A first archetype of boron dipyrromethene-phthalocyanine pentad dye: Design, synthesis, and photophysical and photochemical properties

Article abstract of DOI:10.1039/c4dt00406j

A novel type of phthalocyanine pentad containing four boron dipyrromethene (BODIPY) units at peripheral positions of the phthalocyanine framework has been designed and synthesized for the first time. The Sonogashira coupling reaction between 4,4′-difluoro-8-(4-ethynyl)-phenyl-1,3,5,7-tetramethyl-4-bora-3a, 4a-diaza-s-indacene (Ethynyl-BODIPY) and 2(3),9(10),16(17),23(24)-tetrakis(iodo) zinc(ii) phthalocyanine (Iodo-Pc) has been used for the synthesis of the target compound. The BODIPY-phthalocyanine pentad dye (BODIPY-Pc) has been fully characterized by ¹H NMR, MALDI-TOF mass, FT-IR and UV-Vis spectroscopic techniques and elemental analysis as well. The photoinduced energy transfer process for this dye system was explored in tetrahydrofuran solution. The singlet oxygen generation capability and photodegradation behaviours of this BODIPY-Pc pentad dye were also investigated in DMSO for the determination of the usability of this new type of dye system as a photosensitizer in PDT applications. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4dt00406j

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
A first archetype of boron dipyrromethene-
phthalocyanine pentad dye: design, synthesis, and
photophysical and photochemical properties
Cite this: Dalton Trans., 2014, 43,
7561
Cem Göl, Mustafa Malkoç, Serkan Yeşilot and Mahmut Durmuş*
A novel type of phthalocyanine pentad containing four boron dipyrromethene (BODIPY) units at peri-
pheral positions of the phthalocyanine framework has been designed and synthesized for the first time. The
Sonogashira coupling reaction between 4,4’-difluoro-8-(4-ethynyl)-phenyl-1,3,5,7-tetramethyl-4-bora-
3a,4a-diaza-s-indacene (Ethynyl-BODIPY) and 2(3),9(10),16(17),23(24)-tetrakis(iodo) zinc(II) phthalo-
cyanine (Iodo-Pc) has been used for the synthesis of the target compound. The BODIPY-phthalocyanine
pentad dye (BODIPY-Pc) has been fully characterized by 1H NMR, MALDI-TOF mass, FT-IR and UV-Vis
spectroscopic techniques and elemental analysis as well. The photoinduced energy transfer process for
this dye system was explored in tetrahydrofuran solution. The singlet oxygen generation capability and
photodegradation behaviours of this BODIPY-Pc pentad dye were also investigated in DMSO for the
determination of the usability of this new type of dye system as a photosensitizer in PDT applications.
Received 7th February 2014,
Accepted 9th March 2014
DOI: 10.1039/c4dt00406j
www.rsc.org/dalton
asymmetrical phthalocyanine derivative and this compound
bears one BODIPY group at the peripheral position.20
Introduction
Photodynamic therapy (PDT) is a cancer treatment technique
The target compound in this study is a pentad dye system
that uses nontoxic light-sensitive compounds called photo- that contains four BODIPY groups on the phthalocyanine
sensitizers, along with harmless light having a long wavelength framework. To the best of our knowledge, there is no report
to damage cancer cells.1 Recently, phthalocyanine (Pc) com- about symmetrical BODIPY-substituted phthalocyanines in the
pounds have been mostly used in photodynamic therapy (PDT) literature. Although both types of compounds (BODIPY and
as photosensitizers2,3 besides being utilized in many fields phthalocyanine) have been investigated as photosensitizers
such as industrial,4 technological5,6 and other biomedical themselves in PDT of cancer, there is no report about the
applications.7,8 Phthalocyanine compounds are considered investigation of the photosensitizing properties of BODIPY
to be ideal candidates for PDT of cancer due to their suitable substituted phthalocyanines. In order to check whether this
properties such as long wavelength absorption (near IR), capa- type of photosensitizer is a good candidate or not, the photo-
bility for efficient singlet oxygen generation and having non- physical and photochemical properties were evaluated in the
toxic effects in the absence of light.9 BODIPY (4-difluoro- present work.
