Lanthanide macrocyclic quinolyl conjugates as luminescent molecular-level devices

Article abstract of DOI:10.1021/ja004316i

The Eu(III) tetraazamacrocyclic complexes [Eu·1] and [Eu·2], and the Tb(III) and Yb(III) complexes [Tb·1] and [Yb·2], have been synthesized as luminescent molecular-level devices. The Eu complexes exhibit unique dual pH switching behavior in water under ambient conditions. The delayed Eu emission is reversibly switched on in acid, with an enhancement factor of several hundred for [Eu·1). These observations are consistent with the protonation of the quinoline aryl nitrogen moiety (pK_a ≈ 5.9 for [Eu·1]). The fluorescence emission spectra of these complexes are unaffected by acid, but pronounced changes occur in alkaline solution due to the deprotonation of the aryl amide nitrogen (pK_a ≈ 9.4 for [Eu·1]). [Tb·1] shows a more intriguing pH dependence; Tb emission is switched on only in the presence of H⁺ and in the absence of molecular oxygen, whereas the fluorescence emission properties are similar to those observed with [Eu·1). This behavior can be conveniently described as a molecular-level logic gate, corresponding to a two-input INHIBIT function, A λ B′. The analogous [Yb·2] complex shows no such pH or O₂ dependence.

Full text of DOI:10.1021/ja004316i

12866
J. Am. Chem. Soc. 2001, 123, 12866-12876
Lanthanide Macrocyclic Quinolyl Conjugates as Luminescent
Molecular-Level Devices
,†
†
‡
Thorfinnur Gunnlaugsson,* D o´ nall A. Mac D o´ naill, and David Parker
Contribution from the Departments of Chemistry, UniVersity of Dublin, Trinity College Dublin, Dublin 2,
Ireland, and UniVersity of Durham, South Road, Durham, DH1 3LE, U.K.
ReceiVed December 21, 2000. ReVised Manuscript ReceiVed June 5, 2001
Abstract: The Eu(III) tetraazamacrocyclic complexes [Eu‚1] and [Eu‚2], and the Tb(III) and Yb(III) complexes
[Tb‚1] and [Yb‚2], have been synthesized as luminescent molecular-level devices. The Eu complexes exhibit
unique dual pH switching behavior in water under ambient conditions. The delayed Eu emission is reversibly
switched on in acid, with an enhancement factor of several hundred for [Eu‚1]. These observations are consistent
with the protonation of the quinoline aryl nitrogen moiety (pKa ≈ 5.9 for [Eu‚1]). The fluorescence emission
spectra of these complexes are unaffected by acid, but pronounced changes occur in alkaline solution due to
the deprotonation of the aryl amide nitrogen (pKa ≈ 9.4 for [Eu‚1]). [Tb‚1] shows a more intriguing pH
+
dependence; Tb emission is switched “on” only in the presence of H and in the absence of molecular oxygen,
whereas the fluorescence emission properties are similar to those observed with [Eu‚1]. This behavior can be
conveniently described as a molecular-level logic gate, corresponding to a two-input INHIBIT function, A ∧
B′. The analogous [Yb‚2] complex shows no such pH or O2 dependence.
Introduction
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University of Dublin.
University of Durham.
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J. Am. Chem. Soc., Vol. 123, No. 51, 2001 12867
simple devices can be employed as chemosensors for the
devices. In these complexes the metal center can govern the
response of the device to some external perturbations such as
those arising from ion or molecular recognition. Our goal is
twofold: First we wish to demonstrate the use of such systems
for the signaling of ions and molecules through “off-on”
luminescent signaling. The neutral monoamide complex [Eu‚1]
and the cationic tetraamide complex [Eu‚2] are examples of
such systems. These systems can also be considered as lan-
1
2
detection of ions and molecules in physiological systems and
can conveniently be described as logic operations.1
3
Mimicking logic functions, the basis of modern computing,
is of particular interest; the relationship between the input and
the output may be described by truth tables, where 1 represents
an active input/output and 0 an inactive one.14 Molecular logic
devices have recently been demonstrated, in each case using
fluorescence or phosphorescence as an output, triggered by ionic
1
8
thanide-based luminescent chemosensors, possessing a long-
lived excited state (in the millisecond range), emitting at long
wavelengths (500-700 nm), with large Stokes shifts and line-
like emission bands (10-30 nm bandwidth) under ambient
+
+
13,15
16
(
H , Na , etc.)
or molecular inputs (O2 and â-CD). Being
able to modulate the nature of these devices in a controllable
way could, in principle, lead to the construction of arrays of
molecular-level systems which may be important in the devel-
opment of molecular information processing. The potential of
such a supramolecular system has recently been illustrated by
de Silva and McClenaghan, who demonstrated a molecular-level
arithmetic addition operation on 2-bit integers.17
1
8-21
conditions.
We set out to develop luminescent molecular-level devices,
based on modulating the photophysical properties of metal
complexes, using lanthanide ions as emitting moieties (output
1
8
signal). The quinoline amide-derived macrocyclic Eu(III)
1
9
20
complexes [Eu‚1] and [Eu‚2], the Tb(III) complex [Tb‚1],
and the Yb(III) complex [Yb‚2] can be considered as such
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Second, we wish to develop molecular logic gates by
exploiting the photophysical switching ability of lanthanide ions,
and we have chosen the binary inhibit (INH) logic gate, which
20
has not been previously reported. The neutral Tb(III) complex
(14) Contemporary Logic Design; Katz, R. H., Ed.; Benjamin Cum-
[
Tb‚1] behaves as such a logic gate, reading ionic and molecular
mings: Menlo Park, CA, 1994. Digital Design: A Practical Course; Burger,
P., Ed.; Wiley: New York, 1988.
+
inputs, specifically the presence of H and the absence of
oxygen. The output is a delayed lanthanide emission with the
advantages of long-lived emission, long wavelengths, and line-
like emission bands, leading to a large signal-to-noise ratio and
a high signal quality. Tb(III) was chosen since it has previously
been shown that Tb(III) complexes with a sensitizing chromo-
(
15) Balzani, V.; Credi, A.; Venturi, M. Coord. Chem. ReV. 1998, 171,
3
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2
2
susceptible to quenching by O2. As such, [Tb‚1] is in fact a
chemosensor for O2 in an acidic environment, and O2 may
therefore be considered as a (molecular) logic gate input.
(
(
3
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(
18) Reany, O.; Gunnlaugsson, T.; Parker, D. Chem. Commun. 2000,
4
2
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1
2
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2
000, 93.

12868 J. Am. Chem. Soc., Vol. 123, No. 51, 2001
Gunnlaugsson et al.
Scheme 1. (a) Schematic Representation of Antenna
Connected to a Macrocyclic Lanthanide Emitter, Showing
the Sensitization and Emission from the Lanthanide Ion
Ln(III) after Excitation of the Antenna, and (b) Excitation of
the Lanthanide Ion Now Dependent on the State of the
Receptora
Scheme 2. Synthesis of the R-Chloroamide 3 and the
Ligands 1 and 2
a
In the example shown, a cation must be complexed to the receptor
for an efficient sensitization.
Results and Discussion
Ligands 1 and 2 are derived from 1,4,7,10-tetraazacyclodode-
cane (cyclen), but such eight-coordinated derivatives form
kinetically and thermodynamically stable complexes with lan-
thanide ions, possessing low hydration numbers q e 1 (the
number of coordinated water molecules).1 These complexes
also possess adequate water solubility (submillimolar). Lan-
thanide ions are in general photophysically inert due to their
low molar absorptivities24 and large energy gaps between the
8,23
25
5
emissive and ground states. However, the emissive states, D0
and the 5D4 for Eu(III) and Tb(III), respectively, can be
populated indirectly by using a sensitizing “antenna”, that is, a
chromophore connected to cyclen via a covalent spacer which
transfers its own excited-state energy to the lanthanide ion,
Scheme 1a. Population of these emissive states is accomplished
if the triplet excited state of the antenna is sufficiently long-
lived, and if the triplet (T1) energy of the antenna is close to
5
-1
5
those of D0 Eu(III) (E ) 17 200 cm ) and D4 Tb(III) (E )
-
1 25,26
2
0 500 cm ).
