Vapochromic and mechanochromic phosphorescence materials based on a platinum(II) complex with 4-trifluoromethylphenylacetylide

Article abstract of DOI:10.1021/ic202421d

Planar platinum(II) complex Pt(Me₃SiC≡CbpyC≡ CSiMe₃)(C≡CC₆H₄CF₃-4) ₂ (6) with 5,5′-bis(trimethylsilylethynyl)-2,2′- bipyridine and 4-trifluoromethylphenylacetylide exhibits remarkable luminescence vapochromic and mechanochromic properties and a thermo-triggered luminescence change. Solid-state 6 is selectively sensitive to vapors of oxygen-containing volatile compounds such as tetrahydrofuran (THF), dioxane, and tetrahydropyrane (THP) with phosphorescence vapochromic response red shifts from 561 and 608 nm to 698 nm (THF), 689 nm (dioxane), and 715 nm (THP), respectively. Upon being mechanically ground, desolvated 6, 6·CH₂Cl₂, and 6·¹/₂CH₂ClCH₂Cl exhibit significant mechanoluminescence red shifts from 561 and 608 nm to 730 nm, while vapochromic crystalline species 6·THF, 6·dioxane, or 6·THP affords a mechanoluminescence blue shift from 698 nm (THF), 689 nm (dioxane), or 715 nm (THP) to 645 nm, respectively. When the compounds are heated, a thermo-triggered luminescence change occurs, in which bright yellow luminescence at 561 and 608 nm turns to red luminescence at 667 nm with a drastic red shift. The multi-stimulus-responsive luminescence switches have been monitored by the changes in emission spectra and X-ray diffraction patterns. Both X-ray crystallographic and density functional theory studies suggest that the variation in the intermolecular Pt-Pt interaction is the key factor in inducing an intriguing luminescence switch.

Full text of DOI:10.1021/ic202421d

Article
pubs.acs.org/IC
Vapochromic and Mechanochromic Phosphorescence Materials
Based on a Platinum(II) Complex with 4-
Trifluoromethylphenylacetylide
Xu Zhang,† Jin-Yun Wang,† Jun Ni,† Li-Yi Zhang,† and Zhong-Ning Chen*,†,‡
†State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences,
Fuzhou, Fujian 350002, China
‡State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
Shanghai 200032, China
S
* Supporting Information
ABSTRACT: Planar platinum(II) complex Pt(Me3SiCCbpyCCSiMe3)(CCC6H4CF3-4)2 (6) with 5,5′-bis-
(trimethylsilylethynyl)-2,2′-bipyridine and 4-trifluoromethylphenylacetylide exhibits remarkable luminescence vapochromic and
mechanochromic properties and a thermo-triggered luminescence change. Solid-state 6 is selectively sensitive to vapors of
oxygen-containing volatile compounds such as tetrahydrofuran (THF), dioxane, and tetrahydropyrane (THP) with
phosphorescence vapochromic response red shifts from 561 and 608 nm to 698 nm (THF), 689 nm (dioxane), and 715 nm
(THP), respectively. Upon being mechanically ground, desolvated 6, 6·CH2Cl2, and 6·1/2CH2ClCH2Cl exhibit significant
mechanoluminescence red shifts from 561 and 608 nm to 730 nm, while vapochromic crystalline species 6·THF, 6·dioxane, or
6·THP affords a mechanoluminescence blue shift from 698 nm (THF), 689 nm (dioxane), or 715 nm (THP) to 645 nm,
respectively. When the compounds are heated, a thermo-triggered luminescence change occurs, in which bright yellow
luminescence at 561 and 608 nm turns to red luminescence at 667 nm with a drastic red shift. The multi-stimulus-responsive
luminescence switches have been monitored by the changes in emission spectra and X-ray diffraction patterns. Both X-ray
crystallographic and density functional theory studies suggest that the variation in the intermolecular Pt−Pt interaction is the key
factor in inducing an intriguing luminescence switch.
als based on various metal coordination compounds. External
stimuli cause variations in metallophilic contact, π−π stacking,
H-bonding interaction, or metal−solvent bonding, thus
resulting in an increase or decrease in the MLCT or LLCT
energy level, respectively, which is responsible for the blue or
red shift, respectively, of the phosphorescent emission.
We have been interested in the stimulus-responsive
phosphorescence switch in square-planar bis(σ-acetylide)
platimum(II) complexes with 5,5′-bis(trimethylsilylethynyl)-
2,2′-bipyridine (Me3SiCCbpyCCSiMe3) or 5-(trimethylsi-
lylethynyl)-2,2′-bipyridine (Me3SiCCbpy).7 These planar
platinum(II) complexes exhibit remarkable luminescence
vapochromic or/and mechanochromic properties, inducing
INTRODUCTION
■
It has been demonstrated that square-planar Pt(diimine)(C
CR)2 (R = alkyl or aryl) complexes usually exhibit bright
luminescence at ambient temperature, originating mostly from
3[dπ(Pt) → π*(diimine)]/3[dπ(CCR) → π*(diimine)]
3MLCT/3LLCT triplet excited states.1−5 These planar
molecules favor formation of aggregate species through
intermolecular Pt−Pt and π−π interactions that are highly
sensitive to external stimuli such as solvate, heat, and
mechanical force, triggering intriguing color and luminescence
changes.6−8 Such stimulus-responsive luminescence switches
have extensive applications in sensing, optical recording,
memory, and display. Among various luminescence and color
changes in response to external stimuli, luminescence
vapochromism,6−27 mechanochromism,7c,d,22a,b,23,28−36 and
thermochromism32,37−42 occur frequently in solid-state materi-
3
3
Received: November 10, 2011
Published: May 2, 2012
© 2012 American Chemical Society
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Table 1. Crystallographic Data for 6·CH2Cl2, 6·1/2CH2ClCH2Cl, and 6·THF
6·CH2Cl2
6·1/2CH2ClCH2Cl
6·THF
empirical formula
formula weight
crystal system
space group
a (Å)
C39H34Cl2F6N2PtSi2
966.85
C39H34ClF6N2PtSi2
931.39
C42H40F6N2OPtSi2
954.03
monoclinic
P21/c
monoclinic
P21/c
monoclinic
C2/c
7.1353(7)
38.393(3)
15.2803(17)
96.035(7)
4162.8(7)
4
7.084(3)
37.329(17)
15.811(7)
94.648(7)
4168(3)
4
17.388(7)
39.549(15)
13.504(6)
105.179(8)
8963(6)
8
b (Å)
c (Å)
β (deg)
V (Å3)
Z
ρcalcd (g/cm−3
)
1.543
1.485
1.414
μ (mm−1
)
3.612
3.544
3.241
radiation (λ, Å)
0.71073
293(2)
0.71073
293(2)
0.71073
293(2)
temp (K)
a
R1(Fo)
0.0474
0.0691
0.0733
b
2
wR2(Fo )
0.1701
0.2116
0.2118
GOF
1.020
1.070
1.035
a
b
2
2
R1 = ∑|Fo − Fc|/∑Fo. wR2 = ∑[w(Fo − Fc2)2]/∑[w(Fo )]1/2
.
