Multiphotochromism in an Asymmetric Ruthenium Complex with Two Different Dithienylethenes

Article abstract of DOI:10.1021/acs.inorgchem.7b02023

An asymmetric bis(dithienylethene-acetylide) ruthenium(II) complex trans-Ru(dppe)₂(L1o)(L2o) (1oo) incorporating two different dithienylethene-acetylides (L1o and L2o) was designed to modulate multistate photochromism in view of the well separated ring-closing absorption bands between L1o and L2o. Upon irradiation with appropriate wavelengths of light, complex 1 undergoes stepwise photocyclization and selective photocycloreversion to afford four states (1oo, 1co, 1oc, and 1cc). As a contrast, symmetric complexes trans-Ru(dppe)₂(L1o)₂ (2oo) and trans-Ru(dppe)₂(L2o)₂ (3oo) with two identical dithienylethene-acetylides were synthesized, and the corresponding photochromic behavior was investigated. The photochromic properties of the oxidized species (1oo⁺/1co⁺/1oc⁺/1cc⁺, 2oo⁺/2co⁺/2cc⁺, and 3oo⁺/3co⁺/3cc⁺) were also investigated. The ring-closing absorption bands of one-electron oxidized species 1oo⁺, 2oo⁺, and 3oo⁺ show obvious blue shifts relative to those of 1oo, 2oo, and 3oo, respectively. The ring-closing absorption bands in both neutral and oxidized species grow progressively following oo → oc/co → cc and oo⁺ → oc⁺/co⁺ → cc⁺. As revealed by spectroscopic, electrochemical, and computational studies, complex 1 displays eight switchable states through stepwise photocyclization, selective cycloreversion, and a reversible redox process.

Full text of DOI:10.1021/acs.inorgchem.7b02023

Article
pubs.acs.org/IC
Multiphotochromism in an Asymmetric Ruthenium Complex with
Two Different Dithienylethenes
Jin-Xiang Chen,† Jin-Yun Wang,† Qian-Chong Zhang,† and Zhong-Ning Chen*,†,‡
†State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences,
155 Yangqiao Road West, Fuzhou 350002, China
‡College of Chemistry and Materials Science, Fujian Normal University, Fuzhou, Fujian 350007, China
S
* Supporting Information
ABSTRACT: An asymmetric bis(dithienylethene-acetylide) ruthenium(II) complex
trans-Ru(dppe)2(L1o)(L2o) (1oo) incorporating two different dithienylethene−
acetylides (L1o and L2o) was designed to modulate multistate photochromism in
view of the well separated ring-closing absorption bands between L1o and L2o. Upon
irradiation with appropriate wavelengths of light, complex 1 undergoes stepwise
photocyclization and selective photocycloreversion to afford four states (1oo, 1co, 1oc,
and 1cc). As a contrast, symmetric complexes trans-Ru(dppe)2(L1o)2 (2oo) and trans-
Ru(dppe)2(L2o)2 (3oo) with two identical dithienylethene-acetylides were synthe-
sized, and the corresponding photochromic behavior was investigated. The
photochromic properties of the oxidized species (1oo+/1co+/1oc+/1cc+, 2oo+/
2co+/2cc+, and 3oo+/3co+/3cc+) were also investigated. The ring-closing absorption
bands of one-electron oxidized species 1oo+, 2oo+, and 3oo+ show obvious blue shifts
relative to those of 1oo, 2oo, and 3oo, respectively. The ring-closing absorption bands
in both neutral and oxidized species grow progressively following oo → oc/co → cc
and oo+ → oc+/co+ → cc+. As revealed by spectroscopic, electrochemical, and computational studies, complex 1 displays eight
switchable states through stepwise photocyclization, selective cycloreversion, and a reversible redox process.
still highly challenging to access all the possible switchable
isomers. Particularly, the fully ring-closed isomers in the fused
asymmetric organic molecules are always unattainable.33,34
When ring-closing absorption maxima of two nonequivalent
DTE moieties are sufficiently separated in asymmetric metal-
coordinated systems, it is likely to obtain all four states (oo, co,
oc, cc) through selective photocyclization and cycloreversion
upon irradiation with suitable wavelengths of light.35 Since the
absorption positions of closed-ring DTEs are highly dependent
on the π-conjugation, they can be conveniently modulated by
change of the linking position of thienyl groups to a
cyclopentene moiety.36 In an attempt to obtain multistate
and full color systems, two types of DTE−acetylides, L1o and
L2o (Scheme 1), with a large energy gap between their ring-
closing absorption peaks are elaborately designed for this study.
For L1o, two 3-thienyl groups are bound to a perfluorocyclo-
pentene moiety to achieve a ring-closing absorption peak at 605
nm. The π-conjugation of the closed-ring isomer of L1o is
extended over the whole molecule through the DTE linkage
with a pyrimidyl group. In contrast, the perfluorocyclopentene
moiety in L2o is bound to one benzyl-containing 2-thienyl and
one 3-thienyl so as to give a ring-closing absorption band
centered at 506 nm with a much higher absorption energy than
INTRODUCTION
■
Photochromic diarylethene (DTE) compounds that can
undergo a light-induced reversible transformation between
two isomers have attracted much attention due to their fast
response, remarkable fatigue resistance, and excellent thermal
reversibility1−9 as well as their potential applications in optical
memory storage systems and switching devices.10−21 During
past decades, numerous research effort was devoted to the
development of multiphotochromic systems that incorporate
multiple DTE units into the same structures since they are of
interest for the modulation of optoelectronic properties in
materials and supramolecular systems.3,11,22−24 However, the
resulting multiswitch systems often display partial photo-
cyclization because of facile intramolecular energy transfer
(ET) from the ring-open moiety to a ring-closed one that
prevents further photocyclization.25 Interestingly, when multi-
DTE acetylides are inserted into a metal center, stepwise ring-
closing is attainable, but the systems are still limited.25 In most
cases, the symmetric structures with two or more identical DTE
moieties face difficulty in creating multistates and multi-
colors.25b,26−32 On the other hand, multistate and multicolor
photochromism is likely achieved by incorporating DTE
moieties with different structures into one organic molecule33,34
or a metal center.35 The advantages of the asymmetric systems
over those incorporating identical DTEs lie in their better
feasibility in achieving stepwise and selective photochromism
through irradiation with different wavelengths of light, but it is
Received: August 7, 2017
© XXXX American Chemical Society
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Scheme 1. Asymmetric Ruthenium(II) Complex 1oo and
Symmetric Complexes 2oo and 3oo
RESULTS AND DISCUSSION
■
Synthesis and Characterization. The synthetic routes to
L1o and L2o as well as ruthenium(II) complexes 1oo−3oo
were depicted in Schemes S1 and S2. Asymmetric complex 1oo
(Scheme S1) was prepared by a two-step reaction procedure.
The reaction of cis-Ru(dppe)2Cl2 with 1.2 equiv of L1o in the
presence of NaPF6 produced first ruthenium(II) vinylidene
derivative RuCC-DTE as a yellow intermediate. Stable
complex cis-Ru(dppe)2(L1o)Cl was then accessed in 56% yield
as a yellow product by the addition of Et3N as a base to the
yellow intermediate through a deprotonation process. Further
reaction of cis-Ru(dppe)2(L1o)Cl with 1 equiv of L2o in the
presence of NaPF6 (1.2 equiv) and NEt3 resulted in the
isolation of asymmetric complex 1oo as a yellow solid in 55%
yield. Treatment of cis-Ru(dppe)2Cl2 with 2.5 equiv of L1o or
L2o in the presence of NaPF6 and NEt3 gave complex 2oo
(Scheme S1) or 3oo (Scheme S2), respectively. Complexes
1oo−3oo were readily purified through chromatography on
short alumina columns using dichloromethane as an eluent.
UV−Vis Absorption Spectral Studies. The ring-closure
absorption bands of L1o and L2o were well modulated by
adjusting the linking position of thienyl groups to the
perfluorocyclopentene moiety as well as introducing a
substituent such as pyrimidine or benzyl at the 5-position of
thienyl rings. When a CH2Cl2 solution of L1o was irradiated
with 312 nm light, the colorless solution turned blue because
the ring-closing absorption maximum appeared at 605 nm due
to the formation of L1c. Similarly, the colorless CH2Cl2
solution of L2o turned red with the observation of the ring-
closing peak at 506 nm upon irradiation at 312 nm. As
expected, the ring-closure absorption peaks of free ligands L1
and L2 (Figure S1) are well separated with a wavelength
difference of ca. 100 nm.
that of L1o because the closed-ring form of L2o has a much
shorter π-conjugated system.
