Synthesis and photophysical properties of meso-substituted bisporphyrins: Comparative study of phosphorescence quenching for dioxygen sensing

Article abstract of DOI:10.1021/ic0508573

The 4,6-bis(10-mesityl-5,15-di-p-tolylporpyrinyl)dibenzothiophene (H ₄DPSN) free base was obtained in five steps from commercially available materials. The metalation of DPSN^2- with zinc(II), copper(II), and palladium(II) led to three new homobimetallic systems, (Zn) ₂DPSN, (Cu)₂DPSN, and (Pd)₂DPSN, respectively. The cofacial structures of these molecules offer the possibility of having dioxygen molecules inside the cavity for a period of time, allowing dynamic (collisional) phosphorescence quenching to be more efficient. The bimolecular excited-state deactivation rate constant for deactivation by dioxygen (k _Q: (Pd)₂DPB, 2.98 × 10⁹; (Pd) ₂DPSN, 3.99 × 10⁹; (Pd)₂DPX, 6.94 × 10⁹; (Pd)TPP, 8.95 × 10⁹; (Pd)₂DPS, 8.95 × 10⁹ M^-1 s^-1) of (Pd)₂DPSN, which exhibits an intense phosphorescence at 699 nm, was compared to those observed for (Pd)TPP, (Pd)₂DPS, (Pd)₂DPX, and (Pd) ₂DPB (TPP^2- = tetraphenylporphyrin dianion, DPS ^4- = 4,6-bis[5-(2,8,13,17-tetraethyl-3,7,12,18- tetramethylporphyrinyl)]dibenzothiophene tetraanion, DPX^4- = 4,5-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]-9, 9-dimethylxanthene tetraanion, and DPB^4- = 1,8-bis[5-(2,8,13,17- tetraethyl-3,7,12,18-tetramethylporphyrinyl)]biphenylene tetraanion). These collision-induced deactivation data were interpreted by estimating a series of physical parameters such as the surface area and bisporphyrin radii, the diffusion coefficient of the bismacrocycles, and the theoretical deactivation efficiency for the five compounds addressing the role of steric hindrance of the macrocycles on each other and the aryl groups at the meso positions. For sensing purposes, (Pd)₂DPX is characterized by a Stern-Volmer constant k_SV of 2.91 × 10⁶ M^-1, placing the lower detection limit for [O₂] in solution at 0.58 ppm, which is better than that for (Pd)TPP (k_SV = 2.31 × 10⁶ M^-1; lower detection limit of 0.73 ppm), the classically used monoporphyrin complex.

Full text of DOI:10.1021/ic0508573

Inorg. Chem. 2005, 44, 9232−9241
Synthesis and Photophysical Properties of Meso-Substituted
Bisporphyrins: Comparative Study of Phosphorescence Quenching for
Dioxygen Sensing
Se´bastien Faure,†,‡ Christine Stern,† Roger Guilard,*,† and Pierre D. Harvey*,‡
LIMSAG UMR 5633, UniVersite´ de Bourgogne, 6 bd Gabriel, 21100 Dijon, France, and
De´partement de Chimie de l’UniVersite´ de Sherbrooke, Sherbrooke J1K 2R1, Que´bec, Canada
Received May 27, 2005
The 4,6-bis(10-mesityl-5,15-di-p-tolylporpyrinyl)dibenzothiophene (H4DPSN) free base was obtained in five steps
-
from commercially available materials. The metalation of DPSN2 with zinc(II), copper(II), and palladium(II) led to
three new homobimetallic systems, (Zn)2DPSN, (Cu)2DPSN, and (Pd)2DPSN, respectively. The cofacial structures
of these molecules offer the possibility of having dioxygen molecules inside the cavity for a period of time, allowing
dynamic (collisional) phosphorescence quenching to be more efficient. The bimolecular excited-state deactivation
rate constant for deactivation by dioxygen (kQ: (Pd)2DPB, 2.98
× × ×
109; (Pd)2DPSN, 3.99 109; (Pd)2DPX, 6.94
109; (Pd)TPP, 8.95
×
109; (Pd)2DPS, 8.95
×
109 M-1 s-1) of (Pd)2DPSN, which exhibits an intense phosphorescence
at 699 nm, was compared to those observed for (Pd)TPP, (Pd)2DPS, (Pd)2DPX, and (Pd)2DPB (TPP2
) tetra-
-
-
phenylporphyrin dianion, DPS4
) 4,6-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]dibenzothiophene
-
tetraanion, DPX4
) 4,5-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]-9,9-dimethylxanthene tetraanion,
) 1,8-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]biphenylene tetraanion). These collision-
and DPB4
-
induced deactivation data were interpreted by estimating a series of physical parameters such as the surface area
and bisporphyrin radii, the diffusion coefficient of the bismacrocycles, and the theoretical deactivation efficiency for
the five compounds addressing the role of steric hindrance of the macrocycles on each other and the aryl groups
at the meso positions. For sensing purposes, (Pd)2DPX is characterized by a Stern
−Volmer constant kSV of 2.91
×
106 M-1, placing the lower detection limit for [O2] in solution at 0.58 ppm, which is better than that for (Pd)TPP
(kSV
) 2.31 ×
106 M-1; lower detection limit of 0.73 ppm), the classically used monoporphyrin complex.
Introduction
quently, Chang and collaborators have developed the “Pac-
man” concept, in which the two porphyrin rings are held
together by a rigid spacer such as anthracenyl or biphenylenyl
groups.8-10 Thereafter, new rigid spacers such as DPO, DPX,
The chemistry of cofacial bisporphyrins is currently a topic
of great interest, particularly because of their numerous
applications in catalysis and their photophysical properties.1,2
The first bisporphyrin systems maintained in a face-to-face
configuration by flexible chains were reported by Collman
and their collaborators to mimic hemoproteins.3-7 Subse-
(3) Collman, J. P.; Elliot, C. M.; Halbert, T. R.; Tovrog, B. S. Proc. Natl.
Acad. Sci. U.S.A. 1977, 74, 18.
(4) Collman, J. P.; Chong, A. O.; Jameson, G. B.; Oakley, R. T.; Rose,
E.; Schmittou, E. R.; Ibers, J. A. J. Am. Chem. Soc. 1981, 103, 516.
(5) Collman, J. P.; Anson, F. C.; Barnes, C. E.; Bencosme, C. S.; Geiger,
T.; Evitt, E. R.; Kreh, R. P.; Meier, K.; Pettman, R. B. J. Am. Chem.
Soc. 1983, 105, 2694.
* To whom correspondence should be addressed. E-mail:
Roger.Guilard@u-bourgogne.fr (R.G.), Pierre.Harvey@USherbrooke.ca
(P.D.H.).
(6) Collman, J. P.; Bencosme, C. S.; Durand, R. R.; Kreh, R. P.; Anson,
F. C. J. Am. Chem. Soc. 1983, 105, 2699.
(7) Collman, J. P.; Brauman, J. I.; Collins, T. J.; Iverson, B. L.; Lang,
G.; Pettman, R. B.; Sessler, J. L.; Walters, M. A. J. Am. Chem. Soc.
1983, 105, 3038.
† Universite´ de Bourgogne.
‡ Universite´ de Sherbrooke.
(1) Lindsey, J. S. In The Porphyrin Handbook; Kadish, K. M., Smith, K.
M., Guilard, R., Eds.; Academic Press: San Diego, 2000; Vol. 1, p
45.
(8) Chang, C. K.; Abdalmuhdi, I. J. Org. Chem. 1983, 48, 5388.
(9) Chang, C. K.; Abdalmuhdi, I. Angew. Chem., Int. Ed. 1984, 23, 164.
