Luminescent mononuclear Ag(I)-bis(diphosphine) complexes: Correlation between the photophysics and the structures of mononuclear Ag(I)- bis(diphosphine) complexes

Article abstract of DOI:10.1021/ic900203x

Correlation between the photophysics and the structures of three Ag(I)-bis(diphosphine) complexes ([Ag(dppbz)₂]NO₃ (2 · NO₃), [Ag(dppe)₂]NO₃ (3·NO ₃), and [Ag(dppp)₂]NO₃ (3·NO ₃) (dppbz = 1,2-bis(diphenylphosphino)benzene, dppe = 1,2-bis(diphenylphosphino)ethane, dppp = 1,3-bis(diphenylphosphino)propane) has been investigated using temperature-dependent emission measurements and electrochemical and theoretical methods. All three Ag(I)-bis(diphosphine) complexes have relatively low oxidation potential, which allows metalto-ligand charge transfer (MLCT) contribution in the lowest excited state of the tetrahedral geometry, which is difficult in other Ag(I) complexes. Both 1 · NO₃ and 2 · NO₃ show orange phosphorescence with moderate quantum yield in airfree methanol at room temperature, while 3 · NO₃ is less emissive in solution at room temperature. In all three complexes the temperature-dependent luminescence measurements in EtOH/MeOH 4:1 (v/v) solution indicate the blue-shift of the emission maximum and the increase of the emission intensity on lowering the temperature. In particular, the sequential emission spectral change with decreasing temperature is observed in 1 · NO₃ and 2 · NO₃. In the glass state at 90 K, all three complexes show intense blue phosphorescence. The theoretical calculation using density functional theory (DFT) suggests that the orange and blue emissions mainly originate from the ³MC excited state based on a square-planar geometry and the ³IL+³MLCT excited state based on a tetrahedral geometry, respectively.

Full text of DOI:10.1021/ic900203x

Inorg. Chem. 2010, 49, 805–814 805
DOI: 10.1021/ic900203x
Luminescent Mononuclear Ag(I)-Bis(diphosphine) Complexes: Correlation
between the Photophysics and the Structures of Mononuclear
Ag(I)-Bis(diphosphine) Complexes
Kenji Matsumoto,‡ Takao Shindo,† Naoki Mukasa,† Toshiaki Tsukuda,† and Taro Tsubomura*,†
†Department of Materials and Life Science, Seikei University, 3-3-1 Kichijoji-kitamachi, Musashino, Tokyo,
180-8633, Japan and ‡Department of Chemistry, Faculty of Science, Graduate School, Kyushu University,
Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan
Received February 2, 2009
Correlation between the photophysics and the structures of three Ag(I)-bis(diphosphine) complexes
([Ag(dppbz)2]NO3 (1 NO3), [Ag(dppe)2]NO3 (2 NO3), and [Ag(dppp)2]NO3 (3 NO3) (dppbz = 1,2-bis(diphenyl-
3
3
3
phosphino)benzene, dppe = 1,2-bis(diphenylphosphino)ethane, dppp = 1,3-bis(diphenylphosphino)propane) has
been investigated using temperature-dependent emission measurements and electrochemical and theoretical
methods. All three Ag(I)-bis(diphosphine) complexes have relatively low oxidation potential, which allows metal-
to-ligand charge transfer (MLCT) contribution in the lowest excited state of the tetrahedral geometry, which is difficult in
other Ag(I) complexes. Both 1 NO3 and 2 NO3 show orange phosphorescence with moderate quantum yield in air-
3
3
free methanol at room temperature, while 3 NO3 is less emissive in solution at room temperature. In all three
3
complexes the temperature-dependent luminescence measurements in EtOH/MeOH 4:1 (v/v) solution indicate the
blue-shift of the emission maximum and the increase of the emission intensity on lowering the temperature. In
particular, the sequential emission spectral change with decreasing temperature is observed in 1 NO3 and 2 NO3. In
3
3
the glass state at 90 K, all three complexes show intense blue phosphorescence. The theoretical calculation using
density functional theory (DFT) suggests that the orange and blue emissions mainly originate from the 3MC excited
3
3
state based on a square-planar geometry and the ILþ MLCT excited state based on a tetrahedral geometry,
respectively.
Introduction
superior photophysical properties.6 In particular, multinuc-
lear d10-metal complexes show interesting photolumines-
cence properties such as luminescence thermochromism,
which are achieved by the control of metal-metal bonding
interaction.7 Although there are many reports on lumines-
cent d10-metal complexes, emissive mononuclear Ag(I) com-
plexes have not been studied well because of their potential
photosensitivity and limited luminescent property.6,8
A large number of the luminescent metal complexes have
been studied for the past decades.1,2 Among them in recent
years, d10-metal complexes are anticipated as emissive mate-
rials,3 imaging probes,4 and photocatalysts5 because of their
*To whom correspondence should be addressed. E-mail: tsubomura@
st.seikei.ac.jp. Phone: þ81-422-37-3752. Fax: þ81-422-37-3871.
(1) Photochemistry and Photophysics of Coordination Compounds I and II;
Balzani, V., Campagna, S. Eds.; Springer-Verlag: Heidelberg, 2007.
(2) Evans, R. C.; Douglas, P.; Winscom, C. J. Coord. Chem. Rev. 2006,
250, 2093–2126.
Most recently, it has been reported that the Ag(I) complex
with 1,2-bis(diphenylphosphino)benzene (dppbz), 1 PF6, shows
3
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Tsukuda, T. Inorg. Chem. 2008, 47, 481–486. (b) Yam, V. W.-W.; Cheng, E. C.-C.
Top. Curr. Chem. 2007, 281, 269. (c) Miller, A. J. M.; Dempsey, J. L.; Peters,
J. C. Inorg. Chem. 2007, 46, 7244–7246. (d) Tsuboyama, A.; Kuge, K.; Furugori,
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Z.; Wegh, R. T.; Welter, R. Adv. Mater. 2006, 18, 1313–1316.
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J. Am. Chem. Soc. 2005, 127, 5012–5013. (c) Catalano, V. J.; Moore, A. L. Inorg.
Chem. 2005, 44, 6558–6566. (d) Rasika Dias, H. V.; Diyabalanage, H. V. K.;
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2003, 125, 12072–12073.
