Brilliant reversible luminescent mechanochromism of silver(I) complexes containing o-bis(diphenylphosphino)benzene and phosphinesulfide

Article abstract of DOI:10.1039/b921111j

The Ag(I) complex with o-bis(diphenylphosphino)benzene shows reversible interconversion between blue-emitting (1b) and green-emitting (1g) materials on grinding and heating; comparison of the structure of 1b with another green-emitting crystals (2) having

Full text of DOI:10.1039/b921111j

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Brilliant reversible luminescent mechanochromism of silver(I) complexes
containing o-bis(diphenylphosphino)benzene and phosphinesulfidew
Toshiaki Tsukuda,* Marina Kawase, Ayumi Dairiki, Kenji Matsumoto and Taro Tsubomura*
Received (in Cambridge, UK) 12th October 2009, Accepted 4th January 2010
First published as an Advance Article on the web 15th January 2010
DOI: 10.1039/b921111j
The Ag(I) complex with o-bis(diphenylphosphino)benzene shows
reversible interconversion between blue-emitting (1b) and green-
emitting (1g) materials on grinding and heating; comparison of
the structure of 1b with another green-emitting crystals (2)
having the same formula suggests the chromism results from
intermolecular interactions between adjacent phenylene rings.
e.g. dppaS2ꢀ (Chart 1), have been studied.10 In these complexes,
we have found that a silver(I) complex coordinatedꢀby dppbz
(= o-bis(diphenylphosphino)benzene) and dppaS2 ligands,
[Ag(dppbz)(dppaS2)], shows emitting color change upon
mechanical grinding. Herein, we report the luminescent
properties and mechanochromism of this complex.
Treatment of KdppaS2 and dppbz with AgPF6 in CHCl3
readily gives a mixed-ligand complex, [Ag(dppbz)(dppaS2ꢀ)].
The colorless crystals (1b) obtained by recrystallization
from CHCl3–ether show blue emission upon irradiation of
UV-light. X-Ray suitable crystals of 1b are obtained as
prismatic crystals (Fig. S1, ESIw). The structure of 1b has a
Mechanochromism is the phenomenon of color change caused
by mechanical grinding or pressing of the solid sample and
reversion to the original color by heating or recrystallization,
in which the presence of two different pressure-dependent
stable or metastable states is essential.1 Recently, much
attention has been paid to the photoluminescent compounds
that possess mechanochromic properties in view of unique
optical recording devices or sensing materials involving
luminescence detection. Some organic mechanochromic
substances showing luminescent color change caused by
isomerization or variation of molecular packing on grinding
have been reported.2 For luminescence mechanochromism of
metal-containing compounds, Pt(II),3 Zn(II)4 and Au(I)5
complexes have been reported, in which difference in the
intermolecular interactions is responsible for the change of
emission color for the ground samples.
ꢀ
distorted tetrahedral geometry coordinated by the dppaS2
and dppbz ligands (Fig. 1, black), and no solvent molecules are
found in the unit cell.
When the blue-emitting crystals were ground in a ceramic
mortar, the white powder obtained emits green luminescence
(1g). Emission maximum of 1g occurs at 518 nm, whereas that
of 1b at 458 nm. Since elemental analysis of both 1b and 1g
gave the same values corresponding to [Ag(dppbz)(dppaS2ꢀ)],
the process does not involve adsorption or removal of a
solvent molecule as shown in vapochromic systems.11 Upon
treatment of 1g with drops of CHCl3–hexane (1 : 2), the green
luminescence reverted to blue one (Fig. S2, ESIw). Furthermore,
emitting color of 1g returned to blue on heating at 200 1C for
10 minutes (Fig. 2). The thermal properties of 1g were studied
by differential thermal analysis measurement ranging from 25
to 180 1C (Fig. S3, ESIw). The heating profile of 1g shows a
weak exothermic peak at ca. 120 1C, which is assigned to the
phase transition from 1g to blue-emitting solid, and a clear
endothermic peak at ca. 240 1C, which indicates a thermal
decomposition.
In our groups, extensive studies on the luminescent
properties of d10 metal complexes involving various
phosphines have been reported.6–8 In these complexes,
tetrahedral Pd(0) and Cu(I) complexes have emission bands
generally assigned to 3MLCT transition from the metal center
to the p* orbital on the ligands. Upon MLCT excitation, the
d9 metallic character causes tetragonal flattening distortion, so
luminescent properties based on MLCT transition in d10 metal
complexes depends on the extent of the distortion.9 Recently,
we have turned our attention to phosphine sulfides in order
to prevent oxidation of phosphines and to increase stability
of complexes, therefore luminescent properties of mixed-
ligand d10 complexes with phosphines and phosphine sulfide,
ꢀ
Chart 1 dppaS2 ligand.
