New luminescent fluorenyl-armed linear porphyrin trimers with diphenylacetylene bridges

Article abstract of DOI:10.1016/j.jphotochem.2014.04.024

First a series of porphyrins bearing various fluorenyl donor groups is presented; an intermediate porphyrin bearing three fluorenyl arms (zinc complex 12) and compound 13, bearing only two fluorenyl groups. Then starting from these building blocks, synthesis of new porphyrin trimers 7 and 8, with in totally eight peripheral fluorenyl arms is performed by using a palladium catalyst. Photophysical properties; absorption and luminescence, of new trimers 7 and 8 are presented. We can then compare these properties to those of reference porphyrin monomer TFP (2), as well as to those of porphyrin dendrimers bearing various numbers of fluorenyl arms (3 and 4) and finally to those of the corresponding dimers 5 and 6, which are the precursor models of this work.

Full text of DOI:10.1016/j.jphotochem.2014.04.024

Accepted Manuscript
Title: New luminescent fluorenyl-armed linear porphyrin
trimers with diphenylacetylene bridges
Author: Christine O. Paul-Roth Areej Merhi Dandan Yao
Olivier Mongin
PII:
S1010-6030(14)00169-5
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jphotochem.2014.04.024
JPC 9661
To appear in:
Journal of Photochemistry and Photobiology A: Chemistry
Received date:
Revised date:
Accepted date:
27-2-2014
25-4-2014
26-4-2014
Please cite this article as: C.O. Paul-Roth, A. Merhi, D. Yao, O. Mongin,
New luminescent fluorenyl-armed linear porphyrin trimers with diphenylacetylene
bridges, Journal of Photochemistry and Photobiology A: Chemistry (2014),
http://dx.doi.org/10.1016/j.jphotochem.2014.04.024
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Graphical Abstract
New luminescent fluorenyl-armed linear porphyrin trimers with diphenylacetylene
bridges
Christine O. Paul-Roth,*a,b Areej Merhi,a,b Dandan Yao,a,b Olivier Mongin,a
a Institut des Sciences Chimiques de Rennes, ISCR-UMR CNRS 6226, Université de Rennes 1,
35042 Rennes Cedex
bInstitut National des Sciences Appliquées, INSA-ISCR,
35043 Rennes Cedex
Université Européenne de Bretagne, France
*Corresp. author. Fax: 02 23 23 56 37; Tel.: 02 23 23 63 72,
e-mail: christine.paul@univ-rennes1.fr or christine.paul@insa-rennes.fr
ET
ET
HN
N
N
N
N
N
N
N
N
N
N
M
M
NH
M= Zn Trimer 7
M= 2H Trimer 8
1
Page 1 of 27

New luminescent fluorenyl-armed linear porphyrin trimers with
diphenylacetylene bridges
Christine O. Paul-Roth,*a,b Areej Merhi,a,b Dandan Yao,a,b Olivier Mongin,a
a Institut des Sciences Chimiques de Rennes, ISCR-UMR CNRS 6226,
Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France.
bInstitut National des Sciences Appliquées, INSA-ISCR, 35043 Rennes Cedex, France.
*Corresponding author. Fax: 02 23 23 56 37; Tel.: 02 23 23 63 72
e-mail: christine.paul@univ-rennes1.fr or christine.paul@insa-rennes.fr
ABSTRACT
First a series of porphyrins bearing various fluorenyl donor groups is presented; an
intermediate porphyrin bearing three fluorenyl arms (zinc complex 12) and compound 13,
bearing only two fluorenyl groups. Then starting from these building blocks, synthesis of new
porphyrin trimers 7 and 8, with in totally eight peripheral fluorenyl arms is performed by
using a palladium catalyst. Photophysical properties; absorption and luminescence, of new
trimers 7 and 8 are presented. We can then compare these properties to those of reference
porphyrin monomer TFP (2), as well as to those of porphyrin dendrimers bearing various
numbers of fluorenyl arms (3 and 4) and finally to those of the corresponding dimers 5 and 6,
which are the precursor models of this work.
Keywords : Porphyrins; Fluorene; trimer; diphenylacetylene; Luminescence
1. Introduction
Modular synthetic approaches called great attention for the preparation of
multicomponent systems. The synthesis of photosynthetic or related model systems requires
strategies for joining large number of components into functional arrays. Assemblies of
porphyrins have shown interesting properties for the fabrication of electronic and optical
devices, as well as for the conversion of solar energy.[1] In nature, the photosynthetic light-
harvesting systems (I and II) consist of well-organized porphyrin antennas in sophisticated
three-dimensional structures.[2] Thus, the ability to design and construct molecular
architectures in which the energy flow can be controlled constitutes a great (and timely)
challenge. One approach is to use porphyrins as building blocks and to assemble them by
different coupling methods.
2
Page 2 of 27