spectroscopic measurements were of spectroscopic grade. 5,5′-
Bis(trimethylsilylethynyl)-2,2′-bipyridine (Me3SiCCbpyC
CSiMe3), 1-ethynyl-4-(trifluoromethyl)benzene (HCCC6H4CF3-
4), and Pt(Me3SiCCbpyCCSiMe3)Cl2 were prepared by
synthetic procedures described in the literature.7,43 Other reagents
were purchased from commercial sources and used as received unless
specified otherwise.
significant emission shifts in response to vapors of specific
volatile organic compounds (VOCs) or mechanical grinding.
Aiming at increasing the contrast of stimulus-responsive
luminescence color changes as well as exploring the influence
of various substituents on crystal packing and luminescence
conversion in response to external stimuli, we found a feasible
approach is to increase the 3MLCT/3LLCT level by
introducing electron-donating substituents into Me3SiC
CbpyCCSiMe3 or electron-withdrawing substituents into
phenylacetylide. Considering that introduction of an electron-
withdrawing CF3 group onto phenylacetylide (CCC6H4R)
would lower the HOMO level and increase the
3MLCT/3LLCT energy, Pt(Me3SiCCbpyCC-SiMe3)-
(CCC6H4CF3-4)2 (6) was synthesized to produce blue-
shifted phosphorescent emission (568 and 608sh nm in
CH2Cl2) relative to that of Pt(Me3SiCCbpyCC-SiMe3)-
(CCC6H5)2 (2; λem = 616 nm in CH2Cl2). It is found that
phosphorescent emission in solid materials based on complex 6
is highly sensitive to vapors of some O-heterocyclic VOCs,
heating, and mechanical grinding with multi-stimulus-respon-
sive luminescence switches. In contrast with Pt(Me3SiC
CbpyCCSiMe3)(CCC6H5)2 (1)7b that exhibits lumines-
cence vapochromism to vapors of three halocarbons such as
CH2Cl2, CHCl3, and CH3I with drastic vapochromic red shift
responses, complex 6 is selectively sensitive to vapors of three
O-heterocyclic VOCs with drastic vapochromic red shift
responses from 561 and 608 nm to 698 nm (THF =
tetrahydrofuran), 689 nm (dioxane), or 715 nm (THP =
tetrahydropyrane). Furthermore, unusual blue-shifted or red-
shifted mechanochromic luminescence is exhibited for the
6·VOC complex depending on the solvate VOC, in which the
6·THF complex displays obviously blue-shifted luminescence in
response to mechanical grinding whereas desolvated 6,
6·CH2Cl2, and 6·1/2CH2ClCH2Cl afford remarkably red-shifted
mechanochromic luminescence.
Pt(Me3SiCCbpyCCSiMe3)(CCC6H4CF3-4)2 (6). To a di-
chloromethane (50 mL) solution of 1-ethynyl-4-(trifluoromethyl)-
benzene (85 mg, 0.5 mmol) were added Pt(Me3SiCCbpyC
CSiMe3)Cl2 (123 mg, 0.20 mmol), CuI (1 mg), and diisopropylamine
(2 mL) with stirring for 1 day at ambient temperature. After the
solvents were removed in vacuo, the product was purified by
chromatography on a silica gel column using dichloromethane as the
eluent. Yield: 82% (145 mg). Anal. Calcd for desolvated
C38H32F6N2PtSi2: C, 51.75; H, 3.66; N, 3.18. Found: C, 51.57; H,
3.59; N, 3.29. ESI-MS: m/z 882 [M + H]+. 1H NMR (CDCl3): δ 9.86
(d, 2H, J = 1.6 Hz, bpy), 8.20 (dd, 2H, J = 1.6 Hz, J = 8.4 Hz, bpy),
7.97 (d, 2H, J = 8.4 Hz, bpy), 7.57 (d, 4H, J = 8.0 Hz, C6H4), 7.50 (d,
4H, J = 8.4 Hz, C6H4), 0.28 (s, 18H, CH3). IR (KBr disk): 2117s (C
CPt), 2163m (CCSiMe3), 1250m cm−1 (Si−C).
Physical Measurements. Spectroscopic measurements for un-
ground solid samples were performed using crystalline species isolated
from the solutions. The ground samples were made by mechanically
grinding the crystalline species in an agate mortar. UV−vis absorption
spectra in solutions were measured on a Perkin-Elmer Lambda 25
UV−vis spectrophotometer. UV−vis diffuse reflectance spectra in solid
states were recorded with a Perkin-Elmer Lambda 900 UV−vis−NIR
spectrophotometer. Infrared spectra (IR) were recorded on a Magna
750 FT-IR spectrophotometer with KBr pellets. Elemental analyses
(C, H, N) were conducted on a Perkin-Elmer model 240 C elemental
1
analyzer. H NMR spectra were recorded on a Bruker Advance 400
(400 MHz) spectrometer with SiMe4 as the internal reference.
Electrospray ionization mass spectrometry (ESI-MS) was performed
on a Finnigan LCQ mass spectrometer using dichloromethane and
methanol as mobile phases. Powder X-ray diffraction (XRD)
measurements were recorded on Rigaku miniflex II desktop X-ray
diffractometer and Bruker D8 Advance diffractometer using Cu Kα
radiation. Emission and excitation spectra were recorded on a Perkin-
Elmer LS55 luminescence spectrometer with a red-sensitive photo-
multiplier type R928 instrument. Emission lifetimes in solid states and
degassed solutions were determined on an Edinburgh analytical
instrument (F900 fluorescence spectrometer) using an LED laser with
excitation at 440 nm. The emission quantum yield (Φem) in a degassed
dichloromethane solution at room temperature was estimated using
EXPERIMENTAL SECTION
■
General Procedures and Materials. All operations were
conducted under a dry argon atmosphere using Schlenk techniques
and vacuum-line systems unless otherwise specified. The solvents were
dried, distilled, and degassed prior to use except that those for
[Ru(bpy)3](PF6)2 in acetonitrile as the reference standard (Φem
=
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Scheme 1
0.062).44 To probe the selectivity and reversibility of the vapochromic
properties with respect to specific VOCs, a concentrated CH2Cl2
solution of 6 was put on quartz disks that were purged with N2 to dry.
