The synthesis and optical properties of novel fluorescent iminocoumarins and bis-iminocoumarins: Investigations in the series of urea derivatives

Article abstract of DOI:10.1016/j.dyepig.2009.07.003

The condensation of 3-cyano-7-diethylamino-iminocoumarin with various isocyanates and diisocyanates as C-electrophiles gave a new series of N-substituted iminocoumarins and bis-iminocoumarins. The ten compounds obtained were characterized using IR, ¹H NMR, ¹³C NMR, elemental analysis and mass spectrometry. Their optical properties, studied in dichloromethane by UV/vis absorption and fluorescence spectroscopy, were found to depend strongly upon the nature of the substituent borne by the imino group. For the sake of comparison, the optical properties of selected compounds were also analyzed in ethanol. Of the iminocoumarins studied, the alkylurea derivatives displayed the most interesting spectroscopic characteristics and may be of potential use as novel fluorescent probes in media of various polarity.

Full text of DOI:10.1016/j.dyepig.2009.07.003

Dyes and Pigments 84 (2010) 108–113
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
The synthesis and optical properties of novel fluorescent iminocoumarins
and bis-iminocoumarins: Investigations in the series of urea derivatives
,
a
Mehdi Fakhfakh a, Hamida Turki a, Suzanne Fery-Forgues b , Rachid El Gharbi
*
a Laboratoire de Chimie Applique´e: He´te´rocycles, Corps Gras et Polyme`res, Faculte´ des Sciences de Sfax, 3038 Sfax, Tunisia
b Laboratoire des Interactions Mole´culaires R´eactivite´ Chimique et Photochimique, UMR CNRS 5623, Universite´ Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
The condensation of 3-cyano-7-diethylamino-iminocoumarin with various isocyanates and diisocyanates
as C-electrophiles gave a new series of N-substituted iminocoumarins and bis-iminocoumarins. The ten
compounds obtained were characterized using IR, 1H NMR, 13C NMR, elemental analysis and mass
spectrometry. Their optical properties, studied in dichloromethane by UV/vis absorption and fluores-
cence spectroscopy, were found to depend strongly upon the nature of the substituent borne by the
imino group. For the sake of comparison, the optical properties of selected compounds were also
analyzed in ethanol. Of the iminocoumarins studied, the alkylurea derivatives displayed the most
interesting spectroscopic characteristics and may be of potential use as novel fluorescent probes in media
of various polarity.
Received 9 June 2009
Received in revised form
7 July 2009
Accepted 8 July 2009
Available online 14 July 2009
Keywords:
Iminocoumarin
Bis-iminocoumarin
C-electrophile
Fluorescence
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
fragment in order to elaborate novel materials for applications
based on their optical properties [31–37]. It rapidly appeared that
It is well documented that coumarins are nowadays an impor-
tant group of fluorescent organic compounds [1–7]. They are used
as optical brightening agents and laser dyes, they provide enzyme
substrates for fluorimetric titrations in biomedical analysis, and are
at the basis of numerous fluorescent probes and advanced photo-
physical systems. In contrast, the 2-imino analogues have received
little attention. They have been used for a long time as precursors of
coumarins [8–15] and closely related structures [16]. It has also
been shown that iminocoumarins functionalized at the 3-position
can be used as starting materials to obtain novel heterocyclic
compounds consisting of a benzopyrane moiety fused with pyr-
azole [17], naphthyridine [18], quinoline [18], quinazoline [19,20]
and pyrimidine rings [21–25]. It also appeared more recently that,
besides their obvious interest in heterocyclic synthesis, some imi-
nocoumarins exhibit attractive optical properties [26,27], leading to
nice applications in the field of fluorescent sensors [28,29] and dye-
sensitized solar cells [30]. These compounds offer the distinct
advantage to be easily modified by substitution on the imino group
and they can be adapted for particular applications. Our group
has been working for many years on the synthesis of various
original structures incorporating a coumarinic or iminocoumarinic
3-cyano-7-diethylamino-iminocoumarin (1, Scheme 1) was of
particular interest owing to its excellent fluorescence properties,
similar to those of the corresponding coumarin [35]. As it is
important to know whether these properties are retained after
substitution of the imino group, a systematic study was under-
taken. It showed that the nature of the substituent introduced on
the imino group is indeed of major importance for the spectro-
scopic behaviour of the compound obtained. This means that the
type of coupling used to graft the fluorescent moiety 1 on
a
substrate is determinant for subsequent applications. For
instance, the N-ethoxycarbonylated derivative obtained by reacting
1 with ethylchloroformate as C-electrophilic reagent, was highly
fluorescent [34,35]. Similarly, among the various N-acylated
analogues that were prepared using acid chlorides [36], those
bearing an aryl group directly linked to the ]N–CO– group showed
good fluorescence efficiency in different solvents, and could thus be
used as fluorescent tracers in different media. In contrast, the
derivatives bearing an alkyl group on the imido function were
strongly fluorescent in dichloromethane, but emitted very weakly
in a polar and protic medium such as ethanol. Consequently, we
proposed their use for the fluorescent staining of biological
membranes.
As a continuation of this investigation, it was decided to explore
the effect of other types of substitution of the imino group. To do so,
a series of novel, 3-cyano-7-(diethylamino)-iminocoumarins were
* Corresponding author. Tel.: þ33 5 61 55 68 05; fax: þ33 5 61 55 81 55.
E-mail address: sff@chimie.ups-tlse.fr (S. Fery-Forgues).
0143-7208/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2009.07.003

M. Fakhfakh et al. / Dyes and Pigments 84 (2010) 108–113
109
using the classical formula: Fx ¼ (As ꢁ Fx ꢁ n2x ꢁ Fs)/(Ax ꢁ Fs ꢁ ns2)
where A is the absorbance at the excitation wavelength, F the area
under the fluorescence curve, and n is the refractive index of the
solvents used. Subscripts s and x refer to the standard and to the
sample of unknown quantum yield, respectively. Coumarin 6 in
O
C
CN
NH
H
EtOH
+ NC-CH2-CN
Piperidine
Et2N
OH
Et2N
O
1
ethanol (
F
¼ 0.78) was taken as the standard [38]. Fluorescence
decay was measured with the stroboscopic technique using
a Strobe Master fluorescence lifetime spectrophotometer from PTI.
