Photophysical properties of nonperipherally and peripherally substituted triazatetrabenzcorrole phosphorous dihydroxy and singlet oxygen generation

Article abstract of DOI:10.1016/j.jphotochem.2010.08.001

Triazatetrabenzcorrole (TBC) is the nonplanar analogue of phthalocyanine (Pc), in which one meso-nitrogen is missing. A nonperipherally substituted TBC complex, i.e. tetra(α-phenoxy) TBC phosphorous dihydroxy (POTBC(α-OPh)₄) was synthesized and characterized for the first time together with a peripherally substituted POTBC(β-OPh)₄. The photophysical properties for each POTBC complex and its corresponding zinc Pc counterpart were measured by ground state absorption, steady state fluorescence, single photon counting technique and laser flash photolysis methods. These compounds possess long triplet lifetime, good triplet formation yield. They can effectively photosensitize the generation of singlet oxygen ¹O₂(¹Δ_g). Their fluorescence yield and lifetime are comparable to the corresponding zinc Pcs. The nonperipheral α-OPh exhibits remarkably larger influence than the peripheral β-OPh on the photophysical properties, including: (1) the longer red shift for absorption, fluorescence spectra and T₁-T_n transient spectra and (2) the larger decrease of fluorescence lifetime and triplet lifetime. Although POTBC complexes are nonplanar in the structure, they still show the similar effect of nonperipheral substitution on the photophysical properties as that of the planar ZnPcs.

Full text of DOI:10.1016/j.jphotochem.2010.08.001

Journal of Photochemistry and Photobiology A: Chemistry 215 (2010) 96–102
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Photophysical properties of nonperipherally and peripherally substituted
triazatetrabenzcorrole phosphorous dihydroxy and singlet oxygen generation
Xian-Fu Zhang∗, Jingyao Huang, Huizhi Zhao, Xuefang Zheng, Zhu Junzhong
Chemistry Department, Hebei Normal University of Science and Technology, Qinghuangdao 066004, Hebei Province, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 May 2010
Received in revised form 18 July 2010
Accepted 2 August 2010
Available online 6 August 2010
Triazatetrabenzcorrole (TBC) is the nonplanar analogue of phthalocyanine (Pc), in which one meso-
nitrogen is missing. A nonperipherally substituted TBC complex, i.e. tetra(␣-phenoxy) TBC phosphorous
dihydroxy (POTBC(␣-OPh)4) was synthesized and characterized for the first time together with a
peripherally substituted POTBC(␤-OPh)4. The photophysical properties for each POTBC complex and its
corresponding zinc Pc counterpart were measured by ground state absorption, steady state fluorescence,
single photon counting technique and laser flash photolysis methods. These compounds possess long
triplet lifetime, good triplet formation yield. They can effectively photosensitize the generation of singlet
oxygen 1O2(1ꢀg). Their fluorescence yield and lifetime are comparable to the corresponding zinc Pcs.
The nonperipheral ␣-OPh exhibits remarkably larger influence than the peripheral ␤-OPh on the pho-
tophysical properties, including: (1) the longer red shift for absorption, fluorescence spectra and T1–Tn
transient spectra and (2) the larger decrease of fluorescence lifetime and triplet lifetime. Although POTBC
complexes are nonplanar in the structure, they still show the similar effect of nonperipheral substitution
on the photophysical properties as that of the planar ZnPcs.
Keywords:
Triazatetrabenzcorrole
Phthalocyanine
Corrole
Synthesis
Photophysics
Triplet state
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
of tumor (PDT) [3,4]. We also have been interested in the synthesis
and photophysical properties of TBCs [11].
Triazatetrabenzcorrole (TBC) is a ␲-contracted phthalocyanine
(Pc), as shown in Scheme 1, and was first obtained by Pc reduction in
1981 [1]. TBC is also considered as the ␲-expanded corrole deriva-
tive [2]. TBC and its derivatives, therefore, show the properties
from both corroles and Pcs. TBCs show the ability to stabilize high-
valent oxidation states, possess low oxidation potentials and high
reduction potentials, and exhibit unique spectral characteristics in
UV–vis region [2]. These properties make TBCs attract attentions
recently because of the potential applications as excellent elec-
tron donors and sun light antennas in dye-sensitized solar cells,
photo-medicine in photodynamic therapy of tumors (PDT) [3,4],
and blue-laser dyes.
