ON-OFF luminescence signaling of hybrid organic-inorganic switches

Article abstract of DOI:10.1021/ic400676j

The dyads 1_OFF and 2_OFF were prepared by combining the inorganic luminophores [Ru(phen)₂(2-[imidazol-2-yl]pyridine)] ²⁺ and [Re(CO)₃Cl(2-[imidazol-2-yl]pyridine)] with 2-(anthracen-9-yl)-4-methylphenol as a second photoactive moiety. In both cases, the inorganic unit operates as the emitter, whereas the organic part acts as a controller. Emission of the inorganic luminophore can be reversibly switched ON and OFF by adjusting the energetic level of the ³π-π* state of the appended anthracene unit through either dearomatization using a photohydration or aromatization applying a thermal dehydration. Emission of both switches is reversibly recorded and erased multiple times without significant degradation.

Full text of DOI:10.1021/ic400676j

Article
pubs.acs.org/IC
ON-OFF Luminescence Signaling of Hybrid Organic−Inorganic
Switches
Palani Natarajan* and Michael Schmittel*
Center of Micro- and Nanochemistry and Engineering, Department of Chemistry and Biology, Organische Chemie I, Universitat
̈
Siegen, Adolf-Reichwein-Straße 2, D-57068 Siegen, Germany
S
* Supporting Information
ABSTRACT: The dyads 1OFF and 2OFF were prepared by
combining the inorganic luminophores [Ru(phen)2(2-[imidazol-
2-yl]pyridine)]2+ and [Re(CO)3Cl(2-[imidazol-2-yl]pyridine)]
with 2-(anthracen-9-yl)-4-methylphenol as a second photoactive
moiety. In both cases, the inorganic unit operates as the emitter,
whereas the organic part acts as a controller. Emission of the
inorganic luminophore can be reversibly switched ON and OFF by
3
adjusting the energetic level of the π−π* state of the appended
anthracene unit through either dearomatization using a photo-
hydration or aromatization applying a thermal dehydration.
Emission of both switches is reversibly recorded and erased
multiple times without significant degradation.
deaerated CH3CN) was realized by eradicating the lower lying
nonradiative 3π−π* states of the appended anthracene via
photodimerization. The OFF state was regenerated by
thermally splitting the photodimer. The same group equally
introduced the doubly anthracene-functionalized switch [Ru-
(bpy)2L]2+ (L = 1-bis(anthracenylmethyl)-2-(bipyridyl)-
ethane)9 capitalizing on an intramolecular anthracene photo-
dimerization and thermal cycloreversion for luminescence
readout and erase cycles. For all of these switches, the authors
observed invariable readout stability for multiple cycles without
loss in emission intensities. However, emission erase was not
complete due to the high stability of the photodimer. All these
findings thus indicate that fully reversible luminescent switches
can only be achieved through a proper design of the
concomitant controller unit.1a
Photoexcitation of 2-(anthracen-9-yl)phenol and its deriva-
tives in aqueous solutions is well-known to yield the
corresponding hydrated anthracenyl derivatives (triaryl carbi-
nols) through excited state intramolecular proton transfer
(ESIPT).10 Because this process allows manipulation of the
energy levels of anthracene,10e we utilized our expertise in the
field of Ru2+-luminophores11 to design two novel luminescent
switches (Chart 1) with either [Ru(phen)2(2-[imidazol-2-
yl]pyridine)]2+ or [Re(CO)3Cl(2-[imidazol-2-yl]pyridine)]
subunits as emitter and the 2-(anthracen-9-yl)-4-methylphenol
as a controller. The objective was to modulate luminescence of
the inorganic emitter reversibly by manipulating the triplet
energy level of the appended 2-(anthracen-9-yl)-4-methylphe-
nol via ESIPT photohydration and subsequent dehydration.
INTRODUCTION
■
Molecules that reversibly shift their functional behavior in
response to one or several external stimuli, such as light, heat,
change in pH, electrical field, microenvironment, and so forth,
are called molecular switches.1 While great success stories have
been realized with colorimetric devices,2 luminescent organic
switches often show problems with long-term stability of the
ON (write) and OFF (erase) states because of aggregation,
oxygen quenching, and decomposition.3 Therefore, researchers
have intensified the development of hybrid organic−inorganic
switches with the inorganic units acting as the emitter due to
the more pronounced stability of their redox states, specifically
in presence of heat, light, and water.4,5 Complementarily, the
organic unit takes the part of modulating the inorganic
luminophore. For the latter purpose, anthracene derivatives
have been frequently used, because they are well-known to
3
quench the MLCT emission of numerous second and third
row transition metal complexes, such as Ru2+-, Re+-, Pt2+
1a,4f,5
3
3
polypyridyls, through MLCT→ π−π* energy transfer.
The complexes [Ru(bpy)2L]2+ and [Re(CO)3(Cl)L] with L =
N-(9-anthracenylmethyl)-2-(2-pyridyl)benzimidazole may
serve as representative examples.6 Neither a MLCT based
3
emission (λex = 450−470 nm) nor a 1π−π*/3π−π* anthracene
emission (λex = 355−375 nm) were observed at ambient
conditions.6 Based on this design principle, several groups have
selectively oxidized the appended anthracene chromophore in
Ru/Re-anthracene dyads thus restoring luminescence of the
inorganic unit (vide infra).5,7 Castellano and co-workers8 have
adopted a slightly modified approach using [Ru(bpy)2L]2+ (L =
1-(anthracen-9-yl)-2-(bipyridyl)ethane) as OFF state (Φ <
0.004 in deaerated CH3CN). The ON state with a considerable
MLCT based emission of the ruthenium core (Φ ∼ 0.06 in
Received: March 19, 2013
© XXXX American Chemical Society
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Chart 1. Molecular Structure of Dyads 1OFF and 2OFF, and Their Photo Product 1ON and 2ON, Respectively
a
Scheme 1. Synthetic Routes to Ligand 3 (a) and Dyads 1OFF and 2OFF (b)
a
1
Numbering is only used for H NMR assignments and does not reflect IUPAC nomenclature.
B
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Figure 1. UV−vis absorption spectra of 1OFF (left) and 2OFF (right) in air-equilibrated acetonitrile (purple) and 50% aqueous acetonitrile (blue) (1
× 10−4 M) at room temperature.
a
Table 1. Optical Absorption and PL of 1OFF, 2OFF, 1ON, and 2ON, and Their Model Compounds
T1
b
c
d
ef
,
λabs /nm (10−4 ε/M−1 cm−1
)
λmax /nm
ΦPL
/(cm−1
ND
)
PL
compound
1OFF
210 (102), 240 (sh), 255 (106), 293 (62), 340 (sh), 350 (9), 372 (11), 390 (13), 442 (13),
471 (14)
580−670 (b) <10−3
2OFF
253 (133), 287 (sh), 327 (22), 342 (27), 417 (18)
235 (154), 274 (sh), 462 (21)
600−700 (b) <10−4
ND
1ON
626
616
624
617
430
0.0142
0.0031
17600
18100
15700
16400
14500
2ON
[Ru(phen)3]2+
[Re(Phe-ImPy)]+ 239, 414
244 (173), 305(sh), 411 (26)
f
f
287, 466
0.023
g
g
h
g
i
0.0011
i
9-PA
225, 257, 353, 369, 396
0.53
a
b
Triplet energy values for model compound are taken from the literature.19−21. Absorption spectra were measured in air-equilibrated solutions at 1
c
d
× 10−4 M in 50% aqueous acetonitrile. Emission spectra were recorded in air-equilibrated solutions at 1 × 10−5 M in 50% aqueous acetonitrile. PL
e
quantum yields (ΦPL) were determined using [Ru(bpy)3]2+ as a standard (Φ = 0.028, λexc = 450 nm) in aerated CH3CN-water solution. The triplet
f
g
h
i
energy of 1ON and 2ON were estimated from the onset of their emission spectra. Ref 19. Ref 20. Ref 6. Ref 21. Abbreviations: 9-PA, 9-
phenylanthracene; T1, triplet energy; sh, shoulder; b, broad; ND, not determined.
