Pushing pentacene-based fluorescence to the near-infrared region by platination

Article abstract of DOI:10.1021/om2005645

A series of binuclear platinum complexes of pentacenyl-6,13-diacetylide with different auxiliary ligands were synthesized to probe the effect of metal coordination on electronic spectroscopy and photophysics, to determine the solid-state packing of the co

Full text of DOI:10.1021/om2005645

Article
pubs.acs.org/Organometallics
Pushing Pentacene-Based Fluorescence to the Near-Infrared Region
by Platination
Minh-Hai Nguyen and John H. K. Yip*
Department of Chemistry, National University of Singapore, 3 Science 3 Drive, Singapore, 117543
S
* Supporting Information
ABSTRACT: A series of binuclear platinum complexes of
pentacenyl-6,13-diacetylide with different auxiliary ligands
were synthesized to probe the effect of metal coordination
on electronic spectroscopy and photophysics, to determine
the solid-state packing of the complexes, and to tune
emission energy. The complexes with anionic, π-donating
ligands showed absorption (687−696 nm) and fluorescence
(710−726 nm) lower in energy than those with neutral,
π-accepting ligands (662−666, 675−686 nm). Our work
showed that coordination of Pt ions with π-donating anionic
ligands to pentacenyl-6,13-diacetylide could move the
fluorescence of the organic chromophore to the near-
infrared region (λ em 710−726 nm). The combined perturbations of alkynation and platination lowered the HOMO →
LUMO transition up to 0.34 eV.
LUMO−HOMO gap by stabilizing the LUMO more than the
HOMO.14
INTRODUCTION
■
There is a quest for molecules that display near-infrared (near-
IR) luminescence because of their wide applications in fields
such as bioimaging, organic photovoltaics, optoelectronics, and
photodynamic therapy.1 Various organic and organometallic
chromophores (e.g. porphyrin,2 squararine,3 and aza-dipyrro-
methene4), lanthanide complexes,5 and nanoparticles6a have
been invoked in the development of near-IR emitters.6
Incentive to search for new near-IR chromophores arises
from the possibility that new chromophores would have
different photophysical properties and subcellular localization.
For π-conjugated chromophores, their emissions can be shifted
to the near-IR region by ring substitution of or extension of
π-conjugation of the molecules, which lowers the HOMO−
LUMO gap.1b,7 In our ongoing study of the photochemistry
and photophysics of metalated polycylic aromatic hydrocarbons
(PAHs), our attention was drawn to pentacene, which displays
fluorescence at the low-energy visible region.8 It is envisioned
that the chromophore can be converted into a near-IR emitter
by lowering its HOMO−LUMO gap. An obvious advantage of
pentacene is its intense low-energy visible absorption with an
extinction coefficient of 104 M−1cm−1.9 However, the
compound is known to be unstable10 and it is synthetically
difficult to modify or add substituents to the ring.11
Nonetheless, Anthony et al. demonstrated that 6,13-bis-
(triisopropylsilylethynyl)pentacene (TIPS-pentacene) has high-
er stability,12 and lower energy fluorescence,8,13a and lower first
ionization energy in the gas phase.13b Recent DFT calculations
showed that the red shift of the emission was due to the
inductive effect of the ethynyl groups, which reduced the
Metalation of PAHs is an attractive alternative to tune the
photophysics of the organic molecules.15 The d orbitals of transi-
tion metals would introduce additional manifolds of orbital
interactions and excited states (e.g., MLCT and LMCT). In
addition, heavy transition metals, with their high-energy d orbitals
and large spin−orbit coupling, can alter the photophysics of
PAHs. For instance, attaching a gold(I) or platinum(II) ion to
tetracene and tetracenyldiacetylide could lower the fluorescence
energy up to 0.53 eV16 and switch on the phosphorescence of
pyrene.17 Our study of platinated and aurated pyrenes showed
that the PtII ion has stronger perturbation on the electronic
structures of the PAHs than the more electrophilic AuI ion.17b
This suggests to us the importance of metal−ligand π
interactions in red-shifting the fluorescence of PAHs and the
possibility of shifting the fluorescence of pentacene to lower
energy by platination. Herein we report a synthetic and
spectroscopic study of a series of binuclear [L(Et3P)2PtII]2-
pentacenyl-6,13-diacetylide complexes with different auxiliary
ligands L (Scheme 1). Our results showed that the collective
effect of the ethynyl substitutents and the Pt ions can move the
fluorescence of pentacene to the near-IR region and the extent
of the red shift is sensitive to the electronic properties of L.
EXPERIMENTAL SECTION
■
General Methods. All syntheses were carried out under a N2
atmosphere. All the solvents used for synthesis and spectroscopic
Received: June 29, 2011
Published: November 10, 2011
© 2011 American Chemical Society
6383
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Organometallics
Article
Scheme 1
1
31P{1H} NMR (202.4 MHz, CDCl3): δ 9.63 (s, JPt−P = 2319 Hz).
measurements were purified according to the literature procedures.
trans-Pt(PEt3 )2I2,18 trans-Pt(PBu3 )2I2,19 and 6,13-bis-
(triisopropylsilylethynyl)pentacene20 were prepared according to
reported procedures.
ESI-MS: m/z 1440.0, [M]+.
[I(Bu3P)2PtII]2-pentacenyl-6,13-diacetylide (1b). The compound
was synthesized by following the procedure described for 1a, except
that trans-Pt(PBu3)2I2 was used instead of trans-Pt(PEt3)2I2. The dark
green product was collected from column chromatography (silica gel,
20 cm × 4 cm column, hexane/dichloromethane 4/1, v/v). Yield: 48%.
X-ray-quality crystals of 1b were obtained from CH2Cl2/MeOH at
room temperature. Anal. Calcd for 1b (C74H120I2P4Pt2): C, 50.00; H,
Physical Methods. The UV/vis absorption and emission spectra
of the complexes were recorded on a Hewlett-Packard HP8452A diode
array spectrophotometer and a Perkin-Elmer LS-50D fluorescence
spectrophotometer, respectively. Emission lifetimes were recorded on
a Horiba Jobin-Yvon Fluorolog FL-1057 fluorescence spectrometer.
Cresyl violet was used as a standard in measuring the emission
quantum yields.21 1H and 31P{1H} NMR spectra were recorded on a
Bruker ACF 500 spectrometer. All chemical shifts are quoted relative
to SiMe4 (1H) or H3PO4 (31P). Elemental analyses of the complexes
were carried out in the microanalysis laboratory in the Department of
Chemistry at the National University of Singapore.
1
6.80. Found: C, 50.21; H, 7.01. H NMR (500 MHz, CDCl3): δ 9.31
(s, 4H, H5,7,12,14), 7.90 (dd, J = 3.1, 6.9 Hz, 4H, H1,4,8,11), 7.31 (dd, J =
3.1, 6.9 Hz, 4H, H2,3,9,10), 2.23−2.20 (m, 24H, PCH2CH2CH2CH3),
1.68−1.67 (m, 24H, PCH2CH2CH2CH3), 1.41−1.34 (m, 24H,
PCH2CH2CH2CH3), 0.86−0.83 (t, 36H, PCH2CH2CH2CH3).
1
31P{1H} NMR (202.4 MHz, CDCl3): δ 1.26 (s, JPt−P = 2300 Hz).
