Spectral switching of naphthalimide-coumarin induced by F-

Article abstract of DOI:10.1166/jnn.2015.10420

A highly selective color sensor based on naphthalimide and coumarin was reported. Upon addition of F^-, the solution color changed from pale yellow to deep blue. The sensor shows excellent selectivity against other common anions. The underlying mechanism for the color change is based on the deprotonation/protonation of the dye. Frontier molecular orbitals analysis gives further insight about the signaling mechanism.

Full text of DOI:10.1166/jnn.2015.10420

Article
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Nanoscience and Nanotechnology
Vol. 15, 5370–5373, 2015
Copyright © 2015 American Scientific Publishers
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Spectral Switching of Naphthalimide-Coumarin
Induced by F−
Xiaochuan Li1ꢀ2ꢀ∗ and Young-A Son3ꢀ∗
1Collaborative Innovation Center of Henan Province for Green Manufacturing of Fine Chemicals, Key Laboratory of
Green Chemical Media and Reactions, Ministry of Education, School of Chemistry and Chemical Engineering,
Henan Normal University, Xinxiang, Henan 453007, P. R. China
2Jiangxi Key Laboratory of Organic Chemistry, Jiangxi Science and Technology Normal University,
Jiangxi, Nanchang, 330013, P. R. China
3Department of Advanced Organic Materials Engineering, Chungnam National University, Daejeon, 305-764, S. Korea
A highly selective color sensor based on naphthalimide and coumarin was reported. Upon addition
of F−, the solution color changed from pale yellow to deep blue. The sensor shows excellent selec-
tivity against other common anions. The underlying mechanism for the color change is based on
the deprotonation/protonation of the dye. Frontier molecular orbitals analysis gives further insight
about the signaling mechanism.
Keywords: Naphthalimide, Coumarin, F−, Deep Blue, Frontier Molecular Orbital.
Delivered by Ingenta to: Chinese University of Hong Kong
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Copyright: American Scientific Publishers
1. INTRODUCTION
red or blue by altering the nature of the ring substituent or
that of the imide. This opens up its various application.
Generally, receptor unit was substituted at the 4-position
of 1,8-napthalimides derivatives, which facilitated the inter-
nal charge transfer from the electron-rich naphthalene to
electron-deficient imide when binding of analyte (cation,
anion, or H+). In this report, coumarin, a blue emitter, was
incorporated with 1,8-naphthalimide with –NHNH– as the
bridge unit. Binding at the bridge unit will possibly dis-
turb the electron properties of the dye and consequently
induced change in optical properties. The underlying mech-
anism is effectively controlled by intramolecular PET or
PCT between 1,8-naphthalimide and coumarin.
1,8-naphthalimide and coumarin are typical green and
blue emitters and they have been intensively modified
and functionalized. The frameworks of naphthalimide and
coumarin have been widely used in construction of vari-
ous chemosensors, emitters, device fabrication, and light
absorbers.1–6 Due to the different absorption and emis-
sion wavelength, the two building blocks are attractive
candidates for configuration of the photoinduced electron
transfer (PET) or photoinduced charge transfer (PCT)
type fluorophores. The framework of 1,8-naphthalimide
can be conveniently synthesized according to the reac-
tion between the corresponding 1,8-naphthalic anhydrides
and amine. It allows the production of a large number
family of derivatives. Additionally, the framework of 1,8-
naphthalimide is easy to be modified chemically, especially
at the 3- and 4-position by amino or nitro groups, which
can be transferred to various functional groups and target
to biomolecules. The two positions are also having major
effect on the electronic properties with a consequent influ-
ence on the optical and photo-physical properties.3 Most of
1,8-naphthalimide derivatives are strongly fluorescent with
the emission in the green part of electromagnetic spectrum
and the maximum emission could be modulated towards to
2. EXPERIMENTAL DETAILS
2.1. Materials
All the chemicals were purchased from commercial
sources and used as received. Basic solvents for synthesis
1
were dried using literature methods. H and 13C nuclear
magnetic resonance (NMR) spectra were recorded on a
Brucker AM-400 spectrometer operating at frequencies of
400 MHz for proton, 100 MHz for carbon in DMSO-
d6. Mass spectra measured on a LC-MS (Waters UPLC-
TQD) mass spectrometer. High resolution mass spectra
(HRMS) were measured on a Brucker microOTOF II
Focus instrument. Absorption spectra were measured with
∗Authors to whom correspondence should be addressed.
5370
J. Nanosci. Nanotechnol. 2015, Vol. 15, No. 7
1533-4880/2015/15/5370/004
doi:10.1166/jnn.2015.10420

