Fluorescence of diimidazo[1,2-a:2′,1′-c]quinoxalinium salts under various conditions

Article abstract of DOI:10.1021/jo302531g

The synthesis and photophysical properties of diimidazo[1,2-a:2′, 1′-c]quinoxalinium salts were examined for different counteranions. The ethyl-substituted diimidazo[1,2-a:2′,1′-c]quinoxalinium salt with tosylate anion (categolized in ionic liquid) showed good fluorescence (Φ_F = 0.77) in organic solvent. The 3,10-diphenyldiimidazo[1,2-a: 2′,1′-c]quinoxalinium salts showed absorption and fluorescence peaks resembling those of the former diimidazoquinoxaline. The salt also emitted under various conditions such as in organic solvents, water, and even in the solid state, while retaining a good fluorescence quantum yield (Φ_F = 0.5-0.8). Furthermore, the fluorescence was quenched efficiently through the introduction of an electron-donating substituent on the alkyl side chain.

Full text of DOI:10.1021/jo302531g

Article
pubs.acs.org/joc
Fluorescence of Diimidazo[1,2‑a:2′,1′‑c]quinoxalinium Salts Under
Various Conditions
Shoji Matsumoto,* Hajime Abe, and Motohiro Akazome
Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, Chiba University, 1-33 Yayoicho, Inageku,
Chiba 263-8522, Japan
S
* Supporting Information
ABSTRACT: The synthesis and photophysical properties of diimidazo[1,2-a:2′,1′-
c]quinoxalinium salts were examined for different counteranions. The ethyl-
substituted diimidazo[1,2-a:2′,1′-c]quinoxalinium salt with tosylate anion (categol-
ized in ionic liquid) showed good fluorescence (ΦF = 0.77) in organic solvent. The
3,10-diphenyldiimidazo[1,2-a:2′,1′-c]quinoxalinium salts showed absorption and
fluorescence peaks resembling those of the former diimidazoquinoxaline. The salt
also emitted under various conditions such as in organic solvents, water, and even in
the solid state, while retaining a good fluorescence quantum yield (ΦF = 0.5−0.8).
Furthermore, the fluorescence was quenched efficiently through the introduction of
an electron-donating substituent on the alkyl side chain.
Recently, we reported the luminescent properties of
diimidazo[1,2-a:2′,1′-c]quinoxaline derivatives (1) with a high
quantum yield (∼70%) in the blue region (Chart 1).11 These
INTRODUCTION
■
The development of organic fluorophores is essential for
progress in many areas of chemistry and functional materials
research. Various fluorescence materials based on planar π
conjugation have been explored.1 However, the application of
the chromophores under desired circumstances sometimes
requires consideration at the stage of synthesis planning. For
instance, hydrophilic poly(ethylene glycol) (PEG) has been
attached to fluorophores for dissolution in water, and the PEG
block is sometimes introduced in the early or middle stages of
their synthesis.2 One of the simplest methods for changing the
character of a compound is the formation of the ionic form
when the chromophore possesses an sp2 nitrogen atom in its π
conjugation, such as in pyridine and imidazole. For example,
phosphonated cyanines have been formed by the substitution
reaction of alkyl bromide with benzothiazole.3 They show
enhanced in fluorescent intensity upon the addition of
Ca(ClO4)2. The synthesis and physical properties of a 2,2′-
bibenzimidazolium compound have been investigated by Shi
and Thummel,4 and 2,2′-bibenzimidazolium salts have been
explored as synthetic reagents with electron donors.5 Bielawski
and co-workers reported fluorescent materials consisting of
benzobis(imidazolium) salts,6 which showed interesting phys-
ical and optical properties. Furthermore, compounds containing
an ionic structure in the fused cyclic system also exhibited
fluorescence ability.7,8 This implies that it is also possible to
utilize the ionic structure as a fluorophore. Some imidazolium
salts exist as ionic liquids, which are useful as reaction solvents9
and electrolytes.10 Furthermore, it is possible to provide further
functionality and introduce additional properties at the alkyl
chain in imidazolium-type ionic structures. Therefore, the
ionization of the heterocyclic system has potential for the
development of novel functional materials.
Chart 1
materials have an sp2 nitrogen atom that can introduce a
substituent through alkylation. Herein, we report the physical
properties of diimidazo[1,2-a:2′,1′-c]quinoxalinium salts (2·X),
which showed fluorescence properties resembling those of the
parent diimidazo[1,2-a:2′,1′-c]quinoxalines (1) in organic
solvents. 2·X exhibited luminance under various conditions,
including in the solid state and in aqueous solution.
Furthermore, the quenching of luminance by the introduced
substituent is also demonstrated. Fluorophores with solubility
in water as well as quenching ability are promising materials for
utilization as chemical and biological sensors.12,13
RESULTS AND DISCUSSION
■
Compound 1 was alkylated with alkyl iodide in CH3CN under
reflux to give the corresponding salt 2·I (Scheme 1). Double
alkylation never occurred even with excess alkyl halide present.
The compound (2·OTs) bearing tosylate as the counteranion
was also obtained through the reaction of 1 with alkyl tosylate.
Received: November 21, 2012
Published: February 26, 2013
© 2013 American Chemical Society
2397
dx.doi.org/10.1021/jo302531g | J. Org. Chem. 2013, 78, 2397−2404

The Journal of Organic Chemistry
Article
moieties is more efficient to give crystal packing than that in
the alkyl chain. However, a decrease in melting point of about
100 °C was observed when the phenyl group was attached to
the substituted alkyl group (2f·OTs) (entry 15), which would
be caused by somewhat change in the crystal structure with new
interaction between diimidazoquinoxalinium structure and
phenyl ring on the side chain.
Scheme 1. Formation of Diimidazo[1,2-a:2′,1′-
c]quinoxalinium Salts
The absorption and fluorescence spectra of the diimidazo-
quinoxalinium salts were measured in CH3CN (Table 1). In
comparison with 1a, a slight longer wavelength of the
absorption maximum peak (λmax) was obtained upon the
introduction of alkyl groups in 2a·I (entry 2 and Figure 1). The
The tetrafluoroborate derivative (2a·BF4) was obtained from
2a·I by anion exchange using triethyloxonium tetrafluorobo-
rate.14
The physical properties of 1 and 2·X are summarized in
Table 1. We first examined the influence of the counteranion
and the substituent on the melting point. The melting point
decreased upon the introduction of an ethyl group at the sp2
nitrogen atom in the case of the compounds with no
substituent at the 3- and 10-positions (1a vs 2a·X). The
tosylate anion gave the lowest melting point (89−90 °C)
among the three different anions used (entries 2−4), yielding a
compound that is categorized as an “ionic liquid.”15 On the
contrary, there was little effect on the melting point upon salt
formation in the case of the 3,10-diphenyl compounds (1b vs
2b·OTs) (entries 5 and 7). Similar melting points were
obtained even upon the introduction of linear and branched
alkyl chains (2b·OTs, 2c·OTs, 2d·OTs, and 2e·OTs) (entries
7, 12, 13, and 14). It suggests that the interaction in between
neighboring diphenyldiimidazo[1,2-a:2′,1′-c]quinoxalinium
Figure 1. (a) Absorption (3.0 × 10−5 M in CH3CN) and (b)
fluorescence (3.0 × 10−7 M in CH3CN) spectra of 1a, 2a·I, 2a·BF4,
and 2a·OTs.
