Electrochemical, spectroscopic and microscopic studies of new manganese phthalocyanine complexes in solution and as self-assembled monolayers on gold

Article abstract of DOI:10.1142/S1088424610002471

Four new manganese(III) phthalocyanines (3a-d), octasubstituted at the peripheral position with pentylthio, decylthio, benzylthio, and phenylthio groups, respectively, were synthesized. Their specific electrochemical, spectroscopic and microscopic propert

Full text of DOI:10.1142/S1088424610002471

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2010; 14: 568–581
DOI: 10.1142/S1088424610002471
Published at http://www.worldscinet.com/jpp/
Electrochemical, spectroscopic and microscopic studies of
new manganese phthalocyanine complexes in solution and
as self-assembled monolayers on gold
Megan Coates, Edith Antunes and Tebello Nyokong*
Department of Chemistry, Rhodes University, Grahamstown 6140, South Africa
Received 25 March 2010
Accepted 15 May 2010
ABSTRACT: Four new manganese(III) phthalocyanines (3a–d), octasubstituted at the peripheral position
withpentylthio,decylthio,benzylthio,andphenylthiogroups,respectively,weresynthesized.Theirspecific
electrochemical, spectroscopic and microscopic properties in solution and as self-assembled monolayers
on gold were characterized. The UV-vis spectra confirmed red-shifted Q bands for all the complexes,
due to the effect of the central metal and the electron-donating substituents. Three redox couples were
visible during cyclic voltammetry studies for the four complexes, and spectroelectrochemistry confirmed
the couples as corresponding to MnIIIPc-2/MnIIPc-2 (II) (metal reduction), MnIIPc-2/MnIIPc-3 (III) (ring
reduction) and MnIIIPc-1/MnIIIPc-2 (I) (ring oxidation). Electrochemistry was also used to determine the
blocking characteristics of the MnPc self-assembled monolayers on gold, which proved to be highly
dependent on the type of substituent. Other methods of characterization included Raman spectroscopy,
atomic force and scanning electrochemical microscopy analyses of the SAMs.
KEYWORDS: manganese thiol-derivatised phthalocyanines, cyclic voltammetry, spectroelectro-
chemistry, self-assembled monolayer.
used in this regard to produce a self-assembled mono-
INTRODUCTION
layer (SAM) on gold [1, 4].
Metallophthalocyanines (MPcs) are incredibly diverse
Manganese phthalocyanines (MnPcs) have not been as
and widely studied compounds, as their properties and
extensively studied as some MPcs, like those containing
characteristics can be tailored fairly simply by changing
cobalt as the central metal. MnIIIPcs have typically red-
the central metal and/or the nature of the substituents on
shiftedabsorbancespectrainthevisibleregion(theQband),
the ring [1–3]. MPcs are macrocyclic 18 π-electron sys-
and this can be shifted further to the red by non-peripheral
tems and a variety of substituents can be positioned at four
substituents and the electron-donating properties of groups
different points on each isoiminoindoline ring, resulting in
like those containing sulfur [4–8]. Electron-donating sub-
a large range of products with a common central structure.
stituents can also affect the electrochemical properties of
Electrodes modified with MPcs have been widely
the Pc, making it more easily oxidized but harder to reduce
used to facilitate electrocatalysis of many analytes that
[9]. Mn has a number of oxidation states, ranging from MnI
are otherwise difficult to detect [1]. The substituents on
to MnIV, but it is MnIIPc that has been shown to form a
the Pc ring can also be used to link the MPcs to an elec-
μ-oxo species, PcMnIII–O–MnIIIPc, on absorption of oxy-
trode in order to make a reproducible, stable and uniform
gen with the possibility of monomeric MnIIIPc also forming
sensor surface. Sulfur-containing substituents have been
[5, 10]. Formation of this dimer is highly dependent on the
position, number and type of substituents [5].
SPP full member in good standing
MPc derivatives containing alkyl- and aryl-thio groups
with different central metals are known [4, 7–9, 11–17].
SPP student member
However, mainly tetrasubstituted derivatives of the
MnPcs have been reported [9], with few examples of
*Correspondence to: Tebello Nyokong, email: t.nyokong@
ru.ac.za, tel: +27 46-6038260, fax: +27 46-6225109
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neW manganeSe PhthalOCyanIne COmPlexeS In SOlutIOn
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Scheme 1. Synthetic route for the produced thiol-derivatised metallophthalocyanine complexes. Complex 3a, manganese(III)
octa(pentylthio)phthalocyanine, (OAc)MnPcβ{S(CH2)4CH3}8. Complex 3b, manganese(III) octa(decylthio)phthalocyanine, (OAc)
MnPcβ{(SCH2)9CH3}8. Complex 3c, manganese(III) octa(benzylthio) phthalocyanine, (OAc)MnPcβ(SCH2Ph)8. Complex 3d,
manganese(III) octa(phenylthio)phthalocyanine, (OAc)MnPcβ(SPh)8
octa-substitution in these complexes [11]. Octa-substitution
in MPc complexes has advantages over tetra-substitution
due to isomeric purity, and hence ease of purification and
characterization. The complexes synthesized in this work
are shown in Scheme 1. They are MnIII phthalocyanines
octasubstituted at the peripheral positions with pentylthio
(3a), decylthio (3b), benzylthio (3c) and phenylthio (3d)
groups. Dodecylthio octasubstituted phthalocyanine com-
plexes have been reported for other central metals such as
Cu [13] and Ni [12] as well as hexylthio octasubstituted
phthalocyanine complexes of Cu and Zn [14] and butyl-
thio octasubstituted ZnPc complex [15], but the ligands
of interest in this work have not been reported for MnPc
derivatives. Changes in the structure of the MPc and the
type of central metal can have substantial effects on the
behavior of the complex as an electrocatalyst [9, 18–23]
and on the formation of SAMs [4, 9, 21–24]. SAMs of
the MnPcs were produced by utilizing the high affinity of
sulfur for gold, and their properties were studied in this
work using electrochemical, spectroscopic and micro-
scopic techniques to determine the effect of the alkyl and
aryl substituents on monolayer formation.
the appropriate thiol with 4,5-dichlorophthalonitrile in
the presence of potassium carbonate, which facilitated
a base-catalyzed nucleophilic aromatic displacement
reaction. The success of the reaction was confirmed
by proton NMR analysis, and the clean spectra clearly
showed the alkyl or aryl substituents bonded to the
phthalonitrile through sulfur and resulting in a highly
pure product. Sulfur caused deshielding of the adjacent
CH2 protons on the alkyl substituents, shifting them to
3.01 ppm.
