DSpace at VNU: Sequence-specific synthesis of platinum-conjugated trichromophoric energy cascades of anthracene, tetracene, and pentacene and fluorescent "black chromophores"

Article
pubs.acs.org/Organometallics

Sequence-Specific Synthesis of Platinum-Conjugated
Trichromophoric Energy Cascades of Anthracene, Tetracene, and
Pentacene and Fluorescent “Black Chromophores”
Minh-Hai Nguyen,† Van Ha Nguyen, and John H. K. Yip*
Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore, 117543
S Supporting Information
*

ABSTRACT: A sequence-specific synthesis of trichromophoric energy
cascades containing anthracenyl (A), tetracenyl (T), or pentacenyl (P) rings
is achieved by coupling PtII ions and singly desilylated bis(triisopropylsilylethynyl)acenes (acene = anthracene, tetracene, or pentacene). Four sequences,
T-P-T, P-T-P, A-P-T, and A-T-P, are generated. Absorption spectra of the
triads show intense bands due to the S0 → S1 transitions of the acenes. The AP-T and A-T-P, being able to absorb strongly throughout the entire visible
region, are rare examples of “black chromophores”. Different sequences are
shown to have different emission fingerprints. Emission spectra of A-P-T and
A-T-P show that excitation at the S0 → S1 band of A gives rise to emissions
from the S1 excited states of A, T, and P, implying the presence of energy
transfer from the excited state of A to those of T and P.

■

INTRODUCTION
Many multichromophoric molecules were devised as models
for understanding kinetics of intramolecular energy transfer1 or
electron transfer.2 A subset of the molecules is energy cascades,
which have a stepwise arrangement of electronic excited states
of different chromophores. Energy cascades have been actively
studied as molecular wires and light antenna for artificial

photosynthesis.3 In this regard, various dyads and triads
containing chromophores, such as porphyrins,4 RuII(2,2′bipyridine)3,5 polycyclic aromatic hydrocarbons (PAHs),6 and
BODIPY7 dyes, have been devised.
Efficient energy transfer between chromophores depends on
their distance and orientation as well as their excited state
manifolds. An early study of Meyer et al.8 highlighted the
important role played by an intermediate excited state in
mediating energy transfer from a donor to an acceptor: in a
polymer containing RuII(bipy)3, OsII(bipy)3, and an anthracenyl ring, facile energy transfer from the metal-to-ligand
charge-transfer excited state (3MLCT) of RuII(bipy)3 to the
3
MLCT excited state of OsII(bipy)3 is mediated by the triplet
excited state of the anthracenyl ring that is situated between the
two MLCT excited states in terms of energy. Anthracene (A),
tetracene (T), and pentacene (P) form a homologous series
that has similar electronic structures. As the number of fused
rings increases, the HOMO−LUMO gap decreases,9 and
consequently, the energy of the lowest singlet excited states
S1 of the molecules follows the order A > T > P (Scheme 1).
The clear ordering allows realization of stepwise energy casades
in linear arrays of the three chromophores. In addition,
combining the three acenes in one molecule would lead to a
new excited state manifold that includes not only the S1 excited
© XXXX American Chemical Society

Scheme 1

states but also other excited states such as the lowest triplet
excited states T1.
Schanze and his co-workers pioneered the use of transPtII(L)2(CCR)2 (L = phosphine) to connect different

chromophores to form monodispersed oligomers or molecular
wires that exhibit two-photon absorption,10a nonlinear optical
properties,10b photoinduced charge separation,10c energy transfer,10d or exciton migration.10e Our previous studies11 showed
that desilylation of 5,12-bis(triisopropylsilylethynyl)tetracene
(TIPS-T)12 and 6,13-bis(triisopropylsilylethynyl)pentacene
(TIPS-P),13 which were first synthesized by Anthony et
Received: June 20, 2013

A

dx.doi.org/10.1021/om400578t | Organometallics XXXX, XXX, XXX−XXX


Organometallics

Article

Scheme 2

Scheme 3

al.12,13, generates acetylides that can coordinate to the PtII ion
to form binuclear [I(Et3P)2PtII]2-5,12-diethynyltetracene11a and
[I(Et3P)2PtII]2-6,13-diethynylpentacene,11b and mononuclear
trans-[I(Et3P)2PtII]-{5-ethynyl-12-[(triisopropylsilyl)ethynyl]tetracene} and trans-[I(Et3P) 2PtII]-{6-ethynyl-13-[(triisopropylsilyl)ethynyl]pentacene}.11c It is envisioned that, in
conjugation with bis(triisopropylsilylethynyl)anthracene
(TIPS-A), these molecules can be employed in building triads
that contain the three chromophores shown in Schemes 2 and
3. The dipole of the S1 excited state of the chromophores is
known to be polarized along their long molecular axes.14a−c In

the linear arrangement of the chromophores depicted in
Scheme 2, the dipoles would be aligned along the molecular
axis. This arrangement is expected to facilitate Foster resonance
energy transfer.14d Apart from the excited state energy ordering,
spatial arrangement of different chromophores in a molecule
could affect the direction and efficiency of energy flow. It is,
therefore, essential to develop a programmable approach that
allows specific sequences of the chromophores in the linear
array to be synthesized. Herein, we report the first sequencespecific synthesis of energy cascades that have different
combinations of the chromophores including T-P-T, A-P-T,
B

dx.doi.org/10.1021/om400578t | Organometallics XXXX, XXX, XXX−XXX


Organometallics

Article

tetracene), 9.05 (d, J = 8.2 Hz, 2H, H1-tetracene), 8.28−8.26 (m, 6H,
H7-tetracene, H1,4,8,11-pentacene), 8.12 (d, J = 8.8 Hz, 2H, H10tetracene), 7.50−7.43 (m, 4H, H3,8-tetracene), 7.33−7.29 (m, 6H, H2tetracene, H2,3,9,10-pentacene), 7.23 (t, J = 7.6 Hz, 2H, H9-tetracene),
2.22−2.20(m, 24H, PCH2CH2CH2CH3), 1.89−1.88 (m, 24H,
PCH2CH2CH2CH3), 1.38−1.31 (m, 45H, PCH2CH2CH2CH3, iPr),
0.83 (t, J = 7.6 Hz, 12H, PCH2CH2CH2CH3). 31P{1H} NMR (202.4
MHz, C6D6): δ 5.40 (s, 1JPt−P = 2339 Hz). MALDI-TOF-MS: m/z
2386.76, [M]+.
Synthesis of T-P. To a 250 mL Schlenk flask were charged Pt2P
(0.2 g, 0.11 mmol), iPr2NH (5 mL), 5,12-bis(triisopropylsilylethynyl)tetracene (200 mg, 0.340 mmol), CuI (5 mg), and CH2Cl2 (30 mL). A
CH2Cl2 solution (50 mL) of Bu4NF (20 mg, 0.06 mmol) was slowly