By carefully choosing the antenna, it is
in 1-3 has a high extinction coefficient, and a T1 energy (E )
possible to tune the efficiency of the sensitization by selectively
populating S1 (and subsequently T1) via external perturbation,
for instance by using a recognition moiety, sensitive to the
presence or absence of a targeted species in solution. The
receptor is an intrinsic part of the antenna, and the sensitization
mechanism can be switched on by recognition of the ion or
-
1
2
1 980 cm measured for the protonated form of 3 in glacial
5
5
ethanol) that is close to those of the Eu D0 and Tb D4 emissive
states; it is therefore suitable for efficient Eu and Tb sensitiza-
tion. Importantly, the quinoline possesses a simple recognition
+
element since the aryl nitrogen is also a H acceptor and can
be used to tune the energy transfer from the antenna. This is
achieved by choosing an excitation wavelength that has a low
excitation coefficient in alkaline solution (no or relatively small
absorption), whereas in acidic solution the excitation coefficient
at this wavelength is greatly enhanced due to spectral shifts and
concomitant enhancement in energy transfer to the lanthanide
ion excited state.
Ligand and Complex Synthesis. The syntheses of ligands
1 and 2 are shown in Scheme 2. The R-chloroamide 3 was made
in one step by reacting chloroacetyl chloride with 2-methyl-4-
aminoquinoline at -10 °C in dry THF and 1 equiv of NEt3,
followed by acid-base extraction and single recrystallization,
to yield off-white solids. Monoalkylation of 3 with a molyb-
molecular species appropriate for the receptor; see Scheme 1b
for the recognition of a cation.18 The quinoline chromophore
(23) Beeby, A.; Clarkson, I. M.; Dickems, R. S.; Faulkner, S.; Parker,
D.; Royle, L.; de Sousa, A. S.; Williams, J. A. G.; Woods, M. J. Chem.
Soc., Perkin Trans. 2 1999, 493.
(
24) The extinction coefficient is very small for these ions, ꢀ ≈ 1 [L/mol
-
1
cm ], which is related to Laporte forbidden f-f transitions making direct
excitation difficult.
(25) Stein, G.; W u¨ rzberg, E. J. Chem. Phys. 1975, 62, 208. Sammes, P.
G.; Yahioglu, G. Nat. Prod. Rep. 1996, 1. Richardson, F. S. Chem. ReV.
1
982, 82, 541. Grosby, G. A.; Whan, R.; Freeman, J. J. Chem. Phys. 1962,
6
6, 2943.
(
26) The sensitization mechanism is via inter-system crossing (ISC) from
(
singlet) S1 to T1 of the excited antenna, followed by an intramolecular
energy transfer from T1 to D0 and D4.
5
5

J. Am. Chem. Soc., Vol. 123, No. 51, 2001 12869
denum tricarbonyl complex of cyclen27 at 80 °C in DMF and
K2CO3 yielded 4 after aqueous basic workup, which was reacted
(without further purification) with CH2O and MeP(OEt)2 (4.5
equiv) in refluxing dry THF and in the presence of 4 Å
molecular sieves, to give the phosphinoxymethylated product
2
8
5
. This intermediate was purified by column chromatography
on alumina (gradient elution from CH2Cl2 to 5% MeOH/CH2-
Cl2), followed by basic hydrolysis (D2O, NaOD) at room
temperature to yield the octadentate ligand 1.
The tetrasubstituted ligand 2 was made by reacting the
corresponding R-chloroamides with cyclen in a 4:1 ratio under
an inert atmosphere in dry DMF at 80 °C for 12 h in the
presence of Cs2CO3 and KI (4.1 equiv), followed by acid-base
extraction and recrystallization to give off-white powders. All
1
13
products were analyzed using H NMR, C NMR, IR, elec-
trospray (ES) MS, and elemental analysis or HRMS (ES)
accurate mass determination.
The Eu(III), Tb(III), and the Yb(III) complexes of 1 and 2
were made by reacting, in freshly distilled acetonitrile, equimolar
quantities of the appropriate ligand and the dried Ln(CF3SO3)3
2
9
(
Ln ) Eu, Tb, Yb) salt (2-3 mL per 10 mg of ligand). The
resulting solutions were cooled to room temperature and poured
into 150 mL of dry ether under viscous stirring. In each case
this gave a fine off-white powder which was collected by
centrifugation, followed by purification on alumina (gradient
3
1
elution from CH2Cl2 to 10% MeOH:CH2Cl2). The P NMR
spectrum of the ligand 1 showed two well-defined signals, in a
ratio of 2:1, at 42.9 and 33.5 ppm, whereas [Eu‚1] gave a set
30
of three signals in a ratio of 1:1:1 at 95.4, 85.5, and 83.7 ppm.
For [Tb‚1] only two broad signals were observed at 442 and
1
4
28 ppm, also in a 2:1 ratio. The H NMR of [Eu‚2] showed
signals at 38.2, -5.7, and -9.9 ppm for the ring axial and
equatorial protons, and at -15.8 and -20.0 ppm for the
R-protons of the pendant arm, consistent with a complex
possessing a square antiprismatic geometry with >90% of a
single isomeric species.30 Similar NMR results were observed
for the [Yb‚2] complex.
Figure 1. (a) Corrected absorption spectra of 3 at pH 11 and 2.5. (b)
The corresponding emission spectra.
The fluorescence spectrum of 3 was also pH dependent,
Figure 1b. Upon acidification (from alkaline solution) there was
a band shift from 373 to 357 nm, with an isoemissive point at
Absorption and Fluorescence Investigation of the r-
Chloroamide 3. The UV-vis absorption spectrum of the
R-chloroamide 3 was recorded in water, in the presence of
3
90 nm, and intensity (hypochromic) changes were observed
when the sample was excited at 330 nm. The fluorescence
emission was also investigated when the sample was exited at
-
2
tetramethylammonium perchlorate (2 × 10 M) to maintain a
constant ionic strength. The absorption spectrum of 3 was highly
pH dependent. In alkaline solution an intense absorption band
occurred at 298 nm (log ꢀ ) 3.80), which shifted upon
acidification to 317 nm (log ꢀ ) 4.18), with a new band
appearing at 261 nm (log ꢀ ) 4.00), and with isosbestic points
at 296, 253, and 245 nm, Figure 1a. A pH vs absorption titration
profile of 3 gave a sigmoidal curve, consistent with a simple
ion-binding equilibrium, with a pKa of 6.0 ( 0.1. Further
changes were observed at higher pH corresponding to a pKa of
approximately 10; these changes were too small for accurate
pKa determination. However, potentiometric measurements of
31
the isosbestic point. The quantum yield of fluorescence (ΦF)
was measured in both acid (pH 2-3) and base (pH 11-12) as
0
.064 ( 0.001 and 0.018 ( 0.001, respectively, corresponding
with singlet excited-state lifetimes (τS) of 0.87 ( 0.01 and 1.12
32
(
0.01 ns, respectively. Analysis of the pH vs fluorescence
profile
λex ) 330 nm, λem ) 357 nm) showed that the major changes
(
in the fluorescence spectra were observed in the alkaline range,
Figure 2, corresponding to a process with pKa ) 9.2 ( 0.1.
Much smaller changes were seen for the protonation of the
quinoline nitrogen moiety (pKa ≈ 6).
3
showed two distinct pKa values of 6.18 ( 0.05 and 9.83 (
The fluorescence excitation spectrum of 3 was recorded in
various solvents. These showed that the 317 nm band was
dependent on solvent polarity, shifting to longer wavelength
0
.05, the latter being associated with the deprotonation of the
aryl amide nitrogen.
(
H2O > MeOH > MeCN > Et2O > CH2Cl2) with increasing
(
27) Parker, D. In Macrocyclic Synthesis, a Practical Approach; Parker,
D., Ed.; Oxford University Press: Oxford, England, 1996.
28) Pulukkody, K.; Norman, J. T.; Parker, D.; Royle, L.; Broan, C. J.
J. Chem. Soc., Perkin Trans. 2 1993, 605.
29) Parker, D.; Williams, J. A. G. J. Chem. Soc., Perkin Trans. 2 1996,
581.
30) Aime, S.; Barge, A.; Bruce, J. I.; Botta, M.; Howard, J. A. K.;
Moloney, J. M.; Parker, D.; de Sousa, A. S.; Woods, M. J. Am. Chem. Soc.
999, 121, 5762. Howard, J. A. K.; Kenwright, A. M.; Moloney, J. M.;
Parker, D.; Port, M.; Navet, M.; Rousseau, O.; Woods, M. Chem. Commun.
