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The Effect of Biological Substrates on the Ultrafast Excited‐state Dynamics of Zinc Phthalocyanine Tetrasulfonate in Solution
Author(s) -
Howe L.,
Zhang J. Z.
Publication year - 1998
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1998.tb05169.x
Subject(s) - zinc , excited state , ultrashort pulse , dynamics (music) , phthalocyanine , nanotechnology , chemical physics , materials science , chemistry , optoelectronics , biological system , physics , optics , biology , quantum mechanics , organic chemistry , laser , acoustics
Zinc phthalocyanine tetrasulfonate (ZnPcS 4 ), 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 O 2 creating singlet O 2 , the short lifetime is expected to be unfavorable for producing singlet O 2 . 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 ex‐cited states of ZnPcS 4 have been directly measured in the presence of a model membrane, n‐hexadecyltrimethylammonium bromide (CTAB). The excited‐state dynamics of ZnPcS 4 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 in‐creases the photosensitizing potential of ZnPcS 4 .