Microwave-assisted solvent-free synthesis of fluorescent naphthalimide dyes

Article abstract of DOI:10.1016/j.dyepig.2013.04.004

A series of fluorescent naphthalimide dyes were synthesized via aromatic nucleophilic substitution reaction of 4-bromo-N-alkylnaphthalimides with amines, alkoxides and thiols under microwave irradiation. In this procedure an efficient method for C-N, C-O and C-S bond formation via applying appropriate nucleophiles in the presence of KF/Al₂O₃ under solvent-free conditions is described. Adducts are produced in good to excellent yields and relatively in short times. The optical properties of three dyes as representative derivatives were examined by UV absorption and steady state fluorescence spectroscopy in solvents with different polarity.

Full text of DOI:10.1016/j.dyepig.2013.04.004

Dyes and Pigments 99 (2013) 52e58
Contents lists available at SciVerse ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Microwave-assisted solvent-free synthesis of fluorescent
naphthalimide dyes
*
Ghasem R. Bardajee
Department of Chemistry, Payame Noor University, PO Box 19395-3697, Tehran, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of fluorescent naphthalimide dyes were synthesized via aromatic nucleophilic substitution re-
action of 4-bromo-N-alkylnaphthalimides with amines, alkoxides and thiols under microwave irradia-
tion. In this procedure an efficient method for CeN, CeO and CeS bond formation via applying
appropriate nucleophiles in the presence of KF/Al2O3 under solvent-free conditions is described. Adducts
are produced in good to excellent yields and relatively in short times. The optical properties of three dyes
as representative derivatives were examined by UV absorption and steady state fluorescence spectros-
copy in solvents with different polarity.
Received 4 January 2013
Received in revised form
4 April 2013
Accepted 6 April 2013
Available online 15 April 2013
Keywords:
Ó 2013 Elsevier Ltd. All rights reserved.
Naphthalimide dyes
Microwave irradiation
Synthesis
Solvent-free
Optical property
KF/Al2O3
1. Introduction
those dyes that have a functional group that allows them to be
covalently attached to a macromolecule. Useful functional groups
It has been known for many years that the naphthalimide dyes
are widely used class of dyes due to their versatile applications in
various fields [1,2]. Because of their strong fluorescence and good
photostability, 1,8-naphthalimide derivatives have found applica-
tions in polymer materials [3,4], laser active media [5,6], fluores-
cent markers in biology [7], anticancer agents [8], analgesics in
medicine [9], fluorescence switchers and sensors [10e13], light
emitting diodes [14], electroluminescent materials [15], liquid
crystal displays [16] and ion probes [17e19].
The 4-amino-1,8-naphthalimide dyes are probably still the most
important yellow components for day light fluorescent pigments.
Most applications of 4-amino-1,8-naphthalimide derivatives are as
fluorescent in detergents, textiles, paper, plastics and paints [20e
22]. More recently, 1,8-naphthalimide derivatives have been stud-
ied as DNA intercalators [23,24].
include hydroxyl, carboxyl, and amino groups. For instance com-
pounds of type 1 found different applications due to the occurrence
of different functional groups in their structures (Fig. 1) [29e35].
Compound 1a have been used with considerable success as intra-
cellular markers and naphthalimide 1b has been used for moni-
toring interactions between single stranded desoxyribonucleic
acids and proteins [30]. Another important application of naph-
thalimide dyes includes their use as donor-acceptor pairs for fluo-
rescence resonance energy transfer (FRET) experiments, a powerful
technique for measurement of distances on a nanometer scale. This
technique is widely used in biology, and study of synthetic polymer
systems. For example, continuing our interest in studying aspects of
morphology and miscibility between polymeric phases, we have
recently attached fluorescents compounds of type 1c (Fig. 1) as
donor and acceptor pairs to polymers [32,33]. Also, we have applied
dyes of type 1d as an atom transfer radical polymerization (ATRP)
initiator for the synthesis of chromophore-labeled poly(2-N,N-
dimethylaminoethyl methacrylate) homopolymers (PDMA) which
was used in surface modification of CdSe quantum dots [34]. Thus,
several approaches have been developed for their syntheses which
often consist of limited practical applicability, involving harsh re-
action conditions, multistep syntheses, long reaction times, toxic
solvents or reagents and high temperatures [29,35]. Also some of
these methods suffer from the lack of generality for common
Microwave irradiation technique has been used for the rapid
synthesis of a variety of compounds, and microwave-accelerated
solvent-free organic reactions have received special attention in
recent years [25e28]. Many reactions can proceed fast with the
assistance of microwave irradiation in high yields.