998, 1381.
polarity, an observation consistent with the formation of an
internal charge-transfer (ICT) excited state. The effect of pH
was also investigated; at pH 10.6 only a small band was
3
3
(
(
1
(31) Fluorescence quantum yields were determined using quinine sulfate
in aqueous H2SO4 as standard (Φ ) 0.546): Penedo, J. C.; Mosquera, M.;
Rodriguez-Prieto, F. J. Phys. Chem. A 2000, 104, 7429.
(32) The quantum yields and singlet excited-state lifetimes were measured
at λF max ) 356 and 372 nm for 4, respectively, using single photon counting,
in both aqueous acid and base, by exciting at 330 nm.
(
1
1

12870 J. Am. Chem. Soc., Vol. 123, No. 51, 2001
Gunnlaugsson et al.
Figure 3. Absorption changes for [Eu‚1] (/) and [Eu‚2] (]) measured
Figure 2. Fluorescence intensity changes for 3 as a function of pH.
Scheme 3. Protonated and Deprotonated Forms of 3
at 318 and 256 nm, respectively, as a function of pH.
smaller than that seen with 3. In base it was determined to be
0
.0044 ( 0.0005, whereas in acid it was 0.0098 ( 0.0005; the
corresponding singlet excited-state lifetimes were too short for
accurate determination. The low ΦF in base can be partly
explained by photoinduced electron-transfer (PET) quenching
from one of the amine groups of the macrocycle, whereas in
acid this quenching pathway is mostly suppressed since the
oxidation potential of the amine is increased upon protonation.2
Ground and Singlet Excited-State Investigation of [Eu‚1]
and [Eu‚2]. The absorption spectra of the neutral [Eu‚1]
complex and the cationic [Eu‚2] complex showed λmax at 300
and 299 nm, respectively, and pH-dependent bathochromic shifts
upon acidification with λmax ) 318 nm (log ꢀ ) 4.18) and 314
nm for [Eu‚1] and [Eu‚2], respectively, with a new band being
formed at 261 (log ꢀ ) 4.0) and 262 nm. In both cases the
protonation of the quinoline nitrogen moiety was the main
contributor to the spectral changes. The titration profiles of [Eu‚
1
] and [Eu‚2] measured at 318 and 256 nm, respectively, are
shown in Figure 3. From these measurements pKa values of
.2 ( 0.1 and 10.3 ( 0.1 were determined for [Eu‚1]. A single
6
pKa was difficult to determine for [Eu‚2] as discussed earlier,
but potentiometric titration showed that 4 equiv of base was
consumed upon titration of an acidic solution of [Eu‚2]. These
results are summarized in Table 1.
observed at ∼317 nm, but at pH 2.5 this band had increased
substantially in intensity and shifted to longer wavelength. The
observed sensitivity to pH, in both the absorption and the
excitation spectra, is due to the tuning of the ICT excited state,
which is modified by protonation or deprotonation of the two
nitrogen moieties in 3 as depicted in Scheme 3.
The fluorescence emission spectrum of [Eu‚1], Figure 4,
revealed a λmax ) 375 nm, following excitation at 330 nm in
alkaline solution, with Φ ) 0.026 ( 0.001 and τ ) 2.16 (
F
S
0.01 ns. Upon acid titration, the intensity of this band dramati-
cally reduced, with the formation of a new band at 357 nm (Φ
F
32
) 0.045 ( 0.001 and τ ) 0.83 ( 0.01 ns) and an isoemissive
S
Absorption and Fluorescence Investigation of the Ligands
point at 375 nm. Similar changes were observed for [Eu‚2] when
1
and 2. The ligands 1 and 2 showed pH dependence similar
excited at 330 nm, with λmax ) 377 and an isoemissive point at
375 nm. In each case the fluorescence emission was highly pH
dependent in alkaline pH (pH 8-11), while little or no changes
were seen in acidic solution, indicating that the protonation of
the nitrogen quinoline moiety was not occurring. pKa values of
9.6 ( 0.1 and 9.4 ( 0.1 were determined for [Eu‚1] and [Eu‚2],
respectively, for the changes at 357 nm. The emission properties
of [Eu‚1] were also investigated by exciting the complex at
to that seen in the absorption and the fluorescence spectra of 3.
In the absorption spectra of 1, the major changes were again
due to the protonation of the quinoline nitrogen moiety, pKa )
6
.2 ( 0.1, with smaller changes being observed for the
deprotonation of the amide. In the fluorescence spectra the
opposite effect was observed, with a pKa ) 9.4 ( 0.1 and little
change in acidic media. The quantum yield for 2 was somewhat
3
10 nm and monitoring the intensity at 375 nm. Again the
(33) Valeur, B.; Bourson, J.; Pouget, J.; Keschke, M.; Ernsing, N. P. J.
deprotonation of the aryl amide nitrogen was the main contribu-
tor to the overall emission changes. However, unlike the case
for excitation at 330 nm, the intensity of the 372 nm band
Phys. Chem. 1992, 96, 6545. Valeur, B. In Fluorescent Biomolecules:
Methodologies and Applications; Jameson, D. M., Reinhart, G. D., Eds.;
Plenum: New York, 1989.

J. Am. Chem. Soc., Vol. 123, No. 51, 2001 12871
Table 1. Various Physical Parameters Measured for the Eu(III)
Complexes of 1 and 2
parameters
[Eu‚1]a
300
61
[Eu‚2]b
λ
abs/base (nm)
299
262
2
log ꢀ/base (L/mol cm)
abs/acid (nm)
3.82
318
λ
319
262
2
61
4.2
.0
log ꢀ/acid
4
b
λ
λ
λ
Flu/base (nm)
375
357
581
377
356
581
594
617
652
687
701
b
Flu/acid (nm)
Eu(III) (nm)
5
6
6
6
6
7
93
15
24
54
82
02
c
Φ
Φ
F
/base
0.026
0.045
2.16
0.83
0.71
c
F
/acid
d
τ
τ
τ
τ
q
S
/base (ns)
/acid (ns)
O)/acid (ms)
O)/acid (ms)
(q uncorrected)
d
S
Figure 5. Fluorescence changes as a function of pH when excited at
e
T
(H
(D
2
0.55
1.55
0.8 (1.05)
34
∼6
3
10 nm and monitoring the intensity at 375 (O), and when excited at
e
T
Eu f
2
1.98
330 nm and monitoring the intensity at 372 nm ([).
0.8 (1.07)
∼250
6.2
g
Eu EF
pK
excitation spectrum of [Eu‚1] was also investigated as a function
of solvent polarity and pH. Results were observed similar to
those observed previously with 3; i.e., the excitation spectrum
was solvent polarity dependent, while the 314 nm excitation
band was “switched on” upon acidification.
h
a
10.3
i
j
pK
pK
a
9.4
5.9
9.4
∼5.8
a
a
-2
Measured in water in the presence of 1 × 10 M tetramethylam-
b
Delayed Europium Luminescence Studies of [Eu‚1] and
[Eu‚2] as pH Chemosensors. The most intriguing pH depen-
dence was seen in the delayed Eu(III) luminescence emission
spectra of [Eu‚1] and [Eu‚2]. The Eu(III) emission of [Eu‚1],
when excited at 330 nm in alkaline solution (under ambient
conditions; room temperature and aerated solution) in the range
of 550-720 nm, was found to be of low intensity and was
independent of pH above pH 10. The emission can thus be said
to be “switched off” in alkaline solution. However, the Eu(III)
emission intensity was gradually enhanced, with increasing
acidity, appearing as well-separated emission bands at 581, 593,
monium perchlorate to maintain constant ionic strength. Measured at
c
d
longest wavelength. Measured at λ
F
.
Excitation at 330 nm and
e
observing the decay at λ
F
max. Measured by excitation at 330 nm
and observing the single-exponential decay at 594 nm. Calculated from
the rate constant of deactivation of the Eu(III)* ((10%), values not
f
Eu
shown. Calculated using q ) 1.2(∆kcorr), where ∆kcorr ) (kH O
-
2
K
D O) - 0.25 - 0.075x, in which x ) number of bound amide NH
2
39 g
oscillators.
Eu(III) emission enhancement factors (“ON” vs “OFF”
i
h
state). Measured for the changes in absorption. Measured for changes
in fluorescence (see b). Measured using changes in Eu(III) emission
j
(∆J ) 1).
