New meso-Tetrafluorenylethynyl porphyrin platform

Article abstract of DOI:10.1142/S1088424619500202

To improve conjugation between a central porphyrin core and its peripheral fluorenyl antennae, we have introduced in the meso-Tetrafluorenyl porphyrin (TFP-Bu) unit an ethynyl spacer at the meso positions. By this means, we have synthesized and characterized a new meso-Alkynyl fluorenyl porphyrin (TAFlP). We discuss the effect of this extra extension of the I manifold on the optical properties. This enlarged porphyrin core, TAFlP, is foreseen as a key building block for the design of new dendrimers for theranostic applications. The constant improvement of porphyrin-based dendrimers featuring conjugated fluorenyl dendrons is recalled herein and demonstrates the important role of the central core structure in determining linear and nonlinear optical properties. Further improvement of these properties seems possible with TAFlP-like structures based on observations made for dendrimers recently obtained. This makes the exploration of such new molecular architectures appealing for photodynamic therapy (PDT) and related applications.

Full text of DOI:10.1142/S1088424619500202

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2019; 23: 185–195
DOI: 10.1142/S1088424619500202
Published at http://www.worldscinet.com/jpp/
New meso-tetrafluorenylethynyl porphyrin platform
Xu Zhanga,b and Christine O. Paul-Roth*a
a Univ Rennes, INSA Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes) — UMR 6226,
F-35000 Rennes, France
b Department of Chemistry, College of Chemistry and Chemical Engineering, Chifeng University, Chifeng, China
This paper is part of the 2019 Women in Porphyrin Science special issue.
Dedicated to Dr. Gérard Simonneaux for opening the door of the wonderful world of porphyrins.
Received 7 December 2018
Accepted 21 January 2019
ABSTRACT: To improve conjugation between a central porphyrin core and its peripheral fluorenyl
antennae, we have introduced in the meso-tetrafluorenyl porphyrin (TFP-Bu) unit an ethynyl spacer at
the meso positions. By this means, we have synthesized and characterized a new meso-alkynyl fluorenyl
porphyrin (TAFlP). We discuss the effect of this extra extension of the p manifold on the optical
properties. This enlarged porphyrin core, TAFlP, is foreseen as a key building block for the design of
new dendrimers for theranostic applications. The constant improvement of porphyrin-based dendrimers
featuring conjugated fluorenyl dendrons is recalled herein and demonstrates the important role of the
central core structure in determining linear and nonlinear optical properties. Further improvement of
these properties seems possible with TAFlP-like structures based on observations made for dendrimers
recently obtained. This makes the exploration of such new molecular architectures appealing for
photodynamic therapy (PDT) and related applications.
KEYWORDS: porphyrin, fluorenyl, fluorescence, alkyne.
research in fields more related to photophysics and
material sciences has been undertaken in recent decades.
Symmetrical A4-type porphyrins, substituted at the
INTRODUCTION
There has been great interest in the synthesis of
porphyrin systems because the peripheral substituents
four meso positions, are particularly interesting because
on the macrocyclic core can modulate the physical
the molecules are easily accessible with good yields.
properties at will. Consequently, they present wide
Also very appealing is the synthetic expansion of such
potential applications in different fields such as, for
structures by introducing dendrons at these positions, and
instance, light-harvesting, organic light emitting diodes
the modification of these dendrons for light harvesting.
(OLEDs) or switches. Porphyrin-based systems are
In this respect, many porphyrin-based dendrimers
largely present nowadays, in many applied developments
have been recently synthesized. Their light-harvesting
encompassing by far the numerous bio-related studies
properties can be optimized by connecting highly
in which these macrocycles were initially involved [1a].
absorbing dendrons to the central porphyrin core, with
Stimulated by the fact that the unique photochemical
the former acting as energy donors to the latter, overall
properties of the porphyrin core can be fine-tuned by
behaving like an antenna system [1b]. In particular,
modification of the peripheral substituents, intense
some porphyrins bearing pendant linear oligofluorene
arms have been reported in this context [1c], and for
such assemblies, Fréchet [1d] demonstrated that the
antenna effect was facilitated in dendritic architectures
vs. linear ones. More recently, hyperbranched polymers
*Correspondence to: Christine O. Paul-Roth, tel.: (+33) (0) 2 23
23 63 72, fax: (+33) (0) 2 23 23 63 72, email: christine.paul@
univ-rennes1.fr or christine.paul@insa-rennes.fr.
