Structure-Photoproperties Relationship Investigation of the Singlet Oxygen Formation in Porphyrin-Fullerene Dyads

Article abstract of DOI:10.1007/s10895-017-2123-1

A systematic structure-photoproperties relationship study of the interactions of porphyrin-fullerene dyads with molecular oxygen was conducted on a set of three porphyrin-fullerene dyads, as this approach of related applications - oxygen sensitivity and photo-induced singlet oxygen generation - of such dyads remained to be endeavoured. To promote energy transfers between the porphyrin and fullerene units and limit undesired charge separation, a particular attention was devoted to the choice of the solvents for the photoproperties determination. Toluene, in which in addition the compounds investigated are not aggregated, was selected accordingly. The molecular orbital levels and energy gaps of the dyads were determined by electrochemistry and theoretical calculations. Their ground state absorption, steady-state fluorescence-based oxygen sensitivity and photo-induced singlet oxygen generation were determined. The dyads were designed to benefit from a facilitated synthetic porphyrin-fullerene coupling thanks to an easy access to formyl-functionalized porphyrins. The effect of two structural parameters was investigated: the presence of electron-donating hexyloxy chains at the para position of the meso-phenyl, and the presence of a phenylacetylene spacer. This latest factor appeared to have the most predominant effect on all these properties.

Full text of DOI:10.1007/s10895-017-2123-1

J Fluoresc
DOI 10.1007/s10895-017-2123-1
ORIGINAL ARTICLE
Structure-Photoproperties Relationship Investigation
of the Singlet Oxygen Formation in Porphyrin-Fullerene Dyads
1
1
1
2
Emel Önal & Sevinc Zehra Topal & Ismail Fidan & Savaş Berber
&
1
1
Fabienne Dumoulin & Catherine Hirel
Received: 1 February 2017 /Accepted: 24 May 2017
Springer Science+Business Media New York 2017
#
Abstract A systematic structure-photoproperties relationship
study of the interactions of porphyrin-fullerene dyads with
molecular oxygen was conducted on a set of three
porphyrin-fullerene dyads, as this approach of related applica-
tions - oxygen sensitivity and photo-induced singlet oxygen
generation - of such dyads remained to be endeavoured. To
promote energy transfers between the porphyrin and fullerene
units and limit undesired charge separation, a particular atten-
tion was devoted to the choice of the solvents for the
photoproperties determination. Toluene, in which in addition
the compounds investigated are not aggregated, was selected
accordingly. The molecular orbital levels and energy gaps of
the dyads were determined by electrochemistry and theoretical
calculations. Their ground state absorption, steady-state fluo-
rescence-based oxygen sensitivity and photo-induced singlet
oxygen generation were determined. The dyads were de-
signed to benefit from a facilitated synthetic porphyrin-
fullerene coupling thanks to an easy access to formyl-
functionalized porphyrins. The effect of two structural param-
eters was investigated: the presence of electron-donating
hexyloxy chains at the para position of the meso-phenyl,
and the presence of a phenylacetylene spacer. This latest factor
appeared to have the most predominant effect on all these
properties.
.
.
.
.
Keywords Porphyrin Fullerene Dyad Singlet oxygen
.
.
Fluorescence Electrochemistry Oxygen sensor
Introduction
The interactions of molecular oxygen with photosensitisers in
their excited states [1] is of crucial importance for several appli-
cations such as the photogeneration of singlet oxygen for photo-
dynamic therapy, photocatalysis [2] or the luminescence (fluo-
rescence or phosphorescence)-based oxygen sensing. Porphyrins
are chosen as photosensitisers for these applications, and our
laboratory is strongly involved in their chemistry for photody-
namic therapy [3–5] and oxygen sensing purposes [6, 7].
On the other hand, porphyrin-fullerene dyads or superior
arrays are electron donor-acceptor systems, and as such, ex-
hibit properties suitable for light-harvesting purposes, as they
can behave as photosynthetic antenna or reaction center
mimics [8]. Upon irradiation, fullerene acts as an electron
and energy acceptor group from photo-activated donor por-
phyrin. This can be observed on covalent or supramolecular
Electronic supplementary material The online version of this article
(doi:10.1007/s10895-017-2123-1) contains supplementary material,
which is available to authorized users.
[9] arrays. The nature of the porphyrin-fullerene linkage (flex-
ible or rigid, linear or not, aromatic, ethylenic or acetylenic)
proved to have an important effect on the photophysical prop-
erties of such dyads. [10–16] These electron donor-acceptor
systems can exhibit synergistic properties higher than the sum
of the properties exhibited by each isolated partner [17].
Despite its potential interest asserted by all these consider-
ations, investigation of the interactions of porphyrin-fullerene
dyads with molecular oxygen remains unexplored in a system-
atic manner, a topic we wished to endeavour, with further
*
*
Sevinc Zehra Topal
sztopal@gtu.edu.tr
Catherine Hirel
chirel@gtu.edu.tr
1
2
Department of Chemistry, Gebze Technical University,
4
1400 Gebze, Kocaeli, Turkey
Department of Physics, Gebze Technical University,
1400 Gebze, Kocaeli, Turkey
4

J Fluoresc
photodynamic and optical oxygen sensing usages in mind. A
few porphyrin-fullerene dyads have indeed proved to be good
singlet oxygen generators [18, 19] occasionally used in pho-
todynamic therapy [20, 21], and were previously used as
photoelectrochemical sensors [22] but have never been used-
to the best of our knowledge - as optical oxygen sensing pur-
poses. Although it is acknowledged that energy and/or elec-
tron transfers in porphyrin-fullerene dyads can be affected and
sometimes controlled by i) the polarity of the solvent, ii) the
nature of the porphyrin substituents, iii) adjusting the distance
between the donor and acceptor, [23] systematic investiga-
tions of the effect of structural variations on interactions of
photo-excited porphyrin-fullerene dyads with molecular oxy-
gen are less reported and yet still needed. This paper tackles
this aspect and reports on detailed fundamental investigations
conducted on a set of three dyads (Fig. 1) designed following
different considerations:
far multi-steps syntheses [26–28]. Since we recently de-
veloped a straightforward method [29] to introduce alde-
hyde functions at the meso-position of porphyrins, the
synthetic limitations became the access to mono-meso-
brominated porphyrin. As 5-(4-bromophenyl)-10,15,20-
triphenylporphyrin (1-Br) proved to be tedious to isolate,
porphyrin 2-Br, much easier to purify, was designed. 1-
Br led to dyad 1 while 2-Br is the precursor of dyads 2
and 3. The effect of the electron-donating hexyloxy
chains (dyads 1 vs 2) likely to affect the solubility of the
dyads and to exert an electron-donating effect on their
photoproperties will be accordingly investigated.
The effect of a phenylacetylene moiety. One of our recent
studies demonstrated that the presence of a phenylacetylene
moiety at the meso position of Pd and Pt porphyrins im-
proved their oxygen sensing efficiency [7], a result in line
with other documented results showing that the presence of
triple bond on oxygen-sensing cores improves their perfor-
mances [30]. Hence dyad 3 (Fig. 1) was designed to have
the fullerene rigidly bound to the meso-position of the por-
phyrin via a phenylacetylene unit acting as a spacer which
increases the electron donor-acceptor distance and the π-π
–
–
The relative synthetic accessibility of dyad 1 vs dyads 2
and 3. Fullerene reacts with aldehyde functions via the
Prato reaction [24, 25], thus aldehyde-functionalized por-
phyrins are needed. This type of compounds required so
Fig. 1 Targeted fullerene-porphyrin dyads 1–3 and their interaction with molecular oxygen

