Rational synthetic design of well-defined Pt(bisethynyl)/Zn(porphyrin) oligomers for potential applications in photonics

Article abstract of DOI:10.1039/c0nj00819b

Well-defined oligomers of 1, 2, 3 and 4 units built upon the very soluble bis-1,15-(1,4-ethynylbenzene)-3,7,13,17-tetramethyl-2,8,12,18-tetrakis(n-hexyl) zinc(ii) porphyrin ligand and the trans-bis(tri-n-butylphosphine)platinum(ii) linker, with acetylene

Full text of DOI:10.1039/c0nj00819b

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PAPER
Rational synthetic design of well-defined Pt(bisethynyl)/Zn(porphyrin)
oligomers for potential applications in photonicswz
Guillaume Langlois,ab Shawkat M. Aly,ya Claude P. Gros,b Jean-Michel Barbe*b
and Pierre D. Harvey*ab
Received (in Gainesville, FL, USA) 22nd October 2010, Accepted 13th December 2010
DOI: 10.1039/c0nj00819b
Well-defined oligomers of 1, 2, 3 and 4 units built upon the very soluble bis-1,15-
(1,4-ethynylbenzene)-3,7,13,17-tetramethyl-2,8,12,18-tetrakis(n-hexyl) zinc(II) porphyrin ligand and
the trans-bis(tri-n-butylphosphine)platinum(II) linker, with acetylene or trimethylsilane as end
groups, has been prepared in the presence of a dichloromethane/diethylamine mixture (1 : 1 v/v)
and CuX (X = Cl, I) at room temperature, analogue to a Sonogashira coupling. The new
1
monodisperse organometallic oligomers were characterized by H, 31P NMR, UV-visible
spectroscopies and MALDI-TOF mass spectrometry. The methyl groups placed at the
3,7,13,17-positions induces the locking of the C6H4 fragment in a perpendicular conformation
with respect to the zinc(II) porphyrin chromophore, hence removing conjugation as corroborated
by the almost total absence of spectral shift of the Soret and Q-bands upon increasing the number
of units. Despite this feature, exciton coupling in the Soret band is noted at both room
temperature and 77 K. The photophysical parameters, fluorescence lifetimes and quantum yields
are practically constant going from the monomer, dimer and tetramer, and as a function of the
monitored fluorescence wavelength, all indicating that the excitonic behavior (excitation energy
delocalization) is minimal, which is consistent with the weak exciton coupling constants and the
lack of conjugation of the p-system. The synthetic methodology can provide longer well-defined
oligomers as the presented products were still very soluble even when the number of unit was 4.
assemblies, notably using platinum bisethynyl linkers, trans-
Introduction
CRC–PtL2–CRC (L = PEt3, PBu3), are just in its infancy
based on
a
recent review.4 The mononuclear trans-
The conjugated polyporphyrin assemblies covalently held by
ethynyl bridges for photonic applications have gained an
important place in the design of light harvesting devices and
long-distance electron transports.1–3 The investigations of the
corresponding analogous organometallic version of such
ArCRC–PtL2–CRCAr (Ar = aromatic) species are well-
known for non-linear5 and two-photon absorption properties,6
electronic communication across the backbone,7 luminescence
(notably phosphorescence)8 with occasional excimer forma-
tions.9 All these properties can also be found in the oligomers
(mono- and polydispersed),10,11 and applications of sensorisa-
tion of transition metals,12 charge separation,13 light emitting
diodes14,15 and photocells were reported as well.16–19
a Pierre D. Harvey, De´partement de Chimie, Universite´ de
Sherbrooke, Sherbrooke PQ, Canada J1K 2R1.
E-mail: pierre.harvey@USherbrooke.ca; Fax: 819-821-8017;
Tel: 819-821-7092
Jean-Michel Barbe, Institut de Chimie Moleculaire de l’Universite de
b
Indeed, the earlier syntheses of species, monomers and oligo-
mers of Pt(bisethynyl)/ Zn(porphyrin) systems, were reported by
Russo and collaborators in 2003 and 2004 (Chart 1),20–22 latter
by Chen and collaborators (2006),23 and more recently by us
over the past two years (Chart 1),24–26 including systems where
the metal-metal-bonded Pt2(dppm)2 bridge is used.27 Solubility
is a major challenge in these cases, and so the growth of longer
chain appears challenging at first glance. On the photophysical
point of view, evidence for electronic communications across the
oligomers such as conjugation, singlet and triplet energy transfer
and long-distance heavy atom effect is provided.
´
Bourgogne (ICMUB, UMR 5260), Universite de Bourgogne, Dijon,
´
´
France. E-mail: jean-michel.barbe@u-bourgogne.fr;
Tel: 33 (0)3 80 39 61 12
w This article is part of a themed issue on Molecular Materials: from
Molecules to Materials, commissioned from the MolMat2010
conference.
z Electronic supplementary information (ESI) available: MALDI/
TOF mass spectrum of the reaction mixture during the one-pot
1
reaction of 1b with PtCl2(PBu3)2 (Fig. S1), H and 31P NMR spectra
of the different oligomers and precursors (Fig. S2–13), MALDI/TOF
MS spectra of the different oligomers and precursors (Fig. S14–31) and
IR spectra (KBr) of the different oligomers (Fig. S32–S38). See DOI:
10.1039/c0nj00819b
y On leave from Chemistry Department, Faculty of Science, Assiut
University, Assiut, Egypt.
One common point is that in attempts to prepare long
polymer chains from the conventional ligand substitution
c
1302 New J. Chem., 2011, 35, 1302–1314
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Chart 1
strategy ‘‘Pt–Cl’’ + H–CRCR (with a small amount of CuI)
the incorporation of soluble groups such as hexyls at
the b-position and the control of the stoichiometry of the
reactants are made. The photophysical properties of
representative examples are investigated and the data are in
the same range of previously reported other polydispersed
oligomers of the similar type.25,26 A weak excitonic coupling
is noticed in the Soret bands and a suspected very small increase
in internal conversion rate constant in the S1 state appears
responsible to the very small decrease in fluorescence lifetimes as
the oligomer length increases.
leads only to short and polydispersed oligomers (PD are in the
order of 1.5 to 2.0 based on GPC analysis). The downfall is
that when comes the photophysical characterization of such
1D-oligomeric species, one cannot be certain what is the main
contributor to the photophysical parameters such as emission
lifetimes and quantum yields. The need to find an easy strategy
to prepare any oligomers of a well-defined length is crucial in
the structure-properties relationship.