A redox-active ruthenium(II) moiety is utilized to incorpo-
rate two nonequivalent DTEs (L1o and L2o) because the
reversible oxidation of Ru(II) to Ru(III) can afford more
addressable forms. We describe herein asymmetric ruthenium-
(II) complex 1oo with two different DTEs (L1o and L2o) as
well as symmetric complexes 2oo and 3oo with two identical
DTEs (L1o for 2oo and L2o for 3oo). The oxidized species
1oo+, 2oo+, and 3oo+ are also obtained through the oxidation
of Ru(II) to Ru(III). As expected, stepwise photocyclization/
cycloreversion and a multistate are achieved. It is worth noting
that eight states are accessible in asymmetric ruthenium(II)
complex 1oo through stepwise photocyclization, selective
cycloreversion, and reversible redox processes. Interestingly,
the oxidized species 1oo+, 2oo+, and 3oo+ exhibit near-infrared
(NIR) absorption bands, strikingly different from those in 1oo,
2oo, and 3oo.
Complexes 1oo−3oo display intense absorption bands at ca.
290−370 nm, arising mainly from π → π* IL (intraligand), 4d
(Ru) → π*(dppe) MLCT (metal-to-ligand charge transfer),
and π(one CC−DTE) → π*(the other CC−DTE) LLCT
Figure 1. UV−vis absorption spectral changes of 1oo (a), 2oo (b), and 3oo (c) in toluene (2 × 10−5 M) at ambient temperature upon irradiation at
365 nm, and the absorbance change of 2 (d) at 701 nm upon alternate irradiation at 365 and 700 nm for five cycles.
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(ligand-to-ligand charge transfer) states as supported by the
computational studies (vide infra).
and 1cc) and four colors (colorless, blue, red, and blue-black)
could be attained through stepwise photocyclization and
selective cycloreversion processes upon irradiation of the
solution at the PSS with appropriate wavelengths of light.
The success to attain selective cycloreversion is attributed to
the well-separated absorption bands of L1c and L2c.
Upon irradiation at 365 nm, the colorless toluene solution of
1oo turned blue as the new broad bands appeared increasingly
at 426−850 nm. The broad absorption bands with maxima at
ca. 696 and 524 nm (Figure 1a) originated from the ring-
closing absorptions of L1c and L2c, respectively, due to the
formation of a mixture of singly ring-closed species 1co and
1oc. When the solution was prolonged to be irradiated, the
absorption maxima at 696 and 524 nm enhanced progressively
due to further transformation of 1co/1oc to 1cc. At the
photostationary state (PSS), the solution turned blue-black
with a mixture of 1co and 1cc as verified by NMR studies
(Figure 2 and Figure 3a).
When the colorless solution of 2oo in toluene was irradiated
at 365 nm (Figure 1b), three new bands generated at ca. 395,
474, and 694 nm with the decrease of the bands at 309 and 347
nm. Meanwhile, the solution turned cyan, suggesting the
ongoing photocyclization of L1o → L1c to the singly ring-
closed species 2co (Scheme S3). Upon further irradiation at
365 nm, the absorption intensity of the band centered at 694
nm continually increased, and the absorption maximum
progressively red-shifted to 701 nm, indicating a further
photocyclization reaction of 2co → 2cc at the second L1o to
L1c. As depicted in Figure 1b, the ring-closed absorption
maximum was red-shifted from the initial 694 to 701 nm,
demonstrating unambiguously that stepwise photocyclization
occurred indeed through the conversion process 2oo → 2co →
2cc. On the other hand, the corresponding stepwise cyclo-
reversion reaction of 2cc → 2co → 2oo was observed upon
irradiation of the solution at the PSS with the light of 700 nm.
Notably, stepwise photochromism of complex 2 was monitored
by alternate irradiation at 365 and 700 nm for several cycles
without appreciable photodegradation (Figure 1d).
Irradiation of a toluene solution of 3oo at 365 nm resulted in
an immediate increase in the absorption intensity at 522 nm
with the colorless solution turning red (Figure 1c), which was
assigned to the formation of singly ring-closed species 3co.
Further irradiation of the solution with 365 nm light did not
show an obvious red-shift of the absorption peak, which could
be elucidated from the NMR studies (Figure 3c and Figure S6).
Since the species at the PSS was mainly 3co (73%) with only a
small amount of 3cc (22%), an obvious red-shift could not be
observed.
1
NMR Spectral Studies. The H NMR spectral changes of
1
Figure 2. H NMR spectral changes of 1oo in C6D6 (5 × 10−3 M)
1oo and the corresponding assignments are shown in Figure 2.
1
The H NMR spectrum of complex 1oo displayed thienyl
upon irradiation at 365 nm to the PSS.
protons at 8.55, 6.73, 6.64, and 6.17 ppm together with four
methyl signals at 1.85 (b), 1.75 (d), 1.74 (a), and 1.67 (c) ppm.
When the solution of 1oo in C6D6 was irradiated at 365 nm,
the initial signals of thienyl and methyl protons attenuated
gradually. Meanwhile, new peaks were observed at 7.89, 6.80,
6.15, and 5.60 ppm, which are ascribable to thienyl signals of
the singly ring-closed 1co. Simultaneously, four relative weak
signals occurred at 8.54, 6.67, 5.72, and 5.17 ppm, attributed
probably to the thienyl signals of singly ring-closed 1oc. On the
other hand, the new signals of methyl groups appeared at 2.48,
2.42, 1.75, and 1.65 ppm due to 1co together with four signals
at 1.98, 1.82, 1.79, and 1.73 ppm due to 1oc. The assignment
on the new peaks for 1co and 1oc is based on the integration
area of the peaks as well as the absorption intensity in the UV−
vis absorption spectra in Figure 1a, in which the absorption
intensity of 1co is much greater than that of 1oc. Thus, the
content of 1co is much more than that of 1oc upon the UV
irradiation of the solution. The obvious shifts of these thienyl
and methyl protons imply that the process 1oo → 1co/1oc
took place indeed. Upon further irradiation with 365 nm light,
the thienyl and methyl signals of 1co and 1oc gradually
decreased, and in fact the signals of 1oc disappeared finally
following the 1co/1oc → 1cc process. Three new thienyl
signals were observed at 8.01, 6.82, and 6.70 ppm, whereas
The photocycloreversion was also examined. On the one
hand, when the solution at the PSS was irradiated with 730 nm
light (Figure S2), the absorption band centered at 696 nm
decreased rapidly and nearly disappeared. In contrast, although
the band at 524 nm exhibited some extent of reduction, it still
kept. Such spectral changes suggested that 1cc converted to
1oc through the cycloreversion of L1c to L1o with the blue-
black solution turning red (Scheme 2). On the other hand,
upon irradiation of the solution at the PSS with light at 530 nm
(Figure S3), the absorption maximum at 524 nm decreased
rapidly and bleached finally. By comparison, the band centered
at 696 nm displayed some decrease but still remained without
vanishing as 1cc was converted 1co through the cycloreversion
of L2c to L2o with the blue-black solution turning blue.
Therefore, selective ring-opening at L1c or L2c could be
attained through irradiation at 730 or 530 nm, respectively,
leading to the conversion of 1cc to 1oc or 1co accompanied by
a color change from blue-black into red (1oc) or blue (1co).
Actually, when the solution at the PSS was irradiated at >460
nm, both ligands L1c and L2c exhibited cycloreversion
reactions, resulting in stepwise 1cc → 1oc/1co → 1oo
conversion with a color conversion of blue-black → red/blue →
colorless. As depicted in Scheme 2, four states (1oo, 1co, 1oc,
C
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Scheme 2. Stepwise and Selective Photochromic Processes and Color Conversions of Complex 1 in Toluene Solution
Figure 3. 31P NMR spectral changes of 1oo (a), 2oo (b), and 3oo (c) in C6D6 (5 × 10−3 M) under UV light irradiation at 365 nm to the PSS.
another one was overlapped with that of 1co at 6.15 ppm. At
the same time, two new methyl signals occurred at 2.40 (f) and
2.30 ppm (e), and the other two were observed at 1.75 (h) and
1.65 (g) ppm, which were overlapped with those of 1co. At the
PSS, only the signals of 1co and 1cc were observed (Figure 2).
