The synthesis and optical characterization of novel iminocoumarin derivatives

Article abstract of DOI:10.1016/j.dyepig.2009.10.020

A series of novel long-wavelength, fluorescent, novel iminocoumarin derived dyes were synthesized by extending the π-conjugation and spatial location of the benzimidazolic and iminochromene rings in a planar structure. Several dyes display a fluorescent maxima ≥600?nm whilst others showed fluorescent maxima in the NIR region.

Full text of DOI:10.1016/j.dyepig.2009.10.020

Dyes and Pigments 86 (2010) 6e14
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
The synthesis and optical characterization of novel iminocoumarin derivatives
,
b
a
b
c
Sheng-Tung Huang a , Jia-Liang Jian , Huai-Zu Peng , Kun-Li Wang , Chun-Mao Lin ,
*
Chih-Hung Huang a, Thomas C.-K. Yang b
a Institute of Biotechnology, National Taipei University of Technology, Taipei, Taiwan
b Institute of Chemical Engineering, National Taipei University of Technology, Taipei, Taiwan
c College of Medicine, Taipei Medical University, Taipei, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel long-wavelength, fluorescent, novel iminocoumarin derived dyes were synthesized by
Received 10 August 2009
Received in revised form
22 October 2009
Accepted 25 October 2009
Available online 11 November 2009
extending the
p-conjugation and spatial location of the benzimidazolic and iminochromene rings in
a planar structure. Several dyes display a fluorescent maxima ꢀ600 nm whilst others showed fluorescent
maxima in the NIR region.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Iminocoumarins
Benzopyran dyes
Long-wavelength fluorescent dyes
Chromene
Benzimidazole
Near-infrared region dyes
1. Introduction
to excite the long-wavelength dyes allows the possibility of using
a low-cost excitation light source [6]. However, the full potential of
Fluorescence has long been viewed as a powerful tool for basic
research in the biological sciences, for instance in the development
of new drugs, the assurance of food safety and environmental
quality as well as the clinical diagnosis of diseases, owing to its high
resolution and sensitivity [1]. Recent breakthroughs in fluorescence
microscopy are producing notable improvements in imaging
resolution [2,3]. Such technical advances should have a major
positive impact on the emerging field of cell imaging using single-
molecule methods and help merge the subdisciplines of cell and
molecular biology [4,5]. Bright, long-wavelength (lem > 600 nm)
fluorescent dyes, which emit light in the red or near-infrared (NIR)
region, have recently enjoyed interest as luminescent dyes and as
fluorescent probes for biomolecules. The demand for fluorescent
dyes with a spectral range between 600 and 900 nm has grown
[2e5]. Employing long-wavelength dyes in biological imaging
significantly reduces the background signal due to the lowest
autoabsorption and autofluorescence of biomolecules in the
long-wavelength region of the spectrum. In addition, the low light
scattering and deep penetration of long-wavelength light required
many of these new imaging methods will only be achieved
depending upon the availability of suitable dyes.
Fluorescent coumarin derivatives have been widely used in
many applications from cell biology, medical analysis, lasers,
sensors, to the advanced photophysical systems [7,8]. In contrast,
very few reports have been carried out on the neighboring series
of iminocoumarin dyes. Of the reported iminocoumarin deriva-
tives, the iminocoumarin moiety has been incorporated as
a fluorescence signaling unit in Ca2þ, Zn2þ, or Hþ indicators
[9e11]. In these reports, the molecular structure of these
iminocoumarin moieties incorporate a push-pull functionality,
the N,N-dialkylamino group at the 7-pointion is an electron
donor, while an electron withdrawing group, such as the benz-
imidazole fragment at the 3-position, enhances the fluorescence
efficiency [12]. Despite the spectacular successes that have been
achieved using coumarin or iminocoumarin derived fluorophores
in contemporary pure and applied science; most of these fluo-
rophores illuminate in the blue green region which might limit
these dyes for use in biological applications. Many biological
samples fluoresce on their own, typically in the blue green region
of the spectrum; thus this would interfere with the fluorescence
signals generated from the coumarin or iminocoumarin derived
fluorophores.
* Corresponding author. Tel.: þ886 02 2771 2171; fax: þ886 02 2731 7117.
E-mail address: ws75624@ntut.edu.tw (S.-T. Huang).
0143-7208/$ e see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2009.10.020

S.-T. Huang et al. / Dyes and Pigments 86 (2010) 6e14
7
The iminocoumarin derived fluorophores are known for their
2.2.1. N,N-Diethyl-7-[(4-nitropheyl)imino]-7H-chromeno
high fluorescence ability and efficient quantum yield [12]. The
3-benzimidazol-2-yl-2-iminocoumarin structure 1 is an exten-
sively employed synthon for the preparation of new fluorophores
(Fig. 1). Recently, several groups reported the condensation
reaction between the aromatic aldehydes with 3-benzimidazol-
2-yl-2-iminocoumarin to produce a rigid molecular structure 2
[13,14], or condensed the same synthon with malononitrile to
produce a rigid benzopyran 3 [15] (Fig. 1). However, the fluores-
cence peaks of both the 2 and 3 structural derivatives still fall
short of the long-wavelength region of the spectrum which thus
limited their biomedical applications. Our group recently reported
the synthesis and evaluation of several 3-benzimidazol-2-yl-
2-iminocoumarin derivatives for the dye-sensitized solar cell
applications [16]. We were interested in further exploring the
chemistry of 3-benzimidazol-2-yl-2-iminocoumarin and have
synthesized a series of conformational restricted derivatives i.e.
dyes 4, 5, 6 and 7 (Fig. 2). We envisioned that the spatial fixation
of the benzimidazolic and chromene rings into a planar structure
would enhance electron flow within the conjugated ring system.
Furthermore, we also introduced various electron withdrawing
groups to the C]N group of 3, 4, and 5 to enhance the push-pull
effect on the molecules. We believed that introducing these
structural modifications onto the 3-benzimidazol-2-yl-2-imino-
coumarin could create new fluorophores that would emit in the
long-wavelength region of the spectrum. In this paper, we report
the synthesis of 4, 5, 6 and 7 and also the evaluation of their
optical properties.
