New porphyrin dendrimers with fluorenyl-based connectors: a simple way to improving the optical properties over dendrimers featuring 1,3,5-phenylene connectors

Article abstract of DOI:10.1039/c9nj06166e

Two new meso-tetrafluorenylporphyrin-cored dendrimers 1 and 2 have been synthesized and characterized. The peripheral fluorenyl units of these dendrimers are linked to the central tetrafluorenylporphyrin (TFP) core by original fluorene-based connectors instead of the more classic 1,3,5-phenylene unit. Selected linear and non-linear optical (LO and NLO) properties were determined for these dendrimers via absorption or emission studies and by two-photon excited fluorescence (TPEF) measurements. Dendrimer 1, which has a conjugated and quite rigid structure, exhibits a significantly higher two-photon absorption (2PA) cross-section than dendrimer 2, presenting a non-conjugated and more flexible structure, as well as better luminescence and singlet oxygen activation quantum yields. Both dendrimers exhibit higher 2PA cross-sections than several closely related TFP-based dendrimers previously characterized. However, among them, dendrimer 1 is the only one outperforming all these compounds in terms of 2PA brightness and 2PA oxygen sensitization. Thus, the new type of connector (or dendrimeric node) introduced in 1 appears to be quite appealing for the design of photosensitizers aimed at theranostic uses in the future.

Full text of DOI:10.1039/c9nj06166e

View Article Online
View Journal
NJC
New Journal of Chemistry
Accepted Manuscript
A journal for new directions in chemistry
This article can be cited before page numbers have been issued, to do this please use: X. ZHANG, S. Ben
Hassine, N. Richy, O. Mongin, M. Blanchard-Desce, F. Paul and C. O. Paul-Roth, New J. Chem., 2020,
DOI: 10.1039/C9NJ06166E.
Volume 42
This is an Accepted Manuscript, which has been through the
Number
6
21 March 2018
Pages 3963-4776
Royal Society of Chemistry peer review process and has been
accepted for publication.
NJC
New Journal of Chemistry
rsc.li/njc
A journal for new directions in chemistry
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
ISSN 1144-2546
PAPER
Chechia Hu, Tzu-Jen Lin et al.
Yellowish and blue luminescent graphene oxide quantum dots
prepared via a microwave-assisted hydrothermal route using
H2O2 and KMnO4 as oxidizing agents
rsc.li/njc

Page 1 of 34
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ06166E
New Porphyrin Dendrimers with Fluorenyl-based Connectors:
A Simple Way to improving the Optical Properties over Dendrimers
featuring 1,3,5-Phenylene Connectors
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Xu Zhang,a Sarra Ben Hassine,a,b Nicolas Richy,a Olivier Mongin,a
Mireille Blanchard-Desce,c Frédéric Paul,a 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 Faculté des Sciences de Tunis, Université de Tunis El Manar, Tunisie
c Univ. Bordeaux, Institut des Sciences Moléculaires (CNRS UMR 5255), 33405 Talence, France
*Corresponding author: christine.paul@univ-rennes1.fr or christine.paul@insa-rennes.fr
tel : (+33) (0) 2 23 23 63 72 fax: (+33) (0) 2 23 23 63 72
Electronic Supplementary Information (ESI) available: [details of any supplementary information available
should be included here]. See DOI: 10.1039/x0xx00000x
Abstract: Two new meso-tetrafluorenylporphyrin-cored dendrimers 1 and 2 have been
synthesized and characterized. The peripheral fluorenyl units of these dendrimers are linked to
the central tetrafluorenylporphyrin (TFP) core by original fluorene-based connectors instead
of the more classic 1,3,5-phenylene unit. Selected linear and non-linear optical (LO and NLO)
properties were determined for these dendrimers via absorption or emission studies and by
two-photon excited fluorescence (TPEF) measurements. Dendrimer 1, which has a conjugated
and quite rigid structure, exhibits a significantly higher two-photon absorption (2PA) cross-
section than dendrimer 2, presenting a non-conjugated and more flexible structure, as well as
better luminescence and singlet oxygen activation quantum yields. Both dendrimers exhibit
higher 2PA cross-sections than several closely related TFP-based dendrimers previously
characterized. However, among them, dendrimer 1 is the only one outperforming all these
compounds in terms of 2PA brightness and 2PA oxygen sensitization. Thus, the new type of
connector (or dendrimeric node) introduced in 1 appears quite appealing for the design
photosensitizers aimed at theranostic uses in the future.
Keywords
Porphyrin * fluorene * fluorescence * energy transfer * dendrimer *node
Introduction

New Journal of Chemistry
Page 2 of 34
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ06166E
Stimulated by their remarkable photochemical and redox properties which can be fine-tuned
by modification of the peripheral substituents, porphyrin-based systems are foreseen as key
building blocks for many applied developments nowadays. In this respect, impressive
fundamental research based on porphyrins has been undertaken in fields related to material
sciences and information treatment these last decades,[1, 2] but also in fields related to health,
such as photodynamic therapy (PDT) for instance.[3]
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
In this particular field, their use for PDT has been revived subsequent to the
observation that oxygen sensitization might advantageously be triggered by two-photon
absorption (2PA-PDT),[4] especially when the photosensitizers can be coupled to fluorescent
probes, allowing to perform curing and imaging at the same time in a so-called theranostic
approach.[5, 6] Given that tetraphenylporphyrin (TPP in Scheme 1) or related derivatives are
only modestly fluorescent in their free base form and presents a rather weak two-photon
absorption cross-section, most of the investigations in this field relied on porphyrin conjugates
featuring an expanded -manifold, in order to enhance the 2PA cross-section and also, to
some extent, their fluorescence.[7] However, this expansion was often performed via alkynyl
or alkenyl linkers appended at their meso-positions.[4, 7] As such, it was usually accompanied
by a red-shift of the porphyrin absorptions at lowest energy, reducing thereby the spectral
window available to perform two-photon excitation in a wavelength range devoid of linear
absorption, an important condition to fully benefit from the advantages of two-photon
excitation.
At difference with such approaches, we could recently show with various families of
12]
star-shaped[8-10] or dendrimeric porphyrins,[11,
that by appending fluorene-containing
dendrons at the periphery of a central tetra-arylporphyrin core, fluorescent photosensitizers
with significantly enlarged one-photon brightnesses could be obtained upon increasing the
dendrimer generation. Furthermore, when fully unsaturated dendrons were used such as in An
and Bn (Scheme 1),[11, 12] a significant increase in the two-photon absorption cross-section of
these photosensitizers could be achieved without diminishing the optical window for
excitation.[11, 12] This remarkable property most likely results from the partial disruption of the
-manifold (taking place at the meso positions in the most stable conformers). Furthermore,
2

