Syntheses and characterization of a series of oxacalix[4]arene-linked cofacial bisporphyrins

Article abstract of DOI:10.1142/S1088424610002367

A series of oxacalix[4]arene-linked cofacial bisporphyrins 2-4 have been synthesized as free-bases, biszinc(II) and biscopper(II) complexes. UV-vis, fluorescence and cyclic voltammetric studies were performed on the bisporphyrins. Little electronic intera

Full text of DOI:10.1142/S1088424610002367

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2010; 14: 523–530
DOI: 10.1142/S1088424610002367
Published at http://www.worldscinet.com/jpp/
Syntheses and characterization of a series of
oxacalix[4]arene-linked cofacial bisporphyrins
Lijuan Jiao*a, Yanhua Fangb, Yunyou Zhou*b, Sufan Wanga, Erhong Haoa and
M. Grac¸a H. Vicente*c◊
a Anhui Key Laboratory of Functional Molecular Solids and Anhui Key Laboratory of Molecular Based Materials,
College of Chemistry and Material Science, Anhui Normal University, Wuhu, Anhui 241000, China
b Anhui Key Laboratory of Chemo-Biosensing, College of Chemistry and Materials Science, Anhui Normal
University, Wuhu 241000, China
c Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803, USA
Received 22 January 2010
Accepted 6 April 2010
ABSTRACT: A series of oxacalix[4]arene-linked cofacial bisporphyrins 2–4 have been synthesized
as free-bases, biszinc(II) and biscopper(II) complexes. UV-vis, fluorescence and cyclic voltammetric
studies were performed on the bisporphyrins. Little electronic interactions between the two porphyrin
macrocycles in both the metal-free and biszinc(II) complexes 2 and 3 were observed, while enhanced
electronic communications were observed in the case of 4 bearing two copper(II) metal ions. Geometry
optimizations were carried out using HF/CEP-31G methods to investigate the molecular structures of
these bisporphyrins. Solvent effects on the photophysical properties of these bisporphyrins are also
discussed.
KEYWORDS: oxacalix[4]arene, cofacial bisporphyrins, photophysical, cyclic voltammograms.
Calixarenes have been extensively studied in the past
INTRODUCTION
decade due to their unique conformational cavity struc-
Cofacial bisporphyrins play important roles in diverse
ture and their molecular recognition properties. Por-
fields, as light-harvesting devices [1], energy and electron
phyrin-calix[4]arene conjugates have been synthesized
transfer materials [2], and as catalysts for multi-electron
by several groups [12]. Most of these molecules were
redox catalysis [3]. Among these, rigid spacer-linked
synthesized via the modification of the calixarene frag-
cofacial bisporphyrins, known as Pacman porphyrins,
ment. The total synthesis of these porphyrin-calixarene
have been mostly studied as hosts for small-molecule
conjugates suffers from long synthetic routes and very
reactions [4]. Most often, Pacman porphyrins [5, 6], such
low yields. The efficient synthesis of these bisporphyrins
as DPA (diporphyrin anthracene) [7], DPB (diporphyrin
remains a challenge, as well as the investigation of their
biphenylene) [8], DPX (diporphyrin dimethylxanthene)
properties [13]. Oxacalix[4]arene is a versatile platform
[9], DPD (diporphyrin dibenzofuran) [10] and DPS
that can be easily functionalized. In addition, this plat-
(diporphyrin dibenzothiophene) [11] are linked by rigid
form has a rigid discrete 1,3-alternate conformation with
spacers [7–11] including anthracene, biphenylene, dime-
appreciable flexibility [14] that is limited to a unique
thylxanthene, dibenzofuran and dibenzothiophene units.
form designated “slipped dimer” rather than a “face-to-
face dimer” [15].
Attracted to the interesting conformations of this
oxacalix[4]arene platform and based on the recent
SPP full member in good standing
improved synthetic route of this fragment by Katz et al.
