Photochromic properties of polyoxotungstates with grafted spiropyran molecules

Article abstract of DOI:10.1021/ic401380a

The first systems associating in a single molecule polyoxotungstates (POTs) and photochromic organic groups have been elaborated. Using the (TBA) ₄[PW₁₁O₃₉{Sn(C₆H₄I)}] precursor, two hybrid organic-in

Full text of DOI:10.1021/ic401380a

Article
pubs.acs.org/IC
Photochromic Properties of Polyoxotungstates with Grafted
Spiropyran Molecules
Arnaud Parrot,†,‡ Guillaume Izzet,*,† Lise-Marie Chamoreau,† Anna Proust,† Olivier Oms,‡
Anne Dolbecq,‡ Khadija Hakouk,§ Houda El Bekkachi,§ Philippe Deniard,§ Remi Dessapt,*,§
́
and Pierre Mialane*,‡
†Institut Parisien de Chimie Molec
Jussieu, Case 42, F-75005 Paris, France
́
ulaire, IPCM, UMR CNRS 7201, Universite
́
Pierre et Marie Curie, UPMC Univ Paris 06, 4 Place
de Versailles Saint-Quentin en Yvelines, 45 Avenue des Etats-Unis, F-78035
́ ̀
de Nantes, CNRS, 2 rue de la Houssiniere, BP 32229, 44322 Nantes cedex, France
‡Institut Lavoisier de Versailles, UMR 8180, Universite
Versailles cedex, France
́
§Institut des Mater
́
iaux Jean Rouxel, Universite
S
* Supporting Information
ABSTRACT: The first systems associating in a single molecule
polyoxotungstates (POTs) and photochromic organic groups
have been elaborated. Using the (TBA)4[PW11O39{Sn(C6H4I)}]
precursor, two hybrid organic−inorganic species where a
spiropyran derivative (SP) has been covalently grafted onto a
{PW11Sn} fragment via a Sonogashira coupling have been
successfully obtained. Alternatively, a complex containing a
silicotungstate {PW11Si2} unit connected to two spiropyran
entities has been characterized. The purity of these species has
1
been assessed using several techniques, including H and 31P
NMR spectroscopy, mass spectrometry, and electrochemical
measurements. The optical properties of the hybrid materials
have been investigated both in solution and in the solid state.
These studies reveal that the grafting of SPs onto POTs does not significantly alter the photochromic behavior of the organic
chromophore in solution. In contrast, these novel hybrid SP−POT materials display highly effective solid-state photochromism
from neutral SP molecules initially nonphotochromic in the crystalline state. The photoresponses of the SP−POT systems in the
solid state strongly depend on the nature and the number of grafted SP groups.
include smart windows, multicolor smart painting, UV sensors,
cosmetics, optical switches, and 3D high-density optical data
storage.4 Fortunately, it has been shown that the elaboration of
hybrid organic−inorganic materials based on photochromic
organic molecules may overcome this problem.5 In particular,
sol−gel methods have been developed that enable formation of
spiropyran-based solid-state photochromic materials.6 It has
also been shown that the inclusion of an SP in metal organic
frameworks can strongly stabilize the MC form and can even
lead to an antidromic reversible photochromic behavior.7 Also,
besides these examples where SP molecules are physically
embedded into the cavities of a (meso)porous soft material or a
crystalline coordination network, the covalent connection of SP
chromophores to matrixes has also been made. We can
especially note that SPs have been grafted on polymers.8 In
addition, SP molecules have been connected to coordination
complexes, as exemplified by the characterization of an SP−
porphyrin compound.9 Nonetheless, the optical properties of
1. INTRODUCTION
Photochromic molecules display reversible transformations
induced in one or both directions by electromagnetic radiations
between two states having different absorption spectra.1 Among
the numerous organic compounds that possess such behavior,
the class of spiropyran (SP) molecules has probably been the
most widely studied these last 50 years, because of their high
optical performances and their synthetic accessibility.2 In their
closed form (CS), the colorless SP molecules contain a Cspiro
−
O bond that can be cleaved under near-UV irradiation, leading
to a zwitterionic merocyanin (MC) isomer. This latter,
compared to the CS form, strongly absorbs in the visible
region. The CS form can then be regenerated under thermal
activation or via a photochemical pathway. For a huge majority
of SP molecules, even low power UV irradiations can induce
noticeable CS → MC isomerization in solution. In strong
contrast, very few spiropyrans exhibit such transformation in
the solid state and in ambient conditions.3 Nonetheless, the
elaboration of relevant solid-state photochromic materials is
essential to develop effective photochromic devices in view of
potential technological and marketable applications, which
Received: June 5, 2013
© XXXX American Chemical Society
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Figure 1. Representation of (a, b) the two POT precursors and of (c, d) the two spiropyran molecules used in this study and the SP → MC
isomerization process.
this species have not been investigated in the solid state.