Phosphorous TBC (POTBC), in particular, is among the few TBC
complexes (Si, Ge, Sn) synthesized so far [5]. The peripherally tetra-
substituted POTBCs were later reported by Liu et al. [6–8], Li et al.
[9,10], and the structures were also elucidated by them. Zhang et al.
[11], Antunes and Nyokong [12], and Breusova et al. [13] recently
also reported peripheral tetra-substituted POTBCs. Fox was the first
to synthesize octa-substituted POTBCs [14]. Song and Huang have
shown that sulfonated POTBC is effective for photodynamic therapy
Among the tetra-substituted TBCs reported, we notice that no
nonperipheral modifications have been performed. Nonperipheral
substitution, on the other hand, may exhibit quite different effects
on the properties of TBC from peripheral substitutions, based on
the knowledge from Pc chemistry.
Herein we report the synthesis of a nonperipherally substituted
tetra(␣-phenoxy) POTBC and the measurement of its excited sin-
glet and triplet properties. The purpose is to compare the different
effect of two types of substitution on photophysical properties of
POTBC. ZnPc and its nonperipherally or peripherally substituted
tetra(phenoxy) derivatives were also included to show the simi-
larity and differences of the substitution effect between TBCs and
Pcs.
2. Experimental
2.1. Materials and instruments
Zinc phthalocyanine (ZnPc) was purchased from TCI. The
synthesis of substituted phthalocyanines and POTBC used here
has been reported by us previously [11,15,16]. All the other
reagents were analytical grade and used as received. 1H NMR
spectra were recorded at room temperature on a Bruker dmx
300 MHz NMR spectrometer. MS spectra were recorded either on
∗
Corresponding author. Tel.: +86 3352039067; fax: +86 3352039067.
E-mail address: zhangxianfu@tsinghua.org.cn (X.-F. Zhang).
1010-6030/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2010.08.001

X.-F. Zhang et al. / Journal of Photochemistry and Photobiology A: Chemistry 215 (2010) 96–102
97
Scheme 1. Chemical structures of peripherally substituted ZnPc(␤-OPh)4, POTBC(␤-OPh)4 and nonperipherally substituted ZnPc(␣-OPh)4, POTBC(␣-OPh)4. The highlighted
six-member ring in a ZnPc complex becomes five-member ring in a POTBC compound due to the loss of a meso-nitrogen.
a Bruker APEX II or Autoflex III Maldi-TOF spectrometer. IR spec-
tra were recorded at room temperature on a Shimadzu FTIR-8900
spectrometer.
2.2.2. 2,6(7),10(11),14(15)-Tetraphenoxy-triazatetrabenzcorrole
phosphorous dihydroxy [POTBC(ˇ-OPh)4]
POTBC(␤-OPh)4 was synthesized by the same procedure
mentioned above from peripherally substituted unmetallated
derivative H2Pc(␤-OPh)4. Yield: 0.52 g (27%). IR(KBr) ꢁmax/cm−1
3419(PO–H), 1577, 1527(C N), 1482, 1403, 1341, 1253, 1203, 1131,
1058, 1023, 990, 939(P–OH), 835, 744, 721. UV/Vis (DMF) ꢂmax/nm
416, 446, 600, 630, 656. 1H NMR (CDCl3): ı/ppm 8.75–8.93(4H, m,
Pc–H), 8.37–8.60 (4H, m, Pc–H), 7.81–7.92 (4H, m, Pc–H), 7.65–7.74
(8H, d, phenyl–H), 7.51–7.59 (8H, t, phenyl–H), 7.38–7.46 (4H,
t, phenyl–H). 31P NMR (D5-pyridine) ı/ppm −201.30. MS m/z
(MALDI-TOF): 932.1 [M+], 914.3[M−H2O]+.
2.2. Synthesis
2.2.1. 1,8(11),15(18),22(25)-Tetraphenoxy-triazatetrabenzcorrole
phosphorous dihydroxy [POTBC(˛-OPh)4]
POTBC(␣-OPh)4 was prepared following the procedure in liter-
ature [8,9]. 1.81 g H2Pc(␣-OPh)4 (2.05 mmol) in 20 mL of pyridine
was added into a 50 mL three-necked round-bottomed flask, which
was equipped with reflux condenser and a argon gas inlet tube.
