Chromenone 12-crown-4 substituted zinc phthalocyanine complexes: Investigation of spectral, photophysical and photochemical properties

Article abstract of DOI:10.1016/j.saa.2011.07.003

The synthesis of novel 6,7-[(12-crown-4)-3-[p-(3,4-dicyanophenoxy)phenyl] coumarin (1), 6,7-[(12-crown-4)-3-[p-(2,3-dicyanophenoxy)phenyl]coumarin (2), and their corresponding tetra-(chromenone 12-crown-4)-substituted zinc (II) phthalocyanine complexes (3 and 4) have been prepared. These new compounds have been characterized by elementel analysis, ¹H NMR (1 and 2), MALDI-TOF, IR and UV-Vis spectral data. The fluorescence intensity changes for 1 and 2 by addition of Na⁺ or K⁺ ions have been determined at 25 °C in THF. Intensity of the binding Na⁺- and K ⁺-complexes (1 and 2) have decreased. The effects of the chromenone crown ether on the phthalocyanine molecule concerning photophysical and photochemical properties are also investigated. Photodegredation, singlet oxygen, fluorescence quantum yields, and fluorescence lifetimes of zinc phthalocyanine complexes (3 and 4) are also examined in DMSO.

Full text of DOI:10.1016/j.saa.2011.07.003

Spectrochimica Acta Part A 81 (2011) 690–697
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Chromenone 12-crown-4 substituted zinc phthalocyanine complexes:
Investigation of spectral, photophysical and photochemical properties
Aliye Aslı Esenpınara, Mahmut Durmus¸ b, Mustafa Bulutc,∗
a Kırklareli University, Department of Chemistry, 39100 Kırklareli, Turkey
b Gebze Institute of Technology, Department of Chemistry, P.O. Box 141, Gebze 41400, Kırklareli, Turkey
c Marmara University, Faculty of Art and Science, Department of Chemistry, Kadikoy 34722, Istanbul, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of novel 6,7-[(12-crown-4)-3-[p-(3,4-dicyanophenoxy)phenyl]coumarin (1), 6,7-[(12-
crown-4)-3-[p-(2,3-dicyanophenoxy)phenyl]coumarin (2), and their corresponding tetra-(chromenone
12-crown-4)-substituted zinc (II) phthalocyanine complexes (3 and 4) have been prepared. These new
compounds have been characterized by elementel analysis, 1H NMR (1 and 2), MALDI-TOF, IR and UV–Vis
spectral data. The fluorescence intensity changes for 1 and 2 by addition of Na+ or K+ ions have been
determined at 25 ◦C in THF. Intensity of the binding Na+- and K+-complexes (1 and 2) have decreased.
The effects of the chromenone crown ether on the phthalocyanine molecule concerning photophysi-
cal and photochemical properties are also investigated. Photodegredation, singlet oxygen, fluorescence
quantum yields, and fluorescence lifetimes of zinc phthalocyanine complexes (3 and 4) are also examined
in DMSO.
Received 27 May 2011
Received in revised form 28 June 2011
Accepted 1 July 2011
Keywords:
Coumarin (2H-chromen-2-one)
Crown ether
Phthalocyanine
Fluorescence
Singlet oxygen
Quantum yield
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
into Pc molecules makes it possible to optimize the properties
of the materials used in the semiconductor technology and elec-
Since their accidental discovery over seventy years ago and
subsequent structural elucidation, the phthalocyanines (Pcs) have
been one of the most studied class of functional materials [1,2].
Pcs, remarkably robust and versatile compounds first developed as
industrial pigment, have been applied in a wide range of area such
as photovoltaic devices [3], catalysts [4], gas sensors [5,6], elec-
trochromic displays [7], and photodynamic therapy (PDT) agents
[8,9]. These properties may be modulated by central metals and
huge variety of substitutions attached to the Pc cores [10,11].
By controlling such parameters, diverse functionalities can be
obtained. For example, Pcs containing macrocycles such as crown
ethers show potential applications as ion conducting channel or
heavy metal extraction agents [12,13].
Another interesting group of compounds used as biological
models are crown ethers. Crown ethers, which are capable of selec-
tively binding alkali metal ions, are important building blocks for
constructing specific devices while metal complexation can lead to
a specific response, e.g. a change in electrical conductivity [14–16].
Crown ether substituted phthalocyanines were first synthesized
in 1986 [17–19]. The introduction of crown ether substituents
trochromic devices. The unique ability of crown substituted Pcs
to the cation induced formation of supramolecular heteronuclear
ensembles with ionic conductivity can be used for the design of
materials with new properties [20]. Among crown substituted Pcs,
the tetra crown substituted compounds and their transition metal
complexes are studied the most extensively [21–23].
