Effects of an axial ligand on the reduction potential, proton dissociation, and fluorescence quantum yield of hydroxo(porphyrinato)antimony(V) complexes

Article abstract of DOI:10.1246/bcsj.75.1577

The substituent effects on the reduction potentials (E_1/2^red), the proton dissociation constants of a hydroxo ligand (K_a), and the fluorescence quantum yields (Φ) in aryloxo(hydroxo)tetraarylporphyrinatoantimony(V) complexes were investigated. The E_1/2^red and K_a values were affected by substituents in the axial aryloxo ligand but, little affected by substituents in the porphyrin ring. Since E_1/2^red of tetraarylporphyrinatoantimony(V) complexes were higher than those of other metal-porphyrin complexes, it was suggested that the metal orbital greatly contributed to the LUMO level of the complex which can be related to the E_1/2^red and K_a values. Therefore, the substituent effects of the axial aryloxo ligand on the E_1/2^red and K_a values were attributed to the electron density of the antimony ion, which affected the LUMO level of the complexes. Moreover, the of the porphyrin moiety depended on both the oxidation potential of the axial aryloxo ligands and the polarity of the solvent used. The fluorescences of the porphyrin moiety were quenched by the axial aryloxo ligands at rate constants of 10⁸-10¹¹ s^-1.

Full text of DOI:10.1246/bcsj.75.1577

Bull. Chem.
Soc. Jpn.
75
7
© 2002 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 75, 1577–1582 (2002) 1577
The Chemical
Society of Ja-
pan
The Chemical
Society of Ja-
pan
OB
7
15
Effects of an Axial Ligand on the Reduction Potential, Proton
Dissociation, and Fluorescence Quantum Yield of
Hydroxo(porphyrinato)antimony(Ⅴ) Complexes
Hydroxo(porphyrinato)antimony(Ⅴ) Complexes
T. Shiragami et al.
2002
1577
1582
BCSJA8
0009-2673
01440
12
Tsutomu Shiragami,* Yoshito Andou, Yuichiro Hamasuna, Futoshi Yamaguchi, Kensuke Shima, and
Masahide Yasuda
Department of Applied Chemistry, Faculty of Engineering, Miyazaki University and CREST, JST (Japan Science and
Technology), Gakuen-Kibanadai, Miyazaki 889-2192
13
(Received December 13, 2001)
2001
3
4
The substituent effects on the reduction potentials (E1/2red), the proton dissociation constants of a hydroxo ligand
(Ka), and the fluorescence quantum yields (Φ) in aryloxo(hydroxo)tetraarylporphyrinatoantimony(Ⅴ) complexes were in-
vestigated. The E1/2red and Ka values were affected by substituents in the axial aryloxo ligand but, little affected by sub-
2002
red
stituents in the porphyrin ring. Since E1/2 of tetraarylporphyrinatoantimony(Ⅴ) complexes were higher than those of
1.1
other metal-porphyrin complexes, it was suggested that the metal orbital greatly contributed to the LUMO level of the
complex which can be related to the E1/2red and Ka values. Therefore, the substituent effects of the axial aryloxo ligand on
the E1/2red and Ka values were attributed to the electron density of the antimony ion, which affected the LUMO level of the
complexes. Moreover, the Φ of the porphyrin moiety depended on both the oxidation potential of the axial aryloxo
ligands and the polarity of the solvent used. The fluorescences of the porphyrin moiety were quenched by the axial aryl-
4.9.2
4.13.1
oxo ligands at rate constants of 108 – 1011 s−1
.