J Fluoresc
−
1
conjugation. The effect of this spacer can be studied by
comparing dyads 2 and 3.
them being IR active, at 1428, 1181, 574 and 525 cm [32, 33].
−1
Indeed, three IR bands at 1185, 575 and 525 cm confirm the
successful grafting of the C on the porphyrins (See supporting
60
information). The success of the coupling was also evidenced by
1
1
For each dyad, the determination of the photophysical, pho-
tochemical and electrochemical behaviour, the molecular orbital
levels and energy gaps was comparatively performed with a
structure-property relationship approach. A focus of the interac-
tions of the excited states of these three dyads with oxygen was
completed with two approaches in mind: their potential use as
photodynamic photosensitisers and as molecular oxygen sensors.
Meso-tetraphenylporphyrin (TPP) was used as a reference for all
the measurements performed in these works.
H NMR spectroscopy. The well resolved and representative H
NMR spectra of compound 1-CHO and dyad 1 are presented in
Fig. 2 (See supplementary information for comparative NMR
spectra of 2-CHO, 3-CHO, dyads 2 and 3). The integrated peak
areas ratio is in agreement with the empirical formula and the
1
AB3 asymmetry. The H NMR spectrum of 1-CHO exhibited
six doublets in the aromatic region corresponding to the meso-
phenyl group protons, two doublets at 7.69 and 8.13 ppm for the
6 protons of the ortho-CHAr (H3) and two doublets at 8.21 and
8.32 ppm for meta/para-CHAr (H4,5). The two doublets at 8.21
and 8.32 ppm are allocated to CHAr (H1 and H2). The eight β
Results and Discussion
pyrrole hydrogen atoms were attributed to two doublets at 8.71
(CH7-pyrrole) and at 8.79 (CH6-pyrrole) as well as a single peak
Synthesis and Chemical Characterization
at 8.83 ppm (CH8-pyrrole). Characteristic singlet peak at
1
0.40 ppm typical of the proton of the formyl groups and the
1
The synthesis of the novel porphyrin-fullerene dyads (1–3) was
achieved in two steps, starting from mono-meso-brominated por-
phyrins, 1-Br or 2-Br [31]. 1-Br was prepared by a statistical
Adler reaction using a mixture of benzaldehyde and 4-
bromobenzaldehyde. As chromatographic separations of 1-Br
from the concomitantly formed meso-tetraphenylporphyrin
inner NH shielded protons were observed at −2.84 ppm. H
NMR spectrum of dyad 1 in CDCl /CS solution is less resolved
3
2
due to the presence of C unit, the aromatic signals are broader,
60
but exhibit undoubtedly the expected features and integration
ratios. CS is used as a co-solvent to increase the solubility of
2
the dyads. The aromatic protons for the porphyrin moiety were
observed at 7.72 ppm (b, 12H, CH4,5-Ar-phenyl), 8.15 ppm (b,
6H, CH3-Ar-phenyl 8.22 (b, 4H, CH1, 2-Ar-phenyl) and 8.77
(TPP) proved to be really tedious, a clean mixture of 1-Br and
TPP was engaged in the next step of the synthesis. 2-Br was
prepared by an alkylation reaction on the trihydroxylated
monobrominated derivative 2-Br(OH)3 [5] whose preparation
and separation from the symmetrical tetrahydroxylated porphyrin
derivative was quite easy thanks to their significantly different
polarity. 1-Br (mixed with TPP) and 2-Br were subjected to a
bromine-lithium exchange reaction previously developed in our
group [29], yielding mono-formylporphyrins 1-CHO or 2-CHO
in 35% and 13% respectively, allowing the introduction of a
formyl group directly on the para position of the meso-phenyl
substituent. It has to be noticed that the reactivity of 1-Br is
higher than those of 2-Br, as shorter reaction time was needed
to complete the reaction in higher yield. 2-Br was also subjected
to a Sonogashira reaction with 4-ethynylbenzaldehyde in the
presence of Pd(OAc) , PPh , and dry diisopropylamine/THF
),
(b, 8H, CHpyrrole). Signals of the inner NH were observed at
−2.88 ppm. The signals assigned to the pyrrolidine ring can be
clearly observed as two doublets at 4.34 and 5.04 (Ha and Hb), a
singlet at 5.19 ppm (Hc) and a singlet at 3.09 ppm singlet corre-
sponding to N-CH , all in agreement with the literature [34].
3
Molecular Orbital Levels and Energy Gaps
The band gap energy values define the energy necessary for the
transition of an electron from the HOMO to the LUMO.
Molecular orbital energy levels and HOMO-LUMO energy gaps
give precious information on the potentiality of the dyes for
many applications such as solar cells or photosensitiser [35].
The band gap energy was calculated from LUMO and HOMO
values obtained by CV as well as theoretical calculations.
Calculations of the molecular orbital energy levels and of the
energy gaps were performed to quantify the effects of substituent
and of the spacer.
2
3
(1:1 volume), yielding 24% of 3-CHO, in which the formyl
group is away from the porphyrin macrocycle by a
phenylacetylide spacer.
The Prato reaction [24, 25], a powerful tool to functionalize
fullerene C60 sphere by simply refluxing it in the presence of
an aldehyde in toluene, led to 1 in 62%, 2 in 45% and 3 in 35%
yields (Scheme 1).
Electrochemistry Electrochemistry can be used to characterize
and determine the molecular orbital levels and energy gaps of a
molecule. C is one of most popular electron acceptor (A) com-
1
All compounds were characterized by IR, H NMR and UV-
60
Vis spectroscopies. The IR spectra of formyl-porphyrins 1–3-
pound [36] with up to six one-electron reductions whereas free
base porphyrins are well-known donors (D) with two oxidations,
and particularly with small difference [37] between first and sec-
ond oxidation when substituents located on the para position of
−1
CHO show a typical sharp and intense peak at 1694 cm which
is characteristic of formyl vibration (See supporting information).
C60 possesses 42 fundamentals of various symmetries, four of

J Fluoresc
N
N
N
O
O
N
H
N
N
N
N
NH
HN
N
N
NH
HN
H
N
O
O
O
O
1
2
3
ii
CHO
ii
ii
CHO
N
H
CHO
O
O
N
N
H
N
N
N
N
NH
HN
NH
HN
N
1-CHO
O
O
O
O
i
O
Br
2-CHO
3-CHO
Br
N
N
Pd(OAC)2
PPh3
Diisopropilamine/THF
NH
HN
N
H
i
N
N
H
N
CHO
O
O
2-Br
1-Br
mixture tedious
to separate
Br
TPP
K2CO3, DMF
propionic acid
reflux
HO
Br
CHO
Br
CHO
OH
H
N
N
N
CHO
Br
CHO
H
N
NH
HN
propionic acid
reflux
HO
OH
2-Br(OH)3
Scheme 1 General synthetic pathway i) n-BuLi, Et O, DMF, Ar, −50 °C, ii) sarcosine, toluene, reflux
2
meso-phenyls moieties. The electrochemical behaviour of dyads
–3, TPP and C60 were investigated in o-dichlorobenzene/ace-
tonitrile (4:1) mixture by using cyclic voltammetry (CV)
Fig. 3).
The oxidation and reduction potentials of dyads 1–3 were
summarized in Table 1, and match previous literature reports
with peaks attributable to the fullerene moieties while the remain-
ing ones are due to the porphyrin [38]. Dyad 1 exhibited four
reduction and two oxidation peaks between −2.5 V and +1.0 V.
The first oxidation was observed at 0.572 Vand, the second one
at 0.880 V which were arose from oxidations of porphyrin skel-
eton. Dyad 2 and 3 showed very similar reduction patterns with
small potential shifts. Dyad 2 had lower first oxidation potential
phenyls of the porphyrin core that caused the 0.156 V shift to
negative potentials. First oxidation of dyad 3 occurred at 0.481 V
which was higher than that of dyad 2 (0.416 V) but lower than
that of dyad 1 (0.572 V) due to the presence of the
phenylacetylene spacer which in return avoid lowering the po-
tential. In terms of reductions, the observed first and second
reductions of the dyads (for example at −1.134 V and
−1.536 V for dyad 1) correspond to the first and second reduction
of fullerene whereas the third one corresponds to the first reduc-
tion of the porphyrin macrocycle. However, dyad’s fourth reduc-
tion was attributed to third reduction of C and second reduction
1
(
60
of porphyrin which were overlapped at −2.076 V. Finally, the
electron-donating nature of the three hexyloxy moieties caused
low shifts to negative potentials, and phenylacetylene spacer shift
to positive potentials even if the shift was very slow.
(0.416 V) than dyad 1 did (0.572 V), as anticipated, due to the
electron-donating nature of the three hexyloxy moieties on meso-

J Fluoresc
1
Fig. 2 H NMR of 1-CHO in CDCl
3
and dyad 1 in CDCl /CS
3 2
(1:1, v:v)
HOMO and LUMO energy levels of the three dyads and of
TPP were calculated using the first oxidation and first reduc-
tion values of the dyads in o-dichlorobenzene/acetonitrile
(4:1) vs the HOMO level of ferrocen at −4.8 eV according to
Eqs. 1 and 2 [39].
ÂÀ
Á
Á
Ã
Ã
EHOMO ¼ − Eox−E
ELUMO ¼ − Ered−E
þ 4:8
þ 4:8
ð1Þ
ð2Þ
1
=2ðferroceneÞ
ÂÀ
1
=2ðferroceneÞ
As can be seen from Table 2, substituent and spacer affect-
ed the band gap very efficiently. In presence of fullerene moi-
ety, band gaps remarkably decreased. The lowest band gap
a
Table 1 Redox potentials of processes observed by cyclic
b
+
voltammetry (V vs Fc/Fc )
E
red4
E
red3
E
red2
E
red1
E
ox1
E
ox2
TPP
-
-
-2.032
−1.433
−1.536
−1.548
−1.514
−1.704
−1.033
−1.134
−1.156
−1.108
0.530
-
0.815
-
C
1
2
3
60
-2.354
−2.076
−2.098
−2.039
−1.890
−1.723
−1.758
−1.701
0.572*
0.416
0.481*
0.880*
0.690
0.700
a
All potential values as E1/2 = (Epa + Epc)/ 2 and Epa for * as exception. b
Measured as 0.25 mManalyte in o-dichlorobenzene/acetonitrile (4:1),
0
4 4 3
.1 M Bu NClO , scan rate 100 mV/s, Ag/AgNO (0.01 M) reference
Fig. 3 Cyclic voltammetry profiles of TPP, fullerene C60 and dyads 1–3,
recorded in o-dichlorobenzene/acetonitrile (4:1) at 0.25 mM
electrode, Pt counter electrode, glassy carbon electrode, at room
temperature