Because hydration and dehydration normally occur readily and
quantitatively,12 we expected good signals for readout and full
erase capability, thus overcoming the disadvantages of existing
switches.1 Herein, we report the synthesis and the optical,
photochemical as well as functional behavior of two hybrid
dyads (Chart 1) in aqueous solutions.
characterization of all compounds is provided in the
Experimental Section and detailed further in the Supporting
Information.
Optical Properties. UV−vis absorption and photolumi-
nescence (PL) spectra of 1OFF and 2OFF were recorded in
CH3CN or in a mixture of CH3CN-water (50:50) at ambient
conditions. In both solvent systems, the absorption spectra of
1OFF and 2OFF were basically the sum of the corresponding
subunits’ absorptions with only minor differences in wavelength
maxima and band shapes (Figure 1 and Table 1). For 1OFF, the
spectrum shows two MLCT bands; the lowest energy band at
471 nm corresponds to Ru (dπ)→π* transitions of ligand 3,
whereas the band at 442 nm arises from Ru (dπ)→π* of
phenanthrolines.17 The structured absorptions in the visible
region between 350 and 400 nm are the characteristic
collection of π−π* bands of arylanthracene as well as high
energy MLCT transitions.6,18 Besides, the intense absorptions
in the UV region between 210 and 280 nm arise by admixture
of intramolecular π→π* transitions from phenanthrolines, 2-
(imidazol-2-yl)pyridine and arylanthracene (β-band) moi-
eties.17,18 Analogous transitions, MLCT as well as intraligand
π→π*, were equally noticed in 2OFF (Figure 1), with the
MLCT band being blue-shifted about 54 nm (∼ 2750 cm−1) as
RESULTS
■
Synthesis. The synthetic approach to ligand 3 and dyads
1OFF and 2OFF is outlined in Scheme 1.
A typical procedure to prepare alkylimidazoles involves the
nucleophilic substitution of alkyl halides by sodium or
potassium imidazolates.13 However, all our attempts to prepare
9-(5-(bromomethyl)-2-methoxyphenyl)anthracene from 9-(2-
methoxy-5-methylphenyl)anthracene were met with failure.
Hence, ligand 3 was synthesized by a condensation of 2-
(imidazol-2-yl)pyridine and 2-(anthracen-9-yl)-4-
(hydroxymethyl)phenol at elevated temperature (Scheme
1).14 The imidazole itself was afforded from the cyclo-
condensation of pyridine-2-carboxaldehyde, glyoxal, and
aqueous NH3 in ethanol.15 The anthracene derivative was
prepared in a three-step procedure involving a Pd(0) catalyzed
Suzuki coupling of 9-anthraceneboronic acid and 3-bromo-4-
methoxybenzaldehyde followed by demethylation and reduc-
tion (Scheme 1).16 Compound 1OFF was prepared by reaction
of ligand 3 with [Ru(phen)2Cl2] in ethanol,11 whereas 2OFF was
synthesized in toluene from [Re(CO)5Cl] and ligand 3.6 Full
17
compared to that of 1OFF. A detailed analysis of the UV−vis
profiles indicates that the ground states of both chromophores
in 1OFF and 2OFF are not interfering much, because they are
separated by an aliphatic chain. The well-defined separation of
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1
their absorption bands allowed selective excitation of both
chromophores as of interest. When the PL response of 1OFF
and 2OFF (Supporting Information, Figure S1) was evaluated by
exciting at 350 to 480 nm using an increment of 10 nm,
substantial emission was observed neither from 1OFF (ΦPL
<10−3, λex = 450 nm) nor from 2OFF (ΦPL <10−4, λex = 420
nm), vide infra.6,7c,17 The corresponding excitation spectra for
1OFF and 2OFF were recorded by monitoring MLCT as well as
anthracene, based emissions at 630 and 400 nm, respectively,
and show quite clearly distinct absorption features suggesting
that both chromophores are mutually independent (Supporting
Information, Figures S2 and S3).
NMR, mass spectroscopy, IR and elemental analysis. H NMR
spectra of ligand 3 and its photoproducts 4 and 5 are shown in
Figure 2. Two major changes are visible by comparing the
photoproducts with 3 as the reactant. A new peak appears at
3.90−3.96 ppm, while the signal at 8.68 ppm has disappeared.
In the 13C NMR, two carbons of the photoproducts
dramatically shift upfield to 36.2 and 81.1 ppm from 105.5
1
and 117.1 ppm in ligand 3. It is worth noting that H NMR
spectra of 9-hydroxy-10-hydroanthracenes show a CH2 signal at
3.85−3.98 ppm22 like ligand 3 after photohydration (Figure 2).
Thus, the above changes are characteristic for hydration of 2-
(anthracen-9-yl)alkylphenols.22 Reciprocally, H and 13C NMR
1
Photolysis of 3. As outlined above in our project design the
well-established ESIPT photohydration of 2-(anthracen-9-yl)-4-
methylphenol is considered to switch ON the emission of the
inorganic luminophore in 1OFF and 2OFF. At the onset, we thus
examined the photoreactivity of ligand 3 in aqueous solutions
to probe the influence of the 2-(imidazol-2-yl)pyridine unit on
the photoreactivity of 2-(anthracen-9-yl)-4-methylphenol.
signals of the 2-(imidazol-2-yl)pyridine subunit in ligand 3 were
not affected significantly by photolysis indicating that the
subunit did not react under the experimental conditions.
