Rationally designed fluorescence turn-on sensors: A new design strategy based on orbital control

Article abstract of DOI:10.1021/ic101165k

Herein, we explore a new strategy in the chemo-sensor field for fluorescence amplification upon binding with metal ions based on controlled participation of the nitrogen lone pair orbital. The basic architecture of the sensor entails a fluorophore, the sp² hybridized nitrogen lone pair (-C=N-), and a chelator site referred to as the control part. Though nonplanar and nonfluorescent, compound IC1 achieved pseudo planarity from binding with Zn²⁺ as indicated by the increased fluorescence signal. Its other analogue (IC2) is also planar, and unlike IC1-Zn²⁺ was fluorescent with a lack of binding affinity to metal ions. The time-dependent density functional theory (TDDFT) calculations revealed that the fluorescence amplification was due to the blocking of the nitrogen lone pair orbital; unlikely geometrical rearrangements were insignificant. This could indicate a breakthrough concept in the future design of fluorescent turn-on sensors.

Full text of DOI:10.1021/ic101165k

8
552 Inorg. Chem. 2010, 49, 8552–8557
DOI: 10.1021/ic101165k
Rationally Designed Fluorescence Turn-On Sensors: A New Design Strategy Based
on Orbital Control
†
‡
†
†
†
,‡
Hyo Sung Jung, Kyoung Chul Ko, Jae Hong Lee, Sang Hoon Kim, Sankarprasad Bhuniya, Jin Yong Lee,*
§
§
,†
Youngmee Kim, Sung Jin Kim, and Jong Seung Kim*
†
‡
Department of Chemistry, Korea University, Seoul, 136-704, Korea, Department of Chemistry,
§
Sungkyunkwan University, Suwon 440-746, Korea, and Department of Chemistry and Division of Nano
Sciences, Ewha Womans University, Seoul 120-750, Korea
Received June 10, 2010
Herein, we explore a new strategy in the chemo-sensor field for fluorescence amplification upon binding with metal ions
based on controlled participation of the nitrogen lone pair orbital. The basic architecture of the sensor entails a fluorophore,
the sp hybridized nitrogen lone pair (-CdN-), and a chelator site referred to as the control part. Though nonplanar and
2
2þ
nonfluorescent, compound IC1 achieved pseudo planarity from binding with Zn as indicated by the increased
2þ
fluorescence signal. Its other analogue (IC2) is also planar, and unlike IC1-Zn was fluorescent with a lack of binding
affinity to metal ions. The time-dependent density functional theory (TDDFT) calculations revealed that the fluorescence
amplification was due to the blocking of the nitrogen lone pair orbital; unlikely geometrical rearrangements were insignificant.
This could indicate a breakthrough concept in the future design of fluorescent turn-on sensors.
Introduction
reported pertaining to the signaling mechanisms of photo-
4
induced electron/energy transfer (PET), metal-ligand
Nature has created sophisticated machinery to control the
activities of essential trace elements, which include enzymes,
cofactors with catalytic functions, and structural support
elements in human beings. Since the nineteenth century,
various efforts have been exerted to detect numerous essential,
and indeed, toxic metal ions in biological, as well as in the
natural, environment. Spawned from these efforts, fluore-
scent sensors offer better sensitivity, specificity, and real-time
5
charge transfer (MLCT), intramolecular charge transfer
6
7
(
ICT), excimer/exciplex formation, excited state twisted
8
1,2
intramolecular charge transfer (TICT), and excited-state
intra/intermolecular proton transfer (ESIPT). However,
9
these signaling mechanisms involve the excited state proper-
ties of the chemosensor prior to interaction with guest ions. In
practicality, incorporation of such mechanisms in designing
new fluorescent sensors has proven very unpredictable. It is
therefore highly desirable to discover a useful and new design
strategy for fluorescent sensors based on a relatively straight-
forward concept.
3
monitoring with fast response time over other chemosensors.
To date, a variety of fluorescent chemosensors have been
*
To whom correspondence should be addressed. E-mail: jinylee@
skku.edu (J.Y.L.), jongskim@korea.ac.kr (J.S.K.).