The synthesis and characterization of porphyrinatometal
complexes have been extensively studied from the view points
of biological interests involving the photosynthesis and redox
processes for many years. Therefore, the most intense atten-
tion has been focused on transition-metal and typical low-va-
lent element complexes of porphyrin. On the other hand, a
typical high-valent element is expected to lower the LUMO
and HOMO levels of porphyrinatometal complexes and to co-
valently bond with axial ligands, differing from the transition-
metal complexes.1–3 Our attention has especially been paid to
porphyrinatophosphorus(Ⅴ) and antimony(Ⅴ) complexes hav-
ing the functionalized moieties on axial ligands. We have al-
ready reported the photoinduced intramolecular electron and
energy transfer between a porphyrin ring and axial π-electron
chromophores linked by a methylene chain in porphyrinatoan-
timony(Ⅴ) complexes.4–5 However, there is no information
about the properties of porphyrinatoantimony(Ⅴ) complexes
affected by π-electron chromophores directly coordinated to
an antimony atom as an axial ligand without a methylene
bridge.
vestigated for dihydroxo(tetraarylporphyrinato)antimony(Ⅴ)
complexes (1a–c) having substituents (X = OMe, H, CN) on
the tetraphenylporphyrinato ring and aryloxo(hydroxo)(tetra-
phenylporphyrinato)antimony(Ⅴ) complexes (2a–d) having
substituents (Y = OMe H, F, CN) on the aryloxo axial ligand
(Scheme 1).
Moreover, (m-dimethylaminophenoxo)-(hy-
droxo)(tetraphenylporphyrinato)antimony(Ⅴ) complex (3) was
used for the substituent effect on the fluorescence spectra.
Substituent Effect on Reduction Potentials.
The half
peak of the reduction potentials (E1/2red) of 1a–c and 2a–d are
summarized in Table 1. Figure 1 shows a voltammogram of 1a
as a typical example. The first reduction peaks of 1a–c were
reversible, since the ratio (ipc/ipa) of the peak current intensity
at a cathodic sweep (ipc) to that at an anodic sweep (ipa) were
measured to be 0.8–1.0, and the peak potential differences
(∆Ep) between the cathodic and anodic sweeps at the first re-
duction potential were 40–80 mV, which were theoretically
predicted. Moreover, ∆E values, which are the differences be-
tween the first reduction peaks and the second reduction peaks
of 1a–c, were 0.43–0.48 V. Similar ipc/ipa , ∆Ep values, and ∆E
values were reported for the reversible process of various octa-
ethylporphyrinatometal complexes.6–7 On the other hand, the
oxidation potentials of 1a–c did not show reversible peaks.
Therefore, the reductants of 1a–c were stable compared with
their cation radicals. A similar behavior was observed for 2a–
d. If the reductant generated by the first reduction is the π-rad-
ical anion, this process does not become reversible by the fol-
lowing process (protonation e.t.c.). Therefore, the reductants
can be assigned to a valence change of antimony from five to
four in the reduction process.
Here, we elucidate the effects of an axial aryloxo ligand in
aryloxo(hydroxo)(tetraphenylporphyrinato)antimony(Ⅴ) com-
plexes, ([Sb(tpp)(OH)(OAr)]+; tpp = tetraphenylporphyrinato
group) on their electrochemical properties, proton dissociation
of hydroxo ligand, and excited singlet-state properties.
Results
Hydroxo(tetraarylporphyrinato)antimony(Ⅴ) Complex-
es. The substituent effects on the reduction potential, the pro-
ton dissociation, and the fluorescence quantum yield were in-

1578 Bull. Chem. Soc. Jpn., 75, No. 7 (2002)
Hydroxo(porphyrinato)antimony(ꢀ) Complexes
Scheme 1.
Table 1. Redox Potential and Ka of 1a–c and 2a–d
E1/2red/V
an aqueous KOH solution into a MeCN–H2O (7:3, v/v) solu-
tion of 2a, the absorption maximum (λmax) of the Soret band
was shifted from 419 nm to 422 nm with an isobestic point at
420 nm, as shown in Fig. 2. Upon the addition of HClO4 to an
alkaline solution, the shifted Soret band returned to the origi-
nal position, thus revealing that the spectral change was due to
a reversible proton-dissociation process (Scheme 2). More-
over, no occurrence of the substitution of the phenoxy group
with a hydroxy group was confirmed by FAB-MS measure-
ments of complexes treated by an acid and a base. The proton-
dissociation constant (Ka) of 2a was estimated from the con-
centration of KOH required for a half shift of the maximum
shift in plots of the λmax vs the concentration of KOH (Fig. 2).
