Time-resolved fluorescence anisotropy of Radachlorin and Chlorin e6 in aqueous and organic solutions under one- and two-photon excitation

Abstract

We present results of experimental study of polarized time-resolved fluorescence of the photosensitizers Radachlorin and chlorin e6 in water-alcohol solutions under one- and two-photon excitation by femtosecond laser pulses within the Soret absorption band. Analysis of orthogonal components of polarized fluorescence allowed us to study anisotropy r0 and rotational diffusion time trot of Radachlorin and chlorin e6 in various solutions as a function of excitation wavelength varied within the ranges of 375-425 nm and 750-850 nm. The observed experimental results were as follows. We observed a nonlinear dependence of the anisotropy parameter r0 on the excitation wavelength. The spectral behavior of r0 obtained at one- and two-photon excitation demonstrated opposite trends: at one-photon excitation r0 reached a minimum value of -0.013 at the absorption maximum of 405 nm while at two-photon excitation r0 reached a maximum value of 0.43 at 810 nm. The data obtained on anisotropy for chlorin e6 and Radachlorin fully coincided within the experimental error bars. The rotational diffusion time trot was shown to depend nonlinearly on alcohol concentration in solution but in proportion to solution viscosity. Good correspondence of rotational diffusion times and solution viscosity suggests that the photosensitizers can be used for probing intracellular viscosity. Financial support from Russian Science Foundation under the grant #21-72-10044 is gratefully acknowledged.

Speaker

Ioanna Gorbunova
Ioffe Institute
Russia

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