Time-resolved Luminescence and Singlet Oxygen Formation After Illumination of the Hypericin-Low-density Lipoprotein Complex
Abstract
Time-resolved fluorescence and phosphorescence study of hypericin (Hyp) in complex with low-density lipoproteins (LDL) as well as the evolution of singlet oxygen formation and annihilation after illumination of Hyp LDL complexes at room temperature are presented in this work. The observed shortening of the fluorescence lifetime of Hyp at high Hyp LDL molar ratios (}25:1) proves the self-quenching of the excited singlet state of monomeric Hyp at these concentration ratios.
The very short lifetime (_0.5 ns) of Hyp fluorescence at very high Hyp LDL ratios (}150:1) suggests that at high local Hyp concentration inside LDL molecules fast and ultrafast nonradiative decay processes from excited singlet state of Hyp become more important. Contrary to the lifetime of the singlet excited state, the lifetime (its shorter component) of Hyp phosphorescence is not dependent on Hyp LDL ratio in the studied concentration range.