fine structure was also observed in the absorption spectra,
which suggests that the diimidazoquinoxalinium has a rigid
structure. The fluorescence peak (λem) of 2a·I was at 353 nm
with a 14-nm hypsochromic shift compared with that of 1a
Table 1. Physical Properties of 1 and 2·X
a
b
c
d
entry
compd
Ar
R
X
mp (°C)
solvent
λmax (nm) [ε (M−1 cm−1)]
λem (nm) [ΦF]
1
1a
H
H
H
H
Ph
261
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
THF
307.5 [12200]
311 [13700]
311 [12700]
311 [15500]
329 [14200]
335 [11500]
335.5 [17700]
336.5 [17900]
334 [16800]
334.5 [19100]
334 [19100]
335.5 [17800]
336.5 [17600]
335.5 [18500]
336 [18600]
367 [0.70]
353 [0.68]
353 [0.78]
353 [0.77]
424 [0.47]
2
2a·I
Et
Et
Et
I
157−158
240−241
89−90
3
2a·BF4
2a·OTs
1b
BF4
4
OTs
5
203−204
e
6
428 [0.82]
7
2b·OTs
Ph
Et
OTs
223−224
CH3CN
THF
429 [0.63]
433 [0.72]
429 [0.72]
430 [0.65]
430 [0.66]
428 [0.78]
428 [0.65]
428 [0.22]
427 [0.65]
8
9
H2O
10
11
12
13
14
15
aq NaOH (pH = 11.8)
aq HCl (pH = 2.2)
CH3CN
2c·OTs
2d·OTs
2e·OTs
2f·OTs
Ph
Ph
Ph
Ph
n-Bu
i-Bu
OTs
OTs
OTs
OTs
203−204
209−210
203−204
105−107
CH3CN
n-Hex
CH3CN
−(CH2)3Ph
CH3CN
a
b
c
d
Melting points are uncorrected. Concentration: 3.0 × 10−5 M. Concentration: 3.0 × 10−7 M. Determined by p-terphenyl (ΦF = 0.87, excited at
e
265 nm) as a standard. Determined by quinine sulfate (ΦF = 0.55, excited at 366 nm) as a standard.
2398
dx.doi.org/10.1021/jo302531g | J. Org. Chem. 2013, 78, 2397−2404

The Journal of Organic Chemistry
Article
Figure 3. Fluorescence spectra in the solid state with integration
sphere system: (a) 1a, 2a·I, 2a·BF4, and 2a·OTs excited at 311 nm;
(b) 1b and 2b·OTs excited at 335 nm. ΦF values were determined by
using a calibrated integration sphere system.
Figure 2. (a) Absorption (3.0 × 10−5 M in CH3CN) and (b)
fluorescence (3.0 × 10−7 M in CH3CN) spectra of 1b and 2b−f·OTs.
(entry 2 and Figure 2). The fluorescence quantum yield (ΦF)
remained at ≈70% even upon introduction of an alkyl chain.
No influence of the counteranion was observed on the peaks of
the absorption and fluorescence spectra (2a·I, 2a·BF4, and
2a·OTs) (entries 2−4). However, ΦF differed slightly (0.68 for
2a·I, 0.78 for 2a·BF4, and 0.77 for 2a·OTs).
Interestingly, a change of below 6 nm for λmax and λem was
observed between 1b and 2b·OTs bearing phenyl groups
(entries 5 and 7 in Table 1, and Figure 2), and ΦF was
increased upon changing from the diphenyldiimidazoquinoxa-
line to the diphenyldiimidazoquinoxalinium structure, which is
caused by restriction of the rotation of phenyl ring to introduce
the alkyl chain. Focused on the difference in the alkyl chain,
2e·OTs bearing a long alkyl chain gave a decrease in ΦF (entry
14). This is because nonradiative decay through the motion of
the alkyl chain was increased. However, the phenyl group
attached to the edge of the introduced alkyl group did not affect
the optical properties in the absorption and fluorescence
spectra (entry 15).
rings at the 3- and 10-positions in 1b with a hypsochromic shift
of the emission peak, which is a different result from that
obtained in solution. From these results, it was found that these
3,10-diaryldiimidazoquinoxaline and 3,10-diaryldiimidazoqui-
noxalinium structures potentially have emission properties in
the solid state upon photoirradiation, even though they have
different fluorescence properties in solution.
The solvent effect on the absorption and fluorescence spectra
of 1b and 2b·OTs is represented in Figure 4. Because of its
ionic structure, 2b·OTs could be dissolved in H2O without any
organic cosolvent. A slight influence on the absorption and
fluorescence peaks was observed in both 1b and 2b·OTs.
Although a decrease in ΦF was observed for 1b in a polar
solvent (entries 5 and 6 in Table 1), ΦF of 2b·OTs was
maintained in various solvents (entries 7−11). It was found that
2b·OTs could be utilized as a good fluorophore, emitting in the
visible region even in acidic, basic, and neutral H2O (entries 9,
10, and11).
In order to obtain further information, we investigated the
fluorescence properties of the various materials under different
conditions. As mentioned in our previous paper, 1b shows
luminescence in the solid state.11 Therefore, we examined the
fluorescence properties of diimidazoquinoxalinium derivatives
in the solid state. We selected 1a and 2a·X as the objective
substrates because not only the structural change but also the
counteranion would affect the optical properties under the
aggregated conditions. Compound 1a was illuminated by
photoirradiation with medium quantum yield (ΦF = 0.36)
(Figure 3a). Compounds 2a·BF4 and 2a·OTs also exhibited
photoluminescence with a decrease in ΦF (0.15 and 0.17,
respectively). However, the fluorescence of 2a·I was strictly
quenched because of the heavy atom effect of the iodide
counteranion. The emission peak of 2a·OTs showed a
hypsochromic shift compared with 1a, and 2a·BF4 exhibited
two broadened peaks. Compounds 1b and 2b·OTs also showed
emission in the solid state (Figure 3b). Furthermore, an
increase in ΦF was observed upon the attachment of phenyl
The absorption and fluorescence properties of 1b and
2b·OTs were consistent with the results of DFT calculations.