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X. ZHANG AND C. O. PAUL-ROTH
Fig. 1. Molecular structures of TPP-cored porphyrin dendrimers TPP1-TPP3 and their reference TPP
containing porphyrins with fluorenyl arms have also
been synthesized for light harvesting [1e], while the
group of Okada and Kozaki investigated the use of a
series of multi-porphyrin arrays in conjugated networks
as light-harvesting antenna [1f]. In this field, we also
have recently reported efficient light-harvesting systems
in which 5,10,15,20-tetraphenylporphyrin (TPP) was
linked, via flexible ether bridges, to fluorenyl donor
moieties [1g, h]. One might wonder why there is such
interest in porphyrin-fluorenyl combinations. Actually,
as we have discovered in collaboration with J.A.G.
Williams, that 5,10,15,20-tetrafluorenylporphyrin (TFP)
exhibits a high quantum yield (24%), demonstrating
the capacity of 2-fluorenyl units to strongly enhance
the emission quantum yield of the porphyrin core [1i].
Our aim was then to exploit further this capacity, and
a series of super porphyrins based on the small TPP-
core was targeted. In the first family, the dendrons were
linked via ether bridges to the central core. Four, eight
and sixteen fluorenyl donor moieties were included in
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NEW meso-TETRAFLUORENYLETHYNYL PORPHYRIN PLATFORM
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Fig. 2. TFP-cored porphyrin dendrimers TFP1, TFP2 and TFP3 and the corresponding reference compound TFP-Bu
these dendrons. Then, we wondered about improving
the light-harvesting mechanism by preserving some
p-overlap between the peripheral fluorenyl arms and the
central core [1j]. Indeed, porphyrin-based dendrimers
containing p-conjugated dendrons are expected to
present better energy transfer properties than systems
for which p-conjugation is disrupted, as indicated by
the work of Burn and Samuel on porphyrin dendrimers
with stilbene dendrons for instance [1k]. The meso-
phenyl units of the TPP-core molecule have two easy-to-
functionalize positions (para and meta), accordingly the
corresponding dendrimers were then synthesized. The
optical properties of these porphyrin-based dendrimers,
featuring 2-fluorenyl containing dendrons with extended
p-manifolds on these positions were then studied (Fig. 1).
Such systems present increasing numbers of terminal
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X. ZHANG AND C. O. PAUL-ROTH
fluorenyl units at their periphery, going from 4 to 8 to 16
(TPP1, TPP2 and TPP3, respectively). We have shown
that conjugation between the TPP porphyrin core and
the unsaturated dendrons is more effective in the para-
functionalized systems than in the meta-ones. This better
conjugation improves the photophysical properties of
the para-substituted compounds (TPP1) over the meta-
substituted ones (TPP2, TPP3) [1l], encouraging us
to consider the 2,7-fluorenyl unit as a new spacer, in
replacement of the 1,4-phenyl unit.
Subsequently a series of related compounds in which
2,7-fluorenyl groups were connected directly to the meso
positions of the central porphyrin core (i.e. a dendritic
architecture featuring TFP instead of TPP as a central
core) and still possessing fully conjugated peripheral
arms incorporating fluorene units at both terminal and
internal positions was developed.
A versatile synthetic protocol allowed us to easily
introduce fluorenyl units as internal chromophores
(behaving also as antennae). The effect of this structural
variation on the photophysical properties of the resul-
ting dendrimers was then explored. Dendrimers with
increasing generations going from 1 to 3, were called
TFP1, TFP2 and TFP3, respectively (represented
in Fig. 2) [1 m]. In terms of photophysical properties,
this TFP series exhibits remarkably high luminescence
quantum yields (20–24%) again thanks to a very efficient
energy transfer (ET) from the peripheral fluorenyl units
toward the central porphyrin core. This process is plainly
apparent for dendrimers TFP1 and TFP2, but contrasts
with the dual emission (blue and red) observed for the
big TFP3 compound featuring the largest dendrons at the
meso positions. Such a size limit to the ET was expected
considering the tilted conformation adopted by the inner
meso-fluorenyl groups bearing the peripheral dendrons.
