Synthesis, photophysical, photochemical and electrochemical properties of crown ether bearing coumarin substituted phthalocyanines

Article abstract of DOI:10.1016/j.ica.2011.11.014

Zinc (II), cobalt (II) and copper (II) phthalocyanines substituted at the peripheral (complexes 5, 6 and 7) and non-peripheral (complexes 8, 9 and 10) positions with 7,8-(15-crown-5)-3-(4-oxyphenyl)coumarin groups have been prepared and characterized. The photophysical and photochemical properties of zinc (II) Pc complexes (5 and 8) were also described. The singlet oxygen quantum yields (0.54 for 5, 0.65 for 8) are indicating the potential of the complexes as photosensitizers in applications of PDT. The redox processes of the complexes were identified by voltammetry and in situ spectroelectrochemistry. Alpha and beta-substituted complexes displayed metal- and/or phthalocyanine ring-based redox processes. It was found that the kind of substitution affects the redox processes of the phthalocyanine complexes considerably, due to the difference in their aggregation behaviors.

Full text of DOI:10.1016/j.ica.2011.11.014

Inorganica Chimica Acta 383 (2012) 287–299
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, photophysical, photochemical and electrochemical properties
of crown ether bearing coumarin substituted phthalocyanines
Meryem Çamur a, Mahmut Durmusß b, A. Rıza Özkaya c, Mustafa Bulut c,
⇑
a Kırklareli University, Department of Chemistry, 39100 Kırklareli, Turkey
b Gebze Institute of Technology, Department of Chemistry, P.O. Box 141, Gebze 41400, Turkey
c Marmara University, Department of Chemistry, 34722 Göztepe-Istanbul, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 June 2011
Received in revised form 3 October 2011
Accepted 8 November 2011
Available online 25 November 2011
Zinc (II), cobalt (II) and copper (II) phthalocyanines substituted at the peripheral (complexes 5, 6 and 7)
and non-peripheral (complexes 8, 9 and 10) positions with 7,8-(15-crown-5)-3-(4-oxyphenyl)coumarin
groups have been prepared and characterized. The photophysical and photochemical properties of zinc
(II) Pc complexes (5 and 8) were also described. The singlet oxygen quantum yields (0.54 for 5, 0.65
for 8) are indicating the potential of the complexes as photosensitizers in applications of PDT. The redox
processes of the complexes were identified by voltammetry and in situ spectroelectrochemistry. Alpha
and beta-substituted complexes displayed metal- and/or phthalocyanine ring-based redox processes. It
was found that the kind of substitution affects the redox processes of the phthalocyanine complexes con-
siderably, due to the difference in their aggregation behaviors.
Keywords:
Phthalocyanine
Coumarin
Crown ether
Singlet oxygen
Fluorescence
Electrochemistry
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
mophores have been extensively studied as fluorescent metal indi-
cators, especially for alkaline and alkaline-earth metal ions [18].
Phthalocyanines (Pcs) are planar aromatic macrocycles consist-
ing of four isoindole units presenting an 18 -electron aromatic
Crown ether containing Pcs have been shown to possess a combi-
nation of three very useful properties [19], namely, they have an
p
cloud delocalized over an arrangement of alternated carbon and
nitrogen atoms [1]. Pcs have been an important class of dyes and
pigments since their first synthesis early in the last century [2].
Other areas of current interest include applications in catalysis
[3], chemical sensors [4], electrochromism [5], photodynamic ther-
apy (PDT) [6], nonlinear optical (NLO) materials [7] and liquid crys-
tals [8] as a result of newly synthesized compounds [9].
extended p-conjugated core which plays a key role in the charge
transfer properties of stacked Pcs, they contain crown ethers which
can host alkaline ions and they possess alkyl side chains which
can induce liquid crystalline behavior. Furthermore, crown ether-
substituted Pcs can be stacked to create ion-conducting channels
[20–22]. A combination of these three potentially promising units
(i.e. phthalocyanines, crown ethers and coumarins) for the purpose
of constructing novel supramolecular structures with novel multi-
functional properties have attracted research interests. Attachment
of crown ether and coumarin groups to the Pc ring significantly in-
creases the solubility of Pcs in many organic solvents, leading to
significant advances in research such as biological modeling,
homogeneous catalysis, alkaline or earth alkaline and lanthanide
metal extractions [23,24].
MPc complexes have been proved as highly promising photo-
sensitizers for PDT due to their intense absorption in the red region
of the visible light. High triplet state quantum yields and long trip-
let lifetimes are required for efficient sensitization of them. The
photophysical properties of the Pc dyes are strongly influenced
by the presence and nature of the central metal ion. Complexes
of Pc with transition metals give short triplet lifetimes to these
dyes. Closed shell and diamagnetic ions, such as Zn2+, Al3+ and
Si4+, give Pc complexes with both high triplet yields and long
Coumarin (2H-1-benzopyran-2-one) is the simplest naturally
occurring phenolic substance possessing fused benzene and a-pyr-
one rings. The coumarin derivatives exist in a variety of forms, due
to the various substitutions possible in their basic structure, which
modulate their biological activities [10,11]. Coumarins possess
anti-inflammatory [12], antioxidant [13], antithrombotic [14],
antiviral [15], antimicrobial [16] and anti-carcinogenic [17] prop-
erties. Coumarins exhibit large Stokes shifts, which prevent the
overlap between the excitation and emission spectra, and they
usually have excellent fluorescence quantum yields [18]. Another
interesting group of compounds used as biological models are
crown ethers. Crown-ether derivatives bearing coumarin chro-
⇑
Corresponding author. Tel.: +90 216 3479641/1370; fax: +90 216 3478783.
E-mail
addresses:
mbulut@marmara.edu.tr,
mustafabulut50@gmail.com
(M. Bulut).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.11.014