Different ways to connect porphyrins have been studied earlier; one of the first
examples, in 1976, was the synthesis of diporphyrins and triporphyrins bridged by an ester
bond for energy and electron transfer in biological processes.[3] Later in 1983, porphyrins
connected by ether bond were used for light collecting.[4] Few years later, many other
examples were shown; Therien et al. published a porphyrin dimers and trimers linked at meso
position by two triple bonds as models for light collecting antenna.[5] Assemblies in which the
porphyrins are directly connected by a single bond, usually between the meso positions, have
been prepared by Smith's group.[6] Later, the synthesis of dimers and trimers linked by
ethynyl bond at positions like meso-meso, or meso-beta were proposed.[7-11]
In 2004, we have reported the synthesis of a porphyrin monomer possessing four fluorenyl
arms (TFP, compound 2).[12-16] Surprisingly, TFP exhibited a remarkably high quantum
yield (24%), compared to the reference tetraphenylporphyrin (TPP, compound 1)
demonstrating the capacity of the fluorenyl units to enhance quantum yields (Fig. 1). Then, to
exploite this efficiency, a series of porphyrin dendrimers bearing fluorenyl dendrons was
prepared, namely: 3 and 4.[17, 18] As an applications, we next tested corresponding
platinum(II) complexes in the fabrication of red Organic Light Emitting Diodes (OLEDs).[19-
21]
Also, supramolecular assemblies possessing 12 or 24 fluorenyl arms, using these
efficient building blocks, have been prepared by our group.[22] Very recently, the synthesis
of smaller systems possessing 6 fluorenyl arms like dimers 5 and 6 were synthesised
successfully by our group.[21] Encouraged by these results, we will synthesize trimers of
porphyrins substituted by eight fluorenyls units in the meso position.
Linear porphyrin trimers will be formed by coupling a porphyrin with two iodo groups and
two porphyrins with one terminal alkyne function, catalyzed by a palladium complex. To this
aim, zinc porphyrin with three peripheral fluorenyl groups and one anchoring point (12), as
well as new building block with two peripheral fluorenyl groups and two anchoring points
are described (13).
N
H
N
H
N
N
N
N
H
N
H
N
TPP
C om pound 1
TFP
Com pound 2
3
Page 3 of 27

HN
N
N
N
N
N
N
M
NH
M= Zn Dimer 5
M= 2H Dimer 6
N
N
HN
N
N
N
N
N
N
N
M
M
NH
N
M= Zn Trimer 7
M= 2H Trimer 8
Figure 1:
Monomers 1, 2 and dimers 5, 6 and target trimers 7, 8
Preliminary photophysical results for new trimers 7 and 8, are reported. These results
are first compared to previous data for precursor TFP,[23] secondly to the porphyrin
dendrimers 3 and 4,[17, 18, 22] and finally to the corresponding dimers 5 and 6.[21]
2. Experimental
2.1. General remarks
All reactions were performed under argon and were magnetically 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 other 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 TFP
=
tetrafluorenylporphyrin, TPP
=
tetraphenylporphyrin. 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
4
Page 4 of 27

Spectroscopy), HMBC (Heteronuclear Multiple Bond Correlation) and HMQC
(Heteronuclear Multiple Quantum Coherence). UV spectra were recorded on UVIKON 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 performed at room
temperature (R. T.) with dilute solutions (ca. 10-6M) using an Edinburgh Instruments (FLS
920) spectrometer working in photon-counting mode, equipped with a calibrated quantum
counter for excitation correction. Fluorescence quantum yields were measured using standard
methods; TPP in DCM (= 0.12 at ex = 417 nm) was used as a reference. The reported
fluorescence quantum yields are within ± 10%.
2.2. Synthesis of the Monomers
2.2.1. Synthesis of 5,10,15-tris(9H-fluoren-2-yl)-20-(4-ethynylphenyl)porphyrinato Zn(II)
(12).
First, the synthesis of 4-((trimethylsilyl)ethynyl)benzaldehyde 9 was done following
given reference.[24]
Then, 2-Fluorenecarboxaldehyde (3.00 g, 15.4 mmol), 4-
trimethylsilylbenzaldehyde (1.03 g, 5.1 mmol) and pyrrole (1.4 mL, 20.5 mmol) were added
to distilled chloroform (1.5 L). The expected compound 10 was obtained as a purple solid to
yield 756 mg (15%).[21] For the Synthesis of 5,10,15-tris(9H-fluoren-2-yl)-20-(4-
ethynylphenyl)porphyrin (11): a solution of porphyrin 10 (200 mg, 0.21 mmol) in distilled
DCM (36 mL) and distilled methanol (12 mL) was prepared in a schlenk tube under argon.
Potassium carbonate (145 mg, 1.05 mmol) was added and the reaction mixture was stirred
during 47 h at R.T. The deprotected porphyrin 11 was obtained as a purple powder to yield
187 mg (98%).[21] For the Synthesis of 5,10,15-tris(9H-fluoren-2-yl)-20-(4-ethynylphenyl)-
porphyrinato Zn(II) (12) : A solution of porphyrin 11 (185 mg, 0.2 mmol) in distilled DCM
(127 mL) and distilled methanol (63 mL) was prepared in a schlenk under argon. Then,
Zn(CH3CO2)2.2H2O (220 mg, 1.0 mmol) was added and the reaction mixture was stirred
during 24h at room temperature. The metallated porphyrin 12 was obtained as a purple solid
to yield 188 mg (97%), for complete work up see previous reference of our groups.[21]
2.2.2. Synthesis and characterization of new 5, 15-(9H-fluoren-2-yl)- 10,20-(4-
iodophenyl)porphyrin (13).
5
Page 5 of 27