Synthesis. [I(Et3P)2PtII]2-pentacenyl-6,13-diacetylide (1a). In a
250 mL Schlenk flask was charged trans-Pt(PEt3)2I2 (600 mg, 0.911
mmol), iPr2NH (5 mL), Bu4NF (250 mg, 0.800 mmol), CuI (10 mg),
and CH2Cl2 (30 mL). To the mixture was added a CH2Cl2 solution
(100 mL) of 6,13-bis(triisopropylsilylethynyl)pentacene (100 mg,
0.156 mmol) over 5 h by using an equalizing funnel. The resulting
solution was stirred overnight, and all the solvents were reduced to
dryness. The dark green product was collected from column chro-
matography (silica gel, 20 cm × 4 cm column, hexane/CH2Cl2 2/1
then 1/1, v/v). Yield: 160 mg, 71%. Anal. Calcd for 1a
(C50H72I2P4Pt2): C, 41.68; H, 5.04. Found: C, 41.26; H, 4.72. 1H
NMR (500 MHz, CDCl3): δ 9.34 (s, 4H, H5,7,12,14), 7.92 (dd, J = 3.1,
6.9 Hz, 4H, H1,4,8,11), 7.33 (dd, J = 3.1, 6.9 Hz, 4H, H2,3,9,10), 2.30−
2.26 (m, 24H, PCH2CH3), 1.30−1.23 (m, 36H, PCH2CH3).
ESI-MS: m/z 1777.3, [M]+.
[(C6H5S)(Et3P)2PtII]2-pentacenyl-6,13-diacetylide (2). To a suspen-
sion of 1a (40 mg, 0.028 mmol) in CH2Cl2 (15 mL) was added
thiophenol (0.1 mL, 1 mmol) and NEt3 (0.2 mL, 1.3 mmol). The
resulting mixture was stirred for 2 h, and the solvent was then reduced
by rotavaporation. The addition of excess MeOH afforded a dark
green solid. The product was filtered and thoroughly washed with
MeOH and then dried in vacuo. Yield: 28 mg, 72%. X-ray-quality
crystals of 2 were obtained from CH2Cl2/MeOH at −20 °C. Anal.
Calcd for 2 (C62H82P4Pt2S2): C, 52.98; H, 5.88; S, 4.56. Found: C,
52.79; H, 5.83; S, 4.46. H NMR (500 MHz, CDCl3): δ 9.39 (s, 4H,
5,7,12,14), 7.95 (dd, J = 3.1, 6.3 Hz, 4H, H1,4,8,11), 7.64 (d, J = 7.6 Hz,
4H, o-C6H5), 7.34 (dd, 4H, H2,3,9,10), 7.11 (t, J = 7.6 Hz, 4H, m-C6H5),
6.95 (t, J = 7.6 Hz, 2H, p-C6H5), 2.13−2.08 (m, 24H, PCH2CH3),
1
H
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Organometallics
Article
1.29−1.23 (m, 36H, PCH2CH3). 31P{1H} NMR (202.4 MHz,
scaling; SADABS22b for empirical absorption correction; SHELXTL22c
for space group determination, structure solution, and least-squares
refinements on |F|2. Anisotropic thermal parameters were refined for
the rest of the non-hydrogen atoms. The hydrogen atoms were placed
in their ideal positions. Crystal data and experimental details are
summarized in Table 1
1
CDCl3): δ 13.37 (s, JPt−P = 2409 Hz). ESI-MS: m/z 1404.2, [M]+.
[(C6H5C2)(Et3P)2PtII]2-pentacenyl-6,13-diacetylide (3). To a sus-
pension of 1a (50 mg, 0.035 mmol) in CH2Cl2 (15 mL) was added
CuI (3 mg), triethylamine (5 mL), and phenylacetylene (0.1 mL,
0.892 mmol). Upon stirring for 0.5 h, the suspension turned to a clear
green solution. The resulting mixture was further stirred overnight,
and all the solvents were removed in vacuo. The dark green product
was isolated from column chromatography (basic alumina, 10 cm ×
2 cm column, hexane/dichloromethane 1/1, v/v). Yield 35 mg, 73%.
X-ray-quality crystals of 3 were obtained from CH2Cl2/MeOH at
room temperature. Anal. Calcd for 3 (C66H82P4Pt2): C, 57.05; H,
RESULTS AND DISCUSSION
■
Synthesis and Characterization. The compounds 1a,b
were synthesized by Sonogashira coupling of trans-PtII(PR3)-
I2 (R = Et, Bu) and 6,13-diethynylpentacene, which was
generated in situ from desilylation of TIPS-pentacene. 1a
was sparingly soluble in common organic solvents, frustrat-
ing efforts to obtain single crystals for X-ray diffraction.
1
5.95. Found: C, 57.28; H, 5.44. H NMR (500 MHz, CDCl3): δ
9.38 (s, 4H, H5,7,12,14), 7.91 (dd, J = 3.1, 6.3 Hz, 4H, H1,4,8,11), 7.36
(d, J = 7.5 Hz, 4H, o-C6H5), 7.31 (dd, J = 3.1, 6.3 Hz, 4H, H2,3,9,10),
7.27−7.24 (m, 4H, m-C6H5), 7.16 (t, J = 7.6 Hz, 2H, p-C6H5),
2.29−2.25 (m, 24H, PCH2CH3), 1.36−1.29 (m, 36H, PCH2CH3).
31P{1H} NMR (202.4 MHz, CDCl3): δ 12.32 (s, 1JPt−P = 2369 Hz). ESI-
MS: m/z 1388.3, [M]+.
1
Nonetheless, H and 31P{1H} NMR, high-resolution ESI-
MS, and elemental analysis results confirm the proposed
formulation of the compound. Figure 1 shows the nearly
identical experimental and simulated cluster peaks for [1a]+
(m/z 1440.0). The analogous complex 1b, bearing the more
easily solubilized PBu3, is soluble in many organic solvents,
even hexane.
[(Ph3P)(Et3P)2PtII]2-pentacenyl-6,13-diacetylide-(OTf)2 (4). To a
suspension of 1a (25 mg, 0.017 mmol) in CH2Cl2 was added
AgOTf (25 mg, 0.097 mmol) with stirring at room temperature over
0.5 h in the absence of light. The resulting mixture was filtered under
argon, and excess triphenylphosphine (100 mg) was added. The
solution was stirred for 2 h, and the solvent was then reduced by
rotavaporation. The title compound was precipitated by addition of
excess Et2O. Yield: 32 mg, 92%. Slow diffusion of Et2O into an
acetonic solution at room temperature afforded dark green crystals
suitable for an X-ray crystallography study. Anal. Calcd for 4
(C88H102F6O6P6Pt2S2): C, 52.59; H, 5.12; S, 3.19. Found: C, 52.23;
H, 4.77; S, 3.12. 1H NMR (500 MHz, CDCl3): δ 9.24 (s, 4H,
Complex 2 was obtained from substitution of the iodide ions
in 1a by benzenethiolate, and complex 3 was prepared from
Sonogashira coupling of 1a and phenylacetylene. Complexes 4
and 5 were easily prepared in good yields from halide
abstraction with AgOTf followed by reaction with PPh3 and
pyridine, respectively. Facile substitution of iodides in 1a by
2,6-xylyl isocyanide in CH3CN followed by anion exchange
with LiClO4 afforded the green complex 6. Compounds 2−6
were much more soluble than 1a in solvents such as CH2Cl2,
CHCl3, and CH3CN, making X-ray characterization of the
complexes possible.