The aim of the ongoing research is to synthesize and inves-
tigate photophysical (fluorescence quantum yields and lifetimes)
and photochemical (singlet oxygen generation and photodegre-
dation) properties of zinc phthalocyanine complexes substituted
with chromenone crown ether as potential PDT agent. The biolog-
ical importance of both crown ether and Pc’s it is worthwhile to
combine these two functional molecules into a single compound
via synthetic methology which may also exhibit biological activi-
ties and maybe a potential canditate molecule in the application of
PDT. The crown ether groups as substituents on the Pc framework
can penetrate the cancer cell easily for PDT activation to realize
Na+/K+ ion equilibrium. The investigation of photophysical and
photochemical properties, especially singlet oxygen generation, are
very important for PDT of cancer. In this work, we also report on the
effects of the crown ether functionalized chromenon group as sub-
stituent on the photophysical and photochemical parameters. The
objective is the preparation and characterization of zinc phthalo-
cyanines containing four crown ether moieties on the periphery
through oxy bridges have shown to be good candidate for new
fluorescence sensor to Na+ and K+ ions.
∗
Corresponding author. Tel.: +90 216 3479641/1370; fax: +90 216 3478783.
E-mail addresses: mbulut@marmara.edu.tr, mustafabulut50@gmail.com
(M. Bulut).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.07.003

A.A. Esenpınar et al. / Spectrochimica Acta Part A 81 (2011) 690–697
691
This work also explores the effects of ring substitutions
2.4. Photochemical parameters
on the fluorescence quenching of zinc phthalocyanine by 1,4-
benzoquinone (BQ) using the Stern–Volmer relationship.
2.4.1. Singlet oxygen quantum yields
Singlet oxygen quantum yields (˚ꢁ) of the samples (3 and 4)
were determined in DMSO by using the photo-irradiation set-up
described in the literature [32,33]. Typically, 2 ml portion of the
sample solution (concentration = 1 × 10−5 M) containing the sin-
glet oxygen quencher was irradiated in the Q band region with
2. Experimental
2.1. Materials
the photo-irradiation set-up. Singlet oxygen quantum yields (˚ꢁ
)
Unsubstituted zinc (II) phthalocyanine (ZnPc) and 1,3-
diphenylisobenzofuran (DPBF) were purchased from Aldrich.
Potassium carbonate (K2CO3) was purchased from Fluka.
were determined in air using the relative method with ZnPc as
standard and DPBF as chemical quencher. The Eq. (3) was used for
calculation singlet oxygen quantum yield.
Acetonitrile
(CH3CN),
triethyleneglycolditosylate,
N,N-
dimethylaminoethanol (DMAE), sodium carbonate (Na2CO3),
calcium chloride (CaCl2) and anhydrous zinc acetate (Zn(OAc)2)
were purchased from Acros. Quinoline, dimethylsulfoxide (DMSO)
and dimethylformamide (DMF) were dried as described by
Perrin and Armarego [24] before use. Methanol, n-hexane,
chloroform (CHCl3), dichloromethane (DCM), tetrahydro-
furan (THF), acetone and ethanol were freshly distilled.
4-Nitrophthalonitrile [25], 3-nitrophthalonitrile [26], 6,7-
Std
R · I
abs
RStd · Iabs
˚
= ˚Std
(3)
ꢂ
ꢂ
where ˚Sꢂtd is the singlet oxygen quantum yield for the standard
ZnPc (˚Sꢂtd = 0.67 in DMSO) [34]. R and RStd are the DPBF pho-
tobleaching rates in the presence of the respective samples and
standard, respectively. Iabs and IStd are the rates of light absorption
by the sample and standard, resapbesctively. To avoid chain reactions
induced by DPBF in the presence of singlet oxygen the concen-
tration of quencher was lowered to ∼3 × 10−5 M [35]. Solutions
of sensitizer containing DPBF was prepared in the dark and irra-
diated in the Q band region using the photo-irradiation set-up.
DPBF degradation at 417 nm was monitored. The light intensity was
6.66 × 1015 photons/s cm2 for ˚ꢁ determinations.
dihidroksi-3-[p-(3-4-dicyanophenoxy)phenyl]coumarin
and
6,7-dihidroksi-3-[p-(2-3-dicyanophenoxy)phenyl]coumarin [27]
were synthesized according to reported procedures.
2.2. Equipment
The IR spectra were recorded on a Shimadzu FTIR-8300 using
KBr pellets. 1H NMR spectra were recorded on a Varian 500 MHz
spectrometer in DMSO-d6 for compounds 1 and 2. Mass spec-
tra were performed on a Bruker Daltonics Autoflex III MALDI-TOF
spectrometer. Absorption spectra in the UV–Visible region were
recorded with a Shimadzu 2001 UV and Shimadzu UV-1601
spectrophotometers. Fluorescence excitation and emission spectra
were recorded on a Varian Eclipse spectrofluorometer using 1 cm
pathlength cuvettes at room temperature.
