Synthesis, spectral and redox properties of closely spaced pyrrole-β-position-linked porphyrin-fullerene dyads

Article abstract of DOI:10.1016/j.molstruc.2019.04.013

Two free base meso-tetraphenylporphyrin-fullerene dyads, H₂PMe-C₆₀, H₂POMe-C₆₀, and their zinc complexes, ZnPMe-C₆₀ and ZnPOMe-C₆₀, which the para positions of the meso-tetrasubstituted phenyl groups of the porphyrin core were substituted by methyl(-Me) and methoxyl(-OMe) groups respectively, were synthesized. The porphyrin unit in the synthesized dyads is directly linked to the fullerene entity through the pyrrole-β- position rather than through the traditionally meso-substituted phenyl group, which may be more favorable for electron communication between the donor and the acceptor. They are fully characterized by mass spectrometry, nuclear magnetic resonance, infrared spectroscopy and ultraviolet visible spectroscopy. Experimental results obtained from steady-state fluorescence spectroscopy and cyclic voltammetry show that the coordination of the zinc ions lead to an increase in the singlet excited state energy of the metallated porphyrin unit by about 0.15 eV, and to a reduce in the HOMO level and in the HOMO-LUMO energy gap. The molecular reorganization energy decreases after the electron-donating groups of -Me or -OMe attaching to the para position of the meso-phenyl group of the porphyrin moiety. The results of the energy calculations show that photoinduced electron transfer is thermodynamically favorable for the synthesized porphyrin-C₆₀ dyads. There exists a competition between the photoinduced electron transfer and energy transfer processes from the first singlet excited state of porphyrin core to fullerene moiety. The photoinduced electron transfer rate constant of the dyads were calculated according to Marcus theory. The results indicate that the coordination of metal zinc ions lead to great increase in the electron transfer rate constant. Further, the photoinduced electron transfer rate constant increases in the order ZnP-C₆₀, ZnPMe-C₆₀, ZnPOMe-C₆₀.

Full text of DOI:10.1016/j.molstruc.2019.04.013

Accepted Manuscript
Synthesis, spectral and redox properties of closely spaced pyrrole-β-position-linked
porphyrin-fullerene dyads
Zhen-Yi Wu, Sheng-Yan Yang
PII:
S0022-2860(19)30402-8
DOI:
https://doi.org/10.1016/j.molstruc.2019.04.013
MOLSTR 26385
Reference:
To appear in: Journal of Molecular Structure
Received Date: 23 February 2019
Revised Date: 26 March 2019
Accepted Date: 2 April 2019
Please cite this article as: Z.-Y. Wu, S.-Y. Yang, Synthesis, spectral and redox properties of closely
spaced pyrrole-β-position-linked porphyrin-fullerene dyads, Journal of Molecular Structure (2019), doi:
https://doi.org/10.1016/j.molstruc.2019.04.013.
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ACCEPTED MANUSCRIPT
Synthesis,Spectral and Redox Properties of Closely Spaced
Pyrrole-β-position-linked Porphyrin-fullerene Dyads
,1
Zhen-Yi Wu
Sheng-Yan Yang2
1Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University,
Xiamen, 361005, P.R. China
2College of Chemistry and Material Engineering, Chaohu University, Chaohu 238000, P.R. China
Abstract: Two free base meso-tetraphenylporphyrin-fullerene dyads, H2PMe-C60,
H2POMe-C60, and their zinc complexes, ZnPMe-C60 and ZnPOMe-C60, which the para
positions of the meso-tetrasubstituted phenyl groups of the porphyrin core
were substituted by methyl(-Me) and methoxyl(-OMe) groups respectively , were
synthesized. The porphyrin unit in the synthesized dyads is directly linked to the
fullerene entity through the pyrrole-β- position rather than through the traditionally
meso-substituted phenyl group, which may be more favorable for electron
communication between the donor and the acceptor. They are fully characterized by
mass spectrometry, nuclear magnetic resonance, infrared spectroscopy and ultraviolet
visible spectroscopy. Experimental results obtained from steady-state fluorescence
spectroscopy and cyclic voltammetry show that the coordination of the zinc ions lead
to an increase in the singlet excited state energy of the metallated porphyrin unit by
about 0.15 eV, and to a reduce in the HOMO level and in the HOMO-LUMO energy
gap. The molecular reorganization energy decreases after the electron-donating groups
of -Me or -OMe attaching to the para position of the meso-phenyl group of the
*Corresponding author: Tel: +86-13625010329; fax: +86-592-8818087
E-mail address: zywu@xmu.edu.cn

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porphyrin moiety. The results of the energy calculations show that photoinduced
electron transfer is thermodynamically favorable for the synthesized porphyrin-C60
dyads. There exists a competition between the photoinduced electron transfer and
energy transfer processes from the first singlet excited state of porphyrin core to
fullerene moiety. The photoinduced electron transfer rate constant of the dyads were
calculated according to Marcus theory. The results indicate that the coordination of
metal zinc ions lead to great increase in the electron transfer rate constant. Further, the
photoinduced electron transfer rate constant increases in the order ZnP-C60,
ZnPMe-C60, ZnPOMe-C60.
Introduction
It is currently a hot topic of scientific researches to construct the donor-acceptor (D-A)
systems to simulate natural photosynthesis and to develop novel photoelectron
molecular devices at the molecular level. Porphyrins[1-5], phthalocyanines[6, 7],

