Ligand perturbations on fluorescence of dinuclear platinum complexes of 5,12-diethynyltetracene: A spectroscopic and computational study

Article abstract of DOI:10.1021/om300904b

To understand how the Pt^II ion perturbs the electronic structures of tetracene, 10 dinuclear [X(Et₃P)₂Pt ^II]₂-5,12-diethynyltetracene complexes with different auxiliary ligands were synthesized. Interactions between the Pt^II ion and 5,12-diethynyltetracene were probed spectroscopically and computationally. The dinuclear [X(Et₃P)₂Pt^II] ₂-5,12-diethynyltetracene complexes exhibit red-shifted absorption and fluorescence in comparison with those of 5,12-bis(triisopropylsilylethynyl) tetracene, with the neutral complexes with π-donating auxiliary ligands showing a larger red shift than the cationic complexes with π-accepting ligands. Electronic structures of the complexes and effects of the metal ions and the ligands on the electronic transitions of the complexes were investigated by TD-DFT calculations, the results of which showed that the electronic structure of the 5,12-diethynyltetracene core is perturbed by π interactions with the Pt fragments, the extent of which depends on the energies of the dπ orbitals of the Pt fragments.

Full text of DOI:10.1021/om300904b

Article
pubs.acs.org/Organometallics
Ligand Perturbations on Fluorescence of Dinuclear Platinum
Complexes of 5,12-Diethynyltetracene: A Spectroscopic and
Computational Study
Minh-Hai Nguyen,† Chun-Yuen Wong,*,‡ and John H. K. Yip*,†
†Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543
‡Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong SAR, People’s
Republic of China
S
* Supporting Information
ABSTRACT: To understand how the PtII ion perturbs the
electronic structures of tetracene, 10 dinuclear [X(Et3P)2PtII]2-
5,12-diethynyltetracene complexes with different auxiliary
ligands were synthesized. Interactions between the PtII ion
and 5,12-diethynyltetracene were probed spectroscopically and
computationally. The dinuclear [X(Et3P)2PtII]2-5,12-diethynyl-
tetracene complexes exhibit red-shifted absorption and
fluorescence in comparison with those of 5,12-bis-
(triisopropylsilylethynyl)tetracene, with the neutral complexes
with π-donating auxiliary ligands showing a larger red shift than
the cationic complexes with π-accepting ligands. Electronic
structures of the complexes and effects of the metal ions and
the ligands on the electronic transitions of the complexes were investigated by TD-DFT calculations, the results of which showed
that the electronic structure of the 5,12-diethynyltetracene core is perturbed by π interactions with the Pt fragments, the extent of
which depends on the energies of the dπ orbitals of the Pt fragments.
Interestingly, the complex [I(Et3P)2PtII]2-5,12-diethynyltetra-
cene (1; Chart 1) shows a larger red shift of tetracene-centered
INTRODUCTION
■
Oligoacenes, especially anthracene, tetracene, and pentacene,
have played an important role in the development of low-
dimensional materials, light-harvesting systems, optoelectronics,
Chart 1
and organic electronics.1 It has been demonstrated that
functionalization can increase the stability or solubility of the
oligoacenes and vary their photophysical properties and
electron transfer parameters.2 In addition, functionalization
can change the solid-state packing of the oligoacenes, which is
crucial for properties such as charge mobility and charge
injection barrier.1e,g,3 In most cases, oligoacenes are function-
alized with p-block elements such as halogens, aryls, and
alkynes.4 On the other hand, transition metals have not been
much employed in oligoacene functionalization, despite the
potential for d orbitals to impart redox activity, new structural
moiety, photophysics, and intermolecular interactions to the
oligoacences.5 It is believed that understanding how metals
influence the photophysics of oligoacenes is important in
developing metal−oligoacenes as a new class of organometallic
emitters and devices. Some recent work shows that attaching
platinum(II) and gold(I) to anthracene and pyrene can alter
the photophysics and reactivity of the molecules.6 PtII and AuI
tetracene and 5,12-diethynyltetracene complexes have been
reported recently, and spectroscopic studies of the complexes
showed that metalation together with alkynylation can red-shift
the fluorescence energy of tetracene up to 0.53 eV.7
π → π* absorption and fluorescence than the corresponding
[R3PAuI]2-5,12-diethynyltetracene complexes (R = CH3,
C6H5). We proposed that the PtII ion, being more π-donating
than the AuI, has stronger perturbations on the tetracenyl ring
via metal-to-tetracene π-donation, mediated by the ethynyl
linker. The hypothesis can be tested by a systematic variation of
the electronic properties of the PtII ion. To this end, 10
homologous dinuclear [X(Et3P)2PtII]2-5,12-diethynyltetracene
complexes with different ligands X were synthesized and their
spectroscopy was investigated. A spectroscopic study showed
Received: September 21, 2012
Published: March 5, 2013
© 2013 American Chemical Society
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Organometallics
Article
1
(C58H80P4Pt2Se2): C, 48.07; H, 5.56. Found: C, 48.08; H, 5.71. H
that the electronic structure of the tetracenyl ring is perturbed
by the metal ions. Although X is far from the central
chromophore, it has a significant effect on the spectroscopy
of the complexes, as it is observed that fluorescence of the
neutral complexes with π-donating ligands is consistently red-
shifted from those cationic complexes with π-accepting ligands.
DFT calculations were carried out on model compounds to
provide an explanation for the spectroscopy of the complexes.
NMR (300 MHz, CDCl3): δ 9.40 (s, 2H, H6,11), 8.74 (dd, J = 3.3, 6.7
Hz, 2H, H1,4), 8.00 (dd, J = 3.1, 6.6 Hz, 2H, H7,10), 7.74 (d, J = 5.6 Hz,
4H, o-C6H5), 7.44−7.38 (m, 4H, H2,3,8,9), 7.07−7.05 (m, 6H, m,p-
C6H5), 2.14−2.09 (m, 24H, PCH2CH3), 1.26−1.16 (m, 36H,
PCH2CH3). 31P{1H} NMR (121.5 MHz, CDCl3): δ 10.80 (s, JPt−P
1
= 2392 Hz). ESI-MS: m/z 1450.0, [M]+.