The phthalonitriles were then reacted with manganese(II)
acetate by refluxing in ethylene glycol for 4 or 5 h.Yields
of complexes 3a to 3d ranged from 32 to 74%. The com-
plexes were purified by column chromatography using
Bio-beads, which relies on size-exclusion. The use of a
Bio-bead column instead of the commonly used silica
column was much more effective and provided higher
yields for these complexes. The choice solvent for elu-
tion was CHCl3 as the use of THF as an eluting solvent
resulted in the formation of μ-oxo MnPc species, as
shown by its typical spectrum [8] in Fig. 1 with a peak at
650 nm. μ-oxo MnPc complexes absorb in the 630 to 650
nm region and hence are highly blue-shifted compared
to monomeric MnIIIPc complexes, which commonly have
their Q band near 750 nm or above. The observed μ-oxo
MnPc formation in THF could be a result of the different
amounts of dissolved oxygen in the solvent compared to
chloroform.
RESULTS AND DISCUSSION
Synthesis and characterization
The syntheses of the aryl- and alkyl-thio substi-
tuted phthalonitriles were accomplished by reacting
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Fig. 2. UV-visible spectra of 3a, 3b, 3c and 3d in CHCl3
Fig. 1. UV-visible spectra of 3d showing spectral changes dur-
ing elution from Biobeads column with DCM (a) followed by
THF (b) and (c) in various subsequent fractions
previous work and confirms that the alkyl chain length in
MPc complexes does not significantly affect the Q band
position [12, 16, 25]. The spectral differences between
the two arylthio MnPcs could be attributed to the CH2
group separating the sulfur and the ring for 3c, and so
making it behave more similarly to the alkyl substituents
with regard to electron-donating ability. The electron-
rich phenyl ring in complex 3d, however, could directly
contribute to the electron-donating properties of the
substituents and shift the spectra further to the red. This
indicated that although alkyl chain length does not affect
the electronic properties of the ring, aryl substituents can
play a larger role.
The mechanism for the formation of the μ-oxo dimer
and MnII species was put forward by Lever et al. [10] and
is as follows:
MnIIPc + O2  MnIIIPc(O2)
(1)
(2)
(3)
(4)
(5)
MnIIIPc(O2) + MnIIPc  MnIIIPc–O2–PcMnIII
MnIIIPc–O2–PcMnIII  2MnIVPcO
2MnIVPcO + 2MnIIPc  2MnIIIPc–O–PcMnIII
Net: MnIIPc + O2  2MnIIIPc–O–PcMnIII
The Pcs also had three bands near 405, 465 and 530
nm. The bands between 400 and 550 nm are due to
charge transfer between the metal and the Pc ring [8].
For both 3a and 3b the Q band spectra shifted to 755
nm in THF (data not shown). Figure 2 shows that 3d is
less aggregated than the other Pcs, as judged by the nar-
rower Q band. However, Beer’s law was observed for all
complexes at concentrations less than 9.0 × 10-6 M. Com-
parisons of Q band maxima between similar complexes
(peripherally tetrasubstituted and non-peripherally octa-
substituted, Fig. 3) are shown in Table 1.
Complexes 3c and 3d were soluble in CHCl3, DCM,
THF, DMF and DMSO, whereas 3a and 3b were insoluble
in DMF and DMSO, likely due to their more non-polar
alkyl substituents. Complexes 3a and 3b also showed
good stability in the solvents over time, with little to no
change in their spectra. However, complexes 3c and 3d
exhibited unstable spectra in DMF and THF over time,
with the formation of bands typical of the μ-oxo species,
similar to that shown in Fig. 1, due to the effects of dis-
solved oxygen. It can be seen that the spectra and thus the
color of these Pcs changes depending on the solvent con-
ditions, and care needs to be taken in their preparation.
The UV-visible spectra of complexes 3a to 3d are
shown in Fig. 2 in chloroform. Because of the presence
of manganese and the electron-donating properties of
sulfur, the Q band is highly red-shifted and the com-
plexes are dark red, brown, or dark brown in color. This
is typical of MnIIIPc complexes [9, 11, 16]. The synthesis
used Mn(II) acetate, however, as purification took place
in aerobic conditions the MnIIIPc species was formed, as
outlined in Equation 1 above, and there was no indication
of residual MnIIPc.
For compounds 3a and 7 containing the same chain
length but the latter non-peripherally substituted
Table 1. Electronic absorption spectra of MnIIIPc derivatives
in DCM
Complex
Q band absorbance
Reference
3a
3b
3c
3d
4
768
768
767
773
764
749
745
893
this work
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this work
this work
[4]
Complex 3d was slightly more red-shifted compared
to the other Pcs, with a Q band at 773 nm, while the alky-
lthio-Pcs (3a and 3b) had a Q band at 768 nm and for 3c
it was at 767 nm in DCM (Table 1). The spectra in DCM
were identical to that in CHCl3. This correlates with
5
[9]
6
[9]
7
[11]
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R3
R2
R4
N
R1
OAc
R1
R4
N
N
R3
R2
R2
R3
N
Mn N
N
N
N
R4
R1
R4
R1
R3
R2
Complex
number
3a
Substituent
Abbreviation
Reference
This work
This work
This work
This work
(OAc)MnPcβ{S(CH2 )4CH3}8
(OAc)MnPcβ{(SCH2)9CH3}8
(OAc)MnPcβ(SCH2 Ph)8
(OAc)MnPcβ(SPh)8
R1 = R4 =H; R2 = R3 =
S(CH2 )4CH3
R1 = R4 =H; R2 = R3 =
(SCH2)9CH3
3b
3c
3d
R1 = R4 =H; R2 = R3 =
SCH2Ph
R1 = R4 =H; R2 = R3 =
SPh
(OAc)MnPcα(SPh)4
R2 = R3 = R4 =H; R1 = SPh
R1 = R3 = R4 =H; R2 =
(SCH2)11CH3
4
9
4
5
(OAc)MnPcβ{(SCH2)11CH3}4
(OAc)MnPcβ(SCH2Ph)4
R1 = R3 = R4 =H; R2 = SCH2Ph
R2 = R3 =H; R1 = R4 = S(CH2 )4CH3
9
6
7
(OAc)MnPcα{S(CH2 )4CH3}8
11
Fig. 3. Molecular structures of the compared manganese phthalocyanine complexes
(structures are shown in Fig. 3), the Q band was observed
at 768 nm and 893 nm [11] in DCM, respectively
(Table 1), showing that peripheral substitution caused
an expected blue shift in the Q band compared to non-
peripheral substitution [8].