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naphthalocyanines[8, 9] are often used as the electron donors for D-A systems due to
their excellent light harvesting characteristics in the visible region of the spectrum and
their structural stability, and C60 is used as an electron acceptor[5] because of its
unique three-dimensional structure, low reduction potential and small reorganization
energy of electron transfer. At present, the synthesis and photophysical properties of
the porphyrin-fullerene dyads have been studied intensively. The chlorophyll-like
porphyrin units of these dyads absorb light energy and undergo photoinduced
electron/energy transfer to convert the captured energy into chemical energy. The
efficiency of the photoinduced electron transfer in such D-A dyads depends on the
electronic and spatial structure at the molecular level. To obtain high light-induced
electron transfer efficiency, a photosensitive moiety with a wide light absorption
range and strong electron-pushing characteristics is required. In addition, a long-lived
charge-separated
state
achived
by fast charge separation (CS)
and
slow charge recombination (CR) is also necessary[10]. The efficiency of the
photoinduced electron transfer process is affected by different factors including the
nature of porphyrin moiety[11], geometry[12, 13] and length[14, 15] of the
σ/π-conjugate bridge between D and A, and the property of the modified fullerene[3].
The position of the porphyrin core at which the bridge attached has been shown to
dramatically affect charge transport properties[16, 17]. At present, in-depth studies for the
meso-substituted phenyl porphyrin–C60 dyads have been carried out on the effects of
the conjugation properties, the geometry and the length of the bridge between D and A
on the photoinduced electron transfer properties[3, 12, 15, 18-21]. However, little

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research has been done for the closely spaced pyrrole-β-position-linked
porphyrin-fullerene dyads porphyrin-fullerene dyads and there has only been
one related studypublished so far[22].Due to a short distance, there may exist strong
interactions between the donor and the acceptor,and the modification of
electron-pushing substituents on the porphyrin core and the coordination of metal ions
will exert substantial influence on the electronic structure of porphyrin unit. Thus,
the interaction between donor and acceptor in D-A molecule and the Gibbs free
energy of charge transfer and charge recombination between donor and acceptor can
be tuned by the coordination of metal ions
and the modifications of
the porphyrin core, and to achieve regulation of its light-induced electron transfer.
In this paper, we designed and synthesized two porphyrin-C60 dyads of
5,10,15,20-tetrakis (4-methylphenyl)porphyrin-fullerene ꢀ H2PMe-C60 ꢁ and
5,10,15,20- tetrakis(4-methoxyphenyl) porphyrin-fullereneꢀH2POMe-C60ꢁ, and their
zinc complexes of ZnPMe-C60 and ZnPOMe-C60 (Fig.1), where the porphyrin unit
link to fullerene moiety via β-pyrrolic position, and the p-positions of meso-phenyl
rings of porphyrin unit were substituted by the strong π-donors (methoxyl groups,
-OCH3) and the weak σ-donors (methyl groups, Me-) respectively. . The
electrochemical and photophysical properties of these dyads were studied by using
cyclic voltammetry and steady-state fluorescence spectroscopy. The energy level
diagrams of these dyads were proposed and the photoinduced electron transfer rates
were estimated. The effects of electron-donating substituents at the para position of
the phenyl ring on the driving force of the photoinduced electron transfer, the

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recombination energy and the photoinduced electron transfer rate was discussed.
Results and discussions
Synthesis of dyads(Fig.2): firstly, two fully-symmetric free base porphyrin
compounds(H2PMe and H2POMe) which substituents of -Me or -OMe attaching at
the para position of the meso-phenyl ring were synthesized by using the modified
Adler method, following coordinating to copper ions to activate the β-position of the
meso-porphyrin ringto afford CuPMe, CuPOMe. Then, a formyl group was
introduced into the β position using Vilsmeier formylation, and removing copper ions
by reacting with concentrated sulfuric acid to get the free base tetraphenylporphyrin
formyl-H2PMe and formyl-H2POMe which a formyl group attaching at the β-position.
Finally, free base porphyrin-fullerene dyads of H2PMe-C60 and H2POMe-C60, which
the fullerene pyrrolidine linked the porphyrin unity at the β position directly, were
synthesized by using a 1,3 dipolar addition reaction. . The zinc porphyrin-fullerene
dyads of ZnPMe-C60 and ZnPOMe-C60 were synthesized by reaction of H2PMe-C60or
H2POMe-C60 with zinc acetate. For comparison, we also synthesized
porphyrin-fullerene dyad of ZnP-C60 without substituents on porphyrin core as the
reference compound.
All synthesized dyads were characterized by mass spectrometry, infrared
spectroscopy, ultraviolet visible spectroscopy and nuclear magnetic resonance
spectroscopy. Mass spectra were performed using APCI as the ionization source, and
showed the molecular ion peaks at m/z 1390.2 for H2P-C60, 1446.3 for H2PMe-C60,
1510.3 for H2POMe-C60, 1453.1 for ZnP-C60, 1508.1 for ZnPMe-C60, 1573.5 for

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ZnPMe-C60, which consistent with their molecular formulas C107H35N5, C111H43N5,
C111H43N5O4, ZnC107H33N5, ZnC111H41N5, ZnC111H41N5O4 respectively. The isotope
distribution simulations are also consistent with the experimental values, which prove
that the synthesized compounds are the target products.
1
The H NMR spectra for H2P-C60, H2PMe-C60, H2POMe-C60 showed the proton
peak of N-H in porphyrin ring at about δ -2.65 ppm. Two doublets at δ 3.61-3.74 and
4.56-4.62 ppm are due to the -CH2- group of the pyrrolidine. A singlet signal at
δ2.45-2.49 ppm was attributed to the protons of N-methyl group (N–CH3) of the
pyrrolidine. The signals for the β protons and aromatic protons for porphyrin rings
appear as multiple peaks at δ=6.89-7.56 and 8.13-8.92 ppm.
The infrared spectra (Fig. 3) for H2P-C60, H2PMe-C60, H2POMe-C60 show
strong N-H stretching vibrations of the porphyrin at about 3320, 967cm-1. The
characteristic C60 skeleton vibration absorption appears at 526 cm-1. A weak
absorption peak at ~2771 cm-1 is ascribed to the C-H stretching vibration in N-CH3 of
C60 pyrrolidine. N-H stretching vibrations of the porphyrin at ~3320, 967cm-1
disappear after coordination to zinc ion to form zinc porphyrin-fullerene dyads of
ZnP-C60, ZnPMe-C60, ZnPOMe-C60. In addition, the vibrational peak of the porphyrin
skeleton at 985 cm-1 shifts by ~15 cm-1 to higher wavenumber and the peak intensity
increase, which can be attributed to the enhancement in the molecular symmetry after
coordination to zinc ions, and resulting in the improvement in porphyrin infrared
activity.
The UV-visible spectra for H2P, H2PMe, H2POMe, H2P-C60, H2PMe-C60,