H
5,7,12,14), 8.03−8.01 (m, 4H, H1,4,8,11), 7.89−7.86 (m, 12H, o-C6H5),
7.64−7.63 (m, 18H, m,p-C6H5), 7.48−7.46 (m, 4H, H2,3,9,10), 1.56
(multiplet, 24H, PCH2CH3), 1.10−1.07 (m, 36H, PCH2CH3).
31P{1H} NMR (500 MHz, CDCl3): δ 11.76 (t, JPt−P = 2547 Hz,
1
2JP−P = 22 Hz, PPh3), 9.03 (d, 1JPt−P = 2160 Hz, 2JP−P = 22 Hz, PEt3).
ESI-MS: m/z 855.6, [M − 2OTf]2+.
1
The H NMR spectra of all the complexes exhibit the same
[(C5H5N)(Et3P)2PtII]2-pentacenyl-6,13-diacetylide-(OTf)2 (5). The
compound was prepared by following the procedure for 4, except
that pyridine was used instead of PPh3. Yield: 85%. Dark green crystals
of 5 were grown by slow diffusion of Et2O into a CH2Cl2 solution at
room temperature. Anal. Calcd for 5 (C62H82F6N2O6P4Pt2S2): C,
45.31; H, 5.03; N, 1.70; S, 3.90. Found: C, 45.22; H, 5.07; N, 1.66; S,
pattern of pentacenyl proton signals, which include one singlet
(H5,7,12,14) and two doublet of doublets (H1,4,8,11 and H2,3,9,10),
indicating a D2h symmetry of the complexes in solution.
Similarly, 31P{1H} NMR spectra of all the complexes except 4
1
show sharp singlets with 195Pt satellites. The JPt−P coupling
1
constants of 2074−2409 Hz are consistent with a trans
orientation of the phosphines.15d,23 The spectrum of 4 displays
a doublet and a triplet with intensity ratio 2:1, which are
ascribable to the ligands PEt3 and PPh3, respectively. The
4.19. H NMR (500 MHz, CDCl3): δ 9.17 (s, 4H, H5,7,12,14), 8,74 (d,
J = 5.7 Hz, 4H, o-C5H5N), 8.07 (t, J = 7.6 Hz, 2H, p-C5H5N), 7.87
(multiplet, 4H, H1,4,8,11), 7.78−7.75 (m, 4H, m-C5H5N), 7.35−7.33
(multiplet, 4H, H2,3,9,10), 1.78 (q, 24H, PCH2CH3), 1.26−1.19 (t, 36H,
1
PCH2CH3). 31P{1H} NMR (202.4 MHz, CDCl3): δ 16.56 (s, JPt−P
=
2
magnitude of JP−P (22 Hz) is consistent with the cis
2322 Hz). ESI-MS: m/z 672.1, [M − 2OTf]2+.
orientation of the two ligands.15c,16,24
[(C6H3(CH3)2NC)(Et3P)2PtII]2-pentacenyl-6,13-diacetylide-(ClO4)2
(6). To a suspension of 1 (40 mg, 0.028 mmol) in acetonitrile (10
mL) was added 2,6-xylyl isocyanide (20 mg, 0.151 mmol). When it
was stirred for 2 h, the suspension turned to a clear green solution.
The addition of excess LiClO4 (100 mg) followed by Et2O afforded
the title product, which was collected and dried. Yield: 25 mg, 55%.
Dark green crystals of 6 were grown by slow diffusion of Et2O into a
CH2Cl2 solution at room temperature. Anal. Calcd for 6
(C68H90Cl2N2O8P4Pt2): C, 49.55; H, 5.50; N, 1.70. Found: C,
Crystal Structures. Structures of 1b, 2·2CH2Cl2, 3,
4·2H2O, 5·CH2Cl2, and 6 are shown in Figures 2−7, and
selected bond lengths and angles are given in Table 2. The PtII
ions show a distorted-square-planar geometry with C−Pt−P
angles of 80.2(3)−92.33(14)° and P−Pt−X angles of
87.70(14)−101.89(8)° (X is the donor atom of the ligand L).
The two trialkylphophines are in a trans configuration (P1−
Pt−P2 = 173.11(10)−177.24(3)°), and the Pt−P bond lengths
1
49.60; H, 5.50; N, 1.75. H NMR (500 MHz, CDCl3): δ 9.20 (s, 4H,
II
́
(2.2959(13)−2.321(3) Å) are typical for Pt −tertiary phos-
phine compounds.23b,25 The Pt ions in 4·2H2O show more
severe deviation from the ideal square-planar geometry due to
the steric repulsion between the PEt3 and PPh3 ligands, which
causes the Et3P−Pt−PEt3 linkage to bend toward the
pentacenyl ring (P1−Pt−P2 = 162.48(8)°) and elongation of
H
5,7,12,14), 7.96−7.94 (m, 4H, H1,4,8,11), 7.44−7.42 (m, 4H, H2,3,9,10),
7.38 (t, 2H, p-C6H3), 7.27 (d, 4H, m-C6H3), 2.60 (s, 12H, CH3),
2.37−2.34 (m, 24H, PCH2CH3), 1.41−1.35 (m, 36H, PCH2CH3).
31P{1H} NMR (202.4 MHz, CDCl3): δ 17.11 (s, JPt−P = 2074 Hz).
1
ESI-MS: m/z 724.2, [M − 2ClO4]2+.