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Zeller, M.; Hunter, A. D.; Gray, T. G. Inorg. Chem. 2007, 46, 6218–6220.
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ꢀ
(b) Horvarth, O. Coor. Chem. Rev. 1994, 135/136, 303–324. (c) Li, D.; Che,
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3329.
r
2010 American Chemical Society
Published on Web 01/07/2010
pubs.acs.org/IC

806 Inorganic Chemistry, Vol. 49, No. 3, 2010
Matsumoto et al.
an interesting luminescence property.9 The complex luminesces
orange phosphorescence at room temperature, and when the
temperature decreases until the media is frozen, the emission
changes to intense blue. This phenomenon is known as lumines-
cence thermochromism and occurs when the geometries differ at
high and low temperatures.10 In general, it is established that
some d10-metal complexes with tetrahedral geometry, such as
Cu(I)-bis(diimine) complexes, show flattening distortion in their
triplet metal-to-ligand charge transfer (3MLCT) excited state
because the d9 configuration, which is caused by the charge
transfer, prefers a square-planar geometry.11 Therefore it has
been deduced that the orange and blue emissions observed at
room temperature and low temperature originate from square-
planar and tetrahedral structures, respectively.
Chart 1
Most of the luminescent Ag(I) complexes, however, show
emission due to cluster-centered or ligand-centered excited
states.6 Since an Ag(I) ion is inert to oxidation, the low-
energy MLCT state hardly occurs.8c In fact, the absorption
ties were investigated using electrochemical and tempera-
ture-dependent emission measurements and computa-
tional method. As a result, we found that these Ag(I)
complexes have interesting emission properties which are
different from Cu(I) complexes. In this report, lumines-
cence details of the mononuclear Ag(I) complexes are
discussed.
spectrum of 1 PF6 is similar to that of the free ligand, dppbz,
3
and the accurate assignment of the absorption is difficult.
This is in contrast with luminescent Cu(I) complexes whose
emission states are frequently assigned to MLCT. In addition,
although in tetrahedral Cu(I) complexes the flattening dis-
tortion in the excited state leads to marked reduction of the
Experimental Section
luminescence intensity, 1 PF6 shows a lower-energy and
3
General Procedures. Reagents and solvents were purchased
from commercial suppliers and used without further purifica-
tion unless otherwise noted. Elemental analyses were performed
for C, H, and N elements on a Perkin-Elmer model 2400.
31P{1H} and 1H NMR spectra were taken by a JEOL Lambda
400 Fourier transform spectrometer with Air-VT thermocon-
troller. The references of 31P{1H} and 1H NMR spectra are
external 85% H3PO4 and internal tetramethylsilane, respec-
tively.
longer-life emission in solution (λem
= 670 nm and τ =
max
11 μs in air-free 2-MeTHF)9 with relatively strong intensity
than that of the Cu(I) analogue, [Cu(dppbz)2]BF4 (λem
=
max
556 nm and τ = 244 ns in air-free CH2Cl2).12 This result
shows that 1 PF6 in the excited state has an extraordinarily
3
slow deactivation rate.
We have been interested in the luminescent mononuclear
d
10 metal complexes and reported the photophysical prop-
erties of Pd(0),3a Pt(0),3a,13 Cu(I),14 and Au(I).15 In recent
years, we have also been studying the luminescence proper-
ties of mononuclear Ag(I) complexes. Interestingly, although
it has been reported that the Ag(I) complex with dppe
Synthesis of Complexes. To a methanol solution (50 mL)
containing 1 mmol of a diphosphine ligand (dppbz, dppe, or
dppp) was added a small amount of aqueous solution of silver(I)
nitrate (AgNO3; 0.5 mmol), and the mixture was stirred for 2 h
under dark. After stirring, most of the solvent in the reaction
solution was evaporated and then was cooled. The white powder
of [Ag(diphosphine)2]NO3 was precipitated after cooling for
several hours. The precipitate was filtered off and washed with
diethyl ether. The complex obtained was recrystallized by slow
diffusion of ether into the ethanol solution of a complex. The
31P{1H} and 1H NMR spectra of 1 NO3, 2 NO3 and 3 NO3 are
that is a dppbz analogue, 2 PF6, is non-emissive in solu-
3
tion,16 we discovered that the complex in degassed solution
showed orange phosphorescence similar to 1 PF6. The
3
luminescent properties of three Ag(I)-bis(diphosphine)
complexes (diphosphine = dppbz, dppe, dppp, Chart 1)
which have different electronic and structural proper-
3
3
3
depicted in the Supporting Information, Figures S1-S6.
[Ag(dppbz)2]NO3 (1 NO3). Anal. Calcd. for C60H48Ag1P4-
3
N1O3: C, 67.81; H, 4.55; N, 1.32. Found: C, 67.76; H, 4.45; N,
=
(9) Osawa, M.; Hoshino, M. Chem. Commun. 2008, 6384–6386.
ꢀ
ꢀ ꢀ
1.17. 31P{1H} NMR (160 MHz, CD3OD): δ = 1.94 (1JAgP
(10) (a) Ruben, J.; Dıez, A.; Fernandez, J.; Fornies, J.; Garcıa, A.; Gil, B.;
´
´
1
Lalinde, E.; Moreno, M. T. Inorg. Chem. 2008, 47, 7703–7716. (b) Felder, D.;
Nierengarten, J.-F.; Barigelletti, F.; Ventura, B.; Armaroli, N. J. Am. Chem. Soc.
2001, 123, 6291–6299. (c) Ford, P. C.; Cariati, E.; Bourassa, J. Chem. Rev. 1999,
99, 3625–3647. (d) Wrighton, M.; Morse, D. L. J. Am. Chem. Soc. 1974, 96,
998–1003.
(11) (a) Armaroli, N. Chem. Soc. Rev. 2001, 30, 113–124. (b) Iwamura, M.;
Takeuchi, S.; Tahara, T. J. Am. Chem. Soc. 2007, 129, 5248–5256.
(12) Moudam, O; Kaeser, A.; Delavaux-Nicot, B.; Duhayon, C.; Holler, M.;
230, 267 Hz). H NMR (400 MHz, CD3OD): δ = 7.61-7.55
(m, 8H, Ph), δ = 7.38-7.34 (m, 8H, Ph), δ = 7.18-7.13 (m,
32H, Ph).