(10) Eaton, S. S.; Eaton, G. R.; Chang, C. K. J. Am. Chem. Soc. 1985,
107, 3177.
(2) Harvey, P. D. In The Porphyrin Handbook; Kadish, K. M., Smith, K.
M., Guilard, R., Eds.; Academic Press: San Diego, 2003; Vol. 18, p
63.
9232 Inorganic Chemistry, Vol. 44, No. 25, 2005
10.1021/ic0508573 CCC: $30.25
© 2005 American Chemical Society
Published on Web 11/04/2005

Meso-Substituted Bisporphyrins
Scheme 1
led us to investigate bismacrocycles, because the size of the
cavity formed by the two macrocycles and the spacer allows
small molecules to interact with the metal atoms in an endo
position.23-26 Taking advantage of a recent work by Lindsey
and collaborators for the synthesis of meso-substituted
porphyrins,1,16,27,28 we have synthesized a new bisporphyrin
free base, 4,6-bis(10-mesityl-5,15-di-p-tolylporphyrinyl)-
dibenzothiophene, H4DPSN, in five steps starting from
commercially available materials, along with three homo-
bimetallic complexes, including (Pd)2DPSN. The photo-
physical properties of (Pd)2DPSN and the bimolecular
excited-state deactivation rate constant by oxygen, kQ, are
compared to those of four palladium(II) mono- and bispor-
phyrin systems. The data are analyzed using a theoretical
approach, which consists of evaluating the quenching ef-
ficiency using an estimation of the efficient surface of the
chromophores for O2 interactions.
Experimental Section
Materials. Unless otherwise stated, all reagents and solvents were
used as received. 1,3-Benzoxathiolium tetrafluoroborate29 and
5-mesityldipyrromethane30 7 were synthesized according to litera-
ture methods. 2-MeTHF (g99%, anhydrous and under inert gas),
DDQ (2,3-dichloro-5,6-dicyano-p-benzoquinone), and TMEDA
(tetramethylethylenediamine) were purchased from Aldrich. HgO
(yellow) was purchased from Janssen Chimica. Chromatographic
purification of all compounds was performed with neutral alumina
(Merck; usually Brockmann Grade III, i.e., deactivated with 6%
water) and silica gel (Merck; 70-120 mm), and was monitored by
thin-layer chromatography (Merck 60 F254 silica gel precoated
sheets, 0.2 mm thick) and UV-vis spectroscopy.
Molecular Modeling. Connolly areas were calculated using
Chem3D Ultra 8.0 software. The procedure consisted of computing
a minimum energy structure at the MM2 level, followed by a second
minimization using Gaussian 98 Semiempirical AM1 computation.
Connolly areas31 were obtained with ChemPropStd job. The radius
r(2-MeTHF) was calculated using the Connolly molecular area of
2-MeTHF with probe radius set to 0.
and DPS led to easier routes of synthesis (Scheme 1).11-14
These spacers allowed researchers to vary the intermacro-
cycle Cmeso-Cmeso distance and the interplanar angle. Ac-
cording to a 14-step synthesis and an overall yield of about
0.3%, the synthesis of the free base H4DPS, for instance,
still has room for improvement.13,15 In addition, very little
research has been devoted to the synthesis of meso-
substituted bisporphyrins. Recent works led to very original
synthetic procedures that vary the nature of the bridge and
the porphyrin meso substituents.16
Apparatus. 1H NMR spectra were recorded on a Bruker DRX-
500 AVANCE spectrometer at the Centre de Spectrome´trie Mo-
(17) Harriman, A. Platinum Met. ReV. 1990, 34, 181.
(18) Sinaasappel, M.; Ince, C. J. Appl. Physiol. 1996, 81, 2297.
(19) Demas, J. N.; DeGraff, B. A.; Coleman, P. B. Anal. Chem. 1999, 71,
793A.
(20) Bolze, F.; Gros, C. P.; Harvey, P. D.; Guilard, R. J. Porphyrins
Phthalocyanines 2001, 5, 569.
(21) Okura, I. J. Porphyrins Phthalocyanines 2002, 6, 268.
(22) Mei, E.; Vinogradov, S.; Hochstrasser, R. M. J. Am. Chem. Soc. 2003,
125, 13198.
(23) Le Mest, Y.; L’Her, M.; Collman, J. P.; Hendricks, N. H.; McElvee-
White, L. J. Am. Chem. Soc. 1986, 108, 533.
Similarly, the study of palladium(II) monoporphyrins has
shown their intense phosphorescence and their potential
application for oxygen sensing at the parts per million
level.2,17-22 In this respect, the quest for more efficient sensors
(24) Collman, J. P.; Hutchison, J. E.; Lopez, M. A.; Tabard, A.; Guilard,
R.; Seok, W. K.; Ibers, J. A.; L’Her, M. J. Am. Chem. Soc. 1992,
114, 9869.
(25) Collman, J. P.; Wagenknecht, P. S.; Hutchison, J. E. Angew. Chem.,
Int. Ed. 1994, 33, 1537.
(26) Guilard, R.; Brande`s, S.; Tabard, A.; Bouhmaida, N.; Lecomte, C.;
Richard, P.; Latour, J. M. J. Am. Chem. Soc. 1994, 116, 10202.
(27) Rao, P. D.; Dhanalekshmi, S.; Littler, B. J.; Lindsey, J. S. J. Org.
Chem. 2000, 65, 7323.
(28) Tamaru, S.-i.; Yu, L.; Youngblood, W. J.; Muthukumaran, K.;
Taniguchi, M.; Lindsey, J. S. J. Org. Chem. 2004, 69, 765.
(29) Barbero, M.; Cadamuro, S.; Degani, I.; Fochi, R.; Gatti, A.; Regondi,
V. Synthesis 1986, 1074.
(30) Littler, B. J.; Miller, M. A.; Hung, C.-H.; Wagner, R. W.; O’Shea, D.
F.; Boyle, P. D.; Lindsey, J. S. J. Org. Chem. 1999, 64, 1391.
(31) Connolly, M. L. J. Mol. Graphics 1993, 11, 139.
(11) Chang, C. J.; Deng, Y.; Heyduk, A. F.; Chang, C. K.; Nocera, D. G.
Inorg. Chem. 2000, 39, 959.
(12) Deng, Y.; Chang, C. J.; Nocera, D. G. J. Am. Chem. Soc. 2000, 122,
410.
(13) Bolze, F.; Gros, C. P.; Drouin, M.; Espinosa, E.; Harvey, P. D.; Guilard,
R. J. Organomet. Chem. 2002, 643-644, 89.
(14) Chng, L. L.; Chang, C. J.; Nocera, D. G. J. Org. Chem. 2003, 68,
4075.
(15) Faure, S.; Stern, C.; Guilard, R.; Harvey, P. D. J. Am. Chem. Soc.
2004, 126, 1253.
(16) Barbe, J.-M.; Stern, C.; Pacholska, E.; Espinosa, E.; Guilard, R. J.
Porphyrins Phthalocyanines 2004, 8, 301.
Inorganic Chemistry, Vol. 44, No. 25, 2005 9233

Faure et al.
le´culaire de l’Universite´ de Bourgogne. All chemical shifts (δ) and
coupling constants (J) are given in parts per million and hertz,
respectively. The 1H NMR assignments for the spacers refer to the
numbering in Scheme 1. Microanalyses were performed at the
Universite´ de Bourgogne on a Fisons EA 1108 CHNS instrument.
UV-vis spectra were recorded on a Varian Cary 50 spectropho-
tometer. Mass spectra were obtained in a linear mode with a Bruker
Proflex III MALDI-TOF mass spectrometer using dithranol as
matrix, and with a Kratos Concept 32 S spectrometer in EI mode.
