The Effect of Biological Substrates on the Ultrafast Excited‐state Dynamics of Zinc Phthalocyanine Tetrasulfonate in Solution

Abstract

Zinc phthalocyanine tetrasulfonate (ZnPcS4), a potential photosensitizer for photodynamic therapy (PDT), has been studied using femtosecond laser spectroscopy. The excited-state dynamics in water have been found to be fast (< 80 ps) and dominated by intermolecular aggregation. Since the proposed mechanism for PDT is energy transfer from the triplet excited state of the photosensitizer to triplet O2 creating singlet O2, the short lifetime is expected to be unfavorable for producing singlet O2. This leads to the suggestion that the presence of biological substrates may have an effect on the excited-state dynamics. To test this hypothesis, the lifetimes of the excited states of ZnPcS4 have been directly measured in the presence of a model membrane, n-hexadecyltrimethylammonium bromide (CTAB). The excited-state dynamics of ZnPcS4 in buffer solutions and with human serum albumin (HSA) have also been measured. The presence of HSA and CTAB increases the excited-state lifetime significantly relative to that observed in water. The longer lifetime of ZnPcS4 in CTAB (> 1 ns) indicates that the micellar surface favors monomer formation. By increasing the excited-state lifetime, the surface substantially increases the photosensitizing potential of ZnPcS4.

Zinc Phthalocyanine Photochemistry by Raman Imaging, Fluorescence Spectroscopy and Femtosecond Spectroscopy in Normal and Cancerous Human Colon Tissues and Single Cells

“…On the contrary, in micelles the electronic relaxation appears to be longer than 1 ns. The elongation of the lifetime in micelles is advantageous for PDT because ZnPcS 4 has more time to transfer electronic energy from its triplet state to the triplet state of O 2 , which leads to an increase in the quantum yield of singlet oxygen formation [54].…”

Photosensitizer Binding to Lipid Bilayers as a Precondition for the Photoinactivation of Membrane Channels

“…First, oxygen concentrations in lipid membranes are supposed to be approximately an order of magnitude greater than in the bulk aqueous solution. Second, the singlet oxygen lifetime and the photosensitizer triplet-state lifetime are reported to be longer in membranes relative to aqueous solution (Valenzeno, 1987;Howe and Zhang, 1998;Krasnovsky, 1998;Ehrenberg et al, 1998). The third reason, and probably the most important, is that the activity of singlet oxygen and other reactive oxygen species is confined by their mean diffusion distances.…”

Preparation of Novel Silica Nanoparticles with Controllable Fluorescence Intensity from Porphyrin‐Bridged Silsesquioxane

“…However, the porphyrin was dissolved in water, which would greatly shorten their excited-state lifetime due to the poor solubility and aggregation of most porphyrin derivatives. [27][28][29][30] According to references, 31 the fluorescence decay of porphyrin adsorption on surface of SiO 2 is biexponential which includes a short lifetime of 6.0 ps (95%) and a longer lifetime of 26.2 ps (5%). Figure 7 shows the contour of luminescence and biexponential fitted excited-state lifetime of monodisperse PDSNPs (The decay of THPP in water was not showed due to its poor solubility in water).…”