The stepwise photocyclization 1oo → 1co/1oc → 1cc was
also confirmed by the change of the 31P NMR spectrum
(Figure 3a). The 31P NMR signal of 1oo in C6D6 was first
observed at 53.3 ppm. When the solution was irradiated at 365
nm, the signal at 53.3 ppm gradually decreased and ultimately
disappeared. In the meantime, two new signals emerged at 52.3
and 52.1 ppm due to the photocyclization of L1o and L2o to
generate mixed ring-open/closed species 1co and 1oc,
respectively. Another new signal due to dually ring-closed
species 1cc was observed at 51.4 ppm upon prolonged
irradiation. Meanwhile, the signal of 1oc decreased and finally
vanished at the PSS with gradual enhancement of the signal of
1cc at 51.4 ppm, suggesting the complete conversion of 1oc to
1cc. At the PSS, the percentages of 1co and 1cc were estimated
as 51% and 49% (Table 1 and Figure 3a) as evidenced by the P
signals of 1co and 1cc.
Table 1. Conversion Maxima and Conversion Percentages at
PSS for 1−3
a
b
conversion maximum
contents at PSS
1oo
2oo
3oo
83% (→1co), 24% (→1oc)
94% (→2co)
1co (51%), 1cc (49%)
2co (12%), 2cc (88%)
85% (→3co)
3oo (5%), 3co (73%), 3cc (22%)
a
b
Data obtained with an uncertainty of 10%. Conversion
percentages measured by NMR spectroscopy in C6D6 solutions (5 ×
10−3 M).
gradually, while those of 1oc at 52.1 ppm and 1oo at 53.3 ppm
appeared and progressively enhanced, indicating that 1cc and
1co converted to 1oc and 1oo through selective ring-opening
at L1c. Similarly, upon irradiation of the solution at the PSS
with light of 530 nm (Figure S4b), the signal of 1cc gradually
decayed and finally disappeared. Meanwhile, the signal at 52.3
ppm due to 1co emerged and increasingly enhanced, implying
the selective cycloreversion at L2c, thus leading to the
conversion of 1cc to 1co.
When 2oo in C6D6 was irradiated with UV light at 365 nm
(Figure S5 and Scheme S3), the signals of thienyl protons at
8.54 and 6.63 ppm attenuated gradually and disappeared finally.
Concomitantly, four new signals at 8.52, 7.89, 6.70, and 5.60
ppm appeared and enhanced following 2oo → 2co. Upon
further irradiation at 365 nm to the PSS, two new signals at
Conversely, photochemical cycloreversion at selective ligands
(L1c or L2c) can be obtained by irradiation with specific
wavelengths of light. As expected, when the toluene solution at
the PSS was subsequently irradiated at 730 nm (Figure S4a),
the signals at 51.4 ppm for 1cc and 52.3 ppm for 1co reduced
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Figure 4. Relative content changes of 1oo (a), 2oo (b), and 3oo (c) in C6D6 (2 × 10−3 M) under UV light irradiation at 365 nm to the PSS.
7.90 and 5.68 ppm emerged, while the signals at 8.52, 7.89,
6.70, and 5.60 ppm gradually decreased and almost vanished,
indicating further photocyclization of 2co to 2cc. Meanwhile,
the methyl signals of 2oo at 1.85 and 1.74 ppm decreased
gradually with the formation of 2co. Two methyl signals with
low-field shifts appeared at 2.48 and 2.43 ppm, whereas another
new methyl signal was observed at 1.83 ppm following 2oo →
2co. Upon keeping irradiation at 365 nm, the methyl signals of
2co weakened gradually, and two new signals enhanced
progressively at 2.39 (a″) and 2.45 (b″) ppm due to the
formation of 2cc.
Table 2. Electrochemical Data for Complexes 1−3 with
Various Forms in 0.1 M Solutions of [nBu4N][PF6] in
Dichloromethane
ab
,
E1/2 (ΔEp)
c
Ru-centered
DTEs
d
1oo
1co
2oo
2co
2cc
3oo
3co
0.47 (0.06)
0.44 (0.07)
0.48 (0.06)
0.45 (0.07)
0.43 (0.08)
0.43 (0.05)
0.45 (0.08)
1.20
d
0.94, 1.14
d
1.21
d
0.95, 1.16
0.81, 0.96
d
In the 31P NMR spectrum of 2oo (Figure 3b), the P signal
was observed at 53.3 ppm. Upon irradiation at 365 nm, this
signal gradually reduced and finally vanished, while a new signal
emerged at 52.2 ppm due to the formation of 2co. Upon
keeping irradiation, the signal at 52.2 ppm decreased gradually;
another new signal at 51.3 ppm occurred and enhanced
increasingly due to further conversion of 2co to 2cc. At the PSS
(Table 1 and Figure 4b), the solution contained 12% 2co and
88% 2cc, as estimated by the relative area of P signals of 2co
(52.2 ppm) and 2cc (51.3 ppm).
1.18
d
d
0.89, 1.19
a
Potential data in volts were recorded relative to Ag/AgCl as a
b
reference electrode. ΔEp = Ea − Ec, where Ea and Ec are the anodic
and cathodic potentials, respectively. Potential data from differential
pulse voltammogram (DPV). Anodic potential.
c
d
1
In the H NMR spectrum of 3oo (Figure S6, Scheme S4),
the thienyl protons were observed at 6.89 (H1o) and 6.25 ppm
(H2o) and the methyl signals appeared at 1.83 (a) and 1.97
ppm (b). Upon irradiation of 3oo at 365 nm, both proton
signals of thienyls (H1o and H2o) and methyls (a and b)
decreased gradually accompanied by four new thienyl proton
signals at 6.88 (H′1o), 6.07 (H′1c), 6.24 (H′2o), and 5.27 ppm
(H′2c) due to the formation of 3co. In the same time, the
methyl signals of ring-opened L2o occurred at 1.84 (c′) and
1.97 ppm (d′) with a slight high-field shift, whereas those of
ring-closed L2c were observed at 1.83 (a′) and 2.03 ppm (b′).
Upon further irradiation, two new thienyl signals emerged at
6.04 and 5.25 ppm, and two new methyl signals at 2.06 and
1.93 ppm were also observed, indicating the further conversion
of 3co to 3cc. Upon irradiation at 365 nm (Figure 3c), the P
signal of 3oo at 53.3 ppm gradually attenuated together with
the appearance of a new signal at 52.8 ppm following 3oo →
3co. Keeping irradiation of the solution resulted in another new
signal at 51.8 ppm, suggesting the further formation of 3cc. At
the PSS, the P signal integral ratio indicated the presence of 5%
3oo, 73% 3co, and 22% 3cc (Table 1 and Figure 4c).
Electrochemical Studies. The electrochemical properties
of 1−3 were in situ monitored under UV irradiation at 365 nm
using a cyclic voltammogram (CV) and differential pulse
voltammogram (DPV) in 0.1 M [nBu4N][PF6] dichloro-
methane solutions. The data are summarized in Table 2.
As illustrated in Figure 5, the redox waves of 1oo were
observed at 0.47 V as a quasi-reversible process and 1.20 V as
an irreversible one, attributed to the oxidation of RuII → RuIII
and ring-open DTEs, respectively. Upon irradiation of 1oo with
365 nm light, while the waves at 0.47 and 1.20 V reduced
Figure 5. Plots of cyclic voltammograms (a) and differential pulse
voltammograms (b) of 1oo, 1co, and 1cc in 0.1 M solutions of
[nBu4N][PF6] in dichloromethane.
gradually and disappeared finally, three new oxidation waves
emerged at 0.44, 0.94, and 1.14 V. The reversible wave at 0.44
V corresponds to the oxidation of the RuII center, whereas the
waves at 0.94 and 1.14 V are ascribable to the ring-closed L1c
and the ring-opened L2o of singly ring-closed species 1co,
respectively. The redox wave for 1oc, however, was not
detected because of the low content (<25%) in the mixture.