Anthracenes are recognized for their characteristic optical
properties.23 Thus, absorption and PL analysis were used to
monitor the photoreactivity of 3 at 30 min intervals. In both
channels, the initial absorption/emission intensity of the 2-
(anthracen-9-yl)-4-methylphenol residue in 3 decreased grad-
ually with irradiation time as a result of the loss of
conjugation.10 After 4−5 h of constant excitation at λ = 355
5 nm, the solution of ligand 3 was completely transparent at
anthracene absorption and emission wavelengths (Figure 3)
suggesting that the photoreactive 2-(anthracen-9-yl)-4-methyl-
phenol chromophore did not exist anymore. Eventually, the
following rationalizations were made based on the results of
NMR, mass, UV−vis, and PL studies: (i) upon photolysis, the
2-(anthracen-9-yl)-4-methylphenol unit in 3 undergoes the
well-known ESIPT process and is quantitatively transformed
into the less conjugated hydrated derivative 4,10e (ii) photo-
physical properties and energy levels of the hydrated
anthracenyl residue are quite different from those of the 2-
(anthracen-9-yl)-4-methylphenol unit, and (iii) photoreactivity
Irradiation of 3 at 355
5 nm either in 50% aqueous
CH3CN or in 50% aqueous methanol yielded within 4−5 h the
expected 9-hydroxy- or 9-methoxy-10-hydroanthracene deriva-
tives 4 and 5 (Chart 2).10 Both products were confirmed by
Chart 2. Molecular Structure of Ligand 3 and Its
Photoproducts 4 and 5
Figure 2. 1H NMR spectra (CD2Cl2) of (a) ligand 3 and (b,c) its photoproducts. (b) The photoproduct 4 and (c) the photoproduct 5 are formed
after photolysis of 3 in water-acetonitrile and water−methanol, respectively. Notice the diagnostic signals (CH2, OCH3) of both products located in
the upfield region (marked with a circle). Proton 10-H of the anthracene unit is not present in the aromatic region of the photoproducts.
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Figure 3. Photochemical reaction of ligand 3 in 50% aqueous CH3CN (λex = 355 5) was monitored at 30 min intervals by UV−vis (left) and
luminescence (right) analysis. Notice that the absorption at 240−270 nm increases due to the formation of small aromatic rings from the original
anthracenyl subunit, whose absorption and emission intensities decline.
Figure 4. 1H NMR spectra of (a) 1OFF and (b) its photoproduct 1ON in CD3OD. Notice the diagnostic signal for CH2 in 1ON located in the upfield
region (marked with a circle). Likewise, anthracene proton 10-H disappeared and other protons (1-H to 8-H) underwent upfield shift in the
aromatic region of 1ON
.
of the 2-(anthracen-9-yl)-4-methylphenol in ligand 3 is not
affected substantially by the 2-(imidazol-2-yl)pyridine sub-
stituent.
products display a new signal in the aliphatic region, while
concurrently an aromatic signal is gone. In addition, after
photoexcitation the 1H NMR peaks of the 2-(anthracen-9-yl)-4-
methylphenol units appear upfield shifted by 0.2−0.3 ppm,
whereas signals corresponding to the metal complex unit are
not affected signifycantly. In all, the detected spectral changes
are approximately similar to those noticed for ligand 3 and its
photohydrated product 4 (Figure 2).
The time evolution of the photodearomatization of 1OFF and
2OFF was monitored by absorption and emission measurements.
As shown in Figure 6, the absorption bands between 350 and
400 nm arising from the 2-(anthracen-9-yl)-4-methylphenol
residue in 1OFF and 2OFF completely vanished after 18 h of
photolysis. In this course, a new peak appeared in the high
energy region (λ = 240−255 nm) being diagnostic for the
The quantum yield10a for photogeneration of 4 (Φpdt = 0.071
in 50% aqueous CH3CN) and 5 (Φpdt = 0.126 in 50% aqueous
methanol) (see Chart 2) was assessed through UV−vis
absorption measurements (cf. experimental part).
Photolysis of 1OFF and 2OFF. Both 1OFF and 2OFF were
excited separately in a CH3CN-water mixture (50:50) under
exactly the same conditions as mentioned for 3. Within 18 h,24
1OFF and 2OFF entirely transformed into the hydrated products
1ON and 2ON (Chart 1),25 which were isolated and
characterized by NMR, mass spectroscopy, and elemental
analysis. The 1H NMR spectra of 1OFF and 2OFF as well as their
photoproducts are shown in Figures 4 and 5. Both photo-
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Figure 5. 1H NMR spectra of (a) 2OFF and (b) its photoproduct 2ON in CD3OD. Notice the diagnostic signal for CH2 in 2ON located in the upfield
region (marked with a circle). Likewise, anthracene proton 10-H disappeared and other protons (1-H to 8-H) underwent upfield shift in the
aromatic region of 2ON
.
Figure 6. UV−vis (left) and PL (right) spectra measured after 18 h of photoexcitation (λ = 355 5 nm) of 1OFF (red, λex = 450 nm) and 2OFF (blue,
λex = 380 nm) in 50% aqueous CH3CN. The hump close to 760 nm in the emission corresponds to the Raman line.
formation of small aryl units.10e Clearly, the pendant
anthracene chromophore is dearomatized (destroyed), while
the remaining absorptions persist similar to those of the
corresponding alkyl-functionalized Ru2+ and Re+ chromo-
phores, vide infra. The UV−vis absorption changes were
increasing destruction of the appended organic chromophore
proves that the latter is responsible for the nonemissive nature
5−9
of the inorganic luminophore in 1OFF and 2OFF
.
Luminescence excitation spectra of 1OFF and 2OFF were
measured after 18 h of photolysis monitoring both anthracene-
and MLCT based emissions. While the MLCT-based transition
was clearly discernible between 400 and 460 nm, anthracene-
based transitions were not detected in the spectra (Supporting
Information, Figure S4) indicating that exclusively anthracene
had undergone photodehydration.
utilized to determine the photogeneration quantum yield
10a
Φpdt
for 1ON (Φpdt = 0.018) and 2ON (Φpdt = 0.022)
(Chart 1) in 50% aqueous CH3CN with reference to the
photohydration of 2-(anthracen-9-yl)phenol (Φpdt = 0.09 in
D2O+CH3CN).10e
Luminescence spectra recorded after about 90 min of
Upon preparative photolysis, 1OFF and 2OFF transformed into
the hydrated analogues 1ON and 2ON, as clearly supported by
mass and elemental analysis results. Throughout photolysis, the
inorganic complex of both compounds was not affected because
its MLCT absorption band remained unaltered. Moreover,
optical properties of 1ON, 2ON are rather different from those of
1OFF, 2OFF as apparent from their UV−vis and PL data. The
photolysis already exhibit broad and unstructured peaks (Figure
3
6) at λmax = 626 and 616 nm that are characteristic MLCT
emission for Ru2+ and Re+ complexes, respectively.5,17 To reach
maximum PL intensity at saturation level (no further
enhancement or loss), however, 18 h of photoexcitation are
required.24 The growth of MLCT emission intensity with
3
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Figure 7. Luminescence spectra of 1OFF→1ON (left), and 2OFF→2ON (right) measured at 2 h intervals during photodearomatization (λex = 355
5
nm). Notice that the MLCT emission intensity increases upon irradiation.
Figure 8. Absorption spectra of 1OFF→1ON (left), and 2OFF→2ON (right) measured at 2 h intervals during photodearomatization (λex = 355 5 nm).