Luminescence vapochromic experiments were performed upon
sufficient exposure of the quartz disks to various saturated VOC
vapors at ambient temperature for 5−10 min. A rapid vapochromic
response is usually observed in 15 s to 2 min depending on the sample
thickness in quartz disks. A PMMA film of complex 6 was made on a
quartz slide (2.5 cm × 4 cm) using the spin coating method, in which
the solution was prepared by dissolving complex 6 (10 mg) and
PMMA (polymethylmethacrylate, 40 mg) in dichloromethane (2 mL).
Determination of Crystal Structures. Single crystals of
6·1/2CH2ClCH2Cl, 6·CH2Cl2, and 6·THF were obtained by layering
petroleum ether onto the corresponding solutions of 6 with solvate
VOCs as the solvents. Single crystals sealed in capillaries with mother
liquor were measured on a Saturn 70 CCD diffractometer by the ω
scan technique at room temperature using graphite-monochromated
Mo Kα (λ = 0.71073 Å) radiation. CrystalClear was used for data
reduction and empirical absorption correction. The structures were
determined by direct methods. The heavy atoms were located with an
E-map, and the rest of the non-hydrogen atoms were found in
subsequent Fourier maps. All non-hydrogen atoms were refined
anisotropically, while the hydrogen atoms were generated geometri-
cally and refined with isotropic thermal parameters. The structures
were refined on F2 by full-matrix least-squares methods using
SHELXTL-97.45 For 6·THF, 4-(trifluoromethylphenyl)acetylide and
solvate THF exhibit a statistical distribution with two sets of
corresponding identical groups. The occupancy percentage of atoms
C30−C38 and F4−F6 (4-trifluoromethylphenyl) as well as O01 and
C01−C04 (solvate THF) is 47.4%, whereas that of counterparts
C30B−C38B and F4B−F6B (4-trifluoromethylphenyl) as well as
O01B and C01B−C04B (solvate THF) is 52.6%. Crystallographic data
for 6·CH2Cl2, 6·1/2CH2ClCH2Cl, and 6·THF are presented in Table
1.
Theoretical Calculation Methodology. To gain insight into the
electronic and spectroscopic properties as well as the nature of the
origin of absorption and emission of complex 6, time-dependent
density functional theory (DFT/TD-DFT)46−48 with the gradient-
corrected correlation functional PBE1PBE49 was employed for the
calculations. First, the structural geometry of complex 6 as an isolated
molecule from the solvent phase in the ground state was optimized at
the DFT level of theory without symmetry constraints. To analyze the
spectroscopic properties, 100 singlet and 6 triplet excited states were
obtained to determine the vertical excitation energies in a dichloro-
methane solution by performing the TD-DFT calculations on the basis
of the optimized geometrical structure. The polarized continuum
model method (PCM)50 with dichloromethane as the solvent was
used to calculate all the electronic structures in solution. In these
calculations, the Stuttgart−Dresden (SDD)51 basis set consisting of
the effective core potentials (ECP) was employed for the platinum(II)
and silicon(IV) atoms, and the 6-31G(p,d) polarized double-ζ basis set
was used for the remaining atoms. To precisely describe the electronic
structures, one additional f-type polarization function was imple-
mented for the platinum(II) atom (αf = 0.18).52
To compare transition characteristics that contribute to the
absorption and emission spectra in crystalline species 6·VOC with
different solvate VOCs, TD-DFT calculations were performed on
6·1/2CH2ClCH2Cl and 6·THF using a pair of symmetry-related
platinum(II) moieties (dimeric model) with the shortest intermo-
lecular Pt···Pt distance. As the solvate molecules were found to exert
an insignificant influence on the calculated results, all the calculations
on 6·1/2CH2ClCH2Cl and 6·THF were performed by using a pair of
symmetry-related square-planar platinum(II) moieties with the
shortest intermolecular Pt···Pt distance without considering the
solvate molecules. All calculations were performed with Gaussian 03.53
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together with the C−Pt−N, C−Pt−C, and N−Pt−N angles
are comparable to those in other Pt(Me3SiCCbpyC
CSiMe3)(acetylide)2 complexes.7
RESULTS AND DISCUSSION
■
Synthesis and Characterization. Complex 6 and related
square-planar platinum(II) complexes are shown in Scheme 1.
Crystalline species 6·VOC were obtained from the correspond-
ing solutions with solvate VOCs as the solvents by layering
petroleum ether. The solvate VOC was identified by thermal
analysis and mass spectrometry, thermogravimetric studies, and
1H NMR spectra (Figures S1−S6 of the Supporting
Information). The desolvated crystalline species 6 could be
obtained by removal of the solvate CH2Cl2 or CH2ClCH2Cl in
6·CH2Cl2 or 6·1/2CH2ClCH2Cl at ambient temperature under
vacuum for several hours, which was confirmed by
thermogravimetric studies (Figures S4 and S5 of the
Supporting Information). Nevertheless, desolvated crystalline
species 6 could not be obtained from 6·THF, in which the
solvate THF in 6·THF could not be removed by exposure to
vacuum for 2 h at ambient temperature (Figure S6 of the
Supporting Information).
Planar platinum(II) complex moieties in 6·1/2CH2ClCH2Cl
(Figure S9b of the Supporting Information) and 6·CH2Cl2
(Figure 1b) are packed in an antiparallel pattern with adjacent
Pt···Pt distances being alternately 4.262(11) and 4.482(12) Å
for the former and 4.371(10) and 4.377(10) Å for the latter.