Page 3 of 34
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ06166E
these twisted conformations adopted by the meso aryl groups allow the peripheral dendrons to
behave as efficient light-harvesting antennae, while preserving quite sizeable efficiencies for
two-photon oxygen sensitization at the porphyrin core. This is plainly shown by the relevant
figure of merit (O2) given for several of these compounds in Scheme 1, revealing that among
the members of the two dendrimer families An and Bn represented, the TFP-cored dendrimers
(Bn) are always the most efficient photosensitizers for oxygen.[13] The O2 factor corresponds
to the 2PA singlet oxygen production for a given compound (Ф•σ2max) normalized by that of
TPP. Furthermore, since the luminescence quantum yield (fl) of the central porphyrin is
usually preserved,[11] the one-photon brightness improves with successive generations in a
given family.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
However, in contrast to the one-photon brightness, the two-photon brightness and two-
photon photosensitization (or O2 factor) decrease with increasing dendrimer generations in
each of these dendrimer families.[11, 12] This decrease can be traced back to the weak
electronic communication operative between fluorenyl units through the meta-positions of the
1,3,5-phenylene units used as dendrimeric nodes. As a result, the two-photon absorption
cross-section (2) does not scale anymore with the number of fluorenyl units present in the
peripheral dendrons, presently making the smallest derivatives in each family (A0 and B0) the
most promising two-photon photosensitizers for any applied development. Also possibly in
line with this poor electronic communication, the energy transfer from the periphery to the
central porphyrin does no more take place quantitatively in the generation two dendrimer
B2.[11]
In order to improve further these photosensitizers in their higher generations, we
decided to test another node and to replace the classic 1,3,5-phenylene unit (C1; Scheme 2)
by the new fluorenyl-based unit (C2) in the dendrons. Thus, new TFP-based dendrimer 1,
the analogue of dendrimer B1 featuring these new connectors, was targeted. Likewise to B1, n-
butyl groups were added in position 9 on the terminal fluorene groups to improve the overall
solubility of the dendrimer. In generation one (G1) dendrimer 1, contrary to what is
happening with classic connector C1, the 2-alkynylfluorenyl units on C2 are no more
connected to topologically orthogonal positions[14] and a better electronic communication
3

New Journal of Chemistry
Page 4 of 34
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ06166E
between the various fluorenyl subunits should result. This should positively impact 2 in 1,
and in turn, also positively impact the two-photon brightness and the O2 figure of this
compound. Then, in order to make sure that any improvement of these features is not simply
related to the increase in the number of fluorene units within each dendron (given that the
connector C2 is also a fluorenyl unit), we also targeted the dendrimer 2 featuring c3
connections in place of C2. Likewise to dendrimer 1, dendrimer 2 has four fluorenyl units in
each peripheral dendron, but without any conjugation between three of them. Thus,
comparison between 1 and 2 should allow us to evidence the importance of electronic
conjugation within the dendrons. The C2 connector, substituted in the position 9 by a double
bond linked to two (2-ethynyl)fluorenyl groups, allows electronic conjugation between the
four fluorenyl groups. In contrast, the connector C3, with a tetrahedral carbon in the position 9
featuring saturated extensions on opposite sides of the central fluorene group does not allow
electronic conjugation with the two pendant fluorene groups. The dendrons in 1, with rigid
and entirely planar termini (except for the four butyl chains), will possibly adopt a propeller-
shaped conformation around the porphyrin core, while the dendrons in 2, more flexible,
should adopt a more compact three dimensional structure.
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
4

Page 5 of 34
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ06166E
Bu
Bu
Bu
Bu
5
6
7
8
A0
A1
9
(O2 = 17; fl = 19)
(O2 = 1; fl = 11)
(O2 = 37; fl = 20)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
TPP
Bu
Bu
A
Bu
Bu
=
A
NH
N
N
A
A
HN
Bu
Bu
A
Bu
Bu
TFP
Bu Bu
Bu
Bu
Bu
Bu
Bu
Bu
(O2 = 7; fl = 24)
Bu Bu
Bu
Bu
Bu Bu
Bu
Bu
Bu
Bu
B2
B1
B0
(O2 = 66; fl = 24)
(O2 = 62;fl = 23)
(O2 = 62;fl = 24)
Scheme 1. Selected representatives among two families of tetraarylporphyrin-based dendrimers (An and Bn)
along with the reference compounds TPP and TFP. A figure of merit for two-photon oxygen sensitization ()
measured in CH2Cl2 and their fluorescence quantum yields (fl) measured in toluene are given in parenthesis.
Finally, we will also study compounds 4 and 5, modelizing the new terminal units in 1
and 2, respectively. These model compounds should help us understanding better some of the
photophysical properties of the new dendrimers 1 and 2, in particular the energy transfer (ET)
taking place from peripheral light-harvesting antennae toward the central macrocycle. The
central core of these dendrimers being modelized by the known tetrafluorenylporphyrin
TFPBu.[11]
5

New Journal of Chemistry
Page 6 of 34
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ06166E
In the following, we will now describe (i) the synthesis of the various model compounds
4-5; (ii) the synthesis and characterization of the targeted TFP-based dendrimers 1 and 2
featuring these units as components and (iii) the study of the linear and nonlinear optical
properties, as well as their capability to photosensitize oxygen. Their optical properties,
energy transfer behavior and two photon absorption properties as well as their singlet oxygen
photosensitizing properties will then be compared with those of dendrimer B1 and discussed
in the light of previous results.[11, 12]
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Bu
Bu
TFP-based Dendrimers
c1
Bu
Bu
Bu
Bu
B1
Bu
Bu
=
TFPBu (3)
A
Bu
Bu
Bu
A
Bu
NH
N
Bu
Bu
A
A
Bu
Bu
N
HN
c2
Bu
Bu
c3
A
1
Bu
Bu
2
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Node MODELS
c2
c3
4
5
Scheme 2. The known first generation dendrimer B1 and the targeted analogues 1 and 2, along with the
corresponding TFP “core” model TFPBu and targeted model compounds 4 and 5.
6

Page 7 of 34
New Journal of Chemistry
1
2
3
4
5
View Article Online
DOI: 10.1039/C9NJ06166E
Results and discussion
6
7
8
9
To synthetically access the new dendrimers 1 and 2, a strategy in three steps was used
(Scheme 3), i.e. (i) the synthesis of the bromo-terminated dendrons precursors 6 and 7, (ii) the
synthesis of the tetra((7-ethynyl)fluoren-2-yl)porphyrin (8), standing for TFP-cored
precursor, by the Lindsey method,[15, 16] and finally, (iii) the connection of porphyrin 8 to the
dendron precursors by Sonogashira coupling reactions.[17] During parts (i) and (ii), the
previously discussed model compounds 4 and 5 will also be isolated.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Bu
Bu
Bu
Bu
Acceptor :
A
6
1
Br
NH
N
N
N
NH
N
+
A
Bu
A
Bu
HN
Bu
HN
Bu
7
2
A
8
Br
Scheme 3. Proposed retrosynthetic approach followed to access 1 and 2.
Dendron synthesis
Model Compound 4 and Conjugated Dendron Precursor 6. These molecules were obtained
from commercial fluorenone (9) in a few steps (Scheme 4).
7

New Journal of Chemistry
Page 8 of 34
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ06166E
Br
Br
Br
Br
O
O
5
6
7
8
CBr4 / PPh3
NBS
CBr4 / PPh3
Br
Br
CH2Cl2, 0°C
(70 %)
Methanesulfonic
acid
CH2Cl2, 0°C
(73 %)
9
10
11b
11a
(73 %)
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Pd(PPh3)2Cl2
/ CuI (Cat.)
DMF / iPr2NH, 95°C
Pd(PPh3)2Cl2
/ CuI (Cat.)
DMF / iPr2NH, 95°C
12
(28 %)
12
(79 %)
Br
4
6
Scheme 4. Syntheses of the conjugated dendron precursor 6 and of the corresponding model compound 4.
Treatment with N-bromosuccinimide (NBS) afforded 2-bromofluorenone (10) and further
reaction with the in situ formed dibromomethylene phosphorane afforded the gem-dibromo
derivative 11a. The latter reacted with two equivalents of the terminal alkyne 12[18, 19] to yield
the desired precursor 6 in 42% global yield from 9. In a similar approach, the model
compound 4 was obtained via the intermediate 11b, albeit in a lower global yield (20%).
We observe by 1H NMR, that exchanging oxygen for a CBr2 group causes a large shift
in the peaks of these protons to low field from 7.6 to 8.6 ppm (see Fig. S1; ESI). In the model
compound 4, bearing two fluorenyl antennae in place of the bromine atoms, a further shift to
lower field (8.8 ppm) takes place for this doublet. In non-symmetric compounds such as
bromo intermediate 11a or Dendron 6, the doublet splits, giving a singlet and doublet at low
field (Figure 1). This peculiar 1H NMR signal will therefore be used to assess the presence of
dendrons like 4 in dendrimer 1.
8