Li and Son
Spectral Switching of Naphthalimide-Coumarin Induced by F−
an Agilent 8453 spectrophotometer. The solvents used in
photo-chemical measurement were spectroscopic grade.
All the experiments were done repeatedly, and repro-
ducible results were obtained. Prior to the spectroscopic
measurements, the solutions were deoxygenated by bub-
bling nitrogen through them.
1H NMR (400 MHz, DMSO–d6ꢁ: ꢂ 9.61 (sꢀ1 H),
9.09 ꢃsꢀ1 H), 8.68 (dꢀJ = 8.0 Hz, 1 H), 8.59
(dꢀJ = 8ꢄ0 Hz, 1 H), 8.43 (dꢀJ = 8.0 Hz, 1 H), 8.06
(dꢀJ = 8.0 Hz, 1 H), 7.86 (tꢀJ = 8.0 Hz, 1 H), 7.71
(1 H, s), 7.30 (1 H, tꢀJ = 7.8 Hz), 7.18 (1 H, dꢀJ =
7.1 Hz), 7.10 (1 HꢀdꢀJ = 7ꢄ8 Hz), 4.02 (3 H, s),
3.92 (tꢀJ = 7.2 Hz, 2 H), 1.53–1.61 (mꢀ2 H), 1.31–1.35
(mꢀ2 H), 0.93 (tꢀJ = 7ꢄ6 Hz, 3 H); 13C NMR (100 MHz,
DMSO-d6ꢁ: ꢂ 163.2, 158.4, 156.7, 147.3, 143.7, 133.2,
132.1, 131.8, 131.2, 130.5, 130.3, 129.1, 128.3, 125.0,
124.1, 122.9, 122.0, 119.3, 117.9, 56.2, 42.3, 29.5, 19.6,
13.3; MS (EI, 70 eV) m/z 485 (M+ꢁ; HRMS calcd for
C27H23N3O6 485.1587, found 485.1592.
2.2. Theoretical Calculations
For the theoretical study of excited state photo-physics
of the compound, the Dmol3 program packaged in Mate-
rial Studio was used.7ꢀ8 The ground state geometries and
the frontier molecular orbital of the compound were cal-
culated using the density function theory (DFT) with the
B3LYP hybrid functional and the double numerical plus
d-functions (DND) atomic orbital basis set.
3. RESULTS AND DISCUSSION
The absorption spectrum of N-C was measured in DMF.
An intense absorption peak around 400 nm was observed,
which can be assigned to the intramolecular charge transfer
process of nitrogen atom substituted at 4-position of 1,8-
naphthalimide. The proton of the bridge unit, –NHNH–, is
easy to be removed by Lewis base, such as F−. Therefore,
removing the proton from the bridge unit was investigated
in detail. The titration spectrum of F− was presented in
Figure 2. Upon addition of F−, the absorption peak around
400 nm decreased and a new peak at 610 nm appeared
with the isobestic point at 292, 370, and 462 nm. It indi-
2.3. Preparation and Characterization
The synthesis of naphthalimide-coumarin (N-C)
was depicted in Figure 1. Coumarin (2) was con-
densed between 2-hydroxy-3-methoxy-benzaldehyde and
dimethylmalonate under basic condition. After hydrolysis
by NaOH, coumarin acetic acid (3) was reflux with thionyl
chloride yielding the corresponding acid chloride (4).9