Upon keeping irradiation of the solution of complex 1 at 365
nm, three waves at 0.80, 0.95, and 1.13 V were observed at the
PSS. Since the singly ring-closed 1co (51%) and the fully ring-
closed 1cc (49%) coexisted at the PSS (Table 1), it is
unattainable to separate them as pure samples through
chromatography. At this stage, it is difficult to thoroughly
investigate the electrochemical property of 1cc.
The voltammogram plots of 2oo, 2co, and 2cc (Figure S7)
showed a quasi-reversible wave at ca. 0.40−0.50 V (vs Ag/
AgCl), respectively, due to the oxidation of RuII to RuIII.
Species 2oo also displayed an irreversible wave at 1.21 V, most
likely corresponding to the L1o-centered oxidation process. For
2co, ligand-centered redox process showed two one-electron
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Figure 6. (a) The UV−vis−NIR spectra of switchable eight forms for complex 1 in CH2Cl2. (b) The UV−vis−NIR spectral changes of 1oo+ upon
irradiation at 365 nm. (c) Eight states of complex 1 from stepwise photochemical and electrochemical reactions.
Figure 7. UV−vis−NIR spectra of complexes 2 (a) and 3 (b) in various states in CH2Cl2 solutions (2 × 10−5 M).
oxidation waves at 0.95 and 1.16 V with lower potentials,
ascribed to L1c and L1o in 2co, respectively. Dually ring-closed
species 2cc showed two waves at 0.81 and 0.96 V due to the
sequential oxidation of two ring-closed L1c’s, implying an
obvious electronic interaction between two identical ring-closed
DTE moieties.30 Species 3oo (Figure S8) also displayed a
reversible wave at 0.43 V stemming from the oxidation of the
RuII center together with an irreversible wave at 1.18 V due to
the ring-opened DTE moiety. Compound 3co showed three
oxidation waves at 0.45 (Ru), 0.89 (L2c), and 1.19 V (L2o).
Unfortunately, the low conversion percentages of 3co to 3cc
(ca. 22%) resulted in the absence of distinct electrochemical
changes upon further irradiation of 3co solution at 365 nm.
Spectroscopic Studies on Oxidized Species. In order to
achieve multistate systems, monocationic species were obtained
through the oxidation of RuII into RuIII. On the basis of
electrochemical studies, they (1oo+/1co+/1oc+/1cc+, 2oo+/
2co+/2cc+, and 3oo+/3co+/3cc+) were accessed by the addition
of 1 equiv of [N(C6H4Br-4)3](SbCl6) as an oxidant to the
corresponding solutions of complexes 1oo−3oo.
band at ca. 1273 nm. The ring-closing absorption band
occurred at 515 nm for 1oc+ and 657 nm for 1co+. In the case
of 1cc+, three low-energy bands were observed at 908, 657, and
515 nm. The NIR bands at ca. 908 nm in 1co+/1oc+/1cc+
showed an obvious blue-shift compared with that in 1oo+
(1273 nm), ascribed to their differences in transition character
between ring-closed 1co+/1oc+/1cc+ and ring-open 1oo+ as
revealed by computational studies (vide infra). Moreover, the
ring-closed absorption bands in the visible region due to L1c
and L2c in one-electron oxidized complexes 1co+ (657 nm),
1oc+ (515 nm), and 1cc+ (657 and 515 nm) showed distinct
blue-shifts in comparison with those in 1co (696 nm), 1oc
(524 nm), and 1cc (696 and 524 nm), respectively.
As depicted in Figure 6b, upon irradiation of one-electron
oxidized species 1oo+ with UV light at 365 nm, while the NIR
band centered at 1273 nm decreased gradually, a new NIR
band at 908 nm occurred and grew increasingly. Meanwhile, a
broad composite band composed of the ring-closing absorption
peaks at 515 nm (L2c) and 657 nm (L1c) emerged and
increased progressively following the stepwise photocyclization
1oo+ → 1oc+/1co+ → 1cc+. As a result, complex 1 displays
eight switchable states (1oo/1co/1oc/1cc and 1oo+/1co+/
1oc+/1cc+) through optical and electrochemical stimuli (Figure
6c).
Complex 1oo+ (Figure 6a) displayed a near-infrared (NIR)
absorption band centered at 1273 nm, which was mainly
attributed to L1o/L2o/dppe → Ru(III) LMCT states. By
comparison, both complexes 1oc+ and 1co+ exhibited a new
band centered at 908 nm with a distinct attenuation of the NIR
F
DOI: 10.1021/acs.inorgchem.7b02023
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Inorganic Chemistry
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Similarly, complex 2oo+ exhibited an intense NIR band at ca.
1261 nm (Figure 7a) due to the L1o/dppe → Ru(III) LMCT
state.30 In contrast, 2co+ displayed a weaker NIR band at ca.
1261 nm together with a ring-closing band at 654 nm and
another NIR band at 920 nm. Relative to that in 2co+, the NIR
band at 920 nm became stronger, and the ring-closing band was
shifted to 661 nm in 2cc+ with the complete disappearance of
the NIR band at ca. 1261 nm. The red-shift of the ring-closing
band from 654 nm (2co+) to 661 nm (2cc+) reflects a more
extended π system in 2cc+ than that in 2co+.
+1. The greater involvement of HOMO−3 → LUMO+1 for
2co (48%) than that for 3co (10%) gives a reasonable
explanation to the experimental fact that further ring closure of
2co to 2cc (conversion percentage 88%) is much more facile
than that of 3co to 3cc (conversion percentage 22%). For 2cc
and 3cc, the HOMO/HOMO−1 is uniformly distributed on
the two ring-closed DTE moieties along with a minor
population at the Ru center, while the LUMO/LUMO+1 is
mainly populated on one of the two ring-closed DTE moieties.
The calculated low-energy absorption bands at 706 nm for 2cc
and 543 nm for 3cc due to HOMO → LUMO/LUMO+1 and
HOMO−1 → LUMO/LUMO+1 are all typical of IL and
LLCT (from one DTE to the other) character. The oscillator
strength of low-energy absorption of 3cc is weaker than that of
2cc, implying a smaller portion of 3cc can be obtained upon
irradiation of 3co under UV light.
Complex 3oo+ displayed a NIR band centered at ca. 1265
nm (Figure 7b). For 3co+, a ring-closing band centered at 516
nm and a NIR band at 960 nm were observed, but the NIR
band at ca. 1265 nm became much weaker relative to that of
3oo+. The corresponding absorption bands in 3cc+ were not
detected due to the low conversion percentage.
For 1oo+, the calculated NIR absorption at 1053 nm is
typical of a LMCT state (Lo/dppe to Ru center). The NIR
absorptions of 1co+ are mainly featured with a LLCT state of
L2o → L1c and MLCT transition of Ru → L1c. Likewise, the
NIR absorptions of 1oc+ are primarily assigned to LLCT
character from L1o → L2c and MLCT transition of Ru → L2c.
For 1co+ and 1oc+, the bands in the visible region are typical of
ring-closing absorption of L1c and L2c, respectively, mixed with
some LLCT state from the ring-opened DTE moiety to the
ring-closed one and MLCT transition of Ru → ring-closed
DTE. For 1cc+, the NIR absorption bands result mainly from
Ru → L1c MLCT, π → π* (L2c centered), and L2c → L1c
LLCT states. Due to their difference in transition character, the
NIR absorptions in 1co+/1oc+/1cc+ exhibit distinct blue-shifts
relative to that in 1oo+.
Computational Studies. TD-DFT computational studies
were performed on 1oo/1co/1oc/1cc, 2oo/2co/2cc, and
3oo/3co/3cc together with monocationic 1oo+/1co+/1oc+/
1cc+ (Tables S1−S14). For 1oo−3oo, the HOMO is
distributed on 4d orbitals of ruthenium and two ring-open
DTE−acetylides, whereas the LUMO is localized at one of the
ring-open ligands. The low-energy absorption bands are
ascribable to Ru → DTE−acetylide (MLCT) and DTE−
acetylide (IL) centered transitions, mixed with some LLCT
character from one DTE−acetylide to the other.
