Tetra (4-propargyloxyphenoxy)phthalocyanines: Facile synthesis, fluorescence and thermal properties

Article abstract of DOI:10.1016/j.poly.2017.06.029

The facile method of synthesizing of tetra (4-propargyloxyphenoxy) phthalocyanines with the terminal alkynyl (C[tbnd]C) group is reported. The synthesized phthalocyanines are the unmetallated (H₂TPrOPhOPc) and the metallated complexes of cobalt (CoTPrOPhOPc) and manganese (Mn(OAc)TPrOPhOPc). The fluorescence properties of H₂TPrOPhOPc and Mn(OAc)TPrOPhOPc were investigated. The fluorescence lifetimes (τ_F) for the H₂TPrOPhOPc and Mn(OAc)TPrOPhOPc, evaluated using time correlated single photon counting (TCSPC) technique, were found to be 5.79?ns and 5.50?ns, respectively. The fluorescence quantum yields (Φ_F) were also calculated using a comparative method and were 0.12 for H₂TPrOPhOPc and 0.16 for Mn(OAc)TPrOPhOPc. The CoTPrOPhOPc complex did not show fluorescent properties and this was attributed to the quenching of the excited state by the half-filled metal d-orbitals which are lying below the highest occupied molecular orbitals (HOMO) of the phthalocyanine ring. The CoTPrOPhOPc and Mn(OAc)TPrOPhOPc exhibited excellent thermal stability, which was better than H₂TPrOPhOPc, due to the presence of the cobalt and manganese metal ions at the centre of the phthalocyanine ring. Density functional theory (DFT) calculations predicted the HOMO?LUMO (lowest unoccupied molecular orbitals) gap for H₂TPrOPhOPc, CoTPrOPhOPc and Mn(OAc)TPrOPhOPc to be 2.06?eV, 2.15?eV and 1.75?eV, respectively.

Full text of DOI:10.1016/j.poly.2017.06.029

Accepted Manuscript
Tetra (4-propargyloxyphenoxy) phthalocyanines: facile synthesis, fluorescence
and thermal properties
Daniel Mwanza, Samson Khene, Philani Mashazi
PII:
S0277-5387(17)30447-3
DOI:
http://dx.doi.org/10.1016/j.poly.2017.06.029
POLY 12710
Reference:
Polyhedron
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Received Date:
Revised Date:
Accepted Date:
28 March 2017
20 June 2017
21 June 2017
Please cite this article as: D. Mwanza, S. Khene, P. Mashazi, Tetra (4-propargyloxyphenoxy) phthalocyanines: facile
synthesis, fluorescence and thermal properties, Polyhedron (2017), doi: http://dx.doi.org/10.1016/j.poly.
2017.06.029
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Tetra (4-propargyloxyphenoxy) phthalocyanines: facile synthesis,
fluorescence and thermal properties
Daniel Mwanza, Samson Khene, Philani Mashazi*
Department of Chemistry, Rhodes University, PO Box 94, Grahamstown 6140, South Africa.
Abstract
The facile method of synthesizing of tetra (4-propargyloxy phenoxy) phthalocyanines with
≡C) group
the terminal alkynyl (C
is reported. The synthesized phthalocyanines are the
unmetallated (H2TPrOPhOPc) and the metallated complexes of cobalt (CoTPrOPhOPc) and
manganese (Mn(OAc)TPrOPhOPc). The fluorescence properties of H2TPrOPhOPc and
Mn(OAc)TPrOPhOPc were investigated. The fluorescence lifetimes (τF) for the
H2TPrOPhOPc and Mn(OAc)TPrOPhOPc, evaluated using time correlated single photon
counting (TCSPC) technique, were found to be 5.79 ns and 5.50 ns, respectively. The
fluorescence quantum yields (ΦF) were also calculated using a comparitive method and were
0.12 for H2TPrOPhOPc and 0.16 for Mn(OAc)TPrOPhOPc. The CoTPrOPhOPc complex did
not show fluorescent properties and this was attributed to the quenching of the excited state
by the half-filled metal d-orbitals which are lying below the highest occupied molecular
orbitals (HOMO) of the phthalocyanine ring. The CoTPrOPhOPc and Mn(OAc)TPrOPhOPc
exhibited excellent thermal stability, which was better than H2TPrOPhOPc, due to the
presence of the cobalt and manganese metal ions at the centre of the phthalocyanine ring.
Density functional theory (DFT) calculations predicted the HOMO – LUMO (lowest
unoccupied molecular orbitals) gap for H2TPrOPhOPc, CoTPrOPhOPc and
Mn(OAc)TPrOPhOPc to be 2.06 eV, 2.15 eV and 1.75 eV, respectively.
1

Keywords: Fluorescence, terminal alkynyl, propargyloxyphenoxy, cobalt phthalocyanine,
manganese phthalocyanine, theoretical DFT calculations.
*Corresponding author. Tel: + 27 46 6038846; Fax: +27 46 6225109.
E-mail: p.mashazi@ru.ac.za (P. Mashazi)
2

1
Introduction
Phthalocyanines (Pcs) are a class of coordinated complexes or organometallic complexes
composed of a di-anionic (Pc-2) macrocyclic ring. The di-anionic ring can be complexed
using suitable metal ions to form metallophthalocyanine complexes. Thus, phthalocyanines
exists in two forms, the metallophthalocyanines (MPcs) and the metal-free phthalocyanines
(H2Pcs) that show interesting physicochemical properties. Their interesting properties have
motivated their wide industrial applications such as building blocks in medicinal applications
as photosensitizers, electrocatalysts in chemical sensors, liquid crystals, nonlinear optical
materials and molecular devices [1-7]. The wide applications of phthalocyanine complexes
are universally dependent on the type of central metal ion introduced in the Pc ring cavity and
the type of the functional groups that can be introduced onto the peripheral and non-
peripheral positions of the Pc. The choice of the substituents on the Pc ring allows for
increased solubility for these complexes in various organic and sometimes aqueous solvents.
Amongst the different functional groups that have been studied, the alkynyl (C≡C) group is
of interest in our research due to its rigidity and linearity. The alkynyl functional groups
allows for high exciton and electron coupling between chromophore units [1]. However, a
few alkynyl-substituted Pcs have been synthesized mainly as building blocks in material
synthesis and for polymerization reactions [1,8-10]. The limited investigation of this
≡C)
functional groups is due to the difficulty of synthesizing terminal substituted alkynyl (C
phthalocyanines. Very few research groups have successfully managed to synthesized the Pcs
bearing the terminal alkynyl groups [8,9,11-14]. The majority of research on the alkynyl
substituted phthalocyanines are non-terminal groups or are quickly converted to the triazole
rings before the formation of phthalocyanines [1,15-17]. This work investigate the use of
propargylbromide to achieve the 4-(4-propargyloxy)phenoxy substituted phthalocyanines.
This method can achieve our desired phthalocyanines following a Williamson ether synthesis
3