[Ag(dppe)2]NO3 (2 NO3). Anal. Calcd. for C52H48Ag1P4-
3
N1O3: C, 64.61; H, 5.00; N, 1.45. Found: C, 64.51; H, 4.83; N,
1.58. 31P{1H} NMR (160 MHz, CD3OD): δ = 4.31 (1JAgP
=
232, 267 Hz). 1H NMR (400 MHz, CD3OD): δ = 7.43-7.24 (m,
40H, Ph), δ = 2.55-2.52 (m, 8H, CH2).
[Ag(dppp)2]NO3 (3 NO3). Anal. Calcd. for C54H52Ag1P4-
ꢀ
Accorsi, G.; Armaroli, N.; Seguy, I.; Navarro, J.; Destruel, P.; Nierengarten,
J.-F. Chem. Commun. 2007, 3077–3079.
(13) Abedin-Siddique, Z.; Ohno, T.; Nozaki, K.; Tsubomura, T. Inorg.
Chem. 2004, 43, 663–673.
(14) (a) Tsukuda, T.; Nishigata, C.; Arai, K.; Tsubomura, T. Polyhedron
2009, 28, 7–12. (b) Saito, K.; Arai, T.; Takahashi, N.; Tsukuda, T.; Tsubomura, T.
Dalton Trans. 2006, 4444–4448. (c) Saito, K.; Tsukuda, T.; Tsubomura, T. Bull.
Chem. Soc. Jpn. 2006, 79, 437–441. (d) Tsukuda, T.; Nakamura, A.; Arai, T.;
Tsubomura, T. Bull. Chem. Soc. Jpn. 2006, 79, 288–290.
(15) Saito, K.; Tsukuda, T.; Matsumoto, K.; Tsubomura, T. Bull. Chem.
Soc. Jpn. 2007, 80, 533–535.
(16) Delfs, C. D.; Kitto, H. J.; Stranger, R.; Swiegers, G. F.; Wild, S. B.;
Willis, A. C.; Wilson, G. J. Inorg. Chem. 2003, 42, 4469–4478.
3
N1O3: C, 65.20; H, 5.27; N, 1.41. Found: C, 64.87; H, 5.31; N,
=
217, 253 Hz). H NMR (400 MHz, CD3OD): δ = 7.40-7.21
(m, 40H, Ph), δ = 2.53 (br, 8H, P-CH2), δ = 1.68 (br, 4H,
-CH2-).
1.59. 31P{1H} NMR (160 MHz, CD3OD): δ = -4.88 (1JAgP
1
Photophysics. Absorption and emission spectral measure-
ments were carried out using degassed solutions by repeated
freeze-pump-thaw procedures (at least five times). Absorption
and emission spectrawere measured with a Shimadzu UV-3100PC

Article
Inorganic Chemistry, Vol. 49, No. 3, 2010 807
spectrophotometer and an Ocean Optics QE-65000 scientific-
grade CCD spectrometer, respectively. A grating-monochro-
mated Xe lamp source (lamp: AMKO, Lamphousing A 1000
series; monochromator: Jovin-Ybon, HR 320) was used for the
excitation of the samples. Excitation and solid-state emission
spectra were recorded by a Shimadzu RF-5000 fluorometer. The
low-temperature solid-state emission spectral measurement was
carried out using a SUPRASIL quartz tube and a quartz Dewar
flask. The temperature-dependent emission spectral measure-
ment in an air-free EtOH/MeOH 4:1 (v/v) solution was per-
formed using a custom-made LN2 cryostat (Jecc-Torisha) with a
thermocontroller (Scientific Instruments, Model 9700). Unless
otherwise noted, the temperature-dependent emission spectra
and lifetimes were measured after over 40 min when a tempera-
ture has been set. All emission spectra were corrected using the
LS-1-CAL calibration light source (Ocean Optics). The quan-
tum yields (Φ) of 1 NO3, 2 NO3, and 3 NO3 were calculated by
performed using the CrystalStructure19 (Ver. 3.8) crystallo-
graphic software package. The structure was solved using
SIR9220 and refined with program SHELXL-97.21 The non-
hydrogen atoms were refined anisotropically. The hydrogen
atoms were refined isotropically. Molecular plot was obtained
with the program ORTEP-3.22 The crystallographic data are
given in Supporting Information, Table S1.
Computational Details. All theoretical calculations were per-
formed using Gaussian 0323 for Windows (Ver. 6.1, Revision
E-.01) on the Intel Core2 Quad Q6600 2.4 GHz computer with
2 GB memories. Both geometry optimization by density func-
tional theory (DFT) and time-dependent DFT (TD-DFT)24,25
calculations applied Becke’s 3-parameter hybrid function26
combined with the Lee-Yang-Parr correlation function27
(B3LYP), and the basis set as follows: silver, CEP-121G;
phosphorus, 6-31þG*; carbon, 6-31G*; hydrogen, 6-31G. No
symmetry was used. In the calculation of the triplet state,
unrestricted B3LYP (UB3LYP) was used. In the calculation
of the singlet state, the “UltraFine” option was specified for the
“Int” keyword. In the geometry optimization of all complexes,
the atomic coordinates based on the crystal structure were used
as the initial geometry. The modified GDIIS algorithm28 was
used as the optimization method. No solvent effect was included
for the geometry optimization. In both geometry optimizations
of the singlet and triplet states all four items (Maximum Force,
rms Force, Maximum Displacement and rms Displacement)
were converged or a maximum force became negligible small.
