Determination of the quantum yield of singlet oxygen sensitized by halogenated boron difluoride dipyrromethenes

Article abstract of DOI:10.1134/S0018143917030079

The spectral–luminescent, photophysical, and photochemical properties of dichloro-, dibromo-, and diiodo-derivatives of boron dipyrromethenate (BODIPY) have been studied, as well as the feasibility of generating singlet oxygen (¹O₂) via its photosensitization by the dihalogenated derivatives of BF₂ dipyrromethene in solutions. Quantum yields of singlet oxygen have been determined using 1,3-diphenylisobenzofuran as the ¹O₂ trap. The lowest fluorescence quantum yields have been shown to correspond to the maximum yields of singlet oxygen. It has been found that the best ¹O₂ photosensitizer among the three test dihalotetraphenylaza- BODIPY is dibromotetraphenylaza-BODIPY, which in addition possesses the highest photostability. Diiodotetramethyl-BODIPY results in the singlet oxygen yield close to unity, but it has significantly lower photostability. The yield of singlet oxygen is affected by the solvent. Dibromtetraphenylaza-BODIPY and diiodotetramethyl-BODIPY may find use as a medium in photodynamic therapy and photocatalysis of oxidation reactions.

Full text of DOI:10.1134/S0018143917030079

ISSN 0018-1439, High Energy Chemistry, 2017, Vol. 51, No. 3, pp. 175–181. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © R.T. Kuznetsova, Iu.V. Aksenova, D.E. Bashkirtsev, A.S. Shulev, E.V. Antina, M.B. Berezin, N.A. Bumagina, 2017, published in Khimiya Vysokikh
Energii, 2017, Vol. 51, No. 3, pp. 190–196.
PHOTONICS
Determination of the Quantum Yield of Singlet Oxygen Sensitized
by Halogenated Boron Difluoride Dipyrromethenes
R. T. Kuznetsovaa, *, Iu. V. Aksenovaa, D. E. Bashkirtseva, A. S. Shuleva, E. V. Antinab,
M. B. Berezinb, and N. A. Bumaginab
aTomsk State University, Tomsk, 634050 Russia
bInstitute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, 153045 Russia
*e-mail: kuznetrt@phys.tsu.ru
Received August 26, 2016
Abstract⎯The spectral–luminescent, photophysical, and photochemical properties of dichloro-, dibromo-,
and diiodo-derivatives of boron dipyrromethenate (BODIPY) have been studied, as well as the feasibility of
generating singlet oxygen (1O2) via its photosensitization by the dihalogenated derivatives of BF2 dipyr-
romethene in solutions. Quantum yields of singlet oxygen have been determined using 1,3-diphenylisoben-
zofuran as the 1O2 trap. The lowest fluorescence quantum yields have been shown to correspond to the max-
imum yields of singlet oxygen. It has been found that the best 1O2 photosensitizer among the three test dihalo-
tetraphenylaza-BODIPY is dibromotetraphenylaza-BODIPY, which in addition possesses the highest
photostability. Diiodotetramethyl-BODIPY results in the singlet oxygen yield close to unity, but it has sig-
nificantly lower photostability. The yield of singlet oxygen is affected by the solvent. Dibromtetraphenylaza-
BODIPY and diiodotetramethyl-BODIPY may find use as a medium in photodynamic therapy and photo-
catalysis of oxidation reactions.
