Synthesis and photophysicochemical properties of novel mononuclear rhodium(III) phthalocyanines

Article abstract of DOI:10.1016/j.poly.2011.05.017

Chloro axially-substituted octa(4-isopropylphenoxy)rhodium(III) phthalocyanine, (R)₈PcRhCl (3), was reacted with the nitrogenous bases pyridine (Py) and pyrazine (Pyz) to give the axially-disubstituted octa(4-isopropylphenoxy)rhodium(^III)phthalocyanines [(R) ₈PcRhCl(L)] (4) and (5), L = (Py) and (Pyz), respectively. In this study, the fluorescence quantum yield (ΦF), the phosphorescence quantum yield (Φ_phos) and the photodegradation quantum yield (Φ_pd) values for the newly synthesized rhodium phthalocyanine complexes (RhPcs) 4 and 5 are reported. The complexes have also been fully characterized by elemental analysis, FD mass spectrometry, FT-IR and ₁H NMR spectroscopy.

Full text of DOI:10.1016/j.poly.2011.05.017

Polyhedron 30 (2011) 2045–2050
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and photophysicochemical properties of novel mononuclear rhodium(III)
phthalocyanines
b
Tamer Ezzat Youssef a, , Hanan H. Mohamed
⇑
a Applied Organic Chemistry Department, National Research Center, Dokki 12622, Cairo, Egypt
b Institut für Technische Chemie, Universität Hannover, Callinstrasse 3, D-30167 Hannover, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Chloro axially-substituted octa(4-isopropylphenoxy)rhodium(III)phthalocyanine, (R)8PcRhCl (3), was
reacted with the nitrogenous bases pyridine (Py) and pyrazine (Pyz) to give the axially-disubstituted
octa(4-isopropylphenoxy)rhodium(III)phthalocyanines [(R)8PcRhCl(L)] (4) and (5), L = (Py) and (Pyz),
respectively. In this study, the fluorescence quantum yield (UF), the phosphorescence quantum yield
Received 24 March 2011
Accepted 11 May 2011
Available online 24 May 2011
(
Uphos) and the photodegradation quantum yield (Upd) values for the newly synthesized rhodium phtha-
Keywords:
Rhodium phthalocyanines
Photophysics
Phosphorescence
Photodegradation
locyanine complexes (RhPcs) 4 and 5 are reported. The complexes have also been fully characterized by
elemental analysis, FD mass spectrometry, FT-IR and 1H NMR spectroscopy.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
complexes of the type PcRh(L)CI, [L = 2-methylpyrazine (mepyz),
4,40-bipyridine (bpy) or pyridine (py)] have been prepared and
Phthalocyanines (Pcs) enjoy widespread use as conventional
dyes and pigments, and they have interesting chemical and phys-
ical properties [1,2]. The optical and electronic properties of the
phthalocyanine (Pc) macrocycle make it suitable for a wide range
of technological applications, such as photoconductors in xero-
graphic machines [3], electrochromic displays [4], photovoltaic
materials in solar cells [5,6], systems for fabrication of light emit-
ting diodes (LED) [7], optical limiters [8], dyes at recording layers
in recordable digital versatile discs (DVDs) [9], liquid crystalline
[10] organic conductors [11] and diverse catalytic systems [12].
Pcs have also found importance in a number of applications as
photosensitizers with excellent photosensitizing properties for
photodynamic cancer therapy (PDT) [13–16], due to their good sin-
glet oxygen generation ability [17–19], owing to the intense
absorption in the red region of visible light [20–22].
In the past few years, a considerable amount of research has
been focused on the preparation, chemistry and structure of rho-
dium phthalocyanine complexes [23]. They have been prepared
as Langmuir–Blodgett films [24,25], encapsulated in X and Y type
zeolites [26] or bounded to polymer backbones [27]. Therefore,
they are of great interest to scientists due to their catalytic [28],
electrochemical [29] and photochemical properties [30,31]. A ser-
ies of pure and axially substituted rhodium(III) phthalocyanine
studied earlier by Hanack et al. [32], in addition their cyclic vol-
tammetric properties have been investigated, along with those
for K[RhPc(CN)] [33]. Another series of axially-substituted (octa-
n-pentylphthalocyaninato)(methyl)rhodium(III) complexes has
been synthesized by Chen and Rathke [34]. These complexes are
not able to aggregate due to their special structural features [35].
