Energy transfers in monomers, dimers, and trimers of zinc(II) and palladium(ii) porphyrins bridged by rigid pt-containing conjugated organometallic spacers

Article abstract of DOI:10.1021/ic900840w

A series of linear monomers (spacer-M(P)), dimers (M(P) - spacer-M'(P)), and trimers (M(P)-spacer-M'(P)-spacer-M(P)) of spacer/metalloporphyrin systems (M' = Zn, M = Zn, Pd, P = porphyrin, and spacer = trans-C₆H ₄C≡CPtL₂C≡

Full text of DOI:10.1021/ic900840w

Inorg. Chem. 2009, 48, 7613–7629 7613
DOI: 10.1021/ic900840w
Energy Transfers in Monomers, Dimers, and Trimers of Zinc(II) and Palladium(II)
Porphyrins Bridged by Rigid Pt-Containing Conjugated Organometallic Spacers
Diana Bellows,† Shawkat M. Aly,† Claude P. Gros,‡ Maya El Ojaimi,‡ Jean-Michel Barbe,‡ Roger Guilard,*,‡ and
Pierre D. Harvey*,†
†
‡
ꢀ
ꢀ
ꢀ
Departement de chimie, Universite de Sherbrooke, Sherbrooke, Quebec, Canada, and ICMUB (UMR 5260),
ꢀ
Universite de Bourgogne, Dijon, France
Received February 3, 2009
A series of linear monomers (spacer-M(P)), dimers (M(P)-spacer-M0(P)), and trimers (M(P)-spacer-M0(P)-
spacer-M(P)) of spacer/metalloporphyrin systems (M0 = Zn, M = Zn, Pd, P = porphyrin, and spacer = trans-
C6H4CtCPtL2CtCC6H4- (L=PEt3)) including mixed metalloporphyrin compounds, were synthesized and characterized.
The S1 and T1 energy transfers Pd(P)*fZn(P) occur with rates of ∼2ꢀ109 s-1, S1, and 0.15ꢀ103 (slow component)
and 4.3ꢀ103 s-1 (fast component), T1. On the basis of a literature comparison with a related dyad, the Pt atom in the
conjugated chain slows down the transfers. The excitation in the absorption band of the trans-C6H4CtCPtL2CtCC6H4-
spacer in the 300-360 nm range also leads to T1 energy transfer (spacer* f M(P); M=Zn, Pd) with rates of 104 s-1
.
Introduction
models to mimic these photophysical processes.12-15 Among
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u-bourgogne.fr (R.G.), pierre.harvey@usherbrooke.ca (P.D.H.). Phone: 33
(0)3 80 39 61 11 (R.G.), 819-821-7092 (P.D.H.). Fax: 819-821-8017 (P.D.H.).
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2009 American Chemical Society
Published on Web 07/22/2009
pubs.acs.org/IC

7614 Inorganic Chemistry, Vol. 48, No. 16, 2009
Bellows et al.
Scheme 1. (Top Left) Drawing of LH II Showing the B850 Network, the Non-Interacting B800s, and the Carotenoids; a (Top Right) Drawing of the
Local Environment of the Carotenoids (in Black) and the B800 and B850 Units Stressing the Downhill S1 Energy Transfers and the Possible Slightly
Uphill Transfers (Carotenoid f B850); (Bottom) Structures of the Bacteriochlorophyll a and of the Carotenoid
a The quasi-parallel arrows represent the transition moments of two B850 units.
well-documented among the photosynthetic bacteria.35,36 In
this case, the singlet state energy migration from B800 f
B850 (B=bacteriochlorophyll a) systems occurs in the 1 ps
time scale despite the long center-to-center separation
donor-acceptor separation, and by the fact that π-conjugation
is still possible across the spacer from the presence of the dxy
metal orbital. Energy migrations in the S1 state are noted. This
conclusion bears an important consequence on the anticipated
antenna effect in one-dimensional (1-D) materials built upon
these dyads and monodispersed oligomers (Chart 1).
(∼18 A).37 It is strongly believed that the auxiliary carotenoid
˚
is used as a relay between the donor and acceptor.
Inspired by the observation that S1 energy transfer between
a donor and an acceptor that are not conjugated is possible,
even when separated by 18 A or so, it appears convenient to
Experimental Section
˚
Materials. The porphyrin precursors, a,c-biladiene and 3,30-
diethyl-4,40-dimethyldipyrromethane, were synthesized as pre-
viously reported.38 cis-Dichlorobis(triethylphosphine)-plati-
num(II), trans-dichlorobis(triethylphosphine)platinum(II) were
prepared according to standard procedures.39,40 The following
materials were purchased from commercial suppliers: DDQ
(dichlorodicyanoquinone; Aldrich), triethylphosphine (Aldrich),
diisopropylamine (Aldrich), phenylacetylene (Aldrich), copper(I)
iodide (Aldrich), [(trimethylsilyl)ethynyl]benzaldehyde (Aldrich),
dichloromethane (EMD), platinum(II) chloride (Strem), potas-
sium carbonate (Fisher), ether (ACP), hexane (ACP), ethanol
(Commercial Alcoholsinc.). All the solvents were purified accord-
ing to literature procedures.41 The coupling reactions were
performed under argon using Schlenk techniques, with flame-
dried reaction vessels before use. Silica gel (Merck; 70-120 μm)
was used for column chromatography. Analytical thin layer
design a series of dyads composed of porphyrinoids that
exhibit similar features as that shown above in the natural
system (B800-B850). In that respect, we now wish to report
a series of dimers and trimers (Chart 1) for the investigation of
S1 and T1 energy transfers in unconjugated donor-spacer-
acceptor systems rigidly held by a conjugated organometallic
fragment (-C6H4CtCPtL2CtCC6H4-). The donor and
acceptor are very poorly conjugated owing the quasi right
angle formed by the metalloporphyrin ring and phenyl group.
The choice of a heavy metal (Pt) is driven by the opportunity
to also investigate the T1 state behavior (a state whose
population is enhanced by heavy atom effect), by the dimen-
sion of the atom allowing to reach the desired targeted
(35) Bertini, I.; Gray, H. B.; Stiefel, E. I.; Valentine, J. S. In Biological
Inorganic Chemistry Structure and Reactivity; Stiefel, J. E., Ed.; University
Science Books: Sausalito, CA, 2007; pp 305-316.
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Ahr, K., Ryan, M., O'Neil, J., Wong, V., Ciprioni, J., Mays, M., Tymoczko, N. E.,
Eds.; W. H. Freeman and Company: New York, 2005; pp 725-735.
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2008, 102, 395–405.
ꢀ ^
(38) Guilard, R.; Gros, C. P.; Bolze, F.; Jerome, F.; Ou, Z. P.; Shao, J. G.;
Fischer, J.; Weiss, R.; Kadish, K. M. Inorg. Chem. 2001, 40, 4845–4855.
(39) Kharasch, M. S.; Seyler, R. C.; Mayo, F. R. J. Am. Chem. Soc. 1938,
60, 882–884.
(40) Parshall, G. W. Inorg. Synth. 1970, 12, 26–33.
(41) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purifications of
laboratory chemicals; Pergamon Press: Oxford, 1966.

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7615
Chart 1
chromatography was performed using Merck 60 F254 silica
gel (precoated sheets, 0.2 mm thick). All the reactions were
monitored by thin-layer chromatography and UV-visible
spectroscopy.
the solvent was removed in vacuo, and the crude product was
dissolved in dichloromethane (100 mL), washed with water
(3 ꢀ 500 mL), and dried over MgSO4. The solvent was
removed in vacuo, and the residue was purified by silica
column chromatography (CH2Cl2 as eluent). After evapora-
tion, the title compound 2a was obtained in 86% yield
5-[4-(Trimethylsilyl)ethynylphenyl]-13,17-diethyl-2,3,7,8,12,18-
hexamethyl-porphyrin (1). A mixture of 2.01 g (9.93 mmol) of
4-[(trimethylsilyl)ethynyl]-benzaldehyde and 4.00 g (6.64 mmol)
of a,c-biladiene dihydrobromide38 was dissolved in 500 mL of
hot absolute ethanol. p-Toluenesulfonic acid (8.0 g) in 100 mL
of ethanol was slowly added over 12 h, and the mixture was
stirred under reflux for 48 h. The mixture was cooled to room
temperature, and the solution was evaporated under vacuum.
The residue was dissolved in dichloromethane (500 mL), neu-
tralized with a saturated solution of NaHCO3, and then washed
thoroughly three times with 1 L of water. The organic phase was
dried over MgSO4 and filtered, the solvent was removed in
vacuo. The residue was purified by silica column chromatogra-
phy (CH2Cl2 as eluent). The second fraction was collected,
concentrated, and crystallized from CH2Cl2/MeOH to yield
the title compound (1.9 g; 30% yield) as a purple solid. 1H
NMR (CDCl3) δ (ppm): 10.36 (s, 2H, H-meso), 10.20 (s, 1H,
1
(567 mg) as a red microcrystalline solid. H NMR (CDCl3)
δ (ppm): 10.07 (s, 2H, H-meso), 9.93 (s, 1H, H-meso), 8.01 (d,
2H, JH-H = 8 Hz, H-Phenyl), 7.88 (d, 2H, JH-H = 8 Hz,
3
3
3
H-Phenyl), 4.05 (q, 4H, JH-H =7.6 Hz, CH2), 3.61 (s, 6H,
CH3), 3.52 (s, 6H, CH3), 2.47 (s, 6H, CH3), 1.87 (t, 6H,
3JH-H =7.6 Hz, CH3), 1.28 (s, 9H, Si-CH3). MS (MALDI-
TOF): m/z=684.10 [M]+•; 684.26 calcd for C41H44N4SiZn.
HR-MS (ESI): m/z=685.2706 [M+H]+; 685.2699 calcd for
C41H45N4SiZn, m/z = 707.2539 [M+Na]+; 707.2519 calcd
for C41H44N4NaSiZn. UV-visible (CH2Cl2): λmax nm (ε ꢀ
10-3, M-1 cm-1)=403 (203), 533 (8.9), 569 (9.9).
5-(4-Ethynylphenyl)-13,17-diethyl-2,3,7,8,12,18-hexamethyl-
porphyrin Zinc (2b). To a solution of 5-[4-(2-(trimethylsilyl)-
ethynylphenyl]-13,17-diethyl-2,3,7,8,12,18-hexamethymporphy-
rin zinc 2a (567 mg, 0.829 mmol) in tetrahydrofuran (THF,
100 mL) was added NBu4F (4 mL, 4 mmol, 1 M in THF). After
the mixture was stirred at room temperature for 12 h, the
solution was evaporated under reduced pressure and dissolved
in methylene chloride. The solution was washed with a saturated
NH4Cl solution, 3 times with water and dried over anhydrous
MgSO4. After purification over a silica plug (CH2Cl2 as eluent),
the title compound 2b was isolated in 78% yield (397 mg).
1H NMR (CDCl3) δ (ppm): 9.98 (s, 2H, H-meso), 9.80 (s, 1H,
H-meso), 7.99 (d, 2H, 3JH-H=7.5 Hz, H-Phenyl), 7.88 (d, 2H,
3JH-H=7.5 Hz, H-Phenyl), 3.99 (q, 4H, 3JH-H=7.6 Hz, CH2),
3.54 (s, 6H, CH3), 3.48 (s, 6H, CH3), 3.34 (s, 1H, alcyne), 2.43 (t,
3
H-meso), 8.29 (d, 2H, JH-H =8 Hz, H-Phenyl), 8.04 (d, 2H,
3
3JH-H=8 Hz, H-Phenyl), 3.96 (q, 4H, JH-H=7.6 Hz, CH2),
3.56 (s, 6H, CH3), 3.33 (s, 6H, CH3), 2.32 (s, 6H, CH3), 2.00 (t,
6H, 3JH-H=7.6 Hz, CH3), 1.35 (s, 9H, Si-CH3), -0.85 (s, 1H,
NH), -1.93 (s, 1H, NH). HR-MS (MALDI-TOF): m/z =
622.3503 [M]+•; 622.3492 calcd for C41H46N4Si. UV-visible
(CH2Cl2): λmax nm (ε ꢀ 10-3, M-1 cm-1) = 405 (188), 500
(10.1), 535 (11.1), 570 (11.0), 620 (3.7).
5-[4-(Trimethylsilyl)ethynylphenyl]-13,17-diethyl-2,3,7,8,12,18-
hexamethyl-porphyrin Zinc (2a). 5-[4-(Trimethylsilyl)ethynyl-
phenyl]-13,17-diethyl-2,3,7,8,12,18-hexamethylporphyrin 1
(600 mg, 0.964 mmol) and zinc acetate tetrahydrate
(317 mg, 1.44 mmol) were dissolved in chloroform (70 mL)
and methanol (30 mL) and refluxed for 90 min in the presence
of sodium acetate (790 mg, 9.63 mmol). The metalation
reaction was monitored by UV-visible spectroscopy and
MALDI-TOF mass spectrometry. At the end of the reaction,
3
6H, JH-H =7.6 Hz, CH3), 1.82 (s, 6H, CH3). MS (MALDI-
TOF): m/z = 611.89 [M]+•; 612.22 calcd for C38H36N4Zn.
HR-MS (ESI): m/z = 613.2311 [M+H]+; 613.2304 calcd for
C38H37N4Zn, m/z = 635.2140 [M+Na]+; 635.2124 calcd
for C38H36N4NaZn. UV-visible (CH2Cl2): λmax nm (εꢀ10-3
,
M-1 cm-1)=403 (288), 533 (17.2), 569 (19.3).