4-bromo-1,8-naphthalic anhydride (5) was commercially
available. The active bromo atom of 5 was readily sub-
stituted by hydrazine hydrate and gave 6.10 The final
condensation between the acid chloride and 6 gave the tar-
Delivered by Ingenta to: Chinese University of Hong Kong
cates that only two species co-exist in the equilibrium.
get compound N-C. It was purified rigorously to remove
IP: 46.161.61.76 On: Sat, 18 Jun 2016 05:56:23
The deprotonation of N enhanced the electron-donation
and enlarged the ꢅ conjugated system of naphthalimide,
which contributed to absorption centered at 610 nm. Cor-
respondingly, the pale yellow–green color turned to deep
blue gradually. The deep blue color can also be faded
and recover the pale yellow–green color. The color change
is reversible by repeated addition between F− and H+.
The emission behavior was investigated in various sol-
vents with different polarity. However, its weak emission
behavior in solution state is different from most of the 1,8-
naphthalimide derivatives with strong emission character.
Copyright: American Scientific Publishers
spurious impurities and characterized by standard analyti-
cal techniques including 1H, 13C NMR spectroscopies and
HRMS spectrometry.
To a magnetically stirred solution of N -butyl-6-
hydrazinyl-1,8-naphthalimide (283 mg, 1 mmol) and sev-
eral drops of pyridine in dry chloromethane 60 mL,
an anhydrous dichloro-methane solution of acid chloride
(258 mg, 1 mmol) was added dropwise at room tem-
perature and monitored by TLC. Yellowish solid precip-
itated out of the solution gradually. After the completion
of reaction, yellowish precipitate was filtered and washed
with methanol. Pure product was obtained by recrystal-
lization from ethanol and dried in vacuum with 82% yield
(398 mg).
1.2
0.9
0.6
O
O
O
O
O
O
CHO
OH
(1)
OCH3
(2)
(3)
Cl
OMe
OH
O
OCH3
O
O
OCH3
OCH3
1
3
4
2
[H+] [F-]
n-Bu
N
n-Bu
N
O
O
N
0.3
O
O
O
O
O
O
O
H
O
(4)
(5)
4
N
H
N
(6)
n-Bu
O
O
OCH3
0.0
Br
Br
NHNH2
300
400
500
600
700
800
900
5
6
7
Naphthalimide-courmain (N-C)
Wavelength (nm)
Figure 1. Synthesis of N-C: (1) dimethylmalonate/piperidine/
EtOH/CH3COOH, reflux 6 h; (2) NaOH (10%), reflux; (3) SOCl2, reflux
4 h; (4) n–BuNH2/EtOH, reflux 4 h; (5) NH2NH2 ·H2O/MeOCH2CH2OH,
reflux; (6) CH2Cl2, r.t.
Figure 2. Absorption change of N-C in DMF solution (6.0 × 10−5
M) imparted by deprotonation and protonation with the F− addition
(0–10 eq).
J. Nanosci. Nanotechnol. 15, 5370–5373, 2015
5371

