Synthesis and spectroscopic properties of 4-amino-1,8-naphthalimide derivatives involving the carboxylic group: A new molecular probe for ZnO nanoparticles with unusual fluorescence features

Article abstract of DOI:10.3762/bjoc.9.147

Of a series of 4-substituted 1,8-naphthalimides, fluorescent 4-(6-piperidinyl-1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)benzoic acid (4) was found to be a sensitive molecular probe for ZnO nanoparticles. We investigated in detail one- and two-photon absorption properties of this fluorophore. In nonpolar solvents, the acid 4 absorbs at about 400 nm and fluoresces at 500 nm with a fluorescence lifetime of about 7 ns, similar to the ester 6 and typical of the lifetimes of other derivatives of this type. Although the anionic form of this acid is not fluorescent, partial ionization of 4 in polar solvents, such as ethanol and acetonitrile, is not only accompanied by the expected decrease in the fluorescence quantum yield, but also gives rise to bathochromic shifts of both absorption and fluorescence and dual fluorescence with lifetimes of 0.2-0.3 ns and 6 ns ascribed to the formation of anionic complexes. The interaction with the ZnO surface brings about further considerable changes in the fluorescence patterns.

Full text of DOI:10.3762/bjoc.9.147

Synthesis and spectroscopic properties of
4-amino-1,8-naphthalimide derivatives involving the
carboxylic group: a new molecular probe for ZnO
nanoparticles with unusual fluorescence features
Laura Bekere, David Gachet, Vladimir Lokshin, Wladimir Marine
and Vladimir Khodorkovsky*
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2013, 9, 1311–1318.
Aix Marseille Université, CNRS, CINaM UMR 7325, 13288, Marseille,
France
doi:10.3762/bjoc.9.147
Received: 12 March 2013
Accepted: 05 June 2013
Published: 03 July 2013
Email:
Vladimir Khodorkovsky* - khodor@cinam.univ-mrs.fr
* Corresponding author
Associate Editor: J. A. Murphy
Keywords:
© 2013 Bekere et al; licensee Beilstein-Institut.
License and terms: see end of document.
fluorescence; hydrogen bond; 1,8-naphthalimide; one- and
two-photon absorption; zinc oxide
Abstract
Of a series of 4-substituted 1,8-naphthalimides, fluorescent 4-(6-piperidinyl-1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)benzoic
acid (4) was found to be a sensitive molecular probe for ZnO nanoparticles. We investigated in detail one- and two-photon absorp-
tion properties of this fluorophore. In nonpolar solvents, the acid 4 absorbs at about 400 nm and fluoresces at 500 nm with a fluo-
rescence lifetime of about 7 ns, similar to the ester 6 and typical of the lifetimes of other derivatives of this type. Although the
anionic form of this acid is not fluorescent, partial ionization of 4 in polar solvents, such as ethanol and acetonitrile, is not only
accompanied by the expected decrease in the fluorescence quantum yield, but also gives rise to bathochromic shifts of both absorp-
tion and fluorescence and dual fluorescence with lifetimes of 0.2–0.3 ns and 6 ns ascribed to the formation of anionic complexes.
The interaction with the ZnO surface brings about further considerable changes in the fluorescence patterns.
Introduction
1,8-Naphthalimide derivatives are useful for a variety of appli- imide derivatives have also been reported to be efficient fluo-
cations owing to their strong fluorescence, electroactivity and rescent molecular probes [7,8].
photostability. These compounds can be employed as dyes for
natural and synthetic fibers [1], optical brighteners in deter- Recently, the potential of amino-1,8-naphthalimides as fluores-
gents, textiles, polymeric materials [1-3] and chemiluminiscent cent sensors in living cells has been reviewed [9]. Dendrimers
agents [4]. Owing to the high fluorescence quantum yields involving the amino-1,8-naphthalimide moieties were showed
1,8-naphthalimides are used as laser dyes [5,6]. Some naphthal- to be promising active nondoping emitters [10]. 4-Amino-
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Beilstein J. Org. Chem. 2013, 9, 1311–1318.
