
the pyridine to the zinc centres, the complex is more dissociated. As
a result, the free ligand 7 and corresponding porphyrin dominate in
solution over the adduct, resulting in no apparent bathochromic
shift. Appreciable spectral changes, indicative of dissociation, are
observed upon dilution to 1.0ꢁ10ꢂ6 M. Under these high dilutions
conditions (10ꢂ6 M), axial dissociation takes place, as shown mainly
by a blue shift in absorption and for fluorescence (as we shall see
below), the absorption peaks shifting back to the values observed
for porphyrins 3 and 4. The Soret band in the absorption spectra of
the self-assembled systems 5 and 6 can thus be usefully used to
determine the concentrations at which these labile systems pre-
dominate in solution over their constituents (1.0ꢁ10ꢂ3 M). Notably,
less marked shifts take place with the other absorption bands
detected, such as the fluorene band near 300 nm or these charac-
teristics of the apical ligand 7 near 285 nm.
assigned to a vibronic progression from a Q state: the very weak
band near 720 nm is assigned as Q(2,0) and actually appears as an
extended tail on the Q(1,0) band. The major difference between
them, compared to their corresponding free-bases (1 and 2), is the
remarkable hypsochromic shift of w50 nm for the strongest
emission band Q(1,0) and w70 nm for the second Q(0,0), due to the
metal coordination.5
We then studied the photophysical properties of supramolecu-
lar assemblies 5 and 6. At concentrations around 10ꢂ3 M and using
a front-face (FF) fluorescence detection setup instead of a classical
right-angle (RA) detection setup, we could observe a characteristic
red shift (Fig. 4) for the emission spectra recalling that previously
observed for 3 (Dg(Q1)¼4) or 4 (Dg¼5 nm for Q(1,0) and Dg¼5 nm
for the Q(0,0)). This red shift, already observed in absorption be-
tween 3 and 5 (respectively 4 and 6), is characteristic of the apical
coordination of the pyridine ligand to the metal (Table 2). Notably,
when the fluorescence spectra are recorded for more dilute solu-
tions, no difference can be stated compared to the corresponding
monomer 3 (respectively 4). These results clearly indicate that
supramolecular assemblies 5 and 6 are mainly dissociated at
2.2.2. Luminescence studies. The fluorescence spectra at 25 ꢀC of
the zinc(II) complexes 3 and 4 (Fig. 4) consist of three sub-bands

102
S. Drouet et al. / Tetrahedron 68 (2012) 98e105
N
N
O
N
N
N
O
O
O
N
HD
N
C
N
O
HD
O
HC
HD
HB
HC
HB
HA
N
HB
N
HA
N
HA
Hc
N
Zn
N
N
9.0
7.0
6.0
5.0
8.0
Fig. 2. NMR spectra of zinc complex 5.
concentrations required by the classical right-angle detection
While 7 is essentially non luminescent in the free state, 4 proved
to exhibit properties similar to 3. It emits dominantly red light after
selective UV or visible irradiation. Actually, in case of UV irradiation,
such systems comprising a central zinc porphyrin core linked to
peripheral photon-harvesting fluorene moieties have been shown
to act as efficient relays between the antennas and the Zn atom. For
these compounds, the red luminescence can be obtained from
a large range of excitation wavelengths from UV to red.
We next attempted to compare the photophysical properties of
5 and 6 to these of the starting porphyrin monomers 3 and 4.
However, due to weak coordination of the pyridine end-groups of 7
to the Zn centres, the new assemblies 5 and 6 are quite labile in
solution and exist mostly in the form of their dissociated compo-
nents at concentrations where fluorescence studies are usually
made. This frustrated us from the quantitative determination of the
fluorescence yield of these fascinating assemblies. Nevertheless, at
higher concentrations these assemblies are more stable and pres-
ent distinct properties from their constitutive monomers, as evi-
denced by UVevis and luminescence studies using a front-face
detection setup. We are now planning to investigate their poten-
tial directly in the solid state, by using them directly as active layers
(after deposition or spin coating from very concentrated solutions)
in OLED or related devices.
(10ꢂ6e10ꢂ7 M), (Fig. 5).
2.2.3. Fluorescence quantum yields. The fluorescence quantum
yields FF of these compounds were determined by comparing
with proper calibration standards26 (Table 1). By comparison
with the fluorescence quantum yield of the reference zinc com-
plex of tetraphenylporphyrin ZnTPP (FF¼3.3%), we found that
compound 3 presents an unusually high luminescence quantum
yield of 8.5%. Compound 4 presents a fair luminescence quantum
yield of 3.4%, which is quite similar to that of ZnTPP. The fluo-
rescence quantum yield of the pure organic linker 7 is much
lower (FF¼0.3%).