Notice that the absorption for the 2-(anthracen-9-yl)-4-methylphenol residue decreases during irradiation.
photophysical characteristics of 1ON and 2ON (Table 1) are
actually similar to those of alkyl-functionalized metal
complexes, such as [Ru(phen)2L]2+ with L = 2-(1-methyl-
comparable to those of the corresponding alkyl-substituted
metal complexes, such as [Ru(phen)2L]2+ with L = 2-(1-
methylbenzimidazol-2-yl)pyridine, Φ = 0.01726 and [Re-
(CO)3ClL] with L = 2-(1-ethylbenzimidazol-2-yl)pyridine, Φ
= 0.002.27 The determined PL quantum yields are in agreement
benzimidazol-2-yl)pyridine26 (λmax = 468 nm, λmax = 619
nm) and [Re(CO)3(Cl)L] with L = 2-(1-ethylbenzimidazol-2-
yl)pyridine27 (λmaxabs = 413 nm, λmaxPL = 616 nm), respectively.
Photoinduced and Thermal Switching of Lumines-
cence. To study the suitability of 1 and 2 to act as reversible
ON and OFF luminescence switches, their ON state 1ON/2ON
was produced photochemically and reversed thermally to the
OFF state 1OFF/2OFF. Clean thermal switching could be
achieved by heating 1ON and 2ON at 80−90 °C, as evident
from NMR (Supporting Information, Figures S30 and S31) and
quantum yields (Supporting Information, Table S1).
abs
PL
with NMR findings that 1OFF/2OFF transformed fairly into 1ON
/
2
ON. In OFF → ON photoswitching, the absorption bands
between 350 and 400 nm belonging to the 2-(anthracen-9-yl)-
4-methylphenol residue completely disappeared after 18 h of
excitation (Figure 8). Thus, this moiety is entirely dearomatized
after photolysis.10
Aryl carbinols are unstable and undergo dehydration in acidic
medium,29 as do 9-hydroxy-9-aryl-10-hydroanthracenes that
form 9-arylanthracenes.30 As a result, 1ON/2ON were trans-
formed into 1OFF/2OFF by dehydration. Full conversion was
observed at 80−90 °C within 4 h, while in the presence of
desiccants, such as molecular sieves or acidic alumina, the
transformation was even accomplished at 40−50 °C within
2.5−3 h. Both 1OFF and 2OFF, as obtained by dehydration, were
OFF → ON → OFF switching was monitored by PL and
UV−vis studies taking spectra at 2 h intervals (Figures 7 and 8).
Upon constant irradiation of 1OFF and 2OFF using either a
xenon lamp or a Rayonet photoreactor (λex = 355 5), the
3
intensity of the MLCT emission increased by 120−150 fold
1
(Figure 7) due to formation of 1ON/2ON (Chart 1). After about
18 h of irradiation, no further PL intensity variation was
noticed. At this point, emission quantum yields were
determined by using [Ru(bpy)3]2+ as a standard in aerated
water (Φ = 0.028)28 yielding Φ = 0.0142 and 0.0031 for 1ON
and 2ON, respectively. It is worthy of mention that both PL
emission wavelengths and quantum yields of 1ON and 2ON are
characterized by NMR and mass analysis. As expected, the H
and 13C NMR signals of the dehydrated compounds were
found to be identical to those of 1OFF and 2OFF prepared
independently (Scheme 1 and Supporting Information, Figures
S30 and S31).
The thermal dehydration of 1ON/2ON in dry CH3CN without
any desiccant was monitored over time by absorption and PL
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Figure 9. Reversible switching behavior of 1OFF to 1ON (1OFF↔1ON, left) and 2OFF to 2ON (2OFF↔2ON, right) or vice versa, during photoirradiation
followed by thermal dehydration experiments. 1OFF and 2OFF at start of cycle 1 were produced by thermal dehydration of 1ON and 2ON
.
a
Scheme 2. Proposed Mechanism of Switching in Dyads 1 and 2
a
Notice that the triplet state energy and conjugation of the organic pendant changes during photodearomatization and thermal aromatization (LF −
ligand field of 2-(anthracen-9-yl)-4-methylphenol unit).
studies. At 80−90 °C the initial PL intensity of solutions of 1ON
and 2ON commenced to bleach after 20 min and complete loss
of emission was realized after 4 h. At this time, the MLCT
and monitored its course over 5 cycles (Figure 9). The result
shows that conversion of 1OFF→1ON and 2OFF→2ON and vice
versa takes place cleanly and without substantial degradation
(Supporting Information, Table S1 and Figures S30 and S31).
3
emissions of 1ON at 550−750 nm and of 2ON at 550−700 nm
had disappeared substantially and their quantum yield values
had fallen to <10−3 (Supporting Information, Table S1). The
half-life of the thermal dehydration of 1ON to 1OFF (t1/2 = 154
min) and 2ON to 2OFF (t1/2 = 147 min) was determined at 80
°C by monitoring the decreasing PL intensity over time
(Supporting Information, Figures S32 and S33). In the
absorption channel, the signals for 2-(anthracen-9-yl)-4-
methylphenol fully recovered with ε being comparable to that
of fresh 1OFF and 2OFF. Quantitative transformation to 1OFF and
2OFF was equally corroborated from NMR (Supporting
Information, Figures S30 and S31). Perceptibly, the spectral
changes observed during thermal rearomatization, ON → OFF,
were reversing those of the initial photodearomatization, OFF
→ ON, shown in Figures 7 and 8.
DISCUSSION
■
Mechanism of Luminescence Switching. As mentioned
in the introduction, various anthracene derivatives have been
described to quench the MLCT emissions of appended
transition metal complexes, including those of Ru2+ and Re+
luminophores, via energy transfer (Supporting Information,
Charts S1 and S2).1a,b,4f,5−9 The PL quantum yields of these
dyads were found to be in the order of 10−3 to 10−4 at room
temperature,6,31 with quantum yields increasing >100 fold after
5,7
1
oxidation of anthracene residue with either O2 or H2O2.
Photophysical studies on these multichromophoric systems,32
in particular those with anthracene or perylene decorated
transition metal complexes, reveal no absorption for the
inorganic subunit in the transient absorption spectra. Rather
they exhibit an intense absorption corresponding to the 3π−π*
To check for multiple reversible switching, we performed the
photodearomatization and thermal rearomatization repeatedly
H
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complexes proved to be air- and moisture-stable, which allowed all
measurements to be done at ambient conditions unless otherwise
state of the pendant organic substituent. The sum of these
findings indicates that the MLCT state has been effectively
3
1
stated. H and 13C NMR spectra were recorded on a Bruker Avance
quenched via energy transfer to the lower-lying nonradiative
400 MHz spectrometer in deuterated solvents. Chemical shifts are
reported in δ-scale (ppm) and are referenced to residual protiated
solvent. Infrared spectra were recorded on a Varian 1000 FT-IR
instrument, and the ESI mass spectra were recorded on a Thermo-
Quest LCQ Deca instrument. Elemental analysis was measured using a
EA 3000 CHNS.