procedure. Therefore, this work investigates the facile method for the synthesis of
phthalocyanines bearing terminal alkynyl (C≡C) functional groups. To the best of our
knowledge 4-propargyloxyphenoxy functional groups have never been reported as
substituents on the phthalocyanine ring. The synthesized phthalocyanines were characterized
using various spectroscopic techniques and studied for their thermal and fluorescence
properties.
2
Experimental
2.1 Materials
Deuterated dimethyl sulfoxide (DMSO-d6), deuterated chloroform (CDCl3), 4-
nitrophthalonitrile, cobalt (II) acetate, manganese (II) acetate, lithium metal (stored in
paraffin oil), propargylbromide and hydroquinone were purchased from Sigma Aldrich.
Absolute ethanol (EtOH) and methanol (MeOH) were purchased from SAARCHEM and
used as received. Potassium carbonate (K2CO3), dimethylsulfoxide (DMSO), tetrahydrofuran
(THF), acetone, acetic acid (AcOH), acetonitrile (ACN), dimethylformamide (DMF),
ethylacetate (EtOAc), toluene and 1-pentanol were purchased from Merck chemicals. The
distilled dry DMF was stored dry over alumina before use. Thin layer chromatography (TLC)
and column chromatography was carried out on silica gel (60 Å 70-230 mesh 63-200 µm)
which was purchased from Sigma-Aldrich.
2.2 Equipments
Perkin–Elmer Universal ATR Sampling accessory spectrum 100 FT-IR spectrometer was
used to collect Infra-red spectra for the synthesized compounds and complexes. Proton
4

Nuclear Magnetic Resonance (1H NMR) data was obtained using a Bruker 400 MHz NMR
spectrometer in DMSO-d6 or CDCl3. The NMR data was analysed using MestreNOVA
software for integration and peak picking. Elemental analysis for Carbon, Hydrogen and
Nitrogen (C, H and N) were measured using a Vario-Elementar Microcube ELIII.
A
Shimadzu UV-2550 spectrophotometer and a Chirascan Plus spectropolarimeter equipped
with a permanent magnet with a magnetic field 1 Tesla were used to obtain the electronic
absorption and magnetic circular dichroism (MCD) spectra, respectively. Thermogravimetric
analysis (TGA) was carried out on a Perkin Elmer TGA analyzer. The samples were heated at
0
0
a rate of 10 C/min from 20 to 600 C. The inert atmosphere was created by having a 120
cm3.min-1 flow of nitrogen gas. A time correlated single photon counting (TCSPC) technique
was used to measure fluorescence lifetimes of the studied complexes. The phthalocyanines in
THF were excited at 670 nm with a diode laser (LDH-P 670, 20MHz repetition rate, 44 ps
pulse width, PicoQuant GmbH). Pettier cooled photomultiplier (PMA-C-192-M, PicoQuant
GmbH) was used as the detector. The fluorescence quantum (ΦF) yields for H2TPrOPhOPc
(5) and Mn(OAc)TPrOPhOPc (7) were calculated using a comparative method reported in
literature [18] and using the equation (1) below:
ꢐ
ꢁ
.ꢌ .ꢏ
ꢆꢇꢈꢉꢊꢋ ꢆꢍꢎ
ꢆꢇꢈꢉꢊꢋ
ꢀꢁ =ꢂꢀꢁ(ꢃꢄꢅ)
(1)
ꢐ
ꢁ
.ꢌ
.ꢏ
ꢆꢍꢎ ꢆꢇꢈꢉꢊꢋ
ꢆꢍꢎ
where Fsample and Fstd are the areas under the fluorescence emission spectra of the sample, that
is H2TPrOPHOPc (5) or Mn(OAc)TPrOPhOPc (7), and standard (ZnPc in THF),
respectively. The absorbance of the samples and standard at excitation wavelengths are
respectively Asample and Astd. The refractive indices for the solvent (THF) used for the sample
and standard are also nsample and nstd, respectively. The ΦF(std) is the fluorescence quantum
yield of unsubstituted ZnPc in THF is 0.25 [19]. The absorbance of between 0.04 – 0.05 at
the excitation wavelength was employed.
5

2.3 Density functional theory calculations
Density functional theory (DFT) and time dependent density functional theory (TDDFT)
calculations were performed on Gaussian 03 package [20] running on an Intel/linux cluster.
The modelled complexes were optimized at level of B3LYP geometry optimization with 6-
31G (d) and SSD basis sets. Gausview 4.1 was used for all visualization of molecular orbitals
(MOs) and properties [21]. The B3LYP exchange-correlation density functional employs
Becke’s method for using Lee-Yang Parr’s gradient-correlation, which includes a hybrid of
semi-empirical Hartfee-Fork and DFT exchange.
2.4 Synthesis of unmetallated and metallated phthalocyanines
2.4.1 Synthesis of 4-(4-hydroxyphenoxy)phthalonitrile (3)
A solution of hydroquinone (1, 0.55 g, 5.00 mmol), 4-nitrophthalonitrile (2, 0.79 g, 4.54
mmol) and anhydrous K2CO3 (1.50 g) in 15 mL dry DMSO was stirred at room temperature
for 60 hrs. The reaction was followed using TLC and upon confirmation of the disappearance
of 4-nitrophthalonitrile, the reaction was quenched with a mixture of water and acetic acid in
the ratio 100:1. The crude solid (the product) was filtered, washed with plenty of cold water.
The solids were dissolved in ethylacetate and the column chromatography using a solvent
mixture of ethylacetate and hexane (8:1) as an eluent. The product collected as a second
fraction was dried on air and further at 70 °C to yield 0.80 g (75%) of compound (3) as white
solid crystals. FT-IR (ν, cm-1): 3205 (O-H); 3045 (Ar-H); 2232 (C≡N); 1656 (C=C); 1244
6