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H2POMe-C60, ZnP-C60, ZnPMe-C60, ZnPOMe-C60 were measured using chloroform
as a solvent. As shown in Fig. 4 and Tab. 1, free base porphyrin-fullerene dyads of
H2P-C60, H2PMe-C60, H2POMe-C60 showed 7 peaks at 256, 317-318, 423-429,
520-523, 553-560, 593-598, and 650-656 nm, respectively. The absorption bands due
to C60 appear at 256 and 317-318nm.The strong absorption at 423-429 nm is
attributed to the Soret band of porphyrin unit, and the other four peaks are ascribed to
the Q band of porphyrin. UV-Vis spectra of ZnP-C60,ZnPMe-C60, ZnPOMe-C60 show
five absorption bands at about 256,311-316nm(due to C60ꢁ, 427-430nm(Soret band of
porphyrin), 555-557, 591-599 nm (Q band of porphyrin). The UV-visible spectra
change greatly after the porphyrin unit covalently linked to C60 and further
coordinated to zinc ions to form zinc porphyrin-C60 dyads. Firstly, covalent linkage
of the C60 unit results in a significant red shift in the Soret band. After H2P-C60,
H2PMe-C60, H2POMe-C60 coordinated to zinc ions to form ZnP-C60, ZnPMe-C60,
ZnPOMe-C60, the Soret band is further red-shifted and the number of Q-bands is
reduced from 4 to 2, which may be ascribed to the increases in the symmetry of the
porphyrin unit and in the degeneracy caused by the coordination to metal zinc ions.
For example, after covalently attaching to C60, the Soret band for H2POMe-C60 is red
shifted from 426.6 nm for H2POMe to 428.9 nm, and is further redshifted to 430.7nm
after coordinating to zinc ion to form the dyad of ZnPOMe-C60, which indicates the
existence of a strong interaction between the ground state zinc porphyrin moiety and
the C60 moiety. In addition, various peripheral substituents have marked effects on the
absorption spectra of porphyrins. For example, the Soret band of H2P-C60 appears at

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423.5 nm, and red-shifted to 426.2 nm for H2PMe-C60, to 428.9nm for H2POMe-C60
after the para-H of phenyl group was substituted by –Me and -OMe group
respectively.
Fluorescence measurements were performed on ∼1×10-5M solutions of samples
in dichloromethane by excitation with 510 nm(Figure 5). Fluorescence spectra of H2P,
H2PMe, H2POMe showed an emission band at 648-652 nm. The position of the band
almost remains unchanged after the porphyrin unit attached to C60 to form the dyads
of H2P-C60, H2PMe-C60,H2POMe-C60, but the emission peak strongly quenched by
more than 90% compared with those of their corresponding references H2P, H2PMe,
H2POMe,which mainly be ascribed to the photoinduced electron transfer from the
singlet excited porphyrin to the fullerene moiety. When H2P-C60, H2PMe-C60,
H2POMe-C60 are coordinated to zinc ions to form ZnP-C60, ZnPMe-C60, ZnPOMe-C60,
the emission peaks are all blue-shifted by about 50 nm to 600 nm, and lead to
fluorescence further quenching, indicating that the coordination of metal zinc ions
lead to the increases in the singlet excited state energy of porphyrin moiety and in the
degree of photoinduced electron transfer. The fluorescence emission peak of the
fullerene pyrrolidine was observed at 702nm for H2P-C60, 712nm for H2PMe-C60 and
711.0nm for H2POMe-C60, However, no fluorescence emissions of the fullerene
pyrrolidine was observed for ZnP-C60, ZnPMe-C60, ZnPOMe-C60, indicating that
there exist energy transfer from the free base porphyrin to the C60 moiety for H2P-C60,
H2PMe-C60, H2POMe-C60, but no for zinc porphyrin-fullerene dyads ZnP-C60,
ZnPMe-C60, ZnPOMe-C60.

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In order to estimate the energy of the charge-separated state of the dyads after
photoexcitation, the first oxidation potential of the porphyrin moiety and the first
reduction potential of the fullerene were determined by cyclic voltammetry conducted
in anhydrous toluene/acetonitrile (v/v=3/1) mixed solvent and tetrabutylammonium
tetrafluoroborate as a supporting electrolyte. All potentials are referenced to the
ferrocene/ferrocene+ (Fc/Fc+) couple used as an internal standard. The redox potential
values are summarized in Tab. 2. In the potential range of 0-1.90V, the dyad of
H2PMe-C60 show three single-electron reduction peaks at -1.154, -1.358, -1.716V,
respectively. The first and second reduction peaks can be assigned to the reductions of
fullerene pyrrolidine moiety to C60- and C602-. The third reduction peak is attributed to
the reduction of the porphyrin moiety. The first reduction potential shows a significant
negative shift compared with that of pristine C60 (-1.056V),which can be attributed to
the increase in LUMO energy level caused by the saturation of the double bond of the
C60 moiety[23]. The oxidation potential of H2PMe-C60 appears at about 0.505V, which
is mostly an irreversible process. This is because H+ ion is detached from the center of
the porphyrin ring when the free base porphyrin moiety is oxidized, and transferred to
the tertiary amine of the outer ring. After coordinating to zinc ion, ZnPMe-C60 showed
an oxidation peak at 0.284 Vs Fc/Fc+ which shift by 0.221V to a more negative
potential compared with that of H2PMe-C60, indicating that the coordination of zinc
ions leads to a decrease in HOMO. Two reduction peaks were observed at
-1.032,-1.472V, which corresponding to reductions of C60 and zinc porphyrin moieties,
respectively. The electrochemical HOMO–LUMO gaps for H2PMe-C60 and