Recently, we have initiated a study devoted to the elaboration
of hybrid materials, displaying dual photochromic and electro-
chromic behaviors built from the association of polyoxometa-
lates (POMs), a class of molecular oxides that exhibits an
enormous diversity of structures and properties,10 with
spiropyran molecules. After the characterization of supra-
molecular materials where cationic SP+ act as counterions for
POM species,11 we have successfully performed the covalent
grafting of neutral SP molecules onto the polyoxomolybdate
Anderson platform {MnMo6O18}.12 If these compounds
present solid-state photochromism properties due to a highly
effective CS → MC isomerization, the influence of the POM on
the photochromic performances of the hybrid materials was
mostly limited to the kinetics of photoresponses since the
spiropyran precursor was itself photoactive in the solid state.
To clearly evidence a potential beneficial role of the POM
fragment on the photochromic properties of connected SP
molecules, it is necessary to elaborate covalent SP−POM dyads
incorporating spiropyran units initially nonphotoactive in the
solid state. Herein, we report the first examples of materials
where such SP groups are connected to POM platforms.
Because of their versatilities, and the well-established synthetic
tools that allow their controlled covalent functionalization,13
polyoxotungstates (POTs) have been considered as inorganic
supports. Three compounds, differing by the nature of the POT
(stannotungstate vs silicotungstate), resulting in different
numbers of grafted SPs (one vs two) and different electron
acceptor characters, and by the nature of the SP (spiropyran vs
benzospiropyran), have been characterized, and their photo-
chromic properties have been fully investigated.
2. RESULTS AND DISCUSSION
2.1. Synthesis and Characterization. Recently, some of
us have described new organo-silyl14 and organo-stannyl15
POT-based hybrid platforms enabling the covalent attachment
of organic ligands using Sonogashira couplings. Among others,
two Keggin precursors were obtained. In (TBA)3[PW11O40{Si-
(C6H4I)}2] (TBA.KSi[I], Figure 1a), two {Si(C6H4I)} groups
are connected to the monovacant {PW11} POT, whereas, in
(TBA)4[PW11O39{Sn(C6H4I)}] (TBA.KSn[I], Figure 1b), one
{Sn(C6H4I)} fragment is inserted into the POT. These two
complexes, which then can be covalently bonded to one or two
organic fragments, respectively, have been chosen for
connecting spiropyran entities. This necessitated the use of
SP molecules bearing an alkyne arm. To the best of our
knowledge, it is only very recently that the first alkyne/SP
compound has been reported (SPR, Figure 1c).16 Considering
that this species is not photochromic in the solid state at room
temperature, it has thus been selected for our study. In
addition, the related benzospiropyran BSPR represented in
Figure 1d has been synthesized in order to determine if small
structural variations of the organic fragment can have significant
influences on the optical properties of the targeted materials.
Although this spiropyran has not been previously reported, the
relevant benzoindolenium precursor has already been charac-
terized,17 allowing readily synthesizing BSPR by reacting it with
1
2-hydroxy-5-nitrobenzaldehyde. However, H NMR spectros-
copy revealed that, despite numerous efforts for purifying the
crude spiropyran or by modifying the synthetic protocol, BSPR
1
is obtained as a mixture, with ca. 10%, estimated by H NMR,
of a secondary product. Single crystals of the mixture
(Supporting Information, Table S1) have been obtained, and
X-ray diffraction measurements revealed that the impurity is the
bromopropenyl spiropyran derivative BrBSPR (see the
Supporting Information, Figure S1). Noticeably, the presence
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Figure 2. Representation of the three hybrid spiropyran/polyoxotungstates: (a) TBA.KSn[SPR], (b) TBA.KSn[BSPR], and (c) TBA.KSi[SPR].
of a small amount of such BrBSPR impurities in BSPR does
not prevent its further use, as the Sonogashira reaction is only
effective with alkyne groups.
The cyclovoltammograms (CVs) of SPR, BSPR, TBA.