Synthesis of [C6H5C}C(Et3P)2PtII]2-5,12-diethynyltetracene
(6). To a stirred solution of 1 (77 mg, 0.055 mmol) in THF (10
mL) were added CuI (5 mg), diethylamine (5 mL), and phenyl-
acetylene (0.12 mL, 1 mmol). The resulting mixture was stirred
overnight, and all the solvents were removed in vacuo. The solid
residue was extracted with CH2Cl2, and the title compound was
afforded by the addition of excess MeOH. Yield: 37 mg, 50%. X-ray-
quality crystals of 6 were obtained from CH2Cl2/MeOH at room
temperature. Anal. Calcd for 6 (C62H80P4Pt2): C, 55.60; H, 6.02.
Found: C, 55.31; H, 5.85. 1H NMR (300 MHz, CDCl3): δ 9.39 (s, 2H,
H6,11), 8.74 (dd, J = 3.4, 6.9 Hz, 2H, H1,4), 7.96 (dd, J = 3.0, 6.4 Hz,
2H, H7,10), 7.39−7.33 (m, 8H, H2,3,8,9 and o-C6H5), 7.24−7.22 (m, 4H,
m-C6H5), 7.14 (t, J = 7.2 Hz, 2H, p-C6H5), 2.26−2.20 (m, 24H,
PCH2CH3), 1.35−1.24 (m, 36H, PCH2CH3). 31P{1H} NMR (121.5
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.8
5,12-Bis(triisopropylsilylethynyl)tetracene (TIPS-T)1e and complex 17
were prepared according to the reported methods.
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. Rhodamine 640 (also known as
rhodamine 101)9 was used as a standard in measuring the emission
quantum yields. Emission lifetimes were recorded on a Horiba Jobin-
Yvon Fluorolog FL-1057 spectrometer. 1H and 31P{1H} NMR spectra
were recorded on a Bruker ACF 300 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.
Synthesis of [Br(Et3P)2PtII]2-5,12-diethynyltetracene (2). To a
CH2Cl2 solution of 1 (50 mg, 0.036 mmol) was added AgOTf (19 mg,
0.072 mmol) with stirring at room temperature over 1 h in the absence
of light. The resulting mixture was filtered under argon, and excess
tetra-n-octylammonium bromide was added. The solution was stirred
for 2 h, and the solvent was then reduced by rotary evaporation. The
title compound was precipitated by the addition of excess MeOH.
Yield: 22 mg, 49%. Anal. Calcd for 2 (C46H70Br2P4Pt2): C, 42.60; H,
1
MHz, CDCl3): δ 12.27 (s, JPt−P = 2375 Hz). FAB-MS: m/z 1338.6,
[M]+.
Synthesis of [Ph3P(Et3P)2PtII]2-5,12-diethynyltetracene (7).
The compound was prepared by following the procedure for 2, except
that Ph3P was used instead of tetra-n-octylammonium bromide and the
titled compound was precipitated by the addition of excess Et2O.
Yield: 85%. Slow diffusion of Et2O into a CH2Cl2 solution at room
temperature afforded red crystals suitable for X-ray crystallography
study. Anal. Calcd for 7 (C84H100F6O6P6Pt2S2): C, 51.48; H, 5.14; S,
3.27. Found: C, 51.16; H, 5.03; S, 3.12. 1H NMR (300 MHz, CDCl3):
δ 9.27 (s, 2H, H6,11), 8.62 (dd, J = 3.2, 6.7 Hz, 2H, H1,4), 8.06 (dd, J =
3.4, 6.5 Hz, 2H, H7,10), 7.91−7.46 (m, 34H, H2,3,8,9 and C6H5), 1.71−
1.67 (m, 24H, PCH2CH3), 1.17−1.07 (m, 36H, PCH2CH3). 31P{1H}
1
2
NMR (121.5 MHz, CDCl3): δ 12.91 (t, JPt−P = 2561 Hz, JP−P = 22
Hz, PPh3), 8.62 (d, JPt−P = 2173 Hz, JP−P = 22 Hz, PEt3) . ESI-MS:
1
2
1
5.44. Found: C, 42.60; H, 4.96. H NMR (300 MHz, CDCl3): δ 9.34
m/z 830.7, [M − 2OTf]2+.
(s, 2H, H6,11), 8.69 (dd, J = 3.3, 6.7 Hz, 2H, H1,4), 7.96 (dd, J = 3.0, 6.6
Hz, 2H, H7,10), 7.42−7.37 (m, 4H, H2,3,8,9), 2.17−2.13 (m, 24H,
PCH2CH3), 1.30−1.20 (m, 36H, PCH2CH3). 31P{1H} NMR (121.5
Synthesis of [(Et3P)3PtII]2-5,12-diethynyltetracene (8). The
compound was prepared following the procedure for 7, except that
Et3P was used instead of Ph3P. Yield: 75%. Crystals of 8 were grown
by slow diffusion of Et2O into an acetone solution. Anal. Calcd for 8
(C60H100F6O6P6Pt2S2): C, 43.11; H, 6.03; S, 3.84. Found: C, 43.22; H,
5.86; S, 3.64. 1H NMR (300 MHz, CDCl3): δ 9.18 (s, 2H, H6,11), 8.52
(dd, J = 3.3, 6.7 Hz, 2H, H1,4), 7.93 (dd, J = 3.4, 6.6 Hz, 2H, H7,10),
7.49−7.47 (m, 4H, H2,3,8,9), 2.29−2.17 (m, 36H, PCH2CH3), 1.36−
1.24 (m, 54H, PCH2CH3). 31P{1H} NMR (121.5 MHz, CDCl3): δ
1
MHz, CDCl3): δ 13.54 (s, JPt−P = 2360 Hz). ESI-MS: m/z 1296,
[M]+.
Synthesis of [Cl(Et3P)2PtII]2-5,12-diethynyltetracene (3). The
compound was prepared by following the procedure described above
using tetra-n-butylammonium chloride. Yield: 77%. Anal. Calcd for 3
1
(C46H70Cl2P4Pt2): C, 45.74; H, 5.84. Found: C, 45.41; H, 5.63. H
NMR (300 MHz, CDCl3): δ 9.33 (s, 2H, H6,11), 8.68 (dd, J = 3.1, 6.7
Hz, 2H, H1,4), 7.96 (dd, J = 3.0, 6.6 Hz, 2H, H7,10), 7.40−7.38 (m, 4H,
H2,3,8,9), 2.11−2.07 (m, 24H, PCH2CH3), 1.32−1.21 (m, 36H,
1
2
1
12.60 (d, JPt−P = 2223 Hz, JP−P = 24 Hz, Pcis), 6.38 (t, JPt−P = 2403
2
Hz, JP−P = 24 Hz, Ptrans) . ESI-MS: m/z 686.2, [M − 2OTf]2+.