In spite of that non-optimal p conjugation, the one-
photon brightness of these compounds increases almost
linearly with the number of fluorenyl groups in the
peripheral arms, in line with the existence of the antenna
effect previously mentioned.1m To further improve
the photophysical performance of such dendrimeric
systems, with the aryl groups tilted conformations
should be replaced by another unit permitting to achieve
co-planarity between the central core and an aromatic
system of the peripheral dendrons. In particular, this
can be done by using a meso-substituted tetra-alkynyl
porphyrin as the central unit. We therefore turned our
interest toward meso-ethynylporphyrins.
The first porphyrins of this kind, substituted by one or
two alkynyl groups, were initially targeted as precursors
for the elaboration of conducting polymers [2–3], non-
linear optical (NLO) materials [4, 5], photosynthetic
models [6, 7] and enzyme mimics [8–10]. Most of these
alkynyl-meso-substituted porphyrins contained only
one or two ethynyl moieties. These macrocycles turned
out to present a strong bathochromic shift of their first
absorptions relative to tetraphenylporphyrin [11–15].
This is due to the direct conjugation of the 18p-electronic
system of the macrocycle over the alkynyl group to
the terminal aromatic moieties. As a result, the Soret
(B) band and Q bands are significantly altered [11]. In
consequence, the color of these porphyrins in solution
turns to a brilliant green departing from the typical red
color of tetraphenylporphyrin. Hence the trivial name
of Chlorophyrins was given for arylethynyl-meso-
substituted porphyrins [12–15]. In the tetralkynyl series,
in 1992, Anderson reported a tetra-substituted derivative:
5,10,15,20-tetra-trimethylsilylethynyl-porphyrin (H21)
(see Fig. 3) which was isolated in moderate yield (14%)
[11]. The same year, Hevesi obtained a closely related
Fig. 3. Molecular structures of reported meso-alkynyl porphyrins (H21, H22 and H23-R)
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NEW meso-TETRAFLUORENYLETHYNYL PORPHYRIN PLATFORM
189
(a)
(b)
Fig. 4. (a) Structure of reference compound TFP-Bu and corresponding TFP-based dendrimers; (b) target compound: new meso-
alkynyl fluorenyl porphyrin TAFlP allowing the design of new TAFlP-based dendrimers
compound (H22), but with methyl end-groups substituents
rather than TMS ones. This new tetra-alkynylporphyrin
was isolated with an even lower yield (around 1%)
[16]. Finally, the corresponding aryl-ethynyl derivative
(5,10,15,20-tetra-phenylethynyl)-porphyrin (H23-R) was
also reported the same year, with a yield of 2% by
Hevesi and coworkers [16]. Subsequently, Milgrom
reported the synthesis of related compounds with octyl
or nonyloxy chains appended in the para positions of the
four phenyl groups (H23-R) to increase the solubility of
these compounds [12]. These last porphyrins (H22 and
H23-R) were synthesized with the aim of developing
highly conjugated porphyrin polymers and arrays by
assembling these building blocks together [12, 16].
Based on these tetra-alkynyl meso-substituted precur-
sors, we believe that the related meso-tetra-alkynyl
fluorenyl porphyrin (TAFlP), composed of one central
porphyrin substituted at its meso positions by four
alkynylfluorenyl units, could constitute an interesting
platform for designing new dendrimers for theranostics
(Fig. 4). Indeed expanding the p manifold should
increase 2PA and bring about a red shift in emission
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X. ZHANG AND C. O. PAUL-ROTH
and absorption. We have therefore synthesized TAFlP
porphyrin as a model compound to study its optical
properties and compare them to those of TFP-Bu taken
as reference. TAFlP porphyrin will also be compared
to known tetraalkynyl porphyrins H21, H22 and H23-R
(R = H, C8H17, OC9H19). This molecular assembly
might (i) possess the remarkable fluorescence yield and
brightness of TFP [1i] precursor and (ii) present a fully
conjugated and extended p manifold which will favor the
2PA and also redshift the 2PA and the emission. As usual
(see Figs 1 and 2) butyl chains will be connected to the
peripheral fluorenyl units (in the 9 position) to improve
the solubility of the compound in organic solvents.
selected, in spite of its comparatively low final yield,
mostly for practical and cost-related reasons.
The new compounds were characterized by the usual
methods. The 1H NMR spectra of the known 9,9-dibutyl-
fluorenyl-2-carboxaldehyde and of the new (9,9-dibutyl-
fluorenyl)-2-propiolaldehyde (3) are shown in Fig. 5. We
observe that the aldehyde proton of new compound 3, at
9.46 ppm, is shifted to a higher field (+0.62 ppm) upon
the introduction of the alkynyl function. The multiplets
corresponding to aromatic, as well as n-butyl protons,
present similar shifts for 3 compared to 9,9-dibutyl-
fluorenyl-2-carbaldehyde, but of lower magnitude.