substituted naphthalimide dyes are important yellow compo- Our target derivative was designed to involve the benzoic acid
nents of daylight fluorescent pigments and can be employed as moiety at the N-atom of the 1,8-naphthalimide. At first we used
fluorescent dichroic dyes in liquid-crystal displays [1,2,11].
a general straightforward method involving the hydrolysis of
the chloro substituted imide 1 and eventual substitution of the
In this paper, we report on the synthesis [12], characterization chlorine atom by piperidine. (Scheme 1, Pathway A). The
and one- and two-photon spectroscopic properties of previously pathway A has two major inconveniences. Hydrolysis of inter-
unknown methyl 4-(6-piperidinyl-1,3-dioxo-1H-benzo[de]iso- mediate 1 was successful only under the basic conditions, since
quinolin-2(3H)-yl)benzoate and the corresponding acid. The even prolonged heating of 1 under reflux with a strong mineral
phenyl moiety can serve as a rigid spacer, while the carboxylic acid (HCl or H2SO4) afforded no expected product 2. A mix-
group can function as an anchor for grafting the fluorophore to ture of 6-chloro- and 6-hydroxy-derivatives 2 and 3 were
metal oxide surfaces. This approach to the modification of ZnO obtained upon treatment with a small excess of sodium
nanoparticles produced by femtosecond laser ablation was hydroxide. Pure 6-hydroxy derivative 3 can be obtained in the
demonstrated to afford nanohybrid materials for biophotonic reaction of ester 1 with 4 equivalents of NaOH in boiling water.
applications [13,14].
The reaction of acid 2 with piperidine proceeded slowly and
was accompanied by the formation of a number of unidentified
byproducts.
Results and Discussion
Synthesis and characterization
Yellow 4-amino-1,8-naphthalimides are usually synthesized in To avoid side reactions, we tried another approach that
two steps. The first step is the condensation of 4-chloro- appeared to be effective. The chlorine atom was replaced with
1,8-naphthalic anhydride with amines in 1,4-dioxane or 2-meth- the piperidine moiety in the first step (Scheme 1, Pathway B).
oxyethanol under reflux yielding the corresponding 4-chloro- 4-Piperidinyl-1,8-naphthalic anhydride 5 [1] was condensed
1,8-naphthalimides. The second step involves the substitution of with methyl 4-aminobenzoate and the corresponding ester 6 was
the chlorine atom with aliphatic primary or secondary amines.
isolated in high yield. The target acid 4 was obtained in 69%
Scheme 1: Synthesis and structures of 1,8-naphthalimides.
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yield by hydrolysis of 6 under basic conditions. The reactions 490 nm and the addition of a few drops of ethanolic NaOH
were monitored by thin-layer chromatography (TLC) on silica brings about a red shift and broadening of the fluorescence band
gel eluted with CH2Cl2 or EtOH/CH2Cl2. All synthesized new (Figure 2). Moreover, upon dilution of a solution of 4 in
compounds were characterized by the 1H NMR spectra and the ethanol, the shoulder observed at about 450 nm at the concen-
elemental analyses.
tration of 5 × 10−5 M increases and becomes the major band at
lower concentrations as shown in Figure 3.
Photophysical properties
The spectroscopic properties of 1,8-naphthalimides are strongly
dependent on the substituent at C-4 of the naphthalene ring. In
general, the derivatives with a halogen atom or alkoxy groups
are colorless and exhibit blue fluorecence [15,16], while the
amino-substituted 1,8-naphthalimides are yellow and exhibit
green fluorescence [17].
Derivatives 1, 2, 3, 4 and 6 were characterized by one-photon
absorption and fluorescence spectroscopy (Table 1). In non-
polar, as well as in polar solvents, chloro-substituted intermedi-
ates 1 and 2 exhibit absorption maxima at 341 and 345 nm and
fluorescence maxima at 397 and 401 nm, respectively. In
contrast, the spectroscopic properties of derivatives 3 and 4
depend on the solvent polarity. The absorption and fluores-
cence maxima of 4 in different solvents are collated in Table 2
and the typical spectra are shown in Figure 1. The observed
bathochromic shifts are moderate and the strongest shifts in
absorption (in ethanol) and fluorescence (in acetonitrile) can be
related to partial ionization of the acids 3 and 4 in these
solvents. The pure sodium salt of 4 is not fluorescent and
absorbs at 322 nm (in water). At the same time, the addition of
a few drops of aqueous HCl shifts the fluorescence maximum to
Figure 1: Normalized absorption (solid curves) and fluorescence
(dashed curves) spectra of 4: (1) in cyclohexane; (2) in toluene; and
(3) in CH2Cl2.