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ZnPMe-C60 can be calculated to be 1.659 and 1.326V, respectively, by using their first
oxidation potential and first reduction potential values.
In the cathodic scan for H2POMe-C60, three reduction peaks were located at
-1.058, -1.506, -1.733V, and the first two reduction peaks are attributed to the
reduction of C60 moiety, the first reduction peak slightly shifts to negative potential
with respect to that of pristine C60. The third cathodic peak arises from the reduction
of H2POMe moiety, and an irreversible oxidation peak at 0.521 can be ascribed to the
oxidation of the free base porphyrin moiety.
An oxidation peak at 0.286V was observed for ZnPOMe-C60, which
shifted negatively by 0.235V compared to that of the dyad of H2POMe-C60, and
cathodic peaks at -1.059, -1.488V can be ascribed to the reduction of the C60 moiety.
The electrochemical HOMO–LUMO gaps for dyads of H2POMe-C60 and
ZnPOMe-C60 can be calculated to be 1.579 and 1.345V, respectively by using the
above data.
For H2P-C60, four reduction peaks were observed at -1.063, -1.401, -1.679,
-2.060V. The first two peaks correspond to the reduction of the C60 moiety, and the
latter two originate from the porphyrin moiety. The first peak for the C60 moiety shifts
by 0.007V to negative potential compared with that of pristine C60. An irreversible
peak at 0.521V is ascribed to the oxidation of the free base porphyrin moiety. For
ZnP-C60 two reduction peaks at -1.103V for C60 moiety and 1.553V for zinc porphyrin
unit were observed, and the oxidation potential of zinc porphyrin unitt shifts
negatively by 0.248V to 0.273V. The electrochemical HOMO-LUMO gaps of both

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H2P-C60 and ZnP-C60 are 1.584 and 1.376V, respectively. Thus, the coordination of
the free base porphyrin-C60 to zinc ions leads to the decreases in both the oxidation
potential of the zinc porphyrin unit and the electrochemical HOMO-LUMO gap. The
first oxidation peaks of ZnPMe-C60 ZnPOMe-C60 with -Me and –OMe substituents at
the para position of phenyl group respectively are shifted to more positive potential
with respective to that of ZnP-C60. In addition, their HMO-LUMO values for the two
dyads of ZnPMe-C60, ZnPOMe-C60 are also reduced from 1.376V for ZnP-C60 to
1.316V for ZnPMe-C60 and 1.345V for ZnPOMe-C60.
To gain insight into the molecular geometries and the electronic structures of
free-base/zinc porphyrin-C60 dyads, molecular orbital (MO) calculations were carried
out by using the ab initio B3LYP/6-31G(*) method in the Gaussian 03 package. Fully
optimized ground-state structures are shown in Fig. 6. The calculated center-to-center
distance between the porphyrin unit and the C60 moiety (RC-C) and the radii of the
acceptor (R-) in the optimized structure are almost the same for all porphyrin-C60
0
dyads. They are 18.5 and 4.7
A
, respectively. The radii of the donor (R+) for
H2P-C60,H2PMe-C60, H2POMe-C60 and ZnP-C60, ZnPMe-C60 ꢂZnPOMe-C60 are
0
A
estimated to be 5.6, 6.3, 6.6 and 5.6, 6.3, 6.6 , respectively. A bigger donor radii (R+)
lead to a smaller reorganization energy λ, and result in a larger charge separation rate
constant Kcs. Fig. 6 shows the spatial electron density of HOMO and LUMO of
H2P-C60,H2PMe-C60,H2POMe-C60 and ZnP-C60,ZnPMe-C60ꢂZnPOMe-C60. For the six
dyads, the HOMO is localized on the porphyrin moiety and the LUMO is localized on
the C60 spheroid.

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The charge recombination free energy (ꢀGφCR) of the charge-separated states of
dyads formed after excitation can be estimated by the Rehm Weller method based on
values of the standard redox potentials, the theoretical calculation results, and the
dielectric constant of the solvent used. The energy of the first excited singlet state
(ꢀE0-0) for the dyads in dichloromethane also can be calculated by using the
1
1
fluorescence data which are 1.917eV for H2P*-C60, 1.904eV for H2PMe*-C60,
1
1
1
1.907eV for H2POMe*-C60, 2.069eV for ZnP-C60, 2.062eV for ZnPMe*-C60, and
1
2.072eV for ZnPOMe*-C60. Thus, the charge separation driving force (-ꢀGφCS) can
be further estimated from values of ꢀGφ and ꢀE0-0. The calculated data of ꢀGφ
CR
CS
and ꢀGφ for the six dyads are listed in the Tab. 3. Both ꢀGφ and ꢀGφ show
CR
CS
CR
negative values, indicating that the charge separation and the charge recombination
for the six porphyrin-C60 dyads are all thermodynamically favorable, and the driving
force (-ꢀGφCS) is less than the total reorganization energy (λ) of electron transfer,
indicating that the charge separation process of the dyads is in the normal region of
the Marcus parabola.
1
*
3
It is reported that the lowest excitation energies of C60 and C60* are 1.75 and
1.50 eV[24, 25], respectively, and the formation of the charge-separated state of
˙-
H2PR˙+-C60 by charge-transfer dependent on the solvent polarity. H2P-C60,
H2PMe-C60, H2POMe-C60 show significant fullerene fluorescence peak at about
710nm in dichloromethane, but no observed for ZnP-C60,ZnPMe-C60ꢂZnPOMe-C60.
Thus, the proposed energy diagrams for H2PR-C60 in dichloromethane are as shown in
1
the Fig. 7(a). After H2PR* C60 was formed by the irradiation of the free base
-