After 10 min argon-purged pyridine (10 mL) that contained 6.5 mL
of PBr3 (70.2 mmol) was then added and the resulting mixture
was heated at 90–100 ◦C under stirring and argon atmosphere for
3.5 h. After cooling, the mixture was poured into water and fil-
tered, the solid was washed thoroughly with water. The crude
product was dissolved in THF and purified by column chromatogra-
phy on silica gel using THF-dichloromethane (1:1) as eluent. Yield:
1.03 g (53%). IR(KBr) ꢁmax/cm−1 3433 (PO–H), 1574, 1523(C N),
1485, 1400, 1342, 1250, 1207, 1130, 1060, 1026, 991, 937(P–OH),
833, 746, 725. UV/Vis (DMF) ꢂmax/nm 446, 461, 611, 640, 673.
1H NMR (CDCl3) ı/ppm 8.23–8.94 (4H, m, Pc–H), 7.61–7.97
(4H, m, Pc–H), 7.12–7.57 (24H, m, phenyl–H, Pc–H). 31P NMR
(D5-pyridine) ı/ppm −201.30. MS m/z (MALDI-TOF) 932.3 [M+],
914.5[M−H2O]+.
2.3. Photophysical measurements
Dimethylsulfoxide (DMSO) were dried and redistilled before
use. The absorption and fluorescence spectra, fluorescence quan-
tum yields and excited singlet-state lifetimes were investigated at
room temperature in DMSO.
UV–vis absorption measurements were made with either a
HP 8451A or Shimadzu 4500 spectrophotometer in 10 mm quartz
cuvettes. Sample concentrations were adjusted so that the Q band
absorption maxima were between 0.20 and 1.0 and their respective
concentrations are given in the figures for various measurements.
Fluorescence spectra up to 900 nm were monitored using EI FLS920
instrument, with 0.5 nm slits. All the spectra were corrected for the

98
X.-F. Zhang et al. / Journal of Photochemistry and Photobiology A: Chemistry 215 (2010) 96–102
sensitivity of the photo-multiplier tube. The fluorescence quantum
respectively. Their ratio can be obtained by Eq. (4):
yield (˚f) was calculated by ˚f = FsA0˚0/(F0As), in which F is the
ref
f
Iaref
Ia
1 − 10−A
670
integrated fluorescence intensity, A is the absorbance at excitation
wavelength, the subscript 0 stands for a reference compound and s
represents samples. Zinc phthalocyanine was used as the reference
(˚0f = 0.30) [17]. Excitation wavelengths of 610 nm corresponding
to S0–S1 transitions were employed. The sample and reference solu-
tions were prepared with the same absorbance (Ai) at the excitation
wavelength (near 0.09 per cm). All the solutions were air saturated.
Fluorescence lifetime of S1 was measured by time-correlated
single photon counting method (Edinburgh FLS920 spectropho-
tometer) with excitation at 672 nm diode laser (50 ps FWHM) and
emission was monitored at 690 nm.
=
.
(4)
1 − 10−A
670
To avoid chain reactions induced by DPBF in the presence
of singlet oxygen, the concentration of DPBF was lowered to
∼3 × 10−5 mol dm−3. A solution of sensitizer (absorbance ∼0.65 at
the irradiation wavelength) that contained DPBF was prepared in
the dark and irradiated in the Q-band region. DPBF degradation at
415 nm was monitored. The error in the determination of ˚ꢀ was
∼10% (determined from several ˚ꢀ values).
3. Results and discussion
Transient absorption spectra were recorded in degassed DMSO
(prepared by bubbling with argon for 20 min) with an Edinburgh
LP920 laser flash photolysis system. A Nd:YAG laser (Brio, 355 nm
and 5 ns FWHM) was used as excitation source. The analyzing light
was from a xenon lamp. The laser and analyzing light beams per-
pendicularly passed through a quartz cell with an optical path
length of 1 cm. The signal was displayed and recorded on a Tek-
tronix TDS 3012B oscilloscope and an Edinburgh LP920 detector.