288
M. Çamur et al. / Inorganica Chimica Acta 383 (2012) 287–299
lifetimes and they are good candidate for photocatalytic reactions
such as PDT [25–28].
was additionally placed in the light path before the sample. Light
intensities were measured with a POWER MAX5100 (Molelectron
detector incorporated) power meter.
In this work, we report on the effects of the crown ether bearing
coumarin groups as substituent and the position of the substituent
on the photophysical, photochemical and electrochemical proper-
ties of Zn(II), Co(II) and Cu(II) Pcs. The main feature of the crown
ether groups is that they can hold the alkali cations within their
cavity. Crown ether groups have been preferred as substituent on
the Pc ring because they can penetrate easily into the cell. The
photophysical (fluorescence lifetime and quantum yields) and pho-
tochemical (singlet oxygen and photodegradation quantum yields)
properties were investigated only on the Zn(II) Pc complexes.
Other studied Co(II) and Cu(II) Pc complexes exhibited weak
photophysical and photochemical properties due to the transition
metal nature of Co(II) and Cu(II) atoms. This work also explores
the effects of ring substitutions and position on the fluorescence
quenching of zinc(II) Pcs by 1,4-benzoquinone (BQ) using the
Stern–Volmer relationship. Since PDT activity is mainly based on
singlet oxygen, its production is determined by the dye-sensitized
photooxidation of 1,3-diphenylisobenzofuran (DPBF), a specific
scavenger of this toxic species [29]. The understanding of the redox
properties of the Pc complexes is important in terms of their appli-
cations in many areas. The redox or electron transfer processes of
these complexes occur at either the Pc ring or the metal center.
However, it is not possible to distinguish such processes by vol-
tammetry alone. In situ spectroelectrochemistry provide additional
support for the assignment of these redox processes. Moreover,
spectroelectrochemical studies of Pcs are also important in identi-
fying the effect of aggregation-disaggregation equilibrium of Pcs on
their redox behavior. Therefore, we also investigate the electro-
chemical and in situ spectroelectrochemical behavior of the syn-
thesized Pc complexes.
The cyclic and differential pulse voltammetry measurements
were carried out with a PAR VersoStat II Model potentiostat/galva-
nostat controlled by an external PC and utilizing a three-electrode
configuration at 25 °C. The working electrode was a Pt plate with a
surface area of 0.10 cm2. The surface of the working electrode was
polished with H2O suspension of Al2O3 before each run. The last
polishing was done with a particle size of 50 nm of Al2O3. A Pt wire
served as the counter electrode. Saturated calomel electrode (SCE)
was employed as the reference electrode and separated from the
bulk of the solution by a double bridge. Electrochemical grade tet-
rabutylammonium perchlorate (TBAP) in extra pure DMSO was
employed as the supporting electrolyte at a concentration of
0.10 moldmꢁ3. High purity N2 was used for deoxygenating the
solution at least 20 min prior to each run and to maintain a nitro-
gen blanket during the measurements. In situ spectroelectrochem-
ical measurements were carried out by an Agilent Model 8453
diode array spectrophotometer equipped with the potentiostat/
galvanostat and utilizing an optically transparent thin layer cell
with three-electrode configuration at 25 °C. The working electrode
was transparent Pt gauze. Pt wire counter electrode and a SCE
reference electrode separated from the bulk of the solution by a
double bridge were used.
2.2. Synthesis
2.2.1. Generel procedure for the synthesis of phthalonitriles (3 and 4)
A
mixture of 7,8-dihydroxy-3-[p-(30,40-dicyanophenoxy)
phenyl]coumarin (1) or 7,8-dihydroxy-3-[p-(20,30-dicyanophen-
oxy)phenyl]coumarin (2) (1.00 g, 2.52 mmol), tetraethylene glycol
ditosylate (1.269 g, 2.52 mmol) and anhydrous Na2CO3 (0.535 g,
5.05 mmol) in acetonitrile (CH3CN) (100 ml) was heated to reflux
for 5 days under nitrogen atmosphere. After the removal of
solution by distillation, the precipitate was dissolved in chloroform
(CHCl3), washed with water and dried on Na2SO4. The crude
products were purified by column chromatography on silica gel
with CHCl3 as eluent.
2. Experimental
2.1. Materials and equipment
Unsubstituted zinc (II) phthalocyanine (ZnPc), 1,3-diphenyliso-
benzofuran (DPBF), tetrabutylammonium hydroxide (TBAOH) and
2,3,4-trihydroxybenzaldehyde were purchased from Aldrich. Zinc
(II) acetate, cobalt (II) acetate, copper (II) acetate, sodium carbon-
ate (Na2CO3), sodium acetate (NaOAc) and tetraethylene glycol
ditosylate were purchased from Fluka. All solvents were dried as
described by Perrin and Armarego [30] before use. p-(20,30-Dicy-
anophenoxy)phenylacetic acid [31], 7,8-dihydroxy-3-[p-(30,40-
dicyanophenoxy)phenyl]coumarin (1) [32] and 7,8-dihydroxy-3-
[p-(20,30-dicyanophenoxy)phenyl]coumarin (2) [33] were synthe-
sized and purified according to literature procedures.
2.2.1.1. 7,8-(15-Crown-5)-3-[p-(30,40-dicyanophenoxy)phenyl]couma-
rin (3). Yield: 0.509 g (37%). M.p.: 185 °C. FT-IR (KBr), m
max/(cmꢁ1):
3085–3050 (Ar–CH), 2950-2885 (aliphatic –CH), 2225 (C„N), 1720
(C@O, lactone), 1605 (C@C), 1578–1450 (Ar C@C), 1295–1245 (Ar–
O–Ar), 1184-1112 (Ar–O–C). 1H NMR (CDCl3, 500 MHz): 7.85 (s,
1H, coumarin 4-H), 7.82 (dd, J = 8 and 2 Hz, 2H, Ar–H), 7.79 (d,
J = 8 Hz, 1H, Ar–H), 7.39 (d, J = 2 Hz, 1H, Ar–H), 7.35 (dd, J = 8 and
2 Hz, 1H, Ar–H), 7.27 (d, J = 8 Hz, 1H, Ar–H), 7.18 (dd, J = 8 and
2 Hz, 2H, Ar–H), 6.93 (d, J = 8 Hz, 1H, Ar–H), 4.44 (t, J = 6 Hz, 2H,
–OCH2), 4.29 (t, J = 6 Hz, 2H, –OCH2), 4.04–4.01 (m, 4H, –OC(CH2)2),
3.83–3.78 (m, 8H, –OCCO(CH2)2O(CH2)2). UV–Vis (CHCl3) kmax (nm)
Infrared spectra (IR) were recorded on a Shimadzu FTIR-8300
Fourier Transform Infrared Spectrophotometer using KBr pellets,
electronic spectra were recorded on a Shimadzu UV-2450 and Shi-
madzu UV-2001 UV–Vis spectrophotometers. Elemental analyses
were performed by the Instrumental Analysis Laboratory of the
TUBITAK Marmara Research Centre. 1H NMR spectra were recorded
on a Varian Unity Inova 500 MHz spectrometer using TMS as an
internal standard. Mass spectra were performed on a Bruker Auto-
flex III MALDI-TOF spectrometer using 2,5-dihydroxybenzoic acid
(DHB, 0.02 g/cm3 in THF) as matrix. MALDI samples were prepared
by mixing the complex (0.02 g/cm3 in DMF) with the matrix solu-
(loge): 341 (4.03). MS (MALDI-TOF); calc. for C31H26N2O8: m/z 554
[M]+, found: m/z 577 [M+Na]+. Anal. Calc. for C31H26N2O8: C, 67.15;
H, 4.69; N, 5.05. Found: C, 67.18; H, 4.65; N, 5.07%.
2.2.1.2. 7,8-(15-Crown-5)-3-[p-(20,30-dicyanophenoxy)phenyl]couma-
rin (4). Yield: 0.340 g (24%). M.p.: 170 °C. FT-IR (KBr), m
max/(cmꢁ1):
3070–3052 (Ar–CH), 2915-2870 (aliphatic –CH), 2230 (C„N), 1718
(C@O, lactone), 1606 (C@C), 1507–1457 (Ar C@C), 1292-272 (Ar–
O–Ar), 1119–1074 (Ar–O–C). 1H NMR (CDCl3, 500 MHz): 7.83 (s,
1H, coumarin 4-H), 7.81 (bd, 2H, Ar–H), 7.64 (t, J = 6 Hz, 1H, Ar–
H), 7.53 (d, J = 8 Hz, 1H, Ar–H), 7.27 (d, J = 8 Hz, 1H, Ar–H), 7.22
(d, J = 8 Hz, 1H, Ar–H), 7.20 (dd, J = 8 and 2 Hz, 2H, Ar–H), 6.93
(d, J = 8 Hz, 1H, Ar–H), 4.43 (t, J = 6 Hz, 2H, ꢁOCH2), 4.29 (t,
J = 6 Hz, 2H, –OCH2), 4.04–4.01 (m, 4H, –OC(CH2)2), 3.83–3.78 (m,
tion (1:10 v/v) in
a
0.5 cm3 Eppendorf micro tube. Finally,
1 ꢀ 10ꢁ3 cm3 of this mixture was deposited on the sample plate,
dried at room temperature and then analyzed. 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 radiations, respectively. An
interference filter (Intor, 670 nm with a band width of 40 nm)
8H, –OCCO(CH2)2O(CH2)2). UV–Vis (CHCl3) kmax (nm) (loge): 340