X-ray Crystallography. The diffraction experiments were carried
out on a Bruker AXS SMART CCD three-circle diffractometer with a
sealed tube at 223 K using graphite-monochromated Mo Kα radiation
(λ = 0.710 73 Å). The software used was as follows: SMART22a for
collecting frames of data, indexing reflections, and determining lattice
parameters; SAINT22a for integration of intensity of reflections and
́
the Pt−PEt3 bonds (2.333(2) and 2.346(2) Å). The Pt−PPh3
bond distance of 2.308 (2) Å falls in the normal range of Pt−
26
́
PPh3 bond lengths (2.29−2.37 Å). Despite the different
electronic properties of L, the Pt−C(acetylide) distances in the
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Table 1. Crystal Data for 1b, 2·2CH2Cl2, 3, 4·2H2O, 5·CH2Cl2, and 6
1b
2·2CH2Cl2
3
4·2H2O
5·CH2Cl2
6
empirical formula
formula wt
cryst syst
space group
unit cell dimens
a (Å)
C74H120I2P4Pt2 C64H86Cl4P4Pt2S2 C66H82P4Pt2
C88H106F6O8P6Pt2S2 C63H84Cl2F6N2O6P4Pt2S2 C68H90Cl2N2O8P4Pt2
1777.56
monoclinic
P21/c
1575.31
triclinic
1389.38
monoclinic
P21/n
2045.85
monoclinic
P2/n
1728.4
1648.38
monoclinic
P21/c
triclinic
P1
̅
P1
̅
8.9087(12)
15.686(2)
27.615(4)
90
8.5325(19)
12.255(3)
15.834(4)
95.889(4)
95.537(4)
100.011(4)
1610.8(6)
1
9.3267(12)
10.0902(13)
32.989(4)
90
22.021(4)
9.6457(17)
22.317(4)
90
9.359(5)
19.357(9)
20.162(10)
77.513(9)
85.523(10)
78.643(9)
3494(3)
2
18.470(3)
9.6544(13)
39.616(6)
90
b (Å)
c (Å)
α (deg)
β (deg)
97.571(4)
90
94.049(10)
90
111.396
90
99.540(3)
90
γ (deg)
V (Å3)
3825.4(9)
2
3096.8(7)
2
4413.6(13)
2
6966.5(16)
4
Z
calcd density (g cm−3
)
1.543
1.624
1.49
1.539
1.643
1.572
abs coeff (mm−1
)
4.581
4.706
4.653
3.388
4.292
4.234
F(000)
cryst size (mm3)
1772
786
1388
2060
1720
3304
0.90 × 0.12 × 0.30 × 0.06 ×
0.06
0.30 × 0.12 ×
0.10
0.40 × 0.26 × 0.08
0.60 × 0.10 × 0.04
0.60 × 0.14 × 0.04
0.06
θ range for data collecn (deg) 1.49−27.49
1.30−25.00
2.11−27.50
1.63−25.00
1.34−27.50
1.12−25.00
index ranges
−11 ≤ h ≤ 11 −10 ≤ h ≤ 10
−20 ≤ k ≤ 19 −14 ≤ k ≤ 14
−30 ≤ l ≤ 35 −18 ≤ l ≤ 18
−11 ≤ h ≤ 12 −26 ≤ h ≤ 25
−13 ≤ k ≤ 10 −11 ≤ k ≤ 11
−12 ≤ h ≤ 12
−25 ≤ k ≤ 25
−26 ≤ l ≤ 26
44 567
−20 ≤ h ≤ 21
−11 ≤ k ≤ 11
−47 ≤ l ≤ 44
39 257
−42 ≤ l ≤ 41
21 506
−26 ≤ l ≤ 23
25 105
no. of rflns collected
no. of indep rflns (R(int))
max, min transmissn
26 707
16 877
8775 (0.0397) 5664 (0.0670)
0.7706, 0.1044 0.7655, 0.3326
7087 (0.0442)
7758 (0.0607)
15 964 (0.0853)
0.8471, 0.1827
15 964/133/821
12 264 (0.0738)
0.8489, 0.1856
11 264/603/1025
0.6662, 0.5459 0.7733, 0.3443
no. of data/restraints/params 8775/0/376
5664/0/349
7087/41/348
7758/53/550
a
final R indices (I > 2σ(I))
R1
0.0296
0.0658
1.063
0.0494
0.0999
1.109
0.0366
0.0615
0.0684
0.0603
wR2
0.0845
0.1397
0.1758
0.1396
b
goodness of fit (GOF)
largest diff peak, hole (e Å−3) 2.012, −0.569
R1 = (||Fo| − |Fc||)/(|Fo|); wR2 = [w(Fo2 − Fc2)/w(Fo )]1/2. GOF = [(w(Fo − Fc2)2/(n − p)]1/2. For all crystal determinations, the scan type and
wavelength of radiation used are ω and 0.710 73 Å, respectively.
1.078
1.142
1.033
1.02
1.722, −3.826
2.288, −0.748
2.792, −1.063
14.832, −2.657
2.460, −1.402
a
b
4
2
between the planes and the pentacenyl rings are 59.58, 69.21,
70.83, and 78.24°, respectively.
The pentacenyl rings of 1b, 2·2CH2Cl2, and 4·2H2O are
widely separated (>6 Å) and are parallel in the crystals. It is
noted that some H atoms of the butyl groups (1b) and the
ethyl groups (2·2CH2Cl2 and 4·2H2O) are close to the
pentacenyl rings with calculated H(Bu/Et)−C(pentacenyl ring)
distances of 2.644−2.893 Å, which fall within the range of
C−H···π hydrogen bonds,28 suggesting the presence of these
interactions (Figure 2b).
The pentacenyl rings in the crystals of 3 (Figure 4b) and
5·CH2Cl2 (Figure 6b) slightly overlap in a head-to-tail
fashion, forming staircaselike patterns. The two overlapped
rings in 5·CH2Cl2 are offset along the short axes of the rings.
́
The rings in 3 are uniformly separated by 3.466 Å
Figure 1. (a) ESI-MS cluster peak for [1a]+ and (b) simulated isotopic
distribution for [1a]+.
(perpendicular distance between the mean planes of the
rings), but the rings in 5·CH2Cl2 are alternately separated by
3.477 and 3.422 Å. The distances fall in the range of π−π
́
interactions.29
́
complexes are rather similar (1.984(9)−1.963(9) Å). The Pt−
The pentacenyl rings in the crystal of 6 form a 2D
herringbone pattern (Figure 7b) similar to that of pentacene.
Each pentacenyl ring is involved in edge-to-face C−H···π
interactions with the rings in two adjacent columns. The
interacting rings are nearly perpendicular to each other,
showing a dihedral angle of 87.95°, which is larger than the
corresponding angle (51.78°) in the crystal of pentacene.30 The
terminal H1, H2, H8, and H9 atoms of the pentacenyl ring are
X bond distances are normal.23c,27
In 1b, 2·2CH2Cl2, 3, and 4·2H2O, the coordination planes of
the two Pt ions are parallel to each other and make a dihedral
angles of 89.14, 72.82, 87.45, and 73.12°, respectively, with the
central pentacenyl ring. On the other hand, the two
coordination planes in 5·CH2Cl2 and 6 are staggered (dihedral
angles 54.82 and 32.91°, respectively) and the dihedral angles
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Figure 4. (a) ORTEP plot of 3 (thermal ellipsoids drawn at the 50%
probability level). H atoms and disordered ethyl groups are not shown
for clarity. Color scheme: Pt, green; P, orange; C, gray. (b) π−π
stacking of 3.
Figure 2. (a) ORTEP plot of 1b (thermal ellipsoids drawn at the 50%
probability level). H atoms are not shown for clarity. Color scheme:
Pt, green; P, orange; C, gray; I, purple. (b) Solid-state packing of 1b
showing possible C−H···π interactions between H atoms (light gray)
́
́
of butyl groups and the pentacenyl rings (d1 = 2.704 Å; d2 = 2.845 Å;
́
́
́
́
d3 = 2.876 Å; d4 = 2.853 Å; d5 = 2.845 Å; d6 = 2.883 Å).
Figure 5. ORTEP plot of 4·2H2O (thermal ellipsoids drawn at the
50% probability level). H atoms, anions, and water molecules are not
shown for clarity. Color scheme: Pt, green; P, orange; C, gray.
Absorption and Emission Spectroscopy. Figure 8
shows the absorption spectra of the complexes, and spectral
data are summarized in Table 3. Complex 1a is sparingly
soluble, and therefore only its solution emission was measured.
All the complexes display four absorption bands: a broad intense
vibronic band at 500−770 nm (I), a weak and narrow band
around 435−444 nm (II), a shoulder at 356−377 nm (III), and a
very strong, sharp band at 314−320 nm (IV). The spectra of
pentacene and TIPS-pentacene display similar absorptions,
but at higher energies. The absorption bands are assigned
Figure 3. ORTEP plot of 2·2CH2Cl2 (thermal ellipsoids drawn at
the 50% probability level). H atoms and solvent molecules are not
shown for clarity. Color scheme: Pt, green; P, orange; C, gray; S,
yellow.