The presence of functional groups in dyes plays an important
role in their applications. We use the term functional to refer to
* Tel.: þ98 281 3336366; fax: þ98 281 3344081.
E-mail addresses: rezanejad@pnu.ac.ir, ghrezanejad@yahoo.com.
0143-7208/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2013.04.004

G.R. Bardajee / Dyes and Pigments 99 (2013) 52e58
53
Fig. 1. Some naphthalimide dyes with different functional groups.
R
N
R
N
O
O
O
O
O
O
O
RNH2
Nucleophile (Nu)
KF/Al2O3, MW
DOX, reflux
Nu = amine, alcohols
and thiols
a) R= Isobutyl
b) R= Butyl
Nu
Br
2
Br
3
4
Scheme 1. Synthesis of 4-substituted-1,8-naphthalimide dyes.
nucleophiles like amines, alcohols and thiols [36,37]. In this paper, a
microwave-assisted preparation of a series of fluorescent naph-
thalimide dyes is described in high yields via applying KF/Al2O3 as a
basic support under solvent-free conditions (Scheme 1).
Accordingly, when the 4-bromo-N- isobutylnaphthalimide 3a
(1 mmol, 1 equiv) was treated with isobutylamine (3 mmol, 3 equiv)
in the presence of KF/Al2O3 (0.15 g) under microwave irradiation
(5 min), the naphthalimide dye 4a was obtained in 81% yield (Table 1,
entry 3).
After optimizing the reaction conditions, we tested the gener-
ality of the reaction by using several amines, alcohols and thiols.
A wide range of primary or secondary amines, alcohols and thiols
were examined for CeN, CeO and CeS bond formations as shown
in Tables 2 and 3.
As one can see from Table 2, primary and heterocyclic secondary
amines like isobutylamine, benzylamine, propylamine, pyrolidine,
pipiridine and morpholine have shown higher yields compared to
chain secondary amines (entries 1e8, Table 2). More efforts for the
synthesis of naphthalimide dyes via using hindered amines such as
diisopropylamine or tert-butylamine have failed and no product
was observed. This behavior can be attributed to the competition of
nucleophilicity strength of amines versus their steric effects. In
continue, the bi-functional nucleophiles including ethanolamine
and N-methylethanolamine gave highly regio-selective 2-
hydroxyethyl amine derivatives in good yields (entries 9e10,
Table 2).
To expand the scope of our procedure to other carbon-
heteroatom bond formations, alcohols and thiols were used as
nucleophiles (Table 3). In this regard, different types of alcohols and
thiols including benzyl alcohol, n-butyl alcohol and benzyl
mercaptan were treated with compound 3 in good yields (entries
1e2 and 4, Table 3). The more hindered isopropyl alcohol and tert-
butyl alcohol didn’t work in our practice. A similar method was
applied for ethylene glycol as a bi-functional nucleophile and the
corresponding product was obtained with a reasonable yield (entry
3, Table 3). We believe that basic nature of KF/Al2O3 activates the
nucleophilic groups for taking part in reaction with 4-bromo-N-
alkylnaphthalimides via an aromatic nucleophilic substitution
mechanism.