A solution of p-iodobenzaldehyde (2.12 g, 9.2 mmol), 2-fluorenecarboxaldehyde
(1.80 g, 9.2 mmol) and pyrrole (1.27 mL, 18.4 mmol) in distilled chloroform (1.5 L) was
placed in a two necked flask under an argon atmosphere. The chloroform solution was
degassed by argon bubbling for 20 minutes, the flask was protected from light and boron
trifluoride diethyl etherate; BF3.OEt2 (560 µL) was added with a syringe. The solution was
stirred for 2 hours at room temperature, then, three equiv of the oxidant, p-chloranil (3.78 g,
15.4 mmol) are added and the reaction mixture was refluxed for 1 h (light protection was
removed). After neutralization of the acid catalyst by triethylamine, the solvent was removed,
and the resulting black solid was purified by two column chromatographies (column 1:
CH2Cl2/pentane 1:1; column 2: CH2Cl2/pentane 1:4) affording 407 mg (9%) of the desired
porphyrin 13 as a purple solid. New intermediate porphyrin 13 was characterized; the
1
hydrogen atom-labeling scheme for this synthon is shown in Figure 2. H NMR (400 MHz,
3
3
CDCl3,  in ppm) : 8.95 (d, 4H, JHH = 5.0 Hz, H-pyrrolic); 8.85 (d, 4H, JHH = 5.0 Hz, H-
pyrrolic); 8.40 (s, 2H, Hfluorenyl, H1); 8.26 (d, 2H, 3JHH = 8.0 Hz, Hfluorenyl, H4); 8.17 (d, 2H, 3JHH
3
3
= 8.0 Hz, Hfluorenyl, H3); 8.12 (d, 4H, JHH = 8.0 Hz, Hphenyl, HA); 8.06 (d, 2H, JHH = 7.6 Hz,
3
3
Hfluorenyl, H5); 7.98 (d, 4H, JHH = 8.0 Hz, Hphenyl, HB); 7.70 (d, 2H, JHH = 7.6 Hz, Hfluorenyl,
H8); 7.55 (t, 2H, 3JHH = 7.6 Hz, Hfluorenyl, H6); 7.46 (t, 2H, 3JHH = 7.6 Hz, Hfluorenyl, H7); 4.20 (s,
4H, CH2-fluorenyl); -2.60 (s, 2H, NH). UV-vis (λ max, CH2Cl2, nm) : 288, 424; Q bands : 513,
550, 590, 645. MALDI TOF-MS calcd for C58H36I2N4 : 1043.10294 [MH]+, found
.
1043.15030 [MH]+. Analysis: calcd for C58H36I2N4 3CHCl3: C, 52.30 ; H, 2.81 ; N, 4.00 ;
found C, 51.75 ; H, 2.87 ; N, 2.73.
2.3. Synthesis of Trimers 7 and 8
2.3.1. Synthesis and characterization of new trimer 7.
To
a
solution of
2
equiv of 12, 5,10,15-tris(9H-fluoren-2-yl)-20-(4-
ethynylphenyl)porphyrinato Zn(II) (80 mg, 0.08 mmol) and 1 equiv of 13, 5,15-(9H-fluoren-
2-yl)-10,20-(4-iodophenyl)porphyrin (36 mg, 0.04 mmol), 0.3 equiv of Pd2(dba)3.CHCl3 (11
mg, 0.01 mmol) are added. Then, 2.4 equiv of AsPh3 (25 mg, 0.083 mmol) in 20 mL of
freshly distillate THF and 6 mL of triethylamine were added. This solution was stirred for 5
days at 35 °C under argon. Then, the reaction mixture was cooled at room temperature,
filtered rapidly over silica gel with DCM and evaporated to dryness. The residue was purified
by column chromatography on silica gel using a mixture heptane/DCM 40/60 as an eluent
affording the desired product 7, as a dark red powder with a yield of 10%. The reaction was
6
Page 6 of 27

followed by MALDI-TOF MS as well as by NMR. The hydrogen and carbon atom-labeling
scheme for the porphyrin trimer 7 as well as for precursors 12 and 13 are shown in Figure 2
and 3. This new compound 7 is very soluble in most organic solvents and can be purified by
precipitation (THF, heptane). Compound 7 is well-behaved in silica gel chromatography and
was fully characterized by usual solution spectroscopies (NMR and mass spectrometry) and
1
microanalysis. H NMR (400 MHz, CDCl3,  in ppm) : 9.03 (m, 16H, H-pyrrolic); 8.97 (m,
8H, H-pyrrolic); 8.40 (s, 8H, Hfluorenyl, H1); 8.32 (m, 8H, Hphenyl); 8.26 (m, 8H, Hfluorenyl, H4);
8.17 (m, 8H, Hfluorenyl, H3); 8.06 (m, 16H, 8Hfluorenyl: H5 and 8Hphenyl); 7.69 (m, 8H, Hfluorenyl,
H8); 7.53 (large t, 8H, Hfluorenyl, H6); 7.43 (large t, 8H, Hfluorenyl, H7); 4.21 (m, 16H, 8CH2-
fluorenyl). 13C NMR (CDCl3): 150.6-150.4 (m, Cq, C1-4-6-9-11-14-16-19); 143.8 (Cq, C9”); 141.6
(m,Cq, C4”, C8”, C5”); 133.4 (Cq, C2’, C4’); 132.1 (m, CH, C2-3-7-8-12-13-17-18); 131.3 (C1’); 127.0
(C6’ and C7’);125.2 (C8’); 120.6-120.3 (m, Cq, C5-10-15-20); 120.2 (C5’); 117.8 (C3’); 114.6, 37.1
(C9’). Rf on silica plate using DCM/heptane (60 : 40) : 0.32. UV-vis (λ max, (ε, 10-3 M-1.cm-
1), CH2Cl2, nm) : 265 (160), 429 (1 035), 521 (22), 555 (54), 596 (24), 649 (4). FT-IR (n,
.
KBr, cm-1): 2363 (C≡C). Analysis: calcd for C192H114N12Zn2 6CHCl3 : C, 69.21; H, 3.52; N,
4.89; found C, 68.72; H, 4.06 ; N, 4.31. MALDI TOF-MS calcd for C192H114N12Zn2:
2715.78723 [MH]+; found : 2715.66750 [MH]+.
2.3.2. Synthesis and characterization of the free trimer 8.
Compound 8 was obtained from the bis-zinc complex 7 by acidic treatments as
following: to a solution of 1 equiv of trimer 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 UV-Visible spectrometry to
be sure that zinc was entirely eliminated from the porphyrin macrocycle, to obtain the totally
free and protonated porphyrin trimer. Finally, TEA was added to neutralize this dark green
solution, to obtain the free, but non protonated porphyrin trimer 8. The red solution was
stirred for 30 min at room temperature. Then, the residue was filtered on silica gel using DCM
1
as eluent to afford neutral 8, as a pure product: a dark red powder with 95% yield. H-NMR
(300 MHz, CDCl3, δ in ppm): 9.06 (m, 16H, H-pyrrolic); 9.05 (m, 8H, H-pyrrolic); 8.43 (m, 8H,
Hfluorenyl, H1); 8.28 (m, 16H, Hfluorenyl: H4 and 8Hphenyl); 8.18 (m, 8H, Hfluorenyl, H3); 8.07 (m,
16H, 8Hfluorenyl: H5 and 8 Hphenyl); 7.71 (m, 8H, Hfluorenyl, H8); 7.54 (large t, 8H, Hfluorenyl, H6);
7.44 (large t, 8H, Hfluorenyl, H7); 4.22 (m, 16H, 8CH2-fluorenyl) ; -2.70 (s, 6H, NH). UV-vis (λ
7
Page 7 of 27