UV−vis absorption spectra were recorded on a Varian Cary 100
Bio-UV/Visible spectrometer either in CH3CN or 50:50 aqueous
CH3CN-water. PL spectra and PL quantum yields (ΦPL) and
excitation spectra were measured on a Varian Cary Eclipse
Fluorescence Spectrophotometer with excitation and emission slits
set to either 2.5 or 5 nm. PL quantum yields (ΦPL) were determined
using [Ru(bpy)3]2+ as a standard (Φ = 0.028, λexc = 450 nm)28 in
aerated CH3CN-water solution. The following equation was used for
3π−π* state of the attached organic unit.7,32
Based on these results and the optical properties of
luminescent switches 1OFF/2OFF and their photoproducts
1
ON/2ON, we propose a possible working mechanism and
energy level change during photodearomatization and thermal
aromatization in Scheme 2. A key element of our mechanistic
proposal is that the quenching process MLCT→3π−π* is
3
absent, when the pendant 2-(anthracen-9-yl)-4-methylphenol
in 1OFF/2OFF has undergone ESIPT photohydration to 1ON
2ON
/
.
Generalizations about the Functional Behavior of 1
and 2. The energy levels of anthracene and its derivatives can
be modulated reversibly by different reactions, such as
oxidation and reduction,3k,33 cycloaddition and retro-cyclo-
addition,34 ring closing and opening,35 hydration and
dehydration,10 etc.23 Among oxidation and reduction, cyclo-
addition and retro-cycloaddition, reactions of anthracene have
been extensively employed in the development of molecular
machines, sensors, switches, and so on.1,36 However, the
concept of hydration and dehydration at the anthracene core
has not been explored practically for molecular materials.1 This
omission may be due to the essential need of an aqueous
medium for hydration, where many compounds are either
unstable or insoluble. To the best of our knowledge, we herein
present the first example of a luminescent switch that is
the calculation of ΦPL for 1ON and 2ON
:
Φ = Φ(Iu/Is)(As/Au)(η /η )2
u
s
u
s
with the subscripts “s” and “u” referring to standard and unknown
samples, Au and As to absorbances at the excitation wavelength, Iu and
Is to the integrated emission intensities (i.e., areas under the emission
curves), and ηu and ηs to the refractive indexes of the corresponding
solutions.
General Procedure for the Photohydration.10 A solution of
either ligand 3 or 1OFF or 2OFF (ca. 20 mg) in 4−5 mL of deionized
water-CH3CN (50:50) was irradiated with a Xenon lamp or in a
preparative photoreactor (λex = 355
5) at room temperature.
Progress of the reaction was monitored by UV−vis and PL analysis.
After completion of the reaction (no further change in intensity and/
or shape of a profile), the volatiles were removed under vacuum at
room temperature. The resultant semisolid was dissolved in methanol
and passed through a short pad of Celite column yielding the hydrated
products 4 or 1ON or 2ON in near quantitative yields (>93−97%). In
case of 4 CH2Cl2 was used for purification instead of methanol.
controlled by hydration and/or dehydration. Hybrids 1OFF
/
2OFF and 1ON/2ON are nicely soluble in aqueous medium and
satisfy the basic requirements of molecular switches as their
functional behavior is tuned in response to external stimuli, that
is, light and heat. In addition, they undergo switching, that is,
readout (hydration) and erase (dehydration), quantitatively (by
ΦPL and NMR) and rather rapidly, when compared to how
analogue hybrid switches work in nonaqueous medium.1,4,5,8,9
Complete photohydration of 1OFF and 2OFF happens within 18
h as judged by full MLCT emission gain, whereas analogue
systems operating on either cycloaddition or oxidation of
anthracenes require 24−48 h.7−9,33 Likewise, luminescence is
fully erased by thermal dehydration of 1ON and 2ON after 4 h,
while more than 48 h are required for partial retro-
cycloaddition of anthracenyl adducts.8,9,34
General Procedure for Product Quantum Yield (Φpdt
)
Measurements.10a,e Solutions of substrate, either ligand 3 or 1OFF
or 2OFF, in deionized water−CH3CN (50:50, v/v) and of the standard
2-(anthracen-9-yl)phenol, in 4 M D2O−CH3CN solution, were placed
in two separate quartz cuvettes (3.0 mL). The solutions were purged
with N2 gas over 10 min, then their optical density (OD) was adjusted
to the same value at 350 nm. Subsequently, solutions were irradiated
with a Xenon lamp (λex = 355 5) for about 3.0 h. Thereafter, the OD
for both analyte and standard was measured again, and the loss of OD
vs irradiation time was followed and compared with that of the
unphotolyzed solution. The value of quantum yield was estimated
from the equation described in the literature.10a
= ΔAλ/103ε ΔIa
CONCLUSIONS
Φ
pdt
λ
■
Readout/write behavior of 1OFF and 2OFF was readily tuned by
photohydration involving dearomatization using ESIPT photo-
chemistry, and erase by thermal dehydration of 1ON and 2ON at
moderate temperature. Readout/write cycles were run five times
without fatigue. The ready accessibility, complete reversibility
and the water-mediated functionality of 1OFF and 2OFF may
warrant the exploration of future applications in biological
fluids and settings.
ΔAλ is the loss of OD at 350 nm, ελ is the extinction coefficient at
excitation wavelength, and ΔIa is the number of photons absorbed per
unit volume during the irradiation.
General Procedure for Thermal Dehydration. A solution of
1ON or 2ON (ca. 20 mg) in 5 mL of acetonitrile was heated at 80−90
°C until complete dehydration was seen (4 h). The progress of the
reaction was monitored by UV−vis and PL analysis. After completion
of the reaction, the volatiles were removed under vacuum. The
resultant solid material was dissolved in methanol and passed through
a short pad of Celite column yielding the dehydrated products 1OFF or
2OFF in near quantitative yields (>92−97%).
EXPERIMENTAL SECTION
■
General Aspects. All reactions were performed under a nitrogen
gas atmosphere in oven-dried glassware. The solvents tetrahydrofuran
(THF) and toluene were freshly distilled over sodium, whereas
CH2Cl2 and CH3CN were distilled over CaH2 prior to use. All
reactions were monitored by precoated analytical thin layer
chromatography (TLC) on silica gel/alumina. Column chromatog-
raphy was conducted with silica gel (60−120 mesh). All commercial
chemicals were used as received. All intermediates and metal
Preparation of 9-Anthraceneboronic Acid.37 To a solution of
9-bromoanthracene (1.9 g, 7.5 mmol) in THF (50 mL) kept at −50 to
−60 °C (low temperature maintained by using acetone-liquid nitrogen
bath) was added nBuLi (11.0 mmol) dropwise over 30 min. The
resultant red colored solution was stirred for 1 h at the same
temperature, subsequently trimethyl borate (11.0 mmol) was added
slowly. The reaction mixture was brought to room temperature over a
period of 2 h, then aqueous HCl (5 mL) was added. The volatiles were
I
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Article
removed and the organic material was extracted with ethyl acetate. The
combined extract was dried over Na2SO4 and evaporated. The pure
product was obtained after filtration over a short pad of silica-gel using
30% ethyl acetate in hexane, followed by recrystallization from ethyl
acetate and hexane furnishing 9-anthraceneboronic acid as a pale
yellow solid (1.2 g, 70%): mp 214−219 °C (mp 217 °C);37 Rf 0.41 in
50% ethyl acetate in hexane; 1H NMR (400 MHz, acetone-d6) δ 7.47−
7.50 (m, 4H, 2-, 3-H), 7.86 (s, 2H, −OH), 8.03−8.06 (m, 2H, 4-H),
8.12−8.14 (m, 2H, 1-H), 8.49 (s, 1H, 5-H); 13C NMR (100 MHz,
acetone-d6) δ 111.5, 126.8, 126.9, 128.4, 130.4, 130.9, 133.2, 135.3.