7616 Inorganic Chemistry, Vol. 48, No. 16, 2009
Bellows et al.
5-(4-(Trimethylsilyl)ethynylphenyl)-13,17-diethyl-2,3,7,8,12,18-
hexamethyl-porphyrin Palladium (3a). 5-(4-(Trimethylsilyl)-
ethynylphenyl)-13,17-diethyl-2,3,7,8, 12,18-hexamethylpor-
phyrin 1 (400 mg, 0.642 mmol) and sodium acetate (0.540 g,
6.58 mmol) were dissolved under argon in 80 mL of 1,2-
dichloroethane. The mixture was heated at 110 °C. A palla-
dium acetate solution (157 mg, 0.700 mmol in 15 mL of
methanol) was slowly added over 90 min, and the metalation
reaction was monitored by UV-visible spectroscopy and
MALDI-TOF mass spectrometry. The solution was cooled
to room temperature, washed 3 times with water and evapo-
rated under reduced pressure. After purification on silica
column (CH2Cl2 as eluent), the title compound 3a was iso-
lated in 65% yield (302 mg). 1H NMR (CDCl3) δ (ppm): 10.07
C54H60N4Si2Zn. UV-visible (CH2Cl2): λmax nm (ε ꢀ 10-3
,
M
-1 cm-1)=411 (267), 539 (15.0), 574 (8.0).
5,15-Bis[(4-ethynyl)phenyl]tetraethyl-2,8,12,18-tetramethyl-
3,7,13,17-porphyrin Zinc (4b). This compound was prepared in
93% yield (311 mg, 420.36 mmol) as described for 2b start-
1
ing from 4a (400 mg, 452 mmol). H NMR (CDCl3) δ (ppm):
10.09 (s, 2H, H-meso), 7.96 (d, 4H, 3JH-H=7.5 Hz, H-Phenyl), 7.81
(d, 4H, 3JH-H=7.5 Hz, H-Phenyl), 3.91 (q, 8H, 3JH-H=7.6 Hz,
CH2), 3.26 (s, 2H, alcyne), 2.38 (s, 12H, CH3), 1.68 (t, 12H,
3JH-H=7.6 Hz, CH3). HR-MS (MALDI-TOF): m/z=740.2891
[M]+•; 740.2857 calcd for C48H44N4Zn. UV-visible (CH2Cl2):
λ
max nm (εꢀ10-3, M-1 cm-1)=411 (235), 539 (13.1), 574 (7.1).
trans-Chloro-[5-(4-ethynylphenyl)-13,17-diethyl-2,3,7,8,12,18-
hexamethyl(metal)-porphyrin]bis(triethylphosphine)platinum(II)
(metal=Zn (5), Pd (6)). CuI (0.6 mg, 0.003 mmol) was added
to a mixture of trans-Pt(PEt3)2Cl2 (87.5 mg, 0.174 mmol) and
porphyrin 2b (0.035 mmol) or 3b (0.035 mmol) in CH2-
Cl2/iPr2NH (50 mL, 1:1 v/v). The purple solution was left to
stir overnight under inert atmosphere and refluxed, after which
all volatiles were removed under reduced pressure. The residue
was redissolved in CH2Cl2 and washed 3 times with water and
dried over K2CO3. All solvents were removed under reduced
pressure. The residue was dissolved in a minimum amount of
CH2Cl2 and passed through a silica column using hexane/
CH2Cl2 (40/60) as the solvents.
5. Yield: 69% (72.4 mg) 1H NMR (CDCl3) δ (ppm): 10.15 (s,
2H, H-meso), 10.05 (s, 1H, H-meso), 7.88 (d, 2H, 3JH-H=8.0 Hz,
H-Phenyl), 7.61 (d, 2H, 3JH-H=8.1 Hz, H-Phenyl), 4.10 (q, 4H,
3JH-H=7.6 Hz, CH2), 3.64 (s, 6H, CH3), 3.54 (s, 6H, CH3), 2.54
(s, 6H, CH3), 2.26-2.21 (m, 12H, CH2), 1.89-1.87 (m, 6H,
CH2CH3), 1.34-1.25 (m, 18H, CH3). 31P NMR (CDCl3) δ
(ppm): 16.23. IR (KBr) ν: 2115.1 cm-1 (CtC). Anal. Calcd
(%) for C50H65ClN4P2PtZn (1079.95): C 55.61, H 6.07, N 5.19.
Found: C 55.33; H 6.36, N 4.91. MS (MALDI-TOF): m/z =
1080.24 [M]+•; 1079.95 calcd for C50H65ClN4P2PtZn. UV-
visible (2MeTHF): λmax nm (ε ꢀ 10-3, M-1 cm-1)=328 (27),
411 (302), 540 (18), 576 (11).
6. Yield: 57% (38.9 mg) 1H NMR (CDCl3) δ (ppm): 10.09 (s,
2H, H-meso), 10.03 (s, 1H, H-meso), 7.84 (d, 2H, 3JH-H=7.9 Hz,
H-Phenyl), 7.59 (d, 2H, 3JH-H=8.0 Hz, H-Phenyl), 4.04 (q, 4H,
3JH-H=7.6 Hz, CH2), 3.59 (s, 6H, CH3), 3.48 (s, 6H, CH3), 2.49
(s, 6H, CH3), 2.25-2.19 (m, 12H, CH2), 1.90-1.85 (m, 6H,
CH2CH3), 1.38-1.25 (m, 18H, CH3). 31P NMR (CDCl3) δ
(ppm): 16.23. IR (KBr) ν: 2118.7 cm-1 (CtC). Anal. Calcd
(%) for C50H65ClN4P2PtPd (1120.98): C 53.57, H 5.84, N 5.00.
Found: C 53.85, H 6.09, N 4.81. MS (MALDI-TOF): m/z =
1120.24 [M]+•; 1120.98 calcd for C50H65ClN4P2PtPd. UV-
visible (2MeTHF): λmax nm (ε ꢀ 10-3, M-1 cm-1)=320 (32),
400 (265), 515 (22), 548 (53).
(s, 2H, H-meso), 10.01 (s, 1H, H-meso), 7.94 (d, 2H, 3JH-H
=
8 Hz, H-Phenyl), 7.84 (d, 2H, JH-H = 8 Hz, H-Phenyl),
3
4.02 (q, 4H, 3JH-H=7.6 Hz, CH2), 3.46 (s, 6H, CH3), 2.41 (s,
6H, CH3), 1.87 (t, 6H, JH-H = 7.6 Hz, CH3), 1.54 (s, 6H,
3
CH3), 0.40 (s, 9H, Si-CH3). MS (MALDI-TOF): m/z=726.00
[M]+•; 726.24 calcd for C41H44N4PdSi. HR-MS (ESI): m/z=
727.2457 [M+H]+; 727.2443 calcd for C41H45N4PdSi, m/z=
749.2281 [M+Na]+; 749.2262 calcd for C41H44N4NaPdSi.
UV-visible (CH2Cl2): λmax nm (ε ꢀ 10-3, M-1 cm-1)=395
(137), 513 (8.0), 547 (24.0).
5-(4-Ethynylphenyl)-13,17-diethyl-2,3,7,8,12,18-hexamethyl-
porphyrin Palladium (3b). To a solution of porphyrin palladium
3a (290 mg, 0.399 mmol) in THF (75 mL) was added NBu4F
(2 mL, 2 mmol, 1 M in THF). After the mixture was stirred at
room temperature for 12 h, the solution was evaporated under
reduced pressure and dissolved in methylene chloride. The
solution was washed with a saturated NH4Cl solution, 3 times
with water and dried over anhydrous MgSO4. After purification
over a silica plug (CH2Cl2 as), the title compound 3b was
1
isolated in 96% yield (252 mg). H NMR (CDCl3) δ (ppm):
=
9.97 (s, 2H, H-meso), 9.92 (s, 1H, H-meso), 7.93 (d, 2H, 3JH-H
8 Hz, H-Phenyl), 7.82 (d, 2H, JH-H =8 Hz, H-Phenyl), 4.01
3
3
(q, 4H, JH-H=7.6 Hz, CH2), 3.44 (s, 6H, CH3), 3.29 (s, 1H,
3
alcyne), 2.40 (s, 6H, CH3), 1.85 (t, 6H, JH-H=7.6 Hz, CH3),
1.54 (s, 6H, CH3). HR-MS (ESI): m/z = 655.2074 [M+H]+;
655.2048 calcd for C38H37N4Pd, m/z = 677.1896 [M+Na]+;
677.1867 calcd for C38H36N4NaPd. UV-visible (CH2Cl2): λmax
nm (ε ꢀ 10-3, M-1 cm-1)=395 (142), 513 (9.8), 547 (26.3).
5,15-Bis[4-(trimethylsilyl)ethynyl]phenyl]-tetraethyl-2,8,12,18-
tetramethyl-3,7,13,17-porphyrin Zinc (4a). A solution of 4-
[(trimethylsilyl)ethynyl]benzaldehyde (439 mg, 2.17 mmol) and
3,30-diethyl-4,40-dimethyldipyrromethane38 (500 mg, 217 mmol)
in 250 mL of CH2Cl2 was treated with BF3 OEt2 (0.16 mL).
3
After 30 min, DDQ (1.47 g, 6.51 mmol, 3 equiv) and triethyla-
mine (1.5 mL) were added, and the solution was stirred at room
temperature for 1 h. After evaporation, the residue was dis-
solved in a minimum amount of CH2Cl2 and passed through an
alumina column using CH2Cl2 as the solvent. After removing
of the solvent, the crude porphyrin and zinc acetate dihydrate
(953 mg, 4.34 mmol) were dissolved in CHCl3 (70 mL) and
methanol (30 mL) and refluxed for 90 min in the presence of
sodium acetate (1.18 g, 8.68 mmol). The metalation reaction was
monitored by UV-visible spectroscopy and MALDI-TOF
mass spectrometry. At the end of the reaction, the solvent
was removed, and the crude product was dissolved in CH2Cl2
(100 mL), washed with water (3 ꢀ 500 mL), and dried over
MgSO4. The solvent was removed in vacuo, and the residue was
purified by silica column chromatography (CH2Cl2 as the
solvent). After evaporation, the title compound 4a was obtained
in 22% yield (423 mg) as a red microcrystalline solid. 1H NMR
trans-(Ethynylphenyl)[5-(4-ethynylphenyl)-13,17-diethyl-2,3,
7,8,12,18-hexamethyl-(metal)porphyrin]bis(triethylphosphine)-
platinum(II) (metal=Zn (7), Pd (8)). CuI (0.3 mg, 0.002 mmol)
was added to a mixture of [Pt(PEt3)2(CtCC6H4(M(P)))Cl]
(19.4 mg, 0.0161 mmol) and phenylacetylene (0.00180 mL,
0.0177 mmol) in CH2Cl2/iPr2NH (50 mL, 1:1 v/v). The purple
solution was left to stir overnight under inert atmosphere and
refluxed, after which all volatiles were removed under reduced
pressure. The residue was redissolved in CH2Cl2 and washed 3
times with water and dried over K2CO3. All solvents were
removed under reduced pressure, and the residue was dissolved
in a minimum amount of CH2Cl2 and filtered through a silica
column using hexane/CH2Cl2 (40/60).
7. Yield: 60% (21.8 mg) 1H NMR (CDCl3) δ (ppm): 10.02 (s,
2H, H-meso), 9.84 (s, 1H, H-meso), 7.85 (d, 2H, 3JH-H=7.7 Hz, H-
Phenyl), 7.65 (d, 2H, JH-H =7.8 Hz, H-Phenyl), 7.35 (m, 3H,
(CDCl3) δ (ppm): 10.12 (s, 2H, H-meso), 7.98 (d, 4H, 3JH-H
=
3
3
3
3JH-H = 7.2 Hz, H-Phenyl), 7.26 (d, 2H, JH-H = 6.8 Hz, H-
Phenyl), 4.00 (q, 4H, JH-H=7.6 Hz, CH2), 3.57 (s, 6H, CH3),
7.5 Hz, H-Phenyl), 7.84 (d, 4H, JH-H = 7.5 Hz, H-Phenyl),
3.95 (q, 8H, 3JH-H=7.6 Hz, CH2), 2.41 (s, 12H, CH3), 1.72 (t,
12H, JH-H = 7.6 Hz, CH3), 1.22 (s, 18H, Si-CH3). HR-MS
3
3
3.50 (s, 6H, CH3), 2.53 (s, 6H, CH3), 2.40-2.31 (m, 12H, CH2),
(MALDI-TOF): m/z = 884.3671 [M]+•; 884.3648 calcd for
1.86-1.81 (m, 6H, CH2CH3), 1.42-1.31 (m, 18H, CH3). 31PNMR