The corresponding meso-alkynyl fluorenyl porphyrin
(TAFlP) was also characterized by 1H NMR. The
partial spectrum is compared to reference TFP-Bu
in CD2Cl2 (Fig. 6). As shown, the singlet at 9.69 ppm,
corresponding to eight b-pyrrolic protons is shifted
to a lower field compared to the corresponding signal
of TFP-Bu at 8.92 ppm. This could be because these
b-pyrrolic protons are further removed from ring currents
field of the aromatic units in the arms. An alternative
explanation is that they experience a smaller ring current
from the porphyrin cycle. The second explanation is also
supported by the fact that the singlet at -1.36 ppm of NH
protons is strongly shifted to a lower field compared to
that at -2.57 ppm for TFP-Bu. Thus it seems that the
combination of the alkynyl bridges and fluorenyl units
also causes a decreased electron density at the porphyrin
ring. On the contrary, the electron density of fluorenyl
arms seems to be partially increased, leading to signals
for aromatic protons (H1–5) at higher fields for TAFlP
than for TFP-Bu.
RESULTS AND DISCUSSION
Synthesis and characterization
Two different methods for synthesizing TAFlP were
tested. The first attempt to isolate this molecule was done
via H21 [2a]. As shown in Scheme 1, one equivalent
of the commercial 3-(trimethylsilyl)-2-propynal and
pyrrole were dissolved in distilled CHCl3 under argon.
The reaction was conducted by adapting the reaction
protocol given by Anderson in the literature for H21 [11],
and it allowed the isolation of H21 with a low yield (14%)
[11]. Considering the large quantity of H21 required
for the next step and also the high cost of the starting
material (3-(trimethylsilyl)-2-propynal); this approach
was ultimately not pursued, and a second approach was
tested.
In the second approach, 9,9-dibutyl-fluorenyl-2-
propiolaldehyde 3 was synthesized first as a precursor
and then assembled to obtain the desired TAFlP under
Lindsey’s conditions (Scheme 2). The intermediate
alkyne 2 was prepared in three steps as described earlier
[1l], giving the precursor 3 by exchange of the terminal
proton and carboxylation [17]. The desired new meso-
alkynyl fluorenyl porphyrin TAFlP was finally isolated
albeit with a low yield (3%). This second synthetic
approach (Scheme 2), using for each step well known
reactions and leading to isolation of the precursor 3 in
higher yields than the route first tested, was eventually
UV-vis absorption and emission spectra were next
recorded for the new porphyrin (TAFlP) in CH2Cl2
solution (HPLC level) at room temperature. Molecules
with similar structures, such as H21, H22 and H23-R
reported previously (Fig. 3) [9, 11–16] and TPP, TFP-Bu
were chosen as references to analyze the influence of the
triple bond introduction on the optical properties. When
compared to meso-tetra-alkynylporphyrins, the fluorenyl
rings of TAFlP extend the p manifold of the chromophore,
resulting in bathochromic shifts for all absorption bands
compared to H21, H22 and H23-R, but also compared
to TFP-Bu. TAFlP has several characteristic features
Scheme 1. Syntheses of intermediate H21, following Anderson’s work up (Ref. 11)
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Scheme 2. Synthesis of the new 9,9-dibutyl-fluorenyl-2-propiolaldehyde 3 and of meso-alkynyl fluorenyl porphyrin TAFlP
in the UV-vis region (Fig. 7): (i) an intense Soret band
around 479 nm with a shoulder at 486 nm and two red-
shifted Q bands at 661 and 748 nm, characteristic of the
porphyrin macrocycle, and (ii) an extra absorption due
to alkynylfluorenyl antennae (AFl), around 250–400 nm
(lDendron =319nm)whichcorrespondstoap*←ptransition
of the conjugated dendron. This strong absorption,
largely fluorenyl-based, is absent for reference TFP-Bu,
suggesting that the unconjugated meso-fluorenyl groups
of TFP-Bu absorb above 270 nm [1m], whereas those
of the TAFlP conjugate with the porphyrin core appear
strongly red shifted and more intense.