J Fluoresc
Table 2 Molecular orbital energy
levels and HOMO–LUMO
energy gaps determined from
cyclic voltammetry (CV) and
theoretical (th) calculations
Compound HOMOCV
eV)
LUMOCV
(eV)
HOMO-LUMOCV
(eV)
HOMOth
(eV)
LUMOth
(eV)
HOMO-LUMOth
(eV)
(
TPP
-5.330
−5.372
−5.216
−5.281
−3.096
−3.666
−3.644
−3.692
2.234
1.706
1.572
1.589
−5.159
−5.217
−4.997
−5.006
−2.558
−3.582
−3.544
−3.560
2.601
1.635
1.452
1.445
1
2
3
was found for molecule 2, and this information matches the
shortest absorption wavelength maxima of 2 compared to 1, 3
and TPP (see Table 3).
The double bond on a hexagon-hexagon edge of the C is
60
3
opened to convert the hybridization to sp at the interface. In a
sense the phenyl ring is the bridge between the porphyrin core
and the C . The bridge contains an additional phenyl ring in
6
0
Theoretical Calculations Structure optimization of the inves-
tigated dyads was performed first. Our calculated atomic
structures of the dyads are depicted in Fig. 4 as ball-and-
stick models. The structure optimizations were started from
several initial configurations with reasonable bond lengths
and continued until all force components are lower than
dyad 3, and the phenyl rings are joined by triple bonded C
atoms. In the optimum structure, the two phenyl rings in the
bridge are almost in the same plane. However, we observe that
the rotation of the phenyl rings with respect to each other costs
less than 20 meV and our structure optimizations go through
very shallow energy landscape before reaching to this config-
uration. Therefore, at nonzero temperature the two phenyl
rings may not be in the same plane due to thermal activation.
After obtaining fully relaxed atomic structures, electronic
structures of the dyads 1–3 and TPP were calculated using
GGA, HSE06, and B3LYP exchange-correlation functionals.
As expected, GGA underestimates energy gaps, and this is
corrected by hybrid Exchange-correlation functionals of
B3LYP and HSE06. The HOMO and LUMO levels and en-
ergy gaps listed in Table 2 are calculated in B3LYP Exchange-
correlation functional, which gives the best agreement with
the experiment. Frontier orbitals of the three dyads are shown
in Fig. 4 as 3D iso-density contour plots, where HOMO levels
are indicated by blue-green colors and orange-turquoise colors
are for LUMO levels. There are also several empty states
above the LUMO that are localized on the C60 moiety, and
several filled states below the HOMO level that are localized
on the porphyrin core. The spatial localization of the frontier
orbitals shown in Fig. 4 confirms that the porphyrin act as
donor and the fullerene as acceptor, corroborating the cyclic
voltammetry measurements.
0
.01 eV/Å in conjugate gradient algorithm. For our purposes,
the overlap between the electronic states localized on the por-
phyrin and the π-conjugated bridge states of 3 is important
since the π-conjugated bridge states are expected to be inde-
pendent from the electronic states of the C . The electron
6
0
transfer between the porphyrin core and the C60 moiety
through the bridge is closely related to the dihedral angles
between the phenyl rings of the bridge and the porphyrin core.
Although the phenyl rings were chosen in the plane of
porphyrin cores, the phenyl rings are rotated during the struc-
ture optimizations. On each dyad, a porphyrin core is
surrounded by 4 phenyl rings, and the dihedral angles between
the porphyrin and phenyl planes were determined to be 66° in
all structures. All calculations with a lower initial dihedral
angle value ends up with this dihedral angle. We also find that
the cost of rotating the phenyl rings to increase the dihedral
angle is actually below the thermal energy of the room tem-
perature. Therefore, at nonzero temperatures the dihedral an-
gles may also be larger than the optimum value due to thermal
vibrations. Because of this low energy threshold for phenyl
ring rotations, the structure optimizations took at least thou-
sand molecular dynamics steps. Our results indicate that the
attachment of hexyloxy groups in 2 and 3 compared to 1 do
not significantly affect the dihedral angles. The phenyl ring is
The LUMO levels for all the dyads, shown in Fig. 4, are
3
strictly localized on the C60 moiety because the sp bonded
carbon atoms help to confine the electronic states of the C60
2
3
with sp character. The sp bonding at the interface of the
bridge and the fullerene isolates the electronic states of the
3
connected to the C60 moiety through a sp bonded C atom.
Table 3 Maximum absorption wavelengths (λmax) and logarithmic values of molar extinction coefficients (ε) of dyads 1–3 and TPP in toluene
Compound
Soret or B(0–0)
Qy(1–0)
Qy(0–0)
Qx(1–0)
Qx(0–0)
TPP
419 (5.63)
420 (5.69)
424 (5.36)
424 (5.46)
514 (4.32)
515 (4.41)
518 (4.05)
518 (4.08)
548 (3.95)
549 (4.08)
555 (3.86)
555 (3.96)
591 (3.78)
591 (3.89)
595 (3.55)
595 (3.60)
648 (3.66)
648 (3.74)
651 (3.50)
652 (3.57)
1
2
3

J Fluoresc
Fig. 4 Left: optimized geometries of dyads 1, 2 and 3. Right: HOMO-LUMO orbital schemes as resulted from DFT calculations displaying the donor
and acceptor character of the dyads (the HOMOs and LUMOs are presented in navy blue-green and in orange-turquoise, respectively)
bridging phenyl rings, which are π-conjugated states near the
HOMO and LUMO, from the fullerene states. Therefore,
probability of charge transfer from the C60 moiety to the brid-
ges is greatly reduced by this atomic configuration, playing an
important role in delaying the deactivation of the electronic
excited state through a radiative decay.
Unlike LUMO levels, HOMO levels of the dyads are local-
ized on the porphyrin core and have π-state character. Since the
phenyl rings are not in the plane of porphyrin core, the HOMO
levels have very small contribution on the phenyl rings. The π-
conjugated network is hindered by the rotation of the phenyl
ring and thus the large dihedral angle of 66° is very crucial in
isolating the HOMO level from the π-conjugated electronic
states of the bridging phenyl rings. In fact, there would be no
contribution from the phenyl ring to the HOMO if the dihedral
angle was 90°, for which the phenyl ring is perpendicular to the
porphyrin plane. In view of the fact that the dihedral angles
larger than the optimum value is easily accessible by thermal
activation as mentioned above, the HOMO level has very small
overlap with the electronic states of the bridge. This also re-
duces the probability of radiative decay, giving time for the
energy transfer to vibrational modes. Therefore, the large dihe-
dral angle is a key structural parameter affecting the
photophysical and photochemical properties.
In dyad 3, the addition of a second phenyl ring to the bridge
farther reduces the overlap between the HOMO level and the

