Organometallic oligomers based on bis(arylacetylide)bis(P-chirogenic phosphine)platinum(II) complexes: Synthesis and photonic properties

Article abstract of DOI:10.1021/ic301829x

A series of P-chirogenic oligomers of the type (- C? - /C - aryl - C? - /C - PtL₂ -)_n [L = (R)- and (S)-P(Ph)(iPr)(C₁₇H₃₅); aryl = 1,4-benzene, 2,1,3-benzothiadiazole] along the corresponding achiral analogues (L = PBu ₃) and model complexes PhC? - /CPtL₂C? - /CPh were prepared from the ephedrine strategy and were fully characterized [ ¹H, ³¹P NMR; IR; small-angle X-ray scattering (SAXS); gel permeation chromatography (GPC); thermal gravimetric analysis (TGA); circular dichroism, UV-vis, and luminescence spectroscopy; photophysics, and degree of anisotropy measurements]. From the CD measurements, the chiral environment of the phosphine ligands is modestly felt by the aryl moieties. Concurrently, the TGA shows that the P(C₁₇H₃₅)(Ph)(i-Pr)-containing materials are more stable than those containing the shorter chain ligand PBu₃, and exhibits red-shifted absorption and emission bands compared to those including the PBu₃ ligands. The presence of the long chain on the phosphorus atoms does not greatly alter the photophysical parameters, notably the emission lifetimes, and fast triplet energy transfer terminal* → central unit has been deduced from the absence of luminescence arising from the terminal units.

Full text of DOI:10.1021/ic301829x

Article
pubs.acs.org/IC
Organometallic Oligomers Based on Bis(arylacetylide)bis(P-
chirogenic phosphine)platinum(II) Complexes: Synthesis and
Photonic Properties
Antony Lapprand,† Naïma Khiri,‡ Daniel Fortin,† Sylvain Juge,*,‡ and Pierre D. Harvey*,†,‡
́
†Dep
́
artement de Chimie, Universite
ulaire de l’Universite
* Supporting Information
́
de Sherbrooke, 2500 Boul. Universite,
́
Sherbrooke, Queb
́
ec, Canada J1K 2R1
de Bourgogne, Dijon, France
‡Institut de Chimie Molec
́
́
de Bourgogne (ICMUB, StereochIM), Universite
́
S
ABSTRACT: A series of P-chirogenic oligomers of the type
(CCarylCCPtL2)n [L = (R)- and (S)-
P(Ph)(iPr)(C17H35); aryl = 1,4-benzene, 2,1,3-benzothiadia-
zole] along the corresponding achiral analogues (L = PBu3)
and model complexes PhCCPtL2CCPh were prepared
from the ephedrine strategy and were fully characterized [1H,
31P NMR; IR; small-angle X-ray scattering (SAXS); gel
permeation chromatography (GPC); thermal gravimetric
analysis (TGA); circular dichroism, UV−vis, and luminescence
spectroscopy; photophysics, and degree of anisotropy
measurements]. From the CD measurements, the chiral
environment of the phosphine ligands is modestly felt by the
aryl moieties. Concurrently, the TGA shows that the P(C17H35)(Ph)(i-Pr)-containing materials are more stable than those
containing the shorter chain ligand PBu3, and exhibits red-shifted absorption and emission bands compared to those including
the PBu3 ligands. The presence of the long chain on the phosphorus atoms does not greatly alter the photophysical parameters,
notably the emission lifetimes, and fast triplet energy transfer terminal* → central unit has been deduced from the absence of
luminescence arising from the terminal units.
chiral phosphines expectedly found applications in not only
enantioselective homogeneous catalysis12 but also cluster
chemistry.13 We now wish to report the synthesis of both
enantiomers of the P-chirogenic heptadecylphenyl-i-propylphos-
phine 6 along with the organometallic conjugated polymers
(CCarylCCPt(P(Ph)(i-Pr)(C17H35))2)n
(aryl = 1,4-benzene, 2,1,3-benzothiadiazole ((S)- only); Chart
1). The use of a long alkyl chain aims at verifying whether the
INTRODUCTION
■
Research on chiral polymers and macromolecules for electronic
and optical properties has been the subject of intense research
over the past several decades.1 For organic polymers, research on
photonic properties and applications, including polarized light
sensitive photovoltaic cells,2 polarized reflection devices,3
polarized electroluminescence, and light emitting diodes,4 has
also been performed. The area of coordination and organo-
metallic polymers, the design of P-containing 1-D chiral
materials, is still in its infancy. To the best of our knowledge,
just several chiral organometallic polymers have been reported so
far. These can be separated into two categories; those whose
chirality is transported by the skeleton chain,5 notably among
others, using binapthyl, and those that are P-chirogenic.6
Chart 1
Recently, our group reported a series of conjugated organo-
metallic polymers bearing the trans-bis(ethynyl)bis(phosphine)
unit,7 and applications in the design of photonic devices such as
photovoltaic cells8 and light emitting diodes9 have been made.
Moreover, the rapid electronic communication across the
polymeric chains, investigated by means of energy (ns) and
electron transfers (fs time scale), has also been demonstrated by
us.10 To the best of our knowledge, no P-chirogenic conjugated
organometallic polymer has been designed so far. One of us
reported a series of articles demonstrating how to apply the
ephedrine technology11 to build P-chirogenic ligands. These
chiral environment can be transmitted onto the π-systems of the
aromatics, hence potentially altering their photonic properties.
EXPERIMENTAL SECTION
Materials and General Procedure. All reactions were carried out
under Ar(g) atmosphere in dried glassware with magnetic stirring.
■
Received: August 27, 2012
© XXXX American Chemical Society
A
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Inorganic Chemistry
Article
Solvents were dried prior to use. Tetrahydrofuran (THF) and toluene
were distilled from sodium/benzophenone and stored under Ar(g).
Dichloromethane (CH2Cl2) was distilled from CaH2. Hexane and
propan-2-ol for HPLC were of chromatographic grade and used without
further purification. Isopropyllithium (0.7 M in pentane), methyllithium
(1.6 M in Et2O), n-butyllithium (2.5 M in hexane), 1-bromo-hexadecane
(C16H33Br), 1,4-diazabicyclo[2.2.2]octane (DABCO), BH3·SMe2,
tributylphosphine, K2[PtCl4], [PdCl(η3-C3H5)]2, trimethylsilylacety-
lene (C5H10Si), phenylacetylene, and copper iodide (CuI) were
purchased from commercial source and used as received. (+) and
(−)-Ephedrine were purchased from commercial source and dried by
azeotropic shift of toluene on rotary evaporator. The toluene/HCl
solution was obtained by bubbling HCl gas, and the resulting solution
was titrated before use. 4,7-Bis(ethynyl)-2,1,3-benzothiadiazole was
prepared according to the literature.14 Reactions were monitored by
thin-layer chromatography (TLC) using 0.25-mm precoated silica gel
plates. Visualization was accomplished with UV light and/or appropriate
staining reagents. Flash chromatography was performed with the
indicated solvents using silica gel 60 (particle size 35−70 μm) or
aluminum oxide 90 standardized. The (2R,4S,5R)-(+)-3,4-dimethyl-2,5-
diphenyl-1,3,2-oxazaphospholidine-2-borane 2 and its enantiomer
(2S,4R,5S)-(−)-2 was prepared from appropriate (−)- or (+)-ephe-
drine, as previously described.11 The (Rp)-(+)-N-methyl-N-
[(1S,2R)(1-hydroxy-2-methyl-1-phenyl-2-propyl)]amino-i-propyl-phe-
nylphosphine borane 3 and (R)-(−)- and (S)-(+)-methylphenyl-i-
propylphosphine borane 4 were prepared from the (−)- or
(+)-ephedrine 1, respectively, according to the published procedure.11a
The complexes trans-dichloro-bis(tris-n-butylphosphine)platinum(II)
8,15 trans-bis(4-ethynylbenzene)bis(tris-n-butylphosphine) platinum-
(II) 9,16,17 and (+)-di-μ-chloro-bis{2[1-(dimethylamino)ethyl]phenyl-
C,N}dipalladium,18 and polymers poly(trans-(1,4-diethynylbenzene)-
bis(tris-n-butylphosphine)platinum(II)) 1119,20 and poly[trans-(bis-
4,7-ethynyl-2,1,3-benzothiadiazole)bis(tri-n-butylphosphine)platinum-
(II)] 14,21 were prepared according to reported procedures.