M. Çamur et al. / Inorganica Chimica Acta 383 (2012) 287–299
289
(4.06). MS (MALDI-TOF); calc. for C31H26N2O8: m/z 554 [M]+, found:
m/z 577 [M+Na]+. Anal. Calc. for C31H26N2O8: C, 67.15; H, 4.69; N,
5.05. Found: C, 67.20; H, 4.73; N, 5.07%.
1508–1478 (Ar C@C), 1292–1247 (Ar–O–Ar), 1122–1076 (Ar–O–
C). UV–Vis kmax (DMSO) (nm) (log ): 336 (4.76), 604 (shoulder,
3.82), 676 (4.51). MS (MALDI-TOF, DHB as matrix); calc. for
e
C
124H104N8O32Co: m/z 2275 [M]+, found: m/z 2275 [M]+, 2298
2.2.2. General procedure for the metallo phthalocyanines (5–7, 8–10)
A mixture of 3 or 4 (0.100 g, 0.181 mmol) and metal salt [Zn(A-
cO)2ꢂ2H2O (0.010 g, 0.045 mmol), Co(AcO)2.4H2O (0.012 g,
0.048 mmol) and Cu(AcO)2 (0.009 g, 0.049 mmol] in dry 2-dimeth-
ylaminoethanol (DMAE) (1.5 ml) was refluxed with stirring for
24 h under nitrogen atmosphere. After cooling to room tempera-
ture, methanol (5 ml) was added to precipitate the product. The
green product was filtered and washed with water, methanol, eth-
anol, acetonitrile, ethyl acetate, aceton, acetic acid and diethyl
ether. The crude products were purified by column chromatogra-
phy on silica gel with CHCl3 as eluent.
[M+Na]+. Anal. Calc. for C124H104N8O32Co: C, 65.41; H, 4.57; N,
4.92. Found: C, 65.36; H, 4.51; N, 4.90%.
2.2.2.6. 1(4),8(11),15(18),22(25)-Tetra[7,8-(15-crown-5)-3-(4-oxy-
phenyl)coumarin]-phthalocyaninato copper (II) (10). Yield: 0.052 g
(50%). M.p. >300 °C. FT-IR (KBr),
m
max/(cmꢁ1): 3065–3053 (Ar–
CH), 2924–2870 (aliphatic CH), 1719 (C@O, lactone), 1605 (C@C),
1506–1474 (Ar C@C), 1291–1248 (Ar–O–Ar), 1125–1076 (Ar–O–
C). UV–Vis kmax (DMSO) (nm) (log
e): 339 (4.92), 615 (shoulder,
3.98), 691 (4.73). MS (MALDI-TOF, DHB as matrix); calc. for
C
124H104N8O32Cu: m/z 2280 [M]+, found: m/z 2280 [M]+, 2303
[M+Na]+, 2319 [M+K]+. Anal. Calc. for C124H104N8O32Cu: C, 65.26;
2.2.2.1. 2(3),9(10),16(17),23(24)-Tetra[7,8-(15-crown-5)-3-(4-oxy-
H, 4.56; N, 4.91. Found: C, 65.20; H, 4.52; N, 4.86%.
phenyl)coumarin]-phthalocyaninato zinc (II) (5). Yield: 0.089 g
(86%). M.p. >300 °C. FT-IR (KBr),
m
max/(cmꢁ1): 3078–3036 (Ar–
2.3. Photophysical parameters
CH), 2925–2863 (aliphatic CH), 1719 (C@O, lactone), 1605 (C@C),
1508–1463 (Ar C@C), 1291–1233 (Ar–O–Ar), 1122–1077 (Ar–O–
C). 1H NMR (CDCl3, 500 MHz): 7.83–7.59 (m, 40H, Ar–H), 4.40–
2.3.1. Fluorescence quantum yields and lifetimes
Fluorescence quantum yields (UF) were determined by the
comparative method using Eq. (1) [34,35]:
3.75 (m, 64H, –OCH2). UV–Vis kmax (DMSO) (nm) (loge): 355
(5.25), 619 (shoulder, 4.55), 681 (5.07). MS (MALDI-TOF, DHB as
matrix); calc. for C124H104N8O32Zn: m/z 2281 [M]+, found: m/z
2281 [M]+, 2304 [M+Na]+. Anal. Calc. for C124H104N8O32Zn: C,
65.23; H, 4.56; N, 4.91. Found: C, 65.28; H, 4.61; N, 4.85%.
F ꢂ AStd ꢂ n2
UF
¼
UF ðStdÞ
ð1Þ
FStd ꢂ A ꢂ n2Std
where F and FStd are the areas under the fluorescence emission
curves of the samples (5 and 8) 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 sample and standard, respectively.
Unsubstituted ZnPc (UF = 0.20 in DMSO) [36] was employed as
the standard. Both the sample and standard were excited at the
same wavelength. The absorbance of the solutions was ranged be-
tween 0.04 and 0.05 at the excitation wavelength.
2.2.2.2. 2(3),9(10),16(17),23(24)-Tetra[7,8-(15-crown-5)-3-(4-oxy-
phenyl)coumarin]-phthalocyaninato cobalt (II) (6). Yield: 0.063 g
(61%). M.p. >300 °C. FT-IR (KBr),
m
max/(cmꢁ1): 3085–3050 (Ar–
CH), 2958–2874 (aliphatic CH), 1720 (C@O, lactone), 1601 (C@C),
1512–1465 (Ar C@C), 1295–1240 (Ar–O–Ar), 1120–1040 (Ar–O–
C). UV–Vis kmax (DMSO) (nm) (log
e): 339 (4.95), 595 (shoulder,
4.14), 665 (4.76). MS (MALDI-TOF, DHB as matrix); calc. for
C
124H104N8O32Co: m/z 2275 [M]+, found: m/z 2275 [M]+, 2298
Natural radiative lifetimes (
chem CAD program which uses the Strickler–Berg equation [37].
The fluorescence lifetimes (sF) were evaluated using Eq. (2)
s0) were determined using Photo-
[M+Na]+. Anal. Calc. for C124H104N8O32Co: C, 65.41; H, 4.57; N,
4.92. Found: C, 65.48; H, 4.54; N, 4.96%.
sF
s0
2.2.2.3. 2(3),9(10),16(17),23(24)-Tetra[7,8-(15-crown-5)-3-(4-oxy-
UF
¼
ð2Þ
phenyl)coumarin]-phthalocyaninato copper (II) (7). Yield: 0.063 g
(61%). M.p. >300 °C. FT-IR (KBr),
m
max/(cmꢁ1): 3080–3065 (Ar–
CH), 2960–2848 (aliphatic CH), 1722 (C@O, lactone), 1601 (C@C),
1510–1445 (Ar C@C), 1295–1238 (Ar–O–Ar), 1120–1040 (Ar–O–
2.4. Photochemical parameters
2.4.1. Singlet oxygen quantum yields
C). UV–Vis kmax (DMSO) (nm) (log
e): 341 (4.99), 603 (shoulder,
4.24), 673 (4.64). MS (MALDI-TOF, DHB as matrix); calc. for
C
124H104N8O32Cu: m/z 2280 [M]+, found: m/z 2280 [M]+, 2303
Singlet oxygen quantum yields (UD) of the samples (5 and 8)
were determined as previously explained in detail [38–40]. Typi-
cally, 2 cm3 portion of the samples (5 and 8) solutions (concentra-
tion = 1 ꢀ 10ꢁ5 moldmꢁ3) containing the singlet oxygen quencher
was irradiated in the Q band region with the photo-irradiation
set-up described in references [38–40]. Singlet oxygen quantum
yields (UD) were determined in air using the relative method with
unsubstituted ZnPc (in DMSO) as reference; and DPBF as chemical
quencher for singlet oxygen, using Eq. (3):
[M+Na]+, 2319 [M+K]+. Anal. Calc. for C124H104N8O32Cu: C, 65.26;
H, 4.56; N, 4.91. Found: C, 65.23; H, 4.60; N, 4.95%.
2.2.2.4. 1(4),8(11),15(18),22(25)-Tetra[7,8-(15-crown-5)-3-(4-oxy-
phenyl)coumarin]-phthalocyaninato zinc (II) (8). Yield: 0.057 g
(55%). M.p. >300 °C. FT-IR (KBr),
m
max/(cmꢁ1): 3068–3053 (Ar–
CH), 2915–2863 (aliphatic CH), 1719 (C@O, lactone), 1606 (C@C),
1507–1479 (Ar C@C), 1292–1244 (Ar–O–Ar), 1122–1076 (Ar–O–
C). 1H NMR (CDCl3, 500 MHz): 7.78–7.60 (m, 40H, Ar–H), 4.43-
Std
3.81 (m, 64H, –OCH2). UV–Vis kmax (DMSO) (nm) (loge): 352
R ꢂ I
UD
¼
USDtd
ð3Þ
abs
(5.19), 632 (shoulder, 4.52), 697 (5.22). MS (MALDI-TOF, DHB as
matrix); calc. for C124H104N8O32Zn: m/z 2281 [M]+, found: m/z
2281 [M]+, 2304 [M+Na]+. Anal. Calc. for C124H104N8O32Zn: C,
65.23; H, 4.56; N, 4.91. Found: C, 65.28; H, 4.59; N, 4.95%.
RStd ꢂ Iabs
where USDtd is the singlet oxygen quantum yield for the standard
(
USDtd = 0.67 for unsubstituted ZnPc in DMSO) [41]; R and RStd are
the DPBF photobleaching rates in the presence of the samples (5
2.2.2.5. 1(4),8(11),15(18),22(25)-Tetra[7,8-(15-crown-5)-3-(4-oxy-
and 8) and standard, respectively; Iabs and IStd are the rates of light
abs
phenyl)coumarin]-phthalocyaninato cobalt (II) (9). Yield: 0.076 g
(74%). M.p. >300 °C. FT-IR (KBr),
CH), 2948–2868 (aliphatic CH), 1718 (C@O, lactone), 1608 (C@C),
absorption by the samples (5 and 8) and standard, respectively. To
avoid chain reactions induced by DPBF in the presence of singlet
oxygen [42], the concentration of quencher (DPBF) was lowered
m
max/(cmꢁ1): 3065–3048 (Ar–