The lowest 20 (for Ag(dppe)2 and Ag(dppp)2) or 30 (for Ag-
(dppbz)2) singlet excited states were calculated for the optimized
geometry in the singlet state using TD-DFT. The lowest 10
triplet excited states were computed for each optimized geome-
try in the triplet (for Ag(dppbz)2) and singlet states (for all
complexes). The SCF keyword options were specified as follows:
“Tight, VShift = 500, Maxcycle = 256”. The solvent effect
using polarizable continuum model29 (PCM) was included in the
singlet excited energy calculation, and the chosen solvent was
methanol. The input and output files for all calculations are
described in the Supporting Information. The abbreviations in
the figures and tables are as follows: ES, excited state; f,
3
3
3
the following equation:17
ꢀ
ꢁ ꢀ ꢁꢀ ꢁꢀ
ꢁ
2
ꢀ
ꢀ
n
S
I
A
ꢀ
Φ ¼ Φ
ꢀ
ꢀ
n
S
I
A
where n is the refractive index of the solvent, S is the area of the
corrected emission spectra, I is the intensity of light at the
excitation wavelength, and A is the absorbance at the excitation
wavelength. The asterisk refers to the standard sample. The
excitation wavelengths for 1 NO3, 2 NO3, and 3 NO3 are 330,
3
3
3
312, 300 nm, respectively. Quinine bisulfate in 1 N H2SO4 was
used for the standard of the quantum yield (Φ* = 0.546)18 and
was excited at the same wavelength for each complex (i.e., I*/I=1).
At the excitation wavelength, the absorbance of all samples
except for 3 NO3 is less than 0.1. Since the emission intensity of
3 NO3 is very weak, the value of a slightly larger absorbance
3
3
(0.16) was used. Luminescence decay curves were measured on a
laboratory-made apparatus; the sample was excited with a Nd:
YAG laser (266 nm; Continuum, Minilite), and the emission
light was focused into a Jovin-Ybon H-20 monochromator
equipped with a photomultiplier (Hamamatsu, R-955). The
output of the photomultiplier was acquired by a Tektronix
TDS 5034 Digital Phosphor Oscilloscope.
Electrochemistry. The cyclic voltammetry of 1 NO3, 2 NO3,
and 3 NO3 was carried out under the following conditions:
3
3
(20) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Burla,
M.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
3
€
€
(21) Sheldrick, G. M. SHELXL-97; University of Gottingen: Gottingen,
Germany, 1997.
[Ag(I) complex] = 1 mM, 100 mM tetra-n-butylammonium
hexafluorophosphate (nBu4NPF6) as supporting electrolyte, a
glassy carbon working electrode, an Ag/Agþ reference elec-
trode, a Pt wire counter electrode, scan rate 100 mV/s.
nBu4NPF6 was recrystallized from hot acetonitrile before use.
Before the measurement, deaeration of the solution was carried
out using Ar bubbling during at least 15 min. The voltammo-
gram was taken by a potentiostat (Huso Electrochemical Sys-
tem, HECS 311B 15-01) with a potential sweep unit (Huso
Electrochemical System, HECS 321B) and was recorded using a
X-Y recorder (Riken Denshi, Model F-35CA). The chart was
digitalized by a graph reading software. The potential value
obtained for the Ag/Agþ reference electrode scale was converted
to the Fc/Fcþ scale using the redox potential of Fc/Fcþ obtained
in the same condition as the external reference.
(22) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
(23) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, Jr., J. A.; Vreven, T.; Kudin, K. N.;
Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa,
J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,
S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz,
P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
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B.; Chen, W.; Wong, M. W.; Gonzalez, C.; and Pople, J. A. Gaussian 03,
Revision E.01; Gaussian, Inc.: Wallingford, CT, 2004.
X-ray Crystallographic Analysis.
A single crystal was
mounted in a loop with liquid paraffin. An X-ray diffraction
measurement was made on a Rigaku Saturn CCD area detector
with graphite monochromated Mo-KR radiation, operating at
50 kV and 40 mA at -150 °C. Data were collected and processed
on a PC using CrystalClear software (Rigaku) and was corrected
for Lorentz and polarization effects. All calculations were
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808 Inorganic Chemistry, Vol. 49, No. 3, 2010
Matsumoto et al.
Table 1. Photophysical and Electrochemical Properties of 1 NO3, 2 NO3, and 3 NO3
3
3
3
λabsmax/nma
λemmax at
λemmax at
Eox/Vc
E
red/Vc
complex
(ε/M-1 cm-1
)
295 K/nma (τ/μs)
90 K/nmb (τ/μs)
Φ/%a
(vs Fc/Fcþ)
(vs Fc/Fcþ)
1 NO3
3
273 (3.6 ꢁ 104)
263 (3.7 ꢁ 104)
268 (3.2 ꢁ 104)
680 (28), 445d
693 (12)
445 (2.4 ꢁ 103)
403 (1.1 ꢁ 104)
410 (9.9 ꢁ 103)
8.3
4.2
<0.05
þ0.48 (þ0.36)f
þ0.64 (þ0.44)f
þ0.86 (þ0.39)f
þ0.42
þ0.45
2 NO3
3
3 NO3
3
ca.430 (n. d.)e
a In air-free methanol. b In air-free EtOH/MeOH 4:1 (v/v). c In Ar-saturated acetonitrile. d In solid. e Not determined. f Oxidation potential of the
corresponding free ligand.
Table 2. Calculated Singlet Excited States and Their Transition Energies Related to the Absorption Spectra of 1þ, 2þ, and 3þa
complex
no. of excited state
calculated transition/nm
oscillator strength
main transition (maximum CI coefficient)
assign
1
1þ
2þ
3þ
ES 7
ES 18
ES 1
ES 10
ES 1
ES 12
295.24
270.57
292.50
271.69
288.80
262.36
0.1011
0.1605
0.1769
0.2052
0.1280
0.1518
242 HOMO-1 f 244 LUMO (0.66346)
243 HOMO f 255 LUMOþ11 (0.51487)
219 HOMO f 220 LUMO (0.53506)
219 HOMO f 224 LUMOþ4 (0.58034)
227 HOMO f 228 LUMO (0.55992)
227 HOMO f 234 LUMOþ6 (0.58691)
1IL þ MLCT
1
1IL þ MLCT
1
1IL þ MLCT
1
1IL þ MLCT
1
1IL þ MLCT
1
1IL þ MLCT
a All calculation results are deposited in the Supporting Information
oscillator strength; CI coeff., configuration interaction coeffi-
cient.