(R)-(−)-Heptadecylphenyl-i-propylphosphine Borane 5. This
compound is derived from (−)-ephedrine. In a two necked-flask
equipped with a magnetic stirrer and an argon inlet, a solution of 2.5 g of
(R)-(+)-methylphenyl-i-propylphosphine borane 4 (14.0 mmol) in
THF (10 mL) is added. The mixture is cooled to 0 °C, and 11.2 mL (2.5
M in hexane, 28.1 mmol) of n-butyllithium is slowly added with a syringe
while stirring. After the formation of a white precipitate, the mixture is
stirred for 1 h at 0 °C. 1-Bromo-hexadecane (4.43 g, 14.5 mmol) is
dissolved with a minimum of dry THF (5 mL) before use and added
slowly. The resulting mixture was progressively warmed to room
temperature and stirred for 2 h. After hydrolysis, the aqueous layer is
extracted twice with dichloromethane. The organic layers were dried
over anhydrous MgSO4, and the solvent was removed. The residue was
purified by column chromatography on silica gel using a mixture of
petroleum ether/CH2Cl2 8:2 as eluent. Yield 56%. White solid; mp ≤ 50
°C. [α]D25 = −3.2 (c = 1.0, CHCl3) for 96% ee. Rf = 0.51 (petroleum
ether/CH2Cl2, 8:2). 1H NMR (300 MHz, CDCl3): δ 7.53−7.47 (m, 2H,
CHarom), 7.32−7.23 (m, 3H, CHarom), 1.92 (m, 1H, CH, i-Pr), 1.67 (m,
2H, CH2), 1.48 (m, 2H, CH2), 1.03 (br s, 31H, CH3 and C17H35), 0.93
(dd, 3H, J = 14.4, 7.3 Hz, CH3, i-Pr), 0.80 (t, 3H, J = 6.2 Hz, CH3,
C17H35). 13C NMR (75 MHz, CDCl3): δ 132.51 (d, J = 8.0 Hz, CHarom),
131.1 (d, J = 2.3 Hz, CHarom), 128.6 (d, J = 9.2 Hz, CHarom), 127.5 (d, J =
49.7 Hz, Carom), 31.91 (s, CH2), 31.3 (d, J = 12.7 Hz, CH2), 29.6 (br d, J =
2.7 Hz, CH2), 29.5 (d, J = 3.6 Hz, CH2), 29.3 (d, J = 4.0 Hz, CH2), 29.0
(s, CH2), 25.1 (d, J = 35.5 Hz, CH), 23.0 (s, CH2), 22.8 (s, CH2), 22.7 (s,
CH2), 22.6 (s, CH2), 16.7 (s, CH3), 14.0 (s, CH3). 31P NMR (121 MHz,
CDCl3): δ +24.9 (d, J = 69.2 Hz). ESI-MS: m/z (%) = 427.4 (100) [M +
Na]+.
acetate 9:1 as eluent. After removal of the solvent under vacuum/argon,
the free phosphine was obtained in 98% yield. White solid. H NMR
1
(300 MHz, CDCl3): δ 7.44−7.38 (m, 2H, CHarom), 7.25−7.19 (m, 2H,
CHarom), 7.11 (m, 1H, CHarom), 2.84 (m, 6H, CH and CH2), 1.83−1.55
(m, 4H, CH2), 1.04 (br s, 26H, CH3 and C17H35), 0.90 (dd, 3H, J = 14.7,
7.8 Hz, CH3, i-Pr), 0.78 (t, 3H, J = 7.9 Hz, CH3, C17H35). 13C NMR (75
MHz, CDCl3): δ 137.6 (d, J = 16.2 Hz, Carom), 133.2 (d, J = 18.8 Hz,
CHarom), 128.6 (br.s, CHarom), 127.9 (d, J = 7.0 Hz, CHarom), 31.8 (s,
CH2), 31.3 (d, J = 19.6 Hz, CH2), 29.6 (br.s, CH2), 29.5 (d, J = 7.5 Hz,
CH2), 29.2 (d, J = 6.0 Hz, CH2), 27.1 (d, J = 8.3 Hz, CH), 26.1 (d, J =
14.3 Hz, CH2), 25.1 (d, J = 12.9 Hz, CH2), 22.6 (s, CH2), 19.5 (s, CH3),
19.3 (d, J = 2.3 Hz, CH3), 14.0 (s, CH3). 31P NMR (121 MHz, CDCl3): δ
−7.0. The enantiomeric excess of 6 (92% ee) was determined by
comparison with a racemic sample, by 31P NMR in the presence of
(+)-di-μ-chlorobis{2[1-(dimethylamino)ethyl]phenyl-C,N}-
dipalladium.18c 31P NMR(121 MHz, CDCl3): δ + 43.0 [(R)-
enantiomer].
(S)-Heptadecylphenyl-i-propylphosphine (S)-6. (Yield 98%.)
This enantiomer was prepared using a similar procedure as for (R)-6, but
starting from (S)-methylphenyl-i-propylphosphine borane 5. The
characterization data are identical to those for (R)-6. 31P NMR (121
MHz, CDCl3): δ +41.7 [(S)-enantiomer)].
Synthesis of the Complexes 7 [(S)-7 or (R)-7]. In a first flask, a
solution of HCl 4 M (100 mL) in distilled ethanol (200 mL) was
degassed with argon for 20 min, before use. In a second flask, equipped
with a magnetic stirrer, an argon inlet, and a condensor, 1.0 g of
phosphine 6 (2.5 mmol) and 0.40 g of K2[PtCl4] (1.3 mmol) were
introduced. The alcoholic HCl solution was then added using a cannula.