4-borata-3a-azonia-4a-aza-s-indacene) derivatives have also
The aim of the present study is to synthesize a new type of
been studied as a new class of photosensitizers10,11 besides dye system containing both BODIPY and phthalocyanine units.
using them in light harvesting systems,12 logic gates,13 chemi- It exhibits all the advantages of two different unique groups
cal sensors14 and energy transfer cassettes.15
(BODIPY and phthalocyanine) present on a single molecule
Although there are many individual examples of BODIPY and might be a good candidate in many application areas such
and phthalocyanine compounds, only a few studies about com- as light harvesting systems and PDT.
pounds containing these two groups on the same molecule are
known in the literature. Most of these molecules contain
BODIPY groups as axial substituents on the boron subphthalo-
cyanines or silicon phthalocyanines.16–19 Only one study
published by Torres and co-workers was devoted to the
Experimental
Materials
Tetrahydrofuran (THF), triethylamine (TEA), dichloromethane
(DCM), pentanol and toluene were dried as described by
Perrin and Armarego21 before use. Zinc(II) chloride, zinc(II)
acetate, trifluoroacetic acid (TFA), 2-dimethylaminoethanol
Gebze Institute of Technology, Department of Chemistry, P.O. Box 141, 41400 Gebze,
Kocaeli, Turkey. E-mail: durmus@gyte.edu.tr; Fax: (+)90(262)605 31 01
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 7561–7569 | 7561

View Article Online
Paper
Dalton Transactions
(DMAE), K2CO3, copper(I) iodide, bis(triphenylphosphine)- Photochemical parameters
palladium(II) chloride, dichloro dicyano benzoquinone (DDQ),
Singlet oxygen quantum yield. Singlet oxygen quantum
yield (ΦΔ) of BODIPY-Pc was carried out using the experi-
mental set-up described in the literature.28–30 Typically, a 3 mL
portion of BODIPY-Pc solution (C = 1 × 10−5 M) containing the
singlet oxygen quencher was irradiated in the Q band region
with the photo-irradiation set-up described in ref. 28–30.
Singlet oxygen quantum yield (ΦΔ) was determined in air
using the relative method in DMSO with unsubstituted ZnPc
as a reference. DPBF was used as a chemical quencher for
singlet oxygen in DMSO. Eqn (2) was employed for the
calculations:
trimethylsilylacetylene (TMSA), BF3·OEt2, 4-iodophthalonitrile
and unsubstituted zinc phthalocyanine were purchased from
Aldrich. 1,3-Diphenylisobenzofuran (DPBF) was purchased
from Fluka. Column chromatography was performed on silica
gel 60 (0.04–0.63 mm). 4,4′-Difluoro-8-(4-iodo)-phenyl-1,3,5,7-
tetramethyl-4-bora-3a,4a-diaza-s-indacene
(Iodo-BODIPY),22
4,4′-difluoro-8-(4-ethynyl)-phenyl-1,3,5,7-tetramethyl-4-bora-3a,4a-
diaza-s-indacene (Ethynyl-BODIPY),23 and 2(3),9(10),16(17),23-
(24)-tetrakis(iodo) zinc(II) phthalocyanine (Iodo-Pc)24 were syn-
thesized and purified according to literature procedures.
Std
RI
RStdIabs
ΦΔ ¼ ΦSΔtd
ð2Þ
abs
Equipment
where ΦSΔtd is the singlet oxygen quantum yield for the stan-
dard unsubstituted ZnPc (ΦSΔtd = 0.67 in DMSO).31 R and RStd
Absorption spectra in the UV-visible region were recorded
using a Shimadzu 2101 UV spectrophotometer. Fluorescence
excitation and emission spectra were recorded on a Varian
Eclipse spectrofluorometer using 1 cm pathlength cuvettes at
room temperature. The FT-IR spectrum was recorded on a
Perkin-Elmer Spectrum 100 FT-IR spectrometer. Positive ion
and linear mode MALDI-MS spectra of BODIPY-phthalo-
cyanine pentad dye (BODIPY-Pc) were obtained in dihydroxy-
benzoic acid (as a MALDI matrix) using a Bruker Microflex LT
MALDI-TOF mass spectrometer. The 1H-NMR spectrum was
recorded on a Varian 500 MHz spectrometer in CDCl3
solution.
are the DPBF photobleaching rates in the presence of BODI-
Std
abs
PY-Pc and the standard, respectively. Iabs and I are the rates
of light absorption by BODIPY-Pc and the standard, respect-
ively. To avoid chain reactions induced by DPBF in the pres-
ence of singlet oxygen,32 the concentration of the quencher
(DPBF) was lowered to ∼3 × 10−5 M. Solutions of the sensitizer
and the standard (C = 1 × 10−5 M) containing DPBF were
prepared in the dark and irradiated in the Q band region
using the photoirradiation setup. DPBF degradation at 417 nm
was monitored. A light intensity of 6.7 × 1015 photons s−1 cm−2
was used for ΦΔ determinations.