Keywords: dipyrromethenes, BODIPY, photosensitivity, singlet oxygen, chemical traps
DOI: 10.1134/S0018143917030079
The last decade has seen intense development of a quenched by ambient oxygen, a property that is used
new class of synthetic chemical compounds, the com-
plexes of p- and d-block elements with dipyrromethe-
nes [1, 2], which can significantly alter both chromo-
phore properties (absorption and emission regions and
their intensity) and emission efficiency with fluores-
cence quantum yields of 1 to <0.01, depending on the
central atom and the ligand structure [3]. Therefore,
this class of compounds is the most promising for
studying the relation of the spectral-and-luminescent
properties and photonics of the compounds to their
structure with the aim of the subsequent selection and
synthesis of a particular structure to solve a certain
practical problem of creation of a high-tech optical
device. Thus, alkyl, phenyl, and benzyl derivatives of
boron dipyrromethenate (BODIPY), which have a
fluorescence yield close to unity, can be used as a laser
active medium for both liquid and solid-state tunable
lasers operating in the range of 500–615 nm [3–6].
Introduction of the propargylamino group into the
meso-position of the molecule shifts the spectral char-
to create oxygen sensor media [7, 8]. The replacement
of carbon in the meso-position of the BF2 dipyr-
romethene molecule by nitrogen (aza-BODIPY) leads
to a long-wavelength shift of band maxima in the spec-
tra and a decrease in the fluorescence efficiency [3]
due to the appearance of closely arranged energy states
of different orbital natures and multiplicities, which
increases the probability of intersystem crossing. The
subsequent halogenation of the dipyrromethene core
of aza-BODIPY would further increase the intersys-
tem crossing probability, i.e., the triplet and phospho-
rescence yields, which might enhance the response of
sensor media. However, the study of the luminescence
characteristics of tetraphenylaza-BODIPY has shown
that neither tetraphenylaza-BODIPY nor any of its
halogenated derivative exhibits phosphorescence, a
fact that can be explained by a decrease in the lifetime
of the T1 state as a result of not only nonradiative pro-
cesses of intersystem crossing from the T1 state, but
acteristics to shorter wavelengths (effective generation also the effective quenching of this state by molecular
oxygen to give its singlet form (1O2) [9, 10].
of stimulated emission at 470 nm has been achieved
[5]). Halogen substitution substantially reduces the
efficiency of fluorescence and causes the emergence
of long-lived phosphorescence in both frozen solu-
The formation of singlet oxygen via its photosensi-
tization by organic compounds that have a high triplet
tions and solid matrices at room temperature, which is yield involves energy transfer from the BODIPY triplet
175

176
KUZNETSOVA et al.
Ph
Ph
N
Ph
Ph
Ph
N
B
Cl
Cl
Br
Br
N
N
N
N
B
Ph
Ph
Ph
Ph
Ph
F F
F F
1
2
H3C
CH3
N
I
I
I
I
N
N
N
N
B
B
CH3
H3C
Ph
Ph
F F
F F
3
4
Ph
O
N
S
CH3
+
H3C
N
N
Cl−
CH3
CH3
Ph
5
6
Fig. 1. Structural formulas of (1) dichlorotetraphenylaza-BODIPY (Cl Ph -aza-BODIPY), (2) dibromotetraphenylaza-
2
4
BODIPY (Br Ph -aza-BODIPY), (3) diiodotetraphenylaza-BODIPY (I Ph -aza-BODIPY), (4) diiodotetramethyl-BODIPY
2
4
2
4
(I (CH ) BODIPY), (5) methylene blue (MB), and (6) 1,3-diphenylisobenzofuran (DPBF).
2
3 4
Ph
O
Ph
Ph
O
O
O
1O2
O
O
O
Ph
Ph
Ph
DPBF
DBB
1
Fig. 2. Scheme of the reaction of diphenylisobenzofuran (DPBF) with O to form the UV photoproduct DBB [11].
2
3
OBJECTS AND METHODS OF STUDY
to O2 in the triplet collision complex (reaction (1))
[11, 12]:
Figure 1 shows the structural formulas of the test
photosensitizers, which are BF2 complexes of haloge-
nated dipyrromethenes (1–4); the singlet oxygen trap
diphenylisobenzofuran (DPBF) (6); and the methy-
lene blue (MB) dye (5), which is the currently known
singlet-oxygen photosensitizer [11, 12, 14] used in this
study as the standard with a quantum yield of
[3Т(BODIPY) + 3О2] → S0(BODIPY) + 1О2. (1)
1
Media that generate O2 with a high yield hold
promise for use in photodynamic therapy (PDT) [11–
13] and as photocatalysts for processes based on the
participation of 1O2 in photooxidation reactions [14].
