Nanometer length-dependent triplet - Triplet energy transfers in zinc(11) porphyrin/trans-bis(ethynylbenzene)platinum(11) oligomers

Article abstract of DOI:10.1021/ic900198h

The synthesis and characterization of organometallic oligomers of the type [(p-C₆H₄)C≡CPt(P(nBu)₃) ₆C≡C(p-C₆H₄)-Zn(P)]n with the corresponding models [(C₆H5C≡C)R(P(n-Bu)₃) ₂C≡C(p-C₆ H₄)Zn(P)(p-C₆H ₄)C≡CR(P(n-Bu)₃)₂(C≡CC ₅H₅)], where Zn(P) is zinc(11)-10,20-di(mesityl)- (n = 4, 9) or zinc(11)-10,20-di-n-pentyl-porphyrin (n = 3, 6, 9), are reported. The electronic spectra (absorption, excitation, emission, and transient absorption) and the photophysical properties (emission lifetimes and quantum yields) of these species in 2-methyltetrahyrofuran at 298 and 77 K are presented. Rates for triplet (T₁) energy transfer, k_ET, from the [(p-C ₆H₄C≡C)Pt(P(n-Bu)₃)₂(C≡ C-p-C₆H₄)] spacer to Zn(P) vary from 2.4 × 10 ⁴to 1.3 × 10⁶ s^-1. For the n-pentyl case, a rate dependence of oligomer size is noted as k_ET increases with the number of units, n. This phenomenon is interpreted by the presence of an excitonic process (i.e., delocalization of the energy along the Zn(P) array).

Full text of DOI:10.1021/ic900198h

Inorg. Chem. 2009, 48, 5891–5900 5891
DOI: 10.1021/ic900198h
Nanometer Length-Dependent Triplet-Triplet Energy Transfers in Zinc(II)
Porphyrin/trans-Bis(ethynylbenzene)Platinum(II) Oligomers
Li Liu,† Daniel Fortin, and Pierre D. Harvey*
†
ꢀ
ꢀ
Departement de Chimie, Universite de Sherbrooke, PQ, Canada J1K 2R1. On leave from the Ministry of
Education Key Laboratory for the Synthesis and Application of Organic Functional Molecules, School of
Chemistry and Chemical Engineering, Hubei University, Wuhan 430062, People’s Republic of China
Received January 31, 2009
The synthesis and characterization of organometallic oligomers of the type [(p-C6H4)CtCPt(P(n-Bu)3)2CtC(p-C6H4)-
Zn(P)]n with the corresponding models [(C6H5CtC)Pt(P(n-Bu)3)2CtC(p-C6H4)Zn(P)(p-C6H4)CtCPt(P(n-
Bu)3)2(CtCC6H5)], where Zn(P) is zinc(II)-10,20-di(mesityl)- (n = 4, 9) or zinc(II)-10,20-di-n-pentyl-porphyrin (n = 3,
6, 9), are reported. The electronic spectra (absorption, excitation, emission, and transient absorption) and the
photophysical properties (emission lifetimes and quantum yields) of these species in 2-methyltetrahyrofuran at 298
and 77 K are presented. Rates for triplet (T1) energy transfer, kET, from the [(p-C6H4CtC)Pt(P(n-Bu)3)2(CtC-
p-C6H4)] spacer to Zn(P) vary from 2.4 Â 104 to 1.3 Â 106 s-1. For the n-pentyl case, a rate dependence of oligomer size
is noted as kET increases with the number of units, n. This phenomenon is interpreted by the presence of an excitonic
process (i.e., delocalization of the energy along the Zn(P) array).
Introduction
continues to attract much attention.1-8 Among these, con-
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transfers inspired researchers to explore in more detail
their behavior with respect to the photosynthesis mecha-
nism.9,10 An initial survey clearly showed that energy transfer
The search for new metal-organic molecular and poly-
meric functional materials with optoelectronic applications
*To whom correspondence should be addressed. Tel.: 001-819-821-7092.
Fax: 001-819-821-8017. E-mail: Pierre.harvey@usherbrooke.ca.
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2009 American Chemical Society
Published on Web 06/11/2009
pubs.acs.org/IC

5892 Inorganic Chemistry, Vol. 48, No. 13, 2009
Liu et al.
(ET) increases as the distance between the donor and
acceptor porphyrins decreases.11 Recently, heavy-metal-
containing bis(ethynyl) linkers were used to form con-
jugated carbazole- and fluorene-based bis(ethynyl)-me-
tal polymers (metal=platinum, gold, and mercury), and
their emission spectroscopy and photophysics were in-
vestigated.12 The key feature is that incorporation of a
heavy metal in the backbone of the polymers can enhance
intersystem crossing, hence leading to an increase in the
population of the triplet states.
Bearing this in mind, we designed here several Pt acetylide
conjugated systems combined with metalated porphyrins. A
series of oligomers and polymers containing Pt acetylide and
Zn porphyrins are synthesized and characterized, and their
photophysical properties are investigated. To our knowl-
edge, no other study of energy (donor-acceptor)-containing
organometallic porphyrin polymers exist to date. We
now wish to report the synthesis and characterization of
nano-oligomers of the type [(p-C6H4)CtCPt(P(n-Bu)3)2-
CtC(p-C6H4)Zn(P)]n with the corresponding models
[(C6H5CtC)Pt(P(n-Bu)3)2CtC(p-C6H4)Zn(P)(p-C6H4)CtC-
Pt(P(n-Bu)3)2(CtCC6H5)], where Zn(P) is zinc(II)-10,
20-di(2,4,6-trimethylphenyl)- or zinc(II)-10,20-n- dipentyl-
porphyrin (Chart 1). The electronic spectra and the photo-
physical properties of these species in 2-methyltetrahydrofuran
(2MeTHF) at 298 and 77 K are presented. A discussion on the
triplet-triplet energy transfer, T1 ET, from the [(p-C6H4-
CtC)Pt- (P(n-Bu)3)2CtC(p-C6H4)] chromophore to the
porphyrin moiety is made. We find that the rate for T1 ET
for the olimer with largest number of repeating units is faster
(1.35 Â 106 s-1). This work represents the first example of
detailed investigations that address electronic communication
in the backbone of a conjugated organometallic porphyrin-
containing polymer.
5,15-Bis(mesityl)-10,20-bis(1,4-trimethylsilanylethynylben-
zene)-zinc(II)porphyrin (T1). 5-Mesityldipyrromethane (2.98 g,
11.3 mmol) and 4-trimethylsilylethynylbenzaldehyde (2.28 g,
11.3 mmol) were dissolved in 125 mL of CHCl3 under Ar in a
one-neck round-bottom flask. BF3 O(Et)2 (54 μL) was added to
3
initiate the condensation. The reaction mixture was stirred
for 1 h under Ar. 2,3-Dichloro-5,6-dicyano-1,4-benzoqui-
none (DDQ; 2.56 g, 11.3 mmol) was added to the reaction
mixture, and stirring was continued for another hour. The
solvent was removed. A solution of Zn(OAc)2 2H2O (1.86 g,
3
8.47 mmol) in MeOH (18 mL) was added to the residue in
CHCl3 (100 mL), and the mixture was stirred and refluxed for
2 h. The crude reaction mixture was washed with H2O and
dried over MgSO4. The crude product was then purified by
using chromatography on silica gel with CH2Cl2/hexane (1:2)
as a solvent. This afforded a red solid (1.85 g, 34.4%). 1H
NMR (CDCl3, 400 MHz): δ 0.38 (s, 18 H), 1.82 (s, 12 H), 2.63
(s, 6H),7.28 (s, 4H), 7.87 (d, 4H, J=12 Hz),8.17 (d, 4H, J=12 Hz),
8.79 (d, 4H, J=4.4 Hz), 8.84 (d, 4H, J=4.4 Hz).