max, (ε, 10-3 M-1.cm-1), CH2Cl2, nm) : 263 (299), 427 (1 023), 520 (47), 557 (44), 594 (22),
649 (16). FT-IR (n, KBr, cm-1): 2363 (C≡C). HRMS (ESI) calcd for C192H118N12: 2591.9675
[MH]+; found : 2591.9590 [MH]+. MALDI TOF-MS calcd for C192H118N12: 1296.4874
[M+2H]2+; found : 1296.4870 [M+2H]2+.
3. Results and discussion
3.1. Synthetic strategy
The aim of this work consists in the synthesis of porphyrin trimers composed of two
types of porphyrins: one substituted at three positions by meso fluorenyl units and an
acetylenic group on purpose to future link by a tolane (phenyl-C≡C-phenyl) bridge, another,
in the middle, with two fluorenyl units in the meso positions with two activable iodo groups to
link in trans with two same bridges. The synthetic strategy is based on the coupling of two
metallized A3B porphyrins, and another A2B2 free base. The trisporphyrin assembly is made
by Sonogashira coupling, under conditions optimized by Lindsey.[8, 9]
First, we will describe the synthesis of the intermediate porphyrins 12 and 13,
possessing different anchoring points. In a second time, intermediate 12 and 13 are connected
to obtain the trimer zinc complex porphyrins 7 and finally by dematallation : free trimer 8.
It should be noted that in the conditions used, the non-substituted methylene of the
fluorenyl arm is stable but alkyl chains have often been introduced on the position-9 of the
fluorenyl units to increase the solubility.[25] For this project, due to the encouraging results
obtained for synthesis of the monomers and dimers, this was voluntary avoided.
3.1.1. Preparation of the intermediate zinc porphyrin complex 12
First, the synthesis of 4-((trimethylsilyl)ethynyl)benzaldehyde 9, is done in one step by
Sonogashira coupling reported in 1981.[24] The aldehyde 9 is obtained as a white powder
with a yield of 92%. Then, the protected A3B free-base porphyrin 10, was prepared from two
aldehydes: the fluorenylcarbaldehyde (commercial) and previously prepared 4-
((trimethylsilyl)ethynyl)benzaldehyde 9. The synthesis of porphyrin 10 is made by the method
of Lindsey: it consists in mixed condensation between two different aldehydes and pyrrole
(Scheme 1) as described by us in 2013.[21] Porphyrin 10 is isolated as a purple solid with a
yield of 15%. The porphyrin 10 is then basified to give the free-base porphyrin 11, with the
8
Page 8 of 27

deprotected acetylenic function (Scheme 1). Deprotected porphyrin 11 was obtained as a dark
red-violet powder with a yield of 98%. The free base porphyrin 11 is then metallated in the
presence of 5 equiv of zinc acetate, Zn(CH3CO2)2.2H2O, to give the zinc porphyrin complex
12 (Scheme 1). The zinc complex 12 is obtained as a dark red powder with a yield 97%.[21]
1) a/ BF .OEt cat.
3
2
CHCl
b/ p-chloranil
, CH Cl /MeOH
3
CHO
c/ K2CO3
2
2
N
Zn
N
N
N
H
N
H
CHO
2) Zn(CH3CO2)2.2H2O
CH Cl /MeOH
2
2
TMS
9
12
Scheme 1: Synthesis of zinc porphyrin complex 12
3.1.2. Synthesis and characterization of new porphyrin-free base 13, possessing two fluorenyl
arms.
The second type A2B2 porphyrin, is prepared in one step, according to the method of
Lindsey and consists in mixed condensation between two aldehydes and pyrrole (Scheme 2),
the reaction is by the Lewis acid: BF3.OEt2. Porphyrin 13 is isolated as a violet powder, from
other reaction products (polymers as well as mono fluorenyl, tri fluorenyl, etc.) by several
successive chromatographies on silica gel, with a yield of 9%. New intermediate
diodoporphyrin 13 was characterized; the hydrogen and carbon atom-labeling scheme are
shown in Figure 2.
) BF .OEt cat.
CHO
I
1
3
2
NH
N
N
2) p-chloranil
I
I
CHO
HN
N
H
CHCl3
9 %
13
Scheme 2: Synthesis of new porphyrin-intermediate 13
9
Page 9 of 27

3.1.3. Synthesis and characterization of the new trimer possessing eight fluorenyl arms 7.
We have to link by rigid bridges, three porphyrins with in the middle; one free-base 13
and at the ends; two others zinc metallated 12. These linkers, are phenyl-phenyl triple bonds.
This new trimer possesses in full eight fluorenyl groups directly attached in meso position;
this should exalt the luminescence.
First, the reaction is performed by adding zinc porphyrin complex 12 and free base
diodo-porphyrin 13 in a mixture of (THF/triethylamine) in the presence of a Pd(0) catalyst
and a large excess of triphenylarsine (As(Ph)3) as a ligand (Scheme 3). These conditions
optimized by Lindsey[9, 26] are preferred to standard conditions for Sonogashira coupling
involving copper iodide, in order to avoid any risk of porphyrin copper formation. This
solution was stirred for 5 days at 35 °C under argon, then; the reaction mixture was cooled at
room temperature, filtered rapidly over silica gel with DCM and purified by column
chromatography affording the desired product 7, as a dark red powder with a yield of 10%.
The connection of all three units was confirmed by matrix-assisted laser desorption
ionization time-of-flight mass spectrometry (MALDI-TOF MS) as well as by NMR. The
hydrogen and carbon atom-labeling scheme for the trimer 7 as well as for precursors 12 and
13 are shown in Figure 2 and 3. This new compound 7 is very soluble in most organic
solvents and can be purified by precipitation (THF, heptane). Compound 7 is well-behaved in
silica gel chromatography and was characterized by usual spectroscopies in solution (NMR
and UV-Vis) and microanalysis.
10
Page 10 of 27