Looking at the octasubstituted complex 3c (λQ = 767)
and comparing it to its tetrasubstituted counterpart 6 (λQ =
745), the Q band spectrum was blue-shifted in the tetra-
substituted complex [9]. These results show that the octa-
substituted MnPcs exhibited greater electron-donation by
the substituents than the equivalent tetra-MnPcs, which
can be simply attributed to the greater number of sub-
stituents around the ring.
other is the tetrasubstituted non-peripheral (4), the latter
has a comparatively blue-shifted Q band despite being
non-peripherally substituted [4]. This indicates that the
number of substituents could play a larger role than the
position of these substituents on the electronic properties
of the ring.
Voltammetric and spectroelectrochemical character-
ization
Figure 4 shows the cyclic (CV) and differential pulse
voltammograms (DPV) of complex 3c, representing all
the other MnPcs synthesized. All electrochemical analy-
ses were performed in deaerated DCM using TBABF4 as
an electrolyte.
Comparing complexes 3d (λQ = 773) and 4 (λQ = 764),
one is the peripheral octasubstituted version (3d) and the
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pentylthio groups at the non-peripheral posi-
tions showed reversible behavior [11], most
likely due to the prevention of aggregation by
non-peripheral substitution. The assignments
of these processes were confirmed with spec-
troelectrochemistry, as discussed below.
The MnIIIPc-2/MnIIPc-2 process (II) could
be clearly observed at similar potentials in
all thiol-derivatized MnPcs, Table 2 (except
for 6) [4, 9, 11]. The oxidation of Mn(III) to
Mn(IV) could not be conclusively observed
in the synthesized Pcs in this work, although
the process has been observed before [9, 11,
16]. Process III has been assigned in similar
complexes to either MnIIPc-2/MnIPc-2 [5, 7] or
MnIIPc-2/MnIIPc-3 [7, 9, 11, 16, 22], although
the latter has been reported more frequently.
In this work, spectroelectrochemistry was
used to assign this process to ring reduction.
Fig. 4. Cyclic voltammogram for 3c in DCM containing 0.1 M TBABF4.
Scan rate = 50 mV/s. Inset: DPV
Process I could be attributed to ring oxidation, and it is
in a similar range to that reported in literature [7, 9, 11].
Thiol substituted complexes often decompose during ring
oxidation, and this can contribute to the irreversibility of
process I [7, 9].
The half-wave potentials (E1/2) for 3a–d and other
similar compounds are shown in Table 2. Complexes
3a–d displayed three main redox processes, with ∆E val-
ues from 93 to greater than 200 mV. 3a displayed redox
processes at: E1/2 = +0.97 V (I), E1/2 = -0.35 V (II) and
E1/2 = -1.07 V (III) vs. Ag|AgCl with 3b displaying redox
processes at: E1/2 = +0.94 V (I), E1/2 = -0.46 V (II) and
E1/2 = -1.08 V (III) vs. Ag|AgCl. 3c displayed redox pro-
cesses at: E1/2 = +0.96 V (I), E1/2 = -0.26 V (II) and E1/2
= -0.94 V (III) vs. Ag|AgCl while 3d displayed redox
processes at: E1/2 = +0.88 V (I), E1/2 = -0.34 V (II) and
E1/2 = -1.15 V (III) vs. Ag|AgCl. In some of the com-
plexes, a weak process could be observed around -0.1 V.
This process was attributed to aggregation of the com-
pounds, as the peaks were observed to decrease with
dilution. Plots of peak current (Ip) vs. square root of the
scan rate (v1/2) were linear, suggesting diffusion control
at the electrode surface for all the complexes. Figure 4
shows broad cyclic voltammetry peaks, which are often
observed in MnPc complexes, especially those contain-
ing long-chain substituents [9]. This was also observed
for the tetrasubstituted complexes 5 and 6 (structures
in Fig. 3) [9]. However, complex 7 octasubstituted with
Ease of oxidation and reduction of complexes is
related to the electron-donating or electron-withdrawing
effects of the substituents. Electron-donating substitu-
ents are expected to facilitate easier oxidation and harder
reduction, as they should increase the electron density on
the ring [26, 27]. As aromatic rings are electron donors,
3d should then be more electron-donating than 3c, which
would in turn be more electron-donating than 3a fol-
lowed by 3b. This behavior was partially confirmed by
the absorbance spectra of the compounds (Fig. 2), which
showed the Q band positions of 3a–c at an approximately
equivalent position, while 3d was the most red-shifted as
its phenyl substituents were the most electron-donating.
As expected then, 3a–c were harder to oxidize with regard
to process I when compared to complex 3d. Looking at
process III, 3d was the hardest to reduce (as expected)
with an E1/2 of -1.15 V, with 3a and 3b having similar
values and 3c being the easiest to reduce with an E1/2 of
-0.94 V. The ease in reduction for 3c could be attributed
Table 2. Electrochemical data of thiol-derivatized MnPcs. The compounds were analyzed in DCM containing
TBABF4 and the half-wave potential (E1/2) as V against Ag|AgCl, unless otherwise specified
Complex
MnIIPc-2/MnIIPc-3 (III)
MnIIIPc-2/MnIIPc-2 (II)
MnIIIPc-1/MnIIIPc-2 (I)
Reference
3a
3b
3c
3d
5
-1.07
-1.08
-0.94
-1.15
-0.98
-0.84
-1.24
-0.35
-0.46
-0.26
-0.34
-0.26
-0.08
-0.46
0.97
0.94
0.96
0.88
0.83
0.87
—
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this work
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this work
[9]
6
[9]
7
[11]
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to the aromatic ring being separated from the Pc by a CH2
been observed during oxidation of thio-substituted MPc
complexes [9]. Figure 5(a) illustrates spectral changes
observed on application of potentials more negative than
process II (-0.65 V), clearly showing the reduction of
Mn(III) to Mn(II) as there is a decrease in the Mn(III)
Q band and a growing blue-shifted Q band that correlates
to Mn(II) [4, 8, 9, 11]. The Q band shifted from 768 nm
for the Mn(III) complex to 720 nm for the Mn(II) com-
plex and the color of the complex in the OTTLE cell vis-
ibly changed from red-brown to green. There was also a
decrease in intensity of two of the charge transfer bands
at 465 and 530 nm, with the former disappearing almost
completely and the latter shifting to 540 nm. The spectra
had three clear isosbestic points at 738, 614 and 407 nm
and the value of n was calculated using Q = nFCV to
be approximately equal to 1. Figure 5(b) shows spectral
changes observed on application of potentials more nega-
tive than process III (-1.3 V), with the decrease in the
Q band and the formation of new features between 500
and 650 nm characteristic of ring-based reduction pro-
cesses in Pcs [28], leading to the assignment of this as
MnIIPc-2/MnIIPc-3. The spectral changes were similar to
that reported elsewhere for this process [7, 9, 11]. It has
been shown that the nature of ring substituents are respon-
sible for the formation of MnIIPc-3 as opposed to MnIPc-2
[7] and there was no evidence of the broad Q band form-
ing at around 550 nm that is characteristic of MnI [7],
confirming process III as ring-based reduction. Based on
these results, the processes could be assigned as follows:
group, as this has been observed before with complexes 5
and 6 [9]. No particular trend could be observed for pro-
cess II except that again complex 3c showed the greatest
ease in reduction with an E1/2 of -0.26 V.