ϕ
MB(1O2) = 0.52 [15]. The method for determining the
quantum yield of halo-BODIPY-photosensitized sin-
1
In this regard, the aim of the present spectroscopic
study was to explore the possibility of generating O2
glet oxygen with the use of O2 traps is based on the
1
chemical interaction of DPBF in the ground elec-
1
tronic state (Fig. 2) with excited singlet oxygen O2
and determining its quantum yield via photosensitiza-
tion by dichloro, dibromo, and diiodo derivatives of
tetraphenyl aza-BODIPY, which do not exhibit phos-
phorescence, and their well-phosphorescing analogue
diiodotetramethyl-BODIPY, using the technique of
chemical degradation of 1O2 traps during their interac-
tion with singlet oxygen.
generated via reaction (1).
Quantum yields ΦX(1O2) were determined accord-
ing to Eq. (2) [11, 13]:
ФХ(1О2) = ФМВ(1О2)(k Х k MB
)
,
(2)
МВ
Х
⎡
⎤
×
1 – Т
(
1 – Т
λ exc ) (
)
λ exc
⎣
⎦
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DETERMINATION OF THE QUANTUM YIELD
177
where ΦMB is the known yield of 1O2 sensitized by the
A
0
standard MB, kX is the decay rate of DPBF in a mix-
ture with test dipyrromethenate X, and kMB is the
DPBF decay rate in a mixture with the standard MB.
The rate was determined from the slope (Fig. 3) of the
plot of absorbance A at maximum of the DPBF
absorption band (410 nm) versus the time of irradia-
tion at the sensitizer absorption band (640 or 535 nm),
at which DPBF does not absorb light (i.e., singlet oxy-
gen can be generated via reaction (1) alone). TMB and
TX refer to the transmittance of the solutions with
methylene blue (standard) and the test photosensitizer
(X), respectively, at the excitation wavelength (here,
the factor (1 – Tλexc) takes into account the
light absorbed by the photosensitizer to cause the for-
mation of excited triplet complexes). In the case of
compound 4, the excitation was carried out to its long-
wavelength absorption at λ = 535 nm, at which DPBF
likewise does not absorb light. The standard (MB) was
also excited at this wavelength, and its yield at a wave-
length excitation of 535 nm was evaluated with respect
to that in the case of excitation in the long-wavelength
band (640 nm), since the intensity of the excitation
source at these wavelengths was the same for an SM
2203 spectrometer.
(а)
1 Ar
1
2
3
8
0.6
0.4
0.2
0
10
15
λ, nm
400
500
600
700
(b)
A
0
10
20
30
40
50
60
0.6
0.4
0.2
0
λ, nm
700
400
500
600
The experiment was conducted in the sample com-
partment of the modified SM 2203 spectrometer by
placing in the compartment a cell with the solution of
the photosensitizer–DPBF mixture prepared in the
dark (spectral slit width was 10 nm during irradiation
or 5 nm for recording absorption spectra). To retain
the excitation geometry in different experiments,
close values of transmittance of the mixtures at the
excitation wavelength (T = 0.15–0.2, cBODIPY = 1–2 ×
A
0.8
(c)
0
10 Ar
5
10
0.6
0.4
0.2
15
25
35
50
70
90
120
10−5 mol/L) and close “trap” concentrations (cDPBF
≅
λ, nm
2 × 10−5 mol/L) were chosen. To exclude appreciable
consumption of dissolved molecular oxygen during
0
A
1
400
500
600
700
the generation of O2, the working mixtures were
(d)
sparged with pure oxygen at a constant flow rate
1
(20 cm3/min).