J Fluoresc
π-conjugated bridge states since the HOMO does not pene-
trate to the second phenyl ring in dyad 3, as shown in Fig. 4.
Even a minute dihedral angle between the two phenyl rings of
the bridge is enough to interrupt the π-conjugation network.
Since even larger dihedral angles are possible under thermal
excitations, the overlap between HOMO and the electronic
states of the bridge is further reduced in dyad 3. Therefore
the inclusion of phenylacetylene in the bridge should suppress
radiative decay, and allow better energy transfer to the vibra-
tion modes. On the basis of our calculations, we expect the
highest photochemical activity for dyad 3. In addition, it is
expected that all dyads should have higher photochemical
reactivity than TPP because of the reduced overlap between
the HOMO and LUMO levels, and the isolation of the bridge
states from these frontier orbitals, which is promoted by a
proved to be appropriate for such kind of measurements [40,
41]. The relevance of this choice had to be confirmed by
checking the non-aggregation of the dyads 1–3 and the refer-
ence TPP to prevent aggregation-induced artefact results, as
aggregation affects luminescence properties. Table 3 summa-
rizes the UV-Vis bands and the extinction coefficients for
porphyrin-fullerene dyads 1–3 as well as TPP as reference
compound. The spectra exhibits a strong and sharp Soret band
(at ~420–424 nm) and four weak Q-bands in the visible region
between 515 and 652 nm due to a S0-S1 transition typical of
free porphyrin. Beer-Lambert law plots (Fig. 5) are linear be-
tween 1 and 8 μM concentration range, and thus show no
evidence for aggregation in this range.
The order of their maximum wavelengths was
3 = 2 > 1 > TPP whereas the extinction coefficients show a
quite different trends: 1 > TPP > 3 > 2 with respective log ε
values of 5.69, 5.63, 5.46, 5.36. The small red shift between
TPP and the fullerene-dyads 1–3 reveals a relatively shorter
HOMO-LUMO gap. This effect is more pronounced when
electron donating hexyloxy chains (of about 5 nm for TPP
compared to 2 and 3) are substituted on the porphyrin moie-
ties. These observations are in accordance with the energy
levels of the frontier molecule orbitals determined via electro-
chemical measurements.
3
large dihedral angle and the sp bonded C atom.
Our calculated HOMO-LUMO energy gaps of 1.635,
1
.452, and 1.445 eV for dyads 1, 2, and 3 respectively, are
in good agreement with our experimentally measured values
of 1.706, 1.572, and 1.589 eV. Our calculated HOMO and
LUMO levels, listed in Table 2, indicate that the appearance
of the acceptor level of the fullerene within the energy gap of
TPP reduces the gap to 1.635 eV from 2.601 eV, the value for
TPP. While introducing substituents do not affect the LUMO
level located on the fullerene, the HOMO level is shifted up by
the hexyloxy substituents, and thus reduces the energy gap, in
agreement with our cyclic voltammetry results. This reduction
of the energy gap decreases the lifetime of the excited state,
and thus should decrease the photochemical activity since a
faster electron transfer hinders the energy transfer to vibra-
tions. However, in dyad 3, the atomic structure plays a crucial
role to prevent a radiative decay and thus should improve the
photochemical activity. In case these structural factors domi-
nate, the best photochemical activity should appear for dyad 3.
We expect better photochemical activity if the bridge contains
longer phenylacetylene chain. Our molecular design provides
non-overlapping donor and acceptor levels with a low electron
transfer probability to allow a higher energy transfer to vibra-
tion modes. Our calculations indicate that the length of the
bridge has very small effect on the energy levels and energy
gaps, while the spacer is most likely to have an effect.
Steady-State Fluorescence-Based Oxygen Sensitivity
As the fluorescence of free-base or metalloporphyrins is
known to be strongly quenched by oxygen, either in solution
or in solid matrices (thin films or nanofibers) [6, 7], they are
interesting candidate for optical oxygen sensors. Steady-state
fluorescence data, excitation and emission wavelengths, the
Stokes shifts and the fluorescence quantum yields for dyads
1–3 and TPP were first determined and summarized in
Table 4. The positions of the fluorescence emission maxima
are very similar for dyads 1–3 and TPP. A noticeable
quenching, 97%, 92% and 98% of pophyrin fluorescence by
fullerene was observed for 1, 2 and 3, respectively. The fluo-
rescence quantum yields Φ of the dyads 1, 2 and 3 were
F
found to be 0.003, 0.008 and 0.002, which can be considered
as quasi-nul whereas the value for TPP (used as a reference
standard) is 0.12 in DMF [42]. The presence of hexyloxy
Choice of the Solvent for Photophysical
and Photochemical Measurements
chains (comparison of 2 with 1) increased Φ but on the other
F,
hand dyad 3 exhibited the lowest Φ value in the series. This
F
may be attributed to the spacer as generally triplet bonds shift
the emission maxima to longer wavelength and decrease ΦF.
The oxygen sensing properties of TPP and dyads 1–3 were
investigated in toluene and the results are presented in Fig. 6.
Despite the strong fluorescence quenching, dyads 1, 2 and 3
shows still oxygen sensing ability. Especially the presence of
three hexyloxy donating group on the porphyrin macrocycle
influence the oxygen sensitivity, dyad 2 was the best oxygen
sensing dyad in the series, even more sensitive than TPP (see
Our purpose is to investigate the interactions of the dyads at
their excited states with molecular oxygen, which implies to
promote energy transfer between the porphyrin and the fuller-
ene units, and to limit or inhibit photo-induced electron trans-
fer generating a charge separation, as these two events are
competitive. The nature of the solvent chosen for
photophysical and photochemical measurements is known to
affect their outcome. Non-polar solvents such as toluene

J Fluoresc
Fig. 5 Electronic absorptions of TPP and dyads 1–3 at 1, 2, 4, 6 and 8 μM. Inset: absorbance values vs concentration
Table 4), reaching an I0/I100 value of 2.45. The presence of the
phenylacetylene spacer in dyad 3 decreased the I0/I100 ratio
from 2.45 to 1.50, indicating a negative effect on the
fluorescence-based oxygen sensitivity.
triplet state is reported as 0.98 electron volts (eV), and it fits the
energy gaps of porphyrins as well as the dyads 1–3 as calculated
from cyclic voltammetry measurements [43]. In our study, ΦΔ
values of the dyads were determined by monitoring the
phosphorescence of singlet oxygen at ~1270 nm in toluene. In
more polar solvents, the stabilization of charge transfer state takes
Singlet Oxygen Generation
place, decreasing the efficiency of singlet oxygen generation
1
Singlet oxygen generation is crucial in photodynamic process-
es, and a good photosensitiser must exhibit high singlet oxy-
[18]. Phosphorescence intensities of O vs absorbance for
2
TPP and the dyads 1–3 were presented in Fig. 7, and the
gen quantum yield (Φ ). According to literature (from transi-
quantum yields were summarized in Table 4. Φ values were
Δ
Δ
tion absorption/luminescence measurements), in non-polar
solvent like toluene, the porphyrin-fullerene dyad behaviour
is as follow: the singlet state of porphyrin is quenched by
singlet-singlet energy transfer to the fullerene C , The singlet
calculated using TPP as a reference (Φ = 0.63 in toluene) [44],
Δ
and appeared to be strongly affected by the presence of the
fullerene, as all dyads have higher ΦΔ values than TPP, with
the following trend: TPP (0.63) < 2 (0.70) < 1 (0.78) < 3 (0.81).
6
0
state of fullerene undergoes intersystem crossing to give the
triplet state of fullerene, and this species have a high ability to
react with triplet oxygen to form singlet oxygen.
Dyad 3 exhibited the highest Φ respect to dyads 2 and 1, in
Δ
accordance with the lowest fluorescence quantum yield of 3
compared to 1 and 2. It can be concluded that the presence of
phenylacetylene linker between porphyrin and fullerene have a
positive effect on singlet oxygen generation as the longer
The energy difference for the transition between the lowest
energy of O in the singlet state and the lowest energy in the
2
Table 4 Photophysical and photochemical properties of TPP and dyads 1–3 in toluene (λ em ma x: maximum emission wavelength: Φ
: fluorescence
F
0
quantum yield and I /I100: parameter exhibit oxygen sensitivity and singlet oxygen quantum yield)
em
max1
em
max2
Compound
λ
(nm)
λ
(nm)
Φ
F
Oxygen response (I
0
/I100
)
Φ
Δ
4
2
TPP
651
653
653
653
711
715
715
715
0.120
0.003
0.008
0.002
1.79
1.35
2.45
1.50
0.63
0.78
0.70
0.81
1
2
3

J Fluoresc
…
Fig. 6 Fluorescence spectra of TPP and the dyads 1–3 in toluene upon exposure to oxygen: 0% O
2
(−), 21% O
2
2
(−-), 100% O ( )
distance between the donor and acceptor should favour the ISC
transfer [23]. It should be also noted that for simple fullerene
derivatives ΦΔ is generally >0.9 [45]. These observations are
somewhat opposed to those made for dyad with non-
conjugated spacer [17] but in accordance with other reported
trends [18].
Lifetime of singlet oxygen is an intrinsic characteristic like
emission maxima of singlet oxygen (~1270 nm). It means that
lifetime of singlet oxygen will not change depending on mol-
ecules but will depends on the medium. However, the count
rate during the lifetime of singlet oxygen experiment will
change from one molecule to another molecule in function
of time.
Determination of singlet oxygen luminescence decay for
TPP and dyads 1–3 in toluene have been recorded upon ex-
citation by a spectra LED at 417 nm. Lifetime of singlet oxy-
gen in toluene was found to be 31.4 ± 1.62 μs for all dyads and
TPP, in accordance with the literature value; 29.4 ± 2.94 μs
[46].
During 150 μs, the obtained counts were found to be 9500,
8700, 9800 and 7800 for dyads 1, 2, 3 and TPP, respectively.
Dyad 3 exhibited the highest counts confirming that 3
Fig. 7 Phosphorescence
1
intensities of O
2
(at 1270 nm) vs
absorbance for TPP and dyads 1–
ex
3
.λ :405 nm