The EPR spectrum was recorded in solution on a Bruker ESP 300
spectrometer at the X-band (9.6 GHz), from the Centre de
Spectrome´trie Mole´culaire de l’Universite´ de Bourgogne, equipped
with a double cavity and a liquid nitrogen cooling accessory. The
EPR spectrum was referenced to 2,2-diphenyl-1-picrylhydrazyl
(DPPH) (g ) 2.0036). The IR spectrum was obtained on a Bruker
Vector 22 FTIR spectrophotometer equipped with a high-pressure
Diamond ATR system.
4,6-Bis[(2,2′-dipyrryl)methyl]dibenzothiophene (3). A solution
of 2 (9 g, 37 mmol) and pyrrole (208 mL, 80 equiv) was degassed
with Ar for 30 min until BF3‚OEt2 (0.92 mL, 0.2 eq) was added.
The reaction mixture was stirred for 1 h, quenched with 0.1 M
NaOH, and extracted with CH2Cl2. The combined organic layers
were washed with water and dried over MgSO4, and the solvent
was removed to afford a white solid. After the addition of CH2Cl2,
the resulting solution was poured into cold pentane; the derivative
3 was collected by filtration as a white solid and dried under vacuum
1
(16 g, yield 89%). H NMR (CDCl3): δ 8.05 (d, J ) 7.6, 2H,
H-C3-7, or H-C1-9), 7.97 (s, 4H, H-N), 7.40 (t, J ) 7.6, 2H,
H-C2-8), 7.20 (d, J ) 7.6, 2H, H-C3-7, or H-C1-9), 6.68 (d, 4H,
HR), 6.15 (t, 4H, Hâ), 6.00 (d, 4H, Hâ), 5.74 (s, 2H, Hmeso). 13C
NMR (CDCl3): δ 126.7 and 125.6 (C3-7 or C1-9), 120.9 (C2-8),
117.9 (CR), 108.9 (Câ), 108.2 (Câ), 43.6 (Cmeso). MS (MALDI-
TOF): m/z 472 (M+), 471 calcd for C30H24N4S. Anal. Calcd for
C30H24N4S‚0.2H2O: C, 75.66; H, 5.16; N, 11.77; S: 6.73. Found:
C, 75.40; H, 5.56; N, 12.14; S: 6.43.
Emission and excitation spectra were obtained by using a double
monochromator Fluorolog 2 instrument from Spex. Fluorescence
lifetimes were measured on a Timemaster model TM-3/2003
apparatus from PTI. The source was a nitrogen laser equipped with
a high-resolution dye laser (fwhm ∼ 1500 ps), and the fluorescence
lifetimes were obtained from deconvolution and distribution lifetime
analysis.32 All of the samples were prepared under an inert
atmosphere (in a glovebox, P(O2) < 1-3 ppm) by dissolution of
the different compounds in 2-MeTHF in 1 cm3 quartz cells equipped
with a septum (298 K) or in standard 5 mm NMR tubes (77 K).
Three different measurements (i.e., different solutions) were
performed for each photophysical data type (quantum yields and
lifetimes). The sample concentrations were chosen to obtain an
absorbance of about 0.05. Each absorbance value was measured
five times to gain better accuracy for determining the quantum
yields. The quantum yield of H2TPP (Φ ) 0.11) was used as a
reference for the quantum yields measured at 298 K.33-35 The
quantum yield of H2TPP (Φ ) 0.11) was also used as a reference
for the quantum yields measured at 77 K, which itself was obtained
using (Pd)TPP (Φ ) 0.17; 77 K; MCH ) methylcyclohexane) as
a reference.36,37
4,6-Diformyldibenzothiophene (2). 2 was synthesized using a
modified literature method.38 A solution of n-BuLi (166 mL, 2.5
M in heptane, 0.415 mol) in heptane was added dropwise to a
solution of 1 (30 g, 0.163 mol) in heptane (1.2 L) and TMEDA
(80 mL) under Ar over a period of 30 min. The reaction mixture
was heated, and was stirred under reflux (70 °C) for 15 min. After
the mixture was cooled in an ice bath, DMF (82 mL) was added,
and the reaction mixture was stirred for 30 min at room temperature.
The resulting solution was poured into cold water (6 L), and was
stirred for an additional 2 h. A yellow solid was collected by
filtration and dried under vacuum. Recrystallization in toluene
afforded pure 2 (31 g, yield 79%) as a light yellow solid. 1H NMR
4,6-Bis[(2,2′-bis(1-(p-tolyl)-1,3-benzoxathiolyl)pyrryl)methyl]-
dibenzothiophene (4). To a solution of 3 (2 g, 4.2 mmol) in
acetonitrile (360 mL) and pyridine (1.4 mL) was added 2-(p-tolyl)-
1,3-benzoxathiolium tetrafluoroborate (5.27 g, 0.17 mmol). The
reaction mixture was stirred for 30 min at room temperature, and
then diluted with ethyl acetate (400 mL). The combined organic
layers were washed with water and dried over MgSO4, and the
solvent was removed to obtain 2.8 g of a dark solid.
4,6-bis[(2,2′-bis(1-(p-methylbenzoyl)pyrryl))methyl]diben-
zothiophene (5). HBF4 (34% in water, 6 mL) was added to a
solution of 4 (2.8 g, 2 mmol) in THF (260 mL) containing HgO
(1.8 g, 8.4 mmol). The reaction mixture was stirred for 1.5 h at
room temperature, and diluted with ethyl acetate (400 mL). The
combined organic layers were washed with KI (10% in water), 0.1
M NaOH, and water, and then dried over MgSO4. Removal of the
solvent under vacuum gave a light red solid, which was dissolved
in CH2Cl2/NEt3 (99:1), and filtered through a pad of silica (CH2Cl2).
The second collected derivative was the tetra-acyl compound
(CH2Cl2 with 1% MeOH). Removal of the solvent followed by a
recrystallization in CH2Cl2/heptane afforded an orange solid (1.2
1
g, 63%). H NMR (CDCl3): δ 11.08 (s, 4H, H-N), 8.13 (d, J )
7.5, 2H, H-C3-7, or H-C1-9), 7.67 (d, J ) 7.5, 8H, tolyl), 7.49 (t,
J ) 7.5, 2H, H-C2-8), 7.13 (m, 10H, H-tolyl, and H-C3-7 or
H-C1-9), 6.61 (m, 4H, Hâ), 6.06 (m, 6H, Hâ, and Hmeso), 2.34 (s,
12H, CH3-tolyl). MS (MALDI-TOF): m/z 945 (M+), 944 calcd
for C62H48N4O4S. Anal. Calcd for C62H48N4O4S‚0.2H2O: C, 78.49;
H, 5.14; N, 5.90; S, 3.38. Found: C, 78.23; H, 5.26; N, 6.07; S,
3.23. IR: νCdO 1598 cm-1
.