The excitation source was a flash lamp filled with a mixture of
nitrogen and helium (30/70). Data were collected over 200 chan-
nels with a time-base of 0.1 ns per channel. Analysis of fluores-
cence decay was performed using the multiexponential method
software from PTI.
CN
O
N
C
O
NH R
Et2N
RNCO
2-8
1
CN
N
OCN-R-NCO
O
2.2. Materials
Et2N
O
C
O
NH
R
N
C
N
O
NEt2
H
For synthesis, acid chlorides, isocyanates and di-isocyanates
were purchased from Aldrich. For spectroscopic measurements,
analytical grade dichloromethane was from Prolabo and ethanol
was from SDS.
NC
9-11
OCH3
R =
CH3
2.3. General procedure for the synthesis of iminocoumarin
2
3
4
and bis-iminocoumarin derivatives 2–11
CH3
CH3 CH
3-Cyano-7-(diethylamino)-iminocoumarin 1 was synthesized as
reported previously [33] using the Knoevenagel protocol. Subse-
quently, isocyanate (12 mmol) or diisocyanate (7 mmol)) diluted in
2 ml of chloroform was added dropwise, over 30 min, to a stirred
solution of 10 mmol of 1 in 30 ml of chloroform at 0 ꢀC. The basic
medium was then allowed to reach room temperature. The mixture
was kept under stirring at 20 ꢀC during 30 min (compounds 2, 4, 9
and 10), 45 min (3, 5, 7 and 8), 1 h (11) or 1 h30 (6). The products
obtained were separated by filtration and then washed with
methanol and dried before being characterized.
CH3
CH
CH3
CH3
CH2 CH3
CH
CH3
5
6
7
8
CH3
CH3
CH2
(CH2)4
9
10
11
Scheme 1. Synthesis and chemical structure of compounds 1–11.
The compounds were examined by TLC on silica plates using
chloroform as eluent. Most of them showed a single spot under
excitation at 365 nm. A small amount of compound was system-
atically purified by TLC prior to spectroscopic work.
prepared by condensation of 1 with C-electrophilic reagents such as
isocyanates and diisocyanates. The urea derivatives of seven imi-
nocoumarins and three bis-iminocoumarins were obtained, the
urea group bearing various alkyl and aryl group. The optical prop-
erties of these compounds solubilised in dichloromethane were
studied and compared.
2.3.1. 1-[3-Cyano-7-(diethylamino)-2H-chromen-2-ylidene]-3-
phenylurea (2)
Yield: 86%. m.p. 195 ꢀC. 1H NMR (300 MHz, CDCl3):
d
¼ 1.23
(t, J ¼ 7.0 Hz, 6H, 2 ꢁ CH3), 3.43 (q, J ¼ 7.0 Hz, 4H, 2 ꢁ CH2), 6.49
(d, J ¼ 2.4 Hz, 1H, H8), 6.60 (dd, J ¼ 9.0 Hz, J ¼ 2.4 Hz, 1H, H6), 7.08
(m, 1H, Ph), 7.13 (m, 2H, Ph), 7.23 (d, J ¼ 9.0 Hz, 1H, H5), 7.62 (m, 2H,
Ph), 7.81 (s, 1H, H4), 8.22 (s, 1H, NH). 13C NMR (75 MHz, DMSO):
2. Experimental
2.1. Apparatus
d
¼ 12.62 (CH3), 44.67 (CH2), 92.11 (C3), 96.65 (C8), 106.63 (C6),
Melting points were determined by an Electrothermal 9100
apparatus. Infrared spectra were recorded on a Jasco FT-IR 420
spectrophotometer apparatus (in KBr pellets). 1H and 13C NMR
spectra were obtained with a Bruker WP 200 spectrometer oper-
ating at 300 and 75 MHz, respectively, in CDCl3 or DMSO-d6 with
TMS as internal standard (chemical shifts in ppm). Elemental
microanalyses were performed on an EA1112 analyser from CE
Instruments. Mass spectrometry (CI) was performed on a DSQII
ThermoFisher spectrometer using DCI/NH3 as the ionization mode
(positive mode).
All spectrophotometric measurements were conducted at 25 ꢀC
using a temperature-controlled cell holder. UV/vis absorption
spectra were recorded on a Hewlett–Packard 8452A diode array
spectrophotometer. The estimated experimental error was 2 nm
on the band maximum. Steady state fluorescence work was per-
formed on a Photon Technology International (PTI) Quanta Master
1 spectrofluorometer. All excitation and emission spectra were
109.97 (C10), 116.41 (C^N), 118.95 (Ph), 122.98 (Ph), 129.05 (Ph),
131.52 (C5), 139.92 (Ph), 148.73 (C7), 149.90 (C4), þ153.06 (C9),
156.23 (C2), 157.47 (C]O). IR (KBr) cmꢂ1
:
n
¼ 1656 (C]N), 1685
(C]O), 2225 (C^N), 3344 (NH). Anal. Calcd. for C21H20N4O2: C,
69.98; H, 5.59; N, 15.54%. Found: C, 68.90; H, 5.33; N, 13.99%. MS:
361.1 (M þ Hþ).