6
15, 624, 654, 686, and 702 nm, representing the deactivation
5
7
of the D0 f FJ (J ) 0, 1, 2, 3, and 4) ground states, with at
least a 250-fold luminescence enhancement for ∆J ) 1 and a
Stokes shift of 250-370 nm (for each of the D0 f FJ bands),
Figure 6. The relative intensity of each band is determined by
5
7
5
the Franck-Condon overlap of the two energy levels D0 f
7
25
FJ. For [Eu‚1] the ∆J ) 1 transition showed the largest
intensity changes, but the hypersensitive transitions ∆J ) 2 and
are also significantly enhanced (switched on), indicating that
4
any of these three bands can be used for observing the pH
changes. The lifetime in aqueous (τH O) alkaline solution of the
2
Eu(III) emission of [Eu‚1] was too short to measure accurately
with the available instrumentation, but at pH 1.8 τH O was
2
measured to be 0.71 ms. This significant “off-on” switching
was assigned to the protonation of the quinolyl nitrogen moiety,
as is evident from the Eu(III) emission vs pH profile shown in
Figure 7, which showed a sigmoidal curve in accordance with
simple ion-binding equilibria extending over 2 pH units. From
these changes a pKa of 5.8 ( 0.1 was determined, indicating
that the Eu(III) emission was signaling the protonation of the
remote antenna, a feature not seen in the fluorescence emission
spectrum when excited at 330 nm. Thus, the sensitization of
the Eu excited state is greatly enhanced by protonation, giving
rise to a large increase in the Eu(III) emission.
Figure 4. Fluorescence spectra of [Eu‚1] as a function of pH: 10.7,
0.1, 9.5, 9.1, 8.4, 7.5, 3.8.
1
increased in alkaline solution rather than decreasing (cf. 357
nm band), Figure 5. From these changes a protonation constant
pKa of 9.4 ( 0.1 was determined. The changes in the pH 3-8
range were too small for accurate pKa analysis. The fluorescence
These measurements were repeated by exciting [Eu‚1] at the
isosbestic point and at 310 nm. In these cases the Eu(III)

12872 J. Am. Chem. Soc., Vol. 123, No. 51, 2001
Gunnlaugsson et al.
Figure 8. Changes in the Eu(III) luminescence emission of [Eu‚2] at
5
93 nm (∆J ) 1) when excited at 330 nm, upon addition of acid,
Figure 6. Changes in the Eu(III) luminescence emission of [Eu‚1] at
showing the “switching on” of the emission with increasing acidity in
5
93 nm (∆J ) 1) when excited at 330 nm, upon addition of acid,
the pH range of 10.9-2.7.
showing the “switching on” of the emission with increasing acidity in
alkaline solution the emission was switched off, but it was
switched on at low pH. The largest emission enhancements were
seen for the ∆J ) 1, 2, and 4 transitions with much smaller
changes in the ∆J ) 0 and 3. The luminescent enhancement
factor was also smaller, ca. 30, for ∆J ) 1. The pH vs intensity
profile of [Eu‚2], Figure 7, showed an emission which was
the pH range of 11.4-2.7.
“
switched on” over a broader pH range (pH 6.5-2.5) than in
[Eu‚1]. It may be noted that switching occurred at ca. 1 pH
unit below that of [Eu‚1]. This may be interpreted as indicating
a successive protonation of all the four quinolines (with different
pKa values); these were difficult to determine individually, but
a pKa ) 5.8 was estimated as a reasonable average. Multistep
protonation was confirmed by potentiometric titration. In
addition to the large emission changes, a small inflection in the
metal-based emission was apparent at ca. pH 7 (Figure 7). This
is possibly not a ligand-based feature and may be due to the
deprotonation of a proximate water molecule coordinated to the
metal complex, fulfilling its high coordination requirements.37
Such observations have previously been reported for related
Figure 7. Sigmoidal pH dependence for the lanthanide metal emission
of both [Eu‚1] (b) and [Eu‚2] (0).
3
8
cyclen systems. For [Eu‚1], a similar inflection was seen
around pH 8.5. The emission lifetime for [Eu‚2] at pH 1.8 was
0.55 ms, somewhat smaller than that seen for [Eu‚1] (0.71 ms).
In D2O, the lifetimes (τD2O) for [Eu‚1] and [Eu‚2] were
measured to be 1.98 and 1.55 ms, respectively, which are longer
than those in water, due to the decreased vibrational deactivation
enhancement factor was much smaller than that seen when the
sample was excited at 330 nm, indicating that the suppression
of any active (and competitive) PET from the singlet excited
state of the antenna to the Eu(III) metal ion following proto-
nation was contributing by a factor of 3 to the overall
luminescent enhancements.34 The large emission enhancements
are thus more likely due to increased ease of populating the S1
and subsequently the T1 excited states of the quinoline chro-
mophore at 330 nm in acidic solution versus that in alkaline
solution.35 The protonation of the quinoline nitrogen moiety,
as previously seen in the absorption and the excitation spectra,
is thus mirrored in the Eu(III) emission spectrum. Similar
changes have been defined for the protonation of a sensitizing
3
9
by O-D as compared to O-H oscillators. This behavior is
consistent with an overall hydration state q ) 0.8 for both [Eu‚
1] and [Eu‚2] (after compensating for vibrational quenching
by closely diffusing energy-matched OH oscillators).2
1,40
The pH dependence of the cationic [Yb‚2] complex was very
different from that of the Eu(III) complexes. The absorption
and the fluorescence properties of [Yb‚2], however, were similar
to those observed with Eu(III). Yb(III) complexes are known
to emit in the near-infrared following either direct or sensitized
36
phenanthraidine moiety.
(
37) Parker, D. Coord. Chem. ReV. 2000, 205, 109.
The pH dependence of the Eu(III) emission for the cationic
complex [Eu‚2], Figure 8, was similar to that of [Eu‚1]. In
(38) Aime, S.; Barge, A.; Botta, M.; Parker, D.; De Sousa, A. S. J. Am.
Chem Soc. 1997, 119, 4767.
(39) Dickins, R. S.; Parker, D.; de Sousa, A. S.; Williams, J. A. G. Chem.
(
34) de Silva, A. P.; Gunaratne, H. Q. N.; Rice, T. E. Angew. Chem.,
Commun. 1996, 697.
Int. Ed. Engl. 1996, 35, 2116.
(40) The effect of anion quenching on the Eu(III) emission of [Eu‚1]
was also investigated. At pH 1.85 (fully protonated quinoline) and in the
presence of 0.01 M (CH3)4NClO4, the Eu(III) emission was unaffected (after
dilution correction) upon addition of NaCl or NaNO3 solution (final
(
35) It is also notable that the ΦF and τS for [Eu‚1] are smaller than
those for 4, but the ΦF is much larger than that for 2. Because of this the
population of the T1 might be more efficient than in the case of [Eu‚1]
than [Eu‚2]. However, these features were not investigated any further.
-
-
concentration of 0.2 M and 0.1 M Cl and NO3 respectively). It may be
-
(
36) Parker, D.; Senanayake, K.; Williams, J. A. G. Chem. Commun.
concluded that Cl , which has been shown to quench the singlet excited
1
997, 1777. Parker, D.; Senanayake K.; Williams, J. A. G. J. Chem. Soc.,
states of N-alkylated quinolines (via an electron-transfer mechanism), was
not observed to affect the protonated form of [Eu‚1].
Perkin Trans. 2 1998, 2129.

J. Am. Chem. Soc., Vol. 123, No. 51, 2001 12873
Scheme 4. State Energies for the Protonated Form of the
Quinoline 3 and the Eu(III), Tb(III), and Yb(III)
excitation of the 2F5/2 state of Yb(III).41 Luminescence is
2
2
observed around 980 nm associated with the F5/2 f F7/2
transition.4
1,42
However, emission from [Yb‚2] showed no pH
dependence, unlike that from [Eu‚1] and [Eu‚2]. This is most
2
likely due to the fact that the energy of the F5/2 state (E )
-
1 25
1
0 300 cm ) is much lower than that of the T1 (E ) 21 980
-
1
cm ) of the antenna; the energy gap between the T1 and the
2
F5/2 states is too large for selective tuning of the Yb(III) emitting
-1 25
state; ∆E ) 11 680 cm . The energy gaps for the deactivation
of Eu(III), Tb(III), and Yb(III) emitting states to the relevant
ground states are shown in Scheme 4. The above results show
that the complexes [Eu‚1] and [Eu‚2] display dual luminescent
behavior dependent on pH, whereas [Yb‚2] shows no such
dependence. The fluorescence emission spectra of [Eu‚1] and
[
Eu‚2] are independent of pH in the range of 3-7, while
showing significant pH dependence in alkaline solution, fol-
lowing excitation at 330 nm. The Eu(III) emission possesses
pH sensitivity distinctly different from that of the fluorescence
emission, mirroring the pH changes observed in the absorption
spectrum in the pH range of 3-7. These Eu(III) complexes are
thus interesting candidates for measuring pH in competitive
media, since by simply changing the observation wavelength
and the time gating, changes spanning 10 pH units can be
observed.
