Photochromic metal complexes: Photoregulation of both the nonlinear optical and luminescent properties

Article abstract of DOI:10.1021/ic2025457

A series of dithienylethene (DTE)-containing 2,2′-bipyridine ligands and their zinc(II) diacetate, zinc(II) dichloro, rhenium(I) tricarbonyl bromo, and ruthenium(II) bis(bipyridine) complexes have been designed and synthesized, and their photochromic, photophysical, and quadratic nonlinear optical properties have been studied. Upon UV irradiation at 350 nm, the ligands and complexes undergo ring closure of the DTE units, with a good to excellent photocyclization yield. In the case of the Re(I) and Ru(II) complexes, the photocyclization of the DTE units can also be triggered using visible light, upon excitation into the metal-to-ligand charge-transfer (MLCT) bands at 400 and 490 nm, respectively. Molecular quadratic nonlinear optical (NLO) responses of the complexes have been determined by using either the electrical field induced second harmonic generation (EFISH) or harmonic light scattering (HLS) technique at 1910 nm. These studies reveal a large increase of the second-order NLO activity after UV irradiation and subsequent formation of the ring-closed isomers. This efficient enhancement clearly reflects the delocalization of the -electron system and the formation of strong push-pull chromophores in the closed forms. The combination of the photochromic DTE-based bipyridine ligand with luminescent Re(I) and Ru(II) fragments also allows the photoregulation of the emission, leading to an efficient quenching of the ligand-based 77 K luminescence and demonstrating that the photocontrol of two optical properties, linear and nonlinear, could be achieved by using the same photochromic ligand.

Full text of DOI:10.1021/ic2025457

Article
pubs.acs.org/IC
Photochromic Metal Complexes: Photoregulation of both the
Nonlinear Optical and Luminescent Properties
Lucie Ordronneau,† Hiroyuki Nitadori,‡ Isabelle Ledoux,§ Anu Singh,§ J. A. Gareth Williams,∥
Munetaka Akita,‡ Veronique Guerchais,*,† and Hubert Le Bozec*,†
́
†UMR CNRS 6226-Universite
́
de Rennes 1, Sciences Chimiques de Rennes, Campus de Beaulieu, 35042 Rennes Cedex, France,
‡Chemical Resources Laboratory, Tokyo Institute of Technology, R1-27, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
§Laboratoire de Photonique Quantique et Molec
ulaire, UMR CNRS 8531, Institut d’Alembert, ENS Cachan, 61 avenue du President
Wilson, 94235 Cachan, France
́
́
∥Department of Chemistry, Durham University, South Road, Durham, DH1 3LE, United Kingdom
ABSTRACT: A series of dithienylethene (DTE)-containing
2,2′-bipyridine ligands and their zinc(II) diacetate, zinc(II)
dichloro, rhenium(I) tricarbonyl bromo, and ruthenium(II)
bis(bipyridine) complexes have been designed and synthe-
sized, and their photochromic, photophysical, and quadratic
nonlinear optical properties have been studied. Upon UV
irradiation at 350 nm, the ligands and complexes undergo ring
closure of the DTE units, with a good to excellent
photocyclization yield. In the case of the Re(I) and Ru(II)
complexes, the photocyclization of the DTE units can also be
triggered using visible light, upon excitation into the metal-to-
ligand charge-transfer (MLCT) bands at 400 and 490 nm,
respectively. Molecular quadratic nonlinear optical (NLO) responses of the complexes have been determined by using either the
electrical field induced second harmonic generation (EFISH) or harmonic light scattering (HLS) technique at 1910 nm. These
studies reveal a large increase of the second-order NLO activity after UV irradiation and subsequent formation of the ring-closed
isomers. This efficient enhancement clearly reflects the delocalization of the π-electron system and the formation of strong push−
pull chromophores in the closed forms. The combination of the photochromic DTE-based bipyridine ligand with luminescent
Re(I) and Ru(II) fragments also allows the photoregulation of the emission, leading to an efficient quenching of the ligand-based
77 K luminescence and demonstrating that the photocontrol of two optical properties, linear and nonlinear, could be achieved by
using the same photochromic ligand.
the design of metal-based photoswitchable molecules.8 For
INTRODUCTION
■
example, versatile diarylethene-containing polyimine ligands
and their transition-metal complexes9−15 have been synthesized
and their photochromic behavior has been widely exploited for
the photomodulation of luminescence and electronic proper-
ties.
We have been involved for several years in the use of 4,4′-
disubstituted-2,2′-bipyridines as precursors to dipolar and
octupolar metal complexes for nonlinear optics.16,17 In order
to carry out the photoswitching of the NLO properties, we
recently prepared a new type of 4,4′-bis(ethenyl)-2,2′-bipyridine
The ability to switch on and off the NLO activity of a molecule
is of relevance to the development of molecular photonic
devices, where switching can be achieved by modifying one of
the component parts of the molecule.1,2 Since π-conjugated
connections between donor and acceptor end groups are a
central requirement for obtaining large quadratic nonlinearities,
one strategy to achieve an efficient switching effect concerns the
alteration of the π bridge in response to an external trigger such
as light. In this category, photochromic compounds are
promising candidates for the design of photoswitchable NLO
materials.3−6 Diarylethene (DTE) derivatives are widely used as
the photochromic units, and changes in the π-conjugated chain
of DTE derivatives can be successfully used to control donor−
acceptor interactions.7 Typically, the DTE unit undergoes
reversible interconversion between a nonconjugated open form
and a π-conjugated closed form when irradiated in the UV and
visible spectral ranges, respectively. Recently, the combination
of transition metals and ligands featuring diarylethene units has
received much attention and opened up new perspectives for
ligand functionalized by
a 4-(dimethylamino)-
phenyldithienylethene (DTE) group and the corresponding
zinc bis(acetate) complex (Scheme 1).18 The excellent
photochromic property of this complex was exploited to design
the first example of metal-containing photochromic ligands
allowing an efficient switching of the quadratic NLO properties.
Received: November 24, 2011
Published: April 30, 2012
© 2012 American Chemical Society
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Scheme 1
Scheme 2. Stepwise Synthesis of Photochromic Bipyridyl Ligands
In contrast, by complexation of the same photochromic
bipyridine ligand to the luminescent bis-cyclometalated Ir(III)
center, an efficient photoregulation of the emission was found,
whereas no significant modification of the quadratic NLO
response could be observed accompanying photocyclization,19
due to the weaker contribution of the ILCT vs MLCT
transitions to the quadratic hyperpolarizability. These observa-
tions prompted us to extend our study to another series of
chromophores combining DTE-based bipyridines La,b (a,
NMe2; b, NBu2) with different metallic fragments, namely
the stronger Lewis acid ZnCl2 as well as the Ru(bipy)2 and
Re(CO)3Br moieties, known for their luminescent properties.
2+
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Figure 1. Chemical structures of photochromic bipyridine Zn(II), Re(I), and Ru(II) complexes.
In particular, it was appealing to study the role of the metal
center on the photochromic and NLO activity and, in addition,
to investigate the photoregulation of the emission properties of
the resulting system, as the use of a single photochromic metal
complex for photocontrol of both NLO and luminescence
properties, which could be of interest for the elaboration of
multifunctional molecular materials and hence for optical data
storage, has not been reported yet.15 We describe herein the
synthesis, photochromic, and luminescence properties of these
complexes, together with the quadratic hyperpolarizability of
the open and photocyclized forms, measured by the EFISH and
HLS techniques.
Finally, treatment of diethylphosphonatomethyl-2,2′-bipyri-
dine17d with aldehydes 7a,b under normal Wadsworth-Emmons
conditions afforded the target bipyridine ligands La,b(o) in 55−
60% yield after purification by recrystallization.