The crystal structure of 6·THF (Figure 1a), nevertheless,
exhibits an alternately staggered and anitiparallel packing
pattern to afford a short Pt···Pt distance and a long Pt···Pt
distance [3.255(8) and 4.646(10) Å, respectively]. It has been
revealed that a staggered packing pattern favors formation of a
short Pt···Pt distance (<3.5 Å) whereas an antiparallel pattern
always induces a long Pt···Pt distance (>3.5 Å) for planar bis(σ-
acetylide) platinum(II) complexes with functionalized 2,2′-
bipyridyl ligands.7 The shortest Pt···Pt distance in 6·THF
[3.255(8) Å] is even slightly shorter than those found in
Pt(Me3SiCCbpyCCSiMe3)(CCC6H5)2·CHCl3
[3.302(1) Å]7b and Pt(Me3SiCCbpyCCSiMe3)(C
CC6H4F-4)2·1/2CH2Cl2 [3.315(9) Å]7c with a staggered
packing pattern.
The crystal structures of 6·1/2CH2ClCH2Cl, 6·CH2Cl2, and
6·THF were determined by X-ray crystallography. Crystal
packing diagrams are depicted in Figure 1 for 6·CH2Cl2 and
Host−guest interactions between solvate CH2Cl2 and
platinum(II) moieties exist in the crystal structure of
6·CH2Cl2 (Figure S10 of the Supporting Information),
including the ClC-H···π(CC) interaction and C6H4···ClCH
hydrogen bonds together with intermolecular F···H−C hydro-
gen bonds between CCC6H4CF3-4 and Me3SiCCbpyC
CSiMe3. For 6·1/2CH2ClCH2Cl (Figure S11 of the Supporting
Information), the solvate CH2ClCH2Cl molecules are inserted
into the channels and cavities of the crystal structures and
arranged through a short Cl···Cl contact [3.381(11) Å]
between neighboring CH2ClCH2Cl molecules. The solvate
THF is associated with the platinum(II) moiety in 6·THF
(Figure S12 of the Supporting Information) through
intermolecular interactions, including C−H···O(THF) and
F···H−C(THF) hydrogen bonds.
Photophysical Properties. The UV−vis electronic
absorption spectrum of 6 in CH2Cl2 exhibits high-energy
absorption bands with maxima at 293, 327, and 369 nm due to
mainly ligand-centered transitions together with a broad low-
energy band with the maximum centered at 430 nm, which can
be ascribed to dπ(Pt) → π*(Me3SiCCbpyCCSiMe3)
1MLCT and π(CCC6H4CF3-4) → π*(Me3SiCCbpyC
CSiMe3) 1LLCT transitions.7 The low-energy absorption bands
are solvent-dependent, affording negative solvatochromic
properties (Figure S14 of the Supporting Information), which
are progressively red-shifted with a gradual decrease in solvent
polarity. Upon excitation at wavelengths longer than 320 nm,
complex 6 (Table 2) shows bright yellow solution lumines-
cence with vibronic-structured emission centered at 568
(608sh) nm (Figure S13 of the Supporting Information) and
the lifetime being 0.70 μs in fluid CH2Cl2. A significant Stokes
shift together with a microsecond range of lifetimes reveals that
the emission is phosphorescent in nature with a triplet excited
state.1−8 Compared with that of complex 1 (616 nm),7b the
emission of complex 6 (568 and 608sh nm) in fluid CH2Cl2 is
obviously blue-shifted because of the introduction of an
electron-withdrawing CF3 group onto phenylacetylide, in
which the 3MLCT/3LLCT level is indeed increased. In
comparison with unstructured solution emission in platinum-
(II) complexes Pt(Me3SiCCbpyCCSiMe3)(CCR)2 (R
is C6H5 for 1, CCC6H4F-2 for 2, CCC6H4F-3 for 3, C
Figure 1. Packing diagrams of planar platinum(II) complexes 6·VOC
(VOC = THF or CH2Cl2). (a) Alternately staggered and antiparallel
stacking pattern in 6·THF with short (3.255 Å) and long (4.646 Å)
Pt···Pt distances. (b) Antiparallel pattern in 6·CH2Cl2 with long Pt···Pt
distances (4.262 and 4.482 Å).
6·THF and Figure S9 of the Supporting Information for
6·1/2CH2ClCH2Cl. The platinum(II) centers exhibit a distorted
square-planar coordination environment composed of N2C2
donors from chelating Me3SiCCbpyCCSiMe3 and bis(σ-4-
trifluoromethylphenyl)acetylide. The Pt−C [1.942(10)−
1.962(11) Å] and Pt−N [2.049(8)−2.099(8) Å] lengths
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Upon excitation at wavelengths longer than 320 nm,
crystalline species, including desolvated 6, 6·1/2CH2ClCH2Cl,
and 6·CH2Cl2, exhibit bright yellow luminescence with two
vibronic-structured emission bands centered at 561 and 608 nm
(Table 2). Crystalline species 6·THF, however, displays bright
red luminescence with an unstructured and broad emission
band centered at 698 nm.
Luminescence Vapochromic Properties. Scheme 2
depicts the conversion processes of complex 6 in various
forms of solid states in response to vapor, heat, and mechanical
grinding. The vapo-, thermo-, and mechano-triggered emission
spectral changes of complex 6 are presented in Figure 3.
Photographic images of 6 in PMMA films are shown in Figure
4, showing remarkable luminescence color switches under UV
light (365 nm) irradiation in response to vapor or mechanical
stimuli.
Table 2. Luminescence Data of 6 in CH2Cl2 and Solid State
at Ambient Temperature
sample
sample state
λem (nm)
τem (μs)
Φem (%)
6
CH2Cl2
unground
ground
568 (608sh)
561, 608
730
0.70
0.95
0.09
0.82
0.07
4.07
0.11
4.53
0.06
3.49
10.9
heated
667
6·THF
unground
ground
698
645
6·dioxane
6·THP
unground
ground
689
647
unground
ground
715
645
a
The quantum yield in a degassed dichloromethane solution was
estimated relative to that of [Ru(bpy)3](PF6)2 in acetonitrile as the
standard (Φem = 6.2%).