5,15-n-Pentyl-10,20-bis(1,4-trimethylsilanylethynylbenzene)-
zinc(II)porphyin (T2). 5-n-Pentyldipyrromethane (2.14 g,
9.89 mmol) and 4-trimethylsilylethynyl- benzaldehyde (2.00 g,
9.89 mmol) were dissolved in 125 mL of CHCl3 under Ar in a
one-neck round-bottom flask. BF3 O(Et)2 (54 μL) was added to
3
initiate the condensation. The reaction mixture was stirred
for 1 h under Ar. DDQ (2.25 g, 9.89 mmol) was added to the
reaction mixture, and stirring of the solution was continued
for another hour. The solvent was removed. A solution of
Zn(OAc)2 2H2O (1.63 g, 7.42 mmol) in MeOH (18 mL) was
3
added to the residue in CH2Cl2 (100 mL), and the mixture
was stirred and refluxed for 2 h. The crude reaction mixture was
washed with H2O and dried over MgSO4. The crude product
was purified by using chromatography on silica gel with
CH2Cl2/hexane (1:2) as the solvent. This afforded a red solid
(0.7066 g, 16.6%). 1H NMR (CDCl3, 400 MHz): δ 0.44 (s, 18 H),
0.88-1.00 (m, 6 H), 1.31-1.78 (m, 6H), 2.37-2.50 (m, 4H),
4.58-4.75 (m, 4H), 7.91 (d, 4H, J=12 Hz), 8.07 (d, 4H, J=
12 Hz), 8.75 (d, 4H, J=5.8 Hz), 9.27 (d, 4H, J=6.0 Hz). 13C
NMR (CDCl3, 100 MHz): δ 149.86, 148.64, 143.26, 134.32,
131.67, 130.12, 128.59, 122.10, 120.80, 118.85, 105.27, 101.69,
95.24, 38.68, 35.40, 32.87, 22.77, 14.18, 0.14. EI-MS m/z calcd for
C52H56N4Si2Zn [M]+: 858.59. Found: 856.
Experimental Section
Materials. All reactions were carried out under a nitrogen
atmosphere by using standard Schlenk techniques. Solvents
were dried and distilled from appropriate drying agents under
an inert atmosphere prior to use. Glassware was oven-dried at
about 120 °C. All reagents and chemicals, unless otherwise
stated, were purchased from commercial sources and used
without further purification. The compounds 4-trimethylsi-
lylethynylbenzaldehyde,13 meso-substituted dipyrrometh-
anes (5-mesityl- and 5-n-pentyldipyrromethane),14 trans-
chloro(ethynylbenzene)bis(trin-butyl- phosphine)platinum
(II),15 and trans-[Pt(P(n-Bu)3)2Cl2]16 were prepared accord-
ing to the literature methods.
5,15-Bis(1,4-ethynylbenzene)-10,20-bis(mesityl)zinc(II)por-
phyrin (L1). K2CO3 (1.34 g, 9.70 mmol) was added to a solution
of T1 (1.85 g, 1.94 mmol) in THF and MeOH (v/v=1:1; 100 mL)
and was stirred for 12 h. The solution was evaporated. The crude
product was purified by column chromatography on silica gel
with CH2Cl2/hexane (1:1) as the solvent to yield the pure ligand
as a red solid (1.41 g, 90%). 1H NMR (CDCl3, 400 MHz): δ 1.83
(s, 12 H), 2.64 (s, 6 H), 3.31 (s, 2H), 7.29 (s, 4H), 7.88 (d, 4H, J=
12 Hz), 8.20 (d, 4H, J=12 Hz), 8.80 (d, 4H, J=4.4 Hz), 8.86 (d,
4H, J=4.4 Hz). EI-MS m/z calcd for C54H40N4Zn [M]+: 810.31.
Found: 808.
5,15-Bis(1,4-ethynylbenzene)-10,20-di-n-pentylzinc(II)por-
phyrin (L2). K2CO3 (0.569 g, 4.12 mmol) was added to
a solution of T2 (0.707 g, 0.823 mmol) in a THF and Me-
OH (v/v = 1:1) solution (100 mL) and stirred for 12 h. The
solution was evaporated. The crude product was purified by
column chromatography on silica gel with CH2Cl2/hexane (1:1)
as the solvent, to yield the pure ligand as a red solid (0.500 g,
85%). 1H NMR (CDCl3, 400 MHz): δ 0.97-0.99 (m, 6 H),
1.52-1.80 (m, 4 H), 2.42-2.58 (m, 4H), 3.28 (s, 2H), 4.82-4.93
(m, 4H), 7.88 (d, 4H, J=6.0 Hz), 8.15 (d, 4H, J=6.0 Hz), 8.91 (d,
4H, J=4.4 Hz), 9.51 (d, 4H, J=4.4 Hz). 13C NMR (CDCl3,
100 MHz): δ 150.18, 149.35, 148.81, 143.64, 134.26, 131.86,
131.55, 130.30, 128.89, 121.18, 83.80, 78.03, 38.70, 35.60, 32.84,
22.77, 14.16. EI-MS m/z calcd for C54H40N4Zn [M]+: 714.23.
Found: 712.
(11) Faure, S.; Stern, C.; Guilard, R.; Harvey, P. D. J. Am. Chem. Soc.
2004, 126, 1253.
(12) (a) Wong, W.-Y. J. Inorg. Organomet. Polym. Mater. 2005, 15, 197.
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C. E.; Humphrey, M. G. Coord. Chem. Rev. 2004, 248, 725. (d) Abd-El-Aziz,
A. S. Macromol. Rapid Commun. 2002, 23, 995. (e) Long, N. J.; Williams,
C. K. Angew. Chem. 2003, 115, 2690. Angew. Chem., Int. Ed. 2003, 42, 2586.
(f ) Manners, I. Science 2001, 294, 1664. (g) Bunz, U. H. F. Chem. Rev. 2000,
100, 1605. (h) Wong, W.-Y. Dalton Trans. 2007, 4495. (i) Wong, W.-Y.
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(13) Austin, W. B.; Bilow, N.; Kelleghan, W. J.; Lau, K. S. Y. J. Org.
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Article
Inorganic Chemistry, Vol. 48, No. 13, 2009 5893
Chart 1
Poly[5,15-(trans-bis(1,4-ethynylbenzene)bis(tri-n-butylphosphine)-
platinum(II))-10,20-bis(mesityl)zinc(II)porphyrin] (P1). A mixture
of trans-Pt(P(n-Bu)3)2Cl2 (200 mg, 0.298 mmol) and 1 equiv of
of trans-Pt(P(n-Bu)3)2Cl2 (115 mg, 0.172 mmol) and 1 equiv of
i
L2 (123 mg, 0.172 mmol) was dissolved in Pr2NH-CH2Cl2
(50 mL, 1:1, v/v), and CuI (3 mg) was subsequently added. After
stirring for 12 h at different temperatures (25, 80, and 110 °C
producing three oligomers of different lengths), all of the
volatiles were removed under reduced pressure. The residue
was redissolved in CH2Cl2 and filtered through a short silica
column using CH2Cl2 as a solvent to give a yellow solution of the
polymeric material. The monomer was removed by adding
MeOH to induce a precipitation of the polymer. The monomer
remained soluble. The solid (i.e., the polymer) was filtered and
washed with MeOH. The precipitation and washing were per-
formed three times, to afford a red solid in 70.5% yield (158 mg).
