“…[12,13] Because they have an extended conjugated electronic structure, Pcs exhibit enhanced absorption at wavelengths around 670 nm (ε ≈ 10 5 L mol −1 cm −1 ), which are longer than those of most porphyrins (λ max ≈ 610 nm, ε ≈ 5 × 10 3 L mol −1 cm −1 ) and that penetrate deeper into biological tissues. [14] Specificity required for the applications of Pcs can be governed by modification of the peripheral aromatic rings, by the nature of central chelated metal ions and even by altering the axial ligands. Pcs that have been probed as PSs for PDT include derivatives of zinc(II)-phthalocyanine (ZnPc), silicon(IV)-phthalocyanine (SiPc), and aluminum(III)-phthalocyanine (AlPc).…”