Table 1: Optical properties of derivatives 1–4, 6 in ethanol.
Compound λabs max
λflu max
ε, l mol−1 cm−1
1
2
3
4
6
341
345
342
417
415
397
401
415
535
533
17 700
15 000
16 000
13 400
12 100
Figure 2: Normalized fluorescence spectra of 4 in ethanol
(5 × 10−5 M): (solid line) neutral solution; (dashed) acidified solution;
(dashed-dot) basic solution.
Table 2: Solvent-dependent optical properties of the dye 4.
Solvent
λabs max
λfl max
Cyclohexane
Toluene
CHCl3
391
401
415
405
414
417
412
490
500
519
523
528
535
540
The acid 4 and its ester 6 show strong fluorescence in nonpolar
solvents such as cyclohexane and toluene (quantum yield for 4
is 75 ± 10%), while in polar solvents such as ethanol, the fluo-
rescence intensity of 4 considerably diminishes (quantum yield
≈10%). This phenomenon can also be related to partial ioniza-
tion: the formation of the nonfluorescent anionic species and
fluorescent anionic complex in ethanol, as shown in a simpli-
THF
CH2Cl2
EtOH
Acetonitrile
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Beilstein J. Org. Chem. 2013, 9, 1311–1318.
5.77 ± 0.2 ns. The shifts of the excitation wavelength to the red
inevitably induce a bi-exponential decay with very strong
nonradiative component. A typical decay curve is shown in
Figure 4. Fitting of the experimental data gives fast decay,
0.21–0.3 ns (amplitude 0.95–0.85), depending on the detection
wavelength with a subsequent slow component with
small amplitude of about 0.1 and a typical lifetime between
5.8–6.02 ns (detection at 550 nm) depending on the dye concen-
tration. A Stern–Volmer plot shows a simultaneous static and
dynamic quenching, probably superimposed with FRET
between pure acid 4 and the anionic complex, formed in
ethanol. The full analysis of the formation of these complexes
will be published elsewhere.
Figure 3: Normalized fluorescence spectra of 4 in ethanol at different
concentrations: (solid line) 10−4 M; (dashed line) 10−5 M; (dashed-dot)
10−6 M.
fied form (the potential existence of the acid dimers is omitted)
in Scheme 2. We exclude the possibility of participation of the
amino group in the equilibrium since, according to our prelimi-
nary experiments, the parent compound prepared from
1,8-naphthalic anhydride behaves similarly.
The fluorescence lifetime measurements were performed under
350–450 excitation and detection between 470 and 700 nm in
toluene and ethanol. We observed a strong influence of the
solvent on the photophysical properties of compound 4. In
toluene, at 500 nm (corresponding to the fluorescence
maximum), the fluorescence decay followed a mono-exponen-
tial law with a lifetime equal to 6.98 ns. This value is compa-
rable with the lifetimes of other 4-amino substituted naphthal-
Figure 4: Fluorescence decay profile of 4 from a 10−5 M solution in
ethanol (excitation at 450 nm, detection at 550 nm).
imides without the carboxylic group in ethanol (7.5–10.5 ns The two-photon absorption cross section of 4 in toluene was
[17]). In ethanol, measurements of fluorescence decay time found to amount to about 80 GM at 800 nm. The two-photon
show the complex nature of the deactivation of the excited fluorescence excitation and fluorescence spectra are somewhat
states. Only excitation at short wavelength, 350–360 nm, and narrower than the respective one-photon spectra (Figure 5), but
detection at the blue edge of the emission spectra, 455–470 nm, seem to correspond to the same electronic transitions. The
shows a single exponential decay with lifetime of about dependence of the fluorescence intensity on the square of the
Scheme 2: Possible ionization and complexation of 4 in ethanol.