The light source was a General Electric quartz line lamp
(300 W). A 600 nm glass cutoff filter (Schott) and a water filter
were used to filter off ultraviolet and infrared radiation,
respectively. An interference filter (Intor, 670 nm with a band-
width of 40 nm) was additionally placed in the light path
before the sample. Light intensities were measured using a
POWER MAX5100 (Molectron Detector Incorporated) power
meter.
Photodegradation
quantum
yield. Photodegradation
quantum yield (Φd) measurement of BODIPY-Pc was carried
out using the experimental set-up described in the
literature.28–30 Photodegradation quantum yield was deter-
mined using eqn (3):
ðC0 ꢀ CtÞVNA
Φd ¼
ð3Þ
IabsSt
where C0 and Ct are BODIPY-Pc concentrations before and
after irradiation respectively, V is the reaction volume, NA is
Avogadro’s constant, S is the irradiated cell area and t is the
irradiation time. Iabs is the overlap integral of the radiation
source light intensity and the absorption of BODIPY-Pc. A light
intensity of 2.24 × 1016 photons s−1 cm−2 was employed for Φd
determinations.
Photophysical parameters
Fluorescence quantum yields. Fluorescence quantum yield
(ΦF) of BODIPY-Pc was determined by the comparative method
using eqn (1):25,26
FAStdn2
FStdAnStd
ΦF ¼ ΦFðStdÞ
ð1Þ
2
Synthesis
where F and FStd are the areas under the fluorescence emission
4-[4,4′-Difluoro-8-(4-ethynyl)-phenyl-1,3,5,7-tetramethyl-4-bora-
curves of BODIPY-Pc and the standard, respectively. A and AStd 3a,4a-diaza-s-indacene]phthalonitrile (BODIPY-Pht). 4-Iodo-
are the respective absorbances of BODIPY-Pc and the standard phthalonitrile (33 mg, 0.13 mmol), Ethynyl-BODIPY (46 mg,
at the excitation wavelengths, respectively. n2 and nStd are the 0.13 mmol), PdCl2(PPh3)2 (7 mg, 0.01 mmol) and CuI (4 mg
2
refractive indices of solvents used for BODIPY-Pc and the stan- (0.022 mmol) were added to a Schlenk tube equipped with a
dard, respectively. Unsubstituted ZnPc (ΦF = 0.20 in DMSO)27 magnetic stir bar. A solvent system of THF : Et3N 5 : 2 was well-
was employed as the standard. Both the samples and the stan- degassed under argon for 30 min prior to its addition to the
dard were excited at the same wavelength. The absorbance of reaction mixture. The reaction was quenched with a saturated
the solutions at the excitation wavelength ranged between 0.04 solution of NH4Cl after 24 h. The organic layer was then
and 0.05.
diluted with CH2Cl2 and washed with water and saturated
7562 | Dalton Trans., 2014, 43, 7561–7569
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
NH4Cl. The organic layers were dried over anhydrous MgSO4, BODIPY-Pc was obtained in very low yield (6%) in this syn-
filtered, and the solvent was removed from the filtrate in vacuo thesis strategy (Scheme 1). It could be due to the decompo-
to afford the crude product, which was purified by column sition of the BODIPY units under cyclotetramerization
chromatography (silica gel 4 : 1 hexane : CH2Cl2). Yield: 53 mg conditions such as high temperature. The other strategy is the
(86%). UV/Vis (CHCl3) λmax/nm (log ε): 333 (4.44), 504 (4.80). synthesis of the novel target BODIPY-Pc via a Pd-catalyzed
FT-IR [ATR νmax/cm−1]: 3106 (aromatic-CH), 2959–2858 (ali- Sonogashira coupling reaction between 4,4′-difluoro-8-
phatic-CH), 2234 (–CuN–), 2213 (–CuC–), 1610 (–CvN), 1541 (4-ethynyl)-phenyl-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene
(CvC), 1508, 1468. 1H-NMR (CDCl3): δ, 7.87 (s, 1H, Ar-CH), (Ethynyl-BODIPY) and 2(3),9(10),16(17),23(24)-tetrakis(iodo)
7.79 (d, 1H, Ar-CH), 7.75 (d, 1H, Ar-CH), 7.63 (d, 2H, Ar-CH), zinc(II) phthalocyanine (Iodo-Pc) (Scheme 1). The synthesis of
7.30 (d, 2H, Ar-CH), 5.87 (s, 2H, CH), 2.48 (s, 6H, CH3), 1.35 (s, the targeted novel BODIPY-Pc was achieved through this coup-
6H, CH3). Calc. for C29H21BF2N4: MALDI-TOF-MS m/z: calc. ling reaction in high yield (83%). We concluded that this syn-
474.3; found 474.2 [M]+.
