Carbazole substituted BODIPY dyes: Synthesis, photophysical properties and antitumor activity

Article abstract of DOI:10.1016/j.dyepig.2015.07.025

Abstract In this study, two different BODIPYs containing carbazole groups at the meso position were designed and synthesized. All compounds were fully characterized by elemental analysis, FT-IR, matrix-assisted laser desorption/ionization time-of-flight m

Full text of DOI:10.1016/j.dyepig.2015.07.025

Dyes and Pigments 123 (2015) 32e38
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Carbazole substituted BODIPY dyes: Synthesis, photophysical
properties and antitumor activity
a
a
b
c
a, *
Ibrahim F. Sengul , Elif Okutan , Hakan Kandemir , Erhan Astarcı , Bünyemin Ço s¸ ut
a
Department of Chemistry, Faculty of Science, Gebze Technical University, Gebze, Kocaeli, Turkey
Department of Chemistry, Faculty of Art and Science, Namık Kemal University, Tekirdag, Turkey
Mudurnu Sureyya Astarci Vocational School, Abant Izzet Baysal University, Bolu, Turkey
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 5 June 2015
Received in revised form
In this study, two different BODIPYs containing carbazole groups at the meso position were designed and
synthesized. All compounds were fully characterized by elemental analysis, FT-IR, matrix-assisted laser
desorption/ionization time-of-flight mass spectrometry, 1H and 13C NMR spectroscopy. The photo-
14 July 2015
physical properties of the new compounds were investigated by means of absorption and fluorescence
spectroscopies in dilute dichloromethane solutions. We were also interested in the biological activity of
these two novel carbazole-linked BODIPYs, particularly concerning their ability to inhibit human colon
cancer HT29 cell lines. The photophysical studies revealed strong donoreacceptor interaction between
carbazole and BODIPY and follow the order compound 5 > compound 4. Also, preliminary assay showed
that compound 5 possessed higher cytotoxic activity than compound 4, with IC50 values of 8.3 ng/mL
and 21.7 ng/mL respectively.
Accepted 20 July 2015
Available online 29 July 2015
Keywords:
Carbazole
Energy transfer
Fluorescence
Biological activity
Borondipyrromethenes
Lifetime
© 2015 Elsevier Ltd. All rights reserved.
1. Introduction
functionalization, stability, low redox potential, hole transport
properties, and strong electron donating ability [12e14]. Carbazole-
4
,4-Difluoro-4-borato-3a,4a-diaza-s-indacene (BODIPY) is one
based compounds are attractive as photoelectrical materials and
dyes, as well as for supramolecular recognition and medicinal
chemistry [12]. Such considerations have led to the preparation and
characterization of carbazole conjugated BODIPY chromophores
selected for their specific photophysical properties. Recently, Tour
et al. have demonstrated the preparation of highly fluorescent
BODIPY based nano-cars incorporating carbazole and p-carborane
groups [15]. Long-wavelength fluorescent BODIPYs with mono-
of the important families amongst the highly fluorescent dyes [1].
Since the first synthesis of BODIPY in 1968 by Treibs and co-worker
2], the chemistry of BODIPY has been the subject of intense study
[
and major efforts have been devoted to obtain the well-designed
BODIPY structures [3]. BODIPYs are highly colored compounds
that often show intense florescence. They display highly desirable
properties, such as high fluorescence quantum yields, intense ab-
sorption in the 450e750 nm regions, tunability of absorption range,
and good solubility in most organic solvents [4,5]. Due to the photo-
stable nature and insensitivity towards the environmental pH they
gained attention as fluorescent labels (proteins and DNA) in the
cells [6,7]. The study of the photophysical properties of these
compounds is particularly interesting and highly dependent on the
functional dye systems [8e11].
and di-carbazole groups attached to BODIPYs
a-pyrrole position
exhibited reasonable two-photon absorption cross-section
a
[16e18]. Donor-acceptor carbazole substituted BODIPY dyes were
reported for DSSC (dye sensitized solar cells) application [13,19e21]
and as dye, possessing solid-state red fluorescence and green
metallic luster properties [22]. Also, carbazole-BODIPY derivatives
have been explored for OLED green dopants [3]. As part of an on-
going investigation into the chemistry of carbazole-linked BOD-
IPY, we now report the synthesis and characterization of com-
pounds 4 and 5 (Scheme 1) as well as their absorption and emission
spectroscopy studies in order to investigate the energy transfer
from carbazole unit into the BODIPY core. Moreover, we were also
interested in the biological activities of these two novel carbazole-
linked BODIPYs, particularly concerning their ability to inhibit hu-
man colon cancer HT29 cell lines.