[14a], we have recently reported the synthesis and charac-
terization of a series of oxacalix[n]arene-locked cofacial
*Correspondence to: Lijuan Jiao, email: jiao421@mail.ahnu.
edu.cn; Yunyou Zhou, email: zy161299@mail.ahnu.edu.cn
and M. Graca H. Vicente, email: vicente@lsu.edu
Copyright © 2010 World Scientific Publishing Company

524
L. JIaO et al.
bisporphyrins and higher oligomers [16]. The X-ray
structure of a metal-free bisporphyrin shows a “slipped
dimer” conformation [16]. We envisioned that the intro-
duction of metal ions into the porphyrin macrocycles to
build the corresponding homobimetallic bisporphyrins
would lead to interesting photophysical and electro-
chemical properties for this system. Herein, we report
the synthesis, photophysical and electrochemical proper-
ties as well as the geometry optimization based on HF/
CEP-31G methods of these new bismetallic oxacalix[4]
arene-linked cofacial bisporphyrins 3 and 4 and compare
them to those of the previously reported [16] metal-free
system 2.
Cu(OAc)2·2H2O (100 mg, 0.45 mmol) in 15 mL of meth-
anol. The resulting solution was refluxed until TLC indi-
cated that the reaction was completed. After removal of
the solvents under vacuum, the resulting solid was dis-
solved in a 1:1 mixture of dichloromethane and water
(100 mL). The organic layer was washed with water
(3 × 50 mL) and dried over anhydrous Na2SO4; solvent
was removed under vacuum. The crude product was
purified by column chromatography on silica gel using
dichloromethane for elution. Complex 4 was obtained in
90% yield (71 mg). Anal. calcd. for C100H56Cu2N12O12:
C, 68.84; H, 3.24; N, 9.63%. Found: C, 68.70; H, 3.44;
N, 9.52. MS (MALDI-TOF): m/z 1744.9 (calcd. for
C100H56Cu2N12O12 1744.7).
EXPERIMENTAL
Cyclic voltammetry
Cyclic voltammetry (CV) was conducted in a standard
three-electrode cell with the use of CHI 660 potentiostat-
galvanostat (Shanghai Chenhua Instrumental Coop-
eration Ltd., China). A Pt wire served as the auxiliary
electrode, an Ag/AgCl electrode was used as a reference
electrode, and the glassy carbon electrode (GCE) was
used as a working electrode. The reference electrode was
separated from the bulk of the solution by a bridge filled
with the solution to be investigated. The bridge was then
placed in another tube ending in a lugging capillary tip.
The GC electrode (GCE) was polished consecutively
with diamond paste until a mirror finish was obtained.
The polished electrode was cleaned in an ultrasonic water
bath for 5 min to remove the diamond and carbon parti-
cles. The total volume of the electrolysis cell was 2–5 mL
and concentrations of porphyrins and bisporphyrins solu-
tions were 1 × 10-3 M. Sweep rate was set at 60 mV.s-1.
Constant-potential coulometer was conducted at room
temperature in dry dichloromethane. Trihexyl(tetradecyl)
phosphonium hexafluorophosphate was used as the sup-
porting electrolyte at a concentration of 0.1 M. Deaera-
tion of the solution with high-quality purified nitrogen
was performed before commencing the experiment. All
experiments were carried out in a controlled temperature
room and potentials are reported with respect to the
Ag/AgCl electrode.
General
Reagents were purchased as reagent-grade and used
without further purification unless otherwise stated. Sol-
vents were used as received from commercial suppliers
unless noted otherwise. THF was freshly distilled from
sodium benzophenone ketyl. All reactions were per-
formed in oven-dried or flame-dried glassware unless oth-
erwise stated, and were monitored by TLC using 0.25 mm
1
silica gel plates with UV indicator (60F-254). H NMR
are obtained on a Bruker AV-300 spectrometer at 298 K.