mical properties of these Ag(I)-bis(diphosphine) complexes
are summarized in Table 1. All complexes have an intense
absorption band (ε = ca. 35,000 M-1 cm-1) around 270 nm,
which is similar to those of each ligand (dppbz: 277 nm (ε =
2.0 ꢁ 104 M-1 cm-1) in EtOH/MeOH (4:1 v/v)31a and about
280 nm (ε = ca. 1.8 ꢁ 104 M-1 cm-1) in 2-MeTHF,9 dppe:
251 nm (ε = 1.83 ꢁ 104 M-1 cm-1) in cyclohexane,31b dppp:
252 nm (ε = 1.76 ꢁ 104 M-1 cm-1) in cyclohexane31b). This
suggests that these bands involve an intraligand (IL) char-
acter. In addition, the shoulder bands are observed around
300 nm for all complexes. Since the lower-energy shoulder
band is not observed in the absorption spectra of ligands, this
may be attributed to an IL charge transfer perturbed from a
metal center. Although many luminescent mononuclear Ag-
(I) complexes exclusively show IL excited states, these ab-
sorption bands are assigned as 1IL transitions involving
Results and Discussion
1 NO3, 2 NO3, and 3 NO3 were prepared by the reaction
3
3
3
of a methanol solution of each corresponding diphosphine
with an aqueous solution of AgNO3 and obtained them in
good yield (ca. 80%). The 31P{1H} NMR spectra of 1 NO3,
2 NO3, and 3 NO3 in CDCl3 show two doublets centered at
3
3
3
δ1.12 (1JAgP = 230 and 265 Hz), 3.90 (1JAgP = 232 and 263 Hz),
and -5.39 (1JAgP = 226 and 257 Hz), respectively, in which
the splitting is attributed to the two isotopes of silver, 107Ag
and 109Ag, having each 1/2 of nuclear spin. Their signals in
the complexes show downfield shifts compared with those of
free diphosphines (dppbz: δ -13.4, dppe: δ -12.0, dppp:
δ -17.0). The measurement in a coordinating solvent,
methanol-d4, also gave similar results (see also the Experi-
mental Section). These results indicate that the four phos-
phorus atoms in those complexes are magnetically equivalent
and Ag-P bonds are not fluxional in solution on the NMR
time-scale.
1
significant contribution of MLCT. This is supported by
TD-DFT calculations for the three Ag(I)-bis(diphosphine)
complexes discussed later. The results of the calculations
1
suggest that there are some bands derived from mixed IL
and 1MLCT from 260 to 300 nm (Supporting Information,
Figure S9 and Table 2).
The single crystal of 1 NO3 was obtained by diffusing
3
The cyclic voltammogram (CV) of three Ag(I)-bis-
(diphosphine) complexes in acetonitrile is depicted in
ether into its chloroform solution. The cation in the complex
of 1 NO3 has a C2-symmetry and adopts a distorted tetra-
3
Figure 1. The CV of 1 NO3 shows a reversible redox wave
hedral geometry (Supporting Information, Figure S7). The
crystallographic data are shown in Supporting Information,
Table S1. The Ag-P lengths and P-Ag-P angle are
2.4560(4) and 2.5103(4) A and 80.055(13)°, respectively.
These values are almost identical to those of the correspond-
3
with E1/2 = þ0.45 V versus Fcþ/Fc and ΔE = 0.06 V at room
temperature. In 2 NO3 the voltammogram gives an irrever-
3
sible redox pair. The anodic (Epa) and cathodic (Epc) peak
potentials of 2 NO3 are þ0.64 and þ0.45 V versus Fcþ/Fc,
3
ing PF6 salt, 1 PF6.9 The dihedral angle between the two
respectively. The voltammogram of 3 NO3 gave only an
3
3
anodic peak at þ0.86 V versus Fcþ/Fc. The redox potentials
of Ag(I)-bis(diphosphine) complexes are significantly smaller
than that of [Ag([18]aneS4O2)]PF6 (Epa = þ1.09 V and
Epc = þ0.95 V versus Fcþ/Fc at 253 K) whose ligand is able
to form a stable Ag(II) complex.32 The low redox potential of
Ag(I)-bis(diphosphine) complexes may be attributed to sta-
bilization of the divalent complexes by phosphine ligands
P-Ag-P planes is 85°, indicating that the two chelate planes
are almost orthogonal to each other. These values are within
the range of typical Ag(I)-phosphine complexes.9,30
The absorption spectra of 1 NO3, 2 NO3, and 3 NO3 in
3
3
3
methanol at room temperature are shown in Supporting
Information, Figure S8. The photophysical and electroche-
(30) (a) Affandi, D.; Berners-Price, S. J.; Effendy; Harvey, P. J.; Healy,
P. C.; Ruch, B. E.; White, A. H. J. Chem. Soc., Dalton Trans. 1997, 1411–
1420. (b) Gimeno, M. C.; Jones, P. G.; Laguna, A.; Sarroca, C. J. Chem. Soc.,
Dalton Trans. 1995, 1473. (d) Harker, C. S.W.; Tiekink, E. R. T. J. Coord. Chem.
1990, 21, 287.
(31) (a) This work. (b) Liaw, B.; Orchard, W.; Kutal, C. Inorg. Chem.
1988, 27, 1311–1316.
(32) Huang, D.; Blake, A. J.; McInnes, E. J. L.; McMaster, J.; Davies,
€
E. S.; Wilson, C.; Wolowska, J.; Schroder, M. Chem. Commun. 2008, 1305–
1307.

Article
Inorganic Chemistry, Vol. 49, No. 3, 2010 809
Figure 1. Cyclic voltammograms of Ag(I)-bis(diphosphine) complexes
in acetonitrile at room temperature.
Figure 3. Comparison of the optimized geometries of 1þ in triplet and
singlet states.
emissive. At 77 K all complexes are emissive in the solid state
(Figure 2). In 1 NO3 and 2 NO3, their emission maxima
3
3
show slight blue-shifts in comparison with their free ligands.
This result suggests that the IL excited state is perturbed by
the metal. On the other hand, 3 NO3 shows the same
3
emission spectrum as the free ligand, indicating that the
emission of 3 NO3 in the solid state predominantly originates
3
from the IL excited state.
Under oxygen-free condition, the methanol solutions of
1 NO3 and 2 NO3 show orange luminescence with peak
3
3
maxima at 680 and 693 nm, respectively. The large Stokes
shifts in solution suggest that the structures of these com-
plexesintheexcited stateare considerablydistorted from that
in the ground state.