KSn[I], TBA.KSi[I], TBA.KSn[SPR], TBA.KSn[BSPR], and
TBA.KSi[SPR] are represented in Figure 3. In the +1.00 to
−1.80 V/SCE range, the SPR and BSPR species exhibit only
The coupling between SPR and TBA.KSn[I] or TBA.KSi[I],
using a slight excess of spiropyran and under classical
conditions (room temperature, 8% Pd(PPh3)2Cl2/CuI, DMF,
triethylamine), afforded the targeted materials (TBA)4-
[PW11O39{Sn(C6H4(SPR))}] (TBA.KSn[SPR], Figure 2a)
and (TBA)3[PW11O39{Si(C6H4(SPR))}2] (TBA.KSi[SPR],
Figure 2c), respectively. In analogous conditions but using
BSPR, the compound (TBA)4[PW11O39{Sn(C6H4(BSPR))}]
(TBA.KSn[BSPR], Figure 2b) has been also obtained. These
three species were purified by successive selective precipitations
and the use of ion-exchange and exclusion size chromatog-
raphy. Attempts to isolate single crystals suitable for X-ray
diffraction analysis were unsuccessful. However, the purity of
one reversible monoelectronic reduction wave located at E1/2
=
−1.19 and −1.18 V/SCE, respectively. Considering preceding
electrochemical studies devoted to nitrospiropyrans, it can be
proposed that this process does not involve the formation of
merocyanin and that the extra electron is essentially located on
the nitrobenzene moiety, with the formation of a radical
anion.18 Concerning the POT precursors, they display different
electron acceptor properties according to the nature of the
chemical anchorage (organosilyl vs organotin). Typically, the
organosilyl POT derivatives are easier to reduce than the
organotin ones, due to the one-charge difference. Indeed, the
CVs of TBA.KSn[I] and TBA.KSi[I] exhibit two reversible one-
electron waves (E1/2 = −1.11 and −1.64 V/SCE) and three
reversible one-electron waves (E1/2 = −0.37, −1.01, and −1.66
V/SCE), respectively, corresponding to successive redox
processes centered on the polyoxotungstate frameworks.
Turning now to TBA.KSn[SPR], two reversible waves are
observed at E1/2 = −1.14 and −1.61 V/SCE, with respective
intensities of 2:1. This is thus in perfect agreement with the
structure of TBA.KSn[SPR], considering that the waves
1
the samples was assessed, via H and 31P NMR spectroscopy
(Supporting Information, Figures S2−S4), elemental analysis,
and electrospray ionization mass spectrometry experiments. For
all of them, X−C6H4−CC−CH2− (X = Si, Sn) groups
ensure the connection between the Keggin unit and the SP
molecule(s). To further confirm the composition of these
hybrid species and to evaluate their electronic properties,
electrochemical measurements have also been performed.
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Figure 4. Abs(t) vs t plots for TBA.KSn[SPR] in acetonitrile (T = −20
°C, [TBA.KSn[SPR]] = 3.10−5 mol·L−1) after 0, 5, 10, 15, 20, 30, 45,
60, 75, and 90 min of irradiation at 365 nm. Inset: decay of the Abs(t)
vs t plot at λ = 570 nm for TBA.KSn[SPR] in acetonitrile (T = 20 °C,
[TBA.KSn[SPR]] = 3.10−5 mol·L−1).
Figure 3. Cyclic voltammograms of 10−3 mol·L−1 solutions of SPR
(a), BSPR (b), TBA.KSn[I] (c), TBA.KSn[SPR] (d), TBA.KSn[BSPR]
(e), TBA.KSi[I] (f), and TBA.KSi[SPR] (g) in DMF with 0.1 M
TBAPF6 as electrolyte. The scan rate was 100 mV·s−1, and the
reference electrode was a saturated calomel electrode (SCE).
UV irradiation for 5 min at 20 °C. For all compounds, it was
found that the Abs(t) vs t curves can only be fitted using a
double exponential model (see the Supporting Information,
Table S3, for the quantification of the kinetics constants), a
single exponential model being not suitable (Supporting
Information, Figure S6). Such a phenomenon has already
been observed for many SPs, a plausible explanation being the
existence of different isomers of the MC form in solution.20 It
can also be proposed that, in these compounds, the slowest
process (related to k2) is linked to the isomerization process
and the quickest one (related to k1) to the ring closure.
Interestingly, it can be noted that, whereas k1 is only slightly
affected when the SP is grafted on the POT platform, the
formation of a hybrid material has a significant influence on the
k2 constant.
The solid-state photochromic properties of the three hybrid
SP−POT materials have been investigated in ambient
conditions by diffuse reflectance spectroscopy of microcrystal-
line powders. TBA.KSn[SPR], TBA.KSn[BSPR], and TBA.
KSi[SPR] have an optical gap at 423, 410, and 414 nm,
respectively (Supporting Information, Figure S7). By compar-
ison, the optical gap of (TBA)4H3[PW11O39]a POT
reference that does not contain spiropyran moietiesarises
at a higher energy (342 nm). This shows that the SP moiety
dictates the absorption threshold in the three hybrid
compounds, similarly as in the SP−{MnMo6O18} dyads.12
Very importantly, whereas SPR is nonphotochromic in the
solid state in ambient conditions, the beige powder of TBA.