NH
N
N
N
N
N
N
I
I
H
Zn
HN
Pd2(dba)3
AsPh3
THF / TEA (5:1)
12
13
10 %
N
N
HN
N
N
N
N
N
Zn
Zn
NH
N
N
N
Trimer 7
Scheme 3: Synthesis of trimer 7
3.1.4. Synthesis and characterization of the free trimer 8 possessing eight fluorenyl arms.
This new trimer 8 was obtained from the previous bis-zinc complex 7 by acidic
treatments with a Bronsted acid, like trifluoro-acetic acid (TFA), the dark red DCM solution
turns immediately green. The reaction mixture was stirred and controlled by UV-Vis
spectrometry, to be sure the entire zinc complex is eliminated and to obtain the totally free
and protonated porphyrin trimer. Finally, a base; TEA was added to neutralize acid and to get
a red solution, to obtain the free, not protonated porphyrin trimer 8. Then, the residue was
purified by column chromatography on silica gel using DCM to obtain neutral 8. This free
trimer 8 was characterized by NMR, UV-Vis, and by mass spectrometry (MALDI-TOF MS)
as well as by HRMS.
3.2. NMR studies
The 1H-NMR signals obtained in deuterated chloroform for porphyrins 11, 12, 13 and
finally 7 and 8, were carried out at room temperature.
11
Page 11 of 27

H
H
H
H
H
H
H
H
H '
9
H
H
H
H
H
H
9
H
H
8
H
H
A
H
B
B
A
1
HN
N
N
N
N
N
N
I
I
H
7
H
Cb' Cb
M
NH
H
H
H
H
3
6
H
B
B
H
A
4
5
A
H
H
H
H
H
H
H
H
H
1
3
Compound 13
M = 2H Compound 11
M = Zn Compound 12
H '
9
4
5
H
H
8
9
H
H
6
H
7
Figure 2:
Hydrogen and carbon atom-labeling for porphyrins 11, 12 and for diiodo porphyrin-
intermediate 13.
3.2.1. Characterization of zinc complex 12.
For this zinc complex and for the corresponding free macrocycle 11, there is only a
clear difference for the protons carried by the nitrogen atoms in the heart of the porphyrin;
around -3 ppm, these protons are not observed for the zinc complex 12. The other proton
signals are quite similar.
3.2.2. Characterization of compound 13.
At high field, around -3 ppm, we observe the protons carried by the nitrogen atoms in
the core of the porphyrin. At 4.2 ppm, are the CH2 protons of the two fluorenyl groups. In the
region between 7.5 and 8.5 ppm resonate the aromatic protons (fluorenyl and phenyl) of the
porphyrin meso substituents: we can notice that all the seven protons on the two fluorenyl
arms are equivalent, and in expected position: 8.40 (s, 2H); 8.26 (d, 2H); 8.17 (d, 2H); 8.06
(m, 2H); 7.70 (d, 2H); 7.55 (t, 2H) and 7.46 (t, 2H). At low field; around 9 ppm, there are two
signals, an AB system; two doublets, for four protons each; they are all assigned to the
protons pyrrole-β.
12
Page 12 of 27

H
H
H
H
H
H
H
H
C10
C11
H
HA'
H9'
H
HA'
H
H9''
C9
N
H
HB
HA
HB'
H1
H8
HA
HB
HB'
Cb Cb'
C9
C9
C4
'
HN
N
N
N
N
C6
C5
C4
C14
N
N
N
N
"
C8''
Cb' Cb
C15
C16
Zn
C5
"
C2
'
"
H7
Zn
NH
C1
N
C19
HA'
HB'
HB
HA
HA'
H
HB'
HB
HA
H
H3
H6
H5
H4
C20
H
H
H
H
H
H
H
H
H
H
Trimer 7
Figure 3:
Hydrogen and carbon atom-labeling for new Trimer 7
3.2.3. Characterization of bis zinc trimer 7.
Around -3 ppm, the two protons carried by the nitrogen atoms of the porphyrin-free
base in the center of the trimer are not observed. At 4.2 ppm, there is a large singlet for the
sixteen protons of the CH2 protons of fluorenyl groups. In the region between 7.4 and 8.4 ppm
resonate the aromatic protons (fluorenyl and phenyl) of the porphyrin meso substituents: we
can notice that all the seven protons on the eight fluorenyl arms are equivalent, and in
expected position: 8.40 (s, 8H); 8.26 (m, 18H); 8.17 (m, 8H); 8.06 (m, 8H); 7.69 (m, 8H); 7.53
(t, 8H); 7.43 (t, 8H). Around 9 ppm, there are three signals, a singulet integrating for eight
protons and a doublet for eight protons and another doublet for eight protons as well, assigned
to the protons pyrrole-β, due to the symmetry of this molecule 7. One can note the
disappearance of the singlet corresponding to the acetylenic proton at 3.33 ppm of the starting
zinc porphyrin complex 12 (Figure 4).
3.2.4. Characterization of free trimer 8.
Between this free base and the corresponding bis-zinc complex 7, there is only a clear
difference for the protons carried by the nitrogen atoms in the core of the porphyrin; around -3
ppm, these protons are not observed for the zinc complex 7. The other proton signals are quite
similar (Figure 4).
13
Page 13 of 27