J Fluoresc
1
generates more O . These data confirm that our porphyrin-
spectrometer with an attenuated total reflection (ATR) acces-
sory featuring a zinc selenide (ZnSe) crystal. H NMR spectra
2
1
fullerene dyad, and in particular dyad 3, is good candidates for
biomedical applications, especially after making them water-
soluble as recently reported for related derivatives [47].
were recorded on a Varian 500 MHz spectrometer (with the
deuterated solvents as the lock and tetramethylsilane as the
internal reference). MALDI-MS spectra were acquired in lin-
ear modes with an average of 50 shots on a Bruker Daltonics
Microflex mass spectrometer equipped with a nitrogen UV-
Laser operating at 337 nm, using 2,5-dihydroxybenzoic acid
or nitroanthracene as the matrix.
Conclusions
A set of three porphyrin-fullerene dyads has been designed
and prepared, thanks to a facilitated synthetic procedure of
formylporphyrins, coupled afterwards to fullerene by the
Prato reaction. Two structural parameters were varied: the
presence of electron-donating hexyloxy chains at the para
position of the meso-phenyl, and the presence of a
phenylacetylene spacer between the porphyrin macrocycle
and the fullerene. The effect of these structural variations on
the electrochemistry, molecular orbital levels and energy gaps,
ground state absorption, fluorescence and singlet oxygen gen-
eration of the dyads was comparatively investigated. These
properties were interpreted with the final purpose to determine
their suitability as oxygen sensors or photodynamic
photosensitisers. Dyad 3 containing phenylacetylene spacer
was found to be the best singlet oxygen generator as
phenylacetylene increase the ISC process, whereas dyad 2
with hexyloxy chains but without spacer exhibited higher ox-
ygen sensing ability. Probably because, when hexyloxy
groups are introduced in the molecule, the HOMO-LUMO
gap is affected noticeably. Dyad 2 could be a good candidate
for further incorporation into doped microfilms/ nanofibers.
Dyad 3 with hexyloxy chains and phenylacetylene spacer
could be use in a next step in biomedical photodynamic ap-
plications making them water-soluble, retaining the alkyloxy
chain pattern. Substituting the hexyloxy chains by polyethyl-
ene glycol chains could be a suitable option.
5-(4-Bromophenyl)-10,15,20-Triphenylporphyrin (1-Br)
4-bromobenzaldehyde (0.01 mol, 1.8 g), benzaldehyde
(10.2 mL, 0.1 mol, 10 eqv.) were added to refluxing propionic
acid (250 mL), then pyrrole (7.6 mL, 0.11 mol, 11 eqv.) was
added to the reaction mixture. After refluxing for 1 h, the
reaction mixture was cooled to room temperature and filtered.
The filter cake was washed with methanol and hot water. The
resulting crude mixture were purified on silica gel with n-
hexane/DCM 2:1, 1/1 eluent system. 1-Br + TPP could not
be separated because of their close polarity. A clean mixture of
1-Br + TPP (3 g) was obtained.
5-(4-Bromophenyl)-10,15,20-Tris(4-(Hexyloxyphenyl)
Porphyrin (2-Br) 5-(4-bromophenyl)-10,15,20-
tris(4-(hydroxy)phenylporphyrin (2.56 mmol, 1.9 g), hexyl
bromide (51 mmol, 7.1 mL, 20 eqv.) and K CO (20 g) were
2
3
stirred in DMF (100 mL) at 60 °C over night and the reaction
mixture was poured in water then washed with ethanol.
Purification was achieved by column chromatography on sil-
ica gel with a gradient of eluent from DCM/hexane (1:1).
−1
Yield 43% (2.4 g). FT-IR: ν (cm ). 3315 (NH), 2950 (CH
Ar), 1465 (C = N), 1399 (=C-N), 1174 (C-Hpyrrole), 966
1
porphyrin ring, 787 pyrrole ring, 726 (NH bending). H
NMR: δ (ppm), CDCl , −2.76 (s, 2H, NH), 1.02 (br, 9H,
3
methyl-H), 1.27 (br,6H, CH (12), 1.49 (br,6H, CH (11),
2
2
1
.67(m, 6H, CH (10), 2.04 (m, 6H,CH (9), 4.33 (t, 6H,
2 2
Experimental
Synthesis
CH (8), 7.53 (t, 2H, CHAr-phenyl), 8.13 (br, 2H, CHAr-phenyl),
2
8
.49 (m, 12H, CHAr-phenyl), 8.81–8.89 (br, 8H, CHpyrrole).
MS-MALDI-TOF (m/z): C H BrN O [calcd]: 994.131,
6
2
65
4 3
+
[
found]: 995.301 [M + H] . UV-vis: λ, nm, (CHCl ) 418,
3
Materials and Methods Starting materials were of reagent
grade quality, purchased from Aldrich for Pyrrole (reagent
grade 98%), n-Butyllithium 2.5 M solution in hexane and
anhydrous N,N-dimethylformamide store over molecular
sieve (Aldrich 40,248–250). Whereas diethylether dried max
512, 547, 588, 644.
5-(4-Formylphenyl)-10,15,20-Triphenylporphyrin (1-
CHO) A TPP/1-Br mixture (400 mg) was placed in a
Schlenk tube and was dried by purge-and-refill for at least
three times (nitrogen(g)/vacuum). Under nitrogen (g), dry
diethylether (50 mL) was added with a syringe at room tem-
perature. The purple solution was placed in a liquid nitrogen-
acetone bath at −50 °C for 10 min. And a 5 mL of n-butyl
lithium in hexane (2.5 M; 6.25 mmol) was added, giving rise
to a green resulting mixture that was further stirred for 3 h at
−50 °C. Then, dry DMF (5 mL, 37.5 mmol) was added. The
cooling bath was removed and the green-blue reaction mixture
0
.005% H O (Merck 100,929) and propionic acid were pur-
2
chased from Merck. Fullerene-C , N-Methylglycine
6
0
(
sarcosine), diisopropylamine, 4-ethynylbenzaldehyde were
obtained from Aldrich. Preparative separations were per-
formed by silica gel column chromatography Merck-60 (43–
6
3 mesh) and TLC on aluminum sheets precoated with silica
gel 60F254 (Merck). IR spectra were recorded between 4000
and 600 cm− using a Perkin Elmer Spectrum 100 FT-IR
1