1) Reagan, M.; Bagchi, P.; Sumalekshmy, M.; Fahmi, C. J. Chem. Rev.
009, 109, 4780.
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A. J. M.; McCoy, C. P.; Rademacher, J. T.; Rice, T. E. Chem. Rev. 1997, 97,
515. (b) Kim, J. S.; Quang, D. T. Chem. Rev. 2007, 107, 3780. (c) Kim, H. N.;
Lee, M. H.; Kim, H. J.; Kim., J. S.; Yoon, J. Chem. Soc. Rev. 2008, 37, 1465.
d) Senthilvelan, A.; Ho, I.-T.; Chang, K.-C.; Lee, G.-H.; Liu, I.-H.; Chung, W.-S.
Pursuant to this, Wu et al. recently attempted to establish a
new concept to amplify the fluorescence upon complexation
(
2
þ
2
2
with Zn , whereby CdN isomerization was inhibited in an
(
10
iminocoumarin system, as it is well-known that the conjugated
(
(6) (a) Wang, J. B.; Qian, X. F.; Cui, J. N. J. Org. Chem. 2006, 71, 4308.
1
(b) Coskun, A.; Akkaya, E. U. J. Am. Chem. Soc. 2005, 127, 10464.(c) Chen, C.-T.;
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(
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(
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(
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1
992, 730. (b) Kim, S. K.; Lee, S. H.; Lee, J. Y.; Bartsch, R. A.; Kim, J. S. J. Am.
Lett. 2005, 7, 2133. (b) Jung, H. S.; Park, M.; Han, D. Y.; Kim, E.; Lee, C.; Ham,
S.; Kim, J. S. Org. Lett. 2009, 11, 3378.
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Soc. 2004, 126, 13377.
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Chem. Soc. 2004, 126, 16499. (c) Chang, K.-C.; Su, I.-H.; Senthilvelan, A.;
Chung, W.-S. Org. Lett. 2007, 9, 3363.
(
5) (a) Jung, H. S.; Kwon, P. S.; Lee, J. W.; Kim, J. I.; Hong, C. S.; Kim,
J. W.; Yan, S.; Lee, J. Y.; Lee, J. H.; Joo, T.; Kim, J. S. J. Am. Chem. Soc.
009, 131, 2008. (b) Beer, P. D.; Drew, M. G. B.; Hesek, D.; Shade, M.; Szemes, F.
2
Chem. Commun. 1996, 2161.
pubs.acs.org/IC
Published on Web 08/24/2010
r 2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 18, 2010 8553
a
b
Scheme 1. Synthetic Pathways to IC1-IC3 and Their Crystal Structures
a
2 2 5 2 3
Reagents and conditions: (i) CH (COOC H ) , HCl/AcOH; (ii) POCl , DMF; (iii) 2-(metylthio)aniline, EtOH; (iv) 2-aminobenzenethiol, EtOH;
b
v) Aniline, EtOH. All hydrogen atoms are omitted for clarity. Thermal ellipsoids are shown at the 50% probability level. Crystallographic data have
(
been deposited with the Cambridge Crystallographic Data Centre under CCDC 763946 (IC1), 763947 (IC2), and 763948 (IC3).
lone pair electron was expected to contribute to the fluore-
scence, which could be tuned by modifying the control part or
by the metal coordination. In the present study, a coumarin
moiety was selected as the fluorophore as it is a widely accepted
2
þ
2þ
fluorophore in detection of trace elements (Cu , Zn ) in
biological systems with high quantum yield and comparatively
lower toxicity.
5a,14
The methyl aryl thioether was adapted as
the controlling part. For fluorescence tuning, such as mod-
ulating the nitrogen lone pair orbital contribution, two differ-
ent approaches were adapted: (i) cyclization of the controlling
2
þ
part into the CdN; (ii) Zn coordination to block the
nitrogen lone pair orbital.
Figure 1. Conceptual architecture for the fluorescent sensors.