The luminescence quantum yields of 1 NO3 and 2 NO3 in
3
3
methanol at room temperature are 8.3% and 4.2%, respec-
tively. These values are significantly higher than other lumi-
nescent Ag(I) complexes,2,6,8a and the former is comparable
Figure 2. Emission spectra (uncorrected) of Ag(I)-bis(diphosphine)
complexes (left) and corresponding ligands (right) in the solid state at
77 K.
to thevalue of 1 PF6 inless coordinativesolvent, 2-MeTHF.9
3
having both σ-donor and π-acceptor characters.32,33 Related
ligands (dppbz, dppe, and dppp) show only an irreversible
anodic peak around þ0.4 V versus Fcþ/Fc (Table 1). The fact
The higher quantum yield of 1 NO3 compared with 2 NO3
3
3
may be attributed to the rigid structure with a phenylene
group in the P-P chelate ring. Although it is well-known that
the luminescence of many Cu(I) complexes involving Cu(I)-
bis(diimine) complexes is quenched in the coordinating sol-
vents such as nitriles and alcohols, this result indicates that
these Ag(I)-bis(diphosphine) complexes in the excited state
are not susceptible to the nucleophilic attack of the solvent
molecules. The orange emissions of 1 NO3 and 2 NO3 in the
that a reversible redox pair is found in the CV of 1 NO3
3
shows that the oxidation mechanism is different from that of
the ligand oxidation. Such low oxidation potential and
reversible redox process of the Ag(I) complex should be
ascribed to significant contribution of metal orbitals to the
highest occupied molecular orbital (HOMO), which is shown
by the DFT results. This may explain why the Ag-phosphine
complexes have the excited states with significant MLCT
character, which is difficult in other Ag(I) complexes.
3
3
solution state were completely quenched in the presence of
oxygen. The emissions show the single exponential decay,
and the emission lifetimes of 1 NO3 and 2 NO3 are 28 and
3
3
12 μs, respectively, indicating that these emissions have a
The room-temperature emission spectra of 1 NO3,
3
phosphorescence nature. In the literature16 it has been
2 NO3, and 3 NO3 are shown in Supporting Information,
3
3
described that 2 PF6 is non-emissive in solution. In the
Figure S10. In the solid state 1 NO3 indicates strong blue
luminescence with peak maximum at 445 nm upon excitation
3
3
previous study the emission of the complex might be
quenched by a trace amount of oxygen involved in the media.
at 300 nm, whereas 2 NO3 and 3 NO3 are almost non-
3
3
On the other hand, 3 NO3 shows a very weak emission with a
3
peak maximum around 430 nm, which significantly differs
(33) (a) Shaw, J. L.; Wolowska, J.; Collison, D.; Howard, J. A. K.;
from the emission behaviors of 1 NO3 and 2 NO3. Since the
3
3
€
McInnes, E. J. L.; McMaster, J.; Blake, A. J.; Wilson, C.; Schroder, M.
emission of 3 NO3 in room-temperature solution resembles
3
J. Am. Chem. Soc. 2006, 128, 13827–13839. (b) Walker, N. R.; Wright, R. R.;
Barran, P. E.; Murrell, J. N.; Stace, A. J. J. Am. Chem. Soc. 2001, 123, 4223–
4227.
that of the ligand in the low-temperature solid, the emission
band probably stems from an IL excited state.

810 Inorganic Chemistry, Vol. 49, No. 3, 2010
Matsumoto et al.
Table 3. Observed and Calculated Triplet Transition Energies of 1þ, 2þ, and 3þ
solution
at r. t.
glass at 90 K
(solid at r. t.)
complex
observed
λemmax/nm
Ag(dppbz)2
Ag(dppe)2
Ag(dppp)2
680
693
ca.430
445 (445)
403
410
singlet-optimized
geometry
(crystal structure)
triplet-optimized
geometry
calculated
λemmax/nm
Ag(dppbz)2
Ag(dppe)2
Ag(dppp)2
609.56
a
a
359.49 (356.15)
350.93
347.40
a Not calculated.
Calculation of the optimized geometry of 1þ in the triplet
state by the DFT method shows that it adopts a significantly
flattened geometry (Figure 3). The dihedral angle between the
two P-Ag-P planes of the triplet-optimized geometry of 1þ is
34°, which is significantly smaller than the values for the singlet-
optimized geometry (69°) and that found in the crystal (85°).
The lowest triplet excitation energy for the triplet-optimized
geometry using the TD-DFT method is consistent with the
corresponding observed value (Table 3). The calculation also
suggested that the emission band based on the flattening
distorted geometry stems from the 3MC excited state including
MLCT such as a metal-phosphine dσ*fpπ transition
Figure 4. Molecular orbitals (isovalue = 0.02) related to the lowest
triplet excitation based on the triplet-optimized geometry of 1þ. ES,
excited state; f, oscillator strength; CI coeff., configuration interaction
coefficient.
(Figure 4, Table 4). The emission behavior of 2 NO3 could
3
be also explained in a similar way. Although, in general, for d10
metal ions the MC excited states lie at much higher energy, the
square-planar geometry and the pπ-pπ bonding interaction
between Ag 5p and phosphine 3p orbitals in the lowest
unoccupied molecular orbital (LUMO) may decrease the
energy level of the MC excited states in 1 NO3 and 2 NO3
state in comparison with 1þ and 2þ (Table 4). In general, since
the 3IL excited state undergoes thermal deactivation at room
temperature, 3 NO3 may have poor luminescence. Since the
þ 3
structure of 3 is closer to an ideal tetrahedral geometry than
that of 1þ and 2þ, the relatively strong IL character in
the excited state is probably attributed to the fact that the
d-orbital splitting in 3þ is smaller than that in 1þ and 2þ.
Surprisingly, all excitation spectra at 90 K are consistent
with those at room temperature (Figure 5), especially in
1 NO3 and 2 NO3, despite the large difference between the
3
3
because the square-planar geometry significantly raises the
energy level of the dx2-y2 orbital of silver atom compared
to the tetrahedral geometry and the pπ-pπ bonding interac-
tion decreases the energy level of the silver 5p orbital
(Supporting Information, Figure S11). Therefore, such
pπ-pπ bonding interaction stabilizes a structure of the com-
plex in the excited state, which leads to the high quantum yields
of 1 NO3 and 2 NO3 compared with other luminescent Ag(I)
3
3
emission maxima at room temperature and 90 K. This result
indicates that the absorption species corresponding to the
emission bands at both room temperature and 90 K are the
same. Thus, for 1 NO3 and 2 NO3, the results described here
3
3
3
3
complexes.
can be explained on the basis of flattening distortion which
occurs in the excited state at room temperature, as expected
from the theoretical calculation.