2. Results and discussion
The class of dyes of interest to us, with the general structure 4,
was prepared from the reaction of 4-bromo-1,8-naphthalimides 3
with primary or secondary amines, alcohols and thiols via the
nucleophilic aromatic substitution reaction as shown in Scheme 1.
In the first step, 4-bromo-1,8-naphthalic anhydride 2 was reacted
with the desired amines (butylamine (76%) or isobutylamine (74%))
in boiling 1,4-dioxane (DOX) for an appropriate time intervals to
give intermediate 3 (Scheme 1) [31]. In the next step, compound 3
was reacted with nucleophiles such as primary or secondary
amines, alcohols and thiols using KF/Al2O3 as the base under
solvent-free conditions with microwave irradiation. The comple-
tion of reactions was followed by thin-layer chromatography (TLC)
on silica gel using n-haxane-acetone (3:1) as eluent.
To obtain the optimized reaction conditions, we initially tested the
reaction of isobutylamine with 4-bromo-N-isobutylnaphtha-limide
3a to find the optimum amount of support respecting to higher yield
of the reaction (Table 1). Furthermore, changing the reaction time
showed that the five minutes reaction time has the best efficiency.
Table 1
Effect of different amounts of KF/Al2O3 on the yield of the reaction of isobutylamine
with 4-bromo-N-isobutylnaphthalimide 3a under microwave irradiation.
Entry
KF/Al2O3 (g)
Time (min)
Yield (%)a
1
2
3
4
0.05
0.1
0.15
0.2
5
5
5
5
51
65
81
81
a
All reactions were run under the following conditions: 4-bromo-N-iso-
butylnaphthalimide 3a (1 mmol), isobutylamine (3 mmol) and KF/Al2O3 (0.05e
0.2 g) were placed in a Teflon flask (20 ml) and subjected to microwave irradiation
for 5 min.
In continue we examined the reusability of the catalyst. To this
end, the catalyst was separated and reused after washing with
CH2Cl2 and drying at 90 ꢀC. The reusability of the catalyst was

54
G.R. Bardajee / Dyes and Pigments 99 (2013) 52e58
Table 2 (continued)
Table 2
Synthesis of 1,8-naphthalimide dyes derived from the reaction of different amines
with compounds 3aeb in the presence of KF/Al2O3.
Entry
Amine
Compound 3
Product 4a
Yield (%)b
Entry
Amine
Compound 3
Product 4a
Yield (%)b
7
3a
90
1
3a
81
2
3a
84
8
3a
3a
3a
92
72
61
3
3a
78
9
4
5
6
3b
3b
3a
82
66
87
10
a
All products were characterized by m.p., IR, and 1HNMR, and their physical data
were similar to those reported in the literature [27,29,33].
b
All reactions were run under the following conditions: compound 3 (1 mmol),
amine (3 mmol) and KF/Al2O3 (0.15 g) were placed in a Teflon flask (20 mL) and
subjected to microwave irradiation for 5 min.
checked by the reaction of compound 3a and isobutylamine under
optimized reaction conditions. The results showed that the catalyst
can be used effectively three times without any loss of its activity
(78% after three times recycling). So the recovery and reusability of
this catalyst is a great advantage of the presented method.