H
H
H9
'
H9
H
H
H8
H
H
H
H
H
1
N
N
N
Zn
N
H7
H
H6
H3
H4H5
H
H
HA
H
H
3CH2Fluorenyl
12
HB
-CCH
Hpyrrol
HBenzyl
NH
N
N
I
I
HN
2CH2Fluorenyl
13
HN
N
N
N
N
N
N
NH
HN
N
N
N
N
N
N
N
N
N
Zn
Zn
NH
N
Trimer 7
HN
N
N
HN
N
NH
N
N
NH
NH
N
HN
Trimer 8
Figure 4:
1H-NMR studies (in CDCl3) of Dimer 5 (with a CH2Cl2 peak), trimers 7 and 8, in comparison
to zinc porphyrin complex 12 (on the top) and for diiodo porphyrin-intermediate 13 showing
the shift as indicated by the arrows.
14
Page 14 of 27

3.3. Photophysical properties
3.3.1 Absorption spectra.
The recording of the UV-visible absorption spectra of the porphyrins 11, 12, 13,
dimers 5 and 6, and finally trimers 7 and 8 was carried out at room temperature in
dichloromethane. For these compounds, measurements at different concentrations were
performed; a more concentrated solution is used to display the Q bands and a less
concentrated for the Soret band of porphyrin (Figure 5a). We will first consider the two parent
molecules: free porphyrin 13 and zinc complex 12 and then the new trimer 7.
The UV-visible spectra of free porphyrin 13 exhibit an intense Soret band with a
maximum absorption around 422 nm and four Q bands characteristic of a porphyrin free base
which are located at 513 nm, 550 nm, 590 nm and 645 nm. In addition, there is a broad band
at 288 nm corresponding to the absorption of the two fluorenyl arms (Figure 5a). The Soret
band is slightly red shifted compared to 417 nm for TPP (1), but not as much as for TFP (2)
(426 nm). This tendency in red shifting is observed as well for the Q bands (Table 1). The π-
π* absorption in the UV range is clearly apparent, due to the presence of fluorenyl arms: for
reference compound 2, the four fluorenyls absorb with a maximum absorption peak at 272
nm, while for compound 11 possessing only three arms the absorption is weaker with a
maximum at 275 nm, and for compound 13 with only two fluorenyl arms the absorption is
weaker at 288 nm.
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)).[27-29] Thus, the zinc complex 12 exhibit an
intense Soret band at 426 nm, together with two weak Q-bands in the visible range: located at
554 nm and 595 nm (Table 1). An additional broad band is also observed in UV range which
corresponds to π-π* absorption of the three fluorenyl chromophores. As mentioned before,
the UV absorption, at 273 nm, is weaker for the zinc complex 12 than for reference TFP (2),
due to the smaller number (three vs. four) of fluorenyl groups (Figure 5a).
The absorption spectrum of porphyrin trimer 7 shows the presence of a Soret band at
429 nm and four sub-bands which are located at 521 nm (Qy(0, 1), very weak), 555 nm
(Qy(0, 0), strong), 596 nm (Qx(0, 1), strong) and 649 nm (Qx(0, 0), weak), corresponding to
15
Page 15 of 27

the superposition of visible absorption of a free base porphyrin and two terminal zinc
complexes. This indicates that, in the ground state, no major interaction occurs between the
porphyrin subunits of the trimer, which can be related to the presence of phenyl-ethynyl-
phenyl linkers. In addition, there is a broad band at 265 nm corresponding to the absorption of
the eight fluorenyls arms (Table 1).
3.3.2. Absorption spectra of titration
The formation of free trimer 8 by adding TFA to bis zinc complex 7 was followed by
UV-Visible spectrophotometry (Figure 5b). Dissolution of trimer 7 in neutral DCM solution
results in a UV-Vis spectrum with a maximum absorbance at 429 nm, the evolution of visible
spectra by protonation (adding regular small quantities of TFA) is shown in Fig. 5b. During
this titration, the Soret band, initially at 429 nm, for trimer 7, is red shifted to 461 nm, due to
protonation and consequently loss of encapsulated zinc.
During the evolution of these spectra for protonation steps, we observe an isobestic
point at 440 nm; illustrating the formation of a totally protonated distinct species. For this
hexacation porphyrin trimer, we observe the presence of a band at 461 nm and a broad band
which is located at 684 nm corresponding to the superposition of Vis absorption of similar
protonated porphyrins.[30] No evolution of the spectrum is observed when more acid is
added. Then, this hexacation was neutralized by adding a base (NEt3). The evolution of
visible spectra by basifying is shown in Fig. 5b. Deprotonation occurred upon titration with
NEt3, transforming the hexacation into the free base, so absorbance at 462 nm disappeared
and an isobestic point at 440 nm, is again observed. We can notice that the original spectrum
of trimer 7, is not restored because of the irreversible loss of encapsulated zinc but no partial
degradation is observed. A new compound is obtained corresponding to the neutral species
named free trimer 8. In Figure 5a, the UV-Vis absorption of monomers 11, 12 and 13 are
compared to the absorption of free trimer 8. The profiles of parent monomers 11, 12 (except
Q bands) and 13 are quite similar.
The absorption spectrum of free base porphyrin trimer 8 shows the presence of a Soret
band at 427 nm: this band is slightly blue shifted compared to 429 nm for trimer 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 trimer 7, and the relative intensities are different. They are located at
520 nm (Qy(0, 1); strong), 557 nm (Qy(0, 0); strong), 594 nm (Qx(0, 1); strong) and 649 nm
(Qx(0, 0); weak), corresponding typically to Visible absorption of a free porphyrin. Again,
this confirms that, in the ground state, no major interaction occurs between the porphyrin
16
Page 16 of 27