For 1co, both the HOMO and LUMO are mostly populated
at ring-closed L1c. The LUMO+1 is mostly populated at L2o,
which is responsible for further ring closure.25 The low-energy
absorption of 1co results mainly from the π → π* (L1c) IL
state, mixed with minor 4d(Ru) → π* (L1c) MLCT character.
Similarly, both HOMO and LUMO for 1oc are mostly
distributed on L2c. The LUMO+1 responsible for further
ring-closure is populated on L1o. The electronic transition from
HOMO to LUMO is typical of the π → π* (L2c) IL state,
mixed with some 4d(Ru) → π* (L2c) MLCT character. For
1cc, the HOMOs are mainly contributed by two ring-closed
L1c and L2c, while the LUMO and LUMO+1 are mainly
localized on L1c and L2c, respectively. The calculated ring-
closure absorption at 691 nm (L1c) is featured with π → π*
(L1c) IL and π (L2c) → π* (L1c) LLCT transitions, mixed
with some 4d(Ru) → π*(L1c) MLCT state. Similarly, the
calculated ring-closure absorption at 531 nm is primarily
assigned to π → π* (L2c) IL and π (L1c) → π* (L2c) LLCT
states, mixed with a minor 4d(Ru) → π*(L2c) MLCT state.
The large separation of the two ring-closure absorption bands
at 691 nm (L1c) and 531 nm (L2c) implies that the mixed ring-
open/closed species 1co or 1oc could be obtained
experimentally through selective cycloreversion at L2c or L1c,
respectively. However, the calculated ring-closure absorption of
L2c at 531 nm (oscillator strength of 0.6422) is much weaker
than that of L1c at 691 nm (oscillator strength of 1.0125),
coinciding with the fact that a much smaller content of 1oc
than of 1co could be generated upon irradiation of 1oo under
UV light.
CONCLUSIONS
■
Two different dithienylethene-acetylides, L1o and L2o, that
display a large separation between their ring-closing absorption
peaks were utilized to construct an asymmetric ruthenium(II)
complex 1oo and two symmetric ones 2oo and 3oo. The
oxidized ruthenium(III) species 1oo+, 2oo+, and 3oo+ were also
accessible by the oxidation of RuII to RuIII. They display
distinctly stepwise photocyclization and selective photocyclor-
eversion upon irradiation with suitable wavelengths of light.
The one-electron oxidized RuIII species exhibit NIR absorption
and distinctly blue-shifted ring-closing absorption bands in the
visible region relative to the corresponding RuII ones. Complex
1 presents unique stimuli-responsive features, including (1)
multicolor, four different colors by using light as a trigger; (2)
multistate, eight interconvertible states through light or redox
stimulation; and (3) double addressing modes, via light
irradiation and a reversible redox process. It is concluded that
when the ring-closing absorption bands of two different DTE
moieties are well-separated, four states and four colors can be
achieved upon irradiation with different wavelengths of light.
This asymmetric ruthenium complex with two types of DTE
switches represents an eight-state system triggered simulta-
neously by optical and electrochemical stimuli. Such multistate
and multicolor photochromic switches have potential applica-
tions in photoswitchable full-color displays and multifrequency
of three-dimensional optical memory media.
For 2co and 3co, both the HOMO and LUMO are mostly
located at ring-closed L1c and L2c, respectively. Thus, the low-
energy absorption due to electron promotion from HOMO to
LUMO is typical of L1c and L2c centered states for 2co and
3co, respectively. The LUMO+1 populated primarily on L1o
for 2co and L2o for 3co is favorable for further photo-
cyclization. The calculated UV absorption bands at 303 nm for
2co and 329 nm for 3co indeed involve HOMO−3 → LUMO
EXPERIMENTAL SECTION
General Procedures and Materials. The operations were
performed by Schlenk techniques and vacuum-line systems under a
dry argon atmosphere. Solvents were dried (sodium/benzophenone
■
G
DOI: 10.1021/acs.inorgchem.7b02023
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
for THF and calcium hydride for dichloromethane) and distilled under
an argon atmosphere. cis-Ru(dppe)2Cl2,37 2,5-dibromo-3-methylthio-
phene,38 3-bromo-2-methyl-5-thienyl boronic acid,39 and ((4-
(3,3,4,4,5,5-hexafluorocyclopent-1-en-1-yl)-5-methylthiophen-2-yl)-
ethynyl)trimethylsilane40 were prepared by procedures described in
the literature. Other chemicals were commercially purchased and used
as received.
yellow solid. Yield: 40% (425 mg). 1H NMR (CDCl3, ppm): δ 8.71 (d,
J = 4.92 Hz, 2H), 8.00 (s, 1H), 7.26 (s, 1H), 7.15 (t, J = 4.88 Hz, 1H),
1.99 (s, 3H), 1.93 (s, 3H), 0.27 (s, 9H). 13C NMR (CDCl3, ppm): δ
160.6, 157.3, 146.3, 143.3, 141.1, 132.1, 128.4, 126.0, 124.7, 121.7,
118.9, 99.9, 96.2, 14.9 (CH3), 14.5 (CH3), −0.2 (SiCH3). HRMS
(ESI) m/z calcd for [C24H21F6N2S2Si ]+: 543.0820 [M + H]+. Found:
543.0814. IR (KBr): 2146 cm−1 (CC).
2-(5-Bromo-4-methylthiophen-2-yl)-4,4,5,5-tetramethyl-
1,3,2-dioxaborolane. A dried 250 mL two-neck flask was charged
with 2,5-dibromo-3-methylthiophene (5.2 g, 20 mmol) and dry THF
(100 mL) at −78 °C under an argon atmosphere. The mixture was
stirred at −78 °C for 1 h after n-BuLi (8.8 mL, 22 mmol, 2.5 M) was
dropwise added. Then, the isopropoxyboronic acid pinacol ester (5.3
mL, 26 mmol) was added dropwise and the mixture stirred for 2 h.
After the temperature rose to room temperature, the mixture was
stirred overnight. Then, the mixture was quenched by the addition of a
saturated aqueous solution of NH4Cl (50 mL) and extracted with ethyl
acetate three times. The combined extracts were dried over MgSO4.
The crude product was purified with silica-gel column chromatography
using ethyl acetate as an eluent to afford the compound (4.3 g, 70%) as
a yellow oil. 1H NMR (CDCl3, ppm): δ 7.32 (s, 1H, CH), 2.22 (s, 3H,
CH3), 1.34 (s, 12H, 2-OC(CH3)2). 13C NMR (CDCl3, ppm): δ 139.1,
138.6, 116.9, 84.2, 24.7, 14.9. HRMS (ESI) m/z calcd for
[C11H16BBrO2SNa]+: 326.9981 [M + Na]+. Found: 326.9629.
2-(2-Pyrimidyl)-4-bromo-5-methylthiophene. 2-Bromopyrimi-
dine (2.29 g, 14.4 mol), 2-(4-bromo-5-methylthiophen-2-yl)-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane (3.97 g, 13.1 mol), and tetrakis-
(triphenylphosphine)palladium(0) (0.76 g, 0.66 mmol) were dissolved
in THF (100 mL) with stirring for 15 min. An aqueous (50 mL)
solution of sodium carbonate (12.5 g, 118 mmol) was then added. The
mixture was refluxed with vigorous stirring for 8 h. The reaction
process was monitored by TLC. The product was extracted with ethyl
acetate three times. The combined extracts was dried with MgSO4 and
then concentrated. The residue was purified by silica gel column
chromatography using dichloromethane−petroleum (1:1, v/v) as an
eluent. Yield: 81% (2.7 g). 1H NMR (CDCl3, ppm): δ 8.67 (d, J = 4.88
Hz, 2H), 7.81 (s, 1H), 7.09 (t, J = 4.88 Hz, 1H), 2.46 (s, 3H). 13C
NMR (CDCl3, ppm): δ 160.5, 157.2, 139.5, 139.4, 131.5, 118.6, 110.6,
15.3 (CH3). HRMS (ESI) m/z calcd for [C9H8BrN2S] +: 256.9492 [M
+ H]+. Found: 256.9565.