The mixture was heated under reflux for 4 h, cooled at −78 °C to afford a
yellow solid which was collected in the same temperature by filtration,
washed with ethanol, and dried under vacuum. The resulting residue was
filtered through a chromatography column on silica gel using hexane/
diethyl ether, 9:1. A yellow band was obtained first, containing trans-
{[(i-Pr)(C17H35)(Ph)P]2PtCl2} (7-trans); eluting further with diethyl
ether, an colorless band was collected, which was reduced to dryness to
provide cis-[((i-Pr)(C17H35)(Ph)P)2PtCl2] (7-cis). Yield 54% (ratio 7-
trans/7-cis, 6:4).
t r a n s - D i c h l o r o b i s [ ( R ) - h e p t a d e c y l p h e n y l - i -
propylphosphine]platinum(II) 7-trans. Yield 60%. Bright yellow
solid; mp = 213-215 °C. [α]D25 = −15.8 (c = 1.0, CHCl3) (derived from
1
(−)-ephedrine). Rf = 0.80 (hexane/diethyl ether, 9:1). H NMR (300
MHz, CDCl3): δ 7.65 (m, 4H, CHarom), 7.34 (m, 6H, CHarom), 2.76 (m,
2H, CH, i-Pr), 2.15 (m, 4H, CH2), 1.72 (m, 4H, CH2), 1.39 (m, 6H,
CH2), 1.18 (br.s, 62H, CH3 and C17H35), 0.81 (t, 6H, J = 6.0 Hz, CH3,
C17H35). 13C NMR (75 MHz, CDCl3): δ 133.6 (t, J = 4.0 Hz, CHarom),
130.1 (s, CHarom), 127.6 (t, J = 4.9 Hz, CHarom), 31.9 (s, CH2), 31.4 (t, J =
7.5 Hz, CH2), 30.9 (s, CH), 29.7 (br.s, CH2), 29.6 (s, CH2), 29.5 (s,
CH2), 29.3 (s, CH2), 29.2 (s, CH2), 24.5 (s, CH2), 22.7 (s, CH2), 22.0 (t,
J = 17.3 Hz, CH), 21.0 (t, J = 15.8 Hz, CH2), 18.3 (s, CH2), 17.4 (s,
CH3), 14.1 (s, CH3). 31P NMR (121 MHz, CDCl3): δ +20.0 (s, JPt−P
=
2502 Hz). ESI-MS: m/z (%) = 1068.6 (100) [M + Na]+. HRMS (ESI-
Q-TOF) Calcd for C52H94ClP2Pt [M − Cl]+: 1011.6168. Found:
1011.6181. Anal. Calcd for C52H94P2PtCl2 (1047.25): C 59.64, H 9.05.
Found: C 59.98, H 9.31.
cis-Dichlorobis[(R)-heptadecylphenyl-i-propylphosphine]-
25
platinum(II) 7-cis. Yield 40%. White solid; mp = 82−84 °C. [α]D
=
−5.7 (c = 1.0, CHCl3) (prepared from (R)-6). Rf = 0.10 (hexane/diethyl
ether, 9:1). H NMR (300 MHz, CDCl3): δ 7.23 (t, 2H, J = 8.0 Hz,
1
CHarom), 7.05 (t, 4H, J = 7.6 Hz, CHarom), 6.88 (t, 4H, J = 9 Hz, CHarom),
3.28 (m, 2H, CH, i-Pr), 2.17−1.63 (m, 8H, CH2), 1.47−1.14 (br.s, 62H,
CH3 and C17H35), 0.81 (t, 6H, J = 6.0 Hz, CH3, C17H35), 0.48 (dd, 6H, J
= 13.6, 6.2 Hz, CH3, i-Pr). 13C NMR (75 MHz, CDCl3): δ 131.4 (t, J =
4.0 Hz, CHarom), 130.4 (s, CHarom), 127.8 (t, J = 4.5 Hz, CHarom), 127.1
(d, J = 55.0 Hz, Carom), 31.9 (s, CH2), 31.4 (t, J = 8.3 Hz, CH2), 29.7 (br s,
CH2), 29.6 (s, CH2), 29.5 (s, CH2), 29.3 (s, CH2), 29.2 (s, CH2), 25.2 (s,
CH2), 22.7 (s, CH2), 19.9 (s, CH3), 16.3 (s, CH3), 14.1 (s, CH3). 31P
NMR (121 MHz, CDCl3): δ +9.7 (s, JPt−P = 3610 Hz). ESI-MS: m/z
(%) = 1068.6 (100) [M + Na]+. HRMS (ESI-Q-TOF) Calcd for
C52H94ClP2Pt [M − Cl]+: 1011.6168. Found: 1011.6189. Anal. Calcd
for C52H94P2PtCl2 (1047.25): C 59.64, H 9.05. Found: C 59.62, H 9.36.
(R)-Heptadecylphenyl-i-propylphosphine 6. This compound is
derived from (−)-ephedrine. In a 50 mL two-necked flask equipped with
a magnetic stirrer and an argon inlet, 0.40 g of phosphine borane 5 (1.0
mmol) and 0.56 g of DABCO (5.0 mmol) were dissolved in 10 mL of
toluene. The reaction mixture was heated at 50 °C for 12 h. After
cooling, the crude product was rapidly transferred via a cannula into a
column previously evacuated and filled with argon containing neutral
alumina. The reaction solution was filtered using degassed toluene/ethyl
B
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Dichlorobis[(S)-heptadecylphenyl-i-propylphosphine]-
platinum(II) 7-cis and -trans. These enantiomers were prepared using
a similar procedure as for (R)-7, but starting from (S)-methylphenyl-i-
propylphosphine 6. Their analytical data are identical to the previously
described for (R)-7-cis and (R)-7-trans isomers.
MHz, CDCl3): δ 7.83−7.52 (br, 4H), 7.37 (m, 6H), 6.51 (br, 4H),
3.14−2.78 (m, 2H), 2.64−2.25 (m, 4H), 1.82 (br, 4H), 1.41 (br, 4H),
1.25−1.19 (m, 52H), 1.07 (m, 12H), 0.85 (t, J = 6.5 Hz, 6H). 31P NMR
(162 MHz, CDCl3): δ +20.9 (JP−Pt = 2402 Hz, terminal), +19.1 (JP−Pt
=
2446 Hz). IR: ν(CC) = 2112 cm−1. MS (MALDI TOF): >10 000. Anal.
Calcd for PtC62H98P2: C 67.67, H 8.98. Found: C 67.70, H 8.79. GPC
(polystyrene standards): Mn = 17 700, Mw = 30 300, DPI = 1.71.
Poly[trans-bis(4,7-ethynyl-2,1,3-benzothiadiazole)bis((S)-
heptadecylphenyl-i-propyl phosphine)platinum(II)] (S)-13.
Poly[trans-dichloro-bis(tri-n-butylphosphine)platinum(II)]15
8. For comparison purposes, the characterization data are as follows:
1
yield 68%. H NMR (400 MHz, CDCl3): δ 1.85 (m, 12H), 1.57 (m,
12H), 1.44 (m, 12H), 0.93 (t, J = 7.2 Hz, 18H). 31P NMR (162 MHz,
CDCl3): δ +5.5 (s). m/z (EI): 670 (M+).
1
Yield 78%. H NMR (400 MHz, CDCl3) δ 7.90 (s, 2H), 7.84−7.57
Synthesis of the trans-Bis(ethynylphenyl)bis(phosphine)-
platinum(II) Complexes. Typical Procedure. After three cycles of
vacuum/argon in a round-bottom flask equipped with a magnetic stirrer,
a dichloromethane/diisopropylamine (1:1) mixture (20 mL) was added
by syringe to CuI, trans-PtCl2L2, and an excess of phenylacetylene. After
stirring for 8 h at room temperature under argon, the solvent was
removed, and the residue was purified by column chromatography on
silica. The final product is yellow, which tends to crystallize. A
dichloromethane−hexane mixture of 3:7 and 1:4 was used as eluent
solution for the chiral complex and the achiral complex, respectively.
trans-Bis(1,4-ethynylbenzene)bis(trin-butylphosphine)-
platinum(II)16,17 9. Yield 60%. 1H NMR (400 MHz, CDCl3): δ 7.26
(dd, J = 8.3, 1.4 Hz, 4H), 7.22−7.17 (m, 4H), 7.13−7.07 (m, 2H), 2.20−
2.07 (m, 12H), 1.66−1.56 (m, 12H), 1.44 (dq, J = 14.5, 7.3 Hz, 12H),
(m, 4H), 7.38 (s, 6H), 3.20 (d, J = 60.6 Hz, 2H), 2.86−2.37 (m, 4H),
1.82 (d, J = 45.2 Hz, 4H), 1.47−1.36 (m, 4H), 1.26−1.22 (m, 52H),
1.22−1.19 (br, 12H), 0.89−0.85 (m, 6H). 31P NMR (162 MHz,
CDCl3): δ +24.4 (JP−Pt = 2491 Hz, terminal), 21.9 (JP−Pt = 2480 Hz). IR:
ν(CC) = 2094 cm−1. Anal. Calcd for PtC62H96N2P2S: C 64.28, H 8.35, N
2.42, S 2.77. Found: C 64.30, H 7.98, N 2.60, S 2.58. GPC (polystyrene
standards): Mn = 6050, Mw = 9500, DPI = 1.57.