1H NMR (CDCl3, 400 MHz): δ 0.98-1.07 (m, 36 H), 1.53-1.65
(m, 28 H), 1.73-1.86 (m, 28 H), 2.28-2.36 (m, 24 H), 2.55-2.57
(m, 4 H), 5.00-5.05 (br s, 4 H), 7.26-7.34 (m, 10 H), 7.76 (br s,
4H), 8.11 (br s, 4H), 9.09 (br s, 4H), 9.56 (br s, 4H). 13C NMR
(CDCl3, 100 MHz): δ 150.12, 149.27, 139.84, 134.19, 132.09,
130.82, 128.89, 128.49, 127.86, 124.82, 120.48, 119.96, 109.47,
109.11, 108.90, 108.06, 38.76, 35.73, 32.87, 26.47, 24.52, 24.00,
i
L1 (242 mg, 0.298 mmol) was dissolved in Pr2NH-CH2Cl2
(50 mL, 1:1, v/v), and CuI (3 mg) was subsequently added. After
stirring for 24 h at 298 K, all of the volatiles were removed under
reduced pressure. The residue was redissolved in CH2Cl2 and
filtered through a short silica column using CH2Cl2 as a solvent
to give a yellow solution of the polymeric material. The mono-
mer was removed by adding MeOH to induce a precipitation of
the polymer. The monomer remained soluble. The solid (i.e., the
polymer) was filtered and washed with MeOH. The precipita-
tion and washing were performed three times, to afford a red
1
solid in 54.0% yield (227 mg). H NMR (CDCl3, 400 MHz):
δ 1.05-1.09 (m, 18 H), 1.22-1.26 (m, 12 H), 1.54-1.60 (m,
12 H), 2.17 (s, 12 H), 2.37-2.39 (m, 12 H), 2.65 (s, 6H), 7.26-
7.30 (m, 4H), 7.75 (d, 4H, J=10.4 Hz), 8.14 (d, 4H, J=10.4 Hz),
8.79 (d, 4H, J=6.3 Hz), 8.95 (d, 4H, J=6.3 Hz). 31P NMR
(CDCl3, 160 MHz): δ 4.56 (1JPt-P=3106 Hz). Elem anal. calcd
(%) for (C78H92N4P2PtZn)n: C, 66.54; H, 6.59; N, 3.98. Found:
C, 63.49; H, 5.63; N, 3.14. GPC (THF): Mw=24531, Mn=13262.
Poly[5,15-(trans-bis(1,4-ethynylbenzene)bis(tri-n-butylphosphine)-
platinum(II))-10,20-bis(n-pentyl)zinc(II)porphyrin] (P2). A mixture
22.84, 14.18, 13.95. 31P NMR (CDCl3, 160 MHz): δ 4.72 (1JPt-P
3102 Hz). Elem anal. calcd (%) for (C70H93N4P2PtZn)n: C,
=

5894 Inorganic Chemistry, Vol. 48, No. 13, 2009
Liu et al.
64.04; H, 7.14; N, 4.27. Found: C, 63.84; H, 6.94; N, 3.98. GPC
(THF): Mw=21460, Mn = 9908.
with a Luzchem spectrometer using the 355 nm line of a YAG
laser from Continuum (Serulite) and the 355 nm line from an
OPO module pump of the same laser (fwhm=13 ns).
5,15-Bis(trans-bis(1,4-ethynylbenzene)bis(tri-n-butylphosphine)-
platinum(II))-10,20-bis(mesityl)zinc(II)porphyrin (M1). Treatment
of L1 (119 mg, 0.147 mmol) with 2 equiv of trans-phenylethynyl-
chlorobis(tri-n-butylphosphine) platinum(II) (216.5 mg, 0.2940
mmol) for 12 h at 298 K, in the presence of CuI (3 mg), in
iPr2NH-CH2Cl2 (50 mL, 1:1, v/v) gave the title complex as a red
solid in 74.5% yield (250 mg) after purification on a silica column
using n-hexane/CH2Cl2 (40:60, v/v) as a solvent. 1H NMR
(CDCl3, 400 MHz): δ 1.01-1.05 (m, 36 H), 1.54-1.61 (m, 24
H), 1.74-1.75 (m, 24 H), 1.87 (s, 12 H), 2.29-2.30 (m, 24 H), 2.67
(s, 6 H), 7.24-7.36 (m, 12 H), 7.68 (d, 4H, J=10.4Hz), 8.11 (d, 4H,
Quantum Yield Measurements. For room-temperature mea-
surements, all samples were prepared under an inert atmosphere
(in a glovebox, PO2 <20 ppm) by dissolution of the different
compounds in 2MeTHF using 1 mL quartz cells with a septum
(298 K) or quartz NMR tubes in liquid nitrogen for 77 K
measurements. Three different measurements (i.e., different
solutions) were performed for each set of photophysical data
(quantum yields, ΦF). The sample concentrations were chosen
to correspond to an absorbance of 0.05 at the excitation
wavelength. Each absorbance value was measured five times
for better accuracy in the measurements of emission quantum
yield (ΦF). The ΦF was tretraphenylporphyrin, H2TPP (ΦF =
0.11 in 2MeTHF at 77 K),17 which was checked against (Pd)TPP
(ΦF=0.17 in methylcyclohexane at 77 K).18,19
Crystallographic Data. The crystals were grown by slow
vapor diffusion of hexanes in a CH2Cl2 solution. One single
crystal of 0.50 Â 0.50 Â 0.60 mm3 was mounted using a glass
fiber on the goniometer. Data were collected on an Enraf-
Nonius CAD-4 automatic diffractometer using omega scans
at 198(2) K. The DIFRAC20 program was used for centering,
indexing, and data collection. One standard reflection was
measured every 100 reflections; no intensity decay was observed
during data collection. The data were corrected for absorption
by empirical methods based on ψ scans and reduced with the
NRCVAX21 programs. They were solved using SHELXS-9722
and refined by full-matrix least-squares on F2 with SHELXL-
97.23 The non-hydrogen atoms were refined anisotropically. The
hydrogen atoms were placed at idealized calculated geometric
position and refined isotropically using a riding model. The
CH2Cl2 solvent molecule was disordered.
J=10.4 Hz), 8.81 (d, 4H, J=6.3 Hz), 8.99 (d, 4H, J=6.3 Hz). 13
C
NMR (CDCl3, 100 MHz): δ 150.11, 149.79, 139.26, 137.40,
134.26, 132.38, 130.82, 130.57, 129.05, 128.03, 127.87, 127.63,
124.82, 120.54, 119.12, 109.81, 109.08, 108.90, 108.06, 107.86,
26.47, 24.53, 24.22, 24.01, 21.62, 13.92. 31P NMR (CDCl3, 160
MHz): δ 4.71 (1JPt-P = 3100 Hz). Elem anal. calcd (%) for
C118H157N4P4Pt2Zn: C, 64.10; H, 7.16; N, 2.53. Found: C,
63.84; H, 6.88; N, 2.34.