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Beilstein J. Org. Chem. 2013, 9, 1311–1318.
Figure 5: Normalized one- and two-photon spectra of dye 4 in toluene. Solid curves: one-photon absorption and fluorescence; dashed curves two-
photon fluorescence excitation (the X-axis values are λ/2) and fluorescence spectra. Inset: fluorescence intensity versus (laser power)2 at 800 nm.
laser power shown in the inset (Figure 5) clearly demonstrates ized within the naphthalene and phenyl rings. These results are
the two-photon excitation nature.
in a good agreement with the experiment (Figure 1). It is note-
worthy that both HOMO and LUMO orbitals are delocalized
and involve both the naphthalene moiety and the amino
Quantum mechanical calculations
Quantum mechanical calculations were performed for deriva- substituent (Figure 6a,b). In addition, the phenyl ring is twisted
tive 4 to gain deeper insight into the nature of the longest wave- out of the molecule plane and does not contribute to either
length transition and to estimate the electron donating and orbital. The degree of charge transfer is not large, which
accepting properties of this molecule. The geometry was opti- accounts for the relatively moderate solvatochromism.
mized by using the semiempirical AM1 method and the elec- The calculated IP and EA values are 7.13 and 0.78 eV, respect-
tronic spectra were calculated by using the TD B3LYP/ ively. Derivative 4 should thus exhibit stronger electron-donat-
6-31G(d,p) method. The ionization potential (IP) and electron ing properties and weaker electron-accepting properties than
affinity (EA) were calculated at the B3LYP/6-31G(d,p) level by ZnO [18].
using the energies of the corresponding radical cation and
anion.
Grafting to the surface of ZnO nanoparticles
In order to investigate the behavior of acid 4 as a fluorescent
Thus, the first electronic transition is predicted at 401 nm molecular probe, preliminary experiments on grafting to the
(f = 0.30). It is essentially the HOMO → LUMO transition. The surface of ZnO nanoparticles (NPs) were carried out. The ZnO
next five electronic transitions between 333 and 300 nm are NPs in ethanol were prepared by laser ablation according to
weak (f = 0.001–0.003) and involve mostly the orbitals local- [14]. The typical NP size was 17 nm with the dispersion about
Figure 6: (a) HOMO and (b) LUMO of 4.
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Beilstein J. Org. Chem. 2013, 9, 1311–1318.
25%. A freshly prepared ZnO NP solution in ethanol was added 1H NMR spectra were recorded on a Brucker AC 250 spectrom-
to the 1.4 × 10−6 M solution of 4 in ethanol. Under one-photon eter. Proton chemical shifts are reported in ppm downfield from
CW excitation at 325 nm, the fluorescence intensity of the solu- tetramethylsilane. The elemental analyses were made by the
tion exhibited a four-fold enhancement. A 14 nm blue-shift was Microanalytical Center of Aix-Marseille Université. Melting
also observed (Figure 7). Fluorescence from 4 persists after points were determined on a Büchi-510 apparatus and were not
several centrifugation/washing cycles (which completely corrected. The UV–vis absorption spectra were recorded
remove 4 from the solvent) and the band shape does not with an Ocean Optics USB 4000 spectrometer. The fluores-
undergo further change, thus proving the ZnO surface grafting. cence spectra were recorded with an HORIBA Fluorolog
FL-1057 spectrometer. All spectra were recorded using 1 cm
Conclusion
Derivative 4 involving both the fluorophore moiety and the
quartz cells.
carboxylic group capable of binding the ZnO surface can serve The quantum yield of fluorescence was determined by using
as an efficient molecular probe owing to the high sensitivity to coumarin 153 as a reference in toluene and ethanol at 20 °C.
the polarity of the surroundings. Derivative 2 can also be used
when fluorescence detection at shorter wavelengths is desired. Fluorescence lifetime measurements were performed by using
Moreover, owing to the absence of fluorescence from the time-correlated single photon counting (TCSPC) spectroscopy.
anionic species these compounds can be employed for moni- Femtosecond pulses (150 fs, 80 MHz) generated by a tunable
toring the complex equilibria of carboxylic acids existing in mode-locked Ti:sapphire laser (MaiTai HP, Spectra-Physics,
polar solvent solutions. The detailed quantitative investigation 690–1050 nm) were externally frequency-doubled by a 1 mm
of the behavior of derivatives 2 and 4 and the unsubstituted thick BBO crystal. The pulse repetition rate was reduced to
parent derivative is underway in our laboratory.
