Preparation of a crown-ether-modified lophine peroxide as a guest-sensitive novel chemiluminophore and modulation of its chemiluminescence by metal cations

Article abstract of DOI:10.1016/S0040-4039(01)01572-6

A guest-sensitive chemiluminophore, a novel crown-ether-modified lophine peroxide 1, has been prepared, and its chemiluminescent behavior has been investigated in the presence of alkaline and alkaline earth metal cations. In the presence of Na⁺, the λ_max of the chemiluminescence of peroxide 1 was blue-shifted (505 nm) compared to the case without a metal cation (566 nm). The chemiluminescent intensity was enhanced by addition of Na⁺ while that of Mg²⁺ decreased the intensity.

Full text of DOI:10.1016/S0040-4039(01)01572-6

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 7453–7455
Preparation of a crown-ether-modified lophine peroxide as a
guest-sensitive novel chemiluminophore and modulation of its
chemiluminescence by metal cations†
Hideki Okamoto,* Makoto Owari, Masaru Kimura and Kyosuke Satake
Graduate School of Natural Science and Technology, Okayama University, Tsushima-Naka 3-1-1, Okayama 700-8530, Japan
Received 13 July 2001; revised 23 August 2001; accepted 24 August 2001
Abstract—A guest-sensitive chemiluminophore, a novel crown-ether-modified lophine peroxide 1, has been prepared, and its
chemiluminescent behavior has been investigated in the presence of alkaline and alkaline earth metal cations. In the presence of
Na+, the umax of the chemiluminescence of peroxide 1 was blue-shifted (505 nm) compared to the case without a metal cation (566
nm). The chemiluminescent intensity was enhanced by addition of Na+ while that of Mg2+ decreased the intensity. © 2001 Elsevier
Science Ltd. All rights reserved.
Molecular photodevices, whose properties can be con-
trolled by specific additives, have been extensively
developed1 since the pioneering studies of Vo¨gtle on
chromoionophores.2 For such chromophores, conven-
tionally, absorption and photoluminescent properties
have been controlled through interactions between the
host dyes and specific guests.3
the complex formation between the ionophore part and
guest ions. On the basis of this molecular design, we
have examined the synthesis of a crown-ether-modified
lophine peroxide
1 as a novel chemiluminescent
ionophore. Herein we would like to report our prelimi-
nary results on the preparation of the modified lophine
peroxide 1 and its chemiluminescence studies in which
the chemiluminescent properties of the peroxide 1 were
modulated by metal cations.
Chemiluminescent output provides potent highly sensi-
tive analytical tools.4 Thus, it would be of interest to
construct a chemiluminophore possessing a host func-
tion, which displays change in its chemiluminescent
behavior on addition of a specific guest, since such a
chemiluminophore may serve as a novel, highly sensi-
tive luminescent chemosensor.
It has been reported that the chemiluminescent proper-
ties of lophine peroxide (2,4,5-triphenyl-4H-imidazol-4-
ylhydroperoxide) are affected significantly by
substitution on its phenyl groups.5–7 Therefore, it is
expected that incorporation of an ionophore function
into the phenyl groups of lophine peroxide would
enable control of its chemiluminescent properties
through fine-tuning of the substituent effects based on
Crown-ether-modified triphenylimidazole 3, which is
the precursor of the peroxide 1, was synthesized by
condensation of benzaldehyde 28 and benzil in the
presence of ammonium acetate9 in good yield (Scheme
1).10 The imidazole 3 was converted into the desired
peroxide 1 through a reaction with singlet oxygen in
CH2Cl2 at low temperature.5,11 The resulting solution of
the peroxide 1 was poured into a short silica gel
column, and subsequent elution with MeCN gave a
solution of the peroxide 1 in MeCN.12 The solution of
the peroxide 1 was used for the present chemilumines-
cence measurements without further purification
because the peroxide 1 was not stable enough to be
isolated at room temperature: although the peroxide 1
was durable at 0°C for several hours, it underwent
Keywords: chemiluminescence; chemiluminescent ionophore; lophine
peroxide; aza crown ether.
* Corresponding author. Tel.: +81-(0)86-251-7840; fax: +81-(0)86-
251-7853; e-mail: hokamoto@cc.okayama-u.ac.jp
†
Here we describe a chemiluminescent dye as a chemiluminophore for
convenience, in accordance with the fact that luminescent dyes are
called luminophores.
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)01572-6