(Ar-O-Ar), 1192 (Ar-O); Anal. Calcd. for C14H8N2O2: C, 71.18; H, 3.41; N, 11.86%; Found:
1
C, 70.89; H, 3.65; N, 12.01%. H NMR (400 MHz, d6-DMSO) δ [ppm]: 6.84 – 6.86 (d, 2H,
Ar-H); 7.00 – 7.02 (d, 2H, Ar-H), 7.27 – 7.30 (dd, 1H, Ar-H), 7.66 - 7.76 (d, 1H, Ar-H), 8.04
- 8.06 (d, 1H, Ar-H), 9.60 (s, 1H, O-H).
2.4.2 Synthesis of 4-(4-propargyloxyphenoxy)phthalonitrile (4)
Propargylbromide 80% in toluene (0.45 g, 3.78 mmol) was slowly added to 4-(4-
hydroxyphenoxy) phthalonitrile (0.60 g, 2.54 mmol) dissolved in 15 mL dry DMF under
stirring at room temperature. After 30 min of stirring, finely ground anhydrous K2CO3 (0.50
g, 7.00 mmol) was slowly added to the reaction mixture over a period of 5 hrs. The reaction
was followed using TLC and upon the disappearance of 4-(4-hydroxyphenoxy) phthalonitrile
(3) and the formation of the product, the reaction was quenched with 60 mL of ice water. The
precipitate was filtered, washed with ice cold water followed by methanol (to remove excess
propargylbromide) and dried in the desiccator over P2O5. The crude product was then
recrystallized in methanol to yield 0.52 g (75%) of product (4). FT-IR (ν, cm-1): 3281 (≡C-
H); 3072 (Aromatic C-H); 2877 (Aliphatic C-H); 2231 (C≡N); 2123 (C≡C); 1238 (Ar-O-Ar);
1189 (Ar-O-C). Anal. Calcd. for C17H10N2O2: C, 74.45, H, 3.67; N, 10.21%. Found: C,
1
74.76; H, 3.51; N, 10.09%. H NMR (400MHz, d6-DMSO, δ (ppm)): 3.61 (s, 1H, C≡C-H);
4.82 (s, 2H, CH2); 7.08 – 7.11 (d, 2H, Ar-H); 7.16 – 7.19 (m, 2H, Ar-H); 7.30 – 7.32 (dd,1H,
Ar-H); 7.72 – 7.73 (d, 1H, Ar-H); 8.06 – 8.09 (d, 1H, Ar-H).
7

2.4.3 Synthesis of metal-free tetra (4-propagyloxyphenoxy) phthalocyanine
(H2TPrOPhOPc) (5)
Compound (4, 0.30 g, 1.09 mmol) was added to 5 mL dry 1-pentanol and refluxed for 15 min
until a homogeneous mixture was obtained. Lithium metal (0.25 g) was then added under
reflux, resulting in a green colored reaction. The reaction mixture was then refluxed for
further 3 hrs, after which, the reaction mixture was cooled to room temperature. A mixture of
methanol/acetic acid was added to afford a blue-green precipitate which was filtered. The
precipitate was isolated and treated for 24 hrs with methanol using soxhlet extraction
apparatus to remove the unreacted 4-(4-propagyloxyphenoxy) phthalonitrile (4) and 1-
pentanol. The purity of the metal free phthalocyanine was verified by thin layer
chromatography (TLC) which showed a single spot. The column chromatography (silica gel),
with chloroform as the eluent, was used for further purification of H2TPrOPhOPc (5) . Yield:
0.47 g (39%). FT-IR (ν, cm-1): 3643 (N-H); 3291 (≡C-H); 3046 (Aromatic C-H,); 2918
1
≡C); 1210 (Ar
(aliphatic CH); 2062 (C
-O-Ar), 1095, 1009 (Ar-O-C). H NMR (600MHz,
≡C
CDCl3, δ (ppm)): 2.62 (s, 4H, C -H); 4.73 (s, 8H, CH2); 7.03 (bs, 16H, Ar-H), 7.19 (bs,
12H, Pc-H). Anal. Calcd. for C68H42N8O8: C 74.31, H 3.85, N 10.19; Found: C 74.25, H 3.67,
N 10.32. UV-Vis (THF) λmax, nm (log ɛ): 343 (4.74), 382 (4.42), 608 (4.40), 644 (4.57), 670
(4.91), 708 (4.95).
2.4.4 Synthesis of cobalt (II) tetra (4-propagyloxyphenoxy) phthalocyanine
(CoTPrOPhOPc) (6)
Purified complex 5 (20 mg, 0.018 mmol) and cobalt (II) acetate (4.5 mg, 0.025 mmol) was
added to 3 mL of dry DMF. The reaction mixture was stirred under reflux. The reaction was
followed using UV-Vis and after 3 hours, the split Q-band of H2TPrOPhOPc collapsed to
form a single Q-band. The reaction was allowed to react for further 2 hrs under reflux. The
8

reaction mixture was then cooled to room temperature and methanol/water (1:1) solution was
added to afford a blue precipitate. The precipitate was isolated by filtration and washed three
times with water (20 mL) before drying. The crude product was then purified by column
-1
≡C
chromatography using THF as eluent. Yield: 14 mg (67%). FT-IR (ν, cm ): 3288 ( -H);
≡C); 1262, 1191 (Ar
3062 (Aromatic C-H); 2925 (Aliphatic CH); 2160 (C
-O-Ar); 1118, 1090,
1056, 1026 (Ar-O-C). Anal. Calcd. for 5H2O.C68H40CoN8O8: C, 65.54; H, 4.04; N, 8.99.
Found C, 65.58; H, 3.97; N, 8.76%. UV-Vis (THF) λmax nm (log ɛ): 325 (4.67), 608 (4.23),
667 (4.78).
2.4.5 Synthesis of manganese (III) tetra (4-propagyloxyphenoxy) phthalocyanine
(Mn(OAc)TPrOPhOPc) (7)
Complex 7 was synthesized using a similar procedure as for CoTPrOPhOPc complex (6),
using manganese (II) acetate instead of cobalt (II) acetate. The purified complex 5 (20 mg,
0.018 mmol) and manganese (II) acetate (3.5 mg, 0.025 mmol) was added to 3 mL of dry
-1
≡C
DMF. Yield (15.7 mg) = 72%. FT-IR (ν, cm ): 3287 ( -H); 3047 (Ar-H); 2918, 2849 (CH,
≡C); 1212, 1190 (Ar
aliphatic); 2119 (C
-O-Ar); 1116, 1072, 1049, 1023 (Ar-O-C). Anal.
Calcd for 4H2O.C68H40Mn(OOCCH3)N8O8: C, 65.52; H, 4.01; N, 8.73. Found: C, 65.56; H,
3.86; N, 8.54%. UV-Vis (THF): λmax, nm (log ɛ) 405 (4.81), 505 (4.40), 655 (4.51), 725
(4.86).
9