KSn[SPR] (Figure 5a) gradually shifts to deep purple under
low-power UV excitation (365 nm, 6 W). The photochromic
effect, which is detectable with the naked eye after only 3 s,
does not evolve anymore after 20 min, revealing a very fast
photoresponse and a strong coloration contrast. As observed in
solution, the color change is associated with the growth of the
two absorptions characteristic of the MC form with the more
intense one located at λmax = 584 nm (Figure 5b). Under
similar UV exposure, the powder of TBA.KSi[SPR] develops
the same purple coloration, the maximum of the intense
photogenerated MC absorption band being also located at 584
nm (Supporting Information, Figure S8), however, with a color
change less prononced than that for TBA.KSn[SPR]. In marked
observed at E1/2 = −1.19 V/SCE for SPR and at E1/2 = −1.11
V/SCE for TBA.KSn[I] are merging in TBA.KSn[SPR]. Exactly
the same considerations can be made concerning the TBA.
KSn[BSPR] compound (E1/2 = −1.13 and −1.61 V/SCE).
Finally, four redox processes are observed for TBA.KSi[SPR]
(E1/2 = −0.37, −0.98, −1.18, and −1.66 V/SCE, with relative
intensities 1:2:1:1). Again, the waves centered on the POT
fragment superimpose with that of the spiropyran and the POT
precursors, and confirm the 2:1 SP/POT ratio in TBA.
KSi[SPR]. Overall, these electrochemical measurements are
thus confirming the nature of all the reported compounds and
indicate that the POT and SP are minimally coupled
electronically, as previously observed for organosilyl and
organotin POT-based hybrids bonded to neutral organic
moieties.19
2.2. Optical Properties. The photochromic properties of
the reported materials have been studied both in solution and
in the solid state. As the MC form is unstable in acetonitrile at
room temperature for all of these compounds, the photo-
generation of the MC form in solution has systematically been
performed at −20 °C. Under UV irradiation (365 nm, 6 W),
colorless solutions of TBA.KSi[SPR] and TBA.KSn[SPR] in
acetonitrile quickly shift to purple. As shown in Figure 4, the
color change of TBA.KSn[SPR] is consistent with the
appearance of the MC form that is characterized by two
absorption bands in the visible region, the first one at λmax
around 390 nm, and the second very intense one at λmax = 570
nm. By comparison, this latter arises at λmax = 563 nm for the
irradiated SPR solution (Supporting Information, Figure S5).
These results clearly show that the grafting of SPs on POT
platforms does not significantly alter the optical signature of the
organic moieties in solution except for a very slight bath-
ochromic effect. The kinetics of the MC → CS thermal ring
closure were determined in the dark by following the
absorbance of the MC intense absorption as a function of
time after irradiating the acetonitrile solutions under 365 nm
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for TBA.KSn[SPR] and TBA.KSi[SPR]. It is worth noting that
TBA.KSn[SPR] shows a very fast and intense color change
effect, and the Abs584(t) vs t plot can be well-fitted by a single-
exponential rate law, with the coloration rate constant kc1
=
0.012 s−1. In the case of TBA.KSi[SPR], the coloration rate
significantly deviates from first-order kinetics but can be
adequately fitted using a biexponential rate law with kc1
=
0.003 s−1 and kc2 = 0.018 s−1, kc1 describing the major
contribution (around 77%) of the temporal evolution of
Abs584(t). This could be tentatively explained considering that
(i) two SP molecules are grafted onto the POT unit in TBA.
KSi[SPR] (for only one in the case of TBA.KSn[SPR]), both of
them contributing to the global absorption in the visible, and
(ii) the two MC open forms could be localized in different
environments in the framework. As expected from photographs,
the photocoloration response of TBA.KSi[SPR] is slower and
less intense, despite the two SP units, than for TBA.KSn[SPR],
signifying at first sight that, in ambient conditions, the CS →
MC photoinduced switch could be less effective in TBA.
KSi[SPR] than in TBA.KSn[SPR].
Figure 5. (a) Photographs of powders of TBA.KSn[SPR] after
different 365 nm UV irradiation times (in min). (b) Evolution of the
photogenerated absorption in TBA.KSn[SPR] after 0, 0.166, 0.5, 1, 1.5,
2, 3, 4, 5, 8, 15, and 30 min of UV irradiation (365 nm).
The color fading rates of TBA.KSn[SPR] and TBA.KSi[SPR]
in the solid state were measured in the dark (thermal fading)
and under yellow light, at room temperature, by monitoring the
temporal decay of the absorption band located at λmax = 584 nm
of samples once irradiated under UV excitation for 30 min
(Supporting Information, Figures S11 and S12). Decays can be
well-fitted using a biexponential rate law (see the Supporting
Information, Table S4, for detailed fading kinetic parameters).