5,15-Bis(trans-bis(1,4-ethynylbenzene)bis(tri-n-butylphosphine)-
platinum(II))-10,20-bis(n-pentyl)zinc(II)porphyrin (M2). Treat-
ment of L2 (108 mg, 0.152 mmol) with 2 equiv of trans-phenyl-
ethynylchlorobis(trin-butylphosphine)-platinum(II) (224 mg,
0.304 mmol) for 12 h at 298 K, in the presence of CuI (3 mg),
in iPr2NH-CH2Cl2 (50 mL, 1:1, v/v) gave the title complex as a
red solid in 38.4% yield (122 mg) after purification through
column chromatography using silica and n-hexane/CH2Cl2
(40:60, v/v) as a solvent. 1H NMR (CDCl3, 400 MHz): δ
0.98-1.07 (m, 36 H), 1.53-1.65 (m, 28 H), 1.73-1.86 (m, 28
H), 2.28-2.36 (m, 24 H), 2.55-2.57 (m, 4 H), 5.00-5.05 (m, 4
H), 7.26-7.34 (m, 10 H), 7.68 (d, 4H, J=10.3 Hz), 8.05 (d, 4H,
J=10.7 Hz), 9.02 (d, 4H, J=6.4 Hz), 9.54 (d, 4H, J=6.1 Hz). 13
C
NMR (CDCl3, 100 MHz): δ 150.12, 149.27, 139.84, 134.19,
132.09, 130.82, 128.89, 128.49, 127.86, 124.82, 120.48, 119.96,
109.47, 109.11, 108.90, 108.06, 38.76, 35.73, 32.87, 26.47, 24.52,
24.00, 22.84, 14.18, 13.95. 31P NMR (CDCl3, 160 MHz): δ 4.56
(1JPt-P = 3102 Hz). Elem anal. calcd (%) for C110H157N4-
P4Pt2Zn: C, 62.47; H, 7.48; N, 2.65. Found: C, 62.66; H, 7.70;
N, 2.81.
Results and Discussion
Synthesis and Characterization. Meso-substituted dipy-
rromethanes are synthesized from the reaction of a de-
sired aldehyde in the presence of an excess of pyrrol (neat
solvent) and a mild Lewis acid (e.g., MgBr2) at room
temperature.24 The two functional groups, mesityl and
n-pentyl, are used to test the solubility propensity of the
target polymers. The condensation of 4-((trimethylsilyl)-
ethynyl)benzaldehyde and 5-mesityldipyrromethane is
Instrumentation. Infrared spectra were recorded as powder or
THF solutions using a Perkin-Elmer Paragon 1000 PC or
Nicolet Magna 550 Series II FTIR spectrometer, using CaF2
cells with a 0.5 mm path length. NMR spectra were measured in
appropriate deuterated solvents on a JEOL EX270 or a Varian
Inova 400 MHz FT-NMR spectrometer, with 1H NMR chemi-
cal shifts quoted relative to SiMe4 and 31P chemical shifts
relative to an 85% H3PO4 external standard. Fast-atom bom-
bardment (FAB) mass spectra were recorded on a Finnigan
MAT SSQ710 mass spectrometer in m-nitrobenzyl alcohol
matrices. The molecular weights of the polymers were deter-
mined by gel permeation chromatography (GPC; HP 1050 series
HPLC with visible wavelength and fluorescent detectors) using
polystyrene standards and THF as an eluent, and the thermal
analyses were performed with a Perkin-Elmer TGA6 thermal
analyzer. The UV/vis spectra were recorded on a Hewlett-
Packard diode array model 8452 A at Sherbrooke. The emission
and excitation spectra were obtained using a double monochro-
mator Fluorolog 2 instrument from Spex. Phosphorescence
time-resolved measurements were performed on a PTI LS-100
using a 1 ms tungsten flash lamp. Fluorescence and phosphor-
escence lifetimes were measured on a Timemaster Model TM-
3/2003 apparatus from PTI. The source was a nitrogen laser with
a high-resolution dye laser (fwhm ≈ 1.5 ns), and the fluorescence
lifetimes were obtained from high-quality decays and deconvo-
lution or distribution lifetime analysis. The uncertainties were
about (40 ps on the basis of multiple measurements. The flash
photolysis spectra and the transient lifetimes were measured
initiated with BF3 O(Et)2 and subsequently quenched
3
with DDQ (after 1 h). The free base porphyrins are then
metalled with zinc(II) from zinc acetate (in a CH2-
Cl2/MeOH mixture refluxing 2 h) to form the trimethy-
silane-containing ethynyl derivatives T1 and T2. The
diethynyl zinc porphyrins L1 and L2 are then prepared
by proton-desilylation using K2CO3 in MeOH as the base
(Scheme 1).
Scheme 2 presents the synthesis scheme for the Pt(II)-con-
taining polymers P1 and P2 and their model corresponding
(17) 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.
(18) Harriman, A. J. Chem. Soc. Faraday Trans. 2 1981, 77, 1281.
(19) Murov, S. L.; Carmichael, I.; Hug, G. L. Handbook of Photochem-
istry, 2nd ed.; Marcel Dekker: New York, 1993.
(20) Flack, H. D.; Blanc, E.; Schwarzenbach, D. J. Appl. Crystallogr.
1992, 25, 455.
(21) Gabe, E. J.; Le Page, Y.; Charland, J.-P.; Lee, F. L.; White, P. S.
J. Appl. Crystallogr. 1989, 22, 384.
(22) Sheldrick, G. M. SHELXS-97, release 97-2; Sheldrick, G. M., Ed.;
::
::
University of Gottingen: Gottingen, Germany, 1997.
(23) Sheldrick, G. M. SHELXL-97, release 97-2; Sheldrick, G. M., Ed.;
::
::
University of Gottingen: Gottingen, Germany, 1997.
(24) Laha, J. K.; Dhanalekshmi, S.; Taniguchi, M.; Ambroise, A.;
Lindsey, J. S. Org. Proc. Res. Dev. 2003, 7, 799.

Article
Inorganic Chemistry, Vol. 48, No. 13, 2009 5895
Scheme 1
Scheme 2
dinuclear complexes M1 and M2. These species are prepared
from the reaction of the ligands L1 and L2 with the Pt(II)-
containing mono- and difunctional derivatives trans-Pt(P-
(n-Bu)3)2(CtCC6H5)Cl and trans-Pt(P(n-Bu)3)2Cl2 in the
presence of the ethynyl-activating reactant CuI and a base
(i-Pr2NH). The desired Pt(II) diyne-containing model com-
pounds are readily isolated using a silica column, whereas
the purification of P1 and P2 is achieved by filtering the crude
material through a short column using pure CH2Cl2 as the
solvent. The polydispersity can be improved by precipitating
the polymer-containing CH2Cl2 solution in MeOH. All of the
new metal complexes and polymers are air-stable and gen-
erally exhibit good solubility in chlorocarbons such as
CH2Cl2 and CHCl3.