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7617
(CDCl3) δ (ppm): 12.44. IR (KBr) ν: 2107.5 cm-1 (CtC). Anal.
Calcd (%) for C58H70N4P2PtZn (1145.62): C 60.81, H 6.16, N 4.89.
Found: C 61.09, H 6.31, N 4.55. MS (MALDI-TOF): m/z =
1145.42 [M]+•; 1145.62 calcd for C58H70N4P2PtZn. UV-visible
(2MeTHF): λmax nm (ε ꢀ 10-3, M-1 cm-1)=335 (26), 412 (210),
540 (10), 575 (6).
2.19-(-1.80) (CH2CH3). 31P NMR (MAS) δ (ppm): 5.50. IR (KBr)
ν: 2109.5 cm-1 (CtC). Anal. Calcd (%) for C148H172N12P4Pt2Zn3
(2829.31): C 62.83, H 6.13, N 5.94. Found: C 63.10, H 5.88, N 6.09.
MS (MALDI-TOF): m/z = 2828.85 [M]+•; 2829.12 calcd for
C
148H172N12P4Pt2Zn3. UV-visible (2MeTHF): λmax nm (ε ꢀ 10-3
,
M-1 cm-1)=340 (44), 413 (322), 540 (27), 575 (17).
8. Yield: 45% (10.0 mg) 1H NMR (CDCl3) δ (ppm): 10.07 (s,
2H, H-meso), 10.01 (s, 1H, H-meso), 7.81 (d, 2H, JH-H=7.8 Hz,
H-Phenyl), 7.62 (d, 2H, JH-H=7.8 Hz, H-Phenyl), 7.34 (m, 3H,
13. Yield: 56% (35.1 mg) 1H NMR (MAS) (all bands are very
large) δ (ppm): 7.65 (H-meso), 6.23 (H-phenyl), 3.99-1.88
(CH2CH3), 1.88-(-1.01) (CH2CH3). 31P NMR (MAS) δ
(ppm): 10.97. IR (KBr) ν: 2098.1 cm-1 (CtC). Anal. Calcd
(%) for C148H172N12P4Pt2ZnPd2 (2911.36): C 61.06, H 5.95, N
5.77. Found: C 61.29, H 6.18, N 5.52. MS (MALDI-TOF): m/z=
2910.77 [M]+•; 2911.31 calcd for C148H172N12P4Pt2ZnPd2.
Instruments. 1H NMR spectra for complexes 1-4 were re-
corded on a Bruker DRX-300 AVANCE spectrometer at the
JH-H = 7.5 Hz, H-Phenyl), 7.23 (d, 2H, JH-H = 6.8 Hz, H-
Phenyl), 4.03 (q, 4H, 3JH-H=7.6 Hz, CH2), 3.57 (s, 6H, CH3),
3.47 (s, 6H, CH3), 2.49 (s, 6H, CH3), 2.38-2.30 (m, 12H, CH2),
1.90-1.84 (m, 6H, CH2CH3), 1.54-1.32 (m, 18H, CH3). 31P
NMR (CDCl3) δ (ppm): 12.44. IR (KBr) ν: 2106.1 cm-1 (CtC).
Anal. Calcd (%) for C58H70N4P2PtPd (1186.64): C 58.70, H
5.95, N 4.72. Found: C 58.46, H 5.69, N 5.07. MS (MALDI-
TOF): m/z = 1186.37 [M]+•; 1186.64 calcd for C58H70N4P2-
PtPd. UV-visible (2MeTHF): λmax nm (ε ꢀ 10-3, M-1 cm-1)=
328 (40), 396 (211), 515 (17), 548 (43).
ꢁ
“Plateforme d’Analyse Chimique et de Synthese Moleculaire de
l’Universite de Bourgogne (PACSMUB)”. Chemical shifts are
ꢀ
ꢀ
expressed in ppm relative to chloroform (7.258 ppm). The NMR
spectra for complexes 5-8 were acquired on a Bruker AC-300
spectrometer (1H 300.15 MHz and 31P 121.50 MHz) using the
solvent as a chemical shift standard, except for the 31P NMR,
where the chemical shifts are relative to D3PO4 85% in D2O. All
chemical shifts (δ) and coupling constants (J) are given in ppm
and hertz, respectively. The spectra were measured from freshly
preparedsamples inchloroform. The NMRspectra for complexes
9-13 were characterized in the solid state. 1H MAS NMR
experiments (magic angle spinning) were performed at the Na-
tional Ultrahigh-field NMR Facility for Solids (Ottawa, Canada)
on a Bruker Avance II NMR spectrometer operating at 21.1 T. A
double-resonance 3.2 mm Bruker probe. 1H NMR chemical shifts
were referenced to neat tetramethylsilane (TMS) using adaman-
trans-Bis[5-(4-ethynylphenyl)-13,17-diethyl-2,3,7,8,12,18-he-
xamethyl(metal)-porphyrin]bis(triethylphosphine)platinum(II)
(metal=Zn (9), Pd (10)), and trans-[(5-(4-Ethynylphenyl)-13,17-
diethyl-2,3,7,8,12,18-hexamethyl(palladium(II))-porphyrin)-
[(5-(4-ethynylphenyl)-13,17-diethyl-2,3,7,8,12,18-hexamethyl-
(zinc(II))-porphyrin)]bis(triethylphosphine)platinum(II) (11). CuI
(1.5 mg, 0.0080 mmol) was added to a mixture of trans-Pt-
(PEt3)2Cl2 (38.7 mg, 0.0770 mmol) and the corresponding
porphyrin (0.154 mmol) in CH2Cl2/iPr2NH (50 mL, 1:1 v/v).
The purple solution was stirred overnight under inert atmo-
sphere and refluxed. A redish-purple precipitate was formed,
which was collected by filtration and washed with CH2Cl2 and
dried under vacuum.
1
tane as a secondary chemical shift reference. H MAS NMR
9. Yield: 63% (80.1 mg) 1H NMR (MAS) (all bands are very
large) δ (ppm): 9.07 (H-meso), 6.85 (H-phenyl), 4.50-2.01
(CH2CH3), 2.01-(-1.32) (CH2CH3). 31P NMR (MAS) δ
(ppm): 8.27. IR (KBr) ν: 2115.7 cm-1 (CtC). Anal. Calcd (%)
for C88H100N8P2PtZn2 (1657.60): C 63.76, H 6.08, N 6.76.
Found: C 63.87, H 6.33, N 6.87. MS (MALDI-TOF): m/z =
1657.63 [M]+•; 1657.60 calcd for C88H100N8P2PtZn2. UV-
visible (2MeTHF): λmax nm (ε ꢀ 10-3, M-1 cm-1)=335 (26),
410 (121), 435 (52), 540 (24), 577 (24).
spectra were recorded at a resonance frequency of 900.2 MHz.
Samples were spun at a spinning speed of 20 kHz in 3.2 mm o.d.
ZrO2 rotors. A single pulse sequence with background suppres-
1
sion was used in the H NMR experiments with the r.f. pulse
length of 2.5 mks (pi/2 pulse) and a 10 s relaxation delay between
pulses, which was found sufficient for a complete relaxation. A
total of 64 scans were accumulated in each 1H NMR experiment.
The 31P CP/MAS NMR spectra were acquired using a double-
resonance 2.5 mm MAS Bruker probe at a resonance frequency of
364.4 MHz under 20 kHz MAS. The CP contact time in all
experiments was 3 ms with a delay between acquisitions of 20 s.
SPINAL-64 proton decoupling was used during spectra acquisi-
tion. From 256 to 2048 scans were collected depending on the
amount of sample available. 31P NMR chemical shifts were
referenced to 85% H3PO4 using solid (NH4)H2PO4 (ADP) as a
secondary chemical shift reference. The same ADP sample was
used to setup 31P CP/MAS conditions. The mass spectra were
obtained on a Bruker Daltonics Ultraflex II spectrometer at the
PACSMUB in the MALDI/TOF reflectron mode using dithranol
as a matrix. High resolution mass measurements (HR-MS) were
carried out in the same conditions as previously using PEG ion
series as internal calibrant or on a Bruker Micro-QTOF instru-
ment in ESI mode. The infrared spectra were acquired on a
Bomen FT-IR MB series spectrometer equipped with a base-
line-diffused reflectance. The UV-visible spectra for compounds
1-4 were recorded on a Varian Cary 1 spectrophotometer. The
UV-visible spectra for compounds 5-8 were recorded on a
Hewlett-Packard diode array model 8452A. The emission spectra
were obtained using a double monochromator Fluorolog 2
instrument from Spex. The emission lifetimes were measured on
a TimeMasterModelTM-3/2003apparatusfrom PTI.Thesource
was nitrogen laser with high-resolutiondye laser (fwhm ∼1400 ps)
and the fluorescence lifetimes were obtained from deconvolution
or distribution lifetimes analysis. The uncertainties were about
50-100 ps. Some of the phosphorescence lifetimes were performed
on a PTI LS-100 using a 1 μs tungsten-flash lamp (fwhm ∼1 μs).
The flash photolysis spectra and the transient lifetimes were
10. Yield: 46% (12.6 mg) 1H NMR (MAS) (all bands are very
large) δ (ppm): 9.57 (H-meso), 6.41 (H-phenyl), 4.48-1.71
(CH2CH3), 1.71-(-1.43) (CH2CH3). 31P NMR (MAS) (ppm):
10.31. IR (KBr) ν: 2111.2 cm-1 (CtC). Anal. Calcd (%) for
C88H100N8P2PtPd2 (1739.65): C 60.76, H 5.79, N 6.44. Found: C
60.75, H 5.92, N 6.11. MS (MALDI-TOF): m/z=1738.47 [M]+•
;
1739.65 calcd for C88H100N8P2PtPd2.
11. Yield: 79% (23.1 mg) 1H NMR (MAS) (all bands are very
large) δ (ppm): 8.39 (H-meso), 6.55 (H-phenyl), 4.36-2.09
(CH2CH3), 2.09-(-1.94) (CH2CH3). 31P NMR (MAS) δ
(ppm): 6.74. IR (KBr) ν: 2111.2 cm-1 (CtC). Anal. Calcd (%)
for C88H100N8P2PtPdZn (1698.63): C 62.22, H 5.93, N 6.60.
Found: C 61.96, H 6.17, N 6.37. MS (MALDI-TOF): m/z =
1698.56 [M]+•; 1698.63 calcd for C88H100N8P2PtPdZn. UV-
visible (2MeTHF): λmax nm (ε ꢀ 10-3, M-1 cm-1)=335 (78), 412
(846), 515 (34), 547 (78), 576 (27).
Bis[5-trans-(4-ethynylphenyl)-13,17-diethyl-2,3,7,8,12,18-hexa-
methyl(metal)-porphyrin(bis(triethylphosphine)platinum(II)]-trans-
5,15-bis(ethynylphenyl)-tetra-ethyl-2,8,12,18-tetramethyl-3,7,13,
17-(zinc)porphyrin (metal = Zn (12), Pd (13)). CuI (∼0.3 mg,
∼0.0015 mmol) was added to a mixture of 5 (38.6 mg, 0.0360 mmol)
or 6 (48.2 mg, 0.043 mmol) and [((HCtCC6H4)2(Zn(P))] (16.0 mg,
0.0220 mmol) in CH2Cl2/iPr2NH (50 mL, 1:1 v/v). The purple
solution was left to stir overnight under inert atmosphere and
refluxed. A redish-purple precipitate was formed, which was col-
lected by filtration, washed with CH2Cl2, and dried under vacuum.
1
12. Yield: 61% (24.8 mg) H NMR (MAS) (all bands are very
large) δ(ppm):8.70(H-meso),7.09(H-phenyl),4.69-2.19(CH2CH3),