added to the solution. The mixture was stirred for 12 h, and the solid
obtained from rotary evaporation was subjected to column
chromatography (silica gel, hexane:CH2Cl2 4:1) from which the
dark purple product was isolated. Yield: 70 mg, 30%. Anal. Calcd (%)
for T-P (C105H151IP4Pt2Si): C, 60.56; H, 7.31. Found: C, 60.19; H,
7.22. 1H NMR (500 MHz, C6D6): δ 9.96 (s, 3H, H6-tetracene, H5,7pentacene), 9.84 (s, 2H, H12,14-pentacene), 9.71 (s, 1H, H11tetracene), 9.29 (d, J = 8.2 Hz, 1H, H4-tetracene), 9.04 (d, J = 8.8
Hz, 1H, H1-tetracene), 8.27−8.19 (m, 5H, H7-tetracene, H1,4,8,11pentacene), 8.11 (d, J = 8.9 Hz, 1H, H10-tetracene), 7.48−7.44 (m,
2H, H2,3-tetracene), 7.32−7.22 (m, 6H, H8,9-tetracene, H2,3,9,10pentacene), 2.26−2.18 (m, 24H, PCH2CH2CH2CH3), 1.88−1.86
(m, 12H, PCH2CH2CH2CH3), 1.76−1.75 (m, 12H, PCH2CH2CH2CH3), 1.38−1.30 (m, 45H, PCH2CH2CH2CH3, iPr), 0.85 (t, J
= 7.6 Hz, 12H, PCH2CH2CH2CH3), 0.81 (t, J = 7.6 Hz, 12H,
PCH2CH2CH2CH3). 31P{1H} NMR (202.4 MHz, C6D6): δ 5.36 (s,
1
JPt−P = 2344 Hz), 1.64 (s, 1JPt−P = 2304 Hz). MALDI-TOF-MS: m/z
2082.42, [M]+.
Synthesis of A-P-T. To a 250 mL Schlenk flask were charged 9,10bis(triisopropylsilylethynyl)anthracene (0.15 g, 0.28 mmol), iPr2NH
(5 mL), CuI (5 mg), and CH2Cl2 (30 mL). To the mixture was added
a CH2Cl2 solution (50 mL) of Bu4NF (9 mg, 0.03 mmol) over 5 h,
and then T-P (30 mg, 0.01 mmol) was added to the solution. The
mixture was stirred for 12 h, and the dark brown product was collected
from column chromatography (silica gel, hexane:CH2Cl2 4:1). Yield:
16 mg, 48%. Anal. Calcd (%) for A-P-T (C132H180P4Pt2Si2): C, 67.84;
H, 7.76. Found: C, 67.42; H, 7.42. 1H NMR (500 MHz, C6D6): δ 9.98
(s, 1H, H6-tetracene), 9.97 (s, 2H, H5,7-pentacene), 9.96 (s, 2H, H12,14pentacene), 9.71 (s, 1H, H11-tetracene), 9.31−9.30 (m, 3H, H4tetracene, H4,5-anthracene), 9.07−9.04 (m, 3H, H1-tetracene, H1,8anthracene), 8.28−8.24 (m, 5H, H7-tetracene, H1,4,8,11-pentacene),
8.12 (d, J = 8.8 Hz, 1H, H10-tetracene), 7.57−7.43 (m, 8H, H2,3,6,7anthracene, H2,3,8,9-tetracene), 7.31−7.28 (m, 4H, H2,3,9,10-pentacene),
2.22−2.16 (m, 24H, PCH2CH2CH2CH3), 1.89−1.85 (m, 24H,
PCH2CH2CH2CH3), 1.40−1.27 (m, 66H, PCH2CH2CH2CH3, iPr),
0.85−0.81 (m, 36H, PCH2CH2CH2CH3). 31P{1H} NMR (202.4 MHz,
C6D6): δ 5.39 (s, 1JPt−P = 2337 Hz), 5.33 (s, 1JPt−P = 2337 Hz).
MALDI-TOF-MS: m/z 2336.76, [M]+.
Synthesis of P-T-P. Pt2T (50 mg, 0.03 mmol), iPr2NH (5 mL),

6,13-bis(triisopropylsilylethynyl)pentacene (180 mg, 0.281 mmol),
CuI (5 mg), and CH2Cl2 (30 mL) were added to a 250 mL Schlenk
flask. To the mixture was added a CH2Cl2 solution (50 mL) of Bu4NF
(21 mg, 0.067 mmol) over 5 h. The resulting solution was stirred for
12 h, and the dark blue product was isolated by column
chromatography (silica gel, hexane:CH2Cl2 2:1). Yield: 31 mg, 44%.
Anal. Calcd (%) for P-T-P (C140H184P4Pt2Si2): C, 68.99; H, 7.61.
Found: C, 68.70; H, 7.54. 1H NMR (500 MHz, C6D6): δ 10.00 (s, 2H,
H6,11-tetracene), 9.96 (s, 4H, H5,7-pentacene), 9.70 (s, 4H, H12,14pentacene), 9.35 (dd, J = 3.1, 6.9 Hz, 2H, H1,4-tetracene), 8.34 (dd, J =
3.1, 6.9 Hz, 2H, H7,10-tetracene), 8.21 (d, J = 8.8 Hz, 4H, H4,8pentacene), 8.05 (d, J = 8.8 Hz, 4H, H1,11-pentacene), 7.63 (dd, J =
3.1, 6.9 Hz, 2H, H2,3-tetracene), 7.37 (dd, J = 3.1, 6.9 Hz, 2H, H8,9tetracene), 7.26 (t, J = 8.8 Hz, 4H, H3,9-pentacene), 7.16 (overlapped,
2H, H2,10-pentacene), 2.22−2.20 (m, 24H, PCH2CH2CH2CH3),
1.90−1.88 (m, 24H, PCH2CH2CH2CH3), 1.43−1.29 (m, 66H,
PCH2CH2CH2CH3, iPr), 0.83 (t, J = 7.6 Hz, 24H, PCH2CH2-

A-T-P, and P-T-P (Schemes 2 and 3) and the electronic
spectroscopy of the complexes. The A-P-T and A-T-P are black
chromophores strongly absorbing throughout the entire visible
region and display near-infrared emissions.