Chemical shifts (δ) for 1H NMR spectra are given in ppm
relative to THF-d8 (3.58 and 1.73 ppm). Chemical shift
multiplicities are reported as s = singlet, d = doublet, q =
quartet, and m = multiplet. Mass spectra were obtained on
anAppliedBiosystemsQSTARXL;thematrixusedforthe
MALDI analyses was anthracene. Elemental analysis was
obtained on VarioEL III. 5,15-di(3,5-dihydroxyphenyl)-
porphyrin 1 and oxacalix[4]arene bisporphyrin 2 were
synthesized following previously reported procedures
[16, 17]. The optimized structures of bisporphyrins 2, 3
and 4 were modeled by ab initio HF/CEP-31G method
[18]. The geometrical structure of bisporphyrin 2 was in
consistence with its X-ray structure [16].
Synthesis
Biszinc(II)porphyrin 3 was synthesized by reacting 2
(81 mg, 0.05 mmol) with excess amount of Zn(OAc)2 (92
mg, 0.5 mmol) in a refluxing mixture of chloroform/meth-
anol (60 mL, v/v = 3/1). The crude product was purified
by column chromatography (silica gel, dichloromethane)
to give complex 3 in quantitative yield (87 mg). 1H NMR
(300 MHz; THF-d8): δΗ, ppm 9.06 (s, 2H), 8.71 (br, 16 H),
8.41 (m, 8H), 8.23 (m, 8H), 7.83 (s, 2H), 7.78 (m, 18H),
7.11 (s, 2H). Anal. calcd. for C100H56N12O12Zn2·2CH3OH:
C, 67.59; H, 3.56; N, 9.28%. Found: C, 67.65; H, 3.61;
N, 9.14. HRMS (MALDI-TOF): m/z 1748.2728 (calcd.
for C100H56Zn2N12O12 1748.2715).
UV-vis and fluorescence analysis
UV-visible absorption spectra were recorded on a
Hitachi U-3010 spectrophotometer (190–1100 nm scan
range). Fluorescence emission spectra were recorded
on a Hitachi F-4600 FL spectrophotometer. The slit
widths were 2.5 nm and 5.0 nm for excitation and emis-
sion, respectively. Solvents and reagent for photophys-
cial studies were purchased as analytical grade and were
used freshly distilled. All measurements were recorded
at 20 °C. Fluorescence lifetimes were measured on a
combined steady-state lifetime fluorescence spectrom-
eter model FLS920 (Edinburgh Instruments) and the
fluorescence lifetimes were obtained from deconvolution
Biscopper(II)porphyrin 4. To a solution of 2
(73 mg, 0.045 mmol) in 50 mL of chloroform was added
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SyntheSeS anD CharaCterIzatIOn Of OxaCaLIx[4]arene-LInkeD COfaCIaL bISPOrPhyrInS
525
and distribution lifetime analysis [19]. Fluorescent quan-
upon reaction of porphyrin 1 with 1,5-difluoro-2,4-di-
nitrobenzene, as we have previously reported [16]. The
starting porphyrin 1 can be prepared in multigram scale
by a mixed aldehyde condensation in propionic acid, fol-
lowed by demethylation with BBr3 in dichloromethane
[17]. The homobimetallic coordination complexes 3 and
4 were prepared by direct reaction of 2 with the corre-
sponding metal(II) salts (as shown in Scheme 1). Com-
plex 3 was synthesized in quantitative yield from the
reaction of 2 with Zn(OAc)2 in a methanol/chloroform
mixture and was characterized by 1H NMR, high-resolution
mass spectrometry, and elemental analyses. Complex 4
was obtained in excellent yield (90%) by reaction of 2
with Cu(OAc)2·2H2O in a methanol/chloroform mixture
and was characterized by mass spectra and elemental
analysis.