The laser energy incident at the sample was attenuated to a few mJ
per pulse. Time profiles at a series of wavelengths from which point
by-point spectra were assembled were recorded with the aid of a Pc
controlled kinetic absorption spectrometer. The concentrations of
the target compounds were typically 10 ␮M providing A355 = 0.25
in a 10 mm cuvette.
3.1. Ground state absorption spectra
The UV–vis ground state absorption spectra of the three POT-
BCs and the three ZnPcs (Scheme 1) in DMSO solution at room
temperature are shown in Fig. 1. Both POTBCs and ZnPcs exhibit
the typical spectra of their own kind, respectively. The spectrum of
each compound, no matter it is a POTBC or a Pc complex, shows a
near-UV Soret (B) band region (corresponding to S0 → S2) and vis-
ible Q bands (corresponding to S0 → S1). The B bands in POTBCs,
however, become much stronger than its Q bands in contrast to
that of Pcs. POTBCs also show more vibronic satellite, i.e. Q(0,0),
Q(1,0), Q(2,0) and B(0,0), B(1,0), B(2,0) etc. The Q band absorption
The triplet–triplet absorption coefficients (εT) of the samples
were obtained using the singlet depletion method [18], and the
following equation was used to calculate the εT:
ꢀAT
εT = εS
(1)
ꢀAS
where ꢀAS and ꢀAT are the absorbance change of the triplet
transient difference absorption spectrum at the minimum of the
bleaching band and the maximum of the positive band, respec-
tively, and εS is the ground state molar absorption coefficient at
the UV–vis absorption band maximum. Both ꢀAS and ꢀAT were
obtained from the triplet transient difference absorption spectra.
The triplet quantum yield
paring the ꢀAT of the optically matched sample solution
at 355 nm in 1 cm cuvette to that of the reference,
ZnPc (˚T = 0.65 0.02, εT
(470) = 47,000 1000 M−1 cm−1
˚
T
was obtained by com-
a
) [19], using the equation:
εZTnPc
ꢀAT
˚
T
= ˚ZnPc
,
(2)
T
ꢀAZTnPc
εT
where the superscripts represent the reference, ꢀAT is the
absorbance of the triplet transient difference absorption spectrum
at the selected wavelength, and εT is the triplet state molar absorp-
tion coefficient.
Singlet oxygen quantum yield (˚ꢀ) determinations were car-
ried out using the chemical trapping method [20]. Typically, a
2 mL portion of the respective sample solutions that contained
diphenylisobenzofuran (DPBF) was irradiated at 670 nm in air sat-
urated dimethylsufoxide. ˚ꢀ values were obtained by the relative
method using ZnPc as the reference (Eq. (3)):
k
kref
Iaref
Ia
˚
= ˚ref
,
(3)
ꢀ
ꢀ
where ˚rꢀef is the singlet oxygen quantum yield for the standard
(0.67 for ZnPc in DMSO) [21], k and kref are the DPBF photobleach-
ing rate constants in the presence of the respective samples and
standard, respectively; Ia and Iaref are the rates of light absorption at
the irradiation wavelength of 670 nm by the samples and standard,
Fig. 1. UV–vis absorption spectra of the six compounds in DMSO at room temper-
ature. Concentration is 3.6 ␮M, 5.7 ␮M, and 4.2 ␮M for ZnPc, ZnPc(␤-OPh)4, and
ZnPc(␣-OPh)4, respectively. Concentration is 27 ␮M, 5.4 ␮M, and 2.8 ␮M for POTBC,
POTBC(␤-OPh)4, and POTBC(␣-OPh)4, respectively.

X.-F. Zhang et al. / Journal of Photochemistry and Photobiology A: Chemistry 215 (2010) 96–102
99
Fig. 2. Normalized emission and absorption spectra in DMSO. Emission spectra were measured with excitation at 610 nm (absorbance ∼0.09).
maximum of POTBCs is blue shifted by ca. 15 nm relative to that of
the corresponding ZnPcs, the B band absorption maximum of POT-
BCs, on the other hand, is red shifted significantly by ca. 100 nm.