We now wish to report the syntheses of easily accessible and
well-defined oligomers (monomers, dimers, trimer and tetramer;
Chart 2 and 3) of Pt(bisethynyl)/Zn(porphyrin) systems, where
Experimental section
Materials
The porphyrin precursors, 1a and 1b, were synthesized as
previously reported.28,29 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), potassium carbonate
(Fisher), ether (ACP), hexane (ACP), ethanol (Commercial
Alcohols inc.). All the solvents were purified according to
literature procedures. The coupling reactions were performed
under nitrogen using Schlenk techniques, with flame dried
reaction vessels before use. Silica gel (Merck; 70–120 mm) was
used for column chromatography. Analytical thin layer
chromatography was performed using Merck 60 F254 silica
Chart 2
c
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Chart 3
gel (precoated sheets, 0.2 mm thick). All the reactions were
Trans-chloro-[5-(4-ethynylphenyl)-15-[4-(trimethylsilyl)ethynyl-
phenyl]-3,7,13,17-tetramethyl-2,8,12,18-tetrakis-(n-hexyl)-zinc(II)-
porphyrin]bis(tri-n-butyl-phosphine)-platinum(II) (3a). A mixture
of trans-bis(tri-n-butylphosphine)-dichloro-platinum(II) (152.4 mg,
227.3 mmol) and CuI (5.1 mg, 27 mmol) was solubilized in a
mixture of CH2Cl2/Et2NH (15 mL, 1 : 1 v/v). The porphyrin 1c
(117.2 mg, 56.4 mmol) was solubilized in CH2Cl2 (15 mL) and
added dropwise over 1 h at room temperature. After 30 min of
additional stirring, the solvents were removed in vacuo to afford
a red solid. The porphyrin 1c and trans-bis(tri-n-butylphosphine)-
dichloro-platinum(II) were partially removed by fractional
crystallization (CH2Cl2–CH3OH). The solvents of the fraction
containing the title compound 3a were removed in vacuo. The
resulting red solid was purified using a solution of CH2Cl2–
pentane (20 : 80–30: 70 v/v) containing 0.5% of Et3N to afford
the title compound 3a as a red solid in 49% yield (45.8 mg,
monitored by thin-layer chromatography and UV-visible
spectroscopy.
5,15-Bis(trans-bis(1,4-ethynylbenzene)bis(tri-n-butylphosphine)-
platinum(II))-3,7,13,17-tetramethyl-2,8,12,18-tetrakis(n-hexyl)-
Zinc(II)porphyrin (4). A mixture of the porphyrin 1b (15.0 mg,
15.5 mmol), trans-phenylethynyl-chlorobis(tri-n-butylphosphine)-
platinum(II) (24.0 mg, 32.6 mmol), and CuI (1.0 mg, 5.3 mmol)
was dissolved in CH2Cl2/Et2NH (4 mL, 1 : 1 v/v). The mixture
was stirred at room temperature for 15 min. After removal of
the solvent in vacuo, the resulting mixture was recrystallized
(CH2Cl2–CH3OH). The red solid was washed with CH3OH
and collected with CH2Cl2. The solvent was evaporated in
vacuo and the red solid was recrystallized a second time
(CH2Cl2–CH3OH) to afford 4 as a red solid in 87% yield
(31.8 mg, 13.4 ꢀ mmol). HR-MS (MALDI-TOF): m/z =
2363.3119 [M]+ 2363.2684 calcd for C128H192N4P4Pt2Zn.
31P NMR (161.92 MHz, CHCl3) d (ppm): 3.20. 1H NMR
(300 MHz, CDCl3) d (ppm): 10.17 (s, 2H, H-meso), 7.88 (d,
27.4 mmol). HR-MS (MALDI-TOF): m/z = 1669.8837 [M]+
ꢀ
1669.8715 calcd for C91H137ClN4P2PtSiZn. 31P NMR
(161.92 MHz, CHCl3) d (ppm): 8.15. 1H NMR (400 MHz, CDCl3)
d (ppm): 10.17 (s, 2H, H-meso), 8.04 (d, 2H, 3JH–H = 8.0 Hz, Ph),
3
3
4H, JH–H = 8.0 Hz, Ph), 7.64 (d, 4H, JH–H = 8.0 Hz, Ph),
7.89 (d, 2H, JH–H = 8.0 Hz, Ph), 7.86 (d, 2H,3JH–H = 8.0 Hz,
3
3
7.32 (d, 6H, JH–H = 8.0 Hz, Ph), 7.23 (d, 4H, JH–H = 8.0
3
Ph), 7.61 (d, 2H, 3JH–H = 8.0 Hz, Ph), 4.00–4.93 (br, 12H, CH2),
3
Hz, Ph), 3.97 (t, 8H, JH–H = 7.2 Hz, CH2), 2.54 (s, 12H,
2.53 (s, 6H, CH3), 2.47 (s, 6H, CH3), 2.22–2.11 (br, 16H, CH2),
3
1.77–1.66 (br, 16H, CH2), 1.56 (sextet, 16H, JH–H
CH3), 2.30–2.08 (m, 32H, CH2), 1.81–1.68 (m, 32H, CH2),
1.62–1.32 (m, 40H, CH2), 1.02 (t, 36H 3JH–H = 7.2 Hz, CH3),
3
0.91 (t, 12H, JH–H = 7.2 Hz, CH3).
=
3
7.3 Hz, CH2), 1.49 (quintet, 8H, JH–H = 7.3 Hz, CH2), 1.38
c
1304 New J. Chem., 2011, 35, 1302–1314
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3
(quintet, 8H, JH–H = 7.3 Hz, CH2), 1.02 (t, 18H, JH–H
3
=
(161.92 MHz, CHCl3) d (ppm): 3.34. 1H NMR (400 MHz, CDCl3)
d (ppm): 10.19 (s, 4H, H-meso), 8.05 (d, 4H, 3JH–H = 8.0 Hz, Ph),
7.92 (d, 4H, 3JH–H = 8.0 Hz, Ph), 7.88 (d, 4H,3JH–H = 8.0 Hz, Ph),
7.71 (d, 4H, 3JH–H = 8.0 Hz, Ph), 3.04–3.90 (br, 16H, CH2), 2.58
(s, 12H, CH3), 2.49 (s, 12H, CH3), 2.47–2.49 (br, 12H, CH2),
2.25–2.12 (br, 16H, CH2), 1.95–1.83 (br, 12H, CH2), 1.82–1.70
(br, 16H, CH2), 1.69 (sextet, 12H, 3JH–H = 7.3 Hz, CH2), 1.52-1.45
3
7.3 Hz, CH2), 0.91 (t, 12H, JH–H = 7.3 Hz, CH2), 0.40 (s, 9H,
Si(CH3)3).
Trans-(4-Ethynylphenyl)-[5-(4-ethynylphenyl)-15-[4-(trimethyl-
silyl)-ethynyl-phenyl]-3,7,13,17-tetramethyl-2,8,12,18-tetrakis-
(n-hexyl)-zinc(II)-porphyrin]-bis(tri-n-butylphosphine)-platinum(II)
(2a). The porphyrin 1c (91.2 mg, 43.9 mmol), trans-phenyl-
ethynyl-chlorobis(tri-n-butylphosphine)platinum(II) (38.5 mg,
52.3 mmol) and CuI (8.0 mg, 42.0 mmol) were dissolved in
CH2Cl2/Et2NH (12 mL,1 : 1 v/v). The reaction mixture was
stirred at room temperature for 10 min and was monitored
by TLC. The solvent was removed in vacuo and the residue
was purified by silica gel chromatography (30 : 60 CH2Cl2/
heptane). The resulting red solid was recrystallized (CH2Cl2–
CH3OH) to afford the title compound 2a as a red solid in
66% yield (50.0 mg, 28.8 mmol). HR-MS (MALDI-TOF):
(br, 16H, CH2), 1.44–1.34 (br, 16H, CH2), 1.12 (t, 18H, 3JH–H
=
7.3 Hz, CH3), 0.93 (t, 12H, 3JH–H = 7.3 Hz, CH3), 0.92 (t, 12H,
3JH–H = 7.3 Hz, CH3), 0.41 (s, 18H, Si(CH3)3).
