Photophysical and photochemical properties of Ni(II), Pd(II) and Pt(II) aryloxo and alkylthio derivatised phthalocyanine

Article abstract of DOI:10.1016/j.molstruc.2010.03.047

Several aryloxo (3a-6a and 3b-6b) and alkylthio (3d and 3e) derivatised phthalocyanines were synthesized, characterized and the photochemical and photophysical properties investigated along with those of the previously reported (3c-5c, 4d, 5d, 4e and 5e)

Full text of DOI:10.1016/j.molstruc.2010.03.047

Journal of Molecular Structure 973 (2010) 96–103
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Photophysical and photochemical properties of Ni(II), Pd(II) and Pt(II) aryloxo
and alkylthio derivatised phthalocyanine
*
Taofeek B. Ogunbayo, Tebello Nyokong
Department of Chemistry, Rhodes University, Grahamstown 6140, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 January 2010
Received in revised form 14 March 2010
Accepted 16 March 2010
Available online 21 March 2010
Several aryloxo (3a–6a and 3b–6b) and alkylthio (3d and 3e) derivatised phthalocyanines were synthe-
sized, characterized and the photochemical and photophysical properties investigated along with those
of the previously reported (3c–5c, 4d, 5d, 4e and 5e) complexes. The effects of open-shell metals (Ni(II),
Pd(II) and Pt(II)) on the photophysical and photochemical properties of the phthalocyanine ligands were
investigated. Palladium and platinum improved the triplet quantum yield and singlet oxygen generation
capacities of the unmetalated phthalocyanines (3a–3e) making their complexes candidates for further
investigation in photocatalysis. Ni(II)Pc analogues gave poor results compared with their Pd(II)Pc and
Pt(II)Pc counterparts.
Keywords:
Metal-free phthalocyanine
Nickel phthalocyanine
Palladium phthalocyanine
Platinum phthalocyanine
Fluorescence quantum yield
Triplet quantum yield
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
especially Ni(II), Pd(II) and Pt(II) is essential for possible applica-
tions, such as in PTT. Such studies are scarce in the literature for
Metallophthalocyanine (MPc) complexes containing diamag-
netic central metals are well known as photosensitizers in photo-
dynamic therapy [1,2]. This is due to their ability to efficiently
produce singlet oxygen [1], which mediates photosensitized reac-
tions of MPc complexes. Generally, diamagnetic metals promote
intersystem crossing (ISC), producing long lived triplet excited
states [3–9].
these MPc complexes.
This work reports on the syntheses, and photophysical and pho-
tochemical characterization of metal-free, Ni, Pd and Pt phenoxy
(3a–6a) and benzyloxyphenoxy (3b–6b) phthalocyanine com-
plexes. The syntheses of unmetalated alkylthio derivatives (3d,
3e) are also reported. The choice of substituents (a) (phenoxy)
and (b) (benzyloxyphenoxy) is based on our previous study of
these substituents on MPc complexes containing other central
metals (e.g. OTi(IV), ClIn(IV), ClGa(IV), Cd and Pb) where these li-
gands were found to prevent aggregation in some cases, hence
enhancing photochemical and photophysical behavior of the MPc
complexes [14–18]. NiPc complexes in particular are known to
be highly aggregated even when bulky ligands are employed [19].
The effects of substituents and central metals on the photo-
chemical and photophysical properties for 3a–6a, 3b–6b and 3d,
3e are compared with those of previously reported pentylthio,
octylthio and dodecylthio substituted NiPc (4c–4e) and PdPc (5c–
5e) derivatives and unmetalated pentylthio Pc (3c) [20,21].
Because of considerable d–
cited states, short triplet state lifetimes (
p
interactions which quench the ex-
T) are observed for open-
s
shell MPc complexes. In spite of this theoretical shortcoming PdPcs
are being investigated in the areas of photocatalysis [10,11] be-
cause of their high photostability. The short triplet state lifetimes
implies that MPc complexes decay from the electronically excited
state to the ground state primarily by non-radiative pathways,
releasing their energy in several forms, including heat. Thus the
possibility exists of producing local photosensitized hyperthermal
effects with open shell phthalocyanines leading to specific damage
of the cells and tissues containing the photosensitizer, without
affecting healthy tissues [12]. This is the basis for photothermal
therapy (PTT) of cancer, and nickel octabutyloxyphthalocyanine
and nickel octabutyloxynaphthalocyanine have gained a lot of
attention in this area [13]. Thus, systematic investigation of the
photophysical properties of MPcs containing open-shell metals,
2. Experimental
2.1. Materials
Nickel chloride hexahydrate, palladium chloride and platinum
chloride, potassium carbonate, 8-diazabicyclo{5.4.0}-undec-7-ene
(DBU), diphenylisobenzofuran (DPBF), and phenol were purchased
* Corresponding author. Tel.: +27 46 603 8260; fax: +27 46 622 5109.
E-mail address: t.nyokong@ru.ac.za (T. Nyokong).