From the results of the DFT and TDDFT calculations at the
B3LYP/6-31+G level (Figure 5), the orbitals of both structures
derived in the ground state (from DFT) and excited state (from
TDDFT) were delocalized in the biimidazole moiety and
substituted phenyl groups at the 3- and 10-positions in the
HOMOs of the 1b and 2b cation. The LUMOs also exist in the
biimidazole and phenyl parts with the region on the phenylene
moiety of the diimidazoquinoxaline structure. Therefore, there
is little charge transfer in the ground and excited states, which
leads to a less pronounced solvent effect on λmax and λem. The
orbital energies of both the HOMO and LUMO decrease upon
introduction of an alkyl group to form the diimidazoquinox-
alinium structure. However, there is little change in the energy
separation between the HOMO and LUMO in the 1b and 2b
cation (ΔE = 4.101 eV for 1b and 4.044 eV for 2b cation from
DFT calculations; ΔE = 3.102 eV for 1b and 3.129 eV for 2b
cation from TDDFT calculations). Thus, the small wavelength
2399
dx.doi.org/10.1021/jo302531g | J. Org. Chem. 2013, 78, 2397−2404

The Journal of Organic Chemistry
Article
Figure 4. Absorption (narrow line, 3.0 × 10−5 M) and fluorescence (bold line, 3.0 × 10−7 M) spectra of (a) 1b and (b) 2b·OTs in THF, CH3CN,
H2O, aq NaOH (pH = 11.8), and aq HCl (pH = 2.2).
Figure 5. Orbitals and energies of HOMO and LUMO of 1b and 2b cation estimated by (a) DFT and (b) TDDFT (nstate = 10) calculations for
structure optimization at the B3LYP/6-31+G level.
change in the absorption and fluorescence peaks would be
observed by lowering the orbital energies of the HOMO and
LUMO by the same degrees.
a 3,4,5-trimethoxyphenyl group or an anthryl group on the alkyl
chain are summarized in Table 2 and Figure 8. The data for
2f·OTs, which is their phenyl analogue with a propylene linker,
is also represented for reference. Fluorescence quenching of
2h·OTs and 2i·OTs was observed in dilute conditions (3.0 ×
10−7 M) (entries 3 and 4), whereas 2g·OTs showed
fluorescence with ΦF = 0.50. It is suggested that the length
of the alkyl chain is important for quenching the fluorescence,
and that the propylene linker gives the appropriate alignment
for the interaction between the electron-donating substituent
and the diimidazoquinoxalinium part. In terms of the
quenching ability of the different substituents, it was found
that the fluorescence of 2i·OTs was quenched more effectively
than that of 2h·OTs (ΦF = 0.03 for 2i·OTs vs 0.16 for
2h·OTs). The ionization potential of anthracene (7.23 eV)16 is
lower than that of 1,2,3-trimethoxybenzene (7.74 eV).17
Therefore, we believe that the quenching mechanism can be
explained rationally by the acceptor-excited photoinduced
electron transfer depicted in Scheme 2.18,19 The diimidazoqui-
noxalinium part (A) is excited by photoirradiation to give the
“SOMO” state (Scheme 2 (ii)). When an electron-donating
substrate (B) is present in the appropriate position of A, the
From the consideration of the result of the DFT calculations,
fluorescence quenching of 2b·OTs was observed upon the
introduction of a moiety with electron-donating ability. To
reveal the possibility to such phenomenon directly, the
fluorescent intensity of 2b·OTs under solvent-free conditions
was reduced by mixing about the same volume of 2b·OTs with
each electron-donating substrate, 3,4,5-trimethoxytoluene and
anthracene, whereas they were less effective in 1b which has
higher LUMO orbital energies than 2b cation (Figure 6). Upon
mixing 2b·OTs with anthracene, the fine structure observed in
the fluorescence spectrum shown in Figure 6b is due to
emission from the anthracene. In solution, the quenching
phenomenon was also observed upon the combination of
2b·OTs and 3,4,5-trimethoxytoluene, although an excess of the
donating 3,4,5-trimethoxytoluene (over 100 equiv) was
necessary for efficient quenching (Figure 7).
Furthermore, we examined the intramolecular quenching due
to the electron-donating property of the alkyl chain. The optical
properties of compounds 2g·OTs, 2h·OTs, and 2i·OTs bearing
2400
dx.doi.org/10.1021/jo302531g | J. Org. Chem. 2013, 78, 2397−2404

The Journal of Organic Chemistry
Article
Figure 8. (a) Absorption (3.0 × 10−5 M in CH3CN) and (b)
fluorescence (3.0 × 10−7 M in CH3CN) spectra of 2f−i·OTs.
Figure 6. Fluorescence spectra in solid state excited at 335 nm: (a) 1b
(solid black line), 1b + 3,4,5-trimethoxytoluene (ca. 1:1 (v/v))
(dashed black line), 2b·OTs (solid red line), and 2b·OTs + 3,4,5-
trimethoxytoluene (ca. 1:1 (v/v)) (dashed red line); (b) 1b (solid
black line), 1b + anthracene (ca. 1:1 (v/v)) (dashed black line),
2b·OTs (solid red line), and 2b·OTs + anthracene (ca. 1:1 (v/v))
(dashed red line).
“HOMO” electron of B is easily transferred to the lowering
“SOMO” of A (Scheme 2 (iii)). As a result, further electron
transfer between B and A occurs, followed by nonradiative
decay to reach the ground state (Scheme 2 (iv)). From these
findings, we suggest that the fluorescence of diimidazoquinox-
alinium is controllable by the functionality introduced though
the alkyl side chain at the 1-position.
CONCLUSION
■
We have synthesized various diimidazo[1,2-a:2′,1′-c]-
quinoxalinium salts through substitution reactions with
alkylation reagents and the exchange of the counteranions
and examined their optical properties under various conditions.
Fine fluorescence properties with ΦF ≈ 0.8 were obtained in
solution. The 3,10-diphenyldiimidazaoquinoxalinium deriva-
tives showed absorption and emission peaks resembling those
of the original diimidazoquinoxaline (1b). Furthermore, the
diimidazoquinoxalinium salts exhibited fluorescence in various
Figure 7. Fluorescence spectra (3.0 × 10−5 M in CH3CN) of 2b·OTs
with various amounts of 3,4,5-trimethoxytoluene (excited at 355 nm).
Table 2. Physical Properties of 2·X with Aryl Group Attached
a
b
c
Measured in CH3CN (3.0 × 10−5 M). Measured in CH3CN (3.0 × 10−7 M). Determined by p-terphenyl (ΦF = 0.87, excited at 265 nm) as a
standard.
2401
dx.doi.org/10.1021/jo302531g | J. Org. Chem. 2013, 78, 2397−2404

The Journal of Organic Chemistry
Article
Scheme 2. Proposed Fluorescence Quenching Mechanism
for 2b Based on Photoelectron Transfer
EXPERIMENTAL SECTION
General Information. Melting points were uncorrected. NMR
■
1
measurements were recorded with a 300 MHz spectrometer for H
NMR and with a 75 MHz spectrometer for 13C NMR. Chemical shifts
1
(δ) of H NMR were expressed in parts per million downfield from
tetramethylsilane in CDCl3 (δ = 0) or DMSO-d5 (δ = 2.49) as an
internal standard. Multiplicities are indicated as s (singlet), d
(doublet), t (triplet), q (quartet), quint (quintet), sext (sextet), sept
(septet), m (multiplet), bs (broadened singlet), and coupling
constants (J) are reported in hertz units. Chemical shifts (δ) of 13C
NMR are expressed in parts per million downfield or upfield from
CDCl3 (δ = 77.0) or DMSO-d6 (δ = 39.6) as an internal standard.
