Photodynamics of merocyanine 540 in liquid and membrane systems



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Texas Tech University


The photoisomerization and reorientational dynamics of merocyanine 540 have been studied by using steady-state fluorescence spectroscopy and UV-Vis absorption spectroscopy. The importance of merocyanine 540 is that this fluorophore is being used in photodynamic therapy, particularly in the treatment of leukemia. In order to use this photosensitizer efficiently in medical treatments, its photophysical behavior in living systems must be well-understood. Therefore, this probe should be studied in model systems which are similar to biological systems. Micelles and vesicles have been used as model membrane systems in biomedical research. The photophysics and photodynamics of the probe are not well-established in pure solvent and model systems. In the treatment of leukemia, it is believed that photoisomerization of the probe plays a role in causing the destruction of the cancer cells. To shed light on the photoisomerization reaction, the dye was studied in pure solvents. Radiative rate constants were calculated from steady-state spectra by utilizing the Strickler-Berg equation. After that isomerization constants were obtained from radiative rates and quantum yields. The photoisomerization reaction is discussed in terms of the Kramers theory for activated barrier crossing. The photoisomerization process of the probe was also investigated in micellar solutions. In the case of pure solvents, the high-friction limit of the Kramers theory, in other words, the Smoluchowski limit, is in good agreement with our findings. In the case of micellar solutions, photoisomerization is similar to that in a pure solvent and is close to the Smoluchowski limit.



Carbynes, Meropolymethine, Dyes in medical diagnosis