Carbazole and its derivatives are important class of aromatic
heterocyclic compounds, having long attracted attention from re-
searchers due to their valuable properties, such as facile
*
Corresponding author. Department of Chemistry, Gebze Technical University,
P.O. Box: 141, Gebze 41400, Kocaeli, Turkey. Tel.: þ90 262 6053015; fax: þ90 262
053105.
E-mail address: bcosut@gtu.edu.tr (B. Ço s¸ ut).
6
http://dx.doi.org/10.1016/j.dyepig.2015.07.025
143-7208/© 2015 Elsevier Ltd. All rights reserved.
0

I.F. Sengul et al. / Dyes and Pigments 123 (2015) 32e38
33
Scheme 1. Chemical structure and synthetic pathway of 2e5 and molecular structures of standards 1 and 6.
2
. Experimental
were tried to find an intense molecular ion peak and low frag-
mentation under the MALDI-MS conditions for these compounds.
1,8,9-Anthracenetriol MALDI matrix yielded the best MALDI-MS
spectra. 1,8,9-Anthracenetriol (2 mg/mL in tetrahydrofuran) ma-
trix for compounds 2e6 were prepared. MALDI samples were
prepared by mixing compounds 2e6 (2 mg/mL in tetrahydrofuran)
with the matrix solution (1:10 v/v) in a 0.5 mL eppendorf micro
2.1. Materials
3
The deuterated solvent (CDCl ) for NMR spectroscopy was ob-
tained from Merck. Following chemicals were obtained from Sigma
Aldrich; 9-ethylcarbazole, 2,4-dimethylpyrrole, trifluoroacetic acid,
2
,3-Dichloro-5,6-dicyano-1,4-benzoquinone, trimethylamine, Bo-
tube. Finally 1
dried at room temperature and then analyzed. H and C NMR
spectra were recorded in CDCl solutions on a Varian 500 MHz
spectrometer. Analytical thin layer chromatography (TLC) was
performed on silica gel plates (Merck, Kieselgel 60, 0.25 mm
thickness) with F254 indicator. Column chromatography was per-
formed on silica gel (Merck, Kieselgel 60, 70e200 or
mL of this mixture was deposited on the sample plate,
1
13
ron trifluoride diethyl etherate. Silica gel 60 and dichloromethane
were obtained from Merck Chemicals. 1,8,9-Anthracenetriol for the
MALDI matrix was obtained from Fluka.
3
2.2. Equipment
2
30e400 mesh). Suction column chromatography was performed
Electronic absorption spectra were recorded with a Shimadzu
101 UV spectrophotometer in the UVevisible region. Fluorescence
on silica gel (Merck, Kieselgel 60A, 70e230 mesh).
2
excitation and emission spectra were recorded on a Varian Eclipse
spectrofluorometer using 1 cm pathlength cuvettes at room tem-
perature. The fluorescence lifetimes were obtained using Horiba-
Jobin-Yvon-SPEX Fluorolog 3-2iHR instrument with Fluoro Hub-B
Single Photon Counting Controller at an excitation wavelength of
2.3. The parameters for fluorescence quantum yields
470 nm. Signal acquisition was performed using a TCSPC module.
Mass spectra were acquired in linear modes with average of 50
shots on a Bruker Daltonics Microflex mass spectrometer (Bremen,
Germany) equipped with a nitrogen UV-Laser operating at 337 nm.
FT-IR spectra were recorded on a Bruker Alpha-P in ATR in the
The fluorescence quantum yield values of the samples (4 and 5)
were determined in dichloromethane by comparing with the
fluorescence of Rhodamine 6G as a standard. Fluorescence quan-
F
tum yields (F ) were calculated by the comparative method (Eq.
ꢀ1
ꢀ1
range of 4000 cm e650 cm . Many different MALDI matrices
(1)) [23].

34
I.F. Sengul et al. / Dyes and Pigments 123 (2015) 32e38
F$AStd$n2
was as follows based on literature with a minor revision [29]
(Scheme 1).
F ¼ F ðStdÞ
(1)
F
F
FStd$A$n2
Std
where
F
F
(Std) is the fluorescence quantum yield of standard.
