Abstract
Low frequency vibrations of the native PYP and related systems in solution have been investigated in "time" (fs fluorescence up-conversion) and "frequency" (resonance Raman) domains to elucidate their role in ultrafast photoisomerization reaction dynamics of PYP. Tentative assignments of the oscillatory components to particular vibrations are proposed supported by normal mode calculations based on DFT and ab initio MO methods. It is concluded that the out-of-plane skeleton bending mode of the chromophore, γ16, is responsible for the observed oscillations in native and all mutant PYPs (f1 ∼ 135 cm-1), while in-plane ν'42 and ν'43 modes are probably responsible for oscillations observed in the PYP analogue with locked chromophore. A dynamic model called "trigger mode mediated guidance" has been proposed to explain in simple terms the ultrafast primary process initiating PYP's photocycle. Furthermore, first successful fluorescence dynamics experiments on PYP single crystals with femtosecond time resolution are presented and discussed.