Seikei University, Department of Materials and Life Science,
3-3-1 Kichijoji-Kitamachi, Musashino, 1808633, Tokyo, Japan.
E-mail: tsukuda@st.seikei.ac.jp, tsubomura@st.seikei.ac.jp
w Electronic supplementary information (ESI) available: Experimental
details; figures. CCDC 738876 and 738877 for 1b and 2g. For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/b921111j
Fig. 1 ORTEP drawings of two forms of [Ag(dppaS2ꢀ)(dppbz)]: 1b
(black) and 2 (red).
ꢁc
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Table 1 Selected bonds (A) and angles (1)
1b
2
Ag–S
Ag–P
S–P
2.5805(5), 2.5545(4)
2.5346(5), 2.5725(6)
1.9995(7), 2.0053(6)
2.5392(10), 2.5341(10)
2.4916(8), 2.4980(8)
2.0064(11), 1.9960(14)
S(1)–Ag(1)–S(2)
S(1)–Ag(1)–P(3)
S(1)–Ag(1)–P(4)
S(2)–Ag(1)–P(3)
S(2)–Ag(1)–P(4)
P(3)–Ag(1)–P(4)
Ag(1)–S(1)–P(1)
Ag(1)–S(2)–P(2)
109.76(2)
106.71(2)
120.12(2)
124.45(2)
114.74(2)
78.67(2)
95.67(2)
94.15(2)
110.06(3)
117.30(2)
115.75(2)
120.78(3)
106.52(3)
83.30(2)
96.09(4)
96.23(4)
irradiation of UV-light (2). The space group of 2 is P21/c (#14)
ꢀ
whereas that of 1b is P1 (#2), though the structure of complex
molecules in 2 is similar to that of 1b (Fig. 1, red).
The metal–donor bond lengths of 2 are smaller than those of
1b and thus slight differences of bond angles related to metal
center are observed; e.g. the bond lengths of Ag–P are
2.5347(5) and 2.5725(6) A in 2 whereas the ones in 1b are
2.4916(8), 2.4980(8) A, and therefore the P–Cu–P chelate angle
of 1b is 78.68(2)1, which is smaller than that of 2 (83.30(2)1)
(Table 1). In 1b, the close distances between the carbon atoms
of the phenylene rings of dppbz in adjacent molecules are
3.55 A (for C(41)–C(390)) and 3.66 A (for C(41)–C(380)),
so it suggests that there are noticeable intermolecular interactions
between the phenylene rings of the dppbz ligand (Fig. S5, ESIw).
In 2, such interactions are not observed. The shortest distance
between phenylene rings is long at B7 A (Fig. S6, ESIw).
The emission maximum for 2 in the solid state occurs at
518 nm, which is similar to that of 2 and longer than that of 1b.
In 2, no change of emission color on grinding was observed. In
CH2Cl2 solution, both 1b and 2 show similar emission at
ca. 580 nm. Furthermore, the similarity among the absorption
spectra of 1b, 1g and 2 in solution (Fig. S7, ESIw) suggests that
all of the crystal/solid contains structurally similar Ag(I)
complex. It was reported that the emission maximum of
[Ag(dppbz)2]+ in 2-MeTHF solution occurs at 670 nm, and
that the large Stokes shift observed in solution shows that
flattening distortion occurs in the MLCT excited state.12
Therefore, it is suggested that the emissive excited states of
[Ag(dppbz)(dppaS2ꢀ)] are assigned to MLCT transitions
involving the p* orbital of phenylene ring in dppbz ligand,
and the green emission is based on the flattened geometry.
Fig. 2 Emitting color on irradiation of UV-light (365 nm) of 1b (a)
and 1g (b) and luminescence spectra of 1b and 1g (c); emitting color of
1g and 1b before heating (d) and after heating at 200 1C for 10 min (e).
Fig. 3 Simulated XRD pattern of 1b (upper blue) and observed data
of 1g (middle green) and 1g after heating at 200 1C (lower pale blue).