4
0.5
0.4
0.3
0.2
Fig. 3. Change in the absorption spectra of a DPBF mixture
with the dyes: (a) methylene blue in ethanol, (b) Br Ph -
2
4
aza-BODIPY in acetonitrile, and (c) I Ph -aza-BODIPY in
2
4
5
ethanol, depending on the time of irradiation at λ = 640 nm.
The irradiation time is given in (a, c), minutes and (b) sec-
onds. (d) Dependence of absorbance at the DPBF absorp-
tion band maximum (410 nm) upon the time of irradiation of
mixtures with the dyes (1) methylene blue in
3
2
t, s
0
100
200
300
ethanol, (2) Br Ph -aza-BODIPY
in
2
acetonitrile,
2
4
(3) I (CH ) BODIPY in ethanol, (4) I Ph -aza-BODIPY
2
3 4
4
in acetonitrile, and (5) Cl Ph -aza-BODIPY in acetonitrile.
2
4
Irradiation wavelength: (1, 2, 4, 5) 640 or (3) 535 nm.
HIGH ENERGY CHEMISTRY Vol. 51 No. 3 2017

178
KUZNETSOVA et al.
1
mixtures at wavelengths at which the trap DPBF does
not absorb causes its degradation, whereas the con-
centration of the irradiated photosensitizer itself
remains almost unchanged providing that the irradi-
ated volume of the solution is maintained constant
during the measurement. Based on the processing of
these and other relevant relationships for the four
Hal2-BODIPY species in different solvents, we calcu-
lated by Eq. (2) values for the quantum yield of singlet
oxygen. The calculation results together with the spec-
tral–luminescent, photophysical, and photochemical
properties are given in Tables 1 and 2.
The error of the O2 yield was calculated on the
basis of three independent measurements of the
DPBF decay rate in freshly prepared MB–DPBF
mixtures. The measurement error of the DPBF decay
rate was 5%, and its error in the subsequent calculation
of Φ(1O2) by Eq. (2) was 12%.
Halogenated boron(III) dipyrromethenates were
synthesized at the Institute of Solution Chemistry
(Ivanovo) [16]. As has been noted in [16], Br2Ph4-aza-
BODIPY is unstable in proton-donor alcohols and
electron-donor DMF. The concentration of a Br2Ph4-
aza-BODIPY (compound 2) solution at room tem-
perature is reduced two- to threefold 3 h after its
preparation. It can be assumed that the dye degrada-
tion under these conditions involves the nucleophilic
displacement of the bromine atoms and the subse-
quent reduction of the imine bond of the meso-aza
bridge by the bromide anions and oxidative degrada-
tion of the azadipyrrol core. In inert nonpolar sol-
vents, compound 2 is stable. No effects of this kind
have been detected for compounds 1 and 3: their solu-
tions in ethanol are stored for a long time without sig-
nificant change; i.e., this property is associated with
the dibromo substitution in tetraphenylaza-BODIPY.
In connection with this, compounds 1, 3, and 4 were
studied in ethanol and acetonitrile, and compound 2
was examined in acetonitrile, acetone, cyclohexane,
and toluene (all of the reagent grade) using only
freshly prepared solutions. Methylene blue and DPBF
available from Aldrich were used without further puri-
fication.
The spectral-and-luminescent characteristics of
the mixtures were recorded on a SOLAR SM 2203
spectrofluorimeter (Belarus). Photochemical and las-
ing properties were studied using excitation by the sec-
ond harmonic of an Nd : YAG laser (532 nm,
20 MW/cm2), the lasing and pumping energies were
measured with an OPHIR NOVA II power meter
(Israel) and a Gentec ED100A DUO energy detector
(Canada) with an error 3%, and lasing spectra were
recorded with an AVANTES spectrometer (the Neth-
erlands) accurate to 0.5 nm. Photostability parameters
(absolute quantum yield of phototransformations)
were determined by measuring the change in absor-
bance upon the Nd : YAG second harmonic excitation
(532 nm, 20 MW/cm2) of the compounds, with the
error being 7%. The setup used and the measurement
procedures are detailed in [3, 6, 9].