■

EXPERIMENTAL SECTION

General Methods. All syntheses were carried out in a N2
atmosphere. All the solvents used for synthesis and spectroscopic
measurements were purified according to the literature procedures.15
trans-Pt(PnBu3)2I2,16 9,10-bis(triisopropylsilylethynyl)anthracene,17
5,12-bis(triisopropylsilylethynyl)tetracene,12 and 6,13-bis(triisopropylsilylethynyl)pentacene13 were prepared according to reported
procedures.

Physical Methods. The UV/vis absorption and emission spectra
of the complexes were recorded on a Hewlett-Packard HP8452A diode
array spectrophotometer and a PerkinElmer 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.18 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. MALDI-TOF mass
spectra were recorded on an Autoflex III TOF/TOF mass
spectrometer using α-cyano-3-hydroxycinnamic acid as the matrix.
Synthesis of Pt2P.11b To a 250 mL Schlenk flask were charged
trans-Pt(PnBu3)2I2 (400 mg, 0.47 mmol), iPr2NH (5 mL), Bu4NF (100
mg, 0.32 mmol), CuI (10 mg), and CH2Cl2 (30 mL). A CH2Cl2
solution (100 mL) of 6,13-bis(triisopropylsilylethynyl)pentacene (46
mg, 0.07 mmol) was added to the mixture over 5 h. The resulting
solution was stirred for 12 h, and then the solvent was removed by
rotary evaporation. The solid was subjected to column chromatography (silica gel, hexane:CH2Cl2 4:1) from which the dark green
product was collected. Yield: 62 mg, 48%. Anal. Calcd (%) for Pt2P
(C74H120I2P4Pt2): C, 50.00; H, 6.80. Found: C, 50.21; H, 7.01. 1H
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). 31P{1H} NMR (202.4 MHz, CDCl3): δ
1.26 (s, 1JPt−P = 2300 Hz). ESI-MS: m/z 1777.3, [M]+.
Synthesis of Pt2T. To a 250 mL Schlenk flask were charged transPt(PnBu3)2I2 (1.8 g, 2.1 mmol), iPr2NH (5 mL), Bu4NF (0.42 g, 1.3
mmol), CuI (10 mg), and CH2Cl2 (40 mL). To the mixture was added
a CH2Cl2 solution (60 mL) of 5,12-bis(triisopropylsilylethynyl)tetracene (0.20 g, 0.34 mmol) over 5 h. The resulting solution was

stirred for 12 h and was reduced to dryness, and the dark red product
was collected from column chromatography (silica gel, hexane:
CH2Cl2 4:1). Yield: 0.30 mg, 51%. Anal. Calcd (%) for Pt2T
(C70H118I2P4Pt2): C, 48.67; H, 6.88. Found: C, 48.74; H, 6.67. 1H
NMR (500 MHz, C6D6): δ 9.82 (s, 2H, H6,11), 9.16 (dd, J = 3.1, 6.9
Hz, 2H, H1,4), 8.22 (dd, J = 3.1, 6.3 Hz, 2H, H7,10), 7.51 (dd, J = 3.1,
6.9 Hz, 2H, H2,3), 7.28 (dd, J = 3.1, 6.3 Hz, 2H, H8,9), 2.22−2.19 (m,
24H, PCH2CH2CH2CH3), 1.71−1.69 (m, 24H, PCH2CH2CH2CH3),
1.34−1.30 (m, 24H, PCH2CH2CH2CH3), 0.87−0.84 (t, J = 7.6 Hz,
36H, PCH2CH2CH2CH3). 31P{1H} NMR (202.4 MHz, C6D6): δ 1.59
(s, 1JPt−P = 2307 Hz). ESI-MS: m/z 1727.4, [M]+.
Synthesis of T-P-T. To a 250 mL Schlenk flask were charged Pt2P
(50 mg, 0.03 mmol), iPr2NH (5 mL), 5,12-bis(triisopropylsilylethynyl)tetracene (0.25 g, 0.42 mmol), CuI (5 mg), and CH2Cl2 (40
mL). A CH2Cl2 solution (50 mL) of Bu4NF (21 mg, 0.067 mmol) was
added to the solution over 5 h, and the mixture was stirred for 12 h
before all the solvents were removed by rotary evaporation. The dark
red product was collected from column chromatography (silica gel,
hexane:CH2Cl2 2:1). Yield: 37 mg, 55%. Anal. Calcd (%) for T-P-T
(C136H182P4Pt2Si2): C, 68.43; H, 7.68. Found: C, 68.67; H, 7.74. 1H
NMR (500 MHz, C6D6): δ 9.98 (s, 6H, H6-tetracene, H5,7,12,14pentacene), 9.71 (s, 2H, H11-tetracene), 9.30 (d, J = 8.8 Hz, 2H, H4C