Page 9 of 34
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ06166E
5
6
7
Intermediate
11a
8
9
Br Br
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Br
Dendron 6
Br
9.4
9.2
9.0
8.8
8.6
8.4
8.2
8.0
7.8
7.6
7.4
7.2
1
Figure 1. Partial H NMR spectra of the intermediate 11a and of the corresponding dendron precursor 6 in
CDCl3.
Model Compound 5 and Non-Conjugated Dendron Precursor 7. These molecules were
obtained from commercial 2-bromo-9,9-dibutyl-fluorene (13).[11, 12] The latter molecule, after
reaction with n-BuLi in THF, followed by addition of DMF (Scheme 5), affords the
corresponding fluorene carboxaldehyde intermediate (14). This compound is subsequently
reduced in alcohol and brominated, giving 16 in two steps with 82% overall yield. Different
reagents were tested for the bromination of 15, i.e. CBr4, HBr and NBS,[9, 10, 20, 21] with yields
of 31%, 60% and 86% respectively, but NBS turned out to be the most efficient reagent.
Finally, the model compound 5 and the desired dendron precursor 7, were obtained from 16
after reaction with the commercially available synthons 17a and 17b, respectively. Notably, 7
could not be isolated using the classical method (i.e. Bu4NBr in toluene) and toluene had to be
replaced by DMSO to lead to the desired molecule in a good global yield (59%) from 13.[22, 23]
Likewise, the model compound 5 was isolated in 60% overall yield from 13 by a similar
reaction sequence.
9

New Journal of Chemistry
Page 10 of 34
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ06166E
OH
O
NaBH4
n-BuLi / -78°C
Br
H
THF / DMF
(92 %)
EtOH (abs)
(97 %)
13
14
15
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
THF / 15°C
(86 %)
NBS
PPh3
R = H
Br
(79 %)
2 equiv.
16
Bu4NBr
5
DMSO / NaOH
(50% aq.)
H
H
R = Br
1 equiv.
R
(77 %)
(R = H)
(R = Br)
Br
17a
17b
7
Scheme 5. Syntheses of the non-conjugated dendron precursor 7 and of the corresponding model compound 5.
In contrast to what had been stated for the derivatives discussed previously, no
1
particular H NMR signature could be identified among the aromatic protons of the non-
conjugated dendrons. However, the protons of the methylene bridges (Hb,b’) can now be used
as convenient NMR markers (singlet around 3.5 ppm) of dendron such as 5, providing a
simple spectroscopic mean of monitoring the di-substitution at the position 9 of the central
fluorenyl unit (see Fig. S2; ESI). Furthermore, this signal is also sensitive to the substitution
at the position 2 of the central fluorene, since after introducing the bromo substituent in the 2
position of this fluorene to obtain, this singlet in 5 splits into a well-defined AB multiplet
(ranging from 3.4 to 3.6 ppm) in dendron 7.
Porphyrin Synthesis
Synthesis of the TFP Precursor 8. The synthesis of this porphyrin is obtained following
Lindsey method (Scheme 6).[15, 16] The aldehyde 18[24] was condensed with pyrrole to obtain
10

Page 11 of 34
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ06166E
trimethylsilyl (TMS)-protected porphyrin (19) and then, compound 19 was readily
5
6
deprotected, providing the desired tetra-alkynyl precursor 8 in 28% yield from 18.
7
8
9
Synthesis of Dendrimers 1 and 2. The targeted dendrimers 1 and 2 were then obtained by
coupling deprotected porphyrin 8 with the dendrons 6 and 7, under Sonogashira conditions,[17]
these two dendrimers were obtained as dark red solids in 22% (1) and 29% (2) yields,
respectively (Scheme 6). These new dendrimers were characterized by NMR, elemental
analysis and MALDI MS for 1. In 1H NMR (see ESI), the large single peak detected around 9
ppm which corresponds to the eight equivalent β-pyrrolic protons of the TFP core is
diagnostic of the symmetric structure of these dendrimers. Furthermore, for dendrimer 1, we
can recognize the eight diagnostic protons (H1 and H8) corresponding to the dendron as a
singlet and doublet at high field (8.97 and 8.87 ppm), while for dendrimer 2, a large but
unresolved signal around 3.6 ppm, corresponding to the sixteen protons of the bridging
methylene units of the peripheral dendrons is observed in addition to the eight equivalent β-
pyrrolic protons of the TFP core (see ESI).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
11

New Journal of Chemistry
Page 12 of 34
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ06166E
.
1) BF3 OEt2
CHCl3
2) p-chloranil
NEt3
O
SiMe3
(33 %)
H
NH
N
N
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
18
3) K2CO3
CH2Cl / MeOH
HN
(85 %)
N
H
8
1 equiv.
NH
N
N
HN
6
4.5 equiv.
(22 %)
1
Pd(PPh3)2Cl2 /CuI (cat.)
DMF / iPr2NH, 95 °C
8
7
4.5 equiv.
(29 %)
NH
N
N
HN
2
Scheme 6. Synthesis of the generation one (G1) TFP-cored dendrimers 1 and 2.
12

Page 13 of 34
New Journal of Chemistry
1
2
3
4
5
View Article Online
DOI: 10.1039/C9NJ06166E
Photophysical properties
6
7
8
9
The normalized UV-visible (abs) and emission (em) spectra of the porphyrins 1, 2, of the
precursor porphyrin TFPBu (compound 3; without the extra dendrons) and of the node
models 4, 5 (Scheme 2) were measured in CH2Cl2 at room temperature (Figures 2-4) and
compared to those of the known dendrimers B1 and B0 (Scheme 1). Whereas the former
compound corresponds to the best 2PA photosensitizer among the various first generation
dendrimers characterized by our group, so far, the latter compound corresponds to the lead
compound in this respect. Furthermore, B0 shares also the same extended central TFP
platform with dendrimers 1 and 2.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Absorption spectra
The new dendrimers 1 and 2 have several characteristic features in their UV-visible
absorption spectra (Figure 2): (i) an intense Soret-band around 430 nm and four Q-bands from
520-650 nm, which are typical for free base porphyrin absorptions[25, 26] and (ii) an extra
absorption, around 300-400 nm, which corresponds to a *←  transition of the conjugated
dendrons.[27] This absorption, largely fluorenyl-based, is absent for the model porphyrin
TFPBu (3), suggesting that the unconjugated meso-fluorenyl groups of this compound absorb
below 290 nm,[28-29] whereas the absorption band of the meso-ethynylfluorenyl groups of
precursor 8 is slightly red-shifted and appears at 292 nm. Those of 1 and 2, which have meso-
fluorenylethynylfluorenyl groups, are even more red-shifted (330-350 nm) and more intense,
likewise to what had been previously observed with B0 and B1.[11]
13