Substituent Effect on Fluorescence Quantum Yield.
The fluorescence of 1a–c appeared at λmax of 594–597 nm in
MeCN with Φ of 0.00468–0.0518. Also, the fluorescence
spectra 2a–d appeared at 594–597 nm in MeCN under the ex-
citation of a porphyrinato chromophore at 420 nm. However,
the Φ of 2a (X = OMe) was extremely smaller than those for
2b (X = H), 2c (X = F), and 2d (X = CN) (Table 2). The ab-
sorption spectra of 2a–d were essentially similar to those of
1a–c, except for the appearance of an extra band due to the ax-
ial aryloxo ligand at a shorter wavelength than 300 nm. Thus,
no strong interaction between the porphyrin ring and the axial
aryloxo ligand in the ground state was confirmed by the simi-
larity of the Soret bands between 1a–c and 2a–d. In the case
of 2a, therefore, the occurrence of intramolecular fluorescence
quenching by the axial aryloxo ligand was supposed.
E1/2ox/V
Ka/104
0.83
0.43
1.33
0.56
0.56
3.63
5.33
Firsta) Secondb) ∆Ec)
Pord) Ligande)
1.40
1.40
1.41
1.64
1.50
1.55
1.76
1a
1b
1c
2a
2b
2c
2d
−0.51
−0.51
−0.52
−0.54
−0.46
−0.46
−0.46
−0.99
−0.95
−0.95
−0.90
−0.87
−0.87
−0.85
0.48
0.44
0.43
0.36
0.41
0.41
0.39
0.70
0.93
1.39
1.59
a) The half-peak of first reduction potential of porphyrinato
moiety. b) The half-peak of second reduction potential of
porphyrinato moiety. c) ∆E values were differences
between first and second half-peaks of reduction potentials
of porphyrinato moiety. d) The half-peak of oxidation
potential of porphyrinato moiety. e) The half-peak of oxi-
dation potential of the axial aryloxo ligand.
In the case of 3, having a dimethylaminophenyl group as the
axial ligand, the fluorescence quantum yield was very small,
probably due to intramolecular quenching of the porphyrin
moiety by the axial aryloxo ligand, similar to the case of 2a
mentioned above. However, the addition of HClO4 (3.2 × 10−2
mol dm−3) to a MeCN solution of 3 restored the fluorescence
intensity from 0.002 to 0.015, as shown in Fig. 3. The restora-
tion of the fluorescences by the addition of the acid can be at-
Fig. 1. Cyclic voltammogram of 1a at 0.3 V/s rate in MeCN.
Substituent Effect on the Proton Dissociation Constants
of Hydroxo Ligand in 1a–c and 2a–d. By the addition of

T. Shiragami et al.
Bull. Chem. Soc. Jpn., 75, No. 7 (2002) 1579
Fig. 2. (A) Spectral change of Soret band of 2a in MeCN–H2O (4:1 v/v) solution by the additon of aqueous KOH solution.
(B) Plots of λmax vs the concetration of OH−.
Scheme 2.
Table 2. Fluorescence Properties of 2a–d
c)
2
Φ/10−3 a)
∆G/eVb)
log kq
λmax/nm
2a
0.3
2.4
6.9
−0.84
−0.69
−0.23
−0.03
11.2
10.3
9.6
597, 645
596, 647
594, 647
594, 646
2b
2c
2d
29.8
8.9
a) Fluorescence quantum yields at the excitation at 420 nm
in MeCN.
b) ∆G = E1/2ox−E1/2red−E0–0 where E0–0 = 2.08 eV.
c) kq values were calculated by the following equation: kq
= (Φ0/Φ−1)/τf where τf was 1.7 ns and Φ0 was 0.0518
(Data from Ref. 5).