subunits of the trimer. In addition, as expected, there is a broad UV absorption band at 263
nm corresponding to the absorption of the eight fluorenyl arms. We can notice in Figure 5c,
that in this conjugated system possessing 8 fluorenyl arms and three porphyrin macrocycles;
meaning a ratio (antenna/porphyrin unit) = 2.7, the antenna absorption is however stronger for
trimer 8 than for TFP possessing 4 arms per porphyrin core, so a ratio (antenna/porphyrin
unit) = 4.
a/
17
Page 17 of 27

b/
c/
Figure 5:
a/ Absorption spectra of precursors 11, 12, 13 and new trimer 8 in DCM at room temperature.
b/ Formation of free trimer 8 by protonation of bis zinc complex 7.
18
Page 18 of 27

c/ Absorption spectra of TPP (red), TFP (pink), OOFP (dark blue), SOFP (green) and new
trimer 8 (violet) in DCM at room temperature. All the spectra are normalized to the Soret band
of the spectrum of the reference TPP at 417 nm (concentration ~2.0 10-6 M).
3.3.3. 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 is very weak
whereas the strongest emission band is typically around 600 nm and the second peak is at 
650 nm, due to the metal coordination.[15]
a/
19
Page 19 of 27

b/
c/
Figure 6:
a/ Emission spectra of monomers 11 and 12, dimers 5 and 6, compared to trimers 7 and 8 in
DCM at room temperature. All the spectra are normalized to the spectrum of dimer 7 at 657 nm
(concentration ~2.0 10-6 M).
b/ Fluorescence emission spectrum of 7 in DCM at room temperature upon excitation at 265
nm (red dashed lines) compared to that upon direct excitation of the porphyrins at 429 nm (red
plain).
20
Page 20 of 27

c/ Fluorescence emission spectrum of 8 in DCM at room temperature upon excitation at 270
nm (red dashed lines) compared to that upon direct excitation of the porphyrins at 427 nm (red
plain).
The fluorescence spectra at 25 °C of the zinc(II) complex 12, after excitation in the Soret
band at 426 nm, reveals a strong red fluorescence with a peak maximum at 607 nm and a
second peak, at 655 nm (Fig. 6a). We can notice that the band near 720 nm does not appear for
this complex.
For comparison, the emission spectrum of free compound 11 is also reported. After
excitation in the Soret band, at 425 nm, strong red emission at 657 nm and a weaker peak at
700 nm are observed (Fig. 6a). That means that by emission spectroscopy, we should be able to
clearly distinguish between free base and zinc complex parts of the dimer and trimer
molecules. Concerning dimer 5, actually after excitation in the Soret band, a weak emission at
600 nm, a strong red emission at 657 nm and a weaker peak at 720 nm are observed. Similarly
for trimer 7, after excitation in the Soret band, a weak emission at 609 nm, a strong red
emission at 657 nm and a weaker peak at 722 nm are observed (Fig. 6a). It should be noticed
that the contribution of the zinc complex to the emission of trimer 7 is lower than for dimer 5,
despite trimer 7 contains two zinc porphyrins instead of a single one for dimer 5. This clearly
indicates that in contrast with dimer 5, energy transfer occurs in trimer 7 from the zinc
complex(es) to the central free base porphyrin. In Figure 7, comparison is made between the
emission spectra of dimer 5 (top) and trimer 7 (bottom) with the corresponding solution of the
porphyrin moieties (i. e. the zinc complex 12 and the free base porphyrin 14[16, 31]) in a 1 : 1
and 2 : 1 ratios, respectively. The emission spectrum of dimer 5 closely resembles to that of the
1 : 1 mixture, indicating that almost no energy transfer occurs, whereas for dimer 7, the
intramolecular energy transfer efficiency can be estimated to about 70%.
N
N
N
N
NH
N
N
H
Zn
HN
12
14
21
Page 21 of 27

Figure 7: Top: measured emission spectra of dimer 5, of a solution of the porphyrin moieties 12 and 14 in a 1 : 1
ratio and of the free base acceptor 14 in DCM at room temperature. Bottom: measured emission spectra of trimer
7, of a solution of the porphyrin moieties 12 and 14 in a 2 : 1 ratio and of the free base acceptor 14 in DCM at
room temperature (exc = 429 nm).
Finally, for demetallated dimer 6, and trimer 8 possessing respectively two and three
similar free base moieties, we observe, as expected, two peaks: at 657, 720 nm and 658, 724
nm (Figure 6a).
3.3.4. Fluorescence quantum yields
The fluorescence quantum yields of these compounds were determined by comparing
with a calibration standard of compound 1 (TPP) in degassed toluene solution presenting a
22
Page 22 of 27

fluorescence quantum yield of 0.12,[32] preferentially to a benzene solution with a
fluorescence quantum yield of 0.13.[33]
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 luminescence quantum yields (13 and 14%
respectively) similar to that of the reference 1 (12%). We have shown earlier that increasing
the number of dendrons does not 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
eight or sixteen fluorenyl donor moieties in position 3 and 5, presents the same luminescence
efficiency as the parent TPP compound.[17, 34] For these reasons, recently dimers[21] were
considered and currently trimers with direct connection of fluorenyl on meso position are
presented.
For free trimer 8, a conjugated system possessing 8 fluorenyl arms and three free
porphyrin macrocycles, an interesting luminescence quantum yield (13%) is obtained in non-
degassed DCM, which is similar to that of non-conjugated dendrimers; with 8 or 16 fluorenyl
arms (compounds 3 and 4 respectively) and to that of the reference TPP compound (1), but
not as high as the parent compound TFP (2). However, the brightness (defined by the product
f) of trimer 8 is higher than that to TFP (2), taking into account the very large
absorptivities of 8 (1 023 000 M-1 cm-1 at 427 nm).
The corresponding zinc complexes, monomer 12 and dimer 5 have low luminescence
quantum yield (around 5-7%), but bis zinc trimer 7 presents a quantum yield of 9%, which is
relatively high when zinc complexes are present, higher than reference compound ZnTPP
(3.3%) and parent compound ZnTFP (5%).[15] This can be related to the efficient energy
transfer from the zinc complexes to the central free base. It should also be noticed that the
quantum yield of trimer 7 is also higher than that of dimer 5 (5%), despite trimer 7 contains
two zinc complexes for one single free base porphyrin instead of a one to one ratio for dimer
5, which confirms that the energy transfer is more efficient in trimer 7 than in dimer 5.
(c)