Preparation of 3-(Anthracen-9-yl)-4-methoxybenzalde-
hyde.38 9-Anthraceneboronic acid (1.0 g, 4.5 mmol), 2-bromo-4-
anisaldehyde (1.2 g, 5.4 mmol), and [Pd(PPh3)4] (0.26 g, 5.0 mol %)
were introduced into an initially oven-dried pressure tube under N2.
To this mixture were added THF (30 mL) and saturated aqueous
K2CO3 solution (10 mL). The reaction mixture was refluxed at 85−90
°C for 36 h and then cooled to room temperature. The contents were
extracted with CH2Cl2, dried over Na2SO4, and the solvent was
evaporated. The resultant material was purified by silica gel column
chromatography using 25% CH2Cl2 in hexane, yielding 3-(anthracen-
9-yl)-4-methoxybenzaldehyde as a colorless solid (0.59 g, 43%): mp
161−164 °C (mp 164 °C);38 Rf 0.16 in 2.5% ethyl acetate in hexane;
1H NMR (400 MHz, CD2Cl2) δ 3.93 (s, 3H, 9-H), 7.01 (d, J = 2.4 Hz,
insoluble material was isolated by filtration and further purified by
silica gel column chromatography using 10−30% methanol in CH2Cl2
yielding 3 as a faint yellow solid (0.35 g, 62%): mp 141−146 °C; Rf
0.13 in 20% methanol in CH2Cl2; IR (KBr cm−1) 3463, 3322, 2951,
2934, 2880, 2751, 2671, 1366, 1351, 1332, 1288, 1269, 1226, 1197,
1107, 1097, 958, 895, 878, 871, 852, 844; 1H NMR (400 MHz,
CD2Cl2) δ 5.89 (s, 2H, 10-H), 7.02 (d, J = 1.4 Hz, 1H, 11-H), 7.09−
7.17 (m, 3H, 6-, 7-, 12-H), 7.20 (dd, J = 3.6 Hz, J = 1.2 Hz, 1H, 14-H),
7.33−7.37 (m, 2H, 15-, 8-H), 7.58 (t, J = 7.2 Hz, 2H, 3-H), 7.69−7.75
(m, 3H, 2-, 9-H), 8.08 (d, J = 8.8 Hz, 2H, 4-H), 8.17 (d, J = 8.0 Hz,
1H, 16-H), 8.37 (d, J = 7.6 Hz, 2H, 1-H), 8.49 (d, J = 5.2 Hz, 1H, 13-
H), 8.68 (s, 1H, 5-H); 13C NMR (100 MHz, CD2Cl2) δ 50.9, 105.5,
117.1, 122.6, 122.7, 123.5, 125.2, 126.0, 126.4, 128.9, 129.0, 129.1,
130.2, 130.3, 130.5, 130.7, 132.9, 133.3, 136.7, 140.8, 144.5, 148.2,
150.7; ESI-MS m/z (%) 428.2 (100) [M+1]+. Anal. Calcd for
C29H21N3O: C, 81.48; H, 4.95; N, 9.83. Found: C, 81.22; H, 4.92; N,
9.67.
Photolysis of 3 in CH3CN-Water. Photolysis was performed by
following the general procedure described in the photohydration
section. The photoproduct 4 was obtained in 94−95% yield: mp 121−
125 °C; Rf 0.14 in 20% methanol in CH2Cl2; IR (KBr cm−1) 3510,
3327, 3057, 3045, 2969, 2774, 1635, 1602, 1591, 1536, 1516, 1493,
1453, 1421, 1397, 1322, 1284, 1265, 1239, 1162, 1154, 1039, 1009,
966, 915, 907, 841; 1H NMR (400 MHz, CD2Cl2) δ 3.96 (s, 2H, 5-H),
5.90 (s, 2H, 10-H), 7.02 (d, J = 1.2 Hz, 1H, 11-H), 7.10−7.22 (m, 9H,
2-, 3-, 4-, 6-, 7-, 12-H), 7.25−7.30 (m, 3H, 1-, 9-H), 7.34−7.38 (m, 2H,
15-, 8-H), 7.74 (dd, J = 6.0 Hz, J = 1.6 Hz, 1H, 14-H), 8.18 (d, J = 8.0
Hz, 1H, 16-H), 8.50 (d, J = 4.4 Hz, 1H, 13-H); 13C NMR (100 MHz,
CD3COCD3) δ 36.2, 52.2, 81.1, 123.8, 124.2, 124.4, 125.9, 126.4,
127.6, 128.0, 128.7, 130.5, 130.6, 132.0, 132.1, 132.3, 138.6, 138.8,
140.5, 143.4, 145.8, 150.0, 152.7; ESI-MS m/z (%) 445.8 (100) [M
+1]+. Anal. Calcd for C29H23N3O2: C, 78.18; H, 5.2; N, 9.43. Found:
C, 78.31; H, 5.19; N, 9.46.
Photolysis of 3 in CH3OH-Water. Photolysis was performed by
following the general procedure described in the photohydration
section The photoproduct 5 was obtained in 93−95% yield: mp 119−
122 °C; Rf 0.16 in 20% methanol in CH2Cl2; IR (KBr cm−1) 3494,
3380, 3317, 3091, 2996, 2977, 2964, 2855, 2653, 2624, 2611, 1623,
1603, 1581, 1537, 1489, 1453, 1434, 1385, 1370, 1324, 1305, 1261,
1230, 1199, 1157, 1041, 1030, 1019; 1H NMR (400 MHz, CD2Cl2) δ
3.57 (s, 3H, 21-H), 3.94 (s, 2H, 5-H), 5.89 (s, 2H, 10-H), 7.01 (d, J =
1.2 Hz, 1H, 11-H), 7.09−7.20 (m, 9H, 2-, 3-, 4-, 6-, 7-, 12-H), 7.24−
7.27 (m, 3H, 1-, 9-H), 7.33−7.37 (m, 2H, 15-, 8-H), 7.72 (dd, J = 5.6
Hz, J = 1.6 Hz, 1H, 14-H), 8.17 (d, J = 8.0 Hz, 1H, 16-H), 8.50 (d, J =
4.4 Hz, 1H, 13-H); 13C NMR (100 MHz, CD2Cl2) δ 37.0, 50.9, 70.4,
119.8, 122.5, 122.6, 122.7, 123.6, 125.1, 126.0, 126.7, 126.8, 128.9,
130.2, 130.3, 130.5, 136.7, 140.7, 140.8, 141.7, 143.4, 144.5, 148.2,
150.7; ESI-MS m/z (%) 459.6 (100) [M+1]+. Anal. Calcd for
C30H25N3O2: C, 78.41; H, 5.48; N, 9.14. Found: C, 78.39; H, 5.47; N,
1H, 8-H), 7.39−7.41 (m, 2H, 6-, 7-H), 7.49−7.53 (m, 2H, 3-H),
7.58−7.62 (m, 2H, 2-H), 8.00 (d, J = 8.8 Hz, 2H, 4-H), 8.45 (s, 1H, 5-
H), 8.49 (d, J = 9.2 Hz, 2H, 1-H), 9.79 (s, 1H, 10-H); 13C NMR (100
MHz, CD2Cl2) δ 56.1, 108.9, 114.2, 121.9, 125.6, 126.8, 127.1, 127.2,
127.3, 128.5, 129.9, 130.4, 132.1, 147.2, 151.5, 190.5.