2.3.2. 1-[3-Cyano-7-(diethylamino)-2H-chromen-2-ylidene]-3-
p-tolylurea (3)
Yield: 82%. m.p. 188 ꢀC. 1H NMR (300 MHz, CDCl3):
d
¼ 1.23
(t, J ¼ 7.2 Hz, 6H, 2 ꢁ CH3), 2.33 (s, 3H, CH3-Ph), 3.43 (q, J ¼ 7.2 Hz,
4H, 2 ꢁ CH2), 6.48 (d, J ¼ 2.4 Hz, 1H, H8), 6.57 (dd, J ¼ 10.5 Hz,
J ¼ 2.4 Hz,1H, H6), 7.14 (d, J ¼ 9.6 Hz, 2H, Ph), 7.22 (d, J ¼ 10.5 Hz,1H,
H5), 7.49 (d, J ¼ 9.6 Hz, 2H, Ph), 7.77 (s, 1H, H4), 8.62 (s, 1H, NH). 13
C
NMR (75 MHz,DMSO):
d
¼ 12.22 (CH3), 20.91 (CH3-Ph), 44.82 (CH2),
92.52 (C3), 96.22 (C8), 106.17 (C6), 109.56 (C10),115.98 (C^N),128.98
(Ph), 129.59 (Ph), 131.11 (C5), 131.37 (Ph)), 136.91 (Ph), 148.33
(C7), 149.26 (C4), 152.65 (C9), 155.82 (C2), 156.82 (CO). IR (KBr)
corrected. The fluorescence quantum yields (F) were determined

110
M. Fakhfakh et al. / Dyes and Pigments 84 (2010) 108–113
cmꢂ1
:
n
¼ 1660 (C]N), 1695 (C]O), 2229 (C^N) 3330 (NH). Anal.
2.3.7. 1-[3-Cyano-7-(diethylamino)-2H-chromen-2-ylidene]-3-
isopropylurea (8)
Yield: 71%. m.p. 192 ꢀC. 1H NMR (300 MHz, CDCl3):
Calcd. for C22H22N4O2: C, 70.57; H, 5.92; N, 14.96%. Found: C, 69.90;
H, 5.33; N, 13.99%. MS: 375.1 (M þ Hþ).
d
¼ 1.09 (t,
J ¼ 6.9 Hz, 6H, 2 ꢁ CH3), 1.10 (d, J ¼ 6.6 Hz, 6H, 2 ꢁ CH3(iPr)), 3.40 (q,
J ¼ 6.9 Hz, 4H, 2 ꢁ CH2), 3.81 (m, J ¼ 6.6 Hz, 1H, CH(iPr)), 6.22 (s, 1H,
H8), 6.64 (d, J ¼ 8.4 Hz, 1H, H6), 7.37 (d, J ¼ 8.4 Hz, 1H, H5), 7.39 (s,
2.3.3. 1-[3-Cyano-7-(diethylamino)-2H-chromen-2-ylidene]-3-
(3-methoxyphenyl)urea (4)
Yield: 90%. m.p. 126 ꢀC. 1H NMR (300 MHz, CDCl3):
d
¼ 1.07
1H, NH), 8.21 (s, 1H, H4). 13C NMR (75 MHz, DMSO):
23.42 (CH3(iPr)), 41.80 (CH(iPr)), 44.85 (CH2), 93.57 (C3), 96.54 (C8),
d
¼ 12.74 (CH3),
(t, J ¼ 6.9 Hz, 6H, 2 ꢁ CH3), 3.42 (q, J ¼ 6.9 Hz, 4H, 2 ꢁ CH2), 3.71 (s,
3H, OCH3), 6.36 (d, J ¼ 1.2 Hz, 1H, H8), 6.58 (d, J ¼ 6.9 Hz, 1H, Ph),
6.73 (dd, J ¼ 9.0 Hz, J ¼ 1.2 Hz, 1H, H6), 7.16–7.21 (m, 2H, Ph), 7.31 (s,
1H, Ph), 7.42 (d, J ¼ 9.0 Hz, 1H, H5), 8.35 (s, 1H, H4), 9.79 (s, 1H, NH).
106.57 (C6), 109.70 (C10), 116.56 (C^N), 131.51 (C5), 148.18 (C7),
148.87 (C4), 152.91 (C9), 156.33 (C2), 159.03 (CO). IR (KBr) cmꢂ1
:
n
¼ 1654 (C]N), 1691 (C]O), 2231 (C^N) 3359 (NH). Anal. Calcd.
13C NMR (75 MHz, DMSO):
d
¼ 12.82 (CH3), 44.82 (CH2), 55.46
for C18H22N4O2: C, 66.24; H, 6.79; N,17.17%. Found: C, 66.90; H, 5.33;
(OCH3), 93.00 (C3), 96.84 (C8), 104.99 (C6), 106.23 (Ph), 108.42 (Ph),
110.21 (C10), 111.47 (Ph), 116.57 (C^N), 130.01 (C5), 131.73 (Ph),
141.23 (Ph), 149.04 (C7), 150.01 (C4), 153.28 (C9), 156.41 (C2), 157.50
N, 15.99%. MS: 327.1 (M þ Hþ).
2.3.8. 1-(4-Methyl-1,3-phenylene)bis[3-(3-cyano-7-
(diethylamino)-2H-chromen-2-ylidene]urea) (9)
(Ph), 160.08 (CO). IR (KBr) cmꢂ1
:
n
¼ 1652 (C]N), 1690 (C]O), 2226
(C^N), 3356 (NH). Anal. Calcd. for C22H22N4O3: C, 67.68; H, 5.68; N,
14.35%. Found: C, 66.90; H, 5.33; N, 13.99%. MS: 391.1 (M þ Hþ).