Interestingly, at 90 K, all three Ag(I) complexes in the glass
state (EtOH/MeOH = 4:1) show intense blue and very long-
lived luminescence (Supporting Information, Figure S12,
Table 1). The emission spectra of all complexes are similar
to those in the solid state at 77 K (Figure 2). This result
suggests that the complexes excited at low temperature main-
tain the original (distorted tetrahedral) geometry. In fact, the
lowest triplet excitation energies calculated by the TD-DFT
method based on the singlet-optimized geometries and the
crystal structure of 1þ explain that the distorted tetrahedral
complex exhibits blue-shifted phosphorescence compared to
that of the flattened structure. (Table 3). Furthermore, it is
suggested that the emission band based on the distorted
tetrahedral geometry stems from admixture of 3IL and
3MLCT excited states (Supporting Information, Figure S13,
Table 4). The calculation for the singlet-optimized geometries
of 2þ and 3þ also gave similar results. However, in the case of
To investigate the temperature-dependence of media on
the emission of mononuclear Ag(I)-bis(diphosphine) com-
plexes, the temperature-dependent emission spectra of
1 NO3, 2 NO3, and 3 NO3 were measured at various
3
3
3
temperatures. As the temperature of the solution of 1 NO3
3
decreases from 295 to 150 K, the intensity of emission
increases, and the peak maximum shifts to longer wavelength
up to 755 nm (Figure 6A). 2 NO3 also shows a similar
3
behavior (Figure 6C). Decrease of emission intensity has
been often observed in some d10 complexes with a red-shift of
emission maximum on lowering the temperature.3a,d,10b This
observation is explained by the thermal equilibrium between
singlet and triplet excited states.10b,34 Since in 1 NO3 and
3
(34) Siddique, Z. A.; Yamamoto, Y.; Ohno, T.; Nozaki, K. Inorg. Chem.
2003, 42, 6366–6378.
3
3þ, the pure IL character largely contributes to the excited

Article
Inorganic Chemistry, Vol. 49, No. 3, 2010 811
Table 4. Summary of the Calculated Lowest Triplet Transition for 1þ, 2þ, and 3þa
a All calculation results are deposited in the Supporting Information.
tially changes from red to blue is unprecedented. Similar
emission behavior is also found in 2 NO3 although in a
3
narrow temperature range from 100 to 90 K the sequential
blue-shift occurs. (Figure 6D). Interestingly, in both cases a
rise in the emission intensity after the excitation is observed in
the same temperature range (Figure 8). The observed rise-
times of 1 NO3 at 110 K and 2 NO3 at 100 K are 5 and 7 μs,
3
3
respectively. In addition, the emission intensity after the rise
decays single exponentially. In 2 NO3, especially, the rise of
3
the emission is found in the lower-energy emission band but
not in the higher-energy one (Figure 8 (iv) inset). Since the
absorption species corresponding to both lower- and higher-
energy emission bands are the same (vide supra), these results
indicate that the structure of a complex in the excited state
slowly changes from a tetrahedral geometry showing a
higher-energy emission band to a square-planar geometry
showing a lower-energy emission band. The structural
change in the excited state is generally much more rapid than
the emission process.11b The observed risetimes are signifi-
cantly long, which are comparable with the luminescence
lifetimes. Similar behavior is found in tetranuclear copper(I)
iodide clusters such as [Cu4I4(4-Phpy)4] with different struc-
tures in different excited states (3XLCT and 3CC) which are
poorlycoupled.35 In 1 NO3 and 2 NO3, hence, it is suggested
Figure 5. Excitation spectra (uncorrected) of Ag(I)-bis(diphosphine)
complexes in an air-free EtOH/MeOH 4:1 (v/v) at room temperature
(dotted line) and 90 K (solid line). [1 NO3] = 50 μM, [2 NO3] = 66 μM,
3
3
and [3 NO3] = 59 μM.
3
3
3
that there are two different excited states (3ILþ MLCT and
3MC) corresponding to two different structures (tetrahedral
and square-planar geometries), and that the geometrical
change occurs in a microsecond time scale at the specific
temperature range (90-100 K). At the temperature range,
the non-radiative deactivation of the excited state in the
tetrahedral geometry and the change in the geometry into a
more flattened one should occur with similar rates, and the
radiative rate of the initially populated excited state should be
far slower than the former two rates. With these conditions
satisfied, theobservedresults, that is, thelow-energy emission
has a slow rise, may be reasonably explained. The blue-shift
of the emission maximum in 1 NO3 and 2 NO3 on lowering
3
2 NO3 both emission intensities increase on lowering the
3
temperature, the observed red-shift is not attributed to such
thermal equilibrium. On the other hand, it is well-known that
the Cu(I)-bis(2,9-dimethyl-1,10-phenanthroline) complex
shows large Stokes shift in a non-coordinative solvent at
room temperature, and this is attributed to the structural
change of the complex from tetrahedral to square-planar
geometries in the excited state.11b Considering these findings,
the red-shift found in 1 NO3 and 2 NO3 may be caused by
3
3
the change in the average geometry of the complex with
temperature in the excited state, that is, in a cooled solution
adopts a more flattened geometry than that in a solution at
room temperature. Under 150 K, as shown in Figure 6B, the
emission shows sequential blue-shift with multicolor emis-
sion spectral change and becomes intense and long-lived as
temperature decreases (Figure 7 and Supporting Information,
Table S2). The phenomenon that the emission color sequen-
3
3
the temperature may reflect the sequential suppression of the
flattening distortion around the silver ion in the excited state.
(35) Kyle, K. R.; Ryu, C. K.; DiBenedetto, J. A.; Ford, P. C. J. Am. Chem.
Soc. 1991, 113, 2954–2965.

812 Inorganic Chemistry, Vol. 49, No. 3, 2010
Matsumoto et al.
Figure 6. Temperature-dependent emission spectra of Ag(I)-bis(diphosphine) complexes in an air-free EtOH/MeOH 4:1 (v/v) solution. [1 NO3] = 49 μM,
3
[2 NO3] = 50 μM, and [3 NO3] = 55 μM.