Infrared spectra (IR) were recorded on a KBr disk. UV−vis and PL
spectra were measured in a quartz cell. The absolute fluorescence
quantum yield in solid state was measured with the integrating sphere
unit. Anhydrous CH3CN was distilled from sodium hydride and was
stored with MS 3 Å. Anhydrous CHCl3 was distilled from P2O5 after
washing with MeOH and drying with CaCl2, and was stored with MS
4 Å. Anhydrous THF was distilled from sodium benzophenone ketyl
immediately prior to use. The reactions were performed under
nitrogen atmosphere.
1-Ethyldiimidazo[1,2-a:2′,1′-c]quinoxalinium Iodide (2a·I).
To a solution of diimidazo[1,2-a:2′,1′-c]quinoxaline (1a)11 (62.3
mg, 0.299 mmol) in CH3CN (1.2 mL) was added iodoethane (82.4
mg, 0.528 mmol). The mixture was stirred under reflux conditions for
24 h. After being cooled to room temperature, the reaction mixture
was concentrated in vacuo. From 1H NMR of the crude products, the
reaction proceeded almost quantitatively. The residual mixture was
recrystallized from CH3CN and hexane to give 1-ethyldiimidazo[1,2-
a:2′,1′-c]quinoxalinium iodide (2a·I) (63.2 mg, 0.174 mmol) in 58%
isolated yield as a white solid: mp 240.1−241.1 °C; 1H NMR (DMSO-
d6, 300 MHz) δ 1.57 (t, J = 7.1 Hz, 3H), 4.93 (q, J = 7.2 Hz, 2H), 7.81
(t, J = 7.3 Hz, 1H), 7.88 (t, J = 6.5 Hz, 1H), 7 95 (s, 1H), 8.43 (d, J =
2.1 Hz, 1H), 8.57 (d, J = 7.3 Hz, 1H), 8.60 (d, J = 7.9 Hz, 1H), 8.99 (s,
1H), 9.10 (d, J = 2.2 Hz, 1H); 13C NMR (DMSO-d6, 75 MHz) δ 15.0,
44.7, 115.6, 116.8, 117.7, 118.0, 122.5, 124.4, 124.7, 127.9, 129.4,
129.8, 130.6, 134.1; IR (KBr) 3072, 3021, 1644, 1583, 1503, 1455,
1434, 1332, 774, 677 cm−1. Anal. Calcd for C14H13IN4·3/5H2O: C,
44.84; H, 3.82; N, 14.94. Found: C, 44.88; H, 3.54; N, 14.83.
1-Ethyldiimidazo[1,2-a:2′,1′-c]quinoxalinium Tetrafluorobo-
rate (2a·BF4). To a solution of 1-ethyldiimidazo[1,2-a:2′,1′-c]-
quinoxalinium iodide (2a·I) (36.4 mg, 0.100 mmol) in CH3CN (3
mL) was added a solution of triethyloxonium tetrafluoroborate in
CH2Cl2 (1 M; 0.1 mL, 0.1 mmol). After being stirred at room
temperature for 28 h, the reaction mixture was concentrated in vacuo.
1
From H NMR of the crude products, the reaction proceeded almost
quantitatively. The reaction residue was recrystallized from CH3CN
and hexane to give 1-ethyldiimidazo[1,2-a:2′,1′-c]quinoxalinium
tetrafluoroborate (2a·BF4) (25.8 mg, 79.6 mmol) in 80% isolated
solvents, especially in H2O with ΦF = 0.72, and even
illuminated in the solid state. Therefore, they can be utilized
as fluorophores under various conditions. The long length of
the alkyl chain decreased the fluorescence intensity. The
counteranion such as iodide anion had decreased the
fluorescence in the solid state, but was less effective in solution.
We further examined the electron-donating effect of the
substituent attached on the alkyl side chain, and found that
substrates with electron-donating character led to efficient
quenching of the fluorescence because of the photoelectron
transfer. This result implies that novel functional fluorophores
can be designed using this interaction between the
diimidazoquinoxalinium structure and the group attached on
the alkyl side chain. From these findings, it is suggested that
diimidazoquinoxalinium salts have potential for application not
only as fluorophores utilized under various conditions, but also
in the fields of sensors, biological fluorescence imaging,
biolabeling, and so on. The applications of this diimidazoqui-
noxaline structure as a sensor are under investigation.
1
yield as white solid: mp 156.5−157.8 °C; H NMR (DMSO-d6, 300
MHz) δ 1.56 (t, J = 7.3 Hz, 3H), 4.92 (q, J = 7.2 Hz, 2H), 7.81 (t, J =
7.5 Hz, 1H), 7.88 (t, J = 7.3 Hz, 1H), 7.95 (s, 1H), 8.42 (d, J = 1.6 Hz,
1H), 8.56 (d, J = 7.6 Hz, 1H), 8.58 (d, J = 7.7 Hz, 1H), 8.99 (s, 1H),
9.08 (d, J = 1.8 Hz, 1H); 13C NMR (DMSO-d6, 75 MHz) δ 15.0, 44.7,
115.5, 116.7, 117.7, 118.0, 122.5, 124.4, 124.7, 127.9, 129.4, 129.9,
130.6, 134.1; IR (KBr) 3050, 3022, 1644, 1583, 1505, 1456, 1435,
1333, 774, 678 cm−1. Anal. Calcd for C14H13BF4N4·1/6H2O: C, 51.41;
H, 4.11; N, 17.13. Found: C, 51.68; H, 4.10; N, 16.88.
1-Ethyldiimidazo[1,2-a:2′,1′-c]quinoxalinium p-Toluenesul-
fonate (2a·OTs). To a solution of 1a (63.0 mg, 0.302 mmol) in
CH3CN (1.2 mL) was added ethyl p-toluenesulfonate (104 mg, 0.519
mmol). The mixture was stirred at 60 °C for 24 h. After being cooled
to room temperature, the reaction mixture was concentrated in vacuo.