[20, 30: 4, 5] pyrimido [1, 6-a] benzimidazol-3-amine (4a)
Red solid (54% yield) m.p. > 300 ꢁC. FT-IR v/cmꢂ1 ¼ 2975, 2929,
2871, 1643, 1596, 1553, 1527, 1505, 1427, 1333, 1266, 1234, 1204,
1181, 1135, 1113, 1080, 1005 cmꢂ1 1H NMR (500 MHz, CDCl3):
.
d
¼ 8.71 (d, J ¼ 7.9 Hz, 1H), 8.67 (s, 1H), 8.28 (d, J ¼ 8.9 Hz, 2H), 7.85
(d, J ¼ 7.9 Hz, 1H), 7.51e7.42 (m, 3H), 7.38 (d, J ¼ 8.9 Hz, 2H), 6.76
(dd, J ¼ 9.0, 2.3 Hz, 1H), 6.68 (d, J ¼ 2.3 Hz, 1H), 3.49 (q, J ¼ 7.1 Hz,
4H), 1.27 (t, J ¼ 7.1 Hz, 6H). 13C NMR (125 MHz, CDCl3):
d
¼ 162.1,
156.3, 155.0, 153.3, 145.7,145.0, 144.6,143.4, 136.9, 131.2,131.1, 125.1,
124.7, 124.0, 123.8, 118.9, 116.6, 111.4, 110.3, 104.3, 97.5, 45.4, 12.4.
HRMS-ESI (m/z): [M þ 1] For C27H22N6O3, 478.1753 calcd; 479.1855
found.
2.2.2. N,N-Dibutyl-7-[(4-nitropheyl) imino]-7H-chromeno
[20, 30: 4, 5] pyrimido [1, 6-a] benzimidazol-3-amine (4b)ꢂ1
Red solid (61% yield) m.p. 244e246 ꢁC. FT-IR v/cm ¼ 2957,
2929, 2871, 1639, 1595, 1553, 1525, 1505, 1484, 1421, 1332, 1276,
1218, 1136, 1111, 1097 cmꢂ1
.
1H NMR (500 MHz, CDCl3):
d
¼ 8.70
(d, J ¼ 8.0 Hz, 1H), 8.66 (s, 1H), 8.28 (d, J ¼ 8.9 Hz, 2H), 7.84
(d, J ¼ 8.0 Hz, 1H), 7.49e7.41 (m, 3H), 7.38 (d, J ¼ 8.9 Hz, 2H), 6.72
(dd, J ¼ 9.0, 2.2 Hz, 1H), 6.63 (d, J ¼ 2.2 Hz, 1H), 3.39 (t, J ¼ 7.8 Hz,
4H), 1.66e1.60 (t, J ¼ 7.2, 4H), 1.43e1.36 (m, 4H), 0.99 (t, J ¼ 7.3 Hz,
6H). 13C NMR (125 MHz, CDCl3):
d
¼ 162.1, 156.2, 155.0, 153.7, 145.7,
144.9,143.4, 136.9,131.2,130.9, 125.1,124.7,124.0,123.7, 118.9,116.6,
111.5, 110.3, 104.1, 97.6, 51.5, 29.3, 20.2, 13.9. HRMS-ESI (m/z):
[M þ 1] For C31H30N6O3, 534.2379 calcd; 535.2457 found.
2.2.3. 4-{[3-Diethylamino]-7H-chromeno [20, 30: 4, 5] pyrimidol
[1, 6-a] benzimidazol-7-ylidene] amino} benzonitrile (4c)
Red solid (65% yield) m.p. > 300 ꢁC. FT-IR v/cmꢂ1 ¼ 2974, 2932,
2870, 2214, 1631, 1603, 1555, 1524, 1508, 1492, 1424, 1338, 1276,
1264, 1232, 1200, 1184, 1167, 1133, 1112, 1080, 1012 cmꢂ1. 1H NMR
2. Experimental
2.1. Apparatus and chemicals
(500 MHz, CDCl3):
d
¼ 8.71 (d, J ¼ 8.0 Hz, 1H), 8.66 (s, 1H), 7.85
1H and 13C NMR were obtained on a Bruker AMX-500 spec-
trometer; chemical shifts are reported in ppm relative to tetrame-
thylsilane (d units). Electrospray ionization (ESI) was preformed at
the Analytical Facility of The National Taiwan University. All
chemicals were purchased from Acros, Aldrich or TCI and used
without future purification. The iminocoumarin 1aeb, dyes 3aeb
and 5a were prepared according to the published procedures
[15e19]. Various phenyl isocyanide dichlorides derivatives were
prepared in two steps according to known procedures [20].
(d, J ¼ 8.0 Hz, 1H), 7. 67(d, J ¼ 8.4 Hz, 2H), 7.51e7.41 (m, 3H), 7.35
(d, J ¼ 8.4 Hz, 2H), 6.75 (dd, J ¼ 9.1, 2.3 Hz, 1H), 6.68 (d, J ¼ 2.3 Hz,
1H), 3.49 (q, J ¼ 7.1 Hz, 4H), 1.27 (t, J ¼ 7.1 Hz, 6H). 13C NMR
(125 MHz, CDCl3):
d
¼ 162.0, 156.2, 153.2, 152.7, 145.7, 144.8, 144.6,
136.7, 132.8, 131.3, 131.0, 125.0, 124.1, 124.0, 120.0, 118.9, 116.7, 111.3,
110.3, 105.9, 104.5, 97.5, 45.4, 29.7, 12.4. HRMS-ESI (m/z): [M þ 1]
For C28H22N6O, 458. 1855 calcd; 459.1975 found.
2.2.4. 4-{[3-Dibutylamino]-7H-chromeno [20, 30: 4, 5] pyrimidol
[1, 6-a] benzimidazol-7-ylidene] amino} benzonitrile (4d)ꢂ1
Red solid (65% yield) m.p. 256e258 ꢁC. FT-IR v/cm ¼ 2957,
2931, 2870, 2218, 1636, 1601, 1554, 1527, 1507, 1443, 1421, 1338,
2.2. General procedures for preparing dyes 4aej
1291, 1273, 1256, 1218, 1168, 1135, 1112, 1096 cmꢂ1 1H NMR
.
(500 MHz, CDCl3):
d
¼ 8.71 (d, J ¼ 7.9 Hz, 1H), 8.65 (s, 1H), 7.84
In a flask fitted with a magnetic stirrer was placed iminocou-
marin 1a (3 mmol), phenyl-isocyanide dichlorides (caution:
incompatible with strong oxidizing agents; corrosive) (6 mmol),
and isopropanol (5 ml) and then a catalytic amount of piperidine.