4,6-Bis(10-mesityl-5,15-di-p-tolylporphyrinyl)dibenzothio-
phene (6). Procedure A. A solution of ethylmagnesium bromide
(1 M in THF, 25.2 mL, 10 equiv) was added dropwise to a solution
of 3 (1.2 g, 2.8 mmol) in dry toluene (100 mL) under Ar placed in
a cold bath of water. The reaction mixture was stirred for 30 min
at room temperature, and a solution of p-toluoyl chloride (1.7 mL,
5 equiv) in 13 mL of toluene was added dropwise. The reaction
mixture was stirred for an additional 10 min and, after being
quenched with aq NH4Cl, was extracted with ethyl acetate. The
combined organic layers were washed with water and dried over
MgSO4, and the solvent was removed under vacuum to afford a
red oil. Column chromatography (silica, CH2Cl2/methanol 96:4 with
NEt6) afforded a mixture of acylated products. CH2Cl2 was added,
and the mixture was poured into cold pentane. A solid was collected
by filtration. The solid (1 g), a mixture of acylated compounds as
shown by mass spectroscopy, was then dissolved in dry THF (85
mL) and dry MeOH (15 mL), and was stirred under Ar before
(DMSO): δ 10.58 (s, 2H, CHO), 9.10 (d, J ) 7.3, 2H, H-C3-7
,
or H-C1-9), 8.55 (d, J ) 7.3, 2H, H-C3-7, or H-C1-9), 8.11 (m,
J ) 7.3, 2H, H-C2-8).
(32) Valeur, B. Molecular Fluorescence: Principles and Applications;
Wiley-VCH: Weinheim, Germany, 2002.
(33) Strachan, J.-P.; Gentemann, S.; Seth, J.; Kalsbeck, W. A.; Lindsey, J.
S.; Holten, D.; Bocian, D. F. J. Am. Chem. Soc. 1997, 119, 11191.
(34) Gouterman, M. In The Porphyrins; Dolphin, D., Ed.; Academic
Press: New York, 1978; Vol. III, p 1.
(35) Seybold, P. G.; Gouterman, M. J. Mol. Spectrosc. 1969, 31, 1.
(36) Harriman, A. J. Chem. Soc., Faraday Trans. 2 1981, 77, 1281.
(37) Murov, S. L.; Carmichael, I.; Hug, G. L. Handbook of Photochemistry,
2nd ed.; Marcel Dekker: New York, 1993.
(38) Kadish, K. M.; Burdet, F.; Je´roˆme, F.; Barbe, J.-M.; Ou, Z.; Shao, J.;
Guilard, R. J. Organomet. Chem. 2002, 652, 69.
9234 Inorganic Chemistry, Vol. 44, No. 25, 2005

Meso-Substituted Bisporphyrins
NaBH4 (3 g, 80 equiv) was added step by step over 50 min. The
reaction was monitored by IR spectrometry using as a marker the
1598 cm-1 νCdO band. The reaction mixture was poured into a
saturated solution of NH4Cl in water, and extracted with CH2Cl2.
The combined organic layers were washed with water and dried
over MgSO4, and the solvent was removed to afford a pale yellow
solid. Acetonitrile (850 mL) was added with mesityldipyrromethane
(0.615 g), and after the reaction mixture was degassed in the dark
with Ar for 5 min, TFA was added. The reaction mixture was stirred
for 3 min before we added DDQ (1.42 g, 5.4 mmol) and NEt3 (6
mL). The mixture was stirred for an additional 1 h, and was filtered
through a pad of alumina (eluted with CH2Cl2) until the eluent was
no longer dark. Removal of the solvent afforded a dark solid, which
was redissolved in CH2Cl2/heptane/NEt3 (40:59:1) and filtered
through a pad of silica (CH2Cl2). Removal of the solvent under
vacuum followed by recrystallization in CH2Cl2/heptane afforded
a purple solid (73 mg, yield 4%).
12H, CH3-tolyl), 2.51 (s, 6H, CH3-mesityl), 1.71 (s, 6H, CH3-
mesityl), 1.30 (s, 6H, CH3-mesityl). MS (LSIMS): m/z 1520 (M+),
1520 calcd for C98H72N8SZn2. UV-vis (CH2Cl2) λ (nm) (ꢀ 10-3
M-1 cm-1): 417 Soret (618), 551 (29), 591 (7). Anal. Calcd for
C98H72N8SZn2: C, 77.21; H, 4.76; N, 7.35; S, 2.10. Found: C,
77.35; H, 4.52; N, 7.59; S, 1.86.
4,6-Bis(palladium(II)-10-mesityl-5,15-di-p-tolylporphyrinyl)-
dibenzothiophene (9). Under Ar, 6 (40 mg, 0.03 mmol) was
dissolved in benzonitrile (15 mL), and PdCl2 (20 mg, 3 equiv) was
added. The mixture was stirred under reflux for 15 min. Removal
of the solvent under vacuum gave a purple solid, which was
redissolved in CH2Cl2 (1% NEt3) and filtered through a pad of silica
(CH2Cl2). The first band was collected, and the solvent was
evaporated. The resulting solid was recrystallized in CH2Cl2/MeOH,
and afforded an orange solid (28 mg, yield 61%). 1H NMR
(CDCl3): δ 8.75 (d, J ) 8, 2H, H-spacer), 8.49 (s, 8H, Hâ), 8.47
(d, J ) 4.3, 4H, Hâ), 8.33 (d, J ) 4.3, 4H, Hâ), 8.16 (d, J ) 8, 2H,
H-spacer), 7.93 (t, J ) 8, 2H, H-spacer), 7.75 (d, J ) 7.5, 4H,
H-tolyl), 7.65 (d, J ) 7.5, 4H, H-tolyl), 7.45 (d, J ) 7.5, 4H,
H-tolyl), 7.32 (d, J ) 7.5, 4H, H-tolyl), 7.13 (s, 2H, H-mesityl),
7.02 (s, 2H, H-mesityl), 2.59 (s, 12H, CH3-tolyl), 2.49 (s, 6H, CH3-
Procedure B. A solution of 5 (1 g, 1.05 mmol) in dry THF (85
mL) and dry MeOH (15 mL) was stirred under Ar. NaBH4 (3 g,
0.085 mol, 80 equiv) was added step by step over 50 min. The
reaction was monitored by IR spectrometry using as a marker the
1598 cm-1 νCdO band. The reaction mixture was poured into an
aqueous saturated solution of NH4Cl, and extracted with CH2Cl2.
The combined organic layers were washed with water and dried
over MgSO4, and the solvent was removed to afford a pale yellow
solid. Acetonitrile (850 mL) was added with 7 (0.615 g), and the
reaction mixture was degassed in the dark with Ar for 5 min before
adding TFA (1.96 mL). The reaction mixture was stirred for 3 min,
and DDQ (1.42 g, 5.4 mmol) and NEt3 (6 mL) were added. The
reaction mixture was stirred for an additional 1 h, and filtered
through a pad of alumina (eluted with CH2Cl2) until the eluent was
no longer dark. Removal of the solvent afforded a dark solid, which
was redissolved in CH2Cl2/heptane/NEt3 (40:59:1) and filtered
through a pad of silica (CH2Cl2). Removal of the solvent under
vacuum followed by recrystallization in CH2Cl2/heptane afforded
mesityl), 1.74 (s, 6H, CH3-mesityl), 1.21 (s, 6H, CH3-mesityl). 13
C
NMR (CDCl3) (CH, CH2, CH3 only): δ 134.5 and 133 (CH-tolyl),
132.5, 121.5, and 124 (CH-spacer), 131.5 and 131.7 (CH-â-pyrrole),
129.5 (2 signals, CH-â-pyrrole), 127.9 and 127.7 (2 signals, CH-
mesityl), 21.5 and 21.8 (CH3-mesityl), 22 (CH3-tolyl), 120-142
(7 signals). MS (MALDI-TOF): m/z 1604 (M+), 1605 calcd for
C98H72N8Pd2S. UV-vis (CH2Cl2) λ (nm) (ꢀ 10-3 M-1 cm-1): 412
Soret (481), 524 (51), 555 (7). Anal. Calcd for C98H72N8Pd2S: C,
73.26; H, 4.52; N, 6.98; S, 2.00. Found: C, 73.01; H, 4.20; N, 7.20;
S, 2.30.