3
Results and Discussion
3.1 Synthesis of phthalocyanines (5-7)
The synthesis of phthalocyanines (5 – 7) bearing four 4-propargyloxyphenoxy substituents
was achieved following the procedure in Scheme 1. The synthesis of terminal alkynyl
substituted phthalocyanines involved nucleophilic aromatic substitution between 4-
nitrophthalonitrile and hydroquinone. Potassium carbonate (K2CO3) was a base in
nucleophilic aromatic displacement of nitro group and thus producing the phenolate [22] at
the carbon in position 4. The electron deficient carbon can then undergo nucleophilic attack
from the alcohol functional group of hydroquinone thus producing an ether compound. The
experimental conditions were optimized to favor higher percentage yields of mono
substituted phthalonitrile by using excess hydroquinone concentrations to 4-
nitrophthalonitrile at room temperature as has been reported [23]. According to Zhao et al.
[23], the use of excess hydroquinone concentrations ration to 4-nitrophthalonitrile yields 76%
of the mono-substituted 4-(4-hydroxyphenoxy) phthalonitrile (3). In this work, similar yields
75% were observed from using excess hydroquinone. The pure compound (3) was then
reacted with propargybromide via Williamson ether synthesis to yield the 4-(4-
propargyoxyphenoxy)phthalonitrile (4). The 4-(4-propargyloxyphenoxy)phthalonitrile (4)
was used to form phthalocyanines via cyclotetramerization in the presence of lithium-1-
pentanolate to yield an unmetallated or metal-free phthalocyanine (5). The metal-free
phthalocyanine was then converted into a metallated phthalocyanine complexes using cobalt
(II) acetate and manganese (II) acetate to yield complexes (6) and (7), respectively.
10

(2)
(i)
(ii)
(4)
(3)
(1)
(iii)
(iv)
(5)
(6)M=Co
(7)M=Mn
Scheme 1: Synthesis procedure for the formation of MTPrOPhOPc complexes, with M = H2
(5), Co(II) (6) and Mn(III)OAc (7). (i) and (ii) DMSO, K2CO3, room temperature, 60 hrs; (iii)
Li metal, 1-pentanol, reflux, 3 hours and (iv) MX2 (M = Co or Mn), X (Cl or OAc), dry
DMF, 70°C, 3 hours.
3.2 Characterization of synthesized phthalocyanines (5-7)
3.2.1 FT-IR characterization and elemental analysis
The synthesis and characterization of 4-(4-hydroxyphenoxy)phthalonitrile (3) and 4-(4-
propagyloxyphenoxy)phthalonitrile (4) was confirmed using FT-IR as shown and discussed
in Fig. S1 in the electronic support information (ESI). After successful synthesis of (4), the
11

unmetallated phthalocyanines (H2TPrOPhOPc, 5) was synthesized. Figure 1 shows the FT-
IR spectra of (a) (i) 4-(4-propargyloxyphenoxy)phthalonitrile (4) and (ii) H2TPrOPhOPc (5)
and (b) (i) H2TPrOPhOPc (5), (ii) CoTPrOPhOPc (6) and (iii) Mn(OAc)TPrOPhOPc (7). The
ether (C-O-C) stretches were prominent for both compound (4) and (5) in the range of 1000 -
1200 cm-1. The above results confirmed that the functional groups were retained during the
cyclotetramerization reactions. The most distinctive change in spectra in Fig. 1(a) was the
-1
≡N) stretch at 2231
disappearance of the nitrile (C
cm and the presence of the N-H stretch at
3643 cm-1 confirming the formation of H2TPrOPhOPc (5). The elemental analysis also
confirmed the successful synthesis of (5) with high purity. Figure 1(b) shows the FT-IR
spectra of (i) H2TPrOPhOPc (5), (ii) CoTPrOPhOPc (6) and (iii) Mn(OAc)TPrOPhOPc (7).
The formation of the metal complexes (6) and (7) from the unmetallated phthalocyanine (5)
was confirmed by the disappearance of N-H stretch at 3643 cm-1. The FT-IR absorption
wavenumbers were shifted by either 4 or 40 cm-1 when H2TPrOPhOPc (5) was converted to
CoTPrOPhOPc (6) or Mn(OAc)TPrOPhOPc (7). The C, H and N elemental analysis of (6)
and (7) confirmed their successful synthesis and the data was < 0.4% and within acceptable
range. The elemental analysis showed that complexes (6) and (7) existed as Pc hydrates with
five and four water molecules, respectively. This was not surprising as phthalocyanines are
heterocyclic molecules known to form hydrated complexes with water molecules [24].
Kudrevich and van Lier [25] showed that the number of water molecules also varies and there
is no correlation between the structure and the observed number of water.
12

(a)
(i)
(ii)
3800 3450 3100 2750 2400 2050 1700 1350 1000
Wavenumber (cm-1)
650
(b)
(i)
(ii)
(iii)
3800 3450 3100 2750 2400 2050 1700 1350 1000 650
Wavenumber (cm-1)
Figure 1: FT-IR spectra of (a) (i) 4-(4-propargyloxyphenoxy)phthalonitrile (4) and (ii)
H2TPrOPhOPc (5) and (b) (i) H2TPrOPhOPc (5), (ii) CoTPrOPhOPc (6) and (iii)
Mn(OAc)TPrOPhOPc (7).
The proton NMR (1H NMR) was used for the characterization of 4-(4-hydroxyphenoxy)
phthalonitrile (3), 4-(4-propargyloxyphenoxy)phthalonitrile (4) and the unmetallated
1
phthalocyanine (H2TPrOPhOPc, 5). Figure 2 shows the H NMR of the synthesized (a) (3),
(b) (4) both measured in d6-DMSO and H2TPrOPhOPc (5) measured in CDCl3. For
1
compound (3), the H NMR exhibited a clean spectrum with the protons integrating and
13