The IC1 (hereafter IC represents iminocoumarin) and
its analogues were rationally designed and synthesized with
unique features to demonstrate the fluorescence intensity
changes dependent on the geometry and participation of the
imine lone pair electrons as proposed. Compounds IC1-IC3
were synthesized in high yields as shown in Scheme 1. Purpo-
11
12
nitrogen lone pair electron at the R- or β-positions of the
fluorophore is responsible for fluorescence quenching. Re-
cently, Lippard and co-workers reported NO detection by
2
þ
fluorescence turn-on using Cu complexes, where the nitrogen
13
lone pair orbital plays an important role. They observed
remarkably enhanced fluorescence when the nitrogen lone pair
orbital energy was greatly lowered by NO coordination.
As part of our research projects, these findings have
prompted us to generate a new interaction mechanism for
fluorescence enhancement utilizing the nitrogen lone pair for
the next generation of sensors.
sely, the -SCH group was introduced at the o-position of the
3
aryl imine as a possible binding site with metal ions in the IC1;
nevertheless, the IC3 analogue bore an open structure without
addition of a binding site, and the IC2 analogue was a complete
planar cyclic structure, as shown in Scheme 1. Single crystals of
IC1-IC3 were grown under vapor diffusion of ethyl ether into
CH CN (Scheme 1). The CdN-C-C dihedral angle was
3
1
45.4°, which revealed the twist s-trans conformation of IC1,
Results and Discussion
whereas IC2 was planar (-177.0°).
The conceptual architecture is depicted in Figure 1 where
the -CdN- is located in conjunction with a fluorophore and a
control part at a position βto the -CdN-. The CdN group was
chosen so as to take advantage of the CdN isomerization, as
well as the PET phenomenon in fluorescence. The nitrogen
Compounds IC1 and IC2 show UV absorption centered at
475 and 477 nm, respectively (Supporting Information, Figure
S1), implying absorption of UV light independent of ligand
planarity. However, twisted nonplanar IC1 and IC3 showed
very low fluorescence signal with quantum yields of Φ = 0.01,
f
whereas planar IC2 showed strong green fluorescence at
(
11) (a) Iyoshi, S.; Taki, M.; Yamamoto, Y. Inorg. Chem. 2008, 47, 3946.
b) Parkesh, R.; Lee, T. C.; Gunnlaugsson, T. Org. Biomol. Chem. 2007, 5, 310.
12) (a) Xue, L.; Liu, C.; Jiang, H. Org. Lett. 2009, 11, 1655.
b) Bazzicalupi, C.; Bencini, A.; Biagini, S.; Bianchi, A.; Faggi, E.; Giorgi, C.;
λmax = 518 nm, with a quantum yield (Φ ) of 0.79 (Figure 2
f
(
(
and Table 1). The remarkably high fluorescence in IC2,
compared to IC1, is due to blocking of the nitrogen lone pair
orbital contribution to the excitation by cyclization of the CdN
group; hence, the nitrogen lone pair orbital is prevented from
fluorescence quenching (vide infra). This phenomenon pro-
vokes the possibility of fluorescence enhancement by orbital
control (FEOC). Although the main origin of the fluorescence
(
Marchetta, M.; Totti, F.; Valtancoli, B. Chem.;Eur. J. 2009, 15, 8049.
c) Moore, E. G.; Bernhardt, P. V.; Furstenberg, A.; Riley, M. J.; Smith, T. A.;
Vauthey, E. J. Phys. Chem. A 2005, 109, 3788. (d) Burdette, S. C.; Walkup, G. K.;
Spingler, B.; Tsien, R. Y.; Lippard, S. J. J. Am. Chem. Soc. 2001, 123, 7831.
e) Burdette, S. C.; Frederickson, C. J.; Bu, W. M.; Lippard, S. J. J. Am. Chem.
Soc. 2003, 125, 1778. (f) Kulatilleke, C. P.; de Silva, S. A.; Eliav, Y. Polyhedron
(
(
2
2
006, 25, 2593. (g) Xue, L.; Wang, H. H.; Wang, X. J.; Jiang, H. Inorg. Chem.
008, 47, 4310.