Fig. 3. The change of fluorescence quantum yields of 3 with
HClO4 in MeCN.
tributed to a decrease in the electron-donating ability of the ax-
ial aryloxy group by protonation on the nitrogen atom of the
dimethylaminophenoxo axial ligand (Scheme 3).
The fluorescence spectra of 2b were measured in toluene,
benzene, 1,4-dioxane, tetrahydrofuran, ethyl acetate, dichlo-
romethane, and acetonitrile upon the excitation of porphyrin
Soret band (λ = 420 nm). The emission maxima (λmax) of 2b
were observed at 596 nm independently on the solvent used,
while the fluorescence quantum yield (Φ) depended on the sol-
vent used, as shown in Table 3.
Scheme 3.
Discussion
natometal complex is simultaneously lower and the contribu-
tions of the metal orbital to the LUMO of the complexes are
greater. On the other hand, porphyrinatometal complexes (i.e.
Zn(ꢀ), Ni(ꢀ)) having largely negative reduction potentials
have a higher LUMO level, which can be predominantly af-
fected by the porphyrin orbitals. Previous reports have eluci-
Effects of an Axial Aryloxo Ligand. Scheme 4 shows a
typical energy diagram between the metal orbital and the por-
phyrin orbital. Because the LUMO levels of the high-valent
metal ion are lower, i.e. the reduction potentials of the metal
ion shifts to the positive side, the LUMO level in the porphyri-

1580 Bull. Chem. Soc. Jpn., 75, No. 7 (2002)
Table 3. Fluorescence Quantum Yields of 2b
Hydroxo(porphyrinato)antimony(ꢀ) Complexes
mony(Ⅴ) complex without an interaction with the axial ligand,
the rate constants (kq) for the quenching of porphyrin moiety in
the excited singlet state of 2a–d by the axial aryloxo ligands
were estimated by the following equation, where τf and Φ0 are
the fluorescence lifetime (1.7 ns) and the fluorescence quan-
tum yield (0.0518) of 1b in MeCN, respectively:5
d)
Solventa)
ET(30)b)
Φ0/10−3 c)
Φ/10−3
log kq
TL
33.9
34.5
36.0
37.4
38.1
41.1
46.0
29
28
36
39
40
35
52
21
20
18
2
3
3
8.35
8.37
8.77
10.0
9.8
BZ
DO
TF
EA
DM
AN
kq = (Φ0 / Φ − 1) / τf,
(1)
9.8
10.2
2
The free-energy changes (∆G) of the intramolecular elec-
tron transfer from the axial aryloxo ligand to the excited sin-
glet state of the porphyrin moiety of 2a–d were calculated by
the Rehm–Weller equation (Eq. 2)9 using the oxidation poten-
tials (E1/2ox) of the axial aryloxo ligand, E1/2red of the porphyrin
ring, and the excitation energy (E0-0). The Coulombic term
was estimated to be very small, since a positive charge transfer
from the porphyrinato chromophore to the axial ligands caused
no change in the total charge. Thus, the ∆G values for 2a–d
were calculated to be exoergonic, as shown in Table 2.
a) TL; toluene, BZ; benzene, DO; 1,4-dioxane, TF; tetrahy-
drofuran, EA; ethyl acetate, DM; dichloromethane, and
AN; acetonitrile. b) Empirical solvent parameter. c) Fluo-
rescence quantum yield for 1b. Data from Ref. 5. d) log kq
values of 2b were calculated by the following equation: kq
= (Φ0/Φ−1)/τf where τf for 1b was 1.7 ns.