dx.doi.org/10.1021/om400578t | Organometallics XXXX, XXX, XXX−XXX


Organometallics

Article

Scheme 4

Scheme 5

CH2CH3). 31P{1H} NMR (202.4 MHz, C6D6): δ 5.42 (s, 1JPt−P = 2339
Hz). MALDI-TOF-MS: m/z 2436.73, [M]+.
Synthesis of P-T. Pt2T (0.20 g, 0.116 mmol), iPr2NH (5 mL),
6,13-bis(triisopropylsilylethynyl)pentacene (150 mg, 0.235 mmol),
CuI (5 mg), and CH2Cl2 (30 mL) were added to a 250 mL Schlenck
flask. The mixture was added to a CH2Cl2 solution (50 mL) of Bu4NF
(18 mg, 0.06 mmol). The mixture was stirred for 12 h, and the dark
purple product was isolated by column chromatography (silica gel,
hexane:CH2Cl2 4:1). Yield: 45 mg, 19%. Anal. Calcd (%) for P-T
(C105H151P4Pt2Si): C, 60.56; H, 7.31. Found: C, 60.27; H, 7.32. 1H
NMR (500 MHz, C6D6): δ 9.98 (s, 1H, H6-tetracene), 9.95 (s, 2H,
H5,7-pentacene), 9.84 (s, 1H, H11-tetracene), 9.71 (s, 2H, H12,14pentacene), 9.32 (d, J = 8.5 Hz, 1H, H4-tetracene), 9.19 (d, J = 8.5 Hz,
1H, H1-tetracene), 8.30 (d, J = 8.8 Hz, 1H, H7-tetracene), 8.26 (d, J =
8.2 Hz, 1H, H10-tetracene), 8.20 (d, J = 8.8 Hz, 2H, H4,8-pentacene),
8.05 (d, J = 8.8 Hz, 2H, H1,11-pentacene), 7.60−7.55 (m, 2H, H2,3tetracene), 7.35−7.30 (m, 2H, H8,9-tetracene), 7.25 (t, J = 8.2 Hz, 4H,
H3,9-pentacene), 7.16 (overlapped, 2H, H2,10-pentacene), 2.24−2.17
(m, 24H, PCH2CH2CH2CH3), 1.88−1.85 (m, 12H, PCH2CH2CH2CH3), 1.74−1.71 (m, 12H, PCH2CH2CH2CH3), 1.42−1.29 (m,
45H, PCH2CH2CH2CH3, iPr), 0.87 (t, J = 7.6 Hz, 12H, PCH2CH2CH2CH3), 0.82 (t, J = 7.6 Hz, 12H, PCH2CH2CH2CH3). 31P{1H}
NMR (202.4 MHz, C6D6): δ 5.40 (s, 1JPt−P = 2339 Hz), 1.63 (s, 1JPt−P
= 2312 Hz). MALDI-TOF-MS: m/z 2082.30, [M]+.
Synthesis of A-T-P. To a 250 mL Schlenk flask were charged 9,10bis(triisopropylsilylethynyl)anthracene (0.15 g, 0.28 mmol), iPr2NH
(5 mL), CuI (5 mg), and CH2Cl2 (30 mL). A CH2Cl2 solution (50
mL) of Bu4NF (12 mg, 0.038 mmol) was slowly added to the mixture,
followed by P-T (30 mg, 0.01 mmol). The mixture was stirred for 12 h
and dried by rotary evaporation. The dark brown product was
collected from column chromatography (silica gel, hexane:CH2Cl2
4:1). Yield: 23 mg, 68%. Anal. Calcd (%) for A-T-P (C132H180P4Pt2Si2): C, 67.84; H, 7.76. Found: C, 67.41; H, 7.72. 1H NMR (500 MHz,
C6D6): δ 9.99 (s, 1H, H6-tetracene), 9.97 (s, 3H, H11-tetracene, H5,7pentacene), 9.71 (s, 2H, H12,14-pentacene), 9.35−9.29 (m, 4H, H4,5anthracene, H1,4-tetracene), 9.06 (d, J = 8.2 Hz, 2H, H1,8-anthracene),

8.34−8.29 (m, 2H, H7,10-tetracene), 8.21 (d, J = 8.8 Hz, 2H, H4,8pentacene), 8.05 (d, J = 8.8 Hz, 2H, H1,11-pentacene), 7.65−7.59 (m,
2H, H2,3-tetracene), 7.56−7.50 (m, 4H, H2,3,6,7-anthracene), 7.36−7.32
(m, 2H, H8,9-tetracene), 7.26 (t, J = 8.2 Hz, 2H, H3,9-pentacene), 7.16
(overlapped, 2H, H2,10-pentacene), 2.22−2.19 (m, 12H, PCH2CH2CH2CH3), 2.16−2.13 (m, 12H, PCH2CH2CH2CH3), 1.89−1.81 (m,
24H, PCH2CH2CH2CH3), 1.43−1.28 (m, 66H, PCH2CH2CH2CH3,
i
Pr), 0.86−0.81 (m, 36H, PCH2CH2CH2CH3). 31P{1H} NMR (202.4

MHz, C6D6): δ 5.42 (s, 1JPt−P = 2342 Hz), 5.24 (s, 1JPt−P = 2347 Hz).
MALDI-TOF-MS: m/z 2336.72, [M]+.

■

RESULTS AND DISCUSSION
Syntheses. As shown in Schemes 2 and 3, the
chromophores in the dyads and triads were joined by Pt−C
bonds derived from the ethynyl group of the chromophores
and platinum iodide complexes via copper-catalyzed crosscoupling. An inherent difficulty in the syntheses is that the
sequence-specific arrangement of the chromophores requires
coupling to take place to only one end of the symmetric
building blocks 9,10-bis(triisopropylsilylethynyl)anthracene, 5,12-bis(triisopropylsilylethynyl)tetracene, and 6,13-bis(triisopropylsilylethynyl)pentacene, and Pt2P and Pt2T. The
reactions require single desilyation of the bis(triisopropylsilylethynyl)acenes to form A-SiH, T-SiH, and P-SiH (Schemes 2
and 3), which can be achieved by reacting large excess of the
acenes with Bu4NF in ratios of up to 10:1 (Scheme 4). The
unreacted acenes were easily recovered from column
chromatography. The monosilylated ethynylacenes were
unstable and were coupled to the Pt ion without being
isolated. While double desilylation of bis(triisopropylsilylethynyl)acenes is unavoidable, the tetraplatinum products
arising from coupling of diethynylacenes and Pt2P or Pt2T
were not observed. It could be due to the small amount of the

products and the poor solubility of the large molecules.
Similarly, the formation of the unsymmetrical T-P and P-T
required reacting T-SiH and P-SiH with excess Pt2P and Pt2T,
respectively. It is found that the PnBu3 ligands on the Pt ions
are important for increasing the solubility of the triads in
organic solvents such as CH2Cl2. The analogous complexes of
PEt3 are sparingly soluble or insoluble in most of the organic
solvents.
Structures. Despite numerous attempts, we failed to obtain
single crystals of the complexes for X-ray diffraction. Nonetheless, the proposed structures were confirmed by NMR
spectroscopy, elemental analysis, and high-resolution mass
spectrometry.
All the 1H NMR spectra show signals in the aliphatic
(isopropyl and n-butyl) and aromatic regions (acene). The
D

dx.doi.org/10.1021/om400578t | Organometallics XXXX, XXX, XXX−XXX


Organometallics

Article

Figure 1. (a) MALDI-TOF-MS cluster peak and (b) calculated isotopic distribution for the [A-T-P]+ ion.