The photophysical properties of 1,8-naphthalimides mainly
come from the polarization of the naphthalimide moiety due to the
electron donor-acceptor interaction occurring between the sub-
stituents at C-4 (electron donor) and the carbonyl groups from the
imide structure (electron acceptor) of the molecule. To study the
spectroscopic properties of entitled dyes, the dyes 4g, 4h and 4n
were selected. In Table 4, the spectroscopic properties of these
dyes are summarized. Normalized absorption and emission spectra
for each of these dyes in four different solvents (toluene,

G.R. Bardajee / Dyes and Pigments 99 (2013) 52e58
55
Table 3
dichloromethane (DCM), dimethylformamide (DMF), and acetoni-
trile) are presented in Fig. 2. As one can see from Table 4, the main
absorption band (attributed to the 0e0 vibrational band of a strong
S0eS1 transition) of these dyes is centered between 380 and
446 nm in the aforementioned solvents. The position of the S0eS1
absorption band shows minor solvent-dependent shifts, indicating
a weak charge transfer character for the lowest electronic excitation
in the ground-state geometry. In the other hand, the fluorescence
emission of selected dyes (4g, 4h and 4n) is more solvent depen-
dent. The fluorescence maximum shifts to longer wavelengths in
going from nonpolar to polar solvents, indicative of the charge
transfer nature of the emitting state. For example in Table 4, lem for
4h shifts from 490 nm to 524 nm as the solvent is changed from
toluene (a non-polar solvent) to acetonitrile (a polar solvent). Ex-
amination of the chemical structure of entitled dyes suggests that
the occurrence of an intramolecular charge transfer (ICT) process
may be responsible for their solvent sensitivity. For example for the
dye 4h, the tertiary amino group is an electron donor group and the
imide moiety is an electron-deficient moiety, allowing for the
occurrence of an excited state with some ICT character. Fig. 3 shows
the delocalized forms for dye 4h in a valence bond picture. Struc-
ture A (and zwitterionic structure B) have dominant contributions
to the ground (S0) state, thereby rationalizing the slight sensitivity
of the absorption peak with solvent polarity/polarizability. In the
excited state, however, a larger weight is expected for the charge-
separated structure C. As a result, polar solvents stabilize the
excited state and lead to a red-shifted emission [38e40]. Further-
more dyes 4g and 4h have essentially identical chromophores, with
a secondary amine attached to the 4-position of the naphthalene
ring. The major difference that distinct dye 4g from 4h, is the
presence of 5 member ring of pyrolidine in dye 4h instead of 6
member ring of morpholine containing an oxygen atom. The
aforementioned differences seem to be the origin of some obser-
vations. First, the molar extinction coefficient of the dye 4h is
markedly greater than dye 4g in all of the examined solvents
(Table 4). Second, while the emission spectra of dyes 4g and 4h are
almost in the same range in different solvents, the absorption
spectra shows a red-shifted for dye 4h in examined solvents. This
leads to a smaller Stokes shift for later dye. Finally, there is a small
stoke shift for dye 4g in DMF (Fig. 2 and Table 4). It can be attributed
to the highly stabilized excited state of dye 4g in DMF solvent due to
the presence of oxygen atom of morpholine part in the entitled dye.
We are in the process of investigating these effects, and will report
these studies separately.
Synthesis of 1,8-naphthalimide derived from the reaction of alcohols and thiols with
compounds 3 in the presence of KF/Al2O3.
Entry
Nucleophile
Compound 3
Product 4a
Yield (%)b
1
3b
72
2
3b
70
3
3a
73
4
3a
78
a
All products were characterized by m.p., IR, and 1HNMR, and their physical data
were similar to those reported in the literature [27,29,33].
In continue, the quantum yield (QY) of dyes 4g, 4h and 4n were
calculated according to the method explained in the references
[41]. Briefly, rhodamine 6G in water was selected as a reference
standard (QY ¼ 0.90), and the absorbance for the standard (in
water) and the dyes solutions (in ethyl acetate) at the excitation
wavelengths was measured (6 different solutions for each sample
with an absorbance at excitation wavelength around 0.1). The
fluorescence spectra of each solution were measured and the in-
tegrated fluorescence intensity (that is, the area of the fluorescence
spectrum) was calculated. The areas of the integrated fluorescence
intensity vs. absorbance were plotted. The plot obtained should be a
straight line with a gradient (Grad), which was used to calculate the
quantum yield based on the equation (1):
b
All reactions were run under the following conditions: Compound 3 (1 mmol),
nucleophile (3 mmol) and KF/Al2O3 (0.15 g) were placed in a Teflon flask (20 mL)
and subjected to microwave irradiation for 5 min.