∆G = E1/2ox − E1/2red − E0-0 − Coulombic term
(2)
Figure 4 shows the dependence of log kq on the ∆G in
MeCN. The log kq values decreased remarkably along with an
increase in the ∆G value. Since the fluorescence quenching
proceeded via an intramolecular process, the kq value exceeded
the 1010 order, which was the diffusional-controlled limit when
∆G was −0.84. Moreover, the plots of log kq of 2b in given
solvents vs the empirical parameter ET(30), which show the
scale of the solvent polarity, are shown in Fig. 5.10 The log kq
values increased along with an increase in ET(30), thus sug-
gesting that kq should strongly depend on the used solvent po-
larity.11–13 These results showed that the fluorescence quench-
ing occurred mainly by the electron-transfer process.
Scheme 4.
Thus, in the case of high-valent porphyrinatometal com-
plexes, it is suggested that substituents on the axial aryloxo
ligand remarkably influence the chemical properties of the por-
phyrinatometal complex.
dated that the reduction of porphyrinatometal complexes (met-
al= Zn(ꢀ), Ni(ꢀ), Pb(ꢀ) etc.) occurred mainly in the porphyrin
ring, while the reduction of tetraphenylporphyrinatocobalt(ꢁ)
occurred on the metal-orbitals.8
Based on the above discussion, the LUMO level of high-va-
lent porphyrinatoantimony complexes were suggested to be
predominantly affected by the metal orbitals. Therefore, the
first reduction potentials from Sb(Ⅴ) to Sb(ꢂ), and the proton-
dissociation constants (Ka) should be affected by the substitu-
ents (X) on the axial aryloxo ligand, rather than the substitu-
red
ents (Y) on the porphyrin ring. In fact, E1/2 of 2a–d varied
from −0.54 V (2a; Y = OMe) to −0.46 V (2d; Y = CN),
red
while a small substituent effect of X on E1/2 was observed;
e.g. −0.52 V for 1a (X = OMe) and −0.51 V for 1c (X =
CN). Furthermore, the measured Ka values of 1a–c and 2a–d
are listed in Table 1. Along with an increase in the electron-
withdrawing character of X and Y, the Ka values increased.
The Ka values were strongly affected by the substituents (Y) on
the aryloxo ligand, but were only slightly affected by the sub-
stituents (X) on the porphyrin ring. Thus, both the first reduc-
tion potential and the proton dissociation constants (Ka) were
affected by the substituents (Y) on the axial aryloxo ligand.
Kinetic Treatment for Fluorescence Quenching. Using
1b as a model compound for the hydroxo(porphyrinato)anti-
Fig. 4. Plots of log kq vs ∆G for the fluorescence quenching
of 2 in MeCN.

T. Shiragami et al.
Bull. Chem. Soc. Jpn., 75, No. 7 (2002) 1581
matographed on SiO2 using CHCl3–MeOH (10:1, v/v) as an elu-
ent to give 2a–d and 3.
Dihydroxo[tetra(4-methoxyphenyl)porphyrinato]antimony-
(Ⅴ) Hexafluorophosphate (1a). Yield 79%; UV–vis λmax/nm
(log ε) 431 (5.55), 558 (4.31), 604 (4.45); SIMS m/z 887 (M+); 1H
NMR δ −4.20(2H, brs, OH), 4.14 (12H, s, OMe), 7.41 (8H, d, J =
8.6 Hz, –C6H4–), 8.28 (8H, d, J = 8.6 Hz, –C6H4–), 9.48 (8H, s,
pyrrole).
Dihydroxo[tetra(4-cyanophenyl)porphyrinato]antimony(Ⅴ)
Hexafluorophosphate (1c). Yield 60%; UV–vis λmax/nm (log ε)
416 (5.62), 548 (4.49), 586 (4.30); SIMS m/z 867 (M+); 1H NMR
( in CD3CN) δ 8.28 (8H, d, J = 8.2 Hz, –C6H4–), 8.49 (8H, d, J =
8.2 Hz, –C6H4–), 9.50 (8H, s, pyrrole).
Hydroxo(4-methoxyphenoxo)(tetraphenylporphyrinato)an-
timony(Ⅴ) Hexafluorophosphate (2a).
