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Published on the web April 21, 2012
Design and Synthesis of a Chemiluminescent Solvatochromic Dye
Yutaka Yamagishi, Sang-Hyun Son, Maiko Yuasa, and Koji Yamada*
Section of Materials Science, Faculty of Environmental Earth Science, Hokkaido University,
Kita-ku, Sapporo, Hokkaido 060-0810
(Received February 13, 2012; CL-120117; E-mail: yamada@ees.hokudai.ac.jp)
Chemiluminescent solvatochromic dye has been synthesized
by the condensation of a chemiluminescent moiety into a
fluorescent solvatochromic dye via the Suzuki-Miyaura cross-
coupling. The chemiluminescent wavelength is shifted by
solvent polarity, and ratiometric measurement enables the
accurate determination of the proportion of water in an aqueous
acetone solution.
Figure 1. Molecular design of chemiluminescent solvatochro-
mic dye 1.
Chemiluminescence (CL) refers to the emission of light as
the result of certain chemical reactions. Unlike fluorescence,
CL produces very little background noise as it does not require
an excitation source beam. CL detection is advantageous with
respect to its sensitivity due to high signal-to-noise ratio.1 On the
other hand, CL intensity is easy to change, not only by the
modification of reaction conditions such as temperature, pH, and
solvents used, but also by changing the dye concentration.
However, these effects of these changes are indistinguishable
from each other, and consequently, a number of quantitative
problems associated with CL detection remain to be solved.2,3
In general, ratiometric techniques are preferred for quantitative
measurements because the ratio of intensities is independent
with respect to changes made in dye concentration.4 For
this purpose, ratiometric indicators based on resonance energy
transfer (RET), which exhibit changes in dual emission
intensity, were developed. However, these indicators consist of
large fluorescent protein molecules, and may inhibit many of the
biological reactions to be observed. Meanwhile, it is difficult to
control the distance between dyes (1-10 nm) in fluorescent dye-
based indicators, and the RET mechanism has been applied
almost exclusively to long wavelength emission.5-8 Therefore, a
small and simple dye-based indicator in which CL wavelength is
shifted by microenvironmental changes is required for monitor-
ing biological reactions with high sensitivity and quantitativity.
Fluorescent solvatochromic dyes are chromic dyes in which
the emission wavelength is changed by the polarity of the
solvent molecules surrounding them. These dyes are made up of
small and simple molecules, composed of an electron-donating
group, an aromatic ring, and an electron-withdrawing group.9-11
Recently, we succeeded in preparing a series of fluorescent
solvatochromic dyes by condensation of the electron-donating,
aromatic ring, and electron-withdrawing moieties via Suzuki-
Miyaura cross-coupling reactions.12 Applying the same synthetic
strategy, we have tried to design a chemiluminescent solvato-
chromic dye using CL molecules as the electron-withdrawing
moiety (Figure 1). Phthalhydrazide was selected as the electron-
withdrawing group for the following three reasons: (1) phthal-
hydrazide has a partial luminol structure,13 which is a repre-
sentative CL dye; (2) the two carbonyl groups exhibit strong
electron-withdrawing properties; and (3) the phthalimide group
can be easily converted to a phthalhydrazide group. A 4-
Scheme 1. Synthesis of phthalhydrazide 1.
dihexylaminophenyl group was chosen as the electron-donating
moiety, as the two alkyl chains facilitate purification due to their
high solubility in organic solvents. Thiophene was used as the
aromatic ring as it demonstrates good photophysical properties
in fluorescent solvatochromic dyes.12
The target compound 1 was synthesized as shown in
Scheme 1. A phthalimide intermediate 2 was prepared through
one-pot synthesis using a Suzuki-Miyaura cross-coupling
reaction, and subsequent treatment of 2 with hydrazine afforded
1 in 50% overall yield. Compounds 1 and 2 were readily purified
by silica gel column chromatography due to the presence of
alkyl chains in the electron-donating moiety. Their structures
1
were fully characterized by H and 13C NMR spectra, and ESI-
HRMS data.15
Dye 1 has very low solubility in water due to its hydro-
phobicity. However, an aqueous acetone solution of 1 exhibits
strong chemiluminescence under similar reaction conditions as
for luminol. Furthermore, the CL color changes from blue-green
to greenish yellow, depending on the concentration of water
(Figure 2). To evaluate the effect of solvents on the CL
properties of 1, we measured the CL spectra of 1 in pure
organic solvents of different polarities when added to an
aqueous solution of NaOH, K3[Fe(CN)6], and H2O2. The CL
maximum progressively shifted toward longer wavelengths with
increases in solvent polarity (Figure 3a). The ET(30) value is
Chem. Lett. 2012, 41, 504-506
© 2012 The Chemical Society of Japan
Yamagishi, Yutaka
