70
T.B. Ogunbayo, T. Nyokong / Journal of Molecular Catalysis A: Chemical 337 (2011) 68–76
in 1-CNP, an interference filter (Intor, 750 nm with a band width of
40 nm) was additionally placed in the light path before the sam-
ple, to ensure the excitation of the Q band. For the determination
of singlet oxygen quantum yields of ads–MPc–SWCNT conjugates,
interference filters of 670 nm (for 1a–1e) and 750 nm (for 2a–2c)
were employed.
Triplet quantum yields and lifetimes of the new complexes
(2a–2c) were determined using a laser flash photolysis system; the
excitation pulses were produced by a Nd:YAG laser (Quanta-Ray,
1.5 J/8 ns) pumping a dye laser (Lambda Physic FL 3002, Pyridin 1
in methanol). The analyzing beam source was from a Thermo Oriel
xenon arc lamp, and a photomultiplier tube was used as a detector.
Signals were recorded with a two-channel digital real-time oscillo-
scope (Tektronix TDS 360); the kinetic curves were averaged over
256 laser pulses. Triplet lifetimes were determined by exponential
fitting of the kinetic curves using Origin Pro 7.5 software.
where C0 and Ct are the DPBF concentrations prior to and after irra-
diation, respectively; VR is the reaction volume; t is the irradiation
time per cycle and Iabs is defined by Eq. (3).
˛AI
Iabs
=
(3)
NA
where ˛ = 1 − 10−A(ꢁ) , A(ꢁ) is the absorbance of the sensitizer at the
irradiation wavelength, A is the irradiated area (3.14 cm2), I is the
intensity of light (1 × 1015 photons cm−2 s−1) and NA is Avogadro’s
constant. The singlet oxygen quantum yields (˚ꢃ) were calculated
using Eq. (4).
1
1
1
kd
1
=
+
˚
ꢃ
(4)
˚
˚
ka [DPBF]
DPBF
ꢃ
where kd is the decay constant of singlet oxygen and ka is the rate
constant for the reaction of DPBF with O2(1ꢃg). The value of 1/˚ꢃ
for the PdPc derivatives 2a–2c was obtained as the intercept from
the plot of 1/˚DPBF versus 1/DPBF. The singlet oxygen quantum
yields of ads–MPc–SWCNT conjugates were calculated as described
above, using ADMA as singlet oxygen quencher and substituting it
for DPBF.
2.3. Photocatalysis procedures
tions containing DPBF (90 M) and the Pcs (absorbance ∼ 0.2 at
the irradiation wavelength). Irradiations were done using the set-
up described above, and were repeated until around 80% decay of
DPBF was observed [20]. The absorbance was corrected for that of
the sensitizer in the B band region. Singlet oxygen quantum yields
of the ads–MPc–SWCNT conjugates were determined by suspend-
ing the conjugates in oxygen saturated pH 8.5 buffer solution and
irradiating at the Q band of the phthalocyanine complexes, using
ADMA as a singlet oxygen quencher in aqueous media.
The transformation of 4-NP was monitored through its absorp-
tion peak at 400 nm after each photolysis cycle. A 1 cm path-length
UV–vis spectrophotometric cell, fitted with a tight fitting stopper
was used as the reaction vessel. The pH of the 4-NP solution was
adjusted to 8.5. At this pH, 4-NP is deprotonated. The participation
of 1O2 in the photolysis of 4-NP was further confirmed by the addi-
tion of sodium azide, a singlet oxygen quencher, to the photolysis
reaction containing the 4-NP and suspended ads–MPc–SWCNT.
The photocatalysis products were analysed using gas chro-
matography (GC). For the GC analysis, Agilent Technologies 6820
GC system (HP 5973, HP-1 column) was employed. The photolysed
solutions were filtered to remove the MPc-SWCNT particles before
GC analysis.
Synthesis of 1a–e and 2a (hence 4a) have been reported
[9,18,19]. Synthesis of compound 3 has also been reported [22],
Scheme 1.