4,6-Bis(copper(II)-10-mesityl-5,15-di-p-tolylporphyrinyl)diben-
zothiophene (10). Under Ar, 6 (30 mg, 0.02 mmol), K2CO3 (100
mg), and Cu(OAc)2‚H2O were dissolved in 20 mL of CHCl3/MeOH
(80:20). The mixture was stirred under reflux for 15 min. Removal
of the solvent under vacuum gave a purple solid, which was
redissolved in CH2Cl2, washed with water, and dried over MgSO4.
The solvent was removed. Recrystallization in CH2Cl2/MeOH
afforded a purple solid (32 mg, yield 100%). MS (MALDI-TOF):
m/z 1519 (M+), 1518 calcd for C98H72Cu2N8S. UV-vis (CH2Cl2)
λ (nm) (ꢀ 10-3 M-1 cm-1): 410 Soret (409.0), 540 (17.2), 577
(2.5). Anal. Calcd for C98H72Cu2N8S: C, 77.40; H, 4.77; N, 7.37;
S, 2.11. Found: C, 77.67; H, 5.02; N, 7.07; S, 2.01.
1
a purple solid (50 mg, yield 3.4%). H NMR (CDCl3): δ 8.75 (d,
J ) 8, 2H, H-spacer), 8.55 (d, J ) 5.3, 4H, Hâ), 8.45 (d, J ) 5.3,
4H, Hâ), 8.41 (d, J ) 4.3, 4H, Hâ), 8.35 (d, J ) 4.3, 4H, Hâ), 8.11
(d, J ) 8, 2H, H-spacer), 7.92 (t, J ) 8, 2H, H-spacer), 7.66 (d, J
) 6.4, 4H, H-tolyl), 7.43 (d, J ) 6.4, 4H, H-tolyl), 7.18 (d, J )
6.4, 4H, H-tolyl), 7.12 (s, 2H, H-mesityl), 7.05 (s, 2H, H-mesityl),
7.01 (d, 4H, H-tolyl), 2.49 (s, 6H, CH3-mesityl), 2.47 (s, 12H, CH3-
tolyl), 1.69 (s, 6H, CH3-mesityl), 1.36 (s, 6H, CH3-mesityl), -3.11
(s, 4H, N-H). MS (MALDI-TOF): m/z 1397 (M+), 1397 calcd
for C98H76N8S. UV-vis (CH2Cl2) λ (nm) (ꢀ 10-3 M-1 cm-1): 416
Soret (560), 517 (30), 547 (11), 591 (11), 646 (10). Anal. Calcd
for C98H76N8S‚0.3H2O: C, 83.88; H, 5.50; N, 7.99; S, 2.29.
Found: C, 83.63; H, 5.74; N, 8.29; S,1.86.
Results and Discussion
Syntheses. The syntheses of cofacial meso-substituted
bisporphyrins have already been described. Three routes of
synthesis are possible.
4,6-Bis(zinc(II)-10-mesityl-5,15-di-p-tolylporphyrinyl)diben-
zothiophene (8). Under Ar, 6 (30 mg, 0.02 mmol) was dissolved
in CH2Cl2 (15 mL) and NEt3 (0.5 mL), and a saturated solution of
zinc acetate in MeOH (1 mL) was added. The mixture was stirred
under reflux for 15 min. Removal of the solvent under vacuum
gave a purple solid, which was redissolved in CH2Cl2 (1% NEt3)
and filtered through a pad of silica (CH2Cl2). The first band was
collected, and the solvent was evaporated. Recrystallization in
CH2Cl2/MeOH afforded a purple solid (29 mg, yield 88%). 1H NMR
(CDCl3): δ 8.79 (d, J ) 7.5, 2H, H-spacer), 8.64 (d, J ) 4.3, 4H,
Hâ), 8.62 (d, J ) 4.3, 4H, Hâ), 8.60 (d, J ) 4.3, 4H, Hâ), 8.47 (d,
J ) 4.3, 4H, Hâ), 8.19 (d, J ) 7.5, 2H, H-spacer), 7.96 (t, J ) 8,
2H, H-spacer), 7.85 (d, J ) 7.5, 4H, H-tolyl), 7.70 (d, J ) 7.5,
4H, H-tolyl), 7.39 (d, J ) 7.5, 4H, H-tolyl), 7.36 (d, J ) 7.5, 4H,
H-tolyl), 7.14 (s, 2H, H-mesityl), 7.06 (s, 2H, H-mesityl), 2.63 (s,
One approach consists of the monoprotection of the
corresponding bisaldehyde spacer, allowing the construction
of a first porphyrin macrocycle, according to Lindsey’s
procedure.1 This step is followed by the deprotection and
construction of the second ring as developed by Collman
and co-workers39-42 and other groups.43 The drawbacks are
the extra protection/deprotection steps and the purification
of the monoaldehyde intermediates.
A second strategy was developed independently by Therien
and co-workers44,45 and by Kobuke and co-workers,46 and
(39) Collman, J. P.; Tyvoll, D. A.; Chng, L. L.; Fish, H. T. J. Org. Chem.
1995, 60, 1926.
(40) Collman, J. P.; Chng, L. L.; Tyvoll, D. A. Inorg. Chem. 1995, 34,
1311.
Inorganic Chemistry, Vol. 44, No. 25, 2005 9235

Faure et al.
Scheme 2
consists of the formation of a linear porphyrin-spacer-
porphyrin triad, in which the spacer can be chemically altered
in a way that leads to a cofacial arrangement.
The last method is the direct coupling between a func-
tionalized spacer and two appropriately substituted porphyrin
macrocycles. Examples of such strategies are those using
the Sonogashira coupling.47-50 Similarly, the Suzuki coupling
was employed by Nocera and co-workers14 for this purpose.
Attempts to synthesize the desired products using simpler
procedures and requiring fewer steps were made. The direct
reaction between pyrrole, monoaldehyde, and dialdehyde
spacer, as previously attempted by Collman and co-workers,
was not successful.39 The condensation of 4,6-bis[(2,2′-
dipyrryl)methyl]dibenzothiophene 3 with dialdehyde phen-
yldipyrromethane did not lead to the targeted product, despite
the use of various experimental conditions as previously
reported in the literature.51-54 The coupling between 3 and
diacetylate phenyldipyrromethane as already described for
thesynthesesofmonoporphyrinswasalsonotsuccessful.1,27,55-60
Presumably, the H in the R-position of the pyrrole N-H’s
may be not reactive enough in compound 3.
On the basis of previous procedures reported by Lindsey
and co-workers for mono- and multiporphyrin systems,1,27,61,62
we report the procedure leading to the desired meso-
substituted bisporphyrin 6, H4DPSN. The highly stable
compound 3 is prepared in a high yield from the condensa-
tion of four pyrrolic units onto the dibenzothiophene spacer
2 using BF3‚OEt2 as a catalyst (Scheme 2). Experimental
conditions show that the use of higher-purity diformyl
compound 2 allows the synthesis of 3 without chromatog-
raphy. However, 2 is purified by recrystallization in toluene
prior use. Two routes for the synthesis of bisporphyrin 6
(H4DPSN) starting from 3 have been investigated (Scheme
3). The first one, called A, consists of reacting 3 with EtMgBr
to replace the R H’s on the pyrrole residues, which can be
functionalized by tolylcarbonyl groups.1,27,61,62 Unfortunately,
the target intermediate 5 has not been isolated in pure form.