2.2.4. Energy transfer studies. The emission spectra of 3 and 4
presently used as supramolecular building blocks suggest that the
fluorenyl donor transfers energy with high efficiency to the por-
phyrin acceptor. Indeed, excitation for both zinc complexes at
300 nm (i.e., in the fluorene band) results in the characteristic red
emission of porphyrins (Fig. 4a). As a result, the blue fluorenyl
emission is almost completely quenched for both compounds,
and emission is seen predominantly from the porphyrin ring.
Similar effect could also be observed for the assemblies 5 and 6,
with an emission also coming quasi-exclusively from the por-
phyrins (Fig. 4b).
4. Experimental section
4.1. General procedures
3. Conclusions
We have synthesized and characterized two new threefold
symmetric architectures from two porphyrins bearing numerous
fluorenyl pendant arms and an original isocyanurate tris-pyridyl
tripodal ligand 7. The goal was to obtain luminescent soluble
super-molecular architectures by combining simple and highly
luminescent porphyrin building blocks with very transparent and
stable bridging ligands. These new compounds along with the new
porphyrin monomer 4 and the new ligand 7, were fully character-
ized and their luminescence was studied.
All reactions were performed under argon (with magnetic stir-
ring). Solvents were distilled from appropriate drying agent prior to
use, CH2Cl2 from CaH2, CHCl3 from P2O5 and all other solvents were
HPLC grade. Commercially available reagents were used without
further purification unless otherwise stated. 5,10,15,20-Tetra-9H-
fluoren-2-yl-21H,23H-porphine 1 (TFP) was prepared as described
in our earlier report.16
All reactions were monitored by thin layer chromatography
(TLC) with Merck pre-coated aluminium foil sheets (Silica gel 60

S. Drouet et al. / Tetrahedron 68 (2012) 98e105
103
Fig. 3. (a) UVevis absorption spectra in 10-mm path length cells of compounds 3 (black line), 7 (blue line) in CH2Cl2 at 25 ꢀC at a concentration of ca. 10ꢂ6 M, of a mixture solution of
3 equiv of 3 and 1 equiv of 7 at w10ꢂ6 M concentration (red line) and theoretical absorption spectrum resulting from the additive contribution of 3 equiv of 3 and 1 equiv of 7
(dashed line). (b) Absorption spectra in 1-mm path length cell of compounds 3 and 5 in CH2Cl2 at 25 ꢀC at higher concentration (1.5ꢁ10ꢂ3 M).
with fluorescent indicator UV254). Compounds were visualized
with ultra-violet light at 254 and 365 nm. Column chromatography
was carried out using silica gel from Merck (0.063e0.200 mm).
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 tetramethylsilane (TMS) and coupling con-
stants are in hertz. The assignments were performed by 2D NMR
experiments: COSY (Correlation Spectroscopy), HMBC (Hetero-
nuclear Multiple Bond Correlation) and HMQC (Heteronuclear
Multiple Quantum Coherence). For Hydrogen and/or carbon atom-
labelling for the porphyrin complexes 3, 4 and for the tripodal li-
gand 7, see Fig. 1. High-resolution mass spectra were recorded on
a ZabSpec TOF Micromass spectrometer in FAB mode or ESI positive
mode at the CRMPO. IR spectra were recorded on Bruker IFS 28,
using KBr pellets or in dichloromethane solution. UVevis spectra
were recorded on UVIKON XL from Biotek instruments.
Table 1
Photophysical properties of the zinc fluorenyl porphyrins 3 and 4 and of ligand 7, in
CH2Cl2 solution at 298 K (w10ꢂ6 M)
abs
a
b
abs
a
b
em c
Compound
l
[nm]
3
l
[nm]
3
l
max
Fd
max2
max2
max1
max1
[cmꢂ1
[cmꢂ1
[nm]
Mꢂ1
]
Mꢂ1
]
Tripod 7
ZnTFP (3)
ZnOOFP (4) 269
285
264
102,000 302
76,000 428
216,000 425
93,000 316
0.003e
535,000 608, 657 0.085f
519,000 602, 650 0.034f
4.2. Synthesis of [5,10,15,20-tetra-9H-fluoren-2-yl-21H,23H-
porphinato(2-)]zinc(II) (3)
a
Experimental absorption maxima.
Molar extinction coefficients.
Experimental emission maxima.
Fluorescence quantum yield.
b
c
d
e
f
Free base porphyrin 1 (100 mg, 0.10 mmol) was dissolved in
20 mL of distilled dichloromethane. Zinc acetate dihydrate (108 mg,
0.49 mmol) was added in one portion to the stirred solution. The
Determined relative to anthracene in EtOH (FF¼0.2724).