Yield: 81%. m.p. 233 ꢀC. 1H NMR (300 MHz, CDCl3):
d
¼ 1.05 (t,
J ¼ 6.9 Hz,12H, 2 ꢁ CH3), 2.24 (s, 3H, CH3-Ph), 3.39 (q, J ¼ 6.9 Hz, 8H,
2 ꢁ CH2), 6.32 (s, 2H, 2 ꢁ H8), 6.66 (d, J ¼ 8.7 Hz, 2H, 2 ꢁ H6), 7.13 (d,
J ¼ 8.4 Hz, 1H, Ph), 7.24 (d, J ¼ 8.4 Hz, 1H, Ph), 7.39 (d, J ¼ 8.7 Hz, 2H,
2.3.4. 1-[3-Cyano-7-(diethylamino)-2H-chromen-2-ylidene]-3-
(4-isopropylphenyl)urea (5)
2 ꢁ H5), 7.89 (s, 1H, Ph), 8.26 (s, 2H, 2 ꢁ H4), 9.12 (s, 2H, 2 ꢁ NH). 13
C
Yield: 80%. m.p. 195 ꢀC. 1H NMR (300 MHz, CDCl3):
d
¼ 1.05
NMR (75 MHz, DMSO):
d
¼ 12.72/12.77 (CH3), 17.78 (CH3-Ph), 44.88
(d, J ¼ 6.9 Hz, 6H, 2 ꢁ CH3(iPr)), 1.14 (t, J ¼ 6.9 Hz, 6H, 2 ꢁ CH3), 2.81
(m, J ¼ 6.9 Hz, 1H, CH(iPr)), 3.40 (q, J ¼ 6.9 Hz, 4H, 2 ꢁ CH2), 6.35 (s,
1H, H8), 6.71 (d, J ¼ 9.0 Hz, 1H, H6), 7.14 (d, J ¼ 8.4 Hz, 2H, Ph), 7.41
(d, J ¼ 9.0 Hz, 1H, H5), 7.52 (d, J ¼ 8.4 Hz, 2H, Ph), 8.33 (s, 1H, H4),
(CH2), 93.16/93.22 (C3), 96.59/96.81 (C8),106.69/106.76 (C6),109.93/
110.10 (C10), 112.61 (Ph), 114.90 (Ph), 116.15/116.56 (C^N), 126.91
(Ph), 130.71 (Ph), 131.67 (C5), 136.96 (Ph), 138.15 (Ph), 148.51/148.78
(C7), 156.38 (C4), 153.09/153.19 (C9), 156.38 (C2), 158.73 (C]O). IR
9.72 (s, 1H, NH). 13C NMR (75 MHz, DMSO):
d
¼ 12.81 (CH3), 24.52
(KBr) cmꢂ1
:
n
¼ 1653 (C]N), 1670 (C]O), 2231 (C^N), 3344 (NH).
(CH3(iPr)), 33.37 (CH(iPr)), 44.82 (CH2), 93.11 (C3), 96.81 (C8),106.76
(C6), 110.13 (C10), 116.59 (C^N), 119.18 (Ph), 126.91 (Ph), 131.71 (C5),
137.77 (Ph), 143.21 (Ph), 148.90 (C7), 149.79 (C4), 153.23 (C9), 156.42
Anal. Calcd. for C37H36N8O4: C, 67.67; H, 5.53; N, 17.06%. Found: C,
66.90; H, 5.33; N, 15.99%. MS: 657.3 (M þ Hþ).
(C2), 157.47 (CO). IR (KBr) cmꢂ1
:
n
¼ 1650 (C]N), 1680 (C]O), 2224
2.3.9. 1,1’-[4,4’-Methylenebis(4,1-phenylene)]bis{3-[3-cyano-7-
(diethylamino)-2H-chromen-2-ylidene]urea} (10)
(C^N) 3344 (NH). Anal. Calcd. for C24H26N4O2: C, 71.62; H, 6.51; N,
13.92%. Found: C, 70.90; H, 5.33; N, 13.99%. MS: 403.1 (M þ Hþ).
Yield: 75%. m.p. 220 ꢀC. 1H NMR (300 MHz, CDCl3):
d
¼ 1,09 (t,
J ¼ 6.9 Hz, 12H, 4 ꢁ CH3), 3.42 (q, J ¼ 6.9 Hz, 8H, 4 ꢁ CH2), 3.81 (s,
2H, Ph-CH2-Ph), 6.32 (s, 2H, 2 ꢁ H8), 6.68 (d, J ¼ 8.7 Hz, 2H, 2 ꢁ H6),
7.13 (d, J ¼ 7.8 Hz, 4H, Ph), 7.39 (d, J ¼ 9.0 Hz, 2H, 2 ꢁ H5), 7.53 (d,
J ¼ 7.8 Hz, 4H, Ph), 8.30 (s, 2H, 2 ꢁ H4), 9.74 (s, 2H, 2 ꢁ NH). 13C NMR
2.3.5. 1-[3-Cyano-7-(diethylamino)-2H-chromen-2-ylidene]-3-(2-
isopropyl-6-methylphenyl)urea (6)
Yield: 40%. m.p 125 ꢀC. 1H NMR (300 MHz, CDCl3):
d
¼ 1.10 (d,
J ¼ 9.0 Hz, 6H, 2 ꢁ CH3(iPr)), 1.15 (t, J ¼ 6.9 Hz, 6H, 2 ꢁ CH3), 2.60 (m,
1H, CH(iPr)), 2.77 (s, 3H, CH3-Ph), 3.40 (q, J ¼ 6.9 Hz, 4H, 2 ꢁ CH2),
6.30 (d, J ¼ 2.4 Hz, 1H, H8), 6.70 (dd, J ¼ 8.7 Hz, J ¼ 2.4 Hz, 1H, H6),
7.02 (dd, J ¼ 6.7 Hz, J ¼ 6.9 Hz, 1H, Ph), 7.35 (d, 6.7 Hz, 1H, Ph), 7.35
(d, J ¼ 8.7 Hz, 1H, H5), 7.77 (d, J ¼ 6.9 Hz, 1H, Ph), 8.29 (s, 1H, H4),
(75 MHz, DMSO):
93.11 (C3), 96.82 (C8), 106.77 (C6), 110.13 (C10), 116.57 (C^N), 129.33
d
¼ 12.80 (CH3), 44.82 (CH2), 79.68 (Ph-CH2-Ph),
(Ph), 131.69 (C5), 136.37 (Ph), 148.89 (C7), 149.91 (C4), 153.22 (C9),
156.40 (C2), 157.50 (C]O). IR (KBr) cmꢂ1
:
n
¼ 1650 (C]N), 1691
(C]O), 2229 (C^N) 3355 (NH). Anal. Calcd. for C43H40N8O4: C,
70.48; H, 5.50; N, 15.29%. Found: C, 69.90; H, 5.33; N, 13.99%. MS:
733.3 (M þ Hþ).