Trans-bis[5,15-bis(4-ethynylphenyl)-3,7,13,17-tetramethyl-2,
8,12,18-tetrakis(n-hexyl)zinc(II)porphyrin]bis(tri-n-butylphos-
phine)platinum(II) (5b). The porphyrin 5a (30 mg, 11.2 mmol)
was dissolved in tetrahydrofuran (8.0 mL). NBu4F (70 mL, 1.0 M
in THF) was added and the mixture was stirred at room
temperature for 20 min. The solvent was removed in vacuo.
The resulting red solid was recrystallized (CH2Cl2–CH3OH).
The red solid was washed with CH3OH and collected with
CH2Cl2. The solvent was evaporated in vacuo and the red solid
was recrystallized a second time to afford the title compound
5b as a red solid in quantitative yield (28.4 mg, 11.2 mmol).
m/z = 1735.9453 [M]+ 1735.9418 calcd for C99H142N4P2
ꢀ
PtSiZn. This intermediate was not further characterized and
was used directly in the following deprotection step.
Trans-(4-Ethynylphenyl)-[5,15-bis(4-ethynylphenyl)-3,7,13,17-
tetramethyl-2,8,12,18-tetrakis(n-hexyl)zinc(II)porphyrin]bis(tri-n-
butylphosphine)platinum(II) (2b). The porphyrin 2a (49.8 mg,
28.6 mmol) was dissolved in tetrahydrofuran (20 mL). NBu4F
(200 mL, 1.0 M in THF) was added and the mixture was stirred at
room temperature for 1 h. The solvent was removed invacuo. The
resulting red solid was recrystallized (CH2Cl2–CH3OH). The red
solid was washed with CH3OH and collected with CH2Cl2. The
solvent was evaporated in vacuo and the red solid was recrystal-
lized a second time to afford the title compound 2b as a red
cotton-like microcrystalline solid in 77% yield (36.8 mg,
HR-MS (MALDI-TOF): m/z = 2526.4127 [M]+ 2526.3915
ꢀ
calcd for C152H204N8P2PtZn2. 31P NMR (161.92 MHz,
CHCl3)
d
(ppm): 4.39. 1H NMR (400 MHz, CDCl3)
3
d (ppm): 10.20 (s, 4H, H-meso), 8.07 (d, 4H, JH–H = 8.0
=
Hz, Ph), 7.92 (d, 4H, 3JH–H = 8.0 Hz, Ph), 7.90 (d, 4H,3JH–H
3
8.0 Hz, Ph), 7.70 (d, 4H, JH–H = 8.0 Hz, Ph), 4.04–3.92
(br, 16H, CH2), 3.34 (s, 2H, CH), 2.58 (s, 12H, CH3), 2.48
(s, 12H, CH3), 2.47–2.42 (br, 12H, CH2), 2.21–2.13 (br, 16H,
CH2), 1.94–1.84 (br, 12H, CH2), 1.80–1.70 (br, 16H, CH2),
3
22.1 mmol). HR-MS (MALDI-TOF): m/z = 1663.9088 [M]+
1.67 (sextet, 12H, JH–H = 7.3 Hz, CH2), 1.52–1.45 (br, 16H,
CH2),1.44–1.35 (br, 16H, CH2), 1.11 (t, 18H, 3JH–H = 7.3 Hz,
ꢀ
1663.9023 calcd for C96H134N4P2PtZn. 31P NMR (161.92 MHz,
CH3), 0.93 (t, 12H, 3JH–H = 7.3 Hz, CH3), 0.92 (t, 12H, 3JH–H
=
1
CHCl3) d (ppm): 4.27. H NMR (400 MHz, CDCl3) d (ppm):
3
7.3 Hz, CH3).
10.17 (s, 2H, H-meso), 8.06 (d, 2H, JH–H = 8.0 Hz, Ph), 7.89
(d, 2H, 3JH–H = 8.0 Hz, Ph), 7.87 (d, 2H,3JH–H = 8.0 Hz, Ph),
7.65(d, 2H, 3JH–H =8.0Hz,Ph),7.32(d,2H,3JH–H =7.3Hz,Ph),
7.23(d, 2H, 3JH–H =7.3Hz,Ph),7.15(d,1H,3JH–H =7.3Hz,Ph),
4.00–3.91 (br, 12H, CH2), 3.33 (s, 1H, CH), 2.54 (s, 6H, CH3), 2.47
Trans-bis[5-(4-ethynylphenyl)-15-[trans-bis(1,4-ethynylphenyl)-
bis(tri-n-butyl-phosphine)-platinum(II)]-3,7,13,17-tetramethyl-2,8,
12,18-tetrakis(n-hexyl)-zinc(II)-por-phyrin]bis(tri-n-butylphosphine)-
platinum(II) (6). A mixture of the porphyrin 2b (8.8 mg,
3.5 mmol), trans-phenylethynyl-chlorobis(tri-n-butylphosphine)-
platinum(II) (8.0 mg, 10.9 mmol) and CuI (1.0 mg, 5.3 mmol) was
dissolved in CH2Cl2/Et2NH (4 mL,1 : 1 v/v). The mixture was
stirred at room temperature for 15 min. After removal of the
solvent in vacuo, the resulting mixture was recrystallized
(CH2Cl2–CH3OH). The red solid was washed with CH3OH
and collected with CH2Cl2. The solvent was evaporated
in vacuo and the red solid was recrystallized a second time
to afford 6 as a red solid in 84% yield (11.5 mg, ꢀ2.92 mmol).
HR-MS (MALDI-TOF): m/z = 3925.1390 [M]+ 3925.1238
calcd for C216H320N8P6Pt3Zn2. 31P NMR (161.92 MHz, CHCl3)
d (ppm): 3.34, 3.21. 1H NMR (300 MHz, CDCl3) d (ppm): 10.19
(s, 6H, CH3), 2.25–2.33 (br, 8H, CH2), 2.17 (sextet, 8H, 3JH–H
=
=
7.3 Hz, CH2), 1.80–1.69 (br, 16H, CH2), 1.56 (sextet, 16H, 3JH–H
3
7.3 Hz, CH2), 1.49 (quintet, 8H, JH–H = 7.3 Hz, CH2), 1.39
(quintet,8H, 3JH–H =7.3Hz, CH2), 1.01 (t, 18H, 3JH–H =7.3Hz,
CH3), 0.91 (t, 12H, 3JH–H = 7.3 Hz, CH3).