A
PMMA film containing 1b (1-PMMA), in which
A powder X-ray diffraction of 1g showed only weak and
ambiguous reflections (Fig. 3). Some of the weak peaks are
assigned to unconverted 1b crystals because the 2y values of
the peaks correspond to those of simulated peaks calculated
from the X-ray data of the single crystal of 1b. After heating
the sample of 1g at 200 1C, some sharp diffraction peaks
appeared, which show a better agreement with the simulated
pattern of 1b. The result shows reversible phase conversion
occurs from crystal (1b) to amorphous (1g) on grinding and
heating. An attempt to repeat this blue-to-green emission
cycles was successful at least five times (Fig. S4, ESIw).
dispersion of complex molecules prevents intermolecular
interactions, shows similar luminescent color to that of 2
crystal (501 nm, Fig. S8 (ESIw)). In these observations, blue
emission is only found for 1b crystals, where intermolecular
p–p interactions involving the phenylene rings are present. So
it is suggested that the lack of the intermolecular interaction
involving the phenylene rings is responsible for the green
emission.
It is uncommon that the p–p interaction involving aromatic
rings leads to the blue shift of emission wavelength, because
p–p interaction between aromatic rings usually results in a
bathochromic shift as seen in the formation of excimer of
aromatic systems. For example, emission maximum of
Synthesis of [Ag(dppbz)(dppaS2)] in CH3CN instead of
CHCl3 gives needle crystals which show green emission upon
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[PtII(5pb)Cl] (5dpb = 2,6-bis(5-methyl-2-pyridyl)benzene) at
570 nm was shifted to 670 nm on grinding accompanied by the
formation of excimer.3 Two possibilities can be considered for
the unique blue shift of the emission of 1b. First, the inter-
molecular p–p interaction involving phenylene rings may
cause perturbation of energy level for p* orbitals to form
specific aggregates. It has been reported that columnar stacks
of a tetraphenylpyrene derivative are responsible for blue
emission of the solid and that the disruption of the columnar
structure by pressure leads to the formation of the green
emissive solid with the poorly ordered molecular packing.2a
However, no remarkable difference between diffuse reflectance
spectra of 1g, 1b and 2 was observed (Fig. S9, ESIw), so it may
not be applicable to this case. Alternatively, it is possible that
the intermolecular interaction between adjacent phenylene
rings may prevent some distortion of the ligands on excitation,
which leads to a small Stokes shift. In this case, the excitation
energy of 1g must be similar to that of 1b. Actually, excitation
maximum of 1g is similar to that of 1b (Fig. S10, ESIw).
Considering from these results, we propose that mechanical
grinding leads to a disruption of intermolecular interaction
between phenylene rings of adjacent molecules in 1g solid to
give green emission. 1g may be in the metastable amorphous
phase, and either heating or recrystallization transforms 1g
into more stable 1b in the mechanochromic system.
Notes and references
1 (a) M. K. Beyer and H. Clausen-Schaumann, Chem. Rev., 2005,
105, 2921–2948; (b) H. Bouas-Laurent and H. Durr, Pure Appl.
Chem., 2001, 73, 639–665.
2 (a) Y. Sagara, T. Mutai, I. Yoshikawa and K. Araki, J. Am. Chem.
Soc., 2007, 129, 1520–1521; (b) J. Mizuguchi, N. Tanifuji and
K. Kobayashi, J. Phys. Chem. B, 2003, 107, 12635–12638;
(c) P. L. Gentili, M. Nocchetti, C. Miliani and G. Favaro,
New J. Chem., 2004, 28, 379–386; (d) K. Ariga, T. Nakanishi,
Y. Terasaka, H. Tsuji, D. Sakai and J. Kikuchi, Langmuir, 2005,
21, 976–981.
¨
3 T. Abe, T. Itakura, N. Ikeda and K. Shinozaki, Dalton Trans.,
2009, 711–715.