1
La,b(o) were characterized by H and 13C NMR, UV−visible
spectroscopy, and high-resolution mass spectrometry and gave
1
satisfactory elemental analysis. The H NMR spectra display
classical chemical shifts for the vinyl-bipyridine protons with a
3JH−H vinylic coupling constant of ca. 16 Hz typical for an E
configuration about the double bond. The DTE moieties
exhibit two very close resonance signals for the methyl protons
at ca. 2 ppm and two singlets for the methine protons of the
thiophene rings, as expected for the asymmetrical nature of this
fragment. Ligands La,b(o) show good transparencies in the
visible region, whatever the nature of the R group: the UV−
visible spectra in dichloromethane show an intense absorption
at 340−350 nm which is tentatively assigned to (IL) π → π*
transitions of the bipyridyl moieties with some mixing of the
DTE units.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Ligands and
Complexes. The synthesis of the target bipyridines La,b(o)
was performed according to Scheme 2. The aryl-substituted
DTE aldehydes 7a,b were first obtained by a multistep
procedure: the two thienyl fragments were prepared
independently and then successively connected to the
perfluorocyclopentene ring. The 3-bromo-2-methyl-5-aryl
thiophene compounds 3a,b were prepared in 75−98% yield
by the Suzuki coupling of 1 with the commercially available
arylboronic acids 2a,b. The second thienyl derivative 4,3
bearing a protecting dimethylacetal group, was reacted with
octafluorocyclopentene (C5F8) using a commonly used
procedure to afford 5 in 70% yield. Due to partial deprotection
of the carbonyl group during the chromatographic workup, the
characterization of this synthon was made on the correspond-
ing fully deprotected compound 6. Reaction of 3a,b with 5 in
the presence of n-butyllithium afforded, after subsequent
treatment with p-toluenesulfonic acid (PTSA) in wet
tetrahydrofuran, the desired aldehydes 7a,b in 50−55% yield.
The corresponding Zn(II) complexes (La(o))Zn(OAc)2 and
(La,b(o))ZnCl2 (Figure 1) were readily obtained after room-
temperature treatment of La,b(o) with 1 equiv of zinc diacetate
dihydrate or zinc dichloride in dichloromethane. Reaction of
La(o) with Re(CO)5Br in refluxing anhydrous toluene afforded
fac-(La(o))Re(CO)3Br as brown crystals in 82% yield. The
ruthenium complex [(La(o))(dmbipy)2Ru](PF6)2 (dmbipy =
4,4′-dimethyl-2,2′-bipyridine) was obtained in 60% yield from
the corresponding cis-(dmbipy)2RuCl2 upon treatment first
with 2 equiv of silver triflate in methanol and then reaction with
ligand La(o) in dichloromethane at room temperature, followed
by anion exchange from triflate with hexafluorophosphate. The
complexes (La(o))Zn(OAc)2, (Lb(o))ZnCl2, (La(o))Re-
(CO)3Br, and [(La(o))(dmbipy)2Ru](PF6)2 are soluble in
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chlorinated solvents (CH2Cl2, CHCl3) and were fully
whereas the rhenium complex shows a moderately intense
absorption shoulder at ca. 410 nm which can be assigned as the
dπ(Re) → π*(bipy) transition.
1
characterized by means of H and 13C NMR and UV−visible
spectroscopy and gave satisfactory microanalyses (see the
Experimental Section). Conversely, the very low solubility of
(La(o))ZnCl2, bearing the dimethylamino end group, pre-
vented its complete spectroscopic characterization or further
photochromic and NLO studies. In all cases, that the E
configuration of the double bond is retained upon complex-
ation of the ligand is clearly established on the basis of the large
olefinic protons coupling constant (3JH−H ≈ 16 Hz), showing
that there is no isomerization of the CC linker.
Photochromic Properties of Ligands and Complexes.
For each ligand and complex, the photocyclization process was
monitored by 1H NMR and UV−vis spectroscopy in
dichloromethane. We have already described the photochromic
behavior of ligand La and its zinc diacetato complex,18,20 which
undergo ring closure of both DTE units. Similarly, upon
irradiation at 350 nm, the yellow solutions of Lb(o) and
(Lb(o))ZnCl2 turn green, with the emergence of a new broad
bands at 679 and 714 nm, respectively, attributed to the
intraligand (IL) S0 → S1 transition of the closed DTE form.
The UV−visible spectra of the zinc complexes (in CH2Cl2)
all show an intense band around 360 nm similar to that of the
ligands, which is slightly red-shifted by complexation (Table 1).
1
Their H NMR spectra show the characteristic downfield shift
of the methyl signals by ca. 0.2 ppm and an upfield shift by ca.
0.5−0.6 ppm of the two thiophene protons. According to H
1
Table 1. Electronic Absorption Data for Ligands and
Complexes in the Open and Closed (PSS) forms, Emission
Data in the Open Form, and Percentage Conversion at
Photostationary State
NMR analysis, integration of the methyl groups indicates a
photocyclization yield of 95% and 85% for Lb(o) and
(Lb(o))ZnCl2, respectively, showing that complexation to the
Zn(II) ion does not perturb the photochromic properties of Lb.
We only notice a much slower conversion rate for the zinc
complex as compared to the free ligand (the irradiation time,
under our experimental conditions, to achieve the PSS is 600 s
for La, 1500 s for (La)Zn(OAc)2, 1500 s for Lb, and 2500 s for
(Lb)ZnCl220). As shown in Table 1, the absorption maxima of
the closed-ring forms are dependent on the nature of the donor
groups and metallic fragments. Replacement of NMe2 with the
more strongly donating NBu2 end group induces a small red
shift (Δλ = 10 nm) of the IL band, and complexation to ZnCl2
induces a much larger bathochromic shift (Δλ= 35 nm) than
for Zn(OAc)2, in agreement with the higher Lewis acidity of
ZnCl2 vs Zn(OAc)2.
a
λabs/nm
closed
(PSS)
λem/nm
(τ/μs)
open
ring
b
λabs/nm (ε/M−1
closing/
a
c
compd
cm−1
)
open
%
d
La
La
348 (89 000)
346 (76 300)
360 (76 000)
351 (53 000)
347, 395,
438, 669
95
95
90
85
339, 400,
441, 679
d
(La)Zn(OAc)2
343, 394,
450, 687
(Lb)ZnCl2
342, 390
(sh), 463,
714
(La)Re(CO)3Br
340 (110 000),
380 (sh), 410
(sh)
336, 387,
443, 705
652, 725
(22)
65
62
[(La)(dmbipy)2Ru]
(PF6)2
338 (78 000), 377 336, 387,
(sh), 491 (27
000)
680, 753
(13)
Photocyclizations of (La(o))Re(CO)3Br and [(La(o))-
(dmbipy)2Ru](PF6)2 are also accomplished by irradiation
with UV light at 350 nm, giving rise to lower-energy
absorptions at 705 and 716 nm, respectively, corresponding
to the ring-closed isomers (Figure 2). Thus, a substantial
bathochromic shift of the IL band (Δλ = 36−47 nm) is also
observed upon complexation of La to the Re(I) and Ru(II)
organometallic fragments. The ratio of the methyl signals
between the closed and open DTE units (ring closing) in the
photostationary states (PSS) is lower (60−65%) than those
found for the zinc(II) complexes according to 1H NMR.21 It is
443 (sh),
716
a
b
At 298 K in CH2Cl2. At 77 K in diethyl ether/isopentane/ethanol
c
d
1
(2/2/1, v/v). Determined by H NMR spectroscopy. From ref 18.
The electronic absorption spectra of both the rhenium and
ruthenium complexes also show intense IL absorptions near
340 and 380 nm (shoulders). In addition, the ruthenium
complex displays another broad band in the visible at 490 nm
corresponding to MLCT dπ(Ru) → π*(bipy) transitions,
Figure 2. UV−vis absorption spectra changes of (a) [(La)(dmbipy)2Ru](PF6)2 and (b) (La)Re(CO)3Br in dichloromethane upon excitation at 350
nm.