2-Benzyl-5-bromo-4-methylthiophene. Benzyl chloride (1.30
mL, 11.3 mol), 2-(4-bromo-5-methylthiophen-2-yl)-4,4,5,5-tetrameth-
yl-1,3,2-dioxaborolane (3.12 g, 10.3 mol), and tetrakis-
(triphenylphosphine)palladium(0) (0.60 g, 0.52 mmol) were added
to DME (80 mL) with stirring for 15 min. An aqueous (30 mL)
solution of sodium carbonate (7.5 g, 71 mmol) was then added. The
mixture was refluxed with stirring overnight. The reaction process was
monitored by TLC. The product was extracted with ethyl acetate three
times. The combined organic was dried with Na2SO4 and
concentrated. The product was purified by chromatography on a
silica gel column using petroleum as an eluent. Yield: 59% (1.6 g). 1H
NMR (CDCl3, ppm): δ 7.30−7.21 (m, 5H), 6.46 (s, 1H), 3.99 (s,
2H), 2.09 (s, 3H). 13C NMR (CDCl3, ppm): δ 143.6, 139.6, 136.9,
128.7, 128.6, 127.2, 126.7, 106.9, 36.4 (PhCH2), 15.2 (CH3). HRMS
(ESI) m/z calcd for [C12H12BrS ]+: 268.9743 [M + H]+. Found:
268.9802.
1-(5-Methyl-2-(2-pyrimidyl)-4-thienyl)-2-(2-meth-yl-5-ethyn-
yl-3-thienyl)perfluorocyclo-pentene (L1o). To a THF-methanol
(30 mL, v/v = 1:1) solution of 1-(5-methyl-2-(2-pyrimidyl)-4-thienyl)-
2-(2-methyl-5-trimethylsilylethynyl-3-thienyl)perfluorocyclopentene
(550 mg, 1.01 mmol) was added an excess of anhydrous potassium
carbonate, and the mixture was stirred overnight. Upon removal of the
solvent, the residue was dissolved in dichloromethane (30 mL). The
product was purified by chromatography on a silica gel column using
dichloromethane-petroleum ether (v/v = 1:1) as an eluent to afford to
the product as a yellow solid. Yield: 90% (428 mg). 1H NMR (CDCl3,
ppm): δ 8.71 (d, J = 4.92 Hz, 2H), 7.99 (s, 1H), 7.27 (s, 1H), 7.13 (t, J
= 5.12 Hz, 1H), 3.35 (s, 1H), 1.96 (s, 3H), 1.93 (s, 3H). 13C NMR
(CDCl3, ppm): δ 160.6, 157.3, 146.3, 143.7, 141.2, 132.7, 128.4, 125.9,
124.7, 120.5, 118.9, 82.2, 75.8, 14.9 (CH3), 14.5 (CH3). HRMS (ESI)
m/z calcd for [C21H13F6N2S2]+: 471.0424 [M + H]+. Found:
471.0421. IR (KBr): 2106 cm−1 (CC).
1-(5-Methyl-2-benzyl-4-thienyl)-2-(2-methyl-5-trimethylsily-
lethynyl-3-thienyl)perfluoro-cyclopentene. To a dry THF (40
mL) solution of 2-benzyl-4-bromo-5-methylthiophene (570 mg, 2.13
mmol) at −78 °C was added slowly n-butyllithium (1.6 M in hexane,
1.4 mL, 2.3 mmol). Upon stirring at −78 °C for 1 h, to the above
solution was then added a dry THF (5 mL) solution of ((4-
(3,3,4,4,5,5-hexafluorocyclopent-1-en-1-yl)-5-methylthiophen-2-yl)-
ethynyl)trimethyl-silane (823 mg, 2.13 mmol). The reaction mixture
was stirred at −78 °C for 2 h and put aside at room temperature
overnight before being quenched by the addition of an aqueous
hydrochloric acid solution. The product was extracted with ethyl
acetate and dried with Na2SO4 and then purified by chromatography
on a silica gel column using dichloromethane−petroleum ether (v/v =
1:4) as an eluent. The product was isolated as a yellow solid. Yield:
1
53% (625 mg). H NMR (CDCl3, ppm): δ 7.34−7.20 (m, 5H), 7.19
(s, 1H), 6.51 (s, 1H), 4.06 (s, 2H), 1.88 (s, 3H), 1.67 (s, 3H), 0.25 (s,
9H). 13C NMR (CDCl3, ppm): δ 148.5, 143.4, 141.2, 139.1, 132.5,
129.2, 128.7, 128.6, 126.9, 125.1, 121.4, 121.1, 99.7, 96.4, 36.1
(PhCH2), 15.5 (CH3), 14.2 (CH3), −0.2 (SiCH3). HRMS (ESI) m/z
calcd for [C27H24F6S2SiNa ]+: 577.0891 [M + Na]+. Found: 577.0883.
IR (KBr): 2153 cm−1 (CC).
1-(5-Methyl-2-benzyl-4-thienyl)-2-(2-methyl-5-ethynyl-3-
thienyl)perfluorocyclopentene (L2o). An excess of anhydrous
potassium carbonate was added to a THF−methanol (30 mL, v/v =
1:1) solution of 1-(5-methyl-2-benzyl-4-thienyl)-2-(2-methyl-5-trime-
thylsilylethynyl-3-thienyl)perfluorocyclopentene (571 mg, 1.03
mmol). The mixture was stirred at ambient temperature overnight.
The product was purified by chromatography on a silica gel column
using dichloromethane−petroleum ether (v/v = 1:3) as an eluent to
1
afford the product as a yellow solid. Yield: 92% (457 mg). H NMR
(CDCl3, ppm): δ 7.34−7.22 (m, 5H), 7.20 (s, 1H), 6.52 (s, 1H), 4.06
(s, 2H), 3.33 (s, 1H), 1.90 (s, 3H), 1.67 (s, 3H). 13C NMR (CDCl3,
ppm): δ 148.7, 143.7, 141.3, 139.1, 133.1, 129.2, 128.7, 128.6, 126.9,
125.1, 121.1, 120.2, 82.0, 75.9, 36.1 (PhCH2), 15.4 (CH3), 14.3 (CH3).
HRMS (ESI) m/z calcd for [C24H16F6S2Na ]+: 505.0495 [M + Na]+.
Found: 505.0490. IR (KBr): 2108 cm−1 (CC).
1-(5-Methyl-2-(2-pyrimidyl)-4-thienyl)-2-(2-meth-yl-5-trime-
thylsilylethynyl-3-thienyl)- perfluorocyclopentene. To a dry
THF (40 mL) solution of 2-(2-pyrimidyl)-4-bromo-5-methylthio-
phene (500 mg, 1.96 mmol) at −78 °C was added dropwise n-
butyllithium (1.6 M in hexane, 1.2 mL, 1.9 mmol) with stirring for 1 h.
A dry THF (5 mL) solution of 2-(5-(4-trimethylsilylethynyl)-2-
methylthiophen-3-yl)perfluorocyclopentene (757 mg, 1.96 mmol) was
then added to the above solution. The reaction mixture was stirred at
−78 °C for another 2 h and then put aside at room temperature
overnight before being quenched by the addition of an aqueous
NH4Cl solution. The product was extracted with ethyl acetate and
dried with MgSO4 and then concentrated. The product was purified
through silica gel column chromatography using dichloromethane-
petroleum ether (v/v = 1:2) as an eluent to afford the product as a
cis-Ru(dppe)2(L1o)Cl. cis-Ru(dppe)2Cl2 (137 mg, 0.142 mmol)
and L1o (80 mg, 0.17 mmol) were dissolved in CH2Cl2 (15 mL).
Upon the addition of NaPF6 (29 mg, 0.17 mmol), the solution was
stirred at room temperature for 12 h and then concentrated to 2 mL.
To the solution was added 40 mL of anhydrous diethyl ether, which
produced a precipitate. Upon filtration, the solid was dissolved in 30
mL of CH2Cl2, followed by the addition of NEt3 (1 mL). When the
solution was stirred for 30 min, the solvent was removed under a
vacuum. The residue was chromatographed over a short alumina
column using CH2Cl2 as an eluent. The product was recrystallized
from dichloromethane−hexane to give a yellow solid. Yield: 56% (111
H
DOI: 10.1021/acs.inorgchem.7b02023
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
1
mg). H NMR (CDCl3, ppm): δ 8.71 (d, J = 4.88 Hz, 2H), 8.06 (s,
ACKNOWLEDGMENTS
■
1H), 7.46−6.94 (m, 40H), 7.13 (t, J = 4.90 Hz, 1H), 6.06 (s, 1H), 2.66
(s, 8H), 1.94 (s, 3H), 1.79 (s, 3H). 31P NMR (CDCl3, ppm): δ 48.9.