2.5.1. 3,6-Di(octylthiol)-4,5-dicyanobenzene (4b)
Following literature methods for synthesis of substituted
phthalonitriles [20], 4b was synthesized as follows: octanethiol
(2.01 g, 20 mmol) was dissolved in dimethylsulfoxide (DMSO)
(15 ml) under nitrogen and 3 (2 g, 10 mmol) was added. After stir-
ring for 15 min, finely ground anhydrous potassium carbonate (6 g,
43.4 mmol) was added portion-wise within 2 h with efficient stir-
ring. The reaction mixture was stirred under nitrogen at room
temperature for 12 h. Then water (30 ml) was added and the aque-
ous phase extracted with chloroform (3× 20 ml). The combined
extracts were treated first with sodium carbonate solution (5%), fol-
lowed by water. The solvent was evaporated and the product was
crystallized from ethanol. Yield: 2.4 g (79%). 1H NMR (400 mHz); ı
ppm (CDCl3) 7.52 (2H, s, Ar–H), 3.06–3.02 (4H, t, –CH2), 1.74–1.68
(4H, m, –CH2), 1.48–1.45 (4H, m, –CH2), 1.31–1.29, (16H, m,
–(CH2)4), 0.93–0.90 (6H, m, –CH3). IR (KBr pellets) vmax/cm−1]:
3469, 3094, 3021, 2934, 2871, 2574, 2232(C N), 1827, 1573, 1469,
1226, 1127, 916, 734(C–S), 687, 539.
2.4. Triplet and singlet oxygen quantum yield parameters
Triplet quantum yields were determined using a comparative
method based on triplet decay, using Eq. (1):
2.5.2. 3,6-Di(dodecylthiol)-4,5-dicyanobenzene (4c)
The same method used for the synthesis of 4b was also used for
4c except dodecylthiol was employed instead of octanethiol. The
amounts of reagents used were: dodecanethiol (3.01 g, 20 mmol),
3 (2 g, 10 mmol), potassium carbonate (6 g, 43.4 mmol). Yield: 4.4 g
(85%). 1H NMR (400 mHz); ı ppm (CDCl3): 7.52 (2H, s, Ar–H),
3.04–3.01 (4H, t, –CH2), 2.71–2.68 (4H, m, –CH2), 1.70–1.66, (12H,
m, –(CH2)3), 1.29–1.24, (12H, m, –(CH2)3), 0.93–0.90 (18H, m,
–(CH2)3–CH3). IR (KBr pellets) vmax/cm−1]: 3468, 3090, 3024,
2931, 2868, 2577, 2231(C N), 1822, 1579, 1462, 1353, 1129, 921,
741(C–S), 683.
ꢃASTampleεSTtd
ꢃASTtdεSTample
Sample
T
˚
= ˚STtd
(1)
where ꢃATSample and ꢃATStd are the changes in the triplet state
absorbance of the PdPc derivatives and the standard, respectively.
εSTample and εTStd are the triplet state extinction coefficients for
the triplet state quantum yield for the standard, ZnPc in 1-CNP,
Std
˚
= 0.67 [21]. Triplet lifetimes were determined by exponential
fitTting of the kinetic curves using OriginPro 7.5 software.
The DPBF (or ADMA) quantum yields (˚DPBF) were calculated
using Eq. (2) and the determined extinction coefficient of DPBF in
1-chloronaphthalene (ε1-CNP = 20287 M L−1 cm−1).
2.5.3. 1,4,8,11,15,18,22,25-Octakis(octylthiophthalocyaninato)
palladium(II) (2b)
In
refluxing
pentanol
(10 ml),
3,6-bis(octylthio)-4,5-
dicyanobenzene (4b) (0.42 g, 1 mmol), PdCl2 (0.08 g, 0.45 mmol)
and DBU (1.70 g, 11.17 mmol) were added. The solution was
heated to reflux for 5 h. The solution was then allowed to cool
and the solvent removed under reduced pressure, followed by
(C0 − Ct)VR
˚
DPBF
=
(2)
Iabs
t