1
to π → π* transitions primarily localized in the pentacenyl-
6,13-diacetylide ligand. Pentacene belongs to a class of mole-
cules called alternant hydrocarbons, which exhibit intense
absorptions arising from four electronic transitions, namely
LUMO ← HOMO (1B1u ← 1Ag), LUMO ← HOMO-1 (1B2u ←
directed toward the first and second rings of its two adjacent
pentacenyl rings. The centroid−centroid distance between
the terminal (six-membered) ring of the first molecule and
the second (six-membered) ring of the adjacent molecule is
5.146 Å (4.713 Å for pentacene). The distance is typical for
edge-to-face interactions between aromatic molecules.31
1
1Ag), LUMO+1 ← HOMO (1B2u ← Ag), and LUMO+1 ←
́
HOMO-1 (1B1u ← 1Ag). The second and third transitions lead
to the two degenerate 1B2u excited states, which undergo strong
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Figure 7. (a) ORTEP plot of 6 (thermal ellipsoids drawn at the 30%
probability level). H atoms, anions, and disordered xylyl groups are not
shown for clarity. Color scheme: Pt, green; P, orange; C, gray; N, blue.
(b) Herringbone pattern of the pentacenyl rings of 6. For clarity, only
the rings are shown.
Figure 6. (a) ORTEP plot of 5·CH2Cl2 (thermal ellipsoids drawn at
the 30% probability level). H atoms, anions, and solvent molecules are
not shown for clarity. Color scheme: Pt, green; P, orange; C, gray; N,
blue. (b) π−π stacking of 5·CH2Cl2.
platination and alkynylation collectively red-shifts the transition
up to 2740 cm−1 (0.34 eV).
Interestingly, the complexes can be divided into two
groups on the basis of the energies of their LUMO ←
HOMO transitions. The neutral complexes have similar
LUMO ← HOMO transition energies (λ max 687−696 nm)
which are invariably lower than those of the cationic
complexes (λ max 662−664 nm). In addition, the neutral
complexes show broader bands I. Although the red shift
(440−740 cm−1) is small, it is significant, as it clearly
indicates that the absorption energy is sensitive to the
[L(R3P)2Pt]n+ ions. Notably, while 4−6 do not show any
significant absorption beyond 700 nm, the bands I of 1b, 2,
and 3 extend into the near-IR region.
All the complexes are photoluminescent, and their solution
and solid-state emission spectra are shown in Figures 9 and 10,
respectively. The fluorescence of 1a,b, 2, and 3 spans from 650
to 900 nm and that of 4−6 from 630 to 850 nm. The lifetimes
and quantum yields of the solution emission are given in Table 3.
The nanosecond lifetimes (2.7−8.9 ns) and small Stokes
shifts between the emission and the LUMO ← HOMO
transition suggest the luminescence is LUMO → HOMO
(S1 → S0) fluorescence centered in the pentacenyl ring.
Quantum yields of the emission range from 0.025 to 0.162.
Similar to the case for the absorptions, the fluorescences of the
complexes are red-shifted from the fluorescence of TIPS-
pentacene (λmax = 656 nm) and pentacene (λ max 578 nm) by
430−1470 and 2490−3530 cm−1, respectively. In accord with
the energies of the LUMO ← HOMO transitions, the
emissions of 1a,b, 2, and 3 (λmax 710−726 nm) are 490−
1040 cm−1 lower than those of 4−6 (λmax 675−686 nm). Table 4
shows the percentage of emission intensity at wavelengths
shorter and longer than 700 nm.
configuration interaction to give the high-energy “plus” state
32
−
1B2u and the low-energy “minus” state B2u
.
Although the
+
1
symmetries of the Pt2 complexes and pentacene are different,
there is still a direct correspondence between the four absorp-
tion bands displayed by the complexes and the four electronic
transitions of pentacene. Band I in the spectra of the complexes
1
corresponds to the LUMO ← HOMO (1B1u ← Ag) transition,
which is also known as an S0 (singlet ground state) → S1(the
lowest energy singlet excited state) transition. The intense band
1
IV corresponds to the LUMO+1 ← HOMO-1 (1B1u ← Ag)
transition. The shoulder III is attributed to the transition to the
1
+
+
1
“plus” state B2u (1B2u ← Ag). The weak absorption II is
ascribable to the transition to the “minus” state (1B2u ← Ag),
which is pseudo parity forbidden. The transition is significantly
intensified in the spectra of the complexes, indicating that the
electronic structure of the pentacenyl ring is significantly
perturbed by the Pt ions and the ethynyl groups. Similar
intensification of the forbidden B2u ← Ag transition has been
observed in AuI and PtII pyrene17 and anthracene33 complexes
and is taken as evidence for metal perturbation.
−
1
1
−
1
Comparing the spectra of the complexes with that of TIPS-
pentacene shows that replacing the triisopropylsilyl groups with
the [L(R3P)2Pt]n+ ions (R = ethyl, butyl, n = 1, 2) leads to a
red shift of the four transitions. While band III is red-shifted
only slightly (∼250 cm−1), the energies of the bands I, II, and
IV are lowered by 450−1200, 480−2000, and 400−1000 cm−1,
respectively. The energy of the LUMO ← HOMO transition
(which corresponds to band I of the complexes) of pentacene is
lowered by 1540 cm−1 by substitution of triisopropylsilyle-
thynyl groups at its 6- and 13-positions. Our result shows that
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Table 2. Selected Bond Lengths (Å) and Angles (deg) for the Complexes
Article
a
́
1b
2·2CH2Cl2
3
4·2H2O
5·CH2Cl2
6
Bond Distances
1.971(5)
Pt(1)−C(1)
Pt(1)−X
Pt(1)−P(1)
Pt(1)−P(2)
1.971(4)
1.966(8)
2.363(2)
2.321(2)
2.312(2)
1.975(8)
2.308(2)
2.333(2)
2.346(2)
1.963(9)
2.088(8)
2.302(3)
2.321(3)
1.984(9)
1.928(9)
2.300(3)
2.317(2)
2.6545(3)
2.3081(10)
2.3140(10)
1.990(5)
2.2975(13)
2.2959(13)
Bond Angles
179.1(2)
C(1)−Pt(1)−X
177.48(10)
177.24(3)
90.98(10)
88.13(3)
177.7(3)
176.58(8)
87.4(2)
173.8(2)
162.48(8)
80.2(3)
177.0(4)
173.11(10)
86.5(3)
176.9(4)
174.35(9)
85.3(3)
P(1)−Pt(1)−P(2)
C(1)−Pt(1)−P(1)
X−Pt(1)−P(1)
C(1)−Pt(1)−P(2)
X−Pt(1)−P(2)
176.68(5)
92.33(14)
87.70(14)
87.23(14)
92.68(14)
171.1(5)
92.89(7)
90.8(2)
101.89(8)
82.5(3)
91.3(2)
92.6(3)
86.92(10)
93.90(3)
89.1(3)
89.1(3)
88.97(8)
177.9(8)
95.60(8)
175.9(10)
93.2(2)
93.0(3)
C(1)−C(2)−C(6)
a
177.5(4)
173.7(11)
177.8(10)
X = donor atom of the auxiliary ligand L; L = I, S, C, P, N, C for 1b and 2−6, respectively.