Determined relative to tetraphenyl-porphine in toluene (FF¼0.1225).

104
S. Drouet et al. / Tetrahedron 68 (2012) 98e105
4.3. Synthesis of [5,10,15,20-tetrakis[3,5-bis(9H-fluoren-2-
ylmethoxy)phenyl]-21H,23H-porphinato(2-)]zinc(II) (4)
To a solution of free base porphyrin 2 (60 mg, 28
mmol) in CH2Cl2
(15 mL) was added Zn(OAc)2$2H2O (30 mg, 140 mol) in methanol
m
(7 mL) and the mixture was stirred 2 h at reflux. When metallation
was complete (TLC checking), the reaction mixture was washed
with water, dried over MgSO4 and purified by column chroma-
tography (CH2Cl2) to afford 50 mg of a pink solid ZnOOFP (81%). 1H
NMR (500 MHz, CDCl3, d in ppm): 8.94 (s, 8H, Hb-pyrrolic), 7.68 (d, 8H,
3
3
0
0
0
JH,H¼8 Hz, 8H, H4 ), 7.64 (d, JH,H¼8 Hz, 8H, H5 ), 7.46 (s, 8H, H1 ),
7.45 (d, 3JH,H¼7 Hz, 8H, H8 ), 7.41 (s, 8H, HB), 7.32 (d, JH,H¼7 Hz, 8H,
3
0
3
3
0
0
0
H3 ), 7.28 (t, JH,H¼7 Hz, 8H, H6 ), 7.25 (t, JH,H¼7 Hz, 8H, H7 ), 6.85 (s,
4H, HE), 5.02 (s, 16H, OCH2), 3.75 (s, 16H, H9 and H9 ). 13C NMR
0
00
(125 MHz, CDCl3, d in ppm): 157.6 (CC), 149.9 (C1e4e6e9e11e14e16e19),
00
00
00
00
0
144.6 (CA), 143.5 (C1 ), 143.3 (C8 ), 141.6 (C4 ), 141.2 (C5 ), 135.1 (C2 ),
0
0
0
132.0 (C2e3e7e8e12e13e17e18), 126.8 (C6 ), 126.7 (C7 ), 126.5 (C3 ),
0
0
0
0
125.0 (C8 ), 124.5 (C1 ), 120.7 (C4 ), 119.9 (C5 ), 119.8 (C5e10e15e20),
0
115.3 (CB), 102.2 (CD), 70.6 (CH), 36.8 (C9 ). UVevis (
l
max, CH2Cl2,
nm): 270, 292 and 303 (fluorene), 425 (Soret band), 551 (Q band),
596 (Q band). Anal. Calcd (%) for C156H108N4O8Zn$H2O: C, 83.28; H,
4.93; N, 2.49. Found: C, 82.86; H, 4.88; N, 2.36. MS (ESI-CH2Cl2/
CH3COCH3: 90/10): calcd for C156H108N4O8NaZn: 2251.73508
[MNa]þ. Found 2251.73500 [MNa]þ.
4.4. Synthesis of tripod 7
Fig. 4. (a) Photoluminescence spectra of compound 4 at different excitation wave-
lengths. (b) Photoluminescence spectra of compound 4 and of supramolecular as-
sembly 6 (1.5 10ꢂ3 M) in CH2Cl2 at 25 ꢀC (excitation at 430 nm).
In a Schlenk tube under argon containing a mixture of starting
triyne15 8 (0.50 g, 1.16 mmol), 4-bromopyridine hydrochloride 9
(1.36 g, 7 mmol, 6 equiv), CuI (18 mg, 0.09 mmol, 0.08 equiv) and
PdCl2(PPh3)2 (33 mg, 0.047 mmol, 0.04 equiv) were added dry DMF
(40 mL) and distilled triethylamine (10 mL). After 2 days of stirring
at 70 ꢀC and cooling to room temperature, the solvents were re-
moved by cryoscopic transfer. The reaction mixture was extracted
with CH2Cl2, washed with water and dried over MgSO4. After fil-
tration and evaporation to dryness, the crude product was purified
by column chromatography on neutral aluminium oxide eluting
with pure ethyl acetate first and then a mixture of ethyl acetate/
methanol (95/5), to afford the corresponding product 7 as a beige
mixture was stirred 2 h at reflux. Reaction progress is monitored by
TLC, spotting directly from the organic layer. Then, the solvent was
removed, and the black red residue was chromatographed on silica
gel column with a MeOH/CH2Cl2 mixture (2 %e10 % MeOH). Com-
pound 3, was obtained as a dark red colour powder in a yield of 87%.