Looking at peripheral (3a) vs. non-peripheral (7) sub-
stitution (using the same substituent), complex 3a showed
greater ease in reduction compared to complex 7 [11].
Pc ring oxidation of 7, although attributed to MnIVPc-1/
MnIVPc-2 rather than MnIIIPc-1/MnIIIPc-2 as in this work,
showed that the non-peripheral complex was more easily
oxidized with an E1/2 of +0.75 V [11]. Octasubstituted 3c
proved to be harder to oxidize compared to the tetrasub-
stituted complex 6 containing the same substituent. The
same was true of complex 3b compared to the similar tet-
rasubstituted compound 5 [9], though the chain lengths
were slightly different.
Spectroelectrochemical studies allowed a confident
assignment of the redox couples to be made. Figure 5
shows the spectral changes that occurred for complex 3a,
which were similar to the spectral changes observed for
the other complexes in this work. Oxidation at potentials
of process I resulted in degradation of the complex, as has
MnIIIPc-2 → MnIIIPc-1 + e- (process I)
(6)
(7)
(8)
MnIIIPc-2 + e- → MnIIPc-2
MnIIPc-2 + e- → MnIIPc-3
(process II)
(process III)
Self-assembled monolayers
SAM films were formed by immersing the bare gold
electrode in the desired complex for an average time of
48 h in each case. Formation of SAM films is facilitated
by coordination of the sulfur group (using its lone pair of
electrons) with gold, with the C-S bond remaining intact
as reported previously [18]. Electrochemistry, Raman
spectroscopy, atomic force microscopy (AFM) and scan-
ning electrochemical microscopy (SEM) were used to
characterize the modified gold electrodes and give further
spectroscopic evidence of their formation. For the latter
studies (Raman, AFM and SEM), only 3b and 3d were
used to identify the effect of the different substituents on
the SAM layer as these both showed good blocking char-
acteristics. Gold-coated glass was immersed in the MnPc
solution for 10 days for these analyses, to ensure a fully-
formed SAM and complete coverage.
Inhibition of faradaic processes. Electrochemical
properties of the films are closely related to the extent
to which they inhibit common faradaic processes associ-
ated with the bare gold surface. Figure 6(a) shows oxida-
tion (at +0.21 V vs. Ag|AgCl) and reduction (gold oxide
Fig. 5. UV-vis spectral changes for complex 3a observed using
controlled potential electrolysis at: (a) -0.65 V and (b) -1.3 V.
Electrolyte = DCM with 0.1 M TBABF4
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Fig. 6. Cyclic voltammograms for bare Au, 3a-Au, 3b-Au, 3c-Au and 3d-Au in: (a) 1 M Na2SO4 in pH 4 buffer solution, (b) 1 mM
Fe(NH4)2(SO4)2 in 1 M HClO4, (c) 1 mM K3[Fe(CN)6] in 0.1 M KCl and (d) 1 mM CuSO4 in pH 4 buffer solution. Scan rate = 50
mV/s vs. Ag|AgCl
stripping peak, at +0.15 V vs. Ag|AgCl) of the bare gold
surface in 1 M Na2SO4 in pH 4 buffer solution. As seen
in this figure, there was appreciable passivation of this
process in the presence of all the MPc-SAMs, although
the 3c-SAM was the least effective at blocking the elec-
trode. Gold oxidation was considerably inhibited with
a decrease in intensity of the gold oxide stripping peak,
suggesting that the electrolyte was no longer accessible
to the bare gold surface and confirming SAM formation.
Figure 6(b) shows the cyclic voltammograms
obtained for the bare Au electrode and the SAM-
modified gold electrodes in 1 mM ferrous ammonium
sulfate (Fe(NH4)2(SO4)2) containing 1 M perchloric acid
(HClO4). The clearly resolved quasi-reversible redox
process ([Fe(H2O)6]3+/[Fe(H2O)6]2+) on the bare electrode
was almost completely inhibited on SAMs of 3a and 3b,
only slightly inhibited for the 3d-SAM, and almost com-
pletely uninhibited for the 3c-SAM. The inhibition of this
process on the SAM-modified gold electrodes suggests
the isolation of the gold surface from the electrolyte, con-
firming defect-free SAM formation for 3a and 3b. For 3d,
the voltammograms were distorted, but more resolved for
3c. It is possible that the bulky aryl substituents in 3c and
3d were less effective in blocking the redox process, as
the SAMs they formed appeared to be more permeable
to this analyte.
Figure 6(c) shows the cyclic voltammograms of the
bare Au electrode and the SAM-modified electrodes
in 1 mM solution of [Fe(CN)6]3- containing 0.1 M KCl
as the supporting electrolyte. Unlike the [Fe(H2O)6]3+/
[Fe(H2O)6]2+ redox process in Fig. 6b, the [Fe(CN)6]3-/4-
redox couple was not inhibited on the SAM-modified
electrodes because of the fast nature of electron transfer
for this process. This observation has been reported pre-
viously for adsorbed cobalt tetra-amino phthalocyanine
films on a vitreous carbon electrode [19]. However, the
cathodic-to-anodic peak difference (ΔE) for this process
was larger for SAMs of 3a, 3b and 3d, but the same for
3c. The anodic and cathodic current intensities of the
[Fe(CN)6]3-/4- redox couple on bare gold electrode are
larger than that observed on the SAM-modified elec-
trodes, confirming the formation of the SAM films.