This band shift indicates that the energy gap between S1 and S2 in
POTBCs is remarkably closer than the case in Pcs.
shorter-wavelength feature is the Q(0,0) band and the longer wave-
length one is the Q(0,1) vibronic satellite. The mirror symmetry
exists in Pc compounds between the emission and corresponding
absorption, which contrasts to the case of POTBCs. For POTBCs, two
bands appear in the emission but three bands exist in the absorp-
tions. The shorter-wavelength emission is the Q(0,0) band, while
the longer one should be Q(2,0) band judging from its distance to
the Q(0,0) band. The emission intensity ratio of Q(0,0) over Q(2,0) is
5.3 and not affected by the substitutions. In the absorption spectra
of POTBCs, the absorbance ratio of Q(0,0) over Q(2,0) is 3.9 and also
not varied by the substitutions. The absorbance ratio of Q(0,0) over
Q(1,0), on the other hand, show the tendency of decrease from 2.00
for POTBC to 1.85 of POTBC(␤-OPh)4 and to 1.78 of POTBC(␣-OPh)4.
The ␣-substitution moves the emission maximum to a longer
wavelength than the ␤-substitution, the same as that occurs in the
absorption spectra.
The substitutions in POTBCs with phenoxy, as that in Pcs, do
not change the shape of the spectra but make the peak wavelength
moved to the red direction. The nonperipheral substitution, how-
ever, causes a 19 nm red shift of Q band maximum which is much
larger than a 2 nm red shift by the peripheral substitution. This
trend is similar to the case in Pcs. The larger bathochromic shift of
the nonperipheral substitution is due to the larger coefficients in
linear combinations of atomic orbitals (LCAO) at the nonperipheral
positions of the HOMO than those at the peripheral positions. As
a result, the HOMO level is destabilized more at the nonperipheral
position than that at the peripheral position. Essentially, the energy
gap (ꢀE) between the HOMO and LUMO becomes smaller, resulting
in a bathochromic shift [22,23].
3.3. Fluorescence yields and singlet excited state lifetimes
3.2. Fluorescence emission spectra
The fluorescence quantum yield (˚f) and the lifetime of the low-
est singlet excited state (ꢃf) for each of the six compounds in DMSO
at 295 K are given in Table 1. The time profiles of fluorescence decay
with excitation at 672 nm by a 50 ps laser pulse are displayed in
Fig. 3. Fitting the data by single exponential function gave satis-
factory results for these compounds, and the Chi squared (ꢄ2) for
each fitting is also included in Table 1. The lifetimes are 3.20 ns,
3.00 ns and 2.58 ns for POTBC, POTBC(␤-OPh)4, and POTBC(␣-OPh)4
respectively. The ␣-substitution exerts a larger decrease in ꢃf than
Fluorescence emission spectra for POTBCs in DMSO solutions at
room temperature are shown in Fig. 2 with excitation at 610 nm,
together with the Q band absorptions (left spectra). For all the POT-
BCs, the emission spectra are dominated by S1 → S0 fluorescence,
so are the case of Pcs (not shown). Even if POTBCs were excited at a
B band wavelength, their S2 → S0 fluorescence is still much weaker
compared to that of S1 → S0 fluorescence (not shown). For Pcs, the
Table 1
Photophysical data for S1 state.
ꢂabs, nm
log ε
ꢂem, nm
˚
f
ꢃf, ns
ꢄ2
POTBC
654
656
673
670
678
690
4.18
4.84
4.98
5.44
5.25
5.38
663
670
683
680
690
708
0.36
0.40
0.33
0.30
0.29
0.26
3.20
3.00
2.58
3.41
3.23
3.04
1.23
1.18
1.00
1.11
1.03
1.00
POTBC(␤-OPh)4
POTBC(␣-OPh)4
ZnPc
ZnPc(␤-OPh)4
ZnPc(␣-OPh)4

100
X.-F. Zhang et al. / Journal of Photochemistry and Photobiology A: Chemistry 215 (2010) 96–102
Fig. 3. Time profile of emission decay at 690 nm. The samples were excited at
672 nm (50 ps diode laser). The data were fit by mono exponential functions, Chi
squared values are shown in Table 1.
the ␤-substitution for POTBC, so does the case for ZnPc. ˚f change
in ZnPcs matches their ꢃf change, such that the radiation rate con-
stant kf (=˚f/ꢃf) remains constant (0.88 0.02) × 108 s−1. kf values
of for POTBCs also show no significant change upon the substitu-
tions (1.24 0.11) × 108 s−1. It is therefore due to either internal
conversion (IC) or intersystem crossing that decreases ꢃf in these
compounds.