New Journal of Chemistry
Page 14 of 34
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ06166E
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2. Normalized UV-visible (abs) spectra of new conjugated dendrimers 1, 2 and reference compounds 3, 8
and B1 in CH2Cl2.
After normalizing the spectra on the intensity of the Soret-band (Figure 2), it is clear that the
porphyrin-based transitions (Soret-band and Q-bands) do not show any significant shifts and
that the Q-bands remain of almost constant intensity. Thus, in comparison to B0 or B1, the
new fluorenyl-based connector present in 1 or 2 does not appear to reduce the transparency
window in which these dendrimers can undergo selective two-photon excitation (i.e. the
frequency range devoid of linear absorption).
Table 1. Photophysical data of new dendrimers 1, 2 and bare porphyrin 8, of the model compounds TFPBu (3),
4, 5, reference TPP and of the known dendrimers B0 and B1 in CH2Cl2 at R.T.
UV-visible absorption a /nm
Emission a /nm
b
Φfl
Refs
Ligand-based Soret
(%)
Q-Bands
ex
660
660
em
Absoption
Band
1
2
325
430
521, 557, 593, 652
524, 555, 591, 652
726
725
17
12
This work
This work
309, 341
430
14

Page 15 of 34
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ06166E
TFPBu(3) /
426
/
519, 555, 592, 652
660
410
724
469
18
This work
275,
323,
This work
4
/
0.2
410
274, 308
292
-
5
/
/
273
660
653
660
660
312
724
721
726
725
59
19
11
23
22
This work
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
8
428
417
432
431
520, 558, 594, 652
513, 548, 589, 646
522, 559, 594, 652
520, 557, 597, 652
This work
[11]
TPP
B0
B1
341
333
This work
This work
a Experiments were performed in CH2Cl2 (HPLC grade): Excitation (ex) and emission (em) wavelength maximas.
b
Fluorescence quantum yields were measured in CH2Cl2 (HPLC grade) using H2TPP (fl = 11%) as standard in toluene,
upon excitation at the Soret band.
c For values in toluene, see ref. [11]
.
It should be noted that the Soret bands of 1 and 2 are broader than those of TFPBu (3) and 8,
presumably in relation with the extension of the -manifold after appending the peripheral
dendrons, recalling the broadening previously observed for B0 or B1. This broadening is even
more evident in the case of dendrimer 1, in which the central porphyrin and peripheral
dendrons are fully conjugated. Deeper in the UV region, B0 exhibits a broad and intense
absorption band which maximum appears at 341 nm (vs. 333 nm for B1), corresponding to the
absorption of the four conjugated meso-fluorenyl ethynylfluorenyl groups. Dendrimer 2,
which possesses a nearly similar set of conjugated groups at its meso positions, also exhibit a
very similar absorption band with a maximum at the same wavelength, but along with another
sharper band at 309 nm, which can therefore be attributed to the eight non-conjugated
fluorenes of the flexible antennae. In Dendrimer 1, these two bands seem to overlap, resulting
in an even stronger and broader band with a maximum at 325 nm, i.e. at an intermediate value
between those of Dendrimer 2. This change can now be related to the extra-conjugation
operative between the rigid antennae and the meso-fluorenyl ethynylfluorenyl groups.
15

New Journal of Chemistry
Page 16 of 34
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ06166E
Emission spectra
5
6
7
8
9
Upon excitation in their Soret-band, the Dendrimers 1, 2 and the reference compounds
TFPBu, 8 exhibit a strong red emission, with characteristic porphyrin peaks Q(0,0) and
Q(0,1).[30] After normalizing the emission intensities of these compounds on their Q(0,0)
peaks, they exhibit very similar emission spectra, i.e. a strong Q(0,0) band and a weaker
Q(0,1) band at the same wavelengths (Figure 3). However, the intensity ratios between Q(0,0)
and Q(0,1) are slightly more different for extended compounds 1 and 2 than for shorter ones
TFPBu and 8.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
In contrast, the fluorescence quantum yields are much more impacted by the structural
modifications, even if all these tetrafluorenylporphyrins exhibit higher values than TPP
(Table 1). The quantum yield increases from 11% up to 18 or 19% upon extension of the TFP
platform, i.e. when going to TFPBu (fluorene) or 8 (ethynylfluorene). Both dendrimers 1 and
2, in which antennae are replacing on the peripheral fluorenyls the butyl chains of B0, exhibit
lower fluorescence quantum yields (17% and 12%, respectively) than B0 (23%). They also
fluoresce less than the generation 1 dendrimer B1 (22%). This behavior can probably be
explained by an increase of the internal conversion rate, especially in the case of 2, bearing
eight flexible fluorenylmethyl groups.
Figure 3. The normalized emission (em) spectra of new dendrimers 1, 2 and reference compounds TFPBu (3), 8
and B1 in CH2Cl2.
16

Page 17 of 34
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ06166E
Photophysical properties of the model compounds 4 and 5
5
6
7
8
9
The emission spectra of 4 and 5 were measured in CH2Cl2 and their quantum yield were
derived (Table 1). Considering the significant overlap between model donor emission and
model acceptor absorption, the energy transfer (ET) from the donor fluorenyl dendrons
toward the acceptor porphyrin central core in dendrimers 1-2 is possible. Figure 4 shows the
emission spectra of isolated donors 4 and 5 (dashed lines) and the UV-visible absorption
spectrum of the tetraalkynylporphyrin acceptor 8 (solid line). The absorption band of the
ethynylfluorene moiety of 8 appears in UV region at 292 nm, whereas the maximum of the
intense Soret band is at 428 nm, and the four Q-bands range at 520-650 nm (corresponding
photophysical data are listed in Table 1). When the conjugated 4 was excited at 410 nm, a
broad emission band in the region of 410-700 nm is observed. This emission band overlaps
with the Soret and Q absorption bands of 8 (red hatched area), allowing in principle ET from
dendron 4 towards the porphyrin core. Similarly, upon excitation of 5 at 274 nm, a narrow
emission band has a partial overlap with the absorption spectrum of 8 (blue hatched area),
which means that ET is also possible in this case (Figure 4).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
4
5
TA8 TFP
Figure 4. Overlaps between the emission spectrum of Model 4, considered as the energy donor, and the
absorption spectrum of porphyrin 8, considered as the energy acceptor (red hatched area), and between the
emission spectrum of Model 5 and the absorption spectrum of 8 (blue hatched area) in CH2Cl2.
17

New Journal of Chemistry
Page 18 of 34
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ06166E
Notably, the conjugated dendron Model 4 has a much lower quantum yield than the
unconjugated Model 5, presenting values close to these traditionally found for fluorenyl
derivatives.[8] Quite likely, an efficient non-radiative quenching process is taking place in the
former compound.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Energy transfer from the fluorene units to the porphyrin core in Dendrimers 1 and 2
After excitation in dendron absorption region (300 nm), the conjugated dendrimer 1 exhibits
exclusively a red emission from porphyrin core as shown in Figure 5, which means that the
ET efficiency is close to 100%. The broad emission band from conjugated peripheral
dendrons (modelled by 4) is completely quenched in the ET process, so that the red emission
from the porphyrin core is exclusively seen, likewise to what had been previously observed
[11]
for B0 and B1 For the dendrimer 2, which has non-conjugated dendrons (modelled by 5),
the strong blue dendron emission is not totally quenched, and a very weak dendron emission
band appears at 322 nm in addition to the red porphyrin emission. This dual emission suggests
that ET from dendrons to TFP core is slightly less efficient than for 1, but still near 100%.
Additional data confirm the high efficiency of the ET process: i) the fluorescence quantum
yields upon excitation in the dendron absorption band at 300 nm are exactly the same than
upon excitation at the Soret band at 430 nm (17% for dendrimer 1 and 12% for dendrimer 2),
and ii) the excitation spectra of 1 and 2 closely resemble the corresponding absorption spectra
(see Fig. S3, ESI). The maximum emission at 322 nm indicates that this residual emission
comes from the non-conjugated pending fluorenyls (i.e. the flexible antenna, see Scheme 2),
and not from the conjugated part of the dendrons (which belong to the extended TFP
platform). To conclude, the ET is efficient in both cases, in relation with a good overlap
between the emission spectrum of the dendron donors and the absorption spectrum of the
TFP acceptor (see hatched areas in Figure 4).
18