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Figure 6(d) shows the cyclic voltammograms of the
been reported before for NiPc complexes that some metal
processes are observed when the complexes are absorbed
but not when in solution [1]. The difference between the
free and bound MnPc is associated with the nature of the
SAM and the different solution environments.
bare Au electrode and the SAM-modified electrodes in
1 mM CuSO4 in pH 4 buffer solution. The bulk deposi-
tion of Cu began at 133 mV (vs. Ag|AgCl on the nega-
tive scan) and the maximum of the large underpotential
deposition stripping peak of the Cu occurred at 101 mV
(vs. Ag|AgCl) on the bare Au electrode. This process
was significantly inhibited on the SAM-modified elec-
trodes, indicating SAM formation for 3a, 3b and 3d. The
3c-SAM again showed the least inhibition of the redox
process, indicating that it was not completely blocked.
In general 3a and 3b showed particularly good block-
ing characteristics in all solutions, suggesting that the
benzyl and phenyl groups for 3c and 3d prevent the for-
mation of good SAMs.
Surface coverage. Figure 7 shows the cyclic voltam-
metry profiles obtained for the SAM-modified electrodes
in 1 M HClO4. The redox processes observed in Fig. 7 are
associated with Mn3+/Mn4+ (E1/2 = ~0.23 V vs. Ag|AgCl,
Table 3) as compared to similar compounds [4, 9, 11].
This process was not observed above in solution, and there
were no peaks in this potential range in solution. It has
Surfacecoverage(Γ)foreachSAMwasestimatedfrom
the relevant redox process in Fig. 7 using Equation 9:
Ipa 4(RT)
n2 F2 Aν
(9)
ΓSAM
=
where Ipa is the peak current (A) in Fig. 7 for each SAM,
A is the real surface area of the gold electrode, n is the
number of electron transferred (approximately 1) and the
other symbols have their usual meanings. The real surface
area of the electrode was estimated using the well-
established method [29] applying Equation 10 (Randles-
Sevcik equation). [Fe(CN)6]3- was used as the redox active
species because it has a known diffusion coefficient.
Ipa = (2.69 × 105) n3/2 D1/2 v1/2 AC
(10)
where n is the number of electrons transferred (approxi-
mately 1), D is the diffusion coefficient of the redox
active species (7.6 × 10-6 cm2.s-1 [29]), A is the geometric
surface area (0.0201 cm2), v is the scan rate (0.05 V.s-1)
and C is the bulk concentration of [Fe(CN)6]3- (0.001 M).
Roughness factor of the electrode was calculated to be
1.02 (ratio of Ipa (exptal)/Ipa (theor)), where Ipa (exptal)
and Ipa (theor) are the experimental current and current
calculated using Equation 10, respectively. The geomet-
rical area was used in the estimation of Ipa (theor). The
product of the roughness factor and theoretical surface
area gives the real surface area (0.0205 cm2). Thus the
values of surface coverage obtained on the gold elec-
trode were 0.64 × 10-10 mol.cm-2 for 3a, 0.30 × 10-10 mol.
cm-2 for 3b, 0.42 × 10-10 mol.cm-2 for 3c and 1.45 × 10-10
mol.cm-2 for 3d (Table 3). Except for 3d, these values
are slightly less than the values obtained for a monolayer
coverage of an MPc molecule lying flat on the electrode
[30], which is estimated at 1 × 10-10 mol.cm-2. These val-
ues are, however, still within the range for monolayer
Fig. 7. Cyclic voltammograms for 3a-Au, 3b-Au, 3c-Au and
3d-Au in 1 M HClO4. Scan rate = 50 mV/s vs. Ag|AgCl
Table 3. Electrochemical parameters of SAMs of complexes 3a–d in 1 M HClO4, (formation time = 48 h)
MnPc complex
MnIII/MnII
MnIV/MnIII
Surface concentration
(1010 mol.cm-2)
Reference
3a
3b
3c
3d
4
—
—
0.22
0.24
0.22
0.23
0.30
0.2
0.64
0.30
this work
this work
this work
this work
[4]
[9]a
[9]a
[21]a
—
0.42
—
1.42
-0.2
—
1.1 (24 h)b
0.78 (18 h)b
0.69 (18 h)b
1.1
5
6
—
0.35
—
7
-0.1
a In pH 4 phosphate buffer. b Numbers in brackets refer to the time allowed for SAM formation.
Copyright © 2010 World Scientific Publishing Company
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576
m. COateS et al.
are used to give information beyond the surface-blocking
characteristics (which are easily studied using electro-
chemical techniques), such as whether the MnPcs are
aggregated on the gold surface or whether they form a
uniform layer. SEM is also commonly used to look at the
surface morphology of thin films formed at different tem-
peratures [31]. These methods should be used in conjunc-
tion because although SEM gives a broader view of the
surface with regards to larger (micro-scale) aggregated
clusters, like transmission electron microscopy (TEM), it
does not give an indication of the height of the surface or
aggregation on a smaller (nano) scale [32]. AFM, on the
other hand, indicates clearly whether there is complete
coverage by looking at the difference in the height of
the surface before and after modification [33]. Aggrega-
tion is an important factor in SAM formation, and it can
affect formation of a uniform layer on a surface [32–34]
as well as the electrical properties [35] and reaction of
the sensor with analytes. It could, for example, play a
role in increasing or reducing passivation effects of the
electrode, depending on the nature of the layer.
Figure 9(a) shows the AFM 2D and 3D images of the
gold-coated glass before the formation of SAMs, indi-
cating that the bare gold surface was fairly smooth and
uniform with the small bright areas being attributed pre-
viously to imperfections on the surface [24]. Figure 9(b)
shows the 3b-SAM (alkylthio) and Fig. 9(c) shows the
3d-SAM (arylthio) on gold. The most important data
to take away from AFM are the values for mean thick-
ness and roughness, and any clear indications of com-
plete coverage or the formation of aggregates [34–38].
Figure 9 indicates that there are significant differences
in the topographies of the surfaces. The mean rough-
ness and thickness of the gold-coated glass before SAM
formation are 0.278 nm and 1.643 nm, respectively. The
mean roughness and thickness after the 3b-SAM forma-
tion are 2.081 nm and 8.738 nm, while the mean rough-
ness and thickness after 3d-SAM formation are 1.870 and
8.666 nm, respectively. This increase in the roughness
and thickness of the surface after SAM formation con-
firms the presence of a layer of the MnPcs on the surface.