9.02 (s, 1H, NH). 13C NMR (75 MHz, DMSO):
d
¼ 12.83 (CH3), 20.88
(CH3-Ph), 25.62 (CH3(iPr)), 33.40 (CH(iPr)), 44.95 (CH2), 92.92 (C3),
96.77 (C8), 107.01 (C6), 110.12 (Ph), 110.16 (C10), 116.62 (C^N),
123.23 (Ph),125.65 (Ph),127.32 (Ph),130.90 (C5),132.05 (Ph),144.62
(Ph), 149.00 (C7), 149.77 (C4), 153.13 (C9), 155.22 (C2), 156.40 (CO). IR
2.3.10. 1,1’-(Butane-1,4-diyl)bis{3-[3-cyano-7-(diethylamino)-2H-
chromen-2-ylidene]urea} (11)
(KBr) cmꢂ1
:
n
¼ 1649 (C]N), 1688 (C]O), 2230 (C^N) 3349 (NH).
Yield: 88%. m.p. 265 ꢀC. 1H NMR (300 MHz, CDCl3):
d
¼ 1.09 (t,
Anal. Calcd. for C25H28N4O2: C, 72.09; H, 6.78; N, 13.45%. Found: C,
J ¼ 6.9 Hz, 12H, 4 ꢁ CH3), 1.55 (t, J ¼ 8.6 Hz, 4H, 2 ꢁ CH2), 3.15 (t,
J ¼ 8.9 Hz, 4H, 2 ꢁ CH2), 3.42 (q, J ¼ 6.9 Hz, 8H, 2 ꢁ CH2), 6.28 (s, 2H,
2 ꢁ H8), 6.67 (d, J ¼ 9.0 Hz, 2H, 2 ꢁ H6), 7.37 (d, J ¼ 9.0 Hz, 2H,
2 ꢁ H5), 7.49 (s, 2H, 2 ꢁ NH) 8.22 (s, 2H, 2 ꢁ H4). 13C NMR (75 MHz,
70.90; H, 6.33; N, 13.99%. MS: 417.2 (M þ Hþ).
2.3.6. 1-[3-Cyano-7-(diethylamino)-2H-chromen-2-ylidene]-3-
ethylurea (7)
DMSO):
d
¼ 13.00 (CH3), 40.60 (CH2), 44.90 (CH2), 94.87 (C3), 96.98
Yield: 70%. m.p. 170 ꢀC. 1H NMR (300 MHz, CDCl3):
d
¼ 1.05
(C8), 107.80 (C6), 110.15 (C10), 116.81 (C^N), 132.02 (C5), 148.88 (C7),
(t, J ¼ 6.9 Hz, 6H, 2 ꢁ CH3), 1.05 (t, J ¼ 6.8 Hz, 3H, CH3(EtNH)), 3.11
(q, J ¼ 6.8 Hz, 2H, CH2(EtNH)), 3.42 (q, J ¼ 6.9 Hz, 4H, 2 ꢁ CH2), 6.28
(d, J ¼ 1.8 Hz, 1H, H8), 6.67 (dd, J ¼ 8.7 Hz, J ¼ 1.8 Hz, 1H, H6), 7.37
(d, J ¼ 8.7 Hz, 1H, H5), 7.48 (s, 1H, NH), 8.24 (s, 1H, H4). 13C NMR
150.14 (C4), 154.13 (C9), 155.23 (C2), 157.55 (C]O). IR (KBr) cmꢂ1
:
n
¼ 1653 (C]N), 1688 (C]O), 2228 (C^N), 3350 (NH). Anal. Calcd.
for C34H38N8O4: C, 65.58; H, 6.15; N, 17.99%. Found: C, 66.20; H,
5.33; N, 16.99%. MS: 623.3 (M þ Hþ).
(75 MHz, DMSO):
d
¼ 12.80 (CH3), 25.40 (CH3(EtNH)), 40.50
(CH2(EtNH)), 44.80 (CH2), 93.48 (C3), 96.67 (C8), 106.57 (C6), 109.80
3. Results and discussion
(C10), 116.59 (C^N), 131.56 (C5), 148.34 (C7), 148.84 (C4), 153.01 (C9),
156.35 (C2), 159.57 (CO). IR (KBr) cmꢂ1
:
n
¼ 1671 (C]N), 1699
3.1. Synthesis
(C]O), 2228 (C^N), 3355 (NH). Anal. Calcd. for C17H20N4O2: C,
65.37; H, 6.45; N. 17,94%. Found: C, 66.10; H, 5.33; N, 16.99%. MS:
313.1 (M þ Hþ).
The synthetic procedure was accomplished in two steps
(Scheme 1). Firstly, 3-cyano-7-(diethylamino)-iminocoumarin 1

M. Fakhfakh et al. / Dyes and Pigments 84 (2010) 108–113
111
was prepared using the Knoevenagel condensation of 4-dieth-
0.8
100
80
60
40
20
0
a
ylamino-salicylaldehyde with an equimolecular amount of malo-
nonitrile. Secondly, its N-substitution was performed by reacting 1
with an isocyanate or diisocyanate derivative in chloroform. The
ensuing products were isolated with good purity by simple filtra-
tion. Ten new iminocoumarin and bis-iminocoumarin derivatives
were therefore prepared, all bearing one or two urea functions.
Most of these compounds were obtained in good yields around
80%. It seems that, interestingly, the presence of the diethylamino
group at the 7-position increased the reactivity of the imino group,
due to the strong electron donating effect that is transmitted by
charge transfer. Only for 6 was the yield quite small, probably
because of the steric hindrance due to the substituted aryl group.