The resulting reaction mixture was stirred at reflux temperature for
16 h. The precipitate was filtered and purified by recrystallisation
with DMF to give 4.
(d, J ¼ 7.9 Hz, 1H), 7. 67 (d, J ¼ 8.4 Hz, 2H), 7.49e7.41 (m, 3H), 7.35
(d, J ¼ 8.4 Hz, 2H), 6.72 (dd, J ¼ 9.0, 2.2 Hz, 1H), 6.64 (d, J ¼ 2.2 Hz,
1H), 3.39 (t, J ¼ 7.4 Hz, 4H), 1.66e1.60 (m, 4H), 1.44e1.36 (m, 4H),
0.99 (t, J ¼ 7.3 Hz, 6H). 13C-NM (125 MHz, CDCl3):
d
¼ 162.1, 156.2,
153.6, 152.7, 145.7, 144.8, 144.6, 136.7, 132.9, 131.3, 130.9, 125.0,
124.1, 124.0,118.9,116.7,111.4, 110.2,104.3, 97.7, 51.5, 29.3, 20.2,13.9.
Fig. 1. Chemical structural of 1, 2, and 3.

8
S.-T. Huang et al. / Dyes and Pigments 86 (2010) 6e14
Fig. 2. Synthetic schemes for dyes 4aej, 5aeb, 6aeb, and 7aeb.
HRMS-ESI (m/z): [M þ 1] For C32H30N6O, 514.2481 calcd; 515.2577
HRMS-ESI (m/z): [M þ 1] For C32H30F3N5O, 557.2402 calcd;
found.
558.2501 found.
2.2.5. N,N-Diethyl-7-[(4-trifluoromethyl)imino]-7H-chromeno
[20, 30: 4, 5] pyrimido [1, 6-a] benzimidazol-3-amine (4e)
2.2.7. Methyl 4-{[3-diethylamino]-7H-chromeno [20, 30: 4, 5]
pyrimidol [1, 6-a] benzimidazol-7-ylidene] amino} benzoate (4g)
Red solid (68% yield) m.p. > 300 ꢁC. FT-IR v/cmꢂ1 ¼ 2968, 2924,
2853, 1713, 1638, 1603, 1581, 1552, 1525, 1509, 1423, 1336, 1269,
Red solid (55% yield) m.p. > 300 ꢁC. FT-IR v/cmꢂ1 ¼ 2973, 2932,
2873, 1641, 1607, 1557, 1528, 1507, 1444, 1422, 1324, 1264, 1231,
1202, 1180, 1133, 1111, 1034, 1013 cmꢂ1. 1H NMR (500 MHz, CDCl3):
1232, 1200, 1180, 1132, 1111, 1098, 1045, 1012 cmꢂ1 1H NMR
.
d
¼ 8.74 (d, J ¼ 7.8 Hz, 1H), 8.65 (s, 1H), 7.84 (d, J ¼ 7.8 Hz, 1H), 7. 64
(500 MHz, CDCl3):
d
¼ 8.74 (d, J ¼ 7.8 Hz, 1H), 8.59 (s, 1H), 8.08
(d, J ¼ 8.3 Hz, 2H), 7.49e7.40 (m, 3H), 7.36 (d, J ¼ 8.3 Hz, 2H), 6.71
(d, J ¼ 10.2 Hz, 1H), 6.66 (s, 1H), 3.47 (q, J ¼ 7.1 Hz, 4H), 1.25
(d, J ¼ 8.5 Hz, 2H), 7.83 (d, 7.8 Hz, 1H), 7.46e7.39 (m, 3H), 7.33 (d,
J ¼ 8.5 Hz, 2H), 6.69 (dd, J ¼ 9.0, 2.3 Hz, 1H), 6.62 (d, J ¼ 2.3 Hz, 1H),
3.92 (s, 3H), 3.44 (q, J ¼ 7.1 Hz, 4H), 1.24 (t, J ¼ 7.1 Hz, 6H). 13C NMR
(t, J ¼ 7.1 Hz, 6H). 13C NMR (125 MHz, CDCl3):
¼ 161.8, 156.2, 153.2,
d
151.3, 145.7, 144.4, 144.1, 136.7, 131.3, 131.0, 125.9, 125.8, 125.0,
124.9, 124.0, 123.3, 118.7, 116.7, 111.1, 110.2, 104.2, 97.5, 45.4, 12.4.
HRMS-ESI (m/z): [M þ 1] For C28H22F3N5O, 501.1776 calcd;
502.1899 found.
(500 MHz, CDCl3):
d
¼ 167.4, 161.7, 156.1, 153.0, 152.8, 145.7, 144.5,
144.3,136.3, 131.4, 130.9, 130.5, 124.8, 124.7,123.9,123.1, 118.8,116.7,
111.0, 110.1, 104.5, 97.5, 51.8, 45.3, 12.4. HRMS-ESI (m/z): [M þ 1] For
C29H25N5O3, 491.1957 calcd; 492.2042 found.
2.2.6. N,N-Dibutyl-7-[(4-trifluoromethyl)imino]-7H-chromeno
[20, 30: 4, 5] pyrimido [1, 6-a] benzimidazol-3-amine (4f)ꢂ1
Red solid (61% yield) m.p. 288e290 ꢁC. FT-IR v/cm ¼ 2956,
2930, 2873, 1638, 1605, 1557, 1529, 1506, 1420, 1323, 1290, 1277,
2.2.8. Methyl 4-{[3-dibutylamino]-7H-chromeno [20, 30: 4, 5]
pyrimidol [1, 6-a] benzimidazol-7-ylidene] amino} benzoate (4h)
Red solid (61% yield) m.p. 235e237 ꢁC. FT-IR v/cmꢂ1 ¼ 2956,
2928, 2871, 1712, 1635, 1602, 1557, 1525, 1506, 1423, 1363, 1335,
1218, 1136, 1111, 1064, 1013 cmꢂ1
.
1H NMR (500 MHz, CDCl3):
1277, 1218, 1176, 1135, 1111, 1046, 1015, 822 cmꢂ1
.