The solution IR spectra of these new metal complexes
display a single sharp ν(CtC) absorption peak (not two)
in the range of 2100-2104 cm-1, consistent with a trans
configuration (i.e., D2h symmetry) of the ethynylene
ligands around the metal center. The absence of the
CtCH stretching mode of each compound at around
3300 cm-1 corroborates the successful formation of a M-
CtC bond. The NMR spectral data support the conclu-
sion that these compounds have well-defined and symme-
trical structures. The 31P NMR spectra of the Pt(II)-
containing complexes exhibit a single resonance with a
pair of Pt satellites. Moreover, two distinct 13C NMR
signals for the individual sp carbons are observed, and
they are shifted downfield with respect to the free ligands.
The aromatic region in the 13C NMR spectra reveals a
high degree of structural regularity in the polymers. The
observation of intense molecular ion peaks in the posi-
tive-ion FAB mass spectra confirms the formulas for M1
and M2.
In order to prepare the investigated oligomers/poly-
mers, the reaction time was kept constant at 12 h and the
temperature was varied during the various runs between
20 and 110 °C. For the characterization of the resulting
materials, GPC analysis was used to estimate the mole-
cular weight of each polymer (see data in the Experimen-
tal Section). However, the data should be viewed with

5896 Inorganic Chemistry, Vol. 48, No. 13, 2009
Liu et al.
Table 1. GPC Characterizations of P1 and P2
n (approximate
length/nm)a
polymer code
Mn
Mw
PD (Mw/Mn)
P1(n = 4)
P1(n = 9)
P2(n = 3)
P2(n = 6)
P2(n = 9)
5410
13260
3590
7460
11100
6270
24530
4940
11500
22140
4 (∼10.0)
9 (∼22.5)
3 (∼7.5)
1.16
1.85
1.39
1.54
1.85
6 (∼15.0)
9 (∼22.5)
a Approximated average length of the oligomer (in nm) extracted
from the X-ray dimension of a repetitive unit (see below for M1)
multiplied by the average number of units. In this approximation, the
end group is neglected since its exact nature is not known.
caution in view of the difficulties associated with utilizing
GPC for rigid-rod polymers, which have appreciable
differences in the hydrodynamic behavior from those
for flexible polystyrene polymers (used as comparative
standards). Hence, we would anticipate certain systema-
tic discrepancies in the GPC measurements. However, the
lack of discernible 1H resonance and IR absorption
attributed to the CtC-H end groups in the NMR and
IR spectra suggests the presence of a good degree of
oligomerization for most of these materials, but for the
shorter oligomers, the presence of trans-Pt(P(n-Bu)3)2Cl
as end groups should be strongly suspected. Nonetheless,
the number of units, n, varies from 3 to 9 (Table 1), and we
did find a particular trend relating the synthesis condi-
tions and the resulting average molecular dimension. For
P2, for example, the temperatures were 20, 110, and 80 for
n = 3, 6, and 9, respectively. Attempts were made to
increase the polymer dimensions but all stubbornly failed,
most likely due to the nature of the solubilizing side
groups employed. So, these oligomeric/polymeric materi-
als were investigated as such. The photoelectron diffrac-
tion (PD) is also found to be somewhat large (from 1.16
to 1.85) but is common for the type of reaction employed.
The thermal properties of two representative materials
were investigated. Indeed, P1(n = 9) and P2(n=3) were
examined by thermal gravimetric analysis (TGA) under
nitrogen (Figure 1). The TGA trace for P1(n = 9) exhibits
a first weight loss at about 300 °C, indicative of its
excellent thermal stability. The trace at a higher tempera-
ture is ill-defined, consistent with the polymeric nature of
the solid. The TGA trace for P2(n = 3) exhibits a first
weight loss around 280 °C, also showing a good thermal
stability, but this trace differs from that recorded for P1-
(n = 9), where plateaus are noted with a fast weight loss at
about 410 °C. The rapid weight loss represents 12-20%
of the total mass of the Mn of P2(n=3). This may corres-
pond to a loss of an end group Pt(P(n-Bu)2)3Cl (12%).
The Cl represents only 0.7%. Moreover, polymers P1-
(n=9) and P2(n=3) exhibit a glass transition at ∼116 and
176 °C, respectively (DSC).
Figure 1. TGA traces for P1(n = 9) and P2(n = 3) (heating rate:
20 °C min-1). The end groups are not shown on the structures for con-
venience.
Figure 2. ORTEP representation of M1. The thermal ellipsoids are
presented at 50% probability. The H atoms and solvent crystallization
molecule are omitted for clarity.
During the course of this investigation, one model
compound, M1, crystallized to form crystals suitable for
X-ray analysis (Figure 2). The geometry of the Pt(II)-
containing organometallic fragment is the expected
square planar, and the ligand environment exhibits a
trans geometry, as spectroscopically demonstrated, con-
sistent with the unique ν(CtC) IR absorption. The bond
˚
distances are found to be normal (2.287 and 2.286 A
˚
Figure 3. Normalized UV-vis spectra of L1, M1, P1(n = 4), and
P1(n = 9) in 2MeTHF (298 K). Inset: expansion of the spectrum for
P1(n=9) stressing the splitting of the Soret band.
˚
for Pt-P, 1.995 and 2.009 A for Pt-C, and 2.039 A for
Zn-N, for example). The angle between the xylyl and

Article
Inorganic Chemistry, Vol. 48, No. 13, 2009 5897
Table 2. UV-Vis Absorption Data in 2MeTHF at 298 K
λ
max [nm] (ε Â 10-3 M-1 cm-1 a
)
compds.
Soret region
Q bands
M1
M2
263, 284, 326
262, 286, 327
256, 312
261, 315
264, 289, 317, 338
284, 321
264, 282, 327
249, 313
248, 314
429 (454.8)
431 (93.0)
519 (4.6)
522 (2.4)
519 (4.7)
518 (2.1)
522 (2.7)
520 (3.54)
525 (2.7)
517 (5.7)
521 (2.1)
558 (22.4)
561 (4.6)
599 (11.9)
604 (3.9)
600 (10.4)
599 (5.2)
606 (9.7)
605 (8.7)
604 (12.3)
597 (10.1)
604 (6.7)
P1(n = 4)
P1(n = 9)
P2(n = 3)
P2(n = 6)
P2(n = 9)
L1
427 (396.7), ∼430(sh)
427 (204.1), 435(sh)
434 (226.6), 424(sh)
434 (142.2), 425(sh)
433 (235.5), 426 (sh)
404 (69.3), 425 (923)
405 (30.9), 426 (321)
558 (21.7)
558 (10.2)
561 (12.0)
561 (10.5)
561 (14.4)
556 (33.1)
559 (12.2)
L2
a The absorptivities for the oligomers were calculated using concentrations based on the mass of a repetitive unit.
Chart 2
porphyrin planes is 81.51°, whereas that for the phenyl
and porphyrin is 86.7°, strongly suggesting a weak con-
jugation between the two chromophores. The angle made
by the average plane of the porphyrin and the P-P axis is
64.1°. The angle made by the average porphyrin plane
and the Pt-Pt axis is 6.1°, suggesting that these molecular
objects can be treated as relatively rigid sticks.