(
13) Lim, M. H.; Wong, B. A.; Pitcock, W. H.; Mokshagundam, D.; Baik,
(14) Komatsu, K.; Urano, Y.; Kojima, H.; Nagano, T. J. Am. Chem. Soc.
2007, 129, 13447.
M. H.; Lippard, S. J. J. Am. Chem. Soc. 2006, 128, 14364.

8
554 Inorganic Chemistry, Vol. 49, No. 18, 2010
Jung et al.
3
Figure 2. Fluorescence spectra (excited at 500 nm) of IC1 and IC2 (10 μM) in CH CN solution.
Figure 3. (a) Fluorescence emission spectra of IC1 (10 μM) with various concentrations of Zn(ClO
4
)
2
[0-1.4 equiv, respectively]; (b) Histogram of IC1
-
þ
þ
þ
þ
þ
þ
2þ
2þ
2þ
2þ
2þ
2þ
2þ
2þ
2þ
2þ
2þ
(
10 μM) uponadditionofClO salts of Ag , Li , Na , K , Cs , Rb , Hg , Co , Ba , Mg , Ca , Pb , Cu , Sr , Cd , Zn , andZn þ X (other
4
all metals) (10 equiv, respectively) in CH CN with excitation at 500 nm. (Bars indicate the fluorescence ratio at 532 nm emission). The inset shows the
3
correlation between the fluorescence intensity and zinc concentration.
Table 1. Photophysical DataR
2þ
fluorescence enhancement (∼4,100%) upon binding with Zn
ions over other transition and post-transition metal ions, as
absorbance
max (nm)
emission
max (nm)
relative quantum
2þ
shown in Figure 3. Only Cd shows an obvious fluorescence
change (∼820%). The alkali metal ions were unable to improve
any fluorescence signal as they have feeble bonding affinity
toward the CdO and -S-Me groups. Simultaneously, the
UV absorption is slightly red-shifted to 504 from 475 nm (Sup-
porting Information, Figure S2) and reaches saturation at 1.0
equiv of Zn , implicating a 1:1 complexation of ligand with the
Zn ion. The quantum yield of IC1 in CH CN is also enhanced
upon binding with the Zn ion by a factor of 39, compared with
compound
f
yield (Φ )
IC1
IC2
IC3
IC1 þ Zn
R
475
477
474
504
509
518
508
530
0.01
0.79
0.01
0.39
10
2
þ
Φ : Relative Fluorescence Quantum Yield (fluorescein in 0.1N
f
2
þ
15
NaOH as a reference, Φ
f
= 0.85).
2þ
3
mechanism in this study is basically PET (photoinduced electron
2þ
3a,b
transfer), we here propose the new terminology FEOC with
which one easily guesses the nitrogen lone pair orbital contribu-
tion in the molecular structure rather than the PET contribution.
With only conventional PET, the high quantum yield of IC2
cannot be properly explained. However, the concept of FEOC
can be explained in the non-chelating systems as shown in IC2 as
well as in the chelating systems. Thus, we ensure that FEOC is
more general concept than conventional CHEF.
IC1 alone (Table 1). To understand the complexation ratio of
Zn with IC1, a Job’s plot analysis was performed (Supporting
2þ
Information, Figure S3) and the FAB mass spectrum (Support-
2þ
ing Information, Figure S4) of IC1-Zn complex recorded;
both experimental data indicates a 1:1 complex of IC1 with
2
þ
Zn . The corresponding calculated association constant of IC1
2þ
6
-1 16
for Zn was 1.21 (0.03 ꢀ 10 M . Fortunately, obtainment
To gain insight into the metal ion binding effects upon
the fluorescence behavior of IC1, various cations were added
to the acetonitrile solution to give a noticed and remarkable
(
16) (a) Haugland, R. P. Handbook of Fluorescent Probes and Research
Products, 10th ed.; Molecular Probes, Inc.: Eugene, OR, 2005. (b) Association
constants were obtained using the computer program ENZFITTER, available
from Elsevier-BIOSOFT, 68 Hills Road, CambridgeCB2 1LA, U.K. (c) Connors,
K. A. Binding Constants; Wiley: New York, 1987.
(
15) Paeker, A.; Rees, W. T. Analyst 1960, 85, 587.