7618 Inorganic Chemistry, Vol. 48, No. 16, 2009
Bellows et al.
Scheme 2
measured with a Luzchem spectrometer using the 355 nm line of a
YAG laser from Continuum (Serulite), and the 530 nm line from
OPO module pump by the same laser (fwhm=13 ns).
few decades.44 The porphyrins can be covalently linked to
metal-containing centers by one or multiple carbon-metal
bonds at the meso or β-positions of the porphyrin skeleton.44
In search for new ways to interconnect porphyrins, platinum
acetylide linkages have been previously used to synthesize
conjugated organometallic porphyrin dimers, oligomers, or
dendrimers.45-53
Quantum yields measurements were performed in 2MeTHF at
77 and 298 K. Three different measurements (i.e., different
solutions) were prepared for each photophysical datum (quantum
yields and lifetimes). For the 298 K measurements, the samples were
prepared under inert atmosphere (in a glovebox, PO2 < 50 ppm).
For both temperatures, the sample and standard concentrations
were adjusted to obtain an absorbance of 0.05 or less. This
absorbance was adjusted to be the same as much as possible for
the standard and the sample for a measurement. Each absorbance
value was measured 10 times for better accuracy in the measure-
ments of the quantum yields. The references used for quantum yields
were Pd(TPP) (TPP = tetraphenylporphyrin; Φ = 0.14)42 for
measuring porphyrin quantum yields and 9,10-diphenylanthracene
(Φ=1.0)43 for measuring the spacer quantum yields.
(44) Suijkerbuijk, B. M. J. M.; Klein Gebbink, R. J. M. Angew. Chem.,
Int. Ed. 2008, 47, 7396–7421.
(45) Chen, Y.-J.; Lo, S.-S.; Huang, T.-H.; Wu, C.-C.; Lee, G.-H.; Peng,
S.-M.; Yeh, C.-Y. Chem. Commun. 2006, 1015–1017.
(46) Ferri, A.; Polzonetti, G.; Licoccia, S.; Paolesse, R.; Favretto, D.;
Traldi, P.; Russo, M. V. J. Chem. Soc., Dalton Trans. 1998, 4063–4069.
(47) Harriman, A.; Hissler, M.; Trompette, O.; Ziessel, R. J. Am. Chem.
Soc. 1999, 121, 2516–2525.
(48) Mackay, L. G.; Anderson, H. L.; Sanders, J. K. M. J. Chem. Soc.,
Chem. Commun. 1992, 43–44.
(49) Monnereau, C.; Gomez, J.; Blart, E.; Odobel, F.; Wallin, S.; Fall-
Results and Discussion
::
berg, A.; Hammarstrom, L. Inorg. Chem. 2005, 44, 4806–4817.
(50) Onitsuka, K.; Kitajima, H.; Fujimoto, M.; Iuchi, A.; Takei, F.;
Takahashi, S. Chem. Commun. 2002, 2576–2577.
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Goldoni, A.; Parent, P.; Laffon, C.; Russo, M. V. Chem. Phys. 2004, 296, 87–
100.
Syntheses and Characterization. There has been a
tremendous amount of research devoted to the porphyrin
syntheses with peripheral metal centers over the past
(42) Bolze, F.; Gros, C. P.; Harvey, P. D.; Guilard, R. J. Porphyrins
Phthalocyanines 2001, 5, 569–574.
(43) Eaton, D. F. Pure Appl. Chem. 1988, 60, 1107–1114.
(52) Polzonetti, G.; Ferri, A.; Russo, M. V.; Iucci, G.; Licoccia, S.;
Paolesse, R. J. Vac. Sci. Technol. A 1999, 17, 832–839.
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Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7619
Scheme 3
Scheme 4
The synthetic routes leading to the target porphyrin-
containing derivatives are outlined in Scheme 2a.
readily formed via a two-step one flask reaction of dipyrro-
methane and 4-[2-(trimethylsilyl)ethy;nyl]benzaldehyde at
room temperature (Scheme 2b). The free-base was not iso-
lated but in situ metal insertion allowed us to isolate the zinc
complexes in 22% yield (not optimized). Desilylation of 4a
using NBu4F at room temperature afforded the 5,15-diethy-
nylporphyrin derivative 4b in 93% yield.
The general procedure to synthesize monomeric, dimeric,
and trimeric compounds 5, 6, 8, 9, 10, 12, and 13 involved a
dehydrohalogenation reaction56 between the trans-Pt-
(PEt3)2Cl2 and the appropriate ethynylporphyrin (2b or
3b) in diisopropylamine in the presence of CuI (Schemes 3
and 4). The crude products 5-8 were purified via column
chromatography (silica gel) using hexane/CH2Cl2 (40/60) as
the solvents, and the products were isolated in 45-70%
yields. Complexes 9-13 formed redish-purple precipitates,
which were collected by filtration and washed with CH2Cl2.
The condensation of 4-[2-(trimethylsilyl)ethynyl]benzal-
dehyde with the a,c-biladiene38 afforded the expected free
base porphyrin which can easily be metalated. The two
metalation processes involve palladium acetate and zinc
acetate yield the corresponding metalated porphyrins. The
subsequent elimination of the trimethylsilyl group from the
zinc- and palladium-containing porphyrins with NBu4F in
THF54,55 produced the corresponding ethynyl porphyrins 2b
and 3b in 78% and 96% yields, respectively. The resulting
compounds were then used for the subsequent complexation
with trans-dichlorobis(triethylphosphine)platinum(II)39,40 to
afford various monomers, dimers, and trimers below in good
yields. The trans-substituted porphyrin building block 4a was
(54) Nath, M.; Pink, M.; Zaleski, J. M. J. Am. Chem. Soc. 2005, 127, 478–
479.
(55) Yen, W.-N.; Lo, S.-S.; Kuo, M.-C.; Mai, C.-L.; Lee, G.-H.; Peng,
S.-M.; Yeh, C.-Y. Org. Lett. 2006, 8, 4239–4242.
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S.; Hagihara, N. J. Organomet. Chem. 1978, 145, 101–108.