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1
porphyrin moiety with 515 nm, due to the energy of the singlet excited state H2PR*
*
is higher than that of the radical ion pair and the H2PR-1C60 state, there exists a
competition between the photoinduced electron transfer from the singlet excited state
1 H2PR* to the C60 moiety to form a H2PR˙+-C60˙-, and the energy transfer to form a
*
*
*
H2PR-1C60 . The H2PR-1C60 state would convert to a triplet state (3C60 ) through an
intersystem crossing or to the radical ion pair through electron transfer. Finally, the
charge-separated state is recombinated and quenched into a ground state. The
proposed energy diagrams of the dyads ZnPR-C60 in dichloromethane are shown in
the Figure 7(b). After photoexcitation, zinc porphyrin was excited to form
1(ZnPR)*-C60. There also exists a competition between photoinduced electron transfer
1
˙-
from singlet excited state ZnPR* to C60 moiety to form ZnPR˙+-C60 and energy
*
transfer to form a ZnPR-1C60 . Because the energy of the triplet excited state 3C60* is
highter than that of the free radical ion ZnPR˙+-C60˙-, ZnPR-1C60* undergoes electron
transfer from the ZnPR moiety to 1C60* without forming ZnPR-3C60*. Thus, a radical
ion pair of ZnPR˙+-C60 is produced in above two cases, and finally recombinated to
˙-
ground state.
As can be seen from the data in the table 3ꢂthe charge separation driving force
(−ꢀGφCS) is greatly increased after coordination to zinc ions to form
ZnP-C60,ZnPMe-C60ꢂZnPOMe-C60, and increase the photoinduced electron transfer
rate constant by an order of magnitude. In addition, for ZnP-C60,ZnPMe-C60ꢂ
ZnPOMe-C60, the radius R+ increases with the size of the modifying group increases,
which lead to a decrease in the recombination energy, and result in an increase in the

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photoinduced electron transfer rate.
Conclusions
In summary, this study shows that, in dichloromethane solvent, rapid photoinduced
electron transfer can occur for both free base porphyrin-fullerene dyads and zinc
porphyrin-fullerene dyads which fullerene pyrrolidine direct attached at the β-position
of the porphyrin moiety to produce charge-separated state. The coordination of zinc
ions leads to the increases in both the singlet excited state energy of porphyrin moiety
and the rate constant of the photoinduced electron transfer. For the zinc porphyrin-C60
dyads, the Ket values are increased after the -Me and -OMe groups attached at the para
position of phenyl group. These results may be instructive for the design of such D-A
molecules that are expected to be used in molecular-scale photovoltaic or electronic
devices.
Experimental Methods and Materials
All reagents were of analytical grade and purchased from Sinopharm Chemical
Reagent Co., Ltd. Neutral alumina ( for column chromatography, 200-300 mesh),
activated at 180 °C for 2 h before used. Fullerene[60] (C60 ) was purchased from
Wuda Three-dimensional Carbon Cluster Materials Co., Ltd. in Wuhan City, and used
directly without further processing. The samples were characterized by various
standard analytical techniques, including mass spectrometry (MS) , nuclear magnetic
resonance spectroscopy(NMR), Ultraviolet/visible spectroscopy (UV-Vis),infrared
spectroscopy(IR).The MS spectra were recorded using a Daltonics mass spectrometer
of Bruker (Bremen, Germany); 1H NMR spectra were recorded on a Varian Unity 400

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spectrometer (400 MHz); The UV-vis absorption spectra were measured on a
Shimadzu UV-2501 spectrophotometer. The IR spectra were recorded on a Nicolet
Avatar 360 Fourier transform infrared spectrometer using KBr pellets. The
steady-state fluorescence emission was monitored by a HITACHI F-4500
spectrometer.
Electrochemical experiments were carried out in a conventional three-electrode
system, by using a platinum ball (d=2.2 mm) as the working electrode, a square
platinum sheet (1cm2) as the auxiliary electrode, and a saturated calomel electrode
(SCE) as reference electrode. Tetrabutylammonium hexafluorophosphate (n-Bu4NPF6,
from Alfa Aesar) was used as supporting electrolyt. Toluene and acetonitrile
(chromatography pure, from China National Pharmaceutical Group Chemical Reagent
Co., Ltd) were used without further purification. All other chemicals were reagent
grade. Voltammograms were recorded with a CHI 660C electrochemical analyzer
(Chen Hua Instrument Co., Shanghai, China) in deaerated toluene/acetonitrile (4:1,
v/v) solution containing 0.10 M n-Bu4NBF4 at room temperature. The computational
calculations were performed by the DFT B3LYP/3-21G(*) method with the
GAUSSIAN-03 software package.23 The graphics of frontier orbitals were generated
using the GaussView software.
General Procedure for the Synthesis of 5,10,15,20-tetrakis(4-R-phenyl)porphyrin ,
H2PR (R=H,Me,OMe).
In a 25-ml-two necked round-bottom flask, 60 ml of propionic acid and 40 ml of
nitrobenzene were mixed, and heated to reflux, to which a solution of 40 mmol of