Article
Inorganic Chemistry, Vol. 49, No. 18, 2010 8555
2þ
Figure 4. Quantumyield change ofIC1 byZn coordinationand its crystal structure ofthe complex. Thermal ellipsoids are shown at the 50% probability
˚
level. Hydrogen atoms are omitted for clarity. Select bond lengths (A) and dihedral angles (deg): Zn-O 2.163; Zn-N 2.120; Zn-S 2.748; Zn-Cl1 2.244;
Zn-Cl2 2.205; C1-N-C2-C3 143.8(0). The crystallographic data have been deposited with the Cambridge Crystallographic Data Centre under CCDC
763945.
2
þ
of a crystal structure of IC1-Zn complex (Figure 4) indicated
that the C1dN-C2-C3 dihedral angle was slightly reduced to
stabilized with the resonance electron delocalization; thus, in
IC2, conformational isomerization is almost forbidden.
To further investigate the fluorescence behavior of IC1,
1
43.8°, with retainment of the s-trans configuration. This
structural information suggests that fluorescence enhancement
of IC1 by Zn coordination does not originate from planarity
or C-C rotation as previously reported. Instead, the lone pair
electrons of the imine nitrogen may play a pivotal role in
fluorescent amplification, which strongly suggests the possibility
of fluorescence enhancement by orbital control (FEOC). A similar
experiment was performed for IC3. There was, however, no
significant change in fluorescent signal upon addition of various
ions (Supporting Information, Figure S5), suggesting that the
o-methylthio unit only plays an important role in complexation
2þ
IC2, and IC1-Zn , time-dependent DFT (TDDFT) calcula-
tions were also carried out. The excited state calculations with
TDDFT resulted in oscillator strengths of 0.596, 1.024, and
0.649, and respective absorption wavelengths of 393.0, 406.0,
2
þ
6
2þ
and 413 nm for IC1, IC2, and IC1-Zn . The calculated
wavelengths were consistent with experimental values and
within 60-70 nm deviations, due possibly to solvent effects.
2þ
The origin of the fluorescence in IC1, IC2, and IC1-Zn can
be fully understood based on the nitrogen orbital action. The
molecular orbitals relevant to the most dominant electronic
2
þ
2þ
with Zn in IC1.
oscillators to the absorption for IC1, IC2, and IC1-Zn are
In addition, another experiment was carried out to under-
stand the practical ability of IC1 to sense the Zn ions in the
shown in Supporting Information, Figure S9 and S10.
Importantly, Figure 5 shows the energy levels of the frontier
molecular orbitals, including the nitrogen lone pair orbitals of
2þ
þ
þ
þ
2þ
þ
2þ
presence of other interfering metal ions (Ag , Li , Na , K ,
þ
þ
2þ
2þ
2þ
2þ
2þ
2þ
2þ
Rb , Cs , Hg , Co , Ba , Mg , Ca , Pb , Cu , Sr
,
IC1, IC2, and IC1-Zn , and the electronic configurations of
2þ
Cd ). From this, there is a remarkable fluorescent increment
Supporting Information, Figure S6) but little suppression.
We have also checked the anion effects with various anions in
presence of Zn and found some anion effects of IC1 from
UV absorption and fluorescence spectra (Supporting Infor-
mation, Figure S7). It is probably due to their ionic strength
differences or different coordination mode when they are
ligated by ionofluorophores.