As already proposed for other spiro-derivatives,21 this could be
interpreted as the result of two different structural micro-
environments around the merocyanin forms photogenerated at
the surface of the samples or lying deeper inside the bulk (let us
underline that the UV irradiation does not affect all the bulk of
the samples but is only limited to a small volume under the
surface, which depends on the penetration depth of the UV
light in the materials). During the thermal fading process, the
absorption of both materials exhibits a loss of only about 20%
in intensity, showing that, in the dark, a large part of the UV-
photogenerated zwitterionic MC form remains stabilized in the
polar hybrid framework. The extracted thermal fading rate
constants are kf1 = 1.426 .10−4 s−1 and kf2 = 0.024 s−1 for TBA.
KSn[SPR], and kf1 = 2.282 .10−4 s−1 and kf2 = 0.029 s−1 for
TBA.KSi[SPR] (in each case, kf1 describes the major
contribution of the temporal evolution of the absorption).
For each system, the significant difference in kinetic constant
values kf1 and kf2 and in the amplitudes (A1 and A2) extracted
from the fits could be explained considering at first sight that
the majority of the zwitterionic MC forms are photogenerated
near the surface while a smaller amount is generated deeper in
the bulk. A specific MC molecule near the surface is mostly
surrounded by similar open forms. Thus, the polarity of its local
environment increases and the MC molecule is better
stabilized. Therefore, the MC → CS thermal back conversion
(related to kf1) should be slow. At the opposite, MC forms in
the bulk are mainly surrounded by less polar CS isomers, and
so, they should be less stabilized in the framework. Hence, the
associated thermal MC → CS isomerization (related to kf2)
should be strongly faster. These values are quite comparable
with those of other hybrid materials based on spiropyran
molecules embedded in silica-gel matrixes,22 and they are much
faster than those of the rarest pure spiropyran molecules
developing solid-state photochromism at room temper-
ature.3a,23 Interestingly, the color fading process at room
contrast with TBA.KSn[SPR], TBA.KSn[BSPR] does not
display any significant solid-state photochromic activity in
ambient conditions (Supporting Information, Figure S9), the
color change remaining quasi undetectable by human eyes even
after irradiating the powdered sample under UV excitation for a
period as long as 1 day. This result underlines that small
structural variations of the SP moieties can induce dramatic
damages in the optical properties of the hybrid SP−POT
materials. Nevertheless, TBA.KSi[SPR] and TBA.KSn[SPR]
clearly illustrate that the grafting of SP moleculesinitially
nonphotochromic in the solid stateonto POT fragments is a
powerfull strategy to reach solid materials with strong
photoresponses.
The coloration kinetics of powders of TBA.KSn[SPR] and
TBA.KSi[SPR] at room temperature have been quantified from
the evolution of the photogenerated MC absorption with the
365 nm UV irradiation time t (Supporting Information, Figure
S10), and details of the kinetics parameters are given in the
Supporting Information (Table S4). Because of its very weak
photoresponse, the coloration kinetics of TBA.KSn[BSPR] has
not been investigated. Figure 6 displays the absorption at λmax
=
584 nm (Abs584(t)) as a function of the UV irradiation time t
Figure 6. Abs584(t) vs t plots for TBA.KSn[SPR] ( ) and TBA.
■
●
KSi[SPR] ( ). The lines show the fits of the plots according to rate
laws Abs584(t) = A1(exp(−k1t) − 1) and Abs584(t) = −A1 − A2 +
A1exp(−k1t) + A2exp(−k2t) for TBA.KSn[SPR] and TBA.KSi[SPR],
respectively (R2 are the regression coefficients for the fits).
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data can be obtained free of charge from the Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
4.3. Optical Measurements. Diffuse reflectance spectra were
collected at room temperature on a finely ground sample with a Cary
5G spectrometer (Varian) equipped with a 60 mm diameter
integrating sphere and computer-controlled using the “Scan” software.
Diffuse reflectance was measured from 250 to 1550 nm with a 2 nm
step using Halon powder (from Varian) as reference (100%
reflectance). The reflectance data were treated by a Kubelka−Munk
transformation29 to better locate the absorption thresholds. The
temperature is considerably accelerated when the irradiated
samples are put under yellow light, that is, with energy
corresponding to that of the photogenerated absorption.2 The
absorption loss is about 75% for both materials, and the color
fading rates are more than 3 times faster than in the dark (kf1 =
5.056 .10−4 s−1 and kf2 = 0.076 s−1 for TBA.KSn[SPR], and kf1 =
7.434 .10−4 s−1 and kf2 = 0.035 s−1 for TBA.KSi[SPR]).