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also interesting to note that the photochromic reaction can be
triggered by irradiation of the rhenium and ruthenium
complexes into the low-energy MLCT bands at 400 and 490
nm, respectively. This MLCT photosensitization has been
previously established for a cyclometalated iridium(III)
complex containing a similar DTE-based bipyridine ligand
forms, and as expected, the largest NLO enhancement is
observed with the complex featuring the harder ZnCl2 Lewis
acid associated with the better NBu2 donor group, in agreement
with the higher red shift of the intraligand (IL) transition which
dominates the second-order NLO response. This efficient on/
off switching markedly contrasts with the absence of switching
of the NLO response observed for the cyclometalated
phenylpyridine Ir(III) complex featuring the same photo-
chromic bipyridyl ligand La (Scheme 1), in which the EFISH
response was found to be mainly controlled by a MLCT/
L′LCT process from the cyclometalated phenylpyridine Ir(III)
moiety to the π* orbitals of the bipyridine, and not by an
intraligand transition.19
The harmonic light scattering (HLS) technique was also
used for the molecular first-hyperpolarizability β measurements
of the dicationic ruthenium complex and for comparison of the
neutral Re complex. Unlike EFISH, HLS can be used also for
ionic molecular species and for nondipolar molecules such as
octupolar molecules. The measurements were performed in
dichloromethane at a fundamental wavelength of 1.91 μm, and
the values of ⟨β1.91⟩ and static hyperpolarizabilities ⟨β0⟩25 are
given in Table 3. Much attention has been given to the large β
3
and suggests the intermediacy of the triplet state IL(DTE) in
the photocyclization process.10a Finally, for all ligands and
complexes, excitation at 650 nm, in the absorption band of the
closed forms, leads to the quantitative regeneration of the open
isomers, indicating the fully reversible closed-to-open photo-
isomerization.
Nonlinear Optical Properties. The second-order NLO
responses of the new, neutral, dipolar zinc and rhenium
complexes were determined in CH2Cl2 (concentration 10−3 M)
by the EFISH technique, working with an incident wavelength
of 1.91 μm. The EFISH μβ1.91 values, before and after UV
irradiation, are reported in Table 2, along with that previously
Table 2. EFISH μβ Values Determined at λinc 1910 nm of
Zn(II) and Re(I) Complexes in CH2Cl2
a
a
EFISH open
EFISH after UV irr
ring
Table 3. βHLS Values of Re(I) and Ru(II) in CH2Cl2
closing/
ab
,
ab
,
ac
,
ac
,
d
compd
μβ1.91
μβ0
μβ1.91
μβ0
%
HLS open
HLS after UV irr
e
(La)Zn(OAc)2
(Lb)ZnCl2
200
113
160
4220
3850
5650
2920
1800
1460
2143
1148
90
35
65
65
ring
closing/%
ab
,
ab
,
ab
,
ab
,
105
compd
⟨β1.91
⟩
⟨β0⟩
⟨β1.91
⟩
⟨β0⟩
c
d
(La)Re(CO)3Br
229
325
178
223
965
380
419
65
62
f
(La)Re(CO)3Br
240
187
c
d
[(La)Ru(dmbipy)2]
1113
a
b
c
d
In units of 10−48 esu. Error 20%. Error 5%. Determined by 1H
(PF6)2
e
f
a
b
c
In units of 10−30 esu. Error 15%. Calculated by using the two-
NMR spectroscopy. From ref 18. calculated by using the two-level
d
model and λMLCT value
level model and λMLCT values. Calculated by using the two-level
model and λIL(DTE) values.
reported18 for (La)Zn(OAc)2. The static μβ0 values extrapo-
lated at zero frequency were calculated by using the two-level
model.22 As evidenced in Table 2, the EFISH μβ1.91 values of
(Lb(o))ZnCl2 and (La(o))Re(CO)3Br are very weak and quite
similar to that of (La(o))Zn(OAc)2, as expected by the absence
of conjugation between the amino donor group and the
bipyridyl metal acceptor moieties. A dramatic increase of the
second-order NLO activity is observed after UV irradiation and
subsequent accumulation of the ring-closed isomers: in the case
of (Lb)ZnCl2 the second-order NLO response is increased
almost 14-fold after only 35% of ring closing, while a 21-fold
enhancement is observed after 65% of ring closing which
consists mainly of a mixture of open−closed and closed−closed
isomers in a ca. 2:1 ratio.23 Furthermore, it is also interesting to
note that this latter EFISH μβ0 value is even higher than that
previously reported for (La)Zn(OAc)2 in the PSS (90% of ring
closing), as expected from the higher Lewis acidity of ZnCl2 vs
Zn(OAc)2. A similar, but somewhat less dramatic, behavior is
observed for the rhenium(I) complex, with an increase of μβ0
from 187 × 10−48 to 1148 × 10−48 esu in the PSS (65% of ring
closing). The lower efficiency of the Re(I) complex in
comparison with that of the corresponding Zn(II) complexes
has already been shown in dipolar donor-substituted styryl
bipyridine metal chromophores24 and could be explained by the
presence of two vectorially opposed charge-transfer transitions
(MLCT and ILCT), which contribute to a lowering of the total
NLO response.
responses of bipyridine ruthenium chromophores, such as
octupolar D3 tris-chelate ruthenium complexes, which are
dominated by low-lying ILCT or MLCT excitations, depending
on the electron-donating or -accepting nature of the
substituents on the bipyridyl ligands.17,26 It turned out that
[(La)(dmbipy)2Ru](PF6)2 in its open form also shows a fairly
large ⟨β⟩ value, larger than that of the rhenium complex, which
can be reasonably attributed to low-energy MLCT dπ(Ru) →
π*(bipy) transitions. Upon photocyclization of the DTE, ⟨β0⟩
is found to increase by a factor of ca. 2, a result which is
consistent with an NLO response mainly controlled by the red-
shifted IL transition.
Luminescent Properties. None of the ligands and
complexes display detectable luminescence in solution at
room temperature when excited in the UV or visible bands.
This behavior contrasts with that of the DTE-free counterparts:
the free and Zn complexed 4-(dimethylamino)styrylbipyridine
ligands are emissive at room temperature in fluid solutions.17d
It is likely that the luminescence is inhibited by the competitive
photocyclization pathway of the DTE unit. The rate constant
for cyclization at room temperature will greatly exceed the
rather slow radiative rate constant of the triplet state (typically
around 105 s−1 for Ru and Re complexes). In frozen glasses
upon UV irradiation, we do not observe by UV−vis
spectroscopy any formation of closed-DTE species. As the
photocyclization is inhibited under these experimental con-
ditions, this allows the phosphorescence process to compete
effectively. At 77 K (EPA), only the rhenium and ruthenium
The large enhancement of μβ0 after ring closure clearly
reflects the delocalization of the π-electron system in the closed
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Figure 3. (left) Emission spectrum of [(La(o))(dmbipy)2Ru](PF6)2 at 77 K in diethyl ether/isopentane/ethanol (2/2/1 v/v) (blue line) upon
excitation into the lowest energy absorption band (490 nm) and the corresponding spectrum recorded for the photostationary state (red line).
(right) Corresponding spectra of (La(o))Re(CO)3Br and its PSS.
complexes emit, displaying structured luminescence spectra
with vibronic progressions of 1400−1500 cm−1, typical of
aromatic and/or CC bond vibrations. The emission
characteristics are summarized in Table 1, and the emission
spectra of (La(o))Re(CO)3Br and [(La(o))(dmbipy)2Ru]-
(PF6)2 and their PSS are shown in Figure 3. The long lifetimes
(22 and 13 μs for the Re and Ru complexes, respectively), low
energy, and structured spectra are indicative of emission from a
triplet state predominantly localized on the bpy−CC−Ar
moiety, rather than from the MLCT state.
