Title :

Multiphoton femtosecond laser spectroscopy of anisotropic molecular probes

Abstract :

The talk presents a review of theoretical and experimental investigations of polarized fluorescence in anisotropic molecular probes excited via two-color two-photon transitions by femtosecond laser pulses.  

The molecular probes under study were small biomolecules which are of importance for bio-medical applications: indole, tryptophan, and NADH (nicotinamide adenine dinucleotide). The polarized fluorescence was excited in molecular solutions by simultaneous absorption of two laser photons with different and variable wavelengths thus allowing for tuning of the total excitation energy in the range 4,04-7,09 eV. By alternating the polarization of each of the three photons involved in the photoprocess a set of molecular parameters describing the photoprocess dynamics were determined. Analysis of the results obtained was performed on the basis of ab initio computations of excited state molecular structure and transition dipole moments.  

As pointed out in the talk, the molecular parameter values are very sensitive to the molecular microenvironment thus allowing for investigation of thin details of enegry transfer processes in excited molecules characterized by: anisotropic distribution of molecular axes, lifetimes, rotation correlation times, and the dynamics of nonadiabatic transitions between different potential energy surfaces. As shown, investigation of polarized fluorescence from molecular probes imbedded into biological structures opens a new information channel on protein structure, folding, hydration, and on the mechanizms of redox reactions in living organisms. 

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