When solid 6 is exposed to vapors of VOCs, including
methanol, ethanol, furan, 2-methyltetrahydrofuran, acetone,
acetonitrile, diethyl ether, ethyl acetate, n-hexane, toluene,
benzene, pyridine, various halohydrocarbons, etc., bright yellow
or orange luminescence is always observed with vibronic-
structured emission bands at 561 and 608 nm. Nevertheless,
upon exposure of 6 to vapor of THF, dioxane, or THP, bright
red luminescence is exhibited with a broad, unstructured
emission band centered at 698 nm (THF), 689 nm (dioxane),
or 715 nm (THP). As shown in Figure 5, complex 6 shows
selective phosphorescence vapochromic properties in response
to THF, dioxane, or THP vapor with a drastic vapochromic
response shift. Figure 6 shows reversible emission spectral
changes of solid 6 in response to THF or CH2ClCH2Cl vapor
in the reverse process, showing gradual interconversion
between two vibronic-structured emission bands (561 and
608 nm) and a broad unstructured emission (∼698 nm). The
reversibility and reproducibility of the conversion processes
have been also confirmed by the variations of the XRD
diagrams recorded in a reversible vapochromic
6·1/2CH2ClCH2Cl ⇆ 6·THF cycle. Figure 7 shows dynamic
variations of the XRD patterns in the 6·1/2CH2ClCH2Cl →
6·THF process upon exposure of the 6·1/2CH2ClCH2Cl
sample to a saturated THF vapor as well as the corresponding
variations of the XRD patterns in the 6·THF →
6·1/2CH2ClCH2Cl reverse process upon exposure of the
6·THF sample to CH2ClCH2Cl vapor at ambient temperature.
Consequently, the THF-responsive vapochromic luminescence
switch is totally reversible as demonstrated upon exposure of
the solid sample in THF vapor and another organic vapor
alternately. The conversion processes could be repeated for
several exposure cycles without detectable decomposition of
the solid materials.
CC6H4F-4 for 4, and CCbpy-5 for 5) described previously,7
the vibronic-structured emission spectrum with vibrational
progressional spacing of 1160 cm−1 in complex 6 is typical for
the CC and CN stretching frequencies of the aromatic
rings in Me3SiCCbpyCCSiMe3, suggesting an increased
contribution from Me3SiCCbpyCCSiMe3-based phos-
phorescence. As revealed by DFT studies (Table S3 of the
Supporting Information), the phosphorescent emission in
complex 6 contains indeed a substantial contribution from
the Me3SiCCbpyCCSiMe3 (π → π*) intraligand triplet
excited state as a consequence of introduction of an electron-
withdrawing CF3 group onto phenylacetylide.
The solid-state UV−vis electronic spectra of crystalline
species 6·CH2Cl2, 6·1/2CH2ClCH2Cl, and 6·THF and their
corresponding ground samples are depicted in Figure 2. On
Figure 2. UV−vis electronic spectra of crystalline species (solid lines)
6·CH2Cl2 (cyan), 6·1/2CH2ClCH2Cl (red), and 6·THF (blue) and the
corresponding ground species (dashed lines) together with 6 in a THF
solution (green).
As revealed by X-ray crystallography, both 6·CH2Cl2 and
6·1/2CH2ClCH2Cl exhibit an antiparallel packing pattern in
stacking of planar platinum(II) complex molecules with the
shortest intermolecular Pt···Pt distances being >4.0 Å, implying
that it is impossible to form Pt−Pt contacts. For 6·THF, an
alternately staggered and antiparallel packing pattern gives short
[3.255(8) Å] and long [4.646(10) Å] Pt···Pt distances,
respectively, leading to the formation of a dimeric structure
through intermolecular Pt−Pt interaction, thus resulting in a
one hand, the low-energy bands of crystalline species 6·THF
are obviously red-shifted compared with those of crystalline
species 6·CH2Cl2 and 6·1/2CH2ClCH2Cl. On the other hand,
when the sample are thoroughly mechanically ground, the
corresponding low-energy band is significantly red-shifted for
6·CH2Cl2 and 6·1/2CH2ClCH2Cl whereas it is distinctly blue-
shifted for 6·THF (Figure 2). The XRD measurement revealed
that the XRD patterns vanished entirely for all of the ground
samples, indicating that the regular crystalline state was totally
destroyed by mechanical grinding.7c,d
3
lower MLCT/3LLCT energy level and thus a significant red
shift of the emission as demonstrated by DFT studies (vide
infra).
In our previous studies, it has been demonstrated that
complex Pt(Me3SiCCbpyCCSiMe3)(CCC6H5)2 (1)7b
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Scheme 2. Interconversion Processes for Solid Materials Based on Complex 6
Figure 4. Photographic images of 6 in a PMMA film in response to
CH2Cl2 vapor or mechanical stimuli under UV light (365 nm)
irradiation.
vapochromic luminescence: 562(610sh) nm (acetone) → 617
nm (n-hexane) → 660 nm (ethyl acetate) → 729 nm (CHCl3)
→ 747 nm (THF) depending on the shortest Pt···Pt distance
induced by the inserted solvate molecules in the crystal lattices.
It is demonstrated that the shorter the intermolecular Pt···Pt
distances in 5·VOC with various solvate VOCs, the more red-
shifted the phosphorescence emission due to the lower energy
3
levels of MLCT/3LLCT triplet states. These previous studies
together with the results presented in this study suggest that the
packing patterns in the stacking of planar platinum(II) moieties
and consequently the shortest intermolecular Pt···Pt distances
play a crucial role in determining the emission energy and the
extent of the luminescence vapochromic response. Vapor-
triggered luminescence switches are also affected by other types
of intermolecular interactions, including short π−π contacts
between pyridyl rings of functionalized 2,2′-bipyridine as well as
host−guest interactions between planar platinum(II) moieties
and solvate molecules through C−H···π(CC) and C−H···X
(X = F, Cl, or Br) hydrogen bonds. It appears that the
selectivity of luminescence vapochromism in Pt(Me3SiC
CbpyCCSiMe3)(CCR)2 (R is C6H5, C6H4F, or C6H4CF3)
is highly dependent on the R substituent of the acetylide
ligands. When R is C6H5 (1)7b or C6H4F (2−4),7c
phosphorescence emission in the corresponding platinum(II)
complexes is usually sensitive to vapors of specific halohy-
drocarbons because of the formation of C−H···π(CC) and
C−H···X (XF, Cl) hydrogen bond interactions, thus
stabilizing a staggered crystal packing to afford significant Pt−
Figure 3. Solid-state emission spectra of crystalline and corresponding
ground materials based on complex 6·VOC at ambient temperature.