structures can be rather easily determined from the number of
aromatic signals of each acene in the molecules. Scheme 5
shows the numbering schemes of the protons. For example, the
central tetracenyl ring of the symmetrical P-T-P exhibits only 5
signals for H2,3, H1,4, H6,11, H17,10, and H8,9, whereas the

tetracenyl ring in the unsymmetrical A-T-P displays 10 signals.
Consistent with the symmetric structures of the complexes,
the spectra of P-T-P and T-P-T show five and six signals for the
central tetracenyl ring (H1,4, H2,3, H6,11, H7,10, H8,9) and
pentacenyl ring (H1,4, H2,3, H 5,14 , H7,12, H 8,11, H9,10),
respectively. The H6,11 of the former and the H5,7,12,14 of the
latter are singlet, while the other protons are doublet or double
doublets. The loss of C2-symmetry of the two pentacenyl rings
in P-T-P and the two tetracenyl rings in T-P-T are
characterized by the presence of 12 and 10 signals for the
rings in the spectra of the complexes, respectively. Both spectra
of A-T-P and A-P-T show 8, 10, and 12 signals for the
anthracenyl, tetracenyl, and pentacenyl rings, respectively. The
31 1
P{ H} NMR spectra of the symmetrical T-P-T and P-T-P
show a singlet at δ 5.40 (1JPt−P = 2339 Hz) and δ 5.42 (1JPt−P =
2339 Hz), respectively. In accord with the unsymmetrical
structures of the molecules, two singlets are found in the
spectra of A-P-T and A-T-P at δ 5.33 (1JPt−P = 2337 Hz) and δ
5.39 (1JPt−P = 2337 Hz), and δ 5.40 (1JPt−P = 2342 Hz) and δ
5.24 (1JPt−P = 2347 Hz), respectively. The 1JPt−P values (2304−
2364 Hz) are consistent with a trans-orientation of the
phosphines.19
All the complexes have been characterized by MALDI-TOF
mass spectrometry. The spectra show prominent peaks for
singly charged parent ions [M]+ (see Figures S1−S5 in the
Supporting Information for the MS spectra of the other
complexes). The observed isotopic distributions in the cluster
peaks are essentially identical with the ones calculated
according to the molecular formula. Figure 1 shows the cluster

peak of the parent ion [A-T-P]+ (m/z = 2336.72) and the
calculated isotopic distribution.
Electronic Absorption Spectroscopy. All the complexes
show deep colors that reflect combinations of the acenes in
them. The dyads P-T and T-P are violet, whereas T-P-T and PT-P are purple and Prussian blue. Both A-P-T and A-T-P are
deep brown. The absorption spectra and the colors of the
solutions of the complexes are depicted in Figures 2 and 3, and

Figure 2. UV−vis absorption spectra and colors of CH2Cl2 solutions
of T-P-T (brown), T-P (pink), and A-P-T (blue) at room
temperature.

Figure 3. UV−vis absorption spectra and colors of CH2Cl2 solutions
of P-T-P (green), P-T (red), and A-T-P (black) at room temperature.

the spectral data are summarized in Table 1. The absorption
spectra of the building blocks TIPS-P, TIPS-T, and TIPS-A
can be found in the Supporting Information (Figures S6−S8).
E

dx.doi.org/10.1021/om400578t | Organometallics XXXX, XXX, XXX−XXX


Organometallics

Article

Table 1. UV−vis Absorption Spectroscopic Dataa
complex

band 1
(ε, 104 M−1 cm−1)

P-T-P

697 (4.89),
638 (3.00)
692 (4.21),
635 (2.47)
697 (4.23),
637 (2.49)
659 (3.91)

P-T

652 (2.18)

A-T-P

654 (2.20)

T-P-T
T-P
A-P-T

band 2 (ε, 104 M−1 cm−1)
567 (4.57), 533 (4.24),
497 (2.35)
568 (2.49), 533 (2.21),
497 (1.20)

568 (2.31), 533 (2.10),
586 (3.84), 542 (2.48), 504
(1.13)
578 (3.94), 537 (2.65), 504
(1.21)
582 (4.55), 540 (3.18)

band 4
(ε, 104 M−1 cm−1)

band 3 (ε, 104 M−1 cm−1)

470 (3.71), 444 (3.29),
415 (1.84)

469 (3.69), 442 (3.23),
415 (1.94) (s)

band 5 (ε, 104 M−1 cm−1)

350 (5.11)

319 (27.65), 297 (31.24)

347 (3.79),
338 (3.92) (s)
348 (3.35), 337 (3.61)

318 (28.72), 297 (19.44)

360 (4.77), 338 (5.00)

319 (25.59), 297 (19.24),
279 (16.53)
316 (47.50), 304 (26.30)

357 (3.79), 338 (3.88)

316 (29.05), 303 (20.83)

359 (3.66), 339 (3.62)

316 (29.67), 303 (23.23),
278 (16.20)

a
The extinction coefficients (ε) of vibronic peaks are shown and as the bands 1 of P-T-P, P-T, and A-T-P have no vibronic peak, only the εmax values
are listed.

Figure 4. Emission spectra of T-P-T (red) and T-P (blue) in CH2Cl2 at room temperature (excitation wavelength = 490 nm). Inset: excitation
spectra of T-P-T (red) and T-P (blue) monitored at 720 nm.

The absorption spectra are dominated by intense π → π*
transitions of the acenes. The spectra exhibit two vibronic
bands in ∼600−750 nm (band 1, εmax = (2.18−4.89) × 104
M−1 cm−1) and in ∼450−620 nm (band 2, εmax = (2.31−4.57)
× 104 M−1 cm−1), which correspond, respectively, to the S0 →
S1 transitions of the pentacenyl and tetracenyl rings, which are
the common motifs of the six complexes. The spectra of A-T-P
and A-P-T show an additional band in ∼400−500 nm (band 3,

εmax = (3.69−3.71) × 104 M−1 cm−1), which corresponds to the
S0 → S1 transition of the anthracenyl ring. In addition, all
spectra display a shoulder around 330−380 nm (band 4, εmax =
(3.35−5.11) × 104 M−1 cm−1) and very intense sharp bands
between 280 and 330 nm (band 5, εmax = (2.56−4.75) × 105
M−1 cm−1), which are due to high-energy π → π* transitions
characteristic of the acenes.14a It is noted that all the absorption
bands, especially the S0 → S1 transitions, are red-shifted from
the corresponding transitions of TIPS-A, TIPS-T, and TIPS-P
by 30−50 nm. A similar red shift has been observed in the
spectra of binuclear PtII complexes of diethynyltetracene and
diethynylpentacene and has been attributed to the perturbation
of the Pt ions on the electronic structures of the acenes, mainly
via metal−ligand π-interactions.11 Notably, the triads A-T-P
and A-P-T absorb intensely (ε > 104 M−1 cm−1) throughout the
entire visible region and part of the UV region (280−750 nm),
making them examples of “black chromphores” that efficiently
absorb all visible lights.20