¼ 0.76 in water)
24]. F and FStd are the areas under the fluorescence emission curves
3
.1. Synthesis of compound 4
Rhodamine 6G was employed as the standard (F
F
[
of samples (4 and 5) and the standard, respectively. A and AStd are
the respective absorbance of the samples and standard at the
excitation wavelengths.
solvents used for the sample and standard, respectively. The con-
A 500 mL round bottomed flask was charged with dichloro-
methane (150 mL), and purged with Ar for 20 min. To the flask were
added Compound 1 (0.263 g, 1.18 mmol) and 2,4-dimethylpyrrole
(0.246 g, 2.60 mmol) were dissolved in dichloromethane and stir-
red 20 min and few drops of trifluoroacetic acid was added to the
reaction mixture and stirred for 2e3 h. 2,3-dichloro-5,6-dicyano-p-
benzoquinone (DDQ) (0.16 g, 0.71 mmol) was dissolved in 80 mL of
dichloromethane and added to the reaction mixture. The reaction
mixture was stirred for 2 h at room temperature and triethyl amine
2
2
Std
h
and h
are the refractive indices of
centration of the solutions at the excitation wavelength fixed at
ꢀ
7
ꢀ3
5
ꢁ 10 mol dm . According to the Eq. (2) [25,26], where
FENT is
the energy transfer quantum yield, F (dyad) and F (donor) are
F
F
the fluorescence quantum yields of the dyad (the donor part) and
the donor without connecting to the acceptor, respectively.
(5 mL, 57 mmol) was added to the mixture drop by drop and stirred
for 30 min. BF3. OEt (5 mL, 66 mmol) was added to the mixture
2
FENT ¼ 1 ꢀ FFðdyadÞ=FFðdonorÞ
.4. Cell culture
HT-29 cells were obtained from SAP Institute (Ankara, TURKEY).
(2)
drop by drop. The reaction mixture was stirred at room tempera-
ture 2e3 h and filtered from G4 sintered filter. Solvent was removed
under reduced pressure. Compound 4 has been isolated from col-
umn chromatography with silica gel (4:1; Hexane: Ethylacetate)
Yield: 72 mg (14%).
2
The cells were grown in phenol red free Dulbecco's modified Eagle's
Spectral data of 4: (Found: C 73.45, H 5.96, N 9.54%, C27H26BF N
(441) requires C 73.48, H 5.94, N 9.52%). H NMR (500 MHz, CDCl )
3
2
3
1
medium (DMEM) (high glucose) supplemented with 10% fetal calf
ꢂ
serum,100 units/mL penicillin and 100
in 5% CO
m
g/mL streptomycin at 37 C
d
8.08 (d, J ¼ 7.7 Hz, 1H), 8.00 (s, 1H), 7.55e7.51 (m, 2H), 7.48 (d,
2
in humudified incubator in T25 culture flasks. All culture
J ¼ 8.1 Hz, 1H), 7.34 (dd, J ¼ 8.3, 1.6 Hz, 1H), 7.29e7.26 (m, 1H), 5.98
media were obtained from Biochrom (Berlin, GERMANY). Before
cell viability assays cells in T25 flasks were grown upon reaching
(s, 2H), 4.43 (t, J ¼ 7.2 Hz, 2H), 2.59 (s, 6H), 1.51 (t, J ¼ 7.2 Hz, 3H),
13
3
1.32 (s, 6H). C NMR (126 MHz, CDCl ) d 155.21, 143.51, 143.34,
7
0% in vitro confluency, in the meantime culture media were
140.50, 140.13, 132.44, 126.88, 126.43, 125.46, 125.28, 123.54,
122.78, 121.17, 121.16, 120.74, 120.22, 119.44, 109.19, 108.97, 47.63,
changed every other day. Before quantification assay cells were first
washed with ice-cold Phosphate Buffered Saline (PBS) solution
twice and then subjected to trypsin enzyme for 5 min at 37 C and
activity of trypsin was stopped by the addition of serum containing
DMEM (7 mL medium per ml of trypsin solution), 10
was taken for cell counting by using hemocytometer and cell
concentration was adjusted to 1 ꢁ 10 cells/100
ꢀ
1
37.97, 29.85, 14.79, 14.74, 14.72, 13.96. IR (ATR) ʋmax (cm ): 2955
(aromatic CH), 2920 (aliphatic CH), 2856 (aliphatic CH), 1601 (ar-
omatic C]C), 1546 (aromatic C]C), 1505 (BeF), 1463 (aliphatic
CH), 1370, (aliphatic CH), 1305 (CeN), 1255, 1190, 1155, 1122, 975,
ꢂ
mL of medium
þ
þ
807, 765, 726. MS (MALDI-TOF) m/z (%): 442 [M þ H] , 423 [MꢀF] .