thesis strategy is a suitable way for substitution of the
2(3),9(10),16(17),23(24)-Tetrakis-[4,4′-difluoro-8-(4-ethynyl)- phthalocyanine derivatives via an ethynyl bond. The syn-
phenyl-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene phthalo- thesized tetra-BODIPY substituted Zn(II) phthalocyanine
cyaninato]zinc(II) (BODIPY-Pc). Method A: BODIPY-Pht (40 mg, (BODIPY-Pc) was obtained as a statistical mixture of four regio-
0.084 mmol) and anhydrous zinc(II) acetate (31 mg, isomers (D4h, C4h, C2v and Cs) because the starting compound
0.168 mmol) were heated at reflux temperature in pentanol (Iodo-Pc) bears four iodine substituents in various possible
(4 mL) for 6 h in the presence of DBU (0.1 mL, 0.07 mmol) positions relative to one another with respect to each other.33
under an argon atmosphere. After cooling, the solution was In general, phthalocyanine compounds are hardly ever soluble
dropped into the hot n-hexane. The dark green solid product was in most organic solvents; however, introduction of BODIPY
precipitated and collected by filtration and washed with n-hexane. substituents in the phthalocyanine ring increased the solubi-
The green crude product was purified by column chromatography lity and the target BODIPY-Pc exhibited excellent solubility in
(silica gel CH2Cl2 to 50 : 1 CH2Cl2 : THF). Yield: 2.6 mg (6.3%).
Method B: Iodo-Pc (24 mg, 0.022 mmol), Ethynyl-BODIPY acetate, DMF, toluene, benzene, chloroform and THF).
(75 mg, 0.22 mmol), PdCl2(PPh3)2 (6 mg, 0.0085 mmol) and The novel BODIPY-Pc was fully characterized by general
the most common organic solvents (DMSO, acetone, ethyl
CuI (2 mg, 0.0105 mmol) were added to a Schlenk tube spectroscopic methods (UV-Vis, FT-IR, 1H-NMR and MALDI-
equipped with a magnetic stir bar. A solvent system of THF : TOF mass) and elemental analysis as well. In the FT-IR spec-
Et3N 2 : 1 was well-degassed under an argon atmosphere for trum of BODIPY-Pc, the aromatic and aliphatic CH stretchings
30 min prior to its addition to the reaction mixture. The reac- were observed at 3063 cm−1 and 2956–2851 cm−1, respectively.