4 S. Mizukami, H. Houjou, K. Sugaya, E. Koyama, H. Tokuhisa,
T. Sasaki and M. Kanesato, Chem. Mater., 2005, 17, 50–56.
5 (a) A. L. Balch, Angew. Chem., Int. Ed., 2009, 48, 2641–2644;
(b) H. Ito, S. Tomihisa, O. Naoya, N. Kitamura, S. Ishizaka,
Y. Hinatsu, M. Wakeshima, M. Kato, K. Tsuge and
M. Sawamura, J. Am. Chem. Soc., 2008, 130, 10044–10045;
(c) J. Schneider, Y. A. Lee, J. Perez, W. W. Brennessel,
C. Flaschenriem and R. J. Eisenberg, Inorg. Chem., 2008, 47,
957–968; (d) Y. A. Lee and R. J. Eisenberg, J. Am. Chem. Soc.,
2003, 125, 7778–7779; (e) Z. Assefa, M. A. Omary,
B. G. McBurnett, A. A. Mohamed, H. H. Patterson,
R. J. Staples and J. P. Fackler, Inorg. Chem., 2002, 41, 6274–6280.
6 Pd(0) and Pt(0) complexes: (a) T. Tsubomura, Y. Ito, S. Inoue,
Y. Tanaka, K. Matsumoto and T. Tsukuda, Inorg. Chem., 2008,
47, 481–486; (b) Z. A. Siddique, T. Ohno, K. Nozaki and
T.
Tsubomura,
Inorg.
Chem.,
2004,
43,
663–673;
(c) T. Tsubomura, M. Abe, M. Tarutani, H. Yamada and
T. Tsukuda, Bull. Chem. Soc. Jpn., 2003, 76, 2151–2152;
(d) H. Tominaga, K. Sakai and T. Tsubomura, J. Chem. Soc.,
Chem. Commun., 1995, 2273–2274.
7 Cu(I) complexes: (a) T. Tsukuda, C. Nishigata, K. Arai and
T. Tsubomura, Polyhedron, 2009, 28, 7–12; (b) K. Saito,
T. Tsukuda and T. Tsubomura, Bull. Chem. Soc. Jpn., 2006, 79,
437–441; (c) K. Saito, T. Arai, T. Tsukuda and T. Tsubomura,
Dalton Trans., 2006, 4444–4448; (d) T. Tsukuda, A. Nakamura,
T. Arai and T. Tsubomura, Bull. Chem. Soc. Jpn., 2006, 79,
288–290; (e) T. Tsubomura, N. Takahashi, K. Saito and
T. Tsukuda, Chem. Lett., 2004, 678–679.
Most of the metal complexes showing reversible luminescent
mechanochromism reported so far are Au(I) multinuclear
complexes, which results from modulation of the aurophilic
interactions. The Ag–dppbz system reported herein, which
apparently requires different mechanism for the mechano-
chromism, should provide new mechanistic insights into
mechanochromism. Molecular orbital calculation for inter-
molecular interaction in the Ag–dppbz system may give useful
information on the mechanism of the mechanochromism. In
addition, our studies underway show that the use of dppbz
leads to other complexes showing the luminescent mechano-
chromism. [Ag(dppbz)2]+ and [Ag2I2(dppbz)2] also show
luminescent color change on grinding. As mentioned above,
the presence of phenylene ring between the phosphino groups
of dppbz must be a key of such mechanochromic properties.
Further studies for structural and optical properties of these
complexes in detail will elucidate the mechanism for this type
of chromism.
8 Au(I) complexes: K. Saito, T. Tsukuda, K. Matsumoto and
T. Tsubomura, Bull. Chem. Soc. Jpn., 2007, 80, 533–535.
9 See reviews as follows: (a) A. Barbieri, G. Accorsi and
N.
Armaroli,
Chem.
Commun.,
2008,
2185–2193;
(b) N. Armaroli, Chem. Soc. Rev., 2001, 30, 113–124;
(c) D. V. Scaltrito, D. W. Thompson, J. A. O’Callaghan and
G. J. Meyer, Coord. Chem. Rev., 2000, 208, 243–266;
(d) D. R. McMillin and K. M. McNett, Chem. Rev., 1998, 98,
1201–1219.
10 A. Dairiki, T. Tsukuda, K. Matsumoto and T. Tsubomura,
Polyhedron, 2009, 28, 2730–2734.
11 (a) M. Kato, Bull. Chem. Soc. Jpn., 2007, 80, 287–294;
(b) M. A. Mansour, W. B. Connick, R. J. Lachicotte,
H. J. Gysling and R. J. Eisenberg, J. Am. Chem. Soc., 1998, 120,
1329–1330.
We thank Prof. T. Kojima, Prof. S. Satokawa and Dr K.
Urasaki for the powder X-ray diffraction and the DSC
thermal analysis.
12 M. Osawa and M. Hoshino, Chem. Commun., 2008, 6384–6386.
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Chem. Commun., 2010, 46, 1905–1907 | 1907