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V.P. Chauke et al. / Journal of Photochemistry and Photobiology A: Chemistry 221 (2011) 38–46
˚
2.4.2. Photodegradation quantum yields
For determination of photodegradation quantum yields of the
TaPc or TiPc derivatives, the usual Eq. (2) [26] was employed:
Cu K␣ radiation (ꢀ = 1.5405 A, nickel filter). Data were collected in
the range from 2ꢁ = 5◦ to 60◦, scanning at 1◦ min−1 with a filter
time-constant of 2.5 s per step and a slit width of 6.0 mm. Sam-
ples were placed on a silicon wafer slide. The X-ray diffraction data
were treated using Eva (evaluation curve fitting) software. Baseline
correction was performed on each diffraction.
(C0 − Ct)VNA
˚
=
(2)
P
I
absSt
where C0 and Ct (mol dm−3) are the concentrations of TiPc and
TaPc complexes (5–7) before and after irradiation respectively; V
is the reaction volume; S, the irradiated cell area (2.0 cm2); t, the
irradiation time (s); NA, the Avogadro’s number and Iabs, the over-
lap integral of the radiation source intensity and the absorption
of the Pc (the action spectrum) in the region of the interference
filter transmittance. For experiments where the TiPc and TaPc com-
plexes were irradiated in the presence of AuNPs, any absorption of
the latter was subtracted from the DPBF absorption to avoid any
errors.
2.3. Photochemical methods
General Electric Quartz line lamp (300 W) was employed for the
determination of photodegradation and singlet oxygen quantum
yields, and for the phototransformation of cyclohexene. A 600 nm
glass cut off filter (Schott) and a water filter were used to filter
off ultraviolet and infrared radiations respectively. An interference
filter (Intor, 740 nm with a band width of 40 nm) was addition-
ally placed in the light path before the sample, hence ensuring
excitation at the Q band only (700–780 nm). Light intensities were
measured with a POWER MAX 5100 (Molelectron detector incor-
porated) power meter.
The products for the phototransformation of cyclohexene were
analyzed using an Agilent HP 5890 gas chromatograph (GC), fit-
ted with a flame ionization detector (FID), using a DB-5MS column
(0.25 m length, 0.2 mm internal diameter, 0.25 m film thickness).
The GC parameters were as follows: the initial oven temperature
was at 50 ◦C, maximum oven temperature was 280 ◦C, equilibra-
tion time was 0.15 min, initial ramp rate was 10 ◦C/min at 180 ◦C
for 2 min, the second was 10 ◦C/min at 280 ◦C for 2 min and total
run time was 27 min.
2.4.3. Triplet quantum yields and lifetimes
The solutions for triplet quantum yields and lifetimes were
cell, deaerated using argon and irradiated at the Q band maxima.
Triplet state quantum yields (˚T) of the TiPc (5 and 6) and TaPc
(7) complexes and their AuNPs derivates were determined by the
triplet absorption method. A comparative method [27] using zinc
phthalocyanine as a standard was employed for the calculations,
Eq. (3):
ꢃAT .εSTtd
ꢃASTtd.εT
˚
T
= ˚STtd
.
(3)
where ꢃAT and ꢃASTtd are the changes in the triplet state
respectively. εT and εSTtd are the triplet state molar extinction
coefficients for the TiPc or TaPc derivatives and the standard,
respectively. ˚STtd is the triplet quantum yield for the standard, ZnPc
Reactions were carried out under homogeneous conditions
in toluene. The reaction mixture consisted of complexes 5–7
or 5–7-AuNP mixed with known concentration of the cyclohex-
ene. The reaction mixture was contained in a reaction vessel
maintained at room temperature under constant stirring, and pho-
tolysed using the set-up described above. The reaction was then
monitored by taking samples of the solution and recording UV spec-
tra or gas chromatographs. Light intensity for these studies was
(˚T = 0.65 in toluene [28]). εT and εSTtd were determined from the
molar extinction coefficients of the respective ground singlet state
(εS and εStd), the changes in absorbances of the ground singlet states
S
1.4 × 1017 photons s−1 cm−2
.
(ꢃAS and ꢃAStd) and changes in the triplet state absorptions, (ꢂAT
S
and ꢃASTtd) according to Eqs. (4a) and (4b):
ꢃAT
2.4. Photochemical and photophysical parameters
εT = εS
(4a)
(4b)
ꢃAS
2.4.1. Singlet oxygen quantum yields
ꢃASTtd
ꢃASStd
Quantum yields of singlet oxygen photogeneration by TaPc or
TiPc derivatives in toluene were determined in air (no oxygen bub-
bled) using the relative method with ZnPc as reference and DPBF
as chemical quencher for singlet oxygen, using Eq. (1):
εSTtd = εSStd
2.5. Synthesis of phthalocyanine derivatives
has been reported [29].
Std
abs
RDStPdBFIabs
R
I
DPBF
˚
= ˚Std
.
(1)
ꢂ
ꢂ
2.5.1. 1,(4)-(2-Mercaptopyridine)phthalocyaninato titanium (IV)
oxide (5), Scheme 1
where ˚Sꢂtd is the singlet oxygen quantum yield for the standard,
Under a stream of nitrogen, a mixture of titanium butoxide
(0.25 g, 1.5 mmol), 3-(2-mercaptopyridine)phthalonitrile (3) (0.5 g,
2.1 mmol), DBU (1.66 mL, 12 mmol) and 1-pentanol (10 mL) was
stirred at 160 ◦C for 5 h. After cooling, methanol was added to the
reaction solution. The resulting precipitate was filtered and washed
twice methanol. The mixture was cooled and column chromatog-
raphy over silica was done with CHCl3 as eluent. Yield: 0.38 g (64%).
UV/Vis (toluene): ꢀmax (nm) (log ε) 335(4.45), 642(4.46), 720(5.12).
IR (KBr): ꢄmax/cm−1; 3058 (Ar-H), 1558 (C C), 1523, 1452, 1345,
1201, 1109, 1093 (C–S–C), 898 (Ti O). 1H NMR (CDCl3): ı, ppm:
8.90–9.35 (m, 5H, Pc-H), 8.45–8.89 (m, 7H, Pc-H), 7.75–8.25 (m, 8H,
Pyridyl-H), 7.43-7.68 (m, 8H, Pyridyl-H), Calc. for C52H28N12S4OTi:
Std
are the DPBF
DPBF
photodegradation rates in the presence of a sensitizer under inves-
tigation and the standard respectively. Iabs and IStd are the rates of
abs
light absorption by the sensitizer and standard, respectively.
To avoid chain reactions induced by DPBF in the presence of
singlet oxygen [26], the concentration of DPBF was lowered to
∼3 × 10−5 mol dm−3. Solutions of sensitizer (absorbance = 0.2 at the
irradiation wavelength) containing DPBF were prepared in the dark
and irradiated in the Q band region using the setup described above.
DPBF degradation at 415 nm was monitored. The light intensity for
singlet oxygen studies was 5 × 1015 photons s−1 cm−2
.