Synthesis of [C5H5N(Et3P)2PtII]2-5,12-diethynyltetracene (9).
The compound was prepared following the procedure for 7, except
that pyridine was used instead of Ph3P. Yield: 63%. Slow diffusion of of
Et2O into a CH2Cl2 solution at room temperature afforded red crystals
suitable for an X-ray crystallography study. Anal. Calcd for 9
(C58H80F6N2O6P4Pt2S2): C, 43.72; H, 5.06; N, 1.76; S, 4.02. Found:
1
PCH2CH3). 31P{1H} NMR (121.5 MHz, CDCl3): δ 15.96 (s, JPt−P
= 2388 Hz). ESI-MS: m/z 1208.1, [M]+.
Synthesis of [C6H5S(Et3P)2PtII]2-5,12-diethynyltetracene (4).
To a stirred solution of 1 (44 mg, 0.032 mmol) in CH2Cl2 (10 mL)
were 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 rotary evaporation. The addition of excess MeOH
afforded a deep purple solid. The product was filtered and thoroughly
washed with MeOH and then dried in vacuo. Yield: 27 mg, 63%. X-
ray-quality crystals of 4 were obtained from CH2Cl2/MeOH at room
temperature. Anal. Calcd for 4 (C58H80P4Pt2S2): C, 51.39; H, 5.95; S,
4.73. Found: C, 51.00; H, 5.83; S, 4.67. 1H NMR (300 MHz, CDCl3):
δ 9.39 (s, 2H, H6,11), 8.74 (dd, J = 3.4, 6.9 Hz, 2H, H1,4), 8.00 (dd, J =
3.1, 6.6 Hz, 2H, H7,10), 7.61 (d, J = 8.2 Hz, 4H, o-C6H5), 7.43−7.38
(m, 4H, H2,3,8,9), 7.11−7.06 (m, 4H, m-C6H5), 6.93 (t, J = 6.6 Hz, 2H,
1
C, 43.32; H, 5.22; N, 1.69; S, 4.01. H NMR (300 MHz, CDCl3): δ
9.21 (s, 2H, H6,11), 8,74 (d, J = 4.9 Hz, 4H, o-C5H5N), 8.56 (dd, J =
3.3, 6.6 Hz, 2H, H1,4), 8.07 (t, J = 7.9 Hz, 2H, p-C5H5N), 7.96 (dd, J =
3.4, 6.7 Hz, 2H, H7,10), 7.81−7.76 (m, 4H, m-C5H5N), 7.47−7.42 (m,
4H, H2,3,8,9), 1.80−1.75 (m, 24H, PCH2CH3), 1.27−1.16 (m, 36H,
PCH2CH3). 31P{1H} NMR (121.5 MHz, CDCl3): δ 16.50 (s, JPt−P
=
1
2320 Hz). ESI-MS: m/z 647.1, [M − 2OTf]2+.
Synthesis of [C6H3(CH3)2N}C(Et3P)2PtII]2-5,12-diethynyltetra-
cene (10). To a suspension of 1 (40 mg, 0.029 mmol) in acetonitrile
(5 mL) was added 2,6-xylyl isocyanide (10 mg, 0.076 mmol). When it
was stirred for 1 h, the suspension turned into a clear orange-red
solution. The addition of excess NaOTf (100 mg) followed by Et2O
afforded the title product, which was collected and dried. Yield: 26 mg,
53%. Anal. Calcd for 10 (C66H88F6N2O6P4Pt2S2): C, 46.70; H, 5.22;
p-C6H5), 2.09−2.03 (m, 24H, PCH2CH3), 1.27−1.16 (m, 36H,
1
PCH2CH3). 31P{1H} NMR (121.5 MHz, CDCl3): δ 13.29 (s, JPt−P
=
2412 Hz). ESI-MS: m/z 1354.5, [M]+.
Synthesis of [C6H5Se(Et3P)2PtII]2-5,12-diethynyltetracene (5).
The compound was prepared by following the procedure for 4 using
benzeneselenol. Yield: 67%. X-ray-quality crystals of 5 were obtained
from THF/MeOH at room temperature. Anal. Calcd for 5
1
N, 1.65; S, 3.78. Found: C, 46.60; H, 5.02; N, 1.61; S, 3.70. H NMR
(300 MHz, CDCl3): δ 9.19 (s, 2H, H6,11), 8.54 (dd, J = 3.3, 6.9 Hz,
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Organometallics
Article
Table 1. X-ray Crystal Data for 4−6, 7·2CH2Cl2, 8·0.5C3H6O·H2O, and 9·2CH2Cl2
4
5
6
7·2CH2Cl2
8·0.5C3H6O·H2O
9·2CH2Cl2
empirical formula
C58H80P4Pt2S2
C58H80P4Pt2Se2
C62H80P4Pt2
C86H104Cl4F6O6P6Pt2S2
C61.5H105F6O7.5P6
Pt2 S2
C60H84Cl4F6N2O6P4
Pt2S2
formula wt
cryst syst
space group
unit cell dimens
a (Å)
1355.40
monoclinic
P21/c
1449.20
monoclinic
P21/c
1339.32
triclinic
2129.61
triclinic
1716.56
monoclinic
P21/n
1763.27
monoclinic
C2/c
P1
P1
̅
̅
9.2161(11)
25.684(3)
12.9507(15)
90
8.9050(8)
11.5177(11)
27.949(3)
90
9.5196(48)
17.2407(8)
18.7566(8)
71.520(1)
80.678(1)
81.328(1)
2864.8(2)
2
9.4901(4)
11.5318(5)
20.5678(9)
81.069(1)
89.872(1)
80.764(1)
2194.19(16)
1
22.9582(10)
10.8973(5)
29.5076(13)
90
9.2429(8)
20.0203(17)
37.838(3)
90
b (Å)
c (Å)
α (deg)
β (deg)
109.035
90
93.569
90
91.500(1)
90
95.066(2)
90
γ (deg)
V (Å3)
2897.9(6)
2
2861.1(5)
2
7379.8(6)
4
6794.5(10)
4
Z
calcd density (g cm−3
)
1.553
1.682
1.553
1.612
1.545
1.679
abs coeff (mm−1
)
5.040
6.304
5.027
3.527
4.035
4.376
F(000)
cryst size (mm3)
1352
1424
1336
1068
3456
3504
0.3 × 0.18 × 0.14 0.30 × 0.14 × 0.04 0.40 × 0.16 × 0.08 0.56 × 0.30 × 0.28
0.40 × 0.30 × 0.02 0.78 × 0.16 × 0.10
θ range for data
collection (deg)
1.59−25.00
1.91−25.00
1.15−25.00
1.00−27.50
1.14−25.00
2.11−27.50
index ranges
−10 ≤ h ≤ 10
−30 ≤ k ≤ 25
−15 ≤ l ≤ 14
16478
−10 ≤ h ≤ 10
−13 ≤ k ≤ 13
−15 ≤ l ≤ 14
16058
−11 ≤ h ≤ 11
−20 ≤ k ≤ 20
−22 ≤ l ≤ 22
31021
−12 ≤ h ≤ 12
−14 ≤ k ≤ 14
−26 ≤ l ≤ 26
29069
−27 ≤ h ≤ 27
−8 ≤ k ≤ 12
−34 ≤ l ≤ 35
41224
−11 ≤ h ≤ 11
−24 ≤ k ≤ 26
−41 ≤ l ≤ 49
24544
no. of rflns collected
no. of indep rflns
5102 (R(int) =
0.0872)
5042 (R(int) =
0.0676)
10103 (R(int) =
0.0330)
10053 (R(int) = 0.0379) 12968 (R(int) =