4
mL culture medium.
3.2. Synthesis of compound 5
2.5. Cell viability assay
A 500 mL round bottomed flask was charged with dichloro-
methane (250 mL), and purged with Ar for 20 min. To the flask were
added Compound 3 (1.25 g, 5 mmol) and 2,4-dimethylpyrrole
2.1 g, 22 mmol) were dissolved in dichloromethane and stirred
0 min and few drops of trifluoroacetic acid was added to the re-
action mixture and stirred for 2e3 h. 2,3-dichloro-5,6-dicyano-p-
benzoquinone (DDQ) (2.26 g, 6 mmol) was dissolved in 150 mL of
dichloromethane and added to the reaction mixture. The reaction
mixture was stirred for 2 h at room temperature and triethyl amine
Cell viability was performed by using MTT (3-(4, 5-
dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide) [27]. HT-
4
2
9 cells are plated in 96-well microplates at 1 ꢁ 10 cells/well,
(
2
and incubated overnight for proper attachment in conditions
described elsewhere. Treatments were applied in seven groups in
triplicates along with vehicle control (DMSO only). Cells were
treated with increasing concentrations of mono- and bis-BODIPY
carbazoles 4e5 (0, 5, 10, 25, 50, 100, 250 ng/mL). Data were gath-
ered over 24 by removing cell culture media from the cells, then
(
5 mL, 57 mmol) was added to the mixture drop by drop and stirred
washing with PBS and adding 100
L of 12 mM MTT reagent (Molecular Probes). Cells were further
incubated 4 h and 100 L of 10% SDS solution prepared from 0.01 M
mL of new media which contains
for 30 min. BF3. OEt (5 mL, 66 mmol) was added to the mixture
2
10 m
drop by drop. The reaction mixture was stirred at room tempera-
ture 2e3 h and filtered from G4 sintered filter. Solvent was removed
under reduced pressure. Compound 5 has been isolated from col-
umn chromatography with silica gel (4:1; Hexane: Ethylacetate)
yield: 350 mg (10%).
m
HCl was added. Absorbances of plates were read spectrophoto-
metrically at 570 nm with automatic micro-plate reader (Bio-RAD).
Average results were obtained and cell viability was calculated
according to the formula below:
Spectral data of 5: (Found: C 69.84, H 5.74, N 10.21%,
1
C
(
40
39
H B
2
F
4
N
5
(687) requires C 69.89, H 5.72, N 10.19%). H NMR
%
Cell viability ¼ ½ðAbsorbance of treated cellsÞ=
500 MHz, CDCl
3
)
d
7.94 (s, 2H), 7.58 (d, J ¼ 8.3 Hz, 2H), 7.39 (d,
J ¼ 8.3 Hz, 2H), 5.97 (s, 4H), 4.48 (q, J ¼ 7.0 Hz, 2H), 2.57 (s,12H),1.59
ꢁ
ꢁ
ðAbsorbace of controls untreated cellsÞꢃ
100
1
3
(
1
d, J ¼ 7.1 Hz, 3H), 1.32 (s, 12H). C NMR (126 MHz, CDCl
3
) d 155.49,
55.25, 143.49, 143.07, 142.77, 142.61, 142.14, 140.40, 126.10, 125.76,
1
25.74, 121.11, 120.28, 109.38, 47.49, 29.68, 14.78, 14.58. FT-IR (ATR)
ꢀ1
3
. Synthesis
ʋmax (cm ): 2958 (aromatic CH), 2923 (aliphatic CH), 2853
(aliphatic CH), 1541 (aromatic C]C), 1505 (BeF), 1469 (aliphatic
Compounds 2 and 3 were prepared according to procedures
described previously [28]. The synthesis procedure of compound 6
CH), 1409, (aliphatic CH), 1305 (CeN), 1190, 1155, 973, 807, 765, 726.
MS (MALDI-TOF) m/z (%): 688 [M þ H] , 669 [MꢀF] .