When going from reference TFP-Bu to new porphyrin
TAFlP, a strong red shift (Dl = 53 nm) can be clearly
observed on the normalized absorption spectra for the
porphyrin-based bands due to the alkynyl bridges (Soret
band and Q bands in Fig. 7). It should also be noticed
that generally, free-base porphyrins have four obvious
Q bands, but for TAFlP, only two coalesced Q bands
with a hyperchromic effect are observed in the visible
region. In addition, there is a marked increase in the main
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X. ZHANG AND C. O. PAUL-ROTH
1
Fig. 5. Comparison of complete H NMR spectra of 9,9-dibutyl-fluorenyl-2-carbaldehyde and new (9,9-dibutyl-fluorenyl)-2-
propiolaldehyde (3)
Fig. 6. The partial 1H NMR spectra of new meso-alkynyl fluorenyl porphyrin TAFlP compared to reference TFP-Bu
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NEW meso-TETRAFLUORENYLETHYNYL PORPHYRIN PLATFORM
193
H21 is red-shifted to 451 nm. Also, replacing the TMS
groups of H21 with aryl groups (H23-R), increases the
B- and Q-band red shifts even further.
The emission spectra of TAFlP and the reference
compound TFP-Bu were measured in CH2Cl2 (HPLC
grade) at room temperature. Upon excitation in their
Soret band, they both exhibit the characteristic porphyrin
emission peaks Q(0,0) (Fig. 8). The lowest energy
Q-band absorption is at 748 nm, while the corresponding
fluorescence band appears at 760 nm. The new tetra-
fluorenylethynylporphyrin spectra are also characterized
by small Stokes shifts (∼12 nm) but slightly larger
than for TFP-Bu derivatives (∼10 nm) [19] similar
to the shift reported in 1998 for 5,10,15,20 tetra-
arylethynyIporphyrinato zinc(II) complexes (13 nm)
Fig. 7. Normalized absorption UV-vis spectra of TAFlP
[18]. The proximity of these two bands indicates that
the nuclear configurations of the ground and excited
states of TAFlP are nearly similar. Whereas reference
TFP-Bu emits a typical red luminescence, with two
Q bands (660 and 724 nm), for new TAFlP only a strong
single band Q(0,0) could be detected in the visible region
with a maximum at 760 nm with a large red shift (Dl =
100 nm) compared to TFP-Bu. This intense Q(0,0)
emission band has a part of its emission located in the
near infrared region (shadowed on Fig. 8). Thus, as
for absorption, the presence of the four ethynyl groups
results in a significant red shift in the fluorescence
peak maxima relative to TPP and TFP-Bu derivatives,
resulting in emissions located partly in the near infra-red
region of the spectrum. The detector of the Edinburgh
FS920 Fluorimeter (Xe900) can only collect the signal at
the maximum wavelength of 900 nm, so for the moment
eventually weaker emission band Q(0,1) could not be
detected and in consequence, the quantum yield of this
new porphyrin TAFlP is calculated but maybe under
evaluated. The fluorescence quantum yields, measured in
and reference TFF-Bu in CH2Cl2 (HPLC grade) at room
temperature
Q band absorption (661 nm) relative to that of the B band
(479 nm), and the second Q band (748 nm) appears as
a smaller band on the right side of this main Q band
absorption.
We can notice that the derivative H23-H, which possess
similar ethynylaryl structures to TAFlP, presents similar
spectral profiles and shows only two Q-band absorptions
(Table 1). In contrast, the para-octyl-substituted derivate
of H23-R presents four Q bands but very strongly red
shifted and in this case, this red shift is even larger, going
up to Dl = 79 nm. The porphyrin H22 also presents four
classical Q bands in the visible region [12, 16]. Likewise,
the aryl rings of the tetra-phenylethynylporphyrin (H23-
H), by extending the porphyrin chromophore, resulting in
a bathochromic shift for the B- and Q-absorption bands
compared to those of porphyrin. Thus, compared to short
tetra-phenylporphyrin (TPP), the B band of porphyrin
Table 1. Photophysical data of new meso-alkynyl fluorenyl
porphyrin TAFlP and reported H21, H22 and H23-R and
Refs TFP-Bu, TPP
UV-vis absorption/nm
Emission/nm
Φfl/%
τ/ns
lSoret
419
lQ bands
excited at lSoret
TPP
515, 548, 592, 647
Q (0,0)
Q (0,1)
TFP-Bu
H21a
H22a
426
520, 557, 593, 650
567, 606, 646, 710
517, 563, 602, 647, 708
621, 717
TPP
653
663
660
760
721
730
724
—
11
24
20
—
8.6
8.0
8.2
—
451
TFP
446
TFP-Bu
TAFlP
a
H23H
463
H23C
466
599, 642, 673, 737
600, 653, 744
H
8
17
H
H23OC
472
9
19
TAFlP
479 (486)
661, 748
aData from literature [11–16].