Emission Spectroscopy. The complexes are weakly
emissive with the quantum yield of (0.6−7.7) × 10−3. The
solution emission and excitation spectra of the complexes are
shown in Figures 4−6, and lifetime and quantum yield are
listed in Table 2. All the emissions are fluorescence, which is
Table 2. Emission Spectroscopic Data of the Complexes
complex
T-P-T
T-P
A-P-T
P-T-P

P-T
A-T-P

emission maxima
(λmax/nm)
601,
599,
491,
770
600,
490,

727
720
600, 723

lifetimes (τ/ns)
7.0c, 0.5
7.1c, 0.6
4.7d, 4.0c, 0.5
a

770
604, 778

8.4c, a(770 nm)
4.4d, a(604 nm), a(778 nm)

quantum
yields

(φ × 10−3)b
7.7
4.6
7.4
0.6
3.7
0.8

Not determined. bExcitation wavelength (λem) is 490 nm. cλem = 483
nm. dλem = 373 nm.
a

confirmed by lifetimes of nanosecond order. Despite the
presence of the heavy Pt center, no phosphorescence was
observed. Our previous studies of cyclometalated PtIIanthracene,21 Pt2T,11a and Pt2P11b show no phosphorescence,
and this apparent absence of a heavy atom effect is attributed to
the characteristic large S1−T1 gap of the alternant hydrocarbons,22 which imposes a large Franck−Condon barrier for S1
→ T1 intersystem crossing. The spectra of T-P-T and T-P
F

dx.doi.org/10.1021/om400578t | Organometallics XXXX, XXX, XXX−XXX


Organometallics

Article

Figure 5. Emission spectra of a CH2Cl2 solution of A-T-P excited at 400 nm (brown) and 490 nm (purple) at 298 K. Inset: excitation spectra
obtained by monitoring emission at 600 nm (purple) and 750 nm (brown) (the peak at 375 nm is an artifact).

Figure 6. Emission spectra of a CH2Cl2 solution of A-P-T excited at 400 nm (brown) and 490 nm (purple) at 298 K. Inset: excitation spectra
obtained by monitoring emission at 600 nm (purple) and 730 nm (brown).

lie entirely in the near-infrared region (>700 nm). Excitation at
400 nm, where the absorption of the anthracenyl ring
dominates (ε = 1.36 × 104 M−1 cm−1), gives rise to tetracenyl
and pentacenyl emissions, indicating energy transfer from the
S1(A) to the S1(T) and S1(P), and stepwise excited state
manifold in the triads. Excitation at 490 nm where the
absorption is mainly due to S0 → S1 of the tetracenyl rings leads
to both tetracenyl and pentacenyl emissions. Monitoring the
tetracenyl and pentacenyl emissions gives excitation spectra
(insets of Figures 4 and 5) that are similar to the absorption
spectra, indicating the presence of S1(A) → S1(T), S1(A) →
S1(P), and S1(T) → S1(P) energy transfer.
The relative intensity of the three emissions of A-T-P is
different from that of A-P-T. For A-T-P, the emission intensity
follows the order of A > P ≫ T. On the other hand, the order is
P > A > T for A-P-T. The difference could be due to different
energy transfer rates or different intrinsic photophysics (i.e.,
nonradiative and radiative decay rates) of the chromophores in
the two triads. The relative intensity of the emission, which is
characteristic of each triad, can be taken as the spectroscopic
fingerprint of the different sequences of the three chromophores.

(Figure 4) and P-T (Figure S9 in the Supporting Information)
exhibit two bands at ∼600 and ∼720 nm that are S1 → S0
fluorescent emissions of the tetracenyl ring and the pentacenyl
ring, respectively. Similar emissions were displayed by Pt2diethynyltetracene (λmax = 596 nm)10a and Pt2-diethynylpentacene (λmax = 726 nm).10b Irradiating the complexes at 490 nm,
where the absorption is mainly due to the S0 → S1 transition of

T, leads invariably to pentacenyl emission, suggesting energy
transfer from S1(T) to the S1(P).
It is further corroborated by the excitation spectra of the
complexes obtained by monitoring the pentacenyl emission at
720 nm (Figure 4, inset, and Figure S10, Supporting
Information), which resemble the absorption spectra. The
complexes show different relative intensity of the two emissions
in the complexes. For instance, the pentacenyl emission of T-P
is more intense than its tetracenyl emission but the pentacenyl
emission of P-T is very much weaker (Figure S9, Supporting
Information) than its tetracenyl emission. The two emissions of
T-P-T have similar intensities, but the tetracenyl emission of PT-P is essentially quenched and only the pentacenyl emission is
observed (Figure S9).
Figures 5 and 6 show the emission and excitation spectra of
A-T-P and A-P-T, respectively. Irradiating solutions of the
complexes at 400 nm gives rise to three emission bands at 490,
604, and 778 nm (A-T-P), and 491, 600, and 723 nm (A-P-T)
that are S1 → S0 fluorescence of A, T, and P, respectively. The
triads are visible and NIR emitters as the pentacenyl emissions

■

CONCLUSION
In this study, we demonstrated the sequence-specific syntheses
of triads of anthracene, tetracene, and pentacene. While crosscoupling provides the chemistry required to link up the
G

dx.doi.org/10.1021/om400578t | Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