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para-R-benzaldehyde in 20ml of propionic acid was added gradually, followed by a
solution of 40 mmol of freshly distilled pyrrole in 20 ml of nitrobenzene was slowly
added dropwise. The reaction mixture was refluxed for 45 mins. The color of the
solution gradually changed from light yellow to blue-violet, and finally turned
purple-black. After completion, 25ml of methanol was added, and the mixture was left
to stand overnight at room temp. The resulting precipitate was vacuum filtered and
washed with distilled water and ethanol for 3 times, and dried to give a blue-violet
powder. The crude product was charged onto basic alumina and was purified by
column chromatography on basic alumina with dichloroform/methanol (19:1 v/v) as
eluent.
5 ,10,15,20-tetraphenylporphyrin, H2P Yield 50 %. FTIR (KBr): ν˜ =3318,
1472, 1441, 1072, 980, 965, 799, 701cm-1. 1H NMR (400 MHz, CDCl3, 20oC): δ 8.84
(s, 8H, pyrrole ring), 8.23 (d, J 6.0 Hz, 8H, o- C6H5); 7.72 (d,J 8.0 Hz, p- and m-
C6H5); -2.17 (s, 2H, NH). UV/Vis (CH2Cl2): λmax = 416.8, 514.5, 550.2, 589.6, 646.4
nm. MS (ESI): m/z calcd for C44H30N4, [M+H]+:614.7; found:615.3.
5,10,15,20-tetrakis(4-methylphenyl)porphyrin, H2PMe Yield 45ꢃ. FTIR (KBr):
1
ν˜ =3318, 1472, 1181, 982, 967, 800, 736cm-1. H NMR (400 MHz, CDCl3, 20oC): δ
8.84 (s, 8H),8.09 (d, J 8.5 Hz, 8H),7.54 (d, J 8.5Hz, 8H), 2.70 (s, 12H), -2.68 (br s,
2H). UV/Vis (CH2Cl2): λmax= 418.5, 516.9, 552.0, 590.8, 647.1nm. MS (ESI): m/z
calcd for C48H38N4, [M+H]+:670.8; found: 671.5.
5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin, H2POMe Yield 41%. FTIR
(KBr): ν˜=3318, 2834, 1606, 1469, 1247, 1174, 984, 966, 803, 706cm-1. 1H NMR

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(400 MHz, CDCl3, 20oC): 8.65 (s, 8H), 8.11(d, J 8.5 Hz, 8H), 7.28 (d, J 8.5 Hz, 8H),
4.09 (s, 12H),-2.75 (s, 2H). UV/Vis (CH2Cl2): λmax = 426.6, 518.2, 555.8, 592.7, 649.6
nm. MS (ESI): m/z calcd for C48H38N4O4, [M+H]+: 734.8; found: 735.3.
General Procedure for the Synthesis of 5,10,15,20-tetrakis(4-R-phenyl)porphyrin
copper(II) complexes, CuPR (R=H, Me, OMe ).
0.2 mmol of the corresponding 5,10,15,20-tetrakis(4-R-phenyl)porphyrin was
dissolved in 40 ml of chloroform, to which a saturated solution of copper acetate in
methanol was added. The mixture was magnetically stirred at room temperature, and
the progress of the reaction was monitored by TLC. The reaction is essentially
complete in 2 to 3 hours, and then distilled water (15 ml) is added to wash the organic
layer for 3 times. the organic layer was dried over anhydrous MgSO4, and filtered.
The solvent was removed by rotary evaporation yielding a purple powder.
5,10,15,20-tetrakis(phenyl)porphyrin copper(II) complex, CuP Yield 99%. FTIR
(KBr): ν˜ = 3052, 2921, 1597, 1440, 1345, 1070, 1004, 793, 742, 697cm-1. MS (ESI):
m/z calcd for CuC44H28N4, , [M+H]+: 676.3; found: 677.1.
5,10,15,20-tetrakis(4-methylphenyl)porphyrin copper(II) complex, CuPMe
Yield 96%. MS (ESI): m/z calcd for CuC48H36N4,[M+H]-: 732.4; found: 732.4.
5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin copper(II) complex, CuPOMe
Yield 95%. FTIR (KBr): ν˜ = 2929, 2833, 1606, 1504, 1344, 1286, 1246, 1175, 1036,
998, 805, 720, 604cm-1. MS (ESI): m/z calcd for Cu C48H36N4O4, [M+H]-: 796.4;
found: 795.1.
General Procedure for the Synthesis of β-formyl-5,10,15,20-tetrakis(4-R-phenyl)

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porphyrin copper(II) complexes, Formyl-CuPR (R=H,Me,OMe).
Under the protection of nitrogen, 0.14 mmol of the corresponding
5,10,15,20-tetrakis(4-R-phenyl)porphyrin copper(II) complex was dissolved in 16 ml
of CHCl3, to which 0.75ml of DMF was added with magnetic stirring. The solution
was cooled to 0°C in an ice bath, and then 0.56ml of phosphoryl chloride (POCl3) was
slowly added within 20 mins. The ice bath was removed and stirring was continued at
room temperature for 1 hour, and the solution was continously stirred and heated at 70ꢄ
for 24h. Then 3.606g of NaAc and 14.4ml of distilled water were added in an ice bath
and stirring for another 1h. After separation of the aqueous layer, the organic layer
was washed with 10ml of distilled water for 3 times, then dried over anhydrous
magnesium sulfate and filtered. The solvent was removed by rotary evaporation at
low temperature to afford a crude product. The crude product was dissolved in
dichloromethane and subjected to column chromatography over neutral alumina with
dichloromethane/petroleum ether (v/v=3:1) as the eluent. The third coloured band was
collected and the solvent was removed by rotary evaporation to afford a purple
powder.
β-formyl-5,10,15,20-tetrakis(phenyl)porphyrin copper(II) complex, Formyl-CuP
Yield 87%. FTIR (KBr): ν˜ =3054,2962,2922,2851,1668,1537,1441, 1344,
1261,1059,1033,801,701cm-1. MS (ESI): m/z calcd for CuC45H28N4O, [M+H]-: 704.3;
found: 704.0.
β-formyl-5,10,15,20-tetrakis(4-methylphenyl)porphyrin copper(II) complex,
Formyl-CuPMe Yield 85%. MS (ESI): m/z calcd for CuC49H36N4O, [M+H]-: 760.4;

