Synthesis and Photophysical Studies of Hydrophilic Zinc Phthalocyanine Dendrimers

Phthalocyanines (Pc) and their metalloderivatives (MPc) are two-dimensional 18 π-electron aromatic porphyrin synthetic analogues¹. Due to their excellent photochemical and photophysical properties, together with their chemical versatility, Pcs are perfectly suited for their application as photosensitizers (PS) in photodynamic therapy (PDT).

Pcs exhibit a strong absorption band in the visible region of the UV/vis spectrum from 630 to 750 nm and, in the presence of an appropriate central atom, they yield long-lived triplet excited states and high singlet oxygen photo-production². Yet, although several Pcs disclose their capability to act as photosensitizing agents³, not many of them are soluble in aqueous media⁴.

In this communication, we report the synthesis, photochemical and photophysical characterization of a series of new metallodendrimers built around a zinc phthalocyanine core.  Within the last step of the synthetic route, the terminal esters were hydrolyzed, giving rise to a dramatic change in polarity upon formation of multiply charged species that are very soluble in aqueous media.

Through photochemical and photophysical studies, we corroborated the capacity of these water-soluble species to produce singlet oxygen in air-saturated solution. Moreover, along with increasing dendritic shell, a significant increase in the generation of singlet oxygen was observed. These highly hydrophilic Pc dendrimers may thus be advantageous for the purpose of producing ¹O₂ in biological media by photosensitization.

References

[1] a) G. de la Torre, C.G. Claessens, T. Torres Chem. Commun 2000 (2010); b) G. de la Torre, G. Bottari, U. Hahn, T. Torres Struct. Bond 1, 135 (2010).

[2] a) C.G. Claessens, U. Hahn, T. Torres, Chem. Rec. 8, 75 (2008); b) L.M. Moreira, F.V. dos Santos, J.P. Lyon, M. Maftoum-Costa, C. Pacheco-Soares, N.S. da Silva, Aust. J. Chem. 61, 741 (2008); c) Handbook of Porphyrin Science, K.M. Kadish, K.M. Smith, R. Guilard (Eds.) vol. 4. World Scientific: Singapore, 2010.

[3] a) J.W. Hofman, F. van Zeeland, S. Turker, H. Talsma, S. A. G. Lambrechts, D. V. Sakharov, W. E. Hennink, C. F. van Nostrum, J. Med. Chem. 50, 1485 (2007); b) X.J. Jiang, S. L. Yeung, P. C. Lo,W.P. Fong, D. K. P. Ng, J. Med. Chem. 54, 320 (2011); c) J.T.F. Lau, X.J. Jiang, D.K.P. Ng, P.C. Lo, Chem. Commun. 49, 4274 (2013).

[4] a) N. Nishiyama, Y. Morimoto, W.D. Jang, K. Kataoka, Adv. Drug Deliver. Rev. 61, 327 (2009); b) U. Hahn, F. Setaro, X. Ragàs, S. Nonell, A. Gray-Weale, T. Torres, Phys. Chem. Chem. Phys. 13, 3385 (2011); c) M. Nishida, H. Horiuchi, A. Momotake, Y. Nishimura, H. Hiratsuka, T. Arai, J. Porphyrins Phthalocyanines 15, 47 (2011); d) T.L. Doane, C.H. Chuang, A. Chomas, C. Burda, ChemPhysChem 14, 32 (2013).