The UV-vis data for bisporphyrins 2, 3 and 4 at room
temperature are presented in Table 1 and Fig. 2. The
absorption bands in the Soret and Q regions exhibit the
expected patterns for the corresponding two porphyrin
chromophores (free-base for 2 or metallic for 3 and 4).
The absorption characteristics of 2 and 3 closely approxi-
mate the monomer H2TPP and ZnTPP, respectively, indi-
cating the enlarged distance between the two porphyrin
chromophores in the “slipped dimer” conformer. In com-
parison to 2, little variation in the λmax of the Soret band
was observed for 3. The two Q bands typical of a metal-
loporphyrin were observed for 3, in contrast with those
observed for 2. Therefore, we conclude that the inser-
tion of zinc(II) has little effect on the electronic com-
munication between the two porphyrin macrocycles. The
increased separation decreases π-π overlap and excitonic
coupling between the porphyrin subunits [24]. In contrast,
characteristics of strongly interacting porphyrin sub-units
was observed in 4: the blue shift of the Soret band to 412
nm, and the red shift (by 8 nm) of Q(1,0) and the Q(0,0)
maxima. These results suggest enhanced excitonic inter-
actions with the insertion of copper(II) ions [25].
tum yields were calculated using a secondary standard
method by comparing the areas under the corrected
emission spectrum of the test sample in various solvents
with that of the standard. Dilute solutions (0.01 < A <
0.05) were used to minimize the reabsorption effects and
correction for the solvent refractive index was applied.
H2TPP in dry DMF (ΦF = 0.11 [20]) and ZnTPP in tolu-
ene (ΦF = 0.03 [21]) were used as a fluorescence standard
for the fluorescent quantum yield calculation according
to the absorption of the test sample [22]. Quantum yields
were determined using the following equation [23]:
ΦX = ΦS (IX/IS) (AS/AX) (ηX/ηS)
(1)
where ΦS stands for the reported quantum yield of the
standard, I stands for the integrated emission spectra, A
stands for the absorbance at the excitation wavelength,
and η stands for the refractive index of the solvent being
used (η = 1 when the same solvent was used for both the
test sample and the standard). X subscript stands for the
test sample and S subscript stands for the standard.
RESULTS AND DISCUSSION
Metal-free bisporphyrin 2 with a “slipped dimer”
conformation (Fig. 1) was synthesized in 91% yield
Ph
Ph
HN
N
Ph
NH
Ph
N
N
NH
N
Ph
HN
Ph
O
O
O2N
NO2
O
O
O2N
NO2
The fluorescence data for bisporphyrins 2 and 3 are
presented in Table 1 and Fig. 3. The comparison of the
Fig. 1. “Slipped dimer”conformation of bisporphyrin 2
F
O2N
O2N
O
NO2
O
HO
OH
Ph
Ph
M
N
N
N
N
N
N
N
N
F
O2N
Ph
Ph
M
K2CO3
DMSO
N
NH
N
Ph
Ph
O
O
HN
Ph
Ph
O2N
NO2
Ph
M = 2H
2
i)
ii)
M = Zn(II)
M = Cu(II)
3
4
Scheme 1. Synthesis of oxacalix[4]arene linked cofacial bisporphyrins 2, 3 and 4, reaction conditions: (i) excess Zn(OAc)2, chloro-
form/methanol (v/v = 3/1), refluxing; (ii) excess Cu(OAc)2·2H2O, chloroform/methanol (v/v = 3/1), refluxing