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H. Okamoto et al. / Tetrahedron Letters 42 (2001) 7453–7455
Scheme 1. Reagents and conditions: (i) benzil (0.9 equiv.), AcONH4 (10 equiv.), AcOH, reflux, 1 h, 78%; (ii) O2, methylene blue,
hw, −78°C, CH2Cl2, 30 min; (iii) NBu4OH, MeCN, rt; (iv) AcOH; (v) NBu4OH, MeCN, rt.
slowly spontaneous chemiluminescent reaction at room
temperature.
presence of metal cations is summarized. The spectra
were observed with a multi-channel photodiode array
detector and the intensities were determined by integra-
tion of the chemiluminescence spectra in the 430–670
nm region detected during the chemiluminescent reac-
tion (90 s). In the absence of any additive, peroxide 1
showed a broad chemiluminescent emission band
between 450 and 670 nm (umax 566 nm) [Fig. 1, curve
(a)]. Addition of Li+ or K+ had minimal effect on the
chemiluminescence [Fig. 1, curves (b) and (d), Fig. 2].
On the other hand, in the presence of Na+, the chemilu-
minescent intensity of the peroxide 1 was enhanced
1.5-fold relative to that observed in the absence of a
metal cation (Fig. 2), and the umax shifted to 505 nm (51
nm blue-shifted compared to the case without Na+)
[Fig. 1, curve (c)]. Effects of alkali earth metal cations
on the chemiluminescence were also examined. As
shown in Fig. 2, Ca2+ and Ba2+ displayed no remark-
able effect on the intensity. In contrast, Mg2+ reduced
significantly the chemiluminescent intensity (ca. 0.7 rel-
ative to the case without a metal cation). Therefore, by
means of the addition of metal cations, the chemilu-
minescent intensity of the host chemiluminophore 1
When tetrabutylammonium hydroxide was added to
the MeCN solution of the peroxide 1, bright yellow
chemiluminescence was observed. After disappearance
of the chemiluminescent emission (within 90 s), the
resulting reaction mixture was neutralized carefully
with acetic acid followed by extraction with CH2Cl2 to
give a benzamidine derivative 4 as the sole product.10
For the base-induced chemiluminescent reaction of
lophine peroxide, it has been reported5,11 that lophine
peroxide gives N,N%-dibenzoylbenzamidine as
a
product. Thus, the fact that the benzamidine 4 was
obtained in the present chemiluminescent reaction
confirmed that the peroxide 1 was involved as the key
intermediate of the chemiluminescence.11,13
The effects of metal cations on the chemiluminescence
of peroxide 1 were investigated. Fig. 1 shows the chemi-
luminescence spectra of the peroxide 1, and in Fig. 2,
the relative chemiluminescent intensity observed in the
Figure 2. Relative chemiluminescent intensity of the peroxide
1 (ca. 1.5 mM) in MeCN observed on addition of tetra-
butylammonium hydroxide (MeOH soln, excess) in the pres-
ence of metal cations (25 mM, as perchlorate) at 20°C. The
experimental errors were based on at least three independent
runs.
Figure 1. The chemiluminescence spectra of the peroxide 1
(ca. 1.5 mM) in MeCN observed on addition of tetra-
butylammonium hydroxide (MeOH soln, excess) at 20°C in
the presence of metal cations (25 mM as perchlorate). (a)
Without metal cation; (b) Li+; (c) Na+; (d) K+.