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found: 760.0.
β-formyl-5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin copper(II) complex,
Formyl-CuPOMe Yield 83%. FTIR(KBr): ν˜=2921, 2850, 1665, 1606, 1534,
1504, 1343, 1288, 1246, 1174, 1036, 999, 800, 754.
C49H36N4O5, [M+H]-: 824.4; found: 824.0.
MS (ESI): m/z calcd for Cu
General Procedure for the Synthesis of β-formyl-5,10,15,20-tetrakis(4-R-phenyl)
porphyrin, Formyl-H2PR (R=H,Me,OMe).
Under the protection of nitrogen, 0.14 mmol of the corresponding
β-formyl-5,10,15,20-tetrakis(4-R-phenyl)porphyrin copper(II) complex was dissolved
in 16 ml of CHCl3, to which 0.75ml of DMF was added with magnetic stirring. The
solution was cooled to 0°C in an ice bath, and then 0.56ml of phosphoryl chloride
(POCl3) was slowly added within 20 mins. The ice bath was removed and stirring was
continued at room temperature for 1 hour, followed the solution was stirred and
heated at 70ꢄ for 24h. The solvent was removed by rotary evaporation at low
temperature, and the resulting solid was dissolved in 96% H2SO4 in an ice bath to get
a green clear solution. The reaction was complete after stirring overnight at room
temperature, and then saturated sodium acetate solution was added to adjust the pH to
alkaline, and filtered. The precipitate was washed with chloroform and the aqueous
phase was extracted twice with 30 ml chloroform. The upper aqueous phase was
removed on separating and the chloroform phase was washed three times with 40 ml 5%
NaOH solution and distilled water respectively. The chloroform solution was dried
over anhydrous magnesium sulfate, filtered and rotary evaporated to dryness to get

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the crude product.
The crude product was dissolved in dichloromethane and subjected to column
chromatography over neutral alumina with dichloromethane as the eluent. The third
coloured band was collected and the solvent was removed by rotary evaporation to
afford a purple powder.
β-formyl-5,10,15,20-tetrakis(phenyl)porphyrin, Formyl-H2P Yield 70%. FTIR
(KBr): ν˜ = 3322, 3053, 3026, 1668, 1596, 1500, 1474, 1442, 1385, 1349, 1164, 1073,
1
1002, 963, 799, 700 H NMR (400 MHz, CDCl3, 20oC): δ 9.31 and 9.23(2s, 2H),
8.83~8.58 (m, 6H), 8.23~7.77 (m, 20H, phenyl), -2.17 (s, 2H, NH). UV/Vis
(CH2Cl2):λmax=314.3, 413.7, 525.3, 566.8, 606.2, 664.5 nm. MS (ESI): m/z calcd for
C45H30N4O, [M+H]+: 642.8; found: 643.6.
β-formyl-5,10,15,20-tetrakis(4-methylphenyl)porphyrin, Formyl-H2PMe Yield
68%. FTIR (KBr): ν˜ = 3325, 3022, 2919, 1672, 1556, 1473, 1347, 1221, 1181, 1022,
965, 799, 729cm-1. 1H NMR (400 MHz, CDCl3, 20oC): δ 9.30 9.21(2s,2H),8.85~8.55 ,
8.06-7.15 (m, 22H, P-pyrrole, phenyl), 2.66 (s, 12H, methyl),-2.65(s, 2H; H1-NH).
UV/Vis (CH2Cl2):λmax=315.7, 433.7, 527.3, 570.7, 608.7, 666.3 nm. MS (ESI): m/z
calcd for C49H38N4O: 698.9, [M+H]+; found: 699.5.
β-formyl-5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin, Formyl-H2POMe
Yield 65%. FTIR (KBr): ν˜ = 2929, 2835, 1667, 1605, 1508, 1466, 1347, 1288, 1246,
1175, 1033, 964, 801, 731 cm-1
1H NMR (400 MHz, CDCl3, 20oC): 9.32 9.24 (2s,
2H), 8.65 (s, 6H), 7.90(m, 8H),7.21 (m, 8H), 4.03 (s, 12H),- 2.75 (s, 2H). UV/Vis
(CH2Cl2):λmax= 313.9, 435.8, 530.0, 571.8, 608.3, 671.8 nm. MS (ESI): m/z calcd for

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C49H38N4O5, , [M+H]-: 762.9; found: 762.3.
General Procedure for the Synthesis of free base 5,10,15,20-tetrakis(4-R-phenyl)
porphyrin-fullerene dyads, H2PR-C60 (R=H,Me,OMe).
In
a
round-bottom
flask,
0.14mmol
of
the
corresponding
110mg
β-formyl-5,10,15,20-tetrakis
(4-R-phenyl)porphyrin
(R=H,Me,OMe),
(0.154mmol)of C60 and 63mg(0.7mmol) N-methylglycine (sarcosine) were combined
and dissolved in 125mL of toluene. The reaction mixture was stirred and refluxed at
140-150°C in an oil bath under nitrogen for 18 h. The resultant brown solution was
centrifuged to remove the insoluble impurities, and concentrated at reduced pressure
under nitrogen to about 8ml. The concentrated solution was subject to column
chromatography over neutral alumina with toluene/petroleum ether (2:1 v/v) as the
eluent to remove the unreacted C60, and followed with toluene as the eluent. The
second coloured band was collected and the solvent was removed by rotary
evaporation to get the target product. Yields are calculated based on consumed C60.
5,10,15,20-tetrakis(phenyl)porphyrin-fullerene, H2P-C60 Yield 65%. FTIR (KBr):
ν˜ = 3054, 3021, 2922, 2851, 2780, 1597, 1466, 1441, 1383, 1350, 1222, 1180, 1073,
965, 798, 729, 702, 526 cm-1.
1H NMR (400 MHz, CDCl3, 20oC): δ 9.53 (s, 1H,
P-pyrrole), 8.87~8.58, 8.23~7.77 (m, 26H, P-pyrrole, phenyl), 5.31 (s, 1H,
pyrrolidine), 4.72 (d 1H, J 9.6Hz pyrrolidine), 3.80 (d, 1H, J 9.6Hz pyrrolidine),
2.71 (s, 3H, methyl) and -2.65(s, 2H; H1-NH). UV/Vis (CH2Cl2): λmax= 256.2, 318.2,
423.5, 520.6, 553.4, 593.5, 650.7nm. MS (APCI): m/z calcd for C107H35N5, [M+H]-:
1390.5; found: 1390.2(M).