The solid, a mixture of acylated compounds obtained after
reaction of bisdipyrromethane 3 with p-toluoyl chloride, is
reduced by NaBH4 and reacted with mesityl-dipyrromethane
7. Subsequently, oxidation of the macrocycle ring is obtained
by adding DDQ. H4DPSN 6 was isolated, and purified by
column chromatography.27,61 The second route (B), developed
by Barbero and co-workers,29,63 involves the use of a
benzoxathiol compound to generate the intermediate 4, which
was not isolated from the reaction mixture. This derivative
was converted into 5 by reacting 4 with HgO. Fortunately,
5 was isolated and purified by column chromatography. The
reduction by NaBH4 followed by condensation with dipyr-
romethane 7 and oxidation by DDQ led to the desired
bisporphyrin 6. Both routes give an overall yield of 3-4%
from 3, and about 1.4% from the commercially available
starting materials (five steps). This yield is higher than that
reported for â-substituted H4DPS (0.3%),16 which utilizes a
14-step procedure. The use of acylated bisdipyrromethane
intermediates represents a significant advance in the prepara-
tion of cofacial bisporphyrin systems.
(41) Collman, J. P.; Fish, H. T.; Wagenknecht, P. S.; Tyvoll, D. A.; Chng,
L.-L.; Eberspacher, T. A.; Brauman, J. I.; Bacon, J. W.; Pignolet, L.
H. Inorg. Chem. 1996, 35, 6746.
(42) Hutchison, J. E.; Postlethwaite, T. A.; Chen, C. H.; Hathcock, K. W.;
Ingram, R. S.; Ou, W.; Linton, R. W.; Murray, R. W.; Tyvoll, D. A.;
Chng, L. L.; Collman, J. P. Langmuir 1997, 13, 2143.
(43) Meier, H.; Kobuke, Y.; Kugimiya, S.-I. J. Chem. Soc., Chem. Commun.
1989, 923.
(44) Fletcher, J. T.; Therien, M. J. J. Am. Chem. Soc. 2002, 124, 4298.
(45) Fletcher, J. T.; Therien, M. J. Inorg. Chem. 2002, 41, 331.
(46) Tomohiro, Y.; Satake, A.; Kobuke, Y. J. Org. Chem. 2001, 66, 8442.
(47) Solladie´, N.; Gross, M. Tetrahedron Lett. 1999, 40, 3359.
(48) Kubo, Y.; Murai, Y.; Yamanaka, J.-i.; Tokita, S.; Ishimaru, Y.
Tetrahedron Lett. 1999, 40, 6019.
(49) Brettar, J.; Gisselbrecht, J.-P.; Gross, M.; Solladie´, N. Chem. Commun.
2001, 733.
(50) Jokic, D.; Asfari, Z.; Weiss, J. Org. Lett. 2002, 4, 2129.
(51) Lee, C. H.; Lindsey, J. S. Tetrahedron 1994, 50, 11427.
(52) Li, F. R.; Yang, K. X.; Tyhonas, J. S.; MacCrum, K. A.; Lindsey, J.
S. Tetrahedron 1997, 53, 12339.
(53) Littler, B. J.; Ciringh, Y.; Lindsey, J. S. J. Org. Chem. 1999, 64, 2864.
(54) Geier, G. R.; Riggs, J. A.; Lindsey, J. S. J. Porphyrins Phthalocyanines
2001, 5, 681.
(55) Geier, G. R.; Lindsey, J. S. J. Chem. Soc., Perkin Trans. 2 2001, 677.
(56) Geier, G. R.; Lindsey, J. S. J. Chem. Soc., Perkin Trans. 2 2001, 687.
(57) Geier, G. R.; Littler, B. J.; Lindsey, J. S. J. Chem. Soc., Perkin Trans.
2 2001, 701.
The metalation step proceeds as described in the literature,
and involves the direct complexation with the desired
cation.10,11,64,65 Scheme 4 exhibits the one-step syntheses of
three metal complexes of 6, leading to products 8 ((Zn)2-
DPSN), 9 ((Pd)2DPSN), and 10 ((Cu)2DPSN), which were
obtained in good yields. Compound 8 was synthesized with
the aim of X-ray characterization. Unfortunately, all attempts
to grow suitable crystals for X-ray analysis stubbornly failed.
Compound 9, which exhibits strong phosphorescence proper-
ties (see below) was also prepared. Compound 10 was
investigated because the Cu-Cu distance is easily determined
by EPR methods. Unfortunately, no evidence for Cu(II)-
Cu(II) interaction at half-field transition has been detected
by EPR. This absence of signal led us to conclude that the
Cu-Cu distance is greater than 6-7 Å.9 Table 1 compares
1H NMR for the N-H protons for various cofacial bispor-
phyrin systems.14 For H4DPSN 6, the δ value resembles that
of other “open” bisporphyrin for which the Cmeso-Cmeso
distance is 6.3 Å (or greater). Comparison of the δ values
(58) Geier, G. R.; Littler, B. J.; Lindsey, J. S. J. Chem. Soc., Perkin Trans.
2 2001, 712.
(59) Burrell, A. K.; Officer, D. L.; Plieger, P. G.; Reid, D. C. W. Chem.
ReV. 2001, 101, 2751.
(60) Geier, G. R.; Callinan, J. B.; Rao, P. D.; Lindsey, J. S. J. Porphyrins
Phthalocyanines 2001, 5, 810.
(63) Barbero, M.; Cadamuro, S.; Degani, I.; Flochi, R.; Gatti, A.; Regondi,
V. J. Org. Chem. 1988, 53, 2245.
(61) Lee, C.-H.; Li, F.; Iwamoto, K.; Dadok, J.; Bothner-By, A. A.; Lindsey,
J. S. Tetrahedron 1995, 51, 11645.
(62) Cho, W.-S.; Kim, H.-J.; Littler, B. J.; Miller, M. A.; Lee, C.-H.;
Lindsey, J. S. J. Org. Chem. 1999, 64, 7890.
(64) Loh, Z.-H.; Miller, S. E.; Chang, C. J.; Carpenter, S. D.; Nocera, D.
G. J. Phys. Chem. A 2002, 106, 11700.
(65) Faure, S.; Stern, C.; Espinosa, E.; Douville, J.; Guilard, R.; Harvey,
P. D. Chem.sEur. J. 2005, 11, 3469.
9236 Inorganic Chemistry, Vol. 44, No. 25, 2005

Meso-Substituted Bisporphyrins
Scheme 3
Scheme 4
Table 1. Cmeso-Cmeso Distances and Chemical Shifts of N-H Protons for Cofacial Free Base Bisporphyrins
DPB
DPX
DPA
DPO
5.53
DPS
DPXNa
DPSN
DPONb
d(Cmeso-Cmeso) (Å)
3.80
4.32
4.94
6.3
δc
-7.6
9, 13
-6.42, -6.80
11, 67
-4.98
8, 68
-3.8, -3.91
12, 13, 67
-3.68,-3.75
69
-3.30
14
-3.11
-3.07
14
ref
a DPXN: 4,5-bis[5-(10,15,20-trimesitylporphyrinyl)]-2,7-di-tert-butyl-9,9-dimethylxanthene. b DPON: 4,6-bis[5-(10,15,20-trimesitylporphyrinyl)]diben-
zofuran. c 1H NMR in CDCl3.
of H4DPXN (δ ) -3.30) to those of H4DPX (δ ) -6.42
and -6.80) clearly shows that the use of bulky substituents
at the meso position induces a larger cavity size.