8006 (R(int) =
0.0317)
0.0502)
max, min transmission 0.5389, 0.3132
0.7866, 0.2536
5042/286/432
0.6892, 0.2384
10103/0/625
0.4384, 0.2427
10053/41/556
0.9236, 0.2952
12968/548/923
0.6687, 0.1315
8006/0/394
no. of data/restraints/ 5102/381/507
params
goodness of fit (GOF) 1.126
1.225
1.069
1.154
1.053
1.245
final R indices (I >
2σ(I))
R1 = 0.0844, wR2 R1 = 0.0863, wR2 R1 = 0.0357, wR2 R1 = 0.0395, wR2 =
R1 = 0.0572, wR2 = R1 = 0.0416, wR2 =
= 0.1687
= 0.1717
= 0.0879
0.0974
0.1438
0.0931
largest diff peak, hole 1.944, −1.307
1.432, −2.069
3.947, −1.176
1.841, −1.358
3.350, −2.394
1.886, −2.378
(e Å−3
)
2H, H1,4), 7.98 (dd, J = 3.3, 6.6 Hz, 2H, H7,10), 7.53−7.26 (m, 10H,
H2,3,8,9 and C6H3), 2.56 (s, 12H, CH3), 2.33−2.28 (m, 24H,
PCH2CH3), 1.40−1.29 (m, 36H, PCH2CH3). 31P{1H} NMR (121.5
MHz, CDCl3): δ 17.31 (s, 1JPt−P = 2068 Hz). ESI-MS: m/z 699.3, [M
− 2OTf]2+.
(B3LYP). Frequency calculations were also performed on all the
optimized structures. As no imaginary vibrational frequencies were
encountered, the optimized stationary points were confirmed to be
local minima. Detailed optimized structural data are summarized in the
Supporting Information (Tables S1−S7).
In each TD-DFT calculation, the direction along the Pt−
C(acetylide) is defined to coincide with the z axis of the coordinate
system and the Pt−P bond in the x direction. Stuttgart small-core
relativistic effective core potentials were employed for Pt atoms with
their accompanying basis sets.13 In the geometry optimization
calculations, the 6-31G basis set was employed for C and H atoms14
and the 6-311G basis set for N, P, S, and Se atoms.15 The vertical
transition energies (the first 160 excited states) for the model
complexes were computed at their respective gas-phase-optimized
ground-state geometries using the TD-B3LYP method. The 6-31G*
basis set was employed for C and H atoms in the TD-DFT calculations
in order to enhance the accuracy of calculations. Tight SCF
convergence (10−8 au) was used for all calculations. All the DFT
and TD-DFT calculations were performed using the Gaussian 03
program package (revision D.01).16
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 = 0.71073 Å). The software used were SMART10 for collecting
frames of data, indexing reflections, and determination of lattice
parameters, SAINT10a for integration of intensity of reflections and
scaling, SADABS10b for multiscan absorption correction, and
SHELXTL10c 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 included in all refinements as riding atoms in geometrically
correct positions. The molecule of 7 is equally disordered over two
positions which are related by a C2 rotation around the substituted ring
of the tetracenyl ring. The X-ray crystal data are summarized in Table
1.
Computation Methodology. DFT and TD-DFT calculations
were performed on {[X(PMe3)2Pt]2-5,12-diethynyltetracene}n+ (X =
−SPh (4′), −SePh (5′), −CCPh (6′), n = 0; X = PMe3 (8′), pyridine
(9′), CNPh (10′), n = 2), which were used as models for the
platinum complexes studied in this work. PMe3 was used instead of
PEt3 in the models in order to reduce computational effort. 5,12-
Bis(trimethylsilylethynyl)tetracene and 5,12-diethynyltetracene were
also computed for comparisons. Their electronic ground states were
optimized without symmetry imposed using Becke’s three-parameter
hybrid functional11 with the Lee−Yang−Parr correlation functional12
RESULTS AND DISCUSSION
■
Complex 1 was synthesized from Cu(I)/amine coupling17
between trans-[Pt(PEt3)2I2] and 5,12-diethynyltetracene, which
was produced from desilylation of 5,12-bis-
(triisopropylsilylethynyl)tetracene (TIPS-T) followed by de-
protonation. Except for 6, which was prepared by Cu(I)/amine
coupling of 1 and phenylacetylide, all complexes were
synthesized from 1 by substitution of its iodides with X. The
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Figure 1. ORTEP plot of 4 (thermal ellipsoids drawn at the 30%
probability level). Disordered parts of tetracene and ethyl groups are
not shown for clarity. Color scheme: Pt, green; P, orange; C, gray; S,
blue.
Figure 5. ORTEP plot of 8·0.5C3H6O·H2O (thermal ellipsoids drawn
at the 30% probability level). The anions and solvent molecules are
not shown for clarity. Color scheme: Pt, green; P, orange; C, gray.
Figure 2. ORTEP plot of 5 (thermal ellipsoids drawn at the 30%
probability level). Disordered parts of tetracene and ethyl groups are
not shown for clarity. Color scheme: Pt, green; P, orange; C, gray; Se,
yellow.
