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Triplet Photoreactivity of the Diaryl Ketone Tiaprofenic Acid and Its Decarboxylated Photoproduct. Photobiological Implications
Author(s) -
Encinas Susana,
Miranda Miguel A.,
Marconi Giancarlo,
Monti Sandra
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.tb05221.x
Subject(s) - chemistry , reactivity (psychology) , photochemistry , excited state , derivative (finance) , fluorescence , chromophore , acceptor , medicine , physics , alternative medicine , pathology , quantum mechanics , nuclear physics , financial economics , economics , condensed matter physics
The 2‐benzoylthiophene chromophore of the photosensitizing drug tiaprofenic acid and of its decarboxylated derivative is characterized by a unusually high energy gap between the T 1 (π,π*) and T 2 (n,π*) excited states, which makes this a unique system to study the intrinsic photo‐reactivity of the two states. Weak fluorescence and phosporescence emission were detected at room temperature. Tiaprofenic acid undergoes photodecarboxylation from the triplet manifold as the main reaction. The photoprocess is temperature dependent with activation energy of 7–10 kcal/mol, close to the energy gap between T 1 and T 2 . The decarboxylated product abstracts hydrogen in type I reactions. The involvement of T 2 in the above processes is proposed. Moreover the decarboxylated derivative exhibits reactivity toward phenols, consistent with a participation of the T 1 state as electron acceptor. The observed photoprocesses can account for biological photosensitization reactions, like membrane damage and protein modification.