7620 Inorganic Chemistry, Vol. 48, No. 16, 2009
Bellows et al.
Scheme 5
Attempts to prepare the homometallic trimer contain-
ing three palladium(II)-porphyrins was unfortunately
unsuccessful. Two strategies were investigated. First, we
attempted the demetalation of the starting bisethynyl-
zinc(porphyrin). The demetalation step was readily per-
formed using HCl (Scheme 5A). The following step was
the coordination of palladium. A black insoluble preci-
pitate was obtained but, unfortunately, it was concluded
via spectroscopic comparison with the parent palladium-
containing compounds 3b and 10 that this precipitate was
not the desired product. The second attempted route
consisted of using compound 13 as the starting material
followed by a demetalation process to remove the zinc.
Unfortunately the zinc metal was not removed in
the presence of HCl. Subsequently, a more soluble acid,
the para-toluene sulfonic acid (PTSA), was used
(Scheme 5B). The comparison of the UV-vis spectra
confirmed that the zinc had been removed, hence forming
the desired free base, and that the palladium metals
remained in the peripheral porphyrin macrocycles. Sub-
sequently, the addition of palladium (palladium acetate)
was attempted. A soluble product was indeed obtained,
but the comparison of the signature in the Q-region of the
absorption spectra to compounds 12 and 13 did not
resemble their spectral features. We then concluded that
the desired product was unfortunately not obtained.
All the compounds were fully characterized by analy-
tical and spectroscopic methods. The IR, NMR (1H, and
31P), and mass spectral data shown in the Experimental
Section are consistent with their chemical structures. The
IR spectra of these new metal complexes display a single
sharp ν(CtC) absorption band in the range of 2105-
2120 cm-1. The absence of the CtC-H stretching mode
of each compound around 3300 cm-1 indicates the for-
mation of a CtC;M bond. The NMR spectral data
supports the conclusion that these compounds have well-
defined and symmetric structures. The 31P NMR spectra
of compounds 5 and 6 exhibit a single resonance with a
pair of Pt satellites, which is indicative of the trans
geometry of the phosphine ligands about the platinum.
Spectroscopy and Photophysics. 1. Absorption Spectra.
Absorption Spectra of the Parent PhCtCPtL2CtCPh
Compounds. The UV-vis spectra and MO descriptions
(using density functional theory (DFT) and time-depen-
dent DFT (TDDFT)) of the spacer and parent compounds
of the type RCtCPt(PR03)2CtCR (R=Ph; R0 =Et, Bu)
were previously reported.57-61 Only a brief account of
the relevant information is provided here since this
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Brozik, J. A. J. Phys, Chem. A 2003, 107, 11340–11346.
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Philips, D. L.; Wong, K.-Y.; Zhu, N. J. Am. Chem. Soc. 2005, 127, 13997–
14007.
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J. E.; Stagle, J. E. J. Phys. Chem. A 2006, 110, 13370–13378.
(61) Gagnon, K.; Aly, S. M.; Brisach-Wittmeyer, A.; Bellows, D.; Berube,
J.-F.; Caron, L.; Abd-El-Aziz, A. S.; Fortin, D.; Harvey, P. D. Organome-
tallics 2008, 27, 2201–2214.

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7621
Table 1. Absorption Spectral Data Measured in 2MeTHF at 298 K
λ [nm](ε ꢀ 10-3 M-1 cm-1
)
compound
spacer
Soret band
Q bands
2b
3b
5
6
7
332 (24)
330 (19)
328 (27)
320 (32)
335 (26)
328 (40)
335 (26)
335
410 (342)
396 (237)
411 (302)
400 (265)
412 (210)
396 (211)
410 (121)
400
540 (18) 575 (14)
514 (20) 547 (51)
540 (18) 576 (11)
515 (22) 548 (53)
540 (10) 575 (6)
515 (17) 548 (43)
540 (52) 577 (24)
515 549
8
9
10a
11
12
13a
Figure 1. Emission (blue), excitation (red), and absorption (black)
spectra of the parent compound trans-PhCtCPt(PEt3)2CtCPh in
2MeTHF at 77 K.
335 (78)
340 (44)
340
412 (846)
413 (322)
400
515 (34)547 (78) 576 (27)
540 (27) 575 (17)
420 515 548 580
a The solubility of these compounds in 2MeTHF was not sufficient
enough for accurate absorptivity measurements.
a 0-0 peak at 356 nm was also detected for trans-(2,4,5-
Me3C6H2)CtCPt(PEt3)2CtC(2,4,5-Me3C6H2) in de-
gassed 2MeTHF at 298 K.61 The fluorescence lifetime
(τF) for this latter compound was <0.1 ns, which is
consistent with the weak quantum.61
fragment is used in the monomers, dimers, and trimers
below. Thecomplexesexhibitintenselowestenergyabsorp-
tion bands between 320 and 340 nm. For example, for R=
Ph, these bands are found at 330 (shoulder; ε=43600) and
337 nm (ε=44900 M-1 cm-1).58 Earlier DFT calculations
(B3LYP) for the PhCtCPt(PBu3)2CtCPh parent com-
pound indicated that the highest occupied molecular orbi-
tal (HOMO) is composed of conjugated π-orbital of the
PhCtC unit along with a contribution from the Pt(dxy)
orbital. Concurrently, the lowest unoccupied molecular
orbital (LUMO) consists of the ligand π* orbital only.57
Thus, the lowest energy excitation (i.e., HOMOf LUMO)
for this Pt-containing spacer is a MLCT (metal-to-ligand-
charge-transfer). This assignment is corroborated by the
difference in band shape between the Pt complex (broad)
and PhCtCH (ππ*; narrow). Moreover, a more recent
computational report (TDDFT) pointed out that this first
excitation is in fact a mixture between two contributions,
MLCT (59%) similar to that described above and LMCT
(32%).60 These two transitions arise from two different
vertical but nearly degenerated excitations (difference only
0.04 eV; φgfφu* and φufφg*; where φg and φu and φg* and
φu* are π- and π*-orbitals, respectively, and with g orbitals
including the Pt(dxy) orbital).
Absorption Spectra of the Intermediates and the Spacer/
Porphyrin Systems. Typical absorption spectra of the
porphyrin-containing compounds include the intense
Soret band (S0-S2 transition) and Q-bands (S0-S1 tran-
sition). The UV-visible data and absorptivities of the
target monomeric, dimeric, and trimeric porphyrin deri-
vatives and their synthesis intermediates are presented in
Table 1.
For compounds 5-13, the attachment of trans-C6H4Ct
CPt(PEt3)2Cl or trans-C6H4CtCPt(PEt3)2CtCPh or
trans-C6H4CtCPt(PEt3)2CtCC6H4- residues onto the
porphyrin chromophores resulted in an intensity enhance-
ment of the band in the UV-region (i.e., 300-350 nm) of
the spectrum in comparison with the starting materials 2b
and 3b. This new band is unambiguously characteristic of
the spacer.
Moreover, compounds of the type trans-RCtCPt-
(PBu3)2CtCR (R=Ph, 2,4,5-Me3C6H2, 2,4,6-Me3C6H2)
are strongly phosphorescent at 77 K (in 2MeTHF).61
The phosphorescence bands exhibit a characteristic vi-
bronic progression known for this class of compounds
spreading from 440 to 600 nm with an intense 0-0 peak at
∼450 nm.57 A very weak fluorescence is occasionally obs-
erved, but its intensity is often too weak to allow the
accurate measurements of τF and ΦF. The strong phos-
phorescence coupled to the weak fluorescence is readily
attributed to the heavy atom effect of the Pt metal. For
comparison purposes, the emission spectrum of trans-
PhCtCPt(PEt3)2CtCPh in 2MeTHF at 77 K is pre-
sented in Figure 1.
It was also occasionally noticed that when the fluores-
cence is more intense for some derivatives in comparison
with the parent compounds trans-RCtCPt(PBu3)2Ct
CR, delayed fluorescence was present (see reference 61
for example). These luminescence features were readily
detected from time-resolved spectroscopy in the μs time
scale where both the phosphorescence and the fluores-
cence decays are the same (i.e., the fluorescence/phos-
phorescence intensity ratio is constant). We observed a
similar feature here but this behavior was not investigated
since this was not the purpose of this work.
Emission Spectra of the Synthesis Intermediates. The
emission spectra and quantum yields for compounds
2b-6 in 2MeTHF are listed in Table 2 and are used for
assignment purposes. The recorded spectra are given in
the Supporting Information (Figure SI 1-4).
Emission Spectra of the Spacer/Porphyrin Systems. The
emission spectra of the spacer-porphyrin monomers
7 and 8 (i.e., Zn(P)-C6H4CtCPtL2CtCC6H5 and Pd-
(P)-C6H4CtCPtL2CtCC6H5, respectively), the brid-
ged porphyrin homobimetallic dimers Zn(P)-C6H4Ct
CPtL2CtCC6H4-Zn(P), 9, and Pd(P)-C6H4CtCPtL2-
CtCC6H4-Pd(P), 10, the heterobimetallic dyad Zn(P)-
C6H4CtCPtL2CtCC6H4-Pd(P), 11, and the trimers Zn-
(P)-C6H4CtCPtL2CtCC6H4-Zn(P)-C6H4CtCPtL2-
CtCC6H4-Zn(P) (12) and Pd(P)-C6H4CtCPt-
L2CtCC6H4-Zn(P)-C6H4CtCPtL2CtCC6H4-Pd(P)
(13) where L=PEt3 were investigated in 2MeTHF at 77
and 298 K. The data are listed in Table 3.
2. Emission Spectra. Emission Spectra of the Parent
PhCtCPtL2CtCPh Compounds. The trans-PhCtCPt-
(PBu3)2CtCPh compound exhibits a weak fluorescence
band at room temperature in degassed 2MeTHF solu-
tions, with a 0-0 peak localized at 346 nm and a quantum
yield, ΦF, < 0.0006.57 Similarly, a weak fluorescence with