Page 19 of 34
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ06166E
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 5. The normalized emission spectra of 1 and 2 upon excitation at the dendron band at 300 nm.
Two-photon absorption
Based on the fact that high two-photon absorption (2PA) cross-sections had previously been
[11]
measured for B0 and B1
and other dendrimers possessing as well sixteen fluorenyl
antennae,[10] we next turned our attention to the non-linear optical properties of 1 and 2.
Taking advantage of the good fluorescence of these TFP-cored dendrimers, their TPA cross-
sections (σ2) were determined by investigating their two-photon excited fluorescence (TPEF)
in dichloromethane. Measurements were performed with 10-4 M solutions, using a mode-
locked Ti:sapphire laser delivering femtosecond pulses, following the experimental protocol
described by Xu and Webb.[31] A fully quadratic dependence of the fluorescence intensity on
the excitation power was observed for each sample at all the wavelengths of the spectra
shown in Figure 6, indicating that the cross-sections determined are only due to 2PA. The
shape of these curves reveals the interest of limiting the red-shift of the lowest absorption (Q
bands) in the higher generation dendrimers in order to be able to benefit of a pure two-photon
excitation at highest energy, corresponding also to a better 2PA cross-section.
19

New Journal of Chemistry
Page 20 of 34
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ06166E
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 6. Two-photon absorption spectra of 1, 2, TFPBu (3), B0 and B1 in CH2Cl2.
An obvious increase of σ2 values was observed for both new dendrimers 1 and 2 when
compared to those of reference TFPBu (140 GM at 790 nm). Connection of dendron
precursors 6 and 7 to the TFP core results in a strong improvement of the 2PA properties, up
to a ten-fold increase of the 2PA cross sections in the case of 1 bearing rigid dendrons. The
comparison between 1 and 2 clearly reveals the determining (positive) role of the conjugated
spacer in 1 on 2PA cross-sections. Logically, these dendrons will also contribute to enhance
the two-photon brightness (Фfl·σ2max), which evolves from 25 GM for TFPBu to 247 GM and
101 GM for 1 and 2, respectively (Table 2).
Table 2. Two-Photon Absorption and Brightness Properties of dendrimers 1, 2, TFPBu and
related reference compounds TPP, B0 and B1 in CH2Cl2.
max
max
max
σ2
Фfl·σ2
2PA
/nm
790
Two-photon brightness
enhancement factor c
Compound
1
/GMa
1450
/GMb
247
190
20

Page 21 of 34
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ06166E
2
TFPBu (3)
TPP
790
790
790
790
790
840
140
12d
101
25
78
19
1.3
177
161
1
B0
770
730
136
124
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
B1
a
Intrinsic TPA cross-sections measured in 10-4 M dichloromethane solutions by TPEF in the
femtosecond regime;
b Maximum two-photon brightness in dichloromethane.
c Enhancement factor: Фfl•σ2max of the compounds normalized to that of TPP.
d Data from reference.[32]
Comparison with the known dendrimers B0 or B1 is quite informative.[11] Thus, dendrimer 2
exhibits a 2PA cross-section similar to that of B0 (slightly higher, but within the error margin
for the maximum value at 790 nm) and significantly larger than that of B1, in spite of the
extended dendrimeric structure of the latter, in line with the determining role of the four
conjugated fluorenyl ethynylfluorenyl arms at the meso-positions for 2PA. In contrast,
dendrimer 1 exhibits 2PA cross-sections more than twice as large as those of B0 or B1,
evidencing the additional positive effect of electronic conjugation within the dendrons on
2PA. Due to its lower fluorescence quantum yield relative to B0 or B1, 2 also exhibits lower
two-photon brightness, whereas 1 is the brightest compound of these series (Table 2). This
comparison clearly indicates that the enhancement of the 2PA cross-section observed for 1
actually results both from the increased number of fluorenyl units (one fluorenyl unit
composing the connector) in each dendron but also from the conjugated (rigid) structure of
the C2 connector in 1 which boosts 2PA more than the flexible and non-conjugated C3
connector in 2 (Scheme 2).
Table 3. Oxygen sensitization properties of dendrimers 1, 2 and related reference compounds
TPP, TFPBu, B0 and B1.
Two-photon excited oxygen
a
sensitization enhancement
Compound
1

Ф·σ2max /GM b
factor (O2) c
0.46
667
93
21

New Journal of Chemistry
Page 22 of 34
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ06166E
2
TFPBu (3)
TPP
0.40
0.64
0.60
0.62
0.61
336
90
47
13
1
7.2
477
445
B0
66
62
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
B1
a Singlet oxygen production quantum yield determined relative to TPP in
dichloromethane (Δ[TPP] = 0.60).
b ·2max: Figure of merit of the two-photon excited singlet oxygen production in
dichloromethane.
c
Enhancement factor: ·2max of the compound normalized to that of TPP.
Oxygen sensitization
We also wondered about the oxygen-sensitizing capabilities of 1-2, by comparing their
quantum yields of singlet oxygen generation () with those of TFPBu, B0 and B1 (Table
3).[11] The two new dendrimers exhibit values lower than those of the related reference
compounds, however they still exhibit significant values (40 to 46 %). Dendrimer 1 exhibits
singlet oxygen quantum yields higher than those of flexible dendrimer 2, presumably in
relation with a lower internal conversion rate. The decrease of the singlet oxygen production
is concomitant with a strong increase of the 2PA cross-sections compared to TFPBu. This
counteracting behavior of  and 2max leads in fine to stronger enhancements of the figure of
merit of the two-photon excited oxygen sensitization (2max) relative to TFPBu (up to a
seven-fold increase for dendrimer 1). When comparing the two-photon excited oxygen
sensitization properties of 1 and 2 with those of B0 or B1, similar trends are observed than
previously noticed for the two-photon brightness: 2 is less efficient than B0 or B1, due to its
lower singlet oxygen quantum yield, but 1 is more efficient than B0 or B1, because its lower
 is largely compensated by its much larger 2.
22

Page 23 of 34
New Journal of Chemistry
1
2
3
4
5
View Article Online
DOI: 10.1039/C9NJ06166E
Conclusions
6
7
8
9
Two new conjugated and non-conjugated meso-tetrafluorenylporphyrin-cored dendrimers 1
and 2 have been synthesized and characterized. For these dendrimers the peripheral fluorenyl
units are linked to the central TFP core by original fluorene-based connectors instead of the
more classic 1,3,5-phenylene unit previously used in related compounds. Absorption,
emission and TPEF studies on these dendrimers 1 and 2 reveal that their two-photon
absorption cross-sections are largely enhanced compared to that of TFPBu, ultimately leading
to a better two-photon brightness (Фfl·σ2max) and enlarged two-photon excited oxygen
sensitization (.2max). These results point to a minimal impact of the dendrons on the linear
optical properties, mostly determined by the TFP core, but not on the nonlinear optical
properties which are largely influenced by the peripheral arms. Based on the classical figures
of merit, dendrimer 1, outperforms the best first-generation dendrimer (B1) previously
developed in our group,[11, 12, 33] but also the best porphyrin-based photosensitizer identified so
far (B0) for 2PA oxygen sensitization among these series. Thus, this new rigid and conjugated
fluorenyl-based connector introduced in 1 leads to higher performances than the 1,3,5-
phenylene spacer. This connector ameliorates the electronic communication within the
dendrimeric branches without affecting the relevant linear optical properties for fluorescence
imaging and oxygen photosensitization. It is therefore very promising for applied
developments related to 2PA-PDT, since it enables improving the two-photon absorption
cross-section while permitting a good trade-off with other important photophysical properties
essential for theranostic uses (i.e. the fluorescence and singlet oxygen quantum yields). This
new connector should now be used in the future when designing dendrimers for combined
oxygen photosensitization and two-photon fluorescence imaging. Work is in progress to
improve the water-solubility and the biocompatibility of this system, by replacing the alkyl
chains on the fluorene units with water-solubilizing groups, such as oligoethyleneglycol
chains.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Experimental Section
General
23