tion was quenched with a saturated solution of NH4Cl after The characteristic vibrations were observed at ∼1510 cm−1 for
16 h. The organic layer was then diluted with CH2Cl2 and CvC groups, 2209 cm−1 for –CuC– groups and 1610 cm−1 for
washed with water and saturated NH4Cl. The organic layers –CvN groups. The 1H NMR spectrum of BODIPY-Pc showed
were dried over anhydrous MgSO4, filtered, and the solvent complex patterns due to the isomer mixture. This compound
1
was removed from the filtrate in vacuo to afford the crude was found to be pure by H NMR with all the substituents and
product, which was then purified by column chromatography ring protons observed in their respective regions. The reson-
(silica gel CH2Cl2 to 50 : 1 CH2Cl2 : THF). Yield: 36 mg (83%). ances for the phthalocyanine ring protons were observed
UV/Vis (DMSO) λmax/nm (log ε): 372 (4.84), 502 (5.18), 698 between 8.34 ppm and 7.47 ppm as multiplets. The aromatic
(5.04). FT-IR [ATR νmax/cm−1]: 3063 (aromatic-CH), 2956–2851 protons for benzene groups on BODIPY units were observed at
(aliphatic-CH), 2209 (–CuC–), 1610 (–CvN), 1510 (CvC), 7.99 ppm as multiplets. The CH protons on the BODIPY units
1
1468, 1408. H-NMR (CDCl3): δ, ppm 8.34 (m, 4H, Pc-H), 7.99 were observed at 6.01 ppm as a broad peak. The CH3 protons
(m, 16H, BODIPY-H), 7.47 (m, 8H, Pc-H), 6.01 (br, 8H, CH), on the BODIPY units were observed at 2.54 ppm, 1.89 ppm,
2.54 (s, 12H, CH3), 1.89 (s, 12H, CH3), 1.50 (s, 12H, CH3), 1.18 1.5 ppm and 1.18 ppm as singlets. The mass spectrum of BOD-
(s, 12H, CH3). Calc. for C116H84B4F8N16Zn: C 70.90, H 4.31, IPY-Pc was obtained by the MALDI-TOF-MS technique and the
N 11.42%; found: C 71.67, H 4.81 N 11.21%. MALDI-TOF-MS molecular ion peaks of this compound were found at m/z
m/z: calc. 1962.67; found 1943.58 [M − F]+ and 1962.35 [M]+.
1962.35 as [M]+ and 1943.58 as [M − F]+ (Fig. 1).
The elemental analysis results were also consistent with the
predicted structure of BODIPY-Pc as shown in Scheme 1.
Results and discussion
Ground state electronic absorption and fluorescence spectra
Synthesis and characterization
Fig. 2 shows the normalized absorption spectra of Ethynyl-
In this study, two different synthesis strategies have been BODIPY, Iodo-Pc and BODIPY-Pc in THF. The former two com-
employed for the synthesis of the target BODIPY-zinc(II) pounds were used as references. The electronic spectrum of
phthalocyanine pentad dye (BODIPY-Pc). The first strategy is the newly synthesized BODIPY-Pc shows a panchromatic be-
the base catalyzed cyclotetramerization of BODIPY substituted haviour (Fig. 2) which appears in the absorption over a broad
phthalonitrile (BODIPY-Pht) which is generally used for the spectral region and is able to using an efficient light-harvesting
synthesis of phthalocyanine compounds but the target system. This spectrum contains three main characteristic
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 7561–7569 | 7563

View Article Online
Paper
Dalton Transactions
Scheme 1 Synthesis route of BODIPY-Pc pentad dye. Reagents and conditions: (i) THF/NEt3, [Pd(PPh3)2Cl2], CuI, rt, 24 h; (ii) pentanol, Zn(OAc)2,
reflux, 6 h; (iii) DMAE, ZnCl2, reflux, 18 h (iv) THF/NEt3, [Pd(PPh3)2Cl2], CuI, rt, 16 h.
Fig. 1 MALDI-TOF spectrum of BODIPY-Pc pentad dye.
bands related to the phthalocyanine core (698 nm, ε = 110 571 spectrum of this pentad dye (Fig. 2). For instance, the Q band
and 370 nm, ε = 68 714) and a BODIPY unit (502 nm, ε = based phthalocyanine unit is 18 nm red-shifted when substi-
151 386). The observed single (narrow) Q band at 698 nm is tuted with BODIPY groups. This observed red-shifted Q band
typical for non-aggregated metallophthalocyanine com- indicates that two chromophores (BODIPY and Pc) possess sig-
plexes.34 The B-band is broad due to the superimposition of nificant ground-state electronic interactions.
the B1 and B2 bands in ca. 370 nm regions (Fig. 2). The effect
The aggregation behaviour of BODIPY-Pc was investigated
of the BODIPY substitution on the phthalocyanine skeleton is in the most common organic solvents (acetone, ethyl acetate,
also clearly apparent on inspection of the UV-Vis absorption DMF, toluene, benzene, chloroform, THF, and dichloro-
7564 | Dalton Trans., 2014, 43, 7561–7569
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
Fig. 2 Normalized UV-Vis absorption spectra of BODIPY reference (Ethynyl-BODIPY), zinc phthalocyanine reference (Iodo-Pc) and target BODI-
PY-Pc pentad dye in THF.