7622 Inorganic Chemistry, Vol. 48, No. 16, 2009
Bellows et al.
Table 2. Luminescence Data for the Metalloporphyrin Chromophores 2b-6 in 2MeTHF
λ (nm)
Φb
77 K
298 K
phosphorescence
77 K
298 K
compound
lumophorea
fluorescence
phosphorescence
fluorescence
ΦF
ΦP
ΦF
ΦP
2b
3b
5
Zn(P)
Pd(P)
Zn(P)
Pd(P)
575, 630
703, 785, 830 sh
662, 695, 717sh, 738
706, 788, 830 sh
664, 697, 719, 738
597, 633
549, 600
580, 635
550, 600
0.045
0.026
0.40
0.017
0.35
0.047
545, 575, 597
576, 632
547, 598
668, 742sh
670
0.0016
0.033
0.0015
0.0018
0.045
0.0017
0.032
6
0.0003
a Lumophores Zn(P) and Pd(P) are Zn(II) porphyrin and Pd(II) porphyrin, respectively. b The quantum yields are for the Zn(P) and Pd(P)
chromophores only (λexc = 515 nm in all cases). The uncertainties in quantum yield values are ( 10% based on multiple measurements
Table 3. Luminescence Data Measured in 2MeTHF for 7-13
λ (nm)
Φb
77 K
phosphorescence
298 K
phosphorescence
77 K
298 K
compound
lumophorea
fluorescence
fluorescence
ΦF
ΦP
ΦF
ΦP
7
spacer
Zn(P)
spacer
Pd(P)
spacer
Zn(P)
spacer
Pd(P)
spacer
Pd(P)
Zn(P)
spacer
Zn(P)
spacer
Pd(P)
Zn(P)
442, 463, 476, 490
705, 786, 835sh
442, 460, 477, 490sh
663, 697, 718sh
442
0.042
0.012
0.043
0.35
0.005
0.022
0.005
0.35
575, 632
547, 598
575, 633
547, 598
580, 635
553, 607
581, 635
552, 608
0.039
0.048
8
673
0.0012
0.039
0.0014
0.052
0.0003
0.002
9
707, 788
10
11
440, 467, 490sh
663, 697, 718sh, 736
445
668
0.0013
0.011c
0.0016
0.008c
0.004
0.094c
547
575, 633
663
553
530, 635
664sh
706, 737sh, 786, 826sh
495
715, 798
495, 522
664
698sh, 716, 737
12
13
0.005
0.009
0.005
0.092c
576, 634
580, 636
0.024
0.034
546
579, 636
552
587, 638
0.0003c
0.003c
a Zn(P)=Zn(II) porphyrin, Pd(P)=Pd(II) porphyrin, spacer=C6H4CtCPt(PEt3)2CtCC6H4. b The quantum yields are for the Zn(P) and Pd(P)
chromophores only (λexc=515 nm in all cases). The uncertainties in quantum yield values are ( 10% based on multiple measurements. c Because of the
very strong overlap between the emission arising from the two chromophores, the total quantum yield is provided.
The emission spectra of the spacer-porphyrin mono-
mers 7 and 8in 2MeTHF at 77 K are presented in Figure 2;
the corresponding spectra recorded at 298 K are given in
the Supporting Information (Figure SI 5).
the Pd(P) chromophore in 8 is due to the heavy atom
effect. Concomitantly, the intense emission bands are
observed at 705 and 660 nm for 7 and 8, respectively,
and are assigned to the ππ* phosphorescence of the
metalloporphyrin chromophore.42,62-65
The emission spectra exhibit the signature of both the spacer
and the porphyrin emissions. The phosphorescence originating
The emission spectra for the bridged porphyrin homo-
bimetallic dimers Zn(P)-C6H4CtCPtL2CtCC6H4-Zn-
(P), 9, and Pd(P)-C6H4CtCPtL2CtCC6H4-Pd(P), 10 (L
=PEt3) in 2MeTHF at 77 K are shown in Figure 3. The
corresponding spectra recorded at 298 K are given in
the Supporting Information (Figure SI 6). While the spectra
also exhibit the characteristic emission bands arising
from the spacer and the porphyrins, the relative intensity
of the spacer phosphorescence (λexc =340 nm) versus that
of the porphyrin emission is much smaller than that of
the metalloporphyrin chromophores than what it would
be anticipated for a ratio of 1:2 spacer versus metallopor-
phyrins. In fact, the ΦP’s decrease by another order
of magnitude (∼0.005). This result clearly reinforces the
3
from the ππ* state of the spacer is readily identified in the
430-500 nm region with a 0-0 peak located at ∼440 nm58 (λexc
= 350 nm). In comparison with the parent compounds
trans-(2,4,5-Me3C6H2)CtCPt(PBu3)2CtC-(2,4,5-Me3C6H2)
(ΦP = 0.17)61 and trans-(2,4,6-Me3C6H2)CtCPt(PBu3)2-
CtC(2,4,6-Me3C6H2) (ΦP=0.38),61 the relative inten-
sity of the spacer phosphorescence is smaller for the
spacer/porphyrin systems 7 and 8. Indeed, the ΦP’s
decrease to ∼0.042 for both cases. This result indicates
the presence of a supplementary non-radiative pro-
cess in the spacer/porphyrin systems. Details for the
spacer phosphorescence quantum yields are presented
below.
On the other hand, the typical emissions of both
the zinc(II)- and palladium(II)-porphyrins were also ob-
served (λexc =540 and 510 nm in the Q region, for con-
venience, for 7 and 8, respectively). The ππ* fluorescence
of the metalloporphyrin chromophore was observed at
575 and 630 nm for 7 and at 547 and 597 nm for 8 as weak
intensity bands. The weak intensity of the fluorescence of
(62) Harriman, A. J. Chem. Soc., Faraday Trans. 2 1981, 77, 1281–1291.
(63) Imahori, H.; Hagiwara, K.; Aoki, M.; Akiyama, T.; Taniguchi, S.;
Okada, T.; Shirakawa, M.; Sakata, Y. J. Am. Chem. Soc. 1996, 118, 11771–
11782.
(64) Pekkarinen, L.; Linschitz, H. J. Am. Chem. Soc. 1960, 82, 2407–2411.
(65) Sessler, J. L.; Jayawickramarajah, J.; Gouloumis, A.; Torres, T.;
Guldi, D.; Maldonado, S.; Stevenson, K. J. Chem. Commun. 2005, 1892–
1894.

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7623
Figure 4. Emission (blue and green), excitation (red), and absorption
(black) spectra of Pd(P)-C6H4CtCPtL2CtCC6H4-Zn(P) (L=PEt3) in
2MeTHF at 77 K.
Figure 2. Emission (blue and green), excitation (red) and absorption
(black) spectra of Zn(P)-C6H4CtCPtL2CtCC6H5 (bottom, 7) and
Pd(P)-C6H4CtCPtL2CtCC6H5 (top, 8) in 2MeTHF at 77 K (L =
PEt3).
Figure 5. Emission (blue and green), excitation (red) and absorption
(black) spectra of Zn(P)-C6H4CtCPtL2CtCC6H4-Zn(P)-C6H4-
CtCPtL2CtCC6H4-Zn(P) ((L = PEt3; bottom) and Pd(P)-C6H4-
CtCPtL2CtCC6H4-Zn(P)-C6H4CtCPtL2CtCC6H4-Pd(P) (top)
in 2MeTHF at 77 K.
in 2MeTHF at 77 K is given in Figure 4. The correspond-
ing spectra recorded at 298 K are given in the Supporting
Information (Figure SI 7). The characteristic emission
bands arising from the spacer (in the 400-550 nm
region; broad) and from both the palladium(II)- and
the zinc(II)-porphyrins above 540 nm are readily ob-
served. The Pd(P) fluorescence appears as a weak band
at 545 nm, expected for this heavy metal-containing
dyad, whereas that for the Zn(P) moieties is observed
at 575 and 633 nm. A strong phosphorescence signal
appears at 664 nm, which is readily attributed to the
Pd(P) phosphorescence while the structured phosphor-
escence of the Zn(P) chromophore is observed in the
705-850 nm region. The ΦP of the spacer (0.004) is weak
as anticipated based on the observed data for 9 and 10
above.
Figure 3. Emission (blue and green), excitation (red), and absorption
(black) spectra of Zn(P)-C6H4CtCPtL2CtCC6H4-Zn(P), 9 (bottom),
and Pd(P)-C6H4CtCPtL2CtCC6H4-Pd(P), 10 (top) in 2MeTHF at 77
K (L=PEt3).
assumption that there is the presence of a non-radiative
process efficiently deactivating the spacer excited states in the
spacer/porphyrin systems.
The emission spectrum of the heterobismetallomacro-
cycle (Pd(P)-C6H4CtCPtL2-CtCC6H4-Zn(P)), 11,

7624 Inorganic Chemistry, Vol. 48, No. 16, 2009
Bellows et al.
Table 4. Emission Lifetimes for 2b-8 in 2MeTHF
τ (λemi used; in nm)
77 K
298 K
compound
fluorescence (ns)
phosphorescence
fluorescence (ns)
phosphorescence (μs)
2b
3b
5
6
7
1.71 ( 0.03 (575)
0.17 ( 0.01 (545)
1.68 ( 0.04 (575)
0.14 ( 0.01 (550)
1.66 ( 0.04 (575)
0.16 ( 0.01 (550)
27.8 ( 1.5 ms (780)
1810 ( 5 μs (663)
24.1 ( 0.9 ms (780)
1.45 ( 0.06 (580)
0.10 ( 0.03 (550)
1.37 ( 0.02 (580)
0.07 ( 0.02 (550)
0.88 ( 0.04 (575)
0.07 ( 0.01 (550)
97 ( 1 (665)
1770 ( 10 μs (660) 90 ( 5 μsa (450)a
19.3 ( 0.1 ms (785)
b
b
8
1740 ( 10 μs (660)
a This emission is due to the phosphorescence of the ClPt(PEt3)2CtCC6H4 chromophore. b Too weak to be measured accurately.
Table 5. Emission Lifetimes Measured in 2MeTHF
τ (λemi used; in nm)
77 K
298 K
compound
fluorescence (ns)
phosphorescence
fluorescence (ns)
phosphorescence (μs)
73.3 ( 3.4 (665)
9
10
11
1.70 ( 0.02 (575)
0.19 ( 0.01 (550)
1.69 ( 0.02 (575)
0.16 ( 0.02 (550)a
23.3 ( 1.1 ms (780)
1730 ( 20 μs (660)
0.84 ( 0.02 (575)
0.09 ( 0.01 (550)
0.73 ( 0.08 (580)
too weak (550)
27.5 ( 0.7 ms (785)
205 ( 20 μs (660) 69%
1380 ( 50 μs (660) 31%
24.6 ( 1.2 ms (795)
20.0 ( 0.4 ms (795)
1680 ( 30 μs (660) 50%
244 ( 33 μs (660) 50%
12
13
1.44 ( 0.04 (575)
1.43 ( 0.03 (575)
0.15 ( 0.01 (550)a
0.89 ( 0.03 (580)
0.79 ( 0.04 (575)
0.08 ( 0.01 (550)
a Examples of fast picosecond decays are provided in the Supporting Information (Figure SI 9).
Scheme 6
Similarly, the emission spectra of the trismetal-
The Φe data (ΦF and ΦP) for the metalloporphyrin
chromophores also undergo changes with the structure.
Scheme 6 shows a representative example of the effect of
the structure on the Φe data. Going from 2b f 7 f 9 f 12
in 2MeTHF at 77 K, ΦF should increase with the number
of Zn(P) chromophores in the molecule, but in overall, it
decreases. This observation is consistent with the heavy
metal effect induced by the Pt atoms. On the other hand,
ΦP should increase in the same order, but in overall, it
decreases with some fluctuation. The increase in the
number of chromophores should induce an increase in
ΦP as well observed going from 7 to 9, but the introduc-
tion of the PEt3 ligand also introduces a loose-bolt effect
loporphyrins Zn(P)-C6H4CtC-PtL2CtCC6H4-
Zn(P)-C6H4CtCPtL2CtCC6H4-Zn(P) (12) and Pd-
(P)-C6H4CtCPtL2CtC-C6H4-Zn(P)-C6H4CtC-
PtL2CtC-C6H4-Pd(P) (13) also exhibit the charac-
teristic emissions of both the spacers and porphyrin
macrocycles (Figure 5). The corresponding spectra
recorded at 298 K are given in the Supporting Infor-
mation (Figure SI 8). Unsurprisingly, the ΦP for the
spacer phosphorescence is low (0.005) as for com-
pounds 9, 10, and 11. The spectral and ΦP data for
the studied compounds in 2MeTHF are listed in
Table 3.