2.4.2. Photodegredation quantum yields
Determination of photodegredation quantum yields (˚d) was
carried out as previously described in the literature [32,33]. ˚d was
determined using Eq. (4),
(C0 − Ct) · V · NA
˚
=
(4)
d
Iabs · S · t
Photo-irradiations were done using a General Electric quartz
line lamp (300 W). A 600 nm glass cut off filter (Schott) and a
water filter were used to filter off ultraviolet and infrared radia-
tions 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 with a POWER MAX5100
(Molelectron detector incorporated) power meter.
where C0 and Ct are the concentrations before and after irradi-
ation, respectively. V, NA, S, t and Iabs are reaction volume, the
Avogadro’s constant, irradiated cell area, irradiation time and the
overlap integral of the radiation light source intensity, respectively.
A light intensity of 2.22 × 1016 photons/s cm2 was employed for ˚d
determinations.
2.4.3. Fluorescence quenching by 1,4-benzoquinone (BQ)
2.3. Photophysical parameters
Fluorescence quenching experiments on the substituted zinc
phthalocyanine complexes (3 and 4) were carried out by the addi-
tion of different concentrations of BQ to a fixed concentration of the
complexes (3 and 4), and the concentrations of BQ in the resulting
mixtures were 0, 0.008, 0.016, 0.024, 0.032 and 0.040 M. The fluo-
rescence spectra of substituted ZnPc complexes (3 and 4) at each
BQ concentration were recorded, and the changes in fluorescence
intensity related to BQ concentration by the Stern–Volmer (S–V)
equation [36] as shown in Eq. (5):
2.3.1. Fluorescence quantum yields and lifetimes
Fluorescence quantum yields (˚F) were determined by the com-
parative method using Eq. (1) [28,29]
F · AStd · n2
˚
F
= ˚F (Std)
(1)
FStd · A · n2
Std
where F and FStd are the areas under the fluorescence emission
curves of the samples (3 and 4) and the standard, respectively. A
and AStd are the relative absorbance of the samples and standard at
the excitation wavelength, respectively. n and nstd are the refrac-
tive indices of solvents for the samples and standard, respectively.
Unsubstituted ZnPc (in DMSO) (˚F = 0.20) [30] was employed as
the standard. The absorbance of the solutions was ranged between
0.04 and 0.05 at the excitation wavelength.
I0
= 1 + KSV [BQ]
(5)
I
where I0 and I are the fluorescence intensities of fluorophore in the
absence and presence of quencher, respectively. [BQ] is the concen-
tration of the quencher and KSV is the Stern–Volmer constant which
is the product of the bimolecular quenching constant (kq) and the
ꢀF and is expressed in Eq. (6).
Natural radiative lifetimes (ꢀ0) were determined using Pho-
tochem CAD program which uses the Strickler–Berg equation [31].
The fluorescence lifetimes (ꢀF) were evaluated using Eq. (2).
KSV = kq · ꢀF
(6)
ꢀF
The ratios of I0/I were calculated and plotted against [BQ]
according to Eq. (5), and KSV is determined from the slope.
˚
F
=
(2)
ꢀ0

692
A.A. Esenpınar et al. / Spectrochimica Acta Part A 81 (2011) 690–697
2.5. Synthesis
C 66.18; H 4.12; N 5.32%. Found: C 66.22; H 4.14; N 5.30%. MS
(MALDI-TOF, 2,5-dihydroxybenzoic acid as matrix): m/z 2105 [M]+.
2.5.1.
6,7-[(12-Crown-4)-3-[p-(3,4-dicyanophenoxy)phenyl]coumarin
(1)
2.5.4. 1(4),8(11),15(18),22(25)-Tetrakis[6,7-(12-crown-4)-3-(4-
oxyphenyl)coumarin)]-phthalocyaninato zinc(II) complex
(4)
6,7-Dihydroxy-3-[p-(3,4-dicyanophenoxy)phenyl]coumarin
(1.00 g, 2.50 mmol) and triethylenglycol ditosylate (1.26 g,
2.50 mmol) were dissolved in dry CH3CN (150 ml) under nitrogen
atmosphere and anhydrous Na2CO3 (0.53 g, 5 mmol) was added.
This mixture was stirred for 7 days at 85–90 ◦C and then sol-
vent was evaporated in vacuum. Diluted HCl was added to the
residue and the mixture was extracted with CHCl3 (4 × 30 ml).
