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PHOTOCHEMISTRY OF MEROCYANINE 540
Author(s) -
DAVILA JORGE,
HARRIMAN ANTHONY,
GULLIYA KIRPAL S.
Publication year - 1991
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.1751-1097.1991.tb08460.x
Subject(s) - merocyanine , photochemistry , chemistry , biophysics , photochromism , biology
— The photophysical properties of merocyanine 540 have been determined in methanol solution over a modest temperature range. Triplet state population is inefficient (the limiting triplet quantum yield being 0.25) due to rapid isomerization of the central double bond from the first excited singlet state. Activation energies have been measured for isomerization from the excited singlet state (20 kJ mol ‐1 ) and for conversion of the resultant cis ‐isomer back to the original trans ‐form (63 kJ mol ‐1 ), both processes involving formation of a twisted species. The dye is easily oxidized to give an unstable adduct which decomposes on the sub‐ms timescale. Reversible redox chemistry occurs upon excitation in the presence of electron acceptors. These various observations are discussed in terms of the known chemotherapeutic activity of MC540 and it is concluded that the most probable mechanisms for cytotoxicity involve either local thermal disruption of cell membranes or in siru photogeneration of toxins derived from breakdown of the dye.