Table 4
Spectroscopic properties of dyes 4g, 4h and 4n in different solvents.
a
Dye Solvent
ε ꢁ 10ꢂ4 (Mꢂ1 cmꢂ1
)
labs (nm)b lem (nm)b
Df
4g
4h
4n
Toluene
DCM
DMF
1.39
0.65
1.60
388
392
395
391
433
441
446
442
380
385
389
382
488
508
419
526
490
508
514
524
443
448
473
468
0.022
0.168
0.275
0.305
Acetonitrile 2.06
Toluene
DCM
DMF
2.03
4.31
2.76
Acetonitrile 2.51
FX
¼
FSTðGradX=GradSTÞðhX2
=
h2ST
Þ
(1)
Toluene
DCM
DMF
1.95
7.34
0.97
Where the subscripts ST and X denote standard (rhodamine 6G)
and test samples respectively, is QY, and is the refractive index
Acetonitrile 0.86
F
h
a
of the solvent. The QY of dyes 4g, 4h and 4n was calculated 0.66,
0.74 and 0.71, respectively.
Extinction coefficient.
Wavelengths of maximum absorbance (labs) and emission intensity (lem).
b

56
G.R. Bardajee / Dyes and Pigments 99 (2013) 52e58
Fig. 2. Absorption and emission spectra of compounds 4g, 4h and 4n in toluene (red), dichloromethane (DCM, blue), dimethylformamide (DMF, grey), and acetonitrile (black). (For
interpretation of the references to color in this figure legend, the reader is referred to the web version of this article).
between the ground state and the excited state (in cmꢂ1) on the
refractive index (n) and the dielectric constant (ε) of the solvent.
O
N
O
O
N
O
O
N
O
ꢀ
ꢁ
2
ε ꢂ 1
n2 ꢂ 1
ð
mE
ꢂ
mGÞ2
nA
ꢂ
nF
¼
ꢂ
þ constant
(2)
2n2 þ 1
a3
hc 2ε þ 1
where nA and nF are the wave numbers (cmꢂ1) of the absorption and
emission maxima, respectively. h ¼ 6.6256 ꢁ 10ꢂ27 erg s is Planck’s
constant; c ¼ 2.9979 ꢁ 1010 cm/s is the speed of light; and a is the
radius of the cavity in which the fluorophore resides. mG and mE refer
to the ground state and excited state dipole moments, respectively.
The term inside the brackets in equation (2) is called the orientation
A
B
C
N
N
N
Fig. 3. Different delocalized structures of 4h contributing to the ground and excited
states.
polarizability (
sensitivity of a fluorophore. This plot of Dn
four solvents we examined, is presented in Fig. 4. The calculated
values of f for each solvent are presented in Table 4.
Two important points are obvious from Lippert plot in Fig. 4.
First, the non-linearity of the plots can be regarded as evidence for
the dominant importance of specific solvent effects on the spectral
shifts (general solvent effects can lead to linear Lippert plots).
Second, one can see from the y-axis that the magnitude of the
Stokes shift (Dn) is significantly larger for 4g than for 4h or 4n.
D
f). The slope of the Lippert plot reflects the solvent
(
nA nf) versus f, for the
ꢂ
D
To obtain more information about the solvent sensitivity of the
absorption and emission spectra of these dyes, the Lippert plot is
shown in Fig. 4. The Lippert plot comes from the Lippert equation
[40] which illustrates the dependence of the energy difference
D
3. Conclusions
In summary, we have described the synthesis and character-
ization of a series of fluorescent naphthalimide dyes, which was
prepared by nucleophilic aromatic substitution reaction of 4-
bromo-N-alkylnaphthalimides with amines, alcohols and thiols
under microwave irradiation. The KF/Al2O3 was found to be a mild
and effective basic support for this reaction. The use of this inex-
pensive, clean, and easily available catalyst under essentially
neutral reaction and work up conditions make this protocol prac-
tical and economically attractive. In addition, the optical properties
of 3 selected dyes (4g, 4h and 4n) in different solvents with various
Fig. 4. Lippert plot for dyes 4g, 4h and 4n.

