448
K. Imato and Y. Ooyama
generation can be indirectly estimated from changes in photoabsorption spectra of
scavengers such as 1,3-diphenylisobenzofuran (DPBF, λ
abs
max = 410–420 nm) (Gollnick and Griesbeck 1985) and 1,5-dihydroxynaphthalene (DHN, λ
abs
max = 300 nm)
(Takizawa et al. 2011), which are oxidized by
1 O 2 via [4 + 2] cycloaddition reaction
(Fig. 13.2b). To quantify
1 O 2 generation by the scavenger method, a relative quantum
yield method is commonly used. In the method, Φ sam of a target photosensitizing
dye (sam) can be calculated by comparing changes in photoabsorption spectra of a
scavenger during its reaction with
1 O 2 generated using the target photosensitizing
dye and spectral changes using a standard photosensitizing dye (ref) represented by
methylene blue, as well as comparison with Φ ref as follows (Eq. (13.1)):
sam = ref × [(m sam /m ref ) × (L ref /L sam )]
(13.1)
where Φ sam and Φ ref are
1 O 2 generation quantum yields of target and standard
photosensitizing dyes, respectively, m sam and m ref are slopes in changes of absorbance
at the photoabsorption maximum wavelength (λ
abs
max ) of a scavenger against photoirradiation time using target and standard photosensitizing dyes, respectively, and L sam
and L ref are light harvesting efficiencies of target and standard photosensitizing dyes,
respectively, at photoirradiation wavelength (L = 1 – 10
–A , “A” is absorbance at the
photoirradiation (photoexcitation) wavelength).
Alternatively, the evaluation of changes in fluorescence spectra of a fluorescent
scavenger such as anthracene-9,10-dipropionic acid (ADPA, λ
fl
max = 430 nm) during
its reaction with
1 O 2 via [4 + 2] cycloaddition is also well known as another method
to estimate
1 O 2 generation (Fig. 13.2c) (Aubry et al. 1995).
In addition, the estimation of 4-oxo-TEMPO radicals formed via the reaction of
4-oxo-TEMP, a spin trapping agent, with
1 O 2 by electron paramagnetic resonance
(EPR) spectroscopy enables to indirectly detect and quantify photogenerated
1 O 2
(Fig. 13.2d) (Yamakoshi et al. 2003; Oriana et al. 2013).
As a direct method for detection and quantification of
1 O 2 , a spectroscopic method
for measuring the phosphorescence of
1 O 2 [
1 O 2 →
3 O 2 + hν (1270 nm, 0.98 eV)]
generated by photosensitizing dyes is available but requires an expensive spectrophotometer to detect near-infrared fluorescence (Fig. 13.1c) (Yamakoshi et al.
2003).
13.3 Porphyrin-Based Photosensitizing Dyes
Porphyrin dyes have a strong Soret absorption band at 400–450 nm (ε = −10
6
M
–1 cm
–1 ) and a weak Q absorption band at 500–700 nm (ε = −10
4 M
–1 cm
–1 ),
and therefore, have been expected as excellent PDT dyes with the photosensitizing ability in the phototherapeutic window since the early days. Water-soluble
porphyrin-based photosensitizing dyes can be obtained by introducing sulfonic
acid, sulfonate, carboxylic acid, carboxylate, or N-alkylpyridinium groups into the
K. Imato and Y. Ooyama
generation can be indirectly estimated from changes in photoabsorption spectra of
scavengers such as 1,3-diphenylisobenzofuran (DPBF, λ
abs
max = 410–420 nm) (Gollnick and Griesbeck 1985) and 1,5-dihydroxynaphthalene (DHN, λ
abs
max = 300 nm)
(Takizawa et al. 2011), which are oxidized by
1 O 2 via [4 + 2] cycloaddition reaction
(Fig. 13.2b). To quantify
1 O 2 generation by the scavenger method, a relative quantum
yield method is commonly used. In the method, Φ sam of a target photosensitizing
dye (sam) can be calculated by comparing changes in photoabsorption spectra of a
scavenger during its reaction with
1 O 2 generated using the target photosensitizing
dye and spectral changes using a standard photosensitizing dye (ref) represented by
methylene blue, as well as comparison with Φ ref as follows (Eq. (13.1)):
sam = ref × [(m sam /m ref ) × (L ref /L sam )]
(13.1)
where Φ sam and Φ ref are
1 O 2 generation quantum yields of target and standard
photosensitizing dyes, respectively, m sam and m ref are slopes in changes of absorbance
at the photoabsorption maximum wavelength (λ
abs
max ) of a scavenger against photoirradiation time using target and standard photosensitizing dyes, respectively, and L sam
and L ref are light harvesting efficiencies of target and standard photosensitizing dyes,
respectively, at photoirradiation wavelength (L = 1 – 10
–A , “A” is absorbance at the
photoirradiation (photoexcitation) wavelength).
Alternatively, the evaluation of changes in fluorescence spectra of a fluorescent
scavenger such as anthracene-9,10-dipropionic acid (ADPA, λ
fl
max = 430 nm) during
its reaction with
1 O 2 via [4 + 2] cycloaddition is also well known as another method
to estimate
1 O 2 generation (Fig. 13.2c) (Aubry et al. 1995).
In addition, the estimation of 4-oxo-TEMPO radicals formed via the reaction of
4-oxo-TEMP, a spin trapping agent, with
1 O 2 by electron paramagnetic resonance
(EPR) spectroscopy enables to indirectly detect and quantify photogenerated
1 O 2
(Fig. 13.2d) (Yamakoshi et al. 2003; Oriana et al. 2013).
As a direct method for detection and quantification of
1 O 2 , a spectroscopic method
for measuring the phosphorescence of
1 O 2 [
1 O 2 →
3 O 2 + hν (1270 nm, 0.98 eV)]
generated by photosensitizing dyes is available but requires an expensive spectrophotometer to detect near-infrared fluorescence (Fig. 13.1c) (Yamakoshi et al.
2003).
13.3 Porphyrin-Based Photosensitizing Dyes
Porphyrin dyes have a strong Soret absorption band at 400–450 nm (ε = −10
6
M
–1 cm
–1 ) and a weak Q absorption band at 500–700 nm (ε = −10
4 M
–1 cm
–1 ),
and therefore, have been expected as excellent PDT dyes with the photosensitizing ability in the phototherapeutic window since the early days. Water-soluble
porphyrin-based photosensitizing dyes can be obtained by introducing sulfonic
acid, sulfonate, carboxylic acid, carboxylate, or N-alkylpyridinium groups into the