þ
þ

I.F. Sengul et al. / Dyes and Pigments 123 (2015) 32e38
35
4
. Results and discussion
4.1. Synthesis and structural characterization
9
-Ethylcarbazole 1 was chosen for this study as a linker in order
to generate new carbazole-based BODIPY systems. According to
literature, the carbazole ring systems are easily functionalized and
covalently linked to other molecules [30]. In particular, carbazole
undergo Vilsmeier-Haack formylation to obtain an appropriate
carbazole carbaldehyde using dimethyl formamide and phosphoryl
chloride [29]. This reaction therefore provides a ready entry to
suitable aldehyde precursors for the BODIPY synthesis. The first
step was the formylation of 9-ethylcarbazole 1 by Vilsmeier-Haack
conditions using phosphoryl chloride and dimethyl formamide to
get mono- and diformyl carbazoles 2 and 3 [29]. With the 9-ehtyl-
9
H-carbazole-3-carbaldehyde (2) and 9-ehtyl-9H-carbazole-3,6-
dicarbaldehyde (3) in hand, it was of interest to use 9-ehtyl-
carbazole-3-carbaldehyde (2) as a monomeric model for the
preparation of mono-BODIPY carbazole before extending the
chemistry to bis-BODIPY carbazole. The synthetic strategy for the
preparation mono-BODIPY carbazole involved the treatment of
carbazole-3-carbaldehyde (2) with 2,4-dimethylpyrrole in the
presence of trifluoroacetic acid followed by the oxidation of
dipyrromethane derivatives to dipyrromethenes using DDQ and
finally dipyrromethene precursors were transformed to compound
Fig. 1. Electronic absorption spectra of compounds 4 and 5 in dichloromethane.
spectra of the compounds 4 and 5 exhibited similar features to
other carbazole compounds with a maximum absorption wave-
length at 330 and 347 nm. The longer wavelength band corre-
4
by boron trifluoride etherate in the presence of trimethylamine
sponding to the
ca. 503 nm [6].
pep* transition of the BODIPY moiety appeared at
(
Scheme 1). Identification of the compound 4 was performed
1
13
through FT-IR, H and C NMR spectroscopy, mass spectrometry
and elemental analysis and the results were consistent with the
predicted structures, as shown in the experimental section. The FT-
IR, elemental analysis results and the mass spectral data for the
newly synthesized carbazole substituted BODIPY 4 were consistent
with the assigned formulations. The mass spectra of compounds 4,
was obtained by MALDI-TOF MS using 1,8,9-anthracenetriol as the
MALDI matrix, and the spectrum revealed the peak groups repre-
senting the protonated molecular ions at 442 Da and molecular ion
4
.2.2. Fluorescence spectra
The fluorescence properties of compounds 4 and 5 were
investigated in dichloromethane by both steady state and time
resolved fluorescence techniques. The fluorescence emission
spectra of compounds 4 and 5 were investigated with an excitation
wavelength of 470 nm in dichloromethane at room temperature
Fig. 2). Fluorescence emission peaks were observed at around
12 nm for all the compounds in dichloromethane. The fluores-
cence spectra of 4 and 5 exhibit characteristic emission of BODIPYs
such as narrow bandwidth, small stokes shift and high quantum
yield. When comparing to these two carbazole-linked BODIPY dyes,
the bis-BODIPY carbazole dye (5) showed higher fluorescence
(
5
1
rupture fluor at 423 Da (Fig. 6). Well-resolved H NMR spectra of 4
showed sets of signals for meso-carbazole protons ~ 7e8 ppm re-
gion. The pyrrole rings eCH protons appeared as sharp singlets
3 3
~5.9 ppm and eCH protons ~2.5 ppm and ~1.3 ppm. The eCH and
eCH protons on the carbazole were observed ~1.4 ppm as triplet
2
and ~4.4 ppm as quarted respectively.
With the successful execution of monomeric model in hand,
preparation of related bis-BODIPY carbazole system was examined.
The BODIPY synthetic methodology was again employed for the
preparation of compound 5 (Scheme 1). The targeted compound
bis-BODIPY carbazole 5 was purified by column chromatography
and/or preparative TLC techniques. The structure of the compound
1
13
5
was supported by FT-IR, H and C NMR spectroscopic data. The
1
H NMR spectrum in CDCl
protons ~10.1 ppm as a result of BODIPY formation and displayed
characteristic pyrrole -rings CH protons ~1.3 and ~2.5 ppm as
3
showed the loss of two aldehyde CHO
3
singlets. Further structural verification was obtained via mass
spectrometry, with MALDI-TOF MS using 1,8,9-anthracenetriol as
the MALDI matrix. The spectrum showed the peak groups repre-
senting the protonated molecular ions at 688 Da and molecular ion
rupture fluor at 669 Da, consistent for the bis-BODIPY carbazole 5
(Fig. 6).