The FTIR spectra of compounds 2–11 showed the characteristic
bands of the 3-cyanoimino moiety (C]N, C^N), together with
those specific to each N-substituent. Compared to the FTIR spec-
0.6
0.4
0.2
0
250
350
450
550
650
Wavelength (nm)
100
80
60
40
20
0
0.8
b
trum of 1 (nC]N ¼ 1650 cmꢂ1
,
nC^N ¼ 2223 cmꢂ1) [33], we noted for
N-substituted iminocoumarins that the C]N and C^N bands were
0.6
0.4
shifted toward high frequency, around 1660 and 2230 cmꢂ1
,
respectively. A new NH band appeared in the 3330–3360 cmꢂ1
region for the substituted compounds, while the band associated to
the free imino group NH in 1 (3317 cmꢂ1) disappeared. The 1H NMR
spectra of all compounds were in good agreement with the
proposed structures. It can be noticed that the peak related to NH
appeared around 7–10 ppm, while that related to the free NH group
in 1 was at 8.25 ppm [33]. The structures of the compounds were
also confirmed by 13C NMR spectroscopy and mass spectrometry.
0.2
0
250
350
450
550
650
Wavelength (nm)
4. Optical properties
Fig. 1. UV/vis absorption spectra (dotted lines), normalized fluorescence excitation and
emission spectra (plain lines) of compounds 7 (a) and 9 (b) in dichloromethane.
Concentrations: 1.8 ꢁ 10ꢂ5 M and 1.0 ꢁ 10ꢂ5 M, respectively, for absorption and
1.1 ꢁ10ꢂ6 M and 6.5 ꢁ10ꢂ7 M, respectively, for fluorescence. lem ¼ 476 nm,
lex ¼ 438 nm.
4.1. Optical properties of dyes 2–11 in dichloromethane
All compounds were first studied in dilute solution in
dichloromethane, the data being gathered in Table 1.
4.1.2. Excitation spectra
For fluorescence spectroscopy, the dye concentration was in the
10ꢂ6 M range or below, so absorbance at the excitation wavelength
was kept around 0.05. In these conditions, for all compounds, the
excitation spectrum did not vary with the emission wavelength,
indicating that there is only one emissive species in each sample.
For compounds 2–8 and 11, the excitation spectrum was superim-
posable to the absorption spectrum (see Fig. 1a for 7), showing that
the species visible on the absorption spectrum is actually respon-
sible for fluorescence. In contrast, for 9 (Fig. 1b) and 10, a discrep-
ancy of 10 nm was noticed between the excitation and the
absorption spectrum. Since the purity of the compounds was
checked by TLC, this can be explained by the presence of aggregated
molecules (although those were not detected by absorption spec-
troscopy for 9), or most likely to the presence of conformers that are
visible in the red part of the absorption spectrum, but not
fluorescent.
4.1.1. UV/vis absorption spectra
For UV/vis absorption measurements, the dye concentration
was between 1 ꢁ10ꢂ5 and 2 ꢁ10ꢂ5 M. The spectra of compounds 7
and 9 are given as an example in Fig. 1. All N-substituted imino-
coumarin derivatives showed a maximum around 440 nm, with
a shoulder more or less pronounced around 422 nm. The absorp-
tion spectra of bis-iminocoumarins 9–11 were very close to those of
the monomers. It was checked with compounds 9 and 11 that the
shape and position of these spectra, as well as the molar absorp-
tivity, did not change with concentration between 5 ꢁ10ꢂ4 M and
10ꢂ6 M. The effect of concentration was not studied on compound
10, which is not very soluble in dichloromethane. If we refer to the
unsubstituted iminocoumarin 1, which exhibits two maxima of
similar intensity at 414 and 428 nm [35], we notice that the intro-
duction of the urea group has induced a significant shift towards
long wavelengths.
Table 1
Maximum absorption wavelength (labs), maximum excitation wavelength (lex), maximum emission wavelength (lem), fluorescence quantum yield (
), radiative (kr) and non-radiative (knr) deactivation constants for compounds 2–11 in dichloromethane.
F), fluorescence lifetime
(
s
Compound
labs (nm)
lex (nm)
lem (nm)
F
s
(ns)
kr (108 sꢂ1
)
knr (108 sꢂ1
)
2
3
4
5
6
7
8
9
443
442
443
443
439
439
439
440
440
439
443
442
442
440
442
440
440
430
430
440
488
490
486
488
480
476
476
460
460
478
9.8 (ꢃ0.2) ꢁ 10ꢂ2
1.1 (ꢃ0.2) ꢁ 10ꢂ2
4.7 (ꢃ0.2) ꢁ 10ꢂ2
1.1 (ꢃ0.2) ꢁ 10ꢂ2
0.40 ꢃ 0.02
0.3 ꢃ 0.1
3.1 ꢃ 0.4
0.5 ꢃ 0.2
1.4 ꢃ 0.4
2.6 ꢃ 0.4
3.2 ꢃ 0.2
3.5 ꢃ 0.4
2.8 ꢃ 0.6
2.7 ꢃ 0.2
2.6 ꢃ 0.2
3.26
0.35
0.94
0.79
1.54
2.66
2.11
0.39
0.23
2.31
30.1
3.19
19.1
7.06
2.31
0.47
0.74
3.18
3.48
1.54
0.85 ꢃ 0.03
0.74 ꢃ 0.03
0.11 ꢃ 0.02
10
11
6.1 (ꢃ 0.2) ꢁ 10ꢂ2
0.60 ꢃ 0.03

112
M. Fakhfakh et al. / Dyes and Pigments 84 (2010) 108–113
Table 2
4.1.3. Steady-state emission spectra
Maximum absorption wavelength (labs), maximum excitation wavelength (lex),
The emission spectra of all compounds in dichloromethane
displayed only one band, without any fine structure. It did not
depend on the excitation wavelength. For compounds 2–5 bearing
an aromatic group directly fixed to the ]N–CO–NH– linker, the
emission spectrum peaked at around 488 nm. In contrast, for
compounds 7 and 8 that bear an aliphatic group, the emission
maximum was situated at shorter wavelengths. The spectrum of 6,
which bears a bulky aromatic substituent, is intermediate between
the formers.
maximum emission wavelength (lem) and fluorescence quantum yield (
compounds 6-8 and 11 in ethanol.