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.03.047

T.B. Ogunbayo, T. Nyokong / Journal of Molecular Structure 973 (2010) 96–103
97
as a standard, UF = 0.20 [27], for the determination of fluorescence
quantum yields of all the MPcs synthesized. The sample and the
standard were excited at the same relevant wavelength.
from Sigma Aldrich. Chloroform, methanol (MeOH), 1-chloronaph-
thalene(1-CNP), 1-pentanol, tetrahydrofuran (THF), dimethylform-
amide (DMF), deuterated chloroform (CDCl3) deuterated pyridine
(Pyr-d5) were obtained commercially and dried where necessary
before use. Dimethylsulphoxide (DMSO) was purchased from
SAARCHEM, and dried in alumina before use. Column chromatogra-
phy was performed on silica gel 60 (0.04–0.063 mm). The syntheses
of the phthalonitriles: 1,2-dichloro-4,5-dicyanobenzene (1) [22],
1,2-diphenoxy-4,5-dicyanobenzene (2a) [18], 1,2-bis(benzyloxy-
phenoxy)-4,5-dicyanobenzene (2b) [18,23], 1,2-bis(octylthio)-4,
5-dicyanobenzene (7d) [20] and 1,2-bis(dodecylthio)-4,5-dicyano-
benzene (7e) [24] have been reported in literature. The syn-
theses of phthalocyanine complexes: metal-free 2,3,9,10,16,17,23,
24-octakis(pentylthiophthalocyanine) (3c), 2,3,9,10,16,17,23,24-
octakis(pentylthiophthalocyaninato) nickel(II) (4c), 2,3,9,10,16,17,
23,24-octakis(pentylthiophthalocyaninato) palladium(II) (5c), 2,3,
9,10,16,17,23,24-octakis(octylthiophthalocyaninato) nickel(II)
(4d), 2,3,9,10,16,17,23,24-octakis(octylthioph-thalocyaninato) pal-
ladium(II) (5d), 2,3,9,10,16,17,23,24-octakis(dodecylthiophthaloc-
yaninato) nickel(II) (4e) and 2,3,9,10,16,17,23,24-octakis(dodecyl-
thiophthalocyaninato)palladium(II) (5e), have been reported before
[20,21].
2.3.2. Triplet quantum yields and lifetimes
Triplet quantum yields were determined using a comparative
method based on triplet decay, using Eq. (2):
D
D
ASTample
ꢀ
eSTtd
eSTample
USTample
¼
USTtd
ð2Þ
ASTtd: are the changes in the triplet state absor-
ASTtd
ꢀ
where
D
ASTample and
D
bance of the MPc derivatives and the standard, respectively. eTSample
and eSTtd are the triplet state extinction coefficients for the MPc
derivatives and standard, respectively. USTtd is the triplet state quan-
tum yield for the standard, ZnPc in 1-CNP, USTtd ¼ 0:67 [28].
2.4. Photochemistry
2.4.1. Singlet oxygen quantum yields
The singlet oxygen quantum yield (UD) determinations were
carried out using solutions containing DPBF (90 lM) and the Pcs
(absorbance ꢁ0.2 at the irradiation wavelength). A solution of
the complex (2 ml) contained in a quartz cuvette (1 cm ꢂ 1 cm)
was saturated with oxygen and irradiated using the set-up de-
scribed above. The irradiation and measurement were repeated
until around 80% decay of DPBF was observed [29]. The DPBF
absorbance was corrected for the absorbance of sensitizer at the
respective detection wavelength.
2.2. Equipment
Triplet absorption and decay kinetics were recorded on a laser
flash photolysis system; the excitation pulses were produced by
a Nd: YAG laser (Quanta-Ray, 1.5 J/8 ns) pumping a dye laser
(Lambda Physic FL 3002, Pyridin 1 in methanol). The analyzing
beam source was from a Thermo Oriel xenon arc lamp, and a pho-
tomultiplier tube was used as detector. Signals were recorded with
a two-channel digital real-time oscilloscope (Tektronix TDS 360).
The kinetic curves were averaged over 256 laser pulses. Triplet life-
times were determined by exponential fitting of the kinetic curves
using OriginPro 7.5 software.
For singlet oxygen determination the irradiation was carried
out with a tungsten lamp (100 W, 30 V) perpendicular to the direc-
tion of measurement. A water filter and an interference filter (with
a wavelength close to the absorption maximum of the sensitiser)
were placed in the light beam path of the tungsten lamp. The light
intensity was measured with a power meter. The decay of DPBF
absorption at 421 nm was recorded after each photolysis cycle.
UV–Vis spectra were recorded on a Cary 500 UV/Vis/NIR spectro-
photometer. Fluorescence emission and excitation spectra were re-
corded on Varian Eclipse spectrofluorimeter. 1H NMR spectra were
obtained, in deuterated solvents, using a Bruker EMX 400 MHz
NMR or Bruker Avance II+ 600 MHz NMR spectrometer. FT-IR spec-
tra (KBr pellets) were recorded on a Perkin–Elmer spectrum 2000
FT-IR spectrometer. MALDI-TOF mass spectra were recorded ABI
Voyager DE-STR Maldi TOF instrument at University of Stel-
lenbosch using alpha-cyano-4-hydroxycinnamic acid as a matrix.
The DPBF quantum yield UDPBF was calculated using Eq. (3) and
the determined extinction coefficient of DPBF in 1-chloronaphtha-
lene (
e
1-CNP = 20,287 M Lꢃ1 cmꢃ1).
ðC0 ꢃ CtÞVR
UDPBF
¼
ð3Þ
Iabs ꢀ t
where C0 and Ct are the DPBF concentrations prior to and after irra-
diation, respectively; VR is the solution volume; t is the irradiation
time per cycle and Iabs is defined by Eq. (4).
a
ꢀ A ꢀ I
Iabs
¼
ð4Þ
NA
where
a
= 1–10ꢃA(k), A(k) is the absorbance of the sensitizer at the
irradiation wavelength, A is the irradiated area (3.142 cm2), I is
the intensity of light (8.92 ꢂ 1015 photons cmꢃ2 sꢃ1) and NA is Avo-
gadro’s constant. The singlet oxygen quantum yields UD were cal-
culated using Eq. (5) [30].
1
1
1
kd
1
¼
þ
ꢀ
ꢀ
ð5Þ
UDPBF UD
UD
ka ½DPBFꢄ
where kd is the decay constant of singlet oxygen in respective sol-
vent and ka is the rate constant of the reaction of DPBF with
O2(1Dg). The intercept obtained from the plot of 1/UDPBF versus 1/
DPBF gives 1/UD
.