3.4. Triplet state: nanosecond transient spectra and kinetics
Fig. 4 displays the transient spectra for the three POTBCs with
laser excitation of 5 ns pulse at 355 nm. The samples were dissolved
in DMSO and argon-purged for 20 min before measurement. The
common features of the transient spectra are: (1) the minimum of
negative absorptions in the B- and Q-band region showed peaks
matching the maximum of the corresponding ground state absorp-
tion; (2) the positive absorption is broad, and the shape is similar to
the T1–Tn transient absorptions found previously for other POTBCs
[11]; and (3) the positive bands are separated from the ground state
bleaching with well defined isosbestic points, and the bleaching
recovery kinetics are synchronous to the absorption decay kinet-
ics (Fig. 5), indicating concomitant behavior, i.e. as the positive
absorbing transient decays, the ground state is repopulated. It is
very likely that the transient observable on the nanosecond and
longer time scale has a broad continuous absorption between ca.
350 and ca. 800 nm, superimposed upon which is an intense ground
state bleaching signal.
The positive absorption maximum is 463 nm, 470 nm and
505 nm for POTBC, POTBC(␤-OPh)4, and POTBC(␣-OPh)4, respec-
tively. ␣-OPh is also more effective than ␤-OPh on the red shift
of the transient spectra. The positive molar absorption coefficient
(Table 2) is increased two- and three-folds by ␤-OPh and ␣-OPh
modifications, respectively.
The typical transient decays at the wavelength of positive
absorption maximum are given in Fig. 5. The concomitant bleach-
ing recovery at ground state absorption minimum is also shown.
These curves can all be well fit by the mono exponential func-
Fig. 4. POTBCs transient absorption spectra in argon saturated DMSO with laser
excitation at 355 nm (absorbance was adjusted to ∼0.25).
tion. The lifetimes thus obtained are collected in Table 2. The ꢃT
values are 173 ␮s, 179 ␮s and 118 ␮s for POTBC, POTBC(␤-OPh)4,
and POTBC(␣-OPh)4 respectively. The lifetimes are comparable to
those of Pcs [18], and are sufficiently long for photosensitizing the
production of singlet oxygen.
The triplet lifetimes are shortened dramatically (Table 2) in air
saturated DMSO solutions. The rate constant by oxygen quench-
ing can be evaluated to be ranging from 0.92 × 109 M−1 s−1 to
1.50 × 109 M−1 s−1. This effective oxygen quenching also indicates
that the positive absorptions are due to T1–Tn triplet absorptions.
The transient spectra for the three Pcs were also measured under
the same conditions as that of POTBCs. The typical spectra are

X.-F. Zhang et al. / Journal of Photochemistry and Photobiology A: Chemistry 215 (2010) 96–102
101
Fig. 5. Decay of positive transient signal and recovery of negative ground state
absorption in argon saturated DMSO for POTBCs, excitation with 355 nm laser pulse.
shown in Fig. 6 together with the kinetic decay curves. By using the
same analysis mentioned above, the positive signals are assigned to
T1–Tn transient absorptions. The calculated properties for excited
triplet states are listed in Table 2.
The T1–Tn transient absorptions of Pcs are similar to those of
POTBCs, i.e. a broad band across the whole visible region and the
wavelength of absorption maximum is close to 500 nm. The sub-
stitution effect between two types of complexes is also analogous,
i.e. ␣-phenoxy has a larger influence on the red-shift of absorption
maximum and the increase of absorptivities.
Fig. 6. Phthalocyanines transient absorption spectra in argon saturated DMSO with
laser excitation at 355 nm (absorbance ∼0.25).
˚T/ꢃf, however, shows no big change upon substitution (Table 2).
The summation of ˚T and ˚f in all the cases is less than 1, indicat-
ing the presence of internal conversion (IC). The substitutions, no
matter ␣ or ␤ position, enhance IC in both types of compounds. The
rate constant of IC (kic), evaluated by (1 − ˚f − ˚T)/ꢃf, is changed
upon the substitutions.