is sensitive to CH2Cl2, CHCl3, and CH3I vapors with a
significant vapochromic red shift of the emission from 562 and
603 nm to 762 nm. For bis(σ-fluorophenylacetylide) platinum-
(II) complexes Pt(Me3SiCCbpyCCSiMe3)(CCR)2 (R
is C6H4F-2 for 2, C6H4F-3 for 3, and C6H4F-4 for 4),7c
3
displays luminescence vapochromic behavior only to CHCl3
vapor with a luminescence vapochromic red shift from 556 and
603 nm to 740 nm, whereas 4 is selectively sensitive to CHCl3
and CH2Cl2 vapors with a luminescence vapochromic red shift
from 562 and 608 nm to 765 nm (CHCl3) or 760 nm
(CH2Cl2). Complex Pt(Me3SiCCbpyCCSiMe3)(C
Cbpy)2 (5, CCbpy5-acetylide-2,2′-bipyridine)7a displays
VOC-dependent luminescence vapochromic properties in
response to several vapors, including acetone, n-hexane, ethyl
acetate, CHCl3, and THF, affording a progressively red-shifted
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Figure 5. Photographic images (top) of 6 deposited on quartz slides
upon exposure to selected organic vapors under ambient light and UV
light irradiation (365 nm) and emission spectra (bottom) of 6 in the
solid state upon exposure to various VOC vapors at ambient
temperature, showing a broad unstructured emission centered at
∼698 nm for THF, 689 nm for dioxane, and 715 nm for THP vapor,
and two vibronic-structured bands at ∼561 and ∼608 nm for other
VOC vapors.
Figure 7. XRD diagrams recorded in a reversible vapochromic
6·1/2CH2ClCH2Cl ⇆ 6·THF cycle, showing dynamic variations of the
XRD patterns (c−e) in the 6·1/2CH2ClCH2Cl → 6·THF process upon
exposure of the 6·1/2CH2ClCH2Cl sample to a saturated THF vapor
and those (g−i) in the 6·THF → 6·1/2CH2ClCH2Cl reversed process
upon exposure of the 6·THF sample to CH2ClCH2Cl vapor at
ambient temperature. (a and j) Simulated pattern of
6·1/2CH2ClCH2Cl from X-ray crystallography. (b) Measured pattern
of 6·1/2CH2ClCH2Cl. (f) Simulated pattern of 6·THF from X-ray
crystallography.
6 shows selective phosphorescence vapochromism in response
to O-heterocyclic volatile compounds such as THF, dioxane,
and THP with the emission at 561 and 608 nm being red-
shifted to 698 nm (THF), 689 nm (dioxane), and 715 nm
(THP), respectively. X-ray crystallography reveals that the
staggered crystal packing with a short Pt···Pt distance [3.255(8)
Å] in 6·THF is highly stabilized by host−guest interactions
between the platinum(II) moiety and solvate THF through C−
H···O(THF) and F···H−C(THF) hydrogen bonds that are
probably the force driving complex 6 to display selective
luminescence vapochromism toward THF, dioxane, and THP.
Luminescence Mechanochromic Properties. When
crystalline materials, including desolvated 6, 6·CH2Cl2, and
6·1/2CH2ClCH2Cl, are ground in an agate mortar or crushed
gently on a paper with a spatula, dramatic changes in color and
luminescence with a drastic red shift of the emission are
observed. When these solid samples are thoroughly ground,
bright yellow luminescence with two vibronic-structured
emission bands centered at 561 and 608 nm (Figure 3)
converts immediately to weak red luminescence with a broad
and unstructured band centered at 730 nm, affording a drastic
mechanochromic red shift response. In contrast, when
vapochromic crystalline species 6·THF, 6·dioxane, or 6·THP
is mechanically ground, bright red luminescence centered at
698 nm (THF), 689 nm (dioxane), or 715 nm (THP),
respectively, is obviously blue-shifted to 645 nm with a more
intense red emission, giving a remarkable mechanochromic blue
Figure 6. Emission spectral changes of solid 6·1/2CH2ClCH2Cl sample
in response to THF vapor (top) and 6·THF to CH2ClCH2Cl vapor
(bottom), showing gradual interconversion between two vibronic-
structured emission bands (561 and 608 nm) and a broad
unstructured emission band (∼698 nm).
Pt contact as a consequence of the solvate halohydrocarbon
molecule being inserted into the crystal lattice. In contrast,
when R is C6H4CF3-4, the corresponding platinum(II) complex
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shift response. Both emission spectral and XRD studies suggest
that the ground species from 6·1/2CH2ClCH2Cl (Figure S14 of
the Supporting Information and Figure 8) or 6·THF (Figure
molecules are totally lost with crystalline states converted to
amorphous phases. Nevertheless, the loss of solvate is not a
prerequisite of luminescence mechanochromism for 6·VOC
because desolvated crystalline species 6 exhibits the same
mechanoluminescence as 6·1/2CH2ClCH2Cl. Noticeably, regu-
lar crystal arrangements for both crystalline species
6·1/2CH2ClCH2Cl and 6·THF are totally damaged upon the
samples being thoroughly ground to afford amorphous species,
but they belong to two different amorphous states. The ground
amorphous species from 6·1/2CH2ClCH2Cl displays weak red
luminescence centered at 730 nm, whereas the ground species
from 6·THF is strongly emissive at 645 nm. However, it
appears that heating of both ground species with different
amorphous morphs could result in the same new crystalline
state as suggested by XRD measurements (Figure S21 of the
Supporting Information).
Our previous studies have shown that when the crystalline
materials Pt(Me3SiCCbpyCCSiMe3)(CCR)2 (R is
C6H4F-2 for 2, C6H4F-3 for 3, and C6H4F-4 for 4)7c and
Pt(Me3SiCCbpy)(CCR)2 [R is C6H5 for 7or C6H4But-4
for 8; Me3SiCCbpy = 5-(trimethylsilylethynyl)-2,2′-bipyr-
idine]7d are mechanically ground or crushed, a drastic emission
red shift is always observed with bright yellow or yellow-green
luminescence converted to dark red. Upon being mechanically
ground, planar platinum(II) molecules are likely packed in
proximity through Pt−Pt interaction to form a dimeric or an
aggregate structure, resulting in a conversion from a
3MLCT/3LLCT emissive state in the crystalline state to a
3MMLCT triplet state in the amorphous phase and thus a
significant red shift of the emission. By comparison, solvate-
dependent mechanoluminescence properties in crystalline
materials 6·VOC are observed for the first time. While
crystalline materials such as desolvated 6, 6·CH2Cl2, and
6·1/2CH2ClCH2Cl exhibit a grinding-triggered emission red
shift from vibronic-structured bands at 561 and 608 nm to
unstructured broad emission centered at 730 nm, the emission
at 698 nm (THF), 689 nm (dioxane), or 715 nm (THP) is
distinctly blue-shifted to 645 nm when vapochromic crystalline
materials 6·THF, 6·dioxane, and 6·THP are mechanically
ground. Consequently, this study indicates that mechanical
grinding could lead to a luminescence red shift as well as a blue
shift depending on the solvate molecules, in which mechanical
force not only induces planar platinum(II) molecules to be
packed in the proximity through Pt−Pt or π−π interaction in
most cases but also could disrupt ordered close packing in
stacking of planar platinum(II) moieties.