This structure also provides the opportunity to measure
the average length of the target oligomers. The total
around the central macrocyle in the solid state. On the
other hand, the Soret bands for P1 and P2 exhibit
two components that become clearer as the number of
units increases (see inset). This is due to an exciton
coupling, well-known in linear oligomers and polymers of
porphyrins.26
Luminescence spectra. The photophysical data for all
compounds are summarized in Tables 3 and 4, and the
emission spectra are shown in Figure 2. The two chromo-
phores, Zn(P) (with P=porphyrin chromophore), known
to be strongly fluorescent,27,28 and trans-(C6H5CtC)Pt-
(P-(n-Bu)3)2(CtC-p-C6H5), which is strongly phosphor-
escent, namely, at 77 K, were monitored at 298 and
77 K.25
˚
distance of M1 (outmost para-H to para-H) is ∼ 40 A
(4.0 nm). The length of a repetitive unit ([(C6H5CtC)Pt-
(P(n-Bu)3)2(CtC-p-C6H4)Zn(P)]; Zn(P) = zincporphyr-
ꢀ
˚
in) is ∼ 25 A (2.5 nm), as measured from the outmost
para-H and the first carbon atom of the phenyl group, as
illustrated in Figure 2. Using this measurement, the ave-
rage oligomer lengths are estimated using n, the number
of units, extracted from Mn (GPC; Table 1). These vary
from 7.5 to 22.5 nm.
Spectroscopic and Photophysical Properties. Absorption
spectra. The ligands L1 and L2, model compounds M1 and
M2, and oligomers P1 and P2 exhibit similar absorption
spectra (Figure 3 for L1, M1, P1(n=4), and P1(n=9) as
typical examples, see also Table 2).
For all cases at 298 K in 2MeTHF, the emission spectra
are dominated by the intense fluorescence arising from
the ZnP unit (λ0,0 ≈ 610 nm for M1 and P1, λ0,0 ≈ 616 nm
for M2 and P2). Weaker fluorescence and phosphores-
cence arising from the trans-(p-C6H4CtC)Pt(P(n-
Bu)3)2(CtC-p-C6H4) spacer are depicted in the 400 and
500 nm regions, respectively. Whereas the position of the
phosphorescence λ0,0 peak (≈ 445 nm) of the trans-
(p-C6H4CtC)Pt(P(n-Bu)3)2(CtC-p-C6H4) unit remains
relatively constant for all investigated compounds and
polymers at 298 K (except for a slight red-shift with the
molecular dimension), the band shape changes somewhat
for the oligomer where some vibronic components exhibit
an increase in intensity. Similarly, the λ0,0 of the ZnP
fluorescence undergoes a relatively modest red-shift
going, for example, from 606 to 610, 610, and 611 nm
for L1, M1, P1(n = 4), and P1(n = 9), respectively (the
total shift is 5 nm or 135 cm-1), indicating that the
conjugation is moderate. This is again consistent with
the X-ray structure of the model complex M1 where a
quasi-right angle is made by the average planes of the
The spectra are characterized by three regions. The
ππ*-type Q (500-600) and Soret (400-450 nm) bands are
characteristic of the porphyrin macrocycles. The third
region, 250-400 nm, exhibits lower-intensity bands
belonging to both the porphyrin unit and the [(p-C6H4-
CtC)Pt(P(n-Bu)3)2(CtC-p-C6H4)] moiety. The assign-
ment for the lowest-energy UV band for this latter
Pt-containing unit is a mixture of ligand-to-metal charge
transfer and a metal-to-ligand charge transfer where M is
the Pt atom and L represents the phenylethynyls, as
recently demonstrated for analogous conjugated organo-
metallic polymers (Chart 2, see ref 25 for examples and
the references therein).25
The examination of the peak maxima of Q bands
indicates that there is essentially no red-shift as the
number of repetitive units increases. This observation
indicates that these polymers are more or less not con-
jugated along the chain. All in all, each chromophore
appears π-separated from the others, which is entirely
consistent with the quasi perfect right angle made by the
average planes of the porphyrin ring and the aryl groups
(26) Harvey, P. D. The Porphyrin Handbook; Kadish, K. M., Smith, K.
M., Guilard, R., Eds.; Academic Press: San Diego, 2003; Vol. 18, pp 63-250.
(27) M. Gouterman, M. In The Porphyrins; Dolphin, D., Ed.; Academic
Press: New York, 1978; Vol. III, p 1.
ꢀ
ꢀ
(25) Gagnon, K.; Aly, S. M.; Wittmeyer, A. B.; Bellows, D.; Berube, J. F.;
Caron, L.; Abd-El-Aziz, A. S.; Fortin, D.; Harvey, P. D. Organometallics
2008, 27, 2201.
(28) Seybold, P. G.; Gouterman, M. J. Mol. Spectrosc. 1969, 31, 1.

5898 Inorganic Chemistry, Vol. 48, No. 13, 2009
Liu et al.
Table 3. Fluorescence and Phosphorescence Data
λ
max [nm]a
Φe ((10%)b
compd. or polymer
298 K
77 K
298 K
77 K
M1
[Pt]: fluo: 391; phos: 449
ZnP: fluo: 610, 660
[Pt]: fluo: 397; phos: 446, 511
ZnP: fluo: 616, 665
[Pt]: fluo: 392; phos: 438
ZnP: fluo: 610, 658
[Pt]: fluo: 390; phosp: 452
ZnP: fluo: 611, 659
[Pt]: fluo: 385; phos: 441, 510
ZnP: fluo: 616, 664
[Pt]: fluo: 396; phos: 446
ZnP: fluo: 616, 664
[Pt]: fluo: 396; phos: 446
ZnP: fluo: 616, 662
ZnP: fluo: 606, 656, 720
ZnP: fluo: 612, 664, 726
[Pt] fluo: 385, 397; phos: 416, 446, 473, 496
ZnP fluo: 599, 656, 724; phos: 788
[Pt]: phos: 446, 467, 481, 493
ZnP: fluo: 610, 637, 667; phos: 815 w
[Pt]: fluo: 393, 413; phos: 451, 472, 500, 530
ZnP: fluo: 604, 662, 714; phos: 797 w
[Pt]: fluo: 398, 413; phos: 452, 471, 498, 530
ZnP: fluo: 606, 662, 723; phos: 803 w
[Pt]: phos: 447, 471, 502, 523, 533
ZnP: fluo: 612, 630, 666; phos: 815 w
[Pt]: fluo: 397, 418; phos: 446, 470, 490
ZnP: fluo: 614, 669, 731 w; phos: 822 w
[Pt]: fluo: 393, 418; phos: 450, 472, 495, 523
ZnP: fluo: 615, 638, 667, 703; phos: 823 w
ZnP: fluo: 598, 654, 715; phos: 792 w
ZnP: fluo: 605, 663; phos: 795 w
0.125
0.047
0.071
0.080
0.081
0.086
0.051
0.121
0.081
0.062
0.120
0.163
0.17
M2
P1(n = 4)
P1(n = 9)
P2(n = 3)
P2(n = 6)
P2(n = 9)
0.065
L1
L2
0.074
0.098
0.060
0.11
a Chromophore ZnP=zinc(II)porphyrin, chromophore [Pt]=trans-(C6H4CtC)Pt(P(n-Bu)3)2(CtC-p-C6H4). b Total Φe of the ZnP chromophore
(i.e., fluorescence), λexc=560 nm.