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X. ZHANG AND C. O. PAUL-ROTH
temperature (298 K). UV-vis absorption spectra were
recorded on a BIO-TEK instrument UVIKON XL
spectrometer or on a Jasco V-570 spectrophotometer.
Steady-state fluorescence measurements were performed
on dilute solutions (ca. 10-6 M, optical density < 0.1)
contained in standard 1 cm quartz cuvettes using an
Edinburgh Instrument (FLS920) spectrometer in photon-
counting mode. Fully corrected emission spectra were
obtained for each compound after excitation at the
wavelength of the absorption maximum, with Alex < 0.1
to minimize internal absorption.
Synthesis
9,9-dibutyl-fluorenyl-2-propargylaldehyde (3). In a
Schlenk tube, a mixture of 9,9-dibutyl-2-ethynyl-fluorene
(2) (1.03 g, 3.41 mmol, 1 equiv) was dissolved in dried
THF (10 mL). The reaction medium was degassed by
the freeze-pump-thaw method three times and cooled to
-78°C in a liquid nitrogen-acetone bath.At -78°C, n-BuLi
(2.60 mL, 4.09 mmol, 1.2 equiv) was injected dropwise
to the previous mixture over 30 min. Then the system was
kept stirring at -78°C for more than 3 h. Subsequently
dry DMF (0.53 mL) was injected in the medium and
the reaction was maintained under stirring at -78°C for
another hour. The reaction was then removed from the
cooling bath and stirred overnight at room temperature.
Finally, saturated NH4Cl (aq.) was injected (for quenching
the reaction). The mixture was extracted with ethyl
acetate/water mixtures. After evaporation of the volatiles,
the residue was purified by silica chromatography using
heptane/CH2Cl2 (5:1) as eluent. The desired compound
9,9-dibutyl-fluorenyl-2-propiolaldehyde (3) was isolated
Fig. 8. Comparison of emission spectra of TAFlP and reference
TFP-Bu in the visible region, upon excitation in their Soret band
CH2Cl2 for this new porphyrin TAFlP is found to be 24%
albeit similar to TFP (24%), and higher then TFP-Bu
(20%). In agreement with what had already been noted
earlier about fluorescence. Indeed it was proofed that
fluorescence quantum yield values are significantly
higher for the arylethynyl derivatives (ffl > 20%) and
are among the highest values observed for porphyrinic
species [19]. So, these measurements must be repeated
on a fluorimeter allowing detection further in the near IR
range.
EXPERIMENTAL
Materials
1
as a white powder (623 mg, 55% yield). H NMR
(400 MHz; CDCl3): dH, ppm 9.44 (s, 1H, HCHO), 7.77–
7.75 (m, 2H, H1,3), 7.64–7.62 (m, 2H, H4,5), 7.41–7.35
(m, 3H, H6,7,8), 2.03–1.99 (m, 4H, Ha), 1.13–1.04 (m,
4H, Hc), 0.67 (t, J = 7.2 Hz, 6H, Hd), 0.60–0.52 (m, 4H,
Hb). 13C{1H}NMR (400 MHz, CD2Cl2, ppm): d = 176.6
(CHO), 151.5, 151.1, 144.6, 139.7, 132.5, 128.5, 127.9,
127.1, 123.1, 120.5, 119.9, 117.2, 96.3, 88.8, 55.2,
39.9, 25.9, 23.0, 13.5. HRMS-ESI for C24H27O: m/z =
331.2060 [M]+ (calcd: 331.20619); for C24H26O: m/z =
330.1990 [M]+ (calcd: 330.19837).
Unless otherwise stated, all solvents used in reactions
were distilled using common purification protocols [20],
except DMF and iPr2NH, which were dried on molecular
sieves (3Å). Compounds were purified by chromatography
on silica gel using different mixtures of eluents as specified.