2.3. Photophysical parameters
The values of the fraction of the excited triplet state quenched
by ground state molecular oxygen (S ) were determined using
Eq. (6):
D
2.3.1. Fluorescence quantum yields
Fluorescence quantum yields (UF) were determined by a com-
parative method [25,26], using Eq. (1):
UD
UT
SD
¼
ð6Þ
F ꢀ AStd ꢀ n2
UF
¼
UFðStdÞ
ð1Þ
FStd ꢀ A ꢀ n2Std
2.5. Synthesis
where F and FStd are the areas under the fluorescence curves of the
MPc derivatives and the reference, respectively. A and AStd are the
absorbances of the sample and reference at the excitation wave-
length, and n and nStd are the refractive indices of solvents used
for the sample and standard, respectively. ZnPc in DMSO was used
2.5.1. Metal-free – 2,3,9,10,16,17,23,24-
octakis(phenoxy)phthalocyanine (3a)
A mixture of compound 2a (2.00 g, 6.40 mmol) and DBU
(6.20 ml, 4.00 mmol) was refluxed in 1-pentanol (8 ml), under a

98
T.B. Ogunbayo, T. Nyokong / Journal of Molecular Structure 973 (2010) 96–103
blanket of nitrogen for 8 h. The reaction mixture was allowed to
cool, thereafter, methanol (80 ml) was added and the mixture stir-
red. After stirring, the mixture was filtered, and the resulting solid
sequentially washed with methanol and water and then dried. The
crude product was purified using column chromatography and
DCM as the eluting solvent to afford the title compound as a dark
crude product was purified with column chromatography, using
THF as the eluting solvent to afford the title compound as a dark
green solid. Yield: 0.15 g (88%). UV/Vis [(1-CNP), kmax (nm), (log e)]
708 (5.31), 674 (5.24), 643 (4.76), 611 (4.62). 1H NMR (400 mHz), d,
ppm: (CDCl3) 8.62 (8H, s, PcAH), 7.60–7.00 (72H, m, phenylAH),
5.10 (16H, s, CH2). [IR (KBr pellets) mmax (cmꢃ1)]; 3253(NAH),
3063, 3033, 1602, 1222 (CAOAC), 945, 836, 737. Anal. Calc. For
C136H98N8O16: C, 77.77; H, 4.90, N, 5.34. Found, C, 76.41; H, 5.12,
N, 6.79%.%.
green solid. Yield: 0.14 g (78%). UV/Vis [(1-CNP), kmax (nm), (log e)]
706 (5.31), 672 (5.62), 642 (4.72), 610 (4.58). 1H NMR (400 mHz); d
ppm (CDCl3) 8.53 (8H, s, PcAH), 7.20–7.38 (40H, m, phenylAH).
Calc. MS (ESI–MS) m/z: Calc. 1250.30; Found: 1250.29. [IR (KBr pel-
lets) mmax (cmꢃ1)]; 3289 (NAH), 3061, 3042, 1613, 1270 (CAOAC),
989, 874, 743, 687. C80H50N8O8ꢀH2O. Calc.: C, 75.71; H, 4.10; N,
8.83. Found, C, 74.72; H, 4.07, N, 9.02%.
2.5.6. Nickel – 2,3,9,10,16,17,23,24-octakis(benzyloxyphenoxy)phtha-
locyanine (4b)
A mixture of compound 2b (1.68 g, 3.20 mmol), NiCl2ꢀ6H2O
(0.36 g, 1.50 mmol) and DBU (4.80 ml, 3.00 mmol) was refluxed
in 1-pentanol (8 ml), under a blanket of nitrogen for 24 h. The reac-
tion mixture was allowed to cool, thereafter, methanol (8 ml) was
added and the mixture stirred. The mixture was then filtered and
dried. The crude product was purified by column chromatography,
using THF as the eluting solvent to afford the title compound as a
dark green solid. Yield: 0.13 g (74%). UV/Vis [(1-CNP), kmax (nm),
2.5.2. Nickel – 2,3,9,10,16,17,23,24-octakis(phenoxy)phthalocyanine
(4a)
A mixture of compound 2a (1.00 g, 3.20 mmol), NiCl2ꢀ6H2O
(0.36 g, 1.50 mmol) and DBU (3.20 ml, 2.00 mmol) in 1-pentanol
(8 ml), was refluxed under a blanket of nitrogen for 14 h. The reac-
tion mixture was allowed to cool, thereafter, methanol (80 ml) was
added and the mixture stirred for 1 h, then filtered, and the result-
ing solid sequentially washed with methanol and water and then
dried. The crude product was purified by column chromatography,
using DCM as the eluting solvent to afford the title compound as a
dark green solid. Yield: 0.08 g (75%). UV/Vis [(1-CNP), kmax (nm),
(log
d ppm (CDCl3): 8.72 (8H, s, PcAH), 7.65–7.10 (72H, m, phenylAH),
5.00 (16H, s, CH2). [IR (KBr pellets)
max (cmꢃ1)]; 3052, 3031, 1611,
e
)] 680 (5.40), 648 (4.69), 610 (4.66). 1H NMR (400 mHz);
m
1224 (CAOAC), 955, 820, 734, 694. C136H96N8O16Ni: Calc.: C, 75.73;
H, 4.49, N, 5.19. Found, C, 73.92; H, 5.18, N, 5.12%.
(log e
)] 678 (5.29), 650 (4.65), 610 (4.59). 1H NMR (600 mHz); d
ppm (Pyr-d5) 8.45 (8H, s, PcAH), 7.20–7.36 (40H, m, phenylAH).