EXPERIMENTAL SECTION
■
General Information. All manipulations were performed using
Schlenk techniques under an Ar atmosphere. All solvents were dried
and purified by standard procedures. Spectroscopic grade dichloro-
methane was used for all optical measurements. Compound 4 was
prepared according to a reported procedure, namely by bromination of
5-methyl-thiophene-2-carboxaldehyde, and was subsequently con-
verted into its dimethyl acetal 4-(OMe)2 for further use.3 NMR
spectra were recorded on Bruker DPX 200, AV 300, and AV 500 MHz
1
spectrometers. H and 13C chemical shifts are given versus SiMe4 and
were determined by reference to residual H and 13C solvent signals.
1
Following conversion of solutions of (La(o))Re(CO)3Br and
[(La(o))(dmbipy)2Ru](PF6)2 to the PSS at room temperature
and refreezing to 77 K, a substantial reduction of the 77 K
luminescence is observed (Figure 3). The quenching can be
attributed to intramolecular energy transfer from the triplet
emissive state to the IL state of the closed-ring DTE part of the
molecule: there is extensive overlap of the emission bands of
Attribution of carbon atoms was based on HMBC, HMQC, and
COSY experiments. High-resolution mass spectra (HRMS) were
performed on a MS/MS ZABSpec TOF at the CRMPO (Centre de
Mesures Physiques de l’Ouest) in Rennes. Elemental analyses were
performed at the CRMPO.
Optical Spectroscopy. UV−vis irradiations were performed either
with a Rayonet RPR 100 photochemical reactor equipped with 16
RPR 3500 Å lamps or with a LS series Light Source of ABET
Technologies, Inc. (150 W xenon lamp), with “350FS 10-25”, “450FS
20-25”, and “650FS 10-25” single-wavelength light filters. UV/vis
absorption spectra were recorded using a UVIKON 9413 or Biotek
Instruments XS spectrophotometer using quartz cuvettes of 1 cm path
length (spectroscopic grade dichloromethane was used for all optical
measurements). Steady-state luminescence spectra were measured
using a Jobin Yvon FluoroMax-2 spectrofluorimeter, fitted with a red-
sensitive Hamamatsu R928 photomultiplier tube. The spectra shown
are corrected for the wavelength dependence of the detector, and the
quoted emission maxima refer to the values after correction. Lifetimes
were obtained by multichannel scaling following excitation with a
microsecond-pulsed xenon lamp and detection of the light emitted at
right angles using an R928 photomultiplier tube, after passage through
a monochromator.
em
the Re and Ru chromophores (λmax 652 and 680 nm,
respectively) with the low-energy absorption band of the
abs
acceptor photochromic unit in its closed form (λmax 725 and
753 nm). A similar quenching of the luminescence upon DTE
closure was observed in the previously mentioned cyclo-
metalated iridium complex featuring the same photochromic
ligand.19
CONCLUSION
■
We have presented in this work a full investigation of the
synthesis, characterization, and linear and nonlinear optical
properties of a series of Zn(II), Re(I), and Ru(II) complexes
which incorporate the DTE photochromic unit into the
bipyridine ligand. We have demonstrated that, like the free
DTE-containing bipyridyl ligands, the corresponding com-
plexes undergo reversible ring-closure reactions under light
irradiation, with photocyclization yields ranging from 62 to
90%. The combination of the photochromic DTE-based
bipyridine ligand L with luminescent Re and Ru organometallic
fragments allows the photoregulation of the emission and NLO
properties of the resulting system. This study demonstrates for
the first time that the photocontrol of two optical properties,
linear and nonlinear, could be achieved by using the same
photochromic ligand.
Second-Order NLO Properties. EFISH Measurements. The
molecular quadratic hyperpolarizabilities were measured by the
solution-phase dc electric field induced second harmonic (EFISH)
generation method, which can provide direct information on the
γEFISH = (μβ /5kT) + γ(−2ω; ω, ω, 0)
(1)
λ
intrinsic molecular NLO properties through eq 1, 22where μβλ/5kT is
the dipolar orientational contribution and γ(−2ω;ω,ω,0), a third-order
term corresponding to the mixing of two optical fields at ω and of the
DC poling field at ω = 0, is the electronic cubic contribution to γEFISH
,which is usually negligible with respect to μβλ/5kT. βλ is the
projection along the dipole moment axis of the vectorial component of
the tensor of the quadratic hyperpolarizability, working with an
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Article
incident wavelength λ. All EFISH measurements were carried out in
CH2Cl2 solutions at a concentration of 1 × 10−3 M, working with a
nonresonant incident wavelength of 1.907 μm.
warmed to room temperature and stirred for an additional 16 h. After
addition of 200 mL of water, THF was removed under reduced
pressure, and the residue was extracted with CH2Cl2 (3 × 30 mL). The
combined organic phases were dried over MgSO4, filtered, and
evaporated in vacuo. The residue was extracted with 50 mL of THF.
PTSA (1.2 mmol, 228 mg) and a few drops of water were added. The
reaction mixture was stirred for 16 h at 40 °C. After addition of water
(100 mL), THF was removed under reduced pressure, and the residue
was extracted with CH2Cl2 (3 × 30 mL). The combined organic
phases were dried over MgSO4, filtered, and evaporated in vacuo, and
the residue was chromatographed with silica gel. Elution with a 2/3
dichloromethane/pentane mixture afforded 6 as orange crystals (1.9 g,
HLS Measurements. The HLS technique27,28 involves the detection
of the incoherently scattered second harmonic light generated by a
solution of the molecule under irradiation with a laser of wavelength λ,
leading to the measurement of the mean value of the β × β tensor
product, ⟨βHLS⟩. All HLS measurements were carried out in CH2Cl2
solution at a concentration of 1 × 10−3 M, working with a low-energy,
nonresonant incident radiation of 1.91 μm. The 1.91 μm fundamental
beam was emitted by a high-pressure (30 bar), 50 cm long Raman cell
pumped by a Nd3+:YAG laser operating at 1.06 μm and providing a 10
Hz repetition rate, with pulses of 15 ns duration. Only the
backscattered 1.91 μm Raman emission was collected by use of a
dichroic mirror, in order to eliminate most of the residual 1.06 μm
pump photons. Our reference sample was a concentrated (10−3 M)
solution of ethyl violet, its β value being calibrated at 1.91 μm with
respect to that of the N-4-nitrophenylprolinol (NPP) reference dipolar
molecule, leading to β = 170 × 10−30 esu for ethyl violet at 1.91 μm.
The HLS photons at 955 nm were focused onto the photomultiplier
tube using two collecting lenses (we used a Hamamatsu R632-01
photomultiplier tube). The signal detected was then sampled and
averaged using a boxcar and processed by a computer. The reference
beam was collected at a 45° incidence angle by a glass plate and
focused onto a highly nonlinear NPP powder, which was used as the
frequency doubler. The variation of the scattered second harmonic
intensity from the solution was recorded on the computer as a
function of the reference second harmonic signal provided by the NPP
powder, which scales as the square of the incoming fundamental
intensity. Values for β were then inferred from the slopes of the
resulting lines. The dispersion-free hyperpolarizabilities β0 are inferred
from experimental ones using a two-level dispersion model according
to ref 22.
1
50%). H NMR (200 MHz, CDCl3): δ (ppm) 9.87 (s, 1H, CHO),
6
7.76 (s, 1H, thio), 2.58 (d, JH−F = 3 Hz, 3H, CH3). 13C{1H} NMR
(50 MHz, CDCl3): δ (ppm) 180.1, 151.4, 140.0, 133.8, 119.2, 13.7.
Anal. Calcd for C11H5OF7S: C, 41.52; H, 1.58; S, 10.08. Found: C,
41.27; H, 1.69; S, 10.37. HRMS: m/z 317.9924 [M]+, calcd for
C11H5F7O5S 317.9949.