The synthesis of the rhodium phthalocyanine dimer [(Rhpc2ꢀ)2]
by thermal decomposition of phthalocyaninatorhodium(III) salts
in inert high boiling solvents or under reduced pressure at
T < 350 °C have been also reported previously by Homborg et al.
[36], Nyokong [37], Chen [38] and Liu [39], in addition to their elec-
trochemical properties.
Regarding our previous studies, the nature of the substituents,
such as alkyl, alkoxy chains and bulky groups, either at the periph-
eral position or on the axial position can strongly influence the
essential parameters of a phthalocyanine, such as its solubility,
aggregation behavior, electronic absorption and fluorescence spec-
tral properties [40–43].
Therefore, we have described previously the synthesis, photo-
physical and photochemical properties of indium phthalocyanines
incorporating different types of axial and peripheral substituents
[44]. To our best knowledge, octa(4-isopropylphenoxy)rho-
dium(III)phthalocyanines (RhPcs) 3–5 have not been reported be-
fore. This is the first report describing their synthesis. The rarity
of these phthalocyanines has thus prompted us to study their pho-
tochemical and photophysical properties. The new complexes were
characterized by UV–Vis, FT-IR and 1H NMR spectroscopies, FD
mass spectra and elemental analysis.
⇑
Corresponding author. Present address: Institut für Organische Chemie,
Universität Hannover, Schneiderberg 1B, D-30167 Hannover, Germany. Tel.: +49
(0)15157291577.
E-mail address: tamezzat@yahoo.com (T.E. Youssef).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.05.017

2046
T.E. Youssef, H.H. Mohamed / Polyhedron 30 (2011) 2045–2050
in deoxygenated2-ethoxyethanol (10 ml). The mixture was refluxed
2. Experimental
2.1. General
for 22 h under dry nitrogen. A dark blue solution was formed, cooled
to room temperature and then poured into MeOH/H2O (3:1). The
suspended solution was centrifuged, the precipitated was filtered
off, washed with a methanol/water mixture (1/1, v/v) and dried un-
der vacuum. The crude product (1.2 g) was subjected to column
chromatography over silica gel using a mixture of n-hexane/dichlo-
romethane 5:2 to yield 1.02 g (59%) of complex 3 as a blue violet
powder.
All manipulations were performed under nitrogen by using
standard Schlenk techniques unless otherwise specified. 4,5-Di-
chloro-phthalonitrile (1), 4-(isopropyl)-phenol and rhodium(III)
chloride trihydrate were commercially available (Aldrich) and used
as purchased. All other reagents and solvents were reagent grade
quality, obtained from commercial suppliers and used as received.
Solvents were purified by standard methods and freshly distilled
before use.
IR (KBr) m
(cmꢀ1): 3085 (w), 3050 (s) (Ar-CH), 2950 (s), 2943 (w),
2875 (m), 1602 (CC), 1551 (s), 1460 (s), 1434 (m), 1327 (m), 1215–
1240 (C–O–C), 1179 (s), 1143 (s), 1077 (s), 944 (s), 890 (m), 771
(m), 540 (m). 1H NMR (DMSO-d6) d (ppm): 1.23–1.60 (m, 48H,
16ꢁCH3), 2.7 (hept, 8H, 8ꢁCH-isopropyl), 6.70–7.04 (dd, 32H,
32ꢁArCH-phenoxy), 8.30 (s, 8H, ArCH-Pc). UV–Vis (DMSO), kmax
(nm): 648, 629, 584, 345. MS (FD): m/z (%) 1724.31 (70) (M+). Anal.
Calc. for C104H96ClN8O8Rh: C, 72.44; H, 5.61; N, 6.50. Found: C,
71.89; H, 5.99; N, 7.09%.