the ground and excited states. In IC1, the contribution of the
nitrogen lone pair orbital (HOMO-1) to the excitation is 90%,
subsequently causing fluorescence quenching. However, in IC2,
the nitrogen lone pair orbital (HOMO-4) does not parti-
cipate in the excitation, thus, no fluorescence quenching. It
should be noted that in the case of IC1, the HOMO-1 energy
(-5.442) was slightly lower than the highest occupied molecular
orbital (HOMO) energy (-5.034); furthermore, in IC2, the
HOMO-4 energy (-7.184) was much lower than the HOMO
energy (-5.197). Hence, the nitrogen lone pair orbital is not
involved in the excitation because of the large stabilization of its
(
2þ
To validate the experimental observations, quantum calcula-
tions were executed to verify the fluorescence behavior of IC1,
2þ
analogue IC2, and the chelating complex IC1-Zn . The density
functional theory (DFT) calculations were performed using a
B3LYP exchange functional with 6-31G* basis sets employing a
2þ
lone pair orbital. Nevertheless, when Zn is coordinated to
IC1, the nitrogen lone pair orbital has a strong interaction with
1
7
2þ
suite of Gaussian 03 programs. The calculated lowest energy
structures are shown in Supporting Information, Figure S8. In
IC1, the methyl phenyl thioether group is significantly tilted with
the coumarin moiety, while in IC2, it is almost planar through
the cyclization. The most striking structural feature of IC1 in the
Zn d-orbitals to produce a bonding type (HOMO-6) and
antibonding type (HOMO-4) orbital (Figure 5 and Supporting
Information, Figure S8). The energies of the HOMO-6 and
HOMO-4 are -6.748 and -6.150, lower than the HOMO
energy (-5.714). The nitrogen lone pair orbitals (HOMO-6 and
HOMO-4) are not involved in the excitation, instead HOMO
(8%), HOMO-1 (44%), HOMO-2 (8%), HOMO-3 (17%),
and HOMO-5 (23%) were involved; thus, the nitrogen lone pair
2
þ
Zn coordination is the turning of the methyl phenyl thioether
2þ
group such that the sulfur atom is involved in the Zn co-
ordination together with the nitrogen, oxygen, and two chloride
atoms. The calculated dihedral angles of IC1, IC2, and IC1-
2þ
orbital does not have a quenching effect in IC1-Zn . It should
be noted that this is quite different from the case of IC2 in that
the nitrogen lone pair orbital has no contribution, mainly
2þ
Zn were in good agreement with the experimental crystal
structures, as shown in Supporting Information, Table S1,
Scheme 1, and Figure 4. The planar conformation is highly
2þ
because of the energy lowering in IC2, while in IC1-Zn , the
HOMO-5 is lower lying than the nitrogen lone pair orbital
(HOMO-4) that contributed 23% to the excitation. Thus, the
(
17) Kim, H. J.; Bhuniya, S.; Mahajan, R. K.; Puri, R.; Liu, H.; Ko, K. C.;
Lee, J. Y.; Kim, J. S. Chem. Commun. 2009, 7128.
blocking of the nitrogen lone pair orbital, and hence the

8
556 Inorganic Chemistry, Vol. 49, No. 18, 2010
Jung et al.
2þ
Figure 5. Energy levels of the frontier molecular orbitals of IC1, IC2, and IC1-Zn
.
fluorescence enhancement, can be achieved not only by cycliza-
tion (IC2) but also by metal coordination as well (IC1-Zn ).
geometrical factor, but rather the blocking of the nitrogen
lone pair orbital by metal coordination. We therefore believe
that this new concept will be widely used in the future to
design fluorescence turn-on sensors based on orbital control.
2þ
The quantum calculations revealed that fluorescent amplifi-
2þ
cation of IC1 upon binding with Zn ions was due to the
blocking of nitrogen lone pair electrons rather than conforma-
tional change or attained planarity of the complex. This is sup-
portive of the prediction proffered herein, namely, the possibi-
lity of fluorescence enhancement by orbital control (FEOC).
Experimental Section
General Information and Materials. All fluorescence and UV/
vis absorption spectra were recorded in a Shimadzu RF-5301PC
and a Shinco S-3100 spectrophotometer, respectively. NMR
and mass spectra were recorded at Varian instrument (400
MHz) and JMS-700 MStation mass spectrometer, respectively.
All reagents and cationic compounds such as perchlorate of
Conclusions
We have deviseda newstrategy togeneratenew fluorescent
sensors based on nitrogen lone pair orbital control, referred
to as fluorescence enhancement by orbital control (FEOC).