G.R. Bardajee / Dyes and Pigments 99 (2013) 52e58
57
polarities were studied. It was found that the dyes show a specific
solvent effect and their optical properties are dependent on the
type and nature of substitutions on the position 4 of naphthalimide
moiety.
(d, J ¼ 6.8 Hz, 6H); 2.13 (m, 4H); 2.29 (m, 1H); 3.80 (m, 4H), 4.06 (d,
J ¼ 7.3 Hz, 2H); 6.84 (d, J ¼ 8.7 Hz, 1H); 7.56 (m, 1H); 8.45 (d,
J ¼ 8.6 Hz, 1H); 8.59 (m, 1H). 13C NMR (100 MHz, CDCl3): 20.8; 26.4;
30.1; 47.3; 53.5; 108.9; 111.3; 123.0; 123.4; 131.4; 132.2; 133.8;
134.7; 138.1; 153.0; 164.8; 165.6. HRMS (EI, m/z) calcd. for
4. Experimental
C
C
20H22N2O2 322.1681 (Mþ), Found 322.1690. Anal. Calcd for
20H22N2O2 (322.1): C, 74.51; H, 6.88; N, 8.69. Found: C, 74.58; H,
4.1. Materials
6.75; N, 8.81.
All amines, alcohols, thiols and 4-bromo-1,8-naphthalic anhy-
dride were purchased from Merck or SigmaeAldrich companies.
The course of the synthesis and purity of the products were fol-
lowed by TLC on silica gel plates (Merck, silica gel 60 F254, ready to
use), using ethyl n-hexane-acetone (3:1) as eluent. The eluent for
column chromatography was the same as TLC eluent.
4.4.3. 6-(2-hydroxyethylamino)-2-isobutyl-1H-benzo[de]
isoquinoline-1,3(2H)-dione (4i)
Yield: 72%; m.p. 176e178 ꢀC; 1H NMR (500 MHz, CDCl3):
d 0.87
(d, J ¼ 6.8 Hz, 6H); 2.10 (m, 1H); 3.47 (m, 3H); 3.70 (m, 2H); 3.87 (d,
J ¼ 7.2 Hz, 2H); 6.81 (d, J ¼ 8.8 Hz, 1H); 7.68 (m, 1H); 7.73 (t,
J ¼ 5.6 Hz, 1H); 8.25 (d, J ¼ 8.8 Hz, 1H); 8.43 (d, J ¼ 7.2 Hz, 1H); 8.69
(d, J ¼ 8.8 Hz, 1H). 13C NMR (100 MHz, methanol-d4):
d 20.7; 28.8;
4.2. Instrumentation
46.8; 48.0; 61.1; 105.3; 109.7; 122.0; 123.5; 125.7; 129.4; 131.4;
132.4; 136.1; 152.8; 166.2; 166.8. HRMS (EI, m/z) calcd. for
Melting points were recorded using a Buchi B540 melting point
apparatus and are uncorrected. 1H and 13C NMR spectra were ob-
tained using a bruker (DRX-500 Avance) NMR spectrometers at
ambient temperature. 1H NMR spectra are referenced to tetrame-
thylsilane (0.00 ppm) and 13C NMR spectra are referenced from the
solvent central peak (for example, 77.23 ppm for CDCl3). Chemical
shifts are given in ppm. IR spectra were taken as KBr pellets on an
ABB Bomem MB-100 FTIR spectrophotometer. IR is reported as
characteristic bands (cmꢂ1) at their maximum intensity. A Shi-
madzu UVevisible 1650 PC spectrophotometer was used for
recording absorption spectra in solution. FL spectra were measured
using SCINCO’s Fluorescence Spectrometer FluoroMate FS-2. All
samples were placed in a 1.00 cm quartz cuvette either for UV or
fluorescence measurements.