Figure 9. Tb(III) metal emission dependence of [Tb‚1] when excited
at 330 nm, displaying the output of the molecular INH logic gate: (a)
in aerated acidic solution (red; pH 2.9), and in aerated alkaline solution
(blue; pH 11); (b) in degassed acidic solution (red; pH 2.9), and in
degassed alkaline solution (blue; pH 11). High-intensity output is
achieved only under the conditions of (i) low pH and (ii) degassed
solution (b). Note the difference in the intensity scales for the two
graphs; 0-3.5 for (a) vs 0-90 for (b).
[
Tb‚1] as a Logic Gate: Mimicking the INH Logic
Function. The [Tb‚1] complex also showed a pH dependence
similar to that of the [Eu‚1] complex. Under alkaline and
ambient conditions (non-degassed solution), the Tb(III) emission
was only weak, observed at 491.5, 547.5, 588.0, and 623 nm,
and the emission lifetime was 0.39 ms for the deactivation of
5
7
the D4 f FJ (J ) 6, 5, 4, and 3; Stokes shifts of 160-300 nm
5
7
for each of the Tb D4 f FJ bands). However, upon addition
of an acid (CF3CO2H, pH 2.9), the Tb(III) emission intensity
was enhanced in an analogous way to the Eu(III) emission, but
by a factor of only ca. 1.7 (measured for ∆J ) 5), Figure 9a,
much smaller than that seen for the Eu(III) emission in [Eu‚1]
(
41) Beeby, A.; Faulkner, S. Chem. Phys. Lett. 1997, 266, 116. Faulkner,
S.; Beeby, A.; Dickins, R. S.; Parker, D.; Williams, J. A. G. J. Fluorescence
999, 9, 45.
42) Steemers, F. J.; Verboom, W.; Hofstraat, J. W.; Geurts, F. A. J.;
1
(
Reinhoudt, D. N. Tetrahedron Lett. 1998, 39, 7583. Beeby, A.; Dickins, R.
S.; Faulkner, S.; Parker, D.; Williams, J. A. G. Chem. Commun. 1997, 1401.
Werts, M. H. V.; Hofstraat, J. W.; Geurts, F. A. J.; Verhoeven, J. W. Chem.
Phys. Lett. 1997, 276, 196.
(
factor of ca. ∼250). The fluorescent emission changes were
more apparent, with both a hypsochromic shift (373-357 nm)
and intensity changes (two shoulders at 373 and 357 nm), and

12874 J. Am. Chem. Soc., Vol. 123, No. 51, 2001
Gunnlaugsson et al.
Figure 11. (a) Truth table for the INH logic function; input A
+
corresponds to H , while B corresponds to O
2
, and X is the output
signal (Tb(III) emission). (b) Conventional representation of the INH-
logic gate; an active output signal is obtained when A ) 1 and B ) 0;
i.e., the Tb(III) emission is “switched on” only in the absence of O
and the presence of H
2
Figure 10. Fluorescence emission changes as a function of pH for
Tb‚1] when excited at 330 nm, in the four possible combinations of
+
.
[
aerated/degassed and acidic/basic solutions. These output pattern does
not correspond to the INH function.
ambient conditions; fluorescence was only slightly affected by
the removal of O2.
From these results it is apparent that the Tb(III) emission is
Table 2. Emission Intensities for [Tb‚1] as a Function of Various
+
Combinations of Acid, Base, and O
2
governed by two inputs, namely H and O2. The Tb(III)
+
Tb(III) intenistya,b
gate outputc
emission is “switched on” only in the presence of H and
chemical input
absence of O2 and no other combinations: (i) in the presence
of a base and absence of O2, (ii) in the presence of base and
O2, and (iii) in the presence of acid and O2, based upon the
difference in luminescent enhancement factors, Table 2 (1.7 vs
d
base + O
2
∼1.7
∼3.2
86
∼1.7
0
0
1
0
e
acid + O
base - O
2
2
acid - O
2
5
0). This behavior can be conveniently described using the two-
a
-2
Measured in water in the presence of 1 × 10 M tetramethylam-
b
input logic notation A ∧ B′, Figure 11, where A and B represent
monium perchlorate to maintain constant ionic strength. Measured at
+
c
the two inputs H and O2, respectively, and X represents the
∆
J)5. Representing logic gate output in accordance with Figure 11.
Measured at pH 11.5 in aerated solution. Measured at pH 2.9, [O
10 M after several cycles of degassing using “freeze-pump-thaw”
d
e
2
]
Tb(III) emission. This is the inhibit (INH) logic function, one
of 16 (two-input) logic operations which can be described by
truth tables, and it is a particular integration of the AND and
NOT logic functions. Other logic gate operations have recently
been demonstrated, such as the YES (ID), AND, OR, and NOT
-6
<
technique.
an isoemissive point was observed at 387 nm upon acidification,
Figure 10. Table 2 summarizes these and related results.
5,13
functions by deSilva, and the XOR by Balzani and Stoddart.
As mentioned earlier, the Tb(III) emissions of complexes with
a sensitizing chromophore possessing a triplet energy of ca.
2
The remaining logic functions are the (trivial) ONE and ZERO
gates, the output being 1 and 0, respectively, regardless of the
input, the two-input NAND, NOR, and XNOR gates that satisfy
commutation, and the INH and the IMP gates which do not
50-260 kJ mol- are susceptible to quenching by O2.
1
22
However, when the above measurements were repeated in
degassed solution (“freeze-pump-thaw”, [O2] < 10- M) at
high pH, the Tb emission spectra and lifetime, τTb ) 0.39 ms,
did not change. However, in degassed acidic solution, the Tb(III)
emission exhibited a greater than 50-fold luminescent enhance-
ment for the ∆J ) 5 transition, Figure 9b. Thus, it may be
concluded that the protonation of the quinoline nitrogen was
6
14
satisfy commutation. A three-input INH function has previ-
ously been demonstrated by de Silva et al., but this is the first
time that the more fundamental two-input analogue has been
1
6
demonstrated.
Even though practical integration of such devices to yield
computationally useful machines is not imminent,10 the avail-
ability of a full suite of molecular devices corresponding to
fundamental logic operations may facilitate such a develop-
5
enhancing the population of the D4 state in degassed solution.
The emission lifetime τTb ) 0.98 ms was also greatly increased
from that seen in the aerated solution. The large differences in
enhancement factors are due to competitive quenching of the
T1 state of the antenna by O2. The energy of the T1 state is
4
3
ment. We set out to demonstrate the feasibility of employing
the lanthanide ion complexes as such logic gate mimics, and
[
Tb‚1] is the first example of such a two-input INH logic gate.
Such devices could be of importance in the future once efficient
spatially defined” addressing methods have been devised. Our
results constitute a significant development to molecular
5
-1
close to that of the D4 state (∆E ) 1480 cm ), so both back
“
and forward energy transfer can take place between the two
states (T1 and D4). Quenching of the quinoline T1 by O2 reduces
the population of the D4 state since the intramolecular energy-
5
17
5
computation, not least since the current silicon-based computer
chips are expected to reach their physical limits soon.44
In conclusion, we have made a number of logic devices based
upon lanthanide conjugates derived from cyclen. Protonation
selectively populates the excited states of both the Eu(III) and
transfer step has now to compete with collision quenching by
O2, and Tb(III) emission is “switched off”. Upon degassing the
sample, this quenching process is removed, and the Tb(III)
sensitization is “switched on” with concomitant enhancement
in the Tb(III) emission. The fluorescence spectra of 2 were also
pH dependent, similar to those of [Tb‚1], Figure 10, with both
a hypsocromic shift from 373 to 357 nm (isoemissive point at
(43) For a discussion of the current state of the art of molecular
computing, see: Ball, P. Nature 2000, 406, 118. Reed, M. A.; Tour, J. M.
Sci. Am. 2000, June, 68. Brown, B. New Scientist 1999, 28 Aug, 39.
(
44) Muller, D. A.; Sorsch, T.; Moccio, S.; Baumann, F. H.; Evans-
387 nm) and intensity changes observed upon acidification under
Lutterodt K.; Timp, G. Nature 1999, 399, 759.