1
From H NMR of the crude products, the reaction almost proceeded
quantitatively. The residual mixture and was recrystallized from
CH3CN and hexane to give 1-ethyldiimidazo[1,2-a:2′,1′-c]-
quinoxalinium p-toluenesulfonate (2a·OTs) (36.0 mg, 0.0881 mmol)
1
in 29% isolated yield as white solid: mp 89.4−90.3 °C; H NMR
(DMSO-d6, 300 MHz) δ 1.56 (t, J = 7.3 Hz, 3H), 2.72 (s, 3H), 4.92
(q, J = 7.3 Hz, 2H), 7.09 (d, J = 7.8 Hz, 2H), 7.46 (d, J = 7.9 Hz, 2H),
2402
dx.doi.org/10.1021/jo302531g | J. Org. Chem. 2013, 78, 2397−2404

The Journal of Organic Chemistry
Article
7.81 (t, J = 7.6 Hz, 1H), 7.87 (t, J = 7.6 Hz, 1H), 7 95 (s, 1H), 8.42 (d,
J = 1.5 Hz, 1H), 8.58 (t, J = 7.9 Hz, 2H), 8.98 (s, 1H), 9.08 (d, J = 1.7
Hz, 1H); 13C NMR (DMSO-d6, 75 MHz) δ 15.0, 20.8, 44.7, 115.6,
116.8, 117.7, 118.0, 122.5, 124.4, 124.7, 125.5, 127.9, 128.1, 129.4,
129.8, 130.5, 134.1, 137.6, 145.8; IR (KBr) 3092, 3066, 1644, 1505,
1456, 1432, 1332, 1195, 776, 690 cm−1. Anal. Calcd for
C21H20N4O3S·H2O: C, 59.14; H, 5.20; N, 13.14. Found: C, 59.02;
H, 5.12; N, 13.10.
125.94, 126.4, 126.6, 126.7, 128.1, 128.2, 128.8, 129.4, 129.6, 129.8,
130.2, 130.6, 130.7, 130.79, 130.82, 131.0, 132.6, 135.4, 138.1, 144.4;
IR (KBr) 3055, 2955, 28592, 1645, 1579, 1491, 1468, 1447, 1404,
1203 cm−1. Anal. Calcd for C37H36N4O3S·1/3H2O: C, 71.36; H, 5.93;
N, 9.00. Found: C, 71.33; H, 5.84; N, 8.98.
1-(3-Phenylpropyl)-3,10-diphenyldiimidazo[1,2-a:2′,1′-c]-
quinoxalinium p-Toluenesulfonate (2f·OTs). This compound was
prepared in 56% isolated yield (0.112 g, 0.172 mmol) from 1b (0.110
g, 0.306 mmol) under reflux conditions for 48 h according to a
procedure similar to that mentioned in 2a·OTs: colorless solid; mp
105.1−106.7 °C (CHCl3−Et2O); 1H NMR (CDCl3, 300 MHz) δ 2.24
(s, 3H), 2.53 (quint, J = 7.4 Hz, 2H), 2.90 (t, J = 7.3 Hz, 2H), 5.31 (t, J
= 7.3 Hz, 2H), 6.97 (d, J = 7.9 Hz, 2H), 7.01 (m, 1H), 7.08−7.24 (m,
4H), 7.15 (ddd, J = 1.5, 7.4, and 8.7 Hz, 1H), 7.23 (ddd, J = 1.5, 7.1,
and 8.4 Hz, 1H), 7.48 (dd, J = 1.2 and 8.5 Hz, 1H), 7.53−7.62 (m,
11H), 7.68 (s, 1H), 7.71 (dd, J = 1.4 and 7.6 Hz, 2H), 8.36 (s, 1H);
13C NMR (CDCl3, 75 MHz) δ 21.2, 30.7, 32.6, 50.4, 118.4, 119.6,
1-Ethyl-3,10-diphenyldiimidazo[1,2-a:2′,1′-c]quinoxalinium
p-Toluenesulfonate (2b·OTs). This compound was prepared in 55%
isolated yield (0.115 g, 0.204 mmol) from 3,10-diphenyldiimidazo[1,2-
a:2′,1′-c]quinoxaline (1b)11 (0.135 g, 0.373 mmol) at 60 °C for 24 h
according to a procedure similar to that mentioned for 2a·OTs: pale
1
yellow solid; mp 222.8−224.0 °C (CHCl3−Et2O); H NMR (CDCl3,
300 MHz) δ 1.75 (t, J = 7.2 Hz, 3H), 2.24 (s, 3H), 5.27 (q, J = 7.2 Hz,
2H), 6.97 (d, J = 7.9 Hz, 2H), 7.17 (ddd, J = 1.3, 7.03, and 8.5 Hz,
1H), 7.25 (ddd, J = 1.6, 7.0, and 8.3 Hz, 1H), 7.54−7.61 (m, 12H),
7.70 (s, 1H), 7.75 (diffused d, J = 8.0 Hz, 2H), 8.47 (s, 1H); 13C NMR
(CDCl3, 75 MHz) δ 15.3, 21.1, 46.2, 118.5, 119.6, 124.0, 125.6, 125.9,
126.3, 126.5, 126.7, 128.0, 128.2, 128.7, 129.4, 129.6, 129.7, 130.2,
130.4, 130.56, 130.63, 130.7, 130.9, 132.6, 135.4, 138.1, 144.5; IR
(KBr) 3056, 2981, 1645, 1579, 1491, 1469, 1447, 1403, 1202, 1122
cm−1. Anal. Calcd for C33H28N4O3S: C, 70.69; H, 5.03; N, 9.99.
Found: C, 70.22; H, 5.12; N, 9.90.
123.9, 125.8, 125.9, 126.0, 126.2, 126.4, 126.7, 128.0, 128.1, 128.21,
128.24, 128.7, 129.5, 129.6, 129.7, 130.26, 130.34, 130.6, 130.7, 130.8,
131.0, 132.6, 135.4, 138.2, 140.5, 144.4; IR (KBr) 3056, 1645, 1579,
1491, 1468, 1447, 1405, 1208, 1119, 1033, 1012, 766, 702, 678, 569,
561 cm−1. Anal. Calcd for C40H34N4O3S·1/4H2O: C, 73.32; H, 5.31; N,
8.55. Found: C, 73.32; H, 5.28; N, 8.55.
1-(3-(3,4,5-Trimethoxyphenyl)ethyl)-3,10-diphenyl-
diimidazo[1,2-a:2′,1′-c]quinoxalinium p-Toluenesulfonate
(2g·OTs). This compound was prepared in 97% isolated yield (53.2
mg, 0.0731 mmol) from 1b (27.3 mg, 0.0757 mmol) under reflux
conditions for 48 h according to a procedure similar to that mentioned
1-n-Butyl-3,10-diphenyldiimidazo[1,2-a:2′,1′-c]quinoxa-
linium p-Toluenesulfonate (2c·OTs). This compound was prepared
in 41% isolated yield (48.3 mg, 0.0820 mmol) from 1b (72.1 mg, 0.200
mmol) at 70 °C for 24 h according to a procedure similar to that
mentioned in 2a·OTs: pale yellow solid; mp 202.5−203.6 °C
(CHCl3−Et2O); 1H NMR (CDCl3, 300 MHz) δ 1.01 (t, J = 7.3
Hz, 3H), 1.54 (sext, J = 7.6 Hz, 2H), 2.10 (quint, J = 7.5 Hz, 2H), 2.24
(s, 3H), 5.22 (t, J = 7.5 Hz, 2H), 6.96 (d, J = 7.9 Hz, 2H), 7.16 (ddd, J
= 1.4, 7.2, and 8.7 Hz, 1H), 7.24 (ddd, J = 1.5, 7.2, and 8.4 Hz, 1H),
7.53−7.61 (m, 12H), 7.69 (s, 1H), 7.77 (dd, J = 1.7 and 8.0 Hz, 2H),
8.36 (s, 1H); 13C NMR (CDCl3, 75 MHz) δ 13.6, 19.7, 21.2, 31.9,
50.5, 118.5, 119.7, 124.1, 125.91, 125.93, 126.4, 126.6, 126.7, 128.1,
128.2, 128.8, 129.5, 129.6, 129.8, 130.2, 130.5, 130.7, 130.79, 130.84,
131.0, 132.6, 135.4, 138.2, 144.4; IR (KBr) 3058, 2959, 2872, 1645,
1579, 1492, 1468, 1447, 1403, 1213 cm−1. Anal. Calcd for
C35H32N4O3S: C, 71.40; H, 5.48; N, 9.52. Found: C, 71.19; H, 5.50;
N, 9.41.