F) for
Compound
labs (nm)
lex (nm)
lem (nm)
F
6
7
8
11
432
433
433
430
436
436
436
436
494
490
492
492
0.32 ꢃ 0.02
0.36 ꢃ 0.02
0.37 ꢃ 0.02
>0.24 ꢃ 0.02
Among bis-iminocoumarins, it can be noted that the spectrum
of 11, where the chromophores are linked by an aliphatic chain, was
very close to that of 7 and 8. Surprisingly, compounds 9 and 10,
where the chromophores are linked by an aromatic group, emit at
lower wavelengths than the corresponding monomers.
If a comparison is drawn between compounds 2–11 and the
unsubstituted iminocoumarin 1, it can be seen that the emission
spectra of the substituted compounds were shifted to the red,
except those of 9 and 10 that peaked at exactly the same wave-
length (460 nm).
between the two groups. Concerning bis-iminocoumarins, the kr
and knr values found for 9 and 10 are very close to those found for
the analogous monomer 3, showing that in this case the bis-
coumarin structure leads to no particular effect. But, it is note-
worthy that the kr value for 11 is similar to that found for 7 and 8,
while the knr value was increased. This indicates that new deacti-
vation pathways are opened. This can be due to the overlapping of
both chromophores, which is allowed by the flexibility of the linker,
and leads to the formation of a non-fluorescent intramolecular
excimer. This hypothesis is in line with different studies, which
have shown that such an overlapping actually takes place in bis-
coumarins where the chromophores are connected by aliphatic
chains having 4–8 carbon atoms [39–42].
4.1.4. Fluorescence quantum yields
Concerning the fluorescence quantum yields, the compounds
can be obviously divided in two groups. The alkyl-substituted
compounds
7 and 8 exhibited high fluorescence efficiency
(
F
¼ 0.85 and 0.74, respectively), while the aryl-substituted
4.2. Optical properties of selected compounds in ethanol
compounds 2–5 were less emissive by at least one order of
magnitude.
The spectroscopic study in dichloromethane revealed that
among the compounds investigated, iminocoumarins 6–8 and bis-
iminocoumarin 11 displayed attractive fluorescence properties.
Then, it seemed interesting to us to investigate rapidly the behav-
iour of these compounds in a protic and polar solvent such as
ethanol. The data are gathered in Table 2.
Interestingly, compound 6 was much more emissive than the
other compounds substituted by an aromatic group. This can be
attributed to the strong steric hindrance that may force the
compound in a given conformation or impede free rotation of the
phenyl group.
For bis-iminocoumarin 11, the quantum yield was weaker than
for the monomeric homologues 7 and 8. Regarding now the two
other bis-iminocoumarins 9 and 10, they just behave like the aryl-
substituted homologues 2–5.
It appears that absorption was slightly shifted to short wave-
lengths when passing from dichloromethane to ethanol. Mean-
while, emission was shifted to the red, as normally happens with
this type of compounds, which are sensitive to solvent polarity [34].
Interestingly, all four dyes remain fluorescent in ethanol, meaning
that they could be used as fluorescent tags in media of different
polarity. Note that bis-iminocoumarin 11 was poorly soluble in
ethanol and despite careful filtration, some aggregates may remain
in suspension. Consequently, the actual quantum yield could be
higher than the one indicated here.
4.1.5. Fluorescence lifetimes and deactivation constants
All fluorescence decays measured were monoexponential. The
fluorescence lifetimes varied from several nanoseconds for most of
the compounds to the sub-nanosecond range for 2 and 4. Note that
below 0.7 ns, the values given by our apparatus lack precision and
must be considered with circumspection.
Having determined the fluorescence quantum yield and lifetime
values, the radiative (kr) and non-radiative (knr) deactivation
5. Conclusions
constants were calculated from the classical formula: kr ¼
F/s and
knr ¼ (1 ꢂ )/ (Table 1). Let us recall that, very schematically, a high
F
s
It can be seen in this work that the Knoevenagel-type method
used for synthesis is simple to implement. It allows substituted
iminocoumarins to be obtained with good yields and high selec-
tivity. From a spectroscopic point of view, it was interesting to see
that the nature of the substituent borne by the ]N–CO–NH- linker
strongly governs the behaviour of the compound. This result is
intriguing because the ]N–CO–NH- group was not expected to
transmit the effect of the substituent to the chromophore.
A comparison can be made with the results obtained in
a previous work [36] about N-acyliminocoumarin derivatives,
where the substituents were borne by a ]N–CO- linker. Such
a difference between aromatic and aliphatic substituents was not
encountered in dichloromethane, differences only appearing in
a protic solvent like ethanol. Besides, the N-acyl derivatives directly
substituted by an aromatic group exhibited much better fluores-
cence efficiency than the alkyl derivatives, contrary to what was
observed here. This comparison confirms that the nature of the
modifications brought to the imino group is very important for
value for kr indicates that the energy levels of the molecule are
compatible with high fluorescence efficiency, whereas a high value
for knr suggests that molecular rotations or vibrations, or inter-
molecular interactions, open non-radiative deactivation channels
that compete with fluorescence. In the present case, the analysis of
the photophysical constants reveals that kr decreases and knr
increases markedly when passing from the alkyl-substituted
compounds 7 and 8 to the aryl-substituted compounds 3–5 (The
results obtained for 2 were discarded because of the large uncer-
tainty on the lifetime measurement). This indicates that the loss of
fluorescence efficiency observed with the aryl-substituted
compounds can be attributed to both a disturbance of the energy
levels and a rotation phenomenon that dissipates the excitation
energy. It can be noted for compounds 2 and 4 that the knr value is
particularly high, suggesting that rotation of the phenyl group
actually plays a major role in deactivation of these compounds.