J. Am. Chem. Soc., Vol. 123, No. 51, 2001 12875
Tb(III) complexes. This is reflected in their enhanced emission
properties. The Eu(III) complexes [Eu‚1] and [Eu‚2] are all
highly sensitive to pH, and all display distinct pH switching
ranges: the fluorescence emission spectra show a pronounced
pH dependence in alkaline solution, whereas the delayed Eu(III)
emission is enhanced by several orders of magnitude, i.e.,
stirred for a further hour at -10 °C and for 2 h at room temperature
under an inert atmosphere. The resulting triethylammonium chloride
was filtered off, and the organic layer was washed once with 1.0 M
HCl solution (20 mL). The aqueous acid solution was washed with
CH
extracted three times with CH
layers were dried over K CO , and the solvent was removed under
Cl
2 2
(25 mL), the pH brought to 7.5 using NaHCO
3
, and the solution
2
2
Cl (30 mL). The combined organic
2
3
“
switched on” in acidic solution. These devices can thus be
reduced pressure to give 3 as a yellow oil in 60% yield which
+
considered as luminescent chemosensors for H in competitive
media.45 The Tb(III) emission of complex [Tb‚1] is also pH
dependent, but it is different from that of Eu(III), since the
emission is dependent on the presence or the absence of O2:
crystallized upon standing. Calculated for C H N OCl (%): C, 61.41;
12
11
2
H, 4.72; N, 11.93. Found for C12
(CDCl , 200 MHz): 9.14 (1H, bs, N-H), 8.19 (1H, s, Ar-H), 8.07
1H, d, J ) 8.5 Hz, Ar-H), 7.75 (2H, dd, J ) 8.0 Hz, Ar-H), 7.56
(1H, t, J ) 6.9 Hz, Ar-H), 4.36 (2H, s, CH ), 2.76 (s, 3H, Ar-CH ).
(CDCl , 100.58 MHz): 164.1, 160.1, 148.5, 139.9, 129.9, 129.7,
22.1, 118.5, 111.4, 43.4, 25.8. m/z (% ES ): 234.8 (100, M ), 256.9
11 2
H N OCl: C, 59.98; H, 4.70; N, 11.69.
δ
H
3
(
+
2
3
the Tb(III) emission is only switched on in the presence of H
δ
1
C
3
and the absence of O2, mimicking the function of the 2-bit INH
logic gate A ∧ B′.
+
+
+
(
1
1
20, M + Na ), 200.8 (5), 178.8 (5), 162.7(3), 158.8 (20), 148.7 (5),
18.7 (5). ν (oil)/cm : 3264, 1679, 1618, 1605, 1560, 1534, 1350,
121, 780, 755, 531.
-
1
Experimental Section
Reagents and Solvents. Reagents (obtained from Aldrich) and
1-[N-(2-Methyl-4-quinolyl)carbamoylmethyl]-1,4,7,10-tetraaza-
solvents were purified using standard techniques. Solvents were dried
cyclododecane (4). To a solution of freshly made 1,4,7,10-tetraaza-
cyclododecane-molybdenum tricarbonyl complex (0.37 g, 0.00105
3 2 3 3
over an appropriate drying agent before use: CH CN and N(CH CH )
over CaH , THF over Na with benzophenone as an indicator; DMF
2
mol) in dry DMF (20 mL) was added under an inert atmosphere Cs
2
-
was used directly from a “sure-seal” bottle. 1,4,7,11-Tetraazacyclodo-
decane is commercially available from Strem Chemicals and was used
as received.
CO (0.37 g, 0.00105 mol), and the reaction was stirred for 10 min at
3
80 °C, before addition in one portion of chloro-N-(2-methyl-4-quinolyl)-
ethanamide (3) (0.246 g, 0.00105 mol). The resulting mixture was
stirred for a further 2.5 h at this temperature before the reaction was
allowed to cool to room temperature. The solvent was removed under
reduced pressure, and 1 M HCl (20 mL) was added. This solution was
stirred in air for 12 h before the pH was adjusted to 14 using KOH
pellets. The resulting green solution was filtered and extracted several
Spectroscopy. H and 13C NMR spectra were recorded using Varian
VXR400, Varian Mecury-200, Varity Unity 300, and Varian Unity
Inova-500 spectrometers. Mass spectra were recorded using a VG
Platform II electrospray mass spectrometer with methanol as a carrier
solvent. Elementary analyses were determined using a Carlo ERBA
1
1
106 instrument. Accurate masses were measured by EPSRC National
times with CH
obtained which was dried over K
under reduced pressure to give 4 as a pale yellow oil in 75% yield.
Calculated for C20 O: 370.2481. Found for C20 O: 370.2456.
(CDCl , 200 MHz): 8.34 (d, 1H, J ) 8.4 Hz, Ar-H), 8.26 (1H, s,
Ar-H), 7.99 (1H, d, J ) 8.8 Hz, Ar-H), 7.67 (1H, q, J ) 8.4 Hz,
Ar-H), 7.47 (1H, t, J ) 7.2 Hz, Ar-H), 3.42 (2H, s, CH ), 2.77 (19H,
(CDCl , 100.58
2
Cl
2
(30 mL each time). A pale yellow solution was
MS Service at the University of Swansea. UV absorption spectra were
recorded at 20-25 °C using a UNI-CAM (UV2) spectrometer and on
a Shimadzu UV-2401PC. Fluorescence, excitation emission spectra,
lanthanide emission spectra, fluorescence quantum yields, and lan-
thanide excited-state lifetimes were obtained using a Perkin-Elmer
LS50B. Singlet excited-state lifetimes were measured using an SPC
2
CO , and the solvent was removed
3
H
27
N
6
27 6
H N
δ
H
3
2
FL900 Edinburgh Instrument λext 337 with a N
2
-filled lamp. All spectra
m, Ar-CH
3
and NH-CH
2
2
-CH -NH ring-H). δ
C
3
were measured by excitation at the given wavelength and were corrected
for the wavelength dependence of the photomultiplier tube. Throughout
the titration experiments, the ligand and complex solution were in the
concentration range of (5-7) × 10 M. Aliquots of 3 cm were taken
for absorption and luminescence measurements in standard quartz
cuvetts with a 1 cm path length. Determination of pK values was done
MHz): 170.88, 159.66,149.94, 148.33, 140.45, 124,98, 123.59, 120.74,
120.17, 118.62, 60.52, 53.54, 47.05, 46.96, 45.65, 25.49. m/z (%
+
+
ES ): 371.11 (20, M ), 285.5 (4), 251 (8), 229.9 (20), 186.01 (100,
-5
-3
2+
-1
M ), 155.9 (65), 113 (14), 86.87 (15). ν (oil)/cm : 3210, 2925, 2826,
1686, 1618, 1590, 1560, 1519, 1490, 1457, 1437, 1381, 1366, 1351,
1335, 1270, 1185, 1097, 1061, 985, 751.
