Diarylethene Molecular Photoswitches. Masahiro Irie

12 ps at room temperature and finally leads to the photoproduct via 2A/1ACI(o). Both cyclization and cycloreversion reactions take place via the common CI(o). The cyclization reaction in solution completes within 1 ps, as described before. Therefore, the staying time in the 2Ao state is considered to be less than 1 ps. The time constant of 12 ps reflects the time taken to overcome the barrier 2ATS₁.

      Inferring from the experimental results, the cycloreversion dynamics of 20c is summarized as follows. The 1B state produced by the excitation of the closed‐ring isomer undergoes internal conversion into the 2Ac state with the time constant of 200 fs, which is followed by geometrical rearrangement with vibrational cooling in 3.0 ps. The resultant 2Ac state goes over the activation barrier (2ATS₁) into the 2Ao state with the time constant of 12 ps and finally leads to the open‐ring isomer via the 2A/1ACI(o).

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