2.2. Physical and spectroscopic measurements
1H NMR spectra were measured on
a Bruker ARX 250
(250.133 MHz) NMR spectrometer in DMSO-d6 as the solvent and
TMS as an internal standard; chemical shifts are reported in
ppm. FT-IR spectra were recorded on a Bruker IFS 48 spectrometer
by preparing pellets with KBr. Melting points were measured on an
electrothermal apparatus and were uncorrected. Field desorption
(FD) mass spectra measurements were carried out with a Varian
MAT 711 A spectrometer and reported as mass/charge (m/z). Ele-
mentary analyses were performed on Carlo Erba Elemental Ana-
lyzer 1106. Ground state electronic absorption measurements in
the UV–Vis region were taken in dimethylsulfoxide (DMSO) using
a Perkin–Elmer Lambda 2 spectrophotometer. Fluorescence excita-
tion and emission spectra and the phosphorescence profile were
recorded on a Hitachi F-4500 Pc spectrofluorimeter equipped with
a photomultiplier tube, using 1 cm path length cuvettes at room
temperature. All photo-irradiations were done using a Quartz lamp
(300 W). The light source was equipped with a glass cut off filter
(Schott) and a water filter, respectively, to filter off ultraviolet
and infrared radiations, and cover the red region, 630–750 nm.
Light intensity could be modulated by means of a potentiometer.
2.3.3. Synthesis of 2,3,9,10,16,17,23,24-octa(4-
isopropylphenoxyphthalocyaninato)(chloro)(pyridine)rhodium(III),
[(R)8PcRhCl(py)] (4)
Crude octa(4-isopropylphenoxyphthalocyaninato)(chloro)rho-
dium(III), (3) (0.86 g, 0.5 mmol) was stirred in 5 ml of deoxygen-
ated 2-ethoxyethanol with pyridine (0.6 g) and refluxed for 20 h
under nitrogen. The reaction mixture was left standing to allow
slow cooling and then poured into MeOH/H2O (3:1). The mixture
was then stirred for 2 h. The mixture was centrifuged. The precip-
itate was collected, washed with a methanol/water mixture (1/1,
v/v) and dried. The crude product was purified by column chroma-
tography (silica gel, CHCl3), to remove any excess ligand, and dried
(70 °C, 0.01 Torr), to yield 0.59 g (66%) of complex 4 as a blue/pur-
ple powder.
IR (KBr) m
(cmꢀ1): 3086 (w), 3055 (s) (Ar-CH), 2955 (s), 2948 (w),
2879 (m), 1612 (CC), 1558 (s), 1466 (s), 1440 (m), 1331 (m), 1218–
1238 (C–O–C), 1176 (s), 1140 (s), 1076 (s), 942 (s), 891 (m), 774
(m), 539 (m). 1H NMR (DMSO-d6) d (ppm): 1.33–1.68 (m, 48H,
16ꢁCH3), 2.5 (hept, 8H, 8ꢁCH-isopropyl), 2.6 (d, 1H, Py-Hc), 5.04
(d, 2H, Py-Hb), 5.17 (d, 2H, Py-Ha), 6.60–7.24 (dd, 32H,
32ꢁArCH-phenoxy) , 8.44 (s, 8H, ArCH-Pc). UV–Vis (DMSO), kmax
(nm): 659, 623, 586, 345, 272. MS (FD): m/z (%) 1803.41 (77)
(M+). Anal. Calc. for C109H101ClN9O8Rh: C, 72.60; H, 5.64; N, 6.99.
Found: C, 71.86; H, 6.09; N, 7.19%.
2.3. Synthesis of RhPcs 3–5
2.3.1. Synthesis of 4,5-bis(4-isopropylphenoxy)phthalonitrile (2)
4,5-Dichloro-phthalonitrile (1) (2.84 g, 14.4 mmol) was dis-
solved in DMF (50 ml) under nitrogen and 4-(isopropyl)-phenol
(2.02 g, 14.4 mmol) was added. After stirring for 30 min at room
temperature, finely anhydrous potassium carbonate (5 g,
36.24 mmol) was added in portions over 3 h with efficient stirring.
The reaction mixture was further stirred at 70 °C for 24 h. Then the
mixture was poured into 200 ml ice water, the precipitate that
formed was filtered off, washed with water and methanol, and
then dried. The crude product was recrystallized from methanol
to give 2 as a white crystalline solid (1.90 g, 80.1%). M.p. 172 °C.