Fig. 3 UV-Vis absorption spectra of BODIPY-Pc pentad dye in (a) acetone, ethyl acetate, DMF, THF and (b) toluene, benzene, chloroform, DMSO
(normalized according to the BODIPY absorption maxima) C: ∼6.6 × 10−6 M.
methane) (Fig. 3) to determine a suitable solvent for further pentad dye did not form any aggregated species in this
studies such as singlet oxygen generation and photodegrada- solvent. On the other hand, DMSO is one of the most suitable
tion studies. DMSO was selected for these studies because this solvents for biological studies because this solvent is not toxic
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 7561–7569 | 7565

View Article Online
Paper
Dalton Transactions
Fig. 4 UV-Vis absorption spectra of BODIPY-Pc pentad dye in DMSO at different concentrations. (Inset: plot of absorbance versus concentration.)
Fig. 5 Emission spectra of BODIPY reference (Ethynyl-BODIPY), zinc phthalocyanine reference (Iodo-Pc) and target BODIPY substituted phthalo-
cyanine (BODIPY-Pc) in THF. Excitation wavelength: 480 nm.
at low concentrations. Moreover, the UV-Vis spectra of this expected since there is no absorption at this wavelength
newly synthesized BODIPY-Pc were also recorded at different (Fig. 5).
concentrations (ranging from 1.2 × 10−5 to 2 × 10−6 M)
Energy transfer study
in DMSO (Fig. 4). The studied concentration range obeyed the
Beer–Lambert law for the studied BODIPY-Pc, and 1.0 × 10−5
M
Ethynyl-BODIPY showed a strong fluorescence emission band
at 516 nm when it was excited at 480 nm. However, this band
virtually decreased when excited at the same excitation wave-
length for BODIPY-Pc. Instead, an additional emission band
was observed at 710 nm, which is due to the phthalocyanine
part of this dye. The Iodo-Pc compound did not show any
emission band when excited at 480 nm at the same concen-
tration because this compound does not show any absorption
was decided as the working concentration.
The fluorescence emission peak maximum was observed at
710 nm for BODIPY-Pc when excited at 666 nm. Furthermore,
when this pentad dye was excited from the donor part (at
480 nm), two fluorescence emission peaks were observed at
516 and 710 nm. However, Iodo-Pc did not show any fluo-
rescence emission peak when excited at 480 nm in THF as
7566 | Dalton Trans., 2014, 43, 7561–7569
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
Fig. 6 Normalized absorption and excitation spectra of BODIPY-Pc pentad dye in THF. 710 nm was used as the emission wavelength for the exci-
tation spectrum.
Fig. 7 Absorbance changes during the determination of singlet oxygen quantum yield for BODIPY-Pc pentad dye in DMSO at a concentration of
1.0 × 10−5 M. (Inset: plots of DPBF absorbance versus time.)
in this region. All these investigations indicate that an efficient Singlet oxygen generation study
singlet–singlet energy transfer process in BODIPY-Pc from the
excited BODIPY part to the phthalocyanine unit has occurred. The singlet oxygen generation potential of a photosensitizer is
This energy transfer process is also confirmed by the excitation very important and should be determined for PDT applications
spectrum of BODIPY-Pc which is similar to the absorption because singlet oxygen formation is very noxious and damages
spectrum of this dye in THF (Fig. 6). It is concluded that the tumor cells. In this study, the singlet oxygen generation
the Dexter model which occurs through covalent bonds is the was firstly examined for BODIPY-Pc systems. The singlet
mechanism responsible for energy transfer from donor oxygen quantum yield (ΦΔ) value was determined in DMSO by
BODIPY units to the acceptor phthalocyanine core.35
photochemical methods using diphenylisobenzofuran (DPBF)
The fluorescence quantum yield (ΦF) for Ethynyl-BODIPY in which is a singlet oxygen quencher (Fig. 7). No changes were
THF is 0.55,22 while that for the BODIPY part of BODIPY-Pc observed in the BODIPY and Pc absorption band intensities of
is greatly reduced to 0.08. According to the equation ΦENT
=
the BODIPY-Pc during the ΦΔ determinations (Fig. 7) when
36,37
1 − ΦF(pentad)/ΦF(donor)
where ΦENT is the energy transfer using 30 V light irradiation, indicating that this dye was not
quantum yield, ΦF(pentad) and ΦF(donor) are the fluorescence degraded under this light irradiation during singlet oxygen
quantum yields of the pentad dye (BODIPY-Pc) excited to the determinations. The ΦΔ value of BODIPY-Pc was estimated as
donor part (480 nm) and the donor (Ethynyl-BODIPY), respect- 0.69 in DMSO which is higher than that of the starting Iodo-Pc
ively. The ΦENT value was found to be 0.86, showing that this is compound (ΦΔ = 0.54).38 The substitution of iodine atoms
an efficient energy transfer process for BODIPY-Pc.