The combined organic extracts were washed with water, dried
over CaCl2 and evaporated in vacuum. Crude product was purified
by column chromatography passing through silica gel 60 with
chloroform as eluent and pure chromenone crown ether was
obtained. The compound is soluble in ethanol, methanol, tetrahy-
drofuran (THF), chloroform (CHCl3), dichloromethane (CH2Cl2),
dimethylformamide (DMF) and dimethylsulfoxide (DMSO). Yield:
0.10 g (8%). m.p.: 134–138 ◦C. IR ꢃ(cm−1): 3100–3050 (Ar-CH),
2980–2800 (aliphatic CH), 2200 (C N), 1705 (C O), 1600 (Ar C C),
1245 (Ar-O-Ar). 1H NMR (DMSO-d6, 500 MHz, ı ppm): 8.32 (s, 1H,
lactone-H3), 8.19 (d, 1H, Ar-H6), 8.14 (d, J = 8 Hz, 1H, Ar-H8), 7.86
(dd, J = 8 Hz, 2H, Ar-H4), 7.47 (d, J = 8 Hz, 1H, Ar-H7), 7.30 (d, J = 8 Hz,
2H, Ar-H5), 7.21 (s, 1H, Ar-H1), 7.12 (s, 1H, Ar-H2), 4.18 (m, 4H,
OCH2), 3.80 (m, 4H, OCH2), 3.71 (m, 4H, OCH2). UV–Vis ꢄmax (nm)
(log ε) (THF) (1 × 10−5 M): 363 (5.32). Anal. calcd. for C29H22N2O7:
C 68.23; H 4.34; N 5.49%. Found: C 68.19; H 4.27; N 5.51%. MS
(MALDI-TOF): m/z 510.8 [M]+.
Synthesis and purification were as outlined for 3 except
6,7-[(12-crown-4)-3-[p-(2,3-dicyanophenoxy)phenyl]coumarin
(2) was employed instead of 6,7-[(12-crown-4)-3-[p-(3,4-
dicyanophenoxy)phenyl]coumarin
(1).
The
amounts
of
the reagents employed were: 6,7-[(12-crown-4)-3-[p-(2,3-
dicyanophenoxy)phenyl]coumarin (2) (0.05 g, 0.098 mmol),
Zn(AcO)2 (0.0054 g, 0.024 mmol) dry DMAE (2 ml). The compound
4 is soluble in DMF and DMSO. Yield: 0.045 g (80%), m.p.: > 300 ◦C.
IR ꢃ(cm−1): 3053 (Ar-H), 2918–2861 (aliphatic-CH), 1717 (C
O
lactone), 1614–1569 (C C), 1246 (Ar-O-Ar). UV–Vis ꢄmax (nm)
(log ε) (DMSO) (1 × 10−5 M): 699 (4.83), 669 (4,12), 363 (4.82).
Anal. calcd. for C116H86N8O28Zn: C 66.18; H 4.12; N 5.32%. Found:
C 66.15; H 4.12; N 5.28%. MS (MALDI-TOF, 2,5-dihydroxybenzoic
acid as matrix): m/z 2105 [M]+, 2197 [M+4Na]+.
3. Result and discussion
3.1. Synthesis and characterization
6,7-Dihydroxy-3-[p-(3,4-dicyanophenoxy)phenyl]coumarin
and 6,7-dihydroxy-3-[p-(2,3-dicyanophenoxy)phenyl]coumarin
were reacted with triethylenglycol ditosylate to give the crown
ether analogues (1 and 2) in the presence of Na2CO3 as base in
CH3CN, respectively. The crude products were purified by column
chromatography over silica gel using CHCl3 as eluent and the
chromenone crown ether compounds were obtained in 8% yield
for 1 and in 10% yield for 2 (Scheme 1). The ZnPc complexes show
good solubility in solvents such as DMF and DMSO. The novel
compounds have been characterized by elemental analysis IR, 1H
NMR and MALDI-MS spectroscopy.
2.5.2.
6,7-[(12-Crown-4)-3-[p-(2,3-dicyanophenoxy)phenyl]coumarin
(2)
Synthesis and purification were as outlined for 1 except
6,7-dihydroxy-3-[p-(2,3-dicyanophenoxy)phenyl]coumarin was
employed instead of 6,7-dihydroxy-3-[p-(3,4-dicyanophenoxy)
phenyl]coumarin. The amounts of the reagents employed were:
6,7-dihydroxy-3-[p-(2,3-dicyanophenoxy)phenyl]coumarin
(1.00 g, 2.50 mmol), triethylenglycol ditosylate (1.26 g, 2.50 mmol),
anhydrous Na2CO3 (0.53 g, 5 mmol) in DMF (150 ml). Yield: 0.13 g
(10%). m.p.: 180–184 ◦C. IR ꢃ(cm−1): 3055 (Ar-CH), 2928–2864
(aliphatic CH), 2228 (C≡N), 1714 (C O), 1619–1570 (Ar C C),
1242 (Ar-O-Ar). 1H NMR (DMSO-d6, 500 MHz, ı ppm): 8.28 (s, 1H,
lakton-H3), 7.98 (d, J = 8 Hz, 2H, Ar-H4), 7.92 (t, 1H, Ar-H7), 7.78
(d, J = 8 Hz, 1H, Ar-H6), 7.55 (d, J = 8 Hz, 1H, Ar-H8), 7.41 (d, J = 8 Hz,
2H, Ar-H5), 7.20 (s, 1H, Ar-H1), 7.17 (s, 1H, Ar-H2), 4.11 (m, 4H,
OCH2), 3.82 (m, 4H, OCH2), 3.55 (m, 4H, OCH2). UV–Vis ꢄmax (nm)
(log ε) (THF) (1 × 10−5 M): 355 (3.97), 320 (3.84). Anal. calcd. for
The IR spectra showed two vibration peaks at ca.