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M. Çamur et al. / Inorganica Chimica Acta 383 (2012) 287–299
to ꢃ3 ꢀ 10ꢁ5 moldmꢁ3. Solutions of sensitizer containing quencher
(DPBF) were prepared in the dark and irradiated in the Q band
region using the photoirradiation setup. DPBF degradation at
417 nm was monitored. The light intensity 7.33 ꢀ 1015
photonssꢁ1 cmꢁ2 was used for UD determinations.
2870 cmꢁ1, respectively. The characteristic vibration peaks of the
nitrile (C„N) and carbonyl groups (C@O, lactone) appeared at
2225, 2230 cmꢁ1 and 1720, 1718 cmꢁ1, respectively. The 1H NMR
spectra of 3 and 4 in CDCl3 showed characteristic signals for etheric
(–OCH2CH2O–) protons at 4.44-3.78 ppm for 3 and 4.43–3.78 ppm
for 4. The singlets at 7.85 ppm for 3 and 7.83 ppm for 4 indicated
the presence the proton of coumarin at position of 4. In addition
the chemical shifts of the aromatic protons are observed at 7.82–
6.93 ppm for compound 3 and 7.81–6.93 ppm for compound 4.
Molecular ion peaks were easily identified at m/z = 577 [M+Na]+
for 3 and 4.
2.4.2. Photodegradation quantum yields
Photodegradation quantum yield (Ud) determinations were
carried out using the experimental set-up described in literature
[38–40]. For determination of photodegradation quantum yields
(Ud), the usual Eq. (4) was employed:
The sharp vibration for the C„N groups in the FT-IR spectra of
phthalonitriles 3 and 4 at 2225 and 2230 cmꢁ1, respectively, disap-
peared after conversion into metallo Pcs (5–7 and 8–10). The 1H
NMR spectra of complexes showed ring protons between 7.83–
7.59 ppm for 5 and 7.78–7.60 ppm for 8 as multiplets. Etheric (–
OCH2CH2O–) protons were observed between 4.40–3.75 ppm for
5 and 4.43–3.81 ppm for 8 as multiplets. The MALDI-TOF mass
spectra of Pcs (5–7 and 8–10) confirmed the proposed structures;
molecular ions were easily indentified at m/z: 2281 [M]+ for 5
and 8, 2275 [M]+ for 6 and 9, 2280 [M]+ for 7 and 10. The elemental
analyses for complexes 5–7 and 8–10 gave satisfactory results that
were close to calculated values.
C0 ꢁ Ct ꢂ V ꢂ NA
Ud
¼
ð4Þ
Iabs ꢂ S ꢂ t
where C0 and Ct are the samples (5 and 8) concentrations before and
after irradiation, respectively. V is the reaction volume; S is the irra-
diated cell area (2.0 cm2); t is the irradiation time; NA is Avogadro’s
number and Iabs is the overlap integral of the radiation source inten-
sity and the absorption of the Pc (the action spectrum) in the region
of the interference filter transmittance.
A light intensity of
2.20 ꢀ 1016 photonssꢁ1 cmꢁ2 was employed for Ud determinations.
2.4.3. Fluorescence quenching by 1,4-benzoquinone (BQ)
Fluorescence quenching experiments of Pc complexes (5 and 8)
were carried out by the addition of different concentrations of BQ
to a fixed concentration of the Pc complexes, and the concentra-
tions of BQ in the resulting mixtures were 0, 0.008, 0.016, 0.024,
0.032 and 0.040 moldmꢁ3. The fluorescence spectra of Pc com-
plexes (5 and 8) at each BQ concentration were recorded, and the
changes in fluorescence intensity related to BQ concentration by
the Stern–Volmer (SV) Eq. (5) [43]:
3.2. Electronic absorption spectra
The electronic spectra of the peripherally and non-peripherally
tetra-substituted Pc complexes (5–7, 8–10) showed characteristic
Q band absorptions in DMSO, Fig. 1. The
p–
p⁄ transitions for Q
band absorptions were observed at 681 (5), 665 (6), 679 (7), 697
(8), 676 (9) and 695 nm (10) in DMSO, Table 1. The substitution
of the crown ether and coumarin substituents on the Pc ring in-
creased the wavelength of the Q band. The Q bands of the non-
peripherally metallo Pc complexes were red-shifted 16 nm (be-
tween 5 and 8), 11 nm (between 6 and 9) and 16 nm (between 7
and 10) compared to the peripherally metallo Pc complexes in
DMSO (Fig. 1). The observed red spectral shifts are typical of Pcs
with substituents at the non-peripheral positions and have been
explained [44,45] 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 desta-
bilized upon non-peripherally substitution than peripherally sub-
I0
I
¼ 1 þ KSV½BQꢄ
ð5Þ
where I0 and I are the fluorescence intensities of fluorophore in the
absence and presence of quencher, respectively. KSV is the Stern–
Volmer constant; and this is the product of the bimolecular quench-
ing constant (kq) and the fluorescence lifetime sF (Eq. (6)):
KSV ¼ kqsF
ð6Þ
The ratios I0/I were calculated and plotted against [BQ] accord-
ing to Eq. (5), and KSV determined from the slope.
stitution. Essentially, the energy gap (DE) between the HOMO
3. Results and discussion
and lowest unoccupied molecular orbital (LUMO) becomes smaller,
resulting in a ꢃ20 nm bathochromic shift. The B (Soret) bands of
these complexes exist at 355 nm for 5, 339 nm for 6, 341 nm for
7, 352 nm for 8, 336 nm for 9 and 339 nm for 10.
3.1. Synthesis and characterization
The general synthetic routes for the synthesis of new phthalo-
nitriles (3 and 4), Zn(II), Co(II) and Cu(II) Pcs tetra-substituted at
the peripheral (complexes 5, 6 and 7) and non-peripheral (com-
plexes 8, 9 and 10) positions are given in Scheme 1. 7,8-Dihy-
droxy-3-[p-(30,40-dicyanophenoxy)phenyl]coumarin (1) and 7,8-
dihydroxy-3-[p-(20,30-dicyanophenoxy)phenyl]coumarin (2) were
reacted with tetraethylene glycol ditosylate giving the crown
ethers (3 and 4) in the presence of Na2CO3 in CH3CN. The crude
products (3 and 4) were purified by column chromatography on
silica gel with CHCl3 as eluent. The Zn(II), Co(II) and Cu(II) Pcs
(5–7 and 8–10) were obtained from the dicyano derivatives (3
and 4) and metal salts [Zn(AcO)2ꢂ2H2O, Co(AcO)2ꢂ4H2O and Cu(A-
cO)2, respectively] in DMAE at 150 °C under nitrogen atmosphere.
The novel compounds have been characterized by elemental anal-
ysis, FT-IR, 1H NMR and MALDI-TOFF mass spectroscopy. The
results were in accord with the proposed structures.
The aggregation behavior of the Pc complexes (5–7, 8–10) was
investigated at different concentrations in DMSO. In DMSO, as
the concentration was increased, the intensity of absorption of
the Q band also increased and there were no new bands due to
the aggregated species. Beer–Lambert law was obeyed for all Pc
complexes in the concentrations ranging from 1.2 ꢀ 10ꢁ5 to
2 ꢀ 10ꢁ6 moldmꢁ3
.
Generally in metallo Pc complexes, the peak due to aggregation
is blue shifted with respect to the monomer (called H-type aggre-
gation). However, a less common type of aggregation in solution
(called J-type aggregation) results in a red-shifted peak [46]. While
complex 8 showed a single Q band in DMSO and THF, it showed a
new peak at 739 nm in CHCl3 and CH2Cl2 (Fig. 2). The peak at
739 nm is not due to aggregation. We suggest that this peak is a re-
sult of the splitting in the Q band due to lowering in symmetry ob-
served [47] because of the protonation. In solvents such as
dichloromethane and chloroform (which contain small amounts
of HCl), protonation of the inner nitrogen atoms may occur forming
The FT-IR spectra of 3 and 4 showed vibration peaks for their
aliphatic CH stretching frequency at 2950–2885 and 2915–