C
C
18H20N2O3 312.1474 (Mþ), Found 312.1483. Anal. Calcd for
18H20N2O3 (312.1): C, 69.21; H, 6.45; N, 8.97. Found: C, 69.30; H,
6.49; N, 8.92.
4.4.4. (6-((2-hydroxyethyl)(methyl)amino)-2-isobutyl-1H-benzo
[de]isoquinoline-1,3(2H)-dione) (4j)
Yield: 61%; m.p 115e117 ꢀC; 1H NMR (500 MHz, CDCl3):
d 0.97 (d,
J ¼ 6.6 Hz, 6H); 2.02 (t, J ¼ 5.7 Hz, 1H); 2.23 (m, 1H); 3.08 (s, 3H);
3.50 (t, J ¼ 5.5 Hz, 2H); 3.96 (m, 2H); 4.03 (d, J ¼ 7.2 Hz, 2H); 7.27 (d,
J ¼ 8.1 Hz, 1H); 7.69 (dd, J ¼ 7.4 Hz, 8.4 Hz, 1H); 8.49 (d, J ¼ 8.1 Hz,
1H); 8.57 (dd, J ¼ 1.2 Hz, 7.4 Hz, 1H); 8.61 (dd, J ¼ 1.2 Hz, 8.4 Hz, 1H).
13C NMR (75 MHz, CDCl3):
d 20.5; 27.5; 41.8; 47.1; 58.6; 59.6; 115.5;
116.6; 123.1; 125.6; 126.2; 130.1; 130.5; 131.2; 132.4; 156.4; 164.3;
164.9. HRMS (EI, m/z) calcd. For C19H22N2O3 326.1630 (Mþþ), Found
326.1635. Anal. Calcd for C19H22N2O3 (326.1): C, 69.92; H, 6.79; N,
8.58. Found: C, 69.90; H, 6.86; N, 8.62.
4.3. Synthesis
4.3.1. General procedure for the synthesis of the 1,8-naphthalimide
derivatives under solvent-free conditions assisted with microwave
irradiation
4.4.5. (6-(2-hydroxyethoxy)-2-isobutyl-1H-benzo[de]isoquinoline-
1,3(2H)- dione) (4m)
Yield: 73%; m.p. 146e147 ꢀC; 1H NMR (500 MHz, CDCl3):
d 0.98
The syntheses of compounds 2a and 2b and KF/Al2O3 are re-
(d, J ¼ 6.5 Hz, 6H); 2.01 (bs, 1H); 2.22 (m, 1H); 4.03 (d, J ¼ 7.5 Hz,
2H); 4.19 (m, 2H); 4.40 (t, J ¼ 5.0 Hz, 2H); 7.06 (d, J ¼ 8.0 Hz, 1H);
7.71 (dd, J ¼ 7.0 Hz, 8.5 Hz,1H); 8.54 (d, J ¼ 8.0 Hz,1H); 8.60 (m, 2H).
ported elsewhere [31,42]. To
a mixture of 4-bromo-N-iso-
butylnaphthalimide 2 (1 mmol, 0.331 g) and pyrolidine (3 mmol),
KF/Al2O3 (0.15 g) was added. The resulting mixture was placed in a
Teflon flask (20 mL) and subjected to microwave irradiation. The
mixture was purified over silica gel using n-haxane-acetone (3:1)
to afford the pure product.
13C NMR (75 MHz, CDCl3):
d 20.3; 27.4; 47.2; 61.1; 70.3; 106.2; 115.5;
122.5; 123.3; 126.0; 128.3; 129.5; 131.7; 133.4; 159.8; 164.2; 164.8.