3. CONCLUSION
samples were irradiated with a Fisher Bioblock labosi UV lamp (λexc
=
We have thus reported here the first examples of compounds
based on the covalent association of polyoxotungstates and
organic photochromic molecules. The synthetic approach used
herebased on Sonogashira couplingsallowed us to easily
modulate the nature of the inorganic platform (redox
properties and number of grafted organic molecules), and the
organic chromophore. The purity of all the synthesized
complexes has been unambiguously assessed using multiple
physical techniques, and their optical properties have been
deeply investigated. In solution, it has been observed that the
polyoxotungstate core does not significantly alter the optical
signature of the organic moieties but affects the kinetics of the
MC→ CS thermal ring formation. Furthermore, in the solid
state, it is shown that the grafting of a POT on a
nonphotochromic organic fragment can lead to highly photo-
chromic molecular hybrid compounds. However, this observa-
tion cannot be generalized, and it has been found that very
slight topological modifications can strongly influence the solid-
state photochromic properties of these new molecular systems.
Exploitation of the dual electrochromic and photochromic
properties of these hybrids is under current investigation. We
are also exploring emerging luminescence properties arising
from the covalent combination of such organic and inorganic
components. The results of these studies will be reported soon.
365 nm, P = 6 W). The photocoloration and fading kinetics were
quantified by monitoring the temporal evolution of the absorption
Abs(t), which was defined as Abs(t) = −log(R(t)/R(0)), with R(t) and
R(0) the reflectivity at the time t and at t = 0, respectively.
4.4. Syntheses of the Compounds. 4.4.1. Synthesis of 1,3-
Dihydro-3,3-dimethyl-1-propargyl-6-nitrospiro[2H-1-benzopyran-
2,2-(2H)-indole] (SPR). This compound has been synthesized by a
slight modification of the literature procedure.16 2,3,3-Trimethyl
indolenine (2.000 g, 12.6 mmol) and 2-propyn-1-tosyl (3.957 g, 18.9
mmol) were heated overnight at 70 °C. After cooling down to room
temperature, CH2Cl2 (10 mL) was added to the purple mixture and
the solution was extracted with water (20 mL). The aqueous phase
was then washed with CHCl3 (10 mL) three times and evaporated to
dryness, yielding a green oil that was dissolved in 2-butanone (40 mL).
Piperidin (0.623 g, 7.3 mmol), followed by 2-hydroxy-5-nitro-
benzaldehyde (1.219 g, 7.3 mmol), were then added. The resulting
dark red suspension was heated under reflux (90 °C) for 3 h, cooled
down to room temperature, and then stirred for 15 h. The obtained
suspension was filtered, and the precipitate was washed with 2-
butanone (2 × 3 mL). The filtrate was evaporated and purified
through silica gel chromatography (eluent CH2Cl2) to yield an orange
sticky solid (633 mg; yield: 15%). 1H NMR, 300 MHz, CDCl3: δ 8.04
(dd, J = 9.8, 2.7 Hz, 1H), 8.02 (d, J = 2.6 Hz, 1H), 7.22 (dd, J = 7.60,
1.4 Hz, 1H), 7.13 (dd, J = 7.2, 1.0 Hz, 1H), 7.00 (d, J = 10.4 Hz, 1H),
6.95 (dt, J = 7.6, 7.25, 0.9 Hz, 1H), 6.83 (d, J = 7.8 Hz, 1H,), 6.65 (d, J
= 9.8 Hz, 1H), 5.89 (d, J = 10.4 Hz, 1H), 4.07 (dd, J = 18.1, 2.6 Hz,
1H), 3.85 (dd, J = 18.1, 2.4 Hz, 1 H), 2.10 (t, J = 2.5 Hz, 1H), 1.31 (s,
3H), 1.21 (s, 3H).
4. EXPERIMENTAL SECTION
4.4.2. Synthesis of 1,3-Dihydro-3,3-dimethyl-1-propargyl-6-nitro-
spiro[2H-1-benzopyran-2,2-(2H)-(1H)benzindole] (BSPR). 1,1,2-Tri-
methyl-1H-benzindolenine (2 g, 9.6 mmol) and propargyl bromide
(1.7 g, 14.3 mmol) were suspended in acetonitrile (10 mL) and heated
at reflux for 24 h. The resulting dark blue solution was then cooled
down to room temperature and evaporated. After addition of CH2Cl2
(10 mL), the solution was extracted with water (20 mL). The red
aqueous solution was then washed with CH2Cl2 (10 mL) and CHCl3
(2 × 10 mL). The evaporation of the aqueous phase yielded a red oil
to which was added 2-butanone (7 mL), piperidin (144 mg, 1.69
mmol), and 2-hydroxy-5-nitrobenzaldehyde (283 mg, 1.69 mmol).