M. Çamur et al. / Inorganica Chimica Acta 383 (2012) 287–299
291
HO
HO
HO
O
O
O
O
HO
CN
(1)
O
(2)
CN
CN
O
CN
TsOCH2(CH2OCH)3CH2OTs
CH3CN, Na2CO3
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
(3)
CN
CN
CN
(4)
O
CN
2-Dimethylaminoethanol,150oC, 24 h
Zn(AcO)2.2H2O (for 5 and 8)
Co(AcO)2.4H2O (for 6 and 9)
Cu(AcO)2 (for 7 and 10)
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
N
N
N
M
N
O
O
O
O
O
O
O
N
O
N
O
O
N
O
O
O
O
O
N
O
N
O
O
O
O
O
O
O
N
M
N
O
N
O
O
O
N
N
O
O
O
N
N
O
M= Zn (8), Co (9), Cu (10)
O
M= Zn (5), Co (6), Cu (7)
O
O
O
O
O
O
O
O
O
O
O
O
O
Scheme 1. Synthesis route of new phthalonitriles (3 and 4), zinc (II), cobalt (II) and copper (II) Pc complexes (5–7 and 8–10).
protonated metallo Pc derivatives which are of lower symmetry
than the parent metallo Pc molecule, hence the Q band is split
[48]. The split is not observed in DMSO which is basic and THF
which is neither acidic nor basic. 8 showed a single Q band after
addition of TBAOH (which is an organic base) in CHCl3 solution,
resulting completely deprotonation of the nitrogen atoms in the
Pc core (Fig. 3). 8 also showed a single Q band in CHCl3 which is
neutralized with basic Al2O3 (Fig. 3). Complex 8 contains electron
donating groups at the alpha position, hence close to the nitrogen
atoms, making the latter more basic than for 5, so protonation oc-
curs in 8 but not in 5.
which were similar to absorption spectra with both being mirror
images of emission. The proximity of the wavelength of each com-
ponent of the Q band absorption to the Q band maxima of the exci-
tation spectra for all complexes suggests that the nuclear
configurations of the ground and excited states were similar and
not affected by excitation in DMSO. Fluorescence emission peaks
were observed at 692 nm for 5 and 708 nm for 8 in DMSO (Table
1). The observed Stokes shifts (Table 1) are typical of Pc complexes
in DMSO.
The fluorescence quantum yield (UF) values for the complexes
were found to be 0.09 for 5 and 0.14 for 8 in DMSO, Table 2. The
UF values of Zn(II) Pc complexes (5 and 8) are lower than unsubsti-
tuted Zn(II) Pc in DMSO. The fluorescence quantum yield (UF) va-
lue of non-peripheral Zn(II) Pc complex (8) was higher than
peripheral Zn(II) Pc complex (5).
3.3. Fluorescence spectra, fluorescence quantum yields and lifetimes
The studied Co(II) (6 and 9) and Cu(II) (7 and 10) phthalocya-
nine complexes did not show fluorescence due to the paramagnetic
nature of the Co(II) and Cu(II) metals. Fig. 4 shows the absorption,
fluorescence emission and excitation spectra for Zn(II) Pc com-
plexes (5 and 8) in DMSO (concentration = 2 ꢀ 10ꢁ6 moldmꢁ3).
Zn(II) Pc complexes (6 and 9) showed excitation spectra in DMSO
Fluorescence lifetime (sF) refers to the average time a molecule
stays in its excited state before fluorescing, and its value is directly
related to that of UF; i.e. the longer the lifetime, the higher the
quantum yield of fluorescence. Any factor that shortens the fluo-
rescence lifetime of a fluorophore indirectly reduces the value of