Table 4. Fluorescence and Phosphorescence Lifetimes and Rate Constants for T1 ETa
lifetime
compd. in 2MeTHF
τF(ns) 298 Kb
τP(μs) 77 K
τF(ns) 77 K
kET
λ
exc=345 nm (104 s-1) 77 K
standard
L1
L2
35.0 ( 1.3 [Pt]c
29800 ( 4000 ZnP
21100 ( 1890 ZnP
11800 ( 830 ZnP
12.6 ( 0.8 [Pt]
13600 ( 1380 ZnP
18.8 ( 1.4 [Pt]
14000 ( 500 ZnP
13.2 ( 1.7 [Pt]
8400 ( 13 ZnP
10.5 ( 0.8 [Pt]
11900 ( 510 ZnP
12.3 ( 2.5 [Pt]
10900 ( 500 ZnP
2.9 ( 0.7 [Pt]
8340 ( 300 ZnP
0.73 ( 0.07 [Pt]
1.18 ( 0.06 ZnP
1.11 ( 0.09 ZnP
1.28 ( 0.05 ZnP
3.10 ( 0.03 ZnP
3.34 ( 0.02 ZnP
2.56 ( 0.08 ZnP
M1
5.1 ( 0.6
2.4 ( 0.6
4.7 ( 1.0
6.7 ( 1.0
5.3 ( 1.5
32 ( 7
M2
0.60 ( 0.10 ZnP
1.00 ( 0.18 ZnP
0.93 ( 0.29 ZnP
0.66 ( 0.02 ZnP
0.55 ( 0.01 ZnP
0.51 ( 0.07 ZnP
2.81 ( 0.04 ZnP
2.29 ( 0.05 ZnP
2.38 ( 0.02 ZnP
2.49 ( 0.06 ZnP
2.08 ( 0.03 ZnP
2.51 ( 0.04 ZnP
P1(n = 4)
P1(n = 9)
P2(n = 3)
P2(n = 6)
P2(n = 9)
130 ( 20
a Chromophore ZnP = zinc(II)porphyrin, chromophore [Pt] = trans-(C6H4CtC)Pt-(P(n-Bu)3)2(CtC-p-C6H4). Their corresponding emission
lifetimes were measured using the same excitation wavelengths as indicated in Figure 4. b The τP data of the [Pt] chromophore at 298 K could not be
accurately measured because of the weakness of its emission intensity. c Value extracted from ref 25.
aryls and the porphyrin macrocycle. No phosphorescence
arising from the ZnP chromophore is seen at 298 K.
At 77 K, all of these previous observations are also
noted, but at this temperature, a very weak phosphores-
cence of the ZnP macrocycle now appears at ∼800 nm
(Figure 4). Moreover, the λ0,0 of the ZnP fluorescence also
undergoes a modest red-shift but somewhat relatively
larger than that at 298 K, going for example from 598
to 599, 604, and 606 nm for L1, M1, P1(n=4), and P1(n=
9), respectively (total shift is 8 nm or 220 cm-1), indicating
that the conjugation is slightly accentuated at 77 K. The
change in band shape of the trans-(p-C6H4CtC)Pt(P-
(n-Bu)3)2(CtC-p-C6H4) phosphorescence band is also
notable (Figure 4). This observation, along with the
(modest) red shift of the 0-0 peak with the molecular
dimension, also corroborates the presence of some ex-
tended conjugation at this temperature. To explain this
result, the presence of a change in dihedral angle between
the aryl and porphyrin macrocycle average plane must
take place.
Emission Lifetimes and Triplet State Energy Transfer.
Photoinduced energy transfer processes in conjugated poly-
mers containing the fragment trans-(p-C6H4CtC)Pt-(P(n-
Bu)3)2(CtC-p-C6H4) and related derivatives,25,29 and
dyads containing the ZnP chromophore,30 have been re-
ported before and can be used as a basis for interpretation.
The assignment of the energy donor and acceptor centers is
appropriately made on the basis of the 0-0 peaks (Figure 4
and Table 4) of the fluorescence and phosphorescence
bands. The upper energy donor and lower acceptor are
the (trans-(p-C6H4CtC)Pt(P(n-Bu)3)2(CtC-p-C6H4)) and
ZnP chromophores, respectively (Figure 5).
ꢀ
(29) Fortin, D.; Clement, S.; Gagnon, K.; Berube, J.-F.; Stewart, M. P.;
Geiger, W. E.; Harvey, P. D. Inorg. Chem. 2008, 87, 103.
(30) Faure, S.; Stern, C.; Espinosa, E.; Douville, J.; Guilard, R.; Harvey,
P. D. Chem. Eur. J. 2005, 11, 3469.

Article
Inorganic Chemistry, Vol. 48, No. 13, 2009 5899
Chart 3. Standard (trans-(PhCtC)Pt(P(n-Bu)3)2(CtCPh))25
Taking into account the uncertainties, the τF data of
the zinc(II)porphyrin chromphore (depicted as ZnP in
Table 3) for L1 f M1 f P1(n=4) f P1(n=9) and L2 f
M2 f P2(n = 3) f P2(n = 6) f P2(n = 9) at both
temperatures reveal a slight decrease in τF. The most
notable change in τF data concerns the passages L1 f
M1 and L2 f M2, where a decrease is noted at 77 K. This
decrease is assigned to a heavy atom effect (due to the
incorporation of the Pt atoms in the chain) and the
lengthening of the oligomeric chains, adding vibrational
modes for nonradiative excited state deactivation. The τP
data of the zinc(II)porphyrin chromphore show the same
tendency (i.e., a decrease in τP according to L1 f M1 f
P1(n=4) f P1(n = 9) and L2 f M2 f P2(n = 3) f P2-
(n=6) f P2(n=9)), which is also due to a heavy effect,
which is also particularly notable for the passages L1 f
M1 and L2 f M2, and the lengthening of the oligomeric
chains. These variations in τF and τP data of the ZnP
chromphore occur by a factor of about 2, at the most,
considering the uncertainties.
The τP data for the trans-(C6H4CtC)Pt(P(n-Bu)3)2-
(CtC-p-C6H4) chromophore (i.e., [Pt]) along the same
series also exhibit a more important decrease and heavy
atom effect, and the oligomer chain cannot explain this
larger change. In comparison with the nonfunctionalized
spacer trans-(PhCtC)Pt(P(n-Bu)3)2(CtCPh) (see stan-
dard in Chart 3), the τP values change from 35 μs25 down
to 10.5 (>3 times) and 0.73 μs (>45 times) for P1(n=9)
and P2(n = 9), respectively, hence representing larger
decreases. These supplementary nonradiative processes
promoting excited deactivation of the spacer emission are
T1 ET. The photoinduced electron transfer is unlikely
at 77 K in glassy matrices (because of the very large
reorganization energy) and is rather rare in the triplet
excited states.
Evidence for T1 ET is provided by means of measure-
ments of the transient absorption spectra on the micro-
second time scale (see L1 and M1 for examples; Figure 6).
In the T1-Tn absorption spectrum of L1, for which no
electron transfer is possible, a broad and dissymmetric
band is noted at about 450 nm. For M1, the same band is
observed plus a feature at 800 nm. The latter feature
is due to the T1-Tn absorption band of the trans-
(p-C6H4CtC)Pt(P(n-Bu)3)2(CtC-p-C6H4) unit, on the
basis of the literature (see ref 25 and the references therein).