2.5.7. Palladium – 2,3,9,10,16,17,23,24-octakis(benzyloxyphenoxy)-
phthalocyanine (5b)
Calc. MS (ESI–MS) m/z: Calc. 1306.98; Found: 1306.71. [IR (KBr pel-
lets)
m
max (cmꢃ1)]; 3061, 3032, 1599, 1260 (CAOAC), 965, 801, 748,
Synthesis and purification of 5b was as outlined for 4b except
that PdCl2 was employed instead of NiCl2. The amount of reagents
employed were: 1-pentanol (8 ml), compound 2b (1.68 g,
3.20 mmol), palladium chloride (0.27 g, 1.50 mmol) and DBU
(4.80 ml, 3.00 mmol). Yield: 0.11 g (62%). UV/Vis [(1-CNP), kmax
687. C80H48N8O8NiꢀH2O. Calc.: C, 72.46; H, 3.62, N, 8.45. Found, C,
71.92; H, 3.52, N, 6.98%.
2.5.3. Palladium – 2,3,9,10,16,17,23,24-octakis(phenoxy)phthalocya-
nine (5a)
(nm), (log e
)] 670 (5.25), 603 (4.58). 1H NMR (400 mHz); d ppm
Synthesis and purification of 5a was as outlined for 4a except that
PdCl2 was employed instead of NiCl2. The amount of reagents em-
ployed were: 1-pentanol (8 ml), compound 2a (1.00 g, 3.20 mmol),
PdCl2 (0.27 g, 1.50 mmol) and DBU (3.20 ml, 2.00 mmol). Yield:
(CDCl3) 8.62 (8H, s, PcAH), 7.60–7.00 (72H, m, phenylAH,
phenylAH), 5.10 (16H, s, SACH2). [IR (KBr pellets) mmax (cmꢃ1)];
3065, 3035, 1648, 1207 (CAOAC), 962, 827, 733, 693.
C136H96N8O16Pd Calc.: C, 74.09; H, 4.39, N, 5.08. Found, C, 73.64;
H, 5.90, N, 5.89%.
0.07 g (65%). UV/Vis [(1-CNP), kmax (nm), (log e)] 668 (5.11), 640
(4.41), 602 (4.44). 1H NMR (600 mHz); d ppm (Pyr-d5) 8.43 (8H, s,
PcAH), 7.25–7.42 (40H, m, phenylAH). MS (ESI–MS) m/z: Calc.
1354.14; Found: 1354.20. [IR (KBr pellets) mmax (cmꢃ1)]; 3072,
3039, 1589, 1269 (CAOAC), 988, 882, 746, 688. C80H48N8O8PdꢀH2O
Calc.: C, 69.94; H, 3.50, N, 8.16. Found, C, 68.92; H, 4.12, N, 6.69%.
2.5.8. Platinum – 2,3,9,10,16,17,23,24-octakis(benzyloxyphenoxy)-
phthalocyanine (6b)
Synthesis and purification of 6b was as outlined for 4b except
that PtCl2 was employed instead of NiCl2. The amounts of reagents
employed were: 1-pentanol (8 ml), compound 2b (1.68 g,
3.20 mmol), platinum chloride (0.40 g, 1.50 mmol) and DBU
(4.80 ml, 3.00 mmol). Yield: 0.09 g (49%). UV/Vis [(1-CNP), kmax
2.5.4. Platinum – 2,3,9,10,16,17,23,24-octakis(phenoxy)phthalocya-
nine (6a)
Synthesis and purification of 6a was as outlined for 4a except
that PtCl2 was employed instead of NiCl2. The amount of reagents
employed were: 1-pentanol (8 ml), compound 2a (1.00 g,
3.20 mmol), platinum chloride (0.40 g, 1.50 mmol) and DBU
(3.20 ml, 2.00 mmol). Yield: 0.07 g (61%). UV/Vis [(1-CNP), kmax
(nm), (log e
)] 703 (4.13), 660 (5.22), 594 (4.54). 1H NMR
(400 mHz); d ppm (CDCl3) 8.60 (8H, s, PcAH), 7.70–6.96 (72H, m,
phenylAH), 4.95 (16H, s, CH2) [IR (KBr pellets) mmax (cmꢃ1)];
3052, 3037, 1634, 1261 (CAOAC), 949, 801, 741, 671.
C136H96N8O16Pt. Calc.: C, 71.23; H, 4.22 N, 4.89. Found, C, 68.70;
H, 4.55, N, 5.11%.
(nm), (log e
)] 658 (5.06), 636 (4.53), 593 (4.43). 1H NMR
(600 mHz); d ppm (Pyr-d5) 8.63 (8H, s, PcAH), 7.23–7.45 (40H,
m, phenylAH). Calc. MS (ESI–MS) m/z: Calc. 1443.36; Found:
1443.60. [IR (KBr pellets) mmax (cmꢃ1)]; 3063, 3033, 1602 (C@C),
1251(CAOAC), 966, 852, 745, 688. C80H48N8O8PtꢀH2O. Calc.: C,
65.70; H, 3.28, N, 7.67. Found, C, 64.29; H, 4.13, N, 8.11%.
2.5.9. Metal-free – 2,3,9,10,16,17,23,24,-octakis(octylthio)phtha-
locyanine (3d)
The same method used for 3a was employed for the synthesis of
3d, except 7d was employed instead of 2a. The amounts of re-
agents were: Compound 7d (0.42 g, 1 mmol), DBU (1.66 ml,
2.5.5. Metal-free – 2,3,9,10,16,17,23,24-octakis(benzyloxyphen-
oxy)phthalocyanine (3b)
1 mmol). Yield: 0.37 g (74%), UV/Vis [(1-CNP), kmax (nm), (log e)]
737 (5.15), 710 (5.10), 673 (4.72), 638 (4.62), 452 (4.57). 1H NMR
(400 mHz); d ppm (CDCl3) 8.23 (8H, s, Harom), 3.40–3.37 (16H, t,
SCH2A), 2.10–2.00 (16H, m, CH2A), 1.79–1.75 (16H, m, ACH2),
1.58–1.35 (88H, m, ACH2, CH3). Calc. MS (ESI–MS) m/z: Calc.