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7625
Chart 2
Chart 3
10 (1730 ( 20 μs) suggests very slow T1 energy transfer
(Pd(P) f Zn(P)). On the other hand, the fast components
(205 ( 20 μs for 11 and 244 ( 33 μs for 13) suggest faster
transfer. To explain these components, one may consider
the X-ray structures of the related compounds trans-
RCtCPt(PBu3)2CtCR (Chart 2; R = 2,4,6-Me3C6H2,
2,4,5-Me3C6H2).61
Indeed, the angle formed by the aryl and PtP2(CtC)2
planes are 83 and 30°, respectively. These orientations
cannot exhibit the same electronic communication via
conjugation (across the d orbital of the Pt center). If T1
energy transfer operates dominantly via a Dexter me-
chanism (double electron exchange),69 then orbital over-
lap is clearly important in conjugated systems. The
existence of two (or more) rotamers in solution would
hypothetically lead to different photophysical responses
in energy transfers.
If there are two components for the τP decays for 11 and
13, then we should logically get two as well for the τF
decays. The easiest component to measure is the slow one
(here 0.16 ( 0.02 for 11 and 0.15 ( 0.01 ns for 13), then the
faster one should proportionally be 1 order of magnitude
smaller as well. If this is the case, then the predicted
components should be measured in the 0.020-0.010 ns
time scale, which is within the uncertainty of the method.
The rates for both the S1 and T1 energy transfers can be
calculated using eq 1:67
(decreasing radiative processes to the profit of non-
radiative)66 as well observed going from 2b to 7 (by a
factor of ∼2) and from 9 to 12 (also by a factor of ∼2).
3. Emission Lifetimes and S1 and T1 Energy Transfers
(λexc is in the Q-bands). Emission Lifetimes of the Li-
gands and Intermediates. The emission lifetimes of the
ligands and intermediates (2b-6) measured in 2MeTHF
are given in Table 4. These data are used for comparison
and assignment purposes in the spacer/metalloporphyrin
systems. They appear typical in comparison with other
emission lifetimes and are not discussed further.67 In a
qualitative manner, the trend observed for ΦF and ΦP (see
Scheme 6 for example) follows that of the corresponding
emission lifetimes.
Emission Lifetimes and Pd(P) f Zn(P) S1 and T1
Energy Transfers in the Spacer/Porphyrin Systems 9-
13. On the basis of the position of the 0-0 peaks of the
fluorescence and phosphorescence of the comparison
molecules 2b-8, the Pd(P) and Zn(P) chromophores are
readily assigned as the S1 and T1 energy donor and
acceptor, respectively. A close comparison of τF at 298
and 77 K of the Zn(P) chromophore going from 9 to 11
(Table 5), shows a small decrease (excluding the un-
certainties) consistent with the heavy metal effect (as
one Zn atom is replaced by one Pd). This is interesting
because this subtle “information” is passed across the
61
ꢀ
˚
!
spacer (∼18 A), suggesting communication. The com-
parison of τF of the Pd(P) chromophore going from 10
(for which no energy transfer takes place; donor-spacer-
donor) to 11 also indicates a decrease (also excluding the
uncertainties). In the absence of energy transfer, one
would expect that τF(Pd(P)) would be larger for 11
(since it has only one Pd atom). This is obviously
not the case and this information suggests S1 energy
transfer. Indeed, we have previously reported an exhaus-
tive study on S1 through space energy transfer in cofacial
bisheteromacrocycles (M = Zn, M0 = Pd).68,69 But a
clear evidence for energy transfer comes from the com-
parison of τP(Pd(P)) between 10 and 11, and between 10
and 13. Compound 10 is used as a comparison molecule
for the trimer as well because the synthesis of the
trispalladium(II) porphyrin analogue was unsuccessful
(see above).
1
1
kET
¼
-
ð1Þ
τe τ0e
where,τ0e is the emission lifetime for a comparative do-
nor-donor system where no energy transfer takes place,
and τe is the emission lifetime of the donor in the dyad.
The donor-donor and donor-acceptor systems are 10
and 11, respectively. For 13, the tris-palladium analogue
is not available. The rates for singlet and triplet energy
transfers, kET(S1) and kET(T1) are ∼2 ꢀ 109 s-1 and 0.15 ꢀ
103 (slow component) and 4.3 ꢀ 103 s-1 (fast component),
respectively. The uncertainty on kET(S1) is obviously
large, but this value compares very favorably to that
reported by Osuka and collaborators (kET(S1) = 2.3 ꢀ
109 s-1) in a dyad closely related to compound 11
(Chart 3; Zn(P) and H2(P) are the energy donor and
acceptor, respectively).70 The presence of methyl groups
at the β-position provides the appropriate aryl-porphyrin
chemical environment for acceptable comparison.
Prior to discussing further the energy transfer pro-
cesses, a look at the τP data for 11 and 13 is necessary.
Both compounds exhibit decays with two components
(i.e., 2τP(Pd(P))). The similarity of the long components
(1380 ( 50 μs for 11 and 1680 ( 30 μs for 13) with that for
On the other hand, the kET(T1) values fall short by 1 or
2 orders of magnitude in comparison with structurally
related dyads reported by Albinsson and collaborators
(Chart 4).71 This comparison indicates that the replace-
ment of the aryl group in the Albinsson series by Pt slows
(66) Turro, N. J. Modern Molecular Photochemistry; Benjamin/Cummings
Pub. Co.: Menlo Park, CA, 1978.
(67) Harvey, P. D. In The Porphyrin Handbook; Kadish, K. M., Smith, K.
M., Guilard, R., Eds.; Academic Press: San Diego, CA, 2003; Vol. 18, pp 63-250.
(68) Faure, S.; Stern, C.; Guilard, R.; Harvey, P. D. J. Am. Chem. Soc.
2004, 126, 1253–1261.
(70) Osuka, A.; Tanabe, N.; Kawabata, S.; Yamazaki, I.; Nishimura, Y.
J. Org. Chem. 1995, 60, 7177–7185.
(69) Faure, S.; Stern, C.; Espinosa, E.; Guilard, R.; Harvey, P. D.
Chem.;Eur. J. 2005, 11, 3469–3481.
(71) Jensen, K. K.; van Berlekom, S. B.; Kajanus, J.; Martensson, J.;
Albinsson, B. J. Phys. Chem. A 1997, 101, 2218–2220.

7626 Inorganic Chemistry, Vol. 48, No. 16, 2009
Bellows et al.
Chart 4
Table 6. Emission Lifetimes of the trans-C6H4CtCPt(PEt3)2CtCC6H4 Spacers
and T1 Energy Transfer Rates for Spacer f M(P) (M=Zn, Pd).a
compound
τ
P (monitored at λemi nm)
kET (T1) (s-1
)
7
8
9
10
11
12
13
36.2 ( 0.4 μs (440)
31.1 ( 2.8 μs (460)
24.1 ( 3.6 μs (460)
24.7 ( 2.6 μs (460)
20.0 ( 2.7 μs (460)
weak signal
1.6 ꢀ 104
2.0 ꢀ 104
3.0 ꢀ 104
2.9 ꢀ 104
3.8 ꢀ 104
b
weak signal
b
a In 2MeTHF at 77K. b Too weak to be accurately measured.
Figure 6. Transient absorption spectrum of trans-PhCtCPt-
(PEt3)2CtCPh in 2MeTHF at 77 K (λexc = 355 nm, delay = 0.1 μs).
The negative signal at 430 nm is due to phosphorescence.
down the rates of transfer. The comparison with the
spacer containing a saturated fragment illustrates the
effect of poor conjugation on kET(T1).
Because the fluorescence and phosphorescence life-
times of compounds 12 and 13 resemble that of 10 and
11, the kET values are expected to be in the same range, but
their accurate evaluations are not possible.
(and most likely short as well) for accurate measurements in
the trimers. This behavior is assigned to a T1 energy transfer
(spacer f M(P); M=Zn, Pd) and using eq 1 the kET values
are extracted (Table 6). The data are in the 104 s-1 range, a
range that compares favorably to that reported by Albins-
son and collaborators for structurally related dyads.71 These
values are also faster than that for the T1 Pd(P)* f Zn(P)
transfer in compound 11, again demonstrating clearly that
the bond between the meso-C and the aryl group does not
slow down the T1 transfer but rather the Pt metal does. The
demonstration that T1 energy transfer is the sole process
(i.e., no electron transfer) is provided by transient absorp-
tion spectroscopy in the nanosecond time scale.
Emission Lifetimes When Excited in the Spacer Absorp-
tion Band (around 320 nm) and Triplet Energy Transfer.
(a). Emission Lifetimes of the trans-PhCtCPtL2CtCPh
Spacer and Related Derivatives. For the compounds of the
type trans-RCtCPt(PEt3)2CtCR with R = 2,4,5-Me3-
C6H2, 2,4,6-Me3C6H2, Ph, the τP’s are 85, 50, and 35.0 (
1.3 μs, respectively.61 This trend follows the number of
methyl groups located at the ortho-positions (τP varies as 2
> 1 > 0), and may reflect the relative ease for the aryl
groups to rotate about the Pt-CtC-Ar axis. This mo-
tion, if present, may contribute to the non-radiative relaxa-
tion to the ground state. This feature is important since the
spacers used in this work do not exhibit Me groups at the
ortho-position. However, the rotation is prevented by the
presence of methyl groups placed at the β-positions of the
metalloporphyrin macrocycle. Indeed, for compound 6 we
find τP=90 ( 5 μs. Therefore, the compound exhibiting 85
μs is more suitable for calculating kET’s below.
(b). Phosphorescence Lifetimes of the trans-C6H4-
CtCPtL2CtCC6H4 Spacer in Compounds 7-13. The
spacer τP’s for 7-11 are listed in Table 6. They are in
the same range as the parent compounds trans-RCtCPt-
(PEt3)2CtCR with R = 2,4,5-Me3C6H2, 2,4,6-Me3-
C6H2, Ph discussed above, but quenching is obvious.
The “loose bolt” effect on the emission lifetime is negli-
gible as the macrocycles are rigid components (in com-
parison with the more flexible PEt3 ligands).66
Transient Absorption Spectra and Lifetimes (λexc
=
355 nm). (a). PhCtCPtL2CtCPh Parent Compounds.
For the PhCtCPt(PBu3)2CtCPh compound, the triplet
excited state dynamics can still be accessible from T1-Tn
absorptions. The reported T1-Tn band is located in the
400-700 nm window placed at ∼645 nm. The transient
lifetime is 590 ( 150 ps.72 To increase the lifetime of the
transient species, investigations at 77 K using a Dewar
assembly can be performed. We measured the transient
absorption spectrum of trans-PhCtCPt(PEt3)2CtCPh
(Figure 6). A narrow T1-Tn absorption band is observed
at ∼620 nm, which is in agreement with that reported for
trans-PhCtCPt(PBu3)2CtCPh. The transient lifetime is
36 μs and compares favorably to that of the phosphores-
cence lifetime (35.8 μs) confirming the assignment.
(72) (a) de Santana, H.; Quillard, S.; Fayad, E.; Louarn, G. Synth.
Methods 2006, 156, 81–85. (b) Han, C.-C.; Balakumar, R.; Thirumalai, D.;
Chung, M.-T. Org. Biomol. Chem. 2006, 4, 3511–3516. (c) Nishiumi, T.;
Chimoto, Y.; Hagiwara, Y.; Higuchi, M.; Yamamoto, K. Macromolecules
2004, 37, 2661–2664. (d) Nishiumi, T.; Nomura, Y.; Chimoto, Y.; Higuchi, M.;
Yamamoto, K. J. Phys. Chem. B 2004, 108, 7992–8000. (e) Temme, O.; Laschat,
S.; Frohlich, R.; Wibbeling, B.; Heinze, J.; Hauser, P. J. Chem. Soc., Perkin
Trans. 2 1997, 2083–2085.
The emission lifetimes listed in Table 6 can be separated
into 3 groups: the monomers 7 and 8, dimers 9-11, and
trimers 12 and 13. The lifetimes decrease going from
monomers to dimers, and the intensity becomes too weak