confirming the proposed structure in Scheme 1. The presence of the O-H at 9.60 ppm for
compound (3) and integrating for one proton confirmed that the ether bond formed with one
hydroxyl (OH) group for hydroquinone (1). Additional protons for 4-(4-
hydroxyphenoxy)phthalonitrile (3) were observed in the aromatic region, that is between 6.50
1
ppm and 8.50 ppm. Figure 2(b) shows the H NMR of compound (4). The disappearance of
the OH peak at 9.60 ppm was observed. The presence of the aliphatic protons at 4.83 ppm
≡C
due to CH2 and the alkynyl proton ( -H) at 3.61 ppm confirmed the successful
propargylation of compound (3) to form compound (4). The protons integrated correctly
confirming the purity of the synthesized compound (4). After the successful synthesis of the
4-(4-propargyloxyphenoxy)phthalonitrile (4), the synthesis of metal-free or unmetallated
1
phthalocyanine (H2TPrOPhOPc, 5) was conducted. The H NMR of the metal-free
H2TPrOPhOPc (5) in Fig. 2(c) showed four peaks at 7.19 ppm (broad singlet, bs), 7.03 ppm
(broad singlet, bs), 4.73 ppm (singlet, s) and 2.62 ppm (singlet, s). Upon integration, there
were 12 protons at 7.19 ppm corresponding to the phthalocyanine protons (Pc-H), 16 protons
at 7.03 ppm corresponding to the aromatic protons (Ar-H) from substituents, 8 protons for the
1
≡CH) at 2.62 ppm
aliphatic CH2 at 4.73 ppm and 4 protons for alkynyl (
. The H NMR
spectrum was clean and confirmed the synthesis of H2TPrOPhOPc (5). The NH2 protons were
not observed due to their labile nature and exchange with deuterated solvent. The protons
were slightly shifted due to increased aromaticity from the phthalocyanine ring. The broad
singlets in the aromatic region are typical of the phthalocyanines [26] and due to
phthalocyanine protons (Pc-H) and substituents (Ar-H). These were observed in the proton
NMR of H2TPrOPhOPc and were further attributed to the fact that H2TPrOPhOPc exist as
four constitutional isomers which were not separated. The synthesis of the metallated tetra 4-
(propargyloxy)phenoxy phthalocyanines (MTPrOPhOPc) complexes (6) and (7) followed.
1
The H NMR for CoTPrOPhOPc (6) and MnTPrOPhOPc (7) were not measured due to
14

paramagnetic nature of the metal ions from the two complexes. The H2TPrOPhOPc (5) and
the two complexes (6) and (7) were characterized further using elemental analysis, UV-Vis to
further confirm their successful synthesis.
15

(a)
5
4
3
2'
6
1'
1
2
6
2
4
1
5
3
(b)
5
4
3
2'
1'
2
1
6
6
1
7
2
7
4
5
3
7
1'
2'
O
1
O
6
3
O
(c)
5
2
O
4
N
H
N
N
N
H
N
N
N
N
O
O
O
O
1,2
6
7
3-5
Figure 2: Proton NMR (1H NMR) of (a) 4-(4-hydroxylphenoxy) phthalonitrile (3), (b) 4-(4-
propargyloxyphenoxy) phthalonitrile (4), both measured in d6-DMSO and (c) H2TPrOPhOPc
(5) in CDCl3.
16

3.2.2 UV-Vis and MCD Characterization
Figure 3 shows the electronic absorption of the unmetallated phthalocyanine
(H2TPrOPhOPc, 5) and the metallated complexes (CoTPrOPhOPc, 6) and
(Mn(OAc)TPrOPhOPc, 7) dissolved in THF. The unmetallated phthalocyanine,
H2TPrOPhOPc (5) exhibited a split Q-band with absorption maxima at 670 nm and 708 nm.
The observed split Q-bands are due to electronic transitions from a1u of the highest occupied
molecular orbitals (HOMO) to the doubly degenerate eg orbital of the lowest unoccupied
molecular orbitals (LUMO) [27, 28]. The UV-Vis of compound (5) also showed the B bands
at 382 nm and 343 nm due to transitions from of the π (a2u and b2u) HOMO orbitals to the π*
(eg) LUMO orbitals. The UV-Vis spectra of CoTPrOPhOPc (6) and Mn(OAc)TPrOPhOPc
(7) showed a collapse of the split Q-bands of compound (5) to form single Q-band for
CoTPrOPhOPc (6) at 667 nm and for Mn(OAc)TPrOPhOPc (7) at 725 nm. The observed Q-
band wavelengths are in the same region when compared with the straight chain alkynyl
terminated cobalt phthalocyanine which had a Q-band at 671 nm as reported by Dincer et al.
[8a]. The slight blue or hypsochromic shift to 667 nm of the Q-band for CoTPrOPhOPc (6)
was observed when compared to the work by Dincer et al. [8a] on the aliphatic chain with the
alkynyl terminal functional group. The Mn(OAc)TPrOPhOPc (7) also showed a collapse of
split Q-band of H2TPrOPhOPc (5) to form a single Q-band at 725 nm. The Q-band for (7)
was red shifted upon metalation. The significant red shifting of the Q-band is attributed to
Mn(III) oxidation state due to the acetate axial ligand that was observed in the elemental
analysis. The Mn(II) complexes are weak complexes and this is due to the lack of ligand field
stabilization. Mn(II) complexes behaves more like Group 2 metal ion complexes as opposed
to other divalent d-block metal complexes. Mn(II) has preference for O-donors ligands and
compared with either Mg or Ca. It does have a greater tendency to bind to N-donors. At 107/s
ligand exchange rate for water [29], the Mn(II) has high rate of ligand exchange and is thus
17