2.3.4. Synthesis of 2,3,9,10,16,17,23,24-octa(4-
isopropylphenoxyphthalocyaninato)(chloro)(pyrazine)rhodium(III),
[(R)8PcRhCl(pyz)] (5)
Crude octa(4-isopropylphenoxyphthalocyaninato)(chloro)rho-
dium(III), (3) (0.86 g, 0.5 mmol) was stirred in 5 ml of deoxygen-
ated 2-ethoxyethanol with pyrazine (0.9 g) and refluxed for 20 h
under nitrogen. The reaction mixture was left standing to allow
slow cooling and then poured into MeOH/H2O (3:1). The mixture
was then stirred for 2 h. The mixture was centrifuged. The precip-
itate was collected, washed with a methanol/water mixture (1/1, v/
v) and dried. The crude product was purified by column chroma-
tography (silica gel, CHCl3), to remove any excess ligand, and dried
(70 °C, 0.01 Torr), to yield 0.5 g (61%) of complex 5 as a blue/purple
powder.
IR (KBr) m
(cmꢀ1): 3080 (w), 3053 (s) (Ar-CH), 2956 (s), 2933 (w),
2855 (m), 2230 (CN), 1599 (CC), 1541 (s), 1469 (s), 1435 (m), 1321
(m), 1210–1235 (C–O–C), 1177 (s), 1133 (s), 1070 (s), 940 (s), 889
(m), 777 (m), 539 (m). 1H NMR (DMSO-d6) d (ppm): 1.03–1.30 (m,
12H, 4ꢁCH3), 2.3 (hept, 2H, 2ꢁCH-isopropyl), 6.80 (dd, 8H,
8ꢁArCH-phenoxy), 8.20 (s, 2H, ArCH). MS (EI): m/z (%) 396.49
(90) (M+). Anal. Calc. for C26H24N2O2: C, 78.76; H, 6.10; N, 7.07.
Found: C, 77.92; H, 6.60; N, 7.19%.
IR (KBr) m
(cmꢀ1): 3071 (w), 3049 (s) (Ar-CH), 2965 (s), 2952 (w),
2.3.2. Synthesis of 2,3,9,10,16,17,23,24-octa(4-isopropylphenoxy
phthalocyaninato)(chloro)rhodium(III), [(R)8PcRhCl] (3)
2880 (m), 1610 (CC), 1550 (s), 1463 (s), 1443 (m), 1333 (m), 1220–
1235 (C–O–C), 1173 (s), 1139 (s), 1073 (s), 940 (s), 890 (m), 770
(m), 541 (m). 1H NMR (DMSO-d6) d (ppm): 1.39–1.70 (m, 48H,
16ꢁCH3), 2.6 (hept, 8H, 8ꢁCH-isopropyl), 5.05 (d, 2H, Pyz-Hb),
5.19 (d, 2H, Pyz-Ha), 6.65–7.38 (dd, 32H, 32ꢁArCH-phenoxy),
8.51 (s, 8H, ArCH-Pc). UV–Vis (DMSO), kmax (nm): 661, 622, 588,
347, 270. MS (FD): m/z (%) 1804.40 (72) (M+). Anal. Calc. for
A suspension of rhodium(III) chloride trihydrate (0.3 g) in deox-
ygenated 2-ethoxyethanol (10 ml) was boiled under a stream of
dry nitrogen gas until the water was removed, then added to a
solution of 4,5-bis(4-isopropylphenoxy)phthalonitrile (2) (1.5 g,
4 mmol) and diazabicyclo[5.4.0]undec-7-ene (DBU, 0.45 g, 3 mmol)

T.E. Youssef, H.H. Mohamed / Polyhedron 30 (2011) 2045–2050
2047
C108H100ClN10O8Rh: C, 71.89; H, 5.59; N, 7.76. Found: C, 70.98; H,
3.1. Synthesis and characterization
6.19; N, 7.99%.
The RhPc complex 3 was synthesized directly by cyclotetramer-
ization of 4,5-bis(4-isopropylphenoxy)phthalonitrile (2) in the
presence of the metal salt RhCl3 and diazabicyclo[5.4.0]undec-7-
ene (DBU) as a catalyst in deoxygenated 2-ethoxyethanol. In this
reaction, the long reaction time was necessary for a good yield.
Complexes 4 and 5 were prepared by refluxing the parent crude
chloro rhodium phthalocyanine [(R)8PcRhCl] (3) with an excess
of the corresponding axial ligand in 2-ethoxyethanol, 4: L = pyri-
dine (Py) and 5: L = pyrazine (Pyz), respectively, (see Section 2).
The synthetic routes of the axially substituted rhodium phthalocy-
anines RhPcs 3–5 are shown in Scheme 1.