Poly[trans-bis-(7-ethynyl-2,1,3-benzothiadiazole)bis(trin-
butylphosphine)platinum(II)]21 14. Yield 78%. 1H NMR (400 MHz,
CDCl3): δ 7.36−7.28 (m, 2H), 2.31 (br, 12H), 1.66 (br, 12H), 1.47−
1.40 (br, 12H), 0.93−0.86 (br, 18H). 31P NMR (162 MHz, CDCl3): δ
+8.1 (JP−Pt = 2360 Hz, terminal), 4.29 (JP−Pt = 2330 Hz). IR: ν(CC)
=
2090 cm−1. Anal. Calcd for PtC34H56N2P2S: C 52.23, H 7.22, N 3.58, S
4.10. Found: C 52.20, H 7.19, N 3.30, S 3.88. GPC (polystyrene
standards): Mn = 10 800, Mw = 12 900, DPI = 1.20.
0.92 (t, J = 7.3 Hz, 18H). 31P NMR (162 MHz, CDCl3): δ +4.10 (JP−Pt
2357 Hz). IR: ν(CC)= 2101 cm−1. m/z (EI) 801.
=
Emission Quantum Yields. The quantum yields measurements22
were performed in 2-MeTHF at 298 K. Three different measurements
(i.e., different solutions) were prepared for each photophysical datum
(quantum yields and lifetimes). The solutions for the samples and the
reference were prepared under inert atmosphere in a glovebox.
Solutions prepared for both the reference and the samples were
adjusted to obtain an absorbance around 0.06 where three different
solutions for each measurement were used. Each absorbance value was
measured six times for better accuracy in the measurements of the
quantum yields and was adjusted to be the same as much as possible for
the standard and the sample for a measurement. The reference used for
quantum yield was 9,10-diphenylanthracene22b (Φ298K (2-MeTHF) =
1.0), anthracene22c (Φ298K (MeOH) = 0.20), and H2TPP22d (TPP =
tetraphenylporphyrin; Φ298K = 0.033).
trans-Bis(ethynylphenyl)bis((S)-heptadecylphenyl-i-
1
propylphosphine)platinum(II) (S)-10. Yield 85%. H NMR (400
MHz, CDCl3): δ 7.95−7.82 (m, 4H), 7.50−7.34 (m, 6H), 7.04 (tdd, J =
8.5, 5.2, 3.6 Hz, 6H), 6.89−6.71 (m, 4H), 2.97 (ddd, J = 10.1, 6.8, 3.1 Hz,
2H), 2.60−2.39 (m, 4H), 1.88−1.69 (m, 4H), 1.45−1.37 (m, 4H),
1.36−1.20 (m, 52H), 1.20−1.14 (m, 12H), 0.88 (t, J = 6.8 Hz, 6H). 31P
NMR (162 MHz, CDCl3): δ +21.8 (JP−Pt = 2521 Hz). IR: ν(CC) = 2104
cm−1. MS (MALDI TOF) Calcd for PtC68H104P2: 1177.72. Found:
1177.73. Anal. Calcd for PtC68H104P2: C 69.30, H 8.89. Found: C 69.33,
H 9.19.
trans-Bis(ethynylphenyl)bis((R)-heptadecylphenyl-i-
1
propylphosphine))platinum(II) (R)-10. Yield 94%. H NMR (400
MHz, CDCl3): δ 7.95−7.80 (m, 4H), 7.41 (dd, J = 3.7, 1.9 Hz, 6H),
7.10−6.96 (m, 6H), 6.79 (dd, J = 8.2, 1.4 Hz, 4H), 3.01−2.92 (m, 2H),
2.60−2.40 (m, 4H), 1.84−1.67 (m, 4H), 1.45−1.37 (m, 4H), 1.36−1.20
(m, 52H), 1.20−1.14 (m, 12H), 0.88 (t, J = 6.9 Hz, 6H). 31P NMR (162
MHz, CDCl3): δ +22.8 (JP−Pt = 2521 Hz). IR: ν(CC)= 2105 cm−1. MS
(MALDI TOF) Calcd for PtC68H104P2: 1177.72. Found: 1177.73.
Synthesis of the Oligomers. Typical Procedure. A round-bottom
flask equipped with a magnetic stirrer was loaded with trans-PtCl2L2 and
an equivalent amount of 1,4-diethynylaryl and CuI in catalytic amount.
After three cycles of vacuum/argon, solvent (dichloromethane/
diisopropylamine (1:1) mixture) was added by syringe. After stirring
for 8 h at room temperature under argon, the reaction mixture was
concentrated to a minimum volume and then diluted with cold
methanol until a solid precipitate was obtained, which was washed
repeatedly with cold methanol and dried under vacuum.
Instruments. The NMR spectra (1H, 13C, and 31P) were recorded on
a Bruker 500 AVANCE DRX, 300 AVANCE, or 600 AVANCE II MHz
spectrometer at ambient temperature or in CDCl3 on a Bruker
AVANCE 400 MHz FT-NMR spectrometer using tetramethylsilane as
an internal standard for 1H and 13C nuclei or 85% H3PO4 as an external
standard for 31P nucleus at the Universite
spectra at the Universite
́
de Bourgogne. All NMR
de Sherbrooke were acquired on a Bruker AC-
́
300 spectrometer (1H 300.15 MHz, 13C 75.48 MHz, 31P 121.50 MHz)
or a Varian AS-400 (1H 400.15 MHz, 31P 162.0 MHz) using the solvent
as chemical shift standard, except in 31P NMR, where the chemical shifts
are relative to D3PO4 85% in D2O. Data are reported as s = singlet, d =
doublet, t = triplet, q = quartet, m = multiplet, br s = broad singlet,
integration, coupling constant(s) in Hz. Melting points were measured
on a Kofler bench melting point apparatus and are uncorrected. Optical
rotation values were determined at 25 °C on Perkin-Elmer 341
polarimeter, using a 10 cm quartz vessel. Mass spectral analyses were
performed on BRUKER Daltonics microTOF-Q apparatus or on a
BRUKER AutoflexSpeed MALDI-TOF. The circular dichroism spectra
were measured in dichloromethane on a JACSO J-810 spectropolarim-
eter. Thermogravimetric analysis (TGA) measurements were per-
formed on thermal gravimetric analyzer (model Perkin-Elmer TGA-6)
under a nitrogen flow at a heating rate of 10 °C/min. The DSC spectra
were measured on a TA Q200 differential scanning calorimeter. The gel
permeation chromatography (GPC) measurements were performed on
the Agilent 1050 HPLC system with VWD, using THF as eluent and
polystyrene standards as calibrants. UV−vis spectra were obtained on an
HP-8453 diode array spectrophotometer or on a Varian Cary 300
spectrophotometer. Emission and excitation spectra were measured on a
Photon Technology International (PTI) Fluorescence QuantaMaster
Series QM1 spectrophotometer. The emission lifetimes were measured
on a TimeMaster model TM-3/2003 apparatus from PTI. The source
P o l y [ t r a n s - b i s ( 1 , 4 - e t h y n y l b e n z e n e ) b i s ( t r i n -