New Journal of Chemistry
Page 24 of 34
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ06166E
Unless otherwise stated, all solvents used in reactions were distilled using common
5
6
7
i
purification protocols,[34] except DMF and Pr2NH which were dried on molecular sieves (3
8
9
Å). Compounds were purified by chromatography on silica gel using different mixtures of
1
13
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
eluents as specified. H and C NMR spectra were recorded on BRUKER Ascend 400 and
500 at 298 K. The chemical shifts (in ppm) are referenced to internal tetramethylsilane. 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 2-ethynyl-9,9-dibutyl-fluorene (12),[18,19] (9,9-dibutyl-fluorene-2-yl)carbaldehyde
(14)[7] and 9,9-dibutyl-7-((trimethylsilyl)ethynyl)-fluorene-2-carboxaldehyde (18)[24] were
synthesized as described earlier.
Synthesis of the organic precursors
2-Bromo-9-(dibromomethylene)-9H-fluorene (11a). In a Schlenk tube, 2-bromo-fluoren-9-
one (10) (1.0 g, 3.9 mmol, 1 equiv) and PPh3 (4.05 g, 15.4 mmol, 4 equiv) were dissolved in
distilled and degassed CH2Cl2 under argon. The mixture was cooled to 0 °C in an ice-water
bath. Then, CBr4 (5.12 g, 15.4 mmol, 4 equiv) was added under argon. The mixture was
stirred overnight at 20 °C. After evaporation of the volatiles, residue was further purified by
silica chromatography using petroleum ether as eluent. The title compound was isolated as a
1
yellow powder (1.17 g, 73% yield). H NMR (400 MHz, CDCl3): δ = 8.77 (s, 1H), 8.61 (d,
1H, J = 8.0 Hz), 7.66 (d, 1H, J = 8.0 Hz), 7.55 (s, 2H), 7.43 (t, 1H, J = 8.0 Hz), 7.34 (t, 1H, J =
13
8.0 Hz). C NMR (100 MHz, CDCl3): δ = 139.6, 139.4, 138.5, 137.8, 132.2, 129.6, 129.0,
127.7, 126.0, 121.0, 120.7, 119.6, 93.0, 92.3.
9-(Dibromomethylene)-9H-fluorene (11b). In a Schlenk tube, a mixture of commercial CBr4
(368 mg, 1.1 mmol, 2 equiv) and PPh3 (291 mg, 1.1 mmol, 2 equiv) were stirred in distilled
and degassed CH2Cl2 (2 mL) at 35 oC under argon until the color turned to orange. Then, in
another Schlenk tube, commercial 9-fluorenone (9; 100 mg, 0.55 mmol, 1 equiv) dissolved in
24

Page 25 of 34
New Journal of Chemistry
1
2
3
4
5
6
7
8
View Article Online
DOI: 10.1039/C9NJ06166E
CH2Cl2 (3 mL) and was transferred dropwise into the first Schlenk tube. The mixture was
stirred at 35 oC for 5 h under argon. After evaporation of the volatiles, residue was purified by
silica chromatography using heptane as eluent. The title compound was isolated as a white
9
1
1
powder (130 mg, 70% yield) and characterized by H NMR.[35][(see ESI)] H NMR (400
MHz, CDCl3): δ = 8.61 (d, J = 7.6Hz, 2H), 7.68 (d, J = 8.0 Hz, 2H), 7.42 (t, J = 8.0 Hz, 2H),
7.31 (t, J = 8.0 Hz, 2H).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2,2'-(3-(9H-fluoren-9-ylidene)penta-1,4-diyne-1,5-diyl)bis(9,9-dibutyl-9H-fluorene) (4).
In a Schlenk tube, a mixture of 9,9-dibutyl-2-ethynyl-fluorene (12) (113 mg, 0.4 mmol, 2.5
equiv), 11b (50 mg, 0.15 mmol, 1 equiv), Pd(PPh3)2Cl2 (16.8 mg, 0.04 mmol, 0.6% equiv)
i
and CuI (2.4 mg, 0.04 mmol, 0.6% equiv) were stirred in DMF (1 mL) and Pr2NH (1 mL)
was added under argon. The reaction mixture was degassed by freeze-pump-thaw twice and
o
heated for 48 h at 95 C. After evaporation of the volatiles, residue was further purified by
silica chromatography using pentane as eluent. Orange crystals of the title compound were
obtained (33 mg, 28% yield). 1H NMR (400 MHz, CDCl3): δ = 8.81 (d, J = 4.0 Hz, 2H, HFlu),
7.78-7.66 (m, 10H, HFlu), 7.43-7.33 (m, 10H, HFlu), 2.08-1.98 (m, 8H, CH2-Bu), 1.16-1.07 (m,
8H, CH2-Bu), 0.74-0.59 (m, 24H, J = 8.0 Hz, CH2 & CH3-Bu). MS (MALDI-DCTB) for C60H58:
m/z = 778.4510 [M+H]+ (calcd: 778.45385).
2,2'-(3-(2-bromo-9H-fluoren-9-ylidene)penta-1,4-diyne-1,5-diyl)bis(9,9-dibutyl-9H-
fluorene) (6). In a Schlenk tube, a mixture of 9,9-dibutyl-2-ethynyl-fluorene (12) (300 mg,
1.0 mmol, 2 equiv), 11a (206 mg, 0.5 mmol, 1 equiv), Pd(PPh3)2Cl2 (4.2 mg, 0.01 mmol,
0.6% equiv) and CuI (0.6 mg, 0.01 mmol, 0.6% equiv) were stirred in DMF (2 mL) and
iPr2NH (2 mL) was added under argon. The reaction medium was degassed by freeze-pump-
thaw twice and heated for 48 h at 95 oC. After evaporation of the volatiles, residue was further
purified by silica chromatography using pentane as eluent. The title compound was obtained
1
as an orange powder (340 mg, 79% yield). H NMR (400 MHz, CDCl3): δ = 9.14 (d, J = 1.6
Hz, 1H, HFlu), 8.79 (d, J = 8.0 Hz, 1H, HFlu), 7.79-7.66 (m, 8H, HFlu), 7.60-7.52 (m, 3H, HFlu),
7.43-7.35 (m, 8H, HFlu), 2.13-1.96 (m, 8H, CH2-Bu), 0.90-0.83 (m, 8H, CH2-Bu), 0.73-0.54 (m,
20H, HFlu, CH2 & CH3-Bu). 13C NMR (100 MHz, CDCl3): δ = 151.4, 151.2, 143.3, 142.8,
142.7, 140.4, 140.3, 139.5, 139.3, 139.0, 137.6, 131.9, 131.2, 131.1, 129.6, 128.9, 128.1,
128.0, 127.9, 127.2, 127.1, 126.5, 126.3, 125.7, 123.1, 123.0, 121.3, 120.9, 120.8, 120.7,
25