Accordingly, newly synthesized coumarin derivatives are
unique examples of this category. In IC1, the fluorescence
quenching was dominant because of the nitrogen lone pair
orbital contribution to the excitation, while IC2 gave a
remarkable fluorescence enhancement because of the block-
ing of the nitrogen lone pair orbital contribution by cycliza-
tion and partly because of the planarity and isomeriza-
þ
þ
þ
2þ
þ
2þ
þ
þ
2þ
þ
2þ
2þ
2þ
2þ
2þ
2þ
Ag , Li , Na , K , Cs , Rb , Hg , Co , Ba , Mg , Ca ,
2
Pb , Cu , Sr , Cd , Zn were purchased from Aldrich and
used as received.
General Procedure for the Syntheses.
18
Compound IC1. A portion of iminocoumarin aldehyde (269
mg, 1.0 mmol) and 2-(methylthio)aniline (195 mg, 1.4 mmol)
was combined in absolute ethanol (10 mL) to yield a transient
scarlet precipitate. The solution was stirred under reflux for 4 h,
2þ
tion blocking. However, upon Zn coordination, the IC1
(18) Lim, N. C.; Schuster, J. V.; Porto, M. C.; Tanudra, M. A.; Yao, L.;
showed a significant fluorescence enhancement not due to the
Freake, H. C.; Br u€ ckner, C. Inorg. Chem. 2005, 44, 2018.

Article
Inorganic Chemistry, Vol. 49, No. 18, 2010 8557
and the precipitate was filtrated, washed with absolute ethanol
three times, and recrystallized from C H OH to yield yellow
2 5
crystals (IC1, 320.2 mg, 0.82 mmol) in 82% yield. Mp: 170-
perchlorate salts. After calculating the concentrations of the free
ligand and the complexed form of IC1 from the fluorescence
titration experiments, the association constants were obtained
1
16
1
72 °C; TLC (EtOAc:n-hexane, 1:1 v/v): R = 0.12; H NMR
using the computer program ENZFITTER.
Calculation Details. All theoretical calculations were carried
out within the density functional theory (DFT) approach using a
f
(
400 MHz, CDCl
3
): δ 8.68 (s, 1H), 8.51 (s, 1H), 7.20-7.18 (m,
H), 7.17-7.12 (m, 1H), 7.06-7.04 (m, 1H), 7.02 (s, 1H), 3.33 (q,
J = 5.62 Hz, 4H), 2.91 (t, J = 6.42 Hz, 2H), 2.78 (t, J = 4.00 Hz,
H), 2.46 (s, 3H), 1.99 (m, 4H); C NMR (100 MHz, CDCl3):
63.0, 154.8, 152.9, 149.2, 147.8, 142.1, 134.5, 127.3, 126.6,
25.4, 124.3, 119.5, 118.0, 114.2, 109.0, 106.5, 50.5, 50.1, 27.7,
2
19
suite of Gaussian 03 programs. Geometry optimizations were
performed using Becke’s three-parameter B3LYP exchange-
1
3
2
1
1
2
3
20
21
correlation functional and the 6-31G* basis set. Then, at the
optimized geometries, the time- dependent density functional
theory (TDDFT) calculations were performed to obtain their
excitation properties (transition energies and oscillator strengths).
þ
1.5, 20.6,20.4,15.0. FAB-MS calc. for C H N O S [MþH]
2
3
22
2
2
91.1, found 391.4. Anal. Calcd for C23
H
22
N
2
O
2
S 0.2CH
2
Cl
2
:
3
C, 68.38; H, 5.55, Found: C, 68.48; H, 5.23.
Compound IC2. Synthetic procedures are similar to that of
Acknowledgment. This work was supported by the CRI
program (No. 2010-0000728) from National Research Founda-
tion of Korea (J.S.K.). J.Y.L. acknowledges the NRF grants
(No. 20100001630) and (KRF-2008-313-C00388) funded by
MEST.