292
M. Çamur et al. / Inorganica Chimica Acta 383 (2012) 287–299
Fig. 1. Absorption spectra of substituted zinc (II), cobalt (II) and copper (II) Pc complexes: (A) 5, 6 and 7, (B) 8, 9 and 10 in DMSO. Concentrations: 1 ꢀ 10ꢁ5 moldmꢁ3
.
Table 1
Absorption, excitation and emission spectral data for peripherally and non-peripherally substituted Zn(II), Co(II) and Cu(II) Pcs in DMSO.
Compound
Q band kmax (nm)
log
e
Excitation kEx (nm)
Emission kEm, (nm)
Stokes shift DStokes, (nm)
5
6
7
8
681
665
679
697
676
695
672
5.07
4.76
4.64
5.22
4.80
4.73
5.14
682
–
–
698
–
–
692
–
–
708
–
–
11
–
–
11
–
–
9
10
ZnPca
672
682
10
a
Data from Ref. [64].
UF. Such factors include internal conversion and intersystem cross-
determine its fluorescence lifetime. sF values (Table 2) were calcu-
ing. As a result, the nature and the environment of a fluorophore
lated using the Strickler–Berg equation. Lifetimes of fluorescence

M. Çamur et al. / Inorganica Chimica Acta 383 (2012) 287–299
293
Fig. 2. Absorption spectra of 8 in CHCl3, CH2Cl2, THF and DMSO (concentration: 1 ꢀ 10ꢁ5 moldmꢁ3).
Fig. 3. Absorption spectra of 8 in CHCl3, CHCl3 treated with basic Al2O3 and the addition of TBAOH in CHCl3 solution (concentration: 1 ꢀ 10ꢁ5 moldmꢁ3).
(s
F) were calculated using the Strickler–Berg equation. Using this
Pc complexes (5 and 8) were lower than unsubstituted Zn(II) Pc in
equation, a good correlation has been [35] found for the experi-
mentally and theoretically determined fluorescence lifetimes for
the unaggregated molecules as is the case in this work for 5 and
8 in DMSO. Thus we suggest that the values which obtained using
this equation are a good measure of fluorescence lifetimes. The sF
values of the Zn(II) Pc complexes (5 and 8) were lower than unsub-
stituted Zn(II) Pc complex in DMSO, suggesting more quenching by
substitution.
DMSO.
3.4. Singlet oxygen quantum yields
Singlet oxygen quantum yields (UD) were determined in DMSO
using a chemical method using DPBF as a quencher. The disappear-
ance of DPBF absorption was monitored by UV–Vis spectropho-
tometer. Many factors are responsible for the magnitude of the
determined quantum yield of singlet oxygen including; triplet ex-
cited state energy, ability of substituents and solvents to quench
the singlet oxygen, the triplet excited state lifetime and the effi-
ciency of the energy transfer between the triplet excited state
and the ground state of oxygen. There was no change in the Q band
The natural radiative lifetime (s0) values of Zn(II) Pc complexes
(5 and 8) were longer when compared to unsubstituted Zn(II) Pc in
DMSO. Also the peripheral Pc complex (5) show higher natural
radiative lifetime (
s0) value compared to the non-peripheral Pc
complex (8). The rate constant for fluorescence (kF) values for Zn(II)

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M. Çamur et al. / Inorganica Chimica Acta 383 (2012) 287–299
Fig. 4. Absorption, excitation and emission spectra of (A) complex 5 (excitation wavelength = 645 nm) and (B) complex 8 (excitation wavelength = 665 nm) in DMSO
(concentration: 2 ꢀ 10ꢁ6 moldmꢁ3).
Table 2
Photophysical and photochemical parameters of peripherally and non-peripherally substituted Zn(II) Pcs in DMSO.
a
Compound
UF
sF (ns)
s0 (ns)
kF (ns)
Ud (ꢀ10ꢁ5
)
UD
KSV (Mꢁ1
)
kq/1010 (Mꢁ1 sꢁ1
)
5
8
0.09
0.14
0.20
0.94
1.20
1.22
10.65
8.92
6.80
0.10
0.11
14.70
0.3
1.0
2.6
0.54
0.65
0.67
16.91
19.67
31.90
1.81
1.63
2.61
ZnPcb
a
kF is the rate constant for fluorescence. Values calculated using kF = UF/sF.
Data from Ref. [64].
b
intensity during the UD determinations, confirming that
complexes were not degraded during singlet oxygen studies
(Fig. 5 for complex 8). Zn(II) Pcs (5 and 8) gave good singlet oxygen
quantum yields (UD) (0.54 for 5 and 0.65 for 8, respectively,
Table 2) which are indicating the potential of these complexes as
photosensitizers in applications of PDT.

M. Çamur et al. / Inorganica Chimica Acta 383 (2012) 287–299
295
Fig. 5. A typical spectra for the determination of singlet oxygen quantum yield. This determination was for complex 8 in DMSO at a concentration of 1 ꢀ 10ꢁ5 moldmꢁ3
.
(Inset: plot of DPBF absorbance versus time.)
3.5. Photodegradation studies
Zn(II) Pc complexes (5 and 8) were more stable to degradation
compared to unsubstituted Zn(II) Pc in DMSO. Thus the substitu-
tion of Pc with crown ether bearing coumarin groups seems to in-
crease the stability of the complexes in DMSO.
Degradation of the molecules under irradiation can be used to
study their stability and this is especially important for those mol-
ecules intended for use as photocatalysts. The collapse of the
absorption spectra without any distortion of the shape confirms
clean photodegradation not associated with phototransformation
to visible region absorbing materials. The spectral changes ob-
served for zinc (II) Pc complexes (5 and 8) during confirmed
photodegradation occurred without phototransformation. Phthali-
mide was found to be the photooxidation product following
degradation of MPcs according to the literature [49].
3.6. Fluorescence quenching studies by 1,4- benzoquinone [BQ]
The fluorescence quenching of Pc complexes by 1,4-benzoqui-
none (BQ) in DMSO was found to obey Stern–Volmer kinetics,
which is consistent with diffusion-controlled bimolecular reac-
tions. Fig. 6 shows the quenching of non-peripherally substituted
Zn(II) Pc complex (8) by BQ in DMSO as an example. The slope of
the plots for substituted Zn(II) Pc complexes (5 and 8) shown in
Fig. 6 gave KSV values, listed in Table 2. The KSV values of the
The photodegradation quantum yield (Ud) values of the Pc com-
plexes (5 and 8) in DMSO are given in Table 2. The substituted
Fig. 6. Fluorescence emission spectral changes of 8 (concentration: 1 ꢀ 10ꢁ5 moldmꢁ3) on addition of different concentrations of BQ in DMSO. [BQ] = 0, 0.008, 0.016, 0.024,
0.032, and 0.040 moldmꢁ3. (Inset: Stern–Volmer plots for BQ quenching of zinc (II) Pc complexes (5 and 8).)