1H NMR
d
¼ 8.74 (d, J ¼ 7.9 Hz,1H), 8.61 (s,1H), 7.84 (d, J ¼ 7.9 Hz,1H), 7.64(d,
(500 MHz, CDCl3): d
¼ 8.74 (d, J ¼ 7.9 Hz, 1H), 8.60 (s, 1H), 8.08
J ¼ 8.3 Hz, 2H), 7.47e7.40 (m, 3H), 7.35 (d, J ¼ 8.3 Hz, 2H), 6.70 (dd,
J ¼ 8.9, 2.2 Hz, 1H), 6.62 (d, J ¼ 2.2 Hz, 1H), 3.38 (t, J ¼ 7.8 Hz, 4H),
1.65e1.59 (t, J ¼ 7.2 Hz, 4H), 1.43e1.35 (m, 4H), 0.99 (t, J ¼ 7.4 Hz,
(d, J ¼ 8.5 Hz, 2H), 7.83 (d, 7.9 Hz, 1H), 7.47e7.40 (m, 3H), 7.32 (d,
J ¼ 8.5 Hz, 2H), 6.67 (dd, J ¼ 9.0, 2.2 Hz, 1H), 6.59 (d, J ¼ 2.2 Hz, 1H),
3.92 (s, 3H), 3.36 (t, J ¼ 7.8 Hz, 4H), 1.63e1.58 (t, J ¼ 7.4 Hz, 4H),
1.42e1.34 (m, 4H), 0.98 (t, J ¼ 7.4 Hz, 6H). 13C NMR (500 MHz,
6H). 13C NMR (125 MHz, CDCl3):
d
¼ 161.9, 156.1, 153.5, 151.4, 145.7,
144.6, 144.5, 136.4, 131.4, 130.8, 125.9, 125.8, 125.1, 124.9, 123.9,
123.7, 123.3, 118.8, 116.7, 111.2, 110.1, 104.4, 97.7, 51.5, 29.3, 20.3, 13.9.
CDCl3):
d
¼ 167.4, 161.8, 156.1, 153.4, 152.8, 145.7, 144.6, 144.3, 136.2,
131.4, 130.7, 130.5, 124.8, 124.7, 123.9, 123.1, 118.8, 116.7, 111.1, 110.1,

S.-T. Huang et al. / Dyes and Pigments 86 (2010) 6e14
9
104.5, 97.7, 51.8, 51.4, 29.3, 20.2, 13.8. HRMS-ESI (m/z): [M þ 1] For
d
¼ 8.06 (d, J ¼ 9.2 Hz, 1H), 7.99 (d, J ¼ 7.6 Hz, 1H), 7.62 (t, J ¼ 7.6 Hz,
C33H33N5O3, 547.2583 calcd; 548.2705 found.
1H), 7.56 (t, J ¼ 7.6 Hz, 1H), 7.39 (d, J ¼ 9.2 Hz, 1H), 7.18 (s, 1H), 3.76
(q, J ¼ 7.0 Hz, 4H), 1.33 (t, J ¼ 7.0 Hz, 6H). HRMS-ESI (m/z): [M þ 1]
For C24H18N6O, 406.1542 calcd; 407.1598 found.
2.2.9. N,N-Diethyl-7-[(4-bromophenyl)imino]-7H-chromeno
[20, 30: 4, 5] pyrimido [1, 6-a] benzimidazol-3-amine (4i) ꢂ1
Red solid (68% yield) m.p. 290e292 ꢁC. FT-IR v/cm ¼ 2971,
2928, 2868, 1637, 1590, 1556, 1526, 1510, 1480, 1421, 1339, 1264,
2.4.2. 3-(Dibutylamino)-7-imino-7H-chromeno [30, 20: 3, 4]
pyrido [1, 2-a] benzimidazole-6, 14-dicarbonitrile (5b)
.
1231, 1185, 1133, 1112, 1097, 1077, 1005 cmꢂ1 1H NMR (500 MHz,
Deep blue solid (77% yield) m.p. > 300 ꢁC. FT-IR v/cmꢂ1 ¼ 3305,
2956, 2928, 2871, 2217, 1666, 1621, 1601, 1547, 1508, 1445, 1425,
1359, 1340, 1306, 1278, 1225, 1186, 1153, 1110, 1074. 1H NMR
CDCl3):
d
¼ 8.75 (d, J ¼ 7.7 Hz, 1H), 8.60 (s, 1H), 7.83 (d, J ¼ 7.7 Hz,
1H), 7.49 (d, J ¼ 8.5 Hz, 2H), 7.50e7.40 (m, 3H), 7.21 (d, J ¼ 8.5 Hz,
2H), 6.72 (dd, J ¼ 9.0, 2.3 Hz, 1H), 6.66 (d, J ¼ 2.3 Hz, 1H), 3.48 (q,
J ¼ 7.1 Hz, 4H), 1.26 (t, J ¼ 7.1 Hz, 6H). 13C NMR (500 MHz, CDCl3):
(500 MHz, CDCl3):
d
¼ 8.69 (s, 2H), 7.92 (dd, J ¼ 6.9, 2.3 Hz,1 H), 7.76
(d, J ¼ 9.2 Hz, 1H), 7.46e7.43 (m, 2H), 6.74 (dd, J ¼ 9.2, 2.3 Hz, H),
6.58 (d, J ¼ 2.3 Hz, 1H), 3.43 (t, J ¼ 7.9 Hz, 4H), 1.66 (t, J ¼ 7.1, 4H),
1.47e1.40 (m, 4H), 1.03e1.00 (t, J ¼ 7.4 Hz, 6H). HRMS-ESI (m/z):
[M þ 1] For C28H26N6O, 462.2186 calcd; 463.2253 found.
d
¼ 161.6, 156.1, 153.0, 147.0, 144.2, 136.0, 131.6, 131.5, 130.8, 125.2,
124.8, 123.9, 118.8, 116.8, 116.4, 110.9, 110.1, 104.8, 97.6, 45.4, 29.7,
18.3, 12.4. HRMS-ESI (m/z): [M þ 1] For C27H22BrN5O, 511.1008,
513.0987 calcd; 512.1101, 514.1080 found.