Figure 6. ORTEP plot of 9·2CH2Cl2 (thermal ellipsoids drawn at the
50% probability level). The anions and solvent molecules are not
shown for clarity. Color scheme: Pt, green; P, orange; C, gray; N, light
blue.
Table 2. Selected Bond Lengths (Å) and Angles (deg) of 4−
6
4
Pt(1)−C(1)
Pt(1)−S(1)
Pt(1A)-C(4)
1.99(3)
2.350(4)
1.97(3)
Pt(1)−P(1)
Pt(1)−P(2)
2.305(5)
2.283(5)
C(1)−Pt(1)−S(1)
P(1)−Pt(1)−P(2)
C(1)−Pt(1)−P(2)
168.8(10)
174.84(19)
88.8(11)
S(1)−Pt(1)−P(2)
C(1)−C(2)−C(5)
91.2(2)
172(4)
Figure 3. ORTEP plot of 6 (thermal ellipsoids drawn at the 50%
probability level). Color scheme: Pt, green; P, orange; C, gray.
5
6
Pt(1)−C(1)
Pt(1)−Se(1)
C(1)−Pt(1)−Se(1)
P(1)−Pt(1)−P(2)
C(1)−Pt(1)−P(2)
1.93(3)
Pt(1)−P(1)
Pt(1)−P(2)
Se(1)−Pt(1)−P(2)
C(1)−C(2)−C(5)
2.383(6)
2.248(6)
2.473(5)
174.7(9)
171.5(3)
88.4(11)
89.8(2)
178(3)
Pt(1)−C(1)
Pt(1)−C(7)
C(1)−Pt(1)−C(7)
P(1)−Pt(1)−P(2)
C(1)−Pt(1)−P(2)
2.000(5)
2.001(5)
177.8(2)
178.46(5)
85.59(16)
Pt(1)−P(1)
Pt(1)−P(2)
C(7)−Pt(1)−P(1)
C(1)−Pt(1)−P(1)
C(1)−C(2)−C(5)
2.3004(14)
2.3019(15)
87.43(16)
94.70(15)
178.4(6)
Figure 4. ORTEP plot of 7·2CH2Cl2 (thermal ellipsoids drawn at the
50% probability level). H atoms, the anions, solvent molecules, and the
disordered part of tetracene are not shown for clarity. Color scheme:
Pt, green; P, orange; C, gray.
diethynyltetracene cores with two Pt ions coordinated to the
acetylides. The PtII ions show distorted-square-planar geometry
with typical Pt−C(acetylide) and Pt−P(Et3) bond distances.18
The Pt−C(acetylide) bond distance is not affected by the
different ligand field strengths of the opposite ligands. For
instance, 6−8 have very similar Pt−C(acetylide) bond
distances, despite the different σ-donating and π-accepting
strengths of PhCC−, PPh3, and PEt3. Bond distances
between the metal and other auxiliary ligands are normal.19
cationic 7−10 were isolated as triflate salts. Crystal structures of
4−9 are shown in Figures 1−6, respectively, and the selected
structural parameters are given in Tables 2 and 3. The
tetracenyl rings in 4 and 5 are severely disordered, resulting in
relatively less accurate Pt−C bond distances and X−Pt−C and
P−Pt−C bond angles. All complexes show similar 5,12-
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Table 3. Selected Bond Lengths (Å) and Angles (deg) of
7·2CH2Cl2, 8·0.5C3H6O·H2O, and 9·2CH2Cl2
7·2CH2Cl2
Pt(1)−C(1)
Pt(1)−P(1)
C(1)−Pt(1)−P(3)
P(1)−Pt(1)−P(2)
C(1)−Pt(1)−P(2)
1.987(5)
Pt(1)−P(2)
Pt(1)−P(3)
P(3)−Pt(1)−P(2)
C(1)−C(2)−C(5)
2.3450(12)
2.3170(11)
95.54(4)
2.3347(13)
171.83(15)
164.19(4)
81.53(14)
178.3(6)
8·0.5C3H6O·H2O
Pt(1)−C(1)
Pt(1)−P(2)
C(1)−Pt(1)−P(5)
P(1)−Pt(1)−P(2)
C(1)−Pt(1)−P(2)
1.999(9)
2.360(3)
176.3(3)
160.97(10)
79.9(3)
Pt(1)−P(1)
Pt(1)−P(5)
P(5)−Pt(1)−P(2)
C(1)−C(2)−C(5)
2.338(3)
2.319(3)
96.36(13)
174.0(10)
Figure 8. Emission spectra of 1−6 (solid lines) and 7−10 (dashed
lines) in CH2Cl2 at room temperature. The excitation wavelength is
490 nm.
9·2CH2Cl2 .
Pt(1)−C(1)
Pt(1)−P(1)
C(1)−Pt(1)−N(1)
P(1)−Pt(1)−P(2)
C(1)−Pt(1)−P(1)
1.951(5)
Pt(1)−P(2)
2.3170(12)
2.086(4)
2.3172(12)
177.30(19)
175.33(5)
90.10(15)
Pt(1)−N(1)
N(1)−Pt(1)−P(1)
C(1)−C(2)−C(5)
91.39(11)
175.1(5)
and 9, respectively. There is no stacking of the tetracenyl rings
in the crystals.
Absorption and Fluorescence. UV−vis absorption
spectra of 1−10 are shown in Figure 7, and the spectral data
are given in Table 4. In general, the spectra are similar and
resemble those of substituted tetracenes such as 5,12-
bis(triisopropylsilylethynyl)tetracene in showing three absorp-
tion bandsa very intense band at 290−300 nm (34480−
33330 cm−1; εmax = (0.59−1.45) × 105 M−1 cm−1) and two
moderately intense bands at 340−360 nm (29410−27780
cm−1; εmax = (1.15−2.26) × 104 M−1 cm−1) and 460−630 nm
(21740−15870 cm−1; εmax = (1.25−3.50) × 104 M−1 cm−1).
The last band shows three vibronic peaks.