Analysis of the data presented in Table 1 shows that
substitution of the halogen atoms for the alkyl and
benzyl groups in the 4,4’-position (β-substitution) of
the dipyrromethene core leads to a long-wavelength
shift (10–12 nm) in the spectra and an enhancement
of intersystem crossing as a result of the heavy atom
effect; i.e., a decrease in the fluorescence yield and
appearance of phosphorescence in some cases [1, 5, 7,
8]. In the case of meso-aza substitution, even in the
absence of halogen atoms in the 4,4’-positions, there
is a significant red shift (75 nm) and a decrease in the
fluorescence yield to 0.2 due to the appearance of
energy states differing in type (πσ*, nπ*, ππ*) and
multiplicity; as a result, intersystem crossing is also
enhanced [3, 5]. The introduction of different halo-
gens in the 4,4'-position of aza-BODIPY hardly alters
the position of the absorption and fluorescence bands
(Table 1 and [3]), and the fluorescence quantum
yields depend on the halogen type, making 0.2–0.3 for
Cl2- and I2-Ph4-aza-BODIPY, remaining almost
unchanged as compared with nonhalogenated Ph4-
aza-BODIPY (see [3]). The fluorescence lifetimes
measured are consistent with the data on quantum
yields: the lower the fluorescence yield (i.e., the
greater the contribution of nonradiative processes),
the shorter the fluorescence lifetime (Table 1). Note
that even lasing was obtained in the case of Cl2Ph4-
aza-BODIPY [9, 10]. For Br2Ph4-aza-BODIPY, the
quantum yield and the fluorescence lifetime are an
order of magnitude lower (γfl is as low as 0.02–0.04
and τfl
=
0.08 ns). The fluorescence of
I2(CH3)4BODIPY is also low (γfl = 0.04, Table 1), but
this compound exhibits phosphorescence is solid
media and is used as an oxygen sensor medium [5, 7,
8]. On the other hand, Ph4-aza-BODIPY and its halo-
genated derivatives are not phosphorescent, and the
yield of the T state estimated experimentally and by
quantum-chemical calculation is an order of magni-
tude higher for Br2Ph4-aza-BODIPY than for Cl2-
and I2Ph4-aza-BODIPY [10], a finding that is consis-
tent with the experimental data on photonics
(Tables 1, 2).
RESULTS AND DISCUSSION
Figure 3 shows changes caused by 640 nm irradia-
tion in the absorption spectra of solutions of the pho-
tosensitizers mixed with DPBF (Figs. 3a–3c) and lin-
ear plots of absorbance at the maximum of the DPBF
absorption band versus the irradiation time (Fig. 3d),
as constructed on the basis of these changes. From the
The results given in Table 2 show that all of the test
1
Hal2-BODIPY species generate singlet oxygen O2
presented data it follows that the irradiation of the with varying efficiency depending on the structure of
HIGH ENERGY CHEMISTRY
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2017

DETERMINATION OF THE QUANTUM YIELD
179
Table 1. Spectral–luminescent and photochemical properties of dihalo-BODIPY
e x p [γfl
]
exp
λ
abs, nm
ϕphot
× 105
λfl, nm
(λexc, nm
τfl,
ns
Compound,
solvent
γ fl
(ε, L mol–1сm–1
)
(λexc, nm)
Cl2Ph4-aza-BODIPY, ethanol
645 (50000)
679 (570)
677 (590)
0.9
0.28 (570)
0.06 (290)
0.25 (590)
0.05 (315)
Cl2Ph4-aza-BODIPY*, ethyl acetate
645 (60500)
1.3
Br2Ph4-aza-BODIPY, ethyl acetate
Br2Ph4-aza-BODIPY, toluene
Br2Ph4-aza-BODIPY, acetonitrile
643 (68500)
651 (65000)
639 (38000)
673 (550)
685 (570)
672 (570)
0.08
0.08
0.025 (590)
0.03 (570)
0.13
0.02 (570)
0.003 (310)
Br2Ph4-aza-BODIPY, acetone
641 (39500)
647 (30500)
672 (570)
677 (570)
0.02 (570)
Br2Ph4-aza-BODIPY, cyclohexane