J Fluoresc
was stirred for 3 h more. At room temperature, HCl 5%
250 mL) was added and vigorously stirred for 15 min. The
1.66(b, 6H, CH (9), 2.01 (b, 6H,CH (8), 4.27(b, 6H,
2
2
(
CH (7), 7.30(b, 6H, CH (5
), 7.83(b, 2H, CH (2
2
2
-Ar-phenyl
2
Ar-phe-
mixture was neutralized by NH OH. The resulting pink-red
nyl),7.96 (b, 4H, CH(3,4Ar-phenyl), 8.14 (b, 6H,CH(6Ar-phenyl),
8.27 (b, 2H, CH(1Ar-phenyl), 8.86 (b, 2H, CHpyrrole), 8.91 (s,
6H, CHpyrrole), 10.08 (s, 1H, CHO). MS-MALDI-TOF (m/z)
C H N O [calcd]: 1043.365, [found]: 1043.227 [M + H].
4
emulsion was extracted with chloroform, dried with Na SO
2
4
and evaporated to dryness at 45 °C. 1-CHO free porphyrin
yield 35% 70 mg, calculated on the basis that 200 mg of 1-Br
(
7
0 71 4 4
were present in the TPP/1-Br mixture, as 200 mg of TPP were
recovered) was purified by column chromatography eluted by
diethyl ether/ DCM (1:9). Unreacted TPP (0.2 g) was recov-
UV-vis (λ, nm) (CHCl ) 425, 519, 556, 595, 652.
3
General 1,3-Dipolar Cycloaddition Procedure for Dyads
1–3 A mixture of C60 (8 mg, 0.01 mmol), sarcosine (2 mg,
0.02 mmol, 2 eqv.), and 0.02 mmol (2 eqv) of 1-CHO
(12 mg), 2-CHO (18 mg), 3-CHO (20 mg) in toluene
(60 mL) was refluxed for 2–5 h, then the solvent was removed
under reduced pressure. The crude product was dissolved in
toluene and purified over a silica gel column using toluene/
−
1
ered. FT-IR, ν (cm ): 3313 (NH), 3053 (CH ), 1698
Ar
(
(
C = O), 1601 (C = Cphenyl), 1568 (C = Cpyrrole), 1472
C = N), 1154, (CHpyrrole), 964(CH porp. Ring), 794 (CH pyr.
1
Ring), 720 (NH bending). H NMR δ (ppm) CDCl : −2.84 (s,
3
2
2
8
H, NH), 7.69 (m, 9H, CH(4,5), 8.13 (d, 6H, CH(3), 8.21 (d,
H, CH(2), 8.32 (d, 2H, CH(1), 8.71 (d, 2H, CH(7-pyrrole),
.78 (s, 4H, CH(8-pyrrole), 8.79 (d, 2H, CH(6-pyrrole), 10.31
CS (2:1 then 1:1) as the eluent.
2
(
6
s, H, CHO). MS-MALDI-TOF (m/z) C H N O [calcd]:
45 30 4
42.762, [found]: 643.774 [M + H] . UV-vis (λ, nm)
+
−1
Dyad 1 Yield 62%, 15 mg. FT-IR ν (cm ): 3314 (NH), 2920
CHAr), 1463 (C = N), 1080 (C–Hpyrrole), 964 (C–Hporp.
ring), 796 (C–Hpyr. ring), 72 (NHbending), 1185, 575, 525
(
CHCl ) 420, 515, 559, 592, 649.
3
(
5
(
- ( 4 - F o r m y l p h e n y l ) - 1 0 , 1 5 – 2 0 - T r i s ( 4 -
Hexyloxyphenyl)Porphyrin (2-CHO) The same procedure
as for 1-CHO porphyrin was applied, starting from 2-Br
1
(
C ). H NMR δ (ppm), CS :CDCl (1:1 v/v), −2.88 (s, 2H,
6
0
2
3
NH), 3.09 (s, 3H, N-methyl-H), 4.34, 5.04, 5.19(d, d, s, pyr-
rolidine-H), 7.72 (b, 12H, CH(4,5Ar-phenyl), 8.15 (b, 6H,
CH(3Ar-phenyl), 8.22 (b, 4H, CH(1,2Ar-phenyl), 8.77 (b, 8H,
CHpyrrole). MS-MALDI-TOF (m/z) C107H N [calcd]:
(
2
1
0.2 g, 0.2 mmol), yielding 0.026 g (0.027 mmol, 13%) of
-CHO. FT-IR, ν (cm ): 3312 (NH), 2925 (CHAr),
−
1
35
5
702(C = O), 1506 (C = Cphenyl), 1465 (C = N), 1173,
1
390.492, [found]: 1390.152 [M + H]. UV-vis (λ, nm)
1
(
CHpyrrole), 966 (CH porph. Ring), 801 (CH pyr. Ring). H
(toluene) 422, 516, 551, 593, 651.
NMR: δ (ppm), CDCl –2.72 (s, 2H, NH), 1.01 (b, 9H, meth-
3
yl-H), 1.48,1.55 (b,12H, CH (11,12), 1.66 (m, 6H, CH (10),
2
2
−
1
Dyad 2 Yield 45%, 15 mg. FT-IR ν (cm ): 3311 (NH), 2919
CHAr), 1465 (C = N), 1080 (C–Hpyrrole), 965 (C–Hporp.
2
8
8
2
.01 (m, 6H,CH (9), 4.27 (t, 6H, CH (8), 7.31 (d, 6H, CH (3),
2 2
(
.12 (d, 6H, CH(4), 8.31 (d, 2H, CH(2), 8.41(d, 2H,CH(1),
.78 (d, 2H, CH(5-pyrrole), 8.90 (s, 4H, CH (7-pyrrole), 8.92 (d,
H, CH(6-pyrrole), 10.41 (s, 1H, CHO). MS-MALDI-TOF
1
ring), 798 (C–Hpyr. ring), 732 (NHbending), 574, 526 (C ). H
NMR δ (ppm), CS :CDCl (1:1, v:v), −2.80 (s, 2H, NH),
.36, 1.39, 1.51 (b, 27H, CH (11,12, CH3), 1.68(b,
CH (10), 2.01 (b,CH (9), 3.11 (s, 3H, N-methyl-H), 4.33,
60
2
3
1
(
m/z) C H N O [calcd]: 942.508, [found]: 942.654 [M +
2
6
3 66 4 4
H]. UV-vis (λ, nm) (CHCl ) 424, 519, 555, 595, 652.
2
2
3
5
.05, 5.14 (d, d, s, pyrrolidine-H), 4.25(b, 6H, CH (8), 7.12
2
(
d, 2H, CH(2Ar-phenyl), 7.25 (d, 6H,CH(3Ar-phenyl), 7.53 (d, 2H,
5
(
-(4-Formylphenylethynyl)-10,15,20-Tris(4-
Hexyloxyphenyl)Porphyrin (3-CHO) In tri-necked reac-
tion flask, 2-Br (300 mg, 0.3 mmol), palladium(II) acetate
4 mg, 0.17 mmol) and triphenylphosphine (12 mg) were dis-
solved in degased mixture of dry diisiopropylamine and THF
35 mL/35 mL) under argon. 4-ethynylbenzaldehyde (0.117 g,
CH(1Ar-phenyl), 8.09 (d, 6H, CH(4Ar-phenyl), 8.85 (s, 8H,
CHpyrrole). MS-MALDI-TOF (m/z) C125H N O [calcd]:
1
71
5 3
690.975, [found]: 1690.632 [M + H]. UV-vis (λ, nm)
toluene) 424, 518, 555, 595, 651.
(
(
(
0
2
−1
.9 mmol, 3 eqv.) was added and the solution was refluxed for
days. Water (10 mL) was then added after cooling of the
Dyad 3 Yield 55%, 10 mg. FT-IR ν (cm ): 3314 (NH), 2960
(CHAr), 1465 (C = N), 1086 (C–Hpyrrole), 1014 (C–Hporp.
ring), 794 (C–Hpyr. ring), 721 (NHbending), 525 (C ). H
NMR δ (ppm), CS :CDCl (1:1 v/v), −2.86 (s, 2H, NH), 0.94
(b, 9H, methyl-H), 1.41 (b,12H, CH (10,11), 1.58 (b, 6H,
1
reaction mixture at room temperature. The resulting purple
precipitate was filtered, and washed with hot water.
Purification was achieved by column chromatography on sil-
ica gel with a gradient of eluent from DCM/hexane (1:2 then
6
0
2
3
2
CH (9), 1.93 (b, 6H, CH (8), 2.78 (s, 3H, N-methyl-H),
3.74, 4.85, 5.23 (d, d, s, pyrrolidine-H), 4.18(b, 6H, CH (7),
2
2
−1
1
:1). Yield 24% (75 mg). FT-IR ν (cm ): 3316 (NH), 2950
2
(
CHAr), 2216 (C ≡ C), 1699 (C = O), 1466 (C = N), 1174 (C–
7.19 (b, 6H, CH(5Ar-phenyl), 7.66 (b, 2H, CH(2Ar-phenyl), 7.82
(b, 4H, CH(3,4Ar-phenyl), 8.01(b, 6H,CH(6Ar-phenyl), 8.11 (b,
2H, CH(1Ar-phenyl), 8.78 (b, 8H, CHpyrrole). MS-MALDI-
TOF (m/z) C133H N O [calcd]: 1791.095, [found]:
Hpyrrole), 966 (C–Hporp. ring), 790 (C–Hpyr. ring), 739 (NH
bending). H NMR: δ (ppm), CDCl , –2.70 (s, 2H, NH),
1
1
3
.02(b, 9H, methyl-H), 1.49,1.55(b,12H, CH (10,11),
2
75
5
3