4-(3,3,4,4,5,5-Hexafluoro-2-(2-methyl-5-N,N-dimethylaminophe-
nylthiophenyl-3)cyclopent-1-enyl)-5-methylthiophene-2-carbalde-
hyde (7a). To a solution of 3-bromo-2-methyl-5-phenylthiophene 3a
(2.10 g, 7.12 mmol) in 50 mL of THF, which was cooled to −78 °C,
n
was added dropwise BuLi (2.32 M in hexane, 4.6 mL, 10.7 mmol).
After the reaction mixture was stirred at −78 °C for 1 h, a solution of 5
(2.6 g, 7.12 mmol) in 50 mL of THF was added. After it was stirred at
−78 °C for 1 h and at room temperature for 16 h, the reaction mixture
was hydrolyzed with water, and the solvent was removed in vacuo. The
residue was extracted with CH2Cl2 (2 × 30 mL) and then dried over
MgSO4. After evaporation of the solvent, the residual orange oil was
dissolved in 20 mL of THF, and then PTSA (85 mg, 0.44 mmol) and a
few drops of water were added. After the mixture was stirred at 40 °C
for 16 h, the solvent was removed and the oil was purified by column
chromatography (SiO2, pentane/ethyl acetate 95/5) to give yellow-
1
Synthesis. 3-Bromo-2-methyl-5-(p-dimethylaminophenyl)-
thiophene (3a). In a Schlenk flask, the boronic acid 2a (1.66 g, 10
mmol) and 3,5-dibromo-2-methylthiophene 1 (3.86 g, 15 mmol) were
added to a solution of Na2CO3 (8 g, 75 mmol) and Pd(PPh3)4 (0.58 g,
0.5 mmol) in H2O/THF (40 mL/40 mL). The reaction mixture was
refluxed overnight. The resultant mixture was extracted into 2 × 25
mL of chloroform. The organic layer was first washed with an aqueous
solution of NaCl and then with water (25 mL) and finally dried over
magnesium sulfate. After evaporation of the solvent, the crude product
was purified by column chromatography on silica gel (pentane/
dichloromethane, 75/25) to give 3a as a white powder (2.2 g, 75%).
green microcrystals (1.80 g, 50%). H NMR (500 MHz, CDCl3): δ
(ppm) 9.88 (s, 1H, CHO), 7.80 (s, 1H, thio), 7.42 (d, 3J = 8.8 Hz, 2H,
C6H4−), 7.07 (s, 1H, thio), 6.74 (d, 3J = 8.8 Hz, 2H, C6H4−), 3.02 (s,
6H, NMe2), 2.08 (s, 3H, Me), 1.93 (s, 3H, Me). 13C{1H} NMR
(125.77 MHz, CDCl3): δ (ppm) 182.16 (CHO), 152.00, 150.35,
143.81, 141.64, 139.14, 138.14, 136.43, 134.09, 126.74, 126.61, 125.02,
121.30, 119.45, 116.03, 112.45, 111.16, 40.41, 15.49, 14.45. Anal.
Calcd for C24H19NF6OS2: C, 55.91; H, 3.71; N, 2.72; S, 12.44. Found:
C, 55.41; H, 3.61; N, 2.70; S, 12.49. HRMS: m/z 515.0813 [M]+, calcd
for C24H19NF6OS2 515.0812.
4-(3,3,4,4,5,5-Hexafluoro-2-(2-methyl-5-N,N-dibutylaminophe-
nylthiophen-3-yl)cyclopent-1-enyl)-5-methylthiophene-2-carbalde-
hyde (7b). Following the procedure for 7a, the title compound 7b was
obtained as yellow-green microcrystals (0.5 g, 64%) from 3b (0.5 g,
3
1H NMR (200 MHz, CDCl3): δ (ppm) 7.42 (d, J = 8.7 Hz, 2H,
C6H4), 7.15 (s, 1H, thio), 6.70 (d, 3J = 8.7 Hz, 2H, C6H4), 3.00 (s, 6H,
NMe2), 2.50 (s, 3H, Me). 13C{1H} NMR (50 MHz, CDCl3): δ (ppm)
150.5, 142.5, 131.7, 126.8, 123.6, 122.4, 112.9, 109.9, 40.9, 15.2. Anal.
Calcd for C13H14BrNS: C, 52.71; H, 4.76; N, 4.73; S, 10.82. Found: C,
52.88; H, 4.85; N, 4.82; S, 10.41.
n
1.31 mmol), BuLi (1.6 M in hexane, 1 mL, 1.57 mmol), and 5 (0.48
1
g, 1.31 mmol). H NMR (400 MHz, CD2Cl2): δ (ppm) 9.88 (s, 1H,
3
CHO), 7.83 (s, 1H, thio), 7.39 (d, J = 9.0 Hz, 2H, C6H4−), 7.08 (s,
3
1H, thio), 6.67 (d, J = 9.0 Hz, 2H, C6H4−), 3.34 (m, 4H, CH2N),
3-Bromo-2-methyl-5-(p-dibutylaminophenyl)thiophene (3b).
Following the procedure for 3a, the title compound 3b was obtained
as a yellow powder (2.4 g, 80%) from the boronic acid 2b (2 g, 8
mmol), 3,5-dibromo-2-methylthiophene (1; 2.7 g, 10.5 mmol), and
Pd(PPh3)4 (0.36 g, 0.3 mmol). 1H NMR (400 MHz, CDCl3): δ (ppm)
7.37 (d, 3J = 9.0 Hz, 2H, C6H4−), 6.92 (s, 1H, thio), 6.64 (d, 3J = 9.0
Hz, 2H, C6H4−), 3.30 (m, 4H, CH2N), 2.41 (s, 3H, CH3), 1.60 (m,
2.11 (s, 3H, CH3), 1.96 (s, 3H, CH3), 1.62 (m, 4H, CH2CH2N), 1.40
(sext, 3J = 7.5 Hz, 4H, −CH2CH3), 1.01 (t, 3J = 7.3 Hz, 6H,
−CH2CH3). 13C{1H} NMR (100.62 MHz, CD2Cl2): δ (ppm) 182.01,
151.97, 148.19, 144.09, 141.79, 139.03, 144.09, 141.79, 139.03, 136.29,
126.59, 124.89, 119.90, 118.92, 111,67, 50.65, 29.38, 20.26, 15,21,
14.17, 13.70. Anal. Calcd for C30H31NOF6S2: C, 60.08; H, 5.21; N,
2.34; S, 10.69. Found: C, 60.31; H, 5.34; N, 2.29; S, 10.55. HRMS: m/
z 599.1748, [M]+ calcd for C30H31NOF6S2 599.1746.
3
3
4H, CH2CH2N), 1.38 (sext, J = 7.6 Hz, 4H, CH2CH3), 0.99 (t, J =
7.4 Hz, 6H, CH2CH3). 13C{1H} NMR (100.62 MHz, CDCl3): δ
(ppm) 147.8, 142.3, 130.9, 126.5, 122.7, 120.6, 111.6, 109.35, 50.8,
29.4, 20.4, 14.7, 14.0. Anal. Calcd for C19H26BrNS: C, 59.99; H, 6.89;
N, 3.68; S, 8.43. Found: C, 59.77; H, 6.79; N, 3.85; S, 8.41. HRMS: m/
z 380.1041 [M + H]+, calcd for C19H27NBrS 380.1042.