2.4. Photochemical and photophysical parameters
2.4.1. Fluorescence quantum yields
Fluorescence quantum yields were determined by the compar-
ative method, Eq. (1), [45] using ZnPc in DMSO as a standard,
where (UF) = 0.20 [46,47].
Fx ꢂ AStd
ꢂ
gx2
UF
¼
UFðStdÞ
ð1Þ
FStd ꢂ Ax ꢂ g2Std
All of these axially substituted phthalocyanines were purified
by column chromatography and obtained in a moderate yield
(59% for 3, 66% for 4 and 61% for 5). The structures of the newly
prepared RhPcs complexes were elucidated using elemental analy-
sis, FT-IR, 1H NMR, UV–Vis and FD mass spectroscopy. All the ana-
lytical and spectral data were consistent with the predicted
structures. In the IR spectra, the disappearance of the characteristic
nitrile stretch (C„N) of the phthalonitrile derivative (2) at around
2230 cmꢀ1 indicated the formation of the RhPcs complexes 3–5.
The complexes had good solubility and were mainly monomeric
in solution (DMSO). Further, they were stable in air as solid mate-
rials. The solubility of the mixed axially substituted complexes 4
and 5 were much improved compared to their parent rho-
dium(III)phthalocyanine [(R)8PcRhCl] (3) with a chloro ligand, en-
abling purification by column chromatography and also 1H NMR
measurements in DMSO. These complexes were formed with high
purity, also the substituted pyridine and pyrazine axial ligands
were chosen because of their stability [52]. A simple 1H NMR spec-
trum was obtained for each of the RhPcs complexes 3–5 under or-
dinary conditions (DMSO and room temperature). They all
exhibited well-resolved spectra with sharp peaks in both the aro-
matic and aliphatic regions implying that any aggregation behavior
is totally absent.
where F(x) and F(std) are the areas under the emission curves of the
sample and standard, respectively. A(x) and A(std) are the absor-
bances of the sample and standard, respectively, and g(x) and g(std)
are the refractive indexes of the solvents used for the sample and
standard, respectively. The error in the determination of UF was
10% (determined from several UF values). Both the sample and ref-
erence were excited at the same wavelength. At least three inde-
pendent experiments were performed for the quantum yield
determinations.
2.4.2. Phosphorescence quantum yields
Phosphorescence quantum yields were determined by using the
optically dilute method, Eq. (2), [48] using a solution of 8-meth-
oxypsoralen as a standard, where (Uphos) = 0.17 [49].
Dx ꢂ AStd
ꢂ
gx2
Uphos
¼
UphosðStdÞ
ð2Þ
DStd ꢂ Ax ꢂ g2Std
where Uphos(std) is the phosphorescence quantum yield of the stan-
dard, A(x) and A(std) are the absorbances at the wavelength of the
excitation of the sample and standard, respectively, g(x) and g(std)
are the refractive indexes of the solvents used for the sample and
standard, respectively. D(x) and D(std) are the integrated emission
intensities of the sample and standard, respectively. Both the sam-
ple and reference were excited at the same wavelength. At least
three independent experiments were performed for the quantum
yield determinations.
The conformation of the phenoxy groups in the RhPcs 3–5 was
clarified by the 1H NMR spectra, which showed one environment
for the methyl hydrogens of the iso-propyl groups between 1.23
and 1.70 ppm. The 1H NMR spectrum of 3 showed a variation of
the chemical shifts values to the 1H NMR spectra of 4 and 5 for
the macrocyclic proton resonances due to the presence of the axial
pyridine and pyrazine ligands attached to the rhodium metal. The
FD mass spectra of 3, 4 and 5 confirmed the proposed structures
and these analyses were consistent with the predicted structures.
2.4.3. Photodegradation quantum yields
Determination of photodegradation quantum yields (Upd) was
carried out as previously described in the literature [47,50,51].
Upd was determined using Eq. (3),
3.2. Ground state electronic absorption spectral studies
ðC0 ꢀ CtÞ ꢂ V ꢂ NA
Upd
¼
ð3Þ
The electronic absorption spectra showed monomeric behavior,
evidenced by a single (narrow) Q band for complexes 3 and 5, typ-
ical of rhodium phthalocyanine complexes, (Fig. 1) in DMSO, the Q
bands for RhPcs 3–5 were observed at kmax = 648, 659, 661 nm,
respectively. The Q bands of the mixed axial complexes 4 and 5
were red-shifted by 11–13 nm, when compared to the correspond-
ing chloro-axial RhPc complex 3 in DMSO (Fig. 1 and Table 1). This
observed red spectral shift may due to the attached pyridine (py)
and pyrazine (pyz) rings to the central rhodium metal. The molar
extinction coefficients of the RhPcs 3–5 are listed in Table 1. They
remain almost constant, indicating a pure monomeric form [53].