Copyright © 2010 World Scientific Publishing Company
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526
L. JIaO et al.
Table 1. UV-vis and fluorescence data for bisporphyrins 2, 3 and 4 in dichloromethane at 20 °C
2
Compound
log ε
λabsmax, nm
λem max, nm
ΦF
Lifetime λF, ns (χ )
Soret band
Q bands
H2TPP
5.34
5.67
6.21
6.17
6.02
417
422
418
416
412
514, 547, 592, 648
550, 590
656, 720
602, 650
660, 724
612, 657
—
0.13
0.04
0.12
0.01
—
8.47 (1.00)
1.70 (1.01)
9.28 (0.93)
1.22 (1.03)
ZnTPP
2
3
4
518, 552, 592, 648
550, 590
526, 560 (sh)
Fig. 4. The excited state lifetime of bisporphyrins 2 (dots) and
3 (solid) in dichloromethane measured with time-correlated
single photon counting method fitting with one exponential
Fig. 2. UV-vis spectra of bisporphyrins 2 (solid), 3 (dashes) and
4 (dots) in dichloromethane
of bisporphyrins 2 and 3 were obtained by an interac-
tive nonlinear deconvolution fitting procedure. The fitted
fluorescence lifetime data for 2 and 3 are similar to the
corresponding monoporphyrins (H2TPP and ZnTPP),
respectively. In comparison to 2, bisporphyrin 3 exhibits
a large decrease of the fluorescence lifetime, similar to
the literature result [26], which may be attributed to the
heavy atom effect of zinc(II) metal ions. In addition, the
lifetime decays are all monoexponential, indicating that
only one species is fluorescing. This similarity indicates
that the two porphyrin chromophores in both 2 and 3 have
few interactions, and is consistent with most reported
5,17-substituted derivatives of coneshaped calix[4]arenes
when the open conformation is adapted [27].
Fig. 3. Fluorescence spectra of H2TPP (solid), ZnTPP (dashes),
bisporphyrins 2 (dots) and 3 (dash-dot) in dichloromethane
The solvent effect on the absorption spectra of these
bisporphyrins was also studied and the results are sum-
marized in Table 2. Polar protic solvents, such as metha-
nol and ethanol, cause a blue shift (by 8–9 nm) of the
Soret band for 2 versus H2TPP; on the other hand, polar
aprotic solvents, such as DMSO and THF lead to a red
shift (by 6–12 nm) of the Soret band for 3 vs. ZnTPP. The
increased polarity of the solvent leads to the increased
polarization forces between the solvent and the absorber
(porphyrin), which lowers the energy levels of both the
excited and unexcited states for π-π* transitions. Since
this effect is greater for the excited state, the energy
λemission for 2 vs. H2TPP shows little variation in most of
the solvents studied, with a slight increase of the quan-
tum yield (ΦF). In comparison with ZnTPP, the λemission
of 3 shows a slight red shift (to 612 and 657 nm) in most
solvents studied. These observations are in agreement
with the absorption changes, and indicate little interaction
between the two porphyrin chromophores in 2 and 3.
The fluorescence decay signals and fitted lines are
presented in Table 1 and Fig. 4. The excited lifetimes
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SyntheSeS anD CharaCterIzatIOn Of OxaCaLIx[4]arene-LInkeD COfaCIaL bISPOrPhyrInS
527
Table 2. UV-vis and fluorescence spectra of bisporphyrins 2 and 3 in various solvents
a
a
Solvent
Compounds λabs
,
log ε λem
,
ΦF
Solvent
Compounds λabs
,
log ε λem
,
max
nm
ΦF
max
max
max
nm
nm
nm
acetonitrile
H2TPP
413
5.56 656, 718 0.19 diethyl ether
5.74 657, 721 0.29
H2TPP
414
5.56 654, 718 0.18
6.05 659, 722 0.12
2
404
423
418
2
416
419
418
ZnTPP
5.83 610, 660 0.03
6.10 614, 664 0.01
ZnTPP
5.83 608, 656 0.02
6.10 616, 664 0.03
3
3
methanol
H2TPP
412
5.51 654, 718 0.21 methylene
chloride
H2TPP
417
5.34 656, 720 0.13
2
ZnTPP
3
404
419
416
5.49 658, 721 0.35
5.87 606, 658 0.02
6.09 614, 663 <0.01
2
ZnTPP
3
418
422
416
6.21 660, 724 0.12
5.67 602, 650 0.04
6.17 612, 657 0.01
ethanol
DMSO
THF
H2TPP
413
404
5.62 654, 718 0.18 chloroform
5.77 659, 723 0.25