The resulting dark red suspension was heated under reflux (90 °C) for
3 h, cooled down to room temperature, and then stirred for 15 h. The
suspension was filtered, and the solid was washed with cold 2-
butanone (2 × 3 mL). The filtrate was evaporated and purified
through silica gel chromatography (eluent CH2Cl2) to yield 141 mg of
a powder of BSPR with ca. 10% of 1,3-dihydro-3,3-dimethyl-1-(3-
bromoprop-2-enyl)-6-nitrospiro[2H-1-benzopyran-2,2-(2H)-(1H)-
benzindole] (BrBSPR) as an impurity. 1H NMR, 300 MHz, CDCl3: δ
8.05−7.80 (m, 5H), 7.45 (td, 1H), 7.30 (m, 1H), 7.22 (m, 1H), 7.03
(d, J = 10.4 Hz, 1H), 6.71 (d, J = 10.2 Hz, 1H), 5.96 (d, J = 10.40 Hz,
1H), 4.16 (dd, 1H, J = 18.2, 2.6 Hz, 1H), 3.95 (dd, J = 18.22, 2.50 Hz,
1H), 2.11 (t, J = 2.50 Hz, 1H), 1.66 (s, 3H), 1.39 (s, 3H).
4.1. Methods and Materials. Solvents, including triethylamine,
were dried over suitable reagents and freshly distilled under argon
before use. The reagents 1-tosyl-2-propyne,16 K7[PW11O39]·14H2O,24
[Pd(PPh3)2Cl2],25 1-iodo-4-(triethoxysilyl)benzene,26 1-iodo-4-
(trichlorotin)benzene,15 TBA.KSn[I],15 and TBA.KSi[I]14b were
synthesized according to published procedures. The 1H (300.13
MHz, 400.13 MHz), and {1H} 31P (162 MHz) NMR spectra were
obtained at room temperature in 5 mm o.d. tubes on a Bruker Avance
II 300 or Bruker Avance III 400 spectrometer equipped with a QNP
probe head. IR spectra were recorded from KBr pellets using a Biorad
FT 165 spectrometer. Elemental analyses were performed at the
Institut des Substances Naturelles, Gif sur Yvette, France. Cyclic
voltammetry experiments at a carbon electrode were carried out using
the EG&G model 273A system. A standard three-electrode cell was
used, which consisted of a working vitrous carbon electrode, an
auxiliary platinum electrode, and an aqueous saturated calomel
electrode (SCE) equipped with a double junction.
4.2. X-ray Crystal Structure Determination of BrBSP. A single
crystal of compound BrBSP was selected, mounted onto a glass fiber,
and transferred under a cold nitrogen gas stream. Intensity data were
collected with a Bruker Kappa APEX2 with graphite monochromated
Mo Kα radiation. Unit cell parameter determination, data collection
strategy, and integration were carried out with the APEX 2 suite of
programs. Multiscan absorption correction was applied.27 The
structure was solved by direct methods with SHELXL software.28 All
nonhydrogen atoms were refined anisotropically. All hydrogen atoms
were placed at calculated positions. The crystallographic data and
refinement parameters for BrBSP are summarized in Table S1
(Supporting Information). The crystallographic details are available in
the Supporting Information in CIF format. CCDC no. 940802. These
4.4.3. Synthesis of TBA.KSn[SPR]. In a dried Schlenk flask, SPR
(34.6 mg, 0.1 mmol), TBA4[PW11O39{SnPhI}] (200 mg, 0.05 mmol),
Pd(PPh3)2(Cl)2 (2.3 mg, 0.004 mmol), and CuI (0.8 mg, 0.004 mmol)
were dissolved in 4 mL of dry DMF under an argon atmosphere.
Freshly distilled triethylamine (0.14 mL, 1 mmol) was then added, and
the mixture was stirred for 24 h. The resulting dark red solution was
precipitated with diethyl ether (150 mL), and the orange precipitate
was filtered, redissolved in acetonitrile (10 mL), and stirred with 5 mL
F
dx.doi.org/10.1021/ic401380a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
of Amberlite IR-120 in the TBA+ form. The resulting orange solution
was then precipitated and dried with diethyl ether, yielding an orange
powder (180 mg, Yield: 86%). H NMR, 400 MHz, CD3CN: δ 8.12
ASSOCIATED CONTENT
* Supporting Information
Tables containing crystallographic data, half-wave potentials,
kinetic parameters, and coloration and fading kinetic
■
S
1
(d, J = 2.8 Hz, 1H), 8.01 (dd, J = 9.0, 2.8 Hz, 1H), 7.61 (d + dd, J = 8.2
Hz, JSnH = 96.0 Hz, 2H), 7.32 (d+ dd, J = 8.2 Hz, JSnH = 33.0 Hz, 2H),
7.23 (td, J = 7.7, 1.3 Hz, 1H), 7.18 (ddd, J = 7.7, 1.3, 0.6 Hz, 1H), 7.15
(dd, J = 10.4, 0.7 Hz, 1H), 6.92 (td, J = 7.7, 1.3 Hz, 1H), 6.87 (dt, J =
7.7, 0.7 Hz, 1H), 6.74 (dd, J = 9.0, 0.7 Hz, 1H), 6.00 (d, J = 10.4 Hz,
1H), 4.36 (d, J = 18.4 Hz, 1H), 4.17 (d, J = 18.4 Hz, 1H), 3.15 (m,
32H), 1.64 (m, 32H), 1.38 (sextuplet, J = 7.3 Hz, 32H), 1.31 (s, 3H),
1.19 (s, 3H), 0.97 (t, J = 7.3 Hz, 48H). 31P NMR, 162 MHz, CD3CN:
δ −10.99 (s + d, JSnP = 23.5 Hz). IR (KBr, cm−1): ν 2962 (m), 2933
(m), 2873 (m), 2360 (w), 2340 (w), 1652 (w), 1519 (w), 1482 (m),
1459 (m), 1380 (w), 1337 (w), 1276 (w), 1070 (m), 963 (s), 886 (s),
811 (s), 706 (w), 667 (w), 593 (w), 514 (w), 381 (m), 336 (w), 302
(w), 265 (m). MS (ESI): most intense peaks, {Aggregates}x− m/z
{[KSn[SP]]}4‑ 804.8 (100), calcd 804.8; {H[KSn[SP]]}3− 1072.4 (75),
calcd 1072.1; {TBA·H[KSn[SP]]}2− 1730.4 (25), calcd 1730.3. Anal.