1666.16; Found: 1666.46. [IR (KBr pellets) Umax (cmꢃ1)]; 3452
(NAH), 2949, 2935, 2855, 1669, 1597, 1511, 1469, 1409, 1329,
A mixture of compound 2b (1.68 g, 3.20 mmol) and DBU
(4.80 ml, 3.00 mmol) was refluxed in 1-pentanol (8 ml), under a
blanket of nitrogen for 12 h. The reaction mixture was allowed to
cool, thereafter, methanol (80 ml) was added and the mixture
was stirred for 1 h. The mixture was then filtered and dried. The

T.B. Ogunbayo, T. Nyokong / Journal of Molecular Structure 973 (2010) 96–103
99
1331, 1079, 1021, 939, 871, 751, 682 (CASAC). C96H146N8S8 Calc.:
C, 69.09; H, 8.82, N, 6.71. Found, C, 68.93; H, 8.75, N, 6.56%.
UV–Vis, IR and NMR spectroscopies elemental and mass analysis.
The analyses are consistent with the predicted structures as shown
in the experimental section. 1H NMR of all the molecules were
done in deuterated chloroform except for 4a, 5a and 6a that were
also done in deuterated pyridine.
2.5.10. Metal-free – 2,3,9,10,16,17,23,24,-octakis(dodecylthio)phthalo-
cyanine (3e)
The same method used for 3a was employed for the synthesis of
3e, except 7e was employed instead of 2a. The amounts of reagents
were: Compound 7e (0.53 g, 1 mmol), DBU (1.66 ml, 1 mmol).
3.2. Ground state electronic absorption
Yield: 0.35 g (64%), UV/Vis [(1-CNP), kmax (nm), (log e)] 737
UV/Vis spectra of the complexes showed characteristic absorp-
tions in the Q-band, Figs. 1–3. The Q-bands were observed in the
range 658–709 nm in 1-CNP, Table 1. The spectra of the complexes
in 1-CNP, showed monomeric behavior, evidenced by a single (nar-
row) Q-band at 678, 668, 658 nm (for 4a, 5a and 6a, respectively)
and 680 nm, 670 nm and 660 nm (for 4b, 5b and 6b, respectively),
typical of unaggregated MPcs while spectra of metal-free ana-
logues showed a typical split Q-band at 706 nm and 672 nm for
3a, 708 nm and 674 nm for 3b and 707 nm and 736 nm for both
3d and 3e, (Fig. 3), Table 1. The Q-band of all the thio derivatised
complexes (substituents c, d, and e), Table 1, are red shifted com-
pared to the aryloxy substituted. Red shifting is typical of all thio
substituted phthalocyanine complexes [31].
(5.18), 710 (5.11), 672 (4.72), 638 (4.62), 452 (4.57). 1H NMR
(400 mHz); d ppm (CDCl3) 8.30 (8H, s, Harom), 3.42–3.40 (16H, t,
SCH2A), 2.13–2.09 (16H, m, CH2A), 1.80–1.69 (16H, m, CH2A),
1.50–1.30 (152H, m, CH2, CH3). MS (ESI–MS) m/z: Calc. 2116.91;
Found: 2117.19. [IR (KBr pellets) Umax (cmꢃ1)]; 3449 (NAH),
2962, 2922, 2857, 1666, 1571, 1500, 1467, 1405, 1331, 1319,
1069, 1028, 937, 872, 748, 676 (CASAC). C128H210N8S8 Calc.: C,
72.60; H, 10.00, N, 5.29. Found, C, 71.93; H, 10.42, N, 5.16%.
3. Results and discussion
3.1. Syntheses and characterization
The benzyloxyphenoxy PtPc complex (6b), Fig. 2a and b, also
showed an additional peak on the red side of the Q-band around
709 nm but this extra peak was not noticed in phenoxy derivative
(6a). This extra peak is associated with partial demetallation of the
complex since Pt2+ central metal is unable to completely enter the
central cavity of Pc ring due to its large ionic size. Demetallation
was solvent dependent in that the extra peak was observed in chlo-
rinated solvents as was reported before for CdPc complexes [32].
Studies have shown that, in chlorinated solvents, MPcs undergo
oxidation with the formation of HCl as a by-product [33] which
in certain cases reacts with the MPc to cause demetallation.
Fig. 2c shows that the extra peak disappeared in pyridine. It is also
possible that demetallation occurred during synthesis, this was
evidenced by the presence of the extra peak during synthesis in
1-pentanol, and addition of Zn acetate resulted in the disappear-
ance of the peak as a result of the coordination of the Zn to the cen-
tre of the ring. Attempts to eliminate the demetallated species
using chromatography and eluting with several solvents and their
mixtures were not successful.