Yield 45%. UV–vis
λ
max/nm (log ε) 418 (5.53), 552 (4.27), and 592 (4.04); SIMS m/z
1
873 (M+). H NMR δ −2.90 (1H, br, –OH), 1.52 (2H, d, J =9.2
Hz, –OC6H4–), 3.28 (3H, s, OMe), 5.23 (2H, d, J = 9.2 Hz,
–OC6H4–), 7.86–7.92 (12H, m, Ph), 8.11 (4H, d, J =6.8 Hz, Ph),
8.44–8.47 (4H, m, Ph), 9.42 (8H, s, pyrrole).
Fig. 5. Plots of log kq vs ET (30) for the fluorescence quench-
ing of 2b.
Hydroxo(phenoxo)(tetraphenylporphyrinato)antimony(Ⅴ)
Hexafluorophosphate (2b). Yield 34%. UV–vis λmax/nm (log
ε) 418 (5.51), 550 (4.20), and 590 (3.96); SIMS m/z 843 (M+). 1H
NMR δ −2.90 (1H, br, OH), 1.62 (2H, d, J = 7.9 Hz, OPh), 5.71–
6.07 (3H, m, OPh), 7.68–7.97 (12H, m, Ph), 8.15 (4H, d, J =6.7
Hz, Ph), 8.44 (4H, d, J =6.7 Hz, Ph), 9.48 (8H, s, pyrrole).
4-Fluorophenoxo(hydroxo)(tetraphenylporphyrinato)anti-
Experimental
Instruments and Materials. 1H NMR spectra were taken in
CDCl3 on a Bruker AC250P spectrometer at 250 MHz. SIMS was
obtained on a Hitachi M2000A spectrometer, respectively.
Spectral grades of benzene, toluene, and dichloromethane were
used without any further purification. 1,4-Dioxane and tetrahy-
drofuran were distilled from Na before use. MeCN was distilled
from P2O5 and then CaH2. Phenol, 4-cyanophenol, 4-fluorophe-
nol, 4-methoxyphenol and 3-(dimethylamino)phenol were pur-
chased from Wako Pure Chemical Industries and Nacalai Tesque,
Inc., respectively. Tetra(4-methoxyphenyl)porphyrin ([H2(tmp)])
was obtained form Tokyo Kasei Co. Ltd. According to a reported
method,14 tetra(4-cyanophenyl)porphyrin ([H2(tcp)]) were pre-
pared by the reaction of 4-cyanobenzaldehyde with pyrrole.
Preparation of 1a–c, 2a–d and 3. According to the litera-
ture,15 a pyridine solution (100 mL) of SbBr3 (14 mmol) in the
presence of [H2(tmp)], [H2(tpp)], or [H2(tcp)] (0.7 mmol) was re-
fluxed for 4 h. To the solution, Br2 (1.8 mL) was added to form
[Sb(tmp)Br2]+Br−, [Sb(tpp)Br2]+Br− or [Sb(tcp)Br2]+Br−, re-
spectively. The mixtures were then poured into hexane (200 mL)
to give a precipitate. A CH2Cl2 solution of the precipitate was
washed with hydrobromic acid (47%) and 150 mL of water. After
evaporation, the hydrolysis of crude [Sb(tmp)Br2]+Br−, [Sb(tpp)-
Br2]+Br−, or [Sb(tcp)Br2]+Br− in H2O–MeCN (1:3, v/v) at 60 °C
followed by a treatment with AgPF6 (6.3 mmol) gave [Sb(tmp)-
mony(Ⅴ) Hexafluorophosphate (2c). Yield 13%. UV–vis λmax/
nm (log ε) 419 (5.52), 551 (4.23), and 590 (3.95); SIMS m/z 861
1
(M+). H NMR δ −2.62 (1H, br, OH), 1.50–1.55 (2H, t, J = 8.2
Hz, –OC6H4–), 5.38 (2H, t, J = 8.2 Hz, –OC6H4–) 7.84–7.89
(12H, m, Ph), 8.11 (4H, d, J = 6.8 Hz, Ph), 8.44 (4H, d, J = 6.8
Hz, Ph), 9.40 (8H, s, pyrrole).