1H and 13C NMR spectra were recorded on BRUKER
Ascend 400 and 500 NMR spectrometers at 298 K. The
chemical shifts are referenced to internal tetramethyl-
silane. High-resolution mass spectra were recorded on
different spectrometers: a Bruker MicrOTOF-Q II, a
Thermo Fisher Scientific Q-Exactive in ESI positive
mode and a Bruker Ultraflex III MALDI Spectrometer at
CRMPO (centre regional de mesures physiques de l’Ouest)
in Rennes. Reagents were purchased from commercial
suppliers and used as received. Compounds 9,9-dibutyl-7-
((trimethylsilyl)ethynyl)-fluorene-2-carboxaldehyde and
2-ethynyl-9,9-dibutyl-fluorene (2), were synthesized as
described earlier [1l, 1m].
Meso-alkynyl fluorenyl porphyrin (TAFlP). In a
two-neck flask, a mixture of 9,9-dibutyl-fluorenyl-2-
propiolaldehyde (3) (300 mg, 0.91 mmol, 1 equiv) and
distilled pyrrole (0.06 mL, 0.91 mmol, 1 equiv) were
dissolved in dried chloroform (60 mL) under argon.
After degassing the mixture with argon bubbling for
.
30 min, BF3 OEt2 (0.02 mL, 0.16 mmol, 0.25 equiv) was
injected and the reaction was stirred in the dark for 1 h
under argon at -30°C. Then p-chloranil (315 mg, 1.28
mmol, 0.75 equiv) was added as oxidant, and the reaction
was continued at room temperature. for another hour. At
last, NEt3 (2 mL) was injected, and the reaction medium
was kept stirring for several minutes. After evaporation
Spectroscopic measurements
All photophysical properties were performed with
freshly-prepared air-equilibrated solutions at room
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NEW meso-TETRAFLUORENYLETHYNYL PORPHYRIN PLATFORM
195
of the volatiles, purification of the residual solid was
Tetrahedron 2009; 65: 2975–9781. (h) Drouet S
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D, Zhang X, Mongin O, Paul F and Paul-Roth
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done by silica chromatography using a THF/heptane
(1:10) mixture as eluent. TAFlP was collected as a green
powder (10 mg, 3% yield). 1H NMR (400 MHz; CDCl3):
dH, ppm 9.69 (s, 8H, Hb-pyrrolic), 8.11 (d, 8H, J = 10.5 Hz,
H1,3), 7.96 (d, 4H, J = 7.6 Hz, H4), 7.88–7.85 (m, 4H,
H5), 7.51–7.43 (m, 12H, H6,7,8), 2.30–2.15 (m, 16H, Ha),
1.25–1.17 (m, 16H, Hc), 0.78 (t, 24H, J = 7.3 Hz Hd),
0.75–0.62 (m, 16H, Hb), -1.36 (s, 2H, NH). 13C{1H}NMR
(400 MHz, CD2Cl2, ppm): d = 151.3, 151.2, 142.4, 140.5,
131.1, 127.9, 127.0, 126.1, 123.1, 121.7, 120.1, 103.1,
55.4, 40.3, 29.7, 26.2, 23.2, 13.7. UV-vis (lmax, CH2Cl2,
nm): 319, 479, 661, 748. HRMS-ESI for C112H111N4:
m/z = 1511.8797 [M + H]+ (calcd: 1511.88033).
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CONCLUSIONS
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We have successfully synthesized and characterized
the new meso-tetra-fluorenylethynylporphyrin derivative
(TAFlP). Linear optical measurements reveal better
conjugation between the porphyrin core and the
peripheral fluorenyl-containing antennae, compared to
the TFP-Bu core. This results from the presence of an
yne linkage at the meso positions which allows more
planar conformations. We now look forward to using
similar central platforms for the design of new families
of dendrimers. We hope that the extended and more
conjugated p manifold, besides providing a desirable red-
shift for theranostic applications and high fluorescence
for imaging, will also enhance the 2PA of the central core
allowing for more efficient photosensitizers to be made.
For the moment, extensive studies of the NLO properties
of TAFlP are in progress to verify this point.
Acknowledgments
The authors acknowledge China Scholarship Council
(CSC) for PhD funding (XZ). The authors acknowledge
Dr Frédéric PAUL, Dr Olivier MONGIN for fruitful
discussion and exchange. This project was partially
supported by the departmental committees CD35 and
CD85 of the “Ligue contre le Cancer du Grand-Ouest”.
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J. Porphyrins Phthalocyanines 2019; 23: 195–195