with BODIPY units on the phthalocyanine framework has led
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 7561–7569 | 7567

View Article Online
Paper
Dalton Transactions
Fig. 8 Absorption changes of BODIPY-Pc pentad dye in DMSO during irradiation within 1 min intervals. (Inset: plot of Q band absorbance versus
time.)
to an increase in the singlet oxygen generation efficiency oxygen and it showed moderate stability which is very impor-
which might be derived from the energy transfer from BODIPY tant for photocatalytical applications. As a result, this newly
units to the phthalocyanine moiety.
designed BODIPY-Pc system is able to using efficient light-
harvesting systems and it could also be a good candidate as a
photosensitizer in PDT applications for cancer treatment.
Photodegradation study
Find out the degradation rate of a photosensitizer is crucial
because its excretion degree from the body after PDT activation
should be known. The degradation of the molecules under
light illumination is quantified as photodegradation quantum
yield (Φd). The spectral change during photodegradation is
given in Fig. 8. As indicated in this figure, it is worth empha-
sizing that the absorbance changes of BODIPY units (at
502 nm) for BODIPY-Pc remain stable, while the Q band absor-
bance of the Pc unit decreases during light irradiation (100 V)
because this compound was irradiated by 670 nm close to the
Q band region of phthalocyanine. The Φd value of BODIPY-Pc
was found to be 5.14 × 10−4 which is a moderate value (10−6 to
10−3).39 As a result, this pentad dye showed appropriate stabi-
lity for biological applications such as PDT.
Acknowledgements
This study was supported by the Scientific and Technological
Research Council of Turkey (TUBITAK) (project no.
TBAG-111T066).
References
1 S. B. Brown, E. A. Brown and I. Walker, Lancet Oncol., 2004,
5, 497.
2 R. Bonnet, Chem. Soc. Rev., 1995, 24, 19.
3 J. F. Lovell and P. C. Lo, Theranostics, 2012, 9, 815.
4 P. Gregory, J. Porphyrins Phthalocyanines, 2000, 4, 432.
5 K. Daimon, K. Nukada, Y. Sakaguchi and R. Igarashi,
J. Imaging Sci. Technol., 1996, 40, 249.
6 A. Tracz, T. Makowski, S. Masirek, W. Pisula and
Y. H. Geerts, Nanotechnology, 2007, 18, 485303.
7 S. A. Priola, A. Raines and W. S. Caughey, Science, 2000,
287, 1503.
8 E. Ben-Hur and W. S. Chan, in The Porphyrin Handbook, ed.
K. Kadish, K. M. Smith and R. Guilard, Academic Press,
Boston, 2003, vol. 19, p. 1.
9 M. Durmuş, Photochemical and Photophysical Characteriz-
ation, in Photosensitizers in Medicine, Environment, and
Security, ed. T. Nyokong and V. Ahsen, Springer, New York,
2012, p. 135.
Conclusions
In this study, a novel symmetrical BODIPY-zinc phthalocyanine
pentad dye bearing four BODIPY units connected to the
phthalocyanine core via an ethynyl linkage at peripheral posi-
tions (BODIPY-Pc) was synthesized with a high yield for the
first time and this pentad dye was fully characterized by
various spectroscopic techniques such as 1H-NMR, FT-IR,
UV-Vis, fluorescence, MALDI-TOF spectra and elemental analy-
sis as well. The newly synthesized BODIPY-Pc showed light
absorption over a broad spectral region due to the panchro-
matic behaviour and this pentad dye exhibited efficient energy
transfer from the excited BODIPY units to the phthalocyanine 10 S. G. Awuahab and Y. You, RSC Adv., 2012, 2, 11169.
core. The photodynamic therapy potential of this pentad dye 11 A. Kamkaew, S. H. Lim, H. B. Lee, L. V. Kiew, L. Y. Chung
system was also revealed by determination of singlet oxygen
and K. Burgess, Chem. Soc. Rev., 2013, 42, 77.
generation capability and the stability against light irradiation 12 M. D. Yilmaz, O. A. Bozdemir and E. U. Akkaya, Org. Lett.,
in DMSO solution. The BODIPY-Pc produced efficiently singlet
7568 | Dalton Trans., 2014, 43, 7561–7569
2006, 8, 2871.