296
M. Çamur et al. / Inorganica Chimica Acta 383 (2012) 287–299
substituted Pc complexes (5 and 8) were lower than unsubstituted
Zn(II) Pc in DMSO. The substitution with crown ether bearing cou-
marin groups on the phthalocyanine framework seems to decrease
the KSV values of these complexes in DMSO. The bimolecular
quenching constant (kq) values of the substituted Pc complexes
(5 and 8) were lower than for unsubstituted Zn(II) Pc in DMSO,
thus substitution with crown ether bearing coumarin groups
seems to decrease the kq values of the complexes.
3.7. Electrochemistry and in situ spectroelectrochemistry
Voltammetry and in situ spectroelectrochemistry of the com-
plexes were carried out in de-aerated DMSO containing TBAP.
The voltammetric data of the Pc complexes, including the half-
wave redox potential value versus SCE (E1/2) and anodic-to-catho-
dic peak potential separation (DEp) are listed in Table 3. The num-
ber of electrons transferred is usually unity for all redox processes.
Anyway, in monophthalocyanines, multi-electron processes occur-
ring in one step are not common.
Fig. 7 shows typical cyclic voltammograms of beta- and alpha-
substituted ZnPc complexes, 5 and 8 respectively, at 0.100 Vsꢁ1
scan rate in DMSO/TBAP. As shown in Fig. 7A, beta-substituted
ZnPc, 5 displays four reduction (R1, R2, R3 and R4) and two oxida-
tion (O1’ and O100) couples. It is clear from the well-known electro-
chemistry of metallophthalocyanines that Zn(II) at the center of Pc
core is redox-inactive and thus, these redox couples are Pc ligand-
based [50,51]. The redox signals of 5 are remarkably broad. This
may be due to the presence of aggregated species. The aggregation
of Pc molecules is usually a coplanar association, which results
mainly from the
p– p electron clouds
p⁄ interactions between the
of adjacent Pc macrocycles [52]. Some functionalities such as car-
boxylic acid, ester or alkylamide groups in Pc molecules may also
increase the extent of aggregation, due to additional interactions
such as hydrogen bonding. The coumarins can also build aggrega-
tion at carboxyl groups. On the other hand, the lactone carbonyl of
coumarins can coordinate central metal cations. The presence of
both aggregated and nonaggregated Pc species at equilibrium re-
sults generally in broadening of the redox signals, due to the differ-
ences in the redox potentials of these species. On the contrary of
the redox signals of beta-substituted ZnPc, 5, those of alpha-substi-
tuted ZnPc, 8 are not broad (Fig. 7B). Thus, the redox signals of 8
are better defined than those of 5, probably due to the absence
of aggregated species in TBAP/DMSO in the case of 8. The absence
of aggregated species in solution in the case of alpha-substitution
should be due to its nonperipheral nature, leading to nonplanarity
of the complex.
Fig. 7. Cyclic and differential pulse (inset) voltammograms of 5 ꢀ 10ꢁ4 moldmꢁ3
(A) 5 (B) 9 in TBAP/DMSO.
differences in half-peak potentials, probably resulting from the dif-
ference in polarizing power of central metals. The similarity in
their redox potentials is also observed for alpha-substituted CuPc,
10 and alpha-substituted ZnPc, 8. However, similar to the case for 5
and 8, the comparison of the shape of their redox signals suggested
that there is equilibrium between the aggregated and nonaggregat-
ed species of beta-substituted CuPc, 7 in TBAP/DMSO while the
solution of alpha-substituted CuPc, 10 in TBAP/DMSO does not
involve its aggregated species. The redox processes of 7 and 10
are also Pc ligand-based as Cu(II) at the center of Pc core is
redox-inactive (Table 3) [50].
As shown in Table 3, the redox behavior of beta-substituted
CuPc, 7 is similar to that of beta-substituted ZnPc 5, with small
Table 3
Voltammetric data on Pt in DMSO/TBAP for 5–7, 8–10.
Complex
Ring oxidations
MII/MIII
MII /MI
Ring reductions
a
5 (b-ZnPc)
E1/2 (V)
D
0.63
–
0.56
0.060
0.74
0.120
0.58
0.060
0.75
ꢁ0.81
0.060
ꢁ0.80
0.080
ꢁ0.79
0.070
ꢁ0.78
0.080
ꢁ1.06
–
ꢁ1.16
0.120
ꢁ1.26
0.060
ꢁ1.13
0.110
ꢁ1.24
0.070
ꢁ1.32
0.040
ꢁ1.64
0.060
ꢁ1.42
0.080
ꢁ1.60
–
ꢁ1.40
0.090
ꢁ1.57
–
ꢁ1.63
b
Ep (V)
–
a
8 (
7 (b-CuPc)
10 ( -CuPc)
6 (b-CoPc)
9 ( -CoPc)
a-ZnPc)
E1/2 (V)
b
D
Ep (V)
a
E1/2 (V)
0.65
–
ꢁ1.60
b
D
Ep (V)
–
a
a
E1/2 (V)
b
D
Ep (V)
0.100
aE1/2 (V)
0.36
0.080
0.37
ꢁ0.44
0.200
ꢁ0.40
0.080
ꢁ1.72
b
D
Ep (V)
–
a
a
E1/2 (V)
ꢁ1.35
b
D
Ep (V)
0.060
0.060
a
E1/2 = (Epa + Epc)/2 at 0.050 Vsꢁ1
D
.
b
Ep = Epa + Epc at 0.050 Vsꢁ1
.