J Fluoresc
−
1
5
790.634 [M + H] . UV-vis (λ, nm) (toluene) 424, 518, 555,
95, 652.
equipped with high sensitive Hamamatsu PMT cooled hous-
ing detector (300–1700 nm) in presence of high cut filter
(1250 nm). The system is monitored by a (TCSPC) system
Photophysical and Photochemical Measurements
with the software DataStation and DAS6 (Horiba JobinYvon).
Absorption Optical spectra in the UV-visible region were
recorded on a Shimadzu 2001 UV spectrophotometer using
a 1 cm path length cuvette.
Oxygen Sensing Measurements Oxygen and nitrogen gases
were mixed in the concentration range 0–100% in a gas diluter
(Sonimix 7000A gas blending system). The total pressure was
maintained at 760 Torr. The output flow rate of the gas mixture
was maintained at 550 mL min . Gas mixtures were intro-
duced into the sensing agent containing cuvette via a diffuser
needle under ambient conditions.
−1
Steady-State Luminescence Emission Steady-state lumines-
cence emission spectra were recorded using a Horiba–
JobinYvon Fluorolog-3spectrofluorimeter (FL3-2IHR).
Electrochemical Measurements
Fluorescence Quantum Yield Determinations In our study,
meso-tetraphenylporphyrin (TPP) (Φ = 0.12 in toluene [42])
F
Supporting electrolyte, n-Bu NClO was purchased from
4
4
was used as reference standard. Absorbance and luminescence
spectra of the dyadsand of the reference TPP were measured
under identical conditions (absorbance at both the excitation
wavelengths were 0.05). All solutions were thoroughly deox-
ygenated by nitrogen bubbling through for 3 min. The ratio of
the integrated luminescence intensities of the sample to refer-
ence standard was compared to find out quantum yield thanks
to following Equation.
Aldrich and dried overnight at 50 °C under vacuum.
Ferrocene was supplied by Fluka, anhydrous acetonitrile by
VWR and 1,2-dichlorobenzene by Merck. 3 mm-diameter
glassy carbon working electrode (CHI104), non-aqueous
Ag/Ag + reference electrode with porous teflon tip
(
CHI112), platinum wire counter electrode (CHI115) and
electrode polishing kit (CHI120) were purchased from CH
Instruments. Measurements were carried out on CH
Instruments 842B model work station. The setup was conven-
tional three-electrode cell equipped with glassy carbon work-
ing electrode, platinum wire counter electrode, and Ag/
ꢀ
ꢁ
GradX
GradST
ðφ Þ ¼ ðφ Þ
F
X
F
ST
AgNO reference electrode. The glassy carbon electrode was
Singlet Oxygen Quantum Yield Determination Singlet ox-
ygen productions were measured in toluene by optical method
which are based on comparison between singlet molecular
oxygen phosphorescence in the near infrared region at
3
polished routinely with 0.05 μm alumina powder/water slurry
on pads before running experiments. All measurements of
samples were recorded as reported analyte concentration in
0
.1 M n-Bu NClO electrolyte solutions of o-dichloroben-
~
1270 nm produced by the corresponding dyads and the ref-
4 4
zene/acetonitrile (4:1) mixture. Analyte solutions were
deaerated with Argon purge for 5 min and kept under blanket
of argon during the experiments. All electrochemical mea-
surements were performed at ambient temperature.
Ferrocene was used as internal reference and all potentials
were referenced to ferrocene/ferrocenium (Fc/Fc+) redox cou-
ple. Potentials were reported versus ferrocene/ferrocenium
erence photosensitiser, TPP (ΦΔ = 0.63 in toluene) [44].
1
Phosphorescence signal of O was recorded by Horiba-
2
JobinYvon Fluorolog-3R spectrofluorimeter using 450 W Xe
arc lamp as a light source equipped with high sensitive
Hamamatsu PMT cooled housing detector (300–1700 nm).
In this system, a high cut filter (1250 nm) was used in order
to prevent the interference light below 1250 nm. For this pur-
pose, the absorbance and phosphorescence measurements of
TPP and all dyads were carried out at two different concen-
trations. The phosphorescence intensities were plotted vs ab-
sorbance for TPP and corresponding dyads. Singlet oxygen
(Fc/Fc+) redox couple. Scan rate was 100 mV/s for all CV
experiments.
Computational
quantum yields (Φ ) were calculated according to following
Equation using the ratio of the gradients.
Δ
Structure optimization and electronic structure calculations
are performed in density functional theory. Because of the soft
vibration modes the structure optimizations are found to be
very demanding, and reuire at least thousand molecular dy-
namic steps. We use revised Perdew-Burke-Ernzerhof
(revPBE) [48]. Generalized Gradient Approximation (GGA)
functional for exchange-correlationas implemented in the
SIESTA [49] code. Electronic wavefunctions are expanded
to a double-ζ basis set augmented by polarization orbitals.
ꢀ
ꢁ
GradX
GradST
ðφ Þ ¼ ðφ Þ
Δ X
Δ ST
Singlet Oxygen Lifetime Measurements Phosphorescence
1
lifetime of O2 was recorded by Horiba–JobinYvon
Fluorolog-3R spectrofluorimeter using a pulsed diode
(
SpectraLED −415 emitting 417 nm) as a light source

J Fluoresc
1
3. Imahori H, El-Khouly ME, Fujitsuka M, Ito O, Sakata Y, Fukuzumi
S (2001) Solvent dependence of charge separation and charge re-
combination rates in porphyrin−fullerene dyad. J Phys Chem A
The interaction between the core and valence electrons are han-
dled by Troullier-Martins norm-conserving pseudopotentials
[50] in their fully separable form [51]. Geometry optimizations
1
05:325–332
in the conjugate-gradient algorithm are continued until all force
components on each atom is less than 0.01 eV/Å. Since GGA
underestimates fundamental energy gaps, electronic energy
levels are calculated also in HSE06 and B3LYP hybrid
exchange-correlation functionals using 6-311G** basis set as
implemented in NWChem computer code [52]. Both computer
codes give the same energy levels for GGA functional. The value
of HOMO-LUMO energy gaps are in the best agreement with
the experiment for B3LYP exchange-correlation functional.
14. Kodis G, Liddell PA, Garza L, Clausen PC, Lindsey JS, Moore AL,
Moore TA, Gust D (2002) Efficient energy transfer and electron
transfer in an artificial photosynthetic antenna−reaction center com-
plex. J Phys Chem A 106:2036–2048
1
5. Imahori H, Yamada H, Guldi DM, Endo Y, Shimomura A, Kundu
S, Yamada K, Okada T, Sakata Y, Fukuzumi S (2002) Comparison
of reorganization energies for intra- and intermolecular electron
transfer. Angew Chem Int Ed 41:2344–2347
1
6. Tkachenko NV, Lemmetyinen H, Sonoda J, Ohkubo K, Sato T,
Imahori H, Fukuzumi S (2003) Ultrafast Photodynamics of
Exciplex formation and Photoinduced electron transfer in porphy-
rin−fullerene dyads linked at close proximity. J Phys Chem A 107:
8
834–8844
Acknowledgements Catherine Hirel, Emel Önal and Sevinc Z. Topal
1
1
1
7. Schuster DI, MacMahon S, Guldi DM, Echegoyen L, Braslavsky
SE (2006) Synthesis and photophysics of porphyrin–fullerene do-
nor–acceptor dyads with conformationally flexible linkers.
Tetrahedron 62:1928–1936
acknowledge the Scientific and Technical Research Council of Turkey
(
TUBITAK) for their financial support through the project 111 M139.
The authors thank also Eren Jason Gürbüz for the graphical design of
Fig. 1.
8. Milanesio ME, Alvarez MG, Rivarola V, Silber JJ, Durantini EN
(2005) Porphyrin-fullerene C60 dyads with high ability to form
photoinduced charge-separated state as novel sensitizers for photo-
dynamic therapy. Photochem Photobiol 81:891–897
References
9. Ballatore MB, Spesia MB, Milanesio ME, Durantini EN (2014)
Synthesis, spectroscopic properties and photodynamic activity of
porphyrin–fullerene C60 dyads with application in the photodynam-
ic inactivation of Staphylococcus aureus. Eur J Med Chem 18:685–
1
2
3
.
.
.
Zhao J, Wu W, Sun J, Guo S (2013) Triplet photosensitizers: from
molecular design to applications. Chem Soc Rev 42:5323–5351
Ghogare AA, Greer A (2016) Using singlet oxygen to synthesize
natural products. Chem Rev 116:9994–10034
Topkaya D, Ng S.Y, Bretonnière Y, Lafont D, Chung LY, Lee H B,
Dumoulin F (2016) Iodination improves the phototoxicity of an
amphiphilic porphyrin. Photodiagn Photodyn Ther, 16: 12–14
Topkaya D, Lafont D, Poyer F, Garcia F, Albrieux F, Maillard P,
Bretonnière Y, Dumoulin F (2016) Design of an amphiphilic por-
phyrin exhibiting high in vitro photocytotoxicity. New J Chem 40:
6
94
0. Constantin C, Neagu M, Ion RM, Gherghiceanu M, Stavaru C
2010) Fullerene–porphyrin nanostructures in photodynamic thera-
2
(
py. Nanomedicine 5:307–317
2
1. Huang L, Terakawa M, Zhiyentayev T, Huang Y-Y, Sawayama Y,
Jahnke A, Tegos GP, Wharton T, Hamblin MR (2010) Innovative
cationic fullerenes as broad-spectrum light-activated antimicrobials.
Nanomedicine: NBM 6:442–452
4.
5.
6.
2
044–2050
2
2
2. Wu H, Fan S, Jin X, Zhang H, Chen H, Dai Z, Zou X (2014)
Construction of a zinc porphyrin–fullerene-derivative based
Nonenzymatic electrochemical sensor for sensitive sensing of hy-
drogen peroxide and nitrite. Anal Chem 86:6285–6290
3. Obondi CO, Lim GN, Churchill B, Poddutoori PK, Est A, D'Souza
F (2016) Modulating the generation of long-lived charge separated
states exclusively from the triplet excited states in palladium por-
phyrin–fullerene conjugates. Nano 8:8333–8344
Topkaya D, Arnoux P, Dumoulin F (2015) Modulation of singlet
oxygen generation and amphiphilic properties of trihydroxylated
monohalogenated porphyrins. J Porphyrins Phthalocyanines 19:
1
081–1087
Topal SZ, Önal E, Ertekin K, Oter O, Gürek AG, Hirel C (2013)
Significant sensitivity and stability enhancement of
tetraphenylporphyrin-based optical oxygen sensing material in
presence of perfluorochemicals. J. Porphyrins Phthalocyanines
24. Prato M, Maggini M (1998) Fulleropyrrolidines: a family of full-
fledged fullerene derivatives. Acc Chem Res 31:519–526
25. Tagmatarchis N, Prato M (2003) The addition of azomethine ylides
to [C60]fullerene leading to fulleropyrrolidines. Synlett 3:768–779
26. Maggini M, Scorrano G, Prato M (1993) Addition of azomethine
ylides to C60: synthesis, characterization, and functionalization of
fullerene pyrrolidines. J Am Chem Soc 115:9798
1
7:431–439
Önal E, Ay Z, Yel Z, Ertekin K, Gürek AG, Topal SZ, Hirel C
2016) Design of oxygen sensing nanomaterial: synthesis, encap-
7
.
(
sulation of phenylacetylide substituted Pd(II) and Pt(II) meso-
tetraphenylporphyrins into poly(1-trimethylsilyl-1-propyne) nano-
fibers and influence of silver nanoparticles. RSC Adv 6:9967–9986
Guldi DM (2002) Fullerene-porphyrin architectures; photosynthet-
ic antenna and reaction center models. Chem Soc Rev 31:22–36
Conoci S, Guldi MD, Nardis S, Paolesse R, Kordatos K, Prato M,
Ricciardi G, Vicente MGH (2004) Zilbermann I, Valli L.
Langmuir–Shäfer transfer of fullerenes and porphyrins: formation,
deposition, and application of versatile films. Chem Eur J 10:6523–
8
.
.
2
7. Nierengarten JF, Eckert F, Nicoud JF, Ouali L, Krasnikov V,
Hadziioannou G (1999) Synthesis of a C60-oligophenylenevinylene
hybrid and its incorporation in a photovoltaic device. Chem
Commun 617–618. doi:10.1039/A900829B
8. Ding H, Meng X, Cui X, Yang Y, Zhou T, Wang C, Zeller M, Wang
C (2014) Highly-efficient synthesis of covalent porphyrinic cages
via DABCO-templated imine condensation reactions. Chem
Commun 50:11162–11164
9
2
6
530
1
0. Yamada K, Imahori H, Nishimura Y, Yamazaki I, Sakata Y (1999)
Acceleration of Photoinduced charge separation in porphyrin-C60
dyad with an acetylene spacer. Chem Lett 28:895–896
29. Önal E, Ahsen V, Pécaut P, Luneau D, Hirel C (2015) Bromine–
lithium exchange as a straightforward method to obtain meso-
tetrakis(4-formylphenyl)porphyrin: a versatile intermediate.
Tetrahedron Lett 56:5157–5160
30. Lembo A, Tagliatesta P, Guldi DM, Wielopolski M, Nuccetelli M
(2009) Porphyrin−β-oligo-ethynylenephenylene−[C60]fullerene
11. Imahori H, Sakata Y (1999) nFullerenes as novel acceptors in pho-
tosynthetic electron transfer. Eur. J. Org. Chem. 10,:2445-2457
2. Gust D, Moore TA, Moore AL (2001) Mimicking photosynthetic
solar energy transduction. Acc Chem Rev 34:40–48
1