8 MHz by the means of a pulse-picker (Model 3980, Spectra-
Physics), extending the delay between the consecutive pulses to
126 ns. The generated femtosecond pulses illuminated a 1 cm
Experimental
All starting materials: 4-chloro-1,8-naphthalic anhydride, quartz cell containing the solution under study. The photo-
piperidine, methyl 4-aminobenzoate and solvents were obtained excited fluorescence was collected in a 90° geometry and sent
from Alfa Aesar. 4-Chloro-1,8-naphthalic anhydride and methyl into a subtractive double-monochromator (DH10, Jobin-Yvon)
4-aminobenzoate were crystallized from acetic anhydride before being detected by a silicon avalanche photodiode
and methanol, respectively. Distilled water was used in all (PDM50CTC, Micro Photon Devices). The entrance and exit
experiments.
slit widths of the monochromator ensured 1 nm spectral resolu-
Figure 7: Fluorescence spectra of 4 ethanol (5 × 10−5 M) (dashed curve) before and after the addition of ZnO NPs (solid curve). Excitation wave-
length: 325 nm. The inset shows the same normalized spectra.
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Beilstein J. Org. Chem. 2013, 9, 1311–1318.
tion in the lifetime measurements. Depending on the experi- C20H12ClNO4: C, 65.67; H, 3.31; N, 3.83; found: C, 65.30; H,
ment, a small part of the 700 or 800 nm laser beam was picked 3.24; N, 3.79.
and sent to a photodiode (TDA 200, Picoquant). The laser and
fluorescence signals were subsequently sent to a correlator 4-(6-Chloro-1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-
(PicoHarp 300, Picoquant). The time of arrival of the fluores- yl)benzoic acid (2): Derivative 1 (1.0 mmol, 0.36 g) was
cence photons was measured with 4 ps or 16 ps resolution suspended in water (5 mL) and a solution of sodium hydroxide
depending on the experiment, and the fluorescence temporal (1.3 mmol, 0.05 g) in water (5 mL) was added at room tempera-
decay was reconstructed. The impulsive response function ture. The mixture was heated at 80 °C for 18 h. The homoge-
(IRF) was taken as the decay curve at the excitation wave- neous reaction mixture was acidified with 1 M HCl solution
length (400 nm). The IRF curve was free from the fluorescence until approximately pH 2. The product was filtered, crystallized
signal. From the IRF curves, we estimated the temporal from MeOH and dried. Yield: 63%, 0.22 g; beige powder,
response of the setup as 150 ps FWHM. The data were numeri- mp > 300 °C; 1H NMR (DMSO-d6): δ 7.78 (dd, J1 = 8.49,
cally deconvoluted using the measured IRF and fitted to mono- J2 = 7.54 Hz, 1H), 7.81 (d, J = 7.74 Hz, 2H), 7.91 (d,
or bi-exponential decays, using a commercial program (IgorPro, J = 7.82 Hz, 2H), 8.04 (dd, J1 = 7.15, J2 = 1.30 Hz, 2H), 8.43
Wavemetrics).
