13 Photodynamic Therapy
463
are observed around 750 nm (ε = ~ 10
4 M
–1 cm
–1 ), and [Pt(bdt)(mesBIAN)] exhibits
a moderate Φ value (0.45) (Fig. 13.9c, [Pt(bdt)(mesBIAN)], [Pt(tdt)(mesBIAN)],
[Pt(dmit)(mesBIAN)]) (Adams et al. 2007).
As described above, transition metal-based photosensitizing dyes show high Φ
values, but their photoabsorption remains below 500 nm. To use them efficiently
in the phototherapeutic window, photoabsorption in a longer wavelength region is
required. In addition, their water solubility and low toxicity under no light irradiation
should be improved.
13.10 Conclusions and Perspectives
In this chapter, the photoabsorption properties,
1 O 2 generation characteristics, and
water solubility of photosensitizing dyes for PDT are organized by dye skeleton, and
the advantages and disadvantages of each dye skeleton are highlighted. The introduction of heavy atoms such as bromine and iodine into the dye skeletons promotes ISC
(from S 1 to T 1 ) by enhanced spin–orbit interaction (while decreasing fluorescence
emission), leading to high Φ T values. However, since the introduction of bromine or
iodine atoms causes toxicity under no light irradiation, the development of halogen
atom-free photosensitizing dyes is desired. In recent years, photosensitizing dyes
with high brightness (BT = ε × Φ fl ) and strong phototoxicity (PP = ε × Φ ) have
attracted much interest to achieve both fluorescence imaging and PDT of cancer
cells. In particular, BODIPY dyes promise to be a new group of photosensitizing
dyes for PDT because those without halogen atoms have high BT and PP characteristics. However, the photosensitizing dyes that efficiently generate
1 O 2 shown in this
chapter are based on the existing porphyrin and BODIPY skeletons with photoabsorption in the phototherapeutic window (650–900 nm). At present, the molecular
design and development of new dye skeletons for PDT are stagnant. In the future, to
promote the improvement and spread of early cancer treatment by PDT, addressing
to the construction of a new group of photosensitizing dyes with high BT and PP
characteristics and exploring the possibilities for PDT use are desired.
References
Adams CJ, Fey N, Parfitt M, Pope SJA, Weinstein JA (2007) Synthesis, structures and properties
of a new series of platinum–diimine–dithiolate complexes. Dalton Trans 111:4446–4456. https://
doi.org/10.1039/b709252k
Adarsh N, Shanmugasundaram M, Avirah RR, Ramaiah D (2012) Aza-BODIPY derivatives:
enhanced quantum yields of triplet excited states and the generation of singlet oxygen and their
role as facile sustainable photooxygenation catalysts. Chem Eur J 18:12655–12662. https://doi.
org/10.1002/chem.201202438
Arnaut LG, Pereira MM, D˛ abrowski JM, Silva EFF, Schaberle FA, Abreu AR, Rocha LB, Barsan
MM, Urba´ nska K, Stochel G, Brett CMA (2014) Photodynamic therapy efficacy enhanced by
463
are observed around 750 nm (ε = ~ 10
4 M
–1 cm
–1 ), and [Pt(bdt)(mesBIAN)] exhibits
a moderate Φ value (0.45) (Fig. 13.9c, [Pt(bdt)(mesBIAN)], [Pt(tdt)(mesBIAN)],
[Pt(dmit)(mesBIAN)]) (Adams et al. 2007).
As described above, transition metal-based photosensitizing dyes show high Φ
values, but their photoabsorption remains below 500 nm. To use them efficiently
in the phototherapeutic window, photoabsorption in a longer wavelength region is
required. In addition, their water solubility and low toxicity under no light irradiation
should be improved.
13.10 Conclusions and Perspectives
In this chapter, the photoabsorption properties,
1 O 2 generation characteristics, and
water solubility of photosensitizing dyes for PDT are organized by dye skeleton, and
the advantages and disadvantages of each dye skeleton are highlighted. The introduction of heavy atoms such as bromine and iodine into the dye skeletons promotes ISC
(from S 1 to T 1 ) by enhanced spin–orbit interaction (while decreasing fluorescence
emission), leading to high Φ T values. However, since the introduction of bromine or
iodine atoms causes toxicity under no light irradiation, the development of halogen
atom-free photosensitizing dyes is desired. In recent years, photosensitizing dyes
with high brightness (BT = ε × Φ fl ) and strong phototoxicity (PP = ε × Φ ) have
attracted much interest to achieve both fluorescence imaging and PDT of cancer
cells. In particular, BODIPY dyes promise to be a new group of photosensitizing
dyes for PDT because those without halogen atoms have high BT and PP characteristics. However, the photosensitizing dyes that efficiently generate
1 O 2 shown in this
chapter are based on the existing porphyrin and BODIPY skeletons with photoabsorption in the phototherapeutic window (650–900 nm). At present, the molecular
design and development of new dye skeletons for PDT are stagnant. In the future, to
promote the improvement and spread of early cancer treatment by PDT, addressing
to the construction of a new group of photosensitizing dyes with high BT and PP
characteristics and exploring the possibilities for PDT use are desired.
References
Adams CJ, Fey N, Parfitt M, Pope SJA, Weinstein JA (2007) Synthesis, structures and properties
of a new series of platinum–diimine–dithiolate complexes. Dalton Trans 111:4446–4456. https://
doi.org/10.1039/b709252k
Adarsh N, Shanmugasundaram M, Avirah RR, Ramaiah D (2012) Aza-BODIPY derivatives:
enhanced quantum yields of triplet excited states and the generation of singlet oxygen and their
role as facile sustainable photooxygenation catalysts. Chem Eur J 18:12655–12662. https://doi.
org/10.1002/chem.201202438
Arnaut LG, Pereira MM, D˛ abrowski JM, Silva EFF, Schaberle FA, Abreu AR, Rocha LB, Barsan
MM, Urba´ nska K, Stochel G, Brett CMA (2014) Photodynamic therapy efficacy enhanced by