46
according to published procedures. Potentiometric measurements were
carried out at 298 K using a Molspin 1 mL autotitrator equipped with
a calibrated Carmin microelectrode to measure pH. Data were analyzed
1,4,7-Tris-ethyl(2-ethoxymethylphosphinate)-10-[N-(2-methyl-4-
quinolyl)carbamoyl-methyl]-1,4,7,10-tetraazacyclododecane (5). 1-[N-
(2-methyl-4-quinolyl)carbamoylmethyl]-1,4,7,10-tetraazacyclodode-
cane (4) (0.59 g, 1.587 mmol) was dissolved in dry THF (30 mL). To
this solution was added 4.5 equiv (0.214 g, 7.14 mmol) of paraform-
aldehyde, and the solution was heated at reflux under an inert
atmosphere for 20 min, before addition of 4.5 equiv of methyldiethoxy-
phosphine (0.972 g, 7.14 mmol). The resulting solution was then stirred
and refluxed over 4 Å molecular sieves for a further 12 h. After the
solution cooled to room temperature, the excess paraformaldehyde was
filtered off and the solvent removed under reduced pressure. The oily
residue was dissolved in CH Cl (30 mL) and extracted twice with 0.1
2 2
M HCl solution (20 mL). The pH of the combined acidic solution was
brought up to 13 (using KOH), the solution was extracted three times
2 2 2 3
with CH Cl (20 mL) and dried over K CO , and the solvent was
removed under reduced pressure to give 5 as an oil. The product was
using Superquad and gave pK
a
values within 0.02 pH unit.47
Chloro-N-(2-methyl-4-quinolyl)ethanamide (3). 4-Amino-2-
methylquinoline (3 g, 0.0189 mol) and triethylamine (1.92 g, 0.0190
mol) were dissolved in dry dichloromethane (CH Cl ) (60 mL), and
2 2
the mixture was cooled to -10 °C in an ice/salt bath. To this mixture,
over a period of 20 min, was added chloroacetyl chloride (2.134 g,
0
2 2
.0190 mol) in 20 mL of dry CH Cl . The resulting suspension was
(45) Fluorescent chemosensors have been extensively investigated for
the detection of physiological species in vitro and in vivo. However, the
use of fluorescent chemosensors in vivo has been somewhat restricted by
a poor signal-to-noise ratio, due to short-lived (approximately nanoseconds)
background emission (autofluorescence) and light scattering from an active
biological environment. These problems may be partially overcome by the
use of lanthanide-based signal moieties. The advantage of using the Eu-
further purified by column chromatography on alumina (gradient elution
(
III) emission to report on local pH variations in physiological systems is
from CH
as a yellow oil in 66% yield. Calculated for C32
Found for C32 : 730.3507. δ (CDCl , 200 MHz): 8.18 (2H,
m, Ar-H), 7.99 (1H, d, J ) 8.4 Hz, Ar-H), 7.66 (1H, t, J ) 8.0 Hz,
Ar-H), 7.43 (1H, t, J ) 8.0 Hz, Ar-H), 3.98 (8H, m, 3 CONCH P;
CONHCH P), 2.68 (25H, m, 16 ring-H, 3 CO-CH -CH , Ar-CH ),
.33 (18H, m, 3 CO-CH -CH , 3 P-CH ). δ (CDCl , 50.3 MHz):
2
Cl
2
to 5% MeOH/CH
2
Cl
2
, R
f
) 0.85) to give the product (5)
due to long-lived excited states and long-wavelength emission bands which
give rise to high signal quality, since autofluorescence and light scattering
are overcome under ambient conditions. Human tissues inefficiently absorb
long-wavelength light, and interference from short-lived background
emission is minimized, making these systems feasible for ion detection in
vivo. Such devices are highly desirable for monitoring, for instance, the
changes of pH in the vicinity of cell membranes where pH changes can
often be over several pH units: Bissell, R. B.; deSilva, A. P. J. Chem.
Soc., Chem. Commun. 1991, 1148.
57 6 7 3
H N O P
: 730.3501.
H N O P
57 6 7 3
H
3
2
2
2
3
3
1
1
1
2
3
3
C
3
70.8, 159.79, 148.38, 140.78, 129.07, 124.84, 124.04, 123.48, 120.49,
20.49, 119.39, 118.89, 118.68, 60.08, 59.96, 59.83, 55.47, 54.74, 54.58,
(
46) Connors, K. A. Binding Constants, 1st ed.; John Wiley & Sons:
New York, 1987.
47) Bates, G. B.; Parker, D. J. Chem. Soc., Perkin Trans. 2 1996, 1109.
53.34, 54.26, 54.15, 54.04, 53.39, 53.29,53.01,52.84, 52.68 25.50, 16.51,
+
(
P 3
14.46, 12.69. δ (CDCl , 101.25 MHz): 51.93, 51.62. m/z (% ES ):

1
2876 J. Am. Chem. Soc., Vol. 123, No. 51, 2001
Gunnlaugsson et al.
inert atmosphere. To this solution were added 4 equiv of Cs CO (0.82
g, 2.32 mmol) and KI (0.39 g, 2.32 mmol). After the solution was
stirred at room temperature for 10 min, 4 equiv of chloro-N-(2-methyl-
4-quinolyl)-ethanamide (3) was added, and the resulting mixture was
heated at 80 °C for 24 h. After cooling to room temperature, the reaction
mixture was poured into HCl (20 mL, 0.1 M) and extracted twice with
71.01 (100, M+ + 1), 753.02 (75, M + Na ), 768.68 (10, M + K ),
90 (4), 675.7 (14), 674.87 (50), 652.91 (70), 638.8 (5), 385.16 (38),
46.12 (50), 312.15 (10), 102.0 (90). ν (oil)/cm- : 3416, 2979, 2924,
810, 1697, 1964, 1622, 1603, 1562, 1533, 1444, 1419, 1386, 1333,
297, 1237, 1187, 1096, 1031, 953, 884, 854, 466, 727, 492.
+
+
3
6
3
2
1
2
3
1
1
,4,7-Tris[ethyl(2-methylphosphinic acid)]-10-[N-(2-methyl-4-
quinolyl)carbamoylmethyl]-1,4,7,10-tetraazacyclododecane (1). 1,4,7-
Tris[ethyl(2-ethoxymethylphosphinate)]-10-[N-(2-methyl-4-quinolyl)-
carbamoyl-methyl]-1,4,7,10-tetraazacyclododecane (5) (0.20 g, 2.739
mmol) was dissolved in KOD solution (5 mL of 1.37 M) and stirred at
room temperature for 12 h. The hydrolysis of the ethyl esters was
followed by monitoring the changes in the P NMR spectrum. After
complete hydrolysis, the pH was adjusted to 5.5 and the solvent
removed under reduced pressure. The resulting residue was redissolved
in ethanol, and the inorganic salts were removed using a 0.5 µm syringe
filter (Milex-LCR 0.5 µm). The solvent of the resulting pale yellow
solution was removed under reduced pressure and dried under high
vacuum to give 1 as a light yellow oil in 97% yield. Calculated for
CHCl
layer was then extracted twice with CHCl
were dried over K CO , and the solvent was removed under a reduced
pressure to give 2 as a white solid in 41% yield. Calculated for
3
: 964.4860. Found for C56 : 964.4856. δ (CD -
OD, 300 MHz): 8.14, (4H, d, J ) 8.1 Hz, Ar-H), 7.73 (4H, m, Ar-
H), (8H, d, J ) 8.3 Hz, Ar-H), 7.56, (4H, m, Ar-H), 7.30 (4H, t, J
3
, before adjustment of the pH to 7 using K
2 3
CO . The aqueous
3
, the combined organic layers
2
3
C
56
H
60
N O
12 4
H
60
N
12
O
4
H
3
1
) 7.43 Hz, Ar-H), 4.1-2 (bs, 16H, ring-H), 3.31, (8H, s, NCH
2
CON),
2.10 (12H, s, Ar-CH
3
). δ (CD OD, 100.57 MHz): 172.0.70, 172.00,
C
3
159.34, 159.19, 147.96, 147.88, 129.609, 129.40, 127.390, 125.30,
125.88, 125.29, 121.61, 113.50, 112.95 57 (m), 23.46, 23.06. m/z (%
+
+
+
ES ): 965.15 (2 M ), 987.28 (100, M + Na ), 1003.01 (15, M +
+
-1
C
26
H
45
N
6
O
7
P
3
: 795.1328. Found for C26
H
45
N
6
O
7
P
3
: 795.1326. δ
H
3
(CD -
K ), 804.79 (3). ν (solid)/cm : 3250, 2972, 2825, 1697, 1604, 1623,
1563, 1534, 1498, 1413, 1382, 1305, 1270, 1189, 1105, 999, 948, 870,
761.
OD, 300 MHz): 8.17 (1H, d, J ) 8.7 Hz, Ar-H), 7.81 (1H, t, J ) 8.4
Hz, Ar-H), 7.80 (1H, d, J ) 8.7 Hz, Ar-H), 7.54 (1H, t, J ) 8.4 Hz,
Ar-H), 6.55 (1H, s, Ar-H), 3.58 (1H, d, J ) 5.7 Hz, 1 ring-H), 3.21
Europium(III) 1,4,7,10-Tetrakis[N-(2-methyl-4-quinolylcarbam-
(
2
24H, m, 15 ring-H; Ar-CH
.53 (3H, s, Ar-CH ), 1.204 (9H, m, PO
MHz): 160.05, 154.59, 140.25, 135.11, 127.40, 124.28, 120.40, 116.66,
03.05, 55, 20, 18, 17, 16. δ (CD OD, 100 MHz): 42.95, 33.54. m/z
3
; 3 CONCH
2
P; CONHCH
2
P; CONHCH
2
P),
oylmethyl]-1,4,7,10-tetraazacyclododecane Tri(trifluoromethylsul-
-
3
2
CH ). δ
3
C
(CD OD, 100
3
fonate) ([Eu‚2](CF
3
SO
3
)). 1,4,7,10-Tetrakis[N-(2-methyl-4-quinolyl-
carbamoylmethyl]-1,4,7,10-tetraazacyclododecane (2) (30 mg, 0.031
1
P
3
mmol) was dissolved in dry acetonitrile (2 mL), and 1 equiv of
europium triflate [(CF SO ) Eu] (18.6 mg, 0.031 mmol) was added.