HRMS (EI, m/z) calcd. For C18H19NO4 313.1314 (Mþþ), Found
313.1318. Anal. Calcd for C18H19NO4 (313.1): C, 68.99; H, 6.11; N,
4.47. Found: C, 68.86; H, 6.19; N, 4.55.
4.4. Characterization data for selected compounds
4.4.6. 6-(benzylthio)-2-isobutyl-1H-benzo[de]isoquinoline-
1,3(2H)-dione (4n)
4.4.1. 6-(benzylamino)-2-isobutyl-1H-benzo[de]isoquinoline-
1,3(2H)-dione (4b)
Yield: 78%; m.p. 127e128 ꢀC; IR (film) ymax cmꢂ1: 3063; 2959;
Yield: 84%; m.p. 156e158 ꢀC; IR (film) ymax cmꢂ1: 3355; 2962;
1694; 1650; 1590; 1377; 1240; 1082. 1H NMR (500 MHz, CDCl3):
1684; 1542; 1347; 1261. 1H NMR (500 MHz, CDCl3):
d
1.02 (d,
d
1.02 (d, J ¼ 6.7 Hz, 6H); 2.28 (m, 1H); 4.08 (d, J ¼ 7.4 Hz, 2H), 4.41
J ¼ 6.7 Hz, 6H); 2.29 (m,1H); 4.06 (d, J ¼ 7.4 Hz, 2H), 4.65 (s, 2H); 5.78
(bs, 1H); 6.79 (d, J ¼ 8.4 Hz,1H); 7.45 (m, 5H); 7.65 (t, J ¼ 7.8 Hz,1H);
8.19 (d, J ¼ 8.4 Hz,1H); 8.48 (d, J ¼ 8.4 Hz,1H); 8.63 (d, J ¼ 7.2 Hz,1H).
13C NMR (100 MHz, CDCl3): 22.1; 28.6; 44.5; 48.3; 105.8; 111.3;
120.3; 124.1; 125.5; 126.4; 128.1; 128.8; 130.4; 130.9; 131.3; 134.9;
138.0; 148.8; 164.5; 164.8. HRMS (EI, m/z) calcd. for C23H22N2O2
358.1681 (Mþ), Found 358.1689. Anal. Calcd for C23H22N2O2 (358.1):
C, 77.07; H, 6.19; N, 7.82. Found: C, 77.24; H, 6.01; N, 8.06.
(s, 1H); 7.36 (m, 3H); 7.44 (d, J ¼ 7.2 Hz, 2H); 7.63 (d, J ¼ 7.8 Hz, 1H);
7.78 (t, J ¼ 7.8 Hz, 1H); 8.48 (d, J ¼ 7.8 Hz, 1H); 8.61 (d, J ¼ 8.4, Hz,
1H); . 8.65 (d, J ¼ 7.2 Hz, 1H); 13C NMR (100 MHz, CDCl3): 20.7; 27.8;
38.0; 47.6; 120.2; 123.6; 124.7; 127.11; 128.3; 129.2; 129.3; 130.2;
130.6; 131.2; 132.0; 135.8; 144.7; 164.7; 164.8. HRMS (EI, m/z) calcd.
for C23H21NO2S 375.1293 (Mþ), Found 375.1299. Anal. Calcd for
C23H21NO2S (375.1): C, 73.57; H, 5.64; N, 3.73; S, 8.54. Found: C,
73.70; H, 5.74; N, 3.81; S, 8.68.
4.4.2. 2-Isobutyl-6-(pyrrolidin-1-yl)-1H-benzo[de]isoquinoline-
1,3(2H)-dione (4h)
Acknowledgments
Yield: 92%; m.p. 138e139 ꢀC; IR (film) ymax cmꢂ1: 2961; 1688;
Payame Noor University is thanked for financial support of
this work.
1635; 1405; 1373; 1243. 1H NMR (500 MHz, CDCl3):
d
0.92

58
G.R. Bardajee / Dyes and Pigments 99 (2013) 52e58
[22] Veale EB, Gunnlaugsson T. Bidirectional photoinduced electron-transfer
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