Phthalocyanines are prepared by cyclotetramerization of pht-
halonitriles. Octasubstituted phthalocyanines were synthesized
from 4,5-diphenoxyphthalonitriles (2a), 4,5-bis-(benzyloxyphen-
oxy)phthalonitrile (2b), 4,5-dioctylthiophthalonitrile (7d) and
4,5-didodecylthiophthalonitrile (7e). The syntheses of metallopht-
halocyanine complexes (4a–6a, and 4b–6b) were achieved by
treatment of respective phthalonitriles (2a and 2b) with NiCl2,
PdCl2 and PtCl2, respectively in dry pentanol (Scheme 1). Metal
salts were not included in the synthesis of metal-free phthalocya-
nines (3a, 3b, 3d, and 3e), Schemes 1 and 2. Column and prepara-
tive thin layer chromatography with silica gel was employed to
obtain the pure products from the reaction mixtures. Generally,
phthalocyanine complexes are insoluble in most organic solvents;
however introduction of substituents on the ring increases the sol-
ubility. All complexes (3a–6a, 3b–6b, 3d, 3e) exhibited excellent
solubility in organic solvents such as dichloromethane, chloroform,
THF and toluene but they are only appreciably monomerised in 1-
chloronaphthalene. The new compounds were characterized by
RO
OR
N
N
N
CN
CN
RO
RO
OR
OR
Cl
Cl
CN
CN
RO
RO
MCl2, 1-Pentanol
DBU, Reflux
ROH, DMF
K2CO3, RT
N
M
N
;
N
N
N
1
2
3
RO
OR
R
=
3; M = 2H
4; M = Ni
5; M = Pd
6; M = Pt
(a)
O
=
(b)
Scheme 1. Synthetic routes for oxy-derivatised phthalocyanines.

100
T.B. Ogunbayo, T. Nyokong / Journal of Molecular Structure 973 (2010) 96–103
RS
SR
Cl
Cl
CN
N
N
RSH, DMSO
RS
RS
CN
N
SR
SR
RS
RS
DBU
Pentanol, 2hrs
K2CO3, Stir, 12hrs
N
M
N
CN
;
N
N
N
CN
1
7
RS
SR
3; M = 2H
4; M = Ni
5; M = Pd
R = C5H11 (c)
= C8H17
=C12H25
(d)
(e)
Scheme 2. Synthetic routes for thio-derivatised phthalocyanines.
(a)
(a)
(b)
(b)
Fig. 1. UV–Vis spectra of complexes 3a, 4a, 5a, and 6a: (a) 1-CNP and (b) in DCM
(concentration ꢁ1 ꢂ 10ꢃ6 mol dmꢃ3).
(c)
There is a clear red shifting of the Q-band as the size of the cen-
tral metal decreases on going from PtPc (6a, 6b), to PdPc (5a, 5b)
and NiPc (4a, 4b), Figs. 1 and 2. Red shifting of the Q-band in
MPc complexes is due to the destabilization of the highest occu-
pied molecular orbital (HOMO) [34]. There are some central metals
such as MnIII, PbII and SnIV, which show a large red shift compared
to metals such as NiII, ZnII [35]. The observed red shifting of NiPc
derivative (4a, 4b) compared to PdPc (5a, 5b) and PtPc (6a, 6b)
derivatives, suggests that the former destabilizes the HOMO to a
larger extent than the latter two complexes. In DCM the MPcs dis-
played aggregation as evidenced by the presence of a blue shifted
non-vibrational band in the visible region, Figs. 1b and 2b. The Q-
bands of the monomers in DCM were observed at 669, 660 and
650 nm for 4a, 5a and 6a, respectively, Fig. 1b and 669, 662 and
652 for 4b, 5b and 6b, respectively, Fig. 2b. The peaks due to the
350
450
550
650
750
Wavelength (nm)
Fig. 2. UV–Vis spectra of complexes 3b, 4b, 5b, and 6b in (a) 1-CNP, (b) in DCM and
(c) 6b in 1-CNP (i) and pyridine (ii) (concentration ꢁ1 ꢂ 10ꢃ6 mol dmꢃ3).
aggregates were observed at 613, 604, 599, 615, 597 and 590 nm,
respectively for 4a, 5a, 6a, 4b, 5b and 6b.

T.B. Ogunbayo, T. Nyokong / Journal of Molecular Structure 973 (2010) 96–103
101
Fig. 3. UV–Vis spectra of complexes 3d and 3e in 1-CNP (concentration = 1 ꢂ
10ꢃ6 mol dmꢃ3).
Fig. 4. UV–Vis spectral changes observed on increase in concentration of 6b in 1-
CNP. Inset: Beer–Lambert’s plot for 6b in 1-CNP. Concentration range:
1.0 ꢂ 10ꢃ6 mol dmꢃ3 to 1.3 ꢂ 10ꢃ5 mol dmꢃ3).
The red shifting of the Q-band in 1-CNP compared to DCM
might be due to aromatic nature of 1-CNP. Aromatic solvents have
been known to bring about red shifting of Q-band relative to the
non-aromatic ones [36]. Generally, aggregation is more pro-
nounced in non-coordinating solvents. Thus the observed exten-
sive aggregation in DCM compared to 1-CNP could be due to the
coordinating nature of the later which reduces coplanar associa-
tion of the Pc rings. Fig. 4 shows the concentration dependence
of complex 6b in 1-CNP. As the concentration was increased, the
intensity of the Q-band also increased and there were no new band
due to the aggregated species for the complex. The Beer–Lambert’s
law was obeyed for all of these compounds in 1-CNP for concentra-
spectra is that of the unmetalated species which will fluoresce
more efficiently than the metallated species. There will be more
enhanced intersystem crossing in the metallated complex. The ob-
served emission is that of the unmetallated species with emission
Q-band maximum of 713 nm which is not too different from that of
unmetallated 3b at 716 nm (Table 1).
For complex 3d, Fig. 5b, there is peak-to-peak matching be-
tween excitation and absorption spectra, but there is a decrease
in intensity in the high energy band of the split pair. The excitation
or emission spectra for 4a, 4b, 5a and 6a were too weak to be ana-
lysed accurately. The implication of this is that excited states of
phenoxy derivatised Ni, Pd and Pt phthalocyanines were quenched
faster than alkylthio (only for NiPc and PdPc complexes, attempts
to synthesize PtPc alkylthio derivatives were not successful) and
benzyloxyphenoxy (for PtPc and PdPc) derivatised analogues This
might be due to a specific interactions between the central metals
and phenoxy groups which quench the excited state faster than the
alkylthio or benzyloxyphenoxy analogues.
tions less than 1 ꢂ 10ꢃ5 mol dmꢃ3
.