Compound 6, where rotation is probably impeded, is intermediate

M. Fakhfakh et al. / Dyes and Pigments 84 (2010) 108–113
113
[18] O’Callaghan CN, McMurry TBH, O’Brien JE, Draper SM, Wilcock DJ. J Chem Soc
Perkin Trans 1 1996:1067.
[19] Bilokin YV, Kovalenko SN, Bylov IE, Chernykh VP. Heterocycl Commun
1998;4:257.
subsequent use of the compound, and justifies this type of
investigations.
[20] Kovalenko SM, Vlasov SV, Silin OV, Chernykh VP. J Sulfur Chem 2009;30:53.
[21] O’Callaghan CN, Roy P. Irish Acad 1973;73(B):291.
[22] Borisov AV, Dzhavakhishvili SG, Zhuravel IO, Kovalenko SM, Nikitchenko VM. J
Comb Chem 2007;9:5.
[23] Gorobets NYu, Abakumov VV. Chem Heterocycl Compd 2002;38:1518
[Translation of Khim. Geterotsik. Soedin.].
Acknowledgment
We would like to thank one of the reviewers who kindly helped
us for the nomenclature of our compounds.
[24] Gorobets NYu, Abakumov VV, Borisov AV, Nikitchenko VM. Chem Heterocycl
Compd 2004;40:334 [Translation of Khim. Geterotsik. Soedin.).
[25] Kammoun M, Turki H, Fery-Forgues S, El Gharbi R. Synthetic Commun, in
Press.
References
[1] Christie RM. Rev Prog Color 1993;23:1.
[26] Karasyov AA, Sizova ZA, Doroshenko AO, Maslov VV, Lukatskaya LL,
Rubtsov MI. Funct Mater 2002;9:242.
[2] Krasovitskii BM, Bolotin BM. Organic luminescent materials. Weinheim: VCH;
1988. p. 139–44.
[27] Samsonova LG, Selivanov NI, Gadirov RM, Ishchenko VV, Khilya OV. J Struct
Chem 2007;48:782.
[3] Drexhage KH. Dye lasers. In: Schafer FP, editor. Topics in applied physics 1.
Berlin: Springer; 1973.
[28] Komatsu K, Urano Y, Kojima H, Nagano T. J Am Chem Soc 2007;129:13447.
[29] Liepouri F, Deligeorgiev TG, Veneti Z, Savakis C, Katerinopoulos HE. Cell
Calcium 2002;31:221.
[30] Kandavelu V, Huang HS, Jian JL, Yang TCK, Wang KL, Huang ST. Sol Energy
2009;83:574.
[31] Mhiri C, El Gharbi R, Le Bigot Y. Synthetic Commun 1999;29:3385.
[32] Ammar H, Fakhfakh M, Le Bigot Y, El Gharbi R. Synthetic Commun
2003;33:1821.
[33] Turki H, Abid S, Le Bigot Y, Fery-Forgues S, El Gharbi R. Synthetic Commun
2004;34:3553.
[4] Schwander H, Hendrix P. In: Yamamoto YS, editor. Ulmann’s Encyclopedia of
Industrial Chemistry. 5th ed., vol. A11. Weinheim: VCH; 1988. p. 280–1.
[5] Zahradnik M. The production and application of fluorescent brightening
agents. New York: Wiley and Sons; 1992.
[6] Maeda M. Laser dyes. New York: Academic Press; 1994.
[7] Wagner BD. Molecules 2009;14:210.
[8] Schiemenz GP. Chem Ber 1962;95:485.
[9] Kovalenko SM, Vlasov SV, Chernykh VP. Heteroatom Chemistry 2007;18:341.
[10] Kovalenko SM, Vlasov SV, Chernykh VP. Synthesis 2006:847.
[11] Kovalenko SN, Sytnik KM, Nikitchenko VM, Rusanova SV, Chernykh VP,
Porokhnyak AO. Chem Heterocycl Compd 1999;35:167.
[12] Khilya OV, Shablykina OV, Frasinyuk MS, Ishchenko VV, Khilya VP. Chem Nat
Compd 2005;41:523.
[13] Rusanova SV, Zhuravel IA, Kovalenko SN, Chernykh VP, Baumer VN. Chem
Heterocycl Compd 2004;40:1323 [Translation of Khim. Geterotsik. Soedin.].
[14] Deligeorgiev T, Tsetkova T, Ivanova D, Timtcheva I. Color Technol
2008;124:195.
[34] Turki H, Abid S, El Gharbi R, Fery-Forgues SCR. Chimie 2006;9:1252.
[35] Turki H, Abid S, Fery-Forgues S, El Gharbi R. Dyes Pigments 2007;73:311.
[36] Fakhfakh M, Turki H, Abid S, El Gharbi R, Fery-Forgues S. J Photochem Pho-
tobiol A 2007;185:13.
[37] Kammoun M, Turki H, El Gharbi R, Fery-Forgues S.
2009;46:28.
J Heterocycl Chem
[38] Reynolds GA, Drexhage KH. Opt Commun 1975;13:222.
[39] Leenders LH, Schouteden E, De Schryver FC. J Org Chem 1973;38:957.
[40] Chen Y, Hong RT. J Polym Res 1994;1:285.
[15] Kovalenko SM, Bylov IE, Sytnik KM, Chernykh VP, Bilokin YV. Molecules
2000;5:1146.
[41] Compernolle F, De Schryver FC. Org Mass Spectrom 1976;11:844.
[42] Compernolle F, Schouteden E, De Schryver FC. Org Mass Spectrom
1977;12:226.
[16] Roudier JF, Foucaud A. Synthesis 1984:159.
[17] Borisov AV, Gorobets NYu, Yermolayev SA, Zhuravel’ IO, Kovalenko SM,
Desenko SM. J Comb Chem 2007;9:909.