butylphosphine)platinum(II)] 11. This polymer was synthesized
according to literature procedure.17 It was characterized for comparison
purposes. Yield 73%. 1H NMR (400 MHz, CDCl3): δ 7.1 (br, 4H), 2.07
(br, 12H), 1.55 (br, 12H), 1.43 (br, 12H), 0.91 (br, 18H). 31P NMR
(121 MHz, CDCl3): δ +8.2 (JP−Pt = 2368 Hz, terminal),20 +4.4 (JP−Pt
2356 Hz). IR: ν(CC)= 2099 cm−1.
=
Poly[trans-bis(ethynylphenyl)bis((R)-heptadecylphenyl-i-
1
propylphosphine)platinum(II)] (R)-12. Yield 78%. H NMR (400
MHz, CDCl3): δ 7.94−7.54 (br, 4H), 7.38 (m, 6H), 6.51 (br, 4H),
3.18−2.70 (m, 2H), 2.63−2.20 (m, 4H), 1.77 (br, 4H), 1.42 (br, 4H),
1.29−1.19 (m, 52H), 1.18−0.95 (m, 12H), 0.85 (t, J = 6.7 Hz, 6H). 31P
NMR (162 MHz, CDCl3): δ +20.9 (JP−Pt = 2403 Hz, terminal), +19.1
(JP−Pt = 2446 Hz). IR: ν(CC) = 2112 cm−1. MS (MALDI TOF): >10
000. GPC (polystyrene standards): Mn = 15 700, Mw = 30 700, DPI =
1.94.
Poly[trans-bis(ethynylphenyl)bis[(S)-heptadecylphenyl-i-
1
propylphosphine)platinum(II)] (S)-12. Yield 92%. H NMR (400
C
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was nitrogen laser with high-resolution dye laser (fwhm ∼1400 ps), and
the fluorescence lifetimes were obtained from deconvolution or
distribution lifetimes analysis. The uncertainties were ∼50−100 ps.
The phosphorescence lifetimes were performed on a PTI LS-100 using a
1 μs tungsten-flash lamp (fwhm ∼1 μs). The small-angle X-ray
scattering, SAXS, patterns were collected with a Bruker AXS Nanostar
system equipped with a Microfocus copper anode at 45 kV/0.65 mA,
MONTAL OPTICS, and a VANTEC 2000 2D detector at 67.75 mm
distance from the samples calibrated with a Silver Behenate standard.
The solutions were prepared saturated in distilled THF, and placed in
quartz cells for measurements. The blanks were measured first and
subtracted to the measured data. The diffracted intensities were then
integrated from 0.15 to 5.00° 2θ and treated with Primus GNOM 3.0
program from ATSAS 2.3 software, to determine the particle sizes by
pair distance distribution.23 The collection exposure times were 2000 s/
sample.
Scheme 3. Synthesis of the Oligomers
are called (S)-10 or (R)-10 (or (S)-12 or (R)-12), respectively,
independently of the absolute configuration of the phosphorus
atoms.
RESULTS AND DISCUSSION
■
The materials were characterized by 1H and 31P NMR, IR, and
TGA, and additionally by GPC and SAXS for the oligomers. The
presence of an IR signal in the 2090−2112 cm−1 range attests to
the presence of a coordinated CC−Pt unit. The 31P NMR
resonances appear as a singlet flanked with two satellites due to
the presence of 195Pt (33% natural abundance). The coupling
constants between the 31P and 195Pt nuclei are on the order of
∼2350 (for the P(n-Bu)3 ligands) and ∼2450−2550 Hz (for the
P[(C17H35)(Ph)(i-Pr)]3 ligands) attesting to the presence of the
trans-geometry (details are placed in Table 1). The observation
of the terminal units, ClPtL2- (L = phosphine) was readily made
with a distinct chemical shift and coupling constants (these are
placed in the Experimental Section). The relative proportion of
terminal versus central units suggests that the materials are
indeed the desired oligomers. This was confirmed by GPC
(Table 2) where the degree of polymerization varies between 5
and 16 units. Noteworthy, GPC measures the hydrodynamic
volumes, and consequently the number of units may be
somewhat overestimated. In parallel, SAXS measurements were
performed, and the results indicate that the average molecular
dimension for (R)-12, (S)-12, and 14 are ∼4, 10, and 18 nm,
respectively, while that for (S)-13 is too small to be measured. On
the basis of molecular modeling, 4 units of Pt(P(C17H35)(Ph)(i-
Pr))2-CCC6H4CCH is ∼4.0 nm. This means that the
materials are ∼4, 10, and 18 units long for (R)-12, (S)-12, and 14,
respectively.
Ligand Synthesis. The stereoselective synthesis of the (R)-
and the (S)-monophosphine ligands 6 (as (R)-(−)-6 and (S)-
(+)-6; Scheme 1) was performed in several steps using the
Scheme 1. (+)-Version Leads to the Corresponding (S)-
Derivatives
ephedrine strategy from (+)- and (−)-ephedrine where
compounds 1−4 were already known.11 (R)-(−)- and (S)-
(+)-Methylphenyl-i-propylphosphine borane 4 reacts with n-
BuLi to form the salt LiCH2P(BH3)(Ph)(i-Pr), which reacts with
C16H33Br to generate 5 in 56% yield. Deprotection with DABCO
gives the desired ligands 6 in excellent yields (98%) with an ee of
92% for (R)-6.
Synthesis and Characterization of the Model Com-
plexes and Oligomers. The model complexes were prepared
from the ligands 6, again as the (R)- and (S)-derivatives (Scheme
2). First the platinum(II) complex 7 can be prepared from a
The accuracy of this method increases as the particle size
increases, but all in all, these rigid rod oligomers are best
described as polydispersed materials ranging from 4 to 18 units.
This conclusion is totally consistent with the clear observation of
terminal −PtL2Cl units (L = phosphine) by 31P NMR. No
attempt was made to increase the oligomer length. This allowed
the relative amount of terminal units/central units to remain
large in order to address the triplet excited state energy transfer
phenomenon terminal*→central units (below). Furthermore,
the shorter size of oligomers conveniently allows an easier
analysis of the molecular dynamics from the measurements of the
degree of anisotropy (also below).
Scheme 2. Synthesis of the Model Complexes
The thermal properties of the materials were determined by
thermogravimetric analysis (TGA; Figure 1). The weight loss
starts being obvious (<5%) at 300 (9), 160 ((R)- and (S)-10),
350 (11), 370 ((R)- and (S)-12), 320 ((S)-13), and 150 (14) °C.
The first derivatives of the TGA traces exhibit maxima (inflection
points) and confirm the same trend (the data are placed in Table
1, see graphs in the Supporting Information (SI), Figure S1). The
key feature is that there is a gain in thermal stability upon using
ligand 6 over PBu3. One may suspect that the electron-donating
direct reaction with K2PtCl4. In this case, both cis- (40%) and
trans- (60%) isomers were observed, isolated, and characterized.