H2TPP
418
418
5.61 658, 720 0.08
6.25 661, 724 0.09
2
2
ZnTPP
420
422
5.88 608, 658 0.03
6.05 615, 664 <0.01
ZnTPP
421
416
5.83 604, 648 0.03
6.17 611, 655 0.01
3
3
H2TPP
418
418
5.57 656, 718 0.19 toluene
5.96 658, 723 0.18
H2TPP
418
420
5.60 658, 720 0.09
6.26 659, 722 0.12
2
2
ZnTPP
427
428
5.90 612, 664 0.04
6.23 615, 662 <0.01
ZnTPP
420
418
5.82 604, 650 0.03
6.12 612, 655 0.04
3
3
H2TPP
416
5.55 658, 720 0.02 carbon
tetrachloride
H2TPP
419
5.56 658, 722 0.06
2
ZnTPP
3
416
423
422
6.27 659, 724 0.12
5.91 610, 658 <0.01
6.23 615, 663 0.02
2
ZnTPP
3
420
421
418
6.23 662, 725 0.12
5.86 606, 646 0.04
6.19 615, 657 0.03
ethyl acetate
H2TPP
414
414
419
420
5.59 654, 718 0.13 cyclohexane
6.17 657, 722 0.12
H2TPP
416
408
424
416
5.55 658, 720 0.11
5.87 661, 725 0.16
5.91 602, 644 0.03
6.06 619, 666 0.03
2
ZnTPP
3
2
ZnTPP
3
5.76 606, 656 0.02
6.19 612, 661 0.02
a Room temperature, excited at 500 nm. The reference for quantum yield is H2TPP in DMF 0.11 [20] and ZnTPP in toluene 0.03 [21].
difference between the excited and unexcited states is
slightly reduced, resulting in a small red shift of the Soret
band as observed in 3. On the other hand, the observed
small blue shift for 2 due to the polarity change of the sol-
vent might have arisen from the conformational changes
of calix[4]arene, as described in literature [28–29]. For
example, based on X-ray structures, Love et al. have
observed two different structural motifs of a calixpyrrole
macrocycle in the presence of a protic solvent: a non-
planar bowl-like conformation in ethanol and a Pacman-
type conformation in water [29].
Since the aggregation of these bisporphyrins in solu-
tion may also bring about variation of the absorption spec-
tra, to verify the metal ion effect on the spectral changes
of these molecules, we also investigated the relationship
between the absorption spectra and the concentration of
these bisporphyrins. The absorption maxima were found
to be independent of the concentration of these bispor-
phyrins (typically 10-4~10-6 M). The linear relationship
between the absorption intensity and the concentration
of these bisporphyrins indicates no anomalous behavior
associated to aggregation effects, as previous described
for cofacial bisporphyrins [2, 6, 7c].
The cyclic voltammetric (CV) data for bisporphyrin
2, 3 and 4 are shown in Table 3. All cyclic voltammo-
grams are similar in shape and yielded three or four peaks,
depending on the presence and nature of the metal ions
at the center of the porphyrin macrocycles. The electron
transfers are in all cases diffusion-controlled and yielded
well-defined current-voltage curves with the theoreti-
cal peak separation for a one-electron transfer. H2TPP is
used as a reference, giving two redox peaks (-1.01 V and
-1.32 V) and two oxidation peaks (1.20 V and 1.54 V)
corresponding to the macrocycle-centered reduction and
Copyright © 2010 World Scientific Publishing Company
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528
L. JIaO et al.
Table 3. Cyclic voltammograms (CV) data of 2, 3 and 4 in
dichloromethane under pure N2 atmosphere
above and indicates little electronic interaction between
the two porphyrin macrocycles. The comparison of the
CV data for 3 vs. ZnTPP also shows little variation and
indicates little electronic interactions between the two
porphyrin macrocycles. The voltammogram for 4 was
similar in shape and form to that of 3, and the E1/2 is
proportional to the electronegativity of the central metal
ions as observed for metalloporphyrins with stable two-
valent central metal ions (Zn and Cu)[32]. The overlayed
CV spectra for 4 and CuTPP was shown in Fig. 5, which
indicates the electronic communication between the two
porphyrin macrocyles and is consistent with the photo-
physical changes described above.