2.5. General procedures for preparation of 6aeb and 7aeb
2.2.10. N,N-Dibutyl-7-[(4-bromophenyl)imino]-7H-chromeno
[20, 30: 4, 5] pyrimido [1, 6-a] benzimidazol-3-amine (4j) ꢂ1
Red solid (68% yield) m.p. 232e234 ꢁC. FT-IR v/cm ¼ 2956,
2930, 2872, 1634, 1591, 1553, 1529, 1509, 1481, 1420, 1341, 1273,
1249, 1219, 1130, 1111, 1068, 1007. 1H NMR (500 MHz, CDCl3):
In a flask fitted with a magnetic stirrer placed 2.6 mmol of
either 3aeb or 5aeb, and 26 ml of dry pyridine and heated up to
120 ꢁC under an argon atmosphere. At 120 ꢁC, 4-chlorosulfonyl-
benzoic acid (10 mmol) was added and the ensuing mixture was
stirred overnight. The pyridine in the mixture was removed under
reduced pressure to yield the crude oily product which was added
10 ml of 2 M aq HCl to give blue precipitate. The resulting
crude precipitate was collected, washed with water and methanol
and purified by flash column chromatography (1:25/MeOH:
CH2Cl2).
d
¼ 8.75 (d, J ¼ 7.8 Hz, 1H), 8.61 (s, 1H), 7.83 (d, J ¼ 7.8 Hz, 1H), 7.49
(d, J ¼ 8.5 Hz, 2H), 7.46e7.39 (m, 3H), 7.21 (d, J ¼ 8.5 Hz, 2H), 6.68
(dd, J ¼ 8.9, 2.3 Hz,1H), 6.61 (d, J ¼ 2.3 Hz, H), 3.37 (t, J ¼ 7.8 Hz, 4H),
1.65e1.59 (t, J ¼ 7.2 Hz, 4H), 1.43e1.36 (m, 4H), 0.99 (t, J ¼ 7.4 Hz,
6H). 13C NMR (500 MHz, CDCl3):
d
¼ 161.6, 156.0, 153.4, 147.0, 145.7,
144.2,136.2,131.6,131.4,130.8,125.2,124.8,123.9,118.7,116.8,116.4,
111.1, 110.1, 104.4, 97.7, 51.4, 29.7, 29.3, 20.2, 13.9. HRMS-ESI (m/z):
[M þ 1] For C31H30BrN5O, 567.1634, 569.1613 calcd; 568.1765,
570.1701 found.
2.5.1. 4-({6-Cyano-3-(diethylamino)-7H-chromeno[30, 20: 3, 4]
pyrido [1, 2-a] benzimidazol-7-ylidene} amino) sulfonyl
benzoic acid (6a)
2.3. Procedures for preparing 3-(dibutylamino)-7-imino-7H-
chromeo[30, 20: 3, 4] pyrido [1, 2-a] benzimidazole-
6-carbonitrile (3b)
Deep blue solid (43% yield) m.p. > 300 ꢁC. FT-IR v/cmꢂ1 ¼ 3456,
1614, 1551, 1502, 1465, 1346, 1295, 1182, 1130, 1038, 1010. 1H NMR
(500 MHz, DMSO-d6):
d
¼ 9.04 (s, 1H), 8.53 (d, J ¼ 8.5 Hz, 1H), 8.0
(d, J ¼ 7.0 Hz, 2H), 7.91 (d, J ¼ 9.5 Hz 1H), 7.84 (d, J ¼ 7.6 Hz, 1H), 7.70
(d, J ¼ 7.0 Hz, 2H), 7.50 (t, J ¼ 7.6 Hz, 1H), 7.53 (t, J ¼ 7.6 Hz, 1H), 7.11
(d, J ¼ 9.5 Hz, 2H), 6.87 (s, 1H), 3.61 (q, J ¼ 7.0 Hz, 4H), 1.19 (t,
J ¼ 7.0 Hz, 6H). HRMS-ESI (m/z): [M ꢂ 1] For C30H23N5O5S, 565.1420
calcd; 564.1341 found.
To a solution of 1b (1 mmol) in 3 ml dry 2-methoxyethanol
was added malononitrile (1 mmol), and the solution was stirred
80 ꢁC for 4 h. The mixture was cooled to room temperature and
the red coloured precipitate was filtered and purified by recrys-
tallisation with DMF toꢂ1give 3b as red solid (68% yield). M.p.
296e299 ꢁC. FT-IR v/cm ¼ 3333, 3190, 2957, 2208, 1356, 1276,
1222, 1169, 1124. 1H NMR (500 MHz, DMSO-d6):
d
¼ 8.76 (d,
2.5.2. 4-({6-Cyano-3-(dibutylamino)-7H-chromeno[30, 20: 3, 4]
pyrido [1, 2-a] benzimidazol-7-ylidene} amino) sulfonyl)
benzoic acid (6b)
J ¼ 7.6 Hz, 1H), 8.05 (s, 1H), 8,41 (br, 1H, NH), 7.80 (d, J ¼ 7.6 Hz,
1H,), 7.42 (m, 3H), 6.68 (dd, J ¼ 9.0, 2.1 Hz, 1H), 6.63 (s, 1H), 3.41 (t,
J ¼ 7.9 Hz 4H,), 1.65 (m, 4H), 1.46e1.39 (m, 4H), 1.25e0.98 (m, 6H).
HRMS-ESI (m/z): [M] For C27H27N5O, 437.2216 calcd; 437.2230
found.
Deep blue solid (51% yield) m.p. > 300 ꢁC. FT-IR v/cmꢂ1 ¼ 3452,
2955, 2214, 1640, 1549, 1505, 1471, 1338, 1287, 1222, 1172, 1128,
1037, 1009. 1H NMR (500 MHz, DMSO-d6):
d
¼ 9.04 (s, 1H), 8.52 (d,
J ¼ 8.3 Hz, 1H), 8.01 (d, J ¼ 8.3 Hz, 2H), 7.90 (d, J ¼ 9.2 Hz, 1H), 7.83
(d, J ¼ 8.2 Hz,1H), 7.71 (d, J ¼ 8.3 Hz, 2H), 7.48 (t, J ¼ 8.2 Hz,1H), 7.42
(t, J ¼ 8.3 Hz, 1H), 7.09 (d, J ¼ 9.2 Hz, 1H), 6.84 (s, 1H) 3.53
(t, J ¼ 7.4 Hz, 4H), 1.56e1.55 (m, 4H), 1.35 (m, 4H), 0.92 (t, J ¼ 7.3 Hz,
6H). HRMS-ESI (m/z): [M ꢂ 1] For C34H31N5O5S, 621.2046 calcd;
620.1971 found.
2.4. General preparation of 5a and 5b
To a solution of 5 (20 mmol) in 50 ml of DMF was added
potassium cyanide (40 mmol in 6 ml of water). The solution was
stirred at 40 ꢁC for 1 h, cooled to room temperature and filtered.