(ddd, J1 = 8.49, J2 = 1.22, J3 = 0.63 Hz, 2H), 13.04 (br s,
COOH); Anal. calcd for C19H10ClNO4: C, 64.88; H, 2.87; N,
The two-photon absorption cross section was determined by 3.98; found: C, 64.54; H, 2.80; N, 3.86.
using fluorescence excitation spectroscopy. The same tunable
femtosecond laser source (operating at 80 MHz), was used to 4-(6-Hydroxy-1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-
excite a solution of 4 by two-photon absorption. The laser beam yl)benzoic acid (3): Derivative 1 (1.0 mmol, 0.36 g) was
was spatially extended with a telescope and was focused into suspended in water (5 mL) and a solution of sodium hydroxide
the 1 cm cell containing a solution of 4 in toluene with a NA 0.4 (4.0 mmol, 0.16 g) in water (5 mL) was added at room tempera-
objective lens. The generated fluorescence was collected at 90° ture. The mixture was heated under reflux for 24 h. The homo-
and filtered through a short-pass interference filter. After geneous reaction mixture was acidified with 1 M HCl/H2O
passing through a monochromator (Spectra Pro 500i, Acton) it solution until approximately pH 2. The product was filtered,
was detected by a CCD camera (Roper Scientific). The fluores- crystallized from EtOH and dried. Yield: 48%, 0.20 g; pale
cence spectra were recorded for the excitation wavelengths yellow powder, mp > 300 °C; 1H NMR (DMSO-d6) δ 7.54 (d,
between 700 to 950 nm, in 5 nm steps. Integration time ranged J = 8.69 Hz, 2H), 8.04 (dd, J1 = 8.45, J2 = 7.35 Hz, 1H), 8.08
from 10 ms to 2 s depending on the fluorescence signal level. (d, J = 8.69 Hz, 2H), 8.10 (d, J = 7.90 Hz, 1H), 8.47 (d,
The average laser power was typically kept around 500 mW. J = 7.90 Hz, 1H), 8.61 (dd, J1 = 7.27, J2 = 1.07 Hz, 1H), 8.68
The two-photon absorption spectra were calculated by inte- (dd, J1 = 8.49, J2 = 1.07 Hz, 1H), 11.02 (s, OH); 13.04 (br s,
grating the fluorescence spectra for each excitation wavelength. COOH); Anal. calcd for C19H11NO5: C, 68.47; H, 3.33; N,
The spectra were normalized by the integration time and the 4.20; found: C, 68.31; H, 3.32; N, 4.18.
square of the average laser power. The two-photon absorption
cross section of 4 was determined by comparing the two-photon 4-(1,3-Dioxo-6-(piperidin-1-yl)-1H-benzo[de]isoquinolin-
absorption spectrum with that of rhodamine B (RhB) in 2(3H)-yl)benzoic acid (4): Method A. Derivative 2 (1.0 mmol,
methanol, and by normalizing by its quantum yield. The values 0.35 g) was dissolved in 1,4-dioxane (5 mL), and piperidine
for RhB found in the literature have been determined with the (2 mmol, 0.2 mL) was added at room temperature. The mixture
same typical pulse duration of about 150 fs [19].
was heated under reflux for 8 h. The basic reaction mixture was
neutralized with 1 M HCl solution until approximately pH 6–7.
Methyl 4-(6-chloro-1,3-dioxo-1H-benzo[de]isoquinolin- The product was filtered, crystallized from MeOH and dried.
2(3H)-yl)benzoate (1): To a solution of 4-chloro-1,8-naphthalic Yield: 10%, 0.04 g. Method B. Derivative 6 (1.0 mmol, 0.36 g)
anhydride (2 mmol, 0.46 g) in 1,4-dioxane (10 mL), methyl was suspended in water (5 mL) and a solution of sodium
4-aminobenzoate (6 mmol, 0.90 g) was added at room tempera- hydroxide (1.3 mmol, 0.05 g) in water (5 mL) was added at
ture. The mixture was heated under reflux for 24 h. The prod- room temperature. The mixture was heated at 80 °C for 18 h.