This porphyrin complex (3) was already described earlier.5 For
clarity, the 1H NMR data are however reported below. 1H NMR
0
(500 MHz, CDCl3, d in ppm): 8.97 (s, 8H, Hb-pyrrolic), 8.42 (s, 4H, H1 ),
3
8.28 (d, 3JH,H¼8.2 Hz, 4H, H3 ), 8.20 (d, JH,H¼7.6 Hz, 4H, H4 ), 8.10 (d,
0
0
solid (0.39 g, 51%). 1H NMR (200 MHz, CD2Cl2,
d in ppm): 8.66 (d,
3
3
3
0
0
JH,H¼6.6 Hz, 4H, H5 ), 7.72 (d, JH,H¼6.8 Hz, 4H, H8 ), 7.56 (t,
3
3JH,H¼6 Hz, 6H), 7.78 (d, JH,H¼9 Hz, 6H), 7.52e7.45 (m, 12H). 13C
3
0
0
0
JH,H¼5.7 Hz, 4H, H6 ), 7.46 (t, JH,H¼6.8 Hz, 4H, H7 ), 4.23 (s, 8H, H9
NMR (50 MHz, CD2Cl2): 150.3, 148.6, 134.5, 133.3, 131.1, 129.2, 125.9,
00
and H9 ).
124.0, 92.6, 88.4. IR (KBr, cmꢂ1): 2224 (m,
nC^C), 1778 (vw, C]O),
Excitation
Excitation
hυ
hυ
Energy
DILUTION
Energy
Transfer
Transfer
hυ'
hυ'
F
F
F
F
hυ"
F
hυ"
Zn
Red light
Blue light
Blue light
Zn
Red light
F
F
F
F
F
F
F
Zn
Zn
F
F
F
F
Concentration 10-3
M
Concentration 10-6
M
* NMR concentration
* 1-mm path length UV-Vis
* FF luminescence
* classical 1-cm path length UV-Vis
* classical RA luminescence
Fig. 5. Dissociation of supramolecular systems 5 and 6.

S. Drouet et al. / Tetrahedron 68 (2012) 98e105
105
Table 2
the solution. Fluorescence measurements on dilute solutions
(10ꢂ6 M, optical density <0.1) were performed using a right-angle
detection setup in standard 10-mm quartz cuvettes on an Edin-
burgh Instruments (FLS920) spectrometer equipped with a 450 W
Xenon lamp and a Peltier-cooled Hamamatsu R928P photo-
Photophysical properties of the zinc fluorenyl porphyrins 3 and 4, and of the su-
pramolecular systems 5 and 6 at 1.5ꢁ10ꢂ3 M in CH2Cl2 solution at 298 K
abs
a
em a
Compound
l
[nm]
l
[nm]
max
max
ZnTFP (3)
(ZnTFP)3-tripod (5)
ZnOOFP (4)
556, 598
562, 605
553, 594
558, 599
621, 660
620, 664
604, 654
609, 659
multiplier tube in photon-counting mode. Fully corrected emission
abs
spectra were obtained, for each compound, at lex
¼
l
with an
max
(ZnOOFP)3-tripod (6)
optical density at lexꢃ0.1 to minimize internal absorption. Fluo-
rescence quantum yields were measured according to literature
procedures.24,26 Fluorescence measurements at higher concentra-
tions (10ꢂ3 M) were performed using a front-face detection setup in
1-mm path length quartz cells on a Horiba Jobin-Yvon Fluorolog-3
spectrometer equipped with 450 W Xenon lamp an a Hamamatsu
R928P photomultiplier tube.
a
Experimental absorption and emission maxima.
1717 (vs, C]O). HRMSeESI: calcd for C42H25N6O3 661.1988
[MþH]þ. Found 661.1981.
4.5. Synthesis of supramolecular assembly 5
Acknowledgements
To a solution of zinc complex ZnTFP (3) (50 mg, 49
mmol) in
ꢀ
Funding for the project was obtained from the ‘Universite
CH2Cl2 (15 mL) was added the ligand 7 (10 mg, 15 mol). The re-
m
ꢀ
Europeenne de Bretagne’ (UEB) and from FEDER by an EPT grant in
the ‘MITTSI’ program from RTR BRESMAT. This research was sup-
ported by grants from the ‘Region Bretagne’ (AREDdA.M.) and from
the ‘Ministere National de la Recherche et de la Technologie’
action mixture was stirred at room temperature under argon. After
1 h (TLC checking), the reaction mixture was concentrated and
precipitated with pentane to afford 51 mg (91%) of the desired
supramolecular assembly 5 as a purple solid. 1H NMR (500 MHz,
0
d in ppm): 8.98 (s, 24H, Hb-pyrrolic), 8.40 (large s, 12H, H1 ),
ꢀ
ꢁ
(MNERTdS.D.). The authors are grateful to S. Sinbandhit (CRMPO)
CDCl3,
3
3
for technical assistance and helpful discussions.