After filtration, 20 mmol of elemental bromine was added dropwise
to the filtrate at 0 ꢁC and the ensuing mixture was stirred for an
additional 60 min at this temperature. The resulting precipitate was
collected, washed with water and methanol and purified by double
recrystallisation from DMF.
2.5.3. 4-({6, 14-Dicyano-3-(diethylamino)-7H-chromeno[30, 20:
3, 4] pyrido [1, 2-a] benzimidazol-7-ylidene} amino) sulfonyl
benzoic acid (7a)
Deep blue solid (42% yield) m.p. > 300 ꢁC. FT-IR v/cmꢂ1 ¼ 3446,
2924, 1607, 1547, 1445, 1335, 1232, 1186, 1109, 1035, 1007. 1H NMR
2.4.1. 3-(Diethylamino)-7-imino-7H-chromeno [30, 20: 3, 4]
pyrido [1, 2-a] benzimidazole-6, 14-dicarbonitrile (5a)
(500 MHz, DMSO-d6):
d
¼ 8.51 (d, J ¼ 8.0 Hz, 1H), 7.99 (d, J ¼ 8.0 Hz,
1H), 7.93 (d, J ¼ 7.6 Hz, 1H), 7.79 (d, J ¼ 9.2 Hz, 2H), 7.72 (d,
J ¼ 8.0 Hz, 2H), 7.54e7.49 (m, 2H), 7.22 (d, J ¼ 9.2 Hz, 1H), 6.92 (s,
1H), 3.64 (q, J ¼ 7.1 Hz, 4H), 1.20 (t, J ¼ 7.1 Hz, 6H). HRMS-ESI (m/z):
[M ꢂ 1] For C31H22N6O5S, 590.1372 calcd; 589.1298 found.
Deep blue solid (70% yield) m.p. > 300 ꢁC. FT-IR v/cmꢂ1 ¼ 3293,
2978, 2213, 1643, 1599, 1533, 1504, 1475, 1434, 1334, 1310, 1289,
1260,1185,1151,1111,1079,1015. 1H NMR (500 MHz, acetic acid-d4):

10
S.-T. Huang et al. / Dyes and Pigments 86 (2010) 6e14
2.5.4. 4-({6, 14-Dicyano-3-(dibutylamino)-7H-chromeno[30, 20:
3, 4] pyrido [1, 2-a] benzimidazol-7-ylidene} amino) sulfonyl
benzoic acid (7b)
Table 1
Spectroscopic data of the synthesized dyes measured in DMSO at room temperature.
Dyes
labs (nm)
l
flu (nm)
3
(Mꢂ1 cmꢂ1
)
Stokes shift
fa
Deep blue solid (48% yield) m.p. > 300 ꢁC. FT-IR v/cmꢂ1 ¼ 3447,
1a
4a
4b
4c
4d
4e
4f
4g
4h
4i
437
536
538
532
535
530
532
531
532
529
533
551
553
640
642
570
571
673
676
497
600
601
580
583
573
576
581
576
561
561
577
580
689
694
607
610
715
720
41 318
56 667
53 297
61 802
51 192
60 544
54 455
47 428
35 658
42 869
43 177
23 498
23 732
32 148
30 105
18 128
41 160
12 842
20 613
60
64
63
48
48
43
44
50
44
32
32
26
27
49
52
37
39
42
44
0.37 ꢂ3
8.8 Eꢂ3
9.1 Eꢂ3
5.4 Eꢂ3
5.7 E
2927, 2218, 1634, 1466, 1440, 1338, 1283, 1221, 1181, 1110, 1036,
1007. 1H NMR (500 MHz, DMSO-d6, 350K):
d
¼ 8.52 (d, J ¼ 8.2 Hz,
1H), 7.97 (d, J ¼ 8.2 Hz, 2H), 7.92 (d, J ¼ 7.4 Hz, 1H), 7.80
(d, J ¼ 9.4 Hz, 2H), 7.75 (d, J ¼ 8.2 Hz, 2H), 7.55 (m, 2H), 7.19
(d, J ¼ 9.4 Hz, 1H), 6.85 (s, 1H), 3.59 (t, J ¼ 7.3 Hz, 4H), 1.61 (m, 4H),
1.41e1.36 (m, 4H), 0.94 (t, J ¼ 3.7 Hz, 6H). HRMS-ESI (m/z): [M ꢂ 1]
For C35H30N6O5S, 646.1998 calcd; 645.1931 found.
6.5 Eꢂ3
6.5 Eꢂ3
3.8 Eꢂ3
3.5 Eꢂ3
3.2 Eꢂ3
4.2 Eꢂ3
0.92
0.94
0.19
0.17
0.90
4j
2.6. Optical measurement
3a
3b
5a
5b
6a
6b
7a
7b
Absorption spectra were recorded on a Perkin-Elmer spectro-
photometer. The all fluorescence measurements were made with
using a fluorescence grade quartz cuvette, and a Horiba Jobin Yvon
FluoroMax-4 spectrofluorometer. The fluorescence quantum yields
of the new dyes were determined by comparisons with reference
compound with known quantum yield, and the experimental
procedures were performed by following the published procedure
[21]. The following reference dyes were used: crystal violet
0.89
0.11
0.12
a
Reference dyes are listed in the Experimental section.
(
f
¼ 0.54 in methanol) [22] for 4aej, 3aeb and 6aeb, zinc
from 450 nm to 600 nm with one absorption maxima between 529
and 536 nm depending on the different electron withdrawing
group (Figs. 3 and 4). The fluorescence spectra of dyes 4aej
displayed emission spectra in the visible region from 500 nm to
700 nm with one emission maxima between 573 and 601 nm also
depending on the nature of the electron withdrawing group (Figs. 5
and 6). We observed a drastic bathochromic shift in both the
absorption and emission maxima for dyes 4aej as compared to
iminocoumarin 1. We believe that this bathochromic shift in the
phthalocyanine (
7aeb [23].
f
¼ 0.30 in 1% pyridine in toluene) for 5aeb, and
3. Results and discussion
3.1. Syntheses of dyes
The synthetic schemes of the new dyes 4, 5, 6 and 7 are
outlined in Fig. 2. The new dyes 4aej prepared in one step from
3-benzimidazol-2-yl-2-imunocoumarin 1a or 1b [12]. Thus treat-
ment of the iminocoumarin 1a and 1b with various p-substituted
phenyl isocyanide dichlorides [20] in isopropanol under piperidine
catalysis resulted in formation of the guanidine dyes 4aej in
45e60% yields (Fig. 2). The rigid benzopyran ring structure of 3a
and b were prepared in one step from the corresponding 3-ben-
zimidazol-2-yl-2-imunocoumarin 1a or 1b by condensing with
malononitrile following a previously published procedure [15].