0.04 (570)
0.008 (310)
I2Ph4-aza-BODIPY, ethyl acetate
I2Ph4-aza-BODIPY, ethanol
I2Ph4-aza-BODIPY, cyclohexane
I2(CH3)4BODIPY**, ethanol
646 (77350)
647 (64000)
646 (60500)
535 (51600)
672 (600)
674 (600)
674 (600)
550 (500)
0.26 (600)
0.05 (320)
0.32 (600)
0.06 (320)
0.24 (600)
0.07 (320)
0.04 (500)
0.8
0.18
0.27
35
* Cl Ph -aza-BODIPY in ethyl acetate generates laser radiation: λ = 532 nm, λ = 685 nm, efficiency = 1.3%.
2
4
3 4
exc
las
** I (CH ) BODIPY in ethanol phosphoresces at 77 K: λ
= 792 nm, γ
= 0.6 (λ = 520 nm).
2
phosph
phosph exc
the ligand core, the halogen introduced, and the sol- totransformation is better to use for practical applica-
vent. The maximum value of the yield was obtained for tion; i.e., it is Br2Ph4-aza-BODIPY, whose pho-
Br2Ph4-aza-BODIPY compared with the Cl2- and I2-
totransformation yield is two orders of magnitude
aza-substituted counterparts in the case of irradiating lower (Table 1).
the mixture at 640 nm (Φ(1O2) = 1.73, which was
The less efficient generation of 1O2 by Cl2Ph4-aza-
greater than that for the MB standard). A value close
to unity (within the margin of error) was obtained for
I2(CH3)4BODIPY in ethanol by exciting at 535 nm.
The quantum yields of singlet oxygen for all Hal2Ph4-
aza-BODIPY and MB in polar acetonitrile are greater
than in the nonpolar solvents, a difference that may be
BODIPY compared with Br2Ph4-aza-BODIPY and
I2Ph4-aza-BODIPY is easy to understand: the yield of
triplets in Cl2Ph4-aza-BODIPY solutions is the small-
est because of a lower value of the spin–orbit coupling
operator; hence, as shown in [10], the intersystem
crossing rate constant is 4.5 × 109 s−1 for Br2Ph4-aza-
BODIPY versus 5.7 × 108 s−1 for Cl2Ph4-aza-
BODIPY. The compound I2Ph4-aza-BODIPY “drops
out” of this series, although it must have a higher trip-
let yield according to the above reasoning. As follows
from the data in Table 2, the 1O2 yield in ethanol and
acetonitrile with this photosensitizer is indeed higher
than that with Cl2Ph4-aza-BODIPY, but it signifi-
cantly lower than the yield with Br2Ph4-aza-BODIPY
in the same solvents. Bearing in mind that the yield of
1O2 in the presence of I2(CH3)4BODIPY as a photo-
1
due to different lifetimes of O2 in these media: 60–
75 μs in acetonitrile and 12, 17, and 29 μs in absolute
ethanol, cyclohexane, and toluene, respectively [12,
1
13]. It should be noted that the O2 yield for Br2Ph4-
aza-BODIPY in acetonitrile was found to be greater
than unity, a fact that may be associated with an
increase in the rate of the DPBF reaction with 1O2 in a
specifically solvating solvent, suggesting its passing to
a chain reaction as discussed in [11]. In addition, the
Br2Ph4-aza-BODIPY fluorescence in acetonitrile is
less effective compared with cyclohexane (Table 1),
indicating a greater yield of triplets for this compound sensitizer is higher than that with I2Ph4-aza-BODIPY,
in acetonitrile and also facilitating the transformation
of the mechanism of the reaction shown in Fig. 2 into
the chain mechanism [11]. Of the two most effective
1O2 photosensitizers I2(CH3)4BODIPY and Br2Ph4-
we can assume that the reason behind this distinction
is associated with the nature of substitution with the
Br2 ions, causing the existence of nπ*-type energy
states, which have a substantial effect on the time
aza-BODIPY, the one that is less subject to pho- characteristics of the triplets. As shown above, the sta-
HIGH ENERGY CHEMISTRY Vol. 51 No. 3 2017

180
KUZNETSOVA et al.