The images appear to show some nano-scale aggregation
of the MnPcs, which can be expected as these periph-
erally substituted Pcs are more prone to aggregation
than their non-peripherally substituted derivatives. The
alkylthio-MnPc, 3b, had higher roughness and thickness
factors than the arylthio-MnPc, 3d. This indicates that
the layer was more densely packed because of the long
chains, and is supported by the better blocking charac-
teristics of the 3b-SAM showed in Fig. 6b with regards
to the [Fe(H2O)6]3+/[Fe(H2O)6]2+ redox process. For the
non-peripheral tetrasubstituted complex 4, the inverse of
the above behavior was observed. AFM showed that the
roughness of the surface decreased upon 4-SAM forma-
tion, and this was explained to be a result of the complex
filling in the grooves in the electrode [24]. In this case
the bare gold had an initial roughness of 1.257 nm [24],
Fig. 8. Cyclic voltammograms in 1 mM CuSO4 in pH 4 buffer
solution for Au electrode after: (1) 0 h, (2) 24 h and (3) 48 h
SAM formation in 1 mM 3d in CHCl3. Scan rate = 50 mV/s vs.
Ag|AgCl
coverage. Complexes 4–6 showed higher (compared to
3a–3c) surface coverage values in Table 3, even though
shorter SAM formation times (18 h and 24 h, compared
to 48 h used in this work) were employed, suggesting
that the tetra-substitution may enhance SAM formation.
The importance of allowing the monolayer to form com-
pletely and fully is shown by Fig. 8, where formation
times of 0 h, 24 h, and 48 h for the 3d-SAM on gold are
tested by looking at the electrochemistry of the SAM in
1 mM CuSO4 in pH 4 buffer solution. As seen in this
figure, a formation time of 24 h was not enough to block
the electrode, while after 48 h the monolayer was almost
completely pinhole-free.
Interestingly, the 3c-SAM had an almost similar sur-
face coverage to the 3b-SAM despite the former SAM
showing less inhibition of electrochemical processes at
the electrode. The 3c-SAM consistently displayed poor
blocking of the gold surface in Fig. 6, but the surface
coverage value indicates that this is not because of poor
monolayer coverage. It is likely that the nature of the sub-
stituents, which are bulky and are also able to rotate more
freely around the CH2 group, creates a layer that is more
permeable to the small redox ions and so allowing them
to reach the gold surface. The long alkyl chains, how-
ever, appear to prevent ions from reaching the surface so
easily despite having a similar surface coverage value to
3c. This indicates once again the importance of different
substituents in the formation of these layers.
Raman spectroscopy, AFM and SEM. Gold-coated
glass was employed, in place of a gold electrode, for
probing surface properties of the 3b- and 3d-SAM films.
The formation time was increased to 10 days to ensure
complete coverage of the glass surface with the MnPcs.
The peak characteristic of the Au-S linkage was
observed at ~345 cm-1 in the Raman spectra of the SAMs
[30]. Surface natures of the SAM films were probed using
AFM (in non-contact mode) and SEM. SEM and AFM
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neW manganeSe PhthalOCyanIne COmPlexeS In SOlutIOn
577
Fig. 9. AFM images of (a) bare gold-coated glass, (b) 3b-SAM-modified gold-coated glass and (c) 3d-SAM-modified gold-coated glass
which was far greater than the roughness of 0.278 nm
observed in this work. This could explain the difference
in the behavior of the SAMs. SAMs of complexes 5, 6
and 7 were not analyzed using AFM or SEM. However,
octa- and tetrasubstituted MPcs containing Sn as a cen-
tral metal with non-peripherally substituted long alkyl-
thio chains were shown to increase the roughness of the
gold surface after SAM formation [39], as was observed
in this work. Non-peripheral substituents also appeared
to decrease the occurrence of surface aggregates.
Figure 10 shows the SEM images of gold-coated
glass alone (a), after 3b-SAM formation (b), and
after 3d-SAM formation (c). Although detailed fea-
tures are not visible because the scale does not per-
mit resolution of distinct molecules [35], the bare
gold-coated glass depicts a smoother surface than the
SAM-modified gold-coated glass which showed signs
of aggregation. The SEM images indicate that there
are areas with large clusters of aggregated MnPc mol-
ecules on the surface, as well as the smaller groups
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 577–581

578
m. COateS et al.
Fig. 10. SEM images of (a) bare gold-coated glass, (b) 3b-SAM-modified gold-coated glass and (c) 3d-SAM-modified gold-coated
glass
of aggregated molecules shown by the AFM results.
As with the AFM images, the 3b-SAM appeared to
EXPERIMENTAL
be rougher than the 3d-SAM. Aggregation is known
to be enhanced by the presence of long alkyl chains
Materials
Dimethylsulphoxide (DMSO), dichloromethane
(DCM), tetrahydrofuran (THF), dimethylformamide
(DMF), chloroform (CHCl3), deuterated chloroform
(CDCl3), methanol and ethanol were purchased from
Merck. Manganese(II) acetate, acetone, 1-pentanethiol,
1-decanethiol, thiophenol, tetrabutylammonium tetraflu-
oroborate (TBABF4) and ethylene glycol were obtained
[12], which could account for the greater roughness
of the 3b-SAM in the AFM and the presence of larger
surface clusters in the SEM image. SEM has not been
used to analyze SAMs of complexes 4–7 on gold, but
comparing the difference in topographies of the sur-
faces is another method that can be used to confirm
SAM formation.
Copyright © 2010 World Scientific Publishing Company
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neW manganeSe PhthalOCyanIne COmPlexeS In SOlutIOn
579
from Aldrich. Saarchem provided anhydrous potassium
For SAM studies, the gold electrode was rinsed with
freshly distilled CHCl3 and placed in deaerated CHCl3
containing the MnPc complex for 48 h. Gold-coated glass
was used for surface characterization of the SAM films
using AFM, SEM and Raman. The glass was immersed
in solution of the desired complex in CHCl3 for 10 days
for the latter studies.
carbonate. Benzyl mercaptan was procured from Fluka,
while argon was purchased from Afrox. Bio-beads S-X1
(200–400 mesh) were obtained from Bio-Rad and silica
gel 60 (0.04 to 0.063 mm) was purchased from Merck.
4,5-dichlorophthalonitrile was synthesized according to
a well-known procedure [40, 41] starting from dichlo-
rophthalic anhydride. Solvents were dried and distilled
before use, and all other chemicals and reagents were of
analytical grade and were used as received.
Synthesis
As stated above, the synthesis of 4,5-dichlorophthalo-
nitrile (1) has been reported before [40, 41] and so shall
not be discussed here. The conversion to the required
phthalonitriles followed by formation of the phthalocya-
nine is illustrated in Scheme 1.