easily mobilized. The unmetallated phthalocyanine ligand exist as Pc-2 anion and capable of
coordinating M2+ metal ions. The Mn(II) is inserted within the ring central cavity and
coordinate to the N-atoms. Due to the Mn preference for O-donor ligands, the acetate ligand
bind axially to the metal ion. The formation of Mn(III) results due to the stabilization of the
complex. The acetate ligand is a third ligand (axial ligand) on the manganese atom for
Mn(OAc)TPrOPhOPc (7) and thus increasing the oxidation state to Mn(III). The UV-Vis
spectroscopy confirmed the +3 oxidation state with the red shifted Q-band when compared to
H2TPrOPhOPc (5) and CoTPrOPhOPc (6). The elemental analysis also confirmed that the
presence of the acetate ligand and water molecules. The elemental data confirmed the
structure of the Mn(OAc)TPrOPhOPc (7). The Mn(OAc)TPrOPhOPc complex (7) exhibited
an additional band at 505 nm in THF. This absorption band is either a ligand-to-metal
(LMCT) or metal-to-ligand (MLCT) charge transfer band [30,31].
1.20
(5)
1.00
0.80
(7)
(6)
0.60
0.40
0.20
0.00
300
400
500
600
700
800
Wavelength (nm)
Figure 3: Electronic absorption spectra of H2TPrOPhOPc (5), CoTPrOPhOPc (6) and
Mn(OAc)TPrOPhOPc (7) in THF. Concentration ~1 x 10-5 M.
Figure 4 shows the UV-Vis absorption and magnetic circular dichroism (MCD) spectra of
the synthesized (a) H2TPrOPhOPc (5), (b) CoTPrOPhOPc (6) and (c) MnTPrOPhOPc (7) in
18

THF. Magnetic circular dichroism (MCD) spectroscopy characterization showed that the
main electronic Q(0,0) and B(0,0) band transitions for unmatellated phthalocyanine (5) and
the metallated complexes (6) and (7). The H2TPrOPhOPc (5) showed oppositely-signed
Faraday Ɓ0 terms and an intense Faraday A1 term was observed for CoTPrOPhOPc (6) and
Mn(OAc)TPrOPhOPc (7) [32-35]. The assignment of the various bands on the MCD spectra
has been reported [33-35] and are arranged in descending energy and determined to be C (ca.
210 nm), L (ca. 245 nm), N (ca. 275 nm), B2 (ca. 330 nm), B1 (ca. 370 nm) and Q (ca. 670
nm) bands. The observed spectrum of (5) is typical of the unmetallated phthalocyanine with
no three-fold or higher symmetry [36, 37]. The presence of the Faraday Ɓ0 term for the Q-
band suggests that the eg orbitals of the HOMO are non-degenerate, whilst the Faraday A1
term suggest that the eg orbital of the HOMO are degenerate. The red or bathochromic shift
phenomenon observed for Mn(OAc)TPrOPhOPc (7) is typical of manganese phthalocyanine
complexes with higher oxidation state of +3.
3.2.3 Density functional theoretical calculations
Figure 4 further shows the theoretical bands obtained using TDDFT calculations for the
H2TPrOPhOPc (5) and metal complexes (6) and (7). The theoretical bands were plot on a
secondary axis with diamond tips to elucidate the Q, B1 and B2 bands. The UV-Vis
absorption spectra are similar to those in Fig. 3 and discussed above. The TDDFT results in
Fig.
4
shown
as
diamond
tips
are
summarized
in
Table
S1.
19

Figure 4: UV-Visible absorption and MCD spectra of (a) H2TPrOPhOPc (5), (b) CoTPrOPhOPc (6) and (c) Mn(OAc)TPrOPhOPc (7) in THF.
The calculated bands using TDDFT for the complexes (5) – (7) are plotted on a secondary axis with diamond tips to elucidate the Q, B1 and B2
bands.
20

The TDDFT results for Mn(OAc)TPrOPhOPc (7) further exhibited an additional absorption
bands at 591 nm which is assigned to metal-ligand (MLCT) and 592 nm assigned to ligand-to-
metal (LMCT) charge transfer bands. The LMCT or MLCT are electronic transitions for
Mn(OAc)TPrOPhOPc (7) due to manganese d-orbitals lying between the HOMO-LUMO gap of
the Pc ring, thus allowing for the charge transfer transitions to occur. Since the mixed electron
transitions, the LMCT is much lower in energy than the MLCT. Therefore, the TDDFT
absorption at 592 nm is assigned LMCT and the absorption at 591 nm is assigned MLCT. Due to
the close proximity of these transitions (LMCT and MLCT), the observed band in the UV-Vis
spectrum for Mn(OAc)TPrOPhOPc (7) at 505 nm can either be LMCT or MLCT or both. This
phenomenon has been reported for metal complexes [38].
Figure 5 further shows the isosurfaces for the simulations of a, -a, s, and –s for H2TPrOPhOPc
(5), CoTPrOPhOPc (6) and Mn(OAc)TPrOPhOPc (7) on the y-axis. Michl [39] describes a and –
a as the molecular orbitals (MOs) that have nodal planes which coincide with the yz-plane and
-2
are derived from the HOMO and LUMO of a C16H16 parent perimeter, respectively [36,40].
Whereas the s and –s MOs are described as having the antinodes on the yz-plane. The large
separation between the a and s MOs is due to the incorporation of the aza-nitrogen atoms that
have a higher stabilising effect on the s molecular orbitals. The a, -a, s and –s isosurfaces are
shown in Fig. 5 next to their respective MO energy. The H2TPrOPhOPc (5) exhibited a doubly
degenerate eg with different and distinct isosurfaces corresponding to LUMO (-s) and LUMO+1
(-a). In the UV-Vis spectrum of H2TPrOPhOPc (5), the doubly degenerate eg resulted in the split
Q-bands from the HOMO to LUMO as discussed above.
21

Figure 5: Relative positions of the HOMOs and LUMOs of H2TPrOPhOPc (5), CoTPrOPhOPc
(6) and MnTPrOPhOPc (7). The a, -a, s and –s isosurfaces are also shown.
The CoTPrOPhOPc (6) and Mn(OAc)TPrOPhOPc (7) exhibited a degenerate eg from a collapse
of the doubly degenerate eg of H2TPrOPhOPc (5). The collapse of the doubly degenerate eg to
degenerate eg was a confirmation of the UV-Vis and MCD spectra which showed a single Q-
band and an intense Faraday A1 term for complexes (6) and (7). The isosurfaces corresponding to
–s (LUMO) and –a (LUMO +1) for CoTPrOPhOPc (6) were different but had the same MO
energy and hence the degenerate eg. For Mn(OAc)TPrOPhOPc (7), the isosurfaces for the
degenerate eg were observed at the same MO energy as that of CoTPrOPhOPc (6). The one
isosurface for Mn(OAc)TPrOPhOPc (7) was observed at much lower MO energy value and the
22