2980–2800 cm−1 for compound
1
and 2982–2864 cm−1 for
compound 2 due to aliphatic C–H stretching frequency. The char-
acteristic vibrational peaks of the carbonyl (C O) was appeared in
the region 1705–1714 cm−1. The vibration peaks corresponding to
C–O–C ether chain was appeared in the range 1245–1242 cm−1
.
The characteristic C≡N peaks were also showed at 2220 cm−1 for
compound 1 and 2228 cm−1 for compound 2.
The 1H NMR spectra showed the expected peak resonances
and peak integrals due to the protons of chromenone crown ether
derivatives (1 and 2) in DMSO-d6. The 1H NMR spectra of 1 and 2
showed characteristic signals for etheral (–O–CH2–CH2–O–) pro-
tons at ı 3.71–4.18 ppm for compound 1 and 3.55–4.11 ppm for
compound 2 as multiplets. The singlet peak at ı 8.32 ppm for com-
pound 1 and 8.28 ppm for compound 2 indicated the presence of
lacton protons. In addition, the chemical shifts of the aromatic pro-
tons were observed at between 7.12–8.19 ppm and 7.17–8.28 ppm
for compounds 1 and 2, respectively.
C
29H22N2O7: C 68.23; H 4.34; N 5.49%. Found: C 68.11; H 4.17; N
5.49%. MS (MALDI-TOF): m/z 510.1 [M]+, 511.2 [M+1]+.
2.5.3. 2(3),9(10),16(17),23(24)-Tetrakis[6,7-(12-crown-4)-3-(4-
oxyphenyl)coumarin)]-phthalocyaninato zinc(II) complex
(3)
6,7-[(12-Crown-4)-3-[p-(3,4-dicyanophenoxy)phenyl]coumarin
(1) (0.05 g, 0.098 mmol), Zn(AcO)2 (0.0054 g, 0.024 mmol) and dry
N,N-dimethylamino ethanol (DMAE) (2 ml) were refluxed with
stirring under N2 atmosphere for 24 h. After cooling to room
temperature, the mixture was treated with methanol, and then
the precipitated product was filtered off; washed with water,
methanol, ethanol, acetonitrile, ethyl acetate, aceton, acetic acid
and diethyl ether. The compound 3 is soluble in DMF and DMSO.
Yield: 0.041 g (79%), m.p.: > 300 ◦C. IR ꢃ(cm−1): 3100–3050 (Ar-H),
2985–2800 (aliphatic-CH), 1725 (C O lactone), 1625 (C C), 1230
(Ar-O-Ar). UV–Vis ꢄmax (nm) (log ε) (DMSO) (1 × 10−5 M): 679
(5.02), 648 (4.43), 355 (5.01). Anal. calcd. for C116H86N8O28Zn:
2(3),9(10),16(17),23(24)-Tetrakis[6,7-(12-crown-4)-3-
(4-oxyphenyl)coumarin)]-phthalocyaninato
zinc
(3)
and
1(4),8(11),15(18),22(25)-tetrakis[6,7-(12-crown-4)-3-(4-
oxyphenyl)coumarin)]-phthalocyaninato zinc (4) complexes
have been prepared by cyclotetramerization of novel 6,7-[(12-
crown-4)-3-[p-(3,4-dicyanophenoxy)phenyl] coumarin (1) and
6,7-[(12-crown-4)-3-[p-(2,3-dicyanophenoxy)phenyl]coumarin
(2), respectively. Cyclotetramerization of the dinitril compounds
(1 and 2) to the ZnPc complexes (3 and 4) was confirmed by the
disappearance of the sharp C≡N vibration at 2200 and 2228 cm−1
for compounds 1 and 2, respectively. The IR spectra showed
characteristic vibrational peaks at 3050 cm−1 for complex 3 and

A.A. Esenpınar et al. / Spectrochimica Acta Part A 81 (2011) 690–697
693
HO
O
HO
HO
O
HO
CN
O
CN
O
CN
CN
6,7-dihydroxy-3-[p-(2',3'-dicyanophenoxy)phenyl]coumarin
6,7-dihydroxy-3-[p-(3',4'-dicyanophenoxy)phenyl]coumarin
O
OTs
TsO
O
O
OTs
TsO
O
0
2
Na
CH CN
7 days
2CO3
85-90 C
,
0
3
2
Na
CH CN
7 days
2CO3
85-90 C
,
3
10
9
10
9
1
2
11
O
O
1
2
O
O
11
O
O
O
O
4
5
O
O
11
4
5
CN
O
3
O
9
11
10
4
O
CN
3
5
8
9
10
4
O
2
CN
CN
5
6
8
1
7
6
7
DMAE
Zn(OAc)2
0C
160
0C
DMAE
160