4
4
.2. Photo-physical properties
.2.1. Electronic absorption spectra
The absorption spectra of 4 and 5 were recorded in dichloro-
methane and are shown in Fig. 1. Compounds 4 and 5 showed two
major characteristic absorption bands at 330e350 and 503 nm. The
Fig. 2. Emission spectra of
wavelength ¼ 470 nm.
4
and
5
in dichloromethane. Excitation

36
I.F. Sengul et al. / Dyes and Pigments 123 (2015) 32e38
emission than the mono-BODIPY carbazole dye (4). In the cases
where two different dyes were used, it may result in fluorescence
resonance energy transfer (FRET) [31,32]. Therefore 4 and 5
constitute a potential donoreacceptor pair in energy transfer.
Indeed, all the compounds 4 and 5 exhibited an energy transfer
phenomenon from carbazole unit to the BODIPY core. In order to
obtain more information about the energy transfer, the emission
spectrum of compound 4 with the emission spectra of their refer-
ence compounds 1 and 6 were measured under the same condi-
ꢀ7
ꢀ3
tions (5 ꢁ 10 mol dm in dichloromethane, exc 330 nm) and are
shown in Fig. 5A. In the emission spectrum of compound 4 excited
from carbazole at 330 nm, there is significant quenching of donor
emission at around 350 and 370 nm and enhancement in acceptor
emission at around 510 nm. In addition to that, compound 6 excited
at 330 nm has very weak emission at around 510 nm (Fig. 3A). In
the emission spectrum of compound 5 excited from pyrene at
330 nm, similar results were obtained. There is a significant
quenching of donor emission at around 350 and 370 nm and
enhancement in acceptor emission at around 510 nm (Fig. 3B). This
shows that all increase in emission at 510 nm is coming from en-
ergy transfer from donor groups (Fig. 3A, B). The fluorescence
quantum yields of compounds 4 and 5 in dichloromethane are
0.0022 and 0.0026, respectively. According to Eq. (2), the energy
transfer quantum yield values of 4 and 5 were estimated. The ENT
F
values were found 0.90 for compound 4 and 0.88 for compound 5,
showing that this is a very efficient energy transfer process in 4 and
5
. The lifetimes were also measured with the time correlated single
photon counting (TCSPC) technique in dichloromethane, excited at
70 nm. Our values of the lifetimes were found to be 4.926 and
.073 ns respectively (Fig. 4). These results indicate a strong elec-
tronic interaction between carbazole and the BODIPY.
4
6
4.3. Biological properties
Following synthesis and characterization, our targeted mono-
and bis-BODIPY carbazoles 4 and 5 were subjected to biological
assessment against human colon cancer HT29 cell lines. In vitro
cytotoxic activity of the compounds 4 and 5 were evaluated on
HT29 cells in different concentrations. IC50 values of the novel
carbazole-linked BODIPY were obtained as 21.7 and 8.3 ng/mL over
Fig. 3. Emission spectra of A) 1, 4, 6 and B) 1, 5, 6 in dichloromethane. Excitation
wavelength ¼ 330 nm.
24 h, respectively. Although the mechanism of 4 and 5 in terms of
its toxic effect has not been studied for this cell type yet, there is
Fig. 4. The fluorescence decay profiles of compounds 4 and 5. The Excitation wavelength used was 470 nm, collected at 512 nm.

I.F. Sengul et al. / Dyes and Pigments 123 (2015) 32e38
37
Fig. 5. Effects of the compounds 4 and 5 on viability of HT-29 Cells. Cell proliferation was determined by MTT assay HT-29 cells were treated with different concentrations of the
compounds 4 and 5 (0, 5, 10, 25, 50, 100, 250 ng/mL) over 24 h.
energy transfer between the carbazole and BODIPY, as well as
fluorescence behavior was better on compound 5 than compound
4. A preliminary screening of the targeted BODIPY compounds
developed throughout this body of work showed reasonable
cytotoxic activity against HT29 cell lines.
Acknowledgment
_
We wish to thank TÜBITAK (project number -113Z159) for
financial support.
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