(3) (a) Serin, J. M.; Brousmiche, D. W.; Frechet, J. M. J. Chem.
Commun. 2002, 2605. (b) Bura, T.; Retailleau, P.; Ziessel, R. Angew.
Chem., Int. Ed. 2010, 49, 6659. (c) Diring, S.; Puntoriero, F.; Nastasi,
F.; Campagna, S.; Ziessel, R. J. Am. Chem. Soc. 2009, 131, 6108.
(d) Nakamura, Y.; Aratani, N.; Osuka, A. Chem. Soc. Rev. 2007, 36,
831.
(4) (a) Duan, X.-F.; Wang, J.-L.; Pei, J. Org. Lett. 2005, 7, 4071.
(b) Casanova, M.; Zangrando, E.; Iengo, E.; Alessio, E.; Indelli, M. T.;
Scandola, F.; Orlandi, M. Inorg. Chem. 2008, 47, 10407. (c) Pinto, S.
M. A.; Neves, Â . C. B.; Calvete, M. J. F.; Abreu, A. R.; Rosado, M. T.
S.; Costa, T.; Burrows, H. D.; Pereira, M. M. J. Photochem. Photobiol., A
2012, 242, 59. (d) Liu, X.; Liu, J.; Pan, J.; Chen, R.; Na, Y.; Gao, W.;
Sun, L. Tetrahedron 2006, 62, 3674. (e) Zhu, X.; Wong, W.-K.; Wong,
W.-Y.; Yang, X. Eur. J. Inorg. Chem. 2011, 2011, 4651. (f) Zhao, Z.;
Poon, C.-T.; Wong, W.-K.; Wong, W.-Y.; Tam, H.-L.; Cheah, K.-W.;
Xie, T.; Wang, D. Eur. J. Inorg. Chem. 2008, 2008, 119. (g) Jiang, F.-L.;
Wong, W.-K.; Zhu, X.-J.; Zhou, G.-J.; Wong, W.-Y.; Wu, P.-L.; Tam,
H.-L.; Cheah, K.-W.; Ye, C.; Liu, Y. Eur. J. Inorg. Chem. 2007, 2007,
3365.
(5) (a) Ventura, B.; Barbieri, A.; Barigelletti, F.; Batcha Seneclauze, J.;
Retailleau, P.; Ziessel, R. Inorg. Chem. 2008, 47, 7048. (b) Borgström,
M.; Ott, S.; Lomoth, R.; Bergquist, J.; Hammarström, L.; Johansson,
O. Inorg. Chem. 2006, 45, 4820. (c) Benniston, A. C.; Harriman, A.;
Pariani, C.; Sams, C. A. Phys. Chem. Chem. Phys. 2006, 8, 2051.
(6) (a) Scarpantonio, L.; Tron, A.; Destribats, C.; Godard, P.;
McClenaghan, N. D. Chem. Commun. 2012, 48, 3981. (b) Wan, J.-H.;

Ma, Z.; Liu, F.; Xu, Z.; Wang, H.-Y.; Jiang, H.-J.; Huang, W. J.
Photochem. Photobiol., A 2010, 211, 115. (c) Giribabu, L.; Ashok
Kumar, A.; Neeraja, V.; Maiya, B. G. Angew. Chem., Int. Ed. 2001, 40,
3621. (d) Wong, W. W. H.; Khoury, T.; Vak, D.; Yan, C.; Jones, D. J.;
Crossley, M. J.; Holmes, A. B. J. Mater. Chem. 2010, 20, 7005.
(7) (a) Yin, S.; Leen, V.; Jackers, C.; Beljonne, D.; Van Averbeke, B.;
Van der Auweraer, M.; Boens, N.; Dehaen, W. Chem.Eur. J. 2011,
17, 13247. (b) Dumas-Verdes, C.; Miomandre, F.; Lépicier, E.;
Galangau, O.; Vu, T. T.; Clavier, G.; Méallet-Renault, R.; Audebert, P.
Eur. J. Org. Chem. 2010, 2525. (c) Brizet, B.; Eggenspiller, A.; Gros, C.
P.; Barbe, J.-M.; Goze, C.; Denat, F.; Harvey, P. D. J. Org. Chem. 2012,
77, 3646. (d) Ziessel, R.; Goze, C.; Ulrich, G.; Césario, M.; Retailleau,
P.; Harriman, A.; Rostron, J. P. Chem.Eur. J. 2005, 11, 7366.
(e) Harriman, A.; Mallon, L. J.; Elliot, K. J.; Haefele, A.; Ulrich, G.;
Ziessel, R. J. Am. Chem. Soc. 2009, 131, 13375.
(8) Strouse, G. F.; Worl, L. A.; Younathan, J. N.; Meyer, T. J. J. Am.
Chem. Soc. 1989, 111, 9101.
(9) Haley, M. M.; Tykwinski, R. R. Carbon-Rich Compounds; WileyVCH: Weinheim, Germany, 2006.
(10) (a) Dubinina, G. G.; Price, R. S.; Abboud, K. A.; Wicks, G.;
Wnuk, P.; Stepanenko, Y.; Drobizhev, M.; Rebane, A.; Schanze, K. S. J.
Am. Chem. Soc. 2012, 134, 19346. (b) Liao, C.; Shelton, A. H.; Kim,
K.-Y.; Schanze, K. S. ACS Appl. Mater. Interfaces 2011, 3, 3225.
(c) Liao, C.; Yarnell, J. E.; Glusac, K. D.; Schanze, K. S. J. Phys. Chem.
B 2010, 114, 14763. (d) Li, Y.; Köse, M. E.; Schanze, K. S. J. Phys.
Chem. B 2013, 117, 9025. (e) Keller, J. M.; Glusac, K. D.; Danilov, E.
O.; McIlroy, S.; Sreearuothai, P.; Cook, A. R.; Jiang, H.; Miller, J. R.;
Schanze, K. S. J. Am. Chem. Soc. 2011, 133, 11289.
(11) (a) Nguyen, M.-H.; Yip, J. H. K. Organometallics 2010, 29, 2422.
(b) Nguyen, M.-H.; Yip, J. H. K. Organometallics 2011, 30, 6383.
(c) Nguyen, M.-H.; Yip, J. H. K. Organometallics 2012, 31, 7522.