electron distribution was abserved around the Mn metal ion centre. This was a source of the
MLCT or LMCT bands on the Mn(OAc)TPrOPhOPc (7).
Using DFT calculations, in Fig. 5, the HOMO-LUMO gap for H2TPrOPhOPc (5) was
determined to be 2.06 eV and 2.15 eV for CoTPrOPhOPc (6). The HOMO-LUMO gaps for the
H2TPrOPhOPc (5) and CoTPrOPhOPc (6) were found to be very close to each other. The
HOMO-LUMO gap for Mn(OAc)TPrOPhOPc (7) was 1.75 eV and was observed to be
significantly lower than that of H2TPrOPhOPc (5) and CoTPrOPhOPc (6). The HOMO-LUMO
gap can be reduced by either destabilizing the HOMO or stabilizing the LUMO by the central
metal. The smallest band gap was observed for Mn(OAc)TPrOPhOPc (7) and was attributed to
the fact the dx2-y2 MOs of manganese lies just directly beneath the LUMO of the Pc ligand. This
phenomenon is not observed in CoTPrOPhOPc (6) as the 3d MOs of cobalt lies lower than the
HOMO of the Pc ring. This is the very reason why the electronic spectrum of the
Mn(OAc)TPrOPhOPc (7) is red shifted in both the experimental UV-Vis spectrum and the
TDDFT results in Fig. 3 and Fig. 4. The experimental and theoretical bands are summarized in
Table S1. The observed HOMO-LUMO gaps decreases following this trend CoTPrOPhOPc (6)
> H2TPrOPhOPc (5) > Mn(OAc)TPrOPhOPc (7). Figure 5 further shows the isosurface
mapping of the simulated MOs of H2TPrOPhOPc (5), CoTPrOPhOPc (6) and
Mn(OAc)TPrOPhOPc (7). The isosurfaces show that the HOMOs of the three complexes are
almost the same and they are localized on the four indole rings of the Pc ligand. The localisation
is of π-type and it is due to carbon-carbon atom. The LUMO of (5) is purely of π-type orbitals
comprising of all the nitrogen atoms at the centre of the Pc. The LUMO of CoTPrOPhOPc (6)
shows a little of metal contribution although it is also mainly π-type orbital. The LUMO of
Mn(OAc)TPrOPhOPc (7) is distinctively different from that of H2TPrOPhOPc (5) and
23

CoTPrOPhOPc (6) as observed from the isosurface and arise from the 3d orbital of manganese
central metal ion. The HOMOs of phthalocyanines are contributed by the Pc ring, hence the
observed similarities. However, the observed differences between the LUMOs of the complexes
is due to the closeness of the 3d orbitals of the manganese to the LUMO of the Pc ring. This
results in the HOMO of Mn(OAc)TPrOPhOPc (7) to have a Mn-3d π-system.
3.3 Thermogravimetric analysis of the synthesized phthalocyanines
Since the metallophthalocyanine complexes are chemically and thermally stable organometallic
compounds, their thermal stability has been utilized in the synthesis of carbon nanotubes [41],
especially the unsubstituted CoPc and FePc. The thermal stability of these newly synthesized
phthalocyanines was investigated using the thermogravimetric analysis (TGA). Figure 6 shows
the % weight loss (TGA pertans) and their derivatives (DTG) for (a) H2TPrOPhOPc (5), (b)
CoTPrOPhOPc (6) and (c) Mn(OAc)TPrOPhOPc (7) for the temperature ranging from 20 - 600
°C.
0.05
(a)
100
-0.05
85
-0.15
70
-0.25
55
-0.35
40
-0.45
0
100 200 300 400 500 600
Temperature (°C)
24

0.05
(b)
100
90
80
70
60
0.00
-0.05
-0.10
-0.15
-0.20
0
100 200 300 400 500 600
Temperature (°C)
105
0.05
(c)
0.00
95
85
75
65
-0.05
-0.10
-0.15
-0.20
0
100 200 300 400 500 600
Temperature (°C)
Figure 6: Thermogravimetric analysis (TGA) pertans and their derivatives (DTG) for (a)
H2TPrOPhOPc (5), (b) CoTPrOPhOPc (6) and (c) MnTPrOPhOPc (7) measured from room
temperature (20 °C) to 600 °C.
o
The thermograms show that the complexes decomposes in three steps and at 600 C the residue
was in the range of 50-70% for the different phthalocyanines. The residual percent was high
(70%) for CoTPrOPhOPc (6) and Mn(OAc)TPrOPhOPc (7), when compared to 53% of
H2TPrOPhOPc (5). The thermograms showed that the Pc core ring did not decompose and are
thermally stable, especially the metallated CoTPrOPhOPc (6) and MnTPrOPhOPc (7)
complexes. The thermal stability of the metallated complexes is due to the metal ions at the
centre of the Pc ligand. The Mn(OAc)TPrOPhOPc (7) was even more stable when compared to
25

CoTPrOPhOPc (6) complex. The derivatives of the thermograms (DTG) were investigated and
the decomposition mechanism of the various complexes predicted. The H2TPrOPhOPc (5)
o
showed the first weight loss of 3% at a temperature range of 80-203 C which corresponds to
three water molecules. The results did not agree with the elemental analysis which showed no
water molecules for compound (5). A 20% weight loss was observed between 247 – 350 °C
corresponding to the loss of four propargyloxy groups (4 x -OCH2C≡CH) for (5). This appeared
to be the major weight loss as can be observed in Fig. 6 by the deep trough in the derivative of
the thermogravimetry (DTG). Additional 24% weight loss within the range 372 – 600 °C
corresponded to the loss of phenyl groups from H2TPrOPhOPc (5). The DTG in Fig. 6 showed
that the loss of pheny group occurred in two stages of equal area with two troughs between 372
o
oC and 600 C. The thermograms of CoTPrOPhOPc (6) and Mn(OAc)TPrOPhOPc (7) were
almost similar in shape and also in their % weight loss. They both exhibited an initial 10%
weight loss between 20 - 200°C and was attributed to the loss of five water molecules for
CoTPrOPhOPc (6) and four water molecules plus an axial acetate ligand for
Mn(OAc)TPrOPhOPc (7). It was interesting to observe the correlation and the loss of five water
molecules for CoTPrOPhOPc (6) and four water molecules plus the axial acetate ligand for
Mn(OAc)TPrOPhOPc (7) also observed in the elemental analysis. CoTPrOPhOPc (6) and
Mn(OAc)TPrOPhOPc (7) showed two steps for the loss of four propargyl groups (4 x -
CH2C≡CH) and at the studied temperature range. These two steps decomposition were clearly
observed from their respective DTG. The DTG for CoTPrOPhOPc (6) shows a small trough
between 320-380oC before the bigger one between 380-525oC. However, the DTG of
Mn(OAc)TPrOPhOPc (7) is an opposite of CoTPrOPhOPc (6), in that, the bigger trough was
first observed before the smaller one. It was interesting to observe that the phenoxy moiety did
26