Calcd for PW11SnO42C27H21N2C64H144N4(H2O)2: C, 25.88; H, 4.03;
N, 1.99. Found: C, 25.65; H, 3.95; N, 2.05.
4.4.4. Synthesis of TBA.KSn[BSPR]. This compound was obtained
following the same experimental protocol than that described for TBA.
KSn[SPR], using the raw BSPR compound (36.9 mg, 0.1 mmol)
instead of the SPR one, as an orange powder (174 mg, Yield: 82%).
1H NMR, 400 MHz, CD3CN: δ 8.14 (d, J = 2.8 Hz, 1H), 8.06 − 7.97
(m, 2H), 7.92−7.83 (m, 2H), 7.60 (d + dd, J = 8.2 Hz, JSnH = 96.0 Hz,
2H), 7.46 (ddd, J = 8.3, 6.8, 1.3 Hz, 1H), 7.38−7.29 (m, 3H), 7.29
(ddd, J = 8.3, 6.8, 1.1 Hz, 1H), 7.21 (dd, J = 10.4, 0.7 Hz, 1H), 6.72
(dd, J = 9.1, 0.6 Hz, 1H), 6.08 (d, J = 10.4 Hz, 1H), 4.48 (d, J = 18.6
Hz, 1H), 4.26 (d, J = 18.6 Hz, 1H). 3.15 (m, 32H), 1.65 (s, 3H), 1.64
(m, 32H), 1.38 (sextuplet, J = 7.3 Hz, 32H), 1.36 (s, 3H), 0.97 (t, J =
1
parameters and figures showing structural representations, H
and 31P NMR spectra, Abs(t) vs t plots, double and single
exponential fits, Kubelka−Munk transformed reflectivity vs
wavelength and energy plots, photographs of powders,
evolution of the photogenerated absorption, and temporal
evolution of the absorbance at 584 nm. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: guillaume.izzet@upmc.fr.
*E-mail: remi.dessapt@cnrs-imn.fr.
*E-mail: pierre.mialane@uvsq.fr.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the CNRS, the Minister
̀
e de l′Enseignement
Super
BIOOPOM.
́
ieur et de la Recherche, and the ANR-11-BS07-011-01
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■
7.3 Hz, 48H). 31P NMR, 162 MHz, CD3CN: δ = −10.99 (s + d, JSnP
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(70.6 mg, 0.204 mmol), TBA3[PW11O40{SiPhI}2] (200 mg, 0.05
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1
filtration (130 mg, Yield: 62%). H NMR, 400 MHz, CD3CN: δ 8.11
(d, J = 2.9 Hz, 2H), 8.02−7.94 (m, 1H), 7.73 (d, J = 8.2 Hz, 4H), 7.32
(d, J = 8.2 Hz, 4H), 7.22 (td, J = 7.7, 1.3 Hz, 2H), 7.17 (ddd, J = 7.7,
1.3, 0.6 Hz, 2H), 7.13 (dd, J = 10.4, 0.5 Hz, 2H), 6.91 (td, J = 7.7, 1.3
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(d, J = 10.4 Hz, 2H), 4.36 (d, J = 18.5 Hz, 2H), 4.16 (d, J = 18.5 Hz,
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2874 (m), 2360 (w), 2340 (w), 1609 (w), 1519 (w), 1482 (m), 1458
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3.50; N, 2.27. Found: C, 28.48; H, 3.50; N, 2.10.
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