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
13 A. Coskun, E. Deniz and E. U. Akkaya, Org. Lett., 2005, 7, 27 A. Ogunsipe, J. Y. Chen and T. Nyokong, New J. Chem.,
5187. 2004, 28, 822.
14 O. A. Bozdemir, F. Sozmen, O. Buyukcakir, R. Guliyev, 28 J. H. Brannon and D. Madge, J. Am. Chem. Soc., 1980, 102,
Y. Cakmak and E. U. Akkaya, Org. Lett., 2010, 12, 1400. 62.
15 A. Harriman, G. Izzet and R. Ziessel, J. Am. Chem. Soc., 29 A. Ogunsipe and T. Nyokong, J. Photochem. Photobiol., A:
2006, 128, 10868. Chem., 2005, 173, 211.
16 J. Y. Liu, H. S. Yeung, W. Xu, X. Li and D. K. P. Ng, Org. 30 I. Seotsanyana-Mokhosi, N. Kuznetsova and T. Nyokong,
Lett., 2008, 10, 5421. J. Photochem. Photobiol., A: Chem., 2001, 140, 215.
17 J. Y. Liu, E. A. Ermilov, B. Röder and D. K. P. Ng, Chem. 31 N. Kuznetsova, N. Gretsova, E. Kalmkova, E. Makarova,
Commun., 2009, 1517.
18 E. A. Ermilov, J. Y. Liu, D. K. P. Ng and B. Röder, Phys.
Chem. Chem. Phys., 2009, 11, 6430.
19 J. Y. Liu, Y. Huang, R. Menting, B. Röder, E. A. Ermilov and
D. K. P. Ng, Chem. Commun., 2013, 49, 2998.
S. Dashkevich, V. Negrimovskii, O. Kaliya and
E. Luk’yanets, Russ. J. Gen. Chem., 2000, 70, 133.
32 W. Spiller, H. Kliesch, D. Wöhrle, S. Hackbarth, B. Roder
and G. Schnurpfeil, J. Porphyrins Phthalocyanines, 1998, 2,
145.
20 Y. Rio, W. Seitz, A. Gouloumis, P. Vazquez, J. L. Sessler, 33 M. Durmuş, S. Yeşilot and V. Ahsen, New J. Chem., 2006,
D. M. Guldi and T. Torres, Chem. – Eur. J., 2010, 16, 1929. 30, 675.
21 D. D. Perrin and W. L. F. Armarego, Purification of 34 M. J. Stillman and T. Nyokong, in Phthalocyanines: Pro-
Laboratory Chemicals, Pergamon Press, Oxford, 2nd edn,
perties and Applications, ed. C. C. Leznoff and A. B. P. Lever,
1989.
VCH Publishers, New York, 1989, vol. 1, ch. 3.
22 X. Yin, Y. Li, Y. Zhu, X. Jing, Y. Li and D. Zhu, Dalton 35 B. Albinsson and J. Martensson, J. Photochem. Photobiol. C:
Trans., 2010, 39, 9929.
Photochem. Rev., 2008, 9, 138.
23 J. Godoy, G. Vives and J. M. Tour, Org. Lett., 2010, 12, 1464.
24 E. M. Maya, P. Haisch, P. Vazguez and T. Torres, Tetra-
hedron, 1998, 54, 4397.
25 S. Fery-Forgues and D. Lavabre, J. Chem. Ed., 1999, 76,
1260.
36 K. K. Jensen, S. B. van Berlekom, J. Kajanus, J. Mårtensson
and B. Albinsson, J. Phys. Chem. A, 1997, 101, 2218.
37 K. Kilsa, J. Kajanus, J. Martensson and B. Albinsson,
J. Phys. Chem. B, 1999, 103, 7329.
38 X.-F. Zhang and H.-J. Xu, J. Chem. Soc., Faraday Trans.,
1993, 89, 3347.
26 D. Maree, T. Nyokong, K. Suhling and D. Phillips, J. Por-
phyrins Phthalocyanines, 2002, 6, 373.
39 T. Nyokong, Coord. Chem. Rev., 2007, 251, 1707.
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 7561–7569 | 7569