Trans-bis-[5-(4-ethynylphenyl)-15-[4-(trimethylsilyl)ethynyl-
phenyl]-3,7,13,17-tetramethyl-2,8,12,18-tetrakis(n-hexyl)zinc(II)-
porphyrin]bis(tri-n-butylphosphine)-platinum(II) (5a). The porphyrin
1c (70.6 mg, 34.0 mmol), trans-dichloro-bis(tri-n-butylphosphine)-
platinum(II) (10.3 mg, 15.4 mmol) and CuCl (1.0 mg, 10 mmol) were
dissolved in CH2Cl2/Et2NH (4.0 mL, 1 : 1 v/v).The reaction was
stirred at room temperature for 20 min and was monitored by TLC.
The solvent was removed in vacuo and the resulting red solid was
recrystallized (CH2Cl2–CH3OH). The red solid was washed with
CH3OH and collected with CH2Cl2. The solvent was evaporated
in vacuo and the red solid was recrystallized a second time to afford
the title compound 5a as a red solid in 73% yield (30.0 mg,
3
(s, 4H, H-meso), 7.93 (d, 4H, JH–H = 8.0 Hz, Ph), 7.90 (d,
4H,3JH–H = 8.0 Hz, Ph), 7.69 (d, 4H, 3JH–H = 8.0 Hz, Ph), 7.65
(d, 4H, 3JH–H = 8.0 Hz, Ph), 7.31 (d, 4H, 3JH–H = 8.0 Hz, Ph),
7.22 (br, 6H, Ph), 4.05–3.92 (br, 16H, CH2), 2.58 (s, 12H, CH3),
2.55 (s, 12H, CH3), 2.50–2.40 (br, 12H, CH2), 2.35–2.12 (br,
40H, CH2), 1.95–1.83 (br, 12H, CH2), 1.82-1.60 (br, 52H,
CH2), 1.60–1.46 (br, 40H, CH2),1.45–1.35 (br, 16H, CH2),
11.2 ꢀmmol). HR-MS (MALDI-TOF): m/z = 2670.4435
[M]+ 2670.4705 calcd for C158H220N8P2PtSi2Zn2. 31P NMR
c
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1.11 (t, 18H, 3JH–H
=
7.3 Hz, CH3), 1.02
solubilized in CH2Cl2 (10 mL) to be added over 1 h at room
temperature with a dropping funnel. The mixture was stirred
for an additional 1 h. After removal of the solvent in vacuo, the
resulting mixture was purified by silica gel chromatography
(20 : 60–30–60 CH2Cl2–pentane) with 0.5% Et3N to afford 7a
as a red solid in 20% yield (7.0 mg,ꢀ 1.7 mmol). HR-MS
(MALDI-TOF): m/z = 4232.3957 [M]+ 4232.3259 calcd for
3
(t, 36H, JH–H = 7.3 Hz, CH3),0.93 (t, 12H, JH–H = 7.3 Hz,
3
3
CH3), 0.92 (t, 12H, JH–H = 7.3 Hz, CH3).
Trans-[5-(4-ethynylphenyl)-15-[trans-bis(1,4-ethynylphenyl)-
bis(tri-n-butyl-phosphine)-platinum(II)]-3,7,13,17-tetramethyl-
2,8,12,18-tetrakis-(n-hexyl)-zinc(II)-porphyrin]-[5-(4-ethynyl-
phenyl)-15-[4-(trimethylsilyl)ethynylphenyl]-3,7,13,17-tetra-
ethyl-2,8,12,18-tetrakis-(n-hexyl)-zinc(II)-porphyrin]-bis(tri-
n-butylphosphine)-platinum(II) (8a). A mixture of porphyrin
3a (35.0 mg, 20.9 mmol), porphyrin 2b (31.5 mg, 18.9 mmol)
and CuI (2.0 mg, 10.5 mmol) was dissolved in CH2Cl2/Et2NH
(10 mL,1 : 1v/v). The mixture was stirred at room temperature
for 10 min. After removal of the solvent in vacuo, the resulting
mixture was recrystallized (CH2Cl2–CH3OH). The red solid was
washed with CH3OH and collected with CH2Cl2. The solvent
was evaporated in vacuo and the red solid was recrystallized a
second time to afford 10 as a red solid in 70% yield (43.5 mg,
C
246H348N12P4Pt2Si2Zn3. 31P NMR (161.92 MHz, CHCl3) d
(ppm): 4.39. 1H NMR (400 MHz, CDCl3) d (ppm): 10.20
3
(s, 6H, H-meso), 8.05 (d, 4H, JH–H = 8.0 Hz, Ph), 7.95–7.90
(m, 8H, Ph), 7.88 (d, 4H,3JH–H = 8.0 Hz, Ph), 7.71 (d, 8H,
3JH–H = 8.0 Hz, Ph), 4.04–3.92 (br, 24H, CH2), 2.59 (s, 12H,
CH3), 2.58 (s, 12H, CH3), 2.49 (s, 12H, CH3), 2.48–2.40
(br, 24H, CH2), 2.24–2.12 (br, 24H, CH2), 1.93–1.82 (br, 24H,
3
CH2), 1.81–1.71 (br, 24H, CH2), 1.68 (sextet, 24H, JH–H
=
7.3 Hz, CH2), 1.52–1.45 (br, 24H, CH2), 1.44–1.35 (br, 24H,
CH2), 1.12 (t, 36H, 3JH–H = 7.3 Hz, CH3), 0.92 (m, 36H, CH3),
0.41 (s, 18H, Si(CH3)3).
13.1 mmol). HR-MS (MALDI-TOF): m/z
= 3297.6804
[M]+ 3297.7972 calcd for C187H270N8P4Pt2SiZn2. 31P NMR
ꢀ
5,15-Bis[trans-(4-Ethynylphenyl)-[5,15-Bis(4-ethynylphenyl)-
3,7,13,17-tetra-methyl-2,8,12,18-tetrakis(n-hexyl)zinc(II)por-
phyrin]-bis(tri-n-butylphosphine)-platinum(II)]-3,7,13,17-tetra-
methyl-2,8,12,18-tetrahexyl-Zinc(II)porphyrin (7b). The porphyrin
7a (6.0 mg, 1.4 mmol) was dissolved in tetrahydrofuran
(2.0 mL). NBu4F (10.0 mL, 1.0 M in THF) was added and the
mixture was stirred at room temperature for 20 min. The solvent
was removed in vacuo. The residue was recrystallized
(CH2Cl2–CH3OH). The red solid was washed with CH3OH and
collected with CH2Cl2. The solvent was removed in vacuo and the
(161.92 MHz, CHCl3) d (ppm): 4.39, 4.26. 1H NMR (400 MHz,
3
CDCl3) d (ppm): 10.19 (s, 4H, H-meso), 7.92 (d, 4H, JH–H
8.0 Hz, Ph), 7.87 (d, 4H, JH–H = 8.0 Hz, Ph), 7.70 (d, 4H,
=
3
3JH–H = 8.0 Hz, Ph), 7.65 (d, 4H, JH–H = 8.0 Hz, Ph), 7.33
3
3
3
(m, 2H, JH–H = 8.0 Hz, Ph), 7.23 (m, 3H, JH–H = 8.0 Hz,
Ph), 3.98 (m, 16H, CH2), 2.57 (s, 6H, CH3), 2.55 (s, 6H, CH3),
2.49 (s, 6H, CH3), 2.47 (s, 6H, CH3), 2.46–2.42 (br, 12H, CH2),
2.33–2.25 (br, 24H, CH2), 2.23–2.13 (br, 16H, CH2), 1.94–1.84
(br, 12H, CH2), 1.80–1.71 (br, 28H, CH2), 1.68 (sextet 12H,
3JH–H = 7.3 Hz, CH2), 1.52-1.47 (br, 16H, CH2), 1.43–1.35
red solid was recrystallized
a second time to afford
3
(br, 16H, CH2), 1.11 (t, 18H, JH–H = 7.3 Hz, CH3), 1.02
3
(t, 18H, JH–H = 7.3 Hz, CH3), 0.93 (t, 12H, JH–H = 7.3 Hz,
CH3), 0.92 (t, 12H, 3JH–H = 7.3 Hz, CH3). 0.41 (s, 9H, Si(CH3)3).