could increase the inductive effect, leading to further
decrease of the HOMO−LUMO gaps. The neutral
complexes with π-donating anionic ligands L show the
largest red shifts and, hence, the smallest HOMO−LUMO
gaps. In a recent study, we showed that the absorption and
fluorescence of [I(Et3P)2Pt]2-tetracenyl-5,12-diacetylide
(λ max 572 nm) are lower in energy than those of (Ph3-
PAuI)2-tetracenyl-5,12-diacetylide (λ max 553 nm).16 As the
PtII ions are stronger π-donors than the electrophilic AuI
ion, our finding highlights the effect of metal−acene π
interactions on the energies of the frontier π and π* orbitals
of the acene. It is possible that the small HOMO−LUMO
gaps in 1−3 are due to orbital interactions with [L(Et3P)2Pt]
(L = I−, PhS−, PhC2 ). Our recent study shows that the
−
HOMO of tetracenyl-5,12-diacetylide is higher in energy
than the 5dπ orbitals of the Pt ion in the [I(Et3P)2Pt]+
fragment. Similarly, the 5dπ orbitals of the Pt ions should
be lower in energy than the HOMO of the pentacenyl-6,13-
diacetylide, which is more extensively π-conjugated than
the tetracenyl-5,12-diacetylide. The anionic, π-donating L is
expected to destabilize the dπ orbital of the Pt ions, reducing
the energy gap between the metal orbitals and the HOMO of
pentacenyl-6,13-diacetylide ion (Scheme 2).
Figure 8. UV−vis absorption spectra of 1b (black), 2 (red), 3
(orange), 4 (green), 5 (blue), and 6 (violet) in CH2Cl2 at room
temperature.
While only 34.2−50.57% of the total fluorescence intensity of
4−6 is at wavelengths longer than 700 nm, the emissions of
1a,b, 2, and 3 lie mainly (77.3−87.3% of total emission
intensity) in the near-IR region. Accordingly, the complexes can
be regarded as near-IR emitters. Solids of 1a,b and 2 (λmax
768−779 nm) display emissions lower in energy than the
corresponding solution emissions. The solid-state luminescen-
ces of 1a and 2 are weak, and solids of 3−6 are not emissive.
Given the orbital parentage of the absorption and emission,
the energies of the transitions can be used to gauge the
HOMO−LUMO gaps. In view of the localization of the excited
state in the pentacenyl ring, it is reasonable to assume that the
exchange interaction and electron−electron repulsion in the
lowest energy singlet excited states of the complexes and in
TIPS-pentacene and pentacene are similar. Also, according to
the energies of LUMO ← HOMO transitions, the HOMO−
LUMO gaps follow the order 1a,b, 2, 3 < 4−6 < TIPS-
pentacene < pentacene. Recent computational studies14 showed
that the HOMO−LUMO gap in TIPS-pentacene is reduced
because of the inductive effect of the sp-hybridized ethynyl
substituents, which preferentially stabilize the LUMO more than
the HOMO. The reduced HOMO−LUMO gaps in the Pt2
complexes are partly due to the inductive effect of the ethynyl
groups. Replacing the triisopropylsilyl groups with the positively
charged [L(Et3P)2Pt]2+ (L = pyridine, PPh3, 2,6-xylyl isocyanide)
According to second-order perturbation theory,34 decreasing
the energy gap would increase the extent of metal−ligand
orbital interactions, resulting in a more destabilized HOMO
and LUMO. Since the dπ orbitals are closer in energy to the
HOMO than to the LUMO, the HOMO should be more
destabilized than the LUMO by the π interactions. The overall
result is a decrease of the HOMO−LUMO gap (Scheme 2).
On the other hand, the 5dπ orbitals of the Pt ions in the
cationic complexes should be lower in energy than those of the
neutral complexes. As the gap between the metal and ligand
orbitals increases, the π interactions become weaker and hence
the red shifts of the absorption and fluorescence become
smaller.
Cyclic voltammograms (CVs) of 3 and 5 show two quasi-
reversible oxidation waves at −0.18 and 0.37 V and at 0.08 and
0.60 V (vs Fc+/Fc). The first oxidation of the complexes is
cathodically shifted from the corresponding oxidation of TIPS-
pentacene, which occurs at −0.38 V. It is consistent with the
proposed bonding picture where the HOMOs of the
complexes, which should be mainly localized in the
pentacenyl-6,13-diacetylide, are destabilized by the metal−
ligand π interactions. The fact that the first oxidation potential
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Table 3. Absorption and Emission Spectroscopic Data of the Compounds
emission max
(nm)
band (nm) (ε (10−4 M−1cm−1))
solid
emission
emission quantum
compd
I
II
III
IV
soln state lifetime τfl (ns)
yield Φfl
b
1a
1b
a
a
a
a
710 779
4.0
5.0
a
687 (3.20), 632 (1.78), 586 (0.62) (s) 442 (0.25)
694 (3.04), 637 (1.73), 589 (0.66) (s) 443 (0.32)
696 (3.32), 639 (1.89), 590 (0.66) (s) 444 (0.36)
364 (1.73) (s),
339 (2.86)
318 (28.67) 713 768
0.072
b
2
366 (1.97) (s),
339 (3.48)
319 (24.45) 723 778
3.2
0.025
3
4
377 (2.41)
320 (29.60) 726
314 (25.20) 675
c
c
2.7
8.9
0.025
0.162
664 (3.34), 610 (1.73), 564 (0.59) (s) 435 (0.34), 410
(0.40) (s)
361 (1.33) (s),
331 (3.24)
5
6
666 (2.80), 613 (1.53), 565 (0.54) (s) 436 (0.30), 410
(0.37) (s)
363 (1.45)
315 (26.97) 686
314 (20.73) 677
c
c
6.0
5.8
0.079
0.082
662 (3.80), 609 (2.04), 563 (0.74) (s) 439 (0.44), 413
(0.50), 395 (0.74)
356 (1.70) (s),
341 (3.26) (s)
a
b
c
Not determined accurately because of the poor solubility of 1a. The emission intensity is very weak. Nonemissive.
Table 4. Percentage of Emission Intensity at Wavelengths
<700 nm and >700 nm
compd
<700 nm (%)
>700 nm (%)
1a
1b
2
22.7
18.7
12.2
11.6
65.8
49.3
57.0
77.3
81.3
87.8
88.4
34.2
50.7
43.0
3
4
5
6
Scheme 2
Figure 9. Solution emission spectra of the complexes in CH2Cl2 at
room temperature.
CONCLUSION
■
In this study, we demonstrated that the electronic structure of
pentacenyl-6,13-diacetylide can be perturbed by PtII coordina-
tion. The extent of perturbation, as reflected by the red shift of
the absorption and fluorescence, is sensitive to the electronic
properties of the [L(R3P)2Pt]n+ ions. The π-donating and
anionic auxiliary ligands have stronger perturbation than the
π-accepting, neutral ligands. The fluorescence of the complexes
is mainly based on the pentacenyl ring, and the Pt ions appended
with π-donating, anionic ligands can shift the fluorescence to
the near-IR region. The combined perturbations of alkynation
and platination lowered the LUMO ← HOMO transition up to
0.34 eV.