Table 2. Values for the DPBF degradation rate (k), the factor correcting light absorption at an irradiation wavelength
(1 − Tλ exc), and the quantum yield of singlet oxygen generated by photosensitization with halogenated boron dipyr-
romethenates (Φ(1O2))
Photosensitizer,
(1 – 10–log1/Т) =
(1 – Тλexc) ( 1%)
Ф(1О2)
( 12%)
k = ∆(А0 – Аt)410/∆t:
solvent,
exc, nm
DPBF decay rate × 103 ( 5%), s–1
λ
МВ, ethanol, 640
МВ, acetone, 640
0.85
1.33
1.8
0.75
0.74
0.74
0.29
0.81
0.83
0.74
0.77
0.82
0.82
0.84
0.84
0.85
0.52 [13]
0.84
1.1
МВ, acetonitrile, 640
МВ, ethanol, 535
0.5
0.82
0.02
0.28
0.89
0.83
0.47
0.03
0.19
Cl2Ph4-aza-BODIPY, ethanol, 640
Cl2Ph4-aza-BODIPY, acetonitrile, 640
Br2Ph4-aza-BODIPY, acetone, 640
Br2Ph4-aza-BODIPY, toluene, 640
Br2Ph4-aza-BODIPY, cyclohexane, 640
I2Ph4-aza-BODIPY, ethanol, 640
I2Ph4-aza-BODIPY, cyclohexane, 640
I2Ph4-aza-BODIPY, acetonitrile, 640
I2(CH3)4BODIPY, ethanol, 535
0.032
0.5
1.4
1.33
0.83
0.053
0.35
0.83
2
0.46
1.09
bility of this derivative is lower in proton-donating sol- aza-BODIPY < I2Ph4-aza-BODIPY calls for further
vents. An understanding of this phenomenon invites
further investigation.
investigation to reveal the causes of the selective ability
of the dibromo derivatives as compared to
the dichloro- and diiodo-substituted counterparts
regarding the yield of triplets and generation of singlet
oxygen.
CONCLUSIONS
The efficiency of generation of singlet oxygen via its
photosensitization by halogenated derivatives of
BODIPY has been determined, as well as their spec-
tral–luminescent, lasing, and photochemical proper-
ties, thereby allowing some features of the relation-
ships revealed to be explained.
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p. 4891.
2. Teets, T.S., Partyka, D.V., Undegraff, Y.B., and
Gray, T.G., Inorg. Chem, 2008, vol. 47, p. 2338.
The most effective singlet-oxygen photosensitizers
suitable for practical application are Br2Ph4-aza-
BODIPY and I2(CH3)4BODIPY used at excitation
wavelengths of 640 and 535 nm, respectively: both are
superior in singlet-oxygen generation efficiency to
methylene blue, a well-known photosensitizer for this
spectral region; however, Br2Ph4-aza-BODIPY is 270
times more photostable than I2(CH3)4BODIPY and,
therefore, is preferable for practical use. On the basis
of these photosensitizers, media for photodynamic
therapy and photocatalysis of chemical oxidation
reactions can be created.
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Translated by S. Zatonsky
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