M. Çamur et al. / Inorganica Chimica Acta 383 (2012) 287–299
297
Fig. 8. (A) Cyclic voltammograms of 5 ꢀ 10ꢁ4 mol dmꢁ3 6 in TBAP/DMSO. In situ UV–Vis spectral changes during the controlled potential electrolysis of 6 upon (B) the first
reduction at ꢁ0.70 V vs. SCE, (C) the second reduction at ꢁ1.48 V vs. SCE and (D) the first oxidation at 0.55 V vs. SCE in TBAP/DMSO.
Figs. 8A and 9A shows the cyclic and differential pulse voltam-
mograms of beta- and alpha-substituted cobalt(II) Pcs, 6 and 9,
respectively, in DMSO/TBAP. The redox potentials of 6 or 9 are con-
siderably different in comparison with those of 5, 7, 8 and 10 (Ta-
ble 3). The first reduction and the first oxidation of 6 or 9 occur at
the potentials much less negative than those of 5, 7, 8 and 10. This
difference in the voltammetric behavior is due to the fact that
MPcs, such as MnPc, CoPc and FePc, having a metal that possesses
energy levels lying between the HOMO and the LUMO of the Pc li-
gand, in general exhibit redox processes centered on the metal
[50,53–57]. For CoPc complexes, the first oxidation and first reduc-
tion processes usually occur on the metal center in polar solvents
such as DMF and DMSO. However the first oxidation process usu-
ally occurs on the Pc ring in nonpolar solvents such as DCM and
THF. Therefore, the first reduction (R1) and the first oxidation
(O1) processes of 6 or 9 may be assigned to the [Co(II)Pc(ꢁ2)]/
[Co(I)Pc(-2)]ꢁ and [Co(II)Pc(ꢁ2)]/[Co(III)Pc(ꢁ2)]+ redox couples,
respectively. The second and the third reduction processes (R2
and R3) of these complexes are probably ligand-based and can be
process labeled R1. The concentration of the complexes was
ꢃ5.00 ꢀ 10ꢁ5 moldmꢁ3 in DMSO/TBAP for studies in optically
transparent thin layer cell. The spectrum at the start of electrolysis
indicates the presence of an equilibrium between the aggregated
and monomer species, as judged by remarkably broad Q-band
absorption. The broad Q-band at 665 nm decreases and nearly dis-
appears, while two new bands at 706 and 474 nm appear. At the
same time, the band at 344 nm shifts 332 nm. The red shifting of
the Q-band from 665 to 706 nm and the formation of a new band
at 474 nm indicate the formation of [Co(I)Pc(ꢁ2)]ꢁ species, con-
firming the voltammetric assignment of the couple R1 to
Co(II)Pc(ꢁ2)/[Co(I)Pc(ꢁ2)]ꢁ process [58–62]. However, the Q-band
obtained after the first reduction process is still broad and the
accompanied spectral changes have not well-defined isosbestic
points at specific wavelengths. These observations imply that the
species obtained upon the reduction of aggregated species proba-
bly do not disaggregate after the first reduction process and thus,
there is still equilibrium between aggregated and monomeric
forms of mono-reduced species. During the second reduction, the
Q band decreases without shift (Fig. 8C) and the absorption within
the range of 500–600 nm increases. These spectral changes at the
potential of the couple R2 are characteristic for a ring-based second
assigned to [Co(I)Pc(ꢁ2)]ꢁ/[Co(I)Pc(ꢁ3)]2ꢁ and [Co(I)Pc(ꢁ3)]2ꢁ
/
[Co(I)Pc(ꢁ4)]3ꢁ, respectively [50]. In the cyclic voltammogram of
beta-substituted CoPc, 6, redox signals are remarkably broad
(Fig. 8A), suggesting that complex 6 forms aggregated species in
DMSO/TBAP. In situ spectroelectrochemical measurements in
TBAP/DMSO provided strong support for both the assignment of
the redox processes of 6 and the coupling of its electron transfer
processes by aggregation-disaggregation equilibrium. Fig. 8B
represents in situ UV–Vis spectral changes during the first
reduction of 6 at ꢁ0.70 V versus SCE corresponding to the redox
reduction in Co(II)Pc complex, [Co(I)Pc(ꢁ2)]ꢁ/[Co(I)Pc(ꢁ3)]2ꢁ
.
Fig. 8D displays in situ UV–Vis spectral changes during the first oxi-
dation process. The broad Q band at 665 nm increases in intensity
with red shift to 675 nm and becomes sharp. At the same time, the
B bands decrease. The increase of the Q band with red shift is typ-
ical of a metal-based oxidation in CoPc complexes [58–63], and
thus confirms the voltammetric assignment of Co(II)Pc(ꢁ2)/

298
M. Çamur et al. / Inorganica Chimica Acta 383 (2012) 287–299
sharper Q-absorption band at 680 nm, in comparison with the cor-
responding one for 6 in Fig. 8B or Fig. 8D. During the first reduction
process, the Q-band at 680 nm shifts 692 nm and its shoulder at
614 nm decreases first, and then nearly disappears. At the same
time, the absorption between 700 and 756 nm increases with the
formation of a shoulder around 716 nm and a new band at
473 nm appears (Fig. 9B). These spectral changes are accompanied
by the decrease in the B band at 342 nm and have well-defined
isosbestic points at 310, 385, 563 and 701 and 756 nm. The forma-
tion of a new band at 473 nm and red shifting of the Q band indi-
cate the formation of [Co(I)Pc(ꢁ2)]ꢁ species, confirming the CV
assignment of the first reduction process, R1 to Co(II)Pc(ꢁ2)/
[Co(I)Pc(ꢁ2)]ꢁ process [58–62]. Upon the first oxidation process,
the Q band at 680 nm increases slightly in intensity with red shift
to 689 nm (Fig. 9C). The increase of the Q band with red shift is typ-
ical of a metal-based oxidation in CoPc complexes [58–63], and
thus confirms the voltammetric assignment of Co(II)Pc(ꢁ2)/
[Co(III)Pc(ꢁ2)]+ for the first oxidation process, O1, of 9.
4. Conclusion
In conclusion, we have prepared and characterized new tetra-
substituted zinc (II), cobalt (II) and copper (II) Pcs at the peripheral
(complexes 5, 6 and 7) and non-peripheral (complexes 8, 9 and 10)
positions
with
7,8-(15-crown-5)-3-(4-oxyphenyl)coumarin
groups. The photophysical and photochemical properties of Zn(II)
Pc complexes (5 and 8) were also described. The singlet oxygen
quantum yields (0.54 for 5, 0.65 for 8), which give indication of
the potential of the complexes as photosensitizers in applications
where singlet oxygen is required (Type II mechanism). Thus, these
complexes show potential as Type II photosensitizers and can be
used in photodynamic therapy. Substitution of Pc complexes with
crown ether bearing coumarin groups seems to increase the stabil-
ity of the complexes in DMSO. The fluorescences of the substituted
Zn(II) Pc complexes are effectively quenched by 1,4-benzoquinone
(BQ). The substituted complexes showed lower KSV values when
compared to the unsubstituted Zn(II) Pc in DMSO. Voltammmetric
and in situ spectroelectrochemical measurements indicated that
aggregation tendency of beta-substituted phthalocyanine com-
plexes in DMSO/TBAP is much higher than that of alpha-substi-
tuted ones. The difference in aggregation tendency of compounds
can be attributed to the deviation from planarity in alpha-substi-
tuted molecules as a result of the non-peripheral substitution.
Fig. 9. (A) Cyclic and differential pulse (inset) voltammograms of
2.5 ꢀ 10ꢁ4 moldmꢁ3 9 in TBAP/DMSO. In situ UV–Vis spectral changes during the
controlled potential electrolysis of 9 upon (B) the first reduction at ꢁ0.60 V vs. SCE
and (C) the first oxidation at 0.55 V vs. SCE in TBAP/DMSO.
Acknowledgment
We are thankful to the Research Foundation of Marmara Uni-
versity, Commission of Scientific Research Project (BAPKO) [FEN-
A-090909-0302] for supporting this study.
[Co(III)Pc(ꢁ2)]+ for couple O1 of 6. In addition, the formation of a
sharp Q-band after the first oxidation process implies that mono-
oxidized species are not aggregated, i.e., disaggregation occurs
immediately after the oxidation of aggregated species. As shown
in Table 3, the first reduction and the first oxidation potentials of
beta-substituted CoPc, 6 and alpha-substituted CoPc, 9 are very
similar to each other with small shifts. However, Pc ring-based sec-
ond and third reduction potentials of 9 are more negative than
those of 6. On the contrary of the reduction couples of 6, those of
9 are not broad, probably due to the absence of aggregated species
(Figs. 8A and 9A). It is known that the shape of the alpha-substi-
tuted Pc molecules deviate from planarity, which should be
responsible for the absence of aggregated species since aggregation
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