HRMS (ESI) m/z calcd for [C73H59F6N2P4RuS2]+: 1367.1950 [M−
Cl]+. Found: 1367.2034. IR (KBr): 2056 cm−1 (CC).
We are grateful for financial support from the NSF of China
(21502193, U1405252, 21531008, 21390392, and 21473201),
the 973 project from MSTC (2014CB845603), the CAS/
SAFEA International Partnership Program for Creative
Research Teams, and the Strategic Priority Research Program
of the Chinese Academy of Sciences (XDB20000000).
1oo. To a dichloromethane (20 mL) solution of cis-Ru-
(dppe)2(L1o)Cl (100 mg, 0.071 mmol) and L2o (41.0 mg, 0.085
mmol) were added NaPF6 (14.3 mg, 0.085 mmol) and triethylamine
(1 mL). The reaction mixture was stirred in the dark at ambient
temperature for 1 day. The reaction was monitored by TLC. The
solution was concentrated and chromatographed on a short alumina
column using dichloromethane as an eluent. The yellow-green product
was further purified through recrystallization by layering n-hexane onto
the dichloromethane solution. Yield: 55% (72 mg). 1H NMR (CDCl3,
ppm): δ 8.55 (s, 1H), 8.04 (d, J = 4.80 Hz, 2H), 7.66−6.90 (m, 45H),
6.73 (s, 1H), 6.64 (s, 1H), 6.17 (s, 1H), 6.03 (t, J = 4.80 Hz, 1H), 3.66
(s, 2H), 2.43 (s, 8H), 1.84 (s, 3H), 1.75 (s, 3H), 1.74 (s, 3H), 1.67 (s,
3H). 31P NMR (CDCl3, ppm): δ 53.2. 13C NMR (CD2Cl2, ppm): δ
160.6, 157.3, 146.3, 141.2, 136.0, 134.7, 133.7, 128.7, 128.6, 127.2,
127.1, 126.6, 123.7, 123.4, 118.9, 103.6 (CC), 30.6 (m, CH2P), 14.9
(CH3 ), 14. 3 (CH3 ). HRMS (ESI) m/z calcd for
[C97H74F12N2P4RuS4Na]+: 1871.2429 [M + Na]+. Found:
1871.2453. IR (KBr): 2050 cm−1 (CC).
REFERENCES
■
(1) Myles, A. J.; Branda, N. R. 1,2-Dithienylethene Photochromes
and Non-destructive Erasable Memory. Adv. Funct. Mater. 2002, 12,
167−173.
(2) Kume, S.; Nishihara, H. Photochrome-Coupled Metal Com-
plexes: Molecular Processing of Photon Stimuli. Dalton Trans. 2008,
252, 3260−3271.
(3) Hasegawa, Y.; Nakagawa, T.; Kawai, T. Recent Progress of
Luminescent Metal Complexes with Photochromic Units. Coord.
Chem. Rev. 2010, 254, 2643−2651.
(4) Copley, G.; Moore, T. A.; Moore, A. L.; Gust, D. Analog
Applications of Photochemical Switches. Adv. Mater. 2013, 25, 456−
461.
2oo. To a dichloromethane (20 mL) solution containing cis-
Ru(dppe)2Cl2 (93.9 mg, 0.097 mmol) and L1o (100 mg, 0.213 mmol)
were added NaPF6 (35.8 mg, 0.213 mmol) and triethylamine (1 mL).
The mixture was stirred at ambient temperature for 1 day, and the
reaction was monitored by TLC. The solution was filtrated and
concentrated, which was then chromatographed on a short alumina
column to give a pale green solid using dichloromethane as an eluent.
The product was further purified through recrystallization by layering
(5) Irie, M.; Fukaminato, T.; Matsuda, K.; Kobatake, S. Photo-
chromism of Diarylethene Molecules and Crystals: Memories,
Switches, and Actuators. Chem. Rev. 2014, 114, 12174−12277.
(6) Natali, M.; Giordani, S. Molecular Switches as Photocontrollable
‘‘Smart’’ Receptors. Chem. Soc. Rev. 2012, 41, 4010−4029.
(7) Herder, M.; Schmidt, B. M.; Grubert, L.; Patzel, M.; Schwarz, J.;
Hecht, S. Improving the Fatigue Resistance of Diarylethene Switches.
̈
1
n-hexane onto the dichloromethane solution. Yield: 50% (89 mg). H
J. Am. Chem. Soc. 2015, 137, 2738−2747.
NMR (CDCl3, ppm): δ 8.54 (s, 2H), 8.05 (d, J = 4.84 Hz, 4H), 7.57−
6.95 (m, 40H), 6.64 (s, 2H), 6.04 (t, J = 4.86 Hz, 2H), 2.43 (s, 8H),
1.85 (s, 6H), 1.74 (s, 6H). 31P NMR (CDCl3, ppm): δ 53.3. 13C NMR
(CDCl3, ppm): δ 147.7, 140.9, 139.3, 136.4, 135.9, 134.1, 129.6, 129.0,
128.8, 128.7, 128.6, 127.1, 126.8, 124.2, 121.9, 107.9 (CC), 36.2
(PhCH2), 31.4 (m, CH2P), 15.5 (CH3), 14.3 (CH3). HRMS (ESI) m/z
calcd for [C94H70F12N4P4RuS4Na]+: 1859.2178 [M + Na]+. Found:
1859.2201. IR (KBr): 2050 cm−1 (CC).
(8) Fredrich, S.; Gostl, R.; Herder, M.; Grubert, L.; Hecht, S.
̈
Switching Diarylethenes Reliably in Both Directions with Visible Light.
Angew. Chem., Int. Ed. 2016, 55, 1208−1212.
(9) Wu, M. W.; Wong, H. L.; Yam, V. W.-W. Photochromic
Benzo[b]phosphole Oxide with Excellent Thermal Irreversibility and
Fatigue Resistance in the Thin Film Solid State via Direct Attachment
of Dithienyl Units to the Weakly Aromatic Heterocycle. Chem. Sci.
2017, 8, 1309−1315.
3oo. This compound was prepared by the same synthetic procedure
as that of 2oo except for the use of L2o in place of L1o. Yield: 52% (91
(10) Chen, H.; Cheng, N.; Ma, W.; Li, M.; Hu, S.; Gu, L.; Meng, S.;
Guo, X. Design of a Photoactive Hybrid Bilayer Dielectric for Flexible
Nonvolatile Organic Memory Transistors. ACS Nano 2016, 10, 436−
445.
(11) Irie, M. Diarylethenes for Memories and Switches. Chem. Rev.
2000, 100, 1685−1716.
(12) Tian, H.; Yang, S. J. Recent Progresses on Diarylethene based
Photochromic Switches. Chem. Soc. Rev. 2004, 33, 85−97.
(13) Tian, H.; Wang, S. Photochromic Bisthienylethene as Multi-
function Switches. Chem. Commun. 2007, 38, 781−792.
(14) Tian, H.; Feng, Y. Next Step of Photochromic Switches? J.
Mater. Chem. 2008, 18, 1617−1622.
(15) Kume, S.; Nishihara, H. Photochrome-coupled Metal
Complexes: Molecular Processing of Photon Stimuli. Dalton Trans.
2008, 3260−3271.
(16) Uchida, K.; Yamanoi, Y.; Yonezawa, T.; Nishihara, H. Reversible
On/Off Conductance Switching of Single Diarylethene Immobilized
on a Silicon Surface. J. Am. Chem. Soc. 2011, 133, 9239−9241.
(17) Ko, C.-C.; Wing-Wah Yam, V. Transition Metal Complexes with
Photochromic LigandsPhotosensitization and Photoswitchable
Properties. J. Mater. Chem. 2010, 20, 2063−2070.