The absorption bands are due to tetracene-based π → π*
transitions perturbed by the platinated acetylene groups. On
the basis of previous spectroscopic studies, the vibronic band at
460−630 nm (21740−15870 cm−1) is assigned to the S0 → S1
transition from the singlet ground state (S0) to the lowest
energy singlet excited state S1.7,20 It has been shown that the
extent of perturbations in metalated polycyclic hydrocarbons
can be gauged by red shifts of the S0 → S1 transitions.6a,7,21
The transitions of the Pt complexes which are red-shifted
from that of 5,12-bis(triisopropylsilylethynyl)tetracene (λmax
535 nm; 18690 cm−1) by 580−1450 cm−1, indicating that
platination increases perturbations on the electronic structure
of the tetracenyl ring. The complexes can be divided into two
groups based on the energies of their S0 → S1 transitionsthe
neutral complexes with primarily π-donating ligands (1−6)
have very similar S0 → S1 transition energies (λmax 572 − 580
Figure 7. Absorption spectra of 1−6 (solid lines) and 7−10 (dashed
lines) in CH2Cl2 at room temperature. For the sake of clarity, the
visible absorption bands (400−650 nm) are magnified by 2.5 times.
The CC−C(tetracenyl) linkages are close to linear. The
tetracenyl ring is essentially planar. Dihedral angles between the
coordination planes of the Pt ions and the tetracenyl rings
ranges from 64.02 to 87.85°, probably due to steric repulsion
between the bulky PEt3 and the tetracenyl ring. The two
coordination planes in 7 are parallel but are separated by
dihedral angles of 7.26, 7.88, 13.92, 38.61, and 53.17° in 4−6, 8,
Table 4. Absorption and Emission Spectroscopic Data of the Complexes
soln emission maximum/nm
(cm−1
emission lifetime τfl/
emission quantum yield
complex
S0 → S1 transition/nm (cm−1; ε, 104 M−1cm−1
)
)
ns
Φfl
1
2
3
4
5
6
7
8
9
10
572 (17480; 2.62), 532 (18800; 1.78), 498 (20080; 0.67) (s)
573 (17450; 2.09), 532 (18800; 1.42), 498 (20080; 0.56) (s)
573 (17450; 2.99), 533 (18760; 2.04), 498 (20080; 0.80) (s)
578 (17300; 2.37), 537 (18620; 1.58), 503 (19880; 0.61) (s)
578 (17300; 1.25), 537 (18620; 0.87), 503 (19880; 0.38) (s)
580 (17240; 3.10), 539 (18550; 2.08), 505 (19800; 0.80) (s)
553 (18080; 3.43), 514 (19450; 2.26), 481 (20790; 0.81)
552 (18120; 2.51), 513 (19490; 1.72), 480 (20830; 0.70)
555 (18020; 2.85), 517 (19340; 1.96), 483 (20700; 0.75)
552 (18120; 3.50), 514 (19450; 2.34), 481 (20790; 0.87)
596 (16780)
599 (16690)
599 (16690)
605 (16530)
605 (16530)
608 (16450)
563 (17760)
561 (17830)
570 (17540)
565 (17700)
8.6
9.2
9.3
6.3
2.6
8.7
2.0
3.3
6.5
5.8
0.60
0.58
0.50
0.36
0.13
0.51
0.38
0.45
0.81
0.97
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On the basis of their small Stokes shifts (290−800 cm−1) and
nanosecond lifetimes (2.0−9.3 ns), the emissions are assigned
to metal-perturbed S1 → S0 fluorescence. Despite of the
presence of the heavy atom Pt, phosphorescence arising from
triplet states of the tetracenyl core was not observed. It might
be due to a low rate of intersystem crossing resulting from a
large extent of π conjugation of the ligand, as suggested by
Che.22 The results are in line with previous work on PtII and
AuI tetracenes and 5,12-diethynyltetracenes.7 The emission
bands of the cationic complexes show vibronic shoulders more
distinct than those of the neutral complexes. Analogous to the
absorption spectra, the fluorescence of the neutral complexes is
red-shifted from that of the cationic complexes by 770−1380
cm−1.
Despite the presence of the heavy Pt atoms, no
phosphorescence is observed. The fluorescence quantum yields
(Φfl = 0.13−0.97) of the complexes are comparable with that of
TIPS-T (Φfl = 0.79),1e indicating that replacing the Si(iPr)3
groups with the much heavier Pt ions does not lead to a
significant increase in rate of intersystem crossing from the S1
excited state to the lowest triplet excited state T1. This is
corroborated by the long-lived S1 excited state (τ = 2.0−9.3 ns).
This apparent absence of the so-called “heavy atom effect” has
been observed in other luminescent complexes containing
second (e.g., RhIII)-22a or third-row transition-metal ions (e.g.,
AuI).22b In a recent study, Che et al. showed that the electronic
structures of the organic chromophores play a key role in
controlling the rate of S1 → T1 intersystem crossing in AuI
oligo(phenylethynylene) compounds.22b Our previous study
shows that cyclometalated PtII anthracene complexes only
exhibit fluorescence despite direct coordination of the metal to
the aromatic ring.6b We argued that the absence of
phosphorescence is due to the electronic structure of
anthracene, which being an alternant hydrocarbon, has a large
S1−T1 gap (11500 cm−1)23 because of the strong exchange
interaction between the two unpaired electrons in its
extensively overlapped HOMO and LUMO. The large S1−T1
gap creates an unfavorable Franck−Condon barrier for the S1
→ T1 intersystem crossing. Tetracene is an alternant hydro-
carbon with a large S1−T1 gap of 10800 cm−1.23 It is therefore
possible that the apparent absence of a heavy atom effect in the
present complexes is due to an unfavorable Franck−Condon
barrier for the S1 → T1 intersystem crossing.
Figure 9. Optimized structures and HOMO and LUMO surfaces for
(a) 5,12-diethynyltetracene (LH) and (b) 6′ using the B3LYP
functional (hydrogen atoms are omitted for clarity, surface isovalue
0.02 au).
nm; 17480−17240 cm−1) which are invariably lower than the
transitions (λmax 552−555 nm; 18120−18020 cm−1) of the
cationic complexes (7−10) with primarily π-accepting ligands.
The energy difference between the transitions are small (540−
870 cm−1) but significant, as it suggests different extents or
modes of perturbation in the two classes of complexes.
The complexes are luminescent (Φfl = 0.13−0.97), with the
isocyanide complex 10 being the most emissive. Like the
absorption spectra, fluorescence of the complexes (Figure 8) is
red-shifted from that of 5,12-bis(triisopropylsilylethynyl)-
tetracene (λmax 542 nm; 18450 cm−1) by 620−2000 cm−1.
