Potential energy surface transition path sampling

Free cw-azobenzene, excited at 480 nm displays a biexponential decay of the excited state Si with time constants of 0.1 ps and 0.9 ps. Here the ultrafast kinetic component dominates the absorption change (it contains 90 % of the whole amplitude). A direct interpretation would relate the fast component to a free isomerizational motion, where the most direct reaction path on the Si and So potential energy surface is used without disturbance. The slower process may be assigned to a less direct motion due to hindrance by the surrounding solvent molecules. This interpretation is supported by the observation of the absorption changes in the APB and AMPB peptides. Here both reaction parts are slowed down by a factor of 2 - 3 and both show similar amplitudes The peptide molecules hinder the motion of the azobenzene switch and slow down considerably the initial kinetics. However, in all samples the transition to the ground state is finished within a few picoseconds. 

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