max / nm(a)

max / nm(b)

max / nm

em / nm
f
Porphyrin
UV band
Soret band
417
Q bands
-
513, 548, 589, 646
519, 557, 593, 649
650, 714
0.12
TPP (1)
Free Monomer
(2)
272
426
661, 725
0.24
263
270
423
423
516, 551, 592, 653
517, 552, 590, 647
656, 721
656, 721
0.13
0.14
OOFP(3)
SOFP (4)
23
Page 23 of 27

275
273
288
281
268
265
263
425
426
422
428
426
429
427
518, 555, 594, 649
554, 595
657, 700
607, 655
663, 728
0.21
0.07
0.02
Free 11
Zn (12)
513, 550, 590, 645
diIodo (13)
Dimer (5)
513, 555, 597, 643 600, 657, 720 0.05
521, 557, 595, 650 657, 720 0.17
521, 555, 596, 649 609, 657, 722 0.09
520, 557, 594, 649 658, 724 0.13
Free Dimer (6)
Trimer (7)
Free Trimer (8)
(a) Wavelengths of the absorption maxima in the UV region (200-400 nm range)
(b) Wavelengths of the absorption maxima in the Soret or B band region (400-450 nm range)
(c) Fluorescence quantum yields using TPP in DCM as standard, following excitation into the Soret bands
Table 1:
Photophysical properties of the fluorenyl porphyrins 1, 2, 3 and 4 in dilute CH2Cl2 solution at
298K, and of dimers 5, 6, trimers 7 and 8, zinc complex 12 and free base 11, 13, under the
same conditions for comparison.
3.3.5. Energy transfer from the fluorenes to the porphyrins
The efficiency of energy transfer from fluorenyl donors toward porphyrin acceptors
will now be discussed. Excitation of trimers 7 and 8 in the fluorenyl antennae results in the
red emission of porphyrins with a maximum at 657-658 nm in both cases. Actually, the blue
fluorenyl emission is partly quenched for trimer 8 and almost completely quenched for free
trimer 7, and red emission is seen predominantly from the porphyrin (Figure 6b and c).
We have to notice that, when excited directly at the Soret band, trimer 7 shows a
strong red emission, but the indirect excitation in the UV region shows as well an important
red emission (Fig. 6b). For free trimer 8, when exciting the Soret band, a strong red emission
is observed in comparison to excitation in the UV region. But this is not evidence of
inefficient energy transfer but of a more complex process.[34]
Thus for these trimer compounds, the luminescence can be modulated in a large range
of excitation wavelengths from UV to red, to finally obtain the desired red emission
particularly efficiently for trimer 7.
4. Conclusions and outlook
In summary, a series of intermediate porphyrins bearing fluorenyl donor groups was
presented. Successively, intermediate compounds 12 (bearing three fluorenyl arms), and 13
(bearing two fluorenyl groups and two iodides) have been synthesized. Starting from these
24
Page 24 of 27

building blocks, new trimers 7 and 8, bearing in totally eight peripheral fluorenyl arms were
finally synthesised and fully characterized.
We then compared the detailed luminescence properties of these trimers 7 and 8 with
porphyrin dendrimers 3 and 4, with corresponding dimers 5 and 6, but also with TFP (2),
which was the precursor model of this work. New bis zinc trimer 7 exhibits a relatively high
luminescence quantum yield (9%), higher than reference compound ZnTPP (3.3%) and
parent compound ZnTFP (5%).[15] It shows also an efficient energy transfer from the
fluorenyl arms toward the porphyrins, as well as an efficient energy transfer from the zinc
complexes toward the free base central porphyrin. New free trimer 8 exhibits a relatively high
quantum yield (13%) and energy transfer from the fluorenyl arms toward the porphyrin core
is also observed. Taking into account their large absorptivities, these assemblies of three
porphyrins exhibit larger brightness than the corresponding dimers and monomers.
Perspectives of this work may be to change the bridge connecting the porphyrins of
the assembly to optimize the luminescence properties and the efficiency of the energy transfer
between porphyrins, and eventually extend this work to tetramers or pentamers. We can also
consider grafting dendrons at the periphery of the new trimer, still in the idea of increasing the
number of antennas around the core porphyrins for light collection.
Acknowledgements
The authors are grateful to S. Sinbandhit (CRMPO) for the technical assistance and
helpful discussions. The authors are grateful to Region Bretagne for ARED grant for A.
Merhi, Chinese Scholar Council (CSC) for D. Yao. Partial Funding for the project was
obtained from the “Université Européenne de Bretagne” (UEB) and from FEDER by an EPT
grant in the “MITTSI” program from RTR BRESMAT. C.P.-R. and O.M. thank ISCR for a
"Projet inter-équipes" grant.
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26
Page 26 of 27

Highlights
►Synthesis of new porphyrin trimers within totally eight peripheral fluorenyl arms is are
presented. ► New bis zinc trimer exhibits a relatively high luminescence quantum yield
(9%), higher than reference compound ZnTPP (3.3%) and parent compound ZnTFP (5%).►
We report an efficient energy transfer from the fluorenyl arms toward the porphyrins, as well
as from the zinc complexes toward the free base central porphyrin.
27
Page 27 of 27