Showing papers by "Andrius Baltuška published in 1993"
TL;DR: In this article, the spectral and temporal characteristics of the absorption changes ((Delta) A) of Hp, HpD and PS is measured by picosecond pump-and-probe techniques.
Abstract: The sensitizing hematoporphyrins and related species used in photosensitized tumor therapy (PTT) were revealed to be complex mixtures of monomers, dimers (mainly dihematoporphyrin ether or ester) and aggregates. Time resolved absorption spectroscopy was proved to be helpful for differentiation between these components. The spectral and temporal characteristics of the absorption changes ((Delta) A) of Hp, HpD and PS is aqueous and ethanol solutions were measured by picosecond pump-and-probe techniques. The (Delta) A spectrum of Hp in ethanol solution is formed by the bleaching of steady-state bands and the absorption from the excited S1 state. The (Delta) A of Hp relaxes exponentially with time constant (tau) equals 10 divided by 17 ns (approximately equal to the fluorescence decay time of monomeric Hp). The (Delta) A of HpD in ethanol shows biexponential decay with time constants (tau) equals 10 divided by 17 and (tau) 1 equals 1.5 divided by 4 ns. We suppose that lifetime 1.5 divided by 4 ns reflects the excitation energy relaxation in covalently linked oligomers and (tau) equals 10 divided by 16 ns is the lifetime of excited S1 state of HpD monomers. It should be noted that the (tau) 1 value depends on the existing different oligomers in HpD due to the HpD preparation conditions. The measured (Delta) A kinetics in aqueous Hp and HpD solution showed the different character. It can be fitted with the three exponents with time constants of (tau) 2 equals 100 divided by 200 ps (short component), (tau) 1 equals 1.5 divided by 4 ns (long component) and (tau) about 15 ns (monomeric component). The main changes in excitation relaxation in aqueous solutions is caused by the presence of equilibrium aggregates of porphyrins. We attribute the estimated lifetimes (tau) 2 equals 100 divided by 200 ps and (tau) 1 equals 1.5 divided by 4 ns in aqueous solutions to equilibrium aggregates and/or covalently linked dimers and oligomers of HpD, respectively.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.