New Journal of Chemistry
Page 26 of 34
1
2
3
4
5
6
7
8
View Article Online
DOI: 10.1039/C9NJ06166E
120.4, 120.1, 120.0, 119.9, 103.3, 100.2, 100.1, 89.2, 89.1, 59.7, 55.5, 55.3, 53.6, 40.4, 40.3,
29.8, 29.5, 23.3, 23.2, 14.0. HRMS-ESI for C60H57Br: m/z = 856.3636 [M]+. (calcd:
856.36381).
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(9,9-dibutyl-9H-fluoren-2-yl)methanol (15). In a Schlenk tube, (9,9-dibutyl-fluorene-2-
yl)carbaldehyde (14; 3.0 g, 9.8 mmol, 1 equiv) was dissolved in EtOH (99.6%) under argon.
The mixture was cooled to 0°C in an ice-water bath. Then NaBH4 (444 mg, 11.8 mmol, 1.2
equiv) was added under argon. The system was first stirred for 1 h at 0 oC, then for another 2 h
at 20 °C. The mixture was extracted 3 times with ethyl acetate then washed by brine. After
evaporation of the volatiles, the residue was further purified by silica chromatography using
CH2Cl2/heptane (1:1) as eluent. The title compound was isolated as white crystals (2.94 g,
97% yield) and characterized by 1H NMR by comparison with its known dihexyl analogue.[36]
1H NMR (400 MHz, CDCl3): δ = 7.70-7.67 (m, 2H, HFlu), 7.34-7.29 (m, 5H, HFlu), 4.78 (d, J
= 5.64 Hz, 2H, CH2OH), 1.98-1.94 (m, 4H, CH2-Bu), 1.68 (t, J = 5.84 Hz, 1H, CH2OH), 1.12-
1.03 (m, 4H, CH2-Bu), 0.67 (t, J = 8.0 Hz, 6H, CH3-Bu), 0.63-0.55 (m, 4H, CH2-Bu).
2-(bromomethyl)-9,9-dibutyl-9H-fluorene (16). In a two-neck flask, a mixture of 15 (1.13
g, 3.7 mmol, 1 equiv) and PPh3 (1.06 g, 4.0 mmol, 1.1 equiv) was dissolved in THF (20 mL)
and cooled to 15 oC. Then, NBS (717 mg, 4.0 mmol, 1.1 equiv) was added. The reaction was
stirred for additional 1 h and immediately quenched by cold water. The precipitate was
dissolved in CH2Cl2. The organic extracts were collected, washed with brine and dried over
anhydrous MgSO4. After evaporation of the volatiles, residue was further purified by silica
chromatography using CH2Cl2/hexane (1:5) as eluent. The title compound was isolated as
1
white crystals (639 mg, 86% yield) and characterized by H NMR by comparison with its
known dihexyl analogue.[36] 1H NMR (400 MHz, CDCl3): δ = 7.71-7.65 (m, 2H, HFlu), 7.38-
7.28 (m, 5H, HFlu), 4.62 (s, 2H, CH2Br), 1.99-1.95 (m, 4H, CH2-Bu), 1.13-1.04 (m, 4H, CH2-
Bu), 0.68 (t, J = 8.0 Hz, 6H, CH3-Bu), 0.64-0.67 (m, 4H, CH2-Bu).
2,2'-((9H-fluorene-9,9-diyl)bis(methylene))bis(9,9-dibutyl-9H-fluorene) (5): Commercial
fluorene (17a; 26 mg, 0.16 mmol, 1 equiv) and Bu4NBr (5.0 mg, 0.02 mmol, 10% equiv) were
dissolved in DMSO (2 mL) and then NaOH (50% aq., 0.02 mL) was injected into the mixture.
After the color turning to orange, compound 16 (127 mg, 0.35 mmol, 2.2 equiv) was added
26

Page 27 of 34
New Journal of Chemistry
1
2
3
4
5
6
7
8
View Article Online
DOI: 10.1039/C9NJ06166E
and stirred at 20 °C for 2 h. The mixture was extracted with CH2Cl2 for 3 times, washed with
saturated NaCl and dried over anhydrous MgSO4. After evaporation of the volatiles, residue
was further purified by silica chromatography using heptane as eluent. The title compound
9
1
was isolated as yellow crystals (88 mg, 79% yield). H NMR (300 MHz, CDCl3): δ = 7.55-
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
7.49 (m, 4H, HFlu), 7.34-7.28 (m, 6H, HFlu), 7.24-7.16 (m, 8H, HFlu), 6.70 (d, J = 9.0 Hz, 2H,
HFlu), 6.55 (s, 2H, HFlu), 3.52 (s, 4H, CH2- bridging, Hb,b’), 1.81(m, 4H, CH2-Bu), 1.58 (m, 4H,
CH2-Bu), 1.06-0.93 (m, 8H, CH2-Bu), 0.70-0.62 (m, 12H, CH3-Bu), 0.42-0.17 (m, 8H, CH2-Bu).
HRMS-ESI for C57H62: m/z = 746.4849 [M]+. (calcd: 746.4846); C57H63: m/z = 747.4925
[M+H]+. (calcd: 747.49243);
2,2'-((2-bromo-9H-fluorene-9,9-diyl)bis(methylene))bis(9,9-dibutyl-9H-fluorene)
(7):
Commercial 2-bromofluorene (17b; 186 mg, 0.76 mmol, 1 equiv) and Bu4NBr (24.4 mg,
0.076 mmol, 10% equiv) were dissolved in DMSO (6 mL) and then NaOH (50% aq., 0.05
mL) was injected into the system. After the color turning to orange, compound 16 (619 mg,
1.67 mmol, 2.2 equiv) was added and stirred at 20 °C for 1 h. The mixture was extracted with
CH2Cl2 for 3 times, washed with brine and dried over anhydrous MgSO4. After evaporation of
the volatiles, the residue was further purified by silica chromatography using heptane as
1
eluent. The title compound was isolated as a white powder (480 mg, 77% yield). H NMR
(400 MHz, CD2Cl2): δ = 7.88 (d, J4 = 1.6 Hz, 1H, HFlu), 7.67 (d, J = 7.6 Hz, 1H, HFlu), 7.51-
7.49 (m, 2H, HFlu), 7.40 (t, J = 8.0 Hz, 1H, HFlu), 7.32-7.29 (m, 2H, HFlu), 7.24-7.16 (m, 10H,
HFlu), 6.64 (d, J = 5.8 Hz, 2H, HFlu), 6.58 (s, 2H, HFlu), 3.62-3.51 (m, 4H, CH2- bridging, Hb,b’),
1.83-1.74 (m, 4H, CH2-Bu), 1.66-1.57 (m, 4H, CH2-Bu), 1.09-0.93 (m, 8H, CH2-Bu), 0.63 (t, J =
7.32 Hz, 12H, CH3-Bu), 0.31-0.11 (m, 8H, CH2-Bu). 13C NMR (100 MHz, CD2Cl2): δ = 151.2,
151.1, 150.1, 148.4, 141.5, 140.8, 140.7, 139.5, 136.3, 130.7, 129.3, 128.5, 127.9, 127.3,
127.1, 127.0, 125.4, 125.0, 121.3, 120.6, 120.1, 119.7, 118.7, 58.6, 55.0, 46.5, 40.7, 40.6,
30.3, 26.4, 26.3, 14.3, 14.2. HRMS-ESI for C57H61Br: m/z = 847.3850 [M+Na]+ (calcd:
847.38488); m/z = 825.4040 [M+H]+ (calcd: 825.40294). Anal. Calcd. (%) for C57H61Br: C
82.88; H 7.44. Found: C 82.71; H 7.66.
5,10,15,20-Tetrakis(9,9-dibutyl-7-ethynyl-9H-fluoren-2-yl)porphyrin (8): In a two-neck
flask, a mixture of previously prepared 9,9-dibutyl-7-((trimethylsilyl)ethynyl)-fluorene-2-
carboxaldehyde (18; 689 mg, 1.7 mmol, 1 equiv) and pyrrole (0.17 mL, 1.7 mmol, 1 equiv)
27