1
mg). H NMR (CDCl3, ppm): δ 7.62−6.99 (m, 50H), 6.89 (s, 2H),
6.25 (s, 2H), 3.73 (s, 4H), 2.48 (s, 8H), 1.97 (s, 6H), 1.83 (s, 6H). 31P
NMR (CDCl3, ppm): δ 53.2. 13C NMR (C6D6, ppm): δ 160.8, 156.7,
148.1, 146.4, 141.6, 141.0, 139.2, 134.7, 133.0, 130.5, 130.2, 130.1,
129.1, 129.0, 128.9, 127.2, 126.8, 126.7, 124.6, 124.5, 124.3, 124.1,
122.1, 118.2, 108.1 (CC), 37.2 (PhCH2), 31.4 (m, CH2P), 15.3
(CH3), 14.6 (CH3), 14.3 (CH3), 14.1 (CH3). Yield: 52% (91 mg).
HRMS (ESI) m/z calcd for [C100H78F12P4RuS4Na]+: 1883.2681 [M +
Na]+. Found: 1883.2706. IR (KBr): 2050 cm−1 (CC).
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b02023.
■
S
Tables and figures giving additional spectroscopic,
computational, and electroluminescent data (PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail: czn@fjirsm.ac.cn.
ORCID
Zhong-Ning Chen: 0000-0003-3589-3745
Notes
The authors declare no competing financial interest.
(18) Akita, M. Photochromic Organometallics, A Stimuli-Responsive
System: An Approach to Smart Chemical Systems. Organometallics
2011, 30, 43−51.
(19) Browne, W. R. Photochemistry of Immobilized Photoactive
Compounds. Coord. Chem. Rev. 2008, 252, 2470−2479.
(20) Klajn, R.; Stoddart, J. F.; Grzybowski, B. A. Nanoparticles
Functionalised with Reversible Molecular and Supramolecular
Switches. Chem. Soc. Rev. 2010, 39, 2203−2237.
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DOI: 10.1021/acs.inorgchem.7b02023
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(21) Gust, D.; Andrea
Data and Signal Processing Using Photochromic Molecules. Chem.
Commun. 2012, 48, 1947−1957.
(22) Fihey, A.; Perrier, A.; Browne, W. R.; Jacquemin, D.
Multiphotochromic Molecular Systems. Chem. Soc. Rev. 2015, 44,
3719−3759.
(23) Guerchais, V.; Ordronneau, L.; Le Bozec, H. Recent
Developments in the Field of Metal Complexes Containing Photo-
chromic Ligands: Modulation of Linear and Nonlinear Optical
Properties. Coord. Chem. Rev. 2010, 254, 2533−2545.
́
sson, J.; Pischel, U.; Moore, T. A.; Moore, A. L.
phene) Bearing Disiloxane Moiety in the Substituent. Remarkably
High Solubility in Hexane. Chem. Lett. 2014, 43, 640−642.
(39) Pu, S.; Fan, C.; Miao, W.; Liu, G. The Effect of Substituent
Position upon Unsymmetrical Isomeric Diarylethenes Bearing a
Methoxy Group. Dyes Pigm. 2010, 84, 25−35.
(40) Liu, Y.; Lagrost, C.; Costuas, K.; Tchouar, N.; Le Bozec, H.;
Rigaut, S. A Multifunctional Organometallic Switch with Carbon-Rich
Ruthenium and Diarylethene Units. Chem. Commun. 2008, 6117−
6119.
(24) Zhang, D.; Fan, C.; Zheng, C.; Pu, S. A new Dithienylethene
Dimer with Terminal Tertiary Amine Redox Centers: Electrochemical,
UV-vis-NIR Spectral and Electronic Transfer Charges induced by a
Stepwise Photochromic Process. Dyes Pigm. 2017, 136, 669−677.
(25) (a) Perrier, A.; Maurel, F.; Jacquemin, D. Single Molecule
Multiphotochromism with Diarylethenes. Acc. Chem. Res. 2012, 45,
1173−1182. (b) Arnaud, F.; Denis, J. How Metals Can Help
Multiphotochromism: An Ab Initio Study. J. Phys. Chem. C 2016,
120, 11140−11150.
(26) (a) Hervault, Y.-M.; Ndiaye, C. M.; Norel, L.; Lagrost, C.;
Rigaut, S. Controlling the Stepwise Closing of Identical DTE
Photochromic Units with Electrochemical and Optical Stimuli. Org.
Lett. 2012, 14, 4454−4457.
(27) Roberts, M. N.; Carling, C.-J.; Nagle, J. K.; Branda, N. R.; Wolf,
M. O. Successful Bifunctional Photoswitching and Electronic
Communication of Two Platinum(II) Acetylide Bridged Dithienyle-
thenes. J. Am. Chem. Soc. 2009, 131, 16644−16645.
̀
(28) Zhong, Y.-W.; Vila, N.; Henderson, J. C.; Abruna, H. D.
̃
Transition-Metal Tris-Bipyridines Containing Three Dithienylcyclo-
pentenes: Synthesis, Photochromic, and Electrochromic Properties.
Inorg. Chem. 2009, 48, 7080−7085.
(29) (a) Li, B.; Wu, Y.-H.; Wen, H.-M.; Shi, L.-X.; Chen, Z.-N.
Gold(I)-Coordination Triggered Multistep and Multiple Photo-
chromic Reactions in Multi-Dithienylethene (DTE) Systems. Inorg.
Chem. 2012, 51, 1933−1942. (b) Li, B.; Wen, H.-M.; Wang, J.-Y.; Shi,
L.-X.; Chen, Z.-N. Modulating Stepwise Photochromism in Platinum-
(II) Complexes with Dual Dithienylethene-Acetylides by a Progressive
Red Shift of Ring-Closure Absorption. Inorg. Chem. 2013, 52, 12511−
12520.
(30) Li, B.; Wang, J.-Y.; Wen, H.-M.; Shi, L.-X.; Chen, Z.-N. Redox-
Modulated Stepwise Photochromism in a Ruthenium Complex with
Dual Dithienylethene-Acetylides. J. Am. Chem. Soc. 2012, 134, 16059−
16067.
(31) Xu, G.-T.; Li, B.; Wang, J.-Y.; Zhang, D.-B.; Chen, Z.-N.
Regulation of Charge Delocalization in a Heteronuclear Fe2Ru System
by a Stepwise Photochromic Process. Chem. - Eur. J. 2015, 21, 3318−
3326.
(32) Zhang, D.-B.; Wang, J.-Y.; Jacquemin, D.; Chen, Z.-N.
Spectroscopic and Electrochemical Properties of Ruthenium Com-
plexes with Photochromic Triarylamine-Dithienylethene-Acetylide
Ligands. Inorg. Chem. Front. 2016, 3, 1432−1443.
(33) Higashiguchi, K.; Matsuda, K.; Irie, M. Photochromic Reaction
of a Fused Dithienylethene: Multicolor Photochromism. Angew. Chem.,
Int. Ed. 2003, 42, 3537−3540.
(34) Higashiguchi, K.; Matsuda, K.; Tanifuji, N.; Irie, M. Full-Color
Photochromism of a Fused Dithienylethene Trimer. J. Am. Chem. Soc.
2005, 127, 8922−8923.
(35) Li, B.; Wen, H.-M.; Wang, J.-Y.; Shi, L.-X.; Chen, Z.-N.
Multistate and Multicolor Photochromism through Selective Cyclo-
reversion in Asymmetric Platinum(II) Complexes with Two Different
Dithienylethene-Acetylides. Inorg. Chem. 2015, 54, 11511−11519.
(36) Uchida, K.; Irie, M. A Photochromic Dithienylethene That
Turns Yellow by UV Irradiation. Chem. Lett. 1995, 24, 969−970.
(37) Chaudret, B.; Commenges, G.; Poilblanc, R. Bis-
(dipheny1phosphino)methane Complexes of Ruthenium(o) and
Ruthenium(II). J. Chem. Soc., Dalton Trans. 1984, 1635−1639.
(38) Mori, A.; Ide, K.; Tamba, S.; Tsuji, S.; Toyomori, Y.; Yasuda, T.
Synthesis and Properties of Regioregular Poly(3-substituted thio-
J
DOI: 10.1021/acs.inorgchem.7b02023
Inorg. Chem. XXXX, XXX, XXX−XXX