4,4′-Bis((E)-2-(4-(3,3,4,4,5,5-hexafluoro-2-(2-methyl-5-p-N,N-di-
methylaminophenylthiophen-3-yl)cyclopent-1-nyl)-5-methylthio-
phen-2-yl)vinyl)-2,2′-bipyridine (La(o)). A THF solution (25 mL) of
7a (0. 20 g, 0. 37 mmol) was added to 4, 4′-bis-
(diethylphosphonomethyl)-2,2′-bipyridine (0.076 g, 0.17 mmol) and
tBuOK (0.081 g, 0.72 mmol) at 0 °C. The reaction mixture was stirred
5-Methyl-4-(perfluorocyclopent-1-enyl)thiophene-2-carbalde-
n
hyde (6). BuLi (2.4 M in hexane, 15.6 mmol, 6.5 mL) was added
for 2.5 h at room temperature. After addition of water, the organic
layer was washed with brine and water, dried over MgSO4, filtered, and
concentrated. Crystallization in a CH2Cl2/pentane mixture afforded La
dropwise to a stirred solution of 4 (3.00 g, 12 mmol) in 100 mL of
THF at −78 °C under a nitrogen atmosphere. After 60 min, the
reaction mixture was transferred into a Schlenk tube containing a
solution of perfluorocyclopentene (4.8 mL, 36 mmol) in 20 mL of
THF. The reaction mixture was stirred for 1 h at −78 °C and then
1
as a green powder (0.15 g, 75%). H NMR (200 MHz, CDCl3): δ
(ppm) 8.66 (d, 3J = 5 Hz, 2H, Py6), 8.50 (s, 2H, Py3), 7.55 (d, 3J = 16
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Article
Hz, 2H, CH), 7.40 (d, 3J = 8.6 Hz, 4H, C6H4−), 7.35 (d, 3J = 5 Hz,
2H, Py5), 7.20 (s, 2H, thio), 7.10 (s, 2H, thio), 6.82 (d, 3J = 16 Hz, 2H,
CH), 6.70 (d, 3J = 8.6 Hz, 4H, C6H4−), 3.00 (s, 12H, NMe2), 2.04
(s, 6H, CH3), 2.03 (s, 6H, CH3). 13C{1H} NMR (125.77 MHz,
CDCl3): δ (ppm) 156.43, 150.26, 149.63, 145.06, 143.25, 142.69,
139.59, 139.15, 127.69, 126.58, 126.08, 125.92, 125.56, 125.45, 121.62,
120.75, 119.79, 118.04, 112.48, 40.44, 14.85, 14.48. HRMS: m/z
1179.24920 [M + H]+, calcd for C60H47N4F12S4 1179.2492. Anal.
Calcd for C60H46F12N4S4: C, 61.11; H, 3.93; N, 4.75; S, 10.88. Found:
C, 60.91; H, 4.15; N, 4.56; S, 10.73.
evaporated, and the residue was successively washed with pentane and
1
diethyl ether to afford a black powder (0.125 g, 89%). H NMR (500
3
MHz, CD2Cl2): δ (ppm) 8.71 (d, J = 5.5 Hz, 2H, Py6), 8.29 (s, 2H,
Py3), 7.75 (d, 3J = 5.5 Hz, 2H, Py5), 7.70 (d, 3J = 16.0 Hz, 2H, CH),
7.41 (d, 3J = 8.8 Hz, 4H, C6H4−), 7.38 (s, 2H, thio), 7.11 (s, 2H, thio),
3
6.95 (d, J = 16.0 Hz, 2H, CH), 6.67 (d, 3J = 8.8 Hz, 4H, C6H4−),
3.33 (m, 8H, CH2N), 2.08 (s, 6H, CH3), 2.00 (s, 6H, CH3), 1.61 (m,
8H, CH2CH2N), 1.39 (sext, 3J = 7.6 Hz, 8H, −CH2CH3), 0.99 (t, 3J =
7.3 Hz, 12H, −CH2CH3). 13C{1H} NMR (125.77 MHz, CD2Cl2): δ
(ppm) 149.73, 149.21, 148.84, 148.11, 145.15, 143.80, 139.00, 138.57,
129.96, 129.76, 126.58, 126.32, 125.19, 123.40, 123.15, 119.95, 119.06,
118.41, 111.64, 50.66, 29.68, 20.25, 14.82, 14.30, 13.73. Anal. Calcd for
C72H70N4F12S4ZnCl2·CH2Cl2: C, 55.89; H, 4.63; N, 3.57; S, 8.18.
Found: C, 55.58; H, 4.48; N, 3.65; S, 8.03.
1
Spectroscopic Data of the Photocyclized La(c). H NMR (300
3
MHz, CD2Cl2): δ (ppm) 8.69 (d, J = 5 Hz, 2H, Py6), 8.57 (s, 2H,
3
3
Py3), 7.54 (d, J = 16 Hz, 2H, CH), 7.52 (d, J = 8.6 Hz, 4H,
C6H4−), 7.40 (d, J = 3.7 Hz, 2H, Py5), 6.82 (d, J = 16 Hz, 2H, 
CH), 6.73 (d, 3J = 8.6 Hz, 4H, C6H4−), 6.62 (s, 2H, thio), 6.53 (s, 2H,
thio), 3.10 (s, 12H, NMe2), 2.18 (s, 6H, CH3), 2.16 (s, 6H, CH3).
4,4′-Bis((E)-2-(4-(3,3,4,4,5,5-hexafluoro-2-(2-methyl-5-p-N,N-di-
butylaminophenylthiophen-3-yl)cyclopent-1-nyl)-5-methylthio-
phen-2-yl)vinyl)-2,2′-bipyridine (Lb(o)). To a THF solution at 0 °C
(80 mL) of 7b (0.50 g, 0.83 mmol) and 4,4′-bis-
(diethylphosphonomethyl)-2,2′-bipyridine (0.173 g, 0.38 mmol) was
3
3
1
Spectroscopic Data of the Photocyclized (Lb(c))ZnCl2. H NMR
(500 MHz, CD2Cl2): δ (ppm) 8.74 (d, 3J = 5.5 Hz, 2H, Py6), 8.29 (s,
2H, Py3), 7.76 (d, 3J = 4.7 Hz, 2H, Py5), 7.63 (d, 3J = 15.8 Hz, 2H, 
CH), 7.52 (d, 3J = 8.9 Hz, 4H, C6H4−), 6.77 (d, 3J = 15.9 Hz, 2H, 
CH), 6.70 (d, 3J = 8.9 Hz, 4H, C6H4−), 6.68 (s, 2H, thio), 6.64 (s, 2H,
thio), 3.41 (m, 8H, CH2N), 2.21 (s, 6H, CH3), 2.18 (s, 6H, CH3), 1.63
(m, 8H, CH2CH2N), 1.41 (sext, 3J = 7.4 Hz, 8H, −CH2CH3), 1.02 (t,
3J = 7.3 Hz, 12H, −CH2CH3).