1
in 2a·OTs: colorless solid; mp 263.7−265.0 °C (CHCl3−Et2O); H
NMR (CDCl3, 300 MHz) δ 2.25 (s, 3H), 3.45 (t, J = 7.4 Hz, 2H), 3.76
(s, 3H), 3.80 (s, 6H), 5.52 (t, J = 7.3 Hz, 2H), 6.72 (s, 2H), 6.98 (d, J
= 8.0 Hz, 2H), 7.15 (dt, J = 1.3 and 8.6 Hz, 1H), 7.23 (dd, J = 1.5 and
8.9 Hz, 1H), 7.51−7.62 (m, 12H), 7.69 (dd, J = 1.8 and 7.7 Hz, 2H),
7.71 (s, 1H), 8.47 (s, 1H); 13C NMR (CDCl3, 75 MHz) δ 21.2, 36.3,
51.3, 56.2, 60.7, 106.5, 118.5, 119.6, 124.1, 125.9, 126.2, 126.4, 126.5,
126.7, 128.19, 128.24, 128.7, 129.5, 129.6, 129.8, 130.3, 130.4, 130.6,
130.8, 130.9, 131.0, 132.5, 132.8, 135.4, 136.8, 138.3, 144.4, 153.2; IR
(KBr) 3446, 3093, 3061, 2999, 2941, 2836, 1645, 1591, 1506, 1468,
1409, 1334, 1215, 1206, 1123, 1035, 1013 cm−1. Anal. Calcd for
C42H38N4O6S·1/7CHCl3: C, 68.04; H, 5.17; N, 7.53. Found: C, 67.74;
H, 5.20; N, 7.56.
1-Isobutyl-3,10-diphenyldiimidazo[1,2-a:2′,1′-c]quinoxa-
linium p-Toluenesulfonate (2d·OTs). This compound was
prepared in 33% isolated yield (39.1 mg, 0.0664 mmol) from 1b
(72.1 mg, 0.200 mmol) with 4 equiv of isobutyl p-toluenesulfonate
under reflux conditions for 72 h according to a procedure similar to
that mentioned in 2a·OTs: pale yellow solid; mp 208.7−209.6 °C
1-(3-(3,4,5-Trimethoxyphenyl)propyl)-3,10-diphenyl-
diimidazo[1,2-a:2′,1′-c]quinoxalinium p-Toluenesulfonate
(2h·OTs). This compound was prepared in 92% isolated yield
(0.209 g, 0.281 mmol) from 1b (0.110 g, 0.306 mmol) under reflux
conditions for 48 h according to a procedure similar to that mentioned
1
in 2a·OTs: colorless solid; mp 105.3−107.0 °C (CHCl3−Et2O); H
1
NMR (CDCl3, 300 MHz) δ 2.25 (s, 3H), 2.57 (quint, J = 7.1 Hz, 2H),
2.89 (t, J = 7.3 Hz, 2H), 3.69 (s, 3H), 3.73 (s, 6H), 5.32 (t, J = 7.0 Hz,
2H), 6.42 (s, 2H), 6.98 (d, J = 7.6 Hz, 2H), 7.15 (t, J = 7.6 Hz, 1H),
7.24 (t, J = 8.1 Hz, 1H), 7.50−7.72 (m, 15H), 8.52 (s, 1H); 13C NMR
(CDCl3, 75 MHz) δ 21.2, 30.7, 33.0, 50.5, 56.1, 60.7, 105.5, 118.5,
119.7, 124.0, 125.9, 126.2, 126.3, 126.4, 126.7, 128.2 (thresh high),
128.7, 129.5, 129.6, 129.7, 130.3, 130.4, 130.7, 130.8, 130.9, 131.0,
132.7, 135.4, 136.2, 136.4, 138.4, 144.3, 152.9; IR (KBr) 3056, 2939,
2839, 1645, 1589, 1507, 1468, 1404, 1195, 1214 cm−1. Anal. Calcd for
C43H40N4O6S·6/7CHCl3: C, 62.47; H, 4.88; N, 6.64. Found: C, 62.42;
H, 4.98; N, 6.61.
(CHCl3−Et2O); H NMR (CDCl3, 300 MHz) δ 1.12 (d, J = 6.7 Hz,
6H), 2.34 (s, 3H), 2.52 (nonet, J = 7.0 Hz, 1H), 5.07 (d, J = 7.5 Hz,
2H), 6.96 (d, J = 8.0 Hz, 2H), 7.16 (ddd, J = 1.2, 7.3, and 8.2 Hz, 1H),
7.24 (ddd, J = 1.2, 7.3, and 8.5 Hz, 1H), 7.54−7.63 (m, 12H), 7.68 (s,
1H), 7.78 (dd, J = 1.7 and 7.8 Hz, 2H), 8.29 (s, 1H); 13C NMR
(CDCl3, 75 MHz) δ 19.6, 21.1, 29.2, 57.0, 118.5, 119.6, 124.0, 125.9,
126.29, 126.33, 126.5, 126.7, 128.0, 128.2, 128.7, 129.4, 129.6, 129.7,
130.2, 130.49, 130.53, 130.7, 130.97, 131.00, 132.6, 135.3, 138.1,
144.5; IR (KBr) 3057, 2962, 2873, 1642, 1579, 1492, 1469, 1447,
1402, 1193 cm−1. Anal. Calcd for C35H32N4O3S·2/3CHCl3: C, 64.10;
H, 4.93; N, 8.38. Found: C, 63.81; H, 4.90; N, 8.37.