Zn(OAc)2
24 h Reflux
24 h Reflux
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
N
N
O
O
N
N
Zn
N
O
N
O
O
O
O
N
N
N
N
O
N
O
O
O
O
N
N
N
Zn
O
O
O
O
O
N
O
N
O
O
O
O
O
O
O
O
O
O
4
O
O
O
O
O
O
O
O
O
3
Scheme 1. Synthesis route of the 6,7-[(12-crown-4)-3-[p-(3,4-dicyanophenoxy)phenyl]coumarin (1) 6,7-[(12-crown-4)-3-[p-(2,3-dicyanophenoxy)phenyl]coumarin (2) and
the chromenone crown ether substituted zinc (II) phthalocyanine complexes (3 and 4).
3053 cm−1 for complex 4 due to aromatic C–H stretching, and
2985–2800 cm−1 for complex 3 and 2918–2861 cm−1 for complex
4 due to their aliphatic C–H stretching frequency. The characteristic
vibrational peaks of the carbonyl groups (C O) were appeared at
1725 cm−1 and 1717 cm−1 for complexes (3 and 4), respectively.
The vibrational peaks were observed at 1230 cm−1 for complex
3 and 1246 cm−1 for complex 4 corresponding to C–O–C ether
chains. The mass spectra of complexes (3 and 4) confirmed the
proposed structure. The mass spectral study by the MALDI-TOF
technique on the newly synthesized phthalocyanine complexes
(3 and 4) were identified at m/z: 2105 [M]+ (Fig. 1 for complex 4)
in the presence of 2,5-dihydroxybenzoic acid (DHB) (20 mg/ml in
THF) as a matrix.
and 699 nm for 4 in DMSO. The B band region was observed around
355 nm for 3 and 363 nm for 4 in DMSO, (Table 1). The UV–Vis spec-
tra showed monomeric behavior evidenced by a single (narrow) Q
band, typical for metallated phthalocyanine complexes [37]. Thus
substitution of the ZnPc with chromenon crown ether substituents
increased the wavelength of the Q band. The Q band of the periph-
erally and non-peripherally tetra-substituted ZnPc complexes (3
and 4) were red-shifted 7 nm and 27 nm compared to the unsubsti-
tuted ZnPc in DMSO. Non-peripherally tetra-substituted complex
4 was red-shifted 20 nm compared to the peripherally substituted
ZnPc complex 3 (Fig. 2). The observed red spectral shift is typical of
phthalocyanines with substituents at the non-peripheral positions
and has been explained [38,39] due to linear combination of the
atomic orbitals (LCAO) coefficients at the non-peripheral positions
of the highest occupied molecular orbital (HOMO) being greater
than those at the peripheral positions. As a result, the HOMO level is
more destabilized upon non-peripherally substitution than periph-
erally substitution on the Pc framework. Essentially, the energy gap
3.2. Ground state electronic absorption behavior
The ground state electronic spectra of the compounds showed
characteristic absorption bands in the Q band region at 679 nm for 3

694
A.A. Esenpınar et al. / Spectrochimica Acta Part A 81 (2011) 690–697
Fig. 1. The positive ion and linear mode MALDI-TOF MS spectrum of non-peripherally substituted zinc Pc complex (4). Inset spectrum shows expanded molecular mass
region of the complex.
Table 1
Absorption, excitation and emission spectral data for unsubstituted (ZnPc), and the chromenone crown ether substituted zinc Pc complexes (3 and 4) in DMSO.
Compound
Q band
(Log ε)
Excitation
Emission
Stokes shift
ꢄmax (nm)
ꢄEx (nm)
ꢄEm (nm)
ꢁStokes (nm)
ZnPca
3
4
672
679
699
5.14
5.02
4.96
672
683
698
682
689
710
10
10
11
a
Data from Ref [43].