Iabs ꢂ S ꢂ t
where C0 and Ct are the sample (4 and 5) concentrations before and
after irradiation respectively, V, NA, S, t and Iabs are the reaction vol-
ume, Avogadro’s constant, irradiated cell area, irradiation time and
the overlap integral of the radiation source light intensity, respec-
tively. A light intensity of 3.7 ꢁ 1016 photons sꢀ1 cmꢀ2 was em-
ployed for the Upd determinations.
3. Results and discussion
The general synthesis involves firstly, a nucleophilic aromatic
substitution reaction between a mixture of the commercially ob-
tained 4,5-dichlorophthalonitrile (1) and 4-isopropylphenol at
70 °C in DMF in the presence of K2CO3, to yield the corresponding
phthalonitrile, 4,5-bis(4-isopropylphenoxy)phthalonitrile (2) in
70–80%.
3.3. Interpretation of the photophysical and photochemical data
The photophysical and photochemical parameters of the photo-
sensitising dyes 4 and 5 can be measured in terms of the light har-
vesting property of the dye, i.e. the molar extinction coefficient (
fluorescence quantum yield (UF), phosphorescence quantum yield
e),

2048
T.E. Youssef, H.H. Mohamed / Polyhedron 30 (2011) 2045–2050
Cl
Cl
CN
O
O
CN
CN
4-(isopropyl)-phenol
K2CO
3 , 24 h,
CN
70 °C
1
2
DBU
22 h
RhCl3
2-ethoxyethanol
O
O
O
O
O
O
O
N
O
N
Cl
N
N
N
Cl
N
N
N
N
Rh
N
2-ethoxyethanol
Ligand
N
Rh
N
N
N
, 20 h
L
N
O
N
O
O
O
O
O
O
O
(59 %)
3
4; L=
5; L=
(66 %)
(61 %)
N
N
N
Scheme 1. Synthesis of RhPcs complexes 3–5.
Rhodium phthalocyanine derivatives 4 and 5 showed the same
fluorescence behavior in the solvent used, and the shape of the
excitation spectra were similar to the absorption spectra for both
complexes. Fig. 2 shows the fluorescence emission and excitation
spectra for complex 4 as an example in DMSO. The fluorescence
emission peaks are observed at 662 nm for 4 and 664 nm for 5 in
DMSO (Fig. 3).
The Q-bands in the absorption and emission spectra of com-
plexes 4 and 5 differ by 2 nm, indicating that the nuclear configu-
rations in the ground and excited states of these compounds are
similar and are not affected by excitation, see Table 1. However
in terms of wavelength, the excitation spectra are slightly red-
shifted when compared to the absorption spectra for both com-
plexes. The fluorescence quantum yields (UF) of the rhodium
phthalocyanine complexes 4 and 5 are typical of MPc complexes
in DMSO and are reported in Table 1 [54].
RhPc 3
RhPc 4
RhPc 5
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
400
500
600
700
800
The efficiency of the fluorescence process was measured by the
quantum yield. This parameter is of major importance from which
the whole photophysical behavior can be deduced, and it is com-
monly given with a 10% error [47].
Wavelength (nm)
Fig. 1. UV–Vis spectra of RhPcs 3, 4 and 5 in DMSO.
(
Uphos) and photodegradation quantum yield (Upd). Both com-
plexes were measured in dimethyl sulfoxide (DMSO) at room tem-
perature and the solutions were further filtered before transferring
into a standard spectrophotometer cell.
3.3.2. Phosphorescence behavior and quantum yield studies
As known, rhodium phthalocyanines exhibited both fluores-
cence and moderately intense phosphorescence spectra in solution
at room temperature. The spectra outlined above show that dilute
solutions of the rhodium(III) phthalocyanines 4 and 5 in DMSO ex-
hibit both fluorescence and phosphorescence at room temperature.
The phosphorescence spectra for complexes 4 and 5 are also
3.3.1. Fluorescence behavior and quantum yield studies
The excitation wavelengths used for the fluorescence measure-
ments were k = 669 nm for (4) and k = 667 nm for (5) in DMSO.