1-(3-(9-Anthryl)propyl)3,10-diphenyldiimidazo[1,2-a:2′,1′-
c]quinoxalinium p-Toluenesulfonate (2i·OTs). This compound
was prepared in 32% isolated yield (61.8 mg, 0.0823 mmol) from 1b
(92.4 mg, 0.256 mmol) under reflux conditions for 48 h according to a
procedure similar to that mentioned in 2a·OTs: pale yellow solid; mp
147.1−150.5 °C (CHCl3−Et2O); 1H NMR (CDCl3, 300 MHz) δ 2.25
(s, 3H), 2.72 (sept, J = 7.4 Hz, 2H), 3.91 (t, J = 7.7 Hz, 2H), 5.49 (t, J
= 7.5 Hz, 2H), 7.00 (d, J = 8.0 Hz, 2H), 7.14 (dt, J = 1.4 and 7.2 Hz,
1H), 7.22 (dt, J = 1.4 and 8.7 Hz, 1H), 7.34 (t, J = 8.0 Hz, 2H), 7.41−
7.63 (m, 15H), 7.69 (d, J = 8.1 Hz, 2H), 7.84 (d, J = 8.2 Hz, 2H), 8.14
(s, 1H), 8.39 (s, 1H), 8.40 (d, J = 7.3 Hz, 1H); 13C NMR (CDCl3, 75
MHz) δ 21.2, 24.8, 30.9, 50.4, 118.5, 119.6, 123.9, 124.6, 124.8, 125.6,
1-n-Hexyl-3,10-diphenyldiimidazo[1,2-a:2′,1′-c]quinoxa-
linium p-Toluenesulfonate (2e·OTs). This compound was
prepared in 38% isolated yield (46.9 mg, 0.0760 mmol) from 1b
(72.2 mg, 0.200 mmol) at 70 °C according for 24 h to a procedure
similar to that mentioned in 2a·OTs: pale yellow solid; mp 202.6−
203.6 °C (CHCl3−Et2O); 1H NMR (CDCl3, 300 MHz) δ 0.89 (t, J =
7.0 Hz, 3H), 1.29−1.40 (m, 4H), 1.46−1.57 (m, 2H), 2.11 (quint, J =
7.6 Hz, 2H), 2.24 (s, 3H), 5.21 (t-like, J = 7.6 Hz, 2H), 6.96 (d, J = 7.9
Hz, 2H), 7.16 (ddd, J = 1.3, 7.2, and 8.7 Hz, 1H), 7.24 (ddd, J = 1.5,
7.0, and 8.4 Hz, 1H), 7.54−7.61 (m, 12H), 7.67 (s, 1H), 7.78 (dd, J =
1.8 and 8.0 Hz, 2H), 8.34 (s, 1H); 13C NMR (CDCl3, 75 MHz) δ
14.0, 21.2, 22.4, 26.1, 29.9, 31.2, 50.7, 118.5, 119.7, 124.1, 125.87,
2403
dx.doi.org/10.1021/jo302531g | J. Org. Chem. 2013, 78, 2397−2404

The Journal of Organic Chemistry
Article
125.8, 125.9, 126.0, 126.2, 126.3, 126.6, 128.1, 128.3 (thresh high),
128.8, 128.9, 129.5, 129.6, 129.7, 130.3 (thresh high), 130.4, 130.7,
131.0, 131.4, 132.5, 133.0, 135.3, 138.4; IR (KBr) 3054, 2971, 1642,
1579, 1492, 1467, 1446, 1403, 1193, 1122 cm−1. Anal. Calcd for
C48H38N4O3S·1/4CHCl3: C, 74.23; H, 4.94; N, 7.18. Found: C, 74.49;
H, 5.08; N, 7.25.
(6) (a) Guo, Z.; Song, N. R.; Moon, J. H.; Kim, M.; Jun, E. J.; Choi,
J.; Lee, J. Y.; Bielawski, C. W.; Sessler, J. L.; Yoon, J. J. Am. Chem. Soc.
2012, 134, 17846−17849. (b) Wiggins, K. M.; Kerr, R. L.; Chen, Z.;
Bielawski, C. W. J. Mater. Chem. 2010, 5709−5714. (c) Boydston, A.
J.; Vu, P. D.; Dykhno, O. L.; Chang, V.; Wyatt, A. R., II; Stockett, A. S.;
Ritschdorff, T. E.; Shear, J. B.; Bielawski, C. W. J. Am. Chem. Soc. 2008,
130, 3143−3156. (d) Tang, T.; Coady, D. J.; Boydston, A. J.; Dykhno,
O. L.; Bielawski, C. W. Adv. Mater. 2008, 20, 3096−3099.
(e) Boydston, A. J.; Pecinovsky, C. S.; Chao, S. T.; Bielawski, C. W.
J. Am. Chem. Soc. 2007, 129, 14550−14551.
(7) (a) Namba, K.; Mera, A.; Osawa, A.; Sakuda, E.; Kitamura, N.;
Tanino, K. Org. Lett. 2012, 14, 5554−5557. (b) Namba, K.; Osawa, A.;
Ishizaka, S.; Kitamura, N.; Tanino, K. J. Am. Chem. Soc. 2011, 133,
11466−11469.
(8) Hutt, J. T.; Jo, J.; Olasz, A.; Chen, C.-H.; Lee, D.; Aron, Z. D. Org.
Lett. 2012, 14, 3162−3165.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 13C NMR spectra for new compounds and Cartesian
coordinates of the results of DFT and TDDFT calculations.
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
■
(9) (a) Plechkova, N. V.; Seddon, K. R. Chem. Soc. Rev. 2008, 37,
123−150. (b) Kubisa, P. J. Polym. Sci. Part A: Plym. Chem. 2005, 43,
4675−4683. (c) Jain, N.; Kumar, A.; Chauhan, S.; Chauhan, S. M. S.
Tetrahedron 2005, 61, 1015−1060. (d) Wasserscheid, P.; Keim, W.
Angew. Chem., Int. Ed. 2000, 39, 3772−3789. (e) Earle, M. J.; Seddon,
K. R. Pure Appl. Chem. 2000, 72, 1391−1398.
Corresponding Author
*Tel: +81-43-290-3369. Fax: +81-43-290-3401. E-mail:
smatsumo@faculty.chiba-u.jp.
Notes
The authors declare no competing financial interest.
(10) (a) Fuchigami, T.; Inagi, S. Chem. Commun. 2011, 47, 10211−
10223. (b) Walsh, D. A.; Lovelock, K. R. J.; Licence, P. Chem. Soc. Rev.
2010, 39, 4185−4194. (c) Zakeeruddin, S. M.; Gratzel, M. Adv. Funct.
̈
ACKNOWLEDGMENTS
■
́
Mater. 2009, 19, 2187−2202. (d) Galinski, M.; Lewandowski, A.;
This work was supported by JSPS KAKENHI Grant No.
24550146.
Stępniak, I. Electrochim. Acta 2006, 51, 5567−5580.
(11) Matsumoto, S.; Batmunkh, E.; Akazome, M.; Takata, Y.;
Tamano, M. Org. Biomol. Chem. 2011, 9, 5941−5944.
(12) (a) Kamiya, M.; Asanuma, D.; Kuranaga, E.; Takeishi, A.;
Sakabe, M.; Miura, M.; Nagano, T.; Urano, Y. J. Am. Chem. Soc. 2011,
133, 12960−12963. (b) Yuasa, J.; Mitsui, A.; Kawai, T. Chem.