4-Cyanophenoxo(hydroxo)(tetraphenylporphyrinato)anti-
mony(Ⅴ) Hexafluorophosphate (2d). Yield 37%. UV–vis λmax
/
nm (log ε) 419 (5.54), 550 (4.19), and 591 (3.93); SIMS m/z 868
1
(M+). H NMR δ −2.45 (1H, br, OH), 1.65 (2H, d, J = 8.7 Hz,
–OC6H4–), 6.02 (2H, d, J = 8.6 Hz, –OC6H4–), 7.87–7.94 (12H,
m, Ph), 8.12 (4H, d, J = 6.6 Hz, Ph), 8.47–8.50 (4H, m, Ph), 9.49
(8H, s, pyrrole).
3-(Dimethylamino)phenoxo(hydroxo)(tetraphenylporphy-
rinato)antimony(Ⅴ) Hexafluorophosphate (3).
Yield 44%.
UV-vis λmax/nm (log ε) 419 (5.53), 551 (4.14) and 590 (3.88);
1
SIMS m/z 886 (M+). H NMR δ −2.90 (1H, br, OH), 0.87–1.01
(1H, m, –OC6H4–), 2.14 (6H, s, Me), 2.86 (1H, s, –OC6H4), 5.30–
5.57 (2H, m, –OC6H4–), 7.84–7.90 (12H, m, Ph), 8.12 (4H, d, J =
6.8 Hz, Ph), 8.46 (4H, d, J = 6.8 Hz, Ph), 9.43 (8H, s, pyrrole).
Measurements of Redox Potentials. The oxidation and re-
duction potentials were measured by cyclic voltammetry for
MeCN solution of 1a–c and 2a–d (1×10−2 M) in the presence of a
supporting electrolyte (Et4NBF4; 0.1 M) at a scan rate of 0.3–0.5
V/s at 23 °C on a BAS CV-50W cyclic voltammetry using a car-
bon-disk working electrode, a carbon counter electrode, and an
Ag/AgNO3 reference electrode. The half-peaks of the oxidation
(E1/2ox) and reduction potentials (E1/2red) vs Ag/Ag+ were modified
to those vs SCE by the addition of +0.23 V.
Proton Dissociation Constants. The absorption spectra of a
MeCN–H2O (4:1, v/v, 10 ml) solution containing 1a–c and 2a–d
(2×10−6 mol dm−3) were observed on a Hitachi U2001 spectrom-
eter. The proton dissociation constants for 1a–c or 2a–d were esti-
mated based on the spectral change of the Soret band by the addi-
−
−
(OH)2]+PF6 (1a), [Sb(tpp)(OH)2]+PF6 (1b),5 and [Sb(tcp)-
(OH)2]+PF6− (1c), respectively. The crude products were purified
by the column chromatography on silica gel (Fuji Silysia BW
300) using CH2Cl2–MeOH (10:1, v/v) as an eluent.
Mono-hydrolysis of [Sb(tpp)Br2]+Br− was performed in H2O–
MeCN (6:4) to give [Sb(tpp)(OH)Br]+Br−.5 An MeCN solution
(40 mL) containing [Sb(tpp)(OH)Br]+Br− (0.22 mmol) and the
corresponding phenol derivative (2.2 mmol) was refluxed for 6 h.