Only the trans-isomer was used subsequently for the preparation
of the model complexes and oligomers (Schemes 2 and 3,
respectively). For sake of simplicity, the nomenclature of the
oligomers 10 (or 12) prepared from the phosphine (S)- or (R)-6,
D
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Table 1. Comparison of the 31P−195Pt Coupling Constants, CC Stretching Frequencies, and Maxima of the First Derivative of
the TGA Graphs
a
Peak maxima of the first derivative of the TGA traces.
Table 2. GPC Data in THF and SAXS Results in 2-MeTHF at
298 K
intraligand ππ*, but the presence of the conjugated coordinated
Pt atom renders these transitions prone to be mixed with metal-
to-ligand charge transfer (MLCT) or with ligand-to-metal charge
transfer (LMCT). Indeed, DFT and TDDFT calculations
indicate that the lowest energy electronic transition are
composed of these two contributions, MLCT and LMCT.24
For materials containing the bis-4,7-ethynyl-2,1,3-benzothiadia-
zole unit flanked with identical aromatics on both sides, literature
indicates that a charge transfer occur from the π-system of both
sides, including that of the bis-4,7-ethynyl-2,1,3-benzothiadiazole
residue to the central benzothiadiazole subunit.25 There is no
theoretical study for organometallic complexes containing the
bis-4,7-ethynyl-2,1,3-benzothiadiazole fragment, but it is reason-
able to believe that the same scenario should occur where charge
transfer excited states (more accurately stated as MLCT here)
are the lowest energy states in these materials.
The optical chirality responses of the complexes and oligomers
were addressed using circular dichroism spectroscopy (Figure 4).
First, both (R)-7 and (S)-7 enantiomers were tested against the
achiral complex 8. Clear positive negative and positive responses
are indeed observed between 200 and 330 nm with the strongest
intensity at about 220 nm, and the spectra of the two enantiomers
are the mirror image of each other. The achiral complex 8 gives
the expected zero baseline. Similarly, the CD spectra for (R)-10
and (S)-10 exhibit positive and negative responses in the 200−
360 nm window as well, where the absorption bands are located,
but the signals are attenuated with respect to those for (R)-7 and
(S)-7 for similar concentrations. Nonetheless, the chiral
environments around the aromatic fragment, here benzene, are
felt by the π-system. The CD spectra for (R)-12 and (S)-12 are
polymer
Mn
Mw
PD
DP
SAXS (nm)
(R)-12
(S)-12
(S)-13
14
15 700
17 700
6050
30 700
30 300
9500
1.94
1.71
1.57
1.20
14.2
16.1
5.2
∼4
∼10
a
10 800
12 900
13.8
∼18
a
Too small to be measured.
inductive effect from the alkyl chain being stronger than that for
the phenyl group makes the PBu3 ligand a stronger base than
(R)- and (S)-6 (i.e., 3 vs 2 alkyl chains) rendering the Pt(II)
center of complexes (R)-10, (S)-10, (R)-12, (S)-12, and (S)-13
less electron-rich. Consequently, the more electron deficient Pt
metal would attract more efficiently the CCR anionic ligands.
With this in mind, the resulting Pt−C bond should be somewhat
stronger with the (R)- and (S)-6 ligands than PBu3. This
explanation assumes that the weak segment of the polymer is the
Pt center, and yet, it is the only portion that changes.
Absorption and Circular Dichroism Spectroscopy. The
absorption spectra for (R)-10, (R)-12, 13, and 14 are presented
in Figures 2 and 3 (traces in black) as representative examples
(the others are placed in the SI, Figures S2 and S3), and the data
are summarized in Table 3.
The nature of the electronic transitions for the materials
containing ArCCPtL2CCAr (L = phosphine) has
previously been established both experimentally and by density
functional theory (DFT) and time-dependent density functional
theory (TDDFT) computations. These are found to be mainly
E
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Figure 1. TGA traces of 9−14 (10 °C/min; N2, 50 mL/min).
Figure 2. Absorption (black), excitation (blue), and emission (red)
spectra of (R)-10 (top) and (R)-12 (bottom).
Figure 3. Absorption (black), excitation (blue), and emission (red)
spectra of 14 (top) and (S)-13 (bottom). The signals at ∼820 nm are
due to phosphorescence.
found to be even more attenuated. In one case, the signal
between 280 and 420 nm, where the absorption takes place, is
lost in the noisy baseline. This situation is more apparent where
only a strong negative response is detected at 225 nm for
polymer (S)-13 (similar to that of oligomer (S)-7), and no other
signal is detected above 280 nm (absorption bands are observed
all the way to 550 nm), where the CD signal is compared with
that for the achiral oligomer 14. In order to address why the
ligand chirality environment is not fully transmitted from the
metallic unit to the aromatic, computer modeling is employed
(PCModel, v. 7.0, Serena Software).
The first comparison concerns (R)-7, (S)-7 vs (R)-10, (S)-10.
A previous X-ray study for two geometric isomers trans-(2,4,6-
Me3C6H2CC)2(Bu3P)2Pt(II) and trans-(2,4,5-Me3C6H2C
C)2(Bu3P)2Pt(II) (Chart 2) shows that the angles formed by the
average P2PtC2 plane with that of the aromatic one are 83.0° and
29.8°, respectively.24h Obviously, this phenomenon comes from
a packing effect (more than intramolecular steric effect) and
indicates that the rotation about the CCPt bond is possible
and presumably facile. Figure 5 shows the side view and the view
along the oligomer chain of oligomer (R)-12 constructed with
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Table 3. Absorption Data of the Materials in 2-MeTHF at 298 K
compd
λmax /nm (ε /L mol−1 cm−1
)
9
264 (28 200), 282 (25 300), 316 (21 500), 338 (18 800)
264 (28 000), 286 (21 600), 330 (25 600), 337 (26 800)
264 (30 500), 286 (23 800), 330 (26 500), 337 (27 800)
272 (3190), 301 (3800), 363 (8800)
(R)-10
(S)-10
11
(R)-12
(S)-12
(S)-13
14
268 (12 900), 298 (12 400), 362 (22 400), 386 (28 600)
271 (13 300), 302 (12 200), 362 (22 700), 386 (28 400)
315 (8000), 322 (8000), 329 (8000), 346 (10 000), 486 (9400), 515 (11 200)
261 (13 400), 320 (11 200), 329 (12 300), 340 (16 600), 519 (15 700)
Figure 4. CD spectra of (R)-7, (S)-7, 8, (R)-10, (S)-10, (R)-12, (S)-12, (S)-13, and 14 (in CH2Cl2, 298 K).
toward each other and the P2PtC2 planes are no longer parallel,
forming a screw-shaped polymer rod (Figure 5). This intrinsic
structure brings a first change in local chirality from one unit to
another. However, this is only a really modest alteration.
Subsequently, rotating the P2PtC2 planes of the building blocks
from one another by ∼90° (attempting to minimize the
proximity of the C17H35 alkyl chains) results in the collapse of
these onto the oligomer backbone (Figure 6). The energy
minimized structure exhibits a nonlinear (CCArCC
Pt)n central chain and different angles formed by the average
P2PtC2 plane with that of the aromatic one.
Chart 2. X-ray Angles Formed by the Average P2PtC2 Plane
and That of the Aromatic One24h
Figure 5. Side view and the view along the oligomer chain of oligomer
(R)-12 after energy minimization originally constructed with the
building blocks placed side by side and the P2PtC2 planes and the C17H35
alkyl chains, perfectly parallel.