t
added BuOK (0.17 g, 1.52 mmol). The reaction mixture was then
(La(o))Re(CO)3Br. In a Schlenk tube, under an argon atmosphere,
Re(CO)5Br (0.71 g, 0.176 mmol) and La (0.210 g, 0.178 mmol) were
dissolved in toluene (20 mL) and refluxed at 110 °C overnight in the
dark. The solvent was evaporated, and the resulting dark yellow
residue was dissolved in CH2Cl2. After filtration through Celite,
crystallization in CH2Cl2/pentane mixture afforded a brown powder
(220 mg, 82% yield). 1H NMR (400 MHz, CD2Cl23): δ (ppm) 8.80 (d,
3J = 5.7 Hz, 2H, Py6), 8.26 (s, 2H, Py3), 7.56 (d, J = 16 Hz, 2H, 
stirred for 5 h at room temperature. After addition of water, the
organic layer was washed with brine and water, dried over MgSO4,
filtered, and concentrated. Recrystallization in a CH2Cl2/pentane
mixture afforded Lb as a brown powder (0.425 g, 83%). 1H NMR (500
3
MHz, CD2Cl2): δ (ppm) 8.67 (d, J = 5 Hz, 2H, Py6), 8.56 (s, 2H,
3
Py3), 7.55 (d, J = 16.2 Hz, 2H, CH), 7.41 (m, 6H, C6H4 + Py5),
3
7.23 (s, 2H, thio), 7.11 (s, 2H, thio), 6.92 (d, J = 16.2 Hz, 2H, 
CH), 6.67 (d, 3J = 9.0 Hz, 4H, C6H4−), 3.35 (m, 8H, CH2N), 2.03 (s,
6H, CH3), 1.98 (s, 6H, CH3), 1.61 (quint, 3J = 7.5 Hz, 8H, CH2CH2−
N), 1.40 (sext, 3J = 7.5 Hz, 8H, −CH2CH3), 0.99 (t, 12H, 3J = 7.5 Hz,
−CH2CH3). 13C{1H} NMR (125.77 MHz, CD2Cl2): δ (ppm) 156.29,
149.50, 148.02, 144.99, 143.56, 142.96, 139.72, 138.95, 127.62, 126.53,
126.07, 125.73, 125.37, 125.27, 120.61, 120.05, 119.15, 117.83, 111.64,
50.63, 29.32, 20.24, 14.59, 14.18, 13.70. HRMS: m/z 1346.4312, [M]+
calcd for C72H70N4F12S4 1346.4292. Anal. Calcd for
C72H70F12N4S4·0.5CH2Cl2: C, 62.64; H, 5.15; N, 4.03; S, 9.23.
Found: C, 62.38; H, 5.06; N, 4.12; S, 8.98.
3
CH), 7.47 (d, J = 8.9 Hz, 4H, C6H4−), 7.41 (s, 2H, thio), 7.29 (m,
2H, Py5), 7.16 (s, 2H, thio), 6.74 (d, 3J = 8.9 Hz, 4H, C6H4−), 6.66 (d,
3J = 16 Hz, 2H, CH), 2.99 (s, 12H, NMe2), 2.14 (s, 6H, CH3), 2.09
(s, 6H, CH3). 13C{1H} NMR (125.77 MHz, CD2Cl2): δ (ppm)
197.27, 189.39, 155.99, 152.12, 150.39, 147.31, 145.26, 143.53, 139.24,
138.91, 129.73, 129.39, 126.44, 125.34, 123.13, 123.02, 121.21, 119.90,
119.78, 112.30, 40.08, 14.81, 14.32. HRMS: m/z 1526.1040 [M]+,
calcd for C63H46N4O3F1279BrS4185Re 1526.097 43; m/z 1498.1085 [M
− CO]+, calcd for C62H46N4O2F1279BrS4185Re 1498.102 52. Anal.
Calcd for C63H46BrF12N4O3ReS4·0.5CH2Cl2: C, 48.52; H, 3.01; N,
3.56; S, 8.16. Found: C, 48.50; H, 3.09; N, 3.49; S, 8.16.
1
Spectroscopic Data of the Photocyclized Lb(c). H NMR (500
3
MHz, CD2Cl2): δ (ppm) 8.70 (d, J = 5.0 Hz, 2H, Py6), 8.59 (s, 2H,
3
Py3), 7.50 (m, 6H, CH + C6H4−), 7.41 (d, J = 6.0 Hz, 2H, Py5),
Spectroscopic Data of the Photocyclized (La(c))Re(CO)3Br. 1H
6.79 (d, 3J = 15.5 Hz, 2H, CH), 6.69 (d, 3J = 9.0 Hz, 4H, C6H4−),
6.60 (s, 2H, thio), 6.54 (s, 2H, thio), 3.39 (m, 8H, CH2N), 2.17 (s,
6H, CH3), 2.16 (s, 6H, CH3), 1.64 (m, 8H, CH2CH2N), 1.42 (m, 8H,
3
NMR 400 MHz (CD2Cl2): δ (ppm) 8.90 (d, J = 5.7 Hz, 2H, Py6),
3
3
8.30 (s, 2H, Py3), 7.64 (d, J = 16 Hz, 2H, CH), 7.56 (d, J = 8.9
Hz, 4H, C6H4−), 7.38 (d, 3J = 6.4 Hz, 2H, Py5), 6.75 (m, 6H, C6H4−
+ CH), 6.74 (s, 2H, thio), 6.67 (s, 2H, thio), 3.12 (s, 12H, NMe2),
2.23 (s, 6H, CH3), 2.22 (s, 6H, CH3).
3
−CH2CH3), 1.01 (t, J = 7.0 Hz, 12H, −CH2CH3).
(La(o))Zn(OAc)2. To a CH2Cl2 solution (40 mL) of La (0.322 g,
0.27 mmol) was added Zn(OAc)2·2H2O (0.060 g, 0.27 mmol). The
reaction mixture was stirred for 16 h at room temperature. The solvent
was then evaporated, and crystallization of the residue in a CH2Cl2/
[(La(o))(dmbipy)2Ru](PF6)2. In a Schlenk tube, under an argon
atmosphere, AgOTf (54 mg, 0.21 mmol) and Ru(4,4′-diMe-2,2′-
bpy)2Cl2 (55.7 mg, 0.103 mmol) were dissolved in MeOH (8 mL) for
5 h at room temperature in the dark. To the resulting red solution
were added La (120 mg, 0.102 mmol) and CH2Cl2 (8 mL). After the
mixture was stirred overnight at room temperature in the dark, a large
excess of NaPF6 was added, this mixture was stirred for 6 h, and then
the solvent was evaporated. The residue was suspended in the mixture
of EtOH (5 mL) and H2O (50 mL), filtered, and washed with H2O
and then with diethyl ether. Crystallization in a CH2Cl2/pentane
mixture afforded a dark brown powder (99.0 mg, 60% yield). 1H NMR
(500 MHz, CD2Cl2): δ (ppm) 8.48 (m, 2H, Py3‑DTEbpy), 8.27 (m, 4H,
Py3‑Mebpy), 7.67 (d, 3J = 16 Hz, 2H, CH), 7.62−7.53 (m, 6H,
1
pentane mixture afforded a brown powder (0.35 g, 95%). H NMR
(300 MHz, CDCl3): δ (ppm) 8.75 (br d, 2H, Py6), 8.24 (s, 2H, Py3),
7.62 (d, 3J = 16 Hz, 2H, CH), 7.52 (s, 2H, Py5), 7.46 (d, 3J = 8 Hz,
4H, C6H4−), 7.35 (s, 2H, thio), 7.15 (s, 2H, thio), 6.84 (d, 3J = 16 Hz,
3
2H, CH), 6.73 (d, J = 8 Hz, 4H, C6H4−), 3.00 (s, 12H, NMe2),
2.07 (s, 6H, CH3), 2.05 (s, 6H, CH3), 2.03 (s, 6H, OC(O)CH3).
13C{1H} NMR (75 MHz, CD2Cl2): δ (ppm) 180.0, 150.4, 149.6,
144.6, 143.5, 139.3, 138.9, 129.4, 128.7, 126.4, 126.1, 125.3, 123.8,
122.8, 121.1, 119.5, 117.9, 112.3, 40.11, 21.8, 14.8, 14.3. Anal. Calcd
for C64H52F12N4O4S4Zn·H2O: C, 55.67; H, 3.94; N, 4.06; S, 9.41.
Found: C, 55.47; H, 3.87; N, 3.85; S, 9.32.
3
Py6‑Mebpy+bpyDTE), 7.45 (d, J = 8.8 Hz, 4H, C6H4−), 7.44 (m, 2H,
Spectroscopic Data of the Photocyclized (La(c))Zn(OAc)2. 1H
NMR (200 MHz, CDCl3): δ (ppm) 8.91 (br d, 2H, Py6), 8.16 (s, 2H,
Py3), 7.63 (s, 2H, Py5), 7.58 (d, 3J = 16 Hz, 2H, CH), 7.51 (d, 3J = 8
Hz, 4H, C6H4−), 6.70 (d, 3J = 8 Hz, 4H, C6H4−), 6.68 (d, 3J = 16 Hz,
2H, CH), 6.63 (s, 2H, thio), 6.60 (s, 2H, thio), 3.10 (s, 12H,
NMe2), 2.17 (s, 6H, Me), 2.16 (s, 6H, Me), 2.10 (s, 6H, OC(O)CH3).