Thermo-Triggered Luminescence Changes. When
desolvated 6, 6·1/2CH2ClCH2Cl, or 6·CH2Cl2 is heated at
120 °C, bright yellow luminescence with two vibronic-
structured emission bands at 561 and 608 nm turns into red
luminescence with a broad structureless emission band
centered at 667 nm (Figure 3), suggesting the occurrence of
thermo-triggered luminescence change with the loss of solvate
CH2ClCH2Cl or CH2Cl2. Upon exposure of the heated sample
to CH2ClCH2Cl or CH2Cl2 vapor, the unstructured emission
band centered at 667 nm could reversibly revert to two
vibronic-structured emission bands at 561 and 608 nm in the
original species 6·1/2CH2ClCH2Cl or 6·CH2Cl2. Temperature-
dependent XRD measurement (Figure S20 of the Supporting
Information) on desolvated 6 in the temperature range of 25−
145 °C demonstrates that a crystalline-state transition occurs
indeed at ∼85 °C, as revealed by the distinct variations in XRD
patterns. Heating of 6·THF at 120 °C, however, could not
Figure 8. XRD diagrams in a mechanochromic cycle for
6·1/2CH2ClCH2Cl (top) and 6·THF (bottom), showing the measured
(a) and simulated (f) patterns for the unground sample, the measured
pattern for the ground sample (b), and dynamic variations (c−e) of
the XRD patterns for the ground samples in response to CH2ClCH2Cl
(top) or THF (bottom) vapor in the reversed process.
S15 of the Supporting Information and Figure 8) could
perfectly revert to the original crystalline state upon being
exposed to the corresponding vapors. Upon exposure of the
ground samples to CH2ClCH2Cl or THF vapor, the broad,
unstructured emission band centered at 730 or 645 nm could
progressively revert to two vibronic-structured bands at 561
and 608 nm in response to CH2ClCH2Cl vapor (Figure S15 of
the Supporting Information) or restored to an unstructured
band centered at 698 nm in response to THF vapor (Figure
S16 of the Supporting Information). The XRD studies indicate
that the diffraction patterns of 6·VOC disappear entirely when
they are thoroughly ground7c,d but could be restored perfectly
to the original XRD patterns upon sufficient exposure to the
corresponding VOC vapors. Figure 8 depicts the XRD
diagrams in a mechanochromic cycle for 6·1/2CH2ClCH2Cl
and 6·THF, showing the XRD patterns for the crystalline and
the ground species together with the changes in XRD patterns
during the restoring process from the ground sample in
response to CH2ClCH2Cl or THF vapor.
Thermogravimetric studies (Figures S4−S6 of the Support-
ing Information) show that when 6·VOC (VOC = THF,
CH2Cl2, or CH2ClCH2Cl) is thoroughly ground, solvate VOC
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induce conversion of the emission centered at 698 nm into
emission at 667 nm, in which the luminescence at 698 nm is
instead quenched upon heating. This implies that the loss of
solvate THF gives another desolvated morph, which is different
from that produced by the loss of solvate CH2ClCH2Cl or
CH2Cl2 in 6·1/2CH2ClCH2Cl or 6·CH2Cl2. The XRD
measurements (Figure S19 of the Supporting Information)
reveal unambiguously that upon being heated at 120 °C, the
species formed by the loss of solvate THF differs distinctly
from that produced by loss of solvate CH2ClCH2Cl or CH2Cl2
in 6·1/2CH2ClCH2Cl or 6·CH2Cl2. Thus, our experiments
suggest that desolvated 6 exhibits polymorphism that differs in
their solid-state packing arrangements, including at least three
crystalline and two noncrystalline morphs as demonstrated by
their differences in XRD patterns (Figure S19 of the Supporting
Information). Three crystalline phases are caused by desolva-
tion of 6·1/2CH2ClCH2Cl or 6·CH2Cl2 in vacuum at ambient
temperature with emission at 561 and 608 nm, desolvation by
heating 6·1/2CH2ClCH2Cl or 6·CH2Cl2 at temperatures higher
than 85 °C with emission at 667 nm, and desolvation by
heating 6·THF at 120 °C with the emission quenched. Two
noncrystalline phases originate from desolvation by mechanical
grinding on crystalline species 6·1/2CH2ClCH2Cl and 6·THF
with emission occurring at 730 and 645 nm, respectively.
Nevertheless, heating of the ground species with different
amorphous morphs results in the same new crystalline state
according to the XRD measurements (Figure S21 of the
Supporting Information), in which the emission is always
quenched when the ground species are further heated.
coincide well with the measured UV−vis electronic absorption
(Figure S24 of the Supporting Information) and emission
spectral data.
To interpret the UV−vis and emission spectral differences in
crystalline species 6·VOC with different solvate VOCs and
explore the origin of THF-triggered luminescence vapochrom-
ism, TD-DFT studies were performed on crystalline morphs
6·1/2CH2ClCH2Cl and 6·THF using a pair of square-planar
platinum(II) moieties having the shortest intermolecular Pt···Pt
distance. The relevant calculation data, including molecular
orbital compositions (percentages) and transition properties,
are provided as Supporting Information (Tables S4−S7). To
gain intuitive insight into the changes in the frontier orbitals
resulting from the inserted solvate VOC in crystal lattices,
Figure 9 depicts the energy level of frontier molecular orbitals
DFT Computational Studies. Time-dependent DFT (TD-
DFT) calculations at the PBE1PBE level were conducted to
elucidate the frontier orbital components and spectral transition
characteristics of 6 in a CH2Cl2 solution using the ground-state
structure (Table S1 of the Supporting Information) optimized
by the DFT method. Partial molecular orbital compositions
(percentage) in the ground state and transition properties of 6
are provided as Supporting Information (Tables S2 and S3).