H. Okamoto et al. / Tetrahedron Letters 42 (2001) 7453–7455
7455
could be changed by a factor of 0.7–1.5 relative to that
observed without metal cations.
Basics and Applications; Imai, K., Ed.; Hirokawa Pub-
lishing Co.: Tokyo, 1989; (c) Kimura, M.; Morioka, M.;
Tsunenaga, M.; Hu, Z. Z. ITE Lett. Batter. New Technol.
Med. 2000, 1, 418–421.
The effect of the metal cations on the chemiluminescent
properties could be due to a variety of factors: e.g. the
complex formation of the crown-modified peroxide 1
with a metal cation14 may cause a change in the
efficiency of the excited-product-providing step, or a
change in the fluorescent efficacy of an emitting species
involved in the chemiluminescence. Concerning the
reported chemiluminescenct reaction of lophine perox-
ide,5,6 the conjugate base of the benzamidine 4− has
been expected to be the light emitter in the chemilu-
minescence. However, as the benzamidine 4 underwent
rapid hydrolysis to the dibenzamide 510 in alkaline
media, the fluorescent properties of the benzamidine 4
have not been studied and thus the exact emitting
species in the chemiluminescence of the peroxide 1 has
not been specified. Currently, the factor(s), in which
metal cations control the chemiluminescent properties
of the peroxide 1, have not been determined and a
study to clarify these factors is under way.
5. White, E. H.; Harding, M. J. C. Photochem. Photobiol.
1965, 4, 1129–1155.
6. Philbrook, G. E.; Maxwell, M. A. Tetrahedron Lett.
1964, 1111–1116.
7. Kimura, M.; Nishikawa, H.; Kura, H.; Lim, H.; White,
E. H. Chem. Lett. 1993, 505–508.
8. Dix, J. P.; Vo¨gtle, F. Chem. Ber. 1980, 113, 457–470.
9. Davidson, D.; Weiss, M.; Jelling, M. J. Org. Chem. 1937,
2, 319.
10. Physical data for the novel compounds. Compound 3:
colorless fine needles, mp 191–192°C; 1H NMR (500
MHz, acetone-d6) l 3.55 (s, 4H), 3.60 (s, 8H), 3.60 (t, 4H,
J=6.0 Hz), 3.75 (t, 4H, J=6.0 Hz), 6.77 (m, 2H), 7.25
(brt, 2H, J=7.0 Hz), 7.32 (brt, 4H, J=7.0 Hz), 7.58 (br,
4H), 7.93 (m, 2H); UV (EtOH) umax (log m) 324 nm (4.58);
IR (KBr) wmax 1613, 1118 cm−1
. Anal. calcd for
C31H35N3O4: C, 72.49; H, 6.87, N, 8.18. Found: C, 72.26;
H, 6.83; N, 8.18%. Compound 4: yellow needles, mp
1
212–213°C; H NMR (500 MHz, CDCl3) l 3.63 (s, 4H),
The present results first show that modulation of the
chemiluminescent output of the chemiluminophore 1
was achieved by addition of metal cations. The molecu-
lar design combining a chemiluminophore with an
ionophore provides a basis for novel chemosensors
displaying guest-sensitive chemiluminescent output.
3.64–3.70 (m, 12H), 3.79 (t, 4H, J=6.0 Hz), 6.70 (d, 2H,
J=9.0 Hz), 7.49 (bs, 4H), 7.58 (bs, 2H), 7.91 (d, 2H,
J=9.0 Hz), 8.05 (bs, 2H), 8.33 (bs, 2H), 12.44 (s, 1H);
wmax (KBr) 1702, 1598 cm−1; UV (MeCN) umax (log m) 369
nm (4.09), 4.27 (4.14). Anal. calcd for C31H35N3O6: C,
68.24; H, 6.47, N, 7.70. Found: C, 68.18; H, 6.39; N,
1
8.12%. Compound 5: colorless prisms, mp 170–171°C; H
NMR (500 MHz, DMSO-d6) l 3.32 (s, 4H), 3.53 (m, 8H),
3.58 (t, 4H, J=5.9 Hz), 3.64 (t, 4H, J=5.9 Hz), 6.69 (m,
2H), 7.48 (t, 4H, J=8.0 Hz), 7.59 (dt, 2H, J=8.0, 1.5
Hz), 7.77 (m, 2H), 7.82 (dd, J=8.0, 1.5 Hz) 10.90 (s, 1H);
UV (EtOH) umax (log m) 235 nm (4.15), 338 (4.33); IR
(KBr) wmax 3244, 1692, 1678, 1601, 1118 cm−1. Anal.
calcd for C24H30N2O6: C, 65.14; H, 6.83, N, 6.33. Found:
C, 65.44; H, 6.95; N, 6.27%.
Acknowledgements
This work was supported by a Grant-in-Aid (No.
13740398) from the Ministry of Education, Culture,
Sports, Science and Technology of Japan. H.O. thanks
Professor Dr. Waldemar Adam (University of
Wu¨rzburg) for active discussions and encouragement.
The authors are grateful to the SC NMR Laboratory of
Okayama University for the 500 MHz 1H NMR
measurements.
11. White, E. H.; Harding, M. J. C. J. Am. Chem. Soc. 1964,
86, 5686–5687.
12. As thin-layer chromatography analysis of the MeCN
solution showed only one spot, the peroxide 1 was
obtained in pure form by the present procedure.
13. Hu, Z. Z.; Takami, S.; Kimura, M.; Tachi, Y.; Naruta,
Y. Acta Crystallogr., Sect. C: Cryst. Struct. Commun.
2000, C56, e465–e466.
14. Taking into account the stability constants (Ks) for com-
plexes of aza-15-crown-5 ionophores with alkaline or
alkaline earth metal cations (log Ks ꢀ2–3.5),2,15 under the
present conditions, it is possible that most of the peroxide
1 associated with the metal cations examined.
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