J Fluoresc
triads: synthesis and electrochemical and photophysical characteri-
41. Schuster DI (2000) Synthesis and photophysics of new types of
fullerene–porphyrin dyads. Carbon 38:1607–1614
42. Owens JW, Smith R, Robinson R, Robins M (1998) Photophysical
properties of porphyrins, phthalocyanines, and benzochlorins. Inorg
Chim Acta 279(2):226–231
43. Shinohara H, Tsaryova O, Schnurpfeil G, Wöhrle D (2006)
Differently substituted phthalocyanines: comparison of calculated
energy levels, singlet oxygen quantum yields, photo-oxidative sta-
bilities, photocatalytic and catalytic activities. J Photochem
Photobiol A Chem 184(1–2):50–57
zation of the new porphyrin−oligo-PPE−C60fullerene systems. J
Phys Chem A 113:1779–1793
3
1. Adler AD, Longo FR, Finarelli JD, Goldmacher J, Assour J,
Korsakoff LA (1967) Simplified synthesis for meso-
tetraphenylporphine. J Org Chem 32:476
3
3
3
3
2. Hirsch A, Brettreich M (2005) In fullerenes. Wiley-VCH Verlag
GmbH & Co. KGaA, ch1, pp 1–48. doi:10.1002/3527603492
3. Schettino V, Pagliai M, Ciabini L, Cardini G (2001) The vibrational
spectrum of fullerene C60. J Phys Chem A 105:11192–11196
4. Drovetskaya T, Reed CA, Boyd P (1995) A fullerene porphyrin
conjugate. Tetrahedron Lett 36(44):7971–7974
4
4. Redmond RW, Gamlin JN (1999) A compilation of singlet oxygen
yields from biologically relevant molecules. Photochem Photobiol
7
0(4):391–475
5. Ishida M, Park SW, Hwang D, Koo YB, Sessler JL, Kim DY, Kim
D (2011) Donor-substituted β-functionalized porphyrin dyes on
4
5. Arbogast JW, Darmanyan AP, Foote CS, Rubin Y, Diederich FN,
Alvarez MM, Anz SJ, Whetten RL (1991) Photophysical properties
of sixty atom carbon molecule (C60). J Phys Chem 95:11–12
2
hierarchically structured mesoporous TiO spheres. Highly efficient
dye-sensitized solar cells. J Phys Chem C 115:19343–19354
6. Maggini M, Karlsson A, Scorrano G, Sandonà G, Farnia G, Prato
M (1994) Ferrocenyl fulleropyrrolidines: a cyclic voltammetry
study. J Chem Soc Chem Commun 5:589–590. doi:10.1039/
C39940000589
7. Tu Y-J, Cheng H C, Chao I, Cho C-R, Cheng R-J, Su YO (2012)
Intriguing electrochemical behavior of free base porphyrins: effect
of porphyrin–meso-phenyl interaction controlled by position of
substituents on meso-phenyls. J Phys Chem A 116:1632–1637
8. Pelado B, Abou-Chahine F, Calbo J, Caballero R, de la Cruz P,
Junquera-Hernandez JM, Orti E, Tkachenko NV, Langa F (2015)
Role of the bridge in photoinduced electron transfer in porphyrin–
fullerene dyads. Chem Eur J 21:5814–5825
4
6. Salokhiddinov KI, Byteva IM, Gurinovich GP (1981) Lifetime of
singlet oxygen in various solvents. J Appl Spectrosc 34(5):561–564
7. Guan M, Qin T, Ge J, Zhen M, Xu W, Chen D, Li S, Wang C, Su H,
Shu C (2015) Amphiphilic trismethylpyridylporphyrin-fullerene
3
3
3
4
(C70) dyad: an efficient photosensitizer under hypoxia conditions.
J Mater Chem B 3(5):776–783
4
8. Perdew JP, Burke K, Ernzerhof M (1996) Generalized gradient
approximation made simple. Phys Rev Lett 77(18):3865–3868
9. Soler JM, Artacho E, Gale JD, García A, Junqueran J, Ordejón P,
Sánchez-Portal D (2002) The Siesta method for ab initio order-N
materials simulation. J Phys: Condens Matt 14:2745–2779
0. Troullier N, Martins JL (1991) Efficient pseudopotentials for plane-
wave calculations. Phys Rev B 43:1993–2006
4
5
3
9. Thelakkat M, Schmidt HW (1998) Synthesis and properties of nov-
el derivatives of 1,3,5-tris(diarylamino)benzenes for electrolumi-
nescent devices. Adv Mater 10:219–223
0. Kuciauskas D, Lin S, Seely GR, Moore AL, Moore TA,
Drovetskaya T, Reed C A, Boyd PDW (1996) Energy and photo-
induced electron transfer in porphyrin−fullerene dyads. J Phys
Chem 100:15926–15932
51. Kleinman L, Bylander DM (1982) Efficacious form for model
pseudopotentials. Phys Rev Lett 48(20):1425–1428
52. Valiev M, Bylaska EJ, Govind N, Kowalski K, Straatsma TP, Van
Dam HJJ, Wang D, Nieplocha J, Apra E, Windus TL, de Jong WA
(2010) NWChem: a comprehensive and scalable open-source solu-
tion for large scale molecular simulations. Comput Phys Commun
181(9):1477–1489
4