Commun. 2011, 47, 5807−5809. (c) Liu, Y.; Deng, C.; Tang, L.; Qin,
A.; Hu, R.; Sun, J. Z.; Tang, B. Z. J. Am. Chem. Soc. 2011, 133, 660−
663. (d) Jiang, Y. L.; Patel, P.; Klein, S. M. Bioorg. Med. Chem. 2010,
18, 7034−7042. (e) Meyer, Y.; Richard, J.-A.; Massonneau, M.;
Renard, P.-Y.; Romieu, A. Org. Lett. 2008, 10, 1517−1520. (f) Pires,
M. M.; Chmielewski, J. Org. Lett. 2008, 10, 837−840. (g) Liu, W.; Xu,
L.; Sheng, R.; Wang, P.; Li, H.; Wu, S. Org. Lett. 2007, 9, 3829−3832.
(13) Fei, Z.; Zhu, D.-R.; Yang, X.; Meng, L.; Lu, Q.; Ang, W. H.;
Scopelliti, R.; Hartinger, C. G.; Dyson, P. J. Chem.Eur. J. 2010, 16,
6473−6481.
REFERENCES
■
(1) Recent reports: (a) Yang, S.; You, J.; Lan, J.; Gao, G. J. Am. Chem.
Soc. 2012, 134, 11868−11871. (b) Grybowski, M.; Glodkowska-
Mrowka, E.; Stoklosa, T.; Gryko, D. T. Org. Lett. 2012, 14, 2670−
2673. (c) Chen, J.; Lin, W.; Ma, J.; Xu, H.; Wu, J.; Tang, X.; Fan, Z.;
Wang, P. J. Org. Chem. 2012, 77, 3475−3482. (d) Massue, J.; Frath,
D.; Ulrich, G.; Retailleau, P.; Ziessel, R. Org. Lett. 2012, 14, 230−233.
(e) Matsumoto, S.; Mori, T.; Akazome, M. RSC Adv. 2012, 2, 3379−
3386. (f) Yan, W.; Wang, Q.; Lin, Q.; Li, M.; Petersen, J. L.; Shi, X.
Chem.Eur. J. 2011, 17, 5011−5018. (g) Zhao, D.; Hu, J.; Wu, N.;
Huang, X.; Qin, X.; Lan, J.; You, J. Org. Lett. 2011, 13, 6516−6519.
(h) Hayashi, M.; Toshimitsu, F.; Sakamoto, R.; Nishihara, H. J. Am.
Chem. Soc. 2011, 133, 14518−14521. (i) Shanmugaraju, S.; Joshi, S. A.;
Mukherjee, P. S. J. Mater. Chem. 2011, 21, 9130−9138. (j) Yyagi, P.;
Venkateswararao, A.; Thomas, K. R. J. J. Org. Chem. 2011, 76, 4571−
4581. (k) Goel, A.; Kumar, V.; Chaurasia, S.; Rawat, M.; Prasad, R.;
Anand, R. S. J. Org. Chem. 2010, 75, 3656−3662. (l) Hauck, M.;
(14) Vu, P. D.; Boydston, A. J.; Bielawsk, C. W. Green Chem. 2007, 9,
1158−1159.
(15) (a) Zein El Abedin, S.; Endres, F. Acc. Chem. Res. 2007, 40,
1106−1113. (b) Rogers, R. D.; Voth, G. A. Acc. Chem. Res. 2007, 40,
1077−1078.
(16) Miller, L. L.; Nordelom, G. D.; Mayeda, E. A. J. Org. Chem.
1972, 37, 916−918.
(17) Jacques, P.; Allonas, X.; Burget, D.; Haselbach, E.; Muller, P.-A.;
Sergenton, A.-C.; Galliker, H. Phys. Chem. Chem. Phys. 1999, 1, 1867−
1871.
(18) Doose, S. ChemPhysChem 2009, 10, 1389−1398.
(19) (a) Supur, M.; El-Khouly, M. E.; Seok, J. H.; Kim, J. H.; Kay, K.-
Y.; Fukuzumi, S. J. Phys. Chem. C 2010, 114, 10969−10977.
(b) Kowalczyk, T.; Lin, Z.; Voorhis, T. V. J. Phys. Chem. A 2010,
114, 10427−10434. (c) Gunnlaugsson, T.; Davis, A. P.; Glynn, M.
Chem. Commun. 2001, 2556−2557.
Turdean, R.; Memminger, K.; Schonhaber, J.; Rominger, F.; Muller, T.
̈
̈
J. J. J. Org. Chem. 2010, 75, 8591−8603. (m) Matsumoto, S.; Samata,
D.; Akazome, M.; Ogura, K. Tetrahedron Lett. 2009, 50, 111−114.
(2) (a) Ohyanagi, T.; Nagahori, N.; Shimawaki, K.; Hinou, H.;
Yamashita, T.; Sasaki, A.; Jin, T.; Iwanaga, T.; Kinjo, M.; Nishimura, S.
J. Am. Chem. Soc. 2011, 133, 12507−12517. (b) Blanco-Canosa, J. B.;
Medintz, I. L.; Farrell, D.; Mattoussi, H.; Dawson, P. E. J. Am. Chem.
Soc. 2010, 132, 10027−10033. (c) Liu, W.; Howarth, M.; Greytak, A.
B.; Zheng, Y.; Nocera, D. G.; Ting, A. Y.; Bawendi, M. G. J. Am. Chem.
Soc. 2008, 130, 1274−1284. (d) Susumu, K.; Uyeda, H. T.; Medintz, I.
L.; Pons, T.; Delehanty, J. B.; Mattoussi, H. J. Am. Chem. Soc. 2007,
129, 13987−13996. (e) Latham, A. H.; Williams, M. E. Langmuir
2006, 22, 4319−4326.
̀
(3) Mzieres, M. R.; Duprat, C.; Bellan, J.; Wolf, J. G. Dyes Pigments.
2007, 74, 404−409.
(4) Shi, Z.; Thummel, R. P. J. Org. Chem. 1995, 60, 5935−5945.
(5) (a) Gierz, V.; Melomedov, J.; Forster, C.; Deißler, C.; Rominger,
̈
F.; Kunz, D.; Heinze, K. Chem.Eur. J. 2012, 18, 10677−10688.
(b) Murphy, J. A.; Zhou, S.; Thomson, D. W.; Schoenebeck, F.;
Mahesh, M.; Park, S. R.; Tuttle, T.; Berlouis, L. E. A. Angew. Chem., Int.
Ed. 2007, 46, 5178−5183. (c) Murphy, J. A.; Khan, T. A.; Zhou, S.;
Thomson, D. W.; Mahesh, M. Angew. Chem., Int. Ed. 2005, 44, 1356−
1360.
2404
dx.doi.org/10.1021/jo302531g | J. Org. Chem. 2013, 78, 2397−2404