0
0
8.26 (large d, JH,H¼7 Hz, 12H, H3 ), 8.13 (d, JH,H¼7 Hz, 12H, H4 ),
3
3
0
0
8.05 (d, JH,H¼8 Hz, 12H, H5 ), 7.68 (d, JHH¼7 Hz, 12H, H8 ), 7.52 (t,
3
3
Supplementary data
0
0
JHH¼6 Hz, 12H, H6 ), 7.42 (t, JHH¼6 Hz, 12H, H7 ), 7.34 (d,
3JHH¼8 Hz, 6H, Hphenyl), 7.21 (d, 3JHH¼8 Hz, 6H, Hphenyl), 6.55 (large
3
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tet.2011.10.081.
0
d, JHH¼5 Hz, 6H, HB), 5.71 (v large d, 6H, HA), 4.20 (s, 24H, H9 ,
CH2fluorene). UVevis (l max, CH2Cl2, nm): 263 (fluorene), 303 (li-
gand 7), 428 (Soret band), 554 (Q band), 596 (Q band). FT-IR (KBr,
cmꢂ1): 2221 (m,
n
C^C), 1740 (s, C]O). Anal. Calcd (%) for
n
References and notes
C258H156N18O3Zn3$3CH2Cl2: C, 78.23; H, 4.07; N, 6.29. Found: C,
78.97; H, 4.38; N, 6.23.
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4.6. Synthesis of supramolecular assembly 6
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To a solution of zinc complex ZnOOFP (4) (50 mg, 22
mmol) in
CH2Cl2 (15 mL) was added ligand tripod 7 (5 mg, 7 mol). The re-
m
action mixture was stirred at room temperature under argon. After
1 h (TLC checking), the reaction mixture was concentrated and
precipitated with pentane to afford 48 mg (96%) of desired supra-
molecular assembly 6, as a purple solid. 1H NMR (500 MHz, CDCl3,
3
0
d
in ppm): 8.94 (s, 24H, Hb-pyrrolic), 7.76 (d, JH,H¼8 Hz, 24H, H4 ),
3
0
0
7.75 (d, JH,H¼8 Hz, 24H, H5 ), 7.66 (s, 24H, H1 ), 7.54 (s, 24H, HB),
7.51 (d, 3JH,H¼7 Hz, 24H, H8 ), 7.47 (d, JH,H¼7 Hz, 24H, H3 ), 7.34 (t,
3
0
0
3
3
0
0
JH,H¼7 Hz, 24H, H6 ), 7.27 (t, JH,H¼7 Hz, 24H, H7 ), 7.16 (d,
3JH,H¼8 Hz, 6H, Hphenyl), 7.12 (s, 12H, HE), 7.01 (d, JH,H¼8 Hz, 6H,
3
Hphenyl), 5.90 (large s, 6H, Hpyridine), 5.26 (s, 48H, OCH2), 3.86 (s,
0
00
48H, H9 and H9 ). UVevis (
(ligand 7), 425 (Soret band), 551 (Q band), 591 (Q band). FT-IR (KBr,
cmꢂ1): 2223 (m,
C^C), 1740 (s, C]O). Anal. Calcd (%) for
l max, CH2Cl2, nm): 270 (fluorene), 304
n
n
C510H348N18O27Zn3$3CHCl3: C, 79.87; H, 4.59; N, 3.27. Found: C,
78.82; H, 5.36; N, 3.09.
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22. Gouterman, M. J. Mol. Spectrosc. 1961, 6, 138.
4.7. Photophysical methods
23. Austin, E.; Gouterman, M. Bioinorg. Chem. 1978, 9, 281.
24. Eaton, G. R. Pure Appl. Chem. 1988, 60, 1107.
25. Owens, J. W.; Smith, R.; Robinson, R.; Robins, M. Inorg. Chim. Acta 1998, 279,
226.
26. Demas, J. N.; Crosby, G. A. J. Phys. Chem. 1971, 75, 991.
All photophysical properties measurements have been per-
formed at room temperature (298 K). UVevis absorption spectra
were recorded on a Jasco V-570 spectrophotometer, using 10-mm or
1-mm path length quartz cells, depending on the concentration of