Figure 6. Top: Side view of a fragment of oligomer (R)-12 after energy
minimization originally constructed with the building blocks placed side
by side and the P2PtC2 planes make an angle of ∼90° with respect to
each other. Bottom: Fragment of polymer 11 placed for comparison
purposes.
the building blocks placed side by side and the P2PtC2 planes and
the C17H35 alkyl chains perfectly parallel. After energy
minimization (vide infra), the C17H35 alkyl chains bend slightly
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This computer modeling along with the previous X-ray data
show that the Pt−C rotation is facile and that such rotation leads
to various rotamers (and combination of rotamers along the
oligomer chain) making the local environment of each aromatic
different. Consequently, with the environment being different,
the transmission of the chiral information from the phosphine
onto the π-system of the aromatic units is not homogeneous,
hence resulting in a strong attenuation of the CD signals in the
spectral region above >290 nm. It will be shown below that the
second scenario is highly probable on the basis of anisotropy
data.
Emission and Excitation Spectra. The emission and
excitation spectra for (R)-10, (R)-12, 13, and 14 (as
representative examples) recorded at 298 and 77 K are presented
in Figures 2 and 3 (the others are placed in the SI, Figures S2 and
S3). The fluorescence and phosphorescence bands of (R)-10 and
(R)-12 are the same as those previously reported of the achiral
polymers 11 and 14 and model complexes.21,24 The similarity in
peak positions, band shapes, and activity (presence or not of
fluorescence and phosphorescence) strongly suggest that the
nature of the singlet (S1) and triplet (T1) emissive states are the
same for the chiral and achiral materials. The slight variation in
peak positions between the PBu3- and P(C17H35)(Ph)(i-Pr)3-
containing materials is expected due to the difference in inductive
effect of the alkyl chains. The electronic bands of the latter type
are all red-shifted in comparison with the former type suggesting
that the Pt[P(C17H35)(Ph)(i-Pr)3]2 unit is more electron-rich
than that for Pt(PBu3)2. The fluorescence and phosphorescence
quantum yields at 298 K are placed in Table 4.
Figure 7. The two possible degrees of angular displacement in rigid rod
molecules.
about 10 years ago.27 The lowest energy excited states are 1,3B3u
(1Ag is the ground state), and the S0−S1 transition is allowed and
polarized along the x-axis. This means that, for longer oligomers,
the same polarization feature operates (i.e., along the long axis;
Figure 7). In the light of this simple analysis, rotation around the
long axis should not influence β. Conversely, rotation around the
short axis should.
Oligomers 11, (R)-12, and (S)-12 exhibit fluorescence
lifetimes <300 ps (Table 5). At such short time scale, the
molecule does not have much time to have a significant β value
(i.e., β ∼ 0, r0 ∼ 0.40). Experimentally using λex = 370 nm in the
bulk of the lowest energy band, this expected value of ∼0.40 at
the maximum intensity of the fluorescence at ∼400 nm is indeed
observed (Figure 8). Conversely, the r0 value is drastically
different for the phosphorescence, which exhibits much longer
lifetimes (>700 ns). A change in r0 is obviously expected, and
values approaching 0 (meaning β ∼ 54.7° (magic angle)) are
expected (i.e., the rigid rods have time to tumble prior to
emission).
For oligomers (S)-13 and 14, the fluorescence lifetimes are ∼4
times longer allowing enough time for reorganization of the
oligomer orientations in solution. The minimum r0 values (at
maximum intensity where it is more accurate) are approximately
−0.20 and approximately −0.15 for (S)-13 and 14, respectively
(Figure 9). These values suggest β values of ∼90° (maximum
possible) and ∼80°, respectively. This result is in line with the
GPC and SAXS data (Table 2), which implies that shorter
oligomers (here (S)-13) should tumble more easily (therefore
changing their relative orientation) than longer ones (here 14).
However, the similarity in r0 and β values indicates that both
must have a similar dominant reorganization motion in solution.
The common reorientation must be the rotation along the x axis
with a polymer conformation resembling that shown in Figure 6.
Interestingly, despite the clear evidence of significant amount
of terminal CCPtL2Cl (L = PBu3) units from the 31P
NMR, the corresponding blue-shifted phosphorescence is not
observed. The expected signal is at λem(0−0) = 435 nm,
previously reported for PhCCPt(PBu3)2Cl.20 Moreover,
the phosphorescence decays appear as a single exponential in all
cases, excluding the possibility of having this emission blurred by
the more intense phosphorescence of the central units (i.e.,
PtL2CCC6H4CCPtL2). Recently, evidence of emis-
sions arising from both the terminal and central units was
provided for oligomers comprising the CCPtL2C
C (L = PBu3) or CCPt2(dppm)2CC bridge (Figure
10).28
Table 4. Fluorescence and Phosphorescence Quantum Yields
Measured in 2-MeTHF
298 K
compd
ΦF (×10−3) (λmax; λex, nm)
ΦP (×10−3) (λmax; λex, nm)
11
1.34 (388; 350)
0.26 (404; 350)
0.25 (403; 350)
42.4 (567; 350)
6.82 (569; 350)
1.46 (515; 350)
0.67 (559; 350)
0.67 (556; 350)
0.83 (821; 485)
1.20 (819; 485)
(R)-12
(S)-12
(S)-13
14
Molecular Dynamic and Excited State Lifetimes.
Conversely to the model complexes, the five investigated
oligomers exhibit fluorescence at 298 K. This allows the
measurements of the degree of anisotropy (r0),26 which should
be important in rigid stick-shaped molecules. This method
permits estimation of the change in angular displacement (β)
formed by the transition moment between the moment the
molecule absorbs the light and the moment it emits it. These two
parameters are related by r0 = (2/5)((3 cos2 β − 1)/2).26 For
example, β = 0°, 45°, 54.7°, and 90°, and r0 = 0.40, 0.10, 0.00, and
−0.20, respectively. Prior to discussing the results, relevant
comments are necessary. First, there are two degrees of freedom
in angular displacement (β) as illustrated in Figure 7. On the
basis of molecular dimensions notes in Figures 5 and 6, a rotation
around the long axis (oligomer backbone) should be easier than
that for the short axis. But due to the relative dimension deduced
by GPC and SAXS, rotation around the short axis should also be
effective, although slower.
In these cases, the lowering of the phosphorescence lifetimes
of the end groups versus their model compounds implied the
presence of triplet energy transfers terminal*→central. The
rates, kET(T1), are extracted from kET(T1) = (1/τe) − (1/τeo)
where τe and τeo are the emission lifetimes of the donor, here the
CCPtL2Cl end group (as the 0−0 peak is expected at 435
nm), in the presence and the absence of the acceptor, and here
the central units (as the 0−0 peak is at 443 nm, 77 K),
Second, the complex HCCC6H4CCPtL2-C
CC6H4CCH (L = PBu3; D2h point group) with the x, y, and
z axes as the long axis, the P−Pt−P axis, and the axis
perpendicular to the PtP2C2 plane, respectively, was investigated
H
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a
Table 5. Fluorescence and Phosphorescence Lifetimes in 2-MeTHF
compd
298 K τF (ns)
298 K τP (ns)
77 K τF (ns)
77 K τP (μs)
9
31.7 2.4 (443)
33.2 0.2 (445)
34.2 0.7 (445)
53.0 0.4 (515)
45.6 2.6 (515)
48.1 0.1 (518)
(R)-10
(S)-10
11
b
<0.10 (400)
0.75 0.03 (515)
26.9 1.5 (555)
22.1 1.5 (555)
0.20 0.04 (440)
0.31 0.03 (440)
0.35 0.09 (440)
0.45 0.05 (570)
0.38 0.06 (570)
(R)-12
(S)-12
(S)-13
14
0.27 0.03 (400)
0.16 0.02 (400)
1.22 0.21 (560)
1.26 0.30 (560)
a
The values in parentheses are the emission positions where the measurements were performed. The phosphorescence lifetime at 800 nm for (S)-13
b
and 14 could not be measured due to the low intensity of the signal in this region. Reached detection limit.