the title compound 7a as a red solid in 78% yield (4.5 mg,
3
1.1 mmol). HR-MS (MALDI-TOF): m/z
= 4088.2138
[M]+ 4088.2468 calcd for C240H332N12P4Pt2Zn3. 31P NMR
ꢀ
(161.92 MHz, CHCl3) d (ppm): 4.39. 1H NMR (400 MHz,
Trans-[5-(4-ethynylphenyl)-15-[trans-bis(1,4-ethynylphenyl)-
bis(tri-n-butyl-phosphine)-platinum(II)]-3,7,13,17-tetramethyl-
2,8,12,18-tetrakis-(n-hexyl)-zinc(II)-porphyrin]-[5,15-bis(4-eth
ynylphenyl)-3,7,13,17-tetramethyl-2,8,12,18-tetrakis-(n-hexyl)-
zinc(II)-porphyrin]-bis(tri-n-butylphosphine)-platinum(II) (8b). The
porphyrin 8a (15.9 mg, 4.81 mmol) was dissolved in a mixture of
tetrahydrofuran and dichloromethane (4.0 mL, 1 : 1 v/v).
NBu4F (40.0 mL, 1.0 M in THF) was added and the mixture
was stirred at room temperature for 2 h. The solvent was
removed in vacuo. The resulting red solid was recrystallized
(CH2Cl2–CH3OH). The red solid was washed with CH3OH
and collected with CH2Cl2. The solvent was removed in vacuo
and the red solid was recrystallized a second time to afford
the title compound 8b as a red solid in 98% yield (15.2 mg,
3
CDCl3) d (ppm): 10.20 (s, 6H, H-meso), 8.08 (d, 4H, JH–H
=
8.0 Hz, Ph), 7.95–7.86 (m, 12H, Ph), 7.71 (d, 8H, 3JH–H = 8.0 Hz,
Ph), 4.03–3.83 (br, 24H, CH2), 3.34 (s, 2H, CH), 2.59 (s, 12H,
CH3), 2.58 (s, 12H, CH3), 2.49 (s, 12H, CH3), 2.48–2.42 (br, 24H,
CH2), 2.24–2.16 (br, 24H, CH2), 1.94–1.84 (br, 24H, CH2),
1.81–1.72 (br, 24H, CH2), 1.72–1.62 (br, 24H, CH2), 1.55–1.46
(br, 24H, CH2), 1.45–1.38 (m, 24H, CH2), 1.12
(t, 36H, 3JH–H = 7.3 Hz, CH3), 0.97–0.89 (m, 36H, CH3).
5,15-Bis[trans-(4-Ethynylphenyl)-[5-(4-ethynylphenyl)-15-[trans-
bis(1,4-ethynylphenyl)-bis(tri-n-butylphosphine)-platinum(II)]-
3,7,13,17-tetramethyl-2,8,12,18-tetrakis-(n-hexyl)-zinc(II)-por-
phyrin]bis(tri-n-butylphosphine)-platinum(II)]-3,7,13, 17-tetra-
methyl-2,8,12,18-tetrahexyl-Zinc(II)porphyrin (9). A mixture
of the porphyrin 7b (1.4 mg, 0.34 mmol), trans-phenylethynyl-
chlorobis(tri-n-butylphosphine)platinum(II) (1.0 mg, 1.4 mmol)
and CuCl (0.2 mg, 2 mmol) was dissolved in CH2Cl2/Et2NH
(1.0 mL, 1 : 1 v/v). The solution was stirred at room temperature
for 30 min. After removal of the solvent in vacuo, the residue was
recrystallized (CH2Cl2–CH3OH). The red solid was washed with
CH3OH and collected withCH2Cl2. The solvent was evaporated in
vacuo and the red solid was recrystallized a second time to afford 9
as a red solid in 53% yield (1.0 mg, 0.18 mmol). HR-MS
4.70 mmol). HR-MS (MALDI-TOF): m/z
= 3225.7667
[M]+ 3225.7576 calcd for C184H262N8P4Pt2Zn2. This inter-
mediate was not further characterized and was used directly in
the following coupling step.
ꢀ
5,15-Bis[trans-(4-Ethynylphenyl)-[5-(4-ethynylphenyl)-15-[4-
(trimethylsilyl)-ethynylphenyl]-3,7,13,17-tetramethyl-2,8,12,18-
tetrakis(n-hexyl)-zinc(II)-porphyrin]-bis-(tri-n-butylphosphine)-
platinum(II)]-3,7,13,17-tetramethyl-2,8,12,18-tetrahexyl-Zinc(II)-
porphyrin (7a). A mixture of porphyrin 3a (35.9 mg, 21.5 mmol),
and CuI (1.0 mg, 5.3 mmol) was dissolved in CH2Cl2/Et2NH
(10 mL, 1 : 1 v/v). The porphyrin 1b (8.1 mg, 8.4 mmol) was
(MALDI-TOF): m/z = 5487.1266 [M]+ 5486.9791 calcd for
304H448N12P8Pt4Zn3.