Photophysical Data. Figure 1 and Figure 2 exhibit the
absorption spectra of 6, and 8-10. The Soret band for 6 is
strong and narrow (λmax ) 416 nm), which is characteristic
for weakly or noninteracting meso-substituted porphyrins in
a face-to-face configuration (i.e., no excitonic coupling).15
Table 2 compares the UV-vis data between meso- and
â-substituted mono- and bisporphyrins (H2TPP vs H4DPSN,
H2P vs H4DPB, H4DPS, and H4DPX), and shows that the
Soret band for meso-substituted macrocycles is more intense
Inorganic Chemistry, Vol. 44, No. 25, 2005 9237

Faure et al.
rin dianion) was too small to be measured at 298 K.65 The
emission spectra and photophysical data for the investigated
compounds are presented in Figure 3 and Table 3, respec-
tively. The emission maxima are similar for the mono- and
bisporphyrins in all meso-substituted systems. At 298 K, the
ΦF values for the bisporphyrins are smaller compared to
those of H2TPP. Moreover, the ΦP values for the PdP
chromophore in (Pd)2DPSN is smaller than that observed
for (Pd)TPP. At 77 K, ΦP’s are expectedly larger for all
molecules, but the meso-substituted systems exhibit a larger
increase in ΦP going from 298 to 77 K.
Bimolecular Excited-State Quenching by Oxygen. The
kQ values for five dipalladium bisporphyrins from this work
and the literature are compared. Figure 4 exhibits the graphs
0
of ΦP /ΦP as a function of the diffusion time of O2 in the
0
solution, where ΦP and ΦP are the phosphorescence
Figure 1. Absorption spectra of H4DPSN, (Zn)2DPSN, (Pd)2DPSN, and
(Cu)2DPSN in CH2Cl2 at 298 K.
quantum yields in the absence and presence of oxygen,
respectively, for (Pd2)DPS, (Pd)2DPX, (Pd)2DPB, (Pd)2DPSN,
and (Pd)TPP. This graph is similar to Stern-Volmer plots.
0
air
[O2] is determined using (Pd)TPP as a standard (ΦP /ΦP
) 4850, [O2]dissolved ) 2.1 × 10-3 M under PO ) 0.21
2
atm20,37), allowing for the determination of kQ according to
Φ
0 ) 1 + kQτP[O2] ) 1 + kSV[O2]
(1)
Φ
where kSV is the Stern-Volmer constant and τP is the
phosphorescence lifetime (see Table 4). Comparison of the
data can be made according to Table 5. (Pd)2DPX and
(Pd)2DPB are the most and least sensitive to oxygen,
respectively, (i.e., largest and smallest observed kSV values).
k
SV depends on both kQ and τP (eq 1). In a previous paper,65
it was demonstrated that τP is a function of the Cmeso-Cmeso
distance. As this distance decreases, τP decreases (τP: H4-
DPX > H4DPB), witnessing the presence of excited-state
deactivation due to internal conversion processes promoted
by intermacrocycle collisions or interactions. The incorpora-
tion of bulky tolyl and mesityl groups at meso positions
should greatly reduce these interactions. Indeed, τP((Pd)2-
DPSN) > τP((Pd)2DPS), and in fact, the former bismacro-
cycle exhibits the largest τP of the series. On the other hand,
kQ is small and just larger than that measured for (Pd)2DPB,
which is the bismacrocycle that exhibits the smallest cavity.
A qualitative analysis of the kQ data is given below.
Theoretically, kQ arising from a collisional bimolecular
process (dynamic quenching) is defined as
Figure 2. Absorption spectra of H4DPSN, (Zn)2DPSN, (Pd)2DPSN, and
(Cu)2DPSN in 2-MeTHF at 77 K.
Table 2. UV-Vis Absorption Data in CH2Cl2 at 298 K
λ
max (nm) (ꢀ × 10-3 M-1 cm-1
)
Soret
region
compound
Q-bands
H4DPSN
416 (556)
417 (619)
412 (482)
411 (408)
513 (28)
552 (29)
524 (50)
551 (9)
591 (9)
646 (7)
594 (6)
555 (7)
540 (17)
(Zn)2DPSN
(Pd)2DPSN
(Cu)2DPSN
H2TPP35,a
515 (19.8)
550 (23.3)
524
(Zn)TPP34,35,a 425
589
554
578
626 (4)
576 (11)
538 (43.2)
(Pd)TPP34 a
(Cu)TPP34 a
H2Pb
418
416
402 (154)
410 (270)
398 (180)
kQ ) fQk0
(2)
539
502 (15)
540 (18)
504 (16)
532 (8)
578 (6)
(Zn)Pb
where fQ is the quenching efficiency and k0 the diffusion-
controlled bimolecular rate constant assuming that all col-
lisions lead to excited-state deactivation. The fact that the
absorption spectra are not modified by the presence of O2
in solution confirmed that the observed phosphorescence
(Pd)Pb
H4DPS
398 (309.9) 502 (29.6) 536 (15.0) 570 (14.2) 622 (6.8)
(Zn)2DPS
402 (473.6) 536 (32)
394 (256.9) 516 (23.5) 548 (50.5)
572 (29)
610 (0.29)
(Pd)2DPS68
a In C6H6. b P2- ) 5-phenyl-2,8,13,17-tetraethyl-3,7,12,18-tetrameth-
ylporphyrin dianion.
(66) Lakowicz, J. R. Principles of Fluorescence Spectroscopy, 2nd ed.;
Kluwer Academic/Plenum Publishers: New York, 1999.
(67) Chang, C. J.; Baker, E. A.; Pistorio, B. J.; Deng, Y.; Loh, Z.-H.; Miller,
S. E.; Carpenter, S. D.; Nocera, D. G. Inorg. Chem. 2002, 41, 3102.
(68) Bolze, F. Ph.D. Thesis. University of Burgundy: Dijon, France, 2001.
(69) From molecular modeling MOPAC (AM1).
and red-shifted than that observed for the â species. The
phosphorescence of the (Pd)P monoporphyrin (P2-
)
5-phenyl-2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphy-
9238 Inorganic Chemistry, Vol. 44, No. 25, 2005

Meso-Substituted Bisporphyrins
Figure 3. Emission spectra of H4DPSN, (Pd)2DPSN, and (Zn)2DPSN at 298 K (A) and 77 K (B), and of (Cu)2DPSN at 77 K (B) in 2-MeTHF.
Table 3. Emission Dataa
emissionb λmax (nm)
quantum yieldc,d
lifetimed,e τF (ns), τP (µs)
compound
298 K
77 K
298 K
77 K
298 K
77 K
H4DPSN
655, 719
602, 654
699
655, 715
611, 670
688
729
680, 755
0.06860 (ΦF)
0.02843 (ΦF)
0.03705 (ΦP)
0.1310 (ΦF)
0.0574 (ΦF)
0.1551 (ΦP)
< 0.0001 (ΦP)
0.17f (ΦP)
12.43 (τF)
2.46 (τF)
13.34 (τF)
1.45 (τF)
1388.00 (τP)
45.5 (τP)
1320 (τP)
(Zn)2DPSN
(Pd)2DPSN
(Cu)2DPSN
(Pd)TPP
506.00 (τP)
696, 772
0.02 (ΦP)
258.67 (τP)
a In 2-MeTHF, λexcitation ) 510 nm for free and palladium porphyrins and 540 nm for copper and zinc derivatives; the quantum yield was evaluated by
reference to H2TPP (0.11,)33-35 and the quantum yield for H2TPP (0.11) at 77 K was verified by reference to (Pd)TPP (0.17; 77 K; MCH).36,37 b The
uncertainties in the values of λmax are (1 nm. c The uncertainties in the values of the quantum yields are (10%. d F ) fluorescence, P ) phosphorescence.
e The uncertainties in the values of the lifetimes are (10%. f In methylcyclohexane (MCH).