Spectral Switching of Naphthalimide-Coumarin Induced by F−
Li and Son
100
80
60
40
20
0
LUMO
–3.78 eV
–0.78 eV
–1.97 eV
F–
Cl–
Br–
I–
SO42– NO–3 H2PO4– CO32– ClO–4
Ac–
HOMO
Figure 3. Comparison of percent increase of absorption of N-C in DMF
solution at 610 nm in the presence of 10 equiv different anions.
The observed color change induced by F−/H+ could be
attributed to the deprotonation/pronation from the bridge
unit (–NHNH–). The switch model of color change could
be established based on the cassette of N-C dye with mod-
ulation of F−/H+.
–5.04 eV
N-C
–1.37 eV
N-C-H
–2.53 eV
N-C-2H
Figure 5. Electron density distributions and energies of the frontier
molecular orbitals of N-C.
Figure 3 shows response of N-C towards different
anions. The binding property of N-C towards F− is
remarkable. The absorption of N-C shows barely any
were calculated using DFT and LDA/DN basis set. Further
refinement and optimization on structures were undertaken
using DND/B3LYP basis set.
The size and signs of the highest occupied molecu-
lar orbital (HOMO) and the lowest unoccupied molecular
response with other anions, such as Cl−, Br−, I−, SO42−
,
NO−3 , H3PO4−, CO32−, ClO4−, and CO23−. The highly selec-
tivity of N-C towards F− resulted from the character of
−
Delivered by Ingenta to: ChinesoerbUitnaliv(eLrUsiMtyOo)f HaroeniglluKsotrnatged in Figure 5. It is apparent
strong Lewis base. Generally, OH addition should have
IP: 46.161.61.76 On: Sat, 18 Jun 2016 05:56:23
similar effect as F− addition. Experimental result shows
that the electron density is distributed over naphthalim-
ide unit in HOMO, whereas that of the LUMO localized
Copyright: American Scientific Publishers
that OH− addition can also induce color change from pale
yellow–green to deep blue. However, the solution color of
N-C is unstable in basic condition. It is easy to be decom-
posed about half hours in base conditions and the solution
color changed from deep blue to blue-gray.
away from the naphthalene unit to the coumarin unit. Once
the proton removed from the –NHNH– unit, the electron
density of nitrogen atom increased. And the HOMO dis-
tribution spread partly to the coumarin unit. The second
protonation remove from the bridge unit, the HOMO dis-
tribution will spread more of the electron density to the
coumarin unit. For the LUMO distribution, a regularly
trend was observed with the electron density localization
on the coumarin unit. Only small part of the electron den-
sity left in the naphthalimide unit. According to the char-
acteristics of HOMO/LUMO distribution, the first proton
removing from the bridge unit contribute much more to
the red-shift of absorption band than that of the second
proton. This can be deduced from the energy gap between
HOMO and LUMO. The energy gap estimated to be 1.26,
0.60, and 0.56 eV for N-C, N-C-H, and N-C-2H, respec-
tively. It fits well to the red-shift of absorption band from
400 nm to 610 nm. The higher electron density accumu-
lated on nitrogen atom also enhanced the possibility of
electron transfer after absorbing the photos.
The proposed combining mode was shown in Figure 4.
The occurrence of removing protonation from the bridge
unit (–NHNH–) leads to the electron density increasing at
the nitrogen atom and the PCT process will be enhanced
and red-shifted the absorption band correspondingly.11ꢀ12
To better understand the geometrical, electronic, and
optical properties of N-C, a comprehensive computa-
tional investigation was carried out based on the plat-
form of MS/Dmol3. To reduce the run times in the first
instance, the ground-state energy-minimized structures
O
N
O
O
O
O
O
N
N
F-
F-
N
N
HN
NH
NH
N
O
O
O
O
O
O
O
O
O
4. CONCLUSION
In summary, a new naphthalimide-coumarin dye was
designed and fully characterized. Upon addition of fluo-
ride anion, the maximum absorption band of N-C in DMF
was red-shift from 400 nm to 610 nm and accompanied
OCH3
OCH3
OCH3
N-C
N-C-H
N-C-2H
Figure 4. Concept of deprotonation by F−.
5372
J. Nanosci. Nanotechnol. 15, 5370–5373, 2015

Li and Son
Spectral Switching of Naphthalimide-Coumarin Induced by F−
by the color change to deep blue. The deep blue color of
solution returned to the original color state by H+ addi-
tion. This color change is reversible by repeated addition
of F−/H+. In addition, it shows highly selectivity of N-C
towards F− against other anions. The underlying mecha-
nism is the removing of protonation from the bridge unit
by the F−. Frontier molecular orbitals analysis unequivo-
cally suggests that lower energy gap of N-C-H, and N-C-
2H lead to the absorption band shift to longer wavelength.
In line with the development mentioned above, function-
alized dyes based on the framework of 1,8-naphthalimide
is underway in our lab.
References and Notes
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Acknowledgment: This work was supported by the
National Natural Science Foundation of China (grant No.
21272060), and jianxi key lab of organic chemistry (grant
No. GFZ-KF-201301). This study was supported by Basic
Science Research Program through NRF of Korea funded
by the Ministry of Education, Science and Technology
(Grant No. 2013054767).
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Received: 8 November 2013. Accepted: 14 June 2014.
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J. Nanosci. Nanotechnol. 15, 5370–5373, 2015
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