Compound
Eox, V
Ere, V vs
vs Ag/AgCl
Ag/ AgCl
H2TPP
1.54
1.20
0.89
1.08
1.20
0.81
1.27
-1.01
-1.32
-1.59
-1.64
-1.45
-1.51
-1.50
ZnTPP
1.37
1.42
1.33
1.32
1.62
-1.38
-1.23
-1.06
-1.43
-0.97
CuTPP
2
3
4
We further investigated the distance between the two
porphyrin macrocycles based on the HF/CEP-31G calcu-
lation results [18]. The ab initio HF/Cep-31g optimized
structures of bisporphyrins 2, 3 and 4 are shown in Fig. 6.
The optimized structure for the metal-free bisporphyrin
2 was in agreement with the X-ray structure of this mol-
ecule, with the distance between two porphyrin macro-
cycles at 8.471 Å. In comparison with complex 2, a slight
increase of the distance was observed in bisporphyrin 3
(8.557 Å) after the insertion of Zn2+ into the porphyrin
macrocycles, while a large decrease of the distance was
observed in bisporphyrin 4 (7.108 Å) after the insertion
of Cu2+. The short distance observed in bisporphyrin 4
may account for the enhanced electronic communica-
tion between the two porphyrin macrocycles, which is
in consistence with the photophysical changes and CVs
described above.
Fig. 5. Cyclic Voltammograms of 1 × 10-3 M CuTPP (solid)
and 1 × 10-3 M bisporphyrin 4 (dashes) in dry dichloromethane.
Trihexyl(tetradecyl)phosphonium hexafluorophosphate as the
supporting electrolyte at a concentration of 0.1 M, glassy car-
bon electrode (GCE) as a working electrode, and scan rate at
60 mV.s-1
CONCLUSION
We report the syntheses of a series of cofacial
homobimetallic bisporphyrins, their photophysical
and electronic properties, and HF/CEP-31G computa-
tional results, along with those of a previously reported
metal-free bisporphyrin. We observed little electronic
interaction between the two porphyrin macrocycles
in the free-base and biszinc(II) complexes 2 and 3,
while enhanced electronic interactions were observed
between the two porphyrin macrocycles in 4 bearing two
copper(II) ions.
oxidation reactions, which is consistent with previous
reported values [30]. The comparison of the CV data
of 2 vs. H2TPP shows little variation: two redox peaks
(-1.06 V and -1.45 V) and two oxidation peaks (1.20 V
and 1.33 V). All four reactions were diffusion-controlled
and, in agreement with previous electrochemical results,
the potential difference between anion and cation radi-
cal formation (2.26 V) is 2.25 0.15 V [31]. This result
is consistent with the photophysical changes described
Fig. 6. Tube models of the ab initio HF/CEP-31G optimized structures of bisporphyrins (A) 2, (B) 3 and (C) 4
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J. Porphyrins Phthalocyanines 2010; 14: 528–530

SyntheSeS anD CharaCterIzatIOn Of OxaCaLIx[4]arene-LInkeD COfaCIaL bISPOrPhyrInS
529
Acknowledgements
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This work is supported by the National Nature Sci-
ence Foundation of China (Grants 20802002, 20902004
and 20875002), Anhui Province (Grants 090416221 and
KJ2009A130) and the United States National Science
Foundation (Grant CHE-0911629).
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