not decompose for the metallated complexes owing to their stability upon cobalt and manganese
metal complexation. All the TGAs and DTGs in Fig. 6 show that the phthalocyanines remained
o
stable with the Pc core retained at the studied temperature between 20 - 600 C. The phenoxy
groups were also retained for the CoTPrOPhOPc (6) and Mn(OAc)TPrOPhOPc (7). The stability
of the phenoxy moiety even at high temperatures is attributed to the increased stability of the Pc
ring which in turn stabilizes the substituents. The observed thermal stability of the studied
complexes at the studied temperature followed this trend of increasing stability: H2TPrOPhOPc
(5) < CoTPrOPhOPc (6) < Mn(OAc)TPrOPhOPc (7). The % weight loss and the proposed
chemical structure of lost moiety are summarized in Table S2. The % weight loss on the
CoTPrOPhOPc (6) and Mn(OAc)TPrOPhOPc (7) was very low and could only account for the
propargyl group and not the phenoxy as the found % weight loss for H2TPrOPhOPc (5) was (3
%, 20 %, 24 %); for CoTPrOPhOPc (6) and for Mn(OAc)TPrOPhOPc (7) was similar (10 %, 10
%, 10 %).
Broido’s graphical method [42] was employed to study the degradation mechanism, and
thermodynamic parameters of the synthesized unmetallated (5) and metallated phthalocyanines
(6) and (7). From Equation 2 below, the slope of ln (ln1/y) versus 1/T (K) was used to calculate
the energy of activation (E) of respective decomposition steps [42]:
ꢑꢒ ꢓꢑꢒ ꢕꢔꢖ = − ꢘꢙ + ꢑꢒ ꢓꢘꢚꢙꢛꢜꢖ
(2)
ꢗ
ꢝꢗ
where y is the undecomposed fraction of the sample, E is the energy of activation; R is the gas
constant; Z is the frequency factor; β is the heating rate and Tm is the temperature of the
maximum reaction rate. From Equation 2, the energy of activation of each decomposition step
27

was calculated using a slope of ꢑꢒ ꢓꢑꢒ ꢕꢔꢖ ꢂꢞꢟꢂꢂ ꢠꢔ ꢂequalꢂto − ꢘꢗ . The frequency factor (Z) was
calculated from the same graph using y-intercept equal to ꢑꢒ ꢓꢘꢚꢙꢛꢜꢖ. Figure 7 shows the plot of
ꢝꢗ
ln (ln1/y) versus 1/T (K) for phthalocyanines (5) – (7) at different temperature ranges which
correspond to the degradation event as discussed above for temperature range (TR) (A) TR = 80 to
300°C, (B) TR = 300 to 450 °C and (C) TR = 450 to 600 °C. The various parameters for the
decomposition of the synthesized phthalocyanines (5) – (7) at different intervals are summarized
in Table S3. Table S3 shows the summary of the calculated energy of activation, frequency
factor, linear regression and the rate constants of the respective decomposition steps for the
phthalocyanines (5) - (7) studied in this work. The energy of activation for the first weight loss
in H2TPrOPhOPc (5) is less than that of CoTPrOPhOPc (6) and Mn(OAc)TPrOPhOPc (7). This
trend is expected as there are more molecules of water lost in CoTPrOPhOPc (6) and
Mn(OAc)TPrOPhOPc (7) than in H2TPrOPhOPc (5). This trend is clearly observed in the second
decomposition step in which H2TPrOPhOPc (5) which shows a higher activation energy than
that of CoTPrOPhOPc (6) and Mn(OAc)TPrOPhOPc (7). This is because of the higher number
of the propargyl functional groups are lost in H2TPrOPhOPc (5) than in CoTPrOPhOPc (6) and
Mn(OAc)TPrOPhOPc (7). However, the rate constant shown in Table S3 for the second
decomposition step of the propargyl group was observed to decrease from unmetallated (5) to
metallated phthalocyanine complexes (6) and (7) following this trend of decreasing rate
constants: (5) > (6) > (7). This suggests that the rate of loss of the propagyl group is higher in
H2TPrOPhOPc (5) than in CoTPrOPhOPc (6) which is in turn also higher than
Mn(OAc)TPrOPhOPc (7). On the other hand, this trend in-terms of rate constant, also suggest
that, the propargyl groups on the Mn(OAc)TPrOPhOPc (7) are more thermally stable than on the
CoTPrOPhOPc (6) which is more stable than on the H2TPrOPhOPc (5).
28

-2.00
-2.50
-3.00
-3.50
-4.00
-4.50
-5.00
-5.50
-6.00
-6.50
(a)
5
6
7
y = -2984.2x + 3.178
R² = 0.9942
y = -3817.2x + 3.9596
R² = 0.9965
y = -2599.1x + 1.3325
R² = 0.9947
0.0017 0.00195 0.0022 0.00245 0.0027 0.00295 0.0032
1/T (K)
0.00
(b)
-0.50
-1.00
-1.50
-2.00
-2.50
-3.00
-3.50
-4.00
5
6
7
y = -7616.1x + 11.116
R² = 0.996
y = -6227.2x + 6.8753
R² = 0.9976
y = -3975.4x + 3.8042
R² = 0.999
0.0013
0.00145
0.0016
1/T (K)
0.00175
0.0019
-0.40
5
6
7
(C)
-0.60
-0.80
-1.00
-1.20
-1.40
-1.60
y = -1918.4x + 1.8145
R² = 0.9967
y = -2587.4x + 2.1093
R² = 0.9959
y = -2146.9x + 1.4225
R² = 0.9906
0.00111 0.00121 0.00131 0.00141 0.00151 0.00161 0.00171
1/T (K)
Figure 7: Plots of ln (ln1/y) versus 1/T (K) for complexes (5) – (7) in different temperature
ranges which correspond to the degradation event as discussed above for temperature range (TR)
(A) TR = 80 - 300°C, (B) TR = 300 – 450 °C and (C) TR = 450 – 600 °C.
29