So the transient absorption spectra at 77 K are con-
sistent with T1-Tn absorption signatures with no evi-
dence for charge-separated state, as no other feature is
observed. The rate of energy transfer (kET) is quantified
by kET=(1/τe) - (1/τe°), where τe is the emission lifetime
of the donor in a system where the donor is involved in an
intramolecular energy transfer process and τe° is the
emission lifetime of the donor in the absence of an energy
transfer.26 In this work, τe would be, for M1, M2, P1,
and P2, excited at 345 nm (at 77 K) and τe° would be for
Figure 4. Top: Corrected emission spectra of L1, M1, P1(n=4), and P1
(n = 9) at 298 K in 2MeTHF. Second: Corrected emission spectra of L2,
M2, P2(n = 3), P2(n=6), and P2(n = 9) at 298 K in 2MeTHF. Third:
Corrected emission spectra of L1, M1, P1(n= 4), andP1(n =9)at77K in
2MeTHF. Bottom: Corrected emission spectra of L2, M2, P2(n = 3), P2
(n = 6), and P2(n = 9) at 77 K in 2MeTHF. The λexc values are indicated
in the spectra. X = artifact; [Pt] = trans-(p-C6H4CtC)Pt(P(n-Bu)3)2-
(CtC-p-C6H4); ZnP = zinc(II)porphyrin; (fluo) = fluorescence; (phos)
= phosphorescence.
Figure 5. Energy diagram for the [Pt(P(n-Bu)3)2CtC(p-C6H4)Zn(P)(p-
C6H4)CtC]n polymers and the [(C6H5CtC)Pt(P(n-Bu)3)2(CtC-p-C6H4)-
Zn(P)(p-C6H4)CtCPt-(P(n-Bu)3)2(CtCC6H5)]
model
compounds
([Pt]=(p-C6H4)CtCPt(P(n-Bu)3)2CtC(p-C6H4)). The relevant radiative
(A=absorbance, F=fluorescence, P=phosphorescence) and nonradiative
(isc = intersystem crossing, T1 ET=triplet energy transfer) are indicated.

5900 Inorganic Chemistry, Vol. 48, No. 13, 2009
Liu et al.
interesting to note that this jump (i.e., energy migration
from one ZnP chromophore to another) operates over 18
ꢀ
˚
A (the Cmeso-[spacer]-Cmeso separation; distance ex-
tracted from X-ray data for other spacers).25
Conclusion
A series of 1-D nanometer-sized oligomers built upon a
metalloporphyrin and a rigid linear and conjugated organo-
metallic spacer were prepared and characterized. Moderate
variations of the photophysical data, notably the emission
lifetimes of the metalloporphyrin chromophore (2 folds), are
observed when in the presence of heavy atom effects (Pt) and
when submitted to nonradiative pathways associated with
the increase in chain length. However, when the excitation
takes place directly in the absorption band of the trans-
(p-C6H4CtC)Pt(P(n-Bu)3)2(CtC-p-C6H4) spacer, T1 ET
operates from the spacer (donor) to the zinc(II)porphyrin
(acceptor) with rates, kET, ranging from 104 (slow) to 106 s-1
(intermediate rate). The kET measurements are interesting
since a dependence on the oligomer length is noticed. This
work represents a basic example of the antenna effect (multi-
chromophoric structure with electronic interactions) respon-
sible for harvesting the light and for the migration of the light
energy across a membrane or a material.
Figure 6. Transient absorption spectra of L1 (top) and M1 (bottom)
in 2MeTHF at 77 K excited at 355 nm (delay=1 μs). The transient
absorption band at 800 nm is the T1-Tn absorption of the trans-(p-C6H4-
CtC)Pt(P(n-Bu)3)2(CtC-p-C6H4) spacer.
It is also interesting to note that the (-chromophore-
spacer-)n topology bears some resemblance to the light-
harvesting devices in photosystems of some photosynthetic
bacteria. For example, the purple photosynthetic bacteria
exhibit an LH II device (light-harvesting device II) where a
circular structure of a little bit more than 10 nm composed of
18 bacteriochlorophylls a (B850), nine bacteriochlorophylls a
(B800), and nine glucoside rhodopins (carotenoids) form a
circular grid with upper (18 bacteriochlorrophylls) and lower
rings (alternating nine bacteriochlorophylls and nine carote-
noids) connected by the nine perpendicularly placed carote-
noids.34 All of the components act as molecular antenna for
harvesting light and channeling this energy toward the
reaction center protein (inside LH I). Exciton processes
trans-(PhCtC)Pt(P(n-Bu)3)2(CtCPh) (i.e., 35 μs).25 The
extracted kET values (Table 3) reveal a modest and more
pronounced decrease going from M1fP1(n=4) f P1-
(n=9) and M2 f P2(n=3) f P2(n=6) f P2(n=9), res-
pectively. The latest series exhibits a change of 2 orders of
magnitude for T1 kET, but overall, these rates are respec-
tively modest (104 s-1) and relatively faster (106 s-1) for
these two series. Literature data for porphyrin-containing
assemblies reveal that T1 kET ranges typically between 103
and 109 s-1 26
. As for the reason as to why one substituent
(n-pentyl) leads to faster T1 energy transfers (in compar-
ison with the mesityl) as the chain length increases is
unknown. However, one may speculate that the flexible
chain of the n-pentyl side substitutes may induce a “loose
bolt” effect,31 rapidly draining the excited state energy by
nonradiative pathways (interconversion from the triplet
manifold) down to the ground state. If this is the case, one
localized excited zinc(II)porphyrin being deactivated by
remote n-pentyl groups is most unlikely. The only way to
explain this effect is to have an exciton process allowing
delocalization of the triplet state excitation,32 hence hav-
ing the excited chromophore more efficiently subjected to
excited deactivation by the “loose bolt” effect. Evidence
for exciton phenomena was previously provided and
discussed by Schanze and his collaborators,33 so it is
not new. However, we find in these two series that the
delocalization of this energy spreads over at least nine
units, which is longer than that mentioned by Schanze
(a few units) in the triplet excited states. It is also
˚
between the B800 units, which are separated by ∼20 A
(Mg Mg), occur at an efficient time scale of 500 fs. Here,
3 3 3
the metalloporphyrin and the trans-(p-C6H4CtC)Pt(P(n-
Bu)3)2(CtC-p-C6H4) spacer, although placed in a 1-D ar-
rangement, play the roles of bacteriochlorophylls and carote-
noids, respectively, for the lower ring. The presence of ex-
citonic processes was evidenced here, where the rate of energy
migration gets faster when the number of unit increases.
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 (CEMOPUS). L.L. ac-
ꢀ
knowledges the National Natural Science Foundation
of China (No.20671033) for the purchase of her airplane
tickets.
(31) Turro, N. J. Modern Molecular Photochemistry; Benjamin/
Cummings: Menlo Park, CA, 1978.
(32) Fortin, D.; Turcotte, M.; Drouin, M.; Harvey, P. D. J. Am. Chem.
Supporting Information Available: This material is available
free of charge via the Internet at http://pubs.acs.org.
Soc. 1997, 119, 531.
::
(33) (a) Glusac, K.; Kose, M. E.; Jiang, H.; Schanze, K. S. J. Phys. Chem.
::
B 2007, 111. (b) Muller, J. G.; Atas, E.; Tan, C.; Schanze, K. S.; Kleiman, V.
(34) Harvey, P. D.; Stern, C.; Gros, P. C.; Guilard, R. J. Inorg. Biochem.
2008, 102, 395.
D. J. Am. Chem. Soc. 2006, 128, 4007.