IC1 to give 318.3 mg, 0.85 mmol in 85% yield. Mp: 190 °C; TLC
1
EtOAc:n-hexane, 1:3 v/v): R = 0.3; H NMR (400 MHz,
(
CDCl
f
3
): δ 8.80 (s, 1H), 8.00 (d, J = 8.30 Hz, 1H), 7.93 (d,
J = 7.84 Hz, 1H), 7.47 (t, J = 8.53 Hz, 1H), 7.35 (t, J = 8.30 Hz,
1
H), 7.05 (s, 1H), 3.36-3.29 (m, 4H), 2.94 (t, J = 7.58 Hz, 2H),
13
2
.79 (t, J = 7.17 Hz, 2H), 2.03-1.94 (m, 4H). C NMR (100
): 162.9, 154.9, 153.0, 149.2, 147.9, 142.1, 134.5,
27.4, 126.5, 125.5, 124.4, 119.5, 118.0, 114.2, 109.1, 106.4, 50.5,
Supporting Information Available: X-ray crystallographic
data for IC1, IC2, IC3, and IC1-Zn in CIF format. UV-vis
MHz, CDCl
3
2þ
1
5
absorption spectra (Figures S1-S2). Fluorescence spectra
0.1, 27.7, 21.5, 20.6, 20.4, 15.0. FAB-MS calc. for
(
Figures S5-S6). Calculation (Table S1, Figures S8-S10).
þ
C H N O S [MþH] 375.1, found 375.2. Anal. Calcd for
2
2
18
2
2
NMR and Mass spectrometry spectra for all compounds
(Figures S11-S19). This material is available free of charge
via Internet at http://pubs.acs.org.
C
22
18
H N
2
O
2
S 0.25CH
2
Cl
2
: C, 67.53; H, 4.72, Found: C,
3
6
7.59; H, 4.53.
Compound IC3. Synthetic procedures are similar to that of
IC1 to give 275.5 mg, 0.80 mmol in 80% yield. Mp: 168 °C; TLC
(19) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
1
(
EtOAc:n-hexane, 1:1 v/v): R = 0.14; H NMR (400 MHz,
M. A.; Cheeseman, J. R.; Montgomery, Jr., J. A.; Vreven, T.; Kudin, K. N.;
Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci,
B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada,
M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian,
H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.;Cammi, R.;Pomelli, C.; Ochterski,
J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg,
J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.;Strain, M. C.; Farkas, O.;
Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.;
Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.;
Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill,
P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; and Pople, J. A.
Gaussian 03, revision C02; Gaussian Inc.: Pittsburgh, PA, 2004.
f
CDCl
3
): δ 8.72 (s, 1H), 8.42 (s, 1H), 7.37 (t, J = 7.94 Hz, 2H),
.24 (m, 3H), 6.98 (s, 1H), 3.33 (q, J = 5.62 Hz, 4H), 2.91 (t, J =
7
6
(
1
2
[
1
3
.42 Hz, 2H), 2.78 (t, J = 4.00 Hz, 2H), 1.99 (m, 4H). C NMR
): 162.8, 155.2, 152.7, 151.9, 147.7, 141.3,
29.2, 126.9, 125.9, 121.2, 119.3, 114.0, 108.6, 106.2, 50.2, 49.8,
100 MHz, CDCl
3
9.7, 27.5, 21.2, 20.3, 20.2; FAB-MS calc. for C22
H
20
N
2
O
2
þ
MþH] 345.2, found 345.3. Anal. Calcd for C H N O
3 0.6-
2
2
20
2
2
3
CH OH: C, 74.64; H, 6.22, Found: C, 74.71; H, 6.67.
Spectroscopic Data. Stock solutions (1.00 mM) of the metal
perchlorate salts were prepared in CH CN. Stock solutions of
3
IC1-IC3 (0.3 mM) were prepared in CH CN. For all measure-
3
ments of fluorescence spectra, excitation was at 500 nm with
excitation and emission slit widths at 1.5 nm. UV/vis and fluo-
rescence titration experiments were performed using 10 μM of
(20) (a) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
(
b) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
IC1-IC3 in CH CN with varying concentrations of the metal
(21) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972, 56, 2257.
3