Table 5. HOMO and LUMO Compositions of {[X(PMe3)2Pt]2-5,12-diethynyltetracene}n+
composition/%
5,12-diethynyltetracene
complex
MO
energy/eV
Pt[dxz + px]
PMe3
X
3′
HOMO
LUMO
HOMO
LUMO
HOMO
LUMO
HOMO
LUMO
HOMO
LUMO
HOMO
LUMO+2
HOMO
LUMO
−4.266
−1.975
−4.192
−1.918
−4.185
−1.915
−4.045
−1.780
−8.033
−5.675
−7.876
−5.493
−7.988
−5.655
8.26
4.08
9.16
4.36
8.88
4.05
7.75
3.49
4.54
3.40
4.12
3.93
2.91
1.47
4.93
4.10
4.22
4.19
4.04
4.17
4.60
4.18
5.01
6.10
3.82
3.95
4.00
7.49
86.43
91.71
84.13
91.20
83.28
91.45
86.21
91.92
88.78
87.97
91.60
84.93
92.48
84.26
0.30
0.06
2.23
0.20
3.28
0.21
1.32
0.37
1.53
2.16
0.39
7.08
0.59
6.60
4′
5′
6′
8′
9′
10′
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Figure 10. Orbital interaction between the [X(PMe3)2Pt]n+ moieties and the 5,12-diethynyltetracene dianion in the model complexes (Interactions
are counted to be effective when the percent contribution of the fragments to the model complexes >5%). H and L denote HOMO and LUMO, and
π(Pt) denotes the {Pt[dxz + px] + π(X)} hybrid orbitals of the Pt fragments.
2,6-xylyl isocyanide, the auxiliary ligands in 8′ and 10′ are the
electronically similar PMe3 and phenyl isocyanide, respectively.
The ground-state molecular structures of the model complexes
were optimized at the DFT level (B3LYP). In order to
understand the role played by the metal ions, the electronic
structures of 5,12-diethynyltetracene (LH) and 5,12-bis-
(trimethylsilylethynyl)tetracene (LSi), which model TIPS-T,
were also calculated. In each case, the directions along the Pt−
Cα(5,12-diethynyltetracene) and the Pt−P bonds are defined as
the z and x axes, respectively. Structural parameters of the
optimized structures of the models (Supporting Information,
Tables S1−S7) are in good agreement with the crystal
structures of their corresponding complexes; for example, the
Pt−C bond distances obtained from the X-ray crystal structures
are 1.982(5) and 2.000(5) Å in 6 and 1.951(5) Å in 9 and are
2.022 and 1.975 Å in 6′ and 9′. Figure 9 shows the optimized
structures and HOMO and LUMO surfaces for LH and 6′.
Although all the calculated molecules were optimized with no
symmetry imposed, their ground-state structures have approx-
imate C2v symmetry. The HOMOs (a2) and LUMOs (b1) of
the molecules are dominated by the π and π* orbitals of the
central 5,12-diethynyltetracenyl ring.
An exception is 9′ (n = 2, X = pyridine), for which the
tetracene-based π* orbital is LUMO+2 (LUMO and LUMO+1
are π* orbitals of the pyridine ligands), and accordingly the
HOMO → LUMO+2 transition of 9′ corresponds to the
HOMO → LUMO transitions of the other complexes. The
π(Pt) orbitals mix with the π and π* orbitals of the 5,12-
diethynyltetracene dianion, but their contributions to the
HOMOs and LUMOs (LUMO+2 for 9′) are small (>10% in
both the HOMOs and LUMOs). For the neutral complexes
with π-donating ligands (3′−6′), the Pt[dxz + px] hybrid
Table 6. Comparison of the Vertical Transition Energies for
the Model Compounds and Corresponding Experimental
Data
TD-DFT calculation
exptl data
λmax/nm
excitation energy/nm
(oscillator strength)
transition
(εmax)
LH
LSi
3′
564 (0.1123)
582 (0.2102)
606 (0.3032)
614 (0.3648)
616 (0.3727)
617 (0.3945)
588 (0.3130)
582 (0.2547)
596 (0.4001)
HOMO →
LH
TIPS-T 535
a
LUMO
HOMO →
LUMO
(3.15 × 104)
573
(2.99 × 104)
578
(2.37 × 104)
578
(1.25 × 104)
580
(3.10 × 104)
552
(2.51 × 104)
555
(2.85 × 104)
HOMO →
LUMO
3
4′
HOMO →
LUMO
4
5′
HOMO →
LUMO
5
6′
HOMO →
LUMO
6
8′
HOMO →
LUMO
8
9′
HOMO →
LUMO+2
9
10′
HOMO →
LUMO
10
552
(3.50 × 104)
a
5,12-diethynyltetracene is too unstable to be isolated for spectro-
scopic measurements.
DFT Calculations. To understand the cause of the red shift,
DFT calculations on {[X(PMe3)2Pt]2-5,12-diethynyltetrace-
ne}n+ (n = 0, X = −Cl (3′), −SPh (4′), −SePh (5′), −C
CPh (6′); n = 2, X = PMe3 (8′), pyridine (9′), CNPh
(10′)), as models for the complexes 3−6, 8−10 respectively,
were carried out. The PEt3 groups in the complexes are
replaced with PMe3 in the models. Also, instead of PEt3 and
Figure 11. Energy levels of the HOMOs and LUMOs and the energies associated with the transition between the MOs for LH, LSi, and other model
Pt complexes. For 9′, LUMO+2 is depicted instead of the LUMO.
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Figure 12. Energies of the HOMOs and LUMOs in the model Pt complexes relative to those in LH.
orbitals contribute more to the HOMOs (7.75−9.16%) than to
the LUMOs (3.49−4.36%); for the cationic complexes (8′−
10′), the Pt[dxz + px] hybrid orbitals have small contributions
to both the HOMOs (2.91−4.54%) and LUMOs ((LUMO+2
for 9′, 1.47−3.93%). According to the different extents of the
Pt[dxz + px] hybrid orbital contribution to the frontier orbitals,
one would expect the metal perturbation in 3′−6′ should be
stronger than in 8′−10′. The compositions of the HOMOs and
LUMOs (LUMO+2 for 9′) for the model Pt complexes are
summarized in Table 5.