ꢀ
C
c
1306 New J. Chem., 2011, 35, 1302–1314
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T r a n s -bis[trans-[5,15-bis(4-ethynylphenyl)-3,7,13,17-tetra-
methyl-2,8,12,18-tetrakis(n-hexyl)zinc(II)porphyrin]-[5-(4-ethynyl-
phenyl)-15-[4-(trimethylsilyl)-ethynylphenyl]-3,7,13,17-tetra-
methyl-2,8,12,18-tetrakis(n-hexyl)-zinc(II)-porphyrin]-bis-(tri-
n-butylphosphine)-platinum(II)]-bis-(tri-n-butylphosphine)plati-
num(II) (10a). A mixture of porphyrin 3a (21.0 mg, 12.6 mmol),
porphyrin 5b (11.3 mg, 4.46 mmol) and CuCl (0.5 mg, 5.1 mmol)
was dissolved in CH2Cl2/Et2NH (5.0 mL, 1 : 1 v/v). The
solution was stirred at room temperature for 30 min. After
removal of the solvent in vacuo, the resulting mixture was
recrystallized (CH2Cl2–CH3OH). The red solid was washed
with CH3OH and collected with CH2Cl2. The solvent was
evaporated in vacuo and the red solid was recrystallized
a second time to afford 10a as a red solid in 98% yield
(25.5 mg, 4.40 mmol). HR-MS (MALDI-TOF): m/z =
and CuCl (0.5 mg, 5 mmol) was dissolved in CH2Cl2/Et2NH
(2.0 mL, 1 : 1 v/v). The solution was stirred at room tempera-
ture for 30 min. After removal of the solvent in vacuo, the
residue was recrystallized (CH2Cl2–CH3OH). The red solid
was washed with CH3OH and collected with CH2Cl2. The
solvent was evaporated in vacuo and the red solid was recrys-
tallized a second time to afford 11 as a red solid in 82% yield
(4.1 mg, 5.8 mmol). MS (MALDI-TOF): m/z = 7060.4221
[M]+ 7059.6427 calcd for C392H576N16P10Pt5Zn4 (average
ꢀ
mass). 31P NMR (161.92 MHz, CHCl3) d (ppm): 4.39, 4.27.
1H NMR (400 MHz, CDCl3) d (ppm): 10.21 (s, 4H, H-meso),
10.19 (s, 4H, H-meso), 7.96–7.87 (d, 12H, Ph), 7.71 (d, 16H,
3
3JH–H = 8.0 Hz, Ph), 7.65 (d. 4H, JH–H = 8.0 Hz, Ph), 8.0
(d. 4H, 3JH–H = 8.0 Hz, Ph),7.24 (d. 6H, 3JH–H = 8.0 Hz, Ph),
4.05-3.92 (br, 32H, CH2), 2.59 (s, 24H, CH3), 2.58 (s, 12H,
CH3), 2.55 (s, 12H, CH3), 2.49–2.41 (br, 36H, CH2), 2.25–2.14
(br, 32H, CH2), 1.95–1.82 (br, 36H, CH2), 1.81–1.63 (m, 116H,
CH2), 1.61–1.46 (m, 56H, CH2), 1.45-1.35 (br, 32H, CH2), 1.12
(t, 54H, 3JH–H = 7.3 Hz, CH3), 1.02 (t, 36H, 3JH–H = 7.3 Hz,
CH3), 0.98–0.89 (m, 48H, CH3).
5795.2374 [M]+ 5794.1812 calcd for C334H476N16P6Pt3Si2Zn4.
ꢀ
31P NMR (161.92 MHz, CHCl3) d (ppm): 4.41. 1H NMR
(400 MHz, CDCl3) d (ppm): 10.20 (s, 4H, H-meso), 10.19
3
(s, 4H, H-meso), 8.05 (d, 4H, JH–H = 8.0 Hz, Ph), 7.95–7.91
(m, 12H, Ph), 7.88 (d, 4H,3JH–H = 8.0 Hz, Ph), 7.71 (d, 12H,
3JH–H = 8.0 Hz, Ph), 4.05–3.91 (br, 32H, CH2), 2.59 (s, 24H,
CH3), 2.58 (s, 12H, CH3), 2.48 (s, 12H, CH3), 2.47–2.42 (br,
36H, CH2), 2.25–2.14 (br, 32H, CH2), 1.95–1.84 (br, 36H,
CH2), 1.82–1.64 (m, 68H, CH2), 1.56–1.46 (br, 32H, CH2),
1.46–1.35 (br, 32H, CH2), 1.12 (t, 54H, 3JH–H = 7.3 Hz, CH3),
0.98–0.90 (m, 48H, CH3), 0.41 (s, 18H, Si(CH3)3).
Instruments
1H NMR spectra were recorded on a Bruker DRX 300 MHz
AVANCE spectrometer at the ‘‘Plateforme d’Analyse Chimique
`
´
´
et de Synthese Moleculaire de l’Universite de Bourgogne (PACS-
MUB)’’ or on a Bruker AVANCE III 400 MHz spectrometer
(1H 400.13 MHz and 31P 161.92 MHz) using the solvent as a
chemical shift standard, except for the 31P NMR, where the
chemical shifts are relative to H3PO4 85% in D2O. All chemical
shifts (d) and coupling constants (J) are given in ppm and Hertz,
respectively. The spectra were measured from freshly prepared
samples in chloroform. 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. The UV-visible spectra were recorded on a
Varian Cary 1 spectrophotometer or on a Hewlett-Packard
diode array model 8452A. UV-visible spectra were recorded on
a Hewlett-Packard diode array model 8452A and the emission
spectra were obtained using a double monochromator Fluorolog
2 instrument from Spex. The emission lifetimes were measured
using a TimeMaster Model TM-3/2003 apparatus from PTI.
The source was nitrogen laser with high-resolution dye laser
(fwhm B 1600 ps) and the emission lifetimes were obtained from
deconvolution of decay curves monitored at three different
emission wavelengths. The uncertainties in the lifetimes were
about 10–50 ps based on multiple measurements.
Trans-bis[trans-bis[5,15-bis(4-ethynylphenyl)-3,7,13,17-tetra-
methyl-2,8,12,18-tetrakis(n-hexyl)zinc(II)porphyrin]-3,7,13,17-
tetramethyl-2,8,12,18-tetrakis(n-hexyl)-zinc(II)-porphyrin]-bis
(tri-n-butylphosphine)platinum(II)]-bis(tri-n-butylphosphine)-
platinum(II) (10b). The porphyrin 10a (6.0 mg, 1.0 mmol) was
dissolved in tetrahydrofuran (1.0 mL). NBu4F (1.0 M in THF)
was added and the mixture was stirred at room temperature for
30 min. The solvent was removed in vacuo. The residue was
recrystallized (CH2Cl2–CH3OH). The red solid was washed
with CH3OH and collected with CH2Cl2. The solvent was
removed in vacuo and the red solid was recrystallized a second
time to afford the title compound 10b as a red solid in 83% yield
(4.8 mg, 0.85 mmol). HR-MS (MALDI-TOF): m/z = 5650.2302
[M]+ 5650.1022 calcd for C328H460N16P6Pt3Zn4. 31P NMR
ꢀ
(161.92 MHz, CHCl3) d (ppm): 4.39. 1H NMR (400 MHz,
=
CDCl3) d (ppm): 10.20 (s, 8H, H-meso), 8.08 (d, 4H, 3JH–H
8.0 Hz, Ph), 7.96–7.87 (m, 16H, Ph), 7.71 (d, 12H, JH–H
3
=
8.0 Hz, Ph), 4.05–3.92 (br, 32H, CH2), 3.34 (s, 2H, CH), 2.58
(s, 36H, CH3), 2.49 (s, 12H, CH3), 2.47–2.41 (br, 36H, CH2),
2.25–2.14 (br, 32H, CH2), 1.95–1.82 (br, 36H, CH2), 1.81–1.63
(br, 68H, CH2), 1.52–1.46 (br, 32H, CH2), 1.45–1.35 (br, 32H,
CH2), 1.12 (t, 54H, 3JH–H = 7.3 Hz, CH3), 0.98–0.89 (m, 48H,
CH3).