Fig. 2. (a) Absorption spectra of peripherally (3) and non-peripherally (4) sub-
stituted zinc Pc complexes in DMSO. Concentration = 1 × 10−5 M. (b) Aggregation
behavior of 3 in DMSO at different concentrations: 12 × 10−6 (F), 10 × 10−6 (E),
8 × 10−6 (D), 6 × 10−6 (C), 4 × 10−6 (B), 2 × 10−6 (A) M. (Inset: Plot of absorbance
versus concentration.)
Fig. 3. Absorption, excitation and emission spectra of: (a) for complex 3, (b) for
complex 4 in DMSO. Excitation wavelength = 648 nm for 3, 669 nm for 4 in DMSO.

A.A. Esenpınar et al. / Spectrochimica Acta Part A 81 (2011) 690–697
695
Fig. 4. The effect of alkali cations on the fluorescence intensity (a) for 1 and (b) for 2 during the gradual addition of KSCN, (c) for 1 and (d) for 2 addition of NaSCN in THF.
(ꢁE) between the HOMO and lowest unoccupied molecular orbital
(LUMO) becomes smaller, resulting in a ∼20 nm bathochromic shift.
Beer-Lambert low was obeyed for all studied ZnPc complexes in the
concentrations ranging from 12 × 10−6 to 2 × 10−6 M and both ZnPc
complexes did not show aggregation in these concentrations.
(Fig. 4c and d); because the size of the Na+ ion is more suitable for
the cavity of 12-crown-4 than the size of K+ cation.
The fluorescence quantum yields (˚F) of the studied zinc Pc
complexes are given in Table 2. The ˚F values of peripherally and
non-peripherally substituted zinc Pc complexes are similar and
typical of MPc complexes in DMSO. The ˚F value of the substi-
tuted zinc Pc complex 3 is lower compared to unsubstituted zinc
Pc complex but, complex 4 is higher compared to unsubstituted
zinc Pc complex in DMSO which implies that the position effect of
the chromenon crown ether substituents on the phthalocyanine
framework. The non-peripherally substituted complex (4) show
larger ˚F value, suggesting less quenching of the excited singlet
state by non-peripheral substitution compared to peripheral sub-
stitution.
Lifetimes of fluorescence (ꢀF) are calculated using the
Strickler–Berg equation. Using this equation, a good correlation
has been [29] found for the experimentally and theoretically deter-
mined fluorescence lifetimes for the phthalocyanine molecules as
is the case in this work for 3 and 4 in DMSO solution. While ꢀF
value of peripherally and non-peripherally zinc phthalocyanine
complexes were higher than the ꢀF value of unsubstituted ZnPc
complex. The natural radiative lifetime (ꢀ0) values of peripherally
and non-peripherally tetra-substituted zinc Pc complexes (3 and 4)
were also longer when compared to unsubstituted ZnPc in DMSO.
The rate constants for fluorescence (kF) of tetra-substituted zinc Pc
complexes (3 and 4) were lower than unsubstituted ZnPc complex
in DMSO.
3.3. Fluorescence quantum yields and lifetimes
Fluorescence emission spectra were recorded for compounds (1
and 2) in THF, and in DMSO for zinc Pc complexes (3 and 4). The
emission peaks were observed at 443 nm for 1, 445 nm for 2, 689 nm
for 3 and 711 nm for 4 (Table 1). The excitation spectra of the zinc
Pc complexes (3 and 4) are similar to that of absorption spectra,
and they are mirror images of the fluorescence emission spectra.
Fig. 3 shows the absorption, fluorescence emission and excitation
spectra for zinc complexes (3 and 4) in DMSO.
With the aim of assessing the effect of alkali cations on the flu-
orescence behavior of the crown ether substituted coumarins by
spectral methods, the chromenon crown ether compounds (1 and
2) were dissolved in THF and then an alkali metal salt (NaSCN or
KSCN) solutions in ethanol was added. To avoid any effect arising
from dilution due to the addition of the metal salts to the 1 and 2
solutions, the chromenone crown ether compounds (1 and 2) and
metal salts were prepared at concentrations of 1.233 × 10−5 M for
NaSCN and 1.029 × 10−5 M for KSCN in EtOH, respectively. How-
ever, the addition of NaSCN and KSCN to the chromenone crown
ethers (1 and 2) solutions caused decreasing of the fluorescence
intensity of these compounds indicate that the entrance of the bind-
ing Na+ or K+ cations in the crown ether cavitiy. The fluorescence
intensities of complexes 1 and 2 are least decreased with addition
of KSCN (Fig. 4a and b) but on the contrary, fluorescence intensi-
ties of these complexes are more decreased with addition of NaSCN
3.4. Singlet oxygen quantum yields
Energy transfer between the triplet state of phthalocyanines
and ground state molecular oxygen molecules leads to the pro-

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A.A. Esenpınar et al. / Spectrochimica Acta Part A 81 (2011) 690–697
Table 2
Photophysical, photochemical and fluorescence quenching data for unsubstituted (ZnPc) and the chromenone crown ether substituted zinc Pc complexes (3 and 4) in DMSO.