The origin of the different extents of the Pt[dxz + px] hybrid
orbital contribution to the frontier orbitals can be rationalized
by considering the molecular orbital pictures as the result of the
{[X(Me3P)2Pt]n+}−[5,12-diethynyltetracene dianion] interac-
tion. Figure 10 shows the HOMOs and LUMOs (LUMO+2 for
9′) of the model complexes and their corresponding
compositions from the “frozen” [X(Me3P)2Pt]n+ and 5,12-
diethynyltetracene dianion fragments.
from one-electron excitation from the HOMO to the LUMO
(or HOMO to LUMO+2 for 9′). The absorption maxima
obtained from the TD-DFT calculations is in the order LSi (583
nm) ≈ 8′−10′ (582−596 nm) < 3′−6′ (606−617 nm), which
parallels the trend observed experimentally. Figure 11 depicts
the energy levels of the HOMOs and the LUMOs and the
energies associated with the transition between these MOs for
LH, LSi, and other model Pt complexes.
Figure 12 depicts the energies of the HOMOs and LUMOs
of the model Pt complexes and LSi relative to those in LH,
which can be used to illustrate the reason for the red shift in
absorption and fluorescence from neutral to cationic complexes.
The plot shows that the HOMOs and LUMOs (LUMO+2
for 9′) for 8′−10′ are substantially stabilized (ca. 3 eV) nearly
solely by the inductive effect of the two doubly charged
[X(PMe3)2Pt]2+ units (metal perturbations to these orbitals are
shown to be <5%; see Table 5 and Figure 10). Since the
HOMOs and LUMOs (LUMO+2 for 9′) are stabilized to
nearly the same extent in these cationic complexes, their
HOMO → LUMO transition energies (HOMO → LUMO+2
for 9′) are close to that for LH and LSi. On the other hand, the
HOMOs for 3′−6′ are destabilized to a greater extent (0.7−0.9
eV) than the LUMOs (0.6−0.7 eV), which is a result of
stronger metal perturbation in the HOMOs (5−10%) than in
the LUMOs (<5%). Thus, their HOMO → LUMO transition
energies are red-shifted in comparison with those in 8′−10′.
For the [X(Me3P)2Pt]n+ fragments, mixing of the dxz and px
orbitals of the Pt ion and the π orbitals of the auxiliary ligand X
gives rise to three hybrid orbitals {Pt[dxz + px] + π(X)}, which
are abbreviated as π(Pt) orbitals hereafter. These π(Pt) hybrid
orbitals have π symmetry which are able to interact with the
HOMO and HOMO-6 of the 5,12-diethynyltetracene dianion
fragment to give the HOMO of the model complexes. The
π(Pt) orbitals for the neutral complexes (3′−6′) are higher
lying than those for the cationic complexes (8′−10′) by at least
4 eV because of the lower effective nuclear charge of the Pt ions
in the neutral complexes. Therefore the π(Pt) orbitals in 3′−6′
have better energy matching with the HOMO and HOMO-6 of
the 5,12-diethynyltetracene dianion fragment and thus
contribute more to the HOMOs of the complexes than in
the cases for 8′−10′. The lower HOMO energies for 8′−10′ in
comparison with those for 3′−6′ mainly arise from the higher
nuclear charges of the [X(Me3P)2Pt]n+ fragments in 8′−10′ in
comparison to those in 3′−6′. The LUMOs of the model
complexes (LUMO+2 for 9′) are mainly composed of the
LUMO of the 5,12-diethynyltetracene dianion with some
contribution from the LUMO+1. Again the lower LUMO
energies for 8′−10′ (LUMO+2 for 9′) in comparison with
those for 3′−6′ mainly arise from the higher nuclear charges of
the [X(Me3P)2Pt]n+ fragments.
CONCLUSION
■
Traditionally, the electronic and spectroscopic properties of
oligoacenes are varied by substitution of the H atoms of the
rings with heteroatoms or functional groups. In this work, we
demonstrated that the absorption and fluorescence of Pt2 5,12-
diethynyltetracenes are subject to the influence of auxiliary
ligands which are not directly attached to the ring. Despite the
wide range of electronic properties of the ligands examined in
this study, according to the absorption and emission energies,
the complexes can be classified into two groups: complexes
with anionic π-donating ligands (1−6) and complexes with
neutral ligands (7−10). The S0 → S1 transition associated with
all these complexes are calculated to originate from HOMO →
LUMO transitions (HOMO → LUMO+2 for 9). For 7−10,
the contribution of these orbitals from the [X(Me3P)2Pt]n+
fragments are minimal, as the π(Pt) hybrid orbitals on the
[X(Me3P)2Pt]n+ fragments are too low-lying to interact with
the HOMO and LUMO of the 5,12-diethynyltetracene dianion
fragment; thus, their HOMO → LUMO transition energies
(HOMO to LUMO+2 for 9) are close to that for the ligand LSi.
On the other hand, the {[X(Me3P)2Pt]n+}−[5,12-diethynylte-
tracene dianion] interaction in 1−6 is apparent, and the
Electronic transitions for the model complexes were
calculated using the TD-DFT method. Calculated vertical
transition energies are summarized in Table 6. The calculated
spectra (Supporting Information, Figures S1−S7) of the
models are in good agreement with the experimental spectra:
each of them exhibits a lowest-energy dipole-allowed electronic
transition in the visible region (λmax 588−617 nm) originating
1627
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Organometallics
Article
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HOMO of the 5,12-diethynyltetracene dianion fragment is
perturbed to a greater extent by the π(Pt) hybrid orbitals on
the [X(Me3P)2Pt]n+ fragments, as they are closer to the
HOMO of the 5,12-diethynyltetracene dianion fragment than
the LUMO. Thus, the S0 → S1 transition energies for 1−6 are
red-shifted in comparison with those for 7−10.
ASSOCIATED CONTENT
* Supporting Information
■
S
CIF files, giving crystallographic data for 4−6, 7·2CH2Cl2,
8·0.5C3H6O·H2O, and 9·2CH2Cl2, and Tables S1−S7 and
Figures S1−S7, giving structural parameters of the optimized
structures of the model complexes and their calculated
absorption spectra, respectively. This material is available free
of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail for J.H.K.Y.: chmyiphk@nus.edu.sg.
■
(7) Nguyen, M.-H.; Yip, J. H. K. Organometallics 2010, 29, 2422.
(8) Armarego, W. L. F.; Chai, C. L. L., Purification of Laboratory
Chemicals, 5th ed.; Elsevier: Amsterdam, 2003.
Notes
The authors declare no competing financial interest.
(9) Karstens, T.; Kobs, K. J. Phys. Chem. 1980, 84, 1871.
ACKNOWLEDGMENTS
(10) (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
■
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. The computa-
tional work was supported by a grant from the Hong Kong
Research Grants Council (Project No. CityU 103911).
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.
(11) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(12) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
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