Quantum yields
Trans-bis[trans-[5,15-bis(4-ethynylphenyl)-3,7,13,17-tetra-
methyl-2,8,12,18-tetrakis(n-hexyl)zinc(II)porphyrin]-[5-(4-
ethynylphenyl)-15-[trans-bis(1,4-ethynylphenyl)-bis(tri-n-butyl-
phosphine)-platinum(II)]-3,7,13,17-tetramethyl-2,8,12,18-tetrakis-
(n-hexyl)-zinc(II)porphyrin]-bis(tri-n-butylphosphine)platinum(II)]-
bis(tri-n-butylphosphine)platinum(II) (11). A mixture of the
porphyrin 10b (4.0 mg, 0.71 mmol), trans-phenylethynyl-
chloro-bis(tri-n-butylphosphine)platinum(II) (3.2 mg, 4.3 mmol)
The quantum yields measurements were performed in 2MeTHF
at 298 K using Zn(TPP) (TPP = tetraphenylporphyrin; F =
0.033)30 as a reference. The solutions for the samples and the
reference were prepared under inert atmosphere (in a glove box,
PO o 50 ppm). Solutions prepared for both the reference and
2
the samples were adjusted to obtain absorbencies in the range
of 0.02–0.05 where three different solutions for each measure-
ment were used. The absorbance was adjusted to be the same
c
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New J. Chem., 2011, 35, 1302–1314 1307

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as much as possible for the standard and the sample for each
measurement.
trimethylsilyl groups with TBAF/THF produced the corre-
sponding diethynyl porphyrin 1b in 94% yield (Scheme 2).
A general procedure to synthesize monomeric or oligomeric
compounds could involved e.g. a dehydrohalogenation reac-
tion between the trans-Pt(PBu3)2Cl2 and the appropriate
ethynylporphyrin in a dichloromethane/diethylamine mixture
(1 : 1 v/v), at room temperature in the presence of CuX (X =
Cl, I).31 The mechanism is analog to a Sonogashira coupling.32,33
It is worth noting that copper chloride can be preferred to
copper iodide13 as, in some cases, the yields of the coupling
reactions were higher and the formation of polar by-products
was decreased. This coupling strategy was first used to access
to the porphyrin dimer 5b as described in Scheme 2. Indeed,
reaction of the symmetrical diethynyl porphyrin 1b with trans-
dichlorobis(tri-n-butylphosphine)platinum(II) under N2 and in
the presence of CuI leads to the formation of the expected
porphyrin dimer 5b (as monitored by MALDI/TOF mass
spectrometry). Unfortunately, due to a low selectivity, the
presence of different porphyrin oligomers (trimers, tetramers,. . .)
was also observed by MALDI/TOF mass spectrometry (Fig. S1)
and TLC. Indeed, the main downfall of this first approach is
that the reaction is quite uncontrolled resulting in a complex
mixture of oligomers with different chain lengths (Fig. S1).
Laborious and lengthy chromatographic separations were
attempted affording only small quantities of the desired por-
phyrin dimer 5b. Therefore, this way was not further considered.
This latter result led us to investigate a new one-step
procedure to synthesize porphyrins 5a and 5b. Indeed, the
other possible route to obtain the porphyrin 5a and to avoid
further oligomerization, consists in the coupling reaction of
the unsymmetrical monoethynyl porphyrin 1c (prepared as
described in Scheme 3) with trans-dichlorobis(tri-n-butylpho-
sphine)platinum(II). This key intermediate was successfully
prepared by using only one equivalent of K2CO3 during
the deprotection step. The generation of the latter product
was monitored by MALDI/TOF mass spectrometry until
Results and discussion
Syntheses and characterization
The structures of the Pt(bisethynyl)/Zn(porphyrin) oligomers
are shown in Chart 2 and 3. The symmetrical porphyrin
precursor 1a was prepared as described in the literature
(Scheme 1).28,29 The subsequent elimination of the two
Scheme 1
Scheme 2
c
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1308 New J. Chem., 2011, 35, 1302–1314

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maximization of the experimental conditions. The unreacted
symmetrical porphyrin precursor 1a did not affect any further
coupling reaction and was recovered afterwards. The synthetic
procedure (Scheme 3) was successfully performed by reacting
trans-dichlorobis(tri-n-butylphosphine)platinum(II) with 1c
under the same coupling reaction conditions as indicated
above in Scheme 2. Porphyrin dimer 5a was obtained in a
quantitative yield (Scheme 4). The subsequent deprotection of
the trimethyl silyl group by K2CO3 easily led to 5b in almost
quantitative yield.
MALDI/TOF mass spectrometry. The subsequent reaction of
porphyrin dimer 8a with trans-Pt(PBu3)2Cl2 afforded the
desired tetramer 11 in 30% yield.
The preparation of the porphyrin tetramer 11 was further
improved through the reaction of the symmetrical dimer 5a
with porphyrin 3a using the same coupling conditions as
employed for 6 (Scheme 4) with, in this case, CuI being
replaced by CuCl. It is worth noting that the synthetic strategy
applied to the synthesis of oligomers containing an even
number of porphyrin units (e.g. porphyrin dimers, tetramers)
could also be applied to the preparation of oligomers containing
an odd number of porphyrin units (e.g. porphyrin trimers) as
described in Scheme 5. This was successfully performed by
reacting the diethynyl porphyrin 1b with porphyrin 3a under
the same coupling conditions as above (Scheme 5) leading to
7a and 9 in very good yields.
The synthetic pathway leading to the porphyrin tetramer is
shown in Scheme 3. The key unsymmetrical monoethynyl
porphyrin 1c was used for this synthesis. The synthetic route
to porphyrin tetramer 11 requires first the preparation of the
monoethynyl dimer 8a as successfully performed. Porphyrins
2a and 3a were easily prepared in high yields by coupling, in
the presence of CuI, porphyrin 1c with trans-phenylethynyl-
chlorobis(tri-n-butylphosphine)platinum(II) and trans-bis(tri-
n-butylphosphine)-dichloroplatinum(II), respectively. In both
cases, these coupling reactions were monitored by TLC and
The main advantage of this synthetic method is the step-
by-step control of the oligomers length coupled by a high
solubility due, mainly, to the presence of four long-chain
n-hexyl substituents at the b-positions of the porphyrin
Scheme 3
c
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Scheme 4
macrocycles. The reported products in this work exhibit good
solubility in common solvent.
to form aggregates at high concentrations which modify the
spectral signatures and excited state dynamics.34 But upon
adding bulky groups, such as dendrons for examples, this
aggregation phenomenon has not been observed.35 We also
observed the same phenomenon (i.e. non-aggregation in
oligomers, polymers and model compounds with other bulky
substituents),35,36 even for species containing zinc(II) porphyrin
units well known for forming J-and H-aggregates.10,11 In this
work, the spectra and dynamics were found concentration
independent in the range investigated (typically 10ꢁ6 to 10ꢁ5 M).