Equipment
UV-visible spectra were recorded on a Cary 500 UV/
vis/NIR spectrophotometer. H-nuclear magnetic reso-
1
nance (NMR, 400 MHz) spectra were recorded using
a Bruker AMX 400 MHz NMR spectrometer in CDCl3
using standard 1D pulse programs. Elemental analysis
was done using a Vario-Elementar Microcube ELIII on
the purified Pcs. Spectroelectrochemical studies were
done using a homemade optically transparent thin-layer
electrochemical (OTTLE) cell connected to a Bioanalyti-
cal Systems (BAS) CV 27 voltammograph and using a
Shimadzu Model UV-2550 UV-vis spectrophotometer.
MALDI-TOF mass data was obtained in an α-cyano-4-
hydroxycinnamic acid matrix, on a ABI Voyager DE-STR
MALDI-TOF instrument in positive ion mode, by the
University of Stellenbosch in South Africa. AFM images
were obtained in non-contact mode in air with a CP-11
Scanning Probe Microscope from Veeco Instruments
(Carl Zeiss, South Africa) at a scan rate of 1 Hz. Scan-
ning electrochemical microscopic (SEM) images were
recorded using a Tescan Digital Microscope model scan-
ning electron microscope at the Rhodes University Elec-
tron Microscopy Unit. A Bruker Vertex 70 spectrometer
(fitted with the RAM II module and equipped with a 1064
nm Nd:YAG laser and a liquid nitrogen-cooled germanium
detector) was used to collect the Raman spectral data.
4,5-bis(pentylthio)phthalonitrile (2a). Compound 2a
was synthesized as reported in literature [11] with some
modifications. Briefly, 1-pentanethiol (30.45 mmol)
and 1 (2.0 g, 10.2 mmol) were dissolved in DMSO (15
mL) under argon. The mixture was stirred for 15 min
and ground anhydrous potassium carbonate (5.1 g, 36.9
mmol) was added portion-wise over 2 h with stirring. The
mixture was stirred under an argon atmosphere for 12 h.
Water (100 mL) was then added and the mixture stirred
for 30 min. The precipitate was filtered and washed with
water, followed by recrystallization from ethanol. Yield:
38%. IR (KBr): νmax, cm-1 3075, 2949, 2930, 2859, 2231
(C≡N), 1618, 1563, 1456, 1433, 1350, 1264, 1225, 1112,
929, 900, 869, 731, 682, 605, 527. 1H NMR (400 MHz;
CDCl3; Me4Si): δ, ppm 7.41 (2H, s, Ar-H), 3.01 (4H, t,
S-CH2), 1.76 (4H, m, -CH2), 1.49 (4H, m, -CH2), 1.39
(4H, m, -CH2), 0.93 (6H, t, -CH3).
4,5-bis(decylthio)phthalonitrile (2b). Compound 2b
was synthesized as described above for 2a, using
1-decanethiol (30.5 mmol), DMSO (15 mL) under argon
and 1 (2.0 g, 10.2 mmol). Yield: 56%. IR (KBr): νmax
,
cm-1 3071, 2943, 2921, 2852, 2359, 2340, 2230 (C≡N),
1692, 1614, 1580, 1457, 1343, 1224, 1186, 1108, 1004,
1
929, 899, 870, 831, 761, 735, 668, 609, 528. H NMR
Electrochemical studies
(400 MHz; CDCl3; Me4Si): δ, ppm 7.41 (2H, s, Ar-H),
3.01 (4H, t, S-CH2), 1.75 (4H, m, -CH2), 1.49 (4H, m,
-CH2), 1.28 (24H, m, -CH2), 0.89 (6H, t, -CH3).
4,5-bis(benzylthio)phthalonitrile (2c). Compound 2c
was synthesized as described above for 2a, using ben-
zyl mercaptan (30.5 mmol), DMSO (15 mL) under argon
Cyclic (CV) and differential pulse (DPV) voltammetry
data was obtained using a Bio-Analytical Systems (BAS)
B/W 100 Electrochemical Workstation. Differential pulse
voltammetric analysis was carried out at a pulse ampli-
tude of 50 mV, sample width of 17 msec, pulse width
of 50 msec, pulse period of 200 msec and a scan rate of
20 mV/s. A typical three-electrode system with a silver/
silver chloride (Ag|AgCl) pseudo-reference, platinum
auxiliary and glassy carbon (GCE) working electrode
was used. The potential response of the Ag|AgCl pseudo-
reference electrode was less than the Ag|AgCl (3M KCl)
by 0.015 0.003 V. The GCE was cleaned by polishing
with 0.5 µm alumina on a Beuhler felt pad before use.
DCM containing 0.1 M TBABF4 as a supporting electro-
lyte was used for the electrochemical experiments. The
concentration of the various MnPcs in solution was in the
millimolar (mM) range.
and 1 (2.0 g, 10.2 mmol). Yield: 54%. IR (KBr): νmax
,
cm-1 3060, 3027, 2359, 2336, 2227 (C≡N), 1768, 1719,
1565, 1494, 1452, 1331, 1238, 1115, 1029, 933, 889,
1
873, 778, 712, 694, 633, 530, 483, 465. H NMR (400
MHz; CDCl3; Me4Si): δ, ppm 7.40 (2H, s, Ar-H), 7.31
(10H, m, Ar-H), 4.20 (4H, s, S-CH2).
4,5-bis(phenylthio)phthalonitrile (2d). Compound
2d was synthesized as described above for 2a, using thio-
phenol (30.5 mmol), DMSO (15 mL) under argon and
1 (2.0 g, 10.2 mmol). Yield: 75%. IR (KBr): νmax, cm-1
3075, 2959, 2921, 2850, 2229 (C≡N), 1768, 1714, 1653,
1564, 1473, 1453, 1437, 1384, 1349, 1331, 1259, 1218,
Copyright © 2010 World Scientific Publishing Company
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580
m. COateS et al.
1108, 1022, 924, 883, 799, 758, 693, 528, 489. 1H NMR
(400 MHz; CDCl3; Me4Si): δ, ppm 7.53 (10H, m, Ar-H),
7.01 (2H, s, Ar-H).
H, 3.25; N, 6.96; S, 15.92%. Found: C, 62.72; H, 3.49; N,
6.65; S, 15.08%. MS (MALDI-TOF): m/z 1432 (calcd.
for [M - Ac]+ 1433).