3.3. Fluorescence spectra and quantum yield
The absorption and fluorescence excitation spectra of the
unmetalated derivatives (3a, 3b, 3c, 3d and 3e) are almost identical
(Fig. 5a using 3a as an example), implying that the absorbing spe-
cies do not differ much from the fluorescing species. Metal-free Pcs
are known to fluoresce with only one main peak in non-aqueous
media which has been assigned as the 0–0 transition of the fluores-
cence [37], hence the observation of an unsplit fluorescence Q-
band in Fig. 5a. The fluorescence excitation spectrum of the benzyl-
oxyphenoxy derivative of PdPc (5b) is red shifted from the absorp-
tion spectrum by 11 nm (Table 1), suggesting a change in geometry
upon excitation. Since for the Pt analogue (6b), the peak at 709 nm
is due to partial demetallation discussed above, the excitation
The fluorescence quantum yield (UF) values of 3a, 3b, 3c, 3d and
3e in 1-CNP are 0.21, 0.25, 0.10, 0.13 and 0.15, respectively while
those of the metallated derivatives are expectedly low (<0.01 and
0.012), 6b displayed a higher fluorescence quantum yield (UF) than
6a probably because of the demetallation discussed above, Table 2.
The low fluorescence quantum yield observed for the PdPc and
PtPc complexes is due to open-shell nature of the metals involved
Table 1
Spectral data for all complexes in 1-CNPa.
Complexes
Substituents
kQ(abs) (nm)
kQ(exc) (nm)
kQ(emm) (nm)
3a (M@H2)
4a (M@Ni)
5a (M@Pd)
6a (M@Pt)
3b (M@H2)
4b (M@Ni)
5b (M@Pd)
6b (M@Pt)
3c (M@H2)
4c (M@Ni)b
5c (M@Pd)b
3d (M@H2)
4d (M@Ni)
5d (M@Pd)b
3e (M@H2)
4e (M@Ni)b
5e (M@Pd)b
AOAC6H5
AOAC6H5
AOAC6H5
AOAC6H5
AOAC6H4AOACH2AC6H5
AOAC6H4AOACH2AC6H5
AOAC6H4AOACH2AC6H5
AOAC6H4AOACH2AC6H5
SAC5H11
SAC5H11
SAC5H11
SAC8H17
SAC8H17
SAC8H17
SAC12H25
SAC12H25
SAC12H25
672, 706
678
668
658
674, 708
680
670
660
707, 736
696
698
707, 736
707
698
707, 736
709
698
677, 711
–
–
720
–
–
–
716
–
682
713c
745
730
745
745
740
707
745
730
709
–
674, 709
–
681
709
711, 738
695, 725
738
711, 738
662, 699
701
711, 738
727
703
b
a
b
c
kQ(abs) = Q-band absorption wavelength; kQ(exc) = Q-band excitation wavelength; kQ(emm) = Q-band emission wavelength.
Values from Ref. [20].
Due to demetalated species.

102
T.B. Ogunbayo, T. Nyokong / Journal of Molecular Structure 973 (2010) 96–103
0.1
0.05
0
(a)
(b)
-0.05
-0.1
400
500
600
700
800
-0.15
-0.2
-0.25
-0.3
-0.35
-0.4
400
450
500
550
600
650
Fig. 6. Transient absorption curve for triplet decay curve of 3b in 1-CNP at 520 nm.
Excitation wavelength = 707 nm. Inset: transient absorption spectrum in the
500 nm region.
to enhancement of intersystem crossing by the presence of heavy
central metals. The Ni(II)Pc analogue (4a) did not show any triplet
absorption peak suggesting an extremely short triplet lifetime or
yield. The triplet lifetimes of the molecules reflect their open-shell
nature. 3a which was not metalated showed a lifetime of 55
while 5a (Pd) and 6a (Pt) showed lifetimes of 23 s and 17
respectively, Table 2, demonstrating the effect of d– interaction
ls
l
ls,
p
characteristics of open-shell metal phthalocyanines, this normally
results in lower excited state lifetime. The triplet decay curve in
Fig. 7 obeyed first order kinetics suggesting minimum or absence
of triplet–triplet recombination.
Fig. 5. Absorption and fluorescence (excitation and emission) spectra of (a) 3a and
(b) 3d in 1-CNP excitation wavelength = 620 nm.
Of the octabenzyloxyphenoxy phthalocyanines, the metal-free
analogue (3b) has UT = 0.47 while the Ni(II) analogue (4b) showed
no triplet absorption peak as was the case for 4a. Complexes 5b
(Pd) and 6b (Pt) showed UT = 0.65 and 0.73, respectively (Table 2)
due to enhancement of intersystem crossing by the presence of Pd
and Pt. The lifetime followed the same pattern as octaphenoxy
which promotes d–
p interactions thereby quenching the singlet
state of the complexes. Also the enhanced spin orbit coupling or
low planarity might be responsible in lowering of fluorescence
quantum yields [38].
derivatives with 3b, 5b and 6b, showing lifetimes of 50
and 13 s, respectively.
ls, 20 ls
3.4. Triplet quantum yield and lifetime
l
The alkylthio derivatised phthlocyanines showed triplet quan-
tum yields lower than their oxy-derivatised counterparts. The me-
tal-free analogues (3c, 3d and 3e) gave UT values of 0.39, 0.40 and
Both the triplet quantum yields and lifetimes were determined
by laser photolysis. Transient spectrum (Fig. 6) of complex 3b in 1-
CNP showed a split Q-band characteristic of unmetalated phthalo-
cyanines. Of the octaphenoxy phthalocyanines, the metal-free (3a)
complex showed a triplet quantum yield (UT) of 0.40, while MPc
complexes 5a (Pd) and 6a (Pt) containing the same substituent,
gave UT = 0.51 and 0.62, respectively. The increase in the triplet
quantum yield of the palladated and platinated octaphenoxy
phthalocyanines (compared to unmetalated derivative, 3a) is due
0.38, with triplet lifetimes of 62, 51, 44 ls, respectively, Table 2.