Nucleophilic addition of the nitrile to the chromene ring structure
of 3a and b followed by bromine oxidation gave 5a and 5b in 70%
and 77% yields, respectively [24]. The treatment of either 3aeb
or 5aeb with 4-carboxybenzenesulfonyl chloride gave the
sulfonamide in 6aeb or 7aeb, respectively. The chemical struc-
tures of the newly synthesized iminocoumarin derivatives were
characterized by NMR, IR and mass; all of the characterization
data are listed in the Experimental section. We believe that
compounds 4 should possess the E stereochemistry, and we
assumed compounds 6 and 7 will possess Z stereochemistry on
steric grounds. However, there is no direct evidence at this point
for these stereochemical assignments. Experiments to assist with
the elucidation of the stereochemistry of these dyes are presently
ongoing.
spectra results from the extension of the
p-conjugation and the
spatial fixation of the benzimidazole unit with the C]N bond of
the iminochromene bicycle into the planar guanidine structure
thereby enhancing the electron flow within the conjugation ring
system.
3.2. Spectral characteristics of the dyes 4aej
The basic spectral characteristics of 4aej, such as the absorption
maxima (lmax) and emission maxima (lem), were measured in
dimethyl sulfoxide (DMSO) and the results are presented in Table 1
and Figs. 3e6. In general, the absorption and fluorescence spectra
characteristics for dyes 4aej, which have the same R2 substituents,
exhibited nearly identical spectra for either N-ethyl or N-butyl
substitutions (Table 1 and Figs. 3e6). The electron absorption
spectra of dyes 4aej displayed absorptions in the visible region
Fig. 3. Normalized absorption spectra for dyes 4a, 4c, 4e, 4g, 4i, and 1a in dimethyl
sulfoxide.

S.-T. Huang et al. / Dyes and Pigments 86 (2010) 6e14
11
Fig. 6. Normalized fluorescence spectra for dyes 4b, 4d, 4f, 4h, and 4j in dimethyl
sulfoxide.
Fig. 4. Normalized fluorescence spectra for dyes 4a, 4c, 4e, 4g, 4i, and 1a in dimethyl
sulfoxide.
4i regarding their fluorescence and absorption maxima. Hammett
substituent constants sp versus the fluorescence maxima of dyes
were plotted and the results are shown in Fig. 7 [26]. The positive
sp value due to a substituent and indicates an electron with-
drawing polarization resonance effect of the group upon the
conjugated system; all of the R2 substituents in dyes 4aej have
positive sp values. We observed a linear relationship between the
polarization resonance effects of the electron withdrawing
substitution on R2 in dyes 4aej with their fluorescence maxima; as
the sp value of the R2 increased, the fluorescence maximum value
of the dye shifted toward the red region of the spectra. The nitro
group in 4a and 4b, which has the highest sp values of the
substituents amongst all the dyes tested, induced the strongest
electron withdrawing polarization resonance effects on the
conjugated structure of the dyes; thus their fluorescence spectra
exhibited the greatest red shift among the tested dyes with lmax at
ca 600 nm, while the others short of emission maxima value in the
long-wavelength region. However, we did not observe the same
linear relationship between the sp value of the R2 dyes 4aej with
The introduction of polar substituents into organic chromo-
phores causes a redistribution of the electron density in both the
ground state and the excited state, which can strongly modify their
absorption and fluorescence properties [25]. We also investigated
the correlation between the polarization resonance effects of the
electron withdrawing substitution on R2 of dyes 4a, 4c, 4e, 4g and
Fig. 5. Normalized absorption spectra for dyes 4b, 4d, 4f, 4h, and 4j in dimethyl
sulfoxide.
Fig. 7. Plot of Hammett substituents constant sp versus the fluorescence maxima for
dyes 4a, 4c, 4e, 4g, and 4i.

12
S.-T. Huang et al. / Dyes and Pigments 86 (2010) 6e14
absorption maxima. To summarize, it can be concluded the R2
substituent in dyes 4aej induced a redistribution of the electron
density in both the ground state and the excited state resulting in
shifting of the fluorescence maxima of the dyes toward to the long-
wavelength region.
3.3. Spectral characteristics of the dyes 3, 5, 6, and 7
The spectral characteristics of dyes 3, 5, 6, and 7, such as the
absorption maxima (lmax) and emission maxima (lem) were also
measured in DMSO, and the results are also presented in Table 1
and Figs. 8 and 9. In general, the absorption and fluorescence
spectra characteristics and maxima for dyes 3, 5, 6, or 7 were
nearly identical for either the N-ethyl or N-butyl substitutions
(Table 1). The electron absorption spectra of dye 3a displayed an
absorption in the visible region from 400 nm to 600 nm with an
absorption maximum at 551 and a shoulder peak at 500 nm; the
fluorescence spectra of dye 3a displayed an emission spectra in the
visible region from 500 nm to 700 nm with an emission maximum
at 577 nm (Figs. 8 and 9). We observed a small red shift in both the
absorption maximum (20 nm) and fluorescence maximum
(30 nm) as the
p conjugation in 3a was extended by incorporation
of a 4-carboxybenzenesulfonyl moiety in 6a (Table 1 and Fig. 9).
The bathochromic effect of an electron-withdrawing nitrile at the
4-position in the chromene moiety is known in the chemistry of
optical fluorophores derived from coumarin [24,27]. We observed
a similar dramatic bathochromic shift in both the absorption
(89 nm) and emission (112 nm) maxima as the 4 position of the
chromene moiety in 3a was substituted by an electron-with-
drawing nitrile group in 5a (Table 1 and Figs. 8 and 9). Finally,
Fig. 9. Normalized emission spectra for dyes 3a, 5a, 6a, and 7a in dimethyl sulfoxide.
3.4. Extinction coefficient and quantum yield of dyes
3, 4, 5, 6, and 7
extending the
p
conjugation of 5a with the 4-carbox-
ybenzenesulfonyl moiety also resulted in a small red shift in both
the absorption and emission maximum (Figs. 8 and 9). The dyes 7a
and b exhibited the longest absorption and emission maximum of
the tested compounds, and they showed fluorescence in the NIR
region of the spectrum.