2,3,9,10,16,17,23,24-octakis(pentylthio)phthalo-
cyaninatomanganese(III)(Ac), (OAc)MnPcβ{S(CH2)4-
CH3}8 (3a). Compound 2a (0.9 g, 2.7 mmol),
manganese(II) acetate (0.12 g, 0.71 mmol) and anhy-
drous ethylene glycol (6 mL) were mixed and refluxed
for 4 h at 200 °C under argon. The mixture was allowed
to cool before excess methanol was added to precipitate
out the crude product, which was then purified using a
Bio-Bead S-X1 column eluting with CHCl3. Yield: 72%.
UV-vis (CHCl3): λmax, nm (log ε) 405 (4.2), 465 (4.2),
530 (4.1), 768 (4.5). IR (KBr): νmax, cm-1 2955, 2925,
2856, 2360, 2343, 1701, 1637, 1618, 1551, 1458, 1413,
1376, 1328, 1072, 959, 743, 669, 618, 486. Anal. calcd.
for C72H96N8S8Mn(Ac): C, 61.55; H, 6.91; N, 7.76; S,
17.76%. Found: C, 61.89; H, 7.05; N, 7.02; S, 17.35%.
MS (MALDI-TOF): m/z 1384 (calcd. for [M - Ac]+
1385).
2,3,9,10,16,17,23,24-octakis(decylthio)phthalo-
cyaninatomanganese(III)(Ac), (OAc)MnPcβ{(SCH2)9-
CH3}8 (3b). Complex 3b (MnODTPc) was synthesized
as described above for 3a using compound 2b (1.0 g,
2.1 mmol), manganese(II) acetate (0.10 g, 0.55 mmol)
and anhydrous ethylene glycol (6 mL). Yield: 32%.
UV-vis (CHCl3): λmax, nm (log ε) 405 (4.2), 465 (4.3),
530 (4.2), 769 (4.6). IR (KBr): νmax, cm-1 2955, 2924,
2853, 2360, 2342, 1701, 1654, 1592, 1458, 1414, 1377,
1328, 1073, 960, 782, 743, 669, 597, 509. Anal. calcd.
for C112H176N8S8Mn(Ac) (CHCl3): C, 65.01; H, 8.54; N,
5.28; S, 12.07%. Found: C, 64.61; H, 8.60; N, 4.59; S,
12.63%. MS (MALDI-TOF): m/z 1945 (calcd. for [M -
Ac]+ 1946).
CONCLUSION
The octakis(pentylthio)-, (decylthio)-, (benzylthio)-
and (phenylthio)phthalocyaninato manganese(III) acetate
complexes (3a–d) showed solvent-dependent conversion
to the μ-oxo dimer, as well as a solvent-dependent shift
in the Q band. The different substituents did not greatly
affect the UV-vis spectra of the compounds, but did
appear to have an effect on their electrochemical proper-
ties. Three main redox processes for the complexes were
identified as MnIIIPc-2/MnIIPc-2 (II), MnIIPc-2/MnIIPc-3
(III) and MnIIIPc-1/MnIIIPc-2 (I) and confirmed using spec-
troelectrochemistry. Self-assembled monolayers (SAMs)
of the MnPcs were formed on gold, and showed good
surface coverage in all cases. All the MnPc-SAMs
except 3c showed good blocking characteristics for
gold oxidation, copper UPD and the redox chemistry
of Fe(NH4)2(SO4)2, and even some blocking for
K3[Fe(CN)6], with 3a and 3b being the most effective.
Raman, AFM and SEM also confirmed SAM forma-
tion and good surface coverage, although the latter two
did indicate that there was some aggregation of the Pcs.
The specific behavior of the SAM seemed again to be
dependent on the nature of the substituents. The success-
ful formation of MnPc-SAMs confirms the potential of
these surfaces for use in electrochemical sensors, and
the investigation of the use of these SAMs in sensors is
currently underway in our laboratories.
Acknowledgements
2,3,9,10,16,17,23,24-octakis(benzylthio)phthalo-
cyaninatomanganese(III)(Ac), (OAc)MnPcβ(SCH2 Ph)8
(3c). Complex 3c (MnOBTPc) was synthesized as
described above for 3a using compound 2c (1.3 g, 3.5
mmol), manganese(II) acetate (0.16 g, 0.92 mmol) and
anhydrous ethylene glycol (6 mL). Yield: 74%. UV-vis
(CHCl3): λmax, nm (log ε) 407 (3.9), 472 (3.9), 530 (3.9),
770 (4.0). IR (KBr): νmax, cm-1 2924, 2853, 2360, 2342,
1639, 1617, 1412, 1378, 1327, 1073, 958, 669, 618, 486.
Anal. calcd. for C88H64N8S8Mn(Ac) (CHCl3): C, 63.42;
H, 3.98; N, 6.50; S, 14.88%. Found: C, 64.78; H, 3.73; N,
6.49; S, 15.08%. MS (MALDI-TOF): m/z 1544 (calcd.
for [M - Ac]+ 1545).
The authors would like to thank Ms. S. D’Souza
and Dr. W. Chidawanyika for the AFM images, and
Mr. M. Randall and Ms. S. Pinchuck from the Rhodes Uni-
versity Electron Microscopy Unit for the SEM images.
This work was supported by the Department of
Science and Technology (DST) and National Research
Foundation (NRF) of South Africa through DST/NRF
South African Research Chairs Initiative for Professor of
Medicinal Chemistry and Nanotechnology and Rhodes
University and by DST/Mintek Nanotechnology Innova-
tion Centre (NIC). MC thanks NIC and Rhodes Univer-
sity Henderson for Scholarships.
2,3,9,10,16,17,23,24-octakis(phenylthio)phthalo-
cyaninatomanganese(III)(Ac), (OAc)MnPcβ(SPh)8 (3d).
Complex 3d (MnOPhTPc) was synthesized as described
above for 3a using compound 2d (1.0 g, 2.9 mmol),
manganese(II) acetate (0.13 g, 0.76 mmol) and anhydrous
ethylene glycol (6 mL). Yield: 55%. UV-vis (CHCl3):
λmax, nm (log ε) 462 (4.3), 530 (4.1), 694 (3.9), 773 (4.7).
IR (KBr): νmax, cm-1 2923, 2852, 2361, 2343, 1701, 1637,
1614, 1555, 1438, 1326, 1064, 955, 743, 669, 618, 486.
Anal. calcd. for C80H48N8S8Mn(Ac) (CHCl3): C, 61.87;
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