3
3
metry compared to 1þ and 2þ because of its large bite angle,
in 3þ the flattening distortion in the excited state may hardly
occur by means of the large steric repulsion between the
phenyl groups. The intensities of both emission bands slightly
increase when the temperature decreases to 150 K (Figure 6E).
The appearance of a lower-energy emission band in the range
from 210 to 150 K may be attributed to the reduction of the
non-radiative deactivation from the tetrahedral excited state
with large 3IL character and the stabilization of the flattening
distorted state by decreasing temperature. Under 150 K,
however, the intensity of only the higher-energy emission
band remarkably increases, and the lower-energy emission
band gently weakens (Figure 6F). This result also suggests
that the flattening distortion of the complex in the excited
state hardly occurs at low temperature.
From our findings, the mechanism of the emission for the
three Ag(I)-bis(diphosphine) complexes, 1þ, 2þ, and 3þ,
could be explained as shown in Chart 2. In 1þ and 2þ at room
temperature, the complexes in the IL excited state with
significant contribution of MLCT rapidly undergo the flat-
tening distortion (kf . kT),36 and then show the lower-energy
Figure 7. Temperature dependence of the emission lifetimes for 1 NO3
and 2 NO3 in the range from 295 to 90 K. Inset: Arrhenius plot of the
emission lifetime for 1 NO3.
3
3
3
3
emission originated from the MC excited state based on
square-planar geometry (in Chart 2, the route indicated by
red arrows). At low temperature, since the flattening distortion
does not essentially occur (kT . kf), the complexes emit the
Such emission mechanism may lead to the complicated
temperature dependence of the emission lifetime of 1 NO3
3
3
higher-energy luminescence stemming from the3ILþ MLCT
(Figure 7 inset).
In 3 NO3, in addition to a very weak emission band
3
excited state based on the tetrahedral geometry (in Chart 2,
the route indicated by blue arrows). In the intermediate state
centered around 430 nm observed at room temperature, a
new weak emission band with peak maximum around 680 nm
similar to that for 1 NO3 and 2 NO3 appears on lowering the
(36) Hereat, an observed rate constant for the decay of the excited state
indicates the sum of radiative and non-radiative rate constants.
3
3
temperature. Since 3þ adopts almost ideal tetrahedral geo-

Article
Inorganic Chemistry, Vol. 49, No. 3, 2010 813
Figure 8. Emission decay of 1 NO3 and 2 NO3 in an air-free EtOH/MeOH 4:1 (v/v) solution at different temperatures. 1 NO3: (i) 150, 120, and 110 K;(ii)
3
3
3
100 and 90 K. 2 NO3: (iii) 120 and 100 K; (iv) 90 K. Inset: After 30 min when the temperature was set at 90 K (the spectrum with asterisk in Figure 6D).
3
Chart 2.a
deactivation and flattening distortion are significantly sup-
pressed (kT . kf), the higher-energy emission as well as 1þ
and 2þ is found (in Chart 2, the route indicated by blue
arrows).
Conclusion
We investigated the luminescence properties of three Ag-
(I)-bis(diphosphine) complexes, 1 NO3, 2 NO3, and
3
3
3 NO3, using photophysical, electrochemical, and theoreti-
3
cal methods. These Ag(I) complexes have relatively low
oxidation potential compared with other Ag(I) complexes.
Not only 1 NO3 but also 2 NO3 operate as good orange
3
3
triplet emitters in solution although 2þ has been reported to
a kT = Observed rate constant for the decay of the excited state from a
tetrahedral geometry in rigid media. kS = Observed rate constant for the
decay of the excited state from a square-planar geometry in fluid media.
kf = Observed rate constant for the flattening distortion.
be non-emissive in solution. On the other hand, 3 NO3 is less
3
emissive in solution. In the EtOH/MeOH 4:1 (v/v) glass, all
three complexes show intense blue phosphorescence. The
theoretical calculation using DFT suggests that the orange
3
around the freezing point of media, the emission may occur
from the species having the intermediate geometry depending
on the temperature. On the other hand, in 3þ at room
temperature, since the pure 3IL character largely contributes
to the excited state in comparison with 1þ and 2þ, non-
radiative deactivation is predominant. At low temperature
(but not below freezing point), since non-radiative deactiva-
tion is suppressed, in addition to the higher-energy emission,
the lower-energy emission similar to that of 1þ and 2þ is
observed (in Chart 2, the routes indicated by blue and red
arrows). At sufficient low temperature, since non-radiative
and blue emissions mainly originate from the MC excited
state based on
a square-planar geometry and the
3
3ILþ MLCT excited state based on a tetrahedral geometry,
respectively. Furthermore, the temperature-dependent emis-
sion spectra of 1 NO3 and 2 NO3 indicate the sequential
3
3
emission spectral change on lowering the temperature. A
slow rise in the emission intensity after excitation is observed
in the lower-energy emission. These results support the fact
that there are two different excited states (3ILþ MLCT and
3
3MC) corresponding to two different structures (tetrahedral
and square-planar geometries), and slow flattening distortion

814 Inorganic Chemistry, Vol. 49, No. 3, 2010
Matsumoto et al.
from the former to the latter structures occurs in a certain
temperature range. These findings suggest that the mono-
nuclear Ag(I)-bis(diphosphine) complexes flattened in the
excited state is not susceptible to the nucleophilic attack of
solvent molecules which frequently causes non-radiative
deactivation in luminescent Cu(I) complexes. Therefore,
Ag(I)-bis(diphosphine) complexes have a potential to show
higher luminescence compared to Cu(I) complexes. In addi-
emission property may lead to the application to various
luminescence sensors.
Acknowledgment. This work was financially supported
by the Promotion and Mutual Aid Corporation for Private
Schools of Japan through the Science Research Promotion
Fund and through the High-tech Research Center Project.
Supporting Information Available: Additional figures, com-
putational details, and crystallographic data for 1 NO3 in CIF
tion, as observed in 1 NO3, depending on temperature, the
3
3
phenomenon in which a single complex shows luminescent
color from red to blue is unprecedented. This interesting
format. This material is available free of charge via the Internet
at http://pubs.acs.org.