Figure 10. Solid-state emission spectra of 1a (brown), 1b (black), and
2 (orange) at room temperature.
of 3 (−0.18 V) is lower than that of 5 (0.08 V) indicates that
the HOMO energy of 3 is higher than that of 5, as suggested
by the electronic spectroscopy of the complexes. Complexes
3 and 5 show reduction waves at −1.86 and −1.73 V,
respectively, which are lower than the corresponding
reduction of TIPS-pentacene (−1.50 V), suggesting that
the LUMOs of the complexes are destabilized by the metal−
ligand interactions.
ASSOCIATED CONTENT
■
S
* Supporting Information
CIF files giving crystallographic data for 1b, 2·2CH2Cl2, 3, 4·2H2O,
5·CH2Cl2, and 6, and figures giving cyclic voltammograms of 3, 5,
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Article
5669−5681. (c) Wang, B.-Y.; Karikachery, A. R.; Li, Y.; Singh, A.; Lee,
H. B.; Sun, W.; Sharp, P. R. J. Am. Chem. Soc. 2009, 131, 3150−3151.
(d) Khan, M. S.; Al-Mandhary, M. R. A.; Al-Suti, M. K.; Al-Battashi, F.
R.; Al-Saadi, S.; Ahrens, B.; Bjernemose, J. K.; Mahon, M. F.; Raithby,
P. R.; Younus, M.; Chawdhury, N.; Kohler, A.; Marseglia, E. A.;
Tedesco, E.; Feeder, N.; Teat, S. J. Dalton Trans. 2004, 2377−2385.
(e) Chan, C. K. M.; Tao, C.-H.; Tam, H.-L.; Zhu, N.; Yam, V. W.-W.;
Cheah, K.-W. Inorg. Chem. 2009, 48, 2855−2864. (f) Kim, K.-Y.; Liu,
and TIPS-pentacene. This material is available free of charge via
the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: chmyiphk@nus.edu.sg.
S.; Kose, M. E.; Schanze, K. S. Inorg. Chem. 2006, 45, 2509−2519.
ACKNOWLEDGMENTS
̈
■
(g) Wong, W.-Y.; Ho, C.-L. Acc. Chem. Res. 2010, 43, 1246−1256.
(h) Wong, W.-Y.; Ho, C.-L. Coord. Chem. Rev. 2006, 250, 2627−2690.
(i) Wong, W.-Y. Dalton Trans. 2007, 4495−4510. (j) Wong, W.-Y.;
Harvey, P. D. Macromol. Rapid Commun. 2010, 31, 671−713.
(k) Wong, W.-Y. Macromol. Chem. Phys. 2008, 209, 14−24.
(l) Wong, W.-Y.; Wang, X.-Z.; He, Z.; Djurisic, A. B.; Yip, C.-T.;
Cheung, K.-Y.; Wang, H.; Mak, C. S. K.; Chan, W.-K. Nat. Mater.
2007, 6, 521−527.
We are grateful to Prof. Koh Lip Lin and Ms. Tan Geok Kheng
for determining the X-ray structures. The Ministry of Education
(R-143-000-429-112) of Singapore and the National University
of Singapore are thanked for financial support.
REFERENCES
■
(1) (a) Escobedo, J. O.; Rusin, O.; Lim, S.; Strongin, R. M. Curr.
Opin. Chem. Biol. 2010, 14, 64−70. (b) Qian, G.; Wang, Z. Y. Chem.
Asian J. 2010, 5, 1006−1029.
(16) Nguyen, M.-H.; Yip, J. H. K. Organometallics 2010, 29, 2422−
2429.
(17) (a) Hu, J.; Yip, J. H. K.; Ma, D.-L.; Wong, K.-Y.; Chung, W.-H.
Organometallics 2009, 28, 51−59. (b) Heng, W. Y.; Hu, J.; Yip, J. H. K.
Organometallics 2007, 26, 6760−6768.
(2) (a) Borek, C.; Hanson, K.; Djurovich, P. I.; Thompson, M. E.;
Aznavour, K.; Bau, R.; Sun, Y.; Forrest, S. R.; Brooks, J.; Michalski, L.;
Brown, J. Angew. Chem., Int. Ed. 2007, 46, 1109−1112. (b) Won, D.-H.;
Toganoh, M.; Terada, Y.; Fukatsu, S.; Uno, H.; Furuta, H. Angew. Chem.,
Int. Ed. 2008, 47, 5438−5441.
(3) (a) Arunkumar, E.; Forbes, C. C.; Noll, B. C.; Smith, B. D. J. Am.
Chem. Soc. 2005, 127, 3288−3289. (b) Arunkumar, E.; Fu, N.; Smith,
B. D. Chem. Eur. J. 2006, 12, 4684−4690.
(18) Hannebohn, O.; Klemm, W. Z. Anorg. Allg. Chem. 1936, 229,
225−251.
(19) Rahn, J. A.; Baltusis, L.; Nelson, J. H. Inorg. Chem. 1990, 29,
750−755.
(20) Chen, J.; Subramanian, S.; Parkin, S. R.; Siegler, M.; Gallup, K.;
Haughn, C.; Martin, D. C.; Anthony, J. E. J. Mater. Chem. 2008, 18,
1961−1969.
(4) (a) Zhao, W.; Carreira, E. M. Angew. Chem., Int. Ed. 2005, 44,
1677−1679. (b) McDonnell, S. O.; O’Shea, D. F. Org. Lett. 2006, 8,
3493−3496.
(21) Isak, S. J.; Eyring, E. M. J. Phys. Chem. 1992, 96, 1738−1742.
(22) (a) SMART & SAINT Software Reference Manuals, version 4.0;
Siemens Energy and Automation, Inc., Analytical Instrumentation:
Madison, WI, 1996. (b) Sheldrick, G. M. SADABS: Software for
́
(5) (a) Zucchi, G. l.; Maury, O.; Thuery, P.; Ephritikhine, M. Inorg.
Chem. 2008, 47, 10398−10406. (b) Ronson, T. K.; Lazarides, T.;
Adams, H.; Pope, S. J. A.; Sykes, D.; Faulkner, S.; Coles, S. J.;
Hursthouse, M. B.; Clegg, W.; Harrington, R. W.; Ward, M. D. Chem.
Eur. J. 2006, 12, 9299−9313.
Empirical Absorption Correction; University of Gottingen, Gottingen,
̈
̈
Germany, 1996. (c) SHELXTL Reference Manual, version 5.03; Siemens
Energy and Automation, Inc., Analytical Instrumentation: Madison,
WI, 1996.
̇
(6) (a) Altınoğlu, E. I.; Adair, J. H. Wiley Interdiscip. Rev.: Nanomed.
Nanobiotechnol. 2010, 2, 461−477. (b) Wang, X.-Z.; Wong, W.-Y.;
Cheung, K.-Y.; Fung, M.-K.; Djurisic, A. B.; Chan, W.-K. Dalton Trans.
2008, 5484−5494. (c) Wang, X.-Z.; Wang, Q.; Yan, L.; Wong, W.-Y.;
(23) (a) Yam, V. W.-W.; Tao, C.-H.; Zhang, L.; Wong, K. M.-C.;
Cheung, K.-K. Organometallics 2001, 20, 453−459. (b) Tao, C.-H.;
Zhu, N.; Yam, V. W.-W. Chem. Eur. J. 2005, 11, 1647−1657.