The formation yield of singlet oxygen (˚ꢀ) is also included in
Table 2. The value of ˚ꢀ for a dye is very close to its ˚T, sug-
gesting a very high efficiency of energy transfer from a T1 state
to a molecular oxygen, T1 (PS) + 3O2 → S0 (PS) + 1O2. The rate con-
stant of this process by oxygen quenching (ket) is listed in Table 2
for each compound. The ket values obtained above are compara-
ble to the rate constants obtained for O2 quenching of the triplet
excited states of a variety of porphyrins and phthalocyanines [21].
3.5. Triplet and singlet oxygen formation yield
The formation yield of the lowest triplet excited state (˚T) for
eachofthe sixcompoundsin DMSOat 295 K is givenin Table2. ˚T of
POTBCs is generally lower than that of ZnPcs since their ˚f is higher,
as shown in Table 1. The rate constant of ISC (kisc) calculated by
Table 2
Photophysical data related to triplet state.
ꢂT–T, nm
ꢀεT, 104 M−1
˚
T
ꢃT/Ar, ␮s
ꢃT/air, ␮s
ket, 109 M−1
kisc, 109 s−1
kic, 109 s−1
˚
ꢀ
cm−1
s−1
POTBC
458
470
505
465
480
560
1.00
3.77
4.80
4.50
2.82
2.94
0.45
0.41
0.32
0.60
0.47
0.63
173
0.44
0.52
0.54
0.33
0.39
0.44
1.13
0.96
0.92
1.51
1.27
1.13
0.14
0.14
0.12
0.19
0.15
0.21
0.059
0.063
0.136
0.015
0.074
0.036
0.43
0.35
0.39
0.65
0.50
0.65
POTBC(␤-OPh)4
POTBC(␣-OPh)4
ZnPc
ZnPc(␤-OPh)4
ZnPc(␣-OPh)4
179
118
145
181
75

102
X.-F. Zhang et al. / Journal of Photochemistry and Photobiology A: Chemistry 215 (2010) 96–102
The values are close to one-ninth of the diffusion rate of O2 in the
solvent.
[7] J. Liu, Y. Zhao, F. Zhao, F. Zhang, X. Song, F.T. Chau, Study on phosphorus (III)
complex of tetrabenzotriazacorrole: a novel phthalocyanine-like photosensi-
tizer, J. Photochem. Photobiol. A: Chem. 99 (1996) 115.
[8] J. Liu, F. Zhang, F. Zhao, Y. Tang, X. Song, G. Yao, Complexation of phospho-
rus(III) with a novel tetrapyrrolic phthalocyanine-like macrocyclic compound,
J. Photochem. Photobiol. A: Chem. 91 (1995) 99.
4. Conclusion
[9] J. Li, L.R. Subramanian, M. Hanack, Studies on phosphorus phthalocyanines and
triazatetrabenzcorroles, Eur. J. Org. Chem. (1998).
POTBC(␣-OPh)4 and POTBC(␤-OPh)4 were synthesized to com-
pare the difference of the substitution effect. The photophysical
properties for the POTBCs and ZnPcs were measured by ground
state absorption, steady state fluorescence, single photon count-
ing technique and laser flash photolysis. These compounds possess
long triplet lifetime and good triplet formation yield. They can
effectively photooxidize DPBF through singlet oxygen. POTBCs flu-
orescence yields and lifetimes are comparable to the corresponding
ZnPcs. The nonperipheral ␣-OPh exhibits remarkably larger effect
than the peripheral ␤-OPh on photophysics, including: (1) the
longer red shift of absorption, fluorescence emission and T1–Tn
transient spectra, (2) the larger decrease of fluorescence lifetime
and triplet lifetime. Although POTBCs are nonplanar in structure,
they showed the similar effect of nonperipheral substitution on
photophysical properties as that of the planar ZnPcs.
[10] J. Li, L.R. Subramanian, M. Hanack, Substituted ␣,␤,␥-triazatetrabenzcorrole: an
unusual reduction product of a phthalocyanine, Chem. Commun. (1997) 679.
[11] X.-F. Zhang, Y. Chang, Y. Peng, F. Zhang, Substituted phosphorous triazate-
trabenzocorroles: correlation between structure and excited state properties,
Aust. J. Chem. 62 (2009) 434.