(12) Odom, S. A.; Parkin, S. R.; Anthony, J. E. Org. Lett. 2003, 5,
4245.
(13) 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.
(14) (a) Birks, J. B. Photophysics of Aromatic Molecules; Wiley:
London, 1970. (b) Levitus, M.; Garcia-Garibay, M. A. J. Phys. Chem. A
2000, 104, 8632. (c) Levitus, M.; Garcia-Garibay, M. A. J. Phys. Chem.
A 2000, 104, 8632. (d) Parson, W. W. Modern Optical Spectroscopy
with Excercises and Examples from Biophysics and Biochemistry; SpringVerlag: Berlin, 2007.

chromophores, the success of our approach relies on the
production of monosilylated T-SiH, P-SiH, A-SiH, T-P, and PT, which requires the use of excess TIPS-A/T/P and Pt2P and
Pt2T in order to minimize double desilylation and double
ligation of the Pt ions. Inevitably, the yields of the triads are
low, but fortunately, the unreacted TIPS-A/T/P and Pt
complexes can be recycled from the reaction mixtures by
column chromatography. In principle, the method can be used
to synthesize sequence-specific polymers of the chromophores
such as A-T-P-A-T-P-A-T-P···, although the process is timeconsuming and probably the solubility of the polymer would
decrease as the chain length increases. The triads are energy
cascades as pumping the molecules to higher excited states such
as the S1 of A led to the fluorescence from a lower-energy
excited state such as the S1 of T or P. Different sequences have
different emission spectroscopic fingerprints. Finally, A-T-P
and A-P-T are rare examples of “black chromophores”, which
show strong absorption throughout the entire visible region.

■

ASSOCIATED CONTENT

S Supporting Information
*

MALDI-TOF mass spectra of T-P-T, T-P, A-P-T, P-T-P, and
P-T and emission and excitation spectra of P-T-P and P-T.
This material is available free of charge via the Internet at
.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail:
Present Address
†

Inorganic Chemistry Department, Hanoi University of
Science, 19 Le Thanh Tong, Hanoi, Vietnam.
Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS
We are grateful to the National Environmental Agency,

Environment Technology and Research Program (R-143-000547-490) for financial support.

■

REFERENCES

(1) (a) Bronner, C.; Veiga, M.; Guenet, A.; De Cola, L.; Hosseini, M.
W.; Strassert, C. A.; Baudron, S. A. Chem.Eur. J. 2012, 18, 4041.
(b) Jiménez, A. J.; Marcos, M. L.; Hausmann, A.; Rodríguez-Morgade,
M. S.; Guldi, D. M.; Torres, T. Chem.Eur. J. 2011, 17, 14139.
(c) Cotlet, M.; Vosch, T.; Habuchi, S.; Weil, T.; Müllen, K.; Hofkens,
J.; De Schryver, F. J. Am. Chem. Soc. 2005, 127, 9760. (d) Du, B.;
Harvey, P. D. Chem. Commun. 2012, 48, 2671. (e) Albert-Seifried, S.;
Finlayson, C. E.; Laquai, F.; Friend, R. H.; Swager, T. M.; Kouwer, P.
H. J.; Juríček, M.; Kitto, H. J.; Valster, S.; Nolte, R. J. M.; Rowan, A. E.
Chem.Eur. J. 2010, 16, 10021. (f) Wong, W.-Y. Coord. Chem. Rev.
2005, 249, 971. (g) Aly, S. M.; Ho, C.-L.; Fortin, D.; Wong, W.-Y.;
Abd-El-Aziz, A. S.; Harvey, P. D. Chem.Eur. J. 2008, 14, 8341.
(h) Aly, S. M.; Ho, C.-L.; Wong, W.-Y.; Fortin, D.; Harvey, P. D.
Macromolecules 2009, 42, 6902.
(2) (a) Hankache, J.; Niemi, M.; Lemmetyinen, H.; Wenger, O. S.
Inorg. Chem. 2012, 51, 6333. (b) Wasielewski, M. R. Chem. Rev. 1992,
92, 435. (c) Markovic, V.; Villamaina, D.; Barabanov, I.; Lawson Daku,
L. M.; Vauthey, E. Angew. Chem., Int. Ed. 2011, 50, 7596. (d) Tasior,
M.; Gryko, D. T.; Shen, J.; Kadish, K. M.; Becherer, T.; Langhals, H.;
Ventura, B.; Flamigni, L. J. Phys. Chem. C 2008, 112, 19699. (e) Xie,
Y.; Hill, J. P.; Schumacher, A. L.; Sandanayaka, A. S. D.; Araki, Y.; Karr,
P. A.; Labuta, J.; D’Souza, F.; Ito, O.; Anson, C. E.; Powell, A. K.;
Ariga, K. J. Phys. Chem. C 2008, 112, 10559.
H

dx.doi.org/10.1021/om400578t | Organometallics XXXX, XXX, XXX−XXX


Organometallics

Article

(15) Armarego, W. L. F.; Chai, C. L. L. Purification of Laboratory
Chemicals, 5th ed.; Elsevier: Amsterdam, 2003.
(16) Rahn, J. A.; Baltusis, L.; Nelson, J. H. Inorg. Chem. 1990, 29,
750.
(17) Goldsmith, R. H.; Vura-Weis, J.; Scott, A. M.; Borkar, S.; Sen,
A.; Ratner, M. A.; Wasielewski, M. R. J. Am. Chem. Soc. 2008, 130,
7659.
(18) Isak, S. J.; Eyring, E. M. J. Phys. Chem. 1992, 96, 1738.
(19) (a) Yam, V. W.-W.; Tao, C.-H.; Zhang, L.; Wong, K. M.-C.;
Cheung, K.-K. Organometallics 2001, 20, 453. (b) Khan, M. S.; AlMandhary, 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. (c) Tao, C.-H.; Zhu, N.; Yam,
V. W.-W. Chem.Eur. J. 2005, 11, 1647. (d) Chang, X.; Lee, K.-E.; Il
Jeon, S.; Kim, Y.-J.; Lee, H. K.; Lee, S. W. Dalton Trans. 2005, 3722.
(20) (a) Nazeeruddin, M. K.; Kay, A.; Rodicio, I.; Humphrey-Baker,
R.; Müller, E.; Liska, P.; Vlachopoulos, N.; Grätzel, M. J. Am. Chem.
Soc. 1993, 115, 6382. (b) Zhao, Z.; Cammidge, A. N.; Hughes, D. L.;
Cook, M. J. Org. Lett. 2010, 12, 5138. (c) Bouit, P.-A.; Villegas, C.;
Delgado, J. L.; Viruela, P. M.; Pou-AméRigo, R.; Ortí, E.; Martín, N.
Org. Lett. 2011, 13, 604.
(21) Hu, J.; Lin, R.; Yip, J. H. K.; Wong, K.-Y.; Ma, D.-L.; Vittal, J. J.

Organometallics 2007, 26, 6533.
(22) Michl, J.; Thulstrup, E. W. Tetrahedron 1976, 32, 205.

I

dx.doi.org/10.1021/om400578t | Organometallics XXXX, XXX, XXX−XXX