The extinction coefficient (3) and quantum yields (f) of the dyes
3, 4, 5, 6, and 7 were measured in DMSO and the results are also
summarized in Table 1. The dyes 4aej have retained the extinction
coefficient values (35 658e61 802 Mꢂ1 cmꢂ1) as compared to
coumarin 1; however, dyes 4aej suffer a major fluorescence quench
and their quantum yields (f < 0.2) are much lower than coumarin 1
(Table 1); thus, we are unable to rationalize this observation with
the current experimental data. On the other hand, dyes 3, 5, 6, and 7
are slightly less light absorptive with lower extinction coefficient
values (12 842e41 160 Mꢂ1 cmꢂ1) as compared to coumarin 1
(Table 1). The dyes 3aeb and 6aeb have the highest quantum yields
(
f > 0.84) tested in this study; however, dyes 5aeb and 7aeb,
which contain a nitrile group at the 4 position in the chromene
moiety, exhibit low quantum yields as compared to analogue dyes
3aeb and 6aeb, respectively. We believe that the striking decrease
in the quantum yields for 5aeb and 7aeb might be induced by the
strong electron withdrawing nitrile substitution because a similar
effect has also been observed in other coumarin derivatives [28].
The decrease in the fluorescence efficiency of various coumarin
dyes has generally come to be accepted as due to charge transfer
between the donor and acceptor moieties coupled with an internal
twist in the excited state leading to a nonplanar twisted confor-
mation with a large dipolar character which is known as the
twisted intramolecular charge transfer (TICT) state [29]. The elec-
tron withdrawing nitrile substituents, especially at the 4-position
of the chromene moiety in coumarin dyes further enhances charge
separation, which markedly accelerates the population of the TICT
state; therefore, 4-nitrile substituted coumarin dyes exhibited
a low quantum yield [28]. We postulated that dyes 5aeb and 7aeb
might exhibit the same effect as the coumarin dyes; therefore, dyes
5aeb and 7aeb exhibited low quantum yields. We are currently
designing more experiments to rationalize the possible causes of
inducing a low quantum yield for these synthesized dyes.
Fig. 8. Normalized absorption spectra for dyes 3a, 5a, 6a, and 7a in dimethyl sulfoxide.

S.-T. Huang et al. / Dyes and Pigments 86 (2010) 6e14
13
Table 2
Spectral properties of the dyes in different solvents.
Dyes Dimethyl sulfoxide
Acetonitrile
Chloroforma
labs lflu
labs
lflu
3
(Mꢂ1 cmꢂ1
)
Stokes
shift
fb
labs
lflu
3
(Mꢂ1 cmꢂ1
)
Stokes
shift
fb
3
(Mꢂ1 cmꢂ1
)
Stokes
shift
fb
(nm)
(nm)
(nm) (nm)
(nm) (nm)
4a
4c
4e
4g
4i
3a
5a
6a
7a
536
532
530
531
529
551
640
570
673
600
580
573
581
561
577
689
607
715
56 667
61 802
60 544
47 428
42 869
23 498
32 148
18 128
12 842
64
48
43
50
32
26
49
37
42
8.8 Eꢂ3 527
5.4 Eꢂ3 524
6.5 Eꢂ3 522
3.8 Eꢂ3 523
3.2 Eꢂ3 521
585
557
550
565
548
568
677
603
704
55 439
41 530
80 832
51 764
56 096
25 184
34 778
20 019
14 952
58
33
28
42
27
24
47
38
41
8.8 Eꢂ3 531
3.9 Eꢂ3 529
6.7 Eꢂ3 526
3.1 Eꢂ3 527
3.7 Eꢂ3 525
578
540
541
561
541
562
660
e
50 146
41 646
61 901
58 826
56 232
34 453
61 403
e
47
11
15
34
16
11
29
e
7.8 Eꢂ3
4.5 Eꢂ3
5.8 Eꢂ3
3.8 Eꢂ3
3.5 Eꢂ3
0.92
0.92
0.19
0.90
0.11
544
630
565
663
0.93
0.29
0.91
0.19
551
631
e
0.43
e
e
e
e
e
e
a
Dyes 6a and 7a were in soluble in chloroform.
Reference dyes are listed in the Experimental section.
b
3.5. Effect of solvent polarity for dyes 3, 4, 5, 6, and 7
for High-performance computing for the computer time and
facilities.
The effect of the solvent polarity on the optical properties of
the dyes synthesized in this study was investigated, because
many fluorescent dyes are influenced by the solvent polarity, and
their optical characteristics change (Table 2). All of the synthe-
sized dyes exhibited small blue shifts along with a decreased
solvent polarity (solvent polarity: DMSO > acetonitrile > chlo-
roform), and optical characteristic of the coumarin dyes exhibited
similar trends [30].
In terms of the quantum yields, dyes 4a, 4c, 4e, 4g, 4i showed
almost no fluorescence increase, and retained a low quantum yield
in all of the tested solvent (Table 2). On the other hand, dyes 3a
and 6a exhibited no change in the fluorescence quantum yield as
the polarity of the solvent decreased. In contrast, dyes 5a and 7a
showed an increased fluorescence quantum yield as the polarity of
the solvent decreased. This fluorescence increase of 5a and 7a in
less polar solvents is assumed to be due to the presence of the
electron-donating moieties, which cause the TICT state. The TICT
state is also known to influence the rate of nonradiative relaxation
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A series of novel iminocoumarin derived dyes 4, 5, 6, and 7 have
been designed and synthesized for application as long-wavelength
fluorescent dyes by extending the
p-conjugation and benzimid-
azole unit fixation of the benzimidazolic bicycle and iminochro-
mene into a planar structure. The photophysical characterization
showed that these iminocoumarin derived dyes are suitable for
long-wavelength fluorescent dyes applications, and the dyes 7a and
b showed fluorescent maxima in the NIR region. The present
molecular design based on the iminocoumarin moiety will enable
the synthesis of a variety of dyes containing various functional
groups, paving the way for the exploitation of new long-wave-
length fluorescent dyes. We are currently modifying our design to
optimize the quantum yield and also studying their cytotoxic
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Acknowledgements
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NSC grant 96-2113-M-027-002-MY3 and outstanding project
on solar cell supported by National Taipei University of Tech-
nology is appreciated. We are also grateful to the National Center

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