Table 4. Photophysical Data of Palladium Bisporphyrins Compared to
(Pd)TPPa
lowest
kQ
kSV
detectionb
(ppm)
compound
τP (µs)
(109 M-1 s-1
)
(106 M-1
)
(Pd)2DPX
(Pd)TPP
(Pd)2DPSN
(Pd)2DPS
(Pd)2DPB
440
258
506
210
258
6.94
8.95
3.99
8.95
2.98
2.91
2.31
2.02
1.88
0.77
0.58
0.73
0.83
0.90
2.2
a τP values are phosphorescence lifetimes measured under an atmosphere
of argon; kQ values are excited-state deactivation constant; kSV is the Stern-
Volmer constant. b Lowest detection (5%) based on I ) 0.95 I0.
Table 5. Theoretical Parameters for O2 Quenching, Quenching
Efficiency, and Diffusion-Controlled Bimolecular Rate Constants for
Palladium Bisporphyrins and (Pd)TPP
Figure 4. Graph of ΦP0/ΦP vs diffusion time of O2 (lower scale) and vs
[O2] (upper scale) of the Pd-porphyrin sensors.
a
b
c
d
e
f
rP
Dp
Rp
k0
kQ
fQ
compound (Å) (10-9 m2 s-1
)
(Å) (109 M-1 s-1
)
(109 M- 1s-1
)
(%)
quenching is due to a dynamic quenching process.66 The
collision frequency, Z, is defined as
(Pd)2DPX 8.1
(Pd)TPP 6.6
(Pd)2DPSN 9.5
(Pd)2DPS 9.0
(Pd)2DPB 7.9
0.45
0.56
0.39
0.43
0.46
7.4
8.8
8.6
8.0
7.3
15.6
19.4
17.7
16.8
15.4
6.94
8.95
3.99
8.95
2.98
44
46
22
53
19
Z ) k0[O2]
(3)
a Porphyrin radius. b Diffusion coefficient of the bismacrocycle. c Sum
of the molecular radius of the chromophore and dioxygen. d Theoretical
diffusion-controlled deactivation constant. e Deactivation constant. f De-
activation efficiency.
and k0 can be expressed according to the Smoluchowski
relation37,66
k0 ) 4πNRP(DO + DP)
(4)
2
respectively. The latter can be estimated using the Stokes-
Einstein equation37,66
where N is Avogadro’s number, RP is the collision radius,
i.e., the sum of the radii of the emitting species (a single
chromophore) and quencher (Scheme 5),66 and DO2 and DP
are the diffusion coefficients of O2 and the porphyrin species,
kbT
D )
(5)
6πηr
Inorganic Chemistry, Vol. 44, No. 25, 2005 9239

Faure et al.
Scheme 5
where kb, η, and T are the Boltzman constant, the viscosity
of the medium (η ) 0.575 × 10-3 Pa for 2-MeTHF at 293
K),37 and the temperature, respectively, r is the solvated
molecular radius (i.e., rP for the bisporphyrin, rO2 for O2;
Scheme 5). As molecules are not spherical systems, the
molecular surfaces are computed according to the Connolly
methodology.31 The calculated surfaces are then used to
Figure 5. Examples of computed surfaces for (Pd)2DPB (A), (Pd)2DPS
(B), and (Pd)2DPSN (C).
((Pd)2DPX, (Pd)2DPS) and “closed” ((Pd)2DPSN, (Pd)2DPB)
systems. (Pd)TPP is characterized by an efficiency similar
to that of the bisporphyrins with “open” cavities that are
formed by the two macrocycles and the spacer.
extract rP and rO for a sphere model. This computer
2
methodology requires knowledge of the solvent radius. In
this work, r(2-MeTHF) was also estimated by computations
using the van der Waals radii (r(2-MeTHF) ) 2.89 Å). This
The comparison of the fQ values for (Pd)2DPX, (Pd)2DPS,
and (Pd)2DPB shows that the smaller cavity in the biphen-
ylenyl derivative (Figure 5) prevents efficient quenching by
oxygen. The fact that the fQ((Pd)2DPS)/fQ((Pd)2DPB) ratio
is about 2 strongly suggests that the O2 molecules do not
penetrate inside the cavity in (Pd)2DPB, and indicates that
the two macrocycles screen each other. Similarly, comparison
of the fQ values for (Pd)TPP and (Pd)2DPSN indicates that
the interior of the cavity of the latter system is cluttered.
This can also be observed in Figure 5 when comparing
(Pd)2DPS with (Pd)2DPSN. Again, fQ((Pd)2DPS)/fQ((Pd)2-
DPSN) and fQ((Pd)TPP)/fQ((Pd)2DPSN) ratios of about 2 are
noted.
While the meso-substitution by aryl groups prevents the
two macrocycles in a cofacial arrangement from deactivating
each other, rendering τP longer, steric hindrance prevents O2
from efficiently penetrating inside the cavity. As a conse-
quence, the design for better sensors must take these
parameters into account. It is interesting to note that
(Pd)2DPX is the most sensitive of the porphyrin systems,
but its synthesis requires many steps.
approach represents a crude approximation. For O2, rO
)
2
1.6 Å and DO ) 2.33 × 10-9 m2 s-1.
2
Table 5 compares the calculated parameters and experi-
mental kQ allowing extraction of fQ. Figure 5 shows three
typical examples of computed surface envelopes used to
determine rP and RP. As anticipated, rP is greater for larger
bismacrocycles (example: rP((Pd)2DPSN) > rP((Pd)2DPB)),
and DP’s for the porphyrin molecules are smaller than that
for O2. Similarly, RP’s for â-substituted porphyrins are
smaller than those for the meso-substituted chromophores,
again consistent with the number of substituent C atoms
attached on the porphyrin rings. k0 is calculated from rP, DP,
and RP (eq 4). On the basis of the k0 values, (Pd)TPP, (Pd)2-
DPSN, and (Pd)2DPS are predicted to be the most efficient
O2 sensors if all collisions are efficient from a theoretical
stand point. This basic model assumes that collisions with
the porphyrin chromophore substituents lead to excited-state
deactivation, which is not necessarily always the case. From
the experimental kQ’s, we estimated and compared the fQ’s.
The series can be separated into two groups: “open”
9240 Inorganic Chemistry, Vol. 44, No. 25, 2005

Meso-Substituted Bisporphyrins
Conclusion
prepared at a reasonable price. In this context, the construc-
tion of systems covalently anchored on solid support, both
mono- and bisporphyrin systems, exhibits very interesting
possibilities for future applications in this area.
The results demonstrate the presence of a diffusion
mechanism of O2 toward the chromophore, contrasting with
the static mechanism, which is the source of some contro-
versy in the literature. In terms of efficiency vs cost, (Pd)-
TPP definitely exhibits the best ratio in the studied series.
However, the structural modification for molecular device
improvement of this monoporphyrin complex is not flexible.
Indeed, better sensitivity is obtained when one figures out a
way to increase τP and ΦP via structural modification. This
was found in (Pd)2DPX, for which τP was increased and both
macrocycles remained clearly accessible to O2. By reducing
the number of steps of synthesis for (Pd)2DPSN in this work,
and choosing the appropriate substituents, we found it is
possible that more effective O2 sensing porphyrins could be
Acknowledgment. P.D.H. thanks NSERC (Natural Sci-
ences and Engineering Research Council of Canada) for
support. The support of the CNRS (R.G., UMR 5633) is also
gratefully acknowledged.
Supporting Information Available: Table comparing the λmax
,
Φe, and τe for various related bisporphyrin systems; H and 13C-
{1H} NMR and MS (MALDI-TOF) and EPR spectra for 1-9. This
material is available free of charge via the Internet at http://
pubs.acs.org.
1
IC0508573
Inorganic Chemistry, Vol. 44, No. 25, 2005 9241