Preparation of 2-(Anthracen-9-yl)-4-(hydroxymethyl)-
phenol. To a solution of 3-(anthracen-9-yl)-4-methoxybenzaldehyde
(0.55 g, 1.8 mmol) in 20 mL of CH2Cl2 at 0 °C was added dropwise
1.0 M BBr3 in CH2Cl2 (0.7 mL) under N2 gas atmosphere. The purple
color reaction mixture was stirred overnight, and subsequently it was
quenched with ethanol. The volatiles were removed under vacuum
yielding a semisolid that was taken as such to the NaBH4 reduction.
About 20−25 mL of ethanol and NaBH4 (0.41 g, 1.1 mmol) were
added to the contents. The resultant yellow solution was stirred at
room temperature for about 1 h. Thereafter volatiles were removed,
and the organic material was extracted with ethyl acetate. The
combined extract was dried over Na2SO4 and evaporated. The pure
product was obtained after chromatography over silica gel using 30%
ethyl acetate in hexane, followed by recrystallization from ethyl acetate
and hexane furnishing 2-(anthracen-9-yl)-4-(hydroxymethyl)phenol as
a colorless solid (0.41 g, 74%): mp 252 °C dec.; Rf 0.21 in 25% ethyl
acetate in hexane; 1H NMR (400 MHz, CD2Cl2) δ 1.90 (s, 1H, 17-H),
5.61 (s, 2H, 10-H), 7.46−7.50 (m, 2H, 6-, 7-H), 7.53−7.61 (m, 4H, 2-,
3-H), 7.97 (d, J = 2.4 Hz, 1H, 8-H), 8.02 (d, J = 8.8 Hz, 2H, 4-H), 8.39
(d, J = 9.2 Hz, 2H, 1-H), 8.46 (s, 1H, 5-H); 13C NMR (100 MHz,
CD2Cl2) δ 57.2, 113.2, 121.5, 124.1, 125.2, 126.4, 128.2, 128.6, 129.1,
130.3, 131.5, 131.6, 136.3, 136.5; Anal. Calcd for C21H16O2: C, 83.98;
H, 5.37. Found: C, 83.87; H, 5.38.
9.15.
11
Preparation of 1OFF
.
A suspension of [Ru(phen)2]Cl2 (0.12 g,
Preparation of 2-(Imidazol-2-yl)pyridine.15 To a solution of
pyridine-2-carboxaldehyde (20.0 g, 187 mmol) and 27 mL of 40%
aqueous glyoxal in 40 mL of ethanol at 0 °C was added at once 64 mL
of cold aqueous NH3 (30%). The mixture was stirred at 0 °C for 1 h,
brought to room temperature, and stirred for another 1 h.
Subsequently, all volatiles were removed and extracted with CH2Cl2.
The combined extract was dried over Na2SO4 and evaporated. The
resultant dark brown oil was distilled at 180 °C under vacuum. The
colorless to pale yellow oil solidified on standing (8.0 g, 30%): mp
133−136 °C (mp 135 °C)15; 1H NMR (400 MHz, CD2Cl2) δ 7.16 (s,
2H, 11-, 12-H), 7.25 (dd, J = 4.0 Hz, J = 1.2 Hz, 1H, 14-H), 7.78 (dd, J
= 2.0 Hz, J = 1.6 Hz, 1H, 15-H), 8.20 (d, J = 8.0 Hz, 1H, 16-H), 8.50
(d, J = 4.8 Hz, 1H, 13-H), 11.86 (s, 1H, 18-H); 13C NMR (100 MHz,
CD2Cl2) δ 120.0, 120.1, 123.1, 137.3, 146.4, 148.7, 148.9, 149.0.
Preparation of 3.14 2-(Anthracen-9-yl)-4-(hydroxymethyl)phenol
(0.40 g, 1.3 mmol) and 2-(imidazol-2-yl)pyridine (0.38 g, 2.7 mmol)
were mixed thoroughly with a spatula and heated at 120 °C for 1 h,
later at 140 °C for further 6 h. The yellow semisolid was treated with
80:20 hexane-CH2Cl2 to remove unreacted starting precursors. The
0.21 mmol) and ligand 3 (0.10 g, 0.21 mmol) in 40 mL of 20%
aqueous ethanol was refluxed under N2 for 8 h. After this period, the
wine-red solution was concentrated to about 5−7 mL, then acetone
(20 mL) was added. The resultant red precipitate was isolated by
filtration and washed with a small portion of cold acetone. The pure
product was obtained after filtration over a short pad of silica-gel using
ethanol followed by 10−25% ammonium hexafluorophosphate in
methanol to yield 0.21 g (55%): IR (KBr, cm−1) 3470, 3089, 2864,
1
1608, 1596, 1561, 1514, 1428, 1263, 1116, 954, 840, 733; H NMR
(400 MHz, CD3OD) δ 5.89 (s, 2H, 10-H), 7.23−7.29 (m, 2H, 6-, 7-
H), 7.40−7.51 (m, 6H, 2-, 3-, 8-, 9-H), 7.64 (dd, J = 4.0 Hz, J = 0.8 Hz,
1H, 14-H), 7.73 (d, J = 2.0 Hz, 1H, 11-H), 7.78 (d, J = 2.0 Hz, 1H, 12-
H), 7.91 (d, J = 8.4 Hz, 2H, 4-H), 7.96−8.01 (m, 3H, 1-, 16-H), 8.05−
8.12 (m, 5H, 15-, 19-H), 8.16 (s, 4H, 17-H), 8.35 (s, 1H, 5-H), 8.81−
8.83 (m, 1H, 13-H), 8.89 (dd, J = 6.8 Hz, J = 1.6 Hz, 4H, 18-H), 9.19
(dd, J = 3.6 Hz, J = 1.6 Hz, 4H, 20-H); 13C NMR (100 MHz, CH3OD
+ CD3COCD3, 50:50 v/v) δ 57.7, 101.5, 114.2, 115.4, 120.3, 123.2,
123.9, 126.3, 126.8, 127.0, 127.7, 129.2, 129.4, 130.0, 130.6, 131.1,
131.6, 132.2, 133.4, 133.8, 135.5, 138.1, 138.3, 141.2, 142.6, 143.6,
J
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147.6, 149.8, 152.3; ESI-MS m/z (%) 924.4 (100) [M−Cl]+. Anal.
Calcd for C53H37N7OF12P2Ru: C, 54.00; H, 3.16; N, 8.32. Found: C,
53.93; H, 3.12; N, 8.31.
P.N. In addition, we are indebted to the DFG under Schm 647/
17-1.