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5,10,15,20-tetrakis(4-methylphenyl)porphyrin-fullerene, H2PMe-C60 Yield 62%.
FTIR (KBr): ν˜ =3320,2971, 2919, 2851, 1510, 1461, 1383, 1261, 1218, 1181, 1089,
1041, 966, 880, 799, 732, 526 cm-1. 1H NMR (400 MHz, CDCl3, 20oC): δ 9.34 (s, 1H,
P-pyrrole), 8.85~8.55 , 8.06-7.15 (m, 22H, P-pyrrole, phenyl), 5.24 (s, 1H,
pyrrolidine), 4.41 (d 1H, J 1.2Hz pyrrolidine), 3.56 (d, 1H, J 1.2Hz pyrrolidine),
2.66 (s, 12H, methyl) 2.52 (s, 3H N-CH3(3H)) and -2.65(s, 2H; H1-NH). UV/Vis
(CH2Cl2): λmax= 255.1, 307.1, 426.2, 522.7, 556.4, 595.1, 653.4 nm. MS (APCI): m/z
calcd for C111H43N5, [M+H]-: 1446.6; found: 1446.3.
5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin-fullerene, H2POMe-C60 Yield
60%. FTIR (KBr): ν˜ =3321, 2924, 2851, 16005, 1509, 1462, 1384, 1287, 1246, 1173,
1
1035, 966, 840, 800, 733, 526. H NMR (400 MHz, CDCl3, 20oC): δ 9.40 (s, 1H,
P-pyrrole), 8.93~8.58 , 8.14-6.90 (m, 22H, P-pyrrole, phenyl), 5.38 (s, 1H,
pyrrolidine), 4.58 (d 1H, J 7.6Hz pyrrolidine), 3.74 (d, 1H, J 7.2Hz pyrrolidine),
4.10 (s, 12H, -OCH3), 2.50 (s, 3H N-CH3) and -2.65(s, 2H; -NH). UV/Vis (CH2Cl2):
λmax= 255.5, 317.4, 428.9, 522.7, 559.6, 596.4, 655.2nm. MS (APCI): m/z calcd for
C111H43N5O4: 1510.6, [M+H]-; found: 1510.3.
General Procedure for the Synthesis of 5,10,15,20-tetrakis(4-R-phenyl)
porphyrin zinc (II)-fullerene dyads, ZnPR-C60 (R=H,Me,OMe).
In a round-bottom flask, 0.01mmol of the corresponding dyad H2PR-C60
(R=H,Me,OMe) was dissolved in 4mL of CHCl3 and heated at reflux. A solution of
zinc acetate (5.5mg) in MeOH (2 mL) was added, and the reflux continued for 2h.
The progress of the reaction was monitored by TLC. The mixture was cooled to room

ACCEPTED MANUSCRIPT
temperature and extracted with water (15 mL). The upper aqueous phase was
removed after phase separation and the organic phase was dried over anhydrous
magnesium sulfate, and subject to column chromatography over neutral alumina with
toluene as the eluent. The second coloured band was collected and the solvent was
removed by rotary evaporation to get purple black product.
5,10,15,20-tetrakis(phenyl)porphyrin zinc(II)-fullerene, ZnP-C60 Yield 97%.
FTIR (KBr): ν˜ = 2922, 2851, 1636, 1462, 1440, 1384, 1262, 1072, 1004, 796, 749,
701, 526 cm-1. UV/Vis (CH2Cl2): λmax= 256.2, 312.5, 427.3, 555.1, 591.8 nm. MS
(APCI): m/z calcd for ZnC107H33N5:1453.8, [M+H]-; found:1453.1.
5,10,15,20-tetrakis(4-methylphenyl)porphyrin zinc(II)-fullerene, ZnPMe-C60
Yield 96%. FTIR (KBr): ν˜ = 2922, 2853, 1634, 1459, 1383, 1335, 1261, 1047, 998,
798, 726, 526 cm-1. UV/Vis (CH2Cl2): λmax= 256.9, 312.2, 428.3, 521.9, 555.8, 594.5
nm. MS (APCI): m/z calcd for ZnC111H41N5, [M+H]-:1509.9; found:1508.1.
5,10,15,20-tetrakis(4-methoxyphenyl)porphyrinzinc(II)-fullerene , ZnPOMe-C60
Yield 95%. FTIR (KBr): ν˜ = 2925, 1605, 1510, 1461, 1384, 1336, 1285, 1247, 1174,
1106, 1035, 998, 808 cm-1. UV/Vis (CH2Cl2): λmax= 256.5, 312.3, 430.7, 557.0, 598.3
nm. MS (APCI): m/z calcd for ZnC111H41N5O4, [M+H]-:1573.9; found: 1573.5.
Acknowledgments
The authors gratefully acknowledge the financial support from the National
Natural Science Foundation of China (No. 21771149) and the Natural Science
Foundation of Fujian Province of China (No. 2018J01012, 2013J01057)
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ACCEPTED MANUSCRIPT
Ito, Studies on covalently linked Porphyrin-C-60 dyads: Stabilization of
charge-separated states by axial coordination, Journal of Physical Chemistry A, 106
(2002) 12393-12404.
Fig.1. Structures of the Closely Spaced β-position-Bonded Porphyrin-fullerene Dyads

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