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7627
Figure 7. Transient absorption spectra of 2b (up left), 5 (middle left), 7 (bottom left), 9 (up right), 11 (middle right), and 12 (bottom right) in 2MeTHF at
298 K (λexc = using 355 nm; delay = 0.1 μs). The arrow indicates the absorption band for Zn(P)+
.
a
Chart 5.
a Ar=3,5-(t-Bu)2C6H3.
trans-PhCtCPt(PEt3)2CtCPh parent compound. How-
ever the broadness of this signal and its absence from the
spectra of the Pd(P)-containing analogues (the spectra
are provided in the Supporting Information; Figure SI 10)
suggest that this feature may not be the T1-Tn absorption
of the Pt-containing spacer.
Figure 8. Comparison of the transient absorption spectra of 2b (red), 7
(blue) in 2MeTHF at 298 K (λexc=using 355 nm; delay=0.1 μs) and the
dyad presented in Chart 5 (green; Ar = 3,5-(t-Bu)2C6H3). The green
spectrum is redrawn and modified from reference. 73
The possibility of electron transfer was also considered.
The Zn(P)+ cation generated by a photoinduced electron
transfer in a dyad formed of a Zn(P) chromophore and the
strong electron acceptor C60 (Chart 5) was recently investi-
gated.73 Figure 8 compares the transient absorption spectra
of 2b (red), 7 (blue), and the Zn(P)-C60 dyad presented in
Chart 5 (green; Ar = 3,5-(t-Bu)2C6H3).73 The latter dyad
exhibits a signal centered at about 700 nm for the correspond-
ing Zn(P)+ chromophore, which is significantly different
from the T1-Tn signal of the Pt-containing spacer located at
(b). Transient Absorption Spectra and Lifetimes of the
Synthesis Intermediates 2b-13. The transient absorption
spectra for Zn(P)-containing compounds, 2b, 5, 7, 9,
11, 12, and 13, in 2MeTHF at 298 K (Figure 7) exhibit
two distinctive features. The first one is a strong
absorption characteristic of the porphyrin macrocycle
at ∼470 nm as well exemplified by the spectrum of
compound 2b. This feature is accompanied by a “val-
ley” located at ∼535 nm resembling a bleach of a Q-
band.
The second feature is the presence of a broad band at
∼640 nm for this series except 2b. This broad feature falls
close to the transient T1-Tn absorption at ∼620 nm for the
(73) Tsuji, H.; Sasaki, M.; Shibano, Y.; Toganoh, M.; Kataoka, T.;
Araki, Y.; Tamao, K.; Ito, O. Bull. Chem. Soc. Jpn. 2006, 79, 1338–1346.

7628 Inorganic Chemistry, Vol. 48, No. 16, 2009
Bellows et al.
Figure 9. Left: Transient absorption spectra of 2b (black), 2b þ C60 (blue), and 7 (red) in benzene (up) and ethanol (down). λexc=355 nm; delay=0.1 μs.
Right: Time-resolved transient absorption spectra of 2b (up) and 7 (down) in 2MeTHF at 298 K; λexc=355 nm.
∼640 nm. So this ∼640 nm feature cannot be assigned to the
equivalent Zn(P)+.
cluding mixed metalloporphyrin compounds, where the
spacer is the rigid and conjugated Pt-containing trans-
C6H4CtCPtL2CtCC6H4- fragment were synthesized and
characterized. Both the spacer and the metalloporphyrin
macrocycle are luminescent allowing the monitoring of the
photophysical proerties as a function of structural changes.
The excitation in the Q-bands of the Pd(P) chromophores
leads to S1 and T1 energy transfers to the Zn(P) units (i.e.,
Moreover, the second product of this photoinduced
electron transfer is the radical anion [trans-C6H4-
CtCPtL2CtCC6H4h]. On the basis of the literature,74
the transient absorption spectrum exhibits a low-energy
feature between 1000 and 1400 nm, a range that is not
accessible on our instrument. It also exhibits a higher
energy band at 540 nm, but in our spectra this position
falls at a place where a bleach of a Q-band takes place.
This is particularly true for the Pd(P)-containing com-
pounds where the bleach is more pronounced (i.e., ex-
hibiting a negative signal; Supporting Information,
Figure SI 10).
In an attempt to address the nature of this band, other
tests were performed. Figure 9 exhibits the transient
absorption spectra of compound 2b in the presence and
in the absence of C60 using benzene and ethanol as the
solvents. In the presence of C60, quenching of the triplet
excited state is observed from the decrease of the signal at
450 nm for identical concentrations and delay times.
Moreover, a new transient feature is observed at ∼720
nm. This band is readily assigned to the corresponding
Zn(P)þ cation75 and is clearly absent from the transient
absorption spectra of 7 (Figure 9).
Pd(P)*fZn(P)). The rates are found modest (∼2 ꢀ 109 s-1
,
S1, and 0.15 ꢀ 103 (first component) and 4.3 ꢀ 103 s-1
(second component), T1), which is consistent with the pre-
sence of the spacer, a spacer where the conformation is
limited to a quasi-perpendicular orientation of the aryl and
porphyrin planes (because of the presence of two β-methyl
groups). Importantly, it is concluded that the Pt atom slows
down the transfer when comparing to related dyads that
do not contain a Pt-atom in the conjugated chain. The
excitation in the absorption band of the trans-C6H4-
CtCPtL2CtCC6H4- spacer in the 300-360 nm range also
leads to T1 energy transfer (spacer* f M(P); M=Zn, Pd) and
a decrease in the phosphorescence intensity is observed. The
rates for T1 energy transfer measured by the change in
phosphorescence lifetimes are in the 104 s-1 range. This time
scale lies on the slow side of the list of rates known for
porphyrin-containing molecules.67 This time frame (104 s-1
)
The time-resolved transient spectra show no evidence
for two different species as clearly seen in Figure 9 on the
right-hand side. So species arising from a photoinduced
electron transfer can be ruled out, and the transient
spectra are dominated by the T1-Tn signature of the M(P)
chromophores (M=Zn, Pd). The photophysical events in
this time scale (>13 ns) are only T1 energy transfers.
is faster than that for the T1 Pd(P)*fZn(P) transfers above
(103 s-1), hence corroborating that the spacer-metallopor-
phyrin single bond located on meso-C atom is not the major
barrier slowing down the transfer (but rather the Pt atom in
this case).
These non-radiative processes (S1 and T1 energy transfers)
in these monodisperse oligomers bear direct relevance to
the corresponding metalloporphyrin-containing polymers,
(-spacer-M(P)-)n, as potential materials for photonic
applications (i.e., solar cells).
Conclusion
A series of linear monomers (spacer-M(P)), dimers
(M(P)-spacer-M0(P)), and trimers (M(P)-spacer-M0-
(P)-spacer-M(P)) of spacer/metalloporphyrin systems, in-
Finally, this work stresses the interesting resemblance
between the LH II system (for example) in the purple
photosynthetic bacteria discussed in the Introduction.
Among the phenomena, the energy transfer process S1
B800* f B850 which is very fast (∼1.2 ps time scale) despite
(74) Cardolaccia, T.; Funston, A. M.; Kose, M. E.; Keller, J. M.; Miller,
J. R.; Schanze, K. S. J. Phys. Chem. B 2007, 111, 10871–10880.
(75) Losev, A. P.; Bachilo, S. M.; Volkovich, D. I.; Avlasevich, Y. S.;
Solov’yov, K. N. J. Appl. Spectrosc. 1997, 64, 62–71.
˚
the long center-to-center separation (∼18 A) was suspectedto
use the carotenoid as relay. This work demonstrates that this

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7629
phenomenon is indeed possible since S1 energy transfer
(Pd(P)* f Zn(P)) is possible with a relatively good rate
(∼100 ps time scale). The difference in rates for this compar-
ison is due to the larger change in dipole moment of the
bacteriochlorophyll a chromophore in comparison with the
symmetric metalloporphyrin unit. This choice was based on
synthetic convenience.
The presence of Pt in the spacer allowed monitoring the rates
of transfer in the T1 states. The slow rates observed remind us
that nature elected not to use the T1 energy transfer as a
pathway for energy migration. Indeed, one of the roles of the
carotenoid is to quench the T1 state in LH II if populated. In
addition, the excitation in the absorption band of the organo-
metallic spacer here allowed us to observe. A study of the chain
length dependence on the photophysical properties of longer
oligomers is in progress and will be published in due course.
and managed by the University of Ottawa (www.
nmr900.ca). The Natural Sciences and Engineering Re-
search Council of Canada (NSERC) is acknowledged
for a Major Resources Support grant. The French
Ministry of Research (MENRT), CNRS (UMR 5260)
is also gratefully acknowledged. The authors are also grate-
ful to M. Albini for the synthesis of pyrrole and dipyrro-
methane precursors.
Supporting Information Available: Emission, excitation and
absorption spectra in 2MeTHF at 77 and 298 K of starting
material Zn(P)-C6H4CtCH (2b) and Pd(P)-C6H4CtCH
(3b) (Figure SI 1 and SI 2); and intermediates Zn(P)-C6H4-
CtCPtL2Cl (5) and Pd(P)-C6H4CtCPtL2Cl (6) (Figure SI 3
and SI 4). Emission, excitation and absorption spectra of Zn(P)-
C6H4CtCPtL2CtCC6H6 (7), Pd(P)-C6H4CtCPtL2CtCC6H6
(8) (Figure SI 5), Zn(P)-C6H4CtCPtL2CtCC6H4-Zn(P) (9),
Pd(P)-C6H4CtCPtL2CtCC6H4-Pd(P) (10) (Figure SI 6), Pd-
(P)-C6H4CtCPtL2CtCC6H4-Zn(P) (11) (Figure SI 7), Zn(P)-
C6H4CtC-PtL2CtCC6H4-Zn(P)-C6H4CtCPtL2CtCC6H4-
-Zn(P) (12) and Pd(P)-C6H4CtCPtL2CtC-C6H4-Zn(P)-
C6H4CtCPtL2CtCC6H4-Pd(P) (13) (Figure SI 8). Typical ex-
ample of fluorescence decay of compounds 11 and 13 in 2MeTHF
at 77 K (red) against the lamp profile (black), typical example of
phosphorescence decay of compounds 7 and 8 in 2MeTHF at 77 K
(Figure SI 9), and transient absorption spectra in MeTHF at
298 K of Pd(P)-C6H4CtCH (3b), Pd(P)-C6H4CtCPtL2Cl (6),
Pd(P)-C6H4CtCPtL2CtCC6H6 (8), Pd(P)-C6H4CtCPtL2-
CtCC6H4-Pd(P) (10), and Pd(P)-C6H4CtCPtL2CtCC6H4-
Zn(P)-C6H4CtCPtL2CtCC6H4-Pd(P) (13) (Figure SI 10).
This material is available free of charge via the Internet at http://
pubs.acs.org.
Acknowledgment. This research was supported by the
Natural Sciences and Engineering Research Council of
ꢀ ꢀ
Canada (NSERC), le Fonds Quebecois de la Recherche
sur la Nature et les Technologies (FQRNT), and the
ꢀ
ꢀ
Centre d’Etudes des Materiaux Optiques et Photoniques
de l’Universite de Sherbrooke. The authors thank Dr.
ꢀ
Victor V. Terkikh for the NMR measurements with
access to the 900 MHz NMR spectrometer which was
provided by the National Ultrahigh Field NMR Facility
for Solids (Ottawa, Canada), a national research facility
funded by the Canada Foundation for Innovation, the
Ontario Innovation Trust, Research Quebec, the Na-
tional Research Council Canada, and Bruker Biospin