The examination of the absorption spectra was first made at
room temperature (Fig. 1 and Table 1). The spectra are typical
from other porphyrin compounds. The existence of exciton
couplings denoted as a shoulder on the high energy side of
the Soret band for 6, 9 and 11 at room temperature but not for
All the compounds were fully characterized by spectro-
scopic methods. The NMR (1H, and 31P), and mass spectral
data shown in the Experimental Section are consistent with
their chemical structures.
Absorption and emission spectroscopy
In order to analyze the excited state behavior of the oligomers,
the representative model complexes 4, 6, and 11 were investigated
by means of absorption and emission spectroscopy. During
the course of this investigation, the possibility of aggregation
was also considered. Indeed, compounds of the type trans-
ArCRC–PtL2–CRCAr (even where L = PBu3) are known
c
1310 New J. Chem., 2011, 35, 1302–1314
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Scheme 5
Table 1 Absorption spectral data meaured in THF at 298 K
l [nm](e ꢄ 10ꢁ3 Mꢁ1 cmꢁ1
)
Soret band
Q bands
Compound
Monomers
1b
2b
3b
4
Dimers
5b
6
8b
416 (374)
418 (520)
418 (249)
420 (172)
545 (16)
544 (12)
545 (10)
546 (9)
579 (4)
578 (5)
579 (2)
578 (3)
Fig. 1 UV-vis spectra of 4 (dotted line) and 11 (straight line) in
419 (519)
421 (498)
420 (427)
545 (20)
545 (28)
544 (17)
578 (6)
578 (7)
579 (7)
toluene at 298 K stressing the exciton coupling.
Trimers
7b
9
Tetramers
10b
11
4 when using 2MeTHF as the solvent (Table 2). In order to
confirm the presence of a spectral feature, the 77 K spectra of
4, 6 and 11 were also measured (Fig. 2). At this temperature,
the shoulder is well resolved into a peak allowing one to
measure accurately this constant. Again, this high energy peak
is absent in 4 supporting the exciton coupling assignment. A
coupling constant of 400 cmꢁ1 is observed for 11, which is
weak, but not negligible. This observation appears unusual
when one considers the size of the Pt-containing spacer (Hꢂ ꢂ ꢂH
421 (254)
422 (243)
546 (15)
545 (12)
579 (5)
579 (3)
421 (250)
423 (532)
544 (16)
544 (27)
577 (5)
578 (6)
Table 2 Exciton coupling constants (cmꢁ1
)
Species
Constant (298 K)
Constant (77 K)
distance in trans-ArCRC–PtL2–CRCAr (Ar
= 2,5-
Monomer 4
Dimer 6
Trimer 9
0
0
not measured
C6Me2H3- and 3,5-C6Me2H3) is B18 A.37 The coupling con-
stants increase as the number of units in the chain increases
from 0 to 280 cmꢁ1 at 298 K or 405 cmꢁ1 at 77 K (Table 2).
This observation, i.e. the presence of a long distance inter-
action is also consistent with the recent evidence for efficient
singlet energy transfer in dyads built upon this rigid conju-
gated spacer of the type M(P)–C6H4CRC–PtL2–CR
CC6H4–M0(P) where M and M0 are Pd (donor) or zinc
(acceptor), L is PEt3 and P is hexamethyldiethylporphyrin.24
The photophysical parameters, fluorescence lifetimes (tF)
and quantum yields (FF) are placed in Table 3. The FF data
for 4, 6 and 11 are constant, which is consistent with the lack
170
225
280
325
405
Tetramer 11
of conjugation along the oligomers; the chromophores act
independently. Settle variations cannot be detected because of
the uncertainties of the measurements (ꢃ10%). The possibility
of exciton phenomenon38,39 in the excited states was tested.
The exciton phenomenon may manifest itself by exhibiting
tF being fluorescence wavelength dependent.38 This possibility
was checked (Table 3). All decays turned out to be single
exponential and no strong variation of the tF with the
c
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Fig. 2 Absorption (solid), excitation (dotted . . .), and emission (broken - - -) of 4 (n = 1), 6 (n = 2) and 11 (n = 4) measured in 2MeTHF: (A) At
298 K where lem = 505 nm and lex = 640 nm; (B) At 77 K where lem = 535 nm and lex = 635 nm.
fluorescence wavelength was observed. This observation is
totally consistent with the long distance between the chromo-
phores (B18 A). The other trend is the settle decrease in tF
going from the monomer 4 to dimer 6 and tetramer 11.
Because the change is small, measurements were also repeated
at 77 K. The tF data exhibit an increase upon cooling, which is
Table 3 Fluorescence lifetime and quantum yields
tF(ns)
298 K
77 K
lmon = 575 nmb
lmon = 585 nmb
lmon = 595 nmb
lmon = 575 nmb
w2
tF
w2
tF
w2
tF
w2
tF
a
FF
tFav
4
6
11
0.021
0.021
0.021
0.99
0.71
1.15
1.34 ꢃ 0.02
1.31 ꢃ 0.01
1.30 ꢃ 0.01
1.02
1.32
0.91
1.35 ꢃ 0.02
1.33 ꢃ 0.01
1.30 ꢃ 0.02
1.08
0.79
0.77
1.40 ꢃ 0.02
1.39 ꢃ 0.01
1.34 ꢃ 0.01
1.36 ꢃ 0.02
1.35 ꢃ 0.01
1.31 ꢃ 0.01
0.97
1.14
0.92
1.51 ꢃ 0.08
1.49 ꢃ 0.02
1.45 ꢃ 0.04
a
The quantum yields were measured using lexc = 505 nm and the uncertainties in the measured values were ꢃ 10% based on multiple
b
measurements. The emission wavelength at which the fluorescence lifetime was measured. The uncertainties are those extracted from the
c
deconvolution data. The wavelength corresponding to the first maximum fluorescence emission peak.
c
1312 New J. Chem., 2011, 35, 1302–1314
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consistent with the increase in medium rigidity. The trend
(a decrease in tF with the oligomer length) remains but this
variation is very small. The proposed interpretation for this
decrease in tF is a slight increase in internal conversion rate
constant (kic) as the oligomer gets longer. This slight increase
(rather than a large one) is consistent with the ‘‘rigid stick’’
nature of the oligomers.
(MENRT), CNRS (UMR 5260), and Re
´
gion Bourgogne are
also gratefully acknowledged for support of training periods
for GL in Dijon.
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Conclusion
We reported a methodology that gives easy access to mono-
dispersed oligomers. The key features is that (1) one prepares
end groups such as the trans-C6H5CRCPt(PBu3)2Cl unit
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in lifetimes suggest that kic must increase slightly as the
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a
Acknowledgements
This research was supported by the Natural Sciences and
Engineering Research Council of Canada (NSERC), le Fonds
Que
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be
´
cois de la Recherche sur la Nature et les Technologies
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