Compound
˚
F
␶
(ns)
␶ (ns)
0
akF (s−1) (×108)
˚
d
(×10−4
)
˚
(
KSV (M−1
)
kq/1010 (M−1 s−1
)
F
ZnPcb
3
4
0.20
0.11
0.25
1.22
3.00
7.33
6.80
27.27
29.32
1.47
0.36
0.34
0.26
0.14
0.37
0.67
0.21
0.38
31.90
22.92
18.85
2.61
0.76
0.31
a
kF is the rate constant for fluorescence. Values calculated using kF = ˚F/ꢀF.
[43].
b
Fig. 5. A typical spectrum for the determination of singlet oxygen quantum
yield. These determinations were for compound 4 in DMSO at a concentration of
1 × 10−5 M. (Inset: Plot of DPBF absorbance versus time.)
duction of singlet oxygen. There is a necessity of high efficiency
of transferred of energy between excited triplet state of phthalo-
cyanine and ground state of oxygen to generate large amounts
of singlet oxygen, essential for photocatalytic reactions such as
PDT.
Many factors are responsible for singlet oxygen including;
triplet excited state energy, ability of substituents and solvents to
quench the singlet oxygen, the triplet excited state lifetime and the
efficiency of the energy transfer between the triplet excited state
and the ground state of oxygen. It is believed that during photosen-
sitization, the phthalocyanine molecule is first excited to the singlet
Fig. 6. Fluorescence emission spectral changes and Stern–Volmer plots for 1,4-
benzoquinone (BQ) quenching of 3 (a) and 4 (b) (1.00 × 10−5 M) on addition of
different concentrations of BQ in DMSO. [BQ] = 0, 0.008, 0.016, 0.024, 0.032, 0.040 M.
state and through intersystem crossing forms the triplet state, and
ꢀ
then transfers the energy to ground state oxygen, O2(3 g), gen-
erating excited singlet state oxygen, O2(1ꢁg), the main cytotoxic
species, which subsequently oxidizes the substrate by Type II mech-
anism.
complex (4) is higher than peripherally substituted complex (3) in
DMSO.
There was no change in the Q band intensity during the ˚ꢁ
determinations, confirming that complexes were not degraded
during singlet oxygen studies (Fig. 5 as an example for complex
4 in DMSO). The ˚ꢁ values of zinc phthalocyanine complexes (3
and 4) are lower when compared to unsubstituted ZnPc in DMSO.
3.6. Fluorescence quenching studies by 1,4-benzoquinone (BQ)
Phthalocyanine complexes may also be used as photosynthetic
mimickers. An essential requirement for a good photosynthetic
mimicker is the ability to undergo excited state charge transfer with
ease, and Pc-quinone systems have proved to be favored candidates
for understanding of energy transfer process [41,42].
The fluorescence quenching of zinc phthalocyanine com-
plexes by 1,4-benzoquinone (BQ) in DMSO was found to
obey Stern–Volmer kinetics, which is consistent with diffusion-
controlled bimolecular reactions. Fig. 6 shows the quenching of
complexes 3 and 4 by BQ in DMSO solution. The slope of the plots
shown in inset of Fig. 6 gave KSV value, listed in Table 2. The KSV
values of the peripherally and non-peripherally zinc Pc complexes
(3 and 4) were lower than unsubstituted ZnPc. The substitution
with coumarin and crown ether groups seems to decrease the KSV
values of the complexes in DMSO. The bimolecular quenching con-
stant (kq) values of the substituted zinc phthalocyanine complexes
(3 and 4) were also lower than for unsubstituted ZnPc, but gener-
3.5. Photodegradation studies
Degradation of the photosensitizers under light irradiation can
be used to study their stability and this is especially important for
those photosensitizers intended for use as photocatalysts. The col-
lapse of the absorption spectra without any distortion of the shape
confirms clean photodegradation not associated with phototrans-
formation into different forms of MPc.
Stable zinc phthalocyanine complexes show ˚d values as low as
10−6 and for unstable molecules, values of the order of 10−3 have
been reported [40]. It seems that synthesized zinc Pc complexes (3
and 4) also show similar ˚d values and stability to the known zinc
phthalocyanine complexes. The ˚d values of the peripherally and
non-peripherally zinc Pc complexes are lower than unsubstituted
ZnPc and the ˚d value of the non-peripherally substituted zinc Pc

A.A. Esenpınar et al. / Spectrochimica Acta Part A 81 (2011) 690–697
697
ally, substitution with coumarin and crown ether groups seems to
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Acknowledgement
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