(c) Chang, X.; Lee, K.-E.; Il Jeon, S.; Kim, Y.-J.; Lee, H. K.; Lee, S. W.
Dalton Trans. 2005, 3722−3731.
(24) Chanda, N.; Sharp, P. R. Organometallics 2007, 26, 3368−3373.
(25) Ghosh, S.; Chakrabarty, R.; Mukherjee, P. S. Inorg. Chem. 2009,
48, 549−556.
̌ ́
Cheung, K.-Y.; Ng, A.; Djurisic, A. B.; Chan, W.-K. Macromol. Rapid
Commun. 2010, 31, 861−867.
(7) (a) Pschirer, N. G.; Kohl, C.; Nolde, F.; Qu, J.; Mullen, K. Angew.
̈
Chem., Int. Ed. 2006, 45, 1401−1404. (b) Zhou, G. J.; Wong, W. Y.;
Ye, C.; Lin, Z. Adv. Funct. Mater. 2007, 17, 963−975. (c) Zhou, G.-J.;
Wong, W.-Y. Chem. Soc. Rev. 2011, 40, 2541−2566. (d) Aly, S. M.; Ho,
C.-L.; Wong, W.-Y.; Fortin, D.; Harvey, P. D. Macromolecules 2009, 42,
6902−6916. (e) Liu, L.; Wong, W.-Y.; Poon, S.-Y.; Shi, J.-X.; Cheah,
K.-W.; Lin, Z. Chem. Mater. 2006, 18, 1369−1378.
(26) (a) Al-Resayes, S. I.; Hitchcock, P. B.; Nixon, J. F.; Mingos, D.
M. P. J. Chem. Soc., Chem. Commun. 1985, 365−366. (b) Stang, P. J.;
Kowalski, M. H.; Schiavelli, M. D.; Longford, D. J. Am. Chem. Soc.
1989, 111, 3347−3356.
(8) Maulding, D. R.; Roberts, B. G. J. Org. Chem. 1969, 34, 1734−
1736.
(9) Perkampus, H.-H. UV-VIS Atlas of Organic Compounds, 2nd ed.;
VCH: Weinheim, Germany, 1992.
(27) (a) Johnson, C. A.; Haley, M. M.; Rather, E.; Han, F.; Weakley,
́ ̀
T. J. R. Organometallics 2005, 24, 1161−1172. (b) Arevalo, A.; Bernes,
́
S.; Garcia, J. J.; Maitlis, P. M. Organometallics 1999, 18, 1680−1685.
(c) Constable, E. C.; Housecroft, C. E.; Neuburger, M.; Schaffner, S.;
Shardlow, E. J. Dalton Trans. 2005, 234−235. (d) Crisp, M. G.;
Tiekink, E. R. T.; Rendina, L. M. Inorg. Chem. 2003, 42, 1057−1063.
(28) (a) Nishio, M.; Hirota, M.; Umezawa, Y. The CH/π interaction:
Evidence, Nature, and Consequences; Wiley-VCH: New York, 1998.
(b) Nishio, M.; Hirota, M. Tetrahedron 1989, 45, 7201−7245.
(c) Nishio, M.; Umezawa, Y.; Hirota, M.; Takeuchi, Y. Tetrahedron
1995, 51, 8665−8701. (d) Desiraju, G. R. Acc. Chem. Res. 2002, 35,
565−573. (e) Desiraju, G. R.; Steiner, T. The Weak Hydrogen Bond: In
Structural Chemistry and Biology; Oxford University Press: New York,
1999.
(10) (a) Laquindanum, J. G.; Katz, H. E.; Lovinger, A. J. J. Am. Chem.
Soc. 1998, 120, 664−672. (b) Maliakal, A.; Raghavachari, K.; Katz, H.;
Chandross, E.; Siegrist, T. Chem. Mater. 2004, 16, 4980−4986.
(11) Takahashi, T.; Kitamura, M.; Shen, B.; Nakajima, K. J. Am.
Chem. Soc. 2000, 122, 12876−12877.
(12) Anthony, J. E.; Brooks, J. S.; Eaton, D. L.; Parkin, S. R. J. Am.
Chem. Soc. 2001, 123, 9482−9483.
(13) (a) Coppo, P.; Yeates, S. G. Adv. Mater. 2005, 17, 3001−3005.
(b) Griffith, O. L.; Gruhn, N. E.; Anthony, J. E.; Purushothaman, B.;
Lichtenberger, D. L. J. Phys. Chem. C 2008, 112, 20518−20524.
(14) Kaur, I.; Jia, W.; Kopreski, R. P.; Selvarasah, S.; Dokmeci, M. R.;
Pramanik, C.; McGruer, N. E.; Miller, G. P. J. Am. Chem. Soc. 2008,
130, 16274−16286.
(15) (a) Partyka, D. V.; Esswein, A. J.; Zeller, M.; Hunter, A. D.;
Gray, T. G. Organometallics 2007, 26, 3279−3282. (b) Gao, L.; Peay,
M. A.; Partyka, D. V.; Updegraff, J. B.; Teets, T. S.; Esswein, A. J.;
Zeller, M.; Hunter, A. D.; Gray, T. G. Organometallics 2009, 28,
(29) (a) Anthony, J. E.; Eaton, D. L.; Parkin, S. R. Org. Lett. 2002, 4,
15−18. (b) Lehnherr, D.; Murray, A. H.; McDonald, R.; Ferguson, M.
J.; Tykwinski, R. R. Chem. Eur. J. 2009, 15, 12580−12584. (c) Roesky,
H. W.; Andruh, M. Coord. Chem. Rev. 2003, 236, 91−119. (d) Janiak,
C. Dalton Trans. 2000, 3885−3896.
6391
dx.doi.org/10.1021/om2005645|Organometallics 2011, 30, 6383−6392

Organometallics
Article
(30) Holmes, D.; Kumaraswamy, S.; Matzger, A. J.; Vollhardt, K. P.
C. Chem. Eur. J. 1999, 5, 3399−3412.
(31) (a) Jorgensen, W. L.; Severance, D. L. J. Am. Chem. Soc. 1990,
112, 4768−4774. (b) Paliwal, S.; Geib, S.; Wilcox, C. S. J. Am. Chem.
Soc. 1994, 116, 4497−4498. (c) McNelis, B. J.; Nathan, L. C.; Clark,
C. J. J. Chem. Soc., Dalton Trans. 1999, 11, 1831−1834.
(32) (a) Ham, N. S.; Ruedenberg, K. J. Chem. Phys. 1956, 25, 13−26.
(b) Pariser, R. J. Chem. Phys. 1956, 24, 250−268. (c) Klessinger, M.;
Michl, J. Excited States and Photochemistry of Organic Molecules; VCH:
Weinheim, Germany, 1995.
(33) Hu, J.; Lin, R.; Yip, J. H. K.; Wong, K.-Y.; Ma, D.-L.; Vittal, J. J.
Organometallics 2007, 26, 6533−6543.
(34) Albright, T. A.; Burdett, J. K.; Whangbo, M.-H. Orbital
Interactions in Chemistry; Wiley-Interscience: New York, 1985.
6392
dx.doi.org/10.1021/om2005645|Organometallics 2011, 30, 6383−6392