T.E. Youssef, H.H. Mohamed / Polyhedron 30 (2011) 2045–2050
2049
Table 1
Spectral, fluorescence, phosphorescence and photodegradation parameters for RhPcs 3–5 in DMSO.
RhPc
Qabs kmax (nm) (Log
e
)
Qems kmax (nm)
QExc kmax (nm)
Qphos kmax (nm)
UF
Uphos
Upd(ꢁ105)
3
4
5
648 (4.17)
659 (5.57)
661 (5.43)
698
662
664
648
669
667
786
749
747
0.31
0.33
0.30
0.51
0.56
0.66
1.8
1.3
1.7
Qabs = Q band absorption maximum; Qems = Q band emission maximum; Qphos = Q band phosphorescence maximum; Qexc = Q band excitation maximum; k = wavelength;
= molar extinction coefficient; UF = fluorescence quantum yield; Uphos = phosphorescence quantum yield; Upd = photodegradation quantum yield.
e
produce a substantial stabilizing effect upon the phthalocyanine
macrocycle [50] and therefore there is good comparability be-
tween the different complexes.
Emission
3000
2500
2000
1500
1000
500
RhPc 4
Photodegradation for the mixed axially substituted RhPcs com-
plexes 4 and 5 were characterized by the decrease in the intensity
of the spectra (both the Q and B bands) without shift in maxima or
formation of new bands, when exposed to light and irradiated at
constant time intervals over a period of 60 min. The spectral
changes observed show the decrease of the absorption spectra
without any distortion of the shape, which confirmed that clean
photodegradation occurred without any phototransformation, as
shown in Figs. 4 and 5.
Excitation
Phosphorescence
Photobleaching studies were undertaken in order to determine
the effects of different axial ligands on the stability of rhodium
0
500
600
700
800
2.0
RhPc 4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Wavelength (nm)
0 Sec
1.5
1.0
0.5
0.0
Fig. 2. Excitation, emission and phosphorescence spectra of RhPc 4 in DMSO.
3500
RhPc 5
Emission
3000
0
500
1000
1500
2000
2500
3000
3500
4000
Time (sec)
2500
2000
Excitation
3600 Sec
Phosphorescence
1500
1000
500
0
200
300
400
500
600
700
800
Wavelength (nm)
Fig. 4. The photodegradation of RhPc 4 in DMSO with after irradiation at constant
time intervals over a period of 60 min. (Insert: plot shows the absorbance against
time of irradiation).
500
600
700
800
1.8
1.6
Wavelength (nm)
RhPc 5
Fig. 3. Excitation, emission and phosphorescence spectra of RhPc 5 in DMSO.
2.0
1.4
1.8
1.6
1.2
1.4
0 Sec
1.2
virtually identical to one another, exhibiting a maximum at 749
and 747 nm, respectively, (Table 1). The phosphorescence quan-
tum yield (Uphos) values for 4 and 5 in DMSO are reported in Table
1.
1.0
1.0
0.8
0.6
0.8
0.4
0.2
0.6
0.0
0
500
1000
1500
2000
2500
3000
Time(sec)
0.4
0.2
0.0
3.3.3. Photodegradation behavior and quantum yields studies
Photodegradation (photobleaching) is a process where phthalo-
cyanines are degraded under light irradiation. It is important for
their applications as photocatalysts or as photosensitizers and it
can be used to determine the MPc’s stability.
3000 sec
200
300
400
500
600
700
800
Wavelength (nm)
The photobleaching stabilities of complexes 4 and 5 were deter-
mined in DMSO and in the presence of oxygen because it allows
good solubility and deaggregation. In addition, DMSO appears to
Fig. 5. The photodegradation of RhPc 5 in DMSO with after irradiation at constant
time intervals over a period of 50 min. (Insert: plot shows the absorbance against
time of irradiation).

2050
T.E. Youssef, H.H. Mohamed / Polyhedron 30 (2011) 2045–2050
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listed in Table 1 and are of the order of 10ꢀ5. These values show
that the RhPcs 4 and 5 have high stability in DMSO.
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The excitation spectra of the two complexes 4 and 5 represent
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that the complexes absorbing light in the ground state are the
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4. Conclusions
We have successfully synthesized chlororhodium phthalocya-
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