450
K. Imato and Y. Ooyama
1 O 2 generation characteristics, that is, low (0.06) and high (0.69) Φ values at pH
7.4 and 5, respectively.
Optical, electrochemical, and photosensitizing properties of porphyrin, chlorin,
and bacteriochlorin skeletons have been compared. Bacteriochlorin-based dyes show
Q absorption bands in a 90 nm-longer wavelength region (ca. 740 nm) but moderately lower Φ values than those of porphyrin and chlorine-based dyes (Fig. 13.3b,
H2THPP, H2THPC, H2THPB) (Arnaut et al. 2014).
In recent years, porphyrin-based photosensitizing dyes that have strong twophoton absorption cross section (δ 2 /GM) have been developed to overcome the
disadvantage of porphyrin dyes, i.e., weak Q absorption bands in a short-wavelength
region. Two-photon absorption (2PA) is a phenomenon in which a molecule is excited
by simultaneous absorption of two photons; for example, excitation of a dye by simultaneous absorption of two 1000 nm photons is comparable to that by absorption of one
500 nm photon, which has a double energy gap. Therefore, two-photon-absorbable
dyes enable the use of tissue-permeable near-infrared light and promise two-photon
PDT, in which cancer cells deep in tissues can be selectively killed. For example,
dendronized DenH 2 TPP with enhanced light collection efficiency (290 GM @λ
2PA
= 790 nm), TPA-ZnP with a triphenylamine group (251 GM @λ
2PA
= 830 nm), and
DPP-ZnP with a diketopyrrolopyrrole moiety (2000 GM @λ
2PA
= 910 nm) have
been designed and synthesized as porphyrin-based photosensitizing dyes exhibiting
two-photon absorption characteristics (Fig. 13.3c) (Yao et al. 2015; Hammerer et al.
2014; Schmitt et al. 2015).
As described above, the molecular design and synthesis of new porphyrin-based
photosensitizing dyes have been extensively studied, and the effects of central metals
and substituents on photochemical and electrochemical properties and
1 O 2 generation
efficiency have been also investigated.
13.4 Phthalocyanine-Based Photosensitizing Dyes
Phthalocyanine dyes have a weak Soret absorption band at 300–400 nm and a strong
Q absorption band above 650 nm (ε = ~ 10
5 M
–1 cm
–1 ). Porphyrin dyes show
high light collection efficiency in the Soret absorption bands, whereas phthalocyanine dyes show high light collection efficiency in the Q absorption bands. Therefore, phthalocyanine dyes are expected to be second-generation photosensitizers
for PDT with excellent photosensitizing abilities in the phototherapeutic window.
To render phthalocyanine dyes water-soluble, the introduction of sulfonic acid,
sulfonate, carboxylic acid, and carboxylate into the phthalocyanine skeleton is an
effective way. On the other hand, phthalocyanine dyes form aggregates in solution such as dimers and multimers stacked due to their strong π-π interaction and
hydrophobic interaction. The formation of aggregates not only shifts the Q absorption bands to a short-wavelength region but also deactivates the excited states (energy
deactivation between dyes), thereby reducing the light collection efficiency, Φ T ,
and Φ . The aggregation can be suppressed by introduction of bulky water-soluble
K. Imato and Y. Ooyama
1 O 2 generation characteristics, that is, low (0.06) and high (0.69) Φ values at pH
7.4 and 5, respectively.
Optical, electrochemical, and photosensitizing properties of porphyrin, chlorin,
and bacteriochlorin skeletons have been compared. Bacteriochlorin-based dyes show
Q absorption bands in a 90 nm-longer wavelength region (ca. 740 nm) but moderately lower Φ values than those of porphyrin and chlorine-based dyes (Fig. 13.3b,
H2THPP, H2THPC, H2THPB) (Arnaut et al. 2014).
In recent years, porphyrin-based photosensitizing dyes that have strong twophoton absorption cross section (δ 2 /GM) have been developed to overcome the
disadvantage of porphyrin dyes, i.e., weak Q absorption bands in a short-wavelength
region. Two-photon absorption (2PA) is a phenomenon in which a molecule is excited
by simultaneous absorption of two photons; for example, excitation of a dye by simultaneous absorption of two 1000 nm photons is comparable to that by absorption of one
500 nm photon, which has a double energy gap. Therefore, two-photon-absorbable
dyes enable the use of tissue-permeable near-infrared light and promise two-photon
PDT, in which cancer cells deep in tissues can be selectively killed. For example,
dendronized DenH 2 TPP with enhanced light collection efficiency (290 GM @λ
2PA
= 790 nm), TPA-ZnP with a triphenylamine group (251 GM @λ
2PA
= 830 nm), and
DPP-ZnP with a diketopyrrolopyrrole moiety (2000 GM @λ
2PA
= 910 nm) have
been designed and synthesized as porphyrin-based photosensitizing dyes exhibiting
two-photon absorption characteristics (Fig. 13.3c) (Yao et al. 2015; Hammerer et al.
2014; Schmitt et al. 2015).
As described above, the molecular design and synthesis of new porphyrin-based
photosensitizing dyes have been extensively studied, and the effects of central metals
and substituents on photochemical and electrochemical properties and
1 O 2 generation
efficiency have been also investigated.
13.4 Phthalocyanine-Based Photosensitizing Dyes
Phthalocyanine dyes have a weak Soret absorption band at 300–400 nm and a strong
Q absorption band above 650 nm (ε = ~ 10
5 M
–1 cm
–1 ). Porphyrin dyes show
high light collection efficiency in the Soret absorption bands, whereas phthalocyanine dyes show high light collection efficiency in the Q absorption bands. Therefore, phthalocyanine dyes are expected to be second-generation photosensitizers
for PDT with excellent photosensitizing abilities in the phototherapeutic window.
To render phthalocyanine dyes water-soluble, the introduction of sulfonic acid,
sulfonate, carboxylic acid, and carboxylate into the phthalocyanine skeleton is an
effective way. On the other hand, phthalocyanine dyes form aggregates in solution such as dimers and multimers stacked due to their strong π-π interaction and
hydrophobic interaction. The formation of aggregates not only shifts the Q absorption bands to a short-wavelength region but also deactivates the excited states (energy
deactivation between dyes), thereby reducing the light collection efficiency, Φ T ,
and Φ . The aggregation can be suppressed by introduction of bulky water-soluble