New Journal of Chemistry
Page 28 of 34
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ06166E
were dissolved in dried chloroform (200 mL) under argon. After degassing the mixture with
argon bubbling for 30 min, BF3•OEt2 (0.05 mL, 0.4 mmol, 0.25 equiv) was injected and the
reaction was stirred in dark for 3 h under argon at room temperature. Then oxidant p-chloranil
(315 mg, 1.28 mmol, 0.75 equiv) was added, and the reaction was heated at 60 oC for another
2 h without any protection. After cooling the reaction to room temperature, NEt3 (2 mL) was
injected and then stirring was kept for several minutes. After evaporation of the volatiles,
purification was done by silica chromatography using [CH2Cl2/heptane (1:4)] mixture as
eluent; the porphyrin 19 was collected as a red powder. The crude porphyrin 19 was then
deprotected by K2CO3 (470 mg, 3.4 mmol, 8 equiv) in a mixed solvents CH2Cl2/THF/MeOH
(3:1:1) at 60°C, overnight. At last, the title tetra-alkynyl porphyrin was isolated by silica
chromatography using a CH2Cl2/heptane (1:4) mixture as eluent. The overall yield is 28% for
these two steps. 1H NMR (400 MHz, CDCl3): δ = 8.90 (s, 8H, Hβ-pyr), 8.25-8.19 (m, 8H, HFlu),
8.07 (d, 4H, J = 7.3 Hz, HFlu), 7.91 (d, 4H, J = 7.8 Hz, HFlu), 7.63 (m, 8H, J = 8.0 Hz, HFlu),
3.21 (s, 4H, C≡CH), 2.13 (t, 16H, J = 6.9 Hz, CH2-Bu), 1.21-1.14 (m, 16H, CH2-Bu), 0.92-0.83
(m, 16H, CH2-Bu), 0.79-0.73 (m, 24H, CH3-Bu), -2.60 (s, 2H, NH). 13C NMR (100 MHz,
CDCl3): δ = 151.4, 149.7, 141.9, 141.7, 140.1, 133.9, 131.6, 129.5, 126.9, 120.8, 120.2,
118.4, 88.6, 84.9, 55.5, 40.4, 26.5, 23.3, 14.1. MS (Maldi-DCTB) for C112H110N4: m/z =
1510.869 [M+•] (calcd: 1510.8725). Anal. Calcd. (%) for C112H110N4.EtOH: C, 87.87; H, 7.50;
N, 3.60. Found: C, 87.89; H, 7.59; N, 3.49.
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Conjugated Porphyrin-based Dendrimer (1): In a Schlenk tube, the dendron precursor 6
(100 mg, 0.12 mmol, 4.5 equiv), porphyrin 8 (39 mg, 0.03 mmol, 1 equiv), Pd(PPh3)2Cl2 (4.2
mg, 0.01 mmol, 0.6% equiv) and CuI (0.6 mg, 0.01 mmol, 0.6% equiv) were stirred in DMF
i
(2 mL) under argon. Subsequently, degassed Pr2NH (2 mL) was added and the reaction
o
medium was degassed by freeze-pump-thaw twice and heated for 72 h at 95 C. After
evaporation of the volatiles, residue was purified by silica chromatography using petroleum
ether/THF (30:1) as eluent. The title porphyrin-based dendrimer was isolated as a dark violet
1
powder (26 mg, 22% yield). H NMR (400 MHz, CDCl3): δ = 9.23 (t, J = 8.8 Hz, 4H, HFlu),
8.97 (m, 8H, Hβ-pyr), 8.87-8.83 (m, 4H, HFlu), 8.67-8.50 (m, 4H, HFlu), 8.28 (m, 8H, HFlu),
8.11-8.09 (m, 4H, HFlu), 7.99-7.88 (m, 10H, HFlu), 7.79-7.61 (m, 38H, HFlu), 7.44-7.34 (m,
28

Page 29 of 34
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ06166E
28H, HFlu), 2.27-1.97 (m, 48H, CH2-Bu), 1.19-1.06 (m, 48H, CH2-Bu), 0.78-0.58 (m, 110H, CH2
5
6
13
& CH2-Bu), -2.53 (s, 2H, NH). C NMR (100 MHz, CDCl3): δ = 151.5, 151.4, 151.3, 151.2,
7
8
9
140.4, 140.3, 140.0, 139.8, 138.3, 137.8, 131.2, 131.1, 129.7, 129.4, 128.0, 127.2, 126.5,
123.1, 121.1, 121.0, 120.5, 120.4, 120.2, 120.1, 120.0, 55.4, 55.3, 40.4, 26.1, 23.2, 14.1, 14.0.
MS (ES-CH2Cl2) for C352H336N4: m/z = 2309.3104 [M]2+ (calcd: 2309.3202); MS (MALDI)
for C352H335N4: m/z = 4617.693 [M+H]+ (calcd: 4617.63313). Anal. Calcd. (%) for
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
.
C352H336N4 4CH2Cl2: C, 86.14; H, 6.98; N, 1.14. Found: C, 86.39; H, 7.09; N, 1.26.
Non-conjugated Porphyrin-based Dendrimer (2): In a Schlenk tube, the Dendron precursor
7 (100 mg, 0.14 mmol, 4.5 equiv), the porphyrin 8 (45 mg, 0.03 mmol, 1 equiv), Pd(PPh3)2Cl2
(4.2 mg, 0.01 mmol, 0.6% equiv) and CuI (0.6 mg, 0.01 mmol, 0.6% equiv) were stirred in
DMF (2 mL) under argon. Subsequently, degassed iPr2NH (2 mL) was added and the reaction
o
medium was degassed by freeze-pump-thaw twice and heated for 114 h at 95 C. After
evaporation of the volatiles, residue was purified by silica chromatography using petroleum
ether/THF (30:1) as eluent. The title porphyrin-based dendrimer was isolated as a dark violet
1
powder (38 mg, 29% yield). H NMR (400 MHz, CD2Cl2): δ = 9.00 (s, 8H, Hβ-pyr), 8.31-7.96
(m, 22H, HFlu), 7.77-7.68 (m, 12H, HFlu), 7.50-6.97 (m, 60H, HFlu), 6.71-6.63 (m, 14H, HFlu),
3.63 (s, 16H, CH2-bridging), 2.24-1.64 (m, 48H, CH2-Bu), 1.09-0.75 (m, 72H, CH3-Bu), 0.64-0.23
(m, 96H, CH2-Bu), -2.59 (s, 2H, NH). 13C NMR (100 MHz, CD2Cl2): δ = 151.6, 150.6, 149.6,
149.5, 141.4 141.1, 140.0, 138.8, 136.0, 132.1, 130.9, 130.8 , 128.7, 126.5, 124.9, 124.5,
122.7 , 121.1, 119.4, 119.2, 118.1, 54.5, 45.9, 40.3, 40.1, 29.7, 25.7, 23.1, 22.7, 13,7, 13.6.
.
Anal. Calcd. (%) for C340H350N4 3CH2Cl2: C, 86.78; H, 7.54; N, 1.18. Found: C, 87.39; H,
7.90; N, 1.01.
Spectroscopic Measurements
All photophysical properties have been performed with freshly-prepared air-equilibrated solutions at
room temperature (298 K). UV-Vis absorption spectra were recorded 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
29