(Lb(o))ZnCl2. To a CH2Cl2 solution (20 mL) of Lb (0.130 g, 0.096
mmol) was added ZnCl2 (0.013 g, 0.095 mmol). The reaction mixture
was stirred for 16 h at room temperature. The solvent was then
Py5‑bpyDTE), 7.36 (s, 2H, thio), 7.27 (m, 4H, Py5‑Mebpy), 7.13 (s, 2H,
3
3
thio), 6.96 (d, J = 16 Hz, 2H, CH), 6.76 (d, J = 8.8 Hz, 4H,
C6H4−), 3.01 (s, 12H, NMe2), 2.62 (s, 6H, CH3Mebpy), 2.61 (s, 6H,
CH3Mebpy), 2.04 (s, 6H, CH3DTE), 1.97 (s, 6H, CH3DTE). 13C{1H}
NMR (125.77 MHz, CD2Cl2): δ (ppm) 157.14, 156.37, 156.22,
151.10, 150.75, 150.51, 150.27, 150, 146.01, 144.78, 143.42, 139.50,
138.95, 129.59, 128, 126.43, 126.12, 125, 124.81, 123.65, 123.20,
121.52, 120.68, 119.58, 112.46, 40.27, 21.11, 14.78, 14.27. HRMS: m/z
824.172 36, [M]2+ calcd for C84H70N8F12S4102Ru 824.1735; m/z
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Inorganic Chemistry
Article
−
1793.309 45 [M2+,PF6 ]+, calcd for C84H70N8F12PS4102Ru 1793.3102.
Ko, C. C.; Wong, K. M. C.; Zhu, N.; Yam, V. W.-W. Organometallics
2007, 26, 12−15. (d) Lee, P. H. M.; Ko, C. C.; Zhu, N.; Yam, V. W.-
W. J. Am. Chem. Soc. 2007, 129, 6058−6059. (e) Wong, H.-L.; Tao,
C.-H.; Zhu, N.; Yam, V. W.-W. Inorg. Chem. 2011, 50, 471−481.
(12) (a) N. Roberts, M.; Nagle, J. K.; Finden, J. G.; Branda, N. R.;
Wolf, M. O. Inorg. Chem. 2009, 48, 19−21. (b) Roberts, M. N.;
Carling, C.-J.; Nagle, J. K.; Branda, N. R.; Wolf, M. O. J. Am. Chem.
Soc. 2009, 131, 16644−16645. (c) Roberts, M. N.; Nagle, J. K.;
Majewski, M. B.; Finden, J. G.; Branda, N. R.; Wolf, M. O. Inorg. Chem.
2011, 50, 4956−4966.
Anal. Calcd for C84H70F24N8P2RuS4·CH2Cl2: C, 50.45; H, 3.59; N,
5.54; S, 6.34. Found: C, 50.39; H, 3.67; N, 5.43; S, 6.33.
Spectroscopic Data of the Photocyclized [(La(c))(dmbipy)2Ru]-
(PF6)2. H NMR (500 MHz, CD2Cl2): δ (ppm) 8.48 (m, Py3‑bpyDTE),
1
8.27 (m, Py3‑Mebpy), 7.67−7.60 (m, CH, Py6‑Mebpy+DTEbpy), 7.52 (m,
C6H4−), 7.45 (m, Py5‑DTEbpy), 7.27 (m, 4H, Py5‑Mebpy), 6.77−6.63 (m,
thio + C6H4− + CH), 3.10 (s, 12H, NMe2), 2.62 (m, 2 CH3Mebpy),
2.18 (s, 6H, CH3DTE), 2.15 (s, 6H, CH3DTE), 2.04 (s, 6H, CH3DTE),
1.97 (s, 6H, CH3DTE).
(13) (a) Zhong, Y. W.; Vila, N.; Henderson, J. C.; Flores-Torres, S.;
Abruna, H. D. Inorg. Chem. 2007, 46, 104470−10472. (b) Zhong, Y.-
W.; Vila, N.; Henderson, J. C.; Abruna, H. D. Inorg. Chem. 2009, 48,
991−999.
AUTHOR INFORMATION
Corresponding Author
*E-mail: lebozec@univ-rennes1.fr (H.L.B.).
■
(14) Indelli, M. T.; Carli, S.; Ghirotti, M.; Chiorboli, C.; Ravaglia, M.;
Garavelli, M.; Scandola, F. J. Am. Chem. Soc. 2008, 130, 7286−7299.
(15) Brayshaw, S. K.; Schiffers, S.; Stevenson, A. J.; Teat, S. J.;
Warren, M. R.; Bennett, R. D.; Sazanovich, I. V.; Buckley, A. R.;
Weinstein, J. A.; Raithby, P. R. Chem. Eur. J. 2011, 17, 4385−4395.
(16) (a) Renouard, T.; Le Bozec, H. Eur. J. Inorg. Chem. 2000, 229−
239. (b) Maury, O.; Le Bozec, H. Acc. Chem. Res. 2005, 38, 691−704.
(17) (a) Le Bouder, T.; Maury, O.; Le Bozec, H.; Ledoux, I.; Zyss, J.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
This work has been financially supported by the ANR (BLANC
COMET) and LEA Rennes-Durham (Molecular Materials and
■
́
Catalysis). L.O. thanks the Region Bretagne for a Ph.D. grant.
H.N. is grateful to the ITP (Japan−Europe−US International
Training Program for Young Generation in Molecular Materials
Science for Development of Molecular Devices) and JSPS
(Japan Society for Promotion of Science; research fellowship
DC2) programs for a travel grant.
́ ́
Chem. Commun. 2001, 2430−2431. (b) Senechal, K.; Maury, O.; Le
Bozec, H.; Ledoux, I.; Zyss, J. J. Am. Chem. Soc. 2002, 124, 4561−62.
(c) Le Bouder, T.; Maury, O.; Le Bozec, H.; Bondon, A.; Costuas, K.;
Amouyal, E.; Zyss, J.; Ledoux, I. J. Am. Chem. Soc. 2003, 125, 12884−
́ ́ ́
12899. (d) Maury, O.; Viau, L.; Senechal, K.; Corre, B.; Guegan, J .-P.;
Renouard, T.; Ledoux, I.; Zyss, J.; Le Bozec, H. Chem. Eur. J. 2004, 10,
4454−4466. (e) Viau, L.; Bidault, S.; Maury, O.; Brasselet, S.; Ledoux,
I.; Zyss, J.; Ishow, E.; Nakatani, K.; Le Bozec, H. J. Am. Chem. Soc.
2004, 126, 8386−8387.
(18) Aubert, V.; Guerchais, V.; Ishow, E.; Hoang-Thi, K.; Ledoux, I.;
Nakatani, K.; Le Bozec, H. Angew. Chem., Int. Ed. 2008, 47, 577−580.
(19) Aubert, V.; Ordronneau, L.; Escadeillas, M.; Williams, J. A. G.;
Boucekkine, A.; Coulaud, E.; Dragonetti, C.; Righetto, S.; Roberto, D.;
Ugo, R.; Valore, A.; Singh, A.; Ledoux-Rak, I.; Zyss, J.; Le Bozec, H.;
Guerchais, V. Inorg. Chem. 2011, 50, 5027−38.
(20) All these bis-DTE ligands and complexes undergo the sequential
photocyclization open−open (o,o) → open−closed (o,c)→ closed−
closed (c,c). For photokinetic studies, quantum yield measurements,
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