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THE INTERACTION OF MELANIN WITH 8‐METHOXYPSORALEN: EFFECT ON RADIATIVE and NONRADIATIVE TRANSITIONS. A FLUORESCENCE and PULSED PHOTOACOUSTIC STUDY
Author(s) -
Losi Aba,
Viappiani Cristiano,
Crippa Pier Raimondo
Publication year - 1994
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.1751-1097.1994.tb08224.x
Subject(s) - intersystem crossing , fluorescence , photochemistry , chemistry , quenching (fluorescence) , excited state , photoacoustic imaging in biomedicine , absorption (acoustics) , melanin , singlet oxygen , radiative transfer , triplet state , singlet state , analytical chemistry (journal) , molecule , materials science , oxygen , optics , atomic physics , chromatography , physics , organic chemistry , biochemistry , composite material
–The interaction of 8‐methoxypsoralen (8‐MOP) with synthetic eumelanin was investigated using static and time‐resolved fluorescence and pulsed photoacoustic calorimetry. Due to the strong overlap of the absorption bands of melanin and 8‐MOP, a method is presented to account for the systematic errors introduced by the optical filter effect exerted by each absorbing species in the fluorescence and the photoacoustic measurements. As a preliminary step to the understanding of the nonradiative behavior of the psoralen‐melanin complexes, the photoacoustic parameters of 8‐MOP in various solvents were determined. Spectroscopic data indicate the absence of interaction at the ground‐state level, whereas the singlet excited state of 8‐MOP is quenched by the pigment; the average fluorescence lifetimes are independent of the melanin concentration, thus indicating a static quenching mechanism. The photoacoustic data show that the quenching process involves an increased intersystem crossing probability, which is almost unaffected by the presence of oxygen, as expected for a molecule essentially acting as a type I photosensitizing agent.