3 3 3
-
-
+
+
(% ES ): 646.27 (45 M ), 668.23 (8 Na ), 684.21 (3 K ), 647.32
(
4
20), 645.05 (38), 624.6 (12), 576.69 (11), 548.95 (20), 538.85 (22),
The mixture was heated at 80 °C for 12 h under an inert atmosphere.
After cooling to room temperature, the solution was poured into dry
diethyl ether (100 mL) and stirred vigorously. The product precipitated
out as an off-white suspension which was collected by centrifugation
and dried under high vacuum to give a 46% yield of 3. Calculated for
+
74.95 (13), 380.92 (25), 333.15 (5), 333.24 (M + Na /2), 323.05 (50,
-
-
M /2), 322.23 (70, M /2), 269.00 (100), 222.98 (38), 94.82 (23), 61.87
-
1
(28). ν (oil)/cm : 3250, 2974, 2935, 2835, 1654, 1603, 1566, 1508,
1
451, 1421, 1375, 1295, 1147, 1033, 964, 872, 838, 761, 599.
Europium(III) 1,4,7-Tris[ethyl(2-methylphosphinato acid)]-10-
C
56
H
60
N
12
O
4
Eu: 1116.3860. Found for C56
OD, 300 MHz): 38.18 (Hax), 10-0 (m, aromatic and aliphatic
H), -5.68 (d, Heq, H′ax), -9.88 (s, H′eq), -15.83 (CHCO), -19.92
60 12 4
H N O Eu: 1116.3853.
[
N-(2-methyl-4-quinolyl)-carbamoylmethyl]-1,4,7,10-tetra-
azacyclododecane ([Eu‚1]). 1,4,7-Tris[ethyl(2-methylphosphinic acid)]-
0-[N-(2-methyl-4-quinolyl)carbamoylethyl]-1,4,7,10-tetraazacyclodo-
decane (1) (0.05 g, 0.0775 mmol) was dissolved in dry ethanol (0.1
mL). To this solution was added acetonitrile (8 mL), and the solution
was stirred at room temperature for a few minutes before addition of
H 3
δ (CD
+
+
1
(CHCO). m/z (% ES ): 1115.78 (5, M ), 1265.77 (M + CF
965.02 (3), 708.57 (5), 708.57 (10), 633.50 (M + CF SO /2), 558.45
(M /2), 425 (8), 372.59 (37), 322.68 (100). ν (solid)/cm : 3396, 3357,
3245, 3171, 3017, 1665, 1644, 1603, 1509, 1479, 1407, 1224, 1158,
1027, 1022, 938, 808, 759, 620.
3 3
SO ),
3
3
+
-1
3 3 3
europium triflate [(CF SO ) Eu] (0.051 g, 0.0852 mmol). The solution
was stirred at room temperature for 1 h and then at 50 °C for 1 h. The
solvent was then removed under reduced pressure to give an off-white
solid. The complexation of the Eu(III) ion was monitored by following
Ytterbium(III) 1,4,7,10-Tetrakis[N-(2-methyl-4-quinolylcarbam-
oylmethyl]-1,4,7,10-tetraazacyclododecane, (Tri(trifluoromethylsul-
-
fonate) ([Yb‚2](CF
3
SO
3
)). The procedure from ([Eu‚2]) was adopted,
-
the changes both in the electrospray mass spectrum (ES ) and in the
using 10 mg of 1,4,7,10-tetrakis[N-(2-methyl-4-quinolylcarbamoyl-
methyl]-1,4,7,10-tetraazacyclododecane (2) (0.010 mmol) and 6.43 mg
3
1
P NMR spectrum. The product was purified by column chromatog-
raphy on alumina (gradient elution from CH Cl to 10% MeOH/CH
Cl ) to give the product [Eu‚1] as a yellow solid in 50% yield.
Calculated for C26 Eu: 795.1328. Found for C26
Eu: 795.1324. δ O, 200 MHz): 26.7, 23.7, 18.7, 13.5 (ring Hax),
0 to -5 (bs, Ar-H; P-CH , ring H), -6.2, -7.9, -8.6, -9.6, -10.6,
12.8, -13.5, -16.5 (ring H; NCH ). δ (CH CN, 101 MHz): 95.4,
SO ), 797.25
3), 796.28 (10), 793.96 (9), 793.03 (5), 472.90 (15), 472.20 (21), 470.64
100 CF SO /2), 456.79 (40), 399.83 (9), 338.61 (12), 336.69 (55),
20.75 (53), 298.75 (15). ν (solid)/cm : 3363.6, 2362, 1651, 1612,
2
2
2
-
of ytterbium triflate [(CF
3
SO
3
)
3
Yb] (0.010 mmol). Calculated for
Yb: 1137.4849.
2
C
56
H
60
N O
12 4
Yb: 1137.4860. Found for C56H N O
60 12 4
H
(D
42
N
2
6
O
7
P
3
H
45
N O
6 7
P
3
-
H 3
δ (CD OD, 400 MHz): 37.01 (Hax), 10-0 (m, aromatic and aliphatic
H
H), -6.01 (d, Heq, H′ax), -11.00 (s, H′eq), -16.10 (CHCO), -21.56
+
1
-
8
(
(
3
1
3
(CHCO). m/z (% ES ): 1138.74 (8, M), 1285.79 (8, M + CF
3
SO
3
),
2
P
3
1436.01 (8, M + 2CF
3
SO
3
), 642.39 (100, M + CF SO /2), 567.54 (70,
3 3
-
-
-1
5.5, 83.7. m/z (% ES ): 795.05 (15, M ), 944.93 (10, CF
3
3
M/2). ν (solid)/cm : 3437, 3061, 1612, 1583, 1487, 1440, 1362, 1231,
1223, 1168, 1082, 1025, 963, 912, 838, 784, 838, 784, 756, 632.
3
3
Acknowledgment. We gratefully acknowledge the BBSRC
and the Kinerton Ltd. for financial support, Professor John M.
Kelly and Dr. J. C. Penedo Esteiro for assisting with the triplet
excited state measurements, Dr. Steve Faulkner for Yb(III)
measurements, EPSRC National MS Service at the University
of Swansea for accurate mass determination, Dr. Ritu Kataky
for assisting with potentiometric measurements, and Dr. Hazel
M. Moncrieff for valuable discussions.
-
1
573, 1522, 1242, 1161, 1054, 1026, 760, 630.
Terbiuim(III) 1,4,7-Tris[ethyl(2-methylphosphinato acid)]-10-[N-
(2-methyl-4-quinolyl) carbamoylmethyl]-1,4,7,10-tetraazacyclodo-
decane ([Tb‚1]). The procedure from ([Eu‚1]) was adopted, with the
exception that the reaction was boiled under reflux for 12 h, using 7.3
3 3 3
mg (0.0113 mmol) of 1 and terbium triflate [(CF SO ) Tb] (0.08 g,
0
.0113 mmol). The complexation of the Tb(III) ion was monitored by
+
following the changes in the ES mass spectrum. The product was
further purified by column chromatography on alumina (gradient elution
Supporting Information Available: Absorption pH titration
of [Eu‚1]; fluorescence emission spectra of [Eu‚1] in various
solvents; fluorescence excitation spectra of [Eu‚1] at pH 2.5,
7.47, and 10.64; fluorescence emission-pH profile for 3; and
otentiometric pH measurements of 3, 2, and [Eu‚2] (PDF). This
material is available free of charge via the Internet at
http://pubs.acs.org.
from CH
2
Cl
2
to 10% MeOH/CH
2 2
Cl ) to give the product ([Tb‚1]) in
-
5
8
5% yield. δ
P
(CH CN, 101 MHz): 442 (bs), 428 (bs). m/z (% ES ):
3
+
+
+
02.94 (15, M + 1), 826.30 (13, M + Na ), 802.34 (10, M ), 677.49
+
(4), 550.66 (4), 549.22 (18), 508 (8), 466 (32), 413 (56, M + Na /2),
[
+
4
02.23 (M /2), 393.15 (18), 261.04 (24), 216.75 (55), 215.0 (100).
,4,7,10-Tetrakis[N-(2-methyl-4-quinolylcarbamoylmethyl]-1,4,7,
1
1
0-tetraazacyclododecane (2). 1,4,7,10-Tetracyclododecane (0.1 g,
0
.58 mmol) was dissolved in dry DMF (5 mL) and stirred under an
JA004316I