On the basis of the TD-DFT studies, the intense UV
absorptions below 370 nm are featured with an intraligand
(IL) π → π* transition (Me3SiCCbpyCCSiMe3), mixed
with some 1LLCT/1MLCT character. The low-energy of
HOMO → LUMO, HOMO-1 → LUMO, and HOMO-2 →
LUMO absorption transitions arise primarily from π(C
Figure 9. Plots of the energy level of frontier molecular orbitals
HOMO-5 to LUMO+5 for 6 in a CH2Cl2 solution, solid-state
6·1/2CH2ClCH2Cl, and 6·THF in the ground states by the TD-DFT
method at the PBE1PBE level, together with the electron density
diagrams of the HOMO and LUMO orbitals.
HOMO-5 to LUMO+5 for 6 in a CH2Cl2 solution, solid-state
6·1/2CH2ClCH2Cl, and 6·THF together with the electron
density diagrams of the HOMO and LUMO.
Analogous to those in a CH2Cl2 solution, the corresponding
low-energy absorption and emission in solid-state
6·1/2CH2ClCH2Cl (Tables S4 and S5 of the Supporting
Information) and 6·THF (Tables S6 and S7 of the Supporting
Information) originate primarily from LLCT/MLCT excited
states, comparable to those found in analogues Pt(Me3SiC
CbpyCCSiMe3)(CCR)2 (R is C6H5 for 1, C6H4F-2 for 2,
C6H4F-3 for 3, C6H4F-4 for 4, and bpy for 5).7 Compared with
that in 6·1/2CH2ClCH2Cl (Figure 9), the HOMO level is
significantly higher whereas the LUMO level is slightly lowered
in 6·THF, thus resulting in a much smaller HOMO−LUMO
energy gap in 6·THF (2.39 eV) than in 6·1/2CH2ClCH2Cl
(3.24 eV). Via careful examination of the HOMO compositions
(Tables S4 and S6 of the Supporting Information), we found
1
CC6H4CF3-4) → π*(Me3SiCCbpyCCSiMe3) LLCT and
5d(Pt) → π*(Me3SiCCbpyCCSiMe3) 1MLCT states.
Likewise, the triplet-state emission, which is primarily character-
istic of HOMO → LUMO and HOMO-3 → LUMO
3
transitions, can be ascribed to LLCT/3MLCT triplet excited
3
states together with some IL character of Me3SiCCbpyC
3
CSiMe3. Such a significant contribution from the IL state of
Me3SiCCbpyCCSiMe3 in complex 6 leads to distinctly
vibronic-structured emission at 568 (608sh) nm in a fluid
CH2Cl2 solution, which is strikingly different from the
structureless solution emission bands found in analogues
Pt(Me3SiCCbpyCCSiMe3)(CCR)2 (R is C6H5 for 1,
C6H4F-2 for 2, C6H4F-3 for 3, C6H4F-4 for 4, and bpy for 5).7
The distinctly blue-shifted emission of 6 (568 and 608sh nm)
compared with that of 1 (616 nm)7b in a fluid CH2Cl2 solution
is well elucidated by a larger HOMO−LUMO gap of 6 (3.12
eV) compared to that of 1 (2.904 eV)7b because of the
introduction of an electron-withdrawing CF3 group into
phenylacetylide in 6. Both the calculated singlet and triplet
excitation transitions (Table S3 of the Supporting Information)
2
that the contribution of the dz (Pt) orbital to the HOMO in
6·THF (7.42%) is much larger than that in 6·1/2CH2ClCH2Cl
(0.21%). When the intermolecular Pt···Pt distance is sufficiently
short (<3.5 Å) to form Pt−Pt contacts, it has been
demonstrated that the HOMO is featured with the dσ* nature
2
resulting from σ-overlap between two dz (Pt) orbitals with a
higher energy level in the aggregate species than that of
2
individual the dz (Pt) orbital in the monomeric moiety, thus
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inducing a smaller HOMO−LUMO energy gap that is
significantly perturbed by the Pt···Pt distances.54 As demon-
strated by X-ray crystallography, the antiparallel oriented planar
platinum(II) moieties in 6·1/2CH2ClCH2Cl [4.262(11) Å]
afford a Pt···Pt distance much longer than that in 6·THF
[3.255(8) Å] with two neighboring platinum(II) molecules
arranged in a staggered pattern. Consequently, the DFT studies
of 6·THF and 6·1/2CH2ClCH2Cl reveal unambiguously that
THF-triggered absorption and emission red shifts arise most
likely from remarkably enhanced intermolecular Pt−Pt
interaction upon insertion of solvate THF into the crystal
lattices to induce a staggered pattern of packing of square-
planar platinum(II) moieties. Furthermore, the results of this
DFT study agree well with the data for previously described
complexes Pt(Me3SiCCbpyCCSiMe3)(CCR)2 (R is
C6H5 for 1, C6H4F-2 for 2, C6H4F-3 for 3, and C6H4F-4 for
4),7 in which vapochromic crystalline materials 1·CHCl3,
3·CHCl3, 4·CH2Cl2, and 4·CHCl3 always originate from an
increased contribution from intermolecular Pt−Pt interaction
upon insertion of solvate CHCl3 or CH2Cl2 molecules into
crystal lattices; thus, the 3MLCT/3LLCT emissive state is
converted to a lower energy level.
AUTHOR INFORMATION
Corresponding Author
*E-mail: czn@fjirsm.ac.cn.
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are grateful for financial support from the NSFC
(20931006, U0934003, and 91122006), the 973 project
(2007CB815304) from MSTC, and the NSF of Fujian Province
(2011J01065).
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Vapo-, thermo-, and mechano-responsive phosphorescence
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bis(trimethylsilylethynyl)-2,2′-bipyridine and 4-
(trifluoromethylphenyl)acetylide are described. Depending on
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drastically red-shifted for 6, 6·CH2Cl2, or 6·1/2CH2ClCH2Cl.
Upon being heated to >85 °C, crystalline species 6·VOC,
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shifted to 667 nm. The vapo-, thermo-, and mechano-triggered
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ASSOCIATED CONTENT
■
S
* Supporting Information
(15) Pattacini, R.; Giansante, C.; Ceroni, P.; Maestri, M.; Braunstein,
Figures giving additional UV−vis and emission spectra,
diagrams of XRD patterns, tables and figures giving DFT
calculation data, and an X-ray crystallographic file in CIF format
for the determination of the structures of compounds
6·1/2CH2ClCH2Cl, 6·CH2Cl2, and 6·THF. This material is
available free of charge via the Internet at http://pubs.acs.org.
P. Chem.Eur. J. 2007, 13, 10117.
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