Insertion of nickel into the cavities of these Pc ligands caused dras-
tic reduction in UT values of these molecules with complexes 4c,
4d and 4e having triplet quantum yields of 0.09, 0.04 and 0.04
and reduced of lifetimes of 6, 4 and 2 ls, respectively. However,
insertion of palladium metal into the ligands enhanced the triplet
Table 2
0.012
0.010
0.008
0.006
0.004
0.002
0.000
Photophysical properties of oxy and thio-derivatised phthalocyanines. References in
brackets. Solvent = 1-CNP.
Compounds
UF
UT
sT
(ls)
UD
S
D
3a (M@H2)
4a (M@Ni)
5a (M@Pd)
6a (M@Pt)
3b (M@H2)
4b (M@Ni)
5b (M@Pd)
6b (M@Pt)
3c (M@H2)
4c (M@Ni)
5c (M@Pd)
3d (M@H2)
4d (M@Ni)
5d (M@Pd)
3e (M@H2)
4e (M@Ni)
5e (M@Pd)
0.21
–
–
–
0.25
–
<0.01
0.012
0.10
<0.01 [20]
<0.01 [20]
0.13
<0.01 [20]
<0.01
0.15
<0.01
<0.01
0.40
–
0.51
0.62
0.47
–
0.65
0.73
0.39
0.09
0.47
0.40
0.04
0.42
0.38
0.04
0.40
55
–
23
17
50
–
20
13
62
6
15
51
4
0.05
<0.01
0.49
0.42
0.01
<0.01
0.43
0.39
0.04
<0.01
0.42
0.04
<0.01
0.40
0.04
<0.01
0.39
0.13
–
0.96
0.68
0.02
–
0.66
0.53
0.1
<0.1
0.89
0.1
0.25
0.95
0.11
0.25
0.98
12
44
2
0.0000
0.0001
0.0002
t (s)
0.0003
0.0004
10
Fig. 7. Triplet decay curve for 3a in 1-CNP. Excitation wavelength = 707 nm.

T.B. Ogunbayo, T. Nyokong / Journal of Molecular Structure 973 (2010) 96–103
103
yields but also reduced the lifetime of the molecules with com-
plexes 5c, 5d and 5e showing triplet quantum yields to 0.47, 0.42
and 0.40 and triplet lifetimes to 15, 12 and 10 s, respectively,
Acknowledgements
l
This work was supported by the Department of Science and
Technology (DST) and National Research Foundation (NRF), South
Africa through DST/NRF South African Research Chairs Initiative
for Professor of Medicinal Chemistry and Nanotechnology and
Rhodes University.
Table 2. The increase in the quantum yield by insertion of heavy
metal palladium is due to enhancement of intersystem crossing
through spin–orbit coupling which also reduces the lifetimes.
The nickel analogues of the alkylthio derivatised phthalocyanines
were found to be slightly photoactive while that of oxy-derivatised
showed no photoactivity. The non-display of photoactivity by nick-
el oxy-derivatised phathlocyanines is consistent with what was
observed for nickel octabutoxylphthalocyanines and nickel oct-
abutoxynaphthalocyanines [13] that made them good candidates
for photothermal therapy (PTT). This suggest a specific interaction
between aryloxy substituents and Ni(II) that efficiently quenches
the excited states to a larger extent than the alkylthio substituents.
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Singlet oxygen quantum yields were determined in 1-CNP using
DPBF as a chemical quencher. The disappearance of DBPF was
monitored using UV–Vis spectrometer. Many factors are responsi-
ble for the magnitude of the determined quantum yield of singlet
oxygen including; triplet excited state energy, ability of substitu-
ents to quench the singlet oxygen, the triplet excited state lifetime
and the efficiency of the energy transfer between the triplet ex-
cited state and the ground state of oxygen. The trends in the of sin-
glet oxygen quantum yields (Table 2) is as follows for the phenoxy
and benzyloxyphenoxy complexes: Pd (5) > Pt (6) > H2 (3) > Ni (4).
This trend shows the PdPc derivatives to have higher UD values
than the Pt complexes, yet the latter showed larger triplet quan-
tum yields. This suggests that the PtPc complexes are less efficient
in generating singlet oxygen than the corresponding PdPc deriva-
tives, with low S values for the former complexes. The magnitude
D
of S (=UD/UT) represents the efficiency of quenching of the triplet
D
excited state by singlet oxygen. The variation in the UD values for
the alkylthio complexes was: Ni < Metal-free < Pd.
4. Conclusions
Octakis(benzeloxyphenoxyl)phthalocyanine and octakis(phe-
noxyl)phthalocyanine complexes of Ni(II), Pd(II) and Pt(II) were
successfully synthesized and characterized along with their me-
tal-free analogue and alkylthio derivatised phthalocyanines. The
effects of these open-shell metals on the photophysical and photo-
chemical properties of these oxo and thio substituted phthalocya-
nine ligands were investigated. Palladium and platinum improved
the singlet oxygen generation properties of the ligands while nickel
reduced the capacity. Insertion of each of the metals led to reduc-
tion in the fluorescence quantum yield due to intersystem crossing
[38] M.O. Senge, Chem. Commun. (2006) 243.
and d–p interaction.