Preparation of 2OFF.6 A suspension of [Re(CO)5Cl] (0.15 g, 0.42
mmol) and ligand 3 (0.17 g, 0.42 mmol) in 30 mL of degassed toluene
was refluxed under N2 for 24 h. The reaction mixture was cooled to
room temperature, and the solid was isolated by filtration. The lemon
yellow solid was recrystallized in 30% CH2Cl2 in hexane twice to yield
0.22 g (72%): IR (KBr cm−1) 3456, 2987, 2924, 2821, 2693, 2029,
1919, 1493, 1322, 1286, 1250, 1147, 1065, 956, 902, 883, 866, 851; 1H
NMR (400 MHz, CD3OD) δ 5.87 (s, 2H, 10-H), 7.25−7.26 (m, 2H,
6-, 7-H), 7.47−7.58 (m, 6H, 2-, 3-, 8-, 9-H), 7.63 (dd, J = 3.6 Hz, J =
1.2 Hz, 1H, 14-H), 7.70 (d, J = 2.0 Hz, 1H, 11-H), 7.76 (d, J = 2.0 Hz,
1H, 12-H), 7.95 (d, J = 8.0 Hz, 1H, 16-H), 8.04 (d, J = 2.0 Hz, 1H, 15-
H), 8.05−8.12 (m, 4H, 1-, 4-H), 8.58 (s, 1H, 5-H), 8.80 (d, J = 3.6 Hz,
1H, 13-H); 13C NMR (100 MHz, CD3OD) δ 52.9, 123.9, 125.6, 126.2,
127.1, 127.2, 127.8, 127.9, 128.0, 128.5, 129.9, 131.9, 132.1, 132.9,
135.3, 135.4, 138.6, 139.5, 139.6, 139.7, 144.1, 151.5, 181.2, 190.2;
ESI-MS m/z (%) 700.8 (100) [M−Cl]+. Anal. Calcd for
C32H21N3O4ClRe: C, 52.42; H, 2.89; N, 5.73. Found: C, 52.41; H,
2.92; N, 5.74.
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Preparation of 1ON. This compound was prepared starting from
1OFF by following the general procedure described in the photo-
hydration section (yield 95−97%): IR (KBr cm−1) 3466, 3211, 3106,
3051, 2934, 2811, 1624, 1593, 1552, 1514, 1451, 1354, 1363, 1301,
1
1266, 1212, 1121, 1004, 940, 839; H NMR (400 MHz, CD3OD) δ
3.90 (s, 2H, 5-H), 5.92 (s, 2H, 10-H), 7.10−7.15 (m, 6H, 2-, 3-, 6-,
COH-H), 7.20−7.31 (m, 5H, 1-, 4-, 7-H), 7.47 (d, J = 8.0 Hz, 1H, 8-
H), 7.53 (s, 1H, 9-H), 7.66 (dd, J = 3.6 Hz, J = 1.2 Hz, 1H, 14-H),
7.75 (d, J = 2.0 Hz, 1H, 11-H), 7.81 (d, J = 2.0 Hz, 1H, 12-H), 8.02 (d,
J = 8.0 Hz, 1H, 16-H), 8.07−8.12 (m, 1H, 15-H), 8.16−8.19 (m, 4H,
19-H), 8.27 (s, 4H, 17-H), 8.84 (d, J = 4.0 Hz, 1H, 13-H), 8.98 (dd, J
= 6.8 Hz, J = 1.6 Hz, 4H, 18-H), 9.26 (dd, J = 6.8 Hz, J = 1.6 Hz, 4H,
20-H); 13C NMR (100 MHz, CH3OD+CD3COCD3, 50:50 v/v) δ
38.3, 46.7, 101.4, 114.7, 120.2, 121.6, 123.8, 123.9, 127.0, 128.5, 128.6,
129.3, 129.4, 130.8, 131.4, 131.6, 132.4, 133.1, 133.4, 136.5, 141.6,
142.5, 143.3, 143.4, 145.1, 148.2, 150.0, 152.8; ESI-MS m/z (%) 943.7
(100) [M−Cl]+. Anal. Calcd for C53H39N7O2F12P2Ru: C, 53.18; H,
3.28; N, 8.19. Found: C, 53.14; H, 3.17; N, 8.22.
Martínez-Manez, R., Eds.; The Supramolecular Chemistry of Organic-
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Preparation of 2ON. This compound was prepared starting from
2OFF by following the general procedure described in the photo-
hydration section (yield 94−96%): IR (KBr cm−1) 3398, 3289, 2992,
2911, 2877, 2032, 1915, 1603, 1512, 1401, 1374, 1281, 1254, 1211,
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1
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1054, 929, 876, 857; H NMR (400 MHz, CD3OD) δ 3.94 (s, 2H, 5-
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addition to the anthracenyl units, other organic photochromic systems
such as stilbenes, azo group, spirooxazines, spiropyrans, and
diarylethenes have been used to control the luminescence emission
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modulating their energy levels. Details to those systems are contained
in Chapter 4 of Reference 1b.
H), 5.91 (s, 2H, 10-H), 7.13−7.18 (m, 6H, 2-, 3-, 6-, COH-H), 7.22−
7.28 (m, 5H, 1-, 4-, 7-H), 7.49 (d, J = 8.0 Hz, 1H, 8-H), 7.52 (s, 1H, 9-
H), 7.65 (dd, J = 4.0 Hz, J = 1.2 Hz, 1H, 14-H), 7.72 (d, J = 2.0 Hz,
1H, 11-H), 7.78 (d, J = 2.0 Hz, 1H, 12-H), 7.99 (d, J = 7.2 Hz, 1H, 16-
H), 8.06−8.11 (m, 1H, 15-H), 8.83 (d, J = 4.0 Hz, 1H, 13-H); ESI-MS
m/z (%) 715.8 (100) [M−Cl]+. Anal. Calcd for C32H23N3O5ClRe: C,
51.16; H, 3.09; N, 5.59. Found: C, 51.17; H, 3.12; N, 5.58.
ASSOCIATED CONTENT
* Supporting Information
■
S
Additional PL data, excitation spectra and NMR spectra for all
intermediates and final compounds ON and OFF. This material
is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: schmittel@chemie.uni-siegen.de.
■
(6) (a) Haga, M. Inorg. Chim. Acta 1983, 75, 29. (b) Shavaleev, N.
M.; Bell, Z. R.; Easun, T. L.; Rutkaite, R.; Swanson, L.; Ward, M. D.
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Notes
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Olmsted, J. J. Photochem. Photobiol. A: Chem. 1994, 78, 119.
(b) Szacilowski, K.; Macyk, W.; Drzewiecka-Matuszek, A.; Brindell,
M.; Stochel, G. Chem. Rev. 2005, 105, 2647. (c) Campagna, S.;
Puntoriero, F.; Nastasi, F.; Bergamini, G.; Balzani, V. Top. Curr. Chem.
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The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We would like to thank the Alexander von Humboldt
Foundation (AvH) for a postdoctoral research fellowship to
K
dx.doi.org/10.1021/ic400676j | Inorg. Chem. XXXX, XXX, XXX−XXX

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dx.doi.org/10.1021/ic400676j | Inorg. Chem. XXXX, XXX, XXX−XXX