After the absorption spectra was shifted to a shorter wavelength,
the solvent was evaporated and then solved in CH2Cl2. The
CH2Cl2 solution was washed three times with 50 mL portions of
H2O. After evaporation, the crude product was treated by AgPF6
(2.2 mmol) to exchange the counter anion, and was then chro-

1582 Bull. Chem. Soc. Jpn., 75, No. 7 (2002)
Hydroxo(porphyrinato)antimony(ꢀ) Complexes
tion of 2.5×10−2 cm3 portions of a 1×10−2 mol dm−3 aqueous
KOH solution.16
Uno, J. Organomet. Chem., 611, 551 (2000).
Y. Andou, K. Shima, T. Shiragami, and M. Yasuda, Chem.
Lett., 2001, 1198.
4
Fluorescence Quantum Yields. The fluorescence spectra
were measured on a Hitachi F4500 spectrometer at room tempera-
ture under excitations of the porphyrinato chromophore at 420
nm. The concentrations of solutions of 1b, 2a–d, and 3 were ad-
justed for the absorbance to be less than 0.08 at the excitation
wavelength. According to the reported method,17 the quantum
yields for the fluorescence were determined using a benzene or
MeCN solution of tetraphenylporphyrinatozinc(ꢀ) (the quantum
yield is 0.033 in benzene and 0.029 in MeCN)18 as an actinometer.
The fluorescence spectral change of 3 in MeCN was observed
upon the addition of HClO4 (0.4 – 3.2 × 10−3 mol dm−3) at room
temperature under excitations of the porphyrin chromophore at
420 nm.
5
Y. Andou, K. Shima, T. Shiragami, and M. Yasuda, J.
Photochem. Photobiol. A: Chem., 147, 191 (2002).
6
7
R. S. Nicholson and I. Shain, Anal. Chem., 36, 706 (1964).
J. H. Fuhrhop, K. M. Kadish, and D. G. Davis, J. Am.
Chem. Soc., 95, 5140 (1973).
8
(1966).
9
R. H. Felton and H. Linschitz, J. Am. Chem. Soc., 88, 1113
D. Rehm and A. Weller, Isr. J. Chem., 8, 259 (1970).
10 C. Reichardt, “Solvent Effects in Organic Chemistry,” Ver-
lag Chemie. Weiheim, New York (1978).
11 P. J. F. Derege and M. J. Therien, Inorg. Chim. Acta, 242,
211 (1996).
12 J. W. Park, B. A. Lee, and S. Y. Lee, J. Phys. Chem. B., 102,
8029 (1997).
13 D. M. Guldi, C. P. Luo, M. Prato, E. Dietel, and A. Hirsch,
Chem. Commun., 2000, 373.
14 A. D. Adler, F. R. Longo, J. D. Finarelli, J. Goldmacher, J.
Assour, and L. Korsakoff, J. Org. Chem., 32, 476 (1967).
15 T. Shiragami, K. Kubomura, D. Ishibashi, and H. Inoue, J.
Am. Chem. Soc., 118, 6311 (1996).
16 M. Gouterman, P. Sayer, E.shankland, and J. P. Smith,
Inorg. Chem., 20, 87 (1981).
We would like to thank Prof. H. Inoue, Dr. T. Shimada, and
Dr. S. Takagi, Tokyo Metropolitan University, for their helpful
suggestions. This research was supported by a Grand-in-Aid
for Scientific Research (No. 11750717 and 09750937) from
the Ministry of Education, Science, Sports and Culture.
References
1
T. Barbour, W. J. Belcher, P. J. Brothers, C. E. F. Rickard,
and D. C. Ware, Inorg. Chem., 31, 746 (1992).
Y. Yamamoto and K. Akiba, J. Organomet. Chem., 611,
200 (2000).
T. Ogawa, H. Furuta, M. Takahashi, A. Morino, and H.
17 J. B. Birks, “Photophysics of Aromatic Molecules,” Win-
ley-Interscience, New York (1970), Chap. 4.
18 M. Sirish and B. G. Maiya, J. Photochem. Photobiol. A:
Chem., 77, 189 (1994).
2
3