uct was filtered, purified by crystallization from EtOH, and The homogeneous reaction mixture was acidified with 1 M HCl
dried. Yield: 77%, 0.56 g; pale yellow crystals, mp > 300 °C; solution until approximately pH 2. The product was filtered,
1H NMR (CDCl3) δ 3.94 (s, 3H), 7.39 (d, J = 8.8 Hz, 2H), 7.86 crystallized from MeOH and dried. Yield: 69%, 0.17 g; orange
(d, J = 7.9 Hz, 1H), 7.89 (dd, J1 = 8.5, J2 = 7.3 Hz, 1H), 8.22 (d, crystals, mp > 300 °C; 1H NMR (DMSO-d6) δ 1.60–1.80 (m,
J = 8.8 Hz, 2H), 8.53 (d, J = 7.9 Hz, 1H), 8.67 (d, 6H), 2.9–3.0 (m 4H), 7.36 (d, J = 8.1 Hz, 1H), 7.49 (d,
J = 8.5 Hz, 1H), 8.7 (d, J = 8.5 Hz, 1H); Anal. calcd for J = 8.5 Hz, 2H), 7.84 (dd, J1 = 8.4, J2 = 7.3 Hz, 1H), 8.07 (d,
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Beilstein J. Org. Chem. 2013, 9, 1311–1318.
12.Bekere, L.; Lokshin, V.; Marine, W.; Khodorkovsky, V. Latv. Kim. Z.
2011, 50, 309.
J = 8.5 Hz, 2H), 8.40 (d, J = 8.1 Hz, 1H), 8.47 (d, J = 8.4 Hz,
1H), 8.48 (d, J = 8.1, 1H), 13.00 (br s, COOH); Anal. calcd for
C24H20N2O4: C, 71.99; H, 5.03; N, 7.00; found: C, 71.41; H,
5.10; N, 6.89.
13.Said, A.; Sajti, L.; Giorgio, S.; Marine, W. J. Phys.: Conf. Ser. 2007, 59,
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doi:10.1016/S0143-7208(96)00053-8
6-(Piperidin-1-yl)-1H,3H-benzo[de]isochromene-1,3-dione
(5): Preparation according to [1]. The product was isolated in
82% yield, mp 174–176 °C (lit. [1] 175–176 °C).
16.Grabchev, I.; Petkov, C.; Bojinov, V. Macromol. Mater. Eng. 2002, 287,
904–908. doi:10.1002/mame.200290025
17.Alexiou, M. S.; Tychopoulous, V.; Ghorbanian, S.; Tyman, J. H. P.;
Brown, R. G.; Brittain, P. I. J. Chem. Soc., Perkin Trans. 2 1990,
837–842. doi:10.1039/p29900000837
Methyl 4-(1,3-dioxo-6-(piperidin-1-yl)-1H-benz[de]iso-
quinolin-2(3H)-yl)benzoate (6): 4-Piperidinyl-1,8-naphthalic
anhydride 5 (1 mmol, 0.28 g) was dissolved in 2-ethoxyethanol
(7 mL) and methyl 4-aminobenzoate (3 mmol, 0.45 g) was
added at room temperature. The mixture was heated under
reflux for 24 h. The product was filtered, crystallized from
EtOH and dried. Yield: 89%, 0.34 g; yellow crystals,
mp 280–282 °C; 1H NMR (CDCl3) δ 1.68–1.81 (m, 2H),
1.86–2.0 (m, 4H), 3.24–3.33 (m, 4H), 3.95 (s, 3H), 7.25 (d,
J = 7.2 Hz, 1H), 7.39 (d, J = 8.2 Hz, 2H), 7.72 (dd, J1 = 8.3,
J2 = 7.4 Hz, 1H), 8.21 (d, J = 8.2 Hz, 2H), 8.49 (d, J = 8.5 Hz,
1H), 8.53 (d, J = 8.5 Hz, 1H), 8.61 (d, J = 7.2 Hz, 1H); Anal.
calcd for C25H22N2O4: C, 72.46; H, 5.35; N, 6.76; found: C,
72.03; H, 5.29; N, 6.80.
18.Morkoç, H.; Özgür, Ü. Electronic Band Structure. Zink Oxide.
Fundamentals, Materials and Device Technology; Wiley-VCH:
Weinheim, Germany, 2009; pp 14–26. doi:10.1002/9783527623945
19.Xu, C.; Webb, W. W. J. Opt. Soc. Am. B 1996, 13, 481–491.
doi:10.1364/JOSAB.13.000481
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