Figure 9. Measurements of the degree of anisotropy (r0) for (S)-13 and
14 in 2-MeTHF at 298 K: r0 = ((I∥/I⊥) − 1)/((I∥/I⊥) + 2) with (I∥/I⊥) =
(IVV HH)/(IVH HV) with IVV being the emission intensity measured using
I
I
a vertically and vertically placed polarizers at the excitation and emission
position, and so on. H means horizontally.26.
reported. They were compared to the achiral analogues
containing the trans-Pt[P(PBu)3]2 fragment, and several differ-
ences were noted. First, the P(C17H35)(Ph)(i-Pr)3-containing
materials are more thermally stable than that containing the
shorter chain ligand PBu3. Second, presumably based on
inductive effect, the trans-Pt(P(C17H35)(Ph)(i-Pr))2-containing
oligomers exhibit absorption and emission bands that are more
red-shifted than those bearing the trans-Pt(PBu3)2 residue.
Third, the through space transmission of the chirality environ-
ment to the π-systems of the aromatic bridges is attenuated in the
oligomers, presumably because of the irregular environment
from one unit to the next in the chain based on computer
modeling. Fourth, the presence of the long chain on the
phosphorus atoms does not greatly alter the photophysical
parameters, notably the emission lifetimes. This means that the
long chain must be placed away from the lumophore, which is
located in the middle of the oligomer skeleton. Fifth, the
oligomer nature of the materials conveniently allows demon-
strating that a fast triplet energy transfer terminal*→central takes
places. The comparison with rates for structurally related systems
indicates that the rates must be faster than 3.3 × 105 s−1. These
observations and conclusions on the structure−property
relationship are clearly useful for the future design photonic
materials bearing chiral moieties.
Figure 8. Measurements of the degree of anisotropy (r0) for 11, (R)-12,
and (S)-12 in 2-MeTHF at 298 K: r0 = ((I∥/I⊥) − 1)/((I∥/I⊥) + 2) with
(I∥/I⊥) = (IVVIHH)/(IVHIHV) with IVV being the emission intensity
measured using a vertically and vertically placed polarizers at the
excitation and emission positions, and so on. H means horizontally (λex
= 370 nm).
respectively. The kET(T1) values range from 0.1 × 105 to 3.3 ×
105 s−1 for structurally related oligomers (Figure 10). We
conclude that a fast triplet energy transfer terminal*→central
takes places, presumably with rates larger than 3.3 × 105 s−1,
where evidence for the donor emission is still detectable.
CONCLUSION
■
The ligands (R)-6 and (S)-6 were prepared in several steps using
the ephedrine strategy from (+)- and (−)-ephedrine in ee up to
98%, hence demonstrating its utility. From these chiral species,
three oligomers containing the unit (R)- or (S)-trans-Pt[P-
(C17H35)(Ph)(i-Pr)3]2 have been prepared using the bis-1,4-
ethynylbenzene and bis-4,7-ethynyl-2,1,3-benzothiadiazole as
bridges. To the best of our knowledge, these new materials are
the first P-chirogenic conjugated polymers (as oligomers) to be
I
dx.doi.org/10.1021/ic301829x | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 10. Structures of the known oligomers exhibiting emissions from the terminal and central units.
Lebon, F.; Longhi, G.; Abbate, S.; Famulari, A.; Valdo Meille, S. Chem.
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ASSOCIATED CONTENT
* Supporting Information
Absorption, excitation, and emission spectra of 9, 11, (S)-10, and
(S)-12; TGA 1st derivatives traces of 9−14; table giving the peak
positions in the emission and excitation spectra; table giving the
CD spectroscopic data; and the NMR spectra. This material is
available free of charge via the Internet at http://pubs.acs.org.
■
S
́
(6) (a) Salomon, C.; Fortin, D.; Khiri, N.; Juge, S.; Harvey, P. D. Eur. J.
AUTHOR INFORMATION
Corresponding Author
*E-mail: Pierre.Harvey@USherbrooke (P.D.H.); Sylvain.Juge@
u-bourgogne.fr (S.J.). Phone: 1-819-821-7092 (P.D.H.); +33 (0)
3 80 39 61 13 (S.J.).
■
Inorg. Chem. 2011, 2597−2609. (b) Ouchi, Y.; Morisaki, Y.; Ogoshi, T.;
Chujo, Y. Chem.Asian J. 2007, 2, 397−402.
(7) Wong, W.-Y.; Harvey, P. D. Macromol. Rapid Commun. 2010, 31,
671−713.
(8) Zhan, H.; Lamare, S.; Ng, A.; Kenny, T.; Guernon, H.; Chan, W.-
K.; Djurisic, A. B.; Harvey, P. D.; Wong, W.-Y. Macromolecules 2011, 44,
5155−5167.
Notes
The authors declare no competing financial interest.
(9) (a) Goudreault, T.; He, Z.; Guo, Y.; Ho, C.-L.; Wang, Q.; Zhan, H.;
Wong, K.-L.; Fortin, D.; Yao, B.; Xie, Z.; Kwok, W.-M.; Wong, W.-Y.;
Harvey, P. D. Macromolecules 2010, 43, 7936−7949. (b) Ho, C.-L.;
Chui, C.-H.; Wong, W.-Y.; Aly, S. M.; Fortin, D.; Harvey, P. D.; Yao, B.;
Xie, Z.; Wang, L. Macromol. Chem. Phys. 2009, 210, 1786−1798.
(10) (a) Aly, S. M.; Ho, C.-L.; Wong, W.-Y.; Fortin, D.; Harvey, P. D.
Macromolecules 2009, 42, 6902−6916. (b) Aly, S. M.; Ho, C.-L.; Wong,
W.-Y.; Abd-El-Aziz, A. S.; Harvey, P. D. Chem.Eur. J. 2008, 14, 8341−
8352.
ACKNOWLEDGMENTS
This research was supported by the Natural Sciences and
Engineering Research Council of Canada (NSERC), le Fonds
■
Queb
(FQRNT), the Centre d’Etudes des Mater
Photoniques de l’Universite de Sherbrooke (CEMOPUS) and
́
ec
́
ois de la Recherche sur la Nature et les Technologies
́
iaux Optiques et
́
l’Agence Nationale de la Recherche (France) for the grant
MetChirPhos and the Award of a Research chair of Excellence to
(11) (a) Chaux, F.; Frynas, S.; Laureano, H.; Salomon, C.; Morata, G.;
Auclair, M.-L.; Stephan, M.; Merdes
J.; Henry, J. C.; Bayardon, J.; Darcel, C.; Juge,
S. In Phosphorus Ligands in
̀
, R.; Richard, P.; Ondel-Eymin, M.-
P.D.H.. We thank Dr. Pierre Lavigne (Faculte
́ ́
de Medecine of the
́
S. C. R. Chim. 2010, 12,
Universite de Sherbrooke) for letting us use his circular
́
1213−1226. (b) Darcel, C.; Uziel, J.; Juge,
́
dichroism spectrometer and Dr. J. Bayardon for helpful
discussion and his help in the preparation of this manuscript.
Asymmetric Catalysis Synthesis and Applications; Borner, A., Ed.; Wiley-
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VCH: New York, 2008; Vol. 3, p 1211. (c) Bauduin, C.; Moulin, D.;
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