[12] E.M. Antunes, T. Nyokong, Synthesis, Photophysical properties of tetra- and
octasubstituted phosphorous oxide triazatetrabenzcorrole photosensitizers,
Metal Based Drugs 2008 (2008) 1.
[13] M.O. Breusova, V.E. Pushkarev, L.G. Tomilova, Synthesis of alkyl-substituted
phosphorus phthalocyanines and triazatetrabenzocorroles, Russ. Chem. Bull.
56 (2007) 1456.
[14] J.P. Fox, D.P. Goldberg, Octalkoxy-substituted phosphorus (V) triazatetraben-
zcorroles via ring contraction of phthalocyanine precursors, Inorg. Chem. 42
(2003) 8181.
[15] X.-F. Zhang, Y. Di, F. Zhang, Photoinduced single- and double-electron transfer
in a photosynthetic model consisting of one-acceptor with four equally linked
donors (D4–A), J. Photochem. Photobiol. A: Chem. 203 (2009) 216.
[16] X.F. Zhang, H.J. Xu, Synthesis and photophysical properties of substituted zinc
phthalocyanines, Chem. Res. Chin. Univ. 15 (1994) 917.
[17] P.G. Seybold, M. Gouterman, Porphyrins XIII. Fluorescence spectra and quan-
tum yields, J. Mol. Spectrosc. 31 (1969) 1.
References
[18] I. Carmichael, G.L. Hug, Triplet–triplet absorption spectra of organic molecules
in condensed phases, J. Phys. Chem. Ref. Data 15 (1986) 1.
[19] T.H.T. Thi, C. Desforge, S.G.C. Thiec, Singlet–singlet and triplet–triplet
[1] M. Gouterman, P. Sayer, E. Shankland, J.P. Smith, Porphyrins. 41. Phosphorus
mesoporphyrin and phthalocyanine, Inorg. Chem. 20 (1981) 87.
[2] I. Aviv, Z. Gross, Corrole-based applications, Chem. Commun. (2007) 1987.
[3] Z. Song, F. Zhang, X. Li, C. Shek-Kiu, F. Zhao, Y. Tang, Investigation of a novel
triazatetrabenzcorrole photosensitizer, J. Porphyrins Phthalocyanines 6 (2002)
484.
[4] L. Huang, C. Zhong, F. Zhang, C.H. Tung, Photochemical DNA cleavage by novel
water-soluble sulfonated dihydroxy phosphorus (V) tetrabenzotriazacorrole,
Bioorg. Med. Chem. Lett. 18 (2008) 2152.
[5] M. Fujiki, H. Tabei, K. Isas, New tetrapyrrolic macrocycle: ␣,␤,␥-
triazatetrabenzcorrole, J. Am. Chem. Soc. 108 (1986).
[6] J. Liu, F. Zhang, F. Zhao, Y. Tang, X. Song, Corrigendum to Study on phosphorus
(III) complex of tetrabenzotriazacorrole: a novel phthalocyanine-like photo-
sensitizer, J. Photochem. Photobiol. A: Chem. 99 (1996) 115–119;
J. Photochem. Photobiol. A: Chem. 124 (1999) 165.
intramolecular
transfer
processes
in
a
covalently
linked
porphyrin–phthalocyanine heterodimer, J. Phys. Chem. 93 (1989) 1226.
[20] M.G. Lagorio, L.E. Dicelio, E.A.S. Roman, S.E. Braslavsky, Quantum yield of singlet
molecular oxygen sensitization by copper(II) tetracarboxyphthalocy anine, J.
Photochem. Photobiol. B 3 (1989) 615.
[21] W.R. Redmond, J.N. Gamlin, A compilation of singlet oxygen yields from bio-
logically relevant molecules, Photochem. Photobiol. 70 (1999) 391.
[22] A.B. Anderson, T.L. Gorden, M.E. Kenney, Electronic and redox properties of
stacked-ring silicon phthalocyanines from molecular orbital theory Electronic
and redox properties of stacked-ring silicon phthalocyanines from molecular
orbital theory, J. Am. Chem. Soc. 107 (1985) 192.
[23] M. Konami, M. Hatano, A. Tajiri, Inter-ring overlap integrals in dimer complexes
of phthalocyanines and porphyrins, Chem. Phys. Lett. 166 (1990) 605.